JP3359012B2 - Spot welding robot - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spot welding robot which carries out spot welding by mounting a welding gun on a wrist of an articulated robot, for example.

[0002]

2. Description of the Related Art A welding gun of a spot welding robot has a fixed electrode and a moving electrode. The welding gun is arranged at a hitting position taught in advance. It clamps, applies a pressing force, and applies a welding current to perform spot welding.

In spot welding, it is desirable that the angle of the electrode of the welding gun (the inclination of the electrode with respect to the workpiece at the time of welding) is in the direction perpendicular to the plane (the direction perpendicular to the workpiece). For this purpose, for example, JP-A-6-328268 or JP-A-10-216955 proposes a method of detecting a direction perpendicular to a surface by adding a certain type of sensor. Because of the necessity, the cost was increased.

[0004] A method for detecting the direction perpendicular to the plane without requiring a special device is disclosed in Japanese Patent Application Laid-Open No. 10-143212. In the method disclosed in this publication, a workpiece is clamped between both electrodes having flat ends while the welding gun is angularly displaced about the clamping point. Since the distance between the electrodes is smallest when the electrodes are in the direction perpendicular to the surface, the inclination of the electrodes at this time is detected as the direction perpendicular to the workpiece.

[0005]

However, in the above-mentioned method, it is necessary to use electrodes whose end faces are flat. Detection is possible even when the surface is not flat, but the detection accuracy is greatly reduced. In addition, it is troublesome to replace an electrode having a rounded tip used in a normal welding operation each time.

An object of the present invention is to provide a spot welding robot which does not require a special device and can accurately detect the direction perpendicular to the surface regardless of the shape of the electrode tip.

[0007]

According to the present invention, a welding gun having a pair of openable and closable electrodes is provided on a wrist of a robot, and a predetermined welding point of an object to be welded is sandwiched between both electrodes. In a spot welding robot that performs spot welding by moving one electrode to a plurality of designated points in the vicinity of the welding point of the workpiece, detecting the magnitude of the reaction force when the electrode contacts the workpiece, A spot welding robot characterized by detecting a direction perpendicular to a workpiece to be welded based on a position of a designated point and a magnitude of a reaction force at the designated point.

If one of the electrodes comes into contact with the workpiece while the robot or the electrodes are being moved, the workpiece is elastically deformed to generate a reaction force. The hitting angle at the time of welding is stored in advance as teaching data so as to be straight. In the vicinity of the hit point of the workpiece, set a designated point so that the electrode just touches the surface of the workpiece at multiple locations, and when the electrode is moved to this designated point, if the teaching data is accurate, Since the electrode tip uniformly contacts the workpiece at each designated point, the degree of deformation and the magnitude of the reaction force of the workpiece become equal. However, when the hitting angle of the teaching data deviates from the actual direction perpendicular to the plane, the degree of elastic deformation of the workpiece differs depending on the position of the designated point, and the degree of occurrence of the reaction force differs. That is, the magnitude of the reaction force differs for each designated point.

Therefore, designated points are set at a plurality of locations near the welding point, the reaction force when the electrode is moved to each designated point is detected, and the position of the designated point and the magnitude of the reaction force at the designated point are determined. Based on this, for example, it is possible to detect the direction perpendicular to the workpiece such that the actual direction perpendicular to the surface is on the specified point side where the reaction force is smaller than the hitting angle of the teaching data. When the direction perpendicular to the surface is known, the hitting angle of the teaching data is corrected based on the direction, and the hitting angle can be accurately set as a flat surface.

As described above, according to the present invention, the electrodes are brought into contact with the workpiece at a plurality of locations to detect the direction perpendicular to the surface.
Regardless of the shape of the tip of the electrode, the direction perpendicular to the plane can be accurately detected even when the tip is round. Such detection in the direction perpendicular to the surface can be applied not only to the correction of the teaching data but also to the correction of the hitting angle when the workpiece is displaced during the welding operation.

According to a second aspect of the present invention, the welding gun has a fixed electrode and a moving electrode that is moved by a servomotor, the moving electrode is moved to a designated point by the servomotor, and the moving electrode is A reaction force is obtained based on a current value of the servomotor when the motor comes into contact with the motor.

When moving the moving electrode to the designated point, if the moving electrode comes into contact with the workpiece in the middle of the movement, the servo motor driving the moving electrode moves the moving electrode to the predetermined position against the workpiece. The current supplied to the motor is increased so as to move. That is, the motor current value increases according to the reaction force from the workpiece. Therefore, the magnitude of the reaction force can be detected by detecting the motor current value. In this way, according to the present invention, the magnitude of the reaction force can be detected without providing any special device, so that the direction perpendicular to the workpiece can be detected without increasing the cost.

According to a third aspect of the present invention, the welding gun has a fixed electrode and a moving electrode that is moved by a servomotor. When the robot is moved to move the fixed electrode to a designated point and the electrodes come into contact with each other. And detecting the direction perpendicular to the surface based on the reaction force acting on the robot.

In the present invention, a reaction force is obtained by moving a welding gun by a robot and bringing a fixed electrode into contact with an object to be welded, instead of detecting a reaction force by moving a moving electrode. Also in this case, for example, the current value of the servomotor that drives the robot is detected to determine the reaction force, and the direction perpendicular to the surface can be detected based on the reaction force.

According to the present invention, a plurality of designated points are set on a circle centered on the welding point on a plane passing through the welding point stored in advance and perpendicular to the inclination of the electrode during welding. It is characterized by the following.

According to the present invention, a plurality of designated points are set on a circle centered on the welding point on the surface of the work to be welded. When it is on the designated point side where the reaction force is the smallest with respect to the hitting angle, the direction perpendicular to the plane can be easily detected.

In the prior application, the posture of the gun was changed,
In contrast to the case where the electrode is used to hold the welding point and detect the direction perpendicular to the surface, in the present invention, in the vicinity of the welding point, the electrode is brought into contact with a plurality of points by changing the position and position of the point. Since the perpendicular direction is detected based on the magnitude of the force, the perpendicular direction can be detected more accurately than in the prior application.

[0018]

FIG. 1 is a perspective view showing the appearance of a spot welding robot 1 according to an embodiment of the present invention. The spot welding robot 1 is configured by equipping a wrist 7 of the robot 2 with a 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 displaced in the longitudinal direction 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 vertically displaceable about a horizontal third axis J3. A wrist 7 attached to the tip of the upper arm 6 is attached so as to be angularly displaceable around a fourth axis J4 parallel to the axis of the upper arm 6,
It is attached so as to be angularly displaceable about a fifth axis J5 perpendicular to the axis of the upper arm 6. The spot welding gun 8 attached to the wrist 7 is provided so as to be angularly displaceable about 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 fixed to an end of the gun arm 12. Is done. A moving electrode 13 is provided on the gun arm 12 so as to face the fixed electrode 14 and to be movable in a direction of approaching / separating from the fixed electrode 14. Electrode 1
Reference numerals 3 and 14 are rod-shaped and arranged coaxially with each other. The moving electrode 13 is driven by a welding servomotor Mw provided on the welding gun 8. Also, the joint axes J1 to J6 of the 6-axis articulated robot 2 are also servomotors M1 to M6, respectively.
Driven by M6.

Next, a control configuration of the welding robot 1 will be described. FIG. 2 is a block diagram showing a control configuration of the welding servomotor Mw. Note that other servo motors M1
The configuration of the servo motor Mw is also the same as that of the servo motor Mw, so that the illustration is omitted.

The electrode movement path calculator 22 stores teaching data and a hitting angle correction program described later. The teaching data includes a work operation program for sequentially spot-welding the respective welding points of the workpiece W, which is the workpiece, and the position of the welding gun 8 at the time of welding the respective welding points. The spot position of the welding gun 8 is represented by the coordinate position of the welding point,
And the hitting angle at the time of welding (the moving direction of the moving electrode 13) is given in the absolute coordinate system. The hitting angle is given so as to coincide with the direction perpendicular to the workpiece W.

The moving position command value P from the position controller 20 to the moving electrode 13 is calculated by the electrode moving path calculating unit 22.
When w is given to the servo controller 21, the servo controller 21 outputs a current I according to the movement command value Pw.
w is given to the welding servomotor Mw. by this,
The moving electrode 13 moves forward to the commanded position. For example, at the time of spot welding, the work W is held and pressed by the electrodes 13 and 14.

The position controller 20 changes the attitude of the robot 2 by giving the angle command values P1 to P6 of the axes J1 to J6 to the servo controller 21 to position the welding gun 8 at the designated hitting position. Servo controller 21
Is such that the axes J1 to J6 are at the commanded angles,
Current values I1 to I6 corresponding to the angle command values P1 to P6 are given to the servo motors M1 to M6.

An encoder Ew is attached to the servomotor Mw, and the amount of movement of the movable electrode 13 by the servomotor Mw is detected by the encoder Ew. The detected encoder value is returned to the servo controller 21. The servo controller 21 feedback-controls the servo motor Mw based on the moving position command value Pw from the position controller 20 and the encoder value from the encoder Ew so that the moving electrode 13 moves to the specified moving position. Such a configuration is the same for the servo motors M1 to M6.

Since the servomotors Mw and M1 to M6 are feedback-controlled, the welding robot 1 is moved to a designated position, for example, when the moving electrode 13 is moved forward or the posture of the robot 2 is changed. When the electrode 13 or 14 comes into contact with the work W, the current supplied to each of the servomotors M1 to M6 and Mw is increased or decreased so as to move to a designated position against the work W. That is, since the work W is elastically deformed, the elastic restoring force of the elastically deformed work W acts on the robot 1 as a reaction force. Therefore, the reaction force to the robot 1 can be obtained based on the current values of the servo motors Mw and M1 to M6 when moving the work W against the elastically deformed work W. In the present embodiment, the current values of the servo motors Mw, M1 to M6 are monitored by the monitoring unit 23. For example, the current value when the electrode 13 or 14 reaches the designated position is sent to the electrode moving path calculation unit 22. The input and the reaction force acting on the robot 1 is detected by the electrode movement path calculation unit 22 based on the input.

When spot welding is performed by the welding robot 1, first, the moving gun 13 is separated from the fixed electrode 14, the welding gun 8 is opened, and the welding gun 8 is moved to the hitting position based on the teaching data. Next, the movable electrode 13 is moved to the fixed electrode 14 side to close the welding gun 8, the welding points of the work W are sandwiched between the two electrodes 13 and 14, a predetermined pressing force is applied, and a welding current is applied to perform spot welding. I do.

At this time, it is desirable that the striking angle of the electrode coincides with the direction perpendicular to the surface of the workpiece W. However, the teaching of the welding hit point can be performed relatively accurately, but it is difficult to teach the hitting angle so that the hitting angle is accurately straight. Therefore, in the present invention, the welding hit point is accurately taught in advance, the hitting angle is roughly taught, teaching data is prepared, and the hitting angle is corrected in accordance with the hitting angle correction program stored in the electrode movement path calculating unit 22. The hitting angle of the teaching data is corrected so that the angle is exactly straight. In addition, even if the teaching data is accurate, if the workpiece W is displaced during the welding operation and the hitting angle is not straight, the hitting angle correction program also performs the face-to-face direction with respect to the placed workpiece W during the welding operation. Is detected, and the hitting angle is corrected.

Next, a method of correcting the hitting angle by the electrode moving path calculation unit 22 will be described with reference to the flowchart shown in FIG.

First, in step a1, the welding gun 8 is arranged at a position corresponding to the welding point Pc of the workpiece W. The state at this time is, as shown in FIG.
The tip of No. 4 is in contact with the workpiece W and is in a state of zero touch.

Next, in step a2, as shown in FIG. 5, the welding gun 8 is moved along the axial direction of the electrode toward the fixed electrode 14 by a predetermined distance L1. At this time,
The movable electrode 13 and the workpiece W do not come into contact with each other, and are moved to a position where there is a margin.

Next, in step a3, an electrode moving path is calculated. First, a cone 30 as shown in FIG. 6 is set as the electrode moving path. The cone 30 has a center angle B at the electrode hitting angle at the time of welding at the welding point Pc stored as teaching data, a plane perpendicular to the center axis B passing through the welding point Pc as a bottom surface 32, and fixed to the bottom surface 32. On the electrode 14 side,
The point having the height L1 is defined as the vertex 31 and has an outer peripheral surface that forms an angle α with the axis B. Then, on the extension of the outer peripheral surface of the cone 30, a plurality of, in this embodiment, eight, electrode moving paths C1 to C8 are set toward the vertex 31. A plurality of electrode movement paths C1 to C8 are set at equal angles β on the circumference of the bottom surface 32 of the cone 30. In the present embodiment, eight designated points P1 to P8 are set as β = 45 °, and these designated points are set. P1 to P8
And eight straight lines passing through the vertex 31.

In the next step a4, as shown in FIG.
The moving electrode 13 is moved along the electrode moving paths C1 to C8 to the designated points P1 to P8 on the bottom surface 32, and the current value at each point is detected. That is, first, the posture of the welding gun 8 is changed by the robot 2, and as shown in FIG.
The moving electrode 13 is moved over the electrode moving path C1 above the designated point P1.
Place on top. Next, as shown in FIG. 7, the moving electrode 13 is advanced to the designated point P1 by the servo motor Mw. At this time, the current value of the servo Mw is monitored by the monitoring means 2.
3 and when it reaches the designated point P1,
The current value of the servo motor Mw corresponding to the reaction force when the moving electrode 13 contacts the work W and the work W is elastically deformed is input to the electrode movement path calculation unit 22.

After the moving electrode 13 reaches the designated point P1, the servo motor Mw is rotated in the reverse direction to move the moving electrode 13 backward as shown in FIG. Then, the posture of the welding gun 8 is changed again, and the moving electrode 13 is arranged on the electrode moving path C2 above the designated point P2 as shown in FIG. Then, as described above, the electrode 13 is moved to the designated point P2 (FIG. 7), the current value at this time is detected, and the electrode 13 is retracted (FIG. 7). Thus, each designated point P1 to P8
The current value as the reaction force in the above is detected and input to the electrode movement path calculation unit.

If the teaching data is almost accurate and the hitting angle at the welding point Pc, that is, the inclination of the electrode 13 at the time of welding the welding point Pc matches the direction perpendicular to the plane, the bottom surface 32 of the cone 30
Substantially coincides with the surface of the workpiece W. Therefore, the moving electrode 1 is moved to each of the designated points P1 to P8 on the bottom surface 32 of the cone 30.
When the workpiece 3 is moved, the relative stop position of the movable electrode 13 with respect to the surface of the workpiece W and the degree of deformation of the workpiece W are substantially the same. Therefore, the current value as the reaction force at each of the designated points P1 to P8 is relatively constant at a relatively low value as shown in FIG.

On the other hand, the hitting angle of the teaching data, that is, the center axis B of the cone 30 is perpendicular to the workpiece W in the plane direction C.
On the other hand, as shown in FIG. 9A, in the case of inclination, the designated point P1 side is below the work W (the fixed electrode 14).
Side), and the designated point P5 side is above the work W (the moving electrode 13 side). Therefore, when the electrode 13 is moved to each of the designated points P1 to P8, the elastic deformation of the work W is maximized at the designated point P1, and the current value of the servo motor Mw is maximized. In some cases, the current does not reach the work W, and the current value becomes minimum. Therefore, the current value as the reaction force at each of the designated points P1 to P8 at this time is the highest at the designated point P1, and the designated point P5 side (P4, P5, P6) as shown in FIG. Appear stepwise so that is lowest.

Accordingly, if the difference between the maximum and the minimum of the current value at each of the designated points P1 to P8, and in the example shown in FIG. 9, the difference between the current values at the designated point P1 and the designated point P5 is large, the teaching data It can be determined that the hitting angle is displaced from the in-plane direction C. In this case, it is necessary to correct the teaching data. Conversely, when the difference between the maximum and the minimum of the current values of the designated points P1 to P8 is small, the hitting angle of the teaching data is
Can be determined to substantially match, so there is no need to correct the teaching data.

Therefore, in the next step a5,
The difference between the maximum value and the minimum value of the current value of each of the designated points P1 to P8 is calculated. If the difference is smaller than a predetermined value D, the program for correcting the welding point Pc is terminated without correcting the teaching data, If the difference is equal to or larger than the predetermined value D, the process proceeds to step a6.

When the difference between the maximum value and the minimum value of the current value is large, as shown in FIG. 9A, the hitting angle is inclined toward the side where the current value increases. Therefore, in step a6, the hitting angle is shifted by a predetermined angle θ around the welding hit point Pc to the side where the current value becomes the smallest, and the teaching data is rewritten. At this time, when the electrode 13 does not reach the work W at a plurality of locations and there are a plurality of points where the current value becomes the smallest as shown in FIG. 9B, the point where the current value is the largest (see FIG. 9). In the example shown, the point opposite to the designated point P1 (designated point P5 in the example shown in FIG. 9) is the point having the smallest current value. Further, the angular displacement axis when the hitting angle is shifted by the angular displacement passes through the welding hit point Pc and the designated point (P1) having the maximum current value and the designated point (P1) having the minimum current value.
5) A straight line perpendicular to the straight line connecting (P3 and P7)
Becomes

Then, the process returns to step a3 again.
The electrode movement path is calculated again based on the rewritten hitting angle, the current values at the designated points P1 to P8 are detected in step a4, and the difference between the maximum current value and the minimum current value is determined again in step a5. It is determined whether it is smaller than D or not.

Thus, the difference between the current values is equal to the predetermined value D.
Steps a3 to a6 are repeated until the distance becomes smaller. This makes it possible to correct the hitting angle of the teaching data so as to match the direction perpendicular to the surface of the workpiece W.

The correction of the hitting angle is not limited to the correction of the teaching data, but is also applicable to the correction of the hitting angle when the workpiece W is displaced during the welding operation.

In the above-described embodiment, the moving electrode 13 is moved by the servo motor Mw along the calculated electrode moving path, and the direction perpendicular to the plane is detected by the current value as the reaction force. Not only the case where the movable electrode 13 is moved as described above, the fixed electrode 14 may be moved. In this case, as the electrode moving path, a cone having a vertex on the moving electrode 13 side is set, and a plurality of electrode moving paths are set at equal intervals toward the vertex on the extension of the outer peripheral surface of the cone as described above. A plurality of designated points are set on the bottom surface of the cone in the same manner as described above. The welding gun 8 is moved by the robot 2 so that the fixed electrode 14 moves to each designated point along each electrode moving path set by using the welding gun 8 with the electrodes opened at predetermined intervals, and Detect the reaction force at a point.

The magnitude of the reaction force in this case depends on the servo motors M1 to M5 driving the axes J1 to J6 of the articulated robot 2.
It is calculated from the current value of M6. As described above, these servo motors M1 to M6 are also subjected to feedback control, and the current value changes according to the reaction force from the elastically deformed work W. Therefore, the fixed electrode 14 elastically deforms the work, and the robot 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 by evaluating the amount of change in the current value of the servo motors M1 to M6 at each point.
6 may be weighted and evaluated. Further, for example, the reaction force may be calculated by preferentially selecting the servomotors M4 to M6 of the wrist axes J4 to J6 having a smaller frictional force of the speed reducer than the basic axis.

In the same manner as described above, the hitting angle is corrected by repeating the angular displacement shift of the hitting angle until the difference between the calculated maximum value and the minimum value of the reaction force at each point becomes smaller than a predetermined value. .

The electrode moving path is not limited to the path along the conical surface, and the electrode may be moved so that the electrodes come into contact with a plurality of points near the welding point Pc.

[0047]

As described above, according to the present invention, a plurality of designated points are set in the vicinity of the welding point of the work to be welded, the electrodes are moved to each designated point, and one electrode is brought into contact at a plurality of locations. Since the direction perpendicular to the plane is detected based on the magnitude of the reaction force at each contact point, the direction perpendicular to the plane can be easily and accurately detected regardless of the shape of the tip of the electrode.

Since the direction of the straightness can be detected in this manner, it is not necessary for the operator to visually judge the straightness, and the detection of the straightness at a position where visual confirmation is difficult can be accurately detected. As a result, it is possible to minimize deterioration in welding quality and adverse effects on equipment in spot welding.

Further, since the reaction force is calculated based on the change in the current value of the servomotor, it is not necessary to provide a special detector or the like, and it is possible to perform the direct detection at low cost.

[Brief description of the drawings]

FIG. 1 is a perspective view of a spot welding robot 1 according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a control configuration of the spot welding robot 1.

FIG. 3 is a flowchart illustrating a surface straightness detection method.

FIG. 4 is a view showing a state where a welding gun 8 is arranged at a hitting position.

FIG. 5 is a view showing a state in which the welding gun 8 is moved by a predetermined distance L1 from the hitting position.

FIG. 6 is a diagram illustrating an electrode moving path.

FIG. 7 is a perspective view showing a moving path of a moving electrode 13;

FIG. 8 is a graph showing current values at designated points P1 to P8 when the hit angle is straight.

FIG. 9A is a diagram showing a state in which the hitting angle is deviated from the direction perpendicular to the surface, and FIG. 9B is a graph showing current values at designated points P1 to P8 at that time. It is.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Spot welding robot 2 Articulated robot 20 Position controller 21 Servo controller 22 Electrode movement path calculation part 30 Cone 31 Vertex 32 Bottom surface Mw, M1-M6 Servo motor P1-P8 Designated point Pc welding spot

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B23K 11/11 B23K 11/24

Claims (4)

(57) [Claims] 1. A spot welding robot in which a welding gun having a pair of electrodes that can be opened and closed is mounted on a wrist of a robot, and spot welding is performed by sandwiching a predetermined welding point of an object to be welded between both electrodes. One electrode is moved to a plurality of designated points near the welding point of the object, the magnitude of the reaction force when the electrode contacts the workpiece is detected, and the position of the designated point and the reaction force at the designated point are detected. A spot welding robot for detecting a direction perpendicular to a workpiece based on a size. 2. The welding gun has a fixed electrode and a moving electrode that is moved by a servomotor. The servomotor is used to move the moving electrode to a designated point, and the servo is controlled when the moving electrode comes into contact with the workpiece. The spot welding robot according to claim 1, wherein the reaction force is obtained based on a current value of the motor. 3. The welding gun has a fixed electrode and a moving electrode that is moved by a servomotor, and moves the robot to move the fixed electrode to a designated point. 2. The spot welding robot according to claim 1, wherein a direction perpendicular to the surface is detected based on the force. 4. A plurality of designated points are set on a circle centered on the welding point on a plane passing through the welding point stored in advance and perpendicular to the inclination of the electrode during welding. The spot welding robot according to any one of claims 1 to 3.