JP3903672B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a recording material conveyance technique in an image forming apparatus that forms an image by an electrophotographic method, and more particularly to a recording material conveyance technique at a transfer position where a toner image is transferred to a recording material.
[0002]
[Prior art]
(1) A recording material is conveyed to a transfer position in order to transfer a toner image from an image carrier such as a photoconductor, but a guide member for guiding the recording material to the transfer position in order to prevent image deterioration due to transfer. Needs to be set with high accuracy for the image carrier.
[0003]
In the prior art, the required setting accuracy of the guide member has been achieved by increasing the setting accuracy of the guide member and increasing the accuracy of the mounting position of the guide member with respect to the image forming apparatus main body. .
[0004]
(2) Various recording materials tend to be used in terms of type, size, and the like, and there is a tendency that accuracy is required with respect to the position of an image formed on the recording material as well as image quality.
[0005]
In order to form an image at the correct position on the recording material, it is necessary to convey the recording material to the transfer position in precise synchronization with the image formation on the image carrier. The recording material is conveyed by a registration roller provided upstream.
[0006]
However, it has been found that it is difficult to form an image with the required positional accuracy on various recording materials as described above depending on the synchronous conveyance of the registration rollers. For this purpose, the present applicant provides a sensor for detecting the leading edge of the recording material downstream of the registration roller in Japanese Patent Application No. 11-88573, and uses the detection signal of the sensor to synchronize the image formation and the conveyance of the recording material. And a pre-transfer conveyance roller is proposed between the registration roller and the transfer position. The pre-transfer conveyance roller is provided to stabilize the conveyance of the recording material between the registration roller and the transfer position which are lengthened by the installation of the sensor.
[0007]
[Problems to be solved by the invention]
(1) Recently, with the widespread use of digital image forming apparatuses, as the field of use of image forming apparatuses expands, the types of recording materials used are diversified in terms of types and sizes, and the demand for image quality has become stricter. ing. For this reason, it has become difficult to meet the above requirements only by improving the accuracy of the parts of the guide member and its mounting accuracy as in the prior art.
[0008]
That is, depending on the prior art, the distance between the surface of the guide member and the image carrier is limited to an accuracy of about ± 0.2 mm with respect to the reference value, but this makes it difficult to satisfy the above requirement. It is coming.
[0009]
Accordingly, an object of the first aspect of the present invention is to provide an image forming apparatus capable of forming an image with high positional accuracy on various recording materials.
[0012]
[Means for Solving the Problems]
The object of the present invention is achieved by the invention described below.
[0013]
(1) an image carrier,
Transfer means for transferring a toner image formed on the image carrier to a recording material;
Conveying means for conveying a recording material to a transfer position formed by the image carrier and the transfer means; and
In the image forming apparatus having guide means for guiding the recording material conveyed by the conveyance means to the transfer position,
The guide means includes a first guide member that introduces a recording material to the transfer position, a second guide member that guides the introduced recording material along an image carrying surface of the image carrier, and the first guide member. the positional relationship between the second guide members possess an adjusting member for adjusting a,
The adjustment member is provided at a plurality of locations in the width direction of the conveyance path,
The first guide member and the second guide member are fixed to each other in a part in the width direction of the transport path, and are joined by the adjustment member in another part in the width direction of the transport path. Image forming apparatus.
[0014]
(2) The image forming apparatus according to (1), wherein the adjustment member is a screw .
[0015]
(3) The first guide member and the second guide member are formed of plate-like members, and have a third guide member made of a rotating body that guides the recording material along the image carrier ( 1) or an image forming apparatus according to item (2).
[0016]
(4) The image forming apparatus according to any one of (1) to (3), wherein the guide unit is provided on a frame body that supports the transfer unit .
[0017]
(5) The image forming apparatus according to (4 ), wherein the guide unit is rotatably supported by the frame .
[0018]
(6) In the item (4) , the frame supporting the transfer means is provided with a separation pole for discharging the recording material onto which the toner image has been transferred and separating the recording material from the image carrier. The image forming apparatus described.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a configuration of an image forming apparatus according to an embodiment and an embodiment of the present invention.
[0029]
In FIG. 1, documents are placed on a document feeder 11 of an automatic document feeder 1 with the image surface facing upward, sent out one by one by the operation of a delivery roller 12, and temporarily stopped by a registration roller 13 and the leading edge is stopped. After the adjustment, the material is conveyed to the conveyance drum 14. The image reading unit 2 reads the image surface while the document is integrally rotated counterclockwise along the peripheral surface of the conveyance drum 14, and then branches from the drum surface at a substantially half-turned position. 15 is discharged. The automatic document feeder 1 also has a transport function for duplex scanning in addition to the transport function for single-sided scanning, but this operation is omitted.
[0030]
In the image reading unit 2, the first mirror unit 23 including the light source 23 a and the mirror 23 b reads and sequentially illuminates the passing document at a position directly below the transport drum 14, and is orthogonal to the moving direction of the document. Are reflected by a second mirror unit 24 including a mirror 24a and a mirror 24b disposed on the image sensor 25, and are imaged on a line-shaped image sensor 26 through an imaging lens 25 to be image information. Further, a function is also provided in which a document is placed on a stationary document table 27 and the mirror units 23 and 24 move and read.
[0031]
The image information of the document image read by the image reading unit 2 is subjected to image processing by the image processing means and temporarily stored in the memory as image information.
[0032]
When the image forming unit 3 using the electrophotographic process is activated, stored image information is read out, or screen information transmitted from a personal computer or the like is input to the image writing unit 33, and a laser light emitter (not shown) Then, the laser beam modulated according to the image information performs main scanning exposure on the photosensitive drum 31 as an image carrier by the rotation of the polygon mirror. Then, the main scanning exposure in the axial direction of the photosensitive drum 31 and the sub scanning by the rotation of the photosensitive drum 31 are performed on the photosensitive drum 31 to which the charging potential is applied in advance by the charger 32, and the photosensitive layer is subjected to image information. An electrostatic latent image is formed. The electrostatic latent image is reversely developed with a developer by a developing device 40 as developing means to form a toner image. This developer is, for example, a two-component developer in which a magnetic material having a particle size of about 20 μm is used as a carrier and a resin toner having a particle size of several μm is mixed. And develop. In parallel with this, the recording material is fed from the manual paper feed unit 19 as the recording material supply means or the paper feed tray 7 containing the recording material. The paper feed tray 7 has, for example, three stages 7A, 7B, and 7C, and any one of the paper feed rollers 51A, 51B, and 51C of the transport unit 5 operates to carry out the recording material, and the transport roller 55 and the registration roller The toner is fed to the pair 56 and the pre-transfer conveying roller pair 39 and is fed to the photosensitive drum 31 in synchronization with the toner image on the photosensitive drum 31. As the recording material, paper, a transparent film sheet, or the like is used.
[0033]
The toner image on the photosensitive drum 31 as an image carrier for carrying a toner image is applied with a voltage of opposite polarity by a transfer pole 35 as a transfer means, transferred to a recording material and transferred, and a recording in which the toner image is transferred The material is neutralized at a separation electrode 36 as a separation means, separated from the photosensitive drum 31, conveyed to a fixing device 38 as a fixing means via a conveyance belt, and fixed by fixing a toner by pressure heating of a pair of heat rollers. Then, the paper is discharged from the fixing paper discharge roller 61 of the discharge unit 6 and discharged to the paper discharge tray 64 to form an image based on the image information.
[0034]
On the other hand, the photosensitive drum 31 from which the recording material has been separated is configured such that after the residual potential is removed, the residual toner is removed and cleaned by the cleaning device 37, and the image forming device is put into the next image forming process. The overall control is performed by the control means.
[0035]
Next, the transport unit 5 that transports the recording material to the transfer position TR will be described with reference to FIGS. 2 shows a part for conveying the recording material to the transfer position TR of the conveyance part 5, FIG. 3 shows a part of the conveyance part 5 near the transfer position TR, and FIG. 4 is a plan view of the transfer unit 200. 5 is a view of parts assembled from the guide plates 105, 106, and 107 as viewed from below in FIGS.
[0036]
The transport unit 5 transports the recording material supplied from the paper feed cassette 7 to form a loop immediately upstream of the registration roller pair 56 serving as transport means, a pair of registration rollers 56 and a pair of transport rollers before transfer. 39 is provided to transport the recording material P to the transfer position TR.
[0037]
Reference numerals 101, 102, and 103 are guide plates for the recording material, and the guide plate 101 is inclined to form a loop. Further, the guide plate 103 has a recess, and a sensor S for detecting the side edge of the recording material is provided in the recess. Between the pre-transfer conveyance roller pair 39 and the transfer position TR, guide plates 105 (first guide member), 106 (first guide member) and 107 (second guide member) are provided as guide members.
[0038]
The transfer electrode 35 and the separation electrode 36 are provided in the transfer separation unit 200, and the transfer separation unit 200 is provided with a guide rib 202. Guide plates 105 and 106 as first guide members introduce the leading end portion of the recording material conveyed by the pre-transfer conveyance roller pair 39 to the transfer position TR. The guide plate 107 as the second guide member has a guide surface 107 b that guides the recording material along the peripheral surface of the photosensitive drum 31. The transfer separation unit 200 is accurately positioned at a predetermined position with respect to the photosensitive drum 31 by a known positioning member (not shown).
[0039]
The recording material is supplied to the registration roller pair 56 by the conveying roller 55, temporarily stops at the registration roller pair 56, and a loop is formed at the leading end. The registration roller pair 56 is rotated by the image forming signal and the recording material is sent to the pre-transfer conveyance roller pair 39. A sensor S detects a side edge of the recording material between the registration roller pair 56 and the pre-transfer conveying roller pair 39. The signal of the sensor S that detects the side edge of the recording material is used to control the writing start time in the main scanning direction of the image writing unit 33 that performs exposure on the photosensitive member 3. As described above, in order to control the image formation start timing of the image writing unit 33 based on the output of the sensor S, the distance between the transfer position TR and the sensor S is set larger than the distance between the exposure position and the transfer position. ing. The distance between the exposure position and the transfer position is a distance on the circumferential surface of the photosensitive drum 31.
[0040]
The recording material conveyed by the registration roller pair 56 or the pre-transfer conveyance pair roller 39 is guided by the bent leading end portion 107 b of the guide plate 107 and the roller 108 and moves along the peripheral surface of the photosensitive drum 31. After the toner image is transferred by the electrostatic force due to the charging, the separation electrode 36 is separated from the photosensitive drum 31 by the charge eliminating action. A guide rib 202 guides the recording material at the separation pole 36.
[0041]
Guide plates 105, 106, and 107 for guiding the recording material conveyed by the pre-transfer conveyance roller pair 39 to the transfer position TR are provided on the frame body 201 of the transfer separation unit 200. That is, as shown in FIG. 4B, the guide plate 106 is provided at both ends thereof, and the bent portion 106 a is supported by the frame body 201 by the shaft 110. As shown in FIG. 4B, the guide plate 106 is urged clockwise by a compression spring 111, and is held at a fixed position by a stopper 201a provided on the frame body 201. The upper limit of the guide surface (the upper limit in FIG. 3). ) Is held at a fixed position. FIG. 4B is a partial cross-sectional view taken along line XX in FIG.
[0042]
The guide plate 105 is fixed to the guide plate 106 with a screw 123 at an interval for passing the recording material (see FIG. 3). The guide plate 106 rotatably supports two rollers 108 serving as third guide members for guiding the recording material.
[0043]
A guide plate 107 is further fixed and supported on the guide plate 106. The support structure of the guide plate 107 by the guide plate 106 is shown in FIG. The bent portion 107 c of the guide plate 107 is brought into close contact with the two bent portions 106 c formed on the guide plate 106 and is fixed by the two screws 122. The three bent portions 106b of the guide plate 106 are coupled to the bent portion 107c of the guide plate 107 with three screws 121 as adjustment members. Since a free hole is formed in the bent portion 106 b and a screw hole is formed in the bent 107 c, the distance between the bent 106 b and the bent 107 c is adjusted by turning the screw 121. Therefore, the guide plate 106 and the guide plate 107 are fixedly coupled to each other at the position of the bent portion 106c, but the mutual positional relationship is coupled to be adjustable at the positions of the three bent portions 106b. Reference numeral 1211 denotes a retaining ring for preventing the screw 121 from coming off.
[0044]
As apparent from FIG. 3, the recording material is moved along the front end portion of the guide plate 107, that is, along the photosensitive drum 31 by adjusting the guide plate 107 with respect to the guide plate 106 to which the rotation fulcrum is fixed. A minute gap between the bent leading end portion 107b to be guided and the surface of the photosensitive drum 31 is adjusted. In particular, since the distance from the photosensitive drum 31 is adjusted at both ends of the guide plate 107, appropriate adjustment can be performed.
[0045]
With the above-described adjusting mechanism, the accuracy between the surface of the photosensitive drum 31 and the guide surface of the front end portion 107b of the guide plate 107 is within an error range of ± 0.05 mm with respect to a reference value (for example, 0.5 mm). It becomes possible to set with.
[0046]
In the present embodiment, two rollers 108 face the conveyance path from the two windows 107a provided on the guide plate 107. With this configuration, the recording material can be conveyed more smoothly at the transfer position. Further, an elastic guide plate 120 made of resin is provided on the recording material entrance side of the guide plate 106.
[0047]
Next, the configuration of the pre-transfer conveyance roller pair 39 will be described.
As shown in FIG. 2, in this embodiment, the registration roller pair 56 is driven by a motor M1, and the pre-transfer conveyance roller pair 39 is driven by a motor M2. In any case, the lower rollers 561 and 391 are drive rollers, and the upper rollers 562 and 392 are driven rollers.
[0048]
As shown in FIG. 6, the lower roller 561 and the upper roller 562 of the registration roller pair 56 are one roller formed slightly shorter than the width of the conveyance path (corresponding to the maximum size width of the recording material). In contrast, the upper roller 562 includes three rollers. The lower roller 391 and the upper roller 392 constituting the pre-transfer conveying roller pair 39 are configured by one short roller disposed in the center of the conveying path.
[0049]
The lower roller 561 of the registration roller pair 56 is made of rubber (EPDM), and the upper roller 562 is made of resin (POM: polyacetal resin). The lower roller 391 of the pre-transfer conveying roller pair 39 is made of resin (POM), and the upper roller 392 is made of rubber (EPDM).
[0050]
It is desirable that the registration roller pair 56 has a reliable conveyance performance for the recording material. For this purpose, the lower roller 561 as a driving roller is formed of rubber. On the other hand, it is desirable for the pre-transfer conveyance roller pair 39 to maintain a stable conveyance speed, that is, a linear velocity over a long period of time. For this purpose, a resin roller such as POM, which is a material that hardly wears, is used for the lower roller 391 that is a driving roller. Rubber is used for the upper roller 392 which is a driven roller of the pre-transfer conveying roller pair 39.
[0051]
As a material that constitutes the lower roller 391 that is a driving roller of the pre-transfer conveyance roller pair 39, that is, a material that is hard to wear, has little variation in its radial dimension over a long period of time, and maintains a conveyance speed with very little variation, In addition to the resin, ceramic, metal, and the like can be given.
[0052]
In order to accurately synchronize the conveyance of the recording material by the pre-transfer conveyance roller pair 39 with respect to the photosensitive drum 31, the lower roller 391 is formed by precision machining so that the radius thereof falls within an error range of 0.5%. It is desirable. If the error exceeds 0.5%, there may occur a transfer deviation, a change in image vertical magnification (magnification in the recording material conveyance direction), or the like. In particular, it is desirable to form so as to fall within an error range of 0.15%.
[0053]
As another method of synchronizing the photosensitive drum 31 by finely adjusting the transport speed of the pre-transfer transport roller pair 39, there is a method of using a step motor as the drive motor M2 and adjusting the frequency of the motor drive clock. is there. It is also possible to use both precision machining of the radius of the lower roller 391 that is the driving roller and adjustment of the frequency of the driving clock of the motor M2.
[0054]
In the present embodiment, once the conveyance speed of the pre-transfer conveyance roller pair 39 is adjusted, the adjusted conveyance speed is maintained for a long period of time.
[0055]
In the present embodiment, the rotational speed of the photosensitive drum 31 may be changed. That is, in the present embodiment, the pixel density of the recorded image can be switched between 400 dpi (the number of dots per 25.4 mm, the same applies hereinafter) and 600 dpi. Along with this pixel density conversion, the moving speed of the photosensitive drum 31 is changed. The rotational speed of the lower roller 561 that is the driving roller of the registration roller pair 56 and the rotational speed of the lower roller 391 that is the driving roller of the pre-transfer conveying roller pair 39 are also changed in accordance with the change in the rotational speed of the photosensitive drum 31. Is done. Further, double-sided image formation has a problem due to the formation of a back side image on a recording material that has been shrunk by being heated in the fixing unit 38 when the front side image is formed. Due to this thermal contraction, when the back side image is formed, the moving speed of the photosensitive drum 31 corresponding to the contraction of the recording material is changed, and the conveyance speed of the recording material is changed corresponding to the change. Accordingly, in the double-sided image formation, the driving speed of the lower roller 391 of the pre-transfer conveying roller pair 39 is changed together with the change of the moving speed of the photosensitive drum 31 in the back surface image forming process.
[0056]
Furthermore, in the present embodiment, the lower roller 561 of the registration roller pair 56 and the lower roller 391 of the pre-transfer conveying roller pair 39 are driven independently by the motors M1 and M2, so that the registration roller pair 56 is used for a long time. For example, when the wear is caused by wear, it is possible to correct the fluctuation in the conveyance performance of the registration roller pair 56 by adjusting the rotation speed of the motor M1.
[0057]
【The invention's effect】
According to the first aspect of the present invention, the positional accuracy of the guide member that guides the recording material to the transfer position can be made extremely high, image quality deterioration due to transfer can be prevented, and a high-quality image can be formed. Become. In particular, the image quality is likely to deteriorate at the rear end of the recording material, but such a decrease in image quality at the rear end of the recording material is effectively prevented. Further, since the position of the guide member can be adjusted at each part in the conveyance path width direction, it is possible to cope with a partial image quality problem. Furthermore, since adjustment can be performed with a part of the guide member fixed, fine adjustment is possible.
[0058]
According to the second aspect of the present invention, the guide member can be finely adjusted by a simple adjustment operation.
[0061]
According to the third aspect of the invention, the recording material is guided more smoothly at the transfer position, and an image with high image quality can be formed.
[0062]
According to the invention of claim 4 , since the guide member can be attached and detached together with the transfer means, it becomes easy to eliminate a paper jam at the transfer position. Further, since the guide means is provided on the frame body whose position can be determined with high accuracy with respect to the image carrier, the position accuracy of the guide means before adjustment is relatively high, and the adjustment amount by the adjustment member is small.
[0063]
According to the fifth aspect of the present invention, since the guide member can be displaced by the rigidity of the recording material, the recording material is smoothly conveyed at the transfer position, and a high-quality image can be formed.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a portion of a conveyance unit that conveys a recording material to a transfer position.
FIG. 3 is a diagram illustrating a portion in the vicinity of a transfer position of a transport book.
FIG. 4 is a plan view of a transfer separation unit.
FIG. 5 is a view showing a state in which a guide plate is assembled.
FIG. 6 is a diagram illustrating a registration roller and a pre-transfer conveyance roller.
[Explanation of symbols]
31 Photosensitive drum 35 Transfer pole 36 Separation pole 39 Pre-transfer conveyance roller pair 56 Registration roller pair 101, 102, 103, 104, 105, 106, 107 Guide plate 391, 561 Lower roller M1, M2 Motor

Claims (6)

Image carrier,
Transfer means for transferring a toner image formed on the image carrier to a recording material;
Conveying means for conveying a recording material to a transfer position formed by the image carrier and the transfer means; and
In the image forming apparatus having guide means for guiding the recording material conveyed by the conveyance means to the transfer position,
The guide means includes a first guide member that introduces a recording material to the transfer position, a second guide member that guides the introduced recording material along an image carrying surface of the image carrier, and the first guide member. the positional relationship between the second guide members possess an adjusting member for adjusting a,
The adjustment member is provided at a plurality of locations in the width direction of the conveyance path,
The first guide member and the second guide member are fixed to each other in a part in the width direction of the transport path, and are joined by the adjustment member in another part in the width direction of the transport path. Image forming apparatus. The image forming apparatus according to claim 1, wherein the adjustment member is a screw . The first guide member and the second guide member are formed of plate-like members, and have a third guide member made of a rotating body that guides a recording material along the image carrier. The image forming apparatus according to claim 2. The image forming apparatus according to claim 1 , wherein the guide unit is provided on a frame that supports the transfer unit . The image forming apparatus according to claim 4 , wherein the guide unit is rotatably supported by the frame body . The image forming apparatus according to claim 4 , wherein a separation pole that neutralizes the recording material onto which the toner image is transferred and separates the recording material from the image carrier is provided on the frame that supports the transfer unit. .

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