JPH08305176A - Image forming device - Google Patents

Abstract

PURPOSE: To provide an image forming device capable of preventing the deviation of the image transfer position by enhancing the accuracy of the detection of positioning mark formed on an intermediate transfer body. CONSTITUTION: This image forming device is provided with a positioning mark 426B for adjusting the image transferring position of the belt type transfer body 426 on which multiple transfer of the image is executed, and the positioning mark 426B is constituted of a non-reflective film layer 426B1 and a reflection film layer 426B2. As a result, S/N at the time of optical detection can be enhanced by suppressing reflection from the belt type transfer body itself.

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,
In particular, the present invention relates to an image forming apparatus that uses an intermediate transfer member to perform a primary transfer and a secondary transfer process.

[0002]

2. Description of the Related Art As one of image forming apparatuses, there is an apparatus capable of forming colored images of at least two colors by using developers of plural colors. In such an image forming apparatus, it is necessary to form toner images of three primary colors (cyan, magenta, and yellow) of subtractive color mixture on the recording paper in an overlapping manner. As an example of a color image forming apparatus, as shown in, for example, Japanese Patent Laid-Open No. 52-73738, toner images of respective color components are formed on a photoconductor several times, and the respective color components are formed. There is an image forming apparatus in which a color image is obtained by sequentially transferring the toner images of 1 to 1 sequentially onto a recording paper forming a transfer material.

In such a color image forming apparatus, a clamp mechanism for clamping the end portion of the recording paper is provided to bring the recording paper into close contact with the photoconductor several times. In addition to being complicated, there is a problem that an image cannot be transferred to a clamp portion of the recording paper. Therefore, in order to solve such a problem, first, in the same manner as described above, the toner image for each color component is formed several times on the photoconductor, and the toner image for each color component is formed. To each one in sequence
An image forming apparatus has been proposed which is configured to execute a secondary transfer step to form a color toner image and transfer the color toner image onto a recording sheet all at once. The intermediate transfer member used in the image forming apparatus is a transparent medium resistance material having a volume resistivity of 1 × 10 ⁸ to 10 ¹² Ω · cm and a surface resistivity of 1 × 10 ⁸ to 10 ¹¹ Ω (JISK6911). A belt-shaped member is used (hereinafter, the intermediate transfer member is referred to as an intermediate transfer belt). The intermediate transfer belt is wound around multiple rollers,
A part corresponding to the secondary transfer position of the expanded portion is hung on a pair of rollers and expanded in the horizontal direction.

As a structure for carrying out the secondary transfer, a structure using a transfer bias roller which is arranged so as to face the photoconductor and can be brought into contact with and separated from the back surface of the recording paper contacting the photoconductor, and a corona discharger are used. There is a structure. When a transfer bias roller is used in the above transfer structure, the toner image may be disturbed if it comes into contact with the toner image that is primarily transferred. Until then, it is separated from the photoconductor. For this reason, there is a problem in that the mechanism is complicated due to the need for the contacting / separating mechanism, the apparatus becomes large, and the cost increases.

Therefore, in order to solve such a problem, a corona discharger which can apply a transfer bias in a state of not being in contact with the toner image is used. FIG. 8 shows the structure of the above-mentioned intermediate transfer belt. In FIG. 8, the intermediate transfer belt A has a plurality of rollers B, C, D, E, F1, and F2.
Each of the rollers is moved in the direction of the arrow in the figure via the drive of the roller B, which is a drive unit, among the rollers. The pair of rollers F1 and F2 are juxtaposed in the horizontal direction so as not to hinder the transfer efficiency of the corona discharger H, and the transfer bias from the corona discharger H is generated by flattening the recording paper S. It is set so that the effect can be received uniformly.

On the other hand, the recording sheet S to which the color toner images are collectively transferred is guided by the guide member G provided on the upstream side in the feeding direction of the corona discharger H so that the leading end of the recording sheet S is directed to the extension portion of the intermediate transfer belt A. It is supposed to be done.
The guide member G is set in such a shape that the recording paper S can be introduced above the discharge electrodes of the corona discharger H, and is integrated with the wall portion of the corona discharger H as shown in FIG. A lower guide plate and an upper guide plate facing the lower guide plate. The guide member G has its tip above the discharge electrode of the corona discharger H, and the intermediate transfer belt A.
The recording paper S is arranged at a position where the front end of the recording paper S can abut.

On the other hand, as the operation modes of the intermediate transfer belt A, there are (1) constant speed forward movement method, (2) skip forward movement method, and (3) reciprocating movement (quick return) method.

In the method described in (1), the intermediate transfer belt continues to move at a constant speed even after the toner image of the first color is transferred. In the case of this method, The image processing is performed by setting the timing so that the image front end of the toner image of the next color on which the visible image is processed on the photoreceptor side matches the image front end on the intermediate transfer belt.

In the method described in (2), after the toner image of the first color is transferred, the intermediate transfer belt is separated from the photoconductor and the toner image of the first color is transferred. In this method, the intermediate transfer belt is moved at a high speed in the same direction as before, and when the intermediate transfer belt is moved by a predetermined amount, it is switched to the initial moving speed and brought into contact with the photosensitive member again. This method is used, for example, when the length of the image transferred is shorter than the length of the intermediate transfer belt, and has an advantage that the cycle time for image formation on the photoconductor side can be prevented from becoming long. .

In the method described in (3), after the toner image of the first color is transferred, the intermediate transfer belt is separated from the photoconductor, and the intermediate transfer belt is moved in the reverse direction at a higher speed than before. Then, it waits in a state where the position of the previously transferred toner image matches the position of the toner image of the next color carried on the photoconductor, and again the intermediate transfer belt is brought into contact with the photoconductor. This is a method in which the movement is started in the same direction as the photoconductor and this operation is continued until the transfer of the toner image of the final color.
This method does not move the intermediate transfer belt in the forward direction but controls only the amount of movement that has progressed so far in terms of control of the position where the image position of the intermediate transfer belt is aligned with the image position of the photoconductor. Therefore, there is an advantage that the control becomes simple considering that it is not necessary to secure the moving amount of the intermediate transfer belt so much.

[0011]

By the way, as the material of the intermediate transfer belt, a transparent organic resin film based on a dielectric is used. When an organic resin film is used and the reciprocating method described in (3) above is adopted as the moving method, mechanical elongation occurs in the belt, and it becomes difficult to align the image transfer position for each color. was there. Therefore, conventionally, a part of the belt is provided with a marking for alignment, which is made of a reflection part, and the marking is detected by an optical sensor to control the movement start position of the intermediate transfer belt.

However, when the above-mentioned marking is formed, since the belt itself has a reflectance, if the distinction between the marking and its surroundings is not clear, the S / N ratio deteriorates and the marking can be accurately detected. May not be possible. For this reason, it is difficult to control the movement start position of the intermediate transfer belt, and there is a problem that the transfer position of the image for each color on the intermediate transfer body is likely to shift.

Therefore, in view of the problems in the conventional image forming apparatus, an object of the present invention is to improve the detection accuracy of the marking for alignment formed on the intermediate transfer member and prevent the shift of the image transfer position. An object of the present invention is to provide an image forming apparatus capable of performing the same.

[0014]

In order to achieve the above object, the invention according to claim 1 uses a plurality of color toners to perform a visual image processing on the image carrier with the toners of the respective colors, and then the visual images of the respective colors. In an image forming apparatus that forms a color image by performing a primary transfer of the image and a secondary transfer of the primary-transferred visible image onto a transfer material at a time. A belt-shaped transfer body on which alignment marks for superimposing the images of the respective colors are formed, and the alignment marks on the belt-shaped transfer body are optically detected to start the movement of the belt-shaped transfer body. And an optical detection unit that outputs a signal for controlling the position, wherein the alignment mark is composed of a non-reflection area and a reflection area on the back surface of the image transfer surface of the belt-shaped transfer body. It is characterized by that.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the alignment mark is coated on the surface of the reinforcing portion formed at the widthwise end of the belt-shaped transfer body. It is characterized in that it is composed of a non-reflective film layer and a reflective film layer formed on the surface of the non-reflective film layer.

According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the alignment mark is coated on the back surface of the image transfer surface at the widthwise end of the belt-shaped transfer member. It is characterized by comprising a reflective film layer and a reflective film layer formed on the surface of the non-reflective film layer.

According to a fourth aspect of the present invention, in the image forming apparatus according to one of the first to third aspects, the alignment mark is arranged so as to face the location where the alignment mark is installed. It is characterized in that it has a flat belt-shaped transfer member guide member having an exposing opening, and an optical detection means arranged at a predetermined interval in the vicinity of the belt-shaped transfer member guide member.

[0018]

According to the first aspect of the invention, it is possible to accurately distinguish the incident light from the alignment mark toward the optical detecting means.

According to the second and third aspects of the present invention, the alignment mark should not reduce the S / N ratio between the non-reflective film layer by painting and the reflective film formed on the non-reflective film layer. You can

According to the fourth aspect of the present invention, the positional relationship between the optical detecting means and the mark is made constant by the belt-shaped transfer member guide member.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the drawings.

FIG. 1 shows the overall construction of a color electrostatic image forming apparatus using an intermediate transfer medium, and FIG. 2 shows the construction of the main parts thereof. In these drawings, a writing optical unit 400 as an exposure unit converts a color image data from a color scanner 200 for color-separating and reading an original image and converting the color image data as an electrical signal into an optical signal. The optical writing corresponding to the original image is performed to form an electrostatic latent image on the photoconductor 402 which is an image carrier. The writing optical unit 400 includes a laser emission means (laser diode) 404, an emission drive control section (not shown) thereof, a polygon mirror 406 and a rotation motor 40 thereof.
8, f / θ lens 410, reflection mirror 412 and the like.

The photoconductor 402 rotates counterclockwise as indicated by the arrow. Around the periphery thereof, the photoconductor cleaning unit 414, the charge eliminating lamp 416, the potential sensor 420,
Of the rotary developing device 422 as the developing means, a selected developing device (developing device 438 in the example of FIG. 8), a development density pattern detector 424, an intermediate transfer belt 426 as an intermediate transfer medium, and the like are arranged. . As the intermediate transfer belt, a volume resistivity of 1 × 10 ⁸ to 10 ¹² Ω · cm, a surface resistivity of 1 × 10 ⁸ to 10 ¹¹ Ω (JISK6911), a medium resistance belt, ethylene tetrafluoroethylene (ETFE),
Epichlorohydrin rubber is used. Alternatively,
It may be used as a drum instead of a belt.

The rotary developing device 422 includes a black developing device 428, a cyan developing device 430, and a magenta developing device 4.
32, a yellow developing device 434, and a rotation driving unit (not shown) for rotating each developing device. Each developing device has a developing sleeve that rotates by bringing the brush of the developer into contact with the surface of the photoconductor 402 in order to visualize the electrostatic latent image,
It is composed of a developing paddle or the like that rotates to pump up and stir the developer.

In the standby state, the rotary developing device 422 is
When the copying operation is started at the black developing position, the color scanner 200 starts reading black image data at a predetermined timing,
Based on this image data, optical writing by laser light
Formation of a latent image starts (hereinafter, an electrostatic latent image based on black image data is referred to as a black latent image. The same applies to cyan, magenta, and yellow). In order to develop from the tip of the black latent image, the developing sleeve is started to rotate to develop the black latent image with black toner before the tip of the latent image reaches the developing position of the black developing device.

Thereafter, the developing operation of the black latent image area is continued, but when the trailing edge of the latent image passes the black developing position, the developing position for black is immediately rotated to the next color developing position. The developing device rotates. The operation is completed at least before the leading edge of the latent image formed by the next image data arrives.

When the image forming cycle is started, first, the photosensitive member 402 is rotated counterclockwise as indicated by an arrow, and the intermediate transfer belt 426 is rotated clockwise by a drive motor (not shown). Intermediate transfer belt 426
When one toner image is transferred by the above-mentioned moving method (3), it moves at a high speed in a direction opposite to the moving direction at the time of transfer by a preset amount, and stands by at that position. . The intermediate transfer belt 426 moves in the forward direction again when the toner image of the next color is transferred. At this time, the intermediate transfer belt 426, as shown by the broken line in FIG.
Since it can be moved at a higher speed than that at the time of transferring the toner image in a state of being separated from the photoconductor 406, it is possible to shorten the time required for aligning the image leading end positions at the time of transferring the superimposed toner images.

With the rotation of the intermediate transfer belt 426, black toner image formation, cyan toner image formation, magenta toner image formation, and yellow toner image formation are performed, and finally black (Bk), cyan (C), and magenta. (M) and yellow (Y) are sequentially stacked on the intermediate transfer belt 426 to form a toner image.

First, black image formation is performed as follows. The charger 418 as a charging unit uniformly charges the photoconductor 402 with a negative charge to about −700 V by corona discharge (charging step). Then, the laser diode 404 performs raster exposure based on the black signal (exposure step). In this way, when raster exposure is performed, the exposed portion of the photoconductor 402 that is initially uniformly charged loses the charge proportional to the amount of exposure light, and an electrostatic latent image is formed.

The toner in the developing device 422 is negatively charged by stirring with the ferrite carrier, and the black developing sleeve of the present developing device is negatively charged with respect to the metal base layer of the photoconductor 402 by a power source means (not shown). A bias of a potential in which the direct current potential and the alternating current is superimposed is applied. As a result, the toner does not adhere to the portion of the photoconductor 402 where the electric charge remains, and the black toner is adsorbed to the non-charged portion, that is, the exposed portion, and a black visible image similar to the latent image is formed. Will be formed (developing step).

The intermediate transfer belt 426 is driven by the drive roller 44.
4, transfer counter roller 446, cleaning counter roller 4
It is stretched around 48 and a driven roller group, and is driven and controlled by a drive motor (not shown).

The black toner image formed on the photoconductor 402 is transferred onto the surface of the intermediate transfer belt 426 which is driven at a constant speed in contact with the photoconductor by a belt corona discharger 450 as a primary transfer means ( Primary transfer process).
Hereinafter, the transfer of the toner image from the photoconductor to the intermediate transfer belt is referred to as primary transfer. The discharge efficiency (distribution ratio) of the belt corona discharger 450 is about 20 to 40%. Photoconductor 40
A small amount of untransferred residual toner on the surface of the photoconductor 40
It is cleaned by the photoconductor cleaning unit 414 in preparation for reuse of the secondary color of the second color. The toner collected here is stored in a waste toner tank (not shown) via a collection pipe.

On the intermediate transfer belt 426, the black, cyan, magenta, and yellow toner images sequentially formed on the photoconductor 402 are accurately aligned in sequence,
As a result, a belt transfer image of four colors is formed, and then
A transfer corona discharger 454 as a secondary transfer means is used to collectively transfer to a recording paper as a recording medium (secondary transfer step).

On the photoconductor 402 side, the black process is followed by the cyan process. At a predetermined timing, the reading of the cyan image data by the color scanner starts, and the cyan latent image is written by the laser light writing by the image data. It is formed.

The cyan developing unit 430 has passed the preceding black developing rear end portion with respect to its developing position, and
The rotary developing device 422 before the leading edge of the cyan latent image arrives.
And the cyan latent image is visualized with cyan toner. After that, the development of the cyan developing area is continued, but when the trailing edge of the latent image passes, the cyan developing unit is rotated like the previous black developing device. This is also completed before the leading edge of the magenta latent image reaches.

The image data reading, latent image forming, and developing operations for the magenta and yellow steps are the same as those for the black and cyan steps, and the description thereof is omitted.

Corona discharger 454 as a secondary transfer means
Applies a DC or AC + DC component by the corona discharge method to transfer the overlapping toner image on the intermediate transfer belt onto the recording medium. The distribution ratio is about 20 to 40%, which is similar to the belt transfer corona discharger.

Each recording paper cassette 4 in the paper supply bank 456
58, 460 and 462 are cassettes 464 in the main body of the apparatus.
Various sizes of recording paper different from the size of the recording paper accommodated in are accommodated in the storage cassette of the designated (selected) size paper, and the paper is fed in the direction of the registration roller by the paper feed roller 466. -Transported. Reference numeral 468 in the figure denotes a manual paper feed tray for OHP paper, thick paper, and the like.

At the time when image formation is started, the recording paper is fed from the paper feed port of any one of the above cassettes and stands by at the nip portion of the registration roller pair 470. When the front end of the toner image on the intermediate transfer belt 426 reaches the corona discharger 454, the registration roller pair 470 is driven so that the front end of the recording paper coincides with the front end of the image, and the transfer position between the paper and the image is transferred. Matching is done.

In this way, the recording paper is superposed on the intermediate transfer belt 426 and passes over the corona discharger 454 connected to the positive potential. At this time, the recording paper is positively charged by the corona discharge current, and a substantial part of the toner image is transferred onto the recording paper. Subsequently, when passing through a part of the static elimination brush (not shown) arranged on the left side of the corona discharger 454 in the figure, the recording paper is statically eliminated and the intermediate transfer belt 42
After peeling from 6, the sheet is moved to the conveyor belt 472.

The recording paper to which the four-color superposed toner images have been collectively transferred from the intermediate transfer belt 426 is conveyed to the fixing device 474 by the paper conveying belt 472, and the fixing roller 476 and the pressure roller 478 controlled to a predetermined temperature. The toner image is melted and fixed at the nip portion, sent out of the machine by a pair of discharge rollers 480, and is stacked face up on a copy tray (not shown) to obtain a full-color copy. Intermediate transfer belt 426
The surface of the photoconductor 402 after the image transfer is cleaned by the photoconductor cleaning unit 414 including a brush roller and a rubber blade, and the charge is uniformly discharged by the charge removing lamp 416.

The surface of the intermediate transfer belt 426 after the toner image is transferred onto the recording paper is cleaned by pressing the blade with the blade contacting / separating mechanism again in the cleaning device 452.

In the case of repeat copying, the operation of the color scanner and the image formation on the photoconductor are carried out following the first color image process of the first sheet, and the first sheet of the second sheet is imaged at a predetermined timing.
The process proceeds to the color image process. Further, in the intermediate transfer belt, the second black toner image is primarily transferred to the surface area cleaned by the cleaning device 452 following the batch transfer process of the first four-color superimposed image onto the transfer paper. It After that, the same operation as the first sheet is performed as described above. The above is a description of the copy mode for obtaining four full colors of A4 size horizontal feed. However, in the case of the three-color copy mode or the two-color copy mode, the same operation as the above with respect to the designated color and the number of times is performed. Will be done.

In the single color copy mode, until the predetermined number of sheets are finished, only the developing device of the predetermined color of the rotary developing device 422 is in the developing operation state, that is, the developing position state of the predetermined color, The copying operation is continuously performed while the blade of the cleaning device 452 is pressed against the belt.

Next, A3, which is the longest size for this device
A case where full-color copying is performed in size will be described. It is efficient for a color copy of that size to perform one-color image formation every time the intermediate transfer belt 426 makes one revolution and complete four-color image formation after four rotations. If the length is shortened according to the maximum size as much as possible, there is a problem that the scanner return time is lost in the copy operation of the maximum size.

On the other hand, when the intermediate transfer belt is dimensioned on the assumption of the copy operation in the maximum size which is used less frequently such as A3 size, when the size of the intermediate transfer belt is smaller than that size and used frequently, the size of A4 or B5 is used. However, there is a problem that dead time that does not contribute to image formation increases. Therefore, in the case of copying A3 size, one image is formed while the intermediate transfer belt is rotated twice. That is, after the black toner image is transferred to the belt, the next one cycle of development,
It rotates without being transferred, and development and primary transfer are performed in the next one rotation.

As described above, the so-called "idle rotation" is a method for suppressing the peripheral length of the intermediate transfer belt so as to ensure a predetermined copy speed even in the case of small-sized copying and not to reduce the maximum printable size. It is proposed that a scanner return or other operation be performed during "idle rotation" in which no transfer is performed on the intermediate transfer belt during primary transfer of each color when copying a size close to the circumference of the intermediate transfer belt. Are going to do.

However, in this case, when forming a full-color image, the toner image on the intermediate transfer belt 426 passes through the corona discharger 454 portion six times, and the frequency at which the loose toner adheres to the discharge wire. Will increase.

In any case, in the case of an electrostatic image forming apparatus of the type using the intermediate transfer medium, in the case of color copying, the toner images formed on the surface of the intermediate transfer medium are superposed and transferred so that the toner images are transferred. While being carried on the intermediate transfer medium,
If the present invention is not applied, free toner will pass through the corona discharger 454.
The situation is such that it easily attaches to the discharge wire.

The intermediate transfer belt 426 has a volume resistivity of 1 × 10 ⁸ to 10 ¹² Ω · cm, as described above.
Surface resistivity 1 × 10 ⁸ -10 ¹¹ Ω (JISK6911)
The medium resistance belts such as ethylene tetrafluoroethylene (ETFE) and epichlorohydrin rubber are used. As shown in FIG. 3, the intermediate transfer belt 426 is integrally formed with an extension suppressing reinforcing portion 426A made of polyethylene terephthalate (PET) or the like at the widthwise end portion of the belt orthogonal to the moving direction thereof. ing. The reinforcing portion 426A is located on the back surface of the image transfer surface of the intermediate transfer belt 426. This intermediate transfer belt 426
Alignment marking 426B for aligning the image transfer position regardless of the extension of the belt 426 is provided on the back surface of the.

The positioning marking 426B is composed of a non-reflective film layer 426B1 and a reflective film layer 426B2 located on the surface of the reinforcing portion 426A or the surface in the vicinity of the reinforcing portion 426A. The example shown in FIG. 3 shows a state in which the positioning marking 426B is located near the reinforcing portion 426A. FIG. 4 is a partially enlarged cross-sectional view of a case where an alignment marking 426B is formed on the surface of the reinforcing portion 426A. In FIG. 4, the non-reflection film layer 426B1 forms the lower ground of the reflection film layer 426B2. The black paint is coated with a matte paint in which silicon oxide or the like is mixed. In FIG. 4, the reflective film layer 426B2 is an alumina (Al ₂ layer) integrated on the non-reflective film layer 426B1.
A material such as O ₃ ) is used and configured as a layer capable of reflecting infrared rays by an infrared sensor used as an optical sensor. The reflective film layer 426B2 is a non-reflective film layer 426.
If it does not adversely affect the coating of B1, it can be formed by vapor deposition. In addition to this, a non-reflective film layer 426B can be formed by sticking a seal-shaped one.
Integrate with 1.

Since this embodiment has the above configuration,
On the back surface of the image transfer surface of the intermediate transfer belt 426, a non-reflective film layer 426B1 that does not reflect infrared rays and a reflective film layer 426B2 that can reflect infrared rays are used for alignment marking 426.
B is constructed. The non-reflective film layer 426B1 eliminates the reflection characteristic of the intermediate transfer belt 426 itself and positively suppresses the reflection of infrared rays. Therefore, the reflectance of infrared rays is extremely different from that of the reflective film layer 426B2. be able to. Accordingly, the infrared sensor has a reflective film layer 426.
Since only the reflected light from B2 is incident, the alignment control using the alignment marking 426B becomes easy.

FIG. 5 shows the alignment marking 426.
5, a positioning marking 426B is a non-reflection film layer 426B formed in a film shape.
The reflection film layer 426B2 is previously integrated with the surface of No. 1 by pasting or the like. The positioning marking 426B having such a configuration is attached and installed on the surface of the reinforcing portion 426A of the intermediate transfer belt 426B or the surface in the vicinity thereof. Further, as a modification of the example shown in FIG. 5, a positioning mark 426B is formed by a seal in which a non-reflection film layer 426B1 and a reflection film layer 426B2 are vapor-deposited on the same surface.
The seal may be attached to the surface of the reinforcing portion 426A of the intermediate transfer belt 426 or the surface in the vicinity thereof. According to this, the alignment marking 4
The installation man-hour of 26B is only one.

By the way, the intermediate transfer belt 426 provided with the positioning marking 426 may be bent in a direction perpendicular to the extending direction, and thus the facing distance to the infrared sensor may not be constant. In such a case, even if the infrared rays emitted from the infrared sensor are reflected by the alignment marking, in comparison with the optical path length with respect to the intermediate transfer belt 426 at the regular position indicated by the symbol α in FIG. If the intermediate transfer belt 426 is located at the position indicated by the symbol β, the optical path length will be different, and the position at which the reflected light is incident will also be different. Therefore, the infrared light emitted from the light emitting portion 429A of the infrared sensor 429 which is the optical detecting means does not enter the light receiving portion of the infrared sensor 429B even if it is reflected by the positioning marking 426B. The reflected light of will not be captured properly. As a result, the amount of light received necessary for detecting the alignment marking 426 cannot be obtained, and the marking detection becomes unstable.

Therefore, in the present invention, in order to solve such a problem, a structure is provided for keeping the facing distance between the positioning marking 426B of the intermediate transfer belt 426 and the infrared sensor 429 constant. FIG. 7 shows an embodiment applied to this case. In FIG. 7, the positioning marking 42 provided on the intermediate transfer belt 426 is shown.
A guide member 427 of the intermediate transfer belt 426 having an opening 427A through which the alignment marking can be exposed is disposed at a position facing 6B. The guide member 427 is a guide member that maintains the stretched position of the intermediate transfer belt 426 at a predetermined position, and the infrared sensor 429.
And the marking 426B for alignment are provided at a position where the distance between them can be kept constant.

The guide member 427 is arranged at a position where the forward movement of the intermediate transfer belt 426 is restarted in order to transfer the toner image of each color, and the infrared sensor 427 when the intermediate transfer belt 426 moves to that position. It is designed to keep the distance between and constant.

Further, the guide member 427 is a flat plate member made of a material having a low friction coefficient such as a fluororesin, and does not hinder the movement of the intermediate transfer belt 426 even if the intermediate transfer belt 426 comes into contact therewith. In such a configuration, the intermediate transfer belt 426 has a position of the stretched portion at the infrared sensor 4
It is prevented by the guide member 427 from changing with respect to the position of 29. Moreover, even when the intermediate transfer belt 426 comes into contact with the guide member 427,
No. 26 does not hinder its movement, so that color misregistration is prevented when toner images of respective colors are transferred in multiple.

According to this configuration, the guide member 427 having a characteristic that does not hinder the movement of the intermediate transfer belt 426 is simply arranged so as to face the intermediate transfer belt 426. The optical path length required for detection can be secured. As a result, the alignment marking 426B is detected with certainty, so that the multiple transfer of the toner images of the respective colors can be performed without causing the image position deviation. Moreover,
Even when the guide member 427 is provided, the intermediate transfer belt 42
Since it is possible to prevent the movement of No. 6 from being hindered, it is possible to prevent image shift due to optical detection of the alignment detection marking 426A and prevent image shift due to stabilization of the movement of the intermediate transfer belt 426.

In the above structure, the guide member 42
Although 7 itself is made of a material having a low friction coefficient, the present invention is not limited to this, and a contact layer made of that material may be provided only on the surface in contact with the intermediate transfer belt 426.

Further, as the constitution of the guide member 427, instead of the constitution in which the belt 426 is slid in contact with the intermediate transfer belt 426, a roller rotatable in accordance with the movement of the intermediate transfer belt 426 may be used. Good. In this case,
It suffices to dispose the rollers at a position that does not block the optical path of the infrared rays from the infrared sensor 429, and since it is sufficient that the low friction coefficient material layer is provided on the peripheral surface thereof, it is not necessary to process the opening. It is possible to simplify the configuration.

[0061]

As described above, according to the first aspect of the present invention, since the incident light from the alignment mark toward the optical detecting means can be accurately distinguished, multiple transfer of images is performed. It is possible to prevent the image shift when performing.

According to the second and third aspects of the present invention, the alignment mark does not reduce the S / N ratio between the non-reflective film layer by painting and the reflective film formed on the non-reflective film layer. Therefore, it is possible to improve the consistency of the transfer position of each image when transferring the multiple images.

According to the fourth aspect of the invention, since the positional relationship between the optical detecting means and the mark is made constant by the belt-shaped transfer member guiding member, the accuracy of detecting the mark by the optical detecting means is secured, It is possible to ensure the consistency of the transfer positions when transferring multiple images.

[Brief description of drawings]

FIG. 1 is a schematic diagram schematically showing an overall configuration of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining a main part of a transfer mechanism used in the image forming apparatus shown in FIG.

FIG. 3 is a perspective view illustrating a configuration of a main part of a transfer body used in the transfer mechanism illustrated in FIG.

FIG. 4 is a cross-sectional view for explaining a configuration of an alignment mark provided on the transfer body shown in FIG.

5 is a perspective view for explaining a modified example of the alignment mark shown in FIG.

FIG. 6 is a schematic diagram for explaining a problem with the transfer body shown in FIG.

7 is a perspective view for explaining a guide structure of a transfer body in the transfer mechanism shown in FIG.

FIG. 8 is a schematic diagram for explaining an example of a transfer mechanism using a belt-shaped transfer body.

9 is a schematic diagram for explaining the configuration of a secondary transfer portion in the transfer mechanism shown in FIG.

[Explanation of symbols]

402 Photoreceptor as image carrier 422 Developing device used for image processing 426 Intermediate transfer belt 426A corresponding to belt-shaped transfer member 426A Reinforcing portion 426B Positioning marking 426B1 Non-reflective film layer 426B2 Reflective film layer 427 Guide member 429 Optical Infrared sensor corresponding to detection means 450 Corona discharger for primary transfer 454 Corona discharger for secondary transfer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Takeshi Inventor Takeshi Nakamagome 3-6, Ota-ku, Tokyo, Ricoh Co., Ltd. (72) Inventor Mitsuru Takahashi 1-3-6 Nakamagome, Ota-ku, Tokyo・ Inside Ricoh Co., Ltd.

Claims (4)

[Claims] 1. A toner image of a plurality of colors is used to perform a toner image development process on the image carrier with toners of the respective colors, and then the toner images of the respective colors are primary-transferred. In an image forming apparatus that forms a color image by secondarily transferring the image, it is wound around a plurality of rollers, and a registration mark for superimposing the visible images of each color is formed on a part of the rollers. A belt-shaped transfer member; and an optical detection unit that optically detects a positioning mark on the belt-shaped transfer member and outputs a signal for controlling a movement start position of the belt-shaped transfer member. The image forming apparatus, wherein the alignment mark is composed of a non-reflection area and a reflection area on the back surface of the image transfer surface of the belt-shaped transfer member. 2. The image forming apparatus according to claim 1, wherein the alignment mark is a non-reflective film layer coated on a surface of a reinforcing portion formed at an end portion in the width direction of the belt-shaped transfer body. An image forming apparatus comprising: a reflection film layer formed on the surface of the non-reflection film layer. 3. The image forming apparatus according to claim 1, wherein the alignment mark is a non-reflective film layer coated on the back surface of the image transfer surface at the widthwise end of the belt-shaped transfer member, and the alignment mark. An image forming apparatus comprising a reflection film layer formed on the surface of a non-reflection film layer. 4. The image forming apparatus according to claim 1, wherein the image forming apparatus is disposed so as to face the location where the alignment mark is installed.
A flat plate-shaped belt-shaped transfer member guide member having an opening through which the alignment mark can be exposed; and optical detection means arranged at a predetermined interval in the vicinity of the belt-shaped transfer member guide member. A characteristic image forming apparatus.