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Correction of errors in table position

Naturally, the apparent {x,y} position of the table deviates somewhat from a perfectly uniform, rectilinear coordinate system. When in use as a coordinate measuring machine, the Leitz control system applies software corrections to the apparent positions in order to correct for this effect. Because of the high stability of the machine in its temperature-controlled environment, it is expected that these corrections will remain systematic and fixed for long timescales (> 1 year), and hence that software correction provides a viable means of obtaining an accurate measuring system. Measurement of NPI gauge blocks confirmed that, with corrections in place, the large-scale absolute accuracy of the table (in the absence of the optical system and measuring statically as a coordinate measuring machine) was indeed accurate to micron.

During a scan, some of these systematic errors (the larger component) are removed by applying our own real-time position corrections: others are removed during the image-processing stage.

Mon Aug 5 15:56:21 BST 1996