Brushless Motor Controller Abnormality Detection Adaptation
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Solution Overview
Problem
Existing electric power tools using brushless motors face challenges in setting an appropriate abnormality detection period, leading to false abnormalities at short intervals or potential damage at long intervals, due to the inability to adapt to varying rotation speeds and duty ratios.
Innovation Solution
An electric power tool with a controller that estimates the output interval of position information signals from a rotation position sensor, adjusts the abnormality detection period based on the motor's rotation speed, and executes abnormal deactivation and reactivation with a lower duty ratio to prevent damage and ensure safe operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the abnormality detection period is set to be short, then the response speed to abnormalities is improved, but false abnormality detection occurs during normal operation
Solution Approach 1:
The patent applies dynamics by making the abnormality detection period variable rather than fixed. The control circuit dynamically adjusts the detection period based on the rotation speed of the brushless motor - setting it to a first (longer) period at low speeds and a second (shorter) period at high speeds. This dynamic adaptation resolves the contradiction by matching the detection sensitivity to the actual operational conditions, preventing false detections while maintaining quick abnormality response.
Solution Approach 2:
The patent changes the parameter of the abnormality detection period based on rotation speed. By establishing a relationship between rotation speed and detection period, the system optimizes the detection window appropriately for each operating condition. This parameter change approach allows the system to avoid false positives at low speeds while maintaining fast detection capability at high speeds.
2Reliability
If the abnormality detection period is set to be long, then false abnormality detection is reduced, but power may be supplied to switching elements during abnormal situations causing damage
Solution Approach 1:
The system dynamically adjusts the detection period based on rotation speed to prevent both false detections and damage. At high rotation speeds where the risk of damage is greater, the system uses a shorter detection period, enabling faster abnormality detection and power cutoff. This dynamic response prevents the harmful effect of supplying power to damaged switching elements while avoiding false alarms through appropriate period selection.
Solution Approach 2:
The system takes preliminary anti-action by proactively detecting abnormalities before they cause damage to switching elements. The control circuit continuously monitors position information signals and is prepared to cut off power immediately upon detecting an abnormal pattern, preventing the harmful effect of continued power supply to faulty components.
3Device complexity
If the abnormality detection period is fixed, then the control logic is simple, but it cannot adapt to varying rotation speeds and duty ratios
Solution Approach 1:
The patent implements dynamics by making the detection period adaptive to rotation speed and duty ratio changes. The control circuit automatically adjusts the detection period based on current operating conditions, enabling the system to adapt to varying speeds and duty ratios without requiring complex manual configuration or multiple fixed detection mechanisms.
Solution Approach 2:
The system achieves universality by creating a detection mechanism that works effectively across multiple operating conditions. By establishing detection periods that are appropriate for different rotation speeds and duty ratios, the single abnormality detection function becomes universally applicable throughout the entire operational range of the motor, eliminating the need for separate detection systems for different operating modes.
Data Source
Figure 1
Figure 2~3
Figure 4A~4B
AI summary
The control circuit (14) of an electric tool (1) estimates the output interval of a sensor signal from a hole element (S) on the basis of the rotational speed of a motor (3), and sets an abnormality detection time in accordance with the estimated output interval. After actually detecting the sensor signal from the hole element (S), the control circuit (14) determines that there is an abnormality when a subsequent sensor signal is not verified within the abnormality detection time. The control circuit (14) is provided with an abnormality detection time algorithm in which the abnormality detection time is set shorter the faster the rotational speed of the motor (3), and the abnormality detection time is set longer the slower the rotational speed of the motor.