Modern Mechanical Engineering, 2012, 2, 57-64 Published Online August 2012 (
Parallel Manipulators Applications—A Survey
Y. D. Patel1*, P. M. George2
1Department of Mechanical Engineering, A. D. Patel Institute of Technology, New Vallabh Vidyanagar, India
2Department of Mechanical Engineering, Birla Vishvakarma Mahavidyalaya Engineering College, Vallabh Vidyanagar, India
Email: *
Received February 9, 2012; revised March 25, 2012; accepted April 2, 2012
This paper presents the comparison between serial and parallel manipulators. Day by day, the applications of the paral-
lel manipulator in various field is become apparent and with a rapid rate utilized in precise manufacturing, medical sci-
ence and in space exploration equipments. A parallel manipulator can be defined as a closed loop kinematic chain
mechanism whose end effector is linked to the base by several independent kinematic chains. The classification of
various parallel manipulators is presented herewith. The prime focus of the paper is to realize the parallel manipulators
applications for industry, space, medical science or commercial usage by orienting manipulator in the space at the high
speed with a desired accuracy.
Keywords: Parallel Manipulator; Hexapod; Reconfigurable Parallel Robot; Delta Robots
1. Introduction
Parallel manipulators are widely popular recently even
though conventional serial manipulators possess large
workspace and dexterous maneuverability. The basic
problems with serial one are their cantilever structure
makes them susceptible to bending at high load and vi-
bration at high speed leading to lack of precision and
many other problems. In this paper, parallel manipulators
advantages over the serial one are compared. Hence, in
applications demanding high load carrying capacity and
precise positioning, the parallel manipulators are the bet-
ter alternatives and the last two decades points to the
potential embedded in this structure that has not yet been
fully exploited. Willard L. V. Polard [1] designed and
patented the first industrial parallel robot as shown in
Figure 1. The development of parallel manipulators can
be dated back to the early 1960s, when Gough and
Whitehall [2] first devised a six-linear jack system for
use as a universal tire testing machine. Later, Stewart [3]
developed a platform manipulator for use as a flight
simulator. Since 1980, there has been an increasing in-
terest in the development of parallel manipulators. This
paper highlights the potential applications of parallel
manipulators include mining machines, walking ma-
chines, both terrestrial and space applications including
areas such as high speed manipulation, material handling,
motion platforms, machine tools, medical fields, plane-
tary exploration, satellite antennas, haptic devices, vehi-
cle suspensions, variable-geometry trusses, cable-actu-
ated cameras, and telescope positioning systems and
pointing devices. More recently, they have been used in
the development of high precision machine tools [4] by
many companies such as Giddings & Lewis, Ingersoll,
Hexel, Geodetic and Toyoda, and others. The Hexapod
machine tool [5,6] is one of the widely used parallel ma-
nipulators for various industries.
2. Serial vs Parallel Manipulators
Parallel kinematic manipulators offer several advantages
over their serial counterparts for certain applications.
Figure 1. Pollard’s spatial industrial robot [1].
*Corresponding author.
opyright © 2012 SciRes. MME
Among the advantages are greater load carrying capaci-
ties as total load can be shared by number of parallel
links connected to fixed base, low inertia, higher struc-
tural stiffness, reduced sensitivity to certain errors, easy
controlling and built-in redundancy but smaller and less
dexterous workspace due to link interference, physical
constraints of universal and spherical joints and range of
motion of actuators and suffer from platform singularities.
The abundant use of multi DOF spherical and universal
joints in parallel manipulator not only simplify the kine-
matics, but they also make sure that the legs in the Stew-
art-Gough platforms [7] experience only compressive or
tensile loads, but no shear forces or bending and torsion
moments. This reduces the deformation of the platform,
even under high loads. The fully parallel designs of ro-
bots have all actuators in or near the base, which results
in a very low inertia of the part of the robot that has actu-
ally to be moved. Hence, a higher bandwidth can be
achieved with the same actuation power. This is why
parallel structures are used for, for example, flight simu-
lators and fast pick-and-place robots. Parallel architecture
is always lucrative for many practical applications to
improve robot performance beyond the reach of serial
manipulators as apparent from Table 1. Parallel kinematic
robots have another structure. From the fixed base, a
number of arms and links are coupled in parallel to the
Tool Centre Point. All drive motors/gearboxes can then be
located on the fixed base are used for drilling, welding,
tapping with greater accuracy and repeatability. In par-
ticular, parallel manipulators with fewer than six degrees
of freedom have recently attracted researchers’ attention,
as their employ may prove valuable in those applications
in which a higher mobility is uncalled-for. Arms/links can
then be lightweight and very stiff, minimizing inertia. Ball
joints means link loads restricted to pure tension/compres-
sion, further improving the stiffness/mass ratio. Errors will
not be amplified throughout a parallel structure.
For a parallel kinematic mechanism, the kinematic
equations will be considerably more complex due to the
closed kinematic loops, than for an open (serial) kinematic
structure. Parallel manipulators are also termed as closed
loop manipulators. For development of high performance
robots, models will be required for simulation and per-
formance prediction, and for model based compensation in
the control system to obtain advanced performance. Any
mechanical systems composed of conventional joints, tra-
ditional parallel manipulators suffer from errors due to
backlash, hysteresis, and manufacturing errors in the joints.
In contrast to serial manipulators, there can be presence of
un-actuated or passive joints. The presence of passive
joints and multi-DOF joints makes the kinematic analysis
very different from kinematic analysis of serial manipula-
tors. Direct kinematics is much harder & involves elimina-
tion of passive joint variables in parallel kinematics.
Compare to direct kinematics the inverse kinematics is
much simpler in parallel manipulators. Parallel robots are
intrinsically more accurate than serial robots because their
errors are averaged instead of added cumulatively due to
many parallel links as well as closed loop architecture.
These robots possess many intrinsic characteristics over
serial robots, hence lot of scope of applications in near
future in various fields can be envisaged.
Table 1. Comparison between parallel and serial manipulators.
Type of manipulator
Parallel manipulator Serial manipulator
Type of manipulators Closed loop Open loop
End effectors Platform Gripper
Natural description In Cartesian space In joint space
Location of actuators Near the immobile base On the links
Inertia forces & stiffness Less and high respectively High and less respectively
Design considerations Structure, workspace considerations,
singularities, link interference
Strength and stiffness considerations,
vibration characteristics
Preferred property Stiffness Dexterity
Use of direct kinematics Difficult and complex Straightforward and unique
Use of inverse kinematics Straightforward and unique Complicated
Singularity Static Kinematic
Direct force transformation Well defined and unique Not well defined; may be non-existent,
unique or infinite
Preferred application Precise positioning Gross motion
Copyright © 2012 SciRes. MME
Classification of Parallel Manipulators
Symmetric Planar Spherical Spatial
Symmetrical manipulators has number of limbs equals to
number of degree of freedom, which is also equals to
total numbers of loops. A planar parallel manipulator is
formed when two or more planar kinematic chains act
together on a common rigid platform. Now days, each
leg of a planar parallel manipulator is replaced by a
single wire, the manipulator is referred to as a planar
wire-actuated (or wire-suspended) parallel manipulator.
Spherical manipulators are just able to make the end ef-
fectors movement according to controlled spherical mo-
tions. Especially, spatial parallel manipulators with fewer
degrees of motion than six, but more than three, attracted
the attention of both, the researchers and users.
In the most of the research work, kinematic analysis is
carried by either kinematic constraint equations, screw
theory method, DH Parameters or using the concept of
dual unit quaternion which is really a most efficient for
representing screw displacements of lines for spatial ma-
nipulators [8]. Using the inverse dynamics, the forces
and torques of the actuated joints can be computed for
closed loops configurations of parallel architecture. As
per the literature review, Newton Euler approach is rela-
tively more economical compared to Euler Lagrange
formulation for parallel as well as hybrid manipulators.
3. Industrial Applications
In 1942, a patent was issued to Willard L. V. pollard [1]
for his novel design of automatic spray painting. In fact,
it was never built. It has five degree-of-freedom mo-
tion—three for the position of the tool head, and the
other two for orientation. In 1954, Dr. Eric Gough, an
employee of Donlop Rubber Co., England had developed
a six degree of freedom—the first octahedral hexapod for
universal Tyre Testing Machine [2]. In 1965, Stewart
published a paper in which he proposed a six degree of
freedom parallel platform as a flight simulator [3]. The
Stewart platform comprises six pods, six spherical joints
and six universal joints with 6 degree of freedom as
shown in Figure 2 [9]. Stewart platform has also been
used for the Agile Eye (a spherical Parallel mechanism)
—pointing devices developed by Gosselin and Hamel
[10] at robotics laboratory at Laval University, Canada,
has low inertia and inherent stiffness, the mechanism can
achieve angular velocities superior to 1000 deg/sec and
angular accelerations greater than 20,000 deg/sec2, large-
ly outperforming the human eye. An American engineer,
Klaus Cappel is considered as a third pioneer in field of
parallel robotics. He has developed an octahedral Hexa-
pod Manipulator as motion simulator & was patented in
1967 as shown in Figure 3 [11]. Stewart Platform is also
used for underground excavation device by Arai in 1991
and another application such as milling machines by
Aronson in 1996.
3-DOF spherical parallel mechanism [12] as shown in
Figure 4 has interesting characteristics for practical ap-
plications like worktable, a manipulator, a camera ori-
enting device, a wrist or a motion simulator. Parallel
Robots can offer many advantages for high-speed laser
operations as shown in Figure 5 due to their structural
stiffness and limited moving masses with less power
consumption [13].
Figure 2. Typical Gough Stewar t platfor m [9].
Figure 3. First design of an octahedral hexapod for flight
simulator (courtesy of Klaus Cappel) [11].
Figure 4. Three DOF spherical parallel manipulators [12].
Copyright © 2012 SciRes. MME
Figure 5. Three RUU kinematic chains usage in delta robot
for laser cutting [13].
Figure 6 depicts the parallel cube-manipulators [14]
have characteristics of no singularities in the workspace,
simple form of forward kinematics and existence of a
compliance centre x = y = z = 0 with a added advantages
of high stiffness and compactness used in the fields of
micro-motion manipulators, remote center compliance
(RCC) devices, assembly, planar kinematics machines
and so on.
3.1. Hexapod
The hexapod is one form of parallel manipulator that is
used increasingly in manufacturing, inspection and re-
search. The ultimate hexapod would provide large mo-
tions for massive payloads in up to six degrees of free-
dom with high accuracy, resolution and repeatability.
Recently, during the inverse kinematics error simulation
results indicated that hexapod machine tool could be po-
sitioned with an error less than 0.03 mm and could be
oriented with an error less than 0.000003 rad. The Figure
7 shows hexapods with various actuators with range in
size from 130 mm to 3 m, with load capacities between
0.5 and 1500 kg.
3.2. Delta Robots
3-RPS mechanism is utilized in the machine tool, which
was analyzed using Bezout’s elimination approach for
solving trigonometric non linear equations by Meng-
Shiun Tsai et al. [16] during their research work. The
hybrid machine tool developed by Industry Technology
Research Institute (ITRI) is shown in Figure 8 using the
stated 3-PRS mechanism. The configuration shown in Fig-
ure 9 is utilized as a 3-axis PKM for drilling-tapping
machine tool for point to point high speed accurate con-
trol. Same concept was applied to a machine tool proto-
type developed by Renault Automation Comau, France
with a velocity of 120 m/min. Parallel or delta robotics is
used mainly in the packaging industry, in working with elec-
tronic components, and in the medical and pharmaceutical
Figure 6. Cube manipulators [14].
Figure 7. Hexapods using piezoelectric, electromagnetic and
motor-driven screw actuators [15].
Figure 8. The machin e tool designed by ITRI in Taiwan [16].
Figure 9. Use of linear drives in delta structure for 3-axis
parallel machine tool [17].
Copyright © 2012 SciRes. MME
industries. Most of the time delta robotics is mounted in a
hanging position. This will allow the effector arm to ex-
tend down to a work area, like a conveyor belt. The robot
is made up of two bases, one larger and one smaller. The
smaller end is where all the work is done. These two
platforms are connected by the linkages. Each of these
linkages is powered by a single motor. The linkages are
attached to the main base by a universal joint. This gives
the linkages a great deal of flexibility in the range of
movement, provided it is in unison. The latest versions of
delta robotics have been designed to reduce maintenance
and cleaning. They have been given a smaller footprint
so that occupied space can be kept to a minimum. Vari-
ous styles of delta robots have been created, such as the
stainless steel model that allows for easy wash down
when used in food applications. In sort, this type of con-
figuration is widely applicable as a sorting and collating
in various types of packaging and food industry. Figure
10 shows “FlexPicker”, a 3- or 4-axes axis pick and place
parallel robot for handling of drugs, food, electronic
components etc developed by ABB [18].
As shown in Figure 11, the table tennis game can be
played with a visual feedback using parallel manipulators.
Lagrangian’s dynamics is used for its dynamic analysis
and simulation.
4. Reconfigurable Parallel Robot
A reconfigurable parallel robot consists of a set of inde-
pendently designed modules, such as actuators, passive
joints, rigid links (connectors), mobile platforms and
end-effectors that can be rapidly assembled into various
configurations with different kinematic characteristics
and dynamic behaviors.
Cable-Driven Robots
There are several applications of cable-suspended manipu-
lators [20] such as; Cutting, Excavating and Grading, Shap-
ing and Finishing, Lifting and Positioning, Flexible Fixtur-
ing, cleanup of disaster sites, access to remote areas, ma-
nipulation of heavy payloads. Cable-direct-driven robots
(CDDRs) are a type of parallel manipulator wherein the
end-effector link is supported in-parallel by n cables with n
tensioning motors. Cable-driven robots are very attractive
because of their capabilities for high payloads (comparable
to construction cranes), large range of motion, rapid de-
ployment and easy reconfiguration.
One of the biggest application areas of cable-sus-
pended robots is cargo handling. The idea of a Stewart
platform is replicated in a cable suspended robot as shown
in Figure 12 at University of Delaware. Figure 13 shows
spatial design of 7-cable-suspended robot, with closed
form forward pose kinematics, for automated machining,
construction, sculpting, and related applications. S. La-
houar et al. [22] have determined the new method of col-
lision detection between cable and object recently.
Figure 10. “FlexPicker” [18].
Figure 11. Prototype of robot tennis system [19].
Figure 12. Cable-suspended robot designed and assembled
at University of Delaware [20].
Figure 13. Seven-cable robot with 6-cable passive metrology
(2004) [21].
Copyright © 2012 SciRes. MME
5. Space Applications
Figure 14 shows the Canterbury satellite tracker [23]
system uses parallel mechanism for better orientation.
Now days, the scope of parallel manipulators for spatial
applications is lucrative for researchers. The reconfigur-
able parallel robot (Figure 15) is developed at National
Research Council of Canada for purpose of exploring its
space applications. The robot is made up of two modular
units: 1) slide: a three-DOF prismatic joint system with
fixed-leg length 2) swing: a three-DOF revolute joint
system. The design allows emergency behavior lead to
the saving in building, launching and operating costs for
space applications. The reconfigurable configurations are
considered as part of ultimate intelligent systems.
6. Medical Science
N. Sima’an et al. [21] had investigated best fits robot for
medical applications using parallel architecture. The RSPR
robot is best suitable compared to URS and double cir-
cular triangular robot due to reduce actuator forces &
singular positions. The kinematic structure of Hexapod
robot shown in Figure 16 provides 6 DOF with working
area of 100 × 100 × 50 mm and 15˚ rotation with position
accuracy of 20 µm for different kinds of surgical instru-
ments [25]. The other applications may include in neu-
rosurgery, ENT, Ophthalmology, Spine surgery and or-
thopedics for total knee and hip replacement surgery. The
application of the mechanism shown in Figure 17 was
inspired by the human biological elbow operation and it
was intended to be a medium to seek for functional res-
toration in patients with transhumeral amputation.
3-PUU translational parallel manipulator concept is
used in CPR for chest compression as a rescue breathing
with compression frequency of 100 times per minute as
shown in Figure 18. The same parallel manipulator De-
sign problems for human-machine interfaces are consid-
ered for end-effectors in cable-based parallel manipula-
tors in physiotherapy applications [28] as shown in Fig-
ure 19 developed at the Robotics & Mechatronics Labo-
ratories of the University of Padua, Italy. Parallel robot
architecture for Ultrasound 3D systems are being devel-
oped by Simon Lessard, Ilian Bonev and Pascal Bigras to
potentially replace traditional 2D equipments in the di-
agnosis of vascular disease using multiple 3D ultrasound
examinations on a human patient [29]. Parallel manipu-
lator usage in self propelling endoscope with hydraulic
actuation is noteworthy. Moreover, 3DOF ISOGLIDE3
as a parallel manipulators are developed with fuzzy and
PID controller for clinical use [30].
7. Miscellaneous Applications
Some applications require service robots that are capable
of moving along a vertical plane e.g., wall painting,
Figure 14. Satellite tracker [23].
Figure 15. The re-configurable parallel robot [24].
Figure 16. Use of Stewart platform for precision surgery
Figure 17. Elements of prosthesis using parallel topology
with 3 line actuators [26].
Copyright © 2012 SciRes. MME
Figure 18. Conceptual design of Cardio-pulmonaryresus-
citation (CPR) operation [27].
Figure 19. MariBot—a platform for upper arms using ca-
ble-based parallel manipulator [28].
window washing, non-destructive testing (NDT), sur-
veillance, etc. Ship cleaning/inspection, Welding robot,
Airplane cleaning and inspection, Oil tank inspection,
Nuclear plant inspection, Steal bridge inspection, Clean-
ing and Inspection of glass wall and inspection of pipes
with ultrasonic probe in chemical plants.
NINJA-1 is composed of legs based on a 3D parallel
link mechanism capable of producing a powerful driving
force for moving on the surface of a wall or glass. Weld-
ing tasks at time of assembly as well as during mainte-
nance are accomplished using a hybrid parallel robot
developed for an international thermonuclear experi-
mental reactor (ITER), which is a Vacuum Vessel.
8. Conclusion
Several parallel mechanisms have been conceived and
investigated in the last two decades. Automated welding,
grinding, cutting, inspection, material handling, pipe fit-
ting, oil-well fire fighting, ship building, bridge construc-
tion, air craft maintenance, ship-to-ship cargo handling,
steel erection, etc. are the various areas of applications.
Many prototypes of innovative manipulators and ma-
chine based parallel architecture have been built and
presented in literature. One of the basic features of paral-
lel mechanisms like Stewart platform, Hexaglides, hexa-
pods and delta robots consist of suitable behavior for
dynamical applications where high speed operation makes
important the dynamics of the system. Because of the
stated advantages, with the applications of micromachi-
nes running at very high speed, mechatronics and parallel
structured manipulators in medicine are widely spread in
clinical use. Deep-sea maintenance of oil and gas facili-
ties can be improved and be more effective by explora-
tion of parallel manipulators applications in this area.
Wire driven parallel robotics pay attention for the space
applications for current state of research. A continued
and incessant effort by researchers will grow and evolve
in increasing the capability and effectiveness of various
parallel robotics applications to push towards new ho-
rizons for robotic industry.
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