Constant Velocity Scan Research Articles

Peak Filter Tuning based on Disturbance Spectrum for MIMO High-Precision Scan Stage

In high-precision positioning systems such as scanning machines, the feedback controller tuning needs a lot of time and skills. In particular, a feedback controller tuning with six-degree-of-freedoms (x,y,θz,z,θx,θy) is difficult because of the numbers of controller parameters in each axis. The feedback controllers designed as single-input single-output controllers in each axis may not achieve sufficient performance in multi-input multi-output systems, and stability may not be satisfied because of a coupling problem between each axis. The repetitive disturbance makes the performance worse in a constant velocity scanning motion, and they are conventionally rejected by a peak filter in other applications of high-precision systems such as a hard disk drive. In this paper, we propose a tuning method of a peak filter to suppress a repetitive disturbance which satisfies robust stability conditions for six-degree-of-freedom systems by using convex optimization. The effectiveness of the proposed method is verified by the error in the constant velocity scanning motion.

Yaw error correction of ultra-precision stage for scanning beam interference lithography systems

The stage yaw error is a key factor affecting the phase distortion of gratings produced by scanning beam interference lithography system. In order to solve this problem, a coarse-fine dual-stage mechanism is proposed, in which an ultra-precision fine positioning stage with yaw error correction function is developed. To achieve nanoscale positioning and sub-microradian yaw motion accuracy, four Lorentz motors are used to drive the fine stage. The internal coupling factors and the mechanism of Lorentz motors motion control are analyzed. Besides, the Abbe error caused by the yaw error is investigated. Positioning and scanning experiments are conducted and the outcomes show that maximum yaw error is 0.33 μrad during constant velocity scanning, which completely meets the grating fabrication requirements.

A High Speed Calibration Method for Laser Positioner by Constant Velocity Scanning

This paper describes a high speed calibration method for laser positioner by scanning work area under constant velocity. Laser positioner consists of sinusoidal laser encoder, DC motor and the controller. The encoder has diffraction grating scale and laser optics. It generates sine and cosine outputs according to the travel distance. Qualities of the scale and the optics contribute to the fluctuation of output signal amplitude, DC offset and relative phase. First, the controller collects the output data under constant velocity of 4 samples per 1 sine wave length. The parameter can be estimated by simplified discrete Fourier transform method. Calibration data are collected every quarter sine wave length over all positioner work area. The result is stored in the table then referred by the controller in real time operation. Experiment results are also reported for HDD servo track writer application.

Trajectory Planning and Precision Control of Scan-move for Step-scan Lithography Stage

A trajectory planning method and precision control strategies for scan-move of step-scan projection lithography are investigated. The difference of trajectory planning between step-move and scan-move is firstly discussed. Aiming at the requirements of accuracy and strict synchronization of scan-move,several key issues are analyzed. Considering the accuracy losses in discrete-time implementation of trajectory planning algorithm,the integration strategy in discrete-time domain of precision control of trajectory planning is presented with combination of internal integer integration strategy. Furthermore,a compensation method with a correcting factor of constant velocity scan phase is advanced. Experiment results demonstrate that the proposed trajectory planning algorithm and its precision compensation strategy are accurate and effective. These methods are successfully applied in ultra-precision motion control system of 100 nm step-scan projection lithography equipment.

Projection-Based Iterative Learning Control for Wafer Scanner Systems

In this paper, an iterative learning controller (ILC) that uses partial but most pertinent information in the error signal from previous cycles is employed for precision control of a wafer stage. Typically, ILC schemes use the error signal from the previous cycle for updating the control input. This error contains both repetitive and nonrepetitive components. The nonrepetitive components of the error cause degradation of performance of the ILC scheme. Based on structural information about the plant and the disturbances, we can determine some basis functions along which the repetitive error is concentrated. This information is extracted by projecting the error signal onto the subspace spanned by these basis functions. The projected error signal is then used in the ILC update law. Stability and convergence conditions are presented for this projection-based ILC update law. The proposed idea is motivated by precision control of a wafer stage. For a constant velocity scan by the wafer stage, the major sources of repetitive error are found to be phase-mismatch and force ripple. These effects are mathematically modeled to obtain the subspace spanned by them. The projection-based ILC scheme using this subspace is then implemented on a prototype one DOF stage and its performance is compared to the standard ILC scheme that uses a frequency-domain filtering to remove nonrepetitive components of the error.

A cam-based laser-induced fluorescence scanner for capillary array electrophoresis

Capillary array electrophoresis (CAE) is an important high throughput analytical technique. Laser-induced fluorescence (LIF) has been the dominant detection method for CAE owing to its low limit of detection (LOD) and wide linear dynamic range (LDR). Linear LIF scanners were first used in CAE because linear motions of an objective match well with a common planar array of capillaries. A problem with linear scanners is that the motor is required accelerating/decelerating so that all capillaries can be properly scanned, which makes motion control complicated and reduces the duty cycle. Rotary scanners were developed to overcome this problem. While rotary scanners have been successfully applied in CAE, the capillaries have to be arranged in a circular format, which can be inconvenient in some cases. In this report, we describe a cam-based LIF scanner as an alternative technique for CAE detection. In this system, a rotary motor is mechanically linked with a capillary holder via a cam. During operation, the motor carries the cam in a rotary motion that drives an array of capillaries on the holder to move back and forth across the objective for fluorescence detection. Using this design, the capillaries can be parallel-arranged in a plane while the motor acceleration/deceleration is avoided. To demonstrate the feasibility of this approach, we constructed a prototype instrument with a constant-velocity scanning distance of ∼10 mm, a scanning frequency of 3 Hz and a duty cycle of ∼70%. The scanner exhibited a LOD of 69 pM of fluorescein and a LDR of 3.5 orders of magnitude. Multiplexed capillary SDS-PAGE was performed on this scanner for protein separations.

Data processing of reflection seismic data by use of neural network

The present paper proposes an algorithm for data processing of reflection seismic data using of neural networks. A neural network algorithm was applied to the reading of arrival time of first break signal, the recognition of waveform in seismic trace and the automatic picking of result of constant velocity scan among the various data processing techniques. A layered network with the correct answer, so called, teacher's signal, in training period by the error back propagation algorithm was used. The general procedure of processing of reflection seismic data by use of neural network is as follows. 1. 1. Constitution of the most suitable network for the target processing. 2. 2. Setting of the weight values to all units in the layers and the teacher's signal. 3. 3. Calculation of the output signals from the output layer by activating the network. 4. 4. Estimation of learning signal from the energy of errors between the actual output signal and the teacher's signal. 5. 5. Calculation of the change of weight values by using learning signal so as to minimize the energy of errors between the actual signal and the teacher's signal. 6. 6. Steps (3) to (5) are repeated till the errors fall into the designated limitation or the designated learning count is reached. As a result of model studies, it was determined that the proposed algorithm performed the readings of arrival time of first break signal, the waveform recognition and the automatic picking of velocity analysis result with good accuracy.

ニューラルネットワークの反射法地震探査データ処理への適用

The present paper proposes an algorithm for data processing of reflection seismic data by use of a neural network. The algorithm of neural network was applied to the reading of the first break, the recognition of waveform in seismic trace and the automatic picking of the result of the constant velocity scan among various data processing techniques. A layered network with training by the error back propagation algorithm was used.As a result of model studies, it was clarified that the proposed algorithm performed the first break reading, the waveform detection and the automatic picking of velocity with good accuracy.

Characterization and use of a novel optical position sensor for microposition control of a linear motor

The performance of an optical reflective position sensor is evaluated as the position feedback element in the microposition control of a linear electromagnetic motor. The open loop position sensor characteristics are first measured to determine the analog controller design parameters. The performance of the controller, evaluated using an integrated Michelson interferometer, measures the control loop bidirectional accuracy, hysteresis, long-term stability, and position linearity. Compensation of the small nonlinearity measured required linearization of the input command signal and a practical application is demonstrated with a constant velocity scan of one of the interferometer mirrors. A final result is the submicron square wave modulation of the interferometer output with its scan mirror under closed-loop control using feedback from the reflective position sensor.

On the Synthesis of Straight Line, Constant Velocity Scanning Mechanisms

This paper presents a kinematic synthesis of constant-velocity, straight-line coupler-point motion of two planar mechanisms. After the derivation of synthesis equations, the numerical results of a grid search to determine the linkage dimensions for maximum constant velocity, with minimal straight line error, are presented. Plots of acceleration magnitude, transmission angles, and transverse velocity are presented as a function of the percentage of the constant velocity portion of a cycle of input motion. For a 5R2P Stephenson 6-bar linkage, normalized velocity errors as small as 2 percent can be maintained over 40 percent, or more, of the input cycle. A 7R Watt 6-bar linkage, while not achieving quite as high values as the 5R2P linkage, nevertheless can maintain normalized velocity errors as low as 2.5 percent over as much as 39 percent of the input cycle. These levels of performance must be weighed against unfavorable transmission angles, and in many cases, other undesirable effects, such as large accelerations and large transverse travel. The results show that, in order to maintain minimally acceptable transmission angle requirements, the velocity error and scan fraction requirements may be as little as 2.0 percent and as much as 35 percent, respectively.