3D Force and Displacement Sensor for SFA and AFM Measurements

Abstract

A new device has been designed, and a prototype built and tested, that can simultaneously measure the displacements and/or the components of a force in three orthogonal directions. The "3D sensor" consists of four or eight strain gauges attached to the four arms of a single cross-shaped force-measuring cantilever spring. Finite element modeling (FEM) was performed to optimize the design configuration to give desired sensitivity of force, displacement, stiffness, and resonant frequency in each direction (x, y, and z) which were tested on a "mesoscale" device and found to agree with the predicted values to within 4-10%. The device can be fitted into a surface forces apparatus (SFA), and a future smaller "microscale" microfabricated version can be fitted into an atomic force microscope (AFM) for simultaneous measurements of the normal and lateral (friction) forces between a tip (or colloidal bead probe) and a surface, and the topography of the surface. Results of the FEM analysis are presented, and approximate equations derived using linear elasticity theory are given for the sensitivity in each direction. Initial calibrations and measurements of thin film rheology (lubrication forces) using the "mesoscale" prototype show the device to function as expected.

Development of 3D Force Sensors for Nanopositioning and Nanomeasuring Machine

“…Compared to work done by other group, the four arm titanium foil sensor gives H:V ratio of 1:15 [5], which is lower then one boss full and cross membrane.…”

“…Using the 3σ and the measured sensitivity, the minimum force and displacement can be calculated, which is 9 μN and 1.4 nm, respectively. In comparison to the result of four armed titanium force sensor (160 μN and 840 nm) [5], our sensors have 18 times higher accuracy for force measurement and 600 times for the displacement measurement.…”

“…There are other optical- and laser-based measurements on multi-sensor systems which provide highly accurate measurement on visible surfaces, but it is difficult to use these systems for 3D measurements. This is an important reason why many groups are working on developing a tactile sensor using a four arm structure [5-8] for contact probing.…”

“…Recently, a 3D force sensor has been fabricated using a titanium foil, where a stylus is attached to the centre of the symmetrical four-arm titanium foil structure [5]. The drawback is that the strain gauges are individually glued onto the titanium foil which leads to variations in the position of the strain gauges on the foil.…”

Vision-Based Microforce Measurement With a Large Range-to-Resolution Ratio Using a Twin-Scale Pattern

“…Variations of system behavior and poor signal-to-noise ratio being key features at the microscale, it is then highly important to have the best initial signal quality (displacement or stress). To tackle this key lock, many works propose smart, optimized, or improved designs and combine it with one measurement principle among the most used: capacitive [6]- [8], piezoresistive [9]- [11], strain gauges [12], [13], magnetic [14], [15], or whether optical [10], [16], [17]. Several research teams notably proposed compliant systems with improved shapes and reduced stiffness (notably to improve resolution) [18], [19].…”