welding gun

Abstract

To reduce the size in a width direction, of a welding gun having guide mechanism.SOLUTION: A welding gun 100 comprises: a fixed electrode 11 fixed to an arm 30; a movable electrode 12 held in a holder 22 and provided in an advanceable and retractable manner; a pressurization drive unit 40 that includes a rod portion 41 fixed to the holder 22 holding the movable electrode 12 and moving the holder 22 forward with respect to the arm 30 and that sandwiches a welding object 300 between the movable electrode 12 and the fixed electrode 11 to thereby pressurizes the welding object 300; and a ball spline 50 (guide mechanism) that is disposed to extend parallel to a shaft C3 of the rod portion 41 and guides the holder 22, wherein the rod portion 41 is fixed to the holder 22 at a position eccentric to an extension line of a shaft C1 of the fixed electrodes 11, and the ball spline 50 has only one spline shaft 51 fixed to the holder 22 in a plane including a shaft C2 of the movable electrode 12 and a shaft C3 of the rod section 41.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a welding gun. [Background technology]

[0002] A welding gun used for resistance spot welding has a fixed electrode and a movable electrode arranged opposite each other, and is configured such that a pressure drive unit moves the movable electrode toward and away from the fixed electrode fixed to an arm. In a welding gun configured in this manner, the pressure drive unit advances the movable electrode toward the fixed electrode, and the workpieces placed between the fixed and movable electrodes are sandwiched and pressurized by both electrodes, and a large current is passed between the two electrodes for a short period of time, thereby joining the workpieces.

[0003] The pressure drive unit has a rod that moves linearly, and this rod moves the movable electrode toward the fixed electrode, thereby advancing and retracting the movable electrode. Some pressure drive units are equipped with a rotation prevention mechanism to prevent the rod from rotating around its axis due to a reaction force when pressure is applied between the movable electrode and the fixed electrode while the workpiece is sandwiched between them. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-025877 Summary of the Invention [Problem to be solved by the invention]

[0005] In the case of a welding gun in which the movable electrode is held by a holding member and the rod portion is fixed to the holding member at a position that is eccentric (offset) from the extension of the axis of the fixed electrode, when the tip of the fixed electrode and the tip of the movable electrode clamp the object to be welded, the rod portion pushes against a position on the holding member that is eccentric from the clamping position, causing the rod portion to bend.

[0006] In other words, the holding member receives a reaction force from the fixed electrode toward the rear on the fixed axis of the movable electrode, and receives a load from the rod portion toward the front on the axis pushed by the rod portion, which generates a moment in the holding member, and this moment causes the holding member to try to rotate, causing the rod portion to bend.

[0007] As a result, the movable electrode may become misaligned from the fixed electrode, and the pressure generated by the pressure drive unit may not be applied properly to the workpieces to be welded.

[0008] Therefore, a welding gun has been proposed in which the holding member is supported by a guide mechanism having two round guide rods arranged at two locations along the width direction at a predetermined interval, separate from the position where the rod portion is fixed, thereby suppressing deflection of the holding member and preventing misalignment of the movable electrode.

[0009] However, since the two round guide rods are arranged side by side in the width direction, the width of the welding gun increases, which places greater restrictions on the range in which the welding gun can be moved and used.

[0010] An object of the present invention is to provide a welding gun having the above-mentioned guide mechanism and having a reduced width. [Means for solving the problem]

[0011] The present invention is a welding gun comprising: a fixed electrode fixed to an arm; a movable electrode held by a holding member separate from the arm; a pressure drive unit having a rod portion fixed to the holding member and moving back and forth linearly, wherein the rod portion advances the holding member relative to the arm, thereby applying pressure to the workpiece between the movable electrode and the fixed electrode by sandwiching the workpiece between them; and a guide mechanism extending parallel to the axis of the rod portion and guiding the holding member, wherein the rod portion is fixed to the holding member at a position eccentric to the extension of the axis of the fixed electrode, and the guide mechanism has only one guide rod fixed to any of the movable side part including the movable electrode, the holding member, and the rod portion. [Effects of the Invention]

[0012] According to the welding gun of the present invention, the size in the width direction can be reduced. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a perspective view showing a welding gun according to a first embodiment. [Figure 2] FIG. 2 is a longitudinal sectional view of the welding gun of FIG. 1. [Figure 3] FIG. 2 is a partial cross-sectional perspective view showing the structure of a ball spline in a welding gun. [Figure 4] FIG. 10 is a perspective view showing a welding gun according to a second embodiment. [Figure 5] FIG. 5 is a longitudinal sectional view of the welding gun of FIG. 4. DETAILED DESCRIPTION OF THE INVENTION

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a welding gun according to the present invention will be described with reference to the drawings.

[0015] (Embodiment 1) <Configuration> Fig. 1 is a perspective view showing a welding gun 100 of a first embodiment, Fig. 2 is a longitudinal cross-sectional view of the welding gun 100 of Fig. 1, and Fig. 3 is a partially cross-sectional perspective view showing the structure of a ball spline 50 in the welding gun 100. The illustrated welding gun 100 is one embodiment of the welding gun according to the present invention.

[0016] Welding gun 100 is a gun for resistance spot welding, and is a so-called C-type gun having a C-shaped arm 30, as shown in Fig. 1. Welding gun 100 includes fixed electrode 11, movable electrode 12, holders 21 and 22, arm 30, pressure drive unit 40, ball spline 50, support member 80, and transformer 90.

[0017] In the welding gun 100, a support member 80 is fixed to an arm 30, and a pressure drive unit 40, a ball spline 50, and a transformer 90 are fixed to the support member 80. The fixed electrode 11 is fixed to the arm 30, and the movable electrode 12 is attached to the pressure drive unit 40.

[0018] More specifically, the fixed electrode 11 is fixed to the arm 30 via a holder 21 attached to one end of the C-shape of the arm 30. A detachable and replaceable electrode tip 11a is attached to the tip of the fixed electrode 11.

[0019] The movable electrode 12 is fixed to a holder 22 (holding member) that is separate from the arm 30. The holder 22 is displaceable relative to the arm 30, and by displacing the holder 22 relative to the arm 30, the movable electrode 12 moves forward and backward relative to the fixed electrode 11. The movable electrode 12 is disposed so that its axis is located on an extension of the axis C1 of the fixed electrode 11. A detachable electrode tip 12a is also attached to the tip of the movable electrode 12.

[0020] The pressure drive unit 40 has a rod portion 41. A tip 41a, which is the front end of the rod portion 41 in the front-rear direction L, is fixed to the holder 22 at a position eccentric with respect to an extension of the axis C1. The pressure drive unit 40 linearly advances and retreats the rod portion 41 along an axis C3 parallel to the axis C1. As shown in FIG. 2, the axis C3 of the rod portion 41 is eccentric upward in the height direction H by a dimension h with respect to the axis C1 of the fixed electrode 11.

[0021] The ball spline 50 is an example of a guide mechanism that guides the holder 22, and has high rigidity (high strength) against bending in a direction intersecting the longitudinal direction (direction along the axis C4).

[0022] The ball spline 50 has a single spline shaft 51 (an example of a guide rod), two outer cylinders 52 and 53, and balls 54 (see FIG. 3). As shown in FIG. 3, the spline shaft 51 has two or more passages 51b formed on its outer circumferential surface, each of which extends linearly along an axis C4. The passages 51b may be formed as slant surfaces of ridges protruding from the outer circumferential surface, as shown in FIG. 3, or may be formed as groove surfaces recessed into the outer circumferential surface, as shown in FIG. 3.

[0023] The passage 51b is formed with an arc-shaped cross section having approximately the same diameter as the outer surface (spherical surface) of the ball 54. As a result, the spline shaft 51 is formed with a so-called irregular cross section, in which the cross-sectional contour shape taken along a plane perpendicular to the axis C4 is not a perfect circle. Therefore, even when used alone, the spline shaft 51 has higher rigidity (higher strength) against bending in a direction intersecting the longitudinal direction than a round bar having a perfect circle with the smallest radius in its cross section.

[0024] A tip 51a of the spline shaft 51, which is the front end in the front-rear direction L, is fixed to the holder 22. The position on the holder 22 where the tip 51a of the spline shaft 51 is fixed is a position above the axis C3 to which the rod portion 41 is fixed in the height direction H. In other words, the spline shaft 51 is fixed on the opposite side of the portion where the rod portion 41 is fixed from the portion where the movable electrode 12 is held.

[0025] The two outer cylinders 52, 53 are arranged side by side along the axis C4 direction of the spline shaft 51. The two outer cylinders 52, 53 are each fixed to a frame case 55 and are configured integrally.

[0026] As shown in FIG. 3, a circulation path 53a (52a) is formed on the inner peripheral surface of the outer cylinder 53 (similarly to the outer cylinder 52) to circulate a plurality of balls 54 rolling along the passage 51b of the spline shaft 51.

[0027] When the spline shaft 51 is displaced along the axis C4 relative to the outer cylinders 53, 52 fixed to the frame case 55, the multiple balls 54 sandwiched and arranged between the passage 51b of the spline shaft 51 and the circulation paths 53a, 52a of the outer cylinders 53, 52 move while rolling within the circulation paths 53a, 52a as the spline shaft 51 moves, allowing the spline shaft 51 to be displaced linearly along the axis C4 with high precision.

[0028] In ball spline 50, spline shaft 51 is covered by outer cylinders 52, 53, each having a certain length in the longitudinal direction, with a large number of balls 54 arranged in the longitudinal direction. Therefore, even with this configuration, ball spline 50 has higher rigidity against bending than a simple bar-shaped guide rod.

[0029] The support member 80 includes a top plate 81 , two upper side plates 82 , two lower side plates 83 , a middle plate 84 , and two spacers 85 .

[0030] Top plate 81 is a plate-like body arranged horizontally (on a surface extending in width direction W and front-rear direction L) at the uppermost part in height direction H of support member 80. Top plate 81 is fixed to mounting member 210 that mounts welding gun 100 to robot arm 200.

[0031] The middle plate 84 is a plate-like body that is disposed horizontally below the top plate 81, similar to the top plate 81. A transformer 90 that supplies power to the fixed electrode 11 and the movable electrode 12 is fixed to the upper surface of the middle plate 84.

[0032] The two lower side plates 83 are plate-like bodies arranged vertically (on surfaces extending in the height direction H and the front-rear direction L) on both the left and right sides in the width direction W, with axes C3 and C4 in between.

[0033] The two lower side plates 83 are fixed to the middle plate 84 at the rear of the upper part in the height direction H and in the front-to-rear direction L, sandwiching the middle plate 84 from the outside in the width direction W. The two lower side plates 83 are fixed to the arm 30 at the front of the upper part in the height direction H and in the front-to-rear direction L, sandwiching the arm 30 from the outside in the width direction W via spacers 85, 85. The two lower side plates 83 fix the arm 30 in an orientation such that the axis C1 of the fixed electrode 11 is parallel to the front-to-rear direction L.

[0034] The two lower side plates 83 also secure the pressure drive unit 40 at the lower part in the height direction H, sandwiching it from the outside in the width direction W. The two lower side plates 83 secure the main body of the pressure drive unit 40 (the case portion excluding the rod portion 41, etc.) in an orientation in which the axis C3 of the pressure drive unit 40 is parallel to the front-rear direction L.

[0035] The two lower side plates 83 sandwich and secure the frame case 55 of the ball spline 50 from the outside in the width direction W between the upper and lower portions in the height direction H. The two lower side plates 83 secure the ball spline 50 in an orientation in which the axis C4 of the spline shaft 51 is parallel to the front-rear direction L. As described above, the ball spline 50 and the pressure drive unit 40 are integrally configured via the lower side plates 83, but are not directly fixed to each other.

[0036] Since the arm 30, the pressure drive unit 40, and the ball spline 50 are respectively fixed to the two lower side plates 83 as described above, the axis C1 of the fixed electrode 11, the axis C3 of the pressure drive unit 40, and the axis C4 of the ball spline 50 are arranged parallel to each other and in the same vertical plane (a plane extending in the height direction H and the front-to-rear direction L).

[0037] The two upper side plates 82 are fixed at the top of the height direction H, sandwiching the top plate 81 from the outside in the width direction W, and at the bottom of the height direction H, they are fixed at the two lower side plates 83, sandwiching them from the outside in the width direction W.

[0038] <effect> The operation of the welding gun 100 configured as above will be described below.

[0039] The welding gun 100 is fixed to the robot arm 200 by fixing the top plate 81 of the support member 80 to a mounting member 210 attached to the robot arm 200, and its position and posture relative to the workpiece 300 to be welded are adjusted according to the movement of the robot arm 200.

[0040] Robot arm 200 controls the position and attitude of welding gun 100 so that workpiece 300 is positioned between electrode tip 11a of fixed electrode 11 and electrode tip 12a of movable electrode 12, as shown in FIG.

[0041] In the welding gun 100, a control unit (not shown) controls the pressure drive unit 40 to move the rod unit 41 forward along the axis C3 in the front-to-rear direction L. This causes the holder 22 fixed to the rod unit 41 to move the movable electrode 12 forward along the axis C1 toward the fixed electrode 11.

[0042] At this time, the spline shaft 51, whose tip 51a is fixed to the holder 22, also advances along the axis C4 relative to the outer cylinders 52, 53 fixed to the support member 80 as the holder 22 advances.

[0043] As the movable electrode 12 advances, the electrode tip 11a of the fixed electrode 11 and the electrode tip 12a of the movable electrode 12 face each other on the extension of the axis C1 with the work-piece 300 sandwiched therebetween.

[0044] Then, with the workpiece 300 sandwiched between the electrode tip 11a of the fixed electrode 11 and the electrode tip 12a of the movable electrode 12, the pressure drive unit 40 applies pressure to move the rod unit 41 further forward, causing the fixed electrode 11 and the movable electrode 12 to tightly sandwich and pressurize the workpiece 300 with a predetermined load.

[0045] At this time, the portion of the holder 22 on the axis C3 receives a forward pressure force from the rod portion 41, while the portion of the holder 22 on the axis C1 receives a rearward reaction force from the fixed electrode 11. As a result, a moment that tends to rotate counterclockwise in FIG. 2 is generated in the holder 22. If the holder 22 were to rotate due to this moment, the rod portion 41 fixed to the portion on the axis C3 would bend so that the tip 41a would lower. As a result, the electrode tip 12a of the movable electrode 12 would be misaligned downward from the axis C1.

[0046] In contrast, in the welding gun 100 of this embodiment, a ball spline 50 is fixed to the holder 22. The ball spline 50 is provided along an axis C4 that is parallel to the axis C1 of the rod portion 41. Therefore, in order for the holder 22 to rotate, not only the rod portion 41 but also the ball spline 50 needs to bend.

[0047] However, the ball spline 50 has a high degree of rigidity that cooperates with the rod portion 41 to prevent rotation of the holder 22. Therefore, the rod portion 41 and the ball spline 50 do not bend, and the rod portion 41 maintains its shape along the axis C3, and the ball spline 50 maintains its shape along the axis C4.

[0048] Therefore, the rotation of holder 22 is prevented, and misalignment of electrode tip 12a of movable electrode 12 from its position on axis C1 can be prevented. As a result, welding gun 100 can appropriately apply the pressure force generated by pressure drive unit 40 to work-piece 300.

[0049] Then, while the welding gun 100 applies an appropriate pressure to the workpiece 300 using the movable electrode 12 and the fixed electrode 11 as described above, the control unit controls the transformer 90 to pass current between the fixed electrode 11 and the movable electrode 12, thereby welding the workpiece 300.

[0050] As described above, according to the welding gun 100 of this embodiment, the ball spline 50, which is an example of a highly rigid guide mechanism, is provided in the holder 22 to which the rod portion 41 and the movable electrode 12 are fixed, thereby making it possible to appropriately prevent misalignment of the movable electrode 12.

[0051] Furthermore, welding gun 100 of this embodiment has a configuration in which only one ball spline 50 is provided in the same plane as axis C1 of two electrodes 11, 12 and axis C3 of pressure drive unit 40 (rod portion 41), which allows the size of welding gun 100 in width direction W to be smaller than a configuration in which two or more guide rods are arranged dispersedly in width direction W. This reduces the restrictions on the range in which welding gun 100 can be moved and used.

[0052] Furthermore, welding gun 100 of this embodiment can more efficiently obtain the effect of suppressing misalignment by arranging axes C1, C3, and C4 in the same plane. Specifically, by arranging axes C1, C3, and C4 in the same plane, welding gun 100 has high rigidity against loads along the height direction H in the plane including axes C1, C3, and C4, thereby enhancing the effect of suppressing downward misalignment of electrode tip 12a in the height direction H.

[0053] Furthermore, in the welding gun 100 of this embodiment, the frame case 55 of the ball spline 50 is fixed to the lower side plate 83 (support member 80) rather than directly to the pressure drive unit 40. Therefore, the distance in the height direction H between the rod portion 41 of the pressure drive unit 40 and the spline shaft 51 can be adjusted simply by adjusting the fixing position of the frame case 55 on the lower side plate 83.

[0054] As a result, in welding gun 100, for example, if a configuration is adopted in which dimension h, which is the amount of eccentricity from axis C1 of electrodes 11, 12 to axis C3 to which rod portion 41 is fixed, is increased, the load acting to deflect rod portion 41 increases. However, by adjusting the distance in the height direction H of axis C4 to which ball spline 50 is fixed relative to axis C1 to be larger, the strength of ball spline 50 that resists the load attempting to deflect rod portion 41 can be increased, and misalignment of movable electrode 12 can be suppressed.

[0055] Therefore, for example, in a structure in which the frame case 55 is fixed to the lower side plate 83 using bolts, the holes in the lower side plate 83 through which the bolts pass can be formed in advance as long holes extending in the height direction H, or as multiple holes lined up along the height direction H, which makes it easier to adjust the distance in the height direction H between the rod portion 41 of the pressure drive unit 40 and the spline shaft 51 than when the frame case 55 is fixed directly to the pressure drive unit 40.

[0056] However, the welding gun according to the present invention does not exclude a guide mechanism (for example, ball spline 50) fixed to pressure drive unit 40, and may be directly fixed to pressure drive unit 40.

[0057] The welding gun 100 of the present embodiment is an example in which the ball spline 50 is used as a single, yet highly rigid, guide mechanism, but the welding gun according to the present invention is not limited to one in which the ball spline 50 is used as a highly rigid guide mechanism.

[0058] In other words, the welding gun of the present invention only needs to have a single guide rod as a highly rigid guide mechanism, the guide rod having an axis C4 extending parallel to the axis C3 of the rod portion 41 within a plane including at least the axis C1 of the movable electrode 12 and the axis C3 of the rod portion 41; for example, a guide mechanism having only one guide rod with an irregular cross-sectional contour shape that is not a perfect circle can also be applied.

[0059] In this case, the welding gun of the present invention can more efficiently obtain the effect of suppressing misalignment by arranging the axes C1, C3, and C4 in the same plane.

[0060] In this way, even with a welding gun that employs a guide mechanism having only one guide rod with an irregular cross-sectional contour shape within a plane including the axis C1 of the movable electrode 12 and the axis C3 of the rod portion 41, the movable electrode 12 can be properly supported, and the size of the welding gun 100 along the width direction W can be reduced, thereby reducing the restrictions on the range in which the welding gun 100 can be moved and used.

[0061] In the welding gun 100 of this embodiment, the support member 80 is formed by dividing it into an upper side plate 82 on the upper side in the height direction H and a lower side plate 83 on the lower side, but it is not limited to being divided into upper and lower parts, and the upper side plate 82 and the lower side plate 83 may be configured as an integrated side plate.

[0062] Furthermore, although the welding gun 100 of this embodiment is an example in which the spline shaft 51 of the ball spline 50 is fixed to the holder 22, the welding gun according to the present invention may be one in which the guide rod of the guide mechanism is fixed to any one of the movable parts, which are parts that move relative to the arm and include the movable electrode, the holding member, and the rod part. Therefore, the welding gun 100 may be one in which the spline shaft 51 is fixed to the movable electrode 12 or the rod part 41. The same applies to the following embodiment 2.

[0063] (Embodiment 2) <Configuration> Fig. 4 is a perspective view showing a welding gun 400 of the second embodiment, and Fig. 5 is a vertical cross-sectional view of the welding gun 400 of Fig. 4. The illustrated welding gun 400 is another embodiment of the welding gun according to the present invention.

[0064] 4 and 5, welding gun 400 has the same basic configuration as welding gun 100 of embodiment 1, except that it has holder 122 instead of holder 22. Holder 122 is formed in a shape that is bent at an angle different from that of holder 22 so that axis C2 of movable electrode 12 is inclined at angle θ with respect to axis C1 of fixed electrode 11.

[0065] The movable electrode 12 held by the holder 122 has its electrode tip 12a positioned on an extension of the axis C1 of the fixed electrode 11, and when the holder 122 is moved forward along the axis C3 by the rod portion 41 of the pressure drive unit 40, the electrode tip 12a of the movable electrode 12 is positioned opposite the electrode tip 11a of the fixed electrode 11 on the axis C1.

[0066] The pressure drive unit 40, ball spline 50, and support member 80 of the welding gun 400 are the same as the pressure drive unit 40, ball spline 50, and support member 80 of the welding gun 100. The tip 41a of the rod portion 41 of the pressure drive unit 40 is fixed to the holder 122 at a position eccentric by a dimension h upward in the height direction H with respect to an extension line of the axis C1.

[0067] A tip end 51a of the spline shaft 51 of the ball spline 50 is fixed to a position in the height direction H above the axis C3 of the holder 122 to which the rod portion 41 is fixed.

[0068] <effect> The welding gun 400 configured as above also has the same functions and effects as the welding gun 100 of the first embodiment.

[0069] In addition, since the axis C2 of the movable electrode 12 of the welding gun 400 is inclined at an angle θ with respect to the axis C1 of the fixed electrode 11, when the rod portion 41 exerts a pressure force along the axis C3 on the holder 122, the pressure force transmitted from the holder 122 to the movable electrode 12 has a component force along the axis C2 of the movable electrode 12, and since this component force component has a downward component in the height direction H, the electrode tip 12a of the movable electrode 12 tries to escape downward from on the axis C1.

[0070] In other words, although welding gun 400 of embodiment 2 is configured to be more susceptible to misalignment than welding gun 100 of embodiment 1, the action of ball spline 50 described above can appropriately prevent misalignment of movable electrode 12.

[0071] Therefore, the welding gun 400 can appropriately apply the pressure force generated by the pressure driving unit 40 to the movable electrode 12 . [Explanation of symbols]

[0072] 11 Fixed electrode 12 Movable electrode 22,122 Holder (holding member) 40 Pressure drive unit 41 Rod section 50 Ball spline (guide mechanism) 51 Spline shaft (guide rod) 100,400 welding gun 200 Robot Arm 210 Mounting material 300 Welding object C1,C2,C3,C4 axis

Claims

1. a fixed electrode fixed to the arm; a movable electrode held by a holding member separate from the arm; a pressure drive unit having a rod portion fixed to the holding member and linearly advancing and retreating, the rod portion advancing the holding member relative to the arm, thereby sandwiching and applying pressure to the work-piece between the movable electrode and the fixed electrode; a guide mechanism that is arranged to extend parallel to the axis of the rod portion and guides the holding member, the rod portion is fixed to the holding member at a position eccentric with respect to an extension line of the axis of the fixed electrode, the guide mechanism has only one guide rod fixed to any one of the movable electrode, the holding member, and the movable portion including the rod portion, The welding gun, wherein the guide mechanism is a ball spline.

2. The welding gun according to claim 1 , wherein the holding member is formed in a curved shape so that the axis of the movable electrode is disposed in an inclined position relative to the axis of the fixed electrode.

3. the pressure drive unit, the guide mechanism, and the arm are fixed to support members disposed on both sides of the axis of the rod unit, The welding gun according to claim 1 or 2, wherein the support member is fixed to a mounting member that mounts the welding gun to a robot arm.

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