PMDC Motor Sensor Diagnostics Using Velocity Observer Feedback
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Solution Overview
Problem
Permanent magnet DC motors in power steering systems are susceptible to single point failures due to reliance on a single rotational position encoder, which can be hazardous and lead to inaccurate motor control.
Innovation Solution
A method and system for diagnosing sensor errors in PMDC motors using a position sensor, current sensor, and a motor velocity observer to determine a difference velocity, adjusting an adaptive threshold based on operating conditions, and performing actions in response to detected errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single rotational position encoder is used to measure motor position, then device complexity is reduced, but system reliability deteriorates due to single point failures
Solution Approach 1:
The system changes the parameter of velocity estimation from direct sensor measurement to model-based calculation. By using the motor model to calculate expected velocity from current and voltage commands, the system creates an alternative velocity source that does not depend on the position sensor, thereby improving reliability without adding hardware complexity.
Solution Approach 2:
The invention replaces the mechanical/physical velocity measurement system (position encoder) with an electrical/model-based velocity estimation system. The motor model uses electrical measurements (current, voltage) and mathematical relationships to substitute for the physical position sensor, eliminating the single point of failure while maintaining simplicity.
2Reliability
If sensor error detection is implemented, then system safety is improved, but device complexity increases due to additional diagnostic components
Solution Approach 1:
The system implements feedback by continuously comparing the model-calculated velocity with the position-sensor-measured velocity. This feedback mechanism enables automatic detection of sensor errors when the velocities diverge beyond a threshold, providing safety monitoring without requiring separate diagnostic hardware.
Solution Approach 2:
The motor model serves a dual purpose: it controls the motor operation and simultaneously provides velocity estimation for diagnostic purposes. The same model used for control inherently provides the reference velocity needed for error detection, eliminating the need for separate diagnostic systems and reducing overall complexity.
3Measurement precision
If adaptive threshold adjustment is implemented, then measurement precision is improved for sensor error detection, but device complexity increases
Solution Approach 1:
The velocity threshold is made dynamic rather than fixed. The threshold adapts based on operating conditions such as motor speed and load, allowing the system to maintain high detection precision across varying operational ranges. This dynamic adjustment prevents false alerts while ensuring accurate error detection, achieved through straightforward conditional logic rather than complex mechanisms.
Data Source
AI summary
Technical solutions are described for diagnosing a sensor error in an actuator having a permanent magnet DC (PMDC) motor, including: measuring, by a position sensor, a measured position of the PMDC motor; determining, based on the measured position, an estimated motor velocity; measuring, by a current sensor, a measured current in the PMDC motor; determining, based on the measured current in the PMDC motor, a voltage command for the PMDC motor; determining, based on the measured current and the voltage command, and using a motor velocity observer, an observed velocity of the PMDC motor; determining a difference velocity as a difference between the estimated motor velocity and the observed velocity; determining, based on the difference velocity, the sensor error; and performing an action in response to determining the sensor error.