Optimal Design of a PZT Bimorph Actuator for Minimally Invasive Surgery

A metamodel-based approach is developed to optimize the force and displacement performance of a piezoceramic bimorph actuator. A segmented design with a variable piezoceramic layer thickness is proposed, where the thicknesses of discrete piezoceramic segments are used as the design variables. Design of experiments and metamodeling techniques are employed to construct computationally inexpensive approximations of finite element simulations of the PZT bimorph actuator. The metamodels are then used in lieu of the actual FEM for optimization. Design objectives include maximum tip deflection, maximum grasping force, and maximum work available at the tip. The metamodels are also used to rapidly generate the design space and identify the Pareto frontier for the competing design objectives of maximum deflection and maximum force. The accuracy and efficacy of two types of metamodels —response surfaces and kriging models —are compared in this study. By optimizing the thickness of the piezoceramic layers, and by allowing the voltage applied to each segment to vary, dramatic improvements in deflection and force are obtained when compared to a standard straight bimorph actuator. The motivation for this design is the need in the field of minimally invasive surgery for improved grasping tools, where a pair of optimized bimorph actuators can be used as a simple grasping device.