Angle Coder Error Estimation in Closed-Loop Rotary Control
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Solution Overview
Problem
Existing methods for estimating angular errors in angular encoders of precision rotary devices, such as motion simulators and centrifuges, are inadequate due to random disturbances from friction, leading to unreliable and inaccurate error estimates, especially when the system is in a closed-loop control mode.
Innovation Solution
A method and apparatus for estimating angular errors in a closed-loop system by synthesizing a specific corrector that opens the loop at specific frequencies, allowing for the estimation of encoder errors and torque ripples through a series of controlled tests at constant speeds, followed by a matrix relation to identify and compensate for these errors in real-time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an optical interferometer is used to evaluate encoder errors, then measurement precision is improved, but device complexity increases and the number of measurable positions is limited
Solution Approach 1:
The system uses its own actuator and encoder to measure encoder errors autonomously. The actuator generates torque ripples at known frequencies, and the encoder provides position measurements that are processed to extract error information, eliminating the need for external optical interferometers
Solution Approach 2:
The patent replaces the optical measurement system (interferometer with laser beams and polygonal mirrors) with an electrical/mechatronic system using the actuator's torque ripples and the encoder's position signals. This substitution simplifies the measurement device while maintaining measurement capability
2Manufacturing precision
If the system operates in closed-loop control mode, then position control accuracy is improved, but encoder error estimation reliability deteriorates due to random friction disturbances
Solution Approach 1:
The system exploits the periodic torque ripples generated by the actuator at specific frequencies (fundamental frequency and harmonics related to the number of magnet pairs). By operating at these known frequencies and using spectral analysis, the method can distinguish the deterministic torque ripple signals from random friction disturbances in the closed-loop mode
Solution Approach 2:
The method uses feedback from the encoder position measurements and actuator current signals to estimate encoder errors. By analyzing the relationship between the commanded torque and actual position at specific frequencies, the system can extract encoder error information even when closed-loop control is active and friction is present
3Device complexity
If autonomous methods are used to determine encoder errors, then device complexity is reduced, but measurement precision deteriorates due to friction-induced random disturbances
Solution Approach 1:
The patent uses the periodic torque ripples (mechanical vibrations) generated by the actuator as a reference signal. By operating at specific frequencies related to the actuator's magnetic pole pairs and analyzing the system response through spectral methods, the system can extract encoder error information with high precision without requiring complex external measurement devices
Solution Approach 2:
The method changes the operating parameters by testing at multiple constant rotation speeds and analyzing the spectral content at different frequencies. This allows the system to separate deterministic encoder errors from random friction disturbances through frequency-domain analysis, improving measurement precision while keeping the device simple
Data Source
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AI summary
The invention relates to a method for estimating angular errors of coders for a looped system comprising at least one actuator rotating on an axis and an angle coder producing a position measurement signal, and comprising a calculation device for at least controlling said actuator, the calculation device receiving a setpoint signal as input, as well as the measurement signal, for looping, the calculation device calculating in a corrector a control signal. In a test phase, a specific corrector Cωrj(q) is synthesised for a constant rotation speed ωrj, the corrector having substantially zero gain at said frequency and its harmonics, resulting in an opening of the loop at said frequencies, a matrix relation is established between the position measurements and a function of parameters characterising the coder errors and the torque ripples, the test phase is repeated with different speeds, the matrix relations are concatenated to obtain an identifiable global matrix relation, the encoder error and torque ripple parameters are estimated by resolution of the global matrix relation.