Weight Illusion by Tangential Deformation of Forearm Skin Yuki Kuniyasu Department of Informatics University of Electro-Communications 1-5-1 Chofugaoka, Chofu, Tokyo, JAPAN +81-42-443-5445 kuniyasu@kaji-lab.jp Shogo Fukushima Department of Informatics University of Electro-Communications 1-5-1 Chofugaoka, Chofu, Tokyo, JAPAN +81-42-443-5445 shogo@kaji-lab.jp Masahiro Furukawa Department of Informatics University of Electro-Communications 1-5-1 Chofugaoka, Chofu,Tokyo, JAPAN +81-42-443-5445 furukawa@kaji-lab.jp Hiroyuki Kajimoto Department of Informatics University of Electro-Communications 1-5-1 Chofugaoka, Chofu, Tokyo, JAPAN +81-42-443-5445 kajimoto@kaji-lab.jp ABSTRACT When we perform exercise or undergo rehabilitation, it is helpful to be supported by another person. To get this support, we normally take hold of a person’s arm, and pull it. In this paper, we investigate the use of a special device to produce a “pulling arm” sensation on the forearm. Using a weight comparison task, we performed an experiment to confirm the sensation of illusory external force with our device. We concluded that our current device presented about 10g to 20g weight perception. Categories and Subject Descriptors H5.2. Information interfaces and presentation: User Interfaces – haptic I/O, prototyping. General Terms Performance, Experimentation, Human Factors Keywords Pulling hand, forearm skin, force sensation 1. INTRODUCTION When we perform exercise or undergo rehabilitation, it is helpful to be supported by another person. Many power assisted devices have previously been proposed to replace the person in providing such support [1]. While the device can produce a large amount of force, safety is an issue. On the other hand, there are some passive type haptic devices that use brakes [2]. Although safety is less of a problem, such devices can only guide, but not help. In both cases, bulky structure hinders their practical use. In the practicing rehabilitation field, it is often observed that tiny tactile sensations dramatically change patients’ ability. For example, patients may subjectively feel that their legs were “supported”, when the soles of their feet were merely being touched. This observation suggests that skin sensation might be subjectively felt as an external force. If true, this notion would allow us to produce a “pseudo-power supporting device” that is simply a tactile display, but is interpreted by the user as real support. Such a device is safe, lightweight, and easy to wear. In this paper, we focus on the forearm to produce “pulling arm” sensation. We make the device and perform an experiment that confirms the sensation of illusory external force, by means of a weight comparison task. 1.1 Pulling Arm Sensation We carefully observed the process of one person pulling the arm of another for purposes of support (Figure 1). First, the “puller” takes hold of the other person’s forearm, and pulls it any direction. At this moment, skin deformation and pressure sensations are produced at the forearm in the direction of the pulling forearm (Figure 1: red arrows and green arrow). We focused on the skin deformation and pressure sensation, predicting that if these phenomena were reproduced, one can feel the sensation of illusory external force in any direction. We made the device based on this principle. Figure 1. Process of “pulling arm” sensation 2. Related Works A number of prior devices used internal force as a substitute for external force. Tsetserukou et al. [3] proposed a wearable device attached on the upper and lower arms to reproduce joint torque. However, the apparatus is large and cumbersome for practical use. On the other hand, alternative devices provided the pseudo-force sensation by stimulating the skin. Minamizawa et al. [4] proposed to squeeze the skin of a finger to provide the pseudo external force. Barks et al. [5] produced tangential skin deformation on the arm. Their primary purpose was to provide the direction of arm joint rotation by tweaking the skin. Our work can be considered as a derivation of these prior attempts to produce pseudo-force by skin deformation. We produced tangential skin deformation on the skin of the forearm as the pseudo external force. We believe that our approach meets the criteria for practical applications in a rehabilitation setting. 3. DEVICE DESIGN Figure 2 provides an overview of our device. Briefly, it is composed of two servomotors (Grand Wing Servo-Tech Co., Ltd, GWSMICRO/2BBMG), a rubber band, wristband, strings and acrylic frames. 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