A Review of Smart Materials in Tactile Actuators for Information Delivery

As the largest organ in the human body, the skin provides the important sensory channel for humans to receive external stimulations based on touch. By the information perceived through touch, people can feel and guess the properties of objects, like weight, temperature, textures, and motion, etc. In fact, those properties are nerve stimuli to our brain received by different kinds of receptors in the skin. Mechanical, electrical, and thermal stimuli can stimulate these receptors and cause different information to be conveyed through the nerves. Technologies for actuators to provide mechanical, electrical or thermal stimuli have been developed. These include static or vibrational actuation, electrostatic stimulation, focused ultrasound, and more. Smart materials, such as piezoelectric materials, carbon nanotubes, and shape memory alloys, play important roles in providing actuation for tactile sensation. This paper aims to review the background biological knowledge of human tactile sensing, to give an understanding of how we sense and interact with the world through the sense of touch, as well as the conventional and state-of-the-art technologies of tactile actuators for tactile feedback delivery

A Model that Predicts the Material Recognition Performance of Thermal Tactile Sensing

Tactile sensing can enable a robot to infer properties of its surroundings, such as the material of an object. Heat transfer based sensing can be used for material recognition due to differences in the thermal properties of materials. While data-driven methods have shown promise for this recognition problem, many factors can influence performance, including sensor noise, the initial temperatures of the sensor and the object, the thermal effusivities of the materials, and the duration of contact. We present a physics-based mathematical model that predicts material recognition performance given these factors. Our model uses semi-infinite solids and a statistical method to calculate an F1 score for the binary material recognition. We evaluated our method using simulated contact with 69 materials and data collected by a real robot with 12 materials. Our model predicted the material recognition performance of support vector machine (SVM) with 96% accuracy for the simulated data, with 92% accuracy for real-world data with constant initial sensor temperatures, and with 91% accuracy for real-world data with varied initial sensor temperatures. Using our model, we also provide insight into the roles of various factors on recognition performance, such as the temperature difference between the sensor and the object. Overall, our results suggest that our model could be used to help design better thermal sensors for robots and enable robots to use them more effectively.Comment: This article is currently under review for possible publicatio

Strategies in surface engineering for the regulation of microclimates in skin-medical product interactions

There is a growing number of personal healthcare devices that are in prolonged contact with the skin. The functionality of these products is linked to the interface formed by the contact between the medical apparatus and the skin. The interface can be characterised by its topology, compliance, and moisture and thermal regulating capabilities. Many devices are, however, described to have suboptimal and occlusive contacts, resulting in physiological unfavourable microclimates at the interface. The resulting poor management of moisture and temperature can impact the functionality and utility of the device and, in severe cases, lead to physical harm to the user. Being able to control the microclimate is therefore expected to limit medical-device related injuries and prevent associated skin complications. Surface engineering can modify and potentially enhance the regulation of the microclimate factors surrounding the interface between a product's surface and the skin. This review provides an overview of potential engineering solutions considering the needs for, and influences on, regulation of temperature and moisture by considering the skin-medical device interface as a system. These findings serve as a platform for the anticipated progress in the role of surface engineering for skin-device microclimate regulation

Development of a Tactile Thimble for Augmented and Virtual Reality Applications

The technologies that have gained a renewed interest during the recent years are Virtual Reality (VR) and Augmented Reality (AR), as they become more accessible and affordable for mass-production. The input device which allows us to interact with the virtual environment is a very crucial aspect. One of the main barriers to immerse ourselves in virtual reality is the lack of realistic feedback. The user has to almost rely entirely on visual feedback without any haptic feedback, and this increases the user's workload and decreases the performance. In this thesis, a functional demonstrator of a tactile feedback device which conveys compelling interactions with not just VR, but also AR is presented. The device is designed such that there is realistic feedback for virtual touches and least obstruction during contact of a real object in AR applications. New design principle of introducing small actuators allows the device to be compact and increases its portability. In contrast to actuators that are placed on the finger pad in most of the available input devices for VR, a tactile device with two actuators that are arranged laterally on the finger, so that the underside of the fingertip is free is proposed. The output from these actuators generate a tactile stimulus by stimulating a sense of touch, which helps the user to manipulate virtual objects. The actuators are designed to independently generate vibrations and this coupled tactile feedback enhances the stimulation resulting in a wide variety of stimulation patterns for the sense of touch. Preliminary experimental evaluation for design and location of actuators has been carried out to measure the vibration intensity. In addition, user experiments for design evaluation of the two actuators based on different vibration patterns have also been conducted

Influence of contact conditions on thermal responses of the hand

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.Includes bibliographical references (leaves 82-87).The objective of the research conducted for this thesis was to evaluate the influence of contact conditions on the thermal responses of the finger pad and their perceptual effects. A series of experiments investigated the thermal and perceptual effects of different contact conditions including contact force, contact duration, the object's surface temperature, and its surface roughness. The thermal response of the finger pad was measured using an infrared camera as the contact force varied from 0.1 to 6 N. It was determined that the decrease in skin temperature was highly dependent on the magnitude of contact force as well as contact duration. A second set of experiments investigated the effect of surface texture on the thermal response of the finger pad, and demonstrated, contrary to predictions, that a greater change in skin temperature occurs when the finger is in contact with rougher surfaces. The effect of varying surface texture on the perception of temperature was also investigated. The changes in temperature due to varying surface texture are perceptible, and demonstrate that the perception of surface roughness is not only influenced by changes in temperature, but in turn affects the perception of temperature. The final set of experiments examined the effect of varying the surface temperature of the thermal display on the perceived magnitude of finger force. Over the range of 20 to 38 'C, the surface temperature of the display did not have a significant effect on the perceived magnitude of force. The results of these experiments can be incorporated into thermal models that are used to create more realistic displays for virtual environments and teleoperated systems.by Jessica Anne Galie.S.M

遠隔操作での視覚的力触覚の脳波評価とロボット実装に関する研究

関西大

温度感覚がもたらす運動・感覚作用の医療福祉への応用

人間の皮膚感覚は，皮膚の機械的変形を伝える触覚（本論文では機械的変形を伝える感覚を狭義の触覚とする），温度感覚，痛覚等によって構成されている．このうち触覚については近年，バーチャルリアリティ（VR）等，さまざまな分野への応用もなされている．しかし温度提示の応用は，VRにおける皮膚感覚の一要素としての温度感覚の提示や，保温等による快適性の向上に限定され，いまだ発展途上の研究分野といえる．一方で温度提示は機械的な駆動部を必要とせず，また振動提示等と比べて低コスト，低エネルギーであるため，全身への情報提示に向いている可能性がある．これらのメリットを持ちながら応用が行われない理由として，これまでの温度提示が「温度そのものの知覚」に主眼をおいていたことが挙げられる．しかし，温度提示によってもたらされるものは温度そのものの知覚に限らない．温度感覚は温度の情報を伝達するのみならず，時としてほかの感覚を生起し，さらには人間の運動を誘発する．例えば痛み，痒みの感覚は必ずしも温度提示と不可分の感覚ではないが，伝達する神経は温度を伝達する神経と共通し，実際には温度感覚と不可分の関係にある．また近年の研究では，人間が物体を把持する力の調節に温度感覚が寄与することが示唆されている．このような温度感覚の運動および感覚に与える作用を考えれば，上述した振動等の触刺激提示に対する利点を活用することができるであろう．本論文は単純な温度情報の伝達にとどまらない，温度感覚がもたらす運動・感覚作用に注目し，特に医療福祉分野における応用を提案する．本論文ではこうした温度感覚が身体に与える作用を「純粋に感覚的なもの」，「身体運動に影響を与えるもの」の2つに分類した．温度感覚の身体作用については限定的にしか知られていないが，上記の分類それぞれについて「温度感覚による痛みの生起」と「温度感覚による運動調整」が挙げられる．「純粋に感覚的なもの」として挙げた温度感覚提示が痛みの感覚を生起する現象に着目すると，痒みの鎮静（鎮痒）への応用可能性がある．温度感覚はAδ線維とC線維によって伝達され，同じくAδ，C線維により伝達される痛み，痒みとも密接な関係をもつ．痒みは乾皮症や腎不全，糖尿病等様々な病気の症状として知られるが，なかでも日本国内に約35万人の患者を抱えるアトピー性皮膚炎は非常に重大な問題となっている．現在一般的な痒みの治療法は少なからず副作用の危険性を持つ．特に，アトピー性皮膚炎の治療薬として最も一般的なステロイド薬には多くの重篤な副作用が報告されている．この他の痒みを抑制する方法に，患部を掻きむしる，患部に痛みを与える等がある．いずれも鎮痒効果があることは検証されているが，皮膚を損傷し症状を悪化させる危険性が大きく，治療に用いることは難しいとされる．これに対して本論文では温度錯覚現象Thermal grill illusion（TGI）を用いた鎮痒を提案した．TGIは温冷２つの温度感覚提示によって痛みを生じる現象であり，皮膚を損壊せず痛みを提示することが可能であることから，副作用のない鎮痒手法になる可能性がある．ローラー型の温冷刺激部が皮膚上を回転することで時空間的に交互に温冷刺激を提示し，TGIを生起させるという手法を提案し，複数回の鎮痒デバイスの試作および鎮痒効果の実験を行い，一定の鎮痒効果を有するという結果を得た．またローラーを用いずにTGIを生じさせるために，温度感覚が触覚提示部位に転移する現象であるThermal Referral（TR）を用いる手法を検討し，TRによって転移した温度提示部にTGIが生じることを発見した．さらにTRが全身に適用できることを示した（第4章）．「身体運動に影響を与えるもの」として挙げた温度感覚と把持力調節機能の関係に着目すると，温度感覚検査への応用可能性がある．近年の温度感覚研究では温度感覚の脱出した患者の把持動作に異常がみられることから，Aδ，C線維が伝達する温度感覚が運動機能に関与する可能性が示唆されていた．この知見は人間の温度知覚を，主観的な回答に依らない把持力の変化という客観的な形で表すことができる可能性が大きいことを示している．これまで温度知覚能力を計測する際には，患者の主観的な回答に頼る場合が多く，明確にその能力を計ることが困難であった．無意識的な運動調節が温度の知覚サインとなるのであれば，検診やリハビリの現場で温度，痛みを評価する際の指標としての運用が期待できる．本論文ではより直接的な温度提示と把持力調節の関係を探るため，物体の表面温度を動的に変化させることが可能なキューブ型のマニピュランダムを開発した．被験者が拇指，示指で装置を把持した際の，表面温度の変化に伴う把持力の推移を記録した．温度変化と把持力の関係性を検討したところ，物体表面の温度が増加すると把持力が減少するという関係性を認めた．健常者におけるこのような変化が温度覚由来の調節であることを確かめる目的で，温度感覚が脱失しているCIPA患者4名に同様の課題を行わせたところ，温度変化と把持力変化の間には関連性を認めなかった．また，実験を行った健常者は温度の変化を知覚した一方で把持力が変化したことを認識していなかったことから，温度の変化に伴う把持力調節は無意識的な調節であることが示唆された．これらの結果により，提案手法，デバイスが温度知覚能力の検査に応用可能であることを示した．次に把持動作についてみられた運動調節が姿勢や状況に依存しないものであるか検証を行った．手掌部における実験では温度と加重の推移に関連はみられなかった．これは把持動作に，「把持した物体を落さない」という明確な目的があるのに対し，手掌部の実験の場合明確な目的がなく加重調節の必要がなかったためと考えた．そこで立位という明確な姿勢調整の必要性を持つ条件を用いたが，温度変化と重心の推移の関係は不明確であった．しかし人間が立位姿勢をとるときの自然な重心動揺が実験条件に近いことから，周期をより大きく変更した実験を行った．その結果，温度変化時にわずかではあるが重心の偏りが生じることが示唆された（第5章）．以上のように，本論文は温度感覚のもたらす「温度そのものの知覚」以外の身体作用に注目し，特に医療福祉分野における応用を提案した．温度感覚によって痛覚を生起するという現象を鎮痒に利用できること，温度感覚によって運動調整が生じるという現象を温度知覚機能検査に利用できることを示した．電気通信大学201

Augmenting communication technologies with non-primary sensory modalities

Humans combine their senses to enhance the world around them. While computers have evolved to reflect these sensory demands, only the primary senses of vision and audition (and to an extent, touch) are used in modern communication. This thesis investigated how additional information, such as emotion and navigational assistance, might be communicated using technology-based implementations of sensory displays that output the non-primary modalities of smell, vibrotactile touch, and thermo-touch. This thesis explored using a portable atomiser sprayer to deliver emotional information via smell to mobile phone users, a ring-shaped device worn on the finger to display emotional information using vibration and colours, and an array of thermoelectric coolers worn on the arm to create temperature sensations. Additionally, this thesis explored two methods of signalling temperature using the thermal implementation, and finally, used it in a controlled study to augment the perceived emotion of text messages using temperature. There were challenges with using some of these implementations to display information. Smells produced with the scent technology were ambiguous and highly cognitive, and poor delivery to the user produced undesirable cross-adaption effects when smells lingered and mixed in the environment. The device used to communicate vibrotactile and colour lighting cues neutralized emotions in text messages. Furthermore, temperature pattern discrimination using the thermal implementation was difficult due to non-linear interaction effects that occurred on the skin’s surface, as well as latency resulting from the thermal neurological pathway and the technology used to heat and cool the skin. However, the thermal implementation enabled more accurate user discrimination between thermal signals than what a single stimulator design provided. Furthermore, the utility of continuous thermal feedback, in the context of spatial navigation, was demonstrated, which improved user performance compared to when the user was not presented with any thermal information. Finally, temperature was demonstrated to elicit arousal reactions across subjects using the thermal implementation, and could augment the arousal of text messages, especially when the content of the message was strongly neutral. However, no similar statistical significance was observed with valence, demonstrating the complex implications of using thermal cues to convey emotional information