JPH0511527A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain an image forming device such as a copying device improving paper feeding function and paper detecting function. CONSTITUTION:A 1st roller 24 is controlled so that the circumferential speed of rotation may be lower than that of a 2nd roller 25, and a paper is carried toward a paper path 35 by the 1st roller and a roller which is rotatable with respect to the shaft of the 2nd roller 25. An actuator 34 provided with detection parts 34a and 34b for detecting the paper in two directions is provided on the shaft of the 2nd roller 25. A paper guide (guard film) 55 having elasticity is allowed to flow toward the paper path 35 through a non-contact gap between the 1st and the 2nd rollers 24 and 25 in a state where one end is allowed to play. Furthermore, by turnably providing a switching gate 33 on the shaft of a roller 27 and switching the position of the gate 33 to two directions, the paper is carried toward the paper paths 35 and 43, and a paper path 47.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine having an improved sheet conveying function and a sheet detecting function.

[0002]

2. Description of the Related Art Three rollers which engage with each other in a sheet conveying path are provided, a central roller and one roller form a forward conveying path, and a central roller and the other roller form a backward conveying path. Then, an image forming apparatus for double-sided printing is known in which after the first side is printed, the sheet is fed again into the apparatus from this reverse transport path and the second side is printed. However, the conventional device has the following problems. 1. In the paper reversing / transporting mechanism, the central roller only urges the other two rollers, and the peripheral speed of each roller is constant. For this reason, if the paper conveyance speed is made extremely higher than the fixing roller speed, a soft toner image may be rubbed, the paper image may be soiled, or the roller itself may be soiled with toner. In order to avoid this, if a forward / reverse transport mechanism is provided at a position away from the fixing roller, the device becomes large,
In order to prevent the apparatus from becoming large, if the speed of the sheet reversing / conveying mechanism is made equal to the speed of the fixing roller, the conveying time for printing the second surface becomes long. 2. The paper reversing / conveying mechanism consisting of three rollers must move the paper to the nip part on the opposite side to that in the case of forward conveying when reversing the paper, but curling occurs on the paper that has been fixed. In view of this curl, it is necessary to make the roll diameter sufficiently large. A space for this is required and the device becomes large. 3. Further, as another problem, in an apparatus having a sheet reversing / conveying mechanism and a sheet path switching mechanism, the two are usually arranged at positions separated from each other. Therefore, a paper path connecting the two is required, and as a result, the apparatus becomes large and complicated, and the paper jam becomes difficult to handle because the paper path becomes long.

4. Further, in an apparatus having different paper paths, a method of providing two actuators for detecting papers of different paths and a method of providing an optical sensor corresponding to each path are known. However, the method of providing two actuators not only complicates the mechanism, but also makes it difficult to arrange the actuators for accurate detection. In the case of an optical sensor, it may not be detected in the case of OHP paper or thin paper, and adjustment such as optical axis alignment between the light emitting unit and the light receiving unit is required.

5. Some conventional devices do not use three rollers in the paper reversing / conveying mechanism, but provide independent roller pairs for each and reverse the paper at the paper reversing switching gate, but the device becomes large and complicated. Drive system is required.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-described problems, and maintains the speed of the paper reversing / conveying mechanism at the same level as the speed of the fixing roller, while the paper after the reverse rotation is performed. An object of the present invention is to provide an image forming apparatus capable of downsizing the apparatus by increasing the conveying speed, increasing the image forming processing speed in the case of double-sided printing, and improving the sheet conveying guide means and the sheet detecting means. There is.

[0006]

An image forming apparatus according to the present invention sandwiches a sheet printed on a first side in an image forming section with a first roller and a second roller and conveys the sheet to a forward direction conveying path,
The reversal sheet sent to the sheet reversing unit provided on the downstream side and retransmitted through the sheet reversing unit is nipped by the second roller and the third roller, and fed again to the image forming unit, In an image forming apparatus that ejects paper after surface printing to the outside of the apparatus, means for pressing the first roller and the third roller in the axial center direction of the second roller, and rotation of the first roller slower than rotation of the second roller. Driving means, a fourth roller that is rotatably provided on the shaft of the second roller, is pressed by the first roller, is driven by the peripheral speed of the first roller, and conveys the sheet to the forward direction conveyance path, and the second roller. It is characterized in that it has a roller portion fixedly provided on the shaft of the roller and configured to follow the third roller to feed the paper backward.

Further, a first sheet contact portion, which is swingably held near the second roller and projects toward the first roller from the nip tangent line between the first roller and the second roller, the second roller and the third roller. It is also characterized in that a sheet detecting means having a second sheet contact portion protruding from the nip tangent line of the roller to the third roller side and an operation detecting means for detecting the operation of the sheet detecting means are provided. Further, it is also characterized in that it is provided with an elastic paper guide which is passed through the non-contact gap between the first roller and the second roller in the forward transport direction.

Further, the first and second rollers are provided downstream of the first roller and the second roller, with their tips facing the vicinity of the first roller, the second roller, and the third roller, and centering near the other end. It has a paper guide means that can be switched to a position and is rotatable. When the paper guide means is in the first position, the paper is conveyed to the forward-direction conveyance path, and the reversed paper to be retransmitted via the paper reversing means is moved to the first position. It is also characterized in that it is sent to the nip portion of the two rollers and the third roller, and when it is in the second position, the paper sent by the first roller and the second roller is conveyed in the direction of the third conveying means.

[0009]

With this structure, in the first aspect of the invention, the transport speed of the sheet can be made higher when the sheet is transported in the reverse direction than when it is transported in the forward direction with a simple mechanism. Further, according to the second aspect, the sheet conveyed in the two directions can be detected by one sheet detecting means, and the apparatus can be downsized and simplified. Further, according to the fourth aspect, the paper can be reliably guided to each paper path. Further, in the fifth aspect, the sheet can be guided in three directions by one sheet guiding means, and the apparatus can be downsized and simplified.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of an image forming apparatus according to an embodiment. The schematic configuration of the apparatus will be described with reference to FIG.

An unused sheet is stored in the apparatus, and the sheet feeding cassettes 1 which can be attached to and detached from the apparatus main body are mounted in upper and lower two stages. A paper feed roller 2 for feeding a sheet is provided above the tip of each cassette 1, and upper and lower separation rollers 3 for separating the sheet into one sheet are provided on the apparatus body side at the tip of the cassette 1.

A recording head 5 for recording a latent image on the image carrier 4.
A developing unit 6 for visualizing the latent image with toner, a corona charger 7 for transferring the toner on the image carrier 4 to the fed sheet, and an untransferred toner for the image carrier. A cleaning unit 8 and the like for removing it from above 4 are arranged around the image carrier 4. Between the image carrier 4 and the corona charger 7, that is, the registration roller 9 for conveying the sheet to the transfer unit is provided in the main body of the apparatus.
It is held substantially parallel to the image carrier 4 so that it can rotate and can be disconnected from the drive system.

From the upper sheet feed cassette 1 to the registration roller 9, the first sheet path 11 is formed by the upper surface of the guide A10 and the lower rib of the developing unit 6, and from the lower sheet feed cassette 1 to the registration roller 9. A second paper path 13 is formed by the lower surface of the guide A10 and the upper surface of the guide B12. Furthermore, the lower surface of the guide B12 and the guide C
Third paper path 1 leading to registration roller 9 by 14
5, between the roller H16, the roller A17 and the registration roller 9 provided in the duplex unit, the guide C14 and a part of the transfer unit 18 serve as a paper guide to form the fourth paper path 19. is doing.

These first to fourth paper paths merge into one on the paper feed cassette 1 side of the registration roller 9, and an actuator A20 for detecting the presence or absence of paper is arranged at this portion.

In addition to the corona charger 7 as a main component, the transfer unit 18 is provided with a pinch roller 21 for pressing against the registration roller 9 and a vacuum fan on the downstream side.

A fixing unit 22 for fixing the toner image transferred on the paper to the paper is provided downstream of the transfer unit 18, and a conveying unit 23 for allocating the paper path is provided further downstream thereof. .

The carrying unit 23 is provided with five carrying rollers 24 to 28 as shown in FIG. The sheet conveyed from the fixing unit 5 is guided to the conveying unit 23 from the fifth sheet path 31 formed between the lower surface of the guide D29 and the unit 30. And, it is adapted to communicate with the roller A24 which is pressed by the roller B25. The roller B25 is also pressed by the roller C26.

A sample tray 32 is provided on the downstream side with paper.
A roller D27 and a roller E28 for discharging the sheet are provided, and the roller E28 is pressed by the roller D27. A switching gate 33, which is swingable about its axis, is loosely fitted to the roller D27. Further, an actuator B34 is loosely fitted to the shaft of the roller B25 so as to be swingable about the shaft, and the presence or absence of paper is detected.

In the state shown in FIG. 1, the switching gate 33
However, the fifth paper path 31 is connected to the sixth paper path 35 and is connected to the paper discharge unit 36. In addition, the switching gate 3
In the state where 3 is switched in the horizontal direction, the switching gate 33
However, the fifth paper path 31 is communicated with the paper path 37 to guide the paper to the rollers D27 and E28.

As shown in FIG. 3, the paper discharge unit 36 rotatably holds a roller F38 and a roller G39 which is pressed against the roller F38. An actuator C40 is loosely fitted to the shaft of the roller G39 so as to be swingable about the shaft. Further, a photo interrupter 41 for detecting the operation of the actuator C40 is provided. The rollers F38 and G39 can be rotated forward and backward by a drive mechanism (not shown), and have a function of discharging the paper to the tray 42 at the upper part of the apparatus at the time of normal rotation and a function of sending the paper back into the apparatus at the time of reverse rotation. That is, the sixth paper path 35 communicates with the knit portions of the rollers B25 and C26 when the switching gate 33 is in the state shown in FIG.
A paper path is formed through the seventh paper path 43 to the duplex unit 44.

The duplexer unit 44 is provided with an aligner roller 45 for feeding the sheet in a direction inclined with respect to the sheet conveying direction and a pinch roller 46 pressed by the aligner roller 45. Further, a roller H16 and a roller H17 pressed by the roller H16 for sending the sheet to the registration roller 9 again.
Are provided substantially parallel to the registration roller 9.

The duplex unit 44 is located directly below the transfer unit 18 and can be retrofitted by the user. The toner recovery unit is provided between the transfer unit 18 and the duplex unit 44. The structure is such that is attached.

In the apparatus of the embodiment configured as described above, the sheets fed from the sheet feeding cassette 1 are
The registration roller 9 and the pinch roller 21 pass through any one of the third paper paths to send the image to the transfer portion at a timing with the image, and the corona charger 7 transfers the image onto the paper. After that, the fixing roller 2 of the fixing unit 22
The toner image is fixed on the sheet by the sheets 2a and 22b.
Further, the sheet passes through the fifth sheet path 31 and is nipped by the roller A 24 and the roller B 25, and further the switching gate 33
Guided by the surface 33a of the sheet No. 33a, passed through the sixth paper path 35, nipped by the roller F38 and the roller G39, and discharged to the tray 42 with the printing surface facing down.

In the case of double-sided printing, the trailing edge of the sheet conveyed to the sixth sheet path 35 has rollers A24 and B2.
Actuator B4
By detecting 0 at 0 and reversing the roller F38, the sheet is nipped by the roller B25 and the roller C26 and guided to the duplex unit 44 via the seventh sheet path 43. Further, the side edge portion of the paper is positioned by the liner roller 45, and the fourth paper path 1 is set by the rollers H16 and I17.
It is guided to the registration roller 9 again through 9 and the image is formed on the second side by the process similar to the printing on the first side.

The printed paper is guided to the eighth paper path 47 by switching the switching gate 33 in the horizontal direction as required, and the paper is nipped by the rollers D27 and E28 to the sample tray 32. It can also be ejected with the print side up.

In the apparatus of the embodiment for performing the printing operation as described above, the conveying speed and the nip force of each roller have the relationship shown in the table of FIG. 4 when the peripheral speed of the image carrier 4 is 1. ing.

The feeding speed of the paper feed roller 2 and the separation rollers 3a and 3b is approximately tripled in order to increase the number of prints in a fixed time. Fixing unit 2
The conveyance speed of the second pair of deposition rollers 22a and 22b is set to the image carrier 4
The peripheral speed is set to be substantially the same as that for stabilizing the conveyance of the paper at the transfer unit and reducing the expansion and contraction of the image. Further, the reason why the conveyance speed of the roller A24 and the roller B25 is set to 1.1 times is that tension is applied to the paper sent from the fixing rollers 22a and 22b to reduce the curl. Further, the reason why the conveyance speed of the roller for double-sided printing is increased is that the paper is returned to the registration roller 9 again in a short time to increase the number of prints within a certain time in the double-sided print mode.

In order to increase the number of prints within a predetermined time in the double-sided print mode, the roller conveying speed is increased, and at the same time, the sheet conveying path for double-sided printing is shortened as much as possible, and the time is reduced. There is a demand for a paper transport means that is efficient.

Next, the detailed structure and operation of the transport unit 23 will be described. As shown in FIG. 5, the roller B25 is fitted with two rotatable plastic rollers 25d on its stainless shaft. Rubber rollers 25c fixed to the shaft are formed at two locations on both outer sides thereof, and the outer diameters of the plastic roller 25d and the rubber roller 25c are substantially the same. Both ends of the roller B25 are rotatably fixed to the frame of the unit via bearings, and the reduction gear 48 is fixed to the end on the drive side outside the frame.

The roller A24 has two rubber rollers 24a having the same diameter and three rubber rollers 24b having a smaller diameter fixed to the shaft, and a drive gear 49 is provided at the end of the drive side shaft. The gear 49 meshes with the reduction gear 48 via a small diameter gear. The roller A24 is pressed against the roller B25 by the force of the spring 50 via the bearing. As a result, 2 of roller A24
4a and 25d are in pressure contact with each other, and 24b and 25c face each other with a slight gap.

Since the center distance between the gears 48 and 49 is set wider than the regular interval, the forces of the springs 50 are not received by the gears, and the forces of the springs 50 are all nip between the 24a portion and the 25d portion. helpful.

Also, the roller C26 is fixed to the plastic rollers 26a and 26b having the same diameter, and the roller 26a is replaced by the rubber roller 2 with the spring 50 via the bearings at both ends.
The roller B25 is pressed in contact with 5c.

With such a mechanism, when the reduction gear 48 is driven, the roller B25 is rotated and the roller C26 is rotated by 26.
It is driven by the nip pressure of the 25c portion via the a portion. Further, the roller A24 is driven at a rotational speed slower than that of the roller B25 by the reduction ratio of the reduction gear 48 and the gear 49. Therefore, the 25d portion of the roller B25 is 24a of the roller A24.
Since it is driven by the part, it rotates in the same direction as the shaft at a slow rotation speed. Therefore, if the transport speed of the sheet nipped between the 24a section and the 25d section is 1, the 25c section and the 26c section are conveyed.
It is possible to increase the speed of the sheet conveyed while being nipped to the portion a, for example, 1.7.

Both ends of the roller D27 are rotatably supported by bearings and fixed to the frame.
A gear 49 is fixed to the outside of the frame on the drive side of the roller D27, and a rubber roller 27d having the same diameter is fixed near the center. Two plastic rollers 28a are fixed to the roller E28, and the 28a portion is in contact with the 27d portion of the roller D27, and the roller E28 presses the roller D27 by the springs 50 through the bearings at both ends thereof. The portion 28a has a large diameter in the non-nip portion, and serves to make the paper stiff. As shown in FIG. 6, two idler gears 51, which receive the driving force, are connected from the small diameter gear of the reduction gear 48 fixed to the roller B25, and the driving force is transmitted to the gear 49 fixed to the roller D27.

Next, an actuator B34 for detecting the sheet
The configuration of will be described. The actuator B34 is formed by integral molding with a roller B, as shown in FIG.
Two small diameter portions 25a, 25b provided on the shaft of 25
In addition, the bearing part, which is partially cut off at the outer circumference, is spread and fitted into the bearing part, so that the bearing part is swingably hung around the roller B25. A metal weight is inserted in the 34d portion of the actuator B34, and the swing range is restricted by the weight. The portions 34a and 34b of the actuator B34 that actually contact the paper are the nip tangent line between the roller A24 and the roller B25 and the roller B25 and the roller C, respectively.
It is arranged so as to project longer than the tangent line to the nip 26 and to be located downstream of the nip point in the sheet conveyance. Therefore, only the leading edge of the sheet that is securely nipped presses the actuator B34 and rotates the roller B25 as a center.

The portion 34c of the actuator B34 has a light-shielding function. As shown in FIG. 6, when there is no paper, the moment of the weight 34d makes contact with the photo interrupter 41, and the optical axis of this photo interrupter 41. Is blocking. When the paper pushes 34a or 34b, 3
The sheet 4d is separated from the photo interrupter 41 so that the sheet can be detected.

By configuring the actuator B34 in this way, it is not necessary to provide a new member for holding the actuator B34, and in a compact space, sheets of paper passing through different paper paths conveyed in different directions can be stored. Detection was possible with a set of actuator B34 and photo interrupter 41.

Next, details of the configuration of the switching gate 33 will be described with reference to FIG.
Will be described. The switching gate 33 is formed integrally with the mold, and includes the small diameter portions 27a, 27 of the roller D27.
The bearing portion of which the outer periphery is partially cut is spread and fitted into the positions corresponding to b and 27c, respectively, so that the bearing is swingably fitted to the shaft of the roller D27. Switching gate 3
A boss 33c projects outward from the frame of the unit and is fitted into the stainless-steel link hole 52a of the link 52 at the drive-side end of the unit 3.

The link 52 has one end engaged with the plunger of the solenoid 53 at the U groove 52b, and the hole 5 at the other end.
2c is urged by a spring 54 in the direction opposite to the plunger. 52a, 52b, 52c of the link 52
The parts are arranged on a substantially straight line.

In such a structure, the solenoid 53
When the power is supplied to the switching gate 33, the switching gate 33 rotates downward about the shaft of the roller D27 via the link 52. When the solenoid 53 is turned off, the force of the spring 54 causes the link 52
Moves upward and rotates the switching gate 33 upward. The rotation range of the link 52 is defined by the position of the solenoid 53 and the stopper position of the link 52 (not shown). FIG. 2 shows the position of the switching gate 33 when the solenoid 53 is turned on. At this time, the switching gate 33 serves as a guide for guiding the leading edge of the paper to the sixth paper path 35. It serves to guide the rear end to the seventh paper path 45.

When the solenoid 53 is turned off, the switching gate 33 switches its position in the horizontal direction, and the lower surface 33b of the switching gate 33 serves as a guide forming the eighth paper path.

In this way, centering on the axis of the roller D27,
By rotating the leading ends of the rollers A24, B25, and C26 in the vicinity thereof, it is not necessary to provide a new center of rotation when the switching gate 33 has three paper guide functions, and the apparatus can be made compact. be able to.

Next, details of the structure of the guide film 55 will be described. As shown in FIG. 2, the transport unit 23 includes
A guide D29 is attached so as to be capable of thermal expansion in the direction perpendicular to the paper transport direction. This is because the paper heated by the fixing unit 22 expands due to the heat. This guide D29
Has a lower surface 29a serving as a paper guide surface and an upper surface having
One end of the guide film 55 is fixed with an adhesive.
Since the guide film 55 is arranged at a position close to the fixing unit 22, it is required to have heat resistance and abrasion resistance due to friction with a sheet, so that abrasion resistance is also required.
Therefore, in this example, a polyimide sheet having a heat of 200 μ and a width of 10 mm was used.

The guide film 55 passes through the non-nip portion between the roller A24 and the roller B25, comes into contact with the switching gate 33 by its elastic force, and extends in the direction of the sixth paper path 35,
The edge projects from the unit out of the paper path. The protruding end portion is not fixed, and the width of the guide film 55 is increased so that the end portion does not enter the sixth paper path 35.

In order to make the apparatus compact, the roller A
The diameters of the roller 24, the roller B25, and the roller C26 are designed to be small (about 20 mm in this embodiment). Therefore, the sheet that has passed from the fifth paper path 31 to the sixth paper path 35 is rotated by the reverse rotation of the roller F38. If there is curl at the trailing edge of the paper when trying to guide it to the nip portion of B25 and roller C26, it is difficult to insert it accurately. The elasticity of the guide film 55 causes the gate 33 to switch near the rear end of the paper.
The paper is securely pressed by pressing it against the seventh paper path 4
It has a function to guide you to 3.

The more the guide film 55 is projected near the tip of the roller B25 and the switching gate 33, the greater the effect. At that time, it is provided from the fifth paper path 31 between the roller A24 and the roller B25 so as not to hinder the leading edge of the paper fed from the fifth paper path 31. Since the distance between these two rollers is small, the guide film 55 is made of a thin sheet material so that it does not interfere with the axis of the roller A24. Further, one end of the sixth paper path 35 is made to project out of the path so that a thin guide film 55 can be used in the processing work in case of paper jam.
This is to prevent damage to. Since the guide film 55 is made of a thin sheet-like material, even when the transfer gate of the switching gate 33 is switched, the guide film 55 whose surface 33a has elasticity forms the eighth paper path 47 to form the sample tray. The paper can be discharged to 32.

The roller F38 provided in the paper discharge unit 36 is configured to be reversible in the forward and reverse directions by a driving device (not shown). The timing of switching between normal rotation and reverse rotation is important. The paper having the first side printed, which has been conveyed from the fifth paper path 31, has rollers A24 and B2.
5 further feeds the sheet to the upper side where the transport unit 36 is provided. It is necessary to reverse the roller F38 after the trailing edge of this sheet has surely passed the nip portion of both rollers. If this timing is too early, paper jam occurs, and if it is late, unnecessary time is consumed for transporting the paper.

In this embodiment, when the sheet passes the 40a portion of the actuator B40 described above and the optical axis of the photo interrupter 41 is blocked, or a sequence for reversing the roller F38 after a predetermined time is set, the sheet is fed. Be sure that the rear ends are roller A24 and roller B25.
It is possible to convey the paper in the reverse direction at the timing when the paper passes through the nip portion and at the timing when the waste of time is minimized.

The reversed sheet is nipped by the roller B25 and the roller C26 and is conveyed to the seventh sheet path 43. At this time, the fact that the sheet has been surely conveyed to the seventh sheet path 43 is re-actuated. Since the 34b portion of B34 detects, even if it is not conveyed to the seventh paper path 43, that fact can be detected promptly, and failure or damage of the device can be prevented.

Next, the structure and function of the actuator C40 will be described. In the actuator C40, a roller F38 is held in the paper discharge unit 36 by a drive system (not shown) so as to be rotatable in the forward and reverse directions. Further, the roller G39 is urged and pressed by a spring toward the center of the roller G38 via a bearing. Therefore, it follows the roller F38. A small diameter portion made of stainless steel is provided at substantially the center of the roller G39, and an actuator C40 having a bearing portion with a part of the outer circumference cut out at that portion.
However, the cutout portion is spread and fitted, and is loosely fitted to the roller G39 under its own weight so as to be freely rotatable.

As shown in FIG. 3, the actuator C40 has a tip 40a protruding toward the tray 42,
Due to the moment of the inserted metal weight 40b, the light blocking portion 40c abuts the photo interrupter 41 and blocks the optical axis of the photo interrupter 41.
In this state, it is detected that there is no paper.
Although the 40d portion of the actuator C40 directly contacts the leading edge of the sheet, the angle with the leading edge of the sheet is always small.
It is formed in a substantially arc shape.

When the paper is conveyed from the sixth paper path 35 by the nip portion of the roller F38 and the roller G39, the actuator C40 is lifted by the leading end of the paper and the light shielding portion 4 is moved.
When 0c leaves the optical axis of the photo interrupter 41, the arrival of the paper is detected. When the trailing edge of the paper leaves the roller F38 and the paper falls onto the tray 42, the actuator C40 returns to the original position again by its own weight.

When this printed operation is repeated and the printed paper is stacked in the tray 42 and is in the form of a sticky paper, the tip 40a of the actuator C40 rides on the stacked paper and the light from the photo interrupter 41 is emitted. It will not block. Since the actuator C40 does not block the light of the photo interrupter 41 for a certain time during the paper discharge operation, it is determined that the stacked paper on the tray 42 is a black paper. Based on this determination, a new paper feeding operation is prohibited and the paper information is displayed on a display panel (not shown). The operator removes the paper on the tray 42 based on the paper information, and the paper state is released, and the actuator C4 is released.
0 also returns to the normal position.

This actuator C40 is used only to detect the paper sheets stacked on the tray 42, and is not used to detect a paper jam in the paper transport path or the like. The reason is that it is not possible to distinguish between the case of paper jam and the case of jam, and this actuator C40 is arranged at a position where it is directly contacted from the outside of the device.

By directly attaching the actuator C40 to the roller G39, a new holding member is unnecessary, and the actuator C40 is passed from the upstream side to the downstream side of the nip portion between the roller F38 and the roller G39. By doing so, by making the 40d part arcuate, and by providing the tray 42 with an inclination, the contact angle with the conveyed paper is always kept small, and the shape of the actuator C40 does not damage the leading edge of the paper. Since it is possible to form the protruding length of the tray 42 on the tray 42 into a short shape, when the operator removes the sheets stacked on the tray 42,
This Actuator C40 can be installed out of the way.

As an option, a sorter 56 as shown in FIG. 7 can be attached to the image forming apparatus of this embodiment. A switching gate 57 for switching the sheet path to the tray 42 side or the sorter 56 side is provided on the sorter 56 above the tray 42 and in the vicinity of the rollers F38 and G39. The tip of the switching gate 57 can be switched to a state below or above the nip tangent line of the roller F38 and the roller G39 by a drive mechanism (not shown) around the shaft 57a. Further, the switching gate 57 is cut out at a portion facing the actuator C40, and both sides of the actuator C40 extend to the vicinity of the roller F38.
Therefore, the actuator C40 and the switching gate 57
Does not interfere with its operating range. For this reason, even if sheets are stacked on the tray 42 in the state of a blank sheet, the switching gate 57
Does not interfere with the paper.

Send the paper to the sorter 56 or the tray 42
Whether to eject the paper is determined based on a command from the host computer. When the paper is sent to the sorter 56, the actuator C40 is lifted while the paper is passing. Therefore, the optical axis of the photo interrupter 41 passes through. If the paper passes, the actuator C
40 returns to the original position, and the optical axis of the photo interrupter 41 is blocked. At this time, this actuator C40
Is used for detecting passage of the front and rear edges of paper, not for detecting paper.

As a result, it becomes unnecessary to provide the sorter 56 with a new paper detection sensor. Also, put paper in tray 4
When ejecting onto 2 or in double-sided print mode,
Once a part of the paper is put on the tray 42, and the roller F is again used.
When the paper 38 is fed into the apparatus by reversing 38, the switching gate 57 can be switched and moved to the horizontal position. With this mechanism, even when the length of the paper to be printed on both sides is long and the long portion of the paper comes out from the roller F38 on the tray 42, it is possible to cope with the case where the sorter 56 is not attached.

Further, when the paper is discharged onto the tray 42, the actuator C40 can be used for detecting the paper as in the case where the sorter 56 is not provided. If the sorter 56 is installed and the optical axis of the photo interrupter 41 is not interrupted at the timing when there is no paper while discharging the paper to the tray 42, new feeding for sending to the sorter 56 is immediately prohibited. Then, when the paper on the tray 42 is removed and the optical axis of the photo interrupter 41 is blocked again, the prohibition is released. That is, the actuator C40 is used to detect the leading edge and the trailing edge of the sheet when the sheet is sent to the sorter 56, and to detect the rod sheet when the sheet is discharged to the tray 42. . With such a configuration, the tray 42 and the sorter 56 can be compatible with each other on the device. The present invention is not limited to the above-mentioned embodiments, and can be modified and carried out without changing the gist.

[0060]

According to the present invention, the following effects can be expected.

1. By using three conveyor rollers and using a simple structure and space without using a new drive source, the conveyor speed after reversal could be faster than the conveyor speed before reversal. The paper conveyance speed is set to be about the same as the fixing roller speed to prevent image distortion and toner adhesion to the conveyance roller, and the paper conveyance speed after reversal is increased to return to the image forming unit to reduce loss time. I was able to do it.

2. Since an actuator for paper detection that shares the axis of the central roller of the forward / reverse mechanism is provided, a new member for holding the actuator is not required, and it is possible to detect paper in two paths with one actuator, which is inexpensive and It was possible to have a simple configuration that requires no space.

3. Since the actuator is arranged in the vicinity of the central roller and the protruding portion for detecting the paper is provided on the downstream side of the nip portion, the paper can be detected accurately and reliably at the timing when the paper passes the conveying roller, and the paper can be reversed. It is possible to prevent the paper jam due to the timing shift and reduce the loss of the transport time.

4. By providing the guide film for the paper guide through the gap between the roller shafts, it is possible to smoothly convey the paper from the fifth paper path to the sixth paper path and from the sixth paper path to the seventh paper path, and the three conveyance rollers are provided. Since it is possible to form a small diameter, the device can be made compact.

5. Since the guide film is made of a flexible thin resin sheet and one end is free, it can be passed between rollers with a small diameter, and the paper can be turned over while maintaining the paper running performance. Moreover, the paper path can be easily changed without disturbing the operation of the switching gate.
Furthermore, by freeing one end, it is possible to prevent damage to the guide film when a paper jam occurs.

6. By providing a switching gate for switching the paper path as a paper guide for the sixth paper path, the eighth paper path, and the seventh paper path for paper reversal, it has three functions,
It is possible to reduce the number of paper guides, and since the shaft of the paper conveying means is shared with the center of rotation of the switching gate, a new member and space for holding the switching gate are unnecessary, The device can be downsized and the configuration can be simplified.

[Brief description of drawings]

FIG. 1 is a structural cross-sectional view of an embodiment of the present invention.

FIG. 2 is a sectional view of the transport unit according to the embodiment.

FIG. 3 is a sectional view of the paper discharge unit according to the embodiment.

FIG. 4 is a table showing the relationship between the transport speed of each roller and the nip force.

FIG. 5 is a sectional view illustrating a configuration of each roller of the transport unit.

FIG. 6 is an explanatory diagram of the configuration and operation of an actuator B.

FIG. 7 is an explanatory diagram of the configuration and operation of a switching gate 33.

[Explanation of symbols]

1 ... Paper feed cassette 2 ... Paper feed roller 3
...... Separation roller 4 ...... Image carrier 5 ...... Recording head 6
…… Developing unit 7… Corona charger 8… Cleaning unit 9
...... Registration roller 10 ... Guide A 11 ... First paper path 1
2 ... Guide B 13 ... Second paper path 14 ... Guide C 1
5 ... Third paper path 16 ... Roller H 17 ... Roller I 1
8 ... Transfer unit 19 ... Fourth paper path 20 ... Actuator A 2
1 ... Pinch roller 22 ... Fixing unit 23 ... Conveying unit 2
4 ... Roller A 25 ... Roller B 26 ... Roller C 2
7 ... Roller D 28 ... Roller E 29 ... Guide D 3
0 ... Unit 31 ... Fifth paper path 32 ... Sample tray 3
3 ... Switching gate 34 ... Actuator B 35 ... Sixth paper path 3
6 ... Paper discharge unit 37 ... Paper path 38 ... Roller F 3
9 ... Roller G 40 ... Actuator C 41 ... Photointerrupter 4
2 ... Tray 43 ... Seventh paper path 44 ... Duplex unit 45 ... Aligner roller 46 ... Pinch roller 4
7 ... Eighth paper path 48 ... Reduction gear 49 ... Drive gear 5
0 ... Spring 51 ... Idler gear 52 ... Link 5
3 ... Solenoid 54 ... Spring 55 ... Guide film 5
6 ... Sorter 57 ... Switching gate

Claims (6)

[Claims] 1. A sheet printed on the first side in an image forming section is nipped by a first roller and a second roller, conveyed to a forward direction conveyance path, and fed to a sheet reversing means provided on the downstream side. ,
An image forming apparatus in which a reversal sheet retransmitted via the sheet reversing unit is sandwiched between the second roller and the third roller, fed again to the image forming unit, and the sheet after the second side printing is discharged to the outside of the apparatus. In, means for pressing the first roller and the third roller in the axial center direction of the second roller, means for driving the rotation of the first roller at a speed slower than the rotation of the second roller, and rotation for the shaft of the second roller A fourth roller that is freely provided and is driven by the first roller to follow the peripheral speed of the first roller, and that conveys the paper to the forward conveyance path, and a third roller that is fixedly provided on the shaft of the second roller. An image forming apparatus comprising: a roller unit that is driven to feed a sheet backward. 2. A sheet printed on the first side in an image forming section is sandwiched by a first roller and a second roller, conveyed to a forward direction conveyance path, and sent to a sheet reversing means provided downstream thereof. ,
An image forming apparatus in which a reversal sheet retransmitted via the sheet reversing unit is sandwiched between the second roller and the third roller, fed again to the image forming unit, and the sheet after the second side printing is discharged to the outside of the apparatus. , The first paper contact portion that is swingably held near the second roller and protrudes toward the first roller from the nip tangent line between the first roller and the second roller, and the nip between the second roller and the third roller. An image forming apparatus comprising: a sheet detecting unit having a second sheet contact portion protruding from a tangent line to the third roller side; and an operation detecting unit detecting an operation of the sheet detecting unit. 3. The image forming apparatus according to claim 2, wherein the paper detection means is swingably held by the shaft of the second roller. 4. A sheet printed on the first side in an image forming section is sandwiched by a first roller and a second roller, conveyed to a forward direction conveyance path, and sent to a sheet reversing means provided downstream thereof. ,
An image forming apparatus in which a reversal sheet retransmitted via the sheet reversing unit is sandwiched between the second roller and the third roller, fed again to the image forming unit, and the sheet after the second side printing is discharged to the outside of the apparatus. The image forming apparatus according to claim 1, further comprising an elastic paper guide that is passed in the forward transport path direction through the non-contact gap between the first roller and the second roller. 5. A sheet printed on the first side in an image forming section is sandwiched by a first roller and a second roller, conveyed to a forward direction conveyance path, and sent to a sheet reversing means provided downstream thereof. ,
An image forming apparatus in which a reversal sheet retransmitted via the sheet reversing unit is sandwiched between the second roller and the third roller, fed again to the image forming unit, and the sheet after the second side printing is discharged to the outside of the apparatus. At the downstream of the first roller and the second roller, the tip faces the vicinity of the first roller, the second roller, and the third roller, and switches to the first and second positions with the other end as the center. When the sheet guide means is rotatable, the sheet guide means conveys the sheet to the forward direction conveyance path, and when the sheet guide means is in the first position, the reversal sheet retransmitted through the sheet reversing means is used as the second roller. An image forming apparatus, wherein the sheet is sent to a nip portion of a third roller, and when the sheet is in the second position, the sheet sent by the first roller and the second roller is conveyed in the direction of the third conveying unit. 6. The image forming apparatus according to claim 5, wherein the third conveying means has a roller having at least a rotary shaft, and the paper guiding means uses this roller shaft as a switching center of rotation.