Impact Tool Controller Duty Ratio Adjustment for Screw Fastening
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Solution Overview
Problem
Existing impact tools apply excessive striking force during screw fastening, leading to increased risk of screw damage and reduced efficiency, especially when dealing with small screws or self-drilling screws, as they struggle to balance high fastening torque with precision and speed.
Innovation Solution
The impact tool employs a controller that adjusts the duty ratio of the motor's PWM drive signal from a high to a low setting before the first striking event, using a brushless DC motor with semiconductor switching elements, allowing for precise control of the striking force and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the motor is driven at high duty ratio continuously, then high fastening torque is achieved, but excessive striking force damages screws and reduces precision
Solution Approach 1:
The patent applies periodic action by switching the motor duty ratio between high and low states in synchronization with the hammer-anvil striking cycle. The controller detects striking events and adjusts the PWM duty ratio accordingly: high duty ratio during rotation phases and low duty ratio during striking phases. This periodic modulation enables high fastening torque when needed while preventing excessive striking force that would damage screws.
2Object-affected harmful factors
If the motor speed is reduced to prevent screw damage, then striking force is controlled, but fastening efficiency and operation speed decrease
Solution Approach 1:
The patent implements dynamics by making the motor speed and duty ratio adjustable in real-time based on operational conditions. Rather than maintaining a fixed low speed to prevent damage, the system dynamically increases speed during rotation phases and reduces it during striking phases through PWM control. This dynamic adjustment allows high fastening efficiency during non-striking periods while controlling striking force to prevent screw breakage.
3Power
If high power motor is used for fastening torque, then fastening capability is improved, but power consumption increases and battery life decreases
Solution Approach 1:
The patent applies periodic action to power consumption by using high power only during necessary rotation phases and reducing power during striking phases. The controller modulates the PWM duty ratio periodically, switching between high and low power states synchronized with the hammer-anvil engagement cycle. This enables the use of a high-power motor for adequate fastening capability while significantly reducing average power consumption and extending battery life.
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 enables high-speed and accurate fastening of small screws and self-drilling screws while preventing screw breakage, maintaining efficiency and extending the tool's reliability and battery life by optimizing the striking force.
Implementation Method 1
The brushless DC motor employs a coil (winding) at a stator side and a permanent magnet at a rotor side and has a configuration that power driven by an inverter is sequentially energized to a predetermined coil to rotate the rotor
Implementation Method 2
a position detecting element configured by a plurality of Hall ICs which detect a position of the rotor by detecting a magnetic force of the permanent magnet of the rotor
Implementation Method 3
an inverter circuit which drives the rotor by switching DC voltage supplied from a battery pack, etc., using 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 impact tool and method can include: a motor; a trigger; a controller configured to control driving power supplied to the motor using a semiconductor switching element according to an operation of the trigger; a striking mechanism configured to drive a tip tool continuously or intermittently by rotation force of the motor, the striking mechanism including a hammer and an anvil. The controller drives the semiconductor switching element at a high duty ratio when the trigger is manipulated. The motor can be driven so that the duty ratio is lowered before a first striking of the hammer on the anvil is performed and the first striking is performed at a low duty ratio lower than the high duty ratio.