Electric Power Tool Speed Limiting for Bit Wear Reduction
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Solution Overview
Problem
Electric power tools with drilling functions often cause excessive wear on bits due to high rotation speeds when used with steel plates, leading to reduced bit service life.
Innovation Solution
An electric power tool with a motor, output shaft, drive force transmission, trigger, rotation speed changing circuitry, and rotation speed control circuitry that limits the rotation speed of the bit to a lower speed when the trigger is fully pulled, using a three-stage planetary gear mechanism and an upper limit rotation speed selector to reduce wear and prolong bit life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the trigger is pulled to maximum to increase rotation speed for efficient drilling, then drilling productivity improves, but bit wear increases excessively reducing service life
Solution Approach 1:
The patent applies dynamics by making the rotation speed characteristic changeable based on operating conditions. The rotation speed changing circuitry dynamically adjusts the relationship between trigger pulled amount and output shaft rotation speed, switching between non-limited mode (for high productivity) and limited mode (for bit protection), thereby resolving the contradiction between drilling efficiency and bit service life
Solution Approach 2:
The patent changes the parameter of rotation speed mapping by using rotation speed changing circuitry to modify the maximum rotation speed of the output shaft based on the selected mode. In non-limited mode, the full motor speed range is utilized for high productivity, while in limited mode, the maximum rotation speed is reduced to protect the bit, thus resolving the contradiction through parameter adjustment
2Speed
If high rotation speed is used for drilling steel plates, then drilling speed improves, but excessive wear occurs on the bit
Solution Approach 1:
The system dynamically adjusts the rotation speed output based on the selected mode. In non-limited mode, high rotation speed is provided for drilling speed. In limited mode, the rotation speed changing circuitry caps the maximum output shaft speed to a lower value, reducing bit wear while still providing adequate drilling capability
Solution Approach 2:
The patent applies preliminary anti-action by pre-setting rotation speed limits before excessive wear can occur. The rotation speed changing circuitry is configured in advance to limit the maximum rotation speed in protected mode, preventing the harmful effect of excessive wear before it happens during operation
Data Source
AI summary
An electric power tool includes a motor, an output shaft, a drive force transmission configured to reduce drive speed of the motor and transmit drive force of the motor to the output shaft; a trigger that can be pulled by a user; a rotation speed changing circuitry configured to change a rotation speed of the output shaft that corresponds to a maximum pulled amount of the trigger to a limited rotation speed that is lower than a maximum rotation speed of the output shaft in a non-limited rotation speed mode; and a rotation speed control circuitry configured to control a rotation speed of the motor in correspondence with a pulled amount of the trigger to obtain the rotation speed of the output shaft that is changed by the rotation speed changing circuitry.