Patent Publication Number: US-2017363942-A1

Title: Image projection apparatus, and control method of image projection apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority pursuant to 35 U.S.C. §119(a) to Japanese Patent Application No. 2016-121812 filed on Jun. 20, 2016 in the Japan Patent Office, the disclosure of which is incorporated by reference herein in its entirety. 
     BACKGROUND 
     Technical Field 
     This disclosure relates to an image projection apparatus, and a control method of the image projection apparatus. 
     Background Art 
     Image projection apparatuses that project images on a projection face (e.g., screen) are used in a wide range of fields such as presentations to a large number of persons such as conferences, lecture meetings, educational sites, and home theaters. When the image projection apparatus receives image data transmitted from an information processing apparatus such as a personal computer, a video reproduction device such as a digital versatile disk (DVD) player, an imaging device such as a digital camera, an optical image generation element (or modulation element, image generation element) generates an image based on the received image data, and then the image is projected on a projection face (e.g., screen) through an optical system including a plurality of lenses or the like. 
     The image projection apparatus includes a cooling device such as a cooling fan for cooling heat generated from a light source (lamp), a ballast (stabilizer), and a power supply device disposed in the image projection apparatus. When the cooling fan is operated, an operation sound is generated by rotation of the cooling fan, and a user feels the operation sound as noise sound. This noise sound may not become a problem when the image projection apparatus is used in a large space such as a hall. However, users may feel the operation sound as noise sound when the image projection apparatus is used in a smaller space such as a home theater. 
     JP-H09-164744-A discloses a method of reducing noise sound, in which a noise masking device generates a noise masking sound against the noise sound generated by a drive motor (i.e. noise source) to cancel the noise sound of the drive motor on the auditory sense. 
     In a case of increasing the resolution of images projected by the image projection apparatus, the pixel density of the optical image generation element (modulation element) may be increased by using a greater number of pixels of the optical image generation element. However, the manufacturing cost of the optical image generation element increases. 
     JP-2007-248721-A discloses an image display device that can display a higher resolution image, in which the image display device generates an intermediate image by shifting pixels by moving an optical element without increasing the number of pixels of an optical image generation element. 
     However, when the optical element is moved to shift the pixels in the image projection apparatus (referred to as pixel-shift control), an operation sound is generated when the optical element is moved for the pixel-shift control. Therefore, the operation sound generated by the cooling fan and the operation sound generated by the pixel-shift control occur concurrently, and thereby the number of the noise sources increases. Further, if a noise cancelling device such as a speaker for masking the noise sound is disposed in the image projection apparatus as disclosed in JP-H09-164744-A, the image projection apparatus becomes expensive and increases the size of the image projection apparatus, which are not preferable. 
     SUMMARY 
     As one aspect of the present invention, an image projection apparatus is devised. The image projection apparatus includes a light source to emit light, an image generation unit including an image generation element to generate an image using the light emitted from the light source, an optical unit to guide the light emitted from the light source to the image generation unit, and to enlarge and project the image generated by the image generation unit, a drive unit to change any one of a position of the image generation element and a position of at least a part of the optical unit at specific timing, and a cooling device to cool one or more parts disposed in the image projection apparatus. An operation sound generated by the cooling device while the cooling device is being operated has a given frequency characteristic settable according to a drive frequency of the drive unit. 
     As another aspect of the present invention, a method of controlling an image projection apparatus including a light source to emit light, an image generation unit including an image generation element to generate an image using the light emitted from the light source, an optical unit to guide the light emitted from the light source to the image generation unit, and to enlarge and project the image generated by the image generation unit, a drive unit to change any one of a position of the image generation element and a position of a part of the optical unit at specific timing, and a cooling device to cool one or more parts disposed in the image projection apparatus is devised. The method includes operating the cooling device to cool the one or more parts disposed in the image projection apparatus; and controlling an operation of the cooling device to set frequency characteristic of an operation sound generated by the cooling device according to a drive frequency of the drive unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the description and many of the attendant advantages and features thereof can be readily obtained and understood from the following detailed description with reference to the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of an image projection apparatus of an embodiment of the present invention; 
         FIG. 2  is a side view of the image projection apparatus of  FIG. 1 , and the image projection apparatus projects an image on a screen used as a projection face; 
         FIG. 3A  is a perspective view of an internal configuration of the image projection apparatus of  FIG. 1  from which an outer casing is removed; 
         FIG. 3B  is a perspective view of an encircled portion in  FIG. 3A ; 
         FIG. 4  is a cross-sectional view of a light guide unit, an optical projection unit, an image generation unit, and a light source unit of the image projection apparatus of  FIG. 1 ; 
         FIG. 5A  is a functional block diagram illustrating an example of the image projection apparatus according to the embodiment; 
         FIG. 5B  is an example of a hardware block diagram of a system controller of the image projection apparatus of  FIG. 1 ; 
         FIG. 6  is a perspective view of an image generation unit according to the embodiment; 
         FIG. 7  is a side view of the image generation unit of  FIG. 6 ; 
         FIG. 8  is a perspective view of a fixed unit according to the embodiment; 
         FIG. 9  is an exploded perspective view of the fixed unit of  FIG. 8 ; 
         FIG. 10  illustrates a support structure of a movable plate using the fixed unit of  FIG. 8 ; 
         FIG. 11  is a partially enlarged view of the support structure at a portion A in  FIG. 10 ; 
         FIG. 12  is a bottom view of a top plate according to the embodiment; 
         FIG. 13  is a perspective view of a movable unit according to the embodiment; 
         FIG. 14  is an exploded perspective view of the movable unit of  FIG. 13 ; 
         FIG. 15  is a perspective view of a movable plate according to the embodiment; 
         FIG. 16  is a perspective view of the movable unit of  FIG. 13  from which the movable plate is removed; 
         FIG. 17  illustrates a DMD holding structure of the movable unit of  FIG. 13 , according to the embodiment; 
         FIGS. 18A, 18B, and 18C  illustrate an example of a display state of an image when pixels are shifted; 
         FIGS. 19A and 19B  illustrate another example of a display state of an image when pixels are shifted; and 
         FIG. 20  is an example of frequency characteristic of a noise sound of a cooling fan. 
     
    
    
     The accompanying drawings are intended to depict exemplary embodiments of the present invention and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted, and identical or similar reference numerals designate identical or similar components throughout the several views. 
     DETAILED DESCRIPTION 
     A description is now given of exemplary embodiments of present disclosure. It should be noted that although such terms as first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, it should be understood that such elements, components, regions, layers and/or sections are not limited thereby because such terms are relative, that is, used only to distinguish one element, component, region, layer or section from another region, layer or section. Thus, for example, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of present disclosure. 
     In addition, it should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of present disclosure. Thus, for example, as used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Moreover, the terms “includes” and/or “including”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Furthermore, although in describing views illustrated in the drawings, specific terminology is employed for the sake of clarity, the present disclosure is not limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner and achieve a similar result. Referring now to the drawings, one or more apparatuses or systems according to one or more embodiments are described hereinafter. 
     Hereinafter, a description is given of one or more embodiments of the present disclosure with reference to drawings of  FIGS. 1 to 20 . 
     (Image Projection Apparatus) 
       FIG. 1  is a perspective view of an image projection apparatus  1  of an embodiment of the present invention.  FIG. 2  is a side view of the image projection apparatus  1 , and the image projection apparatus  1  projects an image on a screen S used as a projection face. 
       FIG. 3A  is a perspective view of an internal configuration of the image projection apparatus  1  from which an outer casing  2  is removed.  FIG. 3B  is a perspective view of an encircled portion in  FIG. 3A , in which an optical engine  3  and a light source unit  4  are included. 
     As to the image projection apparatus  1 , there is a demand for making a projection screen larger while making a projection space necessary for the outside of the image projection apparatus  1  as small as possible. Lately, the performance of the optical engine  3  has been improved, with which the image projection apparatus  1  that can achieve a projection image size of 60 inch to 80 inch with a projection distance of 1 m to 2 m has become a mainstream configuration for the image projection apparatus. 
     In case of conventional image projection apparatuses that require a longer projection distance, a conference desk is set between an image projection apparatus and a screen, and the image projection apparatus is placed at a rear side of the conference desk. Lately, with the shortening of the projection distance of the image projection apparatus, the image projection apparatus can be placed at a front side of the conference desk, with which it becomes possible to freely utilize a space behind the image projection apparatus. 
     The image projection apparatus  1  has a lamp as a light source, and many electronic circuit boards inside the image projection apparatus  1 . Therefore, the internal temperature of the image projection apparatus  1  rises after the image projection apparatus  1  is activated and being operated along the time line. Lately, the rise of internal temperature becomes prominent as the size of the casing of the image projection apparatus  1  has been reduced. Therefore, as illustrated in  FIG. 1 , the image projection apparatus  1  includes, for example, an intake port  16  and an exhaust port  17  to introduce air inside the image projection apparatus  1 , and then to exhaust heated air outside the image projection apparatus  1  so that the temperature of the internal components does not exceed heatproof temperature of the internal components. 
     Further, as illustrated in  FIG. 3A  and  FIG. 3B , the image projection apparatus  1  includes, for example, the optical engine  3  and the light source unit  4 .  FIG. 4  is a cross-sectional view of a light guide unit  40  to guide light emitted from the light source unit  4 , an optical projection unit  60 , an image generation unit  50 , and the light source unit  4  when viewed from a top side of the image projection apparatus  1 . The optical engine  3  includes, for example, the light guide unit  40  and the optical projection unit  60  as illustrated in  FIG. 3A  and  FIG. 3B . 
     As illustrated in  FIG. 3A , an intake fan  18  is disposed inside the image projection apparatus  1  near the intake port  16 , and an exhaust fan  19  is disposed inside the image projection apparatus  1  near the exhaust port  17 . When air is introduced from the intake fan  18  inside the image projection apparatus  1 , and then heated air is exhausted from the exhaust fan  19 , the internal space and components of the image projection apparatus  1  can be cooled by a forced air flow. 
     In the image projection apparatus  1 , light (e.g., white light) coming from a light source in the light source unit  4  enters the light guide unit  40  of the optical engine  3 . Inside the light guide unit  40 , the white light is separated into RGB light components, and then guided to the image generation unit  50  via a lens and a mirror. Then, an image is generated by the image generation unit  50  based on modulation signals, and the image is magnified and projected to the screen S by the optical projection unit  60 . 
     As illustrated in  FIG. 4 , the light source unit  4  includes, for example, a light source  30 . The light source  30  employs various lamps such as arc lamps including a high pressure mercury lamp, a xenon lamp or the like. For example, a high pressure mercury lamp is used as the light source  30 . 
     As illustrated in  FIG. 4 , a cooling fan  20  is disposed at one side of the light source unit  4  to cool the light source  30 . The rotation speed of the cooling fan  20  is controlled so that temperature of each part of the light source unit  4  is within the rated temperature range set for each part of the light source unit  4 . Further, the emission direction of the light from the light source unit  4  and the emission direction of the image light from the optical projection unit  60  are set with a relationship of approximately 90 degrees as illustrated in  FIG. 4 . In this description, the cooling fan  20  is used as an example of the cooling device. As long as the cooling device can cool the light source unit  4 , any cooling devices can be used. 
     Further, in the optical engine  3 , the light guide unit  40  includes, for example, a color wheel  5 , a light tunnel  6 , two relay lenses  7 , a flat mirror  8 , and a concave mirror  9 . The color wheel  5  (e.g., disk-shaped rotatable color filter) separates light emitted from the light source  30 . The light tunnel  6  guides the light exiting from the color wheel  5 . Further, the light guide unit  40  includes, for example, the image generation unit  50 . 
     In the light guide unit  40 , as indicated by arrows of  FIG. 4 , the white light, which is the light emitted from the light source  30 , is separated into R (red), G (green), and B (blue) light components time divisionally when the light emitted from the light source  30  passes through the color wheel  5  rotating in one direction. The R (red), G (green), and B (blue) light components exiting from the color wheel  5  enter the light tunnel  6 . The light tunnel  6  is a tube-shaped member having a square-like cross shape, and its internal face is finished as a mirror face. Each of the light components that enters the light tunnel  6  reflects for a plurality of times on the internal face of the light tunnel  6 , and is then emitted as synthesized uniform light to the two relay lenses  7 . Therefore, the light tunnel  6  is used as an optical member to convert the light into uniformed light. 
     Then, the light exiting from the light tunnel  6  enters the two relay lenses  7 , in which the light is condensed while correcting the chromatic aberration along the light axis by the two relay lenses  7 , which is a combination of two lenses. The light exiting from the two relay lenses  7  is reflected by the flat mirror  8  and the concave mirror  9 , and then enters the image generation unit  50 . The image generation unit  50  includes, for example, a digital micromirror device (DMD)  551  used as an image generation element or modulation element. The DMD  551  includes, for example, a plurality of micromirrors, and the plurality of micromirrors configure a substantially rectangular mirror surface. When each of micromirrors is driven by a time division control based on image data, the light is processed and reflected by the DMD  551  to generate an image light. 
     The image generation unit  50  selects the light that is output to the optical projection unit  60  by switching on and off of the micromirrors based on the input signals, and generates the gradation by controlling the micromirrors. Specifically, the light used for a projection image is reflected to a projection lens by the plurality of micromirrors, and the light to be discarded is reflected to an OFF plate by the DMD  551  based on image data in a time division manner. The image light generated by the image generation unit  50  is reflected to the optical projection unit  60 , passes through the plurality of projection lenses disposed in the optical projection unit  60 , and then projected onto the screen S as an enlarged image. 
     Further, the incident side of the two relay lenses  7 , the flat mirror  8 , the concave mirror  9 , the image generation unit  50 , and the optical projection unit  60  inside the light guide unit  40  is covered by a housing, and the mating surface of the housings is sealed with a sealant to configure a dust-proof structure. 
       FIG. 5A  is a functional block diagram illustrating an example of the image projection apparatus  1  according to the embodiment. 
     As illustrated in  FIG. 5A , the image projection apparatus  1  includes, for example, a system controller  10 , a light source controller  11 , a color wheel controller  12 , a DMD controller  13 , a movable unit controller  14 , a fan controller  15 , the cooling fan  20 , a remote control signal receiver  22 , a main operation unit  23 , an input terminal  24 , a video signal controller  25 , a non-volatile memory  26 , a power supply unit  27 , the light source  30 , the light guide unit  40 , the image generation unit  50 , and the optical projection unit  60  to project an image onto the screen S. The image projection apparatus  1  further includes, for example, a remote controller  21  as a remote control means. 
     The system controller  10  performs overall control of the image projection apparatus  1 . Further, the system controller  10  controls various image processing such as contrast adjustment, brightness adjustment, sharpness adjustment, scaling processing, conversion of frame rate of frames per second (fps) (refresh rate (Hz)), frame generation in an pixel shift control operation, display processing such as on-screen display (OSD) of menu information, and various other processing. 
     Further, the system controller  10  is connected with the light source controller  11 , the color wheel controller  12 , the DMD controller  13 , the movable unit controller  14 , the fan controller  15 , the remote control signal receiver  22 , the main operation unit  23 , the video signal controller  25 , and the non-volatile memory  26 , and controls each of these functional units. 
       FIG. 5B  is an example of a hardware block diagram of the system controller  10  of the image projection apparatus  1 , according to the embodiment. As illustrated in  FIG. 5B , the system controller  10  includes, for example, a central processing unit (CPU)  101 , a read-only memory (ROM)  105 , a random access memory (RAM)  103 , and an interface (I/f)  107 , and the functions of the units of the system controller  10  are implemented when the CPU  101  executes programs stored in the ROM  105  in cooperation with the RAM  103 , but not limited thereto. For example, at least part of the functions of the units of the system controller  10  can be implemented by a dedicated hardware circuit such as a semiconductor integrated circuit. The program executed by the system controller  10  according to the embodiment may be configured to be provided by being recorded in a computer-readable recording medium such as a compact disk read only memory (CD-ROM), a flexible disk (FD), a compact disk recordable (CD-R), a digital versatile disk (DVD), and a universal serial bus (USB) memory as a file of an installable format or an executable format. Alternatively, the program may be configured to be provided or distributed through a network such as the Internet. Moreover, various programs may be configured to be provided by being pre-installed into a non-volatile recording medium such as ROM  105 . Further, the hardware block configuration of  FIG. 5B  can be applied to other controllers. 
     The input terminal  24  is an interface for inputting a video signal, and includes, for example, Video Graphics Array (VGA) input terminal such as a D-Sub connector, and a video terminal such as High-Definition Multimedia Interface (HDMI) (registered trademark) terminal, S-VIDEO terminal, and RCA terminal. The image projection apparatus  1  receives a video signal from a video supply apparatus such as a computer or an audio visual (AV) device via a cable connected to the input terminal  24 . Further, in some cases, the image projection apparatus  1  includes a plurality of input terminals  24 . 
     The video signal controller  25  processes a video signal input to the input terminal  24 , and performs various processes such as serial-parallel conversion and voltage level conversion on the video signal. Further, the video signal controller  25  has a signal determination function for analyzing the resolution and frequency of video signals. 
     The non-volatile memory  26  stores data to be used for the image processing of video signal and various other processing. For example, the non-volatile memory  26  can be a non-volatile semiconductor memory such as an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM), and a flash memory. The image projection apparatus  1  can save or store previously set contents (e.g., language setting) in the non-volatile memory  26  even after the power is turned off. 
     The main operation unit  23  is an interface for operating the image projection apparatus  1 , and receives various operation requests from a user. Upon receiving an operation request, the main operation unit  23  reports the operation request to the system controller  10 . The main operation unit  23  is configured, for example, by operation keys (e.g., operation buttons) provided on an outer surface of the image projection apparatus  1 . 
     The remote control signal receiver  22  receives an operation signal from the remote controller  21 . Upon receiving the operation signal from the remote controller  21 , the remote control signal receiver  22  reports the operation signal to the system controller  10 . 
     A user can set various settings by operating the main operation unit  23  or the remote controller  21 . For example, the user can instruct to display a menu screen, select an installation state of the image projection apparatus  1 , a change request of the aspect ratio of the image projection apparatus  1 , a power supply ON/OFF request of the image projection apparatus  1 , a lamp power change request to change light intensity of the light source  30 , an image mode change to change image quality (e.g., high brightness, standard, natural) of a projected image, a freeze request to stop the projected image, an operation mode change request for a pixel-shift control operation, an ON/OFF setting of the pixel-shift control operation, and the like. 
     The fan controller  15  controls the cooling fan  20  so that the temperature in the image projection apparatus  1  and the temperature of the light source  30  are within a specific temperature range such as heatproof temperature range. 
     The power supply unit  27  is connected to each device in the image projection apparatus  1 , and converts an alternating current (AC) power, input from an electrical outlet, into a direct current (DC), and supplies the DC to each device in the image projection apparatus  1 . 
     The light source  30  is, for example, a high pressure mercury lamp, which emits light by a discharge between a pair of electrodes, and the light source  30  irradiates light to the light guide unit  40 . Further, the light source  30  can use a xenon lamp, and a light emitting diode (LED). Further, the light source controller  11  controls ON/OFF of the light source  30  and the light power. 
     The light emitted from the light source  30  is separated into R (red), G (green), and B (blue) light components time divisionally when the light emitted from the light source  30  passes through the color wheel  5  rotating in one direction in the light guide unit  40 , in which each color light exits from the disc-shaped color wheel  5  at each unit time. 
     The color wheel controller  12  controls the rotation movement of the color wheel  5 . 
     The light exiting from the color wheel  5  is condensed on the DMD  551  used as the image generation element in the image generation unit  50  via the light tunnel  6 , the two relay lenses  7 , the flat mirror  8 , and the concave mirror  9 . 
     The image generation unit  50  includes, for example, a fixed unit  51  ( FIG. 6 ) fixed to a frame, and a movable unit  55  movably supported by the fixed unit  51  so that the movable unit  55  can be moved with respect to the fixed unit  51 . The movable unit  55  includes, for example, the DMD  551 . The position of the movable unit  55  with respect to the fixed unit  51  is controlled by the movable unit controller  14 . 
     The movable unit  55  includes, for example, an electromagnetic actuator (e.g., voice coil, magnet) as a drive unit. The movable unit controller  14  controls the amount of current to flow to the drive unit of the movable unit  55  to control the shift amount of the DMD  551 . The shift control of the DMD  551  by the movable unit controller  14  can be turned on/off by operating the main operation unit  23  or the remote controller  21 . When the shift control of the DMD  551  is set to OFF, a normal projection image not performing the shifting of DMD  551  is displayed. 
     The DMD  551  has a substantially rectangular mirror surface configured by the plurality of micromirrors. When each of micromirrors is driven by a time division control based on image data, the light coming from the light guide unit  40  is processed and reflected by the DMD  551  to generate an image light. The DMD controller  13  controls on/off of the micromirrors of the DMD  551 . 
     The light used for a projection image is reflected to the optical projection unit  60  by the plurality of micromirrors of the DMD  551 , and the light to be discarded is reflected to the OFF plate by the DMD  551  based on image data in a time division manner. The image light generated by the image generation unit  50  is reflected to the optical projection unit  60 , passes through the optical projection unit  60 , and then projected onto the screen S as an enlarged image. 
     The optical projection unit  60  includes, for example, a plurality of projection lenses and mirrors. The optical projection unit  60  magnifies or enlarges the image generated by the DMD  551  of the image generation unit  50 , and project the magnified or enlarged image on the screen S. 
     (Image Generation Unit) 
       FIG. 6  is a perspective view of the image generation unit  50  according to the embodiment.  FIG. 7  is a side view of the image generation unit  50  according to the embodiment. 
     As illustrated in  FIG. 6  and  FIG. 7 , the image generation unit  50  includes the fixed unit  51 , and the movable unit  55 . The fixed unit  51  is fixed to a frame of the image projection apparatus  1  while the movable unit  55  is moveably supported by the fixed unit  51 . The fixed unit  51  may be also referred to as a non-movable unit. 
     The fixed unit  51  includes a top plate  511  as a first fixed plate, and a base plate  512  as a second fixed plate. In the fixed unit  51 , the top plate  511  and the base plate  512  are provided in parallel to each other with a given space therebetween. 
     The movable unit  55  includes the DMD  551 , a movable plate  552  as a first movable plate, a coupling plate  553  as a second movable plate, and a heat sink  554 , and the movable unit  55  is movably supported by the fixed unit  51 . 
     The movable plate  552  is provided between the top plate  511  and the base plate  512  of the fixed unit  51 , and is supported by the fixed unit  51  in parallel to the top plate  511  and the base plate  512  and is movably supported by the fixed unit  51  in a direction parallel to the surfaces of the top plate  511  and the base plate  512 . 
     The coupling plate  553  is fixed to the movable plate  552  by interposing the base plate  512  of the fixed unit  51  between the coupling plate  553  and the movable plate  552 . As to the coupling plate  553 , the DMD  551  is fixed to the upper side of the coupling plate  553 , and the heat sink  554  is fixed to the lower side of the coupling plate  553 . The coupling plate  553  is fixed to the movable plate  552 , and is thereby movably supported by the fixed unit  51  together with the movable plate  552 , the DMD  551 , and the heat sink  554 . 
     The DMD  551  is provided on a plane of the coupling plate  553  closer to the movable plate  552 , and is provided movably together with the movable plate  552  and the coupling plate  553 . The DMD  551  includes an image generation plane where a plurality of movable micromirrors are arranged in a lattice pattern. As to each of the micromirrors of the DMD  551 , the mirror surface of each of the micromirrors of the DMD  551  is mounted tiltably about a torsion axis, and each of the micromirrors of the DMD  551  is ON/OFF driven based on an image signal transmitted from the DMD controller  13 . 
     For example, in the case of “ON”, an inclination angle of the micromirror is controlled so as to reflect the light emitted from the light source  30  to the optical projection unit  60 . Further, for example, in the case of “OFF”, an inclination angle of the micromirror is controlled in a direction for reflecting the light emitted from the light source  30  toward the OFF plate. 
     With this configuration, the inclination angle of each of the micromirrors of the DMD  551  is controlled based on the image signal transmitted from the DMD controller  13 , and the DMD  551  modulates the light emitted from the light source  30  and passing through the light guide unit  40  to generate a projection image. 
     The heat sink  554  is an example of a heat radiating unit, and is provided such that at least part of the heat sink  554  is in contact with the DMD  551 . The heat sink  554  is provided for the movably supported coupling plate  553  together with the DMD  551  such that the heat sink  554  is in contact with the DMD  551 , with which the DMD  551  can be efficiently cooled. Based on this configuration, in the image projection apparatus  1  according to the embodiment, the heat sink  554  suppresses an increase of the temperature of the DMD  551  so that occurrence of troubles such as a malfunction or a failure due to the increase of the temperature of the DMD  551  can be reduced. 
     (Fixed Unit) 
       FIG. 8  is a perspective view of the fixed unit  51  according to the embodiment.  FIG. 9  is an exploded perspective view of the fixed unit  51  according to the embodiment. 
     As illustrated in  FIG. 8  and  FIG. 9 , the fixed unit  51  includes the top plate  511  and the base plate  512 . 
     The top plate  511  and the base plate  512  are each formed from a plate member, and have central holes  513  and  514  respectively provided at positions corresponding to the DMD  551  of the movable unit  55 . The top plate  511  and the base plate  512  are provided in parallel to each other by a plurality of supports  515  with a given space therebetween. 
     As illustrated in  FIG. 9 , an upper end of the support  515  is pressed into a supporting hole  516  formed in the top plate  511 , and a lower end of the support  515  where a male screw groove is formed is inserted into a supporting hole  517  formed in the base plate  512 . A plurality of the supports  515  forms a given space between the top plate  511  and the base plate  512  and supports the top plate  511  and the base plate  512  in a parallel manner. 
     Further, a plurality of supporting holes  522  and  526 , each of which rotatably holds a supporting sphere  521 , are formed in the top plate  511  and the base plate  512 , respectively. 
     A cylindrical holding member  523  having a female screw groove in its inner periphery is inserted into the supporting hole  522  of the top plate  511 . The holding member  523  rotatably holds the supporting sphere  521 , and a position adjustment screw  524  is inserted into the holding member  523  from above. The supporting hole  526  of the base plate  512  is covered at its lower end by a lid member  527 , and rotatably holds the supporting sphere  521 . 
     The supporting spheres  521  rotatably held by the respective supporting holes  522  and  526  of the top plate  511  and the base plate  512  are in contact with the movable plate  552  provided between the top plate  511  and the base plate  512  to movably support the movable plate  552 . 
       FIG. 10  illustrates a support structure of the movable plate  552  using the fixed unit  51 .  FIG. 11  is a partially enlarged view of the support structure at a portion A in  FIG. 10 . 
     As illustrated in  FIG. 10  and  FIG. 11 , in the top plate  511 , the supporting sphere  521  is rotatably held by the holding member  523  inserted into the supporting hole  522 . In the base plate  512 , the supporting sphere  521  is rotatably held by the supporting hole  526  whose lower end is covered by the lid member  527 . 
     The supporting spheres  521  are held such that at least part thereof protrudes from the supporting holes  522  and  526 , and are in contact with and supporting the movable plate  552  provided between the top plate  511  and the base plate  512 . The movable plate  552  is supported by the rotatably provided supporting spheres  521  from both sides of the movable plate  552  so as to be supported in parallel to the top plate  511  and the base plate  512  and movably in a direction parallel to the surfaces of the top plate  511  and the base plate  512 . 
     Further, as to the supporting sphere  521  provided on the top plate  511 , an amount of protrusion of the supporting sphere  521  from the lower end of the holding member  523  is changed by adjusting the position of the position adjustment screw  524  that contacts with the supporting sphere  521  at one side of the supporting sphere  521  that is farther from the movable plate  552 . For example, when the position adjustment screw  524  is displaced in the Z1 direction, the amount of protrusion of the supporting sphere  521  decreases, with which a space between the top plate  511  and the movable plate  552  is reduced. Further, for example, when the position adjustment screw  524  is displaced in the Z2 direction, the amount of protrusion of the supporting sphere  521  increases, with which a space between the top plate  511  and the movable plate  552  is increased. 
     With this configuration, by changing the amount of protrusion of the supporting sphere  521  using the position adjustment screw  524 , the space between the top plate  511  and the movable plate  552  can be appropriately adjusted. 
     Further, as illustrated in  FIG. 8  and  FIG. 9 , magnets  531 ,  532 ,  533 , and  534  are provided on the plane of the top plate  511  closer to the base plate  512 . 
       FIG. 12  is a bottom view of the top plate  511  according to the embodiment. As illustrated in  FIG. 12 , the magnets  531 ,  532 ,  533 , and  534  are provided on the plane of the top plate  511  closer to the base plate  512 . 
     The magnets  531 ,  532 ,  533 , and  534  are arranged at four locations so as to surround the central hole  513  of the top plate  511 . Each of the magnets  531 ,  532 ,  533 , and  534  is configured with two cuboid magnets arranged such that their longitudinal directions are parallel to each other, and the two cuboid magnets form a magnetic field effecting the movable plate  552 . 
     The magnets  531 ,  532 ,  533 , and  534  configure a movement unit for moving the movable plate  552  in cooperation with coils that are provided on the upper surface of the movable plate  552  while each of the coils facing the magnets  531 ,  532 ,  533 , and  534 . 
     Further, the number, the locations, and the like of the supports  515  and the supporting spheres  521  provided in the fixed unit  51  are not limited to the configuration illustrated in the embodiment as long as they are capable of movably supporting the movable plate  552 . 
     (Movable Unit) 
       FIG. 13  is a perspective view of the movable unit  55  according to the embodiment.  FIG. 14  is an exploded perspective view of the movable unit  55  according to the embodiment. 
     As illustrated in  FIG. 13  and  FIG. 14 , the movable unit  55  includes the DMD  551 , the movable plate  552 , the coupling plate  553 , the heat sink  554 , a holding member  555 , and a DMD substrate  557 , and is movably supported by the fixed unit  51 . 
     As described above, the movable plate  552  is provided between the top plate  511  and the base plate  512  of the fixed unit  51 , and is supported movably in a direction parallel to the surfaces of the top plate  511  and the base plate  512  by the supporting spheres  521 . 
       FIG. 15  is a perspective view of the movable plate  552  according to the embodiment. 
     As illustrated in  FIG. 15 , the movable plate  552  is formed from a plate member, has a central hole  570  made at a position corresponding to the DMD  551  provided in the DMD substrate  557 , and also has coils  581 ,  582 ,  583 , and  584  provided around the central hole  570 . 
     Each of the coils  581 ,  582 ,  583 , and  584  is formed by an electric wire being wound around an axis parallel to the Z1-Z2 direction, is provided in a recess formed on the side of the movable plate  552  closer to the top plate  511 , and is covered with a cover. The coils  581 ,  582 ,  583 , and  584  configure the movement unit for moving the movable plate  552  in cooperation with the respective magnets  531 ,  532 ,  533 , and  534  of the top plate  511 . 
     The magnets  531 ,  532 ,  533 , and  534  of the top plate  511  and the coils  581 ,  582 ,  583 , and  584  of the movable plate  552  are provided in locations so as to face each other, respectively, in the state that the movable unit  55  is supported by the fixed unit  51 . When a current is made to flow in the coils  581 ,  582 ,  583 , and  584 , a Lorentz force used as a drive force for moving the movable plate  552  is generated by the magnetic field formed by the magnets  531 ,  532 ,  533 , and  534 . 
     When the movable plate  552  receives the Lorentz force as the drive force generated between the magnets  531 ,  532 ,  533 , and  534  and the coils  581 ,  582 ,  583 , and  584 , the movable plate  552  is linearly or rotationally displaced on the X-Y plane with respect to the fixed unit  51 . 
     The magnitude and direction of the current flowing in each of the coils  581 ,  582 ,  583 , and  584  is controlled by the movable unit controller  14 . The movable unit controller  14  controls a movement direction (linear or rotation direction), a movement amount, and a rotation angle of the movable plate  552  by controlling the magnitude and direction of the current flowing in each of the coils  581 ,  582 ,  583 , and  584 . 
     In the embodiment, the coil  581  and the magnet  531  facing each other and the coil  584  and the magnet  534  facing each other disposed at the opposite positions in the X1-X2 direction configure a first drive unit. When a current is made to flow in the coil  581  and the coil  584 , the Lorentz force is generated in the X1 direction or in the X2 direction as illustrated in  FIG. 15 . The movable plate  552  is moved in the X1 direction or in the X2 direction by the Lorentz forces generated between the coil  581  and the magnet  531  and between the coil  584  and the magnet  534 . 
     Further, in the embodiment, the coil  582  and the magnet  532  facing each other and the coil  583  and the magnet  533  facing each other disposed in parallel in the X1-X2 direction configure a second drive unit. Further, the magnet  532  and the magnet  533  are arranged such that the longitudinal directions of the magnet  532  and the magnet  533  are perpendicular to the longitudinal directions of the magnet  531  and the magnet  534 . Based on this configuration, when a current is made to flow in the coil  582  and the coil  583 , the Lorentz force is generated in the Y1 direction or in the Y2 direction as illustrated in  FIG. 15 . 
     The movable plate  552  is moved in the Y1 direction or in the Y2 direction by the Lorentz forces generated between the coil  582  and the magnet  532  and between the coil  583  and the magnet  533 . Further, the movable plate  552  is displaced to rotate on the X-Y plane by a Lorentz force generated between the coil  582  and the magnet  532  and a Lorentz force generated between the coil  583  and the magnet  533 , which are generated in the opposite directions. 
     For example, when a current is made to flow such that a Lorentz force is generated in the Y1 direction by the coil  582  and the magnet  532  and a Lorentz force is generated in the Y2 direction by the coil  583  and the magnet  533 , the movable plate  552  is displaced to rotate clockwise when viewed from the top. Further, when a current is made to flow such that a Lorentz force is generated in the Y2 direction by the coil  582  and the magnet  532  and a Lorentz force is generated in the Y1 direction by the coil  583  and the magnet  533 , the movable plate  552  is displaced to rotate counterclockwise when viewed from the top. 
     Further, a movable range restriction hole  571  is provided in the movable plate  552  at a position corresponding to the support  515  of the fixed unit  51 . The support  515  of the fixed unit  51  is inserted in the movable range restriction hole  571 , and the movable range restriction hole  571  restricts a movable range of the movable plate  552  by coming in contact with the support  515  when the movable plate  552  is largely moved due to, for example, vibration or some abnormality. 
     As described above, in the embodiment, the movable unit controller  14  controls the magnitude or the direction of the current to be made to flow in the coils  581 ,  582 ,  583 , and  584 , with which the movable plate  552  can be moved to any positions within the movable range. 
     Further, the number, the locations, and the like of the magnets  531 ,  532 ,  533 , and  534  and the coils  581 ,  582 ,  583 , and  584 , which function as the movement unit, may be configured in a different manner from that of the embodiment as long as the movable plate  552  can be moved to any positions. For example, the magnets used as the movement unit may be provided on the upper surface of the top plate  511  or may be provided on any plane of the base plate  512 . Further, for example, a configuration in which the magnets are provided on the movable plate  552  and the coils are provided on the top plate  511  or the base plate  512 , may be employed. 
     Further, the number, the locations, the shape, and the like of the movable range restriction hole  571  are not limited to the configuration illustrated in the embodiment. For example, the number of movable range restriction holes  571  may be one or plural. Further, the shape of the movable range restriction hole  571  may be different from that of the embodiment, and may be a rectangle or a circle. 
     As illustrated in  FIG. 13 , the coupling plate  553  is fixed to the lower side (the side closer to the base plate  512 ) of the movable plate  552  movably supported by the fixed unit  51 . The coupling plate  553  is formed from a plate member, has a central hole made at a position corresponding to the DMD  551 , and has bent portions provided at periphery of the coupling plate  553  that are fixed to the lower side of the movable plate  552  by using three screws  591 . 
       FIG. 16  is a perspective view of the movable unit  55  from which the movable plate  552  is removed. 
     As illustrated in  FIG. 16 , the coupling plate  553  has the DMD  551  provided on its upper surface and the heat sink  554  provided on its lower surface. Since the coupling plate  553  is fixed to the movable plate  552 , the coupling plate  553  having the DMD  551  and the heat sink  554  is provided movably with respect to the fixed unit  51  as the movable plate  552  is provided movably with respect to the fixed unit  51 . 
     The DMD  551  is provided on the DMD substrate  557 , and the DMD substrate  557  is sandwiched between the holding member  555  and the coupling plate  553 , with which the DMD  551  is fixed to the coupling plate  553 . As illustrated in  FIG. 14  and  FIG. 16 , the holding member  555 , the DMD substrate  557 , the coupling plate  553 , and the heat sink  554  are overlapped and fixed using stepped screws  560  as fixing units and springs  561  as pressing units. 
       FIG. 17  illustrates a DMD holding structure of the movable unit  55  according to the embodiment.  FIG. 17  is a side view of the movable unit  55 , in which the movable plate  552  and the coupling plate  553  are omitted. 
     As illustrated in  FIG. 17 , the heat sink  554  has a projecting portion  554   a  in contact with the lower side of the DMD  551  through a through hole provided in the DMD substrate  557  in the state that the heat sink  554  is fixed to the coupling plate  553 . Further, the projecting portion  554   a  of the heat sink  554  may be provided such that it is in contact with a position of the lower side of the DMD substrate  557  corresponding to the DMD  551 . 
     Further, to enhance a cooling effect of the DMD  551 , an elastically deformable heat transfer sheet may be provided between the projecting portion  554   a  of the heat sink  554  and the DMD  551 . By providing the elastically deformable heat transfer sheet between the projecting portion  554   a  of the heat sink  554  and the DMD  551 , a thermal conductivity between the projecting portion  554   a  of the heat sink  554  and the DMD  551  is enhanced, and the cooling effect of the DMD  551  by the heat sink  554  is enhanced. 
     As described above, the holding member  555 , the DMD substrate  557 , and the heat sink  554  are overlapped and fixed using the stepped screws  560  and the springs  561 . When the stepped screws  560  are tightened, the springs  561  are compressed in the Z1-Z2 direction, and a force F 1  in the Z1 direction illustrated in  FIG. 17  is generated from the spring  561 . The heat sink  554  is pressed against the DMD  551  by a force F 2  in the Z1 direction due to forces F 1  generated from the springs  561 . 
     In the embodiment, the stepped screws  560  and the springs  561  are provided at four locations, and the force F 2  applied to the heat sink  554  is equal to that obtained by combining the forces F 1  generated in the four springs  561 . Further, the force F 2  from the heat sink  554  acts on the holding member  555  that holds the DMD substrate  557  where the DMD  551  is provided. Consequently, a force F 3  in the Z2 direction corresponding to the force F 2  from the heat sink  554  is generated in the holding member  555 , so that the DMD substrate  557  can be held between the holding member  555  and the coupling plate  553 . 
     A force F 4  in the Z2 direction acts on the stepped screw  560  and the spring  561  from the force F 3  generated in the holding member  555 . Since the springs  561  are provided at the four locations, the force F 4  acting on each of the springs  561  is equivalent to a quarter of the force F 3  generated in the holding member  555 , and is resultantly balanced with the force F 1 . 
     Further, the holding member  555  is a member capable of bending or warping as illustrated by arrow B in  FIG. 17 , and is formed as a plate spring. The holding member  555  is bent or warped by being pressed by the projecting portion  554   a  of the heat sink  554  and a force to push back the heat sink  554  in the Z2 direction is generated, with which it is possible to firmly keep the contact between the DMD  551  and the heat sink  554 . 
     As described above, as to the movable unit  55 , the movable plate  552  and the coupling plate  553  that includes the DMD  551  and the heat sink  554  are movably supported by the fixed unit  51 . The position of the movable unit  55  is controlled by the movable unit controller  14 . Further, the heat sink  554  in contact with the DMD  551  is provided in the movable unit  55 , so that occurrence of troubles such as a malfunction and a failure caused by an increase of the temperature of the DMD  551  can be suppressed, in particular prevented. 
     (Shifting of Pixel (Shifting of DMD)) 
     As described above, in the image projection apparatus  1  according to the embodiment, the DMD  551  that generates a projection image is provided in the movable unit  55 , and the position of the DMD  551  is controlled by the movable unit controller  14  together with the movable unit  55 . 
     For example, the movable unit controller  14  controls the position of the movable unit  55  so as to move the movable unit  55  with a higher speed between a plurality of positions, which are apart from each other by a distance that is less than an arrangement interval of the micromirrors of the DMD  551  with a given cycle corresponding to a frame rate at the time of projecting images. When the movable unit  55  is moved (i.e., position of the DMD  551  is shifted), the DMD controller  13  transmits an image signal to the DMD  551  so as to generate a projection image based on the shifted position of the DMD  551 . 
     For example, the movable unit controller  14  reciprocally moves the DMD  551  with the given cycle between a position PA and a position PB, which are apart from each other by a distance that is less than an arrangement interval of the micromirrors of the DMD  551  in the X1-X2 direction and in the Y1-Y2 direction. At this timing, the DMD controller  13  controls the DMD  551  so as to generate a shifted projection image based on the shifted position of the DMD  551  so that a resolution of the projection image can be made about twice the resolution of the DMD  551 . 
     With this configuration, the movable unit controller  14  moves the DMD  551  together with the movable unit  55  with the given cycle, and the DMD controller  13  controls the DMD  551  so as to generate the projection image based on the position of the DMD  551 , with which the image having a resolution higher than a resolution of the DMD  551  can be projected. 
       FIG. 18A ,  FIG. 18B , and  FIG. 18C  illustrate an example of a display state of an image when pixels are shifted by one-half pixel by performing the pixel-shift control operation or DMD-shift control operation. 
       FIG. 18A  illustrates each pixel S 1  in a state when the display position is not shifted (i.e., state before shifting, first position), and the size of each pixel is XL×YL.  FIG. 18B  illustrates each pixel S 2  in a state (i.e., second position) shifted by one-half pixel (XL/2, YL/2) from the state of  FIG. 18A . An operation mode that shifts pixels between two states in an oblique direction is referred to as a first operation mode. 
     Then, by combining the two images ( FIGS. 18A and 18B ), that is, alternately projecting the two images at each pixel, it is possible to achieve pseudo high resolution as illustrated in  FIG. 18C . In this pixel-shift control operation, the system controller  10  generates two frames for an input video signal of one frame, in which the system controller  10  generates one frame at the first position (first frame) and another frame at the second position (second frame) for the input video signal of the one frame. Then, the movable unit controller  14  controls the movable unit  55  to shift the DMD  551  in the oblique direction, and the first frame and the second frame are projected with a state of shifting pixels for one-half pixel to achieve a higher resolution image as illustrated in  FIG. 18C . 
     In this pixel-shift control operation, it is necessary to project the frames at twice the speed of the input video signal in order to make it look the same as the refresh rate of the input video signal. For example, if the refresh rate of the input video signal is 60 Hz (i.e. frame rate of 60 fps), it is necessary to set a drive frequency (i.e., operation frequency) for driving the movable unit  55  (i.e., DMD  551 ) at 120 Hz under the pixel-shift control operation to project each frame at the first position and each frame at the second position (i.e., projection of one round trip) to perform an image projection, in which high-speed image processing is required. 
     Further, the pixel-shift control operation can be performed differently. For example, it is also possible to shift the DMD  551  in the horizontal direction and the vertical direction into a total of four states under the pixel-shift control operation as illustrated in  FIG. 19A  and  FIG. 19B .  FIG. 19  A and  FIG. 19B  illustrate another example of a display state of an image when pixels are shifted, in which an operation mode uses four display states, which is referred to as a second operation mode. 
       FIG. 19A-A  illustrates each pixel S 1 , which is in a state (i.e., state before shift, first position) when the display position is not shifted.  FIG. 19A-B  illustrates each pixel S 2 , which is in a state (i.e., second position) when the display position is shifted to the vertical direction (i.e., downward direction in  FIG. 19 ) from the first position ( FIG. 19A-A ).  FIG. 19A-C  illustrates each pixel S 3 , which is in a state (i.e., third position) when the display position is shifted to the horizontal direction (i.e., right direction in  FIG. 19 ) from the second position ( FIG. 19A-B ).  FIG. 19A-D  illustrates each pixel S 4 , which is in a state (i.e., fourth position) when the display position is shifted to the vertical direction (i.e., upward direction in  FIG. 19 ) from the third position ( FIG. 19A-C ). Then, the position is returned to the first position from the fourth position by shifting the display position to the horizontal direction (i.e., left direction in  FIG. 19 ). 
     Then, by combining the four images, that is, by projecting the image at each pixel at a high speed, a pseudo high resolution can be achieved as illustrated in  FIG. 19B . 
     As above described, the pixels are shifted between the four positions with a manner of shifting among the four positions with a given sequential order in the second operation mode. In the second operation mode, the system controller  10  generates one frame at each of the first position to the fourth position for an input video signal of one frame, which means the system controller  10  generates four frames, and each frame is set for each of the first position to the fourth position. Then, the movable unit controller  14  controls the movable unit  55  to shift the DMD  551  in the horizontal direction and the vertical direction with a sequential order from the first position, the second position, the third position, and to the fourth position, and then an image is projected while achieving a higher resolution image. 
     In this pixel-shift control operation, it is necessary to project the frames at four times the speed of the input video signal in order to make it look the same as the refresh rate of the input video signal. For example, if the frame rate of the input video signal is 60 Hz (i.e. frame rate of 60 fps), it is necessary to set a drive frequency (operation frequency) for driving the movable unit  55  (i.e., DMD  551 ) at 240 Hz under the pixel-shift control operation to project each frame at each of the first position to the fourth position (i.e., projection of one round trip) to perform an image projection, in which high-speed image processing is required. 
     Further, the image projection apparatus  1  can be configured to selectively executing one of the first operation mode and the second operation mode as required, and further, the image projection apparatus  1  can be configured to execute only one of the first operation mode and the second operation mode. Further, in the embodiment, two example operation modes such as the first operation mode and the second operation mode have been described, but the shift amount and the shift direction in the pixel-shift control operation is not limited to these examples. For example, it is also possible to rotate the projected image by rotating the DMD  551 . 
     (Control of Cooling Fan) 
       FIG. 20  is an example of frequency characteristic of an operation sound of the cooling fan  20  when the cooling fan  20  is driven, in which the operation sound generated by the cooling fan  20  may become a noise sound. In this example case, the noise sound has a fundamental frequency (Hz) value obtained by multiplying the rotation speed of the cooling fan  20  per second (rotation/sec) by the number of blades of the cooling fan  20 . In  FIG. 20 , the fundamental frequency is indicated as a peak value P 1 . Further, a sound pressure increases in a given range around the peak value P 1  by setting the peak value P 1  as the center of the given range. In this example case, a range where the sound pressure becomes higher around the fundamental frequency (i.e., peak value) is referred to as a high sound pressure range, and a high sound pressure range R 1  is set for the peak value P 1 . 
     Further, as illustrated in  FIG. 20 , the noise sound has a peak (e.g., peak values P 2 , P 3 , . . . ) at each of given frequency components (i.e., harmonic sound components) obtained by multiplying the fundamental frequency with an integral number (e.g., two, three, and so on), and also has a high sound pressure range (e.g., high sound pressure range R 2 , R 3 , . . . ) around the peak value of each of the harmonic sound components. 
     For example, if the fundamental frequency of the noise sound (i.e., peak value P 1 ) is 120 Hz, each of the harmonic sound components (i.e., peak value P 2 , P 3  . . . ) becomes 240 Hz, 360 Hz, and so, and the high sound pressure range for the peak value P 1  becomes 110 Hz to 130 Hz. 
     Further, the operation sound (referred to as pixel-shift noise sound) caused by the shift control under the pixel-shift control operation includes the drive frequency for driving the movable unit  55  (DMD  551 ) as a main component as described above. 
     Although the sound volume level of the pixel-shift noise sound is relatively small, when the pixel-shift control operation is switched between ON and OFF, a user may perceive the occurrence or disappearance of the operation sound caused by the pixel-shift control operation, in which the user may perceive the operation sound as a noise sound, and may feel uncomfortable. 
     Further, the cooling fan  20  is disposed in the image projection apparatus  1  as an indispensable cooling means that cools a heat source such as the light source  30 , and when the image projection apparatus  1  is driven, the noise sound generated by the cooling fan  20  constantly occurs. Further, the noise sound generated by the cooling fan  20  has a higher sound pressure compared to the pixel-shift noise sound. 
     Therefore, if the pixel-shift noise sound can be masked by the noise sound generated by the cooling fan  20 , a user may be less likely to perceive the pixel-shift noise sound when the pixel-shift control operation is turned ON, and it becomes possible to improve user comfortableness at the time of use of the image projection apparatus  1 . 
     In view of the above described issue of noise sound, the image projection apparatus  1  of the embodiment is devised. The image projection apparatus (image projection apparatus  1 ) includes, for example, a light source (light source  30 ) to emit light, an image generation unit (image generation unit  50 ) including an image generation element (DMD  551 ) to generate an image using the light emitted from the light source, an optical unit (light guide unit  40 , optical projection unit  60 ) to guide the light emitted from the light source to the image generation unit, and to enlarge and project the image generated by the image generation unit, a drive unit (movable unit  55 , electromagnetic actuator to drive the movable unit  55 ) to change any one of a position of the image generation element and a position of at least a part (e.g., lens) of the optical unit at specific timing (e.g.,  FIGS. 18 and 19 ), and a cooling device (cooling fan  20 ) to cool one or more parts disposed in the image projection apparatus  1 . An operation sound generated by the cooling device while the cooling device is being operated has a given frequency characteristic settable according to a drive frequency of the drive unit. 
     Specifically, by matching the fundamental frequency of the noise sound generated by the cooling fan  20  to the drive frequency of the pixel-shift control operation, the pixel-shift noise sound can be cancelled by the noise sound generated by the cooling fan  20  by a masking effect, and thereby a user may not perceive the noise sound caused by the pixel-shift control operation. Therefore, the user can perceive that the noise sound caused by the pixel-shift control operation is suppressed. 
     Further, if it is difficult to match the fundamental frequency of the noise sound generated by the cooling fan  20  to the drive frequency of the pixel-shift control operation, it is preferable to substantially match the fundamental frequency of the noise sound generated by the cooling fan  20  to the drive frequency of the pixel-shift control operation. For example, by setting the drive frequency of the pixel-shift control operation within the high sound pressure range setting the fundamental frequency of the noise sound generated by the cooling fan  20  as the center of the high sound pressure range of the cooling fan  20 , a user may not perceive the pixel-shift noise sound by the masking effect as similar to a case matching the fundamental frequency of the noise sound generated by the cooling fan  20  to the drive frequency of the pixel-shift control operation. 
     When the fundamental frequency of the noise sound generated by the cooling fan  20  and the drive frequency of the pixel-shift control operation are matched, the masking effect becomes the highest, which is the most preferable. The closer the fundamental frequency of the noise sound generated by the cooling fan  20  and the drive frequency of the pixel-shift control operation, the higher the masking effect. Therefore, it is preferable to make a range where the masking effect becomes higher as a high sound pressure range, and to set the drive frequency of the pixel-shift control operation within this range. 
     When the pixel-shift control operation is performed using, for example, the operation mode of shifting between the two states as illustrated in  FIG. 18 , and the refresh rate of the input image is 60 Hz (i.e., frame rate is 60 fps), the drive frequency of the pixel-shift control operation becomes 120 Hz, and the pixel-shift noise sound having 120 Hz as a main component is generated. Similarly, when the pixel-shift control operation is performed using, for example, the operation mode illustrated in  FIG. 19 , and the refresh rate of the input image is 60 Hz (i.e., frame rate is 60 fps), the drive frequency of the pixel-shift control operation becomes 240 Hz, and the noise sound having 240 Hz as a main component is generated. 
     A value of the drive frequency of the pixel-shift control operation is determined in accordance with the frame rate, and when the drive frequency of the pixel-shift control operation is changed, the display of projected image is directly influenced by the changed drive frequency. Therefore, in the embodiment, the fan controller  15  changes the rotation speed of the cooling fan  20  and/or the number of blades of the cooling fan  20  set in advance such that the fundamental frequency or high sound pressure range of the noise sound generated by the cooling fan  20  is matched to the drive frequency of the pixel-shift control operation to suppress the effect of the noise sound caused by the pixel-shift control operation by using the masking effect. 
     For example, if the drive frequency of the pixel-shift control operation is 120 Hz and the number of blades of the cooling fan  20  is six (6), the fundamental frequency of the noise sound generated by the cooling fan  20  can be set to 120 Hz by rotating the cooling fan  20  at 20 revolutions per second (1200 rpm). Further, if it is difficult to match the fundamental frequency of the noise sound generated by the cooling fan  20  to the drive frequency of the pixel-shift control operation, the number of blades and/or the rotation speed of the cooling fan  20  can be set to values such that the drive frequency 120 Hz of the pixel-shift control operation is set within the high sound pressure range of the noise sound generated by the cooling fan  20 . 
     Further, it may be designed to set or adjust the number of blades of the cooling fan  20  based on the rotation speed. For example, if the drive frequency of the pixel-shift control operation is 120 Hz, and the cooling fan  20  is to be rotated 15 times per second (900 rpm), the fundamental frequency of the noise sound generated by the cooling fan  20  can be set to 120 Hz by setting the number of blades of the cooling fan  20  to eight (8). 
     Further, the rotation speed of the cooling fan  20  and the number of blades of the cooling fan  20  can be set with any values such that the cooling fan  20  can be used as the cooling device of the image projection apparatus  1 . For example, if the rotation speed of the cooling fan  20  is set too high, the noise sound generated by the cooling fan  20  may become too great and may exceed an allowable level defined by a noise sound standard while if the rotation speed of the cooling fan  20  is set too low, the size of the cooling fan  20  is required to be greater to achieve the effective cooling effect. Therefore, it is preferable to determine the rotation speed and the number of blades of the cooling fan  20  in view of these issues. 
     Further, as described above, the noise sound generated by the cooling fan  20  also has a peak in the harmonic sound components of the fundamental frequency. Therefore, if it is difficult to match the fundamental frequency of the noise sound generated by the cooling fan  20  to the drive frequency of the pixel-shift control operation, a frequency that is obtained by multiplying the fundamental frequency of the noise sound generated by the cooling fan  20  with an integral number (e.g., two, three, and so on) and the drive frequency of the pixel-shift control operation are matched or approximated with each other. 
     For example, if the drive frequency of the pixel-shift control operation is 120 Hz and the number of blades of the cooling fan  20  is six (6), and the cooling fan  20  is rotated at 10 revolutions per second (600 rpm), the fundamental frequency of the noise sound generated by the cooling fan  20  becomes 60 Hz. Therefore, a frequency component corresponding to two times of the fundamental frequency of the noise sound generated by the cooling fan  20  can be matched to the drive frequency of the pixel-shift control operation, with which the pixel-shift noise sound can be suppressed by the masking effect. 
     As described above, the image projection apparatus  1  according to the embodiment can perform the pixel-shift control operation for achieving the higher resolution of projection image without disposing a silencer that masks the noise sound caused by the pixel-shift control operation, and the above described configuration of the image projection apparatus  1  can suppress the occurrence of the noise sound in the image projection apparatus  1 , with which a user may not perceive the operation sound of the pixel-shift control operation. 
     Further, in the above-described embodiment, the pixel-shift control operation is performed by shifting the image generation element (e.g., DMD  551 ), but not limited thereto. For example, the pixel-shift control operation can be performed by moving an optical element (e.g., one lens configuring the optical projection unit), in which a drive frequency of a drive unit that shifts the optical element can be set similarly as the drive frequency of the drive unit that controls the shifting of the image generation element (e.g., DMD  551 ). Therefore, by substantially matching the fundamental frequency of the noise sound generated by the cooling fan  20  or the harmonic sound component of the noise sound generated by the cooling fan  20  to the drive frequency of the drive unit that shifts the optical element, the pixel-shift noise sound caused by the shift control of the optical element can be suppressed. 
     In the above-described embodiment, the frequency characteristic of the noise sound of the cooling fan  20  is calculated from factors of the rotation speed of the cooling fan  20  and the number of blades of the cooling fan  20 . Further, the frequency characteristics of the noise sound generated by the cooling fan  20  (such as a range width of the high sound pressure range) may vary depending on other factors such as a total size of the cooling fan  20 , a size of the blades of the cooling fan  20 , and a shape of the blades of the cooling fan  20 . Therefore, it is preferable to match the frequency characteristics of the noise sound generated by the cooling fan  20  to the drive frequency of the pixel-shift control operation in view of these factors. Specifically, the frequency characteristics of the operation sound generated by the cooling fan  20  can be measured when the cooling fan  20  of the image projection apparatus  1  is being operated, and then the rotation speed of the cooling fan  20  can be controlled based on the measured frequency characteristics of the operation sound generated by the cooling fan  20  such that the pixel-shift noise sound can be masked by the operation sound generated by the cooling fan  20 . 
     Further, the above embodiment is applied to the cooling fan  20  set with a given rotation speed and a given number of blades and provided for the light source unit  4 , but the above embodiment can be also applied to control other fans provided in the image projection apparatus  1 . 
     Further, in the above-described embodiment, the image projection apparatus  1  using a digital light processing (DLP) is described as an example of image projection apparatuses, but not limited to thereto. The above embodiment can be applied to any configuration that can perform the pixel-shift control operation. 
     Further, in the above embodiment, a horizontally placed projector is used as an example of the image projection apparatus, but the above embodiment can be also applied to a vertically placed ultra-short focus type projector using an optical reflection. 
     Further, in the above embodiment, the electromagnetic actuator (i.e., electromagnetic drive unit) is used as the drive unit of the image generation element, but not limited thereto. For example, other drive unit can be employed for the image generation element. 
     As to the above described image projection apparatus, the image projection apparatus can suppress the occurrence of noise sound caused in the image projection apparatus even if the pixel-shift control operation is performed. 
     Numerous additional modifications and variations for the modules, the units, and the image projection apparatuses are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the description of present disclosure may be practiced otherwise than as specifically described herein. For example, elements and/or features of different examples and illustrative embodiments may be combined each other and/or substituted for each other within the scope of present disclosure and appended claims.