Mohammad Hossein Saadatzi

A GEOMETRIC CONSTRUCTIVE APPROACH FOR THE WORKSPACE ANALYSIS OF SYMMETRICAL 5-PRUR PARALLEL MECHANISMS (3T2R)

This paper investigates an important kinematic property, the constant-orientation workspace, of five-degree-of-freedom parallel mechanisms generating the 3T2R motion and comprising five identical limbs of the WR type. The general mechanism originates from the type synthesis performed for symmetrical 5DOF parallel mechanism. In this study, the emphasis is placed on the determination of constant-orientation workspace using geometrical interpretation of the so-called vertex space, i.e., motion generated by a limb for a given orientation, rather than relying on classical recipes, such as discretization methods. For the sake of better understanding a CAD model is also provided for the vertex space. The constructive geometric approach presented in this paper provides some insight into the architecture optimization. Moreover, this approach facilitates the computation of the evolution of the volume of the constant-orientation workspace for different orientations of the end-effector.

Optimal multivariable two-degree-of-freedom control of electric wheelchair using non-dominated sorting genetic algorithm-II

Electric wheelchairs (EW) experience various terrains surfaces and slopes as well as occupants with diverse weights. This, in turn, imparts a substantial amount of perturbation to the EW dynamics. In this paper we make use of a two-degree-of-freedom control architecture called disturbance observer (DOB) which reduces sensitivity to model uncertainties while enhancing rejection of disturbances which occur when entering slopes. The feedback loop which is designed via characteristic loci method (CLM) is then augmented with a DOB containing a parameterized low-pass filter. According to the disturbance rejection, sensitivity reduction, and noise rejection of the whole controller, three performance indices are defined which enable us to pick the filters optimal parameters using a multi-objective optimization (MOO) approach called non-dominated sorting genetic algorithm-II (NSGA-II). Finally, experimental results show desirable improvement in stiffness and disturbance rejection of the proposed controller as well as its robust stability.

Forward kinematic problem and constant orientation workspace of 5-RP̲RRR (3T2R) parallel mechanisms

This paper investigates some kinematic properties of a five-degree-of-freedom parallel mechanism generating the 3T2R motion and comprising five identical limbs of the RP̲UR type. In this study, two classes of simplified designs are proposed whose forward kinematic problems have either a univariate or a closed-form solution. The principal contributions of this study are the solution of the forward kinematic problem for some simplified designs—which may have more solutions than the FKP of the general 6-DOF Stewart platform with 40 solutions—and the determination of the constant orientation workspace based on algebraic geometry (Bohemian domes).