Sensors for Robotic Hands: A Survey of State of the Art

Recent decades have seen significant progress in the field of artificial hands. Most of the surveys, which try to capture the latest developments in this field, focused on actuation and control systems of these devices. In this paper, our goal is to provide a comprehensive survey of the sensors for artificial hands. In order to present the evolution of the field, we cover five year periods starting at the turn of the millennium. At each period, we present the robot hands with a focus on their sensor systems dividing them into categories, such as prosthetics, research devices, and industrial end-effectors.We also cover the sensors developed for robot hand usage in each era. Finally, the period between 2010 and 2015 introduces the reader to the state of the art and also hints to the future directions in the sensor development for artificial hands

Objekt-Manipulation und Steuerung der Greifkraft durch Verwendung von Taktilen Sensoren

This dissertation describes a new type of tactile sensor and an improved version of the dynamic tactile sensing approach that can provide a regularly updated and accurate estimate of minimum applied forces for use in the control of gripper manipulation. The pre-slip sensing algorithm is proposed and implemented into two-finger robot gripper. An algorithm that can discriminate between types of contact surface and recognize objects at the contact stage is also proposed. A technique for recognizing objects using tactile sensor arrays, and a method based on the quadric surface parameter for classifying grasped objects is described. Tactile arrays can recognize surface types on contact, making it possible for a tactile system to recognize translation, rotation, and scaling of an object independently.Diese Dissertation beschreibt eine neue Art von taktilen Sensoren und einen verbesserten Ansatz zur dynamischen Erfassung von taktilen daten, der in regelmäßigen Zeitabständen eine genaue Bewertung der minimalen Greifkraft liefert, die zur Steuerung des Greifers nötig ist. Ein Berechnungsverfahren zur Voraussage des Schlupfs, das in einen Zwei-Finger-Greifarm eines Roboters eingebaut wurde, wird vorgestellt. Auch ein Algorithmus zur Unterscheidung von verschiedenen Oberflächenarten und zur Erkennung von Objektformen bei der Berührung wird vorgestellt. Ein Verfahren zur Objekterkennung mit Hilfe einer Matrix aus taktilen Sensoren und eine Methode zur Klassifikation ergriffener Objekte, basierend auf den Daten einer rechteckigen Oberfläche, werden beschrieben. Mit Hilfe dieser Matrix können unter schiedliche Arten von Oberflächen bei Berührung erkannt werden, was es für das Tastsystem möglich macht, Verschiebung, Drehung und Größe eines Objektes unabhängig voneinander zu erkennen

Human and Biological Skin-Inspired Electronic Skins for Advanced Sensory Functions and Multifunctionality

Department of Energy Engineering (Energy Engineering)The electronic skin (e-skin) technology is an exciting frontier to drive next generation of wearable electronics owing to its high level of wearability to curved human body, enabling high accuracy to harvest information of users and their surroundings. Altough various types of e-skins, based on several signal-transduction modes, including piezoresistive, capacitive, piezoelectric, triboelectric modes, have been developed, their performances (i.e. sensitivity, working range, linearity, multifunctionality, etc.) should be improved for the wearable applications. Recently, biomimicry of the human and biological skins has become a great inspiration for realizing novel wearable e-skin systems with exceptional multifunctionality as well as advanced sensory functions. As an ideal sensory organ, tactile sensing capabilities of human skin was emulated for the development of e-skins with enhanced sensor performances. In particular, the unique geometry and systematic sensory system of human skin have driven new opportunities in multifunctional and highly sensitive e-skin applications. In addition, extraordinary architectures for protection, locomotion, risk indication, and camouflage in biological systems provide great possibilities for second skin applications on user-interactive, skin-attachable, and ultrasensitive e-skins, as well as soft robots. Benefitting from their superior perceptive functions and multifunctionality, human and biological skins-inspired e-skins can be considered to be promising candidates for wearable device applications, such as body motion tracking, healthcare devices, acoustic sensor, and human machine interfaces (HMI). This thesis covers our recent studies about human and biological skin-inspired e-skins for advanced sensory functions and multifunctionality. First, chapter 1 highlights various types of e-skins and recent research trends in bioinspired e-skins mimicking perceptive features of human and biological skins. In chapter 2, we demonstrate highly sensitive and tactile-direction-sensitive e-skin based on human skin-inspired interlocked microdome structures. Owing to the stress concentration effect, the interlocked e-skin experiences significant change of contact area between the interlocked microdomes, resulting in high pressure sensitivity. In addition, because of the different deformation trends between microstructures in mutual contact, the interlocked e-skin can differentiate and decouple sensor signals under different directional forces, such as pressure, tensile strain, shear, and bending. In chapter 3, interlocked e-skins were designed with multilayered geometry. Although interlocked e-skin shows highly sensitive pressure sensing performances, their pressure sensing range is narrow and pressure sensitivity continuously decreases with increasing pressure level. The multilayer interlocked microdome geometry can enhance the pressure-sensing performances of e-skins, such as sensitivity, working range, and linearity. As another approach of e-skin with multilayered geometry, we demonstrate multilayered e-skin based on conductivity-gradient conductive materials in chapter 4. The conducive polymer composites with different conductivity were coated on the microdome pattern and designed as interlocked e-skin with coplanar electrode design, resulting in exceptionally high pressure-sensing performances compared with previous literatures. In chapter 5, inspired by responsive color change in biological skins, we developed mechanochromic e-skin with a hierarchical nanoparticle-in-micropore architecture. The novel design of hierarchical structure enables effective stress concentration at the interface between nanoparticle and porous structure, resulting in impressive color change under mechanical stimuli. In chapter 6, we emulate ultrahigh temperature sensitivity of human and snake skin for temperature-sensitive e-skin. The thermoresponsive composite based on semi-crystalline polymer, temperature sensor shows ultrahigh temperature sensitivity near the melting point of semi-crystalline polymer. In addition, integration of thermochromic composite, mimicking biological skins, enables dual-mode temperature sensors by electrical and colorimetric sensing capabilities. Finally, in chapter 7, we summarize this thesis along with future perspective that should be considered for next-generation e-skin electronics. Our e-skins, inspired by human and biological skin, can provide a new paradigm for realizing novel wearable electronic systems with exceptional multifunctionality as well as advanced sensory functions.clos

Piezoelectric Transducers Based on Aluminum Nitride and Polyimide for Tactile Applications

The development of micro systems with smart sensing capabilities is paving the way to progresses in the technology for humanoid robotics. The importance of sensory feedback has been recognized the enabler of a high degree of autonomy for robotic systems. In tactile applications, it can be exploited not only to avoid objects slipping during their manipulation but also to allow safe interaction with humans and unknown objects and environments. In order to ensure the minimal deformation of an object during subtle manipulation tasks, information not only on contact forces between the object and fingers but also on contact geometry and contact friction characteristics has to be provided. Touch, unlike other senses, is a critical component that plays a fundamental role in dexterous manipulation capabilities and in the evaluation of objects properties such as type of material, shape, texture, stiffness, which is not easily possible by vision alone. Understanding of unstructured environments is made possible by touch through the determination of stress distribution in the surrounding area of physical contact. To this aim, tactile sensing and pressure detection systems should be integrated as an artificial tactile system. As illustrated in the Chapter I, the role of external stimuli detection in humans is provided by a great number of sensorial receptors: they are specialized endings whose structure and location in the skin determine their specific signal transmission characteristics. Especially, mechanoreceptors are specialized in the conversion of the mechanical deformations caused by force, vibration or slip on skin into electrical nerve impulses which are processed and encoded by the central nervous system. Highly miniaturized systems based on MEMS technology seem to imitate properly the large number of fast responsive mechanoreceptors present in human skin. Moreover, an artificial electronic skin should be lightweight, flexible, soft and wearable and it should be fabricated with compliant materials. In this respect a big challenge of bio-inspired technologies is the efficient application of flexible active materials to convert the mechanical pressure or stress into a usable electric signal (voltage or current). In the emerging field of soft active materials, able of large deformation, piezoelectrics have been recognized as a really promising and attractive material in both sensing and actuation applications. As outlined in Chapter II, there is a wide choice of materials and material forms (ceramics: PZT; polycrystalline films: ZnO, AlN; polymers and copolymers: PVDF, PVDF-TrFe) which are actively piezoelectric and exhibit features more or less attractive. Among them, aluminum nitride is a promising piezoelectric material for flexible technology. It has moderate piezoelectric coefficient, when available in c-axis oriented polycrystalline columnar structure, but, at same time, it exhibits low dielectric constant, high temperature stability, large band gap, large electrical resistivity, high breakdown voltage and low dielectric loss which make it suitable for transducers and high thermal conductivity which implies low thermal drifts. The high chemical stability allows AlN to be used in humid environments. Moreover, all the above properties and its deposition method make AlN compatible with CMOS technology. Exploiting the features of the AlN, three-dimensional AlN dome-shaped cells, embedded between two metal electrodes, are proposed in this thesis. They are fabricated on general purpose Kapton™ substrate, exploiting the flexibility of the polymer and the electrical stability of the semiconductor at the same time. As matter of fact, the crystalline layers release a compressive stress over the polymer, generating three-dimensional structures with reduced stiffness, compared to the semiconductor materials. In Chapter III, a mathematical model to calculate the residual stresses which arise because of mismatch in coefficient of thermal expansion between layers and because of mismatch in lattice constants between the substrate and the epitaxially grown films is adopted. The theoretical equation is then used to evaluate the dependence of geometrical features of the fabricated three-dimensional structures on compressive residual stress. Moreover, FEM simulations and theoretical models analysis are developed in order to qualitative explore the operation principle of curved membranes, which are labelled dome-shaped diaphragm transducers (DSDT), both as sensors and as piezo-actuators and for the related design optimization. For the reliability of the proposed device as a force/pressure sensor and piezo-actuator, an exhaustive electromechanical characterization of the devices is carried out. A complete description of the microfabrication processes is also provided. As shown in Chapter IV, standard microfabrication techniques are employed to fabricate the array of DSDTs. The overall microfabrication process involves deposition of metal and piezoelectric films, photolithography and plasma-based dry and wet etching to pattern thin films with the desired features. The DSDT devices are designed and developed according to FEM and theoretical analysis and following the typical requirements of force/pressure systems for tactile applications. Experimental analyses are also accomplished to extract the relationship between the compressive residual stress due to the aluminum nitride and the geometries of the devices. They reveal different deformations, proving the dependence of the geometrical features of the three-dimensional structures on residual stress. Moreover, electrical characterization is performed to determine capacitance and impedance of the DSDTs and to experimentally calculate the relative dielectric constant of sputtered AlN piezoelectric film. In order to investigate the mechanical behaviour of the curved circular transducers, a characterization of the flexural deflection modes of the DSDT membranes is carried out. The natural frequency of vibrations and the corresponding displacements are measured by a Laser Doppler Vibrometer when a suitable oscillating voltage, with known amplitude, is applied to drive the piezo-DSDTs. Finally, being developed for tactile sensing purpose, the proposed technology is tested in order to explore the electromechanical response of the device when impulsive dynamic and/or long static forces are applied. The study on the impulsive dynamic and long static stimuli detection is then performed by using an ad hoc setup measuring both the applied loading forces and the corresponding generated voltage and capacitance variation. These measurements allow a thorough test of the sensing abilities of the AlN-based DSDT cells. Finally, as stated in Chapter V, the proposed technology exhibits an improved electromechanical coupling with higher mechanical deformation per unit energy compared with the conventional plate structures, when the devices are used as piezo-actuator. On the other hand, it is well suited to realize large area tactile sensors for robotics applications, opening up new perspectives to the development of latest generation biomimetic sensors and allowing the design and the fabrication of miniaturized devices

Integrated Pressure/Temperature Sensor Array Based on Nickel Conductive Composite

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2014. 2. 홍용택.Implementation of electronic artificial skin has been widely studied, from basic concept to prototypes, for potential applications in robot engineering and prosthetic replacement. Electronic Artificial skin plays a key role of sensing external environment, such as pressure and temperature, and delivering transformed signals either to robot control or human nerve system. In order to truly mimicking human skin, artificial skin at least needs to contain both pressure and temperature sensing elements in an array format. In fact, a couple of trials have been attempted to integrate sensing both elements onto single skin. Combination of commercial temperature sensing chips with printed pressure sensitive resistor or assembly of separately fabricated sensor arrays of each type has been demonstrated. These hybrid type integration or assembly approach renders rather complicated processes and thus increases fabrication cost. For sensing elements, conductive composite materials have been commonly used, whose resistance changes as geometrical dimension changes with applied pressure or temperature. In most cases, the conductive composite materials have been used only for single type of sensing element, either pressure or temperature sensor. It is challenging to differentiate two type of sensing part in one substrate with single conductive composite material and to independently read out each signal. Therefore, there have been no reported researches on using single conducting composite materials to a multi-sensing device. In addition, the conductive composite materials were typically fabricated "on" either flexible or stretchable substrate only after readout active-matrix circuitry was fabricated on the substrate. Therefore, there can be limitation in selection of materials and device structure, and process incompatibility that can makes mass manufacturing of the active-matrix sensor arrays difficult. However, when the sensor arrays are separately fabricated by embedding the sensing elements in the substrate, they can be easily incorporated into passive-matrix system or can be simply laminated on the separately fabricated active-matrix circuitry, as in case of the electronic paper front-plane technology. In this thesis, a simple fabrication method of integrated pressure/temperature sensor arrays by embedding conductive nickel (Ni) particles in poly(dimethyloxane) (PDMS) medium for electronic artificial skin application will be elucidated. The pressure and temperature sensing parts are formed in one pixel but have different heights, which are implemented by introducing a corrugated structure to Ni/PDMS composite with a pre-patterned aluminum mold. Since Ni particles are ferromagnetic materials, Ni/PDMS mixture can be patterned by exposure to patterned magnetic fields. Magnetic field exposure helps both lateral patterning and vertical particle alignment, which directly improved sensitivity and linearity of the sensor. Independent and stable read-out signals for pressure and temperature sensors are successfully obtained even under repeated measurements. This technology has advantages of simple tuning for sensitivity and operation ranges by changing particle concentration and device physical dimension, easy scaling-up to large area by seamlessly bonding small arrays or using large-area magnetic field modulator, and potential implementation of the sensor frontplane for active-matrix backplane read-out circuitry. Electronic artificial skin passive-matrix system with about 10 ppi resolution with the integrated 16 by 16 pressure and 15 by 15 temperature sensor arrays have been finally demonstrated. Furthermore, a highly stretchable electrode with demonstration of a resolution sustaining lighting device by fully utilizing the magnetic patterning/aligning method will be also studied. This stretchable electrode based on conductive composite shows unique property that is negative strain-dependency in electrical resistance. Although cyclic behavior of pure nickel composite needs more improvement, nickel-based composite materials have excellent advantages over other materials in terms of simple patterning and in-situ embedding in the matrix. This novel technology would be one of the key enabling technology in implementing future stretchable electronic display devices.Abstract i Contents ６ List of Figures ９ List of Tables １３ Chapter 1 Introduction １４ 1.1 Motivation １４ 1.2 Human Sense of Touch ２１ 1.2.1 Tactile Receptors ２４ 1.2.2 Thermoeceptor ２６ 1.2.3 Nociceptors ２６ 1.2.4 Kinesthetic Receptors ２７ 1.2.5 Tactile Sensitivity and Acuity ２７ 1.2.6 Stretchability of Human Body ２８ 1.3 Transduction Principles for Electronic Skin Applications ３０ 1.3.1 Piezoresistive ３０ 1.3.2 Piezoelectric ３４ 1.3.3 Capacitive ３５ 1.3.4 Optical ３７ 1.4 The Goal and Outline of This Thesis ４０ Chapter 2 Nickel Conductive Composite Material : Characteristics Enhancement by Magnetic Aligning Method ５６ 2.1 Introduction ５６ 2.2 Theoretical Analysis with the Maxwell Theory and the Effective Medium Theory ６２ 2.3 Materials and Fabrication Method ６７ 2.4 Results and Discussions ６９ 2.4.1 Optical Microscope Measurement ６９ 2.4.2 Electrical Characteristics ７０ 2.5 Conclusion ７５ Chapter 3 Scalable and Stretchable Fully Integrated Pressure/Temperature Sensor Array with Magnetically Aligned and Patterned Nickel Conductive Composite Material ８７ 3.1 Introduction ８７ 3.2 Materials and Fabrication Method ９１ 3.3 Finite Element Analysis for Patterning and Mechanical Characteristics ９５ 3.4 Electrical Characteristics of Integrated Sensor Array １１７ 3.5 Conclusion １２０ Chapter 4 Negatively Strain-Dependent Electrical Resistance of Magnetically Arranged Nickel Composite : Its Application to Highly Stretchable Electrode and Stretchable Lighting Devices １２５ 4.1 Introduction １２５ 4.2 Experimental １３０ 4.3 Results and Analysis １３５ 4.3.1 Electrical Characteristics with Tension Test １３５ 4.3.2 Analysis with Three-dimensional Percolation Theory １３８ 4.3.3 Highly Stretchable Electrode with Ink-jet Printed Silver １４５ 4.4 Resolution Sustainable Stretchable Lighting Device １４９ 4.5 Conclusion １５３ Chapter 5 Conclusion １６２ Abstract in Korean １７０Docto

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Department of Energy EngineeringElectronic skins (e-skins) enabling to detect various mechanical/chemical stimuli and environmental conditions by converting into various electrical and optical signals have attracted much attentions for various fields including wearable electronics, intelligent/medical robotics, healthcare monitoring devices, and haptic interfaces. Conventional e-skins have been widely used for the realization of these applications, however it is still considered that new e-skins with enhanced sensor performances (i.e. sensitivity, flexibility, multifunctionality, etc.) should be developed. In accordance with these demands, two approaches to explore novel functional materials or to modify device architectures have been introduced for enhancing sensor performance and acquiring multifunctional sensing capabilities. Firstly, a synthesis of multifunctional materials combined with conductive fillers (carbon nanotube, graphene oxide) and functional polymer matrix (i.e. ferroelectric polymer, elastomer) can provide the multimodal sensing capability of various stimuli and stretchability. Secondly, controlling design of device structures into various micro/nanostructures enables a significant improvement on sensing capabilities of e-skins with sensitivity and multidirectional force sensing, resulting from structural advantages such as large surface area, effective stress propagation, and anisotropic deformation. Therefore, a demonstration of e-skin combined with the functional composites and uniquely designed microstructures can offer a powerful platform to realize ideal sensor systems for next generation applications such as wearable electronics, healthcare devices, acoustic sensor, and haptic interface devices. In this thesis, we introduce the novel multifunctional and high performance electronic skins combined with various types of composite materials and nature-inspired 3D microstructures. Firstly, Chapter 1 briefly introduces various types of e-skins and the latest research trends of microstructured e-skins and summarizes the key components for their promising application fields. In chapters 2 and 3, mimicked by interlocking system between epidermal and dermal layers in human skin, we demonstrate the piezoresistive e-skins based on CNT/PDMS composite materials with interlocked microdome arrays for great pressure sensitivity and multidirectional force sensing capabilities. In chapter 4, we conduct in-depth study on giant tunneling piezoresistance in interlocking system and investigate systematically on the geometrical effect of microstructures on multidirectional force sensitivity and selectivity in interlocking sensor systems. In chapter 5, we demonstrate the ferroelectric e-skin that can detect and discriminate the static/dynamic touches and temperature inspired by multi-stimuli detection of various mechanoreceptors in human skin. Using the multifunctional sensing capabilities, we demonstrated our e-skin to the temperature-dependent pressure monitoring of artery vessel, high-precision acoustic sound detection, and surface texture recognition of various surfaces. In chapter 6, we demonstrate the linear and wide range pressure sensor with multilayered composite films having interlocked microdomes. In chapter 7, we present a new-concept of e-skin based on mechanochromic polymer and porous structures for overcoming limitations in conventional mechanochromic systems with low mechanochromic performances and limited stretchability. In addition, our mechanochromic e-skins enable the dual-mode detection of static and dynamic forces without any external power. Our e-skins based on functional composites and uniquely designed microstructures can provide a solid platform for next generation eskin in wearable electronics, humanoid robotics, flexible sensors, and wearable medical diagnostic systems.clos

Artificial Skin in Robotics

Artificial Skin - A comprehensive interface for system-environment interaction - This thesis investigates a multifunctional artificial skin as touch sensitive whole-body cover for robotic systems. To further the evolution from tactile sensors to an implementable artificial skin a general concept for the design process is derived. A standard test procedure is proposed to evaluate the performance. The artificial skin contributes to a safe and intuitive physical human robot interaction