Brushless Motor Coil Temperature Estimation Without Sensors
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Solution Overview
Problem
In motors like DC brushless motors used in image forming apparatuses, estimating coil temperature accurately is challenging without a temperature sensor, as it requires space and additional circuitry, and existing methods may not effectively prevent coil overheating due to increased heat generation with output torque.
Innovation Solution
A device comprising an application unit to apply voltage to the motor coils, a detection unit to measure current, and an estimation unit to calculate coil temperature based on current values, allowing for motor control to prevent overheating without a temperature sensor by estimating both stop and operational coil temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a temperature sensor is used to detect the ambient temperature of the motor, then the coil temperature can be accurately estimated, but space for placing the temperature sensor and a corresponding circuit must be provided
Solution Approach 1:
The patent extracts the temperature sensing function from a dedicated temperature sensor and integrates it into the existing current detection unit. By reusing the current detection circuitry already present in the motor control system, the patent eliminates the need for separate temperature sensor hardware while maintaining temperature estimation capability
Solution Approach 2:
The current detection unit is given a dual function: it continues to detect current for motor control while simultaneously estimating coil temperature based on the relationship between current and heat generation. This multi-functionality resolves the contradiction by making existing hardware serve multiple purposes
2Device complexity
If the coil temperature is estimated from the square value of the current value, then the temperature estimation can be performed without a temperature sensor, but the estimation accuracy may be insufficient to effectively prevent coil overheating
Solution Approach 1:
The patent implements a feedback mechanism where the estimated coil temperature is continuously monitored and used to adjust motor control parameters. When the estimated temperature approaches critical thresholds, the system automatically reduces current or adjusts duty cycle to prevent overheating, creating a closed-loop temperature control system that enhances estimation effectiveness
Solution Approach 2:
The patent changes the estimation approach from simple square-value calculation to a more sophisticated model that considers multiple parameters including current magnitude, duty cycle, and thermal accumulation over time. This parameter expansion improves estimation accuracy while maintaining the sensorless approach
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 solution enables accurate coil temperature estimation and control, preventing overheating without the need for a temperature sensor, thus ensuring reliable motor operation and extending the lifespan of the motor coils.
Implementation Method 1
the coil current increases according to the output torque, and heat generation in the coils mounted on the motor also increases
Data Source
AI summary
An estimation unit estimates a first coil temperature in a state where the motor is stopped, and a second coil temperature in a state where the motor is driven, and the control unit controls the driving of the motor based on the first coil temperature and the second coil temperature.