Power Tool Gear Shift Control for User Impact Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Power tools with limited gear sets in their power transmission units experience large differences in speed reduction ratios, leading to significant impacts on users when shifting gears, particularly during tasks like bolt fastening, as the load torque increases suddenly, causing motor locking and user discomfort.
Innovation Solution
A power tool with a motor, a power transmission unit capable of shifting between two gears (H and L), a gear shift actuator, and a control unit that detects load torque and gradually reduces motor output over time after shifting to the lower gear ratio, minimizing sudden torque changes and impacts on the user.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the number of gears in the power transmission unit is limited to two to keep the power tool compact, then the power tool size is reduced, but the difference between speed reduction ratios becomes large causing significant impacts on the user when shifting gears
Solution Approach 1:
The control unit reduces motor output before the gear shift occurs and maintains this reduced output for a predetermined period after the shift. This preliminary action prevents the sudden torque increase that would otherwise occur when shifting to a gear with larger speed reduction ratio, thereby suppressing impacts on the user while maintaining compact two-gear design
2Reliability
If the power transmission unit shifts to a gear with large speed reduction ratio when load torque increases, then the power tool can handle higher load torque, but a large impact is applied from the power tool to the user
Solution Approach 1:
The control unit proactively reduces motor output before and during the gear shift process. This preliminary action ensures that when the power transmission unit shifts to a gear with larger speed reduction ratio to handle increased load torque, the motor output is already reduced, preventing the sudden torque transmission that would create impacts on the user
3Power
If the speed reduction ratio is increased to improve fastening performance, then the fastening capability is enhanced, but the impact on the user increases when the tip tool locks
Solution Approach 1:
The control unit reduces motor output in advance before gear shifts occur, particularly when shifting to gears with larger speed reduction ratios that provide enhanced fastening capability. This preliminary reduction in motor output prevents the situation where locked tip tool would transmit large impacts to the user, while still allowing the power transmission unit to operate in high speed reduction ratio gears for improved fastening performance
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A power tool (10) includes a motor (21) that generates rotational power and a power transmission unit (22) that transmits the rotational power from the motor to an output shaft (25). The power transmission unit is configured to reduce a rotation speed related to the rotational power and be capable of shifting a speed reduction ratio. A gear shift actuator (27) shifts a speed reduction ratio of the power transmission unit. A torque detector (41) detects a load torque applied to the output shaft. A control unit (23) controls the gear shift actuator to shift the speed reduction ratio of the power transmission unit in accordance with the detected load torque. The control unit reduces an output of the motor until a predetermined time elapses from when the control unit increased the speed reduction ratio of the power transmission unit by controlling the power transmission unit.