A Totally Decoupled Piezo-Driven XYZ Flexure Parallel Micropositioning Stage for Micro/Nanomanipulation

This paper reports the design and development processes of a totally decoupled flexure-based XYZ parallel-kinematics micropositioning stage with piezoelectric actuation. The uniqueness of the proposed XYZ stage lies in that it possesses both input and output decoupling properties with integrated displacement amplifiers. The input decoupling is realized by actuation isolation using double compound parallelogram flexures with large transverse stiffness, and the output decoupling is implemented by employing two-dimensional (2-D) compound parallelogram flexures. By simplifying each flexure hinge as a two-degree-of-freedom (2-DOF) compliant joint, analytical models of kinematics, statics, and dynamics of the XYZ stage are established and then validated with finite-element analysis (FEA). The derived models are further adopted for optimal design of the stage through particle swarm optimization (PSO), and a prototype of XYZ stage is fabricated for performance tests. The nonsymmetric hysteresis behavior of the piezo-stage is identified with the modified Prandtl-Ishlinskii (MPI) model, and a control scheme combining the inverse model-based feedforward with feedback control is constructed to compensate the plant nonlinearity and uncertainty. Experimental results reveal that a submicron accuracy 1-D and 3-D positioning can be achieved by the system, which confirms the effectiveness of the proposed mechanism and controller design as well. Note to Practitioners-Motivated by the requirement of developing a decoupled XYZ micropositioning stage for 3-D micro/nanomanipulation uses, a novel spatial parallel mechanism incorporating flexure hinges is presented in this paper, and piezoelectric actuators (PZTs) owning large output force and stiffness are used for actuation. The piezo-stage has the merits of not complicated structure as well as both input and output decoupling properties. By input decoupling, the PZTs are isolated and protected. With output decoupling, the parallel stage behaviors like a serial one, which enables the adoption of single-input-single-output (SISO) controller for each axis. Before the fabrication of the stage, its parameters are optimized to achieve a high resonant frequency under performance constraints in terms of workspace size, input stiffness, and safety of material, etc. Analytical models for the above performances are derived and the optimized stage is fabricated from Al-7075 alloy by the wire electrical discharge machining (EDM) process for experimental demonstrations. The results provide a sound basis in developing an alternative piezo-stage for micro/nanoscale manipulation. The design and control methodology can be extended to other types of stages as well.