Electric Tool Motor Control for High-Speed Fastening
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Solution Overview
Problem
Existing electric tools face challenges in achieving high-speed fastening operations while preventing screw or bolt breakage and temperature increases due to excessive motor output, leading to potential mechanical and thermal stress.
Innovation Solution
Implementing a control method that dynamically adjusts the motor's duty ratio from high to low after a predetermined time, allowing for high-speed operation with reduced mechanical and thermal stress, enabling the use of higher-output motors and preventing torque deficiencies during screw or bolt unfastening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the motor output is increased to achieve high rotational speed and high fastening torque, then productivity is improved, but the screw head may be damaged and the motor temperature increases during continuous operation
Solution Approach 1:
The patent applies dynamics by making the motor output adjustable rather than fixed. The control unit dynamically changes the duty ratio based on operational stage: high duty ratio during initial fastening to achieve high speed, then switches to low duty ratio after seating to prevent overheating and damage. This dynamic adjustment resolves the contradiction between high productivity and reliability.
Solution Approach 2:
The patent implements periodic action through alternating high and low duty ratio periods. The motor operates at high output during the first period (before seating detection) and switches to low output during the second period (after seating detection). This periodic switching allows the system to achieve both high fastening speed and prevent thermal damage to screw heads.
2Productivity
If the motor output is increased to achieve high fastening torque, then productivity is improved, but the motor temperature increases during continuous operation
Solution Approach 1:
The control unit dynamically adjusts the duty ratio based on the fastening stage. During initial fastening when high torque is needed, the duty ratio is set high. After seating is detected, the duty ratio is reduced to low level, preventing excessive temperature rise while maintaining sufficient torque for completing the fastening operation.
Solution Approach 2:
The patent changes the operating parameters (duty ratio) of the motor based on operational conditions. By switching from high duty ratio to low duty ratio after seating detection, the system maintains high fastening torque capability while controlling motor temperature during continuous operation.
3Productivity
If a motor with sufficiently high output is used for high-speed fastening, then productivity is improved, but mechanical stress increases causing temperature rise and potential damage
Solution Approach 1:
The system uses a high-output motor but dynamically controls its operation. The control unit switches from high duty ratio (high stress) during initial fastening to low duty ratio (low stress) after seating detection. This dynamic control allows the use of high-output motors for productivity while reducing mechanical stress and temperature rise during continuous operation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the reliability and lifespan of electric tools by allowing secure unfastening at high outputs and shortening operation times, while preventing damage and temperature increases, thus improving operability and durability.
Implementation Method 1
The brushless DC motor employs a coil (winding) at a rotor-side and a permanent magnet at a stator-side and has a configuration where power driven by an inverter is sequentially energized to a predetermined coil to thus rotate the rotor
Implementation Method 2
a position detecting element configured by a plurality of Hall ICs that detects a position of the rotor by detecting a magnetic force of the permanent magnet of the rotor
Implementation Method 3
an inverter circuit that drives the rotor by switching a direct current voltage supplied from a battery pack and the like with semiconductor switching elements such as FET (Field Effect Transistor) or IGBT (Insulated Gate Bipolar Transistor) and changing energization to the stator winding of each phase
Data Source
AI summary
An electric tool includes: a motor configured to be driven by PWM controlling a semiconductor switching element; a trigger configured to adjust startup and rotation of the motor; a changeover switch configured to switch a rotation direction of the motor between a forward rotation and a reverse rotation; a power transmission mechanism configured to rotate a tip tool by the motor, and a controller configured to control rotation of the motor. When the reverse rotation is set by the changeover switch, the controller PWM controls the semiconductor switching element at a high duty ratio after the trigger is pulled to drive the motor, and thereafter drives the motor at a state where the high duty ratio is changed to a low duty ratio.