projector

Abstract

To achieve a projector that can prevent a deterioration in optical performance due to a change in the shape of a reflection surface caused by a local increase in the temperature of a mirror of the projector.SOLUTION: A projector has: image display means; an imaging optical system that enlarges and projects an image displayed on an image forming unit of the image display means on a projection target surface; and image correction control means 4. The imaging optical system has a lens system LS on which image light from the image forming unit is incident, and a mirror M made of synthetic resin that is arranged on an enlargement side of an aperture stop S of the lens system and has a refractive power. The image correction control means corrects a deterioration of an enlarged image due to an uneven increase in the temperature of the mirror M caused by the intensity distribution of imaging beams of light.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] 2. Description of the Related Art Various types of projectors are known in the art that display an image displayed on an image forming section of an image display means as an enlarged image on a projection surface.

[0003] There are various types of image display devices known, including self-luminous devices that use a one-dimensional or two-dimensional array of tiny light-emitting elements, such as an LED array, to display two-dimensional images through the "distribution of light-emitting elements," and devices that modulate the intensity of illumination light from a light source to form an image using so-called "light valves" such as DMDs (Digital Mirror Devices) or LCD panels.

[0004] The "image forming section" is the "portion where the image to be enlarged and projected is displayed" in an LED array or light valve. The enlarged image projected onto the projection surface (generally the "screen surface") is also referred to as the "projected image" below.

[0005] 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.

[0006] In this optical configuration, the image light beam from the image forming unit enters the lens system, and the light beam that passes through the lens system is reflected by a mirror toward the projection surface. Hereinafter, the image light beam that contributes to the formation of the projected image will also be referred to as the "imaging light beam."

[0007] In a projector, there is a problem of heat generation from the light source (a self-generating type such as the LED array or an illumination light source that irradiates illumination light onto a light valve) that generates an imaging light flux.

[0008] In other words, the enlarged image projected onto the projection surface requires "brightness," but if the amount of light emitted from the light source is increased to brighten the enlarged image, the amount of heat generated by the light source increases, causing thermal deformation of optical elements such as lenses and mirrors, resulting in a deterioration of optical performance.

[0009] Such problems have been known for some time, and Patent Document 1 discloses a technology for adjusting the temperature of an aspherical mirror or its vicinity by cooling or the like in order to deal with deterioration of optical performance caused by thermal deformation of the aspherical mirror in an imaging optical system having a lens system and an aspherical mirror.

[0010] Furthermore, Patent Document 2 discloses a technology for correcting degradation of a projected image, such as astigmatism, caused by temperature changes within a lens barrel that holds a lens system in an imaging optical system composed of a lens system, by displacing a correction lens provided within the lens system in the direction of the optical axis in response to temperature changes.

[0011] The mirror surfaces of mirrors used in projectors have refractive power, so they are often aspherical with a "concave or convex curved shape," and are often made from synthetic resin for ease of forming the surface shape and low cost.

[0012] Increasing the brightness of the enlarged image also increases the "light intensity in a cross section perpendicular to the direction of travel" of the imaging light beam. This light intensity is not uniform on the cross section, nor is it uniform on the reflective surface of the mirror. The "non-uniform light intensity distribution" on the reflective surface of the mirror changes depending on the configuration of the lens system and the relative position of the image forming unit and the lens system. It also changes depending on the image being displayed, but the effect of "changes in the light intensity distribution of the imaging light beam due to changes in the displayed image" is generally small, and the light intensity distribution due to the configuration of the lens system and the "relative position of the image forming unit and the lens system" is approximately constant.

[0013] 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. In mirrors made of synthetic resin, the thermal conductivity of the material is low, and the parts irradiated with the high intensity of the imaging light beam are prone to temperature rise because heat is difficult to dissipate.In addition, because synthetic resin has a high coefficient of thermal expansion, the parts that rise in temperature are prone to "large deformation due to thermal expansion."

[0014] As a result, the temperature rise of the mirror occurs locally (in a spot), and the resulting local deformation of the mirror surface changes the focal position of the light reaching the periphery of the projection surface (screen surface), degrading the resolution at the periphery of the projected image.

[0015] Since the above-mentioned deformation of a mirror made of synthetic resin is "local," the method of "adjusting the temperature by cooling the mirror or its vicinity" as in Patent Document 1 takes time to equalize the temperature of the entire mirror because the thermal conductivity of synthetic resin is low, making it difficult to respond quickly.

[0016] The imaging optical system of Patent Document 2 is composed of a lens system and does not include a mirror made of synthetic resin, so the problem of local deformation of the mirror made of synthetic resin does not exist. Summary of the Invention [Problem to be solved by the invention]

[0017] An object of the present invention is to realize a projector that can effectively correct the deterioration of the optical performance of the imaging optical system caused by deformation of the reflecting surface shape due to localized high temperature caused by uneven intensity of the imaging light beam in the above-mentioned synthetic resin mirror. [Means for solving the problem]

[0018] The projector of this invention is a projector that projects an image displayed on an image forming section of an image display means as an enlarged image onto a projection surface, and includes: an image display means; an imaging optical system that projects an image light beam from the image display means onto the projection surface as an imaging light beam; and an image correction control means that corrects the enlarged image on the projection surface. The imaging optical system includes a lens system that receives the image light beam from the image forming section and has a focal length variable function; and a mirror made of synthetic resin that is positioned on the enlargement side of an aperture stop of the lens system and reflects the imaging light beam and has refractive power. The image correction control means is a means for correcting deterioration of the enlarged image due to uneven temperature rise of the mirror that reflects the imaging light beam, which is caused by the intensity distribution of the imaging light beam, and includes a parameter temperature detection section that detects temperatures at multiple locations on the back side of the mirror and obtains a parameter temperature from the detected multiple temperatures; and a control section that controls the focal length variable function in accordance with the parameter temperature obtained by the parameter temperature detection section to correct deterioration of the enlarged image. [Effects of the Invention]

[0019] According to this invention, it is possible to realize a projector that can effectively correct the deterioration of optical performance caused by local high temperature areas on the reflective surface of a mirror made of synthetic resin and having refractive power. [Brief explanation of the drawings]

[0020] [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 the determination of a parameter temperature of a mirror according to one embodiment. [Figure 4] 10 is a diagram illustrating a control unit for correcting degradation of an enlarged image according to an embodiment. FIG. [Figure 5] 10A to 10C are diagrams illustrating control of degradation correction of an enlarged image in one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0021] FIG. 1 is a conceptual diagram of the imaging optical system of a projector. The imaging optical system includes a lens system LS and a mirror M made of synthetic resin.

[0022] In the drawing, the symbol O denotes the "image display surface on which the image display section is formed" of the image display means, the symbol CMX denotes the color synthesis means, and the symbol AX denotes the optical axis of the lens system of the imaging optical system.

[0023] The image display unit is the "upper half in the drawing" of the image display 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, enters the mirror M, where it is reflected to become the 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.

[0024] That is, the image light beam incident on the lens system LS passes through the lens system LS and the mirror M as an imaging light beam, and emerges as a projection light beam FLX.

[0025] The image display unit is composed of three DMDs (one of which is shown in Figure 1) that display images in each of the three primary colors, R (red), G (green), and B (blue).Light from LED light sources of the corresponding colors is irradiated onto the DMDs, which are reflected as image light of each color, enter the color synthesis means CMX, are synthesized into a color image light beam, and enter the lens system LS.

[0026] The lens system LS has an aperture stop S, and the mirror M is disposed on the enlargement side of the aperture stop S. The mirror M, made of synthetic resin, is a concave mirror in this example and has a "positive refractive power."

[0027] The lens system LS has a "focal length variable function." The symbol FL in Figure 1 denotes a floating mechanism for implementing the focal length variable function, and a cam mechanism (not shown) displaces the movable lens of the floating mechanism in the direction of the optical axis AX to change the focal length.

[0028] As described above, the projector of the present invention has an image correction control means for correcting the deterioration of the enlarged image caused by the uneven temperature rise of the mirror due to the intensity distribution of the imaging light beam.

[0029] The correction is performed as follows. That is, the temperature is detected at multiple locations on the rear surface of the mirror M, and a parameter temperature is obtained from the multiple detected temperatures. Then, the focal length variable function is controlled in accordance with the obtained parameter temperature so as to correct the degradation of the enlarged image.

[0030] For this purpose, the projector has a parameter temperature detection unit and an image correction control means.

[0031] The "parameter temperature" is temperature information for performing image correction control, and is obtained by detecting the temperatures at multiple locations on the rear surface side of the mirror M and from the multiple temperatures detected. For example, if there are n temperature detection locations (n≧2) and the detected temperatures obtained at each location are T1, T2, . . . , Tn, the parameter temperature: TP is determined using these detected temperatures: T1, T2, . . . Tn. For example, the arithmetic average (ΣTi) / n (i=1 to n) of the detected temperatures T1 to Tn can be used as the parameter temperature, or the weighted average (Σmi·Ti / Σmi (i=1 to n) where weights m1 to mn are assigned to each detected temperature can be used as the parameter temperature. Of course, the parameter temperature is not limited to the arithmetic average or weighted average of the detected temperatures.

[0032] The determined parameter temperature: TP is related to the degradation of the projected image. When a non-uniform temperature distribution occurs on the synthetic resin mirror M due to non-uniformity in the intensity distribution of the imaging light beam, the parameter temperature: TP changes accordingly.

[0033] When a non-uniform temperature distribution occurs on the mirror M, the focal length of the imaging optical system, primarily the "distance of the focal position of light reaching the periphery of the projection surface (screen surface)" changes accordingly.

[0034] The amount of change in this focal length (referred to as "Y") and the change in the parameter temperature: TP have a certain correspondence relationship depending on the imaging optical system and the image display means, and this correspondence relationship can be experimentally determined in advance.

[0035] That is, the correspondence relationship between each value of the changing parameter temperature: TP and the amount of change in focal length due to the change in focal position: Y: F, that is, Y=F(TP) can be determined experimentally.

[0036] This focal length change amount Y can be corrected by adjusting the focal length of the lens system of the imaging optical system. That is, the focal length change amount: Y can be canceled by the movement amount: Z of the movable lens of the floating mechanism FL. The relationship between the focal length change amount: Y and the movement amount: Z of the movable lens of the floating mechanism FL is G, that is, Z=G(Y) can also be determined experimentally.

[0037] According to this relationship: Z = G(Y), the amount of movement of the lens: Z can be related to the amount of operation: D(Z) of the lens movement mechanism for realizing the amount of movement: G. A cam mechanism in a normal zoom mechanism can be used as the lens movement mechanism, and in this case, the amount of operation: D(Z) is the "amount of rotation of the drive cam" in the cam mechanism.

[0038] In this way, once the parameter temperature: TP is determined, the movement amount: G of the movable lens of the floating mechanism FL is determined to correct the "change in the distance of the focal position of light reaching the periphery of the projection surface" that occurs when the parameter temperature: TP is generated.Therefore, by displacing the movable lens by the operation amount: D(Z) of the lens movement mechanism in accordance with the parameter temperature: TP, it is possible to effectively correct deterioration of the projected image, mainly in the periphery.

[0039] FIG. 4 is a diagram illustrating the configuration of the image correction control means. The image correction control means includes a temperature detection means 3, a control calculation unit 4, and an adjustment mechanism 5. The control and calculation unit 4 is configured by a microcomputer and controls the temperature detection means 3 .

[0040] The temperature detection stage 3 has a plurality of temperature detectors, for example thermistors. These detectors are controlled by a control and calculation unit 4 to detect the temperature of the mirror M at a plurality of locations on the rear surface of the mirror M made of synthetic resin.

[0041] The temperatures detected by the plurality of thermistors are input to the control calculation means 4, and the parameter temperature determination unit 41 determines the parameter temperature: TP. The correction amount determination unit 42 determines the movement amount of the lens movement mechanism (the aforementioned movement amount: D(Z)) according to the parameter temperature: TP, outputs the determined movement amount to the adjustment mechanism 5, and the adjustment mechanism 5 moves the movable lens according to the input movement amount to perform correction.

[0042] That is, the temperature detection means 3 and the parameter temperature determination unit 41 are a "parameter temperature detection unit", and the correction amount determination unit 42 and the adjustment mechanism 5 are a "control unit".

[0043] This control process continues while the projector is powered on. For example, the temperature of the mirror M is detected, i.e., the detected values ​​of the multiple thermistors are sampled at predetermined time intervals, for example, every 30 seconds or every minute, and the amount of operation D(Z) is also determined according to the time intervals.

[0044] The process of determining the operating quantity: D(Z) based on the parameter temperature: TP can be carried out by sequentially performing calculations based on the above-mentioned relationships: Y=F(TP), Z=G(Y), which have been experimentally determined in advance, in accordance with the parameter temperature: TP, and determining the operating quantity: D(Z) based on Z obtained from the calculation results.

[0045] The parameter temperature: TP and the movement amount: D(Z) (hereinafter simply referred to as "D") are experimentally determined in advance, so instead of the above-mentioned sequential calculation, the relationship between the parameter temperature: TP and the movement amount: D may be stored in the correction amount determination unit 42 as an arithmetic expression or a table, and the movement amount: D corresponding to the determined parameter temperature: TP may be determined by calculating the arithmetic expression or by referring to the table.

[0046] One embodiment will be described below. An imaging optical system as shown in Figure 1 was fabricated. Mirror M is made by stamping a 5mm thick "acrylic synthetic resin" into a concave shape, and then depositing an aluminum reflective film onto the concave surface.

[0047] Figure 2 shows the prototype mirror M.

[0048] LEDs were used as light sources for the three colors R, G, and B, and were reflected by a DMD to form an image light beam corresponding to a white image.The temperature distribution of mirror M was measured from the back side after one hour of continuous operation with a light source wattage of 300 W, and the results shown in Figure 2 were obtained.

[0049] 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 in the areas indicated by symbols A1 and A2 showed a maximum temperature of 31.138°C, 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. The Mirror M is designed for a room temperature of 22 degrees.

[0050] Mirror M is made of synthetic resin and is 5 mm thick. Considering that synthetic resin has low thermal conductivity, the temperature on the front side of mirror M is more than 10 degrees higher than the temperature on the back side in the state shown in Figure 2. 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.

[0051] This degradation of the projected image is corrected as described above with reference to FIG.

[0052] An example of correction is described below. In Figure 3, three thermistors S1, S2, and S3 are placed in contact with the rear surface of mirror M to form a parameter temperature detector (temperature detection means in Figure 4). The positions of these thermistors S1, S2, and S3 are as follows: Thermistor S1 is located on the rear surface of the mirror at the intersection of the optical axis AX of the lens system LS and the reflecting surface of mirror M.

[0053] The thermistor S2 was located in the high temperature area A1 shown in FIG. 2, and the thermistor S3 was located in the high temperature area A2. The image correction control means used is the one shown by reference numeral 4 in FIG.

[0054] That is, the thermistors S1, S2, and S3 were controlled by a control and calculation unit 4 configured as a microcomputer.

[0055] The following description will be made with reference to FIG. 5 showing the operation flow. 5, (S1) to (S14) indicate step numbers of the control process, and "Y" indicates yes and "N" indicates no.

[0056] The control process begins when the projector is powered on (S1). The parameter i for the number of temperature measurements and the parameter j for the number of correction operations both become 1 (S2), thermistors S1, S2, and S3 become operational, and the sampling time is set to 1 minute, and the detected temperature T1 of thermistor S1, the detected temperature T2 of thermistor S2, and the detected temperature T3 of thermistor S3 are input into the control calculation unit 4 (S3).

[0057] Next, the parameter temperature: TP is determined based on the detected temperatures: T1, T2, T3 (S4).

[0058] In this example, the parameter temperature: TP is calculated based on the temperatures T1 to T3 detected by thermistors S1 to S3 using the following formula: TP=(T2+T3) / 2−T1 (Equation 1) This calculation formula is experimentally determined in advance and stored in the storage unit of the control calculation unit 4, and when the temperatures T1 to T3 are sampled, the calculation unit performs calculations according to the calculation formula 1.

[0059] As described above, T2 and T3 are the temperatures of the "high temperature areas A1 and A2" on the rear surface of the mirror, and therefore temperatures T2 and T3 are higher than temperature T1. According to the above calculation formula, the parameter temperature TP is a "positive value."

[0060] The determined parameter temperature: TP is compared with a threshold value: TS as a parameter temperature: TPi identified by the number of temperature measurements parameter: i (S5). The threshold value: TS is experimentally determined in advance as "the temperature representing the state of the mirror M at which correction control is required" and is stored in the memory of the control calculation unit 4.

[0061] If TPi≦TS, there is no need to move the operating lens of the lens system, so the number of times parameter i is increased to i+1 (S6) and the thermistor is sampled again. The sampling cycle is one minute, and sampling is performed one minute after the previous sampling.

[0062] The loop of steps (S3 to S6 to S3) is repeated until the parameter temperature: TP becomes equal to or greater than the threshold value: TS. When the parameter temperature: TP becomes equal to or greater than the threshold value: TS, the parameter temperature: TPi that has become equal to or greater than the threshold value is used to calculate the motor rotation angle: θ. At this time, the correction operation count parameter: j is 1.

[0063] The rotation angle θ of the motor is the aforementioned movement amount D, and is the rotation angle of the motor that moves the movable lens of the floating mechanism FL (FIG. 1) by the cam mechanism. As described above, the relationship between the amount of movement: D and the parameter temperature: TP is experimentally determined and can be stored as a table or as an arithmetic expression. In this example, the rotation angle: θ is calculated using the arithmetic expression: θ=a(TPi) 2 +b(TPi)+c (Equation 2) The calculation is performed according to the following formula.

[0064] [a, b, c] in the calculation formula 2 are constants experimentally determined in advance, and the calculation formula 2 is stored in the memory unit of the control calculation unit 4. The calculation is performed according to the above calculation formula 2 using "TPi" previously determined as the parameter temperature by the calculation unit, and the calculated rotation angle: θ becomes the rotation angle: θj identified by the correction operation count parameter: j (S7).

[0065] The rotation angle θj is compared with θj-1 (S8), and depending on the magnitude, motor operation (S9) or motor reverse operation (S10) is performed.

[0066] When the correction operation count parameter: j is 1, θj-1 becomes θ0, which corresponds to the reference position in the cam rotation. When the correction operation count parameter: j is 2 or more, θj-1 is the rotation angle in the previous correction operation.

[0067] When j≧2, if the rotation angle: θj is greater than the previous rotation angle: θj-1, the movement amount of the movable lens of the floating mechanism FL needs to be increased from the previous time, so in this case the motor is operated in the "positive direction" to increase the movement amount of the movable lens (S9).

[0068] This movement is repeated in a loop between steps S11 and S9 until the lens position of the movable lens becomes appropriate, and when the lens position becomes appropriate, the motor is stopped (S13).

[0069] Conversely, when j≧2, and the rotation angle: θj is smaller than the previous rotation angle: θj-1, the movement amount of the movable lens of the floating mechanism FL needs to be reduced from the previous amount, so in this case the motor is operated in reverse to move the movable lens in the opposite direction (S10).

[0070] This movement is repeated in a loop between steps S10 and S12 until the lens position of the movable lens becomes appropriate, and when the lens position becomes appropriate, the motor is stopped (S13).

[0071] The control of steps S9 to S13 is controlled by the control section of the control calculation means 4.

[0072] When the motor is stopped in step S13, the control calculation means 4 increments the correction operation count parameter j to j+1, returns to step S3, and performs new sampling of the mirror temperature, and the above-described process is repeated.

[0073] The rotation amount of the motor operating and reverse operating in steps S9 to S12 may be "detected and controlled by a potentiometer" or may be controlled by using a stepping motor as the motor.

[0074] 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. As mentioned above, the "non-uniform light intensity distribution" on the reflective surface of the mirror changes depending on the configuration of the lens system and the relative positions of the image forming unit and the lens system, and the temperature distribution of the mirror also changes accordingly. When detecting temperature using multiple thermistors, it is best to select positions appropriate for the temperature distribution of the mirror.

[0075] In the embodiment described above, of the three thermistors, the thermistors S2 and S3 are installed in the local high temperature areas A1 and A2 shown in FIG.

[0076] The temperature distribution pattern generated on mirror M by the imaging light beam differs depending on the "light intensity distribution of the imaging light beam on the mirror." However, since the positional relationship between the image display means, lens system, and mirror is uniquely determined by design, it goes without saying that the number and placement positions of thermistors can be optimized according to the temperature distribution pattern thus determined.

[0077] 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.

[0078] 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.

[0079] 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]

[0080] O. A surface on which an image display unit is formed in the image display means LS lens system M mirror S1, S2, S3 thermistors FL Floating mechanism [Prior art documents] [Patent documents]

[0081] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-145623 [Patent Document 2] Patent No. 7027736

Claims

1. A projector that projects an image displayed on an image forming unit of an image display means onto a projection surface as an enlarged image, an image display means; an imaging optical system that projects an image light beam from the image display means onto the projection surface as an imaging light beam; and an image correction control means that corrects the enlarged image on the projection surface, the imaging optical system includes a lens system that receives the image light beam from the image forming unit and has a focal length variable function, and a mirror that is made of synthetic resin and has refractive power, and is arranged on the enlargement side of an aperture stop of the lens system, and reflects the image light beam; The image correction control means is a means for correcting degradation of the enlarged image caused by uneven temperature rise of the mirror that reflects the imaging light beam due to the intensity distribution of the imaging light beam, and includes a parameter temperature detection unit that detects temperatures at multiple locations on the back side of the mirror and obtains a parameter temperature from the multiple detected temperatures, and a control unit that controls the focal length variable function in accordance with the parameter temperature obtained by the parameter temperature detection unit to correct degradation of the enlarged image.

2. 2. The projector according to claim 1, The parameter temperature is obtained based on temperatures detected by a plurality of thermistors arranged in contact with the rear surface of the mirror.

3. 3. The projector according to claim 2, A projector having three thermistors.

4. The projector according to any one of claims 1 to 3, The variable focal length mechanism is a projector that includes a floating mechanism that displaces a movable lens in the lens system.

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