GB2082427A

GB2082427A - A sensor matrix for display screens

Info

Publication number: GB2082427A
Application number: GB8114581A
Authority: GB
Original assignee: Hewlett Packard France SAS
Current assignee: Hewlett Packard France SAS
Priority date: 1980-07-04
Filing date: 1981-05-13
Publication date: 1982-03-03
Also published as: GB2082427B; JPS5720041U; DE3025318C2; DE3025318A1; FR2486267A1

Abstract

To detect the point of contact of a finger on a display screen, e.g. a CRT, on which an item of displayed data is pointed out, light sources (21) and photodetectors (23) along opposite edges of a rectangular frame (25) surrounding the screen establish a grid of light beams (27), the interruption of one or more in the X and Y directions indicating the co-ordinates. The frame (25) may include integral lenses (33, 35) and mirrors (29, 31) to direct the beams and may be opaque to visible light but transparent to IR to which the sources and detectors are adapted. <IMAGE>

Description

SPECIFICATION A sensor matrix for display screens The steadily increasing use of computers in all areas of life has induced circles concerned with this matter to consider the question how the dialog between man and machine could be facilitated and improved. In this connection, the increasing use of display screens is of particular importance, While originally such display screens were used only to display to the viewer text, graphic representations and other data, trends are now going towards the use of display screens also for the entry of data. To this end, the operator may for instance put his finger on a specific point of a graphic representation displayed on the screen. The point of contact is sensed by suitable sensor means, whereafter its coordinates are entered into the computer where they are evaluated in a suitable manner.

For the purpose of sensing points of contact on the screen surface it has been known to provide in front of the screens viewed from the operators standpoint-a grid of light barriers defining lines and columns. To this end, a series of light sources are arranged along the upper, lower, left and right edges of the display screen, and the focussed beams of the said light sources are detected on the opposite edges of the screen by correspondingly arranged photo detectors. Provided the individual rays are suitably spaced from each other, a finger touching the display screen will interrupt at least one line ray and one column ray. The corresponding output signals of the photo detectors may then be used to determine the coordinates of the point of contact.

In known sensor matrixes of this type, four separate printed circuit boards are required as carriers for the light sources, the photo detectors and for the associated lines and the electronic evaluation means, if any. These printed circuit boards must be arranged in a manner such that the light sources defining the lines are arranged opposite the photo detectors associated with the lines and that the light sources defining the columns are arranged opposite the photo detectors associated with the columns. This not only results in relatively high production expense, but also demands exact adjustment of the individual printed circuit boards during assembly.

It is an object of the invention to provide a sensor matrix for display screens which is easy to produce and does not require any adjustment during assembly.

According to the invention there is provided a sensor matrix for display screens comprising a frame encircling the display screen and carrying light sources and photo detectors coacting therewith to form in front of the display screens viewed from the viewer's standpoint a grid of light barriers defining lines and columns, wherein the light sources and the photo detectors are arranged on common, substantially plane carrier means extending in parallel to the image plane and wherein reflexion means are provided for first reflecting the light beams emitted by the light sources in a direction parallel to the carrier means and then reflecting the light beams thus reflected on the opposite side of the display screen towards the coacting photo detectors.

The sensor matrix of the invention permits all light sources and photo detectors to be arranged on one single printed circuit board.

As a result, their relative position is fixed and no adjustment is needed during assembly.

Preferably the reflexion means take the form of an optical frame formed in one piece with integrally formed surfaces provided at an angle relative to the direction of the rays and having inner faces which provide total reflexion of the light beams. This means can be moulded in one piece from a transparent plastic material.

In a further embodiment of the invention the light sources emit infrared light, the photo detectors are sensitive to infrared light and the optical frame is made of a material which is permeable to infrared light, but impermeable to visible light. This embodiment offers the additional advantage of extreme insensitivity to external light.

Hereafter, the invention will be described by way of one example with reference to the accompanying drawing in which Figure 1 shows a cross-section through a sensor matrix for display screens, and Figure 2 shows a plan view of the printed circuit board used in the embodiment of Fig.

1, in diagrammatic representation.

In Fig. 1, the display screen 1 3 and a cathode-ray tube 11 can be seen. In front of the display screen 1 3 there is arranged a conventional protective screen 1 5 which is in turn covered by a transparent coating 1 7.

A printed circuit board 1 9 carries infrared light sources 21 and photo detectors 23 sensitive to the light emitted by the said light sources 21. Fig. 1 shows only one of each of these elements.

An optical frame 25 consisting of a material which is permeable to infrared light but impermeable to visible light, deflects the light emitted by the light source 21 along a path indicated by the dash-dotted line 27. For this purpose, the optical frame 25 is equipped with surfaces 29 and 31 each inclined by 45 relative to the printed circuit board 1 9 and provided with inner faces which provide total reflexion of the infrared light. Accordingly, the ray emitted by the light source 21 is first deflected in the direction parallel to the display screen 1 3 and then towards the photo detector 23. The surfaces 33 and 35 of the optical frame 25 facing the light sources 21 and the photo detectors 23 are curved in the manner of a lense to focus the light beam.

The optical frame 25 serves at the same time as support for the protective screen 1 5 and the coating 1 7 and carries in addition the printed circuit board 1 9 via a spacer frame 37. As a result, a compact unit is obtained which has all its individual components fitting positively into each other so that no adjustment is needed.

Fig. 2 shows a diagrammatic plan view, viewed from the left in Fig. 1) of the printed circuit board 1 9. It can be seen that the printed circuit board is provided with a large center opening 41 for receiving the cathoderay tube 11. The infrared light sources 21 and the photo detectors 23 are arranged in parallel to the outer edge of the printed circuit board 1 9 so that each of the light sources faces one photo detector whereby a matrixlike grid of light barriers is obtained. Touching of the coating 17 (Fig. 1) at any desired point with the finger will interrupt at least one line ray and one column ray, provided the spacing between the light sources 21 on the one hand and the photo detectors 23 on the other hand is smaller than the thickness of the finger. The point of contact is sensed as the crossing point between the two interrupted light beams. In Fig. 2, an example of such a crossing point is designated as 43.

The electric and/or electronic evaluation of the coordinates of the point of contact thus determined is performed in a conventional manner and no object of the present invention.

Claims

1. A sensor matrix for display screens comprising a frame encircling the display screen and carrying light sources and photo detectors coacting therewith to form in front of the display screens viewed from the viewer's standpoint-a grid of light barriers defining lines and columns, wherein the light sources and the photo detectors are arranged on common, substantially plane carrier means extending in parallel to the image plane and wherein reflexion means are provided for first reflecting the light beams emitted by the light sources in a direction parallel to the carrier means and then reflecting the light beams thus reflected on the opposite side of the display screen toward the coating photo detectors.

2. A sensor matrix in accordance with claim 1, wherein the reflexion means take the form of an optical frame formed in one piece with integrally formed surfaces provided at an angle relative to the direction of the rays and having inner faces which provide total reflexion of the light beams.

3. A sensor matrix in accordance with claim 2, wherein the light sources emit infrared light, the photodetectors are sensitive to infrared light and the optical frame is made of a material which is permeable to infrared light, but impermeable to visible light.

4. A sensor matrix for display screens, substantially as herein described with reference to Figs. 1 and 2 of the accompanying drawings.