Ultra-precision Positioning System Research Articles

A Novel Flexure Piezomotor With Minimized Backward and Nonlinear Motion Effect

Continuous, smooth, and highly linear displacement output with centimeter-scale stroke and nanometer-scale resolution is greatly attractive for an ultraprecision positioning system. On the foundation of piezoelectric actuation and compliant mechanism, a novel linear piezomotor with minimized backward and nonlinear motion property is designed. Specifically, a driving unit capable of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$xy$</tex-math></inline-formula> -direction decoupling displacement output is proposed to make the generated motion linear, and a flexure mechanism is introduced into the contact part to make the motion output continuous and nonbackward. Combined with double driving units and the flexure contact mechanism, a motion generation strategy is presented. For performing the motion generation strategy well, the kinematics model of the piezomotor is established. Then, the dimension parameters are optimized. After theoretical derivations, the piezomotor is analyzed and evaluated by finite-element analysis simulation. Finally, a proper control waveform is designed, and the motion generation performance tests are successfully carried out. The results uniformly confirm that the proposed piezomotor can output ultraprecision motion with 8-nm resolution and 10-mm stroke in a continuous and smooth manner, and the backward and nonlinear effects are successfully minimized within 100 Hz.

Dynamic surface control of bellows-driven ultra-precision positioning system based on nonlinear extended state observer

Dynamic surface control of bellows-driven ultra-precision positioning system based on nonlinear extended state observer

Analysis of an Ultra-precision Positioning System and Parametrization of Its Structural Model for Error Compensation

Conventional compensation of position errors of machine tools relies only on measured values. Due to this principle it is not always possible to compensate the errors in time, especially dynamic ones. Moreover, the relevant control variables cannot always be measured directly. Thus, this approach proves to be insufficient for high precision applications. In this context, a model-based error prediction allows for minimal position errors. However, ultra-precision applications set high demands for the models’ accuracy. This paper presents the design of an accurate and real time-capable structural model of an ultra-precision positioning system. The modeling method for the developed ultra-precision demonstrator is shown and the initial parameter identification is presented.

Ultra-precision positioning system using robust sliding mode observer and control

Abstract In this paper, the robust sliding mode control based on reduced order observer is proposed to overcome the model imperfections in ultra-precision positioning system. The reduced order sliding mode observer enables the states and the estimated outputs to be available for controller design. The manifold of the sliding mode control is composed of the estimated output only instead of system states. Using the reduced order observer, the sliding mode control is designed in output feedback form. The effectiveness of the proposed control algorithm has been proved from the application of an ultra-precision stage.

Identification of Dynamic Model for Ultra-Precision Positioning System

Abstract: In order to improve the control precision of the piezoceramic actuator in precision position system, a dynamic modeling of Ultra-precision Positioning System is proposed. A two-step identification strategy is adopted in this paper. Step 1: The linear model was identified based on step input response by least square method. Step 2: According to the step.1 result, the designed nonlinear observer was applied to estimate the output of hysteresis by Fast Tracking Differentiator. The polynomials are used consistently approximate continuous functions of f(.) and g(.) in the Duhem modeling based on the theorem of the Weierstrass polynomial approximation theory. Recursive least square methods are developed to identify α and the coefficients of the polynomials in Duhem model. At last , the simulation results show applicability, rapid convergence velocity and high calculation accuracy of the algorithm.

PZT 구동 스테이지의 위치 제어 성능 향상을 위한 제어기 설계

This paper describes a new robust control algorithm which can be used to enhance the positioning performance of an ultra-precision positioning system. The working table is supported by flexure hinges and moved by a piezoelectric actuator, whose position is measured by an ultra-precise linear encoder. The system dynamics is very complicated because the movement of the table is governed by both the mechanical characteristics and those of the PZT actuator. So that, the dynamics of the stage was modeled roughly in this paper, and the overall system was formularized to solve the small gain problem. A series of experiments was conducted in order to verify the usefulness of the proposed algorithm. From the experimental results, the positioning performance such as the accuracy, the rise time and the hysteresis nonlinearity were greatly improved.

Multi-scale Alignment and Positioning System – MAPS

Abstract In this article we describe the design of a universal ultra-precision positioning platform to be used in the development of many different nano-manufacturing processes. The system incorporates the concept of employing different interchangeable manufacturing and characterization tools with one ultra-precision positioning system. A multi-linear-motor-driven XY planar stage floating on a thin film of air is used to traverse a substrate through a 10 mm × 10 mm travel range with an XY linear position resolution of less than 1 nm and an angular resolution about the Z axis of 0.05 μrad over a range of about a degree (determined by plane mirror interferometer optics). A piezoelectric transducer (PZT) driven tripod positioning system is used to align each manufacturing and characterization tool with the substrate through a travel range of 40 μm along the Z axis and 245 μrad of rotation about the X and Y axes. The mechanical design, an overview of the system error analysis, preliminary component performance results, and the results of the first micro-imprint fabricated with the machine are presented.

Nano positioning control for dual stage using minimum order observer

A nano positioning control is developed using the ultra-precision positioning apparatus such as actuator, sensor, guide, power transmission element with an appropriate control method. Using established procedures, a single plane X-Y stage with ultra-precision positioning is manufactured. A global stage for materialization with robust system is combined by using an AC servo motor with a ball screw and rolling guide. An ultra-precision positioning system is developed using a micro stage with an elastic hinge and piezo element. Global and micro servos for positioning with nanometer accuracy are controlled simultaneously using an incremental encoder and a laser interferometer to measure displacement. Using established procedures, an ultra-precision positioning system (100 mm stroke and ±10 nm positioning accuracy) with a single plane X-Y stage is fabricated. Its performance is evaluated through simulation using Matlab. After analyzing previous control algorithms and adapting modern control theory, a dual servo algorithm is developed for a minimum order observer to secure the stability and priority on the controller. The simulations and experiments on the ultra precision positioning and the stability of the ultra-precision positioning system with single plane X-Y stage and the priority of the control algorithm are secured by using Matlab with Simulink and ControlDesk made in dSPACE.

Modeling and Control of Ultra Precision Positioning System for a Grating Ruling Machine

This paper presents a system modeling based control scheme of an ultra precision positioning system for a grating ruling machine. Since the positioning system having a long stroke with ultra precision, the positioning system consists of a coarse positioning stage driven by a servo motor and a fine positioning stage driven by a piezoelectric ceramic. In order to improve positional accuracy and remove the noise components of motion, a hybrid control scheme based on the system modeling is implemented. Considering position-dependent and time-dependent behaviors of the stages, a model based LQ controller is utilized to the coarse stage and a PID feedback controller based on neural network is utilized to the fine stage. Experiment results reveal the efficient and robust of the control scheme and show that the positional accuracy has been readily achieved within 8.6 nm.

Structural Feature-Based Model Templates Design for Ultra-Precision Positioning System

Ultra-precision mechanism lies in the core of ultra-precision electromechanical equipment, and is characterized by direct electromagnetic driving, air bearing supporting and ultra-precise vibration-isolation, putting a great challenge on design methodology and tools. This paper presents a model template design method which can provide effective computer aided design and engineering tools for new system design by encapsulating the design methods and design experience of ultra-precision mechanism into series of design templates. The model template contains toolkits both for forward structural design applied to new systems, and for the analysis and optimization of existing systems, as well as mathematical model and visualization tool in physical domain. The model templates are encapsulated and assembled according to the dynamical parameters and specific design parameters. Using planar electromagnetic drive structure in ultra-precision positioning system as an example, this paper discusses the design scheme of structure’s model template in detail, and introduces fast calculation method for magnetic field and visualization program, as well as forward design method for electromagnetic coil structure. Fast scheme design and analysis for ultra-precision mechanism can be achieved by using design templates.

Modeling and Validation of Ultra Precision Positioning System

Base on the significance of understanding research objects, modeling and validation of ultra precision positioning system is studied in this paper. Taking different reduction methods of leaf springs into consideration, a rigid body model and an elastic body model has been developed. Identifying unknown parameters by the least square method, the validation results of two models are compared. The conclusion indicates that the elastic body model is better when the dynamic characteristics of the positioning system before the stable state are concerned and the rigid body model is more appropriate if the accuracy of the whole model is focused.

Augmented sliding-mode control of an ultra-precision positioning system

Abstract In this study, we designed an augmented robust controller for an ultra-precision positioning system. The control algorithm includes modified sliding-mode control with a new switching surface and linear quadratic (LQ) control for optimal feedback gain. A nanometric scale positioning system is especially vulnerable to parameter uncertainties and external disturbances. To solve this problem, we propose an augmented system that adopts two auxiliary states: state estimates and control input. We demonstrated the robust performance of the proposed control algorithm through a comparison with LQ control.

Study on intelligent control system of two-dimensional platform based on ultra-precision positioning and large range

The aim of this paper is to improve the positioning accuracy of the micro-positioning stage constructed by flexure hinge and driven by piezoelectric devices. The micro-positioning stage is the micro-stage of an two-dimensional ultra-precision positioning system with high-speed and large range, which is a typical macro–micro-dual-drive system. Because of the strong nonlinearity of the micro-positioning stage, such as hysteresis and creep, and the influence of the highly accelerated operation of the macro-positioning stage, the traditional PID control cannot achieve good performance. To solve this problem, a PID position controlling system based on adaptive neural-fuzzy inference has been proposed and the structure of this control system is also analyzed. The experimental results show that the performance is effectively improved under the intelligent control method. The repetitive positioning accuracy is improved from 92 nm to 23 nm at the axis X and from 102 nm to 28 nm at the axis Y.

Micro-motion selective-actuation X Y Z flexure parallel mechanism: design and modeling

This paper presents the design of a selective-actuation flexure parallel mechanism that can provide three de-coupled micro-motions along the X -, Y - and Z -axes. This mechanism can be used as an ultra-precision positioning system. The modeling of this flexure parallel mechanism is then established based on a pseudo-rigid-body model with consideration of deformation of the flexure member. The factor of deformation allows us to formulate the accurate kinematics analysis of the flexure mechanism. Via this modeling, dimension and free shape of the mechanism are determined based on the criteria of isotropic resolution transmission scale. An experiment was set up to verify the modeling and the design. The experiment shows the advantage of the proposed model versus the model currently used. The similarity of the resolutions obtained from the experiment and predicted by the optimal design shows the validity of the resolution evaluation and the optimal design.

A Picometer Positioning System using Active Aerostatic Guideway(Precision positioning and control technology)

A novel tri-mode ultraprecision positioning system is proposed. The basic coarse mode for nanometer positioning with long stroke and the fine mode for sub-nanometer positioning are executed by using the Twist-roller friction drive (TFD). The ultra-fine mode utilizes the aerostatic guideway with the Active Inherent Restrictor (AIR) for realizing picometer positioning. The performance of the ultra-fine mode is analyzed and the experimental results of step positioning in the range of sub-nanometer and are shown.

静圧案内面を運動縮小機構として利用した超精密位置決めシステムの開発

A new type of ultraprecision positioning system using an aerostatic guideway with active control system is proposed. The control system employs an Active Inherent Restrictor (abbreviated AIR) invented by the authors. The AIR consists of a piezoelectric actuator having a through hole, one end of which is small enough to function as an orifice when the actuator is embedded in the bearing surface. By changing the length of the piezoelectric actuator, the AIR controls the air film thickness and the position of the table supported aerostatically by the guideway. Owing to aerostatic mechanism, the table displacement nominal to the guideway can be much less than the deformation of the actuator. This means that the aerostatic guideway with the AIR acts as a motion-reduction mechanism. Full stroke of the actuator is 3.5μm, while that of the table is 110nm, then the reduction ratio of this mechanism is about thirty. Dynamic step positioning of the table shows that the settling time is about 30ms and the stewing rate is about 45nm/ms. Static step positioning with various step width shows that the positioning resolution is 50pm. Therefore, the stroke is short, however, the system can be used for picometer positioning. Under step positioning of the table, an aluminum alloy mounted on the table is turned by a single point diamond tool. On the turned surface, micro steps, depth of which is 16nm, can be resolved. This shows that the positioning system can be used to control the depth of cut.

Research and development of an ultraprecision positioning system

This paper describes a positioning system for ultraprecision machine tools. This system has a hydrostatic slide table driven by a hydrostatic lead screw (36 mm diameter, pitch 10 mm) and a laser interferometric positioning system. This means that the table is supported by hydrostatic bearings in any direction absolutely without any mechanical contact. Quite high accuracy of straight motion and positioning is realized and maintained; straightness and angular deviation are better than 50 nm and 2 mu rad respectively, positioning accuracy is about 10 nm within a 200 mm stroke. In addition, the effect obtained by a self-controlled restrictor for screw and by a short-pitch (pitch 6 mm) lead screw is mentioned. The stiffness of the hydrostatic screw in the feed direction can be statically infinite with this restrictor. By the use of this lead screw, positioning accuracy is improved and a 0.1 nm positioning step is possible.

An ultraprecision positioning system using a twist-roller friction drive

For ultraprecision positioning, the use of the twist-roller friction drive is proposed. To improve the positioning accuracy of conventional twist-roller friction drives, the proposed design has two features: (1) the twist angle between the driving shaft and the driven rollers is very small, and (2) the driven rollers are supported by hydrostatic bearings. The twist-roller friction drive is mechanically a kind of lead screw, and the small twist angle makes the lead of the friction drive less than 0.1 mm. The use of hydrostatic bearing is effective for improving the rotational accuracy of the driven rollers and for eliminating the influence of the fluctuation in roller rotation on positioning accuracy. It has been shown by experiments that the resolution of positioning can be less than 10 nm, and the twist-roller friction drive is suitable for an ultraprecision positioning system.