A Survey of Perceptual Feedback Issues in Dexterous Telemanipulation: Part II. Finger Touch Feedback

This paper (Part I1 of 11) surveys the existing touch display technologies in the literature. This survey indicates 5 main approaches to touch feedback, involving visual, pneumatic, vibro-tactile, electro-tactile and Neuromuscular stimulations. A pneumatics approach could use air-jets, air pockets or inflatable bladders to provide touch feedback cues to the operator. Similarly, the vibro-tactile approach could use vibrating pins, voice coils, or piezoelectric crystals to provide tickling sensation to the human operator’s skin to signal the touch. The electro-tactile stimulation method can provide electric pulses, of appropriate width and frequency, to the skin while the neuromuscular stimulation approach provides the signals directly to the primary cortex of the operator’s brain. With regard to this, seventeen (17) devices, most of whom were built for sensory substitution purposes, have been examined and compared for their suitability as touch feedback devices for dexterous telemanipulation. 1 Why Touch Feedback? The goal of this paper (Part I1 of 11) is to evaluate the state-of-the-art technology available for designing and building a master glove capable of providing touch feedback to the human operator so that he can interact with the virtual ,and remote environments in a more realistic sense. In view of this, the paper identifies and analyzes specific concerns that must guide the design of touch feedback masters. A central question to the present paper is: why do we need touch feedback to fingers in a dexterous telemanipulation context? Answer is quite simple and intuitive how many object manipulation tasks could we successfully perform when our fingers are numb or when we are wearing thick gloves? not many. The reason is, simply because we cannot know when the fingers are in touch with the object and when not. The further scientific evidence comes from the following: Therefore, when using a multifingered robotic hand as the slave end effector, providing the human operator with a feedback sensation of touch from the slave fingers would positively enhance the operator’s ability to judge the instance each finger touching something in its surroundings and to know if the grasped object is slipping. Then, the operator will be able to perform telemanipulation tasks in lesser duration .of time and with fewer errors than before. Such an ability is not only desirable but it could be crucial to tasks involving grasping and manipulation of delicate objects. 2 Master Requirements in View 2.1 Existing Touch Feedback Methods In principle, providing the touch feedback involves using the tactile sensor output from the remote slave fingers to trigger a stimulating device mounted on the human operators’ hand. The stimulation to the human operator could be provided either in visual or in tactual form, although in any other form should also be possible. The approaches used thus far in the pertaining literature could be classified as follows: (a) Visual display (b) Pneumatic stimulation (Air jets, Air pockets, Air rings) (c) Vibrotactile stimulation (Vibrating Blunt pins, Vibrating Voice coils, Vibrating Piezoelectric Crystals) (d) Electrotactile stimulation (e) Functional Neuromuscular Stimulation (FNS). In a visual display, the status of touch of the slave fingers is indicated by the appearance of an icon or via displaying the slave finger tip forces, digitally or graphically. When such a display indicate the possibility of loss of touch, the human operator moves his fingers or increases the forces appropriately so that the slave hand corrects itself. Providing a visual display as a substitute for touch feedback is not common and has a strong disadvantage in a telemanipulation situation particularly when the operator is provided with a visual feedback of the remote cite of Touch Feedback . Lack of sensation due to wearing of work gloves proin addition to the visual display of the touch status. longed a test task completion time by and McCormick, 1987). deAs a pneumatic stimulation approach, micro air jets tor’s fingers, Figure la. Alternatively, air pockets that could be placed below each finger digit, shown in Figure lb , could be pressurized so that the pressing sensa. Lack Of touch sensation due to wearing thick (space tion on the fingers will be sensed by operator. The other suit) gloves degraded the tw@Point discrimination approach involves placing inflatable air rings on the finability of humans by 50% and prolonged the average gers of the human operator, as shown in Figure IC. When task completion time by 80% (Chodack and Spampthe rings are pressurized the squeezing sensation on the inato, 1991; see Figure 2 in Part I.). fingers will be interpreted as the signal of touch. pending upon the thickness of the glove (see ,rjaAders could be impinged on the ventral surfaces of the Opera0-7803-1363-1/93 $3.00 8 1993 IEEE 27 1 Figure 1: Three (3) methods of providing touch feedback using pressurized air: (a) air-jet, (b) air-pocket, and (c) air-ring.