Brushless Motor Rotor Position Detection via Back-EMF
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Solution Overview
Problem
Existing image forming apparatuses using brushless motors for rotary polygon mirrors face instability in rotation control due to placement dispersion of Hall elements, making accurate rotor position detection difficult.
Innovation Solution
The apparatus employs a light source, photosensitive member, brushless motor with a stator and rotor, and a control unit that detects the rotor's position based on induced voltages in the coils, eliminating the need for Hall elements by using a voltage detecting unit and energization switching unit to control the motor's rotation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Hall elements are used to detect rotor position, then position detection can be performed, but placement dispersion of Hall elements makes accurate detection difficult and rotation control unstable
Solution Approach 1:
The invention extracts and eliminates the Hall elements from the brushless motor structure. Instead of using Hall elements for rotor position detection, the invention uses the back electromotive force (EMF) generated in the stator coils during motor operation to detect rotor position. This removes the problematic component that caused placement dispersion issues and unstable rotation control.
Solution Approach 2:
The invention introduces the back EMF signal as an intermediary to detect rotor position. The voltage detecting unit measures the back EMF generated in the stator coils, which indirectly provides rotor position information without requiring direct physical sensors near the rotor. This intermediary approach avoids the placement precision issues of Hall elements.
2Ease of operation
If Hall elements are placed near the rotor for position detection, then rotation control can be performed, but the component count and device size increase
Solution Approach 1:
The stator coils serve multiple functions: they generate magnetic fields for motor operation and simultaneously function as sensors for rotor position detection through back EMF measurement. This multi-functionality eliminates the need for separate Hall element sensors, reducing component count and device complexity while maintaining rotation control capability.
Solution Approach 2:
The motor's own operational components (stator coils) provide the detection function. The back EMF generated during normal motor operation is utilized for rotor position detection, making the system self-sufficient without requiring external sensing components. This self-service approach reduces overall device 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
This approach stabilizes the rotation control of the brushless motor, reduces component count and size, and enhances reliability by accurately detecting the rotor's position and rotation speed without Hall elements, thereby improving the image forming process.
Implementation Method 1
a voltage detecting unit that outputs a detection signal based on induced voltages that are generated in the coils by rotation of the rotor
Data Source
AI summary
An image forming apparatus includes: a light source that emits a light beam; a photosensitive member; a brushless motor including a stator where a plurality of coils are placed and a rotor where a plurality of magnets are placed; a rotary polygon mirror, which is rotated by the brushless motor, and which periodically deflects the light beam emitted from the light source to sequentially form scanning lines on the photosensitive member; an energization switching unit that turns on and off energizations of the coils; a voltage detecting unit that outputs a detection signal based on induced voltages that are generated in the coils by rotation of the rotor; and a control unit that controls turning on/off of the energizations by the energization switching unit based on the detection signal.