Cantilever Beam Discontinuity for Force Sensor Stress Isolation
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Solution Overview
Problem
Existing endoscopic tools face challenges in accurately measuring forces during minimally invasive surgery due to stress concentration, strain overload, and nonlinear distribution of forces at the interfaces between the cantilever beam and its components, which affects the reliability and accuracy of force sensing.
Innovation Solution
The design incorporates a cantilever beam with a discontinuity between the active portion with strain sensors and the interface portions, where the cross-sectional area changes to isolate stress concentrations and strain overloads, ensuring a linear stress distribution along the beam length and maintaining consistent force sensing across a full range of motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If strain sensors are placed on the cantilever beam to measure forces, then force sensing capability is improved, but stress concentration and strain overload at the interfaces cause measurement inaccuracy and sensor damage
Solution Approach 1:
The cantilever beam is divided into distinct segments: an active portion with strain sensors, interface portions at the ends, and discontinuities (recessed regions) separating them. This segmentation isolates the sensors from stress concentrations at the interfaces, allowing accurate force measurement while protecting sensor reliability.
Solution Approach 2:
Different portions of the beam are designed with different cross-sectional areas to serve different functions: the active portion has a larger cross-sectional area to provide a linear stress distribution for accurate sensing, while the interface portions have smaller cross-sectional areas to concentrate stresses away from the sensor region. This local differentiation resolves the contradiction between measurement accuracy and sensor protection.
2Volume of moving object
If the cantilever beam is made smaller to reduce instrument size, then device compactness is improved, but stress concentrations and cable forces increase causing sensor damage and reduced cable life
Solution Approach 1:
The beam employs varying cross-sectional areas along its length: the active portion maintains sufficient size for linear stress distribution and sensor protection, while interface portions are reduced in size to minimize stress concentrations. This local quality variation allows compact overall design while protecting against harmful stress effects.
Solution Approach 2:
The harmful stress concentration effects are extracted and isolated to specific interface regions through discontinuities and reduced cross-sectional areas, separating them from the active sensing region. This extraction allows the sensor portion to operate in a protected, linear stress environment even in compact instrument designs.
3Area of stationary object
If the cross-sectional area of the beam is reduced to minimize instrument footprint, then device compactness is improved, but cable friction increases requiring pulleys and contoured surfaces
Solution Approach 1:
The beam design uses different cross-sectional areas in different regions: the active portion maintains adequate dimensions to minimize cable friction, while interface portions are reduced for compactness. This local differentiation allows the instrument to achieve small footprint without excessively increasing cable forces or friction.
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 enhances the accuracy and reliability of force sensing by isolating undesired stresses and maintaining consistent signal outputs, reducing the risk of strain sensor damage and improving the precision of force measurements during surgical procedures.
Implementation Method 1
The design incorporates a cantilever beam with a discontinuity between the active portion with strain sensors and the interface portions, where the cross-sectional area changes to isolate stress concentrations and strain overloads, ensuring a linear stress distribution along the beam length
Implementation Method 2
One or more strain sensors are on the middle portion of the beam... devices that include strain sensors on a cantilever beam coupled to an end effector used to measure forces applied to the end effector during a medical procedure
Data Source
AI summary
A medical device includes a shaft comprising a proximal end portion and a distal end portion. A beam has a proximal end portion, a distal end portion, and a middle portion, and one or more strain sensors are on the middle portion. The proximal end portion of the beam is matingly coupled to the distal end portion of the shaft to form an interface. The beam comprises a discontinuity between the interface and the middle portion of the beam. In some embodiments, the medical device includes a link and the distal end portion of the beam is matingly coupled to the link to form a second interface. A second discontinuity is between the second interface and the middle portion of the beam. In some embodiments, an anchor is coupled to the shaft and the proximal end portion of the beam is matingly coupled to the anchor.