Laser scanning projection technology can project the image defined by the existing CAD digital model to the working surface, in the form of a laser harness profile. This projection is in accordance with the ratio of 1: 1. Through the laser harness contours with high positioning quality, the technical staff can carry out the operation with high precision. In a typical process of the projection, in order to determine the relative positional relationship between the laser projection instrument and the target, it is necessary to place several fixed reference points on the projection target and perform the calibration of projection. This position relationship is the transformation from projection coordinate system to the global coordinate system. The entire projection work is divided into two steps: the first step, the calculation of the projector six position parameters is performed, that is, the projector calibration. In the second step, the deflection angle is calculated by the known projector position parameter and the known coordinate points, and then the actual model is projected. Typically, the calibration requires the establishment of six reference points to reduce the possibility of divergence of the nonlinear equations, but the whole solution is very complex and the solution may still diverge. In this paper, the distance is detected combined with the calculation so that the position parameters of the projector can be solved by using the coordinate values of three reference points and the distance of at least one reference point to the projector. The addition of the distance measurement increases the stability of the solution of the nonlinear system and avoids the problem of divergence of the solution caused by the reference point which is directly under the projector. Through the actual analysis and calculation, the Taylor expansion method combined with the least squares method is used to obtain the solution of the system. Finally, the simulation experiment is carried out by MATLAB, and the precision of the calibration algorithm is analyzed.
In the process of zero-crossing trigger measurement of differential confocal microscope, the sample surface features or tilt will cause the edges can't be triggered. Meanwhile, environment vibration can also cause false triggering. In order to restore the invalid information of sample, and realize high-precision surface topography measurement, Total Variation (TV) inpainting model is applied to restore the scanning images. Emulation analysis and experimental verification of this method are investigated. The image inpainting algorithm based on TV model solves the minimization of the energy equation by calculus of variations, and it can effectively restore the non-textured image with noises. Using this algorithm, the simulation confocal laser intensity curve and height curve of standard step sample are restored. After inpainting the intensity curve below the threshold is repaired, the maximum deviation from ideal situation is 0.0042, the corresponding edge contour of height curve is restored, the maximum deviation is 0.1920, which proves the algorithm is effective. Experiment of grating inpainting indicates that the TV algorithm can restore the lost information caused by failed triggering and eliminate the noise caused by false triggering in zero-crossing trigger measurement of differential confocal microscope. The restored image is consistent with the scanning result of OLYMPUS confocal microscope, which can satisfy the request of follow-up measurement analysis.
To perform the ultra-precision centering and leveling operation of large surface under test in optical and mechanical precision measurements, a novel automatic centering and leveling turntable based on the aerostatic bearing technology is developed. In the functional module of centering, a planar aerostatic bearing and two micro-displacement actuators are utilized to achieve centering operation, and in the leveling functional module, a spherical aerostatic bearing, two microdisplacement actuators and a spring pivot are employed to realize the leveling operation. In the paper, the mathematical models of centering and leveling operation are obtained using coordinate transformation, and coupling between the centering and leveling operation is also analyzed. Furthermore, by using distance-measuring interferometer and autocollimator, the resolutions of centering and leveling operation are measured. Finally, errors of the centering and leveling operation are analyzed and the performance evaluation of the turntable is given. The experimental results show that, with 50Kg load, the leveling operation resolution is better than 1.2″; leveling operation range is ±1<sup>°</sup>; the centering operation resolution is better than 0.05μm; centering operation range is about ±5mm. The developed turntable can satisfy the requirements of ultra-precision, high resolution, wide range, frictionless, high load stiffness, stabilization and small driving force.