Role of Annealing with Electric Field Toward Improvement of Ferroelectric and Electroactive Properties of PVDF Copolymer and Terpolymer Thin Films

The present study elucidates the role of annealing with electric field on lamellar crystalline structure and molecular orientation of polymer chains in ferroelectric copolymer (P(VDF-TrFE)) and ferroelectric terpolymer (P(VDF-TrFE-CFE)) spin-coated thin films. The ferroelectric polymer thin films annealed under an electric field support the growth of nanostructure with an "edge-on" lamellar crystalline structure having in-plane molecular chain orientation. The poled P(VDF-TrFE) thin films have higher remnant polarization (Pr) ≈6.2 µC cm-2 and saturation polarization (Ps) ≈8.2 µC cm-2 at an applied electric field of 250 MV/m compared to unpoled thin films having Pr ≈4.7 and Ps ≈6.2 µC cm-2. Also, poled P(VDF-TrFE) thin films show lower coercive field (Ec) ≈94 MV/m compared to an unpoled thin film having Ec ≈105 MV/m. Similarly, poled PVDF-TrFE-CFE thin film shows better ferroelectric properties having Pr ≈0.4 and Ps ≈5.7 µC cm-2 at an applied electric field of 200 MV m-1 compared to unpoled thin films having Pr ≈0.4 and Ps ≈4.1 µC cm-2. The storage energy efficiency of unpoled and poled P(VDF-TrFE-CFE) thin films is measured to be ≈75% and 80%. Annealing of ferroelectric P(VDF-TrFE) polymer thin films under an electric field demonstrates improved ferroelectric and electroactive properties.

Fiber-Reinforced Equibiaxial Dielectric Elastomer Actuator for Out-of-Plane Displacement

Dielectric elastomer actuators (DEAs) have gained significant attention due to their potential in soft robotics and adaptive structures. However, their performance is often limited by their in-plane strain distribution and limited mechanical stability. We introduce a novel design utilizing fiber reinforcement to address these challenges. The fiber reinforcement provides enhanced mechanical integrity and improved strain distribution, enabling efficient energy conversion and out-of-plane displacement. We discuss an analytical model and the fabrication process, including material selection, to realize fiber-reinforced DEAs. Numerical simulations and experimental results demonstrate the performance of the fiber-reinforced equibiaxial DEAs and characterize their displacement and force capabilities. Actuators with four and eight fibers are fabricated with 100 μm and 200 μm dielectric thicknesses. A maximal out-of-plane displacement of 500 μm is reached, with a force of 0.18 N, showing promise for the development of haptic devices.

Towards high performance and durable soft tactile actuators

Soft actuators are gaining significant attention due to their ability to provide realistic tactile sensations in various applications. However, their soft nature makes them vulnerable to damage from external factors, limiting actuation stability and device lifespan. The susceptibility to damage becomes higher with these actuators often in direct contact with their surroundings to generate tactile feedback. Upon onset of damage, the stability or repeatability of the device will be undermined. Eventually, when complete failure occurs, these actuators are disposed of, accumulating waste and driving the consumption of natural resources. This emphasizes the need to enhance the durability of soft tactile actuators for continued operation. This review presents the principles of tactile feedback of actuators, followed by a discussion of the mechanisms, advancements, and challenges faced by soft tactile actuators to realize high actuation performance, categorized by their driving stimuli. Diverse approaches to achieve durability are evaluated, including self-healing, damage resistance, self-cleaning, and temperature stability for soft actuators. In these sections, current challenges and potential material designs are identified, paving the way for developing durable soft tactile actuators.

Haptic Sensing and Feedback Techniques toward Virtual Reality

Haptic interactions between human and machines are essential for information acquisition and object manipulation. In virtual reality (VR) system, the haptic sensing device can gather information to construct virtual elements, while the haptic feedback part can transfer feedbacks to human with virtual tactile sensation. Therefore, exploring high-performance haptic sensing and feedback interface imparts closed-loop haptic interaction to VR system. This review summarizes state-of-the-art VR-related haptic sensing and feedback techniques based on the hardware parts. For the haptic sensor, we focus on mechanism scope (piezoresistive, capacitive, piezoelectric, and triboelectric) and introduce force sensor, gesture translation, and touch identification in the functional view. In terms of the haptic feedbacks, methodologies including mechanical, electrical, and elastic actuators are surveyed. In addition, the interactive application of virtual control, immersive entertainment, and medical rehabilitation is also summarized. The challenges of virtual haptic interactions are given including the accuracy, durability, and technical conflicts of the sensing devices, bottlenecks of various feedbacks, as well as the closed-loop interaction system. Besides, the prospects are outlined in artificial intelligence of things, wise information technology of medicine, and multimedia VR areas.

Height-renderable morphable tactile display enabled by programmable modulation of local stiffness in photothermally active polymer

Reconfigurable tactile displays are being used to provide refreshable Braille information; however, the delivered information is currently limited to an alternative of Braille because of difficulties in controlling the deformation height. Herein, we present a photothermally activated polymer-bilayer-based morphable tactile display that can programmably generate tangible three-dimensional topologies with varying textures on a thin film surface. The morphable tactile display was composed of a heterogeneous polymer structure that integrated a stiffness-tunable polymer into a light-absorbing elastomer, near-infra-red light-emitting diode (NIR-LED) array, and small pneumatic chamber. Topological expression was enabled by producing localized out-of-plane deformation that was reversible, height-adjustable, and latchable in response to light-triggered stiffness modulation at each target area under switching of stationary pneumatic pressure. Notably, the tactile display could express a spatial softness map of the latched topology upon re-exposing the target areas to modulated light from the NIR-LED array. We expect the developed tactile display to open a pathway for generating high-dimensional tactile information on electronic devices and enable realistic interaction in augmented and virtual environments.

Fingertip tactile sensation via piezoelectric micromachined ultrasonic transducers with an amplified interface

Tactile devices are often used in the field of robotics; however, the development of compact high-resolution tactile devices remains challenging. In this study, we developed a haptic device for force presentation using a DC motor and a tactile sensation device to simultaneously present haptic and tactile stimuli. A microelectromechanical system was selected to maintain the compactness of the tactile device. Piezoelectric micromachined ultrasonic transducers are known for high-power stimulation, and we selected lanthanum-doped lead zirconate titanate as the high-power amplified actuator. A finger mount structure that transfers force for amplifying ultrasonic waves was considered to combine acoustic pressure and aeroacoustics by attaching silicone rubber. The device was fabricated, and the performance of the tactile sensations was evaluated. The developed device uses the novel concept of combining acoustic pressure and aeroacoustics, and its compactness renders it suitable for wearable systems.

Structural and Material-Based Approaches for the Fabrication of Stretchable Light-Emitting Diodes

Stretchable displays, capable of freely transforming their shapes, have received significant attention as alternatives to conventional rigid displays, and they are anticipated to provide new opportunities in various human-friendly electronics applications. As a core component of stretchable displays, high-performance stretchable light-emitting diodes (LEDs) have recently emerged. The approaches to fabricate stretchable LEDs are broadly categorized into two groups, namely "structural" and "material-based" approaches, based on the mechanisms to tolerate strain. While structural approaches rely on specially designed geometries to dissipate applied strain, material-based approaches mainly focus on replacing conventional rigid components of LEDs to soft and stretchable materials. Here, we review the latest studies on the fabrication of stretchable LEDs, which is accomplished through these distinctive strategies. First, we introduce representative device designs for efficient strain distribution, encompassing island-bridge structures, wavy buckling, and kirigami-/origami-based structures. For the material-based approaches, we discuss the latest studies for intrinsically stretchable (is-) electronic/optoelectronic materials, including the formation of conductive nanocomposite and polymeric blending with various additives. The review also provides examples of is-LEDs, focusing on their luminous performance and stretchability. We conclude this review with a brief outlook on future technologies.

Recent Advances in Nanomaterials Used for Wearable Electronics

In recent decades, thriving Internet of Things (IoT) technology has had a profound impact on people's lifestyles through extensive information interaction between humans and intelligent devices. One promising application of IoT is the continuous, real-time monitoring and analysis of body or environmental information by devices worn on or implanted inside the body. This research area, commonly referred to as wearable electronics or wearables, represents a new and rapidly expanding interdisciplinary field. Wearable electronics are devices with specific electronic functions that must be flexible and stretchable. Various novel materials have been proposed in recent years to meet the technical challenges posed by this field, which exhibit significant potential for use in different wearable applications. This article reviews recent progress in the development of emerging nanomaterial-based wearable electronics, with a specific focus on their flexible substrates, conductors, and transducers. Additionally, we discuss the current state-of-the-art applications of nanomaterial-based wearable electronics and provide an outlook on future research directions in this field.

Flexible Electronics and Devices as Human-Machine Interfaces for Medical Robotics

Medical robots are invaluable players in non-pharmaceutical treatment of disabilities. Particularly, using prosthetic and rehabilitation devices with human-machine interfaces can greatly improve the quality of life for impaired patients. In recent years, flexible electronic interfaces and soft robotics have attracted tremendous attention in this field due to their high biocompatibility, functionality, conformability, and low-cost. Flexible human-machine interfaces on soft robotics will make a promising alternative to conventional rigid devices, which can potentially revolutionize the paradigm and future direction of medical robotics in terms of rehabilitation feedback and user experience. In this review, the fundamental components of the materials, structures, and mechanisms in flexible human-machine interfaces are summarized by recent and renowned applications in five primary areas: physical and chemical sensing, physiological recording, information processing and communication, soft robotic actuation, and feedback stimulation. This review further concludes by discussing the outlook and current challenges of these technologies as a human-machine interface in medical robotics.

A Soft Electro-Hydraulic Pneumatic Actuator with Self-Sensing Capability toward Multi-Modal Haptic Feedback

Haptic feedback is appealing for achieving the realistic perception of environmental changes for human bodies in human–computer interaction fields. However, existing haptic actuators have some hurdles such as single mode, poor compatibility, or incomplete tactile information. In this study, we proposed a novel way to generate haptic feedback by designing a soft electro-hydraulic pneumatic actuator (SEHPA) with dual drive modes. The SEHPA was structured with silicone films, a silicone air chamber, flexible electrodes, and an insulating liquid dielectric for good human–machine compatibility. The SEHPA had the advantages of high output force (1.5 N at 10 kPa) and displacement (4.5 mm at 5 kPa), as well as various haptic notifications (0~400 Hz vibration). The electro-hydraulic drive method realized smooth output force changes at the millinewton level (0~40 mN) and output displacement changes at the micron level (0~800 μm), which further enriched the details of the tactile experience. In addition, the self-sensing capability of the SEHPA can be dedicated to monitoring and ensuring precise output. The SEHPAs can be potentially mounted on the fingertips to provide accurate tactile sensation once the manipulator touches an object through teleoperation. More invisible information can also be obtained by customizing various haptic notifications. The excellent response behavior and accurate tactile haptic feedback demonstrate the candidate for teleoperation fields.

A 2-DOF Impact Actuator for Haptic Application

The demand for realistic haptic feedback actuators has increased as mobile devices have increased in popularity. However, most current haptic actuators provide limited 1-DOF tactile sensations, such as vibrations. This paper presents a 2-DOF haptic impact actuator that can provide planar directional (e.g., x and y directional) and magnitude tactile cues to a user. We built an impact actuator that was designed to be of such a size that a user can grasp it with one hand. Multiple electromagnets of the actuator drive a permanent magnet to hit the actuator housing, creating an impact. For the control of the impact direction, we assumed the direction of a magnetic field vector at the centre of the actuator would follow that of a reference vector formed by voltage heading into the electromagnet array. The results of magnetic field measurements support our assumption by showing that the trend of the magnetic field vector coincided with that of the reference voltage vector. Furthermore, the measurement of the impact acceleration showed the trend that the impact direction follows the reference voltage vector.

Haptigami: A Fingertip Haptic Interface With Vibrotactile and 3-DoF Cutaneous Force Feedback

Wearable fingertip haptic devices aim todeliver somatosensory feedback for applications such as virtual reality, rehabilitation, and enhancing hardware/physical control interfaces. However, providing various kinds of feedback requires several Degrees of Freedom (DoF) and high mechanical complexity which are mechanically difficult to achieve at the mesoscale. Using compliant low-profile transmissions embedded in an origami structure and PCBmotors as actuators, we designed and fabricated a novel 3-DoF fingertip haptic device, called Haptigami. This under-actuated system, measuring 36 x 25 x 26 mm and weighing 13 g, can render vibrotactile and cutaneous force feedback. We tested our device by creating a novel experimental protocol and robotic platform allowing quantitative characterization of mechanical performance. The current prototype of Haptigami produces 678 mN in compression, and 400 mN and 150 mN in shear for the Y and X directions, respectively. By virtue of its unique origami-inspired design, Haptigami brings a new direction for future designs of lightweight and compact wearable robots.

Valveless microliter combustion for densely packed arrays of powerful soft actuators

Existing tactile stimulation technologies powered by small actuators offer low-resolution stimuli compared to the enormous mechanoreceptor density of human skin. Arrays of soft pneumatic actuators initially show promise as small-resolution (1- to 3-mm diameter), highly conformable tactile display strategies yet ultimately fail because of their need for valves bulkier than the actuators themselves. In this paper, we demonstrate an array of individually addressable, soft fluidic actuators that operate without electromechanical valves. We achieve this by using microscale combustion and localized thermal flame quenching. Precisely, liquid metal electrodes produce sparks to ignite fuel lean methane-oxygen mixtures in a 5-mm diameter, 2-mm tall silicone cylinder. The exothermic reaction quickly pressurizes the cylinder, displacing a silicone membrane up to 6 mm in under 1 ms. This device has an estimated free-inflation instantaneous stroke power of 3 W. The maximum reported operational frequency of these cylinders is 1.2 kHz with average displacements of ∼100 µm. We demonstrate that, at these small scales, the wall-quenching flame behavior also allows operation of a 3 × 3 array of 3-mm diameter cylinders with 4-mm pitch. Though we primarily present our device as a tactile display technology, it is a platform microactuator technology with application beyond this one.

Viscoelasticity Modeling of Dielectric Elastomers by Kelvin Voigt-Generalized Maxwell Model

Dielectric elastomers (DEs) are polymer materials consisting of a network of polymer chains connected by covalent cross-links. This type of structural feature allows DEs to generate large displacement outputs owing to the nonlinear electromechanical coupling and time-dependent viscoelastic behavior. The major challenge is to properly actuate the nonlinear soft materials in applications of robotic manipulations. To characterize the complex time-dependent viscoelasticity of the DEs, a nonlinear rheological model is proposed to describe the time-dependent viscoelastic behaviors of DEs by combining the advantages of the Kelvin-Voigt model and the generalized Maxwell model. We adopt a Monte Carlo statistical simulation method as an auxiliary method, to the best knowledge of the author which has never reportedly been used in this field, to improve the quantitative prediction ability of the generalized model. The proposed model can simultaneously describe the DE deformation processes under step voltage and alternating voltage excitation. Comparisons between the numerical simulation results and experimental data demonstrate the effectiveness of the proposed generalized rheological model with a maximum prediction error of 3.762% and root-mean-square prediction error of 9.03%. The results presented herein can provide theoretical guidance for the design of viscoelastic DE actuators and serve as a basis for manipulation control to suppress the viscoelastic creep and increase the speed response of the dielectric elastomer actuators (DEA).

A Simple Dynamic Characterization Method for Thin Stacked Dielectric Elastomer Actuators by Suspending a Weight in Air and Electrical Excitation

This paper proposes a simple but effective method for characterizing dielectric elastomer actuators (DEAs), especially for thin stacked DEAs, which are promising for haptic devices but which measure the dynamic elastic modulus with great difficulty. The difficulty of the measurement of such a thin stacked DEA arises from the friction and local deformation of the surface between the DEA and a contact, as shown in this paper. In the proposed method, a DEA is vertically suspended and a weight is attached to it. The proposed method requires no contact with the surface of a DEA and uses only a weighting mass. Experimental results demonstrated the proposed method can estimate almost essential constants, such as the dynamic elastic modulus (Young’s modulus and damping time constant), the electrical constants (permittivity and resistivity), and the coefficient of electromechanical coupling, through the forced vibration induced by voltage actuation.

A Light-Driven Vibrotactile Actuator with a Polymer Bimorph Film for Localized Haptic Rendering

A vibrotactile actuator driven by light energy is developed to produce dynamic stimulations for haptic rendering on a thin-film structure. The actuator is constructed by adopting a thermal bimorph membrane structure of poly(3,4-ethylenedioxythiophene) doped with p-toluenesulfonate (PEDOT-Tos) coated onto a polyethylene terephthalate (PET) film. Upon irradiation of near-infrared (NIR) light, the light energy absorbed at the PEDOT-Tos layer is converted into thermoelastic bending deformation due to the mismatch in coefficient of thermal expansion between PEDOT-Tos and PET. Since the light-induced deformation is reversible, spatially localized, and rapidly controllable with designed light signals, the proposed actuator can produce vibrotactile stimulation over 10 dB at arbitrary areas in the human-sensitive frequency range from 125 to 300 Hz using a low input power of ∼2.6 mW mm^-2, as compared with a complex electrical circuit and high input power needed to achieve such actuation performance. Together with its simple structure based on light-driven actuation, the advent of this actuator could open up new ways to achieve substantial advances in rendering textures at a flexible touch interface.

Development of High Dielectric Electrostrictive PVDF Terpolymer Blends for Enhanced Electromechanical Properties

Electroactive polymers with high dielectric constants and low moduli can offer fast responses and large electromechanical strain under a relatively low electric field with regard to theoretical driving forces of electrostriction and electrostatic force. However, the conventional electroactive polymers, including silicone rubbers and acrylic polymers, have shown low dielectric constants (ca. < 4) because of their intrinsic limitation, although they have lower moduli (ca. < 1 MPa) than inorganics. To this end, we proposed the high dielectric PVDF terpolymer blends (PVTC-PTM) including poly(vinylidene fluoride-trifluoroethylene-chlorofluoro-ethylene) (P(VDF-TrFE-CFE), PVTC) as a matrix and micelle structured poly(3-hexylthiophene)-b-poly(methyl methacrylate) (P3HT-b-PMMA, PTM) as a conducting filler. The dielectric constant of PVTC-PTM dramatically increased up to 116.8 at 100 Hz despite adding only 2 wt% of the polymer-type filler (PTM). The compatibility and crystalline properties of the PVTC-PTM blends were examined by microscopic, thermal, and X-ray studies. The PVTC-PTM showed more compatible blends than those of the P3HT homopolymer filler (PT) and led to higher crystallinity and smaller crystal grain size relative to those of neat PVTC and PVTC with the PT filler (PVTC-PT). Those by the PVTC-PTM blends can beneficially affect the high-performance electromechanical properties compared to those by the neat PVTC and the PVTC-PT blend. The electromechanical strain of the PVTC-PTM with 2 wt% PTM (PVTC-PTM2) showed ca. 2-fold enhancement (0.44% transverse strain at 30 V_pp μm⁻¹) relative to that of PVTC. We found that the more significant electromechanical performance of the PVTC-PTM blend than the PVTC was predominantly due to the electrostrictive force rather than electrostatic force. We believe that the acquired PVTC-PTM blends are great candidates to achieve the high-performance electromechanical strain and take all benefits derived from the all-organic system, including high electrical breakdown strength, processibility, dielectrics, and large strain, which are largely different from the organic–inorganic hybrid nanocomposite systems.

Braille and Morse Code Based Tactile Information Coding and its Applications

Tactile sensing has recently been used in pattern recognition technology for pilots’ posture information and environmental information. Human tactile sensing is limited, however, through control of the spatial distribution and vibration intensity of each contact in the tactile stimulation array, the accuracy, convenience, and comfort of the tactile device can be comprehensively improved. Moreover, the recognition rate of most current flight posture information methods is low. In this paper, the principle of vibration haptic coding is optimized. A combined coding scheme of “vibration [Formula: see text] sequence” is used to recognize pilot’s flight posture. A novel triangular coding scheme is proposed for the first time. Compared to other commonly used coding schemes such as “needle scheme“ and “rectangle scheme”, experimental results show that the triangular coding scheme is 1.5% more accuracy with response time reduced by nearly 1.25s in recognition pilots’ flight posture information.

Tactile display of softness on fingertip

Multi-sensory human-machine interfaces are currently challenged by the lack of effective, comfortable and affordable actuation technologies for wearable tactile displays of softness in virtual- or augmented-reality environments. They should provide fingertips with tactile feedback mimicking the tactual feeling perceived while touching soft objects, for applications like virtual reality-based training, tele-rehabilitation, tele-manipulation, tele-presence, etc. Displaying a virtual softness on a fingertip requires the application of quasi-static (non-vibratory) forces via a deformable surface, to control both the contact area and the indentation depth of the skin. The state of the art does not offer wearable devices that can combine simple structure, low weight, low size and electrically safe operation. As a result, wearable softness displays are still missing for real-life uses. Here, we present a technology based on fingertip-mounted small deformable chambers, which weight about 3 g and are pneumatically driven by a compact and cost-effective unit. Weighting less than 400 g, the driving unit is easily portable and can be digitally controlled to stimulate up to three fingertips independently. Psychophysical tests proved ability to generate useful perceptions, with a Just Noticeable Difference characterised by a Weber constant of 0.15. The system was made of off-the-shelf materials and components, without any special manufacturing process, and is fully disclosed, providing schematics and lists of components. This was aimed at making it easily and freely usable, so as to turn tactile displays of softness on fingertips into a technology 'at fingertips'.

Performance Enhancement of Soft Nanotextured Thermopneumatic Actuator by Incorporating Silver Nanowires into Elastomer Body

To improve performance of thermopneumatic soft actuators, which have recently been developed for various industrial applications, we embedded different nanoscale materials into their elastomer bodies. This yields a significant enhancement in the actuator performance via improving the mechanical and thermal properties of the elastomer bodies. In addition, the use of nanoinclusions diminished losses of the working fluid from the actuators by decreasing vapor leaks through the elastomer body and thus improving longevity. Notably, when using different working fluids with low boiling temperatures, the operating temperature range of the actuators can be lowered and widened. The hybrid approach proposed in this study is expected to advance the industrial feasibility of thermopneumatic actuators.

Creating Accessible Online Floor Plans for Visually Impaired Readers

We present a generic model for providing blind and severely vision-impaired readers with access to online information graphics. The model supports fully and semi-automatic transcription and allows the reader a choice of presentation mediums. We evaluate the model through a case study: online house floor plans. To do so, we conducted a formative user study with severely vision impaired users to determine what information they would like from an online floor plan and how to present the floor plan as a text-only description, tactile graphic, and on a touchscreen with audio feedback. We then built an automatic transcription tool using specialized graphics recognition algorithms. Finally, we measured the quality of system recognition as well as conducted a second user study to evaluate the usefulness of the accessible graphics produced by the tool for each of the three formats. The results generally support the design of the generic model and the usefulness of the tool we have produced. However, they also reveal the inability of current graphics recognition algorithms to handle unforeseen graphical conventions. This highlights the need for automatic transcription systems to return a level of confidence in the recognized components and to present this to the end-user so they can have an appropriate level of trust.

Optimization of the Electrode Arrangement and Reliable Fabrication of Flexible EHD Pumps

Soft robots have great potential to realize machines that interact and coexist with humans. A key technology to realize soft robots is soft fluidic actuators. Previously, we developed a soft pump using the electrohydrodynamics (EHD) phenomenon. EHD is a flow phenomenon, which is generated by applying a high voltage to a dielectric fluid. In this study, we developed flexible high-power-density EHD pumps. First, a pump was fabricated by a simple design with interdigitated electrodes. Second, a mathematical model was used to analyze the pressure generated per length assuming that electric fields only act between neighboring electrodes in a flexible EHD pump with interdigitated electrodes. The results were used to optimize the gap between electrodes to maximize the pressure per length. Third, we used the optimized process to fabricate multiple flexible EHD pumps. The procedure produced pumps easily and reliably. Fourth, we compared the experimental values with the analytical solutions. The good agreement confirmed that the generated pressure per unit length can be approximated in a uniform electric field between neighboring electrodes. Because our flexible EHD pump can operate even when deformed, it has potential for wearable device applications.

Influence of Sparse Contact Point and Finger Penetration in Object on Shape Recognition

Making a virtual object shape recognizable using a haptic display is one of the major themes of haptic research. In previous works, multipoint haptic displays have been developed that had a high contact point density between the users' finger skin and the virtual object. However, the ideal contact point density that enables intuitive shape recognition has not been determined yet. Meanwhile, there is also a fundamental problem; that is, real fingers and virtual objects do penetrate, which cannot be solved with such wearable displays. This article investigated the influence of both contact point density and penetration on the shape recognition performance. We prepared a real testing environment where the user touched the real object, and where we could simulate both the sparse contact point and the penetration. Specifically, users' fingers wore thin film coated with glass particles and they touched the urethane foams that deformed flexibly. The result of experiments showed a broad trend where the sparseness of the contact and the softness of the object influenced the exploration time required to achieve recognition. In addition, the result suggested that the larger contact density could make up for the problem of penetration. We confirmed it by conducting two different tasks: (1) exploring the object surface with the index finger and (2) grasping the object surface with the thumb and the index finger.

Design and Experimental Validation of a 3-DOF Force Feedback System Featuring Spherical Manipulator and Magnetorheological Actuators

This research focuses on the development of a new 3-DOF (Degree of Freedom) force feedback system featuring a spherical arm mechanism and three magnetorheological (MR) brakes, namely two rotary MR brakes and one linear MR brake. The first rotary MR brake is integrated in the waist joint to reflect the horizontal tangent force, the other rotary MR brake is integrated in the shoulder joint to reflect the elevation tangent force, while the linear MR brake is integrated in the sliding joint of the arm to reflect the radial force (approach force). The proposed configuration can reflect a desired force to the operator at the end-effectors of the arm independently in 3 DOFs by controlling the current applied to the coils of the MR brakes. After the introduction, the configuration of the proposed force feedback system is presented. Afterward, the design and conducted simulation of the MR brakes for the systems are provided. The prototype of the force feedback system, which was manufactured for the experiment, is then presented as well as some of the obtained experimental results. Finally, the proposed control system is presented and its implementation to provide a desired feedback force to the operator is provided.

A Unidirectional Soft Dielectric Elastomer Actuator Enabled by Built-In Honeycomb Metastructures

Dielectric elastomer actuators (DEAs) are able to undergo large deformation in response to external electric stimuli and have been widely used to drive soft robotic systems, due to their advantageous attributes comparable to biological muscles. However, due to their isotropic material properties, it has been challenging to generate programmable actuation, e.g., along a predefined direction. In this paper, we provide an innovative solution to this problem by harnessing honeycomb metastructures to program the mechanical behavior of dielectric elastomers. The honeycomb metastructures not only provide mechanical prestretches for DEAs but, more importantly, transfer the areal expansion of DEAs into directional deformation, by virtue of the inherent anisotropy. To achieve uniaxial actuation and maximize its magnitude, we develop a finite element analysis model and study how the prestretch ratios and the honeycomb structuring tailor the voltage-induced deformation. We also provide an easy-to-implement and scalable fabrication solution by directly printing honeycomb lattices made of thermoplastic polyurethane on dielectric membranes with natural bonding. The preliminary experiments demonstrate that our designed DEA is able to undergo unidirectional motion, with the nominal strain reaching up to 15.8%. Our work represents an initial step to program deformation of DEAs with metastructures.

Fluidic Fabric Muscle Sheets for Wearable and Soft Robotics

Conformable robotic systems are attractive for applications in which they may actuate structures with large surface areas, provide forces through wearable garments, or enable autonomous robotic systems. We present a new family of soft actuators that we refer to as Fluidic Fabric Muscle Sheets (FFMS). They are composite fabric structures that integrate fluidic transmissions based on arrays of elastic tubes. These sheet-like actuators can strain, squeeze, bend, and conform to hard or soft objects of arbitrary shapes or sizes, including the human body. We show how to design and fabricate FFMS actuators via facile apparel engineering methods, including computerized sewing techniques that determine the stress and strain distributions that can be generated. We present a simple mathematical model that proves effective for predicting their performance. FFMS can operate at frequencies of 5 Hz or more, achieve engineering strains exceeding 100%, and exert forces >115 times their weight. They can be safely used in intimate contact with the human body even when delivering stresses exceeding 10⁶ Pascals. We demonstrate their versatility for actuating a variety of bodies or structures, and in configurations that perform multiaxis actuation, including bending and shape change. As we also show, FFMS can be used to exert forces on body tissues for wearable and biomedical applications. We demonstrate several potential use cases, including a miniature steerable robot, a glove for grasp assistance, garments for applying compression to the extremities, and devices for actuating small body regions or tissues via localized skin stretch.

Soft Wearable Skin-Stretch Device for Haptic Feedback Using Twisted and Coiled Polymer Actuators

Soft and integrated design can enable wearable haptic devices to augment natural human taction. This paper proposes a novel, soft, haptic finger-worn wearable device based on compliant and adhesive silicone skin and lightweight twisted and coiled polymer (TCP) actuators using ultra high molecular weight polyethylene (UHMWPE) fibers to provide lateral skin stretch sensations. Recently, silicone elastomers have been used in wearable sensors and in haptic applications for their high compliance or adhesion. TCP actuators have also demonstrated high power to weight ratios, large stroke length, simple mechanism, and inherent softness. Lateral skin stretch is sensitive to small motions and has been used for intuitive proprioceptive feedback applications. We combined these characteristics to design and manufacture a wearable, functional haptic prototype. Prototype performance was evaluated using an optical tracking system, a force gauge test bench, and compared to vibrotactile haptic feedback in a experiment with 14 healthy participants. Results showed that participant mean reaction times were comparable to those of a vibrotactile feedback system, though task completion times were longer. This paper is the first to employ TCP actuators for haptic stimulation and could serve as a foundation for future applications involving soft wearable haptics in gaming, health, and virtual reality.

Passive Force-Feedback Gloves With Joint-Based Variable Impedance Using Layer Jamming

Force feedback gloves have a great potential in enhancing the fidelity of virtual reality and teleoperation systems. It is a challenge to develop multifinger and lightweight force feedback gloves. In this paper, we propose a solution using layer jamming sheet (LJS) on each finger joint. In simulating free space, the LJS is soft and easy to deform, which allows the finger joints to move freely with a small resistance force. In simulating constrained space, the LJS becomes stiff, which provides resistance torques to prevent the rotation of finger joints. Possible solutions for mounting the LJS on finger joints are investigated. Mechanical models of the LJS are derived by quantifying the relationship between the bending stiffness and the pressure, material, and geometry of the layer. Experiments are performed to characterize the mechanical behavior of the LJS actuator and to validate the performance of the different design solutions in simulating free space and constrained space. Experimental results indicate the potential of the proposed joint-based LJS-actuated approach in developing lightweight force feedback gloves.

Toward Whole-Hand Kinesthetic Feedback: A Survey of Force Feedback Gloves

Force feedback gloves have found many applications in fields such as teleoperation and virtual reality. In order to enhance the immersive feeling of interaction with remote or virtual environments, glove-like haptic devices are used, which enable users to touch and manipulate virtual objects in a more intuitive and direct way via the dexterous manipulation and sensitive perception capabilities of human hands. In this survey, we aim to identify the gaps between existing force feedback gloves and the desired ones that can provide robust and realistic sensation of the interaction with diverse virtual environments. By examining existing force feedback gloves, the pros and cons of existing design solutions to the major sub-systems including sensing, actuation, control, transmission and structure are discussed. Future research topics are put forward with design challenges being elaborated. Innovative design solutions are needed to enable the utility of wearable haptic gloves in the upcoming virtual reality era.

Fabrication of Dielectric Elastomer Composites by Locking a Pre-Stretched Fibrous TPU Network in EVA

Dielectric elastomer (DE) composites with high electrical breakdown strength and large voltage-induced deformation were developed by retaining pre-stretched thermoplastic polyurethane (TPU) fibers in ethylene vinyl acetate copolymer (EVA). The microstructure of the candidate E-TPU fiber membrane and EVA coated E-TPU (E-TPU/EVA) film were characterized by scanning electron microscopy (SEM). The quasi-static and dynamic mechanical property, and the electromechanical properties, including the dielectric constant, dielectric loss tangent, and electromechanical sensitivity, of the DE composites were evaluated. Initially, tensile tests demonstrated that the DE composites based on E-TPU/EVAs had a higher elongation at break of above 1000% but a low elastic modulus of approximately 1.7 MPa. Furthermore, dielectric spectroscopy showed that the E-TPU/EVA had a dielectric constant of 4.5 at the frequency of 1000 Hz, which was 1.2 times higher than that of pure EVA film. Finally, it was found from electromechanical test that the voltage induced strain of E-TPU/EVA rose to 6%, nearly 3 times higher than that of pure TPU film, indicating an excellent electromechanical property. The DE composites developed have demonstrated the potential to be good candidate materials in the fields of artificial intelligence, biomimicry and renewable energy.

Refreshable Tactile Display Based on a Bistable Electroactive Polymer and a Stretchable Serpentine Joule Heating Electrode

The demand for tactile interactive devices has been growing exponentially as the sense of touch enriches the human-machine interaction experience. However, the tactile devices reported so far cannot offer high-quality performance, compact form factor, and relatively simple system architecture for low-cost production. We report the fabrication of a 4 × 4 pneumatic tactile display with Braille standard resolution using a bistable electroactive polymer (BSEP) thin film and a serpentine-patterned carbon nanotube electrode. The BSEP is a variable stiffness material that exhibits a stiffness change of 3000-fold within the narrow temperature range of 43 ± 3 °C. The carbon nanotube electrode was patterned on the polymer film via a P3R process, Prestretch-Pattern-Protect-Release, which leads to a serpentine-patterned composite electrode that is highly stretchable, retains its high electrical conductivity up to an ∼200% area strain, and provides a fast Joule heating rate of 31 °C/s. The tactile pixels are diaphragm actuators that can be individually controlled to produce 0.7 mm out of plain deformation and greater than 50 g of blocking force by application of local heating and pneumatic pressure. The device can operate under low voltage supply (30 V) and has a lifetime of over 100 000 cycles without much performance degradation. This work could open a path to building compact, user-friendly, and cost-effective tactile devices for a variety of important applications.

A Soft Robotic Wearable Wrist Device for Kinesthetic Haptic Feedback

Advances in soft robotics provide a unique approach for delivering haptic feedback to a user by a soft wearable device. Such devices can apply forces directly on the human joints, while still maintaining the safety and flexibility necessary for use in close proximity to the human body. To take advantage of these properties, we present a new haptic wrist device using pressure-driven soft actuators called reverse pneumatic artificial muscles (rPAMs) mounted on four sides of the wrist. These actuators are originally pre-strained and release compressive stress under pressure, applying a safe torque around the wrist joints while being compact and portable, representing the first soft haptic device capable of real-time feedback. To demonstrate the functional utility of this device, we created a virtual path-following task, wherein the user employs the motion of their wrist to control their embodied agent. We used the haptic wrist device to assist the user in following the path and study their performance with and without haptic feedback in multiple scenarios. Our results quantify the effect of wearable soft robotic haptic feedback on user performance. Specifically, we observed that our haptic feedback system improved the performance of users following complicated paths in a statistically significant manner, but did not show improvement for simple linear paths. Based on our findings, we anticipate broader applications of wearable soft robotic haptic devices toward intuitive user interactions with robots, computers, and other users.

Design of a Wearable Fingertip Haptic Device for Remote Palpation: Characterisation and Interface with a Virtual Environment

This paper presents the development of a wearable Fingertip Haptic Device (FHD) that can provide cutaneous feedback via a Variable Compliance Platform (VCP). The FHD includes an inertial measurement unit, which tracks the motion of the user’s finger while its haptic functionality relies on two parameters: pressure in the VCP and its linear displacement towards the fingertip. The combination of these two features results in various conditions of the FHD, which emulate the remote object or surface stiffness properties. Such a device can be used in tele-operation, including virtual reality applications, where rendering the level of stiffness of different physical or virtual materials could provide a more realistic haptic perception to the user. The FHD stiffness representation is characterised in terms of resulting pressure and force applied to the fingertip created through the relationship of the two functional parameters – pressure and displacement of the VCP. The FHD was tested in a series of user studies to assess its potential to create a user perception of the object’s variable stiffness. The viability of the FHD as a haptic device has been further confirmed by interfacing the users with a virtual environment. The developed virtual environment task required the users to follow a virtual path, identify objects of different hardness on the path and navigate away from “no-go” zones. The task was performed with and without the use of the variable compliance on the FHD. The results showed improved performance with the presence of the variable compliance provided by the FHD in all assessed categories and particularly in the ability to identify correctly between objects of different hardness.

Electro-Active Polymer Based Soft Tactile Interface for Wearable Devices

This paper reports soft actuator based tactile stimulation interfaces applicable to wearable devices. The soft actuator is prepared by multi-layered accumulation of thin electro-active polymer (EAP) films. The multi-layered actuator is designed to produce electrically-induced convex protrusive deformation, which can be dynamically programmable for wide range of tactile stimuli. The maximum vertical protrusion is and the output force is up to 255 mN. The soft actuators are embedded into the fingertip part of a glove and front part of a forearm band, respectively. We have conducted two kinds of experiments with 15 subjects. Perceived magnitudes of actuator's protrusion and vibrotactile intensity were measured with frequency of 1 Hz and 191 Hz, respectively. Analysis of the user tests shows participants perceive variation of protrusion height at the finger pad and modulation of vibration intensity through the proposed soft actuator based tactile interface.

Wearable Haptic Systems for the Fingertip and the Hand: Taxonomy, Review, and Perspectives

In the last decade, we have witnessed a drastic change in the form factor of audio and vision technologies, from heavy and grounded machines to lightweight devices that naturally fit our bodies. However, only recently, haptic systems have started to be designed with wearability in mind. The wearability of haptic systems enables novel forms of communication, cooperation, and integration between humans and machines. Wearable haptic interfaces are capable of communicating with the human wearers during their interaction with the environment they share, in a natural and yet private way. This paper presents a taxonomy and review of wearable haptic systems for the fingertip and the hand, focusing on those systems directly addressing wearability challenges. The paper also discusses the main technological and design challenges for the development of wearable haptic interfaces, and it reports on the future perspectives of the field. Finally, the paper includes two tables summarizing the characteristics and features of the most representative wearable haptic systems for the fingertip and the hand.

Evaluation of Wearable Haptic Systems for the Fingers in Augmented Reality Applications

Although Augmented Reality (AR) has been around for almost five decades, only recently we have witnessed AR systems and applications entering in our everyday life. Representative examples of this technological revolution are the smartphone games "Pokémon GO" and "Ingress" or the Google Translate real-time sign interpretation app. Even if AR applications are already quite compelling and widespread, users are still not able to physically interact with the computer-generated reality. In this respect, wearable haptics can provide the compelling illusion of touching the superimposed virtual objects without constraining the motion or the workspace of the user. In this paper, we present the experimental evaluation of two wearable haptic interfaces for the fingers in three AR scenarios, enrolling 38 participants. In the first experiment, subjects were requested to write on a virtual board using a real chalk. The haptic devices provided the interaction forces between the chalk and the board. In the second experiment, subjects were asked to pick and place virtual and real objects. The haptic devices provided the interaction forces due to the weight of the virtual objects. In the third experiment, subjects were asked to balance a virtual sphere on a real cardboard. The haptic devices provided the interaction forces due to the weight of the virtual sphere rolling on the cardboard. Providing haptic feedback through the considered wearable device significantly improved the performance of all the considered tasks. Moreover, subjects significantly preferred conditions providing wearable haptic feedback.

Encapsulation of Piezoelectric Transducers for Sensory Augmentation and Substitution with Wearable Haptic Devices

The integration of polymeric actuators in haptic displays is widespread nowadays, especially in virtual reality and rehabilitation applications. However, we are still far from optimizing the transducer ability in conveying sensory information. Here, we present a vibrotactile actuator characterized by a piezoelectric disk embedded in a polydimethylsiloxane (PDMS) shell. An original encapsulation technique was performed to provide the stiff active element with a compliant cover as an interface towards the soft human skin. The interface stiffness, together with the new geometry, generated an effective transmission of vibrotactile stimulation and made the encapsulated transducer a performant component for the development of wearable tactile displays. The mechanical behavior of the developed transducer was numerically modeled as a function of the driving voltage and frequency, and the exerted normal forces were experimentally measured with a load cell. The actuator was then tested for the integration in a haptic glove in single-finger and bi-finger condition, in a 2-AFC tactile stimulus recognition test. Psychophysical results across all the tested sensory conditions confirmed that the developed integrated haptic system was effective in delivering vibrotactile information when the frequency applied to the skin is within the 200–700 Hz range and the stimulus variation is larger than 100 Hz.

Relative vibrotactile spatial acuity of the torso

While tactile acuity for pressure has been extensively investigated, far less is known about acuity for vibrotactile stimulation. Vibrotactile acuity is important however, as such stimulation is used in many applications, including sensory substitution devices. We tested discrimination of vibrotactile stimulation from eccentric rotating mass motors with in-plane vibration. In 3 experiments, we tested gradually decreasing center-to-center (c/c) distances from 30 mm (experiment 1) to 13 mm (experiment 3). Observers judged whether a second vibrating stimulator (‘tactor’) was to the left or right or in the same place as a first one that came on 250 ms before the onset of the second (with a 50-ms inter-stimulus interval). The results show that while accuracy tends to decrease the closer the tactors are, discrimination accuracy is still well above chance for the smallest distance, which places the threshold for vibrotactile stimulation well below 13 mm, which is lower than recent estimates. The results cast new light on vibrotactile sensitivity and can furthermore be of use in the design of devices that convey information through vibrotactile stimulation.

A Highly Stretchable and Robust Non-fluorinated Superhydrophobic Surface

Superhydrophobic surface simultaneously possessing exceptional stretchability, robustness, and non-fluorination is highly desirable in applications ranging from wearable devices to artificial skins. While conventional superhydrophobic surfaces typically feature stretchability, robustness, or non-fluorination individually, co-existence of all these features still remains a great challenge. Here we report a multi-performance superhydrophobic surface achieved through incorporating hydrophilic micro-sized particles with pre-stretched silicone elastomer. The commercial silicone elastomer (Ecoflex) endowed the resulting surface with high stretchability; the densely packed micro-sized particles in multi-layers contributed to the preservation of the large surface roughness even under large strains; and the physical encapsulation of the microparticles by silicone elastomer due to the capillary dragging effect and the chemical interaction between the hydrophilic silica and the elastomer gave rise to the robust and non-fluorinated superhydrophobicity. It was demonstrated that the as-prepared fluorine-free surface could preserve the superhydrophobicity under repeated stretching-relaxing cycles. Most importantly, the surface's superhydrophobicity can be well maintained after severe rubbing process, indicating wear-resistance. Our novel superhydrophobic surface integrating multiple key properties, i.e. stretchability, robustness, and non-fluorination, is expected to provide unique advantages for a wide range of applications in biomedicine, energy, and electronics.

Designing sensory-substitution devices: Principles, pitfalls and potential1

An exciting possibility for compensating for loss of sensory function is to augment deficient senses by conveying missing information through an intact sense. Here we present an overview of techniques that have been developed for sensory substitution (SS) for the blind, through both touch and audition, with special emphasis on the importance of training for the use of such devices, while highlighting potential pitfalls in their design. One example of a pitfall is how conveying extra information about the environment risks sensory overload. Related to this, the limits of attentional capacity make it important to focus on key information and avoid redundancies. Also, differences in processing characteristics and bandwidth between sensory systems severely constrain the information that can be conveyed. Furthermore, perception is a continuous process and does not involve a snapshot of the environment. Design of sensory substitution devices therefore requires assessment of the nature of spatiotemporal continuity for the different senses. Basic psychophysical and neuroscientific research into representations of the environment and the most effective ways of conveying information should lead to better design of sensory substitution systems. Sensory substitution devices should emphasize usability, and should not interfere with other inter- or intramodal perceptual function. Devices should be task-focused since in many cases it may be impractical to convey too many aspects of the environment. Evidence for multisensory integration in the representation of the environment suggests that researchers should not limit themselves to a single modality in their design. Finally, we recommend active training on devices, especially since it allows for externalization, where proximal sensory stimulation is attributed to a distinct exterior object.