Position determining and digitizing method and device

• US 4,999,462 A
• Filed: 10/06/1989
• Issued: 03/12/1991
• Est. Priority Date: 10/06/1989
• Status: Expired due to Fees

• Current Assignee: Summagraphics Corp.
• Original Assignee: Summagraphics Corp.
• Inventors: Purcell, Alexander M.
• Primary Examiner(s): SCHREYER, STAFFORD
• Application Number:
  US07/417,870
• Time in Patent Office: 522 Days
• Field of Search: 178/18, 178/19, 340/710
• US Class Current: 178/18.03
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: G06F 3/0441 using active external devices, e.g. active pens, for receiving changes in electrical potential transmitted by the digitiser, e.g. tablet driving signals
• CPC Class Codes: G06F 3/0443 using a single layer of sensing electrodes

Abstract

A coordinate determining system, tablet, and method wherein the tablet is formed of a sequence of triangular electrodes extending in a first direction, with alternate electrodes having their apexes extending in opposite directions perpendicular to the first direction, and the bases of alternate electrodes are aligned to define the sides of the tablet. The cursor is round, having a diameter substantially equal to the length of the bases of the electrodes, and is adapted to be electrostatically coupled to the electrodes. Signals are sequentially applied to the electrodes and voltages generated at the cursor are employed to address look up tables for determining the location of the cursor.

Claims

1. A tablet for a coordinate positioning device comprising a plurality of substantially identically shaped first coplanar electrodes and a plurality of second electrodes coplanar with said first electrodes and shaped substantially identically to said first electrodes, said first electrodes being sequentially arranged in a row extending in a first direction and intermeshed with and insulated from said second electrodes, said first and second electrodes having dimensions in said first direction that continually diminish in opposite directions perpendicular to said first direction, and means for separately coupling each of said electrodes independently to a device.

2. The tablet of claim 1 wherein said electrodes are triangular with bases of said first electrodes defining one side of said tablet and bases of said second electrodes defining the opposite side of said tablet.

3. The tablet of claim 2 wherein said electrodes are isosceles triangular shaped, with the bases thereof extending in said first direction.

13. The tablet of claim 1, wherein said device is a signal source.

14. The tablet of claim 1, wherein said device is a signal processor.

4. A coordinate position determining system comprising a tablet and a cursor;

said tablet comprising a plurality of substantially identically shaped first coplanar electrodes and a plurality of second electrodes coplanar with said first electrodes and shaped substantially identically to said first electrodes, said first electrodes being sequentially arranged in a row extending in a first direction and intermeshed with and insulated from said second electrodes, said first and second electrodes having dimensions in said first direction that continually diminish in opposite directions perpendicular to said first direction;

said cursor being adapted to be moved parallel to and adjacent said tablet and insulated therefrom, said cursor having a round electrode of a diameter whereby said cursor electrode cannot overlie only one electrode and cannot overlie more than three electrodes at any position thereof.

5. The system of claim 4 wherein said electrodes are triangular with bases extending in said first direction, and wherein the diameter of said cursor is substantially equal to the length of said bases.

6. The system of claim 5 wherein said electrodes are isosceles triangle shaped.

7. The system of claim 4 further comprising a source of signals, means for sequentially applying said signals to said electrodes, means for sensing signals generated from said cursor, and means responsive to signals from said cursor for determining coordinate positions of said cursor.

8. The system of claim 7 wherein said means for determining coordinate positions comprises means for addressing a look up table with the absolute value of said signals.

9. The system of claim 7 wherein said means for determining coordinate positions comprises means for addressing a look up table with the ratios of the amplitudes of said signals.

10. The system of claim 4 further comprising a source of signals, means for applying said signals to said cursor, means for sequentially sensing signals generated from said electrodes, and means responsive to signals from said electrodes for determining coordinate positions of said cursor.

11. A method for determining the coordinates of a cursor positioned to be electrostatically coupled to the spaced electrodes of a tablet comprises of a sequence of triangular electrodes extending in a first direction, comprising sequentially applying signals to each said electrode independently of the other electrodes while sensing voltages above a predetermined threshold which are electrostatically coupled to an electrode of said cursor, normalizing said voltages by adjusting their magnitudes proportionally so that the sum of their magnitudes is equal to a constant amount, and addressing a lookup table with said adjusted magnitudes to determine said coordinates.

12. A method for determining the coordinates of a cursor positioned to be electrostatically coupled to the spaced electrodes of a tablet comprised of a sequence of triangular electrodes extending in a first direction, comprising sequentially applying signals to said electrodes while sensing voltages above a predetermined threshold which are electrostatically coupled to an electrode of said cursor, determining whether said voltages have been derived from two or three adjacent electrodes, addressing a first lookup table with a function of said voltages when said voltages have been derived from two adjacent electrodes, and addressing a second lookup table with a function of said voltages when said voltages have been derived from three of said electrodes.

15. A method for determining the coordinates of a cursor positioned to be electrostatically coupled to the spaced electrodes of a tablet comprised of a sequence of triangular electrodes extending in a first direction, comprising applying signals to an electrode of the cursor, selectively sensing signals above a predetermined threshold electrostatically coupled to any of said electrodes from said cursor electrode independently of voltages electrostatically coupled to respective adjacent electrodes, normalizing said sensed voltages by adjusting their magnitudes proportionally so that the sum of their magnitudes is equal to a constant amount, and addressing a lookup table with said magnitudes to determine said coordinates.