Sheet skew feeding correction device and image forming apparatus

A sheet skew feeding correction device has a controller that performs a first mode in which the leading end of the sheet conveyed by the first conveying portion abuts the sheet stopping portion in the first posture, and the sheet is nipped by the second conveying portion operating to convey the sheet while the sheet moves the sheet stopping portion toward the second posture against the urging force of the urging portion and performs a second mode in which the leading end of the sheet conveyed by the first conveying portion abuts the sheet stopping portion in the first posture, the sheet moves the sheet stopping portion against the urging force of the urging portion, and the leading end of the sheet abuts the nip portion of the stopped second sheet conveying portion so that a loop shape is formed in the sheet.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet skew feeding correction device that performs a skew feeding correction of a conveyed sheet and an image forming apparatus such as a copying machine, a facsimile, and a printer including the sheet skew feeding correction device.

2. Description of the Related Art

A sheet fed from a cassette storing sheets therein may be skew-fed during a feeding/conveying operation due to various reasons in which a conveying roller is formed in a tapered shape or the alignment of the conveying roller is deviated from an image forming portion or a transfer portion.

Particularly, when the sheet is picked up from the cassette or the sheets are separated so that the sheets are not conveyed at the same time, the sheet may be easily skew-fed in that the roller has a narrow width or the roller does not sufficiently hold the sheet in the rotation state.

Thus, in order to obtain a satisfactory output image, there is a need to correct the skew feeding of the sheet before an image is transferred onto the sheet in the image forming portion. Further, it is effective when the correction position is near the image forming portion.

As a method of correcting the skew feeding of the sheet, there is known a general method of correcting the skew feeding by causing a sheet leading end to abut a registration roller nip. However, in the skew feeding correction method of causing the sheet leading end to abut the registration roller nip, a loss time for rotating and stopping the registration roller occurs. For this reason, a gap between the sheets which are conveyed continuously needs to be large. Thus, there is a problem in that the productivity (the number of image forming sheets per unit time) is not easily improved.

Here, although a method is practically used in which the sheet leading end abuts a shutter for the skew feeding correction without stopping the registration roller and the shutter is opened by an actuator, the damage of the sheet generated when the sheet abuts the shutter may be a problem depending on the type of sheet.

In order to solve the above-described problems, Japanese Patent Laid-Open No. 7-309481 discloses a sheet skew feeding correction device that performs a skew feeding correction by causing the sheet leading end to selectively abut any one of the registration roller nip and the shutter in response to the type of sheet.

Further, Japanese Patent Laid-Open No. 2011-190026 discloses a configuration in which the urging force of the shutter urged by a spring is switched two levels in accordance with the forward or backward rotation of the registration motor. According to this configuration, it is possible to minimize a difference in skew feeding correction caused by the different stiffness of the sheet as a big problem in the shutter urged by the spring without any loss time caused by the rotation and the stop of the registration roller.

However, in the related art disclosed in Japanese Patent Laid-Open No. 7-309481, when the sheet leading end abuts the registration roller nip, the sheet may be bitten into the registration roller nip, and hence the skew feeding correction may be not sufficiently performed.

Further, in the related art disclosed in Japanese Patent Laid-Open No. 2011-190026, a drive system that changes the spring pressure by the forward or backward rotation of the registration roller becomes complex, and hence an increase in size and cost of the apparatus occurs. Further, in recent days, the type of sheet demanded by the user increases. As a result, it is difficult to handle the type of sheet demanded by all users by the use of two levels of the urging force.

SUMMARY OF THE INVENTION

It is desirable to provide a sheet skew feeding correction device capable of accurately performing a skew feeding correction in response to the type of sheet without using a complex drive system and an image forming apparatus including the same.

A representative configuration according to the present invention in order to achieve the object is a sheet skew feeding correction device including: a first sheet conveying portion that conveys a sheet; a second sheet conveying portion that is disposed at the downstream of the first sheet conveying portion in a sheet conveying direction and conveys a sheet while nipping the sheet; a moving member that includes a sheet stopping portion located at a position on the upstream of a nip portion of the second sheet conveying portion in the sheet conveying direction so as to stop a leading end of the sheet and is movable between a first posture in which the sheet stopping portion stops the leading end of the sheet conveyed by the first sheet conveying portion and a second posture which allows the passage of the sheet; an urging portion that urges the moving member so that the sheet stopping portion is in the first posture; and a controller that controls the first sheet conveying portion and the second sheet conveying portion, performs a first mode in which the leading end of the sheet conveyed by the first conveying portion abuts the sheet stopping portion in the first posture, and the sheet is nipped by the second conveying portion operating to convey the sheet while the sheet moves the sheet stopping portion toward the second posture against the urging force of the urging portion and a second mode in which the leading end of the sheet conveyed by the first conveying portion abuts the sheet stopping portion in the first posture, the sheet moves the sheet stopping portion against the urging force of the urging portion, and the leading end of the sheet abuts the nip portion of the stopped second sheet conveying portion so that the sheet is formed in a loop shape.

DESCRIPTION OF THE EMBODIMENTS

Next, a sheet skew feeding correction device and an image forming apparatus using the same according to embodiments of the invention will be described with reference to the drawings.

First Embodiment

Image Forming Apparatus

FIG. 1is a schematic cross-sectional view illustrating an image forming apparatus including a sheet skew feeding correction device according to a first embodiment.

An image forming apparatus of the embodiment is a color image forming apparatus of an electrophotographic system in which four image forming portions respectively forming yellow, magenta, cyan, and black toner images are disposed in parallel. The image forming portions have the same configuration except that the color of the toner image to be formed is different.

In the image forming portions, photoconductive drums101ato101dare uniformly charged by charging rollers102ato102d, and are exposed in response to the image signals of respective colors from laser scanners103ato103dso that an electrostatic latent image is formed. The electrostatic latent image is developed by development devices104ato104dthrough yellow toner, magenta toner, cyan toner, and black toner. The toner developed on the photoconductive drums is sequentially transferred onto an endless belt-shaped intermediate transfer belt106by primary transfer rollers105ato105d, and hence a full-color toner image is formed on the intermediate transfer belt106. The toner remaining on the photoconductive drums is collected by drum cleaners107ato107d.

Meanwhile, a sheet S is fed from any one of cassette feeding portions111and112or a manual feeding portion113in synchronization with an image forming operation. The sheet S is conveyed by a conveying roller114and is further conveyed toward a registration roller (hereinafter, a “second roller”)116as a second sheet conveying portion through a front registration roller (hereinafter, a “first roller”)115as a first sheet conveying portion. The conveying speed of the sheet S at this time is a speed faster than the circumferential speed (the process speed) of the image forming portion, that is, the photoconductive drum or the intermediate transfer belt. In the embodiment, as an example, the process speed of the plain paper is set to 150 mm/s, and the sheet conveying speed thereof is set to 200 mm/s.

When the sheet S is conveyed toward the second roller116, the skew feeding is corrected by the sheet skew feeding correction device. The configuration and the operation for performing the skew feeding correction will be described below.

After the sheet S of which the skew feeding is corrected by the sheet skew feeding correction device passes by the second roller116, the leading end of the sheet S is detected by a sheet sensor117disposed at a predetermined position in front of a secondary transfer portion118. Then, a controller calculates a timing in which the conveying speed of the sheet S is decreased to 150 mm/s as the process speed by the second roller116so that the leading end of the image formed on the intermediate transfer belt matches the leading end of the sheet S at the secondary transfer portion118.

The toner image on the intermediate transfer belt106is transferred onto the sheet S by a bias voltage applied through a secondary transfer roller109, and is heated and pressed by a fixing unit110so as to be fixed onto the sheet S. Subsequently, the sheet S is discharged to the outside of the apparatus body from a discharging portion119aor119b. Further, the toner remaining on the intermediate transfer belt106while not being transferred at the secondary transfer portion118is collected by an intermediate transfer cleaner108.

Next, the configuration of the sheet skew feeding correction device that performs the skew feeding correction of the sheet will be described.FIG. 2is a perspective view illustrating the second roller116constituting the sheet skew feeding correction device according to the embodiment, andFIG. 3is a cross-sectional view taken along the line B-B ofFIG. 2.

As illustrated in the drawing, the second roller116includes a pair of sheet conveying rotating members including a registration lower roller (hereinafter, a “lower roller”)10and a registration upper roller (hereinafter, an “upper roller”)20of which portions near both ends are rotatably supported by bearings11and21. The lower roller10and the upper roller20are disposed so as to face each other, springs12are hooked to the bearings of both ends thereof, and the lower roller10and the upper roller20are pressed against each other so as to form a nip portion. The second roller116is disposed at a position located at the downstream side in the sheet conveying direction (hereinafter, the “downstream side”) of the first roller115as the first sheet conveying portion and the upstream side in the sheet conveying direction (hereinafter, the “upstream side”) of the secondary transfer portion118.

The lower roller10is formed so that a plurality of rubber rollers10bis integrated with a shaft10ain the longitudinal direction. Here, the outer diameter of the rubber roller10bof the embodiment is φ16.

In the upper roller20, a polyacetal roll20bis integrated with a metal shaft20aso as to face the rubber roller10bformed in the lower roller10. The outer diameter of the roll20bof the embodiment is also φ16.

The second roller116is provided with a shutter arm (a shutter member)30that is rotatable (movable) about the rotation center of the upper roller20. The shutter arm30is provided with a plurality of (in the embodiment, six) semicircular circular-arc regulation pieces31(31ato31f) provided in the longitudinal direction of the upper roller20(the width direction of the sheet S orthogonal to the sheet conveying direction).

The lower front ends of the regulation pieces31are provided with sheet abutting portions (sheet stopping portions)32(32ato32f) abutting the leading end of the conveyed sheet. Each regulation piece31is located between a plurality of nip portions formed by the rubber roller10band the roll20band both ends thereof in the longitudinal direction of the second roller116.

Further, bearings33aand33bare integrated with the regulation pieces31aand31fof both ends, and are rotatably supported by the metal shaft20aof the upper roller20.

In addition, the regulation piece31is disposed at the symmetrical positions about the roller longitudinal direction of the sheet passage path between the upper and lower rollers10and20. Further, the regulation piece31is disposed at a plurality of positions so as to handle the sheet S having various widths.

The regulation piece31is rotatable between a first posture of stopping the sheet leading end and a second posture of allowing the passage of the sheet while a sheet abutting portion32abuts the leading end of the conveyed sheet at a position located at the upstream side of the nip portion of the second roller116and in the vicinity of the nip portion.

FIG. 4is a side view illustrating a mechanism for driving the second roller116. A drive gear41is attached to the shaft10aof the lower roller10. A motor gear42ais attached to a motor42for rotationally driving the lower roller10. The drive gear41and the motor gear42aare connected by an idle gear43so as to be driven.

The shutter arm30is urged by an urging portion so as to be held in the first posture. Next, a structure of urging the shutter arm30will be described.

As illustrated inFIGS. 2 and 4, a spring hook portion34and a stopper portion35are provided at one end side of the shutter arm30in the longitudinal direction, and a tensile coil spring64as an urging portion is hooked between the spring hook portion34and a frame (not illustrated).

The shutter arm30is urged in a counter-clockwise rotation direction (a direction indicated by the arrow B) inFIG. 4by the spring force of the tensile coil spring64. Thus, in a state where the sheet is not conveyed by the second roller116, the stopper portion35of the shutter arm30abuts a protrusion piece36(seeFIG. 2) provided in the image forming apparatus body. Then, the sheet abutting portion32of each regulation piece31is formed so as to be slightly located at the upstream side of the nip portion of the second roller116while being perpendicular to the sheet passage path (the first posture of the shutter arm30illustrated inFIG. 3).

Next, the basic skew feeding correction for the sheet will be described.

(Skew Feeding Correction by Shutter)

FIGS. 5 and 6are diagrams in which the sheet S conveyed toward the second roller116by the first roller115is viewed from the upside of the conveying path. In addition, the rubber roller10bof the lower roller10and the roll20bof the upper roller20are omitted for the description ofFIGS. 5 and 6.

The sheet conveying speed of the first roller115and the second roller116is set so that the first roller115becomes faster by about 1%. This speed difference is set so that the sheet conveying speed of the second roller116is not slower than the sheet conveying speed of the first roller115due to the component error. Ideally, two rollers may have the same conveying speed.

As illustrated inFIG. 5, when the sheet S is conveyed in a skew feeding state in the sheet width direction (a direction orthogonal to the sheet conveying direction A) with respect to the second roller116, the right leading end of the sheet S in the width direction first abuts the sheet abutting portion32fof the right regulation piece31fofFIG. 5.

At this time, since the tensile coil spring64is hooked to the shutter arm30holding the regulation piece31f, the sheet S cannot rotate the regulation piece31and the shutter arm30against the urging force of the tensile coil spring64. Accordingly, in this state, the sheet S is formed in a loop shape while the forward movement of the sheet is disturbed at a portion abutting the regulation piece31f.

Meanwhile, at this time, since the sheet S is conveyed in the skew feeding state, the sheet S does not abut the sheet abutting portion32aof the left regulation piece31aofFIG. 5.

Accordingly, one side (the left side ofFIG. 5) not abutting the regulation piece31ain the sheet S is continuously conveyed by the first roller115. As a result, as illustrated inFIG. 6, the sheet S also abuts the sheet abutting portion32aof the left regulation piece31anot abutting the sheet S so far.

In this state, both sheet abutting portions32aand32fof the regulation pieces31aand31fprovided near both ends of the sheet S abut the sheet S. Then, since the pressing force of the sheet S becomes superior to the urging force of the tensile coil spring64, all regulation pieces31are pressed. In this state, the regulation piece31and the shutter arm30first rotate about the shaft20aof the upper roller20as the rotation center of the shutter arm (the second posture of the shutter member).

In this state, since both ends of the leading end of the sheet S in the sheet width direction abut the sheet abutting portions32of the regulation pieces31, both ends are located at the same position in the sheet conveying direction, that is, the skew feeding is corrected. When the regulation piece31and the shutter arm30rotate, any barrier for the sheet S disappears. Thus, the sheet is conveyed again so as to enter the nip portion of the second roller116while the skew feeding is corrected.

The sheet S entering the nip portion of the second roller116is conveyed toward the secondary transfer portion118while the skew feeding correction state is maintained. In addition, there is a need to convey the sheet subjected to the skew feeding correction by the second roller116in this state. For this configuration, it is desirable to dispose the sheet abutting portion32so that the sheet abutting portion32abutting the sheet leading end is located near the nip portion of the second roller116when the shutter member is located at the first posture.

(Skew Feeding Correction by Nip Portion of Second Roller)

FIGS. 7 to 9are diagrams in which the sheet S conveyed to the second roller116by the first roller115is viewed from the upside of the conveying path.

As illustrated inFIG. 7, when the sheet S is conveyed to the stopped second roller116in the skew feeding state in the sheet width direction (a direction orthogonal to the sheet conveying direction A), the right leading end of the sheet S in the width direction abuts the right end of the right roller nip in the width direction.

Meanwhile, at this time, since the sheet S is conveyed in the skew feeding state, the sheet S does not abut the left end of the left roller nip in the width direction ofFIG. 7.

Due to the controller50, the sheet S is continuously conveyed by the first roller115after a predetermined time elapses from the time point in which the sheet leading end of the sheet S passes by a sheet sensor120(seeFIG. 1) disposed at the upstream side of the second roller116. As a result, as illustrated inFIGS. 8 and 9, the sheet S forms a loop between the first roller115and the second roller116, and the sheet S also abuts the left end of the left roller nip not abutting the sheet S so far in the width direction.

Subsequently, the second roller116starts to rotate, and is conveyed toward the secondary transfer portion118while the skew feeding is corrected.

<Description of Print Job and Skew Feeding Correction Mode Switching Operation>

Next, a skew feeding correction mode switching operation in response to the type of sheet (hereinafter, a “sheet type”) will be described. The image forming apparatus of the embodiment switches two modes by the thickness of the sheet as the skew feeding correction method. The first mode is a mode (hereinafter, a “thin sheet mode”) which is used when a thin sheet having a small basis weight is subjected to the skew feeding correction so that the sheet leading end is evenly adjusted by the urging force of the shutter arm30. The second mode is a mode (hereinafter, a “thick sheet mode”) which is used when a thick sheet having a large basis weight is subjected to the skew feeding correction so that the sheet leading end is evenly adjusted by the nip portion of the second roller116after the skew feeding correction is performed by the shutter arm30.

As described above, since the operation in which the sheet S rotates the regulation piece31and the shutter arm30is performed by the stiffness of the sheet S, the behavior is different in the sheets having a different basis weight.

That is, a force of rotating the regulation piece31and the shutter arm30is relatively small in a sheet (hereinafter, a “plain paper”) having a small basis weight. For that reason, when the urging force of the shutter arm30is too strong, the sheet is buckled or folded. Here, it is desirable that the urging force of the shutter arm30be about 2 to 3 N in the case of the plain paper.

Meanwhile, a force of rotating the regulation piece31and the shutter arm30is relatively large in a sheet (hereinafter, a “thick sheet”) having a large basis weight. For that reason, when the urging force of the shutter arm30is too weak, the regulation piece31and the shutter arm30rotate before the entire leading end of the sheet S conveyed in the skew feeding state abuts the regulation piece31, and hence the skew feeding correction cannot be sufficiently performed.

FIG. 10is a control configuration block diagram of the image forming apparatus according to the embodiment, andFIG. 11is a flowchart illustrating a schematic print job. The operation of the image forming apparatus will be described with reference toFIGS. 10 and 11.

As illustrated inFIG. 10, the controller of the embodiment inputs the thickness of the sheet recognized by the selection of the sheet cassette from a sheet thickness recognition portion56based on the instruction from an operation portion51or a PC52. Further, the controller50inputs detection signals from various sensors such as the sheet sensor120disposed at the upstream side of the second roller116. Then, the controller50drives a feeding motor54driving the conveying roller114, a registration motor42driving the second roller116, and motors53driving the image forming portions such as the photoconductive drum101in response to the above-described signals. Further, the controller controls the driving of the fixing unit110or the discharging portion119(119a,119b).

In the image forming apparatus of the embodiment controlled by the controller, as described above, the process speed is 150 mm/s when the sheet is the plain paper, and the sheet conveying speed to be decreased to the process speed to the front position of the secondary transfer portion118is 200 mm/s. Further, the process speed of the thick sheet and the sheet conveying speed to be decreased to the process speed at the front position of the secondary transfer portion118are respectively 75 mm/s and 100 mm/s as ½ of the plain paper.

In the image forming apparatus, the sheet type set in advance is registered by the operation portion51or the like from a user.

For example, a plain paper having a basis weight of 80 g/m2is set in the cassette feeding portions111and112ofFIG. 1, and a thick sheet having a basis weight of 209 g/m2is set in the manual feeding portion113.

A print job is performed by the PC52directly connected to the image forming apparatus or connected thereto via a network. At this time, the sheet to be used is selected from the cassette feeding portions111and112and the manual feeding portion113(hereinafter, the “feeding portion”) along with the number of copies (S1).

The image forming apparatus determines whether the sheet type set by the selection of the feeding portion such as the cassette is the plain paper or the thick sheet based on the preliminarily registered information (S2).

When the feeding portion having the plain paper set therein is selected, the controller50rotates the registration motor42so that the second roller116rotates at a full speed (in the embodiment, a sheet conveying speed of 200 mm/s) in the sheet conveying direction (S3).

The controller50rotates the registration motor42and sets the speed of the motors53driving the image forming portions such as the photoconductive drum101, the intermediate transfer belt106, and the developing sleeve104so that the circumferential speed becomes a predetermined process speed (S4). That is, in the embodiment, the image forming portions such as the photoconductive drum101, the intermediate transfer belt106, and the developing sleeve104are driven at the circumferential speed of 150 mm/s (S4).

After the speed of the registration motor42and the motor53driving the image forming portion is set, the image forming operation is started (S5).

Further, the feeding motor54starts to be driven at a predetermined timing so that the leading end position of the sheet as the transfer target matches the toner image on the intermediate transfer belt106by the secondary transfer portion118, and the sheet starts to be fed from the selected feeding portions111,112, and113(S6). After the sheet is fed, the sheet is conveyed at the conveying speed (200 mm/s in the case of the plain paper) faster than the speed of the image forming portion.

When the sheet reaches the regulation piece31of the shutter arm30in the first posture, the skew feeding caused by the above-described operation during the conveying operation is corrected (S7). Subsequently, the shutter member rotates to the second posture so that the sheet passing by the shutter is conveyed to the second roller116(S8), and the leading end is detected by the sheet sensor117in front of the secondary transfer portion (S9). Then, the controller50calculates a timing in which the sheet conveying speed is decreased to the process speed so that the sheet leading end matches the leading end of the toner image on the intermediate transfer belt at the secondary transfer portion (S10), and decreases the registration motor42at the timing (S11). That is, when the sheet reaches the sheet sensor117slow, the speed-down timing is delayed. On the contrary, when the sheet reaches the sheet sensor117fast, the speed-down timing is advanced so that the leading end of the toner image on the intermediate transfer belt matches the sheet in the secondary transfer portion118.

Subsequently, the toner image on the intermediate transfer belt106is transferred onto the sheet by the secondary transfer portion118(S21), the toner image is fixed onto the sheet by the heat and the pressure in the fixing unit110(S22), and the sheet is discharged from the discharging portion119selected by a discharging portion switching portion55(S23).

When the feeding portion having a thick sheet set therein is selected, the controller50excites the registration motor42so that the second roller116is maintained in a stop state.

The controller50sets the speed of the motors53driving the image forming portions such as the photoconductive drum101, the intermediate transfer belt106, and the developing sleeve104so that the circumferential speed thereof becomes a predetermined process speed (S12). In the embodiment, the image forming portions such as the photoconductive drum101, the intermediate transfer belt106, and the developing sleeve104are driven at the circumferential speed of 75 mm/s (S12). After the speed of the registration motor42and the motor53driving the image forming portion is set, the image forming operation is started (S13).

Further, the feeding motor54starts to be driven at a predetermined timing so that the leading end position of the sheet matches the toner image on the intermediate transfer belt106by the secondary transfer portion118, and the sheet starts to be fed from the selected feeding portions111,112, and113(S14). After the sheet is fed, the sheet is conveyed at the conveying speed (100 mm/s in the case of the thick sheet) faster than the speed of the image forming portion.

After the sheet passes by the sheet sensor120disposed at the upstream side of the second roller116(S15), the skew feeding caused by the above-described operation in the conveying state is corrected when the sheet reaches the regulation piece31of the shutter arm30(S16).

However, a force of rotating the shutter arm30is relatively large in the thick sheet S having a large basis weight. For that reason, as illustrated inFIGS. 7 and 8, the shutter arm30rotates while the skew feeding correction is not sufficient, and the sheet is conveyed toward the nip portion of the second roller116. Then, when the sheet reaches the nip portion of the second roller116, the skew feeding correction is performed by the above-described operation (S17).

Next, the controller50stops the feeding motor54so as to stop the first roller115while the skew feeding correction is performed (S18). Then, the controller50calculates a timing in which the second roller116starts to rotate so that the sheet leading end matches the leading end of the toner image on the intermediate transfer belt106by the secondary transfer portion118(S19). Then, the second roller116and the first roller115are rotationally driven at the calculated timing. Thus, the sheet is conveyed to the secondary transfer portion118while the skew feeding correction is performed (S20).

Subsequently, the toner image on the intermediate transfer belt106is transferred onto the sheet by the secondary transfer portion118(S21), the toner image is fixed onto the sheet by the heat and the pressure in the fixing unit110(S22), and the sheet is discharged from the discharging portion119selected by the discharging portion switching portion55(S23).

As described above, in the embodiment, the skew feeding correction modes include the thin sheet mode of evenly adjusting the sheet leading end by the urging force of the shutter arm30and the thick sheet mode of evenly adjusting the sheet leading end by the nip portion of the second roller116after the skew feeding correction is performed by the shutter arm30. Since two kinds of skew feeding correction modes are selected in response to the type of sheet, the skew feeding correction can be accurately performed in response to the type of sheet.

Particularly, in the high-stiff sheet such as the thick sheet, the sheet abuts the regulation piece31of the shutter arm30urged by the tensile coil spring64and abuts the nip portion of the stopped second roller116so as to perform the skew feeding correction. Thus, since it is possible to prevent the sheet from being bitten into the nip portion of the second roller116, it is possible to obtain high skew feeding correction ability compared with the case where the skew feeding correction is performed only when the sheet abuts the nip portion of the stopped second roller116.

Further, since the sheet skew correction is not performed only by the urging force of the shutter arm30, it is possible to handle the type of sheet having a wide range of thickness (basis weight). Accordingly, the user can obtain the sheet of which the skew feeding correction is sufficiently performed regardless of the type of sheet. Further, in the embodiment, since there is no need to provide a drive system component used when the urging force of the shutter arm30is switched by the normal or reverse rotation of the registration motor42, the image forming apparatus can be decreased in cost and size.

Further, in the embodiment, as illustrated inFIGS. 5 to 9, a case has been described in which the sheet S is skew-fed in the left direction of the sheet width direction. However, it is obvious that the skew feeding correction can be performed in this way even when the sheet S is skew-fed in the direction (the right direction) opposite to the embodiment.

Further, in the embodiment, a case has been described in which the skew feeding correction is performed while being switched between the first mode and the second mode in response to the thickness of the sheet. However, the skew feeding correction mode may be switched based on the basis weight information of the sheet.

Further, in the embodiment, a case has been described in which the process speed of the plain paper or the thick sheet and the urging force of the shutter arm30have detailed numerical values, but it is obvious that the invention is not limited to these numerical values.

Further, the image forming apparatus of the electrophotographic system has been exemplarily described. However, it is obvious that the skew feeding correction can be also performed on, for example, an inkjet type image forming apparatus or an image reading device such as an image scanner.

Second Embodiment

A sheet conveying apparatus and an image forming apparatus including the same according to a second embodiment of the invention will be described with reference toFIGS. 12 and 13. In addition, the embodiment has the same basic configuration as the first embodiment, but is different from the first embodiment in that the sheet thickness can be detected by the sheet thickness detection portion and the skew feeding correction control is performed in response to the detection result. Here, only the difference from the first embodiment will be described, and the same reference numeral will be given to the component having the same function as the first embodiment.

FIG. 12is a configuration diagram in which the second roller as the registration roller of the second embodiment is viewed from the downstream side.

A plurality of shutter members223is fixed at the same phase (the same positional relation in the rotation direction) with respect to a shutter shaft222extending in parallel to the drive shaft10aof the lower roller10. The shutter shaft222as the rotation shaft of the shutter member223is rotatably supported by a frame (not illustrated). Each of the rolls20bof the plurality of upper rollers20is provided with a communication hole used for the communication therein in the axial direction, and the shutter shaft222is inserted into the communication hole of the roll20bof the upper roller20. Accordingly, the rotation center of the roll20bof the upper roller20substantially matches the rotation center of the shutter shaft222. A shutter cam224to be described later is fixed to the shutter shaft222at the end of the shutter shaft222in the axial direction. The plurality of shutter members223and the shutter cam224fixed to the shutter shaft222rotate along with the shutter shaft222.

Each of the rolls20bof the plurality of upper rollers20is movably supported by a frame (not illustrated), and is provided so as to be urged toward the lower roller10by a conveying roll spring (not illustrated) fixed to the frame (not illustrated) in a press-contact state. In a state where the roll20bof the upper roller20is urged toward the lower roller10, a gap is ensured between the outer peripheral surface of the shutter shaft222and the inner peripheral surface of the communication hole of the roll20b. For this reason, the spring force of the conveying roll spring (not illustrated) is not transmitted to the shutter shaft222. Further, the spring force of the conveying roll spring (not illustrated) does not disturb the rotation of the plurality of shutter members223and the shutter cam224fixed to the shutter shaft222.

The shutter member223is provided with four abutting surfaces223a,223b,223c, and223dprovided at the same interval in the rotation circumferential direction so as to serve as the sheet stopping portions stopping the sheet S while abutting the leading end of the sheet S immediately before the sheet S advances to the nip portion of the second roller116. The abutting surfaces223a,223b,223c, and223dare disposed at the upstream of the nip portion of the second roller116before the sheet leading end contacts each abutting surface of the shutter member223, and stop the leading end of the conveyed sheet.

Next, the shutter cam224will be described. The shutter cam224is used to position the shutter member223in the rotation direction and to set the positions of the abutting surfaces223a,223b,223c, and223dof the shutter member223so that the sheet leading end can be stopped. As illustrated inFIG. 13, the shutter cam224has a substantially square shape in the side view, and the corner thereof is formed in a circular-arc shape. Then, concave portions224a,224b,224c, and224dare formed on the respective sides of the shutter cam224.

The shutter cam224is pressed by the pressing member225, and the pressing member225is journaled to the frame (not illustrated) so as to be rotatable about the rotation shaft portion. Then, the pressing member225is urged toward the shutter cam224by a shutter spring227of which one end (not illustrated) is fixed to the frame and the other end is attached to the pressing member225.

As illustrated inFIG. 13, the front end of the pressing member225is provided with a cam follower226rotatably journaled to the pressing member225. The cam follower226is provided so as to contact the shutter cam224at all times.

With the above-described configuration, when the cam follower226urges the shutter cam224by the spring force of the shutter spring227, the shutter member223is held at a standby position (in a standby state) in the rotation direction. When the abutting surface223aof the shutter member223is located near the nip portion, the cam follower226faces the concave portion224aof the shutter cam224. That is, the cam follower226urged by the spring force of the shutter spring227presses the concave portion224aof the shutter cam224. For this reason, the shutter member223is held at the standby position by the spring force of the shutter spring227. That is, a positioning mechanism that positions the shutter member223to a normal position is formed by the cam follower226urged by the shutter spring227or the concave portions224a,224b,224c, and224dof the shutter cam224.

FIG. 13illustrates a state where the shutter member223is located at the standby position as the sheet leading end stopping posture. When the shutter member223is located at the standby position, at least one of the abutting surfaces223a,223b,223c, and223dof the shutter member223is located at the upstream position near the nip portion of the second roller116.

Further, in the embodiment, each of the shutter shaft222, the shutter member223, and the shutter cam224is formed as a separate member, and the plurality of shutter members223and the shutter cam224are fixed to the shutter shaft222. However, the plurality of shutter members223, the shutter cam224, and the shutter shaft222may be formed as a single molded product by resin.

Next, the basic skew feeding correction for the sheet will be described.

(Skew Feeding Correction by Shutter)

Similarly to the first embodiment, the sheet conveyed in the skew feeding state abuts any one of the abutting surfaces223ato223dof the shutter member223, and hence the sheet is formed in a loop shape while the forward movement of the sheet is disturbed.

For example, as illustrated inFIG. 13, the abutting surface223aof the shutter member223is positioned at the upstream standby position of the nip portion (the first posture). In this case, when both ends of the sheet S abut the abutting surface223aand the pressing force of the sheet S becomes superior to the urging force of the cam follower226pressing the concave portion224aof the shutter cam224by the shutter spring227, the shutter cam224rotates (the second posture).

In the case of the plain paper, when the shutter cam224rotates in the second posture, the skew feeding of the sheet is corrected, and the sheet is conveyed by the rotating second roller116. When the sheet S completely passes by the second roller116, the shutter member223rotates so as to face the next concave portion224bof the shutter cam224by the force of the shutter spring227, and hence the abutting surface223bis positioned at the upstream standby position of the nip portion (the first posture).

Meanwhile, in the case of the thick sheet, the skew feeding is corrected while the sheet abuts the shutter member223, and abuts the nip portion of the stopped second roller116similarly to the first embodiment. In this way, the skew feeding of the sheet is corrected.

<Description of Print Job and Skew Feeding Correction Mode Switching Operation>

Next, a skew feeding correction mode switching operation in response to the type of sheet will be described. In the embodiment, the skew feeding correction mode is switched in response to the sheet thickness detected by a sheet thickness sensor121provided at the upstream side of the second roller116(seeFIG. 1) so as to detect the thickness of the sheet other than the configuration in which the sheet thickness is set from the instruction of the operation portion similarly to the first embodiment. In addition, in the embodiment, the sheet thickness sensor121is disposed at the downstream side of the merging portion of the sheets conveyed from the feeding portions111,112, and113.

FIGS. 14A and 14Bare flowcharts illustrating a schematic print job of the image forming apparatus according to the embodiment. Here, only the difference from the flowchart ofFIG. 11is illustrated.FIG. 15is a block diagram in which the detection signal of the sheet thickness sensor121is also input to the sheet thickness recognition portion56ofFIG. 10illustrating the control block diagram of the first embodiment.

Referring toFIG. 14A, an operation will be described below when the plain paper is set from the operation portion and the sheet thickness detected by the sheet thickness sensor (the sheet thickness detection portion) indicates the plain paper or the thick sheet.

(Sheet Conveying Operation in case of Plain Paper)

When the sheet S is fed from the feeding portion having a plain paper set therein, the sheet S reaches the sheet thickness sensor121after step S6ofFIG. 11(S24). When it is determined that the sheet S is the plain paper by the detection of the sensor, the routine moves to step S7ofFIG. 11similarly to the first embodiment.

Meanwhile, when the sheet S is fed from the feeding portions111,112, and113having a plain paper set therein, the routine proceeds to step S6ofFIG. 11. When it is determined that the sheet is the thick sheet by the sheet thickness sensor121, the speed of the motor53driving the image forming portion is switched to a half speed (S26). Then, the registration motor42is stopped (S27), and the routine moves to step S15ofFIG. 11in order to perform the sheet skew feeding correction in the thick sheet mode.

(Sheet Conveying Operation in case of Thick Sheet)

Next, referring toFIG. 14B, an operation will be described below when the thick sheet is set from the operation portion and the sheet thickness detected by the sheet thickness detection sensor indicates the plain paper or the thick sheet.

When the sheet S is fed from the feeding portions111,112, and113having a thick sheet set therein, the routine proceeds to step S14ofFIG. 11. Here, when it is determined that the sheet is the thick sheet by the sheet thickness sensor121, the routine moves to step S15ofFIG. 11similarly to the first embodiment.

Meanwhile, when the sheet S is fed from the feeding portions111,112, and113having a thick sheet set therein, the routine proceeds to step S14ofFIG. 11. Here, when it is determined that the sheet is the plain paper by the sheet thickness sensor121, the speed of the motor53driving the image forming portion is switched to a full speed (S30). Further, the registration motor42is rotated at a full speed (S31). Then, in order to perform the sheet skew feeding correction in the thin sheet mode, the routine moves to step S7ofFIG. 11.

As described above, in the embodiment, it is possible to switch two kinds of skew feeding correction modes, that is, the thin sheet mode of performing the skew feeding correction by the shutter member223and the thick sheet mode of performing the skew feeding correction at the nip portion of the second roller116after the correction of the shutter member223. Thus, it is possible to accurately perform the skew feeding correction in response to the type of sheet. Particularly, when the high-stiff sheet such as the thick sheet abuts the shutter member223urged by the shutter spring227and abuts the nip portion of the stopped second roller116, it is possible to prevent a problem in which the sheet is bitten into the nip portion of the second roller116. For this reason, it is possible to obtain high skew feeding correction ability compared with the case where the skew feeding correction is performed only by the nip portion of the stopped second roller116.

Further, since the sheet skew correction is not performed only by the urging force of the shutter member223, it is possible to handle the type of sheet having a wide range of thickness (basis weight). Accordingly, the user can obtain the sheet of which the skew feeding correction is sufficiently performed regardless of the type of sheet. Further, since there is no need to provide a drive system component used when the urging force of the shutter member223is switched by the normal or reverse rotation of the registration motor42, the image forming apparatus can be decreased in cost and size.

Further, it is possible to obtain the sheet in which the skew feeding correction is sufficiently performed even by the user's mistake in which the sheet type different from the sheet type set by the feeding portions111,112, and113of the apparatus is input compared with the first embodiment.

Third Embodiment

Next, a sheet conveying apparatus and an image forming apparatus including the same according to a third embodiment of the invention will be described with reference toFIG. 16. The embodiment has the same basic configuration as the second embodiment, but the control configuration is different when the plain paper is conveyed while the thick sheet is set. Here, only the difference from the second embodiment will be described, and the same reference numeral will be given to the component having the same function as the second embodiment.

FIG. 16is a flowchart illustrating a case where the plain paper is conveyed from the feeding portion when the thick sheet is set in the print job of the image forming apparatus according to the embodiment. Here, only the difference from the flowchart ofFIG. 11is illustrated. In addition, the same operation as the second embodiment is performed when the plain paper is conveyed while the plain paper is set, the thick sheet is conveyed while the plain paper is set, and the thick sheet is conveyed while the thick sheet is set.

When the sheet S is fed from the feeding portions111,112, and113having a thick sheet set therein, the routine proceeds to step S14ofFIG. 11. Here, when it is determined that the sheet is the plain paper by the sheet thickness sensor121(S29), the registration motor42is rotated at a half speed (S32). Subsequently, the routine moves to step S7ofFIG. 11.

When the thick sheet is set and conveyed, the motor53driving the image forming portion rotates at a half speed in step S12ofFIG. 11. For that reason, even when the plain paper is detected, the second roller is rotated at a half speed so that the sheet conveying speed matches the image forming speed. Thus, the sheet can be directly conveyed to the second roller116so as to form an image thereon after the skew feeding correction is performed by the shutter member.

Even when the skew feeding correction control is performed as in the embodiment, the same operation and effect as the second embodiment can be obtained.

Fourth Embodiment

Next, a sheet conveying apparatus and an image forming apparatus including the same according to a fourth embodiment of the invention will be described with reference toFIG. 17. Similarly to the third embodiment, the embodiment has the same basic configuration as the second embodiment, but the control configuration is difference when the plain paper is conveyed while the thick sheet is set. Here, only the difference from the second embodiment will be described, and the same reference numeral will be given to the component having the same function as the second embodiment.

FIG. 17is a flowchart illustrating a case where the plain paper is conveyed from the feeding portion when the thick sheet is set in the print job of the image forming apparatus according to the embodiment. Here, only the difference from the flowchart ofFIG. 11is illustrated. In addition, the same operation as the second embodiment is performed when the plain paper is conveyed while the plain paper is set, the thick sheet is conveyed while the plain paper is set, and the thick sheet is conveyed while the thick sheet is set.

When the sheet S is fed from the feeding portions111,112, and113having a thick sheet set therein, the routine proceeds to step S14ofFIG. 11. Here, when it is determined that the sheet is the plain paper by the sheet thickness sensor121(S29), the routine moves to step S15ofFIG. 11.

As described above, in the embodiment, the routine proceeds to step S15similarly to the case where the thick sheet is conveyed even when the plain paper is conveyed while the thick sheet is set. In addition, when the thick sheet is conveyed while the plain paper is set, the routine proceeds to step26after step S25ofFIG. 14A, and the skew feeding correction is performed in the thick sheet mode.

In the embodiment, when the thick sheet is conveyed while the plain paper is set, the skew feeding correction in the thick sheet mode is selected. However, even when the plain paper is conveyed while the thick sheet is set, the skew feeding correction is performed in the thick sheet mode. This is because the skew feeding correction needs to be accurately performed in the thick sheet mode in the case of the thick sheet. However, in the case of the plain paper, the skew feeding correction can be accurately performed even in the thick sheet mode. Above all, in this case, the motor53driving the image forming portion rotates at a half speed even in the plain paper, and hence the print speed becomes slower than the case where the skew feeding correction is performed in the thin sheet mode.

Even when the skew feeding correction control is performed as in the embodiment, it is possible to obtain the sheet in which the skew feeding correction is sufficiently performed even when there is the user's mistake in which the sheet type is erroneously set. Thus, the same operation and effect as the second embodiment can be obtained.

Fifth Embodiment

Next, a sheet conveying apparatus and an image forming apparatus including the same according to a fifth embodiment of the invention will be described with reference toFIG. 18. The embodiment has the same basic configuration as the first embodiment, but is different from the first embodiment in that the second roller is driven to rotate reversely after the skew feeding correction in the thick sheet mode.

FIG. 18is a flowchart illustrating a case where a plain paper is conveyed from the feeding portion having a thick sheet set therein in the print job of the image forming apparatus according to the embodiment. Here, only the difference from the flowchart ofFIG. 11is illustrated.

In the embodiment, when the feeding portion having a thick sheet set therein is selected, the routine is the same as the first embodiment until the skew feeding correction of the sheet is performed by the urging force of the shutter arm30and the skew feeding correction is performed by the abutting the nip portion of the second roller (step S18ofFIG. 11). Subsequently, in the embodiment, the second roller116is reversely driven so as to rotate by a predetermined amount in a direction opposite to the sheet conveying direction (step S33), the sheet leading end bitten into the second roller116is ejected toward the upstream side of the second roller nip, and the rotation of the second roller116is stopped (S34). Subsequently, the routine proceeds to step S19ofFIG. 11.

As described above, in the case of the thick sheet, the skew feeding correction is first performed by the shutter member and the skew feeding correction is performed by the abutting of the nip portion of the second roller116. Thus, it is possible to prevent a problem in which the sheet leading end is bitten into the nip portion of the second roller116. Then, when the second roller116is driven to rotate reversely, the sheet bitten into the nip portion of the second roller116is ejected to the upstream side of the nip portion of the second roller116. Thus, it is possible to reliably prevent a problem in which the sheet intrudes into the nip portion of the stopped second roller116.

In addition, the embodiment illustrates an example in which the configuration of the first embodiment is used as the basic configuration, but it is obvious that the second to fourth embodiments also can be used.

Sixth Embodiment

Next, a sheet conveying apparatus and an image forming apparatus including the same according to a sixth embodiment of the invention will be described with reference toFIGS. 19 to 24. In addition, since the basic configuration and the entire configuration of the image forming apparatus of the embodiment are similar to the first embodiment, only the difference from the first embodiment will be described, and the same reference numeral will be given to the component having the same function as the first embodiment.

In all the above-described embodiments, in the thick sheet mode for the skew feeding correction, the skew feeding correction is performed on the sheet by the urging force of the shutter member and the sheet is caused to abut the nip portion of the second roller so as to perform the skew feeding correction. On the contrary, in the embodiment, in the thick sheet mode for the skew feeding correction, the skew feeding correction is performed only by the shutter member without using the configuration in which the sheet abuts the nip portion of the second roller116. For that reason, the shutter member of the embodiment is provided so as to lock the rotation thereof.

Next, the configuration of a shutter regulation portion (a fixing portion) that switches the shutter member of the embodiment to a state where the sheet stopping portion is rotatable between the first posture and the second posture and a state where the sheet stopping portion is fixed to the first posture will be described.

FIG. 19is a perspective view illustrating the configuration of the shutter member attached to the roller shaft of the second roller,FIG. 20is an explanatory diagram illustrating a state where the sheet abutting portion32is rotatable, andFIG. 21is an explanatory diagram illustrating a state where the rotation of the sheet abutting portion32is locked.

As illustrated in the drawing, a shutter regulation member71is held by the frame (not illustrated) so as to be rotatable about the rotation shaft72as the rotation center. One end of the shutter regulation member71is provided with a connection portion73connected to a plunger81of a shutter solenoid80, and the other end thereof is provided with a shutter locking portion74which engages with an engagement portion39of the shutter arm30so as to fix the shutter arm30in the first posture. As illustrated inFIG. 23, the shutter solenoid80is controlled by the controller50so as to be turned on or off, and serves as an operating portion that locks the shutter locking portion74to the shutter arm30or releases the locking operation.

An urging spring76is connected between a frame (not illustrated) and a spring hook portion75of the shutter regulation member71. In a state where a current is not supplied to the shutter solenoid80, the shutter regulation member71is urged in the direction of the arrow C ofFIG. 20by the urging spring76and is held in the posture ofFIG. 20by a stopper (not illustrated). In this state, the engagement between the shutter locking portion74of the shutter regulation member71and the engagement portion39of the shutter arm30is released, and hence the regulation piece31is rotatable between the first posture and the second posture of allowing the passage of the sheet.

When a current is supplied to the shutter solenoid80so that the plunger81of the shutter solenoid80is pulled in the direction of the arrow D ofFIG. 21, the shutter regulation member71rotates about the rotation shaft72in the direction of the arrow E, and is held in the posture ofFIG. 21by the stopper (not illustrated). In this state, the shutter locking portion74of the shutter regulation member71engages with the engagement portion39of the shutter arm30, and the regulation piece31abuts the leading end of the conveyed sheet so as to be fixed (locked) to the first posture of stopping the sheet leading end.

Next, the control operation of performing the sheet skew feeding correction by the shutter member with the above-described configuration will be described with reference to the flowchart ofFIG. 22.

When the feeding portion having a plain paper set therein is selected, the shutter arm30is rotatable without the locking operation of the shutter regulation member71. When the sheet is conveyed in this state, the skew feeding of the sheet is corrected by the urging force of the shutter arm30similarly to the first embodiment, and the sheet is conveyed to the image forming portion by the second roller116(S1to S23).

Meanwhile, when the feeding portion having a thick sheet set therein is selected and a current is supplied to the shutter solenoid80by the controller50, as described above the regulation piece31of the shutter arm30is fixed to the first posture of stopping the sheet leading end by the shutter regulation member71(S24). In this state, the registration motor42is rotated so that the second roller116rotates in the sheet conveying direction at a half speed (a sheet conveying speed of 100 mm/s) (S25).

Further, the controller50rotates the registration motor42and sets the speed of the motors53driving the image forming portions such as the photosensitive drum, the intermediate transfer belt, and the developing sleeve so that the circumferential speed becomes a predetermined process speed (S26). That is, as described in the first embodiment, the image forming portions such as the photosensitive drum, the intermediate transfer belt, and the developing sleeve are driven at the circumferential speed of 75 mm/s (S26).

After the speed of the registration motor42and the motor driving the image forming portion is set, the image forming operation is started (S27).

Further, the feeding motor54starts to be driven at a predetermined timing so that the leading end position of the sheet as the transfer target matches the toner image on the intermediate transfer belt at the secondary transfer portion, and the sheet starts to be fed from the selected feeding portion (S28).

After the sheet is fed, the sheet is conveyed at a conveying speed (100 mm/s in the case of the plain paper) faster than the speed of the image forming portion.

When the sheet reaches the regulation piece31after the sheet passes by the sheet sensor120in front of the second roller (S29), the sheet leading end abuts the regulation piece31of which the rotation is locked, and hence the skew feeding caused by the above-described operation during the conveying operation is reliably corrected (S30). Then, when the skew feeding correction ends, the shutter member is rotatable while the supply of a current to the shutter solenoid80is prohibited by the controller50(S31).

In the embodiment, the first mode of evenly adjusting the sheet leading end by the urging force of the shutter member and the second mode of causing the sheet leading end to abut the fixed shutter member so as to perform the skew feeding correction are switched. Thus, even in the embodiment, it is possible to appropriately perform the skew feeding correction in response to the type of sheet similarly to the above-described embodiments.

Particularly in the case of the thick sheet, the sheet leading end abuts the shutter member so as to prevent the sheet from being bitten into the nip portion of the second roller. For this reason, high skew feeding correction ability can be obtained compared with the case where the skew feeding correction is performed only by the nip portion of the stopped second roller.

Further, since the sheet skew correction is not performed only by the urging force of the shutter, it is possible to handle the type of sheet having a wide range of thickness (basis weight). Accordingly, the user can obtain the sheet of which the skew feeding correction is sufficiently performed regardless of the type of sheet. Further, since there is no need to provide a drive system component used when the urging force of the shutter member is switched by the forward or backward rotation of the registration motor, the image forming apparatus can be decreased in cost and size.

In addition, even in the embodiment, as in the above-described embodiment, the thickness of the conveyed sheet is detected by the sheet thickness sensor121, and the skew feeding correction mode can be automatically changed in response to the detection result.FIG. 24is a flowchart for this configuration. Here, only the difference from the flowchart ofFIG. 22is illustrated.

After step S6or step S28ofFIG. 22, the sheet reaches the sheet thickness sensor121(S32). When it is determined that the sheet is the plain paper (S33), the image forming motor and the second roller116rotate at a full speed (S34), and the shutter solenoid80is turned off (S35). Then, the routine moves to step S7ofFIG. 22. Meanwhile, when it is determined that the sheet is the thick sheet (S33), the image forming motor and the second roller116are rotated at a half speed (S36), and the shutter solenoid80is turned on (S37). Then, the routine moves to step S29ofFIG. 22.

In this way, it is possible to obtain the sheet in which the skew feeding correction is sufficiently performed even by the user's mistake in which the sheet type different from the sheet type set by the feeding portions111,112, and113of the apparatus is input.

Seventh Embodiment

Next, a sheet conveying apparatus and an image forming apparatus including the same according to a seventh embodiment of the invention will be described with reference toFIGS. 25 to 28. Even in the embodiment, as in the sixth embodiment, the rotation of the shutter member is stopped in the thick sheet mode so as to perform the skew feeding correction, but the locking configuration of the shutter member is different from the sixth embodiment.

FIG. 25is a front view illustrating the second roller116constituting the sheet skew feeding correction device according to the embodiment in a state where the shutter member is locked. Further,FIG. 26illustrates a state where the locking operation for the shutter member is released.

Since a shutter regulation lever90operates the shutter regulation member71, it is possible to switch a state where the regulation piece31is fixed to the first posture of stopping the leading end of the conveyed sheet and a state where the regulation piece is rotatable between the first posture and the second posture of allowing the passage of the sheet.

The shutter regulation member71is held by a frame (not illustrated) so as to be rotatable about the rotation shaft72as the rotation center. One end of the shutter regulation member71is provided with the shutter locking portion74which engages with the engagement portion39of the shutter arm30so as to fix the shutter arm30in the first posture. Further, the other end of the shutter regulation member71is provided with the spring hook portion75, and is connected to the urging spring76by the frame (not illustrated).

The shutter regulation lever90is rotatably attached to the shaft10aof the lower roller through the torque limiter92. The shutter regulation lever90is provided with a boss91which engages with the shutter regulation member71.

When the lower roller10is stopped, the shutter regulation member71is rotated in the direction of the arrow E ofFIG. 25by the urging spring76, and is held in the state ofFIG. 25by a stopper (not illustrated). In this state, the shutter locking portion74of the shutter regulation member71engages with the engagement portion39of the shutter arm30, and the regulation piece31abuts the leading end of the conveyed sheet so as to be fixed in the first posture of locking the sheet leading end.

Meanwhile, when the lower roller10rotates in the sheet conveying direction, the shutter regulation lever90rotates in the direction of the arrow F ofFIG. 26through the torque limiter92. Thus, when the boss91presses the shutter regulation member71, the shutter regulation member71is rotated in the direction of the arrow C ofFIG. 26against the urging spring76, and is held in the state ofFIG. 26by the stopper (not illustrated). In this state, the engagement between the shutter locking portion74of the shutter regulation member71and the engagement portion39of the shutter arm30is released, and the regulation piece31is rotatable between the first posture and the second posture of allowing the passage of the sheet.

Then, when the lower roller10is stopped after the sheet is conveyed, the shutter regulation member71is rotated in the clockwise direction ofFIG. 26by the urging force of the urging spring76, and the shutter member is locked again. Accordingly, the shutter arm30can be locked in the first posture or the locking operation thereof can be released when the rotation of the lower roller10is allowed or prohibited.

<Description of Print Job and Skew Feeding Correction Mode Switching Operation>

Next, a skew feeding correction mode switching operation in response to the type of sheet will be described. The procedure of the print job of the image forming apparatus according to the embodiment is illustrated in the flowchart ofFIG. 27.

When the feeding portion having a plain paper set therein is selected, the image forming motor is driven while the second roller116is rotated so as to start an image forming operation. When the second roller116is rotated, as described above, the regulation piece31is rotatable between the first posture and the second posture of allowing the passage of the sheet. Thus, similarly to the above-described embodiments, the skew feeding of the sheet is corrected by the urging force of the shutter member, and is conveyed to the image forming portion so as to transfer the toner image thereonto (S1to S23).

When the feeding portion having a thick sheet set therein is selected, the controller50excites the registration motor42so that the second roller116is maintained in a stop state. Then, since the rotation of the shutter arm30is fixed as described above in the stop state of the second roller116, the regulation piece31abuts the leading end of the conveyed sheet so as to be fixed in the first posture of stopping the sheet leading end.

Then, the routine proceeds from step S2to step S12, and the procedure to step15is the same as the procedure of the first embodiment. That is, the motor53driving the image forming portion is rotated at a half speed so as to start the image forming operation and to start the sheet feeding operation (S12to S14). Then, when the sheet passes by the sheet sensor120disposed at the front position of the second roller (S15) and reaches the regulation piece31of the shutter arm30, the skew feeding corrected by the above-described operation during the conveying operation is corrected (S16).

Next, the controller50stops the feeding motor54so that the first roller115is stopped in the skew feeding correction state (S18). Then, the controller50calculates the rotation start timing of the second roller116so that the sheet leading end matches the leading end of the toner image on the intermediate transfer belt106by the secondary transfer portion118(S19), and drives the second roller116and the first roller115at that timing. Thus, as described above, the rotation locking state of the shutter arm30is released, and hence the regulation piece31is rotatable between the first posture and the second posture of allowing the passage of the sheet. As a result, the sheet is conveyed to the secondary transfer portion118in the skew feeding correction state (S20).

Subsequently, the toner image is transferred and fixed onto the sheet similarly to the first embodiment, and the print job ends (S21to S23).

Even in the configuration of the embodiment, the same effect as the sixth embodiment can be obtained. Further, in the embodiment, there is no need to use the solenoid as in the sixth embodiment.

In addition, even in the embodiment as in the above-described embodiment, the thickness of the conveyed sheet is detected by the sheet thickness sensor121, and the skew feeding correction mode can be automatically switched in response to the detection result.FIG. 28illustrates a flowchart for the above-described configuration, and only the difference from the flowchart ofFIG. 27is illustrated.

The sheet reaches the sheet thickness sensor121after step S6or step S14ofFIG. 27(S32). When it is determined that the sheet is the plain paper (S33), the image forming motor and the second roller116are rotated at a full speed (S34), and the routine moves to step S7ofFIG. 27. Meanwhile, when it is determined that the sheet is the thick sheet (S33), the image forming motor and the second roller116are rotated at a half speed (S36), and the second roller116is stopped (S37). Then, the routine moves to step S15ofFIG. 27.

In this way, it is possible to obtain the sheet in which the skew feeding correction is sufficiently performed even by the user's mistake in which the sheet type different from the sheet type set by the feeding portions111,112, and113of the apparatus is input.

This application claims the benefit of Japanese Patent Application No. 2014-254695, filed Dec. 17, 2014, which is hereby incorporated by reference herein in its entirety.