Numerical Controller PID Gain Tuning for Spindle Vibration
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Solution Overview
Problem
Existing numerical controllers using PID control face instability due to vibration components generated by spindle rotation, which affect the spindle load and reduce the response speed of the control system, making it difficult to maintain constant load and prolong tool life.
Innovation Solution
A numerical controller that measures or predicts the vibration component caused by spindle rotation and adjusts the PID control gains to isolate the output from these vibrations, using a vibration amplitude specifying unit, gain calculating unit, and speed control unit to ensure the feed speed is unaffected by spindle rotation-induced vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a filter is introduced to reduce the frequency component of noise in spindle load feedback, then the vibration due to spindle rotation is reduced, but the response speed of the PID control decreases
Solution Approach 1:
The spindle load feedback signal is segmented into two components: a vibration component at the spindle rotation frequency and a non-vibration component at other frequencies. By separating these components through frequency-based discrimination, the system can selectively process only the relevant feedback signal for PID control, avoiding the need for a filter that would slow down the response. This segmentation allows the control system to maintain high response speed while eliminating vibration-induced instability.
2Productivity
If the feed speed is controlled to maintain constant spindle load using PID control, then the cycle time is shortened and tool life is prolonged, but the control stability deteriorates due to vibration components
Solution Approach 1:
The system implements a specialized feedback mechanism where the spindle load feedback is processed to extract only the non-vibration component. This is achieved by detecting the vibration component at the spindle rotation frequency and subtracting it from the total feedback signal. The purified feedback signal is then used in the PID control loop, ensuring that the control stability is maintained while still achieving the benefits of constant load control for reduced cycle time and extended tool life.
3Object-generated harmful factors
If the frequency component of noise is reduced by filter settings, then the vibration is suppressed, but the response speed of the control system decreases
Solution Approach 1:
Instead of using a filter with fixed frequency characteristics that slows down the response, the system changes the parameter of the feedback signal by selectively extracting the non-vibration component based on its frequency characteristics. This parameter change approach allows the system to remove noise without introducing the time delay associated with traditional filtering, maintaining fast response speed while suppressing vibration and noise.
Data Source
AI summary
A numerical controller includes: a vibration amplitude specifying unit for specifying an amplitude of a vibration component generated by a blade of a tool being brought into contact with a workpiece at a predetermined cycle, due to rotation of a spindle out of a spindle load; a gain calculating unit for calculating a gain of PID control such that an output of the feed speed is uninfluenced by the amplitude, based on the amplitude of the vibration component specified by the vibration amplitude specifying unit; and a speed control unit for outputting a feed speed of the spindle controlled by the PID control, by using the gain calculated by the gain calculating unit.