WO2009031094A1

WO2009031094A1 - Laser scanning projection device with eye detection unit

Info

Publication number: WO2009031094A1
Application number: PCT/IB2008/053538
Authority: WO
Inventors: Arnd Ritz; Achim Weber; Holger Moench; Willem Hoving
Original assignee: Philips Intellectual Property and Standards GmbH; Koninklijke Philips Electronics NV
Current assignee: Philips Intellectual Property and Standards GmbH; Koninklijke Philips NV
Priority date: 2007-09-04
Filing date: 2008-09-02
Publication date: 2009-03-12
Anticipated expiration: 2010-03-04

Abstract

The present invention relates to a projection device comprising at least one laser light source (2) and a scanning unit (7) arranged for scanning an external projection area (12) within a projection cone (11) with a laser beam (10) emitted from said laser light source (2). The projection device further comprises a detection unit (13) designed to detect the presence of an eye (23) in the projection cone (11) and a control unit (21) designed to lower a projection intensity of the laser beam (10) when an eye (23) is detected. The control unit (21) lowers the intensity only as long as the laser beam (10) scans over a limited region (24) around a detected position of the eye (23) and maintains the projection intensity of the laser beam (10) outside of said limited region (24) in said projection cone (11). The projection device allows a reliable protection of the eye of a person looking directly into the laser beam while the projected image is not significantly disturbed in such a case.

Description

LASER SCANNING PROJECTION DEVICE WITH EYE DETECTION UNIT

FIELD OF THE INVENTION

The present invention relates to a projection device comprising at least one laser light source and a scanning unit arranged for scanning an external projection area within a projection cone with a laser beam emitted from said laser light source. BACKGROUND OF THE INVENTION

Laser sources have recently attracted a lot of interest in the field of projection devices, both for use in handheld projectors as well as for replacement of UHP-lamps in front and rear projection devices. Small sized beamers of only a few cm³ of volume, but still capable of delivering an utilizable picture of about an A4-size, are expected to find a broad application in personal projection. These picobeamers could be realized as stand-alone applications but could also be integrated in handheld devices like smart phones or personal digital assistants (PDA).

For projection of the described kind a laser power of about 100 mW cw is necessary. Laser radiation with such a power, spread by a scanning unit to a projection cone to illuminate the desired projection area, is able to damage the human eye when exposed to the diverging laser beam at a distance too close to the projection device. Due to the dilution of the radiation with increasing distance from the projection device, the level of hazard decreases with increasing distance. The hazardous distance for such a laser beamer with about 100 mW total laser power ranges from about 0.5 m to about 3 m, depending on the details of the projection geometry. A person bringing its eye within this hazard distance into the projection cone could suffer eye damages. This exposure might happen if the projector is suddenly redirected or if someone enters into the projection light cone by walking into the free space between the projector and the projection screen.

US 2005/0035943A1 discloses a laser scanning projection device lowering the laser output power if any object is detected in the projection cone between the projection device and the projection screen. The projection device comprises detection means detecting an intrusion of an object into the projection cone, wherein the detection is conducted relative to a position preceding the laser beam in scan direction. The laser output power is then lowered only in the vicinity of the detected object in order to maintain a high projection quality in the remaining area of the projection screen. SUMMARY OF THE INVENTION It is an object of the present invention to provide a projection device which lowers the risk for damage of the eye when a person gets into the projection cone of the projection device and happens to look directly into the beam and which allows an even less influence on the projected image in such a case compared to the above known projection device. The object is achieved with the projection device according to claim 1.

Advantageous embodiments of this projection device are subject matter of the dependent claims or are disclosed in the subsequent portion of the description.

The proposed projection device comprises at least one laser light source and a scanning unit arranged for scanning an external projection area within a projection cone with a laser beam emitted from said laser light source. The projection device further comprises a detection unit designed to detect the presence of an eye in the projection cone. A control unit of the projection device is designed to lower the projection intensity of the laser beam when an eye is detected in the projection cone, said intensity being lowered only as long as the laser beam scans over a limited region around the detected position of the eye, and to maintain the initial (higher) projection intensity of the laser beam outside of said limited region in said projection cone.

Therefore, compared to the known solutions of the prior art, the detection unit of the proposed projection device is designed to detect the intrusion or presence of an eye of a human being or of an animal in the projection cone, and the laser intensity is only lowered if an eye is detected. This means that the laser power or laser intensity is not lowered if any other object not comprising an eye passes through the projection cone. This also means that the intensity of the laser beam is only lowered in the vicinity of the eye and not in other regions. For example, if a person passing through the projection cone is looking in the direction of the projection screen, no eye is detected by the detection unit and, therefore, the laser intensity is not lowered. If a person passes through the projection cone looking in the direction of the projection device, the laser intensity is lowered only in the close vicinity of the eye(s) and not in other regions, for example in the region of the chest, the arms or the legs of the person. These parts of the person therefore reflect the projected image with the full power resulting in a significantly smaller disturbance of the projected image for the viewer than in a case, in which the laser intensity is lowered in the vicinity of the whole person. The latter case causes, dependent on the person, a significant shade in the projection image.

The intensity of the laser beam in the close vicinity of the eye is lowered to a level which does not cause eye damage. The lowering of the laser beam intensity may for example be selected such that irradiance of the eye is limited to values which conform to the international standards on laser radiation safety (IEC 60825-1). The laser intensity may be reduced by different measures. One preferable measure is the lowering of the laser output power, for example in case of laser diodes by lowering the operation currents of the laser diodes. Nevertheless, also other measures are possible, for example by arranging elements with controllable transmission for the laser wavelengths between the laser light source and the scanning unit which are controlled by the control unit.

With the proposed projection device the risk of damage of the eye for a person getting into the projection cone of the projection device and looking directly into the beam is significantly reduced. Furthermore, since the laser intensity is only reduced in the close vicinity of the position of the eye of the person, the image quality of the projected image is only slightly influenced by such an intrusion. The limited region around the detected position of the eye may be a circle having a typical diameter of an eye which is symmetrically arranged around the detected position of the eye. This limited area may also extend to a diameter which is a factor of 2 to 10 or more of the diameter of the eye, preferably less or equal than a factor of 10 of the diameter of the eye, most preferably less than a factor of 5 of the diameter of the eye.

The detection unit for detecting the intrusion of an eye or the presence of an eye within the projection cone principally may be any device for detecting eyes, for example known from eye tracking applications. Preferably, the detection of the eye is based on the high reflection of infrared radiation by an eye. Eyes of human beings or animals are well known to reflect infrared light to a high degree. Therefore, the detection unit of the proposed projection device preferably comprises an additional IR radiation source which monitors the projection cone. The presence of an eye in this projection cone is then detected by a significantly enhanced reflection of the infrared radiation which is sensed by an appropriate IR sensor of the projection device. This sensor can be a one or two dimensional array of CCD elements. When using an IR laser source for generating an IR laser beam which scans the projection area in the same manner as the scanning laser beam for projection, also only a single CCD element or an appropriate photo diode may be used for sensing the reflected IR radiation.

In a preferred embodiment of the proposed projection device, an additional IR laser source and corresponding beam forming and/or beam deflecting elements are arranged such that the IR laser beam is superimposed on the scanning laser beam, i.e. the laser beam for projection. Therefore, the IR laser beam is scanned on the same path as the scanning laser beam and scans the same positions on the projection screen at the same time. In this case, the scanning unit is shared by the scanning laser beam and the IR laser beam. Due to the fast scanning movement of the scanning laser beam, the exposure time for single pass is very short. This very short time of the eye being in the scanning laser beam of possibly 100 mW total power cannot produce eye damage.

In a further advantageous embodiment of the proposed projection device, the IR laser beam is also scanned on the same scan path using the same scanning unit as the scanning laser beam, but is adapted such that it scans equal positions on the projection screen prior than the scanning laser beam. The IR laser beam can be adapted such that it scans the image lines at the projection screen always some pixels ahead of the scanning laser beam, for example 2 to 10 pixels or 2 to 10 lines. This can be achieved by directing the IR laser beam at a slightly different angle onto the scanning unit. The timely difference between the IR laser beam and the scanning laser beam in irradiating one and the same pixel is preferably selected such that a delay caused by the data processing time required for detection of an eye and controlling of the laser intensity is at least compensated.

It goes without saying that the intensity of the additional IR laser beam is selected sufficiently low to avoid damage of the eye by this laser beam.

In a further advantageous embodiment, the detection unit is designed to measure the distance between the projection device and the detected eye. The control unit then lowers the intensity of the scanning laser beam dependent on the measured distance. This means that the intensity is lowered stronger if the eye is detected at a closer position to the projection device. In order to measure the distance to the eye the detection unit can comprise a distance measuring unit based on time of flight measurement. This measurement uses the phase shift between the emitted and the reflected IR light for determining the distance. An example for such a distance measuring unit is an SMI sensor using the technique of self mixing interference (SMI), which is for example disclosed in US2005/0286589A1.

Since the laser intensity or laser power of the scanning laser beam is controlled by the control unit in real time dependent on the signals of the detection unit, a damage of the eye of a person looking into the projection cone in the direction of the projection device can be reliably prevented. The proposed projection device may be designed as picobeamer, for example for use as handheld device, and may also be included in other handheld devices like smart phones or PDA's. The invention, however, is not restricted to handheld devices. For image projection applications the device preferably comprises at least three laser light sources emitting red (R), green (G) and blue (B) light. The laser beams emitted from these laser light sources may then be combined in a known manner to a single laser beam and directed to the scanning unit.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described herein after. BRIEF DESCRIPTION OF THE DRAWINGS

The proposed projection device is described in the following by way of examples in connection with the accompanying figures without limiting the scope of protection as defined by the claims. The figures show:

Fig. 1 a schematic view of a front projector according to the present invention;

Fig. 2 a more detailed schematic view of the projection device of Fig. 1; Fig. 3 a detail schematically showing exemplary beam paths of the scanning laser beam and the IR laser beam of one embodiment of the proposed projection device; Fig. 4 a schematic view of a further embodiment of the proposed projection device; and

Fig. 5 a schematic view illustrating the operation of the proposed projection device.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 schematically shows a projection device according to the present invention. The projection device 1 comprises a laser light source 2 emitting a laser light beam which is directed to a scanning unit 7 for scanning an external projection screen 12 with the laser light beam to project a desired image on this screen. The output power of the laser light source 2 is modulated as known in the art in order to generate the desired image information. The proposed projection device comprises a detection unit 13 for detecting the presence of an eye of a person or an animal within the projection cone 11 which is defined by the scanning movement of the scanning laser beam. Detection unit 13 is connected to a control unit 21 which controls the output power of the laser light source 2 dependent on the signals from the detection unit 13. If detection unit 13 detects an eye within the projection cone 11 , the laser power of the laser light source 2 is lowered to a non hazardous level for the eye in the vicinity of the detected position of the eye.

This situation is schematically illustrated in Fig. 5 showing the scanning unit 7 and the projection cone 11. If a person 22 enters the projection cone 11 with its eye 23 directed towards the projection device, the detecting unit detects the eye 23 and the control unit 21 in real time lowers the intensity of the scanning laser beam in the vicinity of the eye. This means that the output power of the scanning laser beam is only lowered as long as the scanning laser beam scans the region 24, which is a limited area in the close vicinity of the detected position of the eye 23, and does not lower the intensity in the remaining scanning regions 25. This allows the protection of the eye 23 on the one hand and on the other hand does not significantly disturb the projected image. After detecting an eye 23 in the projection cone 11, this position is stored in the detection unit or control unit to allow the lowering of the laser power in region 24 in the subsequent scans. In these subsequent scans the presence and position of the eye 23 are newly determined and updated.

Fig. 2 shows a more detailed example of the projection device of fig. 1 in a schematic view. In this device 1 three laser light sources 2 emitting red (R), green (G) and blue (B) laser light beams are included. The laser light sources 2 may be for example laser diodes. The divergent laser beams emitted by these laser light sources 2 are collimated by a collimating optics 3 and combined to form one single laser beam 9. The combination is made via dielectric mirrors 4, 5, 6. Dielectric mirror 4 is designed to reflect light in the red wavelength region. Dielectric mirror 5 reflects in the green wavelength region and is transparent in the red wavelength region, whereas dielectric mirror 6 reflects in the blue wavelength region and is transparent in the red and green wavelength regions. The combined single laser beam 9 is directed to a 2D scanning unit 7, which contains at least one scanning mirror 8. In Fig. 2 only for illustrative purposes one scanning mirror 8 is depicted, which is tiltable in the direction of the arrow. The scanning mirror 8 scans a projection screen outside of the device 1 with the laser beam 10 leaving the scanning unit 7. With such a projection device 1, a colored two dimensional image may be projected to the projection screen by appropriately controlling the intensity of the red, green and blue radiation of the laser light sources 2 dependent on the scanning movement of the scanning mirrors of scanning unit 7 and the image information. The detection unit comprises an IR laser light source 14 emitting an IR laser light beam 17 which is superimposed on the combined laser beam 9 using an appropriate dielectric mirror 20 as shown in the figure. Dielectric mirror 20 is transparent in the visible wavelength region and highly reflective in the infrared wavelength region of the IR laser light source 14. Due to this overlaying IR laser light beam the projection area is scanned at the same time with the scanning laser light beam 10 for image generation and with the invisible IR laser light beam 17 at the same positions at the same time. Infrared light which is reflected from the projection screen and from any object intruding into the projection cone 11 takes the same path back to infrared laser light source 14. A portion of this reflected infrared light 18 is deflected by an appropriate beam splitter 16 to an IR sensor 15 for measuring the reflected IR intensity. If the IR laser light beam 17 passes through an eye of a person which has entered the projection cone 11, a significant increase in reflected IR light intensity is detected by sensor 15. Processing unit 19 of the detection unit sends an appropriate signal in such a case to control unit 21. Control unit 21 then immediately lowers the operating current of the laser light sources 2 until the enhanced reflected intensity detected by sensor 15 significantly reduces. This means that the scanning laser beam 10 and the sensing IR laser beam 17 have passed the eye so that the intensity of the scanning laser beam 10 can be increased to its normal level.

In the embodiment of Fig. 2, due to the processing time of the detection unit and the control unit 21, the lowering of the laser beam intensity is deferred with respect to the detection of the eye, but still quick enough in order to avoid a damage of the eye. Fig. 3 shows a detail of a further embodiment, in which the sensing IR laser beam 17 moves slightly in front of the scanning laser beam 10. The scanning direction on the projection screen is indicated with the double arrow in Fig. 3. This advance movement of the sensing laser beam 17 can be achieved by directing this laser beam at a slightly different angle to scanning mirror 8, as schematically indicated in Fig. 3. With such an embodiment, a delay between the impingement of the scanning laser beam 10 on the eye and the lowering of the laser intensity can be avoided by appropriately setting the delay between the sensing laser beam 17 and the scanning laser beam 10. The IR laser beam 17 may also lead in lines. This is in the direction normal to the plane of this figure.

In a further preferred embodiment shown in Fig. 4, in addition to the detection of the eye in the projection cone, also the distance to the eye is measured. Control unit 21 then lowers the laser intensity dependent on this distance such that the laser intensity is lowered to a higher extent when the eye is detected closer to the projection device. In any case, the laser intensity is lowered to such an extent that no damage of the eye can occur by the scanning laser beam. In Fig. 4, the construction of the projection device is similar to the construction of the device of Fig. 2. The difference is the detection unit which in this case comprises a laser sensor based on self mixing interferometry (SMI). With such laser sensors velocities, vibrations and distances can be measured. SMI laser sensors make use of the effect that laser light, which is scattered or reflected back from a target object and reenters the laser cavity, interferes with the resonating radiation and thus influences the output properties of the laser. When the laser is operated not too far above the laser threshold the response of the back coupled light is linear and the resulting variations in output power or frequency contain usable information on the movement or the distance of the target object with respect to the sensor. The laser output signal, which contains the information, is collected via a photo detector, the IR detector 15 in Fig. 4. The laser 14 in this case comprises an end mirror which enables outcoupling of a small portion of the laser light. A known laser sensor based on self mixing interferometry comprises a VCSEL (vertical cavity surface emitting laser) as the laser light source 14. When using such a SMI laser sensor as schematically depicted in Fig. 4, in addition to the detection of the eye also the distance of the eye to the projection device is measured via the phase information of the emitted and reflected infrared light.

While the invention has been illustrated and described in detail in the drawings and forgoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive, the invention is not limited to the disclosed embodiments. The different embodiments described above and in the claims can also be combined. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. For example, although the proposed projection device has been described in these embodiments with three laser sources emitting red, green and blue light, the projection device may also include more than three or less than three laser sources. Furthermore, the sensing infrared laser light beam may also be deflected by a separate scanning unit for monitoring the projection cone.

In the claims the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope of these claims.

LIST OF REFERENCE NUMERALS

1 projection device

2 laser light source

3 collimating optics

4 dielectric mirror

5 dielectric mirror

6 dielectric mirror

7 scanning unit

8 scanning mirror

9 combined laser beam

10 scanning laser beam

11 projection cone

12 projection screen

13 detection unit

14 IR laser light source

15 IR sensor

16 IR beam splitter

17 IR laser beam

18 reflected IR radiation

19 processing unit

20 dielectric mirror

21 control unit

22 person

23 eye

24 region of lowered intensity

25 region of normal intensity

Claims

CLAIMS:

1. A projection device comprising at least one laser light source (2) and a scanning unit (7) arranged for scanning an external projection area (12) within a projection cone (11) with a laser beam (10) emitted from said laser light source (2), the projection device further comprising - a detection unit (13) designed to detect the presence of an eye (23) in the projection cone (11) and

- a control unit (21) designed to lower a projection intensity of the laser beam (10) when an eye (23) is detected in the projection cone (11), said intensity being lowered only as long as the laser beam (10) scans over a limited region (24) around a detected position of the eye (23), and to maintain an initial projection intensity of the laser beam (10) outside of said limited region (24) in said projection cone (11).

2. The projection device according to claim 1 , wherein said control unit (21) is designed to lower said intensity by lowering an output power of the laser light source (2).

3. The proj ection device according to claim 1 , wherein said control unit (21) is designed to select the limited region (24) symmetrical around the detected position of the eye (23).

4. The projection device according to claim 1, wherein the detection unit (13) comprises at least one IR light source arranged to monitor the projection cone (11) from the device (1) to the external projection area (12) and an IR detector (15) arranged to receive IR light reflected from any object intruded into the projection cone (11).

5. The projection device according to claim 4, wherein the IR light source is an IR laser light source (14) emitting an IR laser beam (17).

6. The projection device according to claim 1, wherein the detection unit (13) comprises at least one IR laser light source (14) emitting an IR laser beam (17) which is superimposed to the scanning laser beam (10) such that it scans equal positions of the projection area (12) at the same time as the scanning laser beam (10), and an IR detector (15) arranged to receive IR light reflected from any object intruded into the projection cone (11).

7. The projection device according to claim 1, wherein the detection unit (13) comprises at least one IR laser light source (14) emitting an IR laser beam (17) which is deflected to scan the projection area (12) on the same path and in synchronization with the scanning laser beam (10) such that it scans equal positions of the projection area (12) ahead of the scanning laser beam (10), and an IR detector (15) arranged to receive IR light reflected from any object intruded into the projection cone (11).

8. The projection device according to any one of claims 1 to 7, wherein the detection unit (13) is designed to measure a distance to the eye (23) and to lower the intensity of the scanning laser beam (10) dependent on the measured distance.

9. The projection device according to claim 1, wherein the detection unit (13) is designed to detect the presence of an eye (23) by a significant increase of reflected IR radiation typical for reflection from an eye (23).