A GLOVE INTERFACE WITH TACTILE FEELING DISPLAY FOR

HUMANOID ROBOTICS AND VIRTUAL REALITY SYSTEMS

Michele Folgheraiter, Giuseppina Gini

Politecnico di Milano, DEI Electronic and Information Department

Piazza Leonardo Da Vinci 32, Milan

Dario L. Vercesi

Politecnico di Milano, DEI Electronic and Information Department

Piazza Leonardo Da Vinci 32, Milan

Keywords:

Man-Machine Interfaces, Virtual Reality, Haptic Interfaces, Electro-cutaneous Stimulation.

Abstract:

This paper focuses on the study and the experimentation of a glove interface for robotics and virtual reality

applications. The system can acquire the phalanxes position and force of an operator during the execution of

a grasp. We show how it is possible to use and integrate this data in order to permit the user to interact with

a synthetic world. In particular the system we designed can reproduce tactile and force sensation. Electrodes

and actuators are activated according to the information coming from the real world (position and force of the

user’s ﬁnger) and from a physical model that represents the virtual object. We also report some psychophysical

experiments we conducted on ﬁve subjects, in this case only the electro-tactile stimulator was used in order to

generate a touch sensation.

1 INTRODUCTION

Human-machine interfaces are very important in or-

der to guarantee a good transfer of information from

the human to the machine and vice versa. In many

applications the entity and quality of this informa-

tion exchange can establish the performance and

success of the machine operation (Fahn and Sun,

2000),(J.Adams et al., 2001),(Burdea, 1999).

In robotics, for example, these interfaces are applied

in order to remotely control the manipulation sys-

tem. A good example of tele-manipulated robot is

the ”Robonaut” designed in the NASA Johnson Space

Center’s laboratories (Ambrose et al., 2001). This ro-

bot has a humanoid shape and it is intended for sup-

porting astronauts during EVA (Extra Vehicular Ac-

tivity) activities. In this case, the operator is able to

govern the robot by a glove interface that measures

his arm-hand posture and generates the proper control

signals for the robot’s limbs. In this system, the op-

erator receives two types of feedback from the robot:

the ﬁrst is a force feedback that allows to calibrate the

applied force during an object manipulation, the sec-

ond is a visual feedback that reproduces the robot en-

vironment. For this purpose an HMD (Head Mounted

Display) is used.

Another interesting system is the Rutgers Master II

developed at the Rutgers University. This haptic inter-

face (Bouzit et al., 2002) permits to ﬂex or extend the

subject ﬁngers, with a maximum force of 16 N, using

four pneumatic actuators. Each actuator is equipped

with a position sensor that allows to control the ﬁn-

gers closure according to a model that represents the

virtual world.

The TENS (Transcutaneous Electric Nerve Stimula-

tion) devices are also very interesting in the the ﬁeld

of the haptic interfaces. These systems are capable

to generate a touch sensation without recreating the

physical stimulus, like many other mechanical de-

vices; this means high energy efﬁciency and very

compact devices. Technically, it consists in changing

the membrane potential of some skin receptors with

an electric ﬁeld applied by electrodes on the subject’s

dermis (Kajimoto et al., 1999). Controlling the cur-

rent injected in the tissue, it is possible to modulate

the receptor nerve activation and so the tactile sensa-

tion perceived by the subject.

Thanks to the bigger dimension of the mechanore-

ceptor nerves ( 10 µm) with respect to the pain re-

ceptor ﬁbers (1 µm), it is possible to evoke the touch

sensation and avoid the pain sensation.

Even if big improvements were done in the last

decades, many haptic devices are still unable to gener-

ate a fully immersive sensation, because they operate

outside the human perceiving system. To solve some

of these issues, we have built a device that combines

353

Folgheraiter M., Gini G. and L. Vercesi D. (2005).

A GLOVE INTERFACE WITH TACTILE FEELING DISPLAY FOR HUMANOID ROBOTICS AND VIRTUAL REALITY SYSTEMS.

In Proceedings of the Second International Conference on Informatics in Control, Automation and Robotics - Robotics and Automation, pages 353-360

DOI: 10.5220/0001166703530360

 SciTePress

visual, touch and force feedback in order to give a

more realistic interaction with the virtual world.

In this paper we will show some results obtained with

our custom built force feedback and touch sense glove

that can be worn and can interact in strict contact with

the human touch system. In particular the glove that

we developed can be used for three main purposes:

1. To Explore the capabilities of TENS (Tran-

scutaneous Electric Nerve Stimulation) stimulation in

combination with a virtual simulation system.

2. To Acquire the grasp positions performed by

a human operator in order to train a neural network

to make a robotic hand execute the same task (Fol-

gheraiter et al., 2004).

3. To Use the glove as an haptic interface to interact

with a virtual world.

We did a ﬁrst experiment to explore the possibil-

ities offered by the TENS stimulation for the inves-

tigation of a virtual world. Using a special elec-

trode applied at the ﬁngertip, we evoked vibration and

pressure sensations by injecting an impulsive bipha-

sic current into the skin of the subject, according to

the Gate Theory (Melzack and Wall, 1965). We per-

formed different tests changing some stimulation pa-

rameters like the current injected, the stimulation fre-

quency and the duration of the impulse. We also in-

troduced a force feedback in opposition to the ﬁn-

ger movements in order to emulate the virtual object

rigidity.

2 ARCHITECTURE OF THE

VIRTUAL GLOVE

The system is composed by a glove equipped with 14

angular sensors and 2 force sensors (ﬁgure ).

Angular sensors measure the joint rotation of each

phalanx for every ﬁngers, except for the little one.

Force sensors are connected in series with the tendons

that permit to transfer the force from the actuator to

the ﬁngertip. We realized them cutting and reshaping

commercial sensors, in particular we used ﬂex sensors

and FSE (Force Sensor Resistor).

Three angular sensors are mounted on each ﬁnger

respectively for proximal, middle and distant articular

joints. Two sensors, of the same kind, are mounted

between the thumb and the foreﬁnger to measure ab-

duction and adduction movements.

The glove is also equipped with a light arm-band,

rigidly ﬁxed on it, where we have put the actuator sys-

tem able to bind the ﬁnger movement in its dexterous

space.

Figure 1: The Glove.

2.1 Force feedback system

The force feedback actuator is composed by a servo

connected to the ﬁngertip through two tendons ﬁxed

to the solid plastic bands of the glove (Figure 2). The

tendons run along the ﬁnger length across some pass-

ings. We ﬁxed each tendon so that the servo force

was driven perpendicularly to the movement path of

the ﬁnger. In this way we optimized the force trans-

ferred along the tendon to the ﬁngertip.

Figure 2: Schema of the artiﬁcial tendons.

The virtual object is modelled by its dynamics

equations. The force generated by the object depends

on its mechanical characteristics, to a ﬁrst approxima-

tion we can write the model as following:

(t) = K

x(t) + K

dx(t)

(1)

Where K

is an elastic constant, K

is a damping

constant and x(t) is the penetration rate into the object

surface.

To have the equilibrium, the force generated by the

tendon to the ﬁngertip must be equal to the force gen-

erated by the virtual object (F

). We implemented

a software to calculate this force in real time; taking

ICINCO 2005 - ROBOTICS AND AUTOMATION

354

into account the mechanical structure of our glove, the

equation 1 can be rewritten as equation 2.

(t) =

x(t) + K

dx(t)

cosϕ

(2)

Where ϕ is the angle that the tendon forms with the

last phalanx (see ﬁgure 2).

2.2 Electro-cutaneous stimulation

system

The electro-cutaneous stimulation of the ﬁngertip is

due to an electrode ﬁxed between the glove and the

user’s ﬁnger. The position of the electrode can be ad-

justed to choose the speciﬁc zone that we intend to

stimulate. This is also important to avoid an uncom-

fortable sensation caused by a bad contact position.

Furthermore, we can increase the skin-electrode con-

tact quality using a conductive gel.

To a ﬁrst approximation (Kaczmarek and Webster,

1989), we can model the skin-electrode contact as fol-

lowing (ﬁgure 3).

Figure 3: Electrode schema and realization.

Where R

is the resistance between the electrode

and the conductive gel, R

and C

are the resis-

tance and the capacity of the the electrode-skin inter-

face. According to previous works and empiric tests

(Kaczmarek and Webster, 1989), R

results smaller

than R

and can be ignored to a ﬁrst approximation.

Therefore, if V is the impulse amplitude applied to

the electrode-skin interface, we can write the voltage

value presented on the subject tissue V

as following:

(t) = V (1 − e

−

) (3)

(t) = V e

−

(4)

Equations 3 and 4 represent respectively the rising

and falling voltage characteristic.

We can see from the electrode-skin interface re-

sponse that the behavior is not linear. This represents

a problem for the electro-tactile stimulation because,

with ﬁxed voltage at the electrodes, the current in-

jected can vary with time and so the touch sensation

felt by the subject. To avoid this problem, we can

control the current instead of the voltage.

In its turn the voltage V

generates an electric ﬁeld

into the skin surface that causes a potential on the ex-

ternal membrane of the axon ﬁbre.

In their work (Kajimoto et al., 1999) Kajimoto H. et

al described the equivalent electric membrane model.

They related the potential value of the membrane sur-

face with the corresponding inner value for impulsive

stimulus according to the Hodgkin and Huxley theory

(Hodgkin and Huxley, 1952).

Membrane Voltage (mV)

-20

-40

-60

-80

-100

Time (ms)

20 30 40

Figure 4: Signal built by membranes of nervous axons ac-

cording to the Gate Theory. This picture has been built by a

Hodgkin-Huxley Model simulator (a).

Electrodes are controlled by a custom built TENS-

board able to generate a generic biphasic wave vary-

ing in frequency (1Hz-5KHz) and intensity (0-5mA)

according to the transcutaneous electrical nerve stim-

ulation theory. The area of the positive pulse is nearly

equal to the area of the negative impulse. This is

important to avoid that the electrolysis phenomena

might cause a permanent tissue damage.

The TENS board is divided into two main blocks.

The ﬁrst block realizes the wave generator; it works

at low power and can interact with the PCL-812 A/D

board through 4 dedicated channels. An impulsive

digital signal is presented on the gate of a NPN tran-

sistor that performs a ﬁrst small ampliﬁcation, this re-

alizes the frequency base of the stimulation wave. A

digital potentiometer (RDAC) varies the amplitude of

the voltage signal. The RDAC is controlled through

the 3 remaining digital channels.

The second part of the board ampliﬁes the signal

thanks to a couple of op-amp (Operational Ampli-

ﬁer) and then elevates it through a voltage transformer

connected to the electrode. The transformer elevates

voltage from 5V to 100V and generates the biphasic

wave.

We completed the board introducing some capac-

itors to decouple the two phases of the signal trans-

formation. The output of the op-amp has been also

stabilized by a Boucherot block.

In this way the board is completely controlled by

the digital channels of the same A/D card used for

sensor measurements, and can send out the real-time

value of the current injected in the ﬁnger-tip. We are

A GLOVE INTERFACE WITH TACTILE FEELING DISPLAY FOR HUMANOID ROBOTICS AND VIRTUAL

REALITY SYSTEMS

355

able to control the current injected, making an instan-

taneous control loop (via software), both for safety

and adaptability to different users.

To make different experiments we used two

electro-stimulation channels of the same kind and dif-

ferent kinds of electrodes.

2.3 Acquisition and Control systems

The following schema (ﬁgure 5) presents the whole

acquisition and control process. Each block is de-

scribed by a name and its implementation techniques

(hardware/software).

Sensored

Glove

V-A/FM

Tens Card

Sensor_1

Force_S

COND

P. Board

COND

P. Board

COND

P. Board

Multiplexer

A/D

PCL812

SOFTWARE

Demultiplexer

Virtual Model

Collision Detection

VRML Software

4 bit MUX

HEF4067B

SOFTWARE

Counter

4 Bit

SOFTWARE

Timer

1 Bit

SOFTWARE

RDAC

Control

SOFTWARE

Force

Control

SOFTWARE

Attuator

Servo

SOFTWARE

TENS_1

COND

T. BOARD

COND

T. BOARD

A/D

PCL812

A/D

PCL812

Acquisition System

Control System

Figure 5: The acquisition and control blocks of the entire

process.

All the sensor measurements have been normalized

and multiplexed, using an electronic board and then

broadcasted through a single analogical channel to an

A/D general purpose card (PCL-812) mounted on a

PC executing the xPC-target tool of Matlab. Thanks

to xPC-Target architecture we can build physical in-

terfaces and control levels and execute them on dif-

ferent calculators, T arget and HostP C. Target-PC

plays also the role of implementing a ﬁrst control loop

to determine and generate the real-time value of in-

jected current. A speciﬁc value is assigned by the vir-

tual model according to the object surface characteris-

tics; the control module sends data to the TENS-board

in order to stabilize that value. This is important to

generate similar sensations in different subjects.

Target-Pc is connected, using a RS232 interface,

with a mobile PC that plays the main role in build-

ing the world model. The model is realized through

a VRML ﬁle that can be viewed and analyzed by

a proper C++ program with capabilities of collision

detection, based on v-collide algorithm. The virtual

model simulator is composed by two main parts: a

communication module and an external module. The

communication module plays the role of interfacing

Matlab with the external VRML module. The ex-

ternal module implements the graphical engine and

records all the objects into a tree data base that can be

sent and parsed in real-time by the v-collide functions

in order to determine collisions between objects.

The Host-Pc can realize a second control loop

based on angular-sensor measurements, evaluating

collisions and then, through the actuator system, bind-

ing the ﬁnger movement and sending the proper

electro-cutaneous stimulation to the ﬁnger-tip.

The third and last control loop is made by the

user through a visual interface that shows the virtual

3D model (ﬁgure 6) and enables controls on every

process variables.

Figure 6: The VRML model permits the user to have a vi-

sual feedback.

All the software modules, except to the win32 C++

application for 3D model visualization and collision

detection, are built in Simulink and compiled for real-

time execution in Matlab.

3 ELECTRICAL

TRANSCUTANEOUS

STIMULATION EXPERIMENTS

We can divide our experimentation into two main

phases. At ﬁrst we investigated the role of frequency

and current intensity with an half period pulse width,

then the duty cycle (pulse width) has been varied and

we have recorded the differences felt by the subject.

For each experiment we have prepared a question

set of tested points and a set of possible subject re-

sponses.

3.1 Role played by the stimulation

intensity and frequency

For the ﬁrst experiment, we prepared seven different

frequency tests (from 5Hz to 400Hz), each of them

ICINCO 2005 - ROBOTICS AND AUTOMATION

356

differentiated in four levels of current intensity (from

low to very high). This means we have a global test

set of 28 values for each subject.

The two sets can be described by equation 5 (the

number values are expressed in Hz) and equation 6.

= {5, 10, 20, 50, 100, 200, 400} (5)

= {

Low Middle High V.High

} (6)

Each value of the I

set is deﬁned by the correspon-

dent peak current interval as following:

• IǫLow ⇔ i ≤ 1mA

• IǫMiddle ⇔ (i > 1mA) ∧ (i ≤ 2.5mA)

• IǫHigh ⇔ (i > 2.5mA) ∧ (i ≤ 4mA)

• IǫV eryHigh ⇔ i > 4mA

The ﬁnal question set can be described by the 28

position table described by equation 7.

I = I

× I

(7)

Each sensation produced by the electrical

mechanoreceptor stimulation has two main compo-

nents: the intensity level and the sensation evoked

in the human mind (Bach-Y-Rita et al., 2003). We

prepared two response sets in order to map either

components. The ﬁrst set is composed by six possible

intensity response (from NoSesation to Pain). The

second one has seven elements corresponding to

seven possible sensation felt by users. We can write

the two sets as in equation 8 and equation 9.

= {NoSens., Low, M idd., High, Irrit., P ain}

(8)

= {B., I., V., T., R., W.} (9)

Where the sensation evoked values in the set are

Beats, Itch, Vibration, Tingle, Rasping and Warm.

To make a common guide for each experimenta-

tion we prepared an explicative table in which we

described every elements of each sets. The ﬁnal re-

sponse set is described by the 42 position described

by equation10

R = R

× R

(10)

In this manner the ﬁrst experiment can be described

as following:

∀fǫI

, ∀iǫI

⇔ Resp(f, i)ǫR (11)

For each frequency in the frequency set I

and for

each intensity level in the intensity set I

we note one

response of the response set R.

During the experiment we observed that subjects

felt a starting beat when stimulation started. This beat

could be uncomfortable in many cases. We recorded

subject starting beat sensations at 50Hz and 200Hz for

the middle intensity level.

After the data acquisition we prepared a double en-

tering table where we put the mean and variance of

elements response. For brevity we present only

the shortest version of this table in which we put the

whole data grouped by intensity levels. Data is shown

in ﬁgure7.

Intensity Current Mean Variance

Low 0-1mA 1.14 0.04

Middle 1-2.5mA 2.06 0.02

High 2.5-4mA 3.26 0.06

Very-High 4mA+ 4.09 0.17

Figure 7: Mean and variance values of subject responses.

Values under 1mA (Low) are inappreciable to most

of the subjects. Subjects felt low sensation between

1mA and 2.5mA (Middle). At this level they can

be distracted by other stimuli, like people speaking,

and because of that they forget the current stimula-

tion. This is an important consequence of ﬁlter theory.

Values between 2.5mA and 4mA (High) are strongly

felt by the subjects. In this case subjects cannot be

distracted by other external stimulus. Values up to

4mA (Very-High) are considered strong and uncom-

fortable. In some case subjects feel pain. The high

variance present for this data group suggests us to in-

crement the number of elements of I

decreasing steps

especially for high values (4mA+).

The graphic in ﬁgure 9 shows the subject mean per-

ceived values related to the real intensity of the elec-

trical stimulus. For brevity we present only the 50Hz,

100Hz and 200Hz graphs.

50Hz

100Hz

200Hz

Figure 8: Subject sensations by electric pulse intensity.

As we can see by the graph, the sensation perceived

by the subject grows logarithmical with stimulation

intensity. This supports the Steven’s theory (Darley

et al., 1994) according tp which the sensation felt by

a subject grows following the equation 12.

S = K · I

(12)

Where S is the sensation perceived by the subject,

I is the stimulus entity, K and b are two constants that

A GLOVE INTERFACE WITH TACTILE FEELING DISPLAY FOR HUMANOID ROBOTICS AND VIRTUAL

REALITY SYSTEMS

357

depend on each subject. In the transcutaneous stimu-

lation K and b depend also on the impulse frequency.

This is true if we think that the Hodgkin and Huxley

relation (Hodgkin and Huxley, 1952), between gener-

ator potential and axon activation potentials, suggests

a proportionality between frequency of axons poten-

tial and stimulus intensity. We can realize an empiri-

cal calibration of K and b in order to prepare the per-

sonal subject sensation function.

To study the sensations evoked by the electrical

stimulation, we prepared a second double entering ta-

ble in which we described for each f,i couple the R

element the subject response.

Here we present a shortest version of this table

where we describe all the results grouped by fre-

quency values. The table is shown in ﬁgure 9.

Frequency B. I. V. T. R. W.

5Hz 11 1 0 0 0 0

10Hz 11 2 0 0 0 0

20Hz 7 1 5 2 0 0

50Hz 2 5 7 2 0 0

100Hz 0 1 8 1 3 0

200Hz 0 6 7 1 0 0

400Hz 1 2 6 1 0 4

Figure 9: Subject sensations by frequency values. Beats,

Itch, Vibration, Tingle, Rasping, Warm

From this table we can build a graph related to the

sensations evoked during the experiment (Figure 10).

Beats

Vibration

Itch

Rasping

Tingle

Warm

Figure 10: Data graph of subject sensations by frequency

values.

We can see that at very low frequency (from 5Hz

to 20Hz) subjects feel beats and small pressure sen-

sations. Merkel cells are sensible to that frequency

and seem to be specialized in detection of pressure

and surface deformations. At middle frequency (from

100Hz to 200Hz) a new sensation of vibration was

evoked. Users can’t understand, in many cases, the

period of the impulsive current but can only perceive

a sensation of rapid vibration or grasping object under

the ﬁngertip surface. If we think that grasping sensa-

tion can be related to hard vibration, we can assure

that the 82% of the sensations evoked by a stimulus

of about 100-200Hz can be identiﬁed as a vibration

stimulus. This agrees with the former works that sug-

gested that Pacinian Corpuscles are sensible to vibra-

tion and operate at that frequency (Kajimoto et al.,

1999).

The starting beat tests produced no interesting data.

We could only see that starting beat sensation grows

with intensity. This can be connected to the typical

adaptability (Guyton, 1987) of each mechanoreceptor

in the ﬁngertip.

To determine the maximum frequency that the hu-

man mechanoreceptors may perceive, we tried stimu-

lations at 1.2KHz and 5.0KHz. We noted that no sub-

ject can perceive impulses faster than 5.0KHz. This

value can be assumed as a ﬁrst upper bound.

3.2 Pulse Width Modulation of the

electrical stimulation wave

In the second experiment we tried to demonstrate the

role played by the impulse width of the electrical

stimulation wave. We ﬁxed the frequency at two sig-

niﬁcant values (10Hz - 50Hz) for two intensity levels

and then we asked the subject to describe the differ-

ence perceived varying pulse width from 10% to 90%

of the whole period.

Question sets are described by equation 13, equa-

tion 14 and equation 15.

= {

10Hz 50Hz

} (13)

= {

Middle High

} (14)

= {

10% 90%

} (15)

Where I

describes test frequency values, I

is the

intensity level set and I

is the impulse width values

of the experiment. Response set R

is described by

table 1

Table 1: Response set

Lower

Stronger

Softer

Harder

Faster

Slower

Equal

The Lower and Stronger values mean that the

subject feels the same sensation but perceives some

variation in the intensity level. The Sof ter and

Harder values mean that subject feels the same in-

tensity of the half width impulse but with a less

ICINCO 2005 - ROBOTICS AND AUTOMATION

358

or more clear sensations. The F aster and Slower

values are connected to the perceived sensation of

changed speed. Finally Equal value means that the

subject doesn’t perceive any kind of variation.

The whole experience can be described by equation

16.

∀fǫI

, ∀iǫI

, ∀aǫI

⇔ Resp(f, i, a)ǫR

(16)

Results of the data acquisition are described in ta-

ble shown in ﬁgure 11, where we grouped data by

impulse width.

w L. St. So. H. F. Sl. E.

10% 11 0 0 4 0 0 5

90% 0 9 8 0 1 0 2

Figure 11: Subject responses about sensation driven by

pulse width modulation. Lower, Strong, Softer, Harder,

Faster, Slower and Equal sensation.

Subjects feel lower sensation (Lower) for small

pulse width (10%) but also a clear sensation was

evoked (Harder). For large impulse width (90%)

the subjects feel stronger sensation (Stronger) but

smoother (Softer) than the ﬁrst one. We can use pulse

width modulation in order to evoke clear or smooth

tapping sensation based on the same frequency level.

4 HAPTIC USER INTERFACE

The last experiment we made involved the force feed-

back, the cutaneous touch sense and a visual system.

It can be divided into tree main phases. In the ﬁrst part

we used the force feedback system alone. The PCL-

812 controls the servo angular position every 10ms;

if a touch position is reached, servo reacts by slowing

the ﬁnger movement. We can change the servo speed

and touch position in order to simulate hard or soft

surface of every dimensions.

The second experiment involved both force and cu-

taneous feedbacks. We introduced an electrical stimu-

lation (100Hz, middle intensity level) on the ﬁngertip

when the subject reach the virtual object.

The third part of the experiment introduced the vi-

sual and the collision detection systems. We present

to the subject a VRML virtual model of the human

hand and the objects (Figure 6). When the system de-

tects collisions between the hand and the objects, the

force feedback and the cutaneous stimulation are acti-

vated in order to give to the subject a fully immersive

sensation.

For all the experiments we prepared two virtual ob-

jects of different dimension. For each object we tested

two different force opposition values. We can de-

scribe the question set related to the object dimension

through equation17.

= {

Small Big

} (17)

and the question set related to the object hardness

through equation 18.

= {

Sof t Hard

} (18)

the resulting question set is composed by the 4 po-

sition table described in equation 19.

= I

× I

(19)

Where n is the experimentation number (from 1 to

3). For each part of this experiment, we presented the

virtual object to the subject and then we asked him to

recognize its properties choosing his answers into a

response set of the same kind of I

Subjects recognized object hardness and dimen-

sions in each phase, but only when we introduced

visual system, they were able to assign a correct

shape interpretation for the touched object. Summa-

rizing, with force feedback system only, subjects feel

a movement opposition force but not a real touch-

ing object sensations. Combining force feedback and

electrical touch system, subjects can determine the

contact position accurately but already they do not

feel a real detectable touching sensation. When the

whole system was tested, subjects easily afﬁrmed that

they were touching an object of the correct shape.

This is an important result if we think that the in-

troduction of the visual system produces a lag into the

frame rate of about 50ms (100ms of V-Collide system

to 10ms of Simulink model), ﬁve times higher than

the servo impulse ratio. This lag is due to the algo-

rithm for the collision detection analysis and to the

communications between the two interacting software

tasks.

5 CONCLUSION

In this paper we presented an haptic interface for ap-

plication in virtual reality and for tele-manipulation

systems.

In the ﬁrst part we described the model, the hard-

ware and the software used. In the second part

we presented three main experiments. The ﬁrst ex-

periment explores transcutaneous electrical stimula-

tion frequency in order to evoke vibration and pres-

sure sensations. We can determine, by a calibration

process, the K and b parameters of the Steven law

(Darley et al., 1994) to ﬁx the intensity levels of each

subject. Once we found the correct intensity and fre-

quency of stimulations, we explored the pulse width

modulation capabilities.

A GLOVE INTERFACE WITH TACTILE FEELING DISPLAY FOR HUMANOID ROBOTICS AND VIRTUAL

REALITY SYSTEMS

359

In the last part we tested the force feedback, the

touch display and the visualization system in order to

simulate a virtual object with different hardness and

dimensions. Our results demonstrated how integrat-

ing these three kinds of stimulus offered to the subject

a more realistic interaction with the virtual world.

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