Flexible Dome and Bump Shape Piezoelectric Tactile Sensors Using PVDF-TrFE Copolymer

In this paper, a new mold-transfer method to pattern piezoelectric polymer has been developed and applied to fabricate innovative dome and bump shape polyvinylidene-fluoride-trifluoroethylene (PVDF-TrFE) films. The dome and bump shape PVDF-TrFE films have been successfully fabricated and characterized as a sensing component for flexible tactile sensors. The tactile sensors developed using these polymer microstructures show a high sensitivity which can measure as small as 40 mN force for bump shape sensors and 25 mN for dome shape sensors. The newly developed fabrication method provides a flexible way to pattern the piezoelectric polymer with different shapes and dimensions, including bump and dome shape piezoelectric polymer microstructures. In addition, a selective dc poling method for the PVDF-TrFE film has been developed for fabricating precisely located piezoelectric sensors with minimum crosstalk. The bump and dome shape PVDF-TrFE films developed in this paper can have numerous applications for microcatheters or other minimally invasive biomedical devices.     

基于EIT技术的柔性触觉传感器的设计

随着机器人技术的日益发展,柔性传感器在机器人皮肤上的应用也得到了新的发展。本文提出并研究了一种基于导电聚合物压敏电阻效应的柔性触觉传感器的设计,使用由聚二甲基硅氧烷PDMS（Poly Di Methyl Siloxane）和多壁碳纳米管（MWCNTs）混合而成的导电橡胶作为传感器主体,运用EIT（Electrical Impedance Tomography）技术,设计并制作了本系统的硬件电路,并用其检测、传输导电橡胶的边缘电势数据。最后在计算机中应用工具包EIDORS进行有限元模型和图像重构技术,有效且直观的将导电橡胶上的受力位置表现出来。实验对1~3个目标分别进行了成像,证明了本设计的可行性。     

Development of a flexible three-axial tactile sensor array for a robotic finger

In this paper, we propose a flexible three-axial tactile sensor array for measuring both normal and shear loads. The sensor array has 16 tactile sensor units based on piezoresistive strain gauge. It is constructed on a Kapton polyimide film using advanced polymer micromachining technologies. Thin metal strain gauges are embedded in polyimide to measure normal and shear loads, which are tested by applying forces from 0 to 1?N. The developed sensor unit had a hysteresis error of about 9% and repeatability error of about 1.31%. The sensor showed a good resulting image when pressed by a circle-shaped object with 10?N loads. The proposed flexible three-axial tactile sensor array can be applied in a curved or compliant surface that requires slip detection and flexibility, such as a robotic finger.     

一种新型机器人三维力柔性触觉传感器的设计

基于柔性力敏导电橡胶材料,设计了一种能测量三维力的新型机器人柔性触觉传感器。研究了力敏导电橡胶材料的压阻效应,阐述了触觉传感器的设计思想,分别进行了触觉传感器单元设计和阵列结构设计和研究。获得了计算三维力的数学模型,并通过实验进行了三维力的验证。结果表明,设计的机器人三维力柔性触觉传感器具有设计简单,造价低廉,柔顺性好等优点,而且布置成阵列结构可用于医疗、体育、机器人等领域中检测三维力信息。     

导电橡胶触觉传感器阵列的标定实验研究

导电橡胶传感器是智能机器人服装的核心机件;标定出导电橡胶传感器的压阻特性是实现智能机器人触觉传感服装的核心内容之一;实验中,将导电橡胶安装在柔性阵列电极板里制作成触觉传感器阵列服装。对该传感器提出多种测量方法,确立其标定模型;给出数据建模的一般步骤。指出导电橡胶传感器设计的改进方向与部分方法。     

A flexible encapsulated MEMS pressure sensor system for biomechanical applications

 The use of pressure sensors made of conductive polymers is common in biomechanical applications. Unfortunately, hysteresis, nonlinearity, non-repeatability and creep have a significant effect on the pressure readings when such conductive polymers are used. The objective of this paper is to explore the potential of a new flexible encapsulated micro electromechanical system (MEMS) pressure sensor system as an alternative for human interface pressure measurement. A prototype has been designed, fabricated, and characterized. Testing has shown that the proposed packaging approach shows very little degradation in the performance characteristics of the original MEMS pressure sensor. The much-needed characteristics of repeatability, linearity, low hysteresis, temperature independency are preserved. Thus the flexible encapsulated MEMS pressure sensor system is very promising and shows superiority over the commercially available conductive polymer film sensors for pressure measurement in biomechanical applications. Received: 1 December 1999/Accepted: 17 August 2000     

Embedding conductive patterns of elastomer nanocomposite with the assist of laser ablation

This work introduces a simple and low-cost microfabrication technique utilizing laser ablation to embed conductive elastomer nanocomposite within an insulating bulk elastomer. Nanocomposite consisting of poly(dimethylsiloxane) and a network of carbon nanotubes functions as a piezoresistive sensor material. Microstructures are embedded with the assist of laser ablation which utilizes a focused laser beam to ablate through a thin polymer film following a path programmed via software. This approach eliminates hardware such as photo-mask or stamp, which offers distinct advantages in reducing fabrication time and cost in prototyping of sensor devices. Various patterns of polymer film and embedded nanocomposite are demonstrated with spatial resolution down to 34 μm. To characterize patterning quality, different fabrication conditions are tested and uniformity (width, thickness) data are measured with optical profiling. Sensor prototypes are demonstrated based on the piezoresistive response of nanocomposite under tensile strain. Strain sensors could detect large-range (>45%) tensile strain with sensing a factor of about 4, showing promising feasibility for various sensing applications.     

A 5.8‐in. phosphorescent color AMOLED display fabricated by ink‐jet printing on plastic substrate

Abstract— A flexible phosphorescent color active‐matrix organic light‐emitting‐diode (AMOLED) display on a plastic substrate has been fabricated. Phosphorescent polymer materials are used for the emitting layer, which is patterned using ink‐jet printing. A mixed solvent system with a high‐viscosity solvent is used for ink formulation to obtain jetting reliability. The effects of evaporation and the baking condition on the film profile and OLED performances were investigated. An organic thin‐film‐transistor (OTFT) backplane, fabricated using pentacene, is used to drive the OLEDs. The OTFT exhibited a current on/off ratio of 10⁶ and a mobility of 0.1 cm²/V‐sec. Color moving images were successfully shown on the fabricated display.     

A novel flexible heating element using graphene polymeric composite ink on polyimide film

Microsystem Technologies - In this study, a simple, large and flexible electronic heat generator with graphene polymeric composite ink on a polyimide film was fabricated. A 47-μm thin layer...     

Fabrication of wireless sensors on flexible film using screen printing and via filling

Wireless sensors are fabricated on flexible plastic films by means of screen printing and via-hole filling. The wireless sensors are battery free with data and power transmission functions. The sensors, fabricated on polyethylene terephtalate films, are designed based on RFID technology. Using an additive patterning process known as screen printing, metallization on polymer films is created. Both sides of a polymer film are printed with metallic patterns and connected with micro vias filled with conductive paste. One side of the film consists of printed electrical traces for discrete components like resistors and transistors that would be mounted onto it; the other side consists of a printed inductive coil used for wireless data and power transmission. The micro vias, which have a diameter of 120 μm, are formed by mechanical punching and filled with conductive silver paste. The size of one sensor unit is approximately 2 cm × 1.5 cm; an array of 4 × 7 sensor units are printed over an area of 15 cm × 15 cm on a PET film. Details of manufacturing processes, component assembly and functionality test are presented in this paper.     

Micromachined dissolved oxygen sensor based on solid polymer electrolyte

A silicon microprobe to measure dissolved oxygen levels is described. The sensors are prepared by overlaying platinum thin film electrodes with a solid state proton conductive matrix (PCM) coating. The platinum thin film electrodes are fabricated on silicon substrates by standard photolithographic techniques while the PCM coating is achieved by drop-casting methods. The size and materials of the device make it potentially suitable for medical implantation. The devices are tested in deionized water (DI water), phosphate buffered saline (PBS), and bovine blood serum (BBS). Through linear sweep voltammetry (LSV), single devices are shown to have decent performances in terms of long term stability, reliability, hysteresis, linearity, and sensitivity. Variations among different devices are characterized and correlated. The simplicity and cost effectiveness of the fabrication and packaging procedures and the decent in vitro performances of these devices make them good candidates as miniaturized, disposable, and implantable dissolved oxygen sensors for biological and biomedical use.     

Printing of polymer thin‐film transistors for active‐matrix‐display applications

Abstract— We present a process for active‐matrix flat‐panel‐display manufacture based on solution processing and printing of polymer thin‐film transistors. In this process, transistors are fabricated using soluble semiconducting, conducting, and dielectric polymer materials. Accurate definition of the transistor channel and other circuit components are achieved by direct ink‐jet printing combined with surface‐energy patterning. We have used this process to create 4800‐pixel 50‐dpi active‐matrix backplanes. These backplanes were combined with polymer‐dispersed liquid crystal to create the first ink‐jet‐printed active‐matrix displays. Our process is, in principle, environmentally friendly, low temperature, compatible with flexible substrates, cost effective, and advantageous for short‐run length and large display sizes. As well as polymer‐dispersed liquid crystal, this technology is applicable to conventional liquid‐crystal and electrophoretic display effects.     

机器人压阻阵列触觉数据采样的研究

压阻阵列触觉传感器为减少外接引线，一般来用行列电极结构，给触觉的扫描采样带来了噪声。随着阵列数的增加，提高传感器的频响，将直接影响它的实时处理。为此，设计了一种新的行扫描采样电路，解决了这二方面的问题．     

碳纳米管/PDMS复合材料柔性阵列压力传感器制备与实验

以碳纳米管（CNTs）作为导电填料,聚二甲基硅氧烷（PDMS）为基体材料,采用溶液法制备出CNTs/PDMS导电复合材料。研究了碳纳米管浓度对复合材料的电学特性和压阻特性的影响规律,得到碳纳米管在PDMS中的渗滤区域。通过复合材料的压力灵敏度优化碳纳米管浓度。以制备的复合材料为敏感材料,FPCB工艺加工的柔性基板为电极,设计制备了一种简单结构和工艺的柔性阵列压力传感器。用零电势法设计了阵列电阻读出电路与LabVIEW实现的上位机配合,实现信号读取和显示。最后通过一个应用实例表明,该柔性阵列压力传感器及信号处理系统可以实现压力分布与大小的实时监测,可为柔性阵列压力传感器设计与制备提供参考。     

Electrostatic tactile display with thin film slider and its application to tactile telepresentation systems

A new electrostatic tactile display is proposed to realize compact tactile display devices that can be incorporated with virtual reality systems. The tactile display of this study consists of a thin conductive film slider with stator electrodes that excite electrostatic forces. Users of the device experience tactile texture sensations by moving the slider with their fingers. The display operates by applying two-phase cyclic voltage patterns to the electrodes. The display is incorporated into a tactile telepresentation system to realize explorations of remote surface textures with real-time tactile feedback. In the system, a PVDF tactile sensor and a DSP controller automatically generate voltage patterns to present surface texture sensations through the tactile display. A sensor, in synchronization with finger motion on the tactile display, scans a texture sample and outputs information about the sample surface. The information is processed by a DSP and fed back to the tactile display in real time. The tactile telepresentation system was evaluated in texture discrimination tests and demonstrated a 79 percent correct answer ratio. A transparent electrostatic tactile display is also reported in which the tactile display is combined with an LCD to realize a visual-tactile integrated display system.     

Fabrication of micro sensors on a flexible substrate

Flexible micro temperature and humidity sensors on parylene thin films were designed and fabricated using a micro-electro-mechanical-systems (MEMS) process. Based on the principles of the thermistor and the ability of a polymer to absorb moisture, the sensing device comprised gold wire and polyimide film. The flexible micro sensors were patterned between two pieces of parylene thin film that had been etched using O₂ plasma to open the contact pads. The sacrificial Cr spacer layer was removed from the Cr etchant to release the flexible temperature and humidity sensors from the silicon substrate. Au was used to form the sensing electrode of the sensors while Ti formed the adhesion layer between the parylene and Au. The thickness of the device was 7 ± 1 μm, so the sensors attached easily to highly curved surfaces. The sensitivities of the temperature and humidity sensor were 4.81 × 10⁻³ °C⁻¹ and 0.03 pF/%RH, respectively. This work demonstrates the feasibility and compatibility of thin film sensor applications based on flexible parylene. The sensor can be applied to fuel cells or components that must be compressed.     

A Polymer-Based Flexible Tactile Sensor for Both Normal and Shear Load Detections and Its Application for Robotics

This paper proposes and demonstrates a novel flexible tactile sensor for both normal and shear load detections. For the realization of the sensor, polyimide and polydimethylsiloxane are used as a substrate, which makes it flexible. Thin metal strain gauges, which are incorporated into the polymer, are used for measuring normal and shear loads. The salient feature of this tactile sensor is that it has no diaphragm-like structures. The unit tactile cell characteristics are evaluated against normal and shear loads. The fabricated tactile sensor can measure normal loads of up to 4 N, and the sensor output signals are saturated against loads of more than 4 N. Shear loads can be detected by different voltage drops in strain gauges. The device has no fragile structures; therefore, it can be used as a ground reaction force (GRF) sensor for balance control in humanoid robots. Four tactile unit sensors are assembled and placed in the four corners of the robots sole. By increasing bump dimensions, the tactile unit sensor can measure loads of up to 2 kgf. When loads are exerted on the sole, the GRF can be measured by these four sensors. The measured forces can be used in the balance control of biped locomotion systems.     

Piezoresistive sensor design using topology optimization

Piezoresistive materials, materials whose resistivity properties change when subjected to mechanical stresses, are widely utilized in many industries as sensors, including pressure sensors, accelerometers, inclinometers, and load cells. Basic piezoresistive sensors consist of piezoresistive devices bonded to a flexible structure, such as a cantilever or a membrane, where the flexible structure transmits pressure, force, or inertial force due to acceleration, thereby causing a stress that changes the resistivity of the piezoresistive devices. By applying a voltage to a piezoresistive device, its resistivity can be measured and correlated with the amplitude of an applied pressure or force. The performance of a piezoresistive sensor is closely related to the design of its flexible structure. In this research, we propose a generic topology optimization formulation for the design of piezoresistive sensors where the primary aim is high response. First, the concept of topology optimization is briefly discussed. Next, design requirements are clarified, and corresponding objective functions and the optimization problem are formulated. An optimization algorithm is constructed based on these formulations. Finally, several design examples of piezoresistive sensors are presented to confirm the usefulness of the proposed method.     

A4‐sized flexible ferroelectric liquid‐crystal displays with micro color filters

Abstract— We demonstrated an A4‐paper‐sized flexible ferroelectric liquid‐crystal (FLC) color displays fabricated by using a new plastic‐substrate‐based process which was developed for large‐sized devices. Finely patterned color filters and ITO electrodes were formed on a plastic substrate by a transfer method to avoid surface roughness and thermal distortion of the substrate, which induce disordering of the FLC molecular alignment. The thickness of an FLC/monomer solution sandwiched by two plastic‐film substrates was well controlled over a large area by using flexographic printing and lamination techniques. Molecular‐aligned polymer walls and fibers were formed in the FLC by a two‐step photopolymerization‐induced phase‐separation method using UV‐light irradiation. A fabricated A4‐sized flexible‐sheet display for color‐segment driving was able to exhibit color images even when it was bent.     

A flexible dry micro-dome electrode for ECG monitoring

This paper describes a flexible dry electrode with micro domes on polydimethylsiloxane (PDMS) for the monitoring of electrocardiogram (ECG). The fabrication procedure of this microstructure was mainly composed of melting photoresist, double-PDMS-molding, nickel (Ni) plating and encapsulation between two thin PDMS films. To investigate the performance of the fabricated micro-dome electrode, three dry electrodes with different arrays were fabricated to conduct the contact impendence measurements. ECG signals were measured by both the standard wet electrodes (Ag/AgCl) and dry electrodes. Experimental results showed the dry electrode provided signal quality that was comparable to the standard wet electrode without the need for skin preparation or electrolytic solution. The proposed dry electrode is more comfortable, with less skin irritation and requires no conductive gel. Thus, this flexible dry micro-dome electrode could find potential biomedical applications in health monitoring.