Image formation device

Abstract

To provide an image formation device that can fill the gaps between sheets of paper being continuously fed.SOLUTION: The image formation device includes: a conveyance path S through which the paper is transported; a registration roller 32 provided on the conveyance path S; a pickup roller 31 for supplying the paper; a transport sensor 41 that detects the transported paper; and a control unit that controls the transport of the paper. The conveyance path S is set with: a detection position where the transport sensor 41 is provided; a reference position which is a reference distance KL away from the detection position; and a standby position which is a standby distance TL away from the detection position. The control unit conducts a passing determination to determine whether a trailing edge P1b of a leading paper P1, which is being transported ahead, has passed the reference position when it stops at the registration roller 32. If it has passed the reference position, the leading edge of a subsequent paper P2 is allowed to reach the standby position, and if it has not passed the reference position, the transport of the subsequent paper P2 is halted.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to an image forming apparatus having a transport path along which paper is transported. [Background technology]

[0002] Conventionally, in image forming apparatuses, paper is transported to a transfer device and a fixing device through a transport path. The transport path is provided with registration rollers that temporarily stop the paper to adjust the timing of transfer from the transfer device. In recent years, image forming apparatuses have been required to increase the number of images formed per unit time, and methods for addressing this have been proposed (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-135339 Summary of the Invention [Problem to be solved by the invention]

[0004] A conventional image forming apparatus includes a paper feed unit having a paper feed cassette for storing paper, an image forming unit for forming an image on the paper, a transport path for transporting paper fed from the paper feed cassette, a transport unit for transporting the paper toward an image forming position where an image is formed in the image forming unit, a pair of registration rollers disposed upstream of the image forming position in the paper transport direction for stopping the paper and transporting it back to the image forming position, a control unit for restarting the transport of the paper to the image forming position, and a paper detection sensor for adjusting the paper gap disposed upstream from the pair of registration rollers by a length obtained by adding a predetermined paper gap distance to the length of a predetermined paper size in the paper transport direction, the length being shorter than the paper gap distance required to achieve a target number of images formed per unit time. The control unit does not stop the feeding of a subsequent paper following the preceding paper when the pair of registration rollers stops the preceding paper, and stops the feeding of the subsequent paper when the paper detection sensor detects that the leading edge of the subsequent paper has reached the paper detection position, and restarts the feeding of the subsequent paper when the pair of registration rollers resumes transport of the preceding paper.

[0005] In the image forming apparatus described above, a paper detection sensor is provided at a position determined by the paper size, and whether or not to feed a subsequent paper is determined depending on the timing of detection by the paper detection sensor. Therefore, there is a problem in that it is not possible to appropriately determine the timing to feed a subsequent paper for paper of a different size.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide an image forming device that can reduce the gaps between continuously transported sheets of paper, even if the paper sizes are different. [Means for solving the problem]

[0007] The image forming apparatus according to the present disclosure is an image forming apparatus comprising: a transport path along which paper is transported; a resist member provided on the transport path; a paper feed member that supplies paper to the transport path; a transport sensor provided along the transport path between the paper feed member and the resist member and that detects paper transported on the transport path; and a control unit that controls the transport of paper on the transport path, wherein the transport path has, in the paper transport direction, a detection position where the transport sensor is provided, a reference position that is a first distance downstream from the detection position, and a waiting position that is a second distance downstream from the detection position, and when a preceding paper transported ahead on the transport path stops at the resist member, the control unit performs a passing determination to determine whether the trailing end of the preceding paper has passed the reference position, and if the trailing end of the preceding paper has passed the reference position, the control unit causes the leading edge of a succeeding paper transported behind on the transport path to reach the waiting position, and if the trailing end of the preceding paper has not passed the reference position, the control unit stops the transport of the succeeding paper.

[0008] In the image forming apparatus according to the present disclosure, the second distance may be shorter than the first distance.

[0009] In the image forming apparatus according to the present disclosure, the control unit may be configured to start conveying the subsequent sheet when, after the passage determination, conveying of the preceding sheet that has stopped at the registration member has started.

[0010] In the image forming apparatus according to the present disclosure, the control unit may be configured to set the distance from the detection position to the rear end of the preceding paper that has stopped at the resist member as the first distance, and to set the second distance to a distance shorter than the first distance. [Effects of the Invention]

[0011] According to the present disclosure, whether to transport the subsequent paper is determined based on the position of the trailing edge of the preceding paper, so even if the position of the trailing edge varies due to different paper sizes, the gap between the preceding and subsequent paper can be narrowed. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present disclosure. [Figure 2] FIG. 10 is a schematic explanatory diagram showing a state (part 1) in which a sheet is being transported around the transport sensor. [Figure 3] FIG. 10 is a schematic explanatory diagram showing a state (part 2) in which a sheet is being transported around the transport sensor. [Figure 4] FIG. 10 is a schematic explanatory diagram showing a state (part 3) in which a sheet is being transported around the transport sensor. [Figure 5] FIG. 10 is a schematic explanatory diagram showing a state (part 4) in which a sheet is being transported around the transport sensor. [Figure 6] FIG. 10 is a flowchart showing a process flow relating to passage determination. [Figure 7] FIG. 10 is a schematic explanatory diagram showing a state (part 5) in which a sheet is being transported around the transport sensor. DETAILED DESCRIPTION OF THE INVENTION

[0013] (First embodiment) Hereinafter, an image forming apparatus according to a first embodiment of the present disclosure will be described with reference to the drawings.

[0014] FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present disclosure.

[0015] The image forming apparatus 1 according to the first embodiment of the present disclosure is configured to include an exposure device 11, a developing device 12, a photosensitive drum 13, a cleaning device 14, a charger 15, an intermediate transfer belt device 16, a fixing device 17, a paper feed tray 18, a paper output tray 19, and a conveying path S, and forms multi-color and monochrome images on a specified sheet of paper according to image data transmitted from the outside.

[0016] The image data handled by the image forming apparatus 1 corresponds to a color image using the colors black (K), cyan (C), magenta (M), and yellow (Y). Therefore, four developing devices 12, four photosensitive drums 13, four chargers 15, and four cleaning devices 14 are provided to form four types of latent images corresponding to each color, and are set to black, cyan, magenta, and yellow, respectively, and these constitute four image stations Pa, Pb, Pc, and Pd.

[0017] Photosensitive drum 13 is disposed approximately in the center of image forming apparatus 1. Charger 15 uniformly charges the surface (circumferential surface) of photosensitive drum 13 to a predetermined potential. Exposure device 11 exposes the surface of photosensitive drum 13 to light to form an electrostatic latent image. Development device 12 develops the electrostatic latent image on the surface of photosensitive drum 13 to form a toner image on the surface of photosensitive drum 13. Through the series of operations described above, a toner image of each color is formed on the surface of each photosensitive drum 13. Cleaning device 14 removes and collects residual toner on the surface of photosensitive drum 13 after development and image transfer.

[0018] The intermediate transfer belt device 16 is disposed above the photosensitive drum 13 and includes an intermediate transfer belt 21, an intermediate transfer belt drive roller 22, an intermediate transfer belt driven roller 23, an intermediate transfer roller 24, and an intermediate transfer belt cleaning device 25. Four intermediate transfer rollers 24 are provided, one for each of the image stations for YMCK colors.

[0019] The intermediate transfer belt drive roller 22, the intermediate transfer belt driven roller 23, and the intermediate transfer roller 24 are configured to stretch the intermediate transfer belt 21 and move the surface of the intermediate transfer belt 21 in a predetermined direction (the direction of the arrow C in the figure).

[0020] The intermediate transfer belt 21 rotates in the direction of arrow C, and residual toner is removed and collected by the intermediate transfer belt cleaning device 25. The toner images of each color formed on the surface of each photosensitive drum 13 are sequentially transferred and superimposed to form a color toner image on the surface of the intermediate transfer belt 21.

[0021] The image forming apparatus 1 further includes a secondary transfer device 26 including a transfer roller 26a. A nip area is formed between the transfer roller 26a and the intermediate transfer belt 21, and the paper conveyed through the conveying path S is sandwiched in the nip area and conveyed. As the paper passes through the nip area, the toner image on the surface of the intermediate transfer belt 21 is transferred to the paper.

[0022] The paper feed tray 18 is a tray for storing paper sheets to be used for image formation, and is provided below the exposure device 11. The paper discharge tray 19 is provided above the image forming device 1, and is a tray for placing paper sheets on which images have been formed.

[0023] The conveying path S includes a main path S1 formed in an S-shape and a reverse path S2 that branches off from the main path S1 and then rejoins the two paths, and along the main path S1, there are arranged a pickup roller 31 (an example of a paper feed member), a conveying sensor 41, pre-registration rollers 33, registration rollers 32 (an example of a registration member), a secondary transfer device 26, a fixing device 17, and a paper discharge roller 34. The reverse path S2 branches off between the fixing device 17 and the paper discharge roller 34, passes through a plurality of conveying rollers 35, and then rejoins the two paths between the pre-registration rollers 33 and the registration roller 32.

[0024] The pickup roller 31 is provided near the end of the paper feed tray 18 and is a pickup roller that supplies paper one sheet at a time from the paper feed tray 18 to the transport path S. The registration roller 32 temporarily holds the paper being transported from the paper feed tray 18 and transports the paper to the transfer roller 26a at a timing that aligns the leading edge of the toner image on the photosensitive drum 13 with the leading edge of the paper. The pre-registration roller 33 is a small roller that assists in facilitating the transport of the paper. The transport sensor 41 is a sensor that detects the presence or absence of paper at a detection position opposite the sensor. The transport of paper in the portion of the transport path S from the pickup roller 31 to the registration roller 32 will be described later with reference to FIG. 2.

[0025] The fixing device 17 is of a belt fixing type, with a belt wound around two rollers and an additional roller that presses the belt. The fixing device 17 receives the paper on which the unfixed toner image has been formed, and conveys the paper by sandwiching it between the rollers via the belt. After the fixing, the paper is discharged onto the paper discharge tray 19 by the paper discharge rollers 34.

[0026] Furthermore, when forming an image on the back side of the paper as well as the front side, the paper is transported in the reverse direction from the paper discharge rollers 34 to the reversal path S2, the paper is turned over, the paper is guided again to the registration rollers 32, an image is formed on the back side in the same manner as on the front side, and the paper is then transported to the paper discharge tray 19.

[0027] The image forming apparatus 1 includes a control unit (not shown) that controls the transport of paper along the transport path S. The control unit is one or more CPUs mounted in the image forming apparatus 1, and has a function to control not only the transport of paper but also various operations of the image forming apparatus 1.

[0028] Next, the transport of the paper around the transport sensor 41 will be described with reference to FIG.

[0029] FIG. 2 is a schematic explanatory diagram showing a state (part 1) in which a sheet is being transported around the transport sensor.

[0030] 2, a portion of the conveying path S from the pickup roller 31 to the registration roller 32 is extracted and shown schematically. For the sake of explanation, the direction in which the paper is conveyed on the conveying path S will be referred to as the conveying direction H, and the upstream side in the conveying direction H will sometimes be abbreviated simply as the upstream side, and the downstream side in the conveying direction H will sometimes be abbreviated simply as the downstream side.

[0031] In this embodiment, the transport sensor 41 is provided downstream of the pickup roller 31 and upstream of the pre-registration roller 33. The location at which the transport sensor 41 is provided is not limited thereto, and the transport sensor 41 may be provided anywhere along the transport path S, between the pickup roller 31 and the registration roller 32.

[0032] 2, a sheet of paper (preceding sheet P1) is being supplied to the transport path S from the paper feed tray 18 via the pickup roller 31. The leading edge (preceding sheet leading edge P1a) of the preceding sheet P1, which is being transported first, is positioned between the pre-registration roller 33 and the registration roller 32, and its trailing edge (preceding sheet trailing edge P1b) has reached the detection position of the transport sensor 41. When the preceding sheet P1 advances a little from here, the detection result of the transport sensor 41 switches from a state in which the sheet is detected to a state in which the sheet is not detected, and the control unit can determine that the preceding sheet trailing edge P1b has passed the detection position.

[0033] The pickup roller 31 holds the leading edge (leading edge P2a) of the paper (successor paper P2) stacked on top of the paper feed tray 18, and stands by so that it can quickly supply the succeeding paper P2. In this embodiment, the pickup roller 31 is configured by combining a roller that separates and pulls out a single sheet of paper from the stack of stacked sheets, and a pair of rollers that hold the paper pulled out by the roller. When the roller pulls out a sheet from the stack of sheets, the roller may spin freely, preventing the sheet from being pulled out (paper slippage), which may result in a delay in paper supply. For this reason, a control system is employed that shortens the gap between the preceding paper and the paper being transported in advance by preparing the paper by pulling it out and transporting it a short distance in advance, thereby improving processing speed.

[0034] In the image forming apparatus 1, the control unit calculates the distance that the paper has been transported along the transport path S based on the rotation amount, rotation speed, and rotation time of the various rollers. Therefore, by taking into consideration the detection timing of the transport sensor 41 and the transport distance of the paper, the positions of the leading and trailing edges of the paper can be estimated.

[0035] In the conveying path S, a reference position is set downstream from the detection position by a reference distance KL (an example of a first distance) in the conveying direction H, and a standby position is set downstream from the detection position by a standby distance TL (an example of a second distance). Then, when the registration rollers 32 stop the preceding sheet P1, the control unit performs a passing determination to determine whether the preceding sheet trailing edge P1b has passed the reference position. Next, the positional relationship between the reference distance KL and the standby distance TL, and the details of the passing determination will be described with reference to FIGS. 3 to 6.

[0036] FIG. 3 is a schematic explanatory diagram showing a state (part 2) in which a sheet is being transported around the transport sensor.

[0037] In Figure 3, the preceding sheet P1 is being transported in the transport direction H from the state shown in Figure 2. As described above, on the transport path S, a position that has advanced a reference distance KL downstream from the detection position is set as the reference position. The reference distance KL is set to 15 mm, for example. The preceding sheet P1 has its leading edge P1a reach the registration rollers 32 and is stopped by the registration rollers 32. In addition, the preceding sheet trailing edge P1b has advanced beyond the reference position.

[0038] In this embodiment, when it is determined that the trailing edge P1b of the preceding sheet has passed the reference position, the subsequent sheet P2 is transported to the standby position. Note that the timing at which the transport of the subsequent sheet P2 begins may be changed as appropriate. For example, it may be the timing at which the trailing edge P1b of the preceding sheet has passed the detection position, or transport may not begin immediately but may begin with a slight delay.

[0039] FIG. 4 is a schematic explanatory diagram showing a state (part 3) in which a sheet is being transported around the transport sensor.

[0040] In Fig. 4, the subsequent sheet P2 is transported in the transport direction H from the state shown in Fig. 3. Similar to the reference position, the standby position is a position located downstream from the detection position by a standby distance TL. The standby distance TL is set shorter than the reference distance KL, for example, 5 mm.

[0041] The succeeding sheet P2 is stopped with its leading edge P2a reaching the standby position. Because the standby position is set closer to the detection position than the reference position, a gap (paper gap) is provided between the trailing edge P1b of the preceding sheet and the leading edge P2a of the succeeding sheet. In this way, by setting the distance so that the leading edge P2a of the succeeding sheet does not reach the trailing edge P1b of the preceding sheet, the paper gap can be reduced to an appropriate distance.

[0042] FIG. 5 is a schematic explanatory diagram showing a state (part 4) in which a sheet is being transported around the transport sensor.

[0043] 5, like FIG. 3, shows a state in which the preceding sheet P1 is received by the registration rollers 32, except that the preceding sheet P1 is longer than in the case shown in FIG. 5. The preceding sheet trailing edge P1b has advanced a distance shorter than the reference distance KL and has stopped short of the reference position. In this case, it is determined that the preceding sheet trailing edge P1b has not passed the reference position.

[0044] FIG. 6 is a flow diagram showing a process flow relating to the passage determination.

[0045] In the process flow shown in FIG. 6, the state in which the preceding sheet P1 is being transported is set as the start point.

[0046] In step S01, it is determined whether the transport of the subsequent sheet P2 is permitted. Here, it is sufficient to determine whether the subsequent sheet P2 should be transported based on the number of sheets of paper for which image formation is instructed. It may also be confirmed whether paper is present in the paper feed tray 18, or whether the pickup roller 31 is ready for transport. As a result, if the transport of the subsequent sheet P2 is permitted (step S01: YES), the process proceeds to step S02. On the other hand, if the transport of the subsequent sheet P2 is not permitted (step S01: NO), the process waits until it is permitted.

[0047] In step S02, it is determined whether the preceding sheet P1 is stopped. Here, as shown in FIG. 3, it is determined whether the preceding sheet P1 is stopped with its leading edge P1a received by the registration rollers 32. As a result, if the preceding sheet P1 is stopped (step S02: YES), the process proceeds to step S04. On the other hand, if the preceding sheet P1 is not stopped (step S02: NO), the process proceeds to step S03.

[0048] In step S03, the subsequent sheet P2 is conveyed. Here, conveyance of the subsequent sheet P2 is started when conveyance of the preceding sheet P1, which has stopped at the registration rollers 32, is started. At this time, the leading edge P1a of the preceding sheet has already passed the registration rollers 32, and the preceding sheet P1 is being conveyed toward the transfer roller 26a, which is downstream of the registration rollers 32, and then the process returns to step S02.

[0049] In step S04, it is determined whether the preceding sheet P1 has passed the reference position. Here, a passing determination is made to determine whether the trailing edge P1b of the preceding sheet has passed the reference position as shown in FIG. 3, or whether the trailing edge P1b of the preceding sheet has not passed the reference position as shown in FIG. 5. As a result, if the preceding sheet P1 has passed the reference position (step S04: YES), the process proceeds to step S05. On the other hand, if the preceding sheet P1 has not passed the reference position (step S04: NO), the process proceeds to step S06.

[0050] In step S05, the succeeding sheet P2 is transported to the standby position. Here, as shown in Fig. 4, the succeeding sheet P2 is transported so that the leading edge P2a of the succeeding sheet reaches the standby position, and then the process returns to step S02.

[0051] In step S06, the transport of the succeeding sheet P2 is stopped. Here, the transport can be stopped regardless of the position of the succeeding sheet P2, and even if the leading edge P2a of the succeeding sheet P2 has advanced beyond the pickup roller 31, the transport is immediately stopped, and then the process returns to step S02.

[0052] In this embodiment, whether to transport the subsequent paper P2 is determined based on the position of the trailing end P1b of the preceding paper, so even if the position of the trailing end P1b of the preceding paper varies due to different paper sizes, the gap between the preceding paper P1 and the subsequent paper P2 can be narrowed.

[0053] 6, the process may proceed to step S04 regardless of the result of step S02 the first time. In other words, after making the passage determination corresponding to steps S04 to S06, it may be determined whether to transport the subsequent sheet P2 beyond the standby position. In this way, the passage determination is made and the subsequent sheet P2 is stopped with the paper gap secured, so that the transport of the subsequent sheet P2 can be started together with the preceding sheet P1, thereby improving the processing speed.

[0054] (Second embodiment) Next, an image forming apparatus according to a second embodiment of the present disclosure will be described with reference to the drawings. In the second embodiment, the reference position is set differently from that in the first embodiment. Note that the second embodiment has a configuration substantially similar to that of the first embodiment shown in FIGS. 1 to 6, and therefore a description thereof will be omitted, and only the differences will be described.

[0055] FIG. 7 is a schematic explanatory diagram showing a state (part 5) in which a sheet is being transported around the transport sensor.

[0056] 7, like FIG. 4, shows a state in which the preceding sheet P1 is received by the registration rollers 32 and the succeeding sheet P2 is transported to the standby position. In the first embodiment, the reference position was set using the reference distance KL as a predetermined value. However, in the second embodiment, the reference position is set by varying the reference distance KL according to the position of the preceding sheet trailing edge P1b. Specifically, the reference distance KL is the distance from the detection position to the trailing edge (preceding sheet trailing edge P1b) of the preceding sheet P1 that has stopped at the registration rollers 32. Note that a lower limit may be set for the reference distance KL, and if the preceding sheet trailing edge P1b is close to the detection position, it may be determined that the preceding sheet has not passed the reference position. Furthermore, when varying the reference distance KL, it is preferable to vary the standby distance TL according to the varied reference distance KL within a range of distances shorter than the reference distance KL. In this way, by varying the reference distance KL according to the position of the preceding sheet trailing edge P1b, the gap between the sheets can be efficiently narrowed.

[0057] It should be noted that the embodiments disclosed herein are illustrative in all respects and are not intended to be limiting. Therefore, the technical scope of the present disclosure should not be interpreted solely by the above-described embodiments, but should be defined based on the claims. Furthermore, all modifications within the scope and meaning equivalent to the claims are included. [Explanation of symbols]

[0058] 1. Image forming device 31 Pickup roller (an example of a paper feed member) 32 Registration roller (an example of a registration member) 41 Transport sensor P1 Advance paper P2 subsequent paper S Transport Route

Claims

1. a transport path along which the paper is transported; a resist member provided on the transport path; a paper feed member for feeding paper to the transport path; a transport sensor provided along the transport path between the paper feed member and the registration member, the transport sensor detecting the paper being transported along the transport path; a control unit for controlling the transport of paper along the transport path, the transport path is set with a detection position where the transport sensor is provided, a reference position spaced a first distance downstream from the detection position, and a standby position spaced a second distance downstream from the detection position in a transport direction of the paper; When a preceding sheet transported ahead on the transport path stops at the registration member, the control unit performs a passing determination to determine whether the trailing edge of the preceding sheet has passed the reference position, and if the trailing edge of the preceding sheet has passed the reference position, causes the leading edge of the subsequent sheet transported behind on the transport path to reach the standby position, and if the trailing edge of the preceding sheet has not passed the reference position, stops transport of the subsequent sheet. An image forming apparatus comprising:

2. 2. The image forming apparatus according to claim 1, The second distance is shorter than the first distance. An image forming apparatus comprising:

3. 2. The image forming apparatus according to claim 1, The control unit starts conveying the subsequent sheet when conveying the preceding sheet stopped by the registration member after the passage determination. An image forming apparatus comprising:

4. 2. The image forming apparatus according to claim 1, The control unit sets the distance from the detection position to the rear end of the preceding sheet stopped by the registration member as the first distance, and sets the distance shorter than the first distance as the second distance. An image forming apparatus comprising:

Images