Digitizer with serpentine-type conductor grid having uniform conductor

Abstract

Disclosed herein are position determining apparatus and conductor structures or grids therefor. The conductor structure for each axis includes a number of conductors which are run in a serpentine-type path each with uniform repeat increment. The repeat increment, which is the spacing or span between one run and the next of the same serpentine-type conductor, are uniform for each conductor (but may change from conductor to conductor) and is constrained by a maximum repeat increment, or a minimum repeat increment. In the preferred embodiments, there is at least a constraint on the maximum repeat increment to provide noise immunity. The conductors are arranged for each axis of the grid in a pattern such that signals obtained for that axis may be processed to provide binary numbers in a Gray-type code each unique to a small region of the active area in which the coil center is located. The small region for a given axis corresponds to the space between two immediately adjacent, active conductor portions for that axis, with a possible ambiguity of one space. Small regions in each axis define the coarse location of the coil center. Fine location within a region may be determined from the magnitudes of currents induced in selected runs preferably by interpolation.