Tangential Force Sensor for Low Torque Measurement
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional torque measurement methods are inadequate for measuring very low torque values due to parasitic losses, misalignment issues, and decreased signal-to-noise ratio, making them unreliable for quality control, especially in manufacturing environments where low torque is required to initiate and maintain rotation.
Innovation Solution
A method using a two-dimensional force sensor coupled tangentially to a cylindrical object to measure torque by applying a radial force for non-slip contact and translating the sensor to apply a tangential force, allowing for precise calculation of torque without excessive force that could damage the part or mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If strain gauge is used to measure torque on rotating parts, then torque measurement capability is provided, but parasitic losses and misalignment forces mask the actual torque value when measuring very low torque
Solution Approach 1:
The patent extracts the measurement function from the rotating measurement system by using a stationary force sensor that measures forces on a stationary intermediate element. This separates the measurement apparatus from the rotating part, eliminating parasitic losses from bearing friction and eddy currents that plague traditional rotating strain gauge measurements.
Solution Approach 2:
The patent introduces a stationary intermediate element (such as a pulley or drum) that the rotating part drives through friction or mechanical contact. The force sensor measures forces on this intermediate element rather than directly on the rotating part, providing an indirect measurement pathway that avoids the harmful effects of rotation-induced parasitic losses.
2Volume of moving object
If components are reduced in size to accommodate very-low-torque parts, then measurement system size is reduced, but signal-to-noise ratio decreases due to added shaft flexibility
Solution Approach 1:
The measurement function is extracted from the rotating system and placed in a stationary location. The force sensor remains stationary while measuring forces transmitted through the intermediate element, eliminating the need for flexible rotating shafts and their associated noise problems.
Solution Approach 2:
The patent replaces the traditional mechanical strain gauge measurement system with a force sensor-based system that uses friction or mechanical contact between the rotating part and a stationary intermediate element. This substitution allows for rigid, non-flexible measurement components while maintaining measurement capability.
3Measurement precision
If traditional strain gauge method is used, then torque measurement is possible, but misalignment along the axis of rotation produces forces that mask the actual torque value
Solution Approach 1:
The measurement is extracted from the rotating measurement system to a stationary force sensor. This eliminates the need for perfect collinearity and alignment between rotating components, as the force sensor remains stationary and measures forces on a stationary intermediate element.
Solution Approach 2:
A stationary intermediate element serves as a mediator between the rotating part and the force sensor. This intermediate element can be a pulley, drum, or other mechanical component that translates rotational motion into linear forces that the stationary sensor can measure, eliminating alignment sensitivity.
4Speed
If excessive force is applied to initiate rotation, then rotation can be started, but the part or mechanism may be damaged
Solution Approach 1:
The force sensor measures forces during the periodic process of starting and maintaining rotation. By monitoring the force profile over time, the system can detect when rotation initiates and adjust the applied force accordingly, avoiding excessive force that could damage the part.
Solution Approach 2:
The force sensor provides real-time feedback on the forces required to initiate and maintain rotation. This feedback allows for dynamic adjustment of the driving force, applying only the minimum necessary force to overcome static friction and initiate rotation, then reducing force to maintain constant-speed rotation.
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 enhances sensitivity and precision, eliminating parasitic losses and the need for axial alignment, enabling reliable measurement of low torque values, as demonstrated by the ability to measure torques of 20 Newton millimeters and less with reduced noise, suitable for inline quality-control testing.
Implementation Method 1
A progressively increasing tangential force is then applied in some manner to initiate and maintain the rotation of the part. By measuring the tangential force so applied to the part, the torque required to produce and maintain the rotation of the part can be calculated
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A tangential force sensor (32) is used instead of a coaxial strain gauge to measure the torque required to produce the rotation of a part (10). The force sensor (32) is coupled tangentially to the rotating part (10) through a non-slip contact produced by a force (Fz) applied radially on the part. A progressively increasing tangential force (Fx) produced by translating the force sensor (32) in a direction (XX) normal to the axis of rotation (A) of the part is then applied to initiate and maintain its rotation. The radial force (Fz) applied to the part (10) is judiciously selected and measured such that the part is engaged with enough friction to ensure a non-slip condition. By measuring the tangential force (Fx) applied to the part, the torque characteristics of the rotatable part (10) are determined. By sensing and controlling the radial force (Fx) applied to the part, damage to the part (10) or the mechanism supporting it is avoided.