Graphic communications tablet

• US 3,925,610 A
• Filed: 08/12/1974
• Issued: 12/09/1975
• Est. Priority Date: 08/12/1974
• Status: Expired due to Term

• Current Assignee: Anant Kumar Nigam, Gerhard Martin Sessler, Joseph Charles French
• Original Assignee: Anant Kumar Nigam, Gerhard Martin Sessler, Joseph Charles French
• Inventors: Sessler, Gerhard Martin, French, Joseph Charles, Nigam, Anant Kumar
• Primary Examiner(s): Robinson, Thomas A.
• Application Number:
  US05/496,530
• Time in Patent Office: 484 Days
• Field of Search: 178/18,19,20,DIG.10 179/111E,1.41B 340/365C 307/88ET
• US Class Current: 178/18.03
• CPC Class Codes: G01B 7/004 for measuring coordinates of points
• CPC Class Codes: G06F 3/0445 using two or more layers of sensing electrodes, e.g. using two layers of electrodes separated by a dielectric layer
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes
• CPC Class Codes: G07C 9/35 by means of a handwritten signature

Abstract

A tablet or transducer, for use in a graphical communications system, which comprises a rectangular array of electret transducer elements responsive to the writing pressure of a stylus, such as an ordinary ballpoint pen. The array is formed by a selectively metallized elastic electret film mounted in spaced juxtaposition with a selectively metallized backplate. Performance characteristics are enhanced by ridges or separators between metallized areas and by field effect transistor signal detector circuits. An embodiment including a compliant media between the electret film and the backplate for supplying an output signal whose magnitude is proportional to writing pressure is also disclosed.

Claims

1. Graphic communications apparatus comprising:

an electret film selectively metallized on one surface thereof, said electret film locally deformable in response to the pressure of a writing stylus;

a rigid backplate selectively metallized on one surface thereof, said backplate mounted in spaced juxtaposition with said electret film so that said metallized areas of said backplate are in spaced juxtaposition with said metallized areas of said electret film;

a plurality of ridge means dimensioned for decreasing the rise time of said electret film to improve performance at low writing speeds by reducing the amplitude of the reverse polarity overshoot signal, each of said ridge means interposed between the metallized regions of said backplate; and

means for connecting the metallized areas of said electret film and said backplate to a plurality of output terminals.

2. The graphic communications apparatus of claim 1 further comprising a compliant layer interposed between said backplate and said electret film, said compliant layer having a compliance which imparts a substantially linear relationship between the deformation of said electret film and the electrical output signal of said graphic communications apparatus.

3. The graphic communications apparatus of claim 1 wherein said electret film and said backplate are selectively metallized with a plurality of substantially parallel strips, said electret film mounted with the parallel strips thereon substantially perpendicular to the parallel strips on said backplate.

4. The graphic communications apparatus of claim 3 wherein said means for connecting said metallized strips to said plurality of output terminals includes a plurality of diodes, a first electrode of each diode commonly connected to a common output terminal, and the second electrode of each diode connected to a single one of said metallized strips of said backplate and said electret film.

5. The graphic communications apparatus of claim 4 wherein those diodes connected to said metallized strips of said backplate are poled oppositely to those diodes connected to said metallized strips of said electret film.

6. The graphic communications apparatus of claim 5 further comprising:

a plurality of N-channel field effect transistor source-follower circuits, each of said N-channel source-follower circuits including an N-channel field effect transistor and a resistor, the first electrode of said resistor connected to the source electrode of said N-channel transistor, the second electrode of said resistor connected to said common output terminal, the drain electrode of said N-channel transistor connected to a first source of fixed potential, and the gate electrode of said transistor connected to one of said output terminals, each of said output terminals connected to said gates of said N-channel transistors connected to one of said like-poled diodes; and

a plurality of P-channel field effect transistor source-follower circuits, each of said P-channel source-follower circuits including a P-channel field effect transistor and a resistor, the first electrode of said resistor connected to the source electrode of said P-channel transistor, the second electrode of said resistor connected to said common output terminal, the drain electrode of said P-channel transistor connected to a second terminal of fixed potential, the gate electrode of said P-channel transistor connected to a single one of said output terminals, each of said output terminals connected to one of said diodes of opposite poling to those diodes connected to said gates of said N-channel transistors.

7. A transducer for electrically indicating the position of a writing stylus upon the surface of said transducer comprising:

an elastically deformable electret film, one surface thereof selectively metallized with a plurality of equally spaced parallel conductive strips;

a nonconductive backplate with a plurality of equally spaced parallel conductive strips upon one surface thereof;

a nonconductive rectangular array of ridges, said ridges forming a plurality of substantially rectangular interstitial spaces, said ridges having a height and width between 5 and 10 per cent of the spacing dimension between the metallized strips of said backplate;

means for supporting said electret film in juxtaposition with said backplate such that said metallized strips of said electret film are substantially perpendicular to said metallized strips of said backplate with said ridge structure interposed between said electret and said backplate, the individual ridges of said array of ridges contacting said electret film and said backplate between adjacent ones of said conductive strips; and

means for electrically connecting said conductive strips of said backplate and said conductive strips of said electret film to a plurality of output terminals.

8. The transducer of claim 7 further comprising a compliant media which substantially occupies said interstitial spaces of said rectangular array of ridges, said compliant media having a compliance which imparts a linear relationship between the writing pressure exerted by said writing stylus and the magnitude of the electrical output signal of said transducer.

9. A graphic communications system comprising:

trandsucer means for producing electrical signals indicative of the position of a writing stylus upon the surface of said transducer including an electret film with substantially parallel conductive strips on one surface thereof, said electret film mounted in fixed juxtaposition with a nonconductive backplate having a plurality of conductive strips on the surface thereof nearest said electret film, said parallel conductive strips of said electret film oriented substantially perpendicular to said parallel conductive strips of said backplate;

first detection means connected between said conductive strips of said electret film and a terminal of fixed potential, said first detection means responsive to a signal of a first polarity for determining the first positional coordinate of said writing stylus upon said surface of said transducer;

second detection means connected between said conductive strips of said backplate and said terminal of fixed potential, said second detection means responsive to a signal of second polarity for determining the second positional coordinate of said writing stylus upon said surface of said transducer; and

transmission means for supplying said first and second positional coordinate to remote apparatus for utilization therein.

10. The graphic communications system of claim 9 wherein said transducer means further includes a compliant layer interposed between said electret film and said nonconductive backplate;

and said graphic communications system further comprises third detection means for determining the amplitude of each signal detected by said first and second detection means.