Design optimization of a spatial hybrid mechanism for micromanipulation

Traditional parallel manipulators suffer from errors due to backlash, hysteresis, and vibration in the mechanical joints. The hybrid mechanism is built through the reconfiguration of parallel-serial structure. In this paper, a new 3SPS + RPR spatial hybrid mechanism which has three degrees of freedom (DOF) and can generate motions in a microscopic scale is proposed. As a reliable compliant hybrid mechanism which provides micro/nano scale micromotion with high accuracy, it can be utilized for biomedical engineering and fiber optics industry. The detailed design of the structure is first introduced, followed by the kinematic analysis and performance evaluation. Based on the kinetostatic model, the joint and link compliances of the passive constraining leg are investigated. Second, a finite-element analysis of resultant stress, strain, and deformations is evaluated based upon different inputs of the three piezoelectric actuators. Finally, the genetic algorithms and radial basis function networks are implemented to search for the optimal architecture and behavior parameters in terms of global stiffness/compliance, dexterity and manipulability. The proposed analysis and optimization methodology is intuitive and effective that offers a constructive way for design optimization of the family of parallel/hybrid manipulators.