Patent Description:
There are image forming apparatuses that have an automatic duplex printing function. In such an image forming apparatus, in order to form images on both sides of a sheet, the sheet is conveyed from a sheet storage unit to an image forming portion, an image is formed on one side of the sheet, and then the sheet is reversed and conveyed to the image forming portion again. As discussed in <CIT>, an image forming apparatus having such a function includes a plurality of conveyance roller pairs provided in a sheet conveyance path. For example, the plurality of conveyance roller pairs includes a plurality of drive rollers each configured to rotate by receiving a driving force from the image forming apparatus, and a plurality of driven rollers each configured to be rotated by being brought into contact with a corresponding one of the drive rollers. <CIT> discloses a reversal unit that inverts a sheet conveyed between reversal rollers and guide rollers so that the inverted sheet is guided along a specific conveyance path. The contact nip condition of reversal rollers is released during inversion, based on variation in conveying velocity and conveying path length.

In this case, however, an image forming apparatus including the plurality of conveyance roller pairs needs to provide space for arranging the plurality of drive rollers each configured to receive a driving force from the image forming apparatus and the plurality of driven rollers each configured to be rotated by a corresponding one of the drive rollers. In addition, there is an issue where the cost of the image forming apparatus increases.

According to a first aspect of the present invention, there is provided an image forming apparatus as specified in claims <NUM> to <NUM>.

An image forming apparatus <NUM> according to a first embodiment of the present invention will be described with reference to <FIG>. In the present embodiment, a laser beam printer that forms an image on a sheet at an image forming portion using an electrophotographic method is described as an example of the image forming apparatus <NUM>.

An overall configuration of the image forming apparatus <NUM> will be described with reference to <FIG> is a schematic cross-sectional view of the image forming apparatus <NUM>.

Sheets S stacked and stored in a sheet storage unit <NUM> are fed by a pick roller <NUM>. The sheets S are separated one by one by a feed roller <NUM> and a separation roller <NUM>, and the separated sheet S is conveyed to a first nip portion formed by a drive roller <NUM> and conveyance driven rollers <NUM>. The sheet S is then conveyed to an image forming portion that is a contact portion at which a photosensitive drum <NUM> included in a process cartridge <NUM> and a transfer roller <NUM> are in contact with each other.

In the present embodiment, the image forming portion refers to a portion at which toner serving as developer is transferred onto the sheet S.

In the present embodiment, the contact portion of the photosensitive drum <NUM> and the transfer roller <NUM> is the image forming portion. In the case of a configuration using an intermediate transfer belt, a portion at which developer is transferred from the intermediate transfer belt to the sheet S is the image forming portion.

In a case where an image is to be formed on the sheet S, first, a laser scanner unit <NUM> emits a laser beam to form an electrostatic latent image on the photosensitive drum <NUM> serving as an image bearing member. The electrostatic latent image is developed by a developing unit (not illustrated) to form a toner image on the photosensitive drum <NUM>. The toner image is then transferred onto the sheet S conveyed to the image forming portion formed by the photosensitive drum <NUM> and the transfer roller <NUM>.

The sheet S to which the toner image is transferred is conveyed to a fixing portion including a fixing film <NUM> and a pressure roller <NUM> that is brought into pressure contact with the fixing film <NUM>. At the fixing portion, the sheet S to which the toner image is transferred is heated and pressured to fix the toner image on the sheet S.

In the case of printing on one side (a first side) of the sheet S, the sheet S on which the toner image is fixed is discharged by a discharging/reversing roller <NUM> and a discharging/reversing driven roller <NUM>. In the case of printing on both sides of the sheet S, after a trailing edge of the sheet S passes through the fixing portion, the sheet S is conveyed to a duplex conveyance path by switching of a rotation direction of the discharging/reversing roller <NUM>. The sheet S conveyed through the duplex conveyance path is conveyed to the image forming portion again by the drive roller <NUM>, and a toner image is transferred onto a second side of the sheet S. The toner image is then fixed on the sheet S at the fixing portion, and the sheet S is discharged by the discharging/reversing roller <NUM>.

A configuration of the drive roller <NUM> will be described with reference to <FIG>. <FIG> is a cross-sectional view of the drive roller <NUM> and a vicinity thereof, and illustrates a sheet conveyance path P of the sheet S fed from the sheet storage unit <NUM>. <FIG> is a cross-sectional view of the drive roller <NUM> and the vicinity thereof, and illustrates the sheet conveyance path P of the sheet S in the case of image formation on both sides of the sheet S. <FIG> is a perspective view illustrating a configuration of the drive roller <NUM>. <FIG> is a perspective view illustrating the configuration of the drive roller <NUM> in a state where a drive gear <NUM> and other components of a drive unit <NUM> (see <FIG>) are attached. <FIG> is a perspective view illustrating a configuration of a duplex driven roller unit <NUM>.

As illustrated in <FIG>, the drive roller <NUM> includes a drive shaft 321a and rubber rollers 321b, and is configured to be rotated only in one direction (a counterclockwise direction in <FIG>) by a driving force from a drive source <NUM> (refer to <FIG>) included in the image forming apparatus <NUM>. The configuration for rotating the drive roller <NUM> only in one direction will be described below.

The conveyance driven rollers <NUM> each serving as a first rotation member are configured to be rotated by the drive roller <NUM>. The conveyance driven rollers <NUM> are pressed by conveyance pressing members <NUM> via a conveyance driven roller holder <NUM>, and are rotated together with the drive roller <NUM> (are driven to rotate by the drive roller <NUM>) while being in contact with the drive roller <NUM>. The conveyance driven rollers <NUM> and the drive roller <NUM> form the first nip portion for nipping and conveying the sheet S. The conveyance driven rollers <NUM> are arranged so as to move a leading edge of the sheet S in a direction approaching the image forming portion when the leading edge of the sheet S passes through the first nip portion.

In the present embodiment, each of the conveyance pressing members <NUM> is formed of a metal compression spring. An end portion of the metal compression spring has a shape in which a wire material is extended and in contact with a stay member <NUM> (refer to <FIG>) formed of a sheet metal. Thus, the conveyance pressing members <NUM> are suppressed from being electrically charged due to member-to-member friction.

<FIG> are perspective views each illustrating the configuration of the drive roller <NUM>. As illustrated in in <FIG>, the drive roller <NUM> includes the plurality of rubber rollers 321b provided around the drive shaft 321a, and the conveyance driven rollers <NUM> are respectively in contact with the corresponding rubber rollers 321b to form the first nip portion. In the present embodiment, the five conveyance driven rollers <NUM> and the five rubber rollers 321b form the first nip portion. A drive mechanism of the drive roller <NUM> will be described below.

A conveyance direction of the sheet S before image formation on the first side is indicated by an arrow in <FIG>. The uppermost sheet S of the sheets S stacked in the sheet storage unit <NUM> is conveyed to the first nip portion by the pick roller <NUM> and the feed roller <NUM>. The sheet S is conveyed from the first nip portion in a substantially vertical upward direction, and the image formation on the first side is performed at the image forming portion.

<FIG> is a perspective view illustrating a configuration of the duplex driven roller unit <NUM>. The duplex driven roller unit <NUM> is attached to a drive roller guide <NUM> (refer to <FIG>) using a stay <NUM>. Duplex driven rollers <NUM> each serving as a second rotation member are configured to be pressed by a duplex pressing member <NUM> via a driven roller shaft <NUM>.

In the present embodiment, the configuration including the two duplex driven rollers <NUM> is described, and the two duplex driven rollers <NUM> are arranged at positions facing two of the five rubber rollers 321b of the drive roller <NUM>. The duplex driven rollers <NUM> each serving as the second rotation member are in contact with the drive roller <NUM> at positions different from those of the conveyance driven rollers <NUM> each serving as the first rotation member in a rotation direction of the drive roller <NUM>.

In the present embodiment, the conveyance driven rollers <NUM> are larger in diameter than the duplex driven rollers <NUM>. There are two cases where the sheet S is conveyed to the first nip portion formed by the drive roller <NUM> and the conveyance driven rollers <NUM>. More specifically, there is a case where the sheet S is conveyed to the first nip portion from the sheet storage unit <NUM>, and there is a case where the sheet S is conveyed to the first nip portion from a second nip portion (described below). An angle at which the sheet S enters the first nip portion is different between the two cases. As each of the two types of rollers forming the first nip portion has a larger diameter, the sheet S can be conveyed more stably without being affected by the angle at which the sheet S enters the first nip portion. For this reason, in order to convey the sheet S stably, in the present embodiment, the conveyance driven rollers <NUM> are larger in diameter than the duplex driven rollers <NUM>.

As illustrated in <FIG>, the duplex driven rollers <NUM> are in contact with the drive roller <NUM>, and are configured to be rotated by the rotation of the drive roller <NUM> (are configured to be driven to rotate by the drive roller <NUM>). The duplex driven rollers <NUM> and the drive roller <NUM> form the second nip portion for nipping and conveying the sheet S. More specifically, two of the five rubber rollers 321b, which are in contact with the duplex driven rollers <NUM>, are each in contact with two rotation members (one conveyance driven roller <NUM> as the first rotation member and one duplex driven roller <NUM> as the second rotation member) and form two nip portions (the first nip portion and the second nip portion). The duplex driven rollers <NUM> are arranged so as to move the leading edge of the sheet S in a direction apart from the image forming portion when the leading edge of the sheet S passes through the second nip portion.

In the present embodiment, the drive roller <NUM>, the conveyance driven rollers <NUM>, and the duplex driven rollers <NUM> are disposed below the image forming portion in a vertical direction. When the leading edge of the sheet S passes through the second nip portion formed between the duplex driven rollers <NUM> and the drive roller <NUM>, the leading edge of the sheet S moves downward in the vertical direction. When the leading edge of the sheet S passes through the first nip portion formed between the conveyance driven rollers <NUM> and the drive roller <NUM>, the leading edge of the sheet S moves upward in the vertical direction.

The first nip portion is disposed in the sheet conveyance path P through which the sheet S passes before an image is formed on one side of the sheet S. The first nip portion is disposed between the sheet storage unit <NUM> and the image forming portion in the conveyance direction of the sheet S. The second nip portion is disposed in the sheet conveyance path P through which the sheet S passes during duplex printing for forming images on both sides of the sheet S. More specifically, the second nip portion is disposed in the sheet conveyance path P for conveying the sheet S with an image formed on one side thereof to the image forming portion again.

The drive roller <NUM> receives pressing forces from the conveyance driven rollers <NUM> and the duplex driven rollers <NUM>. However, the respective pressing forces act in directions to cancel each other, and bearings 326a and 326b (refer to <FIG>) receive small forces from the drive roller <NUM>. As a result, wear of the bearings 326a and 326b due to sliding motion with the drive roller <NUM> is reduced.

In <FIG>, the conveyance direction of the sheet S in the case of image formation on the second side is indicated by an arrow. In duplex printing, the sheet S conveyed to the duplex conveyance path by the discharging/reversing roller <NUM> after the image formation on the first side is conveyed to the second nip portion. A length of the sheet conveyance path P from the second nip portion to the first nip portion is shorter than a length of the sheet S supported in duplex printing by the image forming apparatus <NUM>. Thus, the drive roller <NUM>, the conveyance driven rollers <NUM>, the duplex driven rollers <NUM> can convey the sheet S in a state where the sheet S is present at the first nip portion and the second nip portion at the same time.

A guide member <NUM> is provided between the second nip portion and the first nip portion in the sheet conveyance path P to guide the conveyance direction of the sheet S. Because the conveyance direction of the sheet S is largely different between the first nip portion and the second nip portion, the guide member <NUM> is configured to largely curve the sheet conveyance path P of the sheet S. More specifically, the guide member <NUM> guides the sheet S so that a moving direction of the leading edge of the sheet S changes from the direction apart from (away from) the image forming portion to the direction approaching the image forming portion. In other words, the guide member <NUM> guides the sheet S from a downward direction to an upward direction with respect to the vertical direction.

An inner side conveyance guide <NUM> and the drive roller guide <NUM> form a curved guide shape of the inner side of the guide member <NUM>. In addition, an outer side guide rib 361a integrally formed with a door <NUM> (described below), and an outer side conveyance guide <NUM> provided in a main body of the image forming apparatus <NUM> form a curved guide shape of the outer side of the guide member <NUM>.

After the sheet S is conveyed from the second nip portion to the downward direction with respect to the vertical direction along the inner side conveyance guide <NUM>, the sheet S is bent by the outer side guide rib 361a and the outer side conveyance guide <NUM>, and conveyed to the first nip portion while the conveyance direction is changed to the upward direction with respect to the vertical direction.

In this case, in the sheet conveyance path P, while the sheet S is present at the second nip portion and first nip portion at the same time, the sheet S is conveyed in substantially opposite directions at the second nip portion and first nip portion. The sheet S is then conveyed to the image forming portion to form an image on the second side of the sheet S.

Curvature of the curve of the sheet conveyance path P in the guide member <NUM> is determined by the inner side guide shape and the outer side guide shape. In the case of a configuration in which no inner side guide is provided in the guide member <NUM>, the sheet conveyance path P in the guide member <NUM> is formed by an outer periphery of the drive roller <NUM> and the outer side guide shape. Accordingly, curvature of the guide member <NUM> is determined by an outer diameter of the drive roller <NUM>. To achieve stable sheet conveyance, the curvature of the curved portion of the sheet conveyance path P is to be made larger to reduce conveyance resistance of the sheet S with particularly strong stiffness. On the other hand, increasing the outer diameter of the drive roller <NUM> leads to an adverse effect such as a cost increase. The configuration according to the present embodiment achieves stable sheet conveyance by providing guide shapes on the inner side and the outer side of the guide member <NUM> while the outer diameter of the drive roller <NUM> is kept small.

A conveyance speed of the sheet S at each of the first nip portion and the second nip portion depends on a peripheral speed of the drive roller <NUM>. In a conventional configuration in which at least two drive rollers are provided, in order to eliminate manufacturing variation (dimensional tolerance) between outer diameters of the two drive rollers, accurate machining is performed and this leads to a cost increase.

It is also conceivable that wear occurs in the drive rollers due to the conveyance of the sheet S, and wear amounts of the two drive rollers differ. For this reason, there is a possibility that a difference in peripheral speed between the two drive rollers may increase through the use of the image forming apparatus. If there is a difference in peripheral speed between the two drive rollers, i.e., a difference in sheet conveyance speed between the two nip portions, there is a possibility that the sheet S may be slack or pulled and an image defect may occur due to the sheet S being rubbed strongly against the guide member.

On the other hand, in the configuration according to the present embodiment, since the two nip portions are formed using the single drive roller <NUM>, the difference in sheet conveyance speed between the two nip portions is unlikely to occur even if wear occurs in the drive roller <NUM> due to the manufacturing variation of the drive roller <NUM> or the use of the image forming apparatus <NUM>. This makes it possible to suppress the sheet S from being excessively slack or pulled, thereby preventing image defects.

Jam clearance operability of the image forming apparatus <NUM> according to the present embodiment will be described with reference to <FIG> is a cross-sectional view illustrating the drive roller <NUM> and the vicinity thereof in a state where the door <NUM> is opened.

The image forming apparatus <NUM> includes the door <NUM> and a main body frame <NUM> (refer to <FIG>) that accommodates the image forming portion, as a housing of the image forming apparatus <NUM>. The door <NUM> is provided to be openable and closable between an open state and a closed state, around a door rotation shaft 361b (refer to <FIG>) with respect to the main body frame <NUM>. When the door <NUM> is in the open state, the sheet conveyance path P is exposed, so that the user can remove the jammed sheet S.

The duplex driven roller unit <NUM> is held by the drive roller guide <NUM>, and thus the duplex driven rollers <NUM> and the drive roller <NUM> form the second nip portion even when the door <NUM> is in the open state. In the configuration according to the present embodiment, a press-contact force at the second nip portion is applied to the main body of the image forming apparatus <NUM> and is not applied to the door <NUM>. Thus, compared with a case where the press-contact forces of the duplex driven rollers <NUM> are applied to the door <NUM>, it is possible to reduce the stiffness of the door <NUM> and a holding force for holding the closed state of the door <NUM>. Thus, the shape and the holding mechanism thereof can be simplified, which contributes to cost reduction.

In the present embodiment, if a jam occurs, the user can open the door <NUM> to perform a jam clearance operation as indicated by a dotted line in <FIG>. However, in a state where a driving force is transmitted from the drive source <NUM> to the drive roller <NUM>, a large force is to be applied to pull out the sheet S nipped by the drive roller <NUM>.

To address the issue, in the configuration according to the present embodiment, when the door <NUM> is in the open state, the transmission of a driving force from the drive source <NUM> to the drive roller <NUM> is released to improve the jam clearance operability of the user. Because of the release of transmission of a driving force from the drive source <NUM> to the drive roller <NUM>, in a case where the user tries to pull out the jammed sheet S toward an upstream conveyance direction (a direction indicated by an arrow in <FIG>), the drive roller <NUM> can be easily rotated by the movement of the jammed sheet S. Thus, it is possible to perform the jam clearance operation with a small force. Also in a case where the user tries to pull out the jammed sheet S toward a downstream conveyance direction, the drive roller <NUM> can be easily rotated. Thus, it is possible to perform the jam clearance operation with a small force.

A method for transmitting a driving force to the drive roller <NUM> will be described with reference to <FIG> and <FIG>. <FIG> are perspective views each illustrating a configuration of a drive release mechanism. <FIG> are cross-sectional views each illustrating the configuration of the drive release mechanism. In the configuration according to the present embodiment, when the door <NUM> is in the closed state as illustrated in <FIG> and <FIG>, a driving force is transmitted from the drive source <NUM> to the drive roller <NUM>, and when the door <NUM> is in the open state as illustrated in <FIG> and <FIG>, a driving force is not transmitted from the drive source <NUM> to the drive roller <NUM>.

As illustrated in <FIG>, the drive source <NUM> transmits a driving force to a drive gear <NUM>, and the driving force is transmitted to the drive roller <NUM> via a drive transmission member <NUM> and a driven transmission member <NUM>. The drive gear <NUM>, the drive transmission member <NUM>, the driven transmission member <NUM>, the drive roller <NUM>, and the drive shaft 321a are provided on the same rotation shaft. The driven transmission member <NUM> and the drive roller <NUM> are rotated together with the drive shaft 321a.

The drive unit <NUM> is held to be slidable with respect to the drive shaft 321a in a rotation axis direction. The drive unit <NUM> includes the drive gear <NUM> and receives a driving force from the drive source <NUM>. The drive unit <NUM> is urged by a second urging member <NUM> in a direction approaching the drive roller <NUM> with respect to the rotation axis direction, with an urging force F2 (a second urging force) smaller than an urging force F1. In the present embodiment, a spring is used for the second urging member <NUM>.

The drive transmission member <NUM> and the driven transmission member <NUM> have a ratchet shape. Thus, the drive transmission member <NUM> transmits a driving force for rotating the sheet S in the conveyance direction to the driven transmission member <NUM>, but does not transmit a driving force for rotating the sheet S in the opposite direction.

In the state illustrated in <FIG> and <FIG> where the door <NUM> is in the closed state, the drive transmission member <NUM> of the drive unit <NUM> and the driven transmission member <NUM> of the drive shaft 321a are engaged with each other. Thus, when the drive source <NUM> transmits a driving force to the drive gear <NUM>, the drive transmission member <NUM> transmits the driving force to the driven transmission member <NUM> to rotate the drive shaft 321a. In other words, the drive unit <NUM> includes the drive transmission member <NUM> that transmits the driving force received from the drive source <NUM> to the drive shaft 321a. The drive shaft 321a includes the driven transmission member <NUM> that receives the driving force from the drive transmission member <NUM>.

On the other hand, in the state illustrated in <FIG> and <FIG> where the door <NUM> is in the open state, since the drive transmission member <NUM> and the driven transmission member <NUM> are not engaged with each other, the driving force received by the drive gear <NUM> from the drive source <NUM> is not transmitted to the driven transmission member <NUM>. Accordingly, the drive shaft 321a does not rotate, and thus the drive roller <NUM> does not rotate either.

Gear teeth formed on a downstream transmission gear <NUM> are configured to transmit the driving force to the further downstream side, and do not contribute to the driving force transmission to the drive roller <NUM>.

As described above, whether to transmit the driving force from the drive gear <NUM> to the drive roller <NUM> is determined based on whether the door <NUM> is in the open state or the closed state, i.e., whether the drive transmission member <NUM> and the driven transmission member <NUM> are engaged with each other. Next, a description will be given of how the drive transmission member <NUM> and the driven transmission member <NUM> are engaged and the engagement thereof is released in each of the open state and the closed state of the door <NUM>. <FIG> is a perspective view illustrating a drive release member <NUM>, and <FIG> is a perspective view illustrating the door <NUM>.

As illustrated in <FIG>, an opening <NUM> and a pressing surface <NUM> are formed in the drive release member <NUM>. A receiving surface <NUM> is formed on a side surface of the opening <NUM>. As illustrated in <FIG>, a pressure receiving portion 361c is formed on the door <NUM>. The transmission of the driving force to the drive roller <NUM> is released by the drive release member <NUM> and the pressure receiving portion 361c of the door <NUM>. The drive release member <NUM> releases the transmission of the driving force by releasing the engagement of the drive transmission member <NUM> and the driven transmission member <NUM>.

First, an operation performed when the door <NUM> is in the closed state will be described with reference to <FIG> and <FIG>. When the door <NUM> is in the closed state, a driving force is transmitted from the drive source <NUM> to the drive roller <NUM>. The drive release member <NUM> is held to be slidable in the rotation axis direction of the drive roller <NUM>.

An end portion of the drive release member <NUM> is urged by a first urging member <NUM> with the urging force F1 (the first urging force). The direction of the urging force F1 is a direction from the drive roller <NUM> toward the drive gear <NUM> with respect to the rotation axis direction of the drive roller <NUM>. In other words, the image forming apparatus <NUM> urges the drive release member <NUM> with the first urging force in a direction apart from the drive roller <NUM> with respect to the rotation axis direction. In the present embodiment, a spring is used for the first urging member <NUM>.

When the door <NUM> is in the closed state, the pressure receiving portion 361c provided on the door <NUM> and the receiving surface <NUM> of the drive release member <NUM> are in contact with each other. Thus, the urging force F1 applied to the drive release member <NUM> is received by the pressure receiving portion 361c to regulate the sliding movement of the drive release member <NUM>. Thus, the drive unit <NUM> receives the urging force F2 in a direction approaching the drive roller <NUM> with respect to the rotation axis direction, and the drive transmission member <NUM> and the driven transmission member <NUM> are engaged with each other.

In this way, when the door <NUM> is in the closed state, the driving force received by the drive gear <NUM> is transmitted to the drive shaft 321a and the drive roller <NUM>. In this state, there is a space between the pressing surface <NUM> and the drive unit <NUM>. On the other hand, when the door <NUM> is in the open state, the drive release member <NUM> urges the drive unit <NUM> in the direction apart from the drive roller <NUM> with respect to the rotation axis direction.

Next, driving force transmission in case where the door <NUM> is in the open state will be described with reference to <FIG> and <FIG>. When the door <NUM> is in the open state, a driving force is not transmitted from the drive source <NUM> to the drive roller <NUM>. When the door <NUM> is in the open state, the pressure receiving portion 361c is retracted from the opening <NUM> of the drive release member <NUM>.

Accordingly, the drive release member <NUM> is urged with the urging force F1 in a direction from the drive roller <NUM> toward the drive gear <NUM> with respect to the rotation axis direction. The drive release member <NUM> is also urged with the urging force F2 in a leftward direction in <FIG>. The relationship between the urging forces F1 and F2 is as follows: <MAT>.

Thus, the drive release member <NUM> slides in the direction from the drive roller <NUM> toward the drive gear <NUM> with respect to the rotation axis direction. This causes the drive unit <NUM> to slide in the direction from the drive roller <NUM> toward the drive gear <NUM> with respect to the rotation axis direction. Accordingly, the engagement of the drive transmission member <NUM> and the driven transmission member <NUM> is released, so that a driving force is not transmitted from the drive source <NUM> to the drive shaft 321a and the drive roller <NUM>. In this way, when the door <NUM> is in the open state, the driving force received by the drive gear <NUM> is not transmitted to the drive shaft 321a and the drive roller <NUM>.

A description will be given of a function of preventing erroneous detection of the open state or the closed state of the door <NUM> in the configuration according to the present embodiment, with reference to <FIG> and <FIG>. <FIG> is a perspective view of the door <NUM>. <FIG> is a perspective view of the image forming apparatus <NUM> seen from the back side thereof.

As illustrated in <FIG>, the door <NUM> is provided with a detection rib 361e. A slope portion 361d sloped with respect to the urging force F1 is formed on the pressure receiving portion 361c. As illustrated in <FIG>, the image forming apparatus <NUM> is provided with a sensor member <NUM> capable of detecting the closed state of the door <NUM>. When the door <NUM> is in the closed state, the closed state of the door <NUM> is detected by the sensor member <NUM> detecting the detection rib 361e provided on the door <NUM>.

Normally, the image forming apparatus <NUM> permits printing when the door <NUM> is in the closed state. However, if the sensor member <NUM> erroneously detects the closed state of the door <NUM> even though the door <NUM> is not actually in the closed state, the image forming apparatus <NUM> may start printing. Since the door <NUM> forms a part of the duplex conveyance path, if the image forming apparatus <NUM> starts printing when the door <NUM> is not in the closed state, jamming may occur during duplex printing because the duplex conveyance path is not formed in a normal manner. Thus, in one embodiment, the erroneous detection of the open state or the closed state of the door <NUM> can be prevented.

As an example of the erroneous detection of the state of the door <NUM>, the following state is conceivable. The door <NUM> is slightly open with respect to the closed state, and the sensor member <NUM> detects the detection rib 361e but the guide member of the door <NUM> does not function sufficiently as the guide for the sheet S.

With the configuration according to the present embodiment, such erroneous detection can be prevented. When the user performs an operation for changing the door <NUM> from the open state to the closed state (hereinafter referred to as a closing operation), the drive release member <NUM> moves in a direction against the urging force F1 with respect to the rotation axis direction while the receiving surface <NUM> is in contact with the slope portion 361d of the door <NUM>.

At this time, if the user stops the closing operation in the middle or the door <NUM> is not completely closed, the door <NUM>, which is in a state between the open state and the closed state, is pushed back in a direction toward the open state by the slope portion 361d receiving the urging force F1. Thus, the sensor member <NUM> does not detect the detection rib 361e, thereby making it possible to prevent the erroneous detection of the closed state of the door <NUM>.

As another example of the erroneous detection, a case is conceivable where the sensor member <NUM> detects the detection rib 361e but the pressure receiving portion 361c does not press the drive release member <NUM> due to the deformation (the distortion, or the bending) of the door <NUM>. In this state, even in a situation where the drive source <NUM> is to transmit a driving force to the drive roller <NUM>, the transmission of a driving force is not possible.

To prevent the situation, as illustrated in <FIG>, the pressure receiving portion 361c and the detection rib 361e of the door <NUM> are disposed on the same side with respect to a sheet conveyance region in a sheet width direction. With this configuration, the image forming apparatus <NUM> reduces the possibility of erroneously detecting the open state or the closed state of the door <NUM> due to the deformation of the door <NUM>. The pressure receiving portion 361c and the detection rib 361e of the door <NUM> are disposed outside the sheet conveyance region in the sheet width direction.

As described above, according to the present embodiment, the duplex driven rollers <NUM> and the conveyance driven rollers <NUM> are brought into contact with the drive roller <NUM> to form the two nip portions. Therefore, the number of drive rollers that receive a driving force from the drive source <NUM> can be reduced. In addition, the size reduction and cost reduction of the main body of the image forming apparatus <NUM> are achieved by the space saving.

Furthermore, since the sheet S is conveyed at the two nip portions by the same drive roller <NUM>, the difference in the conveyance speed of the sheet S between the two nip portions is unlikely to occur. This makes it possible to suppress the sheet S, which is being conveyed between the two nip portions, from being excessively slack or pulled, thereby preventing image defects.

Moreover, even in a state where the closing operation of the door <NUM> is not completely performed, the erroneous detection of the state of the door <NUM> can be prevented by the drive release mechanism for the drive roller <NUM>.

In the configuration according to the first embodiment where the duplex driven rollers <NUM> and the conveyance driven rollers <NUM> are brought into contact with the drive roller <NUM> to form the two nip portions, it is also possible to provide a mechanism for correcting an inclination of the sheet S in the conveyance direction (hereinafter referred to as a skew of the sheet S). In a second embodiment, a description will be given of a configuration in which a regulation member <NUM> is provided on a downstream side of the pick roller <NUM> and an upstream side of the image forming portion in the conveyance direction of the sheet S in order to regulate the leading edge of the sheet S to correct the skew of the sheet S, with reference to <FIG>. An overall configuration of the image forming apparatus <NUM> according to the present embodiment is similar to that according to the first embodiment, and thus the description thereof will be omitted. The image forming apparatus <NUM> according to the present embodiment will be described with reference to <FIG>.

<FIG> are cross-sectional views each illustrating the regulation member <NUM> and a vicinity thereof. A configuration for forming the first nip portion and the second nip portion is similar to that according to the first embodiment, and thus the description thereof will be omitted. The regulation member <NUM> for regulating the leading edge of the sheet S in the conveyance direction of the sheet S is provided on an upstream side of the first nip portion in the conveyance direction. The regulation member <NUM> is held to be rotatable around a shaft 331a and urged by an urging member <NUM> in a counterclockwise direction in <FIG>. A plurality of correction surfaces 331b is located on the upstream side of the first nip portion in the conveyance direction, and arranged to be bilaterally symmetrical in the width direction of the sheet S.

As illustrated in <FIG>, the uppermost sheet S of the sheets S stacked in the sheet storage unit <NUM> is conveyed to the first nip portion by the pick roller <NUM> and the feed roller <NUM>. Two different places at the leading edge of the sheet S make contact with the correction surfaces 331b of the regulation member <NUM> in the conveyance direction, and a position of the leading edge of the sheet S is regulated by the two places in the conveyance direction, so that the skew of the sheet S is corrected. Then, as illustrated in <FIG>, the regulation member <NUM> is rotated in a clockwise direction in <FIG> by being pressed by the sheet S, so that the sheet S is conveyed to the first nip portion.

Behavior of the sheet S in a period from the image formation on the first side to the image formation on the second side is similar to that according to the first embodiment.

As described above, according to the present embodiment, the regulation member <NUM> is provided on the downstream side of the pick roller <NUM> and the upstream side of the image forming portion in the conveyance direction of the sheet S in order to regulate the leading edge of the sheet S in the conveyance direction of the sheet S, in addition to the configuration according to the first embodiment. This makes it possible to correct the skew of the sheet S to be conveyed to the image forming portion and thereby accurately form an image on the sheet S.

According to the embodiments of the present invention, the size of an image forming apparatus can be reduced by bringing a plurality of driven rollers into contact with one drive roller so as to convey a sheet in different conveyance directions. Cost reduction can also be achieved.

Claim 1:
An image forming apparatus (<NUM>) comprising:
an image forming portion at which developer is transferred onto a sheet;
a drive roller (<NUM>) configured to be rotated by a drive source (<NUM>);
a first rotation member (<NUM>) disposed in contact with the drive roller and configured to be driven to rotate by the drive roller, the first rotation member and the drive roller forming a first nip portion for nipping the sheet; and
a second rotation member (<NUM>) disposed in contact with the drive roller at a position different from a position of the first rotation member in a rotation direction of the drive roller, and configured to be driven to rotate by the drive roller, the second rotation member and the drive roller forming a second nip portion for nipping the sheet,
wherein the drive roller (<NUM>), the first rotation member (<NUM>), and the second rotation member (<NUM>) are arranged so as to move a leading edge of the sheet in a direction approaching the image forming portion in a case where the leading edge passes through the first nip portion, and so as to move the leading edge in a direction apart from the image forming portion in a case where the leading edge passes through the second nip portion, and
wherein the drive roller (<NUM>), the first rotation member (<NUM>), and the second rotation member (<NUM>) are configured to convey the sheet in a state where the sheet is present at the first nip portion and the second nip portion at a same time.