ISR edition:35th location:Paris date:23-26 March 2004
This paper deals with the design and optimization of PKMs specifically developed for applications in the MEMS area. Specifically, the mechanism here considered was at first studied in collaboration with the S.A.M.M. Lab
(Space Automation and Manufacturing Mechanisms Laboratory) of the University of Florida and consists of a mobile
platform supported by 3 legs, symmetrically positioned around it. Each kinematic chain is P-R-S: the platform is
connected to the legs by spherical joints; each leg is then linked to a rack, which slides on a prismatic guide fixed at the base plate, by revolute joints. For the rack actuation the use of the motion devices prototyped and designed by SNL (Sandia National Lab) was adopted. The mechanism is conceived in poly-Si, using surface micromachining techniques and can be competitively applied in the optical transmission field, thanks to the better performance and the positioning accuracy achievable through the sophisticated motion device and the PK architecture. The structure has been analyzed at kinematic and dynamic levels, and then its structural behavior was considered too. In particular, a kinematics optimization was performed, in order to obtain an optimal design in terms of number of DoFs, positioning accuracy and footprint. Analyses results highlighted the advantages of using a simpler variant and the initial architecture configuration has been modified substituting the S-joints with universal joints. Specifically, linking together two couples of revolute joints with orthogonal axes by a L-shape plate, a new configuration of μ−universal joint was designed. The legs have been then rearranged in order to optimise the mobility of the mechanism with respect to its stiffness. Simulations were also performed in the combined multi-body and FEM environments to evaluate stresses in the links and to minimize structural compliances.
After a brief introduction to the technological area of MEMS, the potentialities of PKMs applications in the micro world are presented. Successively, the main mechanical design limitations due to manufacturing constraints are discussed and the minimal set of requirements for the feasibility of complex μ-devices is identified. In Sect.4, the μ−PKM under consideration is described and the variant of the initial architecture proposed, while Sect.5 provides with the FEM design of critical components. Finally, conclusions are drawn.