Remote haptic sharing of elastic soft objects-Real-time estimation and display by contact area control –Kinya Fujita* and Yoshiaki Ikeda*(*)Tokyo Univ. of Agri. & Tech., Japan
E-mail: kfujita@ cc.tuat.ac.jp• Introduction• Stiffness and Size Estimation Experiments

Force display devices enabled to display the sense of elastic objects byrepresenting the reaction force from the objects. The tactile display device,
which represents the fingertip contact area change caused by the fingertip
sinking into the objects, added more realistic sensation about the elasticsoft objects[1,2]. Estimation, transfer and display of the physical properties
of soft objects over the computer network is expected to provide us thefunction to touch and feel the distant objects. Especially, the sharing
between users has potential applications such as remote palpation or haptic
broadcast. This study is focused on to develop a prototype remote haptic
sharing system based on the fingertip contact area control device and to
examine the feasibility of the system.

The results of the real-time estimation of the stiffness and the size of theobjects are shown in figure 4. The objects were 50mm cubes with 0.012,0.035, 0.14 (rubber foam) and 0.7 (silicon rubber) N/mm2 Young’s
modulus. The stiffness estimation errors in steady state were less than10%. The steady state size errors were less than 5% (not shown). It wasdemonstrated that the correct estimation is possible after the first pinch hascompleted.
stiffness (N/mm)

stiffness (N/mm)

estimatedparameters0.012N/mm2
0.15

0.1

0.05

0.3
0.2
0.1
002

4

user B

Fig.1: Concept of remote haptic sharing• System Design- RealReal-time estimation of stiffness and size
The difficulties in the real-time stiffness estimation from the human pinch
are the unknown object size and the deformation of the fingertip. In orderto overcome these difficulties, 1) the stiffness and the size was estimated at
the same time using the regression line, and the data below 0.15N wasomitted. 2) the fingertip deformation property was measured in advanceand subtracted.
force

potentiometer

deformation of(object , finger)

stiffness (N/mm)

user Avirtual
soft object

06time (s)0.14N/mm2

1.510.50246time (s)stiffness (N/mm)

0elastic
soft object

0.035N/mm2

0.4

0.7N/mm265432100240246810time (s)time (s)Fig.4: Estimated stiffness in real-time• Display and Recognition Experiments
The paired-comparison experiment was carried out in five adultvolunteers. The displayed Young’s modulus was calculated from theestimated stiffness. The average cognitive rate of the difference was 90%
as seen in figure 4. It is concluded that the feasibility of the remote haptic
sharing was experimentally demonstrated.

force sensor
force + displacement

Realproperty
0finger displacement

Fig.2: Estimation of the object stiffness

Cognitive rate (%)

100806040
200- Fingertip contact area and force control

0.0110.035

0.0110.14

0.0110.67

0.0350.14

0.0350.67

0.140.67

The pinch of a soft deformable object causes the sinking of the fingertip
and it increases the contact area. The role of this information was greaterthan the reaction force in our former experiment [3]. A contact area control
device with force feedback function was developed [2]. The device
consists of the pneumatic contact area control device and the wire-driven
force feedback device. The contact area was calculated using Hertziancontact theory using the Young’s modulus, which is converted from thetransferred stiffness. The Poisson's Ratio was assume to 0.5. The airpressure to drive the pneumatic contact area control device was controlledusing the pre-measured device property. The reaction force was calculated
based on the stiffness using Hook’s law.

Young's modulus of compared objects (N/mm)

Fig.5: Cognitive rate of the objects• Conclusions
A haptic remote sharing system was proposed, which consists of thefingertip force and contact area display device and sensors to real-time
stiffness estimation. Real-time estimation of the elastic soft objects and therecognition of the transferred and displayed virtual object wasexperimentally demonstrated.

• Acknowledgments
This study was partially supported by a Grant-in-Aid for Scientific Research fromThe Ministry of Education, Culture, Sports, Science and Technology.

finger position
contact
detection

stiffness

driving unit

Hook's law

conversion

Young'smodulus

wire
compression
displacement

Hertziancontacttheory

reaction force

regulator

deviceproperty

air pressure

contact area air pressure

aircompressor
finger position
reaction force

Fig.3: Fingertip contact area control system• References[1] K.Fujita and H.Ohmori, A New Softness Display Interface by Dynamic Fingertip
Contact Area Control, in Proc. 5th World Multiconference on Systemics,
Cybernetics and Informatics, pp.78-82, Jul. 2001
[2] Y.Ikeda and K.Fujita, Display of soft elastic object by simultaneous control offingertip contact area and reaction force, Trans. VRSJ, Vol.9, No.2, pp.187-194,
2004 (in Japanese)[3] H.Sasaki and K.Fujita, Experimental analysis of role of visual information in
hardness cognition displayed by a force display system and effect of alteredvisual information, Trans. VRSJ, Vol.5, No.1, pp.795-8202, 2000 (in Japanese)