JPH11143155A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely actuate a detection member detecting the passing of recording paper by the recording paper supplied to an image transfer part and to make the recording paper being supplied to the transfer part keeping a correct carrying posture through a continuously rotating paper supply roller. SOLUTION: Upper and lower guide plates 51 and 52 are opposedly installed away at a prescribed gap on the carrying surface of recording paper including a driving roller for carrying 340 constituting a paper supply roller, a driven roller for carrying 34 press-contacting with the roller 340 and an actuator 35a of a paper detection sensor 35. Then, a leaf spring member 53 supported on the upper plate 51 is slightly made to press-contact with the lower plate 52. Further, the supplied recording paper is passed through the gap between the spring member 53 and the lower plate 52 to provide proper stiffness to the recording paper and to constitute the device so as to always keep the fixed carrying posture of the recording paper.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine for transferring and fixing a toner image formed on an image carrier by a toner image forming means onto recording paper to obtain an image. In particular, the present invention relates to an image forming apparatus in which a transport unit that transports a recording sheet from a cassette or a tray via a paper feed path to a transfer unit is improved.

[0002]

2. Description of the Related Art In a copying machine that is widely used, an image of a document placed on a document placing table is formed on a rotating image carrier by a scanning exposure optical system to form a latent image. The latent image is conveyed to a post-transfer section after being developed into a toner image. On the other hand, the recording paper taken out of the cassette or tray is conveyed to the registration roller or registration shutter by the conveyance roller, temporarily stopped and waited, and then the front end of the toner image and the front end of the recording paper coincided in the transfer area. The recording paper is conveyed again at a timing, and the toner image is transferred onto the recording paper in the transfer area.

In order to synchronize the conveyance of the recording paper with the scanning timing of the exposure optical system, it is necessary to provide a registration roller or a registration shutter for control.
In order to temporarily put the recording paper in a standby state, a clutch, a solenoid, and the like must be provided to control the state. For this reason, the registration roller and registration shutter have been eliminated, and a paper detection sensor that detects the passage of recording paper has been provided in the paper feed path between the paper feeding unit and the transfer unit. A device has been devised in which the exposure start of the exposure optical system is controlled by timing.

For example, Japanese Patent Application Laid-Open No. 7-77913 discloses that, in an image forming apparatus in which the arrival time from the paper feeding unit to the image forming unit varies depending on the length of the paper, the arrival of the paper between the image forming unit and the paper feeding unit. It is described that a registration sensor for detecting the sheet length and detecting the sheet length is provided, and the exposure in the image forming section is started in accordance with the timing determined by the leading edge registration timing determining means.

[0005]

When the recording paper is once stopped by using a registration roller or a registration shutter, the recording paper is stopped at the stop position, and the recording paper is conveyed, for example, when the recording paper is inclined. The posture of the recording paper in the road is corrected, and then the recording paper is conveyed toward the transfer unit in the corrected posture.

In an image forming apparatus in which a registration roller and a registration shutter are eliminated, the cost of parts can be reduced. On the other hand, a paper detection sensor for detecting arrival of a recording sheet is provided between a paper feeding section and a transfer section. The deviation of the timing of the leading edge of the recording paper alone increases, the inclination of the recording paper sent from the cassette is conveyed to the transfer unit without correction, and the toner image is transferred onto the recording paper in a tilted or offset manner. Was to be done.

A first object of the present invention is to provide an image forming apparatus in which a registration roller and a registration shutter are eliminated, in which the variation in the timing of the leading edge of a sheet is suppressed, and the recording sheet sent out from the cassette is not tilted. Is to provide.

[0008] The recording paper sent from the cassette or tray is conveyed toward the transfer section by a paper conveying roller including a driving roller and a driven roller provided opposite thereto. As the recording paper to be conveyed, a recording paper of a size selected from a plurality of sizes of recording paper is conveyed, and the recording paper is conveyed according to either a center reference or a one-side reference conveyance method. ing. The recording paper transport based on the center is based on the center of the paper width regardless of the paper size.However, the center reference matches the center of the original image scanned by the exposure optical system with the center of the recording paper. Since a high-quality image with a good balance can be obtained, recording paper conveyance based on a center standard is often adopted. However, in this case, since there is no guide in the width direction of the recording paper conveyance in the conveyance path, if the right and left balance of the contact condition of the driven roller with respect to the driving roller of the paper conveyance roller is poor, the recording paper may be inclined. It will be transported.

A second object of the present invention is to directly relate to the presence or absence of a registration roller or registration shutter,
It is an object of the present invention to provide an image forming apparatus in which a sheet conveying roller provided in a recording sheet conveying path performs sheet conveyance without bias.

[0010]

The first object of the present invention is to detect the arrival of a sheet conveyed by sheet detecting means positioned between a transfer position and a sheet feed roller, and to control the exposure optical system based on the signal. In an image forming apparatus that performs scanning in synchronization and performs transfer by adjusting the leading edge timing of a sheet and a toner image, a pair of upper and lower conveyance guides formed continuously on the upstream and downstream sides in the sheet conveyance direction of the sheet detection unit. An image forming apparatus, comprising: an elastic member for arranging a plate and pressing a sheet against one surface of the conveyance guide plate on an upstream side in a sheet conveyance direction with respect to the sheet detection unit (an invention according to claim 1). Also, the arrival of the conveyed sheet is detected by sheet detection means positioned between the transfer position and the sheet feed roller, and the signal is used to synchronously scan the exposure optical system to scan the sheet and toner. In an image forming apparatus that performs transfer at the same timing as the leading edge of an image, a sheet conveyance driven roller disposed symmetrically with respect to an image center is opposed to a sheet conveyance driving roller to convey the sheet, and the sheet corresponding to the image center is conveyed. An image forming apparatus (invention according to claim 2), wherein a substantially central portion of a conveyance driven roller is pressed toward the paper conveyance driving roller, and a paper detection device located between a transfer position and a paper feeding roller. In an image forming apparatus that detects the arrival of a sheet conveyed by a means, synchronously scans the exposure optical system based on the signal, and performs transfer by aligning the leading edge timing of the sheet and the toner image, the cassette or tray is fed. The cassette or tray can be inserted and removed in a direction perpendicular to the direction, and both sides of the cassette or tray are pressed by pressing members arranged in the apparatus main body, and the cassette or tray is pressed. Alternatively, an image forming apparatus (an invention according to claim 3), wherein an abutting portion integrally provided on a tray is configured to abut against a surface parallel to a sheet feeding direction provided on an apparatus main body, and a transfer position and an image forming apparatus. The arrival of the paper being conveyed is detected by paper detection means located between the paper feed roller and the signal, the exposure optical system is scanned in synchronization with this signal, and the transfer is performed by synchronizing the leading edge timing of the paper and the toner image. In the image forming apparatus to be performed, the cassette or the tray can be inserted and removed in a direction perpendicular to the sheet feeding direction, and a side opposite to the sheet feeding side of the cassette or the tray is pressed by a pressing member provided in the apparatus main body, An image forming apparatus (an image forming apparatus) comprising: an abutting portion provided integrally with a cassette or a tray abutting against a cassette guide rail provided on a main body of the apparatus and having a surface orthogonal to a sheet feeding direction. Invention according to claim 4).

A second object of the present invention is to rotatably support a paper transport drive roller between main body panels via a bearing,
In an image forming apparatus having a transport guide plate rotatably supporting a paper transport driven roller provided to face the paper transport drive roller and pressed against the paper transport drive roller, the paper transport drive roller is connected to the main body panel. The image forming apparatus (the invention according to claim 5) is characterized in that the position of the transport guide plate is determined based on an outer diameter portion of a bearing rotatably supported by the mounting guide plate.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the description of an embodiment of the present invention, an image forming apparatus (A) to which the inventions of claims 1 to 4 are applied will be described with reference to a cross-sectional view of FIG.

In FIG. 1, reference numeral 1 denotes a photosensitive drum serving as an image carrier, which is formed by forming a photosensitive layer such as an a-Si layer or an organic photosensitive layer (OPC) on the outer periphery of a substrate, and is indicated by an arrow in a grounded state. Rotate clockwise as shown. Reference numeral 2 denotes a scorotron charger which performs a charging action by corona discharge and gives a uniform potential to the photosensitive drum 1. 3 is a static eliminator before charging (P
In CL), exposure for removing a residual potential is performed prior to image formation.

Reference numeral 4 denotes an image exposure unit which scans and exposes the original image placed on the platen glass 41 onto the photosensitive drum 1. That is, the original image on the platen glass 41 is composed of a first mirror unit 42 including an illumination lamp 42a and a first mirror 42b constituting a scanning optical system, a second mirror 43a and a third mirror 43b positioned in a V shape. The original image is formed by moving exposure of the first mirror unit 42 from the start position at the speed V of the second mirror unit 43 and moving scanning by the second mirror unit 43 at the speed V / 2 in the same direction. The scanning is performed from the section, and a latent image of the original image is formed at the exposure position A on the photosensitive drum 1 rotating via the projection lens 44 and the reflection mirror 45.

Reference numeral 5 denotes a charge erasing LED array which performs exposure for erasing the charge outside the original image frame on the photosensitive drum 1. Reference numeral 6 denotes a developing device which develops and attaches to the latent image portion of the original image on the rotating photosensitive drum 1 to form a toner image.

Reference numeral 7 denotes a transfer electrode. The recording paper conveyed one by one from the paper feed cassette 30 by the half-moon roller 31 reaches the transfer position B through the paper transport path 33, and is transferred from the back of the recording paper by the transfer electrode 7. The toner image on the photoreceptor drum 1 is transferred onto a recording sheet by charging the toner with the opposite polarity.

Reference numeral 8 denotes a separation electrode which performs an AC corona discharge so that the recording paper adhered to the photosensitive drum 1 is separated.
Numeral 9 cleans the residual toner on the photosensitive drum 1 after the transfer by the cleaning device. Numeral 10 denotes a fixing device for fixing the recording paper having the toner image adhered between the heating roller and the pressure roller by nipping and conveying the recording paper. A paper discharge roller 37 discharges the fixed recording paper onto a paper discharge tray 38.

In the image forming apparatus according to the present embodiment, the photosensitive drum 1 is driven, the paper feed roller 32 provided along the paper transport path 33, the transport drive roller 340 is driven, and the developing device 6 is driven.
And the fixing device 10 are driven by one common DC motor, and the first mirror unit 42 and the second mirror unit 43 of the image exposure unit 4 are driven independently by a stepping motor.

In the image forming apparatus of this embodiment, a paper detection sensor 35 in which an actuator 35a and an ON / OFF detection sensor 35b are combined is provided between the paper feed roller 32 and the transfer position B in the paper transport path 33. The stepping motor of the image exposure unit 4 at the start position is driven based on the detection signal when the leading end of the recording paper conveyed without stopping is detected. An optical sensor 46 is provided at the start position of the image exposure unit 4, and the first mirror unit 42 and the second mirror unit 43 always stop at a fixed start position by the detection of the optical sensor 46 except during image formation. It is in a scanning standby state. The distance from the paper detection sensor 35 to the transfer position B is set to be longer than the circumference from the exposure position A to the transfer position B on the photosensitive drum 1. The distance from the paper detection sensor 35 to the transfer position B is set longer than the distance from the optical start position of the first mirror unit to the leading edge of the document.

In the image forming apparatus of this embodiment having the above-described configuration, when the start button (not shown) is turned on, the driving of the DC motor is started. The recording paper discharged by the rotation of the paper feed roller 32 is conveyed along the paper conveyance path 33 at the same speed as the peripheral speed of the photosensitive drum 1 by the rotation of the paper feed roller 32, and the leading end of the recording paper pushes down the actuator 35 a of the paper detection sensor 35. To the transfer position B. When the actuator 35a is depressed, the ON / OFF detection sensor 35b composed of, for example, a light emitting element and a light receiving element detects the passage of the leading end of the recording paper by the thin piece of the actuator 35a passing between the light emitting element and the light receiving element. . A control unit (not shown) starts driving the stepping motor of the image exposure unit 4 after a preset time based on a signal of the leading end of the recording paper from the paper detection sensor 35, and the photosensitive member uniformly charged by the scorotron charger 2 The exposure of the original image is performed on the drum 1 at the exposure position A. The latent image of the original image formed on the rotating photosensitive drum 1 becomes a toner image by the developing device 6 and rotates to the transfer position B. On the other hand, the recording paper that has passed the paper detection sensor 35 is transported to the transfer position B by the transport drive roller 340, and is transferred at the transfer position B with the leading edge of the recording paper moving and approaching at a constant speed coincident with the leading edge of the toner image. Transfer is performed by the electrode 7.

The image forming apparatus to which the invention of claim 5 is applied starts together with the apparatus shown in FIG. 1 at the same time as the start button is turned on without using the sheet detecting means as shown in FIG. A so-called registration roller 340 whose drive start timing is controlled in accordance with the progress of the image forming process.
A, or by providing a registration shutter upstream of the transport driving roller 340 and controlling the opening and closing of the registration shutter so that the recording paper is fed in synchronization with the toner image on the photosensitive drum 1. The configured device is also included.

(Embodiment 1) An embodiment of the invention according to claim 1 will be described with reference to FIG.

FIG. 2 is a sectional view of a main part of the image forming apparatus shown in FIG. 1, and includes the upstream side of the actuator 35a of the paper detection sensor 35 in the recording paper transport direction and the transport drive roller 340. On the downstream side, an upper transport guide plate 51 and a lower transport guide plate 52 which are respectively formed continuously.
Are disposed opposite to each other with a predetermined gap therebetween at a position sandwiching the recording paper conveyance surface.

Further, a leaf spring member 53 as an elastic member is attached to the lower surface of the upper transport guide plate 51 facing the transporting surface of the recording paper, and the lower portion is located on the upstream side of the actuator 35a. Is lightly pressed against the upper surface of the transport guide plate 52 with an even pressure distribution.
Of course, the pressing range by the leaf spring member 53 does not need to be in contact with the entire width of the recording paper, and it is sufficient that the recording paper is always transported in the same state.

Each of the transport guide plates 51 and 52 and the leaf spring member 53 have the above-described actuator 35a inserted through an elongated hole near the center of the transport surface, and the recording paper is transported downward by the leaf spring member 53. The plate 52 is pressed against the plate 52 in a well-balanced manner so that appropriate rigidity is imparted. As a result, the recording paper is maintained in the normal conveyance posture and the
The sheet is fed in a state where the leading ends thereof are aligned with the transport drive roller 340 without bending, bending or skewing even when receiving the resistance of the operation a. Further, since the entry position of the recording paper with respect to the actuator is always regulated in a fixed direction, the timing of the leading edge with the toner image can be stably maintained without being affected by the rigidity, curl, thickness, etc. of the recording paper.

(Embodiment 2) An embodiment of the invention according to claim 2 will be described with reference to FIG.

The recording paper fed to the transport drive roller 340 continues its transport operation by being pinched by the transport driven roller 34 which is pressed against it, and is fed to the transfer position B.

The transport driven roller 34 has a support shaft 34A.
A U-shaped notch formed in each rising portion 51a of the upper transport guide plate 51 so as to be placed at a symmetric position of an image center (indicated by a two-dot chain line) while being rotatably supported by Dropped and supported.

The transport driven roller 34 is provided with a support shaft 34.
A biasing force is accumulated in the torsion spring 54 by engaging the end of the torsion spring 54 wound around the position corresponding to the image center of FIG. The transport driven rollers 34 are pressed against the opposed transport drive rollers 340 with good balance.

As a result, the recording paper is fed to the transfer position B with a normal conveyance posture and a normal conveyance speed under the uniform distribution of the clamping force.

(Embodiment 3) An embodiment of the invention according to claim 3 will be described with reference to FIG. (Sheet Feeding Unit (A)) The sheet feeding cassette 30 has a direction perpendicular to the direction A in which the recording paper (shown by a dashed line) is stored, as shown in the plan view of FIG. The cassette guide members 110A and 110A of the apparatus main body are inserted into the apparatus main body from the direction B.
The pair of abutting portions 30C formed at the tips by the guidance of B contact the cassette abutting member 110C of the apparatus main body and are mounted in the apparatus main body.

The cassette abutting member 110C has an abutting surface that abuts against the abutting portion 30C and is disposed in parallel with the recording paper feeding direction arrow A, whereby the recording paper to be stored is fed. Correctly facing the direction.

Further, the paper feed cassette 30 is shown in FIG.
As shown in (b) and (c), the concave portions 30 are provided on both side surfaces of
A and 30B are formed. On the other hand, rollers R supported by leaf springs 111A and 111B are provided as pressing members on each of the cassette guide members 110A and 110B of the apparatus body opposed to each of the concave portions. At the apparatus position in the apparatus main body, the cassette 30 is locked by the rollers R pressing the respective inclined surfaces of the recesses 30A and 30B. As a result, the close contact state between the abutting portion 30C and the cassette abutting member 110C is maintained, and the position of the image center (indicated by a two-dot chain line) of the recording paper is prevented from changing due to vibration or the like accompanying the paper feeding operation. The recording paper is correctly fed from a predetermined position in a predetermined direction.

The roller R of the paper feed cassette 30
The sheet springs 31A and 1A are locked by the pull-out operation of the sheet feeding cassette 30 from the mounting position.
11B is elastically deformed and easily released.

(Embodiment 4) An embodiment of the invention according to claim 4 will be described with reference to FIG. (Paper feeding section (B))
As shown in the plan view of FIG. 5 (a), the paper feed cassette 30 is inserted into the apparatus main body in the direction indicated by an arrow B perpendicular to the direction A in which the recording paper (shown by a dashed line) is fed. The cassette guide members 110A and 1
A pair of abutting portions 30C formed at the distal end by the guide of 10B
Abuts on the cassette abutting member 110C of the apparatus main body to regulate the position in the insertion direction. The above-mentioned cassette guide member 1
Reference numeral 10B is disposed in a vertical direction so as to be orthogonal to the recording paper feed direction arrow A, and is used as a cassette guide rail when the paper feed cassette 30 is inserted.

Further, the above-mentioned paper feed cassette 30 is shown in FIG.
As shown in (b) and (c), a concave portion 30A is provided on the side surface opposite to the sheet feeding direction, and a pair of abutting portions 30 are provided on the side surface on the sheet feeding side.
D are formed, while a leaf spring 11 is provided on the cassette guide member 110A of the apparatus main body facing the recess 30A.
1A, a roller R supported by the sheet feeding cassette 30 is provided. When the roller R presses the inclined surface of the concave portion 30A at the insertion position in the apparatus main body, the cassette of the abutting portion 30C is set. At the same time as securing the contact with the abutting member 110C, the paper cassette 30 is urged in the paper feeding direction to move the abutting portion 30D into the cassette guide member 110B.
, And set to its mounting position. As a result, the abutting portion 30C and the cassette abutting member 110C,
D and the cassette guide member 110B are kept in close contact with each other, so that the position of the image center of the recording paper (indicated by a two-dot chain line) is prevented from fluctuating due to vibration or the like accompanying the paper feeding operation. Paper is fed correctly in a predetermined direction.

The above-mentioned roller R of the sheet cassette 30 is
The leaf spring 111A is elastically deformed by a pull-out operation from the mounting position of the sheet feeding cassette 30, and is easily released.

(Embodiment 5) An embodiment of the invention according to claim 5 will be described with reference to FIGS.

FIG. 7 shows a main part of the image forming apparatus (B) shown in FIG. 6. The upstream side and the downstream side in the recording paper transport direction including the registration roller 340A are formed continuously. The upper transport guide plate 51 and the lower transport guide plate 52 are opposed to each other with a predetermined gap therebetween at a position sandwiching the recording paper transport surface.

The recording paper transported from the paper feed cassette 30 passes between the upper and lower transport guide plates 51 and 52, and the pressing surface of the registration roller 340A and the transport driven roller 34 pressed against the registration roller 340A. The registration position is adjusted by stopping the registration roller 340A, and the image is transferred between the driven roller 34 and the image transfer position in synchronization with the toner image on the photosensitive drum 1. B is fed.

The transport driven roller 34 is provided with the upper transport guide plate 51 as described in the second embodiment.
While being rotatably supported, the torsional spring 54 presses against the opposing registration rollers 340A by the urging force.

The upper transport guide plate 51 supporting the transport driven roller 34 has a positioning hole 5 for regulating the mounting position of the transport driven roller 34 in the bent portion 510 on the left and right sides.
10A, the positioning hole 510A is engaged with the flange portion 200A corresponding to the outer diameter of the bearing 200 that supports the rotation shaft of the registration roller 340A, and then the main body panel, that is, the left and right substrates 100 of the apparatus main body. It is fixed via a set screw S.

Accordingly, each transport driven roller 34 is installed with a high positional accuracy with respect to each registration roller 340A. As a result, the recording paper is transferred to the transfer position B with a normal transport attitude and transport speed under a uniform distribution of pinching force. Paper is fed.

The present invention is also applicable to an image forming apparatus of the type in which the timing of starting image formation is controlled in accordance with the recording paper feeding process by using the above-described paper detecting means. This is also applied to the transport drive roller 340 instead of the registration roller 340A. Further, by disposing the driven roller 34 at a symmetrical position of the image center of the recording sheet and biasing the roller at a position corresponding to the image center, the conveyance of the recording sheet is more balanced, and accurate feeding is realized.

[0045]

According to the first aspect of the present invention, it is possible to detect the always stable feeding timing by the transport operation of the recording paper itself and to perform the meandering balanced in the left and right direction in the recording paper feeding direction according to the second aspect. In addition, it is possible to maintain the normal and normal conveyance operation, and the invention according to the third and fourth aspects realizes the setting and holding of the recording paper at an accurate paper feeding position, and always discharges the recording paper from the cassette in a proper posture. As a result, an image forming apparatus capable of starting image formation in synchronism with the sheet feeding timing of recording paper and obtaining a high-efficiency and high-quality transfer image is provided.

Further, since the invention according to claims 5 and 7 is extremely efficient in realizing a normal paper feeding operation without tilting or meandering of the recording paper, the recording paper is fed in synchronization with the image forming timing. The present invention is extremely effective when applied to the above-described image forming apparatus in addition to the image forming apparatus of the type of starting paper.

[Brief description of the drawings]

FIG. 1 is a sectional configuration diagram of an image forming apparatus (A) of the present invention.

FIG. 2 is a sectional view of a main part of the device (A).

FIG. 3 is a plan view and a ZZ cross-sectional view of a main part of the device (A).

FIG. 4 is a plan view and a cross-sectional view of a main part of a sheet feeding unit (A).

5A and 5B are a plan view and a cross-sectional view of a main part of a sheet feeding unit (B).

FIG. 6 is a sectional configuration diagram of an image forming apparatus (B) of the present invention.

FIG. 7 is a sectional view of a main part of the device (B).

FIG. 8 is a plan view and a cross-sectional view of a main part of the device (B).

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor drum 2 scorotron charger 4 image exposure unit 6 developing device 7 transfer electrode 9 cleaning device 10 fixing device 30 paper feed cassette 30A, 30B recess 30C abutment unit 34 transport driven roller 35 paper detection sensor 35a actuator 35b ON / OFF Detection sensor 51 Upper transport guide plate 52 Lower transport guide plate 53 Leaf spring member 54 Torsion spring 100 Main substrate 110A, 110B Cassette guide member 110C Cassette abutment member 200 Bearing 200A Flange section 340 Transport drive roller 340A Registration roller

Claims (7)

[Claims] An arrival of a sheet conveyed by sheet detection means positioned between a transfer position and a sheet feed roller is detected, and an exposure optical system is scanned in synchronization with a signal from the sheet detection means to scan the sheet and a toner image. In the image forming apparatus which performs transfer by adjusting the leading edge timing of the paper detecting means, a pair of upper and lower transport guide plates continuously formed on the upstream and downstream sides in the paper transport direction of the paper detecting means are arranged, and An image forming apparatus comprising: an elastic member that presses a sheet against one surface of the conveyance guide plate on an upstream side in a conveyance direction. 2. A sheet detecting device positioned between a transfer position and a sheet feed roller detects arrival of a sheet conveyed, and scans the exposure optical system in synchronization with the signal to detect the arrival of the sheet and a toner image. In the image forming apparatus that performs transfer at the same timing as the leading edge of the sheet, the sheet is transported by causing a sheet transport driven roller disposed symmetrically with respect to the image center to face a sheet transport driving roller, and the sheet transport corresponding to the image center is performed. An image forming apparatus, wherein a substantially central portion of a driven roller is pressed toward the paper transport driving roller. 3. A sheet detecting unit positioned between a transfer position and a sheet feed roller detects arrival of a sheet conveyed, and scans the exposure optical system in synchronization with the signal to detect the arrival of the sheet. In the image forming apparatus that performs transfer at the same timing as the leading edge of the cassette, the cassette or the tray can be inserted and removed in a direction perpendicular to the sheet feeding direction, and both side surfaces of the cassette or the tray are pressed by the pressing members arranged in the apparatus main body. An image forming apparatus, wherein an abutting portion provided integrally with the cassette or the tray abuts against a surface provided in the apparatus main body and parallel to a sheet feeding direction. 4. A sheet detecting device positioned between a transfer position and a sheet feed roller detects arrival of a sheet conveyed, and scans the exposure optical system in synchronization with the signal to detect the arrival of the sheet and a toner image. In the image forming apparatus that performs transfer at the timing of the leading edge of the cassette, the cassette or the tray can be inserted and removed in a direction perpendicular to the paper feeding direction, and the side opposite to the paper feeding side of the cassette or the tray is installed in the apparatus main body. The image is characterized in that it is configured to be pressed by a pressing member so that the abutting portion provided integrally with the cassette or the tray abuts on a cassette guide rail provided on the apparatus main body and having a surface orthogonal to a sheet feeding direction. Forming equipment. 5. A paper transport drive roller rotatably supported between main body panels via a bearing, and a paper transport driven roller provided opposite to the paper transport drive roller and pressed against the paper transport drive roller. An image forming apparatus having a transport guide plate rotatably supported, wherein the transport guide plate is positioned with reference to an outer diameter portion of a bearing rotatably supporting the paper transport drive roller on the main body panel. An image forming apparatus. 6. The image forming apparatus detects arrival of a sheet conveyed by sheet detection means positioned between a transfer position and a sheet feed roller, and performs scanning by synchronizing an exposure optical system based on the signal. 6. The image forming apparatus according to claim 5, wherein the image forming apparatus is configured to transfer the sheet and the toner image at the same timing. 7. The paper transport driven roller is disposed symmetrically with respect to an image center, and presses a substantially central portion of the paper transport driven roller corresponding to the image center toward the paper transport drive roller. The image forming apparatus according to claim 5, wherein: