Motor Position Feedback Upsampling for Low-Speed Encoder Control
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Solution Overview
Problem
Direct-drive permanent magnet motors face challenges in achieving smooth operation at slow speeds due to low-resolution encoders, leading to torque vibrations and insufficient position and velocity feedback, especially when the motor is rotating slowly, such as during elevator operations.
Innovation Solution
A system and method that enhances the resolution of position and velocity feedback by using multiple position determination modules within the motor drive to increment high-resolution counters based on the current value of a traditional counter, averaging these values to provide a more robust approximation of the motor shaft position, which is then used by the speed regulator to improve control accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a low-resolution encoder is used in a direct-drive permanent magnet motor, then the device complexity is reduced and cost is lowered, but the measurement precision of position and velocity feedback deteriorates, causing torque vibrations and insufficient control accuracy during slow-speed operation
Solution Approach 1:
The patent introduces an intermediary processing system between the encoder and the control algorithm. Multiple position determination modules act as intermediaries that sample the encoder signal at different frequencies and integrate counts over multiple sampling periods. This intermediary layer processes the low-resolution encoder output to generate high-resolution position and velocity feedback without requiring a high-resolution encoder hardware
Solution Approach 2:
The patent segments the position determination function into multiple independent modules that operate in parallel. Each module samples the encoder at a different frequency and integrates counts independently. The results from multiple modules are then combined to produce the final high-resolution position and velocity feedback. This segmentation allows the system to achieve high measurement precision through computational integration rather than through a single high-resolution encoder
2Speed
If the motor operates at slow speeds, then the application requirements are met (e.g., elevator smooth operation), but the number of encoder counts received per sampling interval decreases, deteriorating the velocity feedback resolution and control accuracy
Solution Approach 1:
The patent performs preliminary integration of encoder counts over multiple sampling periods before the velocity calculation is needed. By accumulating counts in advance across multiple sampling intervals and multiple determination modules, the system builds up sufficient resolution data even when the motor is rotating slowly. This preliminary action ensures that when velocity feedback is required, high-resolution data is already available
Solution Approach 2:
The patent maintains continuous integration of encoder counts across multiple sampling periods and multiple determination modules. Rather than relying on a single sampling interval, the system continuously accumulates position information from multiple sources and time periods. This continuous integration ensures that velocity feedback resolution is maintained across all operating speeds, including slow-speed operation
Data Source
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AI summary
A motor drive receives a position feedback signal from an encoder operatively connected to a motor. The motor drive executes multiple position determination modules to determine multiple approximate motor shaft positions. On each iteration of a position determination module, the motor drive samples the feedback signal, increments a pulse counter when a new encoder pulse is received, adds the pulse counter to a high-resolution pulse counter register, and calculates an approximate motor position as a function of the value of the high-resolution pulse count register. The motor drive averages the multiple approximate positions, and the result is used by a speed regulator module executed on the same motor drive to achieve the desired operation of the motor. The speed regulator iterates at a slower rate than any of the multiple position determination modules.