Multi-Joint Robot Weaving Control Device Trajectory Precision
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Solution Overview
Problem
Existing control methods for articulated robots performing weaving movements in arc welding fail to accurately correct for amplitude and phase changes due to motor dynamic characteristics and external influences, leading to errors in trajectory precision.
Innovation Solution
A weaving control device that includes a signal computation unit for target position signals, a filter computation unit for low-pass filtering, and a motor control unit with position and speed feedback, along with feed-forward control units to predict and correct for inertia, gravity, friction, and interference forces, ensuring approximately flat frequency characteristics and phase compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If angular instruction values are generated based on weaving frequency and amplitude, then the robot can perform weaving movement, but the motor cannot move exactly according to the instruction values due to motor dynamic characteristics, resulting in trajectory precision degradation
Solution Approach 1:
The patent applies preliminary action by pre-calculating and compensating for motor dynamic characteristics before the actual weaving movement. The control device calculates the gain of the motor feedback system based on control time constants and weaving frequency, then multiplies the weaving signal by the inverse of this gain to obtain corrected angular instruction values. This preliminary correction ensures that the motor output matches the desired weaving amplitude despite dynamic characteristics.
Solution Approach 2:
The patent utilizes feedback by incorporating the motor feedback system's control time constants into the calculation of the gain. The feedback gain is determined based on the motor's dynamic characteristics, and this feedback information is used to correct the angular instruction values in advance, ensuring accurate amplitude control during weaving movement.
2Productivity
If the robot performs weaving movement with high frequency, then productivity improves, but the motor dynamic characteristics cause larger amplitude and phase deviations, worsening trajectory precision
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the correction factor based on the weaving frequency. The gain of the motor feedback system is calculated using the weaving frequency as a parameter, and the angular instruction values are corrected by multiplying with the inverse of this frequency-dependent gain. This allows the system to maintain trajectory precision across different welding speeds and frequencies.
3Manufacturing precision
If complex correction methods are applied to compensate for motor dynamic characteristics, then trajectory precision improves, but the control system complexity increases
Solution Approach 1:
The patent replaces complex mechanical or iterative correction methods with a mathematical calculation approach. Instead of using complex control algorithms or physical compensations, the system calculates the correction factor analytically based on the motor's control time constants and the desired weaving frequency, then applies this correction directly to the angular instruction values. This substitution of mathematical calculation for complex control mechanisms reduces system complexity while maintaining precision.
Data Source
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AI summary
Provided is a weaving control device that is of a multi-joint robot, is able to achieve a high-precision weaving, and suppress the occurrence of error in the weaving movement stemming from the effects of the movement of another joint axis and the dynamic characteristics of the motor driving the joint axis in question. The weaving control device 10 contains: a signal computation unit that computes the target position signal for each axis; a filter computation unit 400 that computes a target command signal resulting from low-pass filter processing of the target position signal; and a motor control unit 2500 that drives each axis with the target command signal as an input. The frequency characteristics of the gain of the motor control unit 2500 are configured in an approximately flat manner, and the dynamic characteristics from the target position to the motor output angle are similar to the filter. A weaving signal correction unit 200 computes a target position signal having a corrected gain on the basis of filter characteristics.