Motor Rotor Position Detection with Offset Cancellation
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Solution Overview
Problem
Conventional methods fail to accurately transmit signals from Hall elements in motors due to external magnetic fields, causing signal offsets that disrupt the detection of rotor position.
Innovation Solution
A motor configuration that includes a first magnetic sensor detecting the rotor's position and a second magnetic sensor positioned π/N radians away in the rotation direction, with a signal amplifier and pulse signal generation unit to cancel offset components caused by external magnetic fields, allowing only the sine wave signals from the rotor to be extracted.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Hall element is used to detect rotor position, then the rotor position can be detected, but an offset occurs in the signal when an external magnetic field is brought close to the motor, causing inaccurate signal transmission
Solution Approach 1:
A second Hall element is introduced as an intermediary sensor positioned at a specific location (shifted by π/N in the rotation direction) to detect the external magnetic field interference separately. The signals from both Hall elements are processed together to extract the rotor position signal while canceling the offset caused by external magnetic fields.
Solution Approach 2:
The external magnetic field interference, which was previously harmful and caused offset, is converted into a useful signal source. By using the second Hall element to detect the same external magnetic field and processing both signals together, the interference is transformed into information that enables offset cancellation and accurate rotor position detection.
2Measurement precision
If conventional offset cancellation methods are used for Hall elements, then offset caused by parasitic capacitance can be canceled, but offset caused by external magnetic fields cannot be removed
Solution Approach 1:
The dual Hall element configuration provides universal offset cancellation capability for multiple types of offset sources. The system can simultaneously cancel offset caused by parasitic capacitance (through conventional methods) and offset caused by external magnetic fields (through the differential processing of the two Hall element signals), making the solution versatile against various interference sources.
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
Effectively removes noise and offset signals from external magnetic fields, ensuring accurate transmission of rotor position signals to the microcontroller with a 50% duty ratio pulse signal, enhancing motor control precision.
Implementation Method 1
a first magnetic sensor that detects a rotational position of a rotor; a second magnetic sensor arranged at a position shifted by π/N in a rotation direction of the rotor
Data Source
AI summary
An offset of an output voltage of a magnetic sensor caused by an external magnetic field is removed. A motor according to a disclosed embodiment includes: a first magnetic sensor that detects a rotational position of a rotor; a second magnetic sensor arranged at a position shifted by π/N in a rotation direction of the rotor with respect to the first magnetic sensor when the number of pole pairs is N; a signal amplifier that amplifies a difference between a first signal which is a signal output from the first magnetic sensor and a second signal which is a signal output from the second magnetic sensor; and a pulse signal generation unit that converts an output signal of the signal amplifier into a pulse signal.