Tactile Sensor Array Research Articles

Woven flexible textile structure for wearable power-generating tactile sensor array

In this paper, we propose and demonstrate a power-generating tactile sensor array in which an energy harvester and an array of tactile sensors are integrated in a single device. The device consists of rows and columns of piezoelectric straps woven on a mesh structure of elastic hollow tubes. The fabricated device, which includes 5 × 5 capacitive tactile sensors in an area of 9 × 9 cm2, is highly flexible and stretchable. When the device was stretched in a lateral direction, the maximum output voltage and power were measured as 51 V and 850 μW, respectively. In addition, the capacitance value employed as a signal for the tactile sensor operation was measured while applying a force vertically to the surface using a force gauge. The initial capacitance and sensitivity of a single cell employed as a tactile sensor were approximately 1.727 pF and 40 fF/N, respectively, within a force range of 2 N.

Abstract P1-02-09: Clinical studies of palpation imaging of the breast on over 1000 patients

Abstract INTRODUCTION Palpation Imaging (PI) of the breast is based on the principles of tactile imaging, a method for measuring the elasticity lesions using a tactile sensor array. PI provides objective data beyond subjective manual palpation by quantifying the shape and hardness of a lesion as well as creating a permanent digital image. PI is also known as "Tactile Imaging", "Mechanical Imaging", "Stress Imaging" or "Computerized Palpation". It quantitatively evaluates mechanical and structural properties of a breast lesion that is altered by tumor growth, and provides a quantitative characterization of the detected lesion. PI is a radiation-free and an inexpensive in comparison to other imaging devices. The purpose of this paper is to evaluate the clinical efficacy of PI by summarizing all clinical studies conducted to date with this technology. METHODS The two step process to identify the clinical presence of a breast cancer include identifying the presence of an abnormality and secondarily to determine if that abnormality is malignant. Not all studies examined each portion of this two-step process. There have been 9 clinical studies involving 1,155 symptomatic patients using PI in the U.S., China, and UK. To examine the ability of PI to detect an abnormal breast mass, we reviewed the sensitivity comparisons with CBE. To determine whether a breast lesion was malignant, we reviewed the analysis of the sensitivity, specificity and accuracy for the standard imaging modalities; mammography, breast ultrasound, clinical breast examinations (CBE) and MRI using pathology as the gold standard. Calcifications were not included because they represent DCIS which does not present clinically and is the subject of over diagnosis. RESULTS All studies included in this initial meta-analysis were on symptomatic patients. To identify the presence of an abnormality, the sensitivity of PI to detect breast masses was 89% in comparison with CBE which was 83%. To identify the presence of breast cancer, • The sensitivity of PI in detecting breast cancer was 85%, in comparison to CBE (59%), mammography (76%) and ultrasound (90%). • The specificity of PI in detecting breast cancer was 79% in comparison to CBE (78%), mammography (71%) and ultrasound (79%). • The Accuracy of PI in detecting breast cancer was 82% comparison with CBE (67%), mammography (74%) and ultrasound (84%). Breast Cancer Detection Comparision Palpation ImagingCBEMammogramUltrasoundSensitivity for Cancer Detection85597690Specificity for Cancer Detection79787179Accuracy for Cancer Detection82677484 CONCLUSIONS A summary of clinical studies conducted on symptomatic patients to date suggest that PI is (a) sensitive in the detection of breast masses and b) identifies breast cancer with similar sensitivity and specificity compared with other standard imaging modalities while being cost effective. PI may fill a gap in developing countries where little breast screening infrastructure exists. Ongoing clinical research with PI is warranted to evaluate its potential in the early diagnosis and screening for breast cancer in the U.S. Citation Format: Cary S Kaufman, Jae S Son, Eli Yered, Armen Sarvazyan. Clinical studies of palpation imaging of the breast on over 1000 patients [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P1-02-09.

Slip classification for dynamic tactile array sensors

The manipulation of objects held in a robotic hand or gripper is accompanied by events such as making and breaking contact and slippage, between the fingertips and the grasped object and between the grasped object and external surfaces. Humans can distinguish among such events, in part, because they excite the various mechanoreceptors in the hands differently. As part of an effort to provide robots with a similar capability, we propose two features that can be extracted from dynamic tactile array data and used to discriminate between hand/object and object/world slips. Both features rely on examining how slippage affects an array of dynamic tactile sensors compared with the way it affects individual elements of the array. In comparison with approaches that require extensive training with particular combinations of objects and skin, the features work for a wide range of frequencies and grasp conditions. The performance and generalizability of the features are verified with testing on three different kinds of sensors and for a range of object textures, grasp forces and slip conditions. Both features demonstrate greater than 85% accuracy in identifying the location of slip.

A modified analytical model to study the sensing performance of a flexible capacitive tactile sensor array

This paper presents a modified analytical model to study the sensing performance of a flexible capacitive tactile sensor array, which utilizes solid polydimethylsiloxane (PDMS) film as the dielectric layer. To predict the deformation of the sensing unit and capacitance changes, each sensing unit is simplified into a three-layer plate structure and divided into central, edge and corner regions. The plate structure and the three regions are studied by the general and modified models, respectively. For experimental validation, the capacitive tactile sensor array with 8 × 8 (= 64) sensing units is fabricated. Experiments are conducted by measuring the capacitance changes versus applied external forces and compared with the general and modified models’ predictions. For the developed tactile sensor array, the sensitivity predicted by the modified analytical model is 1.25%/N, only 0.8% discrepancy from the experimental measurement. Results demonstrate that the modified analytical model can accurately predict the sensing performance of the sensor array and could be utilized for model-based optimal capacitive tactile sensor array design.

Artificial Tactile Sensing of Position and Slip Speed by Exploiting Geometrical Features

Rich information about artificial grasps can be obtained using tactile sensing arrays. However, the complexity of the integration and computation inherent to tactile sensor arrays limits their applicability for prosthetic manipulators. We present an artificial ridged skin that detects the position and speed of a slipping object using a single force sensor. The artificial skin features parallel ridges arranged in a nonuniform configuration. An evolutionary algorithm generates distributions of ridges evaluated by the accuracy and resolution of detecting the position and speed of a slipping object. Slip experiments on real skins featuring ridge distributions generated by the evolutionary algorithm show that ridge arrangement is critical for an improved sensing of object position and slip speed. We report ridge patterns that detect object position and speed with errors as low as 10% at slip speeds of up to 60 mm/s. The artificial skin has an average speed sensing resolution of 10 mm/s, an average position sensing resolution of 15 mm, and is robust to various grip conditions, e.g., speed variation, object weight, and contact area. By exploiting the geometrical features of the artificial skin, enhanced tactile information is acquired. The concept opens a promising avenue for robust and energy-efficient tactile sensing systems.

Resolution Enhancement Method Used for Force Sensing Resistor Array

Tactile sensors are one of the major devices that enable robotic systems to interact with the surrounding environment. This research aims to propose a mathematical model to describe the behavior of a tactile sensor based on experimental and statistical analyses and moreover to develop a versatile algorithm that can be applied to different tactile sensor arrays to enhance the limited resolution. With the proposed algorithm, the resolution can be increased up to twenty times if multiple measurements are available. To verify if the proposed algorithm can be used for tactile sensor arrays that are used in robotic system, a16×10force sensing array (FSR) is adopted. The acquired two-dimensional measurements were processed by a resolution enhancement method (REM) to enhance the resolution, which can be used to improve the resolution for single image or multiple measurements. As a result, the resolution of the sensor is increased and it can be used as synthetic skin to identify accurate shapes of objects and applied forces.

Feedforward Neural Network for Force Coding of an MRI-Compatible Tactile Sensor Array Based on Fiber Bragg Grating

This work shows the development and characterization of a fiber optic tactile sensor based on Fiber Bragg Grating (FBG) technology. The sensor is a 3×3 array of FBGs encapsulated in a PDMS compliant polymer. The strain experienced by each FBG is transduced into a Bragg wavelength shift and the inverse characteristics of the sensor were computed by means of a feedforward neural network. A 21 mN RMSE error was achieved in estimating the force over the 8 N experimented load range while including all probing sites in the neural network training procedure, whereas the median force RMSE was 199 mN across the 200 instances of a Monte Carlo randomized selection of experimental sessions to evaluate the calibration under generalized probing conditions. The static metrological properties and the possibility to fabricate sensors with relatively high spatial resolution make the proposed design attractive for the sensorization of robotic hands. Furthermore, the proved MRI-compatibility of the sensor opens other application scenarios, such as the possibility to employ the array for force measurement during functional MRI-measured brain activation.

A bio-hybrid tactile sensor incorporating living artificial skin and an impedance sensing array.

The development of a bio-hybrid tactile sensor array that incorporates a skin analogue comprised of alginate encapsulated fibroblasts is described. The electrical properties are modulated by mechanical stress induced during contact, and changes are detected by a ten-channel dual-electrode impedance sensing array. By continuously monitoring the impedance of the sensor array at a fixed frequency, whilst normal and tangential loads are applied to the skin surface, transient mechanotransduction has been observed. The results demonstrate the effectiveness and feasibility of the preliminary prototype bio-hybrid tactile sensor.

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.

Development of multi-fingered dexterous hand for grasping manipulation

In this paper, a developed multi-fingered dexterous hand with flexible tactile skin is described. The dexterous hand has 5-fingers with 6-DOFs and each finger is equipped with a small harmonic drive gear and a fine high-power mini actuator. To achieve the goal of grasping with high accuracy, each fingertip is covered with the tactile array sensors for determination of the force between the finger and the grasped object. Some preliminary experiments are conducted to illustrate the performance of the grasping of the developed dexterous hand.

Spatially digitized tactile pressure sensors with tunable sensitivity and sensing range

When developing an electronic skin with touch sensation, an array of tactile pressure sensors with various ranges of pressure detection need to be integrated. This requires low noise, highly reliable sensors with tunable sensing characteristics. We demonstrate the operation of tactile pressure sensors that utilize the spatial distribution of contact electrodes to detect various ranges of tactile pressures. The device consists of a suspended elastomer diaphragm, with a carbon nanotube thin-film on the bottom, which makes contact with the electrodes on the substrate with applied pressure. The electrodes separated by set distances become connected in sequence with tactile pressure, enabling consecutive electrodes to produce a signal. Thus, the pressure is detected not by how much of a signal is produced but by which of the electrodes is registering an output. By modulating the diaphragm diameter, and suspension height, it was possible to tune the pressure sensitivity and sensing range. Also, adding a fingerprint ridge structure enabled the sensor to detect the periodicity of sub-millimeter grating patterns on a silicon wafer.

A flexible capacitive tactile sensor array with micro structure for robotic application

A flexible capacitive tactile sensor array with micro needle structure is proposed in this paper for robotic application. Micro needle layer made of polydimethylsiloxane (PDMS) is sandwiched between the upper electrode layer made of PDMS and the bottom electrode layer fabricated on polyester (PET) film. The PDMS material renders the device adequate flexibility as it can be rolled into a cylinder. The single cell size in the fabricated 4 × 4 sensors array is 0.7 × 0.5 cm2 and the initial capacitance of each cell is 0.86 pF. The fabricated cell shows a sensitivity of 3.26%/mN within the full scale range of 1 kPa. The micro needle structure gives better repeatability and stability. The maximum error during each measurement is about 3.2%, while the minimum error is about 1.2%.

Flexible and stretchable fabric-based tactile sensor

We introduce a novel, fabric-based, flexible, and stretchable tactile sensor, which is capable of seamlessly covering natural shapes. As humans and robots have curved body parts that move with respect to each other, the practical usage of traditional rigid tactile sensor arrays is limited. Rather, a flexible tactile skin is required. Our design allows for several tactile cells to be embedded in a single sensor patch. It can have an arbitrary perimeter and can cover free-form surfaces. In this article we discuss the construction of the sensor and evaluate its performance. Our flexible tactile sensor remains operational on top of soft padding such as a gel cushion, enabling the construction of a human-like soft tactile skin. The sensor allows pressure measurements to be read from a subtle less than 1 kPa up to high pressures of more than 500 kPa, which easily covers the common range for everyday human manual interactions. Due to a layered construction, the sensor is very robust and can withstand normal forces multiple magnitudes higher than what could be achieved by a human without sustaining damage.As an exciting application for the sensor, we describe the construction of a wearable tactile dataglove with 54 tactile cells and embedded data acquisition electronics. We also discuss the necessary implementation details to maintain long term sensor performance in the presence of moisture.

The Feel of MEMS Barometers: Inexpensive and Easily Customized Tactile Array Sensors

This article presents a new approach to the construction of tactile array sensors based on barometric pressure sensor chips and standard printed circuit boards (PCBs). The chips include tightly integrated instrumentation amplifiers, analog-to-digital converters, pressure and temperature sensors, and control circuitry that provides excellent signal quality over standard digital bus interfaces. The resulting array electronics can be easily encapsulated with soft polymers to provide robust and compliant grasping surfaces for specific hand designs. The use of standard commercial off-the-shelf technologies means that only basic electrical and mechanical skills are required to build effective tactile sensors for new applications. The performance evaluation of prototype arrays demonstrates excellent linearity (typically <;1%) and low noise (<;0.01 N). External addressing circuitry allows multiple sensors to communicate on the same bus at more than 100 Hz per sensor element. Sensors can be mounted with as close as 3#5-mm spacing, and spatial impulse response tests show that linear solid-mechanics-based signal processing is feasible. This approach promises to make sensitive, robust, and inexpensive tactile sensing available for a wide range of robotics and human-interface applications.

UT hand I: A lock-based underactuated hand prosthesis

In this paper, a new prototype underactuated hand prosthesis is presented. Its design is based on a robotic finger concept featuring tendon-pulley underactuation, joint coupling, and a series of joint locking mechanisms. The joint locks serve to actively control the degrees of freedom of the four fingers, allowing a single actuator to perform a variety of grasping motions. The thumb is separately actuated by a combination of opposition and flexion motors. Rubber fingertips add compliance to the grasp, and can be equipped with an integrated tactile sensor array. The prototype's kinematics are evaluated, and its functionality is demonstrated by performing a series of grasps. The results show that the UT Hand I provides the advantages of minimal actuation, without reducing its functionality.

Soft Tactile Sensor Arrays for Force Feedback in Micromanipulation

This paper describes the design, fabrication, and experimental validation of a soft tactile sensor array for submillimeter contact localization and contact force measurement in micromanipulation. The geometry and placement of conductive liquid microchannels embedded within the elastic sensor body are optimized to provide high sensitivity for representative micromanipulation tasks and to overcome functional limitations seen in previous soft tactile sensor research. Mechanical testing of the numerically optimized sensor prototype demonstrates sensitivity to normal contact forces of and submillimeter contact localization resolution. Tactile sensing experiments demonstrate the ability to infer the abstract geometries and motions of objects imparting force on the sensor surface by analyzing microchannel deformation patterns.

A dome-shaped piezoelectric tactile sensor arrays fabricated by an air inflation technique

In this paper, we propose and demonstrate a dome-shaped piezoelectric tactile sensor fabricated by an inflation technique. The sensor module consists of a 4×4 dome-shaped cell, an Ag electrode layer, a polyimide film for electrode protection, a bump structure, and a PDMS diaphragm for supporting the sensor. The piezoelectric sensor can convert an applied contact force into an electrical signal by using the piezoelectric effect. A normal force applied to the sensor deforms the cell, and consequently generates an output voltage proportional to the cell deformation. Therefore, by using a dome-shaped structure instead of the conventional flat structure, the tactile sensor can obtain high sensitivity. To make the dome-shaped PVDF film, a simple fabrication process based on an inflation technique for controlling the trapped air has been developed. The dome-shaped PVDF film was successfully fabricated, and then used as a sensing structure for a tactile sensor. In order to compare the sensitivity of the sensor, a flat tactile sensor was fabricated with the same design as the proposed sensor. The achieved sensitivities of the sensor are 6.028×10−3V/mN, 7.89×10−3V/mN, and 8.83×10−3V/mN, for the flat sensor and for two dome-shaped sensors (with h=0.5mm and 1.0mm), respectively. The sensitivity of the proposed device shows a maximum 46.4% greater than that of a conventional flat tactile sensor. Also, through measurements of frequency response and crosstalk, the proposed tactile sensor showed stable performance.

Online Direction Classification and Recognition Using an Intuitive Tactile Communication

This paper proposed an online direction classifying method for constructing an intuitive tactile communication during human-robot cooperation. The proposed approach abstracts a suitable feature set from a tactile array sensor equipped on a hand-bar. This lower computation feature extraction method analyze the weighting values concerned with oriental information from principle component analysis (PCA), together with support vector machines (SVM) classifier for direction classification and recognition. Experimental results showed an average accuracy of 96.3% and a low costs of 512μs with respect to different handle gestures of the 6 touch directions, which is practicable utilized for human-robot cooperation based on tactile recognition.

Development of a Skin-Like Tactile Sensor Array for Curved Surface

In this paper, we develop a skin-like tactile sensor array to measure the contact pressure of curved surfaces. The sensor array is laminated into a thin film 3 mm in thickness and can easily be wrapped around a pencil without damaging its skin-like structure. So far, we have achieved the array containing 8 × 16 sensor elements. Its spatial resolution is 1 element per 9 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> area and it can measure the pressure up to 360 kPa. The sensor-array patch contains three layers. The upper and lower layers are polydimethylsiloxane (PDMS) thin films embedded with the conductor strips formed by PDMS-based silver nanowires (AgNWs) networks. The middle layer is formed by the mixing of nickel powder with liquid PDMS for contact force measurement. Experimental tests have demonstrated that conductor strips on the upper layer can maintain their resistances ~ 23 Ω with increase when the tensile strain is up to 50%. Noted is the conductor made with carbon nanotubes can keep its conductivity unchanged for up to only 40% tensile strain. Through fatigue tests, it is observed that the measured AgNWs/PDMS conductor strip exhibits low and stable resistances. This is one of the most desired behaviors of the stretchable interconnects for signal transmission. The integrated sensor system can successfully measure the contact pressure induced by objects of different shapes. It can be applied on curved or non-planar surfaces in robots or medical devices for force detection and feedback.

Spring-based tactile array for assistive robotic surgical applications

Tactile sensing is highly desirable for robotic surgery, more specifically minimally invasive surgery, during tissue/organ manipulation. For safe handling and safe grasping of tissues, the two most important aspects are the monitoring and controlling of force and the stiffness information that exists at the sensor-tissue interface. In this study, a spring-based tactile sensing system is used to measure both the interacting forces and stiffness in surgical assistive applications. A differential analysis is performed to obtain the stiffness of a compliant object whilst individual elements of the proposed sensing array experience different deflections when they come in contact with the object. A lumped model formulation for tactile array performance shows that larger differences in stiffness between the force sensing elements provide higher sensitivity in evaluating the object stiffness. For benchmarking of our sensing principle, a macro tactile-sensor array is designed and tested. Different stiffness combinations of the sensing elements show an inverse linear relationship between the stiffness of the object and the output signal magnitude of the stiffness sensing unit. The proposed tactile array based on spring-based stiffness sensing has high potential for safe grasping/handling of the tissues when integrated into the jaws of a surgical grasper during the minimally invasive robotic procedures.