Motor Controller Inverse Filter for Vibration Suppression
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Solution Overview
Problem
Conventional motor controllers face incompatibility between vibration suppression and shape accuracy in full-closed control systems, with notch filters causing overshooting and degrading machining accuracy.
Innovation Solution
A motor controller that includes a position command unit, position detector, and velocity controller with a filter F(s) that approximates the inverse characteristic of the transfer characteristic from the motor velocity command to the machine velocity, allowing for effective vibration suppression and shape accuracy in full-closed control systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If notch filters are used inside the servo control loop to suppress low-frequency resonance, then vibration suppression is improved, but trajectory accuracy deteriorates due to overshooting
Solution Approach 1:
Instead of using notch filters that attenuate specific frequencies (which cause overshoot), the patent applies an inverse characteristic filter F(s) that pre-compensates the command signal. The filter has the inverse characteristic of the transfer function from motor velocity command to machine velocity, effectively canceling out the resonant behavior before it occurs, thereby avoiding overshoot while suppressing vibrations.
Solution Approach 2:
The patent changes the filtering approach from frequency-selective attenuation (notch filters) to inverse characteristic compensation. By designing F(s) with parameters that match the inverse of the system's transfer characteristic, the filter transforms the system response to eliminate resonance peaks without introducing phase shifts that cause overshooting.
2Stability of the object's composition
If position command correction is applied in full-closed control system, then vibration suppression is achieved, but machining shape accuracy deteriorates due to direct correction of workpiece shape
Solution Approach 1:
The patent applies inverse characteristic filtering to the position command before it reaches the control loop, rather than correcting the position command after detection. This pre-compensation approach suppresses vibrations by canceling resonant characteristics in advance, while the position command still accurately represents the desired machine trajectory, thus maintaining machining shape accuracy.
3Stability of the object's composition
If notch filters are used to suppress low-frequency resonance, then vibration suppression is improved, but device complexity increases due to adjustable filter ratios
Solution Approach 1:
The patent simplifies the filtering approach by using a fixed inverse characteristic filter F(s) whose parameters are determined by the system's inherent transfer characteristics. This eliminates the need for adjustable filter ratios and complex tuning procedures, reducing device complexity while maintaining effective vibration suppression.
Data Source
AI summary
A motor controller according to one aspect of the present invention is a motor controller for controlling a servo motor that drives a machine, including: a position command unit for outputting a position command of the machine; a position detector for detecting the position of the machine; a position controller for generating a motor velocity command based on the position command output by the position command unit and the machine position detected by the position detector; and a velocity controller for controlling the motor velocity in accordance with the motor velocity command, and is constructed such that the position controller includes a filter F(s) that approximates the inverse characteristic of the transfer characteristic from the motor velocity command to the machine velocity.