JP2007322969A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of accurately aligning the image positions on both sides of a paper even for a high-speed machine. <P>SOLUTION: When forming an image on the front surface of the paper in double-sided printing, reference lines for correction 121 and 122 are formed on the front surface 20a of the paper. The reference lines 121 and 122 are detected by an image position detection means 101, and the detected information is fed back to correct the position of the image on the back surface of the paper, when forming the image on the back surface. During the detection by the image position detection means 101, paper convey speed is changed, to speed for detecting time lower than the normal paper conveying speed, whereby the detection accuracy is improved. When detection is finished, the conveying speed is restored to the normal paper conveying speed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a printer, a copier, and a facsimile machine, and more particularly to an image forming apparatus with improved image position accuracy on both sides of a sheet.

JP 2006-93841 A JP 2006-11285 A

  In recent years, image forming apparatuses such as copiers and printers have started to enter the printing industry due to progress in speeding up. In this industry, the majority of demand is for bookbinding and saddle stitching of printed materials, so printed materials require double-sided image formation on the front and back of the paper, and the image position accuracy on the front and back is higher than ever. Things are required.

  For example, in the case where the printed matter on which the image is formed is cut together, if the image positions on the front and back sides are misaligned, depending on the image, the margin may remain or the image may be missing. It will occur. In other words, it is necessary to match the image edges on the front and back. Further, when performing saddle stitching, it is necessary that the center lines of the images are aligned on the front and back.

  In view of this, the applicant of the present application disclosed in Patent Document 1 previously filed as a detection means for edge line, center line, and paper edge information formed simultaneously with the image formation of the first surface (front surface) during double-sided printing. The image forming apparatus is configured to match the image position and the center of the front and back by performing image formation after performing position correction and magnification correction by feeding back the information at the time of second surface (back surface) image formation. Proposed.

  Also, in Patent Document 2, a reference image for alignment is formed on the front and back surfaces of a sheet, the reference image is read by an image reading unit, and the image position and the back surface of the front surface are read based on the obtained read information. An image forming apparatus adapted to match the image position is disclosed.

  However, since the paper conveyance speed has increased due to the recent increase in the speed of image forming apparatuses, depending on the performance of the detection means / reading means, it is possible to detect image position information such as a reference line with high accuracy. There is a concern that the accuracy of the image position on both sides of the paper required by the user cannot be achieved.

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems in a conventional image forming apparatus and to provide an image forming apparatus capable of aligning image positions on both sides of a sheet with high accuracy even with a high speed machine.

  An object of the present invention is to provide an image forming apparatus capable of forming an image on both sides of a sheet according to the present invention, comprising a detection unit that detects a correction reference line formed on the first side of the sheet, and the detection unit detects the image. In the image forming apparatus that corrects the position of the image formed on the second surface of the sheet based on the position information of the correction reference line, when the correction reference line is detected by the detection unit, the sheet conveyance speed is detected at a predetermined time. It is solved by changing to the conveyance speed.

In addition, it is preferable that the transport speed at the time of detection is slower than the normal paper transport speed.
Further, it is preferable that when the detection unit detects the correction reference line, the transport speed of the transport upstream side paper as well as the detected paper is changed to the transport speed during detection.

Further, it is preferable to change the paper transport speed to the normal paper transport speed immediately after the detection by the detecting means is completed.
Moreover, it is preferable to have a plurality of set speeds as the transport speed during detection.

  In addition, it is preferable that a plurality of stages of tolerances are set as tolerances of the image position errors on both sides of the paper, and the above-described transport speed at detection that can correspond to the tolerance of each stage is provided as a table in advance.

Further, it is preferable that a user can select a stage of an allowable range of the error from an operation unit of the image forming apparatus.
In addition, it is preferable that the user can select the stage of the allowable range of error from an external apparatus connected to the image forming apparatus.

The correction reference line is preferably an end line representing the end of the image area on the paper and a center line representing the center of the image area.
In addition, it is preferable to perform the second surface image position correction of each sheet based on the position information detected by the detection means for the correction reference line formed for each sheet during a series of double-sided image formation.

  Further, during the series of double-sided image formation, the correction reference line is formed only on the first sheet, and the second-side image position correction of each sheet is performed based on the position information detected by the detection unit. Is preferable.

  Further, the correction reference line is formed every time a predetermined number of double-sided images are formed, and the second-side image position correction for the next predetermined number of sheets is performed based on the positional information detected by the detecting means. Is preferable.

  According to the image forming apparatus of the present invention, the sheet conveyance speed is changed to a predetermined detection conveyance speed at the time of detection of the correction reference line by the detection unit, so that the correction reference line can be detected with high accuracy. High-precision image alignment of the double-sided paper image is possible.

With the configuration of the second aspect, the correction reference line can be detected with high accuracy.
According to the configuration of the third aspect, it is possible to prevent interference between the detected paper and other paper and to prevent jamming. Further, the control and configuration are not complicated.

With the configuration of the fourth aspect, it is possible to minimize a decrease in productivity.
With the configuration of claim 5, it is possible to cope with a desired detection accuracy.
According to the configuration of the sixth aspect, it is possible to easily set the sheet conveyance speed that realizes a desired error allowable range in the image positions on both sides of the sheet.

According to the configuration of the seventh aspect, it is possible to easily set the allowable error range of the double-sided paper image requested by the user and easily change the paper conveyance speed to realize it.
With the configuration according to the eighth aspect, it is possible to easily set the allowable error range of the double-sided paper image requested by the user even from an external device, and easily change the paper conveyance speed to realize it.

According to the configuration of the ninth aspect, the position of the back image can be corrected with a simple reference line with high accuracy.
According to the configuration of the tenth aspect, the image positions on both sides of the paper can be aligned with high accuracy to obtain a high-quality double-sided printed matter.

  According to the configuration of the eleventh or twelfth aspect, it is possible to align the image positions on both sides of the sheet while suppressing a decrease in productivity.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a sectional view showing a schematic configuration of a copying apparatus which is an example of an image forming apparatus according to the present invention. In the copying apparatus 100 shown in this figure, an image forming unit 1 is disposed at the center, and a paper feeding unit 2 is disposed immediately below the image forming unit 1. The paper feed unit 2 includes a paper feed tray 21 at each stage. A reading unit 3 for reading a document is disposed above the image forming unit 1. A paper discharge storage unit 4 is formed on the left side of the image forming unit 1, and a sheet on which an image is formed is discharged and stored.

  An image forming unit 6 is disposed in the image forming unit 1, and around a photosensitive drum 61 that is an image carrier, a charger 62 that performs charging processing on the surface of the photosensitive member, and an electrostatic latent image formed on the surface of the photosensitive member. A developing device 63 that visualizes an image, a cleaning device 64 that removes and collects toner remaining on the photoreceptor, and the like are disposed. Above the image forming unit 6, an exposure device 7 for irradiating image information onto the surface of the photosensitive member with laser light is disposed. A transfer device 51 for transferring a toner image formed on the photoconductor 61 onto a sheet is disposed under the photoconductor drum 61. At the side of the transfer device 51, there is disposed a fixing device 52 for fixing the toner image by applying heat and pressure to the toner transferred onto the paper through a pair of rollers. The sheet that has passed through the fixing device 52 is discharged to the discharge storage unit 4 by the discharge roller 53.

  In the paper feed unit 2, unused paper is stored in the paper feed tray 21, and the bottom plate 24 that is rotatably supported raises the uppermost paper to a position where the pickup roller 25 can abut. As the paper feed roller 26 rotates, the uppermost paper is sent out from the paper feed tray 21 and conveyed to the registration roller 23.

  The registration roller 23 is controlled so as to start rotation at a timing so that the conveyance of the paper is temporarily stopped and the positional relationship between the toner image on the surface of the photosensitive drum 61 and the front end of the paper is a predetermined position.

  In the reading unit 3, in order to read and scan a document placed on the contact glass 31, the reading traveling bodies 32 and 33 including a document illumination light source and a mirror reciprocate. Image information scanned by the reading traveling bodies 32 and 33 is read as an image signal into a CCD 35 installed behind the lens 34. The read image signal is digitized and image processed by an image processing unit (not shown). In the image forming unit 1, an electrostatic latent image is formed on the surface of the photosensitive drum 61 by light emission of a laser diode (not shown) in the exposure device 7 based on the image signal processed by the image processing unit. The optical signal from the LD reaches the photosensitive member via a known polygon mirror or lens. An automatic document feeder 30 that automatically feeds a document is attached above the reading unit 3.

  At the time of double-sided printing, the paper after fixing is branched by the branching unit 91, the paper is reversed by the reverse double-sided unit 9, and conveyed to the registration roller 23, the paper skew is corrected by the registration roller 23, and the back image It leads to formation operation.

  The image forming apparatus according to the present embodiment, in addition to the function of a so-called digital copier that reads and digitizes a document and copies it onto paper as described above, transmits and receives image information of the document to and from a remote location by a control unit (not shown). A multifunctional image forming apparatus having a function of a facsimile machine and a so-called printer function for printing image information handled by a computer on paper. The copying machine is set by an operator from an operation unit (not shown). In addition, all images formed by any function are discharged to the paper discharge storage unit 4.

  When the paper is branched by the branching claw 91 and reversed through the reverse double-side unit 9 and discharged from the paper discharge roller 53 through the reverse paper discharge roller 54, the paper stacked in the paper discharge storage unit 4 is The image side is the bottom side, and even if the processing order of documents handled by copy, facsimile, and printer is printed from the first page, the first page is the top when taken out from the paper discharge storage unit 4 It is freed from work such as aligning pages again.

  The image forming apparatus of the present invention aligns the second side (back side) image with respect to the first side (front side) during double-sided image formation, and transports the reverse side duplex unit 9 of FIG. First position image position information is detected by the image position detecting means 101 located in the vicinity of the exit, and an image is formed on the second surface based on the information.

Details of the present invention will be described below.
In the copying apparatus 100 of this example, when forming an image on the first surface (front surface) 20a of the paper during double-sided image formation such as double-sided copying or double-sided printing, the image area is shown in FIG. The end line 121 indicating the end of the image forming area and the center lines 122 and 122 indicating the center of the image forming area are formed together with the original image (the image to be originally copied or printed) by using the special toner.

  In this embodiment, as shown in FIG. 1, a special toner developing unit 102 is attached to the developing device 63, and by applying special toner from the special toner developing unit 102, an end line 121 and a center line 122 are provided. Develop. The selective development with the normal toner for the original image and the special toner for the end line 121 and the center line 122 is performed by, for example, making the latent image potentials of the two different.

  As the special toner, for example, a transparent toner that cannot be seen by human eyes or an erasable toner can be used. Thus, in the case of transparent toner, there is no problem even if the end line 121 and the center line 122 (with the original image) exist on the paper. In the case of erasable toner, the end line 121 and the center line 122 are erased from the paper before the paper is discharged, so that there is no problem on the image. In FIG. 1, as an example of using erasable toner, a reference line erasing unit 103 is disposed immediately before the paper discharge roller 53. When transparent toner is used, it is not necessary to provide the reference line erasing unit 103.

  When the double-sided printed material is a bookbinding document or the like, the center line 122 may be formed only outside the end line 121 as shown in FIG. There is no problem even if the end line 121 and the center line 122 are formed on the paper by cutting from the end line 121 when binding the printed matter. In this case, it is not necessary to form the end line 121 and the center line 122 with the special toner, and the end line 121 and the center line 122 may be formed with normal toner.

  Now, the paper on which the end line 121 and the center line 122 are formed is re-fed to the registration roller 23 with the front and back sides of the paper being reversed by the reversing duplex unit 9. In the present embodiment, an image position detecting unit 101 is disposed near the conveyance exit of the reversing double-sided unit 9, and the end line 121 formed on the surface of the paper to be re-fed by the image position detecting unit 101 and Center lines 122 and 122 and paper edge 123 are detected.

  When transparent toner is used as the special toner, for example, an optical sensor using light outside the visible region is used as the image position detection unit 101 in order to detect the end line 121 and the center line 122 formed by the transparent toner. To do. When erasable toner and normal toner are used, a normal optical sensor can be used as the image position detecting means 101.

  In the present invention, when the image position detection unit 101 detects the end line 121, the center lines 122 and 122, and the paper end 123, the paper conveyance speed is changed from the normal conveyance speed to the detection conveyance speed. In this example, the detection conveyance speed <the normal conveyance speed. Thus, the end line 121, the center lines 122 and 122, and the paper end 123 can be detected with higher accuracy. The detection information obtained with high accuracy is fed back at the time of backside image formation to correct the backside image position, thereby obtaining a high-quality double-sided printed material in which images on both sides of the paper are aligned with higher accuracy. be able to.

  The sheet conveyance speed is returned to the normal conveyance speed after the detection by the image position detection unit 101 is completed. Note that the conveyance speed may be changed only for the detected paper, but the control becomes complicated, and there is a risk of interference between the detected paper and other paper being conveyed. In addition, the conveying speed of all the upstream side sheets is changed at the same time. Thereby, it is possible to suppress a decrease in productivity as much as possible, and to prevent troubles in conveyance such as jam.

  The detection by the image position detection unit 101 may be performed for all sheets on which double-sided image formation is performed. However, in a series of continuous duplex printing, the image position detection unit is used only for the first sheet of the job. It is also possible to perform the detection by 101 and apply the correction value based on the detection information to all the sheets of the job for correction. Alternatively, the correction value may be updated by performing the detection for each predetermined number of sheets. As a result, detection is performed only on the first sheet of the job, or detection is performed for every predetermined number of sheets (not performed on all sheets), so that a reduction in productivity is minimized, and The influence on the surface image can be minimized.

  The present invention is not limited in any way to the correction method at the time of forming the back surface image based on the information on the edge line 121 and the center lines 122 and 122 and the paper edge 123 detected by the image position detection unit 101. The same correction as the correction method described in Patent Document 1 previously proposed by the present inventors can be used.

  The image position information detected by the image position detecting means 101 is an end line 121 and a center line 122 formed on the first surface of the paper 20, but the paper itself or toner is affected by the heat of the fixing device 52. Since local contraction occurs on the sheet, for example, the center line 122 is not strictly centered as shown in FIG. 4 (Xa ≠ Xb, Ya ≠ Yb). In view of this, in the correction of the back surface image proposed in Patent Document 1, the front and back images are aligned by performing center correction and magnification correction so that the region divided by the end line 121 and the center line 122 matches. Is going.

That is, the center correction and the magnification correction are performed by performing the following correction for each area in FIG.
(The image forming area is X in the transport direction and Y in the direction perpendicular to the transport)
Area A and area C: X / 2 as Xa, correction area B and area D: X / 2 as Xb, correction area A and area B: Y / 2 as Ya, correction area C and area D: Y / 2 as Yb Correction to

  As described above, since it is possible to perform image formation by performing correction in each region divided by the center line 122, center correction can be performed. Although this phenomenon may occur due to the humidity control state of the paper 20, the temperature distribution of fixing, and the pressure distribution, it can be dealt with.

  FIGS. 5A and 5B show an example of the image position detection unit 101, where FIG. 5A is a schematic diagram showing a state of detection, and FIG. 5B is a bottom view of the image position detection unit 101. FIG. The image position detecting means 101 shown in this figure is a reflective sensor having a light emitting element 104 and a light receiving element 105, and light emitted from the light emitting element 104 is reflected by the surface 20 a of the paper 20 and enters the light receiving element 105.

  The detection output by such a reflection type sensor is as shown in the graph of FIG. As shown in this graph, the sensor output is maximum when “paper is present”, minimum when “paper is not present” (no output), and small when “end line 121 and center line 122 are detected”. The solid line indicates the paper conveyance speed at detection (<normal conveyance speed), and the broken line indicates the normal paper conveyance speed.

  As can be seen from the graph, the output varies depending on the paper conveyance speed, and the detection accuracy is higher when the conveyance speed is lower for an actual paper edge or image. This is due to paper fluttering between the transport guide members in the sensor unit, loose paper or tension between the transport rollers, and the higher the paper transport speed, the more unstable the paper behavior. Because it becomes. Therefore, ideally, it is better to stop the paper at the time of detection, but in this case, productivity is lowered. In the present embodiment, as described above, the detection accuracy is improved and the productivity reduction is suppressed at a high level by slowing the sheet conveyance speed at the time of detection by the image position detection unit 101 and returning to the normal speed after the detection. be able to.

  By the way, in order to adjust the image position accuracy on both sides of the paper to a higher accuracy (increase the detection accuracy), it is only necessary to lower the detection speed. The copying apparatus 100 according to this embodiment is configured to be able to switch to a plurality of conveyance speeds as detection speeds, and the user sets (selects) a plurality of detection speeds as detection modes from an operation panel (not shown) of the copying apparatus 100. ) You can do it.

  The following Table 1 shows an example in which three (three stages) speeds are set as detection speeds. Here, the allowable range of front and back image position error is set in three stages, and the detection speed that can be detected with the accuracy is made to correspond to the allowable range of each error, so that the double-sided image alignment with the accuracy required by the user is performed. Can be easily obtained. Note that the allowable range of error depends on the performance of the detection means 101, and therefore, an appropriate value may be set according to the performance of the detection means.

In Table 1, the normal conveyance speed and the detection conveyance speed are set to the same V in the “normal mode”, and the front and back image position accuracy is set to “± 1.0 mm”, and the “high accuracy mode” is hereinafter referred to as the detection conveyance speed V. as _B, and front and back image position accuracy "± 0.5 mm", as the detection time of the conveying speed _{V C} as "ultra-high precision mode" is set in the table as "± 0.25 mm" front and back image position accuracy. Of course, V _B is preferably equal to V, and more preferably equal to V _C.

  In this way, by setting the detection transport speed that enables double-sided image alignment with a desired accuracy as a detection mode in the table in advance, the user simply selects the detection mode from the operation panel of the image forming apparatus. Thus, it is possible to easily obtain double-sided image formation with accuracy within an allowable range of desired front and back image position errors.

  When the image forming apparatus of this example is used as a printer, it is preferable that the detection mode can be selected from a connected external device such as a personal computer.

As mentioned above, although this invention was demonstrated by the example of illustration, this invention is not limited to this.
For example, the reference line serving as a reference for the backside image position correction is not limited to the end line and the center line in the illustrated example, and can be an appropriate form of reference line, and the position thereof can be set as appropriate. .

  In addition, the detection unit that detects the reference line can be configured appropriately according to the developer, ink, and the like that form the reference line. In addition, the location of the detection means can also be placed at an arbitrary location within a range in which the back image position can be corrected. Moreover, the conveyance speed at the time of detection can also be set as appropriate, and the number of modes in a plurality of modes is arbitrary.

  Further, the configuration of each part of the image forming apparatus is arbitrary, and the image forming apparatus is not limited to the copying apparatus of the embodiment, but may be a printer, a facsimile, or a multifunction machine having a plurality of functions.

1 is a cross-sectional view showing a schematic configuration of a copying apparatus which is an example of an image forming apparatus according to the present invention. FIG. 6 is a schematic diagram illustrating a correction reference line formed on the sheet surface and a state of detection thereof. It is a schematic diagram which shows another example of the reference line for correction | amendment, and the mode of the detection. It is a schematic diagram which shows a mode that the position of the reference line for correction | amendment shifted | deviated. It is a schematic diagram which shows an example of the detection means which detects the reference line for correction | amendment. It is a graph which shows the example of an output of the detection means.

Explanation of symbols

9 Reversed both sides 20 Paper 20a Paper first side (front side)
23 Registration roller 51 Transfer device 52 Fixing device 61 Photosensitive drum 63 Developing device 100 Copying device 101 Image position detecting means 102 Special toner developing portion 103 Reference line erasing means 121 End line (correction reference line)
122 Center line (reference line for correction)
123 Paper edge

Claims (12)

An image forming apparatus capable of forming an image on both sides of a sheet, the image forming apparatus including a detection unit that detects a correction reference line formed on the first side of the sheet, and position information of the correction reference line detected by the detection unit In the image forming apparatus for correcting the image position formed on the second surface of the paper based on
An image forming apparatus, wherein when the detection unit detects the correction reference line, the sheet conveyance speed is changed to a predetermined detection conveyance speed. The image forming apparatus according to claim 1, wherein the transport speed at the time of detection is slower than a normal paper transport speed. 3. The image formation according to claim 1, wherein when the correction reference line is detected by the detection unit, the conveyance speed of the conveyance upstream side paper as well as the detected sheet is changed to the conveyance speed at the time of detection. apparatus. The image forming apparatus according to claim 1, wherein the sheet conveying speed is changed to a normal sheet conveying speed immediately after the detection by the detecting unit is completed. The image forming apparatus according to claim 1, wherein the detection transport speed has a plurality of set speeds. 6. The detection conveyance speed that can set a plurality of stages of allowable errors as an allowable range of image position errors on both sides of the sheet and can handle the allowable errors of each stage is provided as a table in advance. Image forming apparatus. The image forming apparatus according to claim 6, wherein a user can select a stage of the allowable range of the error from an operation unit of the image forming apparatus. The image forming apparatus according to claim 6, wherein a user can select an error tolerance level from an external device connected to the image forming apparatus. The image forming apparatus according to claim 1, wherein the correction reference line is an end line representing an end of the image area on the sheet and a center line representing the center of the image area. 2. The second-surface image position correction of each sheet is performed based on position information detected by the detecting means for a correction reference line formed for each sheet during a series of double-sided image formation. The image forming apparatus described. At the time of forming a series of double-sided images, the correction reference line is formed only on the first sheet, and the second-side image position correction of each sheet is performed based on the position information detected by the detection means. The image forming apparatus according to claim 1, wherein: The correction reference line is formed every time a predetermined number of double-sided images are formed, and the second surface image position correction is performed on the next predetermined number of sheets based on position information detected by the detecting means. The image forming apparatus according to claim 1, wherein:

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