Sliding-mode control of a flexure based mechanism using piezoelectric actuators

The position control of designed 3 PRR flexure based mechanism is examined in this paper. The aims of the work are to eliminate the parasitic motions of the stage, misalignments of the actuators, errors of manufacturing and hysteresis of the system by having a redundant mechanism with the implementation of a sliding mode control and a disturbance observe. x-y motion of the end-effector is measured by using a laser position sensor and the necessary references for the piezoelectric actuators are calculated using the pseudo inverse of the transformation matrix coming from the experimentally determined kinematics of the mechanism. The effect of the observer and closed loop control is presented by comparing the results with open loop control. The system is designed to be redundant to enhance the position control. In order to see the effects of the redundant system firstly the closed loop control for active 2 piezoelectric actuators experiments then for active 3 piezoelectric actuators experiments are presented. As a result, our redundant mechanism tracks the desired trajectory accurately and its workspace is bigger

Design and optimization of a long travel, two-axis flexural nanopositioning stage

This thesis details the design, computational optimization, and resultant evaluation of a two-axis flexural nanopositioning stage based on a modified version of a double parallelogram flexure which features underconstraint-eliminating features nested within the flexural bearing. The stage was optimized using a response surface model with the seven most sensitive geometric parameters for the flexural bearing as inputs, and the flexure’s peak stress and reaction force at maximum deflection as outputs. This paper shows that—through design optimization—the first resonant mode of a long travel, two-axis flexural nanopositioning stage that has previously been reported in literature can be improved by a factor of two while still maintaining the higher-order resonant modes to be at least an order-of-magnitude higher than the fundamental mode of the stage. This improvement is critical because increasing the fundamental mode without sacrificing the higher order modes will allow for a higher bandwidth controller to be implemented on this nanopositioning stage. The end goal of the positioning stage detailed in this paper is to be implemented within a micro-SLS 3D printer.Mechanical Engineerin

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

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

Design and computational optimization of a flexure-based XY nano-positioning stage

This thesis presents the design and computational optimization of a two-axis nano-positioning stage. The devised stage relies on double parallelogram flexure bearings with under-constraint eliminating linkages to enable motion in the primary degrees-of-freedom. The structural parameters of the underlying flexures were optimized to provide a large-range and high bandwidth with sub-micron resolution while maintaining a compact size. A finite element model was created to establish a functional relationship between the geometry of the flexure elements and the stiffness behavior. Then, a neural network was trained from the simulation results to explore the design space with a low computational expense. The neural net was integrated with a genetic algorithm to optimize the design of the flexures for compactness and dynamic performance. The optimal solutions resulted in a reduction of stage footprint by 14% and an increase in the first natural frequency by 75% relative to a baseline design, all while preserving the same 50mm range in each axis with a factor of safety of 2. This confirms the efficacy of the proposed approach in improving stage performance through an optimization of its constituent flexures.Mechanical Engineerin

Micro position control of a designed 3-PRR compliant mechanism using experimental models

A new compliant stage based on 3-PRR kinematic structure is designed to be used as a planar micro positioner. The mechanism is actuated by using piezoelectric actuators and center position of the stage is measured using a dual laser position sensor. It's seen that manufactured mechanism has unpredictable motion errors due to manufacturing and assembly faults. Thus, sliding mode control with disturbance observer is chosen to be implemented as position control in x-y axes of the center of the mechanism. Instead of piezoelectric actuator models, experimental models are extracted for each actuation direction in order to be used as nominal plants for the disturbance observer. The position control results are compared with the previous position control using linear piezoelectric actuator models and it's seen that the implemented control methodology is better in terms of errors in x and y axes. Besides, the position errors are lowered down to ±0.06 microns, which is the accuracy of the dual laser position sensor

Modelling and design of a flexure-based precision positioning system

The paper presents the model and design of a flexure-based 4 DOF precision positioning system for micro-positioning uses. The positioning system is featured with monolithic architecture, flexure-based joints and ultra-fine adjustment screws. The monolithic structure for the require movements has been optimized with Solidworks Simulation software package. The mathematical model for the output displacements of the positioning system has been verified by resorting to finite element analysis (FEA) using ANSYS software package. The established analytical and (FEA) models are helpful for a reliable architecture optimization and performance improvement of the precision positioning systems

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

Modeling and tracking control of a novel XYθz stage

A XYθz stage is designed and experimentally tested. This developed stage is driven by three piezoelectric actuators (PZTs) and guided by a flexure hinge based mechanism with three symmetric T-shape hinges. It was manufactured monolithically by using wire electrical discharge machining technology. In addition, considering the both electrical and mechanical characteristics, a third-order dynamic model of the 3-DOF system has been established to investigate the relationship between the input voltage and the output displacement of the entire system. The parameters of the third-order dynamic model were estimated by using the system identification toolbox. Furthermore, decoupling control is also proposed to solve the existed coupling motion of the stage. In order to compensate the hysteresis of PZT, the inverse Bouc-Wen model was utilized as a feedforward hysteresis compensator. Finally, extensive experiments were performed to verify the good decoupling and tracking performances of the developed stage

A planar 3-DOF nanopositioning platform with large magnification

AbstractPiezo-actuated flexure-based precision positioning platforms have been widely used in micro/nano manipulation. A conventional major challenge is the trade-off between high rigidity, large magnification, high-precision tracking, and high-accuracy positioning. A compact planar three-degrees-of-freedom (3-DOF) nanopositioning platform is described in which three two-level lever amplifiers are arranged symmetrically to achieve large magnification. The parallel-kinematic configuration with optimised sizes increases the rigidity. Displacement loss models (DLM) are proposed for the external preload port of the actuator, the input port of the platform and the flexible lever mechanism. The kinematic and dynamic modelling accuracies are improved by the compensation afforded by the three DLMs. Experimental results validate the proposed design and modelling methods. The proposed platform possesses high rigidity, large magnification, high-precision circle tracking and high-accuracy positioning