Performance investigations on mechanical design and motion control of plannar parallel manipulators

Abstract

In this study, a new family of planar parallel manipulators namely square shape/U-base planar parallel manipulator starting with an active prismatic joint on each limb is proposed. In order to identify the best configurations of this family, comparative kinematic and dynamic analyses are performed. The kinematic performance is quantified with the local performances indices namely stiffness, payload, manipulability, and isotropy. From the results, it is observed that PPR-PRP-PRP, PRP-PRP-PRP and PRR-PRP-PRP manipulators associated with the equilateral triangle end-effector have better kinematic design aspects as compared to other manipulators of the family of U-base manipulators. Moreover, from the kinematic analysis it is found that the end-effector shape is also influencing the manipulator performance, in other words joint locations of the limbs at the end-effector is influencing the performance. Therefore, further kinematic analyses of top three manipulators with two different end-effector shapes namely an equilateral triangle (three-point contact) and a square (one point contact) are investigated and compared. From the overall results, it is found that the PPR-PRP-PRP and PRR-PRP-PRP manipulators associated with square shape end-effector have better kinematic design aspects. Furthermore, the present research presents a comparative dynamic performance analysis of the top three U-base manipulators in terms of dynamic driving performance measures, dynamic manipulability, force, and energy requirements. From the numerical results, it is iv observed that the PPR-PRP-PRP manipulator provides better performances namely higher manipulability, good payload capability, higher isotropy, better stiffness, better driving performance, less energy and force requirements as compared to other manipulators. The identified best U-base manipulator namely PPR-PRP-PRP is further analysed with its motion capabilities and closed-loop control behavior. In this regard, an improved sliding mode control along with a nonlinear disturbance observer is first designed and compared with other controllers. In view of recent development in soft computing, to minimizing the settling time and steady state error of the manipulator, it also proposes a PID-like fuzzy logic control for the motion control of the PPR-PRP-PRP manipulator. These proposed controllers are employed to obtain a stable, fast tracking response with low sensitivity to the disturbances. The effectiveness and robustness of these controllers are demonstrated through the help of prototype experiments. Experimental results demonstrated that the manipulator along with the proposed controllers display considerably better on motion performance in terms of low tracking errors and high positioning accuracy. Further performance of these controllers is compared with traditional and recently developed controllers. Finally, the usefulness of the proposed PPR-PRP-PRP planar parallel manipulator is presented through the help of two different real-time applications namely a worktable of a vertical milling machine and a passive sitting type lower limb rehabilitation mechanism. In overall, this research work shows the U-base planar parallel manipulators are superior alternatives to conventional motion stages for high speed, high rigidity, high precise positioning, and tracking applications. Note: All three limbs of the manipulator are connected at one point of the end-effector is considered as square/rectangular shape end-effector throughout the present thesis. Also, all three limbs of the manipulator are connected to the end-effector through three different points is named as an equilateral triangle shape end-effector.