Graphic digitizer

Abstract

An X-Y coordinate position locating or measuring digitizing device in which a cursor (inductor), moveable within an electromagnetic field generated by successively activated grid wires, develops a voltage from the field, and, in conjunction with conditioning circuits, yields the electrical intelligence required to indicate its position with a high degree of precision. Currents are successively passed through parallel grid lines for a given axis at discretely separate distances, the resultant successively generated field inducing a time variant voltage at the cursor coil output with amplitude and phase dependent upon the position of the cursor in relation to the actuated grid line. Conditioning circuitry to which the cursor coil output is coupled uniquely detects the phase reversal in the cursor coil output signal, interprets this reversal point in a manner which very accurately and linearly relates cursor position to time, and generates a 'STOP' pulse indicating that the above phase reversal has been sensed. An enable signal initiated at an arbitrary reference point and terminated by the 'STOP' pulse is then used to permit a precision clock to relate the distance of the cursor from this arbitrary point to the time needed to reach the cursor center from that reference point. Cursor position then becomes a function of precisely generated pulses accumulated in a counter.