Patent Publication Number: US-8540242-B2

Title: Image forming apparatus, recording medium detecting apparatus and recording medium detecting method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the priority of U.S. Provisional Application No. 61/326,581, filed on Apr. 21, 2010, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     Embodiments described herein relate generally to an image forming apparatus in which a recording medium such as a sheet is carried via plural carrying paths. Embodiments described herein also relate generally to a recording medium detecting apparatus and a recording medium detecting method. 
     BACKGROUND 
     Conventionally, an image forming apparatus such as a copy machine or printer can form an image on plural types of recording media with different sizes and thicknesses. As the recording media, paper sheets and OHP sheets and the like are used. In the following description, a sheet is used as an example of the recording media. 
     A sheet can be supplied to an image forming unit by manual insertion as well as from a paper supply cassette. In the image forming apparatus, an image forming unit including a photoconductive drum is provided. An image is formed on a sheet supplied from a paper supply cassette or a sheet supplied by manual insertion. 
     By the way, since a sheet is carried to the image forming unit via plural carrying path, a media sensor is installed on each carrying path within the image forming apparatus. Thus, the media sensor discriminates the thickness and type of the sheet passing through each carrying path. 
     However, there is an inconvenience that the arrangement of the media sensor on each carrying path increases the cost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the configuration of an image forming apparatus according to a first embodiment. 
         FIG. 2A  and  FIG. 2B  are explanatory views showing the configuration and operation of a media sensor in the first embodiment. 
         FIG. 3  shows the arrangement of the media sensor and the configuration of a moving mechanism of the media sensor. 
         FIG. 4  shows an example of the moving mechanism. 
         FIG. 5  is an explanatory view showing the operation of the moving mechanism. 
         FIG. 6  shows another example of the moving mechanism. 
         FIG. 7  is a block diagram showing a control system of the image forming apparatus. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, an image forming apparatus includes: 
     an image forming unit which forms an image on a recording medium; 
     a carrying unit which guides the recording medium to the image forming unit via a first carrying path or a second carrying path; 
     a media sensor which is arranged at apart where the first carrying path and the second carrying path merge together, and which discriminates a type of the recording medium; and 
     a moving mechanism which moves the media sensor toward the first carrying path or toward the second carrying path where the recording medium passes. 
     Hereinafter, an image forming apparatus according to a first embodiment will be described with reference to the drawings. The same parts in the drawings are denoted by the same reference numerals. 
       FIG. 1  shows the internal configuration of the image forming apparatus according to the first embodiment. In the following description, an MFP (multi-function peripheral) which is a multi-functional machine is described as an example. However, other image forming apparatuses such as a printer can also be used. 
     In  FIG. 1 , an image forming apparatus  10  has an image forming unit  11  at the center of the apparatus. An automatic document feeder (ADF)  12 , an image reading unit (scanner)  13  and a paper discharge unit  14  are provided in an upper part of the image forming apparatus  10 . A paper supply unit  15  is provided below the image forming unit  11 . An operation panel  16  including an operation unit and a display unit is provided in an upper part of the image forming apparatus  10 . 
     The automatic document feeder (ADF)  12  feeds a document to the image reading unit  13 . The image reading unit  13  reads the document and generates image data. The image forming unit  11  is formed, for example, by a tandem color laser printer and scans a photoconductive member with a laser beam from a laser exposure device  17  and thus generates an image. 
     The image forming unit  11  includes image forming sections  20 Y,  20 M,  20 C and  20 K for the colors of yellow (Y), magenta (M), cyan (C) and black (K). The image forming sections  20 Y,  20 M,  20 C and  20 K are arranged in parallel along the lower side of an intermediate transfer belt  21  as an intermediate transfer medium, from upstream toward downstream. 
     In the following description, components constituting the image forming sections  20 Y,  20 M,  20 C and  20 K are denoted by reference numerals with symbols Y, M, C and K. However, in some cases, the components may be described without the symbols Y, M, C and K. 
     Since the image forming sections  20 Y,  20 M,  20 C and  20 K have the same configuration, the image forming section  20 Y will be described as a representative example. The image forming section  20 Y has a photoconductive drum  22 Y. A charger  23 Y, a developing device  24 Y, a transfer roller  25 Y, a cleaner  26 Y and the like are arranged around the photoconductive drum  22 Y. 
     The intermediate transfer belt  21  moves circularly. For example, semi-conducting polyimide is used in view of heat resistance and wear resistance. The intermediate transfer belt  21  is extended over a driving roller  27  and driven rollers  28 ,  29  and  30 . The intermediate transfer belt  21  faces and can contact the photoconductive drum  22 Y. At a position on the intermediate transfer belt  21  facing the photoconductive drum  22 Y, a primary transfer voltage is applied by the transfer roller  25 Y and a toner image on the photoconductive drum  22 Y is primary-transferred to the intermediate transfer belt  21 . 
     A secondary transfer roller  31  is arranged facing the driving roller  27  over which the intermediate transfer belt  21  is extended. When a sheet S passes between the driving roller  27  and the secondary transfer roller  31 , a secondary transfer voltage is applied by the secondary transfer roller  31  and the toner image on the intermediate transfer belt  21  is secondary-transferred to the sheet S. A belt cleaner  32  is provided near the driven roller  30  on the intermediate transfer belt  21 . 
     An exposure position on the photoconductive drum  22 Y is irradiated with a yellow laser beam from the laser exposure device  17  and a latent image is thus formed on the photoconductive drum  22 Y. The charger  23 Y uniformly charges the entire surface of the photoconductive drum  22 Y, for example, to approximately −700 V. The developing device  24 Y supplies a two-component developer including toner and carrier of each color to the photoconductive drum  22 Y, with a developing roller to which a developing bias of approximately −500 V is applied. The cleaner  26 Y removes residual toner on the surface of the photoconductive drum  22 Y using a blade. 
     Meanwhile, the laser exposure device  17  scans the photoconductive drum  22 Y in the axial direction with a laser beam emitted from a semiconductor laser element. The laser exposure device  17  includes a polygon mirror  17 A, an imaging lens system  17 B, a mirror  17 C and the like. 
     The paper supply unit  15  has plural paper supply cassettes  15 A and  15 B accommodating recording media (sheets or the like) of various sizes. Moreover, the image forming apparatus  10  is provided with a manual insertion tray  33  through which a recording medium is supplied by manual insertion. In the following description, an example of forming an image on a sheet S as a recording medium will be described. 
     In a path from the paper supply cassettes  15 A and  15 B to the secondary transfer roller  31 , pickup rollers  34 A and  34 B to take out the sheet S from the paper supply cassettes  15 A and  15 B, separation rollers  35 A and  35 B, carrying rollers  36  and  37  and a registration roller  38  are provided. In a path from the manual insertion tray  33  to the registration roller  38 , a pickup roller  39  to take out the sheet S and a manual insertion paper supply roller  40  are provided. 
     Moreover, a fixing device  41  is provided downstream of the secondary transfer roller  31 . A paper discharge carrying path  42  is provided from the fixing device  41  to the paper discharge unit  14 . A reverse carrying path  43  is further provided. In the reverse carrying path  43 , a gate  44  is provided to sort the sheet toward the paper discharge unit  14  or toward the reverse carrying path  43 . The reverse carrying path  43  reverses the sheet S and then guides the sheet S in the direction of the secondary transfer roller  31 . The reverse carrying path  43  is used in double-side print or the like. 
     Next, the operation of the image forming apparatus  10  will be briefly described. When image information is inputted from a scanner, personal computer terminal or the like, toner images of yellow (Y), magenta (M), cyan (C) and black (K) are formed by the image forming sections  20 Y to  20 K and the toner images of magenta (M), cyan (C) and black (K) are multiple-transferred to the same position where the toner image of yellow (Y) is formed, on the intermediate transfer belt  21 . Thus, a full-color toner image is provided. 
     The full-color toner image on the intermediate transfer belt  21  is collectively secondary-transferred onto the sheet S by the secondary transfer roller  31 . The sheet S is supplied to the position of the secondary transfer roller  31  from the paper supply cassette  15 A or  15 B or the manual insertion tray  33 . The sheet S to which the toner image is secondary-transferred is sent to the fixing device  41  and the toner image is fixed to the sheet S. 
     The sheet S to which the toner image is fixed is sorted to the paper discharge unit  14  by the gate  44  when the sheet S has the image on one side. In the case of performing double-side print or multiple prints, the sheet S is sorted toward the reverse carrying path  43  by the gate  44  and is carried again to the secondary transfer roller  31 . 
     Meanwhile, after the secondary transfer is finished, the residual toner on the intermediate transfer belt  21  is cleaned by the belt cleaner  32 . The residual toner on the photoconductive drum  22  is removed by the cleaner  26  after the primary transfer of the toner image to the intermediate transfer belt  21 , and the photoconductive drum  22  thus becomes available for the next image forming. 
     The image forming apparatus  10  has plural carrying paths to carry sheets toward the image forming unit  11 . The sheet S is supplied, for example, via a carrying path toward the image forming unit  11  from the paper supply cassettes  15 A and  15 B, a carrying path toward the image forming unit  11  from the manual insertion tray  33 , or a carrying path toward the image forming unit  11  from the reverse carrying path  43 . Since sheets with different sizes and thicknesses are supplied from each carrying path, the type of the sheet (for example, thickness) is detected by a media sensor. 
     The media sensor is expensive. Therefore, arranging the media sensor in each carrying path raises the cost and also increases the installation space. 
     Thus, in the first embodiment, an image forming apparatus is provided in which sheets passing through plural carrying paths are detected by a common media sensor. The media sensor is arranged at a merging point where the plural carrying paths merge together. The media sensor is also made movable in the direction of each carrying path. The position of the media sensor is controlled every time the supply source of the supplied sheet changes. 
     Hereinafter, the media sensor and a moving mechanism of the media sensor will be described. 
       FIG. 2A  and  FIG. 2B  are explanatory views showing a media sensor  50  and the operation of the media sensor. As shown in  FIG. 2A , the media sensor  50  has a roller  52  provided on the outer circumference of a bearing  51 , and a supporting part  53  supporting the roller  52 . The supporting part  53  is rotatable about a fulcrum  55  provided in a body part  54  of the sensor. A magnet is provided at the base of the supporting part  53 . A magnetic sensor is provided in the body part  54 . 
     As shown in  FIG. 2B , the roller  52  of the media sensor  50  can contact the sheet. When sheet S is carried in contact with the roller  52 , the roller  52  rotates around the bearing  51  because of the friction with the sheet S. When the thickness of the sheet S is changed, the supporting part  53  rotates about the fulcrum  55  as indicated by angle α. As the angle of inclination of the supporting part  53  changes, the magnetic force changes. The magnetic sensor in the body part  54  detects magnetic resistance due to the change in the magnetic force and detects the thickness of the sheet S. 
       FIG. 3  shows the position of arrangement of the media sensor  50  and the configuration of the moving mechanism. In the example of  FIG. 3 , the media sensor  50  is arranged at a merging point where a sheet carrying path  61  toward the image forming unit  11  from the paper supply cassette  15 A (or  15 B) and a sheet carrying path  62  toward the image forming unit  11  from the manual insertion tray  33  merge together. 
     Hereinafter, the sheet carrying path from the paper supply cassette  15 A (or  15 B) is called a first carrying path  61 . The sheet carrying path from the manual insertion tray  33  is called a second carrying path  62 . The sheet carrying path toward the secondary transfer roller  31  in the image forming unit  11  after the merging point is called a third carrying path  63 . Besides, the first carrying path  61 , the second carrying path  62  and the third carrying path  63  configure the carrying unit. 
     A moving mechanism  70  to move the media sensor  50  is provided. The moving mechanism  70  moves the media sensor  50  toward the first carrying path  61  (in the direction of arrow A) or toward the second carrying path  62  (in the direction of arrow B) according to the carrying of the sheet S. 
       FIG. 4  shows the configuration of an example of the moving mechanism  70  of the media sensor  50 . In  FIG. 4 , it is assumed that the media sensor  50  moves in left-right directions, so that the movement of the media sensor  50  by the moving mechanism  70  can be easy to understand. The description also assumes that the first carrying path  61  and the second carrying path  62  are symmetrical about the third carrying path  63 . 
     The moving mechanism  70  has a moving member  71  supporting the media sensor  50 . A rack  72  is formed on the moving member  71 . A gear  73  is provided to mesh with the rack  72 . The gear  73  is driven by a motor. As the motor rotates the gear  73  forward and backward, the moving member  71  can move in the direction of arrow A or B. 
     As shown in  FIG. 5 , when the sheet S passes through the first carrying path  61 , the moving mechanism  70  moves the media sensor  50  in the direction of the first carrying path  61  (the direction of arrow A) and presses the roller  52  against the sheet S. Therefore, the media sensor  50  can detect the thickness of the sheet S passing through the first carrying path  61 . 
     When the sheet S passes through the second carrying path  62 , the moving mechanism  70  moves the media sensor  50  in the direction of the second carrying path  62  (the direction of arrow B) and presses the roller  52  against the sheet S. Therefore, the media sensor  50  can detect the thickness of the sheet S passing through the second carrying path  62 . 
     Usually, there are many cases where the image forming apparatus  10  forms an image on the sheet S carried form the paper supply cassettes  15 . Therefore, the media sensor  50  may be situated usually toward the first carrying path  61  and may be moved toward the second carrying path  62  when the sheet S is supplied by manual insertion. 
     As for the timing of detecting the thickness of the sheet S, the thickness is detected in response to an operation on the operation panel  16 . For example, when the user operates the operation panel  16  to set the sheet size and the number of sheets and then presses the copy button, the media sensor  50  is moved in the direction of the first carrying path  61 . Then, every time sheets are sequentially carried, the thickness of each sheet is detected. 
     A sheet sensor  56  is provided on the manual insertion tray  33  ( FIG. 1 ). When the sheet S is placed on the manual insertion tray  33 , the sensor  56  detects the sheet S and the moving mechanism  70  moves the media sensor  50  in the direction of the second carrying path  62 . Then, as the user operates the operation panel  16  to set the sheet size and the number of sheets and then presses the copy button, the media sensor  50  detects the thickness of each sheet carried sequentially via the second carrying path  62 . 
       FIG. 6  shows the configuration of another example of the moving mechanism  70 . In  FIG. 6 , the moving member  71  supports the media sensor  50 . A cam  74  is in contact with the moving member  71 . A spring  75  energizes the moving member  71  so that the moving member  71  is constantly in contact with the cam  74 . The cam  74  is, for example, an elliptic eccentric cam and rotates about a shaft  76 . A motor rotates the shaft  76 , causing the moving member  71  to move in the direction of arrow A or arrow B. 
     The moving member  71  is not limited to the above example and various modifications can be employed. 
       FIG. 7  is a block diagram showing a control system of the image forming apparatus according to the embodiment. In  FIG. 7 , a system control unit  80  includes a CPU and ROM, and controls the image forming unit  11 , the ADF  12 , the image reading unit  13  and the like of the image forming apparatus  10  according to a control program stored in the ROM. 
     The operation panel  16  is connected to the system control unit  80 . As the user operates the operation panel  16 , the system control unit  80  controls the image forming unit  11  and the image reading unit  13 , executing operations such as print, copy, and scan. 
     The system control unit  80  is also supplied with the result of detection from the media sensor  50 . The system control unit  80  controls the image forming unit  11  according to the thickness of the sheet detected by the media sensor  50  and thus adjusts the image forming state. For example, when the sheet S is thick, the amount of toner transferred to the sheet S is increased or the fixing temperature of the fixing device  41  is set to a relatively high temperature. Meanwhile, when the sheet S is thin, the amount of toner transferred to the sheet S is reduced or the fixing temperature of the fixing device  41  is set to a relatively low temperature. 
     The result of detection from the sensor  56  provided on the manual insertion tray  33  is also inputted to the system control unit  80 . The system control unit  80  drives a driving unit  77  according to the result of detection from the sensor  56 . The driving unit  77  is provided with a motor. The motor rotates to rotate the gear  73  or the cam  74  of the moving mechanism  70 . 
     For example, when a sheet is set on the manual insertion tray  33 , the system control unit  80  determines that the apparatus is in the manual insertion mode, and the media sensor  50  is moved in the direction of the second carrying path  62 . When no sheets are set on the manual insertion tray  33 , the system control unit  80  determines that the apparatus is in the normal mode, and the media sensor  50  is moved in the direction of the first carrying path  61 . 
     In the above example, the media sensor  50  is arranged on the sheet carrying path from the paper supply cassettes  15  or the manual insertion tray  33 . However, the media sensor  50  may also be provided at a merging point between the carrying path toward the registration roller  38  from the paper supply cassettes  15  and the carrying path toward the registration roller  38  from the reverse carrying path  43  shown in  FIG. 1 . 
     The reverse carrying path  43  is used for double-side print. The thickness of the sheet varies depending on the amount of toner adhering to both sides of the sheet. Therefore, for example, the amount of the adhering toner transferred to the sheet S can be controlled according to the result of detection from the media sensor  50 . 
     Sheets can also be supplied from an external large-capacity paper supply tray in addition to the paper supply cassettes  15 . Therefore, the media sensor  50  may be arranged at a part where the sheet carrying path from the paper supply cassettes  15  and the sheet carrying path from the large-capacity paper supply tray merge together, and the media sensor  50  may detect the thickness of the sheet in each carrying path. 
     In the embodiment, the technique which is applied to the image forming apparatus is described. However, the technique may also be applied to a recording medium detecting apparatus that does not include the image forming unit  11  but includes the parts downstream of the paper supply unit  15  in terms of the sheet carrying direction and up to the third carrying path  63 , as an independent unit. 
     According to such embodiments, the moving mechanism moves the media sensor  50 , enabling common use of the media sensor  50  in plural carrying paths. Therefore, the installation space for the media sensor  50  need not be increased and the rise in the cost can be restrained. 
     Various modifications can be implemented without being limited to the embodiments. For example, an image can be formed on other recording media than the sheet S, such as OHP sheets. Therefore, the difference in thickness between a paper sheet and an OHP sheet may be discriminate and the image forming state may be controlled. The media sensor  50  may detect light transmittance to discriminate the type of paper, other than detecting the thickness of the sheet S. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. Indeed, the novel apparatus and methods described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the apparatus and methods described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.