JPH0767622B2 - Wrist device in industrial robot and its control method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a wrist device in an industrial robot and a control method thereof, and more particularly to an industrial robot capable of changing a pressing force for each welding site. is there. This is used in the field of robots that automatically and sequentially perform stud welding or arc spot welding on a predetermined portion of a work.

[Conventional technology]

A wrist device in an industrial robot is attached to the tip of a robot arm, and is equipped with various mechanisms such as a swivel, a bend, and a twist so that the wrist itself behaves in a desired manner independently of the movement of the arm. In a welding robot, a welding gun or the like is attached to the tip of such a wrist, and stud welding or arc spot welding can be performed. Therefore, it becomes possible to dispose the tip of the welding gun at a desired welding portion of the work by the drive mechanism governed by the spatial movement control that operates the robot arm and the rotation and bending of the wrist arm. ing.

By the way, for example, in the case of arc spot welding of two stacked steel plates, it is necessary to press one plate against the other plate in order to fly the welding arc, and in the case of stud welding. Is required to exert a large pressing force on the work. Therefore, conventionally, an air cylinder is attached to the tip of the wrist, and a gun and a torch are attached to the end.

In such a configuration, the wrist is moved by the movement of the arm by the space movement control, the posture of the wrist is determined by each mechanism such as the swivel described above, and when the tip of the gun reaches the desired welding site, Air is introduced into the cylinder. The piston rod advances toward the welding site while the wrist position is maintained, and the gun or torch attached to the tip of the piston rod pressurizes the steel plate. When the air having a predetermined pressure is introduced, for example, the upper and lower two steel plates are pressed with a predetermined pressure, and a high voltage is applied to the gun and the torch to weld the work.

[Problems to be Solved by the Invention] According to the pressurization control using such an air cylinder, it is possible to constantly generate an equivalent pressurizing force at a welding site by a constant air pressure obtained from a pressure source. However, the welding force at the welding site depends exclusively on the external force of the air cylinder, etc., and it is necessary to attach piping for supplying high-pressure air to the wrist that moves frequently, which becomes an obstacle when the wrist moves. Sometimes, there are problems such as damage.

In addition, peripheral equipment for operating the air cylinder, such as a pressure source, is required.When operating the robot, spatial movement control related to wrist position and speed and welding gun pressurization control are performed by independent equipment and control systems. Therefore, the robot main body configuration and control system become complicated. Moreover, since the air cylinder normally operates at a constant air pressure, it is not easy to change the pressure depending on the welding site.

As a result, it is necessary to secure the desired welding accuracy at each welding site due to the difference in rigidity at each welding site due to the difference in the press shape given to the work, the variation in the proximity of the stacked plate materials, etc. There is a drawback that a suitable pressing force cannot be generated. In order to change the applied pressure for each welding part, it is possible to introduce, for example, an electromagnetic proportional control valve, but the drive structure in the robot body becomes more complicated, and complicated control is required for that, and the overall cost increases. There is.

By the way, a resistance welding device that arranges a spring on the back of the welding gun and reduces the work pressing force of the welding gun when a large pressing force acts on the welding gun,
It is described in JP-A-59-206177. By allowing the welding gun to be substantially displaced with respect to the gun support by such spring deformation,
A rubbing phenomenon such as the tip of the welding gun sliding sideways on the work can be suppressed, and welding can be performed at a desired position.

However, since the welding gun is supported by the slider and the spring is provided behind the slider, the wrists are arranged in series, so that the wrist becomes longer in the extending direction of the welding gun, and it is necessary to attach a heavy and bulky wrist to the swivel arm. Become. This causes problems such as a reduction in speed in space movement control of the welding gun and a large amount of power required to drive the turning arm and the like. In this example, it is also impossible to detect the pressure reaction force and apply a desired pressing force in consideration of the state of the welded portion of the work.

On the other hand, an example of arranging a pressure sensor behind a spring that absorbs displacement while pressing a welding gun against a work is described in Japanese Patent Laid-Open No. 59-185581. If the sensor for detecting the pressure reaction force is provided behind the welding gun in this way, the above problem can be solved. However, in this example, since the main purpose is to perform temperature compensation of the welding gun that is exposed to an extremely strong electromagnetic field during welding, positive measures are taken to hold the welding gun in the lateral direction. However, there is a drawback that it is difficult to reliably weld the desired part.

Moreover, since the welding is stopped if the pressure applied during welding is not appropriate, the pressure applied by the welding gun cannot be controlled according to the workpiece. Of course, the spatial movement operation for displacing the wrist and the operation related to the speed and the pressurizing operation of the welding gun are independent controls, and there is still a problem that the control system is complicated.

The present invention has been made in view of the above problems, and an object thereof is to be able to absorb an impact load acting on a welding gun and reduce damage to a wrist or the like, and to apply different pressurizing forces set according to a welding site of a work. It can be applied to the welding gun, can surely prevent lateral displacement of the welding gun and can perform stable welding on the workpiece, and peripheral equipment such as an independent air cylinder required for pressurizing the welding gun and its accessories. Eliminating the device so that the robot arm and wrist can be operated smoothly and quickly at all times, and the wrist mechanism is simplified to reduce its weight and the overall configuration of the robot is made smaller and lighter. In addition, the robot arm and wrist are controlled by a group of control systems that can switch between spatial movement control of the arm and wrist and pressure control of the welding gun, and are related to robot operation. To provide a wrist device and a control method for an industrial robot can be simplified control system that.

[Means for Solving the Problems]

According to the present invention, a welding gun is attached to a wrist attached to the tip of a robot arm, and the tip of the welding gun is moved to a desired welding site of a work by causing the wrist to rotate or bend with respect to the robot arm. It is applied to a wrist device in an industrial robot which can be arranged.

1 and 2, a gun base 9 for attaching and fixing the welding gun 7 to the tip portion of the wrist 1 is provided. A base holder 10 is provided on the side of the robot arm 2 of the wrist 1, and a slide hole 12 in the extending direction of the welding gun 7 is formed inside the base holder 10. A slidable slider 11 is fitted in the slide hole 12 and the gun base 9 is fixed to the tip of the slider 11, so that the gun base 9 is fixed to the base holding portion 10.
On the other hand, it is displaced only in the direction of pressurizing the gun and is supported so as not to rotate with respect to the wrist 1. Slide hole in the base holder 10
Springs 15 and 16 that are concentric with 12 and that absorb the backward displacement of the gun base 9 are interposed. Then, between the contact plate 18 and the gun base 9 for transmitting the elastic force of the springs 15 and 16 to the welding gun 7, the welding gun 7 is pressed by the robot.
That is, the pressure sensor 19 for detecting the pressure reaction force from the work 17 that acts on the is provided.

According to a second aspect of the present invention, a welding gun is attached to a wrist attached to the tip of a robot arm, and a drive mechanism for operating the robot arm and rotating or bending the wrist with respect to the robot arm by space movement control is used. The present invention is applied to a method for controlling a wrist device in an industrial robot in which the tip can be placed at a desired welding portion of a work.

The feature is that, with reference to FIG. 2, the robot arm 2 and the wrist 1 are displaced by the space movement control of the robot, and when the welding gun 7 reaches a desired welding site on the work 17, the wrist 1 is moved. Pressurization control that presses the welding gun 7 against the work 17 is added to the space movement control that has been displaced (see the switching logic 21 in FIG. 3), and when the welding gun 7 pressurizes the welding site, Welding gun 7 supported spontaneously
Of the welding gun 7 is allowed and the pressure reaction force generated at that time is detected, and the detected pressure value is fed back in the pressure control until the pressure of the welding gun 7 reaches the set value at the welding site. That is, the pressurization is controlled by using a drive mechanism that operates by space movement control.

〔The invention's effect〕

According to the present invention, the gun base is displaced only in the gun pressing direction with respect to the base holding part and is supported so as not to be rotatable with respect to the wrist. It is possible to perform stable welding on. Further, since the spring for absorbing the backward displacement of the gun base is concentric with the slide hole in the base holding portion, the impact load acting on the welding gun is absorbed and damage to the wrist or the like is suppressed. Moreover, the displacement guide mechanism and the displacement absorbing mechanism of the gun base are concentrically and compactly formed inside the base holding part, which simplifies and reduces the weight of the wrist structure and reduces the weight that acts on the robot arm. The burden etc. can be reduced.

A pressure sensor that detects the pressure reaction force from the work that acts on the welding gun due to the pressure operation of the robot is installed between the backing plate and the gun base to transmit the elastic force of the spring to the welding gun. Since it is provided, it becomes possible to generate a suitable pressing force stored in advance for each welding site by feedback pressurization control based on the detected pressure value. In addition, peripheral equipment such as an air cylinder required for pressurizing the welding gun and its auxiliary equipment are not required, and it is possible to prevent a large load from being applied to the robot body and to interfere with a workpiece having a complicated shape. Less
The robot arm and wrist can always be operated smoothly and quickly.

In the second aspect, the welding gun pressure detected by the pressure sensor can be adjusted to a desired value. Not only that, the pressure control is reflected in the drive mechanism that was governed by the space movement control system that displaces the robot arm and wrist, and pressure control is performed without attaching a pressure device such as an air cylinder to the wrist. The pressurizing operation can be given by a group of robot control systems which are added to the space movement control.

[Examples] Hereinafter, a wrist device and a control method thereof in an industrial robot according to the present invention will be described in detail with reference to the drawings showing an example thereof.

FIG. 2 is a schematic view of the vicinity of a robot wrist 1 to which the present invention is applied, in which a swivel 3, a bend 4, and a twisting or bending mechanism such as a twist 5 as necessary are provided at the tip of a robot arm 2. . Arm 2 with such a wrist attached
Is operated by being driven by a motor of a drive mechanism (not shown), and is bent and rotated, and at the same time, swiveled with respect to the robot main body 6 to allow the robot to perform a desired operation. The wrist 1 can be operated independently of the movement of the arm 2 by each rotating mechanism such as the swivel 3 described above, and all these movements are performed based on the spatial movement control of the robot. The wrist 1 is provided at the tip thereof with a welding gun 7 for stud welding, arc spot welding, or the like, and a gun mounting portion 8 for mounting a torch or the like.

The gun mounting portion 8 has an expandable / contractible structure, and as shown in FIG. 1, a gun base 9 for mounting and fixing a welding gun on the front surface, and a base holding portion provided on the arm 2 side of the wrist 1. Ten
It consists of On the back of the gun base 9, for example, a suitable number (one in the figure) of sliders 11 extending in the pressurizing direction are provided in a protruding manner, and the sliders 11 are formed on the inner peripheral portion of the base holder 10. It is fitted in the hole 12.

A slide bearing 13 is interposed in the slide hole 12 so that the slider 11 can slide in the axial direction of the slide hole 12. In this way, the slider 11 is
Therefore, the gun base 9 is displaced only in the pressurizing direction of the welding gun 7 and cannot rotate with respect to the wrist 1. Therefore, the gun base 9 does not rotate in the gun mounting portion 8 and the displacement is allowed only in the pressing direction 14 of the welding gun.

Between the above-mentioned gun base 9 and base holding part 10, the gun base
The springs 15 and 16 are arranged in a double arrangement such as two coils that urge the 10 away from the wrist 1 with a constant force and absorb the displacement in the gun pressing direction.
This is arranged in the center of the inside of the slide hole 12 in the base holder 10, and the sliders 11 and 11 and the springs 15 and 16 are concentrically arranged. Care is taken not to lengthen in the pressurizing direction.

When the welding gun 7 presses the work 17 (see FIG. 2), the springs 15 and 16 are mounted on the gun base 9 by the gun base 9.
In addition to being able to move backward, the displacement is absorbed and suppressed so that a sudden pressure reaction force does not act on the wrist 1 or a pressure sensor 19 described later during pressure operation.

A pad plate 18 is provided so that the elastic force of the springs 15 and 16 can be transmitted to exert an urging force on the welding gun 7. The pad plate 18 and the gun base to which the elastic force is transmitted are provided. A pressure sensor 19 is provided between the table 9 and the table 9. This pressure sensor
Reference numeral 19 denotes a load cell or the like, which detects the pressure reaction force from the work 17 generated by the contraction of the springs 15 and 16 described above, which is proportional to the pressure force in the pressure control. The detected pressure signal is input as an electric signal via a cord 20 to a strain amplifier (not shown) or the like. Incidentally, the gun base 9 has a structure that does not come out of the base holding portion 10, and only the initial elastic force of the springs 15 and 16 acts on the pressure sensor 19 when the welding gun 7 is not in a pressurized state.

By the way, the position feedback loop and the velocity feedback loop that have been conventionally adopted are formed in the control system of the robot.In addition to those space movement control systems, a switching logic for the pressurization control system and both control systems is provided. It has been incorporated. In this example, not only in the space movement control system, but also in the pressure control system, a feedback loop that cannot be applied when the air cylinder is used as the pressure device is adopted.

In the wrist device having such a configuration, the work 17 can be pressure-welded by pressing the welding gun 7 from the base holding portion 10 as described below.

First, when the wrist 1 is moved to a predetermined welding site of the work 17, the switching logic 21 shown in FIG. 3 is turned off, and the command signal of the pressurization set value 22 in the pressurization control system is cut off, and the space is released. Each drive mechanism is operated by movement control.
In response to the position command 23 in the space movement control system, the arm 2 is appropriately operated, and the wrist 1 turns and bends by the swivel 3 or the like. Feedback control indicated by a broken line is applied based on a signal from the encoder 24 so that the music piece and the wrist 1 reach a position taught in advance. At that time, the movement speed of the wrist 1 or the like is also compared with the speed detected by the tacho generator 26 attached to the motor 25 that drives the wrist 1, and the movement speed is as indicated by the one-dot chain line so as to reach the specified speed. Feedback control is performed.

When the wrist 1 moves and the tip of the welding gun 7 reaches a desired welding site of the work 17 by the space movement control, the switching logic 21 is automatically turned on, and the welding gun 7 is controlled by the space movement control of the robot described above. A pressure control function for pressing the work 17 is added. Since the welding gun 7 is restrained at its welding site based on the space movement control, the arm 2 and the wrist 1
The work 17 is pressurized by the increment of the current flowing through the motor 25 that drives each of the operating mechanisms.

The spring 1 interposed in the gun mounting part 8 when the pressure is increased.
The gun base 9, which is pressed against 5,16, has springs 15,16
While retracting, is retracted in the direction of the base holding unit 10. As a result, even if the welding gun 7 suddenly abuts on the work 17, the impact force acting on the welding gun 7 is mitigated, the generation of a sudden pressure reaction force is suppressed, and the impact is transmitted to the wrist 1. Be relieved.

As described above, the welding gun 7 is displaced against the elastic force of the springs 15 and 16, but is not rotated or laterally displaced with respect to the base holding portion 10, and therefore, the welding gun 7 is not pressed during the pressing operation. The posture of No. 7 is reliably held at the desired welding site. Since the gun base 9 is supported by the springs 15 and 16, the pressure sensor 19 installed between the backing plate 18 and the gun base 9 does not receive a sudden pressure reaction force and is detected. The signal does not become unstable with shock.

The force exerted on the gun mounting portion 8 by pressurization is detected by the pressure sensor 19 and is input to the control portion via a strain amplifier or the like. If this input value does not reach the predetermined pressurization value at the welded part, each drive mechanism operated by the space movement control is operated by the pressurization control, and the feedback control shown by the chain double-dashed line in FIG. 3 is performed. The pressurizing operation is continued until the signal from the pressurizing set value 22 matches.

When the set value is reached, the applied pressure is maintained, and welding voltage is applied to perform welding. When the welding at the site is completed, the switching logic 21 is automatically turned off, the feedback loop for pressurization control is broken, the wrist is displaced by the spatial movement control to the next welding site taught, and The work on the work is continued successively by the control by the procedure. In this way, the spatial movement control of the robot arm or wrist and the pressurization control of the welding gun are executed by a group of control systems that can be switched, and the control system related to the robot operation can be simplified.

In the above welding work, the welding force may be the same at the welding site, but if different welding forces are taught or input separately in advance for each welding site, the welding force will be changed for each welding site of the workpiece. be able to. As a result, the pressurization according to the rigidity of the work is realized, and the welding accuracy is secured and the welding work is facilitated. As can be seen from this, it is not necessary to attach an independent drive device such as an air cylinder to the wrist to pressurize the welding gun,
Therefore, peripheral devices can be omitted. As a result, consideration for avoiding obstacles around the robot arm and wrist when operating is reduced as much as possible, and size reduction and weight reduction of the robot body and wrist are promoted. It is also possible to prevent a large load from being applied to the robot body, and it is possible to avoid interference with a work having a complicated shape.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram of a welding gun mounting portion in a wrist device of an industrial robot of the present invention, FIG. 2 is a schematic diagram of the vicinity of a wrist portion of an industrial robot to which the present invention is applied, and FIG. 3 is a robot. 3 is a control system block diagram of FIG. 1 ... wrist, 2 ... robot arm, 7 ... welding gun,
9 ... Gun base, 10 ... Base holder, 11 ... Slider,
12 …… Slide hole, 15,16 …… Spring, 17 …… Workpiece, 18 …… Patch plate, 19 …… Pressure sensor, 21 …… Switching logic.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shinji Fujita 1-1 Kawasaki-cho, Akashi-shi, Hyogo Kawasaki Heavy Industries Ltd. Akashi factory (72) Inventor Yoshitaka Sakamoto 1 Toyota-cho, Toyota-shi, Aichi Toyota Automobile Within the corporation (56) References JP 59-206177 (JP, A) JP 59-185581 (JP, A) Actual development Sho 58-125677 (JP, U)

Claims (2)

[Claims] 1. A welding gun is attached to a wrist attached to the end of a robot arm, and the wrist makes a desired operation on the work by rotating, bending, or the like with respect to the arm. In a wrist device for an industrial robot that can be arranged at a welding site, a gun base for mounting and fixing the welding gun is provided at a tip part of the wrist, and a robot arm side of the wrist. Is provided with a base holding portion, and a slide hole in the extending direction of the welding gun is formed inside the base holding portion, and a slidable slider is fitted in the slide hole and the slider is inserted. By fixing the gun base to the tip of the base, the gun base is displaced only in the gun pressurizing direction with respect to the base holding part and is non-rotatably supported with respect to the wrist. A spring that absorbs the backward displacement of the gun base is concentric with the slide hole in the base holding part, and a pad plate and a gun base for transmitting the elastic force of the spring to the welding gun. A wrist device in an industrial robot, characterized in that a pressure sensor for detecting a pressure reaction force from a work acting on the welding gun by a pressure operation of the robot is provided between the base and the base. 2. A welding gun is attached to a wrist attached to the tip of a robot arm, and the welding is performed by a drive mechanism for operating the robot arm and rotating and bending the wrist with respect to the arm by spatial movement control. A method for controlling a wrist device in an industrial robot, which is capable of arranging a tip of a gun at a desired welding portion of a work, wherein the robot arm and the wrist are displaced by spatial movement control of the robot, and the welding is performed. When the gun reaches a desired welding site on the work, pressure control for pressurizing the welding gun to the work is added to the space movement control that displaces the wrist, and the welding gun pressurizes the welding site. At this point, the retracting of the welding gun supported elastically was allowed, and the pressure reaction force generated at that time was detected. While feeding back the pressure value in pressurization control,
A method for controlling a wrist device in an industrial robot, wherein pressurization control is performed using a drive mechanism that operates by spatial movement control until the pressure applied by the welding gun reaches a set value at the welding site.