Motor Torque Ripple Compensation via Rotor Angle Profiles
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Solution Overview
Problem
DC brushless motors exhibit torque ripples due to non-uniform torque output at different rotation angles with the same input current, affecting their performance in applications like teleoperative surgery, where precise force control is crucial.
Innovation Solution
A method and system for torque compensation, involving determining a torque profile for each motor, storing a compensation profile based on rotor angle, and adjusting the input signal to the motor during operation to minimize torque ripples, using a processor and memory in a control system for a teleoperative medical device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed nominal mapping between input current and torque output is used, then the motor control is simple, but torque ripples occur causing non-uniform torque output at different rotation angles
Solution Approach 1:
The system performs preliminary characterization of the motor's torque profile by measuring torque output at multiple rotation angles across multiple revolutions. This preliminary data collection enables the creation of a compensation profile that is stored and applied during normal operation, eliminating torque ripples without requiring complex real-time calculations.
Solution Approach 2:
The system changes the input current parameter dynamically based on the rotor angle. By applying angle-dependent current adjustments derived from the measured torque profile, the system compensates for torque ripples and achieves uniform torque output throughout the rotation cycle.
2Manufacturing precision
If torque compensation based on torque profile and rotor position is implemented, then torque output uniformity is improved, but control system complexity increases
Solution Approach 1:
The compensation profile is pre-calculated and stored in memory based on measured torque data at various rotation angles. During operation, the controller simply retrieves the appropriate compensation value from the stored profile based on the current rotor angle, avoiding complex real-time torque calculations while achieving uniform torque output.
Solution Approach 2:
The system uses its own measured torque profile data to generate the compensation profile internally. By characterizing its own torque ripples and creating a self-correction mechanism, the motor control system eliminates the need for external calibration or complex control algorithms.
3Manufacturing precision
If multiple separate compensation profiles are stored for different motors, then individual motor torque ripples are compensated accurately, but memory requirements and data management complexity increase
Solution Approach 1:
The system divides the compensation data into separate profiles for each motor, allowing individualized torque ripple compensation. Each motor's unique torque profile is measured and stored separately, enabling precise compensation tailored to each motor's characteristics without interfering with other motors.
Solution Approach 2:
The compensation profiles are stored in an efficient parameterized format that captures the essential torque ripple characteristics. By representing the compensation data as angle-dependent current adjustments rather than raw torque measurements, the system reduces the effective data storage requirements while maintaining compensation accuracy.
Data Source
AI summary
A method for torque compensation of a motor associated with a medical instrument includes determining a torque profile for a motor, the torque profile defining torque output as a function of rotor angle and during operation of the motor, compensating for deviations in the torque profile by adjusting an input signal to the motor, the compensating being based on the torque profile and rotor position.