EP0991972A2

EP0991972A2 - Projection device

Info

Publication number: EP0991972A2
Application number: EP99916841A
Authority: EP
Inventors: Gerd Rieche; Dietrich Schmidt; Jürgen PUDENZ; Hans-Jürgen Meissner; Hans-Joachim STÖHR; Eberhard Piehler; Rainer Schnell
Original assignee: Carl Zeiss Jena GmbH
Current assignee: Jenoptik AG
Priority date: 1998-04-28
Filing date: 1999-03-19
Publication date: 2000-04-12
Also published as: WO1999056166A2; WO1999056166A3; JP2002508093A; US6580469B1

Abstract

The invention relates to a projection device, comprising a matrix (50) for producing a video image, said matrix being located in an image plane, an optical system (9) for projecting the video image onto a screen, and a light source (3, 30) for illuminating the matrix (50). According to the invention, a device is provided with which the whole video image can be evenly illuminated.

Description

Projection device

The invention relates to a projection device with a matrix located in an image plane for generating a video image, with optics for projecting this video image onto a screen and with a light source for illuminating the matrix

Such a technology is known from the video projection devices which are already commercially available today, in which an LCD matrix, like a slide in a slide projector, is installed between a light source and an optical system and is imaged by the latter on a screen

The LCD matrix is controlled, for example, for the display of video images. With the aid of the technology known from slide projection, a video image can be displayed as a large image on a screen. This large image technology is considered future-oriented, since electronic picture tubes can no longer be used with very large images

In addition to the above-mentioned through projection known from slides, an incident light projection with an LCD, as is known from episcopes, would also be suitable for this, the LCD then hitting in the image plane of the epsicope structure

If you want to use the incident light projection method, you can use a mirror matrix instead of the LCD matrix.A matrix of this type is available, for example, as a circuit from the company Texas Instruments.These are several matrix-type tilting mirrors, one for each pixel, digitally controlled in one of the digital ones In this case, a tilting mirror reflects the full light intensity, in the other state the mirror receives and reflects the light at an angle at which it can no longer be thrown onto the screen.This means that the corresponding image point is then on the screen except for small amounts of scattered light dark

The different Lichthel ability to display the gray or color value of a pixel is adjusted by applying a suitable pulse train to the mirror, so that for each pixel, only an intermediate value between full light intensity and dark is detected by an observer's eye

A disadvantage of the known episcope and slide projection method is, however, that a very high light output of the light source is required, the heat output of which could destroy the LCD, for example. That is why such projectors also require a high cow wall, which makes these devices heavy, unwieldy and expensive

In the case of the tilting mirror technique, the usual episcope technique is also unsuitable, since in the former the best image is achieved when the light only reaches the matπx at a defined angle, precisely that Setting angle of the tilting mirror for the dark value so that the light source from the mirror is only opposed to a small area of practically zero for reflection

However, the defined angle cannot be set with a concave mirror structure, as is known, for example, from episcopes for illuminating an image. In the case of illumination which is expediently carried out at a defined angle in tilting mirrors, much greater light losses must therefore be expected than in the known episcope technique

The object of the invention is to reduce the power loss of such projectors as much as possible and thus to create a compact video device of the generic type, in which the cooling problem is reduced despite the compact design

The object is achieved in that an arrangement is provided with which the video image is uniformly illuminated, and in particular a device for mixing the light of the light source via multiple reflections is provided between the light source and the Matπx and the mixed light from the device onto the Matπx is directed

The device according to the invention for mixing the light from the light source is used to generate a luminance on the matrix that is as uniform as possible. In the case of conventional lamps, there is an uneven luminance due to the turning ice or the volume that is always required for emitting light, which is why there is always a certain unevenness in the illumination It should therefore be taken into account that the light spot generated on the slide, on the image to be projected or on the LCD matrix should always be widened further than its dimensions, so that a light field which is as homogeneous as possible is possible. The resulting light losses are, however, reduced according to the invention by the fact that Light in the device for mixing reflects back and forth several times before it leaves this device again, so that the origin of each light bundle is lost from the emission volume of the light source. The light field thus generated then assigns to the device after leaving the device Mixing a very uniform luminance. Such a device for mixing can be, for example, an optical fiber or a mirror system for reflecting back and forth

The resulting advantage of mixing, which results in particular with regard to the required performance, can easily be illustrated by means of a numerical example. If conventional technology only assumed that an area which was twice as large as that required for the area of the image had to be illuminated the edge length is reduced by up to half with uniform illumination according to the invention. This means that only a quarter of the power is then required due to the device for mixing

The extreme gain due to the device provided for mixing according to the invention thus results from all things in that the size of the light spot is better adapted to the area of the image. The drastic reduction in performance that can be achieved in this way follows from the square dependence of the size of the light spot on the edge length to be illuminated Unexpectedly, however, it has also been found that the video images generated with the aid of the mixing device are of significantly higher quality than those without the device. This is primarily attributed to the fact that the more uniform illumination of the matrix according to the invention also allows a better reproduction of the image content

In a preferred development of the invention it is provided that the matrix is a matrix of digitally controllable tilting mirrors. In comparison with the aforementioned LCD matrices, the advantages of the mixing device are particularly advantageous with these matrices, with which, since the light in the essentially occurs only from the direction of the device for mixing, can also set a defined angle

As already explained above, a defined angle is expedient in the case of mirror mats, which can be maintained particularly easily by means of a corresponding geometric design of the projection device and a suitable geometric arrangement of the device for mixing with respect to the matrix

The light losses can be further reduced in particular if, according to an advantageous development of the invention, a coupling optic is provided between the light source and the device for mixing. The coupling optic ensures that the greatest possible amount of light from the light source enters the device for mixing, thus preventing it also avoidable loss of light

In the same way, another development of the invention has an advantageous effect on reducing the amount of light required, in which coupling-out optics are provided between the device for mixing and the matrix, with which the matrix can be illuminated. In particular, the angle for illuminating the matrix can be controlled in the case of the digitally controllable ones Adjust the tilting mirror with the decoupling optics by means of an appropriate geometric design so that the highest possible contrast for high-quality images can be achieved

According to a preferred development of the invention, it is further provided that a field lens is arranged in front of the matrix. With the aid of the field lens, for example, a magnification effect can be achieved with which an adjustment for the light leaving the device for mixing can be carried out particularly well on the image field to be illuminated , since the adjustment accuracy is increased due to the magnifying effect of the field lens. This makes it easier to bring the light spot and image field to cover. Above all for mass production, it becomes possible because of the simplification thereby advantageously to make the light field for illuminating the matrix particularly small dimensioning This feature also has a positive effect on performance savings

Scattering mirror surfaces with a subsequent focusing optics could be used as a device for mixing. Furthermore, optical fibers serve this purpose, which, however, then had to be rigidly attached so that the image field can shift when their position changes. In particular, however, it has proven to be advantageous if the device for mixing a body according to a development of the invention m has the shape of a geometric prism, in the base of which the light from the light source is introduced and from the top surface of which the mixed light for illuminating the matrix has been removed.This creates an effective mixture during the transport of light over the length of the geometric prism, while the light on it Side surfaces are reflected back and forth In particular, this development of the invention also has the advantage that such bodies can be easily manufactured, as a result of which devices according to the invention are particularly cost-effective for the consumer sector

In an advantageous development of the invention, it is provided that the geometric prism has a rectangular base, the aspect ratio of which is determined by the aspect ratio of the video image formed by the matrix

Here one makes use of the fact that the light emerging from the cover surface allows an adaptation of the two aspect ratios of the cover surface of the prism shape to that of the video image, in particular uniform illumination in all directions. When adapting the two aspect ratios, however, it should be noted that the aspect ratio by mirrors , Diaphragms, lenses, etc. in the light path behind the device for mixing the light emanating from it could be changed. The aspect ratios are determined in this context so that the light emerging from the body illuminates the matrix evenly in both planar extents export as an internally mirrored tube. This means that practically all of the light falling into the entrance of the device for mixing can be transmitted to the exit. However, it turned out to be considerably cheaper if the jacket compartments were used for mixing en body is not mirrored and the mixture takes place via multiple reflections due to total reflection on this lateral surface. This means that the mirroring can be saved, which is extremely advantageous for an inexpensive video device, in particular for the consumer market

In a preferred development of the invention it is provided that the ratio of the length of the prism axis to the lateral extent is greater than

5 / vV

where n denotes the calculation index of the material. In this relationship, one makes use of the knowledge that with light being reflected back and forth at least five times, a mixture that is sufficient for video projection already takes place. With the specified limit, the smallest length for the p-shaped can be Determine the body in order to achieve an effective device for mixing with at the same time small dimensions. The dimensions should not be too large, so that the projection device remains compact. When dimensioning the prism length of the mixing device, it is therefore recommended to stay below 100 to 200 reflections polygonal body is also inexpensively made of glass In the case of total reflection in particular, however, light losses can occur due to incorrect mounting of the prism, which, due to bending or contact of a holder with the polygon-shaped body, can in some cases prevent the totally reflective behavior of the body. In order to keep such light losses as low as possible, according to an advantageous development of the invention, it is provided that a holder for the body is made from a sheet metal with a thickness of less than 1 mm and in particular less than 0.5 mm, the holder only touches the body with an edge of this dimension. Due to the possible small contact surface of the holder on the polygonal body, light losses with the given dimensions are negligible.

Furthermore, according to a preferred development of the invention, a corresponding holder is characterized in that a holder for the body made of spring sheet metal is provided, the spring tension of which acts perpendicular to the prism axis and pulls the body perpendicular to the prism axis against an edge of the housing as an abutment and in that Shell surface of the body is provided a groove in which engages a spring attached to the housing.

A colored image display is also possible with the help of such matrices. One possibility is to provide a color wheel with different color filters between the light source and the matrix, which filters different colors of the light sequentially due to rotation, the information on the matrix being set synchronously with the current color of the light falling on the matrix. In a preferred development of the invention, this color wheel is arranged between the light source and the device for mixing. This location is particularly suitable because scattering in or on the color wheel, for example due to imperfections of the material or due to surface dust, is compensated for by the subsequent mixing, so that even with such errors, a high-quality video image is also possible.

According to a preferred development of the invention it is provided that an adjusting element for aligning the light emerging from the device for mixing is arranged behind the device for mixing on the matrix.

As has already become clearer above, it is particularly advantageous, in order to avoid light losses, in particular in the case of the small areas to be illuminated intended for tilting mirror matrices, if the light emitted from the device for mixing can be adjusted to the matrix. For this purpose, a single adjusting element is provided, the structure of which becomes clearer from an exemplary embodiment presented later.

The following explanations refer primarily to tilting mirror matrices as a matrix:

Due to the required low divergence for complete absorption when the video picture is switched dark and the desired high light intensity when switching on brightly so that a large screen can be illuminated, problems arise with a compact design, since on the one hand a long light path is to be created and on the other hand the power loss is economical should not lead to heat build-up in the components. With regard to the heat balance in particular, it should be noted that the Kφpspiegelmatπx is a micromechanical semiconductor device that works reproducibly only within a limited temperature range

In a preferred development of the invention it is provided that the light source is arranged close to the tilting mirror matrix and at an angle at which the light beam is directed away therefrom, and that a folded optical light path is provided for transmitting a light beam emitted by the light source to the tilting mirror matrix

With the folded optical light path, the corresponding length is set so that the light striking the tilt mirror mat has a suitably low divergence. However, according to the invention, it also fulfills another purpose, namely the light of the light source, which according to the invention is not directed directly onto the tilt mirror mat Redirect image display

That the light source is arranged in the vicinity of the tilt mirror mat, the light bundle being directed away from the tilt mirror mat, has two advantages. First, cooling, for example by means of a fan, can be provided in such a way that both the luminous volume, in particular a filament, of the light source as the tilting mirror matrix is also cooled by a single element. Secondly, the cooling leads to very stable and reproducible video images, since the entire heat of loss arises in the vicinity of the tilting mirror matrix, which means that the tilting mirror switches to other states, for example to display a darker video image. only a slight change in their heating due to the then increased absorption, so that the tilting mirror matrix is kept substantially temperature-stable by cooling and uniform heating by the light source. That is, the reproducibility of the images is essentially u n dependent on the image content displayed over time, in contrast to other arrangements. This enables a particularly compact video device to be created

In order to keep the required amount of light as small as possible so that the warmth problem is reduced even further, in a preferred further development of the invention it is provided that the folded optical light path is effected with two deflecting mirrors, between which a light guide extends due to the restriction to essentially two Deflecting mirror, the effort is reduced. The light guide provided ensures, in particular, a high light homogeneity, so that the tilting mirror matrix can be illuminated uniformly. This leads to a lower light output for the light source, since in principle only the flat area of the tilting mirror matrix needs to be illuminated the light guide is homogenized due to the back and forth reflection, that is, a uniform light spot is created for illuminating the tilt mirror matrix, which enables a particularly good image quality

In a preferred development of the invention it is provided that the light guide is a rectangular rod made of transparent material for the light of the light source with a cross-section adapted to the tilt mirror mat. In such a rectangular rod, the light, as is known from other light guides, is guided by total reflection was able to form such a rod with mirror layers, but is a In contrast, simple rod, for example made of glass, can be manufactured particularly inexpensively, as a result of which the price is reduced, which is particularly advantageous for the consumer sector

The cross-section adapted to the tilting mirror was selected for the further training in order to use almost all of the light emerging from the rod to illuminate the matπx by mapping the starting surface of the rod onto the tilting mirror mat. Due to this measure, a light source of lower power can be used than if the Edge of the tilt mirror matrix had to be illuminated over large areas. This measure also drastically reduces the heat problem

For the same purpose, according to an advantageous development of the invention, an coupling optic is provided between the light source and the rectangular rod for focusing the light bundle onto an input surface of the light guide. As a result of this measure, as much light as possible from the light source is coupled into the light guide, so that the power requirement of the light source is due then lower light losses can be reduced, which in turn reduces the warmth problem

According to another preferred development of the invention, a color wheel is provided between the coupling optics and the input surface of the light guide. A color wheel is known in the described generation of video images with tilting mirror matrices for displaying color images. With the color wheel, different color filters are sequentially connected in front of the light source, so that the Light source can be forwarded from different colors The tilt mirror matrix is controlled synchronously with the respective light color with the different color separations, e.g. the colors red, green and blue (R, G, B,). The impression of a color image is created by overlaying the color separations due to the Sluggishness of the eye

With regard to this development of the invention, the arrangement of the color wheel is particularly advantageous. Due to its position between the coupling optics and the input surface of the light guide, it is far from the heat-affected parts of the device, as can be seen in particular from an exemplary embodiment. In the exemplary embodiment, an air flow can also be used to cool the Aiming the light source and the tilt mirror mat simultaneously on the color wheel. A particular advantage of this arrangement is that light intensity fluctuations due to inhomogeneities of the color wheel and dust on its surface are also homogenized by the light guide, which leads to a particularly good image quality

The bundle of light can be aligned particularly well to reduce the power of the light source if, according to a preferred development of the invention, a zyhnderform adjustment element is provided in the folded optical light path, wherein a deflection mirror of the folded optical light path is attached in the adjustment element, with which the light of the light source onto the Tilting mirror matrix can be aligned For a particularly good alignment with the tilting mirror matrix, it is also advantageous if the entire light is focused on the tilting mirror matrix. According to a preferred development of the invention, an optical system for focusing the light beam on the tilting mirror matrix is arranged in the adjusting element is As has already been made clear in the case of the rectangular rod, it is particularly advantageous if a rectangular light surface is imaged on the tilting mirror mat. The focusing which is possible for this purpose can be carried out, for example, with the optical system which is arranged within the adjusting element by changing the location of the adjusting element Suitable focusing conditions can always be set when adjusting

In this regard, a preferred development of the invention further provides that a rectangular, light-emitting area fed by the light source is formed in front of the adjusting element and the adjusting element has an at least two-sided system with which the light-emitting area is imaged on the tilting mirror matrix

The rectangular area can be formed by the aforementioned rectangular rod. Further designs for the area fed by the light source are also possible and can be implemented, for example, by providing a rectangular aperture in the beam path

According to a preferred development of the invention, it has been found to be particularly advantageous for the compactness with good imaging properties if the imaging scale of the at least two-sided system is between 1 and 5. In the exemplary embodiment specified later, a reduction factor of 2 was chosen in particular

A favorable light output combined with a lower heat output results due to an improved adjustment possibility according to an advantageous development of the invention in that a field lens is arranged in front of the tilt mirror matrix. The adjustment is made easier in particular because the field lens makes the desired angle to the tilt mirror matrix, essentially the for optimal dark / light conditions, also during adjustment, the adjustment is also made easier because the field lens enables a large movement of the adjustment element into a small movement of the light beam on the tilting mirror matrix. This improved adjustment option is particularly necessary for a commercial video device, because the light path can be adjusted more easily, even with a very compact design of the device, and the light spot generated by the light source on the tilting mirror matrix is almost completely effortless with only small, tolerable cover The edge region of the tilt mirror mat can be guided one above the other

In particular, it is provided according to a further development of the invention that the light beam directed via the optical light path onto the Kippspiegelmatπx is directed through the field lens onto the Kippspiegelmatπx, while the light reflected from the Kippspiegelmatπx into the lens is unaffected by the field lens and enters the lens. This is for an increase in compactness is required, since the field lens then no longer interferes when it leaves the tilting mirror matrix. This can be achieved, among other things, by a special design of the field lens, in which a hole is drilled in the lens for the light reflected from the matrix

For a particularly inexpensive design of the video device, in particular also for the requirement of compactness, it is provided according to a preferred development of the invention that the field lens is vertical has a part-circular cross-section to the optical axis, in particular a semicircular cross-section, which is arranged between the incident light beam and tilting mirror, an opening defined by the deviation from the circular shape being between the tilting mirror matrix and the lens

The compactness of a video device of the type mentioned can also be increased in accordance with a further development of the invention, in which a final deflecting mirror is provided in the optical light path, which directs the light bundle out of a plane of the optical light path lying from this deflecting mirror and onto the tilting mirror mat optical path, the light is guided in three dimensions instead of one level

The invention is further illustrated in the following description of exemplary embodiments in conjunction with the drawing

1 shows a schematic illustration of the mixing chip used in the invention,

Fig. 2 is a schematic representation of a mixture based on a polygonal body

3 shows a perspective view of a projection system designed according to the invention with a tilting mirror matrix,

4 shows another perspective view of the projection system from FIG. 3,

5 shows a section through the projection system according to FIG. 3 and FIG. 4 according to the line A-A drawn in FIG. 4,

6 shows a beam guide with an adjusting element and the tilting mirror inside the

Exemplary embodiment from FIG. 3 to FIG. 5,

7 shows a sectional drawing of the adjusting element shown in FIG. 6,

8 shows an arrangement as in FIG. 1, but with a folded light path and additional

Color wheel

1 shows the basic principle with which a light bundle 2 is homogenized to improve the illumination of a matrix used for displaying a video image. The light bundle comes from a lamp, such as a halogen lamp, an arc lamp or the like, which is installed in a reflector and From there, an essentially parallel bundle of light emerges. The lamp and reflector form the light source 3

Such a light bundle 2 generally has angular divergences. The emission volume, which is formed, for example, by a luminous filament, also shines in the light source 3 an inhomogeneous spatial intensity distribution If one wants to direct such a light beam onto an LCD matrix or tilt mirror matrix, then such inhomogeneities on this matrix would cause uneven illumination, from which the problem of the image display on the LCD matrix or tilt mirror matrix suffers. According to the prior art, expediently a larger area is illuminated than the matrix, above all to reduce the influence of the decrease in light intensity due to angular divergence and spatially inhomogeneous light distribution towards the edges of the matrix

In the example of FIG. 1, however, a device for mixing 5 is provided, with which a homogenization of the luminance is brought about in such a way that only the desired area of the matrix can be illuminated with only a slight overlap of the edges. This leads to a higher luminance on the tilting mirror matrix. or it can save power for the light source 3, so that the cow wall is reduced because a light source 3 of lower intensity than conventional can be used

In the schematically drawn example of FIG. 1, the device for mixing 5 is a plane-parallel plate which is mirrored on both sides penetrated by the light bundle 2. The light bundle 2 is reflected in the plane-parallel plate by back and forth reflection of the individual light beams, as in FIG. 1 by arrows is indicated, widened and homogenized. This gives an almost homogeneous bundle of light at the exit of the device for mixing, so that the matrix only has to be illuminated in a field which corresponds approximately to the extent of the tilting mirror matrix. Lateral drops in the luminance in the edge regions contribute only little to the overall lighting and the resulting loss of light can be neglected compared to the lighting otherwise generated in the prior art without a device for mixing 5

The principle of image display with a matrix is additionally indicated in FIG. 1. A schematically illustrated Krppspiegelmatπx from a plurality of mirrors 7 directs the reflected light for the video image set on the tilting mirror matrix into a lens 9, which in turn projects the image onto a screen

All tilting mirrors are shown in FIG. 1 set for maximum reflection, except for a mirror 7 'which only opposes the edge of the photo 2. Only a little light, or only scattered light, is directed into the lens 9 by this mirror. This mirror 7' is therefore shown on the screen as a dark field. The tilting mirrors described here are available from Texas Instruments, USA

For a video image for which different mirrors 7, 7 'of the tilting mirror matrix are assigned to create the appropriate luminance for each pixel, such mirrors 7, 7', if they can only be controlled digitally, like the mirrors that are commercially available today , quickly switched back and forth for maximum reflection or minimum reflection. To this end, the tilting mirrors 7, 7 'are subjected to pulse trains, the dark / light keying behavior for each pixel of which is proportional to the brightness desired for this

In the device for mixing 5 shown in FIG. 1, it is advisable to provide at least the upper side facing the light source 3 with dielectric mirror layers in such a way that the jerk reflection results in Light source 3 remains as small as possible. For example, with suitably polarized light, arranging the plane-parallel plate in FIG. 1 at the Brewster angle also serves the same purpose

The jerk reflection is not disadvantageous even in the embodiment of FIG. 1, since the reflector provided in the light source 3 reflects jerk reflected light back onto the device for mixing 5. However, the widening of the light bundle 2 caused by the jerk reflection is then greater

As the preceding discussion shows, the device shown schematically in FIG. 1 for mixing, if, for example, dielectric layers or polarizers become necessary, is very complex, so that in the commercial field, where the price must be taken into account essentially, such mixing devices should avoid as much as possible

In contrast, another alternative shown in FIG. 2 is proposed, in which the device for mixing 5 is designed as a polygonal body. Only a section of the polygonal shape is shown in FIG

Light that falls from the base surface 1 1 of the body is reflected back and forth on the outer surface of the polygon, i.e. the individual polygon sides 12 and 13 due to total reflection because of the different angles of incidence and incidence of the individual rays of the light bundle 2, which always exist with extended light sources when entering the base area 11, a bundle of light 2 can be suitably homogenized with the device for mixing 5 shown in FIG. 2, the degree of homogenization essentially depending on the dimensions selected

2 shows two sizes, d for the length of the polygonal body and a for its lateral extent. The dimension d should not be too small so that enough reflections can take place. For practical use, a number of at least five reflections has been found Likewise, the lateral extension a of the polygon-shaped body, which is used here as a device for mixing 5, should be chosen so large that the tilting mirror mat 7 is fully illuminated. In this regard, an optics was used in the exemplary embodiment explained in more detail below, with which the exit surface 14 is mapped onto the tilting mirror matrix. Furthermore, the exit surface was kept rectangular in order to achieve the best possible illumination of the crooked mirror matrix with regard to the adaptation of the shape

Based on the above considerations of at least five times the reflection, the relationship arises with respect to the total reflection angle α

tan (α) = - 5a According to the Snel us calculation law, however, the following applies to air

n where n is the calculation mdex of the material of the polygonal body. Based on the known relationships between the angular functions, an estimate is made for the lower limit of the ratio of the length d to the lateral extension a of the polygonal body

d 5

-> a V n ² - \

If you want to avoid light losses due to light rays that enter at a very flat angle α and are not totally reflected, you can also mirror the side surfaces 12, 13 of the jacket. However, it has been shown that it is for reasons of cost and because the loss of light while observing the above estimated relationship remains in justifiable areas, it is cheaper to use total reflection in a polygonal body

This principle of homogenization was realized in a practical exemplary embodiment, which is explained in more detail below with reference to FIGS. 3 to 7. FIGS. 3 and 4 show different perspective views of the exemplary embodiment, from which the various features thereof can be found

A 120 W lamp 30 is used as the light source 3 here, which was already provided with a reflector by the manufacturer for the parallelization of light, the light of which is focused on the entry surface of a polygonal body 34 with the aid of an optical system 32. In order to increase the compactness of the device described by way of example To achieve, a deflection mirror 36 is provided between the optical system 32 and the rectangular body 34. Furthermore, a color wheel 40 is arranged between the lamp 30 and the polygonal body 34. This color wheel 40 has various segments 42, 44, 46 and 48, which are associated with dielectric filter layers for the colors red, green, blue and white are provided and with which the light bundle emerging from the lamp 30 is color filtered. The color wheel 40 rotates faster than 10 revolutions per second, so that light bundles of all colors given by the color filter on the color wheel within a period due to the sluggishness of the eye tspanne be directed to the Kippspiegelmatπx The information on the Kippspiegelmatπx 15 is controlled according to the currently effective color filter with the corresponding color separation, so that a colored image is captured in the eye of a viewer of the video image

Because of the focusing coupling optics 32, the light spot on the color wheel 40 is minimally expanded, so that the tilt mirror mat 50 for switching off misinformation by mixed colors when passing segment boundaries between the segments 42, 44, 46 or 48 at the focus of the light beam only needs to be switched dark for a short time These times are considerably longer in known devices, so that light losses are reduced due to this optical system 32 and the special arrangement of the color wheel 40 in the focus and in front of the polygonal body

The polygonal body 34 serves as a device for light mixing in order to compensate for inhomogeneities of the light emanating from the lamp 30 via reflections as far as possible polygonal body 34 multiple total reflections, so that at the output 52 of the polygonal body 34 a uniform, because of its rectangular cross-section, rectangular field is created.The light emerging from the surface 52 is deflected in an optical system designed as an adjusting element 54 with a mirror and then onto the Krppspiegelmatπx 50 thrown. Further details on this are described in the following FIGS. 6 and 7. However, it is noteworthy with this arrangement that the color wheel 40 is arranged in front of the polygonal body 34 intended as a device for mixing and homogenizing and not behind it and also any dust on this averaged by mixing with the polygonal body 34

The Kippspiegelmatπx 50 in the exemplary embodiment consisted of 845 x 600 tilting mirrors with dimensions 17 μm x 17μm. The polygonal body 34 had a suitably large length of 75 mm with an entry area of 4.8 mm x 7 mm, which is sufficient for the light at the The selected material, in the exemplary embodiment glass, suffers from total reflection more than 5 reflections of the individual beams of the light bundle 2 as it passes through the entry surface to the exit surface of the polygonal body 34. This dimensioning has proven to be extremely advantageous for a complete mixture

In the section shown in FIG. 5, the polygonal body 34 can be seen even more clearly. In the exemplary embodiment, this has a rectangular cross section in order to image the light emerging from its exit surface 52 via the optical elements described in more detail below on the likewise rectangular tilting mirror matrix. The polygonal body also exists Body 34 made of glass, so that the uniformity for low light losses can be produced with standard methods, because the uniformity of the polygonal body 34 is extremely useful for maintaining the total reflection conditions

In order to also reduce distortion of the polygonal body 34 and an abolition of total reflection conditions by contacting the jacket surfaces on a holder, which could lead to light loss, a holder 56 is provided, which is bent from a simple sheet metal that is less than 0.5 mm thickness This held the polygonal body 34 via a clamp Because of the small contact surface, practically hien-shaped, with a maximum extension perpendicular to the line alignment of the clamp of 0.5 mm, light losses that could arise locally due to the cancellation of the total reflection conditions are limited, the smaller the Is the better the undesired total reflection losses are avoided

The holder 56 is also designed to be resilient and pulls the polygonal body downward, as shown in FIG. 5, against edges 57 designed as cutting edges. These cutting edges also only have a small area as a support, as a result of which light losses have also been reduced. Against axial displacement of the body 39 is in this a groove, not shown, is provided, into which engages a spring which is also hidden in this view and which is arranged on a part of an adjustable part by screws The further beam path behind the polygonal body up to the tilting mirror matrix 50, from which the video image is projected onto a screen via an objective 60, can be seen in particular in FIG. 6. A bundle of light 62 emerging from the polygonal body 34 is passed over the adjusting element containing a mirror 64 54 to another mirror 66, which directs the bundle of light 62 out of the plane in which the bundle of light 62 is guided beforehand, directed toward the tilt mirror mat 50

The bundle of light reflected by this is then guided into the objective 60, which projects the image electrically set on the tilting mirror matrix on a screen.To improve the adjustment by means of the adjusting element 54, a field lens 68 is provided for reducing its movements by once the defined angle for the smallest Maintain intensity in the dark state on the tilting mirror matrix and on the other hand make the adjustment more sensitive

In order that the light coming from the tilting mirror matrix 50 remains uninfluenced by the field lens 68 and a very compact device is nevertheless possible, the field lens 68 is designed in the form of a part circle. In the exemplary embodiment, a semicircular field lens 68 was used. However, it would also be possible to insert a into a conventional circular field lens 68 to drill a suitable large opening for the light reflected by the tilting mirror matrix or to expose it in some other way

The mirror 66 and the field lens 68 in geometric relation to the tilting mirror matrix 60 and the adjusting element 54 were designed in such a way that after adjustment with the adjusting element 54, almost optimal imaging conditions always prevail

In order to create a compact video device, it has proven to be particularly advantageous to use the field lens 68 and possibly other optical elements, such as a lens in the adjusting element 54, to provide a reduction in the rectangular cross section of the exit surface of the polygonal body in the range from 5 to 1 A reduction by a factor of 2 was therefore used in the exemplary embodiment

As can be seen in particular from FIG. 3, the adjusting element 54 is fixed with a clamp 70, which is fastened to a base plate with screws 72. The adjustment takes place with loosened screws 72. The adjusting element 54 allows both rotation and displacement due to its cylindrical shape the tilting mirror matrix 50 to and from it. Both movements are sufficient to completely align the bundle of light guided by the lamp 30 via the subsequent optical elements to the tilting mirror matrix 50. In particular, the rotary movement of the adjusting element 54 is due to its cylindrical shape and its adapted mounting in the base plate suitable for the device to bring the rectangular beam of light 62 emerging from the polygonal body 34 to cover with the rectangular surface of the tilting mirror matrix. The possible shift in the direction of the light beam path also allows the light beam to focus better on the tilting mirror matrix 50 due to the fact that this shifting movement simultaneously adjusts an optical system 76 provided in the adjusting element 54 on the optical axis, which makes focusing possible. As can be seen in particular from FIG. 3, the adjusting element 54 is held in a trough-shaped depression and in principle has other walls contact only with two straight lines This type of storage, in particular by forming inclined walls of the trough, allows both simple and reproducible rotation and a displacement of the adjusting element 54

The details of the adjusting element 54 can be seen in the section shown in FIG. 7. The polygonal body 34 is in particular guided into the adjusting element 54. A recess 78 is provided in the adjusting element 54. The light is then guided and focused via a three-arm optical system 76 The axis coincides with the cylinder axis of the adjusting element 54, which simplifies the adjustment in particular because the focusing by displacement and the alignment by rotation are decoupled from one another

By means of the optical system 76 and the field lens 68, an image of the exit surface of the polygonal body 34 on the tilting mirror matrix of 1 2 is achieved. Other reduction factors are also possible. However, the aim is to keep this factor between 1 and 5 so that optimal adjustment properties are at the same time more compact Construction are possible

As can already be seen from the example according to FIGS. 3 and 4, the device has a folded beam path which has some special features compared to known radiation paths. For this purpose, FIG. 1 will be briefly discussed again

1 shows a light source 3, from which an almost parallel bundle of light 2 is emitted. For this purpose, the light source 3 is equipped with a filament, a gas discharge or arc lamp, the light of which is parallelized with the reflector indicated schematically in FIG. 1. This light is conspicuous a tilting mirror matrix consisting of a plurality of tilting mirrors arranged in rows and columns. The tilting mirrors, as previously described, are loaded with the information of a video image. The untilted tilting mirrors 7 fully reflect the incident light into the lens 8, which the tilting mirror matrix then depicts on a screen Furthermore, a tilting mirror 7 'is indicated schematically in FIG. 1, which is opposed to the light beam 2 at its set angle. This means that only a little scattered light can fall into the lens 8 from this tilting mirror

Since such light sources 1 are usually extended light sources which have a high beam product even when the bundle of light 2 is approaching parallel, there are 2 different light beams of different angles in the bundle of light, so that the required dark / light behavior can only be achieved if the light source 1 is arranged at a certain distance from the tilting mirror matrix 3. This contradicts, for example, the requirement to create a particularly compact video device. In order to provide a compact device, it is known in optics to use a folded light path, i.e. to guide the beam path with several deflecting mirrors in one plane or in space. There are various possibilities for this given

Unexpectedly, however, the way specified in FIG. 8 is to provide a folded light path in which the light source is arranged in the vicinity of the tilting mirror matrix and that originating from the light source Beam 2 directed away from the tilting mirror matrix is preferable to other ways of folding a light path. It would be expected that the power loss generated by the light source 3, given the high light outputs for displaying video images with a screen diagonal of approximately 2 m and larger, would heat up the tilting mirror matrix to such an extent that it may no longer work properly. However, a significant advantage is gained in that a single cooling stream 6 can be used, for example only a single fan, which cools both the tilting mirror matrix and light source 3. With other folds of the light path, two fans would possibly be necessary for cooling because of the large distance required between the tilting mirror matrix and the light source 3. The advantage of an arrangement according to FIG. 2 therefore has an increased compactness. Another advantage results from the fact that the uniform heat dissipation of the lamp 3 and the cooling flow 6 on the tilting mirror matrix set a constant temperature which has an extremely favorable effect for the display of reproducible images. In other cases, the tilting mirror matrix, the power loss of which depends on the image content due to the different number of tilted tilting mirrors 7 ′, would provide poorer image quality.

With smaller light outputs of the lamp 3, one can even dispense with a fan for generating the cooling flow 6. The cooling current is created solely by convection when lamp 1 and the tilting mirror matrix are located on the top of the video device, since the heat generated rises and thus creates a suction for cooler air from below.

In order to make it clear how the structure shown in FIG. 8, in particular also with regard to cooling, affects other components, a color wheel 10 is also shown in this figure. Such color wheels are used to be able to display colored images.

The previously described exemplary embodiment of a projection device for imaging a video image displayed on a tilting mirror matrix is given only by way of example. As has already been made clear above, by setting different distances, using different polygonal bodies, lamps or optics, different optimizations can be carried out depending on the given requirements.

Claims

Expectations

1. Projection device with a matrix (50) located in an image plane for generating a video image, with optics (9) for projecting this video image onto a screen and with a light source (3, 30) for illuminating the matrix (50), characterized by an arrangement with which the video image can be illuminated evenly.

2. Projection device according to claim 1, characterized in that between the light source (3) and the matrix (50) a device (5) for mixing the light of the light source (3) is provided via multiple reflections and the mixed light from the device (5 ) from the matrix (50).

3. Projection device according to claim 2, characterized in that the matrix (50) is a matrix (50) of digitally controllable tilting mirrors (7, 7 ').

4. Projection device according to claim 2 or 3, characterized by a coupling optics (32) between the light source (3, 30) and the device (5) for mixing.

5. Projection device according to one of claims 2 to 4, characterized in that between the device (5) for mixing and the matrix (50) a coupling optics (76) is provided with which the matrix

(50) can be illuminated.

6. Projection device according to one of claims 2 to 5, characterized by a field lens (68) in front of the matrix (50).

7. Projection device according to one of claims 2 to 6, characterized in that the device (5) for mixing has a body (34) in the form of a geometric prism, in the base of which

Light from the light source (3, 30) is introduced and the mixed light for illuminating the matrix (50) is removed from its top surface (52).

8. Projection device according to claim 7, characterized in that the geometric prism has a rectangular base, the aspect ratio of which is determined by the aspect ratio of the video image formed by the matrix (50).

9. Projection device according to claim 7 or 8, characterized in that the outer surface of the body (34) is not mirrored and the multiple reflection takes place due to total reflection on this outer surface.

10. Projection device according to claim 9, characterized in that the ratio of the length of the prism axis to the lateral extent is greater than

where n is the calculation index of the material.

1 1. Projection device according to claim 9 or 10, characterized in that the body (34) is held by point or line-shaped storage in the projection device.

12. Projection device according to claim 1 1, characterized in that a holder (56) for the body (34) made of sheet metal with a thickness of less than 1 mm and in particular less than 0.5 mm is provided, which has only one edge this dimension is applied to the body (34).

13. Projection device according to claims 9 to 12, characterized in that a holder (56) for the

Body (34) is provided from resilient sheet metal, the spring tension acts perpendicular to the prism axis and pulls the body (34) perpendicular to the prism axis against an edge of the housing as an abutment and that a groove is provided in a lateral surface of the body (34) in which a spring attached to the housing engages.

14. Projection device according to claims 2 to 13, characterized in that a color wheel (40) is provided for color video display and this color wheel (40) between the light source (30) and the device

(5) is arranged for mixing.

15. Projection device according to one of claims 2 to 14, characterized in that an adjusting element (52) for aligning the light emerging from the device (5) for mixing on the matrix (50) is provided behind the device (5) for mixing.

16. Projection device according to claim 1, characterized in that the light source (1, 30) near the matrix (50) and at an angle at which the light beam (2) is directed away from this, is arranged and that a folded optical light path for Transmission of a light bundle (2) emitted by the light source (3, 30) to the tilting mirror matrix (50) is provided.

17. Projection device according to claim 16, characterized in that the folded optical light path is effected with two deflecting mirrors (36, 76), between which an optical fiber extends as a device for mixing. 18 projection device according to one of claims 16 and 17, characterized in that a zyhnderfbrmiger adjusting element (54) is provided in the folded optical light path, in which a deflecting mirror (36, 76) of the folded optical light path is attached and with which the light of the light source ( 3, 30) can be aligned with the matrix (50)

19 projection device according to claim 18, characterized in that an optical system for focusing the light beam (2) on the Matπx (50) is provided in the adjusting element (54)

20 Projection device according to claim 19, characterized in that a rectangular, highly emissive, from the light source (3, 30) fed surface (52) is formed in front of the adjusting element (54) and the adjusting element (54) has an at least two-sided system (76) , with which the light-emitting surface (52) is imaged on the matrix (50)

21 Projection device according to claim 20, characterized in that the imaging scale of the at least two nous system (76) is between 1 and 5

22 Projection device according to one of claims 1 to 21, characterized in that a field lens (68) is arranged in front of the matrix (50)

23 Projection device according to claim 22, characterized in that the light beam (2) directed via the optical light path onto the matrix (50) is directed through the field lens (68) onto the matrix (50), while that of the matrix (50) in the lens (8, 60) reflects reflected light from the field lens (68) into the lens (8, 60) unaffected

24 Projection device according to claim 23, characterized in that the field lens (68) perpendicular to its optical axis has a part-circular cross section, in particular a semicircular cross section, which is arranged between the incident light beam (2) and the matrix (50), one through the deviation from the circular shape defined opening between the matrix (50) and the objective (8, 60)

25 projection device according to one of claims 16 to 25, characterized by a last deflecting mirror (36, 76) which directs the light bundle (2) out of a plane of the optical light path lying in front of this deflecting mirror (66) and onto the matrix (50)