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# Moire Input Tablet

IP.com Disclosure Number: IPCOM000079406D
Original Publication Date: 1973-Jun-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 3 page(s) / 48K

IBM

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Keyes, RW: AUTHOR

## Abstract

One method of entering information into a computer is by positioning a probe on a flat surface. Described is apparatus for locating the position of the probe electronically.

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Moire Input Tablet

One method of entering information into a computer is by positioning a probe on a flat surface. Described is apparatus for locating the position of the probe electronically.

Light and dark lines can be made to move rapidly across a surface by moving patterns that produce Moire fringes. For example, two patterns of Fresnel rings displaced with respect to one another are known to produce a set of linear Moire fringes. When one of the patterns is moved with respect to the other, the spacing between the Moire lines changes. Thus, when the pattern is moved, alternate light and dark stripes will pass a point. If a probe containing a photosensor is located at the point, the passage of light stripes can be observed and the position of the probe can be determined by counting the light cycles.

Referring to the figure, the Fresnel Moire pattern shown on tablet 12 is produced by a set of alternating light and dark concentric circular rings, each having the same area. The radius of the first circle is b, the radius of the second circle is b square root of 2, and the radius of the nth circle is b square root of n. A second Fresnel pattern is produced on a second tablet 10 in such a way that the center of the rings is located at a point some distance away from the tablet. Now if the two tablets are superimposed, a Moire pattern of parallel alternating dark and light stripes will appear. If the two patterns are displaced by a distance s, then the n(1)th circle of one pattern will coincide with the n(2)th circle of a second pattern when the following expression is satisfied b square root of n(1) = s + b square root of n(2) The spacing of the dark rings around the nth ring is 2 x d(b square root of Jn)/dx = b/n/1/2/. The spacing between the straight Moire lines will be that between the coincidences of...