Load Cell Diaphragm Thickness Gradient for Strain Homogeneity
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Solution Overview
Problem
Existing load cells experience inaccuracies in weight measurement due to varying local strain on the diaphragm depending on the radius, making it complex to determine weight values within predefined error limits.
Innovation Solution
The load cell design ensures analogous strain behavior by adjusting the thickness and arrangement of strain gauges, particularly by compensating for the larger circumference with a smaller thickness at the larger radius, and optimizing the placement and orientation of strain gauges to achieve symmetrical strain distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If strain gauges are arranged at different radii on the diaphragm to detect strain, then the ability to detect weight is improved, but the measurement precision deteriorates due to varying local strain depending on the radius
Solution Approach 1:
The diaphragm is designed with non-uniform thickness distribution, where the thickness varies as a function of the radial distance from the central axis. Specifically, the thickness is greater at smaller radii and smaller at larger radii, following a relationship that compensates for the varying strain distribution. This local quality variation ensures that strain gauges at different radii experience comparable strain magnitudes, enabling accurate weight measurement across the entire diaphragm surface.
2Manufacturing precision
If the diaphragm thickness is uniform across all radii, then the manufacturing precision is improved, but the measurement precision deteriorates due to inconsistent strain distribution
Solution Approach 1:
The diaphragm thickness parameter is intentionally made variable rather than uniform. The thickness is designed to decrease with increasing radial distance from the central axis, following a specific functional relationship that compensates for the geometric strain variation. This parameter change allows the diaphragm to maintain consistent strain characteristics across different regions while remaining manufacturable through standard fabrication processes.
3Measurement precision
If the diaphragm thickness decreases with increasing radius, then the measurement precision is improved by equalizing strain distribution, but the manufacturing precision may be affected due to varying thickness requirements
Solution Approach 1:
The diaphragm employs a deliberately designed non-uniform thickness distribution where local quality varies according to the radial position. The thickness is greater near the central axis and progressively smaller toward the outer edge, creating a gradient that compensates for the increasing circumference and strain variation at larger radii. This local quality variation is achieved through standard manufacturing techniques while ensuring consistent strain behavior across the diaphragm.
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 the accuracy of weight measurement by ensuring consistent strain magnitude across different regions, facilitating precise evaluation of the Wheatstone bridge signal and reducing manufacturing deviations.
Implementation Method 1
several, in particular at least four or exactly four, strain gauges arranged on an underside of the membrane for detecting a stretching and/or compressing deformation of the spring body
Implementation Method 2
the strain gauges are electrically connected to a Wheatstone bridge or as part thereof
Implementation Method 3
an annular deformation section, which is designed as a circular membrane... for detecting a stretching and/or compressing deformation of the spring body
Data Source
Figure 1~2
Figure 3~4
Figure 5A
AI summary
The invention relates to a load cell comprising a spring body rotationally symmetrical about a central axis with an outer bearing ring, an upwardly projecting inner force application element, and an annular deformation section, which is designed as an annular membrane and via which the bearing ring and the force application element are rigidly connected to each other, and several strain gauges arranged on an underside of the membrane for detecting a stretching and/or compressing deformation of the spring body, wherein the strain gauges are electrically connected to a Wheatstone bridge or as part thereof, wherein at least one first strain gauge, in particular two first strain gauges, are arranged on a first circle with a first radius around the central axis of the spring body, and at least one second strain gauge, in particular two second strain gauges, are arranged on a second circle with a second radius.which is larger than the first radius, lies around the central axis of the spring body. The average thickness of the annular diaphragm is greater in the region of the first strain gauge(s) than the average thickness in the region of the second strain gauge(s).