Proc. SPIE. 11053, Tenth International Symposium on Precision Engineering Measurements and Instrumentation
KEYWORDS: Mathematical modeling, Sensors, Magnetism, Control systems, Laser scanners, Projection systems, System identification, Chemical oxygen iodine lasers, Laser systems engineering, RGB color model
Galvanometric scanning systems are high inertial behavior and high-speed movement widely that be used in laser marking, drilling, full screen projecting and so on. Therefore, the presented galvanometric scanning system and its applications for laser projector system. In includes a galvanometric unit, motor, position detector and control circuit. All components were discussed and developed by this study. The magnetic rotor and a stator magnet are the main components of the scanner system. The moving magnet is composed of NdFeB material and the stator consists of the coil. In addition, the moving capacitive sensor is used to receive signal feedback. The driver is assembled by the high response performance OP-amplifier circuit. Finally, frequency domain methods were used to identify the scanning system.
In general, the drop-in and cell-mounted assembly are used for standard and high performance optical system respectively. The optical performance is limited by the residual centration error and position accuracy of the conventional assembly. Recently, the poker chip assembly with high precision lens barrels that can overcome the limitation of conventional assembly is widely applied to ultra-high performance optical system. ITRC also develops the poker chip assembly solution for high numerical aperture objective lenses and lithography projection lenses. In order to achieve high precision lens cell for poker chip assembly, an alignment turning system (ATS) is developed. The ATS includes measurement, alignment and turning modules. The measurement module including a non-contact displacement sensor and an autocollimator can measure centration errors of the top and the bottom surface of a lens respectively. The alignment module comprising tilt and translation stages can align the optical axis of the lens to the rotating axis of the vertical lathe. The key specifications of the ATS are maximum lens diameter, 400mm, and radial and axial runout of the rotary table < 2 μm. The cutting performances of the ATS are surface roughness Ra < 1 μm, flatness < 2 μm, and parallelism < 5 μm. After measurement, alignment and turning processes on our ATS, the centration error of a lens cell with 200mm in diameter can be controlled in 10 arcsec. This paper also presents the thermal expansion of the hydrostatic rotating table. A poker chip assembly lens cell with three sub-cells is accomplished with average transmission centration error in 12.45 arcsec by fresh technicians. The results show that ATS can achieve high assembly efficiency for precision optical systems.
An absolute measurement method involving a computer-generated hologram to facilitate the identification of manufacturing form errors and mounting- and gravity-induced deformations of a 300-mm aspheric mirror is proposed. In this method, the frequency and magnitude of the curve graph plotted from each Zernike coefficient obtained by rotating the mirror with various orientations about optical axis were adopted to distinguish the nonrotationally symmetric aberration. In addition, the random ball test was used to calibrate the rotationally symmetric aberration (spherical aberration). The measured absolute surface figure revealed that a highly accurate aspheric surface with a peak-to-valley value of 1/8 wave at 632.8 nm was realized after the surface figure was corrected using the reconstructed error map.
Considering the system performance of the projection lens, not only surface quality of the optics shall be concerned, misalignment between each optics and the wavefront distortion contributed by the mounting stress and gravity are also the factors degraded the optical performance. This article introduces the opto-mechanical design and stress-free assembly process of the reflective mirror subsystem with 300 mm in outer diameter of an I-line lithographic projection lens.
The flexure with mounting position pass through the center gravity of the mirror can be adopted as supporting mechanism to prevent the gravity distortion. The distortion due to temperature difference can be avoided by adopting CLERACREAM®-Z glass ceramic and INVAR for material of reflective mirror and supporting flexure respectively. The adjustment mechanism of the mirror subsystem integrates the concepts of Kinematic and exact constraint to provide six degrees of freedom (6DoF) of posture adjustment of the mirror. Furthermore, the assembly process of the flexure which minimizes the mounting stress on the mirror is presented. In the end of this article, interferometric performance test of the reflective mirror after opto-mechanical assembly compared with the measurement result in manufacturing stage is also presented. With the proposed opto-mechanical design and stress-free mounting process of the mirror, the surface distortion contributed by the amount of mounting stress and gravity effect is less than P-V 0.02 wave @632.8 nm.
This study proposes an absolute measurement method with a computer-generated hologram (CGHs) to assist the identification of manufacturing form error, and gravity and mounting resulted distortions for a 300 mm aspherical mirror. This method adopts the frequency of peaks and valleys of each Zernike coefficient grabbed by the measurement with various orientations of the mirror in horizontal optical-axis configuration. In addition, the rotational-symmetric aberration (spherical aberration) is calibrated with random ball test method. According to the measured absolute surface figure, a high accuracy aspherical surface with peak to valley (P-V) value of 1/8 wave @ 632.8 nm was fabricated after surface figure correction with the reconstructed error map.