Motor Control Device Position Holding Lock Detection
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Solution Overview
Problem
Conventional motor control systems for DC motors in image forming apparatuses often erroneously detect the lock state in position holding mode, leading to premature shutdown and failure to maintain the rotational position of the motor, which can result in sheet misalignment and damage to the motor or driver circuit.
Innovation Solution
The motor control system employs a PWM control signal with alternating rotational directions for each driving period in position holding mode, preventing the count value from exceeding a threshold and avoiding erroneous lock state detection by resetting the count value for each period, thereby ensuring accurate position holding without shutting off the motor drive signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the duty of the pulse signal is monitored to detect lock state, then the lock state can be detected, but the position holding state is erroneously detected as lock state
Solution Approach 1:
The patent applies dynamics by making the detection threshold adaptive rather than fixed. The threshold is dynamically adjusted based on the operational state (normal drive vs. position holding), allowing the system to distinguish between genuine lock states and normal position holding operations. This resolves the contradiction by making the detection system flexible enough to accommodate different operational modes while maintaining accurate lock detection.
Solution Approach 2:
The patent changes the parameter being monitored from simple duty ratio to a combination of duty ratio and its rate of change. By incorporating the temporal derivative of the duty signal, the system can differentiate between static position holding (where duty is constant) and dynamic lock conditions (where duty changes rapidly), thereby resolving the detection ambiguity.
2Object-affected harmful factors
If voltage application is stopped upon lock state detection, then switching device damage is prevented, but motor position cannot be held in position holding state
Solution Approach 1:
The patent implements feedback by continuously monitoring the duty signal and its rate of change, and using this information to control voltage application. The system provides feedback to the control unit, which then decides whether to stop voltage based on the actual operational context. This prevents false shutdowns during position holding while still protecting against genuine lock states that could damage switching devices.
Solution Approach 2:
The patent makes the voltage control dynamic by adjusting it based on real-time analysis of the duty signal characteristics. Rather than a static on/off control, the system dynamically modulates voltage application according to the detected operational state, ensuring both device protection and position maintenance.
3Speed
If the count value threshold is set low for quick lock detection, then lock state is detected quickly, but position holding state is frequently misidentified as lock state
Solution Approach 1:
The patent changes the detection parameter from absolute duty ratio to the rate of change of duty ratio. This transformation allows the system to detect lock states based on the speed of duty change rather than the duty value itself, enabling quick detection of sudden lock conditions while ignoring the steady-state conditions of position holding.
Solution Approach 2:
The patent employs periodic sampling and analysis of the duty signal over time intervals. By analyzing the temporal pattern and rate of change rather than single instantaneous values, the system can distinguish between transient position holding variations and sustained lock conditions, reducing false detections while maintaining quick response.
Data Source
Figure 1
Figure 2(a)~3(c)
Figure 4~5(b)
AI summary
A motor control device (10) supplies a drive control signal to a drive circuit (20) that drives a motor (30) at a constant period using a motor drive signal based on the drive control signal, and shuts off the motor drive signal when a count value counted by a counter (23) that reset the count value if a state of the motor (30) changes exceeds a threshold corresponding to a plurality of driving periods of the motor (30). The motor control device (10) includes: a control unit (11) that controls a setting unit (14) to set a rotational direction of the motor (30) to a first rotational direction and a second rotational direction reverse to the first rotational direction at the constant period alternately, when a drive mode of the motor (30) is a position holding mode to drive the motor (30) so as to hold a rotational position of the motor (30).