Earth electrode clamp device

Abstract

To provide a clamp device capable of clamping an overlapping part with a pair of earth electrodes regardless of a power supply portion by the earth electrodes.SOLUTION: An earth electrode clamp device 10 includes: a first earth electrode 11 that can come into contact with an overlapping part 3 of multiple plate-like members 1, 2; a second earth electrode 12 that can clamp the overlapping part 3 with the first earth electrode 11; a first clamp member 13 to which the first earth electrode 11 is attached; a second clamp member 14 to which the second earth electrode 12 is attached; and a cylinder 15 which can apply clamping force to both of the earth electrodes 11, 12. A cylinder part 15a of the cylinder 15 is attached to the first clamp member 13, a piston rod part 15b of the cylinder 15 is attached to the second clamp member 14, and the overlapping part 3 can be clamped by both of the earth electrodes 11, 12 by driving the piston rod part 15b of the cylinder 15 in a retracting direction.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an earth electrode clamping device, and more particularly to a technique for clamping a welding target with an earth electrode for spot welding. [Background technology]

[0002] As is well known, there is a type of spot welding called indirect spot welding (see, for example, Patent Document 1). In indirect spot welding, welding is performed by passing current between an abutting electrode and an earth electrode in a state in which the electrode is positioned offset from being coaxially opposed to the workpiece. This welding method is often used, for example, when direct spot welding cannot be used due to space restrictions, or in places where it is desired to avoid leaving an indentation caused by direct spot welding on one side.

[0003] On the other hand, when this type of welding is performed, the earth electrode is pressed against the workpiece from only one side, so the contact area with the workpiece is likely to be insufficient due to insufficient pressure. If resistance heating is performed in this state, defects such as welding or electrochemical deposition may occur around the contact area between the earth electrode and the workpiece. The occurrence of such defects should be avoided because they lead to a decrease in welding quality.

[0004] Therefore, as a means for solving the above problems, the present applicant has proposed a spot welding device that enables a new contact mode of the earth electrode (see Patent Document 2). In this spot welding device, a pair of electrodes attached coaxially and facing each other to a welding gun are both used as earth electrodes (first and second earth electrodes), and the first and second earth electrodes are respectively brought into contact with and clamped against overlapping portions of plate-like members to be welded by a driving means of the welding gun, thereby increasing the contact area. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2006-159235 A [Patent Document 2] JP 2016-59937 A Summary of the Invention [Problem to be solved by the invention]

[0006] In view of the recent environment surrounding the manufacturing industry, it is necessary to consider clamping a different part from the conventional one with an earth electrode to supply power in preparation for drastic changes in the manufacturing line of the welding object. Here, when the two welding electrodes provided in the welding gun are each used as an earth electrode as described above, there is a problem that the range of use is limited. That is, a welding gun is generally structured such that a pair of welding electrodes arranged coaxially opposite to each other are connected and supported by an arm portion, and a drive device for pressing and driving one of the welding electrodes is arranged coaxially rearward of the welding electrode. Therefore, depending on the power supply portion by the earth electrode, the arm portion or the drive device may interfere with the surroundings of the power supply portion, making it difficult or impossible to approach the power supply portion.

[0007] In view of the above circumstances, a technical problem to be solved in this specification is to provide a clamping device that can perform clamping with a pair of earth electrodes regardless of the location to which power is supplied by the earth electrodes. [Means for solving the problem]

[0008] The above-mentioned problems are solved by the earth electrode clamping device according to the present invention. That is, this clamping device is an earth electrode clamping device including a first earth electrode capable of contacting an overlapping portion of a plurality of plate-like members, a second earth electrode capable of clamping the overlapping portion between itself and the first earth electrode, a first clamping member to which the first earth electrode is attached, a second clamping member to which the second earth electrode is attached, and a cylinder capable of applying a clamping force to both earth electrodes, characterized in that a cylinder portion of the cylinder is attached to the first clamping member, a piston rod portion of the cylinder is attached to the second clamping member, and the piston rod portion of the cylinder is configured to be driven in a retracting direction so that the overlapping portion can be clamped by both earth electrodes.

[0009] In this way, in the earth electrode clamping device according to the present invention, the cylinder portion of the cylinder for applying the clamping force is attached to the first clamping member, the piston rod portion of the cylinder is attached to the second clamping member, and the piston rod portion of the cylinder is driven in a retracting direction so that the overlapping portion can be clamped by both earth electrodes. Therefore, the cylinder can be positioned offset from the coaxial line of the earth electrodes. In addition, a large member such as an arm portion for connecting and supporting a pair of earth electrodes, as in a welding gun, is not required. Therefore, the cylinder can be positioned in parallel with the pair of earth electrodes, for example, and the entire device can be made compact. If the clamping device can be made compact, the power supply portion can be approached without worrying about interference with the surroundings, and the versatility of the earth electrodes can be increased.

[0010] In the earth electrode clamping device according to the present invention, the first clamping member may be supported so as to be slidable along the driving direction of the cylinder.

[0011] As described above, in the clamping device according to the present invention, the first and second earth electrodes are connected to each other via the first and second clamping members and the cylinder so that the distance between them can be changed. Therefore, for example, with the first earth electrode in contact with the overlapping portion, the piston rod portion of the cylinder is driven in a retracting direction to move the second clamping member closer to the first clamping member, so that the second earth electrode attached to the second clamping member comes into contact with the overlapping portion. Therefore, by continuing to retract the piston rod portion, the overlapping portion can be pressurized and clamped by both earth electrodes. On the other hand, with the above-mentioned means, the second earth electrode is pressed more strongly than the first earth electrode, so that the load is concentrated on the surface of the second earth electrode, leading to the early wear of the second earth electrode. By pressing the first earth electrode against the overlapping portion in advance with an appropriate pressure force, the load acting on both earth electrodes can be made closer to equal, but in that case, for example, it becomes necessary to attach the first clamping member to a robot arm capable of handling high loads and control it with high positional accuracy. Such a configuration is very time-consuming and expensive, and is not suitable for a mass-produced product manufacturing line.

[0012] In consideration of the above, in the earth electrode clamp device according to the present invention, at least one of the first clamp member and the second clamp member is supported so as to be slidable along the driving direction of the cylinder. When the piston rod portion is retracted, if the second earth electrode abuts on the overlapping portion first, the first earth electrode receives a reaction force from the overlapping portion. Here, if the first clamp member is supported so as to be slidable along the driving direction of the cylinder, the first clamp member moves in the direction of the reaction force while sliding. As a result, the first earth electrode starts to move toward the overlapping portion and abuts on it before the pressing force of the second earth electrode increases. Therefore, it is possible to clamp the overlapping portion with both earth electrodes without concentrating the load on one earth electrode (the second earth electrode). Therefore, each earth electrode can be used for a long period of time, and the replacement life can be extended. In addition, if the first clamp member can be moved toward the overlapping portion as the piston rod portion is retracted, there is no need to abut the first earth electrode against the overlapping portion in advance, much less to control the pressing force. Therefore, the positioning of the first earth electrode does not need to be performed with such high precision, and it is possible to simplify the related equipment (and thus to reduce the size and cost).

[0013] Furthermore, when the first clamp member is slidably supported as described above, in the earth electrode clamp device according to the present invention, the second clamp member may be supported slidably along the driving direction of the cylinder.

[0014] In this way, by supporting the second clamp member as well as the first clamp member slidably along the driving direction of the cylinder, depending on the magnitude relationship between the retraction force and the sliding resistance of each clamp member, when the piston rod portion is retracted, the first earth electrode may start to approach the overlapping portion before the second earth electrode abuts on the overlapping portion. Therefore, the timing at which the first earth electrode abuts on the overlapping portion can be made closer to the timing at which the second earth electrode abuts on the overlapping portion, which makes it possible to apply pressure to the overlapping portion as evenly as possible. In addition, by supporting the second clamp member slidably, the posture of the second clamp member and therefore the second earth electrode when retracted and therefore when abutting on the overlapping portion are stabilized. Therefore, it is possible to clamp the overlapping portion at a more accurate position.

[0015] In the earth electrode clamping device according to the present invention, the contact surface of at least one of the earth electrodes with the overlapping portion may be formed of a knitted body made by weaving conductive linear bodies.

[0016] For example, in reality, the surface of a plate-like member constituting an automobile body has few completely flat portions, and most of the portions are curved. Therefore, if the surface of each earth electrode that contacts the overlapping portion is formed flat, it will come into contact with the surface of the overlapping portion of the plate-like member, leading to a situation where heat is easily generated. In contrast, if the surface of the earth electrode (the contact surface with the overlapping portion) is formed of a knitted body made of conductive linear bodies woven together, the knitted body will deform to follow the surface of the overlapping portion when the earth electrode contacts the overlapping portion. Therefore, the earth electrode and the overlapping portion can be contacted at many points via the linear bodies of the knitted body, and the contact area can be increased. If the contact area is increased, it is possible to avoid a situation where the current is concentrated, and it is possible to prevent a situation where excessive heat is generated locally. In addition, by providing a device dedicated to clamping the earth electrode as in the present invention, the shape of the earth electrode can be set arbitrarily, so that the shape (for example, a rectangular shape with a high ratio of the long side) and dimensions of the earth electrode and the knitted body can be set according to the form of the portion to be clamped (the overlapping portion).

[0017] The earth electrode clamping device described above is capable of clamping the overlapping portion with a pair of earth electrodes regardless of the position or shape of the overlapping portion, which is the part to which power is supplied by the earth electrode, and therefore can be suitably provided, for example, as a spot welding device including this earth electrode clamping device and a welding electrode that can abut against the overlapping portion. Effect of the Invention

[0018] As described above, according to the present invention, it is possible to provide a clamping device capable of clamping an overlapping portion with a pair of earth electrodes regardless of the location to which power is fed by the earth electrodes. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a front view of an earth electrode clamping device according to an embodiment of the present invention. [Diagram 2]2 is an enlarged view of a contact surface of the earth electrode shown in FIG. 1. [Diagram 3] FIG. 2 is a front view for explaining an example of a manner in which the earth electrode clamp device shown in FIG. 1 is attached to an overlapping portion, showing a state immediately after starting the retraction operation of the cylinder. [Figure 4] FIG. 2 is a front view for explaining an example of a manner of mounting the earth electrode clamp device shown in FIG. 1 to the overlapping portion, showing a state in which one earth electrode has first come into contact with the overlapping portion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] An embodiment of the earth electrode clamping device according to the present invention will be described below with reference to the drawings. In the following description, an example will be described in which the earth electrode clamping device is disposed below the overlapping portions of the welding objects and the overlapping portions are clamped in a horizontal direction.

[0021] Fig. 1 shows a front view of an earth electrode clamping device 10 according to one embodiment of the present invention. As shown in the figure, this earth electrode clamping device 10 clamps and grounds an overlapping portion 3 (members shown by two-dot chain lines in Fig. 1) of a plurality of plate-like members 1, 2 to be welded, and includes a first earth electrode 11, a second earth electrode 12, a first clamping member 13, a second clamping member 14, and a cylinder 15. In this embodiment, the earth electrode clamping device 10 further includes a sliding support member 16 that slidably supports each of the clamping members 13, 14. Each element will be described in detail below.

[0022] The first earth electrode 11 and the second earth electrode 12 each have an abutment surface 11a, 12a that contacts the overlapping portion 3 and serves as a clamping surface. In this embodiment, both of the abutment surfaces 11a, 12a are configured with a knitted body 18 formed by weaving conductive linear bodies 17 into a predetermined shape (see FIG. 2). In this case, for example, a copper wire is used for the conductive linear bodies 17. This knitted body 18 is fixed to the electrode bodies 11b, 12b of the earth electrodes 11, 12.

[0023] The shape of the abutment surfaces 11a, 12a (the shape of the knitted body 18 in this embodiment) is arbitrary, and for example, by forming the knitted body 18 into a rectangular sheet shape as shown in Figure 2, the abutment surfaces 11a, 12a are shaped to imitate the rectangular sheet-shaped knitted body 18.

[0024] Both the first clamp member 13 and the second clamp member 14 have main body portions 13a, 14a and conductive portions 13b, 14b attached to the main body portions 13a, 14a. The conductive portions 13b, 14b have arm portions 13b1, 14b1 extending horizontally from their upper ends, and corresponding earth electrodes 11, 12 are attached to the tips of the arm portions 13b1, 14b1. These conductive portions 13b, 14b are connected to the ground side conductive portion 20a of the base 20 via the conductive flexible portions 19a, 19b. As a result, the respective earth electrodes 11, 12 are electrically connected to the ground side conductive portion 20a via the conductive portions 13b, 14b and the conductive flexible portions 19a, 19b.

[0025] The cylinder 15 can apply the clamping force of the overlapping portion 3 to the first earth electrode 11 and the second earth electrode 12, and an air cylinder is used, for example. The cylinder 15 is arranged in the horizontal direction, that is, along the opposing direction of the pair of earth electrodes 11 and 12. Here, the cylinder portion 15a of the cylinder 15 is attached to the body portion 13a of the first clamp member 13, and the piston rod portion 15b is attached to the body portion 14a of the second clamp member 14. Thus, the second earth electrode 12 and the second clamp member 14 are connected to the first earth electrode 11 and the first clamp member 13 via the cylinder 15. Here, the above-mentioned clamping force can be applied to both earth electrodes 11 and 12 by disposing the overlapping portion 3 between the first earth electrode 11 and the second earth electrode 12 (as shown by the two-dot chain line in FIG. 1) and driving the cylinder 15 in a direction in which the piston rod portion 15b is retracted. FIG. 1 shows the piston rod portion 15b in an extended state. In this state, a horizontal gap G larger than the thickness dimension t of the overlapping portion 3 to be clamped is formed between the contact surface 11a of the first earth electrode 11 and the contact surface 12a of the second earth electrode 12 (see FIG. 1).

[0026] The sliding support member 16 has sliding parts 21a, 21b that can slide along a linear direction, and a guide part 22 that can support the sliding parts 21a, 21b and guide the sliding of the sliding parts 21a, 21b. In this embodiment, two sliding parts 21a, 21b are provided, and each sliding part 21a, 21b is attached to the main body part 13a of the first clamp member 13 and the main body part 14a of the second clamp member 14. Each sliding part 21a, 21b is configured to be able to independently reciprocate on a common horizontal straight line. In this case, the first sliding part 21a, the first clamp member 13, the first earth electrode 11, and the cylinder part 15a of the cylinder 15 are slidable together. Also, the second sliding part 21b, the second clamp member 14, the second earth electrode 12, and the piston rod part 15b of the cylinder 15 are slidable together.

[0027] The guide portion 22 of the sliding support member 16 configured as above is attached to a base 20 which is the ground side of the earth electrode clamp device 10. The sliding support member 16 can be configured as an LM guide, for example, but is of course not limited to this. Any mechanical element can be applied as long as it has the above configuration.

[0028] In this embodiment, the piston rod portion 15b and the body portion 14a of the second clamp member 14 are connected via a floating joint 23. This allows the piston rod portion 15b to slide in the same direction while absorbing the inclination of the piston rod portion 15b relative to the second clamp member 14.

[0029] Next, an example of a mode of use of the earth electrode clamping device 10 having the above configuration will be described.

[0030] First, the earth electrode clamping device 10 is arranged as shown in Fig. 1. That is, the earth electrode clamping device 10 is arranged so that the overlapping portion 3 of the plurality of plate-like members 1, 2 to be clamped is located between the contact surface 11a of the first earth electrode 11 and the contact surface 12a of the second earth electrode 12. Any means can be used for this arrangement. For example, although not shown, a lifting device can be installed below a line along which a welding target such as a body composed of the plurality of plate-like members 1, 2 is transported, and the earth electrode clamping device 10 can be raised and lowered by this lifting device, so that the earth electrodes 11, 12 approach the overlapping portion 3 only when clamping is required. Alternatively, the earth electrode clamping device 10 can be attached to the tip of a robot arm (not shown), and the robot arm can be driven to bring the earth electrodes 11, 12 toward the overlapping portion 3.

[0031] After that, the cylinder 15 is driven in a direction to retract the extended piston rod portion 15b. As a result, the second clamp member 14 connected to the piston rod portion 15b starts to move in the same direction as the piston rod portion 15b, and the second earth electrode 12 attached to the second clamp member 14 starts to move integrally with the second clamp member 14. Here, for example, as shown in FIG. 3, when the second earth electrode 12, which moves integrally with the second clamp member 14 first, abuts against the overlapping portion 3, the first clamp member 13 receives a reaction force from the overlapping portion 3. Here, since the first clamp member 13 is supported so as to be slidable along the driving direction of the cylinder 15, the first clamp member 13 moves in the direction of the reaction force, that is, in a direction approaching the second clamp member 14 horizontally while sliding (see FIG. 3). As a result, the first earth electrode 11 starts to move toward the overlapping portion 3 and abuts against it before the pressure of the second earth electrode 12 increases. Therefore, the overlapping portion can be clamped by both earth electrodes 11, 12 without the load being concentrated on the second earth electrode 12 (see FIG. 4).

[0032] Alternatively, although not shown, in the present embodiment, when the first clamp member 13 and the second clamp member 14 are both slidably supported by the sliding support member 16, when the second clamp member 14 starts to move toward the first clamp member 13 due to the retraction operation of the cylinder 15, the first clamp member 13 starts to move in the horizontal direction toward the second clamp member 14 before the second earth electrode 12 abuts against the overlapping portion 3, depending on the magnitude relationship between the retraction force of the cylinder 15 and the sliding resistance of the second clamp member 14 against the guide portion 22. In this case, the first earth electrode 11 and the second earth electrode 12 abut against the overlapping portion 3 at very close timing, so that the overlapping portion 3 can be clamped with a further reduced load acting on the second earth electrode 12 compared to the case where the second earth electrode 12 abuts against the overlapping portion 3 first.

[0033] By passing current through a welding electrode (not shown) while clamping overlapping portion 3 with a pair of ground electrodes 11, 12 in the above-described manner and while the welding electrode is in contact with the weld area, indirect spot welding can be performed on the weld area.

[0034] As described above, in the earth electrode clamp device 10 according to this embodiment, the piston rod of the cylinder 15 for applying the clamping force is driven in a retracting direction to clamp the overlapping portion with both earth electrodes, so that the cylinder can be arranged offset from the coaxial line of the earth electrodes. In addition, a large member such as an arm portion for connecting and supporting the pair of earth electrodes 11, 12 as in a welding gun is not required. This allows the earth electrode clamp device 10 to be configured compactly. In particular, as shown in FIG. 1, the pair of earth electrodes 11, 12 and the cylinder 15 are arranged in parallel so that the central axis of the cylinder 15 and the central axis passing through the pair of earth electrodes 11, 12 are parallel, so that the earth electrode clamp device 10 can be made more compact. If the earth electrode clamp device 10 can be made smaller in size, the overlapping portion 3, which is the power supply portion, can be approached without worrying about interference with the surroundings, so that the versatility of the earth electrodes 11, 12 can be improved.

[0035] In addition, in this embodiment, the first clamp member is supported slidably along the driving direction of the cylinder, so that when the first earth electrode 11 receives a reaction force from the second clamp member 14 due to the retraction of the piston rod portion, the first clamp member 13 moves in the direction of the reaction force while sliding. This allows the first earth electrode 11 to start moving toward the overlapping portion 3 before the pressure force of the second earth electrode 12 against the overlapping portion 3 increases. This makes it possible to clamp the overlapping portion 3 while applying pressure equally with both earth electrodes 11, 12, avoiding a situation in which the load is concentrated on one earth electrode (second earth electrode 12). This allows the earth electrodes 11, 12 to be used for a long period of time, and makes it possible to extend the replacement life.

[0036] In particular, as in this embodiment, by supporting the second clamp member 14 slidably along the sliding direction of the cylinder 15, depending on the magnitude relationship between the retraction force and the sliding resistance of each clamp member 13, 14, when the piston rod portion 15b is retracted, the first earth electrode 11 may start approaching the overlapping portion 3 before the second earth electrode 12 abuts against the overlapping portion 3. Therefore, the timing at which the first earth electrode 11 abuts against the overlapping portion 3 can be made closer to the timing at which the second earth electrode 12 abuts against the overlapping portion 3, thereby making it possible to apply pressure to the overlapping portion 3 as evenly as possible. In addition, by supporting the second clamp member 14 slidably, the posture of the second clamp member 14 and therefore the second earth electrode 12 when retracted and therefore the posture when abutting against the overlapping portion 3 are stabilized. Therefore, it is possible to clamp the overlapping portion 3 at a more accurate position.

[0037] Although one embodiment of the present invention has been described above, it goes without saying that the earth electrode clamping device according to the present invention is not limited to the above-mentioned exemplary configuration, and various modifications are possible within the scope of the present invention. [Explanation of symbols]

[0038] 1,2 Plate-shaped member 3. Overlapped section 10 Earth electrode clamp device 11,12 Earth electrode 11a,12a Contact surface 11b,12b Electrode body 13,14 Clamping member 13a, 14a Main body 13b,14b Conductive part 13b1,14b1 Arm 15 cylinders 15a Cylinder section 15b Piston rod part 16 Sliding support member 17 linear body 18 organization 19a,19b Conductive flexible part 20 Base 20a Ground side conductive part 21a, 21b each sliding part 22 Information Department 23 Floating joint G Horizontal gap t Thickness dimension (overlapped part)

Claims

1. a first earth electrode capable of contacting a portion where the plurality of plate-like members are overlapped; a second earth electrode capable of clamping the overlapping portion between the first earth electrode and the second earth electrode; a first clamp member to which the first earth electrode is attached; a second clamp member to which the second earth electrode is attached; and A clamping device for an earth electrode, comprising: a cylinder capable of applying a clamping force to both of the earth electrodes, A cylinder portion of the cylinder is attached to the first clamp member, a piston rod portion of the cylinder is attached to the second clamp member, and The cylinder is disposed so that the pair of earth electrodes are positioned offset from a center line of the cylinder, The earth electrode clamping device is configured so that the piston rod portion of the cylinder can be driven in a retracting direction to clamp the overlapping portion with both of the earth electrodes.

2. 2. The earth electrode clamping device according to claim 1, wherein at least one of the first clamping member and the second clamping member is supported slidably along a driving direction of the cylinder.

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