Strain Gage Fixation for Axial Load Measurement Accuracy
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Solution Overview
Problem
Surgical stapling devices with strain gages face accuracy issues due to unintended forces and bending stresses, which affect the measurement of axial loads during stapling and cutting procedures.
Innovation Solution
A strain gage assembly with multiple strain gages configured to measure axial loads directly, eliminating off-axis loading by computing force vector magnitude and direction, or using a ball-in-socket configuration to allow rotational freedom, thereby reducing the impact of bending stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If strain gages are used to measure axial loads in surgical stapling devices, then force awareness feedback is provided, but bending stresses from off-axis forces reduce measurement accuracy
Solution Approach 1:
A spherical interface is introduced as an intermediary between the strain gage housing and the load path. This sphere allows rotational freedom and accommodates off-axis forces while ensuring that only axial loads are transmitted to the strain gages, thereby eliminating bending stresses and improving measurement accuracy
Solution Approach 2:
The load path is segmented into distinct functional zones: a spherical interface that handles rotational freedom and off-axis forces, a strain gage mounting section that measures only axial loads, and separate structural support elements. This segmentation isolates the strain gages from harmful bending moments while maintaining overall structural integrity
2Measurement precision
If strain gages are mounted in the elongate body, then force awareness feedback is achieved, but small variations in component location and force direction negatively impact accuracy
Solution Approach 1:
The housing is designed with dynamic compliance through the spherical interface, allowing it to adapt to variations in force direction and component positioning. This dynamic adjustment capability eliminates the need for precise static alignment, reducing manufacturing complexity while maintaining measurement accuracy
Solution Approach 2:
The design changes the mechanical parameters of the housing to include rotational degrees of freedom and compliant mounting features. These parameter changes allow the system to tolerate variations in component location and force direction without compromising measurement accuracy
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
The solution effectively eliminates the effect of off-axis loading, providing accurate measurements of axial loads and improving the consistency of staple formation and tissue cutting by directly measuring uniaxial tensile stress, enhancing the precision and reliability of surgical stapling devices.
Implementation Method 1
a plurality of strain gages disposed about the extension portion of the housing. The plurality of strain gages is configured to measure an axial load on the trocar assembly
Data Source
AI summary
A strain gage assembly for use in a circular stapling device includes a housing having a base portion, an extension portion, and a flange disposed on a free end of the extension portion. A plurality of strain gages is disposed about the extension portion. An anchor supports the housing, and a support is received about the housing and in engagement with the anchor. The strain gages are configured to measure an axial load on the trocar assembly received within the longitudinal passage of the housing. The anchor includes a cylindrical portion having an end and a rim disposed about the end of the cylindrical portion. The anchor defines a cylindrical recess and an opening in communication with the cylindrical recess. The cylindrical recess receives the flange when the extension portion is received within the opening. The support includes a collar for supporting a reload assembly of the circular stapling device.