Self-Calibrating Micro-Fabricated Load Cell for High-Resolution Force Measurement
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Solution Overview
Problem
Current micro-mechanical test frames lack the necessary force and displacement range, resolution, and versatility for accurately characterizing small-scale materials and structures, with existing MEMS load cells being limited in their ability to measure forces with resolutions in the 1-100 nN range and achieve large displacements while allowing optical access for strain mapping.
Innovation Solution
A self-calibrating micro-fabricated load cell comprising a resonant double-ended tuning fork force sensor and a phase-locked loop circuit for detecting frequency changes upon external load application, enabling precise measurement of forces with a resolution of 7 nN and a compressive load range of 0.085N, and integrated with a micro-mechanical test frame for characterization of materials and structures at small scales.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If resonant MEMS load cells are used, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent employs a resonant double-ended tuning fork (DETF) structure that utilizes mechanical vibration at its resonant frequency to detect force measurements. The resonant oscillation of the tuning fork tines provides enhanced sensitivity for detecting small forces, achieving resolutions in the 1-100 nN range while maintaining a relatively simple micro-fabricated structure.
Solution Approach 2:
The patent implements a phase-locked loop (PLL) circuit that provides feedback control to maintain the tuning fork at its resonant frequency. The PLL detects frequency shifts caused by applied forces and adjusts the drive signal accordingly, enabling precise force measurement through frequency modulation while keeping the overall system architecture manageable.
2Measurement precision
If resonant frequency detection is used, then measurement precision is improved, but ease of operation deteriorates
Solution Approach 1:
The patent implements a self-calibrating mechanism where the system automatically determines its own calibration factors by measuring the resonant frequency of the tuning fork structure. The scale factor and offset are computed autonomously through frequency measurements at known states, eliminating the need for external calibration instruments or manual calibration procedures.
3Productivity
If micro-mechanical test frame is used, then productivity is improved, but adaptability deteriorates
Solution Approach 1:
The patent designs a universal micro-mechanical test frame platform that can characterize various microstructures including wires, films, and three-dimensional structures. The system achieves versatility through software configuration and interchangeable sample mounting mechanisms, allowing the same hardware platform to perform mechanical characterization across different material types and geometries without requiring physical reconfiguration.
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 a cost-effective, ultra-sensitive load cell with a dynamic range of 140 dB and a scale factor of 216 kHz/N, capable of characterizing small-scale materials with unprecedented force and displacement resolution and range, and is adaptable to various microstructures, allowing for accurate mechanical characterization without the need for external calibration instruments.
Implementation Method 1
a resonant double ended tuning fork force sensor and a phase locked loop circuit for detection of frequency changes upon external load application to the resonant double ended tuning fork force sensor
Data Source
AI summary
Self calibrating micro-fabricated load cells are disclosed. According to one embodiment, a self calibrating load cell comprises a resonant double ended tuning fork force sensor and a phase locked loop circuit for detection of frequency changes upon external load application to the resonant double ended tuning fork force sensor.