Dynamic Notch Filtering for Multi-Axis Oscillation Control
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Solution Overview
Problem
Mechanical oscillations in multi-axis control systems, such as robots, occur due to backlash and flexing in mechanical linkages, leading to positioning errors and reduced productivity due to the need for increased settling time or reduced acceleration/deceleration rates.
Innovation Solution
A dynamic notch filter is implemented in each motor drive of the multi-axis control system, with its operation updated based on position and loading, allowing for faster update rates and reduced oscillations by filtering out undesired frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional mechanical linkages with backlash and compliant couplings are used, then the system can accommodate manufacturing tolerances and mechanical flexibility, but mechanical oscillations occur during acceleration and deceleration, requiring increased settling time or reduced acceleration rates
Solution Approach 1:
The patent replaces mechanical solutions (rigid couplings, reduced backlash mechanisms) with a control system solution. A dynamic notch filter is implemented in the motor drive control system to attenuate oscillations at specific frequencies. This allows the mechanical system to maintain its compliant couplings and backlash for tolerance accommodation while the control system electronically filters out the harmful oscillations, thereby maintaining both productivity and stability.
Solution Approach 2:
The patent changes the parameters of the control system by implementing a dynamic notch filter that adjusts filter frequencies and depths based on operating conditions. The filter dynamically modifies control parameters (gain, frequency attenuation) to counteract oscillations during different phases of motion (acceleration, deceleration, positioning), allowing high acceleration rates without excessive oscillation.
2Speed
If higher acceleration and deceleration rates are used to improve productivity, then throughput increases, but mechanical oscillations increase due to excitation of spring-mass systems in the mechanical linkages
Solution Approach 1:
Instead of mechanically reducing oscillation sources (which would limit acceleration capability), the patent uses a control system approach. The dynamic notch filter in the motor drive attenuates oscillations generated during high acceleration and deceleration events, allowing the system to maintain high acceleration rates while suppressing harmful mechanical oscillations through electronic filtering.
Solution Approach 2:
The dynamic notch filter acts as an intermediary between the motor control system and the mechanical linkage. It processes the control signals to preemptively counteract oscillations before they fully develop in the mechanical system, or attenuates them after generation, thereby mediating between the high acceleration commands and the oscillation-prone mechanical components.
3Measurement precision
If settling time is increased to allow oscillations to decay, then positioning accuracy improves, but productivity decreases due to reduced throughput
Solution Approach 1:
The patent replaces passive waiting for oscillations to decay naturally (which requires time) with an active control solution. The dynamic notch filter actively suppresses oscillations at their source frequencies, causing them to decay much faster or be prevented entirely. This maintains positioning accuracy while dramatically reducing the settling time required, thereby improving throughput.
Solution Approach 2:
The dynamic notch filter is configured to preemptively counteract oscillations before they significantly impact positioning. By filtering at the anticipated oscillation frequencies during acceleration and deceleration phases, the system prevents large oscillations from developing, reducing the time needed for settling while maintaining accuracy.
Data Source
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AI summary
A system and method for reducing mechanical oscillations in a multi-axis control system provides a first command for a dynamic notch filter at a first update rate to multiple motor drives. Each motor drive is operatively connected to a motor for an axis in the multi-axis control system. Each motor drive receives a second command for desired operation of the motor at a second update rate. Operation of the dynamic notch filter in each motor drive is changed as a function of the first command at the first update rate, and each motor drive generates a desired output voltage for desired operation of the motor at a third update rate. The third update rate is faster than the second update rate, the second command is passed through the dynamic notch filter to generate a filtered command, and the desired output voltage is generated as a function of the filtered command.