COMPARATIVE OF HAPTIC INTERFACES FOR ROBOT-ASSISTED

SURGERY

J. M. Azor

ın, J. M. Sabater, N. Garc

ıa, F. J. Mart

ınez, L. Navarro

Dpto. de Ingenier

ıa de Sistemas Industriales, Universidad Miguel Hern

andez

Avenida de la Universidad s/n, Elche (Alicante), 03202 Spain

R. J. Saltar

DISAM, ETSII, Universidad Polit

ecnica de Madrid

C/Jos

e Guti

errez Abascal 2, Madrid, 28006 Spain

Keywords:

Haptic interfaces, robot-assisted surgery, telesurgery, surgical simulation.

Abstract:

This paper presents a comparative of different non-speciﬁc haptic interfaces that could be used for robot-

assisted surgery. The purpose of this analysis is to determine which master interface has the best performance

for a speciﬁc task in which the master-slave scale factor is less than one. Three haptic interfaces have been

considered: two commercial masters, one with serial conﬁguration, the PHANToM 1.5 prototype master, and

one with spherical setup, the Microsoft Force Feedback 2 Sidewinder; and other one non commercial with a

parallel architecture designed in our laboratory, the Magister-P. Two experiments performed to measure the

ﬁdelity of the haptic interfaces have been described and the results obtained have been discussed on this paper.

1 INTRODUCTION

Robot-assisted surgery has became a new research fo-

cus of the robotics community during the last years.

The followed objective is to develop “a partnership

between man (the surgeon) and machine (the robot)

that seeks to exploit the capabilities of both to do a

task better than either can do alone” (Taylor et al.,

1991). Telesurgery and surgical simulators belong to

this new robotics area. Telesurgery allows surgeons to

perform remote surgical operations using robots and

haptic interfaces. On the other hand, surgical sim-

ulators are based in virtual environments where the

surgeon uses a haptic interface to control the med-

ical robot. These virtual environments incorporate

accurate and reliable mathematical models of the hu-

man body part that is going to be operated and of the

rigid bodies of the medical apparatus involved. Sur-

gical simulators can be applied to surgical training

uhnapfel et al., 2000), avoiding the use of other ex-

pensive learning techniques as experiments with ca-

davers, and to biomedical research. In addition, these

surgical simulators become an indispensable tool in

telesurgery, since any action performed by the sur-

geon over the patient can be veriﬁed in the simulator

before it would be executed by the remote robot.

Nowadays, a great research effort is being made

on the robot assisted surgery, and several universi-

ties and enterprisers have presented their develop-

ments with applications on orthopedic, microsurgery,

laparoscopy,...(Cleary and Nguyen, 2001). Neverthe-

less, as it is suggested on (Taylor and Stoianovici,

2003), it is necessary to made signiﬁcant advances on

several aspects, like the interface technology, where

better surgeon-machine interfaces are needed. The

work presented here is focused on this aspect, and it

presents some discussion of a comparative analysis of

different general purpose haptic interfaces that would

be able to be used as robot-assisted surgery input de-

vices. Although near almost the actual developments

use particular devices designed for an speciﬁc task, as

for example the Laparoscopic Engine of Immersion

for endoscopic surgical systems, our interest is made

such tasks with general purpose haptic interfaces, so

we can take beneﬁt of the different kinematic struc-

tures of master and slave to improve the ergonomics

and/or the manipulability of the surgical tools. Two of

the used interfaces are commercially available, while

the third one has been designed in our laboratory.

To our knowledge, there are not many research

works in the literature that analyzes which haptic in-

terface achieves a better behavior in determined surgi-

cal interventions. Some work has been done trying to

obtain general indexes that help us to classify the per-

formance of haptic devices (Moreyra and Hannaford,

1998),(Hayward and Astley, 1996). The purpose of

the current analysis is to discuss the desirable char-

acteristics of a haptic interface to be used for robot-

375

M. Azorín J., M. Sabater J., García N., J. Martínez F., Navarro L. and J. Saltarén R. (2005).

COMPARATIVE OF HAPTIC INTERFACES FOR ROBOT-ASSISTED SURGERY.

In Proceedings of the Second International Conference on Informatics in Control, Automation and Robotics - Robotics and Automation, pages 375-378

DOI: 10.5220/0001159103750378

 SciTePress

Figure 1: Masters considered in the analysis: Microsoft

Force Feedback (right), Phantom (center), and Magister-P

(left).

assisted surgery.

The paper is organized as follows. Section 2 de-

scribes the three haptic interfaces that have been used

in the comparative analysis, explaining its character-

istics. The experiments performed and the results ob-

tained are showed in section 3. Finally the main con-

clusions of the paper are summarized in section 4.

2 MASTER INTERFACES FOR

ROBOT-ASSISTED SURGERY

In this section, the three haptic interfaces used on this

work are presented. All the experiments are limited

to a 1 DOF of the interfaces, trying to mimic the force

sensed on the movement along the axis of a typical

endoscopic device. We assume that a minimally in-

vasive surgery (MIS) is simulated. In MIS the op-

eration is performed with instruments and viewing

equipment inserted in the human body through small

incisions (typically less than 10mm in diameter). The

main advantage of this technique is the limited trauma

to healthy tissue, reducing the post-operative hospital

stay of the patient (Ortmaier, 2002). However this

technique has a difﬁcult learning process since the

surgeon must learn to navigate using visual informa-

tion provided by cameras with non orthogonal optical

to the scene observed.

The three master used are the low-price spherical

Microsoft Force Feedback (MMF- ﬁg. 1 - a)), the well

known 6 d.o.f. serial arm Phantom master 1.5 Proto-

type (ﬁg. 1 - b)), and a parallel conﬁguration device,

the Magister-P (ﬁg. 1 - c)). The spherical and the

serial master are commercially available, while the

parallel master has been designed in our laboratory

(Sabater et al., 2004). All devices incorporate force

feedback. Force feedback improves the task perfor-

mance in spite of the necessity of having a measure of

the force/torque sensor in the robot that executes the

operation. Without force feedback, the forces that the

surgeon feels only depends on the master character-

istics, independently of the remote environment situ-

ation. This way, e.g., the surgeon can not determine

the quantity of forces to exert in a suture operation if

only exists visual feedback.

On many of the recent developed systems, the force

reﬂection is neglected. This could be accepted by the

moment that, in a real classic MIS technique, the real

forces sensed by the surgeon are minimal. Neverthe-

less, if our future goal is not to copy the classical MIS

techniques, but to give the surgeon new tools that al-

low him to increment the useful information that way

the surgical procedures can be improved, it is neces-

sary to have an accurate force reﬂection system.

About the number of DOF, the Phantom and

Magister-P masters have 6 DOF, while the Microsoft

Force Feedback master has only 3 DOF (spherical

motion with 2DOF force feedback). Therefore any

device have the same number of DOF that the laparo-

scopic instrument (4 DOF). Next, how these masters

can be used in an endoscopic operation is explained:

Microsoft Force Feedback Master. This device has

only 3 DOF to control the 4 DOF of the laparo-

scopic slave, so the use of additional master but-

tons is necessary. The ascend and descend motion

of the tool can be achieved with the motion of the

joystick Y axis (ﬁg. 1-a)). In this way, the force

feedback is possible when the tool interacts with

the deformable object. The Z-axis rotation move-

ment can be achieved with the Z-axis joystick rota-

tion movement, and the XY rotation movement of

the tool around the fulcrum point can be achieved

with the movement XY of the joystick at same time

a button is pressed.

Phantom Master. At this device it is necessary to

constraint (or neglect) 2 DOF in order to control

the 4 DOF of the surgical tool. The ascend and de-

scend motion of the tool can be linked with the Z

movement of the Phantom ﬁnal effector. The Z-

axis movement can be achieved with the Z-rotation

of the Phantom, and the fulcrum XY rotation can

be represented by the XY translation movement of

the device. That way 2 rotation DOF of the effector

of the Phantom are neglected.

Magister-P Master. The ascend and descend motion

of the tool corresponds to the Z movement of the

lower platform (ﬁg. 1-c)). The 3 orientation DOFs

of the surgical tool are given by the orientation of

the lower platform. The X and Y position of the

ﬁnal effector are neglected, and are only used to

increase the ergonomic feeling of the surgeon.

The most important features of the devices that are

related with the task they are going to be used are

summarized on table 1.

ICINCO 2005 - ROBOTICS AND AUTOMATION

376

Table 1: Main features of used devices

MFF Phantom Magister

DOF 3 6 6

Conﬁguration Spherical Serial Parallel

Prog. Interface DirectX Ghost C-interface

Range Forces 0-4 N 0-8.5 N 0.3-90 N

Bandwidth ≈ low 1000Hz 320 Hz

Linearity almost

at low range no linear linear no linear

The three master devices have enough bandwidth

for the designed experiments. Nevertheless, for a high

ﬁdelity haptic rendering, devices must have at least

300 Hz or higher, so the MFF is not an appropriate

device. Besides, the DirectX library does not permit

to modify the frequency of the haptic loop. All the

same, the designed experiments try to measure the

performance of the kinesthetic rendering (at frequen-

cies lower than 0.5 Hz) in a low velocity task, as a

surgical operation, so the three devices are valid ones

from the point of view of bandwidth. Mechanically

speaking, the Magister-P has some fabrication errors

that make that we need to overcome a friction thresh-

old to render forces.

3 EXPERIMENTAL RESULTS

At this section the setup of the comparative experi-

ments is explained. The results are plotted and some

comments for their use as master devices in an endo-

scopic robotic surgery are made.

Two psychophysical kind of experiments have been

performed over a group of users with previous ex-

perience with the three master devices. Users have

made each experiment twice, with at least one day

between them. A total of 10 users (6 male and 4 fe-

male) have done a number of 40 experiments. The

goal of the ﬁrst group of experiments is to get data

of the force/torque interaction of the surgeon with the

master device, measuring the minimum force sensed,

what is related with the capability of detecting little

deformations on a deformable tissue. Similarly, the

second group of experiments tries to determine the

minimum difference on the increment of force/torque

that can be sensed, what is related with the ability of

distinguish between similar tissues.

Forces and torques are needed to be introduced to

the devices to make the experiments. In the Phan-

tom case, the Ghost library allows directly to program

them in cartesian space. In the Magister-P case, our

own library takes care of the calibration test to allow a

MFFdata

Phantomdata

Magister-pdata

Figure 2: Experiment 1 results

direct input of forces/torques in cartesian space. Nev-

ertheless, in the MFF case, the DirectX library does

not allow to introduce force/torque values on carte-

sian or joint spaces. Instead of that, the own library

units are used. That way, a previous experiment of

dynamometry-calibration to ﬁnd the relation of these

units with the force values must to be done. Next,

each one of the experiments is detailed and the results

are plotted.

3.1 Minimum sensed force value

On this experiment, starting with a null value of the

displayed force/torque, the value is being increased

each 2 seconds a determined value F

inc

/τ

inc

until the

users is being able to sense the force, recording the

value of this force. The process has been made with

two different increment values for each master. Figure

2 shows the results of the minimum force experiment.

Some remarkable aspects are:

• The ﬁrst time the experiment is done (upper part of

ﬁgure 2), the operators use to detect the force ear-

lier when the increment is the higher one. Besides,

there are signiﬁcant differences when the increment

is one or another.

• The second time the experiment is done (down part

of ﬁgure 2), the difference between the two incre-

ments is reduced, and the torque is detected earlier

in general.

• In the Magister-P experiments, the minimum value

is above 0.4 N, due to the friction threshold that this

device has.

3.2 Minimum increment of force

perceived by the user

The goal of this experiment is to get the minimum

difference between consecutive forces that a user can

feel. This experiment tries to evaluate the ability of

the devices to display the changes on the stiffness of

the tissues.

To make this experiment, an initial force/torque

nominal value (F

nom

/τ

nom

) has been chosen for each

COMPARATIVE OF HAPTIC INTERFACES FOR ROBOT-ASSISTED SURGERY

377

MFFdata

Phantomdata

Magister-pdata

Figure 3: Experiment 2 results

master. This value is kept constant during a period of

time (at least one second) and next the force/torque

increment (F

inc0

/τ

inc0

) is added to this value and

rendered. If the operator feels the increment, the

value of the increment is reduced a certain quantity

red

/τ

red

), and the experiment in repeated with the

new values. This process is repeated while the opera-

tor feels the increment. The last value of increment is

noted as a result. Figure 3 plots the results obtained

on the two experiments made with the different mas-

ters. The average data are:

• In general, users detect a lower torque increment

(∆

) when the nominal initial value is the lowest.

• On the second experiment, the values are lower

than in the ﬁrst one.

3.3 Comparative aspects

Some conclusions can be obtained from the previous

experiments:

• In the ﬁst experiment, in all the devices, when the

increment of forces is small enough, and working

in low frequencies, some users get used to this in-

crement, and they do not detect the force until its

value is signiﬁcantly higher than when the incre-

ment is given in bigger steps. This is because the

human sensors that work at low frequencies are

fast adaption sensors, and they get used to the new

value of the force.

• The mechanical conﬁguration of the devices plays

an important role in the ability of the users to feel

forces. The workspace is also a key parameter.

The ability of translation in the Phantom and in

the Magister-P provokes that the user can move his

hand, hiding some forces, and so that force values

are smaller on the spherical conﬁguration.

• In all the cases, on the second turn of the exper-

iments, values are smaller, due to the experience

acquired by users on the ﬁrst turn.

4 CONCLUSION

A comparative analysis of general purpose haptic de-

vices in a robotic assisted surgery environment has

been made. The studied devices are not task-speciﬁc

devices, and they can be used on other teleoperation

tasks.

All the master devices have the capacity of ren-

dering forces to the operator. Using this feature, the

comparative is focused on this rendering ability, and it

tries to determine the minimum change in the stiffness

of a tissue that could be perceived by the operator-

surgeon. For that, the experiments have been limited

to the input of a determined force/torque on an axis

for each device.

Future work must include the rendering of forces

on arbitrary directions, considering the isotropy of

each device. Besides, the workspace and the er-

gonomics of each device are also parameters that must

be included on a deeper study.

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