WO2009004559A1

WO2009004559A1 - Touch screen system

Info

Publication number: WO2009004559A1
Application number: PCT/IB2008/052611
Authority: WO
Inventors: Christian N. Presura; Jan F. Suijver; Bernardus H. W. Hendriks; Nenad Mihajlovic; Galileo J. Destura
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2007-07-02
Filing date: 2008-06-30
Publication date: 2009-01-08

Abstract

A touch screen system (10) is disclosed that comprises a plurality of light emitters, which are used either for backlighting a screen or for generating an image thereon. A plurality of light detectors (d) detects light emitted by the light emitters and reflected or scattered from a touch member (20). The position of the touch member (20) with respect to the screen is determined based on the light detected by at least some of the light detectors.

Description

Touch screen system

FIELD OF THE INVENTION

The present invention relates to touch screen systems.

BACKGROUND OF THE INVENTION Large and small displays are more and more common in our life. Adding touch screen capabilities to them is desirable because of the added functionality that they offer. Typically, users prefer to interact in an intuitive way by touching of a screen with their own hands, over having to use external devices such as a keyboard or a mouse.

The following basic systems are currently used to recognize a person's touch: systems that sense pressure by making use of local changes in resistance or capacitance between two foils mounted on top of the screen and systems that make use of surface acoustic wave detection. For both of these the major problem lies in the added cost that they bring to the device, and as a result no large-scale market acceptance has occurred.

Most of the systems consist of a normal glass panel that is covered with a special layer. Accidental puncturing with a sharp instrument can easily damage this layer, and in addition the layer may block some of the light given by the display. Furthermore, the very real cost-issue, combined with the absence of a roadmap to realistically reduce these costs in the foreseeable future, implies that these displays will never become commercially interesting for low-income countries. This is especially a problem for an educational environment, where the benefit touch-screen displays bring to students and teachers alike can be huge.

The patent application US 2002/0067348 Al discloses an alternative touch screen system to the basic systems described herein above. The system uses a plurality of infrared ("IR") transmitters and receivers positioned along the edges of the screen, for determining with high resolution the location of a touch between the IR transmitters and receivers using on-axis and off-axis detection. The touch screen system uses, in conjunction with the on-axis and off-axis detection, a coarse and fine sweep of the transmitters and receivers to increase the resolution of identified touch location. Also this system has the drawback of added costs caused by the considerable number of infrared transmitters and receivers that are needed.

It is an object of the invention to provide an improved display screen with touch recognition functionality.

SUMMARY OF THE INVENTION

This and other objects of the invention are achieved by a system according to claim 1. Favorable embodiments are defined by the dependent claims 2-13.

According to an aspect of the invention a touch screen system is provided comprising a plurality of light emitters, which are used either for backlighting a screen or for generating an image thereon. It comprises a plurality of light detectors for detecting light emitted by the light emitters and reflected or scattered by a touch member. The position of the touch member with respect to the screen is determined based on the light detected by at least some of the light detectors. According to the invention, light emitters that are present in standard screen systems are used for obtaining the touch screen functionality, thereby avoiding significant additional costs for the system. Furthermore, the system according to the invention creates the possibility of having a multiple entrance at one time, meaning that if two touch members approach the screen at two different locations, the system is able to detect both locations. The system comprises touch detection means for detecting that the touch member touches the screen. Preferably, the touch detection means are adapted for detecting the touch if the amount of light scattered by or reflected from the touch member is larger than a threshold value. In this way, the touch may be detected in a simple and reliable way.

Preferably, at least some of the light emitters are adapted for working also as light detectors. In this way, the addition of none-standard equipment to the screen system for obtaining the touch functionality is minimized.

According to a first alternative embodiment the light emitters adapted for working also as light detectors are LEDs. At least some of the LEDs are periodically switched into a light detection mode. Preferably, the LEDs are switched into the light detection mode and back to a light emitting mode at a rate imperceptible by the human eye. In this way, the switching is not noticeable for the user and the touch screen functionality is obtained without degrading the quality of the image or backlighting generated by the light emitters. According to a second alternative embodiment the light emitters are adapted for working as light emitter and light detector at the same time. This functionality may be for example provided by laser sensors. Also, this embodiment enables touch screen functionality without degrading the quality of the image or backlighting generated by the light emitters. Preferably, the light emitters are positioned in an array, so that the light strength over the screen is roughly equal.

The invention may be advantageously used in LCD systems and in particularly in systems comprising an LCD layer and a diffusive layer comprising a plurality of light emitters for backlighting. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and its numerous objects and advantages will become more apparent to those skilled in the art by reference to the following drawings, in conjunction with the accompanying specification, in which:

Fig. 1 shows a side view of an embodiment of the system according to the invention.

Fig. 2 shows a front view of the embodiment depicted in Fig. 1. Fig. 3 shows a block diagram of the embodiment depicted in Fig. 1.

Throughout the figures like reference numerals refer to like elements.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Referring now to Figures 1-3, an embodiment of the system according to the invention will be described. Figure 1 shows a side view of a touch screen system 10 for detecting the position of a touch member 20, such as a pen or a user's finger close to the screen's surface. It comprises a LCD layer 30 and a plurality of LEDs incorporated into a diffusive layer 40 behind the LCD layer 30. The LEDs are arranged in an array as shown in Figure 2 and are used for backlighting. LED-based backlighting solutions for larger LCD monitors and televisions are known as such. They significantly improve color rendering. In addition, the energy savings can also be significant if the backlighting system is designed for high-energy efficiency. According to the invention the LEDs are used both for backlighting, as well as for recording the position of touch member 20 close to the screen's surface, creating thus a touch screen at the same time.

It is known that LEDs can work not only as light sources i.e. for emitting light but also as photo-detectors. If the current is suppressed to the LED for a short time, the LED will not emit light. In this reverse mode, external incoming light excites electrons from the valence band to the conduction band, which produce a current when a voltage is applied. Here the LED works as a photodiode.

According to an embodiment of the invention this feature is used to make a combined LCD display with LED backlight and touch screen sensor. Most of the time, the LEDs will be turned on in order to generate light for displaying a certain image. However, from time to time, at a rate imperceptible by the human eye (switch off time is approximately 0.1 ms), some of the LEDs are turned off and used as photodiodes. They can detect the proximity of the touch member 20 with the help of the illumination by the other LEDS that are switched on.

In other words, light reflected by the LEDS that are switched on is partly scattered or reflected by the touch member 20, and captured by the LEDs that work as photodiodes, (referred to as "d" in Figures 1 and 2).

The LEDs that are turned off may be selected in several ways. They may be equally spread over the screen, as is shown in Figure 2. However, they may also be selected in a smart way, for example near LEDs that emit much light. This will result in more light being scattered or reflected to the LEDs that are turned off, enabling a more reliable detection of the position of the touch member 20.

The system comprises LED drive electronics 50 for turning the LEDs on and off. Electronic circuits for switching LEDs between a light emitting mode and a light detecting mode, in which the LEDs work as photodiodes, are well known in the art. A skilled person may select such a known circuit for use in the system according to the invention without difficulty. Such a known electronic circuit for switching LEDs between light emitting and light detection mode is described for example in the patent US 6,449,437 Bl. The system 10 also comprises means 60 for reading the voltage over the LEDs that are working as photodiodes. This voltage is a measure for the light intensity detected by the LED.

The system 10 may further comprise means 70 for detecting the position of the touch member 20 near the screen surface and for detecting a touch of the screen by the touch member 20 based on the detected light intensities by the LEDs. These means may however also be located in an external device, such as a computer. A high intensity detected by a LED means that the touch member 20 is located nearby the LED and a low intensity means that the touch member 20 is located far away from the LED. A touch of the screen by the touch member 20 may for example be detected if the total detected light is larger than a threshold value. The position and touch detection means 70 are preferably implemented by means of a suitably programmed processor.

The invention has been described with reference to a LCD display with LEDs used for backlighting. However, it may be extended to other types of screen systems having a LED as a light-source. One such application may be a LED display. A LED display is an ordered collection of LEDs that can display an image, such as alphanumeric text or animated graphics.

Furthermore, instead of LEDs, also other devices may be used that can work both as light detector and light emitter. An example of such a device is a laser sensor, such as the Twin-eye™ laser sensor commercialized by Philips. This device uses the principle of Self- Mixing Interferometry (SMI) for detecting scattered light. SMI occurs when part of the emitted light from a laser is coupled back into the laser cavity. The interference between the incoming light in the laser cavity and the light already present in the laser cavity creates power fluctuations of the laser. These power fluctuations are measured with a photodiode. A laser sensor can emit and detect light at the same time, so there is no need for including switching circuits in the system, such as in the case that LEDs are used as light emitters/detectors .

Finally, it is possible to use separate light emitters and light detectors instead of devices that are capable of performing both the function of emitting light and the function of detecting light. The light detectors should be arranged in substantially the same two- dimensional plane as the light emitters, preferably in between them. In this case the number of light detectors should be small compared to the number of light emitters, so that the quality of the backlighting or of the image generated by the light emitters remains acceptable. As will be recognized by those skilled in the art, the innovative concepts described in the present application can be modified and varied over a wide range of applications.

Accordingly, the scope of patented subject matter should not be limited to any of the specific exemplary teachings discussed, but is instead defined by the following claims. Any reference signs in the claims shall not be construed as limiting the scope thereof.

Claims

CLAIMS:

1. Touch screen system (10) comprising: a plurality of light emitters, which are used either for backlighting a screen or for generating an image thereon; and a plurality of light detectors (d) for detecting light emitted by the light emitters and reflected or scattered by a touch member (20).

2. Touch screen system (10) according to claim 1 comprising position determining means (70) for determining the position of the touch member (20) with respect to the screen based on the light detected by at least some of the light detectors.

3. Touch screen system (10) according to claim 1, further comprising touch detection means (70) for detecting that the touch member (20) touches the screen.

4. Touch screen system (10) according to claim 3 wherein the touch detection means (70) are adapted for detecting the touch if the amount of light scattered by or reflected from the touch member (20) is larger than a threshold value.

5. Touch screen system (10) according to claim 1 wherein at least some of the light emitters are adapted for working also as light detectors.

6. Touch screen system (10) according to claim 5 wherein the light emitters adapted for working also as light detectors are LEDs.

7. Touch screen system (10) according to claim 6 comprising switching means (50) for periodically switching at least some of the LEDs into a light detection mode.

8. Touch screen system (10) according to claim 7, wherein the switching means (50) are adapted for switching the at least some of the plurality of LEDs into the light detection mode and back to a light emitting mode.

9. Touch screen system (10) according to claim 8, wherein the switching of the plurality of LEDs into the light detection mode and back to a light emitting mode occurs at a rate imperceptible by the human eye.

10. Touch screen system (10) according to claim 5 wherein the light emitters adapted for working also as light detectors are adapted to work as light emitter and light detector at the same time.

11. Touch screen system (10) according to claim 10 wherein the light emitters adapted for working also as light detectors are laser sensors.

12. Touch screen system (10) according to claim 1 wherein the light emitters are positioned in an array.

13. Touch screen system (10) according to claim 1, being an LCD display.

14. Touch screen system (10) according to claim 13 comprising an LCD layer (30) and a diffusive layer (40) with the plurality of light emitters for backlighting.