JP2009300772A - Illumination optical system and image projecting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an illumination optical system which is low in loss, favorable in balance in terms of a light quantity of each color light, and compact in size. <P>SOLUTION: The illumination optical system 100 includes: a first LED (Light Emitting Diode) light source 21G that emits first color light, a second LED light source 21B that emits second color light; a third LED light source 21R that emits third color light; first and second photosynthetic parts 23a, 23b for synthesizing the first color light, the second color light and the third color light so that they may align on the same optical axis. The first and second photosynthetic parts 23a, 23b have the first dichroic mirror 23a which transmits the first color light and reflects the second color light to thereby synthesize the first color light and the second color light, and the second dichroic mirror 23b which transmits the first color light and the second color light that have been synthesized by the first dichroic mirror 23a, and reflects the third color light to thereby synthesize the first color light, the second color light and the third color light. An angle formed of the normal line of the first dichroic mirror 23a and the normal line of the second dichroic mirror 23b is equal to or larger than 60° and smaller than 90°. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an illumination optical system that emits illumination light to a modulation element and an image projection apparatus that projects illumination light modulated by the modulation element.

  2. Description of the Related Art Conventionally, as an apparatus for viewing images, there is an image projection apparatus that modulates light emitted from a light source by a modulation element and projects an image on a screen or the like. As an illumination optical system of this image projection apparatus, for example, one having a configuration in which light from a plurality of light sources such as light emitting diodes having different wavelengths is combined by a light combining unit such as a prism or a dichroic mirror and guided to a modulation element is known. .

  As an example of an illumination optical system of a conventional image projection apparatus, for example, what is disclosed in Non-Patent Document 1 will be described with reference to FIG. FIG. 5 is a diagram for explaining a partial configuration of a conventional illumination optical system. As shown in FIG. 5, the conventional illumination optical system includes two dichroic mirrors 123a and 123b, a mirror 125, a plurality of light sources 121R, 121G, and 121B, and a front surface thereof. Are provided with collimator lenses 122R, 122G, and 122B, a condenser lens 124, and a rod integrator 126, respectively. In such an illumination optical system, the light emitted from the light source 121B is reflected by the dichroic mirror 123a and further reflected by the dichroic mirror 123b. The light emitted from the light source 121G passes through the dichroic mirror 123a and is reflected by the dichroic mirror 123b. The light emitted from the light source 121R is reflected by the mirror 125 and passes through the dichroic mirror 123b. In this way, all the light emitted from the light sources 121R, 121G, and 121B is combined on the same optical axis and is incident on the condenser lens 124 and the rod integrator 126. Thus, the illumination optical system described in Non-Patent Document 1 combines and emits light from a plurality of light sources without including a prism. Although not shown, the synthesized light is guided to the modulation element, modulated by the modulation element, and enlarged and projected onto the screen by the projection optical system.

  As another conventional illumination optical system, for example, Patent Document 1 has two crossed dichroic mirrors, and a plurality of LED (Light Emitting Diode) chips are arrayed as one light source. An illumination optical system using an arranged LED light source is disclosed. By using two dichroic mirrors, loss due to the gap occurs at the intersection of the dichroic mirrors. However, in the illumination optical system of Patent Document 1, by using a plurality of LED chips, Since the output is increased, the output of light emitted from the illumination optical system does not become too low, and sufficiently bright light can be emitted.

As another conventional illumination optical system, for example, Patent Document 2 discloses an illumination optical system that uses a prism as a light combining unit without using a light combining unit that intersects two dichroic mirrors. Yes. In general, in a prism, since a gap generated at the intersection when two dichroic mirrors are used is extremely small, loss can be reduced, but it is difficult to ensure reflection of a P-polarized component. There is a problem. That is, when the LED used as the light source emits randomly polarized light, loss due to the polarization component occurs, so that efficient color synthesis cannot be performed. However, the illumination optical system disclosed in Patent Document 2 is configured to include such a prism with little loss due to the polarization component. Thereby, the illumination optical system disclosed in Patent Document 2 has little loss and enables efficient color synthesis.
SID 04 DIGEST 26.1: RGB LED Illuminator for Pocket−Sized Projectors JP-A-2005-316406 JP 2004-70018 A

  However, the illumination optical system disclosed in Non-Patent Document 1 has a problem that, in the synthesis of each color light, the number of times each color light is reflected is large, the optical path length becomes long, the size is increased, and the efficiency is deteriorated. In addition, the illumination optical system disclosed in Patent Document 1 has a problem that the number of LEDs to be used increases, resulting in an increase in cost and an increase in power consumption. In addition, when a plurality of light sources are used, loss tends to occur in the synthesis of their optical paths. In addition, the use of a plurality of light sources is considerably more disadvantageous than the case of using a single LED having the same light emitting area. In addition, when a single LED is used in the configuration shown in Patent Document 1, loss due to a gap at the intersection of the dichroic mirror is unavoidable. The illumination optical system disclosed in Patent Document 2 uses a prism, but the prism is expensive and heavy. Therefore, there is a problem that the cost of the illumination optical system itself increases and is heavy. Moreover, loss due to dichroic characteristics such as loss of the P-polarized component is unavoidable.

  Moreover, since the output of each light source of each color light is different, it is necessary to adjust the light quantity balance of each color light in an illumination optical system. Specifically, among the blue light, red light, and green light LED light sources, the output of the blue light source is too high compared to the other two light sources. Therefore, it is necessary to increase the emission duty ratio of the red light source and the green light source, which are lower in output than the blue light source, and the characteristics of the pulse light emission are not fully utilized. In order to use pulsed light emission effectively, it is desirable that the illumination optical system has a configuration that can adjust the balance of the amount of light of each color.

  The present invention has been made in view of the above-described circumstances, and an object thereof is an illumination optical system that has low loss, has a good balance of the amount of light of each color, and can be miniaturized, and such an illumination optical system. It is providing the image projector provided with.

  As a result of various studies, the present inventor has found that the above object is achieved by the present invention described below. That is, an illumination optical system according to an aspect of the present invention includes a first LED light source that emits first color light, a second LED light source that emits second color light, a third LED light source that emits third color light, and the first LED light source. An illumination optical system including a light combining unit configured to combine color light, the second color light, and the third color light on the same optical axis, wherein the light combining unit transmits the first color light and transmits the second color light. A first dichroic mirror that combines the first color light and the second color light by reflecting the first color light, the first color light and the second color light combined by the first dichroic mirror are transmitted, and the third color light is transmitted. A second dichroic mirror that combines the first color light, the second color light, and the third color light by reflecting, and a normal line of the first dichroic mirror; and the second dichroic mirror The angle between the normal line is less than 60 degrees or more 90 °.

  Thus, by arranging the first dichroic mirror and the second dichroic mirror so that the angle formed by the respective normal lines is 60 degrees or more and less than 90 degrees, the optical path length of the first color light is shortened, and other An optical path of colored light can be secured. Thereby, since the efficiency of the first color light can be improved, the balance of the amount of light of each color light caused by the difference in the light emission efficiency of each LED light source can be improved, and the size can be reduced. Further, since it is not necessary to use the intersection of the first dichroic mirror and the second dichroic mirror as an optical path, no light loss occurs. Further, since the light combining unit is configured by a dichroic mirror, the weight does not increase as in the case of using a prism.

  In the illumination optical system described above, it is preferable that an angle formed by the optical axis of the second color light incident on the first dichroic mirror and a normal line of the second dichroic mirror is 75 degrees or more.

  Thereby, the optical axis of the 2nd color light which injects into a 1st dichroic mirror can be arrange | positioned so that it may follow a 2nd dichroic mirror surface substantially. Therefore, since the first dichroic mirror can be brought closer to the second LED light source, the first LED light source can be brought closer to the emission side, and the optical path length of the first color light can be shortened.

In the illumination optical system described above, the light emission efficiency of the second LED light source is higher than the light emission efficiency of either the first LED light source or the third LED light source, and the optical path length from the first LED light source to the illuminated portion is L1. And the optical path length from the second LED light source to the illuminated part is L2, and the optical path length in terms of air from the third LED light source to the illuminated part is L3,
L3 ≦ L1 <L2
It is preferable to satisfy the relationship.

  Thereby, since the optical path lengths of the other color lights are shorter than the optical path lengths of the second color lights having high luminous efficiency, the efficiency of the color lights other than the second color lights can be improved.

  In the illumination optical system described above, the light emission efficiency of the first LED light source is preferably higher than the light emission efficiency of the third LED light source.

  As a result, the optical path length of the third color light having a low light emission efficiency is shorter than the optical path lengths of the other color lights, so that the efficiency of the third color light can be improved.

  In the above illumination optical system, the second color light emitted from the second LED light source is blue light, the first color light emitted from the first LED light source is red light or green light, and the third LED light source. It is preferable that the third color light emitted by is a color light different from the second color light among red light or green light.

  Thereby, the blue light emitted from the blue LED light source with the highest luminous efficiency can be arranged in the optical path with the lowest efficiency. Therefore, when performing appropriate white display, the light emission duty ratio of each color light can be balanced and optimized. Thereby, illumination light with good chromaticity and brightness performance can be emitted.

  In the illumination optical system described above, it is preferable that the first color light is green light, and an angle formed by an optical axis of the first color light and a normal line of the first dichroic mirror is less than 45 degrees.

  Thereby, the loss of the green light which permeate | transmits a 1st dichroic mirror can be decreased. Here, in the first dichroic mirror that transmits green light and transmits blue light, since the emission wavelengths of green light and blue light are relatively close, the transmission angle of green light is dependent on the incident angle with respect to the cutoff wavelength. A large impact. That is, when the incident angle is large, the incident angle dependent loss of the dichroic mirror characteristics increases, and the loss due to color synthesis increases.

  In the illumination optical system described above, the first dichroic mirror and the second dichroic mirror include a multilayer body in which layers having different refractive indexes are alternately stacked, and the first dichroic mirror and the second dichroic mirror Of the multilayer body of at least one of the mirrors, the refractive index of the low refractive index layer is preferably 1.8 or more.

  Thereby, the incident angle dependence with respect to the cutoff wavelength in at least one of the first dichroic mirror and the second dichroic mirror can be reduced. Specifically, a dichroic mirror made of a material that increases the average refractive index of each layer in the multilayer body has a small incident angle dependency on the cutoff wavelength. Here, in the first dichroic mirror and the second dichroic mirror, when one of the two color lights is reflected and the other is transmitted, if the wavelength bands of the respective color lights are close to each other, the incident angle dependence on the cutoff wavelength It is preferable that the property is small. Therefore, for example, in a dichroic mirror that reflects one of green light and blue light and transmits the other, it is preferable that the refractive index of a low refractive index layer in the multilayer body is 1.8 or more.

  In the illumination optical system described above, the first LED light source, the second LED light source, and the third LED light source are each single, and are incident from each of the first LED light source, the second LED light source, and the third LED light source. It is preferable to have a collimator optical system that makes the reflected light substantially parallel light.

  Thereby, the light emitted from each LED light source is incident on each dichroic mirror after the emitted light beam is collimated by the collimator optical system. Therefore, the influence of the incident angle dependency on the cutoff wavelength in the dichroic mirror is small. Therefore, there is little loss of light quantity.

  In the illumination optical system described above, it is preferable that the collimator optical systems in the first LED light source, the second LED light source, and the third LED light source have components having a common shape.

  As a result, parts having the same shape can be used, resulting in cost reduction.

  Further, in the above-described illumination optical system, a condensing optical system that condenses the light beams of the first color light, the second color light, and the third color light combined on the same optical axis by the light combining unit, and A rod integrator that has an incident end at the condensing position of the condensing optical system, converts the incident light into a uniform intensity distribution and emits the light, and a relay that guides the light emitted from the rod integrator to the illuminated part side It is preferable to have an optical system.

  Thereby, it is possible to irradiate illumination light uniformly and efficiently to a necessary region of the modulation element.

In the above illumination optical system, the focal length of the collimator optical system of the third LED light source is FL, the focal length of the condensing optical system is FC, and the air from the third LED light source to the incident end of the rod integrator If the converted optical path length is P3,
1.8 × (FL + FC) ≦ P3 ≦ 2.2 × (FL + FC)
It is preferable to satisfy the relationship.

  Thereby, when the color light which requires the most efficiency is the third color light, the arrangement of the third LED light sources can be the most efficient arrangement. By setting it as such an arrangement | positioning, the light emission part of a 3rd LED light source and the incident end of a rod integrator can be optically conjugate | conjugated by a collimator optical system and a condensing optical system. In addition, since both the third LED light source side and the rod integrator side can be in a telecentric relationship, the luminous flux can be incident on the rod integrator without increasing the angular distribution width so that illumination can be efficiently performed.

  In the illumination optical system described above, it is preferable that the first LED light source, the second LED light source, and the third LED light source emit light sequentially.

  In this way, by sequentially emitting light from each LED light source, a color image can be displayed by color time division. An LED light source is suitable for such time-division illumination because it emits light by pulsed light, allowing more current to flow than in continuous light emission and bright light emission.

  An image projection apparatus according to an aspect of the present invention is modulated by the illumination optical system according to any one of claims 1 to 12 and a modulation element that modulates illumination light from the illumination optical system. A projection optical system for projecting illumination light.

  Thereby, a bright projection image with good color reproducibility and color balance can be obtained.

  Further, in the above-described image projection apparatus, at least one of the illumination optical system and the projection optical system has a variable diaphragm mechanism, and the first LED light source and the second LED according to an opening state of the variable diaphragm. It is preferable that the light emission amount ratios of the light source and the third LED light source are different.

  Thereby, the light quantity ratio of each color light that changes by adjusting the diaphragm is corrected by changing the light emission quantity ratio of each LED light source according to the diaphragm, and stable color reproduction can be achieved. In order to change the light emission amount ratio, specifically, there are methods such as changing the current supplied to each LED light source or changing the light emission duty ratio of each color light.

  The reason that the light amount ratio of each color light is changed by adjusting the diaphragm is that the optical path length condition of each color light is different. A. This is because the (Numerical Aperture) distribution state is different, and the intensity distribution in the pupil of the optical system of each color light is different. Thereby, when the aperture is changed, the color balance of each color light changes.

  According to the present invention, it is possible to provide an illumination optical system that is low loss, has a good balance of the amount of light of each color, and can be reduced in size, and an image projection apparatus including such an illumination optical system.

  Embodiments according to the present invention will be described below with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted.

  An image projection apparatus according to an embodiment of the present invention will be described. First, the configuration of the image projection apparatus according to the embodiment of the present invention will be described. FIG. 1 is a diagram for explaining a configuration of an image projection apparatus according to the present embodiment. FIG. 2 is a view showing the arrangement of members in a part of the illumination optical system according to the present embodiment.

  As shown in FIG. 1, an image projection apparatus 100 according to an embodiment includes an illumination optical system 2, a total reflection prism 6, a DMD (Digital Micromirror Device) 7 that is a modulation element, a projection optical system 8, and a controller. 9, a diaphragm control unit 10, a DMD drive circuit 11, a red LED drive circuit 12R, a green LED drive circuit 12G, and a blue LED drive circuit 12B.

  The illumination optical system 2 includes a red LED light source (third LED light source) 21R, a green LED light source (first LED light source) 21G, and a blue LED light source (second LED light source) 21B, which are light sources, and a plurality of lenses corresponding thereto. First dichroic mirror 23a which is a light combining unit for combining the color light from each of the collimator optical systems 22R, 22G and 22B and the red LED light source 21R, the green LED light source 21G and the blue LED light source 21B into the same optical axis. And a second dichroic mirror 23b, a condensing optical system 24, a rod integrator 26, a relay optical system 27, a variable stop 28, and an entrance lens 29.

  The red LED light source 21R, the green LED light source 21G, and the blue LED light source 21B are controlled by the red LED drive circuit 12R, the green LED drive circuit 12G, and the blue LED drive circuit 12B, respectively, and emit light of each color from the light emitting surface. The shape of the light emitting surface of each LED light source 21R, 21G, 21B is, for example, a rectangle of about 4.6 mm × about 2.6 mm with an aspect ratio of about 16: 9, and the display area of DMD7 (for example, 20.7 mm × 11 .7 mm). The collimator optical systems 22R, 22G, and 22B make each color light from the red LED light source 21R, the green LED light source 21G, and the blue LED light source 21B substantially parallel and enter the first dichroic mirror 23a or the second dichroic mirror 23b. These collimator optical systems 22R, 22G, and 22B are all configured by, for example, three positive meniscus lenses that are convex on the projection side, and the focal length may be, for example, about 15.2 mm. The collimator optical systems 22R, 22G, and 22B may be configured by parts having a common shape. As a result, parts having the same shape can be used, resulting in cost reduction.

  The first dichroic mirror 23a only needs to reflect blue light and transmit green light. The second dichroic mirror 23b only needs to have a property of reflecting red light and transmitting blue light and green light. More specifically, the first dichroic mirror 23a transmits green light and reflects blue light to synthesize the optical axes of green light and blue light. The second dichroic mirror 23b transmits the green light and the blue light synthesized by the first dichroic mirror 23a and reflects the red light, thereby synthesizing the optical axes of the green light, the blue light, and the red light.

  Here, the red light reflected by the second dichroic mirror 23b has a relatively long emission wavelength with respect to both the transmitted blue light and green light, but the blue light reflected by the first dichroic mirror 23a is The emission wavelength is relatively close to the transmitted green light. Specifically, the emission wavelength of blue light is about 465 nm, the emission wavelength of green light is about 525 nm, and the emission wavelength of red light is about 625 nm. As described above, when one of the two color lights is reflected and the other is transmitted, when the wavelength bands of the respective color lights are close to each other, it is preferable that the incident angle dependency on the cutoff wavelength is small. Therefore, in such a case, it is preferable that the first dichroic mirror 23a has as small an incident angle dependency as possible of the cut-off wavelength (transmittance 50%) for transition from the blue light reflection band to the green light transmission band. . Therefore, it is preferable that the first dichroic mirror 23a has as little incident angle dependency as possible with respect to the cutoff wavelength in green light. In other words, it is preferable that the green light is transmitted without being reflected even when the incident angle of the green light is increased. Therefore, more specifically, the configuration of the first dichroic mirror 23a will be described with reference to Table 1.

Table 1 shows an example of the constituent material of the first dichroic mirror 23a. The first dichroic mirror 23a has a multilayer structure in which materials having different refractive indexes are periodically stacked. Table 1 shows the material configuration of each layer of the first dichroic mirror 23a. The first dichroic mirror 23a has a structure of 0 to 28 layers, and the unit of the physical film thickness of each layer is nm. As shown in Table 1, the first dichroic mirror 23a has a refractive index of 1.8 between white plate glass (0 layer) and SiO ₂ (28 layers), and is a mixture of SiO ₂ and Nb ₂ O ₅ . A low refractive index layer formed of a material and a high refractive index layer having a refractive index of 2.3 and formed of Nb ₂ O ₅ are alternately formed. Here, in order to reduce the incident angle dependency on the cutoff wavelength, it is better to form the multilayer body using a material having a high average refractive index. That is, the refractive index of the low refractive index layer may be increased. For example, the low refractive index layer preferably has a refractive index of 1.8 or more.

  The transmittance characteristic of the first dichroic mirror 23a having such a configuration will be described with reference to FIG. FIG. 3 is a graph showing the transmittance characteristics of the first dichroic mirror and the emission wavelength of each color light. The horizontal axis in FIG. 3 indicates the wavelength (nm), and the vertical axis indicates the transmittance (%). The two-dot chain line is the transmittance of incident light having an incident angle of 30 degrees with respect to the first dichroic mirror 23a. The alternate long and short dash line represents the transmittance of incident light with an incident angle of 20 degrees with respect to the first dichroic mirror 23a. The thin solid line represents the transmittance of incident light having an incident angle of 40 degrees with respect to the first dichroic mirror 23a. A thin broken line indicates the emission wavelength of blue light, a thick broken line indicates the emission wavelength of green light, and a thick solid line indicates the emission wavelength of red light. As can be seen from FIG. 3, the transmittance at all incident angles is approximately 100% in the wavelength bands of green light and red light. This indicates that green light and red light are transmitted through the first dichroic mirror 23a even if they are incident at these incident angles. However, in the wavelength band of blue light, the transmittance at all incident angles is low, indicating that it is reflected. That is, it can be seen that the first dichroic mirror 23a is sufficient to have the configuration shown in Table 1. As the incident angle increases, the incident angle dependency of the cut-off wavelength is affected. Therefore, it is preferable that the incident angle of green light with respect to the first dichroic mirror 23a is less than 45 degrees. The green light is collimated and then incident on the first dichroic mirror 23a. Since the green light at the time of incidence has an angular distribution of about ± 10 degrees, this embodiment is used for efficient color synthesis. In the embodiment, the incident angle of green light is 30 degrees.

  The condensing optical system 24 condenses the green light, the blue light, and the red light, in which these optical axes are combined, and enters the rod integrator 26. The condensing optical system 24 is composed of, for example, two positive meniscus lenses convex on the light source side, and has a focal length of about 26 mm, for example.

  The rod integrator 26 has its incident end at the condensing position of the condensing optical system 24 to make the intensity distribution of the light emitted from the condensing optical system 24 uniform. For example, it is a prismatic glass having a quadrangular cross section, and light incident on the inside from one end face is repeatedly totally reflected on the side face, and the illuminance distribution of incident light is emitted uniformly. The rod integrator 26 may have a structure having a hollow structure and a mirror surface on the inner surface. The cross-sectional shape of the rod integrator 26 is, for example, about 7.9 mm × about 4.4 mm, and is arranged so as to match the light source images in the red LED light source 21R, the green LED light source 21G, and the blue LED light source 21B. Thereby, the light from the red LED light source 21R, the green LED light source 21G, and the blue LED light source 21B efficiently enters the rod integrator 26. For example, an LED light source image of about 7.9 mm × about 4.4 mm is formed at the incident end of the rod integrator 26 by the collimator optical systems 22R, 22G, and 22B and the condensing optical system 24.

  Here, referring to FIG. 2, the first dichroic mirror 23a, the second dichroic mirror 23b, the red LED light source 21R, the green LED light source 21G, the blue LED light source 21B, the collimator optical systems 22R, 22G, 22B, and the condensing optical system. A more specific arrangement in the 24 and the rod integrator 26 will be described.

  In the present embodiment, among the red LED light source 21R, the green LED light source 21G, and the blue LED light source 21B, the light emission efficiency of the blue LED light source 21B is relatively high, so even if the efficiency of the blue LED light source 21B is reduced, We decided to increase the efficiency of other colors. Specifically, the optical path length of red light is not increased, and both the red LED light source 21R side and the rod integrator 26 side are in a telecentric relationship. Moreover, although the optical path length of green light is long and the telecentric relationship is somewhat disrupted, efficiency is ensured by suppressing them as much as possible. In addition, blue light has a long optical path length and the telecentric relationship is broken, so the efficiency is lowered. However, the brightness of the illumination light is increased in total when considering the color balance during white display.

  Specifically, the angle formed by the normal line of the first dichroic mirror 23a and the normal line of the second dichroic mirror 23b is 60 degrees or more and less than 90 degrees. More preferably, it is 60 degrees or more and 80 degrees or less. In the illumination optical system described above, it is preferable that the angle formed by the optical axis of the blue light incident on the first dichroic mirror and the normal line of the second dichroic mirror 23b is 75 degrees or more. Thereby, the optical path length of green light can be further shortened. That is, the optical axis of the blue light incident on the first dichroic mirror 23a can be arranged so as to be substantially along the surface of the second dichroic mirror 23b. Therefore, since the first dichroic mirror 23a can be brought closer to the blue LED light source 21B side, the green LED light source 21G can be brought closer to the rod integrator 26 side. Thereby, the optical path length of green light can be shortened.

  As shown in FIG. 2, the green LED light source 21G is disposed in an optical path through which green light passes through the first dichroic mirror 23a and the second dichroic mirror 23b. More specifically, green light is incident on the first dichroic mirror 23a at an incident angle of 30 degrees and is transmitted. Blue light emitted from the blue LED light source 21B is reflected by the first dichroic mirror 23a. Specifically, the blue light is incident on the first dichroic mirror 23a at an incident angle of 30 degrees and is reflected. With this arrangement, the green light and the blue light are combined on the same optical axis. The second dichroic mirror 23b is arranged such that its normal is 67.5 degrees with the normal of the first dichroic mirror 23a. Therefore, the normal line of the second dichroic mirror 23b is arranged so as to be at an angle of 82.5 degrees with the optical axis of the blue light emitted from the blue LED light source 21B. Therefore, the optical axes of the blue light and the green light synthesized by the first dichroic mirror 23a enter the second dichroic mirror 23b at an incident angle of 37.5 degrees and are transmitted therethrough. The red light emitted from the red LED light source 21R is reflected by the second dichroic mirror 23b. Specifically, red light enters the second dichroic mirror 23b at an incident angle of 37.5 degrees and is reflected. Thereby, the red light is combined with the blue light and the green light combined with the same optical axis on the same optical axis.

  In the present embodiment, light does not enter the intersecting portion of the first dichroic mirror 23a and the second dichroic mirror 23b in this way, so that no light loss occurs. Further, since it is not necessary to use a prism, the weight and size are not increased, and loss due to polarization characteristics is small. Further, since the incident angle of the green light to the first dichroic mirror 23a can be reduced, there is no loss depending on the incident angle at the first dichroic mirror 23a.

Moreover, the luminous efficiency of the blue LED light source 21B is higher than the luminous efficiency of both the red LED light source 21R and the green LED light source 21G, and the green LED light source 21G has higher luminous efficiency than the red LED light source 21R. From this, when the optical path length in terms of air between each LED light source 21R, 21G, 21B and the illuminated part is L1, L2, L3,
L3 ≦ L1 <L2
It is preferable to satisfy the relationship. Thereby, the balance of the efficiency of each color light can be adjusted in consideration of the light emission efficiency of each LED light source 21R, 21G, 21B. In addition, the optical path length between each LED light source 21R, 21G, 21B and the to-be-illuminated part means from each LED light source 21R, 21G, 21B to the incident end of the rod integrator 26.

  For example, the optical path length in terms of air from the incident end of the rod integrator 26 to the red LED light source 21R is 83.4 mm, and the optical path length in terms of air from the incident end of the rod integrator 26 to the green LED light source 21G is 98.mm. The optical path length in terms of air from the incident end of the rod integrator 26 to the blue LED light source 21B may be 115.5 mm.

  Here, the light source images of the respective colors are formed at the incident end of the rod integrator 26. With respect to red light, both the light source side and the rod integrator 26 side are imaged in a substantially telecentric relationship, and the angle spread is increased. Therefore, the transmission loss in the subsequent optical system is reduced. The arrangement of each member having such a telecentric relationship will be described with reference to FIG.

Here, FIG. 4 is a diagram showing the positional relationship between the rod integrator and the LED light source, FIG. 4 (A) is a diagram showing the positional relationship between the red LED and the rod integrator, and FIG. 4 (B) is a green LED or It is a figure which shows the positional relationship of blue LED and a rod integrator. In FIG. 4, the collimator optical systems 22R, 22G, and 22B and the condensing optical system 24 are schematically represented by thin lenses. As shown in FIG. 4A, when the focal length of the collimator optical system 22R is FL and the focal length of the condensing optical system 24 is FC, the distance between the collimator optical system 22R and the red LED light source 21R is FL, The distance between the collimator optical system 22R and the condensing optical system 24 may be FL + FC, and the distance between the condensing optical system 24 and the rod integrator 26 may be FC. In this case, the light emitted perpendicularly to the light emitting surface of the red LED light source 21R enters the rod integrator 26 perpendicularly and enters the angular distribution without spreading. Therefore, if the optical path length in terms of air from the red LED light source to the incident end of the rod integrator 26 is P3,
1.8 × (FL + FC) ≦ P3 ≦ 2.2 × (FL + FC)
It may be arranged so as to meet the conditions. As a result, both the red LED light source side and the rod integrator 26 side are imaged in a substantially telecentric relationship. With such an arrangement, N.I. can be achieved without widening the angular distribution of light rays that are emitted with a relatively strong radiation intensity and perpendicular to the LED light emitting surface. A. The light can enter the rod integrator 26 without increasing the value of (Numerical Aperture). Thereby, these light beams can be sufficiently used as illumination light for the DMD 7. Further, the image of the red LED light source 21R is formed on the incident surface of the rod integrator 26 and is efficiently introduced into the rod integrator 26.

  Further, for example, the optical path length from each of the LED light sources 21G and 21B for green light and blue light to the incident end of the rod integrator 26 is longer than the optical path length of red light. Specifically, the distance between each collimator optical system 22G, 22B and the condensing optical system 24 is extended. If this extended distance is α, the positional relationship among the LED light sources 21G and 21B, the collimator optical systems 22G and 22B, and the condensing optical system 24 is as shown in FIG. That is, the distance between each collimator optical system 22G, 22B and each LED light source 21G, 21B is FL, the distance between each collimator optical system 22G, 22B and the condensing optical system 24 is FL + FC + α, and the condensing optical system 24 And the distance between the rod integrator 26 is FC. As a result, light rays emitted vertically from the light emitting surfaces of the LED light sources 21G and 21B are incident on the rod integrator 26 at an incident angle δ according to the emission positions (image heights). As a result, the angular distribution of rays illuminating the DMD 7 increases by δ. Therefore, although the optical path lengths of green light and blue light are increased by α, it is preferable to reduce the value of α to reduce the deviation angle δ from the telecentric state. For example, since the incident angle of the green light is 30 degrees as described above, the angle formed by the normal line of the first dichroic mirror 23a and the optical axis of the green light is 30 degrees. By reducing this angle, the green LED light source 21G can be arranged closer to the rod integrator 26.

  The relay optical system 27 is composed of a plurality of relay lenses, passes the light emitted from the rod integrator 26, and emits it to the variable stop 28. The variable diaphragm 28 is for adjusting the diaphragm, and includes a diaphragm motor 28a for performing a diaphragm operation. That is, the variable aperture 28 regulates the light flux of light emitted from the relay optical system 27. For example, the diaphragm may be switched between F2.5 and F8. When priority is given to brightness, open the aperture to F2.5 to allow more light to reach the screen. When priority is given to contrast, the aperture can be closed to F8 and the stray light component can be cut to improve the contrast. Note that the optical axes of the relay optical system 27 and the variable stop 28 coincide with the optical axis of the rod integrator 26. For example, the magnification of the relay optical system 27 is about 2.7 times, and the size of the light source image formed on the DMD 7 surface is, for example, about 21.3 mm × about 11.9 mm.

  The entrance lens 29 is bonded to the total reflection prism 6 to make the light from the variable aperture 28 telecentric. The entrance lens 29 may not be provided, and the total reflection prism 6 may have the same function as the entrance lens 29 by processing the incident surface of the total reflection prism 6 into a curved surface.

  The total reflection prism 6 includes a first prism 6a and a second prism 6b. An air gap is formed at the boundary between the first prism 6a and the second prism 6b, and light incident through the air gap is totally reflected by the incident angle. Whether it is transparent or not. The total reflection prism 6 is installed so that light incident on the first prism 6a of the total reflection prism 6 from the entrance lens 29 is totally reflected on the critical surface 6c that is a boundary with the air gap. The light reflected by the critical surface 6 c propagates through the first prism 6 a, is emitted to the outside of the total reflection prism 6, and is installed so as to irradiate the DMD 7. The exit end of the rod integrator 26 and the display area of the DMD 7 are conjugate, and the shape of the exit end of the rod integrator 26 and the shape of the display area of the DMD 7 are substantially similar. Thereby, the display area of DMD7 can be illuminated efficiently.

  DMD 7 is a modulation element. The DMD 7 has a plurality of micromirrors that are driven according to the image signal of the image to be displayed. Each of these micromirrors corresponds to one pixel and is arranged in a matrix. Then, the light supplied from the total reflection prism 6 is modulated according to the image signal. Specifically, the micromirror has a deflection axis that forms an angle of 45 degrees with respect to the rectangular display area, and is tilted by ± 12 degrees according to the image signal. Thereby, the reflection direction of the light irradiated to the micromirror can be changed. The deflection direction of the micromirror changes according to the image signal. The light reflected in one inclined state of the DMD 7 travels in the direction passing through the projection optical system 8 via the total reflection prism 6. The light reflected in the other inclined state is reflected through the total reflection prism 6 in a direction not incident on the projection optical system 8 or a direction not transmitted through the projection optical system 8. Note that, instead of the DMD 7, for example, a modulation element may be configured by a reflective or transmissive liquid crystal display device.

  The projection optical system 8 is an optical system for enlarging and projecting the light modulated by the DMD 7 onto a screen (not shown) as a projection surface. For example, the projection optical system 8 may be a double zoom lens whose focal length can be changed from 22.6 mm to 45.2 mm, and can change the screen size up to double at the same projection distance. The projection optical system 8 includes a variable diaphragm 8a for adjusting the diaphragm and a diaphragm motor 8b for operating the variable diaphragm 8a. The projection optical system 8 regulates the light beam in the projection optical system 8. For example, the diaphragm may be switched between F2.5 and F8. When priority is given to brightness, the aperture is opened to F2.5 so that more rays can reach the screen. When priority is given to contrast, the aperture can be closed to F8 and the stray light component can be cut to improve the contrast.

  The diaphragm control unit 10 controls the operation of the diaphragm motors 28a and 8b in accordance with a command from the controller 9, thereby adjusting the diaphragm amounts of the variable diaphragms 28 and 8a. The DMD drive circuit 11 controls the modulation operation of the DMD 7. As described above, the DMD 7 has a micromirror, and by changing the tilt angle of the micromirror, the reflection direction of the irradiated light is changed to select whether to project on the screen. . Therefore, the DMD drive circuit 11 controls the tilt direction of each micromirror of the DMD 7 so that a desired image is projected on the screen according to a command from the controller 9. The red LED drive circuit 12R, the green LED drive circuit 12G, and the blue LED drive circuit 12B control the light emission of the red LED light source 21R, the green LED light source 21G, and the blue LED light source 21B according to a command from the controller 9. The red LED light source 21R, the green LED light source 21G, and the blue LED light source 21B emit pulse light. By adjusting the light emission duty ratio, various desired colors can be expressed. In response to a command from the controller 9, the red LED drive circuit 12R, the green LED drive circuit 12G, and the blue LED drive circuit 12B adjust the light emission duty ratio of the red LED light source 21R, the green LED light source 21G, and the blue LED light source 21B.

  The controller 9 controls the diaphragm control unit 10, the DMD drive circuit 11, the red LED drive circuit 12R, the green LED drive circuit 12G, and the blue LED drive circuit 12B to control the overall operation of the image projection apparatus 100.

  Next, the operation of the image projection apparatus 100 according to the embodiment will be described. The controller 9 receives the video signal, generates a timing signal for dividing the period of one frame or one field in synchronization with the video signal, and sends the timing signal to the DMD driving circuit 11. The DMD driving circuit 11 generates a red image signal, a green image signal, and a blue image signal in accordance with the timing signal, and sequentially switches and outputs the image signals for each color. Based on the image signals The DMD 7 is driven. As a result, in the DMD 7, individual micromirrors are sequentially driven during one frame or one field.

  On the other hand, the controller 9 synchronizes with the drive timing of each micromirror of the DMD 7 so that the red LED light source 21R, the green LED light source 21G, and the blue LED light source 21B are sequentially turned on, respectively, The circuit 12G and the blue LED drive circuit 12B are controlled. As a result, in the DMD 7, the red LED light source 21R, the green LED light source 21G, and the blue LED light source 21B are turned on in synchronization with the drive timing of each micromirror, and the light of each color is sequentially switched, and each collimator optical system 22R, 22G. , 22B, and is transmitted and reflected by the first dichroic mirror 23a or the second dichroic mirror 23b, passes through the condensing optical system 24, the rod integrator 26, and the relay optical system 27, and is connected to the DMD 7 via the total reflection prism 6. Imaged. Red, green, and blue images formed on the DMD 7 are sequentially switched and projected onto the screen by the projection optical system 8. Further, the controller 9 controls the diaphragm control unit 10 to drive the diaphragm motors 28a and 8b to adjust the diaphragm amounts of the diaphragms 28 and 8a, thereby controlling the contrast or brightness of the image.

  In addition, the emission intensity of the red LED light source 21R, the green LED light source 21G, and the blue LED light source 21B is controlled, for example, any two LEDs emit light at the same time, or the emission intensity of a specific LED is reduced. The luminance may be controlled by reducing the light emission intensity of the LED.

  In addition, since the optical path length of each color light is different and the distribution state of the angle component in each color light is different, the relative light quantity ratio of each color light is different and the color tone is changed by adjusting the aperture. For example, when the light emission duty ratio is blue: green: red = 1: 1: 1, a predetermined white is obtained with a light quantity ratio of blue: green: red = 0.9: 1: 1.1 when the aperture is F2.5. Suppose you are expressing. When this is narrowed down to F8, the light quantity ratio of each color light changes, for example, blue: green: red = 0.8: 1: 1.2. It becomes white with a low temperature, and the same white as in F2.5 cannot be expressed. In this case, the input current at the time of blue light emission is multiplied by 0.9 / 0.8≈1.1 times to increase the light amount by 1.1 times, and the input current at the time of red light emission is 1.1 / 1. The amount of light may be increased by a factor of 0.9 by setting 2≈0.9. Thereby, the light quantity ratio of blue: green: red = 0.9: 1: 1.1 can be obtained, and the same white as in the case of F2.5 can be expressed. The same effect can be obtained by changing the light emission duty ratio to blue: green: red = 1.1: 1: 0.9 instead of changing the input current.

Hereinafter, simulations are performed on the image projection apparatus according to the present embodiment and the image projection apparatuses described in Non-Patent Document 1, Patent Document 1, and Patent Document 2 described above, and measurement results are shown. As the LED light source of each image projector, Phlatlight (registered trademark); PT120, which is an LED light source of Luminus, was assumed. And the brightness simulation at the time of driving this LED light source with a rated voltage and a recommended current was performed. As an example, the chromaticity in the case of white display is (x, y) = (0.314, 0.351)
It was. This is in accordance with the chromaticity which is a standard in digital cinema. At this time, in the image projector according to the present embodiment, the brightness is 645 lumens, and the light emission duty ratio is
R: G: B = 34.6%: 48.1%: 17.3%
It became.

Further, in the image projection apparatus according to the configuration of Non-Patent Document 1, the brightness is 585 lumens, and the light emission duty ratio is
R: G: B = 34.9%: 48.6%: 16.5%
It became. In this configuration, since the optical path length from the LED light source to the rod integrator is relatively long, the transmission efficiency on the optical axis is equivalent to that of the image projection apparatus according to the present embodiment, but from a location away from the optical axis. Since the transmission efficiency of the emitted light beam is low, it is darker than the image projection apparatus according to the present embodiment.

In the configuration of Patent Document 1, the brightness is 621 lumens, and the light emission duty ratio is
R: G: B = 35.9%: 48.0%: 16.1%
It became. In the case of this configuration, in the optical path length from the LED light source to the rod integrator, the optical path length of the red light is equivalent to the configuration of the image projection apparatus according to the present embodiment, and this point is efficient, but crossed. Due to the loss due to the gap at the intersection of the dichroic mirror, the transmission efficiency is lower and darker than the image projection apparatus according to the present embodiment.

In the configuration of Patent Document 2, the brightness is 612 lumens, and the light emission duty ratio is
R: G: B = 32.6%: 51.9%: 15.5%
It became. In the case of this configuration, in the optical path length from the LED light source to the rod integrator, the optical path length of red light is equivalent to the configuration of the image projector according to the present embodiment, and there is almost no gap due to the intersection of the dichroic mirrors. In this respect, the efficiency is good, but due to the loss due to the characteristics of the dichroic mirror, the transmission efficiency is lower and darker than the image projection apparatus according to the present embodiment.

  As described above, the result that the image projection apparatus according to the present embodiment is brighter than the conventional image projection apparatus was obtained.

  In addition, when the LED light source is driven at a rating and, for example, white of chromaticity that is a reference for digital cinema is displayed, blue tends to be excessive. Therefore, the red and green light emission duty ratios are correspondingly increased. However, if the light emission duty ratio is excessively increased, the cooling cannot be sufficiently performed and the light emission efficiency is lowered. Therefore, it is desirable to suppress the light emission duty ratio to 50% or less.

  In addition, if the light emission duty ratio of blue light is too small, there is a risk that the gray scale cannot be expressed sufficiently when the gray scale is expressed by time division. Therefore, at least the light emission duty ratio of blue light is set to 20% or more. It is desirable. Further, in order to sufficiently secure the light emission duty ratio of blue light, it is necessary to reduce the output such as reducing the current supplied to the blue LED light source. Further, when the blue light emission duty ratio is increased, the light emission duty ratios of the green light and the red light are reduced accordingly, and as a result, the brightness is significantly reduced.

  Also in this respect, the image projection apparatus according to the present embodiment has a relatively large light emission duty ratio of blue light, and thus obtains a brighter and richer projection image than the conventional image projection apparatus. be able to.

  In order to express the present invention, the present invention has been properly and fully described through the embodiments with reference to the drawings. However, those skilled in the art can easily change and / or improve the above-described embodiments. It should be recognized that this is possible. Therefore, unless the modifications or improvements implemented by those skilled in the art are at a level that departs from the scope of the claims recited in the claims, the modifications or improvements are not covered by the claims. To be construed as inclusive.

It is a figure for demonstrating the structure of the image projector which concerns on this Embodiment. It is the figure which showed arrangement | positioning of each member in a part of illumination optical system concerning this Embodiment. It is the graph which showed the transmittance | permeability characteristic of the 1st dichroic mirror, and the emission wavelength of each color light. FIG. 4A is a diagram showing the positional relationship between the rod integrator and the LED light source, FIG. 4A is a diagram showing the positional relationship between the red LED and the rod integrator, and FIG. 4B is a diagram showing the positional relationship between the green LED and the rod integrator. FIG. It is a figure for demonstrating the one part structure of the conventional illumination optical system.

Explanation of symbols

2 Illumination optical system 6 Total reflection prism 6a First prism 6b Second prism 6c Critical surface 7 DMD
8 Projection optical system 8a, 28 Variable aperture 8b, 28a Aperture motor 9 Controller 10 Aperture controller 11 DMD drive circuit 12R Red LED drive circuit 12G Green LED drive circuit 12B Blue LED drive circuit 21R Red LED light source 21G Green LED light source 21B Blue LED Light source 22R, 22G, 22B Collimator optical system 23a First dichroic mirror 23b Second dichroic mirror 26, 126 Rod integrator 24 Condensing optical system 27 Relay optical system 28 Variable aperture 28a Aperture motor 29 Entrance lens 100 Image projection device 121R, 121G, 121B Light source 122R, 122G, 122B Collimator lens 123a, 123b Dichroic mirror 124 Condenser lens 125 Mirror

Claims (14)

The first LED light source that emits first color light, the second LED light source that emits second color light, the third LED light source that emits third color light, the first color light, the second color light, and the third color light are the same. An illumination optical system including a light combining unit for combining with an optical axis,
The light combining unit transmits the first color light and reflects the second color light to combine the first color light and the second color light, and the first dichroic mirror combined with the first dichroic mirror. A second dichroic mirror that synthesizes the first color light, the second color light, and the third color light by transmitting the first color light and the second color light and reflecting the third color light;
An illumination optical system, wherein an angle formed between a normal line of the first dichroic mirror and a normal line of the second dichroic mirror is 60 degrees or more and less than 90 degrees.   The illumination optical system according to claim 1, wherein an angle formed by an optical axis of the second color light incident on the first dichroic mirror and a normal line of the second dichroic mirror is 75 degrees or more. The luminous efficiency of the second LED light source is higher than the luminous efficiency of either the first LED light source or the third LED light source,
The optical path length from the first LED light source to the illuminated part is L1, the optical path length from the second LED light source to the illuminated part is L2, and the optical path length in terms of air from the third LED light source to the illuminated part is L3
L3 ≦ L1 <L2
The illumination optical system according to claim 1 or 2, wherein the relationship is satisfied.   The illumination optical system according to claim 3, wherein the light emission efficiency of the first LED light source is higher than the light emission efficiency of the third LED light source.   The second color light emitted from the second LED light source is blue light, the first color light emitted from the first LED light source is red light or green light, and the third color light emitted from the third LED light source is red. The illumination optical system according to any one of claims 1 to 3, wherein the illumination optical system is color light different from the second color light among light and green light.   The illumination optical system according to claim 5, wherein the first color light is green light, and an angle formed between an optical axis of the first color light and a normal line of the first dichroic mirror is less than 45 degrees.   The first dichroic mirror and the second dichroic mirror each include a multilayer body in which layers having different refractive indexes are alternately stacked, and at least one of the multilayer body of the first dichroic mirror and the second dichroic mirror. The illumination optical system according to any one of claims 1 to 6, wherein a refractive index of a layer having a low refractive index is 1.8 or more.   The first LED light source, the second LED light source, and the third LED light source are each single, and a collimator that makes light incident from each of the first LED light source, the second LED light source, and the third LED light source substantially parallel light. The illumination optical system according to claim 1, further comprising an optical system.   The illumination optical system according to claim 8, wherein each of the collimator optical systems in the first LED light source, the second LED light source, and the third LED light source has components having a common shape. Furthermore, a condensing optical system that condenses the light beams of the first color light, the second color light, and the third color light synthesized on the same optical axis by the light synthesis unit,
A rod integrator that has an incident end at a condensing position of the condensing optical system, converts the incident light into a uniform intensity distribution, and emits it;
The illumination optical system according to claim 8, further comprising a relay optical system that guides the light emitted from the rod integrator to the illuminated portion side. When the focal length of the collimator optical system of the third LED light source is FL, the focal length of the condensing optical system is FC, and the optical path length in terms of air from the third LED light source to the incident end of the rod integrator is P3,
1.8 × (FL + FC) ≦ P3 ≦ 2.2 × (FL + FC)
The illumination optical system according to claim 10, satisfying the relationship:   The illumination optical system according to claim 1, wherein the first LED light source, the second LED light source, and the third LED light source emit light sequentially.   13. An image projection comprising: the illumination optical system according to claim 1; a modulation element that modulates illumination light from the illumination optical system; and a projection optical system that projects the modulated illumination light. apparatus.   At least one of the illumination optical system and the projection optical system has a variable diaphragm mechanism, and the amount of light emitted from the first LED light source, the second LED light source, and the third LED light source according to the opening state of the variable diaphragm. The image projection device according to claim 13, wherein the ratios are different.

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