JPH0368791B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a control method for an automatic seam welding device that can automatically seam weld workpieces such as fuel tanks for two-wheeled vehicles using a robot. .

(Prior Art) The applicant of the present application previously disclosed in Japanese Patent Application No. 58-227829 that a workpiece is held by a vertical wrist shaft provided at the wrist at the operating end of the robot via a workpiece holder. An automatic seam welding device has been proposed in which the welded portion is guided by the movement of each lower moving member of the robot including the wrist shaft and sent between a pair of upper and lower electrode rolls provided in a seam welding machine.

(Problem to be Solved by the Invention) In a seam welding machine, the welded part of the workpiece is forcibly fed by an electrode roll, so in the above device, the robot is operated in synchronization with the rotation of the electrode roll. However, due to slippage between the workpiece and the electrode roll, the actual feed amount of the workpiece by the electrode roll and the feed amount of the workpiece due to robot movement may not match, and as a result, the electrode roll relative to the workpiece may There is a problem in that the direction of movement of the electrode roll deviates from the normal direction, causing the electrode roll to come off the welded part or interfere with the workpiece.

The present invention provides a control method that solves the above problems by automatically detecting a mismatch between the actual feed rate of the workpiece by the electrode roll and the feed rate of the workpiece due to the movement of the robot and correcting the trajectory. Its purpose is to provide.

(Means for Solving the Problems) In order to achieve the above object, the present invention uses the actual torque acting on the vertical wrist shaft that holds the workpiece via the workpiece holder and the actual torque applied to the workpiece by the electrode roll. When the feed rate and the workpiece feed rate due to robot movement match, the deviation from the normal torque acting on the wrist shaft is detected, and the rotational speed of the electrode roll and the torque applied to the workpiece are adjusted according to this deviation. The direction of movement of the electrode roll can be changed.

(Function) Torque related to the movement of the workpiece being sent in the horizontal direction by the electrode rolls acts on the vertical wrist axis located at a position offset from the part where the workpiece is held by the pair of upper and lower electrode rolls. If the actual feed amount of the workpiece by the rolls and the feed amount of the workpiece by the movement of the robot do not match, for example, if the former feed amount decreases than the latter feed amount due to the workpiece slipping, the wrist axis will be affected by the electrode roll. A reaction force corresponding to the difference between the two feed amounts acts in the direction opposite to the feed direction of the workpiece, and thus the actual torque acting on the wrist shaft is smaller than the normal torque when the two feed amounts match by this reaction force. By detecting the deviation between the two torques, the difference between the two feed amounts is detected.

Then, by changing the rotational speed of the electrode roll according to this torque deviation, both feed amounts will match, and by changing the direction of movement of the electrode roll with respect to the workpiece, the welding trajectory of the electrode roll can be adjusted to the normal trajectory. Accurate seam welding can be achieved by restoring the seam.

(Example) Referring to FIG. 1, 1 indicates a seam welding machine,
At the front of the welding machine 1, there is a pair of upper and lower electrode rolls 2 ₁ ,
2 ₂ and drive motors 3 ₁ , 3 ₂ for the respective rolls 2 ₁ , 2 ₂ are provided at the rear of the upper electrode roll 2 .
₁ is pivotally supported by an electrode holder 5 ₁ that is raised and lowered by a pressurizing cylinder 4, and is rotationally driven by a drive motor 3 ₁ via a knurl gear 6, and a lower electrode roll 2
₂ is pivotally supported by an immovable electrode holder ₅₂ and rotationally driven by a drive motor _32. Furthermore, a robot 7 is mounted on the upper surface of the welding machine 1, and a wrist portion 8 at the operating end of the robot 7 is mounted on the upper surface of the welding machine 1. Vertical wrist shaft 9
A workpiece W consisting of a fuel tank for a two-wheeled vehicle is held via a workpiece holder 10, and a welding part Wa consisting of a butt flange around the workpiece W is placed on the lower electrode roll ₂₂ at a predetermined welding start point. Lowering the upper electrode roll 2 ₁ in the mounted state,
Both rolls 2 ₁ and 2 ₂ are driven to rotate with the welded portion Wa sandwiched between the rolls 2 ₁ and 2 ₂ ,
In synchronization with this, each movable member of the robot 7 including the wrist shaft 9 is operated according to the taught data, and the welding part Wa is continuously fed between the rolls 2 ₁ and 2 ₂ to perform automatic seam welding. I decided to do this.

In the illustrated robot 7, both electrode rolls 2 are mounted on a base 11 fixed on the top surface of the seam welding machine 1.
_A robot main body ₁₂ is pivotably mounted on the top of the robot main body 12 so as to be pivotable about a vertical axis X passing through the center of the robot main body 12; , a second arm 14 extending downward is provided at the tip of the first arm 13 so as to be swingable in the front-rear direction, and the second arm 14 is always maintained in a constant posture by an appropriate parallel mechanism at the lower end of the second arm 14. A wrist shaft 9 is vertically mounted on the wrist shaft 9, which is rotatably driven by a drive motor 15 mounted on the wrist shaft 9 via an internal bevel gear (not shown). A workpiece holder 10 is attached to the lower end of the shaft 9 via a cross joint 16.

In the automatic seam welding apparatus configured as described above, according to the present invention, when the actual feed amount of the workpiece W by the electrode rolls 2 ₁ and 2 ₂ matches the feed amount of the workpiece W by the movement of the robot 7. The deviation between the normal torque acting on the wrist shaft 9 and the actual torque acting on the wrist shaft 9 is detected, and the rotational speed of the electrode rolls 2 ₁ and 2 ₂ and the impact on the workpiece W are determined according to this deviation. The direction of movement of the electrode rolls 2 ₁ and 2 ₂ is changed.

To explain this in more detail, when _the workpiece W is sent in the direction _{of the} arrow A _in FIG _. , 2 ₂ , the robot 7 operates as instructed, so the wrist shaft 9 moves as shown by the imaginary line in FIG.
Prior to the feeding of the workpiece W by the rolls 2 ₁ and 2 ₂ , the workpiece W is moved in the workpiece feeding direction, and the workpiece W is tilted using the holding part O by the rolls 2 ₁ and 2 ₂ as a fulcrum,
The traveling directions of the rolls 2 ₁ and 2 ₂ with respect to the workpiece W deviate from the normal direction. At this time, a reaction torque acts on the wrist shaft 9 in a direction opposite to the workpiece feeding direction, that is, in a counterclockwise direction in FIG. 2, and the actual torque acting on the wrist shaft 9 is equal to the normal torque mentioned above. As a result, by detecting the deviation between the actual torque and the normal torque,
The difference between the feed amount of the workpiece W due to the movement of the robot 7 and the actual feed amount of the workpiece W by the electrode rolls 2 ₁ and 2 ₂ is detected, and the rolls 2 ₁ and 2 ₂ are adjusted according to this torque deviation. By changing the rotational speed and traveling direction of the rollers and performing feedback control so that the torque deviation becomes zero, the welding trajectories of the rolls 2 ₁ and 2 ₂ return to normal trajectories and accurate seam welding is performed.

Note that the moving direction of the rolls 2 ₁ and 2 ₂ is such that the rotation axis X of the robot body 12 is located on a vertical line passing through the clamping part O. It can be easily changed by tilting using the fulcrum as the fulcrum.

Here, the torque deviation can be detected, for example, from a change in the drive current of the drive motor 15 of the wrist shaft 9. That is, the a line in _{FIG .}
If the normal drive current change characteristics are such that the amount of feed of the work W by When the torque becomes larger than the normal torque as mentioned above, the drive current correspondingly becomes larger than the normal current value as shown by the b line.Thus, by memorizing the change characteristics of the a line, If the deviation from the actual drive current is detected, the torque deviation can be detected.

It is also possible to detect torque deviation by attaching a strain gauge 17 to the wrist shaft 9, as shown in FIG. 4. In this case, as shown in FIG. The elastic member 9a is fixed by baking to cause a relatively large twist depending on the torque, and a strain gauge 17 is attached to the circumferential surface of the elastic member 9a so that the torque can be detected with good sensitivity.

(Effects of the Invention) As described above, according to the present invention, the rotational speed and the direction of movement of the electrode roll are changed according to the deviation between the actual torque acting on the wrist axis and the normal torque. Even if the welding trajectory of the electrode roll deviates from the normal trajectory due to a mismatch between the actual feed rate of the workpiece and the feed rate of the workpiece due to the movement of the robot, the welding trajectory of the electrode roll is automatically returned to the normal trajectory to perform accurate seam welding. It has the effect that can be obtained.

[Brief explanation of drawings]

Fig. 1 is a side view of an example of automatic seam welding equipment to which the method of the present invention is applied, Fig. 2 is a diagram explaining the principle of action of torque on the wrist axis, and Fig. 3 is a change in the drive current of the drive motor. FIG. 4 is a side view of the wrist portion of an embodiment in which a strain gauge is attached to the wrist shaft, and FIG. 5 is an enlarged side view of the main parts thereof. DESCRIPTION OF SYMBOLS 1... Seam welding machine, 2 ₁ , 2 ₂ ... Electrode roll, 7... Robot, 8... Wrist part, 9... Wrist shaft, 15... Drive motor, 17... Strain gauge, W
...Work, Wa...Welding section.

Claims (1)

[Scope of Claims] 1. A workpiece is held via a workpiece holder on a vertical wrist shaft provided at the wrist at the operating end of the robot, and the workpiece is moved by movement of each movable member of the robot including the wrist shaft. A control method for an automatic seam welding device in which the welded part is guided and fed between a pair of upper and lower electrode rolls provided in a seam welding machine, the method comprising controlling the actual feed amount of the workpiece by the electrode rolls and the movement of the robot. The deviation between the normal torque acting on the wrist shaft and the actual torque acting on the wrist shaft when the feed rate of the workpiece matches the workpiece feed rate is detected, and the rotation of the electrode roll is adjusted according to this deviation. 1. A control method for an automatic seam welding apparatus, characterized in that the speed and direction of movement of the electrode roll relative to a workpiece are changed. 2. The control method for an automatic seam welding apparatus according to claim 1, wherein the torque deviation of the wrist shaft is detected from a change in the drive current of a drive motor of the wrist shaft. 3. The control method for an automatic seam welding apparatus according to claim 1, wherein the torque deviation of the wrist shaft is detected using a strain gauge attached to the wrist shaft.