JP2006078927A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which generates no shift between image formation areas on top and reverse sides, especially, in both-surface printing by equalizing the distances from both ends of recording paper to an image formation area. <P>SOLUTION: On a recording paper conveyance path along which the recording paper 20 is conveyed, a form end detecting means capable of detecting both the ends of the recording paper 20 during the conveyance is arranged in a direction perpendicular to the recording paper conveyance direction, and based upon detection information from the form end detecting means, the width-directional center of the recording paper 20 is calculated to make the width-directional center of the image formation area meet the width-directional center of the recording paper 20. In both-surface printing, widths of the recording paper 20 on the top and reverse sides are compared by a storage means of storing the detection information from the form end detecting means to perform magnification error correction based upon the found shrinkage rate of the recording paper 20, and the width-directional center of the recording paper 20 is calculated to perform image formation control. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a facsimile, a printer, and a printing machine, and more specifically, has a control mechanism for adjusting the position of an image formed on an image forming medium. The present invention relates to an image forming apparatus.

In recent years, in an image forming apparatus, a lateral registration accuracy similar to that of a printing press has been demanded. Particularly recently, an electrostatic latent image is formed on the surface of the photosensitive member, the electrostatic latent image is developed, and the developed image on the photosensitive member is transferred to a recording sheet fed from a paper feeding unit. In many cases, an image forming apparatus having a double-sided printing function is used, in which a recording sheet printed on one side is re-fed to a photoconductor while being reversed through a re-feeding path. With regard to this double-sided printing, there is an increasing demand for accurately matching the printing positions of the front and back surfaces of the recording paper.
In a general image forming apparatus, in order to prepare an image forming area, the start timing for writing a latent image on a photosensitive member is made constant so that the horizontal registration on the writing start side is aligned, and image forming control (recording paper) The control of forming an image at a position of what mm from the end) is performed.

For example, in Patent Document 1, the leading edge of a recording sheet conveyed from a paper feeding unit and the leading edge of an image corresponding to a document formed on the recording sheet are detected, that is, based on the detected leading edge position, that is, An image forming apparatus capable of automatically adjusting the re-start timing (delay time) of the registration motor with respect to the start timing of the scan motor so that the front-end position of the recording paper matches the front-end position of the image corresponding to the document formed on the recording paper. It is disclosed. As a result, the adjustment of the tip position is automatically adjusted for each copying machine, so that the work time for the adjustment can be shortened, and the tip position can be easily adjusted by automatic adjustment even when adjustment is necessary again. Can do.
However, since the invention described in Patent Document 1 is a mechanism for positioning from the edge of the recording paper, in the case of double-sided printing, the writing start side is reversed between the front and back, so that image formation on the front and back of the recording paper is performed. As a result, the area is shifted.
In Patent Document 2, a reference mark is printed on a process medium such as an intermediate belt, the position of the reference mark in the main scanning direction and the sub-scanning direction is detected, and the position of each color image to be superimposed is registered based on the detection result. (Registration) is disclosed.
However, the present invention is not for equalizing the printing positions of the front surface and the back surface of the recording paper.

As a proposal for responding to the problem of preventing the lateral deviation of the transfer paper during double-sided printing, for example, a proposal for detecting the positional deviation of the recording paper and correcting the position of the image at the time of printing on the back side (patent) References 3 to 5).
However, at the time of double-sided printing, heat and pressure are once applied to the paper at the fixing unit, so that the recording paper is slightly shrunk at the time of backside printing. Even if image formation is performed in advance in consideration of the shrinkage amount of the recording paper, the shrinkage amount differs depending on the type of the recording paper, the moisture content, etc., and this causes a problem of slight deviation.

Japanese Patent Laid-Open No. 9-081009 JP-A-6-118735 JP-A 61-275774 JP-A 61-275775 JP-A 61-275780

  Therefore, in view of the above circumstances, the present invention provides an image forming apparatus in which the distance from both ends of the recording paper to the image forming area is the same by controlling the image forming operation, and the image forming area is not shifted between the front and back sides particularly during double-sided printing. It is an issue to provide.

In order to solve the above problems, the present invention is characterized by the following.
1. The image forming apparatus of the present invention includes an image carrier that carries a latent image, a charging device that uniformly charges the surface of the image carrier by a charging member to which a voltage is applied from the outside, and a surface of the charged image carrier. An exposure device that performs exposure based on image data and writes an electrostatic latent image; a developing device that supplies toner to the latent image formed on the surface of the image carrier and visualizes the image; An image forming apparatus comprising: a transfer unit configured to transfer a visible image onto a recording paper; and a recording paper transporting path for transporting the recording paper, and a direction orthogonal to the recording paper transporting direction on the transporting path. A paper edge detection unit capable of detecting both ends of the recording paper during conveyance is provided, and the center of the recording paper width direction is calculated based on the detection information from the paper edge detection unit, and the image forming area width is calculated at the center of the recording paper width direction. Image formation control is performed so that the center of the direction matches. That.
2. The image forming apparatus according to the present invention includes: In the invention described in the above, the recording means includes a storage means for storing detection information from the paper edge detection means, and the recording paper width detected at the first time is compared with the recording paper width detected at the second time in double-sided printing. The shrinkage rate is calculated, the magnification error is corrected based on the shrinkage rate, and the center of the recording paper width direction is calculated based on the second detection information from the paper edge detection means, and the image in the center of the recording paper width direction is calculated. Image formation control is performed so that the center of the formation region is matched.
3. The image forming apparatus according to the present invention includes: Or 2. In the invention described in item 1, the sheet edge detecting means is a non-contact sensor including a plurality of light emitting elements and light receiving elements.
4). In addition, the image forming apparatus of the present invention includes: In the invention described in item 1, the paper edge detection sensor detects the edge of the recording paper depending on whether or not the light from the light emitting element is blocked by the recording paper being conveyed.
5. The image forming apparatus according to the present invention includes: Or 2. In the invention described in (1), the sheet edge detecting means is a reduction optical system using an optical system / a CCD sensor of equal magnification.
6). The image forming apparatus according to the present invention includes: Or 4. In the invention described in the above, the paper edge detecting means bisects the center of the conveyance path width direction to the reference so as to sufficiently cover the maximum / minimum width of the recording paper that can be conveyed in a direction orthogonal to the recording paper conveyance direction. It is characterized by being.
7). The image forming apparatus according to the present invention includes: Or 4. In the invention described in the paragraph, the paper edge detecting means is divided into a predetermined length, arranged in a contrast from the center in the conveyance path width direction, and has a moving means capable of moving the paper edge detecting means in parallel. Then, the moving means moves the paper edge detecting means in accordance with the size of the paper to be conveyed.

  By means for solving the above-mentioned problems, the image forming apparatus of the present invention can provide an image in which the distance from the both ends of the recording paper to the image forming area is the same on the left and right sides. It is possible to provide an image with no deviation in the image forming area.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to the present invention. In the figure, an image forming unit 1 is disposed at substantially the center of the image forming apparatus, 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. If necessary, another sheet feeding device 22 can be added. Above the image forming unit 1, a reading unit 3 for reading a document is disposed. A paper discharge storage section 4 is formed on the left side of the image forming section 1, and the recording paper 20 on which the image is formed is discharged and stored.
In the image forming unit 1, a plurality of image forming units 6 are arranged in parallel on a belt-shaped intermediate transfer belt 5, and each image forming unit 6 has a drum-shaped image carrier (hereinafter referred to as a photoconductor). A charging device 62 for charging the surface of the photoconductor 61, an exposure device 7 for irradiating the photoconductor surface with laser light on the surface of the photoconductor 61, and a static image formed by exposing the surface of the photoconductor 61 around 61. A developing device 63 that visualizes the electrostatic latent image and a cleaning device 64 that removes and collects toner remaining on the photoreceptor 61 are disposed. As an image forming process, the intermediate transfer belt 5 rotates to form a single color image.
First, yellow (Y) toner is developed by the yellow (Y) image forming unit 6 and transferred to the intermediate transfer belt 5. Next, the magenta (M) image forming unit 6 develops the magenta toner and transfers it to the intermediate transfer belt 5. Next, cyan toner is developed in the cyan (C) image forming unit 6 and transferred to the intermediate transfer belt 5. Finally, black (BK) toner is developed and transferred to the intermediate transfer belt 5.
Further, there are a transfer device 51 for transferring the four color toner images developed on the intermediate transfer belt 5 to a recording paper, and an intermediate transfer cleaning device 52 for removing and collecting the toner remaining on the surface of the intermediate transfer belt 5 after the transfer. , Each is arranged.
Further, a fixing device 8 for fixing the toner on the recording paper from which the toner image is obtained is disposed downstream of the image forming device (means) (downstream in the recording paper conveyance path). The recording paper 20 that has passed through the fixing device 8 is discharged and stored in the discharge storage unit 4 by a discharge roller 41.
At the time of double-sided printing, the paper is branched by the branching unit 91, the recording paper 20 is reversed via the double-sided device 9, the skew of the recording paper 20 is corrected by the registration roller 23, and the back side image forming operation is reached.
In the paper feeding unit 2, unused recording paper 20 is accommodated in the paper feeding tray 21, and the bottom plate 24 that is rotatably supported is a position at which the uppermost recording paper 20 can come into contact with the pickup roller 25. Raise to. The uppermost recording paper 20 is sent out from the paper supply tray 21 by the rotation of the paper supply roller 26 and is conveyed to the registration roller 23. The registration roller 23 temporarily stops the conveyance of the recording paper 20 and controls the rotation to start at a timing so that the positional relationship between the toner image on the surface of the photoreceptor 61 and the leading edge of the recording paper 20 becomes a predetermined position. Is done.
Further, in the reading unit 3, in order to perform reading scanning of a document (not shown) placed on the contact glass 31, 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 subjected to image processing. Based on the image-processed signal, an electrostatic latent image is formed on the surface of the photoreceptor 61 by light emission of a laser diode (not shown, hereinafter referred to as LD) in the exposure device 7. The optical signal from the LD reaches the photosensitive member 61 via a known polygon mirror or lens. An automatic document feeder 3 for automatically feeding a document onto the contact glass 31 is attached above the reading unit 3.

The image forming apparatus of the present invention scans, reads and digitizes a document as described above, digitizes it and copies it onto the recording paper 20, in addition to the function as a so-called digital color copying machine, and controls the image of the document by a control device (not shown). This is a multi-function image forming apparatus having a facsimile function for exchanging information with a remote place and a so-called printer function for printing image information handled by a computer on a recording sheet.
All images formed by any of the functions are discharged and stored in one discharge storage unit 4.
Further, when the recording paper 20 is branched by the branching claw 91, reversed through the double-sided device 9, and discharged from the paper discharge roller 41 through the reverse paper discharge roller 92, the recording paper 20 is stacked in the paper discharge storage unit 4. The recorded recording paper 20 is in a state where the image surface is the lower surface. As a result, even if the original, which is handled by copying, facsimile, or printer, is processed from the first page and printed, the first page is the top when it is taken out from the discharge storage unit 4, and the page is aligned again. It is possible to achieve a state where it is not necessary to perform the operation.

FIG. 2 is a schematic diagram of the sheet edge detecting means of the present invention. As shown in FIG. 2, the sheet end detection unit of the present invention is disposed on the conveyance path of the image forming apparatus in a direction perpendicular to the sheet conveyance direction. In addition, the paper edge detection means is configured to have a detection width that can sufficiently detect the maximum size of the conveyed paper.
Note that if the paper end detection means is disposed on the transport path upstream of the image forming unit 1, it is possible to obtain information for performing image formation control, but the recording paper 20 further moves. If the width of the recording paper 20 is detected in a state where it is not, a detection value with no variation can be obtained. For this reason, it is preferable that the recording paper 20 is temporarily put on standby by a registration roller (hereinafter referred to as a registration unit) 23, and a paper edge detecting means is provided at a position where the edge of the recording paper 20 can be detected in this state.
As long as the end of the recording paper 20 can be detected without variation, the location of the paper end detection means is not limited to this.

FIG. 4 is a schematic diagram of a sheet end detection unit including a plurality of light emitting elements and light receiving elements. As shown in the drawing, a light emitting portion and a light receiving portion are arranged with the recording paper 20 being conveyed in between, and the end of the recording paper 20 is detected by whether or not the light from the light emitting portion is blocked by the recording paper 20. . In this embodiment, the width of the recording paper 20 is obtained by numbering sequentially from the left light receiving element in the figure, subtracting the numbers at both ends of the light shielding area, and multiplying this by the arrangement interval of the light receiving elements. Further, since the value obtained by halving the calculated width of the recording paper 20 is the median value in the width direction of the recording paper 20, the image area center is coincident with the center of the recording paper 20 in the width direction. Formation control (adjusting image formation start timing) is performed.
In this way, by performing image formation control so that the center of the image forming area coincides with the center of the recording paper width direction, it is possible to perform image formation in which the distance from both ends of the recording paper 20 to the image forming area is the same on the left and right.
In the case of double-sided printing in particular, the horizontal registration on the writing start side is aligned by making the start timing of writing latent image on the photoreceptor 61 constant as in the prior art, and image formation is performed from a fixed position at the end of the recording paper 20. In the control mechanism of performing, since the writing start side is reversed between the front and back, the front and back image forming areas of the recording paper 20 are shifted as a result.
On the other hand, the image forming apparatus of the present invention performs image formation control so that the center of the recording paper 20 in the width direction and the center of the image forming area coincide with each other by the above-described procedure. Can be eliminated.
Note that the paper edge detecting means is configured to be in a non-contact configuration including a plurality of light emitting elements and light receiving elements as described above, thereby detecting both ends of the recording paper 20 without applying a load to the recording paper 20 being conveyed. There is an effect that can be.

FIG. 5 is a flowchart showing a process in image formation according to the present invention. Here, a case where double-sided printing is performed on one sheet of recording paper 20 will be described.
The recording paper 20 conveyed from the paper supply unit 2 in response to the double-sided printing command is detected at its edge by the paper edge detection means, and based on this detection information, the recording paper width / recording paper width direction center is calculated, and the image forming area The image forming operation is performed so that the center coincides with the center in the recording paper width direction. At this time, the calculated recording paper width is stored by a storage unit such as a memory. The recording paper 20 on which an image has been formed and fixed by a fixing device (hereinafter, referred to as a fixing unit) 8 is conveyed along the double-sided conveyance path and is conveyed again to the image forming unit 1. The recording paper 20 whose edge is detected again by the paper edge detecting means is contracted from before the passage of the fixing unit 8 by passing through the fixing unit 8 and being applied with heat and pressure.
The width of the recording paper 20 and the center of the recording paper 20 in the width direction after being conveyed through the double-sided conveyance path are calculated based on information detected by the paper edge detection means after passing through the fixing unit 8. The shrinkage rate is calculated by comparing the width of the recording paper 20 calculated here with the width of the recording paper 20 stored in the storage unit before passing through the fixing unit 8. With this value, magnification error correction at the time of printing on the back side is performed.
In general, magnification error correction is performed at the time of printing on the back side, but in this case, a fixed magnification correction is performed without considering the paper type of the recording paper 20 and its state.
However, since the shrinkage rate varies depending on the paper type, moisture content, and the like, more effective magnification error correction can be performed by reflecting the recording paper 20 paper width information corresponding to each state sequentially.
In addition to correcting the magnification error by comparing only the recording paper width information, the length of the recording paper 20 before and after passing through the fixing unit 8 is also measured, and the result of comparing the lengths of the recording paper is reflected in the magnification error correction. In this case, the correction accuracy can be further improved.
Thereby, even during double-sided printing, it is possible to eliminate the deviation of the image forming areas of the front and back images due to passing through the fixing unit 8.

FIG. 6 is a schematic diagram showing a case where a reduction optical system / equal magnification CCD sensor is used for the paper edge detection means of the present invention. The edge of the recording paper 20 is detected in the detection area of the CCD sensor shown in the figure.
The CCD sensor can perform detection with high accuracy without imposing a load on the recording paper 20 being conveyed. On the other hand, if the detection area is enlarged while maintaining the detection accuracy, the cost is significantly increased. Therefore, it is not preferable. For this reason, it is necessary to consider the configuration and the like so as to reduce the detection area other than the paper edge detection range.

FIG. 3 is a schematic view showing a case where the paper edge detecting means of the present invention is divided into two and provided symmetrically.
As shown in the figure, the paper edge detection means is arranged with a fixed left and right gap from the center of the conveyance path, leaving a detection area where the edges of the recording paper 20 from the minimum size to the maximum size can be sufficiently detected. Has been established. As described above, by disposing the sheet end detection means so as to omit the detection area that is not necessary for detecting the end portion of the recording sheet 20, it is possible to reduce the disposition space and cost without degrading the detection accuracy. .

FIG. 7 is a schematic configuration diagram of the sheet edge detecting means of the present invention provided with moving means.
In the figure, the paper edge detecting means mounting member provided at the top is provided with two paper edge detecting means comprising a light emitting part / light receiving part of a certain length according to the present invention, and this is contrasted from the conveyance center. Arrange. The paper end detection means mounting member has a mechanism for controlling the movement of the recording paper 20 to be detected by a known movement means (not shown) such as rack and pinion + STM.
By adopting such a configuration, it is possible to deal with recording paper 20 of all sizes by the paper edge detection means having the minimum necessary detection width, and the paper edge detection sensor is made compact while maintaining the detection function. And cost can be reduced.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to the present invention. It is the schematic of the paper end detection means of this invention. It is the schematic which shows the case where the paper edge detection means of this invention is divided into two and provided symmetrically. It is the schematic of the paper end detection means which consists of a several light emitting element and a light receiving element. It is a flowchart which shows the process in the image formation of this invention. FIG. 5 is a schematic diagram showing a case where a reduction optical system / equal magnification CCD sensor is used for the paper edge detection means of the present invention. It is a schematic block diagram of what provided the movement means in the paper edge detection means of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image formation part 2 Paper feed part 20 Recording paper 21 Paper feed tray 22 Another paper feeder 23 Registration roller 24 Bottom plate 25 Pickup roller 26 Paper feed roller 3 Reading part 3 Automatic document feeder 31 Contact glass 32, 33 Traveling body 34 Lens 35 CCD sensor 4 Paper discharge storage unit 41 Paper discharge roller 5 Intermediate transfer belt 51 Transfer device 52 Intermediate transfer cleaning device 6 Image forming unit 61 Photoconductor 62 Charging device 63 Development device 64 Cleaning device 7 Exposure device 8 Fixing device 9 Double-side device 91 Branching part 92 Reverse paper discharge roller

Claims (7)

An image carrier for carrying a latent image;
A charging device that uniformly charges the surface of the image carrier with a charging member to which a voltage is applied from the outside;
An exposure device that exposes the charged image carrier surface based on image data and writes an electrostatic latent image;
A developing device that supplies toner to the latent image formed on the surface of the image carrier to visualize the latent image;
In an image forming apparatus comprising: transfer means for transferring a visible image on the surface of the image bearing member to a recording paper;
The image forming apparatus has a recording paper transport path for transporting recording paper,
A paper edge detection means capable of detecting both ends of the recording paper during conveyance in a direction perpendicular to the recording paper conveyance direction is disposed on the conveyance path,
An image forming apparatus characterized in that, based on detection information from the paper edge detecting means, the center of the recording paper width direction is calculated, and image forming control is performed so that the center of the image forming area width direction coincides with the center of the recording paper width direction. . The image forming apparatus according to claim 1.
The image forming apparatus includes a storage unit that stores detection information from the sheet edge detection unit,
During double-sided printing, the recording paper width detected the first time is compared with the recording paper width detected the second time, the shrinkage rate of the recording paper is obtained, magnification error correction is performed based on the shrinkage rate, and the paper edge detection An image forming apparatus characterized in that the center of the recording paper width direction is calculated based on the second detection information from the means, and image forming control is performed so that the center of the image forming area coincides with the center of the recording paper width direction. The image forming apparatus according to claim 1, wherein
The image forming apparatus, wherein the sheet end detection means is a non-contact sensor including a plurality of light emitting elements and light receiving elements. The image forming apparatus according to claim 3.
The image forming apparatus, wherein the sheet end detection sensor detects the end of the recording sheet based on whether or not light from the light emitting element is blocked by the recording sheet being conveyed. The image forming apparatus according to claim 1, wherein
The image forming apparatus, wherein the paper edge detecting means is a reduction optical system using an optical system / equal magnification CCD sensor. The image forming apparatus according to claim 1, wherein:
The sheet edge detecting means is divided into two parts from the center in the conveyance path width direction so as to sufficiently cover the maximum / minimum width of the recording sheet that can be conveyed in a direction perpendicular to the recording sheet conveyance direction. An image forming apparatus. The image forming apparatus according to claim 1, wherein:
The paper edge detecting means is divided into a predetermined length and arranged in a contrast from the center in the conveyance path width direction, and includes a moving means capable of moving the paper edge detecting means in parallel.
An image forming apparatus characterized in that the paper edge detecting means is moved by the moving means in accordance with the size of paper to be conveyed.

Images