Motor Control Cogging Torque Compensation in Tilted Axes
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Solution Overview
Problem
Existing motor control systems struggle to accurately calculate cogging torque compensation when components due to gravitational torque or other factors are superimposed on the torque command during constant slow-speed feed operations, leading to improper compensation and increased motor speed fluctuations.
Innovation Solution
A motor control apparatus that includes a torque command monitoring unit, an approximation calculation unit, a second torque command calculation unit, and a frequency analyzing unit to isolate and remove non-cogging torque components, allowing for precise calculation of cogging torque compensation by performing frequency analysis on the cleaned torque command waveform.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If frequency analysis is performed directly on the torque command during slow-speed feed operation, then cogging torque compensation can be calculated, but the calculation becomes inaccurate when gravitational torque or other components are superimposed on the torque command
Solution Approach 1:
The patent extracts and removes non-cogging torque components (such as gravitational torque and monotonically varying components) from the torque command before performing frequency analysis. This is achieved by calculating approximation components that represent these external disturbances and subtracting them from the original torque command, thereby isolating the cogging torque components for accurate analysis.
Solution Approach 2:
The patent segments the torque command into distinct components: cogging torque components and non-cogging torque components (such as gravitational torque). By dividing the torque command waveform into these separate elements, the system can analyze each component independently, allowing accurate extraction of cogging torque characteristics even when other forces are present.
2Adaptability or versatility
If the motor is used in a tilted axis configuration, then the motor can perform feed operations on inclined surfaces, but gravitational torque components are superimposed on the torque command making cogging compensation calculation difficult
Solution Approach 1:
The patent introduces an intermediary processing step that calculates approximation components representing gravitational torque and other external disturbances. These approximation components act as intermediaries that bridge the gap between the raw torque command (containing mixed components) and the cleaned torque command suitable for frequency analysis, enabling accurate cogging torque extraction in tilted axis configurations.
3Productivity
If simple Fourier transform is applied to the torque command, then frequency analysis can be performed quickly, but proper compensation cannot be obtained when monotonically increasing or decreasing components are present
Solution Approach 1:
The patent performs preliminary actions by calculating approximation components and removing non-cogging torque elements from the torque command before conducting frequency analysis. This pre-processing step eliminates monotonically varying components and gravitational torque influences, ensuring that the subsequent Fourier transform or frequency analysis operates on a cleaned signal that accurately represents only the cogging torque characteristics.
Data Source
AI summary
A motor control apparatus that can calculate a proper amount of cogging torque compensation even in cases where components due to other factors than cogging torque (for example, components due to gravitational torque, etc.) are superimposed on a torque command being output during constant slow-speed feed operation. The motor control apparatus includes: a torque command monitoring unit which monitors a torque command when the motor is caused to operate at a constant speed; an approximation calculation unit which calculates a torque command approximation component by approximation from the torque command monitored over an interval equal to an integral multiple of the cogging torque period of the motor; a second torque command calculation unit which calculates a second torque command by subtracting the torque command approximation component from the torque command; a second torque command frequency analyzing unit which extracts frequency components, each at an integral multiple of the fundamental frequency of the cogging torque, by performing frequency analysis on the thus calculated second torque command; and a cogging compensation amount calculation unit which calculates the amount of cogging compensation from the amplitude and phase of the extracted frequency components.