Abstract:
A component manipulating method includes recognizing, computing, and manipulating. The recognizing is a process in which a position and an attitude of a measured object is recognized by taking an image of a light spot group of the measured object with a camera, the measured object having the light spot group including a plurality of light spots, based on a light image expressing light spots constituting the light spot group on an image taken with the camera. The computing is a process in which a position and an attitude of the component are computed based on the position and the attitude of the recognized measured object and also on geometric arrangement positions of the measured object and the component. The manipulating is a process in which a robot being used to perform operations on the component is manipulated based on the computed position and the attitude.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Applications No. 2009-074360 and No. 2009-074343 filed on Mar. 25, 2009. 
     BACKGROUND 
     Technical Field 
     The present invention relates to a component manipulating method, a component extracting method, a component assembling method, a component manipulating apparatus, a component extracting apparatus, and a component assembling apparatus. 
     SUMMARY 
     According to an aspect of the invention, there is provided a component manipulating method including: 
     recognizing a position and an attitude of a measured object by taking an image of a light spot group of the measured object with a camera, the measured object and a component of a manipulating target being supported in predetermined positions of a component support, the measured object having the light spot group including plural light spots, serving as a measurement target of a position and an attitude, based on a light image expressing light spots constituting the light spot group on an image taken with the camera; 
     computing a position and an attitude of the component based on the position and the attitude of the measured object recognized in the recognizing as well as geometric arrangement positions of the measured object supported by the component support and the component; and 
     manipulating a robot to perform operations on the component based on the position and the attitude computed in the computing, the robot being used to perform operations on the component. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is an explanatory view of a conventional component extracting method; 
         FIG. 2  illustrates an alignment tray that is stopped while placed on a lifting and lowering mechanism; 
         FIG. 3  is an explanatory view illustrating a measuring method employed in the following exemplary embodiments; 
         FIGS. 4 and 5  are explanatory views illustrating a component extracting method according to a first exemplary embodiment of the invention; 
         FIGS. 6 through 9  illustrate processes of a component extracting method according to a second exemplary embodiment of the invention; 
         FIG. 10  is a view explaining the process in which the uppermost alignment tray in the stacked alignment trays is detached and stacked in another site by a robot; 
         FIGS. 11A and 11B  illustrate a LED board fixed to the alignment tray; 
         FIGS. 12A ,  12 B,  12 C, and  12 D illustrate positions in which the LED board or LEDs are fixed to the alignment tray; 
         FIG. 13  is an explanatory view of a conventional component assembling method; 
         FIG. 14  is an explanatory view illustrating a measuring method; 
         FIGS. 15A ,  15 B, and  15 C are explanatory views illustrating a component assembling method according to a third exemplary embodiment; 
         FIG. 16  is an explanatory view illustrating the component assembling method of the fourth exemplary embodiment; 
         FIG. 17  is an explanatory view illustrating a component assembling method according to a fifth exemplary embodiment; 
         FIG. 18  is an explanatory view illustrating the component assembling method of a sixth exemplary embodiment; 
         FIG. 19  illustrates a position in which the LED board is fixed; 
         FIG. 20  is a schematic diagram illustrating a configuration of a main part in the image forming apparatus; 
         FIG. 21  is a perspective view illustrating a robot used to assemble a photoreceptor assembly; 
         FIG. 22  is a perspective view illustrating an assembly pallet and a frame made of a resin supported by the assembly pallet; 
         FIG. 23  is a perspective view illustrating an alignment tray and cleaning members arranged on the alignment tray; 
         FIG. 24  is a perspective view illustrating a state in which the robot comes close to the alignment tray before the cleaning member is extracted; 
         FIG. 25  is a perspective view illustrating a state in which the robot extracts one of the cleaning members on the alignment tray; 
         FIG. 26  is a perspective view illustrating a state in which the robot sucking the cleaning member comes close to the assembly pallet; 
         FIG. 27  is a perspective view illustrating a state in which the cleaning member has been assembled in the frame; 
         FIGS. 28 and 29  are perspective views illustrating the photoreceptor assembly after the assembly when the photoreceptor assembly is viewed from different angles; 
         FIG. 30  illustrates the frame; 
         FIG. 31  illustrates a state in which the cleaning member has been assembled in the frame; 
         FIG. 32  illustrates a state in which the photoreceptor assembly has been assembled; 
         FIG. 33  illustrates a state in which a photoreceptor assembly retaining member is further assembled; 
         FIG. 34  is a partially enlarged perspective view illustrating the state of  FIG. 33 . 
         FIG. 35  illustrates a state in which the support plate has been further assembled; 
         FIG. 36  is a partially enlarged perspective view illustrating a state immediately before the support plate is assembled; 
         FIG. 37  illustrates a state in which a rear cover has been further assembled; 
         FIG. 38  is a partially enlarged perspective view illustrating the state of  FIG. 37 ; 
         FIG. 39  illustrates a state in which a front cover has been further assembled; 
         FIG. 40  is a partially enlarged perspective view illustrating a state immediately before the front cover is assembled; and 
         FIG. 41  illustrates a state in which a charging device has been further assembled. 
     
    
    
     DETAILED DESCRIPTION 
     A conventional component extracting method will be described as a comparative example, and then various exemplary embodiments of the invention will be described. 
       FIGS. 1A and 1B  are an explanatory view of a conventional component extracting method. 
       FIG. 1A  is a side view illustrating a conveying mechanism that conveys an alignment tray  162 A on which components  113 A are put, and  FIG. 1B  is a plan view of the conveying mechanism. The alignment tray corresponds to an example of the component support of the invention. 
     The alignment tray  162 A on which components  113 A are put is placed on a conveying stage  164 A is conveyed in a direction of an arrow A, the alignment tray  162 A located at a leading end in the A-direction is placed on a lifting and lowering mechanism  165 A, and the alignment tray  162 A is stopped by abutting on an abutment  166 A. After the alignment tray  162 A is stopped, a robot  13  manipulates the component  113 A. More particularly, the robot  13  extracts the component  113 A from the alignment tray  162 A. 
     At this point, when the alignment tray  162 A is stopped by abutting on the abutment  166 A, sometimes the alignment tray  162 A is inclined by an abutment impact of the alignment tray  162 A on the abutment  166 A. 
       FIG. 2  illustrates the alignment tray  162 A that is stopped while placed on the lifting and lowering mechanism  165 A. 
     Broken lines of  FIG. 2  indicate a regular position and a regular attitude of the alignment tray  162 A. 
     Frequently the alignment tray  162 A is placed on the conveying stage  164 A in a cursory attitude, and sometimes the alignment tray  162 A is inclined when abutting on the abutment  166 A of the lifting and lowering mechanism  165 A. In this way, sometimes the alignment tray  162 A is stopped with a displacement or an inclination as illustrated in  FIG. 2 . 
     The robot  13  is programmed to grasp and extract the component  113 A from the alignment tray  162 A on the assumption that the alignment tray  162 A abuts on the abutment  166 A to be stopped in the correct attitude at the regular position. Accordingly, when the alignment tray  162 A is stopped with the displacement or inclination, the robot  13  cannot grasp the component  113 A and extract the component  113 A from the alignment tray  162 A. 
     As described above, in the conventional component extracting method, there is a problem that the robot  13  may not be able to grasp and extract the component  113 A from the alignment tray  162 A when the alignment tray  162 A is inclined. 
     Various exemplary embodiments of the invention will be described based on the comparative example. 
       FIG. 3  is an explanatory view illustrating a measuring method employed in the following exemplary embodiments. 
     An LED board  1120  and a camera  130  are illustrated in  FIG. 3 . Plural LEDs  1121  and  1122  are disposed on the LED board  1120 . 
     In the following exemplary embodiments, measuring accuracy is enhanced by employing the measuring method in which LEDs  1121  disposed on a surface of the LED board  1120  and another LED  1122  located slightly above the surface of the LED board  1120  are used. 
     The measuring method based on the image taken with the camera  130  is basically as follows. The position and attitude of the camera  130  are previously known, LEDs  1121  on the LED board  1120  are taken with the camera  130 , and the directions of LEDs  1121  are obtained when the positions of the images of LEDs  1121  are viewed from the camera  130 . The directions of LEDs  1121  viewed from the camera  130  are obtained because a relative positional relationship among LEDs  1121  is previously known. Therefore, the plane defined by LEDs  1121 , that is, the position and attitude of the LED board  1120  are obtained from the pieces of information. Alternatively, dimensions of the images of LEDs  1121  may be used using the camera  130  on which an imaging lens having a large spherical aberration is mounted. When the imaging lens having the large spherical aberration is used, the images of LEDs  1121  become indistinct images having substantially elliptical shapes, and the dimensions of the image depend on a distance from the camera  130  to each LED  1121 . With this phenomenon, the distance from the camera  130  to each LED  1121  is obtained based on dimensions of the image of LED  1121 . Similarly the directions of LEDs  1121  viewed from the camera  130  are obtained from the position of the image taken with the camera  130 . 
     The two conventional measuring methods may be used at the same time. 
     When the directions and distances of three LEDs  1121  on the LED board  1120  are obtained, the three-dimensional positions of LEDs  1121  are obtained, and the plane defined by three LEDs  1121  is obtained, that is, the position and attitude of the LED board  1120  on which three LEDs  1121  are disposed are obtained. 
     In  FIG. 3 , four LEDs  1121  are provided on the surface of the LED board  1120 . The fourth LED  1121  is used to improve the accuracy when the position and attitude of the LED board  1120  is measured. Alternatively, the position of the fourth LED  1121  is changed for each LED board  1120 , and the fourth LED  1121  may be used as ID in order to specify the ID board. 
     When the LED board  1120  is fixed to the predetermined position of the alignment tray  162 A of  FIGS. 1A and 1B , the position and attitude of the LED board  1121  are obtained, and the position and attitude of the component  113 A on the alignment tray  162 A are also obtained. When the position and attitude of the component  113 A supported by the alignment tray  162 A are obtained, the robot  13  can correctly grasp the component  113 A whose position and attitude are obtained. 
     In the above-described measuring methods, although the directions of LEDs  1121  viewed from the camera  130  are measured with significantly high accuracy, the accuracy of distance between the camera  130  and each LED  1121  is lower than the accuracy of direction. 
     Therefore, another LED  1122  may be added to improve resolution of the distance, as described below. 
     As described above, the additional LED  1122  is disposed while perpendicularly spaced apart from the reference plane (at this point, the reference plane is overlapped with the surface of the LED board  1120 ). 
     In  FIG. 3 , the camera  130  is disposed in a posture, in which the camera  130  is orientated toward the reference plane from a position where an imaging optical axis is not matched with a perpendicular P passing through LED  1122  to the surface (the triangular reference plane formed by three LEDs  1121 ) of the LED board  1120 . When the images of LEDs  1121  and  1122  are taken with the camera  130  while the camera  130  is disposed at the position where the imaging optical axis is not matched with the perpendicular P, a difference in relative position on the imaging screen between LEDs  1121  on the surface of the LED board  1120  and one LED  1122  located slightly above the surface of the LED board  1120  is varied according to the imaging direction. 
     The measuring method in which the difference in relative position on the imaging screen between LEDs  1121  and LED  1122  is utilized may be employed in addition to any one of or both of the above-described conventional measuring methods. Thereby, the position and attitude of the reference plane, that is, the position and attitude of the LED board  1120  in  FIG. 3  can be measured with accuracy higher than that of the conventional measuring method. 
       FIGS. 4A and 4B  are views similar to that of  FIGS. 1A and 1B .  FIGS. 4 and 5  are explanatory view illustrating a component extracting method according to a first exemplary embodiment of the invention. 
       FIG. 4A  is a side view illustrating a conveying mechanism that conveys an alignment tray  162  on which components  113  are put, and  FIG. 4B  is a plan view of the conveying mechanism. 
     Referring to  FIGS. 4A and 4B , the conveying mechanism includes an alignment tray loading plate  161  on which the alignment tray  162  is loaded, and the LED board  1120  (see  FIG. 3 ) is mounted on the alignment tray loading plate  161 . An example in which the LED board  1120  is directly mounted on the alignment tray will be described later. 
     In the example of  FIGS. 4A and 4B , the alignment tray  162  on which the components  113  are put is placed on the conveying stage  164  while loaded on the alignment tray loading plate  161 , the alignment tray  162  is conveyed in the direction of the arrow A, and the alignment tray  162  located at a leading end in the A-direction is placed on a lifting and lowering mechanism  165 , and the alignment tray  162  is stopped by abutting on an abutment  166 . 
     As with the conventional component extracting method of  FIGS. 1A and 1B , frequently the alignment tray loading plate  161  is placed on the conveying stage  164  in a cursory attitude, and sometimes the alignment tray  162  is inclined when abutting on the abutment  166  of the lifting and lowering mechanism  165 . Therefore, sometimes the alignment tray  162  is stopped with the displacement or inclination as illustrated in  FIG. 5 . 
     The component assembling method of the first exemplary embodiment will be described with reference to  FIGS. 4A and 4B . 
     The alignment tray loading plate  161  is conveyed in the direction of the arrow A by the conveying stage  164  while loading many components  113  thereon, and the alignment tray loading plate  161  is stopped by abutting on the abutment  166  of the lifting and lowering mechanism  165 . The LED board  1120  of  FIG. 3  is provided in a predetermined position of the alignment tray loading plate  161 . In the first exemplary embodiment, the LED board  1120  corresponds to an example of the measured object of the invention. 
     A robot  120  is installed above the position where alignment tray loading plate  161  is stopped. The robot  120  includes a robot arm  121  and a robot hand  122  used to extract the component  113 . The camera  130  is fixed to the robot hand  122 . 
     The camera  130  is used in the measurement, and a control unit  140  controls an operation of the camera  130 . The control unit  140  also controls the position and attitude of the robot  120 . The control unit  140  acts as both the image-taking control unit and component extraction control unit of the invention, and the control unit  140  also corresponds to the control unit of the invention. The control unit  140  includes a computer and a control program executed by the computer. 
     When the camera  130  takes the images of LEDs  1121  and  1122 , a position and attitude recognizing unit  150  can accurately specify the position and attitude of the reference plane, that is, the position and attitude of the alignment tray loading plate  161  on which the LED board  1120  is fixed to the top surface of the alignment tray loading plate  161  in  FIG. 3  based on the images of LEDs  1121  and  1122 . 
     When the position and attitude of the alignment tray loading plate  161  are accurately specified, a position and attitude computing unit  151  computes the position and attitude of the component  113  based on the position and attitude of the alignment tray loading plate  161 , the robot hand  122  faces the component  113  of the alignment tray loading plate  161  under the control of the control unit  140  as illustrated in  FIGS. 4A and 4B , and the component  113  is accurately grasped and extracted. 
     In the first exemplary embodiment, the camera  130  and the robot  120  are integral with each other. Alternatively, the camera  130  and the robot  120  may be spaced apart from each other. When the camera  130  and the robot  120  are spaced apart from each other, although the moving mechanisms for the robot  120  and camera  130  are separately required, it is not necessary that the robot  120  perform a useless operation for the imaging, and it is not necessary that the camera  130  perform a useless operation for extracting the component  113 . Therefore, a lifetime extension of the moving mechanism may be expected because the useless motion is reduced. 
     As to a method of supplying electric power to light LEDs  1121  and  1122 , a battery is mounted on the LED board  1120 , and the battery may supply the electric power to LEDs  1121  and  1122 . Alternatively, a coil or an antenna is mounted on the LED board  1120 , and the electric power may be supplied from the outside by electromagnetic induction or radio wave to light LEDs  1121  and  1122 . In such cases, it is not necessary to mount the expendable battery on the LED board  1120 , thereby improving maintenance reliability. 
     A retroreflector may be used instead of LEDs  1121  and  1122  of the first exemplary embodiment. The retroreflector has a characteristic in which light incident to the retroreflector is reflected in the incident direction. The retroreflectors are disposed instead of LEDs  1121  and  1122 , the retroreflectors are illuminated with light from the side of the camera  130 , and the light reflected from the retroreflector is received by the camera  130 . The measurement equal to that of LEDs  1121  and  1122  can be performed, and no electric power is required for the retroreflector, thereby improving the maintenance reliability. 
     In the case of the retroreflector, it is not necessary to supply the electric power to the side of assembly plate  110 , or it is not necessary to place an electric power supply on the side of assembly plate  110 . Therefore, the retroreflector is suitable to an explosion-proof environment. 
     In  FIGS. 4A and 4B , the camera  130  takes the image from immediately above the LED board  1120 . As described above, the measurement accuracy is enhanced in the case of use of the operation method in which the camera  130  is moved obliquely upward with respect to the LED board  1120  to use displacement between LEDs  1121  and LED  1122  on the LED board  1120 . 
     Thus, the component extracting method and component extracting apparatus, in which the robot can securely grasp and extract the component supported in the predetermined position on the alignment tray, can be realized in the first exemplary embodiment. 
       FIGS. 6 to 9  illustrate processes of a component extracting method according to a second exemplary embodiment of the invention. 
     In  FIGS. 6 to 9 , the same constituent as the first embodiment of  FIGS. 4A and 4B  is designated by the same numeral, and the description is omitted. The component extracting method of the second exemplary embodiment differs from that of the first exemplary embodiment in that the LED board  1120  in  FIG. 3  is placed on the alignment tray  111 . 
     In the component extracting method of the second exemplary embodiment, when the robot  120  is located in an initial position as illustrated in  FIG. 6 , the camera  130  takes the image of the LED board  1120  on the alignment tray  11  located in the uppermost stage in the stacked alignment trays  111 . 
     When the robot  120  is located in the initial position, the camera  130  is located immediately above the LED board  1120 . A worker roughly stacks alignment trays  111 , and the camera  130  is located immediately above the LED board  1120  when the alignment tray  111  is placed in a standard position. Therefore, sometimes the LED board  1120  is deviated from immediately below the camera  130  depending on the position in which the alignment tray  111  is actually placed. However, it is assumed that the LED board  1120  sufficiently enters a view angle of the camera  130  when the robot  120  is located in the initial position. 
     As illustrated in  FIG. 6 , when the robot  120  is located in the initial position, the camera  130  performs a first-stage measurement of position and attitude. 
     In the LED board  1120 , one LED  1122  is located slightly above other LEDs  1121  (see  FIG. 3 ). In the case of the first-stage measurement, the camera  130  is located immediately above the LED board  1120 , and the measuring method has relatively low distance resolution. Therefore, even if one LED  1122  is located slightly above other LEDs  1121 , because LED  1122  does not contribute too much to the improvement of the accuracy for specifying the position and attitude of the LED board  1120 , the position and attitude are specified with relatively low accuracy in the first-stage measurement. In the second exemplary embodiment, the position and attitude of the LED board  1120  are obtained with accuracy higher than that of the first-stage measurement. 
     Therefore, based on the position and attitude of the LED board  1120  obtained by the first-stage measurement, the robot  120  is moved to a position in which the measurement can accurately be performed in principle (see  FIG. 7 ). The position in which the measurement can accurately be performed is a position in which an imaging optical axis is not matched with a perpendicular to the LED board  1120  from the camera  130 , and the position in which the measurement can accurately be performed is a position in which LED  1122  located slightly above other LEDs  1121  in  FIG. 3  is largely displaced on the image taken with the camera  130 . 
     In the second exemplary embodiment, not only the position of the camera  130  is moved, but also the attitude of the camera  130  is changed such that the LED board  1120  is placed on an imaging optical axis of the camera  130 . 
     A second-stage measurement is performed after the camera  130  is moved to the position in which the measurement can accurately be performed (see  FIG. 8 ). 
     In the second-stage measurement, because LED  1122  in  FIG. 3  is located slightly above the plane (surface of the LED board  1120 ) formed by other LEDs  1121 , LED  1122  is displaced on the image taken with the camera  130 , thereby obtaining the position and attitude of the LED board  1120  with high accuracy. 
     The position and attitude of the LED board  1120  are accurately specified by the second-stage measurement, the position and attitude of the alignment tray  111  on which the LED board  1120  is placed in the predetermined position are also accurately specified, and the position and attitude of each of the plural components  11  put in the predetermined positions on the alignment tray  111  are also accurately specified. 
     As illustrated in  FIG. 9 , the robot hand  122  is placed in the position and attitude while facing the component  113  to be extracted from the alignment tray  111 , and the robot hand  122  grasps the component  113  to extract the component  113  from the alignment tray  111 . Because the position and attitude of the component  113  to be extracted are accurately specified, a risk of failing to grasp the component  113  by the robot hand  122  or a risk of failing to grasp the component  113  by the robot hand  122  to extract the component  113  from the alignment tray  111  may be largely reduced. 
     All the components  113  in the uppermost alignment tray  111  are extracted, and the uppermost alignment tray  111  becomes empty. Then the uppermost alignment tray  111  is detached from the stacked alignment trays  111 , and the similar work is performed to the new uppermost alignment tray  111 . 
     In the second exemplary embodiment, the uppermost empty alignment tray  111  may manually be detached, or the robot  120  may detach the uppermost empty alignment tray  111 . The configuration in which the alignment tray  111  is detached with the robot  120  will be described later with reference to parts (a) to (f) of  FIG. 10 . 
     In the second exemplary embodiment illustrated in  FIGS. 6 and 9 , as illustrated in  FIGS. 7 and 8 , the camera  130  is moved to take an oblique attitude so as to be orientated toward the LED board  1120  in the second-stage measurement. Alternatively, the camera  130  is orientated toward the same direction as the perpendicular P, and the images of LEDs  1121  and  1122  on the LED board  1120  may be taken with the camera  130  in the position displaced from the center of the image. In such cases, because an aberration of the imaging lens of the camera  130  is caused by the displacement of the LEDs  1121  and  1122  from the center of the image, preferably, the aberration of the imaging lens may be taken into account. 
     In the second exemplary embodiment, when the position and attitude of the LED board  1120  are specified, the measurement is divided into the first-stage measurement and the second-stage measurement to perform the accurate measurement. When the placement position and attitude of the alignment tray  111  are predicted to be not largely varied, the first-stage measurement may be omitted, and the second-stage measurement may directly be performed to specify the directions and distances of LEDs  1121  and  1122  on the assumption that the LED board  1120  is in the standard position and attitude. 
     A process in which the uppermost alignment tray  111  in the stacked alignment trays  111  is detached and stacked in another site by the robot  120  will be described. 
     Parts (a) to (f) of  FIG. 10  are views explaining the process in which the uppermost alignment tray  111  in the stacked alignment trays  111  is detached and stacked in another site by the robot  120 . 
     Parts (a) to (f) of  FIG. 10  sequentially illustrate the process. 
     Part (a) of  FIG. 10  illustrates a state in which the robot  120  extracts all the components  113  from the uppermost alignment tray  111  in the component extracting process after the recognizing process of  FIGS. 6 to 9 . 
     In part (a) of  FIG. 10 , the control unit  140  includes a counter, the control unit  140  uses the counter to count the number of components every time the robot  120  extracts the component  113  from the alignment tray  111  (see  FIGS. 6 and 9 ), and the control unit  140  determines whether the value counted with the counter reaches the number of components on the alignment tray  111 . When determining that the alignment tray  111  becomes empty, the control unit  140  moves the robot  120  and the camera  130  onto the LED board  112 , and the control unit  140  recognizes the position and attitude of the LED board  1120  again to confirm the position in which the alignment tray  111  is grasped (see part (b) of  FIG. 10 ). At this point, unlike the conventional measuring method (two-dimensional recognition), the attitude of the alignment tray can three-dimensionally be recognized based on the image expressing the fourth LED on the LED board  1120 . As illustrated in part (c) of  FIG. 10 , the robot  120  grasps a projection located in the center of the alignment tray  111 , and the robot  120  detached the empty alignment tray  111 . As illustrated in part (d) of  FIG. 10 , the robot  120  moves the grasping alignment tray  111  to another site. The robot  120  moves the empty alignment tray  111 , and the camera  130  reaches the neighborhood of the position in which the empty alignment trays  111  are stacked. At this point, the control unit  140  causes the camera  130  to take the image of the LED board  1120  to confirm the site where the empty alignment trays  111  are stacked, and the moved alignment tray  111  is stacked on the uppermost alignment tray  111  in the stacked empty alignment trays  111 . Then the control unit  140  returns the robot  120  to the state of part (a) of  FIG. 10 , and the robot  120  starts to extract the component  113  on the next alignment tray  111 . 
     In parts (a) to (f) of  FIG. 10 , the control unit  140  uses the counter to count the number of components every time the robot  120  extracts the component  113 , and the control unit  140  determines whether the alignment tray becomes empty. Alternatively, LED is provided in each position in which the component  113  is supported by the alignment tray  111 , the light emitted from LED is obstructed by the existence of the component  113  while the component is supported by the alignment tray  111 , the light emission appears by the extraction of the component  113 , and the control unit  140  may count the number of LEDs in which the light emission appears, thereby determining whether the alignment tray  111  becomes empty. 
       FIGS. 11A and 11B  illustrate the LED board  1120  fixed to the alignment tray  111 , and  FIGS. 12A ,  12 B,  12 C, and  12 D illustrate positions in which the LED board  1120  or LEDs  1121  and  1122  are fixed to the alignment tray  111 . 
     In the second exemplary embodiment, it is necessary that geometric arrangement positions of the LED board  1120  and the component  113  previously positioned in the alignment tray  111  are clear. 
       FIG. 11A  illustrates a state, in which fixing portions called snap-fit joint SN are provided in the alignment tray  111  and the LED board  1120  is fixed to the alignment tray  111  by the snap-fit joints SN.  FIG. 11B  illustrates the alignment tray  111  having a configuration in which screws are inserted in screwing holes SCH to fix the LED board  1120  to the alignment tray  111 . Both the configurations of  FIGS. 11A and 11B  may be employed, and any configuration may be employed as long as the LED board  1120  is fixed to the alignment tray  111  such that the geometric arrangement positions of the component  113  and LEDs  1121  and  1122  on the LED board  1120  are unambiguously determined. 
     The LED board  1120  may be located in an end portion of the alignment tray  111  as illustrated in  FIG. 12A , and The LED board  1120  may be located in the center of the alignment tray  111  as illustrated in  FIG. 12B . As illustrated in  FIG. 12C , two LED boards  1120  may be provided at diagonal positions of the alignment tray  111 . The measurement accuracy is enhanced when the two LED boards  1120  are provided at diagonal positions. As illustrated in  FIG. 12D , LEDs  1121  and  1122  may be provided in the center and four corners of the alignment tray  111 . 
     A component assembling method will be described below. 
     First, a conventional component assembling method will be described as a comparative example. Then, a novel measuring method applied to a component assembling method of the invention will be described, and various exemplary embodiments of the invention will be described. 
     Parts (a) to (f) of  FIG. 13  are explanatory views of a conventional component assembling method. 
     Part (a) of  FIG. 13  illustrates a state in which an assembly pallet  210  is stopped at an assembly point by colliding with an abutment  215  when conveyed to the assembly point. 
     Part (b) of  FIG. 13  illustrates a state in which the assembly pallet  210  is positioned by the positioning pin  214  to assemble the second component  213  in order to prevent the movement of the assembly pallet  210  after the state of Part (a) of  FIG. 13   
     Part (c) of  FIG. 13  illustrates a state in which, instead of positioning the assembly pallet  210  by the positioning pin  214 , a lifting and lowering mechanism  216  is used to lift and position the assembly pallet  210  immediately after the assembly pallet  210  is stopped. 
     Part (d) of  FIG. 13  illustrates manipulation of a first component  211 . More particularly, part (d) of  FIG. 13  illustrates a state in which a second component  213  is assembled in the first component  211  after the state of part (c) of  FIG. 13 . Although not illustrated, the robot is placed in the assembly point, and the second component  213  is automatically assembled in the first component  211  on the assembly pallet by the robot after the assembly pallet is stopped. In the following description, it is assumed that the robot is placed in the assembly point to assemble the second component  213  in the first component  211 . 
     A conventional component assembling method will be described with reference to parts (a) to (d) of  FIG. 13 . 
     The first component  211  is put on the assembly pallet  210 . The assembly pallet  210  is conveyed in a direction of an arrow D by a conveying stage  212  while the first component  211  is put thereon, and the assembly pallet  210  is stopped in the position of part (a) of  FIG. 13  by abutting on an abutment  215  (includes a pin in the example of parts (a) to (d) of  FIG. 13 ). Because the assembly pallet  210  is possibly inclined by the abutment impact at the time the assembly pallet  210  is stopped, a mechanism  214  of part (b) of  FIG. 13  or a mechanism  216  of part (c) of  FIG. 13  is provided to position the assembly pallet  210  immediately after the assembly pallet  210  is stopped. The positioning pin is slid in the mechanism  214 . The assembly pallet  210  is lifted and lowered in the mechanism  216 . 
     The robot assembles the second component  213  in the first component  211  put on the accurately positioned assembly pallet  210 . 
     As described above, in the conventional component assembling method, it is necessary to provide the positioning mechanism and the like, which causes a problem in that the facilities are enlarged. 
     Various exemplary embodiments of the invention will be described based on the conventional component assembling method. 
       FIG. 14  is an explanatory view illustrating a novel measuring method used in the following exemplary embodiments. 
     An LED board  2120  and a camera  230  are illustrated in  FIG. 14 . 
     Plural LEDs  2121  and a LED  2122  are disposed on the LED board  2120 . LEDs  2121  disposed on the surface of the LED board  2120  and LED  2122  disposed slightly above the surface of the LED board  2120  are fixed to the LED board  2120 . 
     In the following exemplary embodiments, the novel measuring method is used to measure the position and attitude of the LED board  2120 , thereby enhancing the measurement accuracy. 
     The conventional measuring method based on the image taken with the camera  230  is basically as follows. At this point, it is assumed that LEDs  2121  disposed in the surface of the LED board  2120  are measured. 
     The position and attitude of the camera  230  are previously known, the images of LEDs  2121  on the LED board  2120  are taken with the camera  230 , and the directions of LEDs  2121  are obtained when the positions of the images of LEDs  2121  are viewed from the camera  230 . The directions of LEDs  2121  viewed from the camera  230  are obtained because a relative positional relationship among LEDs  2121  is previously known. The plane defined by LEDs  2121 , that is, the position and attitude of the LED board  2120  are obtained from the pieces of information. Alternatively, dimensions of the images of LEDs  2121  may be utilized by using the camera  230  on which an imaging lens having a large spherical aberration is mounted. When the camera  230  on which the imaging lens having the large spherical aberration is mounted is used, the images of LEDs  2121  become indistinct images having substantially elliptical shapes, and the dimensions of the image depend on a distance from the camera  230  to each LED  2121 . With this phenomenon, the distance from the camera  230  to each LED  2121  is obtained based on dimensions of the image of LED  2121 . 
     When the directions and distances of three LEDs  2121  on the LED board  212  are obtained, the three-dimensional positions of three LEDs  2121  are obtained, and the position and attitude of the reference plane defined by three LEDs  2121  are obtained, that is, the position and attitude of the LED board  2120  on which the three LEDs  2121  are disposed are obtained. The two conventional measuring methods may be used at the same time. In  FIG. 14 , four LEDs  2121  are disposed on the surface of the LED board  2120 . The fourth LED  2121  is used to improve the accuracy when in measuring the position and attitude of the LED board  2120 . Alternatively, the position of the fourth LED  2121  may be changed for each LED board  2120 , and the fourth LED  2121  may act as ID for specifying the LED board. 
     When the LED board  2120  is fixed to a predetermined position of the assembly pallet  210  of  FIGS. 13A ,  13 B,  13 C, and  13 D, the position and attitude of the LED board  2121  are obtained, and the position and attitude of the first component  211  on the assembly pallet  210  are obtained. When the position and attitude of the first component  211  supported by the assembly pallet  210  are obtained, the first component  211  can correctly be assembled in the second component  211  on the assembly pallet  210  even if the assembly pallet  210  is inclined. 
     In the above-described conventional measuring methods, although the direction of each LED  2121  viewed from the camera  230  is measured with significantly high accuracy, the accuracy of distance between the camera  230  and each LED  2121  is lower than the accuracy of direction. 
     Therefore, another LED  2122  is added to improve the resolution of the distance. 
     As described above, the additional LED  2122  is disposed while perpendicularly spaced apart from the reference plane (overlapped with the surface of the LED board  2120 ). 
     In  FIG. 14 , the camera  230  is disposed in a posture, in which the camera  230  is orientated toward the reference plane from a position where the optical axis of the imaging lens is not matched with a perpendicular P passing through LED  2122  to the surface (the triangular reference plane formed by three LEDs  2121 ) of the LED board  2120 . When the images of LEDs  2121  and  2122  are taken with the camera  230  while the camera  230  is disposed in the position where the imaging optical axis is not matched with the perpendicular P, a difference in relative position on the imaging screen between LEDs  2121  in the surface of the LED board  2120  and one LED  2122  located slightly above the surface of the LED board  2120  is varied according to the imaging direction. 
     Thus, the novel measuring method may be employed in addition to the conventional measuring methods. In the novel measuring method, by utilizing the difference in relative position on the imaging screen between LEDs  2121  and LED  2122 , the position and attitude of the reference plane, that is, the position and attitude of the LED board  2120  of  FIG. 14  can be measured with accuracy higher than that of the conventional measuring method, that is, the measurement of the directions and distances of LEDs  2121  disposed in a planar manner in the surface of the LED board  2120 . 
       FIGS. 15A ,  15 B, and  15 C are explanatory views illustrating a component assembling method according to a third exemplary embodiment of the invention. 
       FIGS. 15A ,  15 B, and  15 C illustrate an example in which the novel measuring method of  FIG. 14  is employed as similar to parts (a) to (d) of  FIG. 13 . Although described in detail later, the use of the novel measuring method can eliminate the positioning mechanisms  214  and  216  that are necessary in parts (a) to (d) of  FIG. 13 . 
     The component assembling method of the third exemplary embodiment will be described with reference to  FIGS. 15A ,  15 B, and  15 C. 
       FIG. 15A  illustrates a state in which the assembly pallet  210  is stopped at the assembly point by the abutment  215  (including a lifting and lowering pin) after the assembly pallet  210  is conveyed to the assembly point.  FIGS. 15B and 15C  illustrate states in which the assembly pallet  210  is inclined by the impact at the time the assembly pallet  210  is stopped after the state of  FIG. 15A . 
     The first component  211  is placed on the assembly pallet  210 . The assembly pallet  210  is conveyed in the direction of the arrow D by the conveying stage  212  while the first component  211  is put thereon, and the assembly pallet  210  is stopped in the position of  FIG. 15A  by abutting on the abutment  215 . The LED board  2120  of  FIG. 14  is provided in a predetermined position of the assembly pallet  210 . In the third exemplary embodiment, the LED board  2120  corresponds to an example of the measured object of the invention. 
     The robot  220  is disposed above the assembly pallet  210  stopped at the assembly point. The robot  220  includes the robot arm  221  and a robot hand  222  used to assemble the component  213 . The camera  230  is fixed above the LED board  2120  of the assembly pallet  210 . 
     A control unit  240  controls the operation of the camera  230 . The control unit  240  controls the position and attitude of the robot  220 . The control unit  240  acts as both the image-taking control unit and component extraction control unit of the invention. For example, the control unit  240  includes a computer and a control program executed by the computer. 
     When the camera  230  takes the image of the LED board  2120 , a position and attitude recognizing unit  250  can accurately specify the position and attitude of the reference plane, that is, the position and attitude of the assembly pallet  210  in which the LED board  2120  is fixed to the top surface of the assembly pallet  210  in  FIGS. 15A ,  15 B, and  15 C based on the image of the LED board  2120 . As with the control unit  240 , the position and attitude recognizing unit  250  includes a computer and a position and attitude recognizing program executed by the computer. The computer may be shared by the position and attitude recognizing unit  250  and the control unit  222 . A position and attitude computing unit  251  also includes a computer and a position and attitude computing program executed by the computer. The computer may be shared by the position and attitude computing unit  251 , the control unit  240 , and the position and attitude recognizing unit  250 . 
     Even if the assembly pallet  210  is inclined as illustrated in  FIGS. 15B and 15C , the position and attitude of the assembly pallet  210  are accurately specified, the position and attitude computing unit  251  computes the position and attitude of the first component  211  based on the position and attitude of the assembly pallet  210 . Therefore, under the instruction of the control unit  240 , the robot hand  222  is disposed while facing the first component  211  of the assembly pallet  210  as illustrated in  FIG. 15C , and the second component  213  is correctly assembled in the first component  211 . 
     In the third exemplary embodiment, it is assumed that the camera  230  is fixed. Alternatively, the camera  230  may be moved to take the image of the LED board  2120  from an optimal position. When the camera  230  is movable, the camera  230  may rigidly be integral with the robot  220 . In such cases, the position and attitude is integrally changed, and the moving mechanism dedicated to the camera  230  can be eliminated. 
     As to a method of supplying electric power to light LEDs  2121  and  2122 , a battery is mounted on the LED board  2120 , and the battery supplies electric power to LEDs  2121  and  2122 . Alternatively, a coil or an antenna is mounted on the LED board  2120 , and the electric power may be supplied from the outside by electromagnetic induction or radio wave to light LEDs  2121  and  2122 . In such cases, it is not necessary to mount the expendable battery on the LED board  2120 , thereby improving the maintenance reliability. 
     The retroreflector may be used instead of LEDs  2121  and  2122  of the third exemplary embodiment. The retroreflector has the characteristic in which the light incident to the retroreflector is reflected in the incident direction. The retroreflectors are disposed instead of LEDs  2121  and  2122  on the LED board  2120 , the retroreflectors are illuminated with light from the side of the camera  230 , and the light reflected from the retroreflector is received by the camera  230 . The measurement equal to that of LEDs  2121  and  2122  can be performed, and no electric power is required for the retroreflector, thereby improving the maintenance reliability. 
     In the case of the retroreflector, it is not necessary to supply the electric power to the side of assembly pallet  210 , or it is not necessary to place an electric power supply on the side of assembly pallet  210 . Therefore, the retroreflector is suitable to the explosion-proof environment. 
     A component assembling method according to a fourth exemplary embodiment of the invention will be described below. 
       FIG. 16  is an explanatory view illustrating the component assembling method of the fourth exemplary embodiment of the invention. In  FIGS. 16 to 18 , the position and attitude recognizing unit  250 , position and attitude computing unit  251 , and control unit  240  illustrated in  FIGS. 15A ,  15 B, and  15 C are omitted and referred to as needed. 
     The component assembling method of the fourth exemplary embodiment illustrated in  FIG. 16  is similar to the component assembling method of the third exemplary embodiment illustrated in  FIGS. 15A ,  15 B, and  15 C. 
     The LED board  2120  and a first component  272  are put in predetermined positions on an assembly pallet  271 . The LED board  2120  is identical to that of  FIG. 14 . The assembly pallet  271  is conveyed in the direction of the arrow D by a conveying stage  279  while the LED board  2120  and the first component  272  are put thereon, and the assembly pallet  271  is stopped in the position of  FIG. 16  by abutting on an abutment  215  (not illustrated). 
     The camera  230  is fixed in the position and attitude so as to obliquely take the image of LED board  2120  on the stopped assembly pallet  271 . When the position and attitude of the LED board  2120  are obtained, the position and attitude of the first component  272  put in the predetermined position on the same assembly pallet  271  are also obtained. 
     On the other hand, the robot hand  222  grasps a second component  273 . The second component  273  is one that is assembled in the first component  272  on the assembly pallet  271 . The robot  220  changes the position and attitude thereof based on the pieces of information on the position and attitude of the first component  272  obtained from the image taken with the camera  230 . The robot  220  disposes the second component  273  such that the second component  273  faces the first component  272  on the assembly pallet  271 , and the robot  220  assembles the second component  273  in the first component  272 . 
     In the fourth exemplary embodiment, it is assumed that the camera  230  is fixed. Alternatively, a moving mechanism may be provided to change the position and attitude of the camera  230 . 
       FIG. 17  is an explanatory view illustrating a component assembling method according to a fifth exemplary embodiment of the invention. A difference with the fourth exemplary embodiment of  FIG. 16  will be described. 
     In the component assembling method of the fifth exemplary embodiment of  FIG. 17 , the LED board  2120  is obliquely fixed in a predetermined position of the assembly pallet  271 , and the camera  230  is fixed so as to take the image of the obliquely fixed LED board  2120  from immediately above. 
     Therefore, the camera  230  can be fixed immediately above the LED board  2120  while the position and attitude of the LED board  2120  are accurately obtained by obliquely taking the image of the LED board  2120  with respect to the perpendicular, thereby reducing a facility installation space. 
       FIG. 18  is an explanatory view illustrating the component assembling method of the sixth exemplary embodiment of the invention. A difference from the fourth exemplary embodiment of  FIG. 16  will be described. 
     The camera  230  is rigidly fixed in the fourth exemplary embodiment of  FIG. 16 . On the other hand, in the sixth exemplary embodiment of  FIG. 18 , the camera  230  is fixed to the robot hand  222 , and the camera  230  is moved along with the robot hand  222 . 
     As illustrated in  FIG. 18 , when the camera  230  is fixed to the robot  220 , interference between the robot  220  and the camera  230  can securely be avoided during the assembly, and a degree of freedom is improved in moving the robot  220  during the assembly. 
     The position in which the LED board  2120  is fixed to the assembly pallet  210  will be described. 
     Parts (a) to (c) of  FIG. 19  illustrate a position in which the LED board  2120  is fixed. 
     Part (a) of  FIG. 19  illustrates a position in which the LED board  2120  used in the sixth exemplary embodiment is fixed. When the LED board  2120  is fixed to the position of part (a) of  FIG. 19 , even if the assembly pallet  210  is rotated as illustrated in the right of part (a) of  FIG. 19 , the position and attitude of the assembly pallet  210  are accurately recognized after the rotation, thereby assembling the second component  213  in the first component  211 . 
     Although the accuracy is sufficiently ensured only by fixing the LED board  2120  in the position of part (a) of  FIG. 19 , two LED boards  2120  may be provided in diagonal positions as illustrated in part (b) of  FIG. 19  in order to further enhance the accuracy. As illustrated in part (c) of  FIG. 19 , four LEDs  2121  may respectively be provided in four corners of the assembly pallet while LED  2122  is provided in the center of the assembly pallet. In the configuration of part (c) of  FIG. 19 , the assembly pallet  210  can be miniaturized compared with the configurations of parts (a) and (b) of  FIG. 19 . 
     Finally a component assembling method according to a seventh exemplary embodiment of the invention will be described below. First an outline of an image forming apparatus predicated on the component assembling method of the seventh exemplary embodiment will be described. 
       FIG. 20  is a schematic diagram illustrating a configuration of a main part in the image forming apparatus. 
     Referring to  FIG. 20 , an image forming apparatus  2100  includes four image forming portions  2110 Y,  2110 M,  2110 C, and  2110 K. The image forming portions  2110 Y,  2110 M,  2110 C, and  2110 K include photoreceptors  2111 Y,  2111 M,  2111 C, and  2111 K, charging devices  2113 Y,  2113 M,  2113 C, and  2113 K, exposure devices  2114 Y,  2114 M,  2114 C, and  2114 K, development rollers  2112 Y,  2112 M,  2112 C, and  2112 K, primary transfer rollers  2120 Y,  2120 M,  2120 C, and  2120 K, and cleaning members  2115 Y,  2115 M,  2115 C, and  2115 K, respectively. The photoreceptors  2111 Y,  2111 M,  2111 C, and  2111 K are rotated in the direction of the arrow A. 
     In the image forming apparatus  2100 , full-color printing can be performed, and suffixes Y, M, C, K of the components designate components for forming yellow, magenta, cyan, and black images. 
     The image forming apparatus  2100  also includes an intermediate transfer belt  2130 , a secondary transfer roller  2140 , a tension roller  2131 , and an image information processing unit  2150 . The intermediate transfer belt  2130  is circulated in the direction of the arrow B. The image information processing unit  2150  transmits image information to each of the image forming portions  2110 Y,  2110 M,  2110 C, and  2110 K. 
     The image information processing unit  2150  separates the image information fed from the outside into yellow, magenta, cyan, and black pieces of image information, and the image information processing unit  2150  transmits the yellow, magenta, cyan, and black pieces of image information to the exposure devices  2114 Y,  2114 M,  2114 C, and  2114 K, respectively. 
     A basic image forming operation performed by the image forming apparatus  2100  will be described below. 
     In the image forming apparatus  2100 , the yellow image forming portion  2110 Y starts toner image formation, and the charging device  2113 Y imparts predetermined charges to a surface of the photoreceptor  2111 Y rotated in the direction of the arrow A. Then, in response to the image information transmitted from the image information processing unit  2150 , the exposure device  2114 Y irradiates the surface of the photoreceptor  2111 Y with exposure light corresponding to the yellow image to form an electrostatic latent image. The development roller  2112 Y develops the electrostatic latent image using yellow toner, thereby forming a yellow toner image on the photoreceptor  2111 Y. The toner image is transferred to the intermediate transfer belt  2130  by the action of the primary transfer roller  2120 Y. 
     At this point, a developer containing toner and magnetic carriers is used in the image forming apparatus  2100 . In the developer, the magnetic carrier is coated with an external additive in order to secure a toner charging characteristic. The electrostatic latent image formed on the photoreceptor according to the image information is developed by the toner contained in the developer. After a developer cartridge filled with the developer is loaded in the image forming apparatus  2100 , only the toner is refilled, and the toner and the magnetic carrier are mixed, whereby the toner is negatively charged while the external additive of the magnetic carrier is positively charged. 
     In the intermediate transfer belt  2130 , the magenta image forming portion  2110 M performs the toner image formation such that the magenta toner image that is of the next color reaches the primary transfer roller  2120 M in synchronization with the time the yellow toner image transferred onto the intermediate transfer belt  2130  reaches the primary transfer roller  2120 M of the next color image forming portion  2110 M. The magenta toner image is transferred to the intermediate transfer belt  2130  by the action of the primary transfer roller  2120 M while superimposed on the yellow toner image of the intermediate transfer belt  2130 . 
     Then, the cyan and black image forming portions  2110 C and  2110 K perform the toner image formation in the similar timing, and the toner images are sequentially transferred to the intermediate transfer belt  2130  by the action of the primary transfer rollers  2120 C and  2120  while superimposed on the yellow and magenta toner images of the intermediate transfer belt  2130 . 
     The secondary transfer roller  2140  finally secondary-transfers the multicolor toner image transferred onto the intermediate transfer belt  2130  to a sheet  2150 , and the multicolor toner image is conveyed in the direction of the arrow C along with the sheet  2150 . Then a fixing device (not illustrated) fixes the multicolor toner image to the sheet  2150  to form the color image. 
     After the toner images are transferred to the intermediate transfer belt  2130 , the cleaning members  2115 Y,  2115 M,  2115 C, and  2115 K scrape out the toner remaining on the photoreceptors  2111 Y,  2111 M,  2111 C, and  2111 K from the surfaces of the photoreceptors  2111 Y,  2111 M,  2111 C, and  2111 K. The waste toner scraped out by the cleaning member is conveyed in a direction perpendicular to the paper plane of  FIG. 20  by a mechanism (not illustrated), and the waste toner is discharged to a waste toner receiving tank (not illustrated). 
     When the yellow image forming portion  2110 Y is cited as an example, the photoreceptor  2111 Y, the charging device  2113 Y, and the cleaning member  2115 Y are assembled into one photoreceptor assembly by the component assembling method of the invention, and disposed in the image forming apparatus  2100 . The same holds true for other image forming portions. 
     The component assembling method of the seventh exemplary embodiment will be described by taking the photoreceptor assembly for example. 
       FIG. 21  is a perspective view illustrating a robot used to assemble the photoreceptor assembly. 
     A robot arm  2201  and a robot hand  2202 , which constitute a robot  2200 , are illustrated in  FIG. 21 . The robot hand  2202  includes suction pads  2203  that suck (an example of “grasp” of the invention) and lift the component by evacuation. A measuring camera  2290  is fixed to the robot hand  2202 . The position and attitude are freely changed in the robot hand  2202 . 
       FIG. 22  is a perspective view illustrating an assembly pallet  2300  and a frame  2410  supported by the assembly pallet  2300 . The frame  2410  is a resin component. The frame  2410  is a frame of the photoreceptor assembly, and the frame  2410  is one of the components constituting the photoreceptor assembly. 
     Four retaining pieces  2301  are fixed onto the assembly pallet  2300 , and an LED board  2310  is fixed to the assembly pallet  2300  by the retaining pieces  2301 . Three measuring LEDs  2311 , LED  2312 , and LED  2313  are provided on the LED board  2310 . LED  2312  is used as ID for distinguishing the LED board  2310  from other LED boards. LED  2313  is fixed slightly above the LED board  2310 . Three LEDs  2311  and one LED  2313  are used to measure the position and attitude of the LED board  2310 . The arrangement position of one LED  2312  depends on the LED board  2310 , and the arrangement position is specified to distinguish the LED board  2310  from other LED boards. Because the method of obtaining the position and attitude of the LED board  2310  using LEDs  2311  and  2313  on the LED board  2310  is similar to that of  FIG. 14 , the detailed description is omitted. 
     Referring to  FIG. 22 , two retaining pieces  2302  and two positioning pins  2303  are provided in the assembly pallet  230 . The two retaining pieces  2302  are used to retain the frame  2410 , and the two positioning pins  2303  are used to position the frame  2410  on the assembly pallet  2300 . Two positioning holes  2411  are made in the frame  2410 , and the positioning pins  2303  are inserted in the positioning holes  2411  while the frame  2410  is mounted on the retaining piece  2302 , thereby previously disposing the frame  2410  in a predetermined position of the assembly pallet  2300 . 
     The LED board  2310  and the frame  2410  are disposed in the predetermined positions on the assembly pallet  2300 , and the position and attitude of the frame  2410  are unambiguously obtained by obtaining the position and attitude of the LED board  2300 . 
       FIG. 23  is a perspective view illustrating an alignment tray and cleaning members arranged on the alignment tray. 
     Ten cleaning members  2420  are arranged in an alignment tray  2330  of  FIG. 23 . The cleaning members  2420  correspond to the cleaning members  2115 Y,  2115 M,  2115 C, and  2115 K of  FIG. 20 , respectively. The cleaning member  2420  of  FIG. 23  is a composite component including a rubber component  2421  and a sheet-metal component  2422 . The rubber component  2421  is in direct contact with the photoreceptor. The rubber component  2421  is supported by the sheet-metal component  2422 . 
     The alignment tray  2330  includes ten storage grooves  2331 , and each of the cleaning members  2420  is stored in each of the storage grooves  2331 . Therefore, the cleaning member  2420  is maintained in predetermined position and attitude on the alignment tray  2330 . 
     A recess  2332  is provided in the alignment tray  2330 , and the LED board  2340  is fitted in the recess  2332 . The LED board  2340  is fitted in the recess  2332  to fix the LED board  2340  in predetermined position and attitude. 
     The LED board  2340  includes three LEDs  2341  and one LED  2343 , and the positions of three LEDs  2341  and one LED  2343  are identical to those of LED board  2310  of  FIG. 22 . LED  2342  differs from LED  2312  on the LED board  2310  of  FIG. 22  in the arrangement position. This is because the arrangement position is varied for each LED board to use LED  2342  as ID for specifying the LED board. 
     For the LED board  2340  of  FIG. 23 , the position and attitude of the LED board  2310  are recognized by the measurement of a camera  2290 , and the position and attitude of each of the cleaning members  2420  arranged on the alignment tray  2330  are obtained based on the position and attitude of the LED board  2310 . The robot  2200  of  FIG. 21  extracts one of the cleaning members  2420  arranged on the alignment tray  2330  to assemble the cleaning member  2420  in the frame  2410  of  FIG. 22 . 
     A procedure of assembling the cleaning member  2420  in the frame  2410  will be described below. 
       FIG. 24  is a perspective view illustrating a state in which the robot  2200  comes close to the alignment tray  2330  before the cleaning member  2420  is extracted. 
     Then, the camera  2290  measures the position and attitude of the LED board  2340 , thereby the position and attitude of the cleaning member  2420  are recognized, and the suction pad  2221  of the robot hand  2220  are controlled in the position and attitude so as to face the cleaning member  2420  to be extracted. 
       FIG. 25  is a perspective view illustrating a state in which the robot  2200  extracts one of the cleaning members  2420  on the alignment tray  2330 . 
     The suction pad  2203  of the robot  2200  faces the cleaning member  2420  to be extracted on the alignment tray  2330 , the suction pad  2203  is pressed against the cleaning member  2420  to suck the cleaning member  2420  by evacuation, and the cleaning member  2420  is directly lifted, thereby extracting the cleaning member  2420  from the alignment tray  2330 . 
       FIG. 26  is a perspective view illustrating a state in which the robot sucking the cleaning member comes close to the assembly pallet. 
     When the robot  2200  comes close to the assembly pallet  2330 , the camera  2290  attached to the robot  2200  measures the position and attitude of the LED board  2310 , thereby the position and attitude of the frame  2410  are recognized. Then the robot  2200  is moved such that the cleaning member  2420  sucked by the suction pad  2203  of the robot hand  2202  faces the frame  2410  fixed to the assembly pallet  2300 . 
       FIG. 27  is a perspective view illustrating a state in which the cleaning member  2420  is assembled in the frame  2410 . 
     After the cleaning member  2420  faces the frame  2410 , the cleaning member  2420  is assembled in the frame  2410  as illustrated in  FIG. 27 . Then, the suction of the suction pad  2203  is released, and the robot  2200  is raised to separate the suction pad  2203  from the cleaning member  2420 . 
     After the cleaning member  2420  is assembled in the frame  2410 , various members are sequentially assembled in the assembling manner similar to that of the cleaning member  2420 . 
       FIGS. 28 and 29  are perspective views illustrating the photoreceptor assembly after the assembly when the photoreceptor assembly is viewed from different angles. 
     Referring to  FIGS. 28 and 29 , a photoreceptor assembly  2400  includes the frame member  2410 , a photoreceptor  2430 , a photoreceptor retaining member  2440 , a support plate  2450 , a rear cover  2460 , a front cover  2470 , and a charging device  2480 . The photoreceptor  2430  corresponds to one of the photoreceptors  2111 Y,  2111 M,  2111 C, and  2111 K of  FIG. 20 , and the charging device  2480  corresponds to one of the charging devices  2113 Y,  2113 M,  2113 C, and  2113 K of  FIG. 20 . 
     The cleaning member  2420  (for example, see  FIG. 25 ) initially assembled in the frame  2410  is not illustrated in  FIGS. 28 and 29  because the cleaning member  2420  is covered with the photoreceptor  2430 . 
     The photoreceptor retaining member  2440  and the support plate  2450  support a rear end and a front end of the photoreceptor  2430 , respectively. A rear part and a front part of the photoreceptor assembly  2400  are covered with the rear cover  2460  and the front cover  2470 , respectively. However, an opening  2461  is formed in the rear cover  2450  in order to transmit a torque to the photoreceptor  2430 . A board  2471  is fixed to the front cover  2470 , and a storage unit in which the cumulative number of rotations of the photoreceptor  2430  is recorded is mounted on the board  2471 . 
     A procedure of assembling the components constituting the photoreceptor assembly  2400  will be described below. 
       FIG. 30  illustrates the frame  2410 . 
     Although not illustrated in the above drawings because of unnecessity, a marker is added in the following drawings in order to identify an assembly stage, as described below. Desirably, the images of the markers such as LED and the retroreflector are clearly taken with the camera  2290  (see  FIG. 21 ). 
     A support plate identifying marker  2501 , a cleaning member identifying marker  2502 , a photoreceptor identifying marker  2503 , and a charging device identifying marker  2504  are formed in the frame  2410  of  FIG. 30 . 
       FIG. 31  illustrates a state in which the cleaning member  2420  is assembled in the frame  2410 . 
     Referring to  FIG. 31 , the cleaning member identifying marker  2502  (see  FIG. 30 ) is covered with the cleaning member  2420  by assembling the cleaning member  2420  in the frame  2410 , and the camera  2290  or a worker easily recognizes that the cleaning member  2420  is assembled in the frame  2410 . 
       FIG. 32  illustrates a state in which the photoreceptor  2430  is assembled. 
     The photoreceptor identifying marker  2503  which is seen until then (see  FIG. 31 ) is covered by assembling the photoreceptor  2430 . Therefore, the camera  2290  or the worker easily recognizes that the photoreceptor  2430  is assembled. 
       FIG. 33  illustrates a state in which the photoreceptor retaining member  2440  is further assembled, and  FIG. 34  is a partially enlarged perspective view illustrating the state of  FIG. 33 . 
     A new photoreceptor retaining member identifying marker  2505  is added to the photoreceptor retaining member  2440 , and the camera  2290  or the worker easily recognizes that the photoreceptor retaining member identifying marker  2505  is newly added in addition to the support plate identifying marker  2501  and the exposure device identifying marker  2504 . Therefore, the camera  2290  or the worker recognizes that the photoreceptor retaining member  2440  is assembled. 
       FIG. 35  illustrates a state in which the support plate  2450  is further assembled, and  FIG. 36  is a partially enlarged perspective view illustrating a state immediately before the support plate  2450  is assembled. 
     As illustrated in  FIG. 36 , the support plate  2450  is assembled so as to be inserted in the direction of the arrow E from the front end of the photoreceptor  2430 . Although the support plate identifying marker  2501  is seen before the support plate  2450  is assembled, the support plate identifying marker  2501  is covered by assembling the support plate  2450 . Because the camera  2290  or the worker recognizes that the support plate identifying marker  2501  is covered, the camera  2290  or the worker recognizes that the support plate  2450  is assembled. 
       FIG. 37  illustrates a state in which the rear cover  2460  is further assembled, and  FIG. 38  is a partially enlarged perspective view illustrating the state of  FIG. 37 . 
     A new rear cover identifying marker  2506  is added to the rear cover  2460 , and the camera  2290  or the worker recognizes that the rear cover identifying marker  2506  is added. Therefore, the camera  2290  or the worker easily recognizes that the rear cover  2460  is assembled. 
       FIG. 39  illustrates a state in which the front cover  2470  is further assembled, and  FIG. 40  is a partially enlarged perspective view illustrating a state immediately before the front cover  2470  is assembled. 
     As illustrated in  FIG. 40 , the front cover  2470  is assembled in the support plate  2450  so as to be pressed against the support plate  2450  in the direction of the arrow F from the front side. 
     A new front cover identifying marker  2507  is added to the front cover  2470 . Because the new front cover identifying marker  2507  is added to the front cover  2470 , the camera  2290  or the worker easily recognizes that the front cover  2470  is added. 
       FIG. 41  illustrates a state in which the charging device  2480  is further assembled. 
     When the charging device  2480  is assembled, the charging device identifying marker  2504  is covered with the charging device  2480 . Therefore, the camera  2290  or the worker easily recognizes in one glance that the charging device  2480  is assembled. 
     As described above, according to the assembly stage of each component constituting the photoreceptor assembly, the marker is formed such that a pattern in which the marker appears is changed, so that the camera or the worker easily recognizes the assembly stage at a glance. 
     As used herein, the term of “grasp” shall mean not only that the component is mechanically sandwiched, but also the component is lifted by vacuum suction of the component, magnetic attraction of the component with an electromagnet, and the like. 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The exemplary embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling other skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.