Touch-panel input device

• US 6,310,614 B1
• Filed: 07/14/1999
• Issued: 10/30/2001
• Est. Priority Date: 07/15/1998
• Status: Expired due to Term

• Current Assignee: SMK Corporation
• Original Assignee: SMK Corporation
• Inventors: Tanaka, Hiroshi, Maeda, Toshifumi
• Primary Examiner(s): Shalwala, Bipin
• Assistant Examiner(s): Osorio, Ricardo
• Application Number:
  US09/353,224
• Time in Patent Office: 839 Days
• Field of Search: 345/173, 345/174, 345/176, 345/177, 178/18.03, 178/18.05, 178/18.01, 178/18.02, 178/18.04, 178/18.06, 178/18.07, 178/18.1
• US Class Current: 345/173
• CPC Class Codes: G06F 3/045 using resistive elements, e.g. a single continuous surface or two parallel surfaces put in contact

Abstract

Two transparent conductive panels are separated by a perimeter of elastic adhesive that forms a sealed gap in which transparent insulative fluid is interposed. The fluid has suspended conductive particles and a refraction index close to that of the panels to improve light transmittance through the device. The conductive particles and small gap width improves response time and prevents formation of a vacuum in the gap. The panels are connected to a position detection circuit that determines coordinate position of an applied pressure point. Spacers in the gap reduce the chance of response to accidental large-area contact which would result in an erroneous position command. The elasticity of the adhesive and the small gap width provide better temperature variation tolerance in addition to improved consistency and reliability of operation.

Claims

1. A touch-panel input device comprising:

at least first and second transparent plates having faces opposed to one another and substantially parallel;

a portion of said opposing faces of said at least first and second transparent plates being transparent electrically conductive surfaces with uniform surface resistance;

a transparent insulative fluid interposed in a gap between said first and second transparent plates, said fluid having a refraction index close to that of said transparent plates;

conductive particles dispersed in said fluid with specific gravities substantially identical to that of said fluid;

at least one of said at least first and second transparent plates capable of resiliently flexing toward an other of said transparent plates, whereby an electrical relationship is changed between said conductive surfaces; and

said relationship is related to a coordinate position on said device.

2. A touch-panel input device according to claim 1, wherein:

said relationship is a voltage drop across a resistance provided by an electrical connection through said conductive particles; and

said voltage drop is related to said coordinate position on said device by a proportional relationship.

3. A touch-panel input device according to claim 1, wherein said gap is substantially uniform with a width in the range of from 5 to 50 microns.

4. A touch-panel input device according to claim 1, further comprising:

an elastic adhesive disposed around a perimeter of said conductive surfaces, whereby said opposing faces are bonded together;

said adhesive provides a seal, whereby said fluid is sealed in said gap; and

said adhesive is composed substantially of solids.

5. A touch-panel input device according to claim 4, wherein said transparent insulative fluid has a viscosity with a surface tension within said gap that overcomes a weight of said fluid, thereby preventing formation of a vacuum cavity in said gap when an orientation of said device is changed.

6. A touch-panel input device according to claim 2, wherein said transparent conductive surfaces are transparent conductive layers disposed on said transparent plates with uniform thickness.

7. A touch-panel input device according to claim 6, wherein said transparent conductive layers are composed of Indium Titanium Oxide (ITO).

8. A touch-panel input device according to claim 6, further including:

electrical connection leads on opposing ends of each of said transparent conductive layers;

an external connector;

said leads connected to said external connector; and

said external connector effective to provide electrical connection to each of said leads from a device external to said touch-panel input device.

9. A touch-panel input device according to claim 8, wherein:

each of said transparent conductive layers includes a plurality of parallel strips; and

said pluralities on said opposing faces being substantially perpendicular to each other.

10. A touch-panel input device according to claim 8, wherein said external connector is electrically connected to an external device having a circuit effective to measure a selected voltage drop along a path through said conductive surfaces and particles to determine a coordinate position indicated by said electrical connection between said transparent conductive surfaces through said conductive particles.

11. A touch-panel input device according to claim 10, wherein:

said circuit includes a DC voltage source;

a controller for controlling input/output and switches;

a first switch connected in series between said voltage source and a first lead on said flexible transparent conductive surface;

a second switch connected in series between said voltage source and a first lead on said rigid transparent conductive surface;

a third switch connected in series between a second lead on said flexible transparent conductive surface and ground;

a fourth switch connected in series between a second lead on said rigid transparent conductive surface and ground;

an input of an analog to digital converter connected through a fifth switch to said second leads on said conductive surfaces;

said controller receiving an output of said analog to digital controller; and

said controller effective to control said switches to measure a first voltage across a first resistor network formed by contact between said transparent conductive surfaces and to measure a second voltage across a second resistor network formed by said contact, thereby effective to determine a coordinate position of said contact.

12. A touch-panel input device according to claim 6, further including:

a transparent barrier layer between said fixed transparent plate and said transparent conductive layer disposed on said fixed transparent plate; and

said barrier layer effective to prevent contamination of said fluid.

13. A touch-panel input device according to claim 1, further including a transparent hard coat layer on an external surface of said flexible transparent plate.

14. A touch-panel input device according to claim 1, further including:

regularly spaced insulative protrusions disposed on at least one of said conductive surfaces; and

a thickness of said insulative protrusions is substantially less than said width of said gap.

15. A touch-panel input device according to claim 14, wherein said protrusions are 5 microns in thickness or less.

16. A touch-panel input device according to claim 15, wherein said conductive particles have an outside diameter in a range of from 1 to 4 microns.

17. A touch-panel input device according to claim 14, wherein said conductive particles have an outside diameter less than said thickness of said protrusions.

18. A touch-panel input device according to claim 1, wherein:

said conductive particles have a core with a smaller specific gravity than that of said fluid;

said conductive particles have a conductive material covering with a specific gravity greater than that of said fluid; and

dimensions of said core and said covering are adjusted to provide said conductive particles with overall specific gravities substantially identical to that of said fluid.

19. A touch-panel input device according to claim 18, wherein said conductive particles are dispersed in said fluid with a density in the range of from 2 to 30 particles per square millimeter in a projection of said fluid on a plane defined by one of said conductive surfaces, whereby said electrical relationship between said conductive surfaces through said particles is avoided when said device is inactive.

20. A touch-panel input device according to claim 18, wherein said covering has a specific gravity in the range of from 2.5 to 16.

21. A touch-panel input device according to claim 18, wherein said conductive particles have an outside diameter less than said width of said gap.

22. A touch-panel input device according to claim 21, wherein said conductive particles have an outside diameter in a range of from 1 to 15 microns.

23. A touch-panel input device according to claim 4, wherein said elastic adhesive is sufficiently elastic to permit said electrical relationship to change by application of external pressure near said perimeter without loss of resiliency or adversely affecting said sealed gap.

24. A touch-panel input device according to claim 4, wherein said elastic adhesive exhibits elasticity sufficient to permit said flexible transparent plate to move resiliently in a direction parallel to said rigid transparent plate.

25. A touch-panel input device comprising:

at least first and second transparent plates having faces opposed to one another and substantially parallel;

transparent electrically conductive layers disposed on each of said opposing faces, said conductive layers having substantially uniform surface resistance;

electrical connection leads disposed on opposing ends of said conductive layers;

pairs of said connection leads of said conductive layers defining a coordinate axis;

spaced apart insulative protrusions on at least one of said conductive layers effective to slightly increase and evenly distribute pressure applied to said transparent plates needed to cause contact between said conductive layers;

said protrusions having a thickness substantially less than said width of said gap;

transparent insulative fluid interposed in said sealed gap, said fluid having a refraction index close to that of said transparent plates; and

conductive particles dispersed in said fluid, said particles having specific gravities substantially identical to that of said fluid and having outer diameters less than said thickness of said protrusions.

26. A touch-panel input device according to claim 25 further comprising:

an external connector connected to said leads;

a position detection circuit connected to said external connector;

at least one of said transparent plates capable of resiliently flexing to change an electrical relationship between said conductive layers; and

said change in said relationship being measurable by said circuit effective to determine a point on said coordinate axis where said change in said relationship occurs.

27. A touch-panel input device according to claim 25, further including:

a transparent barrier layer between one of said conductive layers and said transparent plates; and

a transparent hard coat layer on an external surface of another of said transparent plates.

28. A touch-panel input device comprising:

first and second conductive surfaces facing each other separated by a distance across a sealed space;

at least said first conductive surface being transparent;

a transparent insulative fluid substantially filling said sealed space;

a proportion of transparent conductive particles in said insulative fluid;

said distance exceeding a dimension of said conductive particles, whereby said conductive particles normally remain out of contact with at least one of said first and second conductive surfaces; and

said first conductive surface being deformable inward sufficiently to force at least one of said conductive particles into electrical contact with said first and second conductive surfaces, whereby an electrical resistance between said first and second conductive surfaces is changed.

29. A touch-panel input device according to claim 28, further including an array of insulative spacers spaced apart on at least one of said first and second conductive surfaces.

30. A touch-panel input device according to claim 28, wherein:

said first and second conductive surfaces are separated by an elastic adhesive; and

said adhesive forms a border of said sealed space.