Sheet conveying device

Abstract

To provide a sheet conveying device capable of performing appropriate skew correction without being affected by back tension of a paper feeding section.SOLUTION: A sheet conveying device of the present invention comprises: a paper feed section 30 that feeds and transports sheets loaded on a paper feed tray 30a; a resist roller 31 that applies skew correction to sheets transported from the paper feed section 30; a nip release section 60 that releases the nip of sheets by the paper feed section 30 after the sheets reach the resist roller 31; and a control section 70 that controls the paper feed section 30, the resist roller 31 and the nip release section 60.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a sheet conveying device that conveys a sheet fed from a sheet feeding unit toward a conveying unit.

Background Art

[0002] Conventionally, in a printing device that performs printing processing on a sheet such as printing paper conveyed on a conveyance path, the sheet may be conveyed obliquely, which may affect the printing processing or cause jams.

[0003] Therefore, skew correction is performed on the sheet being conveyed. For example, a printing device has been proposed in which a sheet fed from a sheet feeding unit is skew-corrected by a registration roller, and then the sheet is sent out from the registration roller to a conveying unit such as a conveying belt, and printing processing is performed during conveyance by the conveying unit.

[0004] Also, in Patent Document 1, it has been proposed to perform skew correction during conveyance of a sheet by separating registration rollers in a direction perpendicular to the conveyance direction of the sheet and independently controlling each separated registration roller. In Patent Document 1, a sheet feeding unit for feeding a sheet is provided upstream of the registration roller, and control is performed so as not to be affected by the upstream sheet feeding unit by performing skew correction while forming slack between the sheet feeding unit and the registration roller.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the case of external sheet feeding where the distance between the resist roller and the sheet feeding unit is relatively short, proper skew correction may not be achievable due to the influence of the back tension from the sheet feeding unit. For example, in the case of long sheets such as A3, if an appropriate slack cannot be formed between the sheet feeding unit and the resist roller, the sheet feeding unit will nip the rear end of the sheet, resulting in insufficient skew correction during conveyance.

[0007] Also, even if skew correction is possible, phenomena such as the sheet returning to its original skewed state may occur due to the impact received from the influence of the back tension when it occurs. In addition, in the case of external sheet feeding, it is necessary to stop the conveyance operation (assist control) of the sheet feeding unit before transporting the next sheet, and phenomena such as the sheet returning to its original skewed state may occur due to the impact during the stop.

[0008] Furthermore, depending on the type of sheet, the way slack is formed differs, and it is more difficult to form slack in thick paper and the like, making it more susceptible to the influence of external sheet feeding.

[0009] Taking a longer distance between the sheet feeding unit and the resist roller (conveyance distance) is advantageous for the skew correction ability, but the main body housing becomes larger, and due to layout constraints, it is necessary to arrange the sheet feeding unit and the resist roller in a narrow range. Also, when using a separated resist roller as in Patent Document 1, there is a problem that the straightness of sheet conveyance is weaker compared to a single resist roller, and it is more likely to skew.

[0010] In view of the above circumstances, an object of the present invention is to provide a sheet conveyance device capable of performing appropriate skew correction without being affected by the back tension of the sheet feeding unit.

Means for Solving the Problems

[0011] The sheet conveying device of the present invention includes a sheet feeding unit that feeds and conveys the sheets stacked on the sheet feeding table, a registration roller that performs skew correction on the sheets conveyed from the sheet feeding unit, a nip release unit that releases the nip of the sheets by the sheet feeding unit after the sheets reach the registration roller, and a control unit that controls the sheet feeding unit, the registration roller, and the nip release unit.

Effects of the Invention

[0012] According to the sheet conveying device of the present invention, after the sheet reaches the registration roller, the nip of the sheet by the sheet feeding unit is released, so that appropriate skew correction can be performed without being affected by the back tension of the sheet feeding unit.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0014] Hereinafter, an inkjet printing apparatus using an embodiment of the sheet conveyance device of the present invention will be described in detail with reference to the drawings. The inkjet printing apparatus of this embodiment is characterized by nip release in the sheet feeding unit. First, the overall configuration will be described. FIG. 1 is a diagram showing a schematic configuration of the inkjet printing apparatus 1 of this embodiment. The up-down, left-right directions shown in FIG. 1 are the up-down, left-right directions of the inkjet printing apparatus 1 of this embodiment. The front side of the paper surface in FIG. 1 is the front direction, and the back side of the paper surface is the back direction. Also, the right direction shown in FIG. 1 is the conveyance direction of the sheet P, the left side is the upstream side in the conveyance direction, and the right side is the downstream side in the conveyance direction.

[0015] The inkjet printing apparatus 1 of this embodiment includes a sheet feeding unit 30, a registration sensor RS, a registration roller 31, a skew correction sensor CS, a conveyance roller 32, four line heads 33, a conveyance unit 34, a circulation conveyance path CR, first to fifth circulation conveyance rollers 35 to 39, a paper discharge roller 40, a first reverse conveyance roller 41, a reverse roller 42, and a second reverse conveyance roller 44.

[0016] The sheet feeding unit 30 includes a sheet feeding table 30a, a scraper 30b, a separating plate 30c, and a pickup roller 30d.

[0017] The sheet feeding table 30a has a plurality of sheets P (for example, printing paper) stacked thereon. The scraper 30b rotates in contact with the upper surface of the sheet P stacked on the sheet feeding table 30a. The separating plate 30c is composed of a high-friction member such as a rubber plate provided on the downstream side in the conveyance direction of the sheet P with respect to the scraper 30b. The pickup roller 30d is rotatably provided above the separating plate 30c and conveys the sheet P by separating it between the pickup roller 30d and the separating plate 30c.

[0018] The scraper 30b and the pickup roller 30d are driven by a first sheet feeding drive motor 50 (see FIG. 4).

[0019] The scraper 30b presses against the uppermost sheet P stacked on the sheet feeder 30a with a predetermined pressure, and conveys the sheet P downstream by the frictional force. Even if a plurality of sheets P are taken out by the scraper 30b, the separating plate 30c and the pickup roller 30d separate only one sheet and convey it to the downstream resist roller 31. In this way, the sheet feeding unit 30 takes out the sheets P stacked on the sheet feeder 30a one by one and conveys them to the resist roller 31.

[0020] The scraper 30b and the pickup roller 30d rotate in the direction of conveying the sheet P by the first sheet feeding drive motor 50, but at the time of conveying the sheet P by the resist roller 31, assist control is performed. In the assist control, during the conveyance of the sheet P by the resist roller 31, the sheet P is conveyed at a conveyance speed faster than that of the resist roller 31, thereby forming a slack in the sheet P. Then, thereafter, the conveyance speed is decelerated so that the slack is gradually eliminated. The assist control will be described in detail later.

[0021] Further, in the present embodiment, a nip release unit 60 (see FIG. 4) for releasing the nip of the sheet P by the scraper 30b and the pickup roller 30d is provided. The nip release unit 60 has a rotation mechanism and a mechanical mechanism using a solenoid or a motor, and lifts the scraper 30b upward (in the direction of arrow A shown in FIG. 1) or rotates it freely with an electromagnetic clutch or the like, and rotates the separating plate 30c downward (in the direction of arrow B shown in FIG. 1) to release the nip of the sheet P. The timing of nip release of the nip release unit 60 will be described in detail later.

[0022] The resist roller 31 is a pair of rollers provided on the downstream side in the sheet P conveyance direction with respect to the pickup roller 30d and configured to sandwich (nip) the sheet P. The resist roller 31 is driven by a second sheet feeding drive motor 51 (see FIG. 4).

[0023] The registration roller 31 abuts against the leading end of the sheet P conveyed from the sheet feeding unit 30 in the conveying direction, corrects the skew of the sheet P by this abutment, and then conveys the sheet P toward the conveying roller 32 provided on the downstream side in the conveying direction at a predetermined timing.

[0024] As shown in FIG. 2, the registration roller 31 of the present embodiment is provided separately into two in a direction orthogonal to the conveying direction of the sheet P. The front registration roller shown in FIG. 1 is referred to as a first registration roller 31a, and the rear registration roller is referred to as a second registration roller 31b. The first registration roller 31a and the second registration roller 31b are each independently controlled. The conveying speeds of the first registration roller 31a and the second registration roller 31b are independently controlled according to the skew state of the sheet P, and thereby the skew correction of the sheet P is performed.

[0025] In addition, the driven-side rollers of the first registration roller 31a and the second registration roller 31b have a crown shape. Thereby, the straightness of the conveyed sheet P can be improved, and the skew correction can be performed more appropriately.

[0026] The registration sensor RS is disposed between the pickup roller 30d and the registration roller 31, and detects the conveyed sheet P. The detection signal by the registration sensor RS is output to a control unit 70 (see FIG. 4) described later, and the control unit 70 controls the start and stop of rotation of the registration roller 31 based on the detection signal of the registration sensor RS.

[0027] The skew correction sensor CS is disposed between the resist roller 31 and the conveyance roller 32 and detects the conveyed sheet P. The skew correction sensor CS is provided corresponding to the first resist roller 31a and the second resist roller 31b, respectively. The skew correction sensor CS corresponding to the first resist roller 31a is referred to as the first skew correction sensor CS1, and the skew correction sensor CS corresponding to the second resist roller 31b is referred to as the second skew correction sensor CS2. The first skew correction sensor CS1 and the second skew correction sensor CS2 are provided at a predetermined interval in a direction orthogonal to the conveyance direction of the sheet P.

[0028] Detection signals from the first skew correction sensor CS1 and the second skew correction sensor CS are output to the control unit 70 (see FIG. 4). The control unit 70 controls the rotation speed of the resist roller 31 based on the detection signals of the first skew correction sensor CS1 and the second skew correction sensor CS2 to perform skew correction.

[0029] FIG. 3 is a diagram for explaining the flow of skew correction in the present embodiment. First, as shown in FIG. 3A, the sheet P conveyed by the pickup roller 30d reaches the resist roller 31. In the example shown in FIG. 3A, the leading edge of the sheet P reaches the second resist roller 31b before the first resist roller 31a due to the skew of the sheet P.

[0030] If the sheet P is conveyed as it is in the state shown in FIG. 3A, as shown in FIG. 3B, the leading edge of the sheet P is detected first by the second skew correction sensor CS2 corresponding to the second resist roller 31b, and then the leading edge of the sheet P is detected by the first skew correction sensor CS1 corresponding to the first resist roller 31a.

[0031] Based on the difference Tsnr in the detection times of the detection signal of the second skew correction sensor CS2 and the detection signal of the first skew correction sensor CS1, the control unit 70 calculates the correction distance D ROL as follows. D ROL = conveyance speed V1 × Tsnr × (D1 / D2) Conveying speed V1: The conveying speed of the pickup roller 30d D1: The distance between the first resist roller 31a and the second resist roller 31b (the distance in the direction orthogonal to the conveying direction) D2: The distance between the first skew correction sensor CS1 and the second skew correction sensor CS2 (the distance in the direction orthogonal to the conveying direction)

[0032] And the control unit 70 forms a slack so that the leading ends of the sheet P are aligned by decelerating the conveying speed of the second resist roller 31b based on the correction distance D ROL The slack is eliminated by subsequent assist control

[0033] The conveying roller 32 nips the sheet P that has been skew-corrected by the resist roller 31 and conveys it toward the conveying unit 34. The conveying roller 32 is driven by a conveying roller drive motor 53 (see FIG.  4).

[0034] The conveying unit 34 includes a conveying belt 34a and a platen roller 34b. The conveying belt 34a is formed of an annular endless belt and has a number of suction holes formed therein. The conveying belt 34a is looped around four platen rollers 34b extending in a direction orthogonal to the conveying direction. The sheet P conveyed by the conveying roller 32 is conveyed to the annular conveying belt 34a. Then, the sheet P is adsorbed onto the conveying belt 34a by the suction of a suction fan (not shown) installed on the back side of the conveying road surface of the conveying belt 34a and conveyed at a predetermined conveying speed. While the sheet P is being conveyed by the conveying belt 34a, ink is ejected from the line head 33 onto the sheet P, whereby printing processing is performed on the sheet P. The platen roller 34b is driven by a platen roller drive motor 54 (see FIG. 4).

[0035] Each line head 33 has a plurality of inkjet heads arranged in a direction orthogonal to the conveyance direction of the sheet P. As shown in FIG. 1, the four line heads 33 are arranged at predetermined intervals along the conveyance path of the sheet P. The four line heads 33 eject inks of C (cyan), M (magenta), Y (yellow), and K (black), respectively.

[0036] The sheet P subjected to printing processing by the four line heads 33 is conveyed on the circulation conveyance path CR by the first to fifth circulation conveyance rollers 35 to 39 arranged on the circulation conveyance path CR.

[0037] And, a switching mechanism 43 for switching whether to guide the sheet P to the paper discharge roller 40 side or to the first inversion conveyance roller 41 side is provided ahead of the fifth circulation conveyance roller 39.

[0038] When performing single-sided printing, the single-sided printed sheet P is guided to the paper discharge roller 40 side by the switching mechanism 43 and discharged onto the paper discharge tray 45. On the other hand, when performing double-sided printing, the single-sided printed sheet P is guided to the first inversion conveyance roller 41 side by the switching mechanism 43.

[0039] The sheet P guided to the first inversion conveyance roller 41 by the switching mechanism 43 is conveyed by the first inversion conveyance roller 41 toward the inversion roller 42.

[0040] The inversion roller 42 conveys the sheet P toward the inversion table 46, and by conveying it back from the inversion table 46, conveys the sheet P with the front and back sides inverted toward the second inversion conveyance roller 44.

[0041] Then, the sheet P with the front and back sides inverted is conveyed again to the registration roller 31 by the second inversion conveyance roller 44, and is conveyed by the registration roller 31 toward the conveyance unit 34 again at a predetermined timing. And, printing processing is performed on the back surface of the sheet P by the line head 33.

[0042] The sheet P with printing processed on its back surface is conveyed by the first to fifth circulation conveyance rollers 35 to 39, and is conveyed to the paper discharge tray 45 by the paper discharge roller 40 via the switching mechanism 43.

[0043] FIG. 4 is a block diagram showing a schematic configuration of the control system of the inkjet printing apparatus 1 of the present embodiment.

[0044] The control unit 70 controls the entire inkjet printing apparatus 1, and includes a CPU (Central Processing Unit), a semiconductor memory, a hard disk, and the like. The control unit 70 executes a program stored in advance in a storage medium such as a semiconductor memory or a hard disk, and controls the operations of each part of the inkjet printing apparatus 1 by operating an electric circuit.

[0045] In particular, as described above, the control unit 70 of the present embodiment performs skew correction of the sheet P by the resist roller 31, and controls to release the nip of the sheet P by the paper feeding unit 30 so that the skew-corrected sheet P does not skew again.

[0046] Hereinafter, the operations of paper feeding, skew correction, and nip release from the paper feeding unit 30 will be described with reference to the timing chart shown in FIG. 5. The timing chart shown in FIG. 5 is a diagram showing changes in the conveyance speeds of the paper feeding unit 30 (the scraper 30b and the pickup roller 30d) and the first resist roller 31a and the second resist roller 31b.

[0047] First, the control unit 70 starts the rotation of the scraper 30b and the pickup roller 30d at the timing of time t1 shown in FIG. 5, feeds out the sheet P from the paper feed table 30a, and starts conveyance toward the resist roller 31. At this time, the first resist roller 31a and the second resist roller 31b also start rotating at the timing of time t1.

[0048] Specifically, the control unit 70 rotates the scraper 30b, the pickup roller 30d, the first resist roller 31a, and the second resist roller 31b at a predetermined acceleration, stops the acceleration when the conveyance speed of the sheet P reaches V1, and conveys the sheet P at the conveyance speed V1.

[0049] Then, when the sheet P is detected by the resist sensor RS (time t2), the control unit 70 rotates the scraper 30b and the pickup roller 30d again at a predetermined acceleration and increases the speed to a conveyance speed V2 that is higher than the conveyance speed V1. By making the conveyance speed V2 of the scraper 30b and the pickup roller 30d higher than the conveyance speed V1 of the first resist roller 31a and the second resist roller 31b in this way, assist control is performed, and a slack of the sheet P is formed between the sheet feeding unit 30 and the resist roller 31.

[0050] Then, after the control unit 70 conveys the sheet P at the conveyance speed V2 of the scraper 30b and the pickup roller 30d for a predetermined time, deceleration is started at time t3 to set the conveyance speed to V3 (corresponding to the first conveyance speed of the present invention). Note that the relationship between the conveyance speed V1 and the conveyance speed V3 is V3≧V1. Also, during conveyance at the conveyance speed V3, the first resist roller 31a and the second resist roller 31b remain at the conveyance speed V1. In the present embodiment, since the pickup roller 30d has a weaker frictional force than the first resist roller 31a and the second resist roller 31b and the sheet P is likely to slip, the slack of the sheet P is maintained or gradually eliminated even with the relationship V3≧V1.

[0051] Then, for example, when the leading end of the sheet P is detected by the second skew correction sensor CS2 at time t4 due to the skew of the sheet P as shown in FIG. 3, and then the leading end of the sheet P is detected by the first skew correction sensor CS1 at time t5, the control unit 70 calculates the time Tsnr, which is the difference between time t5 and time t4. Then, the control unit 70 calculates the correction distance D ROL based on the time Tsnr as described above, and the correction distance D ROLBased on this, the conveyance speed of the second resist roller 31b is decelerated for a predetermined time. By this deceleration of the second resist roller 31b, skew correction of the sheet P is performed.

[0052] Subsequently, the control unit 70 decelerates the scraper 30b and the pickup roller 30d from time t6, makes the speed slower than the conveyance speed V3, and conveys the sheet P at a conveyance speed V4 (corresponding to the second conveyance speed of the present invention). Thereby, the slack of the sheet P is further eliminated.

[0053] Then, while the sheet P is being conveyed at the conveyance speed V4, it is nipped by the conveyance roller 32. By nipping with the conveyance roller 32 in this way, it is possible to prevent the skew of the sheet P from occurring again. Also, it is preferable to control so that slack remains in the sheet P at the time when it is nipped by the conveyance roller 32. Thereby, it is possible to prevent back tension from being applied between the pickup roller 30d and the conveyance roller 32, and it is possible to prevent the skew of the sheet P from occurring again.

[0054] Also, when the sheet P is nipped by the conveyance roller 32, the control unit 70 controls the nip release unit 60 to release the nip of the sheet P in the sheet feeding unit 30.

[0055] Then, the control unit 70 decelerates the scraper 30b and the pickup roller 30d from time t7 and sets the conveyance speed to zero.

[0056] The slack of the sheet P is completely eliminated after the sheet P is nipped by the conveyance roller 32. At that time, as described above, the nip of the sheet P by the sheet feeding unit 30 is released by the nip release unit 60, so back tension does not occur between the resist roller 31 and the sheet feeding unit 30, and it is possible to prevent the sheet P from skewing again and perform appropriate skew correction.

[0057] Furthermore, even when the conveyance speed of the sheet feeding unit 30 becomes zero, similarly, the nip of the sheet P by the sheet feeding unit 30 is released by the nip release unit 60. Therefore, no back tension occurs between the resist roller 31 and the sheet feeding unit 30, and it is possible to prevent the sheet P from skewing due to the stop of the sheet feeding unit 30.

[0058] Also, in the present embodiment, as described above, the conveyance speed of the sheet feeding unit 30 (the scraper 30b and the pickup roller 30d) is once decreased from the conveyance speed V2 to the conveyance speed V3, then decreased to the conveyance speed V4, and then stopped at zero. That is, it is stopped after decelerating in two stages of the conveyance speed V3 and the conveyance speed V4. Therefore, for example, the conveyance speed V4 when the slack of the sheet P is completely eliminated can be set to a slow speed. Thus, for example, when the slack of the sheet is completely eliminated before the nip of the sheet feeding unit 30 by the nip release unit 60 is released, the impact of the sheet P at the time of slack elimination can be reduced, and the phenomenon that the sheet P returns to the original skewed state can be suppressed.

[0059] Then, the sheet P is conveyed by the resist roller 31 and the conveyance roller 32 and delivered to the conveyance unit 34. After the rear end of the sheet P passes through the pickup roller 30d, the nip release state by the nip release unit 60 is eliminated and the scraper 30b and the deflector plate 30c return to the original state between the time t7, and the feeding of the next sheet P is started from the time t7.

[0060] Also, in the timing chart shown in FIG. 5, the conveyance speed of the sheet feeding unit 30 is decelerated in two stages from the conveyance speed V2 to the conveyance speed V3 and the conveyance speed V4. However, the present invention is not limited to this. For example, as in the timing chart shown in FIG. 6, it may be decelerated in only one stage of the conveyance speed V3. In this case, it is preferable that the deceleration α1 when decelerating from the conveyance speed V3 to zero is smaller than the deceleration α2 in the case of the timing chart shown in FIG. 5. Thereby, similarly to the case of two-stage deceleration, the impact of the sheet P at the time of slack elimination can be reduced, and the phenomenon that the sheet P returns to the original skewed state can be suppressed.

[0061] In addition, in the assist control of the inkjet printing apparatus 1 of the above embodiment, the deceleration speed may be changed according to the size of the sheet. Specifically, when the sheet is small, there are few cases where back tension is generated by the nip in the sheet feeding unit 30, and when the sheet is large, back tension is more likely to occur. Therefore, the deceleration speed may be made smaller as the sheet is larger. Thereby, the influence of the back tension can be made smaller.

[0062] In addition, in the assist control of the inkjet printing apparatus 1 of the above embodiment, the conveyance speed of the sheet feeding unit 30 may be changed according to the type of sheet, the size of the sheet, or the set amount of slack. Specifically, for example, when the sheet is thick paper, it is difficult to form slack, and the influence of back tension is large. Therefore, the conveyance speed of the sheet feeding unit 30 may be made smaller compared to the case of plain paper. Also, as described above, when the sheet is larger, the influence of back tension is greater, so it is preferable to increase the set amount of slack. Therefore, the conveyance speed of the sheet feeding unit 30 may be increased as the sheet is larger (as the set amount of slack is larger). Thereby, the influence of the back tension can be made smaller.

[0063] In the inkjet printing apparatus 1 of the above embodiment, for the registration roller 31, a configuration separated in the direction orthogonal to the conveyance direction is used. However, the present invention is not limited to this, and a registration roller composed of a single roller may be used. Also, when using a single registration roller, the rotation start timing of the registration roller may be made later than the rotation start timing of the pickup roller 30d, and the sheet P may be brought into contact with the registration roller in a stopped state of rotation. After skew correction is performed by this contact, the registration roller may be started to rotate at a predetermined timing.

[0064] Furthermore, the present invention is not limited to the above-described embodiments, and components can be modified and embodied without departing from the gist thereof at the implementation stage. Also, various inventions can be formed by appropriately combining a plurality of components disclosed in the above embodiments. For example, all the components shown in the embodiments may be appropriately combined. Needless to say, various modifications and applications are possible within the scope not departing from the gist of the invention.

[0065] Regarding the present invention, the following additional remarks are disclosed.

[0066] (Supplementary Note 1) The sheet conveying device of the present invention includes a sheet feeding unit that feeds and conveys a sheet stacked on a sheet feeding tray, a registration roller that performs skew correction on the sheet conveyed from the sheet feeding unit, a nip release unit that releases the nip of the sheet by the sheet feeding unit after the sheet reaches the registration roller, and a control unit that controls the sheet feeding unit, the registration roller, and the nip release unit.

[0067] (Supplementary Note 2) In the sheet conveying device described in Supplementary Note 1, it can be provided with a conveying roller that nips the sheet sent out from the registration roller, and the control unit can control the nip release unit to release the nip of the sheet by the sheet feeding unit after the sheet reaches the conveying roller.

[0068] (Supplementary Note 3) In the sheet conveying device described in Supplementary Note 1 or Supplementary Note 2, the control unit performs assist control to form a slack in the sheet by conveying the sheet by the sheet feeding unit at a conveying speed faster than that of the registration roller during the conveyance of the sheet by the registration roller, and controls the conveying speed of the sheet feeding unit so that the slack is gradually eliminated, and the assist control can be performed so that the slack remains until the sheet conveyed by the registration roller reaches the conveying roller.

[0069] (Supplementary Note 4) In the sheet conveying device described in Supplementary Note 3, the control unit can eliminate slack by decelerating the conveying speed of the paper feeding unit, and can change the deceleration speed according to the size of the sheet.

[0070] (Supplementary Note 5) In the sheet conveying device described in Supplementary Note 3 or Supplementary Note 4, the control unit can eliminate slack by controlling the conveying speed of the paper feeding unit to a second conveying speed smaller than the first conveying speed after decelerating the conveying speed of the paper feeding unit to the first conveying speed.

[0071] (Supplementary Note 6) In the sheet conveying device described in any one of Supplementary Notes 3 to 5, the control unit can change the conveying speed of the paper feeding unit in the assist control according to the type of sheet, the size of the sheet, or the set amount of slack.

Explanation of Reference Signs

[0072] 1 Inkjet printing device 30 Paper feeding unit 30a Paper feed table 30b Scraper 30c Spreading plate 30d Pickup roller 31 Registration roller 32 Conveying roller 33 Line head 34 Conveying unit 34a Conveying belt 34b Platen roller 40 Discharge roller 42 Reversing roller 43 Switching mechanism 45 Discharge table 46 Reversing table 50 First paper feeding drive motor 51 Second paper feeding drive motor 53 Conveying roller drive motor 54 Platen roller drive motor 60 Nip release unit 70 Control unit CR Circulating conveying path CS Diagonal correction sensor P sheet RS resist sensor

Claims

1. A sheet feeding unit that feeds out and conveys a sheet stacked on a sheet feeding table, A registration roller that performs skew correction on the sheet conveyed from the sheet feeding unit, A nip release unit that releases the nip of the sheet by the sheet feeding unit after the sheet reaches the registration roller, A sheet conveying device comprising the sheet feeding unit, the registration roller, and a control unit that controls the sheet feeding unit, the registration roller, and the nip release unit.

2. Comprising a conveying roller that nips the sheet sent out from the registration roller, The sheet conveying device according to claim 1, wherein the control unit controls the nip release unit to release the nip of the sheet by the sheet feeding unit after the sheet reaches the conveying roller.

3. The control unit performs assist control to form a slack in the sheet by conveying the sheet by the sheet feeding unit at a conveying speed faster than that of the registration roller during the conveyance of the sheet by the registration roller, and controls the conveying speed of the sheet feeding unit so that the slack is gradually eliminated, and performs the assist control so that the slack remains until the sheet conveyed by the registration roller reaches the conveying roller. The sheet conveying device according to claim 2.

4. The sheet conveying device according to claim 3, wherein the control unit eliminates the slack by decelerating the conveying speed of the sheet feeding unit and changes the deceleration speed according to the size of the sheet.

5. The sheet conveying device according to claim 3, wherein the control unit decelerates the conveying speed of the sheet feeding unit to a first conveying speed and then controls it to a second conveying speed smaller than the first conveying speed to eliminate the slack.

6. The sheet conveying device according to claim 3, wherein the control unit changes the conveying speed of the sheet feeding unit in the assist control according to the type of the sheet, the size of the sheet, or the set amount of the slack.

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