Sheet conveyance device

Abstract

To provide a sheet conveyance device capable of appropriately restarting conveyance of a sheet by re-driving a conveyance roller without bothering a user with manual work.SOLUTION: A time from when driving of a conveyance roller is started until when a first sensor 21 detects a sheet is measured, and is stored in a memory 62 as TL. After a predetermined time passes since the first sensor 21 detects the sheet 3, driving of a registration roller 15 is started. When a second time which is a time from when the driving of the registration roller 15 is started until when a second sensor 22 detects the sheet 3, exceeds a threshold value, the driving of the registration rollers 15 is temporarily stopped, and then TCON which is a time from when re-driving of the conveyance roller is started until when the driving of the registration roller 15 is started, is determined based on the TL stored in the memory 62, the registration roller 15 is controlled to start the driving after the lapse of the TCON from when the re-driving of the conveyance roller is started.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a sheet conveying device for conveying a sheet.

Background Art

[0002] Conventionally, a sheet conveying device provided with a registration roller for correcting the posture of a sheet has been proposed. Here, the registration roller is composed of a pair of rollers that can rotate in a stop state or in a direction opposite to the conveying direction. The sheet is fed toward the registration roller, and the tip of the sheet is aligned along the pair of rollers by deflecting the sheet. Then, when the registration roller is rotated in the conveying direction with the tip of the sheet along the pair of rollers, the skew is eliminated.

[0003] As an example of a sheet conveying device provided with such a registration roller, for example, Japanese Patent Application Laid-Open No. 2014-031245 discloses an image forming apparatus provided with an MP (multi-pass) tray (also called a manual feed tray) used when printing using a sheet different from a sheet normally used such as cardboard or colored paper. In this image forming apparatus, a conveyance path for a sheet from the MP tray is provided so as to merge into a conveyance path from a sheet feeding tray for storing a sheet normally used to a printing unit. And, in order to make the sheet not skewed at the printing unit, the above registration roller is provided in the conveyance path between the printing unit.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Here, in the sheet conveying device as disclosed in Patent Document 1 above, the conveyance amount of the sheet for creating the deflection necessary for correcting skew in the resist roller is calculated based on the timing when a sensor disposed upstream in the conveyance direction with respect to the resist roller detects the passage of the leading edge of the sheet. That is, after a predetermined time has elapsed since the upstream sensor detects the leading edge of the sheet (the timing when it is estimated that the necessary deflection can be created), the rotational drive of the resist roller in the paper conveyance direction is started.

[0006] On the other hand, the sheet conveying device includes, upstream of the resist roller, a conveying roller for conveying the sheet to the resist roller on the conveyance path and forming a deflection. For this conveying roller, in order to prevent a plurality of sheets from being conveyed during one sheet conveying operation, the conveyance time (the drive time of the conveying roller) is designed in advance so that the conveyance amount during one sheet conveying operation is shorter than the length of the sheet. As a result, for example, if slip occurs between the conveying roller and the sheet at the start of sheet conveyance, the conveyance distance becomes shorter than expected, and while the drive of the resist roller is started when the sheet passes the upstream sensor, a situation may occur where the sheet does not reach the position of the resist roller by a slight amount. Conventionally, when the above situation occurs, it becomes an error, and there has been a problem that the user is forced to remove the sheet remaining in the conveyance path without any abnormality. Also, although it is conceivable to re-drive the conveying roller after once stopping the drive of the resist roller, since the leading edge of the sheet has already passed the upstream sensor, a new problem arises in that it is impossible to specify an appropriate timing for starting the drive of the resist roller in order to correct the posture of the sheet.

[0007] The present invention has been made to solve the above-described conventional problems, and an object thereof is to provide a sheet conveying device that enables appropriate resumption of sheet conveyance by re-driving the conveying roller without bothering the user even when the above situation occurs.

Means for Solving the Problems

[0008] To achieve the above object, the sheet conveying apparatus according to the present application includes a conveying roller that conveys a sheet and stops conveying after a predetermined conveying time has elapsed after the start of driving, a registration roller that is downstream of the conveying roller in the sheet conveying direction, corrects the posture of the sheet conveyed by the conveying roller, and further conveys the sheet downstream, a first sensor that is upstream of the registration roller in the sheet conveying direction and detects the passage of the sheet, a second sensor that is downstream of the registration roller in the sheet conveying direction and detects the passage of the sheet, a memory, and a controller. The controller measures the time from the start of driving of the conveying roller until the first sensor detects the sheet, stores it in the memory as a first time, starts driving the registration roller after a predetermined time has elapsed since the first sensor detected the sheet, and when a second time, which is the time from the start of driving of the registration roller until the second sensor detects the sheet, exceeds a threshold value, once stops driving the registration roller, and based on the first time stored in the memory, determines a third time, which is the time from the start of redriving the conveying roller until the start of driving the registration roller, and after determining the third time, redrives the conveying roller, and controls to start driving the registration roller after the third time has elapsed since the start of redriving the conveying roller. Note that "conveying is stopped after the conveying time has elapsed" may mean that the rotation of the conveying roller itself is stopped after the conveying time has elapsed, or the conveying roller may be separated from the sheet while rotating. Also, "starting driving of the registration roller" means driving the registration roller in the direction of conveying the sheet downstream in the conveying direction, and by performing this driving, the posture of the sheet that has reached the position of the registration roller by the conveying by the conveying roller is corrected and then conveyed further downstream.

Advantages of the Invention

[0009] The sheet conveyance device according to the present application having the above configuration can appropriately resume the conveyance of the sheet by re-driving the conveyance roller without bothering the user even in a situation where, for example, at the start of sheet conveyance, slip occurs between the conveyance roller and the sheet, resulting in a shorter conveyance distance than expected and the sheet passing the first sensor on the upstream side, thereby starting the driving of the registration roller while the sheet has not reached the position of the registration roller by a small amount. Further, when the conveyance roller is re-driven, it is also possible to drive the registration roller at an appropriate timing for correcting the posture of the sheet.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0011] Hereinafter, an embodiment in which the sheet conveyance device according to the present application is embodied in a printer as an image forming apparatus will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a main part showing the printer 1 of this embodiment. In the following description, an embodiment in which the sheet conveyance device is embodied in the printer 1 will be described. However, the "sheet conveyance device" can be embodied not only in printing devices such as printers (e.g., laser printers and inkjet printers), but also in various devices having a function of conveying sheets, such as copiers, facsimile machines, and multifunction machines equipped with a printer function and a scanner function. Further, the "sheet" is not limited to paper sheets as recording media, and also includes OHP sheets, films, and the like.

[0012] [Overall Configuration of Printer] The printer 1 according to this embodiment is a monochrome laser printer using an electrophotographic method, and prints a desired image on the sheet 3. However, the printer 1 may be a color laser printer. The printer 1 includes a main body housing 2, a feeder unit 4 for feeding a sheet 3 as a recording medium inside the main body housing 2, an image forming unit 5 for forming an image on the fed sheet 3, and the like. Hereinafter, among the above components, the main body housing 2 and the feeder unit 4 will be described in more detail.

[0013] (Main Body Housing) In the main body housing 2, a detachable opening 6 for detaching and attaching the process cartridge 18, which is a part of the image forming unit 5, is formed in one side wall, and a front cover 7 for opening and closing the detachable opening 6 is provided.

[0014] This front cover 7 is rotatably supported by a cover shaft (not shown) inserted through the lower end thereof. As a result, when the front cover 7 is closed about the cover shaft, as shown in FIG. 1, the detachable opening 6 is closed by the front cover 7, and when the front cover 7 is opened (tilted) with the cover shaft as a fulcrum, the detachable opening 6 is opened, and the process cartridge 18 can be detached from and attached to the main body housing 2 through this detachable opening 6.

[0015] In the following, in this printer 1 and the process cartridge 18, the side where the front cover 7 is provided is defined as the "front side", and the opposite side is defined as the "rear side". Also, when the printer 1 is viewed from the front side, the right side (the back side of the paper surface) is defined as the "right side", and the opposite side (the front side of the paper surface) is defined as the "left side".

[0016] Although not shown, on the upper surface of the main body housing 2, a user IF (user interface) for providing information to the user and receiving the user's operations is arranged. The user IF is, for example, a touch panel having a function as a display.

[0017] (Feeder unit) The feeder unit 4 includes a paper feed tray 8 detachably mounted at the bottom inside the main body housing 2, a separation roller 9 and a separation pad 10 provided above the front end of the paper feed tray 8, and a paper feed roller 11 provided on the rear side of the separation roller 9 (the upstream side in the conveyance direction of the sheet 3 with respect to the separation pad 10).

[0018] Also, the feeder unit 4 is provided with a paper dust removal roller 12 disposed opposite above the front side of the separation roller 9 (the downstream side in the conveyance direction of the sheet 3 with respect to the separation roller), and an opposing roller 13 disposed opposite to the paper dust removal roller 12. And the first conveyance path 14 of the sheet 3 has a shape that is folded back rearward in a U shape from the vicinity of the arrangement of the paper dust removal roller 12, and a registration roller 15 composed of a pair of upper and lower rollers is arranged below the process cartridge 18 on the further downstream side in the conveyance direction.

[0019] Further, on the upstream side of the resist roller 15 in the sheet conveyance direction, a first sensor 21 for detecting the passage of the sheet 3 (more precisely, the leading edge of the sheet) in the first conveyance path 14 is arranged. Similarly, on the downstream side of the resist roller 15 in the sheet conveyance direction, a second sensor 22 for detecting the passage of the sheet 3 (more precisely, the leading edge of the sheet) in the first conveyance path 14 is arranged. Incidentally, the first sensor 21 and the second sensor 22 include actuators 21a, 22a that are rotatable about a rotation axis and a photosensor (not shown). When the actuators 21a, 22a fall due to contact with the sheet 3 passing through the first conveyance path 14, the photosensor near the rotation axis of the actuators 21a, 22a detects that the actuators 21a, 22a have fallen, that is, the passage of the sheet 3.

[0020] Incidentally, the first sensor 21 is used to determine the driving timing of the downstream resist roller 15 as described later, and the second sensor 22 is also used to determine the timing for executing the printing process in the image forming unit 5 downstream (print position adjustment for the sheet).

[0021] Inside the paper feed tray 8, a paper pressing plate 16 on which the sheets 3 can be stacked is provided. The paper pressing plate 16 is supported so as to be swingable at the rear end, whereby the front end is movable in the vertical direction.

[0022] Also, at the front end of the paper feed tray 8, a lever 17 for lifting the front end of the paper pressing plate 16 upward is provided. The lever 17 is supported so as to be swingable about a lever axis (not shown) at a position below the front end of the paper pressing plate 16, and the front end is in contact with the front end of the lower surface of the paper pressing plate 16. Thus, when a rotational driving force in the counterclockwise direction in the drawing is input to the lever axis, the lever 17 rotates with the lever axis as a fulcrum, and the front end of the lever 17 lifts the front end of the paper pressing plate 16.

[0023] When the front end of the paper pressing plate 16 is lifted, the sheet 3 at the uppermost position on the paper pressing plate 16 is pressed by the paper feeding roller 11, and paper feeding is started toward the separation position between the separation roller 9 and the separation pad 10 by the rotation of the paper feeding roller 11.

[0024] On the other hand, when the paper feed tray 8 is detached from the main body housing 2, the rotation drive shaft that was input to the lever shaft is no longer input, and the paper pressing plate 16 moves downward at the front end by its own weight and assumes a state along the bottom surface of the paper feed tray 8. In this state, the sheet 3 can be stacked on the paper pressing plate 16.

[0025] The sheet 3 sent out toward the separation position by the paper feeding roller 11 is reliably separated and fed one by one when it is sandwiched between the separation roller 9 and the separation pad 10 by the rotation of the separation roller 9. The fed sheet 3 is folded back along the U-shaped first conveyance path 14. More specifically, the fed sheet 3 is first conveyed obliquely upward in the front direction by the separation roller 9 and the separation pad 10, and after passing between the paper dust removal roller 12 and the counter roller 13 where the paper dust is removed, it is conveyed to the registration roller 15.

[0026] The registration roller 15 is composed of a pair of upper and lower rollers facing each other, and after correcting the posture of the sheet 3, it conveys the sheet 3 toward the transfer position of the image forming unit 5 (the nip position between the photosensitive drum and the transfer roller, which is the position where the toner image on the photosensitive drum is transferred to the sheet 3).

[0027] Here, a more detailed description of the method for correcting the posture of the sheet 3 by the registration roller 15 is as follows. The registration roller 15 is basically in a stopped state (it may rotate in the direction opposite to the conveyance direction), and in this state, the sheet is fed into the registration roller 15, and the tip of the sheet is aligned along the roller pair of the registration roller 15 by deflecting the sheet. Then, when the registration roller 15 is rotated in the conveyance direction with the tip of the sheet 3 aligned along the roller pair, the skew is eliminated.

[0028] Here, in order to create the deflection necessary for correcting skew by the resist roller 15, the timing at which the resist roller 15 starts rotating in the conveyance direction is determined based on the timing at which the first sensor 21 upstream detects the passage of the sheet 3. More specifically, the driving of the resist roller 15 is started after a predetermined time has elapsed since the first sensor 21 detects the passage of the sheet 3 (the time required for the sheet 3 that has passed through the first sensor to reach the resist roller 15 and form the necessary deflection).

[0029] Note that the correction of the posture of the sheet 3 by the resist roller 15 is performed in the same manner not only for the sheet 3 fed from the paper feed tray 8 but also for the sheet 3 fed from the MP (multi-pass) tray (also called the manual feed tray) 41. Note that the printer 1 is provided with a conveyance path (the second conveyance path 54 described later) for the sheet 3 from the MP tray 41 so as to merge into the first conveyance path 14 from the paper feed tray 8 that stores the sheet 3 normally used to the transfer position of the image forming unit 5.

[0030] Subsequently, the multi-pass mechanism (manual paper feed mechanism) 42 provided in the printer 1 having the above configuration will be described below. Note that FIG. 2 is a cross-sectional view of the main part showing the state where the MP tray 41 is opened. The printer 1 has, in addition to a paper feed mechanism that conveys the sheet 3 from the paper feed tray 8 to the transfer position of the image forming unit 5 via the first conveyance path 14, a multi-pass mechanism 42 that conveys the sheet to the transfer position manually from the front side of the printer 1. That is, the multi-pass mechanism 42 is a part of the feeder unit 4.

[0031] The front cover 7 is formed with a rectangular opening 40 penetrating therethrough, and an MP tray 41 is provided to cover this. Specifically, the MP tray 41 is configured to include a cover portion 43 that serves as the front wall of the main body housing 2, and a tray portion 44 on which the manual feed sheet 3 is loaded. As shown in FIG. 2, the cover portion 43 is pivotally supported with respect to the main body housing 2 via a rotation axis 43a at the lower end side, and can be opened and closed about the rotation axis 43a. It is locked with the inner surface portion facing upward, and the tray portion 44 is provided on this inner surface portion. Note that, as shown in FIG. 2, when the MP tray 41 is opened, the tray portion 44 is in a posture where the side closer to the rotation axis 43a (the insertion tip side of the sheet 3) is inclined downward.

[0032] Also, the MP tray 41 is provided with a guide mechanism 49 having a pair of guide ribs 48 (only the left one is shown in FIGS. 1 and 2) that guide the conveyance of the sheet 3 by sandwiching both ends in the width direction of the sheet 3 loaded on the tray portion 44 when the MP tray 41 is opened. Since these pair of guide ribs 48 are slidable between a position where they approach each other and a position where they are separated from each other, the MP tray 41 can stack sheets 3 of any size in a stacked manner.

[0033] This guide mechanism 49 is located behind the upper end of the folded tray portion 44 (the space above the multi-pass mechanism 42) when the MP tray 41 is in the closed state (see FIG. 1), and slides along the guide groove 50 to be located on the rear end side of the tray portion 44 when the MP tray 41 is in the opened state (see FIG. 2).

[0034] Also, as shown in FIG. 2, the multi-pass mechanism 42 includes an MP paper feed roller (pickup roller) 51, an MP separation roller (separation roller) 52, and an MP separation pad 53 that is pressed against the MP separation roller 52 in an opposing state. And, in a state where the MP separation roller 52 and the MP separation pad 53 are in opposing contact, the MP separation pad 53 is pressed toward the MP separation roller 52 by the biasing force of a biasing member (not shown). That is, the multi-pass mechanism of the present embodiment is configured as a twin roller system including the MP paper feed roller 51 and the MP separation roller 52, with the MP paper feed roller 51 arranged on the MP tray 41 side and the MP separation roller 52 arranged behind it. Note that the “transport roller” described in the claims includes the MP paper feed roller 51 and the MP separation roller 52.

[0035] Then, the uppermost sheet 3 stacked on the MP tray 41 is fed by the rotation of the contacting MP paper feed roller 51, and after being sandwiched between the MP separation roller 52 and the MP separation pad 53, it is separated and fed one by one by their cooperation. The fed sheet 3 enters from the confluence point X near the downstream end in the transport direction of the first transport path 14 through the second transport path 54 and is sent toward the registration roller 15 side.

[0036] More specifically, the partition member 55 sandwiched between the first transport path 14 and the second transport path 54 has a side cross-sectional shape along the U shape of the first transport path 14, and has a shape that slopes downward as it goes forward from the confluence point X as the uppermost position. In short, the space on the upper surface side of the partition member 55 is a downwardly inclined space that widens downward as it goes forward from the confluence point X. And, in this downwardly inclined space, a roller unit 56 that pivotally supports the MP paper feed roller 51 and the MP separation roller 52 in a state where they are exposed downward is provided, and as will be described later, the MP paper feed roller 51 moves up and down within this downwardly inclined space.

[0037] The MP separation pad 53 is arranged in the middle of the inclined upper surface of the partition member 55, and the MP separation roller 52 is arranged to face it from above and the two are in a pressed state.

[0038] Next, a drive mechanism for conveying the sheets 3 stacked on the MP tray 41 by the MP feed roller 51 and the MP separation roller 52 will be briefly described.

[0039] The roller unit 56 is configured by rotatably mounting the MP feed roller 51 and the MP separation roller 52 on a common bearing member. Specifically, the MP feed roller 51 is integrally provided with a gear on the side thereof on the same axis, and these are rotatably supported on the front end side of the bearing member. On the other hand, the MP separation roller 52 is also integrally provided with a gear on the side thereof on the same axis, and these are rotatably supported on the rear end side of the bearing member. The gear of the MP feed roller 51 and the gear of the MP separation roller 52 are connected via another gear between them. As a result, the MP separation roller 52 rotates when a driving force is applied from a driving motor (not shown), and the MP feed roller 51 rotates accordingly.

[0040] Moreover, the roller unit 56 is configured so that the MP feed roller 51 side can swing around the MP separation roller 52. Specifically, the MP feed roller 51 can move between an elevated position (position shown in FIG. 2) where the MP feed roller 51 is separated from the upper surface of the partition member 55 and a lowered position where the MP feed roller 51 can abut against the upper surface of the partition member 55. The above-mentioned elevated position and lowered position are switched by a cam mechanism that operates when a solenoid (not shown) is turned on. In particular, when the MP feed roller 51 is in the lowered position, the MP separation roller 52 is driven to rotate so that the sheet 3 stacked on the MP tray 41 can be picked up. Note that, as shown in FIG. 2, when the MP feed roller 51 is in the elevated position, it is at the same height as the MP separation roller 52, which is the uppermost position, and when the MP feed roller 51 is in the lowered position, it is at a lower position than the MP separation roller 52.

[0041] Further, the roller unit 56 can switch between a state where a gear is engaged and a state where the gear is not engaged between an input gear to which a driving force from a driving motor (not shown) is input and the gears of the MP paper feed roller 51 and the MP separation roller 52 to be connected, by means of a cam mechanism. In the state where the gear is engaged, the MP paper feed roller 51 and the MP separation roller 52 are rotationally driven by the driving force from the driving motor. On the other hand, in the state where the gear is not engaged, the driving force from the driving motor cannot be transmitted, and the MP paper feed roller 51 and the MP separation roller 52 can rotate freely.

[0042] Next, the operation content when the sheet 3 is conveyed by the driving mechanisms of the MP paper feed roller 51 and the MP separation roller 52 will be briefly described. Here, before the solenoid is turned ON (initial state), it is in the home position. In the home position, the MP paper feed roller 51 is in the raised position separated from the sheet 3, and further, no driving force is applied to the MP paper feed roller 51 and the MP separation roller 52, and they are in a free-rotation state.

[0043] When the solenoid is turned ON, first, the MP paper feed roller 51 moves to the lowered position where it contacts the upper surface of the sheet 3 located on the upper surface of the partition member 55, by means of a cam mechanism that operates triggered by the turning ON of the solenoid. However, the MP separation roller 52 continues to be able to rotate freely. Note that the solenoid is a trigger for operating the cam mechanism, and thus it is turned OFF immediately after being turned ON and the operation of the cam mechanism is started.

[0044] After that, further, a state is achieved where a gear is engaged between an input gear to which a driving force from a driving motor (not shown) is input and the gears of the MP paper feed roller 51 and the MP separation roller 52 to be connected, by means of the cam mechanism. In accordance with the driving of the driving motor driven in synchronization, the MP separation roller 52 is rotationally driven. Along with this, the MP paper feed roller 51 is also driven as a follower. As a result, the feeding of the sheet 3 on the MP tray 41 is started, and the sheets are separated one by one at the opposing position between the MP separation roller 52 and the MP separation pad 53, and the separated sheets 3 pass through the second conveyance path 54.

[0045] Then, after a predetermined time has elapsed since the MP paper feed roller 51 has reached the lowered position and the MP paper feed roller 51 and the MP separation roller 52 have started rotational driving (i.e., the conveyance of the sheet 3 has started), the MP paper feed roller 51 returns to the raised position by the cam mechanism as well. At this point, the gears are meshed between the input gear to which the driving force from the drive motor is input and the gears of the connected MP paper feed roller 51 and MP separation roller 52, and the MP separation roller 52 and the MP paper feed roller 51 are rotationally driven. The conveyance of the sheet 3 that has already been picked up from the MP tray 41 continues by the MP separation roller 52, but it is in a state where a new sheet 3 cannot be picked up from the MP tray 41. After that, the meshing with the input gear to which the driving force from the drive motor is input is released by the cam mechanism, and the MP paper feed roller 51 and the MP separation roller 52 return to the free-wheeling state. That is, the conveyance of the sheet by the MP paper feed roller 51 and the MP separation roller 52 is stopped. Incidentally, the time from when the MP paper feed roller 51 reaches the lowered position and the MP paper feed roller 51 and the MP separation roller 52 start rotational driving until the driving is stopped, that is, the time from when the conveyance of the sheet 3 by the drive mechanism of the MP paper feed roller 51 and the MP separation roller 52 starts until the conveyance is stopped, is defined as the "conveyance time". Thus, the conveyance operation for one sheet 3 stacked on the MP tray 41 is completed. Incidentally, when conveying a plurality of sheets 3, the above operation is repeatedly executed.

[0046] Here, in the printer 1, the timing at which the MP paper feed roller 51 is returned to the raised position after the start of conveyance (the timing at which picking up a new sheet 3 from the MP tray 41 is made impossible) is such that the shape of the cam of the cam mechanism is adjusted so that the trailing edge of the separated sheet 3 passes before the opposing position between the MP separation roller 52 and the MP separation pad 53. In particular, it is set based on the length in the conveyance direction of the smallest size sheet 3 used in the printer 1. Thereby, it is possible to prevent a plurality of sheets from being conveyed for one conveyance operation of the sheet 3.

[0047] By performing the above-described conveying operation, as a result of the conveying operation on the sheet 3 stacked on the MP tray 41, the sheet 3 is conveyed along the second conveying path 54, and further from the merging point X, it is conveyed to the resist roller 15 through the first conveying path 14. At the resist roller 15, as described above, a warp is formed in the sheet 3 and then the posture of the sheet 3 is corrected. After that, the sheet 3 is conveyed toward the transfer position of the image forming unit 5 by driving the resist roller 15.

[0048] Here, the conveying distance of the sheet 3 in one conveying operation by the driving mechanisms of the MP paper feed roller 51 and the MP separation roller 52 is designed to be a distance (for example, 128 mm) sufficient for the leading edge of the sheet 3 to reach the resist roller 15 and form a warp. However, in the present embodiment, as will be described later, if slippage occurs between the MP paper feed roller 51 and the MP separation roller 52 and the sheet 3, particularly when the conveyance of the sheet 3 starts (especially while the leading edge of the sheet is between the MP paper feed roller 51 and the MP separation roller 52), the conveyance distance by the driving mechanisms of the MP paper feed roller 51 and the MP separation roller 52 becomes shorter than the assumed distance (128 mm), and it may happen that the conveyance stops before reaching the position of the resist roller 15 (the cam mechanism automatically stops the conveyance by the MP paper feed roller 51 and the MP separation roller 52 after a predetermined conveyance time has elapsed as described above). In such a case, the above-described conveying operation may be performed again on the same sheet 3. Details of the conveying operation to be performed again will be described later.

[0049] [Electrical Configuration of Printer] FIG. 3 shows the electrical configuration of the printer 1. The printer 1 includes a controller 61, a memory 62, a user IF 63, a network IF (communication interface) 64, a solenoid 65, a paper feed drive motor 66, a resist drive motor 67, a first sensor 21, and a second sensor 22. In FIG. 3, the configuration related to the conveyance of the sheet 3 is particularly extracted and shown, and actually, for example, a configuration related to printing is also separately included. These components are connected to a bus and can communicate with each other. Note that "IF" is an abbreviation of Interface.

[0050] The controller 61 is composed of a CPU, an ASIC (abbreviation for Application Specific Integrated Circuit), etc. On the other hand, the memory 62 is an embedded memory, and may be composed of a combination of ROM, RAM, NVRAM, SSD, HDD, etc. The ROM, RAM, and NVRAM included in the controller 61, which are used when executing various programs, may also be regarded as part of the memory 62.

[0051] The memory 62 stores programs executable by the controller 61. In this embodiment, mainly, the processing of the controller 61 according to the instructions described in the program is shown. That is, the processing such as "judgment", "selection", "calculation", "decision", "specification", "acquisition", "reception", "control", etc. in the following description represents the processing of the controller 61. Note that "acquisition" is used as a concept that does not require a request. That is, the process of the controller 61 receiving data without a request is also included in the concept of "the controller 61 acquiring data". Also, the "data" in this specification is represented by a bit string readable by the controller. And data with the same substantial meaning content but different formats shall be treated as the same data. The same applies to the "information" in this specification.

[0052] Furthermore, in addition to the above program, the memory 62 also stores the currently received print job and the time measured during the sheet conveyance described later.

[0053] The user IF 63 is a touch panel with the function of a display. It is interposed between the user operating the printer 1 and the controller 61, and functions as a user interface that provides various information to the user and accepts the user's operations. Note that the surface of the user IF 63 is a liquid crystal display. In particular, in this embodiment, it is used to display the "error display screen" and the like, which will be described later, and provides guidance such as the fact that printing on the sheet 3 could not be completed normally. Also, with the user IF 63, the user can select various options, buttons, icons, objects, etc. displayed on the liquid crystal display using the touch panel. However, the user interface for accepting the user's operations is not limited to the touch panel and may be physical keys. That is, a liquid crystal display and physical keys may be provided as the user interface.

[0054] In this embodiment, for the sake of convenience, the objects operated and selected by the user using the printer 1 or the administrator managing the printer 1 are described as "options", "buttons", "icons", "objects", etc., but they may be replaced with other words.

[0055] The network IF 64 is a network IF that connects the printer 1 to the network wirelessly or by wire. For example, the printer 1 can receive a print instruction (including image data to be printed) transmitted from a terminal (such as a PC) connected to the same network via the network IF 64, and can execute printing according to the received print instruction.

[0056] The solenoid 65 is an actuator included in the drive mechanism of the aforementioned MP paper feed roller 51 and MP separation roller 52, and is turned on by the controller 61 when starting to convey the sheet 3 stacked on the MP tray 41. When the solenoid is turned on, as described above, the MP paper feed roller 51 moves to the lowered position where it abuts against the upper surface of the sheet 3 positioned on the upper surface of the partition member 55 by the cam mechanism. Further, the driving force from the paper feed drive motor 66 becomes transmissible to the MP paper feed roller 51 and the MP separation roller 52, and the paper feed of the sheet 3 on the MP tray 41 is started. That is, the solenoid 65 serves as a trigger for starting the conveyance of the sheet 3.

[0057] Also, the paper feed drive motor 66 is a motor that serves as the drive source for the MP paper feed roller 51 and the MP separation roller 52. Similarly, the registration drive motor 67 is a motor that serves as the drive source for the registration roller 15. Further, although not shown in the figure, motors that serve as drive sources for other rollers such as the separation roller 9 and the paper feed roller 11 are also connected to the controller 61 in the same manner. However, instead of having a drive source for each roller, for example, a mechanism may be provided in which a single motor drives a plurality of rollers via an electromagnetic clutch or the like, and the controller 61 controls the ON-OFF timing of the electromagnetic clutch. The controller 61 can control each motor (rotation direction and torque) by controlling the current flowing through the motor.

[0058] Further, as described above, the first sensor 21 is a sensor that is upstream of the resist roller 15 in the sheet conveyance direction and detects the passage of the sheet 3 (more precisely, the leading edge of the sheet) in the first conveyance path 14 (FIGS. 1 and 2). Similarly, the second sensor 22 is a sensor that is downstream of the resist roller 15 in the sheet conveyance direction and detects the passage of the sheet 3 (more precisely, the leading edge of the sheet) in the first conveyance path 14. Note that the first sensor 21 and the second sensor 22 include actuators 21a and 22a that are rotatable about a rotation axis and a photosensor (not shown). When the actuators 21a and 22a fall into contact with the sheet 3 passing through the first conveyance path 14, the photosensor near the rotation axis of the actuators 21a and 22a detects that the actuators 21a and 22a have fallen, that is, that the sheet 3 has passed. Note that the sensor that detects the passage of the sheet 3 in the first conveyance path 14 may be a non-contact type sensor such as a proximity sensor or a reflection sensor instead of a physical switch.

[0059] [Control Processing by Controller] Subsequently, among the various control processes executed by the controller 61 of the printer 1 having the above configuration, the control process particularly executed in printing the sheet 3 from the MP tray 41 will be described with reference to FIGS. 4 and 5. FIGS. 4 and 5 are flowcharts of the printing process of the printer 1. The printing process is a process executed after the power of the printer 1 is turned on and a printing instruction (particularly a printing instruction from the MP tray 41) is received from a terminal (such as a PC) connected to the same network via the network IF 64. Note that each process shown in the flowcharts in FIGS. 4 and 5 below is stored in the memory 62 provided in the printer 1 and is executed by the controller 61.

[0060] First, in step (hereinafter abbreviated as S) 1, the controller 61 initializes a timer (timer value = 0). Note that the timer is used to measure the elapsed time from the start of driving (solenoid ON) of the MP paper feed roller 51 and the MP separation roller 52 as described later.

[0061] Subsequently, in S2, the controller 61 turns on the solenoid 65. As described above, the solenoid 65 is an actuator included in the drive mechanism of the MP paper feed roller 51 and the MP separation roller 52. Note that since the solenoid 65 is a trigger for operating the cam mechanism, it is turned off immediately after being turned on and the operation of the cam mechanism is started. Also, when the solenoid 65 is turned on, as described above, the MP paper feed roller 51 moves to the lowered position where it abuts against the upper surface of the sheet 3 located on the upper surface of the partition member 55 by the cam mechanism, and the driving force from the paper feed drive motor 66 driven in synchronization is transmitted to the MP paper feed roller 51 and the MP separation roller 52, and the paper feed of the sheet 3 on the MP tray 41 is started. Also, the measurement of the timer is started.

[0062] Next, in S3, the controller 61 determines whether the current value of the timer is less than T1 (the first upper limit time). T1 is a value determined in advance for each model, and when it is assumed that the sheet 3 is conveyed from the MP tray 41 as expected, it is the time (theoretical value) from when the driving of the MP paper feed roller 51 and the MP separation roller 52 is started (solenoid ON) until the conveyed sheet 3 is expected to pass the first sensor 21, plus a certain margin (margin value, for example, 3 sec).

[0063] And when it is determined that the value of the timer is less than T1 (S3: YES), it is further determined whether the passage of the sheet 3 is detected by the first sensor 21 (S4). Note that the first sensor 21 is a sensor that detects the passage of the sheet 3 (more precisely, the leading edge of the sheet) in the first conveyance path 14 on the upstream side in the sheet conveyance direction with respect to the resist roller 15 as described above (FIGS. 1 and 2).

[0064] And when it is determined that the value of the timer is less than T1 and the passage of the sheet 3 is detected by the first sensor 21 (S4: YES), the current value of the timer, that is, the time from when the driving of the MP paper feed roller 51 and the MP separation roller 52 is started (solenoid ON) until the first sensor 21 detects the sheet 3 is stored in the memory 62 as TL (the first time) (S5). Also, the value of the timer is once initialized to 0 (measurement continues).

[0065] On the other hand, when it is determined that the value of the timer is less than T1 and the passage of the sheet 3 is not detected by the first sensor 21 (S4: NO), the process returns to S3.

[0066] On the other hand, when the first sensor 21 does not detect the sheet 3 and the timer value exceeds T1 after the driving of the MP paper feed roller 51 and the MP separation roller 52 is started (solenoid ON) (S3: NO), the process proceeds to S6. In the case of proceeding to S6, for example, reasons such as the sheet cannot be picked up from the MP tray 41, paper jams occur, or the sheet is not set on the MP tray 41 in the first place can be considered.

[0067] In S6, the controller 61 once initializes the value of the timer to 0 (measurement continues). Also, 0 is set as the initial value of the count value that counts the number of retry times of the sheet conveyance operation.

[0068] Subsequently, in S7, the controller 61 turns on the solenoid 65. Thereby, the conveyance operation of the sheet 3 is started again by the driving mechanism of the MP paper feed roller 51 and the MP separation roller 52. Since the details are the same as those in S2, the description is omitted.

[0069] Next, in S8, the controller 61 determines whether the value of the timer is less than T1 (the first upper limit time).

[0070] And when it is determined that the value of the timer is less than T1 (S8: YES), it is further determined whether or not the passage of the sheet 3 is detected by the first sensor 21 (S9). As a result, when it is determined that the value of the timer is less than T1 and the passage of the sheet 3 is detected by the first sensor 21 (S9: YES), the process proceeds to S5. On the other hand, when it is determined that the value of the timer is less than T1 and the passage of the sheet 3 is not detected by the first sensor 21 (S9: NO), the process returns to S8.

[0071] On the other hand, when it is determined that after the driving of the MP paper feed roller 51 and the MP separation roller 52 is started (solenoid ON) in S7, the first sensor 21 has exceeded T1 without detecting the sheet 3 (S8: NO), the process proceeds to S10.

[0072] In S10, the controller 61 once initializes the value of the timer to 0 (measurement continues). Also, the count value for counting the number of retries of the sheet conveyance operation is incremented by 1.

[0073] Thereafter, in S11, the controller 61 determines whether or not the count value for counting the number of retries of the sheet conveyance operation has reached '3', that is, whether or not the sheet 3 could not be detected by the first sensor 21 even though the process flow of S7 to S9 was tried three times.

[0074] And if the count value for counting the number of retries of the sheet conveyance operation is less than '3' (S11: NO), the process returns to S7. On the other hand, when the count value for counting the number of retries of the sheet conveyance operation reaches '3', that is, when it is determined that the sheet 3 could not be detected by the first sensor 21 even though the process flow of S7 to S9 was tried three times (S11: YES), the process proceeds to S12.

[0075] In S12, the controller 61 displays an error display screen on the user IF 63. Also, the conveyance operation of the sheet 3 by the drive mechanisms of the MP paper feed roller 51 and the MP separation roller 52 is stopped. The error display screen displays a message indicating that the printing process could not be executed. Thereby, the user can grasp that the printing process could not be completed.

[0076] On the other hand, in S13 executed after the above S5, the controller 61 determines whether the current timer value, that is, the time since the passage of the sheet 3 was detected by the first sensor 21 has reached TLS (predetermined time). Note that TLS is preset for each model, and is a time obtained by adding a certain margin (margin value, for example, 1 sec) to the time (theoretical value) required for the sheet 3 that has passed through the first sensor 21 to reach the resist roller 15 and form the required deflection.

[0077] And, when it is determined that the current timer value is less than TLS, that is, the time since the passage of the sheet 3 was detected by the first sensor 21 is less than TLS (S13: NO), it waits until the timer value reaches TLS. On the other hand, when it is determined that the current timer value is equal to or greater than TLS, that is, TLS has elapsed since the passage of the sheet 3 was detected by the first sensor 21 (S13: YES), it proceeds to S14.

[0078] In S14, the controller 61 drives the resist drive motor 67 (or, when it is via an electromagnetic clutch, turns on the clutch), and starts driving the resist roller 15 in the direction of conveying the sheet 3 downstream in the conveyance direction. As a result, after correcting the posture of the sheet 3 that has reached the position of the resist roller 15 by the conveyance operation of the MP paper feed roller 51 and the MP separation roller 52, it is conveyed further downstream.

[0079] After that, in S15, the controller 61 determines whether the current timer value, that is, the time since the passage of the sheet 3 was detected by the first sensor 21, is less than TLS + T2 (threshold value). Note that T2 is a value determined in advance for each model, and assuming that the sheet 3 is being conveyed downstream by the drive of the resist roller 15 as expected, it is the time (theoretical value) from the start of the drive of the resist roller 15 until the sheet 3 is expected to reach the second sensor 22, plus a certain margin (margin value, e.g., 1 sec).

[0080] And when it is determined that the timer value is less than TLS + T2 (S15: YES), it is further determined whether the passage of the sheet 3 has been detected by the second sensor 22 (S16). Note that the second sensor 22 is a sensor that detects the passage of the sheet 3 (more precisely, the leading edge of the sheet) in the first conveyance path 14 on the downstream side of the sheet conveyance direction with respect to the resist roller 15 as described above (FIGS. 1 and 2).

[0081] And when it is determined that the timer value is less than TLS + T2 and the passage of the sheet 3 has been detected by the second sensor 22 (S16: YES), the value obtained by adding T3 to the current timer value, that is, the time from the start of the drive of the resist roller 15 until the sheet 3 reaches the second sensor 22, is stored in the memory 62 as TIMP (S17). Then, the process proceeds to S18. Note that T3 is a value determined in advance for each model, and assuming that the sheet 3 is being conveyed downstream by the drive of the resist roller 15 as expected, it is the time (theoretical value) until the sheet 3 reaches the transfer position of the image forming unit 5 (the nip position between the photosensitive drum and the transfer roller, where the toner image on the photosensitive drum is transferred to the sheet 3) after passing through the second sensor 22. That is, the timing of image formation by the image forming unit 5 is controlled by the time from when the sheet 3 passes through the first sensor 21 until it passes through the second sensor 22 (in other words, the timing when the sheet 3 passes through the second sensor 22).

[0082] On the other hand, if it is determined that the value of the timer is less than TLS + T2 and the second sensor 22 has not detected the passage of the sheet 3 (S16: NO), the process returns to S15.

[0083] On the other hand, if the second time, which is the time from the start of driving the resist roller 15 until the second sensor 22 detects the sheet 3, exceeds TLS + T2 (S15: NO), the process proceeds to S20. Here, the conveyance distance of the sheet 3 in one conveyance operation by the drive mechanisms of the MP paper feed roller 51 and the MP separation roller 52 is designed to be a distance sufficient for the leading end of the sheet 3 to reach the resist roller 15 and form a deflection (for example, 128 mm). The case where the second time exceeds TLS + T2 is, for example, when slippage occurs between the MP paper feed roller 51 or the MP separation roller 52 and the sheet 3 at the start of conveyance of the sheet 3 (especially when the leading end of the sheet is between the MP paper feed roller 51 and the MP separation roller 52), so that the actual conveyance distance by the drive mechanisms of the MP paper feed roller 51 and the MP separation roller 52 becomes shorter than the assumed distance (128 mm), and the first sensor 21 has passed but the conveyance stops before reaching the position of the resist roller 15 (the cam mechanism automatically stops the conveyance by the MP paper feed roller 51 and the MP separation roller 52 after a predetermined conveyance time has elapsed as described above). In such a case, the conveyance operation is performed again after S20.

[0084] Also, in S18, the controller 61 determines whether or not the current value of the timer, that is, the time since the passage of the sheet 3 was detected by the first sensor 21, has reached TIMP. Note that TIMP is set to the timing of image formation by the image forming unit 5 as described above, and the fact that the time since the passage of the sheet 3 was detected by the first sensor 21 has reached TIMP means that it is an appropriate timing for performing image formation on the sheet 3 by the image forming unit 5.

[0085] And when it is determined that the current timer value is less than TIMP, that is, the time elapsed since the passage of the sheet 3 was detected by the first sensor 21 is less than TIMP (S18: NO), it waits until the timer value reaches TIMP. On the other hand, when it is determined that the current timer value is TIMP or more, that is, TIMP has elapsed since the passage of the sheet 3 was detected by the first sensor 21 (S18: YES), the process proceeds to S19.

[0086] In S19, image formation (printing) on the sheet 3 is performed by the image forming unit 5. Note that since the content of the image forming process by the image forming unit 5 is already known, the description is omitted. Thereafter, the sheet 3 on which the image has been formed is discharged from the discharge port provided on the upper surface of the main body housing 2 by driving a paper discharge roller or the like.

[0087] On the other hand, in S20, the controller 61 determines whether or not the sheet size to be conveyed is equal to or larger than a predetermined size. Note that the sheet size to be conveyed is the sheet size designated as the printing target in the received print instruction.

[0088] Also, the predetermined size that is the determination condition in S20 is determined by the conveyance distance (theoretical value, for example, 128 mm) that enables the conveyance of the sheet 3 in one conveyance operation by the drive mechanisms of the MP paper feed roller 51 and the MP separation roller 52. Specifically, it satisfies the condition that the length in the conveyance direction is longer than twice the conveyance distance and is the smallest size within the paper sizes that the printer 1 can handle, for example, A5.

[0089] And when it is determined that the sheet size to be conveyed is equal to or larger than the predetermined size (S20: YES), the process proceeds to S22. On the other hand, when it is determined that the sheet size to be conveyed is less than the predetermined size (S20: NO), there is a possibility that a plurality of sheets may be conveyed by performing the conveyance operation again.

[0090] Therefore, in S21, the controller 61 displays an error display screen on the user IF63. Also, the conveyance operation of the sheet 3 by the drive mechanisms of the MP paper feed roller 51 and the MP separation roller 52 is stopped. The error display screen displays a message indicating that the printing process could not be executed. Thereby, the user can grasp that the printing process could not be completed.

[0091] On the other hand, in S22, the controller 61 temporarily stops the drive of the registration roller 15. Also, the value of the timer is temporarily initialized to 0 (measurement continues).

[0092] Subsequently, in S23, the controller 61 calculates TCON (third time) as the timing to start the drive of the registration roller 15 after restarting the conveyance operation of the sheet 3 by the drive mechanisms of the MP paper feed roller 51 and the MP separation roller 52. Here, during normal operation, the drive timing of the registration roller 15 is determined based on the timing when the passage of the sheet 3 is detected by the first sensor 21. Specifically, it is after TLS (the time required to form the necessary deflection until reaching the registration roller 15) has elapsed since the passage of the sheet 3 is detected by the first sensor 21 (S13). However, at the time of S23, as shown in FIG. 6, the leading edge of the sheet 3 has already passed the first sensor 21 (S4: YES), and although the registration roller 15 is driving, the passage of the second sensor 22 cannot be detected (S15, S16: NO). Therefore, it is expected that the leading edge of the sheet 3 is stopped in a state located between the first sensor 21 and the registration roller 15. Since there is no such thing as paper jamming, it is possible to make the sheet 3 reach the registration roller 15 by restarting the conveyance operation of the sheet 3 by the drive mechanisms of the MP paper feed roller 51 and the MP separation roller 52. However, since it is already in a state after the leading edge of the sheet 3 has passed the first sensor 21, in the conventional method, when restarting the conveyance operation of the sheet 3 by the drive mechanisms of the MP paper feed roller 51 and the MP separation roller 52, it is not possible to specify the appropriate timing to start the drive of the registration roller 15 for correcting the posture of the sheet.

[0093] Therefore, in S23, the controller 61 calculates TCON as an appropriate timing to start driving the registration roller 15 after restarting the conveyance operation of the sheet 3 by the driving mechanisms of the MP paper feed roller 51 and the MP separation roller 52 according to the following formula (1) or (2). Note that formula (1) and formula (2) are substantially the same formula. TCON = (L - (T0 - TL) × V) / V + R / V ····(1) TCON = L / V - (T0 - TL) + R / V ····(2) L = Distance from the first sensor 21 to the registration roller 15 T0 = Conveyance time TL (first time) = Time from when the driving of the MP paper feed roller 51 and the MP separation roller 52 is started (solenoid ON) in S5 until the first sensor 21 detects the sheet 3 V = Conveyance speed of the sheet by the driving mechanisms of the MP paper feed roller 51 and the MP separation roller 52 R = Registration amount (Conveyance amount of the sheet to create the deflection required to correct skewing)

[0094] Note that in formula (2) above, TCON indicates the time obtained by subtracting the difference between the conveyance time T0 and TL, that is, the time the sheet 3 is conveyed after passing the first sensor 21 until it stops as shown in FIG. 6, from L / V + R / V. Note that L / V + R / V is the time (theoretical value) required for the sheet 3 that has passed the first sensor 21 to reach the registration roller 15 and form the required deflection when conveyed as expected, and also corresponds to TLS (predetermined time) which is the determination condition in S13. Therefore, TCON calculated by the above formula (2) is the time (theoretical value) required for the sheet to reach the registration roller 15 from the stop position shown in FIG. 6 and form the required deflection. Note that a certain margin (margin value, for example, 1 sec) may be added further.

[0095] Subsequently, in S24, the controller 61 turns on the solenoid 65. Thereby, the conveyance operation of the sheet 3 by the driving mechanisms of the MP paper feed roller 51 and the MP separation roller 52 is executed again. Details are the same as in S2 and thus are omitted.

[0096] After that, in S25, the controller 61 determines whether the current timer value, that is, the time elapsed since the conveyance operation of the sheet 3 by the drive mechanisms of the MP paper feed roller 51 and the MP separation roller 52 was resumed has reached the TCON calculated in S23 or not.

[0097] And, when it is determined that the current timer value is less than TCON, that is, the time elapsed since the conveyance operation of the sheet 3 by the drive mechanisms of the MP paper feed roller 51 and the MP separation roller 52 was resumed is less than TCON (S25: NO), it waits until the timer value reaches TCON. On the other hand, when it is determined that the current timer value is equal to or greater than TCON, that is, TCON has elapsed since the conveyance operation of the sheet 3 by the drive mechanisms of the MP paper feed roller 51 and the MP separation roller 52 was resumed (S25: YES), it proceeds to S26.

[0098] In S26, the controller 61 drives the resist drive motor 67 (or when it is via an electromagnetic clutch, turns on the clutch), and starts driving the resist roller 15 in the direction of conveying the sheet 3 downstream in the conveyance direction. As a result, after correcting the posture of the sheet 3 that has reached the position of the resist roller 15 by the re-conveyance operation by the MP paper feed roller 51 and the MP separation roller 52, it conveys the sheet 3 further downstream.

[0099] After that, in S27, the controller 61 determines whether the current timer value, that is, the time elapsed since the conveyance operation of the sheet 3 by the drive mechanisms of the MP paper feed roller 51 and the MP separation roller 52 was resumed is less than TCON + T2 (threshold value) or not. Note that T2 is a value determined in advance for each model, and when it is assumed that the sheet 3 is being conveyed downstream by the drive of the resist roller 15 as expected, it is the time obtained by adding a certain margin (margin value, for example, 1 sec) to the time (theoretical value) until the sheet 3 is expected to reach the second sensor 22 after starting the drive of the resist roller 15.

[0100] If it is determined that the value of the timer is less than TCON + T2 (S27: YES), it is further determined whether the second sensor 22 has detected the passage of the sheet 3 (S28). Incidentally, as described above, the second sensor 22 is a sensor that is downstream of the resist roller 15 in the sheet conveyance direction and detects the passage of the sheet 3 (more precisely, the leading edge of the sheet) in the first conveyance path 14 (FIGS. 1 and 2).

[0101] If it is determined that the value of the timer is less than TCON + T2 and the second sensor 22 has detected the passage of the sheet 3 (S28: YES), the current value of the timer, that is, the value obtained by adding T3 to the time from when the conveyance operation of the sheet 3 by the drive mechanisms of the MP paper feed roller 51 and the MP separation roller 52 is resumed until the sheet 3 reaches the second sensor 22, is stored in the memory 62 as TIMP (S29). Then, the process proceeds to S31. Incidentally, T3 is a value determined in advance for each model, and is the time (theoretical value) expected until the sheet 3 reaches the transfer position of the image forming unit 5 (the nip position between the photosensitive drum and the transfer roller, which is the position where the toner image on the photosensitive drum is transferred to the sheet 3) after passing through the second sensor 22, assuming that the sheet 3 is being conveyed downstream by the drive of the resist roller 15 as expected. That is, the timing of image formation by the image forming unit 5 is controlled by the time from when the conveyance operation of the sheet 3 by the drive mechanisms of the MP paper feed roller 51 and the MP separation roller 52 is resumed until the sheet 3 passes through the second sensor 22 (in other words, the timing when the sheet 3 passes through the second sensor 22).

[0102] On the other hand, if it is determined that the value of the timer is less than TCON + T2 and the second sensor 22 has not detected the passage of the sheet 3 (S28: NO), the process returns to S27.

[0103] On the other hand, if the time from when the conveyance operation of the sheet 3 by the drive mechanisms of the MP paper feed roller 51 and the MP separation roller 52 is restarted until the second sensor 22 detects the sheet 3 exceeds TCON + T2 (S27: NO), the process proceeds to S30. Here, when shifting to S30, it is a state where the sheet 3 cannot reach the position of the registration roller 15 even if the second conveyance operation is performed. However, in this embodiment, the third conveyance operation will not be performed. The reason is that although the sheet size to be conveyed satisfies the condition that the length in the conveyance direction is longer than twice the conveyance distance (S20: YES), it is unknown whether the condition is satisfied that it is longer than three times. Therefore, there is a risk that a plurality of sheets may be conveyed by performing the third conveyance operation. Also, the distance from the first sensor 21 to the registration roller 15 is short, and the fact that the sheet 3 cannot reach the registration roller even if the conveyance operation is restarted from the state of passing the first sensor 21 may indicate that some abnormality has occurred rather than just a slip.

[0104] Therefore, in S30, the controller 61 displays an error display screen on the user IF63 without performing the third conveyance operation. Also, the conveyance operation of the sheet 3 by the drive mechanisms of the MP paper feed roller 51 and the MP separation roller 52 is stopped. The error display screen displays a message indicating that the printing process could not be executed. Thereby, the user can grasp that the printing process could not be completed.

[0105] Also, in S31, the controller 61 determines whether the current timer value, that is, the time from when the conveyance operation of the sheet 3 by the drive mechanisms of the MP paper feed roller 51 and the MP separation roller 52 is restarted has reached TIMP. Note that TIMP is set to the timing of image formation by the image forming unit 5 as described above. The fact that the time from when the conveyance operation of the sheet 3 by the drive mechanisms of the MP paper feed roller 51 and the MP separation roller 52 is restarted has reached TIMP means that it is an appropriate timing to perform image formation on the sheet 3 by the image forming unit 5.

[0106] And, when it is determined that the current timer value is less than TIMP, that is, the time elapsed since the conveyance operation of the sheet 3 by the drive mechanisms of the MP paper feed roller 51 and the MP separation roller 52 was restarted is less than TIMP (S31: NO), it waits until the timer value reaches TIMP. On the other hand, when it is determined that the current timer value is TIMP or more, that is, TIMP has elapsed since the conveyance operation of the sheet 3 by the drive mechanisms of the MP paper feed roller 51 and the MP separation roller 52 was restarted (S31: YES), it shifts to S32.

[0107] In S32, image formation (printing) on the sheet 3 is performed by the image forming unit 5. Note that the details of the image formation process by the image forming unit 5 are already known, so the description is omitted. After that, the sheet 3 on which the image has been formed is discharged from the discharge port provided on the upper surface of the main body housing 2 by driving a discharge roller or the like.

[0108] As described in detail above, in the printer 1 according to the present embodiment, the MP paper feed roller 51 and the MP separation roller 52 (hereinafter collectively referred to as the conveyance roller) that convey the sheet 3 and stop the conveyance after a predetermined conveyance time has elapsed after the start of driving, and the registration roller 15 that corrects the posture of the sheet conveyed by the conveyance roller on the downstream side in the sheet conveyance direction of the conveyance roller and further conveys it to the downstream side, the first sensor 21 that detects the passage of the sheet on the upstream side in the sheet conveyance direction with respect to the registration roller 15, the second sensor 22 that detects the passage of the sheet on the downstream side in the sheet conveyance direction with respect to the registration roller 15, the memory 62, and the controller 61 are provided. The controller 61 measures the time from the start of driving the conveyance roller until the first sensor 21 detects the sheet, stores it as TL in the memory 62 (S5), starts driving the registration roller 15 after a predetermined time has elapsed since the first sensor 21 detects the sheet 3 (S14), and when the second time, which is the time from the start of driving the registration roller 15 until the second sensor 22 detects the sheet 3, exceeds the threshold value, once stops driving the registration roller 15 (S22), and based on TL stored in the memory 62, determines TCON, which is the time from the start of redriving the conveyance roller until the start of driving the registration roller 15 (S23). After determining TCON, redrives the conveyance roller (S24), and starts driving the registration roller 15 after TCON has elapsed since the start of redriving the conveyance roller (S26). Therefore, for example, when slip occurs between the conveyance roller and the sheet at the start of sheet conveyance, the conveyance distance becomes shorter than expected, and the sheet passes through the first sensor 21 on the upstream side, causing the driving of the registration roller 15 to start, while the sheet only slightly reaches the position of the registration roller 15. Even in such a situation, it is possible to appropriately resume sheet conveyance by redriving the conveyance roller without bothering the user. Also, when redriving the conveyance roller, it is possible to drive the registration roller 15 at an appropriate timing for correcting the posture of the sheet. In addition, since the controller 61 determines TCON by subtracting the difference between the conveyance time and TL from a predetermined time, it is possible to calculate, as TCON, the time required to reach the resist roller 15 from the stop position and form the necessary deflection. In addition, when the first sensor 21 does not detect the sheet and exceeds a predetermined first upper limit time (T1) after the controller 61 starts driving the conveyance roller, the controller 61 drives the stopped conveyance roller again. Therefore, even if a situation occurs where, for example, at the start of sheet conveyance, slippage occurs between the conveyance roller and the sheet, resulting in a shorter conveyance distance than expected and the sheet not reaching the first sensor 21, it is possible to appropriately resume sheet conveyance by re-driving the conveyance roller without bothering the user. In addition, since the controller 61 re-drives the conveyance roller based on the second time exceeding the threshold up to a predetermined number of times, it is possible to prevent multiple sheets from being conveyed by re-driving the conveyance roller. In addition, the conveyance roller includes an MP paper feed roller 51 that contacts the sheet placed on the MP tray 41 and feeds the sheet, and an MP separation roller 52 that separates the sheets fed by the MP paper feed roller 51 one by one. Since the first sensor 21 is on the conveyance path between the MP separation roller 52 and the resist roller 15, even if the sheet fed from the MP tray 41 stops on the conveyance path, it is possible to appropriately resume sheet conveyance by re-driving the MP paper feed roller 51 and the MP separation roller 52 without bothering the user. Also, in particular, compared to paper feeding from the paper feed tray 8, paper feeding from the MP tray 41 is more likely to cause slippage between the rollers, but it is possible to solve this problem. In addition, when the second sensor 22 does not detect the sheet and exceeds a predetermined second upper limit time after the controller 61 starts re-driving the conveyance roller, the controller 61 stops driving the resist roller 15 and displays a message on the display unit (S30). Therefore, when sheet conveyance cannot be performed even after re-driving the conveyance roller, it is possible to notify the user to that effect. Further, it has an image forming unit 5 that forms an image on a sheet conveyed downstream in the conveyance direction with respect to the resist roller 15. Since the controller 61 controls the timing of image formation by the image forming unit 5 based on the time from when the re-driving of the conveyance roller starts until the second sensor 22 detects the sheet (S29, S31), even when the conveyance roller is re-driven, it is possible to perform image formation at an appropriate position of the sheet. In addition, since the drive mechanism of the conveyance roller has a cam mechanism that stops conveyance after the conveyance time has elapsed when driving starts, and a solenoid 65 that determines the timing of starting driving, the start and stop of driving of the conveyance roller can be realized by a mechanical structure instead of electrical control. Further, when the size of the sheet is less than a predetermined size, the controller 61 stops the driving of the resist roller 15 and displays a message on the display unit without re-driving the conveyance roller even when the second time exceeds the threshold value (S21). Therefore, it is possible to prevent a plurality of sheets from being conveyed by the re-driving of the conveyance roller. In addition, since the predetermined size is determined by the distance that the sheet can be conveyed by the driving of the conveyance roller during the conveyance time, in a printer corresponding to sheets of a plurality of types of sizes, it is possible to appropriately resume the conveyance of the sheet only for a sheet for which there is no risk of a plurality of sheets being conveyed by the re-driving of the conveyance roller by performing the re-driving of the conveyance roller.

[0109] Note that the present invention is not limited to the above-described embodiment, and it goes without saying that various improvements and modifications can be made without departing from the gist of the present invention. For example, in the present embodiment, an example in which the printing process shown in FIGS. 4 and 5 is executed for a sheet conveyed from the MP tray (multi-purpose tray) 41 has been described. However, it is also possible to execute the printing process shown in FIGS. 4 and 5 in the same manner for a sheet conveyed from the paper feed tray 8. In that case, the separation roller 9, the paper dust removal roller 12, and the opposing roller 13 correspond to the conveyance roller.

[0110] Further, in the above embodiment, when the second time, which is the time from the start of driving the resist roller 15 until the second sensor 22 detects the sheet 3, exceeds TLS + T2 (S15: NO), the conveyance operation of the sheet 3 by the drive mechanism of the MP paper feed roller 51 and the MP separation roller 52 is executed again only once. However, it may be repeated two or more times.

[0111] Further, in the above embodiment, the printer 1 is described as an example of the sheet conveyance device. However, for example, it may be a copying machine, a facsimile device, a multifunction machine having a printer function and a scanner function, or the like.

Explanation of Signs

[0112] 1... Printer (sheet conveyance device), 15... Resist roller, 21... First sensor, 22... Second sensor, 41... MP tray, 51... MP paper feed roller, 52... MP separation roller, 61... Controller, 62... Memory, 63... User IF, 65... Solenoid

Claims

1. A sheet conveying device comprising: a conveying roller that conveys a sheet and stops conveying after a predetermined conveying time has elapsed after the start of driving; a register roller that is located on the downstream side of the conveying roller in the sheet conveying direction, corrects the posture of the sheet conveyed by the conveying roller, and further conveys the sheet downstream; a first sensor that is located on the upstream side of the register roller in the sheet conveying direction and detects the passage of the sheet; a second sensor that is located on the downstream side of the register roller in the sheet conveying direction and detects the passage of the sheet; a memory; and a controller, wherein the controller, measures the time from the start of driving of the conveying roller until the first sensor detects the sheet, stores it in the memory as a first time, starts driving the register roller after a predetermined time has elapsed since the first sensor detected the sheet, when a second time, which is the time from the start of driving of the register roller until the second sensor detects the sheet, exceeds a threshold value, once stops driving the register roller, and based on the first time stored in the memory, determines a third time, which is the time from the start of re-driving the conveying roller until the start of driving the register roller, and after determining the third time, re-drives the conveying roller and controls to start driving the register roller after the third time has elapsed since the start of re-driving the conveying roller.

2. The controller, determines the third time by subtracting the difference between the conveying time and the first time from the predetermined time. The sheet conveying device according to claim 1.

3. The controller, when, after the start of driving of the conveying roller, the first sensor does not detect the sheet and a predetermined first upper limit time is exceeded, re-drives the stopped conveying roller. The sheet conveying device according to claim 1.

4. The controller, the re-driving of the conveying roller based on the fact that the second time exceeds the threshold value is performed up to a predetermined number of times. The sheet conveying device according to claim 1.

5. further comprising a sheet tray, The conveying roller includes a pickup roller that contacts a sheet placed on the sheet tray to feed the sheet, and a separating roller that separates the sheets fed by the pickup roller one by one. The sheet conveying device according to any one of claims 1 to 4, wherein the first sensor is on a conveyance path between the separating roller and the registration roller.

6. The sheet conveying device according to claim 5, wherein the sheet tray is a multi-purpose tray on which the user places the sheet by hand.

7. It further has a display unit. The controller When the second sensor does not detect a sheet after starting the re-driving of the conveying roller and exceeds a predetermined second upper limit time, the controller stops the driving of the registration roller and displays a message on the display unit. The sheet conveying device according to any one of claims 1 to 4, characterized in that.

8. It has an image forming unit that forms an image on the sheet conveyed on the downstream side in the conveyance direction with respect to the registration roller. The controller The sheet conveying device according to any one of claims 1 to 4, wherein the controller controls the timing of image formation by the image forming unit based on the time from when the re-driving of the conveying roller is started until the second sensor detects a sheet.

9. The drive mechanism of the conveying roller has a cam mechanism that stops the conveyance after the conveyance time has elapsed when the drive is started, and a solenoid that determines the timing of starting the drive. The sheet conveying device according to any one of claims 1 to 4, characterized in that.

10. It further has a display unit. The controller When the size of the sheet is less than a predetermined size, Even when the second time exceeds the threshold value, the controller stops the driving of the registration roller without re-driving the conveying roller and displays a message on the display unit. The sheet conveying device according to any one of claims 1 to 4, characterized in that.

11. The sheet conveying device according to claim 10, wherein the predetermined size is determined by the distance that the sheet can be conveyed by the driving of the conveying roller during the conveyance time.

Images