JP3136874B2 - Welding gun positioning method for 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 welding gun positioning method for a welding robot, which is mounted on a welding robot and performs a welding operation.

[0002]

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

[0003]

As described above, in a welding robot having a servo gun operated by a servomotor, a fixed welding tip fixed to the welding gun and a movable welding tip movable toward and away from the fixed welding tip are provided. has a tip, anti face, and teaching clogging teaching operation of strike position to a workpiece can be advantageously positioned to the work by the movable welding tip which is driven by a servo motor is carried out with high precision, welding There is a problem that it is not easy to regenerate the welding tip as taught when the work is performed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has been made to be able to easily position a welding tip of a welding gun mounted on a welding robot with respect to a workpiece and to perform a teaching operation and a robot operation. It is an object of the present invention to facilitate reproduction operation.

[0005]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention has a fixed welding tip and a movable welding tip movable forward and backward with respect to the fixed welding tip, and drives the movable welding tip. A positioning method of a welding gun equipped with a servomotor, wherein the fixed welding tip and the movable welding tip are moved via a workpiece in a state where a tip of the fixed welding tip and a tip of the movable welding tip are at a predetermined initial interval. Moving the welding gun to an initial position where the welding tip is opposed, and driving the servomotor to allow the movable welding tip to contact the work so that the current value of the servomotor changes from a low load state to a high load state. Advancing the movable welding tip until it changes, and moving the welding gun by the welding robot to move the fixed welding tip toward the workpiece. Rutotomoni wherein is a movable welding tip welding gun positioning method of welding robot and a step of advancing movement while in contact with the workpiece.

[0006]

In the present invention having the above construction, first, the welding gun, that is, the gun arm is moved to the initial position with respect to the work, and then the servomotor is driven to move the movable welding tip toward the work. When the movable welding tip comes into contact with the work due to this forward movement, the current value of the servo motor changes from a low load state to a high load state. By detecting this with a current value detector, the movable welding tip is automatically changed. Is stopped. Next, the robot shaft is driven to move the gun arm so as to move the fixed welding tip forward toward the surface of the work. At this time, the movable welding tip is driven forward so that the movable welding tip comes into contact with the surface of the work. When both welding tips come into contact with both surfaces of the work, this is detected and positioning is completed. Therefore, the two welding tips are easily positioned with a desired contact pressure with respect to the workpiece.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on one 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, and a pedestal 10 attached to a base (not shown) is provided with a swivel 11 which can swing in the direction of arrow J1. A robot shaft 12 is attached to 11 so as to be swingable in the direction of arrow J2. The robot axis 12 has 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. At the end of the robot shaft 13, a servo gun, that is, a welding gun 14 is attached so as to be swingable and rotatable in the direction indicated by arrow J5 and rotatable in the direction of arrow J6. Therefore, the illustrated robot R has a function of a total of six 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) with the fixed welding tip 21. Are provided. A servo motor 23 for moving the movable welding tip 22 toward and away from the fixed welding tip 21 is attached to the gun arm 15. This servo motor 23
The control of a total of seven axes, including the operation of, is controlled by the robot controller 24 shown in FIG.

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

FIG. 3 is a schematic diagram showing a state in which a welding operation or a teaching operation is being performed on a panel, ie, a work W, using the above-mentioned welding robot R. In FIG. Reference numeral 22 indicates a state where the workpiece W is in contact with the workpiece W, and broken lines indicate a state where the welding tips 21 and 22 are opened.

FIG. 4 is a diagram showing a procedure for positioning the welding tips 21 and 22 at predetermined positions on the workpiece W.
The welding robot R is driven to move the welding gun 14, that is, the gun arm 15, to the initial position as shown in FIG. At this time, as shown, in a state where the fixed welding tip 21 and the movable welding tip 22 are at a predetermined initial interval LT, the tips 21 and 22 face each other via the work W. It is set as follows.

Under this initial position, first, the servomotor 23 is driven at a low speed in order to move the movable welding tip 22 forward toward the workpiece W. This servo motor 23
The current value supplied to is constantly monitored,
As shown in FIG. 4B, when the movable welding tip 22 comes into contact with the surface of the work W, the current value supplied to the servomotor 23 exceeds a predetermined current value. Change to a state. When this is detected, the drive of the servomotor 23 is stopped. As a result, the movable welding tip 22 is moved to the distance L shown in FIG.
This means that only U has moved.

Next, the robot shaft is driven to move the gun arm 15 so that the fixed welding tip 21 comes into contact with the surface of the workpiece W, that is, the surface on the opposite side to which the movable welding tip 22 is in contact. If the movable welding tip 22 is moved as it is, the movable welding tip 22 in contact with the surface of the work W is separated from the workpiece W. Is moved forward at a speed corresponding to the moving speed of the gun arm 15. FIG. 4C shows a state in which the movable welding tip 22 is moved forward in correspondence with the gun arm 15 so that the welding tips 21 and 22 come into contact with the surface of the workpiece W. Therefore, the movable welding tip 2
2 is, finally, the thickness L of the workpiece W from the initial interval LT.
It will move forward by a distance less the dimension of P. The fact that the movable tip 22 has moved forward by the value of the final forward movement, that is, the value of (LT-LP) is detected by counting the moving distance of the movable welding tip 22.

When the welding tips 21 and 22 are released from the work W, the gun arm 15 is moved so that the fixed welding tip 21 is separated from the surface of the work W,
The movable welding tip 22 is moved backward by driving the servomotor 23. FIG. 4D shows a state in which the opening operation has been completed.

In this manner, the positioning of the welding tips 21, 22 with respect to the workpiece W is completed, and a teaching operation of storing the movement trajectories of the welding tips 21, 22 in the memory of the control device of the welding robot R is performed. in case of,
The teaching operation is performed according to the above-described procedure. On the other hand, when performing spot welding on the workpiece W, the welding operation is performed by reproducibly moving the gun arm 15 and the welding tips 21 and 22 as taught.

FIG. 5 shows a main part of a control circuit of the welding robot in which the teaching operation and the reproducing operation are performed as shown in FIG. When performing welding work using the welding robot R, the microprocessor CPU 30 serving as a control unit main body includes an operation panel 31 for inputting a command start signal and the like to the welding robot R, and a teaching operation to the welding robot R. A teaching pendant or teaching box 32 for inputting various signals when performing a teaching operation, and a current value detector 33 for detecting a current value supplied to the servomotor 23 are connected via respective interfaces (not shown). Have been.

From the CPU 30, the robot shaft 12,
Motor 34 for driving the robot axis for driving the 13 and the like
And the servo motor 23 via an interface (not shown).
Various memories such as M36 are connected to the CPU 30.

Next, the operation procedure of the welding gun positioning method for the welding robot of the present invention will be described with reference to the flowcharts shown in FIGS. First, when the operator operates the keys of the teaching box 32 and instructs the start of the teaching operation in step S1, the step of moving the gun arm 15 toward the initial position where spot welding is to be performed on the workpiece W is executed. (Step S
2). In this step, the teaching box 3
The operation is performed by operating the key 2 to drive the welding robot R to move the gun arm 15 to an arbitrary position. In the process of moving to the initial position, the welding tips 21 and 22 are separated from each other by an initial distance LT. The value of the initial interval LT is stored in advance in the memory of the control circuit. As shown in FIG. 4A, at the initial position, the movable welding tip 22 is separated from the workpiece W by a distance LU and the fixed welding tip 21 is separated by a distance LL. , LL can be set arbitrarily.

When the operator turns on the pressurizing command switch of the teaching box with the gun arm 15 moved to the initial position, this is determined in step S3.
Step S4 is executed, and the movable welding tip 22 moves forward at a low speed by the servo motor 23. The operating speed and motor drive current value at this time are stored in a memory in advance, and are read out to drive the servomotor 23 normally at low speed and low current. The low speed is set for the safety of the work, and the low current is set for the purpose of reliably detecting that the movable welding tip 22 has come into contact with the workpiece W. When the servo motor 23 is driven, the current value of the servo motor 23 is monitored by the current value detector 33 in step S5.

The movable welding tip 22 is attached to the workpiece W as shown in FIG.
When the contact is made as shown in FIG.
Changes instantaneously from the low load state to the high load state. This is because the work W is sufficiently positioned and fixed by a fixing member (not shown), and the reaction force is large. When the state changes to the high load state, the current value detected by the current value detector 33 increases, and if it is determined in step S6 that the value exceeds the current value stored in the memory in advance, In S7, the servo motor 23 is stopped.

Next, in step S8, the robot shafts 12, 13 are driven by the motors for driving them.
The gun arm 15 is driven at a low speed to bring the fixed welding tip 21 into contact with the surface of the work W. With this,
Even if the gun arm 15 moves, the movable welding tip 22 moves forward by the same distance at the same speed as the moving speed of the fixed welding tip 21 by the gun arm 15 so that the movable welding tip 22 does not separate from the surface of the workpiece W. (Step S9). For example, the moving distance of the fixed welding tip 21 is XR
If the moving speed is VR, the movable welding tip 22 has the same speed VR and moves in the opposite direction -XR.

If it is determined in step S10 that the movable welding tip 22 has moved by the full stroke, that is, the distance of LT-LP, then in step S11 the servo motor 2
3 and the movement of the robot axis are stopped, and the positioning of the teaching point is completed in step S12.

After the positioning of the teaching position is completed in this way, when the operator inputs a command for the opening operation in step S13, the opening operation in step S14 is executed. In this opening operation, the speed and the moving distance of the fixed welding tip 21 away from the work W are determined by the gun arm 15.
In order to separate the movable welding tip 22 from the workpiece W at the same speed, the movable welding tip 2
It is necessary to move the fixed welding tip 21 in a direction opposite to that of the fixed welding tip 21 at twice the moving speed of 2. As shown in FIG. 4D, the fixed welding tip 21 is separated from the workpiece W by the distance LLa due to the movement of the gun arm 15, and the servo motor 23
When the movable welding tip 22 is separated from the workpiece W by the distance LUa by the drive of the above, the total moving distance of the movable welding tip 22 is LUa + LLa. In the opening operation, as shown in FIG.
It is not necessary to return the interval between the two to the initial interval LT.

In step S15, the two welding tips 21, 2 are driven by the drive of the robot shaft and the servomotor 23.
When it has been detected that the position No. 2 has moved to the predetermined opening limit position, the opening positioning operation is completed. The above-described procedure is a procedure for teaching operation of the welding robot. When the welding robot is reproduced to perform the welding operation, the robot axis and the servomotor are driven as taught.

As described above, in the welding gun positioning method of the present invention, the operator only has to operate the welding robot to move the gun arm to an arbitrary initial position.
Thereafter, the movable welding tip 22 and the fixed welding tip 21 automatically move to a predetermined pressing position,
The teaching reproduction operation can be easily performed in a short time. In addition, the two welding tips 21 and 22 come into contact with the work W with a desired load, so that a problem such as overload does not occur. In other words, in the method of positioning the welding gun with an equalizer generally used conventionally, the welding tip 2
When the wears 1 and 22 are worn, the movable welding tip 22
In a state where the load is applied to the work W by a distance corresponding to the amount of wear, the spot welding is performed after the welding gun 14 is moved until the fixed welding tip 21 contacts the work W. The work W receives a reaction force that moves the welding gun 14 in addition to the pressing force. However, in this embodiment, since the fixed welding tip 21 and the movable welding tip 22 are automatically positioned by moving to the predetermined pressing position, the welding tips 21 and 22 are automatically positioned.
Even if 2 is worn, problems such as overloading do not occur. Further, when the deformation of the work W is prevented, the shapes of the works to be welded can be maintained. Therefore, when a predetermined welding position of the work W is pressed by the welding tips 21 and 22 to bring the works into contact with each other, a desired contact area can be obtained with a smaller pressing force, and a predetermined conduction resistance can be obtained. .

When the force applied to the workpiece W is reduced in this way, even if the workpiece is directly pressed by the welding tips 21 and 22, dents of the welding tips 21 and 22 are not formed on the workpiece W. Therefore, in order to prevent dents, a back bar (not shown) between the workpiece W and the welding tips 21 and 22 becomes unnecessary. This back bar often requires a special one for each welding position, for example, under the sill or the arch part of the wheel house, and for each model,
When such a back bar is not required, the cost of assembling the vehicle is extremely reduced, and workability is significantly improved.

FIG. 8 shows the shape of the tip of the welding tip in contact with the outside of the vehicle body, that is, the surface that affects the appearance of the vehicle.
And the abutting portion is, for example, a diameter d =
By having a flat portion of about 10 mm to 20 mm, the pressing force per unit area of the contact portion may be further reduced to more reliably prevent dents.

Particularly, as compared with a conventional spot welding gun operated by a pneumatic cylinder, there is obtained an advantage that the positioning property and the quietness are extremely excellent.

[0029]

As described above, according to the present invention, there is provided a welding gun having a fixed welding tip fixed to a gun arm and a movable welding tip which is movable toward and away from the fixed welding tip by a servomotor. The effect that the positioning of the welding tip with respect to the work at the time of teaching and at the time of reproduction can be performed extremely easily can be obtained, and the positioning can be performed with high accuracy without causing variation among operators.

[Brief description of the drawings]

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

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

FIG. 3 is a schematic view showing an operation state of the welding robot.

FIG. 4 is a front view showing a positioning step in the method for positioning a welding gun according to the present invention.

FIG. 5 is a block diagram showing a control circuit of the welding robot of the present invention.

FIG. 6 is a flowchart showing an operation state of the positioning method of the present invention.

FIG. 7 is a flowchart showing an operation state of the positioning method of the present invention.

FIG. 8 is a side view showing another embodiment of the welding tip of the present invention.

[Explanation of symbols]

10 ... pedestal, 11 ... swivel table, 12 ...
Robot axis, 13 ... robot axis, 14 ... welding gun,
15 ... Gun arm, 21 ... Fixed welding tip, 22
... Movable welding tip, 23 ... Servo motor, 30 ... CP
U, 31: Operation panel, 32: Teaching box, 34: Robot axis drive motor, R: Robot, W: Work.

Claims (1)

(57) [Claims] 1. A method for positioning a welding gun, comprising: a fixed welding tip; and a movable welding tip capable of moving forward and backward with respect to the fixed welding tip, wherein a servomotor for driving the movable welding tip is mounted. A step of moving a welding gun to an initial position where the fixed welding tip and the movable welding tip face each other via a work in a state where the tip of the fixed welding tip and the tip of the movable welding tip are at a predetermined initial interval. Driving the servo motor to advance the movable welding tip until the movable welding tip comes into contact with the work and the current value of the servo motor changes from a low load state to a high load state; and The welding gun is moved by a robot to bring the fixed welding tip close to the work and bring the movable welding tip into contact with the work. Welding gun positioning method of welding robot and a step of advancing movement while keeping.