Spindle Motor Load Filtering With Variable Time Constants
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Solution Overview
Problem
Large load fluctuations in spindle motors of machine tools make automatic control of feed rates difficult and lead to machining abnormalities, as existing methods require increasing time constants for filtering, which reduces responsiveness.
Innovation Solution
A motor control device with a first low-pass filter that calculates a time constant based on spindle rotation and cutting tooth count, allowing for variable time constants to minimize load fluctuations and maintain responsiveness, and a second low-pass filter with a fixed time constant for averaging torque command values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a first-order filter with a large time constant is used to suppress load fluctuation, then load fluctuation is suppressed, but responsiveness of control deteriorates
Solution Approach 1:
The patent applies dynamics by making the time constant variable rather than fixed. The time constant calculation unit dynamically adjusts the time constant based on spindle rotation speed and cutting tooth count, allowing the filter to adapt its smoothing strength to match the actual machining conditions and frequency characteristics of load fluctuations.
Solution Approach 2:
The patent changes the parameter of time constant from a fixed value to a variable value that depends on spindle rotation speed and cutting tooth count. This parameter change allows the filter to optimize its performance for different operating conditions, suppressing load fluctuation effectively while maintaining responsiveness.
2Device complexity
If a fixed time constant is used for filtering, then the filter structure is simple, but it cannot adapt to different spindle rotation speeds and cutting conditions
Solution Approach 1:
The patent makes the filter adaptive by dynamically calculating the time constant based on spindle rotation speed and cutting tooth count. This allows the simple filter structure to adapt to different machining conditions without requiring complex multi-stage filtering systems.
Solution Approach 2:
The filter system performs self-adjustment by automatically calculating the appropriate time constant based on the current operating conditions (spindle speed and cutting tooth count). The time constant calculation unit enables the system to self-optimize without external intervention, adapting to different machining scenarios.
Data Source
AI summary
A motor control device is a motor control device which controls a spindle motor of a machine tool, the device including: a low-pass filter which averages torque command values or drive current values of the spindle motor and calculates averaged load information of the spindle motor; and a time constant calculation unit which calculates, as a time constant of the low-pass filter, a first time constant based on a cut-off frequency according to the rotation number of the spindle driven by the spindle motor, or a second time constant based on a cut-off frequency according to a value produced by multiplying a of cutting tooth number of a tool by the rotation number of the spindle.