VECTOR TABLET DIGITIZING SYSTEM

• US 3,875,331 A
• Filed: 11/08/1973
• Issued: 04/01/1975
• Est. Priority Date: 11/08/1973
• Status: Expired due to Term

• Current Assignee: National Computer Services Limited (Acer, Inc.)
• Original Assignee: Ralph D. Hasenbalg
• Inventors: Hasenbalg, Ralph D.
• Primary Examiner(s): Robinson, Thomas A.
• Application Number:
  US05/413,773
• Time in Patent Office: 509 Days
• Field of Search: 340/146.35Y,347AD 178/18,19,20 318/567,568,576,615,616 235/61.6A,61.6B,197 33/1M 35/9C
• US Class Current: 178/18.01
• 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

An electrostatic digitizing system is provided, which includes an X, Y digital tablet and a stylus as a graphic input unit, which serves to digitize drawings, or the like, and which may be used in a variety of graphics applications and systems. The surface of the tablet emits a changing electrostatic field which is detected by the tip of the stylus. The field is time multiplexed to provide three necessary functions, which will be referred to as the X-axis digitize function, the Y-axis digitize function, and the pen near detect function. The circuitry to be described incorporates a potentiometric feedback system whereby the stylus senses only an error value. The circuitry is also such that attenuation at the stylus input does not directly affect the operation of the system. The embodiment of the system to be described is constructed to incorporate anti-toggle and overscale features, as well as an adjustable margin feature.

Claims

1. An electrostatic digitizing system comprising:

an X-Y digital tablet providing a changing electrostatic field over a plane surface;

a stylus movable over the plane surface of the tablet and capacitively coupled thereto for detecting the electrostatic field at predetermined X,Y coordinates;

first circuitry including an X register and a Y register and connected to said tablet for producing exciting potentials therefor so as to create said field; and

second circuitry coupled to said stylus and to said first circuitry and including a counter for controlling the digital contents of the registers in accordance with the position of the stylus on the tablet surface and for controlling said exciting potentials as a function of the position of the stylus on said surface.

2. The electrostatic digitizing system defined in claim 1, in which said digital tablet includes a first series of electric wires extending in spaced and parallel relationship across the plane surface;

first resistor means interconnecting the wires of the first series;

means for introducing a first exciting potential across said first resistor means;

a second series of wires extending across the surface in spaced and parallel relationship at right angles to the wires of the first series;

second resistor means interconnecting the wires of the second series; and

means for introducing a second exciting potential across said second resistor means.

3. The electrostatic digitizing system defined in claim 2, and which includes a conductive ring mounted on said surface and surrounding the wires of the first and second series and spaced outwardly therefrom;

and circuit means for introducing a voltage to the conductive ring to cause the ring to inhibit the output of the stylus when the stylus is positioned outside the limits of the wires of the first and second series.

4. The electrostatic digitizing system defined in claim 1, in which said first circuitry includes time multiplexing means connected to said counter for causing the counter to control the digital contents of the register on a time multiplex basis.

5. The electrostatic digitizing system defined in claim 1, in which said first circuitry includes a digital/analog converter for converting the digital contents of the registers into corresponding analog exciting potentials for application to the tablet.

6. The electrostatic digitizing system defined in claim 1, in which said second circuitry includes logic circuit means for producing an output signal when the stylus is brought within a predetermined distance of the surface of said tablet.

7. The electrostatic digitizing system defined in claim 1, in which said first circuit means includes manually adjustable potentiometer means effectively to adjust the margin of the surface of the tablet.

8. The electrostatic digitizing system defined in claim 1, and which includes aN over-scale logic circuit connected to said counter to inhibit the control of either of said X and Y registers when the corresponding register is either full or empty.

9. The electrostatic digitizing system defined in claim 1, and which includes an anti-toggle circuit connected to said counter to inhibit the control of the least significant bit of the contents of either the X or Y registers when a null condition is approached.

10. An electrostatic digitizing system comprising:

and X-Y digital tablet providing a changing electrostatic field over a plane surface;

a stylus movable over the plane surface of the tablet and capacitively coupled thereto for detecting the electrostatic field at predetermined X-Y coordinates;

first circuitry connected to said tablet for producing exciting potentials therefor so as to create said field; and

second circuitry coupled to said stylus and to said first circuitry for controlling said exciting potentials as a function of the position of the stylus on said surface and in which said second circuitry controls said exciting potentials so as to produce a null in the electrostatic field at the position of the stylus.