JP2001087864A - Spot welding gun - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spot welding gun which prevents a deformation of a work to be welded at a pressing time caused by a deviation in a position of the work etc., without using a equalizing device. SOLUTION: A drive source of the spot welding gun 21 raises/lowers an output shaft 42. The output shaft 42 is connected to the middle of a link 43 of a butting transmission manners 41, and an upper electrode tip 26 is connected to the one end of the link 43 through an arm 24. To the other end of the link 43, an arm 25 having a lower electrode tip 27 is connected through a reversal manners 40. When the output shaft 42 is lowered, each of the electrode tips 26, 27 is brought close to other, and the welding gun 21 is closed. When the one electrode tip butts the work 90 to be welded, the movement of the butted electrode stops, the movement of the other electrode tip is continued through the link 43 and both electrodes butt the work 90 to be welded. After that, pressurization is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spot welding gun mounted on, for example, a wrist of an articulated robot and performing spot welding.

[0002]

2. Description of the Related Art In conventional spot welding using a welding gun, a welding gun is positioned so that an object to be welded comes into contact with a lower electrode tip fixed to the welding gun, while an upper electrode tip which moves up and down is used. Lower to sandwich the workpiece,
Further, by applying a welding force and applying a welding current between the two electrode tips, the workpieces are joined to each other. In automatic spot welding by a welding robot, a welding gun is attached to a wrist of an articulated robot, and the welding gun is sequentially positioned at a welding position previously taught by the welding robot.

FIG. 8A is a front view showing a welding position of the workpiece 5. As shown in FIG.
Is positioned so as to come into contact with the lower electrode 1, the upper electrode 2 is lowered to sandwich the workpiece 5 between the electrode tips 1 and 2,
Perform spot welding by applying pressure.

When the pressing position deviates from a predetermined position, that is, as shown in FIG. 8B, when the lower electrode 1 is positioned so as to be separated from the workpiece 5, When the electrode 2 is lowered, the pressing force of the upper electrode 2 cannot be received by the lower electrode 1, and FIG.
As shown by the phantom line in (b), the workpiece 5 is deformed, and the pressing force of the upper and lower electrode tips 1 and 2 becomes unbalanced, resulting in a decrease in welding quality. Such problems are caused by variations in the positioning of the workpiece or welding gun during teaching and repeat, wear of the electrode tips 1 and 2, and deflection of the gun arm during pressurization.

Conventionally, a wrist of a welding robot and a welding gun are connected to each other via an equalizing device in order to prevent the above-described deformation of the work to be performed when the workpiece is pressurized.
The equalizing device floats and supports the welding gun in the vertical direction, and is configured to absorb the positional deviation of the workpiece by moving the welding gun up and down. An example of such an equalizing device is disclosed, for example, in Japanese Utility Model Laid-Open No. Hei 5-18774.

However, when the equalizing device is provided, the welding gun becomes larger correspondingly, so that the welding robot must be of a type having a large payload, and the investment cost of the welding robot increases.

Further, when the size of the welding gun is increased, interference with the work to be welded becomes a problem, and the application site of the welding operation is limited.

In the equalizing apparatus, when one of the electrode tips comes into contact with the workpiece first, the other electrode tip is moved together with the welding gun by the reaction force of the contacted electrode tip to contact the workpiece. Since the electrodes are brought into contact with each other, the impact of the electrode tip which comes into contact with the electrode firstly increases, the consumption of the electrodes increases, and when the workpiece is thin, the workpiece is deformed.

[0009] Instead of using such an equalizing apparatus, there is a method of lifting the lower electrode chip by performing an equalizing operation on a robot arm. When performing this equalizing operation, the upper electrode also moves upward, so that there is no use in the equalizing stroke operation. As a result, there is a problem that an accurate product without distortion cannot be produced at high speed.

As a method for solving such a problem, Japanese Patent Application Laid-Open No. Hei 7-116856 discloses a method using two actuators for independently driving an upper electrode chip and a lower electrode chip. In this method, both electrode tips are individually moved, and when one of the electrode tips comes into contact with the workpiece, the contact is detected,
Stop the actuator that drives one of the contacting electrode tips, continue driving the other actuator,
When the other electrode tip comes into contact with the workpiece and is detected, spot welding is performed by applying pressure to both actuators.

[0011]

However, in the above-mentioned prior art, since two actuators are required for the welding gun, the welding gun is still large and heavy. In addition, since it is individually detected whether or not each electrode tip has come into contact with the work to be welded, and each actuator is controlled accordingly, the control becomes complicated.

It is an object of the present invention to uniformly pressurize a workpiece even if there is a displacement of the workpiece without using an equalizing device or two actuators. An object of the present invention is to provide a spot welding gun capable of preventing deformation of an object.

[0013]

According to a first aspect of the present invention, there is provided a pair of electrode tips which are arranged to face each other and which are moved by a driving source in a direction of approaching and separating from each other. In a spot welding gun that sandwiches an object to be welded with a tip and performs spot welding by applying pressure by the drive source, the spot welding gun is connected to both electrode tips, and both electrode tips move in a direction approaching each other, and one of the electrode tips is moved. A spot welding gun characterized in that it includes a contact transmitting means that, when it first comes into contact with a work to be welded, uses the contacted electrode tip as a fulcrum and continues to move only the other electrode tip.

According to the present invention, while the welding gun is positioned at a predetermined position with respect to the workpiece, one electrode tip and the other electrode tip are simultaneously synchronized by the drive source in a direction approaching each other. Start moving. When the workpieces are not displaced, the two electrodes move at the same time, so that a pair of electrodes abut the workpieces at the same time, and the two electrodes can simultaneously pressurize. Further, the time can be reduced as compared with the conventional case in which only one electrode is moved.

When one of the electrode tips comes into contact with the workpiece first due to a displacement of the workpiece or the like, the movement of the contacted electrode tip is stopped, and the contacted electrode tip is supported as a fulcrum. As a result, only the movement of the other electrode tip is continued by the contact transmitting means, and both electrodes reliably contact the workpiece.

After the two electrode tips come into contact with the object to be welded in this way, a pressure is applied to the object to be welded to perform spot welding.

After the two electrode tips are securely brought into contact with the workpiece, pressurization by the two electrode tips is started. Therefore, even if the welding gun or the workpiece is misaligned, The pressing force of the electrode tip can be received by the other electrode tip, and the deformation of the workpiece during pressurization can be prevented, and finally the workpiece can be uniformly pressed. This can also reduce the impact sound.

Further, in the present invention, unlike the equalizing device which floats and supports the welding gun, a contact transmitting means interposed between the two electrode tips and continuing only the movement of the other electrode tip with the contacted electrode tip as a fulcrum. By using the method, accurate uniform pressurization can be realized without causing an increase in the size and weight of the configuration as in the equalizing apparatus, and the deformation of the workpiece during pressurization can be reliably prevented.

Further, unlike the equalizing apparatus, the movement of the electrode tip which is not in contact with the welding gun is not moved together with the welding gun, but the movement of only the electrode tip is continued.
The impact when the electrode tip comes into contact is small, and the wear of the electrode tip and the deformation of the workpiece can be prevented. Further, without using the equalizing device, the pressing force is balanced by the action of the contact transmitting means even when the distance to the workpiece is different between one chip and the other chip.

Further, since the two electrodes are driven synchronously without performing the equalizing operation by the equalizing device as in the prior art, the speed of the welding point is increased, and the distortion and deformation at the time of pressurizing the workpiece are prevented. can do.

Further, unlike the prior art using two actuators, it is not necessary to individually detect whether one of the electrode tips has come into contact with the work to be welded, and control is facilitated.

According to a second aspect of the present invention, the driving source comprises:
It has an output part that moves in parallel to the approaching and separating directions of the electrode tip, one of the electrode tips moves in the same direction as the moving direction of the output part by the output part of the drive source, and the other electrode tip drives The source is moved in a direction opposite to the one of the electrode tips by an inverting means for inverting a moving direction of the output section of the source.

According to the present invention, by using the reversing means, both the one electrode tip and the other electrode tip can be moved by one drive source, so that it is not necessary to use two actuators and it is possible to perform welding. The size and weight of the gun can be reduced.

According to a third aspect of the present invention, the drive source is an electric motor, and detects that both electrode tips have contacted the workpiece based on the current value of the motor or the displacement of the output portion. Pressurization is started in response to the detection.

According to the present invention, whether or not the electrode tip has contacted the workpiece is detected based on the current value of the motor or the displacement of the output portion of the motor such as an encoder.
For example, there is no need to separately provide a sensor or the like, and the configuration is simplified.

According to a fourth aspect of the present invention, the contact transmitting means has a link mechanism.

According to a fifth aspect of the present invention, in the link mechanism, one end is connected to one electrode tip so as to be angularly displaceable, the other end is connected to an inversion means so as to be angularly displaceable, and a driving source is connected to an intermediate part. Are connected to each other so as to be angularly displaceable, and the output unit has a link that moves in the direction of approaching and moving away from the electrode tip.

According to the present invention, when the link is pushed down by, for example, the output portion of the drive source, the upper electrode tip, which is one electrode tip connected to one end of the link, is lowered and the other end of the link is moved to the other end. The lower electrode tip, which is the other electrode tip, is raised by the connected inverting means, and both electrode tips move in directions approaching each other. here,
For example, if the upper electrode tip first contacts the workpiece,
With one end of the link to which the upper electrode tip is connected as a fulcrum, the output of the drive source continuously pushes down the link, whereby the lower electrode tip continues to rise. By using the link mechanism in this manner, the electrode tips that have previously contacted the workpiece are stopped, the movement of the electrode tips that are not in contact with the workpiece is continued, and both electrode tips are reliably welded. It can be held in contact with an object.

According to a sixth aspect of the present invention, the link is connected to one of the electrodes and the reversing means via an intermediate link so as to be angularly displaceable.

According to the present invention, since the link and one of the electrodes and the reversing means form a multistage link via the intermediate link, the one of the electrodes and the reversing means can be smoothly driven in a predetermined direction.

According to a seventh aspect of the present invention, the output section of the driving source is connected to the center of the link.

According to the present invention, since the output of the drive source is connected to the center of the link, the drive force of the drive source can be applied uniformly to both electrode tips. As a result, the pressing force of both electrodes becomes equal, and the welding quality can be improved.

The output section of the driving source according to the eighth aspect is connected to a position shifted from the center of the link.

For example, when welding a thin plate and a thick plate, it is necessary to shift the center of heat generation at the time of energization from the center. For this purpose, there is a method of providing a difference in the pressing force of the electrode tip. According to the present invention, it is possible to easily provide a difference in the pressing force by shifting the connection position between the output portion of the drive source and the link from the center.

According to a ninth aspect of the present invention, the contact transmitting means is provided with a clutch for preventing and permitting an angular displacement between the output portion of the drive source and the link. Sometimes, the angular displacement between the link and the output unit is prevented for a predetermined time or a predetermined distance, and the angular displacement between the link and the output unit is allowed during pressurization.

According to the present invention, a clutch is interposed between the output portion and the link, and when the electrodes start approaching each other, the clutch prevents angular displacement between the output portion and the link, thereby synchronizing the two electrodes. Thus, it is possible to reliably start the approach.

After a lapse of a predetermined time or a predetermined distance from the start of the approach, the clutch allows the angular displacement between the output portion and the link at a position where neither electrode comes into contact with the workpiece. By this and the function of the contact transmitting means, both electrode tips can be reliably brought into contact with the workpiece.
After the two electrode tips come into contact with each other, a pressing force is applied to the link by the drive source, so that the pressing force can be uniformly applied to the workpiece by the two electrode tips.

According to a tenth aspect of the present invention, when the two electrode tips start separating from the workpiece, angular displacement between the link and the output portion is prevented for a predetermined time or a predetermined distance. .

According to the present invention, when the two electrode tips start to separate from the work to be welded, the clutch prevents the link from being displaced angularly between the link and the output portion for a predetermined time or a predetermined distance, thereby synchronizing the two electrodes with each other. The separation operation can be started.

According to the eleventh aspect of the present invention, a spring biasing means is provided between the output portion of the drive source and the link and biases the link toward a predetermined neutral position. I do.

According to the present invention, by providing the spring biasing means, when the welding gun is closed, the two electrodes can simultaneously start the approach operation. Further, when the welding gun is opened, both electrode tips can be simultaneously separated from the workpiece.

According to a twelfth aspect of the present invention, the reversing means has a rack and a pinion.

According to a thirteenth aspect of the present invention, the reversing means includes a first rack that is driven to be displaced in the same direction as an output portion of a drive source, a pinion that meshes with the first rack, and a first rack that meshes with the pinion. And a second rack that is driven to be displaced in the opposite direction.

According to the present invention, when the link is pushed down by the driving source, the first rack connected to the other end of the link is pushed down, and the first rack is meshed with the first rack through the pinion meshed with the first rack. The two racks are pushed up, and the upper electrode tip, which is the other electrode tip connected to the second rack, rises. As described above, the moving direction of the drive source can be easily reversed by the reversing means using the rack and the pinion.

[0045]

FIG. 1 is a schematic view showing the entire configuration of a spot welding apparatus 11 having a spot welding gun 21 according to the present invention, and FIG. 2 is a sectional view showing the configuration of the spot welding gun 21. The spot welding device 11 includes a welding gun 2
1, a welding robot 61, and a control unit 71, and the welding gun 21 is attached to the wrist 6 of the welding robot 61.
5 attached. The opening, closing, pressurizing operation of the welding gun 21 and the operation of the welding robot 61 are controlled by the control means 71.

As shown in FIG. 2, the welding gun 21 includes a housing 22, arms 24, 25, an upper electrode tip 26,
The lower electrode chip 27, the driving source 30, the contact transmitting means 41 and the inverting means 40 are included.

The drive source 30 comprises a servomotor 35 and a ball screw 32 having an output shaft 42. The ball screw 32 has a screw shaft 23 rotatably supported by the housing 22 via a bearing, and a nut 33 screwed to the screw shaft 23, and the screw shaft 23 is moved in both forward and reverse directions by a servomotor 35. It is driven to rotate. The rotation of the screw shaft 23 causes the nut 33 to move up and down in the axial direction of the screw shaft 23. The nut 33 is connected to an output shaft 42 supported on the housing 22 so as to be vertically displaceable.
As a result, the output shaft 42 is driven up and down together with the nut 33. The servo motor 35 is provided with an encoder 36, and the position of the output shaft 42 can be detected by detecting the rotation amount of the servo motor.

The contact transmitting means 41 has a link 43,
The output shaft 42 of the ball screw 32 is connected to the center of the link 43 by a pin 53 so as to be freely angularly displaceable. The arm 24 is connected to one end 43 a of the link 43 via a connecting member 44, and the upper electrode tip 26 is attached to the lower end of the arm 24. The arm 24 is supported by the housing 22 so as to be vertically displaceable. The intermediate link 44 is connected to one end 43a of the link 43 by a pin 54 so as to be angularly displaceable.
A lower end is connected to an upper end of the arm 24 by a pin 55 so as to be angularly displaceable.

The reversing means 4 is provided at the other end 43b of the link 43.
0, the other arm 25 is connected, the tip of the other arm 25 faces the lower end of the one arm 24, and the lower electrode tip 27 is attached. The reversing means 40 is the first
It has a rack 50, a pinion 51 and a second rack 52. The first rack 50 is supported by the housing 22 so as to be able to move up and down, and the pinion 51 meshes with the first rack 50,
The second rack 52 is rotatably supported by the housing 22.
Is engaged with the pinion 51 and the base 25 of the other arm 25 is
a.

An intermediate link 46 is attached to the other end 43b of the link 43 via a pin 56 so as to be angularly displaceable, and the lower end of the connecting member 46 is connected to the first rack 5 via a pin 57.
0 is connected so as to be freely angularly displaced.

Therefore, when the output shaft 42 of the drive source 30 is lowered, the link 43 is lowered, and accordingly, the arm 24 and the upper electrode 26 connected to one end 43a of the link 43 are lowered. At the same time, the first rack 50 connected to the other end 43b of the link 43 descends.
The first rack 50 is connected to a second rack 52 via a pinion 51.
When the first rack 50 descends, the second rack 52 rises. Since the other arm 25 is integrally fixed to the second rack 52, the arm 25 and the lower electrode 27 are raised accordingly.

When the output shaft 42 is lowered in this way, the upper electrode 26 is lowered and the lower electrode 27 is raised at the same time, and the welding gun 21 is closed. At this time, the upper electrode tip 26 and the lower electrode tip 27 can be closed to the contact position. Further, the output shaft 42 of the drive source 30
Is raised, the upper electrode tip 26 is raised, the lower electrode tip 27 is lowered, and the welding gun 21 is opened by the action opposite to that described above.

Next, the configuration of the spot welding apparatus 11 will be described with reference to FIG. The upper electrode tip 26 and the lower electrode tip 27 are connected to a welding transformer (not shown). The welding transformer is connected to a welding power source (not shown) via a controller 62 having a timer function. The controller 62 is connected to the control means 71. The welding robot 61 has six control axes, and is driven by a servomotor provided for each control axis.

The movement of the welding robot 61 is controlled by control means 71.
Is controlled by The control means 71 teaches a plurality of welding positions, and the welding robot 61 positions the welding gun 21 at the taught welding position. The position information from each control axis of the welding robot 61 is input to the control means 71, and based on these, the position information of the welding gun 21 moved by the welding robot 61 is grasped. The control means 71 includes an encoder 36 for detecting the position of the output shaft 42 for opening and closing the electrode tips 26 and 27.
Is detected.

The control means 71 has a function of calculating the trajectory of the welding robot 61 itself, and the servo motor 3
5, a function of detecting whether or not both electrodes 26, 27 have contacted the workpiece 90, and a load current corresponding to the pressing force set for each welding point. And a function to instruct both electrodes 2
When it is detected that the parts 6, 27 have contacted the workpiece 90,
The load current corresponding to the set pressure is commanded.

Next, the spot welding apparatus 11 of the present embodiment
The operation of will be described. The spot welding apparatus 11 of the present embodiment is used, for example, for spot welding a vehicle body of an automobile. In an automobile assembly line, a vehicle body, which is a workpiece 90, is intermittently moved by a conveyor, and spot welding is performed when the vehicle body stops. When the vehicle body is positioned at a predetermined position, the welding robot 21 moves toward the welding position by the welding robot 61 in the standby state, and performs a spot welding operation.

FIG. 3 shows a spot welding gun 2 during a welding operation.
6 is a time chart showing a current value and an encoder value of one servo motor 35. At time t1, welding gun 2
1 is a fully open position, that is, the output shaft 42 is at the upper limit position,
It is assumed that the upper electrode 26 and the lower electrode 27 are located at positions separated from each other as much as possible.

When the welding operation is started at time t1, first, a current is supplied to the servomotor 35 in the direction in which the electrode tips 26 and 27 are closed, here, in the plus direction, and the output shaft 42 is lowered. As a result, the arm 24 and the upper electrode tip 26 descend, and the arm 25 and the lower electrode 27 start to rise via the reversing means 40.

At time t2, one of the electrode tips, for example, the lower electrode tip 27,
, The movement of the lower electrode tip 27 stops, but the link 43 of the contact transmitting means 41 is connected to the lower electrode tip 27 side, that is, the pin 56 of the other end 43 b, the intermediate link 46 and the rack 50. The arm 24 and the lower electrode tip 26 connected to the one end 43a of the link 43 continue to move downward, with the pin 57 connecting the two to the fulcrum as a fulcrum. As described above, since the link 43 and the reversing means 40 are connected by the multi-stage link via the intermediate link 46, the link 43 can operate smoothly. This is one end 43a of the link 43
The same applies to the intermediate link 44 connected to.

Further, the lower electrode tip 27 is
When it comes into contact with the servo motor 35, as shown in FIG.
Load current rises.

At time t3, when the upper electrode tip 26 comes into contact with the workpiece 90, the current value of the servomotor 35 sharply increases. Therefore, based on the increase in the current value, the control means 71 can determine that the two electrode tips 26 and 27 have come into contact with the workpiece 90. That is, a current value is set in advance, and it is determined that both electrodes have contacted the workpiece 90 when the load current of the servomotor 35 fed back exceeds the set current value.

Another method of detecting that both electrodes have contacted the workpiece 90 is that the interval between the electrode tips 26 and 27 becomes smaller than a predetermined interval based on the encoder value of the servomotor 35. When judged, both electrode tips 2
6 and 27 may be determined to have come into contact with the workpiece 90. If the encoder value of the servomotor 35 does not change for a predetermined time or more, both electrode tips 26 and 27 contact the workpiece 90. It may be determined that they touched each other.

At time t3, both electrode tips 26, 27
When the control means 71 detects that the object has come into contact with the workpiece 90, the control means 71 supplies a load current corresponding to the pressing force corresponding to the welding position to the servomotor 35 to apply a pressing force to the workpiece 90. As described above, since the pressing force is applied after confirming that the two electrode tips 26 and 27 have securely contacted the workpiece 90, even if the position of the workpiece 90 is shifted,
The workpiece 90 can be evenly pressed, and the workpiece 9
0 is reliably prevented from being deformed.

After pressurizing at time t3, a predetermined welding current is passed at time t4 after a predetermined time has elapsed, and after a predetermined time has elapsed, energization is stopped at time t5. Thus, spot welding is performed.

At the next time t6, a current is supplied in a direction opposite to that when the servomotor 35 is pressurized, here in a minus direction. Then, the welding gun 21 starts to be opened, and both electrode tips 2
6, 27 begins to separate.

As described above, since the lower electrode tip 27 contacts the workpiece 90 first, the link 43 is inclined so that the other end 43b to which the upper electrode tip 26 is connected is upward. When the output shaft 42 is pulled up, the other end 43b of the link 43 first reaches the upper limit position at time t7, and the lower electrode 27 stops rising.

When the pulling up of the output shaft 42 is further continued, the link 4 is pivoted around the other end 43b of the link 43 as a fulcrum.
3, the upper end 26a continues to rise, and the upper end 26a of the link 43 reaches the upper limit position at time t8, and the welding gun 21 is fully opened. Note that, between the time t7 and t8 when the upper electrode tip 26 is raised, the current to be supplied is greater than when the two electrode tips 26 and 27 are moved.

FIG. 3 shows a state in which the welding gun 21 is closed from the fully open position, the welding operation is performed, and the state is returned to the fully open position again. Open to a predetermined intermediate position and move to the next welding position.

As described above, in the present embodiment, even when the workpiece 90 is displaced, after the upper electrode tip 26 and the lower electrode tip 27 abut on the workpiece 90, the welding is performed. Since the pressurization of the object 90 is started, it is possible to surely prevent the deformation of the object 90 during pressurization without using an equalizing device as in the related art. Also, since there is no equalizing device, the welding gun 21 can be reduced in size and weight by that much. Therefore, the carrying weight of the welding robot 21 can be small and can be dealt with by a small-sized welding robot, and the investment cost of the welding robot 21 can be reduced. Further, the downsizing of the welding gun 21 enables a welding operation in a narrow space, and the applicable range of the welding operation by the welding gun 21 can be expanded.

Conventionally, in order to teach the welding point to the welding robot, a welding gun is brought closer to the workpiece at each of the welding points, and the lower electrode is brought into accurate contact with the workpiece so that the pressure in the pressing direction is reduced. Positioning must be performed very strictly, and teaching takes a lot of time. In this embodiment, the final positioning of the electrode tips 26 and 27 in the pressing direction at the time of repetition is performed automatically, so to speak, by a link mechanism, and the distance between the upper electrode tip 26 and the lower electrode tip 27 is determined by the distance from the workpiece 90. Even if the pressure is different, the pressure is balanced. Therefore, the positioning of the electrode tips 26 and 27 in the pressing direction in the teaching operation may be rough, and the teaching operation can be sped up.

In addition, since the positioning of the electrode tips 26 and 27 in the pressing direction in the teaching operation may be rough, teaching (off-line teaching) on computer graphics is possible instead of teaching using the actual workpiece 90. Becomes In other words, in teaching work, the positioning accuracy of the surface parallel to the workpiece is not required to be very high because it does not greatly affect the quality. Have a great effect on the quality of the product. Therefore, if positioning in the pressing direction can be automatically and accurately performed as in the present embodiment, offline teaching can be performed.

Further, in this embodiment, by setting the connection position of the output shaft 42 of the drive source 30 to the center of the link 43, the pressing force can be applied evenly to the workpiece.

If there is a difference in the pressing force between the two electrode tips, the contact resistance between the electrode tip having a small pressing force and the workpiece is greater than the contact resistance between the electrode tip having a large pressing force and the workpiece. At the time of energization, the center of heat generation of the workpiece is shifted to the electrode tip side where the pressing force is small. As a result, the diameter of the nugget at the joint surface of the workpiece decreases, and the shear strength of the workpiece decreases. Also,
If the welding current is increased so that the nugget diameter at the joint surface of the work becomes the required value, the work to be welded on the electrode side with a small pressing force will melt too much, causing spatters to scatter and electrode tips to be welded. Is generated.

In this embodiment, by using the link mechanism, it is possible to accurately pressurize evenly, to make the contact resistance of both electrodes uniform, and to make the heat generation center at the time of energization coincide with the joint surface of the workpiece. As a result, a nugget is formed so as to have a maximum shape at the joint surface, high-quality welding with high shear welding strength is obtained, and spatter and chip welding are less likely to occur.

FIG. 4 is a front view showing a contact transmitting means 74 of a spot welding gun according to another embodiment of the present invention. In the contact transmitting means 74 of the present embodiment, a clutch 75 is further provided on the link 43. Note that other configurations are the same as those of the spot welding apparatus 11 described above, and a description thereof will be omitted.

The clutch 75 is connected to the output shaft 42 of the drive source 30.
And an electromagnetic clutch that is interposed between the contact transmission means 41 and the link 43 and includes a friction plate fixed to the link 43 side, a friction plate fixed to the output shaft 42 side, and an electromagnetic solenoid. When a blocking command is given from the controller, the friction plate on the link 43 side and the friction plate on the output shaft 42 are clamped by the electromagnetic solenoid, and angular displacement between the link 43 and the output shaft 42 is prevented. Further, when an allowance command is given from the controller, the electromagnetic solenoid separates the friction plate, and the angular displacement between the link 43 and the output shaft 42 is allowed.

Next, the operation of the clutch 75 will be described with reference to the time chart of FIG. The clutch 75 prevents angular displacement between the output shaft 42 and the link 43 until the welding operation is started and the output shaft 42 moves for a predetermined time or a predetermined distance from the proximity operation start time t1 of each of the electrode tips 26 and 27 until the output shaft 42 moves. ing. Thus, when the approach operation is started, the two electrodes 26 and 27 can be surely simultaneously started to move in the approach direction. Note that the predetermined time or the predetermined distance is a time or a distance during which the electrode tips 26 and 27 do not contact the workpiece 90. In the case of the present embodiment, at most the time until the time t2 or the position at the time t2. Up to the moving distance of the output shaft 42.

After a lapse of a predetermined time or after moving a predetermined distance,
The clutch 75 is turned on by an allowance command from the controller.
The angular displacement between the output shaft 42 and the link 43 is allowed. Thereby, as described above, by the action of the contact transmission means,
Even if one of the electrodes comes in contact with the workpiece first, the movement of the other electrode is continued, and both electrode tips 2
6, 27 can be reliably brought into contact with the workpiece 90.

Further, at time t3, both electrodes 26, 2
After confirming the abutment of 7, when the pressing force is applied by increasing the load current of the servo motor 25, the pressing force from the output shaft 42 acts equally on each of the electrode tips 26 and 27, and the workpiece 90 is accurately positioned. Can be evenly pressed.

After the pressurization is completed, at time t6, the clutch 75 is moved to the output shaft 4 by the stop command from the controller.
The angular displacement between the link 2 and the link 43 is prevented again. By fixing the link 43 in this manner, the electrode tips 26 and 27 simultaneously move in the separating direction when the welding gun 21 is opened, and the electrodes 26 and 27 can be simultaneously separated from the workpiece 90. .

When the output shaft 42 is raised for a predetermined time or a predetermined distance from time t6, the clutch 75 is again connected to the output shaft 42 and the link 43 by an allowable signal from the controller.
Is allowed. Note that the predetermined time or the predetermined distance is a time until one end of the link 43 reaches the upper limit position, or a moving distance of the output shaft 42,
In the present embodiment, at most the time is selected as the time until time t7 or the movement distance of the output shaft 42 to the position at time t7.

By providing the clutch 75 in this manner, synchronization can be reliably performed at the start of approach and at the start of separation.

FIG. 5 is a front view showing a contact transmitting means 79 of a spot welding gun according to still another embodiment of the present invention. In the contact transmitting means 79 of this embodiment, a spring urging means 78 is further provided on the link 43. Note that other configurations are the same as those of the spot welding apparatus 11 described above, and a description thereof will be omitted.

The spring urging means 78 is connected to one of the links 43.
a tension coil spring 76 connected from the side a to the output shaft 42 and a tension coil spring 77 connected from the other side 43b of the link 43 to the output shaft 42, and in a natural state where no external force acts, the spring urging means The link 43 is held at a neutral position perpendicular to the output shaft 42 by the spring forces of 76 and 77.

By providing such a spring biasing means 78, the two electrode tips 26, 2 are started when the welding gun starts approaching, similarly to the function of the clutch 75 described with reference to FIG.
7 can be simultaneously moved in the approach direction without fail, and both electrode tips 26, 2 can be moved even when the welding gun is opened.
7 can be simultaneously separated from the workpiece 90.

FIG. 6 is a front view showing a contact transmitting means 80 of a spot welding gun according to still another embodiment of the present invention. Note that the configuration other than the contact transmitting means 80 is the same as that of the spot welding gun 21 described above, and a description thereof will be omitted.

In the contact transmitting means 80 of the present embodiment, the position where the link 43 and the output shaft 42 are attached is shifted from the center of the link 43. Therefore, when the output shaft 42 is pressed down to apply a pressing force, a difference is generated between the upper electrode tip 26 and the lower electrode tip 27. In the state shown in FIG. 6, the connection position between the output shaft 42 and the link 43 is
3 is closer to the one end 43a than the center of the output shaft 4.
When 2 is pressed down, a large pressing force can be applied to the upper electrode tip 26 connected to the one end 43a.

Therefore, for example, as shown in FIG.
In the work 94 in which one thin plate 93 is superimposed on one thick plate 92, the pressing force of the upper electrode tip 26 located on the thin plate 93 side can be made larger than the pressing force of the lower electrode tip 27. . Thereby, the lower electrode tip 27
The contact resistance between the upper electrode chip 26 and the thin plate 93 becomes larger than the contact resistance between the upper electrode chip 26 and the thin plate 93, the center of heat generation during energization is shifted toward the thick plate 92, and the thickness of the nugget N is reduced.
It becomes thinner on the third side, and the occurrence of spatter and chip welding can be effectively prevented.

As described above, by displacing the connection position between the output shaft 42 and the link 43 from the center of the link 43, it is easy to intentionally provide a difference in the pressing force. Therefore, by shifting the connection position according to the thickness of the workpiece, welding can be performed in an optimum state. Further, for example, a plurality of connectable positions may be formed along the link 43, and the connection position may be appropriately adjusted according to the combination of the thicknesses of the workpieces.
May be movable along the link 43 to adjust the connection position for each welding location.

[0090]

As described above, according to the present invention, after the two electrode tips are brought into contact with the workpiece by the contact transmitting means,
Since both electrode tips are configured to be evenly pressed, the pressing force of one electrode tip can be received by the other electrode tip even if there is a displacement of the workpiece without using an equalizing device, Deformation of the workpiece can be prevented, pressure can be evenly applied, and defective products can be prevented.

Further, when one electrode tip comes into contact with the workpiece, the movement of the other electrode tip is continued with the contacted electrode tip as a fulcrum. It can be brought into contact with the weldment.

Further, by using the reversing means, both electrode tips can be moved by one drive source without using two actuators, and the size and weight of the welding gun can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of a spot welding apparatus 11 according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a configuration of a spot welding gun 21.

FIG. 3 is a time chart of a current value of a servomotor 35 and an encoder value.

FIG. 4 is a front view showing a configuration of a contact transmission means 74 of a spot welding gun according to another embodiment of the present invention.

FIG. 5 is a front view showing a configuration of a contact transmitting means 79 of a spot welding gun according to still another embodiment of the present invention.

FIG. 6 is a front view showing a configuration of a contact transmission means 80 of a spot welding gun according to still another embodiment of the present invention.

FIG. 7 is a diagram showing a state when two plates having different plate thicknesses are welded.

FIG. 8 is a diagram showing a state where the workpiece is accurately positioned and a state where the workpiece is displaced.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Spot welding apparatus 21 Welding gun 26 Upper electrode tip 27 Lower electrode tip 30 Drive source 41, 74, 79, 80 Contact transmission means 40 Inversion means 53 Link 50 First rack 51 Pinion 52 Second rack 61 Welding robot 71 Control means 75 clutch 78 spring biasing means

Claims (13)

[Claims] 1. A pair of electrode tips which are arranged to face each other and which are moved by a driving source in a direction of approaching and separating from each other, sandwiching an object to be welded between these electrode tips, and applying a force by the driving source. In a spot welding gun that performs spot welding by pressing, when connected to both electrode tips, both electrode tips move in the direction approaching each other, and when one of the electrode tips comes in contact with the workpiece first, A spot welding gun comprising: a contact transmitting means for setting the contacted electrode tip side as a fulcrum and continuing only the movement of the other electrode tip. 2. The driving source has an output portion that moves in parallel to the approaching and separating directions of the electrode tip, and one of the electrode tips is driven by an output portion of the driving source in the same direction as the moving direction of the output portion. The spot welding gun according to claim 1, wherein the other electrode tip is moved, and the other electrode tip is moved in a direction opposite to the one electrode tip by a reversing means for reversing a moving direction of an output portion of the drive source. 3. The electric motor according to claim 1, wherein the drive source is an electric motor, and detects that both electrode tips are in contact with the workpiece based on a current value of the motor or an amount of displacement of an output unit. 3. The spot welding gun according to claim 2, wherein the pressure is started. 4. The spot welding gun according to claim 2, wherein said contact transmitting means has a link mechanism. 5. The link mechanism has one end connected to one electrode tip so as to be angularly displaceable, the other end connected to an inverting means so as to be angularly displaceable, and the output part of the drive source to the intermediate part being angularly displaceable. The spot welding gun according to claim 4, further comprising a link that is freely connected, and has a link that moves toward and away from the electrode tip by the output portion. 6. The spot welding gun according to claim 5, wherein the link, the one electrode, and the reversing means are connected via an intermediate link so as to be angularly displaceable. 7. The spot welding gun according to claim 5, wherein an output of the driving source is connected to a center of the link. 8. The spot welding gun according to claim 5, wherein the output of the drive source is connected to a position shifted from the center of the link. 9. The contact transmitting means is provided with a clutch for preventing and permitting an angular displacement between an output portion of a drive source and a link, and the clutch is provided for a predetermined time or a predetermined distance at the time of starting approach of both electrode tips. The spot welding gun according to any one of claims 5 to 8, wherein angular displacement between the link and the output unit is prevented, and angular displacement between the link and the output unit is allowed during pressurization. 10. The clutch for a predetermined time or a predetermined distance when the two electrode tips start to separate from the workpiece,
The spot welding gun according to claim 9, wherein angular displacement between the link and the output unit is prevented. 11. A spring biasing means interposed between an output portion of the drive source and the link, the spring biasing means for biasing the link toward a predetermined neutral position is provided.
The spot welding gun according to any one of Items 1 to 8, 12. The apparatus according to claim 2, wherein said reversing means has a rack and a pinion.
The spot welding gun as described in (1). 13. The reversing means includes: a first rack that is displaced and driven in the same direction as an output section of a drive source; a pinion that meshes with the first rack; a pinion that meshes with the pinion, and is displaced in a direction opposite to the first rack. The spot welding gun according to claim 12, further comprising a second rack to be driven.