Digitizer tablet

• US 4,213,005 A
• Filed: 12/13/1978
• Issued: 07/15/1980
• Est. Priority Date: 12/13/1978
• Status: Expired due to Term

• Current Assignee: Eugene A. Cameron
• Original Assignee: Eugene A. Cameron
• Inventors: Cameron, Eugene A.
• Primary Examiner(s): Robinson, Thomas A.
• Application Number:
  US05/968,841
• Time in Patent Office: 580 Days
• Field of Search: 178/18, 178/19, 178/20, 178/87, 340/146.3 SY, 340/567, 340/347 AD, 346/139 C, 318/568
• US Class Current: 178/18.07
• CPC Class Codes: G06F 3/046 by electromagnetic means

Abstract

A system for precisely determining the location of a cursor on a work surface with respect to a grid of coordinate conductors. The system is based on the time-distance relationship of current sheets caused to move sequentially along each axis of the work surface, and the detection of each current sheet as it approaches and passes an operator-movable sensor. A number of the grid wires are simultaneously energized with a fixed energization pattern which steps along the conductors, thereby generating the current sheet and consequent magnetic field which translate along the plane of the conductors parallel to the conductors. A preferred means responsive to the time of passage of the current sheet comprises an inductive pickup coil having a diameter approximately equal to the width of the current sheet and means for sensing current induced in the pickup coil. Preferably, the grid conductors are energized with substantially fixed constant currents. Among the important advantages of the invention are enhanced signal levels with improved signal to noise ratios, improved immunity to extraneous noise, relative insensitivity to minor inaccuracies in the placement of the grid wires in the manufacture of the tablet, excellent resolution, and a high degree of stability. Moreover, the system, through several discoveries, is characterized by a relative lack of undue complexity, while serving well its intended function.

Claims

1. A system for locating the position of a cursor along a coordinate axis, said system comprising:

a plurality of parallel conductors spaced along the axis and defining a locus;

means for sequentially energizing said conductors in simultaneously energized lesser pluralities with a fixed energization pattern which steps along said plurality of conductors, thereby generating a current sheet which translates along the locus of and parallel to said conductors;

means for sensing the passage of a particular portion of the current sheet across a reference point carried by the cursor; and

means responsive to the time of passage of the particular portion of the current sheet for generating an output signal representing the position of the cursor along the coordinate axis.

2. A system according to claim 1, wherein said conductors are uniformly spaced and wherein the energization pattern steps along at a uniform rate.

3. A system according to claim 2, which further comprises means for energizing said conductors with constant currents.

4. A system according to claim 1, wherein the fixed energization pattern comprises all of said lesser plurality of conductors being energized.

5. A system according to claim 4, which further comprises means for energizing said conductors with constant currents.

6. A system according to claim 4, wherein said lesser plurality comprises seven conductors.

7. A system according to claim 1, wherein said cursor carries an inductive pickup coil.

8. A system according to claim 7, wherein the diameter of said inductive pickup coil is approximately equal to the width of the current sheet along its direction of translation.

9. A system according to claim 8, wherein said means for sensing the passage of a particular portion of the current sheet includes means for sensing current induced in said inductive pickup coil.

10. A system according to claim 7, wherein said means for sensing the passage of a particular portion of the current sheet includes means for sensing current induced in said inductive pickup coil.

11. A system according to claim 10, which further comprises means for energizing said conductors with constant currents.

12. A system according to claim 10, wherein said current sensing means comprises a current-to-voltage converter.

13. A system according to claim 10, wherein said means for sensing the passage of a particular portion of the current sheet comprises a low pass frequency filter for generating a waveform envelope representative of current induced in said inductive pickup coil.

14. A system according to claim 13, wherein said means for sensing the passage of a particular portion of the current sheet further comprises:

a first comparator responsive to the waveform envelope crossing a threshold;

a second comparator responsive to the waveform envelope crossing another threshold for generating a timing signal; and

means for enabling said second comparator only in response to said first comparator.

15. A system according to claim 14, wherein said second comparator is enabled for a predetermined interval selected to allow response to the waveform crossing the other threshold when the portion of the current sheet actually crosses the reference point and selected to minimize the possibility of response to the waveform crossing the other threshold due to an extraneous noise signal.

16. A system according to claim 1, which further comprises means for energizing said conductors with constant currents.

17. A system according to claim 1, wherein said conductors comprise insulated wires bonded to a ferromagnetic substrate.

18. A system according to claim 1, wherein said conductors comprise wires bonded to a glass substrate.

19. A system according to claim 1, wherein said means for sequentially energizing said conductors in simultaneously energized lesser pluralities comprises:

a serial-in/parrallel-out shift register having outputs connected to energize corresponding ones of said conductors;

means for clocking said serial-in/parallel-out shift register; and

means synchronized with said clocking means for serially entering data into said serial-in/parallel-out shift register in accordance with the fixed energization pattern.

20. A system according to claim 19, wherein said means for serially entering data comprises a parallel-in/serial-out shift register having its parallel data inputs connected to fixed logic levels in accordance with the fixed energization pattern and having its serial input connected to a fixed logic level appropriate to establish the trailing edge of the current sheet.

21. A system for locating the position of a cursor on a surface, said system comprising:

a conductor grid including a first plurality of parallel conductors spaced along a first axis in a plane parallel to the surface, and including a second plurality of parallel conductors spaced along a second axis perpendicular to said first axis, also in a plane parallel to the surface, such that the conductors of said second plurality are perpendicular to the conductors of said first plurality;

means for sequentially energizing the conductors in simultaneously energized lesser pluralities with a fixed energization pattern which steps first along said first plurality of conductors and then along said second plurality of conductors, thereby generating a first current sheet which translates along the plane of and parallel to the conductors of the first plurality followed by a second current sheet which translates along the plane of and parallel to the conductors of the second plurality;

means for sensing the passage of a particular portion of each of the current sheets across a reference point carried by the cursor;

means responsive to the times of passage of the particular portions of the current sheets for generating an output signal representing the coordinate position of the cursor on the surface.

22. A system according to claim 21, which further comprises means for energizing said conductors with constant currents.

23. A system according to claim 21, wherein said cursor carries an inductive pickup coil.

24. A system according to claim 23, wherein said means for sensing the passage of the particular portions of the current sheets includes means for sensing current induced in said inductive pickup coil.

25. A system according to claim 24, wherein said current sensing means comprises a current to voltage converter.

26. A system according to claim 23, wherein the diameter of said inductive pickup coil is approximately equal to the widths of the generated current sheets.

27. A system according to claim 26, wherein said means for sensing the passage of the particular portions of the current sheets includes means for sensing current induced in said inductive pickup coil.

28. A system according to claim 26, which further comprises means for energizing said conductors with constant currents.

29. A sensing arrangement for use in a system for locating the position of a cursor along a coordinate axis of the type which sequentially energizes a plurality of parallel conductors spaced along the axis to produce a current wave which translates along the axis, and which responds to the time of passage of the current wave across the cursor to generate an output signal representing the position of the cursor along the coordinate axis, said sensing arrangement comprising:

an inductive pickup coil carried by the cursor; and

means for sensing current induced in said inductive pickup coil.

30. A system according to claim 29, wherein said current sensing means comprises a current-to-voltage converter.

31. In a system for locating the position of a cursor along a coordinate axis of the general type which sequentially energizes a plurality of parallel conductors spaced along the axis to produce a current wave which translates along the axis, and which includes means responsive to the time of passage of the current wave across the cursor to generate an output signal representing the position of the cursor along the coordinate axis, means for sensing the time of passage of a particular portion of the current sheet across a reference point carried by the cursor, which means for sensing comprises:

an inductive pickup coil carried by the cursor;

means responsive to a signal induced in said pickup coil as the current wave passes for generating a waveform envelope;

a first comparator responsive to the waveform envelope crossing a threshold;

a second comparator responsive to the waveform envelope crossing another threshold for generating a timing signal; and

means for enabling said second comparator only in response to said first comparator.

32. A system according to claim 31, wherein said second comparator is enabled for a predetermined interval selected to allow response to the waveform crossing the other threshold when the portion of the current sheet actually crosses the reference point and selected to minimize the possibility of response to the waveform crossing the other threshold due to an extraneous noise signal.