Parallelogram Load Cell Axial Force Isolation
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Solution Overview
Problem
Existing load cells struggle to accurately measure axial forces due to the presence of bending loads, which introduces significant errors in applications like lower limb prosthetics and robotics, leading to inappropriate device reconfiguration and potential user safety issues.
Innovation Solution
A load cell with a substantially planar parallelogram linkage that isolates axial force measurements by using resilient links and a preload mechanism to constrain motion primarily along the longitudinal axis, coupled with sensors to detect separation and calculate load, thereby minimizing the impact of bending loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional load cells are used to measure axial forces, then the measurement system is simple, but bending loads introduce significant errors in the axial force measurement
Solution Approach 1:
The load cell is segmented into multiple functional components: a first member, a second member, resilient links, and a sensor. This segmentation allows each component to perform a specific function - the members transmit load, the resilient links provide compliance and isolation, and the sensor measures displacement - thereby improving measurement accuracy while keeping the overall structure manageable
Solution Approach 2:
Resilient links serve as intermediary elements between the first and second members. These links mechanically couple the members while isolating the sensor from bending loads through their compliant nature. The resilient links transfer only axial forces to the sensor, effectively filtering out bending load components and improving measurement precision
2Measurement precision
If additional sensors are added to compensate for bending load errors, then measurement accuracy improves, but device complexity and maintenance costs increase
Solution Approach 1:
The invention extracts and isolates the axial force measurement function from the bending load interference. By using the parallelogram linkage mechanism with resilient links, the system separates axial and bending load paths, allowing a single sensor to measure only axial forces accurately without needing additional sensors to compensate for bending errors
Solution Approach 2:
The resilient links perform multiple functions simultaneously: they mechanically couple the first and second members, provide compliance to isolate the sensor from bending loads, and ensure that only axial forces are transmitted to the sensor. This multi-functionality eliminates the need for additional compensation sensors
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 provides accurate axial force measurements with minimal bending load components, enhancing the control and stability of prosthetic, orthotic, and robotic devices, reducing complexity and maintenance costs by eliminating the need for additional sensors.
Implementation Method 1
the links can be substantially rigid or resilient. In the case of resilient links, the links can be configured to resist substantially any forces not substantially parallel to a plane of the flexible planar parallelogram linkage
Implementation Method 2
The preloading can be provided via a preload element mechanically coupling the first member and the second member. Exemplary preload elements include spring-loaded shoulder bolts or tension springs
Implementation Method 3
the sensor includes at least one generating element for generating a magnetic field disposed on a first of the first member and the second member and at least one detecting element disposed on a second of the first member and the second member, where the at least one detecting element is configured for detecting magnetic field variation and generating the at least one signal based on the magnetic field variation
Data Source
AI summary
A device includes a first member and a second member disposed in series along a longitudinal axis. The device also includes links coupling first joints of the first member to second joints of the second member. The first and second members and the links arranged to define a planar parallelogram linkage. The devices also include a resilient element disposed between the first member and the second member, the first member and the second member preloaded against the resilient element. The first member and the second member are preloaded to provide an arrangement of the first and the second joints in which a motion of the first joints with respect to the second joints is constrained to a direction substantially parallel to the longitudinal axis. The devices further include a sensor for generating a signal indicating a separation between the first member and the second member.