Accurate characterisation of hole size and location by projected fringe profilometry

The ability to accurately estimate the location and geometry of holes is often required in the field of quality control and automated assembly. Projected fringe profilometry is a potentially attractive technique on account of being non-contacting, of lower cost, and orders of magnitude faster than the traditional coordinate measuring machine (CMM). However, we demonstrate in this paper that fringe projection is susceptible to significant (hundreds of µm) measurement artefacts in the neighbourhood of hole edges, which give rise to errors of a similar magnitude in the estimated hole geometry. A mechanism for the phenomenon is identified based on the finite size of the imaging system’s point spread function and the resulting bias produced near to sample discontinuities in geometry and reflectivity. A mathematical model is proposed, from which a post-processing compensation algorithm is developed to suppress such errors around the holes. The algorithm includes a robust and accurate sub-pixel edge detection method based on a Fourier descriptor of the hole contour. The proposed algorithm was found to reduce significantly the measurement artefacts near the hole edges. As a result, the errors in estimated hole radius were reduced by up to one order of magnitude, to a few tens of µm for hole radii in the range 2-15 mm, compared to those from the uncompensated measurements

Accurate characterisation of hole geometries by fringe projection profilometry

Accurate localisation and characterisation of holes is often required in the field of automated assembly and quality control. Compared to time consuming coordinate measuring machines (CMM), fringe-projection-based 3D scanners offer an attractive alternative as a fast, non-contact measurement technique that provides a dense 3D point cloud of a large sample in a few seconds. However, as we show in this paper, measurement artefacts occur at such hole edges, which can introduce errors in the estimated hole diameter by well over 0.25 mm, even though the estimated hole centre locations are largely unaffected. A compensation technique to suppress these measurement artefacts has been developed, by modelling the artefact using data extrapolated from neighboring pixels. By further incorporating a sub-pixel edge detection technique, we have been able to reduce the root mean square (RMS) diameter errors by up to 9.3 times using the proposed combined method

Reduction of systematic errors in structured light metrology at discontinuities in surface reflectivity

In measuring 3D shape with structured light techniques, systematic errors arise in the neighbourhood of discontinuities in reflectivity or geometry. A mechanism for this phenomenon is proposed, based on the finite size of the imaging system’s point spread function. A theoretical analysis for the phase errors in a phase-shifting projected fringe system is given, from which a correction algorithm to minimise the systematic errors is presented. In this algorithm, a closed form expression for the errors based on the intensity values and the phase values in a neighbourhood excluding the affected region is used to remove the estimated error from the measured phase values within the affected region. Experiments on samples with both linear and circular discontinuities in reflectivity demonstrated respective reductions in systematic errors by factors of 2.5× and 3×

Various abnormal pollen grains of this triple hybrid.

<p>Various abnormal pollen grains of this triple hybrid.</p

Flowers with two kind color of this triple hybrid at the same time (pink and white) and the stigma and stamen with yellow pollen grains of this hybrid.

<p>Flowers with two kind color of this triple hybrid at the same time (pink and white) and the stigma and stamen with yellow pollen grains of this hybrid.</p

The resources of the SSR polymorphism in trispecific hybrid.

<p>The resources of the SSR polymorphism in trispecific hybrid.</p

Abnormal meiosis behavior of the hybrid with several micronuclei of various sizes (different polyads) in telophase II.

<p>Abnormal meiosis behavior of the hybrid with several micronuclei of various sizes (different polyads) in telophase II.</p

Accessions in this study and its characteristics.

<p>Accessions in this study and its characteristics.</p

Whole semi-bush plant with crawl growth characteristic and long epidermis hair in the stem, heart and thick leaf style of this triple hybrid.

<p>Whole semi-bush plant with crawl growth characteristic and long epidermis hair in the stem, heart and thick leaf style of this triple hybrid.</p

Amplification results for three <i>Gossypium herbaceum</i> × <i>G</i>. <i>raimondii</i> F1 hybrids and two parents using 4 representative SSR primer pairs.

<p>A) BNL4053. B) NAU2026. C) NAU1157. D) NAU1164 respectively.1-5: <i>G</i>. <i>herbaceum</i>, hybrid plant 1, hybrid plant 2, hybrid plant 3, and <i>G</i>. <i>raimondii</i>, respectively. The novel bands produced in hybrid plants were indicated by arrows.</p