Two-dimensional absolute position measurement

摘要

A scale 1 and scale reader 2 are disclosed which may be used to determine absolute position of the reader with respect to the scale in two directions. In an embodiment of the invention a chequered pattern is produced on a scale and blocks of the pattern may be imaged on a detector 5 and decoded. The blocks contain bits of information which define an absolute position. The pattern may be used also for incremental measurement.