JP2011113055A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus carrying out optimal correction for meandering of an intermediate transfer belt and skewing of transfer paper so that no distortion may appear in an image by simultaneously detecting the meandering of the intermediate transfer belt and the skewing of the transfer paper without providing respective individual means for detecting the meandering of the intermediate transfer belt and the skewing of the transfer paper. <P>SOLUTION: The optimal correction can be applied simultaneously to a correction means for correcting the skewing of the transfer paper and a correction means for correcting the distortion of a transfer body in real time since an image that is transferred to the transfer paper and a residual toner image can be simultaneously photographed by one image sensor by using the image sensor which continuously photographs so that the image transferred on the transfer paper and the residual toner image on a transfer body surface may be put into the same image frame. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine or a laser printer, and more particularly to an improvement in technology for correcting image misregistration.

  In recent years, image forming apparatuses using an intermediate transfer member as an image carrier for transferring a toner image onto a transfer paper have been widely used because of the need for high-quality image formation. A toner image formed on the surface of a photosensitive drum or the like that is a primary transfer member is transferred to an intermediate transfer belt that is a secondary transfer member, and is then secondarily transferred from the intermediate transfer belt to a transfer sheet.

  For example, in an image forming apparatus of a tandem type, an intermediate transfer belt is stretched around a driving roller and a driven roller. In order to form a toner image on the surface of the stretched intermediate transfer belt, a photosensitive drum of each color (magenta (M), cyan (C), yellow (Y), black (Bk)) It is disposed so as to face the primary transfer roller. In the image forming method of this image forming apparatus, first, an electrostatic latent image is formed on the circumferential surface of the photosensitive drum by the image writing unit of each photosensitive drum, and each toner image obtained by developing this electrostatic latent image is converted into a toner image. An image is formed by performing multiple transfer onto the intermediate transfer belt, and further transferring the toner image on the intermediate transfer belt onto the transfer paper conveyed. For this reason, misalignment is likely to occur when the toner images formed on the photosensitive drums are transferred to the intermediate transfer member and superimposed, and the transfer paper is skewed when the transfer paper is transported. There are two problems that the transfer paper and the toner image are misaligned during the transfer.

  The cause of the positional deviation and the conveyance skew may be that the member of the drum mounting portion expands or contracts due to the temperature variation in the apparatus, or the speed fluctuation or meandering occurs in the intermediate transfer belt or the conveyance belt.

  In order to solve this problem of misregistration, in Patent Document 1, a toner image of a registration mark is formed on each photosensitive drum, which is directly transferred onto an intermediate transfer belt, and each color registration mark is detected by a sensor. A method has been proposed in which relative positional deviation is obtained by detection, and based on the amount of positional deviation, adjustment of the writing timing for forming an electrostatic latent image for each photosensitive drum and phase control of a polygon mirror are proposed. ing. Further, in Patent Document 2, a sensor for detecting the meandering of the intermediate transfer belt is disposed, and the meandering of the intermediate transfer belt is corrected by detecting the meandering of the intermediate transfer belt and tilting the driven roller or the like. Has been proposed.

  Further, in Patent Document 3, in order to solve the occurrence of skew of the transfer paper during conveyance, a plurality of skew detection sensors are provided to measure the skew amount of the transfer paper, and the skew of the transfer paper is corrected by the skew correction roller. A scheme has been proposed.

  However, the technique disclosed in the above document is designed to cope with the image shift and distortion caused by the speed fluctuation of the intermediate transfer belt, the meander and the skew of the transfer paper, and the skew of the intermediate transfer belt and the skew of the transfer paper. Therefore, the structure of the image forming apparatus is complicated, and it is difficult to reduce the size and the cost.

JP 2000-71522 A JP 2006-030598 A JP 2002-284399 A

  Therefore, in order to solve the above-described problems, the present invention can reduce the speed of the intermediate transfer body, the meander and the skew of the transfer paper without separately providing means for detecting the speed of the intermediate transfer body and the meander and the skew of the transfer paper. An object of the present invention is to provide an image forming apparatus capable of optimally correcting the speed of the intermediate transfer member and the meandering and the skew of the transfer paper so that the image is not misaligned or distorted.

In order to achieve this object, the present invention has the following configuration.
According to a first aspect of the present invention, there is provided an image sensor that continuously captures an image transferred to a transfer sheet and a residual toner image on the surface of the image carrier so as to enter a frame of the same image, and a continuous image captured by the image sensor. The present invention relates to an image forming apparatus that detects states of an image transferred to the transfer paper and a residual toner image on an image carrier based on the image forming apparatus.

  According to a second aspect of the present invention, the image forming apparatus further includes a control unit, and the control unit transfers an image transferred to the transfer paper sent from the image sensor and a residual toner image on the image carrier. The image forming apparatus according to claim 1, further comprising a detection unit that analyzes a moving amount of the continuous image and detects a skew of the transfer paper and a speed and meander of the image carrier based on the analysis result. Relates to the device.

  According to a third aspect of the present invention, as the movement amount of the continuous image sent from the image sensor by the detection means, the motion vector of the image transferred to the transfer paper and the motion vector of the residual toner on the surface of the transfer body are used. The image forming apparatus according to claim 2, wherein the calculation is performed.

  According to a fourth aspect of the present invention, there is provided skew correction means for correcting skew of the transfer paper and / or the image carrier based on detection of skew of the transfer paper and speed and meandering of the image carrier by the detection means. The image forming apparatus according to claim 2, further comprising an image carrier correcting unit that corrects the speed and / or the meandering.

  According to a fifth aspect of the invention, there is provided the image forming apparatus according to any one of the first to fourth aspects, wherein the image carrier is an intermediate transfer body for transferring a plurality of color toner images in a superimposed manner.

According to the first aspect of the present invention, the image sensor that continuously captures the image to be transferred onto the transfer paper and the residual toner image on the surface of the transfer body so as to enter the frame of the same image is provided. Since the image transferred to the transfer paper and the residual toner image can be taken at the same time, it is not necessary to separately provide means for detecting the state of the image transferred to the transfer paper and the image on the image carrier. The image forming apparatus can be reduced in size.
In addition, the image sensor needs to be accurately positioned on the apparatus main body. However, by reducing the number of sensors, it is possible to reduce positioning means provided in the apparatus, adjustment work during assembly, and the like.
Furthermore, since the image transferred to the transfer paper by one image sensor and the residual toner image on the image carrier are detected, an error in the relative position of the sensor does not occur compared to detection by a separate image sensor. . Therefore, when the detected individual images are compared, it is possible to accurately compare without performing processing for correcting the position error.

  According to the second aspect of the present invention, the movement amount of the image transferred to the transfer sheet sent from the image sensor and the continuous image of the residual toner image on the image carrier is analyzed, and the transfer is performed based on the analysis result. Since the detecting means for detecting the skew of the paper and the speed and meandering of the image carrier is provided, the state of the apparatus can be detected in real time.

  According to the invention of claim 3, since the motion vector of the image transferred to the transfer paper and the motion vector of the residual toner on the surface of the image carrier are calculated as the movement amount of the continuous image, the skew of the transfer paper and the The speed and meandering of the image carrier can be controlled in real time.

  According to the invention of claim 4, the skew correction means for correcting the skew of the transfer paper and / or the speed of the image carrier based on the detection of the skew of the transfer paper and the speed and meandering of the image carrier by the detection means. Since the image carrier correction means for correcting meandering is provided, optimal correction for image formation can be performed in real time, and a high-quality image can always be obtained.

  According to the fifth aspect of the present invention, in the image forming apparatus in which the image carrier is an intermediate transfer body that transfers a plurality of color toner images, the state of the image on the transfer paper and the residual toner image on the intermediate transfer body By detecting this in real time, a high-quality color image can be obtained.

1 is a schematic sectional view of an image forming apparatus according to the present invention. FIG. 6 is a diagram illustrating Nth and N + 1th consecutive images captured by an image sensor of the image forming apparatus according to the present invention. It is a figure showing the image and motion vector which were image | photographed with the image sensor of the image forming apparatus which concerns on this invention. FIG. 4 is a diagram illustrating an example of an actual image captured by an image sensor of the image forming apparatus according to the present invention. It is a figure showing the motion vector of an example of the actual image image | photographed with the image sensor of the image forming apparatus which concerns on this invention. 1 is a diagram of an embodiment of a distortion correction unit of an image forming apparatus according to the present invention. 1 is a diagram of an embodiment of skew correction means of an image forming apparatus according to the present invention. FIG. 3 is a control flow diagram of the image forming apparatus according to the present invention.

An image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic sectional view of an image forming apparatus according to the present invention.

  The image forming apparatus according to the present invention shown in FIG. 1 includes a paper feeding device (1) for transporting transfer paper, skew correction means (2) for correcting skew of the transported transfer paper, and / or an image carrier ( In the case of the embodiment of FIG. 1, the image carrier correction means (not shown) for correcting the speed and meandering of the intermediate transfer member (3) and the secondary transfer roller (4) cooperate with the transfer paper. Each color (magenta (M), cyan (C), yellow (Y), black is printed on the surface of the intermediate transfer device (5) for forming a toner image on the surface and the surface of the intermediate transfer member (3) provided in the intermediate transfer device (5). A primary transfer device (7) having a photosensitive drum (6) for transferring the toner of (Bk)) as a toner image, a toner image transferred to a transfer paper, and a residual toner image on the surface of the intermediate transfer member (3). An image sensor (8) that continuously shoots within the same image frame; Eteiru.

  The image forming apparatus according to the present invention includes a control unit (9) for controlling the skew correction unit (2) and / or the image carrier correction unit. The control unit has detection means for analyzing the movement amount of the continuous image sent from the image sensor (8) and detecting the skew of the transfer paper and the speed and meandering of the image carrier. Based on this, an accurate control signal is transmitted to the skew correction means (2) and / or the image carrier correction means, and the correction means is controlled in real time. The image sensor (8) continuously shoots the toner image transferred to the transfer paper and the residual toner image on the surface of the intermediate transfer member (3) so as to enter the same image frame. Accordingly, the image on the transfer paper and the residual toner on the surface of the intermediate transfer member (3) can be continuously photographed simultaneously by one image sensor. Therefore, it is possible to easily and accurately analyze the moving amount of the image, and it is not necessary to perform correction between a plurality of image sensors.

Here, the moving amount of the image will be described.
The Nth and N + 1th consecutive images taken by the image sensor (8) are taken as shown in FIG. When the characters “A” and “B” in the frame of the photographed image move in a certain direction on the Nth and N + 1th respectively, the movement amounts of “A” and “B” are as shown in FIG. It can be expressed as a motion vector. A motion vector (optical flow) is a velocity field of each point on the screen. Various methods of motion vector calculation have been proposed, but can be roughly classified into two. One method is a method in which an arbitrary region in the Nth image is compared with the N + 1th image to find the most similar region, and a vector is calculated from the amount of movement. Another method is a method in which the amount of change in luminance (brightness) in an image is the same, that is, a method of solving by partial differential calculation with the amount of change in luminance gradient being constant. By the above method, a motion vector (amount of movement of x and y components on the image) as shown in FIG. 3 can be obtained.

  FIG. 4 is an example of an actually captured image. The Nth and N + 1th consecutive images taken by the image sensor (8) are taken as shown in FIG. The transfer paper (paper) shows a formed image on which characters are transferred, and the image carrier (belt) shows residual toner. Since the residual toner is used to determine the motion vector of the residual toner on the transfer body, the motion vector can be calculated by remaining slightly on the image carrier. When a motion vector is calculated for the image shown in FIG. 4, a result as shown in FIG. 5 is obtained. The calculated motion vectors are: motion vector Vpi = (Vpix, Vpiy) of the transfer paper portion, motion vector Vbi = (Vbix, Vbiy), (i = 0, 1, 2,... (Observation point) of the image carrier. , X, and y can be expressed by respective components). For the calculation of the amount of movement of the image, the sum Svpk and Svbk (k = x, y) of the respective motion vectors is obtained, and the x and y components are compared. Svby represents the amount of movement in the direction perpendicular to the transfer direction of the transfer body. As shown in FIG. 5, when the value of Svby is not 0, the target image of the motion vector moves in the direction perpendicular to the conveyance direction of the image carrier, and represents the amount of distortion of the transfer member. Svpy represents the amount of movement in the direction perpendicular to the transfer sheet conveyance direction. Therefore, the movement amount represented by Svpy-Svby represents the skew amount of the transfer paper after subtracting the distortion of the image carrier.

6 and 7 are diagrams for explaining a correction method by the distortion correction unit and the skew correction unit. Hereinafter, the correction method will be described in detail with reference to the drawings.
FIG. 6 is a diagram of an embodiment illustrating a distortion (meandering) correction unit of the intermediate transfer member.
As described above, the total meandering amount of the intermediate transfer member as an embodiment of the image carrier can be represented by Svby. Therefore, in order to correct the meandering of the intermediate transfer member (3), the intermediate transfer member (3) is corrected so that Svby becomes zero. As this correction method, as shown in FIG. 6, one of the driven roller (10) and the driving roller (11) that stretches the intermediate transfer member (3) is substantially the same as the other roller. Although the method of correcting by tilting from a parallel position is mentioned, it is not limited to this method.

FIG. 7 is a schematic diagram illustrating a skew correction unit in transfer paper transfer.
As described above, the total skew amount of the transfer paper can be expressed by Svpy. Therefore, in order to correct the skew of the transfer paper, the skew correction is performed so that Svpy becomes zero. As shown in FIG. 7, the skew correction unit includes a pair of skew correction rollers (13) and (14) on the downstream side in the conveyance direction of the transfer paper conveyance roller (12). Each of the skew correction rollers (13) and (14) includes different driving means (motors) (15) and (16). Examples of the skew correction method include a method of correcting the transfer paper conveyance skew by changing the rotation speed of the skew correction rollers (13) and (14) when the transfer paper is conveyed. It is not limited.

  The control unit can continuously process the distortion correction and the conveyance skew correction of the transfer body shown in FIGS. 6 and 7, and can perform feedback control based on the correction. Thereby, more accurate correction can be performed.

FIG. 8 is a flowchart showing a control method of the correction unit of the image forming apparatus according to the present invention.
With reference to FIG. 8, the control method of the correction means will be described in detail.

で計算する。評価関数は、得られた動きベクトルを均一化するために用いられる。連続撮影された搬送中の転写紙を剛体と仮定した場合、転写紙部及び転写体部の動きベクトルＶｐｉとＶｂｉは、それぞれ全て同一の値となる。しかしながら、転写紙には、様々な種類の用紙が存在するため、転写紙全てを剛体と仮定することはできない。従って、動きベクトル間のばらつきを均一化する必要がある。そこで、評価関数を使用して、動きベクトルの総和を算出し、計算された動きベクトルＶｐｉ及びＶｂｉに含まれる乱れや異なる動きベクトルを均一化して評価を行う。評価関数で計算した場合、Ｓｖｐｙが転写紙のスキュー量の総和であり、Ｓｖｂｙが転写体の歪み量の総和となる。次いで、制御部は、通過する転写紙に対してＳｖｐｙ＝０、Ｓｖｂｙ＝０もしくはＳｖｐｙ−Ｓｖｂｙ＝０となるように中間転写体の蛇行補正手段及びスキュー補正手段に制御信号を送り、補正制御を行う。 When the transfer paper that has passed through the transfer section passes through the image sensor, images of the transferred transfer paper surface are continuously captured using the image sensor. The captured image is sent to the control unit and the amount of movement is calculated. The control unit obtains the motion vector Vpi of the transfer paper being conveyed and the motion vector Vbi (i = 1, 2,..., N: measurement points) of the transfer unit being conveyed from the obtained continuous images. This is evaluated function Svpk =

Calculate with The evaluation function is used to make the obtained motion vector uniform. When it is assumed that the continuously transferred transfer paper being conveyed is a rigid body, the motion vectors Vpi and Vbi of the transfer paper portion and the transfer body portion are all the same value. However, since there are various types of transfer paper, it is not possible to assume that the transfer paper is a rigid body. Therefore, it is necessary to make the variation between motion vectors uniform. Therefore, the sum of motion vectors is calculated using the evaluation function, and the disturbances and the different motion vectors included in the calculated motion vectors Vpi and Vbi are equalized and evaluated. When calculated with the evaluation function, Svpy is the total skew amount of the transfer sheet, and Svby is the total distortion amount of the transfer body. Next, the control unit sends a control signal to the meandering correction unit and the skew correction unit of the intermediate transfer member so that Svpy = 0, Svby = 0, or Svpy−Svby = 0 for the passing transfer paper, and correction control is performed. Do.

  When the control signal sent from the control unit is a control signal for correcting the motion vector so that Svpy = 0 and Svby = 0, the roller (10) of the intermediate transfer device as shown in FIG. (11) By tilting one of the shafts, the meandering of the intermediate transfer member is corrected and controlled so that Svby = 0, and the rotational speed of the skew correcting rollers (13) and (14) is controlled as shown in FIG. As a result, correction control is performed so that Svpy = 0. If the control signal sent from the control unit is a control signal for correcting the motion vector so that Svpy−Svby = 0, whether the meandering of the intermediate transfer member is corrected by the correction unit. Alternatively, correction control is performed so that the skew amount of the transfer paper is corrected and Svpy−Svby = 0. The correction control is performed in real time.

  The image forming apparatus having the intermediate transfer member (belt) as the image carrier has been described above. However, the present invention relates to an image forming apparatus that does not include the intermediate transfer member, specifically, a photosensitive drum that is an image carrier. The present invention is also applicable to an image forming apparatus that transfers a toner image to transfer paper. In this case, the image sensor (8) may be arranged so that the toner image transferred to the transfer paper and the residual toner image on the surface of the photosensitive drum (6) are continuously photographed simultaneously.

  The image forming apparatus according to the present invention can be suitably used for various copying machines, printers, and FAX machines.

DESCRIPTION OF SYMBOLS 1 ... Paper feeder 2 ... Skew correction means 3 ... Intermediate transfer body 4 ... Secondary transfer roller 5 ... Intermediate transfer device 6 ... Photoconductor drum 7 ... Primary transfer Device 8... Image sensor 9... Control unit 10 .. Driven roller 11 .. Drive roller 12 .. Transfer paper transport roller 13... Skew correction roller 14. Driving means

Claims (5)

An image sensor that continuously shoots the image transferred to the transfer paper and the residual toner image on the surface of the image carrier so as to enter the frame of the same image;
An image forming apparatus that detects states of an image transferred to the transfer paper and a residual toner image on an image carrier based on continuous images taken by the image sensor. The image forming apparatus further includes a control unit,
The control unit analyzes a moving amount of an image transferred from the image sensor to be transferred to the transfer paper and a continuous image of a residual toner image on the image carrier, and based on the analysis result, the transfer paper 2. The image forming apparatus according to claim 1, further comprising detection means for detecting the skew of the image and the speed and meandering of the image carrier. The detection unit calculates a motion vector of the image transferred onto a transfer sheet and a motion vector of residual toner on the surface of the transfer body as the movement amount of the continuous image sent from the image sensor. Item 3. The image forming apparatus according to Item 2.   Based on the detection of the skew of the transfer paper and the speed and meandering of the image carrier by the detecting means, the skew correction means for correcting the skew of the transfer paper and / or the speed and / or meander of the image carrier is corrected. The image forming apparatus according to claim 2, further comprising an image carrier correction unit configured to perform the operation.   The image forming apparatus according to claim 1, wherein the image carrier is an intermediate transfer member that transfers toner images of a plurality of colors in an overlapping manner.

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