Successively electromagnetically scanned x-y grid conductors with a digitizing system utilizing a free cursor or stylus

• US 4,080,515 A
• Filed: 01/12/1977
• Issued: 03/21/1978
• Est. Priority Date: 06/17/1975
• Status: Expired due to Term

• Current Assignee: GTCO Corporation (GTCO Calcomp, Incoporated)
• Original Assignee: GTCO Corporation (GTCO Calcomp, Incoporated)
• Inventors: Anderson, Raymond W.
• Primary Examiner(s): Sloyan, Thomas J.
• Application Number:
  US05/758,818
• Time in Patent Office: 433 Days
• Field of Search: 178/18, 178/19, 235/61.6 A, 340/347 AD, 340/347 M, 33/1 M
• US Class Current: 178/18.07
• CPC Class Codes: G06F 3/046 by electromagnetic means

Abstract

A position digitizing device in which a cursor, moveable within a field generated by successively activated grid wires, developes 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 at discretely separate distances, the resultant successively positioned fields successively inducing voltages at the cursor coil output dependent upon the position of the cursor in relation to the actuated grid line. Conditioning equipment to which the cursor output is coupled mixes the cursor output with a reference and introduces circuitry responsive to the rate at which the grid currents are successively stepped to translate the cursor output to a time variant wave form. A reference point developed from that wave form is then used to permit a precision clock to relate the distance of the cursor from a grid line to the time needed to reach the reference point. Cursor position then becomes a function of precisely generated pulses accumulated in a counter.

Claims

1. Apparatus for determining the position of a selected point on a grid comprising

an oscillator;

a cursor including a coil moveable on said grid;

first means for supplying a signal from said oscillator to X and Y conductors in said grid;

switching means for scanning said X and Y conductors so as to provide said signal to said conductors individually in sequence;

said coil in said cursor detecting said signals in said conductors;

a filter coupled to the output of said coil;

second means for supplying a reference signal from said oscillator;

third means for frequency modulating said reference signal with the output of said filter;

frequency modulation discriminator means coupled to the output of said third means;

a second filter coupled to the output of said discriminator means for producing a signal envelope each time said conductors are scanned;

fourth means coupled to the output of said second filter for detecting the zero crossing point of said signal envelope;

X and Y counters;

fifth means coupling the output of said fourth means to said counters; and

sixth means for coupling the output of said oscillator to said counters;

whereby the outputs of said fourth means and said oscillator are operable to stop each counter at a value indicative of cursor position.

2. The apparatus of claim 1 wherein said oscillator input comprises

a crystal oscillator.

3. The apparatus of claim 1 wherein said first means for supplying said signal comprises

a crystal oscillator;

a divider coupled to the output of said crystal oscillator; and

a decoder and filter coupled to the output of said divider.

4. The apparatus of claim 1 wherein said frequency modulation discriminator means comprises

a phase locked loop.

5. The apparatus of claim 1 wherein said switching means comprises

a clock decoder;

and

a counter for detecting the initiation and termination of each scan.

6. The apparatus of claim 1 further comprising

means for positioning said coil a predetermined distance from said grid.

7. Apparatus for determining the position of a selected point on a grid having X and Y conductors comprising an oscillator;

a cursor including a coil moveable on said grid;

first means for supplying a signal from said oscillator to said coil;

switching means for scanning said X and Y conductors in sequence so as to detect the output signal of said coil;

a filter coupled to the output of said switching means;

second means for supplying a reference signal from said oscillator;

third means for frequency modulating said reference signal with the output of said filter;

frequency modulation discriminator means coupled to the output of said third means;

a second filter coupled to the output of said discriminator means for producing a signal envelope each time said conductors are scanned;

fourth means coupled to the output of said second filter for detecting the zero crossing point of said signal envelope;

X and Y counters;

fifth means coupling the output of said fourth means to said counters; and

sixth means for coupling the output of said oscillator to said counters;

whereby the outputs of said fourth means and said oscillator are operable to stop each counter at a value indicative of cursor position.

8. The apparatus of claim 7 wherein said oscillator input comprises

a crystal oscillator.

9. The apparatus of claim 7 wherein said first means for supplying said signal comprises

a crystal oscillator;

a divider coupled to the output of said crystal oscillator; and

a decoder and filter coupled to the output of said divider.

10. The apparatus of claim 7 wherein said frequency modulation discriminator means comprises

a phase locked loop.

11. The apparatus of claim 7 wherein said switching means comprises

a clock decoder;

and

a counter for detecting the initiation and termination of each scan.

12. The apparatus of claim 7 further comprising

means for positioning said coil a predetermined distance from said grid.

13. Apparatus for determining the position of a selected point on a grid comprising

an oscillator;

a cursor including a coil moveable on said grid;

means for supplying a signal from said oscillator to X and Y conductors in said grid;

switching means for scanning said X and Y conductors so as to provide said signal to said conductors individually in sequence;

said coil in said cursor developing a signal envelope each time said grid is scanned;

a filter coupled to the output of said coil;

means for supplying a reference signal from said oscillator;

means for frequency modulating said reference signal with the output of said filter;

means for detecting the null in said cursor signal envelope;

means for coupling said modulated output to said means for detecting said null;

X and Y counters;

means for coupling the output of said means for detecting said null to said counters; and

means for coupling the output of said oscillator to said counters;

whereby the outputs from said means for detecting said null and said oscillator are operable to stop each counter at a value indicative of cursor position.

14. The apparatus of claim 13 wherein said means for detecting said null comprises

a phase locked loop discriminator.