Electric Power Tool Motor Control via Torque Feedback
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Solution Overview
Problem
Electric power tools experience a decrease in actual rotational speed due to increased load torque, leading to insufficient torque generation and potential motor lockup, especially at low speeds, as the Hall signal variation does not accurately reflect the motor's rotational speed.
Innovation Solution
Incorporating a torque detector and correction circuit in the electric power tool to detect load torque and adjust the drive command value, ensuring the motor receives the necessary power to maintain desired rotational speed, thereby preventing a decrease in actual rotational speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the motor rotates at low speed, then the Hall signal variation interval becomes longer, but the actual rotational speed becomes lower than the calculated rotational speed leading to insufficient torque
Solution Approach 1:
The patent implements a feedback mechanism where the microcomputer continuously monitors the actual rotational speed via Hall signals and compares it with the calculated rotational speed. When a discrepancy is detected (actual speed lower than calculated speed), the system automatically increases the drive command value to compensate for the insufficient torque, ensuring reliable motor operation at low speeds
Solution Approach 2:
The patent dynamically changes the drive command value parameter based on the detected rotational speed discrepancy. When the motor operates at low speeds and the Hall signal variation interval increases, the system adjusts the drive command value upward to maintain adequate torque generation, transforming a static control parameter into a dynamic one that adapts to operating conditions
2Force
If the calculated rotational speed is higher than the actual rotational speed, then the torque generated by the motor becomes insufficient, but increasing torque may cause motor lockup
Solution Approach 1:
The patent employs dynamic control of the drive command value that continuously adapts to the motor's actual operating state. Rather than applying a fixed torque increase, the system dynamically adjusts the drive command value based on real-time feedback from Hall signals, allowing the torque to be optimized for each instantaneous operating condition and preventing both insufficient torque and motor lockup
Solution Approach 2:
The system uses feedback from Hall signals to continuously monitor actual rotational speed and automatically adjusts the drive command value to maintain optimal torque. This closed-loop control ensures torque is increased only when needed and at the appropriate magnitude, preventing motor lockup while ensuring sufficient torque generation
Data Source
AI summary
An electric power tool in one aspect of the present disclosure includes a motor, an output shaft, a torque detector, a correction circuit, and an output circuit. The correction circuit corrects a drive command value based on load torque detected by the torque detector. The drive command value indicates a magnitude of electric power to be supplied to the motor. The output circuit outputs a drive signal indicating the drive command value. The drive circuit (i) receives the drive signal from the output circuit and (ii) supplies electric power in accordance with the drive signal to the motor to drive the motor.