Motor Controller Position Feedback Correction via Commutation Switches
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Solution Overview
Problem
Incremental encoders in motor control systems are prone to errors due to electrical noise, which accumulate over time and affect the accuracy of position feedback, especially at high speeds, as noise characteristics resemble the encoder signal, making noise suppression techniques ineffective.
Innovation Solution
A motor controller system that combines incremental and absolute encoding, where a first incremental encoder provides high-speed position feedback, periodically compared to a second absolute encoder signal to detect and correct cumulative errors, using commutation switches as the absolute encoder to eliminate the need for a separate system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If incremental encoder is used for position feedback, then high data rate and low cost are achieved, but cumulative errors from electrical noise accumulate over time affecting accuracy
Solution Approach 1:
An intermediary correction circuit is introduced that periodically compares the incremental encoder's synthesized absolute position with the actual absolute position from the absolute encoder. This correction circuit acts as a mediator to detect and correct cumulative errors in the incremental encoder feedback without disrupting the high-speed incremental encoding process.
Solution Approach 2:
A feedback mechanism is implemented where the correction circuit continuously monitors the position feedback from the incremental encoder and compares it with the absolute encoder reference. When discrepancies are detected, the system generates correction signals to compensate for cumulative errors, creating a closed-loop error correction system.
2Speed
If incremental encoder signal is used to drive commutation counter, then high-speed commutation control is achieved, but noise-induced errors accumulate affecting control reliability
Solution Approach 1:
The system performs preliminary error detection and correction by periodically comparing the incremental encoder-derived position with the absolute encoder reference before these errors can significantly impact control reliability. This proactive approach prevents noise-induced errors from accumulating to critical levels.
Solution Approach 2:
A feedback loop is established where the correction circuit monitors commutation counter accuracy and provides real-time correction signals. This feedback mechanism ensures that noise-induced errors are continuously detected and compensated, maintaining control reliability at high commutation speeds.
3Measurement precision
If separate absolute encoder system is added for error correction, then cumulative error detection capability is improved, but device complexity increases
Solution Approach 1:
The correction circuit is designed to serve multiple functions: it compares incremental and absolute position signals, detects cumulative errors, generates correction signals, and provides error notifications. This multi-functional approach consolidates what could be separate systems into a single integrated correction unit, reducing overall system complexity.
Solution Approach 2:
The patent combines the incremental encoder high-speed capabilities with the absolute encoder accuracy by merging their functions through a unified correction circuit. This integration allows the system to leverage both encoder types synergistically rather than operating them as separate, complex subsystems.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This combination reduces cumulative errors while maintaining high data rates, allowing for accurate and precise control of motor position, with automatic error correction and notification features to prevent damage from large error changes.
Implementation Method 1
the position encoder may be an incremental encoder (e.g., providing a pair of quadrature phased sine or square waves) defining a direction and magnitude of change of motor position
Implementation Method 2
the position encoder may be an absolute encoder, for example, generating a unique code (e.g., a Gray code) defining an absolute position of the rotor
Implementation Method 3
the commutation switches in brushless DC motors employ non-contacting rotor position sensors, such as Hall-effect sensors, to eliminate the wear, sparking, and friction accompanying the use of brushes
Data Source
AI summary
A motor controller employs absolute encoder signals to periodically assess the existence of cumulative error in a position signal derived from an incremental encoder signal. In one embodiment the absolute encoder signals are extracted from commutation switches of the motor eliminating the need for a separate absolute encoder.