Servo Motor Rotational Angle Measurement Correction for Spot Welding
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Solution Overview
Problem
Aging mechanical elements in spot welding guns lead to increased sliding resistance and torque, causing inaccurate rotational angle measurements due to hysteresis and potential false detection, especially when electrodes are worn or deformed, resulting in inefficient welding operations.
Innovation Solution
A measuring method and device that acquire and correct rotational angles by comparing reference and measured electrode positions using multiple acquisition steps, monitoring current and torque, and image analysis to account for changes in mechanical elements' deterioration, ensuring accurate contact detection without relying on increased threshold values or torque limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If threshold values or torque limits are increased to account for increased sliding resistance due to aging, then the movable electrode can operate under deteriorated conditions, but false detection occurs where the movable electrode contacts the opposite electrode even though such contact is not actually made
Solution Approach 1:
The patent applies preliminary action by acquiring a rotational angle correction amount before actual measurement. The system stores correction amounts obtained when mechanical elements are in good condition, then applies these corrections during operation to compensate for aging effects without needing to adjust threshold values or torque limits, thereby maintaining both reliability and measurement precision
Solution Approach 2:
The patent implements feedback by continuously monitoring the difference between commanded and actual rotational angles, using this feedback to apply appropriate correction amounts. The system adjusts the measured rotational angle based on stored correction data, enabling accurate contact detection despite changes in sliding resistance due to aging
2Force
If the first threshold value is set relatively large to account for increased sliding resistance, then the movable electrode can push through increased resistance, but due to hysteresis of the speed reducer, the movable electrode may not maintain contact with the opposite electrode
Solution Approach 1:
The patent replaces mechanical threshold-based contact detection with a rotational angle-based detection system. Instead of relying on force thresholds that must be increased to overcome aging, the system measures rotational angle deviations and applies correction amounts, eliminating the need to increase mechanical thresholds while maintaining reliable contact detection
Solution Approach 2:
The patent changes the detection parameter from force/threshold-based to rotational angle-based. By monitoring rotational angle deviations and applying correction amounts stored from calibration periods, the system maintains accurate contact detection without needing to adjust mechanical parameters like threshold values or torque limits
3Object-affected harmful factors
If torque limit is set to prevent opposite electrode from contacting workpiece by securing sufficient distance, then safety is improved, but time is taken to secure sufficient distance and testing needs to be performed during production operation
Solution Approach 1:
The patent applies preliminary action by acquiring rotational angle correction amounts during initial installation or calibration when mechanical elements are in good condition. These correction amounts are stored and applied during operation, eliminating the need for time-consuming setup procedures and enabling immediate safe operation without compromising workpiece protection
Solution Approach 2:
The patent creates a copy of the rotational angle characteristics from the calibration period and applies this copied data during operation. By storing and reusing correction amounts obtained during calibration, the system maintains accurate contact detection and safe operation without needing to repeat time-consuming setup procedures
Data Source
AI summary
As a correction amount is acquired a deviation between a first rotational angle of a servo motor when a reference movable electrode is brought into contact with a reference opposite electrode and a second rotational angle of the motor when the reference movable electrodes pushes in the reference opposite electrode with a predetermined pressing force; and a third rotational angle of the servo motor when a movable electrode to be measured pushes in an opposite electrode to be measured with the same pressing force is corrected based on the correction amount.