Inertia Estimation Controller Using Sine-Wave Excitation
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Solution Overview
Problem
Existing methods for estimating the inertia of an article driven by an electric motor are inefficient due to long operation times, limited operation range, instability in motor control, variability in estimation accuracy, and noise interference, especially when the inertia changes with workpiece attachment or detachment.
Innovation Solution
A controller system that uses a sine-wave command to estimate inertia by averaging peak current and acceleration values over multiple cycles, allowing for rapid and accurate inertia calculation, and adjusts position and speed gains to stabilize motor control, reducing noise influence and operation time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If inertia is estimated by operating the motor for a relatively long period to stabilize generated torque, then estimation accuracy is improved, but operation time increases and productivity decreases
Solution Approach 1:
The patent applies periodic action by using a sine-wave command that periodically varies torque demand. By analyzing the motor's response to this periodic excitation signal, the inertia estimation can be performed rapidly without requiring long stabilization periods. The periodic sine-wave command allows the system to extract inertia information from the oscillating response, achieving accurate estimation in a short time frame.
2Productivity
If inertia is estimated using current feedback and acceleration feedback during motor operation, then real-time estimation is enabled, but noise in feedback signals deteriorates estimation accuracy
Solution Approach 1:
The patent converts the harmful effect of noise in feedback signals into a benefit by using periodic sine-wave excitation. The regular, predictable nature of the sine-wave command allows the system to distinguish between the desired response signal and random noise through spectral analysis or averaging techniques. The periodic excitation creates a strong signal at a known frequency that can be easily separated from noise components.
3Reliability
If the motor operation range is limited in a machine tool, then the machine tool can operate within safe boundaries, but sufficient operation range for inertia estimation cannot be obtained
Solution Approach 1:
The patent resolves this contradiction by using periodic sine-wave commands that operate within the motor's safe operating range while still providing sufficient excitation for accurate inertia estimation. The sine-wave signal can be tuned to appropriate amplitudes and frequencies that keep the motor within reliable operating boundaries while generating enough dynamic response to accurately determine inertia parameters.
4Adaptability or versatility
If workpiece replacement is performed frequently, then production flexibility is improved, but sufficient time for inertia estimation cannot be obtained
Solution Approach 1:
The patent enables rapid inertia estimation through periodic sine-wave excitation, reducing the estimation time to a fraction of what traditional methods require. This rapid estimation capability allows the system to quickly adapt to workpiece changes, maintaining high production flexibility while ensuring accurate inertia values are obtained for each new workpiece configuration.
Data Source
AI summary
A controller and a control system capable of estimating inertia of an article to be driven in a short period of time, with a small operation range of an electric motor. The controller for the motor has an inertia estimating part which includes a sine-wave command generating part which adds a sine-wave command to a torque command for the motor; a current feedback sampling part which obtains a current value of the motor; a speed feedback sampling part which obtains a speed feedback of the motor; an acceleration calculating part which calculates an acceleration value based on the speed feedback; and an estimated inertia calculating part which estimates the inertia of the article, based on a representative current value, a representative acceleration value and a torque constant of the motor, which are calculated from current and acceleration values in a plurality of cycles of the sine-wave command and stored in a sampling data storing part.