3-Phase Motor Current Sensor Calibration for Surgical Robotic Actuators
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Solution Overview
Problem
Surgical robotic arms experience motor torque ripple due to distortion in phase currents, leading to rough actuation and adverse impacts on higher layer control algorithms, necessitating a calibration procedure for accurate phase current sensing and a power-on self-test to verify the integrity of phase current sensing.
Innovation Solution
A method for calibrating 3-phase motor current sensing during a power-on self-test involves monitoring the output of a first phase current sensor while adjusting phase voltages until it reaches a zero reference, capturing and storing calibration data from second and third phase current sensors, and applying this data during normal operation to adjust current sensor outputs for improved accuracy, thereby compensating for manufacturing variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If phase current sensing is performed without calibration, then the device complexity is reduced, but the measurement precision of phase current deteriorates due to manufacturing variations in current sensors
Solution Approach 1:
The patent applies preliminary action by performing calibration during the power-on self-test phase, before the motor begins normal operation. The calibration data is pre-computed and stored in memory during manufacturing or initial setup, then automatically applied during runtime to compensate for sensor variations without requiring real-time calibration procedures.
Solution Approach 2:
The system performs self-calibration during the power-on self-test sequence. The motor controller automatically executes the calibration routine, captures the calibration data from current sensors, and applies the compensation without external intervention. The system also performs self-verification by comparing newly computed calibration data against previously stored data to ensure sensing integrity.
2Object-generated harmful factors
If accurate phase current sensing is implemented through calibration, then the motor torque ripple is reduced, but the power-on self-test procedure complexity increases
Solution Approach 1:
The patent merges the calibration function with the existing power-on self-test procedure. The calibration data capture, verification, and application are integrated into the standard self-test sequence that already executes during motor initialization. This combination allows the system to perform both functions without adding separate dedicated calibration hardware or procedures.
Solution Approach 2:
The system implements feedback by capturing calibration data from current sensors during self-test, comparing the newly computed calibration data against previously stored calibration data, and using this comparison to verify sensing integrity. The calibration controller adjusts the current sensor outputs based on the verified calibration data to minimize torque ripple during normal operation.
3Measurement precision
If calibration data is captured and stored for each phase, then the current sensing accuracy is improved, but the memory requirements and data processing increase
Solution Approach 1:
The patent applies local quality by capturing and storing calibration data separately for each phase current sensor. The calibration controller captures outputs from specific phase current sensors (e.g., second and third phase sensors when first phase current is zero) and stores phase-specific calibration data that can be applied locally to compensate for variations in each individual sensor without requiring full-system recalibration.
Data Source
AI summary
A 3-phase motor driver circuit has a first input to be coupled to an output of a first phase current sensor, and a second input that represents a zero reference. A controller adjusts one or more of a first phase voltage, a second phase voltage, and a third phase voltage, until a comparison between the first input and the input indicates that the first input has reached the zero reference, and in response the controller captures an output of a second phase current sensor and an output of a third phase current sensor. The controller then stores, in memory, calibration data that is based on the captured outputs of the second and third phase current sensors. Other aspects are also described.