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.     

A flexible three-axial capacitive tactile sensor with multilayered dielectric for artificial skin applications

In this paper, a new flexible three-axial force sensor was designed and investigated, which was composed of four capacitors, and the mechanism was based on the capacitance change induced by an applying three-axial force. For the configuration of the electrodes, four sensing electrodes and a public electrode were in the same plane, which was based on fringe effect theory. Different from the traditional dielectric layer with single material, this multilayered dielectric consisted of both the air gap and polydimethylsiloxane. The structure of the multilayered dielectric changed under the external/applied force, leading to variation of dielectric constant ε, which caused the capacitance change. Measurement results showed that the full-scale range of detectable force was around 0–10 N for all three axes. The average sensitivities of the force sensor units were 0.0095, 0.0053, and 0.0060 N⁻¹ for the normal, X-axis, and Y-axis shear forces, and more test proved its high potential for application in skin-like sensing field.

     

Design and fabrication of a flexible three-axial tactile sensor array based on polyimide micromachining

This paper describes the design and fabrication of a flexible three-axial tactile sensor array using advanced polyimide micromachining technologies. The tactile sensor array is comprised of sixteen micro force sensors and it measures 13 mm × 18 mm. Each micro force sensor has a square membrane and four strain gauges, and its force capacity is 0.6 N in the three-axial directions. The optimal positions of the strain gauges are determined by the strain distribution obtained form finite element analysis (FEA). The normal and shear forces are detected by combining responses from four thin-film metal strain gauges embedded in a polyimide membrane. In order to acquire force signals from individual micro force sensors, we fabricated a PCB based on a multiplexer, operational amplifier and microprocessor with CAN network function. The sensor array is tested from the evaluation system with a three-component load cell. The developed sensor array can be applied in robots’ fingertips, as well as to other electronic applications with three-axial force measurement and flexibility keyword requirements.     

Design and fabrication of a hybrid silicon three-axial force sensor for biomechanical applications

This paper presents the design and development of a silicon-based three-axial force sensor to be used in a flexible smart interface for biomechanical measurements. Normal and shear forces are detected by combining responses from four piezoresistors obtained by ion implantation in a high aspect-ratio cross-shape flexible element equipped with a 525 μm high silicon mesa. The mesa is obtained by a subtractive dry etching process of the whole handle layer of an SOI wafer. Piezoresistor size ranges between 6 and 10 μm in width, and between 30 and 50 μm in length. The sensor configuration follows a hybrid integration approach for interconnection and for future electronic circuitry system integration. The sensor ability to measure both normal and shear forces with high linearity (99%) and low hysteresis is demonstrated by means of tests performed by applying forces from 0 to 2 N. In this paper the packaging design is also presented and materials for flexible sensor array preliminary assembly are described.     

基于PVDF的三维力机器人触觉传感器的设计

当机器手抓取时物体受力信息检测是抓取过程顺利进行的基础,检测三维方向上的力便可充分反映物体的受力信息。当前用于抓取过程中三维力检测的触觉传感器还存在着一些不足,基于此,论文拟设计一种基于PVDF的三维力机器人触觉传感器。论文展示了传感器的结构设计,建立了压电薄膜及传感头结构的数学模型,设计了调理电路并对传感器进行测试和验证,结果表明该传感器能有效检测机器手抓取过程中的三维力信息。     

压阻式触觉传感器对法向力和剪切力的检测

灵活的触觉传感器应该具有像皮肤一样的功能,能够检测施加力的大小和方向.改进的压阻式触觉传感器,主要由中心芯和4个侧壁组成,法向力和剪切力的感测元件不同.将压阻式触觉传感器嵌入到一个聚二甲基硅氧烷(PDMS)弹性体中,以实现力的柔性检测.通过仿真分析,得到此种触觉传感器对法向力的检测范围为600 Pa~65 kPa,可测得的最小剪切力为900 Pa.通过进一步分析,得到施加法向力和剪切力时法向力感测元件阻值的变化曲线,可得此种触觉传感器能够有效降低法向力感测元件与剪切力感测元件之间的干扰.所开发的触觉传感器可以灵活检测施加的法向力和剪切力,可应用于机器人手臂和假肢上.     

An optical tactile sensor for manipulators

A touch sensor for robots was designed, built and demonstrated. It is based on a deformable elastic reflective surface and optical fiber technology. The device is relatively immune to electromagnetic noise and may be used in environments where it is important to protect sensitive electronic equipment from such noise. The sensed touch pattern is easily read and interpreted by a computer using current video technology. The design allows for extremely high spatial resolution (2100 sensitive spots per square inch achieved here). Spatial resolution must be traded off with sensor pad thickness to retain adequate sensitivity.     

基于光学的触觉传感器电路设计

相较于电信号触觉传感器,基于光学的触觉传感器性能更好,受外界环境影响小,抗干扰性能更高.触觉传感器以弹性材料模拟人体皮肤,在弹性材料内部有标记点阵列.用摄像头拍摄标记点的图像,通过测量弹性材料受力发生形变时标记点阵列的位移情况来求解出力的分布情况,进一步计算出触觉信息.传感器采用EP4CGx30为主处理芯片,采用双层电路堆叠的方式实现,总尺寸为40mm×20mm×15 mm.     

Multiplexed piezoelectric polymer tactile sensor

An electrically multiplexed robotic tactile sensor has been realized using a monolithic silicon-integrated circuit coupled to a piezoelectric polyvinylidene fluoride (PVDF) film. The integrated circuit incorporates 25 sensor electrodes arranged in a symmetrical 5 × 5 matrix. Each electrode occupies a 600 × 600 m?m square area, and they are separated from each other by 600 m?m. A 25-m?m thick PVDF film was experimentally determined to be compatible with the fabrication process, and also yielded very favorable tactile sensing performance characteristics. The response of the tactile sensor is essentially linear for loads spanning 0.8 to 60 g force (gmf). The response bandwidth is 33 Hz, the hysteresis level is very small, and crosstalk is not a significant problem. A novel precharge bias scheme has been implemented to stabilize the pre- and postload sensor response. A rudimentary tactile object image measurement process was evaluated to recognize the shapes of circular, rectangular, toroidal, and hexagonal loads.     

面向视频感知的静电力触觉渲染方法

针对视觉障碍的人获取视频等数字媒体信息受限的问题, 为扩展视频等数字媒体信息的触觉感知通道,提出一种面向视频感知的静电力触觉渲染方法。首先,采用基于像素点的视频帧处理算法,根据手指触摸位置获取当前视频帧的目标像素点,然后将目标像素点彩色信息从RGB模型转换为HSI模型,利用像素点色调分量来映射静电力激励信号频率参量,结合像素点亮度和饱和度分量来映射静电力激励信号幅度参量,合成静电力触觉激励信号,实现对实时视频的触觉渲染和感知。最后,设计动态色彩感知实验和亮度辨识感知实验,结果表明,该方法可实现对视频中物体信息的触觉感知,动态识别平均正确率达90.6%,色彩辨识平均正确率达69.4%,亮度辨识平均正确率达80.0%,所提方法能有效提取视频中的动态特征信息,增强视频触觉渲染的实时性。     

柔性触觉传感器主要技术

结合理论分析和文献报道对现有柔性触觉传感器的主要技术进行了归纳总结,主要包括微机电系统(MEMS)的压阻原理,通过惠斯顿电桥将力转换成电量的基本原理,基于新型材料聚偏二氟乙烯(PVDF)的压电特性,电介质的力学性质与电学性质的耦合作用,以及基于导电橡胶的柔性触觉传感器导电机理和压阻效应。概述了3种主要技术物理特性,总结了3种主要技术应用在柔性触觉传感器上的优缺点和在各个领域上的实际应用,提出了触觉传感器一些有待解决的问题和研究方向。     

Robust bin-picking system using tactile sensor

ABSTRACT

This paper presents a robust bin-picking system utilizing tactile sensors and a vision sensor. The object position and orientation are estimated using a fast template-matching method through the vision sensor. When a robot picks up an object, the tactile sensors detect the success or failure of the grasping, and a force sensor detects the contact with the environment. A weight sensor is also used to judge whether the lifting of the object has been successful. The robust and efficient bin-picking system presented herein is implemented through the integration of different sensors. In particular, the tactile sensors realize rope-shaped object picking that has yet to be made possible with conventional picking systems. The effectiveness of the proposed method was confirmed through grasping experiments and in a competitive event at the World Robot Challenge 2018.     

A multi-purpose dynamic and tactile sensor for robot manipulators

In this article, a multi-purpose tactile/acceleration sensor system made of newly developed thick polymeric piezoelectric material and capable of sensing acceleration, contact force and pressure is developed and evaluated using analytical and experimental techniques, The sensor system is discretized and modeled by a single degree of freedom second order system from which equations of electromechanical dynamics are formulated to evaluate its performance. Analytical solutions are compared favorably with experimental results.     

Development of a sensor system for collecting tactile information

This paper presents the development of a sensor system for collecting tactile information. An active sensing system using the piezoelectric effect and the pyroelectric effect of a PVDF (Polyvinylidene fluoride) film is proposed. The active sensing is designed with human motions for tactile perception in mind. First, as the pretest, the distinction examination of six fabrics with different textures is carried out through human tactile perception. Next, the proposed sensor system is assembled. The sensor is composed of a PVDF film and a soft rubber. The surface of the sensor can be heated through temperature control. The sensor is attached on the tip of a robot finger driven by a piezoelectric bimorph strip and the root of the finger is mounted on a linear slider. Two kinds of active sensing are introduced. First, the heated sensor is contacted with an object and pyroelectric output signals are collected in order to obtain the information on tactile warmth. Next, the heated sensor is slid over the object and piezoelectric output signals are collected in order to obtain the information on feelings of vibration. Through the discussion about each sensing, three indexes representing features of the collected data are extracted and proposed as the sensor outputs for the evaluation of tactile sensation. The measurement using the sensor system is done on the samples used in the distinction examination. Comparison with the results shows that the sensor system extracts features on feelings of vibration and warmth.     

覆盖层材料对触觉传感器空间分辨率的影响

通过有限元计算 ,分析了弹性覆盖层材料对触觉传感器空间分辨率的影响 ,给出了一些覆盖层材料的选择准则。     

Development of tactile sensor for measuring hair touch feeling

In this paper, a tactile sensor system for evaluation of human hair under dry and wet conditions is developed. The polyvinylidene fluoride (PVDF) film is used as the sensory material. The sensor consists of an acrylic base, a silicone rubber, a PVDF film. A surface projection is put on the PVDF film as the contacting part. The sensor output is obtained by contacting and scanning objects. Panels imitating the physical and chemical properties of human hair surface are fabricated and used as measuring objects for stable measurement. Panels cleaned down with several kinds of hair-care products are measured by the sensor. By comparison between the sensor output and human sensory evaluation, it was confirmed that the sensor outputs have a good correlation with human sensory evaluation. It was found that the sensor system is available for monitoring hair conditions in both dry and wet conditions.     

Micromechanical force sensors based on SU-8 resist

This paper presents an innovative approach to develop highly sensitive 3D force sensors. In order to increase the probing sensitivity by using a material with low Young’s Modulus, a novel force sensor design based on SU-8 polymer is realized. Therefore, a low cost fabrication process is developed accompanied by design studies and an estimation of mechanical properties of the deforming elements. This paper will present the fabrication process as well as a distinguishing set of test results, analytical results, and simulations on the characterization of the presented SU-8 force sensor. The novel SU-8 design consists of an SU-8 boss-membrane with integrated piezoresistive elements. The SU-8 membranes are structured using photolithography. The SU-8 micromechanical structures are characterized to determine film stresses, bending stiffness, displacement of the stylus, and breaking points. Included in these tests are measurement of the stress behavior at different process steps and simulation of stress distribution in the membrane at different directions of loading. In addition a comparative analytical investigation of the structures is carried out particularly with regard to the displacement of the stylus.     

用于昆虫足力测试的三维微力传感器

介绍一种三维微力传感器的结构和工作原理,该传感器量程为-0.01~0.01N,分辨力为10μN,用于测量昆虫爬行时足底与接触面间的三维接触力。通过运用Ansys有限元分析软件,对这种结构的传感器进行结构静力分析和模态分析,验证这种结构传感器用于小量程三维接触力测量的可行性。昆虫爬行足力试验测试以及相关的试验数据表明:可以满足生物试验要求。     

一种新型柔性触觉阵列传感器信号处理电路设计

依据一种利用压阻特性的3×3点阵的柔性触觉传感器,设计了针对这种新型柔性触觉传感器的信号处理电路。该电路能完成信号放大、阵列信号的选通、A／D转换以及通过LED电路对其信号的采集。并详细地阐述了电路的原理和所用芯片的功能。所设计的信号处理电路能够判断出这种触觉传感器单元所受三维加载力的大小和位置。通过在正向压力的加载试验,验证了电路的可行性。     

Object imaging with a piezoelectric robotic tactile sensor

A two-dimensional, electrically multiplexed robotic tactile sensor was realized by coupling a piezoelectric polyvinylidene fluoride (PVDF) polymer film to a monolithic silicon integrated circuit (IC). The IC incorporates 64 sensor electrodes arranged in a symmetrical 8×8 matrix. Each electrode occupies a 400×400 μm square area, and they are separated from each other by 300 μm. A 40-μm-thick piezoelectric PVDF polymer film was attached to the electrode array with an electrically nonconductive methane adhesive. The response of the tactile sensor is linear for loads spanning 0.8-135 grams-of-force (gmf) (0.00-1.35 Newtons (N)). The response bandwidth is 25 Hz, the hysteresis level is tolerable, and, for operation in the sensor's linear range, taxel crosstalk is negligible. The historically persistent stability and response reproducibility limitation associated with piezoelectric-based tactile sensors has been solved by implementing a novel pre-charge voltage bias technique to initialize the pre- and post-load sensor responses. A rudimentary tactile object image measurement procedure for applied loads has been devised to recognize the silhouette of a sharp edge, square, trapezoid, isosceles triangle, circle, toroid, slotted screw, and cross-slotted screw