JP2020175972A - Sheet conveying device and sheet processing device - Google Patents

Abstract

To provide a sheet conveying device and an image forming device with a high skew correcting performance for a sheet.SOLUTION: A sheet conveying device comprises a conveying unit, a skew correcting unit 5 for correcting a skew of a sheet conveyed from the conveying unit, and a controlling unit 110. The skew correcting unit 5 comprises: a skew correcting roller 501; a holding member 502 for forming a holding unit N2 between the holding member and the skew correcting roller 501; and a switching unit 102 which is interposed on a power transmission path 100 from a driving source 101 to the skew correcting roller 501 and can switch between a first state where a driving force from the driving source 101 can be transmitted to the skew correcting roller 501 and a second state where the driving force from the driving source 101 cannot be transmitted to the skew correcting roller 501. The controlling unit 110 controls the switching unit 102 so that it brings the state of the leading end of the sheet into the second state when the leading end of the sheet enters the holding unit N2. Further, the controlling unit 110 controls the switching unit 102 so that it changes the state of the leading end of the sheet from the second state to the first state after the leading end of the sheet passes through the holding unit N2.SELECTED DRAWING: Figure 2

Description

The present invention relates to a sheet transport device and a sheet processing device for transporting sheets.

Conventionally, as an image forming apparatus such as an electrophotographic method, a configuration in which a sheet housed in a feeding cassette is conveyed to an image forming unit by a sheet conveying apparatus is widely known. The sheet transport device corrects the posture of the sheet that is tilted in the process of being transported from the feed cassette, and prevents the image formed by the image forming unit from being transferred to the sheet in a tilted state. A correction unit is provided. In the conventional skew correction unit, a shutter member that locks the tip of the conveyed sheet and applies a load is provided, and the obliquely conveyed sheet is formed with a deflection to correct the skew and correct the skew. Later, a configuration has been proposed in which the shutter member is retracted by the sheet. In the case of this configuration, the shutter member must be able to retract even with a thin paper having a low rigidity of the sheet, and it is necessary to set the load applied to the sheet by the shutter member to be weak. In that case, in the case of thick paper having a high rigidity of the sheet, the sheet could not be sufficiently bent, and the performance of correcting the skew was deteriorated. For this reason, Patent Document 1 proposes a configuration in which a lock mechanism is provided on the shutter to increase the load on thick paper and improve the skew correction performance.

Japanese Unexamined Patent Publication No. 2014-133640

However, the configuration of Patent Document 1 requires a complicated mechanism, and even when the lock mechanism is provided, the load cannot be increased in proportion to the rigidity of the sheet. Therefore, there is a possibility that a sheet having a higher rigidity cannot sufficiently form the deflection.

Therefore, an object of the present invention is to provide a sheet transport device and a sheet processing device having high sheet skew correction performance.

One aspect of the present invention includes a transport unit that transports sheets, a skew correction unit that is provided on the downstream side of the transport unit in the sheet transport direction and that corrects skew of the sheet that has been transported from the transport unit. A control unit for controlling the skew correction unit is provided, and the skew correction unit forms a sandwiching portion between the skew correction roller and the skew correction roller in contact with the skew correction roller. The sandwiching member, the drive source for rotationally driving the skew correction roller, and the power transmission path from the drive source to the skew correction roller are interposed, and the driving force from the drive source is transmitted to the skew correction roller. A switching unit that can switch between a first state that can be transmitted and a second state that cannot transmit the driving force from the driving source to the skew correction roller is provided, and the control unit is provided by the transport unit. The switching portion is controlled so that the switching portion is in the second state when the tip of the conveyed sheet enters the sandwiching portion, and after the tip of the sheet has passed through the sandwiching portion, the second state is changed to the second state. The sheet transport device is characterized in that the switching unit is controlled so as to be in one state and transmit the driving force from the driving source to the skew correction roller.

According to the present invention, the input of the driving force to the skew correction roller can be connected and disconnected by the switching portion. Therefore, in a state where the driving force to the skew correction roller is not input, it is possible to correct the skew of the sheet at the sandwiching portion between the skew correction roller and the holding member, depending on the thickness of the sheet. The load applied to the seat can be changed. As a result, the skew correction performance of the sheet can be improved. Further, after the tip of the sheet has passed through the sandwiching portion, the second state is changed to the first state, and the skew-corrected sheet can be conveyed by the skew correction roller.

It is the schematic sectional drawing which shows the image forming apparatus which concerns on 1st Embodiment. It is a perspective view explaining the structure of the skew correction part. It is schematic cross-sectional view explaining the statics model when a sheet is sandwiched by a pair of skew correction rollers. It is a graph which showed the load applied to the sheet in the skew correction roller pair. (A) It is a figure which shows the state just before the skewed sheet is sandwiched by the skew correction roller pair. (B) It is a figure which shows the state which the front side of the tip of a sheet is sandwiched by a pair of skew correction rollers and receives a load. (C) It is a figure which shows the state which the tip of the sheet pushes out the skew correction roller pair. (A) It is a figure which shows the state which the tip of the sheet passed through the sandwiching part of the skew correction roller pair. (B) It is a figure which shows the state just before the rear end of a sheet passes through the sandwiching part of the skew correction roller pair, and the succeeding sheet is sandwiched by the skew correction roller pair. It is a graph which showed the skew correction factor of a sheet. It is a graph which showed the sound pressure generated at the time of the skew correction of a sheet. (A) It is a perspective view which showed the modification of the skew correction roller pair. (B) It is a perspective view which showed the other modification of the skew correction roller pair. (A) It is a perspective view which shows the double-sided refeeding roller pair which concerns on 2nd Embodiment. (B) It is a side view which shows the state which the double-sided refeeding roller pair sandwiched the sheet in the sandwiching part. (A) It is a perspective view which shows the modification of the skew correction roller pair. (B) It is a perspective view of the skew correction roller pair shown in FIG. 11 (a). It is a perspective view which shows the other modification of the skew correction roller pair.

Hereinafter, an image forming apparatus including the sheet conveying apparatus according to the present embodiment will be described with reference to the attached drawings. In this embodiment, an example in which a laser printer is used as the image forming apparatus will be described. Further, in the following description, the sheet includes not only plain paper but also special paper such as coated paper, recording material having a special shape such as envelope and index paper, and plastic film and cloth for overhead projectors. It shall be a paper. Further, the manuscript is also included in the concept of the sheet, and the manuscript may be a blank sheet or may have an image formed on one side or both sides. In addition, the surface of the image forming apparatus facing the user is referred to as a front surface, the surface opposite to the front surface is referred to as a back surface, and the front-back direction of these image forming apparatus is referred to as a front-back direction. Further, the direction orthogonal to the front-back direction is referred to as the width direction.

<First Embodiment>
FIG. 1 is a schematic cross-sectional view showing the configuration of the image forming apparatus 1 as viewed from the front side of the apparatus. As shown in FIG. 1, the image forming apparatus 1 forms an image by an electrophotographic recording method, and conveys a sheet from the apparatus main body 2, the feeding cassette 3 as a sheet accommodating portion, and the feeding cassette 3. The sheet transport unit 4 is provided. Further, the image forming apparatus 1 forms an image on both sides of the sheet, the image forming unit 6 that forms an image on the sheet, the fixing unit 7 that fixes the toner image on the sheet, and the discharging unit 8 that discharges the sheet. It is provided with a double-sided transport unit 9 for transporting the sheet at the time of the operation.

The feeding cassette 3 has a loading plate 30 for loading the sheet S, and the loading plate 30 can be raised to a position where the uppermost surface of the sheet S comes into contact with the feeding roller 41a for feeding the sheet S. is there. When the uppermost surface of the sheet S comes into contact with the feeding roller 41a, the sheet S is fed to the separation nip portion N1 formed by the transport roller 41b and the separation roller 42 by the feeding roller 41a rotating in the direction of arrow R1 shown in the drawing. Will be done. The sheets S are separated one by one at the separation nip portion N1 and then conveyed toward the skew correction portion 5.

The sheet transport unit 4 includes a transport roller 41b as the transport unit described above, and a skew correction section 5 provided on the downstream side of the transport roller 41b in the sheet transport direction. The skew correction unit 5 includes a skew correction roller pair 50 having a skew correction roller 501 as a first rotating body and a holding roller 502 as a second rotating body or a holding member. A sandwiching portion N2 is formed between the correction roller 501 and the sandwiching roller 502. Further, a driving force is transmitted from the driving source 101 to the skew correction roller 501, and the driving source 101 is controlled by a control signal from the control unit 110 (see FIG. 2). Further, an electromagnetic clutch 102 is interposed on the power transmission path 100 between the drive source 101 and the skew correction roller 501, and by controlling these drive sources 101 and the electromagnetic clutch 102, the skew correction roller The drive / non-drive of the pair 50 is controlled. That is, the skew correction unit 5 is controlled by the control unit 110.

The tip of the sheet S conveyed by the transfer roller 41b is loaded by the skew correction roller pair 50. Due to the load, the tip of the sheet S is aligned with the sandwiching portion N2 of the skew correction roller pair 50, and the skew is corrected. The tip of the sheet S whose skew is corrected passes through the holding portion N2 of the skew correction roller pair 50 due to the conveying force of the conveying roller 41b and the rigidity of the sheet S. A detection sensor 65 for detecting the presence or absence of a sheet is arranged downstream of the sheet transporting direction of the sandwiching portion N2 of the skew correction roller pair 50 and upstream of the image forming portion 6. The detection sensor 65 is a sensor that detects the passage of the seat holding portion N2, and the control unit 110 engages with the above-mentioned electromagnetic clutch 102 based on the detection sensor 65 detecting the tip of the seat S. It is in a combined state. When the electromagnetic clutch 102 is engaged, a driving force is input to the skew correction roller pair 50, and the skew-corrected sheet S is moved to the image forming unit 6 by the skew correction roller pair 50 that is rotationally driven. Be transported. The details of the mechanism by which the skew correction roller pair 50 corrects the skew will be described later.

The image forming unit 6 includes a photoconductor drum 61 as an image carrier, an exposure means 62, a developing means 63, and a transfer roller 64. The image forming unit 6 starts the image forming operation when the control unit 110 receives the image signal, and the photoconductor drum 61 is rotationally driven. In the rotation process, the photoconductor drum 61 is uniformly charged by a charging means (not shown), and is exposed by the exposure means 62 according to the image signal. As a result, an electrostatic latent image is formed on the surface of the photoconductor drum 61, and then the toner image is formed on the surface of the photoconductor drum 61 by being developed by the developing means 63. The transfer roller 64 abuts on the photoconductor drum 61 to form a transfer nip TN. The toner image formed on the surface of the photoconductor drum 61 is transferred to the sheet S conveyed by the skew correction roller pair 50 at the transfer nip TN, and then heated and pressurized in the fixing portion 7 to form the sheet. It is fixed on S. The sheet S on which the toner image is fixed by the fixing portion 7 is discharged to the discharge tray 82 by the discharge roller pair 81 of the discharge unit 8.

When double-sided printing is performed, the sheet S on which the toner image is fixed by the fixing portion 7 is guided to the double-sided conveying portion 9. Specifically, first, the transport path switching flapper 91 is moved to the position of the dotted line in FIG. 1 by an actuator (not shown). The sheet S passes over the upper surface of the transport path switching flapper 91 and is delivered to the reverse transport roller pair 92. When the rear end of the sheet S reaches the upper surface of the transport path switching flapper 91, the transport path switching flapper 91 is moved to the position of the solid line in FIG. 1 by an actuator (not shown). After that, the reversing transfer roller pair 92 is reversely driven to transfer the sheet S to the double-sided transfer roller pair 93. The sheet S is conveyed along the reversing transfer path by the double-sided transfer roller pair 93 and the double-sided refeed roller pair 94, and is guided to the skew correction unit 5 again. Then, the above-mentioned printing operation is performed on the back surface of the sheet.

<Structure of skew correction unit>
Next, the detailed configuration of the skew correction unit 5 will be described with reference to FIG. FIG. 2 is a perspective view of the skew correction unit including the above-mentioned skew correction roller pair 50. As shown in FIG. 2, the skew correction roller 501 includes a plurality of roller portions 501a and 501b made of silicon rubber (two in the present embodiment) and a skew correction roller as a rotation axis made of metal. It is composed of a shaft 501c. Each of these two roller portions 501a and 501b is a cylindrical member whose outer peripheral shape is circular when viewed from the axial direction, and has a predetermined interval in the axial direction with respect to the skew correction roller shaft 501c. It is fixed. In the following description, the roller portion 501a on the front side of the main body will be referred to as a front skew correction roller portion, and the roller portion 501b on the back side will be referred to as a back skew correction roller portion.

The front skew correction roller portion 501a and the back skew correction roller portion 501b are press-fitted to the above-mentioned skew correction roller shaft 501c so as to be arranged at equal positions on the left and right with respect to the center of the sheet S to be conveyed. Has been done. The skew correction roller shaft 501c is rotatably held by a frame (not shown). Further, the holding roller 502 is also configured to include two roller portions (hereinafter, referred to as holding roller portions) 502a and 502b on the front side and the back side. Each of the holding roller portions 502a and 502b has an integrally formed holding roller shaft 502c, which is rotatably engaged with the holding roller holding portion 503a which is a recess formed in the holding roller holder 503. Is held at. The holding roller holder shaft 503b, which is integrally formed with the holding roller holder 503, is rotatably held by a frame (not shown). When the holding roller holder 503 is urged by the holding spring 504, the two holding roller portions 502a and 502b come into contact with the front skew correction roller portion 501a and the back skew correction roller portion 501b, respectively, to form the holding portion N2. Will be done. That is, the holding spring 504 can be said to be an urging member that applies a holding pressure between the skew correction roller 501 and the holding roller 502 as a holding member in the holding portion N2. In the present embodiment, the sandwiching roller 502 is urged against the skew correction roller 501 by the sandwiching spring 504 to form the sandwiching portion N2. You may. Further, the skew correction roller 501 and the sandwiching roller 502 may be configured to be urged toward each other. That is, the holding spring 504 may be an urging member that urges either one of the skew correction roller 501 and the holding roller 502 toward the other. Further, the urging member may be formed not only by a spring but also by, for example, rubber.

Further, the skew correction roller shaft 501c is arranged so that the skew correction roller gear 505 rotates integrally. The driving force is transmitted to the skew correction roller gear 505 from the above-mentioned drive source 101 via a power transmission path 100 including a gear train (not shown). Further, as described above, the electromagnetic clutch 102 is arranged on the power transmission path from the drive source 101 to the skew correction roller 501. In the present embodiment, the electromagnetic clutch 102 constitutes a switching unit. Then, an engaged state (first state) in which the driving force from the drive source 101 can be transmitted to the skew correction roller 501 and an released state (first state) in which the driving force from the drive source 101 cannot be transmitted to the skew correction roller 501. It is possible to switch to (2 states) and. In the present embodiment, since the drive source 101 is also a drive source for the photoconductor drum 61 as an image carrier, the control unit 110 obliquely engages / disengages the electromagnetic clutch 102. Controls the drive / non-drive of the row correction roller 501.

Specifically, the control unit 110 includes a CPU 111 as a calculation unit, a RAM 112 and a ROM 113 as a storage unit, and a transfer control program for driving and controlling the skew correction roller 501 is stored in the ROM 113. .. The control unit 110 controls the drive / non-drive of the skew correction roller 501 according to this program. In the present embodiment, the skew correction roller 501 immediately after the tip of the sheet S passes through the holding portion N2. The drive is transmitted only until the rear end of the seat comes off. When the electromagnetic clutch 102 is engaged and the driving force is transmitted, the skew correction roller 501 rotates in the direction of arrow R2 in the drawing and conveys the sandwiched sheet S to the transfer nip TN of the image forming unit 6. To do.

That is, in the skew correction roller pair 50, until the tip of the seat S passes through the holding portion N2, the electromagnetic clutch 102 is in the released state and only driven rotation is performed, and the tip of the seat S is driven. It is driven after passing through the sandwiching portion N2. That is, when the tip of the sheet S is sandwiched by the sandwiching portion N2, both the skew correction roller 501 and the sandwiching roller 502 are driven rollers that rotate driven by the sheet passing through the sandwiching portion N2. ..

Further, in the present embodiment, the skew correction roller pair 50 constitutes a registration roller pair which is a transfer roller pair immediately before the transfer nip TN of the image forming unit 6. Therefore, the control unit 110 performs an image forming operation in the transfer nip TN of the image forming unit 6 so that the tip of the sheet S whose skew is corrected coincides with the writing start position of the image on the image carrier. In addition, it is necessary to transport the sheet S. More specifically, the control unit 110 determines the timing for engaging the electromagnetic clutch 102 based on the timing at which the detection sensor 65 detects the tip of the sheet S and the timing at which the image is formed. Further, the control unit 110 releases the electromagnetic clutch 102 based on the detection sensor 65 detecting the rear end of the seat S to stop the driving of the skew correction roller 501. Further, the control unit 110 starts the processing operation of the image forming unit (sheet processing unit) based on the detection of the tip of the sheet beyond the holding unit N2 by the detection sensor 65. In this way, by controlling the drive start timing and the drive stop timing based on the detection result of the detection sensor 65, the space between the papers can be shortened and the productivity can be improved.

The drive start timing of the skew correction roller 501 may be set based on the predicted time from the start of feeding of the sheet S. Further, for example, when the drive source 101 is a motor dedicated to driving the skew correction roller 501, the timing of entering the sheet S into the transfer nip TN is changed by changing the transport speed of the sheet S of the skew correction roller 501. May be adjusted. That is, the control unit 110 may control the rotation speed of the skew correction roller 501, for example, based on the detection sensor 65 detecting the tip of the sheet. Further, in this case, by stopping the drive source 101 with the electromagnetic clutch 102 engaged, the rotation of the skew correction roller 501 can be stopped faster. When the drive start timing and drive stop timing of the skew correction roller 501 are set by the predicted time, the time setting for surely passing the front end of the seat and the time setting for surely passing the rear end of the seat are set. , A sufficient margin is required.

<Static model of skew correction section>
Next, a mechanism for applying a load to the seat by the skew correction roller pair 50 will be described. FIG. 3 is a schematic cross-sectional view showing a statics model in a state where a sheet S assumed to be a rigid body is sandwiched between the sandwiching portions N2 of the skew correction roller pair 50. In the present embodiment, when the line connecting the centers of the skew correction roller 501 and the sandwiching roller 502 is the x direction in FIG. 3 for simplification of the description, the sheet S is oriented in the y direction orthogonal to the x direction. It was assumed to be transported. As shown in FIG. 3, a holding force P is generated in the holding roller 502 by the holding spring 504, and the holding force P causes the sheet S to be in contact with the skew correction roller 501 at the contact point of the skew correction roller 501. It receives a normal force Na in the direction orthogonal to the tangent line. Similarly, the sheet S receives a normal force Nb at the contact point with the holding roller 502 in a direction orthogonal to the tangent line of the holding roller 502. Further, when the friction coefficient of the surface of the skew correction roller 501 is μ1 and the friction coefficient of the holding roller 502 is μ2, the sheet S receives the friction force μ1 · Na in the tangential direction of the skew correction roller 501, and the holding roller 502 It receives a frictional force of μ2 ・ Nb in the tangential direction. When the pinching force P is applied in the x direction, the skew correction roller shaft 501c is fixed in both the xy directions, so that the load F received by the sheet S is as follows. In the following equation, the angle between the tangent line of the skew correction roller 501 and the sheet is θa, and the angle between the tangent line of the sandwiching roller 502 and the sheet is θb. Further, since the influence of the sliding resistance and moment of inertia of the skew correction roller pair 50 and the slip with the seat is small, it is omitted.

Here, the outer peripheral surfaces of the roller portions of the skew correction roller 501 and the sandwiching roller 502 are formed so that the inclination of the tangent line in the sandwiching portion N2 increases as the inclination of the tangent line increases away from the nip point of the sandwiching portion N2 in the circumferential direction. It is a curved surface. Therefore, when considering the thickness of the sheet S, as the thickness of the sheet becomes thicker, θa and θb each approach 90 °, so that the load F received by the sheet S also increases. FIG. 4 is a graph showing the measured values of the load F on the vertical axis. As shown in FIG. 4, the load of plain paper (sheet thickness t = 0.1 mm) was about 100 gf, whereas that of thick paper (sheet thickness t = 0.2 mm) was about 140 gf, and the load became large. ing.

<Slanting correction mechanism of skew correction section>
Next, the mechanism of skew correction by the skew correction unit will be described. 5 (a) to 5 (c) and 6 (a) and 6 (b) are schematic cross-sectional views for explaining the skew correction mechanism when the front side of the tip of the sheet S is skewed so as to precede it. Specifically, FIG. 5A shows a state immediately before the skewed sheet S is sandwiched between the skew correction roller pairs 50. FIG. 5B shows a state in which the front surface side of the tip of the sheet S is sandwiched between the skew correction roller pairs 50 and is subjected to a load. FIG. 5C shows a state in which the tip of the sheet S pushes the skew correction roller pair 50 apart. FIG. 6A shows a state in which the tip of the sheet S has passed through the sandwiching portion of the skew correction roller pair 50. FIG. 6B shows a state immediately before the rear end of the sheet S passes through the sandwiching portion of the skew correction roller pair 50 and the succeeding sheet S2 is sandwiched by the skew correction roller pair 50. Further, the left side in the figure shows the front skew correction roller portion 501a side, and the right side shows the back skew correction roller portion 501b side.

As shown in FIG. 5A, just before the front end of the sheet S is sandwiched between the front skew correction roller portion 501a and the sandwiching roller portion 502a, the tip of the back surface side of the sheet S is still in the sandwiching portion N2. It is far upstream. At this time, the above-mentioned electromagnetic clutch 102 is released, and the skew correction roller pair 50 is a driven roller pair for which no drive is input. Then, when the sheet S is further conveyed by the transfer roller 41b, the front end of the sheet S is sandwiched by the sandwiching portion N2 and receives the load F as described above. When the rigidity of the sheet S is low and the tip of the sheet S receives the load F, the sheet S is provided on the upstream side of the skew correction roller pair 50 as shown in the front side of FIG. 5 (b). It bends so as to approach the upstream guide 58 of the line correction unit. While the front side of the seat S is bent, the tip of the back side of the seat S is continuously conveyed and approaches the holding portion N2.

When the seat S can no longer be bent, the front end side of the seat S pushes the holding portion N2 apart with a force larger than the load F, and exceeds (passes) the holding portion N2 as shown in FIG. 5 (c). .. That is, when the sheet S cannot be bent, the conveying force of the sheet S becomes larger than the load F as shown in the following equation, and the tip of the sheet S penetrates the holding portion N2.

That is, in the holding spring 504 as the urging member, the holding force received from the skew correction roller 501 and the holding roller 502 when the tip of the sheet is inserted into the holding portion N2 is larger than the carrying force received by the sheet from the transfer roller 41b. Is also configured to be weak. At this time, the front skew correction roller portion 501a is driven to rotate in the R2 direction due to the frictional force with the seat S. At the same time, the rear skew correction roller portion 501b fixed via the skew correction roller shaft 501c also rotates in the R2 direction. Since the back skew correction roller portion 501b is rotating, the back end of the sheet S sandwiched between the back skew correction roller portion 501b and the sandwich roller portion 502b is conveyed without receiving the load F. To. Therefore, the back side of the seat S does not bend. As a result, there is a difference in the amount of deflection between the front side and the back side of the sheet S, that is, the distance actually carried, so that the skew of the difference can be corrected.

After the tip of the sheet S passes through the holding portion N2, a driving force is input to the skew correction roller 501 as shown in FIG. 6A, and the front and back skew correction roller portions 501a and 501b rotate in the R2 direction. Then, the sheet S is conveyed to the image forming unit 6 downstream. When the sheet S is conveyed and the rear end of the sheet S passes through the front and back skew correction roller portions 501a and 501b holding portions N2 as shown in FIG. 6B, the skew correction roller 501 is driven. It will be released and will be in a stopped state. In the case of continuous paper passing, the drive must be stopped immediately before the subsequent sheet S2 reaches the holding portion N2 of the skew correction roller pair 50. When the sheet S2 is skewed, the skew correction operation in the sandwiching portion N2 of the skew correction roller pair 50 is repeated as described in FIGS. 5A to 5C described above.

From the above mechanism, the relationship between the sheet S and the skew correction roller 501 is such that the torque such as the sliding resistance of the skew correction roller 501 is T and the radius is r, and the friction coefficient between the sheet S and the skew correction roller 501 is set. Assuming that μ1, the following equation is obtained.

After the sheet S has passed the holding portion N2 of the skew correction roller pair 50 by the transfer roller 41b, the sheet S is transmitted downstream by the frictional force between the surface of the skew correction roller 501 and the holding roller 502. Will be transported to. At the same time, so that the tip of the skew-corrected sheet S does not skew again, slip occurs between the sheet S and the skew correction roller 501, and the sheet S does not skew until it reaches the transfer nip TN. It is necessary to set the coefficient of friction of the roller surface and the sliding resistance of the roller.

In the case of a sheet having high rigidity and being hard to bend, the performance of correcting skew may be deteriorated, but in the configuration of the present embodiment, the influence of the deterioration can be reduced. Since the rigidity is greatly affected by the thickness of the sheet, a sheet with high rigidity generally has a thicker thickness. As described in the statics model, in the configuration of the present embodiment, when the sheet is thick, the load F received by the sheet becomes large. Therefore, since it becomes easier to bend, it is possible to maintain the performance of correcting skew even even if the sheet has high rigidity. FIG. 7 is a graph comparing the skew correction factor in the conventional shutter configuration and the configuration of the present embodiment. The skew correction factor on the vertical axis of the graph indicates what percentage of the skew amount of the sheet could be corrected by the skew correction unit, and is a value calculated by the following formula.

As shown in FIG. 7, in the conventional skew correction technology using a shutter, as shown by the broken line, the skew correction factor of plain paper is about 65%, whereas that of thick paper is about 45%. It will drop. On the other hand, in the configuration of the present embodiment shown by the solid line, the skew correction factor of the plain paper can be improved to about 65%, while the skew correction factor of the thick paper can be improved to about 70%. The skew correction factor in FIG. 7 also changes depending on the shape of the skew correction section upstream guide 58.

As described above, in the present embodiment, the electromagnetic clutch 102 is provided as the switching unit, and the sheet is skewed by the holding portion N2 of the skew correction roller pair 50 in which the electromagnetic clutch 102 is released and the driving force is not input. I am correcting. That is, in the present embodiment, the control unit 110 controls the electromagnetic clutch 102 so that the tip of the sheet conveyed by the transfer unit is in the released state (second state) when it enters the holding portion N2. .. Further, after the tip of the seat has passed through the holding portion N2, the electromagnetic clutch 102 is changed from the released state to the engaged state (first state) so that the driving force from the drive source 101 is transmitted to the skew correction roller 501. I'm in control. Therefore, with a simple configuration, the load applied to the sheet sandwiched by the sandwiching portion N2 can be changed according to the thickness of the sheet, and the skew correction performance for the sheet, particularly the thick paper, can be improved. Further, the skew correction roller pair 50 also functions as a pre-transfer roller pair (registration roller pair) because another transport roller pair for transporting the sheet is not arranged between the skew correction roller pair 50 and the image forming portion 6. Therefore, the device can be made compact.

Further, as a secondary effect, reduction of suddenly generated sound can be mentioned. In the case of the configuration in which the sheet collides with the protruding shutter portion as in the conventional configuration, when the tip of the sheet S contacts the shutter portion, the speed of the sheet decreases in a minute time, so that a loud collision noise is generated. .. On the other hand, in the case of the configuration of the present embodiment, since the sheet S enters the sandwiching portion N2 that gradually becomes narrower, the speed of the sheet gradually decreases. Therefore, the collision sound can be reduced. FIG. 8 is a graph in which the sound pressure when the sheet is conveyed by the two configurations of the conventional shutter configuration and the configuration of the present embodiment is actually measured and compared. The horizontal axis of the graph represents the time during transportation, and the vertical axis represents the sound pressure. The time when the sheet collides with the shutter, the time when the sheet is sandwiched by the sandwiching portion N2 of the skew correction roller pair 50, and the time when the sheet enters the nip of the pre-transfer roller pair are all set to about 120 ms. As shown in the figure, in the conventional shutter configuration shown by the broken line, a collision sound (SP1) is generated when the tip of the sheet collides with the shutter. In addition, a collision sound (SP2) when the shutter comes into contact with the seat when it tries to return to the initial position is also generated. On the other hand, in the configuration of the present embodiment shown by the solid line, no loud collision sound is generated even at the time of entering the holding portion N2, and the sound equivalent to that when entering the nip of the pre-transfer roller pair, which is a normal transport roller pair. Only occurred.

<Modification example 1>
In the present embodiment, the two roller portions 501a and 501b made of silicon rubber are press-fitted into the skew correction roller shaft 501c, respectively. However, the present invention is not limited to this, and for example, as shown in FIG. 9A, the roller portion of the skew correction roller may be configured as one roller portion 2501 long in the axial direction. Further, as shown in FIG. 9B, the roller portion of the sandwiching roller may be formed as one roller portion 2502 long in the axial direction. Further, each of these configurations may be combined. Further, in the present embodiment, the configuration in which the sheet is bent to correct the skew is described, but the present invention is not limited to this, and a configuration in which the sheet is rotated by applying a load to correct the skew may be used. ..

<Second Embodiment>
Next, a second embodiment of the present invention will be described. The present embodiment is different from the first embodiment in that the double-sided refeeding roller pair 94 is a skew correction roller pair. Therefore, in the following description, only the points different from those of the first embodiment will be described, and the same configurations as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted. To do.

As shown in FIG. 10A, the double-sided refeeding roller pair 94 includes a double-sided refeeding roller 941 and a sandwiching roller 942. The double-sided refeeding roller 941 includes two roller portions 941a and 941b made of silicon rubber, and a double-sided refeeding roller shaft 941c which is a rotating shaft made of metal. The front refeed roller portion 941a, which is a roller portion on the front side of the main body, and the rear refeed roller portion 941b, which is a roller portion on the back side, are left and right with respect to the center of the sheet to be transported (the center of transfer of the sheet). It is evenly press-fitted into the double-sided refeeding roller shaft 941c. The double-sided refeed roller shaft 941c is rotatably held by a frame (not shown).

The holding roller 942 also includes a holding roller portion 942a on the front side, a holding roller portion 942b on the back side, and a holding roller shaft 942c formed of metal. The holding roller portions 942a and 942b on the front side and the back side are rotatably held with respect to the holding roller shaft 942c, and both ends of the holding roller shaft 942c are fixed by a frame (not shown). The sandwiching roller shaft 942c is urged in the direction of the double-sided refeeding roller 941 by the sandwiching spring 944, and the sandwiching roller portions 942a and 942b are in contact with the front refeeding roller portion 941a and the rear refeeding roller portion 941b, respectively. , The sandwiching portion N2 is formed.

Further, the double-sided refeeding roller shaft 941c is arranged so that the double-sided refeeding roller gear 9405 is integrally rotated. The double-sided refeeding roller gear 945 transmits a driving force from the drive source 101a via a power transmission path 100a including a gear train (not shown). Further, an electromagnetic clutch 102a is arranged on the power transmission path from the drive source 101a to the double-sided refeeding roller 941. The control unit 110a engages / disengages the electromagnetic clutch 102a to control the drive / non-drive of the double-sided refeed roller 941. The double-sided refeeding roller 941 transmits the driving force only from immediately after the front end of the seat passes through the holding portion N3 until the rear end of the seat comes out, and rotates in the direction of arrow R2 in the drawing to hold the sandwiched seat. Transport toward the downstream.

In double-sided transport, double-sided transport includes skew caused by the left-right difference when the sheet S is flipped by the reversing transport roller pair 92, and skew caused by the left-right mounting accuracy of the transport guide composed of separate units. It may be necessary to improve the skew peculiar to the part 9. By providing the double-sided refeed roller pair 94 with the skew correction function, the skew correction can be performed in two steps together with the skew correction unit 5, and the left and right sides of the sheet tip can be reliably aligned. In particular, compared to the short transport path from the feed cassette 3 to the image forming unit 6 due to miniaturization, the length of the reverse transport path is long, and the sheet S may be skewed during double-sided transport. In a high image forming apparatus, the skew of the sheet can be effectively removed.

Further, the drive start timing and drive stop timing of the double-sided refeed roller 941 can be set from the estimated arrival time of the seat. Further, a sheet detection sensor is provided immediately after the double-sided refeed roller pair 94, and the drive start timing and drive stop timing of the double-sided refeed roller 941 are determined based on the detection of the front end and the rear end of the seat S by the sensor. You may control it. Further, the skew correction roller pair having the above-described configuration may be formed by the double-sided transfer roller pair 93. That is, after the image is formed on one side in order to form an image on both sides of the sheet, the skew correction roller pair is formed by the transfer roller pair in the sheet transfer device that conveys the sheet toward the image forming unit 6 again. You may.

<Modification 2>
In addition, in the present invention, for example, the skew correction roller pair may be configured by the transport roller pair in the sheet transport device in the ADF (for example, the transport roller pair immediately before the image reading unit). Further, in both the first and second embodiments, the material of the skew correction roller is silicon rubber, and the skew correction roller shaft is a metal shaft. However, this is not the case, for example, the shaft and the roller are integrally made of resin. It may be formed in. At that time, as shown in the above equation of Equation 3, the skew correction roller may be set to be rotated by the sheet. Further, although the number of skew correction roller portions is two in the above-described embodiment, the number may be larger than the number.

Further, as shown in FIGS. 11A and 11B, the holding roller shaft 3502c formed on the holding roller 3502 is rotatably fixed to a frame (not shown), and the roller portions 3501a and 3501b of the skew correction roller 3501 are fixed. May be formed of a soft material such as foam rubber. Then, the sandwiching portion N3 may be formed by causing the sandwiching roller 3502 to bite into the skew correction roller 3501. According to this configuration, the skew correction ability can be improved with a simpler configuration by using the elastic force of the holding roller 3502 and the skew correction roller 3501 as the urging means for applying the holding force to the seat.

Further, in the above-described embodiment, the detection sensor 65 for detecting the presence or absence of the sheet is composed of a flag that abuts on the tip of the sheet S and rotates, and a photosensor that detects the movement of the flag. It may be composed of other sensors such as a sound wave sensor and an encoder. For example, as shown in FIG. 12, the encoder 4501d is fixed to the skew correction roller shaft 4501c of the skew correction roller 4501 so as to rotate integrally, and the rotation detection sensor 59 detects the rotation of the skew correction roller 4501. You may do so. With this configuration, it is possible to detect that the skew correction roller 4501 has started rotating by the sheet S, so that it is possible to detect the tip of the sheet S. The driving of the skew correction roller 4501 may be started by detecting the tip of the sheet S. Further, the skew correction roller 4501 may be driven and stopped by detecting the rear end of the sheet S. Further, the encoder 4501d continues to rotate during the sheet S transfer, but the encoder 4501d stops when a transfer failure occurs and the sheet S stops. Therefore, it is possible to detect transport defects.

Further, the sandwiching portion of the skew correction portion does not necessarily have to be formed by a pair of rollers. For example, the skew correction roller 501,251,3501,4501 and a non-rotating body that abuts on the skew correction roller. The contact pad may be used as a holding member. In this case, the surface of the contact pad is preferably curved, but may be flat. In addition, a groove or the like may be formed on the surface of the skew correction roller described above. In the above-described embodiment, it has been explained that the roller portion of the skew correction roller is formed so that the outer peripheral surface is circular when viewed from the direction of the rotation axis. However, in the concept of this circular shape, the above groove Is also included when is formed on the roller surface. That is, in the present embodiment, the oblique correction roller 501, 251 and 3501, 4501 may have a curved surface whose outer peripheral surface changes the load applied to the sheet according to the thickness of the sheet. In addition, the skew correction roller may be a hollow roller as well as a solid roller, and the hollow roller includes one composed of a film.

Further, in the above-described embodiment, the control unit 110 is configured to drive and control the skew correction roller pair 50 regardless of the type of seat or the like, but the present invention is limited to this. Absent. For example, the drive of the skew correction roller is controlled according to the sheet type information preset by the user and the sheet characteristic information (for example, basis weight, rigidity, surface property) by the discriminating means for discriminating the sheet characteristics. You may. Specifically, the control of driving / non-driving the skew correction roller is applied only to the seat having a predetermined basis weight or more, and the skew correction roller is always driven for the sheet having a predetermined basis weight or less. You can also do it. That is, the user may include the setting means 200 for setting the sheet type (see FIG. 1), and the control unit 110 may control the switching unit 102 based on the sheet type set by the setting means 200. Further, the discriminating unit 201 for discriminating the characteristics of the sheet is provided (see FIG. 1), and the control unit 110 may control the switching unit 102 based on the characteristics of the sheet discriminated by the discriminating means 201.

According to this configuration, an appropriate holding force can be set according to the type of seat. When the setting means 200 and the discriminating means 201 are provided, the control unit changes the electromagnetic clutch 102 as the switching unit from the released state to the engaged state based on the seat type information and the seat characteristic information. The switching timing may be changed. That is, between thin paper and thick paper, skew correction is more difficult to correct in thick paper, and when switching the state of the electromagnetic clutch 102 is determined by time, in the case of thick paper, the skew correction time is longer than that of thin paper. It is desirable to increase the margin). Therefore, for example, the thick paper and the thin paper may be determined from the sheet type information and the sheet characteristic information, and in the case of the thick paper, the timing of transition from the released state to the engaged state may be delayed. .. In addition, the switching portion may be any one as long as it can connect and disconnect the power input to the skew correction roller as well as the electromagnetic clutch 102. For example, a dog clutch or a swing of a gear. It may be something that connects and disconnects the power transmission by motion. The above-mentioned discriminating means 201 is a so-called media sensor, and includes, for example, an ultrasonic sensor and a CMOS sensor.

Further, in the above-described embodiment, an example of applying the present invention to an electrophotographic image forming apparatus has been shown, but the present invention is not limited to this, and for example, an inkjet image forming apparatus and the like may be used. It may be applied to an image forming apparatus other than the electrophotographic method. Further, even if it is an electrophotographic image forming apparatus, it may be provided in an image forming apparatus such as a copying machine, a facsimile, and a multifunction device having these functions in addition to a laser printer. Further, in the above-described embodiment, the image forming unit 6 is provided as a sheet processing unit for processing the sheet downstream of the skew correction roller pair 50 in the sheet transport direction, but the present invention is not limited to this. .. For example, an image reading unit for reading the image of the sheet described above, a stapler (sheet binding unit) for binding the sheet in the sheet post-processing device, and a puncher (sheet perforation unit) for forming holes in the sheet may be used as the sheet processing unit. good. Further, in the above description, the image forming apparatus has been described as an example of the sheet processing apparatus. For example, the image reading apparatus may be a sheet processing apparatus, or the sheet post-processing apparatus may be a sheet processing apparatus.

1: Image forming device, 4: Sheet conveying device (sheet conveying section), 5: Skew correction section, 6: Image forming section, 41b: Transfer section (conveying roller), 65: Detection sensor, 100: Power transmission path, 101: Drive source, 102: Switching unit (electromagnetic clutch), 110: Control unit, 200: Setting means, 201: Discriminating means, 501: Skew correction roller, 501a, 501b: Roller part, 501c: Rotation axis (skew) Correction roller shaft), 502: Holding member (holding roller), 504: Bending member (holding spring), N2: Holding part

Claims (15)

The transport unit that transports the sheet and
A skew correction unit provided on the downstream side of the transport unit in the sheet transport direction to correct the skew of the sheet transported from the transport unit, and a skew correction unit.
A control unit that controls the skew correction unit is provided.
The skew correction unit
With the skew correction roller,
A holding member that comes into contact with the skew correction roller and forms a holding portion between the skew correction roller and the skew member.
A drive source for rotationally driving the skew correction roller and
The first state in which the driving force from the driving source can be transmitted to the skew correction roller by interposing on the power transmission path from the driving source to the skew correction roller, and the driving force from the driving source are described. A second state that cannot be transmitted to the skew correction roller and a switching unit that can be switched to are provided.
The control unit controls the switching unit so that the second state is reached when the tip of the sheet conveyed by the conveying unit enters the holding portion, and the tip of the sheet comes out of the holding portion. After that, the switching unit is controlled so as to change from the second state to the first state and transmit the driving force from the driving source to the skew correction roller.
A sheet transfer device characterized by this. The skew correction unit includes an urging member that applies a holding pressure between the skew correction roller and the holding member in the holding portion.
The urging member is configured such that the holding force received from the skew correction roller and the holding member when the tip of the sheet is inserted into the holding portion is weaker than the carrying force received by the sheet from the carrying portion. ing,
The sheet transport device according to claim 1, wherein the sheet transport device is characterized by this. It is equipped with a detection sensor that detects the passage of the sandwiched portion of the seat.
The control unit switches the switching unit from the second state to the first state based on the detection sensor detecting the tip of the sheet.
The sheet transport device according to claim 1 or 2, wherein the sheet transport device is characterized by the above. The control unit stops driving the skew correction roller based on the detection sensor detecting the rear end of the seat.
The sheet transport device according to claim 3, wherein the sheet transport device is characterized. The control unit controls the rotation speed of the skew correction roller based on the detection sensor detecting the tip of the sheet.
The sheet transport device according to claim 3 or 4, wherein the sheet transport device is characterized by this. The detection sensor is a sensor that detects a sheet on the downstream side of the sandwiching portion in the sheet transport direction.
The sheet transport device according to any one of claims 3 to 5, wherein the sheet transport device is characterized by this. Equipped with a setting means for the user to set the sheet type
The control unit controls the switching unit based on the type of sheet set by the setting means.
The sheet transport device according to any one of claims 1 to 6, wherein the sheet transport device is characterized by this. Equipped with a discriminating means for discriminating the characteristics of the sheet
The control unit controls the switching unit based on the characteristics of the sheet determined by the determination means.
The sheet transport device according to any one of claims 1 to 6, wherein the sheet transport device is characterized by this. The sheet transport device according to claim 8, wherein the discriminating means discriminates the characteristics of the sheet including at least one of the basis weight, the rigidity, and the surface property of the sheet. The skew correction roller
A rotation axis extending in a direction orthogonal to the sheet transport direction,
A plurality of cylindrical roller portions fixed to the rotation axis at predetermined intervals, and the like.
The sheet transport device according to any one of claims 1 to 9, wherein the sheet transport device is characterized by this. The sandwiching member is a roller arranged so as to face the skew correction roller.
The sheet transport device according to any one of claims 1 to 10, wherein the sheet transport device is characterized by this. A sheet processing unit that processes sheets and
The sheet transport device according to any one of claims 1 to 11, which transports a sheet toward the sheet processing unit, is provided.
A sheet processing device characterized by this. The sheet processing unit is any one of an image forming unit that forms an image on the sheet, an image reading unit that reads an image of the sheet, a sheet perforating unit that creates holes in the sheet, and a sheet binding unit that binds the sheet.
12. The sheet processing apparatus according to claim 12. In the sheet transport direction, a transport roller pair for transporting the sheet is not arranged between the skew correction roller and the sheet processing unit.
The sheet processing apparatus according to claim 12 or 13. The one according to any one of claims 12 to 14, wherein the control unit starts a processing operation of the sheet processing unit based on the detection of the tip of the sheet beyond the sandwiching unit. Sheet processing equipment.

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