GB2132359A - Determining co-ordinates of a point electrically - Google Patents

Abstract

An input device for a display unit in a computer terminal comprises a first insulating sheet 2 having thereon a first resistance layer 3 having first terminals at opposite edges thereof and first insulating projections 5, a second insulating sheet 9 having thereon a second resistance layer 10 having second terminals at opposite edges thereof and second insulating projections 12, and an intermediate insulating terminal plate 6 having conductive films 8a, 8b on respective surfaces thereof and sandwiched by and between the insulating projections 5, 12 on the insulating sheets 2, 9, the first and second terminals extending perpendicularly to each other. When pressure is applied with a stylus 14, the resistive layers 3, 10 are brought into contact with their respective adjacent conductive films 8b, 8a and voltages are applied alternately across the first and second terminals, whereby the x and y co- ordinates of the contact point can be determined. <IMAGE>

Description

SPECIFICATION Input device Background of the invention The present invention relates to an input device for use in a display unit such for example as a CRT display unit used as a computer peripheral device, and more particularly to an input device having a pressure-sensitive panel energizabie in response to pressing engagement of a stylus with the panel for producing a signal indicative of the stylus position.

Various input devices of the type described are known in the art. One known input device includes a panel composed of electrodes serving as thinfilm switches for issuing signals when their contacts are brought into mutual contact. Another form of input device comprises an optical matrix table including light sources and photosensors for detecting the coordinates of an object placed in an optical path. According to still another input device, a pressure-sensitive panel detects the pressure with which a stylus is pressed against the panel. A resilient-panel input device can detect the coordinates of a point where the panel is touched from the time it takes for a surface wave to be transmitted over the panel from the point.

The electrode-contact panel is the simplest in construction and least costly among the prior input devices. This type of coordinate input device comprises a thin-film keyboard switch composed of a transparent plastic film with a thin metal film such as of Ag, Pd or a thin metal-oxide film such as of In203 deposited over a prescribed area on the plastic film by way of vacuum evaporation or sputtering. This arrangement is disadvantageous in that the contact resistance is high, the yield is poor because of mechanical weakness, and the device has a short service life. According to a modified input device, thin-film electrodes are made of a synthetic resin material with fine powder of electrically conductive metal dispersed therein.However, the metal powder is not dispersed uniformly, no correct coordinates can be detected on the input device, and the device is of no sufficient mechanical strength.

Summary of the invention With the foregoing prior difficulties in view, it is an object of the present invention to provide an input device which is simple in construction, less costly, of an increased mechanical strength, and capable of detecting coordinates correctly.

According to the present invention, there is provided an input device comprising a first insulating sheet having formed thereon a first resistance layer having first terminal leads at opposite ends thereof and first insulating projections, a second insulating sheet formed thereon a second resistance layer having second terminal leads at opposite ends thereof and second insulating projections, and an intermediate terminal plate having electrically conductive films respectively on both surfaces thereof and sandwiched by and between the insulating projections on the and second insulating sheets, the first and second terminal leads extending perpendicularly to each other.

The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.

Brief description of the drawings FIG. 1 is a fragmentary cross-sectional view of an input device according to the present invention: FIG. 2 is a plan view of a first insulating sheet, a first resistance layer, and first terminal leads in the input device of FIG. 1; FIG. 3 is a plan view of an intermediate terminal plate; FIG. 4 is a plan view of a second insulating sheet, a second resistance layer, and second terminal leads in the input device of FIG. 1; FIG. 5 is a fragmentary cross-sectional view of the input device as it is in operation.

Description of the preferred embodiment As shown in FIG. 1, an input device according to the present invention comprises a substrate 1, a first rectangular insulating sheet 2 placed on the substrate 1 and composed of a film of polyimide, polyester, for example, a first rectangular resistance layer 3 coated uniformly on the insulating sheet 2 and made of electrically conductive paint which is a mixture of carbon and a suitable electrically conductive material, and first terminal leads 4 formed at the ends of the resistance layer 3 in the direction of the X-axis (that is, at a pair of opposite sides of the rectangular resistance layer 3) as shown in FIG. 2.

The terminal leads 4 are in the form of electrodes deposited on the resistance layer 3 as thin electrically conductive films of metal such as Ag, Cu, for example, the terminal leads 4 extending for external connection. A given voltage will be applied between the terminal leads 4, 4.

A matrix of small insulating projections 5 is integrally formed on the resistance layer 3 by means of printing or the like. An intermediate terminal plate 6 shown in FIG. 3 is placed on the small insulating projections 5. The intermediate terminal plate 6 comprises an insulating film, electrically conductive films 8a, 8b of silver paste, for example, deposited on both surfaces of the insulating film, and terminals 8a', 8b' of silver paste, for example, deposited on the both surfaces of the insulating film.

The input device also includes a second insulating sheet 9 of the same construction as that of the first insulating sheet 2 as illustrated in FIG.

4. A second rectangular resistance layer 10 is uniformly coated on the insulating sheet 9, and second terminal leads 11 are formed on the ends of the resistance layer 10 in the direction of the Y-axis (that is, at another pair of opposite sides of the rectangular resistance layer 10). The terminal leads 11 are in the form of electrodes deposited on the resistance layer 10 as thin electrically conductive films of metal such as Ag, Cu, for example, the terminal leads 4 extending for external connection. A given voltage will be applied between the terminal leads 11, 11.

A matrix of small insulating projections 12 is integrally formed on the resistance layer 10 by means of printing or the like. The second resistance layer 10 on the second insulating sheet 9 is placed in confronting relation to the first resistance layer 3. The projections 5, 12 on the first and second resistance layers 3, 10 are disposed in confronting relation with each other with the conductive films 8a, 8b therebetween being sandwiched by the projections 5, 1 2.

When the second insulating sheet 9 is placed in face-to-face relation to the first insulating relation 2, the second terminal leads 11 extend in crisscross relation to the first terminal leads 4, that is, the first terminal leads 4 are arranged in spaced relation in the direction of the X-axis and the second terminal leads 11 are arranged in spaced relation in the direction of the Y-axis.

As shown in FIG. 1 , the second insulating sheet 9 is covered on its upper surface with a flexible insulating protective sheet 13.

A prescribed voltage is impressed between the terminal leads 4 spaced in the direction of the X-axis and also between the terminal leads 11 spaced in the direction of the Y-axis. More specifically, the voltage is applied alternately between the terminal leads 4 and between the terminal leads 11 so that signals can be detected at different times in the directions of the X- and Y-axis.

The terminal 8a' leading from the conductive film 8a on the intermediate terminal plate 6 is electrically connected to a terminal of a circuit including the second resistance layer 10, while the terminal 8b' leading from the conductive film 8b on the intermediate terminal plate 6 is electrically connected to a terminal of a circuit including the first resistance layer 3.

Operation of the input device thus constructed will be described. When a pointed stylus 1 4 is pressed against the insulating protective sheet 13 at a point P as shown in FIG. 5, the insulating protective sheet 13, the second insulating sheet 9 and the second resistance layer 10 are depressed downwardly until the second resistance layer 10 between adjacent small insulating projections 1 2 is brought into contact with the conductive film 8a on the intermediate terminal plate 6. At this time, resistances of the members electrically present from the point P to the terminal leads 11 can be detected to allow detection of the coordinates of the point P in the direction of the Y axis.

Then, the conductive film 8b and the first resistance layer 3 as they spaced from each other by the projections 5 are brought into mutual contact for thereby permitting detection of the coordinates of the point P in the direction of the axis X. Since the voltage is alternately applied between the terminal leads 4, 11, the X- and Y-coordinates of the point P can alternately be recognized.

The input device of the foregoing construction is simple in structure and less costly to fabricate.

When the insulating sheet is pushed at one point, the upper and lower resistance layers are forced more stably into contact respectively with the conductive films on the intermediate terminal plate then the resistance layers would be brought into mutual contact. Since bidirectional potentials are detected respectively as correct fractions of the resistances of the independent resistance layers, the accuracy of coordinate detection is increased.

The projections 5, 12 may be positioned or spaced so that the electrodes will be prevented from making unwanted contact and noise will be removed. The projections 5, 12 may be formed on the intermediate terminal plate.

Although a certain preferred embodiment has been shown and described, it should be understood that many changes and modifications may be made therein without departing from the scope of the appended claims.

Claims (6)

1. An input device comprising a first insulating sheet having formed thereon a first resistance layer having first terminal leads at opposite ends thereof and first insulating projections, a second insulating sheet formed thereon a second resistance layer having second terminal leads at opposite ends thereof and second insulating projections, and an intermediate terminal plate having electrically conductive films respectively on both surfaces thereof and sandwiched by and between said insulating projections on said first and second insulating sheets, said first and second terminal leads extending perpendicularly to each other.

2. An input device according to claim 1, wherein said insulating projections are integrally formed as a matrix on said first and second resistance layers, respectively.

3. An input device according to claim 1, including a flexible insulating protective sheet covering an upper surface of said second insulating sheet.

4. An input device according to claim 1, wherein a voltage will be applied alternately between said first terminal leads and between said second terminal leads.

5. An input device according to claim 1, wherein said electrically conductive films on said intermediate terminal plate are electrically connected to said resistance layers disposed in confronting relation to said electrically conductive films, respectively.

6. An input device substantially as hereinbefore described with reference to the accompanying drawings.