Brushless Motor Current Limiting for Coil Temperature Control
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Solution Overview
Problem
Brushless motors in image forming apparatuses face frequent failures due to excessive coil temperature caused by unexpected increases in motor load, which can be exacerbated by downsizing, and overly limiting coil current hinders proper load handling during normal operation.
Innovation Solution
A motor control apparatus that dynamically adjusts the coil current limit value based on detected average current values over a predetermined time period, reducing the limit when it exceeds a threshold to prevent temperature rises, while allowing for load variation handling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the motor is downsized to reduce image forming apparatus size, then the apparatus size is reduced, but the coil temperature increases due to higher current density and limited heat dissipation capacity
Solution Approach 1:
The patent implements dynamic adjustment of the coil current limit value based on operating conditions. The control unit monitors motor operation and adjusts the current limit in real-time, allowing higher currents when cooling is effective and lower currents when heat accumulation risk increases. This dynamic approach resolves the contradiction by enabling the downsized motor to operate safely despite higher current density.
Solution Approach 2:
The patent changes the parameter of current limit value based on operating time and thermal conditions. By adjusting this critical parameter dynamically, the system optimizes the balance between power output and thermal safety in the downsized motor, preventing coil temperature exceedance while maintaining operational effectiveness.
2Reliability
If the coil current is excessively limited to prevent motor failure, then coil temperature is controlled, but the motor cannot properly handle load variation under normal operation
Solution Approach 1:
The patent employs dynamic current limiting where the current limit value is adjusted based on operating time and thermal conditions rather than using a fixed limit. This allows the motor to handle load variations properly during normal operation while preventing overheating and failure, thus resolving the contradiction between reliability and adaptability.
Solution Approach 2:
The control unit continuously monitors motor operation and adjusts the current limit based on feedback from operating conditions and thermal state. This feedback mechanism enables the system to maintain reliability by preventing failure while preserving load handling capability through adaptive current control.
3Temperature
If a fixed current limit is applied to prevent overheating, then coil temperature is controlled, but the motor performance deteriorates during transient load increases
Solution Approach 1:
The patent replaces fixed current limiting with dynamic current limiting that adapts to transient conditions. The control unit allows higher current during transient load increases when thermal risk is low, then reduces current when operating time increases and heat accumulation becomes significant. This resolves the contradiction by maintaining both temperature control and performance during transients.
Solution Approach 2:
The patent implements preliminary thermal management by adjusting current limits based on accumulated operating time before thermal damage occurs. This preventive approach allows the motor to maintain high performance during brief transients while progressively managing heat buildup, preventing both overheating and performance deterioration.
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
Prevents motor failures by maintaining coil temperature within safe limits under overload conditions while ensuring proper handling of load variations during normal operation, thereby reducing the risk of image defects and maintaining rotor speed.
Implementation Method 1
an unexpected increase of motor load may result in a rise of coil temperature due to an increase of current flowing through the coil of the motor
Data Source
AI summary
The motor control apparatus includes: a setting unit configured to set a limit value of coil current flowing through a coil of a motor; a current supply unit configured to supply the motor with the coil current in a range not exceeding the limit value set by the setting unit; a detection unit configured to detect a current value of the coil current; and a comparison unit configured to compare an average value of the current value detected by the detection unit over a predetermined time period with a first threshold value. When the average value has exceeded the first threshold value, the setting unit updates the limit value in a decreasing manner.