projector

Abstract

To provide a projector capable of preventing optical performance from deteriorating due to a change of a reflection surface shape caused by local temperature rise of a mirror of the projector.SOLUTION: A projector comprises: an image display element and an image formation optical system enlarging and projecting an image displayed on an image formation part of the image display element onto a projected surface. The image formation optical system includes a lens system LS receiving image light from the image formation part, and a resin-made mirror M disposed on an enlargement side of an aperture diaphragm S and having refractive power. The projector further comprises: a thermistor 21 detecting a temperature of a reflection surface of the mirror at a prescribed site on the rear side of the reflection surface; cooling means including a Peltier element 22 and heat conductive members 11-13 and cooling an area region including the prescribed site; and control means 30 steadily controlling cooling of the area region by the cooling means based on temperature detection by the thermistor.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a projector. [Background technology]

[0002] Various types of projectors have been known in the past that enlarge and project an image displayed on the image forming section of an image display element onto a projection surface. Various types of image display elements, such as DMDs (Digital Mirror Devices) and LCD panels, are known as "light valves," and the image forming section is the "portion of the light valve where the image to be enlarged and projected is displayed." Hereinafter, the image enlarged and projected onto the projection surface (generally the "screen surface") will also be referred to as the "projected image" or "enlarged image." A widely known optical configuration of a projector is one that combines a lens system and a "mirror having refractive power" as optical elements to achieve a short projection distance. In such a configuration, an imaging light beam that enters the lens system from the image forming unit and passes through the lens system is reflected by a mirror toward the projection surface. The enlarged image projected onto the projection surface must be bright, but making the enlarged image brighter increases the intensity of the imaging light beam, raising the temperature of the lens system and mirrors, which are optical elements, 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, particularly degrading field curvature and chromatic aberration, and also easily reducing resolution due to the effects 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 deviations of lenses within a lens barrel are 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 the portion of the imaging light beam incident on the reflecting surface of the mirror where the light intensity is high, a local high temperature portion is formed on the mirror surface. The mirror surface of a mirror used in a projector is a concave mirror with positive power, and therefore has a curved shape. From the viewpoint of ease of manufacture and low cost, the mirror is 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, and the temperature easily rises. 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 local deformation of the mirror surface can easily significantly degrade resolution, causing the aforementioned field curvature and chromatic aberration, even with a temperature rise of just 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. Summary of the Invention [Problem to be solved by the invention]

[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. [Means for solving the problem]

[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. [Effects of the Invention]

[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. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a conceptual diagram of an imaging optical system of a projector. [Figure 2] 10A and 10B are diagrams illustrating the temperature distribution on the rear surface of the mirror due to the intensity distribution of the imaging light beam. [Figure 3] FIG. 2 is a diagram illustrating temperature control of a mirror according to one embodiment. [Figure 4] 3A and 3B are diagrams illustrating temperature control of a mirror in one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] FIG. 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. Also, 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 figure" of surface O, and is disposed displaced upward in the figure with respect to the optical axis AX. The image light beam from the image display unit enters lens system LS via color synthesis means CMX, and after emerging from lens system LS, enters mirror M, where it is reflected to become 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 figure.

[0012] The image display element uses a laser light source with the three primary colors of R (red), G (green), and B (blue) to be 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] We prototyped an imaging optical system as shown in Figure 1. Mirror M was made by stamping a 5mm thick acrylic synthetic resin into a concave shape. Figure 2 shows the prototype mirror M.

[0015] Lasers were used as light sources for the three colors R, G, and B, with a light source wattage of 300 W. An image light beam corresponding to a white image was emitted, and the temperature distribution of mirror M after one hour of continuous operation 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 back side. The three-dimensional shape of the mirror is "a shape that bulges outward toward the front of the drawing in Figure 2." The temperature distribution showed a maximum temperature of 31.138°C in the areas indicated by symbols A1 and A2, and in the area indicated by symbol A3, the temperature changed continuously from 29.227°C to 27.316°C as it moved away from areas A1 and A2, and in the outer area A4, the temperature decreased continuously from 27.316°C to 22.539°C at the outermost part (the outer periphery of mirror M) as it moved outward. The temperature change in the temperature distribution was smooth. Mirror M is designed for a room temperature of 22 degrees.

[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, lens system LS, and mirror M is uniquely determined by design, so the temperature distribution pattern that occurs as described above is almost 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 properties was prevented as follows. That is, 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 detection 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] FIG. 3 shows a part of the configuration of one embodiment. 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 the Peltier element 22 is controlled by a control means (not shown) based on the detected temperature, and the mirror M is cooled from the rear side by the heat conducting members 11, 12, and 13. The thermistor 21 detects the temperature of the rear surface of the mirror M by bringing its heat-receiving surface into contact with the rear surface of the mirror, but the position to be detected is a predetermined position, i.e., the position of a "local high-temperature area included in the temperature rise area caused by the light intensity distribution on the reflective surface," and in the example being described, this is a fixed position in area A1 shown in Figure 2, i.e., "within the area with the highest temperature." Note that area A2 is also in the same temperature area as area A1, so temperature detection by the thermistor 21 may be performed in either area A1 or A2, and in this example, it is performed in area 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 according to the curved surface of the rear surface of the mirror, and are 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. As shown in FIG.

[0024] 4 is a diagram illustrating 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 diagrams 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, just like the heat conducting members 11 and 12.

[0026] The heat-conducting members 11, 12, and 13 shown in FIG. 3 are integrally formed. The heat conducting members 111 etc. of the heat conducting members 11, 12, 13 are integrated with one another, and their mirror-side surfaces are curved to match the shape of the back surface of the mirror M, and are provided in close contact with the back surface of the mirror M. These integrated heat conducting members 111 etc. are made by processing aluminum sheet metal, and are 1 mm thick at their thinnest parts, with the surface opposite the back surface of the mirror being a cylindrical surface.

[0027] Thermally conductive sheets 111 and 122, as well as a thermally conductive sheet provided on conductive member 13 (not shown), are attached to the cylinder surface. Thermally conductive sheet 111 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 thermistors 21 are cylindrical with a diameter of 1 mm and a length of 3 mm, and the end face on the mirror M side abuts against the back surface of the mirror M. The position at which the thermistors 21 abut is an appropriate position (for example, the center) within the region A1 shown in FIG. 2.

[0029] A Peltier element 22 is pressed against the surface of the heat conduction sheet 112 of the heat conduction 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 a shape of "a forest of thin cylinders standing like a pinholder" 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 performed constantly while the projector is in operation. That is, when the projector starts operating and the light source is turned on, the temperature of area A on the back surface of mirror M is detected by thermistor 21. Control means 30 performs cooling using Peltier element 22 in accordance with the detected temperature. The cooling action of Peltier element 22 extends to the back surface of mirror M via 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 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 that is cooled includes the area A3 shown in FIG.

[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 field curvature and chromatic aberration, caused by thermal deformation of the mirror surface.

[0034] Although the preferred embodiment of the invention has been described above, the invention is not limited to the specific embodiment described above, and unless otherwise specifically limited in the above description, various modifications and changes are possible within the spirit of the invention as described in the claims. 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 perform temperature control. However, in the case of the embodiment described above, only one Peltier element is required, and therefore it 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 of the heat conducting member that constitutes the heat conducting member, but this is not limiting and copper, nickel, etc. may also be used. Instead of configuring the heat conducting member with a heat conducting member and a dielectric heat conducting sheet, 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." [Explanation of symbols]

[0041] O. Surface on which the image display part of the image display element is formed LS lens system M mirror 11, 12, 13 Heat conduction material 21 Thermistor 22 Peltier element 23 Heat sink [Prior art documents] [Patent documents]

[0042] [Patent Document 1] Patent No. 6285569

Claims

1. a thermistor that detects the temperature of a predetermined position on the reflecting surface of the mirror on the back side of the reflecting 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; and a control means that constantly controls the cooling of the area by the cooling means based on the temperature detection by the thermistor, and the predetermined position is the position of a local high temperature portion included in a temperature rise area caused by the light intensity distribution of the imaging light beam on the reflecting surface.

2. 2. The projector according to claim 1, The projector, wherein the cooling means has a Peltier element and a sheet-like heat conducting means for conducting heat from the area to the Peltier element.

3. 3. The projector according to claim 1, further comprising a heat sink for dissipating heat on the rear side of the Peltier element.

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