JP2008203309A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus with printing quality improved by applying necessary tension of an image forming part in accordance with a web. <P>SOLUTION: A first conveying means is a pair of web conveying tractors equipped with pin members which can be engaged in feed holes provided at both ends of the web, and a second conveying means is a web suction conveying belt provided to be opposed to the surface on an opposite side to the image forming surface of the web. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image on a conveyed web.

  In an image forming apparatus that forms an image on a web, the web is transported by engaging a pin member of a web transport tractor mounted on the image forming apparatus with a web feed hole and driving the web transport tractor.

  However, when a web having feed holes is used, it is necessary to cut both ends of the web having feed holes after printing, and the work is complicated.

  For this reason, there has been put to practical use an apparatus that uses a web without a feed hole and carries the web by a conveyance roller instead of the web conveyance tractor. Furthermore, in order to meet the diversifying needs of customers, an image forming apparatus capable of using both a web having a feed hole and a web having no feed hole has been put into practical use.

  Since the web having the feed holes is transported by the web transport tractor and the web having no feed holes is transported by the transport rollers, both mechanisms are mounted on one image forming apparatus. Here, when a web having no feed hole is transported, if the transport roller is used on the downstream side of the image forming unit, the image may be disturbed. That is, when an image is formed using an electrophotographic process, the image on the web after passing through the image forming unit is in an unfixed state. Therefore, when the transport roller is in contact with the unfixed image, the image can be easily obtained. It will be disturbed.

  Therefore, in the above case, a web suction / conveying belt that sucks and conveys the surface of the web opposite to the image forming surface is used.

  3 and 4 show a conventional example. A movable buffer 5 is provided between the image forming unit 1 and the fixing unit 2, and the movable buffer 5 is pressed against the web 3 by a torsion coil spring 6, and the web length between the image forming unit 1 and the fixing unit 2 is adjusted. The position is changed accordingly.

  Here, a case where the web conveyance of the fixing unit 2 is performed by the heating roller 7 and the pressure roller 8 is shown. On the other hand, the conveying means of the web 3 of the image forming unit 1 is different between a web having a feed hole and a web having no feed hole.

  In the case of a web having a feed hole, web transport tractors 4a and 4b are arranged at the upstream and downstream portions of the image forming unit 1, and the pin members of the tractors 4a and 4b are engaged with the web feed hole, and the tractor is driven. Conveying.

  In the case of a web having no feed hole, as shown in FIG. 4, web transport rollers 9a and 9b are provided upstream of the image forming unit 1, and the driven roller 9b is pressed against the drive roller 9a by a spring (not shown). Web transport.

  Further, in the downstream part of the image forming unit 1, a plurality of holes are opened in two shafts sandwiching a box having static pressure by a suction blower (not shown) so as not to contact the image surface of the web 3. A web suction / conveying belt 10 is used which hangs a belt and sucks and conveys the web 3 at the hole portion.

  Here, the drive shafts of the tractor 4a and the conveying roller 9a, and the tractor 4b and the suction belt 10 are coaxial, and each drive shaft is connected to a web feed motor (not shown) by a timing belt (not shown). .

JP 2002-293461 A JP 2001-335206 A JP-A-10-171189

  In the above conventional example, two pairs of web conveyance tractors are provided in the upstream and downstream portions of the image forming unit in order to convey a web having feed holes, and upstream of the image forming unit in order to convey a web having no feed holes. Since the conveyance roller is provided in the part and the web suction conveyance belt is provided in the downstream part, the apparatus configuration is complicated.

  Moreover, since the web conveyance tractor and the conveyance roller or the web suction conveyance belt are coaxially mounted in order to suppress the expansion of the apparatus size, the tractor is arranged on the left and right in the web width direction, and the conveyance roller and the suction belt are It is arranged between the left and right tractors.

  When using the narrow web, the tractor is brought close to the width of the web, so when using the narrowest web of the equipment specification, the transport roller between them is not interfered when the tractor is brought closest. And the suction belt needs to be reduced in size in the width direction.

  In the case of a web having feed holes, the web feed holes are engaged with the pin members of the tractor before and after the image forming portion, and the web tension therebetween is substantially constant regardless of the web. However, in the case of a thick web or a wide web, the rigidity is strong, and the web swells in the image forming unit, and as a result, the web of the image forming unit may rub against the photosensitive member, thereby causing a decrease in print quality.

  This is because when the web is moved away from or in contact with the photoconductor at the start of printing or when printing is stopped, the relative linear velocity of the web and the photoconductor should be separated in the range that does not change during continuous printing. Since the web is swollen at the part, the web linear speed does not reach the linear speed during continuous printing at the start of printing, or the web linear speed is lower than the linear speed during continuous printing when printing is stopped. Since the web comes into contact with the photoconductor in a state where the web is in contact, the image on the photoconductor or the image on the web that has already been transferred is rubbed, resulting in a decrease in print quality.

  In anticipation of this, when the web tension between the tractors before and after the image forming unit is increased, there is a conflicting problem such that the feed hole portion is deformed (hole galling) in the thin web. In addition, the web tension of the image forming unit is almost constant by engaging the web feed hole with the pin members of the front and rear tractors, but when viewed in detail, due to dimensional errors in the parts and assembly of the front and rear tractors, The intervals between the pin members are slightly different.

  For this reason, the tension of the image forming portion of the web varies with the pitch (usually 1/2 inch) of the pin member of the tractor. The relative position of the web and the photosensitive member also periodically changes with the pin pitch of the tractor, and as a result, the blur of the pin pitch of the tractor appears in the image on the web. Customers' demand for print quality is increasing, and if this phenomenon is suppressed by improving the accuracy of parts and assembly, the apparatus becomes very expensive.

  Considering the case of transporting a web without feed holes, the suction belt basically slips with a slightly larger feed amount than the transport rollers in order to apply tension to the web in the image forming unit. The tension of the web is determined by the conveying force of the suction belt. However, since the width of the suction belt is smaller than the width of the web to be conveyed, the conveying force is insufficient, and the web tension between the conveying roller and the suction belt is necessary. In some cases, the value cannot be secured, and as a result, the web of the image forming unit rubs against the photoconductor to cause a decrease in print quality.

  In order to solve this problem, if the suction force of the suction belt is increased in order to secure the conveyance force, the paper will be deformed at the suction point in the case of a thin web, resulting in poor print quality and contact of the fixing unit with the preheating plate. There is a conflicting problem such as a defect causing a fixing failure.

  Furthermore, in order to secure the web tension of the image forming unit, the suction belt has a slightly larger feed amount than the conveying roller, so that the distance that the web is fed during the printing stop operation and the acceleration distance of the web at the start of printing When the web is returned, the web length between the conveying roller and the suction belt (image forming unit) becomes longer, causing the web to loosen. As a result, the web rubs against the photoconductor as described above. May be reduced.

  Further, if the apparatus has a means for transporting a web having no feed hole, the web having the feed hole can be transported by the same mechanism, however, the transport roller and the suction belt slip. Since there is a possibility, the reliability of conveyance is inferior as compared with a method in which a pin member is engaged with a web feed hole and transported, and the advantages of a web having a feed hole are not utilized.

  The present invention provides an image forming unit that forms an image on a web to be transported, a first web transport unit provided upstream in the web transport direction with respect to the image forming unit, and a web transport direction with respect to the image forming unit. In the image forming apparatus including the second web conveying unit provided in the downstream portion, the first conveying unit includes a pair of web conveying tractors including pin members that can be engaged with feed holes provided at both ends of the web. The second conveying means is a web suction / conveying belt provided opposite to the surface of the web opposite to the image forming surface.

  According to the present invention, in an image forming apparatus that conveys a web, it is possible to give a necessary web tension in an image forming unit according to the web, and as a result, it is possible to provide an image forming apparatus with improved print quality. . Moreover, the conveyance reliability of the web having the feed holes can be maintained, and the configuration can be simplified to provide an inexpensive apparatus.

  An embodiment of the image forming apparatus of the present invention will be described with reference to the drawings.

  FIG. 1 and FIG. 2 are simplified views showing only the web conveyance mechanism disposed in the upstream and downstream portions of the image forming section of the image forming apparatus.

  In FIG. 1, the web transport tractor 4a and the web transport roller 9a are disposed on the same drive shaft, and the drive shaft of the web suction transport belt 10 and the drive shaft of the web transport tractor 4a are timing belts (not shown). It is connected to a rotary drive shaft of a web feed motor (not shown), and performs forward / reverse operation in conjunction with it.

  Usually, in the case of an image forming apparatus that uses a web having a feed hole, the image forming unit has a pair of tractors in the upstream and downstream portions in the web transport direction. The web conveyance tractor 4a is installed only in the upstream portion, and the web suction conveyance belt 10 is used in the downstream portion in the web conveyance direction with respect to the image forming unit.

  The suction belt 10 uses the same mechanism as used when a web having no feed holes is used. Therefore, the tractor disposed in the rear stage of the image forming unit in the prior art is not essential.

  Since the feed hole of the web 3 is engaged with the pin member of the tractor 4a in front of the image forming unit, the web 3 does not slip, and the carry amount of the web 3 is determined by the carry amount by the tractor 4a. It does not reduce the reliability of conveyance, which is an advantage of the web having.

  FIG. 1 shows an example in which the suction belt 10 is enlarged using a vacant space by eliminating the tractor at the rear stage of the image forming unit in the case of an image forming apparatus for both webs with and without feed holes. Yes.

  When a narrow web is used, the shutter member 11 for changing the suction width moves in accordance with the web width inside the suction belt mechanism, and the actual suction width is adjusted. When a wide web is used, the shutter member 11 moves in the direction in which it expands. Various moving methods such as a method of connecting the shutter member 11 and a drive motor (not shown) with a belt (not shown) are conceivable.

  The conveyance force for feeding the web of the suction belt is determined by the suction force and the suction area. Among these, the suction force is uniform in a sealed space, so by changing the suction area according to the web width, In the case of a wide web, a larger conveying force can be given than a narrow web. However, the suction force is a value that does not cause deformation even in the case of a thin web. This value is determined experimentally.

  When the tractor 4b and the suction belt 10 are provided coaxially on the rear stage of the image forming unit as in the conventional example, the suction belt 10 between the left and right tractors must be reduced in size, and the wide web can be reduced. There is a conflicting problem that the web deforms when the suction force is increased in order to ensure the conveyance force due to insufficient conveyance force, but the present invention provides the necessary conveyance force according to the web width without deforming the web. Is possible.

  As a result, the web tension of the image forming unit can be given a necessary tension according to the web width, and the deterioration of the print quality caused by the swell of the web being rubbed against the photoreceptor can be suppressed.

  Here, FIG. 1 shows a configuration in which the shutter member 11 is moved inside the suction belt. For example, a plurality of narrow suction belts 10 are arranged, and the number of suction belts 10 used is changed according to the web width. However, the same effect can be exhibited. Although there is a difference between the tractor 4a and the transport rolls 9a and 9b as the transport means in the front stage of the image forming unit, the transport force is applied to the web in the subsequent stage of the image forming unit regardless of whether the web with or without feed holes is used. By using a suction belt that can be changed accordingly, the print quality can be improved in the same manner.

  FIG. 2 shows the case of a printing apparatus that can use only a web having feed holes. The front stage of the image forming unit uses a tractor to maintain the conveyance reliability of the web having the feed holes, and the rear side of the image forming unit uses a suction belt. In order to secure the web tension of the image forming unit, the suction belt is set to have a slightly larger feed amount than the tractor, and therefore the web is always pulled in the traveling direction.

  Accordingly, the web tension of the image forming unit is always constant, and it is possible to suppress image blurring caused by fluctuations in the tension of the image forming unit due to an error in the pin pitch of the tractor before and after the image forming unit. The same applies to the case of using a web having feed holes in a dual-purpose machine with or without feed holes.

  Further, in the case of a printing apparatus that can use only a web having a feed hole, if the conveyance force of the suction belt can be changed according to the web as in FIG. 1, the tension necessary for the web in the image forming unit. Needless to say, the print quality can be improved as described above.

  Furthermore, the present invention cuts the suction force of the suction belt 10 during the operation of returning the web 3 during the printing operation. Then, the conveyance force of the suction belt 10 is lost, the web 3 is returned by the tractor 4a or the conveyance rollers 9a and 9b at the front stage of the image forming unit, and the reaction force of the buffer unit is loaded at the rear stage of the image forming unit and the web 3 is always tensioned. It is pulled in the state. Accordingly, the web slack of the image forming unit during the returning operation, which has occurred due to the difference in the feeding amount of the suction belt and the front stage of the image forming unit in the prior art, is reduced, and as a result, the web is suppressed from rubbing against the photoconductor and the print quality is improved. improves.

  Here, as an example of cutting the suction force as a means for reducing the feeding amount of the suction belt during the return operation, the suction force or suction area is reduced so that the web is not substantially conveyed, or the suction belt is Various means are conceivable, such as providing a clutch mechanism in the connection path between the drive shaft and the paper feed motor and disconnecting the clutch mechanism so as not to drive the suction belt during the return operation.

It is a schematic diagram of the conveyance mechanism of the printing apparatus which shows one Example of this invention. It is a schematic diagram of the conveyance mechanism of the printing apparatus which shows one Example of this invention. It is a schematic block diagram of the printing apparatus which shows one Example of a prior art. It is a schematic diagram of the conveyance mechanism of the printing apparatus which shows one Example of a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image formation part 2 Fixing part 3 Web 4a, 4b Web conveyance tractor 5 Movable buffer 6 Torsion coil spring 7 Heating roller 8 Pressure roller 9a Web conveyance drive roller 9b Web conveyance driven roller 10 Web suction conveyance belt 11 Shutter member

Claims (2)

  An image forming unit that forms an image on the web to be conveyed, a first web conveying unit provided upstream in the web conveying direction with respect to the image forming unit, and a downstream unit in the web conveying direction with respect to the image forming unit In the image forming apparatus including the second web transport unit, the first transport unit is a pair of web transport tractors including pin members that can be engaged with feed holes provided at both ends of the web. 2. The image forming apparatus according to claim 2, wherein the second conveying unit is a web suction conveying belt provided to face a surface of the web opposite to the image forming surface.   When the third conveying means is provided between the pair of web conveying tractors and image formation is performed on the web having the feeding hole, the web is conveyed by the web conveying tractor and the web suction conveying belt, The image forming apparatus according to claim 1, wherein when image formation is performed on a non-web, the web is conveyed by a third conveyance unit and the web suction conveyance belt.

Images