Patent Publication Number: US-2015069245-A1

Title: Human body detector, human body-detecting method, electric device, and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is based on and claims priority from Japanese Patent Application No. 2013-187465, filed on Sep. 10, 2013, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND 
     Field of the Invention 
     The present invention relates to a human body detector using an infrared sensor, a human body-detecting method, an electric device including the human body detector, and an image-forming apparatus including the human body detector. 
     In reaction to recent social conditions, various electric devices, office machines and so on (hereinafter, referred to as an electric device) having an energy conservation function have been developed, manufactured, and distributed. The electric device includes inside thereof a pyroelectric-type infrared sensor, for example. When the output voltage signal from the pyroelectric-type infrared sensor is under a threshold which is predetermined according to design, the electric device determines that a user is absent there around, and enters into a static mode (for example, power saving mode). On the other hand, when the output voltage signal from the infrared sensor exceeds the threshold, the electric device determines that the user is standing near the electric device, and immediately changes its mode to an operating mode from the static mode. In fact, an electric device is already known in which energy saving is realized by setting the operating mode only when the user comes closer to the device, and setting the static mode when the user is not standing around the device (for reference, see Japanese Patent Laid-open Publication No. 06-242226 and Japanese Patent Laid-open Publication No. 2009-288498). 
     An optimum electric power-control to achieve energy conservation can be realized if a user who is standing in an area adjacent to an electric device for operation can be detected. However, the pyroelectric-type infrared sensor has a problem derived from its characteristic feature such that it is difficult to detect the static state of the user in a detection target area. When the user stands in front of the electric device for operating with no substantial movement (or with very small movement which cannot be detected by a pyroelectric-type infrared sensor), the electric device suddenly changes its mode from the operating mode to the static mode even though the user is still using the device. Thus, such a sudden change significantly decreases the user-friendliness of the device. 
     SUMMARY 
     The present invention has been made in view of the above problem, and an object of the present invention is to provide a human body detector including an infrared sensor, which can reliably detect the presence of a human body in a designated area. 
     A human body detector according to embodiments of the present invention includes, an infrared sensor which detects a light amount change of infrared rays which enter from a detection target area, and a controller which determines the presence or absence of a human body in the detection target area according to the light amount change of the infrared rays, wherein the infrared sensor is configured to detect the light amount change of the infrared rays which enter from a plurality of cell sections which are formed by dividing the detection target area, and arranged two-dimensionally in the detection target area, and 
     the controller is configured to identify an outer peripheral area including cell sections provided along a portion in the outer periphery of the detection target area through which the human body can pass, and an inside area including cell sections other than those in the outer peripheral area, determine the presence of the human body in the detection target area when the light amount change of the infrared rays which enter from the cell sections in the inside area is detected, and determine the absence of the human body in the detection target area when the light amount change of the infrared rays is not detected for a predetermined period in all of the cell sections after the light amount change of the infrared rays which enter from the cell sections in the outer peripheral area is detected. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the specification, serve to explain the principle of the invention. 
         FIG. 1  is a block chart illustrating a configuration of an electric device  10  including a human body detector according to a first embodiment of the present invention. 
         FIG. 2  is a side view illustrating a configuration of infrared sensors  11  and  12  shown in  FIG. 1 . 
         FIG. 3  is an upper surface view illustrating a detailed configuration of a circuit substrate  22  shown in  FIG. 2 . 
         FIG. 4  is a schematic view illustrating viewing fields  1  to  4  of the infrared sensor  11  shown in  FIG. 1 . 
         FIG. 5  is a block chart illustrating a detailed configuration of a signal-processing circuit  32  shown in  FIG. 3 . 
         FIG. 6  is a waveform chart illustrating the behavior of infrared ray-sensing elements S 1  to S 4  shown in  FIG. 3 . 
         FIG. 7  is a schematic view illustrating an aspect in which a human body  51  enters into the viewing field  1  of the infrared sensor  11  shown in  FIG. 1 . 
         FIG. 8  is a waveform chart illustrating output voltages V 1 - 1  to V 1 - 4  of the infrared ray-sensing elements S 1  to S 4  under the condition as shown in  FIG. 7 . 
         FIG. 9  is a timing chart illustrating the behavior of a signal-processing circuit  32  under the condition as shown in  FIG. 7 . 
         FIG. 10  is a schematic view illustrating aspects in which the human body  51  enters into, stops, passes through the viewing fields  1  to  4  of the infrared sensor  11  shown in  FIG. 1 , and an aspect in which the human body  51  travels away from the infrared sensor  11 . 
         FIG. 11  is a waveform chart illustrating the output voltage V 1 - 1  to V 1 - 4  of the infrared ray-sensing elements S 1  to S 4  in the aspect in which the human body  51  stops in the viewing fields  1  to  4  and travels away from the infrared sensor  11  under the condition as shown in  FIG. 10 . 
         FIG. 12  is a waveform chart illustrating the output voltage V 1 - 1  to V 1 - 4  of the infrared ray-sensing elements S 1  to S 4  in the aspect in which the human body  51  passes through the viewing fields  1  to  4  under the condition as shown in  FIG. 10 . 
         FIG. 13  is a schematic view illustrating the aspect in which the human body  51  enters into the detection target area of the infrared sensors  11  and  12  shown in  FIG. 1   
         FIG. 14  illustrates output signals of the infrared sensors  11  and  12  in an aspect in which the human body  51  travels in an outer peripheral area under the condition as shown in  FIG. 13 . 
         FIG. 15  illustrates output signals of the infrared sensors  11  and  12  in an aspect in which the human body  51  passes through both outer peripheral area and inside area under the condition as shown in  FIG. 13 . 
         FIG. 16  illustrates output signals of the infrared sensors  11  and  12  in an aspect in which the human body  51  travels in the inside area under the condition as shown in  FIG. 13 . 
         FIG. 17  illustrates output signals of the infrared sensors  11  and  12  in an aspect in which the human body  51  stands still in the inside area under the condition as shown in  FIG. 13 . 
         FIG. 18  is a flowchart illustrating a human body-detecting process which is performed by a sensor controller  13  shown in  FIG. 1 . 
         FIG. 19  is a block chart illustrating a configuration of an electric device  10  including a human body detector according to a modified example of the first embodiment of the present invention. 
         FIG. 20  is a block chart illustrating a configuration of an electric device  10 A including a human body detector according to a second embodiment of the present invention. 
         FIG. 21  is a schematic view of an image-forming apparatus according to an example of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, with reference to the drawings, embodiments of the present invention will be described. 
     First Embodiment 
       FIG. 1  is a block chart illustrating a configuration of an electric device  10  including a human body detector according to the first embodiment of the present invention. The electric device  10  includes a human body detector including infrared sensors  11  and  12  and a sensor controller  13 . The human body detector has a detection target area (area surrounded by thick dotted line in  FIG. 1 ) which is defined according to detection ranges of the infrared sensors  11  and  12 . In the aspect shown in  FIG. 1 , the detection target area is adjacent to the electric device  10  and expands in the horizontal direction in relation to the ground surface. In  FIG. 1 , the overhead view of the electric device  10  and its detection target area are shown. The infrared sensors  11  and  12  detect the light amount change of the infrared rays which enter from the detection target area. The sensor controller  13  determines the presence or absence of the human body  51  in the detection target area based on the light amount change of the infrared ray. The electric device  10  further includes a power source controller  14 , and the power source controller  14  sets the electric device  10  to the operating mode or the static mode under the control of the sensor controller  13  when the electric device  10  is turned on. The sensor controller  13  sets the electric device  10  to the operating mode when it determines the presence of the human body in the detection target area, and sets the electric device  10  to the static mode when it determines the absence of the human body in the detection target area. 
     The configuration of the human body detector in  FIG. 1  will be described as follows. 
     The infrared sensors  11  and  12  are configured to detect the light amount change of the infrared rays which enter from each of cell sections which are formed by segmenting the detection target area and are arranged two-dimensionally in the detection target area. The infrared sensor  11  includes a first infrared sensor array including a plurality of infrared ray-sensing elements having first viewing fields  1  to  4  which are different from, and are adjacent to each other. For example, in the infrared sensor  11 , the viewing fields  1  to  4  are configured by segmenting the detection target area in a radial fashion. The infrared sensor  12  includes a second infrared sensor array including a plurality of second infrared ray-sensing elements having second viewing fields A to D which are different from, and are adjacent to each other. For example, in the infrared sensor  12 , the viewing fields A to D are configured by segmenting the detection target area in a radial fashion. The infrared sensors  11  and  12  are disposed in a chassis of the electric device  10  so as to have a predetermined distance therebetween. The first viewing fields  1  to  4  intersect with the second viewing fields A to D. Each cell section is formed such that one of the first viewing fields  1  to  4  intersects with one of the second viewing fields A to D. 
     The sensor controller  13  identifies an outer peripheral area including cell sections which are arranged along a portion in the outer periphery of the detection target area in which the human body can pass through, and an inside area including cell sections other than the cell sections in the outer peripheral area. For example, the human body never passes through the portion adjacent to the chassis of the electric device  10  in the outer periphery of the detection target area shown in  FIG. 1 . Therefore, the cell sections arranged along such a portion are detected as the cell sections in the inside area, not in the outer peripheral area. In the aspect shown in  FIG. 1 , the sensor controller  13  identifies the cell sections included in the viewing field  1  which is the most distant from the infrared sensor  12  in the viewing fields  1  to  4  of the infrared sensor  11  as the cell sections in the outer peripheral area. The sensor controller  13  identifies the cell sections included in the viewing field A which is the most distant from the infrared sensor  11  in the viewing fields A to D of the infrared sensor  12  as the cell sections in the outer peripheral area. In addition, the sensor controller  13  identifies the cell sections which are not in the outer peripheral area as the cell sections in the inside area. 
     The sensor controller  13  performs a human body-detecting process as shown in  FIG. 18  so as to determine the presence or absence of the human body in the detection target area. The sensor controller  13  determines the presence of the human body in the detection target area when the light amount change of the infrared rays which enter from the cell sections in the inside area is detected. The sensor controller  13  determines the absence of the human body in the detection target area when the light amount change of the infrared rays is not detected for certain periods in all of the cell sections after the light amount change of the infrared rays which enter from the cell sections in the outer peripheral area is detected. Thereby, even when the infrared sensors  11  and  12  do not detect the light amount change of the infrared rays because the user stands still in front of the electric device  10 , the human body detector does not fail and detect absence of the human body, and thus, it can reliably detect the presence of the human body in the detection target area. The detailed description regarding the human body-detecting process will be made later with reference to  FIG. 18 . 
     The sensor controller  13  may determine the light amount change of the infrared rays which enter from the cell sections in the outer peripheral area when it detects the light amount change of the infrared rays in a plurality of adjacent cell sections (for example, two) of the cell sections in the outer peripheral area. Thereby, the light amount change of the infrared rays which enter from the cell sections in the outer peripheral area can be reliably detected. In this case, the viewing fields  1  to  4  and viewing fields A to D of the infrared sensors  11  and  12  are configured such that the human body occupies the two cell sections which are adjacent to each other when the human body stands in the outer peripheral area. 
       FIG. 2  is a side view illustrating the configuration of the infrared sensors  11  and  12  in  FIG. 1 . The infrared sensors  11  and  12  include a lens  21 , a circuit substrate  22 , and a package  23  which are configured integrally in layers. The lens  21  has an optical micro lens. The circuit substrate  22  includes an infrared ray sensing element and a signal-processing circuit ( FIG. 3 ). The package  23  includes an insulant and an electric pole such as a supply terminal, an earth terminal, or an output signal terminal, which is provided so as to be exposed in part from the insulant. The circuit substrate  22  is sandwiched by the lens  21  and the package  23  for protection. 
       FIG. 3  is an upper surface view illustrating the detailed configuration of the circuit substrate  22  in  FIG. 2 . The circuit substrate  22  includes an infrared sensor array  31  including four infrared ray-sensing elements S 1  to S 4 , and the signal-processing circuit  32 . The infrared ray-sensing elements S 1  to S 4  are arranged linearly on the center part of the circuit substrate  22 . The infrared rays which enter into the infrared sensors  11  and  12  from the detection target area are condensed by the lens  21  ( FIG. 2 ) and enter into the infrared ray-sensing elements S 1  to S 4 . The output voltages of each of the infrared ray sensing elements S 1  to S 4  are sent to the signal-processing circuit  32 . The signal-processing circuit  32  is arranged in the area adjacent to the infrared sensor array  31 . 
       FIG. 4  is a schematic view illustrating the viewing fields  1  to  4  of the infrared sensor  11  in  FIG. 1 . As described above, in the infrared sensor  11 , the viewing fields  1  to  4  are configured by segmenting the detection target area in a radial fashion. Accordingly, the lens  21  and the infrared ray-sensing elements S 1  to S 4  of the infrared sensor  11  are configured so that the infrared rays from the viewing fields  1  to  4  enter into each of the infrared ray-sensing elements S 1  to S 4 . For example, each of the viewing fields  1  to  4  does not share any portions to be configured exclusively. The infrared sensor  12  and the viewing fields A to D thereof have a similar configuration to the infrared sensor  11  and the viewing fields  1  to  4  thereof. 
       FIG. 5  is a block chart illustrating the detailed configuration of the signal-processing circuit  32  in  FIG. 3 . The signal-processing circuit  32  includes amplifiers  41 - 1  to  41 - 4 , switches SW 1  to SW 4 , standard voltage sources E 1  and E 2 , a comparator  42 , preregisters PR 1  to PR 4 , registers R 1  to R 4 , and an interface circuit  43 . 
       FIG. 6  is a waveform chart describing the behavior of the infrared ray-sensing elements S 1  to S 4  in  FIG. 3 . An increase or a decrease of the output voltages V 1 - 1  to V 1 - 4  of the infrared ray-sensing elements S 1  to S 4  when the light amount of infrared rays which enter from the viewing fields  1  to  4  (or viewing fields A to D) changes depends on the relationship between the temperature of the human body and the background temperature. When the human body temperature is lower than the background temperature, the output voltages V 1 - 1  to V 1 - 4  of the infrared ray-sensing elements S 1  to S 4  increase only in the case in which the light amount of the infrared rays which enter from the viewing fields  1  to  4  (or viewing fields A to D) changes, and the output voltages V 1 - 1  to V 1 - 4  exceed the predetermined upper limit threshold. On the other hand, when the human body temperature is higher than the background temperature, the output voltages V 1 - 1  to V 1 - 4  of the infrared ray-sensing elements S 1  to S 4  decrease only in the case in which the light amount of the infrared rays which enter from the viewing fields  1  to  4  (or viewing fields A to D) changes, and the output voltages V 1 - 1  to V 1 - 4  fall below the predetermined lower limit threshold. 
     Referring to  FIG. 5  again, the output voltages V 1 - 1  to V 1 - 4  of the infrared ray-sensing elements S 1  to S 4  are amplified by the amplifiers  41 - 1  to  41 - 4 . The switches SW 1  to SW 4  are connected to the output terminals of the amplifiers  41 - 1  to  41 - 4 . The switches SW 1  to SW 4  operate under the control of the sensor controller  13 , and always send only one signal from the output signals of the amplifiers  41 - 1  to  41 - 4 . Hereinafter, the output signals of the amplifiers  41 - 1  to  41 - 4  which are sent to the comparator  42  are referred to as a detected voltage V 2 . The standard voltage source E 1  generates the predetermined upper limit threshold voltage Vth 1 , and the standard voltage source E 2  generates the predetermined lower limit threshold voltage Vth 2 . The comparator  42  determines whether the detected voltage V 2  is within the range which is equal to or lower than the predetermined upper limit threshold voltage Vth 1  and equal to or higher than the predetermined lower limit threshold voltage Vth 2  (window range) as a window comparator. When V 2  is higher than Vth 1  or V 2  is lower than Vth 2 , the output signal V 3  of the comparator  42  becomes high level, and when V 2  is equal to or higher than Vth 2  and V 2  is equal to or lower than Vth 1 , the output signal V 3  of the comparator  42  becomes lower level. It depends on the relationship between the temperature of the human body and the temperature of the background whether the detected voltage V 2  exceeds the upper limit threshold Vth 1  or it falls below the lower limit threshold Vth 2 . In the case in which the human body temperature is lower than the background temperature, when the light amount of the infrared rays changes, the detected voltage V 2  exceeds the upper limit threshold Vth 1 . In the case in which the human body temperature is higher than the background temperature, when the light amount of the infrared rays changes, the detected voltage V 2  falls below the lower limit threshold Vth 2 . The switches SW 1  to SW 4  are turned on in order of “SW 1  to SW 2  to SW 3  to SW 4  to SW 1  to . . . ”. Thereby, the comparator  42  evaluates whether the detected voltages V 2  which correspond to each output voltage V 1 - 1  to V 1 - 4  of the infrared ray-sensing elements S 1  to S 4  are within the window range or not by time-sharing. The output signal V 3  of the comparator  42  is stored in the preregisters PR 4 , PR 3 , PR 2 , and PR 1 . The preregisters PR 4 , PR 3 , PR 2 , and PR 1  configure a shift register circuit. When the output signal V 3  of the comparator  42  which corresponds to each output voltage V 1 - 1  to V 1 - 4  of the infrared ray-sensing elements S 1  to S 4  is stored in the preregisters PR 1  to PR 4 , the data in the preregisters PR 1  to PR 4  is sent to the registers R 1  to R 4  by batch transmission. The interface circuit  43  transmits the data of the registers R 1  to R 4  to the sensor controller  13  by serial transmission when it receives the reading request signal from the sensor controller  13 . 
     Hereinafter, with reference to  FIGS. 7 to 12 , the fundamental behavior of the human body detector in  FIG. 1  will be described. 
       FIG. 7  is a schematic view illustrating an example in which the human body  51  enters into the viewing field  1  of the infrared sensor  11  in  FIG. 1 .  FIG. 8  is a waveform chart illustrating the output voltage V 1 - 1  to V 1 - 4  of the infrared sensors S 1  to S 4  under the condition indicated in  FIG. 7 . As soon as the human body S 1  enters into the viewing field  1 , the light amount of the infrared rays which enter into the infrared ray-sensing element S 1  changes, so the output voltage V 1 - 1  of the infrared ray-sensing element S 1  changes. 
       FIG. 9  is a timing chart describing the behavior of the signal-processing circuit  32  under the condition as indicated in  FIG. 7 .  FIG. 9  illustrates the behavior of each signal in the signal-processing circuit  32  in a short period T 1  shown in  FIG. 8 . In  FIG. 9 , “SW 1  to SW 4 ” indicate each signal which is provided from the sensor controller  13  toward the switches SW 1  to SW 4 . The switches SW 1  to SW 4  close when the signals are at high level, and open when the signals are at low level. As described above, when the output signal V 3  of the comparator  42  which corresponds to each output voltages V 1 - 1  to V 1 - 4  of the infrared ray-sensing elements S 1  to S 4  is stored in the preregisters PR 1  to PR 4 , the data in the preregisters PR 1  to PR 4  is sent to the registers R 1  to R 4  by batch transmission. According to  FIG. 9 , only the detected voltage V 2  which corresponds to the output voltage V 1 - 1  of the infrared ray-sensing element S 1  exceeds the upper limit threshold voltage Vth 1 , so that only the data of the resister R 1  rises to be high level, and the data of the registers R 2  to R 4  falls to be low level. 
       FIG. 10  is a schematic view illustrating aspects in which the human body  51  stops, passes through, or travels away from the infrared sensor  11  when the human body  51  enters into the viewing fields  1  to  4  of the infrared sensor  11  in  FIG. 1 . Herein, the experiment is provided so as to detect the presence of the human body  51  in the viewing fields  2  and  3  in  FIG. 10 . In the first aspect, the human body  51  enters into the viewing fields  2  and  3  through the viewing field  1 , and stops. In the second aspect, the human body  51  passes through the viewing fields  1  to  4 . In the third aspect, the human body  51  passes through the viewing field  1 , enters into the viewing fields  2  and  3 , and travels in the direction which is away from the infrared sensor  11 .  FIG. 11  is a waveform chart illustrating the output voltages V 1 - 1  to V 1 - 4  of the infrared ray-sensing elements S 1  to S 4  in the aspects in which the human body  51  stops or travels away from the infrared sensor  11  under the condition as indicated in  FIG. 10 .  FIG. 12  is a waveform chart illustrating the output voltages V 1 - 1  to V 1 - 4  of the infrared ray-sensing elements S 1  to S 4  in an aspect in which the human body  51  passes through the viewing fields  1  to  4  under the aspect as shown in  FIG. 10 . According to  FIG. 11 , the aspect in which the human body stops and the aspect in which the human body travels away from the infrared sensor  11  cannot be distinguished only with the detected result of the infrared sensor  11 . Therefore, it is difficult to detect the presence or absence of the human body  51  in the viewing fields  2  and  3 . This is because the infrared sensor  11  in  FIG. 11  can detect the motion of the human body  51  in the transverse direction but it is difficult to detect the motion of the human body  51  in the vertical direction easily. 
     Subsequently, with reference to  FIGS. 13 to 18 , the human body-detecting method by using the human body detector in  FIG. 1  will be described. Herein, the human body is expected to travel in the vertical direction in addition to traveling in the lateral direction. 
       FIG. 13  is a schematic view illustrating an example in which the human body  51  enters into the detection target area of the infrared sensors  11  and  12  in  FIG. 1 . Herein, the human body  51  moves in the inside area from the left side of the outer peripheral area, and stands still therein. When the human body  51  moves toward the inside area from the outside of the detection target area, the human body  51  always passes through the outer peripheral area. Then, the human body  51  moves in the inside area after traveling through both of the outer peripheral area and inside area.  FIG. 14  illustrates the output signals of the infrared sensors  11  and  12  when the human body  51  travels in the outer peripheral area under the condition indicated in  FIG. 13 .  FIG. 15  illustrates the output signals of the infrared sensors  11  and  12  when the human body  51  travels through both of the outer peripheral area and inside area under the condition indicated in  FIG. 13 .  FIG. 16  illustrates the output signals of the infrared sensors  11  and  12  when the human body  51  travels in the inside area under the condition indicated in  FIG. 13 .  FIG. 17  illustrates the output signal of the infrared sensors  11  and  12  when the human body  51  stands still in the inside area under the condition indicated in  FIG. 13 . 
     The performance of the human body detector in  FIG. 1  will be described as follows. 
     First, the electric device  10  enters into the static mode immediately after completing the initialization upon power-on. In the case in which the human body  51  already stands in the inside area at the time of power-on of the electric device  10 , the sensor controller  13  sets the electric device  10  to the operating mode when the light amount change of the infrared rays which enter from one of the cell sections in the inside area is detected. 
     Next, an example in which the human body  51  does not stand in the inside area at the time of power-on, and the human body  51  enters into the inside area from the outside of the detection target area after the power-on will be described. In order to enter into the inside area, the human body must always pass through the outer peripheral area. Accordingly, when the human body enters into the inside area from the outside of the detection target area, the light amount change of the infrared rays which enter from two adjacent areas of the outer peripheral area is detected, and then the light amount change of the infrared rays which enter from one of the cell sections in the inside area is detected. When the above condition is satisfied, the sensor controller  13  determines the presence of the human body  51  in the inside area, and changes the static mode of the electric device  10  to the operating mode. 
     On the other hand, an example in which the human body travels away toward the outside of the detection target area from the inside area will be described. In this case, the human body always passes through the outer peripheral area. Therefore, when the human body travels away toward the outside of the detection target area from the inside area, the light amount change of the infrared rays which enter from one of the cell sections in the inside area is detected. Then, the light amount change of the infrared rays which enter from the adjacent two cell sections in the outer peripheral area is detected. The human body may move between the inside area and the outer peripheral area in a short period while using the electric device  10 . In this regard, the repetition of mode change between the static mode and the operating mode in the electric device  10  causes lack of user-convenience. Therefore, the sensor controller  13  changes the mode of the electric device  10  from the operating mode to the static mode only in the case in which no light amount change of the infrared rays is detected in all cell sections for the predetermined period after the light amount change of the infrared rays which enter from the cell sections in the outer peripheral area is detected. 
     The following descriptions are made to summarize the above-described behavior. 
       FIG. 18  is a flow chart illustrating the human body-detecting process which is performed by the sensor controller  13  in  FIG. 1 . In Step S 11 , the power source of the electric device  10  is turned on. In Step S 12 , the sensor controller  13  sets the electric device  10  to the static mode. In Step S 13 , the sensor controller  13  determines whether the human body  51  is detected in the inside area or not. When the result is “YES”, the step proceeds to Step S 14 , and when the result is “NO”, the step proceeds to Step S 18 . In Step S 14 , the sensor controller  13  sets the electric device  10  to the operating mode. In Step S 15 , the sensor controller  13  determines whether the human body is detected in the outer peripheral area or not. When the result is “YES”, the step proceeds to Step S 16 , and when the result is “NO”, the step goes back to Step S 14 . In Step S 16 , the sensor controller  13  determines whether the human body is not detected for the predetermined period or not. When the result is “YES”, the step proceeds to Step S 17 , and when the result is “NO”, the step proceeds to Step S 18 . In Step S 17 , the sensor controller  13  sets the electric device  10  to the static mode. In Step S 18 , the sensor controller  13  determines whether the human body is detected in the outer peripheral area or not. When the result is “YES”, the step goes back to Step S 13  and when the result is “NO”, the step goes back to Step S 12 . 
     The above-described human body-detecting method is summarized as follows. The sensor controller  13  determines that the human body continues to exist in the detection target area until the human body enters in the outer peripheral area again after moving toward the inside area from the outer peripheral area. The sensor controller  13  determines that the absence of the human body in the detection target area only in the case in which the light amount change of the infrared rays cannot be detected in all of the cell sections for a certain period after the human body passes toward the outer peripheral area from the inside area and moves away from the outer peripheral area. 
     The algorithm of the human body-detecting method shown in  FIG. 13  is installed in the sensor controller  13 . 
     The algorithm of the human body-detecting method shown in  FIG. 13  may be modified as long as the movement between the inside area and the outer peripheral area can be detected. 
     According to the above-described human body-detecting method, the presence of the human body in the detection target area can be reliably detected. 
       FIG. 19  is a block chart illustrating the configuration of the electric device  10  including the human body detector according to the modified example of the first embodiment of the present invention. The human body detector in  FIG. 1  specifies the cell sections arranged along the portion adjacent to the electric device  10  in the outer periphery of the detection target area as they are not in the outer peripheral area but in the inside area, under the assumption that human body does not pass through such a portion. Therefore, the human body detector in  FIG. 1  can keep the larger inside area. However, if the possibility in which the human body passes through the cell sections in such a portion can be considered, the cell sections where the human body may pass through can be detected as the cell sections in the outer peripheral area. The human body detector in  FIG. 19  has a configuration in which an outer peripheral area and inside area are different from each other compared with the human body detector in  FIG. 1 . Referring to  FIG. 19 , the cell sections in the outer peripheral area are provided in all directions in relation to the inside area. The cell sections of the outer peripheral area are not limited to those in the examples shown in  FIG. 1  and  FIG. 19 , but they may be arranged along the portion in the outer periphery of the detection target area where the human body can pass through. 
     In addition, the example in  FIG. 1  includes the infrared sensor array in each of infrared sensors  11  and  12  arranged horizontally to the ground surface so that the detection target area can be expanded horizontally to the ground surface. The infrared sensors  11  and  12  can be arranged in any places and directions as long as the viewing fields of the infrared sensors  11  and  12  include the common area. For example, the infrared sensors  11  and  12  can be provided in the vertical direction to the ground surface. 
     In addition, the example in  FIG. 1  includes each infrared sensor  11  and  12  including four infrared ray-sensing elements S 1  to S 4 , but it may include another number of infrared ray-sensing elements. 
     The inside area is configured by a plurality of cell sections so that the coordinate can be assigned to each cell section. Therefore, the sensor controller  13  can determine the still standing position of the human body standing in the inside area, and determine the traveling direction of the human body in the inside area. By using such information, the sensor controller  13  may control the electric device  10  more accurately. For example, an example in which an illumination device is provided as the electric device  10  is described. In such a case, when the motion of the human body coming close to the illumination device in the inside area is detected, the human body detector can control the illumination to be brightened gradually. In reverse, when the motion of the human body moving away from the illumination device in the inside area is detected, the human body detector can control the illumination to be dimmed gradually. 
     Second Embodiment 
       FIG. 20  is a block chart illustrating a configuration of an electric device  10 A including the human body detector according to a second embodiment of the present invention. The electric device  10 A includes a human body detector having an infrared sensor  11 A and a sensor controller  13 A, and a power supply controller  14 . The human body detector is not always limited to include the infrared sensors  11  and  12  of two 1D infrared sensor arrays as shown in the figures. For example, it can include an infrared sensor  11 A of a single 2D infrared sensor array. The infrared sensor  11 A is configured to detect the light amount change of the infrared rays which enter from each of a plurality of cell sections which are formed by dividing the detection target area. The cell sections are provided two-dimensionally in the detection target area. The human body detector in  FIG. 20  can perform the human body-detecting process as shown in  FIG. 18  similar to the human body detector in  FIG. 1 . 
     Third Embodiment 
       FIG. 21  provides an example of an image-forming apparatus  500 . 
     The image-forming apparatus  500  is, for example, a tandem type color printer which prints multi-color images by superimposing and transferring black, yellow, magenta, and cyan color toner images onto sheets of paper. The image-forming apparatus  500  as shown in  FIG. 21  comprises an optical scan apparatus  100 , four photoconductive drums  30 A to  30 D, a transfer belt  40 , a paper feed tray  60 , a paper feed roller  54 , a first resist roller  56 , a second resist roller  52 , a fuse roller  50 , a paper discharge roller  58 , a not-shown controller collectively controlling the respective components, and a housing  501  in a rectangular solid shape accommodating the components. 
     A paper discharge tray  501   a  on which printed sheets are discharged is formed on the top surface of the housing  501 . The optical scan apparatus  100  is disposed under the paper discharge tray  501   a.    
     The optical scan apparatus  100  scans the photoconductive drum  30 A with a light beam for black image components modulated by image information supplied from a higher-level device (such as personal computer). Similarly, it scans the photoconductive drum  30 B with a light beam for cyan image components, the photoconductive drum  30 C with a light beam for magenta image components, and the photoconductive drum  30 D with a light beam for yellow image components. 
     The four photoconductive drums  30 A to  30 D are cylindrical members and have photoconductive layers on their surfaces which become electrically conductive when illuminated with a light beam. They are disposed with an equal interval in an X-axis direction under the optical scan apparatus  100  in  FIG. 21 . 
     The photoconductive drum  30 A is disposed at an end portion of a reverse X-axis direction (left side in  FIG. 21 ) inside the housing  501  so that its longitudinal direction is to be the Y-axis direction. The photoconductive drum  30 A is rotated by a not-shown rotation mechanism clockwise (as indicated by black arrows in  FIG. 21 ). An electric charger  302 A at the 12 o&#39;clock position (upper side), a toner cartridge  33 A at 2 o&#39;clock position and a cleaning case  301 A at the 10 o&#39;clock position are disposed around the photoconductive drum  30 A. 
     The electric charger  302 A is disposed with a predetermined clearance over the surface of the photoconductive drum  30 A with its longitudinal direction as the Y-axis direction. It electrically charges the surface of the photoconductive drum  30 A with a predetermined voltage. 
     The toner cartridge  33 A includes a cartridge body containing a toner of black image components and a developing roller charged with a voltage of reverse polarity of that of the photoconductive drum  30 A, and the like. The toner cartridge  33 A supplies the toner in the cartridge body to the surface of the photoconductive drum  30 A via the developing roller. 
     The cleaning case  301 A is provided with a cleaning blade of a rectangular shape with its longitudinal direction as the Y-axis direction, and it is disposed so that one end of the cleaning blade comes in contact with the surface of the photoconductive drum  30 A. The toner adhering on the surface of the photoconductive drum  30 A is removed by the cleaning blade along with the rotation of the photoconductive drum  30 A and collected in the cleaning case  301 A. 
     The photoconductive drums  30 B,  30 C,  30 D with the same structure as that of the photoconductive drum  30 A are placed in sequence on the right side of the photoconductive drum  30 A with a predetermined interval. They are rotated by a not-shown rotation mechanism clockwise (as indicated by the black arrows in  FIG. 21 ). Similarly to the photoconductive drum  30 A, electric chargers  302 B,  302 C,  302 D, toner cartridges  33 B,  33 C,  33 D, and cleaning cases  301 B,  301 C,  301 D are disposed around the photoconductive drums  30 B,  30 C,  30 D, respectively. 
     The electric chargers  302 B,  302 C,  302 D with the same structure as that of the electric charger  302 A are disposed to electrically charge the surfaces of the photoconductive drums  30 B,  30 C,  30 D with a predetermined voltage, respectively. 
     The toner cartridges  33 B,  33 C,  33 D include cartridge bodies containing toners of cyan, magenta, yellow image components and developing rollers charged with a voltage of reverse polarity of that of the photoconductive drums  30 B,  30 C,  30 D, and the like, respectively. The toner cartridges  33 B,  33 C,  33 D supply the toners in the cartridge bodies to the surfaces of the photoconductive drums  30 B,  30 C,  30 D via the developing rollers, respectively. 
     The structure and function of the cleaning cases  301 B,  301 C,  301 D are the same as those of the cleaning case  301 A. 
     Hereinafter, a unit of the photoconductive drum  30 A, the electric charger  302 A, the toner cartridge  33 A, and the cleaning case  301 A is to be referred to as the first image-forming station; likewise, a unit of the photoconductive drum  30 B, the electric charger  302 B, the toner cartridge  33 B, and the cleaning case  301 B as the second image-forming station, a unit of the photoconductive drum  30 C, the electric charger  302 C, the toner cartridge  33 C, and the cleaning case  301 C as the third image-forming station, and a unit of the photoconductive drum  30 D, the electric charger  302 D, the toner cartridge  33 D, and the cleaning case  301 D as the fourth image-forming station. 
     The transfer belt  40  is a free end ring-like member and rolls over driven rollers  40   a ,  40   c  placed under the photoconductive drums  30 A,  30 D, respectively, and rolls over a drive roller  40   b  which is placed at a slightly lower position than the driven rollers  40   a ,  40   c . The upper end surface of the transfer belt  40  is in contact with the lower end surfaces of the photoconductive drums  30 A,  30 B,  30 C,  30 D. The transfer belt  40  is rotated counterclockwise (as indicated by the black arrows in  FIG. 21 ) by counterclockwise rotation of the drive roller  40   b . A transfer charger (transfer unit)  48  is applied with a voltage of a reverse polarity of that of the electric chargers  302 A,  302 B,  302 C,  302 D and is placed close to one end of the transfer belt  40  in the X-axis direction (right side in  FIG. 21 ). 
     The paper feed tray  60  of a substantially rectangular solid shape is placed under the transfer belt  40  and contains stacked-up paper sheets  61  for printing. The paper feed tray  60  has a feeder outlet of a rectangular shape close to one end of the upper surface thereof in the X-axis direction (right side in  FIG. 21 ). 
     The paper feed roller  54  extracts paper sheets  61  one by one from the paper feed tray  60  to feed them to a gap formed between the transfer belt  40  and the transfer charger  48  via the first resist roller  56  composed of a pair of rotary rollers. 
     The fuse roller  50  is composed of a pair of rotary rollers, and applies heat and pressure to the paper sheets  61  to feed the paper sheets  61  to the discharge roller  58  via the resist roller  52  composed of a pair of rotary rollers. The discharge roller  58  is composed of a pair of rotary milers and discharges the paper sheets  61  to the discharge tray  501   a.    
     The image-forming apparatus  500  includes the human body detector according to the embodiments of the present invention. 
     The human body detector, human body-detecting method, electric device, and image-forming apparatus according to the embodiments of the present invention include configurations as follows. 
     According to a human body detector of the first aspect of the present invention, in the human body detector comprising an infrared sensor which detects a light amount change of infrared rays which enter from a detection target area, and a controller which determines the presence or absence of a human body in the detection target area according to the light amount change of the infrared rays, 
     the infrared sensor is configured to detect the light amount change of the infrared rays which enter from a plurality of cell sections which are formed by dividing the detection target area, and arranged two-dimensionally in the detection target area, and 
     the controller is configured to identify an outer peripheral area including cell sections provided along a portion in the outer periphery of the detection target area through which the human body can pass, and an inside area including cell sections other than those in the outer peripheral area, determine the presence of the human body in the detection target area when the light amount change of the infrared rays which enter from the cell sections in the inside area is detected, and determine the absence of the human body in the detection target area when the light amount change of the infrared rays is not detected for a predetermined period in all of the cell sections after the light amount change of the infrared rays which enter from the cell sections in the outer peripheral area is detected. 
     According to the human detector of the second aspect of the present invention, in the human body detector according to the first aspect, 
     the infrared sensor includes a first infrared sensor array including a plurality of first infrared ray-sensing elements having for each first viewing fields which are adjacent to and different from each other and a second infrared sensor array including a plurality of second infrared ray-sensing elements having for each second viewing fields which are adjacent to and different from each other, 
     each first viewing field intersects with each second viewing field one another, and 
     each cell section is a section in which one of the first viewing fields intersects with one of the second viewing fields. 
     According to the human body detector of the third aspect of the present invention, in the human body detector according to the second aspect, 
     the first infrared sensor array is configured so that the first viewing fields are formed by dividing the detection target area in a radial fashion, and 
     the second infrared sensor array is configured so that the second viewing fields are formed by dividing the detection target area in a radial fashion. 
     According to the human body detector of the fourth aspect of the present invention, in the human body detector according to the second or third aspect, 
     the first and second infrared sensor arrays are provided horizontally or vertically to a ground surface. 
     According to the human body detector of the fifth aspect of the present invention, in the human body detector according to any one of the first to fourth aspects, 
     the controller determines that the light amount of the infrared rays which enter from the cell sections in the outer peripheral area changes when the light amount change of the infrared rays is detected in a plurality of cell sections which are adjacent to each other in the cell sections in the outer peripheral area. 
     According to an electric device of the sixth aspect of the present invention, in the electric device including the human body detector according to any one of the first to fifth aspect, 
     the electric device has an operating mode and a static mode; 
     the controller sets the electric device to the operating mode when the controller determines the presence of the human body in the detection target area, and sets the electric device to the static mode when it determines the absence of the human body in the detection target area. 
     According to the electric device of the seventh aspect of the present invention, in the electric device including the human body detector according to the third aspect, 
     the electric device includes a chassis; 
     the first and second infrared sensor arrays are provided in the chassis with a predetermined distance therebetween; 
     the controller identifies the cell sections included in the first viewing field which is the most distant from the second infrared sensor array in a plurality of first viewing fields and the cell sections included in the second viewing field which is the most distant from the first infrared sensor array as the cell sections in the outer peripheral area, and identifies the cell sections other than those in outer peripheral area as the cell sections in the inside area, 
     the electric device has the operating mode and the static mode, and 
     the controller sets the electric device to the operating mode when it determines the presence of the human body in the detection target area, and sets the electric device to the static mode when it determines the absence of the human body in the detection target area. 
     An image-forming apparatus according to the eighth aspect of the present invention includes the human body detector according to the first aspect. 
     According to a human body-detecting method of the ninth aspect of the present invention, in the human body-detecting method which determines the presence or absence of a human body in a detection target area according to a light amount change of infrared rays which enter into an infrared sensor from the detection target area, the infrared sensor being configured to detect light amount change of the infrared rays which enter from a plurality of cell sections which is formed by dividing the detection target area, and arranged two-dimensionally in the detection target area, 
     the human body-detecting method comprises: 
     a step of identifying an outer peripheral area including cell sections which are provided along a portion in an outer peripheral of the detection target area through which the human body can pass, and an inside area including cell sections other than those in the outer peripheral area; 
     a step of determining the presence of the human body in the detection target area when the light amount change of the infrared rays which enter from the cell sections in the inside area is detected; and 
     a step of determining the absence of the human body in the detection target area when the light amount change of the infrared rays is not detected for a predetermined period in all cell sections after the light amount change of the infrared rays which enter from the cell sections in the outer peripheral area is detected. 
     The human body detector according to the embodiments of the present invention can be applied to an appropriate electric device in which the operating mode and the static mode can be switched in response to the presence of a human body. The electric devices include a printer complex machine and an illumination device. The human body detector according to the embodiments of the present invention can be also applied to an image-forming apparatus according to the third embodiment. 
     In accordance with the human body detector according to the present invention, the presence of the human body in the predetermined area can be reliably detected by using the infrared sensor. 
     Although the embodiments of the present invention have been described above, the present invention is not limited thereto. It should be appreciated that variations may be made in the embodiments described by persons skilled in the art without departing from the scope of the present invention.