JPH06155036A - Device for positioning welding gun of welding robot - Google Patents

Abstract

PURPOSE:To perform spot welding for the desired welding position with high accuracy by moving a robot shaft interlocking with generation of the pressurizing force for works by the welding gun. CONSTITUTION:The pressurizing force is applied to the works by both welding tips 21 and 22 by driving a servomotor 23 from the zero touch position of both welding tips 21 and 22. In this case, the correction data where the deformation quantity of a gun arm 15 caused by the pressurizing force and the contraction quantity of the respective welding tips 21 and 22 are stored in a storage medium in advance are read out, the pressurizing force of the eservomotor 23 and the displacement quantity of the gun arm 15 are added and the robot shaft and the servomotor 23 are driven. Consequently, the welding tips 21 and 22 can weld the works without displacing for the works and the welding quality can be improved without working unnecessary external force.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding gun positioning device for a welding robot, which is mounted on a welding robot and positions a welding gun for spot welding for performing a welding operation at a predetermined position on a work.

[0002]

2. Description of the Related Art In a welding robot for spot welding used to weld a work such as a panel material, in recent years, a welding motor is operated by a servomotor in order to quickly operate the welding gun. This type of welding gun is used.

[0003]

In the welding robot having the servo gun operated by the servo motor as described above, there is an advantage that the moving distance of the welding tip can be accurately controlled by the servo motor, while the conventional robot has the advantage. In this welding robot, the gun driving servomotor and the welding robot are not linked, and the positioning accuracy of the welding tip becomes low. Also, if the welding robot is not displaced when the welding gun is driven, the welding tip will be displaced with respect to the work piece, and unnecessary external force will be applied to the welding tip and the work piece, making it impossible to perform highly accurate welding. Not only that, but there was a problem that the life of the chip would be shortened.

The present invention has been made in view of the above problems of the prior art, and is intended to enable a welding tip mounted on a robot shaft of a welding robot to be accurately positioned at a predetermined position of a work. To aim.

[0005]

According to the present invention for achieving the above object, a fixed welding tip and a movable welding tip for welding a work by the fixed welding tip are provided on a robot shaft of a welding robot. A gun arm, and a servomotor attached to the gun arm to move the movable welding tip forward toward the fixed welding tip,
A current value detecting means for detecting a current value of the servo motor, a displacement amount storing means for storing a displacement amount of the robot shaft due to the deformation of the gun arm when the workpiece is pressed by the welding tips, and Drive amount storage means for storing the drive amount of the movable welding tip when the workpiece is pressed by the welding tip, and the fixed welding tip and the movable portion when positioning the gun arm of the welding robot at the position of the workpiece. A zero-touch position where the welding tip comes into contact with the workpiece, a calculation means for calculating a target position of each of the welding tips by adding a correction value called from the displacement amount storage means and the drive amount storage means, and When the servomotor is driven to pressurize the work with both chips, whether the pressurizing force reaches a predetermined pressurizing force or not Which is a positioning device of the welding gun of the welding robot and a pressure determining means for determining based on a detection signal from the current value detecting means.

[0006]

In the present invention having the above-described structure, when spot welding a work by a welding gun, first, the gun arm is moved by the welding robot so that each of the welding tips comes into contact with the work, that is, the zero touch position. . Then, the servo motor is driven and the movable welding tip moves forward toward the fixed welding tip,
Considering that the gun arm is deformed due to the pressure applied to the work by the welding tip at this time, and the welding tip is also elastically contracted and deformed, first, the displacement of the robot arm caused by the deformation of the gun arm is stored in the displacement amount storage means. The amount is read from the displacement amount storage means, and the driving amount of the movable welding tip by the servo motor is read. The robot axis is driven in accordance with the read correction values, and the servo motor is driven. As a result, the contact attitude of both welding tips with respect to the workpiece does not change,
The welding position is set as the stationary position.

Whether or not both welding tips have a predetermined pressing force depends on whether or not the current value from the current value detecting means for detecting the current value of the servo motor has reached a predetermined current value. It is automatically discriminated by discriminating by.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on an embodiment of the present invention shown in the drawings. FIG. 1 is a view showing an example of a welding robot R having a servo gun. A pedestal 10 attached to a base portion (not shown) is provided with a swivel base 11 which is swivelable in the direction of arrow J1. A robot shaft 12 is mounted on 11 so as to be swingable in the direction of arrow J2. Then, the robot axis 12 is attached to the robot axis 1.
3 is mounted so as to be swingable in the direction indicated by arrow J3 and rotatable in the direction indicated by arrow J4. A servo gun, that is, a welding gun 14 is attached to the tip of the robot shaft 13 so as to be swingably rotatable in a direction indicated by an arrow J5 and rotatable in an arrow J6 direction. Therefore, the illustrated robot R has a total of 6 axes.

The welding gun 14 has a C-shaped gun arm 15. The gun arm 15 has a fixed welding tip 21 and a movable welding tip 22 for welding a work (not shown) by the fixed welding tip 21. And are provided. A servo motor 23 for moving the movable welding tip 22 forward and backward toward the fixed welding tip 21 is attached to the gun arm 15. This servo motor 23
The total of 7 axes including the operations described above are controlled by the robot controller 24 shown in FIG.

FIG. 2 is a diagram showing the details of the gun arm 15 shown in FIG. 1. The drive rod 25 having the movable welding tip 22 mounted on the tip thereof slides axially on a bearing 26 mounted on the gun arm 15. It is movably supported. A pulley 27 provided on a main shaft of a servo motor 23 attached to the gun arm 15 and a nut portion 28 fitted to a ball screw portion formed outside the drive rod 25 are connected by a timing belt 29. Therefore, when the servomotor 23 is driven, the nut portion 28 rotates via the belt 29, and the portion of the ball screw that meshes with the nut portion 28 causes the drive rod 25 to slide in the axial direction.

FIG. 3 shows welding tips 21 and 22 for welding a work W using the welding robot R shown in FIG.
3A and 3B, the welding robot R first conveys the gun arm 15 to the work W to a predetermined position as shown in FIG. 3A. In this state, the robot axes 12 and 13 are driven by the welding robot R, and as shown in FIG. 3B, the fixed welding tip 21 comes into contact with the surface of the work W and the movable welding tip 22 moves to the servo motor 23. Driven to contact the opposite surface of the work W. This state is a zero-touch state, that is, each of the chips 21 and 22 has only contacted the surface of the work W, and the pressing force is not applied to the work W. The positions of the tips of the chips 21, 22 in this state, that is, the zero-touch positions, are P1, P2, and the posture of the gun arm 15 is as shown by the solid line in FIG. In this state, the servo motor 23
When is driven, a pressing force is applied to the work W by both the chips 21 and 22, as shown in FIG.

When the work W is pressed by the two chips 21 and 22 in this manner, the gun arm 15 itself is elastic as shown by the two-dot chain line in an exaggerated manner in order to clearly show the deformed state in FIG. In addition to being deformed, both chips 21 and 22 themselves are elastically deformed in the axial contracting direction. Therefore, if the movable welding tip 22 is moved forward by the servo motor 23 in the zero-touch state as shown in FIG. 3B, the gun arm 15 may apply an unnecessary external force to the workpiece W in the vertical direction. Both chips 21 and 22 are work W
Since the pressure is applied in a state of being displaced, the pressure points of the chips 21 and 22 with respect to the work W move, which makes it impossible to perform highly accurate welding work.

Therefore, considering that the gun arm 15 is elastically deformed as shown by the chain double-dashed line in FIG.
From the zero touch position P2 in the case where no pressure is applied to the virtual pressure end position P4, the work W is apparently positioned at the same position as before the pressure is applied at the end of pressurization.
The robot axis is moved so as to move the distance XR shown in (C). Further, when no pressure is applied to both tips 21 and 22, the tip of the movable welding tip 22 becomes XG.
The servomotor 23 is driven so as to reach the virtual pressurization end position P3. As a result, both chips 21,
If the work W does not exist between the two chips, the respective chips 21, 22 will be at the positions indicated by the chain double-dashed line in FIG. 3C. 21 and 22 elastically contract and deform and the gun arm 15 elastically deforms, so that the relative positions of the tips 21 and 22 with respect to the work W do not change,
Both tips 21 and 22 are in close contact with both surfaces of the work W, as shown in FIG. 3C, without applying an unnecessary external force to the work W.

As described above, according to the present invention, the pressing point of both chips 21 and 22 is applied to the work W when the pressing force is applied to the work W by both the chips 21 and 22. It does not shift with respect to it, so to speak, the pressure point is kept stationary. Therefore, in the present invention, the contact point of the fixed welding tip 21 with the work W accompanying the elastic deformation of the gun arm 15 including the contraction deformation due to the elastic deformation of the fixed welding tip 21 itself at the time of pressurization. By correcting the displacement of the robot axis, so to speak, welding is performed in a stationary state. This correction data is obtained in advance as described later and the displacement amount is stored in the storage means. Further, for the elastic contraction deformation amount after the pressurization of the movable welding tip 22 itself, the correction value of the driving force by the servo motor 23 required from the zero touch position to the end of the pressurization is obtained in advance.

Next, how to obtain the correction data when the gun arm 15 is pressurized will be described.
The relationship between the amount of deformation and the pressure applied by the servo motor 23 is
There is a predetermined relationship as shown in FIG. 5, and the displacement amount δa of the gun arm 15 when the pressing force on the work W is set to a desired pressing force Fa can be obtained. This is obtained in advance according to the material, thickness, etc. of the workpiece W to be welded, and is stored as the displacement amount XR in the displacement amount storage means in the control device. Similarly, the drive amount correction value for driving the servo motor 23 from the zero touch position until the pressing force Fa is applied is stored in the drive amount storage means as the drive amount supplement XG.

Whether or not the movable welding tip 22 has reached a predetermined pressure amount is detected by detecting the current value of the servo motor 23. The tips of the welding tips 21 and 22 will wear as the work W is repeatedly welded. As described above, after the welding tips 21 and 22 are positioned with high precision on the work W by zero touch, the welding tips 21 and 22 should not be displaced with respect to the work W, that is, the welding tip 21 should be on the work W. , 22
In order to set the pressure to be relatively stationary and to apply pressure, it is necessary to position the tip portions of the welding tips 21 and 22 with high accuracy. Therefore, in order to always grasp the positions of the tips of the welding tips 21 and 22, the wear amount of the tips of the welding tips 21 and 22 is periodically measured, and the wear amount data is stored in the storage means in the control device. I have to.

FIG. 6 is a view showing an apparatus for measuring the amount of wear of the welding tips 21 and 22, in which the fixed post 29 is provided with two limit switches LS1 and LS2, one above and one below the limit switch.
As shown in FIG. 6, by moving the gun arm 15 by operating the robot with the movable welding tip 22 retracted, first, the movable welding tip 22 is moved toward the upper limit switch LS1. Thereby, the wear amount of the movable welding tip 22 is detected from the movement amount of the gun arm 15 when the limit switch LS1 is turned on. Similarly, the amount of wear of the fixed welding tip 21 is detected by bringing the fixed welding tip 21 into contact with the lower limit switch LS2. By correcting the wear amount data of the welding tips 21 and 22 detected in this way, the welding tips 21 and 22 are positioned with respect to the workpiece W with high accuracy.

FIG. 7 is a block diagram showing the control circuit of the positioning device for the welding gun of the welding robot according to the present invention.
2 limit switch LS1 for detecting the amount of wear,
When LS2 is connected and the wear amount is measured,
As shown in FIG. 2, by contacting the tips of the welding tips 21 and 22 with the limit switches LS1 and LS2, the CPU 30 wears the limit switches LS1 and LS2 based on the moving amount of the gun arm 15 and the driving amount of the servo motor 23 when they are turned on. The amount is calculated, and each amount of wear is stored in the amount-of-wear storage medium 31a. Further, as described above, the displacement amount storage medium 31b for storing the displacement amount XR of the robot axis due to the deformation of the gun arm 15 when the workpiece W is pressed by the welding tips 21 and 22 is connected to the CPU 30, and A drive amount storage medium 31c for driving the movable welding tip 22 until the pressurization of the work W is completed by the tips 21 and 22 is connected to the UPU 30. These storage media are composed of non-volatile memories and external storage media. Each of the storage media 31b and 31c has
As described above, various correction data are stored according to the thickness of the work, etc. When the welding start is instructed, if the type of the work is input using the keys of the operation panel 33, the predetermined correction is performed. The data will be specified. Also,
The ROM 32 is a memory that stores control data for controlling the operation of basic movements of the robot.

An input command signal from the operation panel 33 is sent to the CPU 30. By inputting a key provided on the operation panel 33, the start of the robot or the start of the teaching operation is instructed. To be done.
Further, a detector 34 for detecting the current value of the servo motor is connected to the CPU 30, and it is determined whether or not the pressure applied to the work W by the movable welding tip 22 described above has reached a predetermined pressure. It is detected by. A control signal is sent from the CPU 30 to various robot axis drive motors 35 incorporated in the robot, and a control signal is also sent to a servo motor 23 for operating the movable welding tip 22. Will be sent.

Next, the operation procedure of the welding gun positioning apparatus of the present invention will be described with reference to the flow charts shown in FIGS. First, when the welding start switch provided on the operation panel 33 is turned on in step S1 while power is supplied to the welding robot, both welding tips 2 previously stored in the wear amount storage medium 31a are stored.
The correction values of the wear amounts of 1 and 22 are read in step S2. Based on each correction value, both welding tips 21,
The zero-touch positions P1 and P2 of 22 are calculated by the CPU 30 in step S3. According to this calculation result, the movable welding tip 21 is moved to the zero touch position,
PU is set as the moving distance data of the movable welding tip 21, and PL is set as the moving distance data of the robot axis for driving the fixed welding tip 21 so that the fixed welding tip 22 moves to the zero touch position. It will be set (step S4).

When the robot axis and the servo motor 23 are driven in step S5 based on the respective movement distance data, as shown in FIG.
1 and 22 move to the zero touch position. Next, if it is determined in step S6 that the touch panel has moved to the zero touch position, in step S7, the correction value X for generating the pressing force stored in the drive amount storage medium 31c is stored.
By reading G and adding it to the value of P1 in step S8, the target position P3 of the movable welding tip 22 is obtained, and this target position P3 is commanded as the position PU of the movable welding tip 22 in step S9. Similarly,
In step S10, the value of the gun arm deformation amount correction value XR stored in the displacement amount storage medium 31b is read out and added to the value of P2 in step S11 to obtain the target position P4 of the fixed welding tip 21. Then, the target position P4 is set to the position P of the fixed welding tip 21
Instructed as L in step S12. In this way, CP
The target positions of both welding tips are calculated by U30.

When the processes of steps S9 and S12 are completed, step S13 is executed to drive the robot axis and the servo motor 23. Next, in step S14, the detection of the current value of the gun axis motor, that is, the servo motor 23 is started, and the movement distance of the robot axis is counted in step S15 in order to detect whether or not the robot axis has moved a predetermined distance. Then, in step S16, it is determined whether or not the positioning is completed by detecting in step S17 whether or not the current value of the servo motor 23 has reached a predetermined current value and whether or not the robot axis has moved a predetermined moving distance. Is judged. If YES is determined in steps S16 and S17, a positioning completion signal is output in step S18.

In this way, both welding tips 21, 22
When the servomotor 23 is driven from the zero-touch position to apply a pressing force to the work W by both welding tips 21 and 22, the deformation amount of the gun arm 15 and the contraction amount of each welding tip 21 and 22 due to the pressing force. Since the correction data stored in the storage media 31b and 31c in advance is read and the pressing force of the servo motor 23 and the displacement amount of the gun arm 15 are added to drive the robot axis and the servo motor, the welding tip 21, No. 22 is not displaced with respect to the work W, so to speak, the work W can be welded at the stationary position. As a result, the welding tips 21 and 22 do not exert an unnecessary external force on the work W, and the welding quality is significantly improved.

Since the welding tips 21 and 22 are worn out as the welding work is performed, the work of periodically measuring the amount of wear is performed after the welding work is completed a predetermined number of times. The procedure of measuring the amount of wear will be described based on the flowchart shown in FIG. If execution of the wear amount measurement operation is instructed by the measurement start switch in step S20, the welding robot R is driven in step S21 to position the gun arm 15 to the measurement position of the fixed block 29 shown in FIG. To be done. When the gun arm 15 is conveyed to the predetermined measurement position, the gun arm 15 is moved at a low speed in step S22. For example, if the wear amount of the movable welding tip 22 is to be measured, the gun arm 15 is moved upward. By this, step S
If it is detected in 23 that the limit switch LS2 is turned on, the movement of the gun arm 15 is stopped in step S24, the position data of the robot axis at that time is taken in in step S25, and the new welding tip 21 The difference in positioning, that is, the wear amount is calculated in step S26, and the wear amount data is calculated in step S27.
Store in a.

If NO in step S28, the gun arm 15 is returned to the measurement position again to measure the amount of wear of the fixed welding tip 21, and the same operation is performed. To measure the amount of wear of the fixed welding tip 21, the gun arm 15 is moved downward. In this way, the wear amount of both welding tips 21 and 22 is measured, and the correction data is stored in the wear amount storage medium 31a.

As a method for measuring the amount of wear, in addition to the method shown in FIG. 6, both welding tips are clamped on both sides of the fixing member, and the tip of the tip is determined from the change in the current value of the servo motor at that time. Alternatively, the wear amount may be measured.

[0027]

As described above, according to the present invention, the robot axis is moved in association with the generation of the pressing force on the workpiece by the welding gun, so that the spot can be spotted at a desired welding position with high accuracy. In addition to being able to perform welding, it was possible to position the welding tip at a predetermined position on the work at high speed, thereby improving productivity and reducing cost. Further, unnecessary external force does not act on the work such as the panel material, the life of the tip can be maintained for a long time, and the welding quality is improved.

[Brief description of drawings]

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

2 is a front view showing details of the gun arm shown in FIG. 1,

FIG. 3 is an enlarged front view of essential parts showing an operating state of the welding gun positioning device of the present invention;

FIG. 4 is a front view showing a deformed state of the gun arm,

FIG. 5 is a graph showing the relationship between the force applied to the work by the servo motor and the deformation of the gun arm,

FIG. 6 is a front view showing a wear amount detecting device for a welding tip,

FIG. 7 is a block diagram showing a control circuit in a welding gun positioning device of the welding robot of the present invention;

FIG. 8 is a flowchart showing an operating state of the positioning device of the present invention,

FIG. 9 is a flowchart showing an operating state of the positioning device of the present invention,

FIG. 10 is a flowchart showing an operating state of the welding robot when measuring the wear amount of the welding tip.

[Explanation of symbols]

10 ... 10 ... Pedestal, 11 ... Revolving base, 12 ... Robot axis,
13 ... Robot axis, 14 ... Welding gun, 15 ... Gun arm, 21 ... Fixed welding tip, 22 ... Movable welding tip, 2
3 ... Servo motor, 30 ... CPU (arithmetic means, pressing force determining means), 31a ... Wear amount storage medium, 31b ... Displacement amount storage medium, 31c ... Drive amount storage medium, 33 ... Operation panel,
35 ... Robot axis drive motor, R ... Robot, W ... Work.

Claims (1)

[Claims] 1. Attached to a robot axis of a welding robot,
A gun arm provided with a fixed welding tip and a movable welding tip for welding a work by the fixed welding tip, a servomotor attached to the gun arm, and moving the movable welding tip forward toward the fixed welding tip, A current value detecting means for detecting a current value of the servo motor; a displacement amount storing means for storing a displacement amount of the robot shaft due to the deformation of the gun arm when the workpiece is pressed by the welding tips; Drive amount storage means for storing the movable welding tip drive amount when the work is pressed by the welding tip, and the fixed welding tip and the movable portion when positioning the gun arm of the welding robot at the position of the work. At the zero touch position where the welding tip contacts the work,
Calculation means for calculating the target position of each of the welding tips by adding the correction values called from the displacement amount storage means and the drive amount storage means, and driving the servomotor to move the workpiece by the both tips. A welding gun positioning device for a welding robot, comprising: a pressurizing force determining means for determining whether or not the pressurizing force has reached a predetermined pressurizing force based on a detection signal from the current value detecting means when pressurizing.