Electrostatic pattern-coupled digitizer

• US 4,705,919 A
• Filed: 02/21/1985
• Issued: 11/10/1987
• Est. Priority Date: 02/21/1985
• Status: Expired due to Fees

• Current Assignee: Satish K. Dhawan
• Original Assignee: Satish K. Dhawan
• Inventors: Dhawan, Satish K.
• Primary Examiner(s): SCHREYER, STAFFORD
• Application Number:
  US06/704,329
• Time in Patent Office: 992 Days
• Field of Search: 178/18, 178/19, 178/20
• US Class Current: 178/18.03
• CPC Class Codes: G06F 3/0442 using active external devices, e.g. active pens, for transmitting changes in electrical potential to be received by the digitiser

Abstract

A digitizer in which position of a free moving cursor or stylus over a digitizing surface is determined by electrostatic coupling of the cursor with three coplanar electrodes imbedded in the digitizing tablet. The electrodes consist of a repetitive sawtooth pattern to determine position in one axis, the sawtooths interleaved with progressively wider, repetitive stripes to determine position in another axis. The third electrode covers the remainder of the coplanar surface area. Only three electrode signals are required to be electronically processed to determine absolute vertical and horizontal position of the cursor over the digitizing tablet by a ratiometric measurement. The signals from the electrodes are processed synchronously to reject noise.

Claims

1. A digitizer comprising:

A. a digitizer tablet having two electrodes, the first electrode having a pattern that varies with a first coordinate in a two-coordinate system and the second electrode having a pattern that varies with the second coordinate in the two-coordinate system;

B. a cursor movable on the digitizer tablet, the cursor including a coupling electrode for electrostatic field coupling with the first and second patterned electrodes of the digitizer tablet;

C. signal generating means connected for inputting an electrical signal to the coupling electrode of the cursor, thereby establishing electrostatic field coupling with and electrical signals on each of the first and second patterned electrodes, the electrical signals on the first and second patterned electrodes being indicative of the position of the cursor in the two-coordinate system; and

D. electronic means for calculating the coordinates of the cursor in the two-coordinate system from the electrical signals on the first and second patterned electrodes.

2. A digitizer as defined in claim 1 wherein the first and second patterned electrodes are coplanar.

3. A digitizer as defined in claim 2 wherein the two-coordinate system is the orthogonal X-Y axis coordinate system and one of the first and second patterned electrodes comprise a plurality of conductive stripes connected together along one end, the stripes having progressively increasing width starting from a side of the tablet and extending toward an opposite side of the tablet, and the other patterned electrode comprises a plurality of elongated sawtooths interleaved between the stripes, the sawtooths also being connected together at one end thereof, whereby one of the patterned electrodes provides an X-axis indicating signal and the other patterned electrode provides a Y-axis indicating signal.

4. A digitizer as defined in claim 3 and further comprising a balance electrode coplanar with the stripe and sawtooth patterned electrodes and occupying the space therebetween, whereby the sum of the stripe, sawtooth and balance electrodes constitutes the total output signal of the digitizer tablet and the X-axis coordinate of the cursor is proportional to the X-axis signal divided by the sum of the stripe, sawtooth and balance electrodes, and the Y-axis coordinate position is proportional to the Y-axis signal divided by the sum of the stripe, sawtooth and balance electrode signals.

5. A digitizer as defined in claim 4 wherein the field of the coupling electrode of the cursor is circular and covers at least four stripes and sawtooths.

6. A digitizer as defined in claim 4 wherein the coupling electrode of the cursor has a central opening transparent to the tablet surface, in which a mark indicates the center of the coupling electrode.

7. A digitizer as defined in claim 5 wherein the tablet further comprises a perimeter shield electrode coplanar with and surrounding the stripe, sawtooth and balance electrodes, for shielding them against interference.

8. A digitizer as defined in claim 5 wherein the cursor further comprises a shield electrode positioned on the opposite side of the cursor coupling electrode from the digitizer tablet and separated from the cursor coupling electrode by a dielectric spacer, for shielding the cursor coupling electrode from interference.

9. A digitizer as defined in claim 8 wherein the cursor shield electrode is larger than and overhangs the cursor coupling electrode.

10. A digitizer as defined in claim 9 wherein the digitizer tablet further comprises a planar ground electrode positioned on the opposite side of the stripe, sawtooth and balance electrodes from the cursor coupling electrode and separated from the stripe, sawtooth and balance electrodes by a dielectric layer of the digitizer tablet.

11. A digitizer as defined in claim 4 wherein the stripes of the stripe patterned electrode are evenly spaced apart and progressive increase of the width of the stripe electrodes is approximately 0.001 inch, and the sawtooths of the sawtooth patterned electrode are evenly spaced apart.

12. A digitizer as defined in claim 11 wherein there are at least four each striped and sawtooth electrodes per inch.

13. A digitizer as defined in claim 4 wherein the digitizer tablet comprises first and second layers of dielectric material with the first and second patterned electrodes and the balance electrode therebetween.

14. A digitizer as defined in claim 13 wherein the first and second patterned electrodes and the balance electrode comprise a conductive material deposited on one of the first or second layers of dielectric material.

15. A digitizer as defined in claim 13 wherein the first and second patterned electrodes and the balance electrode comprise a conductive ink printed on a thin film of dielectric material and said film is deployed between the first and second layers of dielectric material.

16. A digitizer as defined in claim 13 and further comprising a perimeter shield electrode surrounding the first and second patterned electrodes and the balance electrode, the perimeter shield electrode being positioned between the first and second layers of dielectric material.

17. A digitizer as defined in claim 13 wherein the first layer of dielectric comprises the top surface of the digitizer tablet on which the cursor is used, and further comprising a ground plane electrode substantially covering the second dielectric on the opposite side from the first and second patterned electrodes and the balance electrode.

18. A digitizer as defined in claim 4 wherein the input to the cursor coupling electrode is an alternating current electrical signal, and the electrical output signals from the stripe, sawtooth and balance electrodes are also alternating signals at the same frequency, wherein the output signals from the stripe, sawtooth and balance electrodes are detected synchronously with the input signal, thereby minimizing interference and providing a high signal-to-noise ratio in the output of the digitizer tablet.

19. A digitizer as defined in claim 18 wherein the frequency of the input signal is in the range of 10 KHZ to 1 MHZ.

20. A digitizer comprising:

A. a digitizer tablet having two electrodes, the first electrode having a pattern that varies with a first coordinate in a two-coordinate system and the second electrode having a pattern that varies with the second coordinate in the two-coordinate system;

B. a cursor movable on the digitizer tablet, the cursor including a coupling electrode for coupling with the first and second patterned electrodes of the digitizer tablet;

C. signal generating means connected for inputting an electrical signal alternately to the first and second patterned electrodes of the digitizer tablet, thereby establishing electrostatic field coupling with and an electrical signal on the coupling electrode of the cursor, the signal on the cursor coupling electrode being alternately indicative of the position of the cursor in each coordinate of the two-coordinate system; and

D. electronic means for calculating the coordinates of the cursor in the two-coordinate system from the signals coupled to the cursor electrode from the first and second patterned electrodes.

21. A digitizer as defined in claim 20 wherein the first and second patterned electrodes are coplanar.

22. A digitizer as defined in claim 21 wherein the two-coordinate system is the orthogonal X-Y axis coordinate system and one of the first and second patterned electrodes comprises a plurality of conductive stripes connected together along one end, the stripes having progressively increasing width starting from a side of the tablet and extending toward an opposite other side of the tablet, and the other a plurality of elongated sawtooths interleaved between the stripes, the sawtooths also being connected together at one end thereof, whereby one of the patterned electrodes provides an X-axis indicating signal to the cursor coupling electrode and the other patterned electrode provides a Y-axis indicating signal to the cursor coupling electrode.

23. A digitizer as defined in claim 22 and further comprising a balance electrode coplanar with the stripe and sawtooth patterned electrodes and occupying the space therebetween, whereby the sum of the stripe, sawtooth and balance electrodes constitutes the total output signal of the digitizer tablet and the X-axis coordinate of the cursor is proportional to the X-axis signal divided by the sum of the stripe, sawtooth and balance electrodes, and the Y-axis coordinate position is proportional to the Y-axis signal divided by the sum of the stripe, sawtooth and balance electrode signals.

24. A digitizer as defined in claim 23 wherein the input to the first and second patterned electrodes and balance electrode is an alternating current electrical signal, and the electrical output signals from the cursor coupling electrode are also alternating signals at the same frequency, wherein the output signals from the cursor coupling electrode are detected synchronously with the input signals, thereby minimizing interference and providing a high signal-to-noise ratio in the output of the digitizer tablet.

25. A digitizer comprising:

A. a digitizer tablet having two electrodes, the first electrode having a pattern that varies with a first coordinate in a two-coordinate system and the second electrode having a pattern that varies with the second coordinate in the two-coordinate system;

B. a stylus movable on the digitizer tablet, the stylus including a coupling electrode for electrostatic field coupling with the first and second patterned electrodes of the digitizer tablet;

C. signal generating means connected for inputting an electrical signal to the coupling electrode of the stylus, thereby establishing electrostatic field coupling with and electrical signals on each of the first and second patterned electrodes, the electrical signals on the first and second patterned electrodes being indicative of the position of the stylus in the two-coordinate system; and

D. electronic means for calculating the coordinates of the stylus in the two-coordinate system from the electrical signals on the first and second patterned electrodes.

26. A digitizer comprising:

A. a digitizer tablet having two electrodes, the first electrode having a pattern that varies with a first coordinate in a two-coordinate system and the second electrode having a pattern that varies with the second coordinate in the two-coordinate system;

B. a stylus movable on the digitizer tablet, the stylus including a coupling electrode for coupling with the first and second patterned electrodes of the digitizer tablet;

C. signal generating means connected for inputting an electrical signal alternately to the first and second patterned electrodes of the digitizer tablet, thereby establishing electrostatic field coupling with and an electrical signal on the coupling electrode of the stylus, the signal on the stylus coupling electrode being alternately indicative of the position of the stylus in each coordinate of the two-coordinate system; and

D. electronic means for calculating the coordinates of the stylus in the two-coordinate system from the signals coupled to the stylus electrode from the first and second patterned electrodes.

27. A digitizer as defined in claim 26 wherein the first and second patterned electrodes are coplanar.