JP2002365880A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately align a primary transferred image on a recording medium even though the speed of an intermediate transfer belt is varied. SOLUTION: The intermediate transfer belt 11 is transported along a specified transport path, and a toner image is transferred as the primary transferred image. An image detection sensor 71 is arranged between a photoreceptor unit and a secondary transfer position positioned on a most downstream side on the transport path, and a controller 72 starts the supply of the recording medium to the secondary transfer position in accordance with timing in which the image detection sensor detects the primary transferred image. When the time needed to feed the recording medium to the secondary transfer position is set as (t), the feeding speed of the intermediate transfer body is set as (s), a distance from the photoreceptor unit positioned on the most downstream side to the position of the image detection sensor is set as L, the length of a longest recording medium capable of being used is set as L0 , and a distance from the position of the image detection sensor 71 to the secondary transfer position is set as (x), the relations of x>s×t and also L>L0 are stipulated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic process, and more particularly, to an image forming apparatus for forming an image using an intermediate transfer member.

[0002]

2. Description of the Related Art Generally, an electrophotographic image forming apparatus (image forming apparatus) using a so-called intermediate transfer member when forming a color image using an electrophotographic process is known. In this image forming apparatus, cyan (C), magenta (M),
A photoreceptor unit having a photoreceptor drum is provided for each color of yellow (Y) and black (BK). That is, it has a photoconductor unit for cyan, a photoconductor unit for magenta, a photoconductor unit for yellow, and a photoconductor unit for black. Then, the electrostatic latent images formed on the four photosensitive drums are developed using cyan toner, magenta toner, yellow toner, and black toner, respectively, to obtain toner images of respective colors. After the respective color toner images are sequentially primary-transferred to the intermediate transfer member, the transfer image transferred to the intermediate transfer member is secondary-transferred and fixed to a recording medium (paper) to obtain a color image.

Each photoconductor unit has a photoconductor drum. Around the photoconductor drum, a charger, an exposure unit, a developing device, a transfer device (primary transfer device), a cleaning unit, and a charge removal unit ( Eraser) is located. After the surface of the photosensitive drum is uniformly charged by the charger, an electrostatic latent image is formed on the surface of the photosensitive drum by the exposure unit. Thereafter, the developing device develops the electrostatic latent image to form a toner image on the photosensitive drum, and the transfer device transfers the toner image on the photosensitive drum to the intermediate transfer member. Then, the residual toner remaining on the photosensitive drum is removed by the cleaning unit, and further, the surface of the photosensitive drum is discharged by the discharging unit.

As described above, after the toner image is transferred as a primary transfer image to the intermediate transfer member in each photoconductor unit, the primary transfer image is transferred onto a recording medium using a secondary transfer device, for example. A secondary transfer image is obtained. After that, the secondary transfer image on the recording medium is fixed to the recording medium by the fixing unit to obtain a color image.

In the above-described image forming apparatus, an endless belt-shaped transfer member (hereinafter, referred to as an intermediate transfer belt) rotating in a predetermined direction is generally used as the intermediate transfer member. Each of the photoconductor units described above is arranged. The above-mentioned secondary transfer device is disposed downstream of the intermediate transfer belt in the rotation direction.

In the above-described image forming apparatus, when the primary transfer image on the intermediate transfer belt is secondarily transferred onto a recording medium, the primary transfer image is transferred onto a recording medium sent from a recording medium supply device (for example, a sheet feeding device). The images need to be precisely registered.

Further, in a color image forming apparatus,
As with the monochrome image forming apparatus, various types of recording media are used. For example, when an OHP film is used as the recording medium, the monochrome image forming apparatus simply fixes the secondary transfer image on the OHP film. However, in the color image forming apparatus, when the OHP film is used as a recording medium, sufficient fixability is required due to the requirement of transparency and color development of an image fixed on the OHP film. Therefore, it is necessary to reduce the printing speed (transfer speed). As described above, in the color image forming apparatus, it is necessary to adjust the printing speed according to the type of the recording medium. For example, according to the type of the recording medium, the rotation speed of the photosensitive drum and the rotation speed of the intermediate transfer belt are required. Is set.

However, if the rotation speed of the intermediate transfer belt is changed, the time required for the transfer image primary-transferred to the intermediate transfer belt to reach the secondary transfer unit changes, and accordingly, the recording medium It is necessary to adjust the timing of sending the recording medium from the supply device.

For this reason, for example, a detected portion (for example, a projection, a hole, or a reflection surface) is formed on the intermediate transfer belt, and a position detection sensor for detecting the detected portion is disposed. 2. Description of the Related Art A detected portion is detected by a position detection sensor. Then, when a predetermined time elapses after the detection of the detected portion, the recording medium is sent out.

Since the rotation speed of the photosensitive drum and the rotation speed of the intermediate transfer belt are interrelated, a detected portion is formed on the last photosensitive drum, and the detected portion is detected. You may make it detect with a sensor. Also in this case, the recording medium is sent out after a predetermined time has passed since the detection of the detected portion.

[0011]

However, as described above, if the recording medium is sent from the recording medium supply device when a predetermined time has elapsed after the detection of the detected portion, the intermediate Due to the fact that the rotational speed of the transfer belt itself is detected, the timing at which the primary transfer image actually reaches the secondary transfer unit may be shifted. That is, the primary transfer image cannot be accurately positioned on the recording medium. When the rotation speed of the photosensitive drum and the rotation speed of the intermediate transfer belt are set according to the type of the recording medium,
Since the rotation speed is different for each recording medium, an error at the time of alignment becomes larger.

Japanese Patent Laying-Open No. 2000-284555 (conventional example) discloses an example in which a sensor for detecting an image is disposed on a secondary transfer roller as an image forming apparatus. The deviation from the image recording position is measured. That is, in this conventional example, after the secondary transfer, the amount of displacement of the registration mark is detected, and only the displacement of the image is detected, so that the primary transfer image can be accurately aligned on the recording medium. Is difficult.

In any case, there has been a problem that, if the speed of the intermediate transfer belt fluctuates, the primary transfer image cannot be accurately positioned on the recording medium.

An object of the present invention is to provide an image forming apparatus capable of accurately positioning a primary transfer image on a recording medium even when the speed of an intermediate transfer belt fluctuates.

[0015]

According to the present invention, there are provided a plurality of photoreceptor units for developing toner images by developing an electrostatic latent image formed on an image carrier provided for each color. An intermediate transfer body that is conveyed along a predetermined conveyance path and the toner image is transferred as a primary transfer image, wherein the photoconductor units are arranged along the conveyance path, and are downstream of the conveyance path. An image forming apparatus that forms an image by transferring the primary transfer image to a recording medium at a secondary transfer position positioned on the side of the photosensitive member positioned at the most downstream of the plurality of photoconductor units on the transport path An image detection sensor disposed between the body unit and the secondary transfer position, and starting supply of the recording medium to the secondary transfer position according to a timing at which the image detection sensor detects the primary transfer image. Control means The image forming apparatus is obtained which is characterized by having a.

In the present invention, on the transport path of the intermediate transfer member,
The primary transfer image on the intermediate transfer member is detected by an image detection sensor disposed between the photosensitive member unit positioned at the most downstream of the plurality of photosensitive member units and the secondary transfer position, and according to the detection result. To control the conveyance of the recording medium. Therefore, the primary transfer image can be accurately positioned on the sheet as compared with the case where the detected portion is provided on the intermediate transfer belt and the conveyance of the sheet is controlled based on the detection result.

At this time, the time required for the recording medium to be conveyed is started or resumed and conveyed to the secondary transfer position is t, the conveying speed of the intermediate transfer body is s, and the recording medium is positioned at the lowermost stream. When the distance from the photoconductor unit to the position of the image detection sensor is L, the length of the longest usable recording medium is L ₀ , and the distance from the position of the image detection sensor to the secondary transfer position is x. Where x> s × t and L
> L ₀ is defined.

[0018] Thus, because regulates the relationship x> s × t a and L> L _0, even if there is a variation in the conveyance speed of the intermediate transfer body, one caused by the deviation of the conveying speed primary The shift amount of the transferred image can be reduced to a negligible level.

In addition, a detection image for detecting the leading end of the primary transfer image may be transferred to the intermediate transfer body in addition to the primary transfer image. When a detected image is detected, an image detection signal is sent to the control means. Further, since the primary transfer image is sequentially transferred to the intermediate transfer body, a visual image for position detection is transferred between the primary transfer images, and the image detection sensor detects the visual image when the visual image is detected. An image detection signal may be sent to the control means.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. The dimensions of the components in the illustrated example,
Materials, shapes, relative arrangements, and the like are not intended to limit the scope of the present invention, but are merely illustrative examples, unless otherwise specified.

First, referring to FIG. 1, the illustrated image forming apparatus includes an endless belt-shaped intermediate transfer member 11 as an intermediate transfer member.
(Hereinafter, this intermediate transfer member is referred to as an intermediate transfer belt). A plurality of photoconductor units (toner image forming units) are arranged along the rotation direction of the intermediate transfer belt 11 (conveying direction: indicated by solid arrows in the drawing). In the illustrated example, four photoconductor units 21 to 24 are arranged along the intermediate transfer belt 11. For example, from the left side in the figure, a yellow photoconductor unit, a magenta photoconductor unit, and a cyan photoconductor unit , And a photoconductor unit for black. In FIG. 1, for convenience of explanation, only the photoconductor drums 21a to 24a provided in the photoconductor units 21 to 24, respectively, are shown.
Other components are omitted.

Primary transfer rollers 31 to 34 are arranged opposite the photosensitive drums 21a to 24a, and the intermediate transfer belt 11 is sandwiched between the photosensitive drums 21a to 24a and the primary transfer roller. As shown, the intermediate transfer belt 11 is supported by support rollers 41 to 43 and is conveyed in the direction of the solid line arrow in the figure. , A secondary transfer roller 51 is disposed. And
The intermediate transfer belt 11 is held between the support roller 42 and the secondary transfer roller 51. Paper (not shown) is supplied between the secondary transfer roller 51 and the intermediate transfer belt 11 via a registration roller 52 from a paper feeding device (not shown).

In image formation, the surface of the photosensitive drum 21a is uniformly charged, and then the photosensitive drum 21a is exposed to form an electrostatic latent image on the surface of the photosensitive drum 21a.
Thereafter, the electrostatic latent image is developed to form a toner image on the photosensitive drum 21a.

The toner image on the photosensitive drum 21a is transferred to the intermediate transfer belt 11 by the primary transfer roller 31. Then, after the residual toner remaining on the photosensitive drum 21a is removed, the surface of the photosensitive drum 21a is discharged.

Also on the photosensitive drums 22a to 24a, toner images are formed in the same manner as the photosensitive drum 21a, and the toner images formed on the photosensitive drums 22a to 24a are sequentially transferred by the primary transfer rollers 32 to 34 to intermediate transfer. The image is transferred onto the belt 11. That is, in each of the photoconductor units 21 to 24, the toner image is transferred to the intermediate transfer belt 11 as a primary transfer image. In this way, for example, cyan, magenta, yellow, and black toner images are sequentially superimposed on the intermediate transfer belt 11 and transferred.

As described above, the toner image (primary transfer image) transferred to the intermediate transfer belt 11 is sent toward the secondary transfer roller 51 as the intermediate transfer belt 11 is conveyed. Then, the toner image (primary transfer image) on the intermediate transfer belt 11 is transferred to the sheet by the secondary transfer roller 51 (secondary transfer). A fixing unit (not shown) is disposed downstream of the sheet in the conveyance direction, and the secondary transfer image transferred to the sheet is pressed and heated to the sheet by the fixing unit to be fixed.

The support roller (counter electrode roller) 43
A cleaning blade (not shown) is disposed to face the surface of the intermediate transfer belt 11 by the cleaning blade.

Here, with reference to FIG. 2, a conventional paper feed control will be described to facilitate understanding of the paper feed control according to the present invention.

Now, it is assumed that a detected portion is formed on the intermediate transfer belt 11, and the detected portion is detected by a position detection sensor (not shown). The position detection sensor sends out a position detection signal when detecting the detected portion.
In response to the position detection signal, a control unit (not shown)
That is, the photoconductor units 21 to 24 are drive-controlled based on the position detection timing. Thus, after the electrostatic latent images are formed on the photosensitive drums 21a to 24a, a toner image is formed. Then, as described above, the toner images of each color are sequentially transferred onto the intermediate transfer belt 11.

The control unit includes photoconductor units 21 to 24
After the start of the drive control, that is, the time (first time) from when the position detection signal is received to when the primary transfer image reaches the secondary transfer position is set according to the rotation speed of the intermediate transfer belt 11. At the same time, a time (second time) from when the registration roller 52 is driven to when the sheet reaches the secondary transfer position is set. Therefore, the control unit drives the registration roller 52 to send the sheet to the secondary transfer position when a predetermined time determined according to the first and second times elapses after receiving the position detection signal. That is, the control unit sets the predetermined time (T
After a), the registration roller 52 is driven to feed the sheet to the secondary transfer position.

In other words, the control unit starts the control of the photosensitive units 21 to 24 (the photosensitive drums 21a to 21a).
4a), a predetermined time (T
After a), the registration roller 52 is driven (registration start). Then, the sheet is sent to the secondary transfer position by the registration roller 52, and the primary transfer image on the intermediate transfer belt 11 is transferred to the sheet by the secondary transfer roller 51.

However, in the above-described paper feed control, if the transport speed of the intermediate transfer belt 11 is shifted before the secondary transfer is performed, the supply timing of the sheet is shifted due to the shift in the transport speed. Will be. That is, when the paper reaches the secondary transfer position, the primary transfer image is shifted from the secondary transfer position due to the shift amount of the transport speed (the shift amount at the secondary transfer position is Deviation x
Ta).

More specifically, as shown in FIG. 2, when the conveying speed of the intermediate transfer belt 11 is higher than a normal belt speed (theoretical value), a predetermined time (from the start of latent image formation (latent image writing)). After the elapse of Ta), when the registration roller is driven, the primary transfer image reaches the secondary transfer position before the sheet (image precedes).

On the other hand, if the conveyance speed of the intermediate transfer belt 11 is lower than the theoretical value, when the paper feed roller is driven after a predetermined time (Ta) has elapsed from the start of writing the latent image, the paper becomes earlier than the primary transfer image. It will reach the secondary transfer position (image delay).

As described above, in the conventional paper feed control, if the transport speed of the intermediate transfer belt 11 fluctuates for some reason, the primary transfer image on the intermediate transfer belt 11 cannot be accurately positioned on the paper. In order to prevent such a problem, for example, the transport speed of the intermediate transfer belt 11 must be precisely controlled.

Here, an example of paper feed control according to the present invention will be described with reference to FIGS.

In the illustrated example, an image detection sensor (for example, a CCD) 71 is used in place of the position detection sensor, and the image detection sensor 71 is connected to the photosensitive drum 24 a on the conveyance path of the intermediate transfer belt 11. It is arranged between the next transfer position. The image detection sensor 71 is connected to a paper feed control device 72, and the paper feed control control device 72 controls the driving of the registration roller 52 as described later.

Now, the time required for the paper to be transported from the registration roller 52 to the secondary transfer position is t, the transport speed of the intermediate transfer belt 11 is s, and the primary transfer position of the final stage (that is, the photosensitive drum 24a The distance from the contact point A) with the primary transfer roller 34 to the position of the image detection sensor 71 is L,
Length of the longest sheet available (the length of the longest sheet available the conveying speed in a mode capable of varying the intermediate transfer belt 11) as L _0, the secondary from the position where the image detecting sensor 71 is installed When the distance to the transfer position is x, x> s
And a × t defines the relation of _L> L _0. At this time, from the position where the image detection sensor 71 is arranged, the secondary transfer position (T)
The time required for the primary transfer image to reach is represented by x / s.

When the image detection sensor 71 detects the leading end of the primary transfer image, it provides an image detection signal to the paper feed control device 72. Upon receiving the image detection signal from the image detection sensor 71, the paper feed control device 72 drives the registration roller 52 and starts the conveyance of the paper after a predetermined control time Tb has elapsed. The control time Tb is substantially equal to x / s, and the control time Tb elapses immediately after at least a part of the primary transfer is completed and the secondary transfer is performed. And
The control time Tb may be set slightly longer than the time (t) required for the sheet to reach the secondary transfer position T from the registration roller 52 (nip portion R of the registration roller). As a result, the control time Tb can be set shorter than the predetermined time Ta described with reference to FIG. That is, while the predetermined time Ta shown in FIG. 2 starts from the start of writing the latent image, the control time Tb shown in FIG. 3 starts from the time when the image detection sensor 71 detects the primary transfer image.
<Ta.

Note that a visible image for detecting a transferred image may be formed at the tip of the primary transferred image. Then, when the image detection sensor 71 detects a visible image, it sends out an image detection signal. This makes it easier to detect the primary transfer image.

Further, in the above-described image forming apparatus, since a primary transfer image (color transfer image) is continuously formed, a visible image for detecting the transfer image is formed between the primary transfer images. You may. In the above-described example, the conveyance of the sheet is started by controlling the driving of the registration roller 52. However, the driving of the sheet feeding roller and the conveyance roller may be controlled. When the predetermined control time Tb elapses after receiving the image detection signal from, the conveyance of the sheet may be started.

As is apparent from the above description, after the primary transfer image is detected by the image detection sensor 71, the transport speed of the intermediate transfer belt 11 is maintained during the time until the primary transfer image reaches the secondary transfer position. Even if the gap occurs, as described above,
Since the relationship of x> s × t and L> L ₀ is defined, the shift amount of the primary transfer image at the secondary transfer position is at most the shift amount of the transport speed × Tb. And the control time Tb
Is extremely shorter than the predetermined time Ta described with reference to FIG. 2, so that the shift amount of the primary transfer image due to the shift of the transport speed is negligibly small.

That is, when the belt speed is higher than the theoretical value shown in FIG. 3, the registration start is advanced accordingly, but since the control time Tb is extremely short, the deviation amount of the primary transfer image is negligibly small. Similarly, when the belt speed becomes slower than the theoretical value shown in FIG. 3, the registration start is delayed correspondingly, but since the control time Tb is extremely short, the shift amount of the primary transfer image is negligibly small. . Generally, the speed fluctuation of the intermediate transfer belt 11 is extremely small.

As described above, the primary transfer image on the intermediate transfer belt is detected by the image detection sensor, and the conveyance of the sheet is controlled based on the detection result. In this case, the primary transfer image can be more accurately positioned on the sheet as compared with the case where the conveyance of the sheet is controlled based on the detection result.

[0045] Further, as described above, by defining the relationship x> s × t a and L> L _0, because by placing the image sensor, for example, there is a variation in the conveyance speed of the intermediate transfer belt 11 However, the shift amount of the primary transfer image caused by the shift of the transport speed can be reduced to a negligible amount.

If a visual image for detecting a transferred image is formed at the leading end of the primary transferred image, the image detection sensor 71 sends an image detection signal when detecting the visual image. The position of the image itself can be detected more accurately and easily.

Further, in the above-described image forming apparatus, since the primary transfer image (color transfer image) is formed continuously, the above-mentioned visible image for detecting the transfer image is formed between the primary transfer images. This makes it possible to accurately and easily perform individual positions of the continuously formed primary transfer image.

[0048]

As described above, according to the present invention, the intermediate transfer member is disposed between the secondary transfer position and the photosensitive unit located at the most downstream of the plurality of photosensitive units on the transport path of the intermediate transfer member. The detected image detection sensor detects the primary transfer image on the intermediate transfer body, and controls the conveyance of the recording medium according to the detection result. As compared with the case where the conveyance of the sheet is controlled based on the result, there is an effect that the primary transfer image can be accurately positioned on the sheet.

Further, the recording medium is transported to the secondary transfer position.
T, and the transport speed of the intermediate transfer member
s, image detection from the photoconductor unit positioned at the most downstream
The distance to the position of the output sensor is L, the longest record that can be used
The length of the medium is L₀, Secondary transfer from the position of the image detection sensor
When the distance to the position is x, x> s × t and L> L
₀Stipulates the relationship between
Even if the feed speed fluctuates, the
It is possible to make the deviation amount of the next transfer image so small that it can be ignored.
There is an effect that can be cut.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of an image forming apparatus according to the present invention.

FIG. 2 is a diagram for explaining conventional paper feed control.

FIG. 3 is a diagram for explaining sheet feed control in the image forming apparatus shown in FIG. 1;

[Explanation of symbols]

Reference Signs List 11 Intermediate transfer belt 21, 23, 23, 24 Photoconductor unit 31, 32, 33, 34 Primary transfer roller (conductive elastic roller) 41, 42, 43 Support roller 51 Secondary transfer roller 52 Registration roller 71 Image detection sensor 72 Paper feed control device

Continued on the front page F-term (reference) 2H027 DA21 DE02 DE09 ED16 EF09 2H030 AB02 AD05 AD17 BB02 BB42 BB46 BB56 BB63 2H200 FA04 FA17 GA12 GA23 GA47 HA02 HB12 JA02 JB17 JB20 JC03 JC09 JC20 PB13 3F049 AA02 EA02 LA03

Claims (4)

[Claims] 1. A plurality of photoreceptor units provided for each color to develop an electrostatic latent image formed on an image carrier to form a toner image, and are transported along a predetermined transport path. An intermediate transfer member on which the toner image is transferred as a primary transfer image, wherein the photoconductor units are arranged along the transport path, and at a secondary transfer position located downstream of the transport path. In an image forming apparatus that forms an image by transferring the primary transfer image to a recording medium, the image forming apparatus may be configured such that a photoconductor unit positioned at the most downstream of the plurality of photoconductor units on the transport path and the secondary transfer position An image detection sensor disposed therebetween, and control means for starting supply of the recording medium to the secondary transfer position in accordance with a timing at which the image detection sensor detects the primary transfer image, Image shape Equipment. 2. The method according to claim 1, wherein the time required for the recording medium to be conveyed is started or resumed and conveyed to the secondary transfer position is t, the conveyance speed of the intermediate transfer body is s, and the photosensitive member positioned at the most downstream position. When the distance from the body unit to the position of the image detection sensor is L, the length of the longest usable recording medium is L ₀ , and the distance from the position of the image detection sensor to the secondary transfer position is x, x> s × t a and the image forming apparatus according to claim 1, characterized in that the relation of L> L ₀ is defined. 3. A detection image for detecting a leading end of the primary transfer image is transferred to the intermediate transfer body in addition to the primary transfer image, and the image detection sensor detects the detection image when detecting the detection image. 2. The image forming apparatus according to claim 1, wherein an image detection signal is sent to the control unit. 4. A primary transfer image is sequentially transferred to the intermediate transfer body, a visual image for position detection is transferred between the primary transfer images, and the image detection sensor detects the visual image. 2. The image forming apparatus according to claim 1, wherein an image detection signal is sent to the control unit when the control is performed.