Patent Publication Number: US-11660882-B2

Title: Image forming apparatus including jam detection part provided with photoelecetric sensor

Description:
INCORPORATION BY REFERENCE 
     This application is based on and claims the benefit of priority from Japanese patent application No. 2020-162191 filed on Sep. 28, 2020, which is incorporated by reference in its entirety. 
     BACKGROUND 
     The present disclosure relates to an image forming apparatus which forms an image on a sheet. 
     An apparatus in which a document is read by a reading device disposed below a target glass while the document passes a document conveyance path is known. In the apparatus, by passing a cleaning sheet in place of the document through the document conveyance path, the target glass (the document conveyance path) is cleaned. 
     However, in the above-described technique, it is difficult to know a cleaning time for the target glass (the document conveyance path). Therefore, in the above-described technique, the cleaning operation can be performed only after the occurrence of reading failure or conveyance failure of the document. 
     SUMMARY 
     In accordance with an aspect of the present disclosure, an image forming apparatus includes a reflective photoelectric sensor and a controller. The reflective photoelectric sensor emits light to an object to be detected, receives the light reflected on the object and outputs an electric signal corresponding to a quantity of the reflected light. The object to be detected includes a facing surface area and a sheet on the facing surface area. The controller detects whether the sheet exists on the facing surface area in accordance with an output of the photoelectric sensor. The controller stores, as a threshold of the output of the photoelectric sensor, a first threshold for determining that the sheet does not exist on the facing surface area and a second threshold for determining that the sheet exists on the facing surface area, and determines that the facing surface area is contaminated to cause decreasing in the quantity of reflected light when the output of the photoelectric sensor is within a range between the first threshold and the second threshold. 
     The other features and advantages of the present disclosure will become more apparent from the following description. In the detailed description, reference is made to the accompanying drawings, and preferred embodiments of the present disclosure are shown by way of example in the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a sectional view schematically showing an image forming apparatus according to one embodiment of the present disclosure. 
         FIG.  2    is a block diagram showing a controller and the others of the image forming apparatus according to the embodiment of the present disclosure. 
         FIG.  3    is a sectional view showing a part of a right side portion of the image forming apparatus according to the embodiment of the present disclosure. 
         FIG.  4    is an enlarged sectional view showing a downstream side portion of a first conveyance path in the image forming apparatus according to the embodiment of the present disclosure. 
         FIG.  5    is an enlarged sectional view showing the downstream side portion (during the sheet conveying) of the first conveyance path in the image forming apparatus according to the embodiment of the present disclosure. 
         FIG.  6    is a graph showing an output of a photoelectric sensor in the image forming apparatus according to one embodiment of the present disclosure. 
         FIG.  7    is a flowchart showing a jam detection method in the image forming apparatus according to the embodiment of the present disclosure. 
         FIG.  8    is a block diagram showing a controller and the others in a first modified example of the image forming apparatus according to the embodiment of the present disclosure. 
         FIG.  9    is a flowchart showing a gam detection method in the first modified example of the image forming apparatus according to the embodiment of the present disclosure. 
         FIG.  10    is a block diagram showing a controller and the others in a second modified example of the image forming apparatus according to the embodiment of the present disclosure. 
         FIG.  11    is a sectional view showing the right side portion of the image forming apparatus in a cover half-open state, in the second modified example of the image forming apparatus according to the embodiment of the present disclosure. 
         FIG.  12    is a sectional view showing the downstream side portion of the first conveyance path of the image forming apparatus in a cover half-opening state, in the second modified example of the image forming apparatus according to the embodiment of the present disclosure. 
         FIG.  13    is a graph showing an output of a photoelectric sensor in the image forming apparatus according to the second modified example of one embodiment of the present disclosure. 
         FIG.  14    is a graph showing an output of a photoelectric sensor in the image forming apparatus according to the third modified example of one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, with reference the attached drawings, one embodiment of the present disclosure will be described. “L”, “R”, U″ and “D” marked in the drawings respectively show “left”, “right”, “upper” and “lower”. In these drawing, a front side of the paper surface on which the drawings are drawn is defined as “a front side”. In the specification, although the terms showing a direction and a position are used, they are used only for convenience of explanation and does not limit the technical scope of the present disclosure. 
     [Outline of Image Forming Apparatus] 
     With reference to  FIG.  1    to  FIG.  3   , an image forming apparatus  1  will be described.  FIG.  1    is a view (a front view) schematically showing an inner structure of the image forming apparatus  1 .  FIG.  2    is a block diagram showing a controller  20  and the others of the image forming apparatus  1 .  FIG.  3    is a sectional view showing a part of the right side portion of the image forming apparatus  1 . 
     The image forming apparatus  1  is an inkjet type color printer in which an ink droplet is ejected to form an image on a sheet P. As shown in  FIG.  1   , the image forming apparatus  1  includes a box-shaped housing  2 . In the lower portion of the housing  2 , a sheet feeding cassette  3 A in which the sheet P is placed is stored, and a manual sheet feeding tray  3 B on which the sheet P is manually placed is provided on the right side surface of the housing  2 . On the upper portion of the left side surface of the housing  2 , a sheet discharge tray  4  on which the image formed sheet P is stacked is provided. 
     In the right side portion in the housing  2 , a first conveyance path  6  along which the sheet P is conveyed from the sheet feeding cassette  3 A to an image forming part  12  provided substantially in the center portion of the housing  2  is formed. On the upstream portion of the first conveyance path  6 , a sheet feeding part  10 A is provided, and on the downstream portion of the first conveyance path  6 , a registration roller  11  is provided. The downstream end of the first conveyance path  6  is connected to a sheet feeding path  5  of the manual sheet feeding tray  3 B, and on the sheet feeding path  5 , a sheet feeding part  10 B is provided. The sheet feeding part  10 A has a function of feeding the sheet P from the sheet bundle placed in the sheet feeding cassette  3 A, and the sheet feeding part  10 B has a function of feeding the sheet P from the sheet bundle placed on the manual sheet feeding tray  3 B. 
     The image forming part  12  is provided with a plurality of (for example, four) line heads  13  for ejecting the ink droplets. Each line head  13  has a plurality of ejection heads  13 A corresponding to each of the inks of black, cyan, magenta and yellow. Each ejection head  13 A has a nozzle surface (not shown) to which a plurality of ejection nozzles (not shown) is opened, and ejects the ink (a liquid) from the ejection nozzles. Each ejection head  13 A communicates with an ink pack (not shown) containing the ink of each color via a tube (not shown), and the ink is supplied from the ink pack to the ejection head  13 A. 
     A conveyance belt  14  is stretched around a plurality of stretching rollers  14 A disposed below the image forming part  12 . A plurality of through-holes (not shown) is formed in the conveyance belt  14 , and a suction part  14 B for generating a negative pressure in the through-holes of the conveyance belt  14  at a position facing the image forming part  12  is disposed inside the conveyance belt  14 . On the left side (on the downstream side in the conveyance direction) of the image forming part  12 , a decurl device  15  is provided for correcting the curl of the sheet P by conveying the sheet P while holding the sheet P therebetween. 
     In the left side portion in the housing  2 , a second conveying path  7  along which the sheet P is conveyed from the decurl device  15  toward the sheet discharge tray  4  is formed. A branch member  9  is provided in the middle of the second conveyance path  7 , and a sheet discharge part  16  is provided on the downstream portion of the second conveyance path  7 . The branch member  9  switches the discharge destination of the sheet P to the sheet discharge tray  4  and to a third conveyance path  8  described later. The sheet discharge part  16  has a function of discharging the image-formed sheet P to the sheet discharge tray  4 . 
     In the upper portion in the housing  10 , the third conveyance path  8  along which the sheet P is conveyed from the branch member  9  in the middle of the second conveyance path  7  to the registration roller  11  is formed. In the middle of the third conveyance path  8 , an inversion part  17  for tuning the sheet P upside down is provided. 
     On the first to the third conveyance paths  6  to  8 , a plurality of conveyance rollers pairs  18  for conveying the sheet P is provided. One of the conveyance rollers pair  18  is a drive roller which is rotationally driven by receiving a driving force from a motor or the like, and the other of the conveyance rollers pair  18  is a driven roller which rotates as the drive roller rotates (not shown). The conveyance rollers pair  18  is rotated while holding the sheet P to convey the sheet P toward the downstream side of the first to the third conveyance paths  6  to  8 . 
     The image forming apparatus  1  is provided with a display part  19  which displays various information to a user or the like. The display part  19  is attached, for example, on the right upper portion of the front side surface of the housing  2 . The display part  19  is a so-called touch panel, and is a display device for displaying information (character string, picture, etc.) and also an input device for allowing the user or the like to input or select information by being touched by the user. Around the display part  19 , an input part such as a button is provided (not shown). The display part  19  is not limited to the touch panel, but may be a liquid crystal display or the like. 
     The image forming apparatus  1  (inside the housing  2 ) is provided with a controller  20  which suitably controls various control target devices. As shown in  FIG.  2   , the controller  20  includes an arithmetic processing part  21 , a storage part  22  and an interface part  23 . The arithmetic processing part  21 , the storage part  22  and the interface part  23  are electrically connected to each other. 
     The arithmetic processing part  21  is a processer executing various arithmetic processing according to program and data stored in the storage part  22 . The storage part  2  contains a random access memory (RAM), a read only memory (ROM) and an auxiliary storage device such as a semiconductor drive. The storage part  22  stores the program and the data used in the image forming apparatus  1 . To the interface part  23 , the control target devices such as the image forming part  12  and the display part  19  are electrically connected. To the interface part  23 , an external terminal such as a personal computer is connected via a network or the like (not shown). The controller  20  may be achieved by a logic circuit mounted on an integral circuit board (a hardware) in place of the processer executing the program. 
     [Image Forming Processing] 
     With reference to  FIG.  1   , the image forming processing performed by the image forming apparatus  1  will now be described. The controller  20  appropriately controls the various control target devices and performs the image forming processing as follows. 
     The sheet feeding parts  10 A and  10 B send the sheet P fed from the sheet feeding cassette  3 A or the manual sheet feeding tray  3 B to the first conveyance path  6  or the sheet feeding path  5 . The registration roller  11  performs a skew correction by temporarily blocking the sheet P (for one-side printing), and sends the sheet P to the conveyance belt  14  before printing in accordance with the ejection timing of ink droplets from the line head  13 . The sheet P is attracted on the conveyance belt  14  and conveyed to the downstream side by traveling the conveyance belt  14 . The image forming part  12  (the line heads  13 ) ejects the ink droplets on the sheet P on the conveyance belt  14  to form a full-color image on the sheet P (print). The sheet P passing below the image forming part  12  is released from being attracted on the conveyance belt  14  and is sent to the decurl device  15 . The decurl device  15  corrects the curl generated on the sheet P. 
     When the one-side printing is to be performed, the branch member  9  opens the second conveyance path  7  and closes the third conveyance path  8 . The sheet P printed on one side is discharged to the discharge tray  4  through the second conveyance path  7 . 
     When the both-side printing is to be performed, the branch member  9  closes the second conveyance path  7  and opens the third conveyance path  8 . The sheet P printed on one side enters the third conveyance path  8 , is turned upside down in the inversion part  17 , and is conveyed toward the registration roller  11  again. Thereafter, an image is formed on the back surface of the sheet P in the same order as in the above-described one-side printing, and the curl of the sheet P printed on both sides is collected and discharged to the sheet discharge tray  4 . 
     [Structure for Treating of Jam] 
     By the way, the sheet P being conveyed may be jammed in the middle of the first to the third conveyance paths  6  to  8 . The housing  2  is provided with an openable/closable door or the like for removing the sheet P jammed in the first to the third conveyance paths  6  to  8 . 
     As shown in  FIG.  1   , as an example of the door or the like, a cover  30  for removing the sheet P jammed in the first conveyance path  6  or the third conveyance path  8  is attached to the right side surface of the housing  2  in an openable and closable manner. The cover  30  is turned around a turning shaft  31  provided horizontally in the lower end portion. The cover  30  and the housing  2  are provided with a locking structure (not shown) for fixing the closed cover  30 , and the cover  30  is provided with a lever (not shown) for releasing the locking of the cover  30 . The user pulls the lever to release the locking of the cover  30 , rotates and opens the closed cover  30  around the turning shaft  31 , opens the first conveyance path  6  and the third conveyance path  8 , and removes the jammed sheet P (performs the jam treatment). 
     As shown in  FIG.  3   , on the inner surface of the cover  30 , opposite side conveyance members  6 B and  8 B constituting a part of the first conveyance path  6  and the third conveyance path  8  are provided. The opposite side conveyance members  6 B and  8 B face main body side conveyance members  6 A and  8 A provided inside the housing  2  with a gap in a state where the cover  30  is closed. The gaps formed between the main body side conveyance members  6 A and  8 A and the opposite side conveyance members  6 B and  8 B serve as the first and the third conveyance paths  6  and  8 . For example, the drive roller of the conveyance rollers pair  18  is supported by the main body side conveyance members  6 A and  8 A, and the driven roller of the conveyance rollers pair  18  is supported by the opposite side conveyance members  6 B and  8 B. 
     [Jam Detection Part] 
     The image forming apparatus  1  is provided with a jam detection part  35  which detects that the sheet P is jammed on the first to the third conveyance paths  6  to  8  and the conveyance belt  14  (jam). Hereinafter, with reference to  FIG.  1    to  FIG.  6   , the jam detection part  35  will be described.  FIG.  4    is an enlarged sectional view showing the downstream side portion of the first conveyance path  6 .  FIG.  5    is an enlarged sectional view showing the downstream side portion of the first conveyance path  6  (during the conveying of the sheet S).  FIG.  6    is a graph showing an output of a photoelectric sensor  36 . 
     As shown in  FIG.  2   , the jam detection part  35  is constituted by a plurality of photoelectric sensors  36  and the controller  20 . The photoelectric sensors  36  have the same structure, and one photoelectric sensor  36  provided on the downstream side of the first conveyance path  6  will be describe mainly.  FIG.  2    shows one photoelectric sensor  36 . 
     &lt;Photoelectric Sensor&gt; 
     As shown in  FIG.  1   , the photoelectric sensors  36  are disposed at suitable positions (for example, near the conveyance rollers pair  18 ) on the first to the third conveyance paths  6  to  8 . The photoelectric sensors  36  are provided at positions facing the conveyance belt  14  on the upstream side and on the downstream side of the image forming part  12  in the conveyance direction. The photoelectric sensors  36  are electrically connected to the interface part  23  via an analog-to-digital conversion circuit (not shown) (see  FIG.  2   ). The photoelectric sensor  36  emits light toward an object to be detected, receives the reflected light reflected by the object to be detected, and outputs an electric signal (a voltage) corresponding to a quantity of the reflected light. More specifically, the photoelectric sensor  36  is a reflective type analog sensor having a light emitting part  36 A for emitting the light and a light receiving part  36 B for receiving the reflected light (see  FIG.  4   ), and outputting a voltage that changes depending on an increase or decrease in the quantity of reflected light (the quantity of received light). The photoelectric sensor  36  decreases the voltage as the quantity of received light (the quantity of reflected light) increases (see  FIG.  6   ). That is, the increase or decrease in the output (the voltage) of the photoelectric sensor  36  is inversely proportional to the increase or decrease in the quantity of received light (the quantity of reflected light). 
     In the specification, the term “an object to be detected” includes a facing surface area and the sheet P on the facing surface area. Also, in the specification, the term “the facing surface area” includes a plurality of path facing surface areas  37  provided at suitable positions on the conveyance belt  14  (see  FIG.  1   ) and on the first to the third conveyance paths  6  to  8 . In the present specification, for convenience of explanation, the conveyance belt  14  and the path facing surface areas  37  are collectively referred to as “the path facing surface area or the others  37 ”. 
     As shown in  FIG.  3   , each of the path facing surface areas  37  is provided at a position facing the photoelectric sensor  36 . Each path facing surface area  37  is formed on a member constituting the first to the third conveyance paths  6  to  8 , and has a plane substantially parallel to the light emitting part  36 A and the light receiving part  36 B of the photoelectric sensor  36 . Some of the path facing surface areas  37  are provided on the opposite side conveyance members  6 B and  8 B of the cover  30 , and some of the photoelectric sensors  36  are provided on the main body side conveyance members  6 A and  8 A facing the opposite side conveyance members  6 B and  8 B. 
     The conveyance belt  14  and the path facing surface areas  37  are processed to suppress reflection of light. For example, the conveyance belt  14  is colored in a dark color so as to suppress reflection of light (not shown). For example, a nonwoven fabric or the like is attached to the plane of the path facing surface area  37  (not shown). The plane of the path facing surface area  37  may be colored in a dark color like the conveyance belt  14 . 
     Although the photoelectric sensor  36  is provided on the upstream side and on the downstream side of the image forming part  12 , the photoelectric sensor  36  may be provided only on either the upstream side or the downstream side of the image forming part  12 . The photoelectric sensor  36  may be provided between the line heads  13  adjacent to each other in the conveyance direction (not shown). It is sufficient that at least one photoelectric sensor  36  is provided in the first to the third conveying paths  6  to  8 . 
     &lt;Controller&gt; 
     The controller  20  determines the presence or absence of the sheet P on the path facing surface area or the others  37  in accordance with the output of the photoelectric sensor  36 . The storage part  22  of the controller  20  stores a threshold value of the output of the photoelectric sensor  36 . More specifically, as shown in  FIG.  2   , the storage part  22  stores (records) a first threshold T 1  for determining that the sheet P does not exist on the path facing surface area or the others  37 , and a second threshold T 2  for determining that the sheet P exists on the path facing surface area or the others  37 . The first threshold T 1  is set to a value higher than the second threshold T 2  (see  FIG.  6   ). In the present specification, the expression “the sheet P exists (does not exist) on the path facing surface area or the others  37  (on the facing surface area)” means that the sheet P actually exists (does not exist) on the path facing surface area or the others  37 , and also includes that the sheet P faces (does not face) so as to cover the path facing surface area  37  from the lower side or from the lateral side. 
     The controller  20  includes a determination part  24  for determining the presence or absence of the sheet P by comparing the electric signal (the voltage) output from the photoelectric sensor  36  with each of the thresholds T 1  and T 2  stored in the storage part  22 . The determination part  24  is provided as a function of the controller  20 , and is realized by the arithmetic processing part  21  executing arithmetic processing according to the program and the data stored in the storage part  22 . 
     [Output of Photoelectric Sensor] 
     For example, as shown in  FIG.  4   , when the sheet P does not exist on the path facing surface area or the others  37 , the light emitted from the light emitting part  36 A of the photoelectric sensor  36  is reflected by the path facing surface area or the others  37 , and the reflected light is incident on the light receiving part  36 B of the photoelectric sensor  36 . Since the path facing surface area or the others  37  is processed to suppress reflection of light, the quantity of reflected light is very small. Accordingly, the photoelectric sensor  36  outputs a voltage equal to or larger than the first threshold T 1  which indicates that the sheet P does not exist on the path facing surface area or the others  37  (see the solid line shown in  FIG.  6   ). In  FIG.  6   , for convenience of explanation, the output (the voltage) of the photoelectric sensor  36  is shown by the straight line, but actually, since the photoelectric sensor  36  is an analog sensor, the output of the photoelectric sensor  36  has an irregularly oscillating waveform. 
     On the other hand, as shown in  FIG.  5   , when the sheet P exists on the path facing surface area or others  37 , the light emitted from the light emitting part  36 A of the photoelectric sensor  36  is reflected by the sheet P, and the reflected light is incident on the light receiving part  36 B of the photoelectric sensor  36 . Since the sheet P reflects the light easily than the path facing surface area or the others  37 , the quantity of reflected light at this time is larger than the quantity of reflected light when reflected by the path facing surface area or the others  37 . Accordingly, the photoelectric sensor  36  outputs a voltage equal to or lower than the second threshold value T 2  indicating that the sheet P exists on the path facing surface area or the others  37  (see the solid line shown in  FIG.  6   ). The determination part  24  determines whether a predetermined time elapses after the output of the voltage of the second threshold T 2  or less, and determines that a sheet jam has occurred if the voltage of the second threshold T 2  or less has been output even after the predetermined time is elapsed. A timer function for measuring the time is provided as a function of the controller  20 . The predetermined time for the sheet jam determination is preset and stored in the storage part  22 . 
     By the way, when the image forming processing is repeated, the conveyance belt  14  and the path facing surface area  37  may become dirty with paper powder, ink, or the like, the quantity of reflected light on the path facing surface area or the others  37  may be increased, and the output of the photoelectric sensor  36  may be decreased (see the blank arrow in  FIG.  6   ). Then, as shown by the two-dot chain line in  FIG.  6   , the photoelectric sensor  36  may output a voltage lower than the first threshold T 1  and higher than the second threshold T 2 . When the output of the photoelectric sensor  36  is within a range between the first threshold T 1  and the second threshold T 2 , the determination part  24  determines that the path facing surface area or the others  37  is contaminated to decrease the quantity of reflected light. That is, the value within the range between the first threshold T 1  and the second threshold T 2  includes a threshold indicating that maintenance of the path facing surface area or the others  37  is required. The maintenance of the path facing surface area or the others  37  shows, for example, cleaning of the path facing surface area or the others  37  or replacement of the path facing surface area or the others  37 . 
     [Jam Detection Method] 
     Next, with reference to  FIG.  7   , a jam detection method (a jam detection processing) using the jam detection part  35  will be described.  FIG.  7    shows a flowchart showing the jam detection method. The controller  20  performs the jam detection method (the jam detection processing) in parallel with the image forming processing. The controller  20  performs the jam detection processing for all of the photoelectric sensors  36 , but in the following description, the jam detection processing for one photoelectric sensor  36  will be described. 
     First, the controller  20  receives a voltage (an electric signal) output from the photoelectric sensor  36  (S 1 ). The electric signal output from the photoelectric sensor  36  is analog-digital inverted and then stored in the storage part  22  or a cash memory of the arithmetic processing part  21 . The controller  20  continues to receive the electric signal output from the photoelectric sensor  36  at a predetermined time interval from the start to the end of the image forming processing. 
     Next, the determination part  24  compares the stored electric signal with the first threshold T 1  (S 2 ). When the electric signal (the voltage) is equal to or larger than the first threshold T 1  (Yes in S 2 ), the determination part  24  determines that the sheet P does not exist on the conveyance belt  14  and the first to the third conveyance paths  6  to  8 , and the processing returns to the reception of the output from the photoelectric sensor  36  (S 1 ). 
     On the other hand, when the electric signal is smaller than the first threshold T 1  (No in S 2 ), the determination part  24  compares the electric signal with the second threshold T 2  (S 3 ). When the electric signal (the voltage) is equal to or smaller than the second threshold T 2  (Yes in S 3 ), the determination part  24  starts measuring a time, and determines whether the measured time (Tp) is a predetermined time (T) (S 4 ). When the measured time (Tp) is the predetermined time (T) or shorter (Tp≤T (NO in S 4 )), the processing returns to the reception of the output of the photoelectric sensor  36  (S 1 ), and the above determinations of S 2  and S 3  are executed again. 
     On the other hand, when the measured time (Tp) is longer than the predetermined time (T) (Tp&gt;T (YES in S 4 )), the determination part  24  determines that the sheet jam occurs around the photoelectric sensor  36 , and stores the determination result in the storage part  22 . The controller  20  immediately stops (interrupts) the image forming processing (S 5 ), and displays information (character strings, picture drawings, etc.) indicating the occurrence of sheet jam, the occurrence position of the sheet jam and the others on the display part  19  (S 6 ). 
     The user checks the information displayed on the display part  19 , opens the door provided in the housing  2  such as the cover  30 , and removes the jammed sheet P (performs the jam treatment processing). The controller  20  determines that the jam treatment processing is performed based on the detection of the opening/closing of the door of the housing  2  and the output result of the photoelectric sensor  36 , deletes the determination result of the occurrence of the sheet jam stored in the storage part  22 , returns the display of the display part  19  to the normal display, and performs the interrupted image forming processing again. 
     Returning to the step (S 3 ) where the electric signal output from the photoelectric sensor  36  is compared with the second threshold T 2 , when the electric signal (the voltage) is smaller than the first threshold T 1  and exceeds the second threshold T 2  (No in S 3 ), the determination part  24  determines that the path facing surface area or the others  37  is contaminated, and stores the determination result in the storage part  22 . The controller  20  causes the display part  19  to display information (character string, picture, etc.) indicating that maintenance of the path facing surface area or the others  37  is necessary (S 7 ). When it is determined that the path facing surface area or the others  37  is contaminated, the controller  20  does not interrupt the image forming processing, but the controller  20  may interrupt the image forming processing. Further, when it is determined that the path facing surface area or the others  37  is contaminated, the controller  20  does not interrupt the new image forming processing, but the controller  20  may interrupt the new image forming processing. 
     The user checks the information displayed on the display part  19 , opens the door provided in the housing  2  such as the cover  30 , and carries out the maintenance of the conveyance belt  14  and the path facing surface area  37 . The controller  20  determines that the maintenance is carried out based on the detection of the opening/closing of the door of the housing  2  and the output result of the photoelectric sensor  36 , deletes the determination result of the occurrence of the contamination stored in the storage part  22 , and returns the display of the display part  19  to the normal display. 
     When it is determined that the path facing surface area or the others  37  is contaminated even after the user carries out the cleaning, the controller  20  causes the display part  19  to display information indicating that the path facing surface area or the others  37  needs to be replaced. The work of replacing the path facing surface area or the others  37  is preferably performed by a specialized operator. 
     According to the image forming apparatus  1  according to the embodiment described above, by detecting that the output of the photoelectric sensor  36  is lower than the first threshold T 1  even though the sheet P does not exist on the path facing surface area or the others  37 , it can be estimated that the path facing surface area or the others  37  is contaminated with paper powder, ink or the like. Thus, it becomes possible to detect the time of cleaning for the path facing surface area or the others  37 . As a result, it becomes possible to perform the maintenance, such as cleaning, of the path facing surface area or the others  37  before the occurrence of problems such as the sheet jam or the like that cause the driving of the image forming apparatus  1  to stop. In addition, it becomes possible to inhibit the sheet jam from being erroneously detected even when the sheet jam does not occur (erroneous detection). Furthermore, the photoelectric sensor  36  for the jam detection can also be used for contamination detection of the path facing surface area or the others  37 . Thus, compared with a case where a dedicated sensor for detecting the contamination of the path facing surface area or the others  37  is separately provided, it becomes possible to make the structure around the path facing surface area or the others  37  simple and to reduce the manufacturing cost. 
     Further, according to the image forming apparatus  1  according to the present embodiment, it becomes possible to inform the user or the like through the display part  19  that the path facing surface area or the others  37  is contaminated and the maintenance such as cleaning is required. Thus, the user or the like can clean the path facing surface area or the others  37  before the occurrence of the sheet jam. 
     MODIFIED EXAMPLES 
     Next, modified examples of the image forming apparatus  1  according to the present embodiment will be described with reference to  FIG.  8    to  FIG.  14   .  FIG.  8    is a block diagram showing the controller  20  and the others of the image forming apparatus  1  according to the first modified example.  FIG.  9    is a flowchart showing the jam detection method of the image forming apparatus  1  according to the first modified example.  FIG.  10    is a block diagram showing the controller  20  and the others of the image forming apparatus  1  according to the second modified example.  FIG.  11    is a sectional view showing a part of the right side portion of the image forming apparatus  1  according to the second modified example in a state where the cover  30  is half-opened.  FIG.  12    is a sectional view showing the downstream side portion of the first conveyance path  6  of the image forming apparatus  1  according to the second modified example in a state where the cover is half-opened.  FIG.  13    is a graph showing an output of the photoelectric sensor  36  of the image forming apparatus  1  according to the second modified example.  FIG.  14    is a graph showing an output of the photoelectric sensor  36  of the image forming apparatus  1  according to the third modified example. In the description of the following modified examples, the same reference numerals are marked to the same or corresponding components (steps) of the image forming apparatus  1  according to the above-described present embodiment, and the description of the same or corresponding components (steps) is omitted. 
     First Modified Example 
     In the above-described image forming apparatus  1  according to the present embodiment, the user manually cleans the path facing surface area or the others  37 . On the other hand, the image forming apparatus  1  according to the first modified example further includes, for example, a cleaning part  40  which cleans the path facing surface area or the others  37  (see  FIG.  8   ). 
     The cleaning part  40  includes a cleaning member coming into contact with the surface of the conveyance belt  14  and the plane of the path facing surface area  37 , and a drive part which rotates or reciprocates the cleaning member (not shown). The cleaning member may be, for example, a cleaning roller whose outer circumferential surface is made of a waste or a brush, or an elastically deformable blade (not shown). The drive part includes a drive source such as an electric motor and a solenoid, and a power transmission mechanism such as a gear train and a cam for connecting the drive source and the cleaning member (not shown). The drive part is electrically connected to the controller  20  (the interface part  23 ) and is controlled by the controller  20  to be operated. For example, the drive part moves the cleaning roller to a position in contact with the path facing surface area or the others  37 , and rotates the cleaning roller around an axis. In addition, the drive part moves the blade to a position in contact with the path facing surface area or the others  37 , and reciprocates and linearly moves the blade. In this way, dirt, such as paper dust and ink, adhering to the surface of the conveyance belt  14  and the plane of the path facing surface area  37  is removed. 
     As shown in  FIG.  9   , in the jam detection method (the jam detection processing), when the determination part  24  determines that the contamination occurs in the path facing surface area or the others  37  (NO in S 3 ), and stores the determination result in the storage part  22 . The controller  20  causes the display part  19  to display information indicating that maintenance of the path facing surface area or the others  37  is necessary (S 7 ), and waits for completion of the image forming processing (NO in S 8 ). When the image forming processing is completed (YES in S 8 ), the controller  20  causes the cleaning part  40  to clean the path facing surface area or the others  37  (S 9 ). After the cleaning by the cleaning part  40  is completed, the controller  20  deletes the determination result of the contamination occurrence stored in the storage part  22  and returns the display of the display part  19  to the normal display. If it is determined that the path facing surface area or the others  37  is contaminated even after the cleaning part  40  performs the cleaning, the controller  20  causes the display part  19  to display information indicating that the path facing surface area or the others  37  needs to be replaced. 
     In the image forming apparatus  1  according to the first modified example of the present embodiment described above, the cleaning part  40  can automatically clean the path facing surface area or the others  37 . Thus, it becomes possible to omit the labor for the user to perform the cleaning work manually. 
     When it is determined that the contamination occurs in the path facing surface area or the others  37 , the controller  20  may cause the display part  10  to display a button for selecting either cleaning by the cleaning part  40  or manual cleaning by the user (not shown). 
     In the image forming apparatus  1  according to the first modified example, the cleaning is performed such that the cleaning part  40  moves while contacting with the path facing surface area or the others  37 , but the present disclosure is not limited to this. For example, the cleaning part may include a compressed air source for compressing air and a nozzle for blowing the compressed air to the path facing surface area or the others  37  (not shown). The cleaning part may blow the air to the path facing surface area or the others  37  to remove dirt adhering to the path facing surface area or the others  37 . 
     Second Modified Example 
     The image forming apparatus  1  according to the second modified example is configured to detect a half-open state of the cover  30  by at least one of the path facing surface area  37  provided on the opposite side conveyance members  6 B and  8 B of the cover  30  and the photoelectric sensor  36  facing the path facing surface area  37 . The half-open state of the cover  30  means a so-called half-door state in which the cover  30  cannot be opened by closing the side surface of the housing  2 , but is not completely closed (see  FIG.  11   ). In  FIG.  11    and  FIG.  12   , as an example, the photoelectric sensor  36  provided on the downstream side of the first conveyance path  6  and the path facing surface area  37  detect the half-open state of the cover  30 . 
     As shown in  FIG.  10   , the storage part  22  of the controller  20  stores a third threshold T 3  in addition to the first threshold T 1  and the second threshold T 2 . The third threshold value T 3  is set to a value higher than the first threshold value T 1  (see  FIG.  13   ). In other words, the third threshold T 3  is set to a value on the side opposite to the second threshold T 2  with respect to the first threshold T 1  and outside a predetermined range from the first threshold T 1 . The third threshold T 3  is a threshold value for determining that the cover  30  is in the half-open state. 
     When the sheet P does not exist on the path facing surface area or the others  37  and the cover  30  is in the half-open state (see  FIG.  11   ), a distance between the photoelectric sensor  36  and the path facing surface area  37  is slightly longer than that when the cover  30  is completely closed (see  FIG.  12   ). The two-dotted chain line shown in  FIG.  12    indicates the position of the path facing surface area  37  when the cover  30  is completely closed. Therefore, the reflected light reflected by the path facing surface area or the others  37  becomes weaker (the quantity of light decreases) than that when the cover  30  is completely closed, and as shown in  FIG.  13   , the photoelectric sensor  36  outputs a voltage exceeding the third threshold T 3  set higher than the first threshold T 1 . The determination part  24  of the controller  20  determines that the cover  30  is in an open state when the voltage exceeds the third threshold T 3 . When the output of the photoelectric sensor  36  is equal to or larger than the first threshold T 1  and equal to or less than the third threshold T 3 , the determination part  24  determines that the sheet P does not exist on the path facing surface area or the others  37 . 
     The controller  20  receives the electric signal (the voltage) from the photoelectric sensor  36  before performing the image forming processing, and when the electric signal exceeds the third threshold T 3 , the determination part  24  determines that the cover  30  is in the half-open state. In this case, the controller  20  does not perform the image forming processing, and causes the display part  19  to display information indicating that the cover  30  is not completely closed. The user checks the information displayed on the display part  19 , and closes the half-opened cover  30  completely. 
     The controller  20  performs the image forming processing when the electric signal is equal to or larger than the first threshold T 1  and equal to or smaller than the third threshold T 3 , and executes the jam detection method (the jam detection processing) in parallel with the image forming processing. In principle, since the cover  30  is not opened during the image forming processing, the electric signal from the photoelectric sensor  36  does not exceed the third threshold T 3  during executing the jam detection processing. 
     According to the image forming apparatus  1  according to the second modified example of the embodiment described above, the photoelectric sensor  36  used for detecting the sheet jam and detecting the contamination of the path facing surface area  37  can also be used for detecting the half-open state of the cover  30 . Thus, the structure around the cover  30  can be made simple and the manufacturing cost can be reduced as compared with a case where a dedicated sensor for detecting the half-open state of the cover  30  is separately provided. 
     Further, according to the image forming apparatus  1  according to the second modified example, it becomes possible to inform the user or the like through the display part  19  that the cover  30  is not properly closed. Thus, the user or the like can properly close the half-opened cover  30 . 
     The features of the image forming apparatus  1  according to the second modified example may be applied to the image forming apparatus  1  according to the first modified example. 
     Third Modified Example 
     In the image forming apparatus  1  according to the present embodiment (the first to the second modified examples are included.), the output (the voltage) of the photoelectric sensor  36  is increased or decreased in inverse proportion to the quantity of received light (the quantity of reflected light), but the present disclosure is not limited thereto. As shown in  FIG.  14   , the photoelectric sensor  36  in which the output (the voltage) increases or decreases in proportion to the quantity of received light (the quantity of reflected light) may be employed (a third modified example). That is, the photoelectric sensor  36  may be designed to increase the output (the voltage) as the quantity of received light (the quantity of reflected light) increases. In this design, the first threshold T 1  is set to a value lower than the second threshold T 2 . The photoelectric sensor  36  outputs the voltage equal to or lower than the first threshold T 1  when the sheet P does not exist on the path facing surface area or the others  37 , and the photoelectric sensor  36  outputs the voltage equal to or higher than the second threshold value T 2  when the sheet P exists on the path facing surface area or the others  37 . When the photoelectric sensor  36  outputs the voltage higher than the first threshold T 1  and lower than the second threshold T 2 , the determination part  24  determines that the contamination has occurred in the path facing surface area or the others  37 . The third threshold T 3  is set to a value lower than the first threshold T 1  (not shown). 
     The jam detection method (the jam detection processing) described in the description of this embodiment (the first to the third modified examples are included, the same shall apply hereinafter) is only an example, and the order of each step (each step) may be changed within a range without contradiction. 
     Further, in the image forming apparatus  1  according to the present embodiment, although the cover  30  is provided on the right side surface of the housing  2 , it is not limited thereto, and the cover may be provided on the left side surface, the front side surface, the rear side surface, the upper surface, etc. of the housing  2  in an openable and closable manner (not shown). When the cover constitutes any one of the first to the third conveyance paths  6  to  8  and the path facing surfaces  37  are provided in these covers, the half-open state of the cover can be detected from the output result of the photoelectric sensor  36 . 
     In the image forming apparatus  1  according to the present embodiment, the path facing surface area  37  is provided on the opposite side conveyance members  6 B and  8 B of the cover  30 , and the photoelectric sensor  36  is provided on the main body side conveyance members  6 A and  8 A, but the present disclosure is not limited thereto. Conversely, the photoelectric sensor  36  may be provided on the opposite side conveyance members  6 B and  8 B of the cover  30 , and the path facing surface area  37  may be provided on the main body side conveying members  6 A and  8 A (not shown). 
     In the image forming apparatus  1  according to the present embodiment, the information (warning) such as the occurrence of sheet jam, the contamination of the path facing surface area  37 , and the half-open state of the cover  30  is displayed on the display part  19 , but the present disclosure is not limited thereto. For example, the image forming apparatus  1  may be provided with a speaker (not shown), and the controller  20  may execute a control to flow a warning sound or a sound corresponding to the above-described information from the speaker in addition to displaying the information on the display part  19 . 
     Further, in the image forming apparatus  1  according to the present embodiment, although the turning shaft  31  of the cover  30  is provided in the horizontal direction in the lower portion of the housing  2 , the turning shaft  31  may be provided in the upper-and-lower direction on either left side and right side of the housing  2  (the cover  30 ) (not shown). 
     The image forming apparatus  1  according to the present embodiment is a color printer, but it is not limited thereto, and may be a monochrome printer, a copying machine, a facsimile, etc. Although the image forming apparatus  1  is an ink-jet type printer, it is not limited thereto, and an electrophotographic type image forming apparatus (a printer, a copying machine, a facsimile, etc.) may be used, and it is also possible to detect that the path facing surface portion  37  is contaminated with a paper powder, a toner, or the like (not shown). 
     The description of the above embodiment shows one aspect of the image forming apparatus according to the present disclosure, and the technical range of the present disclosure is not limited to the above embodiment. The present disclosure may be modified, substituted, or modified in various ways without departing from the spirit of the technical idea, and the claims include all embodiments which may be included within the scope of the technical idea.