Takashi Mitsuda mitsuda@md.okayama-u.ac.jp Faculty of Health Sciences Okayama University Medical School 2-5-1 Shikata-cho, OKAYAMA 700-8558 JAPAN Sachiko Kuge SHARP Corporation Masato Wakabayashi Department of Robotics Ritsumeikan University Sadao Kawamura Department of Robotics Ritsumeikan University Presence, Vol. 11, No. 6, December 2002, 569 –577 © 2002 by the Massachusetts Institute of Technology Wearable Force Display Using a Particle Mechanical Constraint Abstract A particle mechanical constraint (PMC) is a soft vinyl tube containing Styrofoam beads. It can be freely compressed, elongated, bent, twisted, or otherwise manipu- lated in all degrees of freedom. Evacuation of the air inside the tube makes the PMC rigid so that it maintains whatever shape it has been given. The stiffness of the PMC is proportional to the reduction in internal pressure below atmospheric pres- sure. Viscosity is also controlled virtually by changing the inside air pressure in pro- portion to the speed of transformation of the PMC. We used a PMC to develop a wearable force display that provides the sensation of coming into contact with a wall or of moving in water with viscosity, in addition to that of moving in air. PMC is an inherently passive device that never exerts excessive force if it were to mal- function. In short, it is suitable as a wearable human interface because it is light, soft, and safe. 1 Introduction A force display generally requires an actuator that exerts a force on the human body. Examples of such actuators include a robot arm (Brooks, Young, Batter, & Kilpatrick, 1990; Kazerooni & Guo, 1993; Bergamasco et al., 1994), a wire system driven by a servo motor (Ishii & Sato, 1994; Kawamura, Ida, Wada, & Wu, 1995) and a pneumatic cylinder (Burdea, Zhuang, Roskos, Deborah, & Langrana, 1992). These systems carry a risk of exerting excessive force accidentally, and these wearable interfaces could be lethal to the user if they were to malfunction. To overcome this problem, devices that exert a force in a passive way have been investigated. Sakaguchi, Fukusumi, and Furusho (2000) developed a passive force display using a manipulandum with ER brakes. This system provides a reaction force to the hand via the braking torque of the manipulandum. Colgate (1996) developed a passive force display using nonholonomic joints. This system exerts a reaction force to the hand through a handle with a wheel that rotates against the direction of movement. Because these systems do not create any power by themselves, they are intrinsi- cally safe. However, it is difficult to increase the degrees of freedom of such systems while suppressing their weight and size. In the present study, we examined a novel passive device called a particle mechanical constraint, which consists of Styrofoam beads and vinyl films, mak- ing it lighter and softer than previous passive devices. It is driven by vacuum pressure, and so it is safer than electric devices when broken. Aldridge, Carr, England, Meech, and Solomonides (1996) developed a similar passive device that, using an amorphous blob filled with fine particles, provides the sensation Mitsuda et al. 569