Flexible Piezoelectric Tactile Sensor Array for Dynamic Three-Axis Force Measurement

Abstract

A new flexible piezoelectric tactile sensor array based on polyvinylidene fluoride (PVDF) film is proposed for measuring three-axis dynamic contact force distribution. The array consists of six tactile units arranged as a 3 × 2 matrix with spacing 8 mm between neighbor units. In each unit, a PVDF film is sandwiched between four square-shaped upper electrodes and one square-shaped lower electrode, forming four piezoelectric capacitors. A truncated pyramid bump is located above the four piezoelectric capacitors to improve force transmission. A three-axis contact force transmitted from the top of the bump will lead to the four piezoelectric capacitors underneath undergoing different charge changes, from which the normal and shear components of the force can be calculated. A series of dynamic tests have been carried out by exerting sinusoidal forces with amplitudes ranging from 0 to 0.5 N in the x-axis, 0 to 0.5 N in the y-axis, and 0 to 1.5 N in the z-axis, separately. The tactile units show good sensitivities with 14.93, 14.92, and 6.62 pC/N in the x-, y-, and z-axes, respectively. They can work with good linearity, relatively low coupling effect, high repeatability, and acceptable frequency response in the range of 5–400 Hz to both normal and shear load. In addition, dynamic three-axis force measurement has been conducted for all of the tactile units. The average errors between the applied and calculated forces are 10.68% ± 6.84%. Furthermore, the sensor array can be easily integrated onto a curved surface, such as robotic and prosthetic hands, due to its excellent flexibility.

Flexible Shear and Normal Force Sensor Using only One Layer of Polyvinylidene Fluoride Film

“…We demonstrated how to make piezoelectric force sensors in a very simple fabrication process that can detect not only the normal but also the shear forces. Previous studies have been able to detect three-axis forces, but electrode patterning is essential, which involves complex processes such as lithography and sputtering [21,25,26]. In our method, this work makes it possible to detect biaxial forces simply by embedding a commercial piezoelectric film into the PDMS.…”

“…In contrast, the piezoelectric ones have the characteristic advantage of being self-powered, i.e., they generate electrical signals under external mechanical inputs [22,23]. With this benefit, several studies have been performed with piezoelectric force sensors that can measure shear forces [20,21,[24][25][26]. Specifically, therein, some researchers have assembled polydimethylsiloxane (PDMS) bump structures on flat or micropillar-type polyvinylidene fluoride (PVDF) and have used electrodes of specific shapes for effective sensing, resulting in the detection of shear and normal forces.…”

Physical sensors for skin‐inspired electronics

“…Piezoelectric‐type mechanical sensors can convert dynamic pressures into electrical signals via piezoelectric materials with the advantages of high sensitivity and fast response, which are widely used in dynamic monitoring . Piezoelectric effect refers to the spatial separation of positive and negative charges generated by an applied force, inducing by rearrangement of dipoles (Figure A) .…”

Ultrathin and Wearable Microtubular Epidermal Sensor for Real‐Time Physiological Pulse Monitoring

“…To overcome this, researchers have deposited conductive layers of carbon nanotubes, [8,15,16] nanoparticles, [17] nanowires, [18][19][20] and 2D materials, [21] onto stretchable substrates, resulting in an overall high mechanical deformability. The functional layers are usually further concealed into a multilayered matrix in patch format that contains a number of circuits sensitive to force-stimulated changes in capacitance, [28] piezoelectricity, [29,30] triboelectricity, [31] and resistance. [27] However, these restrict designs and integration of operational elements in a planar environment.…”

“…The microtube facilitates the deployment of liquid metallic alloy eGaIn which serves as a thin flexible conduit with excellent electrical conductivity and mechanical deformability. The functional layers are usually further concealed into a multilayered matrix in patch format that contains a number of circuits sensitive to force-stimulated changes in capacitance, [28] piezoelectricity, [29,30] triboelectricity, [31] and resistance. The self-sustaining fiber-like shape of the sensor is entirely conformal to human interfaces due to its ability to twist around 3D curvatures and objects.…”