Position detection device and position detection method for workpiece to be welded

Abstract

The present invention provides a position detection device and a position detection method for a workpiece to be welded. The position detection device includes a spot welding gun having a pair of electrodes adapted to be disposed opposite each other across the workpiece; a robot for holding either one of the spot welding gun and the workpiece in a manner movable relate to each other; a servo motor for allowing the pair of electrodes to approach the workpiece and separate from the workpiece; a physical quantity detection section for detecting a physical quantity correlative to a torque of the servo motor when the servo motor allows one of the pair of electrodes to approach a surface of the workpiece so that the one of the pair of electrodes abuts against the surface of the workpiece; a position detection section for detecting positions of the pair of electrodes; a storage section for storing the physical quantity detected by the physical quantity detection section and a value detected by the position detection section; and a computation section for calculating a contact start time at which the one of the pair of electrodes comes into contact with the surface of the workpiece based on time-series data of the physical quantity stored in the storage section, and computing a position of the workpiece at the contact start time based on the value detected by the position detection section stored in the storage section.

Description

technical field [0001] The present invention relates to a welding workpiece position detection device and a welding workpiece position detection method for detecting the position of a spot welded workpiece. Background technique [0002] In the case of using a robot to perform spot welding of a workpiece through automatic operation, if the workpiece position (spot welding point position) recorded in the work program deviates from the actual workpiece position, overloading of the workpiece or incorrect flow may occur. Problems such as excessive welding current lead to a decrease in welding quality. Therefore, conventionally, the position of the workpiece is detected in advance before spot welding, and the position of the spot welding point is corrected based on the position of the workpiece. [0003] In the system described in Japanese Patent No. 4233584 (JP4233584B), a workpiece is placed between a movable electrode and a counter electrode of a spot welding gun, and the mova...

AI Technical Summary

Problems solved by technology

However, the torque of an actual servo motor tends to rise slowly after the movable electrode comes into contact with the workpiece surface

Therefore, at the moment when the motor current exceeds a predetermined value, the movable electrode has sufficiently pressed the surface of the workpiece and is in a state of being moved from the contact position, and when the motor current exceeds a predetermined value, it is judged that the movable electrode has been in contact with the workpiece surface, so Cannot detect workpiece position with high accuracy

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