Brushless Motor Rotor Position Correction via Induced Voltage
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Solution Overview
Problem
Brushless motors with high magnetic poles suffer from significant detection errors in rotational position due to assembly errors in Hall element sensors, affecting control accuracy, especially in high-output applications.
Innovation Solution
An electric working machine with a rotational position sensor, detector, calculator, and memory processor that corrects detection errors by calculating a correction value based on differences between sensor and detector readings, using induced voltages in windings to accurately determine rotor position, even with assembly errors, and stores this correction value for improved control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Hall elements are used to detect rotational position, then the brushless motor can be controlled, but detection errors increase with assembly errors and number of magnetic poles
Solution Approach 1:
The patent introduces an intermediary correction mechanism that mediates between the Hall element sensor and the actual rotor position. A correction value is calculated based on the difference between Hall element detection results and detector results, then applied to compensate for assembly errors. This intermediary correction layer resolves the contradiction by maintaining control functionality while improving measurement precision.
Solution Approach 2:
The patent replaces the purely mechanical/Hall-element-based detection system with a hybrid system that incorporates electrical detection through induced voltages in windings. The detector uses electromagnetic induction to measure rotor position independently of mechanical assembly errors, substituting the error-prone mechanical sensing approach with an electrical measurement approach that is inherently more accurate.
2Power
If the number of magnetic poles is increased for high output, then motor power increases, but detection errors of rotational position increase
Solution Approach 1:
The patent implements a feedback mechanism where the detector continuously monitors the actual rotor position through induced voltages, and this information is fed back to calculate correction values for the Hall element readings. The feedback loop compensates for the increased detection errors that occur with higher pole counts, allowing the motor to maintain high power output while preserving rotational position detection accuracy.
3Measurement precision
If correction value calculation is performed continuously, then detection accuracy is maintained, but memory update frequency and system complexity increase
Solution Approach 1:
The patent employs periodic action by calculating and updating correction values only at specific intervals or under specific conditions (such as when the motor is inertially rotated), rather than continuously. This periodic update strategy maintains detection accuracy while reducing computational burden and memory update frequency, thereby lowering system complexity.
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
The system accurately corrects detection errors, enhancing control precision of brushless motors by minimizing assembly-related errors and maintaining accuracy across varying rotational speeds, reducing the need for frequent memory updates and alerting users to potential abnormalities.
Implementation Method 1
The rotational position sensor detects a rotational position of the rotor based on a variation in a magnetic field associated with rotation of the rotor
Implementation Method 2
The detector detects the rotational position of the rotor based on induced voltages individually generated in each of the plurality of windings
Data Source
AI summary
An electric working machine according to one aspect of the present disclosure comprises a brushless motor, a rotational position sensor, a detector, and a calculator. The calculator detects, when the brushless motor is inertially rotated, a difference between a detection result obtained by the rotational position sensor and a detection result obtained by the detector and calculates a correction value, based on the difference, for correcting the detection result obtained by the rotational position sensor.