A MIXED PIEZOELECTRIC AND ELECTROMAGNETIC ACTUATION DEVICE FOR DRY AND WET MANIPULATION

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1 A MIXED PIEZOELECTRIC AND ELECTROMAGNETIC ACTUATION DEVICE FOR DRY AND WET MANIPULATION Alexandru IVAN,3, Mihaita ARDELEANU, Ion LUNGU3, Valentin GURGU3, Marius IONITA3,Veronica DESPA, Adrian CATANGIU CNRS UMR55, Enise, LTDSB, Université de Lyon, 69365, France Dept. of Materials, Installations and Robots, Valahia University of Targoviste 35, Romania Dept. of Electronics,Telecomm. and Energetics, Valahia University of Targoviste 35, Romania Abstract - The paper presents the design, characterization and further micro-manipulation demonstration of a four-dof (Degrees of Freedom) micro-gripper based on piezoelectric and on electromagnetic actuation mechanisms. Displacement range of >µm and sub-micrometric resolution is achieved in the gripper transverse directions. Unlike most available grippers which operate in a gle direction, the proposed piezo-magnetic device is capable of independent arm movement in two directions each, thus significantly increag its manoeuvrability. Operations of pick-and-place have been demonstrated in both dry and wet (liquid) environments, as may be seen in Fig.. The device may be featured with different tips (also called end-effectors) which could adapt to various objects like small mechanical parts or biocells, whose size may vary from µm down to µm. Single cell isolation, injection and testing become thus possible. Keywords: Micromanipulator, displacement measurement, electromagnetic actuator, piezoelectric actuator, direct kinematic.. Introduction This presentation introduces the design and the main characteristics of a four-dof (degrees of freedom) microgripper based on piezoelectric and on electromagnetic bending mechanisms. The actuation is in the two transverse and orthogonal directions with a sub-micrometric positioning accuracy and a convenient working range (>µm). Mechatronics tends nowadays towards more compact and fully automated devices, being spread from macro to micro scale applications. Speaking about mechatronics, it is necessary to remember about the flexibility too [-6], that is a concept applied in micro assembly automation, for example, and the specific methods need a working space model for precise positioning of each micro object both for clamping and assembling of parts. Simultaneously with technological development, it was remarked that the possibility to fabricate micro- and nano-actuators oriented to mechatronic structure actuation system at the low level of forces and couples [7]. The overall micro-prehension devices are designated for clamping and manipulating object with the basic dimension included into [ ] micrometers. In certain conditions, this kind of devices will operate to mechanical prehension/clamping with nanometric accuracy in positional control [8, 9]. The mechatronics actuality is based on different unconventional actuating types that far exceed the limits of classical ones []. A micromanipulation system supposes extremely accuracy for positioning, existence of improved endeffectors, automation software and, not at least a platform for manipulation. However, all these presented elements don't guarantee the success of manipulation operations, without an adapted to real technical need for the concept of design, regarding manipulating instrument. A variety of microgrippers have been designed for multiple fields of applications, for the ability of working in different environments (dry or wet) and for to enlarge the moving range of flexure structures [-6]. Depending of reciprocal orientation between endeffectors and manipulating object, we can distinguish two manipulation strategies. -Continuous manipulation (the object can occupy every intermediary position into a range delimited by two extreme points). -Discrete manipulation (the object can occupy just certain place points prior established). To assure the success and the efficiency for one micromanipulation operation consisting of clamping and positioning of a micro-object, it has to take in account complex aspects regarding the existing specific forces. For that reason the challenge consists into detailed study of these forces (electrostatical, Van der Waals and others.) dominated by surface effects [7- ]. 56 The Romanian Review Precision Mechanics, Optics & Mechatronics, 5, Issue 48

2 Figure : Michelson Schematic representation of the main manipulation techniques. a) direct contact manipulation (micro-gripper); b) mechanical alignment; c) vacuum prehension; d) electrostatic clamping; e) capillary gripping; f) Van der Waals gripping; g) Localised freezing; h) collaborative manipulation (multiple actuators); i) liquid environment manipulation; j) vibration-induced displacement; k) snap-locking method.[gauthier M. (editor), Regnier St. (editor) - Robotic MicroAssembly, IEEE Press Editorial Board, ].. Principle of operation This is an assembly composed by a metallic case that constitutes the support for elements that generate a magnetic field, respectively two pairs of permanent magnets coils (Fig.). These magnetic systems induce independently magnetic forces in specific compliant arms. The compliant joint can be assimilated like a rotary articulation. In fact we can speak about a displacement of a beam that is bended under magnetic action. Figure : Schematic of micro-gripper Adding another two piezo-elements to the first arms, the displacement spectrum is extended with two orthogonal movement possibilities. The final effectors are passive elements that assure the contact with manipulated object. Optionally, the metallic case can be adapted for a series of magnetic sensors for mechanical movements seng. 3. Electromagnetic actuation This type of actuation is based on existence of two forces, respectively magnetic force Fm and elastic force. The first one has a great controllability through electrical handling (coil current) and the second depends proportionally by displacements. In this way it s relatively simple to obtain a mathematical model for direct and invers kinematics cases. The coil-magnet interaction amplifies the magnetic effect. The positioning of magnet on beam element is determined by maximal displacement of arm and the needed gripping force. In Fig.3 is presented an electromagnetically actuated arm. The main components and functions of this actuation type: Compliant fixed-free beam; Coil-magnet interaction; Mechanical lever amplification; Main gripping task. The electro-magnetic displacements into <xoy> plan are the effects of a three independent elements: () Interaction between permanent magnets mounted on the arms, produces its flexures, generating static equilibrium state. () Magnetic force Fm (Fig.3), generated through interaction between permanent magnet and the coil corresponding for a certain arm. (3) Mechanical stiffness that assures the returning to static equilibrium state when the electric circuit is off. Figure 3: Schematic of electromagnetic principle Applying a current (Ic) into coil circuit, the magnetic field induces a proportional force Fm that creates displacements for permanent magnet and solidary with it to entire beam. The Romanian Review Precision Mechanics, Optics & Mechatronics, 5, Issue 48 57

3 4. Piezoelectric actuation The main components and functions of this actuation type: - Flexural actuator; - Dual-layer PZT; - Vertical alignment, lift/descent tasks. The piezoelectric actuation allows for each end-effector the vertical displacement on Z axis in Fig.4. In the same time was perfected an experimental frame that provided real data regarding the device one arm s displacements. Direct kinematic for one hybrid arm of device The specialists in robotics developed the kinematic models to describe the interrelation between cause (motor movement) and effect (execution elements movement). In this case, shown in Fig., for each of two device s arms we can to apply the direct kinematic model to determinate the end-effector s displacement formula for a given input. Direct kinematics uses transfer matrices, starting from fixed element (base element) and ending with effector element (terminal element) of the kinematic chain. In Fig. 6 are represented the orientation frames associated for device structure. Figure 4: Piezoelectric elements (design-left, real- right) Note: The end-effectors are integrated (original design of FEMPTO-ST Institute, Besancon, France) This fact is essential for end-effectors alignment and a good object manipulation in up-down direction. The actuator consists into glued plates ug a conductive adhesive. The effective principle of actuation in this case is shown in Fig.5. Figure 5: Schematic of piezoelectric principle The adhesive influence on stiffness of bimorph homogenous PZT is shown in figure 6, where it s observable the deformation for both cases: classic bimorph and bimorph with adhesive. On observe that the displacements in the second case are reduced compared with those from first case. With this second type of actuation ends this hybrid structural combination of device. In next chapters it will be presented a theoreticalexperimental parallel. A mathematical model was defined ug transfer matrices theory from robotics. Figure 6: Direct kinematic joint points As is shown, it was established five important points to calculate transfer matrices, for each of two arms. The final characteristic points are P and P corresponding to each arm. The coordinates (x, y, z) of P represent the goal of this chapter. For P coordinates are similarly obtained. The notations used in next formulas are: Fm Magentic force generated by coil. E Young modulus. Iz Inertia torque (depends by beam section). xk yk zk The coordinates in <O-XYZ> frame for considered points. g & p offsets for X and Z axis. The final transfer matrix is obtained by multiplication of elementary (sequential) matrices conform with (). (5) 5 T () k T k 58 The Romanian Review Precision Mechanics, Optics & Mechatronics, 5, Issue 48

4 The obtained result for P total matrices is shown in (). Fm y cos E Iz Fm y E Iz Fm y E Iz Fm y cos E Iz Fm y Fm y g x Fm E Iz ( y3 y4) xcos y 3 E Iz 3E Iz Fm y y cos Fm y E Iz ( y3 y4) x y E Iz p z p Fm y y y E Iz () x ee y ee g x y y F y E I z F y F y E I z 3 E I z m m m y y x cos y y 3 4 F y m m y 3 y4 cos x E I z E I z F y Fm y E I z (3) (4) zee z p p (5) The relations (3), (4) and (5) represent the coordinates of end-effector P. The input data for calculus session is Fm magnetic force that was experimental determined in the lab, ug a complex schema and an ultra-precise electronic balance with six digit capacity calculation in gram weight case. The Fm values order is mili-newton (mn). The material for beams is a biocompatible steel ( E mn / m ), the geometrical sections of these are the same ( m ) and the inertial torque 8 4 ( 6,67 m ). I z 5. Experimental frame for end-effector displacement measurements The experimental frame included a set of elements that created capacity to generate smallest displacements at end-effector characteristic point for one of two arms of the device. In Fig.7 are shown these elements: displacements and the real ones. Figure 8: Experimental frame As is presented previously in relations (3) and (4), the Fm is the function argument. To compare is needed to have the same argument for displacement functions (analytical & experimental). The specific constants of analytic mathematical relations are E (Young modulus) and Iz (Inertia torque). The afferent values of these constants are theoretical ones provided by specialised literature and specific calculus. The most important part of the fabricated arm is shown in Fig. 9. As it can see the material aspect indicates a relative homogeneity in superficial layers and the real shapes versus theoretical forms are relative too. Figure 7: Experimental frame schematic block Microgripper (actuation device); Command block that generate the adequate signals for actuators; Displacement transducer with a great measurement resolution. The entire experiment was directed to obtaining a comparative analyse between analytic calculated Figure 9: Detail of real fabricated arm The Romanian Review Precision Mechanics, Optics & Mechatronics, 5, Issue 48 59

5 Table contains the experimental determination of force depending by coil current (I). Table. Left Arm Force Function No. I Measurement I Measurement No. ma gf N ma gf mn The resulted approximation function is defined by relation (6) and it was used for generating the force values in analytical calculus of displacements. F m I. 8 ImN (6) Finally, in Fig. can be seen the overlaid graphics for a given force range [-8, 8] (mn). The maximal error value is % in the extreme of 8 mn force. The minimal error values (under %) correspond of central force range [-6,6] (mn). Figure : Comparison between analitical and experimental data 6. Conclusions Obtaining of micromanipulation device became possible ug a simple designing concept. The 3D metal prototyping machine offered the possibility to fabricate the specific carcase of microgripper. The analytic mathematical model generated very close values by the real determined ones and that represents that the fabrication process was a professional one. The device can be integrated into micro assembly stations because the accuracy and repeatability are very high. Entire process of command can be automated through adding of CCD sensors and image procesg algorithms. That represents a future intention for our scientific team. Regarding the wet manipulation, the terminals must be adapted for specific phenomena. For example, capacity to move very precise the arms of microgripper device can be applied for a chemical manipulation in liquid environment, ug specific substances that permit attraction between a impregnated terminal and certain biologic cells. Also the precise terminals displacements can be utile for microfluidic systems to create on/off inputs/outputs and in this way the applicability of the device become universal. 7. References [] K. B. Ye, B. J. Nelson, A CAD model based tracking system for visually guided microassembly, Robotica (5) Vol.3, pp [] Q. Zhou, A. Aurelian, B. Chang, C. del Corral, H. N. Koivo, Microassembly system with controlled environment, Journal of micromechtaronics vol., pp. 7 48,. [3] B. E. Kratochvil, K. B. Yes V. Hess, B. J. Nelson, Design of a visually guided 6 DOF micromanipulator system for 3D assembly of hybrid MEMS, Proceedings of the 4th International Workshop on Microfactories, October 4. [4] A. Ferreira, C. Cassier, S. Hirai, Automatic microassembly system assisted by vision servoing and virtual reality, IEEE/ASME Transactions on Mechatronics, vol. 9, no., pp , 4. [5] L. Wang, S. Kim, Automatic micropart assembly of 3-Dimensional structure by vision based control, Journal of Mechanical Science and Technology (8) pp [6] E. D. Kunt, K. Cakir, A. Sabanovic, A workstation for microassembly, Control & Automation, 7. MED '7. Mediterranean Conference on, vol., no., pp.-6, 7-9 June 7. [7] actuatoare-si-nanotehnologii-in-mecatronica/. [8] M. Gauthier (editor), St. Regnier (editor), Robotic MicroAssembly, IEEE Press Editorial Board (). [9] T. Păunescu, I. Stareţu, Tendinţe şi realizări în domeniul microprehensoarelor, Buletin AGIR, nr./, pag.4-. [] capitol5.pdf [] Y. Jia, Q. Xu, MEMS Microgripper Actuators and Sensors: The State-of-the-Art Survey, Recent Patents on Mechanical Engineering 3, Vol. 6, No.. 6 The Romanian Review Precision Mechanics, Optics & Mechatronics, 5, Issue 48

6 [] Beyeler F, Neild A, Oberti S, Bell DJ, Sun Y, Dual J, et al. Mono-lithically fabricated microgripper with integrated force sensor for manipulating microobjects and biological cells aligned in an ultra-sonic field. J Microelectromech Syst. 7; 6(): 7-5. [3] Chen L, Liu B, Chen T, Shao B. Design of hybrid-type MEMS microgripper. Proceedings of the International Conference on Manufacturing Automation. Hong Kong, Aug, 9. [4] Z. Mohd, N. Mohd, B. Shirinzadeh, Y. Tian, Development of a novel flexure-based microgripper for high precision micro-object manipulation, Sensors and Actuators A: Physical 5. (9): [5] B. P. Solano, J. A. Gallant, D. Wood, Design and optimisation of a microgripper: Demonstration of biomedical applications ug the manipulation of oocytes. Design, Test, Integration & Packaging of MEMS / MOEMS, 9. MEMS / MOEMS'9. Symposium on. IEEE, 9. [6] Y. Zhou, E. Diller, M. Sitti, Micromanipulation ug rotational fluid flows induced by remote magnetic micro-manipulators, Journal of Applied Physics.6 (): 649. [7] N. Maluf, An introduction to Microelectromechanical Systems Engineering, Artech House, Inc.685 Canton Street Norwood, MA 6 (4). [8] Gh. Gheorghe, L. Bădiță, Micro şi nanotehnologii avansate în mecatronică, Bucureşti, Ed. CEFIN (9). [9] M. Avram, C. Bucşan, Hydraulic and Pneumatic Actuating Systems with Piezoelectric Actuators, The Romanian Review Precision Mechanics, Optics & Mechatronics, vol.43, pp. 7- (3). [] L. Petit, C. Prelle, E. Doré, F. Lamarque, M. Bigerelle, Four discrete positions electromagnetic actuator: modelling and experimentation, TMECH The Romanian Review Precision Mechanics, Optics & Mechatronics, 5, Issue 48 6