Brushless Motor Rotor Position Detection via Induced Voltage
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Solution Overview
Problem
The existing image forming apparatuses using brushless motors for rotating rotary polygon mirrors face challenges in accurately detecting the rotor position due to placement dispersion of Hall elements, leading to unstable rotation control.
Innovation Solution
The image forming apparatus employs an energization switching unit, a voltage detecting unit, and a control unit to control coil energizations based on induced voltages, reducing electric power supply to electric components during detection periods to enhance signal accuracy and increase the upper limit of electric power supplied to coils during rotation control, thereby improving detection accuracy and preventing inadequate start-up of rotation control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Hall elements are placed in a vicinity of the rotor to detect rotor position, then the position detection can be implemented, but the placement dispersion of Hall elements makes it difficult to detect the position accurately, leading to unstable rotation control
Solution Approach 1:
The invention extracts the position detection function from Hall elements and implements it through induced voltage detection in the coils. By removing the Hall elements and using the existing coil structure for dual purposes (energization and detection), the placement dispersion problem is eliminated. The detection is performed by measuring induced voltages in the coils during specific time periods when no energization is applied, enabling accurate rotor position detection without additional components.
Solution Approach 2:
The coils in the brushless motor are given dual functionality: they serve both as energization coils for motor operation and as detection coils for rotor position sensing. During specific time periods, the coils detect induced voltages to determine rotor position, while during other periods, they receive energization for motor rotation. This multi-functionality eliminates the need for separate Hall elements and their associated placement issues.
2Productivity
If electric power is supplied to electric components during detection period, then the components can operate, but the power supply interferes with the detection signal accuracy, making it difficult to detect rotor position accurately
Solution Approach 1:
The invention implements periodic switching between detection mode and energization mode. During detection time periods, electric power supply to the electric components is stopped to enable accurate induced voltage measurement. During other time periods, full power is restored for component operation and motor energization. This periodic alternation ensures that detection and operation do not interfere with each other, maintaining both accuracy and productivity.
Solution Approach 2:
The detection of rotor position is performed preliminarily before the main operation phase. By detecting the rotor position first during a dedicated detection period, the system establishes the initial conditions needed for subsequent accurate energization control. This preliminary detection ensures that the rotor position is known before power-intensive operations begin, preventing interference between detection signals and operation currents.
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 improves the accuracy of detection signals and ensures stable rotation control by providing sufficient electric power to the brushless motor during detection periods, preventing situations where rotation control cannot be adequately started.
Implementation Method 1
a voltage detecting unit that outputs a detection signal based on induced voltages generated in the coils by rotation of the rotor
Data Source
AI summary
An image forming apparatus includes: a light source; a brushless motor including a stator and a rotor; a rotary polygon mirror rotated by the brushless motor to form scanning lines on a photosensitive member; an energization switching unit turning on/off energizations of the coils; a voltage detecting unit outputting a detection signal based on induced voltages generated in coils of the stator by rotation of the rotor; a motor controlling unit turning on/off of the energizations by the energization switching unit based on the detection signal; an electric component that operates during formation of the scanning lines; and a power supply controlling unit which, in a detecting period of the detection signal for starting a rotation control of the brushless motor, reduces an amount of electric power supplied to the electric component to less than in a period of the formation of scanning lines after the detecting period.