Tactile displays

Besides microfluidics the human-machine interaction, especially the imaging systems, could enormously benefit from the availability of large-scale integrated actuator systems. Such systems could provide an additional mechanical data channel intended for the sense of touch of the human, which is a very sensitive aesthesia. A first impression about the performance of a high-resolution tactile display gives the artificial skin (Fig. 15a). 

Koo IM, Jung K, Koo JC, Nam JD, Lee YK, Choi HR (2008) Development of soft-actuator-based wearable tactile display. IEEE Trans Robotics 24 549... 

Carpi F, Frediani G, De Rossi D (2010) Hydrostatically coupled dielectric elastomer actuators for tactile displays and cutaneous stimulators. EAPAD 2010, Proc SPIE 7642 76420E-1-76420E-6. doi 10.1117/12.847562... 

Tactile display of spatial patterns on the skin uses three main types of transducers [Kaczmarek et al, 1991 Kaczmarek and Bach-y-Rita, 1995]. Static tactile displays use solenoids, shape-memory alloy actuators, and scanned air or water jets to indent the skin. Vibrotactile displays encode stimulation intensity as the amplitude of a vibrating skin displacement (10-500 Hz) both solenoids and piezoelectric transducers have been used. Electrotactile stimulation uses 1-100 mm -area surface electrodes and careful waveform control to electrically stimulate the afferent nerves responsible for touch, producing a vibrating or tingHng sensation. 

Kaczmarek, K.A. and Bach-y-Rita, P 1995. Tactile displays. In W. Barfield and T. Furness (Eds.), Virtual... 

Reed, C. M., Rabinowitz, W.M., Durlach, N.l.etal. 1992. Analytic study of the Tadoma method improving performance through the use of supplementary tactile displays. J. Speech Hear. Res. 35 450. Sataloff, J., Sataloff, R.T., and VassaUo, L.A. 1980. Hearing Loss, 2nd ed. Philadelphia, PA, Lippincott. Saunders, F.A., Flill, W.A., and Franklin, B. 1981. A wearable tactile sensory aid for profoundly deaf children. /. Med. Syst. 5 265. 

Presence Teleoperators and Virtual Environments is a bimonthly journal focusing on advanced human-machine interface issues. In an effort to develop tactile displays without moving parts, our laboratory has demonstrated simple pattern recognition on the fingertip [Kaczmarek et al., 1997] and tongue [Bach-y-Rita et al, 1998] using electrotactile stimulation. 

Reed, C.M., Rabinowitz, W.M., Durlach, N.I. et al. 1992. Analytic study of the Tadoma method Improving performance through the use of supplementary tactile displays. /. Speech Hear. Res. 35 450. 

A common actuator is a tactile display that is lightweight and can be built into a shirt (e.g., www.elitac.nl). This system can be used to orient the athlete or for optimal pacing. When the speed is too low, pressure sensors in the back may stimulate the athlete to speed up similarly, actuators on the chest make signal a mruier to reduce running speed. 

Jaffe and Howse, 1979). The first scouts to find leaf material recruit other workers exclusively, and do not join in leaf-cutting for up to an hour. Scouts recruit nest-mates both by the traU pheromone and by tactile displays. As in Solenopsis, the degree of recruitment is modulated by the strength of the trail, but in the case of Atta this is not dependent on the number of recruiting ants, so that individuals apparently regulate the amount of trail pheromone they deposit, based upon the information they have about the quality and quantity of food available. 

Konyo, M., Tadokoro, S., Takamori, T. and Oguro, K. (2000) Artificial tactile display using soft gel actuators. Proceedings of the IEEE International Conference on Robotics and Automation, 3416-21. 

IPMC Based Tactile Displays for Pressure and Texture Presentation on a Human Finger... 

Tactile sensation is an important cue for us to find a subtle difference in handling objects. For a robotic telemanipulation surgery, tactile displays, which produce virtual cutaneous sensation on human hands, provide haptic feedback to the operators for finding diseases carefully and manipulating tools dexterously. For virtual reahty apphcations in medicine, such as rehabilitation and psychotherapy, a tactile display can also contribute to human emotional responses because tactile sensation is highly related to both our comfort and wonder. Many researchers have developed tactile displays and haptic interfaces, as reported by Benali-Khoudja [1] and Hayward [2]. However, it is difficult for conventional tactile displays to synthesize rich and complex tactile sensation arbitrarily. 

The most characteristic feature of tactile sensation is the variety of perceptual contents reflected, from physical factors such as rigidity, elasticity, viscosity, friction and the surface shape of the target material. It is interesting that tactile receptors in human skin cannot sense the physical factors directly. They only detect the inner skin deformation caused by contact with the object. This fact suggests that a tactile display does not have to reproduce the same physical factors of the material to represent virtual touch. In other words, virtual touch needs only to reproduce the internal deformations in the skin. Furthermore, reproduction of only the nervous activities of the tactile receptors can provide the virtual touch regardless of the inner... 

In addition, active perceptual processes based on touch by movement by hands are quite important for human tactile perception. Hand movement is used consciously or actively to clarify material properties. Gibson [5] reported that active touch is superior to passive touch in quality and quantity. For the conventional tactile displays, however, it was difficult to perform touch movement freely in a 3-D space due to the limits of the size and weight of the device. 

In this chapter, we introduce the wearable tactile display and the tactile synthesis method using IPMC actuators. Our display can represent texture feeling and pressure sensation by controlling three physical characteristics roughness, softness and Metion. 

Conventional tactile displays could hardly control delicate tactile sensation, because it was difficult to make fine distributed stimuli on a human skin under the limitations of their actuators, such as magnetic oscillators, piezoelectric actuators, shape memory alloy actuators, pneumatic devices, and so on. EAP materials have many attractive characteristics as a soft and light actuator for such a stimulation device. 

Wide frequency range A tactile display can stimulate several tactile receptors selectively by ehanging frequency ranges because eaeh taetile receptor has different time response eharaeteristies for vibratory stimulation [9]. The required frequency range is from 5 to 200 Hz to stimulate all kinds of tactile reeeptors. The response speed of an IPMC is fast enough to make a vibratory stimulation on a skin higher than 200 Hz. This means that an IPMC ean stimulate all receptors seleetively. 

Figure 8.3 Overviews of the wearable tactile display (a) close-up of the IPMC stimulator (b) mounted on a finger.

Figure 8.5 Wearable tactile display system in response to virtual contact motion.

For the IPMC tactile display, selective stimulation is realized by changing drive frequencies, using the receptors response characteristics. It was confirmed by a subject s introspection that the contents of sensation vary with the change of drive frequency as follows ... 

As evaluation indexes of the roughness sensation, nine kinds of close-set lead balls that had different diameters from 0.5 to 10 mm were used. The wearable tactile display system shown in Figure 8.5 was used. The amplitudes of the stimulations were fixed at 6.0 V (= the maximum input) and each offset was 0.5 V. The offset was needed to avoid an insensitive zone caused by shortage of amplitudes of the actuators. The subjects put the device on the right middle finger. They touched the index with their left hand at the same time. There was no restriction on time to explore. The subjects were six males in their twenties. 

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