WO2008056297A1

WO2008056297A1 - Laser projector with automatic security

Info

Publication number: WO2008056297A1
Application number: PCT/IB2007/054395
Authority: WO
Inventors: Arnd Ritz
Original assignee: Philips Intellectual Property & Standards Gmbh; Koninklijke Philips Electronics N. V.
Priority date: 2006-11-08
Filing date: 2007-10-30
Publication date: 2008-05-15

Abstract

A projection apparatus and method are described. A projector includes a freely displaceable casing 14, in which a laser light source 24 and a modulation and projection arrangement are included. Light 26 from the light source 24 is modulated according to image data and projected into a projection region outside of the casing 14 to form an image 22 on a screen 12. A security unit has an inertial sensor 40, 44, 46 for detecting acceleration and/or movement of the casing 14. A movement value (ω, A) corresponding to a movement of the casing 14 leading to a displacement of the projection region is determined. The movement value (ω, A) is compared to a movement threshold (ωT1, AT1), (ωT2, AT2). If the movement value is above the threshold, the intensity of the projected light 20, 20a is reduced, or the projected light is turned off.

Description

LASER PROJECTOR WITH AUTOMATIC SECURITY

Field of the invention

The present invention relates to a projection apparatus and a method for operating a projection apparatus. More particularly, the invention relates to a projection apparatus comprising a freely displaceable enclosure and a laser light source within the enclosure.

Background of the invention

A plurality of different types of projectors are known, which project modulated light into a projection region to form a visible image there. In conventional video projectors, the light from a high intensity light source, such as a discharge lamp, is modulated in a light valve according to video image data and projected onto a screen.

Such projectors are available with relatively small size and weight, so that they are freely displaceable.

It has already been proposed to use a laser light source within such a projector. Laser based projectors are expected to find widespread use in home video and gaming applications. In order to enable high quality projection, sufficient light output of up to several watts of light radiation per primary color may be necessary. However, this is an amount of laser radiation, which under adverse conditions can be harmful to people, especially to the human eye.

US-A-2005/007562 shows different embodiments of laser video projectors with safety devices. A laser beam source outputs a laser beam and modulates the laser beam based on an image signal. A scanning unit scans the laser beam output over a screen. In one embodiment shown in US-A-2005/007562, a front-type projector is shown, where the laser beam source and scanning unit are included within an enclosure, and the light is projected outside of this enclosure. The scanning unit comprises an oscillating mirror, which is mounted in a way such that in case of failure of the unit driving the mirror, the mirror assumes a safe position where the laser beam is prevented from being emitted outside of the enclosure. In a further embodiment according to US-A-2005/007562, there is provided a rear-type projector. An enclosure comprises a laser light source, scanning unit and a screen. The modulated light is projected on the backside of the screen, within the enclosure. If due to a screen defect laser light is emitted outside of the enclosure, this is detected by a screen monitoring security device, and further operation of a laser is interrupted. Also, the reflecting mirror is monitored for damage, burning, pin holes or the like, and in case of any abnormality, laser operation is also interrupted. Further, vibration sensors may be provided within the enclosure to avoid a risk of emission of a laser beam outside of the enclosure, if the enclosure is damaged, e. g. intentionally or by an earth quake. In this case also operation of the laser is interrupted if a detected vibration of the enclosure is higher than a predetermined amplitude.

It is an object of the present invention to provide a projector with improved security to avoid eye injuries caused by laser radiation.

Summary of the invention

This object is solved by a projection apparatus according to claim 1 and an operating method according to claim 10. Dependent claims refer to preferred embodiments of the invention.

According to the invention, the projection apparatus comprises a freely displaceable enclosure. The term "freely displaceable" here refers to a projector with an enclosure, or casing, which in total size and weight is dimensioned such that it may be moved and re-positioned. Preferably, the projector may be portable, i. e. dimensioned such that it may easily be carried by a single person. This is to be understood in contrast to stationary mounted projectors, which are fixed to a further structure, such that they may no longer be freely positioned independent of that structure. As laser projectors are expected to be feasible in small sizes, the enclosure is preferably that of a handheld device, which may be a stand alone handheld projector, or the projector functionality may be added to that of PDA, Smartphone, Camera of the like. The term handheld is to be understood as a mobile device (i.e. which works without cable connection) that can easily be held with one hand.

Within the enclosure, a laser light source and a modulation and projection arrangement are mounted to generate modulated laser light and project it into a projection region outside of the enclosure. A will become apparent from the preferred embodiments, modulation may be effected optically (i.e. on the generated laser light) and/or electronically (i.e. on the laser light source).

According to the invention, a security unit is provided with at least one inertial sensor. As will become apparent with the description of preferred embodiments, an inertial sensor may detect movement and/or acceleration, which may comprise both linear and rotational movement and/or acceleration by measuring effects, such as forces or deflection, caused by inertia influence on a mass object. Depending on the type of sensor and the signal processing, the sensor may deliver an output indicating one or more of the following: linear displacement, tilt, rotation, angular or linear velocity, rotational or linear acceleration. As these are closely related, they will in the following only be referred to as "movement".

An inertial sensor may detect movement of the structure it is mounted on without any mechanical, electrical or otherwise connection to a reference point. Thus, the projector can sense movement of its enclosure itself, without any dedicated further connection or calibration being necessary.

According to the invention, a security unit is provided to determine a movement value, compare the movement value to a movement threshold, and, in case the movement value exceed the threshold, turn off the projected light or reduce its intensity to an eye-safe level. The movement value, which corresponds to a movement of the enclosure leading to a displacement of the projection region, may be calculated from the output of one or more of the sensors in different ways. In a simple embodiment, the sensor output value is directly compared to the threshold. Alternatively, a calculation of a movement value may be derived from the sensor output based on one or more consecutive sensor output values and also additional values.

According to a preferred embodiment, the movement value is composed of at least two values, a motion value and a speed value. The motion value indicates an amount of displacement and/or rotation, e.g. how far a projector has been displaced, or how many degrees it has been rotated. The speed value indicates a change rate, e.g. linear or angular velocity. The threshold value correspondingly also comprises a pair of values, a motion threshold value and a speed threshold value. The comparison is effected such that the movement value is only above the threshold if both the motion value and the speed value are above their threshold counterparts. This serves to eliminate false alarms. If, for example, the projector moves quiet rapidly, but only a minimal distance/angle, this will not lead to a significant security issue with regard to eye safety. Thus, if only the speed value is above the speed threshold, but the motion value remains below the motion threshold, there is no need to turn off or reduce the intensity of the projected light. The same may be true for a large displacement with low speed.

It should be emphasized that although the security unit is described here as a separate unit of the projector, it need not be implemented as an entirely separate assembly within the projector. Instead, the security unit may be implemented as part of an electric circuit also serving other purposes within the operation of the projector. Specifically, it is possible to implement the function of the security unit as instructions being executed on a processor unit which also executes instructions for serving other purposes, e. g. the main processor of the projector.

A projector according to the invention thus has a built-in security function that helps to avoid situations where displacement of the projector could lead to persons being exposed to laser radiation. As projectors become smaller and easier to handle, there is a risk that during operation they may be unintentionally displaced, so that the projected light cone is swept in an unforeseeable manner through the room. This type of movement may be detected by the sensor, so that the security unit interrupts or limits operation of the laser to avoid exposing viewers to hazardous light levels.

Since inertial sensors are robust, widely available and are simply mounted - without the need for any further connection or calibration - the invention helps to greatly improve security with only minimal further outlay.

According to a preferred embodiment of the invention, the inertial sensor is adapted to sense rotation about at least one rotation axis. It is also possible to have one or more sensors arranged to sense rotation about two or more axes. Preferably, the rotation axis is not parallel to, but includes an angle with the optical axis, i. e. the center direction into which the modulated light is projected. It is preferred that the angle is at least 30°, most preferably the rotation axis is at least substantially perpendicular, i. e. arranged at 90 +/- 10° with regard to the optical axis.

According to further preferred embodiments, the inertial sensor may be either an accelerometer or a gyroscope. A corresponding accelerometer includes at least a proof mass and a deflection sensing circuit. In case of acceleration acting on the enclosure, e. g. if the projector is suddenly moved, the proof mass will be deflected by inertial forces acting on it, and the deflection (or corresponding forces) are measured by a deflection sensing circuit. In the case of a gyroscope, a moving mass is provided, which may be e. g. spinning. In case of movement occurring in a direction which is arranged at an angle with the spin axis, there is a tendency to resist the change in orientation due to gyroscopic inertia. The deflection and/or reaction force of the spinning mass is sensed by a sensing circuit. Alternatively, the mass may also be vibrating, as described in WO-A-97/27459. According to a further preferred embodiment, the movement value is compared to a first threshold value. In case that the movement value exceed the threshold, the projector is operated in a way that only light of reduced intensity is projected, which operation may be referred to as dimmed or safe mode. Preferably, in the dimmed mode, the intensity is reduced to an eye-safe level, preferably confirming to the limits set in international standards IEC-60825 and CIE S 009.

In a particularly preferred embodiment, instead of the video image according to the video data, only a (preferably constant) pattern image is projected in the dimmed mode. Especially preferred is a pattern, which shows the extent of the image region. The image region is the region, where in normal operation the displayed image is created by the modulated light. In the dimmed mode, a pattern showing the extent of this image region is displayed, which allows a user to position the projector, e. g. aiming at a projection screen. For example, the projected pattern may be a simple frame pattern showing the outer bounds of the image region.

According to a further preferred embodiment, there may be a second movement threshold value defined. The second movement threshold value will typically correspond to greater or faster movement than the first movement threshold value. In case that the second movement threshold value is exceeded, the projected light is turned off. This may be achieved e.g. by turning off the laser light source, closing a light value of the modulation and projection arrangement so that no light is projected, or by using further means, such as shutters. Preferably, the turned-off mode entered if the second threshold is exceeded will leave the projector off permanently. Operation is resumed only upon user input.

Brief description of the drawings

The above and other objects, features and advantages of the present invention will become apparent from the following description of preferred embodiments, in which:

fig. 1 shows a schematical, perspective view of a first embodiment of a projector projecting an image onto a screen; fig. 2 shows a schematical representation of the projector of fig. 1; fig. 3 shows a schematical, perspective view of a second embodiment of a projector projecting an image onto a screen and fig. 4 shows a schematical representation of the projector of fig. 3.

Detailed description of embodiments

As shown in fig. 1, a projector 10 is positioned in front of a screen 12. The projector, of which only a casing 14 is visible, is a portable projector, i. e. it is dimensioned in size and weight such that it can easily be carried by a single person. As shown in fig. 2, the projector 10 comprises a modulation and projection arrangement 18 comprising optics 16 through which modulated light 20 is projected onto the screen 12 to create an image 22 there. The direction, into which the modulated light 20 is projected will be referred to as the projection region. An optical axis is defined as the line from the center of the beam outlet of the projector 10 to the center of the projection region. The image projected by projector 10 represents video data (not shown) supplied to projector 10 being projected such that the display image is an image according to the video data, i. e. with different brightness and/or color in different parts of the image 22.

To create the image 22, the projector 10 comprises a laser light source 24, which creates a beam of laser light 26 within the modulation and projection arrangement 18, the laser beam 26 is enlarged by suitable optics 28 and fed to a two- dimensional light valve 30, which - as known from conventional non-laser projectors - selectively lets the laser light pass through to create a modulated light bundle 34, which is projected through optics 16 as modulated light 20.

The operation of projector 10 is controlled by a central controller 36, which is a microprocessor unit executing a control program. The central controller 36 performs all control functions within the projector 10. It feeds the video data to the light valve 30 so that the laser light 26 is modulated accordingly. Also, the control unit 36 controls operation of the laser light source 24.

The general operation of the above described parts of projector 10 are generally known to the skilled person and will therefore not be further explained in detail. Especially, it should be noted that while the schematic drawing of fig. 2 shows only an arrangement to create an image of a single color, it will usually be preferable to operate the projector 10 to display an image 22 including multiple colors. This may be achieved, e. g. by using multiple laser light sources delivering light 26 of different color, or by sequential color rendering. According to the shown embodiment of the invention, the projector 10 comprises an inertial sensor 40. In the preferred embodiment, the inertial sensor 40 is an integrated dual-axis miniature gyroscope sensor. The sensor 40 is fixed within the casing 14 of projector 10. Its sensor axes X and Y are aligned with the projector 10 so that they are both arranged at right angles with the optical axis (i. e. the central direction into which the modulated light 20 is projected). In the typical substantially horizontal arrangement of projector 10, as shown in fig. 1, the X-axis is arranged vertically, while the Y-axis is arranged horizontally. The sensor may be, e. g. of the vibration type as available from Gyration, Inc.

The sensor 40 detects angular acceleration of the projector 10 and its casing 14 about the X- and Y-axes. Corresponding sensor outputs CCx, CCy are delivered from sensor 40 to controller 36. These values indicate the angular acceleration, i.e. the change in angular speed of the projector 10 about the respective axis. The angular acceleration values can be integrated once to yield angular velocity values ω_x, ω_y, and a second time to yield the amount of rotation A_x, A_y of the projector. Thus, the values A_x, Ay indicate also the sweep of the projection region, i. e. the angles by which the modulated light 20 is swept across the screen 12, leading to an displacement of image 22 on the screen 12.

Within controller 36, the sensor values CCx, CCy are processed as follows: From the start of the system (or preferably, as explained below, only after accumulation is triggered by sensor values) the continuously measured sensor values (angular acceleration) CCx, CCy are integrated once over time to deliver angular speed values ω_x, ω_y, and a further time to yield angular sweep values A_x, A_y.

For each axis X, Y, the obtained movement value pairs (ω, A) are continuously compared to predefined threshold pairs (ω_Ti, A_Ti) and (ω_T2, A_T2).

Comparison is effected by comparing the value of angular velocity ω (speed value) to the corresponding speed threshold values ω_Ti, ω_T2 and by comparing the angular sweep value A (motion value) to the corresponding thresholds A _Ti, A _T2- As a result of this comparison, the movements value pair (ω, A) is only considered to be above threshold if both values are above their corresponding threshold values.

As long as the movement value remains less than the first threshold, operation is continued normally. - If for one axis X, Y, the movement value pair (ω, A) exceeds the first threshold (coχi, A_Ti), but remains lower than the second threshold (coχ2, A_T2), controller 36 switches projector 10 to safe mode. In the safe mode, laser light source 24 is operated at reduced power, such that light output levels are eye-safe. At the same time, modulation of the modulated light 20 according to image data is stopped. Instead, light valve 30 is driven by controller 36 in a way to display only a simple frame image consisting of lines designating the outer boundaries of image 22. Operation in this safe mode is continued as long as the continuously sensed and calculated movement values (ω, A) remain above the first (but below the second) threshold. If the movement value falls below the first threshold, operation in the safe mode is nevertheless continued for a predetermined safety period of time, in order to give a user time to accommodate to a new projection situation. After this safety period, projection is automatically resumed.

If a movement value exceeding the second threshold (ω_T2, A_T2) is detected, controller 36 turns off the laser light source 24. In this case, the projector 10 does not return to normal operation by itself, but has to be manually restarted by a user's external input.

The threshold values may vary depending on the type of projector 10. As a preferred embodiment, the first threshold may be chosen e. g. at coχi corresponding to a movement of 10°/s and a sweep of A_Ti = 5°, indicating a major redirection of the image. The predetermined safety period for re-powering may be chosen to be e. g. at 3 s.

The second movement threshold value is intended to indicate a particularly safety relevant movement of the projector, e. g. very fast movement as would occur if the projector falls off a table. Correspondingly, the second threshold value C0χ2 may be chosen e.g. to correspond to 30°/s and a sweep A_T2 of 10°.

In the following, a data processing algorithm will be outlined as an example of how the sensor values may be digitally processed within the central controller 36 to achieve the above behavior. It should be understood by the skilled person that this processing should serve only as an example, and that actual data processing may be organized differently for different projector applications. In particular, more optimized algorithms may be employed that require less processing capacity and memory from the central controller 36.

The sensor delivers the values α_x, α_y at a certain rate (e.g. 100 Hz). The rate should be high enough to quickly react to any security relevant situation in time. For example, the rate could be 50 Hz, depending on the sensor used. These values are continuously stored to a memory within the central controller 36 in such a way that the values from the latest 5 seconds are available to the system. In a first step of data processing the product of each acceleration value α with the accompanying time interval (e.g. 1/100 Hz = 0,01 s) gives the change in velocity within this time interval. The summation of all the changes deliveres the actual velocity. A like processing of the velocity data gives the sweep angle A_x A_y of the projector. In combination, the described processing deliveres the complete state of movement of the projector.

For the control process it is assumed that the projector when switched on is in a safe and stable position. So the movement values are cleared at that time. As very small and slow movements can not produce a hazardous situation as addressed with this invention, the control mechanism does not accumulate data as long as the acceleration values of the sensor are below a predefined trigger threshold value. In case an acceleration value above the trigger threshold is detected, the process described above is started and velocity and change in position (i.e. the sweep angle since start) is derived and compared to the threshold values for that axis. In case the projector has not been turned off but the velocity went below threshold, the memory may be cleared after a few seconds in order to prevent a long-term built-up of values due to sensor biasing, that would cause safety actions without need.

In operation of the projector 10, the security function thus implemented within controller 36 will work as follows: As long as the projector 10 is positioned in a stationary manner, video projection will occur normally. Also, minor impact leading to only very limited or slow movement of the projector 10 will not influence operation. If however, the projection region is substantially redirected, as may occur either intentionally if the user tries to adjust the position of the image 22 on the screen 12 or unintentionally by pushing of the projector or tripping over the cables, the projector will enter the safe mode and only project an (eye-safe) frame. The user may thus still use this frame to position the image, but the redirection ofthe projection region will not cause an eye hazard.

In case the movement is too fast and/or too large, the controller 36 will turn off further light projection. Fig. 3, fig. 4 show a second embodiment of aprojector 10a. Since the second embodiment in large parts corresponds to the first embodiment, only differences will be explained. Like parts are designated by like reference numerals.

The projector 10a according to the second embodiment also projects an image 22 onto a screen 12. However, in contrast to the projector 10 of the first embodiment, the image is not projected as a modulated light bundle 20, but as a single scanning light beam 20a which is continuously scanned over the area ofthe image 22 in a raster scanning manner, i. e. in lines 21. Scanning of the laser beam is achieved by a scanning device 30a within the casing 14, where a pair of tilt mirrors (or alternatively a two- axes deflection mirror) deflects an incident laser light beam 26 emitted from laser light source 24 to achieve the raster scan. The scanning unit 30a and the laser light source 24 are controlled by central controller 36. An image 22 is displayed according to video data by controlling the intensity ofthe laser light beam 26 in accordance with the present aim ofthe scanning beam 20a at each point in time. This setup is generally known to the skilled person, so that further details of construction and control of the light source 24 and the modulation and projection arrangement 18 will not be further discussed. As also known, the laser light beam 26 may be generated by multiple laser light sources of different color and time- modulated intensity to project a color image 22.

Identically to the first embodiment, an inertial rotation sensor 40 is provided delivering sensor values CCx, 0Cγ indicating rotation about the X- and Y-axes. Additionally, acceleration sensors 44, 46 are provided. The acceleration sensors 44 and 46 are piezoelectric sensors acting as dynamic force and acceleration detector. An inertial mass is provided over a piezo material. In case of an acceleration of the sensor in the direction of the sensor axis, the mass element presses against the piezo material leading to a sensor output signal indicating the amount of acceleration in the sensor direction. As an example, capacitive micromachined accelerometers, available e.g. fromFreescale Semiconductor Inc., could be used. In the described embodiment, accelerometer 44 a_x is arranged with its sensor direction in the X-axis and delivers an acceleration sensor value in this direction, while accelerometer 46 is arranged in the direction of the Y-axis, delivering an acceleration value a_γ.

A controller 36 processes the different sensor values CC_x, α_γ , a_x, a_γ. These are, for each sensor value, separately processed and compared to two thresholds as described above: By once and twice integrating the value over time, a motion and a speed value are obtained. These are continuously compared to the two threshold pairs. If the first threshold is exceeded for any of the measured movements (rotational movements around X axis, rotational movement around Y axis, linear movement in X direction, linear movement in Y direction), safe mode is entered. Similarly, if for any of the values the second threshold is exceeded, the projector is turned off until it is manually restarted.

The invention has been illustrated and described in detail in the drawings and foregoing description. Such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.

As an example of a possible modification, different movements may be sensed. While the above description does not show a detection of movement in the direction (or rotation around) the optical axis, such movement may also be detected and compared to predefined thresholds. This especially applies to linear movements in the direction of the optical axis, because this may lead to creating an eye hazard in a place which previously was far enough away from the device. While in the above examples either a raster scan or a two-dimensional light valve were described, it is alternatively also possible to provide a one-dimensional light valve and scan the resulting line bundle over the screen.

In the claims, the word "comprising" does not exclude other elements, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain 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.

Claims

CLAIMS:

1. Projection apparatus comprising a freely displaceable enclosure (14), and within said enclosure (14) a laser light source (24), a modulation and projection arrangement (18) for modulating light (26) from said light source (24) according to image data and for projecting said modulated light (20, 20a) into a projection region outside of said enclosure (14), and a security unit including at least one inertial sensor (40, 44, 46) for detecting acceleration and/or movement of the enclosure (14), where said security unit is adapted to determine a movement value (ω, A) corresponding to a movement of said enclosure (14) leading to a displacement of said projection region, and to compare said movement value (ω, A) to a movement threshold (GO_T, A_X) and turn off or reduce the intensity of said projected light (20, 20a) if said movement value (ω, A) is above said movement threshold (CO_T, A_T).

2. Apparatus according to claim 1, where said inertial sensor (40) is adapted to sense rotation about at least one rotation axis (X, Y).

3. Apparatus according to claim 2, where - said modulated light (20, 20a) is projected into the direction of an optical axis, and said rotation axis (X, Y) is arranged at an angle with the optical axis.

4. Apparatus according to one of the above claims, where - said inertial sensor (44, 46) is an accelerometer including a proof mass and a deflection sensing circuit.

5. Apparatus according to one of the above claims 1-3, where said inertial sensor (4) is a gyroscope including a moving mass and a deflection and/or reaction force sensing circuit.

6. Apparatus according to one of the above claims, where said movement value comprises at least a motion value (A) indicating an amount of displacement and/or rotation and a speed value (ω) indicating a change rate of an amount of displacement and/or rotation, - and said threshold value comprises a motion threshold value (C0r) and a speed threshold value (A_τ), and said security unit is adapted to compare said movement value to said threshold value such that said movement value is above said threshold value only if said motion value (A) is above said motion threshold value (A_T), - and said speed value (ω) is above said speed threshold value (C0r).

7. Apparatus according to one of the above claims, where said security unit is adapted to compare said movement value (ω, A) to at least a first movement threshold value (α>τi, A_Ti), - and in case that movement value exceeds that first movement threshold value, to operate said modulation and projection arrangement (18) and/or said light source (24) such that only light of reduced intensity is projected.

8. Apparatus according to claim 7, where - said modulation and projection arrangement (18) is adapted to project said modulated light (20, 20a) to display an image (22) within an image region, and said security unit is adapted, in case said movement value (ω, A) exceeds said first movement threshold value (CO_TI, A_Ti), to drive said modulation and projection arrangement (18) and/or said light source (24) to project light displaying a pattern image showing the extent of said image region.

9. Apparatus according to one of the above claims, where said security unit is adapted to compare said movement value (ω, A) to a second movement threshold value (ωχ₂, A_T2), - and in case said movement value (ω, A) exceeds said second movement threshold value, to operate said modulation and projection arrangement (18) and/or said light source (24) so that said projected light is turned off.

10. Method for operating a projection apparatus including a freely displaceable enclosure (14), and within said enclosure (14) a laser light source (24) by operating said laser light source (24) to generate laser light (26), modulating said laser light (26) according to image data and projecting said modulated light (34) into a projection region outside of said enclosure (14), sensing acceleration and/or movement of the enclosure (14) using at least one inertial sensor (40, 44, 46) to determine a movement value (ω, A) corresponding to a movement of said enclosure (14) leading to a displacement of said projection region, and comparing said movement value to a movement threshold (coχ, Ax), turning off or reducing the intensity of said projected light (20, 20a) if said movement value is above said movement threshold.