A novel voice coil motor-driven compliant micropositioning stage based on flexure mechanism

This paper presents a 2-degrees of freedom flexure-based micropositioning stage with a flexible decoupling mechanism. The stage is composed of an upper planar stage and four vertical support links to improve the out-of-plane stiffness. The moving platform is driven by two voice coil motors, and thus it has the capability of large working stroke. The upper stage is connected with the base through six double parallel four-bar linkages mechanisms, which are orthogonally arranged to implement the motion decoupling in the x and y directions. The vertical support links with serially connected hook joints are utilized to guarantee good planar motion with heavy-loads. The static stiffness and the dynamic resonant frequencies are obtained based on the theoretical analyses. Finite element analysis is used to investigate the characteristics of the developed stage. Experiments are carried out to validate the established models and the performance of the developed stage. It is noted that the developed stage has the capability of translational motion stroke of 1.8 mm and 1.78 mm in working axes. The maximum coupling errors in the x and y directions are 0.65% and 0.82%, respectively, and the motion resolution is less than 200 nm. The experimental results show that the developed stage has good capability for trajectory tracking

Design of 3-legged XYZ compliant parallel manipulators with minimised parasitic rotations

This paper deals with the design of 3-legged distributed-compliance XYZ compliant parallel manipulators (CPMs) with minimised parasitic rotations, based on the kinematically decoupled 3-PPPRR (P: prismatic joint, and R: revolute joint) and 3-PPPR translational parallel mechanisms (TPMs). The designs are firstly proposed using the kinematic substitution approach, with the help of the stiffness center (SC) overlapping based approach. This is done by an appropriate embedded arrangement so that all of the SCs associated with the passive compliant modules overlap at the point where all of the input forces applied at the input stages intersect. Kinematostatic modelling and characteristic analysis are then carried out for the proposed large-range 3-PPPRR XYZ CPM with overlapping SCs. The results from finite element analysis (FEA) are compared to the characteristics found for the developed analytical models, as are experimental testing results (primary motion) from the prototyped 3-PPPRR XYZ CPM with overlapping SCs. Finally, issues on large-range motion and dynamics of such designs are discussed, as are possible improvements of the actuated compliant P joint. It is shown that the potential merits of the designs presented here include a) minimised parasitic rotations by only using three identical compliant legs; b) compact configurations and small size due to the use of embedded designs; c) approximately kinematostatically decoupled designs capable of easy controls; and d) monolithic fabrication for each leg using existing planar manufacturing technologies such as electric discharge machining (EDM)

A novel actuator-internal micro/nano positioning stage with an arch-shape bridge type amplifier

This paper presents a novel actuator-internal two degree-of-freedom (2-DOF) micro/nano positioning stage actuated by piezoelectric (PZT) actuators, which can be used as a fine actuation part in dual-stage system. To compensate the positioning error of coarse stage and achieve a large motion stroke, a symmetrical structure with an arch-shape bridge type amplifier based on single notch circular flexure hinges is proposed and utilized in the positioning stage. Due to the compound bridge arm configuration and compact flexure hinge structure, the amplification mechanism can realize high lateral stiffness and compact structure simultaneously, which is of great importance to protect PZT actuators. The amplification mechanism is integrated into the decoupling mechanism to improve compactness, and to produce decoupled motion in X- and Y- axes. An analytical model is established to explore the static and dynamic characteristics, and the geometric parameters are optimized. The performance of the positioning stage is evaluated through finite element analysis (FEA) and experimental test. The results indicate that the stage can implement 2-DOF decoupled motion with a travel range of 55.4×53.2 μm2, and the motion resolution is 8 nm. The stage can be used in probe tip-based micro/nano scratching

Creative design and modelling of large-range translation compliant parallel manipulators

Compliant parallel mechanisms/manipulators (CPMs) are parallel manipulators that transmit motion/load by deformation of their compliant members. Due to their merits such as the eliminated backlash and friction, no need for lubrication, reduced wear and noise, and monolithic configuration, they have been used in many emerging applications as scanning tables, bio-cell injectors, nano-positioners, and etc. How to design large-range CPMs is still a challenging issue. To meet the needs for large-range translational CPMs for high-precision motion stages, this thesis focuses on the systematic conceptual design and modelling of large-range translational CPMs with distributed-compliance. Firstly, several compliant parallel modules with distributed-compliance, such as spatial multi-beam modules, are identified as building blocks of translational CPMs. A normalized, nonlinear and analytical model is then derived for the spatial multi-beam modules to address the non-linearity of load-equilibrium equations. Secondly, a new design methodology for translational CPMs is presented. The main characteristic of the proposed design approach is not only to replace kinematic joints as in the literature, but also to replace kinematic chains with appropriate multiple degrees-of-freedom (DOF) compliant parallel modules. Thirdly, novel large-range translational CPMs are constructed using the proposed design methodology and identified compliant parallel modules. The proposed novel CPMs include, for example, a 1-DOF compliant parallel gripper with auto-adaptive grasping function, a stiffness-enhanced XY CPM with a spatial compliant leg, and an improved modular XYZ CPM using identical spatial double four-beam modules. Especially, the proposed XY CPM and XYZ CPM can achieve a 10mm’s motion range along each axis in the case studies. Finally, kinematostatic modelling of the proposed translational CPMs is presented to enable rapid performance characteristic analysis. The proposed analytical models are also compared with finite element analysis

Development of a piezo-driven 3-DOF stage with T-shape flexible hinge mechanism

This paper presents a 3-DOF (Degree of freedom) stage with T-shape flexible hinge mechanism for the applications in the precision measurement equipments and micro/nano manipulation systems. The stage is driven by three piezoelectric actuators (PEAs) and guided by a flexible hinge based mechanism with three symmetric T-shape hinges. The proposed T-shape flexible hinge mechanism can provide excellent planar motion capability with high stability, and thus guarantee the outstanding dynamics characteristics. The theoretical modeling of the stage was carried out and the stiffness and the dynamic resonance frequency have been obtained. The kinematic model of the 3-DOF stage was established and the workspace has been analyzed. The characteristics of the stage were investigated using finite element analysis (FEA). Experiments were conducted to examine the performance of the stage, through this stage, X-axis translational motion stroke of 6.9 µm, Y-axis translational motion stroke of 8.5 µm and rotational motion stroke along Z-axis of 289 µrad can be achieved. A hybrid feedforward/feedback control methodology has been proposed to eliminate the nonlinear hysteresis, the trajectory tracking performances and to reduce external disturbance of the 3-DOF stage

Design and analysis of symmetric and compact 2R1T (in-plane 3-DOC) flexure parallel mechanisms

Symmetry is very necessary in flexure mechanisms, which can eliminate parasitic motions, avoid buckling, and minimize thermal and manufacturing sensitivity. This paper proposes two symmetric and compact flexure designs, in-plane 3-DOC (degree of constraint) mechanisms, which are composed of 4 and 6 identical wire beams, respectively. Compared to traditional leaf-beam-based designs, the two present designs have lower stiffness in the primary motion directions, and have smaller stiffness reduction in the parasitic directions. Analytical modelling is conducted to derive the symbolic compliance equations, enabling quick analysis and comparisons of compliances of the two mechanisms. A prototype has been tested statically to compare with analytical models

Design and analysis of a compliant parallel pan-tilt platform

In combination of the advantages of both parallel mechanisms and compliant mechanisms, a compliant parallel mechanism with two rotational DOFs (degrees of freedom) is designed to meet the requirement of a lightweight and compact pan-tilt platform. Firstly, two commonly-used design methods i.e. direct substitution and FACT (Freedom and Constraint Topology) are applied to design the configuration of the pan-tilt system, and similarities and differences of the two design alternatives are compared. Then inverse kinematic analysis of the candidate mechanism is implemented by using the pseudo-rigid-body model (PRBM), and the Jacobian related to its differential kinematics is further derived to help designer realize dynamic analysis of the 8R compliant mechanism. In addition, the mechanism’s maximum stress existing within its workspace is tested by finite element analysis. Finally, a method to determine joint damping of the flexure hinge is presented, which aims at exploring the effect of joint damping on actuator selection and real-time control. To the authors’ knowledge, almost no existing literature concerns with this issue