Design of a Flexure-Based XYZ Micropositioner With Active Compensation of Vertical Crosstalk

This paper presents the design and development of a new flexure-based XYZ micropositioner with a hybrid kinematic configuration. A piezoelectric-driven Z stage is embedded into a parallel-kinematic XY stage actuated by two voice coil motors. The XYZ micropositioner features a sizeable workspace with a compact architecture, which benefits from employing deployable mechanisms and mixed actuators. One uniqueness is that the Z-axis crosstalk error of the XYZ micropositioner is compensated by the closed-loop motion control of the Z stage, which achieves a constant vertical position of the center platform when performing planar motion tasks. Analytical models have been derived based on fixed-guided beam theory to assess the driving stiffness of the mechanism. The finite element analysis is carried out to verify the accuracy of the derived models. A prototype system of the XYZ micropositioner is fabricated with the dimension of 116 mm $\times116$ mm $\times45$ mm (i.e., 216 mm $\times216$ mm $\times45$ mm with actuators). Experimental results indicate that it obtains a workspace of 4.15 mm $\times4.06$ mm $\times0.04$ mm with a crosstalk of less than 1% among the three axes. With the active control of the Z-axis position, the vertical crosstalk error has been dramatically reduced from 7.333 to $1.719~\mu \text{m}$ . The proposed design provides a promising approach to enable pure planar motion for ultrahigh precision applications requiring optical or electron focusing, such as electron beam lithography. Note to Practitioners—Flexure-based micropositioners are essential for the semiconductor manufacturing process, atomic force microscopy, and microassembly, due to their high precision and reliability. Many applications demand a planar motion without vertical crosstalk to realize ultrahigh precision operation. For the first time, this paper proposes the concept design of an XYZ micromanipulator by utilizing a Z stage to compensate for the vertical crosstalk error generated by the X/Y-axis motion, which is not considered and is difficult to realize in conventional XY flexible stage design. The simulation has confirmed the effectiveness of the derived analytical models. The XYZ micropositioner’s static and dynamic characteristics are then experimentally evaluated on a fabricated prototype. The travel stroke, coupling displacement, driving stiffness, and resonant frequency have been tested. Experimental results reveal that the active compensation has significantly diminished the Z-axis parasitic errors. The performance comparison results validate the superiority of the proposed concept design.

I. Introduction

Owing to its benefits of no friction, no clearance, monolithic structure, and ease of miniaturization, flexure-based mechanisms have been implemented in a variety of precision devices, including micropositioners, microgrippers, and other micromanipulators [1], [2], [3], [4], [5], [6], [7]. In particular, the compliant micropositioner is popularly applied in the fields of biomedical engineering, advanced manufacturing, micromanipulation, and microassembly [8], [9], [10], [11], [12], [13], [14]. According to the number of motion degrees of freedom (DOF), flexible translational micropositioners can be categorized into three types, i.e., one-dimension (1-D) (X/Y), 2-D (XY), and 3-D (XYZ) stages [15], [16], [17]. As the dimension of motion increases, so does its design and manufacture complexity. Given their operational flexibility and functional integration, flexure-based XYZ micropositioners are demanded in various application circumstances.