Absolute position coordinate determining device employing a single phase

Abstract

A two dimensional digitizing system comprising two systems at right angles, each system having at least two conducting grid systems. Each grid system is comprised of a number of windings with a pitch distance D and an equal number of windings with a pitch distance D+.DELTA.d, where .DELTA.d is a small increment in distance. These windings produce a number of voltages whose amplitude varies cyclically as an AC excited cursor coil is moved in a direction at right angles to the conductors in a plane parallel to the plane of the conductors. Active or passive networks are provided for converting the grid voltages into signals whose phase with reference to the cursor coil excitation current varies linearly with cursor position. These signals are cyclic in nature going through a phase displacement of 360 degrees when the cursor moves through distance D in the case of one grid winding and a distance D+.DELTA.d in the case of the other grid winding. A single phase measuring system is used to provide a signal linearly related to cursor position by producing an output signal proportional to the phase difference between these two signals. This signal can be used to provide non ambiguous absolute positioning of a cursor coil on a digitizer tablet providing the maximum dimension of the tablet is less than ##EQU1## The system is used either alone or combined with a cyclical position signal to provide a more precise coarse/fine digitizing system.