Patent Publication Number: US-2012027426-A1

Title: Image forming apparatus and image forming method

Description:
BACKGROUND OF THE INVENTION 
     The present application claims priority on Japanese Patent Application No. 2010-168093, filed Jul. 27, 2010, the content of which is incorporated herein by reference. 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus and an image forming method. 
     2. Description of the Related Art 
     Conventionally, according to a recording paper transportation mechanism of an image forming apparatus such as a multi functional peripheral or a printer and the like, a registration roller is used to adjust the timing at which an image is written out. The registration roller is also used to correct a skewing. Normally, a recording paper, which was set inside a paper feeding cassette, is sent to a registration roller via an intermediate roller. When the intermediate roller sends the recording paper to a halting registration roller, a positioning of the tip of the recording paper is conducted there. In addition, a deflection in the upper-lower direction is formed. Thereafter, the registration roller and the intermediate roller are driven. Thus, the recording paper is transported to an image forming unit. A driving unit of a roller may be configured in many ways. For example, a drive motor may be attached individually to a roller. In another configuration, a drive motor and a clutch may be used in combination. For instance, according to a printer, based on considerations on cost, one drive motor drives each of the rollers, while a clutch controls the rotations. 
     However, in recent years, the speed of image formation has increased. Accordingly, the speed at which recording paper is transported is also increasing. As a result, a lagging in the response in the linking and releasing of the clutch of the intermediate roller has triggered a problem in which the amount of deflection of the recording paper cannot be controlled to be a predetermined amount at the registration roller. Consequently, a position of an image copied on a recording paper might be displaced. 
     Therefore, an image forming apparatus is suggested such that the rotational speed of the intermediate roller is controlled so that the dispersion in the switchover time of the clutch of the intermediate roller is absorbed. As a result, the amount of paper sent out by the intermediate roller is adjusted to be a predetermined amount. In this way, the amount of deflection at the registration roller is maintained to be constant. 
     However, since there is a dispersion in the response time of the registration roller, the amount of time it takes for a recording paper to reach an intermediate copying belt or a photoreceptive drum, located in a down stream side in the direction in which the recording paper is transported, also varies as well. As a result, the position at which an image is copied to a recording paper deviates. 
     SUMMARY OF THE INVENTION 
     In order to achieve the above object, the present invention employs the following. 
     Namely, an image forming apparatus according to an aspect of the present invention includes an image forming unit forming an image on a recording paper, a registration roller transporting the recording paper to the image forming unit, a post-registration roller detection unit provided at a down stream side of the registration roller in a direction in which the recording paper is transported, the post-registration roller detection unit detecting the recording paper transported by the registration roller and a control unit adjusting a timing in which the image forming unit forms the image on the recording paper based on a timing at which the post-registration roller detection unit detects the recording paper. 
     In addition, an image forming method according to an aspect of the present invention includes a registration step transporting a recording paper and registering with a registration roller, a post-registration roller detection step detecting the recording paper, transported by the registration roller, at a down stream side of the registration roller in a direction in which the recording paper is transported and a control step adjusting a timing at which an image is formed on the recording paper based on a timing at which the recording paper is detected in the post-registration roller detection step. 
     Effect of the Invention 
     According to the present invention, the timing at which an image is formed on a recording paper by the image formation unit is adjusted based on a timing at which a post-registration roller detection unit detects the recording paper. 
     In this way, according to the present invention, the timing at which an image is formed may be synchronized based on the timing at which a recording paper, already transported by the registration roller, is detected. As a result, it is possible to prevent a condition in which the position of the image on the recording paper is deviated due to a lag in the response time of the registration roller. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a skeletal configurative diagram of a printer A according to an embodiment of the present invention. 
         FIG. 2  is a diagram showing a paper transporting mechanism of a printer A according to an embodiment of the present invention. 
         FIG. 3  is a diagram showing a condition in which a paper is transported in a printer A according to an embodiment of the present invention. 
         FIG. 4  is a diagram showing another condition in which a paper is transported in a printer A according to an embodiment of the present invention. 
         FIG. 5  is a diagram showing another condition in which a paper is transported in a printer A according to an embodiment of the present invention. 
         FIG. 6  is a diagram showing another condition in which a paper is transported in a printer A according to an embodiment of the present invention. 
         FIG. 7  is a flowchart showing an operation of a printer A according to the above embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, an embodiment of the present invention is described with reference to the attached diagrams. 
     As shown in  FIG. 1 , a printer (image forming apparatus) A according to the present embodiment is connected to a plurality of client computers via a local area network. When a printing instruction is received from a client computer, an image is formed on a recording medium (hereinafter referred to as a recording paper  200 ) based on an electrophotographic method. As shown in  FIG. 1 , the printer A is configured so that a recording paper  200  is provided by a pick up roller  12   a  of a paper feeding unit  12  and paper feeding rollers  12   b.  A timing of a tip of a recording paper  200 , which was transported by an intermediate roller  12   e,  is adjusted at the registration roller  12   f . Thereafter, the recording paper  200  is sent to an image formation unit  13 . 
     Meanwhile, at the image formation unit  13 , an electrostatic latent image is formed on a peripheral surface of a photoreceptor drum  131 , as described later. Then, a toner image is formed based on this electrostatic latent image. 
     The photoreceptor drum  131  is cylindrical. The photoreceptor drum  131  is placed so as to be elongated in a depth direction seen from a front surface of the printer A. The photoreceptor drum  131  is rotated by a drive unit (not diagrammed) such as a motor. The speed of rotation of the drive unit can be adjusted. The photoreceptor drum  131  is rotated in the direction of the peripheral surface when an image is formed. 
     A charging unit  132  is placed opposite to the photoreceptor drum  131 . The charging unit  132  evenly charges a peripheral surface of the photoreceptor drum  131  to a positive or a negative polarity. 
     The laser scanning unit  136  irradiates a laser beam to a peripheral surface of a charged photoreceptor drum  131 . In this way, the laser scanning unit  136  creates an electrostatic latent image on a surface of the photoreceptor drum  131  according to an image data. 
     A development unit  133  provides a toner to a peripheral surface of the photoreceptor drum  131 . In this way, the development unit  133  develops a toner image based on the electrostatic latent image on the peripheral surface of the photoreceptor drum  131 . 
     A cleaning unit  135  removes toner remaining on the photoreceptor drum  131  after a toner image is transferred to a recording paper  200  from the photoreceptor drum  131 , and after a toner is transferred to a recording paper  200  by a transfer roller  134   a , described later. 
     Next, a paper transportation mechanism is described with reference to  FIG. 2 . The intermediate roller  12   e  is driven and rotated by an intermediate roller driving unit  21  connected via an intermediate roller clutch  20 . The intermediate roller  12   e  is provided at an upper stream side of the registration roller  12   f  with respect to a direction in which the recording paper  200  is transported. The intermediate roller  12   e  transports a recording paper  200 , transported from a paper feeding cassette which is not diagrammed, to the registration roller  12   f.  The intermediate roller  12   e  creates a deflection on the recording paper  200 , as shown in  FIG. 3 , between the intermediate roller  12   e  and the registration roller  12   f.    
     The registration roller  12   f  is driven and rotated by a registration roller driving unit  23 , which is connected via the registration roller clutch  22 . The registration roller  12   f  transports a recording paper  200 , transported from the intermediate roller  12   e,  to the transfer roller  134   a.    
     The transfer roller  134   a  is placed opposite to the photoreceptor drum  131 . The transfer roller  134   a  is driven and rotated by a driving source such as a motor and the like. In this way, a recording paper  200  is sandwiched between the transfer roller  134   a  and the photoreceptor drum  131 . The transfer roller  134   a  transfers a toner image, formed upon the photoreceptor drum  131 , on a recording paper  200  by applying a transfer current. After this transfer, the recording paper  200  is transported to fixing rollers  16 . 
     The fixing rollers  16  include a heating roller  16   a  and a pressure roller  16   b.  A heater is included inside the heating roller  16   a.  The pressure roller  16   b  is welded to the heating roller  16   a.  The fixing roller  16  heats the recording paper  200  and applies pressure to the recording paper  200  by transporting and sandwiching the recording paper  200 , to which a toner image has been copied, with two rollers  16   a  and  16   b.  In this way, the fixing rollers  16  fix a toner image on the recording paper  200 . The recording paper  200 , to which a toner image has been fixed by the fixing rollers  16 , is transported to paper ejection rollers  18  which are not diagramed. 
     The pre-registration roller sensor  26  included in the pre-registration roller detection unit is placed between the intermediate roller  12   e  and the registration roller  12   f . In other words, the pre-registration roller sensor  26  is placed in front of the registration roller  12   f  (at an upper stream side) in a direction in which the recording paper  200  is transported. The pre-registration roller sensor  26  emits light towards a transportation path. The pre-registration roller sensor  26  detects a recording paper  200  based on a reflected light. Further, the pre-registration roller  26  outputs the detection result to an image formation engine  24  as a detection signal. 
     The post-registration roller sensor  27  included in the post-registration roller detection unit is placed in the rear of the registration roller  12   f  (at a down stream side) in a direction in which the recording paper  200  is transported. The post-registration roller sensor  27  emits light towards a transportation path. The post-registration roller sensor  27  detects a recording paper  200  based on a reflected light. Further, the post-registration roller  27  outputs the detection result to an image formation engine  24  as a detection signal. 
     Under the control of the image formation engine  24 , the intermediate roller clutch  20  switches to a connected condition or a disconnected condition. Under the connected condition, a rotational driving force from the intermediate roller driving unit  21  can be transmitted to the intermediate roller  12   e.  Under the disconnected condition, the rotational driving force is not transmitted to the intermediate roller  12   e.    
     The intermediate roller driving unit  21  is a driving source of a motor and the like. The intermediate roller driving unit  21  is connected to a roller axis of the intermediate roller  12   e  via the intermediate roller clutch  20 . Under the control of the image formation engine  24 , the intermediate roller driving unit  21  drives and rotates the intermediate roller  12   e.    
     Under the control of the image formation engine  24 , the registration roller clutch  22  switches to a connected condition or a disconnected condition. Under the connected condition, a rotational driving force from the registration roller driving unit  23  can be transmitted to the registration roller  12   f.  Under the disconnected condition, the rotational driving force is not transmitted to the registration roller  12   f.  Therefore, the registration roller clutch  22  can rotate the registration roller  12   f  or halt the rotation of the registration roller  12   f  while maintaining the condition in which the registration roller driving unit  23  is rotated. 
     The registration roller driving unit  23  is a driving source such as a motor. The registration roller driving unit  23  is connected to a roller axis of the registration roller  12   f  via a registration roller clutch  22 . Under the control of the image formation engine  24 , the registration roller driving unit  23  drives and rotates the registration roller  12   f.    
     The display unit  25  is a liquid crystal monitor, for example. The display unit  25  displays various screens including an image and/or a letter based on a signal inputted by the image formation engine  24 . 
     The image formation engine  24  includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and an interface circuit which performs an input and output of signals with each of the components described above. The image formation engine  24  controls the overall operation of the printer A based on a control program stored in the ROM. Incidentally, the control program stored in the ROM includes an image formation control program. The image formation engine  24  controls the timing at which an electrostatic latent image is formed on the photoreceptor drum  131  based on this image formation control program. Incidentally, the details of the operations performed by the image formation engine  24  are given below, with the operations of the printer A being described as an example. 
     Next, a paper supplying operation and a paper transporting operation of a printer A according to the present embodiment are described in detail with reference to  FIGS. 3-6 . 
     First, a user, who is trying to make a printout using the printer A, first operates a client computer (not diagrammed), and transmits a printing instruction to the printer A. 
     When the image formation engine  24  receives a printing instruction from a client computer, and when an image is formed on a first sheet, the deflection of a recording paper  200  is adjusted by adjusting a timing at which the intermediate roller  12   e  is halted based on a timing at which the recording paper  200  is detected by the pre-registration roller sensor  26 , as shown in  FIG. 3  (step S 1 ). In other words, when an image is formed on a first sheet, the image formation engine  24  rotates the intermediate roller  12   e  by switching the condition of the intermediate roller clutch  20  from a disconnected condition to a connected condition. Thus, according to the image formation engine  24 , a recording paper  200 , transported from a paper feeding cassette (not diagrammed), is transported towards the registration roller  12   f  by the intermediate roller  12   e.  Incidentally, at this stage, the rotation of the registration roller  12   f  is halted. Further, when the pre-registration roller sensor  26  detects a first recording paper  200 , and after a predetermined amount of time has passed, the image formation engine  24  switches the condition of the intermediate roller clutch  20  from a connected condition to a disconnected condition. Further, the image formation engine  24  halts the intermediate roller  12   e.  ( FIG. 4 ) Incidentally, the “predetermined amount of time” refers to the period of time from the moment when the recording paper  200  passes through the pre-registration roller sensor  26  to the moment at which a predetermined deflection is formed under a condition in which the recording paper  200  is pressed against the registration roller  12   f.    
     After step S 1 , the image formation engine  24  makes the intermediate roller  12   e  and the registration roller  12   f  wait under a condition in which the rotations are halted and under a condition in which the deflection is formed on the recording paper  200 . During this time, the fixing roller  16  performs initial preparation for forming an image, such as heating. When the initial preparation for forming an image is completed, the condition of the intermediate roller clutch  20  is switched from a disconnected condition to a connected condition, as shown in  FIG. 5 . Thus, the intermediate roller  12   e  is rotated. At the same time, the condition of the registration roller clutch  22  is switched from a disconnected condition to a connected condition. Thus, the registration roller  12   f  is rotated. Further, the recording paper  200  is transported towards the photoreceptor drum  131  (step S 2 ). In this way, while the initial preparation for forming an image is performed, the recording paper  200  is made to wait between the intermediate roller  12   e  and the registration roller  12   f,  instead of waiting at a paper feeding cassette. As a result, an image formation may be started immediately after the initial preparation has been completed. 
     After step S 2 , when the recording paper  200 , transported by the registration roller  12   f,  is detected by the post-registration roller sensor  27 , the image formation engine  24  adjusts a timing at which an image is formed on a recording paper  200  based on a timing at which the post-registration roller sensor  27  detects this recording paper  200  (step S 3 ). In other words, as shown in  FIG. 6 , the image formation engine  24  adjusts the timing at which an image is formed on a recording unit based on a timing at which the post-registration roller sensor  27  detects the recording unit, after the photoreceptor drum  131  rotates, the charging unit  132  evenly charges the surface of the photoreceptor drum  131 , and an electrostatic latent image is formed by the laser scanning unit  136 . In this way, it is possible to prevent the position of the image on the recording paper  200  from deviating. 
     When the image formation in step S 3  is completed, the image formation engine  24  moves on to forming an image on a second sheet. When an image is formed on a second sheet or other subsequent sheets, the image formation engine  24  adjusts the deflection of the recording paper  200  by adjusting a timing at which the registration roller  12   f  is rotated based on a timing at which the recording paper  200  is detected by the pre-registration roller sensor  26  (step S 4 ). In other words, when an image is formed on a second sheet or other subsequent sheets, the image formation engine  24  makes the condition of the intermediate roller clutch  20  a connected condition. Thus, the intermediate roller  12   e  continues to be rotated. At the same time, the image formation engine  24  makes the condition of the registration roller clutch  22  a disconnected condition. Thus, the registration roller  12   f  is halted. Further, when the pre-registration roller sensor  26  detects the second sheet of recording paper  200 , and a predetermined amount of time has passed, the image formation engine  24  makes the condition of the registration roller clutch  22  a connected condition. Thus, the image formation engine  24  makes the registration roller  12   f  rotate. As a result, the recording paper  200  is transported towards the transfer roller  134   a.  Incidentally, the “predetermined amount of time” refers to the period of time from the moment when the recording paper  200  passes through the pre-registration roller sensor  26  to the moment at which a predetermined deflection is formed under a condition in which the recording paper  200  is pressed against the registration roller  12   f.    
     After step S 4 , when the recording paper  200 , transported by the registration roller  12   f,  is detected by the post-registration roller sensor  27 , the image formation engine  24  adjusts the timing at which an image is formed on this recording paper  200  based on the timing at which the recording paper  200  is detected by the post-registration roller sensor  27  (step S 5 ). In other words, similar to step S 3  described above, the image formation engine  24  synchronizes the timing at which an image is formed on the recording paper  200  by making the laser scanning unit  136  create an electrostatic latent image on a peripheral surface of the photoreceptor drum  131  based on a timing at which the recording paper  200  is detected by the post-registration roller sensor  27 . 
     After step S 5 , the image formation engine  24  determines whether or not an image formation has been completed (step S 6 ). When the determination result of step S 6  is “YES,” i.e., when the image formation is completed, the image formation engine  24  halts the operation. When the determination result of step S 6  is “NO,” i.e., when the image formation is not completed, the image formation engine  24  returns to step S 4 , and once again performs steps S 4  and S 5 . 
     As described above, according to the present embodiment, a timing at which an image is formed on a recording paper  200  is adjusted based on a timing at which a post-registration roller sensor  27  detects the recording paper  200 . In this way, according to the present embodiment, a timing of image formation is synchronized based on a timing at which a recording paper  200 , already transported from the registration roller  12   f,  is detected. As a result, it is possible to prevent the position of the image on the recording paper  200  from deviating due to a delay in the responsiveness of the registration roller clutch  22  of the registration roller  12   f.    
     A preferable embodiment of the present invention has been described above. However, the present invention is not limited by the above embodiment. Components and configurations may be added, omitted, replaced, and other alterations may be made within the gist of the present invention. For example, the following variations are possible. 
     In the embodiment described above, the intermediate roller  12   e  and the registration roller  12   f  were controlled using the detection results of the pre-registration roller sensor  26 . In addition, the timing of image formation was adjusted using the detection result of the post-registration roller sensor  27 . However, the present invention is not limited by this configuration. For example, the detection results of the pre-registration roller sensor  26  and the post-registration roller sensor  27  may be used to detect a position at which a recording paper  200  is jammed. 
     In particular, when only the pre-registration roller sensor  26  is detecting the recording paper  200 , the image formation engine  24  detects that a paper jam has occurred near the pre-registration roller sensor  26 . When a detection has not been made by the pre-registration roller sensor  26  and the post-registration roller sensor  27 , the image formation engine  24  determines that a paper jam has occurred at a location in front of the pre-registration roller sensor  26  or at a rear of the post-registration roller sensor  27  in a direction in which the recording paper  200  is transported. When a detection has been made by the pre-registration roller sensor  26  and the post-registration roller sensor  27 , the image formation engine  24  determines that a paper jam has occurred between the pre-registration roller sensor  26  and the post-registration roller sensor  27 . When a detection is made by the post-registration roller sensor  27 , the image formation engine  24  determines that a paper jam has occurred near the post-registration roller sensor  27 . 
     Furthermore, when the image formation engine  24  detects a paper jam as described above, and when only the pre-registration roller sensor  26  has detected the recording paper  200 , the image formation engine  24  makes a display on the display unit  25  indicating that an operation may be conducted by an easy access from a frontal surface such as opening and closing the cassette. When a detection has not been made by the pre-registration roller sensor  26  and the post-registration roller sensor  27 , the image formation engine  24  makes a display on the display unit  25  indicating that an operation may be performed by an access only from a rear side of the machine. When a detection has been made by the pre-registration roller sensor  26  and the post-registration roller sensor  27 , the image formation engine  24  makes a display on the display unit  25  indicating that a desorption of a component or a processing unit such as a photoreceptor drum  131  and a development unit  133 . When a detection is made by the post-registration roller sensor  27 , the image formation engine  24  makes a display on the display unit  25  indicating that an operation may be made by an access only from a rear side of the machine if a sensor of the fixing unit has made the detection. When a detection is made by the post-registration roller sensor  27 , the image formation engine  24  makes a display on the display unit  25  indicating that a desorption of a component or a processing unit such as a photoreceptor drum  131  and a development unit  133 . Furthermore, in cases of a detection of other paper jams, the image formation engine  24  displays an operation according to a conventional manner. (for example, cases in which a recording paper  200  is not sent to a registration unit after the recording paper  200  is fed, and the like) 
     According to the embodiment described above, the intermediate roller  12   e  continued to be rotated when an image was formed on the second sheet and/or other subsequent sheets of recording paper  200 . However, the present invention is not limited to this configuration. Regardless of whether the recording paper  200  is the first sheet, second sheet, or other subsequent sheets, the intermediate roller  12   e  may be halted after a predetermined amount of time has passed after the pre-registration roller sensor  26  detects the recording paper  200 , and a deflection on the recording paper  200  may be adjusted. 
     In addition, the above image forming apparatus may be configured as follows: the image forming apparatus further includes: a pre-registration roller detection unit provided at an upper stream side of the registration roller in the direction in which the recording paper is transported, the pre-registration roller detection unit detecting the recording paper transported by the registration roller; and an intermediate roller provided at a further upstream side of the pre-registration roller detection unit, the intermediate roller transporting the recording paper to the registration roller. Here, the control unit halts the intermediate roller after a predetermined amount of time based on a timing at which the pre-registration roller detection unit detects the recording paper. 
     Here, a disconnected condition may be made when the intermediate roller is halted. 
     Further, the recording paper being transported may be a first sheet on which the image is formed. 
     In addition, the above image forming apparatus may be configured as follows: the control unit detects a position at which the recording paper is jammed based on a detection result of the pre-registration roller detection unit and a detection result of the post-registration roller detection unit. 
     In addition, the above image forming apparatus may be configured as follows: the image forming apparatus further includes an intermediate roller provided at an upper stream side of the registration roller in the direction in which the recording paper is transported, the intermediate roller transporting the recording paper to the registration roller; and a pre-registration roller detection unit provided between the intermediate roller and the registration roller, the pre-registration roller detecting the recording paper transported from the intermediate roller to the registration roller. Here, the control unit rotates the registration roller after a predetermined amount of time based on a timing at which the pre-registration roller detection unit detects the recording paper. Here, the control unit rotates the registration roller after a predetermined amount of time based on a timing at which the pre-registration roller detection unit detects the recording paper. 
     In addition, the above image forming apparatus may be configured as follows: the recording paper being transported is a second sheet on which the image is formed or a subsequent sheet on which the image is formed. 
     In addition, the above image forming method may be configured as follows: the image forming method further includes a pre-registration roller detection step detecting the recording paper, transported by the registration roller, at an upper stream side of the registration roller in a direction in which the recording paper is transported; and a halting step halting an intermediate roller after a predetermined amount of time after the recording paper is detected in the pre-registration roller detection step. Here, the intermediate roller is located at a position at a further upper stream side compared to a position at which the recording paper was detected in the pre-registration roller detection step. The intermediate roller transports the recording paper to the registration roller. 
     The present invention is not limited by the embodiments described above.