Brushless Motor Rotor Position Detection via Optical Timing
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Solution Overview
Problem
The existing image forming apparatuses using brushless motors face challenges in accurately detecting the rotor position at high speeds or during acceleration, leading to inaccurate phase switching control due to prolonged regeneration periods and increased regeneration period to cycle ratios, which complicates the detection of the rotor position based on inductive voltage.
Innovation Solution
The apparatus employs a light sensor to detect the timing of a light beam reflected by a rotating polygon mirror and acquires information about the relationship between this timing and the inductive voltage reaching a reference value in non-energization states, allowing for phase switching control of the brushless motor without relying on Hall elements, using a processor to manage this process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If rotor position detection is performed based on inductive voltage in brushless motors operating at high speeds or during acceleration, then the detection accuracy deteriorates due to prolonged regeneration periods, but using Hall elements or other sensors increases device complexity and cost
Solution Approach 1:
The patent introduces a light sensor as an intermediary device to detect rotor position indirectly through the polygon mirror's rotation, rather than directly measuring inductive voltage from the motor coils. The light sensor detects reflected light from the rotating polygon mirror, providing a reliable reference signal for determining rotor position without being affected by the motor's electrical state during acceleration or high-speed operation
Solution Approach 2:
The patent replaces the electrical measurement method (inductive voltage detection) with an optical measurement method (light reflection detection). By using a light source, light sensor, and rotating polygon mirror, the system converts the electrical problem of inductive voltage detection into an optical detection problem that is not affected by the motor's regeneration period or electrical noise during acceleration
2Reliability
If rotor position is detected using inductive voltage during high-speed operation, then the regeneration period to cycle ratio increases causing detection errors, but adding sensors like Hall elements increases apparatus cost and size
Solution Approach 1:
The polygon mirror serves as an intermediary mechanical element that couples the motor's rotation to the light sensor. The light sensor detects the rotation of the polygon mirror, which is directly driven by the motor, providing a reliable indicator of rotor position that is independent of the electrical conditions during acceleration or high-speed operation
Solution Approach 2:
The patent substitutes the electrical sensing mechanism with an optical-mechanical sensing mechanism. The light source emits light that reflects off the rotating polygon mirror surfaces, and the light sensor detects these reflected light beams, converting mechanical rotation into detectable optical signals that are not affected by electrical noise or regeneration periods
3Device complexity
If no sensors are used for rotor position detection, then device complexity and cost are reduced, but detection accuracy deteriorates under high-speed and acceleration conditions due to prolonged regeneration periods
Solution Approach 1:
The system uses a light sensor as an intermediary detection device that indirectly measures rotor position through the polygon mirror's rotation. This intermediary approach allows the system to maintain simple motor construction without Hall elements while achieving reliable position detection through optical means that are not affected by the motor's electrical regeneration period
Solution Approach 2:
The patent replaces the electrical inductive voltage measurement system with an optical detection system using a light source, light sensor, and rotating polygon mirror. This substitution enables accurate rotor position detection under high-speed and acceleration conditions without requiring additional sensors on the motor, as the optical system is immune to electrical noise and regeneration effects
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 method enables accurate phase switching control of the brushless motor across various operational states, including high speeds and accelerations, by utilizing the phase difference between light sensor signals and inductive voltage signals, ensuring reliable rotor position detection and apparatus performance.
Implementation Method 1
detect first timing at which the light sensor receives a light beam emitted from the light source and reflected by one of the plurality of mirror surfaces
Implementation Method 2
an inductive voltage being generated in at least one coil in a non-energization state due to rotation of the rotor
Data Source
AI summary
A brushless motor has a rotor and a stator, the stator having coils corresponding to respective phases of the brushless motor. A polygon mirror has a plurality of mirror surfaces and is configured to rotate together with the rotor. When executed by the processor, the instructions cause the processor to: detect first timing at which the light sensor receives a light beam emitted from the light source and reflected by one of the plurality of mirror surfaces when the rotor is rotating; acquire first information identifying a relationship between the first timing and second timing at which an inductive voltage reaches a particular reference value, the inductive voltage being generated in at least one coil in a non-energization state due to rotation of the rotor; and perform a phase switching control of the brushless motor based on the first timing and the first information.