Comparison of asphere measurements by tactile and optical metrological instruments

Bergmans, Rob; Nieuwenkamp, H.; Kok, Gertjan; Blobel, G.; Nouira, Hichem; Küng, Alain; Baas, M.; Tevoert, M; Baer, Goran; Stuerwald, Stephan

doi:10.1088/0957-0233/26/10/105004

Cited by 11 publications

(11 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In this situation, comparisons are a key factor in gaining new insights. Comparisons [6][7][8][9] have shown that, while some progress has been achieved, further improvements are also necessary. Most of the specimens used in these comparison studies were conventional spherical or aspherical surfaces made of glass.…”

Section: Introductionmentioning

confidence: 99%

Round robin comparison study on the form measurement of optical freeform surfaces

Fortmeier¹,

Schachtschneider²,

Lédl³

et al. 2020

J. Eur. Opt. Soc.-Rapid Publ.

View full text Add to dashboard Cite

A round robin comparison of freeform form measurements was carried out by the project partners and stakeholders of a European metrology research project. Altogether six measuring instruments were considered: five different (pointwise and areal) optical devices and one tactile device. Three optical freeform surfaces were used for the comparison measurements, where two specimens were measured by five instruments and one specimen by four instruments. In this paper, the evaluation methods and results of this round robin are presented for the three freeform surfaces made from a temperature-stable material, Super Invar ®. The freeforms had diameters of 40 mm, 50 mm and 100 mm and best-fit radii of 39.75 mm (convex), 40.9 mm (convex) and 423.5 mm (concave). For comparison, the bilateral pointwise differences between the available measurements were calculated. The root-mean-square values of these differences ranged from 15 nm to 110 nm (neglecting spherical contributions) and provided an insight into the status of typical freeform measurement capabilities for optical surfaces.

show abstract

Section: Introductionmentioning

confidence: 99%

Round robin comparison study on the form measurement of optical freeform surfaces

Fortmeier¹,

Schachtschneider²,

Lédl³

et al. 2020

J. Eur. Opt. Soc.-Rapid Publ.

View full text Add to dashboard Cite

show abstract

“…The decreasing number of elitists would significantly speed up the convergence speed in the first stage of the iteration process with many elitists, and keep the exploitation ability in the later stage by removing the elitists for more potential trials. The elitists are selected by ascending order of fitness function evaluations and used in calculating the Mean i of TLBO in (21). This ETLBO makes it easy to achieve the desired searching results with low computational complexity.…”

Section: Elitist Strategymentioning

confidence: 99%

“…Among various surface fitting algorithms, the polynomial approximation is the most popular one. The desirable properties of Zernike polynomials, such as orthogonality, rotational symmetry, relation to classical Seidel aberrations, and simple representation, have made it the most popular basis function for analyzing optical surfaces [19][20][21]. Ares and Royo studied the fitting performance of Zernike polynomials, and found that low-degree Zernike polynomials are suitable for fitting simple wavefronts [22].…”

Section: Introductionmentioning

confidence: 99%

An inline surface measurement method for membrane mirror fabrication using two-stage trained Zernike polynomials and elitist teaching–learning-based optimization

Liu

Chen

Yang

et al. 2016

Meas. Sci. Technol.

View full text Add to dashboard Cite

The accuracy of surface measurement determines the manufacturing quality of membrane mirrors. Thus, an efficient and accurate measuring method is critical in membrane mirror fabrication. This paper formulates this measurement issue as a surface reconstruction problem and employs two-stage trained Zernike polynomials as an inline measuring tool to solve the optical surface measurement problem in the membrane mirror manufacturing process. First, all terms of the Zernike polynomial are generated and projected to a non-circular region as the candidate model pool. The training data are calculated according to the measured values of distance sensors and the geometrical relationship between the ideal surface and the installed sensors. Then the terms are selected by minimizing the cost function each time successively. To avoid the problem of ill-conditioned matrix inversion by the least squares method, the coefficient of each model term is achieved by modified elitist teaching–learning-based optimization. Subsequently, the measurement precision is further improved by a second stage of model refinement. Finally, every point on the membrane surface can be measured according to this model, providing more the subtle feedback information needed for the precise control of membrane mirror fabrication. Experimental results confirm that the proposed method is effective in a membrane mirror manufacturing system driven by negative pressure, and the measurement accuracy can achieve 15 µm.

show abstract

“…[6][7][8]). Another attempt to compare different measurement principles was carried out in an EMRP project in 2015 [9]. However, the number of specimens and participants brought together in this study by CC UPOB e.V.…”

Section: Introductionmentioning

confidence: 99%

Interlaboratory comparison measurements of aspheres

Schachtschneider

Fortmeier

Stavridis

et al. 2018

Meas. Sci. Technol.

View full text Add to dashboard Cite

The need for high-quality aspheres is rapidly growing, necessitating increased accuracy in their measurement. A reliable uncertainty assessment of asphere form measurement techniques is difficult due to their complexity. In order to explore the accuracy of current asphere form measurement techniques, an interlaboratory comparison was carried out in which four aspheres were measured by eight laboratories using tactile measurements, optical point measurements, and optical areal measurements. Altogether, 12 different devices were employed. The measurement results were analysed after subtracting the design topography and subsequently a best-fit sphere from the measurements. The surface reduced in this way was compared to a reference topography that was obtained by taking the pointwise median across the ensemble of reduced topographies on a Cartesian grid. The deviations of the reduced topographies from the reference topography were analysed in terms of several characteristics including peak-to-valley and root-mean-square deviations. Root-mean-square deviations of the reduced topographies from the reference topographies were found to be on the order of some tens of nanometres up to 89 nm, with most of the deviations being smaller than 20 nm. Our results give an indication of the accuracy that can currently be expected in form measurements of aspheres.

show abstract

Comparison of asphere measurements by tactile and optical metrological instruments

Cited by 11 publications

References 6 publications

Round robin comparison study on the form measurement of optical freeform surfaces

Round robin comparison study on the form measurement of optical freeform surfaces

An inline surface measurement method for membrane mirror fabrication using two-stage trained Zernike polynomials and elitist teaching–learning-based optimization

Interlaboratory comparison measurements of aspheres

Contact Info

Product

Resources

About