JP2005215482A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simply correct image shifts due to the difference between the linear velocity of an image carrier, such as an intermediate transfer body and the linear velocity of a secondary transfer belt. <P>SOLUTION: A toner image pattern, stipulated beforehand, is formed on an intermediate transfer drum 18 and this toner image pattern is detected by a density detection sensor 21 and outputted as an intermediate transfer body linear velocity detection value. Furthermore, the toner image pattern on the intermediate transfer drum is transferred to the secondary transfer belt 20 and made to be a transfer toner image pattern. In the density detection sensor 22, the transfer toner image pattern is detected, and the linear velocity of the transfer belt is outputted as the transfer belt liner velocity detection value. In a CPU, linear velocity adjustment control of the secondary transfer belt is carried out, according to the intermediate transfer body linear velocity detection value and the transfer belt linear velocity detection value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile machine, and more particularly to a color image forming apparatus that forms a color image using an intermediate transfer member.

  In general, in a color image forming apparatus using an intermediate transfer drum as an intermediate transfer member, there is one using a secondary transfer belt as a secondary transfer device. In such a color image apparatus, a speed difference of a specified value or more between the peripheral speed of the intermediate transfer drum and the linear speed (rotational speed) of the secondary transfer belt due to manufacturing errors, aging, or changes in the surrounding environment. When such a speed difference occurs, a so-called image shift (color shift) may occur when the toner image is secondarily transferred onto the recording paper.

  On the other hand, in order to cope with the color misregistration caused by the peripheral speed difference between the photosensitive drum and the intermediate transfer drum, the photosensitive drum is driven by the drum driving motor via the output gear and the drum driving gear, and the intermediate transfer drum is changed to another one. The drum drive motor is driven via the output gear and the input gear, and the photosensitive drum and the intermediate transfer drum are driven by friction while being pressed against each other. The angular velocity of the intermediate transfer drum due to the friction with the photosensitive drum and the drum drive motor When the difference between the angular velocity of the intermediate transfer drum and the intermediate transfer drum is large, a torque proportional to the difference is transmitted to the intermediate transfer drum by a torque limiter (see Patent Document 1).

JP 2003-156899 A (pages 3 to 5, FIGS. 1 and 2)

  Incidentally, in the image forming apparatus described in Patent Document 1, although the color shift caused by the peripheral speed difference between the photosensitive drum and the intermediate transfer belt is taken into consideration, the peripheral speed of the intermediate transfer drum and the secondary transfer belt are considered. No consideration is given to the image misalignment caused by the difference between the rotation speed and the color image formation in which the toner image on the intermediate transfer drum is secondarily transferred onto a recording sheet using a secondary transfer belt to form an image. In the apparatus, there is a problem that image shift such as color shift cannot be prevented. In particular, when the secondary transfer belt is brought into contact with the intermediate transfer belt in order to secondarily transfer the image already formed on the intermediate transfer drum to the recording paper, another image is being formed on the intermediate transfer drum. In some cases, if there is a linear velocity difference between the intermediate transfer drum and the secondary transfer belt that exceeds a specified value, the linear velocity of the intermediate transfer drum becomes linear before and after the secondary transfer belt is brought into contact with the intermediate transfer belt. Color shift occurs due to the change due to the difference.

  Therefore, in view of the problems of the prior art, the present invention provides a peripheral speed (linear speed) of an image carrier such as an intermediate transfer body and a rotational speed (linear speed) of a secondary transfer belt in an image forming apparatus using a secondary transfer belt. It is an object of the present invention to provide an image forming apparatus capable of easily correcting an image shift caused by a difference from the speed.

  Accordingly, in order to solve the above problems, the present invention provides an image forming apparatus having an image carrier on which a toner image is formed and a transfer belt for transferring the toner image on the image carrier to a recording medium. First toner image pattern forming means for forming a predetermined toner image pattern on the carrier, and a first linear velocity for detecting the linear velocity of the image carrier and outputting it as a first linear velocity detection value. Detecting means; second toner image pattern forming means for transferring a toner image pattern on the image carrier to the transfer belt to form a transfer toner image pattern; and detecting the transfer toner image pattern to detect the transfer belt A second linear velocity detection means for outputting the linear velocity as a second linear velocity detection value; and a linear velocity adjustment for performing linear velocity adjustment control of the transfer belt in accordance with the first and second linear velocity detection values. And having means It is intended.

  In the present invention, for example, the image bearing member is an intermediate transfer member, and the first linear velocity detection means detects a toner image pattern formed on the intermediate transfer member to determine the linear velocity of the intermediate transfer member. Obtained as the first linear velocity detection value. In this case, for example, a density sensor that detects the density of the toner image pattern is used as the first and second linear velocity detection means, and the density sensor used as the first linear velocity detection means is an image density. It is also used as a density sensor used for control. The toner image pattern has a plurality of different color patterns.

  In the present invention, the image bearing member includes a photosensitive drum and an intermediate transfer member, and a toner image pattern formed on the photosensitive drum is primarily transferred to the intermediate transfer member and then the intermediate transfer member. The toner image pattern is secondarily transferred to the transfer belt to form the transfer toner image pattern, and the intermediate transfer member is driven to rotate following the photosensitive drum. The linear velocity of the drum may be detected.

  As described above, the image forming apparatus according to the present invention forms a predetermined toner image pattern on the image carrier, detects the linear velocity of the image carrier, obtains the first linear velocity detection value, and The toner image pattern on the carrier is transferred to the transfer belt to form a transfer toner image pattern, and the transfer toner image pattern is detected to obtain the linear velocity of the transfer belt as the second linear velocity detection value. Since the linear velocity adjustment control of the transfer belt is performed according to the linear velocity detection value of 2, the image misalignment caused by the difference between the linear velocity of the image carrier and the linear velocity of the transfer belt can be easily corrected. There is.

  In the present invention, when the toner image pattern formed on the intermediate transfer member is detected to obtain the linear velocity of the intermediate transfer member as the first linear velocity detection value, the density sensor is used to control the image density. Since it is also used as a concentration sensor used when performing the above, there is an effect that an increase in cost can be prevented with few additional parts.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.

  Referring to FIG. 1, FIG. 1 is a diagram showing an example of a color image forming apparatus according to the present invention. Here, each color of yellow (Y), magenta (M), cyan (C), and black (BK) is shown. A color image forming apparatus using the above will be described as an example. The illustrated image forming apparatus 10 includes a photosensitive drum 11, and around the photosensitive drum 11, a charging device 12, a Y developing device 13, an M developing device 14, a C developing device 15, and a BK developing device 16. The photosensitive drum 11 is in contact with an intermediate transfer drum 18 that is an intermediate transfer body. On the other hand, an intermediate transfer drum cleaning unit 19, a secondary transfer belt 20, and a density detection sensor 21 are disposed around the intermediate transfer drum 18.

  As shown in the figure, the secondary transfer belt 20 includes a driving roller 20a and a driven roller 20b, and a belt body 20c is stretched between the driving roller 20a and the driven roller 20b, and density detection is performed corresponding to the driving roller 20a. A sensor 22 is arranged.

  Referring also to FIG. 2, the photosensitive drum 11 is rotationally driven by the photosensitive member driving unit 31. In the illustrated example, the intermediate transfer drum 18 abuts on the photosensitive drum 11 and responds to the rotation of the photosensitive drum 11. Rotate. That is, the intermediate transfer drum 18 is driven by the photosensitive drum 11. The rotational speed of the photoconductor drum 11 is detected by the photoconductor linear speed detector 32. For example, a position detection mark is formed on the flange or the like of the photosensitive drum 11, and the linear velocity of the photosensitive drum 11 is detected by detecting the mark by the photosensitive linear velocity detection unit 32, thereby detecting the photosensitive linear velocity. The CPU 33 drives and controls the photosensitive member driving unit 31 in accordance with the photosensitive drum linear velocity detection value output from the unit 32.

  The drive roller 20a of the secondary transfer belt 20 is driven by the transfer belt drive unit 34, whereby the belt body 20c rotates. The rotational speed (linear speed) of the secondary transfer belt 20 is detected as a transfer belt linear speed detection value by a density detection sensor (transfer belt linear speed detection unit) 22 as described later, while the rotation of the intermediate transfer drum 18 is detected. The speed (linear speed) is detected as an intermediate transfer body linear speed detection value by a density detection sensor (intermediate transfer body linear speed detection unit) 21. The transfer belt linear velocity detection value and the intermediate transfer member linear velocity detection value are given to the CPU 33, and the CPU 33 determines the transfer belt drive unit based on the transfer belt linear velocity detection value and the intermediate transfer member linear velocity detection value as described later. 34 is driven and controlled.

  When forming a color image, the surface of the photosensitive drum 11 is charged by the charger 12, and then the surface of the photosensitive drum 11 is exposed by an exposure unit (not shown) according to the image data. An electrostatic latent image is formed on the drum 11. The electrostatic latent image on the photosensitive drum 11 is developed by the Y developing unit 13 to be a Y toner image, transferred to the intermediate transfer drum 18 (primary transfer), and the residual Y toner remaining on the photosensitive drum 11 is It is removed by the photoconductor cleaning unit 17.

  In this way, an M toner image, a C toner image, and a BK toner image are sequentially formed on the photosensitive drum 11 by the M developing device 14, the C developing device 15, and the BK developing device 16. Next transfer is performed to superimpose each color, and a color toner image is formed on the intermediate transfer drum 18. Then, the secondary transfer belt 20 is brought into contact with the intermediate transfer drum 18 in order to perform secondary transfer.

  The color toner image on the intermediate transfer drum 18 is secondarily transferred onto a recording sheet (not shown) conveyed from a paper feeding device (not shown) by the secondary transfer belt 20 at the secondary transfer position, and the conveying belt. (Not shown) is sent to a fixing unit (not shown) where the color toner image on the recording paper is fixed. Thereafter, the recording sheet is discharged to a discharge tray (not shown) via a discharge path (not shown). After the secondary transfer, the toner remaining on the intermediate transfer drum 18 is removed by the intermediate transfer drum cleaning unit 19.

  The density of the toner image formed on the intermediate transfer drum 18 is detected by the density detection sensor 21, and is supplied to a control device (not shown in FIG. 1) as an image density detection signal. The density detection sensor 21 is, for example, a reflection type sensor. The density detection sensor 21 sends light to the intermediate transfer drum 18 and outputs a voltage signal corresponding to the reflected light reflected from the toner image on the intermediate transfer drum 18. To do. Then, the CPU 33 performs image density control according to the voltage value indicated by the voltage signal.

  By the way, between the peripheral speed of the intermediate transfer drum 18 and the rotational speed of the secondary transfer belt 20, a set value of a speed difference (for example, the line of the secondary transfer belt 20 with respect to the linear speed of the intermediate transfer drum 18). A difference in speed may occur with respect to the speed (which is set to 1.00 times) (for example, a speed difference may occur due to manufacturing errors, aging, or changes in the surrounding environment). If there is such a speed difference, an image shift such as a color shift may occur when the image is secondarily transferred to a recording sheet. That is, when the intermediate transfer drum 18 carries two sheets (two pages) of toner images, color deviation occurs in the second sheet of toner images. That is, at the time of continuous printing, the second image starts to be formed to improve the printing speed when the first image formation is completed, and the secondary transfer belt 20 is brought into contact with the intermediate transfer drum 18 for the secondary transfer. At this time, if the linear velocity difference between them is equal to or greater than a specified value, the linear velocity of the intermediate transfer drum 18 changes before and after the contact of the secondary transfer belt 20, and color misregistration occurs.

  In order to prevent the above-described color misregistration, here, the CPU 33 performs linear speed adjustment control (transfer belt linear speed adjustment) of the secondary transfer belt 20 every predetermined number of printed sheets (for example, 4,000 printed sheets). Control). Referring to FIG. 3, in the transfer belt linear velocity adjustment control, the CPU 33 performs image formation control to form toner images on the photosensitive drum 11 in the order of Y, M, C, and BK. These toner images are sequentially transferred to the intermediate transfer drum 18 to form a speed measurement reference pattern (toner image pattern: hereinafter simply referred to as a reference pattern) on the intermediate transfer drum 18 as shown in FIG. The speed measurement reference pattern may also be used as an image density detection pattern used for image density detection for maintaining an appropriate image density of the toner image formed on the intermediate transfer drum 18. In the following example, since the image density detection pattern is also used as the speed measurement reference pattern, it is not necessary to separately measure the image density and the speed measurement, so that the waiting time until the image formation is reduced for the user. There is an advantage.

  As described above, since toner images are formed on the photosensitive drum 11 in the order of Y, M, C, and BK, the reference pattern is a pattern arranged in the order of BK, C, M, and Y. In the example shown in FIG. 3A, BK, C, M, and Y each have five pattern bodies 41 to 44. In BK, the width of each pattern body 41 is L1, and each pattern The interval between the writing ends of the body 41 is L2. Similarly, in C, the width of each pattern body 42 is L1 ′, the interval between the write ends of each pattern body 42 is L2 ′, and in M, the width of each pattern body 43 is L1 ″. The interval between the write ends of each pattern body 43 is L2 ″. In Y, the width of each pattern body 44 is L1 "', and the interval between the write ends of each pattern body 44 is L2"'.

  The reference pattern on the intermediate transfer drum 18 is detected by the density detection sensor 21, and for example, the intermediate transfer body linear velocity detection value shown in FIG. 3B is output as a voltage signal from the density detection sensor 21. Since the cycle of the voltage signal becomes shorter as the linear velocity of the intermediate transfer drum 18 becomes faster, the CPU 33 can know the linear velocity of the intermediate transfer drum 18 according to the cycle of the voltage signal. In the example shown in FIG. 3B, a density detection sensor is used in which the amplitude of the voltage signal increases as the reflected light from the reference pattern decreases, and as shown in FIG. A density detection sensor may be used in which the amplitude of the voltage signal decreases as the amount of reflected light decreases.

  The reference pattern formed on the intermediate transfer drum 18 as described above is then transferred to the secondary transfer belt 20 (recording paper is not fed during this speed adjustment control). The reference pattern transferred to the secondary transfer belt 20 is detected by the density detection sensor 22, and the transfer belt linear velocity detection value shown in FIG. 3D is output from the density detection sensor 22 as a voltage signal. Since the cycle of this voltage signal becomes shorter as the linear velocity of the secondary transfer belt 18 becomes faster, the CPU 33 can know the linear velocity of the secondary transfer belt 18 according to the cycle of the voltage signal. 3D is a waveform corresponding to FIG. 3B, and FIG. 3E is a waveform corresponding to FIG.

  Now, as shown in FIG. 3B or 3C, if the period of the voltage signal output from the concentration detection sensor 21 changes as t11, t12, t13, t14,... The linear velocity of the intermediate transfer drum 18 is obtained according to the average value or the representative value. Similarly, assuming that the period of the voltage signal output from the density detection sensor 22 has changed to t21, t22, t23, t24,..., The CPU 33 causes the secondary transfer belt according to the average value or representative value of these periods. 20 linear velocity is obtained.

  The CPU 33 compares the linear velocity of the intermediate transfer drum 18 obtained as described above with the linear velocity of the secondary transfer belt 20, finds a deviation, and determines the rotation speed of the transfer belt drive unit 34 according to the deviation. adjust. Until the next speed adjustment control is performed, the CPU 33 controls the transfer belt drive unit 34 at the adjusted rotational speed. The reference pattern transferred to the secondary transfer belt 20 is cleaned by a cleaning device (not shown) after speed adjustment control.

  In this way, if the speed of the secondary transfer belt 20 is adjusted using the reference pattern, an image shift caused by the difference between the linear speed of the intermediate transfer drum 18 and the linear speed of the secondary transfer belt 20 is eliminated. It can be easily corrected.

  In the above example, the example in which the speed adjustment control is performed for each predetermined number of printed sheets has been described. For example, when the ambient atmosphere (for example, humidity) changes by a predetermined value or more, the speed adjustment control is performed. You may do it. In the above-described example, the reference pattern is detected by the density detection sensor 21 to obtain the linear velocity detection value of the intermediate transfer drum 18, but the intermediate transfer drum 18 is driven by the photosensitive drum 11. Thus, the speed adjustment control of the secondary transfer belt 20 is performed in accordance with the photosensitive drum linear velocity detection value obtained by the photosensitive member linear velocity detection unit 32 and the transfer belt linear velocity detection value obtained from the density detection sensor 22. It may be. In this case, the photosensitive drum 11 becomes an image carrier for speed detection. In the above example, the reference patterns arranged in the order of BK, C, M, and Y are given as an example. However, the order of colors is not limited, and the linear velocity is detected using at least one of the reference patterns. Is also possible.

  By the way, if the linear velocity of the secondary transfer belt 20 becomes slower than the linear velocity of the intermediate transfer drum 18, a transfer defect occurs when the toner image is secondarily transferred from the intermediate transfer drum 18 to the recording paper. There is. In order to prevent such problems, the linear speed of the secondary transfer belt 20 is increased by ± 0.0% to + 0.5% with respect to the linear speed of the intermediate transfer drum 18.

  For example, when the linear speed of the secondary transfer belt 20 is set to + 0.25% faster than the linear speed of the intermediate transfer drum 18, the CPU 33 detects the intermediate transfer body linear speed detection value and the transfer belt linear speed detection value. Accordingly, the speed adjustment control is performed so that the linear velocity of the secondary transfer belt 20 is + 0.25% faster than the linear velocity of the intermediate transfer belt 18. In any case, the CPU 33 adjusts the linear velocity of the secondary transfer belt 20 in accordance with the linear velocity detection value and the transfer belt linear velocity detection value of the photosensitive drum 11 or the intermediate transfer drum 18 that is an image carrier. Become.

  As is apparent from the above description, the image carrier is an intermediate transfer drum and / or a photosensitive drum, and the CPU 33, the developing devices 13 to 16, the charger, the exposure device, and the like are collectively referred to as the first and the second. Used as the second toner image pattern forming unit, the first linear velocity detecting unit is the photosensitive member linear velocity detecting unit 32 or the intermediate transfer member linear velocity detecting unit 21, and the second linear velocity detecting unit is the transfer belt line. This is a speed detection unit 22. Further, the CPU 33 functions as a linear speed adjusting means. Further, although the image bearing member is an intermediate transfer drum which is an intermediate transfer member, it is obvious that the present invention can be applied to a photosensitive member (photosensitive drum, photosensitive belt, etc.).

  A predetermined toner image pattern is formed on the image carrier, the linear velocity of the image carrier is detected to obtain a first linear velocity detection value, and the toner image pattern on the image carrier is transferred to a transfer belt. The transfer toner image pattern is detected, the transfer toner image pattern is detected, and the linear velocity of the transfer belt is obtained as the second linear velocity detection value, and the transfer belt line is determined according to the first and second linear velocity detection values. Since the speed adjustment control is performed, the image misalignment caused by the difference between the linear velocity of the image carrier and the linear velocity of the transfer belt can be easily corrected, so that it can be applied to a color image forming apparatus such as a copying machine or a printer. .

1 is a cross-sectional view schematically showing an example of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing a control system used in the image forming apparatus shown in FIG. 1. 2A and 2B are diagrams for explaining speed adjustment control in the image forming apparatus illustrated in FIG. 1, in which FIG. 1A is a diagram illustrating a reference pattern for speed measurement, and FIG. FIG. 4C is a diagram showing another example of the output from the intermediate transfer body density detection sensor, FIG. 4D is a diagram showing an example of the output from the secondary transfer belt density detection sensor, and FIG. It is a figure which shows the other example of the output from the density | concentration detection sensor for secondary transfer belts.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 11 Photoconductor drum 12 Charger 13 Yellow (Y) developing device 14 Magenta (M) developing device 15 Cyan (C) developing device 16 Black (BK) developing device 17 Photoconductor cleaning unit 18 Intermediate transfer drum 19 Intermediate Transfer drum cleaning unit 20 Secondary transfer belt 21 Intermediate transfer member linear velocity detection unit (density detection sensor)
22 Transfer belt linear velocity detector (density sensor)
31 Photoconductor Drive Unit 32 Photoconductor Linear Speed Detection Unit 33 CPU
34 Transfer belt drive

Claims (5)

In an image forming apparatus comprising: an image carrier on which a toner image is formed; and a transfer belt that transfers the toner image on the image carrier to a recording medium.
First toner image pattern forming means for forming a predetermined toner image pattern on the image carrier;
First linear velocity detection means for detecting the linear velocity of the image carrier and outputting the first linear velocity detection value;
A second toner image pattern forming means for transferring a toner image pattern on the image carrier to the transfer belt to form a transfer toner image pattern;
Second linear velocity detection means for detecting the transfer toner image pattern and outputting the linear velocity of the transfer belt as a second linear velocity detection value;
An image forming apparatus comprising: a linear velocity adjusting unit that performs linear velocity adjustment control of the transfer belt in accordance with the first and second linear velocity detection values. The image carrier is an intermediate transfer member;
The first linear velocity detection means detects a toner image pattern formed on the intermediate transfer member and obtains the linear velocity of the intermediate transfer member as the first linear velocity detection value. The image forming apparatus according to claim 1.   3. The image forming apparatus according to claim 2, wherein a density sensor that detects the density of the toner image pattern is used as the first and second linear velocity detection means.   4. The image forming apparatus according to claim 3, wherein the toner image pattern includes a plurality of different color patterns. A photosensitive drum and an intermediate transfer member are used as the image carrier,
The toner image pattern formed on the photosensitive drum is primarily transferred to the intermediate transfer member, and then the toner image pattern on the intermediate transfer member is secondarily transferred to the transfer belt to form the transfer toner image pattern.
The intermediate transfer member is driven to rotate following the photosensitive drum,
2. An image forming apparatus according to claim 1, wherein said first linear velocity detecting means detects a linear velocity of said photosensitive drum.

Images