| Compared with serial-structure-based manipulators, parallel manipulators have potential advantages in terms of stiffness, payload, etc. In certain applications that require less than six degrees of freedom (or lower mobility) task motions, parallel manipulators are especially more suited than their serial counterparts. In this dissertation, we study a new design method, called “Integrated Design Method”, for the design of lower-mobility parallel manipulators. The design parameters of the integrated design method consist of both mechanical structure parameters such as link length, mass, mass center location, etc. and control parameters such as PID feedback gains. All these design parameters would be included in the kinematic and dynamic models of the selected parallel manipulator candidate. In addition to rigid body kinematics and dynamics, we also studied the kinematics and dynamics of lower-mobility parallel manipulators with flexible links/joints. With the derived model, several performance indexes, such as workspace, condition number, motion type error and lowest natural frequency of flexible parallel manipulators, were defined and formulated. Then, the design problem was translated into an optimization problem by proper combination of these performance indexes, and the two groups of design parameters could be obtained simultaneously.;A planar parallel manipulator, named the HKUST Planar-Delta, was selected to validate the design theory. Mechanical parameters such as the link shape and controller parameters such as the PD feedback gains were chosen as the design variables. Kinematic and dynamic models considering link flexibility were derived and identified by simulations and experiments. With the design specification extracted from the positioning stage of LED wire bonding machines, a multi-objective optimization problem was formulated and solved. Finally from the experimental results, it can be concluded that using the integrated design method, the lowest natural frequency of the Planar-Delta was increased by 30% averagely while other requirements on the workspace and accuracy were all satisfied. |
