JP3337448B2 - Positioning method of spot welding gun - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for moving a spot welding gun mounted on an articulated robot and for positioning a fixed electrode at a position in contact with a workpiece.

[0002]

2. Description of the Related Art A typical prior art relating to such a method for positioning a spot welding gun is disclosed in Japanese Patent Laid-Open No. 6-2185.
No. 54 discloses this. In this prior art, the distance between the fixed electrode of the spot welding gun and the movable electrode that can approach and separate from the fixed electrode is set to a predetermined initial distance, and then,
The moving electrode is moved to make contact with the work to be welded (hereinafter, sometimes referred to as a work), and furthermore, the spot welding gun is moved so that the fixed electrode approaches the work and the moving electrode is brought into contact with the work. While moving the spot welding gun at a speed corresponding to the moving speed of the spot welding gun, the movement of the moving electrode and the spot welding gun is stopped when the total moving distance of the moving electrode becomes equal to a value obtained by subtracting the work thickness from the initial interval. A method for positioning a spot welding gun is disclosed.

[0003]

In the prior art, when performing spot welding, it is necessary to set the interval between the fixed electrode and the movable electrode to a predetermined initial interval, and to set the thickness of the work for each hitting position. is there. Therefore, there is a problem that these settings are troublesome and the efficiency of the spot welding operation is reduced. In addition, when there is a gap between the stacked workpieces, it is difficult to accurately set the thickness of the workpiece, which may cause poor welding.

An object of the present invention is to provide a positioning method capable of simply and accurately positioning a spot welding gun regardless of the thickness of a workpiece.

[0005]

The present invention comprises a fixed electrode,
A movable electrode that is disposed opposite to the fixed electrode and that can move toward and away from the fixed electrode by a clamping servomotor, and each axis is attached to an articulated robot driven by the servomotor to remove the workpiece; In the method for positioning a spot welding gun for spot welding, each of the servomotors for driving each axis of the articulated robot is controlled so that the object to be welded is interposed between a movable electrode and a fixed electrode. Moving the gun to position the spot welding gun at the hitting point in a plane parallel to the welding surface of the workpiece, and controlling the clamping servomotor that drives the moving electrode to weld the moving electrode Step of moving until contact with the object, and controlling each servo motor driving each of the axes, while approaching the fixed electrode of the spot welding gun toward the object to be welded By controlling the clamping servomotor, the moving electrode is moved at a speed corresponding to a moving speed at which the fixed electrode of the spot welding gun approaches the workpiece, and brought into contact with the workpiece. The current value of each servomotor that drives each axis is monitored, and the reaction force to the articulated robot when the fixed electrode comes into contact with the workpiece and elastically deforms the workpiece is determined. Stopping the servo motors for driving the respective axes and the clamping servo motor when the magnitude of the force reaches a predetermined value.

According to the present invention, after the spot welding gun is moved so that the workpiece is interposed between the two electrodes, the moving electrode is moved toward the workpiece. When the moving electrode comes into contact with the workpiece, the current value of the clamping servomotor increases, so that the contact between the moving electrode and the workpiece can be detected from the level of the current value. Next, the spot welding gun is moved by each servo motor driving each axis of the articulated robot to bring the fixed electrode closer to the workpiece. At this time, the moving electrode is moved at a speed corresponding to the moving speed of the spot welding gun so as to keep the moving electrode in contact with the surface of the workpiece. When the fixed electrode comes into contact with the workpiece, the workpiece is elastically deformed and a reaction force to the articulated robot is generated. The reaction force is obtained, and the magnitude of the obtained reaction force reaches a predetermined value. Then, the movement of the fixed and movable electrodes is stopped.

[0007] Thereby, the contact between the moving electrode and the work and the contact between the fixed electrode and the work can be individually detected, so that the interval between the moving electrode and the fixed electrode is not set to a predetermined initial interval. In addition, the spot welding gun can be easily and accurately positioned regardless of the thickness of the work to be welded interposed between the electrodes. Also, when moving the spot welding gun to bring the fixed electrode close to the workpiece, the moving electrode moves so as to keep in contact with the workpiece. The object receives the pressing force from the fixed electrode while being supported by the moving electrode, and can be made to move ignoring the influence of the gap even if there is a gap between the stacked workpieces.

Further, the present invention has a fixed electrode, and a moving electrode which is arranged to face the fixed electrode and which can be moved toward and away from the fixed electrode by a clamping servomotor, and each axis is driven by the servomotor. In the method for positioning a spot welding gun mounted on an articulated robot to spot-weld an object to be welded, each servomotor driving each axis of the articulated robot is controlled so that the object to be welded is fixed to a moving electrode. Moving the spot welding gun so as to be interposed between the electrode and the step of positioning the spot welding gun at a hitting position in a plane parallel to the welding surface of the workpiece;
By controlling each servo motor for driving each axis, the fixed electrode of the spot welding gun is approached toward the workpiece, and further, the current value of each servo motor for driving each axis is monitored. Calculates the reaction force to the articulated robot when the workpiece comes into contact with the workpiece and elastically deforms the workpiece. When the magnitude of the determined reaction force reaches a predetermined value, each axis is driven. Stopping the respective servomotors, and controlling the clamping servomotor that drives the moving electrodes to move the moving electrodes until they come into contact with the workpiece to be welded. It is.

According to the present invention, after the spot welding gun is moved so that the workpiece is interposed between the two electrodes, the fixed electrode is moved closer to the workpiece. When the fixed electrode comes into contact with the workpiece, the workpiece is elastically deformed and a reaction force to the articulated robot is generated. Therefore, the reaction force is obtained, and the magnitude of the obtained reaction force becomes a predetermined value. Upon reaching, the movement of the fixed electrode is stopped. Next, the moving electrode is moved toward the workpiece by the clamping servomotor. When the moving electrode comes into contact with the workpiece, the current value of the clamping servomotor increases, so that the contact between the moving electrode and the workpiece can be detected from the level of the current value.

Thus, the contact between the movable electrode and the workpiece and the contact between the fixed electrode and the workpiece can be individually detected, so that the interval between the movable electrode and the fixed electrode is set to a predetermined initial interval. The spot welding gun can be easily and accurately positioned without setting, regardless of the thickness of the work interposed between the two electrodes. In addition, since the movement and the movement of the fixed electrode are performed individually, and the movement of the fixed electrode is brought into contact with the surface of the workpiece, the movement of the movable electrode is started. There is no. Therefore, the spot welding gun can be accurately positioned with respect to the workpiece by simple control.

According to the present invention, there is provided a fixed electrode, and a movable electrode which is disposed opposite to the fixed electrode and which can be moved toward and away from the fixed electrode by a clamping servomotor, and each axis is driven by the servomotor. In the method for positioning a spot welding gun mounted on an articulated robot to spot-weld an object to be welded, each servomotor driving each axis of the articulated robot is controlled so that the object to be welded is fixed to a moving electrode. Moving the spot welding gun so as to be interposed between the electrode and the step of positioning the spot welding gun at a hitting position in a plane parallel to the welding surface of the workpiece;
A step of controlling the clamping servomotor that drives the moving electrode to move the moving electrode until it comes into contact with the workpiece, and controlling each servomotor that drives each of the axes to fix the fixed electrode of the spot welding gun. By moving the moving electrode at a speed corresponding to the moving speed at which the fixed electrode of the spot welding gun approaches the work to be welded by controlling the clamping servomotor while approaching the work to be welded. To the articulated robot when the moving electrode comes into contact with the workpiece and elastically deforms the workpiece by monitoring the current value of each servomotor that drives each axis. When the fixed electrode comes into contact with the work to be welded and the magnitude of the obtained reaction force becomes equal to or less than a predetermined value, the servo motors for driving the respective axes and the clamping servo motors are stopped. Work A method of positioning a spot welding gun which comprises and.

According to the present invention, after the spot welding gun is moved so that the workpiece is interposed between the two electrodes, the movable electrode is moved toward the workpiece. When the moving electrode comes into contact with the workpiece, the current value of the clamping servomotor increases, so that the contact between the moving electrode and the workpiece can be detected from the level of the current value. Next, the spot welding gun is moved by each servo motor driving each axis of the articulated robot to bring the fixed electrode closer to the workpiece. At this time, the moving electrode moves at a speed corresponding to the moving speed of the spot welding gun so as to keep the moving electrode in contact with the surface of the workpiece. After the moving electrode comes into contact with the work, the moving electrode pushes down the work and causes the work to undergo elastic deformation. When the work is elastically deformed, a reaction force to the articulated robot is generated, and the magnitude of the reaction force is obtained and monitored. After that, when the fixed electrode contacts the work and pushes the work back to the moving electrode side, the amount of elastic deformation of the work decreases and the magnitude of the reaction force of the articulated robot also decreases, so the magnitude of the reduced reaction force When the magnitude of the obtained reaction force becomes equal to or less than a predetermined value, the movement of the fixed and movable electrodes is stopped.

Thus, the contact between the moving electrode and the work and the contact between the fixed electrode and the work can be individually detected, so that the interval between the moving electrode and the fixed electrode is not set to a predetermined initial interval. In addition, the spot welding gun can be easily and accurately positioned regardless of the thickness of the work to be welded interposed between the electrodes. Further, when the magnitude of the reaction force becomes equal to or less than a predetermined value, the movement of the fixed and movable electrodes is stopped, so that the positioning of the spot welding gun can be performed with almost no elastic deformation of the work.

In the present invention, the reaction force is calculated from the amount of change in the current value of each servomotor when the fixed electrode comes into contact with the workpiece and elastically deforms the workpiece. It is characterized in that it is one selected from those evaluated by weighting the amount of change in the current value and those calculated from the amount of change in the current value of each servo motor of the wrist axis.

According to the present invention, since a plurality of types of reaction force determination methods are set, it is possible to select a method of obtaining the reaction force most suitable for the workpiece. Therefore, the contact between the fixed electrode and the workpiece can be accurately detected, and the positioning of the spot welding gun can be performed so that the elastic deformation of the workpiece is minimized.

According to another aspect of the present invention, there is provided a fixed electrode, and a movable electrode disposed opposite to the fixed electrode and capable of moving toward and away from the fixed electrode by a clamping servomotor, and each axis is driven by the servomotor. In the method for positioning a spot welding gun mounted on an articulated robot to spot-weld an object to be welded, each servomotor driving each axis of the articulated robot is controlled so that the object to be welded is fixed to a moving electrode. Moving the spot welding gun so as to be interposed between the electrode and the step of positioning the spot welding gun at a hitting position in a plane parallel to the welding surface of the workpiece;
A step of controlling the clamping servomotor that drives the moving electrode to move the moving electrode until it comes into contact with the workpiece, and controlling each servomotor that drives each of the axes to fix the fixed electrode of the spot welding gun. By moving the moving electrode at a speed corresponding to the moving speed at which the fixed electrode of the spot welding gun approaches the work to be welded by controlling the clamping servomotor while approaching the work to be welded. The current when the fixed electrode comes into contact with the workpiece and changes the current value of the clamping servomotor by monitoring the current value of the clamping servomotor that drives the respective axes. Stopping the servomotors for driving the respective axes and the clamping servomotor when the obtained current value reaches a predetermined value. It is a down method of positioning.

According to the present invention, after the spot welding gun is moved so that the workpiece is interposed between the two electrodes, the moving electrode is moved toward the workpiece. When the moving electrode comes into contact with the workpiece, the current value of the clamping servomotor increases, so that the contact between the moving electrode and the workpiece can be detected from the level of the current value. Next, the spot welding gun is moved by each servo motor driving each axis of the articulated robot to bring the fixed electrode closer to the workpiece. At this time, the moving electrode is moved at a speed corresponding to the moving speed of the spot welding gun so as to keep the moving electrode in contact with the surface of the workpiece. When the fixed electrode comes into contact with the workpiece, the moving electrode comes into contact with the fixed electrode via the workpiece and cannot move any more, so that the current value of the clamping servomotor further increases. Therefore, the increased current value is obtained, and when the obtained current value reaches a predetermined value, the movement of the fixed and movable electrodes is stopped.

Thus, the contact between the movable electrode and the work and the contact between the fixed electrode and the work can be individually detected, so that the interval between the movable electrode and the fixed electrode does not have to be set to a predetermined initial interval. In addition, the spot welding gun can be easily and accurately positioned regardless of the thickness of the work to be welded interposed between the electrodes. Also, by monitoring the current value of the clamping servomotor driven independently, it is possible to detect the contact between both electrodes and the work, so that it is not necessary to monitor the current value of each servomotor, and the spot welding gun Can be easily and accurately positioned with a simple configuration.

[0019]

FIG. 1 is a perspective view showing the appearance of a spot welding robot 1 to which the present invention can be suitably applied. The spot welding robot 1 includes an articulated robot 2 (hereinafter, sometimes abbreviated as a robot) and a spot welding gun 8.

The robot 2 is a 6-axis vertical articulated robot and has a base 4 fixed to the floor, a lower arm 5, an upper arm 6, and a wrist 7. The lower arm 5 is attached to the base 4 so that the lower end can pivot about a vertical first axis J1 and can be angularly displaced about a horizontal second axis J2. The base end of the upper arm 6 is attached to the upper end of the lower arm 5 so as to be angularly displaceable about a horizontal third axis J3. A wrist 7 attached to the distal end of the upper arm 6 is mounted so as to be angularly displaceable about a fourth axis J4 parallel to the axis of the upper arm 6, and is angularly mounted about a fifth axis J5 perpendicular to the axis of the upper arm 6. Displaceably mounted. Spot welding gun 8 attached to this wrist 7
Is provided so as to be angularly displaceable around a sixth axis J6 perpendicular to the fifth axis.

The spot welding gun 8 has a base 9 attached to the wrist 7 and a U-shaped gun arm 12 fixed to a lower portion of the base 9, and a fixed electrode 14 is provided at an end of the gun arm 12. Fixed. A moving electrode 13 is provided on the gun arm 12 so as to be opposed to the fixed electrode 14 and move in a direction approaching and moving away from the fixed electrode 14. The movable and fixed electrodes 13 and 14 are rod-shaped and arranged coaxially.
The moving electrode 13 is driven by a clamping servomotor Mw provided on the spot welding gun 8. Each axis J1 to J6 of the articulated robot 2 is a servo motor M
1 to M6, these servo motors M1
Through M6, the posture of the robot 2 is controlled. The axes J4 to J6 are called wrist axes.

Next, a control configuration of the spot welding robot 1 will be described. FIG. 2 shows the servomotor M of the first axis J1.
FIG. 3 is a block diagram showing a control configuration of the first embodiment. The other servo motors M2 to M6 and the clamping servo motor Mw have the same configuration as the servo motor M1, and are not shown.

The teaching data of the spot welding robot 1 is stored in the memory 22 as storage means. The teaching data includes a work operation program for sequentially spot-welding the respective welding points of the workpiece W to be welded, and a hit point position, which is the position and attitude of the spot welding gun 8 when welding the respective welding points. . The hitting position is given by a position in the absolute coordinate system, and the attitude is given by the inclination of the electrode (the moving direction of the movable electrode 13) during welding in the absolute coordinate system. The present invention provides teaching data for positioning the spot welding gun 8 at the hitting position as described below.

The position controller 20 changes the posture of the robot 2 by giving angle command values P1 to P6 of the axes J1 to J6 to the servo controller 21 based on the teaching data.
The spot welding gun 8 is positioned at the designated hitting position. The servo controller 21 supplies current values I1 to I6 corresponding to the angle command values P1 to P6 to the servo motors M1 to M6 so that the axes J1 to J6 have the commanded angles.

An encoder E1 is attached to the servomotor M1, and a rotation angle of the servomotor M1 around the first axis J1 is detected by the encoder E1. The detected encoder value is returned to the servo controller 21.
The servo controller 21 performs feedback control of the servo motor M1 based on the angle command value P1 from the position controller 20 and the encoder value from the encoder E1 so that the first axis J1 is at the designated angular position. The same applies to the servomotors M2 to M6 and the clamping servomotor Mw.

At the time of teaching to teach the work operation to the spot welding robot 1, each axis J1 to J
Based on the encoder value of No. 6, the absolute coordinates of the hit point position and the inclination of the electrode are stored in the memory 22 as the teaching position.

The current values of the servomotors M1 to M6 and the clamping servomotor Mw are detected and monitored by the monitoring means 23. The calculating means 24 calculates the reaction force based on the amount of change in these current values as described later.

In order to position the spot welding gun 8 at a predetermined hitting point, after positioning in a plane parallel to the welding surface of the work W, a direction perpendicular to the welding surface of the work W, that is, movement is performed. It is necessary to position the electrode 13 in the moving direction. The former positioning is relatively easy because it is performed in a plane. In the latter positioning, it is necessary to bring the movable and fixed electrodes 13 and 14 into contact with one and the other surfaces of the workpiece W, respectively. Since the moving electrode 13 is independently driven by the clamping servo motor Mw as described above, the contact between the moving electrode 13 and the work W is accurately detected by monitoring the current value of the clamping servo motor Mw. can do. On the contrary,
The fixed electrode 14 is fixed to the spot welding gun 8,
Further, since the position and the attitude of the spot welding gun 8 are controlled by the servomotors M1 to M6 of the respective axes of the robot 2, that is, a plurality of servomotors,
It is difficult to detect the contact between the fixed electrode 14 and the work W even if the current values of M6 to M6 are individually monitored.

The present inventor has conducted various studies on a method for detecting contact between the fixed electrode 14 and the work W. As a result, when the fixed electrode 14 comes into contact with the work W, the work W is elastically deformed and a reaction force is generated. Therefore, it has been found that the contact between the fixed electrode 14 and the workpiece W can be detected by monitoring the magnitude of the reaction force.

The magnitude of the reaction force is determined by the articulated robot 2
Are calculated from the current values of the servo motors M1 to M6 that drive the respective axes J1 to J6. As described above, these servo motors M1 to M6 are also subjected to feedback control, and the current value changes in accordance with the reaction force from the elastically deformed work W. In the case where a reaction force acts on 2, the reaction force can be obtained based on the amount of change in the current value. The reaction force may be calculated from the amount of change in the current value of the servo motors M1 to M6 at each point, or may be evaluated by weighting the amount of change in the current value of the servo motors M1 to M6. Also, for example,
Wrist axis J4 ~ with smaller frictional force of reducer than basic axis
The reaction force may be calculated by preferentially selecting the servo motors M4 to M6 of J6.

FIG. 3 is a flow chart for explaining a method for positioning a spot welding gun according to a first embodiment of the present invention. FIG. 4 shows a positioning procedure of the method for positioning a spot welding gun shown in FIG. FIG. In the present embodiment, the workpiece W, which is an object to be welded, is fixed at a predetermined position with the welding surface substantially horizontal.

In step a1, the spot welding gun 8 is moved to a predetermined horizontal position. The predetermined position is the workpiece W
Is a spot welding position in a horizontal plane parallel to the welding surface of the above, and is set as described above. As shown in FIG. 4A, the spot welding gun 8 moves the workpiece W to the fixed electrode 14.
And the moving electrode 13 is manually guided so as to be interposed. In the present embodiment, the distance between the two electrodes is the
It is not necessary to set the predetermined initial interval as in −218554, but an arbitrary interval. After step a2, the movement of the spot welding gun is automatically performed.

In step a2, the moving electrode 13 moves vertically toward the workpiece W. This movement is performed by controlling the clamping servomotor Mw. The moving speed and the motor drive current value are set in advance to a low speed and a low current, respectively, and are stored in the memory 22. These values are set to low speed and low current because the moving electrode 13
This is for accurately detecting the contact between the workpiece and the work W. In step a3, the current value of the clamping servomotor 13 is detected and monitored by the monitoring means 23. The moving electrode 13 is shown in FIG.
When the workpiece W comes into contact with the workpiece W as shown in (2), the current value of the clamping servomotor Mw increases.

In step a4, the clamping servomotor M
It is determined whether the current value of w is equal to or greater than a predetermined reference current value A1. If this determination is negative, step a
Returning to step 3, the monitoring of the current value is continued, and if this determination is affirmative, it is determined that the moving electrode 13 is in contact with the workpiece W, and the process proceeds to step a5. In step a5, the clamping servomotor Mw is stopped.

In step a6, the spot welding gun 8 moves in the vertical direction to move the fixed electrode 14 toward the work W. This movement is performed by the servo motors M1 to M6.
This is performed by driving each of the axes J1 to J6 at a low speed. In this case, if the moving electrode 13 is moved as it is, as shown in FIG.
Is moved away from the work W, the moving electrode 13 is moved at a speed corresponding to the moving speed of the spot welding gun 8 so that the moving electrode 13 is kept in contact with the work W as shown in FIG. Let it. In step a7, the current values of the servo motors M1 to M6 are detected and monitored by the monitoring means 23.

In step a8, a reaction force is calculated. The calculation of the reaction force is performed based on the amount of change in the current value of each of the servomotors M1 to M6 as described above. When the current value does not change, that is, when the fixed electrode 14 and the work W
When is not in contact, the reaction force is zero. When the fixed electrode 14 contacts the workpiece W as shown in FIG.
The work W is elastically deformed, and the current value changes in each of the servomotors M1 to M6, and the reaction force is calculated. The magnitude of the reaction force is
It increases as the change in the current value increases.

At step a9, it is determined whether or not the magnitude of the reaction force is equal to or greater than a predetermined reference value C1. If this determination is negative, the process returns to step a7, and the monitoring of the current values of the servo motors M1 to M6 and the calculation of the reaction force are continued. If this determination is affirmative, it is determined that the fixed electrode 14 is in contact with the workpiece W, and the process proceeds to step a10. In step a10, the servomotors M1 to M6 and the clamping servomotor Mw are stopped, and the positioning of the spot welding gun 8 is completed. The hitting position of the spot welding gun 8 thus obtained is stored in the memory 22 as teaching data.

As described above, in the present embodiment, the fixed electrode 1
4 and the workpiece W are detected based on the amount of change in the current value of each of the servomotors M1 to M6, and the contact between the moving electrode 13 and the workpiece W is determined based on the level of the current value of the clamping servomotor Mw. Therefore, the contact between the movable electrode 13 and the work W and the contact between the fixed electrode 14 and the work W can be individually detected. Therefore, the spot welding gun 8 can be accurately positioned without setting the interval between the movable electrode 13 and the fixed electrode 14 to a predetermined initial interval and regardless of the thickness of the work W interposed between the electrodes. Can be done.

When the spot welding gun 8 is moved to bring the fixed electrode 14 close to the work W, the movable electrode 13 moves so as to maintain the state of contact with the work W. At the time of contact, the work W is subjected to a pressing force from the fixed electrode 14 while being supported by the moving electrode 13, so that even if there is a gap between the stacked works W, the work W is caused to ignore the influence. Can be. Further, since a method of obtaining the reaction force that is most suitable for the work W can be selected, the contact between the fixed electrode 14 and the work W can be detected with high accuracy. Therefore, the positioning of the spot welding gun can be performed such that the elastic deformation of the work W is minimized.

Further, in this embodiment, the teaching position is corrected as follows. As described above, in the present embodiment, the moving electrode 13 moves first and contacts the workpiece W,
First, the work W is elastically deformed so as to be pushed downward.
This elastic deformation gives a reaction force from the workpiece W to the moving electrode 13 and increases the current value of the clamping servomotor Mw.
Thereafter, the fixed electrode 14 moves and comes into contact with the work W, and is elastically deformed so as to push the work W upward. This elastic deformation generates a reaction force to the robot 2 and
Finally, the work W is pushed upward in the opposite direction. Since the push-up amount corresponds to the reference value C1, the accuracy of the teaching position can be further improved by correcting the teaching position downward by a distance corresponding to the reference value C1.

FIG. 5 is a flowchart for explaining a method for positioning a spot welding gun according to a second embodiment of the present invention. In the present embodiment, the workpiece W is fixed at a predetermined position with the welding surface substantially horizontal.

In step s1, the spot welding gun 8 is manually guided and moved to a predetermined horizontal position as in step a1 in FIG. In step s2, the spot welding gun 8 moves in the vertical direction, and causes the fixed electrode 14 to approach the work W.

In steps s3 to s5, a reaction force is calculated in the same manner as in steps a7 to a9 in FIG. 3, and the presence or absence of contact between the fixed electrode 14 and the work W is determined based on the magnitude of the reaction force. Is determined. If the determination is negative, the process returns to step s3 to continue monitoring the current values of the servomotors M1 to M6 and calculate the reaction force. If the determination is positive, the process proceeds to step s6. In step s6, the servo motors M1 to M6 are stopped.

In steps s7 to s9, the presence or absence of contact between the moving electrode 13 and the work W is determined based on the level of the current value of the clamping servomotor Mw, as in steps a2 to a4 in FIG. If this judgment is negative,
Returning to step s8, monitoring of the current value is continued, and if affirmative, the process proceeds to step s10. In step s10, the clamping servomotor Mw is stopped, and the positioning of the spot welding gun 8 is completed. The hitting position of the spot welding gun 8 thus obtained is stored in the memory 22 as teaching data.

As described above, in the present embodiment, the movement and the movement of the fixed electrodes 13 and 14 are performed individually, and
After moving the movable electrode 4 to contact the lower surface of the work W, the movable electrode 13 moves until the movable electrode 13 contacts the upper surface of the opposite side of the work W. This eliminates the need to move the moving and fixed electrodes 13 and 14 at the same time.
It is not necessary to move the movable electrode 13 so as to keep the state in contact with the workpiece W during the movement of the workpiece. Therefore, the spot welding gun 8 can be accurately positioned with a simple control. Further, similarly to the first embodiment, the interval between the movable electrode 13 and the fixed electrode 14 does not need to be set to a predetermined initial interval, and regardless of the thickness of the work W interposed between the electrodes. The positioning of the spot welding gun 8 can be performed accurately. In addition, since it is possible to select a method of obtaining a reaction force most suitable for the work W, the fixed electrode 14 and the work W
Can be detected with high accuracy.

Further, in the present embodiment, the correction of the teaching position is performed as follows. As described above, in the present embodiment, the fixed electrode 14 moves first and contacts the workpiece W,
The work W is elastically deformed so as to be pushed upward. Thereafter, the moving electrode 13 moves and comes into contact with the workpiece W, and the current value of the clamping servomotor Mw is increased. At this time, since the fixed electrode 14 is in contact with the workpiece W, the movable electrode 1
No. 3 cannot push down the work W. Therefore,
The work W remains pushed upward. Since the push-up amount corresponds to the reference value C1, if the teaching position is corrected to be lower by the distance corresponding to the reference value C1 as in the first embodiment, the accuracy of the teaching position can be improved. Can be more enhanced.

FIG. 6 is a flowchart for explaining a spot welding gun positioning method according to a third embodiment of the present invention. In the present embodiment, the workpiece W is fixed at a predetermined position with the welding surface substantially horizontal.

In steps b1 to b5, exactly the same processing as in steps a1 to a5 in FIG. 3 is performed. Therefore, description is omitted. In step b6, the spot welding gun 8 and the moving electrode 13 are moved. In this process, the spot welding gun 8 is moved to move the fixed electrode 14 closer to the work W as well as to move the movable electrode 13 in contact with the work W, as in step a6 of FIG. This is performed by moving the electrode 13 at a speed corresponding to the moving speed of the spot welding gun 8. In step b7, the current values of the servo motors M1 to M6 are detected and monitored by the monitoring means 23. In step b8, the reaction force is applied to each servomotor M1 as described above.
Calculated based on the amount of change in the current value of M6.

Thus, steps b6 to b8 are apparently the same as steps a6 to a8. Step b6
In order to clarify a substantial difference between the steps b6 to b8 and the steps a6 to a8, the processing of the steps b6 to b8 will be described in further detail. The moving electrode 13 keeps the state in contact with the surface of the work W, and pushes down the work W to
Causes elastic deformation. When elastic deformation occurs in the work W, a reaction force to the robot 2 is generated, and the magnitude of the reaction force is obtained and monitored. Thereafter, when the fixed electrode 14 comes into contact with the work W and pushes back the work W, the amount of elastic deformation is reduced, and the magnitude of the reaction force is also reduced. In step b8 of the present embodiment, the magnitude of the reaction force decreasing in this way is sequentially calculated. On the other hand, in step a8 of the first embodiment, the magnitude of the reaction force that is increased in this manner after the work W is pushed up is calculated sequentially after the decrease.

At step b9, it is determined whether or not the magnitude of the reaction force is equal to or less than a predetermined reference value C2. The value of reference value C2 is, for example, zero. If the determination is negative, the process returns to step b7 to return to each of the servomotors M1 to M6.
The monitoring of the current value and the calculation of the reaction force are continued. If this determination is affirmative, it is determined that the fixed electrode 14 has come into contact with the workpiece W, and the process proceeds to step b10. Step b10
Then, the servomotors M1 to M6 and the clamping servomotor Mw are stopped, and the positioning of the spot welding gun 8 is completed. The spot welding gun 8 thus obtained
Are stored in the memory 22 as teaching data.

As described above, in the present embodiment, when the magnitude of the reaction force falls below the predetermined reference value C2, the movement of the spot welding gun 8 and the movable electrode 13 is stopped. The positioning can be performed with almost no elastic deformation of the work W. Further, the present embodiment can further achieve the same effects as those of the first embodiment.

FIG. 7 is a flow chart for explaining a method of positioning a spot welding gun according to a fourth embodiment of the present invention, and FIG. 8 is a graph showing a temporal transition of a current value of a clamping servomotor Mw. is there. In the present embodiment,
The work W is fixed at a predetermined position with the welding surface substantially horizontal.

In steps c1 to c5, the same processing as in steps a1 to a5 in FIG. 3 is performed. Therefore, duplicate description will be omitted. At time t1 in FIG. 7, the movement of the movable electrode 13 in step c2 is started.
The current value for driving the clamping servo motor Mw is A0
It is. At time t2, the current value of the clamping servomotor Mw increases and reaches the reference current value A1, and the determination in step c4 becomes positive. That is, it is determined that the moving electrode 13 has contacted the upper surface of the work W.

In step c6, the spot welding gun 8 and the movable electrode 13 are moved. In this process, the spot welding gun 8 is moved to move the fixed electrode 14 closer to the work W as well as to move the movable electrode 13 in contact with the work W, as in step a6 of FIG. This is performed by moving the electrode 13 at a speed corresponding to the moving speed of the spot welding gun 8. In step c7, the current value of the clamping servomotor Mw is detected and monitored by the monitoring means 23.

In step c8, the clamping servomotor M
It is determined whether the current value of w is equal to or greater than a predetermined reference current value A2. The reference current value A2 is a value determined in advance by a test as described later, and is set based on the increment of the current value of the clamping servomotor Mw caused when the fixed electrode 14 comes into contact with the work W. If the determination in step c8 is negative, the process returns to step c7 to continue monitoring the current value. If the determination in step c8 is affirmative, that is, the current value of the clamping servomotor Mw increases as in the state at time t3 in FIG.
When the number reaches 2, the fixed electrode 14 is determined to be in contact with the workpiece W, and the process proceeds to Step c9. In step c9, the movement of the spot welding gun 8 and the moving electrode 13 is stopped, and the positioning of the spot welding gun 8 is completed. The hitting position of the spot welding gun 8 thus obtained is stored in the memory 22 as teaching data.

In this embodiment, the setting of the reference current value A2 is performed as follows. As described above, in the present embodiment, the moving electrode 13 moves first and contacts the workpiece W,
The work W is elastically deformed so as to be pushed downward. Thereafter, the fixed electrode 14 moves and comes into contact with the work W, and pushes the work W back upward, so that the amount of elastic deformation pushed downward is reduced. Therefore, at this time, the reference current value A2 may be set such that the amount of the elastic deformation by the fixed electrode 14 is equal to the amount of the elastic deformation by the movable electrode 13.

As described above, in the present embodiment, not only the contact between the movable electrode 13 and the work W but also the contact between the fixed electrode 14 and the work W are detected by monitoring the current value of the clamping servomotor Mw. be able to. Further, since the clamping servomotor Mw drives the movable electrode 13 alone, it is sufficient to monitor one current value, and the first and second embodiments need to monitor the current value of each servomotor.
Control can be simplified as compared with the embodiment. Therefore, the positioning of the spot welding gun can be easily and accurately performed with a simple configuration. Also, in the present embodiment,
The same effects as in the first embodiment can be obtained.

[0058]

As described above, according to the first aspect of the present invention, the distance between the movable electrode and the fixed electrode does not need to be set to a predetermined initial distance, and the welded member interposed between the two electrodes. Regardless of the thickness of the object, the positioning of the spot welding gun can be performed easily and accurately. Also, when the fixed electrode contacts the workpiece, the workpiece receives the pressing force from the fixed electrode while being supported by the moving electrode. Can be ignored.

According to the second aspect of the present invention, in addition to the effect of the first aspect, since it is not necessary to simultaneously move the fixed electrode and the movable electrode, the spot welding gun can be accurately covered with simple control. It can be positioned with respect to the workpiece.

According to the third aspect of the present invention, in addition to the effect of the first aspect, the spot welding gun can be positioned with almost no elastic deformation of the workpiece.

According to the fourth aspect of the present invention, it is possible to select a method of obtaining a reaction force that is most suitable for the work to be welded, so that contact between the fixed electrode and the work can be detected with high accuracy. The positioning of the spot welding gun can be performed so that the deformation of the work is kept to a minimum.

According to the fifth aspect of the present invention, in addition to the effect of the first aspect, by monitoring the current value of the clamping servomotor, only the contact between the moving electrode and the workpiece can be prevented. In addition, since the contact between the fixed electrode and the workpiece can be detected, the positioning of the spot welding gun can be easily and accurately performed by simple control.

[Brief description of the drawings]

FIG. 1 is a perspective view showing the appearance of a spot welding robot 1 to which the present invention can be suitably applied.

FIG. 2 is a block diagram showing a control configuration of a servomotor M1 of a first axis J1.

FIG. 3 is a flowchart illustrating a method for positioning a spot welding gun according to the first embodiment of the present invention.

FIG. 4 is a view showing a positioning procedure of the spot welding gun positioning method shown in FIG. 3;

FIG. 5 is a flowchart illustrating a method for positioning a spot welding gun according to a second embodiment of the present invention.

FIG. 6 is a flowchart for explaining a spot welding gun positioning method according to a third embodiment of the present invention.

FIG. 7 is a flowchart illustrating a method for positioning a spot welding gun according to a fourth embodiment of the present invention.

FIG. 8 is a graph showing a temporal transition of a current value of the clamping servomotor Mw.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Spot welding robot 2 Articulated robot 5 Lower arm 6 Upper arm 7 Wrist 8 Spot welding gun 12 Gun arm 13 Moving electrode 14 Fixed electrode 20 Position controller 21 Servo controller 22 Memory 23 Monitoring means 24 Calculation means M1-M6 Servomotor Mw Servo motor

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B23K 11/11 B23K 11/24 B25J 13/08

Claims (5)

(57) [Claims] 1. A multi-joint type having a fixed electrode and a moving electrode disposed opposite to the fixed electrode and capable of moving toward and away from the fixed electrode by a clamping servomotor, wherein each axis is driven by the servomotor. In a positioning method of a spot welding gun mounted on a robot to spot-weld an object to be welded, controlling each servomotor driving each axis of the articulated robot so that the object to be welded moves between a movable electrode and a fixed electrode. Moving the spot welding gun so as to be interposed therebetween, and positioning the spot welding gun at a hitting position in a plane parallel to the welding surface of the workpiece, and a clamping servomotor for driving a moving electrode. Controlling and moving the moving electrode until it comes into contact with the workpiece; and controlling each servomotor driving each of the axes to fix the fixed electrode of the spot welding gun to the workpiece. And moving the moving electrode at a speed corresponding to the moving speed at which the fixed electrode of the spot welding gun approaches the workpiece by contacting the workpiece by controlling the clamping servomotor. And the current value of each servomotor driving each axis is monitored, and the reaction force to the articulated robot when the fixed electrode contacts the workpiece and elastically deforms the workpiece. And stopping the servomotors for driving the respective axes and the clamping servomotors when the magnitude of the obtained reaction force reaches a predetermined value. Positioning method. 2. A multi-joint type having a fixed electrode, and a moving electrode disposed opposite to the fixed electrode and capable of moving toward and away from the fixed electrode by a clamping servomotor, wherein each axis is driven by the servomotor. In a positioning method of a spot welding gun mounted on a robot to spot-weld an object to be welded, controlling each servomotor driving each axis of the articulated robot so that the object to be welded moves between a movable electrode and a fixed electrode. Moving the spot welding gun so as to be interposed therebetween, positioning the spot welding gun at a hitting position in a plane parallel to the welding surface of the workpiece, and a servo motor for driving each of the axes. By controlling the fixed electrode of the spot welding gun toward the workpiece, the current value of each servomotor for driving each axis is monitored, and the fixed electrode contacts the workpiece. Then, the reaction force to the articulated robot when the workpiece is elastically deformed is obtained, and when the magnitude of the obtained reaction force reaches a predetermined value, each servo motor driving each axis is stopped. A method for positioning a spot welding gun, comprising: a step of controlling a clamping servomotor that drives a moving electrode to move the moving electrode until the moving electrode comes into contact with a workpiece. 3. A multi-joint type having a fixed electrode and a moving electrode disposed opposite to the fixed electrode and capable of moving toward and away from the fixed electrode by a clamping servomotor, wherein each axis is driven by the servomotor. In a positioning method of a spot welding gun mounted on a robot to spot-weld an object to be welded, controlling each servomotor driving each axis of the articulated robot so that the object to be welded moves between a movable electrode and a fixed electrode. Moving the spot welding gun so as to be interposed therebetween, and positioning the spot welding gun at a hitting position in a plane parallel to the welding surface of the workpiece, and a clamping servomotor for driving a moving electrode. Controlling and moving the moving electrode until it comes into contact with the workpiece; and controlling each servomotor driving each of the axes to fix the fixed electrode of the spot welding gun to the workpiece. And moving the moving electrode at a speed corresponding to the moving speed at which the fixed electrode of the spot welding gun approaches the workpiece by contacting the workpiece by controlling the clamping servomotor. And the current value of each servomotor driving each axis is monitored, and the reaction force to the articulated robot when the moving electrode comes into contact with the workpiece and elastically deforms the workpiece. When the fixed electrode is in contact with the workpiece, when the magnitude of the obtained reaction force is equal to or less than a predetermined value, a step of stopping each servo motor for driving each axis and the clamping servo motor. A method for positioning a spot welding gun. 4. The reaction force is calculated from the amount of change in the current value of each servomotor when the fixed electrode comes into contact with the workpiece and elastically deforms the workpiece. 4. The method according to claim 1, wherein the weighted change amount is one selected from a weighted change amount and a change amount calculated from a change amount of the current value of each servomotor of the wrist axis. 3. The method for positioning a spot welding gun according to item 1. 5. A multi-joint type having a fixed electrode and a moving electrode which is arranged to face the fixed electrode and which can be moved toward and away from the fixed electrode by a clamping servomotor, and each axis of which is driven by the servomotor. In a positioning method of a spot welding gun mounted on a robot to spot-weld an object to be welded, controlling each servomotor driving each axis of the articulated robot so that the object to be welded moves between a movable electrode and a fixed electrode. Moving the spot welding gun so as to be interposed therebetween, and positioning the spot welding gun at a hitting position in a plane parallel to the welding surface of the workpiece, and a clamping servomotor for driving a moving electrode. Controlling and moving the moving electrode until it comes into contact with the workpiece; and controlling each servomotor driving each of the axes to fix the fixed electrode of the spot welding gun to the workpiece. And moving the moving electrode at a speed corresponding to the moving speed at which the fixed electrode of the spot welding gun approaches the workpiece by contacting the workpiece by controlling the clamping servomotor. In this state, the current value of the clamping servomotor that drives each axis is monitored, and the current value when the fixed electrode contacts the workpiece to change the current value of the clamping servomotor is determined. Stopping the servomotors for driving the respective axes and the clamping servomotor when the obtained current value reaches a predetermined value.