Image forming apparatus

Abstract

An image forming apparatus is disclosed. The image forming apparatus includes an image forming portion, a reversing roller pair, a reversing motor. A controller controls rotation of the reversing motor in a first feeding mode for a sheet having a first length and in a second feeding mode for a sheet having a second length shorter than the first length. The controller performs a first acceleration control in the first feeding mode in which the reversing motor rotating in a first rotation direction is accelerated from a predetermined speed to a first target speed faster than the predetermined speed after a trailing end of the sheet passes through the image forming portion, and performs a second acceleration control in the second feeding mode in which the reversing motor rotating in the first rotation direction is accelerated to a second target speed slower than the first target speed after the trailing end of the sheet passes through the image forming portion.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus for forming an image on a sheet of a recording medium. Background Technology

[0002] Generally speaking, in the field of image forming apparatuses such as printers and fax machines, the following structural arrangement is known: after an image is formed on a sheet of recording medium, the sheet is turned upside down by a pair of reverse rollers and then the image forming apparatus discharges the sheet.

[0003] A reversal is a sheet conveying operation in which the sheet of recording medium is temporarily stopped after being conveyed in a first direction by a pair of reverse rollers, and then conveyed in a second direction opposite to the first direction.

[0004] In turning operations such as the aforementioned turning operation, when two or more sheets of recording media are continuously transported, one of the two consecutively transported sheets may collide with the sheet immediately preceding it while the first sheet and the second sheet are being transported in the second and first directions, respectively. When the subsequent sheet collides with the previous sheet, both sheets may become damaged. Therefore, conventional turning operations such as the aforementioned turning operation cannot be considered desirable. In particular, if an attempt is made to increase the productivity of the image forming apparatus by reducing the sheet interval during continuous printing operations, the two consecutively transported sheets are even more likely to collide with each other.

[0005] A pair of reverse rollers are initially accelerated to a target speed faster than the image forming speed at a preset timing for conveying the sheet of recording medium in the first direction (forward rotation). Then, the pair of reverse rollers are temporarily stopped to begin conveying the sheet in the second direction (reverse direction). Then, as the pair of reverse rollers begin rotating in the second direction, they are accelerated to the same speed as the aforementioned target speed. The pair of reverse rollers are then driven at the target speed until the rear end of the sheet passes the clamping portion of the pair of reverse rollers. In other words, the sheet of recording medium is accelerated to the target speed by a pair of reverse rollers to reduce collisions between the sheets of two recording media being continuously conveyed in the image forming apparatus.

[0006] The reverse rollers described in Japanese Patent Application Publication No. 2006-182475 are driven by the forward or reverse rotation of a motor. To prevent malfunctions that tend to occur when the motor switches between forward and reverse rotation directions, a preset time length is required between the period of forward rotation and the period of reverse rotation of the motor. However, in the case where the map forming apparatus described in Japanese Patent Application Publication No. 2006-182475 is configured such that its pair of reverse rollers are accelerated to a target speed, the additional time required to accelerate or decelerate the motor necessitates increasing the time the apparatus remains stationary, potentially reducing the apparatus's productivity.

[0007] Furthermore, in recent years, there has been a desire for image forming apparatuses that offer high productivity but can form images on any of a variety of recording media sheets of different lengths. The requirements for preventing the sheets of two recording media being continuously transported from colliding with each other, and for providing sufficient time for the image forming apparatus to remain stationary, are influenced by the sheet length. Summary of the Invention

[0008] Therefore, the main objective of the present invention is to provide an image forming apparatus that, regardless of the sheet length, can keep a pair of opposing rollers stationary for a sufficient period of time to prevent damage to the sheets of two recording media being continuously transported, and also has high productivity.

[0009] According to one aspect of the present invention, an image forming apparatus is provided, comprising: an image forming section configured to form an image on a sheet; a reverse roller pair configured to feed the sheet in a first direction and then reverse the sheet and feed it in a second direction opposite to the first direction in order to redirect the sheet having the image formed by the image forming section; a reverse motor configured to rotate in a first rotational direction and feed the sheet in the first direction, and to rotate in a second rotational direction opposite to the first rotational direction and feed the sheet in the second direction; and a controller configured to feed the sheet in a first feeding mode and a second feeding mode. The controller controls the rotation of the reverse motor. In the first feeding mode, a sheet of a first length is fed; in the second feeding mode, a sheet of a second length shorter than the first length is fed. In the first feeding mode, the controller performs a first acceleration control, in which, after the rear end of the sheet passes the image forming section, the reverse motor rotating in the first rotation direction is accelerated from a predetermined speed to a first target speed faster than the predetermined speed. In the second feeding mode, the controller performs a second acceleration control, in which, after the rear end of the sheet passes the image forming section, the reverse motor rotating in the first rotation direction is accelerated to a second target speed slower than the first target speed.

[0010] Other features of the invention will become clear from the following description of exemplary embodiments (with reference to the accompanying drawings). Attached Figure Description

[0011] Figure 1 This is a schematic cross-sectional view of the printer in the first embodiment of the present invention.

[0012] Figure 2 This is a schematic diagram of the combination of a branch conveying unit and a reverse conveying unit.

[0013] Figure 3 It is a block diagram of the control sequence.

[0014] Figure 4A It is a line graph representing the first driving sequence.

[0015] Figure 4B It is a line graph representing the second driving sequence.

[0016] Figure 5A It is a line graph showing the length of time the reverse motor is driven in the forward direction during the first drive sequence.

[0017] Figure 5BIt is a graph showing the length of time the reverse motor is driven in the forward direction during the second drive sequence.

[0018] Figure 6 It is a graph showing the duration of the reverse motor being reverse-driven in the first drive sequence.

[0019] Figure 7 This is a flowchart of the sheet material conveying control.

[0020] Figure 8 yes Figure 7 The remainder of the flowchart for sheet transport control is shown in the figure.

[0021] Figure 9 This is the flowchart for the first conveyor control.

[0022] Figure 10 This is a flowchart of the second conveyor control.

[0023] Figure 11 This is a flowchart of the first conveying control in the second embodiment of the present invention.

[0024] Figure 12 This is a flowchart of the second conveying control in the second embodiment.

[0025] Figure 13 This is a schematic cross-sectional view of the overall printer in the third embodiment of the present invention. Detailed Implementation

[0026] <Example 1>

[0027] [Overall Structure]

[0028] The first embodiment of the present invention will be described first. Printer 1 is an image forming apparatus. Printer 1 is a full-color laser beam printer. Printer 1 belongs to the electrophotographic type. In addition, printer 1 belongs to the so-called intermediate transfer type and is also a tandem type.

[0029] Unlike so-called direct transfer image forming apparatuses, intermediate tandem image forming apparatuses do not require holding the recording medium sheet on the transfer drum, transfer belt, etc. Therefore, they can handle many types of transfer media, such as significantly thick paper sheets and coated paper sheets. Furthermore, one of their specific features is that multiple images can be processed simultaneously, one-to-one, in their multiple image forming sections; additionally, multiple monochrome images of different colors that constitute a panchromatic image are transferred all at once. Therefore, they are ideal from a high productivity perspective.

[0030] refer to Figure 1The printer 1 includes a feed unit 10, an extraction unit 20, transport units 30 and 40, an image forming unit 50, a fixing device 58, and a branch transport unit 60. The printer 1 also includes a reverse transport unit 70, a reverse draw unit 80, and a duplex mode transport unit 90.

[0031] The image forming unit 50 is equipped with: four processing boxes 51Y, 51M, 51C, and 51Bk, which form four monochrome toner images of different colors, more specifically, yellow (Y), magenta (M), cyan (C), and black (K) toner images; and four exposure devices 52Y, 52M, 52C, and 52Bk. Incidentally, although the four processing boxes 51Y, 51M, 51C, and 51Bk differ in the colors of the images they form, they are structurally identical. Therefore, only the structure and image forming process of processing box 51Y will be described; processing boxes 51M, 51C, and 51Bk will not be described.

[0032] The processing cartridge 51Y includes a photosensitive drum 52, a charged roller, a developing device 53, and a cleaner 54. The photosensitive drum 52 is made by coating the outer peripheral surface of an aluminum cylinder with an organic photoconductive material layer. The photosensitive drum 52 is rotated by a motor. The image forming unit 50 is equipped with an intermediate transfer belt 501, which is driven cyclically by a motor in the direction indicated by arrow B. The intermediate transfer belt 501 is suspended by a combination of a tension roller 502, a drive roller 503, and a secondary transfer inner roller 504 located inside the ring (belt ring) forming the intermediate transfer belt 501. Inside the ring forming the intermediate transfer belt 501, primary transfer rollers 55Y, 55M, 55C, and 55Bk are deployed. Outside the belt ring, a secondary transfer outer roller 56 is deployed opposite to the secondary transfer inner roller 504.

[0033] The fixing device 58 has a fixing clamping section 58a, through which a sheet of recording medium is conveyed while being held clamped between two rollers of the fixing device 58. The feeding unit 10 includes a lifting plate 11 that moves upward or downward while holding the sheet of recording medium in layers; and a feeding section 12 that feeds the sheet on the lifting plate 11 into the main assembly of the printer 1. In this embodiment, the feeding section 12 employs an air conveying method that feeds the sheet of recording medium one sheet at a time into the main assembly of the printer 1 by pneumatically separating (suctioning) the sheet. However, this embodiment is not intended to limit the scope of the invention. For example, the invention is also compatible with roller conveying type feeding sections that use pick-up rollers or the like to feed the sheet of recording medium into the main assembly, and electrostatic adsorption type feeding sections that use electrostatic force to feed the sheet of recording medium into the main assembly of the printer 1.

[0034] Next, the image forming operation performed by the printer 1 constructed as described above will be described. When the image forming signal is input from a personal computer or the like into the exposure apparatus 52Y, the laser beam is projected onto the outer peripheral surface of the photosensitive drum 52 of the processing cartridge 51Y and is simultaneously modulated by the image forming signal.

[0035] Before the laser beam is projected onto the photosensitive drum 52, the outer peripheral surface of the photosensitive drum 52 is uniformly charged to a preset polarity and potential level by a charged roller. Therefore, when the laser beam is projected from the exposure device 52Y through the reflector onto the outer peripheral surface of the photosensitive drum 52, an electrostatic latent image is formed on the outer peripheral surface of the photosensitive drum 52. This electrostatic image on the photosensitive drum 52 is developed into a yellow (Y) toner image by the developing device 53; a yellow (Y) toner image is formed on the outer peripheral surface of the photosensitive drum 52.

[0036] In the same manner, laser beams from exposure devices 52M, 52C, and 52Bk are projected onto the photosensitive drums of each of processing cartridges 51M, 51C, and 51Bk, thereby creating a one-to-one toner image of red (M), cyan (C), and black (K) on the photosensitive drums. After the toner image is formed on the photosensitive drum, the toner image is transferred to the intermediate transfer belt 501 via primary transfer rollers 55Y, 55M, 55C, and 55Bk, thereby producing a full-color toner image on the intermediate transfer belt 501. The full-color toner image is then conveyed via the intermediate transfer belt 501, rotated by motor 503, to the secondary transfer clamping section T2 formed by the secondary transfer inner roller 504 and the secondary transfer outer roller 56. Toner remaining on the photosensitive drum 52 is recovered by cleaner 54. Incidentally, the image forming process used to create four monochromatic toner images of different colors is performed at regular intervals, whereby the downstream monochromatic toner image is overlaid on the upstream toner image.

[0037] In parallel with the progress of image forming processing, the recording medium sheet S is fed from the sheet feeder unit 10 into the main assembly of the printer 1, and then conveyed to a pair of alignment rollers 71 via the alignment unit 40. In the event that the sheet S is accidentally conveyed at an angle, its orientation is corrected by the alignment unit 40. The sheet is then conveyed to the secondary transfer clamping section T2 at a preset conveying time. The full-tone toner image on the intermediate transfer belt 501 is transferred to the first surface (top surface) of the sheet S by a secondary transfer bias applied to the outer secondary transfer roller 56. Toner residue on the intermediate transfer belt 501 is recovered by the belt cleaner 2.

[0038] After the toner image is transferred onto the film S of the recording medium, the film S is conveyed to the fixing device 58 by the predetermined film transport section 57. The film S is then guided to the fixing clamping section 58a of the fixing device 58, where a combination of a preset amount of heat and a preset amount of pressure is applied to the film S and the toner image thereon. Therefore, the toner image is fixed to the film S. That is, the toner image is melted, and then, as the toner image cools, it becomes permanently attached to the film S. After being conveyed by the fixing device 58, the film S is conveyed by the branch transport unit 60 to the discharge tray 500 or the reverse transport unit 70. Incidentally, the branch conveying unit 60 can be used to perform a so-called face-down conveying sequence, that is, when the sheet S is discharged into the discharge tray 500, the sheet S is turned upside down so that the first surface of the sheet S - that is, the surface of the sheet S that has just been transferred with the image in the secondary transfer clamping part T2 - is face down.

[0039] When an image is formed on only one of the two surfaces of the recording medium sheet S, the sheet S is conveyed from the branch conveyor unit 60 to the discharge tray 500. When an image is formed on both surfaces of the sheet S, the sheet S is conveyed from the branch conveyor unit 60 to the reverse conveyor unit 70 and pulled into the reverse pull unit 80. Then, the sheet S is turned by the combination of the reverse conveyor unit 70 and the reverse pull unit 80. After turning, the sheet S is conveyed from the reverse conveyor unit 70 to the duplex pattern conveyor unit 90. Then, the sheet S is guided to the pull unit 20. Thereafter, an image is formed on the second surface (back surface) of the sheet S in the secondary transfer clamping section T2. ​​Then, the sheet S is discharged into the discharge tray 500.

[0040] [Structure of the branch conveyor unit and the structure of the reverse conveyor unit]

[0041] Next, the structures of the branch conveying unit 60 and the reverse conveying unit 70 will be described. (Refer to...) Figure 2 The branch conveying unit 60 includes: an inlet conveying channel 61 that guides the recording medium sheet S when it is conveyed to the fixing device 58; and a straight conveying channel 63 that extends linearly from the inlet conveying channel 61. Additionally, the branch conveying unit 60 includes: a reverse merging channel that extends linearly from the straight conveying channel 63; and a reverse pre-conveyor channel 64 that branches off from the downstream end of the inlet conveying channel 61 in a direction different from the straight conveying channel 63 in the sheet conveying direction. Furthermore, the branch conveying unit 60 includes: a reverse conveying channel 71 that extends downward from the reverse pre-conveyor channel 64; and a reverse post-conveyor channel 66 that connects the reverse conveying channel 71 to the reverse merging channel 68.

[0042] A first switching member 62 is provided at the branch point between the linear transport channel 63 and the reverse pre-transport channel 64. When the sheet exits from the inlet transport channel 61, the first switching member 62 can switch between the position where it guides the sheet S of the recording medium into the linear transport channel 63 and the position where it guides the sheet S into the reverse pre-transport channel 64. The first switching member 62 is driven by a switching motor 238.

[0043] A second switching member 65 is provided at the branch point between the reverse pre-conveyor channel 64 and the reverse post-conveyor channel 66. The second switching member 65 is held by the pressing member 65a in a position that guides the sheet S into the reverse post-conveyor channel 66 when the sheet S passes through the inlet conveyor channel 61. When the sheet S is conveyed from the inlet conveyor channel 61 to the reverse pre-conveyor channel 64, the sheet S advances into the inlet conveyor channel 61 against the pressure from the pressing member 65a while pressing the second switching member 65.

[0044] The inlet conveying channel 61 is provided with a pair of first pull rollers 201 driven by a first pull motor 231 and a first detection unit 221 positioned downstream of the first pull rollers 201 in the sheet conveying direction. The reverse pre-conveying channel 64 is provided with a pair of second pull rollers and a pair of third pull rollers 203 driven by a second pull motor 232 and a second detection unit 222 positioned between the pair of second pull rollers 202 and the pair of third pull rollers 203.

[0045] The reverse conveying channel 71 is equipped with a pair of reverse rollers 71 capable of rotating backward and forward and also capable of turning the sheet S. The pair of reverse rollers 72 are driven by a reverse motor 234. The reverse rear conveying channel 66 is equipped with a pair of conveying rollers 205 and a pair of conveying rollers 206 that convey the sheet S toward the reverse merging channel 68. These pairs of conveying rollers 205 and 206 are driven by a conveying motor 235. Furthermore, the reverse rear conveying channel 66 is equipped with a third detection unit 223, which is positioned between the pair of conveying rollers 205 and the pair of conveying rollers 206 in the sheet conveying direction. The reverse merging channel 68 is equipped with a pair of discharge rollers 207 driven by a discharge motor 237. The first detection unit 221, the second detection unit 222, and the third detection unit 223 detect the sheet S at their respective detection points.

[0046] [Control Sequence]

[0047] Figure 3 This is a block diagram of the control sequence for printer 1. (Reference) Figure 3The printer 1 has a control unit 600, which includes a CPU 601, RAM 602, and ROM 603. The control unit 600 reads various programs from the ROM 603 and executes these programs. The RAM 602 serves as the working area for the CPU 601. The control unit 600 can be connected to an external PC and other devices via I / O 604.

[0048] The CPU 601 is connected to the control section 412, which includes a control panel. Users can issue commands such as changing various operating settings of the printer 1 and starting a print job. The CPU 601 is connected to the first detection section 221, the second detection section 222, and the third detection section 223 via an A / D converter 610. Furthermore, the CPU 601 is connected to the first pull motor 231, the second pull motor 232, the switching motor 238, the reversing motor 234, the conveying motor 235, and the discharge motor 237 via a driver 620.

[0049] [Control of the reverse motor]

[0050] Next, the control of the reverse motor 234, which controls the operation of a pair of reverse rollers 72 used to turn the sheet S of the recording medium, is described. First, the CPU 601 rotates the reverse motor 234 forward (i.e., in the first rotation direction) so that the printer 1 performs a turning operation using the pair of reverse rollers 72. Therefore, as... Figure 2 As shown, sheet S is conveyed by a pair of reverse rollers 72 in a first direction D1. Then, CPU 601 stops the reverse motor 234 to temporarily stop the pair of reverse rollers 72. Then, CPU 601 causes the reverse motor 234 to rotate backward (i.e., in a second rotation direction D1, opposite to the first rotation direction) to convey sheet S in a second direction D2 (i.e., opposite to the first direction D1) using the pair of reverse rollers 72.

[0051] As described above, to ensure that the reverse motor 234 does not malfunction when its rotation direction changes between forward and backward, a preset time length is required for the reverse motor 234 to stop driving the pair of reverse rollers 72. Unless this preset time length is ensured to stop the reverse motor 234, its operation will be problematic; that is, the reverse motor 234 will operate incorrectly. Furthermore, to change the speed of the reverse motor 234—that is, to start and stop it—time is required for acceleration and time for deceleration. Unless sufficient time is provided for these operations, the reverse motor 234 will end up operating unsteadily when it stops.

[0052] Furthermore, to prevent collisions between the preceding sheet S and the following sheet S during the reversing operation when two recording media sheets S are continuously transported, it is desirable to complete the reversing of the preceding sheet S as quickly as possible. Therefore, control is implemented to accelerate the sheet S as quickly as possible to complete the reversing of the sheet S. However, from the perspective of image quality, it is difficult (and undesirable) for the image forming unit 50, which is the image forming unit, to transport the sheet S at a high speed. Therefore, the desired timing for accelerating the reverse motor 234 is immediately after the rear end of the sheet S exits from the image forming unit 50.

[0053] The printer 1 in this embodiment is capable of forming images on sheets of various recording media of different lengths. Therefore, the longer the sheet S, the more likely the reverse motor 234 is to begin acceleration when the leading edge of the sheet S is downstream of a pair of reverse rollers 72. For example, when using a sheet S with a recording medium of a first length (hereinafter referred to as a long sheet), the reverse motor 234 begins acceleration when the leading edge of the sheet is in a first position. When using a sheet with a recording medium of a second length shorter than the first length (hereinafter referred to as a short sheet), the reverse motor 234 begins acceleration when the leading edge of the sheet is in a second position upstream of the first position in the sheet transport direction. Therefore, the point at which the sheet S begins acceleration, with reference to the leading edge of the sheet S, is influenced by the size of the sheet S.

[0054] In this embodiment, the image forming unit 50 includes a fixing device 58, and the reverse motor 234 can accelerate from the processing speed Vp after the rear end of the sheet S exits from the clamping part 58a of the fixing device 58. The processing speed Vp, which is a preset speed, is the image forming speed corresponding to the speed at which the sheet S is conveyed through the secondary transfer clamping part T2. Incidentally, in this embodiment, the printer 1 is configured such that the reverse motor 234 begins to accelerate after the trailing edge of the sheet S has advanced a distance C after exiting the fixing clamping part 58a. The value of distance C is set taking into account variations in sheet length and inconsistencies in sheet detection performed by the sheet detection sensor. The value of distance C is a margin used to ensure that the rear end of the sheet S exits from the fixing clamping part 58a before the reverse motor 234 begins to rotate.

[0055] In this embodiment, the length of the image forming section 50—that is, the distance between the fixing clamping section 58a and the clamping sections of the pair of reverse rollers 72—is shorter than the longest sheet length that can be conveyed by the printer 1 according to the printer specifications. To describe in more detail, the distance between the fixing clamping section 58a and the clamping sections of the pair of reverse rollers 72 is shorter than the length of the long sheet mentioned above (first length) and longer than the length of the short sheet mentioned above (second length).

[0056] Therefore, when conveying a long sheet S of recording medium, the sheet S remains clamped by the fixing clamp 58a when the pair of reverse rollers 72 receive it. Thus, when the pair of reverse rollers 72 receive the long sheet S of recording medium, the speed Vf1 of the reverse motor 234 is equal to the processing speed Vp (Vf1 = Vp). Then, after the trailing edge of the long sheet exits the fixing clamp 58a, the reverse motor 234 accelerates from the processing speed Vp to a first target speed Va1 and is conveyed a distance C (Vf1 = Vp). <Va1)。

[0057] On the other hand, when conveying short sheets, the trailing edge of the sheet S will emerge from the fixing clamping part 58a when the pair of reverse rollers 72 receive the sheet S. Therefore, the speed Vf2 of the reverse motor 234 when the pair of reverse rollers 72 receive the sheet S can be set to a second target speed Va2, which is greater than the processing speed Vp (Vf2 = Va2 > Vp).

[0058] Incidentally, for the sake of simplicity, it is hereafter assumed that the speed of the reverse motor 234 is the same as the speed of the conveying sheet S. For example, it is assumed that the sheet conveying speed when the reverse motor 234 is driven at a first target speed Va1 is the same as the first target speed Va1. That is, it is assumed that the speed of each motor is equal to the circumferential speed of each roller driven by the corresponding motor.

[0059] In this embodiment, the reverse motor 234 is driven at a speed that allows the long sheet to be conveyed. Figure 4A The line in the middle (first line) indicates that the reverse motor 234 is driven to convey the short sheet at a speed determined by the following: Figure 4B The second line in the diagram represents [the line]. (See reference.) Figure 4A When conveying a long sheet, the reverse motor 234 is accelerated to a processing speed Vp (=Vf1) to receive the sheet and is driven at this speed for a preset time length. Then, after the trailing edge of the long sheet exits from the fixing clamp 58a, the reverse motor 234 is accelerated to a first target speed Va1 and further conveyed to a distance C. Then, the reverse motor 234 is driven at the first target speed Va1 for a preset time length.

[0060] Subsequently, the reverse motor 234 is decelerated so that it changes its rotational direction at a timing that causes the trailing edge of the long sheet to pass the second switching member 65. Then, the reverse motor 234 remains stationary for a preset time length Tr. Then, the reverse motor 234 begins to rotate backward and is accelerated to a first discharge speed Vr1. Then, once the trailing edge of the long sheet has exited the clamping portion of a pair of reverse rollers 72, the reverse motor 234 stops.

[0061] Next, refer to Figure 4BIn the case of conveying short sheets, the reverse motor 234 is accelerated to a second target speed Va2 (>Vp) to receive the sheet. After the pair of reverse rollers 72 receive the sheet, the reverse motor 234 rotates at the second target speed Va2 for a preset time length.

[0062] Subsequently, the reverse motor 234 is decelerated so that its direction changes at a timing that causes the trailing edge of the short sheet to pass the second switching member 65. Then, the reverse motor 234 remains stationary for a preset time length Tr. Then, the reverse motor 234 begins to rotate in the reverse direction and is accelerated to the second discharge speed Vr2. Then, the reverse motor 234 stops when the trailing edge of the short sheet exits the clamping portion of a pair of reverse rollers 72.

[0063] [Feasibility of recording media delivery]

[0064] From the viewpoint of the feasibility of transporting the recording medium according to the present invention, we will discuss the values ​​to be set for the first target speed Va1 and the second target speed Va2, as well as the first discharge speed Vr1 and the second discharge speed Vr2.

[0065] The productivity setting of printer 1 determines the time length Tp that can be given to turn a single sheet of recording medium. The time length Tp includes the time length Tk during which the reverse motor 234 is driven to turn a single sheet of recording medium (including the time Tr during which the reverse motor 234 remains stationary) and the time length Ts during which the reverse motor 234 can remain stationary waiting for the next sheet. From the perspective of giving the reverse motor 234 sufficient stationary time length Ts, it is desirable that the time length Tk be as short as possible.

[0066] Hereafter, the time length Tk used for long sheets is referred to as time Tk1, and the time length Tk used for short sheets is referred to as time Tk2. Next, refer to... Figure 5A and Figure 5B Time Tk1 and time Tk2 are analyzed and simplified to be expressed in the form of the following mathematical formulas (1) and (2), respectively. Incidentally, for simplification, the time length during which the reverse motor 234 accelerates from low speed (Vp) to high speed (Va1) is included in the low speed conveying time length, and the time length during which the reverse motor 234 is accelerated for discharge is included in the discharge time length.

[0067] Tk1 = (time for acceleration) + (time for low-speed conveying) + (time for high-speed conveying) + (time for changing the direction of the reverse motor 234) + (time for discharge) + (time for deceleration) = (Vp / a) + (L1 / Va1) + (L2 / Va1) + (Tr) + (L3 / Vr1) + (Vr1 / d)...(1)

[0068] Tk2=(time for acceleration)+(time for high-speed conveying)+(time for changing the direction of reverse motor 234)+(time for discharge)+(time for deceleration)=(Va2 / a)+(L2 / Va2)+(Tr)+(L3 / Vr2)+(Vr2 / d)...(2)

[0069] Vp: Processing speed

[0070] a: Acceleration

[0071] d: deceleration

[0072] L1: Low-speed conveying distance

[0073] L2: High-speed conveying distance

[0074] L3: Discharge conveying distance

[0075] Va1: First target velocity

[0076] Va2: Second target speed

[0077] Vr1: First discharge velocity

[0078] Vr2: Second discharge velocity

[0079] Tr: Length of stillness

[0080] Here, acceleration a, deceleration d, and time length Tr are constants determined by constants related to the performance of the reverse motor 234, and L1 to L3 are constants determined by the sheet length. The processing speed Vp is a constant determined by the image forming requirements. Therefore, they are not treated as variables. That is, the first target speed Va1, the second target speed Va2, the first discharge speed Vr1, and the second discharge speed Vr2 can be listed as variable parameters.

[0081] First, regarding the time length Tk1, we are concerned with the first target velocity Va1. We assume the first discharge velocity Vr1 is constant. Then, the time length Tk1 has a term (L2 / Va1) that is inversely proportional to the first target velocity Va1, and the other terms can be considered constants. The term (L2 / Va1) that is inversely proportional to the first target velocity Va1 can then be expressed as follows: Figure 5A The image shows that, in Figure 5A The horizontal axis represents Va1, while the vertical axis represents Tk1. That is, the time length Tk1 is inversely proportional to the velocity Va1 of the first target.

[0082] Next, regarding the time length Tk1, we focus on the second target velocity Va2, and assume the second discharge velocity Vr2 is constant. Then, the time length Tk2 has a term proportional to the time length Tk2 (Va2 / a) and an inversely proportional term to the second target velocity Va2 (L2 / Va2), and the other terms can be considered constants. Therefore, (Va2 / a) + (L2 / Va2) can be expressed as follows: Figure 5B The image shows that, in Figure 5B The horizontal and vertical axes represent Va2 and Tk2, respectively. That is, the time length Tk2 is inversely proportional to the second target velocity Va2, and it reaches its minimum value (f2) when Va2 = g2. Regarding the time length Tk2, it gradually increases as the second target velocity Va2 increases beyond the value g2.

[0083] Therefore, the time length Tk1 used to transport long sheets is inversely proportional to the first target speed Va1, but if the second target speed Va2 increases excessively, the time length Tk2 used to transport short sheets increases. Therefore, in this embodiment, the first target speed Va1 is set to be greater than the second target speed Va2 (Va1>Va2).

[0084] Therefore, the shorter time length Tk1 improves the productivity of printer 1 when conveying long sheets. Furthermore, as mentioned above, in the sheet conveying direction, the point where the conveying speed of printer 1 increases when using long sheets is located downstream of the point where the conveying speed of printer 1 increases when using short sheets. However, the first target speed Va1 is faster than the second target speed Va2. Therefore, collisions between two sheets conveyed consecutively can be prevented. That is, sheet damage to printer 1 can be reduced.

[0085] Setting the first target speed Va1 to a high value increases the time required for the reverse motor 234 to accelerate to the first target speed Va1 and the time required to decelerate the reverse motor 234 from the first target speed Va1. However, when the pair of reverse rollers 72 receive the long sheet, the reverse motor 234 is rotating at the processing speed Vp. Therefore, setting the first target speed Va1 to a high value has little effect on the stationary time length Tr and the non-rotation time length Ts, thus allowing sufficient stationary time Tr and stopping time Ts to be provided for the reverse motor 234. Therefore, failure of the reverse motor 234 can be prevented.

[0086] On the other hand, when the pair of reverse rollers 72 receive the short sheet, the reverse motor 234 has been accelerated to a second target speed Va2, which is faster than the processing speed Vp. Therefore, setting the second target speed Va2 to a high value, similar to the first target speed Va1, affects the rest time length Tr and the stop time length Ts. Therefore, by setting the second target speed Va2 to be slower than the first target speed Va1, sufficient rest time Ts can be provided for the reverse motor 234, thereby reducing the likelihood of malfunctions in the reverse motor 234. Furthermore, after the speed of the reverse motor 234 increases from the second target speed Va2, which is faster than the processing speed Vp, the pair of reverse rollers 72 receive the short sheet. Therefore, the productivity of the printer 1 can be improved.

[0087] Next, assume that the first discharge velocity Vr1 and the second discharge velocity Vr2 are constant. Time Tk1 has a term inversely proportional to the first discharge velocity Vr1 (L3 / Vr1) and a term proportional to the first discharge velocity Vr1 (Vr1 / d), and other terms can be considered constant. Similarly, time Tk2 has a term inversely proportional to the second discharge velocity Vr2 (L3 / Vr2) and a term proportional to the second discharge velocity Vr2 (Vr2 / d), and other terms can be considered constant.

[0088] (L3 / Vr1)+(Vr1 / d) can be expressed as follows: Figure 6 The image shows that, in Figure 6 The horizontal axis represents Va1 and the vertical axis represents Tk1. That is, as the first discharge velocity Vr1 increases, time Tk1 gradually decreases, and becomes minimum at time point f3 when Vr1 = 3. Then, as the first discharge velocity Vr1 becomes significantly greater than the value g3, time Tk1 gradually increases. Incidentally, (L3 / Vr2) + (Vr2 / d) is similar to... Figure 6 The expression (L3 / Vr1)+(Vr1 / d) is shown, and time Tk2 also has a similar trend to time tk1.

[0089] Therefore, excessively increasing the first discharge speed Vr1 and the second discharge speed Vr2 increases the length of time Tk1 and time Tk2. On the other hand, from the viewpoint of preventing collisions between two sheets that are being driven continuously, increasing the first discharge speed Vr1 and the second discharge speed Vr2 is advantageous.

[0090] The longer sheet begins acceleration later than the shorter sheet and travels a longer distance via the reverse conveying channel 71. Therefore, the longer the two sheets being conveyed consecutively, the more likely they are to collide. Thus, within the range of the first drive sequence—that is, within the range where sufficient stopping time Tr and resting time Ts can be provided—collision between the two sheets can be prevented by increasing the first discharge speed Vr1. Therefore, in this embodiment, the first discharge speed Vr1 is set to be faster than the second discharge speed Vr2.

[0091] [Sheet conveying control]

[0092] Next, refer to Figures 7 to 10 The flowchart in the document describes the sheet feed control during a print job performed by printer 1 in this embodiment. (See reference...) Figure 7 The user inputs the weight and size of the recording medium sheet, the operating mode (face-up mode, face-down mode, duplex mode, etc.), print count (K), etc., through the operation control unit 412, and starts the printer 1 to begin the printing job (S1). Incidentally, the operation to be performed in step S can be performed by an external PC, smartphone, etc. connected to the printer 1.

[0093] When a printing job begins, the Nth sheet is fed by the feed conveyor 12 (step S2). Incidentally, if the sheet being fed at the beginning happens to be the first sheet in the printing job, the Nth (=1)th sheet is fed. Next, the control unit 600 uses the image forming unit 50 to cause the printer 1 to form an image on the first surface of the sheet (step S3). Then, the control unit 600 drives the first pull motor 231 and the second pull motor 232 at a processing speed Vp to rotate a pair of first pull rollers 201, a pair of second pull rollers 202, and a pair of third pull rollers 203 (step S4).

[0094] Next, the control unit 600 determines whether the sheet being conveyed causes the first detection unit 221 to open, that is, whether the leading edge of the sheet has reached the first detection unit 221 (step S5). If the first detection unit 221 is open ("Yes" in S5), the control unit 600 determines whether the sheet is being conveyed to form an image on its first surface, that is, whether the sheet has been flipped (step S6).

[0095] If it is determined that the sheet is being fed to form an image on its first surface ("Yes" in step S6), the control unit 600 determines whether the current print job is set to face-up printing (step S7). If it is set to face-up printing ("Yes" in step S7), or if it is determined in step S6 that no sheet is being fed to form an image on the first surface of the sheet ("No" in step S6), the control unit 600 proceeds to step S11, in which the control unit 600 flips the first switching member 62 toward the straight conveyor channel 63 (step S11).

[0096] Therefore, the sheet is delivered from the straight conveyor channel 63 to the reverse merging channel 68, and then discharged into the discharge tray 500 via a pair of discharge rollers 207 (step S12). Next, the control unit 600 determines whether the discharged sheet (the Nth sheet) is the Kth sheet, which is the last sheet in the current operation (step S13). If the sheet is the Kth sheet ("Yes" in step S13), the control unit 600 ends the operation. If the sheet is not the Kth sheet ("No" in step S13), the control unit 600 increments N by 1 (step S14) and returns to step S2.

[0097] If the job does not require face-up printing in step S7 (No in step S7), the control unit 600 flips the first switching member 62 toward the reverse pre-feed channel 64 (step S8). Then, the control unit 600 determines whether the sheet being fed has activated the second detection unit 222, that is, whether the leading edge of the sheet has reached the second detection unit 222 (step S9). If the second detection unit 222 has been activated (Yes in step S9), the control unit 600 determines whether the current job is set to face-down printing (step S10). If the current job is a face-down printing job, the sheet is turned by a pair of reverse rollers 72 so that the first surface of the sheet on which the image has just been formed faces down. Then, the sheet is discharged.

[0098] If the current operation is not face-down (No in step S10), the control unit 600 conveys the sheet to the double-sided conveying unit 90 (step S15) and returns to step S3. That is, an image is formed on the second surface of the sheet, and then, after undergoing steps S3-S6 and S11-S12, the sheet is discharged into the discharge tray 500.

[0099] If the current job is set to face-down printing in step S10 (Yes in step S10), the control unit 600 determines whether the length of the sheet is greater than a preset length L (step S16). If it is greater than the preset length L (Yes in step S16), the control unit 600 performs first transport control as a first transport mode (step S20). If it is not greater than the preset length L (No in step S16), the control unit 600 performs second transport control as a second transport mode (step S40). In other words, when transporting a long sheet (whose length is greater than the preset length L), first transport control is performed. When transporting a short sheet (whose length is not greater than the preset length L), second transport control is performed. The first transport control and the second transport control will then be described.

[0100] Upon completion of the first or second control, the sheet is discharged into the discharge tray 500. While the sheet is being discharged, the control unit 600 determines whether the discharged sheet (i.e., the Nth sheet) is the Kth sheet, which is the last sheet in the current operation (step S17). If the sheet is the Kth sheet ("Yes" in step S17), the control unit 600 ends the operation. If it is determined that the sheet is not the Kth sheet ("No" in step S17), the control unit 600 increments N by 1 (step S18) and returns to step S12.

[0101] [First Conveyor Control]

[0102] Next, refer to Figure 9 The flowchart in the diagram describes the first transport control. As described above, the first transport control is a transport control performed by the branch transport unit 60 and the reverse transport unit 70 to control the transport of long sheets when the printer 1 is in face-down printing mode.

[0103] refer to Figure 9 At the start of the first transport control, the control unit 600 begins driving the reverse motor 234 at a processing speed Vp (step S21). Then, it begins counting the delay time until the timing for accelerating the sheet. As the preset time length (delay) elapses, the control unit 600 accelerates the first pull motor 231, the second pull motor 232, and the reverse motor 234 to a first target speed Va1 (steps S22 and S23). Incidentally, the timing for the delay time to elapse is the same as the timing for the trailing edge of the sheet to be transported a distance C after exiting the image forming unit 50. Incidentally, the distance C is optional. Steps S22 and S23 constitute the first acceleration control.

[0104] In the first conveying control for conveying long sheets, when a pair of reverse rollers 72 receive the sheet, the sheet is held clamped by the fixing clamp 58a. Therefore, when the leading edge of the long sheet reaches the pair of reverse rollers 72, the speed Vf1 of the reverse motor 234 is equal to the processing speed Vp.

[0105] Next, the control unit 600 determines whether the rear end of the sheet has exited the clamping portion of the pair of third pull rollers 203 (step S24). If it is determined that the rear edge of the sheet has exited the clamping portion of the pair of third pull rollers 203 ("Yes" in step S24), the control unit 600 decelerates the first pull motor 231 and the second pull motor 232 to the processing speed Vp (step S25). The reason why the control unit 600 decelerates the first pull motor 231 and the second pull motor 232 to the processing speed Vp is to prepare for the feeding of the next sheet.

[0106] Incidentally, once the trailing edge of the sheet emerges from the clamping portion of the pair of first pull rollers 201, the control unit 600 decelerates the first pull motor 231 and the second pull motor 232 to the processing speed Vp. Subsequently, once the trailing edge of the sheet emerges from the clamping portion of the pair of third pull rollers 203, the second pull motor 232 can be decelerated to the processing speed Vp.

[0107] Next, the control unit 600 determines whether the trailing edge of the sheet has passed the second switching member 65 (step S26). If it is determined that the trailing edge of the sheet has passed the second switching member 65 ("Yes" in step S26), the control unit 600 stops the reverse motor 234 (step S27). The control unit 600 counts the stop time Tr (step S28). Once the stop time Tr has elapsed, the control unit 600 starts driving the reverse motor 234, the conveying motor 235, and the discharge motor 237 in the reverse direction (second rotation direction) at a first discharge speed Vr1 (steps S28 and S29). Driving the reverse motor 234, the conveying motor 235, and the discharge motor 237 in the reverse direction (second rotation direction) causes the sheet to be conveyed toward the reverse rear conveying channel 66 and a pair of discharge rollers 207.

[0108] Incidentally, steps S27 to S29 constitute a first discharge control for accelerating the reverse motor 234 to a first discharge speed Vr1 in the second rotational direction after the motor is temporarily stopped to turn the sheet.

[0109] Next, the control unit 600 determines whether the trailing edge of the sheet has emerged from the clamping portion of the pair of reverse rollers 72 (step S30). If it is determined that the trailing edge of the sheet has emerged from the clamping portion of the pair of reverse rollers 72 ("Yes" in step S30), the control unit 600 stops the reverse motor 234 (step S31). Then, the control unit 600 determines whether the trailing edge of the sheet has emerged from the clamping portion of the pair of conveyor rollers 206 (step S32). If it is determined that the trailing edge of the sheet has emerged from the clamping portion of the pair of conveyor rollers 206 ("Yes" in step S32), the control unit 600 stops the conveyor motor 235 (step S33).

[0110] Subsequently, the control unit 600 determines whether the trailing edge of the sheet has emerged from the clamping portion of the pair of discharge rollers 207 (step S34). If it is determined that the trailing edge of the sheet has emerged from the clamping portion of the pair of discharge rollers 207 ("Yes" in S34), the control unit 600 determines that the sheet has just been discharged into the discharge tray 500 and stops the discharge motor 237 (step S35). That is, the first conveying control ends.

[0111] [Second Conveyor Control]

[0112] Next, follow Figure 10 The flowchart in the diagram describes the second transport control. As described above, the second transport control is the transport control performed by the branch transport unit 60 and the reverse transport unit 70 when the printer 1 is operating in a face-down mode and using short sheets.

[0113] refer to Figure 10 When the second transport control begins, the control unit 600 starts counting the time until a delay time has elapsed to determine the point at which the sheet needs to be accelerated (step S41). Once the delay time has elapsed, the control unit 600 accelerates the first pull motor 231 and the second pull motor 232 to the second target speed Va2 (step S42). Furthermore, the reverse motor 234 is driven at the second target speed Va2 (step S43). Incidentally, the timing of the delay time coincides with the point at which the trailing edge of the sheet has just been transported a distance C past the fixing clamp 58a, that is, the point at which the trailing edge of the sheet has just exited the image forming unit 50. Steps S41 and S43 constitute the second acceleration control.

[0114] In the second conveying control performed when conveying short sheets, the trailing edge of the sheet moves past the fixing clamping section 58a when the pair of reverse rollers 72 receive the sheet. Therefore, the speed Vf2 at which the reverse motor 234 starts driving when the leading edge of the sheet reaches the pair of reverse rollers 72 can be set to a second target speed Va2 that is faster than the processing speed Vp.

[0115] Incidentally, the distance C is optional. That is, after a preset time has elapsed after the first extraction motor 231 and the second extraction motor 232 have started to accelerate to the second target speed Va2, the reverse motor 234 can be accelerated to the second target speed Va2.

[0116] Subsequently, steps S44 to S48 are referenced. Figure 9 Steps S24 to S28 of the first conveying control described are the same. Therefore, they are not described in detail. After the stop time Tr in step S48, the control unit 600 drives the reverse motor 234, the conveying motor 235, and the discharge motor 237 in the reverse direction (second rotational direction) at the second discharge speed Vr2 (step S49). While the reverse motor 234, the conveying motor 235, and the discharge motor 237 are driven in the reverse direction, the sheet is conveyed toward a pair of discharge rollers 207 through the reverse rear conveying channel 66.

[0117] Incidentally, steps S47 to S49 constitute a second discharge control for accelerating the reverse motor 234 to a second discharge speed Vr2 in the second rotational direction after the reverse motor 234 is temporarily stopped to turn the sheet. Steps S50 to S55 are referenced. Figure 10 Steps S30 to S35 in the first conveying control described are the same. Therefore, they are not described in detail.

[0118] Incidentally, in the above description of the first embodiment, the second transport control is described with reference to the case where the number of sheets simultaneously transported through printer 1 is one. However, this embodiment is not intended to limit the scope of the invention. That is, the invention is also compatible with the following situation: two or more sheets are continuously transported while providing a preset sheet interval, such that two or more sheets are simultaneously transported through printer 1. In this case, the routes from step S13 to step S14 and from step S17 to step S18 are eliminated to enable the continuous transport of two or more sheets through printer 1.

[0119] As described above, in this embodiment, the printer 1 is configured such that a first transport control is performed when the printer 1 is in face-down mode and the recording medium is a long sheet, and a second transport control is performed when the printer 1 is in face-down mode and the recording medium is a short sheet. That is, when the printer 1 is configured such that its reverse motor 234 can accelerate or decelerate to improve the productivity of the printer 1, the timing at which the printer begins to accelerate from the leading edge of the reference sheet is variable, and the probability of two sheets being continuously transported by the printer colliding with each other is variable.

[0120] Therefore, in this embodiment, the first target speed Va1 and the first discharge speed Vr1 in the first transport control are set to be faster than the second target speed Va2 and the second discharge speed Vr2 in the second transport control. Thus, the productivity of printer 1 can be increased while preventing sheet damage, and the reverse motor can remain stationary for a sufficient period of time, regardless of the sheet length.

[0121] [Example 2]

[0122] Next, a second embodiment of the invention will be described. However, the second embodiment is essentially the same as the first embodiment, except that in the second embodiment, the printer 1 maintains a constant speed at which it ejects the sheet, regardless of the sheet length. Therefore, structural components of the printer 1 in this embodiment that are structurally similar to their counterparts in the first embodiment are not illustrated or given the same reference numerals and are not described.

[0123] The duration of reverse drive of the reverse motor 234 has a term inversely proportional to the duration of time (e.g., L3 / Vr1) and a term proportional to the duration of time (Vr1 / d). Therefore, there exists an appropriate speed to satisfy the speed of the reverse motor 234 and the duration of its drive. Thus, in this embodiment, regardless of the sheet length, the speed at which the reverse motor 234 is driven during sheet discharge is set to a third discharge speed Vr3. The value of the third discharge speed Vr3 is related to... Figure 6 The value g3 is the same. During this period, the reverse motor 234 is driven in reverse for the shortest time length f3.

[0124] Figure 11 This is a flowchart of the first conveying control in the second embodiment. Figure 12 This is a flowchart of the second conveying control in the second embodiment. Besides step S69, Figure 11 Reference Figure 9 The flowchart described is the same. Except for step S89, Figure 12 Reference Figure 10 The flowcharts described are the same. In steps S69 and S89, the control unit 600 drives the reverse motor 234, the conveying motor 235, and the discharge motor 237 in the reverse direction (second rotation direction) at a third discharge speed Vr3 (steps S69 and S89).

[0125] As described above, in this embodiment, regardless of the sheet length, the reverse motor 234 is driven in reverse at a speed set to the third discharge speed Vr3. Therefore, high productivity of printer 1 can be maintained while providing sufficient stop time Tr and rest time Ts for printer 1.

[0126] [Example 3]

[0127] Next, a third embodiment of the present invention will be described. The printer in the third embodiment is structurally identical to the printer 1 in the first embodiment, except that, in the third embodiment, its image forming portion, similar to the image forming portion in the first embodiment, includes a cooling unit 300. Therefore, structural features of the printer in this embodiment that are identical to those of the printer in the first embodiment are not described, or are given the same reference numerals in the drawings as those in the first embodiment.

[0128] In recent years, printer productivity has increased significantly. Therefore, the following situation sometimes occurs: after the toner image is fixed onto the film by heat and pressure in the fixing section, but before the toner image cools down, the toner image on the recording medium sheet is clamped by a pair of transport rollers. If the toner image is clamped by the pair of transport rollers before being fixed onto the film, the toner image ends up with an impression from the clamping portion of the pair of transport rollers, which is undesirable from a print quality point of view.

[0129] Therefore, in this embodiment, as Figure 13 As shown, the printer 103, which is the image forming apparatus in this embodiment, is provided with an image forming unit 50C including a cooling section 300. The cooling section 300 has a top belt 301 and a bottom belt 302 for conveying the sheet. After being transferred onto the sheet in the secondary transfer clamping section T2 and fixed by the fixing device 58, the toner image comes into contact with the top belt 301. The cooling section 300 is configured such that the inner surface of the top belt 301 is cooled by a heat sink. Therefore, the toner image is efficiently cooled when it comes into contact with the top belt 301. Incidentally, the cooling section 300 can be configured such that air is blown onto the fins of the heat sink. Alternatively, the cooling section 300 can be configured without the top belt 301. In this case, the cooling section 300 is configured such that the top surface of the sheet is cooled by an airflow generated by a fan when the sheet is conveyed by the bottom belt 302.

[0130] From the viewpoint of the performance of the cooling section 300, it is desirable that the sheet is not accelerated until its trailing edge exits the cooling section 300. Therefore, in this embodiment, after the trailing edge of the sheet has exited the cooling section 300 and been conveyed to a distance C, the first pull motor 231, the second pull motor 232, and the reverse motor 234 are accelerated to a first target speed Va1 or a second target speed Va2. Figure 9 and Figure 10 The second conveying control in this embodiment is different from the conveying control in the first embodiment. Figures 7 to 10 ) or the transport control in the second embodiment ( Figures 11 to 12 It is the same. Therefore, it is not described.

[0131] As described above, in this embodiment, the image forming unit 50C, which is an image forming section, has a cooling section 300. Therefore, the printer 3 in this embodiment can efficiently cool the toner image on the sheet, and thus has better image quality than the printers in the first and second embodiments.

[0132] [other]

[0133] Incidentally, the description of the first embodiment does not address the relationship between the first discharge speed Vr1, the second discharge speed Vr2, the first target speed Va1, and the second target speed Va2. However, this relationship can be configured such that the first discharge speed Vr1 and the second discharge speed Vr2 are equal to the first target speed Va1 and the second target speed Va2, respectively. This arrangement allows the first target speed Va1 and the first discharge speed Vr1 of the reverse motor 234 to be at their maximum speeds, thereby enabling more efficient use of the reverse motor 234 in terms of performance. Furthermore, needless to say, the first discharge speed Vr1 and the second discharge speed Vr2 can be different from the first target speed Va1 and the second target speed Va2, respectively.

[0134] Furthermore, in any of the embodiments of the present invention described above, printers 1 and 103 are so-called electrophotographic types. However, these embodiments are not intended to limit the scope of the invention. For example, the present invention is also compatible with so-called inkjet-type image forming apparatuses that form images on a sheet of recording medium by ejecting liquid ink from nozzles.

[0135] The present invention is also compatible with image forming systems or apparatuses having a program configured via a network or storage medium and having a computer, the program enabling the system or apparatus to perform one or more functions of the image forming apparatus described above, the computer having one or more processors capable of reading and executing the program. Furthermore, the present invention is also compatible with circuits (e.g., ASICs) capable of performing one or more functions of the image forming apparatus described above.

[0136] While the invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the appended claims should be given the broadest interpretation to include all such modifications and equivalent structures and functions.

Claims

1. An image forming apparatus, comprising: An image forming section, the image forming section being configured to form an image on a sheet; The reverse roller pair is configured to feed the sheet in a first direction and then reverse the sheet and feed it in a second direction opposite to the first direction in order to turn the sheet through the image forming section. A reverse motor is configured to rotate in a first rotational direction and feed the sheet to the reverse roller pair in the first direction, and to rotate in a second rotational direction opposite to the first rotational direction and feed the sheet to the reverse roller pair in the second direction. as well as A controller is configured to control the rotation of the reverse motor in a first feeding mode and a second feeding mode, wherein a sheet having a first length is fed in the first feeding mode and a sheet having a second length shorter than the first length is fed in the second feeding mode. In the first feeding mode, the controller performs a first acceleration control, in which, after the rear end of the sheet passes the image forming section, the reverse motor rotating in the first rotation direction is accelerated from a predetermined speed to a first target speed that is faster than the predetermined speed. In the second feeding mode, the controller performs a second acceleration control, in which, after the rear end of the sheet passes the image forming section, the reverse motor rotating in the first rotation direction is accelerated to a second target speed that is slower than the first target speed.

2. The image forming apparatus according to claim 1, wherein, The predetermined speed is the image forming speed corresponding to the sheet feeding speed during image formation by the image forming section.

3. The image forming apparatus according to claim 1, wherein, The distance between the image forming portion and the reverse roller pair in the sheet feeding direction is shorter than the first length and longer than the second length.

4. The image forming apparatus according to claim 1, wherein, In the first feeding mode, the reverse roller pair is driven at the predetermined speed after the leading edge of the sheet reaches the reverse roller pair, and in the second feeding mode, the reverse roller pair is driven at a second target speed when the leading edge of the sheet reaches the reverse roller pair.

5. The image forming apparatus according to claim 1, wherein, When the first surface of the sheet on which the image is formed by the image forming section is turned by the reverse roller pair and the sheet changes from the upper surface side to the lower surface side, the first acceleration control and the second acceleration control are executed.

6. The image forming apparatus according to claim 1, wherein, In a first feeding mode, the controller performs a first discharge control, in which the reverse motor, which is stopped once to turn the sheet, is accelerated to a first discharge speed in a second rotational direction. In a second feeding mode, the controller performs a second discharge control, in which the reverse motor, which is stopped once to turn the sheet, is accelerated to a second discharge speed in a second rotational direction that is slower than the first discharge speed.

7. The image forming apparatus according to claim 1, wherein, The image forming portion includes a fixing portion, which is configured to fix the toner image transferred onto the sheet to the sheet at a clamping portion, and After the film passes through the fixing section at the rear end, the controller performs either a first acceleration control or a second acceleration control.

8. The image forming apparatus according to claim 1, wherein, The image forming section includes a cooling section configured to cool the toner image transferred onto the sheet, and After the sheet passes through the cooling section at its rear end, the controller performs either a first acceleration control or a second acceleration control.

9. An image forming apparatus, comprising: An image forming section, the image forming section being configured to form an image on a sheet; The reverse roller pair is configured to feed the sheet in a first direction and then reverse the sheet and feed it in a second direction opposite to the first direction in order to turn the sheet through the image forming section. A reverse motor is configured to rotate in a first rotational direction and feed the sheet to the reverse roller pair in the first direction, and to rotate in a second rotational direction opposite to the first rotational direction and feed the sheet to the reverse roller pair in the second direction. as well as A controller is configured to control the rotation of the reverse motor in a first feeding mode and a second feeding mode, wherein a sheet having a first length is fed in the first feeding mode and a sheet having a second length shorter than the first length is fed in the second feeding mode. In the first feeding mode, the controller performs a first acceleration control, in which the reverse motor rotating in the first rotation direction is accelerated from a predetermined speed to a first target speed that is faster than the predetermined speed. In the second feeding mode, the controller performs a second acceleration control, in which the reverse motor rotating in the first rotation direction is accelerated to a second target speed that is slower than the first target speed.

Images