Power Tool Torque Control via Motor Speed Monitoring
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Solution Overview
Problem
Existing power tools, such as impact wrenches, often cause damage to screws or workpieces due to excessive torque during screwing operations, as they lack effective mechanisms to adapt torque based on specific screwing situations, leading to potential damage.
Innovation Solution
A method and control unit that dynamically adjust the torque of the electric motor by determining a speed limit based on the screwing conditions, such as screw diameter, thread pitch, and workpiece hardness, and reduce or switch off the motor if the speed exceeds this limit during percussion operation, thereby preventing damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the electric motor maintains high torque during screwing operation, then the screwing process is completed faster, but the screw or workpiece may be damaged
Solution Approach 1:
The patent applies dynamics by making the torque characteristic of the electric motor adjustable and time-dependent. The control unit modifies the torque profile during the screwing operation based on detected speed variations, transitioning from high torque at the beginning to reduced torque when the seated position is approached, thereby adapting the force application to the changing mechanical conditions throughout the screwing process
Solution Approach 2:
The patent implements feedback by continuously monitoring the speed of the electric motor during operation and using this information to control the torque. When the speed exceeds a predetermined limit (indicating the screw has reached its seated position), the control unit responds by reducing torque, creating a closed-loop control system that prevents damage while maintaining efficient screwing
2Object-affected harmful factors
If the torque is limited to prevent damage, then the screwing operation becomes safer, but the screwing process takes longer
Solution Approach 1:
The patent applies periodic action by dividing the screwing operation into distinct phases with different torque characteristics. During the initial phase, high torque is applied to quickly drive the screw into the workpiece. When the seated position is detected (through speed monitoring), the torque is periodically adjusted to a lower level to complete the operation safely, creating a two-stage periodic torque profile that optimizes both speed and safety
3Device complexity
If a fixed speed limit is used to detect seated position, then the control is simpler, but it may not adapt to different screwing situations
Solution Approach 1:
The patent applies parameter changes by using a predetermined speed limit as a detectable parameter to identify the seated position of the screw. This speed threshold serves as a critical parameter that triggers the torque reduction, providing a simple yet effective method to adapt the control system to various screwing situations without requiring complex algorithms or multiple sensors
Data Source
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Figure 3
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AI summary
The invention relates to a method for operating a power tool (10) for screwing a screw (61) into a workpiece (110). After the power tool is activated, an electric motor (20) is driven in order to screw the screw into the workpiece, wherein the rotational speed of the electric motor is ascertained while screwing the screw during a specified starting time of an impact operation (t2) of the power tool. After the starting time, a rotational speed of the electric motor is ascertained, and a torque of the electric motor is at least reduced (t5) if the ascertained rotational speed of the electric motor exceeds a specified rotational speed threshold.