Differential Magnetic Load Cells for Compact Low-Hysteresis Sensing
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Solution Overview
Problem
Existing non-contact position measurement technologies lack the necessary resolution for compact load cell applications requiring high sensitivity and low hysteresis for measuring small displacements, especially in force and torque measurements, and often require large overlapping areas for low noise measurements.
Innovation Solution
The development of differential magnetic load cells using magnetic field generating devices and sensing devices, such as Hall effect sensors, arranged in pairs across a flexure to measure displacement non-contactly, allowing for precise measurement of small forces and torques without the need for large overlapping areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If non-contact magnetic field measurement is used for high resolution displacement sensing, then measurement precision is improved, but device area increases due to large overlapping areas required for low noise measurement
Solution Approach 1:
The patent changes the physical parameters of the magnetic field configuration by using opposing magnetic poles arranged in a differential configuration. This creates a magnetic field gradient that is highly sensitive to displacement while requiring minimal overlapping area. The parameter change from single-pole to dual-pole opposing configuration enables high resolution measurement in a compact geometry.
Solution Approach 2:
The patent transitions from measuring magnetic field strength in one dimension to measuring the gradient of the magnetic field across multiple dimensions. By arranging sensors to detect changes in the magnetic field gradient caused by displacement, the system achieves high measurement precision without requiring large overlapping areas, effectively utilizing spatial dimensionality to enhance sensitivity.
2Reliability
If strain gauge bonding is used for force measurement, then measurement reliability is improved, but hysteresis and temperature dependence increase
Solution Approach 1:
The patent replaces the mechanical bonding system of strain gauges with a non-contact magnetic field sensing system. This substitution eliminates the physical bond between the sensor and the measured structure, thereby removing the source of hysteresis and temperature-dependent bonding failures while maintaining measurement reliability through the differential magnetic sensing configuration.
Solution Approach 2:
The patent introduces a magnetic field as an intermediary between the force application point and the measurement system. Instead of directly bonding a sensor to the structure, the magnetic field serves as a non-contact mediator that transmits displacement information from the flexure to the sensors, eliminating direct mechanical contact and its associated hysteresis problems.
3Volume of moving object
If compact load cell geometry is used, then device size is reduced, but measurement precision deteriorates due to insufficient overlapping area
Solution Approach 1:
The patent changes the operational parameters of the magnetic sensing system by utilizing magnetic field gradients rather than absolute field strength measurements. This parameter change allows the system to achieve high measurement precision in a compact volume, as the gradient-based differential measurement is more sensitive to small displacements and does not require large sensor-magnet overlapping areas.
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 approach enables compact, low-hysteresis force and torque measurement devices with high sensitivity and resolution, capable of accurately measuring small displacements, reducing noise and eliminating the need for large overlapping areas, thus enhancing the precision and robustness of load cell applications.
Implementation Method 1
uses the magnetic field instead of the electric field for non-contact displacement measurement
Implementation Method 2
The magnetic field sensing devices can be one of a number of room-temperature magnetic field sensing technologies, including Hall-effect sensors
Data Source
AI summary
Magnetic load cells that measure force and/or torque are constructed from magnets and one or more arrays of magnetic field sensors. The magnetic field sensors are structured in a tight array where the array is attached to a first portion of a frame. The magnets are operated in pairs polarized in opposition to one-another. In particular, pairs of concentric magnets create sharp field boundaries. The magnets are attached to a second portion of the frame with the magnets separated from the array of field sensors by a small gap. The second portion of the frame is free to displace or rotate in relation to the first portion of the frame when a force or torque is applied to it. The displacement results in a measurable differential change in magnetic field reported by the array that can be sampled and processed to relate to the applied force or torque.