BDC Motor Ripple Detection for Sensorless Speed and Position Feedback
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Solution Overview
Problem
Existing brushed direct current (BDC) motor systems face challenges in accurately measuring motor speed and position without the need for costly and complex encoder-based or sensor-based systems, which are typically required for precise closed-loop control.
Innovation Solution
The method involves sensing coil current and motor voltage to count discontinuities, generating a ripple count, and using a computational model to estimate angular frequency and position, allowing for accurate speed and position estimation within the motor control circuitry without external sensors, while correcting for false and ghost pulses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If encoder-based or sensor-based measurement systems are used, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The motor system uses its own existing components (commutator, brushes, coil current) to generate measurement signals. The commutation process inherently produces current discontinuities that serve as speed and position indicators, eliminating the need for separate measurement systems.
Solution Approach 2:
The patent extracts measurement information from the existing coil current signal by detecting discontinuities during commutation. Instead of adding a separate measurement system, it extracts speed and position data from the current already flowing through the motor windings.
2Measurement precision
If encoder-based or sensor-based measurement systems are used, then measurement precision is improved, but manufacturing cost increases
Solution Approach 1:
The motor uses its own commutation process to generate measurement signals, requiring no additional sensors or encoders. This self-measurement capability eliminates the need for expensive external components while maintaining measurement functionality.
Solution Approach 2:
The patent uses simple, inexpensive signal processing techniques applied to existing current measurements rather than expensive encoder hardware. The measurement is achieved through basic electronic circuitry that detects current discontinuities, significantly reducing component costs.
3Device complexity
If ripple counting is used for speed measurement, then device complexity is reduced, but measurement precision deteriorates due to false and ghost pulses
Solution Approach 1:
The patent applies feedback by comparing the measured angular position against the expected commutation angle. When discrepancies are detected (indicating false or ghost pulses), the system corrects the ripple count to maintain accurate speed and position measurements.
Solution Approach 2:
The system takes preliminary action by detecting and correcting false and ghost pulses before they significantly affect measurement accuracy. The comparison with commutation angle allows early identification and correction of counting errors.
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 approach improves the accuracy of rotational speed and position estimation, integrating speed and position measurement into an integrated circuit, eliminating the need for external sensors and reducing system complexity and cost.
Implementation Method 1
counting ripples in the armature coil current or back electromagnetic force (back emf) that occur from commutation
Implementation Method 2
a DC motor generates mechanical torque from the rotation of an electromagnetic rotor in a magnetic field in response to current applied to the rotor coil
Data Source
AI summary
A motor control system and method for controlling a brushed direct current (BDC) motor using a feedback loop based on a corrected ripple count. Motor control circuitry, for example implemented in digital logic such as a microcontroller, receives a coil current signal and a motor voltage signal. Discontinuities in the coil current signal, such as caused by commutation of the BDC motor, are counted to generate a ripple count. An observer function derives an angular frequency model estimate for the values of the coil current and motor voltage signals using a computational model for the motor. A corrected ripple count is generated based on a comparison of a commutation angle of the motor with an angular position based on the angular frequency model estimate over a time interval between discontinuity pulses. A motor drive signal is adjusted based on the corrected ripple count.