FYP Mechanical

HAPTIC MANIPULATOR
SIX DEGREE OF FREEDOM DESIGN AND BUILD
Ali tayebisadrabadi
School of Mechanical Engineering,University of Birmingham,Birmingham,United Kingdom
Abstract: This paper addresses the design modification of a haptic device containing six degree-of-
freedom (6-DOF). The structure composes of three prismatic joints to create linear motions as well as
three rotary joints for rotational motions. Six joints enable the haptic device to control a parallel robot.
Different topologies are investigated and designed, where stability and ease of planning the path are
considered. Based on critical evaluation, finite element and dynamic analysis, combination of three
prismatic followed by three rotational elements provide the optimum design. Design and build of an
existing manipulator were validated and improved using finite element analysis (FEA). Obtained results
are used to improve the design in order to reduce stress created by external forces. Dynamic analysis
developed demonstrates the calculation for particular motion forces that are required in the system. The
diameter of the pinion is optimized to convey a design that is extensively user friendly, as well as
having enough strength for motions. Also a new design and build was proposed using the same
topology with different material. Finite element and dynamic analyses were also carried out on this
design, and the new haptic manipulator was constructed. The two designed and built robots were
compared in terms of performance, and their behaviour is discussed.
Keywords: Haptic manipulator, Topology, Optimum design, Finite element analysis .
1 INTRODUCTION
The aim of this project is design development of 6-
DOF haptic robot for controlling of parallel robots.
Larger work volume, simpler structure to be
prototyped as well as having a design that is more
economical and light-weight compared to previous
designs were constantly considered during the
research procedure. In order to achieve this aim, the
initial objective is to review the current state of the art
to be able to highlight the importance of this research
as well as finding the methods used in previous works
in haptic design and build field. The shortcomings of
previous works enabled the researcher to evaluate the
topology combinations commonly used in practice
and study of an existing design and build as the next
objective. This is followed by proposal of a new
design and build that is referred to as the improved
design. The final objective is to compare the two
designs as well as pinpointing the improvement in
built haptic manipulator.
As mentioned before haptic manipulators are used
to control parallel robots, which are used in several
applications. Most of these applications are
categorized in industrial segment. Rehabilitation
robots are among these applications for master and
slave robots where 3 or 6-DOF haptic controllers are
used [1]. With respect to the applications of 6-DOF
manipulators in minimal invasive surgery and totally
computer aided surgeries [2, 3], the quality of
performance of these robots is of significant
importance. Medical surgery is one of the applications
that allow the operator to be in a different place; as an
example laparoscopic surgery can be mentioned [4].
Different designs were developed for particular
applications since 1940s [5, 6], for instance Tele-
operation as a new method is also considered in
medical surgery which can be conducted employing a
6-DOF serial robot mentioned in works by Hung &
Na [7]. Multi-DOF manipulators can easily simulate
new methods and provide remarkable characteristics
for modern surgeries [4], however, these applications
are not the aim of this research and therefore are not
further elaborated. The aim constantly requires
stability, strength and light-weight structure of the
manipulator to control the parallel robot more
efficiently to fulfil its requirements for the
applications mentioned above.
As haptic device is one of the useful tools to control
the robots; especially parallel robots; complex

HAPTIC MANIPULATOR
SIX DEGREE OF FREEDOM DESIGNAND BUILD
Email address:axt139@bham.ac.uk(Ali Tayebisadrabadi) 2
kinematic of parallel robots is the reason for
investigating various methods of control. Therefore,
the designs of most of haptic structures are usually 3
or 6-DOF in parallel mechanisms. The haptic devices
are robots with human interface in order to sense
control feedback created by motor force in the system,
for instance, feedback linearization with traditional
feedback linearization (TFL) approach is mentioned in
works by Yang et al [8]. Developed feedback system
is used for path planning of parallel robots [8]. Haptic
devices create communication path between human
and robot that would make user aware of any
limitations and singularities throughout the path
motion [9].
One of the important concepts in this research is
linear motion. 6-DOF serial robot for haptic
application require three linear and three rotational
motions respecting to fixed coordinates on the base of
the system. There are different topologies and
methods to create the linear and rotational motions of
the system. The linear motions can be created by
linear actuator, motor and lead screw, and motor and
rack and pinion. Comparing various elements to be
used in design, the lead screw cannot be easily moved
using the linear force. It is difficult for user to move
the structure by exerting torque to the system. On the
other hand, linear actuator needs high power for
motion and is also expensive for properties that are
necessary to be considered in design. In this case the
best option for moving the structure in both ways
(motor and user) which is also economical is the rack
and pinion Figure 1.a) shows ball screw mechanism
and figure 1.b) simply demonstrates rack and pinion
and its movement.
Figure 1: a) ball screw elements [10], b) rack and pinion [11]
Another important concept considered in validation of
design is the motor. Motor is an important part of
every designed device. Direct current (DC) motor and
servo motor are two well-known types of motors for
controlling. Servo motor’s input is angular motion that
the motor requires to rotate, controlled by macro
controller; where DC motor generates more power as
well as being smaller in size and also being more
economical. The input of this type of motors is
voltage that causes difficulty of control with high
accuracy requirements.
For this particular research, the work undertaken is
compared to an existing haptic robot built in the
robotics laboratory, in school of mechanical
engineering, the University of Birmingham. In this
section the previous work covered in the related
literature is briefly introduced, followed by the
specifications of the existing robot in the robotics
laboratory.
One of the most important aspects of haptic
manipulators is topology chosen for design. There are
various combinations of joints in 6-DOF manipulators
which are used to control parallel robots. Based on the
current state of the art, there are various aspects of
topology covered; such as design and manufacturing
of 6-DOF manipulators for industrial application [12],
different methods and approaches for control of 3 and
6-DOF by various researchers, study of
manipulability, static condition and power
consumption initiated, with the purpose of
optimization and finally kinematic conditioning index
in micro surgical manipulators, which shows the
effect of rotation or translation in performance
increment [13].
The important factor is the control procedure that
varies based on design approach; which is simpler in
cobotics compared to robotics [14].As an example
adaptive controller in system identification for
Hexaglide can be mentioned [15]. The accuracy of
control over robot is enhanced considering the
environmental effects on the motion, [16];
temperature and pressure are two environmental
factors which are explained in methodology section.
There are other methods such as Sobh et al who
proposed a 6-DOF manipulator as software package
for personal computers [17]. However, number of
degrees of freedom and application purposes are the
key factors for design of haptic devices. There are
number of researches that have considered different
structures of 6-DOF robots for various applications.
These consider the flexibility and low-weight
structure of such devices to enhance the efficiency of
a)
b)

HAPTIC MANIPULATOR
the system [18, 19]. In general, the design needs to be
user friendly as well as fulfilling stability
requirements. On the other hand, the design needs to
be developed based on economical material choice;
that provides sufficient yield stress in order to move
through the motion with high accuracy.
Prior to all these factors, planar parallel robots were
used in design and optimization of workspace
determination with respect to global dexterity
variation [20]. Ueberle and Buss presented a design
optimization for VISHARD 6 in modularity,
workspace and force capacity using experimental
information [21]. The same rules were applied to
define an optimized model for a haptic interface
device and consequently, FEA was conducted to
validate the design [22]. Borras also implemented a
characterization on topology of the singularity
locations while corresponding to uncoupled motion in
the workspace [23]. Besides, they conducted a
topology optimization considering workspace
limitation or interference in leg [23]. Generally with
forward and inverse dynamics of manipulators,
Jacobian matrix can be estimated and design
parameters for kinematic analysis can be evaluated
through workspace, as well as global maximum force
and global isotropic indices [24].
The parameters considered in design are able to
identify the singular points of the parallel robot and
optimum path motions. In other studies relative
optimizations for 6-DOF haptic manipulators were
considered [25]. Based on research by Yoon and Ryu
a rotary rotary rotary (RRR) joint combination was
employed to achieve better workspace in parallel
manipulator. The study also indicates use of forward
and inverse dynamics for mobile joysticks and three
connecting bars that lead to more appropriate
estimation of Jacobian matrix calculation [26].
Geometry and design optimizations were also
observed in Delta parallel manipulator by Kosinska
[27], where optimum design method that satisfies the
desired workspace orientation at the boundary of the
translation was investigated. As it is described, and
with respect to complicated dynamics of any new
robotic system, there are different types of dynamic
restrictions which lead to optimization of topology
definition.
The review of current state of the art results in
motivation for the researcher to study the wide range
of available designs for 6-DOF manipulators that
could be used in control of parallel robots. Different
design features were considered to obtain the optimal
design and consequently finite element software
employed for final design validation. These are
presented in methodology section. It is proposed that
topology optimizations should be conducted first,
followed by validation using finite element software
that eventually assists in manufacturing procedure to
be launched for prismatic prismatic prismatic rotary
rotary rotary (PPPRRR) model. The results of analysis
and discussions are presented in sections 3 and 4,
respectively. The concluding remarks of this research
are elaborated in section 5, followed by
recommendations for future researches in this area.
2 METHODOLOLOGY
In this section, the objectives are explained. Firstly the
topologies were studied and investigated, where
crucial parameters that are necessary for the required
application were evaluated against each other.
Stability, user friendly performance and ease of
identification of the measure of the motion are among
the important parameters that are investigated based
on different possible topology combinations for 6-
DOF. Secondly, FEA is applied on possible selected
topologies to identify the weakness of the system in
order to select the most practicable configuration for
the desired application. Three topologies are designed
by computer aided design (CAD) software for more
investigation. The next stage is evaluation and
improvement of design of the existing manipulator
and finally, the new design and build is explained.
The concepts and parameters affecting the design and
build used in the methodology are explained in the
following paragraphs.
The design of the system in this research is improved
to increase the stiffness and stability. Dynamics of the
models are simulated by the use of SolidWorks to
identify motor power for particular motion. Applying
the motors to the assembly designed in
SOLIDWORKS will simulate the torque exerted by
motors through the motions as well as position of
end effecter based on defined coordinate in the
CAD model. In this section performance of
motors is analysed via operation to define the
optimum speed and force through the motion.
The important component in assembly is gear
transferring the force from motor. Size of gear
diameter is optimized to increase the system
performance.
The product design specification (PDS) of the system
is provided in the following sections as performance,
environment, maintenance, size and material.
Moreover, topology investigation, CAD model, FEA,

HAPTIC MANIPULATOR
dynamic simulation and design improvements are
covered in following sections where the results are
presented in section 3.
Performance
Based on review of literature it is investigated that
in terms of performance the haptic device should have
six degree of freedom to support the simulated
motions. The motions include three translational and
three rotational motions about the coordinate system.
There should be low friction between the parts to
make the motion as smooth as possible.
Environment
Environment includes temperature and pressure. The
best temperature range for human interface is 20 to 35
C0
. The pressure range suggested for this study is
between 0.7 to 2 atm.
Maintenance
Maintenance of the system is controlling constrains
and connections between the parts in order to prevent
vibration and collapse of the system.
Size
Based on the application requirements, the required
motions in x, y and z are provided in table1.
Table 1: The required translation and rotation motions
Material
The weight of the model is important in order to
make the system user friendly for motions provided.
Apart from the weight, the strength of material used in
construction is also important in order to provide
enough stiffness for the system. In Cartesian robots,
controlling the Z-axis is the most difficult part of the
design. According to the literature review, the applied
material for these robots can be variable based on
more specific requirements, budget and availability. In
this case the aluminium elements were available in the
robotics laboratory. The existing manipulator is also
assembled and built using aluminium elements.
However, the new proposed design and build material
changed to Polytetrafluoroethylene (PTFE).
2.1 Topology
As mentioned in PDS, various topologies can be
used for designing 6-DOF robot. The advantages and
disadvantages of different topologies are indicated in
Table 2, in results section. P and R notations represent
prismatic and rotational joints, respectively. Different
topologies are compared in terms of stability,
workspace, user feedback, weight, motor power,
kinematic complexity, path planning and user friendly
performance. These are the critical factors in
assessment of efficiency and performance of the
design and build of haptic manipulator that are
selected based on current literature. Stability of the
systems is determined by capability of the model to
stay in position after motion. In most cases, two
rotational components connected in series in the base
of the system reduce the stability. User feedback is a
parameter that is most important for the user in order
to recognize the motion imported to the model.
The weight of the system is based on the component
sizes while the material used for construction of
components is assumed to be the same for all the
topologies. Different required parts for each
configuration is modelled in SolidWorks. The assign
material for all parts is the same. Therefore, the
weight of each component can be obtained by
software based on size and volume of the parts.
Therefore, the weight of each configuration could be
estimated by allocating the required parts
Motor power that is required in the system is
obtained by considering applied force (especially
weight of the structure) on each axis. . In this
investigation, the axis having more applied force is
considered for each topology. Previously the weight
of each topology and weight on each axis was
determined by SOLIDWORKS software. Therefore,
the minimum power required for a motor is the weight
of components in that direction. For the listed
topologies the weight of system effects mostly on
translation motion in Z-axis and rotation motion
around X and Y-axes. Kinematic of each topology is
developed by considering the rotational and
translational motions and order of joint positions.
However, the important factor for inverse kinematic
methodology is identification of the boundary
condition and motion limitation of each joint.
Calculating the amount of joint operation is much
more challenging for complex structures. The
elements of the motion matrix should be determined
in order to find the position of end-effector; which
makes it difficult for the user to follow the desired
path. Path planning is the complex factor that is
needed more investigation. However, in topologies
that the rotational components are placed as the base
of system will effect on translational motion that make
Direction Translation
Motions
Rotational
Motions
X 150 mm 360o
Y 150 mm 360o
Z 100 mm 360o

HAPTIC MANIPULATOR
them different with the value expecting by the user.
End effector position is not accurate with the user
motions User-friendly performance is a parameter
used to identify ease of use of the system by the
operator. Refer to section 3.1 for topology results.
2.2 Finite element analysis of topologies
The FEA of the three topologies which were found
as most suitable for this application was developed in
SolidWorks. In the models the force applied to each
system is based on the direction of motion that user
could exert to that. Boundary conditions of
simulations are assumed to be the same for all three
topologies. The results of FEA are presented in
section 3.2.
2.3 Dynamic analysis of topologies
In order to carry out dynamic analysis, Motion
applied on all configurations to achieve motor
properties. The simulation results are presented in
section 3.3.
2.4 Design improvement of existing manipulator
Finite element and dynamic analyses were
carried out on three selected topologies. The existing
haptic manipulator in robotics laboratory of
University of Birmingham is a PPPRRR combination
that is already built (figure 2. a). As FEA was
performed on this robot, based on results obtained, it
was concluded that the robot can be modified to
improve its performance. Among the problems
encountered in practice two main ones can be
highlighted: 1) the weight of the components of this
robot cause a lot of stress and bending momentum on
the system and 2) also the z-axis motor is not
powerful enough to crate movement in this direction.
The changes in design include changing the position
of Z-axis in the structure to distribute the bending
momentum on the whole structure. Also unnecessary
components were removed from the model to reduce
effect of the weight in Z direction. And finally the
total size of the system in X and Y directions were
reduced to decrease the volume of the model in order
to make it more user friendly and more importantly
decrease the bending momentum effect.
Figure 2: a) existing manipulator, b) improved design
2.5 New design and build
As many problems were encountered in the existing
built manipulator, a new design and build was
proposed.In the new design redundant material was
omitted from the structure.It is demonstrated in figure
3. As it can be observed the weight along the Z-axis
was significantly reduced from 0.11 to 0.065
kilograms by considering the same material.
The FEA was applied on the new design in order to
validate the stiffness through the motions of this
model. Results of FEA are presented in section 3.5.
Figure3: New design with reduced weight along Z direction.
a)
b)

HAPTIC MANIPULATOR
3 Results
3.1 Topology
Factors investigated for different topologies are
defined in previous section. The summary of factors
and twenty two prismatic and rotary combinations
used for haptic manipulator application are presented
in Table 2. The numbers are estimations based on
review of literature. The resultant of all these factors
is presented as the total value. Based on the results of
the total value, three topologies which are most
suitable were considered and further investigated.
The comparisons are presented in the following
sections.
PPPRRR
In this combination, three linear motions are
designed as the base of the system while the
rotational elements are attached on the top. The main
advantages of this system are stability and high
accuracy in managing the motion. However, putting
the rotational parts on top of the system makes the
motion more difficult in Z direction due to high
amount of load applied on it.
Table 2: result of topology comparisons
RPPPRR
In order to reduce the weight of the system in Z
direction in PPPRRR model, rotational part around Z
direction is allocated in the base of the system.
Putting rotational part in different positions of design
reduces the accuracy of motions as well as user
friendly factor. Another drawback is that high power
motor is required to rotate the system around Z axis
due to additional weight of the system and friction
force created between parts.
RRRPPP
Putting all rotational parts in bottom of design as
the base makes the motions in Z direction smoother
by a significant amount; however the stability of
design is drastically reduced. As the kinematic of
the system changes in this configuration,
identification of the amount of translational motion
would be more challenging for the user.
Topology Stability Workspace User
feedback
Weight Motor
power
Kinematic
complexity
Path
planning
User
friendly
Total
score
PPPRRR 7 4 8 6 5 5 8 8 51
PPRPRP 5 4 3 3 3 4 3 3 28
PPRPRR 5 3 3 4 2 4 3 3 27
PPRRRP 5 4 5 5 4 4 4 4 35
PRPPRR 5 4 3 4 3 3 3 3 28
PRPRPR 2 4 3 4 4 3 3 3 26
PRPRRP 4 4 3 3 3 4 3 3 27
PRRPPR 3 4 2 4 4 4 3 3 27
PRRPPR 4 4 3 2 2 3 3 4 25
PRRPRP 3 4 4 3 4 3 3 3 27
PRRRPP 5 5 3 2 3 4 4 3 29
PRRRPP 3 4 3 3 3 4 4 3 27
RPPPRR 6 4 5 5 5 5 5 6 41
RPPRPR 4 4 3 2 4 3 4 4 27
RPPRRP 4 4 4 4 5 5 5 5 36
RPRPPR 2 4 3 2 4 2 1 1 19
RPRPRP 4 4 2 2 2 4 1 1 20
RPRRPP 3 4 3 4 4 2 3 3 26
RRPPPR 4 6 4 6 4 3 3 4 34
RRPPRP 3 5 3 5 4 3 3 3 29
RRPRPP 3 6 3 6 3 3 4 3 31
RRRPPP 4 7 5 6 4 5 3 3 37

HAPTIC MANIPULATOR
3.2 Finite element analysis of topologies
SolidWorks results of FEA of the three
topologies of PPPRRR, RPPPRR and RRRPPP are
presented in figure 4. The maximum value of the
force applied on the system is assumed to be 50N.
As the results clearly show,the stress applied to the
system in RPPPRR is less than other
configurations. Detailed figures of this section are
attached in Appendix.
3.4 Dynamic analysis
The dynamics of two different topologies (3P-3R,
R-3P-2R) are analysed while the motion
demonstrating in table.1 is applied in both systems.
Table 3: Applied Motionto configuration
Parameter θ φ ψ X Y Z
Motion 200
200
200
20
mm
20
mm
50
mm
The following motion is applied to R-3P-2R and
3P-3R. As the results shown in figures below, the
motors’ force for R-3P-2R is less than that of the
3P-3R one. In the other hand the motors for
rotational part especially in Z direction is making
advantage for 3P-3R assembly.
The results of motor performance demonstrate in
figures below while motors 1, 2 and 3 are linear
motors in X, Z and Y direction respectively. As
well as rotory motors 1, 2 and 3 are allocating for
motor placing in X, Z and Y directions
respectively.
Figure 5: a) rotational motor PPPRRR, b) linear motor force PPPRRR
Figure 4: FEA of a) PPPRRR, b) RRRPPP and c) RPPPRR
0
10
20
30
40
50
60
0.000 1.000 2.000 3.000 4.000 5.000 6.000
Torque(N.mm)
Time(s)
Rotory Motor 1 Rotory Motor 2
Rotory Motor 3
a)
19.5
20
20.5
21
21.5
22
22.5
23
23.5
24
24.5
0.000 2.000 4.000 6.000
Time (s)
Linear Motor 1
Linear Motor 2
Linear Motor 3
b)
b)
Force(N)
c)a)

HAPTIC MANIPULATOR
Figure 6: a) rotational motor RPPPRR, b) linear motor RPPPRR
The weight of component for assembly
(PPPRRR) in z direction is 0.40 kilograms. The
weight of components on assembly (RPPPRR) is
0.14 kilograms. The weight on Z direction is
reduced by 65%.
However, put the rotation part as a base changing
the direction coordinate system for linear motions.
That causes difficulty for the user to identify the
desire motion in XY plan. The comparisons of
FEA, dynamic analysis and adjustability for haptic
application make the 3P-3R the best topology
rather than others. The most crucial key for the
considered topology is reducing the weight in Z-
direction
3.4 Design improvement of existing manipulator
As explained in section 2.4 the existing built
robot was analysed and improved. Investigation of
the design revealed that large quantity of weight of
the structure applied on the system in Z direction
has caused high amount of pressure on the motor;
also making motion in Z direction difficult for the
user. Therefore, apart from modification of the
existing result (figure 2.b), a new design and build
was proposed.
3.5 New design
The FEA carried out in SolidWorks with the
purpose of stiffness profile through motions. As
figure 8 shows, the applied pressure on the system
has reduced in this design compared to the existing
manipulator. The stiffness of the system has
increased due to weight reduction. In this particular
analysis the effect of gear on the system was
ignored. The assumed applied forces on the system
are weight of the components as well as exerted
user force in different directions which was
considered as 50 N.
The main advantage of this design is reduced
structure volume. As the results of FEA on each
part reveal, reducing the size of the parts increases
the stiffness. Moreover, smaller size in the
assembly reduces effects of created bending
momentum. The results of induced bending
momentum in the system are high amount of
backlash and vibrations when the robot is
operating. Therefore, the accuracy of the system
was reduced for path planning simultaneously
controlling that is required transferring data in
millisecond. Each insignificant error in the data
provided causes unpredictable motions in the robot.
Figure 7: FEA Result of the new design
3.6 Developing Gear features for Z axis
In this section, the diameter of gear used in the
design is investigated with the aim of making the
haptic system user friendly. Size of the gear
diameter is a crucial factor for moving the parts by
the motor and transmitting forces exerted by the
user. The formulation was developed to calculate
0
10
20
30
40
50
60
0.000 2.000 4.000 6.000
Torque(N.mm)
Time (s)
Rotory motor1
Rotory motor 2
Rotory motor 3
a)
0
2
4
6
8
10
12
0.000 2.000 4.000 6.000
Force(N)
Time (s)
linear motor 1 Linear motor 2
linear motor 3
b)

HAPTIC MANIPULATOR
the maximum size of the gear that could be used in
the system based on motor characteristics. The
example presented below is for the existing haptic
manipulator.
The force that gear is able to transmit could be
identified using equations 2.a and 2.b:
𝑇 =
d
2
wt Equation 2. a
𝑤𝑡 =
60×(10)3
×𝐻
𝜋×𝑁×𝑚×𝑛
Equation 2. b
Where,𝑤𝑡 is transmitted load in kN, n is speed
(rev/min), m is module (mm), N is number of teeth
in the gear and H is power in kW that could be
calculated from equation.4.
Combining equations 2.b and 3, transmitted force is
derived in equation.6.
m × N = d Equation 3
Where, d is gear diameter (mm).
H(kW) =
T(Nm) ∗ ω(rpm)
60 ×
1000
2π
Equation 4
Where motor torque is 4.1 kg.cm (0.41Nm) and 𝜔
is 0.21
𝑠
𝑑𝑒𝑔𝑟𝑒𝑒
(44𝑟𝑝𝑚 ).
H(kW) =
0.41 ∗ 44
60 ×
1000
2π
= 1.88 ∗ 10−3(kW)
Equation 5
wt =
60 × (10)3
× 1.88 ∗ 10−3
πdn
Equation 6
wt /Sf ≥ (mg + Ff) × 10−3
Where, 𝑆𝑓 is factor of safety and it is considered as
1.4 in this optimization.
1.4 × 5 × 10−3
≤
0.68
d
Equation 7
𝑑 ≤ 97𝑚𝑚
On the other hand the maximum applied force by
the user is assumed to be 10N for this study.
Therefore, moving the robot in positive direction of
Z-axis is derived from equation.8.
f − mg = m
v2
r
Equation 8
10 ≥ 0.5 × (
0.32
𝑟
+ 9.81)
𝑑 ≥ 16 𝑚𝑚
By comparing the optimum size of the gear
diameter from both points of view, the best size for
the gear diameter is 16 mm.
3.7 Prototype of 6 DOF Robot
In order to design a 6-DOF robot, three actuators
and three rotational motors are needed to make the
desired movements. There are two types of joints
are used in prototype prismatic and rotational
joints. Based on desired application, three linear
motions in X, Y and Z and three rotational α, β and
γ have been considered. This configuration can
make a 6 DOF robot that moving in the whole
space. DC motor is the best choice for rotational
motion according to its power and small size.
However, for linear motions several systems can be
used to transfer the rotational motions of the motor
to linear motions. As it was investigated in
previous section (section 1), the rack and pinion is
used for mention application. The main material
that is used in robot prototype is Teflon that has a
good strength with low weight. The low weight of
the material is crucial factor in the proposed model.
Selected material enhances the performance of
design in Z-axis that was the structural weakness in
previous designs. Material of rack and pinion is
selected steel In order to improve the accuracy of
the system as FEA analysis shows high stress on
this part of design (Fig.7). Fig.8 shows the final
assembly of the prototyped robot.
Figure 8: prototyped Model

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Discussion
The obtained results of FEA and dynamic
simulation reveal the best topology and motor
specification required for current application.
However, in the optimum design the weight on Z
direction reduced to enhance motor performance
working in Z direction. The size of the component
is optimized in order to reduce the bending
momentum on the system creating by user.
Dynamics motion of device simulated by software
in order to identify the motor forces required for
new design. The following study the weight of
components and friction is considered in order to
find the motor force. Figure 9 show the torque and
force that required for allocated position and
orientation respectively.
By comparing the motor torque results by previous
designs that were simulated in section 3.4, the
dramatic reduction of required torque for same
motion with same boundary condition is arguable.
However, the crucial motor reaction is in z
direction. Based on dynamic results the required
force in Z-axis is 5.85N. Comparing the results in
section 3.4 the required force is reduced due to
significant changes in structure of design.
Figure 9: a) Motor Torque for rotational motion
b) Motor force for translation motion
Structure and weight of system have significant
effects on the friction and external force that are
exerted to the system.
Conclusion
This project addresses the best possible
configuration of a 6 DOF serial robot for haptic
application. Different topologies are compared in
case of stiffness and dynamic. However result of
FEA and Dynamics reveal that 3P-3R is the best
possible topology for the considered application.
The modifications applied on the design in order to
enhance the performance of the system. Dynamics
of system was simulated to identify suitable motors
with enough power for motions in X, Y and Z
directions. Calculating the optimum size of gear
radius using in the systemfor transmitting the force
enhances the efficiency of system. The low weight
and low cost model is prototyped for considered
application. However the results of FEA and
dynamic simulation on different design of 3R-3P
topology reveals that the proposed structure has
higher stiffness as well as needing the lower motor
power for particular motions.
Future work and recommendation
Experimental results by providing the particular
path for the system to validate the accuracy of the
design for haptic application. The produced tool for
the control of parallel robot should apply on the
motorized assembly to experiment the haptic
interface.
6. Acknowledgements
First and foremost, thank you God for your
guidance and kindness that has always been with
me.
Many thanks to Dr. Saadat, your unconditional help
and support throughout the entire course, especially
during the research project, made this research
possible. No progress was possible without your
valuable supervision. You continually and
convincingly communicate the spirit of adventure
regarding research.
I would like to express my deep appreciation to Mr.
Che Zulkheiri, whose guidance and help supported
me throughout this year.
In addition, I would like to thank my parents for
their constant motivation and support for my
education
0
5
10
15
20
25
0.000
0.400
0.800
1.200
1.600
2.000
2.400
2.800
3.200
3.600
4.000
4.400
4.800
Torqe(N.mm)
Time (sec)
Motor 1 Motor 2
Motor 3
a)
4.4
4.6
4.8
5
5.2
5.4
5.6
5.8
6
0.000
0.440
0.880
1.320
1.760
2.200
2.640
3.080
3.520
3.960
4.400
4.840
Time (sec)
Linear Motor X Linear Motor Z
Linear Motor Y
b)
Force(N)

HAPTIC MANIPULATOR
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[16] Khan, S., Andersson, K. and wikandeti, J.
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HAPTIC MANIPULATOR
Appendix I
Abbreviation
CAD Computer-Aided Design
DOF Degree-Of-Freedom
P Prismatic
R Rotation
TFL traditional feedback linearization
DC direct current
FEA Finite element analysis
Appendix II
Polytetrafluoroethylene properties
Property Value
Density 2200 kg/m3
Thermal diffusivity 0.124 mm²/s
Young’s modulus 0.5 GPa
Yield strength 23 MPa
Tensile Strength 2,000~5,000 psi
Specific Gravity 2.18
Melting point 621 K
Thermal Expansion 135 · 10−6
K−1
Coefficient of Friction 0.02
Table1
Appendix III
Motor specifications
Gear Ratio 298.1
Unloaded RPM (3V) 34
Unloaded RPM (6V) 70
Unloaded Current (3V) 40 mA
Unloaded Current (6V) 52 mA
Stall Current (3V) 340 mA
Stall Current (6V) 650 mA
Stall Torque (3V) 23.98 oz-in (1727 g-cm)
Stall Torque (6V) 46 oz-in (3313 g-cm)
Length 0.91" (33.1mm)
Width 0.47" (12mm)
Height 0.39" (10mm)
Shaft Size 7mm long; 3mm diameter
Weight 0.35 oz (10.0g)
Table2

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Appendix IV
Finite element analysis
Figure1: PPPRRR

HAPTIC MANIPULATOR
Figure 2: RRRPPP
Figure 3: RPPPRR

HAPTIC MANIPULATOR
Appendix V
Parts which designed in solidworks for topology investigation
(Figure a, b, c, d, e, f, g, h, I, j and k)
a)
b)
c)
d)
e)
f)

HAPTIC MANIPULATOR
k)
j)
h)g)
i)

HAPTIC MANIPULATOR
FEA in some parts applied to improve the design
(Figure a, b and c)
b)
a)

HAPTIC MANIPULATOR
c)

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