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STUDY OF VARIOUS COMPLIANT MICROMECHANISM AND INTRODUCTION OF A COMPLIANT MICROMOTION REPLICATING MECHANISM

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STUDY OF VARIOUS COMPLIANT MICROMECHANISM AND INTRODUCTION OF A COMPLIANT MICROMOTION REPLICATING MECHANISM Powered By Docstoc
					  International Journal of Mechanical Engineering
                           JOURNAL OF MECHANICAL(IJMET),
INTERNATIONAL6359(Online) Volume 3, Issue and Technology © IAEME ISSN 0976 –
  6340(Print), ISSN 0976 –                        3, Sep- Dec (2012)
                                                                     ENGINEERING
                          AND TECHNOLOGY (IJMET)

ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)                                                     IJMET
Volume 3, Issue 3, September - December (2012), pp.574-582
© IAEME: www.iaeme.com/ijmet.asp
Journal Impact Factor (2012): 3.8071 (Calculated by GISI)
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         STUDY OF VARIOUS COMPLIANT MICROMECHANISM AND
    INTRODUCTION OF A COMPLIANT MICROMOTION REPLICATING
                         MECHANISM
                             Bhagyesh Deshmukh1, Dr. Sujit Pardeshi2
     1
      (Assistant Professor, Mechanical Department, WIT Solapur, India, dbhagyesh@rediff.com)
     2
       (Associate Professor, Mechanical Department, Government College of Engineering COEP,
                                 Pune, India, ssp.mech@coep.ac.in)

   ABSTRACT

           In the era of miniaturization, the necessity to design and develop micromechanisms and
   micro-components has increased. Micromechanisms find a wide range of applications in the field
   of medicine, surgery, satellite, spacecraft engineering and telecommunication systems etc.
   Miniaturization inherits along with it various advantages, challenges and issues. Achieving
   precision, accuracy and manufacturing of such systems is a challenging task and these
   parameters drive the performance obtained from the system. Microsystems involve development
   of Micromechanisms for a typical application in order to achieve desired motion/force transfer.
   A compliant mechanism provides a joint less alternative (which overcomes the limitation of
   conventional rigid body mechanism like back lash, lubrication etc.) and is a vital parameter
   which needs to be considered while designing a micromechanism. The current paper is a review
   of various compliant micromechanisms communicated by different researchers and discussion on
   their merits, limitations and applications is included. A compliant pantograph has been proposed
   for a typical application, wherein it is required to replicate as well as amplify the input motion.

   KEYWORDS: Micromechanisms, Replication of motion, Compliant pantograph.

   1. INTRODUCTION

         Miniaturization    has    inherited   the    necessity   to    design     and     develop
   micromechanisms/components and significant research & development activities have boosted in
   this field. Establishment of MEMS technology has further accelerated the need for
   micromanipulation/displacement and micro-positioning. Micro-motion devices are expected to
   deliver high positioning accuracy and potentially have wide applications in the industry like in
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development of Microfactories/Table top precision micro setups etc. Miniaturization is
associated with various advantages and challenges; a smaller system has lower inertia of mass
enabling quick response from the system. The overall performance of the system is an
outcome/result of precise and accurate behavior of various systems/components involved.
However, precision, accuracy and manufacturing of such systems is a challenging task and these
parameters drive the resulting performance obtained. Microsystems involve development of
Micro mechanism for desired motion/force transfer.
       Traditional rigid body mechanisms consist of rigid links connected with movable joints
and are capable of transforming linear motion into rotational or force into torque. These
mechanisms are adversely affected by issues such as friction, wear, lubrication, backlash etc. and
hence these mechanisms cannot be used for precise applications. A new class of mechanisms
known as compliant mechanisms has hence gained significant importance in MEMS.
        Compliant mechanisms [1, 2] are designed to derive mobility from elastic deformation of
particular element (i.e. flexural hinge or a relatively long flexible segment of a mechanism);
which use strain energy to transform input energy components into a desired output
displacement/motion. Compliant mechanisms provide a joint less alternative which overcomes
the limitations of conventional rigid body mechanisms. They are monolithic structures and
require no assembly, however manufacturing them requires selection of appropriate techniques
viz. WEDM, Laser Machining, ECM etc. The current paper is a review of compliant
micromechanisms communicated by various researchers [3-11] and their merits, limitations and
probable applications are discussed. A compliant pantograph has been proposed for a typical
application, wherein it is required to replicate and amplify the input motion.
   1. OBJECTIVES OF CURRENT WORK
      •   To study the micro mechanisms communicated by various researchers [3-11].
      •   To propose another flexure based micromechanism in the family, capable of
          transmitting motion/force linearly and replicating the input motion.

   2. REVIEW OF VARIOUS MICROMECHANISMS
        The various compliant micromechanisms surveyed are prioritized depending on the
resultant functionality desired from the micromechanism.
        Y. Tiana et. al. [3] presented a table positioning mechanism for a grinder comprising of
flexure hinges as shown in Figure 1. A piezoelectric actuator is mounted on the base and
located against the center of the bottom of the moving platform through a ball tip. The
moving platform can traverse forward and backward (up and down) on a parallel flexure
mechanism .The hinges provide lateral stiffness for the moving platform as well as spring
preload for the piezo-electric actuator (PZT). The guarantee of perfectly achieving the motion
depends upon the accurate manufacture of profile as per design and hence the flexure hinges are
manufactured using the wire electro discharge machining (WEDM) technique. This
mechanism provides a self retracting and precise table positioning however it cannot provide
displacement amplification.


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                      Fig. 1 Piezo-driven flexure-based mechanism [3]

       Ranier Clement et al [4] have presented a RRR (3 rotational) type compliant positioning
system as shown in Figure 2. The mechanism comprises of piezoelectric actuation elements
along with compliant body. Flexure hinges deform with respect to other portions of the material
to enact sense of motion and force transfer. This RRR compliant mechanism is actuated with
three PZT actuators embedded in a piece of complaint material. This mechanism is a general
purpose parallel manipulator that has many applications like manipulator, scanning stage etc.
Amplification of motion may not be the desired function of such type of mechanism.




                           Fig. 2 Model of PZT–RRR mechanism [4]


         Oscar Chaides [5] illustrated the use of Flexure based micromechanism in the positioning
of a system in Micro-EDM as shown in Figure 3. In Micro-EDM (µEDM), the tool and work
piece are not in direct contact, and the tool motion is small relative to the part. The micro
positioner shown in Figure 3 is intended to provide horizontal linear motion to acrylic tank filled
with dielectric fluid. This micromechanism is used to get a reduction 10 times in displacement.
This caused excessive deflection in simulation as seen in Figure 3. This may reduce the fatigue
life of the mechanism and hence the flexure hinges are to be checked for fatigue failure.

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                  Fig.3 Flexure based motion amplifier used in Micro EDM [5]
        Compliant mechanisms are widely used in micro-grippers. The micro-clasp gripper presented by
Sandeep Krishnan and Laxman Saggere [6], conceptually illustrated in Figure 4 is a planar mechanism
comprising of two main components, an end-effector that can be lowered down from top and
folded/unfolded around an object by the action of a linear actuator and a compliant mechanism.
The mechanism transforms the force and displacements from the actuator to the end-effector. The end-
effector is a closed-loop structure with a hollow interior. The folding and unfolding actions of the end-
effector structure around an object lying within the structure boundaries causes “clasping” and
“unclasping” of the object.




                            (a)                                      (b)
      Fig.4 Conceptual diagram of the micro-clasp gripper (a) open and (b) closed [6]
       In the area of microgrippers, A. Nikoobin N and M. Hassani Niaki [7] studied various
microgrippers as shown in Figure 5 (a) and (b). Sudarshan Hegde & G.K.Ananthasuresh [8] have worked
on a microgripper as shown in Figure 5 (c). These grippers are used for the gripping of micro objects
where attention is on the gripping action and allied motion transfer.




            (a)                                  (b)                                    (c)
                                   Fig. 5 Various Microgrippers [7,8]


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       A. Nikoobin N and M. Hassani Niaki [7] discussed the concept of Displacement
Amplification Factor (DAF) which is the ratio between output displacement (jaw displacement)
                                                                       echanism.
and input displacement applied from the micro actuator to the gripper mechanism.




                                                 Factor (DAF) [7]
               Fig. 6 Displacement Amplification F

                               ,
        As shown in Figure 6, DAF = d2/d1, where d1 is the actuator displacement and d2 is the
jaw displacement. Higher the value of this factor, the gripping range increases and the gripper
                                                     he
can manipulate higher dimension micro objects. The actuation range of micro actuators, like
  iezoelectric
piezoelectric actuators, is low and a mechanism with a high displacement amplification factor is
desirable to increase the gripping range. On the other hand, according to the lever principle,
                                                                             force
increasing the output displacement in the arms leads to decrease in gripping force.
                                                                                mechanism
        The Researchers have worked on various displacement amplification mechanisms. The
following Figure7, Figure 8 and Figure 9 show Compliant Motion Amplifier (CMA)
micromechanisms.




Fig. 7 Dimension and flexure hinge parameters of          Fig.8 A bridge type displacement
            the designed CMA [9]                                            [10
                                                                  amplifier [10]
        A bridge type amplification mechanism as shown in Figure 7 is presented by John
                                 ure
Michael Acob et al [9] and Figure 8 is presented by Qingsong Xu & Yangmin Li, [10]. It has
been reported that these mechanisms provides large amplification ratio and are compact in size.
                             fier
The output end of the amplifier is usually connected to a specific device for drives. Qingling Liu
                                                          displacement
et al [11] have also presented a similar design for Micro-displacement amplification as shown in
Figure 9.




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          Fig. 9 Symmetrical micro-displacement amplification mechanism [11]
These mechanisms have a horizontal input and vertical output, used in many industrial
applications with a PZT actuator.
        Qingling Liu et al [11] have reported the presence of a lateral displacement in a lever arm
based micromechanism as shown in Figure10. Lever arm based micromechanisms are hence
least useful in a typical application involving directional constraints though they can provide a
large displacement amplification.




                              Fig. 10 Lateral error in Lever arm [11]

   3. FINDINGS OF LITERATURE SURVEY

        The literature review of various compliant micromechanisms was carried out. The
micromechanisms have been used to provide displacement, its amplification, and reduction.
Many of them are based on the lever arm principle and are least capable of providing linear
directional movements. The aspect of obtaining amplification/reduction and replication from the
micromechanism has not been considered/communicated in the present available literature.

   4. NEED OF A COMPLIANT 5 BAR MICROMECHANISM

       The aspect of obtaining amplification/reduction and replication of input motion from the
micromechanism has not been considered and needed to be addressed. Hence a compliant
pantograph has been proposed with following objectives.
• In plane linear motion/force transfer.
• To replicate the input motion.
• To obtain geometric amplification and reduction.

   5. GEOMETRIC MODELING OF A PANTOGRAPH

        Pantograph is a well established mechanism that is used to replicate/imitate and
amplify/reduce the motion on selecting the proper link lengths. The required amplification or
reduction can be obtained from mechanism when input is given at point ‘D’ or ‘E’ respectively.
Figure 11 represents a pin joint parallelogram ABCD. It is made up of bars connected by turning
pairs. The bars AB and BC are extended to points O and E respectively, such that points O-D-E
are collinear.



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                                 Fig.11 Rigid Link Pantograph.

For a pantograph,


Taking 2OA=OB=60 units, and 2AD =BE=45 units,



         Thus, for all relative positions of the bars the ∆OAD and ∆OBE are similar and the points O-D-E
are collinear. It may be proved that point E traces out the same path as described by point D. In similar
way, if input is given at point E, reduction of motion can be obtained at point D. In consideration of use
of the mechanism for linear motion, let point ‘O’ be constrained and the points ‘D’ and ‘E’ move to some
new positions D′ and E′ as shown in Figure 12.




                       Fig. 12 Geometric analysis of rigid link pantograph

                                                           ′
                                                           ′
        It is very clear that the imaginary line DD′ is parallel to the traced parallel line EE′. Hence, if
point D is constrained to move in vertical direction, point E will provide vertical amplified motion.
Similarly, if point E is constrained to move in a straight line, then point D will trace out a straight line
parallel to the former but motion will be reduced. Considering above dimensions, Geometric
Amplification of the mechanism is expected to be almost twice based on the above link length analysis.
Based on above analysis, a Compliant Pantograph is presented below as shown in Figure 13




                                       Fig.13. Compliant Pantograph

        This Compliant Pantograph is expected to provide Geometric amplification (almost twice) at the
output point E when linear input is given at point D. Advantage of this mechanism is the linear directional
output for linear input which is required for most of the micro-positioning stages.

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6.   CONCLUSION

       The micromechanisms communicated by various researchers have considered force and
motion transfer as per the functional need. However hardly any mechanism communicated is
capable of force as well as motion transfer along with amplification/reduction in motion. A
compliant pantograph is proposed for transmitting motion and force linearly by replicating the
input motion.

        Compliant mechanisms offer a joint less alternative to overcome the limitations of
conventional rigid body mechanisms such as backlash, lubrication etc. Manufacturing of the
hinge requires selection of appropriate techniques viz. WEDM, Laser Machining, ECM etc.
These Compliant mechanisms are designed to derive expected mobility from elastic deformation
of flexure hinges. Since the hinges are subjected to fluctuating/reverse loading, the hinge design
is a critical aspect. Critical analysis of flexure hinges needs to be carried out as it is the most
important parameter and success of compliant micromechanism depends on the performance of
the flexure hinges. A Pseudo Rigid Body Model [1,2] method has been proposed for the
simplified design of flexure hinges, wherein the hinges are modeled as torsional springs and the
compliant mechanism is then treated as a rigid body mechanism for further analysis. A
comprehensive study of different aspects discussed needs to be carried out in the analysis of
compliant micromechanism which are the need of industry.

7.   ACKNOWLEDGMENT

       The authors dedicate this work to late Prof. Dr. S. R. Kajale for his contribution in
developing Microsystems Engineering laboratory (funded under DST-FIST program), at College
of Engineering Pune, without his constant encouragement and support this work wouldn’t have
been possible.

REFERENCES

[1] Larry Howell, Compliant mechanism (Willey International) pp 2–10
[2] Lobontiu N, Compliant mechanisms design of flexure hinges (CRC Press,2002) pp 1–6
[3] Y. Tiana, D. Zhanga, B. & Shirinzadehb, “Dynamic modelling of a flexure-based mechanism
for ultra-precision grinding operation”, Precision Engineering 35 (2011), pp 554–565
[4] Ranier Clement, J.L.Huang, Z.H.Sun, J.Z.Wang & W.J.Zhang, “Motion and stress analysis of
direct-driven compliant mechanisms with general-purpose finite element software”, Springer-
Verlag London On line Published 15th June 2012.
[5] Oscar Chaide and Horacio Ahuett-Garza, “Design and characterization of a linear
micropositioner based on solenoid and compliant mechanism”, Mechatronics 21 (2011), pp
1252–1258
[6] Sandeep Krishnan and Laxman Saggere, “Design and development of a novel micro-
clasp gripper for micromanipulation of complex-shaped objects”, Sensors and Actuators A
176 (2012) 110– 123


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[7] A. Nikoobin n and M. Hassani Niaki,” Deriving and analyzing the effective parameters in
microgrippers performance”, Scientia Iranica Transactions B: Mechanical Engineering (2012) pp
1-10
[8] Sudarshan Hegde and G.K.Ananthasuresh, “Design of Single-Input-Single-Output Compliant
Mechanisms for Practical Applications Using Selection Maps”, Journal of Mechanical Design
August 2010, Vol.132 pp 081007-1 to 081007-8
 [9] John Michael Acob, Vangjel Pano, and P.R. Ouyang, “Optimization of a Compliant
Mechanical Amplifier Based on a Symmetric Five-Bar Topology”, ICIRA 2012, Part II, LNAI
7507(2012), pp. 323–332
[10] Qingsong Xu and Yangmin Li, “Analytical modeling, optimization and testing of a
compound bridge-type Compliant displacement amplifier”, Mechanism and Machine Theory 46
(2011) pp 183–200
[11] Qingling Liu et al, “Design and Analysis of Compliant Symmetrical Micro-Displacement
Amplification Mechanism”, Proceedings of the 3rd ICMEM International Conference on
Mechanical Engineering and Mechanics, Beijing, P. R. China, October 2009. pp 21−23




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