Design and control of flexure based XYϑZ stage

This article presents the design and control of an ultraprecision XYϑ_Z stage with nanometer accuracy. The stage has a plane mechanism and symmetric hexagonal structure which consists of a monolithic flexure hinge mechanism with three piezoelectric actuators and six flexures preserving the plane motion. The symmetric design reduces the effect of temperature gradient on the structure. Because the relationship between design variables and system parameters are quite complicated and there are some trade-offs among them, it is very difficult to set design variables manually and optimal design procedure is used. The objective of design is maximizing the 1^st resonant frequency to improve the dynamic characteristics. The reason is that the stage must move with heavy load of about 20 kg. The higher resonant frequency also makes the stage stiffer and stronger against the dynamic force and moment. This paper describes the procedures of selecting parameters for the optimal design and a mathematical formulation for the optimization problem. The stage was designed to attain ±10 um in the X- and Y-direction and ±90arcsec in the yaw direction at the same time and have the 1^st resonant frequencies of 455.5 Hz in X- and Y-direction and 275.3 Hz for yaw direction without load. The stage was fabricated according to the optimal design results and experimental results indicate that the design procedure is effective. A conventional PI control results are presented for ultraprecision motion.     

Computational parametric analysis and experimental investigations of a compact flexure-based microgripper

This paper presents a flexure-based piezoelectric actuated microgripper for high precision grasping/releasing tasks. The design of the microgripper consists of a three-stage amplification and transmission mechanism, and the parallel grasping technique. A bridge-type mechanism and two sequential lever-type mechanisms are symmetrically connected to amplify the output displacement of the embedded piezoelectric actuator. The parallelogram mechanisms assist in linearizing the output displacement of both jaws of the microgripper. The computational analysis is conducted to investigate the effect of the dimensional parameters on the characteristics of the microgripper. A computational parametric optimization methodology is established to achieve the required attributes of the microgripper. The design optimization resulted in a compact design, a high displacement amplification ratio, and a large output displacement of the microgripper. The experimental studies are conducted to investigate the key characteristics of the microgripper such as the displacement amplification ratio, the output displacement, tracking performance. Further, the parasitic motion, input-end and output-end motion resolution of the microgripper are identified. The experimental results indicate that the compact microgripper can achieve a high displacement amplification ratio and large output displacement with a high positioning accuracy.     

高增益PID控制器实现纳米定位

建立了高增益PID闭环控制系统,在"直流伺服电机＋滚珠丝杠"驱动机构上实现了大范围的纳米定位。对于"伺服电机＋滚珠丝杠"驱动系统来说,摩擦是实现纳米定位精度的主要障碍,它影响着系统微动特性并导致稳态误差。针对这种驱动系统,在根据标定参数计算得到的线性传递函数的基础上,设计高增益不完全微分、比例反馈PID控制器,配置闭环控制系统的极点为负实轴上的多重极点,避免了摩擦力建模和补偿。实验结果表明,该高增益闭环控制系统有效地抑制了摩擦等非线性因素的影响,在系统的宏动和微动特性阶段都可以实现单步的纳米定位并取得了一致的响应,10 nm~10 mm阶跃响应的稳态误差不超过±2 nm。     

超精密气浮工件台的微振动及其抑制

超精密气浮工件台系统是当前主流光刻机中的核心子系统,要求具有纳米级的重复定位精度和同步运动精度.这种系统所采用的气浮轴承如果设计不当,会导致系统发生微幅振动,从而影响系统精度.文章通过分析微振动的成因和影响因素,提出了相应的抑制措施,保障了超精密气浮工件台系统的精度实现.     

基因测序仪运动平台的高精度定位控制

为了实现对基因测序仪运动平台的高精度定位控制,建立了基因测序仪运动平台控制系统。对该系统所采用的数学建模、模型辨识、控制器设计、输入整形等方法进行研究。根据运动平台动力学方程和永磁同步直线电机电压-推力关系构建了运动平台数学模型,利用频域扫描法在实物实验的基础上辨识出运动平台的模型参数。最后,基于运动平台模型设计了双闭环控制器和前馈控制器组成的复合控制器来保证运动平台的稳定性和高精度,同时根据整个系统的主导极点设计了输入整形器以抑制运动平台的残余振荡。实验结果表明:加入了输入整形的复合控制器将运动平台的稳态重复定位精度从±1.47μm提高到±0.354μm。较传统复合控制器,本文提出的方法能使基因测序仪运动平台更快进入可用重复定位精度范围,并基本满足基因测序仪采集图像时所需的稳定性强、精度高等要求。     

An ultraprecision stage for alignment of wafers in advanced microlithography

We present an ultraprecision stage specially designed to align wafers for the microlithography of integrated circuit patterns of sub-0.3 μm design rules. The whole stage mechanism is composed of two individually operating xyθ-stages: a global stage to provide initial coarse alignment of wafers in stepping mode; and a micro stage to produce fine controlability in nanometer range. The global stage is configured with three linear motors kinematically linked to produce xyθ-motions without resorting to precision guideways. The micro stage corrects positional errors in the global stage by activating three piezoelectric microactuators housed in an elastic flexure. These two stages are simultaneously controlled as a dual servo system, because the main emphasis is given to achieving an overall positioning reproducibility of 20 nanometers in xyθ-motions in aligning wafers of 200-mm size.     

磁悬浮式纳米级微动工作台的理论分析与建模研究

磁悬浮式微动工作台由于运动平台和驱动机构采用非接触式的磁悬浮驱动技术而易于实现大范围纳米级精度的微运动。本文构建了一种新型的磁悬浮微动工作台，从理论上对磁悬浮式微动工作台的运动机理进行了详尽分析，建立了磁悬浮式微运动的电磁驱动模型，用Matlab对磁悬浮式微动工作台的运动控制进行了仿真研究，结果表明，设计的磁悬浮式微动工作台能达到纳米级的微运动。本文的研究成果为磁悬浮式微动工作台的设计及其控制提供了理论基础。     

大行程纳米级定位工作台的结构设计

考虑采用静态三步拼接曝光法的扫描干涉场曝光系统的性能与工作台的定位精度及稳定性相关,设计了一种大行程、高精度二维工作台以提高其定位精度。采用摩擦驱动和压电陶瓷微位移机构组合的方式构成宏、微进给机构,由闭式气体静压导轨带动工作台实现沿X、Y两个方向的光栅分度与扫描运动。优化设计了摩擦驱动机构和气体静压导轨结构,并对工作台整体结构固有频率进行了有限元分析。使用自准直仪检测了导轨在X、Y方向的直线性,结果显示其两方向偏航和俯仰精度均在±0.04μm以内。使用激光干涉仪检测了导轨在X方向的定位精度和定位噪声,结果表明,对X向行程为220mm、Y向行程为300mm的工作台,其X方向的定位精度优于±5nm,定位稳定性可达±25nm。得到的结果满足扫描干涉场曝光系统工作台纳米级定位精度的要求。     

超声波电机在三维微细电火花加工中的应用

论述了三维微细电火花加工系统的发展前景,搭建了一台微细电火花加工系统的原型样机.在该系统中,使用超声波电机做驱动装置,为微细电火花加工构造了可实现纳米级微量进给的运动平台,并进行了初步的平台定位精度检测.实验结果证明系统运行良好,运动平台能够达到很高的定位精度.课题在设计实用的精密微量进给机构的电机选择上,探索了新的方法.     

Submicrometer overshoot control of rapid and precise positioning

Precise-positioning technique is relatively well developed. However, it is still difficult to avoid an overshoot or to limit the overshoot within a submicrometer in a rapid and precise positioning. Inspired by recent studies on microdynamics, a control algorithm based on the variable structure control (VSC) method is proposed to achieve an overshoot smaller than 0.2 μm and rapid, precise positioning (a 0.5 mm 1 cm positioning with a steady-state error smaller than 30 nanometer in 0.5 s) with a linear motor drive stage. The stage is guided by a rolling ball guide and with a 10 nm resolution laser interferometer as its position sensor. Some characteristic values in the friction model of microdynamics are included to design the controller. Therefore, we found a way to achieve rapid, precise, and Small overshoot positioning by combining mechanism design system identification, lubrication, and controller design techniques.     

基于柔顺机构的两自由度微动精密定位平台的分析与设计

基于柔性铰链变形原理设计了一种压电驱动的两自由度柔顺机构微动精密定位平台.首先建立了平台的刚度、固有频率和强度的分析模型,通过优化设计得出了平台的最优结构尺寸.利用有限元软件仿真分析验证了设计模型和优化结果的正确性.最后制造了原型样机,进行了实验,对平台进行了标定并分析了平台的定位误差.     

Comprehensive analysis of the influence of structural and dynamic parameters on the accuracy of nano-precision positioning stages

Nano-precision positioning stages are characterized by rigid-flexible coupling systems. The complex dynamic characteristics of mechanical structure of a stage, which are determined by structural and dynamic parameters, exert a serious influence on the accuracy of its motion and measurement. Systematic evaluation of such influence is essential for the design and improvement of stages. A systematic approach to modeling the dynamic accuracy of a nano-precision positioning stage is developed in this work by integrating a multi-rigid-body dynamic model of the mechanical system and measurement system models. The influence of structural and dynamic parameters, including aerostatic bearing configurations, motion plane errors, foundation vibrations, and positions of the acting points of driving forces, on dynamic accuracy is investigated by adopting the H-type configured stage as an example. The approach is programmed and integrated into a software framework that supports the dynamic design of nano-precision positioning stages. The software framework is then applied to the design of a nano-precision positioning stage used in a packaging lithography machine.     

一种新型三维精密位移系统的设计与分析

研究开发了一种新型的大行程、纳米级和计量型三维精密位移系统。精密位移系统采用模块化结构设计，三个方向的驱动机构均采用完全相同的设计结构，分别称为X、Y、Z向一维工作台。位移系统在X、Y、Z三个方向采用粗、精两级驱动，并分别装有计量光栅。其中X、Y两个方向的驱动机构水平放置且为上下层叠式，Z方向上的驱动机构垂直放置。各方向粗驱动采用交流伺服电机配合精密丝杠和直线导轨进行驱动，精驱动采用压电陶瓷微位移器配合柔性铰链进行驱动，每个方向的两级驱动共用一套计量光栅，从而保证了位移系统的大行程、纳米级和计量型。介绍了位移系统的结构设计，分析了位移系统的位移分辨率、位移系统的计量原理以及位移系统的运动性能，从而为位移系统的设计提供理论依据。     

基于柔度比优化设计杠杆式柔性铰链放大机构

分析与研究了柔性铰链的柔度特性,用于柔性放大机构的优化设计。提出了一个通用的柔度比参数λ,探讨了具有不同柔度比λ的柔性铰链主要输出位移形式的灵敏度,分析了它对常用柔性铰链的柔度特性的影响规律。然后,以柔性铰链的柔度比λ为基本参数,在考虑柔性铰链转动中心偏移量的基础上,推导了二级杠杆式柔性铰链放大机构放大率的理论计算方法,并依据柔性铰链的柔度比特性提出了柔性放大机构的优化设计方法。开展了有限元仿真和实验研究。结果显示,优化后的柔性放大机构的放大率比优化前的放大率分别提高了0.234和0.23。实验表明,依据柔性铰链的柔度比λ对柔性放大机构进行优化设计能够有效地提高柔性放大机构的位移放大率与工作行程,进而提高放大机构的末端运动及定位精度。     

Hybrid controller of a linear piezoelectric walking stage relying on stack/shear piezoelectric actuators

This paper proposes a hybrid control strategy of a novel linear piezoelectric walking stage based on two sorts of piezoelectric actuators, which takes the load variation into account. The proposed stage consists of two parallel 4-bar lever amplification mechanisms with flexure hinges actuated by piezoelectric stacks to heighten the vertical distance (that is more tolerable to the assembly discrepancy), two compression springs (that is able to maintain a fixed linear position without powering), and two shear piezoelectric actuators (that can achieve longer and equivalent to walking motion) in a small form factor. The proposed stage has two operating modes, namely a coarse positioning mode with a more extensive travel range and a fine positioning mode with a nanometer-level resolution, to possess excellent performance for the linear piezoelectric walking stage of load variations. One multimodal switching controller and one feedforward-feedback controller conduct the coarse mode and fine mode, respectively. The optimal frequency for a specific load is obtained through a backpropagation neural network in the multimodal switching control. In the feedforward-feedback control, the inverse mathematical model based on the Bouc-Wen hysteresis model is used to mitigate the hysteresis effect in the feedforward part while the proportional–integral–derivative controller in the feedback part handles the external system disturbances. Experimental results show the proposed hybrid coarse/fine mode control strategy's effectiveness to satisfy an efficient and accurate positioning task.     

Practical control of precision positioning mechanism with friction

This paper describes the practical control of precision positioning mechanisms with friction. In a controller design, the microdynamic characteristic of these mechanisms is taken into account. First, the behavior of an experimental mechanism immediately before stopping is examined experimentally and its characteristics, namely, the micro- and macrodynamic ones are modeled. Next, a practical control method is proposed for the mechanism. The controller is designed based on the nominal characteristic trajectory following (NCTF) controller design procedure. It consists of a nominal characteristic trajectory (NCT) and a PI compensator. The NCT is determined using an open-loop time response of the mechanism and is represented on a phase plane. The compensator is used to make the mechanism motion follow the NCT and to stop the motion at the origin of the phase plane. Although the compensator is designed based on the microdynamic characteristic, it is useful in a wide working range. The positioning performance of the system with the proposed controller is examined in comparison with those of the system with conventional PID controllers. These results prove that the system with the proposed controller has a better positioning performance than those with conventional PID controllers and its positioning resolution is higher than 50 nm.     

Integrating mechanism synthesis and topological optimization technique for stiffness-oriented design of a three degrees-of-freedom flexure-based parallel mechanism

This paper introduces a new design approach to synthesize multiple degrees-of-freedom (DOF) flexure-based parallel mechanism (FPM). Termed as an integrated design approach, it is a systematic design methodology, which integrates both classical mechanism synthesis and modern topology optimization technique, to deliver an optimized multi-DOF FPM. This design approach is separated into two levels. At sub-chain level, a novel topology optimization technique, which uses the classical linkage mechanisms as DNA seeds, is used to synthesize the compliant joints or limbs. At configuration level, the optimal compliant joints are used to form the parallel limbs of the multi-DOF FPM and another stage of optimization was conducted to determine the optimal space distribution between these compliant joints so as to generate a multi-DOF FPM with optimized stiffness characteristic. In this paper, the design of a 3-DOF planar motion FPM was used to demonstrate the effectiveness and accuracy of this proposed design approach.     

Precision tracking of a piezo-driven stage by charge feedback control

This paper presents a novel approach for precisely controlling the motion of a piezo actuator embedded in a mechanical stage without using a displacement sensor. A piezo actuator has a high displacement resolution, but the positioning performance is degraded by hysteresis between the applied voltage and resultant displacement. However, an electromechanical model of a piezo actuator suggests that the charge flowing in the actuator is directly related to the dynamic response of the piezo displacement. Therefore, this study directly measured the charge stored in a piezo actuator, and achieved dynamic reference tracking of the actuator's displacement by regulating the charge flowing through the actuator to follow a predefined trajectory.This novel approach requires neither specially designed charge amplifier circuits nor implementation of an inverse hysteresis model. The complete model identification and the digital controller design procedure for a piezo-driven mechanical stage are presented. The charge feedback controller is designed according to the dynamic characteristics of both the actuator and the stage, so that instability is minimized relative to using a charge amplifier. The experimental results confirm satisfactory tracking performance, and reveal the influence of model uncertainties on the system performance.     

基于自校正的纳米工作台控制

利用在线参数估计和自校正控制算法设计一个自校正控制器,以解决纳米工作台因各参数变化而其精确的数学模型难以确定,因而影响定位精度的问题。Matlab仿真结果表明该算法能够克服由扰动引起的系统参数变化对系统精度的影响,其控制性能优良。     

Control of an equipment for fabricating periodic nanostructure

This study presents the control for an equipment that is designed for fabricating periodic nanostructures. This equipment can generate the patterns required for nanostructure production using direct writing laser lithography. The equipment incorporates a direct writing laser lithography instrument, a linear motor-driven long-stroke stage (X, Y), a piezoelectric-driven two degrees of freedom (2-DOF) nano-stage (Y, θ_z), a 3-DOF laser interferometer measurement system, and a system control unit. The working stage of this equipment is combined by a long-stroke stage and a nano-stage; therefore, it can provide long-stroke and high-precision positioning. The feedback signal for this stage is obtained using a 3-DOF laser interferometer measurement system. Integral sliding-mode controllers are used to control the linear motor-driven stage and PID controllers are used to control the piezo-stage for precision positioning. This paper presents the design of the controllers and the control results. Experimental results show that satisfactory writing results can be obtained at a 100 mm/s scan speed.