parallel robot, control, robotics

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68
ISSN 1392 - 1207. MECHANIKA. 2008. Nr.6(74)
Modelling, design and control of 3DOF medical parallel robot
S.-D. Stan*, R. B?lan**, V. M?tie?***
*Technical University of Cluj-Napoca, C. Daicoviciu 15, 400020 Cluj-Napoca, Romania, E-mail: [email protected]
**Technical University of Cluj-Napoca, C. Daicoviciu 15, 400020 Cluj-Napoca, Romania,
E-mail: [email protected]
***Technical University of Cluj-Napoca, C. Daicoviciu 15, 400020 Cluj-Napoca, Romania,
E-mail: [email protected]


1. Kinematics of the 3 DOF ISOGLIDE3 parallel robot

Robot usage outside of the automobile, appliance,
undersea, space, and hazardous materials industries has
increased over the past decade. Robots have potential for
enormous benefit to the medical field, but researchers must
proceed with care to ensure human safety. With the rising
cost of medicine, automation may be one way to make
medicine affordable [1-3].
The trend is to work side-by-side with specialists
of other fields so as to gain insight into the problems hith-
erto remaining untouched. One such environment has been
the hospitals in general and the operation theatres in par-
ticular where it is seen that the abilities of a surgeon carry-



ing out a difficult surgical operation gets enhanced by
Fig. 2 ISOGLIDE3 parallel robot realized at Mechatronics
working side-by-side with such robots. Those robots,
Department
popularly known as medical robots are meant for tackling
the three main areas of medicine - surgery, hospital service
The mobile platform can be visualized as a square
and rehabilitation. The most popular and demanding appli-
whose side length 2L is defined by B1, B2, and B3 points.
B
B
B
cation areas amongst those is surgery [4-6]. The high pre-
The fixed base is defined by three guide rods that pass
cision of the robot manipulator, minimally invasive access,
through A1, A2, and A3 points, respectively (Fig. 3).
enhanced prospects for tele-surgery are some of the rea-
Fixed coordinate frame originates at the point O.
sons behind the justification of a robotic approach to sur-
In Fig. 3, the reference frame XYZ is attached to the fixed
gery.
base. All links are connected then to the mobile platform or
Industrial robots are being used in the operating
the end-effector (Fig. 4).
room, and two classes of robot systems can be defined in
this area: robots that assist the surgeon in surgery, and ro-
bots that actually perform the surgery. The following dis-
cussion comprises a 3 DOF parallel robot that can be used
for surgery. The structure of the 3 DOF ISOGLIDE3 paral-
lel robot is shown in Fig. 1, where a mobile platform is
coupled with the fixed base by three legs of type PRRR
(Prismatic Revolute Revolute Revolute). The realized ro-
bot made at Mechatronics Dept. is presented in Fig. 2.


Fig. 3 Kinematic scheme of 3 DOF ISOGLIDE3 parallel
robot

The three revolute joint axes at each of these links
are parallel to the ground connected prismatic joint axis,
and are located at points Ai, Mi, and Bi, respectively. Also,
B
the three prismatic joint axes passing through points Ai, for
i = 1, 2, 3, are parallel to the X, Y, and Z axes, respectively.

The first prismatic joint axis lies on the X-axis;

the second prismatic joint axis lies on the Y-axis; while the

Fig. 1 CAD design of 3 DOF ISOGLIDE3 parallel robot
third prismatic joint axis is parallel to the Z-axis.


69
limited moving masses, and advantageous robot behaviour.
SimMechanics generated model of the ISOGLIDE3 paral-
lel robot is presented in Fig. 6.



Fig. 4 The mobile platform of 3 DOF ISOGLIDE3 parallel
robot
Consequently, the location of point P is deter-
mined by the intersection of three planes. The forward and
inverse kinematic analysis is trivial. A simple kinematic


relation can be written as
Fig. 6 SimMechanics generated model of the ISOGLIDE3
parallel robot
?x? ?d1 ?
The interface is based on virtual reality approach
? ?
? ?
y = d


? ? ? 2 ?
in order to provide the user with an interactive 3D graphi-
? z? ?d ?
? ? ? 3 ?
cal representation of the parallel robot. The interface was
designed to give a novice user an intuitive tool to control
This robot architecture was also implemented and
any kind of mechanical structure (serial, parallel or hy-
known in the literature under the name of ISOGLIDE3-T3
brid), requiring no programming skills. Computer based
[7, 8], Orthogonal Tripteron [9], or CPM [10].
simulation allows mimicking a real life or potential situa-

tions. SimMechanics models, however, can be interfaced
2. Trajectory planning of ISOGLIDE3 parallel robot
seamlessly with ordinary Simulink block diagrams. For

example, this enables the user to design mechanical and
A path is defined as the sequence of robot con-
the control system in one common environment. Virtual
figurations in a particular order without regard for timing
model interface of the ISOGLIDE3 parallel robot is pre-
of these configurations while trajectory is concerned when
sented in Fig. 7.
each part of the path must be obtained thus specifying tim-
ing.
Control of the robot is implemented using a joint-
based control scheme. In such a scheme, the end effecter is
positioned by finding the difference between the desired
quantities and the actual ones expressed in the joint space.
Simulink model of the ISOGLIDE3 parallel robot is pre-
sented in Fig. 5.



Fig. 7 ISOGLIDE3 virtual reality robot interface

In addition, Virtual Reality Toolbox for

Fig. 5 Simulink model of the ISOGLIDE3 parallel robot
MATLAB makes it possible a more realistic rendering of
bodies. Arbitrary virtual worlds can be designed with Vir-
The first tests on the prototype encourage the di-
tual Reality Modelling Language (VRML), and interfaced
rection of the research: the chosen control algorithms em-
to the SimMechanics model. The procedure of modelling
phasize peculiar characteristics of the parallel architecture
in Virtual Realty in details is described in [11].
and, in particular, good dynamic performance due to the



70
3. Simulation results
900

along x-axis

800
along z-axis
along y-axis
The sample trajectory of the end-effector is cho-
700
sen to be a circular path with the radius of 0.3 meters and
] 600
t
o
ns
its center is O (0, 0, 0).
e
w 500
N
This path is designed to be completed in 7 sec-
c
e
[
400
or
onds when the end-effector reaches the starting point
F
or 300
P
c
t
uat
1(0.3, 0, 0) again with constant angular velocity ? =
A 200
= 0.5? rad/sec. The end-effector path is shown in Fig. 8.
100
The desired force obtained from the actuators to
0
move the end-effector of the ISOGLIDE3 parallel robot
-100
along the desired trajectory is shown in Fig. 9. Dynamic
0
1
2
3
4
5
6
7
Time [seconds]

model was presented in [10]. Optimal design of parallel

Fig. 11The desired force obtained from actuators
robots can be found in [7-16].


4. Conclusions

The paper presents modeling, design and control
simulations of ISOGLIDE3 medical parallel robot. This
robot was realized at Dept. of Mechatronics, Technical
University of Cluj-Napoca.
Also a Virtual Reality Interface for the 3 DOF
ISOGLIDE3 parallel robot (IG3PR) control is presented.
An evaluation model from the Matlab/SimMechanics envi-
ronment was used for the simulation. An interactive tool
for dynamic system modeling and analysis was presented
in Virtual Reality environment of this ISOGLIDE3 parallel
robot. The main advantages of this parallel manipulator are
that all the actuators can be attached directly to the base,

that closed-form solutions are available for the forward and

inverse kinematics, and that the moving platform maintains
Fig. 8 End-effector path for the circular trajectory
the same orientation throughout the entire workspace.
40

By means of SimMechanics, the authors consid-
along X axis
along Y axis
ered robotic system as a block of functional diagrams. Be-
20
sides, such software packages allow visualizing motion of
0
n
s
)
mechanical system in 3D virtual space. Especially non-
wto
Ne
experts will benefit from the proposed visualization tools,
-20
o
r
c
e
(
as they facilitate modeling and interpretation of results.
a
t
o
r F
tu
Ac -40

5. Acknowledgment
-60

-80 0
1
2
3
4
5
6
7
This work was financially supported by CNMP
Time [seconds]

through the grants no. 3280 (PARTENERIATE type), title
Fig. 9 The desired force obtained from the actuators
of the project ‘Complex mechatronics systems for medical
applications’ and CNCSIS 1072 (IDEI type), title of the
project ‘Researches regarding the advanced control with
applications in mechatronics’.

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MODELLING, DESIGN AND CONTROL OF 3DOF
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?????????? ????????????
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Machine Science-IFToMM 11.-Tianjin, China, 2004.

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? ?????? ???????????? ??????????? ???????-
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???????, ???????? ?????????? ???????????? ???????
bots. -The 18th International DAAAM Symposium ISOGLIDE3. ????? ??????????? ???????????? ?????-
Intelligent Manufacturing & Automation: Focus on ???? ????????????, ??????????????? ??? ???????????-
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?? ?????????? ???????????? ??????? ? ????? ?????-
27th October 2007, University of Zadar, Zadar, ???? ???????. ????????? ????????? ???????????? ?
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???????????? ? ??????????? ?????, ? ?????????? ??-
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???????? ???????????? ? ??????? MATLAB, Simulink ?
DOF parallel kinematics machines. -Proc. Appl. Math.
SimMechanics. ?? ????????? ? ??????? ??????????-
Mech. -Berlin: Willey PAMM, 2006, 6, p.705-706.
???? ????????????? ????, ?????????????? ??????

ISOGLIDE3 ?????????? ????? ??????? ?????????,

????????, ??? ??????????? ????? ??????. ??-?? ???
S.-D. Stan, R. B?lan, V. M?tie?
????????, ??????? ???????????? ????????????? ????-
?????????? ???????????? ????? ? ????? ?????????
TRIJ? LAISV?S LAIPSNI? MEDICININIO
??????? ????? ?????????????? ? ????????.
LYGIAGRE?IOJO ROBOTO MODELIAVIMAS,

PROJEKTAVIMAS IR VALDYMAS
Received August 25, 2008
R e z i u m ?
Accepted September 25, 2008
Straipsnyje supažindinama su lygiagre?iojo robo-
to ISOGLIDE3 projektavimu ir jo valdymo imitavimu.


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