Rotary Impact Tool Speed Control via Pseudo-Detection
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Solution Overview
Problem
Existing rotary impact power tools experience response delays and irregular impacts when the drive shaft rotates at low speeds due to temporary detection of zero speed, leading to motor stalling and inconsistent tool performance.
Innovation Solution
The rotary impact power tool incorporates a speed controller that sets a detection time frame and uses a pseudo-detection speed to generate control signals, ensuring consistent impact even at low speeds, with load detection and adaptive control modes to manage varying loads and prevent motor stalling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the drive shaft rotates at low speed while generating impact, then the motor can operate under heavy load, but the speed detection becomes inaccurate (detected speed approaches zero), causing response delay and temporary stalling
Solution Approach 1:
The patent introduces a pseudo-detection speed as an intermediary value to replace the inaccurate detected speed when the drive shaft rotates at low speed. The speed controller determines whether the detected speed is accurate based on a determination value comparison, and substitutes it with a predefined pseudo-detection speed that reflects the actual low-speed rotation state, thereby resolving the measurement inaccuracy without affecting the impact generation
Solution Approach 2:
The patent changes the speed parameter representation by introducing a determination value that compares the detected speed against a threshold. When the detected speed falls below the threshold (indicating low-speed rotation), the system switches from using the detected speed to using a pseudo-detection speed, effectively changing the parameter used for control decisions based on the operating condition
2Measurement precision
If the speed controller waits for accurate speed detection before generating control signals, then the control precision is improved, but the response time increases, causing irregular impact
Solution Approach 1:
The patent applies preliminary action by pre-defining pseudo-detection speed values that correspond to different low-speed operating conditions. When the drive shaft is detected to be rotating at low speed, the controller immediately uses the pre-calculated pseudo-detection speed to generate control signals, eliminating the waiting time for accurate speed detection while maintaining control precision through the predetermined speed values
3Device complexity
If the motor is allowed to stall temporarily to detect zero speed accurately, then the speed measurement is simplified, but the impact regularity deteriorates
Solution Approach 1:
The patent implements feedback by continuously monitoring the detected speed and comparing it with the determination value. When the detected speed indicates low-speed rotation (detected speed < determination value), the system provides feedback to switch to using pseudo-detection speed, ensuring that the control system adapts to the current operating condition and maintains impact regularity without allowing the motor to stall
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 enables regular and consistent impact across a wide range of rotation speeds, particularly under heavy loads, by maintaining motor rotation and preventing delays, thus improving tool performance and user control.
Implementation Method 1
The speed of the drive shaft is detected by a detector which includes magnetic sensors disposed adjacent to a permanent magnet rotor of the motor
Data Source
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AI summary
A impact power tool includes a motor (10) rotating a drive shaft (22), an output shaft (40) holding a tool bit, and a hammer (30) coupled to the drive shaft. The hammer is rotatable together with the drive shaft and is engageable with an anvil (42) fixed to the output shaft so as to give a rotary impact to the output shaft. The tool includes a speed commander (110) generating a target speed intended by a user, and a speed detector (130) for detection of a speed of the drive shaft. A speed controller (120) generates a control signal for driving the motor by referring to the target speed (ST) and the detected speed (SD). The speed controller provides a detection time frame, and to adopt a predefined pseudo-detection speed as a substitute for the detected speed when no speed detection is available within the detection time frame. Accordingly, even if no speed detection continues, i.e., the motor is stalled over the detection time frame, the speed controller can successfully generate the control signal by making the use of the pseudo-detection speed, thereby continues to rotate the drive shaft for generating the impact regularly and consistently without causing a delay.