Importance

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Abstract

Apparatus for determining the distance, accurate to within an error of no more than 1 mm, from a first position to a second position. The apparatus includes a distance marker that includes a first strip having a sequence of uniformly spaced light-reflecting (or light-transmitting) regions in one embodiment and includes a second strip having a sequence of uniformly spaced light-reflecting (or light-transmitting) regions, the two strips being positioned parallel and adjacent to each other with the positions of the light-reflecting (or light-transmitting) regions of the first strip being translated relative to the positions of the light-reflecting (or light-transmitting) regions of the second strip by a fixed translation distance. The apparatus also includes a light sensor positioned adjacent to the strip to sense each such light-reflecting region (or light-transmitting region) and/or each non-reflecting region (or non-transmitting region) as that region moves past the light sensor. When the strip is extended to measure the distance from the first position to the second position, the number of light-reflecting (or light-transmitting) regions and/or non-reflecting (or non-transmitting) regions moving past the light sensor is counted to determine the distance. When the extended portion of the distance marker is reduced in length, the counting process is reversed to determine a new distance. The number of strips on the distance marker can be increased to N.gtoreq.3 for improved distance measurement accuracy.

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First Claim