Abstract:
A group of light spots dispersed and disposed three-dimensionally to be disposed not in one plane on an object-to-be-measured are shot by a camera. A position and an attitude of the object-to-be-measured are recognized based on an optical image representing each of the light spots included on a shot image by the camera.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority under U.S.C. 119 from Japanese Patent Application No. 2009-074378, filed on Mar. 25, 2009. 
     SUMMARY 
     According to an aspect of the invention, a position/attitude recognizing method includes: 
     a first shooting process of shooting, by a camera, a group of light spots on an object-to-be-measured on which the group of light spots are arranged, the group of light spots including a plural light spots which are dispersed and disposed three-dimensionally to be disposed not on one plane; and 
     a first recognizing process of recognizing a position and an attitude of the object-to-be-measured based on an optical image representing each of the plural light spots included in the group of light spots on a first shot image obtained by the shooting in the first shooting process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating one example of a part holding method using the conventional measuring method; 
         FIG. 2A  is a schematic diagrams illustrating a problem of the part holding method illustrated in  FIG. 1 ; 
         FIG. 2B  is a schematic diagrams illustrating a problem of the part holding method illustrated in  FIG. 1 ; 
         FIG. 3  is an explanatory diagram of a new measuring method which is employed in the following exemplary embodiments; 
         FIG. 4  illustrates processes of a part holding method as a first exemplary embodiment of the present invention; 
         FIG. 5  illustrates processes of a part holding method as a first exemplary embodiment of the present invention; 
         FIG. 6  illustrates processes of a part holding method as a first exemplary embodiment of the present invention; 
         FIG. 7  illustrates processes of a part holding method as a first exemplary embodiment of the present invention; 
         FIG. 8  is a plan view an arranging tray carrying plate and an arranging tray employed in the part holding method of the second exemplary embodiment of the present invention; 
         FIG. 9A  is a side view illustrating a transfer mechanism of the arranging tray carrying plate on which the arranging tray  62  is placed; 
         FIG. 9B  is a plan view illustrating a transfer mechanism of the arranging tray carrying plate on which the arranging tray is placed; 
         FIG. 10  illustrates the arranging tray carrying plate  61  and the arranging tray in a state where they are placed on the elevating mechanism and stop; 
       The processes illustrated in  FIG. 11  correspond to the processes illustrated in  FIGS. 4  in the first exemplary embodiment illustrated in  FIGS. 4 to 7 ; 
       The processes illustrated in  FIG. 12  correspond to the processes illustrated in  FIGS. 5  in the first exemplary embodiment illustrated in  FIGS. 4 to 7 ; 
       The processes illustrated in  FIG. 13  correspond to the processes illustrated in  FIGS. 6  in the first exemplary embodiment illustrated in  FIGS. 4 to 7 ; 
       The processes illustrated in  FIG. 14  correspond to the processes illustrated in  FIGS. 7  in the first exemplary embodiment illustrated in  FIGS. 4 to 7 ; 
         FIG. 15  illustrates a process of a part holding method of a third exemplary embodiment of the present invention; 
         FIG. 16  illustrates a process of a part holding method of a third exemplary embodiment of the present invention; 
         FIG. 17  illustrates a process of a part holding method of a third exemplary embodiment of the present invention; 
         FIG. 18  illustrates a process of a part holding method of a third exemplary embodiment of the present invention; 
         FIG. 19  is an explanatory diagram of a part arranging method and a part assembling method as a fourth exemplary embodiment of the present invention; 
         FIG. 20  is an explanatory diagram of a part arranging method and a part assembling method of a fifth exemplary embodiment of the present invention; 
         FIG. 21  is an explanatory diagram of a part arranging method and a part assembling method of a sixth exemplary embodiment of the present invention; 
         FIG. 22  is a schematic block diagram of an essential portion of the image forming apparatus; 
         FIG. 23  is a perspective view of a robot used for assembling the photosensitive body assembly; 
         FIG. 24  is a perspective view illustrating an assembling palette and a frame body which is a resin part supported by the assembling palette; 
         FIG. 25  is a perspective view illustrating the arranging tray and the cleaning members arranged on the arranging tray; 
         FIG. 26  is a perspective view illustrating a state where the robot approaches the arranging tray before the cleaning member is taken out; 
         FIG. 27  is a perspective view illustrating a state where one of the cleaning members on the arranging tray is taken out by the robot; 
         FIG. 28  is a perspective view illustrating a state where the robot which sucks the cleaning member approaches the assembling palette; 
         FIG. 29  is a perspective view illustrating a state where the cleaning member is assembled into the frame body; 
         FIG. 30  is a perspective view of the photosensitive body assembly after the assembling operation; 
         FIG. 31  is a perspective view of the photosensitive body assembly after the assembling operation as viewed from different view points from  FIG. 30 ; 
         FIG. 32  illustrates the frame body; 
         FIG. 33  illustrates a state where the cleaning member is assembled into the frame body; 
         FIG. 34  illustrates a state where the photosensitive body is further assembled; 
         FIG. 35  illustrates a state where the photosensitive body holding body is further assembled; 
         FIG. 36  is a partially enlarged perspective view of that state; 
         FIG. 37  illustrates a state where the support plate is assembled; 
         FIG. 38  is a partially enlarged perspective view illustrating a state immediately before the support plate is assembled; 
         FIG. 39  illustrates a state where the rear cover is further assembled; 
         FIG. 40  is a partially enlarged perspective view of the state; 
         FIG. 41  illustrates a state where the front cover is further assembled; 
         FIG. 42  is a partially enlarged perspective view illustrating a state immediately before the front cover is assembled; and 
         FIG. 43  illustrates a state where the charger is further assembled. 
     
    
    
     DETAILED DESCRIPTION 
     A conventional measuring method is explained first as a comparative example and then, various exemplary embodiments of the present invention will be explained. 
       FIG. 1  is a schematic diagram illustrating one example of a part holding method using the conventional measuring method. 
     In  FIG. 1 , arranging trays  11  are stacked in multiple layers. On each arranging tray  11 , an LED board  12  and multiple parts  13  which are to be taken out from the arranging tray  11  are arranged. 
     A robot  20  is placed on an upper portion of the stacked arranging trays  11 . The robot  20  includes a robot arm  21  and a robot hand  22  for taking out the parts  13 . A camera  30  is fixed to the robot hand  22 . A position and an attitude of the robot  20  are controlled by a controller  40 . Since the camera  30  is fixed to the robot hand  22 , movement and an attitude of the camera  30  are controlled in unison with the movement and an attitude of the robot hand  22 . The controller  40  also controls holding the parts  13  by the robot hand  22 , and controls shooting of the camera  30 . The controller  40  includes a computer and a control program which is executed in the computer for example. 
     Multiple LEDs  12   a  are disposed on each of the LED boards  12 . Basically, if three LEDs  12   a  are disposed on the LED board  12  at a distance from one another, images of these three LEDs  12   a  obtained by shooting them are input to a position/attitude recognizing section  50 , a position and an attitude thereof is obtained by calculation in the position/attitude recognizing section  50 . In the position/attitude recognizing section  50 , a position and an attitude of a triangle plane whose apexes are these respective three LEDs  12   a  are obtained, and a position and an attitude of the LED board  12  is recognized. The LED board  12  is fixed to a predetermined position of the arranging tray  11 , and the plural parts  13  on the arranging tray  11  are also disposed at respective predetermined positions. The position/attitude recognizing section  50  recognizes positions and attitudes of the parts  13  on the arranging tray  11  based on the information. Like the controller  40 , the position/attitude recognizing section  50  may also include a computer and a position recognizing program which is executed in the computer. This computer may be the same computer included in the controller  40 . 
     The measuring method based on an image shot by the camera  30  is basically as follows. That is, a position and an attitude of the camera  30  are known, images of the LEDs  12   a  on the LED board  12  are shot by the camera  30  whose position and attitude are known, and directions of the LEDs  12   a  as viewed from the camera  30  are obtained from the positions of the images of the LEDs  12   a  on the shot image are obtained. A relation between relative position of the LEDs  12   a  is known and therefore, if the directions of the LEDs  12   a  as viewed from the camera  30  are obtained, a plane determined by the LEDs  12   a , i.e., the position and the attitude of the LED board  12  are obtained from the information. 
     Alternatively, a size of an image on a shot image of each LED  12   a  may be utilized using a camera  30  having a shooting lens having a large spherical aberration. If a camera  30  having a shooting lens of a large spherical aberration is used, an image on a shot image of each LED  12   a  becomes out of focus as being substantially circularly. Further, a size of the image differs depending upon a distance from the camera  30  to each LED  12   a . Utilizing this fact, the distance from the camera  30  to each LED  12   a  is obtained based on the size of the image of the LED  12   a . A direction of each LED  12   a  as viewed from the camera  30  is obtained from a position of the image on the shot image in the same manner as that described above. The directions and distances of the three LEDs  12   a  on the LED board  12  are obtained in this manner, a three dimensional positions of the three LEDs  12   a  are obtained, and a plane determined by the three LEDs  12   a , i.e., the position and the attitude of the LED board  12  are obtained. Although two examples of the conventional measuring methods have been introduced here, these methods may be combined and used. 
     The LED board  12  is fixed to the predetermined position of the arranging tray  11  as described above. Therefore, if the position and the attitude of the LED board  12  are obtained, a position and an attitude of the arranging tray  11  itself are also obtained, and a position and an attitude of each part  13  on the arranging tray  11  are also obtained. 
     If the position and the attitude of each part  13  are obtained, the robot  20  causes the robot hand  22  to face the part  13  and sequentially takes out the part  13  from the arranging tray  11 . If all of the parts  13  on the arranging tray  11  which is stacked on the uppermost layer are takes out, the vacant arranging tray  11  itself is removed from the uppermost layer of the stack, and a new arranging tray  11  which newly comes top by the removal is subjected to the same processing. 
       FIGS. 2A and 2B  are schematic diagrams illustrating a problem of the part holding method illustrated in  FIG. 1 . 
     In the case of the above-described measuring method, the directions of the LEDs  12   a  as viewed from the camera  30  are measured fairly precisely, but the distance resolution is low, and a distance between the camera  30  and each LED  12   a  may only be measured with low precision. 
     Therefore, there are possibilities that the part  13  may not be held as illustrated in  FIG. 2A  or the robot hand  22  collides against the part  13  or the arranging tray  11  as illustrated in  FIG. 2B . If there occurs a collision, the part  13  may not be held and the part  13  may be damaged. 
     Considering the comparative examples, various exemplary embodiments of the present invention will be explained. 
       FIG. 3  is an explanatory diagram of a new measuring method which is employed in the following exemplary embodiments. 
     Here, an LED board  120  and a camera  30  are illustrated. 
     Four LEDs  121  are disposed at distances from each other on a surface of the LED board  120 , and one LED  122  is disposed at a position slightly rising from the surface of the LED board  120 . Positions of these total five LEDs  121  and  122  are known. 
     Three of the four LEDs  121  disposed on the surface of the LED board  120  are LEDs for determining a position and an attitude of a triangular reference surface (in here, i.e., a triangular surface which is superposed on the surface of the LED board  120 ) whose apexes correspond to the three LEDs  121 . An arranged position of the remaining one LED  121  disposed on the surface of the LED board  120  differs depending upon the individual LED boards  120 . This remaining one LED  121  is an LED which has a function as an ID (Identification) for specifying this particular LED board  120  from other LED boards  120 . Alternatively, all of the four LEDs  121  may be utilized for recognizing the position and the attitude of the LED board  120  to further enhance the recognition precision. 
     The one LED  122  is disposed at a position separated away from the reference surface (superposed on the surface of the LED board  120 ) in a perpendicular direction. 
     In  FIG. 3 , the camera  30  is placed in such an attitude that the camera  30  is facing toward the reference surface from a position where a normal P passing through the LED  122  toward the surface of the LED board  120  (the triangular reference surface formed by the three LEDs  121 ) and an optical axis of the shooting lens do not match with each other. In such manner, if the camera  30  is placed at the position where the normal P and the optical axis do not match with each other and images of the LEDs  121  and  122  are shot by the camera  30  which is placed at the position, a deviation manner of a position on the shot images of the LEDs  121  being on the surface of the LED board  120  and the one LED  122  being at the position slightly rising from that surface differs depending upon the shooting direction. 
     If one or both of the two examples of the above-described conventional measuring methods are employed and a difference of the deviating manner of position on the shot image of the LEDs  121  and  122  is utilized, the position and the attitude of the reference surface, i.e., the position and the attitude of the LED board  12  in the example illustrated in  FIG. 3  may be specified with higher precision than the conventional measuring method. 
       FIGS. 4 to 7  illustrate processes of a part holding method as a first exemplary embodiment of the present invention. 
     The same elements as those of the comparative example illustrated in  FIGS. 1 and 2  are designated with the same symbols, and explanation thereof is omitted. The first exemplary embodiment is different from the comparative example in that in the first exemplary embodiment, the LED board  120  illustrated in  FIG. 3  is placed on the arranging tray  11 . Further, control contents of the robot  20  and the camera  30  by the controller  40  and calculation by the position/attitude recognizing section  50  for recognizing the position and attitude are also different from those of the comparative example illustrated in  FIGS. 1 and 2 . The controller  40  controls and the position/attitude recognizing section  50  recognizes the position and attitude as are described below. 
     In the case of the part holding method as the first exemplary embodiment, as illustrated in  FIG. 4 , an image of the LED board  120  on the uppermost arranging tray  11  among the stacked arranging trays  11  is shot by the camera  30  when the robot  20  is in the initial position. 
     When the robot  20  is in the initial position, the camera  30  is located directly above the LED board  120 . However, the stacked arranging trays  11  are roughly placed on a stage by an operator, the camera  30  is located directly above the arranging tray  11  which is placed at a standard position, and the LED board  120  may be deviated from a location directly below the camera  30  in some cases depending upon a position where the arranging tray  11  is actually placed. The LED board  120  sufficiently falls within a shooting angle of view of the camera  30  when the robot  20  is in the initial position. 
     Here, first, a first position and an attitude measurement are performed by the camera  30  when the robot  20  is in the initial position as illustrated in  FIG. 4 . 
     According to the LED board  120  employed here, the one LED  122  is located at a position slightly rising from the other LEDs  121  as illustrated in  FIG. 3 , but in the case of the first measurement, since the camera  30  is located substantially directly above the LED board  120  and the distance resolution is low, even if the one LED  122  is located at the slightly higher position, the precision for specifying the position and attitude of the LED board  120  is not enhanced so much and thus, in this first measurement, the position and attitude are specified with low precision. 
     Next, based on the position and attitude of the LED board  120  obtained by the first measurement, the robot  20  is moved to a position where the measurement may be carried out with the highest precision in principle (see  FIG. 3 ). The position where the measurement may be carried out with high precision is a position where a shooting optical axis of the camera  30  and a normal passing through the slightly rising LED  122  illustrated in  FIG. 3  toward the LED board  120  do not match with each other, and is a position where a deviation of the shooting position of the slightly rising LED  122  illustrated in  FIG. 3  on the shot image by the camera  30  is large. 
     In the first exemplary embodiment, not only the position of the camera  30  is moved, but also the attitude of the camera  30  is changed so that the LED board  120  is placed on the shooting optical axis of the camera  30 . 
     After the camera  30  is moved to a position where measurement with high precision may be carried out, the second shooting is carried out (see  FIG. 6 ). 
     In this second measurement, in addition to the conventional measuring method, due to the fact that the LED  122  illustrated in  FIG. 3  is placed on the position rising from the plane (surface of the LED board  120 ) formed by the other LEDs  121 , a measurement based on the fact that the position on the shot image is deviated is carried out, thereby obtaining the position and attitude of the LED board  120  precisely. 
     By the second measurement, the position and attitude of the LED board  120  are specified precisely, the position and attitude of the arranging tray  11  where the LED board  120  are placed at the predetermined position are also specified precisely, and positions and attitudes of the plural parts  13  placed on predetermined positions on the arranging tray  11  are also specified precisely. 
     Next, as illustrated in  FIG. 7 , the robot hand  22  is placed at a position and an attitude right opposed to a part  13  to be taken out from the arranging tray  11 , the part  13  is held by the robot hand  22  and taken out from the arranging tray  11 . Since the position and attitude of the part  13  to be taken out are precisely specified, failure of the holding of the part  13  by the robot hand  22  and the taking out operation of the grasped part  13  from the arranging tray  11  may largely be reduced. 
     All of the parts  13  in the uppermost arranging tray  11  are taken out and the upper most arranging tray  11  becomes empty, the uppermost arranging tray  11  itself is detached from the uppermost layer, and the same operation is carried out for the next arranging tray  11  which newly comes top. 
     The uppermost empty arranging tray  11  may be detached manually or by the robot  20 . 
     Here, in the case of the first exemplary embodiment illustrated in  FIGS. 4 to 7 , the camera  30  is moved in the diagonal attitude oriented to the LED board  120  during the second shooting operation as illustrated in  FIGS. 5 and 6 , but the camera  30  may be oriented in the same direction as that of the normal P so that an images of the LEDs  121  and  122  on the LED board  120  are taken at a position deviated from the center of the shooting screen of the camera  30 . In this case, aberration of the shooting lens of the camera  30  generated when the LEDs  121  and  122  are deviated from the center of the shooting screen may be taken into consideration. 
     In this first exemplary embodiment, when the position and attitude of the LED board  120  are specified, measurement with high precision is carried out in the first shooting operation and the second shooting operation separately, but when it may be expected that a position where the arranging tray  11  is placed and an attitude of the arranging tray  11  when it is placed are not largely varied, the first shooting operation may be omitted, the second shooting operation may be carried out on the assumption that the LED board  120  is in a standard position and attitude, and the directions and the distances of the LEDs  121  and  122  may be measured. 
     In the first exemplary embodiment, the position and attitude of the camera  30  and the robot  20  may be integrally changed. In this case, one moving mechanism suffices, but the robot  20  and the camera  30  may separately move. In this case, moving mechanisms for the robot  20  and for the camera  30  are separately required, but it is unnecessary to cause the robot  20  to perform a wasteful operation for shooting an image, it is unnecessary to cause the camera  30  to perform a wasteful operation for taking out the part  13 , waste operations are reduced and thus lifetime of the moving mechanism is increased. 
     Although an electricity supplying method for illuminating the LEDs  121  and  122  is not referred to in the first exemplary embodiment, a battery may be mounted on the LED board  120  and electricity may be supplied to the LEDs  121  and  122  from the battery. Alternatively, a coil or an antenna may be mounted on the LED board  120 , electricity may be supplied externally by electromagnetic induction or radio wave, and the LEDs  121  and  122  may be illuminated by the supplied electricity. In the latter case, it is unnecessary to mount a battery which is a consumable item on the LED board  120 , and maintainability may be enhanced. 
     A retroreflector may be used instead of the LEDs  121  and  122  in the first exemplary embodiment. The retroreflector has characteristics to reflect incident light thereto in its incident direction. If the retroreflector is provided instead of the LEDs  121  and  122  on the LED board  120  and it is illuminated from a camera  30  side and the reflected light is shot by the camera  30 , the same measurement as that when the LEDs  121  and  122  are provided may be carried out, and since the retroreflector itself does not require electricity, maintainability may be enhanced also in this case. 
     In the case of the retroreflector, since it is unnecessary to supply electricity to the arranging tray  11  or to provide an electricity generating source, this is suitable for an explosionproof environment. 
     Next, a part holding method according to a second exemplary embodiment of the present invention will be explained. In the second and subsequent exemplary embodiments, illustration of elements corresponding to the controller  40  and the position/attitude recognizing section  50  illustrated in  FIGS. 4 to 7  is omitted to avoid illustration complexity in the drawings. 
       FIG. 8  is a plan view an arranging tray carrying plate and an arranging tray employed in the part holding method of the second exemplary embodiment of the present invention. 
     In the second exemplary embodiment, an arranging tray  62  is placed on an arranging tray carrying plate  61 . The arranging tray carrying plate  61  includes arranging tray fixing portions  611  at positions corresponding to four corners of the arranging tray  62 . The arranging tray  62  is carried on the arranging tray carrying plate  61  in a state where the arranging tray  62  is reliably positioned by the arranging tray fixing portions  611 . The parts  13  which are to be taken out are placed on the predetermined positions on the arranging tray  62 . The LED board  120  is fixed to a predetermined position of the arranging tray carrying plate  61 . The LED board  120  has a shape illustrated in  FIG. 3 . Four LEDs  121  are provided on the surface of the LED board  120  and one LED  122  is provided on a location slightly rising from the surface. If the position and attitude of the LED board  120  are recognized by a measurement similar to that described above, a position and an attitude of the arranging tray  62  carried on the arranging tray carrying plate  61  are uniquely determined, and positions and attitudes of the plural parts  13  placed on the arranging tray  62  are also uniquely determined. 
       FIG. 9A  is a side view and  FIG. 9B  is a plan view illustrating a transfer mechanism of the arranging tray carrying plate on which the arranging tray  62  is placed. 
     In a state where the arranging tray  62  on which the parts  13  are placed is carried on the arranging tray carrying plate  61 , the arranging tray  62  which is placed on the transfer stage  64 , transferred in the direction of the arrow A and located at the top in the direction of the arrow A is placed on elevating mechanism  65  and abuts against an abutment portion  66  and stops. 
       FIG. 10  illustrates the arranging tray carrying plate  61  and the arranging tray  62  in a state where they are placed on the elevating mechanism  65  and stop. 
     A broken line in  FIG. 10  illustrates normal position and an attitude of the arranging tray carrying plate  61 . 
     The arranging tray carrying plate  61  is placed on the transfer stage  64  with an appropriate attitude in many cases, or the arranging tray carrying plate  61  is inclined when it abuts against the abutment portion  66  of the elevating mechanism  65 , and is deviated in position or inclined and stops as illustrated in  FIG. 10  in some cases. 
     Here, even if the arranging tray carrying plate  61  is deviated in position or inclined and stops on the elevating mechanism  65  as illustrated in  FIG. 10 , a position and an attitude of the arranging tray carrying plate  61  are precisely recognized by shooting of the LEDs  121  and  122  (see  FIG. 3 ) disposed on the LED board  120  by the camera  30  and by recognizing the position and attitude of the LED board  120  based on the shot image, and the position and attitude of the arranging tray  62  and positions and attitudes of the parts  13  placed on the arranging tray  62  are also precisely determined. After the position and attitude of the part  13  are precisely determined, the robot hand  22  is right opposed to the part  13  whose position and attitude are precisely determined and reliably holds the part  13 , and the part  13  is reliably taken out from the arranging tray  62 . When all of the parts  13  on the arranging tray  62  placed on the arranging tray carrying plate  61  which moves from the transfer stage  64  to the elevating mechanism  65  are taken out, the elevating mechanism  65  is lowered in the direction of the arrow B, the arranging tray carrying plate  61  on which an empty arranging tray  62  is placed is delivered to the transfer stage  64  from the elevating mechanism  65 , and is transferred in the direction of the arrow C by the transfer stage  64 . 
     The elevating mechanism  65  again rises and receives a next arranging tray carrying plate  61  which has been transferred by the transfer stage  64  in the direction of the arrow A. 
     By repeating the above-described operation, the parts  13  on the plural arranging trays  62  placed on the plural arranging tray carrying plates  61  are taken out in succession. 
       FIGS. 11 to 14  illustrate processes of the holding and taking out method of the parts  13  on the arranging tray  62 . 
     The processes illustrated in  FIGS. 11 to 14  correspond to the processes illustrated in  FIGS. 4 to 7  in the first exemplary embodiment illustrated in  FIGS. 4 to 7 . That is, in the second exemplary embodiment, the shape of the arranging tray  62  is different, the way to obtain a position and an attitude of the LED board  120 , the holding method and the taking out method of the part  13  are the same as those of the first exemplary embodiment illustrated in  FIG. 4 to 7  except that the arranging tray  62  is placed on the arranging tray carrying plate  61  and the LED board  120  is fixed to the arranging tray carrying plate  61 . Therefore, detailed explanation is omitted here. 
       FIGS. 15 to 18  illustrate processes of a part holding method of a third exemplary embodiment of the present invention.  FIGS. 15 to 18  respectively correspond to  FIGS. 4 to 7  in the first exemplary embodiment. 
     Here, the robot hand  22  holds parts  70 . 
     The part  70  is formed with retroreflectors  71  due to a mode of its surface. The retroreflector  71  has characteristics that irrespective of from which direction the retroreflector  71  receives incident light, the retroreflector  71  returns reflection light in the same direction as the incident direction of the incident light. The retroreflectors  71  correspond to the LEDs  121  and  122  on the LED board  120  illustrated in  FIG. 3 , and four or more retroreflectors  71  are formed in total at positions on the surface of the part  70  at predetermined distances from one another. A triangular reference surface having three apexes corresponding to three of the four or more retroreflectors  71  is determined. The remaining one retroreflector  71  is place data position slightly separated away from the reference surface toward a normal to the reference surface. 
     In the third exemplary embodiment, the camera  30  includes an annular light source  32  surrounding the shooting lens  31  located on a front surface thereof. The annular light source  32  is for illuminating the retroreflectors  71  formed on the part  70 . If each retroreflector  71  receives illumination light from the annular light source  32 , the retroreflector  71  reflects the light toward the camera  30 . The camera  30  carries out shooting while capturing the reflection light, and the position and attitude of the part  70  are recognized based on the shot image. 
     The third exemplary embodiment illustrated in  FIGS. 15 to 18  is different from the first exemplary embodiment illustrated in  FIGS. 4 to 7  in the above-described points. That is, in the first exemplary embodiment illustrated in  FIGS. 4 to 7 , a position and an attitude of the LED board  120  are obtained from the LEDs  121  and  122  on the LED board  120 , a position and an attitude of the part  13  are obtained based on this, the part  13  is held by the robot hand  22  and is taken out from the arranging tray  11 . In the third exemplary embodiment illustrated in  FIGS. 15 to 18 , reflection light from the retroreflector  71  which is an alternative to the LED is captured, a position and an attitude of the part  70  itself are obtained, and the part  70  is held and brought up by the robot hand  22 . Except these points, the obtaining way of the position and the attitude of the part  70  and the holding method of the part  70  are common to those of the first exemplary embodiment illustrated in  FIGS. 4 to 7 , and explanation of the common portion is omitted. 
       FIG. 19  is an explanatory diagram of a part arranging method and a part assembling method as a fourth exemplary embodiment of the present invention. Illustration and explanation of points which are obvious from the above-explained first to third exemplary embodiments are omitted. 
     Here, the LED board  120  and a first part  72  are placed on predetermined positions on the assembling palette  71 . The LED board  120  has the shape explained with reference to  FIG. 3 . The assembling palette  71  is transferred by the transfer stage  79  in the direction of the arrow D in a state where the LED board  120  and the first part  72  are placed on the assembling palette  71 , and the assembling palette  71  abuts against the abutment portion (not illustrated) and stops substantially at a position illustrated in  FIG. 19 . 
     The camera  30  is fixed to such a position and an attitude that the camera  30  may diagonally shoot an image of the LED board  120  on the stopped assembling palette  71 . That is, in this fourth exemplary embodiment, two stage measurements are not carried out unlike the first exemplary embodiment illustrated in  FIGS. 4 to 7 , and only one stage measurement corresponding to the second measurement of the first exemplary embodiment is carried out. With this, the measuring time is reduced as compared with a case where two measurements are carried out as in the first exemplary embodiment. When the stopped position and the stopped attitude of the assembling palette  71  are not largely varied, the image shooting operation and the measurement may be carried out only once from the position inclined from the normal of the LED board  120  as in the fourth exemplary embodiment illustrated in  FIG. 19  and the position and attitude of the LED board  120  may be obtained. If the position and attitude of the LED board  120  are obtained, a position and an attitude of the first part  72  placed on the predetermined position of the same assembling palette  71  are also obtained. 
     On the other hand, the robot hand  22  holds a second part  73 . The second part  73  is assembled on the first part  72  on the assembling palette  71 . The robot  20  changes its position and attitude based on information of a position and an attitude of the first part  72  obtained based on a shot image taken by the camera  30 , brings the second part  73  right opposed to the first part  72  on the assembling palette  71 , and assembles the second part  73  on the first part  72 . 
     From a viewpoint that the second part  73  is assembled on the first part  72 , the fourth exemplary embodiment corresponds to one exemplary embodiment of the part assembling method of the present invention, and from a viewpoint that the second part  73  is placed on the assembling palette  71 , the fourth exemplary embodiment also corresponds to one exemplary embodiment of a part arranging method of the invention. 
     Although the camera  30  is fixed in the fourth exemplary embodiment, a moving mechanism for changing a position and an attitude of the camera  30  may be provided, the camera  30  is moved independently from the robot  20  and measurements may be carried out in two stages like the first exemplary embodiment illustrated in  FIGS. 4 to 7 . 
       FIG. 20  is an explanatory diagram of a part arranging method and a part assembling method of a fifth exemplary embodiment of the present invention. Here, differences of the fifth exemplary embodiment over the fourth exemplary embodiment illustrated in  FIG. 19  are explained. 
     In the case of the fifth exemplary embodiment illustrated in  FIG. 20 , the LED board  120  is diagonally fixed to a predetermined position on the assembling palette  71 , and the camera  30  is fixed to a position where the camera  30  may shoot an image directly above the LED board  120  which is diagonally fixed. 
     With this, an effect that an image of the LED board  120  may be shot from a diagonal direction with respect to the normal and a position and an attitude of the LED board  120  are obtained precisely is maintained as it is, and since the camera  30  may be fixed directly above the LED board  120 , installation space may be reduced. 
       FIG. 21  is an explanatory diagram of a part arranging method and a part assembling method of a sixth exemplary embodiment of the present invention. Here, differences of the sixth exemplary embodiment over the fourth exemplary embodiment illustrated in  FIG. 19  will be explained. 
     In the case of the fourth exemplary embodiment illustrated in  FIG. 19 , the camera  30  is fixed such that it may not move. In the case of the sixth exemplary embodiment illustrated in  FIG. 21 , however, the camera  30  is fixed to the robot hand  22  as in the first exemplary embodiment illustrated in  FIGS. 4 to 7  and the camera  30  moves together with the robot hand  22 . 
     Even when a position and an attitude are obtained by shooting the LED board  120  only diagonally without carrying out the measurement in two stages, the camera  30  may be fixed to the robot  20  as illustrated in  FIG. 21 . If the camera  30  is fixed to the robot  20 , interference between the robot  20  and the camera  30  may reliably be avoided at the time of assembling operation, and a freedom degree of movement of the robot  20  for assembling operation is enhanced. 
     Next, a seventh exemplary embodiment in which all of the position/attitude recognizing method, the part holding method, the part arranging method and the part assembling method of the present invention are included is explained. First, an outline of an image forming apparatus which is a prerequisite thereof will be explained. 
       FIG. 22  is a schematic block diagram of an essential portion of the image forming apparatus. 
     As illustrated in  FIG. 22 , the image forming apparatus  100  includes four image forming units  110 Y,  110 M,  110 C and  110 K. The image forming units  110 Y,  110 M,  110 C and  110 K respectively include photosensitive bodies  111 Y,  111 M,  111 C and  111 K which rotate in the direction of the arrow A, chargers  113 Y,  113 M,  113 C and  113 K, exposure apparatuses  114 Y,  114 M,  114 C and  114 K, developing rolls  112 Y,  112 M,  112 C and  112 K, primary transfer rolls  120 Y,  120 M,  120 C and  120 K, and cleaning members  115 Y,  115 M,  115 C and  115 K. 
     The image forming apparatus  100  may print in full color. Symbols Y, M, C and K added to the ends of the elements explained above represent elements for forming image of yellow, magenta, cyan and black, respectively. 
     The image forming apparatus  100  also includes an intermediate transfer belt  130  which runs in the direction of the arrow B, a secondary transfer roll  140 , a tension roller  131 , and an image information processor  150  which sends image information to the image forming units  110 Y,  110 M,  110 C and  110 K. 
     The image information processor  150  decomposes image information which is input from outside into image information of each color, and sends the image information to the exposure apparatuses  114 Y,  114 M,  114 C and  114 K. 
     A basic image forming operation of the image forming apparatus  100  will be explained. 
     In the image forming apparatus  100 , a toner image forming operation by the yellow image forming unit  110 Y is started, and predetermined electric charge is applied to a surface of the photosensitive body  111 Y which rotates in the direction of the arrow A by the charger  113 Y. Next, the surface of the photosensitive body  111 Y is irradiated with exposure light corresponding to the yellow image produced by the exposure apparatus  114 Y in accordance with image information which is sent from the image information processor  150 , and an electrostatic latent image is formed. The electrostatic latent image is developed with yellow toner by the developing roll  112 Y, and the yellow toner image is formed on the photosensitive body  111 Y. The toner image is transferred to the intermediate transfer belt  130  by the action of the primary transfer roll  120 Y. 
     In the image forming apparatus  100 , toner and developer agent including magnetic carrier coated with external additive for securing the electric charging characteristics of the toner are used, and the electrostatic latent image formed on the photosensitive body in accordance with the image information is developed with toner among the developer agent. In the image forming apparatus  100 , after a developer agent cartridge is filled with such developer agent is mounted in the apparatus, only toner filling is performed, the toner and the magnetic carrier are mixed, the toner is negatively charged and the external additive of the magnetic carrier is positively charged. 
     At the timing when a yellow toner image transferred on the intermediate transfer belt  130  reaches the primary transfer roll  120 M of the image forming unit  110 M of the next color, a toner image is formed by the magenta image forming unit  110 M so that the magenta toner image which is the next color image reaches the primary transfer roll  120 M. The magenta toner image formed in this manner is superposed and transferred on the yellow toner image on the intermediate transfer belt  130  by the action of the primary transfer roll  120 M. 
     Next, cyan and black toner image forming operations by the image forming units  110 C and  110 K are carried out at the timing similar to that explained above, and these toner images are sequentially superposed and transferred on the yellow and magenta toner images of the intermediate transfer belt  130  by the action of the primary transfer rolls  120 C and  120 . 
     The multi-color toner images transferred on the intermediate transfer belt  130  in this manner is finally secondary transferred on a paper sheet  150  by the secondary transfer roll  140 , the multi-color toner image is conveyed in the direction of the arrow C together with the paper sheet  150 , the toner image is fixed by a fixing device (not illustrated), and a color image is formed on the paper sheet  150 . 
     Toner remaining on the photosensitive bodies  111 Y,  111 M,  111 C and  111 K after the image is transferred to the intermediate transfer belt  130  is scraped off from the photosensitive bodies  111 Y,  111 M,  111 C and  111 K by the cleaning members  115 Y,  115 M,  115 C and  115 K and the toner becomes toner waste. The scraped toner waste is conveyed in a direction perpendicular to the paper surface of  FIG. 22  by a mechanism (not illustrated), and is discharged into a toner waste receiving tank (not illustrated). 
     In the case of the yellow image forming unit  110 Y for example, the photosensitive body  111 Y, the charger  113 Y and the cleaning member  115 Y are assembled into one photosensitive body assembly, and this is disposed in the image forming apparatus  100 . The same procedure is taken for other image forming units also. 
     A seventh exemplary embodiment of the present invention will be explained as an assembling example of the photosensitive body assembly. 
       FIG. 23  is a perspective view of a robot used for assembling the photosensitive body assembly. 
     Here, a robot arm  201  and a robot hand  202  included in a robot  200  is illustrated. The robot hand  202  includes a suction pad  203  which sucks (one example of holding according to the present invention) a part by vacuum suction to bring the part up. A measuring camera  290  having a shooting lens of great spherical aberration is fixed to the robot hand  202 . A position and an attitude of the robot hand  202  are freely changed. 
       FIG. 24  is a perspective view illustrating an assembling palette and a frame body which is a resin part supported by the assembling palette. The frame body  410  is a frame body of the photosensitive body assembly and is one of parts included in the photosensitive body assembly. 
     Four holding pieces  301  are fixed to the assembling palette  300 , and an LED board  310  is fixed to the assembling palette  300  by the holding pieces  301 . The LED board  310  is provided thereon with three measuring LEDs  311 , an LED  312  which is used as an ID for specifying the LED board  310  from other LED boards, and one LED  313  fixed to a position slightly higher than the LED board  310 . The three LEDs  311  and the one LED  313  are used for measuring the position and the attitude of the LED board  310 . The position of the one LED  312  differs depending upon the LED board  310 , the LED board  310  may be distinguished from other LED boards by specifying the position of the LED  312 . A method for obtaining the position and attitude of the LED board  310  using the LEDs  311  and  313  on the LED board  310  is the same as the above-explained exemplary embodiments, and detailed explanation thereof is omitted. 
     The assembling palette  300  includes two holding pieces  302  for holding the frame body  410 , and two positioning pins  303  for positioning the frame body  410  on the assembling palette  300 . The frame body  410  is provided with two positioning openings  411 . The frame body  410  is placed on the holding pieces  302 , and the positioning pins  303  are inserted into the positioning openings  411 . With this, the positioning pins  303  are placed on predetermined positions of the assembling palette  300 . 
     As explained, the LED board  310  and the frame body  410  are disposed at determined positions on the assembling palette  300 . A position and an attitude of the frame body  410  are uniquely obtained by obtaining the position and the attitude of the LED board  310 . 
       FIG. 25  is a perspective view illustrating the arranging tray and the cleaning members arranged on the arranging tray. 
     Ten cleaning members  420  are arranged on the arranging tray  330  illustrated in  FIG. 25 . Each cleaning member  420  corresponds to one of the cleaning members  115 Y,  115 M,  115 C and  115 K illustrated in  FIG. 22 . Each cleaning member  420  illustrated in  FIG. 25  is a combined part of a rubber part  421  which is in direct contact with the photosensitive body and a sheet metal part  422  which supports the rubber part  421 . 
     The arranging tray  330  includes ten accommodating grooves  331  in which the cleaning member  420  is accommodated one each. One cleaning member  420  is accommodated in each of the accommodating grooves  331 . With this, predetermined position and attitude of each cleaning member  420  are maintained on the arranging tray  330 . 
     The arranging tray  330  is provided with a recess  332  in which the LED board  340  is fitted, and the LED board  340  is fitted in the recess  332 . The LED board  340  is fitted in the recess  332 , and predetermined position and attitude of the LED board  340  on the arranging tray  330  are fixed. 
     The LED board  340  includes three LEDs  341  and one LED  343  at the same positions as those of the LED board  310  illustrated in  FIG. 24 . A position of another LED  342  is different from that of the LED  312  on the LED board  310  illustrated in  FIG. 24 . This is because that the LED  342  functions as an ID for specifying the LED board by changing the position of the LED  342  on an LED board to LED board basis. 
     Concerning the LED board  340  in  FIG. 25  also, a position and an attitude of the LED board  310  are recognized by measurement by the camera  290  and based on this, a position and an attitude of each cleaning member  420  arranged on the arranging tray  330  are obtained. One of the cleaning members  420  arranged on the arranging tray  330  is taken out by the robot  200  illustrated in  FIG. 23 , and the cleaning member  420  is assembled into the frame body  410  illustrated in  FIG. 24 . 
     An assembling order of the cleaning member  420  into the frame body  410  will be explained below. 
       FIG. 26  is a perspective view illustrating a state where the robot  200  approaches the arranging tray  330  before the cleaning member  420  is taken out. 
     Then, the camera  290  measures a position and an attitude of the LED board  340 , a position and an attitude of the cleaning member  420  are grasped based on this, and a suction pad  221  of a robot hand  220  is controlled to assume a position and an attitude right opposed to a cleaning member  420  to be taken out. 
       FIG. 27  is a perspective view illustrating a state where one of the cleaning members  420  on the arranging tray  330  is taken out by the robot  200 . 
     The robot  200  brings the suction pad  203  at a position right opposed to one of the cleaning members  420  which is to be taken out this time and then, the suction pad  203  is pushed against the cleaning member  420 , the cleaning member  420  is sucked by the suction pad  203  by vacuum adsorption, the cleaning member  420  is brought up as it is, and the cleaning member  420  is taken out from the arranging tray  330 . 
       FIG. 28  is a perspective view illustrating a state where the robot which sucks the cleaning member approaches the assembling palette. 
     The robot  200  which approaches the assembling palette  300  measures a position and an attitude of the LED board  310  by the camera  290  mounted on the robot  200 , a position and an attitude of the frame body  410  are obtained based on this, and the robot  200  moves such that the cleaning member  420  sucked by the suction pad  203  of the robot hand  202  assumes a position and an attitude right opposed to the frame body  410  fixed to the assembling palette  300 . 
       FIG. 29  is a perspective view illustrating a state where the cleaning member  420  is assembled into the frame body  410 . 
     After the cleaning member  420  is opposed to the frame body  410  as described above, the cleaning member  420  is assembled on the frame body  410  as illustrated in  FIG. 29 . Then, the suction force generated by the suction pad  203  is released, the robot  200  moves upward and the suction pad  203  is separated from the cleaning member  420 . 
     After the cleaning member  420  is assembled into the frame body  410 , later-described various members are sequentially assembled in the same manner as that of the assembling operation of the cleaning member  420 . 
       FIGS. 30 and 31  are perspective views of the photosensitive body assembly after the assembling operation as viewed from different view points from each other. 
     Here, a frame body  410 , a photosensitive body  430 , a photosensitive body holding body  440 , a support plate  450 , a rear cover  460 , a front cover  470  and a charger  480  are illustrated as constituent parts of the photosensitive body assembly  400 . The photosensitive body  430  corresponds to one of the photosensitive bodies  111 Y,  111 M,  111 C and  111 K illustrated in  FIG. 22 , and the charger  480  corresponds to one of the chargers  113 Y,  113 M,  113 C and  113 K illustrated in  FIG. 22 . 
     The cleaning member  420  (see  FIG. 27  for example) which is first assembled into the frame body  410  is covered with the photosensitive body  430  and is not illustrated in  FIGS. 30 and 31 . 
     The photosensitive body holding body  440  and the support plate  450  support a rear end and a front end of the photosensitive body  430 , respectively. The rear cover  460  and the front cover  470  cover a rear portion and a front portion of the photosensitive body assembly  400 , respectively. The rear cover  460  is formed with an opening  461  for transmitting a rotation and driving force to the photosensitive body  430 . A board  471  on which a memory for storing the number of cumulative rotation number of the photosensitive body  430  is fixed to the front cover  470 . 
     Next, an assembling procedure of the parts included in the photosensitive body assembly  400  will be explained. 
       FIG. 32  illustrates the frame body  410 . 
     In the drawings which are described below have marks for discriminating assembling steps as is described below, and the marks are omitted in the above explanation because they are unnecessary. These marks may be LEDs or retroreflectors which may clearly be shot by the camera  290  (see  FIG. 23 ). 
     The frame body  410  illustrated in  FIG. 32  is formed with a support plate discriminating mark  501 , a cleaning member discriminating mark  502 , a photosensitive body discriminating mark  503  and a charger discriminating mark  504 . 
       FIG. 33  illustrates a state where the cleaning member  420  is assembled into the frame body  410 . 
     Here, the cleaning member  420  is assembled into the frame body  410 , the cleaning member discriminating mark  502  (see  FIG. 32 ) is covered with the cleaning member  420 , and it is possible to easily recognize that the cleaning member  420  is assembled into the frame body  410  by means of the camera  290  or eyes of an operator. 
       FIG. 34  illustrates a state where the photosensitive body  430  is further assembled. 
     By assembling the photosensitive body  430 , the photosensitive body discriminating mark  503  (see  FIG. 33 ) which may be seen until then is covered. With this, it is possible to easily recognize that the photosensitive body  430  is in the assembled state by the camera  290  or eyes of an operator.  FIG. 35  illustrates a state where the photosensitive body holding body  440  is further assembled, and  FIG. 36  is a partially enlarged perspective view of that state. 
     The photosensitive body holding body  440  is formed with the photosensitive body holding body discriminating mark  505  which is a new mark. It is recognized by the camera  290  or by the eyes of the operator that the photosensitive body holding body discriminating mark  505  is newly added in addition to the support plate discriminating mark  501  and the charger discriminating mark  504 , thereby recognizing that the photosensitive body holding body  440  is in the assembled state. 
       FIG. 37  illustrates a state where the support plate  450  is assembled.  FIG. 38  is a partially enlarged perspective view illustrating a state immediately before the support plate is assembled. 
     As illustrated in  FIG. 38 , the support plate  450  is assembled such that it is inserted from the front end of the photosensitive body  430  in the direction of the arrow E. Before the support plate  450  is assembled, the support plate discriminating mark  501  may be seen, but when the support plate  450  is assembled, the support plate discriminating mark  501  is covered. It is recognized by the camera  290  or the eyes of the operator that the support plate discriminating mark  501  is covered. With this, it is recognized that the support plate  450  is in the assembled state. 
       FIG. 39  illustrates a state where the rear cover  460  is further assembled.  FIG. 40  is a partially enlarged perspective view of the state. 
     The rear cover  460  is formed with a rear cover discriminating mark  506  which is a new mark. It is recognized by the camera  290  or the eyes of the operator that the rear cover discriminating mark  506  is added and with this, it is easily recognized that the rear cover  460  is in the assembled state. 
       FIG. 41  illustrates a state where the front cover  470  is further assembled.  FIG. 42  is a partially enlarged perspective view illustrating a state immediately before the front cover  470  is assembled. 
     As illustrated in  FIG. 42 , the front cover  470  is assembled into the support plate  450  such that the front cover  470  is pushed against the support plate  450  from front in the direction of the arrow F. 
     This front cover  470  is formed with a front cover discriminating mark  507  which is a new mark, and since the front cover discriminating mark  507  is newly added, it may easily be recognized by the camera  290  or the eyes of the operator that the front cover  470  is in the assembled state. 
       FIG. 43  illustrates a state where the charger  480  is further assembled. 
     When the charger  480  is assembled, the charger discriminating mark  504  is covered with the charger  480 . With this, it is recognized by the camera  290  or the operator at a glance that the charger  480  is in the assembled state. 
     By forming the marks whose patterns are varied in accordance with assembling steps of the parts included in the photosensitive body assembly as described above, it is possible to easily recognize the assembling step at a glance by the camera or the operator. 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purpose 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 embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others 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.