JP7600032B2 - Conveyor - Google Patents

Description

The present invention relates to a conveying device for conveying media.

Printing devices are known that print on paper as a medium while transporting the paper. In such printing devices, multiple paper sensors (medium detection units) are arranged along the paper transport path to detect paper jams, etc.

In such printing devices, paper dust generated by the transport of paper can adhere to and accumulate on the paper sensor. This accumulation of paper dust can cause the paper sensor to remain on or cause chattering in the paper sensor, which can lead to erroneous detection of paper by the paper sensor.

One technology for dealing with problems caused by paper dust in printing devices is disclosed in Patent Document 1. In this technology, multiple sensors for detecting paper dust are placed on the paper transport path, and a message is displayed on the operation panel encouraging cleaning of the area where paper dust has accumulated, based on the amount of accumulated paper dust detected by the paper dust detection sensors.

JP 2009-20370 A

As with the technology of Patent Document 1, by arranging multiple sensors for detecting paper dust, it is possible to determine the timing when each of the multiple paper sensors needs to be cleaned. This allows the paper sensors to be cleaned at the appropriate time, reducing false detection of paper by the paper sensors. However, providing multiple sensors for detecting paper dust leads to an increase in the size of the device and a more complex circuit design.

On the other hand, if only one sensor for detecting paper dust is provided and the timing for cleaning all paper sensors is determined based on the amount of accumulated paper dust detected by that sensor, there is a risk that paper sensors that do not need cleaning will also be cleaned. This is because the amount of accumulated paper dust in each paper sensor can differ depending on conditions such as the orientation of each paper sensor.

The present invention has been made in consideration of the above, and aims to provide a transport device that can reduce unnecessary cleaning of the media detection section while minimizing the size of the device and the complexity of the circuit design.

To achieve the above object, the transport device of the present invention is characterized by comprising: a dust detection unit having a light-emitting unit arranged along a transport path along which media is transported and a light-receiving unit that receives the light emitted by the light-emitting unit; a plurality of media detection units arranged along the transport path to detect media; and a determination unit that, when the amount of light received by the light-receiving units is attenuated due to a media transport operation, calculates a judgment addition value for each media detection unit through which the media has passed based on the amount of attenuation of the amount of light received by the light-receiving units during the media transport operation and the installation conditions of the media detection units through which the media has passed, and determines that cleaning is required for the media detection units for which the judgment value obtained by accumulating the judgment addition values exceeds a predetermined judgment threshold.

The conveying device of the present invention can reduce unnecessary cleaning of the media detection unit while preventing the device from becoming larger and the circuit design from becoming more complex.

1 is a schematic configuration diagram of a printing device according to an embodiment. FIG. 2 is a control block diagram of the printing apparatus shown in FIG. 1 . FIG. 13 is a diagram showing a sensor table. 4 is a flowchart illustrating the operation of the printing device. 4 is a flowchart illustrating an operation of the printing device. 4 is a flowchart illustrating an operation of the printing device. 4 is a flowchart illustrating an operation of the printing device. 4 is a flowchart illustrating an operation of the printing device. 4 is a flowchart illustrating an operation of the printing device. 11 is a diagram showing an example of a transition of a determination value of a paper sensor. FIG. 13 is a view showing a sensor table for explaining an example of a calculation result of a determination value of a paper sensor through which a paper has passed during a paper transport operation; FIG. 13 is a diagram showing an example of a sensor table when a determination value of a paper sensor exceeds a determination threshold value for the first time; FIG.

The following describes an embodiment of the present invention with reference to the drawings. The same or equivalent parts and components are designated by the same or equivalent reference numerals throughout the drawings.

The embodiments shown below are examples of devices that embody the technical idea of this invention, and the technical idea of this invention does not specify the materials, shapes, structures, arrangements, etc. of each component part to those described below. The technical idea of this invention can be modified in various ways within the scope of the claims.

Figure 1 is a schematic diagram of a printing device provided with a conveying device according to an embodiment of the present invention. Figure 2 is a control block diagram of the printing device shown in Figure 1. In the following description, the top, bottom, left, and right directions on the paper surface in Figure 1 are defined as the top, bottom, left, and right directions.

In FIG. 1, the path indicated by the thick line is the transport path along which paper (corresponding to the medium) P is transported. Of the transport paths, the path indicated by the solid line is the normal path RC, the path indicated by the dashed line is the reversal path RR, the paths indicated by the dashed line are the paper discharge paths RD1 and RD2, and the path indicated by the two-dot chain line is the paper feed path RS. In the following explanation, upstream and downstream refer to upstream and downstream in the transport path.

As shown in Figures 1 and 2, the printing device 1 according to this embodiment includes a paper feed unit 2, a print transport unit 3, a printing unit 4, a first paper discharge unit 5, an upper transport unit 6, a second paper discharge unit 7, an inversion unit 8, an operation panel 9, a memory unit 10, a control unit (corresponding to a determination unit) 11, and a housing 12 that houses or holds each unit. Note that the transport device is made up of each unit of the printing device 1 other than the printing unit 4.

The paper feed unit 2 feeds paper P. The paper feed unit 2 includes an external paper feed tray 21, an external paper feed roller 22, an internal paper feed tray 23, an internal paper feed roller 24, a vertical transport roller 25, an external paper feed motor 26, an internal paper feed motor 27, and paper sensors 28A and 28B (corresponding to a medium detection unit). Note that the alphabetical suffixes in the reference symbols for the paper sensors 28A, 28B, etc. may be omitted to refer to them collectively.

The external paper feed tray 21 is where the paper P used for printing is loaded. The external paper feed tray 21 is installed with a portion exposed to the outside of the housing 12.

The external paper feed rollers 22 take out the paper P stacked on the external paper feed tray 21 one sheet at a time and transport it along the paper feed path RS toward the registration rollers 31 described below.

The internal paper feed tray 23 is where the paper P used for printing is loaded. The internal paper feed tray 23 is located inside the housing 12.

The internal paper feed roller 24 picks up the paper P stacked on the internal paper feed tray 23 one sheet at a time and sends it out to the paper feed path RS.

The vertical transport rollers 25 transport the paper P removed from the internal paper feed tray 23 along the paper feed path RS toward the registration rollers 31 described below.

The external paper feed motor 26 drives and rotates the external paper feed roller 22 and the vertical transport roller 25. The external paper feed motor 26 can be connected/disconnected to the external paper feed roller 22 and the vertical transport roller 25 via a clutch (not shown). The clutch switches the drive of the external paper feed roller 22 and the vertical transport roller 25.

The internal paper feed motor 27 drives and rotates the internal paper feed roller 24 and the vertical transport roller 25.

The paper sensor 28A detects paper P taken out from the external paper feed tray 21 and transported along the paper feed path RS. The paper sensor 28B detects paper P taken out from the internal paper feed tray 23 and transported along the paper feed path RS. The paper sensors 28A and 28B are reflective optical sensors, and consist of digital sensors that output a signal indicating the presence or absence of paper. The paper sensor 28A is installed facing downward along the paper feed path RS near the upstream side of the junction of the path from the external paper feed rollers 22 to the registration rollers 31 and the path from the internal paper feed rollers 24 to the registration rollers 31 on the paper feed path RS. The paper sensor 28B is installed horizontally (facing right) along the paper feed path RS near the upstream side of the vertical transport rollers 25.

The print transport unit 3 transports the paper P transported from the paper feed unit 2 or the inversion unit 8. The print transport unit 3 includes a registration roller 31, a registration motor 32, a belt platen unit 33, a belt platen motor 34, and paper sensors 28C and 28D.

The registration rollers 31 temporarily stop the paper P conveyed from the paper feed section 2 or the inversion section 8, and then convey it toward the belt platen section 33. The registration rollers 31 are arranged along the normal path RC, downstream of the junction of the paper feed path RS and the inversion path RR.

The registration motor 32 rotates the registration roller 31.

The belt platen section 33 transports the paper P conveyed from the registration rollers 31 along the horizontal portion of the upstream area of the normal path RC.

The belt platen motor 34 drives the belt platen section 33.

The paper sensor 28C (corresponding to the medium detection section and dust detection section) detects the paper P transported from the registration rollers 31 towards the belt platen section 33. The paper sensor 28C is also used to determine whether cleaning is required due to the accumulation of paper powder (dust) in the paper sensors 28A-D and the paper sensors 28E-L described below. The paper sensor 28C is a transmissive optical sensor having a light emitting section 28a and a light receiving section 28b, and is an analog sensor that outputs a signal indicating the amount of light received by the light receiving section 28b.

The light-emitting unit 28a emits light upward toward the normal route RC. The light-receiving unit 28b receives the light emitted by the light-emitting unit 28a. The light-receiving unit 28b is installed facing downward, facing opposite the light-emitting unit 28a across the normal route RC.

The paper sensor 28C is disposed along the normal path RC near the downstream side of the registration rollers 31. The downstream side of the registration rollers 31 is the position on the transport path of the paper P where paper dust is most likely to accumulate.

The paper sensor 28D (corresponding to the medium detection unit) detects the paper P being transported from the belt platen unit 33 toward the switching unit 36 described below. The paper sensor 28D is a digital sensor similar to the paper sensors 28A and 28B. The paper sensor 28D is installed facing downward along the normal path RC near the downstream side of the belt platen unit 33.

The printing unit 4 has multiple inkjet heads (not shown) and prints by ejecting ink from the inkjet heads onto the paper P transported by the belt platen unit 33. The printing unit 4 is disposed above the belt platen unit 33.

The first paper discharge unit 5 guides the printed paper P to a post-processing device (not shown) connected downstream of the printing device 1. The first paper discharge unit 5 includes a switching unit 36 and a paper sensor 28E (corresponding to a medium detection unit).

The switching unit 36 switches the transport path of the paper P between the normal path RC and the paper discharge path RD1. The switching unit 36 is located at the branching point between the normal path RC and the paper discharge path RD1.

The paper sensor 28E detects the paper P transported along the paper discharge path RD1. The paper sensor 28E is a digital sensor similar to the paper sensors 28A and 28B. The paper sensor 28E is installed facing downward along the paper discharge path RD1 downstream of the switching unit 36.

The upper transport section 6 transports the paper P transported from the belt platen section 33 to the second paper discharge section 7 or the inversion section 8. The upper transport section 6 includes two pairs of upward transport rollers 41, an upward transport motor 42, four pairs of horizontal transport rollers 43, a horizontal transport motor 44, and paper sensors 28F to 28J (corresponding to the media detection section).

The ascending conveying rollers 41 convey the paper P conveyed by the belt platen unit 33 to the upper horizontal conveying rollers 43. The ascending conveying rollers 41 are arranged along the ascending portion of the middle stream of the normal route RC.

The upward conveying motor 42 drives and rotates two pairs of upward conveying rollers 41.

The horizontal transport rollers 43 transport the paper P transported by the ascending transport rollers 41 to the paper discharge section 5 or the inversion section 8. The most downstream horizontal transport roller 43 is located in the upstream area of the inversion route RR. The other horizontal transport rollers 43 are located in the horizontal portion of the downstream area of the normal route RC.

The horizontal conveying motor 44 drives and rotates the four pairs of horizontal conveying rollers 43.

Paper sensors 28F-28I detect paper P transported along the upward portion of the middle stream area and the horizontal portion of the downstream area of normal route RC. Paper sensor 28J detects paper P transported from the most downstream horizontal transport roller 43 to the reversing roller 61, which will be described later. Paper sensors 28F-28J are digital sensors similar to paper sensors 28A and 28B.

The paper sensor 28F is installed horizontally (facing left) along the normal path RC between the upstream ascending conveyor roller 41 and the downstream ascending conveyor roller 41. The paper sensor 28G is installed facing downward along the normal path RC between the downstream ascending conveyor roller 41 and the most upstream horizontal conveyor roller 43.

The paper sensor 28H is installed facing downward along the normal path RC between the most upstream horizontal transport roller 43 and the second horizontal transport roller 43 from the upstream side. The paper sensor 28I is installed facing downward along the normal path RC near the downstream side of the third horizontal transport roller 43 from the upstream side. The paper sensor 28J is installed facing downward along the reversal path RR near the downstream side of the most downstream horizontal transport roller 43.

The second paper discharge unit 7 discharges the printed paper P. The second paper discharge unit 7 includes a switching unit 51, a paper discharge roller 52, a paper discharge motor 53, a paper discharge tray 54, and a paper sensor 28K (corresponding to a medium detection unit).

The switching unit 51 switches the transport path of the paper P between the paper discharge path RD2 and the reverse path RR. The switching unit 51 is located at the branch point of the paper discharge path RD2 and the reverse path RR.

The paper discharge rollers 52 transport the paper P that has been guided to the paper discharge path RD2 by the switching unit 51 and discharge it onto the paper discharge tray 54. The paper discharge rollers 52 are disposed along the paper discharge path RD2 between the switching unit 51 and the paper discharge tray 54.

The discharge motor 53 drives the discharge roller 52 to rotate.

The paper discharge tray 54 is where the paper P discharged from the second paper discharge section 7 is stacked. The paper discharge tray 54 is located at the downstream end of the paper discharge path RD2.

The paper sensor 28K detects the paper P being transported to the paper discharge tray 54 by the paper discharge rollers 52. The paper sensor 28K is a digital sensor similar to the paper sensors 28A and 28B. The paper sensor 28K is installed facing downward along the paper discharge path RD2 between the paper discharge rollers 52 and the paper discharge tray 54.

When performing double-sided printing, the reversing unit 8 reverses the paper P that has been printed on one side and transports it to the print transport unit 3. The reversing unit 8 includes a reversing roller 61, a reversing motor 62, a refeed roller 63, a refeed motor 64, a switching gate 65, and a paper sensor 28L (corresponding to a medium detection unit).

The reversing rollers 61 switch back the paper P conveyed by the horizontal conveying rollers 43 and convey it to the re-feed rollers 63. The reversing rollers 61 are disposed downstream of the most downstream horizontal conveying rollers 43 along the reversing path RR.

The reversing motor 62 drives the reversing roller 61 to rotate.

The refeed roller 63 transports the paper P that has been switched back and inverted by the reversing roller 61 to the registration roller 31. The refeed roller 63 is disposed on the reversing path RR between the reversing roller 61 and the registration roller 31.

The refeed motor 64 drives the refeed roller 63 to rotate.

The switching gate 65 guides the paper P conveyed by the horizontal conveying roller 43 to the reversing roller 61. The switching gate 65 also guides the paper P switched back by the reversing roller 61 to the re-feed roller 63. The switching gate 65 is located near the three centers of gravity of the most downstream horizontal conveying roller 43, the reversing roller 61, and the re-feed roller 63.

The paper sensor 28L detects the paper P that is switched back by the reversing roller 61 and transported to the refeed roller 63. The paper sensor 28L is a digital sensor similar to the paper sensors 28A and 28B. The paper sensor 28L is installed sideways (facing left) along the reversing path RR near the upstream side of the refeed roller 63.

The operation panel 9 accepts input operations from the user and displays various screens, etc. The operation panel 9 includes a display unit 71 and an input unit 72.

The display unit 71 displays various screens, etc. The display unit 71 has a liquid crystal display panel, etc.

The input unit 72 accepts input operations by the user and outputs operation signals corresponding to the operations. The input unit 72 has various operation keys, a touch panel, etc.

The memory unit 10 stores the sensor table 81 shown in FIG. 3. The memory unit 10 is composed of a HDD (Hard Disk Drive) etc.

As shown in FIG. 3, the sensor table 81 holds the orientation of each paper sensor 28 (sensor orientation coefficient K), the judgment value H, the judgment threshold Ht, the number of sheets N (corresponding to the number of passing sheets), and the number of sheets Nt.

The orientation of the paper sensor 28 is set so that it can detect paper P being transported along the transport path at the position where the paper sensor 28 is installed. For example, as described above, the orientation of the paper sensor 28A is downward.

The sensor orientation coefficient K is a coefficient that is multiplied by the attenuation D of the amount of light received by the light receiving section 28b of the paper sensor 28C before and after the paper transport operation (corresponding to the medium transport operation) when calculating the judgment sum value C described below. The sensor orientation coefficient K is set to a larger value in the direction in which paper dust is more likely to accumulate on the paper sensor 28. In the example of Figure 3, the sensor orientation coefficients K for the upward, horizontal, and downward directions are set to 1.0, 0.5, and 0.25, respectively.

The value of the sensor orientation coefficient K is not limited to the above example, and the orientation of the paper sensor 28 is not limited to upward, sideways, or downward, but may be further classified, for example.

The judgment value H is a value for determining whether or not cleaning of the paper sensor 28 is necessary. The judgment value H is a value obtained by accumulating the judgment addition value C from the first paper transport operation after cleaning of the paper sensor 28 to the most recent paper transport operation. If the paper sensor 28 has never been cleaned, the judgment value H is a value obtained by accumulating the judgment addition value C from the first paper transport operation after starting to use the paper sensor 28 (after starting to use the printing device 1) to the most recent paper transport operation. The judgment value H of each paper sensor 28 is reset when the paper sensor 28 is cleaned, and H = 0 is set.

The judgment addition value C indicates the degree of increase in the amount of paper dust accumulation on the paper sensor 28 due to a series of paper transport operations. When the amount of light received by the light receiving section 28b is attenuated by the paper transport operation, the judgment addition value C is calculated for the paper sensor 28 through which paper passed (paper P passed) during the paper transport operation, based on the amount of attenuation D and the orientation of the paper sensor 28 (sensor orientation coefficient K), which is an installation condition of the paper sensor 28.

Specifically, the judgment addition value C of the paper sensor 28 where paper has passed (paper P has passed) during the paper transport operation in which the amount of light received by the light receiving section 28b has attenuated is calculated by the following formula (1):

C = K × D ... (1)
Whether or not paper passes through each paper sensor 28 is determined by the settings of single-sided/double-sided printing, the paper feed source (external paper feed tray 21 or internal paper feed tray 23), and the paper discharge destination (whether the paper P is discharged from the first paper discharge section 5 or the second paper discharge section 7) during the paper transport operation (printing operation), as described below.

The judgment threshold Ht is a threshold for judging whether or not cleaning of the paper sensor 28 is necessary from the judgment value H. The judgment threshold Ht of each paper sensor 28 is set in advance based on experiments, etc. The judgment threshold Ht of each paper sensor 28 is changed if a false detection of paper P occurs in the paper sensor 28 before the judgment value H exceeds the judgment threshold Ht, as described below.

The number of sheets of paper P passed through the paper sensor 28 from the first paper transport operation after the paper sensor 28 is cleaned to the most recent paper transport operation. If the paper sensor 28 has never been cleaned, the number of sheets of paper P passed through the paper sensor 28 from the first paper transport operation after the paper sensor 28 begins to be used (after the printing device 1 begins to be used) to the most recent paper transport operation. The number of sheets of paper N passed through each paper sensor 28 is reset to N=0 when the paper sensor 28 is cleaned.

The number of sheets of paper that have passed through threshold Nt is a value for determining whether or not cleaning of the paper sensor 28 is necessary based on the number of sheets of paper that have passed through N. For each paper sensor 28, the number of sheets of paper that have passed through when the judgment value H first exceeds the judgment threshold Ht after the paper sensor 28 starts to be used (after the printing device 1 starts to be used) is set as the number of sheets of paper that have passed through threshold Nt. After the number of sheets of paper that have passed through threshold Nt is set, even if the judgment value H does not exceed the judgment threshold Ht, if the number of sheets of paper that have passed through N exceeds the number of sheets of paper that has passed threshold Nt, it is determined that cleaning of the paper sensor 28 is necessary.

The control unit 11 controls the operation of each part of the printing device 1. The control unit 11 is configured with a CPU, RAM, ROM, etc.

The control unit 11 executes a printing operation in which the printing unit 4 prints on the paper P while the print transport unit 3 transports the paper P. Here, the printing operation includes a paper transport operation. When the amount of light received by the light receiving unit 28b of the paper sensor 28C is attenuated by the paper transport operation, the control unit 11 calculates a judgment addition value C for each paper sensor 28 through which paper has passed based on the amount of attenuation D during the paper transport operation and the orientation of the paper sensor 28 through which paper has passed, and calculates a judgment value H by accumulating the judgment addition values C. The control unit 11 then determines that the paper sensor 28 for which the judgment value H exceeds the judgment threshold Ht needs to be cleaned.

Next, the operation of the printing device 1 will be explained with reference to the flowcharts in Figures 4 to 9.

When a print job is input, in step S1 of FIG. 4, the control unit 11 acquires the amount of light received by the light receiving unit 28b of the paper sensor 28C. The amount of light received by the light receiving unit 28b acquired by the control unit 11 here is the amount of light received at the start of a series of paper transport operations (printing operations), and is the amount of light received in a state in which the paper sensor 28C is not detecting paper P (there is no paper P between the light emitting unit 28a and the light receiving unit 28b).

Next, in step S2, the control unit 11 starts the printing operation. Here, the control unit 11 performs single-sided printing or double-sided printing according to the single-sided/double-sided printing setting in the print job.

For single-sided printing, the control unit 11 controls the paper feed unit 2 to sequentially take out unprinted paper P from the external paper feed tray 21 or the internal paper feed tray 23 and feed it to the print transport unit 3. Here, the control unit 11 controls the paper feed unit 2 to sequentially feed the paper at a timing according to the drive timing of the registration rollers 31 that send out each paper P so that each paper P is transported at a predetermined interval between sheets on the belt platen unit 33. This allows multiple sheets of paper P to be transported simultaneously on the transport path.

The fed paper P is sent to the belt platen unit 33 by the registration rollers 31 and transported by the belt platen unit 33. At this time, the paper P is printed with ink ejected from the inkjet head of the printing unit 4.

In single-sided printing, when paper P is discharged by the first discharge unit 5, the printed paper P is transported by the belt platen unit 33 and guided to the discharge path RD1 by the switching unit 36, and is transported along the discharge path RD1 and discharged.

When paper P is discharged by the second discharge unit 7 in single-sided printing, the printed paper P is transported by the belt platen unit 33 and guided by the switching unit 36 along the normal path RC to the upper transport unit 6. In the upper transport unit 6, the paper P is transported by the upward transport rollers 41 and the horizontal transport rollers 43. The paper P is then guided by the switching unit 51 to the discharge path RD2 and discharged by the discharge rollers 52 to the paper discharge tray 54.

In the case of double-sided printing, the control unit 11 controls the paper feed unit 2 to sequentially feed unprinted paper P at a timing that doubles the time between the feeding timing of each paper P compared to the feeding timing during single-sided printing.

The fed paper P is printed by the printing unit 4 while being transported by the belt platen unit 33, just as in single-sided printing. After single-sided printing, the paper P is transported from the belt platen unit 33 to the upper surface transport unit 6, where it is transported by the ascending transport rollers 41 and horizontal transport rollers 43. The paper P is then guided to the reversal route RR by the switching unit 51.

The paper P guided to the reversing path RR is guided to the reversing rollers 61 by the switching gate 65 in the reversing unit 8, switched back by the reversing rollers 61, and guided to the refeed rollers 63 by the switching gate 65. The paper P is then re-fed by the refeed rollers 63 to the printing transport unit 3, where it is sent to the belt platen unit 33 by the registration rollers 31.

Here, the paper P after single-sided printing is refed at a timing such that it is sent to the belt platen unit 33 alternately with the unprinted paper P that is fed in sequence. As described above, in double-sided printing, the time between the feeding timing of each paper P is twice as long as in single-sided printing. Therefore, it is possible to insert the paper P after single-sided printing between the unprinted paper P, and refed the paper P after single-sided printing alternately with the feeding of the unprinted paper P.

After printing on one side, the paper P is inverted by the inversion unit 8 and sent to the belt platen unit 33 with the unprinted side facing up. Then, while the paper P is transported by the belt platen unit 33, the printing unit 4 prints on the unprinted side. The paper P that has been printed on both sides is discharged by the first paper discharge unit 5 or the second paper discharge unit 7 in the same manner as the printed paper P during single-sided printing described above.

In double-sided printing, as described above, unprinted paper P is fed alternately with re-feeding of paper P after single-sided printing, so that printing on one side of unprinted paper P and printing on the unprinted side of paper P after single-sided printing are alternately performed on the belt platen unit 33. This allows double-sided printing to be performed with the same productivity per side as when printing on one side.

Since the printing operation is performed as described above, the path that the paper P takes is determined by the settings of single-sided/double-sided printing, the paper feed source (external paper feed tray 21 or internal paper feed tray 23), and the paper discharge destination (whether the paper P is discharged from the first paper discharge section 5 or the second paper discharge section 7). Therefore, in a series of paper transport operations (printing operations), the paper P passes through some of the paper sensors 28 out of the paper sensors 28A-28L, and whether or not paper passes through each paper sensor 28 is determined by the settings of single-sided/double-sided printing, the paper feed source, and the paper discharge destination.

Specifically, in single-sided printing, when the paper source is the external paper feed tray 21 and paper P is discharged by the first paper discharge section 5, paper passes through paper sensors 28A, 28C to 28E, but no paper passes through the other paper sensors 28.

In single-sided printing, when the paper source is the external paper feed tray 21 and paper P is discharged by the second paper discharge section 7, paper passes through paper sensors 28A, 28C, 28D, 28F to 28I, and 28K, but no paper passes through the other paper sensors 28.

In single-sided printing, when the paper source is the internal paper feed tray 23 and paper P is discharged by the first paper discharge section 5, paper passes through paper sensors 28B to 28E, but no paper passes through the other paper sensors 28.

In single-sided printing, when the paper source is the internal paper feed tray 23 and paper P is discharged by the second paper discharge section 7, paper passes through paper sensors 28B-28D, 28F-28I, and 28K, but no paper passes through the other paper sensors 28.

In double-sided printing, when the paper source is the external paper feed tray 21 and paper P is discharged by the first paper discharge section 5, paper passes through paper sensors 28A, 28C to 28J, and 28L, but no paper passes through the other paper sensors 28. One sheet of paper P passes through paper sensors 28C and 28D twice.

In double-sided printing, when the paper source is the external paper feed tray 21 and paper P is discharged by the second paper discharge section 7, paper passes through paper sensors 28A, 28C, 28D, 28F to 28L, but no paper passes through the other paper sensors 28. One sheet of paper P passes twice through paper sensors 28C, 28D, 28F to 28I.

In double-sided printing, when the paper source is the internal paper feed tray 23 and paper P is discharged by the first paper discharge section 5, paper passes through paper sensors 28B to 28J and 28L, but no paper passes through the other paper sensors 28. One sheet of paper P passes through paper sensors 28C and 28D twice.

In double-sided printing, when the paper source is the internal paper feed tray 23 and paper P is discharged by the second paper discharge section 7, paper passes through paper sensors 28B-28D and 28F-28L, but no paper passes through the other paper sensors 28. One sheet of paper P passes twice through paper sensors 28C, 28D, and 28F-28I.

After the printing operation starts, in step S3 of FIG. 4, the control unit 11 determines whether a jam of paper P has been detected. Specifically, the control unit 11 determines that a jam has been detected when the error between the detection timing of paper P and its theoretical value is equal to or greater than a threshold value in at least one of the paper sensors 28A-28L.

If it is determined that a jam has not been detected (step S3: NO), in step S4, the control unit 11 determines whether the printing operation has ended. Here, when printing and paper ejection for the number of sheets printed in the print job are completed, the printing operation ends, and the paper transport operation also ends. If it is determined that the printing operation has not ended (step S4: NO), the control unit 11 returns to step S3.

If it is determined that the printing operation has ended (step S4: YES), in step S5, the control unit 11 updates the number of sheets of paper N in the sensor table 81 for each paper sensor 28 through which paper passed during the most recent paper transport operation.

Specifically, for each paper sensor 28 through which paper passed in the most recent paper transport operation, the control unit 11 calculates the number of sheets of paper P that passed during that paper transport operation to the number of sheets of paper P that passed at the start of that paper transport operation (the number of sheets of paper P that passed in the sensor table 81), thereby calculating the number of sheets of paper P that passed at the end of that paper transport operation. Then, the control unit 11 updates the number of sheets of paper P that passed in the sensor table 81 for each paper sensor 28 through which paper passed to the calculated number of sheets of paper P. Here, for paper sensors 28 through which one sheet of paper P passes twice in double-sided printing, each pass is counted as one pass.

Next, in step S6, the control unit 11 acquires the amount of light received by the light receiving unit 28b of the paper sensor 28C. The amount of light received by the light receiving unit 28b acquired by the control unit 11 here is the amount of light received at the end of a series of paper transport operations, and is the amount of light received in a state in which the paper sensor 28C has not detected the paper P.

Next, in step S7, the control unit 11 determines whether the amount of light received by the light receiving unit 28b has attenuated due to the paper transport operation. If the amount of light received by the light receiving unit 28b at the end of a series of paper transport operations is smaller than the amount of light received by the light receiving unit 28b at the start of the series of paper transport operations, the control unit 11 determines that the amount of light received by the light receiving unit 28b has attenuated.

If it is determined that the amount of light received by the light receiving unit 28b has attenuated (step S7: YES), in step S8, the control unit 11 calculates the judgment value H at the end of the most recent paper transport operation for each paper sensor 28 through which paper passed. The control unit 11 then updates the judgment value H in the sensor table 81 for each paper sensor 28 through which paper passed.

Specifically, the control unit 11 calculates the attenuation amount D by subtracting the amount of light received by the light receiving unit 28b at the end of the most recent paper transport operation from the amount of light received by the light receiving unit 28b at the start of the most recent paper transport operation. Next, the control unit 11 calculates the judgment addition value C for each paper sensor 28 through which paper has passed using the above-mentioned formula (1). Then, the control unit 11 adds the calculated judgment addition value C for each paper sensor 28 through which paper has passed to the judgment value H (judgment value H in the sensor table 81) at the start of the most recent paper transport operation to calculate the judgment value H at the end of the paper transport operation. Then, the control unit 11 updates the judgment value H in the sensor table 81 for each paper sensor 28 through which paper has passed to the calculated judgment value H.

Next, in step S9, the control unit 11 determines whether there is a paper sensor 28 whose judgment value H exceeds the judgment threshold value Ht.

If it is determined that there is a paper sensor 28 whose judgment value H exceeds the judgment threshold Ht (step S9: YES), in step S10, the control unit 11 determines whether or not there is a paper sensor 28 whose judgment value H exceeds the judgment threshold Ht and whose paper count threshold Nt has not been set. Here, when the paper sensor 28 starts to be used (when the printing device 1 starts to be used), the paper count threshold Nt has not been set.

If it is determined that among the paper sensors 28 whose judgment value H exceeds the judgment threshold Ht, there is a paper sensor 28 for which the paper passing number threshold Nt has not been set (step S10: YES), in step S11, the control unit 11 sets the paper passing number N of that paper sensor 28 to the paper passing number threshold Nt.

As a result, the control unit 11 sets the number of sheets of paper N passed when the judgment value H first exceeds the judgment threshold value Ht for each paper sensor 28 after the paper sensor 28 starts to be used as the number of sheets of paper passed threshold value Nt.

Next, in step S12 of FIG. 5, the control unit 11 determines whether or not there is a paper sensor 28 whose judgment value H exceeds the judgment threshold Ht and whose number of sheets N passing through is different from the number of sheets N passing through threshold Nt.

If it is determined that the paper sensor 28 whose judgment value H exceeds the judgment threshold Ht includes a paper sensor 28 whose number of sheets N passing through is different from the number of sheets N passing through threshold Nt (step S12: YES), in step S13, the control unit 11 changes the number of sheets N passing through the paper sensor 28. Specifically, the control unit 11 sets the number of sheets N passing through the paper sensor 28 to the new number of sheets N passing through threshold Nt.

As a result, after setting the sheet number threshold Nt for each paper sensor 28, if the sheet number N when the judgment value H exceeds the judgment threshold Ht differs from the sheet number threshold Nt, the control unit 11 sets the sheet number N to the new sheet number threshold Nt.

Next, in step S14, the control unit 11 instructs the user to clean the paper sensor 28 whose judgment value H has exceeded the judgment threshold Ht. Specifically, the control unit 11 causes the display unit 71 to display a message urging the user to clean the paper sensor 28 whose judgment value H has exceeded the judgment threshold Ht, as well as the position of the paper sensor 28, etc.

In this way, the control unit 11 determines that cleaning is necessary for the paper sensor 28 whose judgment value H has exceeded the judgment threshold value Ht, and instructs the user to clean it.

Next, in step S15, the control unit 11 determines whether cleaning of the paper sensor 28 is complete. Here, the control unit 11 determines that cleaning of the paper sensor 28 is complete when a user operation is performed on the input unit 72 to notify the printing device 1 that cleaning of the paper sensor 28 is complete. If the control unit 11 determines that cleaning of the paper sensor 28 is not complete (step S15: NO), it repeats step S15.

If it is determined that cleaning of the paper sensor 28 is complete (step S15: YES), in step S16, the control unit 11 resets the judgment value H and the number of sheets of paper N in the sensor table 81 for the paper sensor 28 that has been cleaned. This completes the series of processes.

If it is determined in step S10 that there is no paper sensor 28 for which the paper count threshold Nt has not been set among the paper sensors 28 for which the judgment value H has exceeded the judgment threshold Ht (step S10: NO), the control unit 11 proceeds to step S12 in FIG. 5.

If it is determined in step S12 that among the paper sensors 28 whose judgment value H exceeds the judgment threshold Ht, there is no paper sensor 28 whose number of sheets N passing through is different from the number of sheets N passing through threshold Nt (step S12: NO), the control unit 11 proceeds to step S14.

If it is determined in step S7 that the amount of light received by the light receiving unit 28b has not attenuated (step S7: NO), and if it is determined in step S9 that there is no paper sensor 28 whose judgment value H exceeds the judgment threshold value Ht (step S9: NO), in step S17, the control unit 11 determines whether there is a paper sensor 28 whose number of sheets of paper N exceeds the number of sheets of paper threshold value Nt.

If it is determined that there is a paper sensor 28 whose number of sheets N has exceeded the number of sheets Nt (step S17: YES), the control unit 11 proceeds to step S14 in FIG. 5 and instructs the user to clean the paper sensor 28 whose number of sheets N has exceeded the number of sheets Nt.

In this way, when the number of sheets N passing through each paper sensor 28 exceeds the number of sheets N passing through threshold Nt, even if the judgment value H does not exceed the judgment threshold Ht, the control unit 11 judges that cleaning of the paper sensor 28 is necessary and instructs the user to clean it.

If the control unit 11 determines that there is no paper sensor 28 whose number of sheets N passed exceeds the number of sheets Nt passed threshold (step S17: NO), the series of processes ends.

If it is determined in step S3 that a jam has been detected (step S3: YES), the control unit 11 stops the printing operation in step S18 of FIG. 6. This also stops the paper transport operation.

Next, in step S19, the control unit 11 updates the number of sheets of paper N in the sensor table 81 for each paper sensor 28 through which paper passed during the most recent paper transport operation.

Here, when the paper transport operation is stopped due to the detection of a jam, the series of paper transport operations up to the point of the stop is the most recent paper transport operation. The method for calculating the number of sheets of paper N is the same as the method described in step S5 above. The paper P that is stopped at a position detected by the paper sensor 28 at the time the paper transport operation is stopped due to the detection of a jam may or may not be included in the paper P that has passed the paper sensor 28.

After step S19, the control unit 11 proceeds to step S20. The processes of steps S20 to S22 are the same as the processes of steps S6 to S8 described above.

After step S22, in step S23, the control unit 11 determines whether the jam was detected due to erroneous detection of paper P by the paper sensor 28.

Specifically, the control unit 11 causes the display unit 71 to display a message instructing the user to check whether or not there is paper P at the position of the paper sensor 28 where the jam was detected. Then, when a user operation is performed on the input unit 72 to notify the printing device 1 that there is no paper P at the position instructed to be checked, the control unit 11 determines that the jam was detected due to erroneous detection of paper P by the paper sensor 28. Note that the method of determining erroneous detection is not limited to this.

If it is determined that the jam was detected due to erroneous detection of paper P by the paper sensor 28 (step S23: YES), in step S24 of FIG. 7, the control unit 11 determines whether the judgment value H of the paper sensor 28 that erroneously detected the paper P is less than the judgment threshold value Ht.

If it is determined that the judgment value H of the paper sensor 28 that erroneously detected the paper P is less than the judgment threshold Ht (step S24: YES), in step S25, the control unit 11 changes the judgment threshold Ht of the paper sensor 28. Specifically, the control unit 11 sets the judgment value H of the paper sensor 28 to a new judgment threshold Ht.

As a result, when an erroneous detection of paper P occurs in the paper sensor 28 before the judgment value H reaches the judgment threshold Ht, the control unit 11 sets the judgment value H in the paper sensor 28 at the time when the erroneous detection of paper P occurs as the new judgment threshold Ht for the paper sensor 28.

After step S25, the control unit 11 proceeds to step S26. Also, if it is determined in step S24 that the judgment value H of the paper sensor 28 that erroneously detected the paper P is equal to or greater than the judgment threshold value Ht (step S24: YES), the control unit 11 proceeds to step S26. The processing of steps S26 to S34 is the same as the processing of steps S9 to S17 described above.

Here, in step S31, when the control unit 11 instructs the user to clean the paper sensor 28, it also instructs the user to remove the paper P remaining in the printing device 1 due to the stop of the printing operation. As a result, when the paper sensor 28 is cleaned, the paper P remaining in the printing device 1 is also removed, and when the cleaning of the paper sensor 28 is completed, the removal of the paper P remaining in the printing device 1 is also completed.

After step S33, the control unit 11 proceeds to step S35. Also, if it is determined in step S34 that there is no paper sensor 28 in which the number of sheets N passed through exceeds the number of sheets Nt passed through threshold (step S34: NO), the control unit 11 proceeds to step S35.

In step S35, the control unit 11 acquires the amount of light received by the light receiving unit 28b of the paper sensor 28C. The amount of light received by the light receiving unit 28b acquired by the control unit 11 here is the amount of light received at the start of a series of paper transport operations (printing operations) after the printing operation is resumed, and is the amount of light received in a state in which the paper sensor 28C has not detected the paper P.

Next, in step S36, the control unit 11 resumes the printing operation based on the print job that was stopped due to the detection of the jam. After this, the control unit 11 returns to step S3 in FIG. 4.

If it is determined in step S21 of FIG. 6 that the amount of light received by the light receiving unit 28b has not attenuated (step S21: NO), in step S37 of FIG. 8, the control unit 11 determines whether the jam was detected due to erroneous detection of the paper P by the paper sensor 28.

If it is determined that the jam was detected due to erroneous detection of paper P by the paper sensor 28 (step S37: YES), in step S38 of FIG. 8, the control unit 11 changes the judgment threshold Ht of the paper sensor 28 that erroneously detected paper P. Specifically, the control unit 11 sets the judgment value H of the paper sensor 28 to a new judgment threshold Ht. After this, the control unit 11 proceeds to step S31 of FIG. 7.

Here, if step S21 in FIG. 6 is judged as "NO" and step S37 in FIG. 8 is judged as "YES", the judgment value H of the paper sensor 28 that erroneously detected the paper P remains the judgment value H at the start of the most recent paper transport operation. Therefore, the erroneous detection of the paper P occurred before the judgment value H of the paper sensor 28 exceeded the judgment threshold Ht. By the processing of step S38 described above, the control unit 11 sets the judgment value H at the time when the erroneous detection of the paper sensor 28 that erroneously detected the paper P occurred before the judgment value H exceeded the judgment threshold Ht as the new judgment threshold Ht for the paper sensor 28.

If it is determined in step S37 that the jam was not detected due to erroneous detection of paper P by the paper sensor 28 (step S37: NO), in step S39, the control unit 11 determines whether there is a paper sensor 28 in which the number of sheets N passed through has exceeded the number of sheets Nt passed through threshold.

If it is determined that there is a paper sensor 28 where the number of sheets N passed through exceeds the number of sheets Nt passed through threshold (step S39: YES), the control unit 11 proceeds to step S31 in FIG. 7.

If it is determined that there is no paper sensor 28 in which the number of sheets N passing through exceeds the threshold number of sheets Nt (step S39: NO), in step S40, the control unit 11 instructs the user to clear the jam (remove the paper P remaining in the printing device 1). Specifically, the control unit 11 causes the display unit 71 to display a message instructing the user to clear the jam, as well as the position of the paper P remaining in the printing device 1, etc.

Next, in step S41, the control unit 11 determines whether or not jam removal is complete. Here, the control unit 11 determines that jam removal is complete when a user operation is performed on the input unit 72 to notify the printing device 1 that jam removal is complete. If the control unit 11 determines that jam removal is not complete (step S41: NO), it repeats step S41. If the control unit 11 determines that jam removal is complete (step S41: YES), it proceeds to step S35 in FIG. 7.

If it is determined in step S23 that the jam was not detected due to erroneous detection of paper P by the paper sensor 28 (step S23: NO), the control unit 11 proceeds to step S42 in FIG. 9. The processes in steps S42 to S47 are the same as those in steps S9 to S13 and S17 described above.

If it is determined in step S45 that there is no paper sensor 28 in which the number of sheets N passed exceeds the number of sheets Nt passed threshold (step S45: NO), the control unit 11 proceeds to step S31 in FIG. 7. Also, after step S46, the control unit 11 proceeds to step S31 in FIG. 7.

If it is determined in step S47 that there is a paper sensor 28 whose number of sheets N has exceeded the number of sheets Nt (step S47: YES), the control unit 11 proceeds to step S31 in FIG. 7. If it is determined that there is no paper sensor 28 whose number of sheets N has exceeded the number of sheets Nt (step S47: NO), the control unit 11 proceeds to step S40 in FIG. 8.

By processing the flowcharts of Figures 4 to 9 as described above, when the amount of light received by the light receiving portion 28b of the paper sensor 28C is attenuated by the paper transport operation, as described above, the judgment addition value C is calculated for each paper sensor 28 through which paper passed during the paper transport operation, and the judgment value H is calculated by accumulating the judgment addition values C.

An example of the change in the judgment value H of the paper sensor 28 calculated in this manner is shown in FIG. 10. In FIG. 10, a positive value for the attenuation amount D indicates that the amount of light received by the light receiving unit 28b has attenuated, and a negative value for the attenuation amount D indicates that the amount of light received by the light receiving unit 28b has increased.

One paper transport operation consists of a continuous series of paper transport operations. For example, if the paper transport operations for the number of sheets printed in a print job are performed without stopping along the way, then that series of paper transport operations is considered to be one paper transport operation. Also, for example, if the paper transport operation stops once during a print job due to the detection of a jam, then the series of paper transport operations up to the stop is considered to be one paper transport operation, and the series of print transport operations from resumption to completion is also considered to be one paper transport operation. The same applies if the paper transport operation stops multiple times along the way.

In the example of Figure 10, the judgment value H exceeds the judgment threshold value Ht at the end of the 28th paper transport operation, so it is determined that cleaning of the paper sensor 28 in the example of Figure 10 is necessary at this point.

Here, due to the influence of the transport air currents generated by the paper transport, the amount of paper dust accumulated on the paper sensor 28C may decrease, and the amount of light received by the light receiving unit 28b may increase before and after the paper transport operation. That is, as described above, the attenuation amount D may become a negative value. However, even if the amount of paper dust accumulated on the paper sensor 28C has decreased, this does not necessarily mean that the amount of paper dust has also decreased in the other paper sensors 28. For this reason, the printing device 1 calculates the judgment addition value C of each paper sensor 28 through which paper has passed only when the amount of light received by the light receiving unit 28b has decreased, and calculates the judgment value H by accumulating the judgment addition values C. The judgment value H of the paper sensor 28C is calculated in the same way. This makes it possible to prevent a delay in the time when it is determined that the paper sensor 28 needs to be cleaned.

Next, we will explain an example of the calculation results of the judgment value H of each paper sensor 28 through which paper passed during a certain paper transport operation.

The paper transport operation in this example is a paper transport operation in a printing operation in which, in single-sided printing, the paper source is the external paper feed tray 21 and paper P is discharged by the second paper discharge section 7. In this case, as described above, paper is passing through paper sensors 28A, 28C, 28D, 28F to 28I, and 28K, but not through the other paper sensors 28.

In addition, the number of printed sheets in this example is 10. The judgment value H of each paper sensor 28 at the start of the paper transport operation in this example is assumed to be that shown in FIG. 3. The amount of attenuation due to this paper transport operation is assumed to be D = 15.

In this example, the judgment sum C of paper sensor 28A is calculated as C = 3.75 using the above-mentioned formula (1). Then, by adding the judgment sum C = 3.75 to the judgment value H = 5 of paper sensor 28A in Figure 3, the judgment value H = 8.75 of paper sensor 28A is calculated as shown in Figure 11.

Similarly, the judgment value H for each of the paper sensors 28C, 28D, 28F to 28I, and 28K is calculated as shown in FIG. 11. In addition, "10" is added to the number of sheets of paper N for each of the paper sensors 28A, 28C, 28D, 28F to 28I, and 28K in FIG. 3, resulting in the number of sheets of paper N shown in FIG. 11.

Next, FIG. 12 shows an example of the sensor table 81 when the judgment value H of the paper sensor 28 first exceeds the judgment threshold Ht.

In this example, at the end of a paper transport operation, the judgment value H of each of the paper sensors 28G-28I exceeds the judgment threshold Ht for the first time after the paper sensors 28G-28I start to be used. This causes the paper sensors 28G-28I to determine that cleaning is required. Furthermore, for each of the paper sensors 28G-28I, the number of sheets of paper passed at the end of this paper transport operation is N = 10,000.

In this example, after the paper transport operation is completed, the judgment value H and the number of sheets N of paper sensors 28G to 28I in the sensor table 81 are reset (H=0, N=0) as shown in FIG. 12. In addition, the number of sheets Nt thresholds of paper sensors 28G to 28I are set to 10,000.

In this example, for paper sensors 28 other than paper sensors 28G to 28I, the judgment value H has never exceeded the judgment threshold value Ht since the start of use, and as shown in FIG. 12, the paper count threshold value Nt has not been set.

As described above, in the printing device 1, when the amount of light received by the light receiving section 28b of the paper sensor 28C is attenuated by the paper transport operation, the control section 11 calculates the judgment addition value C for each paper sensor 28 through which paper has passed based on the attenuation amount D during the paper transport operation and the orientation of the paper sensor 28 through which paper has passed, and calculates the judgment value H by accumulating the judgment addition values C. Then, the control section 11 determines that the paper sensor 28 whose judgment value H exceeds the judgment threshold value Ht needs to be cleaned. This makes it possible to determine the timing when cleaning is required for each of the multiple paper sensors 28 with only one analog sensor for measuring the degree of paper dust accumulation, the paper sensor 28C. Therefore, unnecessary cleaning of the paper sensor 28 can be reduced while preventing the device from becoming larger and the circuit design from becoming more complicated. In addition, since unnecessary cleaning of the paper sensor 28 can be reduced, maintenance time can be shortened.

In addition, the printing device 1 uses the orientation of the paper sensor 28 as an installation condition for the paper sensor 28 to calculate the judgment value H, so that in a printing device 1 that has multiple paper sensors 28 installed in various orientations, it is possible to determine the timing when each paper sensor 28 needs to be cleaned.

In addition, in the printing device 1, the control unit 11 sets the number of sheets N when the judgment value H first exceeds the judgment threshold Ht for each paper sensor 28 as the number of sheets N passed as the number of sheets passed threshold Nt. After setting the number of sheets passed threshold Nt, the control unit 11 determines that cleaning is required for the paper sensor 28 for which the number of sheets N passed exceeds the number of sheets passed threshold Nt even if the judgment value H does not exceed the judgment threshold Ht. In this way, by also using the number of sheets passed threshold Nt to determine whether cleaning of the paper sensor 28 is required, the timing when cleaning of each paper sensor 28 is required can be determined with higher accuracy.

In addition, in the printing device 1, after setting the sheet count threshold Nt for each paper sensor 28, if the number of sheets N passed when the judgment value H exceeds the judgment threshold Ht differs from the sheet count threshold Nt, the control unit 11 sets the number of sheets N passed as a new sheet count threshold Nt. By updating the sheet count threshold Nt in this way, it is possible to further improve the accuracy of determining when each paper sensor 28 needs to be cleaned.

In addition, in the printing device 1, when an erroneous detection of paper P occurs in a paper sensor 28 before the judgment value H reaches the judgment threshold Ht, the control unit 11 sets the judgment value H of the paper sensor 28 at the time when the erroneous detection of paper P occurs as the new judgment threshold Ht of the paper sensor 28. By updating the judgment threshold Ht in this way, it is possible to further improve the accuracy of determining when cleaning is required for each paper sensor 28.

In addition, in the printing device 1, the paper sensor 28C, which functions as a sensor for measuring the degree of paper dust accumulation, also serves as a sensor for detecting the paper P. This allows the number of paper sensors 28 to be reduced, thereby preventing the device configuration from becoming too complicated.

In addition, the paper sensor 28C may be a dedicated sensor for measuring the degree of paper dust accumulation.

Conditions other than the orientation of the paper sensor 28 may be used as installation conditions for the paper sensor 28 to calculate the judgment value H. For example, if the degree of generation of the transport airflow differs depending on the position of the paper sensor 28 on the transport path, and the ease of paper dust accumulation differs depending on the position of the paper sensor 28 on the transport path, the position of the paper sensor 28 on the transport path may be used as an installation condition for the paper sensor 28 to calculate the judgment value H. The orientation of the paper sensor 28 may be combined with other conditions as an installation condition for the paper sensor 28 to calculate the judgment value H.

The present invention is not limited to the above-described embodiment as it is, and in the implementation stage, the components can be modified and embodied without departing from the gist of the invention. In addition, various inventions can be formed by appropriately combining multiple components disclosed in the above-described embodiment. For example, some components may be deleted from all the components shown in the embodiment.

[Additional Notes]
This application discloses the following inventions.

(Appendix 1)
a dust detection unit having a light emitting unit disposed along a transport path along which a medium is transported and a light receiving unit that receives light emitted by the light emitting unit;
a plurality of medium detection units arranged along the transport path and configured to detect a medium;
a judgment unit that, when the amount of light received by the light receiving unit is attenuated due to a media transport operation, calculates a judgment addition value for each media detection unit through which the medium has passed based on the amount of attenuation of the amount of light received by the light receiving unit during the media transport operation and the installation conditions of the media detection unit through which the medium has passed, and judges that cleaning of the media detection unit is necessary when the judgment value obtained by accumulating the judgment addition values exceeds a predetermined judgment threshold.

(Appendix 2)
2. The conveying device according to claim 1, wherein the installation conditions include an orientation of the medium detection unit.

(Appendix 3)
The conveying device described in Appendix 1 or 2, characterized in that the judgment unit resets the judgment value and the number of media sheets passing through the media detection unit after cleaning, and in each media detection unit, the number of sheets passing when the judgment value first exceeds the judgment threshold is set as the passing number threshold, and after the passing number threshold is set, if the passing number exceeds the passing number threshold even if the judgment value does not exceed the judgment threshold, it judges that cleaning of the media detection unit is necessary.

(Appendix 4)
The conveying device described in Appendix 3 is characterized in that, in each of the media detection units, after setting the passing number threshold, if the number of passing sheets when the judgment value exceeds the judgment threshold is different from the passing number threshold, the judgment unit sets the passing number to a new passing number threshold.

(Appendix 5)
The conveying device described in any of Appendices 1 to 4, characterized in that the judgment unit resets the judgment value in the media detection unit after cleaning, and if a false detection of a medium occurs in the media detection unit before the judgment value reaches the judgment threshold, the judgment value in the media detection unit at the time the false detection of the medium occurred is set as a new judgment threshold for the media detection unit.

(Appendix 6)
6. The conveying device according to claim 1, wherein the dust detection unit also serves as one of the plurality of medium detection units.

REFERENCE SIGNS LIST 1 Printing device 2 Paper feed section 3 Printing transport section 4 Printing section 5 First paper discharge section 6 Upper transport section 7 Second paper discharge section 8 Reversing section 9 Operation panel 10 Memory section 11 Control section 28A to 28L Paper sensor 28a Light-emitting section 28b Light-receiving section 81 Sensor table P Paper RC Normal path RD1, RD2 Paper discharge path RR Reversing path RS Paper feed path

Claims (6)

a dust detection unit having a light emitting unit disposed along a transport path along which a medium is transported and a light receiving unit that receives light emitted by the light emitting unit;
a plurality of medium detection units arranged along the transport path and configured to detect a medium;
a judgment unit that, when the amount of light received by the light receiving unit is attenuated due to a media transport operation, calculates a judgment addition value for each media detection unit through which the medium has passed based on the amount of attenuation of the amount of light received by the light receiving unit during the media transport operation and the installation conditions of the media detection unit through which the medium has passed, and judges that cleaning of the media detection unit is necessary when the judgment value obtained by accumulating the judgment addition values exceeds a predetermined judgment threshold. The transport device according to claim 1, characterized in that the installation conditions include the orientation of the medium detection unit. The conveying device according to claim 1 or 2, characterized in that the judgment unit resets the judgment value and the number of media passing through the media detection unit that has been cleaned, and in each of the media detection units, the number of passing sheets when the judgment value first exceeds the judgment threshold is set as the passing sheet number threshold, and after the passing sheet number threshold is set, if the passing sheet number exceeds the passing sheet number threshold even if the judgment value does not exceed the judgment threshold, it is judged that the media detection unit needs cleaning. The conveying device according to claim 3, characterized in that, in each of the media detection units, if the number of passing sheets when the judgment value exceeds the judgment threshold after the passing sheet number threshold is set is different from the passing sheet number threshold, the judgment unit sets the passing sheet number to a new passing sheet number threshold. The conveying device according to any one of claims 1 to 4, characterized in that the judgment unit resets the judgment value in the media detection unit that has been cleaned, and if an erroneous detection of a medium occurs in the media detection unit before the judgment value reaches the judgment threshold, the judgment value in the media detection unit at the time the erroneous detection of a medium occurs is set as a new judgment threshold for the media detection unit. The conveying device according to any one of claims 1 to 5, characterized in that the dust detection unit also serves as one of the multiple medium detection units.