Brushless Motor Initial Position Detection via Electrical Angle Control
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Solution Overview
Problem
Brushless motors lack an effective method for accurately detecting the initial position of the rotor without a position sensor, leading to potential misalignment and operational issues during power-on and rotation control.
Innovation Solution
A control device that includes an obtaining unit for rotation information and a controller to gradually change the electrical angle of the rotating magnetic field, detecting the initial position when the rotor's rotation direction changes and the difference in rotation amounts becomes smaller than a threshold, allowing precise control of the rotor's position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a position sensor is used to detect the initial position of the rotor, then the position detection accuracy is improved, but the device complexity and cost increase
Solution Approach 1:
The patent extracts the position detection function from a dedicated position sensor and implements it through the existing encoder by analyzing rotation information. The controller detects the initial position by monitoring rotation direction changes and rotation amounts during a change control period, eliminating the need for a separate position sensor while maintaining detection accuracy
Solution Approach 2:
The system uses its own encoder (already present for rotation control) to perform the additional function of initial position detection. The encoder's rotation information is processed by the controller to determine initial position without requiring external sensors, making the system self-sufficient
2Productivity
If the electrical angle is changed rapidly to reach operating speed quickly, then the productivity is improved, but the measurement precision of initial position detection deteriorates
Solution Approach 1:
The patent implements a change control period during which the electrical angle is gradually changed before normal operation begins. During this preliminary phase, the controller monitors rotation direction changes and rotation amounts to accurately detect the initial position. After successful detection, the system transitions to normal operation mode, ensuring both accurate detection and quick productivity
3Device complexity
If no initial position detection method is implemented, then the device complexity is reduced, but the reliability of motor operation deteriorates due to potential misalignment
Solution Approach 1:
The patent implements a feedback mechanism where the controller continuously monitors rotation information from the encoder during the change control period. By detecting when the rotation direction changes and the rotation amount meets specific criteria, the system feedback-determines the initial position, ensuring reliable motor operation without adding complex hardware
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
Enables accurate initial position detection of the rotor, reducing the risk of misalignment and operational issues, and ensuring smooth power transmission and control of the load attached to the motor.
Implementation Method 1
a controller to specify a current that is provided to a coil of the brushless motor to control a rotating magnetic field generated by the coil
Data Source
AI summary
A control device includes an obtaining unit that obtains rotation information indicating an amount of rotation and a rotation direction of a rotor of a brushless motor; and a controller that specifies a current to be provided to a coil of the brushless motor to control a rotating magnetic field generated by the coil by performing change control for gradually changing an electrical angle of the rotating magnetic field, detecting, as an initial position of the rotor, a position in which the rotor faces magnetic poles generated at an electrical angle when the rotation direction obtained during the change control changes from a first direction to a second direction and a difference between the amount of rotation in the first direction and that in the second direction obtained during the change control becomes smaller than a first threshold, and controlling the rotating magnetic field in accordance with the initial position.