The effects of distinctive parameters such as revolute joint angle or spherical joint location of mobile platform in a 6-DOF 6-RUS parallel manipulators on workspace, kinematic, and dynamic indices are investigated in this study to select proper structure commensurate with performance. Intelligent multi-objective optimization method is used to design the manipulator. Considering distinctive parameters, relevant relations for developing inverse kinematic and Jacobin matrix are obtained. In order to study dynamic properties, mass matrix is obtained from calculating the total kinetic energy of the manipulator. After modifying multi-objective Bees algorithm, it used to optimize the manipulator structure considering all geometrical parameters with proper constraints. In addition of comparison of three well known 6-RUS manipulators' types, variation diagram of workspace, local and global dynamics and kinematics performance indices have been drawn with respect to structural parameters variation and limitation of these parameters with proper value are determined. Moreover, considering all dimensional parameters, Pareto front line of multi objective optimization of structure is presented based on dynamic and kinematic performance in pre-determined workspace. Based on the results, a fairly comparison among various types of 6-RUS manipulators can be conducted and the most appropriate set of dimensional parameters are selected based on specific demand. are made of mobile platform which is connected to a fixed platform by several parallel arms. Parallel manipulators can be classified based on degree of freedom, number of arms, order of joints in each arm and type of actuator (Merlet, 2006). according to this, various 6-DOF parallel manipulators have been proposed. One of the most important 6-DOF parallel manipulators is 6-RUS manipulators that revolute joint, universal joint, and spherical joint are used in each arm, respectively.A 6-RUS manipulators has some advantages that the most important one, is low weight of movable parts because of installing motor in the fixed platform. Therefore, bigger and cheaper electrical motors can be used. In addition, thinner connecting rod can be used to the mobile platform that conclude reduction of collision of links to each other (Bonev, 2002). Moreover, these manipulators can be balanced statically (Gosselin and Wang, 2000). Although this type of manipulator has some disadvantages such as bending in connecting rods and complicated mechanical analysis. Also, because of great number of chains, connecting the fixed base with the moving platform, and movment limitations of passive joints, such as spherical and universal, workspace of the 6-RUS manipulators are restericted. To overcome such drawbacks, some researchers demonstrate the tendency for the use less than 6-degree-of-freedom parallel mechanisms (Chablat and Wenger, 2003;Gosselin et al., 2007;Clavel, 1991) and for 6-dof applications hybrid manipulators are studied (Caro et al., 2015).The first 6-RUS manipulator was proposed b...

Squeeze film damping is an important factor in the dynamic stability of the bi‐axial microelectromechanic systems. The purpose of this article is to provide an analytical solution for calculating the air squeeze film damping in bi‐axial torsional micro‐mirrors, considering the changes of pressure distribution in rotation around different axes. This is the first time that has been done for a circular micro‐mirror. One of the advantages of bi‐axis micro‐scanners compared to single‐axis types is the larger space covered by the scan in different axes. To calculate the pressure distribution in different rotation of micro‐mirror and also to achieve the squeeze film damping torque, Reynolds nonlinear equations have been used in polar coordinates, which have been solved by Taylor series expansion and also by eigenfunction expansion method. The results are verified with previous research in single‐axis mode. The results also show that with increasing gap between the micro‐mirror and the scanner substrate, the coefficient squeeze film damping will be less, but if the air gap is not changed, increasing the micro‐mirror radius will increase the damping coefficient. When the radius of micro‐mirror decrease, in order for the damping coefficient to be higher, the angle of rotation of the micro‐mirror must be greater too. The results of this article can be used for accurate modeling of squeeze film damping in micro‐scanners, control of dual‐axis torsion micro‐mirrors, and improvement of their efficiency.

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