JP2004139037A - Transfer-position correcting method and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high quality image at a high printing speed by improving color registration accuracy during transfer in image forming apparatus of a system in which toner images are superposed and transferred. <P>SOLUTION: Mark patterns in the form of toner images of respective colors are formed. A speed at which a transfer belt 10 is moved during a period of time that the marks are read by a reflection-type photosensor 20 is compared with a speed at which the transfer belt 10 is moved during regular image formation in which transfer paper is carried on the transfer belt 10. If there is a difference between them, the operation of writing the speed difference is corrected. The speed at which the transfer belt 10 may be calculated by detecting a pre-formed mark patterns on the transfer belt 10 with the reflection-type photosensor 20. Alternatively, it may be calculated using a rotational speed in which the drive system for the transfer belt 10 is rotated. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a transfer position correction method for correcting a toner transfer position when transferring toner on an image carrier onto a recording material, and when transferring toner on a latent image carrier to an intermediate transfer member. The present invention relates to an image forming apparatus.

As this type of image forming apparatus, for example, latent images of each color are formed on a latent image carrier such as a photoreceptor, and these are formed into toner images by a developing unit, and then transferred onto a recording material such as transfer paper. There is a color image forming apparatus for forming an image. As the transfer method that can be adopted in such a color image forming apparatus, the following three methods can be mainly mentioned. The first transfer method is an intermediate transfer method in which toner images of respective colors formed on a latent image carrier are sequentially superimposed and transferred onto an intermediate transfer member, and then transferred onto a recording material. The second transfer method is a direct transfer method in which toner images of respective colors formed on a latent image carrier are sequentially superimposed and directly transferred onto a recording material conveyed while being carried on a recording material conveying member. . The third transfer method is a method in which the first and second transfer methods are combined.
The first transfer method is suitable for outputting a high-quality image, but has the disadvantage that the printing speed tends to be slow. In addition, the second transfer method can increase the printing speed, but has the disadvantage that it is technically difficult to align the toner transfer positions of the toner images of the respective colors, and that a defective image is easily generated. Further, the third transfer method can output a high-quality image at a high printing speed, but has the disadvantage that the apparatus becomes large and the cost increases.
In recent years, along with the demand for high-quality images, a balance between cost and printing speed has also been demanded, and in order to meet such demands, the second transfer method has attracted attention. However, in order to form a high-quality image by employing the second transfer method, it is necessary to overcome a very difficult technical problem of accurately aligning the toner transfer positions between the toner images of the respective colors as described above. Must.

As a technique for accurately aligning the toner transfer positions between the toner images of the respective colors, for example, a technique proposed in Patent Document 1 can be used. According to this technique, a mark pattern is formed on an intermediate transfer belt, the mark pattern being an array of marks of each color toner arranged in the belt moving direction. Then, each mark of each mark pattern is detected by a sensor, and the amount of deviation between the detected position and the ideal position is calculated to correct the toner transfer position of each color toner. This technique employs an intermediate transfer method (the first transfer method), and corrects a toner transfer position generated at the time of primary transfer from a latent image carrier to an intermediate transfer belt. (The above-described second transfer method). That is, if a plurality of mark patterns are similarly formed on the recording material transporting member, the mark patterns are detected by a sensor, and the amount of deviation between the detected position and the ideal position is calculated. Can be corrected.
Patent Document 2 discloses a technique in which encoders are incorporated in each of a drive motor of a photoconductor and a drive motor of a transfer drum that conveys a recording material, and feedback control is performed so that the periods of the encoder outputs match. Have been. This technique employs a direct transfer method (the above-described second transfer method), and is a so-called one-drum type in which toner images of respective colors are sequentially formed on one photosensitive member and are sequentially transferred onto a recording material. This is a technique relating to an image forming apparatus. In this technique, a transfer position is not corrected by detecting a mark made of toner, but is corrected by detecting a mark provided in advance in a drive system.
In Patent Documents 1 and 2, the toner transfer position is corrected by changing the surface moving speed of the intermediate transfer body or the transfer drum. However, the toner transfer position can be similarly corrected by changing the start timing of writing the latent image on the latent image carrier.

JP-A-8-245331 JP 62-226167 A

According to the techniques disclosed in Patent Document 1 and Patent Document 2, it is possible to reduce the deviation of the toner transfer position in the image forming apparatus employing the direct transfer method. However, the reduction effect is still insufficient. This has been found by the present inventors to be caused by the following problem.
That is, if the technique of Patent Document 1 is applied, the mark pattern is transferred onto the recording material conveying member by the same process as the actual image forming process, and the toner transfer position is adjusted so that the transfer position matches the ideal position. Will be corrected. As described above, the technique of Patent Document 2 performs correction based on the actually transferred toner (mark pattern), and thus does not perform correction based on the actually transferred toner. A higher correction effect can be obtained. However, when the technique of Patent Document 1 is applied, the transfer of the mark pattern performed to correct the toner transfer position is usually performed on a recording material conveying member in a state where the recording material is not supported (non-supported state). Do. This is because if the recording is performed while the recording material is carried, the mark pattern is transferred onto the recording material, and the recording material is wasted. On the other hand, the transfer of the toner image in the actual image forming process is performed on the recording material carried on the recording material transport member in a state where the recording material is carried (supported state). Since the load applied to the recording material conveying member differs between the supported state and the non-supported state, the surface moving speed of the recording material conveying member also differs. Therefore, even if the technique of Patent Document 1 having a high correction effect is applied due to the difference in the surface moving speed, in the actual image forming process, the toner transfer position is necessarily shifted between the toner images of each color. Occurs.
Note that this problem occurs not only when transferring from the latent image carrier to the recording material but also when transferring from the latent image carrier to the intermediate transfer member. Therefore, the above problem can also occur during the primary transfer in the intermediate transfer type color image forming apparatus.

Further, the technique disclosed in Japanese Patent Application Laid-Open No. H11-157400 discloses that when transferring a toner image on a latent image carrier onto a recording material carried and conveyed by a recording material conveying member, the toner image is moved from a desired position on the recording material. It can also be applied to the problem of mistransfer. Specifically, a mark made of toner is formed on a recording material conveying member, the mark is detected by a sensor, and a deviation amount between the detected position and an ideal position is calculated to transfer the toner from the latent image carrier. Correct the position. However, in this case, the mark transfer is usually performed on a non-supported recording material transport member in order to eliminate waste of the recording material. Therefore, as described above, in the actual image forming process, the toner image is transferred from a desired position on the recording material due to a difference in the surface moving speed of the recording material transport member between the supported state and the non-supported state. The problem occurs. This problem occurs, for example, when performing secondary transfer in a color image forming apparatus of an intermediate transfer system, or when transferring a black toner image on a latent image carrier (image carrier) onto a recording material in a monochrome image forming apparatus. Can occur.

The present invention has been made in view of the above background, and an object of the present invention is to transfer a toner image to a desired position on a transfer-receiving member on which a toner image such as a recording material or an intermediate transfer member is transferred. It is an object of the present invention to provide a transfer position correction method and an image forming apparatus capable of improving the correction accuracy when correcting the toner transfer position.

In order to achieve the above object, according to the first aspect of the present invention, the toner on the image carrier is transferred onto a recording material conveyed while being carried on a recording material conveying member. A transfer position correcting method for correcting a toner transfer position of a toner, wherein a mark made of toner is formed on the image carrier, and the mark is transferred to the recording material conveying member. A shift amount detecting step of detecting a shift amount between a transfer position of the mark transferred to the recording material conveying member and an ideal position; and a transfer position of the mark based on the shift amount detected in the shift amount detecting step. A correction step of correcting the toner transfer position so as to match the ideal position. In the transfer position correction method, a first speed detection for detecting a surface moving speed of the recording material conveying member in a state where the recording material is carried Process and recording material carried A second speed detecting step of detecting a surface moving speed of the recording material conveying member in a state where the recording medium is not moved, and a difference between the surface moving speed detected in the first speed detecting step and the surface moving speed detected in the second speed detecting step. A difference detecting step of detecting, and the correcting step corrects the toner transfer position based on the difference detected in the difference detecting step and the shift amount detected in the shift amount detecting step. It is assumed that.
Further, according to the invention of claim 2, the toner on the latent image carrier is primarily transferred onto an intermediate transfer member, and the toner primarily transferred on the intermediate transfer member is transferred onto a recording material which is conveyed. A transfer position correcting method for correcting a toner transfer position on the intermediate transfer member during the primary transfer in an image forming apparatus that performs a secondary transfer while bringing a recording material into contact with the intermediate transfer member, the method comprising: A mark transfer step of forming a mark made of toner on the intermediate transfer body, and transferring the mark on the intermediate transfer body, and a deviation amount between a transfer position of the mark transferred to the intermediate transfer body in the mark transfer step and an ideal position. Transfer position correction including a shift amount detecting step for detecting, and a correcting step for correcting the toner transfer position based on the shift amount detected in the shift amount detecting step so that the transfer position of the mark coincides with the ideal position. In the method, the state that the recording material is in contact A first speed detecting step of detecting a surface moving speed of the intermediate transfer member in the first step, a second speed detecting step of detecting a surface moving speed of the intermediate transfer member in a state where the recording material is not in contact with the first speed detecting step, A difference detecting step for detecting a difference between the surface movement speeds detected in the first speed detecting step and the second speed detecting step, and the correcting step includes the difference detected in the difference detecting step and the deviation. The toner transfer position is corrected based on the amount of deviation detected in the amount detection step.
According to a third aspect of the present invention, there is provided an image carrier, a toner image forming means for forming a toner image on the image carrier, a recording material transporting member for transporting the recording material while the recording material is carried on the surface, and Transfer means for transferring the toner on the image carrier onto the recording material conveyed by the recording material conveying member; and forming a mark made of toner on the image carrier, and transferring the mark to the recording medium by the transfer means. A shift amount detecting means for detecting a shift amount between the mark transfer position and the ideal position when the mark is transferred onto the material conveying member; and, based on the shift amount detected by the shift amount detecting means, the mark transfer position is set to the ideal position. And a correction means for correcting the toner transfer position on the recording material so as to coincide with the correction means. In the state where the recording material is carried The toner transfer position is determined based on the difference between the surface moving speed of the recording material conveying member and the surface moving speed of the recording material conveying member in a state where the recording material is not carried, and the shift amount detected by the shift amount detecting means. Is corrected.
According to a fourth aspect of the present invention, in the image forming apparatus of the third aspect, the toner image forming means includes a latent image writing means for writing a latent image on the image carrier, and a toner image formed by developing the latent image. And a developing means for developing.
According to a fifth aspect of the present invention, in the image forming apparatus of the fourth aspect, the image forming apparatus includes a plurality of the image carriers, and each toner image on each image carrier is recorded on a recording material conveyed by the recording material conveying member. Are transferred by the transfer means so as to overlap each other to form a color image. The correction means controls the toner transfer of each toner image so that the positions of the toner images on the recording material coincide with each other. The position is corrected.
According to a sixth aspect of the present invention, in the image forming apparatus of the second, third, fourth, or fifth aspect, the surface moving speed of the recording material transporting member in a state where the recording material is not carried is determined by detecting the displacement amount. Preferably, the mark is to be transferred onto the recording material transporting member.
According to a seventh aspect of the present invention, there is provided a latent image carrier, toner image forming means for forming a toner image on the latent image carrier, and an intermediate transfer member on which the toner on the latent image carrier is primarily transferred. A primary transfer means for primary-transferring the toner on the latent image carrier onto the intermediate transfer member; and a primary transfer means for bringing the recording material and the intermediate transfer member into contact with the conveyed recording material. A secondary transfer means for secondary-transferring the toner image on the intermediate transfer member, and forming a mark made of toner on the latent image carrier, and transferring the mark to the intermediate transfer member by the primary transfer means A shift amount detecting means for detecting a shift amount between the mark transfer position and the ideal position, and the intermediate position such that the mark transfer position matches the ideal position based on the shift amount detected by the shift amount detecting means. A correction unit that corrects a toner transfer position on a transfer body. A speed detecting means for detecting a surface moving speed of the intermediate transfer body, wherein the correcting means comprises: a surface moving speed of the intermediate transfer body in a state where the recording material is in contact; The toner transfer position is corrected based on the difference between the surface transfer speed of the intermediate transfer member and the deviation amount.
According to an eighth aspect of the present invention, in the image forming apparatus of the seventh aspect, the image forming apparatus has a plurality of the latent image carriers, and the toner images on the latent image carriers are overlapped with each other on the intermediate transfer member. The color image is formed by primary transfer by primary transfer means. The correction means includes a toner transfer position for each toner image such that the positions of the toner images on the intermediate transfer member coincide with each other. Is corrected.
According to a ninth aspect of the present invention, in the image forming apparatus according to the seventh or eighth aspect, the surface moving speed of the intermediate transfer member in a state where the recording material is not in contact is determined by setting the mark to detect the deviation amount. It is characterized in that it is used for transfer onto the intermediate transfer member.
According to a tenth aspect of the present invention, in the image forming apparatus according to the fourth, fifth, sixth, seventh, eighth or ninth aspects, the correction means changes a latent image writing start timing by the latent image writing means. And the correction of the toner transfer position.
According to an eleventh aspect of the present invention, in the image forming apparatus of the third, fourth, fifth or sixth aspect, the correction means corrects the toner transfer position by changing a surface moving speed of the recording material conveying member. It is characterized by being.
According to a twelfth aspect of the present invention, in the image forming apparatus of the seventh, eighth or ninth aspect, the correction unit corrects the toner transfer position by changing a surface moving speed of the intermediate transfer body. It is characterized by the following.
According to a thirteenth aspect of the present invention, in the image forming apparatus according to the second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth, eleventh, or twelfth aspect, the speed detecting means includes the recording material conveying member A plurality of speed detection marks provided on the intermediate transfer member or a driving force transmitting member for transmitting a driving force to the intermediate transfer member are detected, and the recording material conveyance is performed based on detection timings of the plurality of speed detection marks. The moving speed of the member or the surface of the intermediate transfer member is detected.
According to a fourteenth aspect of the present invention, in the image forming apparatus of the thirteenth aspect, the plurality of speed detection marks are provided on a surface of the recording material transporting member opposite to a surface on which the recording material is carried, or The intermediate transfer member is provided on a surface of the intermediate transfer member opposite to a surface to which the toner is transferred.
According to a fifteenth aspect of the present invention, in the image forming apparatus according to the thirteenth aspect, the plurality of speed detection marks are formed on the image carrier or the latent image carrier on the carrier surface or the transfer surface. Are provided in a portion which does not face an image forming area where a toner image can be formed.
According to a sixteenth aspect of the present invention, in the image forming apparatus of the fifteenth aspect, a process cartridge in which the image carrier or the latent image carrier and at least a part of the toner image forming unit are integrated is provided in the apparatus main body. On the other hand, it is configured to be detachable in the surface direction of the carrying surface or the transferred surface, and is configured such that the attaching / detaching path does not cross the plurality of speed detection marks on the carrying surface or the transferred surface. It is characterized by the following.

In the transfer position correcting method according to the first and second aspects and the image forming apparatus according to the third to sixteenth aspects, the mark transfer position and the ideal position when the mark made of toner is transferred onto the recording material conveying member or the intermediate transfer body are determined. The toner transfer position is corrected based on the deviation amount.
Here, in the transfer position correcting method according to the first aspect and the image forming apparatus according to the third aspect, as described above, the surface moving speed is different depending on whether the recording material conveying member is in the supported state or in the non-supported state. Is different. Therefore, even if the correction is performed only by the shift amount obtained based on the mark transferred to the recording material transporting member in the non-carrying state, the normal image forming in which the toner image is transferred to the recording material on the recording material transporting member in the carrying state At times, a shift corresponding to the speed difference remains. Therefore, in the present method and the present apparatus, the surface moving speeds of the recording material conveying member in the supported state and the non-supported state are respectively detected, and the difference is detected. Then, the toner transfer position is corrected based on the difference as well as the deviation amount. As a result, it is possible to correct the toner transfer position so as to eliminate a deviation corresponding to a difference between the surface moving speed of the recording material conveying member in the supported state and the non-supported state.
On the other hand, in the transfer position correcting method according to the second aspect and the image forming apparatus according to the fourth aspect, the secondary transfer is performed while the recording material is in contact with the intermediate transfer body. The secondary transfer is usually started after the primary transfer is started and before the primary transfer is completed. Therefore, while the primary transfer to the intermediate transfer member is being performed, the recording material comes into contact with the intermediate transfer member. Here, the load applied to the intermediate transfer member is different between the state where the recording material is in contact (contact state) and the state where the recording material is not in contact (non-contact state), so that a difference occurs in the surface moving speed. . Therefore, the surface movement speed of the intermediate transfer member changes during the primary transfer. Therefore, even if the toner transfer position after the change is corrected only by the shift amount obtained based on the mark transferred to the intermediate transfer member in the non-contact state, the shift corresponding to the speed difference remains. Therefore, in the present method and the present apparatus, the surface movement speeds of the intermediate transfer body in the contact state and the non-contact state are respectively detected, and the difference is detected. Then, the toner transfer position is corrected based on the difference as well as the deviation amount. As a result, the toner transfer position can be corrected so as to eliminate a deviation that may occur after the surface moving speed of the intermediate transfer body changes during the primary transfer.

As described above, according to the first to thirteenth aspects of the present invention, the correction accuracy when correcting the toner transfer position so that the toner is transferred to a desired position can be improved by using the non-carrying recording material conveying member or the non-contact state. There is an excellent effect that the toner transfer position can be increased by using only the shift amount obtained based on the mark transferred to the intermediate transfer member as compared with the conventional method of correcting the toner transfer position.

[Embodiment 1]
Hereinafter, an embodiment in which the present invention is applied to a tandem-type color image forming apparatus of a direct transfer system (hereinafter, this embodiment is referred to as “Embodiment 1”) will be described with reference to the drawings.
FIG. 2 is a schematic configuration diagram illustrating an example of the image forming apparatus according to the first embodiment.
The image data is converted into image data of each color for color recording consisting of M (magenta), C (cyan), Y (yellow), and K (black), and then is converted to an exposure device 5 as a latent image writing unit. Is sent. The exposure device 5 exposes the photoconductors 6M, 6C, 6Y, and 6K for M, C, Y, and K as image carriers, respectively, and writes an electrostatic latent image. Each of the electrostatic latent images is developed with each toner by each of the developing devices 7M, 7C, 7Y, and 7K as developing means, and is formed into a toner image. Therefore, the toner image forming unit of the first embodiment includes the exposure device 5 and the developing units 7M, 7C, 7Y, and 7K. On the other hand, the transfer paper as the recording material is transported from the paper feed cassette 8 while being carried on a paper transport belt 10 as a recording material transport member. Then, the toner images of the respective colors on the respective photoreceptors are sequentially transferred and superimposed on transfer paper conveyed by transfer units 14M, 14C, 14Y, and 14K as transfer units, and then the fixing device 15 as a fixing unit. Is established by The transfer paper after fixing is discharged outside the machine.

The paper transport belt 10 is a translucent endless belt supported by a driving roller 11, a tension roller 12, and a driven roller 13. In the paper transport belt 10, the tension of the paper transport belt 10 is kept substantially constant because the tension roller 12 applies tension to the paper transport belt 10 by an urging means (not shown). The paper transport belt 10 is driven at a reference belt moving speed (surface moving speed) of 100 mm / sec. In the first embodiment, the distance between the respective photoconductors is 100 mm.

Next, a method for detecting the belt moving speed (surface moving speed) of the paper transport belt 10 and a configuration related thereto will be specifically described.
FIG. 3 is an enlarged view of one end in the width direction of the paper transport belt 10. As shown in the figure, at the widthwise end of the paper carrying surface (outer peripheral surface) of the paper transport belt 10, a plurality of fixed marks 16 as speed detection marks arranged at regular intervals in the belt moving direction are provided. ing. In the first embodiment, the fixed mark 16 is provided on a portion of each of the photoconductors 6M, 6C, 6Y, and 6K that does not face an image forming area where a toner image can be formed. This is because, if it is provided in a portion facing the image forming area, the toner adheres to the fixed mark 16 and the mark detection accuracy deteriorates. The fixed mark 16 may be provided on the surface (inner peripheral surface) of the paper transport belt 10 opposite to the paper carrying surface. In this case, since the toner does not adhere to the fixed mark 16, the position where the fixed mark 16 is provided is not particularly limited. Thereby, for example, the fixed mark 16 can be provided also in the central portion in the belt width direction. The mark pattern 17 made of the toner described above is naturally formed on the portion of the paper transport belt 10 facing the image forming area as shown in the figure.
The fixed mark 16 is provided on the paper transport belt 10 by printing on the paper transport belt 10, laser marking, or attaching a separately created mark. The intervals between the fixed marks are desirably in the range of about 100 to 10000 μm, and all are desirably equal.

In the first embodiment, each of the photoconductors 6M, 6C, 6Y, and 6K is integrated with at least one of a charging unit, developing units 7M, 7C, 7Y, and 7K, and a cleaning unit provided around the photoconductors. Constructs a process cartridge. The process cartridge is configured to be detachable from the image forming apparatus main body. When removing this process cartridge from the apparatus main body, the process cartridge is pulled out in the direction shown by arrow A in the figure. When the process cartridge is attached to the apparatus main body, the process cartridge is inserted in the direction opposite to the arrow A in the figure. Therefore, the first embodiment is configured such that the attachment / detachment path of the process cartridge does not cross the fixing mark 16 on the paper transport belt 10. Specifically, the process cartridge is configured to be inserted into and removed from the front side of the image forming apparatus, and the fixed mark 16 is provided at an end of the paper transport belt 10 located at the back side of the image forming apparatus. ing. With such a configuration, it is possible to prevent the fixing mark 16 from being stained by toner spilling from the process cartridge when the process cartridge is attached or detached.

固定 The fixed mark 16 is detected by a fixed mark sensor 18. The fixed mark sensor 18 is constituted by a reflection-type optical sensor similarly to a reflection-type optical sensor 20 for detecting a mark pattern described above, and detects the fixed mark 16 in the same manner. The mark detection signal output from the fixed mark sensor 18 is sent to a control unit (not shown). Then, the control unit detects the belt moving speed (surface moving speed) of the paper transport belt 10 from the detection timing of the mark detection signal and the mark interval of the fixed mark 16.

Next, a description will be given of a correction mode for correcting a toner transfer position in order to prevent a deviation of the toner transfer position during transfer. This correction mode is executed at the time other than the normal image forming operation, specifically, for example, when the operator performs a specific operation.
When the correction mode is executed, the image forming apparatus first forms a test mark pattern on each of the photoconductors 6M, 6C, 6Y, and 6K. More specifically, the exposure device 5 causes the photoconductors 6M, 6C, 6Y, and 6K to have a front side (hereinafter, referred to as a “front side”) and a rear side (hereinafter, referred to as a “rear side”) on each of the photoconductors 6M, 6C, 6Y, and 6K. , An electrostatic latent image corresponding to the mark pattern is written. Then, this is developed by each of the developing units 7M, 7C, 7Y and 7K. The mark patterns thus formed are transferred onto the paper transport belt 10 driven at the reference belt moving speed by the transfer units 14M, 14C, 14Y, and 14K, respectively. In this correction mode, the mark pattern is transferred onto the paper transport belt 10, so that the correction mode is executed in a state where the transfer paper is not carried on the paper transport belt 10. In the first embodiment, by forming a plurality of such mark patterns, the accuracy of detecting the amount of deviation between the mark transfer position of the mark pattern and the ideal position is increased, and the reliability is improved.

After the mark patterns of the respective colors have been transferred onto the paper transport belt 10 in this way, these mark patterns are then read by the reflection type optical sensor 20. In the first embodiment, since the mark patterns are formed on the front side and the rear side of each photoconductor, the reflection type optical sensors 20 are respectively arranged at positions corresponding to these. The mark pattern includes M, C, Y, and K marks, a straight mark group parallel to the main scanning direction (the width direction of the paper transport belt 10), and a diagonal mark group that forms an angle of 45 ° with the main scanning direction. Are formed on the front side and the rear side, respectively. The reflection-type optical sensor 20 includes a light-emitting element, an integrator, an amplifier, and the like, and transmits transmitted light emitted from the light-emitting element and transmitted through the paper transport belt 10 through a slit (not shown) by a photoelectric conversion element such as a phototransistor. Receive light. In the first embodiment, a phototransistor is used as a light receiving element. When the phototransistor receives light, the impedance between the collector and the emitter becomes low, and the emitter potential, that is, the output signal level of the reflection type optical sensor 20 increases. When the mark pattern reaches the sensor position with the movement of the paper transport belt 10, the mark blocks light, so that the impedance between the collector and the emitter of the transistor becomes high, and the emitter potential decreases. Therefore, the mark detection signal output from the reflection type optical sensor 20 fluctuates depending on whether or not there is a mark pattern at the sensor position. The mark detection signal is A / D-converted at a predetermined pitch, and then sent to a control unit (not shown).

The control unit includes an arithmetic unit, a memory, and the like, and performs various calculations and controls each unit based on a mark detection signal from the reflection type optical sensor 20. Hereinafter, the processing operation of the control unit in the correction mode will be described.
FIG. 1 is a flowchart showing the flow of the processing operation of the control unit.
The control unit detects the belt moving speed (surface moving speed) of the paper transport belt 10 during the image forming operation performed before executing the correction mode using the fixed mark sensor 18 (S1), and detects this. Store in memory. The belt moving speed at this time is a state in which the transfer paper is being carried. When the correction mode is started in response to the execution command of the correction mode (S2), first, each part of the image forming apparatus is controlled to form a mark pattern on each of the photoconductors 6M, 6C, 6Y, and 6K. A mark pattern is formed on the paper transport belt 10 (S3). When the mark pattern formed in this way is detected by the reflection type optical sensor 20, the A / D converted mark detection signal is input to the control unit (S4). Further, after the correction mode is started, the belt moving speed (surface moving speed) of the paper transport belt 10 while the mark pattern is transferred onto the paper transport belt 10 is detected using the fixed mark sensor 18. (S5), and this is stored in the memory. The belt moving speed at this time is a state where the transfer paper is not carried. In the first embodiment, the belt moving speed is also detected by using the fixed mark sensor 18. However, the belt moving speed can be detected by using the reflection type optical sensor 20 that detects the above-described mark pattern. Further, as a method of detecting the belt moving speed of the paper transport belt 10 in S1 and S5, another method can be used. For example, the rotational speed of the drive roller 11 is detected at any point in a drive system such as a drive force transmitting member such as the drive roller 11 and a drive gear, and the belt movement speed of the paper transport belt 10 is calculated from the detection result. You may do so.

Thereafter, the control unit calculates the amount of deviation between the transfer position of each mark and each ideal position from the signal reception interval between the marks and the belt conveyance speed detected in S5 based on the mark detection signal. (S6). Specifically, the transfer position on the paper transport belt 10 where the mark made of the M toner first transferred onto the paper transport belt 10 is transferred is set as an ideal position, and this ideal position and other colors (C, Y, The amount of deviation from the transfer position of the mark K) is calculated. Then, the control unit sets a latent image writing start timing (hereinafter, “writing”) such that the transfer position of the mark of the other color (C, Y, K) matches the ideal position (the transfer position of the M mark). Timing) is temporarily calculated for each of these other colors (C, Y, K) (S7). Specifically, a correction value of how early or late the currently set writing timing is calculated by dividing each deviation amount calculated in S6 by the belt conveyance speed detected in S5. . Then, the corrected write timing is calculated by adding the correction value to the currently set write timing.

The calculation processing in S6 and S7 can be simplified as follows.
The waveform of the ideal mark detection signal when the mark of the other color is transferred so that the mark of the other color matches the transfer position of the M mark on the paper transport belt 10 driven at the belt moving speed detected in S5 is stored in advance. . Then, the waveform of the mark detection signal from the reflection type optical sensor 20 is compared with the ideal waveform, and the shift amount (time) for these other colors is obtained. Since the deviation amount obtained in this manner is the same as the above-described correction value, if this deviation amount is added to the currently set writing timing, the corrected writing timing can be similarly calculated.

Here, as described above, the belt moving speed at the time of transferring the mark pattern 17 onto the paper transport belt 10 is different from the belt moving speed at the time of actually performing the image forming operation. Therefore, this difference causes a shift in the toner transfer position. Thus, in the first embodiment, in order to correct the writing timing by feeding back this deviation, the paper transport belt 10 carries the transfer paper (when the paper is passed) and the paper transport belt 10 does not carry the transfer paper (when the paper is not transported). (At the time of paper: in the correction mode). Hereinafter, this point will be described in detail.

FIG. 4 is a graph showing the belt moving speed of the paper transport belt 10 when paper is not passed and when paper is passed. Note that the reference belt moving speed is 100 mm / sec as described above. In this example, for simplification of the description, an example is given in which the belt moving speed of the paper transport belt 10 during non-sheet passing is equal to the reference belt moving speed. As can be seen from this graph, the belt moving speed during paper passing is 1 mm / sec slower than the belt moving speed during non-paper passing. In this graph, the transfer start time of the photoconductor 6M for M in which the transfer is performed first is set to 0 sec.

FIG. 5 is a graph obtained by integrating the respective belt moving speeds of the graph shown in FIG. 4 and showing the distance that the surface of the paper transport belt moves after the transfer of the photoconductor 6M for M starts. In this graph, the travel distance during non-paper passing and the travel distance during paper passing are overlapped and displayed, but strictly speaking, the position during paper passing is slightly lower than during non-paper passing. are doing. Note that the moving distance shown in this graph is a point on the paper transport belt 10 located at the transfer position at the time of the start of transfer of the M photoconductor 6M where transfer is first performed (hereinafter, referred to as a “reference point”). ).

FIG. 6 is a graph showing the difference between the moving distance of the paper transport belt obtained by integrating the reference belt moving speed and each moving distance shown in FIG. As described above, since the belt moving speed during non-sheet passing is equal to the reference belt moving speed, the difference in the moving distance is 0 mm. On the other hand, since the belt moving speed at the time of paper passing is lower than the reference belt moving speed by 1 mm / sec, the difference from the moving distance increases with time in proportion to the difference in the belt moving speed.

FIG. 7 is a graph showing the relationship between the reference point (transfer start point of the photoconductor 6M for M) on the paper transport belt 10 and the photoconductors 6M, 6C, 6Y, 6K in the graph shown in FIG. 5 is a graph showing a difference from a point (transfer start point) on the paper transport belt 10 at which the toner transfer of the toner image is started. As is clear from this graph, since all the transfer start points corresponding to the respective photoconductors coincide with the reference points, all the differences are 0 mm.

FIG. 8 is a graph showing a difference between a reference point on the paper transport belt 10 and a transfer start point corresponding to each of the photoconductors 6M, 6C, 6Y, and 6K in the graph shown in FIG. Since the belt moving speed at the time of paper passing is lower than the reference belt moving speed, the reference point on the paper transport belt, which is the transfer start point of the M photoconductor 6M, and the other color photoconductors 6C, 6Y, and 6K. There is a difference from the transfer start point. Originally, it is ideal that the toner transfer positions corresponding to the photoconductors 6C, 6Y, and 6K coincide with the above-described reference position when the paper is passed. If these coincide, the so-called color shift does not occur. However, when the belt moving speed at the time of paper passing does not match the reference belt moving speed, as shown in FIG. 8, the toner transfer positions corresponding to the photoconductors 6C, 6Y, and 6K may be made to coincide with the reference position. Can not. Therefore, at the time of actual image formation, it is not possible to transfer the color toner images transferred from the photoconductors 6C, 6Y, and 6K such that the leading ends of the M toner images already transferred on the transfer paper coincide with each other. This causes a so-called color shift. In the case of this example, the amount of deviation from the reference point (the transfer start point of the M photoconductor 6M) on the paper transport belt 10 is 3 mm for the K photoconductor 6K and 3Y for the Y photoconductor 6Y when read from FIG. Is 2 mm, and 1 mm for the C photoconductor 6C.

In the case of this example, the belt moving speed during non-sheet passing is equal to the reference moving speed. Therefore, when the write timing of the other photoconductors 6C, 6Y, and 6K with respect to the write timing of the M photoconductor 6M is corrected using only the difference at the time of non-sheet passing shown in FIG. The write timing is as shown in the upper part of Table 1 below. However, even if such correction is performed, since the actual image formation is performed while the paper is passed, the belt moving speed of the paper transport belt 10, that is, the moving speed of the transfer paper at the time of the actual image formation is not passed. It is different from the belt moving speed at the time of paper. Therefore, even if the writing timing is corrected using only the difference at the time of non-sheet passing, at the time of actual image formation, as shown in FIG. 8, the toner transfer positions of the photoconductors 6C, 6Y, and 6K are set to the reference position ( (Ideal position), and color shift occurs. Therefore, in the first embodiment, the write timing is corrected as shown in the lower part of Table 1 below.

More specifically, the write timing shown in the lower part of Table 1 is obtained as follows.
In the above example, the belt moving speed of the paper transport belt 10 in the correction mode (non-paper passing) is 100 mm / sec, and the belt moving speed of the paper transport belt 10 during paper passing is 99 mm / sec. The other photoconductors 6C, 6Y, and 6K with respect to the writing timing to the M photoconductor 6M in the correction mode are respectively 1 second, 2 seconds, and 3 seconds later. These times are equal to the time from when the reference point on the paper transport belt 10 passes through the transfer area of the M photoconductor 6M to when it reaches the transfer area of each of the photoconductors 6C, 6Y, and 6K in the correction mode. . Here, the inter-axis distance between the photoconductors is 100 mm as described above. Therefore, the time required for the transfer paper sucked and conveyed by the paper conveyance belt 10 to move between the photoconductors at the time of paper passing is 100 [mm] / 99 [mm / sec] = 1.01 sec. Therefore, the write timing for the C photoconductor 6C needs to be corrected after 1.01 sec, which is further delayed by 0.01 sec from the write timing (after 1 sec) corrected using only the difference in the correction mode. . It is necessary to correct Y and K in the same way.

As shown in FIG. 1, the control unit obtains a difference between the belt moving speed Va at the time of sheet passing detected at S1 and the belt moving speed Vb at the time of correction mode (non-sheet passing) detected at S5. . Then, the ratio of the difference to the belt moving speed in the correction mode (at the time of non-sheet passing) is calculated. That is, (Vb-Va) / Vb is calculated. This ratio is (100 [mm / sec] -99 [mm / sec]) / 100 [mm / sec] = 0.01 in the above example. Then, a numerical value obtained by multiplying this ratio by each write timing (C: 1 sec, Y: 2 sec, K: 3 sec) corrected using only the difference in the correction mode is a correction value (C: 0. 01 sec, Y: 0.02 sec, K: 0.03 sec) (S8). This correction value is added to the write timing calculated in S7.

As described above, in the first embodiment, based on the difference between the belt moving speed between the sheet passing time and the correction mode (non-sheet passing time) obtained in S8 and the deviation amount calculated in S6, the corrected Is obtained. The control unit controls the exposure device 5 so that the writing timing of the photoconductors 6C, 6Y, and 6K of the other colors (C, Y, and K) becomes the corrected writing timing obtained in this manner. Is changed (S9). As a result, the toner of each color toner image is transferred from each of the photoconductors 6M, 6C, 6Y, and 6K onto the transfer paper carried and conveyed on the paper transport belt 10 so that the leading ends of the toner images of each color coincide with each other. The transfer position is corrected. Therefore, in the subsequent image formation, a high-quality image without color shift can be obtained.

In the first embodiment, the case where the color shift is prevented in the direct transfer type tandem type color image forming apparatus has been described. However, the transfer position where the transfer position of the toner image transferred onto the transfer paper is shifted from a desired position is described. The same can be applied to displacement. For example, by using the same method as in the first embodiment, it is possible to prevent the transfer position of the toner image from shifting when transferring the leading end of the toner image to a position 2 mm from the leading end of the transfer paper. In this case, even when the image is transferred by a direct transfer type one-drum type color image forming apparatus, or at the time of secondary transfer by a tandem type or one-drum type color image forming apparatus employing an intermediate transfer type, the toner image is transferred. The displacement can be prevented. The same applies to the case where the transfer position of the toner image is prevented from being shifted during the transfer of the monochrome image forming apparatus. However, the direct transfer type tandem type color image forming apparatus exemplified in the first embodiment is superior to other color image forming apparatuses in that a high quality image can be formed at a high speed. .

[Embodiment 2]
Next, an embodiment in which the present invention is applied to an intermediate transfer type tandem type color image forming apparatus (hereinafter, this embodiment is referred to as “Embodiment 2”) will be described with reference to the drawings.
FIG. 9 is a schematic configuration diagram illustrating an example of the image forming apparatus according to the second embodiment.
The exposure device 5 as a latent image writing unit in the present image forming apparatus is the same as that in the first embodiment. Further, the toner image forming means including the photoconductors 6M, 6C, 6Y, and 6K for M, C, Y, and K as image carriers and the developing devices 7M, 7C, 7Y, and 7K as developing means is also described above. This is similar to the first embodiment. In the second embodiment, each color toner image on each photoconductor is primary-transferred on an intermediate transfer belt 110 as an intermediate transfer body by primary transfer rollers 114M, 114C, 114Y, and 114K as primary transfer means. Are superimposed. The composite toner image formed on the intermediate transfer belt 110 in this way is transferred by the secondary transfer roller 214 as a secondary transfer unit while the conveyed transfer paper and the intermediate transfer belt 110 are in contact with each other. It is secondarily transferred onto paper. Thereafter, the transfer sheet is fixed by a fixing device 15 as a fixing unit, and the transfer sheet after fixing is discharged outside the apparatus.

The method for detecting the belt moving speed of the intermediate transfer belt 110 and the configuration thereof are the same as in the case of detecting the belt moving speed of the paper transport belt 10 in the first embodiment.
In the second embodiment, in order to prevent the toner transfer position from being shifted during the primary transfer, a correction mode is executed to correct the toner transfer position. The operation of the control unit in the correction mode is almost the same as in the first embodiment.

Specifically, the control unit detects the belt moving speed (surface moving speed) of the intermediate transfer belt 110 during the image forming operation performed before executing the correction mode using the fixed mark sensor, and detects the speed. Store in memory. This detection is performed when the transfer paper is being passed. Therefore, the belt moving speed at this time is a state in which the transfer paper is in contact with the intermediate transfer belt 110 in the secondary transfer area. When the correction mode is started, a mark pattern is formed on each of the photoconductors 6M, 6C, 6Y, and 6K, a mark pattern is formed on the intermediate transfer belt 110, and the reflection pattern is formed. It is detected by an optical sensor. Further, after the correction mode is started, the belt moving speed (surface moving speed) of the intermediate transfer belt 110 while the mark pattern is transferred onto the intermediate transfer belt 110 is detected using the fixed mark sensor, This is stored in the memory. The belt moving speed at this time is a state in which the transfer paper is not in contact.

After that, based on the mark detection signal, the control unit calculates the amount of deviation between the transfer position of each mark and each ideal position from the signal reception interval between the marks and the belt conveyance speed in the correction mode. Specifically, as in the first embodiment, the transfer position on the intermediate transfer belt on which the mark made of M toner transferred first on the intermediate transfer belt 110 is set as the ideal position. Then, the amount of deviation between the ideal position and the transfer position of the mark of another color (C, Y, K) is calculated. Then, the control unit sets the writing timing such that the transfer position of the mark of these other colors (C, Y, K) coincides with the ideal position (the transfer position of the M mark). Y, K).

Here, in the second embodiment, the belt movement speeds in a state where the intermediate transfer belt 110 is in contact with the transfer paper (at the time of paper passing) and a state where the intermediate transfer belt 110 is not in contact (at the time of non-paper passing: in the correction mode) are respectively detected. are doing. This is to eliminate the deviation of the toner transfer position caused by the difference between the belt moving speed when transferring the mark pattern 17 onto the intermediate transfer belt 110 and the belt moving speed when actually performing the image forming operation. It is.
To explain this point in detail, in the second embodiment, the secondary transfer is performed while the transfer paper and the intermediate transfer belt 110 are in contact with each other. The secondary transfer is started after the primary transfer of the M photoconductor 6M is started and before the primary transfer of the K photoconductor 6M is completed. In the second embodiment, the transfer paper comes into contact with the intermediate transfer belt 110 at the timing when the primary transfer of the M photoconductor 6M is completed. Due to this contact, the load applied to the intermediate transfer belt 110 increases, so that the belt moving speed of the intermediate transfer belt 110 after the transfer paper contacts the intermediate transfer belt 110 becomes slower than that before the contact. That is, the surface moving speed of the intermediate transfer belt 110 changes during the primary transfer. Therefore, even if the toner transfer position after the change is corrected only by the shift amount obtained based on the mark transferred to the intermediate transfer belt 110 in the non-contact state, the shift corresponding to the speed difference remains. . Therefore, in the second embodiment, as described above, the surface movement speed of the intermediate transfer belt 110 in the contact state and the non-contact state is detected, and the difference is detected. Then, the toner transfer position is corrected based on the difference as well as the deviation amount.

Specifically, the control unit detects the belt moving speed (belt moving speed at the time of contact) of the intermediate transfer belt 110 during the image forming operation performed before executing the correction mode, as in the first embodiment. Then, this is stored in the memory. Then, when the correction mode is executed, first, in a state where the transfer paper is not passed, a writing is performed such that the transfer position of the mark of another color (C, Y, K) matches the ideal position (the transfer position of the M mark). And a first writing speed according to the surface moving speed of the intermediate transfer belt 110 in the non-contact state. Further, the belt movement speed (belt movement speed at the time of non-contact) while the mark pattern is being transferred onto the intermediate transfer belt 110 is detected and stored in a memory. Then, from the difference between the belt moving speed at the time of contact and the belt moving speed at the time of non-contact, the second writing speed after the surface moving speed of the intermediate transfer belt 110 is changed by the contact of the transfer paper is calculated. Then, in the subsequent image formation, first, writing of another color (C, Y, K) is performed at the calculated writing timing and the first writing speed. Thereafter, when the timing at which the transfer paper comes into contact with the intermediate transfer belt 110, that is, the timing at which the primary transfer of the M photoconductor 6M ends, the writing speed of the exposure device 5 is changed to the second writing speed. Continue writing. Accordingly, the toner images of the respective color toner images transferred from the photoconductors 6M, 6C, 6Y, and 6K onto the intermediate transfer belt 110 are aligned with each other even after the transfer paper contacts the intermediate transfer belt. The transfer position is corrected. Therefore, in the subsequent image formation, a high-quality image without color shift can be obtained.

As described above, in the second embodiment, the write control after the correction is set based on the difference between the belt moving speed at the time of contact and the belt moving speed at the time of non-contact and the amount of deviation. Thus, the toner transfer positions of the respective color toner images are corrected such that the positions of the respective color toner images primarily transferred from the respective photoconductors 6M, 6C, 6Y, 6K onto the intermediate transfer belt 110 match each other. Therefore, in the subsequent image formation, a high-quality image without color shift can be obtained.

In the first and second embodiments, the case where the toner transfer position is corrected by changing the writing timing by the exposure device 5 has been described. However, the toner transfer position can be similarly corrected by changing the surface moving speed of the paper transport belt 10 or the intermediate transfer belt 110. Specifically, for example, the surface moving speed at the time of actual image formation is equal to the ratio of the difference between the surface moving speed at the time of paper passing and the surface moving speed at the time of non-paper passing to the surface moving speed at the time of non-paper passing. Speed up.

As described above, the image forming apparatus according to the first embodiment includes the photoconductors 6M, 6C, 6Y, and 6K as image carriers, toner image forming means for forming a toner image on these photoconductors, and transfer as a recording material. A paper transport belt 10 serving as a recording material transport member for transporting the paper with the paper carried on its surface, and transferring the toner on the photoconductors 6M, 6C, 6Y, and 6K onto the transfer paper transported by the paper transport belt. Transfer units 14M, 14C, 14Y, and 14K as transfer means for performing the transfer. In addition, the present apparatus forms a mark made of toner on the photoconductors 6C, 6Y, and 6K, and transfers the mark to the ideal position when the mark is transferred onto the paper transport belt 10 by the transfer units 14C, 14Y, and 14K. The reflection type optical sensor 20 as a shift amount detecting means for detecting the shift amount of the M photoconductor 6M from the mark transfer position, and a control unit are also provided. Further, the present apparatus is provided with a control unit as correction means for correcting the toner transfer position on the transfer paper based on the detected shift amount so that the mark transfer position matches the ideal position. The apparatus has a fixed mark 16, a fixed mark sensor 18 as a speed detecting means for detecting the surface moving speed of the paper transport belt 10, and a control unit. The toner transfer position is determined on the basis of the difference between the belt moving speed (surface moving speed) of the paper transport belt 10 and the belt moving speed of the paper transport belt 10 in a state where the transfer paper is not carried, and the above-mentioned deviation amount. to correct. That is, the first speed detecting step of detecting the belt moving speed of the paper transport belt 10 in a state where the transfer paper is carried, and the belt moving speed of the paper transport belt 10 in a state where the transfer paper is not carried. A second speed detecting step for detecting, and a difference detecting step for detecting a difference between the respective belt moving speeds detected in these steps, based on the difference detected in the difference detecting step and the amount of deviation. The toner transfer position is corrected by a transfer position correction method having a correction step of correcting the toner transfer position. Therefore, the toner transfer position can be corrected so that there is no deviation corresponding to the difference between the belt moving speeds of the paper transport belt 10 in the supported state and the non-supported state.
In the first embodiment, the toner image forming unit includes an exposure device 5 serving as a latent image writing unit that writes a latent image on the photoconductors 6M, 6C, 6Y, and 6K. It has developing devices 7M, 7C, 7Y and 7K as developing means for forming an image. Therefore, the present image forming apparatus employs a so-called direct transfer method, and is superior to image forming apparatuses employing other transfer methods in that an image can be formed at a high speed.
Further, the image forming apparatus according to the first embodiment has a plurality of photoconductors 6M, 6C, 6Y, and 6K, and the toner images on the photoconductors are overlapped with each other on transfer paper conveyed by the paper conveyance belt 10. The transfer is performed by the transfer units 14M, 14C, 14Y, and 14K to form a color image. Then, the control unit corrects the toner transfer position of each toner image so that the positions of the toner images on the transfer paper coincide with each other. Therefore, in color image formation, a high-quality image without color shift can be formed. Moreover, since the present image forming apparatus is a tandem-type color image forming apparatus employing a so-called direct transfer method, as described above, it is possible to form high-quality images at a high speed. Better than forming equipment.
Further, in the first embodiment, the belt moving speed of the paper transport belt 10 in a state where the transfer paper is not carried is determined when the mark is transferred onto the paper transport belt 10 in order to detect the deviation amount. It is. The load applied to the paper transport belt 10 changes depending on whether toner transfer is performed or not, so that the belt moving speed changes. Therefore, by using the belt moving speed when the toner is transferred in the same manner as in the actual image formation as in the first embodiment, it is possible to reduce the error between the actual image formation and the actual image formation. And the correction accuracy can be improved. Further, it is not necessary to separately prepare a mode for detecting the belt moving speed of the paper transport belt 10 in a state where the transfer paper is not carried, and waste of processing time can be eliminated.
On the other hand, the image forming apparatus according to the second embodiment includes photoconductors 6M, 6C, 6Y, and 6K as latent image carriers and an exposure device 5 as a toner image forming unit that forms a toner image on these photoconductors. And developing units 7M, 7C, 7Y, 7K, and an intermediate transfer belt 110 as an intermediate transfer body on which toner on the photoconductor is primarily transferred. Further, the present apparatus is conveyed to primary transfer rollers 114M, 114C, 114Y and 114K as primary transfer means for primary transferring toner on the photoconductors 6M, 6C, 6Y and 6K onto the intermediate transfer belt 110. A secondary transfer roller 214 is provided as secondary transfer means for secondary-transferring the toner image on the intermediate transfer belt while bringing the transfer paper into contact with the intermediate transfer belt 110 on the incoming transfer paper. Further, the present apparatus forms a mark made of toner on the photoreceptors 6C, 6Y, and 6K, and the mark transfer position when the mark is transferred onto the intermediate transfer belt 110 by the primary transfer rollers 114C, 114Y, and 114K. A reflection type optical sensor as a shift amount detecting means for detecting a shift amount from the mark transfer position of the M photoconductor 6M, which is a position, and a control unit are also provided. The apparatus also includes a control unit as a correction unit that corrects the toner transfer position on the intermediate transfer belt 110 based on the detected shift amount so that the mark transfer position matches the ideal position. . The control unit includes a fixed mark, a fixed mark sensor, and a control unit as a speed detecting unit that detects a belt moving speed of the intermediate transfer belt 110. The toner transfer position is corrected based on the difference between the belt moving speed and the belt moving speed of the intermediate transfer belt 110 in a state where the transfer paper is not in contact, and the above-described deviation amount. That is, the first speed detection step of detecting the belt moving speed of the intermediate transfer belt 110 when the transfer paper is in contact, and the belt moving speed of the intermediate transfer belt 110 when the transfer paper is not in contact. A second speed detecting step for detecting, and a difference detecting step for detecting a difference between the respective belt moving speeds detected in these steps, based on the difference detected in the difference detecting step and the amount of deviation. The toner transfer position is corrected by a transfer position correction method having a correction step of correcting the toner transfer position. Therefore, the toner transfer position can be corrected so that there is no deviation corresponding to the difference in the belt moving speed of the intermediate transfer belt 110 in the state where the transfer paper is in contact with the transfer paper.
Further, the image forming apparatus of the second embodiment has a plurality of photoconductors 6M, 6C, 6Y, and 6K, and the primary transfer roller 114M on the intermediate transfer belt 110 so that the toner images on the respective photoconductors overlap each other. , 114C, 114Y, and 114K to form a color image by primary transfer. Then, the control unit corrects the toner transfer positions of the respective toner images so that the positions of the respective toner images on the intermediate transfer belt 110 coincide with each other. Therefore, in color image formation, a high-quality image without color shift can be formed.
In the second embodiment, the belt moving speed of the intermediate transfer belt 110 in a state where the transfer paper is not in contact with the intermediate transfer belt 110 when the mark is transferred onto the intermediate transfer belt 110 in order to detect the deviation amount. It is. Since the load applied to the intermediate transfer belt 110 changes depending on whether the toner is transferred or not, the belt moving speed changes. Therefore, by using the belt moving speed when the toner is transferred in the same manner as in the actual image formation as in the second embodiment, the error between the actual image formation and the belt movement can be reduced. And the correction accuracy can be improved. Further, there is no need to separately prepare a mode for detecting the belt moving speed of the intermediate transfer belt 110 in a state where the transfer paper is not carried, and waste of processing time can be reduced.
In the first and second embodiments, the control unit corrects the toner transfer position by changing the writing timing that is the timing at which the exposure device 5 starts latent image writing. With such correction, the toner transfer position can be corrected more easily and accurately than other correction methods. On the other hand, as described above, by changing the belt moving speed of the paper transport belt 10 in the configuration of the first embodiment, the belt moving speed of the intermediate transfer belt 110 is changed in the configuration of the second embodiment. By changing, the toner transfer position can be corrected.
Further, a plurality of fixed marks 16 as speed detection marks provided on the paper transport belt 10 in the first embodiment and the intermediate transfer belt 110 in the second embodiment are detected, and the detection timing of these fixed marks is detected. , The surface moving speed (belt moving speed) of the paper transport belt 10 and the intermediate transfer belt 110 is detected. Thus, the belt moving speed can be accurately detected by a simple method. Therefore, the correction accuracy can be improved. The same effect can be obtained by providing the speed detection mark on a driving force transmitting member such as a gear for transmitting a driving force to the paper transport belt 10 or the intermediate transfer belt 110.
Further, as described in the first embodiment, the plurality of fixed marks 16 may be provided on the surface of the paper transport belt 10 opposite to the surface on which the transfer paper is supported. With this arrangement, it is possible to prevent the toner from adhering to the fixed mark 16 and deteriorating the mark detection accuracy. As a result, a high correction accuracy can be stably obtained. In the configuration of the second embodiment, the same effect can be obtained by providing the fixed mark 16 on the surface of the intermediate transfer belt 110 opposite to the surface to which the toner is transferred.
In the first and second embodiments, the plurality of fixed marks 16 are formed by forming toner images on the photoconductors 6M, 6C, 6Y, and 6K on the carrier surface or the transfer target surface. It is provided in a portion that does not face the image forming area to be obtained. Thereby, it is possible to prevent the toner from adhering to the fixed mark 16 and deteriorating the mark detection accuracy.
In the first and second embodiments, at least one of the photoconductors 6M, 6C, 6Y, and 6K, the charging unit serving as the toner image forming unit, the developing units 7M, 7C, 7Y, and 7K, and the cleaning unit is provided. Together, they constitute a process cartridge. The process cartridge is configured to be detachable from the image forming apparatus main body in the surface direction of the support surface or the transfer receiving surface, and has a plurality of fixing paths on the support surface or the transfer receiving surface. It is configured not to cross the mark 16. With such a configuration, it is possible to prevent the fixing mark 16 from being stained by toner spilling from the process cartridge when the process cartridge is attached or detached.

5 is a flowchart illustrating a flow of a processing operation of a control unit included in the image forming apparatus according to the first embodiment. FIG. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus. FIG. 2 is an enlarged view of one end in a width direction of a paper conveying belt included in the image forming apparatus. 9 is a graph showing the belt moving speed of the paper transport belt in the correction mode (when paper is not passed) and when paper is passed. 5 is a graph showing the distance traveled by the surface of the paper transport belt after the transfer of the M photoconductor is started, which is obtained by integrating each belt moving speed in the graph shown in FIG. 4. 6 is a graph showing a difference between each moving distance shown in FIG. 5 and each moving distance of the paper transport belt obtained by integrating the reference belt moving speed. In the graph shown in FIG. 6, the reference point (the transfer start point of the M photoconductor) on the paper conveyance belt and the transfer start point on the paper conveyance belt at which the toner transfer from each photoconductor starts in the correction mode. The graph which shows the difference with. 7 is a graph showing a difference between a reference point (transfer start point of the M photoconductor) on the paper transport belt and a transfer start point corresponding to each photoconductor in the graph shown in FIG. 6. FIG. 2 is a schematic configuration diagram illustrating an example of an image forming apparatus according to a second embodiment.

Explanation of reference numerals

Reference Signs List 5 Exposure device 6M, 6C, 6Y, 6K Photoconductor 7M, 7C, 7Y, 7K Developing device 10 Paper transport belt 14M, 14C, 14Y, 14K Transfer device 16 Fixed mark 17 Mark pattern 18 Fixed mark sensor 20 Reflective optical sensor 110 Intermediate transfer belt 114M, 114C, 114Y, 114K Primary transfer roller 214 Secondary transfer roller

Claims (16)

A transfer position correction method for correcting a toner transfer position on a recording material when transferring toner on an image carrier onto a recording material conveyed while being carried on a recording material conveyance member,
A mark transfer step of forming a mark made of toner on the image carrier, and transferring the mark on the recording material conveying member;
A shift amount detecting step of detecting a shift amount between a transfer position and an ideal position of the mark transferred to the recording material conveying member in the mark transfer step,
A correction step of correcting a toner transfer position so that a transfer position of the mark is coincident with the ideal position based on the shift amount detected in the shift amount detection step.
A first speed detecting step of detecting a surface moving speed of the recording material conveying member in a state where the recording material is carried;
A second speed detecting step of detecting a surface moving speed of the recording material conveying member in a state where the recording material is not carried;
A difference detecting step of detecting a difference between the surface moving speeds detected in the first speed detecting step and the second speed detecting step,
The transfer position correcting method, wherein the correcting step corrects the toner transfer position based on the difference detected in the difference detecting step and the shift amount detected in the shift amount detecting step. The toner on the latent image carrier is primarily transferred onto an intermediate transfer member, and the recording material and the intermediate transfer member are transferred onto a recording material on which the toner primarily transferred onto the intermediate transfer member is conveyed. A transfer position correcting method for correcting a toner transfer position on the intermediate transfer body at the time of the primary transfer in an image forming apparatus that performs a secondary transfer while making contact with the transfer device,
A mark transfer step of forming a mark made of a toner on the image carrier, and transferring the mark on the intermediate transfer body;
A shift amount detection step of detecting a shift amount between a transfer position and an ideal position of the mark transferred to the intermediate transfer body in the mark transfer step,
A correction step of correcting a toner transfer position so that a transfer position of the mark is coincident with the ideal position based on the shift amount detected in the shift amount detection step.
A first speed detection step of detecting a surface movement speed of the intermediate transfer member in a state where the recording material is in contact with the first transfer member;
A second speed detection step of detecting a surface movement speed of the intermediate transfer body in a state where the recording material is not in contact with the recording medium;
A difference detecting step of detecting a difference between the surface moving speeds detected in the first speed detecting step and the second speed detecting step,
The transfer position correcting method, wherein the correcting step corrects the toner transfer position based on the difference detected in the difference detecting step and the shift amount detected in the shift amount detecting step. An image carrier;
Toner image forming means for forming a toner image on the image carrier,
A recording material transport member that transports the recording material in a state of being carried on the surface,
Transfer means for transferring the toner on the image carrier to a recording material conveyed by the recording material conveying member;
Forming a mark made of toner on the image carrier, and detecting a shift amount between a mark transfer position and an ideal position when the mark is transferred onto the recording material conveying member by the transfer unit;
An image forming apparatus comprising: a correction unit configured to correct a toner transfer position on the recording material based on the shift amount detected by the shift amount detection unit so that the mark transfer position matches the ideal position.
Having a speed detecting means for detecting the surface moving speed of the recording material conveying member,
The correction means is configured to calculate a difference between a surface moving speed of the recording material conveying member in a state where the recording material is supported and a surface moving speed of the recording material conveying member in a state where the recording material is not supported, and the deviation amount. An image forming apparatus, wherein the toner transfer position is corrected based on a shift amount detected by a detection unit. The image forming apparatus according to claim 3,
An image forming apparatus, wherein the toner image forming means includes a latent image writing means for writing a latent image on the image carrier, and a developing means for developing the latent image to form a toner image. The image forming apparatus according to claim 4,
Forming a color image by transferring a plurality of toner images on each image carrier onto the recording material conveyed by the recording material conveying member by the transfer means so as to overlap each other; And
The image forming apparatus according to claim 1, wherein the correction unit corrects a toner transfer position of each toner image such that a position of each toner image on the recording material coincides with each other. The image forming apparatus according to claim 2, 3, 4, or 5,
The surface moving speed of the recording material conveying member in a state where the recording material is not carried is a time when the mark is transferred onto the recording material conveying member in order to detect the deviation amount. Image forming device. A latent image carrier,
Toner image forming means for forming a toner image on the latent image carrier,
An intermediate transfer member on which the toner on the latent image carrier is primarily transferred;
Primary transfer means for primary transferring the toner on the latent image carrier onto the intermediate transfer body;
Secondary transfer means for secondary-transferring the toner image on the intermediate transfer member while bringing the recording material and the intermediate transfer member into contact with the conveyed recording material;
A shift amount detecting means for detecting a shift amount between a mark transfer position and an ideal position when a mark made of toner is formed on the latent image carrier and transferred to the intermediate transfer body by the primary transfer means. When,
An image forming apparatus comprising: a correction unit configured to correct a toner transfer position on the intermediate transfer body based on the shift amount detected by the shift amount detection unit so that the mark transfer position matches the ideal position. ,
Having a speed detecting means for detecting the surface moving speed of the intermediate transfer body,
The correcting means is configured to calculate a difference between a surface moving speed of the intermediate transfer member in a state where the recording material is in contact and a surface moving speed of the intermediate transfer member in a state where the recording material is not in contact, and the amount of deviation. An image forming apparatus that corrects the toner transfer position. The image forming apparatus according to claim 7,
A plurality of the latent image carriers are formed, and a color image is formed by primary transferring the toner images on the latent image carriers on the intermediate transfer member so as to overlap each other. ,
The image forming apparatus according to claim 1, wherein the correction unit corrects the toner transfer positions of the respective toner images so that the positions of the respective toner images on the intermediate transfer member coincide with each other. The image forming apparatus according to claim 7, wherein
An image forming method, wherein the surface moving speed of the intermediate transfer body in a state where the recording material is not in contact with the intermediate transfer body is used when the mark is transferred onto the intermediate transfer body in order to detect the deviation amount. apparatus. The image forming apparatus according to claim 4, 5, 6, 7, 8, or 9,
The image forming apparatus according to claim 1, wherein the correction unit corrects the toner transfer position by changing a latent image writing start timing by the latent image writing unit. The image forming apparatus according to claim 3, 4, 5, or 6,
The image forming apparatus according to claim 1, wherein the correction unit corrects the toner transfer position by changing a surface moving speed of the recording material conveying member. The image forming apparatus according to claim 7, 8 or 9,
The image forming apparatus according to claim 1, wherein the correction unit corrects the toner transfer position by changing a surface moving speed of the intermediate transfer body. The image forming apparatus according to claim 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12,
The speed detecting means detects a plurality of speed detecting marks provided on the recording material conveying member or the intermediate transfer member, or a driving force transmitting member for transmitting a driving force to the recording material conveying member or the intermediate transfer body, and detects the plurality of speed detecting marks. An image forming apparatus for detecting a moving speed of the recording material conveying member or the surface of the intermediate transfer body based on a mark detection timing. The image forming apparatus according to claim 13,
The plurality of speed detection marks are provided on the surface of the recording material conveying member opposite to the surface on which the recording material is carried, or on the surface of the intermediate transfer member opposite to the surface to which the toner is transferred. An image forming apparatus provided on a surface. The image forming apparatus according to claim 13,
The plurality of speed detection marks are provided on a portion of the carrier surface or the transfer receiving surface that is not opposed to an image forming area where a toner image can be formed on the image carrier or the latent image carrier. An image forming apparatus comprising: The image forming apparatus according to claim 15,
A process cartridge in which the image carrier or the latent image carrier and at least a part of the toner image forming means are integrated with each other is configured to be detachably attached to the apparatus main body in the surface direction of the carrier surface or the transfer surface. An image forming apparatus, wherein the attaching / detaching path does not cross the plurality of speed detection marks on the carrier surface or the transfer surface.

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