Internal Strain Gauge Load Cell Instrumentation for Harsh Conditions
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Solution Overview
Problem
Existing strain gauge load cells are not adequately protected from external agents and mechanical stresses, leading to damage and reduced reliability in heavy applications.
Innovation Solution
The strain gauges are applied within cavities of a monolithic elastic element using a printed circuit with an adhesive layer, where the strain gauge is joined to the internal surface via polymerized glue, ensuring protection and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If strain gauges are positioned on the external surface of the pin, then the load cell can detect and record load forces, but the strain gauges are exposed to external agents and mechanical elements that can damage them
Solution Approach 1:
The strain gauges are positioned inside a cavity within the pin structure, nesting the sensitive component within the protective body of the load cell. This internal positioning protects the strain gauges from external damage while maintaining the load detection function through the elastic element's deformation.
Solution Approach 2:
The pin is divided into functional zones: an external elastic element for force transmission and an internal cavity for housing the strain gauges. This segmentation separates the protective structural function from the sensitive measurement function, allowing each to be optimized independently.
2Reliability
If strain gauges are protected with resins and/or metal plates, then they are protected from external agents, but the protection mechanisms increase device complexity and may interfere with structural elements
Solution Approach 1:
Instead of adding protective layers in the external dimension (resins and metal plates covering the strain gauges), the solution moves the strain gauges to an internal dimension (inside the cavity). This dimensional relocation provides protection without adding external protective structures that complicate installation and maintenance.
3Ease of manufacture
If strain gauges are glued on external surfaces, then the manufacturing process is simple, but the strain gauges are vulnerable to damage in heavy applications
Solution Approach 1:
The strain gauges are nested inside the cavity of the pin, providing mechanical protection while maintaining the simple gluing manufacturing process. The cavity structure itself serves as the protective element, eliminating the need for additional protective materials.
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 method effectively protects the strain gauges, enhancing their reliability and precision while allowing use in severe conditions at reduced production costs.
Implementation Method 1
an adhesive layer, so as to be able to temporarily associate it with an internal wall of the abovementioned cavity
Implementation Method 2
stabilize the joining of the strain gauge or gauges to the elastic element by means of polymerization of a glue applied to only the strain gauge/gauges
Data Source
Figure 1~3
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Figure 8~9
AI summary
A method for internally instrumenting a strain gauge load cell, comprises: preparing a monolithic elastic element (2) of a load cell (1), wherein the monolithic elastic element (1) has a cavity (3); preparing at least one printed circuit (5) comprising at least one strain gauge (15), wherein the printed circuit (5) has a first face (11) configured to be coupled to the monolithic elastic element (2) and a second face (13) opposite the first face (11), wherein an adhesive layer (12) is placed on at least part of the first face (11) except at the strain gauge (15); applying a layer of glue (22) on the first face (11) and substantially only at the strain gauge (15); inserting the printed circuit (5) in the cavity (3), making the adhesive layer (12) adhere to an internal surface (4) of the cavity (3); pressing the strain gauge (15) against the internal surface (4) so as to make the layer of glue (22) polymerize and to stably join the strain gauge (15) to the internal surface (4).