Laser welding device

Abstract

A laser welding apparatus that irradiates a welding spot with a laser beam to form a joined portion in which joining target members are joined together at an irradiation position with the laser beam, the laser welding apparatus comprising: a beam device (110) that outputs the laser beam, wherein the laser beam output from the beam device (110) is defined as an incident beam; a diffractive optical element (130) that emits an irradiated beam toward the irradiation position from an incident point of the incident beam; an incident point changing unit (140) that changes a position of the incident point; and a control device (180) which controls the beam device (110) and the incident point changing unit (140), wherein the diffractive optical element (130) comprises a first region (131) and a second region (132) which are arranged adjacently, the first region (131) is a region in which a diffraction grating is formed, the diffraction grating radiating the radiated beam having a first power density distribution profile different from a power density distribution profile of the incident beam, the second region (132) is a region having a surface profile different from a surface profile of the first region (131) and radiating the radiated beam having a second power density distribution profile different from the first power density distribution profile, and the control device executes a connection control to control the incident point changing unit (140) to move at least one point in the incident point across a boundary between the first region (131) and the second region (132) during the radiation of the laser beam from the radiation device (110), characterized in that the second region (132) is a region in which no diffraction grating is formed.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThe present invention relates to a laser welding apparatus. More specifically, the present invention relates to a laser welding apparatus for performing laser welding with a laser beam irradiated after the laser beam has entered a diffractive optical element (DOE).2. Description of Related ArtLaser welding using a laser beam is performed for joining a plurality of members into a single welded structural body. An example of production joined by such laser welding may include batteries. Generally, batteries are configured to include electrode bodies formed of positive and negative electrode plates within housings. In a manufacturing process of such batteries, after the electrode bodies are accommodated inside case bodies from respective openings, a joining step of sealing the openings of the case bodies with sealing plates, then joining the case body and the sealing plates by laser welding, is carried out in some cases. In the joining step, laser welding is performed along welding lines at a position where the openings of the case bodies and side surfaces of the sealing plates are opposed to each other.For example, Japanese Patent Publication JP 2013-220 462 A describes a technique for joining a case body and a sealing plate by irradiating a welding line between the case body and the sealing plate with a low density laser beam having a lower power density and high density laser beams each having a higher power density than the low density laser beam. In JP 2013-220 462 A, while both the case body and the sealing plate are widely irradiated with the low-density laser beam, the high-density laser beams are irradiated such that light spots of the high-density laser beams are arranged within a light spot of the low-density laser beam. The above low-density laser beam and the above high-density laser beams are embodied by beamforming a single laser beam with a DOE. After the temperature is increased to some extent by the low density laser beam, the high density laser beams may be applied. With this configuration, it is possible to prevent rapid increase in temperature at an irradiated portion with the high density laser beams, thereby preventing bumping (jumping) or the like at the welded portion. Subsequently, the low density laser beam is applied to the irradiated portion irradiated with the high density laser steels. With this configuration, it is possible to prevent rapid decrease in temperature at the irradiated portion with the high density laser beam, thus suppressing generation of fractures or the like. It is described that it is accordingly possible to suppress generation of welding defects.US 2015 / 0 260 985 A1 describes a laser processing apparatus and a laser processing method, wherein a laser beam emitted from a laser oscillator is positioned on a minute diffraction pattern or over two or more minute diffraction patterns provided in a diffraction optical element by a moving unit. A laser beam given a desired beam profile is reflected at an angle at which the laser beam is irradiated by a scanning unit to a target position on a processed object. The laser beam is transmitted through the lens unit whose position in the Z-axis direction is controlled so that a focal point of the lens unit corresponds to the surface of the processed object. The object to be processed is irradiated with a laser beam converged by the lens unit and having a desired laser beam profile to realize the desired processing.JP 2012-110 905 A describes a method and an apparatus for welding that stably weld a case and a high-quality sealing plate together to produce a power device such as a secondary battery, an electric double layer capacitor, and so on. The welding apparatus welds welding workpieces of elements by scanning with a laser beam and sweeping a point of a workpiece relative to a scanning direction of the welding workpieces, the laser beam being a beam including workpieces, one workpiece having a first power density and the other workpiece being located within the first workpiece and having a second power density that is higher than the first power density.The document JP 2000-280 085 A describes another laser processing apparatus. A laser light emitted from a laser light source is adjusted in its light volume by an ND filter of a variable light volume part. The laser light output from the variable light volume part is incident on a variable aperture to form waveforms. The laser light output from the variable aperture is then incident on a light modulator. The light modulator includes a rotating disk, a rotating axis, a pulse motor, or the like. The rotary disk is a transmission type on the surface of which a plurality of diffraction optical elements are formed. The pulse motor for rotating the rotary disk is driven by the control of a control unit while being synchronized with an output timing of the laser light to selectively emit the laser light against the desired diffraction optical elements.In laser welding, it is preferable to perform more flexible control depending on the condition of joining target portions or to form a desired joined portion in a shorter time.SUMMARY OF THE INVENTIONIt is an object of the present invention to provide a laser welding apparatus capable of performing laser welding by more flexible control.This object is achieved by a laser welding device according to claim 1 or claim 3. Advantageous further developments are specified in the dependent patent claims.A laser welding apparatus is a laser welding apparatus that irradiates a welding point with a laser beam to form a joined portion in which joining target elements are joined together at an irradiation position with the laser beam, the laser welding apparatus comprising: a beam device that outputs the laser beam, the laser beam output from the beam device being defined as an incident beam; a diffractive optical element that irradiates an irradiated beam toward the irradiation position from an incident point of the incident beam; an incident point changing unit that changes a position of the incident point; and a controller that controls the beam device and the incident point changing unit, wherein the diffractive optical element comprises a first region and a second region that are adjacently disposed, the first region is a region, in which a diffraction grating is formed, the diffraction grating radiating the radiated beam having a first distribution profile of power density different from a distribution profile of power density of the incident beam, the second region being a region having a surface profile different from a surface profile of the first region and radiating the radiated beam having a second distribution profile of power density different from the first distribution profile of power density, and the controller performs connection control to control the incident point changing unit to move at least one point in the incident point across a boundary between the first region and the second region during the radiation of the laser beam from the beam device.The laser welding device is capable of switching the irradiation pattern formed at the irradiation position to the irradiation pattern having a different power density distribution profile during irradiation of the laser beam. It is possible to set the power density at each part in the irradiation position to be at an arbitrary level without changing the output of the laser beam or the like. Thereby, it is possible to perform laser welding by more flexible control and to form the joined portion simultaneously in a shorter time.In the above laser welding device, the second region is a region where no diffraction grating is formed. This is because it is possible to produce the diffractive optical element capable of forming the irradiation pattern having different distribution profiles of power densities at a lower cost by reducing the area where the diffraction grating is formed. In addition, in the region where no diffraction grating is formed, it is possible to irradiate the irradiation position with the incident beam output from the beam device and entering the diffractive optical element without changing the distribution profile of the power density; consequently, it is possible to set the power density at the position concerned to be the maximum.Alternatively, in the above laser welding apparatus, the first region is a region that radiates the radiated beam including parts having a maximum power density in the first power density distribution profile within an outer periphery region different from a central region that is a part having a maximum power density in the second power density distribution profile. This is because it is possible to selectively use the irradiation pattern that achieves a larger molten amount of the outer peripheral portion than a molten amount of the central portion and the irradiation pattern that achieves a larger molten amount of the central portion than a molten amount of the outer peripheral portion.In the above laser welding apparatus, in the joining controller, it may be configured that the controller controls the welding point at the irradiation position to be disposed in the central region, controls the incident point changing unit to set the position of the incident point to be closer to the second region than is the position of the incident point before a predetermined start time elapses after the start time elapses from a start of irradiation of the laser beam from the irradiation device, and controls the irradiation position not to move relative to the joining target members during irradiation of the laser beam from the irradiation device. In the spot welding, it is possible to suppress generation of errors due to laser passing caused by the laser beam transmitted through the gap at the welding point of the joining target members and applied to the member disposed on the opposite side to the laser beam irradiation side of the joining target members.In the above laser welding apparatus, the laser welding apparatus may further include a moving unit that moves at least one of the irradiation position and the joining target members with respect to each other, wherein in the joining controller, the controller may execute a scan control to control the moving unit to move the irradiation position such that a welding line formed by a plurality of continuous welding points extends through the central region. This is because, in the laser welding performed along the welding line, it is possible to form the irradiation pattern having different distribution profiles of the power densities at an arbitrary irradiation position on the welding line.In the above laser welding apparatus, in the connection controller, the controller may control the incident point changing unit to set the position of the incident point to be closer to the second region than is the position of the incident point before a lapse of a predetermined initial time after the initial time has elapsed from a start of irradiation of the laser beam from the irradiation device. Since no melted portion is formed at the start time of the joining control, a gap is likely to be present at a position of the welding point of the joining target members located at the start position. Thus, it is possible to suppress generation of errors caused by the laser passage through the gap at the above start position.In the above-described laser welding apparatus, the second region may be a region in which a central point is formed in the central region by the irradiated beam, the first region may be a region in which a first outer edge point and a second outer edge point are formed by the irradiated beam in the outer edge region, the first outer edge point and the second outer edge point respectively forming vertices of a triangle together with the central point, and the controller may execute, in the scan control, control such that an intermediate part between the first outer edge point and the second outer edge point and the central point are made to pass through the welding point on the welding line in the order of the intermediate part between the first outer edge point and the second outer edge point and the central point. This is because it is possible to execute the scan control while forming the melted portion by the first outer edge point and the second outer edge point and securely filling the gap ahead to the central point with this melted portion. Thereby, it is possible to suppress the laser passage in the scan control.In the above-described laser welding apparatus, the second region may be a region in which a central point is formed in the central region by the irradiated beam, the first region may be a region in which four outer edge points each forming vertices of a rectangle surrounding the central point are formed in the outer edge region by the irradiated beam, and the controller may execute, in the scan control, control such that an intermediate part between a first outer edge point and a second outer edge point that are adjacently disposed among the outer edge points, the central point, and an intermediate part between a third outer edge point and a fourth outer edge point that are outer edge points different from the first outer edge point and the second outer edge point are each made to be, passing through the welding point on the welding line in the order of the intermediate part between the first outer edge point and the second outer edge point that are adjacently disposed among the outer edge points, the central point, and the intermediate part between the third outer edge point and the fourth outer edge point that are the outer edge points different from the first outer edge point and the second outer edge point. This is because it is possible to execute the scan control while forming the melted portion by the first outer edge point and the second outer edge point and securely filling the gap ahead to the central point with the melted portion. Thereby, it is possible to suppress the laser passage in the scan control. In addition, it is possible to suppress rapid decrease in the temperature of the melted portion formed by the passage of the central point by the third outer edge point and the fourth outer edge point. By doing so, it is possible to suppress fractures or the like caused by the rapid decrease in the temperature of the melted portion.In the above laser welding device, the second region may be a region in which a central point is formed in the central region by the irradiated beam, the first region may be a region in which a first outer edge point and a second outer edge point located at a position different from that of the first outer edge point are formed in the outer edge region by the irradiated beam, and the controller may control, in the scan control, the central point to move along the welding line, control the first outer edge point to move forward to the central point along a first outer edge lane that is a lane parallel to the welding line, and control the second outer edge point to move rearward to the central point along a second outer edge lane that is a lane parallel to the welding line. This is because it is possible to execute the scan control while forming the melted portion by the first outer edge point and securely filling the gap ahead to the central point with this melted portion. Thereby, it is possible to suppress the laser passage in the scan control. In addition, it is possible to suppress, by the second outer edge point, rapid decrease in the temperature of the molten portion formed by the passage of the central point. By doing so, it is possible to suppress fractures or the like caused by the rapid decrease in the temperature of the molten portion.In the above-described laser welding apparatus, before the joining control is executed, the control means may execute provisional fixing control to irradiate a part of each provisional position on the welding line with the laser beam to form a provisional fixed portion at the provisional position, and the control means may control, in the provisional fixing control, the incident point changing unit to set the position of the incident point to be within the first range. This is because it is possible to suppress a deviation between the joining target members during the joining control with the formation of the provisionally fixed portion, thereby forming the actual joined portion by the joining control. With respect to the formation of the provisionally fixed portions, it is possible to suppress errors caused by the laser passage by using the laser welding device to form the joined portion.In the above-described laser welding apparatus, the laser welding apparatus may further include a gap output unit that detects a gap at the welding point on the welding line formed by making the connection target members face each other and outputs the detection of the gap, wherein the controller in the connection control, when the gap at the welding point detected by the gap output unit is equal to a predetermined gap threshold value or more, may execute laser control to control the incident point changing unit to set the position of the incident point to be closer to the first range than the position of the incident point is when the output gap is less than the gap threshold value. The joined portion tends to be formed properly by setting the power density in the outer edge region to be larger and setting the power density in the central region to be smaller as the gap is larger. On the other hand, the joined portion tends to be formed properly by setting the power density in the outer peripheral region to be smaller and setting the power density in the central region to be larger as the gap is smaller. Specifically, it is possible to properly form the joined portion by using the irradiation pattern having the power density distribution profile defined depending on the dimension of the gap.In the above-described laser welding apparatus, when the welding line is in a rectangular shape as a whole, the controller may start the sensing control from a start position, the start position being the welding point disposed in a longer side of the welding line, and the controller may execute the sensing control along the welding line through one round to the start position after the start. Deformation of the joining target members tends to be smaller by starting formation of the joined portion from the welding point disposed on a longer side of the welding line rather than starting formation of the joined portion from the welding point disposed on a shorter side of the welding line. Thereby, it is possible to properly form the joined portion while suppressing deformation of the joining target members.In the above-described laser welding apparatus, the irradiation device may adjust a laser output value, which is an output value of the output laser beam, during irradiation of the laser beam. This is because it is possible to perform laser welding while adjusting a maximum value and a minimum value of power density in the irradiation pattern.According to an aspect of the present invention, it is possible to provide the laser welding apparatus capable of performing the laser welding by more flexible control.Brief Description of the DrawingsFeatures, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like reference numerals denote like elements. The following are shown: FIG. 1 shows a perspective illustration of a battery according to a first exemplary embodiment; FIG. 2 is a schematic diagram showing a configuration of a laser welding apparatus according to the first embodiment; FIG. 3 is a drawing explaining a laser beam scanning method in which the welding apparatus according to the first embodiment is used; FIG. 4 shows a plan view of a diffractive optical element and a sliding unit; FIG. 5 is a drawing showing an irradiation pattern of the laser beam formed with an incident point disposed in a formation region of the diffractive optical element; FIG. 6 is a drawing showing an irradiation pattern of the laser beam formed with an incident point overlapping a boundary between the formation region and the non-formation region of the diffractive optical element; FIG. 7 is a drawing showing the irradiation pattern of the laser beam formed with an incident point disposed in the non-forming region of the diffractive optical element; FIG. 8 is a drawing showing a relationship between a slide position of the slide unit and proportions of power densities in the irradiation pattern; FIG. 9 is a drawing showing proportions of power densities in the irradiation pattern when the shift position is located at a position where the incident point is to be located in the formation region of the diffractive optical element; FIG. 10 is a drawing showing portions of power densities in the irradiation pattern when the shift position is located at a position where the incident point overlaps a boundary between the formation region and the non-formation region of the diffractive optical element; FIG. 11 is a plan view of the battery used for explaining a scan control of the laser beam in connection control according to the first embodiment; FIG. 12 is a partial plan view of the battery near a start position of the connection control; FIG. 13 is a sectional view of a straight portion before the connection control is executed; FIG. 14 is a sectional view of a curved portion before the connection control is executed; FIG. 15 is a drawing showing depths of the respective connected portions formed in embodiments and comparative examples; FIG. 16 is a drawing explaining how a provisionally fixed portion is formed by using only a single light spot, which is different from the embodiment; FIG. 17 is a drawing showing a measurement state in which a gap is measured by a laser displacement sensor in a gap detection step according to a third embodiment; FIG. 18 is a drawing showing measurement results of gaps by using the laser displacement sensor; FIG. 19 is a drawing showing a relationship between the ratio of the power density of a central point and a depth of the joined portion for each gap; FIG. 20 is a drawing showing a relationship between each gap and the ratio of the power density of the central point to form a proper connected portion; FIG. 21 is a drawing showing a gap shift position table; FIG. 22 is a schematic drawing showing a configuration of the welding apparatus according to a fourth embodiment; FIG. 23 is a plan view of the welding apparatus according to the fourth embodiment; FIG. 24 is a plan view of the battery used for explanation of laser welding sensing control in connection control according to the fourth embodiment; FIG. 25 is a drawing showing irradiation patterns according to variations; FIG. 26 is a drawing showing irradiation patterns according to variations different from those of FIG. 25 ; FIG. 27 is a drawing explaining how laser welding is performed with the irradiation patterns according to variations of FIG. 26 ; FIG. 28 is a drawing showing irradiation patterns corresponding to variations different from those of FIGS. 25 and 26 ; FIG. 29 is a drawing explaining how laser welding is performed with the irradiation patterns according to variations of FIG. 28 ; and FIG. 30 is a drawing explaining variations of the diffractive optical element.DETAILED DESCRIPTION OF THE EMBODIMENTSPreferred embodiments for embodying the present invention will be described below in detail with reference to the drawings.[First Embodiment]FIG. 1 is a perspective view showing an appearance of a battery 1 which is a joining target of laser welding according to the present invention. As shown in FIG. 1, the battery 1 has an appearance in a flat shape. As shown in FIG. 1, the battery 1 includes a positive electrode terminal 40 and a negative electrode terminal 50. the battery 1 is a secondary battery that is rechargeable via the positive electrode terminal 40 and the negative electrode terminal 50. As the battery 1, lithium ion secondary batteries and nickel-hydrogen storage cells can be exemplified.The battery 1 includes a case body 10. An opening 11 used for accommodating the electrode body inside the case body is formed on an upper part of the case body 10. The opening 11 of the case body 10 is sealed by a sealing plate 20 in FIG. 1. In the present embodiment, materials of the case body 10 and the seal plate 20 are aluminum in both cases.The positive electrode terminal 40 and the negative electrode terminal 50 are provided on the sealing plate 20. The sealing plate 20 is provided with a solution filling opening sealing member 60 for sealing a solution filling opening through which the inside is filled with the electrolytic solution. The solution filling port sealing member 60 is attached after the inside of the case body 10 is filled with the electrolytic solution from the solution filling port.In the battery 1 according to the present embodiment, the case body 10 and the sealing plate 20 are joined to each other by the laser welding. Specifically, the case body 10 and the sealing plate 20 are joined to each other by fitting the sealing plate 20 into the opening 11 of the case body 10 and performing laser welding to irradiate a welding line between the case body 10 and the sealing plate 20 with the laser beam.A joined portion 30 is formed on the welding line between the case body 10 and the sealing plate 20 by a round by the laser welding. Specifically, in the apparent view of the battery 1 as shown in FIG. 1, the opening 11 (inner wall surface 13) of the case body 10 and a side surface 21 of the sealing plate 20 are indicated by reference numerals for the purpose of description. However, actually, the opening 11 (the inner wall surface 13) of the case body 10 and the side surface 21 of the sealing plate 20 are not present on an outer side of the battery 1, because they are melted in the vicinity of the opening 11 and the side surface 21 and mixed with each other into the joined portion 30.Referring to FIG. 2, a welding device 100 that performs laser welding according to the present embodiment will be described. FIG. 2 is a schematic diagram showing a configuration of the welding apparatus 100 for irradiating the battery 1 with a laser beam L. As shown in FIG. 2, the welding apparatus 100 includes a laser oscillator 110, a collimator 120, a diffractive optical element (DOE) 130, a galvano scanner 150, an Fθ lens 160, and a protection lens 170.The laser oscillator 110 is a emitter capable of generating a laser beam and emitting the generated laser beam. The collimator 120, the diffractive optical element 130, the galvano scanner 150, the Fθ lens 160, and the protection lens 170 are arranged in an optical path of the laser beam output from the laser oscillator 110 in this order. The welding device 100 is capable of projecting the laser beam toward the battery 1 from a lower surface of the protection lens 170.The collimator 120 is capable of adjusting the laser beam output from the laser oscillator 110 and entering through an optical fiber 111 to be in a parallel state. The diffractive optical element 130 is capable of adjusting an irradiation pattern of the laser beam. Specifically, the diffractive optical element 130 is capable of emitting the laser beam that has entered as a laser beam having a power density distribution profile different from that of the laser beam at the time of entering. In FIG. 2, the laser beam before entering the diffractive optical element 130 is indicated as an incident beam Li. The laser beam L irradiating the battery 1 is a radiated laser beam resulting from the incident beam Li radiated from an incident point of the diffractive optical element 130.The diffractive optical element 130 is attached to a slide unit 140. The shifting unit 140 is capable of shifting the diffractive optical element 130 with respect to the incident beam Li. The diffractive optical element 130 and the shifter 140 will be described in detail below.The galvanoscanner 150 includes a pair of reflecting mirrors (galvanomirrors) 151, 152. An angle of each reflecting mirror 151, 152 is adjusted by rotating the reflecting mirror 151, 152 by a motor. The Fθ lens 160 is used for correcting a scanning speed of the laser beam to be constant.The galvano scanner 150 is capable of accurately irradiating a predetermined position with the laser beam L by rotating the reflecting mirrors 151, 152. That is, the galvano scanner 150 is capable of irradiating an arbitrary welding point with the laser beam L by rotating the reflecting mirrors 151, 152. The galvano scanner 150 may be a scanning unit capable of scanning the welding line formed by a plurality of continuous welding spots with the laser beam L at a high speed. As shown in FIG. 3, the welding apparatus 100 according to the present embodiment is capable of irradiating a formation position of the joined portion 30 (welding line) of the battery 1 with the laser beam L through one round by rotating the reflecting mirrors 151, 152.The welding apparatus 100 includes a controller 180 to control each component. The controller 180 is capable of controlling irradiation of the laser beam via the laser oscillator 110. The control device 180 controls a sliding movement via the sliding unit 140. The controller 180 further controls scanning with the laser beam L via the galvano scanner 150.FIG. 4 shows a plan view of the diffractive optical element 130 and the sliding unit 140 of the welding device 100. In FIG. 4, the incident beam Li enters the diffractive optical element 130 from the front side in the depth direction of the drawing. FIG. 4 shows an incident point LP where the incident beam Li has entered. In the present embodiment, the incident point LP is not a point having a zero dimension but a point having a certain area.As shown in FIG. 4, the diffractive optical element 130 includes a formation region 131 and a non-formation region 132. The formation region 131 is a region having a quadrangular outer shape disposed at a center of the diffractive optical element 130. The non-formation region 132 is a region disposed around the quadrangular formation region 131 in a manner to surround this formation region 131. Thus, in the diffractive optical element 130, the formation region 131 and the non-formation region 132 are adjacently arranged as shown in Fig. 4. A side of a boundary between the formation region 131 and the non-formation region 132 formed along four sides of the outer shape of the formation region 131 is shown as a boundary 133 in FIG. 4. The diffractive optical element 130 is configured by a material through which the laser beam can be transmitted into both the formation region 131 and the non-formation region 132. An example of the material of the diffractive optical element 130 may comprise, for example, quartz glass.The formation region 131 of the diffractive optical element 130 is a region where a diffraction grating is formed. Thus, in the forming region 131, while the incident beam Li enters the forming region 131, the incident beam Li can be irradiated from the incident point LP to form an irradiation pattern derived from an interference fringe by diffraction of the laser beam at the irradiation position.Meanwhile, in the diffractive optical element 130 according to the present embodiment, the non-formation region 132 is a region where no diffraction grating is formed. Thus, in the non-formation region 132, when the incident beam Li enters the non-formation region 132, the incident beam Li can be transmitted through the incident point LP to form an irradiation pattern at the irradiation position. In the present embodiment, even when the incident point LP is disposed within the non-formation region 132, the laser beam transmitted through the incident point LP is a radiated beam radiated from the incident point LP.As shown in FIG. 4, the slide unit 140 includes a movable part 141 and a fixed part 142. The movable part 141 is slidably movable with respect to the fixed part 142. In the sliding unit 140 according to the present embodiment, the movable part 141 is movable within a plane of the diffractive optical element 130.As shown in FIG. 4, the diffractive optical element 130 is fixed to the movable part 141. Thus, the sliding unit 140 can move the diffractive optical element 130 in the plane in a sliding manner. The slide unit 140 according to the present embodiment is slidably movable in a range from a slide position A indicated by a solid line to a slide position D indicated by an alternate long and two short dash line in FIG. 4. By this configuration, the shifter 140 according to the present embodiment is capable of moving the incident point LP on the diffractive optical element 130.The shift position A indicated by the solid line in FIG. 4 is in a state where the incident point LP of the incident beam Li is located at a center in the formation region 131 of the diffractive optical element 130. This means that, at the shift position A, the incident beam Li only enters the formation region 131 of the diffractive optical element 130. For example, the incident beam Li enters only the formation region 131 of the diffractive optical element 130 until at least one point in the incident point LP comes out of the formation region 131 during the sliding movement from the sliding position A to the sliding position D.Meanwhile, at the shift position D indicated by an alternate long and two short dash line, the incident point LP of the incident beam Li is in a state where the incident point LP is located in the non-formation region 132 of the diffractive optical element 130. Specifically, the incident beam Li enters only the non-formation region 132 of the diffractive optical element 130 at the shift position D. For example, during the sliding movement from the sliding position A to the sliding position D, the incident beam Li enters only the non-forming region 132 of the diffractive optical element 130 after the entire incident point LP has come out of the forming region 131.From the shift position A to the shift position D, it is possible to set the shift unit 140 in a state in which the incident beam Li enters both the formation region 131 and the non-formation region 132 of the diffractive optical element 130. For example, while at least one point of the incident point LP comes out of the formation region 131 and the incident point LP completely comes into the non-formation region 132, the incident beam Li enters both the formation region 131 and the non-formation region 132. Specifically, in a state where the incident point LP overlaps the boundary 133 between the formation region 131 and the non-formation region 132, the incident beam Li enters both the formation region 131 and the non-formation region 132.An irradiation pattern P formed by the incident beam Li having entered the diffractive optical element 130 is shown in each of FIGS. 5, 6, and 7. Each irradiation pattern P shown in FIGS. 5, 6, and 7 is formed on respective upper surfaces of the case body 10 and the sealing plate 20 that are the irradiation position with the laser beam L irradiated from the incident point LP.Specifically, FIG. 5 shows the irradiation pattern P of the laser beam L formed while the incident point LP is located within the formation region 131. As shown in FIG. 5, the irradiation pattern P formed while the incident point LP is located within the formation region 131 includes an outer edge point group SG indicated by oblique line shading. The outer edge point group SG is configured by eight outer edge points S 11, S 12, S 21, S 22, S 31, S 32, S 41, S 42. All the outer edge points of the outer edge point group SG are disposed within an outer edge region A 2 disposed around a central region A 1 in the irradiation pattern P. As shown in FIG. 5, in the state where the incident point LP is located within the formation region 131, the irradiation pattern P does not have a point in the central region A 1. Specifically, the formation region 131 of the diffractive optical element 130 according to the present embodiment is a region that radiates the radiated beam such that parts having the maximum power density are disposed inside the outer edge region A 2 when the incident beam Li enters.FIG. 6 shows the irradiation pattern P of the laser beam L formed while the incident point LP overlaps the boundary 133 between the formation region 131 and the non-formation region 132. As shown in FIG. 6, the irradiation pattern P formed while the incident point LP overlaps the boundary 133 is configured by the outer edge point group SG indicated by the oblique line shading and a central light point S 0 indicated by a point shading. The central point S 0 is located within the central region A 1 in the irradiation pattern P.FIG. 7 shows the irradiation pattern P of the laser beam L formed while the incident point LP is located within the non-formation region 132. As shown in FIG. 7, the irradiation pattern P formed while the incident point LP is located within the non-formation region 132 is configured by the central point S 0 indicated by the dot hatching. As shown in FIG. 7, the irradiation pattern P formed while the incident point LP is located within the non-formation region 132 does not have a point in the outer edge region A 2. In the present embodiment, the central area A 1 is defined as a position at which the central point S 0 is formed. Thus, in the present embodiment, the non-formation region 132 of the diffractive optical element 130 is a region that radiates the radiated beam such that the central point S 0 becomes a part having the maximum power density when the incident beam Li enters.The outer edge light point group SG indicated by the oblique line shading is formed by the incident beam Li that has entered the forming region 131 of the diffractive optical element 130. In other words, the outer edge point group SG is formed by the laser beam L, which is the incident beam Li irradiated into the forming region 131. Specifically, in the forming region 131 of the diffractive optical element 130 according to the present embodiment, a diffraction grating that generates the outer edge point group SG in the outer edge region A 2 is formed due to an interference fringe formed by diffracting the incident beam Li.In the formation region 131, regardless of the position of the incident point LP, the diffraction grating is formed such that a diffracted beam of a first order or more of the incident beam Li that has entered the formation region 131 forms the respective light spots of the outer edge spot group SG. Specifically, either when the incident point LP is located at the center of the formation region 131, or when the incident point LP is located near an end of the formation region 131, the respective light spots of the outer edge spot group SG are formed by the laser beam L irradiated from the incident point LP into the formation region 131.Meanwhile, the central light spot S 0 indicated by the spot shading is formed by the laser beam L (zero-order beam), which is the incident beam Li that has entered the non-forming region 132 of the diffractive optical element 130 and transmitted through the non-forming region 132 at the incident point LP.As shown in FIGS. 5 and 6, the outer edge point group SG in the irradiation pattern P is arranged radially around the central point S 0 arranged in the central region A 1. Specifically, the outer edge points S 11, S 12 of the outer edge point group SG are disposed at an upper right side of the central point S 0. The outer edge points S 21, S 22 are disposed at a lower right side of the central point S 0. The outer edge points S 31, S 32 are disposed at a lower left side of the central point S 0. The outer edge points S 41, S 42 are disposed at an upper left side of the central point S 0.The upper right side outer edge points S 11, S 12 and the upper left side outer edge points S 41, S 42 are each arranged in a positional relationship in which a triangle having vertices defined by one of the outer edge points S 11, S 12 and one of the outer edge points S 21, S 22 together with the central point S 0 is formed. The lower right side outer edge points S 21, S 22 and the lower left side outer edge points S 31, S 32 are each arranged in a positional relationship in which a triangle having vertices defined by one of the outer edge points S 21, S 22 and one of the outer edge points S 31, S 32 together with the central point S 0 is formed. The lower left side outer edge points S 31, S 32 and the upper left side outer edge points S 41, S 42 are each disposed in a positional relationship in which a triangle having vertices defined by one of the outer edge points S 31, S 32 and one of the outer edge points S 41, S 42 together with the central point S 0 is formed. Specifically, for example, the outer edge point S 11 and the outer edge point S 41 are arranged together with the central point S 0 at respective positions corresponding to vertices of a triangle.In addition, the upper right side outer edge points S 11, S 21, the lower right side outer edge points S 21, S 22, the lower left side outer edge points S 31, S 32, and the upper left side outer edge points S 41, S 42 are arranged in a positional relationship in which a rectangle having a respective vertex defined by a point of each pair of the outer edge points is formed. Further, the outer edge point group SG is arranged in a manner to surround the central point S 0 through the rectangle.Gaps are provided between the left outer edge points S 31, S 32, S 41, S 42 and the right outer edge points S 11, S 12, S 21, S 22 of the outer edge point group SG, respectively. In addition, gaps are also provided between the upper outer edge points S 11, S 12, S 41, S 42 and the lower outer edge points S 21, S 22, S 31, S 32. The respective gaps between the left outer edge points and the right outer edge points in the outer edge point group SG and the respective gaps between the upper outer edge points and the lower outer edge points in the outer edge point group SG are set to be equal to or larger than a gap provided in the welding line described below.The central point S 0 and each outer edge point of the outer edge point group SG in the irradiation pattern P are not zero-order points, but have certain areas. In the present embodiment, each point of the outer edge point group SG has the same area as that of the central point S 0. Specifically, a sum of the areas of the respective points of the outer edge point group SG is eight times as large as the area of the central point S 0.The slide unit 140 according to the present embodiment can switch the irradiation pattern P to each irradiation pattern P shown in FIGS. 5, 6, and 7 by a slide motion. Specifically, the shift unit 140 varies the position of the incident point LP of the incident beam Li on the diffractive optical element 130, thereby respectively adjusting the outer edge point group SG and the central point S 0 to appear or not to appear in the irradiation pattern P. With this configuration, it is possible to vary the irradiation pattern P.FIG. 8 is a graph showing a relationship between the slide position of the slide unit 140 and the power density. A horizontal axis in FIG. 8 represents the slide position of the slide unit 140. A vertical axis of FIG. 8 represents a ratio of the power density.In addition, FIG. 8 shows a graph of a ratio of the power density of the outer edge point group SG indicated by a solid line and a graph of a ratio of the power density of the central point S 0 indicated by a broken line. The graph of the ratio of the power density of the outer edge point group SG indicated by the solid line shows a ratio of the power density of one of the eight points configuring the outer edge point group SG.As shown in FIG. 8, the left end of the horizontal axis represents that the slide unit 140 is disposed at the slide position A. The right end of the horizontal axis represents that the slide unit 140 is disposed at the slide position D. A slide position B indicated on the horizontal axis represents that the slide unit 140 is disposed at a boundary between a state in which the incident point LP is located in the formation area 130 and a state in which the incident point LP overlaps the boundary 133.Within a range where the slide position is located more leftward than the slide position B, that is, the incident point LP is located within the formation region 131, the irradiation pattern P shown in FIG. 5 is formed. Within a range where the shift position is located more to the right than the shift position B, that is, the incident point LP overlaps the boundary 133, the irradiation pattern P shown in FIG. 6 is formed. Specifically, at the shift position C within a range where the incident point LP of FIG. 8 overlaps the boundary 133, the irradiation pattern P shown in FIG. 6 is formed. In addition, at the slide position D within a range where the incident point LP is located within the non-formation region 132, the irradiation pattern P shown in FIG. 7 is formed.As shown in the graphs of FIG. 8, the power density of the outer edge point group SG becomes a maximum within a range from the slide position A to the slide position B. This is because the incident beam Li enters only the formation region 131 of the diffractive optical element 130, regardless of the shift position of the shift unit 140 within the range from the shift position A to the shift position B. Within the range from the shift position A to the shift position B, the power density ratio of a single point of the outer edge point group SG is approximately 12.5%, because the outer edge point group SG is configured by eight points.The power density of the outer edge point group SG is gradually decreased from the slide position B toward the slide position D, becoming zero at the slide position D. This is because an overlapping area between the incident point LP and the formation area 131 becomes smaller as the slide position comes closer to the slide position D. Thus, the proportion of the incident beam Li entering the formation region 131 becomes smaller. At the shift position D, the entire incident point LP is located out of the formation region 131 of the diffractive optical element 130, so that no incident beam Li enters the formation region 131.Meanwhile, the power density of the central point S 0 within the range from the slide position A to the slide position B is zero. This is because, within the range from the shift position A to the shift position B, the entire incident point LP is outside the non-forming region 132 of the diffractive optical element 130, and no incident beam Li enters the non-forming region 132. The power density of the central point S 0 is gradually increased from the slide position B toward the slide position D and becomes a maximum of 100% at the slide position D. As the slide position comes closer to the slide position D, an overlapping area between the incident point LP and the non-formation region 132 becomes larger. Thus, the proportion of the incident beam Li entering the non-formation region 132 becomes larger. At the shift position D, the entire incident point LP is located within the non-formation region 132 of the diffractive optical element 130, so that the incident beam Li enters only the non-formation region 132.As can be seen from FIG. 8, the welding apparatus 100 according to the present embodiment can control the relationship between the power density of the outer edge point group SG and the power density of the central point S 0 in the irradiation pattern P by the sliding movement of the sliding unit 140. As a result, the welding apparatus 100 is capable of varying the distribution profile of the power density in the irradiation pattern P.Specifically, for example, FIG. 9 shows ratios of the power densities of the respective points in the irradiation pattern P when the slide unit 140 is disposed at the slide position A. As shown in FIG. 9, as mentioned above, the ratio of the power density of each point of the outer edge point group SG is approximately 12.5% because the outer edge point group SG is configured by eight points. It is apparent from FIG. 9 that no central point S 0 appears in the irradiation pattern P with respect to the shift position A. This means that the power density at the central point S0is zero.In contrast, FIG. 10 shows ratios of the power densities of the respective points in the irradiation pattern P when the slide unit 140 is disposed at the slide position C. Unlike the case at the slide position A shown in FIG. 9, when the slide position is located at the slide position C, the central point S 0 appears as shown in FIG. 10. The proportion of the power density of the central point S0 becomes a maximum. At the slide position C, the ratio of the power density of each point of the outer edge point group SG is decreased more than that at the slide position A. The reason for this is that at the slide position C, the overlapping area between the incident point LP and the formation region 131 is smaller than that at the slide position A, thus decreasing the ratio of the incident beam Li entering the formation region 131.It has been found that the distribution profile of the power density in FIG. 10 is different from that in FIG. 19. Specifically, the power density distribution pattern of the irradiation pattern P with respect to the shift position A shown in FIG. 9 has a power density of 0% at the central point S 0, and has a power density of approximately 12.5% at each point of the outer edge point group SG. In contrast, the distribution profile of the power density of the irradiation pattern P with respect to the shift position C has a power distribution of approximately 14% at the central point S0, and has a power density of approximately 10.75% at each point of the outer edge point group SG.Accordingly, when the slide unit 140 slides from the slide position A to the slide position C, the power density distribution profile of the irradiation pattern P varies. Conversely, the power density distribution profile of the irradiation pattern P also varies as the slide unit 140 slides from the slide position C to the slide position A. That is, the welding apparatus 100 according to the present embodiment is capable of varying the distribution profile of the power density of the irradiation pattern P by the sliding movement of the sliding unit 140 during irradiation with the laser beam L.The configuration of varying the distribution profile of the power density of the irradiation pattern P is not limited to a change from the state in which the incident point LP is located within the formation region 131 to the state in which the incident point LP overlaps the boundary 133, and vice versa, by the sliding movement of the sliding unit 140. That is, when the sliding movement of the sliding unit 140 is performed within the range in which the incident point LP overlaps the boundary 133, it is also possible to vary the distribution profile of the power density of the irradiation pattern P. Specifically, when the position of the incident point LP is changed within the range in which the incident point LP overlaps the boundary 133, the position of each point of the irradiation pattern P is not changed, but the distribution profile of the power density may be varied. In other words, the welding apparatus 100 according to the present embodiment is capable of varying the power density distribution profile of the irradiation pattern P by moving the sliding unit 140 such that at least one point of the incident point LP moves over the boundary 133 of the diffractive optical element 130. With this configuration, the welding apparatus 100 according to the present embodiment is capable of flexibly controlling the distribution profile of the power density of the irradiation pattern P.In the present embodiment, the joined portion 30 (FIG. 1 ) is formed in the battery 1 by performing the joining step using the welding apparatus 100 described above. The controller 180 of the welding apparatus 100 performs connection control on the laser oscillator 110 to emit the laser beam L in the connection step. During connection control, the controller 180 according to the present embodiment controls the slide unit 140 to slide. In the connection control, the controller 180 according to the present embodiment further performs scan control to control the galvanoscanner 150 to scan the welding line with the laser beam.FIG. 11 is a plan view of the battery 1 before the connection step. In the battery 1 shown in FIG. 11, the connected portion 30 (FIG. 1 ) is not yet formed. FIG. 11 shows a state in which the sealing plate 20 is inserted into the opening 11 of the case body 10. Thus, the inner wall surface 13 of the opening 11 of the case body 10 and the side surface 21 of the sealing plate 20 are in a state of opposing each other. In the joining step according to the present embodiment, laser welding is performed along the welding line 80 of an opposing portion 70 in which the inner wall surface 13 of the case body 10 and the side surface 21 of the sealing plate 20 are opposed to each other.As shown in FIG. 11, the opposing portion 70 before the joining step has a gap G between the inner wall surface 13 of the opening 11 of the case body 10 and the side surface 21 of the sealing plate 20. This gap G is used for smoothly inserting the sealing plate 20 into the opening 11 of the case body 10.As shown in FIG. 11, the battery 1 in a flat shape has a longitudinal direction along the X-axis direction extending in a lateral direction and a short-length direction along the Y-axis direction extending in a vertical direction. Thus, the welding line 80 has a substantially rectangular shape having a longitudinal direction extending in the X-axis direction and a short-length direction extending in the Y-axis direction. The welding line 80 includes longitudinal sections X 1, X 2 that are straight sections extending parallel to the X-axis direction. The welding line 80 includes short-length sections Y 1, Y 2 that are straight sections extending in parallel to the Y-axis direction. In addition, the weld line 80 includes curved sections R 1, R 2, R 3, R 4 each of which connects corresponding two straight sections.In the joining step according to the present embodiment, laser welding for scanning the welding line 80 with the laser beam through a round in a clockwise direction from a start position T indicated at the short-length section Y 1 is performed using the welding apparatus 100. Thus, the controller 180 performs the joining control to control the laser oscillator 110 to output the laser beam, and in this joining control, also performs the scanning control to control the galvanoscanner 150 to scan the welding line 80 with the laser beam. The start position T is one of a plurality of continuous welding points formed on the welding line 80.In the scan control, the controller 180 performs positive short-length scan control to control the galvano scanner 150 to scan the short-length section Y 1 with the laser beam from the start position T in an arrow direction YW 1 that is a positive direction of the Y axis. In the scan control, the controller 180 also performs positive longitudinal scan control to control the galvanoscanner 150 to scan the longitudinal section X 1 with the laser beam in an arrow direction XW 1, which is a positive direction of the X axis. In the scan control, the controller 180 further performs negative short-length scan control to control the galvano scanner 150 to scan the short-length section Y 2 with the laser beam in an arrow direction YW 2 that is a negative direction of the Y axis. In addition, the controller 180 also performs negative longitudinal scan control in the scan control to control the galvanoscanner 150 to scan the longitudinal section X 2 with the laser beam in an arrow direction XW 2 that is a negative direction of the X axis.In the above-mentioned first positive short-length scan control, a part of the short-length section Y1 located on the side of the longitudinal section X2 from the start position T is irradiated with no laser beam. Thus, in the scan control after the negative longitudinal scan control, in order to irradiate the part of the short length section Y1 located on the side of the longitudinal section X2 from the start position T with the laser beam, the positive short length scan control for scanning the section concerned with the laser beam in the arrow direction YW1 is performed again.The controller 180 executes the first to fourth curved scan controls to cause the galvanoscanner 150 to scan the respective curved sections R1, R2, R3, R4 with the laser beam between two sequential controls of the positive short-length scan control, the positive longitudinal scan control, the negative short-length scan control, the negative longitudinal scan control, and the positive short-length scan control, respectively. Specifically, in the scan control, the controller 180 according to the present embodiment executes the positive short-length scan control, the first curved scan control, the positive longitudinal scan control, the second curved scan control, the negative short-length scan control, the third curved scan control, the negative longitudinal scan control, the fourth curved scan control, and the positive short-length scan control in this order.The vicinity of an end position of the scan control may moderately overlap the vicinity of the start position T. This is because the case body 10 can be continuously connected to the sealing plate 20 along the welding line 80. Thus, in the second positive short-length scan control, the galvanoscanner 150 can be controlled to continuously perform the scanning with the laser beam to some extent after the scanning reaches the start position T.In the connection control according to the present embodiment, as the irradiation patterns P with the laser beam, the irradiation patterns P shown in FIGS. 5 and 6 are used. The X axis and the Y axis are indicated in each of FIGS. 5 and 6, respectively. The welding apparatus 100 according to the present embodiment applies the laser beam having the irradiation pattern P shown in each of FIGS. 5 and 6 at a rotational position at which the battery 1 shown in FIG. 11 coincides with the X axis and the Y axis. Specifically, the welding device 100 applies the laser beam such that the rotational position of the battery 1 coincides with the rotational position of the irradiation pattern P in each scan control. More specifically, when the irradiation pattern P shown in FIG. 5 is used, the slide unit 140 is set to the slide position A. When the irradiation pattern P shown in FIG. 6 is used, the slide unit 140 is set to the slide position C. In the present embodiment, whichever irradiation pattern P is formed, control is performed so that the welding line 80 extends through a center of the central region A 1 of the irradiation pattern P.FIG. 12 is a plan view partially showing the vicinity of the start position T of the battery 1. FIG. 12 shows the irradiation pattern P of the laser beam applied along the welding line 80 at respective positions. Specifically, at the start position T at which the connection control is started, the controller 180 controls the slide unit 140 to be set to the slide position A to form the irradiation pattern P including only the outer edge point group SG at the start position T.As shown in FIG. 12, the outer edge point group SG is formed at the start position T on the case body 10 and the sealing plate 20. Specifically, at the start position T, the outer edge points S 31, S 32, S 41, S 42 of the outer edge point group SG are formed on the case body 10, and the outer edge points S 11, S 12, S 21, S 22 are respectively formed on the sealing plate 20.After the connection control is started, the controller 180 according to the present embodiment controls the slide unit 140 to be set to the slide position A until a predetermined initial time has elapsed, and then, at the time when the initial time elapses, controls the slide unit 140 to move slidably to the slide position C. Specifically, after the initial time has elapsed, the position of the incident point LP on the diffractive optical element 130 is controlled to be closer to the non-formation region 132 as compared with the position thereof before the initial time elapses. In other words, after the initial time has elapsed, the area of the incident point LP overlapping the formation region 131 of the diffractive optical element 130 is set to be smaller than the corresponding area before the initial time elapses. With this configuration, the laser beam having the irradiation pattern P with respect to the slide position A is applied to the position of the start position T until the start time elapses, and then the laser beam having the irradiation pattern P with respect to the slide position C is applied after the start time elapses. The controller 180 controls the sliding movement of the slide unit 140 without stopping the irradiation of the laser beam from the laser oscillator 110. Thereby, the welding device 100 according to the present embodiment can vary the distribution profile of the power density of the irradiation pattern P in a shorter time, thus reducing a time required for the laser welding.At the time when the initial time elapses, the controller 180 controls the slide unit 140 to slidably move from the slide position A to the slide position C, and controls the galvano controller 150 to start scanning with the laser beam. As shown in FIG. 12, in the irradiation pattern P shown in the vicinity of the end point of the short-length section Y 1 located at a position ahead from the start position T in the arrow direction YW 1, the central point S 0 and the outer edge point group SG are formed. The central point S 0 is formed on the welding line 80.In the connection control, while the shift unit 140 is controlled to be set to the shift position C, the positive short-length scan control, the first curved scan control, the positive longitudinal scan control, the second curved scan control, the negative short-length scan control, the third curved scan control, the negative longitudinal scan control, the fourth curved scan control, and the positive short-length scan control are executed in this order. With this configuration, in the joining step, it is possible to perform laser welding along the welding line 80 by one round.FIG. 13 shows a sectional view of the short-length sections Y 1, Y 2 and the longitudinal sections X 1, X 2. As can be seen from FIG. 13, when the gap G is present and the gap G is irradiated with the laser beam L, the laser beam L may possibly pass through the gap G, that is, laser passage may possibly occur. When the laser passage occurs, the electrode body and other parts housed inside the housing body 10 may be damaged.To cope with this, in the present embodiment, at the start position T, the connection control is started while the slide unit 140 is set to the slide position A. As described above, at the slide position A, the laser beam is applied to the case body 10 and the sealing plate 20, but no laser beam is applied to the gap G existing in the welding line 80. Thus, it is configured that until the start time when the slide unit 140 is set to the slide position A has elapsed, the laser passage of the laser beam with respect to the irradiation pattern P is prevented from occurring.In the present embodiment, the initial time is defined to be an approximate time period required for a melted portion formed by the outer edge point group SG to reach the gap G, filling the gap G with this melted portion. The initial time may be predefined by performing tests previously.After the initial time has elapsed, when the slide unit 140 is set to the slide position C and the central point S 0 is formed on the welding line 80, the melted portion is already present at the position corresponding to the central point S 0, thus no gap G is present. Specifically, it is configured that after the initial time has elapsed and when the slide unit 140 is set to the slide position C, occurrence of the laser passage of the laser beam with respect to the irradiation pattern P is prevented.In the short-length positive scan control, after the initial time has elapsed, control is performed such that an intermediate part between first and second outer edge points that form vertices of a triangle together with the central point S 0 and the central point S 0 are each caused to pass through each welding point of the welding line 80 in the order of the intermediate part between first and second outer edge points that form vertices of the triangle together with the central point S 0 and the central point S 0. Specifically, in the short-length positive scan control, the intermediate part between the outer edge points S 11, S 12, which are the first outer edge point, and the outer edge points S 41, S 42, which are the second outer edge point, is made to pass through the welding point on the welding line 80. The central point S 0 is then made to pass through the welding point on the welding line 80 through which the intermediate part between the outer edge points S 11, S 12 and the outer edge points S 41, S 42 has already passed. That is, in the short-length positive scanning control, the outer edge dots S 11, S 12, S 41, S 42 are formed at a position ahead of the central dot S 0 in the scanning direction in the arrow direction YW 1. The outer peripheral points S 41, S 42 are formed at a position on the case body 10 in front of the central point S 0, and the outer peripheral points S 11, S 12 are formed at a position on the sealing plate 20 in front of the central point S 0.Accordingly, in the short-length positive scan control, a part of the case body 10 located ahead of the central point S 0 is melted by the outer edge points S 41, S 42, and a part of the sealing plate 20 located ahead of the central point S 0 is melted by the outer edge points S 11, S 12 at the same time. In the positive short-length scan control, it is possible to perform the scan with the laser beam while filling the gap G in advance to the central point S 0. Accordingly, in the positive short-length scan control, after the start time has elapsed, it is configured to prevent the laser passage of the laser beam from occurring with respect to the irradiation pattern P.The positive longitudinal scan control, the negative short-length scan control, and the negative longitudinal scan control, which are the scan control in the other straight sections, are executed in the same manner as that of the positive short-length scan control described above. Specifically, for example, in the positive longitudinal scan control, the intermediate part between the first outer edge point outer edge points S 11, S 12 and the second outer edge point outer edge points S 21, S 22 that form vertices of a triangle together with the central point S 0 is first made to pass through each welding point on the welding line 80. The central point S 0 is then made to pass through the welding point on the welding line 80 through which the intermediate part between the outer edge points S 11, S 12 and the outer edge points S 21, S 22 has already passed. In the positive longitudinal scanning control, the outer peripheral points S11, S12, S21, S22 are also formed in advance to the central point S0 in the scanning direction of the laser beam. In addition, in the positive longitudinal scan control, the outer edge points S 11, S 12 are formed on the case body 10, and the outer edge points S 21, S 22 are formed on the sealing plate 20. Accordingly, in each straight portion, it is configured to prevent occurrence of the laser passage of the laser beam with respect to the irradiation pattern P.In the short-length positive scan control according to the present embodiment, the intermediate part between each two adjacent first and second outer edge points among the outer edge points that respectively form vertices of a rectangle surrounding the central point S 0 is caused to pass through the welding point on the welding line 80. The central point S 0 is then caused to pass through the welding point on the welding line 80 through which the intermediate part of the first and second outer edge points has already passed. Subsequently, the intermediate part between the third and fourth outer edge points different from the first and second outer edge points among the outer edge points that respectively form the vertices of the rectangle is made to pass through the welding point on the welding line 80 through which the central point S 0 has already passed. Specifically, in the short-length positive scan control, the intermediate part between the first outer edge point outer edge points S 11, S 12 and the second outer edge point outer edge points S 41, S 42 is first made to pass through the welding point on the welding line 80. The central point S 0 is then made to pass through the welding point on the welding line 80 through which the intermediate part between the outer edge points S 11, S 12 and the outer edge points S 41, S 42 has already passed. Subsequently, the intermediate part between the outer edge points S 21, S 22, which are the third outer edge points, and the outer edge points S 31, S 32, which are the fourth outer edge points, is made to pass through the welding point on the welding line 80 through which the central point S 0 has already passed. Specifically, in the short-length positive scan control, the outer edge points S 11, S 12, S 41, S 42 are formed at positions forward to the central point S 0, and the outer edge points S 21, S 22, S 31, S 32 are formed at positions rearward to the central point S 0. Further, the outer edge points S 31, S 32 are respectively formed at a part of the case body 10 located rearward of the central point S 0, and the outer edge points S 21, S 22 are formed at a part of the sealing plate 20 located rearward of the central point S 0.With this configuration, in the short-length positive scan control, it is possible to suppress rapid decrease in the temperature of the case body 10 located rearward of the central point S 0 by the outer edge points S 31, S 32. It is also possible to suppress rapid decrease in the temperature of the sealing plate 20 located rearward of the central point S 0 by the outer edge points S 21, S 22. Accordingly, in the positive short-length scan control, by suppressing the rapid decrease in the temperature of the melted portion formed after the central point S 0 passes through, it is possible to perform the laser beam scan while suppressing generation of fractures or the like. In other words, it is possible to suppress occurrence of the laser pass by using the outer edge points located ahead of the central point S 0, and also suppress generation of fractures or the like by using the outer edge points located rearward of the central point S 0.The positive longitudinal scan control, the negative short-length scan control, and the negative longitudinal scan control, which are the scan control in the other straight sections, are executed in the same manner as that in the positive short-length scan control described above. Specifically, for example, in the positive longitudinal scan control, the intermediate part between the outer edge points S 11, S 12, which are the first outer edge point, and the outer edge points S 21, S 22, which are the second outer edge point, is caused to pass through each welding point on the welding line 80. The central point S 0 is then made to pass through the welding point on the welding line 80 through which the intermediate part of the outer edge points S 11, S 12 and the outer edge points S 21, S 22 has already passed. Subsequently, the intermediate part between the outer edge points S 31, S 32, which are the third outer edge points, and the outer edge points S 41, S 42, which are the fourth outer edge points, is made to pass through the welding point on the welding line 80 through which the central point S 0 has already passed. Specifically, the outer peripheral points S 11, S 12, S 21, S 22 are formed at positions ahead of the central point S 0, and the outer peripheral points S 31, S 32, S 41, S 42 are formed at positions rearward of the central point S 0. Further, the outer edge points S 41, S 42 are formed on a part of the case body 10 rearward of the central point S 0, and the outer edge points S 31, S 32 are formed on a part of the sealing plate 20 rearward of the central point S 0. Thereby, in each straight section, it is configured that the laser passage of the laser beam with respect to the irradiation pattern P is suppressed as well as rapid decrease in the temperature of the melted portion is suppressed, thus preventing generation of fractures or the like.In the positive short-length scan control, the positive longitudinal scan control, the negative short-length scan control, and the negative longitudinal scan control according to the present embodiment, as described above, the slide unit 140 is set to the slide position C, whereby the welding line 80 where the joined portion 30 is formed is irradiated with the laser beam having a higher power density. Thus, it is possible to form the melted portion having a deeper depth in a shorter time. Accordingly, it is possible to increase the scanning speed of the laser beam in the positive short-length scan control, the positive longitudinal scan control, the negative short-length scan control, and the negative longitudinal scan control. Accordingly, it is possible to suppress generation of errors due to the laser pass, and to perform the laser welding in the joining step in a shorter time.As shown in FIG. 12, in the curved section R 1, the outer edge point S 12 located at a head position of the outer edge point group SG in the scanning direction of the laser beam passes over the gap G. In the curved section R 1 shown in a sectional view of FIG. 14, a supporting surface 12 is provided at a downward position of the inner wall surface 13 of the opening 11 of the case body 10 in a manner to protrude inward from the inner wall surface 13. The supporting surface 12 is a surface used for accommodating an inner surface 22 of the sealing plate 20 fitted into the opening 11 of the case body 10.In the curved section R 1, even when the laser beam L enters the gap G with respect to the outer edge points S 2 of the outer edge point group SG, the laser beam L that has entered irradiates the supporting surface 12 of the case body 10.The configuration is the same in the curved sections R 2, R 3, R 4 different from the curved section R 1. Superficially, in the curved sections R 2, R 3, R 4, it is also configured that the outer edge point located at the head of the outer edge point group SG in the scanning direction of the laser beam passes over the gap G. Thus, in each of the curved sections R 2, R 3, R 4, as shown in the sectional view of FIG. 14, the support surface 12 is also provided at a downward position of the inner wall surface 13 of the opening 11 of the case body 10 in a manner protruding inward from the inner wall surface 13. Thereby, in the curved sections R 2, R 3, R 4, it is also configured to prevent occurrence of the laser passage of the laser beam with respect to the irradiation pattern P.No laser beam scanning is performed from the start of connection control until the start time elapses, and the laser beam scanning is started after the start time elapses. However, the laser beam scanning may be started before the initial time elapses.However, while the slide unit 140 is set to the slide position A, no central point S 0 is formed on the welding line 80, and thus a longer time is likely to be required for forming the melted portion having a sufficient depth than in the case where the slide unit 140 is set to the slide position C. Thus, when the laser beam scan is started before the start time elapses, the scanning speed of the laser beam before the start time elapses may be slower than the scanning speed after the start time elapses.On the other hand, after the initial time has elapsed and the slide unit 140 has been made to slide to the slide position C, the scanning speed of the laser beam may be set to be faster than that before. This makes the time required for connection control shorter. Specifically, in the welding apparatus 100, in order to perform the connection control in a shorter time while the slide unit 140 is set to the slide position C, the scanning speed of the laser beam may be set to be faster than the scanning speed while the slide unit 140 is set to the slide position A.In addition, when the slide unit 140 is controlled to move slidably from the slide position A to the slide position C after the laser beam scanning is started, the laser beam scanning may be stopped once before the slide movement, and the laser beam scanning may be restarted after the slide movement is completed. However, the slide unit 140 may be controlled to move slidably from the slide position A to the slide position C while the laser beam scanning is being performed. When the laser beam scanning is stopped, the time required for the connection control becomes longer by the time spent stopping the scanning. Thus, the incident point LP is changed while the laser beam scanning is performed at the same time, thereby reducing the time required for the connection control.In the present embodiment, no supporting surface 12 shown in the sectional view of FIG. 14 is required at any part in each straight section of the case body 10. Accordingly, in the present embodiment, a case body having a simple shape having no protrusion such as the supporting surface 12 in the straight sections can be used as the case body 10. For example, when the case body 10 is formed using a mold, this mold can be produced at a lower cost.When parts in which the supporting surfaces 12 are formed and parts in which no supporting surfaces 12 are formed are both present on the welding line 80, the joined portion 30 may not be formed uniformly over the parts having the supporting surface 12 and the parts having no supporting surface 12. This is because a heat capacity becomes different between the parts having the supporting surfaces 12 and the parts having no supporting surfaces 12. That is, in the present embodiment, it is possible to uniformly form the joined portion 30 in the longitudinal sections X 1, X 2 and the short-length sections Y 1, Y 2 that are straight sections.As indicated by alternate long and two short dash lines in FIGS. 13 and 14, a groove 23 may be formed on the upper surface of the sealing plate 20. The groove 23 may be formed on the upper surface of the sealing plate 20 along the side surface 21 by a round. This is because it can be suppressed that a quantity of heat supplied to the sealing plate 20 by the irradiating laser beam in the connection control is transferred to the inside of the sealing plate 20. Specifically, the vicinity of the side surface 21 of the sealing plate 20 can be appropriately heated and melted by the laser beam.In the above description, the shift unit 140 is set to the shift position A after the connection control is started until the initial time elapses. However, the slide position of the slide unit 140 until the initial time elapses is not limited to the slide position A, but may be any slide position in which the incident point LP is located within the formation area 131. This is because, in the state where the incident point LP is located within the formation region 131, the distribution profile of the power density of the irradiation pattern P of the laser beam becomes the same as that in the state where the slide unit 140 is located at the slide position A.In the above description, after the initial time has elapsed, the slide unit 140 is set to the slide position C. However, the slide position of the slide unit 140 after the initial time has elapsed is not limited to the slide position C, but may be any slide position within a range in which the incident point LP overlaps the boundary 133. When there is another shift position preferable for the distribution profile of the power density of the irradiation pattern P formed more than the shift position C, it is preferable to set the shift unit 140 to this shift position.The connection control may be performed when the case body 10 is fixed. This is because the case body 10 is fixed to accurately perform the laser beam scanning along the welding line 80. The case body 10 can be fixed by holding the outer side surfaces of the case body 10 from the X-axis direction and the Y-axis direction in FIG. 11.In the welding apparatus 100 according to the present embodiment, as the diffractive optical element 130, one including the formation region 131 and the non-formation region 132 is used. The distribution profile of the power density of the irradiation pattern P becomes different depending on the state in which the incident point LP is located in the formation region 131 or the state in which the incident point LP overlaps the boundary 133. Specifically, the present embodiment realizes the diffractive optical element 130 capable of varying the irradiation pattern P to have a plurality of different distribution profiles of the power densities while reducing the area on which the diffraction grating is formed. Accordingly, it is possible to achieve a reduction in cost for the diffractive optical element 130.When the slide unit 140 is set to the slide position A, it is possible to radiate a radiated beam having a higher power density to the outer edge point group SG of the outer edge region A 2 rather than the central point S 0 of the central region A 1. When the slide unit 140 is set to the slide position C, it is possible to radiate a radiated beam with a higher power density to the central point S 0 of the central area A 1 rather than to the outer edge point group SG of the outer edge area A 2 in the irradiation position. That is, by setting the slide unit 140 to the slide position A, it is possible to increase a melt amount in the outer peripheral area A 2. On the other hand, by setting the slide unit 140 at the slide position C, it is possible to increase a melt amount in the central region A 1. In the present embodiment, it is possible to perform laser welding by selectively increasing the amount of melting in the central region A 1 or increasing the amount of melting in the outer peripheral region A 2.The present inventors have carried out the test described below to verify advantageous effects of connection control using the welding device 100 according to the present embodiment. The present test has been performed in an embodiment and comparative examples 1, 2 which are different from the present embodiment.Specifically, in the respective embodiment and Comparative Examples 1, 2, laser welding has been performed by respective different joining controls in the short-length section Y 1 of the battery 1 described above. In the embodiment, the connection control has been executed such that the slide unit 140 has been set to the slide position A until the initial time has elapsed, and the slide unit 140 has been set to the slide position C after the initial time has elapsed. Specifically, in the embodiment, the connection control has been executed while at least one point of the incident point LP has been moved over the boundary 133 by control of the slide unit 140. In the connection control in the embodiment, laser beam scanning has not been performed until the initial time has elapsed, and laser beam scanning has been started after the initial time has elapsed.Meanwhile, in Comparative Example 1, the connection control has been executed such that the slide unit 140 has been set to the slide position A from the start to the completion of the control. In Comparative Example 2, the connection control has been executed such that the slide unit 140 has been set to the slide position C from the start to the completion of the control. In each of Comparative Examples 1, 2, the connection control has been performed while the incident point LP is fixed with respect to the diffractive optical element 130 without slidably moving the slide unit 140. In each of Comparative Examples 1, 2, as in the embodiment, no laser beam scanning has been carried out until the initial time has elapsed, and the laser beam scanning has been started after the initial time has elapsed.Fig. 15 shows results of the present test. In FIG. 15, a horizontal axis indicates a position in the short length section Y 1, and a more right position in the horizontal axis indicates a more downstream position in the laser beam scanning direction. The start position T at which the connection control has been started is indicated in the horizontal axis. A vertical axis indicates a depth of each connected portion formed by irradiation with the laser beam. The depth of each connected portion has been obtained by considering a section of the connected portion formed after each connection control of the embodiment and the comparative examples 1, 2 has been performed.As shown in FIG. 15, in the embodiment, the joined portion having a depth deeper than that in Comparative Examples 1, 2 has been formed over the entire short-length section Y 1 where the joining control has been executed. That is, in the embodiment, at the initial time when the joining control has been started, the vicinity of the welding line 80 could be melted to a sufficient depth by the outer edge point group SG. In addition, during the laser beam scanning after the elapse of the initial time, the laser beam scanning has been performed in a manner that the central point S 0 having a higher power density has been formed on the welding line 80 that has been the joined portion forming position.In the embodiment, as described above, before the initial time has elapsed, the slide unit 140 has been set to the slide position A to irradiate the gap G with no laser beam. Thus, the laser passage at the gap G has been suppressed before the initial time has elapsed. As described above, after the initial time has elapsed, the fused portion has been formed at a pre-position in the scanning direction of the central point S0 by the outer edge point group SG. Thus, in the embodiment, after the initial time has elapsed, the laser passage at the gap G has also been suppressed.In contrast, it was found that over the entire short length section Y 1, the joined portion formed in Comparative Example 1 had a depth that was about half as deep as that of the joined portion of the embodiment. This is because, in Comparative Example 1, the welding line 80 that was the bonded portion forming position has not been irradiated with a laser beam. In Comparative Example 1, the slide unit 140 has been set to the slide position A from the start to the completion of the connection control. Accordingly, in Comparative Example 1, the laser passage at the gap G was suppressed.In Comparative Example 2, the joined portion had a shallower depth in the vicinity of the start position T. This is because the slide unit 140 has been set to the slide position C from the start of the connection control and the power density has been lower at the outer edge point group SG, so that the vicinity of the welding line 80 has not been sufficiently melted. In Comparative Example 2, the depth of the joined portion has gradually become deeper as the laser beam scanning has advanced, and thus the joined portion having substantially a constant depth has been formed. It was found that the depth of the joined portion at the position concerned was not as deep as in the comparative example, but was moderately deep. However, in Comparative Example 2, the slide unit 140 has been set to the slide position C even at the start time of the connection control. Thus, in Comparative Example 2, the laser passage has occurred at the gap G from the start of the connection control.In the present test, it has been verified that the laser passage can be suppressed appropriately in the embodiment according to the present embodiment. In the embodiment according to the present embodiment, the joined portion having a depth deeper than that in Comparative Examples 1, 2 has been formed over the entire short-length section Y 1 in which the connection control has been performed. Accordingly, in the present test, in the embodiment according to the present embodiment, it is verified that it is possible to increase the scanning speed of the laser beam scan to be faster than that in both Comparative Examples 1, 2 and form the joined portion having a desired depth.As described above in detail, the joining step of joining the case body 10 and the sealing plate 20 to each other is performed by using the welding device 100. The welding device 100 comprises the diffractive optical element 130 and the sliding unit 140. The diffractive optical element 130 includes the forming region 131 and the non-forming region 132 which are adjacently arranged. The shifter 140 is controlled to change the position of the incident point LP of the incident beam Li entering the optical element 130, thereby varying the power density distribution profile of the irradiation pattern P. In this way, it is possible to perform laser welding through flexible control. While controlling the laser oscillator 110 to output the laser beam, the controller 180 of the welding apparatus 100 controls the slide unit 140 to move slidably from the slide position A to the slide position C. Specifically, while the laser oscillator 110 outputs the laser beam, at least one point in the incident point LP is moved over the boundary 133 by controlling the slide unit 140. By doing so, it is possible to suppress generation of errors as well as to form the joined portion in a shorter time.[Second Embodiment]The second embodiment will be described below. In the present embodiment, unlike the first embodiment, a provisional fixing step for forming provisional fixed portions on the welding line is performed in advance before the joining step. A battery as a connection target is the same as that in the first embodiment. In the present embodiment, the procedure described below is performed: 1. provisional fixing step and 2. joining step.„1. Provisional fixing step" will be described below. The present step is carried out before "2nd joining step". The present step is carried out while the sealing plate 20 is inserted into the opening 11 of the case body 10, as shown in FIG. 11. In the present step, a part of the welding line 80 is irradiated with the laser beam to melt a portion irradiated with the laser beam into a provisionally fixed portion. In the present embodiment, the provisional portions are formed in total at eight positions indicated by provisional positions K in FIG. 11. The case body 10 and the sealing plate 20 are partially joined to each other at the provisional positions K at which the provisional fixed portions are formed.In the present step, the welding apparatus 100 described above is also used. In the present step, the controller 180 of the welding apparatus 100 is configured to execute provisional fixation control. The controller 180 also controls the laser oscillator 110 to output the laser beam. The controller 180 controls the galvanoscanner 150 in a manner to irradiate each provisional position K with the laser beam. In the provisional fixing control according to the present embodiment, the controller 180 does not perform laser beam scanning via the galvano scanner 150 during irradiation of the laser beam. However, the laser beam scanning may be performed in the vicinity of each provisional position K along the welding line 80 within a shorter range than the welding line 80.In addition, in the provisional fixing control, the controller 108 according to the present embodiment controls the slide unit 140 to be set to the slide position A. Specifically, in the present embodiment, during execution of the provisional fixing control, the slide unit 140 does not execute a slide motion.The irradiation pattern P formed in the provisional fixing control includes only the outer edge point group SG shown in FIG. 5 because the slide unit 140 is set to the slide position A. Thus, in the provisional fixing control, no central point S 0 is formed at the provisional position K. That is, in the provisional fixing control, it is configured to prevent occurrence of the laser passage of the laser beam with respect to the irradiation pattern P.After "1st provisional fixing step", "2nd joining step" is carried out. In the present embodiment, "2nd joining step" is performed in the same manner as in the first embodiment. In other words, this step is performed by the joining control to perform laser welding along the welding line 80 through one round using the welding device 100. That is, in the joining step according to the present embodiment, it is also possible to suppress generation of errors due to the laser pass or the like and to simultaneously perform the laser welding in a shorter time.In the connection control, as described above, the scanning with the laser beam is performed along the welding line 80 by one round. For example, in the case of using the sealing plate 20 having a thinner thickness and a lower thickness, when the joining step is performed without performing the provisional fixing step, the sealing plate 20 may possibly be deformed while the laser beam scanning is performed along the welding line 80. This deformation of the sealing plate 20 is caused by local temperature increase due to laser beam irradiation or by the sealing plate 20 being pulled by the joined portion 30 formed.For example, when the sealing plate 20 is deformed, the side surface 21 of the sealing plate 20 separates from the inner wall surface 13 of the opening 11 of the case body 10 at the opposing portion 70 where the joined portion 30 is not yet formed. When the side surface 21 of the sealing plate 20 is apart from the inner wall surface 13 of the opening 11 of the case body 10, a melted portion is not properly formed by the irradiation of the laser beam at a position where the inner wall surface 13 is deviated from the side surface 21; thus, connection errors may possibly be caused at the position.To cope with this, in the present embodiment, the provisional fixing step is performed before the joining step to partially join the case body 10 and the sealing plate 20 to each other. In the joining step, it is configured to suppress a deviation between the inner wall surface 13 of the opening 11 of the case body 10 and the side surface 21 of the sealing plate 20 during the laser beam scanning along the welding line 80 by one round. With this configuration, it is possible to properly form the joined portion 30 in an annular shape along the welding line 80 by one round in the joining step.FIG. 11 shows the provisional positions K at a total of eight positions. However, the provisional positions K may be provided at arbitrary positions, and the number thereof may be an arbitrary number.When there are the longitudinal sections X 1, X 2 as in the present embodiment, there is a tendency that a deviation occurs between the inner wall surface 13 of the opening 11 of the case body 10 and the side surface 21 of the sealing plate 20 at a position far from the start position T at which the connection control is started. Thus, the plurality of provisional positions K may be provided in the longitudinal sections X 1, X 2.In the present embodiment, the welding device 100 may be used in the provisional fixing step in addition to the joining step. In other words, the provisional fixing step and the joining step may be performed by a control of a single welding device 100 to perform the provisional fixing control and the joining control. This is because the welding device 100 is capable of performing the laser welding by the flexible controller. Further, it is not necessary to provide an additional device for executing the provisional fixing step.For example, as shown in a plan view of FIG. 16, when the provisional fixing step is performed by using an irradiation pattern PH having only the central point S 0, it is impossible to irradiate the provisional position K with the laser beam with respect to the irradiation pattern PH at the start time of this irradiation. This is because at the start time of irradiation with the laser beam, the gap G is present at the provisional position K.Thus, when the irradiation pattern PH is used, as shown by an alternate long and two short dash line in FIG. 16, at the start time of irradiation with the laser beam, the laser beam having the irradiation pattern PH should be applied to the sealing plate 20, for example. After the sealing plate 20 has been melted and the melted portion fills the gap G, the laser beam having the irradiation pattern PH should be moved to the provisional position K to melt the vicinity of this provisional position K of the case body 10 as well. In this case, however, it is impossible to melt the vicinity of each provisional position K of the case body 10 until the melted portion of the sealing plate 20 fills the gap G; accordingly, a longer time is required for the provisional fixing step.In contrast, when the provisional fixing step performed by the provisional fixing control using the welding device 100 according to the present embodiment, it is possible to irradiate each provisional position K with the laser beam at the start time of irradiation. This is because the irradiation pattern P shown in FIG. 5 used in the provisional fixing control is configured only by the outer edge point group SG, so that no laser passage is caused even when the provisional position K is irradiated with the laser beam. It is possible to melt the vicinity of the provisional position K between the case body 10 and the sealing plate 20 by the laser beam having the irradiation pattern P applied to the provisional position K at the start time of irradiation with the laser. Thus, according to the present embodiment, it is possible to execute the provisional fixing step in a shorter time.As shown in FIG. 16, when the provisional fixing step is performed by using the laser beam having the irradiation pattern PH configured only by the central point S 0, it is impossible to form the groove 23 in the vicinity of each provisional position K; thus, it is necessary to provide a section H in which no groove 23 is present. As described above, when the provisional fixing step is performed using the laser beam having the irradiation pattern PH, it is necessary to irradiate the sealing plate 20 with the laser beam having the irradiation pattern PH in order to melt the sealing plate 20 at the start time of the laser beam irradiation and fill the gap G with this melted portion. Accordingly, when the groove 23 is formed in the portion H, an amount of the melted portion of the sealing plate 20 melted by the laser beam having the irradiation pattern PH becomes smaller; thus, a longer time is required to fill the gap G with the melted portion at the provisional position K. It may be impossible to properly fill the gap G at the provisional position K if the amount of the melted portion is too small.In addition, when the section H in which no groove 23 is formed is provided, it may be impossible to uniformly form the joined portion 30 during the connection control. Connection errors may possibly be caused at a position corresponding to the above-mentioned section H. This is because the section H has a different heat capacity from those of the other sections in which the groove 23 is formed.In contrast, in the provisional fixing step performed by the provisional fixing control using the welding apparatus 100 according to the present embodiment, the laser beam can be applied to the provisional position K at the start time of the laser beam irradiation, thus it is not necessary to provide the section H that does not include the groove 23. Thus, the groove 23 can be formed on the sealing plate 20 by one round. Accordingly, it is possible to suppress connection failures as well as to form the connected portion 30 smoothly without causing connection failures.The provisional fixing control may be performed with the case body 10 fixed. In the present embodiment, the case body 10 can be held and fixed before the provisional fixing control is executed, and after the connection control is executed, this fixing can be released. Both the provisional fixing step and the joining step may be performed at a time with this single holding.In the above description, in the provisional fixing step, the slide unit 140 is set to the slide position A. However, the slide unit 140 in the provisional fixing control may be set not only to the slide position A but also to any slide position within a range where the incident point LP is located in the formation region 131. In the state where the incident point LP is located in the formation area 131, the distribution profile of the power density of the irradiation pattern P of the irradiating laser beam becomes the same as that in the state where the slide unit 140 is set to the slide position A.As described above in detail, in the present embodiment, the provisional fixing step is also carried out in addition to the joining step. In the provisional fixing step, the welding device 100 is also used, and the provisional fixing step is performed by allowing the welding device 100 to execute the provisional fixing control. In the provisional fixing control, the welding device 100 controls the slide unit 140 to be set to the slide position A, and each provisional position K is irradiated with the laser beam to form the provisional fixed portion. Consequently, no laser pass takes place in the provisional fixation control. In addition, it is possible to reduce the time required for provisional fixation control. After the provisional fixing step, the same joining step as that in the first embodiment is performed by the joining control performed by the controller 180 of the welding apparatus 100. Accordingly, it is possible to suppress generation of errors in connection control and also to form the connected portion 30 having higher quality by connection control.[Third Embodiment]The third embodiment will be described below. In the present embodiment, unlike the above embodiments, a gap detecting step for detecting a dimension of a gap between the inner wall surface of the opening of the case body and the side surface of the sealing plate on the welding line is performed before the joining step. The battery as a connection target in the connection step is the same as that in the first embodiment. The present embodiment is carried out in the following procedure: 1. provisional fixing step, 2. gap detection step, and 3. connection step.In the present embodiment, the welding device 100 is used in "1st provisional fixing step" and "3rd joining step". The welding device 100 is controlled to execute the provisional fixing control in "1st provisional fixing step" and execute the joining control in "3rd joining step". In the present embodiment, "1st provisional joining step" is the same as in the second embodiment. However, in the present embodiment, the connection control executed in "3rd connection step" is different from that in the above-described embodiments. "3rd connection step" according to the present embodiment will be described in detail below.In the present embodiment, "2nd gap detection step" is performed before "3rd connection step". "2nd gap detection step" will be described below. In the present step, a laser displacement sensor 190 shown in FIG. 17 is used. The laser displacement sensor 190 is attached to the welding apparatus 100 of each of the above embodiments. Specifically, the welding apparatus 100 according to the present embodiment includes the laser displacement sensor 190 in addition to the configurations described in the above embodiments. The battery 1 shown in FIG. 17 is in a state where a connected portion is not yet formed. However, the provisionally fixed portions are already formed.As shown in FIG. 17, measurement is performed on the battery 1 using the laser displacement sensor 190. A measurement position by the laser displacement sensor 190 is a central position in the longitudinal direction on the upper surfaces of the case body 10 and the sealing plate 20.FIG. 18 shows measurement results of the battery 1 by the laser displacement sensor 190. In FIG. 18, measurement positions are shown on a horizontal axis, and heights are shown on a vertical axis. As shown in FIG. 18, the measurement results represent respective heights at the upper surfaces of the case body 10 and the sealing plate 20. Portions having lower levels than the respective upper surfaces of the case body 10 and the sealing plate 20 appear between the case body 10 and the sealing plate 20.Thus, these lower level portions between the case body 10 and the sealing plate 20 can be detected as gaps G 1, G 2, respectively. The gap G 1 is a gap G at a center of the longitudinal section X 1, and the gap G 2 is a gap G at a center of the longitudinal section X 2. Thus, the respective detected positions of the gaps G 1, G 2 correspond to welding points disposed at respective centers of the longitudinal sections X 1, X 2 on the welding line 80. It is possible to detect respective dimensions of the gaps G1, G2 based on the measurement results shown in FIG. 18.The controller 180 of the welding apparatus 100 first obtains respective detected dimensions of the gaps G 1, G 2 in "3rd joining step" before starting the joining control. The controller 180 of the welding apparatus 100 according to the present embodiment performs the joining control depending on the obtained dimensions of the gaps G 1, G 2. Specifically, in the connection control, the controller 180 according to the present embodiment performs laser control to vary the slide position of the slide unit 140 depending on the obtained dimensions of the gaps G 1, G 2.Here, there is a correlation between the dimension of the gap G and the slide position when the gap G and the slide position can properly form the connected portion. A description regarding the relationship will be provided below. FIG. 19 is a graph showing a relationship between a ratio of the power density of the central point S 0 and a depth of a formed connected portion. In FIG. 19, a horizontal axis represents the proportion of the power density of the central point S 0, and a vertical axis represents the depth of the joined portion. At an end portion of a left position of the horizontal axis, a proportion of the power density of the central point S 0 when the slide position of the slide unit 140 is located near the slide position A is shown. At an end portion of a right position in the horizontal axis, a proportion of the power density of the center point S 0 when the slide position of the slide unit 140 is located near the slide position D is shown.In FIG. 19, a graph of the gap G having a dimension of 10 μm is indicated by a solid line, and a graph of the gap G having a dimension of 50 μm is indicated by a broken line. These graphs have been obtained by observing sections of respective joined portions between the case body 10 and the sealing plate 20 provided with the gaps G having the respective dimensions on the welding line 80, and the joined portions have been formed by being irradiated with the laser beam for a certain time while the slide unit 140 has been set at different slide positions.As shown in FIG. 19, it has been found that in the gap G of 10 μm, the joined portion having a deeper depth can be formed as the ratio of the power density of the central point S 0 is higher. Specifically, it has been found that in the gap G of 10 μm, the connected portion having a deeper depth is likely to be formed when the slide unit 140 is set to a slide position that is closer to the slide position D.On the other hand, it has been found that in the gap G of 50 μm, the joined portion having a deeper depth can be formed as the ratio of the power density of the central point S 0 is lower. Specifically, it has been found that in the gap G of 50 μm, the connected portion having a deeper depth is likely to be formed when the slide unit 140 is set to a slide position that is closer to the slide position A.FIG. 19 shows a depth DT of the connection portion. The depth DT is a depth of the joined portion required for properly joining the case body 10 and the sealing plate 20 to each other. Specifically, it has been found that in the gap G of 10 μm, in order to correctly form the joined portion, it is preferable to form the irradiation pattern P having a ratio of a power density of the central point S 0 equal to or more than a ratio PT 2 illustrated on the horizontal axis. Thus, the ratio of the power density of the central point S 0 may be defined to be the ratio PT 2 or more to form the proper connected portion when the gap G is 10 μm.On the other hand, it has been found that in the gap G of 50 μm, in order to correctly form the joined portion, it is preferable to form the irradiation pattern P with a ratio of a power density of the central point S 0 equal to or less than a ratio of PT 1 illustrated on the horizontal axis. Thus, the ratio of the power density of the central point S 0 may be defined to be the ratio PT 1 or less to form the proper connected portion when the gap G is 50 μm.By obtaining graphs as in FIG. 19 for respective gaps G having different dimensions, it is possible to define the ratio of the power density of the central point S 0 for each gap G having each dimension that can properly form the connected portion.FIG. 20 is a graph showing a relationship between the gap G and the ratio of the power density of the central point S 0. FIG. 20 shows the graph formed to define the proportion of the power density of the central point S0that can properly form the connected portion depending on each dimension of the gap G.As shown in FIG. 20, the ratio of the power density of the central point S 0 that can properly form the connected portion becomes smaller as the gap G becomes larger. On the basis of this, it has been found that it is preferable to set the slide unit 140 to a slide position that is closer to the slide position A as the gap G is larger. Specifically, it has been found that it is preferable to set the position of the incident point LP to a position that is closer to the formation region 131 as the gap G is larger. In other words, it has been found that it is preferable to set an area of the incident point LP overlapping the formation region 131 of the diffractive optical element 130 to be larger as the gap G is larger. This relationship is referred to as a gap-slide position relationship.In the laser control, the controller 180 according to the present embodiment controls the slide unit 140 based on the above-described gap-slide position relationship. Thus, the controller 180 according to the present embodiment includes a storage unit 181 indicated by an alternate long and two short dash line in FIG. 2, and stores a gap shift position table shown in FIG. 21 in the storage unit 181.The gap-slide position table shown in FIG. 21 is generated based on the aforementioned gap-slide position relationship. Specifically, the gap slide position table shown in FIG. 21 is defined such that the slide position of the slide unit 140 is closer to the slide position A as the gap G is larger.The gap shift position table shown in FIG. 21 is defined such that when the gap G is equal to or less than a gap GT 1 shown on the horizontal axis, the shift position is set to a shift position C 1. When the slide unit 140 is set to the slide position D, the irradiation pattern P is configured only by the central point S 0, and thus the laser passage may be caused even if the gap G is small. Thus, when the gap G is equal to or less than the gap GT 1, the slide unit 140 is set to the slide position C 1, thereby filling the gap G in advance to the central point S 0 with the melted portion formed by the outer edge point group SG.The gap slide position table shown in FIG. 21 is generated such that when the gap G is equal to or more than a gap GT 2 shown on the horizontal axis, the slide position is set to the slide position A. As described above, within a range from the shift position A to the shift position B where the incident point LP is located within the formation region 131, the incident beam Li enters only the formation region 131 of the diffractive optical element 130. Thus, even if the slide position of the slide unit 140 is changed within the range in which the incident point LP is located within the formation region 131, the irradiation pattern P of the irradiating laser beam becomes the same.In the connection step according to the present embodiment, the controller 180 obtains respective dimensions of the gaps G 1, G 2 detected in the gap detection step before execution of the connection control. However, the gaps G 1, G 2 detected in the present embodiment are the respective gaps G in the longitudinal sections X 1, X 2. Thus, in the short length sections Y1, Y2 and the curved sections R1, R2, R3, R4 different from the longitudinal sections X1, X2, the connection control is performed in the same manner as in the first embodiment. The connection control in the present embodiment is also the same as that in the above-described embodiments in parts other than the laser control performed in the longitudinal sections X 1, X 2.Specifically, in the present embodiment, at the start time of the connection control, the controller 180 controls the slide unit 140 to be set to the slide position A, and as shown in FIG. 12, only the outer edge point group SG is formed at the start position T. After the initial time has elapsed, the slide unit 140 is controlled to move slidably from the slide position A to the slide position C to start the positive short-length scan control for scanning the short-length section Y1 with the laser beam. Subsequent to the positive short-length scan control, the first curved scan control for scanning the curved section R 1 with the laser beam is executed.When the first curved scan control is completed, the controller 180 performs the laser control. Specifically, in the laser controller, the slide unit 140 is controlled to slidably move from the slide position C to a slide position corresponding to the gap G 1. By the completion of the first curved scan control, the controller 180 refers to the gap shift position table (FIG. 21 ) based on the gap G 1, defining the shift position corresponding to the gap G 1.By the laser control, the slide unit 140 is controlled to be set to the slide position corresponding to the gap G 1, and the longitudinal section X 1 is scanned with the laser beam by the positive longitudinal scanning control at the same time. In this way, the proper connected portion 30 can be formed in the longitudinal section X1. The reason for this is that it is possible to adjust the power density of the central point S 0 in the irradiation pattern P to be a power density sufficient for forming the proper connected portion at the position corresponding to the dimension of the gap G 1, and to perform the positive longitudinal scan control at the same time. Of course, when the slide position defined based on the gap G 1 with reference to the gap slide position table is the slide position C, it is not necessary to control the slide unit 140 to move slidably in the laser controller.Upon completion of the positive longitudinal scan control, the controller 180 controls the slide unit 140 to slidably move to the slide position C. In addition, while the shift unit 140 is controlled to be set to the shift position C, the second curved scan control, the negative short-length scan control, and the third curved scan control are respectively executed to scan the curved section R 2, the short-length section Y 2, and the curved section R 3 with the laser beam, respectively.Upon completion of the third curved scan control, the controller 180 performs the laser control. Upon completion of the third curved scan control, the slide unit 140 is controlled to slidably move from the slide position C to a slide position corresponding to the gap G 2. Thus, by the completion of the third curved scan control, the controller 180 refers to the gap shift position table based on the gap G 2 to define the shift position corresponding to the gap G 2. By the laser control, the slide unit 140 is controlled to be set to the slide position corresponding to the gap G 2, and the longitudinal section X 2 is scanned with the laser beam by the negative longitudinal scanning control at the same time. Accordingly, the proper connected portion 30 can be formed in the longitudinal section X2 as in the longitudinal section X1.Upon completion of the negative longitudinal scan control, the controller 180 controls the slide unit 140 to slidably move to the slide position C. In addition, while the slide unit 140 is controlled to be set to the slide position C, the fourth curved scanning control and the positive short-length scanning control are respectively executed to scan the curved section R 4 and the short-length section Y 1 with the laser beam. When the scan control is executed by one round to the start position C, then the connection control is completed.Specifically, the welding apparatus 100 according to the present embodiment includes the laser displacement sensor 190 that detects the gaps G 1, G 2 for the respective welding points at the centers of the longitudinal sections X 1, X 2 on the welding line 80 and outputs the detection of the gaps G 1, G 2. In the laser control, the controller 180 refers to the gap shift position table (FIG. 21 ) based on the gaps G 1, G 2 detected by the laser displacement sensor 190 to define the respective shift positions. Specifically, the shift position is defined by considering a plurality of gap thresholds for each gap G 1, G 2, determining whether each gap G 1, G 2 is equal to or more or less than another specific gap threshold represented on the horizontal axis of the gap shift position table, and then defining a shift position corresponding to a shift position within a range of the above-mentioned plurality of specific gap thresholds to which each gap G 1, G 2 belongs. For example, as shown in FIG. 21, when the gap G 1 is within a range of a gap threshold GT 3 or more and less than a gap threshold GT 4, a shift position E corresponding to the range of the gap threshold GT 3 or more and less than the threshold GT 4 is determined. For example, in the power density distribution profile at the shift position E, the power density of the center point S 0 is smaller, and the power density of the outer edge point group SG is larger than that in the power density distribution profile at the shift position C corresponding to a shift position within a range of less than the gap threshold GT 3. For example, in the power density distribution profile at the shift position E, the power density of the central point S 0 is larger, and the power density of the outer edge point group SG is smaller than that in the power density distribution profile at the shift position A corresponding to a shift position within a range of the gap threshold GT 4 or more. Specifically, in the laser control, the controller 180 according to the present embodiment controls the position of the incident point LP such that when the gap G is equal to or more than a predetermined gap threshold, the power density of the central point S 0 becomes smaller, and the power density of the outer edge point group SG becomes larger than that in the case of having the gap G smaller than the predetermined gap threshold. In other words, in the laser control, when the gap G is equal to or more than a predetermined gap threshold, the incident point LP is set to a position closer to the formation area 131 via the slide unit 140 than that in the case of the gap G being smaller than the gap threshold. By this configuration, when the gap G is equal to or more than the predetermined gap threshold, the area of the incident point LP overlapping the formation region 131 of the diffractive optical element 130 is set to be larger than that in the case of the gap G being smaller than the gap threshold.On the other hand, in the laser control, the controller 180 controls the position of the incident point LP such that when the gap G is smaller than the predetermined gap threshold, the power density of the central point S 0 becomes larger and the power density of the outer edge point group SG becomes smaller than that in the case of the gap G being equal to or more than the predetermined gap threshold. Specifically, in the laser control, when the gap G is less than the predetermined gap threshold, the incident point LP is set to a position closer to the non-formation region 132 via the slide unit 140 than that in the case of the gap G being equal to the gap threshold or more. By this configuration, when the gap G is smaller than the predetermined gap threshold value, the area of the incident point LP overlapping the formation region 131 of the diffractive optical element 130 is set smaller than that in the case of the gap G being equal to the threshold value or more. In this way, the welding device 100 is controlled to perform the laser welding by the flexible control depending on the dimension of a gap G.In the present embodiment, in the above description, the laser control is executed only in the longitudinal sections X 1, X 2. However, the laser control may also be performed in the short length sections Y 1, Y 2 different from the longitudinal sections X 1, X 2. The laser control is also performed in each short-length section Y 1, Y 2 to form, in each short-length section Y 1, Y 2, the proper connected portion 30 by the laser beam having the irradiation pattern P whose power density distribution profile is formed depending on the dimension of each gap G. When the laser control is also performed in the short length sections Y 1, Y 2, the respective dimensions of the gaps G in the short length sections Y 1, Y 2 can be detected in the gap detecting step.In the present embodiment, in the above description, in the gap detection step, the gap G is detected at the center of each longitudinal section X 1, X 2. However, the detection position of the gap G in the gap detection step is not limited to the middle. It should be noted that the gap G in each longitudinal section X1, X2 very likely varies at the corresponding center. Thus, when it is desired to detect the gap G at a position in the longitudinal section X1, X2, the center can be used as a detection position as in the present embodiment.In the present embodiment, the provisional fixing step is not an essential step. This means that only the gap detecting step and the connecting step can be performed. In the present embodiment, the gap detecting step is executed after the provisional fixing step. This order may be reversed. After the provisional fixing step, the case body 10 and the sealing plate 20 are fixed to each other via the provisional fixed portions, so that the dimension of the gap G is prevented from varying. In contrast, before the provisionally fixed portions are formed, the case body 10 and the sealing plate 20 are not fixed to each other, and thus the gap G may possibly vary. In other words, when the gap detection step is performed before the provisional fixing step, the dimension of the gap G detected in the gap detection step may possibly become different from the dimension of the gap G in the joining step. Accordingly, by executing the gap detecting step after the provisional fixing step, it is possible to execute the gap detecting step to detect the gap G fixed after the provisional fixing step. Thus, in the present embodiment that performs the gap detection step after the provisional fixing step, it is possible to more favorably form the joined portion 30.In the present embodiment, the gap detection step is performed by using the laser displacement sensor 190. However, the gap detection step not limited to the laser displacement sensor 190 may be performed using another measurement device. Specifically, the gap detection step may be performed using, for example, a visual system.In the present embodiment, the laser control is executed based on the gap shift position table shown in FIG. 21. However, if accuracy is not required as accurately for the power density portion of the central point S 0, the slide unit 140 may be set to, for example, either the slide position A or the slide position C based on the obtained dimension of the gap G. Specifically, in the laser control, when the obtained dimension of the gap G is equal to or more than the predetermined gap threshold, the slide unit 140 may be set to the slide position A, and when the obtained dimension of the gap G is less than the predetermined gap threshold, the slide unit 140 may be set to the slide position C. As the gap threshold value in this case, for example, the gap threshold value GT 2 represented on the horizontal axis of the gap shift position table shown in FIG. 21 may be used.In the present embodiment, as described above, the laser control is performed by moving only the position of the incident point LP on the plane of the diffractive optical element 130 by the sliding motion of the sliding unit 140. In the laser control, in addition to the slide movement of the slide unit 140, a laser output value that is an output value of the laser beam output from the laser oscillator 110 may be changed.When the laser control is executed by changing the slide position of the slide unit 140 as well as controlling the laser output value of the laser oscillator 110, the slide position and the laser output value by which the proper connected portion 30 can be formed depending on the dimension of the gap G can be obtained in advance. In addition, a laser table relating to the shift position and the laser output value may be formed depending on the dimension of the gap G, and this laser table may be stored in the storage unit 181 of the controller 180. In the laser control, the laser table may be referred to depending on the dimension of the gap G obtained in the gap detecting step, the shift position and the laser output value suitable for the detected dimension of the gap G are defined, and the connecting step is performed based on the shift position and the laser output value.As described above, the laser control is executed by changing the laser output value of the laser oscillator 110, thereby increasing or decreasing the power density of each point in the irradiation pattern P as a whole. In other words, it is possible to perform laser welding by more flexible control. For example, it is possible to execute the connection control in a further shortened time by increasing the laser output value. It is also possible to easily adjust the depth of the connected portion to be formed by increasing or decreasing the laser output value. Consequently, the relationship between the dimension of the gap G and the shift position in the laser table does not always need to satisfy the aforementioned gap-shift position relationship.As described above in detail, the gap detection step for detecting the gap G between the case body 10 and the sealing plate 20 is performed on the welding line 80 before the joining step. In the gap detection step, the gap G is detected by the laser displacement sensor 190. In the joining step, the controller 180 of the welding apparatus 100 performs the joining control while performing the laser control to set the slide unit 140 to the slide position depending on the dimension of the gap G.[Fourth Embodiment]The fourth embodiment will be described below. In the present embodiment, as in the third embodiment, the gap detecting step for detecting the dimension of the gap between the inner wall surface of the opening of the case body and the side surface of the sealing plate is performed on the welding line. However, in the present embodiment, the joining step is performed while the gap detecting step is performed, which is different from the third embodiment in which the gap detecting step is performed before the joining step.FIG. 22 shows a welding device 200 according to the present embodiment. The welding apparatus 200 includes the laser oscillator 110, the collimator 120, the diffractive optical element 130, and the controller 180, which are the same as those of the welding apparatus 100 according to the first embodiment. The welding apparatus 200 according to the present embodiment includes a condenser lens 270 disposed downstream of the diffractive optical element 130 in the optical path of the laser beam. The controller 180 according to the present embodiment also includes the storage unit 181 indicated by the alternate long and two short dash line in FIG. 22, and the gap shift position table indicated in FIG. 21 is stored in the storage unit 181. The greatest difference of the welding device 200 from the welding device 100 according to the above embodiments is that the welding device 200 does not include a galvano scanner 150 but includes a laser displacement sensor 290 on the side surface.FIG. 23 is a plan view of the welding device 200. As shown in FIG. 23, the laser displacement sensor 290 of the welding device 200 is rotatably movable about the central point S 0 of the irradiation pattern P formed by the welding device 200. Specifically, the laser displacement sensor 290 is movable by the rotation from a first position 291 indicated by a solid line, a second position 292, a third position 293, and a fourth position 294 indicated by alternate long and two short dash lines, respectively.In the present embodiment, the welding device 200 is fixed to a front end of a robot arm so as to be movable with respect to the battery 1. Specifically, the controller 180 of the welding apparatus 200 of the present embodiment is capable of moving the irradiation pattern P together with the welding apparatus 200 along the welding line 80 during execution of the scan control, which is different from the first embodiment. Specifically, the controller 180 according to the present embodiment executes the positive short-length scan control, the first curved scan control, the positive longitudinal scan control, the second curved scan control, the negative short-length scan control, the third curved scan control, the negative longitudinal scan control, the fourth curved scan control, and the positive short-length scan control in this order by a movement of the robot arm.The controller 180 of the present embodiment executes the laser beam scanning along the short length section Y 1 in the positive direction of the Y axis as shown in FIG. 23 in the positive short length scanning control. The controller 180 performs the laser beam scanning along the longitudinal section X 1 in the positive direction of the X axis shown in FIG. 23 in the positive longitudinal scanning control. In the negative short-length scan control, the controller 180 performs the laser beam scan along the short-length section Y 2 in the negative direction of the Y axis shown in FIG. 23. In the negative longitudinal scan control, the controller 180 performs the laser beam scan along the longitudinal section X 2 in the negative direction of the X axis shown in FIG. 23.The controller 180 according to the present embodiment controls a rotational position of the laser displacement sensor 290 in the positive short-length scan control, the positive longitudinal scan control, the negative short-length scan control, and the negative longitudinal scan control. Specifically, during the positive short-length scan control, the rotational position of the laser displacement sensor 290 is set to the first position 291. During the positive longitudinal scan control, the rotational position of the laser displacement sensor 290 is set to the second position 292. During the short-length negative scan control, the rotational position of the laser displacement sensor 290 is set to the third position 293. During the negative longitudinal scan control, the rotational position of the laser displacement sensor 290 is set to the fourth position 294.The controller 180 according to the present embodiment sequentially controls the laser displacement sensor 290 to detect the dimension of the gap G with respect to the positive short-length scan control, the positive longitudinal scan control, the negative short-length scan control, and the negative longitudinal scan control. In other words, the detection of the dimension of the gap G in advance to the irradiation pattern P is always performed in the positive short-length scan control, the positive longitudinal scan control, the negative short-length scan control, and the negative longitudinal scan control, respectively. The detection of the gap G by the laser displacement sensor 290 is performed at predetermined constant intervals. Thus, the detection of the dimension of the laser gap G by the laser displacement sensor 290 is performed at a plurality of welding points on the welding line 80.The controller 180 according to the present embodiment detects the gap G in advance of the irradiation pattern P and performs the laser control based on the detected dimension of the gap G at the same time. The configuration of the laser controller is the same as that according to the third embodiment. Specifically, in the laser control, the slide position of the slide unit 140 is controlled based on the gap-slide position table.Accordingly, it is possible to execute the connection control while the laser control is executed by the longitudinal sections X 1, X 2 and the short-length sections Y 1, Y 2. Specifically, it is possible to perform the laser welding by the flexible controller. Accordingly, the welding apparatus 200 according to the present embodiment is capable of forming the proper joined portion 30 by the longitudinal sections X 1, X 2 and the short-length sections Y 1, Y 2 being the straight sections. Even if variation of the gap G occurs at the center of one of the straight sections, it is possible to perform laser welding while controlling the position of the slide unit 140 to be set to a slide position depending on the dimension of the varied gap G.As described above, in the present embodiment, the joining step is performed while the gap detection step for detecting the gap G between the case body 10 and the sealing plate 20 is performed on the welding line 80. The welding device 200 performs the detection of the gap G in advance to the irradiation pattern P and at the same time performs the joining control while performing the laser control for controlling the slide unit 140 to be set to the slide position depending on the dimension of the gap G.[Fifth Embodiment]The fifth embodiment will be described below. In the present embodiment, the configuration of the welding device and other elements are the same as those according to the second embodiment. As for the second embodiment, in the present embodiment, the provisional fixing step is also performed. However, in the present embodiment, the connection control and the scan control are started from the longitudinal section, which is different from the second embodiment in which the connection control and the scan control are started from the short length section.The present embodiment will be described with reference to FIG. 24. FIG. 25 is a plan view of the battery 1 as in FIG. 11, however, in FIG. 24, the arrangement of the start position T and the provisional positions K is different from that in FIG. 11. Specifically, in the present embodiment, the position of the start position T is set in the longitudinal section X 1 as shown in FIG. 24. In the present embodiment, the number of provisional positions K is six positions, which is less than eight positions in FIG. 11 as shown in FIG. 24.In the present embodiment, as in the second embodiment, the provisional fixing step and the joining step are performed in this order. That is, the provisional fixing step is first carried out. The provisional fixing step according to the present embodiment is performed by the provisional fixing control by the welding device 100 as in the second embodiment, except for the number of provisional positions K that is smaller than that in the second embodiment.Subsequently, in the joining step according to the present embodiment, laser welding is performed by using the welding apparatus 100 to perform laser beam scanning along the welding line 80 in a clockwise direction from the start position T indicated in the longitudinal section X 1 by one round. In the present embodiment, in the connection control, the scan control is executed to control the galvano scanner 150 to perform the laser beam scan along the welding line 80.Specifically, the controller 180 of the present embodiment starts the scan control by the positive longitudinal scan control. In the first positive longitudinal scan control, no laser beam is applied toward a part of the longitudinal section X 1 located on the short-length section Y 1 side from the start position T. Thus, in the scan control after the positive short-length scan control, in order to irradiate the part of the longitudinal section X 1 located on the short-length section Y 1 side from the start position T with the laser beam, the positive longitudinal scan control for scanning the section in the arrow direction XW 1 with the laser beam is performed again. Specifically, in the scan control, the controller 180 according to the present embodiment executes the positive longitudinal scan control, the second curved scan control, the negative short-length scan control, the third curved scan control, the negative longitudinal scan control, the fourth curved scan control, the positive short-length scan control, the first curved scan control, and the positive longitudinal scan control in this order.In the present embodiment, the controller 180 controls the slide unit 140 to be set to the slide position A after the connection control is started until the initial time elapses; after the initial time elapses, the controller 180 controls the slide unit 140 to slidably move to the slide position C. Thereby, in the present embodiment, it is also configured to prevent the laser passage from occurring in the vicinity of the start position T. Also, in the present embodiment, the slide movement of the slide unit 140 is performed without stopping the irradiation of the laser beam from the laser oscillator 110. Thereby, in the present embodiment as well, it is possible to vary the distribution profile of the power density of the irradiation pattern P in a shorter time, thus reducing the time required for the laser welding.By starting the connection control according to the present embodiment from the start position T, it is possible to reduce deformation of the sealing plate 20 more than in the second embodiment. Specifically, in the second embodiment having the start position T in the short length section Y 1, for example, when the joined portion is formed at the start position T, the deviation between the inner wall surface 13 of the opening 11 of the case body 10 and the side surface 21 of the sealing plate 20 of the short length section Y 2 may become larger. The short-length section Y2 is disposed at a diagonal position to the start position T, thus the associated distance is far from the start position T. Consequently, for example, when deformation is caused at a part of the sealing plate 20 located in the vicinity of the start position T, the deformation in the vicinity of the start position T increases to a larger deformation in the short-length section Y 2 that is diagonal to the start position T.In contrast, in the present embodiment, since the start position T is set in the longitudinal position X 1, each position on the welding line 80 has a shorter distance from the start position T than in the second embodiment. Thus, in the present embodiment, even if deformation occurs due to formation of the joined portion in the vicinity of the start position T in the longitudinal section X 1, the deformation at this start position T is prevented from causing a larger deviation between the inner wall surface 13 of the opening 11 of the case body 10 and the side surface 21 of the sealing plate 20 on the welding line 80. Accordingly, the present embodiment is capable of forming the joined portion on the welding line 80 better than the second embodiment.In addition, in the present embodiment, since the deviation between the case body 10 and the sealing plate 20 is suppressed in the joining control, it is possible to reduce the number of provisional positions K in the provisional fixing control. The provisionally fixed portions are provided for the purpose of suppressing the deviation between the case body 10 and the sealing plate 20 in the joining control; thus, as the deviation becomes smaller, less provisionally fixed portions may be required. Thus, in the present embodiment, it is possible to complete the provisional fixing control in a shorter time. This is because the number of provisional positions K can be reduced.As described above in detail, in the present embodiment, the connection control and the scan control are executed in the connection step from the start position T located in the longitudinal section X 1. Thus, it is possible to further suppress generation of errors in the joining step. In addition, the number of provisional positions K in the provisional fixing step can be reduced. Accordingly, the provisional fixing step can be performed in a shorter time.[Variations]Variations of the above-described embodiments will be described below. First, variations of the irradiation pattern will be explained. FIG. 25 shows variation 1, 2 of the irradiation pattern. In a variation table 1, 2 in FIG. 25, an upper row of the table shows the respective irradiation patterns formed respectively when the incident point LP is located in the formation region 131 of the diffractive optical element 130. A middle line of the table shows the respective irradiation patterns formed respectively when the incident point LP is located within the non-formation region 132 of the diffractive optical element 130. Further, a lower row of the table shows the respective irradiation patterns formed respectively when the incident point LP overlaps the boundary 133 between the formation region 131 and the non-formation region 132 of the diffractive optical element 130. As shown in FIG. 25, in each of the variations 1, 2, the irradiation pattern formed when the incident point LP is disposed within the formation region 131 of the diffractive optical element 130 is different from those in the above-described embodiments. On the other hand, when the incident point LP is located in the non-formation region 132 of the diffractive optical element 130, each of the variations 1, 2 has an irradiation pattern including the central point S0 located in the central region A1, as in the above-described embodiments.Specifically, the irradiation pattern shown in the upper row of Variation 1 in FIG. 25 includes the outer edge point group SG that is less than that of the irradiation pattern P shown in FIG. 5. In Variation 1, the formation region 131 of the diffractive optical element 130 may be considered to include a diffraction grating that radiates the radiated beams with respect to the respective points of the outer edge point group SG shown in the upper row in FIG. 25. In the irradiation pattern shown in the lower row of Variation 1 in FIG. 25, both the outer edge point group SG and the central point S 0 emerge. Accordingly, in Variation 1, as in the above-described embodiments, in the laser welding, it is possible to form irradiation patterns having different distribution profiles of the power densities by changing the position of the incident point LP on the diffractive optical element 130.In the irradiation pattern shown in the upper row of the variation 2 in FIG. 25, the central point S 0 is formed in addition to the outer edge point group SG of the irradiation pattern P shown in FIG. 5. In Variation 2, the formation region 131 of the diffractive optical element 130 may be considered to include the diffraction grating that radiates the radiated beam with respect to the points of the outer edge point group SG and the central point S 0 as shown in the upper row in FIG. 25. In Variation 2, as shown in FIG. 25, both the irradiation pattern in the upper row and the irradiation pattern in the lower row have the same number and the same arrangements of the respective points. However, in Variation 2, unlike the irradiation pattern in the upper row in the irradiation pattern in the lower row, the central point S 0 has a higher power density than that of the outer edge point group SG. Thus, also in Variation 2, as in the above-described embodiments, in the laser welding, it is possible to form irradiation patterns having different distribution profiles of the power density by changing the position of the incident point LP on the diffractive optical element.The X axis and the Y axis are added to the irradiation patterns of each variation 1, 2 in FIG. 25 as in those in FIGS. 5, 6, and 7 according to the above-described embodiments. The laser welding using the irradiation pattern of each variation 1, 2 can be performed in the same manner as the laser welding using each irradiation pattern P in FIGS. 5, 6, and 7 according to the above-described embodiments. Thereby, it is possible to perform the laser welding by the flexible control.Next, variations of the irradiation pattern different from those in FIG. 25 will be described with reference to FIG. 26. In a table for respective variations 3 to 6 in FIG. 26, an upper row of the table shows the respective irradiation patterns formed respectively when the incident point LP is located within the formation region 131 of the diffractive optical element 130. A middle line of the table shows the respective irradiation patterns formed respectively when the incident point LP is located within the non-formation region 132 of the diffractive optical element 130. Further, a lower row of the table shows the respective irradiation patterns formed respectively when the incident point LP overlaps the boundary 133 between the formation region 131 and the non-formation region 132 of the diffractive optical element 130. As shown in FIG. 26, in each of Variations 3 to 6, the irradiation pattern formed when the incident point LP is located within the formation region 131 of the diffractive optical element 130 is different from those in the above-described embodiments. On the other hand, when the incident point LP is located within the diffractive optical element non-forming region 132, each of the variations 3 to 6 has an irradiation pattern including the central point S0 located in the central region A1, as in the above-described embodiments.Specifically, the irradiation pattern shown in the upper row of Variation 3 in FIG. 26 includes the outer edge point group SG corresponding to the outer edge points S 11, S 12, S 41, S 42 of the irradiation pattern P shown in FIG. 5. Each irradiation pattern shown in the upper row of variations 4, 5 in FIG. 26 has smaller outer edge point groups SG than those in variation 3, and has a different arrangement from that in variation 3 associated therewith. The irradiation pattern shown in the upper row of the variation 6 in FIG. 26 has the same number of the outer edge point group SG as that in FIG. 3, but has a configuration thereof different from that in the variation 3.In the irradiation pattern shown in the lower row of each of variations 3 to 6 in FIG. 26, both the outer edge point group SG shown in the upper row and the central point S 0 shown in the middle row protrude. Thus, in each of the variations 3 to 6, as in the above-described embodiment, in the laser welding, it is possible to form the various irradiation patterns having different distribution profiles of the power densities by changing the position of the incident point LP on the diffractive optical element 130. This means that it is possible to perform the laser welding by the flexible controller. In each of Variations 3 to 6, the formation region 131 of the diffractive optical element 130 may be considered to include the diffraction grating that radiates the radiated beam with respect to each point of the outer edge point group SG as shown in the upper row in FIG. 26.In the case of executing the scan control in the laser welding using the irradiation pattern of each of the variations 3 to 6 in FIG. 26, a direction indicated by an arrow Z added to each irradiation pattern may be set to be the scanning direction. For example, when the scan control is performed in the laser welding using the irradiation pattern of the variation 4, the scan control may be performed in the manner shown in FIG. 27.FIG. 27 shows that a welding line 95 of an opposing position 90 where surfaces 93, 94 to be joined of two joining target members 91, 92 are opposed to each other is a straight line section. FIG. 27 shows an irradiation pattern P 4 related to Variation 4. the irradiation pattern P 4 is configured by the central point S 0 and the outer edge point group SG formed by a first outer edge point S 51 and a second outer edge point S 52, which respectively form vertices of a triangle together with the central point S 0.In Fig. 27, the left end is a start position of the connection control and the scanning control, and as indicated by the arrow Z, the scanning direction of the laser beam scanning is a rightward direction. Thus, as shown in FIG. 27, in the scan control using the irradiation pattern P 4, the intermediate part between the first outer edge point S 51 and the second outer edge point S 52 and the central point S 0 are caused to pass through the welding point on the welding line 95 in the order of the intermediate part between the first outer edge point S 51 and the second outer edge point S 52 and the central point S 0.Thereby, in the scan control using the irradiation pattern P 4, the first outer edge point S 51 and the second outer edge point S 52 are formed in advance to the central point S 0 in the scanning direction indicated by the arrow Z. In addition, the first outer edge point S 51 is formed on the connection target member 91 in front of the central point S 0, and the second outer edge point S 52 is formed on the connection target member 92 in front of the central point S 0, respectively.In FIG. 27, after the connection control is started and until the start time elapses, when the gap ahead to the central point S 0 is filled with the welding portion formed by the first outer edge point S 51 and the second outer edge point S 52, the incident point LP may be set to be set within the formation region 131. After the initial time has elapsed, the position of the incident point LP may be changed while the laser beam is irradiated to set the incident point LP to a position overlapping the boundary 133 between the formation region 131 and the non-formation region 132. The scan control may be started while the position of the incident point LP is further changed. Thereby, it is possible to prevent occurrence of the laser pass to suppress generation of errors, and to connect the two connection target members 91, 92 to each other along the welding line 95 in a shorter time.Variations of the irradiation pattern different from those in FIGS. 25 and 26 will be described with reference to FIG. 28. In a table for respective variations 7 to 9 in FIG. 28, an upper row of the table shows the respective irradiation patterns of the variations 7 to 9 formed respectively when the incident point LP is located within the formation region 131 of the diffractive optical element 130. A middle line of the table shows the respective irradiation patterns formed respectively when the incident point LP is located within the non-forming region 132 of the diffractive optical element. Further, a lower row of the table shows the respective irradiation patterns formed respectively when the incident point LP overlaps the boundary 133 between the forming region 131 and the non-forming region 132 of the diffractive optical element. As shown in FIG. 28, in each of Variations 7 and 9, the irradiation pattern formed when the incident point LP is disposed within the formation region 131 of the diffractive optical element 130 is different from those in the above-described embodiments and Variations 1 to 6, In Variation 8, the area and arrangement of the outer edge point group SG in the irradiation pattern are the same as that of Variation 3, but as shown in FIG. 28, in Variation 8, the direction of the arrow Z, which is the scanning direction, is different from that of Variation 3. In each of the variations 7 to 9, the irradiation pattern includes the central point S 0 disposed within the central region A 1 as in the above-described embodiments, when the incident point LP is disposed within the non-formation region 132 of the diffractive optical element 130.Specifically, the irradiation pattern shown in the upper row of variation 7 in FIG. 28 includes the outer edge point group SG corresponding to the outer edge points S 11, S 12, S 31, S 32 of the irradiation pattern P shown in FIG. 5. The irradiation pattern shown in the upper row of the variation 8 in FIG. 28 includes the outer edge point group SG corresponding to the outer edge points S 11, S 12, S 21, S 22 of the irradiation pattern P shown in FIG. 5. In the irradiation pattern shown in the upper row of the variation 9 in FIG. 28, the number of the outer edge point group SG is smaller than that of the variation 7, and the arrangement thereof is different from that of the variation 7.In Variation 8, only the rotational position is different from that of Variation 3, and the area and arrangement of the outer edge point group SG are the same as those of Variation 3. Thus, with respect to each irradiation pattern of Variation 3 and Variation 8, the power density distribution profile becomes the same between Variation 3 and Variation 8 when the power density ratio of the central point S 0 and the power density ratio of the outer edge point group SG become the same between Variation 3 and Variation 8.In each of the variations 7 to 9, in the irradiation pattern shown in the lower row in FIG. 8, both the outer edge point group SG shown in the upper row and the central point S 0 shown in the middle row protrude. Thus, in each of the variations 7 to 9, as in the above-mentioned embodiments, in laser welding, it is possible to form various irradiation patterns having different distribution profiles of power density by changing the position of the incident point LP on the diffractive optical element 130. This means that it is possible to perform the laser welding by the flexible controller. In each of Variations 7 to 9, the formation region 131 of the diffractive optical element 130 may be considered to include the diffraction grating that radiates the radiated beam with respect to each point of the outer edge point group SG shown in the upper row in FIG. 28.In the case of executing the scan control in the laser welding using the irradiation pattern of each variation 7 to 9 in FIG. 28, the direction indicated by the arrow Z added to each irradiation pattern may be used as the scanning direction. For example, when the scan control is performed in the laser welding using the irradiation pattern of the variation 9, the scan control may be performed in a manner shown in FIG. 29.FIG. 29 shows that the welding line 95 of the opposing position 90 at which the surfaces 93, 94 to be joined of the two joining target members 91, 92 are opposed to each other is in a straight section. FIG. 29 shows an irradiation pattern P 9 related to the variation 9. the irradiation pattern P 9 is configured by the central point S 0 and the outer edge point group SG formed by a first outer edge point S 61 and a second outer edge point S 62 arranged at different positions.In Fig. 29, the left end is the start position of the connection control and the scanning control, and the scanning direction of the laser beam is a rightward direction indicated by the arrow Z. As shown in FIG. 29, in the scan control using the irradiation pattern P 9, the central point S 0 may be moved along the welding line 95. Further, in the scan control, the first outer edge point S 61 may be moved ahead to the central point S 0 along a first track 96 provided parallel to the welding line 95. In addition, in the scan control, the second outer edge point S 62 may be moved rearward of the central point S 0 along a second track 97 provided parallel to the welding line 95.Thereby, in the scan control using the irradiation pattern P 9, the first outer edge point S 61 is formed in advance to the central point S 0 in the scanning direction indicated by the arrow Z. In addition, the second outer peripheral point S62 is formed rearward of the central point S0 in the scanning direction indicated by the arrow Z. Further, the first outer edge point S 61 is formed on the connection target member 92 forward to the central point S 0, and the second outer edge point S 62 is formed on the connection target member 91 rearward to the central point S 0, respectively.In FIG. 29, at the start time of the connection control, the incident point LP may be set to be located within the formation region 131 of the diffractive optical element 130 until the start time when the gap located ahead of the central point S 0 is filled with the melted portion formed by the first outer edge point S 61 has elapsed. After the initial time has elapsed, the position of the incident point LP may be changed while the laser beam is irradiated to set the incident point to a position overlapping the boundary 133 between the formation region 131 and the non-formation region 132. The scan control can be started while the position of the incident point LP is further changed. Thereby, it is possible to prevent occurrence of the laser pass to suppress generation of errors, and to connect the two connection target members 91, 92 to each other along the welding line 95 in a shorter time.In the scan control of FIG. 29 using the irradiation pattern P 9, it is also possible to suppress rapid temperature decrease of the melted portion formed after the central point S 0 passes through by using the second outer edge points S 62. By doing so, it is possible to perform laser welding while suppressing generation of fractures and the like.When laser welding is performed on the welding line 80 in a rectangular shape of the battery 1 using the irradiation pattern of each of the variations 3 to 9, it may be configured that the sensing control is performed while the rotational position between the battery 1 and the irradiation pattern P is varied, unlike the above-described embodiments. Specifically, when laser welding is performed using the irradiation pattern of each variation 3 to 9, laser beam scanning may be performed while rotating the irradiation pattern to align the direction of the arrow Z along the welding line 80. Thus, the diffractive optical element 130 can be rotated with respect to the battery 1, for example. Alternatively, the battery 1 may be rotated with respect to the diffractive optical element 130, for example.Variations of the diffractive optical element will be described below. In the above-described embodiments, examples using the diffractive optical element 130 configured by the formation region 131 including the diffraction grating at the corresponding center and the non-formation region 132 not including a diffraction grating therein and surrounding the formation region 131 outside have been explained. However, as shown in FIG. 30, for example, a diffractive optical element 230 including a first forming region 231 and a second forming region 232 each including the diffraction grating may be used.When the irradiation pattern P is formed in each of FIGS. 5, 6, 7 using the diffractive optical element 230, the diffraction grating that irradiates the irradiated beam with respect to the outer edge point group SG of FIG. 5 from the incident point LP of the incident beam Li may be formed in the first formation region 231. In addition, the diffraction grating that radiates the radiated beam from the incident point LP of the incident beam Li with respect to the central point S 0 in FIG. 7 may be formed in the second formation region 232.The shift unit is set to the shift position A shown in FIG. 30 to locate the incident point LP within the first formation region 231 of the diffractive optical element 230, thereby forming the irradiation pattern P shown in FIG. 5. The shift unit is set to the shift position D shown in FIG. 30 to locate the incident point LP within the second formation region 232 of the diffractive optical element 230, thereby forming the irradiation pattern P shown in FIG. 7. Further, the shift unit is set to the shift position F shown in FIG. 30 to arrange the incident point LP at a position overlapping a boundary 233 between the first formation region 231 and the second formation region 232 of the diffractive optical element 230, thereby forming the irradiation pattern P shown in FIG. 6.In the case of using the diffractive optical element 230 instead of using the diffractive optical element 130, it is also possible to vary the irradiation pattern P to have multiple different distribution profiles of the power densities, as in the case of using the diffractive optical element 130.The present embodiment is used merely as an example of the present invention and is not intended to limit the present invention in any way. Accordingly, the present invention can be naturally modified and changed in various ways within the scope of the present invention. For example, in spot welding forming a dotted welded portion on a joined point of an opposing portion where surfaces to be joined of two joining target members are opposed to each other, it is not necessary to perform the laser beam scanning. Specifically, for example, irradiation of the welding point with the laser beam may be started in the connection control after the slide unit 140 is set to the slide position A; after the initial time has elapsed, the slide unit 140 may be controlled to move slidably from the slide position A to the slide position C. At this time, the welding point may be set within the central region A 1 in the irradiation pattern P. By doing so, after the connection control is started until the initial time has elapsed, it is possible to suppress the laser passage through gaps by using the outer edge point group SG, thus suppressing generation of errors. After the initial time has elapsed and the gap is filled, it is possible to form the dotted connected portion having a sufficient depth at each welding point using the central point S 0 in a shorter time.For example, the laser beam scanning along the welding line may also be performed by moving the joining target members with respect to the laser beam. In addition, the laser beam scanning on the welding line can be performed by relatively moving both the welded target members and the laser beam.For example, in the above-described embodiments, the position of the incident point of the incident beam on the diffractive optical element is changed by the sliding motion of the sliding unit 140. However, the position of the incident point of the incident beam on the diffractive optical element may be changed using other configurations different from the configuration of using the shifter 140. For example, a rotating element for rotating the diffractive optical element around the rotation axis provided parallel to the optical axis of the incident beam may be used at a position different from the optical axis of the incident beam. Thus, the position of the point of incidence of the incident beam on the diffractive optical element can also be changed by rotation of the rotating element. Alternatively, the position of the point of incidence of the incident beam on the diffractive optical element can be changed by changing the incident beam with respect to the diffractive optical element. In this case, it may be considered to move an optical fiber disposed upstream of the diffractive optical element in the optical path of the laser beam. It may also be configured to provide a reflecting mirror at an upstream position of the diffractive optical element in the optical path of the laser beam to change an angle of the diffractive optical element with respect to the optical path of the laser beam, thereby changing the position of the incident point of the incident beam on the diffractive optical element. The position of the incident point of the incident beam on the diffractive optical element can also be changed by moving both the diffractive optical element and the optical path of the laser beam. However, as in the above-described embodiments, the welding apparatus can be configured in a simple structure by using the sliding unit for slidably moving the diffractive optical element.In the above-described embodiments, for example, it has been described that the position of the incident point of the incident beam on the diffractive optical element is selectively changed between the position within the formation region 131 and the position overlapping the boundary 133. However, the position of the incident point of the incident beam on the diffractive optical element may be changed, for example, within a range where the position overlaps the boundary 133. In such a case, by changing the position of the incident point of the incident beam on the diffractive optical element, it is possible to vary the distribution profile of the power density in the irradiation pattern.Of the above-described embodiments, only the third embodiment describes an example of changing the laser output value of the laser oscillator. However, the laser output value of the laser oscillator may be changed naturally in the other embodiments different from the third embodiment as long as the power density distribution profile can be improved, or the like.In each of the above embodiments, the case of using the transmission type diffractive optical element in which the diffraction grating that emits the transmitted laser beam is formed has been explained in detail. However, the present invention is not limited to such a transmission type diffractive optical element, and is also applicable to a case of using a reflection type diffractive optical element in which the diffraction grating that emits the reflected laser beam is formed.In each of the above embodiments, the case of using the light spots of the irradiation pattern each having a circular shape has been explained. However, the irradiation pattern may be configured by light spots each having a shape other than a circular shape, such as a polygonal shape such as a triangle or an oval shape.In each of the above-described embodiments, the case of using the case body and the sealing plate both made of aluminum as the joining target members has been specifically explained. However, the material is not limited to aluminum, and the present invention is applicable to a combination of any other materials as long as the materials can be joined together by laser welding. Of course, the present invention is also applicable to laser welding for joining target members other than a battery.A laser welding apparatus according to the present invention includes a diffractive optical element, an incident point changing unit, and a controller. The diffractive optical element comprises a first region in which a diffraction grating is formed which emits an emitted beam having a first distribution profile of a power density which is different from a distribution profile of a power density of the incident beam. The diffractive optical element further comprises a second region having a surface profile different from a surface profile of the first region and emitting a radiated beam having a second power density distribution profile different from the first power density distribution profile. The control device performs connection control to move at least one point in the incident point over a boundary between the first region and the second region during irradiation of the laser beam.

Claims

A laser welding apparatus that irradiates a welding point with a laser beam to form a joined portion in which joining target elements are joined to each other at an irradiation position with the laser beam, the laser welding apparatus comprising: a beam device (110) that outputs the laser beam, the laser beam output from the beam device (110) being defined as an incident beam; a diffractive optical element (130) that irradiates an irradiated beam toward the irradiation position from an incident point of the incident beam; an incident point changing unit (140) that changes a position of the incident point; and a controller (180) that controls the beam device (110) and the incident point changing unit (140), wherein the diffractive optical element (130) comprises a first region (131) and a second region (132), adjacently arranged, the first region (131) is a region where a diffraction grating is formed, the diffraction grating radiating the radiated beam having a first distribution profile of a power density different from a distribution profile of a power density of the incident beam, the second region (132) is a region having a surface profile different from a surface profile of the first region (131) and radiating the radiated beam having a second distribution profile of a power density different from the first distribution profile of the power density, and the controller performs connection control to control the incident point changing unit (140), at least one point in the incident point to move across a boundary between the first region (131) and the second region (132) during emission of the laser beam from the irradiation device (110), characterized in that the second region (132) is a region in which no diffraction grating is formed.The laser welding apparatus according to claim 1, wherein the first region (131) is a region that radiates the radiated beam, comprising parts having a maximum power density in the first power density distribution profile within an outer edge region (A2) different from a central region (A1) that is a part having a maximum power density in the second power density distribution profile.A laser welding apparatus that irradiates a welding point with a laser beam to form a joined portion in which joining target elements are joined to each other at an irradiation position with the laser beam, the laser welding apparatus comprising: a beam device (110) that outputs the laser beam, the laser beam output from the beam device (110) being defined as an incident beam; a diffractive optical element (130) that irradiates an irradiated beam toward the irradiation position from an incident point of the incident beam; an incident point changing unit (140) that changes a position of the incident point; and a controller (180) that controls the beam device (110) and the incident point changing unit (140), wherein the diffractive optical element (130) comprises a first region (131) and a second region (132), adjacently arranged, the first region (131) is a region where a diffraction grating is formed, the diffraction grating radiating the radiated beam having a first distribution profile of a power density different from a distribution profile of a power density of the incident beam, the second region (132) is a region having a surface profile different from a surface profile of the first region (131) and radiating the radiated beam having a second distribution profile of a power density different from the first distribution profile of the power density, and the controller (180) performs connection control to control the incident point changing unit (140), To move at least one point in the incident point over a boundary between the first region (131) and the second region (132) during the emission of the laser beam from the beam device (110), characterized in that the first region (131) is a region emitting the emitted beam comprising parts having a maximum power density in the first distribution profile of the power density within an outer edge region (A2) different from a central region (A1) being a part having a maximum power density in the second distribution profile of the power density.The laser welding apparatus according to claim 2 or 3, wherein in the connection control, the control device (180) controls the welding point at the irradiation position to be disposed within the central region (A1), controls the incident point changing unit (140) to set the position of the incident point to be closer to the second region (132) than the position of the incident point before a predetermined start time elapses after the start time elapses from a start of irradiation of the laser beam from the irradiation device (110), and controls the irradiation position so as not to relatively move with respect to the connection target members during irradiation of the laser beam from the irradiation device (110).The laser welding apparatus according to claim 2 or 3, further comprising a moving unit that moves at least one of the irradiation position and the joining target members with respect to the other thereof, wherein in the joining control, the control device (180) performs scan control to control the moving unit to move the irradiation position such that a welding line formed by a plurality of continuous welding points extends through the central region (A1).The laser welding apparatus according to claim 5, wherein in the connection control, the control device (180) controls the incident point changing unit (140) to set the position of the incident point to be closer to the second region (132) than is the position of the incident point before the predetermined initial time has elapsed after the initial time has elapsed from a start of irradiation of the laser beam from the irradiation device (110).The laser welding apparatus according to claim 5 or 6, wherein the second region (132) is a region in which a central point is formed in the central region (A1) by the irradiated beam, the first region (131) is a region in which a first outer edge point and a second outer edge point are formed by the irradiated beam in the outer edge region (A2), the first outer edge point and the second outer edge point respectively form vertices of a triangle together with the central point, and the controller (180), in the scan control, performs control such that an intermediate part between the first outer edge point and the second outer edge point and the central point are made to pass through the welding point on the welding line in the order of the intermediate part between the first outer edge point and the second outer edge point and the central point.The laser welding apparatus according to claim 5 or 6, wherein the second region (132) is a region in which a central point in the central region (A1) is formed by the irradiated beam, the first region (131) is a region in which four outer edge points each forming vertices of a rectangle surrounding the central point are formed in the outer edge region (A2) by the irradiated beam, and the controller (180), in the scan control, performs control such that an intermediate part between a first outer edge point and a second outer edge point that are adjacent among the outer edge points, the central point, and an intermediate part between a third outer edge point and a fourth outer edge point that are outer edge points different from the first outer edge point and the second outer edge point are each made to flow, passing through the welding point on the welding line in the order of the intermediate part between the first outer edge point and the second outer edge point that are adjacently disposed among the outer edge points, the central point, and the intermediate part between the third outer edge point and the fourth outer edge point that are the outer edge points different from the first outer edge point and the second outer edge point.The laser welding apparatus according to claim 5 or 6, wherein the second region (132) is a region in which a central point in the central region (A1) is formed by the irradiated beam, the first region (131) is a region in which a first outer edge point and a second outer edge point located at a different position from that of the first outer edge point are formed in the outer edge region (A2) by the irradiated beam, and the controller (180) controls, in the scan control, the central point to move along the welding line, controls the first outer edge point to move forward to the central point along a first outer edge trace that is a trace parallel to the welding line, and controls the second outer edge point to move rearward to the central point along a second outer edge trace, which is a trace parallel to the welding line.The laser welding apparatus according to any one of claims 5 to 9, wherein, before the joining control is executed, the control means (180) executes provisional fixing control to irradiate a part of each provisional position on the welding line with the laser beam to form a provisional fixed portion at the provisional position, and the control means (180) in the provisional fixing control controls the incident point changing unit (140) to set the position of the incident point to be within the first range (131).The laser welding apparatus according to any one of claims 5 to 10, further comprising a gap output unit that detects a gap at the welding point on the welding line formed by making the connection target members face each other and outputs the detection of the gap, wherein the controller (180), in the connection control, when the gap at the welding point detected by the gap output unit is equal to a predetermined gap threshold value or more, performs laser control to control the incident point changing unit (140) to set the position of the incident point to be closer to the first region (131) than the position of the incident point is when the output gap is less than the gap threshold value.The laser welding apparatus according to any one of claims 5 to 11, wherein when the welding line is in a rectangular shape as a whole, the controller (180) starts the scan control from a start position, the start position being the welding point disposed in a longer side of the welding line, and the controller (180) performs the scan control along the welding line through one round to the start position after the start.The laser welding apparatus according to any one of claims 1 to 12, wherein the irradiation device (110) adjusts a laser output value, which is an output value of the output laser beam, during irradiation of the laser beam.

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