Tunable Ripple-Counting Circuit for Accurate Rotary Position Detection
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Solution Overview
Problem
Existing rotary position detection methods for brushed DC motors face challenges in accuracy due to adaptability issues under changing conditions such as supply voltage, coil current, and loading, leading to missed ripples or false indications in sensorless ripple counting.
Innovation Solution
A tunable circuit that adjusts its operation based on measured voltage and current signals to filter and count ripples, using a bandpass filter with a tunable center frequency and passband width, compensating for errors in rotational speed estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If ripple counting is used for speed and position detection, then the complexity is reduced compared to mechanical sensors, but the accuracy deteriorates under changing motor conditions
Solution Approach 1:
The patent implements dynamic adaptation by continuously adjusting the filter parameters (center frequency and bandwidth) based on the estimated rotational speed. The system transitions from a static filter to a dynamic one that tracks speed variations, allowing the ripple counting method to maintain accuracy under changing motor conditions while keeping the overall system complexity low compared to mechanical sensors.
Solution Approach 2:
The patent changes the parameters of the bandpass filter (center frequency and bandwidth) based on the estimated speed to optimize ripple detection. By adapting these parameters dynamically, the system maintains measurement precision without requiring complex mechanical sensor hardware, thus resolving the contradiction between simplicity and accuracy.
2Device complexity
If a fixed bandpass filter is used for ripple detection, then the device complexity is reduced, but the adaptability to changing motor conditions deteriorates
Solution Approach 1:
The system implements dynamics by making the filter parameters variable rather than fixed. The center frequency and bandwidth are continuously adjusted based on the estimated speed, enabling the system to adapt to changing motor conditions such as varying supply voltage and loading while maintaining a relatively simple overall architecture.
Solution Approach 2:
The patent employs feedback by using the estimated speed information to adjust the filter parameters. This closed-loop approach allows the system to automatically adapt to changing conditions without increasing complexity significantly, as the feedback signal is derived from the same ripple counting process.
3Measurement precision
If mechanical sensors are used for position detection, then the accuracy is improved, but the device complexity and cost increase
Solution Approach 1:
The patent replaces mechanical sensors with an electronic ripple counting system that uses bandpass filtering and signal processing to detect rotor position. This substitution eliminates the need for physical sensors while achieving comparable accuracy through adaptive filtering techniques that track speed variations and optimize ripple detection.
Solution Approach 2:
The system creates an electrical copy of the mechanical sensor functionality by processing the current signal to extract position information. Through adaptive bandpass filtering and ripple counting, the system replicates the position detection capability of mechanical sensors without requiring physical contact or additional hardware components.
Data Source
AI summary
In some examples, an apparatus includes a filter having first and second inputs, a current signal input, and an output. The apparatus also includes a speed observer having a voltage signal input, a current signal input, and an output, the output of the speed observer coupled to the second input of the filter. The apparatus also includes a ripple counter having an input and an output, the input of the ripple counter coupled to the output of the filter. The apparatus also includes a ripple processor having first and second inputs, and an output, the first input of the ripple processor coupled to the output of the ripple counter, the second input of the ripple processor coupled to the output of the speed observer, and the output of the ripple processor coupled to the first input of the filter.