JPH0631462A - Positioning controller for spot welding robot - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a low cost, low weight positioning control device for a robot for spot welding capable of accurate positioning. A storage unit for storing the relationship between the pressure applied to the object to be welded by the electrode tip in the spot welding gun and the deformation amount of the spot welding gun, and based on the relationship stored in the storage unit. The position of the spot welding gun is corrected by the control unit so that no stress is generated in the support.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention automatically corrects the supporting position of a spot welding gun to an optimum position according to the amount of deformation of the spot welding gun caused by the pressure applied to the work piece by the electrode tip. The present invention relates to a controller for a spot welding robot.

[0002]

2. Description of the Related Art At present, spot welding performed on a vehicle body is performed by a dedicated spot welding gun attached to a robot. An example of this welding gun is shown in FIG. In this spot welding gun 1, one electrode tip 2 is vertically moved by a servomotor 3 in the directions A and B shown in the drawing. This vertical movement is performed by the ball screw 4 which engages with the servo motor 3. In the spot welding gun 1 using the servo motor 3 as a drive source, the positioning with respect to the spot for spot welding can be accurately performed by using the correction function of the robot. When pressure is applied to an object,
As shown in FIG. 6, the gun arm 5 is elastically deformed in the outward direction in the drawing according to the applied pressure. For this reason, pressing by the servo motor 3 is required at the time of pressurization, and this pressing is absorbed or corrected by the floating mechanism 6 having the structure shown in FIG.

[0003]

However, in the spot welding robot using the floating mechanism 6 as described above, although the position correction can be performed to some extent by using the correction function on the robot side, it is very accurate. It is not suitable for positioning, and the provision of such a mechanism leads to size increase, cost increase, and weight increase.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide a low-cost, low-weight positioning control device for a robot for spot welding capable of accurate positioning. .

[0005]

SUMMARY OF THE INVENTION To achieve the above object, the present invention is configured to position a spot welding gun attached to the tip of an arm based on teaching data and spot weld an object to be welded. In the spot welding robot described above, a storage means for storing the relationship between the pressing force of the electrode tip of the spot welding gun against the object to be welded and the deformation amount of the spot welding gun, and the storage means are stored in the storage means. A correction means for correcting the support position of the spot welding gun based on the relationship.

[0006]

In the present invention thus constructed, the correction means determines the deformation amount of the spot welding gun, the pressure applied to the object to be welded by the electrode tip stored in the storage means and the spot welding gun. Calculation is performed based on the relationship with the deformation amount, and the support position of the spot welding gun is corrected to an optimum position where no stress is generated based on the calculation result.

For this reason, it is no longer necessary to provide a floating mechanism as in the prior art, and highly reliable spot welding can be performed with improved positioning accuracy, and cost and size can be reduced. Become. Further, as the weight is reduced, the operating performance is improved.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a spot welding robot.

As shown in the figure, the operation of the spot welding robot 10 shown in the figure is controlled by a robot controller 11. This spot welding robot is of a 7-axis type, and a spot welding gun 1 is attached to its working end. The first axis turns the entire spot welding robot 10 in the J1 direction, and the second axis moves the working end in the vertical direction, that is, the J2 direction with reference to the first axis. The third axis similarly moves the working end in the vertical direction, that is, the J3 direction, with the second axis as a reference. The fourth axis is for rotating the working end in the J4 direction in the figure with reference to the third axis. The fifth axis is for moving the working end in the J5 direction in the figure based on the fourth axis. The sixth axis is for rotating the working end in the J6 direction in the figure with reference to the fifth axis. The seventh axis moves the electrode tip 2 of the spot welding gun 1 attached to the working end up and down in the J7 direction in the figure. The spot welding gun 1 is not supported by the floating mechanism, but is directly attached to the sixth shaft.

The robot control device 2 comprehensively controls the above-mentioned 7-axis operations based on the data taught in advance to position the electrode tip 2 at a predetermined position with respect to the workpiece. Spot welding is performed at that position.

FIG. 2 is a schematic block diagram of a positioning control device for a spot welding robot according to the present invention. In the robot control device 11, a controller 15 as a correction means for generally controlling the operation of the spot welding robot 10, and based on a signal from the controller 15, the operation of each of the seven axes is performed. Servo control units 20A to 20G for controlling each are provided. The six servo control sections 20A to 20F control the operation of each axis arm of the main body of the spot welding robot 10, and the servo control section 20G is the electrode tip of the spot welding gun 1. It controls the operation of item 2. In the control unit 15,
A storage unit 16 is provided as a storage unit that stores the relationship between the pressure applied to the electrode tip 2 and the deformation amount of the gun arm 5.

FIG. 3 is a detailed block diagram of the servo control section. The servo control unit controls the operation amount of the connected servo motor 3, and the operation amount of the servo motor 3 is fed back by a signal from the encoder 19. The encoder 19 gives position feedback to the control unit 15, and at the same time, gives feedback of a position command and a speed command to the servo control unit itself.

The servo control unit calculates the rotation speed of the servo motor 3 based on the position command output from the control unit 15, and calculates a current command to be supplied to the servo motor 3 based on the speed command. Based on this current command, a predetermined voltage is applied to the servomotor 3 and a predetermined current is supplied. The current controller 21 controls, based on the current limit command output from the control unit 15, a function of controlling the servo motor 3 so as not to be supplied with a current equal to or more than the current limit, and a current which is currently supplied to the servo motor 3. It has a function of notifying the control unit 15. Since this current value is proportional to the pressure applied to the object to be welded by the electrode tip 2, the control unit 15 calculates a correction amount based on the deformation of the gun arm 5 based on this current value.

FIG. 4 is a structural diagram of a spot welding gun 1A controlled by the apparatus of the present invention. This gun 1A
The basic structure of is the same as that shown in FIG.
This gun 1A is different from the conventional one in that it is directly attached to its sixth shaft without the floating mechanism 6.

The apparatus of the present invention is configured as described above, and this apparatus operates as follows based on the flowchart of FIG.

First, the controller 15 of the robot controller 11
Controls the operation of the servo control unit of each axis based on the data taught in advance, and the spot welding gun 1
The electrode tip 2 is positioned at a predetermined pressurizing point of the workpiece, that is, the welding point (S1). When this positioning is completed, the servo motor 3 is driven to narrow the gap between the electrode tips 2 and press the workpiece to a predetermined pressure. Since this pressure is proportional to the value of the current flowing through the servomotor 3, the controller 15 grasps the pressure based on the current monitor feedback signal from the current controller 21 (S2). The correction of the deformation amount of the gun arm 5 that deforms with the applied pressure is performed based on the data stored in the storage unit 16. Specifically, the storage unit 16 stores the pressure applied to the electrode tip 2 and the amount of deformation of the gun arm 5 associated therewith, but the control unit 15 stores the storage unit 1 in the storage unit 1.
The correction amount is calculated with reference to the deformation amount parameter stored in S6 (S3). The control unit 15 corrects the position data of each axis based on the deformation amount parameter and positions the electrode tip 2 at a predetermined calculation position (S4, S5). By the above processing, it is possible to completely eliminate the positional deviation of the electrode tip 2 due to the deformation of the gun arm 5 that occurs when the electrode tip 2 is pressed against the object to be welded.

The above flow chart may be such that each step is processed in real time,
Further, the steps S2 to S4 may be processed off-line in advance.

[0018]

As described above, according to the present invention, the supporting position of the electrode tip is corrected to a position where no stress is generated according to the pressure applied to the electrode tip. Therefore, it is necessary to provide a floating mechanism as in the prior art. As a result, highly reliable spot welding can be performed with the improvement of positioning accuracy, and cost and size can be reduced. Further, as the weight is reduced, the operating performance is improved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a spot welding robot.

FIG. 2 is a schematic block diagram of a positioning control device for a spot welding robot according to the present invention.

FIG. 3 is a detailed configuration diagram of a servo control unit shown in FIG.

FIG. 4 is a structural diagram of a spot welding gun of a spot welding robot according to the present invention.

FIG. 5 is a flow chart of the device of the present invention.

FIG. 6 is a structural diagram of a conventional spot welding gun.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Spot welding gun 2 ... Electrode tip 3 ... Servo motor 4 ... Ball screw 5 ... Gun arm 11 ... Robot controller 15 ... Control unit 16 ... Memory unit 19 ... Encoder 20A-20F ... Servo control unit 21 ... Current controller

Claims (1)

[Claims] 1. A spot welding robot configured to position a spot welding gun attached to the tip of an arm on the basis of teaching data and spot-weld an object to be welded. An electrode in the spot welding gun. A storage unit that stores the relationship between the pressure of the tip on the workpiece and the deformation amount of the spot welding gun, and the support position of the spot welding gun based on the relationship stored in the storage unit. A positioning control device for a spot welding robot, comprising: a correction means for correcting.