JP4446620B2 - Image forming apparatus - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to an image forming apparatus such as a copy, a FAX, or a printer having a function of forming an image on both sides of a transfer sheet.
[0002]
[Prior art]
Examples of the image forming apparatus having an image forming function on both surfaces of the transfer paper include the image forming apparatuses described in Japanese Patent No. 2840734, Japanese Patent Application Laid-Open No. 8-113432, and Japanese Patent Application Laid-Open No. 7-267461.
[0003]
The image forming apparatus described in Japanese Patent No. 2840734 has been proposed in order to improve the fact that the switchback portion of the transfer paper protrudes to the operation surface side and to improve the jam handling performance. Is performed in the vicinity of the main body outlet and at different positions.
[0004]
A common feature of these prior arts is that a branching claw for selecting whether the transfer paper is discharged or conveyed to the switchback part after fixing is provided, and another second branching means is required in the switchback part. It is a thing. In Japanese Patent No. 2840734, detailed description of the second branching unit is omitted.
[0005]
In any example, the conveyance path after fixing is curved so as to draw a turn to the left and right. This is intended to save space by arranging registration rollers, photoconductors, and fixing rollers in a straight line in the vertical direction so that the size in the width direction of the machine can be accommodated within the projected area of the maximum size transfer paper. In such a case, it is necessary to bend the conveyance path left and right in order to go to the paper discharge tray and the reverse path.
[0006]
Further, the fixing roller portion is usually controlled at a temperature of about 150 ° C. to 200 ° C. in order to melt the toner by heat and fix the toner onto the transfer paper. For this reason, since the transfer paper after fixing is heated and is in a high temperature state, the shape of the guide sheet and the posture of the transfer paper during conveyance due to the difference in linear velocity of the rollers are likely to remain as a habit, for example, downstream rollers It is a well-known fact that when the downstream roller is slower than the upstream roller due to the difference in linear velocity between the two and the upstream roller, the transfer paper will be wavy and the shape will remain as is. In order to prevent undulation, the linear speed of the downstream roller is set to be faster than that of the upstream roller, and the transfer paper is pulled and conveyed.
[0007]
However, as described above, when the conveyance path after fixing is curved, if the linear speed setting of the downstream roller is set faster than that of the upstream roller, the transfer paper is pulled and stretched. Therefore, the toner (image) fixed on the transfer paper is rubbed against the guide plate and the guide rib, and the image is streaked or the toner accumulates on the guide plate and the rib (the guide plate is The transfer paper that passes through is soiled, or the transfer paper is caught by the accumulated toner, causing jamming.).
[0008]
As a countermeasure against such a problem, by installing a roller that rotates at a place where the image of the guide plate or the guide rib rubs, the roller is rotated so as to contact the roller while the transfer paper is stretched. It is known to prevent image rubbing.
[0009]
In addition, the branching means described above is generally a method in which the branching claw is driven by an electromagnetic solenoid or the like and is controlled in timing with the transfer paper. However, the electromagnetic solenoid is costly, so the cost can be reduced. From the point of view, an elastic thin plate of about 0.2 mm or less made of PET film or the like is pressed against the opposing guide plate, or in some cases, a small gap is provided so that the transfer paper passes between them. Thus, a method is known in which the elastic thin plate guides the sheet toward the re-feeding path during switchback.
[0010]
However, in this method, since the transfer paper after fixing is often curled by heat, the elastic thin plate or a small gap between the elastic thin plate and the guide plate is often caught at the time of switchback. It is a problem that the nature is low.
[0011]
[Problems to be solved by the invention]
The object of the present invention is to prevent the image surface of the transfer paper strained by the difference in the conveyance speed of the conveyance roller pair from rubbing against the guide plate and the rib, and the tip of the inverted transfer paper is caught by the elastic thin plate and becomes the switchback portion. An object of the present invention is to propose an image forming apparatus capable of preventing the occurrence of a jam.
[0012]
Another object of the present invention is to propose an image forming apparatus capable of preventing the occurrence of rubbing and jamming even on transfer paper having a large size.
[0013]
Still another object of the present invention is to prevent a jam from occurring due to undulation caused by thermal deformation of an elastic thin plate.
[0014]
[Means for Solving the Problems]
The present invention is located on the upstream side of the first branching portion that branches so that the transfer paper on which the image is formed on the first surface is discharged to the discharge tray or conveyed to the reverse branching portion. The first conveying roller pair and the transfer sheet fed from the first branching section to the reversing branching section are transported to the switchback transport path and then reversed so as to be guided to the refeed transport path. In an image forming apparatus including a second branch portion and a second pair of transport rollers provided in the switchback transport portion path, the second branch portion is provided so as to protrude into the transport path. And an elastic thin plate provided so as to protrude close to the entrance from the fixing device side of the conveyance path at a position lower than the top of the guide roller so as to be close to the guide roller. .
[0015]
The guide roller is divided into a plurality in the width direction of the transfer paper, each of which is rotatably attached to and supported by an attachment member lower than the guide roller formed on the guide plate, and the tip of the elastic thin plate Is characterized in that it is formed in a concavo-convex shape so as to be close to each of the guide roller and the mounting member.
[0016]
Further, the elastic thin plate and the member to which the elastic thin plate is attached are characterized in that both have a linear expansion coefficient substantially the same material.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0018]
FIG. 1 is a longitudinal side view of a main portion showing an embodiment of an image forming apparatus of the present invention, and FIG. 2 is an enlarged longitudinal side view showing a transfer paper entering and conveying state at the transfer paper reversing branching portion. FIG. 3 is an enlarged longitudinal side view showing the reverse conveyance state.
[0019]
The paper feed roller 1 extracts the uppermost paper of the transfer paper 3 loaded on the paper feed tray 2, separates the multi-feed paper by friction with the friction pad 4, and conveys it to the registration roller pair 6 through the guide roller 5. Then, the front end is brought into contact with the registration roller pair 6 to correct the oblique feeding.
[0020]
In parallel with this, the image information formed is processed, and the photosensitive member 8 by the charging roller 7 is ready for writing exposure by the writing light 9 according to the image information. The registration roller pair 6 is driven at a timing matching with the image formed by exposing the transfer sheet 3 to resume the transfer paper 3.
[0021]
The electrostatic latent image formed by exposing the photoconductor 8 with the writing light 9 is developed by the developing roller 10 into a toner image, and the transfer paper 3 is transferred at a position where the transferred transfer paper 3 contacts the photoconductor 8. The toner image is transferred to the first surface of the transfer paper 3 by applying an electric field and pressure from the back surface of the transfer paper 11. The toner remaining on the surface of the photoconductor 8 after the transfer is removed by the cleaning blade 12.
[0022]
The transfer paper 3 onto which the toner image has been transferred is sent to a fixing device constituted by a fixing roller 13 that also serves as a first conveying roller pair and a pressure roller 14, and the toner image is fixed on the transfer paper 3 by heating and pressing.
[0023]
In the single-sided image forming mode in which an image is formed on only one side of the transfer paper 3, the branching claw 16 is indicated by a broken line in the downstream of the fixing device. The position shown is controlled by an electromagnetic solenoid (not shown), and the transfer paper 3 sent out from the fixing device is sent to the paper discharge roller pair 17 and conveyed so as to be discharged onto the paper discharge tray 18. The upper portion of the paper discharge tray 18 is closed by the placed scanner 19.
[0024]
In the double-sided image forming mode in which images are formed on both sides of the transfer paper 3, the branching claw 16 is controlled to the posture indicated by the solid line, and the transfer paper 3 sent out from the fixing device is transferred to the second branching portion that is the transfer paper reverse branching portion. To send.
[0025]
As shown in an enlarged view in FIGS. 2 and 3, the second branch portion is branched by the guide plates 20 a to 20 c so that the switchback transport path 21 side is bent at an obtuse angle toward the switch pack portion, and the sheet refeed transport is performed. A reversal branch portion of the modified T-junction in which the path 22 side branches at an acute angle is formed. Then, a guide roller 23 having a length approximately the maximum width of the transfer paper 3 is provided so as to protrude into the branch path from the guide plate 20a side where the transport path is branched at an obtuse angle, and the guide path is branched at an acute angle. An elastic thin plate 24 is attached and fixed to the guide plate 20b so as to project from the guide roller 23 toward the guide roller 23 and to close the entrance from the fixing device side of the conveyance path at a position lower than the top of the guide roller 23. The elastic thin plate 24 is preferably a PET film.
[0026]
The second branch portion configured as described above enters the switchback conveyance path 21 while the transfer sheet 3 fed out from the fixing device is bent so as to lift the elastic thin plate 24, and enters the switchback conveyance path 21. Enter in the direction of the switchback with the pair 25. The switchback conveyance path 21 opens to the upper portion of the paper discharge tray 18, and the reverse roller pair 25 sends the transfer paper 3 to the paper discharge tray 18 until the reverse sensor 26 detects the rear end of the transfer paper 3. The reversing roller pair 25 stops in a state where the rear end portion of the transfer paper 3 is held when the reverse sensor 26 detects the rear end of the transfer paper 3. At this time, the transfer paper 3 is stopped in a state where the rear end thereof passes between the guide roller 23 and the elastic thin plate 24. FIG. 2 shows the transfer paper conveyance state.
[0027]
Thereafter, the reversing roller pair 25 is reversed and the transfer paper 3 is conveyed so as to be pulled back from the switchback portion. The tip of the elastic thin plate 24 after the transfer paper 3 passes is returned from the bent state due to its elasticity, and is positioned lower than the guide roller 23 in the branch path. Then, it is lifted by the guide roller 23 and passes through the upper side of the elastic thin plate 24 and enters the refeed conveyance path 22. FIG. 3 shows this transfer paper conveyance state.
[0028]
Thereafter, the re-feed conveyance path 22 conveys the transfer paper 3 by the conveyance roller pairs 27, 28, 29 and the guide roller 30, and comes into contact with the registration roller pair 6 in a state in which the transfer paper 3 is reversed. .
[0029]
Thereafter, as described above, the transfer paper 3 is conveyed to form an image on the second surface. The transfer sheet 3 on which the image has been formed on the second surface is conveyed toward the discharge roller pair 17 by the branching claw 16 and discharged onto the discharge tray 18.
[0030]
Reference numeral 31 denotes a transport roller pair for transporting transfer paper from a lower paper feed tray (not shown).
[0031]
By configuring the second branch portion in this way, even if the reversing roller 25 sets the linear speed slightly higher than the fixing roller 13, the guide roller 23 protruding into the branch path prevents the image from rubbing. Can do. The branching claw 16 and the guide plate 20a are positioned so as not to touch the image surface of the transfer paper 3 even when the transfer paper 3 is in tension between the fixing roller 13, the guide roller 23, and the reverse roller 25.
[0032]
In the second branch portion, when the transfer paper 3 is reversed in the transport direction and the transfer paper 3 enters the refeed transport path 22 from the switchback transport path 21, it collides with the tip of the elastic thin plate 24 and jams. In order to prevent the occurrence of this, it is desirable that the gap between the guide roller 23 and the elastic thin plate 24 is small and stable.
[0033]
4 to 6 show modifications for stabilizing the gap between the guide roller 23 and the elastic thin plate 24 being small.
[0034]
In this modification, the guide roller 23 is divided into four in the width direction. Each guide roller 23 is configured to be rotatably supported on a rib 20d that is an attachment member formed integrally with the guide plate 20a. Each rib 20d is formed to be lower than the outer diameter of the guide roller 23 so as not to jump out onto the conveying surface. The opposing elastic thin plate 24 has a concavo-convex shape at the tip, the concave portion is opposed to the guide roller 23, the convex portion is opposed between the guide rollers 23, and the difference between the concave portion and the convex portion is the difference between the guide roller 23 and the guide roller 23. The gap between the ends of the elastic thin plate 24 is set to be uniform at each position so as to match the difference between the ribs 20d on both sides. This gap is set to be within 1 mm at the maximum, and even if the linear gap becomes 0 mm or less due to the overlap, the elastic thin plate 24 is pushed against the transfer paper 3 when the transfer paper 3 arrives from the fixing device side. The thickness of the elastic thin plate 24 and the attachment (sticking) position are set so as to be elastically deformed so as to lift up.
[0035]
In order to keep the relative relationship between the guide roller 23 and the elastic thin plate 24 stable, it is desirable that the amount of thermal deformation of the elastic thin plate 24 heated above the fixing device is small.
[0036]
FIG. 7 shows an embodiment for reducing the amount of thermal deformation of the elastic thin plate 24 in each of the embodiments.
[0037]
The elastic thin plate 24 is attached to the guide plate 20b by adhesion. The occurrence of thermal deformation is greatly affected by the difference in the thermal linear expansion coefficient between the guide plate 20b and the elastic thin plate 24. Therefore, the guide plate 20b and the elastic thin plate 24 are formed of a material having the smallest difference in the thermal linear expansion coefficient (the same). It is desirable. In this embodiment, the guide plate 20a and the elastic thin plate 24 are both formed using the same material PET (thermal expansion coefficient is about 3 × 10 ⁻⁵ mm / mm / ° C.).
[0038]
In the image forming apparatus configured as described above, the transfer paper 3 fed from the fixing roller 13 to the T-shaped reverse branching portion by the branching claw 17 enters the switchback transporting path 21 and is transported by the pair of reverse rollers 25. The guide roller 23 protrudes into the branching path at the second branching section where the transfer paper 3 in the switchback transporting path 21 enters the refeeding transporting path 22 by reversing the reversing roller pair 25. Since the elastic thin plate 24 is provided so as to protrude from the re-feed conveyance path 22 side toward the guide roller 23 at a position lower than the top of the guide roller 23,
Even when the reversing roller 20 has a faster conveying speed than the fixing roller 13 and the pressure roller 14 in the fixing device, the image surface of the transfer paper 3 can be prevented from rubbing against the guide plate, and the reversing roller 20 is reversibly conveyed. Since the leading edge of the transfer paper 3 is pushed up by the guide roller 23 and enters the refeed conveyance path 22 so as to move away from the elastic thin plate 24, a space-saving (longitudinal conveyance path) and low-cost and simple configuration ( By using a branching claw or an electromagnetic solenoid for the branching part of the switchback part, it can be reversed and conveyed without causing a jam.
[0039]
Further, a plurality of guide rollers 23 are provided in the width direction of the transfer paper 3, and ribs 20 d for supporting the guide rollers 23 are formed so as not to protrude from the guide rollers 23, and the tip of the elastic thin plate 24 is formed. By forming the concave-convex shape so as to be close to the guide roller 23, it is possible to cope with the large-size transfer paper 3, and the effect of reducing the occurrence of jam can be further improved.
[0040]
Furthermore, the elastic thin plate 24 and the guide plate 20b, which is a member to which the elastic thin plate 24 is attached, have substantially the same coefficient of thermal linear expansion, thereby preventing the occurrence of undulation due to the thermal deformation of the elastic thin plate 24 and the transfer paper. 3 can further increase the jam prevention effect.
[0041]
【The invention's effect】
As described above, according to the present invention, the second branching unit for transporting the transfer sheet fed to the reversing branching unit after being transported to the switchback transporting path so as to be reversed and guided to the refeeding transporting path. And a guide roller provided so as to protrude into the conveyance path, and a tip of the guide roller so as to close the entrance from the fixing device side of the conveyance path at a position lower than the top of the guide roller so as to be close to the guide roller Therefore, the image surface of the tensioned transfer paper is prevented from rubbing against the guide plate and the rib due to the difference in the transport speed of the pair of transport rollers provided with the elastic thin plate, and the tip of the inverted transfer paper is caught on the elastic thin plate. It is possible to prevent a jam from occurring in the switchback portion.
[0042]
Further, according to the present invention, the guide roller is divided into a plurality in the width direction of the transfer paper, and each of the guide rollers is rotatably attached to and supported by an attachment member lower than the guide roller formed on the guide plate. Since the leading end of the thin plate is formed in a concavo-convex shape so as to be close to each of the guide roller and the mounting member, it is possible to prevent rubbing and jamming even on a large transfer paper.
[0043]
Furthermore, according to the present invention, since the elastic thin plate and the member to which the elastic thin plate is attached are made of a material having substantially the same linear expansion coefficient, it is possible to prevent a jam from occurring due to undulation due to thermal deformation of the elastic thin plate. it can.
[Brief description of the drawings]
FIG. 1 is a longitudinal side view of a main part showing an embodiment of an image forming apparatus of the present invention.
2 is an enlarged vertical side view illustrating a transfer paper entering and conveying state at a transfer paper reversing branching portion in the image forming apparatus shown in FIG.
3 is an enlarged vertical side view of a transfer paper reversal conveyance state at a transfer paper reversing branching portion in the image forming apparatus shown in FIG. 1;
4 is an exploded perspective view of a guide plate and a guide roller showing a modification of the transfer paper reversing branching portion in the image forming apparatus shown in FIG.
5 is a side view showing a relationship between a guide roller and an elastic thin plate in the transfer paper reversing branching portion shown in FIG. 4;
6 is a top view showing a relationship between a guide roller and an elastic thin plate in the transfer paper reverse branching portion shown in FIG. 4. FIG.
FIG. 7 is a perspective view showing an attached state of the elastic thin plate to the guide plate in the image forming apparatus of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Paper feed roller 2 Paper feed tray 3 Transfer paper 8 Photoconductor 13 Fixing roller 14 Pressure roller 16 Branching claw 17 Paper discharge roller pair 20a-20c Guide plate 21 Switchback conveyance path 22 Re-feed conveyance path 23 Guide roller 24 Elasticity Thin plate 25 reverse roller

Claims (3)

A first branching portion that branches so that the transfer paper on which an image is formed on the first surface is discharged to the discharge tray or conveyed to the reversing branching portion, and a first transport located upstream of the first branching portion And a second branch for conveying the transfer sheet fed from the first branching unit to the reversing branching unit after being transported to the switchback transporting path and then reversed and guided to the refeeding transporting path. An image forming apparatus including a second transport roller pair provided in the switchback transport path,
The second branching portion protrudes so as to block the entrance from the fixing device side of the conveying path at a position lower than the top of the guide roller, and a guide roller provided so as to protrude into the conveying path. An image forming apparatus comprising an elastic thin plate provided so as to be close to a guide roller. The guide roller is divided into a plurality in the width direction of the transfer paper, each is rotatably attached to and supported by an attachment member lower than the guide roller formed on the guide plate, and the tip of the elastic thin plate is The image forming apparatus according to claim 1, wherein the image forming apparatus is formed in a concavo-convex shape so as to be close to each of the guide roller and the attachment member. 3. The image forming apparatus according to claim 1, wherein the elastic thin plate and the member to which the elastic thin plate is attached are made of a material having a linear expansion coefficient that is substantially the same.

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