Study of various compliant micromechanism


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Study of various compliant micromechanism

  1. 1. INTERNATIONAL6359(Online) Volume 3, Issue and Technology © IAEME ISSN 0976 – International Journal of Mechanical Engineering 6340(Print), ISSN 0976 – JOURNAL OF MECHANICAL(IJMET), 3, Sep- Dec (2012) ENGINEERING AND TECHNOLOGY (IJMET)ISSN 0976 – 6340 (Print)ISSN 0976 – 6359 (Online) IJMETVolume 3, Issue 3, September - December (2012), pp.574-582© IAEME: Impact Factor (2012): 3.8071 (Calculated by GISI) © 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, 2 (Associate Professor, Mechanical Department, Government College of Engineering COEP, Pune, India, 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 574
  2. 2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEMEdevelopment of Microfactories/Table top precision micro setups etc. Miniaturization isassociated with various advantages and challenges; a smaller system has lower inertia of massenabling quick response from the system. The overall performance of the system is anoutcome/result of precise and accurate behavior of various systems/components involved.However, precision, accuracy and manufacturing of such systems is a challenging task and theseparameters drive the resulting performance obtained. Microsystems involve development ofMicro mechanism for desired motion/force transfer. Traditional rigid body mechanisms consist of rigid links connected with movable jointsand are capable of transforming linear motion into rotational or force into torque. Thesemechanisms are adversely affected by issues such as friction, wear, lubrication, backlash etc. andhence these mechanisms cannot be used for precise applications. A new class of mechanismsknown as compliant mechanisms has hence gained significant importance in MEMS. Compliant mechanisms [1, 2] are designed to derive mobility from elastic deformation ofparticular 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 outputdisplacement/motion. Compliant mechanisms provide a joint less alternative which overcomesthe limitations of conventional rigid body mechanisms. They are monolithic structures andrequire no assembly, however manufacturing them requires selection of appropriate techniquesviz. WEDM, Laser Machining, ECM etc. The current paper is a review of compliantmicromechanisms communicated by various researchers [3-11] and their merits, limitations andprobable applications are discussed. A compliant pantograph has been proposed for a typicalapplication, 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 theresultant functionality desired from the micromechanism. Y. Tiana et. al. [3] presented a table positioning mechanism for a grinder comprising offlexure hinges as shown in Figure 1. A piezoelectric actuator is mounted on the base andlocated against the center of the bottom of the moving platform through a ball tip. Themoving platform can traverse forward and backward (up and down) on a parallel flexuremechanism .The hinges provide lateral stiffness for the moving platform as well as springpreload for the piezo-electric actuator (PZT). The guarantee of perfectly achieving the motiondepends upon the accurate manufacture of profile as per design and hence the flexure hinges aremanufactured using the wire electro discharge machining (WEDM) technique. Thismechanism provides a self retracting and precise table positioning however it cannot providedisplacement amplification. 575
  3. 3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME Fig. 1 Piezo-driven flexure-based mechanism [3] Ranier Clement et al [4] have presented a RRR (3 rotational) type compliant positioningsystem as shown in Figure 2. The mechanism comprises of piezoelectric actuation elementsalong with compliant body. Flexure hinges deform with respect to other portions of the materialto enact sense of motion and force transfer. This RRR compliant mechanism is actuated withthree PZT actuators embedded in a piece of complaint material. This mechanism is a generalpurpose 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 positioningof a system in Micro-EDM as shown in Figure 3. In Micro-EDM (µEDM), the tool and workpiece are not in direct contact, and the tool motion is small relative to the part. The micropositioner shown in Figure 3 is intended to provide horizontal linear motion to acrylic tank filledwith 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 fatiguelife of the mechanism and hence the flexure hinges are to be checked for fatigue failure. 576
  4. 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME Fig.3 Flexure based motion amplifier used in Micro EDM [5] Compliant mechanisms are widely used in micro-grippers. The micro-clasp gripper presented bySandeep Krishnan and Laxman Saggere [6], conceptually illustrated in Figure 4 is a planar mechanismcomprising of two main components, an end-effector that can be lowered down from top andfolded/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 variousmicrogrippers as shown in Figure 5 (a) and (b). Sudarshan Hegde & G.K.Ananthasuresh [8] have workedon a microgripper as shown in Figure 5 (c). These grippers are used for the gripping of micro objectswhere attention is on the gripping action and allied motion transfer. (a) (b) (c) Fig. 5 Various Microgrippers [7,8] 577
  5. 5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep Dec (2012) © IAEME Sep- A. Nikoobin N and M. Hassani Niaki [7] discussed the concept of DisplacementAmplification Factor (DAF) which is the ratio between output displacement (jaw displacement)and input displacement applied from the micro actuator to the gripper mechanism. echanism. Fig. 6 Displacement Amplification F Factor (DAF) [7] 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 grippercan manipulate higher dimension micro objects. The actuation range of micro actuators, like hepiezoelectric actuators, is low and a mechanism with a high displacement amplification factor is iezoelectricdesirable to increase the gripping range. On the other hand, according to the lever principle,increasing the output displacement in the arms leads to decrease in gripping force. force The Researchers have worked on various displacement amplification mechanisms. The mechanismfollowing 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] amplifier [10] [10 A bridge type amplification mechanism as shown in Figure 7 is presented by JohnMichael Acob et al [9] and Figure 8 is presented by Qingsong Xu & Yangmin Li, [10]. It has urebeen reported that these mechanisms provides large amplification ratio and are compact in size.The output end of the amplifier is usually connected to a specific device for drives. Qingling Liu fieret al [11] have also presented a similar design for Micro-displacement amplification as shown in displacementFigure 9. 578
  6. 6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME Fig. 9 Symmetrical micro-displacement amplification mechanism [11]These mechanisms have a horizontal input and vertical output, used in many industrialapplications with a PZT actuator. Qingling Liu et al [11] have reported the presence of a lateral displacement in a lever armbased micromechanism as shown in Figure10. Lever arm based micromechanisms are henceleast useful in a typical application involving directional constraints though they can provide alarge 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. Themicromechanisms 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 lineardirectional movements. The aspect of obtaining amplification/reduction and replication from themicromechanism 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 themicromechanism has not been considered and needed to be addressed. Hence a compliantpantograph 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 andamplify/reduce the motion on selecting the proper link lengths. The required amplification orreduction 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 turningpairs. The bars AB and BC are extended to points O and E respectively, such that points O-D-Eare collinear. 579
  7. 7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME Fig.11 Rigid Link Pantograph.For a pantograph, OA AD ൌ OB BETaking 2OA=OB=60 units, and 2AD =BE=45 units, OA AD 30 22.5 1 ൌ ൌ ൌ ൌ OB BE 60 45 2 Thus, for all relative positions of the bars the ∆OAD and ∆OBE are similar and the points O-D-Eare collinear. It may be proved that point E traces out the same path as described by point D. In similarway, if input is given at point E, reduction of motion can be obtained at point D. In consideration of useof the mechanism for linear motion, let point ‘O’ be constrained and the points ‘D’ and ‘E’ move to somenew positions D′ and E′ as shown in Figure 12. Fig. 12 Geometric analysis of rigid link pantograph OD OD′ ൌ OE OE′ It is very clear that the imaginary line DD′ is parallel to the traced parallel line EE′. Hence, ifpoint 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 lineparallel to the former but motion will be reduced. Considering above dimensions, GeometricAmplification 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 theoutput point E when linear input is given at point D. Advantage of this mechanism is the linear directionaloutput for linear input which is required for most of the micro-positioning stages. 580
  8. 8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME6. CONCLUSION The micromechanisms communicated by various researchers have considered force andmotion transfer as per the functional need. However hardly any mechanism communicated iscapable of force as well as motion transfer along with amplification/reduction in motion. Acompliant pantograph is proposed for transmitting motion and force linearly by replicating theinput motion. Compliant mechanisms offer a joint less alternative to overcome the limitations ofconventional rigid body mechanisms such as backlash, lubrication etc. Manufacturing of thehinge requires selection of appropriate techniques viz. WEDM, Laser Machining, ECM etc.These Compliant mechanisms are designed to derive expected mobility from elastic deformationof flexure hinges. Since the hinges are subjected to fluctuating/reverse loading, the hinge designis a critical aspect. Critical analysis of flexure hinges needs to be carried out as it is the mostimportant parameter and success of compliant micromechanism depends on the performance ofthe flexure hinges. A Pseudo Rigid Body Model [1,2] method has been proposed for thesimplified design of flexure hinges, wherein the hinges are modeled as torsional springs and thecompliant mechanism is then treated as a rigid body mechanism for further analysis. Acomprehensive study of different aspects discussed needs to be carried out in the analysis ofcompliant micromechanism which are the need of industry.7. ACKNOWLEDGMENT The authors dedicate this work to late Prof. Dr. S. R. Kajale for his contribution indeveloping Microsystems Engineering laboratory (funded under DST-FIST program), at Collegeof Engineering Pune, without his constant encouragement and support this work wouldn’t havebeen 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 mechanismfor 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 ofdirect-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 linearmicropositioner based on solenoid and compliant mechanism”, Mechatronics 21 (2011), pp1252–1258[6] Sandeep Krishnan and Laxman Saggere, “Design and development of a novel micro-clasp gripper for micromanipulation of complex-shaped objects”, Sensors and Actuators A176 (2012) 110– 123 581
  9. 9. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME[7] A. Nikoobin n and M. Hassani Niaki,” Deriving and analyzing the effective parameters inmicrogrippers performance”, Scientia Iranica Transactions B: Mechanical Engineering (2012) pp1-10[8] Sudarshan Hegde and G.K.Ananthasuresh, “Design of Single-Input-Single-Output CompliantMechanisms for Practical Applications Using Selection Maps”, Journal of Mechanical DesignAugust 2010, Vol.132 pp 081007-1 to 081007-8 [9] John Michael Acob, Vangjel Pano, and P.R. Ouyang, “Optimization of a CompliantMechanical Amplifier Based on a Symmetric Five-Bar Topology”, ICIRA 2012, Part II, LNAI7507(2012), pp. 323–332[10] Qingsong Xu and Yangmin Li, “Analytical modeling, optimization and testing of acompound 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-DisplacementAmplification Mechanism”, Proceedings of the 3rd ICMEM International Conference onMechanical Engineering and Mechanics, Beijing, P. R. China, October 2009. pp 21−23 582