Investigation of compact positioning systems and a linear actuator based on compliant mechanisms

Abstract

The applications of piezoelectric actuators (PEAs)­-based Compliant precision posi­tioning systems are popular in both academic and industrial applications, including precision machining, microscope, multi-­degree­-of­-freedom (DoF) systems and micro manipulation. Unlike conventional rigid motion pairs, compliant mechanisms deliver motions via the elastic deformations of the material, which feature no backlash and friction, high precision and resolution, and free of lubrication, thus achieving high res­olution as well as repeatability. However, the commercial PEAs generally have limited output displacements of dozens of hundreds of microns, hindering their further appli­cations to some extent. Precision positioning systems with large motion ranges are required in some applications such as microinjection and IC assembly. In general, the larger motion range the stage has, the bulker the stage is, and there is a tradeoff between larger work space and compact overall structural dimensions. Developing compact pre­cision positioning stages is in demand to some instruments. For instance, the majority of the commercial atomic force microscopes (AFMs) require compact PEA tube scan­ners. Moreover, the cross axis coupling is a problem that causes positioning errors of the compliant mechanisms with parallel kinematic principle, and thus requires further study. In this thesis, for the sake of developing compliant precision positioning stages with compact structures, good decoupling performances and large motion strokes, two kinds of 3­-DoF compliant positioning systems and a foldable 2­-DoF compliant posi­tioning systems are devised. Besides, a new linear actuator based on the parasitic motion principle (PMP) is proposed to achieve the long working stroke of the piezoelectric actuator. The main research parts are listed as follows: The first part presents a new precision XYZ compliant parallel­-kinematic stage with compact structure. In comparison with the existing parallel triaxial positioning stages, the newly designed stage features more compact size in the height. The design of the stage incorporates a Z­-shaped flexure hinge (ZFH) based mechanism to produce decoupled motions in both the z-­axis and the y­-axis. The matrix-­based method is used to determine the input stiffness of the proposed stage, and the finite element analysis (FEA) method is adopted to validate the results. In the second part, to obtain a monolithically fabricated compact XYZ stage with no assembly errors, a novel 3-­DoF parallel compliant manipulator inspired by the Tripteron mechanism is devised. Due to its unique configuration, the newly designed manipula­tor has the advantages of a compact structure and being free of assembly errors. The input stiffness of the manipulator is calculated based on the compliance matrix model­ing method, and it is confirmed by the FEA method. The third part focuses on investigating a foldable precision positioning stage, which has two states, namely the deployable state and fold state. The presented stage incorporates the compliant rolling­-contact element (CORE) joint into the design to con­nect the amplification mechanism and motion platform. The FEA method is employed to perform the static coupling test and modal analysis of the stage. The bridge type amplifier and other two modified amplifier mechanisms are presented and their ampli­fication ratio as well as dynamic performances are compared. A foldable stage is then developed, and its cross­-coupling and dynamic performances are investigated. The fourth part reports a new PMP linear actuator based on the symmetrical Z­-shaped compliant mechanism to meet the demand of designing PEAs with long work­ing stroke and high resolution. The mechanism design and the working principle of the newly designed linear actuator are elaborated. The theoretical model of the sym­metrical Z shaped compliant mechanism deformation is established, and is verified by the simulation analysis. The performance of the actuator is also investigated through experimental experiments on a built prototype. To sum up, three compact compliant precision positioning systems with different DoFs are developed, and a novel long­-stroke PMP linear actuator is designed in this thesis. The original contributions and significance can be concluded as follows: (1) A novel parallel 3­-DoF XYZ compliant precision positioning stage is devised, which has a more compact size in the height. (2) A new triaxial parallel-­kinematic compliant manipulator inspired by the Tripteron mechanism is developed, which features struc­ture compactness and free of assembly error. (3) A foldable precision positioning stage is investigated, which has two states, namely the deployable state and fold state. (4) A novel PMP linear actuator is proposed and studied, which provides a large motion stroke.