JPH0242303B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a control device for a spot welding robot.

Conventional technology Spot welding robots were introduced in August 1981, for example.
10th, published by Sankaido Co., Ltd. “Internal combustion engine; Vol21No.267;8
Monthly Special Issue; Trends in Industrial Robotics Technology” No.
As shown on pages 51 and 52, an X-shaped welding gun is attached to the tip of a multi-axis arm, and the multi-axis arm is played back according to a program that teaches spot welding positions on the workpiece to spot weld the workpiece. It is designed to be welded. There are two types of spot welding robots (hereinafter simply referred to as welding robots): hydraulic types that use hydraulic pressure as the drive source for the playback, and electric types that use electric power.However, the hydraulic type requires maintenance, is slow to respond, and requires less equipment. Due to their large size, they are no longer preferred due to their energy saving requirements, and electric models are increasingly being used.

Problems to be Solved by the Invention However, in the case of the above-mentioned electric type, as shown in FIG. 3, the welding gun 1 is moved by calculating the distance and direction to the target value, which is the spot welding position. When the welding gun 1 reaches the target spot welding position, it is pressurized by the pressurizing drive source 1a, and when the workpiece 3 is held between the welding electrode rods 2 facing each other, the welding electrode rod 2 is Arm part 1 supporting
b is deflected as shown by the imaginary line, and this deflection causes the arm 4 of the spot welding robot on which the welding gun 1 is attached to be pushed back in the direction of arrow It is determined that the clamping position has deviated from the program spot welding position, and in an attempt to correct the deviation △l, the electric servo motor is driven while the workpiece 3 of the welding gun 1 is pressurized and clamped. The welding electrode rod 2 is pushed in the direction of the arrow Y, _which is opposite to the arrow
In addition to the required pressure shown by arrow F ₂ , spot welding is performed with the application of an abnormal external force, so as the spot welded part of workpiece 3 is softened by the welding current, it is pushed forward and raised. dent 5
Also, some of the raised parts scatter and adhere to the area around the spot welding area, resulting in spatter marks 6. These dents 5 and spatter marks 6 are ground by a grinder after spot welding, which makes the finishing work troublesome and is also economically disadvantageous.

Therefore, the present invention focuses on the fact that the deflection of an X-shaped welding gun is proportional to the applied pressure, and provides a control device for a spot welding robot that can prevent the aforementioned dents and spatter marks.

Means for Solving the Problems In the present invention, an X-shaped welding gun is attached to the arm, and an electric servo motor is provided as a drive source that plays back spot welding positions on the workpiece according to a memorized program. The welding robot has a storage unit that stores the spot welding position of the workpiece by teaching, a calculation processing unit that outputs a playback command according to a program in this storage unit, and a processing unit that outputs a playback command according to the playback command from the calculation processing unit. a servo motor drive unit that drives the electric servo motor; a pressurization drive unit that drives a pressurization drive source of the welding gun in response to a command from the arithmetic processing unit to end the movement of the welding gun to the target value; A transformer supplies welding current to the welding electrode rod of the welding gun in response to a command from the arithmetic processing section to end pressurization of the welding gun; The output of the servo motor drive section is reduced between the arrival of the pressurization end command and the arrival of the welding current supply start command, and the servo motor drive section is reduced for each spot welding completion command of the welding gun from the arithmetic processing section. and control means for restoring the output of the device to a predetermined value.

Operation When the arithmetic processing unit outputs a playback command according to the program in the storage unit, the electric servo motor drives the playback to move the welding gun to the spot welding position on the workpiece, and the welding gun moves to the spot welding position on the workpiece. When the spot welding position is reached, the pressure drive source operates to pressurize and clamp the spot welding position of the workpiece with the welding electrode rod of the welding gun, while the control means controls the output of the servo motor drive unit to prevent the arm from falling due to its own weight, for example. reduce to the extent that it is obtained. In this state, the transformer supplies a welding current of a predetermined value to the welding electrode rod for a predetermined time, and the welding electrode rod spot-welds the spot welding position of the workpiece. When the spot welding of the workpiece is completed, the control means returns the output of the servo motor drive section to a predetermined value, and one cycle of spot welding is completed.

In other words, while the spot welding position of the workpiece is being pressurized and clamped by the welding electrode rod of the welding gun and spot welding is being performed by supplying welding current, the control means reduces the output of the servo motor drive section, which causes the welding gun to Stop driving the electric servo motor that is attempting to correct the position due to deflection. As a result, the workpiece is spot welded while the push-back force from the welding robot to the workpiece due to the deflection of the welding gun is removed. Each time the spot welding of the workpiece is completed, the control means returns the output of the servo motor drive section to a predetermined value. As a result, the movement speed of the welding robot to the target value, which is the spot welding position of the workpiece, and the working speed of the pressurizing operation of the welding gun become normal speeds controlled by the arithmetic processing section.

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, in which the same parts as those of the conventional structure are denoted by the same reference numerals.

As shown in FIG. 1, 10 is a welding robot, which has an X-shaped welding gun 1 on an arm 10a.
It is equipped with an electric servo motor (not shown) as a drive source that plays back spot welding positions on the workpiece according to a stored program. The welding robot 10 also includes a storage section 11, an arithmetic processing section 12, a servo motor drive section 13, a pressure drive section 14, a transformer 15, and a control means 16.

Here, the storage section 11 is adapted to store spot welding positions on the workpiece through teaching.

The arithmetic processing section 12 is adapted to output a playback command according to the program in the storage section 11.

The servo motor drive unit 13 is adapted to drive the electric servo motor (not shown) in response to a playback command from the arithmetic processing unit 12.

The pressure drive section 14 drives the pressure drive source 1a of the welding gun 1 in response to a command from the arithmetic processing section 12 to end the movement of the welding gun 1 to the target value.

The transformer 15 is adapted to supply a welding current of a predetermined value to the welding electrode rod 2 of the welding gun 1 for a predetermined period of time in response to a command from the arithmetic processing section 12 to end pressurization of the welding gun 1 .

The control means 16 controls the servo motor drive between the arrival of the command to end the movement of the welding gun 1 to the target value and the command to end the pressurization of the welding gun 1 from the arithmetic processing unit 12 and the arrival of the command to start supplying the welding current. The output of the servo motor drive section 13 is lowered, and the output of the servo motor drive section 13 is returned to a predetermined value each time the arithmetic processing section 12 commands the welding gun 1 to complete spot welding.

The execution of the control in the above embodiment will be explained according to the flowchart shown in Fig. 2.First, the distance and direction to the target value, which is the spot welding position of the workpiece, are calculated in the section, and the difference value is calculated by the servo. It is supplied to the motor drive section 13. Next, in a section, it is determined whether the welding gun 1 has reached the target value. If the target value of the welding gun 1 has not been reached, the section processing continues. When the welding gun 1 reaches the target value, the section pressurizes the welding gun 1, and the section adjusts the output voltage of the servo motor drive unit 13, which attempts to correct the position of the deflection of the welding gun 1, by reducing the arm's own weight. decreases to the extent that it can be prevented. Next, it is checked in the section whether pressurization of the welding gun 1 is completed or not, and it is determined in the section whether the output voltage of the servo motor drive section 13 has decreased. When the welding gun 1 pressurizes to a required value and the output voltage of the servo motor drive unit 13 decreases, the section outputs a welding current supply signal to the transformer 15. If the welding gun 1 is not pressurized yet, the section is continued. If the output voltage of the servo motor drive unit 13 has not decreased, the section is continued. Next, check whether the spot welding is completed at the section. If the spot welding is not completed, continue the section. When spot welding is completed, the section outputs a welding current cut-off signal to the transformer 15, the section releases the pressure on the welding gun 1, and
section returns the output voltage of the servo motor drive unit to the required value.

Next, check the operation of these sections in section , and if the operation is completed, check in section whether the spot welding position is the final spot welding position of the program, and if it is not the final position, proceed to the next program in section. Move to the target and repeat from section to section.

Effects of the Invention As described above, according to the present invention, the push-back force from the welding robot to the workpiece due to the deflection of the welding gun can be reduced without impeding the movement speed of the welding robot to the target value and the pressurizing operation of the welding gun. Since it can be removed, it is possible to prevent dents and spatter marks that require finishing work, and to perform spot welding at low cost and with high quality.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
This figure is a flowchart of the same embodiment, and FIG. 3 is an explanatory diagram of the operation of a conventional spot welding robot. 1... Welding gun, 10... Welding robot, 16
...control means.

Claims (1)

[Scope of Claims] 1. A spot welding robot equipped with an X-shaped welding gun on an arm and an electric servo motor as a drive source that plays back spot welding positions on a workpiece according to a stored program, comprising: a storage unit that stores spot welding positions by teaching; an arithmetic processing unit that outputs a playback command according to a program in the storage unit; and a drive unit that drives the electric servo motor in accordance with the playback command from the arithmetic processing unit. a servo motor drive section that drives a pressurization drive source of the welding gun in response to a command from the arithmetic processing section to end the movement of the welding gun to a target value; a transformer that supplies welding current to the welding electrode rod of the welding gun in response to the pressurization end command; and arrival of the welding gun movement end command to the target value and the welding gun pressurization end command from the arithmetic processing section. The output of the servo motor drive unit is reduced between the time when the welding current supply start command arrives, and the output of the servo motor drive unit is returned to a predetermined value every time the welding gun is commanded to complete spot welding from the arithmetic processing unit. A control device for a spot welding robot, comprising: a control means for controlling the spot welding robot;