Force Torque Sensor with Serpentine Beams and Overload Protection
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Solution Overview
Problem
Conventional force/torque sensors face limitations in withstanding high forces and torques beyond their design range due to the similarity in stiffness between deformable and overload features, leading to premature failure and increased stress measurements.
Innovation Solution
The use of serpentine or spiral deformable beams with a higher overall length, reducing their stiffness while maintaining high stiffness in overload beams, creates a significant ratio of stiffness after overload activation, allowing the sensor to handle higher forces and torques before failing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If deformable beams are made shorter and stiffer, then measurement precision is improved, but the sensor fails prematurely under overload conditions
Solution Approach 1:
The sensor is divided into two distinct functional segments: deformable beams for measurement and overload beams for protection. The deformable beams are made shorter and stiffer for precise measurement, while the overload beams are designed as separate sacrificial elements that fail first under overload conditions, preventing damage to the measurement components.
Solution Approach 2:
Overload beams are designed as sacrificial, replaceable components that are intentionally made weaker than the deformable beams. When overload occurs, the overload beams fail first in a controlled manner, protecting the more expensive and critical measurement system. These overload beams can be easily replaced without affecting the sensor's measurement capabilities.
2Force
If deformable beams are made longer and more flexible, then the sensor can withstand higher forces, but measurement precision decreases
Solution Approach 1:
The force tolerance function is segmented between two beam types: deformable beams for measurement and overload beams for high-force protection. The deformable beams remain short and stiff for precise measurement, while the overload beams provide the additional force tolerance through their sacrificial failure mechanism.
Solution Approach 2:
The patent changes the structural parameters of the beam system by introducing overload beams with specific geometric characteristics (longer length, lower stiffness) that differ from the deformable beams. This parameter differentiation allows the system to achieve both high force tolerance and precise measurement by assigning different parameter sets to different functional components.
3Strength
If overload beams are made stiffer, then the sensor structure is stronger, but the ratio of post-overload stiffness to pre-overload stiffness decreases
Solution Approach 1:
Different parts of the sensor have different stiffness characteristics tailored to their specific functions. The overload beams are designed with lower stiffness to ensure they fail first under overload, while the deformable beams maintain higher stiffness for precise measurement. This local differentiation of mechanical properties creates the desired stiffness ratio at overload activation.
Solution Approach 2:
The patent employs parameter changes by designing overload beams with specific geometric parameters (length, cross-section) that result in lower stiffness compared to the deformable beams. This parameter differentiation ensures that when overload occurs, the stiffness ratio between post-overload and pre-overload states is optimized for protecting the measurement system.
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 design increases the number of cycles before metal fatigue and the maximum force/torque the sensor can withstand, with a sharp inflection in the strain/force curve at overload actuation, enhancing the sensor's durability and accuracy.
Implementation Method 1
strain gages 1-6 translate strains at the beams' surfaces, caused by mechanical deformation of the beams, into electrical signals
Implementation Method 2
one or more overload beams close the overload gap, establishing rigid contact to both the TAP and MAP, nominally halting further relative motion between the TAP and MAP
Data Source
AI summary
A force/torque sensor includes a plurality of serpentine or spiral deformable beams connecting a TAP and MAP. These classes of shapes increase the overall length of the deformable beams, which reduces their stiffness. In addition to the deformable beams is a plurality of straight overload beams, each connected at a first end to one of the TAP and MAP, and separated from the other of the TAP and MAP at the second end by an overload gap of a predetermined width. Over a first range of forces and torques, strain gages on the deformable beams transduce compressive and tensile strains into electrical signals, which are processed to resolve the forces and torques. Over a second range of forces and torques greater than the first range, the overload beams close the overload gap, establishing rigid contact to both the TAP and MAP. The stiffness of the sensor in the second range of forces and torques is greater than over the first range.