Patent Publication Number: US-9411036-B2

Title: Light source position detection apparatus, light source tracking apparatus, control method and program

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a National Stage entry of International Application No. PCT/JP2012/082550, filed Dec. 14, 2012. The disclosure of the priority application is incorporated in its entirety herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a light source position detection apparatus, a light source tracking apparatus, a control method and a program. 
     BACKGROUND ART 
     Conventionally, sun tracking sensors are known which use a light position sensor made up of a quadrant photodiode or single element or the like. A sun tracking sensor disclosed in Patent Literature 1 forms an image of sunlight on a quadrant photodiode and a processing circuit outputs X and Y coordinate position signals. Using the X and Y coordinate position signals outputted from the sun tracking sensor enables automatic sun tracking. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Laid-Open Patent Publication No. 05-126563 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, conventional sun tracking sensors using a light position sensor made up of a quadrant photodiode or single element or the like have a problem that an error of ±0.01° or above occurs with respect to an optical axis of light actually emitted from the sun. For example, a tracking type photovoltaic power system is known which drives a solar panel using information outputted from a sun tracking sensor, for example, so that the solar panel is always oriented toward a direction orthogonal to the sunlight. For such a tracking type photovoltaic power system, a condensing type solar panel is used in recent years in order to improve power generation efficiency. In the case of a condensing type solar panel, since light is condensed using a Fresnel lens, errors of ±0.1° due to the sun tracking sensor are added up, preventing light emitted from the sun from being accurately radiated onto solar cells and causing conversion efficiency to deteriorate. Furthermore, light condensed by the Fresnel lens may be condensed at a position different from the solar battery cell, causing damage to the device due to an abnormal temperature rise. In this way, there is a demand for further improvement of accuracy with which the position of the sun is detected in recent years. 
     Furthermore, when the sun is hidden behind clouds, the quantity of light emitted from the sun decreases depending on how the sun is hidden, and the conventional sun tracking sensor has a problem that it cannot detect the position of the sun. Moreover, although it is possible to detect the position of the sun to a certain extent depending on how the sun is hidden, light emitted from the sun is scattered by clouds and the light quantity is also detected from parts other than the sun. Therefore, when the sun is hidden behind clouds, there is a problem that it is not possible to accurately detect the position of the sun due to influences of the quantity of light scattered by clouds. 
     The present invention has been implemented in view of the above-described problems and it is an object of the present invention to accurately detect the position of a light source. It is another object of the present invention to accurately detect the position of a light source even when the light source is hidden behind clouds, for example. 
     Solution to Problem 
     A light source position detection apparatus according to the present invention includes a condensing section that condenses light emitted from a light source to be detected, an image pickup device that receives the light condensed by the condensing section, and a control section that detects a position of the light source to be detected based on per-pixel light reception information received by the image pickup device, in which the control section changes a shutter speed of the image pickup device according to a quantity of the light emitted from the light source to be detected and adjusts the quantity of the light received by the image pickup device. 
     A light source tracking apparatus according to the present invention includes a light source sensor provided with a condensing section that condenses light emitted from a light source to be detected and an image pickup device that receives the light condensed by the condensing section, a control section that detects a position of the light source to be detected based on per-pixel light reception information received by the image pickup device and outputs a drive signal based on the detected position of the light source to be detected, and a drive section that moves the light source sensor based on the drive signal and tracks the light source to be detected, in which the control section changes a shutter speed of the image pickup device according to a quantity of the light emitted from the light source to be detected and adjusts the quantity of the light received by the image pickup device. 
     A method for controlling a light source tracking apparatus according to the present invention is a method for controlling a light source tracking apparatus including a condensing section that condenses light emitted from a light source to be detected, an image pickup device that receives the light condensed by the condensing section, and a control section that detects a position of the light source to be detected based on per-pixel light reception information received by the image pickup device, in which the control section changes a shutter speed of the image pickup device according to a quantity of the light emitted from the light source to be detected and adjusts the quantity of the light received by the image pickup device. 
     A program according to the present invention is a program for controlling a light source position detection apparatus including a condensing section that condenses light emitted from a light source to be detected, an image pickup device that receives the light condensed by the condensing section, and a control section that detects a position of the light source to be detected based on per-pixel light reception information received by the image pickup device, in which the program causes the control section to execute a process of changing a shutter speed of the image pickup device according to a quantity of the light emitted from the light source to be detected and adjusting the quantity of the light received by the image pickup device. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to accurately detect the position of a light source. It is also possible to accurately detect the position of the light source even when the light source is hidden, for example, behind clouds. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating an external configuration of a light source tracking apparatus of the present embodiment. 
         FIG. 2  is a diagram illustrating an internal configuration of the light source tracking apparatus of the present embodiment. 
         FIG. 3  is a diagram illustrating a configuration of a light source sensor according to a first embodiment. 
         FIG. 4  is a flowchart showing processing of the light source tracking apparatus of the present embodiment. 
         FIG. 5  is a diagram for describing clipping processing of the present embodiment. 
         FIG. 6  is a diagram for describing processing of tracking the sun of the present embodiment. 
         FIG. 7  is a diagram showing a comparison between the light source sensor of the present embodiment and a conventional light source sensor. 
         FIG. 8  is a diagram illustrating a configuration of a light source sensor according to a second embodiment. 
         FIG. 9  is a diagram illustrating a configuration of a light source sensor according to a third embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a light source tracking apparatus  10  according to the present embodiment will be described with reference to the accompanying drawings. The embodiments which will be described below will describe a case where a light source to be detected (hereinafter, referred to as “light source”) is assumed to be the sun and the light source tracking apparatus  10  tracks the sun. 
     (First Embodiment) 
       FIG. 1  is a diagram illustrating an example of an external configuration of the light source tracking apparatus  10 . 
     As shown in  FIG. 1 , the light source tracking apparatus  10  includes a base  11 , a first driving stand  12 , a second driving stand  13 , a light source sensor  30  or the like. 
     The base  11  is, for example, grounded to the earth and rotatably supports the first driving stand  12  around a vertical axis (v-axis). 
     The first driving stand  12  rotates around the vertical axis (v-axis) by an azimuth tracking motor  26  which will be described later. Furthermore, the first driving stand  12  rotatably supports the second driving stand  13  around a horizontal axis (h-axis). 
     The second driving stand  13  rotates around the horizontal axis (h-axis) by an elevation angle tracking motor  28  which will be described later. The light source sensor  30  is attached to the second driving stand  13  via a reference surface  13   a  of the second driving stand  13 . A mounting section  14  for mounting a pyrheliometer or sun photometer is set up in the second driving stand  13  for when the light source tracking apparatus  10  is used as a meteorological sensor, for example. 
     The first driving stand  12  and the second driving stand  13  rotate respectively, and the light source tracking apparatus  10  can thereby orient the light source sensor  30  in a given direction. 
       FIG. 2  is a diagram illustrating an example of an internal configuration of the light source tracking apparatus  10 . 
     As shown in  FIG. 2 , the light source tracking apparatus  10  includes a CPU  21 , a memory  22 , a clocking section  23 , a power supply section  24 , a drive section controller  25 , the azimuth tracking motor  26 , a driver  27 , the elevation angle tracking motor  28 , a driver  29  and a light source sensor  30  or the like. The light source tracking apparatus  10  performs a process of detecting a position of a light source and a process of tracking the light source. Furthermore, the CPU  21 , the memory  22 , the clocking section  23 , the power supply section  24  and the light source sensor  30  of the light source tracking apparatus  10  function as a light source position detection apparatus  41  that detects the position of a light source. 
     The CPU  21  is an example of a control section and controls the whole light source tracking apparatus  10 . The CPU  21  executes a program stored in the memory  22  and performs a process of detecting the position of the light source or a process for causing the drive section controller  25  to track the light source based on the detected position of the light source. 
     The memory  22  includes a non-volatile memory such as ROM or EEPROM and a volatile memory such as RAM. The non-volatile memory stores programs to be executed by the CPU  21 , thresholds and a table or the like used when the CPU  21  performs processing. The volatile memory is used as a work memory of the CPU  21 . 
     The clocking section  23  clocks the current date and the current time. The CPU  21  acquires time information as the current date and time from the clocking section  23 , and can thereby determine a rough estimate of light quantity emitted from the sun on a sunny day (when the sun is not hidden behind clouds). 
     The power supply section  24  supplies power to drive each component of the light source tracking apparatus  10 . The power supply section  24  may be an AC power supply that receives power from a power supply plug or rechargeable battery or the like. 
     The drive section controller  25  moves the light source sensor  30  based on an instruction from the CPU  21 . More specifically, the drive section controller  25  controls an orientation of the light source sensor  30  by driving the azimuth tracking motor  26  and the elevation angle tracking motor  28  via the driver  27  and the driver  29 . 
     The azimuth tracking motor  26  is an example of a drive section and rotates the first driving stand  12  around the vertical axis as shown in  FIG. 1 . Along with the rotation of the first driving stand  12 , the light source sensor  30  mounted on the second driving stand  13  via the first driving stand  12  also rotates around the vertical axis. 
     The elevation angle tracking motor  28  is an example of the drive section and causes the second driving stand  13  to rotate around the horizontal axis as shown in  FIG. 1 . Along with the rotation of the second driving stand  13 , the light source sensor  30  mounted on the second driving stand  13  also rotates around the horizontal axis. 
     The light source sensor  30  receives light emitted from the sun and transmits the received light information to the CPU  21 . The light source sensor  30  adjusts the quantity of light received from the sun based on an instruction from the CPU  21 . The configuration of the light source sensor  30  will be described later with reference to  FIG. 3 . 
     Furthermore, an external device  40  such as a personal computer (PC) can be connected to the light source tracking apparatus  10 . For example, the user can directly instruct the light source tracking apparatus  10  via an external device  40  or rewrite a program, thresholds and a table or the like stored in the memory  22 . When the light source tracking apparatus  10  is used to perform tracking so that, for example, the light receiving surface of the solar panel is oriented toward a direction orthogonal to the sun, the external device  40  can be connected to a drive apparatus that drives the orientation of the light receiving surface of the solar panel. 
     Additionally, the light source tracking apparatus  10  may also include an input section that directly receives an instruction from the user. 
     Next, the light source sensor  30  will be described with reference to  FIG. 3 . 
     The light source sensor  30  includes a case  31 , a condensing lens  32 , an image pickup device  33 , a neutral density filter  34 , a visible light interrupting/infrared light pass filter  35  or the like. 
     The case  31  is formed, for example, into a hollow shape and supports the condensing lens  32 , the image pickup device  33 , the neutral density filter  34  and the visible light interrupting/infrared light pass filter  35  to their respective predetermined positions. Reference surfaces  31   a  and  31   b  are formed on outer surfaces of the case  31 . The reference surface  31   a  is a surface along a direction orthogonal to a light receiving surface  33   a  of the image pickup device  33 . The reference surface  31   b  is a surface parallel to the light receiving surface  33   a  of the image pickup device  33 . By mounting the light source sensor  30  on the second driving stand  13  via the reference surface  31   a  and the reference surface  31   b  of the case  31 , it is possible to accurately mount the light source sensor  30  on the second driving stand  13 . Moreover, by forming the reference surface  31   a  and the reference surface  31   b , it is possible to accurately mount the light source sensor  30  on other light source tracking apparatuses. 
     The condensing lens  32  functions as a condensing section that condenses light emitted from the sun on the light receiving surface  33   a  of the image pickup device  33 . 
     As the image pickup device  33 , a CCD (charge coupled device), CMOS (complementary metal-oxide semiconductor) or the like can be used. The image pickup device  33  with the suitable size and number of pixels can be used depending on a light source. 
     The image pickup device  33  receives light condensed by the condensing lens  32  for each pixel, converts the received light to charge and stores the charge, and converts the stored charge to electric signals. The image pickup device  33  transmits the converted electric signals to the CPU  21  as light reception information. The light reception information includes brightness information (or gradation information) of 0 to 255, for example, that increases/decreases according to the quantity of light received for each pixel. Here, brightness “0” corresponds to a case where no light is received and no charges is stored, and brightness “255” corresponds to a case where light is received and charge is stored up to a saturation level. Since the CPU  21  can acquire per-pixel brightness information, the CPU  21  can detect at which position of the light receiving surface  33   a  of the image pickup device  33  light is condensed. 
     Furthermore, the image pickup device  33  includes a mechanism of a so-called electronic shutter. More specifically, the image pickup device  33  can adjust the quantity of received light by changing, namely, extending or shortening a charge storage time. This process of changing the charge storage time corresponds to a process of changing the shutter speed. The shutter speed is changed based on an instruction of the CPU  21 . 
     For example, when the brightness information received by the CPU  21  includes a pixel of brightness “255”, since a saturation level of charge is reached, it is difficult to detect an accurate position of the light source. In this case, the CPU  21  can acquire light reception information suitable for detecting the position of the light source by increasing the shutter speed of the image pickup device  33  (shortening the charge storage time). 
     On the other hand, when the brightness information received by the CPU  21  includes more small brightness, noise may be mixed therein, and so it is difficult to detect an accurate position of the light source. In this case, the CPU  21  reduces the shutter speed of the image pickup device  33  (extends the charge storage time), and can thereby acquire light reception information suitable for detecting the position of the light source. 
     The neutral density filter  34  is a filter that reduces the quantity of light condensed by the condensing lens  32  and emitted to the image pickup device  33 . In the present embodiment, the neutral density filter  34  is preferably a filter that reduces light so that the charge stored in the image pickup device  33  does not reach the saturation level when the quantity of light emitted from the sun is a maximum (for example, on a sunny day in the summer). Note that the filter that reduces light is not limited to the neutral density filter  34  but may also be a heat ray cutting filter. 
     The visible light interrupting/infrared light pass filter  35  is a filter that interrupts visible light out of the light emitted from the sun and allows infrared light to pass therethrough. The visible light interrupting/infrared light pass filter  35  is an example of infrared light image forming means for forming images of infrared light on the light receiving surface  33   a  of the image pickup device  33  without forming images of visible light on the light receiving surface  33   a  of the image pickup device  33 . On sunny days, since light emitted from the sun directly reaches, it is possible to detect the position of the sun by receiving visible light. On the other hand, when the sun is hidden behind clouds, light emitted from the sun is scattered by clouds. Even when the scattered visible light is received, it is difficult to accurately detect the position of the sun. Thus, the present embodiment takes advantage of the nature of infrared light that the infrared light has a longer wavelength than visible light, and is hardly scattered by clouds and passes through clouds. More specifically, visible light interrupting/infrared light pass filter  35  interrupts visible light scattered by clouds and causes the infrared light passing through clouds to be emitted to the light receiving surface  33   a  of the image pickup device  33 . Since the image pickup device  33  also has spectral sensitivity of infrared light which is closer to the long wavelength side than visible light, even when the sun is hidden behind clouds, the CPU  21  can acquire light reception information suitable for detecting the position of the sun from infrared light. 
     Next, a process by the light source tracking apparatus  10  of tracking the sun will be described with reference to a flowchart in  FIG. 4 . Here, a case will be described where the position of the center of gravity of solar energy is detected. The flowchart in  FIG. 4  is implemented by the CPU  21  executing a program stored in the memory  22 . Note that light emitted from the sun is condensed at any one position of the light receiving surface  33   a  of the image pickup device  33  of the light source sensor  30 . 
     In step S 10 , the CPU  21  acquires the light quantity of a light source via the image pickup device  33 . More specifically, the CPU  21  instructs the image pickup device  33  to pick up images at a predetermined shutter speed stored in the memory  22  in advance. The image pickup device  33  receives the light of the sun emitted via the condensing lens  32 , the neutral density filter  34  and the visible light interrupting/infrared light pass filter  35  at the instructed shutter speed and transmits light reception information to the CPU  21 . 
     In step S 11 , the CPU  21  changes the shutter speed of the image pickup device  33  according to the quantity of light emitted from the sun and adjusts the quantity of the light received by the image pickup device  33 . More specifically, the CPU  21  determines the shutter speed based on the brightness information of the light reception information received from the image pickup device  33  in step S 10 . The memory  22  stores a table that associates, for example, a maximum value of brightness with an optimum shutter speed corresponding to the maximum value of brightness. In this table, for example, when the maximum value of brightness is close to “255” (when brightness is large), a higher shutter speed is associated and when the maximum value of brightness is close to “0” (when brightness is small), a lower shutter speed is associated. The CPU  21  acquires the maximum value of brightness and looks up the table stored in the memory  22  and thereby determines the shutter speed associated with the maximum value of brightness. Therefore, when the quantity of light emitted from the sun is large, the maximum value of brightness increases, and therefore the CPU  21  determines a higher shutter speed. On the other hand, when the sun is hidden behind clouds and the quantity of light emitted from the sun is small, the maximum value of brightness is small, and so the CPU  21  determines a lower shutter speed. Here, although the quantity of light emitted from the sun is determined using the maximum value of brightness, for example, an average brightness value may also be used. In this case, the CPU  21  determines a higher shutter speed when the average brightness value of a pixel is large and determines a lower shutter speed when the average brightness value of a pixel is small. For example, as the shutter speed, the CPU  21  preferably determines a shutter speed so that brightness smaller than 255 is outputted when the maximum value of brightness is brightness greater than a predetermined threshold A used in step S 13  which will be described later. 
     In step S 12 , the CPU  21  instructs the image pickup device  33  to pick up images at the shutter speed determined in step S 11 . The image pickup device  33  receives the light of the sun emitted via the condensing lens  32 , the neutral density filter  34  and the visible light interrupting/infrared light pass filter  35  at the instructed shutter speed and transmits light reception information including brightness information to the CPU  21 . 
     In step S 13 , the CPU  21  performs a clipping process of clipping part of the brightness information received from the image pickup device  33 . Here, the clipping process will be described with reference to  FIG. 5 .  FIG. 5( a )  is a diagram illustrating an image of an object in which part of the sun is hidden behind a cloud, with an image of the sun being formed on the light receiving surface  33   a  of the image pickup device  33 . Here, suppose the horizontal direction corresponds to the x-axis and the vertical direction corresponds to the y-axis. 
       FIG. 5( b )  and  FIG. 5( c )  illustrate, in graph, brightness information of pixels along a line I-I in  FIG. 5( a ) . Note that in  FIG. 5( b )  and  FIG. 5( c ) , since the shutter speed is adjusted to an optimum one by aforementioned step S 11 , brightness information suitable for detecting the position of the light source is acquired. 
       FIG. 5( b )  illustrates brightness information when an image of light also including visible light is formed without using the visible light interrupting/infrared light pass filter  35 . As shown in  FIG. 5( b ) , since visible light out of the light emitted from the sun is scattered by clouds, high brightness appears even in the part of the cloud. Therefore, although the actual center of gravity of solar energy is a position shown by an arrow T, the center of gravity is detected as a position shown by an arrow F 1  due to scattering of visible light. 
     On the other hand,  FIG. 5( c )  illustrates brightness information when visible light is interrupted using the visible light interrupting/infrared light pass filter  35 , infrared light is allowed to pass and an image thereof is formed. As shown in  FIG. 5( c ) , by interrupting visible light, light scattered by clouds is interrupted and infrared light passes through the clouds, and so high brightness appears only in the part of the sun. Therefore, the position shown by an arrow F 2  which is a position close to the arrow T of the actual center of gravity of solar energy is detected as the center of gravity. 
     In this way, by using the visible light interrupting/infrared light pass filter  35 , it is possible to prevent scattering of visible light by clouds even when the sun is hidden behind clouds. 
     The CPU  21  performs a clipping process of clipping brightness information equal to or lower than a predetermined threshold out of the acquired brightness information. To be more specific, the process carried out by the CPU  21  will be described. Here, suppose the horizontal direction of the light receiving surface  33   a  is the x-axis and the vertical direction is the y-axis, and brightness of a pixel at coordinates (x, y) is f(x, y). When f(x, y) is equal to or lower than the predetermined threshold A, the CPU  21  performs a process (clipping process) of assuming f(x, y)=0 on all pixels. Note that the threshold A is preferably a value whereby brightness resulting from light scattered by clouds can be rounded down.  FIG. 5( d )  illustrates, in graph, brightness information obtained by assuming brightness equal to or less than the predetermined threshold A to be 0. As shown in  FIG. 5( d ) , performing the clipping process allows the detected position of the center of gravity to match the actual center of gravity of the solar energy shown by the arrow T. 
     In step S 14 , the CPU  21  calculates the center of gravity of solar energy. More specifically, the CPU  21  calculates coordinates of the center of gravity (Xg, Yg) using f(x, y) after the clipping process according to the following Equation 1. This process allows the CPU  21  to accurately detect the position of the sun. 
     
       
         
           
             
               
                 
                   
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     In step S 15 , the CPU  21  performs a process for causing the drive section controller  25  to track a light source based on the detected position of the sun. More specifically, the CPU  21  calculates distances in the x direction and y direction between the center coordinates of the light receiving surface  33   a  of the image pickup device  33  and the coordinates of the center of gravity of solar energy. Next, the CPU  21  calculates an angle of inclination of the optical axis of the sun with respect to the light source sensor  30  based on the calculated distances. The CPU  21  may also calculate the angle of inclination by looking up a table stored in the memory  22  that associates the distances in the x direction and the y direction with angles of inclination or may geometrically calculate the angle of inclination based on the distances in the x direction and the y direction. 
       FIG. 6  is a diagram illustrating a situation in which there is a distance of Δx between the coordinates of the center of gravity of energy of light emitted from the sun and the center coordinates. In this case, from Δx, the CPU  21  calculates Ox as the angle of inclination of the optical axis of the sun. 
     The CPU  21  transmits information on the angle of inclination calculated to track the sun to the drive section controller  25 . The drive section controller  25  transmits drive signals to the azimuth tracking motor  26  and the elevation angle tracking motor  28  based on the information on the angle of inclination transmitted from the CPU  21 . As the azimuth tracking motor  26  and the elevation angle tracking motor  28  operate in response to the respective drive signals, the first driving stand  12  and the second driving stand  13  move. The movement of the first driving stand  12  and the second driving stand  13  allows the optical axis of the sun to accurately match the center coordinates of the light source sensor  30 , and the sun tracking process thereby ends. 
     The light source tracking apparatus  10  continues the processes from step S 10  to step S 15  all the time, and can thereby track the sun with high accuracy. 
       FIG. 7  shows a graph obtained by plotting positions when a conventional light source tracking apparatus using an optical position sensor and the light source tracking apparatus  10  according to the present embodiment respectively detect an identical light source. In  FIG. 7 , the horizontal axis denotes a position when the light source is moved at a predetermined interval and the vertical axis denotes a position of the light source detected by each light source tracking apparatus. A broken line in the graph corresponds to a regression straight line of plots outputted from the conventional light source tracking apparatus and a solid line in the graph corresponds to a regression straight line of plots outputted from the light source tracking apparatus  10  of the present embodiment. 
     As shown in  FIG. 7 , the plots outputted by the conventional light source tracking apparatus are not located on the regression straight line, and a determining coefficient R 2  that indicates a correlation is R 2 =0.5087 showing a low correlation. On the other hand, the plots outputted by the light source tracking apparatus  10  of the present embodiment are located substantially on the regression straight line, and a determining coefficient R 2  that indicates a correlation is R 2 =0.9975 showing quite a high correlation. It has been successfully proven that the light source tracking apparatus  10  of the present embodiment can reduce an error of the angle of inclination with respect to the optical axis of the light source to ±0.001° or less, and can detect the position of the light source with high accuracy. 
     Therefore, for example, when a pyrheliometer is attached to the mounting section  14  of the light source tracking apparatus  10 , the pyrheliometer tracks the sun with high accuracy, and can thereby accurately measure an amount of solar radiation. Furthermore, for example, when the CPU  21  sends the calculated angle of inclination to the drive apparatus of the solar panel, the solar panel can always track the sun with high accuracy in a direction orthogonal to the sun, and can thereby improve conversion efficiency. In the case of a condensing type solar panel in particular, light is condensed by a Fresnel lens and errors are thereby added up, and such errors of the conventional light source tracking apparatus will prevent accurate radiation of light onto a solar battery cell. Using the light source tracking apparatus  10  of the present embodiment makes it possible to minimize errors and so the light source tracking apparatus  10  is also applicable to a condensing type solar panel. 
     Note that although a case has been described in step S 10  of the aforementioned embodiment where the CPU  21  instructs the image pickup device  33  to pick up images at a predetermined shutter speed stored beforehand in the memory  22 , the present invention is not limited to this case. For example, the memory  22  may store, beforehand, a table that associates time information of the current date and time with a shutter speed. This table associates, for example, the winter season or morning and evening times with slow shutter speeds and associates the summer season or daytime with quick shutter speeds. In this case, the CPU  21  acquires time information on the current date and time from the clocking section  23  and acquires a shutter speed associated with the time information by looking up the table stored in the memory  22 . Next, the CPU  21  indicates the acquired shutter speed to the image pickup device  33 , and can thereby acquire light reception information suitable for when determining the shutter speed in step S 11 . 
     Furthermore, the processes in step S 10  and step S 11  may be repeated until light reception information suitable for detecting the position of the sun can be acquired. That is, after determining the shutter speed in step S 11 , the process returns to step S 10  and instructs the image pickup device  33  to pick up images at a determined shutter speed. After that, when light reception information suitable for detecting the position of the sun can be acquired, the CPU  21  can proceed to step S 12 . 
     A case has been described in the aforementioned embodiment where the visible light interrupting/infrared light pass filter  35  is used as the infrared light image forming means, but the present invention is not limited to this case. For example, the condensing lens  32  itself may be a lens that forms images of infrared light that passes through clouds on the image pickup device  33  without forming images of visible light on the image pickup device  33 . 
     (Second Embodiment) 
     A case has been described in the first embodiment where the condensing lens  32  is used as a condensing section that condenses light emitted from the sun on the light receiving surface  33   a  of the image pickup device  33 . The present embodiment will describe a case where a pinhole is used as the condensing section. 
       FIG. 8  is a diagram illustrating a configuration of a light source sensor  50  according to a second embodiment. Note that components identical to those in the light source sensor  30  of the first embodiment are assigned identical reference numerals and description thereof will be omitted as appropriate. 
     The light source sensor  50  includes a case  51 , an image pickup device  33  or the like. 
     The case  51  is formed, for example, into a hollow shape, and a pinhole  51   a  is formed as a condensing section that condenses light emitted from the sun on the light receiving surface  33   a  of the image pickup device  33 . The pinhole  51   a  also has a function of reducing the quantity of light radiated onto the image pickup device  33 . Moreover, reference surfaces  31   a  and  31   b  similar to those in the first embodiment are formed on outer surfaces of the case  51 . 
     According to the present embodiment, it is possible to condense the light condensed by the pinhole  51   a  on the light receiving surface  33   a  of the image pickup device  33 , and thereby detect the position of the sun with high accuracy as in the case of the first embodiment. It is also possible to simplify the configuration of the light source sensor  50  compared to the first embodiment, and thereby reduce the manufacturing cost. 
     (Third Embodiment) 
     A case has been described in the first embodiment and the second embodiment where the condensing lens  32  or the pinhole  51   a  is used as the condensing section. The present embodiment will describe a case where a wide-angle lens is used as the condensing section. 
       FIG. 9  is a diagram illustrating a configuration of a light source sensor  60  according to a third embodiment. Note that components identical to those in the light source sensor  30  of the first embodiment are assigned identical reference numerals and description thereof will be omitted as appropriate. 
     The light source sensor  60  includes the case  31 , a wide-angle lens  61  and the image pickup device  33  or the like. 
     The wide-angle lens  61   b  can condense even light emitted at a large angle of inclination (e.g., 50°) of the optical axis of the sun on the light receiving surface  33   a  of the image pickup device  33 . Using the wide-angle lens  61  in this way allows the light source sensor  60  of the present embodiment to detect the position of the sun over a wide range. 
     Therefore, the light source sensor  60  of the present embodiment is suitable for use to detect a light source that moves faster than the sun (e.g., missile) or when setting up the light source tracking apparatus  10  on a water surface (e.g., ship). The light source sensor  60  of the present embodiment may be configured of a plurality of components in combination with the light source sensor  30  of the first embodiment or the light source sensor  50  of the second embodiment. For example, the light source sensor  30  (first light source sensor) and the light source sensor  60  (second light source sensor) may be placed in parallel and mounted on the second driving stand  13 . In this case, the CPU  21  can detect and track a rough position of the sun based on the light reception information acquired from the light source sensor  60  (after aforementioned step S 10  to step S 15 ) first, and then detect and track an accurate position of the sun based on the light reception information acquired from the light source sensor  30  (aforementioned step S 10  to step S 15 ). By configuring the light source tracking apparatus  10  in this way, it is possible to track the light source early and accurately even when detecting a light source that moves faster than the sun or when setting up the light source tracking apparatus  10  on a water surface (e.g., ship). Note that a fish-eye lens or the like may be used as the wide-angle lens  61 . 
     (Fourth Embodiment) 
     A case has been described in the first embodiment where the CPU  21  calculates the center of gravity of solar energy, but the present invention is not limited to this case. The CPU  21  may also calculate the center of gravity of graphics (geometric center of gravity) when the shape (contours) of the sun is seen as graphics. When calculating the geometric center of gravity, a binarization process may be executed instead of the clipping process in step S 13  in the flowchart in  FIG. 4 . 
     That is, in step S 13 , the CPU  21  executes the binarization process based on the brightness information received from the image pickup device  33 . More specifically, the CPU  21  uses a predetermined threshold A as a boundary, and performs the process on all pixels by assuming f(x, y)=0 when f(x, y) is equal to or below a predetermined threshold A, and f(x, y)=1 when f(x, y) is greater than the predetermined threshold A. 
     In step S 14 , the CPU  21  calculates center of gravity coordinates (Xg, Yg) using f(x, y) after the binarization process according to the aforementioned Equation 1. The CPU  21  can calculate a position of the geometric center of gravity of the sun through this process. 
     In the light source tracking apparatus  10 , the user can set whether to calculate an energy center of gravity or calculate a geometric center of gravity via a PC of the external device  40  or the like. The CPU  21  calculates the energy center of gravity or geometric center of gravity according to the setting. Note that the user may set whether to calculate an energy center of gravity or calculate a geometric center of gravity depending on the purpose of tracking the light source. 
     Although the present invention has been described together with various embodiments so far, the present invention is not limited to these embodiments alone, but can be changed within the scope of the present invention or the respective embodiments can be combined. 
     For example, a case has been described in the aforementioned embodiments where the light source is the sun, but the present invention is not limited to this case. The present invention is applicable to any light source as long as it is a light source that emits light. 
     A case has been described in the aforementioned embodiments where the image pickup device  33  transmits brightness information of 0 to 255 for each pixel, but without being limited to this case, for example, brightness information of 0 to 127, 0 to 511 or the like may be transmitted. 
     A case has been described in the aforementioned embodiments where the azimuth tracking motor  26  and the elevation angle tracking motor  28  are used as the drive sections, but without being limited to this case, any drive section may be used as long as it can track a light source. 
     A case has been described in the aforementioned embodiments where the light source tracking apparatus  10  includes the drive section controller  25 , but the CPU  21  may include the function of the drive section controller  25  and the drive section controller  25  may be omitted. 
     The present embodiment can also be implemented by supplying a program for implementing the aforementioned processes to the light source tracking apparatus  10  via a network or various storage media and the CPU  21  of the light source tracking apparatus  10  reading and executing the supplied program. The present invention may be a storage medium that records the program. 
     INDUSTRIAL APPLICABILITY 
     The present invention can be used for a light source position detection apparatus or a light source tracking apparatus or the like.