Fabrication Of Tactile Sensor Research Articles

Fully 3D printed flexible, conformal and multi-directional tactile sensor with integrated biomimetic and auxetic structure

Tactile sensors play a crucial role in the development of biologically inspired robotic prostheses, particularly in providing tactile feedback. However, existing sensing technology still falls short in terms of sensitivity under high pressure and adaptability to uneven working surfaces. Furthermore, the fabrication of tactile sensors often requires complex and expensive manufacturing processes, limiting their widespread application. Here we develop a conformal tactile sensor with improved sensing performance fabricated using an in-house 3D printing system. Our sensor detects shear stimuli through the integration of an auxetic structure and interlocking features. The design enables an extended sensing range (from 0.1 to 0.26 MPa) and provides sensitivity in both normal and shear directions, with values of 0.63 KPa−1 and 0.92 N−1, respectively. Additionally, the sensor is capable of detecting temperature variations within the range of 40−90 °C. To showcase the feasibility of our approach, we have printed the tactile sensor directly onto the fingertip of an anthropomorphic robotic hand, the proximal femur head, and lumbar vertebra. The results demonstrate the potential for achieving sensorimotor control and temperature sensing in artificial upper limbs, and allowing the monitoring of bone-on-bone load.

Development of a Highly Sensitive Wearable Tactile Sensor on Fabric by Using Conductive Inks Based on Electrical Contact Resistance (ECR) Change Mechanism

Front Cover: In article number 2100130 by Yen-Wen Lu and co-workers, a fabric tactile sensor, based on the fact that contact resistance between two surfaces changes when pressure is applied, is developed by using a screenprinting technique for subtle pressure sensing (<10 kPa) at high sensitivity. Wrist pulse measurements and spatial pressure mapping using the sensors with wireless modules are demonstrated for wearable health monitoring and internet-of-things applications.

Recent Applications of Different Microstructure Designs in High Performance Tactile Sensors: A Review

Flexible tactile sensors have become one of the most attractive research areas because of its great application prospect in electronic skin, healthcare monitoring and artificial intelligence. However, there are still great challenges in mimicking the human skin's strong ability of tactile perception to the changes of external physical information. Nowadays, in addition to flexible polymers and conductive materials, the microstructure of sensing units is a key factor to improve the performance of tactile sensors such as sensitivity, fast response and robustness. In recent years, a variety of novel microstructure designs have been applied to applications of tactile information perception and numerous corresponding processing methods have also been developed, which provides a wealth of enlightening solutions for the production of electronic skins. Herein, a large number of research results of tactile sensor devices are systematically reviewed according to different three-dimensional geometric shapes of the microstructures which are grouped into several categories. At the same time, relevant processing technologies employed, working principles and chief performance characteristics are also briefly described. Relative merits of different types of microstructure applications are clearly elaborated through the classification and comparison of multiple microstructure geometries in this paper to provide valuable reference for sensing microstructure design and fabrication of tactile sensors in corresponding engineering applications. Moreover, current difficulties and challenges in fabrication of flexible microstructures and future investigative directions pertaining to this field have been discussed.

A Sensitive Piezoresistive Tactile Sensor Combining Two Microstructures.

A tactile sensor is an indispensable component for electronic skin, mimicking the sensing function of organism skin. Various sensing materials and microstructures have been adopted in the fabrication of tactile sensors. Herein, we propose a highly sensitive flexible tactile sensor composed of nanocomposites with pyramid and irregularly rough microstructures and implement a comparison of piezoresistive properties of nanocomposites with varying weight proportions of multi-wall nanotubes and carbon black particles. In addition to the simple and low-cost fabrication method, the tactile sensor can reach high sensitivity of 3.2 kPa−1 in the range of <1 kPa and fast dynamic response of 217 ms (loading) and 81 ms (recovery) at 40 kPa pressure. Moreover, body movement monitoring applications have been carried out utilizing the flexible tactile sensor. A sound monitoring application further indicates the potential for applications in electronic skin, human–computer interaction, and physiological detection.

3D Printing Technologies for Flexible Tactile Sensors toward Wearable Electronics and Electronic Skin.

3D printing has attracted a lot of attention in recent years. Over the past three decades, various 3D printing technologies have been developed including photopolymerization-based, materials extrusion-based, sheet lamination-based, binder jetting-based, power bed fusion-based and direct energy deposition-based processes. 3D printing offers unparalleled flexibility and simplicity in the fabrication of highly complex 3D objects. Tactile sensors that emulate human tactile perceptions are used to translate mechanical signals such as force, pressure, strain, shear, torsion, bend, vibration, etc. into electrical signals and play a crucial role toward the realization of wearable electronics and electronic skin. To date, many types of 3D printing technologies have been applied in the manufacturing of various types of tactile sensors including piezoresistive, capacitive and piezoelectric sensors. This review attempts to summarize the current state-of-the-art 3D printing technologies and their applications in tactile sensors for wearable electronics and electronic skin. The applications are categorized into five aspects: 3D-printed molds for microstructuring substrate, electrodes and sensing element; 3D-printed flexible sensor substrate and sensor body for tactile sensors; 3D-printed sensing element; 3D-printed flexible and stretchable electrodes for tactile sensors; and fully 3D-printed tactile sensors. Latest advances in the fabrication of tactile sensors by 3D printing are reviewed and the advantages and limitations of various 3D printing technologies and printable materials are discussed. Finally, future development of 3D-printed tactile sensors is discussed.

Scalable fabric tactile sensor arrays for soft bodies

Soft robots have the potential to transform the way robots interact with their environment. This is due to their low inertia and inherent ability to more safely interact with the world without damaging themselves or the people around them. However, existing sensing for soft robots has at least partially limited their ability to control interactions with their environment. Tactile sensors could enable soft robots to sense interaction, but most tactile sensors are made from rigid substrates and are not well suited to applications for soft robots which can deform. In addition, the benefit of being able to cheaply manufacture soft robots may be lost if the tactile sensors that cover them are expensive and their resolution does not scale well for manufacturability. This paper discusses the development of a method to make affordable, high-resolution, tactile sensor arrays (manufactured in rows and columns) that can be used for sensorizing soft robots and other soft bodies. However, the construction results in a sensor array that exhibits significant amounts of cross-talk when two taxels in the same row are compressed. Using the same fabric-based tactile sensor array construction design, two different methods for cross-talk compensation are presented. The first uses a mathematical model to calculate a change in resistance of each taxel directly. The second method introduces additional simple circuit components that enable us to isolate each taxel electrically and relate voltage to force directly. Fabric sensor arrays are demonstrated for two different soft-bodied applications: an inflatable single link robot and a human wrist.

Large-sized fabric tactile sensors for detecting contacted objects

The authors previously proposed a type of fabric tactile sensor produced by weaving artificial hollow fibres such as clothes. In this study, the authors enlarged its size by using a handloom and investigated the characteristic of the contacted object detection. The authors produced two kinds of fabric tactile sensors having different sizes 87.5×52.0 mm and 180.0×56.0 mm. The pitch values of the detection point at the horizontal and the vertical directions were 7.0 and 7.0 mm, respectively, in the former sensor, and they were 18.0 and 14.0 mm, in the latter one. The authors evaluated the detection performance of the developed fabric tactile sensors, and obtained that the variation of the sensor outputs among the detecting points was less than 1.5% when the concentrated force was applied to the each sensing point. The sensor output increased with increasing applied load, and it depended on the size of the contacted objects. From this result, the authors conducted that the sensor output was the same when the applied pressure on the fabric was the same, even if the contacted areas were different. The developed fabric sensor also successfully detected the two-dimensional shape of the contacted objects.

Fabric tactile sensor composed of ball-shaped umbonal fibre for detecting normal and lateral force

The authors previously proposed an artificial hollow fibre for use as a microelectromechanical systems (MEMS) material to produce a wearable sensing system and developed a fabric tactile sensor to apply to it. In this Letter, the authors developed a ball-shaped projection for producing the umbonal fibre to improve sensing performance for normal- and lateral-forces detection. An adhesive was manually dropped on the fibre to form the ball-shaped projection structure by surface tension. Its typical diameter was 1.0 mm. The entire surface of the umbonal fibre was then coated with metal and insulation layers. Finally, the umbonal hollow fibre, two weft hollow fibres, a brass wire and cotton yarn were woven together to produce the fabric tactile sensor. The sensor output linearly increased with the increase in applied normal force because of the ball-shaped projection. The sensor output obtained from the two weft fibres increased with the increase of the applied lateral force. It also demonstrated excellent repeatability.

Fabrication of a wearable fabric tactile sensor produced by artificial hollow fiber

An artificial-hollow-fiber structure as a new material for MEMS was developed and applied to a novel type of fabric tactile sensor. The artificial hollow fiber was fabricated by uniformly deposited metal and insulation layers on the surface of an elastic tube. A special rotating mechanism for uniformly depositing a metal layer on the tube surface during sputtering was developed. A rectangular-shaped fabric tactile sensor was produced by combining artificial hollow fibers and typical cotton yarns, like a cloth. The sensor can detect a contact force by measuring changes in capacitance at all intersection points of the artificial hollow fibers. Two different types of wearable-tactile-sensor glove, a patched type and a direct knit type, were also fabricated, and it was confirmed that both types can detect a normal load by measuring the capacitance change.

537 繊維状触覚センサにおける力学的変形モデルとそれによる力検出評価(T04 MEMS技術を用いたヒューマンインターフェース,大会テーマセッション,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

We previously proposed the novel type of the fabric tactile sensor produced by weaving the artificial hollow fibers. We this time constructed the theoretical fiber deformation model in the fabric tactile sensor. We at first conducted the deformation model of the single and crossed hollow fibers by applying the material mechanics, and also constructed the model showing how the contact area (sensor output) changes with the changes of the applied load or the fiber deformation. We then verified the conducted mode by the experiments, in which we used five different sized hollow fibers. The conducted fiber deformation model adequately agreed with the experimental results. The hollow fiber linearly deformed with the increase of the applied loads in the both conditions, and the spring constant linearly depended on the third power of the ratio between the thickness and the radius. We finally developed the glove-type of the tactile sensor, and experimentally evaluated its performance.