Structure Comparison and Optimal Design of 6-RUS Parallel Manipulator Based on Kinematic and Dynamic Performances

Abstract

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...

Design of Dynamic Controllers for Continuous Paths on Parallel Platforms (Slide Modes and PD+)

“…It consists of guiding the trajectories of the system to a sliding surface in the phase diagram, which exists if in the vicinity the tangent or velocity vectors point in the direction of said surface as described in equation 4and (5).…”

“…On the other hand, there are closed kinematic chains, characterized by having rigidity in high speed applications and accelerations of up to 50 times the value of gravity [4,5,6]. For its design, complex kinematic and dynamic calculations are required, due to non-linear behaviours, internal singularities, reduced workspace and non-acted joints [7,8].…”

Kinematics analysis and testing of novel 6-P-RR-R-RR parallel platform with offset RR-joints

“…The parallel structure is different from the usual three-legged 6-DOF parallel mechanisms: 3- R R P S chains, 42 3- RP SR chains, 43 3- RP RS chains, 44 3- P R P S chains, 45 3-3- PP SR chains, 46 3- PP SP chains, 47 and 3-RRRS chains. 48 And it is also different from the common six-legged 6-DOF parallel mechanisms: 6-S P S chains 2 (this type of mechanisms is usually called a Stewart platform), 6-U P S chains 49 (this type of mechanisms is the most frequently used in applications, and is usually called as a Gough platform or a Hexapod), 6- P US chains 50 (the first example of such architecture), 6- R US chains 51,52 (this type of chain was first presented by Hunt), 6-U C U chains, 53 6-RR C RR chains, 31,32,54 6- P FF chains, 34 and other 6-DOF parallel platform with miscellaneous chains. 55–57…”

Design Optimization of 6-RUS Parallel Manipulator Using Hybrid Algorithm

“…C. Bonilla and A. Alexander proposed a solution for the optimization of the orientation workspace of the Stewart 6-RUS platform using the PSO algorithm [7]. Mirshekari et al presented a structure comparison and optimal design of 6-RUS parallel manipulator based on kinematic and dynamic performances, where the 6-RUS manipulator structure is optimized using the modified multi objective Bees Algorithm [8].…”

“…Three samples of the most well-known 6-RUS group manipulators are classified in [8], and these samples include Hunt type (Hunt, 1983), Hexa (Pierrot, 1990) and a manipulator named Zamanov type (Merlet, 2006) ( Fig. 1).…”