WO2009003510A1

WO2009003510A1 - Lens for laser projection

Info

Publication number: WO2009003510A1
Application number: PCT/EP2007/056576
Authority: WO
Inventors: Henning Rehn; Oliver Drumm
Original assignee: Osram Gesellschaft mit beschränkter Haftung
Priority date: 2007-06-29
Filing date: 2007-06-29
Publication date: 2009-01-08
Also published as: TW200909975A

Abstract

The invention discloses an apparatus and a method for compensating for at least one non-linearity which arises as a result of movement of a light deflection device, particularly as a result of oscillation of at least one deflection mirror in a laser projection system, wherein the apparatus has a lens system having at least one lens which provides a distortion which compensates for the non-linearities, and also a projection system, particularly a laser projection system, having such an apparatus.

Description

Lens for laser projection

Technical area

The present invention relates to a device and a method for correcting nonlinearities arising from movements of light deflecting devices, in particular the variable speed of a projected onto a screen spot, laser projection systems, and a projection system, in particular a Laserpro ^¬ jektionssystem with such a device.

State of the art

In projection systems using a laser and a deflector for imaging, the projection beam generated by the laser must be moved at a very high speed on the projection plane to produce the image. For this, a rapidly rotating polygonal mirror for the Zeilenab ^¬ steering and an oscillating mirror for the horizontal Ablen ^¬ effect is used for example. However, there are also vibrating (micro) mirrors in two axes, which make the use of two mirrors unnecessary. In order to build up an image by means of such a mirror, it is set in a harmonic oscillation, which causes the corresponding deflection of the projection beam.

The disadvantage of this, however, is that due to the vibra ^¬ movement movement, the speed of the spot on the screen over the deflection Ü is not constant. This leads to the fact that in the edge area of the image, ie at the reversal points of the oscillation movement, the spot velocity slower, which would result in a higher brightness at constant laser power.

In order to produce a uniformly bright image, according to the prior art, the power of the lasers at the reversal points, ie toward the edge of the image, is reduced in relation to the value in the center of the image. Because of this dimming of the order ^¬ periodic points a light loss of up to 60% is produced.

Since the power output of lasers, in particular of laser projectors, usually has to be limited due to a limited maximum power of the available laser sources and also the requirements regarding eye safety, it is often not possible to simply increase the light intensity in the center of the image increase, whereby the possible image brightness of such a laser projection system is limited.

In the prior art, DE 10 2004 027 674A1 proposes to compensate for the non-linearities of the mirror oscillations by correspondingly adapting the time span during which the energy used for the representation of a pixel is emitted. For this purpose, Kings ^¬ NEN example, be adjusted when using a pulsed La ^¬ serstrahls the time intervals between the pulses. Since one pixel is generated from a plurality of pulses, its brightness can be controlled by the number of pulses generated by the pixels.

A disadvantage of this prior art, however, is that a complex control for the laser is necessary. This means a considerably increased electronic effort, which in turn makes the entire laser projection system more expensive. ert. In addition, the possible image brightness is also reduced here.

Presentation of the invention

The object of the present invention is, therefore, an on ^¬ direction and provide a method by which the efficiency of a laser projection system is increased by reducing dimming losses.

This object is achieved by an apparatus and a method for compensating at least one nonlinearities ty which result from movement of a Lichtablenkeinrich-, in particular at a vibration of at least one deflection mirror in a laser projection system is formed, - in particular from variations in a Spotge ^¬ speed of a projection - wherein the pre ^¬ direction, a lens system having at least one lens comprises up, which provides a distortion that compensates for the nonlinearity, and a projection system comprising such a device.

The inventive Upstream of Linsensys ^¬ tems - that a lens - between the mirror and process jektionsebene can be achieved that the distortion of the lens system, the speed fluctuations of a spot completely or partially eliminated. According to the invention be ^¬ acts so the distortion, that the amount of Ge ^¬ speed of the image projected on a screen spots is constant or at least minor variations on ^¬ has, as in the prior art. As a result, temporally equidistant pixels are generated, so that even with variable mirror speed and constant laser power have the same brightness on ^¬ by the laser pixels generated. The lens system can consist of a single lens, but is advantageously made up of several lenses. Advantageously, cylindrical lenses can also be used.

The use of an f-theta lens for a Laserpro ^¬ jektionssystem is described in DE 4324849, but this distortion is designed. In contrast, ^¬ but on targeted manner to the image recorded the presented optics to said linearization effect be ^¬ riding determine.

In a particularly preferred embodiment, in which the mirror oscillation takes place about a first and a second axis, wherein the angular amplitudes for the first and second axes may be different, the distortion of the image is tuned to the greater of the angular amplitudes. The mirror itself is preferably a micromirror oscillating in two axes, which may preferably have a size of 0.5 mm to 1.5 mm.

In another preferred embodiment, the distortion along one direction of the spot movement may be provided by means of the lens system while along the other axis the varying pixel brightness is compensated electronically as in the prior art, ie by reducing the laser power at the image edge. This has the advantage that the rapid movement of the lens system is corrected, in particular at different velocities along the axes ^¬ union, while along the slow moving direction of the light intensity is dimmed. This can increase the efficiency the light output can be increased by more than 20%. In this case, advantageously, a cylinder lens system can be used.

If, as a further embodiment, showing a ro- used tationssymmetrisches lens, must be into account ^¬ Untitled that due to the distortion of the present invention initially a pillow-shaped portion is projected. To get a rectangular image, the corners of this area must be hidden electronically. This causes a certain loss of light, which is however surpassed by the overall light gain achieved, so that even in this embodiment, an over ^¬ over the prior art by at least 10% higher Effi ^¬ ciency is achieved.

It is particularly advantageous if the lens system provides a positive or negative angular magnification. As a result, with regard to the requirements of eye safety, a higher total luminous flux can be permitted because they ultimately relate to the maximum luminance in the projection system and reduce the luminance at the same luminous flux compared to the original double angle amplitude of the mirror oscillation by imaging enlarged projection angles.

It is particularly advantageous according to the invention before use ^¬ direction in a laser projection system comprising a plurality of laser sources of different wavelength. Such laser projection systems can be designed as individual ^devices or in mobile phones, digital cameras, Embedded camcorder, PDA or multimedia ^playback devices.

Further advantages and preferred embodiments are defined in the subclaims, the description and the drawings.

Brief description of the drawings

The invention will be explained in detail by means of execution ^¬ examples. The embodiments shown in the figures are purely exemplary in nature and should not be used to limit the scope of the invention to the illustrated embodiments. The figures show:

Fig. 1 is a schematic representation of a temporal

A laser power for the projection of a constant brightness image in a two-axis oscillating mirror according to the prior art;

2 a schematic representation of the luminous flux losses due to the dimming on the vertical and horizontal image edge as a function of the deflection angle (= double tilt angle) of the mirror;

3 is a schematic representation of a preferred embodiment of the invention according Kom ^¬ compensation of the variable spot speed leading distortion for different Winkelampli- tuden the mirror oscillation; 4 shows a schematic representation of the image projected onto a screen without an objective and with an objective providing the distortion according to the invention;

Fig. 5 shows a first, particularly preferred Ausführungsbei ^¬ game for an inventive lens system for monochromatic laser light;

Fig. 6 is a schematic representation of the distortion provided by the lens system shown in Fig. 5;

Figure 7 shows a second, particularly preferred Ausführungsbei ^¬ play of the lens system according to the invention for a laser projection system with three laser wavelengths. and

FIG. 8 A schematic representation of the distortion provided by the lens system shown in FIG. 7.

Preferred embodiment of the invention

In on the flying-spot-principle-based projection systems, preferably in laser projection systems, the laser light ^¬ bundle used for the formation of the image is deflected by moving mirrors. The image content is displayed on the screen in that the laser power is modulated by the image information corresponding to the current spot position.

For the vertical and horizontal deflection of the laser ^¬ beam, the mirror is usually harmonic Vibrations offset. The vibration used most frequently is a sine wave, which causes a movement of the spot on the screen, which can be expressed mathematically ^¬ table (such calculations are for a sinusoidal oscillation in a similar manner mög ^¬ Lich).

The vibration of a scanner mirror in a plane

θ = θ _m ήnωt (1) causes an angular velocity of the mirror of

θ = 6> _m ωcos ωt = ω-] θ ² - θ ² (2)

If the angle of the beam reflected at the mirror is referred to the axis with 3 = 2 θ, the impact point on the screen is given by the equation

y _o = z-tan3 (3)

given. This leads to a spot speed of

and at the edge {θ → θ _m and y ₀ -> 0)

yo + tyo j

Ky ₀ ) - f - (5)

to greater brightness at the reversal points.

At these reversal points, therefore, the state of the art is used to produce a uniformly bright image Reduces the laser power, resulting in a light loss of up to 60%.

Fig. 1 shows such an attenuated laser output signal for an image constant brightness, the Ablenkspie- gel vibrations in two directions executes each with a different period, and wherein the Abschwä ^¬ deviations of the laser output signal is to be seen in accordance with the Spie ^¬ gelbewegung.

Fig. 2 shows the resulting light losses as a function of the angular amplitude of the mirror oscillation for conventional dimmed laser projectors, wherein on the x-axis, the angle amplitude in ° and on the y-axis, the loss in% are. Since mirrors with Winkelamplitu ^¬ can be realized only with great difficulty to over 10 ° in the present state of the art, the minimum occurring at RESIZE ^¬ ßeren angles can hardly be achieved; the dimming losses will therefore be on the order of 60%.

To compensate for this loss of light, a device, in particular a lens system of at least one lens is introduced Inventions according to the scanning mirror, which provides a distortion that kom ^¬ compensated variable spot velocity due to the mirror oscillation.

A lens, which in the projected image Ver ^¬ drawing

y _W -f * nS ₍₆₎

/ * Tanύ introduces, changes the location of the laser spot on Projekti ^¬ onsschirm according to

y (S) = fton3 (β + ϊ) = y _o (β + ϊ) (7) According to the invention, a constant speed is to be achieved by a correspondingly selected distortion

y = f (1 + tan ² 3) (ß (3) + l) + tan S ^ - 3 = const. (8) dθ

the spot can be reached on the screen.

The distortion resulting from solving this equation

ß {3) = & _m cot 3 aresin 1 (9)

causes a constant amount of spot speed on the screen

y {β) = f3 _m aresine - = y _m arcsin (sin ωt) (10)

As a result, a lens with this pattern of distortion linearizes the spot movement in one dimension, ie for one axis of oscillation of the mirror. For the A ^¬ set this compensation method in two dimensions, that is, for a rectangular image representation means of a vibrating with- in two mutually orthogonal axes mirror analogous considerations are required.

3 schematically shows the course of the distortion for different angular amplitudes of the mirror oscillation, wherein the distortion in% and on the y axis are shown on the x-axis. Axis of the angle to the optical axis of the lens is plotted in °.

The graphs 2, 4, 6 show in comparison the distortions for three different angular amplitudes; wherein the graph 2 shows the course of the distortion for a mirror with an angular amplitude of 10 °, graph 4 for a mirror with an angular amplitude of 15 ° and graph 6 for a mirror with an angular amplitude of 20 °.

Since the oscillation amplitude predetermines the course of the distortion, in the case of mirror oscillation in two axes with different amplitudes, the linearization can only be exact along one axis. With the commonly clotting ^¬ gen differences between two angular amplitudes of the distortion is a large part of the advantages of the invention described remain effective for one of them or at an intermediate value at design; the variation of the spot speed along the other axis is still significantly lower in this case than without compensation. Remaining deviations of the location and the speed of the spot from the ideal case can be compensated electronically.

For this purpose, information about desired and actual coordinates of the projected pixels can be stored in suitable form in a corresponding electronic device and the instantaneous deflections of the mirror can be incorporated in real time. The same electronic device can then take over the compensation of a remaining color in the lens design transverse chromatic aberration; Transformations of the image usually implemented in projectors such as keystone correction, mirroring and the correction of the image flying-spot projection typical distortion ("bow") can also be located here.

In addition, the electronic device can be designed to provide a difference between existing and optimum distortion for pixels outside the oscillation direction corrected by the device according to the invention.

In addition, the electronic device may contain pre-vomit ^¬-assured information on the optical properties of the projection system and advantageously be Kings ^¬ nen also include real-time data for the elongation of the mirror vibration.

It is particularly advantageous when the electronic Before ^¬ direction to compensate for the variation of the spot motion caused by the vibration mirror by means of dimming and / or coordinate transformation provides.

When lens design itself is the one aberrationsbe- bordered spot size, ie, the waist or the Laserbün ^¬ del interpret on the screen so that it is slightly smaller than the theoretical pixel size at the desired on ^¬ solution of the projection system. Thus, neither too high demands on the lens are made, nor is the resolution affected by crosstalk of the pixel information. In the course of the investigations, it has also been found that the depth of field of the projection is not significantly reduced in comparison with the case of a laser beam guided onto the screen without an objective lens. Color cross errors can be permitted within certain limits and be compensated electronically by taking into account the information about the corresponding positional deviation on the screen during the conversion of the image information into the laser current.

4 schematically shows the image regions illuminated on a projection surface, for: a generated image ^without device 8 ^{according to the} invention, a generated image with device 10 according to the invention, region 12 indicating the then usable rectangular region. Due to the cushion-shaped distortion, which depends on the distance from the optical axis, unusable corners 14, which have to be blanked out electronically, are produced. Despite this blanking, nevertheless, a light gain of approximately 10% compared with the prior art can be achieved with the device according to the invention.

Alternatively, cylindrical lens systems can also be used; for example, the movement of the spot for the fast axis, ie the horizontal deflection, and the nonlinearity along the other axis as in the prior art, can be compensated by dimming the laser at the edge of the image. In this case, the light losses Betra ^¬ gen half of what you would have without taking Whether ^¬ objectively accepted.

Ultimately, the objective of mutually orthogonally oriented cylindrical lens systems, or even free-form surfaces can be made to achieve the two-dimensional case, a dependency of the distortion of two orthogona ^¬ len angular coordinates without mixing term; Thus, in the end, one would still use the above described avoid protruding corners and the associated light losses.

Fig. 5 shows an advantageous embodiment of the lens system according to the invention, which is designed for monochromatic light, ie a laser wavelength. By means of the lens system shown schematically in Fig. 5 is achieved, the distortion shown schematically in Fig. 6 for monochromatic laser radiation at a Wel ^¬ lenlänge of 540 nm and a maximum angle of the scan mirror of 10 ° and a projection distance of 1 m. The lens system is designed so that the spot size but ^¬ rationsbedingte is smaller than the nominal Pi ^¬ xelgröße at VGA resolution, so that there are in the final composed image no uncertainty contributions due to a crosstalk of the pixel information.

Fig. 7 shows a particularly preferred Ausführungsbei ^¬ game of the lens system according to the invention for a laser projection system with three laser wavelengths that emit light in the range of 450 nm, 540 nm and 640 nm. The assumed tilt angle of the scanner mirror is in the ^¬ sem illustrated embodiment 5 ° and the projection distance is again 1 m. The exemplary ^embodiment shown here can be used, for example, for television sets. The distortion provided by the lens system in FIG. 7 is shown in FIG.

Likewise, as in the example for the monochrome laser, aberration-induced spot size is smaller than the pixel size, so that no additional blurring is introduced into the projected image. Disclosed is an apparatus and a method for compensating for at least one non-linearity, which is caused by a movement of a light deflecting device, in particular by a vibration of at least one deflecting mirror in a laser projection system, wherein the device comprises a lens system with at least one lens, the one Provides distortion compensating for the non-linearities and a projection system, in particular a laser projection system, with such a device.

Claims

claims

1. A device for compensating at least one non-linearity, which is formed by a movement of a Lichtab ^¬ steering device, in particular by a vibration of at least one deflecting mirror, in a laser projection system, characterized in that the device comprises a lens system with at least one lens that provides a distortion ready ^¬ which compensates the non-linearity.

2. Device according to claim 1, wherein the non-linearity compensated by the device is a variation in a spot speed on a projection ^surface .

3. A device according to claim 2 or 3, wherein the light deflecting means is a vibrating in two axes micromirror.

The device of claim 3, wherein the mirror vibration is a sinusoidal or sine-like vibration.

5. Apparatus according to claim 3 or 4, wherein the vibrations in the direction of the first and the second axis takes place at a different frequency.

6. Apparatus according to claim 3, 4 or 5, wherein the mirror has a diameter of 0.5 mm to 1.5 mm.

7. Device according to one of the preceding claims, wherein the distortion is positive, in particular pillow-shaped.

8. Device according to one of the preceding claims, wherein the distortion of the lens system to a

Angle amplitude of a mirror vibration direction is tuned.

9. Apparatus according to claim 8, wherein the distortion of the lens system is tuned to a maximum angle amplitude of the mirror oscillations.

10. Apparatus according to claim 8 or 9, wherein the device further comprises an electronic device which adjusts the distortion for the other Spie ^¬ gelschwingungsrichtung.

11. The apparatus of claim 10, wherein the electronic device provides the adjustment by means of dimming and / or coordinate transformation.

12. Device according to claim 10 or 11, wherein the electronic device provides data in real time for the elungation of the mirror oscillations.

13. The apparatus of claim 5 and 11 or 12, wherein the distortion of the lens system provides the compensation for the faster vibration direction and the electronic device provides the compensation for the slow vibration direction.

14. Device according to one of the preceding claims, wherein the lens system provides an angular magnification.

15. Device according to one of the preceding claims, wherein the lens system has at least one cylindrical lens.

16. A method for compensating for nonlinearity at least one non caused by a movement of a Lichtab ^¬ steering device, in particular by a vibration of at least one deflection mirror in a laser ^¬ projection system is formed, characterized in that a correction device is used comprising a lens system with at least one lens that records an image written by a light beam such that the nonlinearity is compensated.

17. The method of claim 16, wherein a device according to any one of claims 1 to 15 is used.

18. Projection system, with which an image is written by means of a light beam onto a projection surface, with a Lichtbündel donating ^{Lichtquel ¬} le and a light deflecting device that deflects the emitted light beam from the light source in the direction of the projection surface such that the Lichtbün- del on the Projection generated an image, since ^¬ characterized in that between the light deflection device and the projection surface a Vorrich- to compensate for at least one non-linearity, which is caused by the movement of the light deflecting device, according to one of claims 1 to 15 arranged.

19. A projection system according to claim 18, wherein the light deflection device is a scanner mirror, in particular a two-axis oscillating micromirror.

The projection system according to claim 18 or 19, wherein the movement of the light deflecting means is a sinusoidal or sine-like vibration.

21. A projection system according to any one of claims 18 to 20, wherein the light source is a laser or a laser system.

22. The projection system of claim 18, further ^comprising an electronic device that controls the power of the light source.

23. The projection system according to claim 22, wherein the electronic device contains previously stored information about the optical properties of the projection system and / or provides data in real time for the elongation of the mirror oscillations.

24. The projection system according to claim 18, wherein the extent of an area illuminated by the light beam on the projection surface after passing through run the device is less than or equal to the required pixel size.

25. A projection system according to any one of claims 18 to 24, further comprising an electronic device adapted to correct lateral color aberrations.

26. A projection system according to any one of claims 18 to 25, wherein the generated image is constructed line by line.

27. A projection system according to any one of claims 18 to 25, wherein the generated image is constructed by a Lissajous figure.

28. The projection system of any one of claims 18 to 27, wherein the projection system a Laserprojektionssys ^¬ system, in particular a TV is.

29. The projection system of any one of claims 18 to 28, wherein the projection system a Laserprojektionssys ^¬ system, in particular a mobile projection system or embedded in a mobile terminal Projekti ^¬ onssystem is.

30. A projection system according to any one of claims 18 to 29, wherein an incident on the projection surface luminous flux is between 5 Im and 30 Im.