Structure Design of a New Compliant Gripper Based on Scott-Russell Mechanism Qingsong Xu, Member, IEEE Abstract— This paper presents the structure design and analysis of a novel compliant gripper based on the Scott- Russell (SR) mechanism. An SR mechanism in combination with a parallelogram mechanism enables the achievement of a pure translation of the gripper tips, which is attractive for practical micromanipulation and microassembly applications. As compared with traditional pure-translation grippers, the reported SR-based one exhibits a simple structure as well as compact dimension due to the full use of the in-plane space. The kinematics model of the gripper mechanism is established and finite-element analysis simulations are carried out to verify the structure design. The results not only demonstrate the feasibility of the proposed SR-based gripper design but reveal a promising performance of the gripper when driven by a piezoelectric stack actuator. Moreover, several variations of the gripper structure are presented as well. I. INTRODUCTION Robotic micro- and nano-handling systems are important to realize automated manipulation and assembly of objects in micro- and nanometer scales [1]. As a crucial device in micro-handling systems, microgripper has attracted in- tensive attentions from both academia and industry. Based on different driving principles, various types of microgrip- pers have been previously proposed, such as electrostatic [2], electrothermal [3], and piezoelectric microgrippers [4]. Particularly, piezoelectric actuator is attractive thanks to its property of quick response speed and ultrahigh positioning resolution [5], [6]. Therefore, piezoelectric stack actuator (PSA) is employed for the drive in this research. Concerning the structure design, a great number of mi- crogrippers have been devised using compliant mechanisms. The reason lies in that, as compared with the traditional bearings, compliant mechanisms produce motion by making use of elastic deformation of the material. Hence, compliant mechanisms offer some advantages in terms of backlash- free, friction-free, and lubrication-free [7]–[11]. However, most of the existing microgrippers are constructed with two arms which work based on rotary motion [12]. It is known that the reaction force will appear at the contact points once the gripper tips make contact with the target object. When grasping some object with curved surface, the reaction force may push the grasped object away from the gripper tips [13]. Hence, it is desirable to device microgrippers whose tips This work was supported in part by the Macao Science and Technology Development Fund under Grant 070/2012/A3 and in part by the Research Committee of the University of Macau under Grants MYRG083(Y1-L2)- FST12-XQS and MYRG078(Y1-L2)-FST13-XQS. The author is with the Department of Electromechanical Engineering, Faculty of Science and Technology, University of Macau, Av. Padre Tom´ as Pereira, Taipa, Macao, China qsxu@umac.mo provide a pure translational motion [14], [15]. Nonetheless, majority of parallel-motion grippers possess a complicated structure [13], [14], which complicates the analysis and fabrication procedures. The motivation of this research is to devise a new parallel- motion gripper with simple structure. Specifically, a Scott- Russell (SR) mechanism and a parallelogram mechanism is adopted to design the structure of each gripper arm. SR mechanism has been previously employed to develop micropositioning systems. For instance, two SR mechanisms were used in [16] to construct a two-level amplification of PSA stroke for the actuation of a micropositioniner. An optimal design of the SR-based micropositioning mechanism was presented in [17] with the aim of achieving a maximum amplification of the small displacement of PSA. More re- cently, an SR mechanism was employed in [18] to device an ultraprecision rotary micropositioning stage. However, limited effort has been made in the literature towards the extension of SR mechanism to gripper design. In this paper, a novel compliant gripper is devised based on the SR mechanism. It is shown that the employment of the SR mechanism facilitate the structure design of a gripper with simple architecture. In comparison with tradi- tional microgrippers, the proposed SR-based gripper allows the generation of a simple structure. Moreover, a compact dimension is achieved since the in-plane area has been fully used. The feasibility and performance of the proposed gripper is validated through finite-element analysis (FEA) simulations. In the remainder of this paper, the mechanism design process of an SR-based compliant gripper is presented in Section II, where kinematics model is establish to predict the displacement output of the gripper mechanism. Section III presents static and dynamic analyses which are conducted by resorting to FEA simulations. Discussions about the gripper performance and future work are reported in Section IV. Finally, Section V concludes this paper. II. MECHANISM DESIGN Fig. 1 shows a CAD model of the devised compliant gripper. The flexure hinge-based gripper mechanism is de- signed by a proper arrangement of the SR and parallelogram mechanisms. The gripper is actuated by a piezoelectric stack actuator (PSA). A preloading screw is used to adjust the preloading force between the PSA and gripper mechanism. The gripper structure consists of two SR mechanisms as well as two parallelograms. The SR mechanisms are used to amplify the PSA stroke. The role of the two parallelogram 978-1-4799-2744-9/13/$31.00 ©2013 IEEE Proceeding of the IEEE International Conference on Robotics and Biomimetics (ROBIO) Shenzhen, China, December 2013 1623