Electric Tool Control Device for Recoil Force Reduction
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Solution Overview
Problem
Portable electric power tools face challenges in maintaining a compact size due to the increased size of power transmission units with multiple speed-changing gears, leading to large differences in speed reduction ratios, which result in excessive recoil forces when shifting to high speed reduction gears, especially during improper fastening tasks.
Innovation Solution
An electric power tool with a motor, power transmission unit, speed shift actuator, torque detector, and controller that detects load torque and rotation speed to prevent excessive speed reduction ratio changes, deactivates the motor when locking is detected, and performs a slow start upon reactivation to minimize recoil forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the number of speed changing gears in the power transmission unit is increased, then the speed reduction ratio can be changed more frequently, but the overall size of the electric power tool increases
Solution Approach 1:
The power transmission unit is designed with a variable speed reduction ratio mechanism that can dynamically adjust between different gear ratios (first speed reduction ratio and second speed reduction ratio) based on operating conditions. This allows the system to adapt to different speed requirements without requiring multiple fixed gears, thereby reducing the overall number of components and size of the power transmission unit while maintaining versatile speed changing capability.
2Volume of moving object
If the difference in speed reduction ratio between gears is increased, then the size of the power transmission unit is reduced, but the recoil force applied to the user increases when shifting to high speed reduction gear
Solution Approach 1:
The control unit continuously monitors the rotational speed of the output shaft and automatically shifts between different speed reduction ratios based on the detected speed. When the output shaft rotational speed exceeds a predetermined threshold, the control unit switches to a gear with a different speed reduction ratio. This feedback-based automatic shifting ensures smooth transitions and prevents sudden large changes in speed reduction ratio that would cause excessive recoil force, while still allowing for significant ratio differences to maintain compact size.
3Reliability
If the speed reduction ratio is increased to handle high load torque, then the motor can overcome tighter fastening conditions, but excessive recoil force is applied to the user when the motor is locked
Solution Approach 1:
The control unit proactively monitors the rotational speed of the output shaft and predicts potential motor locking conditions by detecting when the speed exceeds predetermined thresholds. Before the motor becomes locked and generates harmful recoil force, the control unit preemptively shifts the speed reduction ratio to an appropriate gear level. This preliminary action prevents the motor from operating in a locked state, thereby protecting the user from excessive recoil force while still enabling the motor to handle tight fastening conditions when appropriate.
Data Source
Figure 1
Figure 2A~2D
Figure 3~4
AI summary
An electric tool (10) is provided with a power transmission unit (22) for decelerating and then transmitting the rotational power of a motor (21) to an output shaft (25), a shift actuator (27) for changing the deceleration rate of the power transmission unit, a torque detection unit (41) for detecting the load torque applied to the output shaft (25), and a control unit (23) for controlling the shift actuator (27) so as to change the deceleration rate of the power transmission unit in accordance with the detected load torque. The control unit (23) does not increase the deceleration rate of the power transmission device and determines that the motor was locked when the load torque detected by means of the torque detection unit increased within a predetermined time from a threshold value of a shifting condition set to increase the deceleration rate to a threshold value of a locking condition set to detect that the motor was locked.