A Palm-Worn Haptic Display for Bimanual Operations
in Virtual Environments
Kouta Minamizawa, Sho Kamuro, Naoki Kawakami, and Susumu Tachi
School of Information Science and Technology, The University of Tokyo
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japankouta_minamizawa@ipc.i.u-tokyo.ac.jp,
sho_kamuro@ipc.i.u-tokyo.ac.jp,
kawakami@star.t.u-tokyo.ac.jp, tachi@star.t.u-tokyo.ac.jp
http://star.t.u-tokyo.ac.jp/

Abstract. We propose a wearable haptic display that indicates the pressure andvibration on the palm for bimanual operations in virtual reality environments.
This system aims to provide the touch and stroke sensations of virtual objects orvirtual creatures. We constructed a prototype device that can reproduce verticaland shearing forces on the palm and evaluate the capability of the proposed
method to recognize the existence of a virtual object in one-handed and twohanded operations.
Keywords: Haptic Display, Bimanual Operation, Virtual Reality.

1 Introduction
Recently, immersive display systems for virtual reality applications, such as CAVE
[1] and TWISTER [2], have been researched and developed. These display systems
can provide highly immersive virtual environments that enable us to experience not
only with wide view but also with active behaviors such as gaze and gestures. In thewalk-through mixed reality environment, by using a see-through HMD (HeadMounted Display) such as TOWNWEAR [3], we can view virtual objects in the realworld and walk around. In these systems, the haptic interface should be bimanual andwearable so as to provide natural haptic feedback to enhance the existence of thevirtual objects and improve their operability without disturbing the motion and behavior of the users [4]. There are several wearable haptic displays that can be used inimmersive projection environments, such as CyberTouch [5] and HapticGEAR [6].
On the other hand, some researches have been done from other perspectives inthese years. Inaba and Fujita [7] have showed that simple constrictive pressures on thefingers resemble a grip sensation, and Nakamura et al. [8] have demonstrated that anungrounded device can indicate the internal force of an object. These researches havebeen aimed at realizing the practical use of human perceptual characteristics and perceptual illusions in the design of haptic devices so as to retain the reality of the haptic
sensation, while downsizing the device. We have also proposed a wearable haptic
display to present the mass [9] and internal dynamics [10] of virtual objects; the device employs dual motors and generates vertical and shearing forces on theM. Ferre (Ed.): EuroHaptics 2008, LNCS 5024, pp. 458–463, 2008.
© Springer-Verlag Berlin Heidelberg 2008

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fingerpads. Our inference that the tactile sensation on the fingerpads can alternate theproprioceptive sensation on arm suggests that wearable haptic displays of virtual
reality or mixed reality systems can be more compact and indicate more realistic sensations.
In this paper, we propose a palm-worn haptic display that indicates a tactile sensation on the palm by using a simple method. By using the device, users can touch virtual
objects without any disturbance in their motion and gestures, as shown in figure 1.

Fig. 1. Conceptual drawing of haptic interaction by using the proposed palm-worn haptic display. The users are touching or holding a virtual object.

2 Prototype Device
In our previous research [11], we proposed a simple method for reproducing verticaland shearing forces; the method employed dual motors and a belt. The forces on thefingerpads could indicate reliable grasping sensations, even when there were no proprioceptive sensations on the wrist and arm. In this study, we attempted to apply thismethod to the palm, as shown in figure 2, and constructed a prototype device by using
two motors (Maxon Moter Corp., RE 10, 1.5 W, great ratio = 1:16), as shown infigure 3.

Fig. 2. Conceptual drawing of the proposed method

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Fig. 3. Constructed prototype device

3 Experiments
3.1 Single-Handed Recognition of Virtual WallIn this experiment, we evaluated the recognition accuracy of the proposed device inindicating a virtual wall. Figure 4 shows the experimental setup for this experiment.
One infrared LED was attached to the device and the position of the hand was measured by using an infrared camera. Appearance of the experiment is shown in Figure 5.
We used Wii Remote (Nintendo Co. Ltd., 2006) as a Bluetooth infrared camera. Position sensing was performed at a resolution of 0.5 mm and a frequency of 200 Hz. Fivemale subjects (aged 21–25) were asked to wear the haptic display on the right hand,
and they were blindfolded with an eye mask. White noise was provided to both ears tomask the sound of the motors. They placed their right arm on the armrest and could
move their arm right and left. A virtual wall was positioned on the left side of thehand randomly at a distance of 50 mm to 140 mm in the direction of the x-coordinate.

Fig. 4. Coordinate setting of the experiment

When reproducing the force on the palm, we attempted to study two haptic feedback conditions. Under a pressure-only condition, the vertical force on the palm

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increased in direct proportion to the overshoot of the hand position from the positionof the virtual wall. Under an impact-pressure condition, a 30-ms vertical force wasreproduced as the impact force, in addition to the pressure, at the instant when thewall was touched. The subjects moved their right hand from x = 0 toward the left andstopped when they felt that they were pressing against the wall tightly. The subjects
were allowed to grope for the virtual wall twice in one trial. Twenty trials were performed for each condition and each subject.
Figure 6 shows the average and standard deviation of the difference between therecognized position and the position at which the virtual wall was set for each condition and subject. It shows that the haptic feedback of the impact force is effective in
improving the accuracy of recognition of the position.

difference between the set position
and the recognized position (mm)Fig. 5. Experimental setup
40condition 1condition 235302520151050subject 1 subject 2 subject 3 subject 4 subject 5 averageFig. 6. Result of the experiment on single-handed recognition of virtual wall

3.2 Two-Handed Recognition of Virtual Solid
In this experiment, we evaluated the accuracy of the proposed device in indicating avirtual solid. The experimental setup was the same as that in the former experiment.
The subjects wore the devices on both their hands; they were blindfolded with an eyemask and white noise was provided to their ears. Five male subjects (aged 21–25)
were asked to spread their hands to shoulder width. A virtual solid with a specific462

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width was virtually set between the right and left hands. The subjects then closed theirhands slowly and the distance between the two hands was measured in real-time.
When the distance was equal to the width of the virtual solid, the vertical forces withimpulse (discussed in section 3.1) were displayed on both hands. The subjects stopped
closing their hands when they perceived that they were definitely holding something.
The width of the virtual solid was set randomly from 190 mm to 280 mm. Forty trials
were performed for each subject.
Figure 7 shows the average and standard deviation of the recognized width of thevirtual solid for each of the widths set.

300
280260240220200180160180200220240

260

280

300

Fig. 7. Result of the experiment of two-handed recognition of virtual solid. The dotted line
shows the desired value where the recognized size is equal to the set size.

3.3 Discussions
Comparing the standard deviations of the recognized size in two experiments, it isshown that the standard deviation in two-handed recognition has an inclination to besmaller than that in single-handed recognition. This result assumes that the recognition of the object was performed based on not only the haptic feedback but also thepostural sense of arms in bimanual operations.
In these experiments, the subjects stated that they felt that they touched or held
something like a tennis ball, not like a wall or a box. It is considered that this perception occurred due to the lack of a haptic sensation on the fingers. When we holdsomething with both hands, the palms are pushed, and the fingers are free, it implies
that a fist-sized object is being held. The combination of the haptic sensations on thepalm and fingers is required to represent various-sized objects.

4 Conclusions and Future WorkIn this paper, we have suggested that the method of reproducing vertical and shearing
forces by using dual motors and a belt is effective for not only the fingers but also theA Palm-Worn Haptic Display for Bimanual Operations in Virtual Environments

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palm. We have confirmed the availability of the wearable haptic display that indicatesthe pressure and vibration on the palm. This system can reproduce the sensation oftouching or holding an object in bimanual operations in virtual reality environments.
So far, we have evaluated only the effectiveness of a vertical force on the palm.
The shearing force is considered to cause a stroke sensation. The combination of thetouch and stroke sensations would improve the recognition of virtual objects. The
multimodal combination with visual sensation in bimanual operations in virtual environments should also be studied.

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