FlexTorque: Innovative Haptic Interface for Realistic Physical Interaction
in Virtual Reality
Dzmitry Tsetserukou*

Katsunari Sato

Alena Neviarouskaya

Naoki Kawakami

Susumu Tachi

The University of Tokyo

DC Motor
Motorholder
Stopper
Pulleys
Supporter
Shaft
Timing belt

Figure 1: Augmented Arm Wrestling

1

Figure 2: FlexTorque haptic display

Introduction

In order to realize haptic interaction (e.g., holding, pushing, andcontacting the object) in virtual environment and mediated haptic
communication with human beings (e.g., handshaking), the force
feedback is required. Recently there has been a substantial needand interest in haptic displays, which can provide realistic andhigh fidelity physical interaction in virtual environment. The aimof our research is to implement a wearable haptic display forpresentation of realistic feedback (kinesthetic stimulus) to thehuman arm. We developed a wearable device FlexTorque thatinduces forces to the human arm and does not require holding any
additional haptic interfaces in the human hand. It is completely
new technology for Virtual Reality that allows user to explore
surroundings freely. The concept of Karate (empty hand) Haptics
proposed by us is opposite to conventional interfaces (e.g., Wii
Remote, SensAble’s PHANTOM, SPIDAR [Murayama et al.
2004]) that require holding haptic interface in the hand, restricting
thus the motion of the fingers in midair.

2Principle and Technologies

The idea behind the novel torque display FlexTorque is toreproduce human muscle structure, which allows us to performdexterous manipulation and safe interaction with environment indaily life. When we hold a heavy object in a palm, its weight
produces torques in the wrist, elbow, and shoulder joint. Eachmuscle generates a torque at a joint that is the product of its
contractile force and its moment arm at that joint to balance gravity
force, as well as inertial forces, and contact forces. The muscle
with tendon in series acts like a rope pulling on a lever.
The structure of the developed torque display FlexTorque ispresented in Fig. 2. FlexTorque is made up of two DC motors(muscles) fixedly mounted into plastic Motor holder unit, Belts(tendons), and two Belt fixators. The operation principle of thehaptic interface is as follows. When DC motor is activated, it pullsthe belt and produces force generating the flexor torque Tflex. The
oppositely placed DC motor generates the extensor torque Text.
Therefore, the couple of antagonistic actuators produces a net
torque at the user elbow joint Tnet= Tflex - Text.
The essential advantage of the structure of FlexTorque device is*e-mail: dima_teterukov@ipc.i.u-tokyo.ac.jp

Copyright is held by the author / owner(s).
SIGGRAPH Asia 2009, Yokohama, Japan, December 16–19, 2009.
ISBN 978-1-60558-858-2/09/0012

Figure 3: Augmented collisionthat heaviest elements (DC motors, shafts, and pulleys) arelocated on the part of upper arm, which is nearest to the shoulder.
Therefore, user’s arm undergoes very small additional loading.
The rest of components (belts, belt fixators) are light in weightand do not load the human muscles considerably. Each unit iscompact and light in weight (60 grams). This was achieved due tothe use of plastic and duralumin materials in manufacturing themain components. The Supporter surface has concave profile tomatch the curvature of human arm surface.

3. Applications
The main features of FlexTorque are: (1) it presents high fidelitykinesthetic sensation to the user according to the interactiveforces; (2) it does not restrict the motion of the human arm; (3) it
has wearable design; and (4) it is extremely safe in operation.
These advantages allow a wide range of applications in virtualand augmented reality systems and introduce a new way of gameplaying. A number of games for sport experiences, which provide
a natural, realistic, and intuitive feeling of immersion into virtualenvironment, can be implemented. The Arm Wrestling game thatmimics the real physical experience is currently underdevelopment (Fig. 1). The user wearing FlexTorque and Headmounted display (HMD) can play either with a virtual character ora remote friend for more personal experience. The motion of thearm and exerted force are detected by the sensors. The virtual
representation of players’ arms are shown on the HMD. While
playing against a friend, user sees the motion of arms andexperiences the reaction force from rival.
The contact and collision with virtual object can be presented
through FlexTorque as well (Fig. 3). In case of contact or collision,
the net torque produced by the haptic display restrains the further
movement of the user’s arm. The vibration of the human arm (e.g.,simulation of driving a heavy truck) can be realized throughalternate repeatable jerks of torque of antagonistic motors. Thus,
operator can perceive the roughness of a road surface.

References
MURAYAMA, J., BOUGRILA, L., LUO, Y., AKAHANE, K., HASEGAWA, S.,HIRSBRUNNER, B., SATO M., 2004. SPIDAR G&G: A Two-Handed
Haptic Interface for Bimanual VR Interaction, In Proceedings ofInternational Conference EuroHaptics, pp. 138-146.