projector

Abstract

Provided is a projector with which it is possible to prevent deterioration of optical performance resulting from a change in the shape of a reflection surface caused by local temperature increase in a mirror of the projector. The projector comprises an image display element and an image-forming optical system for enlarging and projecting an image displayed on an image-forming part of the image display element on a projection surface, the image-forming optical system having a lens system LS on which image light from the image-forming part is made incident and a synthetic resin mirror M that is placed on the enlargement side of an aperture stop S of the lens system and has refractive power, the projector also comprising: a thermistor 21 that detects, at the reverse-surface side of the reflective surface of the mirror, the temperature at a predetermined position on the reflective surface; a cooling means that includes a Peltier element 22 and heat-conductive members 11‒13, the cooling means cooling an area region including the prescribed position; and a control means 30 that constantly controls the cooling of the area region by the cooling means on the basis of the temperature detected by the thermistor.

Description

Projector

[0001] The present invention relates to a projector.

[0002] Various types of projectors have been known for displaying an image by enlarging and projecting an image displayed on an image forming unit of an image display element onto a projection surface. Various image display elements, such as DMDs (Digital Mirror Devices) and liquid crystal panels, are known as "light valves." The image forming unit is the portion of the light valve where the image to be enlarged and projected is displayed. The image enlarged and projected onto the projection surface (generally a "screen surface") is also referred to as the "projected image" or "enlarged image." A widely known optical configuration of a projector achieves a short projection distance by combining a lens system and a "mirror with refractive power" as optical elements. In this configuration, light beams entering the lens system from the image forming unit and passing through the lens system are reflected by the mirror toward the projection surface. Brightness is required for the enlarged image projected onto the projection surface. However, brightening the enlarged image increases the light intensity of the imaging light beam, raising the temperature of the optical elements, such as the lens system and mirror, and easily causing thermal deformation of the lenses and mirrors in the lens system. Such thermal deformation changes the inherent optical characteristics of the optical elements, and in particular tends to deteriorate field curvature and chromatic aberration, and also tends to lower resolution due to the influence of thermal deformation of the optical elements. Conventionally, as a measure to suppress fluctuations in optical characteristics due to temperature rise of optical elements, a technology has been known in which temperature deviation of lenses in a lens barrel is eliminated by cooling or heating a part of the "lens barrel that holds the lens system" of a projection optical system consisting only of a lens system (Patent Document 1).

[0003] The light intensity of the imaging light beam is not uniform across its cross section, and the light intensity is not uniform on the reflective surface of the mirror either. The "non-uniform light intensity distribution" on the reflective surface of the mirror changes depending on the configuration of the lens system and the positional relationship between the image forming unit and the lens system, and also changes depending on the image displayed, but the effect of "changes in the light intensity distribution of the imaging light beam due to the displayed image" is generally small, and the light intensity distribution depending on the configuration of the lens system and the positional relationship with the image forming unit is approximately constant.

[0004] In areas of high light intensity in the imaging light beam incident on the reflective surface of a mirror, localized high-temperature areas are formed on the mirror surface. The mirror surfaces of mirrors used in projectors are concave mirrors with positive power, so they have a curved shape. Because of ease of manufacturing and low cost, mirrors are often made of synthetic resin. Because synthetic resins have low thermal conductivity, heat is not easily dissipated in areas irradiated with the high light intensity of the imaging light beam, causing the temperature to rise easily. Furthermore, because synthetic resins have a high coefficient of thermal expansion, areas where the temperature rises are prone to "large deformation due to thermal expansion." As a result, the temperature rise occurs locally (in spots), and the resulting localized deformation of the mirror surface can significantly degrade resolution, including the aforementioned field curvature and chromatic aberration, even with a temperature increase of only a few degrees from room temperature.

[0005] Such deterioration in optical performance is caused by "local distribution of high temperature areas occurring on the mirror," and is therefore difficult to resolve using the method of Patent Document 1.

[0006] SUMMARY OF THE INVENTION An object of the present invention is to realize a projector that can prevent the deterioration of optical performance caused by the change in the shape of the reflecting surface resulting from the local temperature rise of the mirror.

[0007] The projector of this invention comprises an image display element and an imaging optical system that enlarges and projects an image displayed on the image forming section of the image display element onto a projection surface, the imaging optical system comprising a lens system into which image light from the image forming section is incident, and a mirror made of synthetic resin and having refractive power that is arranged on the enlargement side of the aperture stop of the lens system, the projector also comprising a thermistor that detects the temperature of a predetermined position on the reflective surface of the mirror on the back side of the reflective surface, a cooling means that includes a Peltier element and a heat conducting member and cools an area including the predetermined position by bringing the heat conducting member into contact with the back side, and a control means that constantly controls the cooling of the area by the cooling means based on the temperature detection by the thermistor, the predetermined position being the position of a local high temperature area included in a temperature rise area caused by the light intensity distribution of the imaging light beam on the reflective surface.

[0008] According to this invention, it is possible to realize a projector that effectively prevents deterioration of optical performance caused by local high temperature areas on the reflective surface of a mirror having refractive power.

[0009] 1 is a conceptual diagram of an imaging optical system of a projector; FIG. 2 is a diagram illustrating a temperature distribution on the rear surface of a mirror due to the intensity distribution of an imaging light beam; FIG. 3 is a diagram illustrating temperature control of a mirror according to an embodiment; and FIG. 4 is a diagram illustrating temperature control of a mirror according to an embodiment.

[0010] 1 is a conceptual diagram of the imaging optical system of a projector. The imaging optical system has a lens system LS and a mirror M. In the figure, the symbol O indicates the surface on which the image display portion of the image display element is formed. Furthermore, the symbol CMX indicates a color synthesis means, and the symbol AX indicates the optical axis of the imaging optical system.

[0011] The image display unit is the "upper half in the drawing" of the surface O, and is disposed displaced upward in the drawing with respect to the optical axis AX. The image light beam from the image display unit enters the lens system LS via the color combining means CMX, and after emerging from the lens system LS, is incident on the mirror M, where it is reflected to become a projection light beam FLX, which is then enlarged and projected as a projection image onto a screen (not shown) provided on the left side of the drawing.

[0012] The image display element uses a laser light source that emits the three primary colors of R (red), G (green), and B (blue), which are incident on a single-panel DMD, and the DMD's ON and OFF lights are synchronized with the light source to display colors.

[0013] The lens system LS has an aperture stop S, and the mirror M is disposed on the enlargement side of the aperture stop S. In this example, the mirror M is a concave mirror and has a "positive refractive power."

[0014] An imaging optical system as shown in Figure 1 was fabricated. The mirror M was made by stamping an acrylic synthetic resin with a thickness of 5 mm to form a concave shape. Figure 2 shows the prototype mirror M.

[0015] As light sources, lasers were used for the three colors R, G, and B, respectively, and the light source wattage was set to 300 W. An image light beam corresponding to a white image was emitted, and after one hour of continuous operation, the temperature distribution of the mirror M was measured from the back side, and the results shown in Figure 2 were obtained.

[0016] Mirror M is a concave mirror, and Figure 2 shows it viewed from the rear side. The three-dimensional shape of the mirror is "a shape that bulges convexly toward the front of the drawing in Figure 2." The temperature distribution shows that the areas indicated by symbols A1 and A2 have a maximum temperature of 31.138°C. The area indicated by symbol A3 changes continuously from 29.227°C to 27.316°C as it moves away from areas A1 and A2. The outer area A4 decreases continuously from 27.316°C to 22.539°C at the outermost edge (the outer periphery of mirror M) as it moves outward. The temperature change in the temperature distribution is smooth. Mirror M is designed for a room temperature of 22°C.

[0017] In areas A1 and A2, the temperature was approximately 10 degrees higher than the design temperature of 22 degrees, and in these areas the surface side of the mirror M underwent uneven thermal expansion, which acted to weaken the positive refractive power, resulting in field curvature, chromatic aberration, and degradation of resolution.

[0018] The positional relationship between the image display element, the lens system LS, and the mirror M is uniquely determined by design, so the temperature distribution pattern that occurs as described above is approximately uniquely determined. Therefore, the occurrence of temperature distribution can be suppressed by temperature control, which will be described below.

[0019] The deterioration of the optical characteristics was prevented as follows: The temperature at a predetermined position on the reflecting surface of the mirror M was detected by a thermistor on the back side of the reflecting surface, and based on the temperature detected by the thermistor, the mirror M was cooled from the back side by a cooling means including a Peltier element and a heat conducting member.

[0020] A part of the configuration of one embodiment is shown in Fig. 3. In Fig. 3, reference numerals 11, 12, and 13 denote heat-conducting members, reference numeral 21 denotes a thermistor, and reference numeral 22 denotes a Peltier element.

[0021] That is, the temperature of the mirror M is detected by the thermistor 21, and based on the detected temperature, a control means (not shown) controls the Peltier element 22, which cools the mirror M from the backside using the heat-conducting members 11, 12, and 13. The thermistor 21 detects the temperature of the backside of the mirror M by bringing its heat-receiving surface into contact with the backside of the mirror M, and the detection position is a predetermined position, i.e., the position of a "local high-temperature portion included in a temperature rise region caused by the light intensity distribution on the reflective surface," and in the example being described, this is the fixed position in region A1 shown in Figure 2, i.e., "within the region with the highest temperature." Note that region A2 is also in the same temperature region as region A1, so temperature detection by the thermistor 21 may be performed in either region A1 or A2, and in this example, it is performed in region A1.

[0022] The heat-conducting members 11, 12, and 13 are made of a material with high thermal conductivity, and their surfaces facing the mirror M are curved to match the curved surface of the rear surface of the mirror, so as to be in close contact with the rear surface of the mirror M. The Peltier element 22 is pressed against the heat-conducting member 11 so that the heat-conducting member 11 is sandwiched between its cooling surface and the rear surface of the mirror, thereby cooling the heat-conducting member 11. The heat-conducting members 12 and 13 are integrated with the heat-conducting member 11. Therefore, the cooling effect of the Peltier element 22 extends from the heat-conducting member 11 to the heat-conducting members 12 and 13, and ultimately extends from the rear surface of the mirror M to the area covered by the heat-conducting members 11, 12, and 13.

[0023] FIG. 4 is a diagram illustrating the mirror M, the heat conducting members 11 and 12, the thermistor 21, the Peltier element 22, and the control means 30.

[0024] 4 is a diagram showing the relationship between the mirror M, the heat conducting member 12, and the thermistor 21, and the right side of the upper diagram of Fig. 4 is a diagram for explaining the relationship between the mirror M, the heat conducting member 11, and the Peltier element 22. In these diagrams, the up-down direction of the diagram corresponds to the up-down direction of the image display unit shown in Fig. 1.

[0025] As shown in the upper diagram of Fig. 4, the heat conducting member 11 is made up of a heat conducting member 111 and a heat conducting sheet 112, and the heat conducting member 12 is made up of a heat conducting member 121 and a heat conducting sheet 122. Although not shown in Fig. 4, the heat conducting member 13 shown in Fig. 3 is also made up of a heat conducting member similar to the heat conducting members 111 and 121 and a heat conducting sheet similar to the heat conducting sheets 112 and 122, like the heat conducting members 11 and 12.

[0026] The heat conducting members 11, 12, and 13 shown in Fig. 3 are integrated with one another. The heat conducting members 111 and the like of the heat conducting members 11, 12, and 13 are integrated with one another, and their mirror-facing surfaces are curved to match the shape of the rear surface of the mirror M and are provided in close contact with the rear surface of the mirror M. These integrated heat conducting members 111 and the like are made of processed aluminum sheet metal, with a thickness of 1 mm at their thinnest part, and the surface opposite the rear surface of the mirror M being a cylindrical surface.

[0027] Thermally conductive sheets 112 and 122, as well as a thermally conductive sheet provided on a heat-conducting member 13 (not shown), are attached to the cylinder surface. The thermally conductive sheet 112 and the like are made of a sponge-like dielectric material with good thermal conductivity and a thickness of about 2 mm.

[0028] Small circular holes with a diameter of about 1 mm are formed in the heat conduction member 121 and the heat conduction sheet 122 of the heat conduction member 12, and thermistors 21 are fitted into these holes. The thermistor 21 is cylindrical with a diameter of 1 mm and a length of 3 mm, and its end face on the mirror M side abuts against the back surface of the mirror M. The abutting position of the thermistor 21 is an appropriate position (for example, the center) within the area A1 shown in FIG. 2.

[0029] A Peltier element 22 is pressed against the surface of the thermally conductive sheet 112 of the heat conducting member 11. The Peltier element 22 has a square shape with an area of ​​the pressed-in surface of 40 mm x 40 mm. In this embodiment, a heat sink 23 for heat dissipation is provided on the back of the Peltier element 22 to promote heat dissipation from the Peltier element 22. The heat dissipation portion of the heat sink 23 has the shape of a "flock of thin cylinders standing in a pinholder shape" on one side of a thin flat plate.

[0030] The control means 30 has an input section that receives temperature information from the thermistor 21, an output section that outputs a drive voltage for driving the Peltier element 22, and a calculation section that determines the drive voltage in accordance with the temperature information, and controls the cooling of the mirror M from the back side.

[0031] This cooling control is always performed while the projector is in operation. That is, when the projector starts operating and the light source is turned on, the thermistor 21 detects the temperature of area A on the back surface of the mirror M. The control means 30 performs cooling using the Peltier element 22 in accordance with the detected temperature. The cooling action of the Peltier element 22 extends to the back surface of the mirror M via the heat-conducting members 11, 12, and 13, cooling an area including areas A and B. This temperature control is feedback control that keeps the temperature detected by the thermistor 21 at a predetermined temperature, for example, 22 degrees.

[0032] The cooling effect extends to the area on the rear surface of the mirror covered by the heat conducting members 11, 12, and 13, and in this embodiment, the area including the area A3 shown in FIG. 2 is cooled.

[0033] This temperature control effectively prevents the formation of a temperature rise pattern on the mirror M due to irradiation with an imaging light beam of non-uniform intensity, and effectively prevents degradation of resolution, such as image plane curvature and chromatic aberration, caused by thermal deformation of the mirror surface.

[0034] Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the specific embodiment described above, and various modifications and variations are possible within the spirit and scope of the invention as defined in the claims unless otherwise specifically limited in the above description. For example, in Fig. 3, instead of providing the Peltier element 22 on the heat-conducting member 11, two Peltier elements may be provided separately on the heat-conducting members 12 and 13 to control the temperature. However, in the case of the embodiment described above, only one Peltier element is required, which can be implemented at lower cost than such an embodiment.

[0035] The temperature distribution pattern on the mirror generated by the imaging light beam will differ depending on the light intensity distribution on the image-forming element side, but as mentioned above, the positional relationship between the image display element, lens system, and mirror is uniquely determined by design, so it goes without saying that the position of the thermistor, the shape and size of the area on the back surface of the mirror covered by the heat-conducting member, the number and arrangement of the Peltier elements, etc. can be optimized in accordance with the temperature distribution pattern thus determined.

[0036] In the above embodiment, aluminum is used as the material for the heat conducting member that constitutes the heat conducting member, but this is not limited to this and other materials such as copper, nickel, etc. Also, instead of configuring the heat conducting member with a heat conducting member and a dielectric heat conducting sheet as in the above embodiment, a highly heat conductive graphite sheet or the like may be provided alone directly on the rear surface of the mirror.

[0037] That is, the heat-conducting member may be constituted by a sheet-like heat-conducting means that conducts heat from a high-temperature area on the rear surface of the mirror to the Peltier element.

[0038] Furthermore, since the mirror is provided on the enlargement side of the aperture stop of the lens system, it can be the optical element on the most enlargement side of the imaging optical system as in the embodiment described above, but it is also possible to arrange one or more lenses that constitute the lens system on the enlargement side of the mirror.

[0039] Furthermore, in the above embodiment, a mirror having a concave reflecting surface is shown, but depending on the imaging optical system, a mirror having a convex reflecting surface may also be used.

[0040] The effects described in the embodiments of the present invention are merely a list of preferred effects resulting from the invention, and the effects of the invention are not limited to "those described in the embodiments."

[0041] O: Surface on which an image display portion of an image display element is formed LS: Lens system M: Mirror 11, 12, 13: Heat conducting member 21: Thermistor 22: Peltier element 23: Heat sink

[0042] Patent No. 6285569

Claims

1. A projector having an image display element and an imaging optical system that enlarges and projects an image displayed on the image forming unit of the image display element onto a projection surface, the imaging optical system having a lens system into which image light from the image forming unit is incident, and a mirror made of synthetic resin and having refractive power that is arranged on the enlargement side of the aperture stop of the lens system, the projector also having a thermistor that detects the temperature of a predetermined position on the reflective surface of the mirror on the back side of the reflective surface, a cooling means that includes a Peltier element and a heat conducting member and cools an area including the predetermined position by bringing the heat conducting member into contact with the back side, and a control means that constantly controls the cooling of the area by the cooling means based on the temperature detection by the thermistor, the predetermined position being the position of a local high temperature area included in a temperature rise area caused by the light intensity distribution of the imaging light beam on the reflective surface.

2. A projector according to claim 1, wherein said cooling means comprises said Peltier element and sheet-like heat conducting means for conducting heat from said area to said Peltier element.

3. A projector according to claim 1 or 2, wherein a heat sink for dissipating heat is provided on the rear side of said Peltier element.

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