Platform Load Sensing System with Separated Load Path
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Solution Overview
Problem
Existing platform load sensing systems face inaccuracies due to the direct transfer of forces and moments, leading to complex mechanisms with large errors in vertical load measurement, as they fail to isolate the platform load from its associated moment.
Innovation Solution
A platform load sensing system with a controlled load path using pivotally connected sides and upper and lower link assemblies, where the platform load is transferred through a shear beam load cell, separating the load from its moment, and utilizing a spherical surface and load cell to ensure perpendicular loading, thereby minimizing tangential components and enhancing accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If platform supports are directly bolted to the boom without allowance for relative vertical motion, then the structure is simple and rigid, but the rotator weldment receives forces from two sources (vertical load and moment) making it difficult to separate the loads for accurate sensing
Solution Approach 1:
The platform support structure is segmented into distinct functional components: upper and lower bearing links for moment transfer, a load member (carriage bolt) for vertical load transfer, and a load cell for sensing. This segmentation separates the moment load path from the vertical load path, allowing accurate measurement of vertical load while maintaining structural integrity.
Solution Approach 2:
The load member (carriage bolt) acts as an intermediary element between the platform support and the load cell. It specifically transfers only the vertical load component to the load cell while allowing moment forces to be transferred through the bearing links, thus isolating the sensing element from moment interference.
2Measurement precision
If complex mechanisms with springs are used to separate vertical load from moment, then load separation is attempted, but large errors in actual vertical load measurement occur
Solution Approach 1:
The moment transfer function is extracted from the load path and assigned to the upper and lower bearing links. This allows the vertical load to be taken out and transferred independently through the load member to the load cell, eliminating the interference between moment and vertical load that plagues spring-based mechanisms.
Solution Approach 2:
The complex spring-based mechanical separation mechanism is replaced with a simpler pivoting link assembly. The bearing links with pivot points provide the necessary moment transfer capability without the complexity and measurement errors associated with spring mechanisms. The spherical surface and pivot points create a kinematic constraint system that naturally separates the load paths.
3Adaptability or versatility
If the load cell is exposed to both vertical load and moment forces, then the structure is simple, but the sensing system performance deteriorates due to inability to meet specific vertical load sensing requirements
Solution Approach 1:
The load path control structure implements local quality by designing specific geometric features at critical interfaces: spherical surfaces at pivot points and a specifically shaped load member head. These local geometric features ensure that only vertical forces are transmitted to the load cell while moment forces are directed through the bearing links, providing the adaptability needed for precise vertical load sensing.
4Measurement precision
If tangential components of applied load are present at the load cell interface, then the structure is simpler, but measurement accuracy decreases
Solution Approach 1:
Spherical surfaces are used at the pivot points of the bearing links and at the interface between the load member and load cell. These curved surfaces ensure that contact forces are always directed along the normal to the spherical surface, which is configured to be perpendicular to the load cell's sensitive axis. This eliminates tangential components that would otherwise cause measurement errors.
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 achieves more accurate load measurements by isolating the platform load from its moment, reducing errors and improving the overall precision of the load sensing system, while also providing a control system for error detection and operational adjustments.
Implementation Method 1
a metal block with an engineered shape and an integral electrical strain gage, so that the strain gage output can be directly interpreted as a force
Data Source
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AI summary
A platform load sensing system connected between a boom and a platform includes an upper bearing link connecting the boom side to the platform side, and a lower bearing link connecting the boom side to the platform side. The upper and lower bearing links are configured to allow for relative motion between the boom side and the platform side. A load member is secured to the platform side between the upper and lower bearing links, and a load cell is secured to the boom side. A load moment on the platform side is functionally eliminated by the upper and lower bearing links, and a vertical load on the platform side is transferred through the load member to the load cell.