We present a profilometry for measuring aspheric surface, which determines the curvature from the sub-aperture topography along two orthogonal directions and then reconstructs the entire surface profile from the measured curvature data. The entire surface was divided into a number of sub-apertures with overlapping zones. Each sub-aperture was measured using white-light scanning interferometry to avoid any optical alignment error along an optical axis. Simulation studies are also presented based on the mathematical model. The proposed mathematical model was also experimentally tested on freeform surfaces using white-light scanning interferometry under deveolpment.
We present a method of aspheric surface reconstruction from the curvature data along two orthogonal directions. The curvature is an intrinsic property of the artifact, which does not depend on the positioning error of a measuring sensor. In this paper, we showed that the curvature method is suitable for aspheric surface reconstruction along one direction and expanded this algorithm to two directions. Computer simulations were undertaken to explore the possibility of three-dimensional surface reconstruction. The simulation results and the position error diagnosis showed that the curvature method is robust against various positioning errors.
Increasing demand for highly accurate freeform aspheric surfaces requires accurate and efficient measurement
techniques. One promising possibility uses a sub-aperture scanning system that measures local curvature variations
across the part. In this paper, we develop and demonstrate two different data processing algorithms, a zonal approach
using Southwell integration method and a modal approach leveraging Zernike curvature basis, that reconstruct the
surface 3-dimensional profiles from the curvature data. The performance of suggested methods and the sensitivity to
noise is diagnosed for various SNR (Signal-to-Noise Ratio) cases.
We present a non-contact type monitoring system specially devised to control the cutting depth on the grinding process.
This system comprises a one axis scanning stage and the imaging system using line camera and collimated white light
source. Experimental results prove that the proposed system is useful, especially for the monitoring system in grinding
the piston groove on the cylinder with a few micrometers accuracy in the dozens of millimeter area.
We present a method of three dimensional shape measurement from the curvature data, which are obtained from the
subaperture topography along the diagonal direction of artifact by using white-light scanning interferometry. The
curvature is an intrinsic property of the artifact, which does not depend on the positioning errors of measuring sensor.
Experimental results prove that the proposed method is useful, especially for large-scale optical surface profile
measurement with nanometer accuracy.
The current version of this paper has had a correction made to it at the request of the author. Please see the linked Errata for further details.
In heavy industry, especially in the shipbuilding process, 3D profile measurement of large-scale hull pieces is needed for fabrication and assembly. Currently, using many kinds of templates made of wood or plastic still do an important role as a standard ruler. We suggest an efficient method of 3D profile measurement to obtain the xyz-coordinates of curvature plates. The measurement system comprises multiple line structured laser sources and performs profile measurement by projecting structured light source on the object surface. The measurement results show that measurement accuracy is within the boundary of accuracy required in the shipbuilding process.
We present a method of aspheric surface profile measurement based on the principle of curvature sensor, which
measures the curvature of subaperture topography along a line and then reconstructs the entire profile from the
measured local curvature data. The subaperture topography is obtained by using white-light scanning interferomtery to
avoid the optical alignment error along an optical axis. Test measurement results demonstrate that the proposed method
and system is well suited for the aspheric surface profile measurement.
We present a method of free-form surface profile measurement using white-light scanning interferometry. This method is based on the principle of curvature sensor which measures the local curvature under test along a line. The profile is then reconstructed from the curvature data on the each point. Unlike subaperture-stiching method and slope detection method curvature sensing have strong points from a geometric point of view in measuring the free-form surface profile. Curvature is related to second derivative terms of surface profile and an intrinsic property of the test piece, which is independent of its position and tip-tilt motion. The curvature is measured at every local area with high accuracy and high lateral resolution by using White-light scanning interferometry.
The Geometry Measuring Machine (GEMM) of the National Institute of Standards and Technology (NIST) is a profilometer for free-form surfaces. A profile is reconstructed from local curvature of a test part surface, measured at several locations along a line. For profile measurements of free-form surfaces, methods based on local part curvature sensing have strong appeal. Unlike full-aperture interferometry they do not require customized null optics. The uncertainty of a reconstructed profile is critically dependent upon the uncertainty of the curvature measurement and on curvature sensor positioning. For an instrument of the GEMM type, we evaluate the measurement uncertainties for a curvature sensor based on a small aperture interferometer and then estimate the uncertainty in the reconstructed profile that can be achieved. In addition, profile
measurements of a free-form mirror, made with GEMM, are compared with measurements using a long-trace profiler, a coordinate measuring machine, and subaperture-stitching interferometry.
We present a point-diffraction interferometer specially devised for the profile measurement of rough surfaces that are difficult to be measured with conventional two-arm interferometers. The diffraction interferometer comprises multiple two-point-diffraction sources made of a pair of single-mode optical fibers, and performs an absolute profile measurement by projecting multiple fringe patterns on the object surface and then fitting measured phase data into a global geometrical model of multilateration. Test measurement results demonstrate that the proposed point-diffraction interferometer is well suited for the warpage inspection of microelectronics components with excessive height irregularities, such as unpolished backsides of silicon wafers and plastic molds of integrated-circuit chip packages.
We present a method of 3-D profile measurement to obtain the xyz-coordinates of complex surfaces based on multipoint diffraction interferometry. This method uses multiple sets of diffraction light sources, each of which is made of two single-mode optical fibers emitting spherical wavefronts. Fringe patterns generated by the interference of two spherical wavefronts are illuminated on the target surface, whose phases are precisely determined by using phase-shifting technique. Finally, measured phase information is directly related to the xyz-coordinates of the target surface utilizing principles of multilateration.