Patent Publication Number: US-11383945-B2

Title: Image forming apparatus that controls feeding operation

Description:
BACKGROUND 
     Field 
     The present disclosure relates to an operation in the case in which a recording material remains inside an image forming apparatus, such as a copier or a printer. 
     Description of the Related Art 
     In known image forming apparatuses, such as a copier and a printer, a recording material may remain inside during feeding operation in some cases. In the case in which such a feeding failure (hereinafter referred to as a jam) occurs, it is necessary to remove the remaining recording material from inside the apparatus. 
     Japanese Patent Laid-Open No. 2004-280076 describes an image forming apparatus including a sheet feeding roller that feeds sheets of paper from a cassette to a conveying path and a sensor that is placed on the conveying path and detects sheets. In the case in which the sensor does not detect any sheet of paper for a period from when the sheet feeding operation is started by the sheet feeding roller to when a predetermined period elapses since, the image forming apparatus determines that a sheet feeding delay jam has occurred. 
     The sheet feeding delay jam occurs when, for example, the sheet feeding roller cannot properly feed a sheet of paper placed on the cassette because the sheet feeding roller slips. In this case, if a user does not remove the sheet of paper by opening a cover of the image forming apparatus, the sheet remaining inside the apparatus may be automatically output by the image forming apparatus rotating again, for example, the sheet feeding roller. In this respect, Japanese Patent Laid-Open No. 2004-280076 describes a control in which, only in the case in which a sheet feeding delay jam has occurred, the image forming apparatus automatically recovers from a jam without waiting for a user&#39;s operation for the image forming apparatus, such as an operation for opening the cover. With such a control, the user does not need to open the cover, and thus, the usability of the image forming apparatus is improved. 
     However, sheets cannot be always output automatically when a sheet feeding delay jam occurs. For example, when a sheet of paper is changed in an accordion fold shape in the conveying path at a position between a cassette and a sensor and jammed at the position, the sheet cannot be automatically discharged from the apparatus. Hence, when using the control described in Japanese Patent Laid-Open No. 2004-280076, remaining sheets cannot be removed in some cases and the image forming apparatus thus cannot recover from the jam. 
     SUMMARY 
     According to an aspect of the present disclosure, an image forming apparatus includes a stacking unit configured to stack a recording material, a feeding unit configured to feed the recording material stacked on the stacking unit, a detection unit configured to detect the recording material fed by the feeding unit, a determination unit configured to determine that a feeding failure has occurred when the detection unit does not detect the recording material until a time when a predetermined period elapses since the feeding unit has started a feeding operation for the recording material, a count unit configured to count a number of times the feeding operation is performed for a single sheet of the recording material, and a control unit configured to control the feeding operation for the recording material and to stop the feeding operation when the determination unit determines that the feeding failure has occurred, wherein, in a case in which the number of times the feeding operation is performed that is counted by the count unit by a time when the feeding failure has occurred is smaller than a threshold, the control unit restarts the feeding operation that has been stopped without waiting for a user&#39;s operation for the image forming apparatus, and wherein, in a case in which the number of times the feeding operation is performed that is counted by the count unit by the time when the feeding failure has occurred is equal to or greater than the threshold, the control unit waits for the user&#39;s operation for the image forming apparatus while the feeding operation is stopped. 
     Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an overall configuration diagram of an image forming apparatus. 
         FIG. 2  is a control block diagram of the image forming apparatus. 
         FIGS. 3A to 3C  are timing charts of image forming operation. 
         FIG. 4  is a flowchart when a feeding failure occurs in a first embodiment. 
         FIG. 5  is a flowchart when a feeding failure occurs in a second embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     First Embodiment 
     Overall Configuration Diagram 
     Referring to  FIG. 1 , the overall configuration of a color image forming apparatus is described. In this embodiment, a laser beam printer is used as an example of a color image forming apparatus. 
     Image Forming Section 
     A laser beam printer  100  (hereinafter referred to as the printer  100 ) includes four image forming stations. The first station forms yellow (Y) toner images, the second station forms magenta (M) toner images, the third station forms cyan (C) toner images, and the fourth station forms black (K) toner images. Since each image forming station has the same configuration, the configuration of the first station is described here as a representative. 
     The first station includes a photosensitive drum  1   a . The photosensitive drum  1   a  is formed by laminating multiple layers of functional organic materials including a carrier generating layer on which electric charges are generated by the light applied to a metal cylinder and a charge transport layer that is used to transport the generated electric charges. The outermost layer of the multiple layers has a low electrical conductivity and is an almost insulating layer. In addition, the first station includes a charging roller  2   a . The charging roller  2   a  abuts the photosensitive drum  1   a  and charges uniformly the surface of the photosensitive drum  1   a  while being rotated by the rotation of the photosensitive drum  1   a . A voltage to which a direct current voltage or an alternating current voltage has been added is applied to the charging roller  2   a  and electricity is discharged in fine air gaps positioned upstream and downstream of a contact nip portion between the surface of the charging roller  2   a  and the surface of the photosensitive drum  1   a , and as a result, the photosensitive drum  1   a  is charged. In addition, the first station includes a development unit  8   a . The development unit  8   a  is constituted by a development roller  4   a  abutting the photosensitive drum  1   a , a non-magnetic one-component developer  5   a  (hereinafter referred to as the toner  5   a ), and a developer blade  7   a . In addition, the first station includes a cleaning unit  3   a . The cleaning unit  3   a  cleans untransferred toner remaining on the photosensitive drum  1   a . The photosensitive drum  1   a  to the development unit  8   a  integrally form a process cartridge  9   a  that is attached to a main body of the printer  100  in an attachable and detachable manner. In addition, the first station includes a scanner unit  11   a . The scanner unit  11   a  applies to the photosensitive drum  1   a  a scanning beam  12   a  modulated in accordance with an image signal. The scanner unit  11   a  may be a light emitting diode (LED) array. In addition, the first station includes a primary transfer roller  81   a . A charging bias power source  20   a , a developing bias power source  21   a , and a primary-transfer bias power source  84   a  are coupled respectively to the charging roller  2   a , the development roller  4   a , and the primary transfer roller  81   a  to apply voltage. 
     The configuration of the first station is as described above and the second, third, and fourth stations all have the same configuration. The components of the second, third, and fourth stations are indicated by respectively adding b, c, or d instead of a after the same numerals as those of the components of the first station. 
     An intermediate transfer belt  80  is supported by three rollers as stretching members, namely a secondary transfer facing roller  86 , a drive roller  14 , and a tension roller  15 , and as a result, the tension in the intermediate transfer belt  80  is maintained. The intermediate transfer belt  80  loops in the direction indicated by the arrow in  FIG. 1  by being driven by the drive roller  14 . Discharging members  23   a  to  23   d  are disposed downstream with respect to the respective primary transfer rollers  81   a  to  81   d  in the direction in which the intermediate transfer belt  80  loops. The drive roller  14 , the tension roller  15 , the discharging members  23   a  to  23   d , and the secondary transfer facing roller  86  are electrically grounded. A cleaning roller  88  cleans untransferred toner remaining on the intermediate transfer belt  80 . A cleaning bias power source  89  is coupled to the cleaning roller  88  to apply voltage. 
     Next, an image forming process is described. The photosensitive drum  1   a  in the first station is formed by coating the outer circumferential surface of an aluminum cylinder with an organic photoconductive layer (OPC). The photosensitive drum  1   a  is supported by flanges at its both ends in a rotatable manner and rotates in the direction indicated by the arrow in  FIG. 1  by the driving force transmitted from a drive motor not illustrated in the drawing to one end of the photosensitive drum  1   a . The photosensitive drum  1   a  and the intermediate transfer belt  80  moves at substantially the same speed. The charging roller  2   a  is a conductive roller. The charging roller  2   a  abuts the surface of the photosensitive drum  1   a  and charging bias voltage is applied to the charging roller  2   a  by the charging bias power source  20   a , and as a result, the surface of the photosensitive drum  1   a  is uniformly charged. The scanner unit  11   a  includes a polygon mirror to which a beam of light corresponding to an image signal is applied by a laser diode not illustrated in the drawing. In this manner, the scanner unit  11   a  forms an electrostatic latent image on the photosensitive drum  1   a . The development roller  4   a , which abuts the photosensitive drum  1   a , is rotated by the drive of a drive motor not illustrated in the drawing and voltage is applied to the development roller  4   a  by the developing bias power source  21   a , and as a result, the development roller  4   a  supplies the yellow toner  5   a  to the photosensitive drum  1   a . In this manner, the development roller  4   a  forms a toner image on the photosensitive drum  1   a . Following the same image forming process, toner images are formed on photosensitive drums  1   b  to  1   d  in the second, third, and fourth stations. As described above, a magenta toner image is formed on the photosensitive drum  1   b , a cyan toner image is formed on the photosensitive drum  1   c , and a black toner image is formed on the photosensitive drum  1   d . The primary transfer rollers  81   a  to  81   d  are disposed on the inner side of the intermediate transfer belt  80  such that the primary transfer rollers  81   a  to  81   d  are in contact with the intermediate transfer belt  80  while respectively facing the four photosensitive drums  1   a  to  1   d . By applying voltage to the primary transfer rollers  81   a  to  81   d  from primarily-transfer bias power sources  84   a  to  84   d , negatively charged toner images formed on the photosensitive drums  1   a  to  1   d  are transferred in series on the intermediate transfer belt  80 . In this manner, a color toner image is formed on the intermediate transfer belt  80 . 
     Sheet Feeding Conveyance Section 
     Multiple sheets of paper P (recording materials) are placed on a cassette  16  (a stacking unit). When the sheets of paper P are fed from the cassette  16 , firstly, the cassette bottom plate  29  is lifted up by driving a lift-up motor (not illustrated), and as a result, the sheets of paper P placed on the cassette  16  are lifted up. When a sheet plane sensor  40  detects the sheets of paper P, the lift-up operation accordingly ends. The topmost sheet of the sheets of paper P that have been lifted up comes into contact with a pickup roller  17  and the sheets of paper P are individually fed by the rotation of the pickup roller  17 . A registration sensor  35  detects the leading edge of the sheet of paper P that is fed. Here, the leading edge of the sheet of paper P denotes the edge positioned downstream in the transport direction of the sheet of paper P. Conveying the sheet of paper P continues for a predetermined period after the registration sensor  35  detects the leading edge of the sheet of paper P, and when the leading edge of the sheet of paper P reaches a temporary stop position  36 , conveying the sheet of paper P is suspended. 
     Subsequently, conveying the sheet of paper P that has been fed by the pickup roller  17  is restarted by a registration roller  18 . The registration roller  18  conveys the sheet of paper P to a secondary transfer position so as to match the leading edge of the image formed on the intermediate transfer belt  80  with the leading edge of the sheet of paper P at a merge point  37 . The secondary transfer position is a contact portion between a secondary transfer roller  82  and the intermediate transfer belt  80 . A secondary-transfer bias power source  85  is coupled to the secondary transfer roller  82  to apply voltage. When the sheet of paper P is conveyed, by applying voltage to the secondary transfer roller  82 , an electric field is formed between the secondary transfer roller  82  and the secondary transfer facing roller  86  that are placed to face each other and dielectric polarization occurs between the intermediate transfer belt  80  and the sheet of paper P. This causes electrostatic attraction force between the intermediate transfer belt  80  and the sheet of paper P. As a result, the toner image formed on the intermediate transfer belt  80  is transferred to the sheet of paper P. 
     Fixing Section 
     A fixing unit  19  applies heat and pressure to the sheet of paper P and fixes the transferred toner image on the sheet of paper P. The fixing unit  19  includes a fixing belt and an elastic pressure roller. While the fixing belt is sandwiched between the elastic pressure roller and a belt guide member not illustrated in the diagram, the elastic pressure roller and the belt guide member form a fixing nip portion of a given length to cause a given level of contact pressure at the fixing nip portion. In the state in which the temperature of the fixing nip portion is adjusted to a predetermined temperature, the sheet of paper P on which the unfixed toner image is formed is conveyed to the fixing nip portion between the fixing belt and the elastic pressure roller. At this time, the sheet of paper P enters the fixing nip portion such that the image plane faces upward, that is, faces the fixing belt, and is conveyed in a sandwiched manner along with the fixing belt through the fixing nip portion while the image plane is in close contact with the outer surface of the fixing belt. In the process in which the sheet of paper P is conveyed in a sandwiched manner along with the fixing belt through the fixing nip portion, heat is applied to the sheet of paper P at the fixing belt, and as a result, the toner image that has been unfixed is fixed on the sheet of paper P by the heat. Subsequently, the sheet of paper P on which the toner image is fixed is output to an output tray  38  from the fixing unit  19 . 
     Control Block Diagram 
       FIG. 2  is a block diagram illustrating a system configuration of the printer  100 . A controller  201  is configured to execute mutually communicate with a host computer  200  and an engine controller  202 . The controller  201  receives image information and a print instruction from the host computer  200 , analyzes the received image information, and converts the image information into bit data. The controller  201  then transmits for each sheet of paper P a print start instruction and a video signal to a central processing unit (CPU)  211  and an image processing GA  212  via a video interface unit  210 . 
     The controller  201  transmits to the CPU  211  via the video interface unit  210  information about print color mode selection (information about monochrome printing or color printing) according to the print instruction transmitted from the host computer  200 . When printing can be started, the controller  201  transmits the print start instruction to the CPU  211  via the video interface unit  210 . The CPU  211  prepares for printing in accordance with the information transmitted from the controller  201  and waits for the print start instruction transmitted from the controller  201 . When receiving the print start instruction, the CPU  211  instructs control units (an image forming control unit  213 , a fixing control unit  214 , and a sheet feeding conveyance control unit  215 ) to start printing operation in accordance with the printing condition determined by the controller  201 . 
     When receiving an instruction for starting printing operation, the image forming control unit  213  starts preparing for image forming. When notified by the image forming control unit  213  that the preparation for image forming is completed, the CPU  211  outputs to the controller  201  a /TOP signal that indicates a basic time at which a video signal is output. When receiving the /TOP signal from the CPU  211 , the controller  201  outputs video signals corresponding to the respective colors at the basic time indicated by the /TOP signal. When receiving the video signals from the controller  201 , the image processing GA  212  transmits image forming data to the image forming control unit  213 . The image forming control unit  213  forms an image in accordance with the image forming data received from the image processing GA  212 . 
     When receiving the instruction for starting printing operation, the sheet feeding conveyance control unit  215  starts a sheet feeding operation (a feeding operation). The sheet feeding conveyance control unit  215  causes the pickup roller  17  to rotate by rotating a stepping motor  240  as a sheet feeding motor by using a motor-driver integrated circuit (IC) not illustrated in the drawing and then starting a pickup solenoid  241  after a predetermined period. In this manner, the sheet of paper P is fed from the cassette  16 . The sheet feeding conveyance control unit  215  stops conveying the sheet of paper P in a temporary manner at the time when the leading edge of the sheet of paper P reaches the temporary stop position  36  in accordance with e time when the registration sensor  35  detects the leading edge of the sheet of paper P that is fed. The CPU  211  projects, in accordance with the /TOP signal as the basic time, the time when the position of the leading edge of the toner image formed on the intermediate transfer belt  80  reaches the merge point  37 . The CPU  211  instructs the sheet feeding conveyance control unit  215  to restart the temporary stopped conveyance of the sheet of paper P in such a manner as to not miss the projected time. The sheet feeding conveyance control unit  215  accordingly restarts conveying the sheet of paper P in response to the instruction for restarting the conveyance of the sheet of paper P as a result, the toner image can be transferred to the desired or predetermined position of the sheet of paper P. 
     When the registration sensor  35  does not detect the leading edge of the sheet of paper P for a period from when the sheet feeding operation is started by the pickup roller  17  to when a predetermined period elapses since, the sheet feeding conveyance control unit  215  determines that a sheet feeding failure (a feeding failure) has occurred. The sheet feeding failure that has occurred here is a sheet feeding delay jam. The sheet feeding conveyance control unit  215  notifies the controller  201  of sheet feeding failure information via the video interface unit  210 . The controller  201  displays on a display  203 , which is, for example, an operation panel, information that needs to be reported to a user on the basis of the sheet feeding failure information received from the engine controller  202 . 
     When receiving the instruction for starting printing operation, the fixing control unit  214  starts preparing for fixing. The fixing control unit  214  starts adjusting the temperature in accordance with printing information to not miss the time when the sheet of paper P on which the toner image has been transferred is conveyed to the fixing control unit  214 . The fixing control unit  214  fixes the toner image on the sheet of paper P and then outputs the sheet of paper P to the output tray  38 . 
     Feeding Failure Cases 
     The sheet feeding failure described above, that is, the sheet feeding delay jam is described in detail. The sheet feeding delay jam is divided into the following three cases. 
     The first case: the state in which the sheet of paper P is fed by the pickup roller  17  from the cassette  16  to the conveying path, but the leading edge of the sheet of paper P the leading edge of the sheet of paper P stops in the conveying path at a position beyond the cassette  16  and cannot reach the registration sensor  35  (the shape of the sheet of paper P is not changed). 
     The second case: the sheet of paper P placed on the cassette  16  cannot be properly picked up by the pickup roller  17  and remains in the cassette  16  (the shape of the sheet of paper P is not changed). 
     The third case: the leading edge of the sheet of paper P is stuck in the conveying path at a position before the registration sensor  35  and the sheet of paper P is jammed in a changed shape. 
     The first case is caused by the decrease in conveying force due to the abrasion of the pickup roller  17 . The conveying force of the pickup roller  17  is affected by the type of the sheet of paper P placed on the cassette  16 . The third case is likely to occur when the leading edge of the sheet of paper P placed on the cassette  16  is folded. 
     It is considered that the second case is caused when, for example, the sheet of paper P is not placed at a proper position on the cassette  16 . For example, the position of the trailing edge guide plate that guides the position of the trailing edge of the sheet of paper P is inappropriate. As another cause, it is considered that a user may stack on the cassette  16  the sheets of paper P more than a predetermined number (overstacking). Among these cases of sheet feeding delay jam, the second case that is caused by the user&#39;s erroneous operation is most likely to occur in the market. 
     Among these cases, in the third case, to restart the printing operation and the sheet feeding operation performed by the printer  100 , the user needs to remove the sheet of paper P from inside the apparatus. This is because the shape of the jammed sheet of paper P is changed and the sheet of paper P thus cannot be automatically output from the apparatus. By contrast, in the first and second cases, since the shape of the sheet of paper P is not changed, the sheet of paper P may be automatically output to outside the apparatus. When the sheet of paper P can be automatically output to outside the apparatus, the printer  100  can restart the printing operation and the sheet feeding operation without the user&#39;s operation for removing the sheet of paper P from inside the apparatus. 
     Since the known image forming apparatuses cannot distinguish these three cases from each other, the known image forming apparatuses notifies the user of the occurrence of sheet feeding failure in every case and every time displays for the user on the display  203  a message indicating that the sheet inside the apparatus should be removed. In other words, the known image forming apparatuses suggest the user&#39;s operation performed for the printer  100  also in the first and second cases in which the printer  100  can automatically recover without the user&#39;s operation for removing the sheet of paper P, and as a result, the usability is reduced. Especially in the second case, since no sheet of paper P stops in the conveying path, the user cannot find the sheet of paper P to be removed when opening a cover or the cassette  16  of the printer  100 . As a result, the usability is reduced. 
     Similarly, to the known image forming apparatuses, the printer  100  according to this embodiment also cannot distinguish the three cases from each other, but the printer  100  calculates which case has occurred in accordance with the number of times the sheet had been fed until the sheet feeding failure occurred and determines whether the user&#39;s recovery operation is necessary. When it is determined that the user&#39;s recovery operation is unnecessary, the printer  100  notifies the user of only the event in which the sheet feeding failure has occurred and does not provide the user with a message for suggesting the user&#39;s operation for the printer  100 , such as a message indicating that the sheet inside the apparatus should be removed. Subsequently, the printer  100  automatically returns to the normal condition. When it is determined that the user&#39;s recovery operation is necessary, the printer  100  notifies the user of the event in which the sheet feeding failure has occurred and provides the user with the message for suggesting the user&#39;s operation for the printer  100 . Subsequently, the printer  100  waits for the user&#39;s recovery operation. 
     Timing Charts of Normal Image Forming Control 
       FIGS. 3A to 3C  are timing charts of image forming performed by the printer  100  according to this embodiment. Firstly, referring to  FIG. 3A , the normal image forming control is described. 
     When receiving a print start instruction from the controller  201 , the engine controller  202  starts preparing for image forming. After the preparation is completed, the engine controller  202  outputs a /TOP signal ( 311   a ) to the controller  201 . When receiving the /TOP signal ( 311   a ), the controller  201  outputs video signals corresponding to yellow, magenta, cyan, and black, which are not illustrated in the timing chart, and forms images. In the case in which the engine controller  202  receives multiple print start instructions from the controller  201 , the engine controller  202  outputs a subsequent /TOP signal ( 312   a ) in accordance with the image size and the image interval. 
     A sheet feeding motor ( 320 ) is driven at the time when the engine controller  202  receives a print start instruction from the controller  201 . Subsequently, a sheet feeding pickup solenoid ( 330 ) is driven for a predetermined period ( 331   a ) and the sheet of paper P placed on the cassette  16  is fed. The registration sensor  35  detects the leading edge of the sheet of paper P that is being fed ( 341   a ), and the engine controller  202  then controls the sheet of paper P to be conveyed to the temporary stop position  36  and stops conveying the sheet of paper P at the temporary stop position  36  in a temporary manner ( 321   a ). The engine controller  202  restarts conveying the sheet of paper P ( 313   a ) miss the time when the leading edge of the toner image formed on the intermediate transfer belt  80  reaches the merge point  37  ( 314   a ), and as a result, an image is formed at a desired or predetermined position of the sheet of paper P. With regard to the second and subsequent sheets of paper P, the sheet of paper P is not stopped at the temporary stop position  36 , but the engine controller  202  controls the speed of the sheet feeding motor ( 320 ) in accordance with the time when the registration sensor  35  detects the leading edge of the sheet of paper P ( 342   a ). The engine controller  202  accelerate or decelerate ( 322   a ) the speed of the sheet feeding motor ( 320 ) to match the leading edge of the sheet of paper P with the leading edge of the toner image at the merge point  37 . Periods of sheet feeding failure window ( 351   a  and  352   a ) are periods in which the engine controller  202  determines the occurrence of sheet feeding failure. Details of the sheet feeding failure window intervals will be described later. 
     Timing Chart When Feeding Failure Occurs 
       FIGS. 3B and 3C  are timing charts when a sheet feeding failure occurs.  FIG. 3B  is a timing chart when a sheet feeding failure occurs in the case in which the sheet feeding counter indicates 1.  FIG. 3C  is a timing chart when a sheet feeding failure occurs in the case in which the sheet feeding counter indicates 2. Here, the sheet feeding counter counts the number of times the sheet feeding operation is performed by the pickup roller  17 . 
     The image forming operation and the sheet feeding operation for the first sheet of paper is the same as those described with reference to  FIG. 3A  and the control for the second sheet is described below. At the time when the sheet feeding pickup solenoid is driven in the feeding control, 1 is added to the count of the sheet feeding counter ( 360 ). When the leading edge of the sheet of paper P is properly detected by the registration sensor  35 , 1 is subtracted from the count of the sheet feeding counter. A jam window ( 350 ) corresponds to periods ( 331   b  to  314   b  and  332   b  to  315   b ), which is from the time when the sheet feeding pickup solenoid is driven in the feeding control to the time when the leading edge of the image formed on the intermediate transfer belt  80  reaches the merge point  37 . 
     The /TOP signal for the second sheet ( 312   b ) is output after the period corresponding to the image size and the image interval elapses since the /TOP signal for the first sheet ( 311   b ) has been output. The sheet feeding operation for the second sheet is performed after the period corresponding to the sheet size and the feeding interval elapses since the first sheet has been fed ( 331   b ). Specifically, the engine controller  202  drives the sheet feeding pickup solenoid for the second sheet for a predetermined period ( 332   b ), as a result, the second sheet of paper P is fed. At the time of starting the sheet feeding pickup solenoid for the second sheet ( 332   b ), 1 is added to the count of the sheet feeding counter. 
     The sheet feeding conveyance control unit  215  then waits until the registration sensor  35  detects the leading edge of the sheet of paper P. In the case in which the registration sensor  35  does not detect the leading edge of the sheet of paper P until the period of the sheet feeding failure window ( 352   b ) passes, the sheet feeding conveyance control unit  215  determines that a sheet feeding failure has occurred ( 353   b ) and compares the present value of the sheet feeding counter ( 360 ) and a threshold. In this embodiment, the threshold is set as 2. In the case of  FIG. 3B , the value of the sheet feeding counter ( 360 ) is 1 and the threshold is 2, and therefore, the sheet feeding counter (1)&lt;the threshold (2). 
     In this case, the sheet feeding conveyance control unit  215  determines that the present case is probably a no pick-up sheet feeding failure, that is, the second case of sheet feeding delay jam, and notifies the controller  201  of the determination result via the video interface unit  210 . The determination is made by using the concept as follows. As described above, the second case of sheet feeding failure is most likely to occur in the market. Therefore, in this embodiment, when the value of the sheet feeding counter ( 360 ) is 1, it is determined that the second case of sheet feeding failure has occurred. 
     When receiving the notification about the second case of the sheet feeding failure from the engine controller  202 , the controller  201  notifies the user of only the event in which the sheet feeding failure has occurred via the display  203  and automatically performs the recovery operation. At this time, the controller  201  does not provide via the display  203  a message for suggesting the user&#39;s operation for the printer  100 . The recovery operation here includes, for example, the operation of automatically outputting the sheet of paper P remaining in the apparatus and the operation of cleaning the image formed on the photosensitive drums  1   a  to  1   d  and the intermediate transfer belt  80 . 
       FIG. 3C  is a timing chart illustrating the printing operation after a sheet feeding failure has occurred in  FIG. 3B  and the automatic recovery operation has been accordingly performed. When receiving a /TOP signal ( 311   c ), the controller  201  starts image forming. The sheet feeding motor ( 320 ) starts when a print start instruction is received from the controller  201 . The engine controller  202  then drives the sheet feeding pickup solenoid ( 330 ) for a predetermined period ( 331   c ) and causes the sheet of paper P placed on the cassette  16  to be fed. 
     The sheet feeding conveyance control unit  215  adds 1 to the count of the sheet feeding counter ( 360 ) at the time of the sheet feeding operation ( 331   c ). Afterwards, in the case in which the registration sensor  35  detects the leading edge of the sheet of paper P by the time when a predetermined period elapses, the sheet feeding conveyance control unit  215  sets the value of the sheet feeding counter as 0 and properly performs the printing operation. 
     Conversely, in the case in which the registration sensor  35  does not detect the leading edge of the sheet of paper P by the time when the predetermined period elapses, the sheet feeding conveyance control unit  215  retries the sheet feeding operation ( 332   c ). Concerning the first sheet of paper P, since the time spent until the leading edge of the image reaches the merge point  37  is long, there is still enough time after the sheet feeding is succeeded in the sheet feeding operation that is retried. The sheet feeding conveyance control unit  215  adds 1 to the count of the sheet feeding counter ( 360 ) at the time of retrying the sheet feeding operation ( 332   c ). The sheet feeding conveyance control unit  215  then waits until the registration sensor  35  detects the leading edge of the sheet of paper P. In the case in which the registration sensor  35  does not detect the leading edge of the sheet of paper P until the period of a sheet feeding failure window ( 351   c ) passes, the sheet feeding conveyance control unit  215  determines that a sheet feeding failure has occurred ( 352   c ) and compares the present value of the sheet feeding counter ( 360 ) and the threshold. In the case of  FIG. 3C , the value of the sheet feeding counter ( 360 ) is 3 and the threshold is 2, and therefore, the sheet feeding counter (3)≥the threshold (2). 
     In this case, the sheet feeding conveyance control unit  215  determines that the present case is probably the third case of sheet feeding delay jam and notifies the controller  201  of the determination result via the video interface unit  210 . The determination is made by using the concept as follows. By the time when the present sheet feeding occurs, the sheet feeding operation has been performed twice. In the case in which a sheet feeding failure occurs after the sheet feeding operation has been performed twice, the sheet feeding failure may be caused by a reason other than no pick-up, such as an issue in the conveying path. Therefore, in this embodiment, when the value of the sheet feeding counter ( 360 ) is 2 or more, it is determined that the third case of sheet feeding failure has occurred. 
     When receiving the notification about the third case of sheet feeding failure from the engine controller  202 , the controller  201  notifies, via the display  203 , the user of the event in which the sheet feeding failure has occurred and the suggestion for removing the remaining sheet from the conveying path. The user accordingly checks the remaining sheet, and when necessary, removes the remaining sheet, and then instructs, via the display  203 , the printer  100  to perform the recovery operation. 
     Flowchart When Sheet Feeding Failure Occurs 
       FIG. 4  is a flowchart when a feeding failure occurs in this embodiment. The control following the process illustrated as the flowchart in  FIG. 4  is performed by the engine controller  202  in accordance with a program stored in a read only memory (ROM) or a random access memory (RAM) that are not illustrated in the drawing. 
     Firstly, when the print start instruction is received from the controller  201 , the CPU  211  instructs the sheet feeding conveyance control unit  215  to perform sheet feeding. The sheet feeding conveyance control unit  215  drives the stepping motor  240 , and then drives the pickup solenoid  241  for a predetermined period, and as a result, the sheet of paper P placed on the cassette  16  is fed (S 401 ). The sheet feeding conveyance control unit  215  then adds 1 to the count of the sheet feeding counter (S 402 ). In S 403 , the sheet feeding conveyance control unit  215  determines whether the registration sensor  35  detects the leading edge of the sheet of paper P. 
     When the registration sensor  35  detects the leading edge of the sheet of paper P, the sheet feeding conveyance control unit  215  subtracts 1 from the count of the sheet feeding counter in S 404 . The process then proceeds to S 405 . In S 405 , in accordance with the position of the leading edge of the image formed on the intermediate transfer belt  80  and the time when the registration sensor  35  detects the leading edge of the sheet of paper R it is determined whether the sheet feeding conveyance control unit  215  needs to perform acceleration or deceleration control. 
     In the case in which both the acceleration and deceleration controls are unnecessary, for example, in the case in which the sheet feeding operation is performed for the first sheet, the sheet feeding conveyance control unit  215  causes the sheet of paper P to be conveyed to the temporary stop position (S 406 ) and then stops the stepping motor  240  (S 407 ). The sheet feeding conveyance control unit  215  subsequently restarts conveying the sheet of paper P to not miss the timing of moving the image formed on the intermediate transfer belt  80  (S 408 ). In the case in which the acceleration or deceleration control is necessary, for example, in the case in which the sheet feeding operation is performed for the second or subsequent sheet during continuous printing, the sheet feeding conveyance control unit  215  accelerates or decelerates the speed of the stepping motor  240  and causes the sheet of paper P to be conveyed in such a manner as to not miss the timing of moving the image formed on the intermediate transfer belt  80  (S 409 ). 
     By contrast, in the case in which it is determined in S 403  that the registration sensor  35  does not detect the leading edge of the sheet of paper P, the sheet feeding conveyance control unit  215  checks the sheet feeding failure window in S 410 . When the period of the sheet feeding failure window has not passed, the sheet feeding conveyance control unit  215  determines in S 415  whether sheet feeding can be performed at this time. Whether sheet feeding can be performed at this time is determined in most cases in accordance with whether the pickup roller  17  has rotated one revolution at the time. In the case in which it is determined in S 415  that sheet feeding can be performed at this time, the process returns to S 401  and the sheet feeding conveyance control unit  215  retries sheet feeding. In the case in which it is determined in S 415  that sheet feeding cannot be performed at this time, the process returns to S 403  and the sheet feeding conveyance control unit  215  waits again until the leading edge of the sheet of paper P is detected. 
     In the case in which the registration sensor  35  does not detect the leading edge of the sheet of paper P by the time when it is determined in S 410  that the period of the sheet feeding failure window has passed, the sheet feeding conveyance control unit  215  compares the value of the sheet feeding counter and the threshold (S 411 ). In the case in which it is determined in S 411  that the value of the sheet feeding counter is equal to or greater than the threshold, the sheet feeding conveyance control unit  215  notifies the controller  201  that the third case of sheet feeding failure has occurred. When receiving the notification of the occurrence of the third case of sheet feeding failure, the controller  201  notifies, via the display  203 , the user of the occurrence of sheet feeding failure and suggests to the user checking the remaining sheet in the conveying path and checking the placement condition of the sheet of paper P on the cassette  16  (S 412 ). After performing the necessary operation, the user notifies, via, for example, the display  203 , the controller  201  of the completion of the user&#39;s operation. The controller  201  checks the completion of the operation (S 413 ) and performs the recovery operation of the printer  100  (S 414 ). 
     In the case in which it is determined in S 411  that the value of the sheet feeding counter is less than the threshold, the sheet feeding conveyance control unit  215  notifies the controller  201  that the second case of sheet feeding failure has occurred. When receiving the notification indicating that the second case of sheet feeding failure has occurred, the controller  201  notifies, via the display  203 , the user of the occurrence of sheet feeding failure (S 416 ). The sheet feeding conveyance control unit  215  then automatically performs the recovery operation of the printer  100  (S 417 ). 
     As described above, in this embodiment, when a sheet feeding failure has occurred, the condition of the sheet remaining inside the apparatus is calculated in accordance with the number of times the sheet feeding operation has been performed in the preceding period and corresponding operations are performed accordingly, and as a result, the usability can be improved/refined. 
     Second Embodiment 
     In this embodiment, the threshold is changed in accordance with the type of the sheet of paper P placed on the cassette  16  in the first embodiment. The main part of this embodiment is identical to that of the first embodiment and only the part different from that of the first embodiment is described here. 
     In the description of the cassette  16  according to the first embodiment, the lift-up operation is mentioned. The lift-up operation is such that the sheet plane sensor  40  measures the position of the sheet plane of the topmost sheet of the sheets of paper P stacked on the cassette  16  and lifting up the cassette bottom plate  29  is accordingly stopped at an appropriate position. In this manner, the level of the sheet plane is maintained at a level appropriate for the sheet feeding operation. In the lift-up operation, the appropriate level cannot be measured when a particular type of the sheet of paper P is placed on the cassette  16 . 
     In the description of the first embodiment, it is assumed to use a sheet of plain paper. In this embodiment, for example, it is assumed to place on the cassette  16  a type of the sheet of paper P that is relatively thick, such as an envelope. When the cassette  16  is opened and then closed, the lift-up operation is performed until the sheet plane sensor  40  enters in an ON state. In the configuration in which the pickup roller  17  is movable, as the result of bringing down the pickup roller  17  into contact with the envelope after the lift-up operation, the level of the sheet plane may be lower than that of plain paper due to the weight of the pickup roller  17  or the thickness of the envelope. This is because the air layer inside the envelope is constricted. When the condition of the sheet plane sensor  40  is changed from the ON state to an OFF state, it is accordingly determined that the level of the sheet plane is lowered. In this situation, the level of the sheet plane is not maintained at an appropriate level, and thus, the printer  100  needs to perform an operation to deal with this condition, such as an additional lift-up operation. 
     Flowchart of Feeding Control in Accordance with this Embodiment 
       FIG. 5  is a flowchart of feeding control according to this embodiment. The control following the process illustrated as the flowchart in  FIG. 5  is performed by the engine controller  202  in accordance with a program stored in a ROM or a RAM that are not illustrated in the drawing. The detailed description of the steps except for S 503 , S 504 , and S 513  is omitted because they are identical to the corresponding steps in the first embodiment. 
     When the sheet feeding operation is started (S 501 ), the sheet feeding conveyance control unit  215  performs a lift-up operation and then brings the pickup roller  17  into contact with the sheet of paper P. In S 503 , the sheet feeding conveyance control unit  215  determines whether the sheet plane sensor  40  can detect the sheet plane without any change. In the case in which the sheet plane sensor  40  cannot detect the sheet plane, it is assumed that the level of the sheet plane is lower than expected as the result of bringing the pickup roller  17  into contact with the sheet plane as described above. In this case, the sheet feeding conveyance control unit  215  performs an additional lift-up operation (S 504 ). 
     In S 513 , the sheet feeding conveyance control unit  215  determines the threshold in accordance with the type of the sheet of paper P placed on the cassette  16 . The type of the sheet placed on the cassette  16  is determined in accordance with the information about a user selection media received from the controller  201  via the video interface unit  210 . In this embodiment, it is assumed that the information about the user selection media received from the controller  201  indicates envelope and the threshold is changed from 2 for plain paper to 4 for envelope. In S 514 , the threshold (4) that has been changed and the value of the sheet feeding counter are compared with each other, and accordingly, the details of the sheet feeding failure is determined as described above. Specifically, no pick-up is more likely to occur in the case of envelope compared to the case of plain paper, and therefore, the threshold, in accordance with which it is determined that the third case of sheet feeding delay jam occurs, is determined as a greater number than that of plain paper. Since the threshold in the case of envelope is 4, the sheet feeding operation illustrated in  FIG. 3C  is repeated twice. 
     As described above, in this embodiment, the condition of the sheet remaining inside the apparatus is more highly accurately calculated by changing the threshold in accordance with the type of the sheet of paper P and corresponding operations are performed accordingly, and as a result, the usability can be improved/refined. 
     While this embodiment describes the case in which the threshold is changed by using the information about a user selection media reported from the controller  201 , the case should not be construed in a limiting sense. The threshold may be changed in accordance with, for example, the determination result of whether the type of the sheet of paper P placed on the cassette  16  is plain paper or envelope, which is determined by determining whether the sheet plane sensor  40  has entered in the OFF state as in S 503  in the flowchart in  FIG. 5 . 
     Furthermore, while this embodiment describes the control in which the movable pickup roller  17  is brought into contact with the sheet of paper P after the lift-up operation, the configuration should not be construed in a limiting sense. When the information about the user selection media can be obtained anytime from the controller  201 , the pickup roller  17  is not necessarily movable. 
     Moreover, while the first and second embodiments describe the configuration in which the sheet of paper P is fed from the cassette  16  attached to the main body of the printer  100  in an attachable and detachable manner, the configuration should not be construed in a limiting sense. The present disclosure can be applied to the configuration in which the sheet of paper P is fed from a manual feeding tray (not illustrated) attached to the main body of the printer  100  in a non-detachable manner. Here, the manual feeding tray is a stacking unit that is exposed outside the main body of the printer  100  and on which the sheet of paper P can be placed. 
     Further, the first and second embodiments describe the example of a laser beam printer, the image forming apparatus to which the present disclosure is applied is not limited to this example and may be a printer using another printing method, such as an ink jet printer, or a copier. 
     In the present disclosure, when a feeding failure has occurred, the condition of the sheet remaining inside the apparatus is calculated and a corresponding operation is performed accordingly, and as a result, the usability can be improved/refined. 
     Embodiment(s) of the present disclosure can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may include one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random access memory (RAM), a read-only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like. 
     While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2018-125008, filed Jun. 29, 2018, which is hereby incorporated by reference herein in its entirety.