Rotary Impact Tool Speed Control for Reliable Hammer-Anvil Strikes
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Solution Overview
Problem
Rotary impact tools face issues with reduced impact force due to high rotational speeds causing the hammer to hit the anvil before full displacement, leading to durability issues and inefficient work processes, and excessive load reduction resulting in delayed tightening.
Innovation Solution
An electric power tool with a motor, impact mechanism, and control circuit that uses pulse-width modulation to maintain a constant rotational speed through proportional-integral control, ensuring the hammer reliably strikes the anvil and optimizing motor current control for consistent performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the motor rotational speed is increased to improve tightening speed, then productivity is improved, but the hammer hits the anvil before full displacement reducing impact force and durability
Solution Approach 1:
The patent applies dynamics by making the motor rotational speed variable rather than constant. The control circuit dynamically adjusts the rotational speed based on the operational phase: high speed during non-impact rotation to improve productivity, and reduced speed during impact to ensure the hammer fully displaces and strikes the anvil correctly, preventing durability issues
Solution Approach 2:
The patent changes the rotational speed parameter according to the operational state. The control circuit detects impact occurrence and adjusts the motor speed parameter accordingly - maintaining higher speeds when no impact occurs to improve tightening speed, and reducing speed when impact is detected to ensure proper hammer displacement and strike, thus resolving the contradiction between productivity and reliability
2Reliability
If constant rotation control is applied to maintain consistent motor speed, then impact force reliability is improved, but work time increases and work efficiency decreases
Solution Approach 1:
The patent applies periodic action by alternating between high-speed rotation phases and controlled impact phases. During non-impact periods, the motor operates at high speed to minimize work time. When impact is detected, the speed is temporarily reduced to ensure reliable impact force. This periodic switching resolves the contradiction by achieving both efficiency and reliability at different stages of the operational cycle
3Reliability
If the motor speed is reduced to ensure proper hammer displacement, then anvil durability is improved, but impact force is reduced and tightening is delayed
Solution Approach 1:
The patent makes the motor speed dynamic, switching between high speed and reduced speed based on the operational phase. High speed is maintained during rotation phases to ensure proper hammer displacement accumulates, while speed is reduced only during impact moments to ensure accurate strikes. This dynamic adjustment resolves the contradiction between displacement accuracy and tightening efficiency
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 solution enhances usability by maintaining consistent rotational speed, reducing fluctuations, and improving work efficiency by ensuring reliable impact force application and preventing premature hammer-anvil contact, thus extending anvil durability and reducing work time.
Implementation Method 1
The control circuit is configured to control a motor current based on a pulse-width modulation signal
Implementation Method 2
The first motor control includes controlling the motor current in accordance with the pulse-width modulation signal based on a drive duty ratio. The basic duty ratio is set in accordance with a first target rotational speed of the motor. The proportional duty ratio is proportional to a speed error.
Data Source
AI summary
An electric power tool in one aspect of the present disclosure includes a motor, an impact mechanism, an impact detector, and a control circuit. The control circuit controls a motor current based on a drive duty ratio in a first driving term. The first driving term corresponds to a time period from when the motor is started until impact is detect. The drive duty ratio corresponds to a sum of a basic duty ratio and a proportional duty ratio. The control circuit controls the motor current so that an actual rotational speed of the motor is consistent with a target rotational speed after elapse of the first driving term.