Guanhao Liang

Flexible Capacitive Tactile Sensor Array With Truncated Pyramids as Dielectric Layer for Three-Axis Force Measurement

This paper presents a flexible capacitive tactile sensor array embedded with a truncated polydimethylsiloxane pyramid array as a dielectric layer. The proposed sensor array has been fabricated with 4 × 4 sensor units. The measurement ranges of forces in the x-axis, y-axis, and z-axis are 0-0.5, 0-0.5, and 0-4 N, respectively. In the range of 0-0.5 N, the sensitivities of the sensor unit are 58.3%/N, 57.4%/N, and 67.2%/N in the x-axis, y-axis, and z-axis, respectively. In the range of 0.5-4 N, the sensitivity in the z-axis is 7.7%/N. Three-axis force measurement has been conducted for all the sensor units. The average errors between the applied and calculated forces are 11.8% ± 6.4%. The sensor array has been mounted on a prosthetic hand. A paper cup and a cube are grasped by the prosthetic hand and the three-axis contact force is measured in real time by the sensor array. Results show that the sensor can capture the three-axis contact force image both in light and tight grasping. The proposed capacitive tactile sensor array can be utilized in robotics and prosthetic hand applications.

Modeling and Analysis of a Flexible Capacitive Tactile Sensor Array for Normal Force Measurement

This paper presents an analytical model to analyze the flexible capacitive tactile sensor array for normal force measurement. The tactile sensor array consists of six layers, including a bottom polyethylene terephthalate film, a lower copper plate, a polydimethylsiloxane film, an upper copper plate, a polyimide (PI) film, and a top PI bump, respectively. By simplifying the sensing unit into a two-layer structure, an analytical model is developed to study the normal force prediction. Finite element modeling (FEM) is conducted to analyze the deformation of the sensing unit, and is compared with the analytical model. Results show that analytical model predicted deformation matches well with the FEM analysis. The change of capacitance verse normal force is obtained, and can be utilized for accurate normal force measurement. Based on the established analytical model, the behaviors of the proposed sensor are analyzed by applying uneven force and shear force.

An analytical model for studying the structural effects and optimization of a capacitive tactile sensor array

This paper presents an analytical model to study the structural effects of a capacitive tactile sensor array on its capacitance changes and sensitivities. The tactile sensor array has 8 × 8 sensor units, and each unit utilizes the truncated polydimethylsiloxane (PDMS) pyramid array structure as the dielectric layer to enhance the sensing performance. To predict the capacitance changes of the sensor unit, it is simplified into a two-layered structure: upper polyethylene terephthalate (PET) film and bottom truncated PDMS pyramid array. The upper PET is modeled by a displacement field function, while each of the truncated pyramids is analyzed to obtain its stress–strain relation. Using the Ritz method, the displacement field functions are solved. The deformation of the upper electrodes and the capacitance changes of the sensor unit can then be calculated. Using the developed model, the structural effects of the truncated PDMS pyramid array and the PDMS bump on the capacitance changes and sensitivities are studied. To achieve the largest capacitance changes, the dimensions have been optimized for the sensor unit. To verify the developed model, we have fabricated the sensor array, and the average sensitivities of the sensor unit to the x-, y-, and z-axes force are 0.49, 0.50, and 0.32% mN−1, respectively, while the model predicted values are 0.54, 0.54, and 0.35% mN−1. Results demonstrate that the developed model can accurately predict the sensing performance of the sensor array and could be utilized for structural optimization.

A flexible tactile sensor array based on pressure conductive rubber for three-axis force and slip detection

This paper presents a novel flexible tactile sensor array with the capabilities to measure three-dimensional (3D) forces and slip occurrence by using the INASTAMOR pressure conductive rubber as the sensing material. The tactile sensor array has 3 × 3(= 9) sensing units, and each unit has a three-layered structure: bottom electrode, middle conductive rubber chips, and top PDMS bump. The structural design, 3D force and slip detection principles, fabrication process of this sensor array are presented. The fabricated sensor array has a spatial resolution of 7 mm. 3D force measurement and slip detection performances of this sensor array are characterized experimentally. Results demonstrated that the sensor array can measure 3D forces. The full-scale range and sensitivities of force measurements for x-, y- and z-axes are 5 N, 5 N, 20 N and 0.65 V/N, 0.67 V/N, 0.23 V/N, respectively. Results also showed the sensor array could detect slipping by using the discrete wavelet transform (DWT) to analyze the measured force data. Thus, the proposed flexible tactile sensor array could be applied to robot hand grasping application that requires slip detection and 3D contact force measurement.

A flexible capacitive tactile sensor array with high scanning speed for distributed contact force measurements

This paper presents an 8×8 (=64) capacitive tactile sensor array with integrated four capacitance-digital-converter (CDC) scanning circuit for three-axis force measurement. For the structural design of the sensor array, the upper and lower electrodes generate four capacitors in one sensing unit and decompose the contact force into three-axis force components. To enhance the flexibility, a thinner PDMS bump (0.5 mm) and truncated pyramid dielectric layer with finer dimensions are utilized. To increase the scanning speed, we divide the sensor array into four regions and using four CDC circuits to simultaneously measure the capacitance changes of these regions. The sensor array is mounted onto a hand finger for grasping of a paper cup. Results showed that the sensor array can detect the distributed contact force at high scanning speed, thus could be utilized in robotic grasping applications.

A Micro-wires Based Tactile Sensor for Prosthesis

Tactile sensor is indispensable in prosthesis for object manipulation. This study presented a novel tactile sensor based on the conductive micro-wires that can measure the normal and shear forces. The developed sensor consists of four layers, from bottom to top are the substrate supporting, polyimide based matrix circuit, micro-wire based sensing, and top surface bump layers, respectively. To improve the sensing performance, structural dimensions were optimized. According to the optimization results, analytical models and finite element analysis FEA were conducted to study the normal and shear force sensing performance of the sensor. To develop the tactile sensor, the carbon-black based conductive polymer was firstly fabricated, and then the conductive micro-wires were manufactured by using the method of micro-contact printing μCP. The results demonstrate that the machined micro-wires have dimensions of 250 μm in width and 50 μm in height.

Design and simulation of bio-inspired flexible tactile sensor for prosthesis

In human hand skin, there are four kinds of mechanoreceptors with different sensing mechanisms to detect both gentle touch and high pressure. In this study, an integrated bio-inspired tactile sensor array, which consists of a capacitive layer and a pressure-sensitive-rubber (PSR) based layer, is designed for prosthesis application. The capacitive layer can detect the low-pressure, while the PSR-based layer is designed to detect the high-pressure. The capacitive layer and PSR-based layer are integrated together with space resolution of 2 mm and 1 mm, respectively. For the designed sensor array, the finite element analysis (FEA) is conducted to study the effects of the dimensions of polyimide in capacitive layer and the Youngs modulus of the conductive rubber in PSR-based layer on the sensing performance. The simulation results show that the developed bio-tactile sensor array is highly sensitive in both low and high pressure range.

Flexible Tactile Sensor Array Mounted on the Curved Surface: Analytical Modeling and Experimental Validation

This paper presents an analytical model to study the sensing performance of the flexible capacitive tactile sensor array when mounted on a curved surface. To predict the deformation of the sensor unit, a cylindrical coordinate is constructed for the upper Polyethylene Terephthalate (PET) and truncated pyramids dielectric layer. The displacement functions model is developed and solved by using the Ritz method. Then, this model is utilized to investigate the capacitance change of the sensor unit and the model-calculated results are compared with the experiment data. Both model calculated and experiment measured results indicate that the capacitances of the sensor array are increased by about 30% when the sensor is mounted on the curved surface with a radius of curvature of 10 mm. Due to the bending effects of the curved surface, the sensitivities of the sensor array are decreased based on the model calculation and are confirmed by experimental validation. Thus, results demonstrate that the developed analytical model can accurately predict the sensing performance of the tactile sensor array on the curved surface and could be utilized for the real applications. [2016-0235]

Preliminary experimental study on the sensing performance of a capacitive tactile sensor array mounted on curved surfaces

In real applications, the capacitive tactile sensor array usually needs to be mounted on curved surfaces. To study the effect of curved surfaces on the sensing performance of the sensor array, we have fabricated the sensor array with 4 × 4 sensor units. Four types of rigid and flexible curved surfaces are selected to mount the sensor array, with radius of curvature of +∞, 40 mm, 30 mm, and 20 mm. The initial capacitances of the sensor array increase as the radius of the surfaces decrease. By applying normal and shear forces to the sensor unit mounted on the curved surfaces, we have found that as the radius of the surface decrease, the capacitance increases faster when the sensor is mounted on 40 mm curved surfaces, and increases slower on 30 mm and 20 mm curved surfaces. The shear forces in the x- and y-axes cause symmetric and asymmetric capacitance changes to the sensor unit, respectively. The flexible curved surfaces can induce larger capacitance changes to the sensor unit, compared with the rigid ones.