Showing papers by "Jinchun Hu published in 2012"

A Holistic Self-Calibration Algorithm for $xy$ Precision Metrology Systems

Abstract: Self-calibration technology is an important approach with the utilization of an artifact plate with mark positions that are not precisely known to calibrate the precision metrology system. In this paper, we study the self-calibration of xy precision metrology systems and present a holistic self-calibration algorithm based on the least squares method. The proposed strategy utilizes three traditional measurement views of an artifact plate on the xy metrology stage and provides relevant symmetry, transitivity, and redundancy. The misalignment errors of all measurement views, particularly errors of the translation view, are totally determined by detailed mathematical manipulations. Consequently, a least-squares-based robust estimation law is synthesized to calculate the stage error even under the existence of random measurement noise. Computer simulation validates that the proposed method can accurately realize the stage error when there is no random measurement noise. Furthermore, the calculation accuracy of the proposed scheme under various random measurement noises is studied, and the results verify that the proposed algorithm can effectively attenuate the effects of random measurement noise. The proposed strategy, in fact, provides a well-understood solution to the xy self-calibration problem for engineers in practical applications.

Stochastic information gradient algorithm with generalized gaussian distribution model

Abstract: This paper presents a parameterized version of the stochastic information gradient (SIG) algorithm, in which the error distribution is modeled by generalized Gaussian density (GGD), with location, shape, and dispersion parameters. Compared with the kernel-based SIG (SIG-Kernel) algorithm, the GGD-based SIG (SIG-GGD) algorithm does not involve kernel width selection. If the error is zero-mean, the SIG-GGD algorithm will become the least mean p-power (LMP) algorithm with adaptive order and variable step-size. Due to its well matched density estimation and automatic switching capability, the proposed algorithm is favorably in line with existing algorithms.

Space six-freedom degrees article locating system based on two-dimensional sensitive sensor

Abstract: The invention discloses a space six-freedom degrees article locating system based on two-dimensional sensitive sensor, which is invented for locating photoetching machine silicon table and a masking table. The system comprises a semiconductor laser, an optical fiber collimator, optical fiber, an optical fiber divider, an optical filter, three PSD sensors and a signal processing system. Laser from the semiconductor laser shoots the optical fiber collimator; then the optical fiber is divided into three paths and transmitted; the background light is filtered by the optical filter and received by the PSD sensor; the positions of the laser spots on the three PSD sensors are processed by the signal processing system to acquire the posture of the space six-freedom degrees article. The locating system uses non-contact measurement, which can avoid influence of cable on the accuracy of platform motion. Meanwhile, the locating system has characteristics of high locating precision, rapid response, simple structure, low cost and the like.

A novel planar 3D magnetic position measurement methodology using linear Hall sensors

Abstract: A novel planar 3D magnetic position measurement methodology using linear Hall sensors is proposed. The measurement methodology can achieve micrometer-order resolution and unlimited range in planar translational 2-DOF (degree-of-freedom), as well as unrestricted range in planar rotational motion. This work presents the methodology and simulation of planar 3-DOF motion measurements of a platen above a Halbach magnet matrix. This methodology includes the arrangement of the linear Hall sensors and the associated position-calculation algorithm to determine the position and orientation through the sensor measurements. Simulation results for ideal cases emphasize the validity of this new measurement methodology and that with Gaussian noise inputs imply strong sensitivity to the noise at some special positions or areas.

Three-dimensional stage self-calibration: A general theory framework

Abstract: In this paper, a general self-calibration theory framework is presented for three-dimensional precision stages to determine the stage error Four measurement views of a cubic artifact on the three-dimensional precision stage are utilized to provide the symmetry, transitivity and redundance The firstorder components of the stage error, ie, the nonorthogonality and the scale difference, are determined through the first three measurement views And the residual components of the stage error are then figured out by a least-square based calculation law, which completes the stage error determination Additionally, the parasitic errors related to the artifact and the misalignment errors of all measurement views can all be identified through algebraic manipulations Computer simulation is finally carried out and the results validate that the proposed algorithm can accurately realize the stage error The proposed scheme actually provides a framework as a principle to solve the three-dimensional self-calibration problem for practical engineers

Two-dimensional, position-sensitive sensor-based system for positioning object having six degrees of freedom in space

Abstract: A two-dimensional, position-sensitive sensor-based system for positioning an object having six degrees of freedom in space, used for positioning of a silicon table and mask table of a lithography machine. The system comprises mainly a semiconductor laser (1), an optical fiber collimator (2), optical fibers (3, 7, 10, and 13), an optical fiber splitter (4), filter plates (6, 9, and 12), three PSD sensors (5, 8, and 11), and a signal processing system. Laser emitted by the semiconductor laser (1) is irradiated onto the optical fiber collimator (2), then transmitted respectively via three paths by the optical fiber splitter (4), and received by the PSD sensors (5, 8, and 11) after having background light filtered out by the filter plates (6, 9, and 12), while the positions of laser spots on the three PSD sensors (5, 8, and 11) are processed by the signal processing system to acquire the position and orientation of the object having six degrees of freedom in space. The positioning system uses contactless measurement, thus preventing the precision of platform movements from being affected by a cable, while at the same time providing characteristics of great positioning precision, expedited response, simple structure, and reduced costs.

Degree of freedom (DOF) vibration isolating device of linear electric motor and motion control method thereof

Abstract: The invention discloses a degree of freedom (DOF) vibration isolating device of a linear electric motor and a motion control method thereof. The vibration isolating device comprises a balance block, an anti-drifting driving unit and a control unit, wherein the upper surface of the balance block is fixedly connected with a stator of a linear electric motor, the lower surface of the balance block is connected with a base by virtue of a first air bearing; the anti-drifting driving unit is used for controlling the position of the balance block, and connected with the balance block by virtue of a second air bearing; the anti-drifting driving unit comprises an anti-drifting linear electric motor, an optical grating scale and a guide rail. The motion control method has the following two technical schemes: in the first technical scheme, a second optical grating scale signal is used as a feedback signal to be input to the control unit so as to perform variable stiffness and nonlinear control on the balance block; and in the second technical scheme, a first optical grating scale signal and the second optical grating scale signal are used as the feedback signals to be input to the control unit so as to obtain a centroid displacement signal of an electric motor rotor and the balance block and perform nonlinear anti-drifting control on the balance block.

Research on the application of Edlén’s formulation in compensation for ultra-precision motion platform’s measurement using an interferometer:

Abstract: The measurement accuracy of an interferometer is largely affected by the refractive index of air. Compared with the direct compensation method, the indirect compensation method is more suitable for compensation for an ultra-precision motion platform using an interferometer. However, the indirect compensation method depends on the air refractive index’s formula, which is empirical and not entirely accurate. It seems that the application of the indirect compensation method in a high-precision measured object is hampered. Considering that the repeat positioning accuracy of some application objects such as lithography’s ultra-precision platform is the highest requirement while the positioning accuracy is less demanding, this means that repeat measuring accuracy is the main factor. For these objects, this paper proposed a hypothesis of Birch and Downs’s revised Edlen’s formula firstly and derived the relation between the repeat measuring accuracy and the repeatability of environmental parameters on this basis ...