Simplified Design of Haptic Display by Extending
One-point Kinesthetic Feedback to Multipoint Tactile Feedback
Kouta Minamizawa*1*3*2, Domenico Prattichizzo and Susumu Tachi*3*1

The University of Tokyo, Japan
University of Siena, Italy*3
Keio University, Japan*2ABSTRACT
For designing a simple and more realistic haptic feedback system,
we propose integrating an underactuated mechanism with onepoint kinesthetic feedback from the arm with multipoint tactile
feedback. By focusing on the division of roles between thecutaneous sensation in fingers and the proprioception in the arm.
We have implemented a prototype system that provides
kinesthetic feedback to the arm and tactile feedback to the fingers,
examined the difference of weight recognition according to theapplied point of kinesthetic feedback, and confirmed theeffectiveness of the proposed method.
Keywords: Haptic display, underactuation
Index Terms: H.5.2 [INFORMATION INTERFACES ANDPRESENTATION]: User Interfaces—Haptic I/O; H.1.2[MODELS AND PRINCIPLES] User/Machine Systems—Human
information processing
1

proprioception on the arm via a stick or a ball driven by motors. In
these systems, although the kinesthetic sensation in the arm is well
represented, the posture of the hand is fixed, and the tactile
sensations in the fingers are summed up; therefore, the user cannot
grasp a virtual object with his/her hand. These grounded haptic
displays have been applied to multifingers in several researches[6]. However, these methods are highly complex and difficult toapply in a wearable or portable device because the mechanicallinkages have to be fixed to a desk or the ground. Therefore, asimplified design method for a highly realistic wearablemultifinger haptic display is required.
Realistic haptic feedback systems that can be applied tomultifingers have been realized using ungrounded haptic displays[7][8][9]. In our previous research [10], we focused on the verticaland tangential forces generated on each fingerpad because of theinteraction between a human finger and an object, and developed afinger-worn haptic display shown in figure 1. The vertical force
and tangential force on the user’s fingerpad are reproduced bypulling up the belt on the fingerpad using dual motors on thedorsal side of the finger.

INTRODUCTION

In recent times, there has been an increasing demand for realistic
haptic feedback for the intuitive operation of computer graphicsystems or entertainment systems and for highly immersive virtual
reality environments such as CAVE [1] and TWISTER [2]. A
number of user interface devices with haptic feedback functions,such as CyberTouch (CyberGlove Systems LLC) and theDualShock controller (Sony Computer Entertainment, Inc., 1997)
have been developed. However, their haptic feedback is limited
only to vibrations because a suitable method for providing haptic
feedback through a small and portable/wearable device has notbeen established thus far. Glove-type haptic displays such as
Rutgers Master II [3] can provide force sensations to all fivefingers of the hand simultaneously. These devices can present a
grasping force with the aid of a wearable device; however, thesedevices are complex and heavy, and the sensation of weight of avirtual object cannot be represented. To realize highly realistic
haptic feedback, the tactile sensations and kinesthetic sensations ineach finger and arm have to be reproduced; however, it is difficultfor a device to reproduce all these sensations. A number ofresearches have been conducted to simplify haptic devices by
sorting the sensations to be represented. PHANToM [4] andSpidar [5] are types of grounded haptic displays that apply*1e-mail: kouta@tachilab.org
e-mail: prattichizzo@ing.unisi.it*3e-mail: tachi@tachilab.org*2IEEE Haptics Symposium 201025 - 26 March, Waltham, Massachusetts, USA
978-1-4244-6820-1/10/$26.00 ©2010 IEEE

Figure 1. The finger-worn haptic display using dual motors

It has been confirmed that estimating the grasping force and theobject weight can reasonably reproduce tactile sensations onfingers. However, these ungrounded haptic displays cannot beused for objects heavier than a few hundred grams because of theabsence of kinesthetic sensations in the fingers and the arm. It is
known that the cutaneous sensation in the fingers and theproprioception in the arm play different roles in estimating theweight of the grasped object. In order to design an optimalmechanism for multifinger haptic displays that strike a balance
between the simplicity of the device and the quality of therepresented sensation, we examine the division of roles between
tactile sensation and kinesthetic sensation and their synergeticeffects.
2PROPOSED METHOD

In the proposed method, the user wears a small tactile display oneach finger and a single kinesthetic display somewhere on the arm.
Each tactile display delivers the contact information between thevirtual object and a finger, and the kinesthetic display delivers thetotal force due to the weight and the inertia of the object. Figure 2257

shows conceptual illustration of the tactile display worn on theindex finger and thumb and the kinesthetic display worn on theforearm. In this configuration, although the proprioceptions on theelbow and shoulder are the same as those when grasping a realobject, there is a lack of proprioception on the fingers and thewrist. This missing haptic information can result in difficulties
during object manipulation. However, as compared tocumbersome kinesthetic displays worn on each finger, thisconfiguration has considerable benefits: the kinesthetic
mechanism can be underactuated and the total system can besimplified.

finger, and “tactile + forearm” denotes the threshold when thekinesthetic feedback was applied on the forearm in addition to thetactile feedback on the index finger. This result shows that theone-point kinesthetic extension was effective, especially when thevirtual object was heavier than 200 g, where the JND became
worse when the kinesthetic extension was not applied. A
considerable difference was not observed according to the applied
point. By comparing the required working area and the degrees offreedom for the kinesthetic display, it appeared reasonable toapply the one-point kinesthetic extension on the forearm because it
requires only four degrees of freedom, whereas seven degrees offreedom are required to apply the kinesthetic extension on thepalm.

Figure 2. Conceptual illustration of proposed system
Figure 3. Experimental setup under “tactile + palm” condition

3EXPERIMENTS FOR APPLIED POINTSKINESTHETIC EXTENSIONOFONE-POINT

In this section, we compare the just notified difference (JND)
when reproducing the weight of a virtual object under fourconditions: applying kinesthetic feedback on the palm, wrist, andforearm, and applying no kinesthetic feedback.
In the experimental setup, we used a finger-worn haptic display[10] for tactile feedback, and the OMEGA.3 haptic device (ForceDimension Inc.) for kinesthetic feedback. The finger-worn haptic
display was attached on the index finger of the subject, and thekinesthetic display was worn on the palm, wrist, or forearm. We
placed urethane forms between the arm and OMEGA.3 tominimize the cutaneous stimuli on the arm and fixed the arm andOMEGA.3 using a Velcro strap as shown in figure 3. The subjects
were asked to wear headphones with white noise and a blindfold;they were also asked to extend their index fingers with the padside up. Constant stimuli were provided to three male subjects inthis experiment. As a standard stimulus, a virtual weight of 50,
100, 200, or 400 g was represented by both the tactile display andthe kinesthetic display for 1 s. After an interval of 1 s, anothervirtual weight that was 70%, 80%, 90%, 100%, 110%, 120%, or
130% of the standard stimulus was represented randomly as a test
stimulus for 1 s. The subjects then stated whether the weight of thevirtual object that acted as the test stimulus was “heavier” or “notheavier” than that that provided as the standard stimulus according
to the two-alternative forced-choice procedure. Thirty-five trials
were performed for each standard stimulus, with each test stimulus
appearing five times. It took approximately 5 min to conduct a setof 35 trials. We performed 16 sets of trials for four types ofstandard stimuli under the four-abovementioned conditions oneach subject.
Figure 4 shows the JNDs of the virtual weight on each applied
point of kinesthetic extension. In this figure, “tactile only” denotes
the threshold when kinesthetic feedback was not applied and only
tactile feedback was applied, “tactile + palm” denotes thethreshold when the kinesthetic feedback was applied on the palmin addition to the tactile feedback on the index finger, “tactile +wrist” denotes the threshold when the kinesthetic feedback wasapplied on the palm in addition to the tactile feedback on the index

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standard weight [g]Figure 4. JNDs on each applied point of kinesthetic extension.
The vertical axis of the graph shows the 75% differential
limens with a ratio to each standard stimulus.

4EXPERIMENTS FOR EFFECTIVENESSKINESTHETIC EXTENSIONOFONE-POINT

We constructed a prototype of a haptic interaction system with
one-point kinesthetic extension on the forearm and then examinedthe effectiveness of this system by comparing JNDs between thefour conditions shown in figure 5. Similar to the previous
experimental setup, we used a finger-worn haptic display [10] fortactile feedback and the OMEGA.3 haptic device for kinesthetic
feedback.
- Condition 1, “real object”: A lightweight cube (side: 5 cm) wasfixed on the kinesthetic display. Double-sided tapes were placedon the sides of the cube to increase friction. The subject held thecube between the index finger and thumb, and then, the virtual
weight was applied.
- Condition 2, “kinesthesia on forearm”: The kinesthetic display
was fixed on the forearm of the subject. The subject was asked tohold the lightweight cube with bare fingers to fix the posture ofthe hand. Urethane forms were placed between the arm and thedevice, and the subject felt little cutaneous sensation on theforearm.

- Condition 3, “tactile on fingertips”: The subject was asked towear the tactile displays on the index finger and thumb and holdthe lightweight box.
- Condition 4, “integration”: According to the proposed method,
the subject was asked to wear the tactile displays on the index
fingers and thumb and the kinesthetic display on the forearm.
Then, the subject held the lightweight cube in the same manner as
under the other conditions.
The subjects were asked to wear headphones with white noise
and a blindfold. Constant stimuli were provided to three malesubjects in this experiment. As a standard stimulus, a virtual
weight of 100, 200, 300, or 400 g was represented by both thetactile display and kinesthetic display for 1 s. After an interval of 1s, another virtual weight (85%, 90%, 95%, 100%, 105%, 110%, or(1) real object(2) kinesthesia on forearm

115% of the standard stimulus under condition 1; 70%, 80%, 90%,100%, 110%, 120%, or 130% of the standard stimulus under theother conditions) was represented randomly as a test stimulus for 1s. The subjects then stated whether the weight of the virtual object
that acted as the test stimulus was “heavier” or “not heavier” thanthat the standard stimulus according to the two-alternative forcedchoice procedure. For each standard stimulus, five trials wereperformed in the order of standard stimulus -> test stimulus, andfive more trials were performed in the reverse order. It took about
10 min to conduct a set of 70 trials for one standard stimulus. We
performed 16 sets of trials for four types of standard stimuli under
the four conditions. Therefore, the total number of trials was 1120
for each subject. The subjects took a break for a few minutes
between each set of trials.

(3) tactile on fingertips(4) integration

Figure 5. Experimental setup in each condition
standard weight = 100 g

200 g

300 g

400 g

(1) real object(2) kinesthesia on forearm(3) tactile on fingertips(4) integration

Figure 6. Experimental result of typical subject.
In each graph, the vertical axis represents the ratio of “heavier” responses, and the horizontal axis represents the weight of test stimuli.

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Figure 7. Recognition thresholds for all subjects under eachexperimental condition

division of roles between the cutaneous sensation on the fingers
and proprioception on the arm while grasping an object, we apply
underactuated kinesthetic feedback on the forearm and small
tactile displays on the fingers. We construct a prototype systemand examine that the proposed system can represent haptic
sensations with a high resolution for a wide range of weights. As afuture work, we will implement a wearable haptic interaction
system for multifingers that can represent a more realistic
sensation than the conventional systems.
As a future work, we are designing a wearable kinesthetic
display on the basis of the underactuation of kinesthetic feedback.
Although the kinesthetic display used in the experimental setup
was a grounded device, our proposed method shows a possibilityof designing a wearable multi-fingered haptic display that
reproduces both kinesthetic sensation on the arm and tactie
sensation on the fingers with a small number of actuators.
ACKNOWLEDGEMENT
This work has been supported by CREST of Japan Science andTechnology Agency, and Grant-in-Aid for JSPS Fellows (192781).
REFERENCES[1]Figure 8. Recognition performances under each condition
normalized with “real object”

Figure 6 shows the ratio of “heavier” responses in each set oftrials for a typical subject. Figure 7 shows the integrated result of
five subjects, and figure 8 shows the performances of haptic
feedback under each condition calculated by dividing the 75%
differential limens under each condition by that under the “realobject” condition. These results show that when we used only
kinesthetic feedback on the arm and the standard weight wassmall, the performance of weight representation was poor. Further,when we used only tactile feedback on the fingers and thestandard weight was large, the performance was poor. However,the proposed system that integrates kinesthetic feedback on thearm and tactile feedback on the fingers could represent the virtual
weight with a highly stable performance around 0.7 for every
weight. Although the debasement in performance of the integrated
condition relating to the real object condition is attributed to thelack of kinesthetic feedback on the wrist and the fingers, the mostimportant thing of the proposed method is to design the balance
between the performance of haptic feedback and the complexityof the system for various purposes. It was also suggested that thetactile sensation on the finger has high accuracy in small range, on
the other hand, the proprioception on the arm has low accuracy inwide range. This results show that the complementary relationshipbetween the fingers and the arm.
5CONCLUSION

In this paper, we propose a design principle for a simplified
haptic display that integrates the tactile feedback on the fingers
and the kinesthetic feedback on the arm. By focusing on the260

C. Cruz-Neira, D. Sandin, and T, DeFanti: Surround-screen
Projection-based Virtual Reality: The Design and Implementation ofthe CAVE. in Proceedings of ACM SIGGRAPH 1993 ComputerGraphics Conference, ACM SIGGRAPH, pp. 135–142, 1993
[2] S. Tachi, T. Maeda, Y. Yanagida, M. Koyanagi, Y. Yokoyama: AMethod of Mutual Tele-existence in a Virtual Environment, inProceedings of ICAT 1996, pp. 9–18, 1996
[3] M. Bouzit, G. Burdea, G. Popescu and R. Boian: The Rutgers Master
II—New Design Force-Feedback Glove, IEEE/ASME Transactions
on Mechatronics, Vol. 7, No. 2, pp. 256–263, 2002
[4] Thomas H. Massie and J. K. Salisbury: The PHANToM Haptic
Interface: A Device for Probing Virtual Objects, in Proceedings ofASME Winter Annual Meeting, DSC-Vol.55-1, pp. 295–300,Chicago, IL, USA, 1994
[5] S Kim, S Hasegawa, Y Koike, M Sato: Tension Based 7-DoF ForceFeedback Device: SPIDAR-G. in Proceedings of IEEE Virtual
Reality 2002, 2002.
[6] S Walairacht, Y Koike, M Sato: String-Based Haptic Interface
Device for Multi-fingers. in Proceedings of IEEE Virtual Reality
2000, 2000
[7] N. Nakamura and Y. Fukui: Development of Fingertip Type Nongrounding Force Feedback Display. in Proceedings of 1st Joint
Eurohaptics Conference and Symposium on Haptic Interfaces forVirtual Environment and Teleoperator Systems, pp. 582–583,Tsukuba, Japan, 2005
[8] K. Minamizawa, S. Kamuro, S. Fukamachi, N. Kawakami and S.
Tachi: GhostGlove: Haptic Existence of the Virtual World. 35th Int.
Conf. on Computer Graphics and Interactive Techniques(SIGGRAPH 2008), Los Angeles, CA, USA, 2008
[9] T. Aoki, H. Mitake, S. Hasegawa and M. Sato: Haptic Ring:Touching Virtual Creatures in Mixed-Reality Environments. 36th Int.
Conf. on Computer Graphics and Interactive Techniques(SIGGRAPH 2009), New Orleans, LA, USA, 2009[10] K. Minamizawa, H. Kajimoto, N. Kawakami and S. Tachi, Wearable
Haptic Display to Present Gravity Sensation - Preliminary
Observations and Device Design. in Proceedings of 2nd Joint
Eurohaptics Conference and Symposium on Haptic Interfaces for
Virtual Environment and Teleoperator Systems, pp. 133–138,
Tsukuba, Japan, 2005