This paper compares two kinds of cylinder stitching algorithm: global error homogenization stitching algorithm and Legendre Fourier polynomial fitting algorithm. The former uses the overlapping regions between adjacent sub-apertures, which can obtain high accurate results but need more time on data acquisition; Legendre-Fourier polynomial fitting stitching algorithm without overlapping regions need less aperture and short measure time but lack of high frequency information. Its stitching results easily affected by the position error of sub aperture, which is more suitable for in-situ measurement.
Since the cylinder surface is closed and periodic in the azimuthal direction, existing stitching methods cannot be used to yield the 360° form map. To address this problem, this paper presents two methods for stitching interferometry of cylinder: one requires overlap regions, and the other does not need the overlap regions. For the former, we use the first order approximation of cylindrical coordinate transformation to build the stitching model. With it, the relative parameters between the adjacent sub-apertures can be calculated by the stitching model. For the latter, a set of orthogonal polynomials, termed Legendre Fourier (LF) polynomials, was developed. With these polynomials, individual sub-aperture data can be expanded as composition of inherent form of partial cylinder surface and additional misalignment parameters. Then the 360° form map can be acquired by simultaneously fitting all sub-aperture data with LF polynomials. Finally the two proposed methods are compared under various conditions. The merits and drawbacks of each stitching method are consequently revealed to provide suggestion in acquisition of 360° form map for a precision cylinder.
Subaperture stitching interferometry has been proven to be a promising method for precision metrology of aspheric surfaces. However, due to the aspheric departure, selection of F/number of the transmission sphere for aspheres is more complicated than spheres or flats. This paper proposed an optimization method to determine the maximum subaperture width based on the slope resolution of the standard interferometer. With it, the transmission sphere is selected with an optimal F/number. On the basis of the transmission sphere and overlap rate, we not only can ensure the fringes of off-axis subapertures are resolvable by the interferometer, but also can minimize the number of subapertures required to cover the full aperture of the surface. Finally, some numerical examples are given to illustrate the procedure, and also to verify the validity of our proposed method.
This paper presents a misalignment aberrations calibration method for the interferometric testing of
cylindrical surface. This approach is based on a simple polynomials function, which is deduced by
analyzing the geometry of the misalignment aberrations and perfectly describes the relationship
between the misalignment aberrations and the corresponding adjustment errors. A least-squares
algorithm for calibration of the misalignment aberrations was implemented towards the measured
phase data, and the adjustment errors can be estimated through the proposed mathematical model. Then
by subtracting the fitting function from the measured phase data, the misalignment aberrations and the
genuine deviation of the test cylindrical surface can be completely separated. By means of simulation
and experimental results, the repeatability and accuracy of the technique are discussed.
The surface microstructure of engine cylinder is critical to its performance. To reduce wear and generated noise, a submicron
and even nanometer smooth surface is required, so more requirements are needed for traditional measurement.
While interferometric optical profilers are often used for testing surface microstructure and this technique is both
noncontact and nondestructive, we set up a cylindrical interferometric measurement system to get the surface shape of
engine cylinder wall. This system includes the interferometer, the cylindrical wave converter and a platform with five-dimensional
precise adjustment. Considering the aberration affected by the real experiment condition, it is almost
impossible to measure the surface profile of the tested object with displacement from a best-fit reference cylinder. In this
paper, we set up a model to simulate the interferogram when the axis of measured object is off the cylindrical focus line.
As the actual experiment environment, there are four situations about the position error of measured object and the exit
pupil wave surface formula for each case can be built by the physical optics. If tested object center is slightly displaced
from the focal line, the formula of the wave surface can be simplified. Then we can get the interferogram by using the
formula. The paper also compares the simulation results with the ones by Zemax software to verify the testing mode.
This paper presents a novel approach to generate object-adapted fringe, which based on scattered data
interpolation. It can effectively solve the problems of the existing methods, such as complicated
computation process and low accuracy. It needn't map the projector pixels coordinate onto the camera
coordinate, only map the camera pixels coordinate onto projector coordinate. The phase of integer
pixels of projector coordinate can be interpolated in the term of phase distribution of wanted fringe
pattern. Compared to the presently algorithms, the advantages of this algorithm are simple and highly
efficiency. This paper expatiates on the principle of the object-adapted fringe generation method using
scattered data points. Simulation analysis and experiment results prove the validity and feasibility of
the new approach. We also have compared the result between this new approach and other existing
methods.
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