Introduction

It is well known that sense of touch is inevi-table for understanding the real world. The use of force feedback to enhance computer-human interaction has often been discussed. A haptic interface is a feedback device that generates sensation to the skin and muscles, including a sense of touch, weight and rigidity. Compared to ordinary visual and auditory sensations, haptics is difficult to synthesise. Visual and auditory sen-sations are gathered by specialised organs, the eyes and ears. On the other hand, a sensation of force can occur at any part of the human body, and is therefore inseparable from actual physi-cal contact. These characteristics lead to many difficulties when developing a haptic interface. Visual and auditory media are widely used in everyday life, although little application of haptic interface is used for information media.

Haptic interface presents synthetic stimu-lation to proprioception and skin sensation. Proprioception is complemented by mechano-receptors of skeletal articulations and muscles. There are three types of joint position receptors: free nerve ending as well as Ruffini and Pacinian corpuscles. Ruffini corpuscle detects static force. On the other hand, Pacinian corpuscle has a function to measure acceleration of the joint angle. Position and motion of the human body is perceived by these receptors. Force sensation is derived from mechanoreceptors of muscles; muscle spindles and Goldi tendons. These recep-tors detect contact forces applied by an obstacle in the environment.

Skin sensation is derived from mechanorecep-tors and thermorecepters of skin. Sense of touch

29History of haptic interface Hiroo Iwata

is evoked by those receptors. Mechanoreceptors of skin are classified into four types: Merkel disks, Ruffini capsules, Meissner corpuscles, and Pacinian corpuscles. These receptors detect edge of object, skin stretch, velocity, and vibra-tion respectively.

The tactile display that stimulates skin sen-sation is a well-known technology. It has been applied to communication aids for blind person as well as master system of teleoperators. A sense of vibration is relatively easy to produce, and a good deal of work has been done using vibration displays [1, 2]. The micro-pin array is also used for tactile displays. Such a device has enabled the provision of a teltaction and com-munication aid for blind persons [3, 4]. It has the ability to convey texture or 2-D geometry [5].

The major role of tactile display is to convey sense of fine texture of object’s surface. The lat-est research activities of tactile display focus on selective stimulation of mechanoreceptors of skin. As mentioned at the beginning of this sec-tion, there are four types of mechanoreceptors in the skin: Merkel disks, Ruffini Capsules, Meissner Corpuscles, and Pacinian Corpuscles. Stimulating these receptors selectively, various tactile sensa-tions such as roughness or slip can be presented. Micro air jet [6] and micro electrode array [7] are used for selective stimulation.

These tactile display technologies cannot stimulate proprioception, although it is inevita-ble to understand the real world as well as virtual environment. External force should be applied to stimulate mechanoreceptors of skeletal articula-tions and muscles. Device for generation of such force has difficulty in its implementation. This chapter focuses on history of development of haptic interface that stimulate proprioception.

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HOMO-HAPTICUS.DE - BOOK HUMAN HAPTIC PERCEPTION, GRUNWALD M (ED.) - BIRKHÄUSER

HOMO-HAPTICUS.DE - BOOK HUMAN HAPTIC PERCEPTION, GRUNWALD M (ED.) - BIRKHÄUSER

356 V. Haptic interfaces and devices

1990: Epoch of haptic interface

There were several roots of haptic interface and they were coincidently published in 1990. Brooks began in 1967 a project to develop visual+haptic display for 6-D force fields of interacting protein molecules [8, 9]. The first haptic system, GROPE-1, employed 2-D movable platform (Fig. 1). A small knob was attached to the platform that can be positioned within a horizontal plane two inch-es square. Potentiometers sense its x and y posi-tion; servomotors exert x and y force. Both are connected to the computer driving an associated visual display. This was the first haptic device that present virtual environment. Later they introduced the Argonne ARM, a 6DOF (degree of freedom) force reflective teleoperator. It was integrated with stereoscopic large screen (Fig. 2). The system was developed for the molecular docking task. The final system, GROPE-III, proved that force significantly contributes to the task

giving the lowest potential energy of the docked combination.

Minsky developed a haptic system, called Sandpaper, designed for experimenting with feel-ing texture [10]. The force display technology used in the system was a motor-driven 2DOF joystick (Fig. 3). The software created very small virtual springs which pull the user’s hand toward low regions and away from high regions of a tex-ture’s depth map. It also created feel-able phys-ics such as variable viscosity soups, springs, and yo-yos. The research was the beginning of theory of haptic rendering.

In 1988, the author started research into design of haptic interface for natural interaction in virtual environment. We proposed a concept of the Desktop Force Display and the first proto-type was published in 1990 [11, 12]. The device applies force to the fingertips as well as the palm. Figure 4 shows overall view of the system. It was the first exoskeleton designed for haptic interac-tion in virtual environment.

Figure 2. grOPe-iiiFigure 1. grOPe-i

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HOMO-HAPTICUS.DE - BOOK HUMAN HAPTIC PERCEPTION, GRUNWALD M (ED.) - BIRKHÄUSER

HOMO-HAPTICUS.DE - BOOK HUMAN HAPTIC PERCEPTION, GRUNWALD M (ED.) - BIRKHÄUSER