National Physical Laboratory

Two-Dimensional Grid Plate Standards

Grid Plates
X-Y Two-Dimensional Grid Plate

NPL has developed a new range of non-contact dimensional standards designed to calibrate the co-planar axes of industrial imaging systems and vision inspection machines.

NPL has developed a new range of non-contact dimensional standards designed to calibrate the co-planar axes of industrial imaging systems and vision inspection machines. These non-contact standards provide traceability to the SI unit of length, the Metre and can be measured with sub-micrometre accuracy. They can aid customers seeking formal accreditation, for example, to UKAS or ISO requirements.

The standards are chrome on glass and have working areas from 250mm x 250mm to 650mm x 650mm. The chrome layer bears metrology structures composed of target dies, set on a square grid that has a nominal pitch of 25mm. Each die is made up of chrome and clear circles, crosses and squares. The nominal external dimensions of these features start from 30┬Ám, with each successive feature being twice the size of the previous, up to 1mm. This enables the co-ordinates of the features to be measured using different optical magnifications. Each artefact has supplementary patterns including linear scales, grids and optical linewidths, designed for the linear calibration of a vision system's optical viewing head.

Grid Plates Supplimentary Patterns

Where high precision calibration and verification of the imaging system is required, a new multi-functional Optical Dimensional Standard is available, consisting of a single high-precision calibration plate bearing a vast range of different scales, designed to meet virtually all optical dimensional calibration needs.

Vision Inspection Machine

Non-Contact Dimensional Metrology - Contract Measurement Service

Vision inspection machines make it possible to measure complex, precisely fabricated items and materials such as automotive and aerospace components, printed circuit boards, microelectronic circuits and features that cannot be accessed by conventional contact type machines and gauges. Measurements can be obtained from thin or soft workpieces; and brittle, elastic or moving parts can be measured accurately and quickly, as the measurement technique is neither invasive nor destructive. This is advantageous in a production environment, allowing quality control and real time feedback to be readily integrated into the manufacturing process. Vision inspection machines are used in many diverse industries, with typical users including pharmaceuticals, food production, engineering, electronics and aerospace.

For organisations that do not have their own vision machines, or who require particularly high accuracy, the laboratory provides a contract measurement service and consultancy. Artefact sizes up to 1200mm x 1000mm x 500mm can be accommodated, and the capabilities of the machines at NPL have been enhanced by laser interferometry and advanced mathematical algorithms designed in-house, to optimise the measurement uncertainty.

Uncertainties:

On high specification grid plates sub-micrometre measurement uncertainties can potentially be achieved.

Key features:

  • Standards are available for sale, or customer supplied artefacts can be measured.
  • Traceable to the Iodine Stabilised Laser.
  • A wide variety of scale designs and artefact dimensions can be accommodated.
  • Measurements can be made with transmitted or reflected illumination.
  • Various scale supporting mechanisms available.
Last Updated: 25 Mar 2010
Created: 5 Sep 2007

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