Design and characterization of a fabric-based softness display

To enable a realistic tactile interaction with remote or virtual objects, softness information represents a fundamental property to be rendered via haptic devices. What is challenging is to reduce the complexity of such an information as it arises from contact mechanics and to find suitable simplifications that can lead an effective development of softness displays. A possible approach is to surrogate detailed tactile cues with information on the rate of spread of the contact area between the object and the finger as the contact force increases, i.e. force/area relation. This paradigm is called contact area spread rate. In this paper we discuss how such a paradigm has inspired the design of a tactile device (hereinafter referred to as Fabric Yielding Display, FYD-2), which exploits the elasticity of a fabric to mimic different levels of stiffness, while the contact area on the finger indenting the fabric is measured. In this manner, the FYD-2 can be controlled to reproduce force-area characteristics. In this work, we describe the FYD-2 architecture and report a psychophysical characterization. FYD-2 is shown to be able to accurately reproduce force-area curves of typical objects and to enable a reliable softness discrimination in human users

Haptics: Science, Technology, Applications

This open access book constitutes the proceedings of the 13th International Conference on Human Haptic Sensing and Touch Enabled Computer Applications, EuroHaptics 2022, held in Hamburg, Germany, in May 2022. The 36 regular papers included in this book were carefully reviewed and selected from 129 submissions. They were organized in topical sections as follows: haptic science; haptic technology; and haptic applications

Doctor of Philosophy

dissertationVirtual reality is becoming a common technology with applications in fields such as medical training, product development, and entertainment. Providing haptic (sense of touch) information along with visual and audio information can create an immersive vi

The Change in Fingertip Contact Area as a Novel Proprioceptive Cue

Humans, many animals, and certain robotic hands have deformable fingertip pads [1, 2]. Deformable pads have the advantage of conforming to the objects that are being touched, ensuring a stable grasp for a large range of forces and shapes. Pad deformations change with finger displacements during touch. Pushing a finger against an external surface typically provokes an increase of the gross contact area [3], potentially providing a relative motion cue, a situation comparable to looming in vision [4]. The rate of increase of the area of contact also depends on the compliance of the object [5]. Because objects normally do not suddenly change compliance, participants may interpret an artificially induced variation in compliance, which coincides with a change in the gross contact area, as a change in finger displacement, and consequently they may misestimate their finger’s position relative to the touched object. To test this, we asked participants to compare the perceived displacements of their finger while contacting an object varying pseudo-randomly in compliance from trial to trial. Results indicate a bias in the perception of finger displacement induced by the change in compliance, hence in contact area, indicating that participants interpreted the altered cutaneous input as a cue to proprioception. This situation highlights the capacity of the brain to take advantage of knowledge of the mechanical properties of the body and of the external environment

Requirements for a tactile display of softness

Developing tactile displays is an important aspect of improving the realism of feeling softness in laparoscopic surgery. One of the major challenges of designing a tactile display is to understand how the perception of touch can be perceived with differences in material properties. This project seeks to address this limitation by investigating how the interaction of material properties affects perception of softness and to present the perception of softness through a tactile display. The first aim explores how the interaction of material properties affects perception of softness through the use of two psychophysical experiments. Experiments used a set of nine stimuli representing three materials of different compliance, with three different patterns of surface roughness or with three different coatings of stickiness. The results indicated that compliance affected perception of softness when pressing the finger, but not when sliding; and that compliance, friction and thermal conductivity all influenced the perception of softness. To achieve the second aim of reproducing various levels of softnesses, the tactile display was built at the University of Leeds. The displayed softness was controlled by changing the contact area and tension of a flexible sheet. Psychophysical experiments were conducted to evaluate how well humans perceive softness through the display. The data was analysed using MatLab to plot psychometric functions. The results indicated that the tactile display might be good for some applications which need to compare between simulated softnesses, but it might be insufficient for other applications which need to compare between simulated softness and real samples

On the Role of Haptic Synergies in Modelling the Sense of Touch and in Designing Artificial Haptic Systems

This thesis aims at defining strategies to reduce haptic information complexity, with minimum loss of information, to design more effective haptic interfaces and artificial systems. Nowadays, haptic device design can be complex. Moreover, the artificial reproduction of the full spectrum of haptic information is a daunting task and far to be achieved. The central idea of this work is to simplify this information by exploiting the concept of synergies, which has been developed to describe the covariation patterns in multi-digit movements and forces in common motor tasks. Here I extend and exploit it also in the perceptual domain, to find projections from the heterogeneous information manifold, generated by the mechanics of touch, and what can be actually perceived by humans. In this manner, design trade-off between costs, feasibility and quality of the rendered perception can be individuated. With this as motivation, referring to cutaneous sensing, I discuss the development of a fabric-based softness display inspired by ``Contact Area Spread Rate'' hypothesis as well as the characterization of an air-jet lump display method for Robot-assisted Minimally Invasive Surgery. Considering kinaesthesia, I analyze the problem of hand posture estimation from noisy and limited in number measures provided by low cost hand pose sensing devices. By using the information about how humans most frequently use their hands, system performance is enhanced and optimal system design enabled. Finally, an integrated device, where a conventional kinaesthetic haptic display is combined with a cutaneous softness one, is proposed, showing that the fidelity by which softness is artificially rendered increases

Polyvinylidene fluoride - based MEMS tactile sensor for minimally invasive surgery

Minimally invasive surgery (MIS) procedures have been growing rapidly for the past couple of decades. In MIS operations, endoscopic tools are inserted through a small incision on human's body. Although these procedures have many advantages such as fast recovery time, minimum damage to human body and reduced post operative complications, it does not provide any tactile feedback to the surgeon. This thesis reports on design, finite element analysis, fabrication and testing of a micromachined piezoelectric endoscopic tactile sensor. Similar to the commercial endoscopic graspers, the sensor is teeth like in order to grasp slippery tissues. It consists of three layers; the first layer is a silicon layer of teeth shapes on the top and two supports at the bottom forming a thin plate and a U-Channel. The second layer is a patterned Polyvinylidene Fluoride (PVDF) film, and the third layer is a supporting Plexiglas. The patterned PVDF film was placed on the middle between the other two layers. When a concentric load is applied to the sensor, the magnitude and the position of the applied load are obtained from the outputs of the sensing elements which are sandwiched between the silicon supports and the Plexiglas. In addition, when a soft object/tissue is place on the sensor and load is applied the degree of the softness/compliance of the object is obtained from the outputs from the middle PVDF sensing elements, which are glued to the back of the thin silicon plate. The outputs are related to the deformation of the silicon plate which related to the contacting object softness. The sensor has high sensitivity and high dynamic range as a result it can potentially detect a small dynamic load such as a pulse load as well as a high load such as a firm grasping of a tissue by an endoscopic grasper. The entire surface of the tactile sensor is also active, which is an advantage in detecting the precise position of the applied point load on the grasper. The finite element analysis and experimental results are in close agreement with each other. The sensor can potentially be integrated with the gasper of a commercially available endoscopic graspe

Haptics: Science, Technology, Applications

This open access book constitutes the proceedings of the 12th International Conference on Human Haptic Sensing and Touch Enabled Computer Applications, EuroHaptics 2020, held in Leiden, The Netherlands, in September 2020. The 60 papers presented in this volume were carefully reviewed and selected from 111 submissions. The were organized in topical sections on haptic science, haptic technology, and haptic applications. This year's focus is on accessibility

Design and development of new tactile softness displays for minimally invasive surgery

Despite an influential shortcoming of minimally invasive sugary (MIS), which is the lack of tactile feedback to the surgeon, MIS has increasingly been used in various types of surgeries. Restoring the missing tactile feedback, especially information which can be obtained by the palpation of tissue, such as detection of embedded lump and softness characterization is important in MIS. The present study aims to develop tactile feedback systems both graphically and physically. In graphical rendering approach, the proposed system receives signals from the previously fabricated piezoelectric softness sensors which are integrated with an MIS grasper. After processing the signals, the tactile information is displayed by means of a color coding method. Using the graphical images, the softness of the grasped objects can visually be differentiated. A physical tactile display system is also designed and fabricated. This system simulates non-linear material properties of different soft objects. The system consists of a linear actuator, force and position sensors and processing software. A PID controller is used to control the motion of a linear actuator according to the properties of the simulated material and applied force. Graphical method was also examined to render the tactile information of embedded lumps within a soft tissue/object. The necessary information on the size and location of the hidden features are collected using sensorized MIS graspers. The information is then processed and graphically rendered to the surgeon. Using the proposed system surgeons can identify presence, location and approximate size of hidden lumps by grasping the target object with a reasonable accuracy. Finally, in order to determine the softness of the grasped object, another novel approach is taken by the design and fabrication of a smart endoscopic tool equipped with sensors for measuring the applied force and the angle of the grasper jaws. Using this method, the softness/compliance of the grasped object can be estimated and presented to the surgeo

Haptics Rendering and Applications

There has been significant progress in haptic technologies but the incorporation of haptics into virtual environments is still in its infancy. A wide range of the new society's human activities including communication, education, art, entertainment, commerce and science would forever change if we learned how to capture, manipulate and reproduce haptic sensory stimuli that are nearly indistinguishable from reality. For the field to move forward, many commercial and technological barriers need to be overcome. By rendering how objects feel through haptic technology, we communicate information that might reflect a desire to speak a physically- based language that has never been explored before. Due to constant improvement in haptics technology and increasing levels of research into and development of haptics-related algorithms, protocols and devices, there is a belief that haptics technology has a promising future