Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N9/00—Details of colour television systems
  • H04N9/12—Picture reproducers
  • H04N9/31—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM]
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
  • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
  • G02B26/10—Scanning systems
  • G02B26/12—Scanning systems using multifaceted mirrors
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N9/00—Details of colour television systems
  • H04N9/12—Picture reproducers
  • H04N9/31—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM]
  • H04N9/3129—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM] scanning a light beam on the display screen

Definitions

• the invention relates to a device, in particular designed as a projection head, for the projection of a video image, a line mirror with at least one mirror surface for deflecting a light beam in the line direction of the video image and an image mirror
• the mirrors used for this are called line mirrors and image mirrors in accordance with their function.
• a polygon mirror is often used as the line mirror, which makes the high deflection speeds possible for displaying a video image.
• other mirrors with high switching speeds are also known, such as very small galvanometer mirrors, which already allow the display of video images with low point density, so that there is hope that such mirrors will be available in the future for very fast line deflection.
• line mirrors in the following this means primarily polygon mirrors. But this does not mean a limitation. The only thing that matters is that the line mirror, by rotating or tilting about an axis of rotation, allows a high speed for changes in the angle of light beams.
• a video image is imaged using the line mirror and the image mirror, however, in contrast to the conventional picture tube, laser beams are used instead of electron beams.
• the color and brightness information for each pixel of the video image is carried out by a suitable modulation of the laser beam, preferably before the deflection by the line mirror and image mirror.
• Such a laser projection system is described for example in DE 43 24 848 C2.
• a first device for laser beam generation, laser modulation and beam combination of laser light of different colors is spatially separated from a second device, which consists solely of a line mirror, tilting mirror and a transfer optics.
• the light transmission between the first device and the separate rastering second device takes place via an optical fiber.
• the device which is also referred to below as the projection head, essentially consists of a biaxial deflection device, in particular with a polygon mirror and a tilting mirror following in the direction of light propagation, which can also be followed by an expansion lens.
• a laser projection system in which a device consisting of dichroic mirrors for combining several laser light bundles into a single light bundle is also provided in the projection head. Furthermore, an image mirror lying in front of the polygon mirror is provided in a projection device according to JP 363-306417, that is to say in a different arrangement compared to that in the German publication specified above.
• the projector also contains the light sources for the colors red, green and blue.
• the brightness and color-modulated light beam is first directed onto a line mirror designed as a polygon mirror, the one
• Image mirror also designed as a polygon mirror, follows.
• the image mirror used in this case would have to have a large mirror surface in order to completely capture the light beam already deflected in the line direction.
• a curved mirror is provided so that the usually sufficient mirror surface area of the polygon mirror is optically widened.
• the light beam is first directed onto a polygon mirror and then fed to an image mirror via a lens. So you need an additional lens.
• an imaging optical system is used between two deflecting mirrors.
• This optical system is arranged as relay optics between the image mirror and the line mirror and serves to create a common imaging point for both deflection directions.
• This technique is widely used.
• EP 0 488 903 B1 and US Pat. No. 5,051,834 each provide relay optics between the line mirror and the image mirror.
• Beam path between the light deflection devices disadvantageous because they cause light loss and the important beam parameters for image display, such as. B. deteriorate the required low divergence of the light beam. Furthermore, due to the additional optical elements and the optical paths required as a result, there is also an increased space requirement. In addition, all optical ones in the beam path lead
• the normals of the mirror surfaces are perpendicular to the axis of rotation.
• the surface normals of the mirror surfaces are inclined at an angle ⁇ to the axis of rotation.
• the object of the invention and its developments is to optimize a known device for projecting video images with a light beam, in particular in such a way that the effort for control and / or optical elements is reduced compared to known devices.
• the task is solved with respect to the control effort based on the prior art mentioned in the introduction in that the light beam at the position of the line mirror at which it is directed into the center of the video image, in the main projection direction, at an angle
• the angle ⁇ has a value of 90 ° and ⁇ is chosen to be 0 °.
• Other angles ⁇ and the resulting ⁇ would lead to an elliptical shape of the beam profile on the mirror surface of a line mirror, so that, especially at angles greater than 45 °, increased accuracy would be required for the mirror surfaces of the line mirror, because then the optical imaging properties would be less favorable . This would require a greater effort to manufacture the line mirror, especially if the manufacturing accuracy is to be less than 2 ".
• At least a part of the device is provided by means of a base plate with which this part or the device itself can be fastened on a floor or on a ceiling, and the axis of rotation of the line mirror for an oblique projection at an angle to this base plate arranged.
• this device for intensity and color modulation of the respective illuminated image point is provided, this device also taking into account and correcting trapezoidal distortions for the projection angle given by the oblique projection.
• the simple attachment with the aid of a base plate to a ceiling makes the device particularly user-friendly, since with conventional ceiling heights, regardless of the location of the observer, the projecting part, the projection head or the device itself is not in the line of sight of an observer of the video image.
• the intended angular position for inclined projection and the possibility of correction for keystone distortion are few complex. In principle, the distortions that occur at a given projection angle are known and can be taken into account by the fact that the line information in the
• Distortion of extended lines is read faster from an image memory and written in a reduced area of the rasterized lines.
• the angle of the axis of rotation to the base plate is equal to the angle of the oblique projection between the main projection direction and the normal to a projection surface ⁇ 10 °.
• the device for intensity and color modulation is spatially separated from the at least part of the device and between the device and the device is an optical fiber coupling for transmitting what is subsequently deflected by the line scan
• the projection head the projecting part mentioned, only has to be provided with an image mirror and a line mirror and any expansion optics which are spatially separated from the much heavier components, for example the lasers.
• the projection head the projecting part mentioned, only has to be provided with an image mirror and a line mirror and any expansion optics which are spatially separated from the much heavier components, for example the lasers.
• Coupling with an optical fiber is also possible in a simple manner. With suitable plug contacts in the projection head and the other device for connecting to the optical fiber, it can also be easily installed. If, on the other hand, a mirror device for transmitting the light from the projection head to the rest of the device were to be provided, a coupling would be considerably more complex, especially since the adjustments of the mirrors then required could hardly be carried out by a non-specialist.
• an image mirror is arranged downstream of the line mirror at a distance of less than 4 cm in the direction of propagation of the light beam, which in turn is then followed by an expansion lens. It is particularly advantageous that the image mirror is arranged downstream of the line mirror. In the reverse order, the Line mirrors and thereby the space required in the projection head mentioned as an example become significantly larger. The same applies if an additional optical system for "optical
• Line mirror and image mirror is kept very short. In this regard, it has proven to be particularly advantageous if the distance between these two mirrors is less than 4 cm, because the expansion optics for the enlarged entrance pupil can then be designed and corrected without great effort with regard to different deflection points for image and line deflection.
• the specified distance of up to 4 cm also leaves enough space for the movement of an image mirror. Due to the fact that this further development makes it possible to dispense with relay lens systems, light losses and imaging errors, in particular also due to dust on the lenses or inhomogeneities in the lens material, are significantly reduced.
• the beam quality of the light beam is therefore significantly better than in other known projection systems.
• Expansion optics are known for example from DE 43 24 849 C2.
• this document specifies a lens system corrected according to the tangent condition. From this publication, however, it can also be seen that such optics can be implemented with more than two stages.
• the expansion optics have an exactly two-stage afocal corrected according to the tangent condition
• Lens system is. Accordingly, a two-stage system is selected from the technical scope, which also has the advantage over other solutions, namely that the effort can be kept lower due to the smaller number of lenses. Furthermore, light losses due to scattering and reflections are advantageously reduced, in a similar manner to that described above with regard to the relay system.
• a first lens of the expansion optics in the Range from 10 mm to 100 mm from the image mirror. This size range enables the position and size of the entrance pupil, the size of the projection head and also a size
• Correction for different deflection points between the image mirror and the line mirror can be optimized without much effort, especially because the relay system mentioned above can then be dispensed with.
• a major problem that has so far only been solved with great effort when imaging with line and / or image mirrors is the occurrence of ghost images, which can arise, for example, from the fact that a polygon mirror is usually installed in a housing with a light entry and a light exit opening, whereby this opening is hermetically sealed with a plane-parallel transparent plate.
• the light beams reflected by the plane-parallel plate hit the mirror surfaces of the polygon mirror again and appear offset to the desired image during image generation.
• Such ghosting could be reduced in the usual way by coating, that is, by applying suitable dielectric layers on this window.
• a light-permeable body is provided in a light path which is traversed by the light bundle after reflection from the line mirror, and which has an inclination to the axis of rotation of the line level in all points caused by the rasterization is greater than 1 ° and is in particular in the range 2 ° to 10 °.
• the first lens for example a relay lens between the line mirror and the image mirror or a widening lens according to DE 43 24 849 C2, is suitable for this
• polygon mirrors are usually used in a housing under reduced pressure and / or a special gas filling, such as helium, because of the rapid rotational speed, so that a window for light inlet and outlet must be provided, ghost images of these plane-parallel plates used as windows are almost always observed as a disruptive effect.
• the body, which is partially transparent to light, the window is plane-parallel Is plate, which is provided in particular for the closure of a housing against the surrounding atmosphere for the polygon mirror.
• the device in particular the projection head, is particularly simple, but if, according to an advantageous development of the invention, the deflection device for the
• the line mirror and the image mirror is a combination of a polygon mirror and a tilting mirror.
• Figure 1 is a schematic representation of a projection system with oblique projection
• FIG. 2 is a schematic representation of a projection head to illustrate the principles that are used according to the invention and its developments;
• FIG. 3 shows a representation of a polygon mirror encapsulated in a housing from two views to explain the formation and avoidance of ghost images
• Figure 4 is a schematic representation of a polygon mirror from two views to explain different angles and angular relationships
• Figure 5 is a graphical representation of the dependence of a particularly favorably chosen angle of incidence ⁇ of a light beam on a mirror surface of a polygon mirror as a function of the inclination of the mirror surface ⁇ in connection with a diagram for illustrating the angles shown.
• the projection head is then on one for attachment, for example to the ceiling or the floor of the room in which a laser projection of video images is planned
• Base plate mounted to which all components are aligned so that ideal angle conditions are always possible regardless of the installation location and the projection conditions. If the invention is also shown here in an exemplary embodiment with particularly favorable configurations of the projection head, it is, however, not restricted to one projection head. The knowledge gained in this way can also be transferred to devices for laser projection in which the projection head is not mechanically and optically separated from the laser.
• FIG. 1 The structure of such a projection device 50 is shown schematically in FIG. 1.
• a device 40 three light beams in the colors red, green and blue are generated by lasers 34 and then controlled by means of modulators 35 with regard to the light intensity.
• the three laser light bundles are then combined with a device 36 to form a single parallel beam and are coupled into an optical fiber 4, which transports the light bundle to a projection head 60, after which it is coupled out therein.
• the coupled-out light beam 5 is scanned in two orthogonal directions, so that an image is formed on the screen 71, similar to the known projection method using electron beams on the screen of a television tube.
• oblique projection i.e. If the light bundle 5 is in the center of the rastered image, in the main projection direction 28, it strikes the screen 71 at two angles ⁇ , notably, as shown, at two angles other than 90 °.
• the image is then not exactly rectangular, but in the most general case is shown, as is indicated in FIG. 1 by the grid 70.
• the lines illustrated by broken lines in this grid field 70 can also be curved, as will be discussed in more detail later.
• the recorded image thus created can generally be corrected by electronics 33, which ensure that the laser beam 5 is modulated in the way in which the illuminated spot on the rectangular screen is concerned. Outside the image area given by the screen 71, the laser beam 5 is then blanked.
• the projection head 60 is constructed from a polygon mirror 12, a tilting mirror 16 and an expansion lens 37.
• the polygon mirror 12 serves for line screening, the tilting mirror 16, on the other hand, for screening perpendicular to the line direction, the
• This polygon mirror 12 has a plurality of mirror surfaces 14. With a rapid rotation of the polygon mirror about the axis of rotation 24, the light falls on each passing mirror surface
• Polygonal mirrors 12 are usually used for line latching in order to achieve high pixel densities and the high speed required as a result. However, with lower requirements for this mirror, it is also possible to use tilting mirrors. If the inertia is reduced, for example by reducing these tilting mirrors, an increase in speed is also expected, so that generally a line mirror is meant which allows a line detent by rotation about an axis of rotation, albeit in the following
• the expansion optics is an essentially afocal lens system that is corrected according to the tangent condition.
• Such lens systems are particularly suitable for widening the angular range rastered by the polygon mirror 12 and tilting mirror 16, since they permit a distortion-free and color-independent widening of the angular range.
• the tangent of the starting angle is in constant relation to the tangent of the angle of incidence.
• a projection head is shown by way of example in FIG. 2, in which the entire deflection device is located in a housing 2.
• the light modulated according to a video information, as described, is coupled in via a light guide 4, parallelized with a lens 6 and directed via two mirrors 8 and 10 onto a polygon mirror 12 for line deflection.
• a tilting mirror 16 For the image deflection of the video image, a tilting mirror 16 with an axis of rotation perpendicular to the
• Axis of rotation 24 of the polygon mirror 12 is provided.
• the angular position of the tilting mirror 16 and the polygon mirror 12 are oriented such that the video image is projected perpendicular to the plane of the drawing in FIG. In this direction there is also the expansion optics 37, with which the video image that can be reached with the mirrors 12 and 16 is enlarged.
• the projection head according to FIG. 2 has another special feature, because it is arranged so that it can rotate about an axis 18 by means of a bearing 21.
• a motor not shown, is provided for driving. Because of the rotation, brand new ones will be used for show and marketing applications Possibilities are opened up in which a video image is to be temporarily projected in other directions.
• the light bundle is coupled in on the axis 18 and also in the same direction to it.
• the already explained deflection of the light beam is provided with the help of the mirrors 8 and 10.
• These levels ensure that the light beam of the Polygo may be incident 12 at an angle ⁇ e on the mirror surfaces 14 'napts.
• This angle ⁇ e is related to other angles, as will be explained in more detail below with reference to FIG. 4.
• FIG. 3 shows a polygon mirror in two views.
• polygon mirror 12 is usually encapsulated in a housing 13 so that it can be operated under negative pressure and / or in a helium atmosphere in order to enable the high speeds required at all. For this reason, a glass body 20 is usually provided for closing off the housing 13.
• the lenses of a subsequent expansion lens can also produce a similar effect.
• the polygon mirror 12 could also work together with the tilting mirror 16 in a common housing under negative pressure, in which case, for example, the window could also be arranged behind the tilting mirror 16.
• any body made of transparent material has no 100 percent transmission. This means that part of the transmitted light is always reflected back. Depending on the position of the mirrors 16 or 14, this partial light is reflected again by the mirrors and can produce a shifted “ghost image” in the image field of the video image to be generated.
• a different route was chosen for the projection head of Figure 2. As can be seen in Figure 3 below, the glass body 20 was arranged at an angle ⁇ to the incident light beam chosen that any light reflected by the vitreous is reflected in areas that are not detected by the mirrors 14 and 16 when deflected.
• the curvature of the first lens is also selected such that reflected light does not strike mirrors 14 and 16 again.
• the angle ⁇ is chosen so large that the light reflected multiple times by the polygon mirror is not detected by the image mirror 16.
• the curvature or inclination does not have to be particularly large, because it has been shown that with the dimensions, as already stated in the introduction, in order to design a polygon mirror as optimally as possible, angles ⁇ of 1 ° are sufficient. The same effect is achieved when tilted by the angle ⁇ .
• This offset V denotes the distance between the axis of rotation and the projection direction of the polygon mirror 12 and is dimensioned with the radius r of the polygon mirror (see FIG. 3) as r * sin (aJ2).
• the glass body 20 is also shown here, which is located between the polygon mirror 12 and the tilting mirror 16. As previously indicated, such a glass body 20 can also be between the tilting mirror 16 and one
• Screen 22 may be provided, as is illustrated by the vitreous 20 '. However, it also applies that the inclination ⁇ 'should be chosen so that reflected light does not fall back on the tilting mirror 16 and the polygon mirror 12.
• the body 20 or the body 20 ' is inclined perpendicular to the deflection direction of the polygon mirror, since experience has shown that a significantly lower inclination in this direction is required in order to avoid ghosting. It was also observed that small angles below 10 ° are completely sufficient.
• the angle of inclination of the surfaces of the bodies 20 and 20 'to the projection direction should be greater than 1 ° and should be between 2 ° and 10 °.
• the angle is also small enough so that the different refraction in the glass body 20 or 20 'does not produce any undesired color separation due to the dispersion of conventional materials.
• the following information relates to an optimization of a projection head with a light beam with a diameter d in the order of 1 to 10 mm with a screen diagonal of greater than 1 m for HDTV or PAL. This takes into account that all optical components have a space requirement that is not optically effective, such as
• the diameter d of the light beam is essentially determined by the geometric resolution and the distance between the projector and the projection surface and thus offers an essential basis for the geometric dimensioning of all optical assemblies. In particular, this results in and the video standard used also the minimum line deflection angle ß and the
• Image deflection angle ⁇ is a parameter that has proven to be particularly suitable as reference points for the dimensioning in the exemplary embodiment of FIG. 2 due to practical considerations:
• the radius of the polygon mirror r should be around 20 mm, the distance d from the axis of rotation 24 of the polygon mirror should be 40 mm and the previously mentioned offset V should be in the range from 0 to 10 mm. In particular, an offset V of 5 mm was used in the exemplary embodiment.
• a point 26 can also be seen in FIG. 4, which denotes the axis of rotation of the image mirror 10.
• the quantities s, t and w shown in FIG. 4 denote the distance between the axis of rotation of the image mirror 16 and its reflecting surface in the directions shown.
• the angle ⁇ should be 90 °.
• 90 ° +/- 10 ° has been found to be particularly advantageous for the compactness of a projection head. This applies in particular to an arrangement of the deflection device as a combination of a polygon mirror and a tilting mirror.
• the angle ⁇ should be greater than 90 ° - ⁇ / 2, so that shading of the image is avoided. It should also not be larger than 120 ° because the
• Reflection conditions for the light beam are then less favorable.
• the distance d between the axis of the line mirror to the projection axis should also satisfy the condition d-r ⁇ 4 cm. At such distances, it is possible to dispense with relay optics with which the deflection point of the polygon mirror 12 with the deflection point of the
• Image of the mirror 16 is brought to congruence.
• the different deflection points of the two mirrors affect the design of a subsequent expansion lens only slightly. Because of the small distance provided, additional optical elements, such as the relay optics mentioned, can be saved, thereby avoiding unnecessary light losses.
• the first lens of the expansion optics should also be in the range of 10 mm to 100 mm behind the image mirror, the reflecting surfaces of the polygon mirror 12 and the image mirror 16 being in the entrance pupil of the expansion optics and the optical axis of the expansion optics with the main projection axis is identical.
• the entrance pupil of the expansion optics is at a distance of less than 80 mm and in particular less than 30 mm in front of the first lens apex.
• An angle ⁇ is also shown in FIG. 4, which relates to another mirror surface inclination of a mirror surface 14 'indicated by a broken line.
• an angle ⁇ of 90 ° was used, because it was observed at all other angles that the lines can then only be displayed in a curved manner.
• other angles ⁇ are also possible if one takes into account that line curvatures of the order of 3% are hardly perceived by the eye. This is sufficient for the display of a video image, but does not provide the required accuracy for CAD applications if the image is not distorted before the display so that it is equalized again due to the mirror surface angle ⁇ , which is different from 90 °.
• the curve 32 drawn was obtained with the aid of curve fitting.
• the curve can be described by formula
• the angle of incidence ⁇ as shown in FIG. 5, can be determined for each ⁇ in such a way that the effort for an equalization of the displayed images is determined by means of
• a tilting mirror can be used instead of the specified polygon mirror 12.
• an acousto-optical modulator could also be used for one of the two deflection devices, a bi-level mirror or a polygon mirror.
• the usual deflection angles ⁇ and ß are smaller, but this could be compensated for by suitable expansion optics.
• the values given are essentially independent of such changes and it will be easy for the person skilled in the art to modify the information accordingly when replacing individual components by their alternative embodiments.

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• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• General Physics & Mathematics (AREA)
• Transforming Electric Information Into Light Information (AREA)
• Mechanical Optical Scanning Systems (AREA)
• Lenses (AREA)

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• 1998
  • 1998-12-23 DE DE19860017A patent/DE19860017A1/de not_active Withdrawn
• 1999
  • 1999-12-07 KR KR1020007009166A patent/KR20010041123A/ko not_active Application Discontinuation
  • 1999-12-07 WO PCT/EP1999/009617 patent/WO2000040035A1/de not_active Application Discontinuation
  • 1999-12-07 EP EP99959386A patent/EP1057347A1/de not_active Withdrawn
  • 1999-12-07 AU AU16575/00A patent/AU1657500A/en not_active Abandoned
  • 1999-12-07 JP JP2000591815A patent/JP2002534704A/ja active Pending

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