Force Sensor Thermal Expansion Suppression via Material Matching
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Solution Overview
Problem
Force sensors used in robot arms face accuracy issues due to thermal expansion differences between the case body and strain body, causing variations in the zero point and reduced detection accuracy.
Innovation Solution
A force sensor design featuring a cylindrical main body and movable body with circular openings, first and second stoppers, and strain sensors, where the second stopper is configured as a thermal expansion suppressing member made of the same material as the strain body to maintain consistent thermal expansion and prevent excessive deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the case body and strain body are constituted of materials different from each other in coefficient of thermal expansion, then the case body can be made lighter or stronger, but the strain body receives a strain concomitant with the expansion or contraction of the case body, causing zero point variation and reduced detection accuracy
Solution Approach 1:
The invention applies different material properties to different parts of the structure. The case body is made of a material with high strength and stiffness, while the strain body is made of a material with high elasticity modulus and low thermal expansion coefficient. This local differentiation allows each component to have optimized properties for its specific function, resolving the contradiction between case body strength and measurement precision.
Solution Approach 2:
The invention changes the material parameters (coefficient of thermal expansion, elasticity modulus) of the strain body to be different from the case body. Specifically, the strain body uses a material with a lower coefficient of thermal expansion and higher elasticity modulus, which prevents thermal strain on the strain body while maintaining the structural integrity of the case body, thus improving detection accuracy without sacrificing strength.
2Weight of moving object
If the case body and strain body are constituted of materials different from each other in coefficient of thermal expansion, then the case body can be made lighter, but the strain body receives a strain concomitant with the expansion or contraction of the case body, causing zero point variation and reduced detection accuracy
Solution Approach 1:
The invention applies different material properties to different parts of the structure. The case body is made of a material with high strength and stiffness, while the strain body is made of a material with high elasticity modulus and low thermal expansion coefficient. This local differentiation allows each component to have optimized properties for its specific function, resolving the contradiction between case body weight and measurement precision.
Solution Approach 2:
The invention changes the material parameters (coefficient of thermal expansion, elasticity modulus) of the strain body to be different from the case body. Specifically, the strain body uses a material with a lower coefficient of thermal expansion and higher elasticity modulus, which prevents thermal strain on the strain body while maintaining the structural integrity of the case body, thus improving detection accuracy without sacrificing weight efficiency.
3Measurement precision
If a thermal expansion suppressing member is added to prevent zero point variation, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The invention merges the thermal expansion suppressing member with the existing case body structure. The strain body is positioned and fixed within the case body in such a way that the case body itself serves as the thermal expansion suppressing member. This integration eliminates the need for separate thermal expansion suppression components, improving measurement accuracy while minimizing the increase in device complexity.
Solution Approach 2:
The case body is designed to serve multiple functions: structural support, housing for the strain body, and thermal expansion suppression. By making the case body multi-functional, the invention avoids adding separate components for thermal expansion suppression, thus improving measurement accuracy without significantly increasing device complexity.
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 enhances measurement accuracy by stabilizing the zero point and preventing excessive deformation of the strain body, improving safety and reliability while allowing for downsizing and weight reduction of the sensor.
Implementation Method 1
if the case body and strain body are constituted of materials different from each other in coefficient of thermal expansion, if the case body expands or contracts by the ambient temperature variation, the strain body receives a strain concomitant with the expansion or contraction of the case body
Data Source
AI summary
In a force sensor according to one embodiment, a main body is cylindrical. A cylindrical movable body is movable with respect to the main body and includes at least three circular openings in the outer circumference thereof. A strain body is fixed to the main body and the movable body and is deformable according to the movement of the movable body. Strain sensors are provided on the strain body. A first stopper is arranged inside each of the openings and includes a first outer circumferential surface including a first outer diameter less than a diameter of the opening. A cylindrical second stopper is arranged separate from a first inner circumferential surface of the main body by a first distance, includes a second outer circumferential surface of a second outer diameter less than a diameter of the first inner circumferential surface.