Since the cylinder surface is closed and periodic in the azimuthal direction, traditional stitching interferometry cannot be used to yield the 360° form map. This paper describes a full cylinder stitching interferometry based on the first-order approximation of cylindrical coordinate transformation. First, it introduces cylindrical projection, which allows us to determine the overlap region of the cylinder without ambiguity. Second, the relationship between the variations of radial coordinates and the movement errors of the rotational stage is derived from the first-order approximation of cylindrical coordinate transformation. Based on this relation, a cylinder stitching model is built to connect all sub-apertures together. Finally, we experimentally validate the proposed method by measuring a precision metal shaft. The high resolution and repeatability shown in the experimental results demonstrate our approach to be an attractive and promising technique in the field of precision measurement.
Measurement of steep acylindrical surface has the difficulty with respect to its large localized slope, which may lead to irresolvable fringe densities in off-axis subapertures. To address this problem, we analyze the departure of off-axis acylindrical subapertures, and propose a measurement strategy by yawing the cylinder null. When the cylinder null is yawed with different angles, variable mounts of acylindrical wavefronts are generated to compensate most of the aberrations for different off-axis subapertures. Thus, the fringe densities are drastically reduced within the vertical dynamic range of interferometers. To connect all subaperture together, we also propose an acylindrical stitching approach. Experimental results demonstrate that an acylindrical lens with a departure of up to 81µm from the best-fitting cylinder can be measured using the proposed method. More importantly, it does not require an additional reconfigurable optical null, making the measurement system simple and inexpensive.
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