Brushless Motor Speed Control for Image Forming Apparatus
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Solution Overview
Problem
In image forming apparatuses using brushless motors, accurate rotation control is challenging due to placement dispersion of Hall elements, leading to unstable rotation and prolonged startup times for subsequent image forming operations, especially when the motor is inertially rotated and induced voltages cannot be detected.
Innovation Solution
The apparatus employs an energization switching unit and a voltage detecting unit to control coil energizations based on induced voltages, maintaining a low-speed rotation during non-image forming periods where induced voltages can still be detected, allowing for early startup of the next image forming operation while reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the brushless motor is allowed to rotate by inertia after image forming operation ends, then power consumption is reduced, but rotation control becomes unstable and induced voltages cannot be detected
Solution Approach 1:
The patent applies dynamics by transitioning the motor from a static high-speed state to a dynamic low-speed state after image forming operations. The control unit dynamically adjusts the rotation speed based on operational phases: maintaining high speed during image forming, then transitioning to a specific low-speed range (500-2000 rpm) where induced voltages remain detectable. This dynamic speed adjustment resolves the contradiction by enabling power savings through speed reduction while preserving the ability to detect induced voltages for stable rotation control.
Solution Approach 2:
The patent changes the operational parameters of the brushless motor, specifically the rotation speed, to resolve the technical contradiction. By setting the rotation speed to a specific range (500-2000 rpm) after image forming operations, the system maintains induced voltage detection capability while reducing power consumption. This parameter change allows the motor to operate in a state that balances energy efficiency with control stability, preventing the rotor from rotating too fast (wasting energy) or too slow/stop (losing induced voltage detection).
2Use of energy by moving object
If the rotation speed is reduced to save power, then energy consumption decreases, but induced voltages cannot be detected and control becomes difficult
Solution Approach 1:
The patent precisely controls the rotation speed parameter within a specific range (500-2000 rpm) to resolve the contradiction between power consumption and induced voltage detection. This parameter optimization ensures that the motor rotates slowly enough to save energy but fast enough to generate detectable induced voltages. The control unit monitors and maintains this critical speed range, enabling accurate measurement of induced voltages while achieving significant power savings compared to continuous high-speed operation.
3Ease of operation
If Hall elements are used for position detection, then rotation control can be achieved, but placement dispersion leads to inaccurate detection and unstable control
Solution Approach 1:
The patent extracts the position detection function from the Hall element-based system and implements it through induced voltage detection instead. By removing the physical Hall elements and their associated placement dispersion problems, the system uses the naturally occurring induced voltages in the motor coils to determine rotor position. This extraction eliminates the measurement precision issues caused by Hall element placement while maintaining rotation control capability through the induced voltage signals.
Solution Approach 2:
The patent applies self-service by using the motor's own operational characteristics (induced voltages generated during rotation) for position detection, rather than relying on separate sensing components like Hall elements. The induced voltages that are inherently generated by the motor's operation are utilized for control feedback, making the system self-sufficient and eliminating the need for additional sensors that introduce placement errors. This self-service approach improves measurement precision while maintaining ease of operation.
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 rotation control and reduces power consumption by maintaining the brushless motor at a speed where induced voltages can be detected, enabling quicker startup and minimizing power wastage during idle periods.
Implementation Method 1
a voltage detecting unit which outputs a detection signal based on induced voltages that are generated in the coils by rotation of the rotor
Data Source
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AI summary
An image forming apparatus (1) includes: a light source (15) that emits a light beam; a photosensitive member (10); a brushless motor (33) including a stator (35) and a rotor (36); a rotary polygon mirror (16) rotated by the brushless motor (33); an energization switching unit (37A) that turns on/off energizations of the coils; a voltage detecting unit (39) that outputs a detection signal based on induced voltages generated in coils of the stator by rotation of the rotor; and a motor controlling unit (38) that controls the turning on/off of the energizations by the energization switching unit (37A) based on the detection signal. In a non-image forming period after one image forming operation, the motor controlling unit performs a low-speed process where the motor controlling unit maintains a rotation speed of the brushless motor at a speed, which is lower than a speed in the image forming operation, and at which the induced voltages are detectable by the voltage detecting unit.