Development of a novel flexure-based microgripper for high precision micro-object manipulation
Introduction
Grasping methodologies have been at the forefront among the subjects of interest by microsystem researches ever since the micro-scale products started to dominate the global market. It is undeniable that miniaturization in systems has implicated in every aspect of our life ranging from health, communication, entertainment, transportation, etc. Therefore, the demand to accomplish fully integrated multifunctional MEMS devices has stimulated extensive researches on micromanipulation methodologies and devices to ultimately achieve fully automated microassembly procedure. Most of the microsystem researchers in academia have been focusing on three critical assembly components that determine the accomplishment of microassembly procedure namely the development of high precision grasping devices, nano-measurement technologies and ultra precision stage positioning [1], [2], [3], [4], [5], [6]. The integration of these components will pave boundless opportunity for the establishment of wide range of microdevices that incorporate sensor, actuator and control architectures. Most of the microassembly procedures nowadays profoundly rely on human dexterities to operate the precision devices and instruments which technically account for large portion of production cost. Furthermore, the repetitive and intricately demanding assembly task will gradually afflict the operator's sensibility and focus and thus increases the susceptibility of human bound errors associated with the operator's stress and eye strain. Furthermore, the precision associated with assembling diminutive components determines the quality and reliability of the finished product and this stringent requirement should be meticulously considered when developing microtechnology based product. Extensive researches in haptics and virtual technology have also contributed to the advancement in microassembly system to enable better understanding towards microworld which involves different physics in contrary to macrodomain [7], [8].
As one of the essential components in microassembly process, the development of fully automated microhandling devices to enable accurate and high precision object manipulation has been undergoing for many years with promising results. It was found from the diverse micrograsping models in literature that researchers have predominantly emphasized on three major components during model development namely novel microfabrication techniques [9], [10], new actuation methodologies [11], [12], [13] and manipulation of different materials [14], [15], [16]. The establishment of novel microfabrication technique and the development of smart structures have advanced the grasping technologies and enable compact, highly compliant, and monolithic mechanism to be realized. The fabrication techniques such as Electro Discharge Machining (EDM), LIGA, surface, bulk and laser micromachining, and photo lithography have paved a decisive breakthrough to the persisting constraints in micrograsping methodology particularly associated with the object-gripper compatibility, surface to surface interaction between the object and the gripper's jaws and nonlinearity during operation [9], [10], [17], [18]. Furthermore, the realization of monolithic structure also demands the employment of different actuation strategy to satisfy the stringent requirements in precision microhandling operation since the application of conventional motor to drive the microgripper is insufficient to comply with the specifications. The development of novel actuation techniques over the years has proven to be decisive to enable model downsizing and further advancement in micrograsping technology. Common actuating techniques conventionally employed to provide the driving input to the grasping mechanism can be classified into four major categories namely thermal, piezoelectric, electrostatic and electromagnetic actuating concepts [12], [15], [19], [20], [21].
Section snippets
Motivation
There are several essential design considerations and challenges arise in developing a gripper mechanism that operates within limited workspace. The inability of rigid hinge based gripper to meet the requirement of high accuracy object manipulation which involves pick and place operations, part maneuvering for insertion, bonding and mounting process requires a different modeling strategy that incorporates compactness, high compliance motion and controllability attributes. A practical and widely
Modeling and analysis
Fig. 2 provides the basic geometrical model of the mechanism which is composed of several rigid bodies joined together by series of flexure hinges which govern the primary movement of the gripper. The model will be subsequently transformed into rigid body mechanism by replacing the flexible segment into equivalent rigid joint and torsional spring as illustrated in Fig. 3. This approach will simplify the model to enable conventional rigid body kinematic analysis to be performed for further
Mechanism prototype
Fig. 7, Fig. 8 represent the prototype of the grasping mechanism accompanied by the corresponding individual components. Piezo-actuator (model AE505D16) from Thorlab™ was employed to provide high resolution driving input to the grasping mechanism with normal operating range between 0 and 100 V. The gripper was fabricated out of Aluminum 7075T6 plate using wire EDM technique with minimum achievable tolerance of 20 and 200 μm was employed to enable intricate cutting on several crucial section of
Experimental result and discussion
Fig. 12 provides the overall set-up for conducting series of experiments to obtain various correlations governing the performance of the gripper. The set-up is composed of data acquisition and imaging devices, voltage supply instrument and grasping mechanism. The actuator output voltage can be controlled via the piezoelectric controller (model MDT693) from Thorlabs™ which can operate in either manual or automatic modes. An electronic linear measuring instrument from Tesatronic™ (model TTA 20)
Conclusion
This paper detailed on the development of a compliant based microgripper utilizing hybrid designing concept. The unification of two compliant structures namely flexure hinge and cantilever beam within the mechanism mainframe has proven to be decisive in satisfying the stringent requirements in performing high accuracy and fidelity object manipulation within microdomain. A combinatory modeling approach was adopted via the utilization of PRBM and FEA techniques to expedite the prototyping
Acknowledgment
This research is funded by Australian Research Council, ARC Discovery-DP0668052, ARC LIFE-LE 0668508, ARC Discovery-DP0450944, and ARC LIFE-LE0453629.
Mohd Nashrul Mohd Zubir received BEng degree in mechanical engineering from University of Malaya (UM), Malaysia, in 2004. He works as an academic staff in UM and currently pursuing a master degree in Monash University, Australia. His fields of interest include flexure based mechanism, micro/nano manipulation and micrograsping.
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Mohd Nashrul Mohd Zubir received BEng degree in mechanical engineering from University of Malaya (UM), Malaysia, in 2004. He works as an academic staff in UM and currently pursuing a master degree in Monash University, Australia. His fields of interest include flexure based mechanism, micro/nano manipulation and micrograsping.
Bijan Shirinzadeh received engineering qualifications: BE (mechanical), BE (aerospace), MSE (mechanical), and MSE (aerospace) from the University of Michigan, and PhD in mechanical engineering from University of Western Australia (UWA). He has held various positions in academia and industry. Dr. Bijan Shirinzadeh is currently an associate professor, and the director of Robotics & Mechatronics Research Laboratory (RMRL) which he established in 1994, in the Department of Mechanical Engineering at Monash University, Australia. His current research interests include haptics, medical robotics, laser-based measurements and sensory-based control, micro/nano manipulation systems, systems kinematics and dynamics, and automated manufacturing.
Yanling Tian received BEng degree in mechanical engineering from Northwest Institute of Light Industry, China, in 1997, and MSc and PhD degree in mechanical engineering from Tianjin University, China, in 2002 and 2005 respectively. From 2005 to 2006, he worked as a postdoctoral research fellow and then held an associate professor position in the School of Mechanical Engineering at Tianjin University. He also worked as visiting scholar at Hong Kong University of Science and Technology, China, and University of Warwick, UK, in 2001 and 2006, respectively. Dr. Yanling Tian is currently a postdoctoral research fellow in the Robotics and Mechatronics Research Laboratory (RMRL), Department of Mechanical and Aerospace Engineering at Monash University, Australia. His research interests include micro/nano manipulation, mechanical dynamics, finite element method (FEM), surface metrology and characterisation.