Feed Axis Control Unit Frequency Characteristic Measurement
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Solution Overview
Problem
Existing methods for measuring frequency characteristics in feed axis drive systems are inaccurate due to friction and lost motion, leading to reduced gain characteristics and inability to optimize feedback-control controllers, and cause fretting issues with sine wave excitation.
Innovation Solution
A method involving a feed axis control unit that uses a constant velocity command with a sine wave of predetermined amplitude less than the velocity reference value, and resampling input and output signals to correct amplitude attenuation, allowing for accurate frequency characteristic measurement without fretting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If white noise or M-sequence signal is used to measure frequency characteristic, then measurement can be performed, but friction and lost motion reduce gain characteristic and cause inaccurate measurement
Solution Approach 1:
The patent changes the excitation signal from white noise or M-sequence to a sine wave signal with specifically controlled amplitude parameters. The amplitude is set to be larger than the lost motion amount to overcome friction and nonlinear spring characteristics, ensuring accurate frequency characteristic measurement without being affected by these detrimental factors.
2Measurement precision
If sine wave signal is used to excite all frequencies, then frequency characteristic can be measured, but measurement time increases and fretting occurs due to continuous excitation
Solution Approach 1:
The patent employs periodic sine wave excitation at each frequency point to measure frequency characteristics. This periodic approach allows for efficient measurement without requiring continuous excitation across all frequencies simultaneously, thereby reducing measurement time and preventing fretting caused by prolonged vibration.
3Object-affected harmful factors
If small amplitude signal is used for excitation, then measurement can be performed, but friction and lost motion decrease gain characteristic and prevent accurate measurement
Solution Approach 1:
The patent applies preliminary anti-action by setting the excitation amplitude to be larger than the lost motion amount before measurement begins. This pre-established amplitude condition ensures that the excitation signal overcomes the nonlinear spring characteristic and friction forces, preventing these harmful factors from degrading measurement accuracy.
4Force
If velocity reference value is not considered, then excitation can be applied, but amplitude may be too large causing excessive displacement
Solution Approach 1:
The patent implements dynamic adjustment of excitation amplitude based on the velocity reference value. The amplitude is set proportional to the velocity reference value, creating a dynamic relationship that adapts to different operating conditions. This ensures the amplitude is sufficiently large to overcome friction and lost motion while remaining proportional to prevent excessive displacement.
Data Source
AI summary
A method measures a frequency characteristic at a feed axis control unit configured to drive a motor in accordance with a velocity command value to control a velocity or a position of a movable portion of a driven body. The velocity command value includes a velocity reference value from a host device or a velocity command calculator and a sweep signal swept in order to measure the frequency characteristic. The method includes moving the feed axis in one direction by commanding the velocity reference value where a moving velocity of the feed axis is constant, exciting by providing a sine wave having an amplitude less than a magnitude of the velocity reference value to the sweep signal, and measuring the frequency characteristic of a feed axis drive system including the motor.