Elsevier

Sensors and Actuators A: Physical

Volume 205, 1 January 2014, Pages 156-163
Sensors and Actuators A: Physical

Numerical simulation and experimental investigation of a topologically optimized compliant microgripper

https://doi.org/10.1016/j.sna.2013.11.011Get rights and content

Highlights

  • Conceptual mechanism of microgripper is designed through topology optimization.

  • Impractical manufacturing regions are found senseless regions from the results.

  • In post optimization process, flexure hinges are replacing the senseless regions.

  • Flexure hinges parameter are evaluated through experimentally and numerically.

  • Graphical position analysis is carried out to evaluate the design of mechanism.

Abstract

In this research work, the compliant based microgripper is developed and the performance of the microgripper is studied through numerical simulation and experiential techniques. Conceptual design of microgripper is developed through topology optimization which is logical, authenticate and effortless among other mechanism design methods such as Mechanism synthesis, Pseudo Rigid Body Model (PRBM) and inverse method. In conceptual design of microgripper, node to node connections were developed and show the hinge locations of the mechanism. These locations were replaced by introducing suitable flexure hinges. The effect of flexure hinges at the node-to-node contact regions need to be analyzed for its critical geometric parameter. The important critical geometric parameter of flexure hinges are varied and analyzed through Finite Element Method (FEM) and experimental studies. In experimental technique, Shape Memory Alloy (SMA) wire is employed to actuate the microgripper. Equivalent rigid body model of the mechanism using Graphical Position Analysis (GPA) to the compliant mechanism is developed for comparing the output displacement.

Introduction

In recent years, precision manipulations of microsized components are inevitable in the micro engineering such as micro assembly, micro robotics, electronics, optics, drug delivery, tissue manipulation and minimally invasive surgery [1], [2], [3], [4], [5], [6]. Microgripper is an essential component to manipulate micro-parts precisely. A typical microgripping system consists of a pair of jaws for holding the micro object, actuators to provide input displacement and mechanisms for transmitting the motion from actuator to jaws. These three segments of micro-gripping system are significant in precision manipulation of micro object. In micro physics, the surface forces such as Van der Waals forces and electro static forces are influencing more than the inertial forces like gravitational force. An appropriate selection of a micro gripper geometry (for example, reducing the contact area between object and gripper jaw) and materials can reduce adhesion between gripper jaws and the object [7]. Another fundamental component of microgripping system is an actuator which supplies an input displacement to mechanism. Various actuation techniques have been used such as electro-thermal actuators [8], [9], electrostatic actuators [10], [11], [12], [13], piezo-electric actuators [14], electro-magnetic actuators [15], SMA actuators [16], [17], [18], [19], [20], and fluidic microactuators [21]. Among the various types of actuation systems, a piezoelectric actuator and SMA actuators have been widely used for actuating the microgripper. SMA actuation system has various advantages such as simplicity, safety and high power-to-weight ratio, low cost. Ni–Ti based SMAs are possessed with an excellent corrosion resistance and biocompatibility. The limitations are low energy efficiency, limited bandwidth due to heating and cooling restrictions, degradation, fatigue and small strains [16].

Another most important part of microgripping system is the mechanism design. In mechanism design, the input force/displacement required to actuate the jaws of the gripper is precisely transmitted. Hence, the traditional joints cannot be used to avoid assembly error, manufacturing error, friction between the assembled component and wear due to friction to confirm the precision motion. This leads to design a suitable joint less mechanism design, called monolithic compliant mechanism design. Various methods are involved in designing a compliant mechanism design such as mechanism synthesis [22], [23], PRBM [24], optimization technique [25], inverse methods [26] and intuitive gripper design [27]. Among various methods, structural optimization technique has proven that it is more general and efficient. Conceptual design of mechanism can be generated using structural optimization. The structurally developed design identifies the location of hinges in the mechanism. In these locations, flexure hinges are introduced to replace the conventional joints. Flexure hinges are the members in the mechanism region which utilizes the material flexibility or the compliance nature to transfer the motion between two neighboring rigid members.

In this research work, microgirpper is designed and developed for the purpose of microassembly and also can be used in bio research because the material of the microgripper and SMA wire is biocompatible. Moreover, the microgripper is designed with lengthy jaw which allows the modification of the geometrical parameter of the gripper jaw relating to application. For example, rough surface can be created in the contact area of the jaws with the object, spherical shaped tips for a special application such as cell manipulation and Teflon wire grasping [38] and bean can be modified as cantilever for measuring the stiffness through its deflection [39]. Initially a conceptual design of microgripper is developed using topological optimization technique. Flexure hinges were integrated into the conceptual design to remove senseless region developed during the topological optimization process. Critical geometric parameters of the flexure hinges were studied to find the suitable design of flexure hinges. Micro manufactured gripper (made up of Stainless Steel (SS) 316) is experimentally investigated and numerical simulations have been performed to evaluate the efficiency of this model with the results obtained through graphical analysis of equivalent rigid body model.

Section snippets

Design of microgripper

Designing a microgripper is a critical task of the designer and is highly difficult to handle the objects at micro level with precision movement. Hence, adopting compliant based mechanism design is more appropriate for designing microgripper. Designing a compliant mechanism, the topology optimization is the most efficient and logical technique. A primary or conceptual mechanism design has been developed using topology optimization technique. An open source for mechanism design developed in

Results and discussion

The microgripper mechanism is investigated through graphical, numerical and experimental techniques. Fig. 15 shows the performance of the compliant mechanism with conventional rigid body mechanism, from that the output displacement of the compliant based microgripper is closer to the conventional rigid body mechanism for the minimum input displacement. Geometrical advantage of the mechanism also calculated as approximately 5 from the graphical position analysis, 4.8 from the finite element

Conclusion

In this research work, a systematic methodology is developed for the design of a compliant mechanism based microgripper and its functional characteristics are verified experimentally as well as numerically. The conceptual design of mechanism for the microgripper is developed through topology optimization technique. The critical geometrical parameters influencing the precision motion of the flexure hinge design are investigated numerically and particularly, gripping force and geometrical

R. Bharanidaran, born in Kallakurichi, Tamilnadu, India on 4th July 1985. He received his M.E. degree in Computer Aided Design from Anna University, Chennai, India in 2008. He obtained his Bachelor degree in Mechanical Engineering from Anna University, Chennai, India in 2006. He worked as software programmer in CADS software, Chennai for six month and as an Assistant Professor in KCG college of Technology, chennai for One year. Currently he is pursuing his Doctoral Degree in the area of Micro

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      However, the optimization space used is both computationally complex and non-convex, which limits its use in multi-DOF mechanisms [13]. Compliant mechanisms such as bridge-mechanisms, microgrippers, force-inverters, and simple multi-DOF stages have been optimized [14–17]. For a detailed survey see [18].

    • Design of compliant mechanisms using continuum topology optimization: A review

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      Great efforts have been made by various researchers who attempted to remove the de facto hinges to obtain CMs with distributed compliance. These efforts can be broadly classified into the following five categories: (I) second-stage design operation strategy [164–166], (II) modified finite element discretization [84,109,167–170], (III) modified optimization procedure [42,171–176], (IV) imposition of length scale control [99–101,177–185], and (V) hinge-free objective functions [159–161,171,186–194]. For the design of CMs using continuum topology optimization, it was Yin and Ananthasuresh [160] who first tried to develop new optimization formulations to overcome the point flexure problem.

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      Nevertheless, optimizing sections within an otherwise heuristically designed mechanism can yield significant improvements. Topology optimization has previously been used to optimize micro-grippers, bridge-amplifiers, and flexure hinges [21–24]. Further, early results on leaf flexure optimizations were reported in Ref. [25].

    • Topology optimisation of bridge input structures with maximal amplification for design of flexure mechanisms

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      Consequently, the impact on the optimal choice of bridge topology and element sizing as the load is modified is analysed. Topology optimisation techniques have been applied to some areas of micro/nano positioner design, however the heuristic approach is the most prevalent in this field [28,29]. Characterisation of optimal bridge structures will allow a hybrid design approach, where heuristic techniques could be used with optimal flexural elements to assemble complex multi-DOF mechanisms, which would be hard to discover using local gradient based solvers.

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    R. Bharanidaran, born in Kallakurichi, Tamilnadu, India on 4th July 1985. He received his M.E. degree in Computer Aided Design from Anna University, Chennai, India in 2008. He obtained his Bachelor degree in Mechanical Engineering from Anna University, Chennai, India in 2006. He worked as software programmer in CADS software, Chennai for six month and as an Assistant Professor in KCG college of Technology, chennai for One year. Currently he is pursuing his Doctoral Degree in the area of Micro System Design at National Institute of Technology, Tiruchirappalli, Tamilnadu, India.

    T. Ramesh, born in Chidambaram, Tamilnadu, India on 3rd May 1972. He received his PhD degree in Mechanical Engineering from Bharathidasan University, India in 2006 and M.E. degree in Engineering Design from Government College of Technology, Coimbatore, India in 1997. He obtained his Bachelor degree in Mechanical Engineering from Madras University in 1995. Presently he is working as an Assistant Professor in the department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli, Tamilnadu, India. He has published more than 20 technical papers in the international journals. His fields of research interest are finite element method, MEMS and Microsystems, Biomaterials and Composite Materials. He is a life member of ISTE (Indian Society for Technical Education).

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