18th International Conference on Artificial Reality and Telexistence 2008

TeleTA: Teleoperation System with Tactile Feedback aimed at Presentation of the
Physical Contact on Entire Robot Arm Surface to the Human Operator
Dzmitry Tsetserukou
University of Tokyo
7-3-1 Hongo, Bunkyo-ku, Tokyo

Susumu Tachi
University of Tokyo
7-3-1 Hongo, Bunkyo-ku, Tokyo

dima_teterukov@ipc.i.u-tokyo.ac.jp

http://tachilab.org/

Abstract
The paper focuses on the teleoperation system designed
to achieve high level of maneuverability of robot arm in
unstructured and dynamic environment. The humanoperator directs the robot arm to the target position, while
manipulator sensory system provides safe physicalinteraction with environment. In order to achieveawareness of collision and to support operator withvaluable information, we elaborated approach tocontacting force vector calculation and delivering thisinformation to the operator’s skin through tactile display.
The analysis of different types of haptic display showed that
increasing tactile information density does not obviously
lead to the quality of information presentation. Thus, weconcentrated on the development of a new type ofapparatus that accounts for effectiveness of the information
presentation, power consumption, ergonomics, andusability for particular teleoperation task. The applicationof proposed design can be extended for VR systems,
wearable information systems, etc.

1. Introduction
Telerobotic systems allow a robot manipulator to becontrolled from a physically separate location. Robot arm iscommanded by human operator supervising the advance of
operation. The operator has to execute skilful manoeuvres
to avoid collisions and direct the robot to its goal position.
In virtual environment, the simulated bodies havepredefined coordinates, and many effective collision
detection algorithms have been already elaborated. When
we consider the real indoor environments, known obstacles(e.g. chairs, tables, etc.) and unknown obstacles (persons
approaching the robot, unmapped environment, etc.)
change their location dynamically. Moreover, the object
shape, speed and position can also alter in unpredictableway. In order to provide the robot with detailed real-timeenvironment view it is imperative to use sensor data.
In many remote-controlled systems visual, force, andaudio channels deliver operator the information about

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scene. The main issues in using visual feedback are narrowvisible area and occlusion of view by robot arm. Anotherchallenge is significant time delay in such applications oftelerobotics as controlling the robot in space station fromthe earth or in case when operator and robot are located at a
distant places. Failing feedback cues user cannot avert
unexpected collision. Even if the human operator has clear
picture what is happening in remote side, he has inherent
difficulty with planning collision-free motion of the entire
manipulator body [1].
The only effective solution of such challenge is to endow
robot arm with ability to safely contact with environment in
an autonomous manner. Lumelsky et al. [2] proposed tocover manipulator with a sensitive skin capable ofdetecting nearby objects. An array of infrared proximity
sensors delivers the information about obstacles
obstructing arm motion to the control system. The
algorithm of motion planner manoeuvres the robot arm
avoiding impact.
Recently proposed sophisticated imaging systems, suchas stereovision and laser scanning, presume usage ofexpensive detectors and complex signal processing
techniques. They sense only narrow space around the robot
body. The concept of sensor array composed of ultrasonicrangefinders and infrared detectors is described in [3].
Researchers are pursuing the goal of the development of arobust proximity sensor system with application in mobile
robotics, taking advantage of high performance/cost ratioof the components and low computational demands of thedetection method. Due to the specular nature of ultrasonicwaves reflection, the only objects normally located to thesensor acoustic axis can be accurately detected. As it comesto infrared sensor, one of the most important problems islimited measuring performance. The amplitude from theinfrared sensor largely depends on reflectivity of the object
and changes with the target distance in non-liner manner.
There is high possibility that proximity sensors fail todetect obstacle along the robot trajectory. In this case an
immediate vicinity of the target can mislead robot control
system invoking the abrupt change in the speed resulting inharm of the environment.
We argue that robot should be mainly controlled not toavoid the collision but rather to ensure safe contact

18th International Conference on Artificial Reality and Telexistence 2008

interaction with environment through gathering thecomprehensive information about objects (shape, stiffness,texture, location, fixation, etc.). Conventional approaches
to handle the interaction between a manipulator andenvironment are based on impedance control of a robot arm
according to applied force vector measured at the
manipulator wrist [4]. However, the rest parts of the robot
body (forearm, elbow, upper arm, shoulder, and torso) arepresenting significant danger not only to human being, butalso to the robot structure itself. Safety can be improved byintentionally introducing compliance at the mechanicaldesign level [5]. However, elements with high compliancenegatively affect the performance of a robot.
The paper focuses on the teleoperation system TeleTA(Teleoperetion system with wearable Tactile display on theoperator arm surface providing Awareness about slave
robot collision) designed by us to achieve high level ofmaneuverability of robot arm in unstructured dynamic
environment and to perform cooperative tasks with humans
in a safe manner. We announce several distinctive
contributions in this paper. New remote robot and sensory
system for the operation in cluttered environment weredeveloped. Distributed optical joint torque sensors andlocal admittance controllers endow our robot arm with thedistinctive capability of safe interaction with surroundings
along entire manipulator surface. The developed remoterobot is equipped with the tactile sensor enabling to detect
coordinates of the contact point. The force vector direction
on the entire robot arm surface (including joints) can becalculated from the values of joint torques and contact
point coordinates. The algorithm of the force vector
calculation is given in the paper.
Although the teleoperated robot can contact withobstacle in a safe manner, unawareness of the user about
contacting force and actual position still remains safety
problems. It is because of limits on joint ranges andpossible torque sensor overloading. Besides, in the casewhen operator fulfills violent maneuver the humancooperating with robot can be injured. These facts raise thesecond question: delivering the tactile cues to the operator.
The issues of optimal representation of contact
information are discussed in the paper. The developed
ergonomic bracelet-shaped tactile display BraTact intended
for presenting the force vector information to the operator
skin in intuitive way is described.
The remainder of paper is structured as follows. Section
2 presents the teleoperation system TeleTA. Section 3
describes the robot sensory system and data processing
algorithms. The approach to calculation of contact force
vector and experimental results are introduced in Section 4.
In Section 5, we focus on the techniques of tactile
information presentation and detail the development stagesof haptic display BraTact. Section 6 concludes the paperand discusses the future work.

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2. Teleoperation system TeleTA
The teleoperation system TeleTA aimed at performing
the cooperative tasks with humans and operating in
unstructured environment is shown in Fig. 1.

Position,
velocity

Opticaltorquesensorsa) Operator cockpit.
Tactile displayb) Master arm.

Tactileskinc) Remote robot.

Figure 1: Robot teleoperation system TeleTA.

Master side (Fig. 1(a)) includes exoskeleton robot arm
with 6 DOF (Fig. 1(b)) to direct the slave robot arm andtactile display BraTact to present cutaneous stimulation
when collision or contact with object is detected. The
orientation of the human elbow is controlled by the tilt
sensor.
From the safety point of view, to minimize injures incase of collision, most of the parts of teleoperated robot arm(Fig. 1(c)) were manufactured from aluminium alloys toobtain as much lightweight structure as possible. The robot
links were designed in round shape to reduce impact force.
The distribution of robot arm joints replicates the humanarm structure in order to make it easy to operate usingkinesthetic sensation.
To
removemechanicalsubsystems
without
disassembling the main structure when the failures do
occur, we have been using a modular approach while
designing anthropomorphic robot arm. Therefore, we
selected CSF-series gear head type of harmonic drive
instead of compact and lightweight component one. The
harmonic drive offers such advantages as accurate
positioning, high torque capability, torsional stiffness, andhigh single stage ratios. Developed teleoperated robot arm
has 4-DOF: Roll, Pitch, Yaw joints of a shoulder, and Pitch
joint of an elbow. Such orthogonal disposition of the axes
simplifies the installation of the torque sensors and motor
drives into the joints, allowing thus avoidance of
application of additional belt driven actuators. The 3D
CAD model of the developed arm and coordinate systems
based on Denavit-Hartenberg convention are represented inFig. 2.

18th International Conference on Artificial Reality and Telexistence 2008

Yaw

Z1
Y2
Z2

Torque sensor in
Shoulder Pitch,Roll, Yaw, andElbow Joints

J2

Y1

+

Z0

Y0
+
X0 +
Pitch
Roll
J1

X1

X2

L1
J3

Z4

Y4

X4

Y3

J4

X3
Z3

Z5

L2

Y5

X5

Figure 2: 3D CAD arm model and coordinate systems.

Each joint is equipped with optical torque sensor directly
connected to the output shaft of harmonic drive. The sizes
and appearance of the arm were chosen so that the sense ofincongruity during interaction with human is avoided. We
kept the arm proportions the same as in average height
Japanese male, aged 25: upper arm length L1 - 0.308 m;
upper arm circumference - 0.251 m (diameter 0.080 m);
forearm length L2 - 0.241 m; forearm circumference - 0.189m (diameter 0.06 m). The motors are equipped withmagnetic encoders having 512 pulses per revolution.

3. Robot sensory system
Proposed sensory system patterns on the human tactile
system. Our sense of touch can be separated intokinesthetic and coetaneous. Kinesthetic stimulations,produced by forces exerted on body, are sensed bymechanoreceptors in the joints, tendons, and muscles
enabling us to estimate forces being applied to body. When
we hold a heavy object in a palm, its weight produces
torques in the wrist, elbow, and shoulder joint. Each muscle
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, mechanical constraints of joints,
inertial forces, and contact forces [6]. Thus, we canmanipulate the object and feel its weight. On the contrary,mechanoreceptors in the skin layers are responsible forcutaneous stimulation sensation. Different types of tactile
corpuscles allow us sensing thermal properties of object,pressure, vibration frequency, pain, and stimuli localization.
Merkel cells and Meissner’s corpuscles provide the mostprecise localization of touch, as they have smallest
receptive fields and are also more sensitive to pressure
applied by a small probe. Very fine spatial resolution of thehuman skin allows performing tactile discrimination of
surface texture and shape by fingertips. For practicalimplementation of the proposed approach we developed

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sensory system of the robot arm that includes optical torquesensors distributed into each joint (to measure applied
force) and tactile skin (to detect contact point).
The robot arm is covered with Kinotex tactile sensor
measuring the pressure intensity through amount ofbackscattered light falling on photodetector [7]. The
sensitivity, resolution, and dynamic range of this artificial
skin are comparable to those of a human. The taxels
displaced with 21.5 mm in X and 22 mm in Y direction
make up 6x10 array.
In technical specifications of the Kinotex sensor, theability of force measurement is indicated. However, thefollowing shortcomings complicate the accurate
measurement of the applied force: temperature dependencyof the transducer constant, fragility while mechanicaloverloading, large hysteresivity, high non-linearity of theoutput, limited sensing range, etc. Additionally, the tactile
sensors detect and measure the spatial distribution of forces
perpendicular to a predetermined sensory area and, hence,cannot evaluate the vector components of applied force.
Thus, the most appropriate application of such tactile
sensors is the contact area recognition and the measurementof relative pressure distribution in the contact region on the
robot body surface. The task of load measurement isaccomplished by the developed optical torque sensors
enabling torque measurement with high accuracy.
In order to recognize the contact region, we employed
the watershed algorithm, an image processing
segmentation technique that splits an image into areas
based on the topology of the image [8]. The adopted
algorithm is processed as follows: departing from the local
maximum, the new taxel is included into the contact area
only if within the 3x3 array surrounding it there is an othertaxel of greater or equal pressure intensity already included
into the water stream.
The accurate estimation of the contact point can beobtained by computing the center of gravity of the contact
pattern c(xc,yc) of the neighborhood Ω by:⎛ ∑ xi f i ( xi , yi ) ∑ yi fi ( xi , yi ) ⎞⎜ x , y∈Ω⎟,
x , y∈Ωc ( xc , yc ) = ⎜,f i ( xi , yi )∑ fi ( xi , yi ) ⎟⎟⎜ x∑
x , y∈Ω⎝ , y∈Ω⎠(1)

where fi(xi,yi) is the pressure intensity level of the taxel iwith coordinates (xi,yi).
The artificial skin sensor generates the data stream
processed by the developed Win32 C++ application. The
program analyses the tactile pattern and calculates thenumber of contacts and the center of gravity of the contact
pattern based on the pressure distribution information. The
example of contact area image obtained by using Kinotex
skin is presented in Fig. 3.

18th International Conference on Artificial Reality and Telexistence 2008

0

0

0

0

0

0

0

0

0

15

0

0

0

0

4

7

0

0

0

0

114

190

0

0

0

26

1303 754

4

0

0

59

859

463

0

0

0

553

796

0

0

0

0

0

0

12

0

0

0

0

0

0

0

0

0

0

0

0

0

0

torque values. The forces ifi acting in the coordinate systemof each joint produce moments ini (Eq. (2)). The joint
torques are derived by taking Z component of the moments
applied to the link (Eq. (4)).
ycni = i +1i R i +1ni +1 + i PCi × i Fi + i Pi +1 × i +1i R i +1 fi +1(2)

f i = i +1i R i +1 f i +1 + i Fi
τ = i nT i Zˆ ,

(3)

i
i

xc

a) Digital imageib) Visual image

Figure 3: Representations of the contact area.

In order to facilitate the realization of torquemeasurement in each arm joint, we developed opticaltorque sensors. The novelty of our method is application of
the ultra-small size photointerrupter (PI) RPI-121 assensitive element to measure relative motion of sensor
components. The dimensions of the PI (3.6 mm × 2.6 mm ×
3.3 mm) and its weight of 0.05 g allow realization ofcompact design. The optical torque sensor is set between
the driving shaft of the harmonic transmission and driven
shaft of the joint (Fig. 4). When the load is applied to therobot joint, the magnitude of the output signal from the PI
corresponds to the exerted load.
Shieldi(4)iwhere i+1iR is the matrix of rotation between links i+1 and icalculated using Denavit-Hartenberg notation; iPi+1, iPCi are
the vectors locating the origin of the coordinate system i+1
in the system i, and contact point, respectively; iFi is thecontact force.
Let us consider the case when force is applied to theupper arm of the robot. Using the Eq. (2), (3) we have:2

1⎡ 0 ⎤ ⎡ F2 x ⎤ ⎡ LF 2 F2 z ⎤n2 = ⎢⎢ LF 2 ⎥⎥ × ⎢⎢ F2 y ⎥⎥ = ⎢⎢ 0 ⎥⎥ ;⎣⎢ 0 ⎦⎥ ⎣⎢ F2 z ⎦⎥ ⎣⎢ − LF 2 F2 x ⎦⎥⎡ s2
n1 = ⎢⎢ 0
⎢⎣c2

c2
0
− s2

0 ⎤ ⎡ LF 2 F2 z ⎤ ⎡ LF 2 F2 z s2 ⎤1 ⎥⎥ ⎢⎢ 0 ⎥⎥ = ⎢⎢ − LF 2 F2 x ⎥⎥ .
0 ⎥⎦ ⎢⎣ − LF 2 F2 x ⎥⎦ ⎢⎣ LF 2 F2 z c2 ⎥⎦

(5)

PI

The components of the applied force vector and force
magnitude are derived from:θ2

F2 x = τ 2 ( − LF 2 ) ; F2 z = τ1 ( LF 2 c2 ) ;τθ1SpringHarmonic
drive

Figure 4: Torque sensor of the elbow joint.

The spring members attached to the first, second, andthird/fourth joints were designed to measure torque of ±12.5 Nm, ± 10.5 Nm, ± 4.5 Nm, and have resolution of
10.77 mNm, 9.02 mNm, and 4.31 mNm, respectively. Eachsensor was calibrated by means of attachment of reference
weights to the lever arm. Non-linearity of 2.5 % of Full
Scale was calculated using maximum deviated value fromthe best-fit line.
The developed optical torque sensors have highdependability, good accuracy (even in electrically noisy
environment), low price, compact sizes, light weight, andeasy manufacturing procedure.

4. Calculation of contact force vector
The proposed algorithm of computing the force vector atany contact point on entire teleoperated robot arm employs
information about the contact point coordinates and joint

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F2 =

( F2 x ) + ( F2 z ) .
2

2

(6)

The value of the applied force projection on the axis Y is
not required because the upper arm cannot move in thisdirection. For the case when the force acts on the forearm
we have the following algorithm to obtain the contact force
vector:( τ 2 + F4 z ( LF 4c3c4 + L2c3 ) + F4 x ( LF 4 s3 + L2 s3c4 ) )( L2 s3 s4 )(7)
F4 x = τ 4 LF 4 ; F4 z = τ3 ( LF 4 s4 ) ,F4 y =

where c2, c3, c4, s3, and s4 are abbreviations for cos(θ2),
cos(θ3), cos(θ4), sin(θ3), and sin(θ4), respectively; L2, LF2,and LF4 are the lengths of the moment arms.
To evaluate the feasibility of the proposed approach, theexperiments were conducted. During the experiment, theobject was moved along the upper arm surface according to
the curve shown in Fig. 5(c). While contacting, the torquevalues measured at the first and second joint (τ1, τ2) vary in18th International Conference on Artificial Reality and Telexistence 2008

accordance with Fig. 5(a). The contact force vector
projections (F2x, F2z) and force vector length F2 obtained
from Eq. (6) are represented in Fig. 5(b). The trajectory of
the end point of the contact force vector is shown in Fig.
5(d).
2.0

Applied torque τEXT, Nm

1.5
1.0
0.5
0.0

-0.5
Applied torque τ1
Applied torque τ2

-1.0
-1.5
0

Contact force components F2, N

a)

8

12

16

12

16

Time t, sec
12
8
4
0
-4
F2
F2z
F2x

-8

-12

0

Contact point location y, mm

b)

4

4

8

Time t, sec

200
180
160
140
120
100
80

120

Contact force component Fz2 , N

c)

140

160

180

200

220

Contact point location x, mm
8
6
4
2
0
-2
-4
-6
-8
-12

d)

-10

-8

-6

-4

-2

Contact force component Fx2 , N

0

Figure 5: Experimental results.

Robot sensory system and proposed algorithm havedemonstrated the ability of contact force vector calculation.

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5. Development of the ergonomic tactile
display BraTact
While interacting with objects in VR or manipulating therobot, human sensory system has to process a plenty of
information cues. Generally, users of VR or teleoperation
systems extensively utilize vision and hearing channels. In
some cases haptic displays can present the information in
more intuitive way.
In order to deliver the sense of object touch to theoperator, the force-feedback devices [9, 10] (generatingkinesthetic stimuli) and tactile-feedback system [11](evoking cutaneous stimuli on local area of the skin) are
widely applied. The devices of former type are able to exert
strong forces on human body and limit user motion in anatural manner. However, they are cumbersome, havenarrow workspace, and enable to generate force only at thehuman hand. When it comes to the contact presentation on
the human arm, tactile displays are preferable ones. They
can convey contact cues [12], direction [13] and distance[14] information. Recently, haptic gadgets displaying
information on a large area of the human body are gaining
increased attention by researchers.
In [15], the authors pursue the goal of ensuring the safety
during low visibility helicopter landing. This paper
introduces the study on alternative approach of flightinformation presentation through tactile display instead ofvisual display. The tactile suit comprises belts with 31
tactors around the waist and a column of 21 tactors on theback. This tactile display supplies the pilot withinformation on groundspeed and altitude. Experimental
results showed that landing manoeuver performance indegraded visual environment was significantly improved
when groundspeed and altitude were presented on tactile
display. Yang et al. [16] presented vibro-tactile wear
endowing human with tactile perception of interaction
object in VR and allowing to direct the motion of the limbs.
Tactile display has cylindrical fashion to be worn on the
torso of a user with array of 60 vibration motors. Fromexperimental results researchers concluded that design oftactile feedback system should account for what factor ismore critical: information accuracy or object presence. In[17], reconfigurable, wearable system TactaVest fordelivering vibro-tactile stimuli aimed at enhanced
human-computer interaction is presented. The tactors were
mounted on the body at the locations having a highprobability of contacting virtual object (namely, shoulder,elbow, belt placement area and breast). The authors madevaluable proposal for improvement of garments design,tactor placement, and wiring.
It can be seen from the papers presented above that,typically, the huge amount of sensors are arranged inregular grid pattern and attached to the human body. The
researchers faced the question: is it really necessary to18th International Conference on Artificial Reality and Telexistence 2008

employ many tactors making device heavy, withcomplicated wiring system and uncomfortable design? Is
increasing number of tactors the effective way to convey
tactile information?
It should be mentioned here, that heavy tactile display
placed on the arm surface degrades the mobility andincreases joint muscle loading. Moreover, the higher
density of conveyed tactile information the less attention
user pays to target task (move in VR, observe situation,
manipulate the object, direct the robot arm, etc.), thus
leading to important information loss. Therefore, we haveto find out the approach to effective presentation of tactile
information.
For the time present, insignificant attempts were made to
optimize the design of tactile display in such a way that it
can be informative, ergonomic, lightweight, wearable,
intuitively understandable in use, comfortable in wearing,with small power consumption and friendly design. In thispaper, we propose the tactile display design that satisfies
mentioned demands for delivering the contact force vector
information to the operator.
During teleoperation user has to move arm in extensive
way. Additional weight on the arms will cause theoverloading of the operator muscles. On the other hand,display should not restrict the motion range of the humanarm. Therefore, the main issue we have to face in designing
the tactile display is to make it compact and lightweight. In
contrast to the method of covering the whole arm surface
with tactile garment, we are proposing to use two tactile
bracelets worn on the middle parts of the forearm and upperarm. The force vector is coded as follows: (1) the tactor
operating on the arm surface represents the force direction,and (2) the magnitude of the contact force is conveyed byvibration intensity.
The developed tactile bracelet BraTact incorporates six
vibration motors with holders linked by elastic band.
Proposed shape takes advantage of the facts that we alreadyused to wear bracelet-shaped watches and accessories, andthat such shape of the tactile display can fit to the humansof different sizes. It should be noted that in traditional
design all tactors are attached to one piece of stretchy
substrate [16] and wrapped by tight fitting wristband or
T-shirt that allows vibrations to propagate along thestructure deteriorating the tactor localization by user. In ourdesign each tactor is separated from neighboring units thatenhances the discrimination of the tactile pattern.
Several attempts were made to explore the human tactile
patterns for effective communication with mobile devices.
It was found that identification accuracy at the nine tactor
locations on the dorsal side of the wrist ranges from 22% to76% [18]. The participants of the study were generally
better at identifying the tactor location across the back of
the arm than along the arm. Chen et al. [19] examined thehuman ability to localize a single vibration source on dorsal

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and volar sides of the forearm near wrist. For theexperiments a 3-by-3 tactor array was placed on the dorsal
and volar parts of the wrist, respectively. An important
finding was that on average only 4 tactor locations could becorrectly identified on both sides of the wrist.
Despite the conclusion mentioned above, we use numberof tactors exceeding the recommended in [19]. Based on
our assumption that the tactile sensitivity in the middle
parts of the human forearm or upper arm is higher than thatof a wrist due to the size of circumference, we decided todesign BraTact for these parts. Moreover, to enhance thelocalization ability, we arrange the tactors in a zigzag
pattern. To ensure the close contact of the tactor with theskin and the adaptation to different sizes of the potential
users, the holders are connected by elastic band. The layoutof tactile system BraTact is shown in Fig. 6.

Figure 6: Tactile display BraTact.

It was reported that maintaining permanent contact of thetactor with the skin is crucial issue [20]. The holder was
designed in such a way that flat vibration motors protrude
and contact arm directly. The 3D prototype of the tactor
unit is presented in Fig. 7.
Vibration motor
Dummytactor

Cover

Lugs

Wiring hole
Figure 7: The link of the tactile bracelet.

The inner surface of the holder has concave profile to18th International Conference on Artificial Reality and Telexistence 2008

match the curvature of human arm surface. The curvatureof the holder surface of 39 mm was calculated on the basisof the forearm circumference value of average Japanesemale (it equals to 246 mm). To balance the position of thelink on the skin, the additional dummy tactor is provided.
The most fragile parts of the holder are lugs intended fortactor link fixation on flexible band. To find out the optimal
sizes of the lug cross-section, we performed FEM analysis.
The initial data are material of the holder (ABS plastic) andmaximum force applied to the lug by stretched band (4 N).
The results of analysis of plastic holder using FEM
demonstrate FEM model (Fig. 8(a)), displacement in m
(Fig. 8(b)), strain (Fig. 8(c)), and von Mises stress σVonMises
in N/m2 (Fig. 8(d)).

a)

b)

c)

d)

Figure 10: BraTact attached to the human arm.

The small flat coreless vibration motors FM34F withdiameter of 12 mm and thickness of 3.4 mm produce tactile
stimulation on human skin [21]. They have operating
voltage range of 2.5-3.5 V, corresponding frequency rangeof 181-236 Hz, and vibration quality of 1.8 G. The control
signal is generated by PC, based on information about
calculated force vector. A/D board feeds cue to the motor
driver hardware that supplies corresponding voltage to thevibration motor (Fig. 11).

PC

A/D

Figure 8: FEM analysis results.

Figure 9: Prototype of the tactile bracelet.

To supply the power to the tactors, thin wires withoverall diameter of 0.5 mm were used. The flexible tubes
wrap wires protecting them from breaking. Compact
connector socket was designed to unite vibration motor
wiring with control board.
It can be seen form Fig. 10 that the developed BraTact
display is compact and fits the arm very well.

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Wires

Wires

Motor Drivers

Tactile display

Figure 11: Control system of BraTact.

We use non-inverting amplifier to control the current of
the vibration motor. The results of calibration of one tactor
are presented in Fig. 12. During experiment we increased
the input voltage of operational amplifier and recorded thecurrent value in vibration motor circuit.
Vibration motor current, mA

Factor of safety of 2.5 was derived based on the
maximum von Mises stress criterion. Thus, designed
structure can guarantee overloading protection. The
holders were produces by using 3D printer. The
disassembled link and tactile bracelet are shown in Fig. 9.

100
80
60
40
20
20

40

60

80

Op-Amp input voltage, mV

100

Figure 12: Control system of BraTact.

The control box with vibration motor drivers is shown in
Fig. 13. To connect the driver box with tactile display the18th International Conference on Artificial Reality and Telexistence 2008

lightweight shielded wire cable was deployed.

Figure 13: Control box.

The initial intensities of the tactors were adjusted to beequal. Through controlling the vibration motor current wechange vibration motor rotational speed and, hence,vibration intensity.

6. Conclusions and future research
The increasing complexity of tasks performed byteleoperation systems requires to deliver and display tactile
information to the human operator effectively in order toensure safe interaction with environment. The sensory
system of the developed slave robot supports the local
admittance controllers with information on exerted force toaccomplish compliant interaction. We argue that to present
the interaction information effectively the usage of only
two bracelets on upper and lower arms is better solution
than employment of large grid of tactors on the human arm.
According to our approach, the contact state can bepresented by force vector. The direction of the force
perpendicular to the arm surface is represented by locationof the tactor; and force magnitude is represented by thistactor vibration intensity.
Our future study will be directed to the detailed
investigation of the force vector perception. First, thediscrimination of the tactors will be examined through user
study. Then, we will conduct study on contacting force
magnitude presentation through assignment of different
vibration intensities. We are also considering designing thecompact tactile displays for delivering the tactile
information to the user’s fingers.

Acknowledgments. The research is supported in part by aJapan Society for the Promotion of Science (JSPS)
Postdoctoral Fellowship for Foreign Scholars.

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