Papers by Keyword: Autocollimator

Abstract: For the needs of laser autocollimator in image acquisition and processing, designed the hardware circuit based on FPGA and DSP as the control core, detailed the system hardware composition. Image sensor initialization and configuration were elaborated, cached the image data by double buffering technique. By reading the cache data, pretreatment, spot extraction, calculating barycentric coordinates and data fitting, the high precision of angle measurement was obtained. The system design is reasonable, the hardware circuit is reliable, and the video capture image is clear. The functionality of image acquisition and processing is achieved.

Abstract: In order to convenient the design of the autocollimator interface, this paper introduces the design of hardware and software of the autocollimator interface, and detailed analysis some key links. The SPI extension module (EEPROM) based on abundance on-chip resource of TMS320F2812 DSP is used to storage the equivalent of misalignment angle; The CAN extension module (CAN bus) based on CAN module is used to communicate with other computers; SCI extension module (RS232) is used which is convenient for the system debugging, and extension interfaces are left. Meanwhile, the corresponding design of software is also given in the paper. Prototype tests show that the design of the autocollimator interface can fully satisfy the requirements of the system. The design experience can be referred in similar engineering.

Abstract: Large aspheric mirrors with diameter over 300 millimeters with high surface accuracy are wildly used in many areas such as astronomical telescopes. Interferometers are widely used in profile measurement of optical flat and sphere. However, standard reference aspheric surface which is necessary for this method is difficult to make. Scanning defletometry based on ESAD (Extended Shear Angle Difference) is used to measure ultra-precise large near-flat and slight curved optical surface with the accuracy of sub-nanometer. However, it is not possible for it to measure aspheric surface because of the limitation of the measuring range of autocollimators. We proposed a new measuring method to scan the surface of a large aspheric optical surface using autocollimator with rotatable optical devices fixed on linear motion stage. To eliminate the influence of the pitching error of the scanning stage, we use two mirrors reflecting laser comes from autocollimator, which have the same effect with a pentaprism used in ESAD. To enlarge the measuring range of the autocollimator, we use a rotatable mirror to fit the changes of the slope of the mirror surface under measurement. The error analysis of the method is done. Measurement of an optical flat mirror and a sphere mirror with diameter of 50 mm and biggest slope of 6000 arc-second are done. The rotatable optical devices that we designed are proved effective on eliminating the pitching error of the moving stage.

Abstract: To develop a high precision Micro Coordinate Measuring Machine (Micro-CMM), it is important to evaluate an X-Y stage on the Micro-CMM. A precision multi-probe measurement system has been designed and developed for simultaneously measuring the yaw and straightness errors of the X-Y stage. In the system, an autocollimator measures the yaw error of the stage, and two laser interferometers measure the profile of a standard mirror which is fixed on the X-Y stage. The straightness error is reconstructed by the application of simultaneous equation and least-squares methods, and the uncertainty associated with the multi-probe method is simulated. When the interval of the laser interferometers equals 10 mm, the standard deviation of multi-probe method using the high accuracy autocollimator and the laser interferometers is about 10 nm. The simulation results satisfy our purpose for the uncertainty of 50 nm, and practical considerations are discussed.

Abstract: A movable pentaprism is a key element in deflectometric profilers, where it directs the beam of an angle measuring device towards the surface under test and enables at the same time the flexible lateral displacement of the beam footprint on the surface. The beam deflection angle of the pentaprism is robust with regard to changes in its angular orientation. Optimal stability is achieved, however, only when the angle measuring device, the pentaprism, and the surface have initially been properly aligned. A newly developed procedure enables the rapid and accurate in-situ adjustment of all angles of the optical components in deflectometric set-ups with an uncertainty of several microrad. In combination with precision mechanical stages, variations in the prism’s deflection angle (caused by changes in its angular orientation) can then be limited to the nanorad level.

Abstract: To overcome the limitations of conventional interferometry, a technique has been developed which allows the absolute topography measurement of near-plane and slightly curved optical surfaces of arbitrary size with low measurement uncertainty. The Extended Shear Angle Difference (ESAD) method combines deflectometric and shearing techniques in a unique way to minimize measurement errors and to optimize measurand traceability. A device for the topography measurement of optical surfaces up to 500 mm in diameter, achieving sub-nanometer repeatability, reproducibility and uncertainty, was built at the Physikalisch-Technische Bundesanstalt (PTB). The ESAD method is optimally suited for creating a primary standard for straightness and flatness with highest accuracy by which the three-flat test or liquid mirrors can be replaced as starting points of the traceability chain in flatness measurement. In the following, the improved ESAD device which uses optimized opto-mechanical components is presented. Central aspects of the proper design and use of deflectometric systems are highlighted, including the optimal use of pentaprisms.