Thin-Film Force Sensor for Power Tool Torque Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing rotary power tools, such as drills and screwdrivers, face inaccuracies and inefficiencies in torque sensing due to mechanical clutches that wear out and electronic clutches that rely on indirect measurements like current or motor speed, which are poor indicators during high motor acceleration and deceleration, and lack responsiveness.
Innovation Solution
A force sensing electronic clutch is implemented, featuring a thin film force sensing resistor coupled to a stationary element of the transmission, generating an electronic signal for direct torque measurement, with a controller comparing this signal to a threshold value to initiate protective operations, and optionally using a current sensing clutch for calibration and operation in reverse direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a mechanical clutch is used for torque sensing, then the tool can interrupt power output when torque exceeds a threshold, but the mechanical parts add a great deal of additional length to the tool and the clutch wears out over time
Solution Approach 1:
The patent replaces the mechanical clutch system with an electronic clutch that uses a force sensor to directly sense reaction torque on the transmission. The force sensor generates an electronic signal that is processed by a controller to interrupt power delivery when torque exceeds a threshold, eliminating the need for mechanical clutch parts and reducing tool length while improving reliability
Solution Approach 2:
The patent extracts the torque sensing function from the mechanical clutch mechanism and implements it as a separate force sensor coupled to a stationary element of the transmission. This allows the torque sensing function to be performed independently without the wear and length issues of mechanical clutch components
2Device complexity
If current sensing is used for electronic clutch, then the tool can infer torque indirectly, but current is a poor indicator of load torque during high motor acceleration and deceleration
Solution Approach 1:
The patent replaces indirect current-based torque inference with direct force sensing using a force sensor coupled to a stationary element of the transmission. This direct mechanical-to-electrical transduction provides accurate torque measurement during all operating conditions including high acceleration and deceleration, eliminating the measurement errors inherent in current-based methods
Solution Approach 2:
The patent introduces a force sensor as an intermediary element that directly couples the transmission to an electronic sensing system. This intermediary provides a direct measurement path from the mechanical torque to an electronic signal, bypassing the need to infer torque from motor current and providing accurate measurements during dynamic operation
3Device complexity
If current sensing is used for electronic clutch, then the tool can measure torque indirectly, but the response time is poor as the current reading lags the actual output torque
Solution Approach 1:
The patent replaces the indirect current sensing method with a direct force sensor that mechanically couples to the transmission. This direct coupling provides immediate torque sensing with fast response time, as the force sensor directly transduces mechanical torque to an electronic signal without the lag inherent in current-based measurement methods
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 provides a compact, accurate, and responsive torque sensing system that reduces tool length and eliminates inaccuracies, enabling effective protective operations and continuous calibration to maintain precision over time and temperature variations.
Implementation Method 1
a force sensor that senses a reaction torque transmitted from the end effector to at least a portion of the transmission. The sensor is configured to generate a first electronic signal corresponding to an amount of the reaction torque.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A method of limiting an output torque in a power tool (10) having a housing (12), a motor (20) and a transmission (22) disposed in the housing (12), and an output end effector (24) coupled to the transmission (22), the method comprising providing a force sensor (42) coupled to a substantially stationary element of the transmission (22); receiving a first electronic signal from the force sensor (42) that corresponds to a value of a reaction torque transmitted from the end effector (24) to the substantially stationary element of the transmission (22); comparing the first electronic signal to a second electronic signal corresponding to a desired threshold torque value; and initiating a protective operation when a value of the first electronic signal indicates that the reaction torque has exceeded the desired threshold torque value.