JP2008046356A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that a white frame is formed around an image, because the moving distance of an intermediate transfer member is changed by tension control for making the tension of a belt type image carrier constant, and the positional relation of the image to recording material is changed due to the change in the moving distance thereof. <P>SOLUTION: A mark sensor moving on a circular arc nearly centering on a transfer position is arranged on the path of the intermediate transfer member whose moving speed is changed by the tension control, the variation of the moving distance of the image caused when adjusting the tension is detected. On the basis of the detected signal, the conveying speed of the recording material is temporarily lowered or start timing of a conveying means which conveys the recording material in synchronism with image formation is adjusted. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to a technique for forming an image at a correct position on a recording material.

  In the image forming apparatus, by synchronizing the recording material conveyance of the conveying unit with the image formation in the image forming unit, an image is formed at a predetermined position of the recording material. By improving and improving the accuracy of recording material conveyance, an image is formed at the correct position on the recording material.

In Patent Document 1, in the case of double-sided image formation, an alignment mark is formed at the time of front-side image formation, and alignment is performed at the time of back-side image formation using the formed mark. It has been proposed to reduce the positional deviation of.
JP 2002-169447 A

  In the case of a document mainly composed of a character image or an image with a frame in which a margin is formed around the condition, the conditions regarding the positional relationship between the recording material and the image are relatively mild, and even if there is a positional deviation of about 1 mm. , Often acceptable.

  However, when a photographic image or a pattern image is formed without a frame, the conditions imposed on the positional relationship between the image and the recording material are severe, and even if there is a deviation of 1 mm or less, the deviation is conspicuous and is not allowed.

  Recently, image forming apparatuses are often used as output of digital cameras or as printing apparatuses for color images, and clear the conditions required for borderless photographic images and pattern images. Is desired.

  However, it has been difficult for the prior art to satisfy such needs. In Patent Document 1, when a toner image is formed on a belt, an alignment mark is formed and position adjustment is performed using the mark. However, the movement of an image on the belt caused by belt tension adjustment is performed. Since the adjustment with respect to the distance fluctuation is not performed, the slight deviation between the leading edge of the image and the leading edge of the recording material as described above cannot be corrected by the method of Patent Document 1.

  As described above, the conventional image position adjusting means cannot correct a slight deviation between the leading edge of the image and the leading edge of the recording material.

  An object of the present invention is to provide an image forming apparatus capable of correcting a slight deviation between an image leading edge and a recording material leading edge.

The object is achieved by the following invention.
1.
A belt-shaped image carrier, an image forming unit that forms a toner image on the image carrier, a transfer unit that transfers a toner image formed on the image carrier to a recording material, and image formation in the image forming unit In an image forming apparatus having a conveying unit that conveys a recording material toward a transfer position formed by the transfer unit synchronously,
A tension control unit that is provided between the image forming unit and the transfer position and maintains a constant tension of the image carrier, and is supported by a support member that is rotatable about the transfer position. Tension control means,
A mark sensor supported by the support member and displaced integrally with the tension control means for detecting a mark on the image carrier formed in a predetermined positional relationship with the toner image; and
An image forming apparatus comprising: a control unit that controls a conveyance speed of the conveyance unit based on an output of the mark sensor.
2.
The control means performs control to temporarily change the transport speed before the leading edge of the recording material reaches the transfer position, and changes the transport speed to determine the length of time for transporting the mark sensor. 2. The image forming apparatus according to 1 above, wherein control is performed based on
3.
A recording material sensor for detecting a recording material between the conveying unit and the transfer position; and the control unit controls the conveying speed of the conveying unit based on a leading edge detection signal of the recording material sensor. 3. The image forming apparatus as described in 1 or 2 above.
4).
A belt-shaped image carrier, an image forming unit that forms a toner image on the image carrier, a transfer unit that transfers a toner image formed on the image carrier to a recording material, and image formation in the image forming unit In an image forming apparatus having a conveying unit that conveys a recording material toward a transfer position formed by the transfer unit synchronously,
A tension control unit that is provided between the image forming unit and the transfer position and maintains a constant tension of the image carrier, and is supported by a support member that is rotatable about the transfer position. Tension control means,
A mark sensor supported by the support member and displaced integrally with the tension control means for detecting a mark on the image carrier formed in a predetermined positional relationship with the toner image; and
An image forming apparatus comprising: a control unit that adjusts a starting point of the transport unit based on an output of the mark sensor.
5.
A recording material sensor configured to detect a recording material between the conveying unit and the transfer position; and the control unit controls the start point of the conveying unit based on a leading edge detection signal of the recording material sensor. 5. The image forming apparatus as described in 4 above.
6).
6. The image forming apparatus according to any one of 1 to 5, wherein the image forming unit forms the mark on the image carrier.
7).
The moving distance of the image carrier from the detection position of the mark sensor to the transfer position is approximately equal to the recording material conveyance distance from the detection position of the recording material sensor to the transfer position. The image forming apparatus according to 5.

  In the first aspect of the present invention, even if the moving distance of the belt-shaped image carrier changes due to belt tension control, the conveying speed of the conveying means is adjusted in accordance with the change in the moving distance. An image is formed at the correct position, and even when a photographic image or a pattern image without a border is formed, there is no margin at the border and a high-quality image is formed.

  According to the second aspect of the present invention, a slight deviation of the start position of the recording material in the conveying means for conveying the recording material in synchronization with image formation is also corrected. Therefore, a high-quality image is formed.

The present invention will be described below with reference to illustrated embodiments, but the present invention is not limited to these embodiments.
<Image forming apparatus>
FIG. 1 is a diagram showing an overall configuration of an image forming apparatus according to an embodiment of the present invention.

  An endless belt-like intermediate transfer member is formed by an image forming unit Y for forming a yellow toner image, an image forming unit M for forming a magenta toner image, an image forming unit C for forming a cyan toner image, and an image forming unit K for forming a black toner image. 10 is arranged to face.

  A recording material storage unit 20 is disposed below, and the recording materials P stored in the recording material storage unit 20 are conveyed one by one, and the transfer device 16 passes through a transfer position TR where it contacts the intermediate transfer body 10. After that, the toner image on the recording material P is fixed through the fixing device 23.

  R2 is a registration roller as a conveying unit that conveys the recording material P in synchronization with image formation in the image forming units Y, M, C, and K.

  The intermediate transfer member 10 as an image carrier is stretched around a plurality of rollers 11 to 14 and a tension roller R1, and circulates and moves as indicated by arrows. The intermediate transfer member 10 is supported substantially horizontally by the rollers 11 and 12 and travels at a transfer position where primary transfer is performed.

  The roller 13 constitutes a backup roller facing the transfer device 16 and is grounded.

  The transfer device 16 includes a transfer roller, and a transfer voltage for transferring the color toner image on the intermediate transfer body 10 to a recording material is applied to the transfer roller.

  The tension R1 is a tension control unit that is urged by a spring 18 and applies a constant tension to the intermediate transfer member 10. The intermediate transfer member 16 is intermediate between the roller 12 that horizontally supports the intermediate transfer member 10 and the transfer device 16. Press contact with the body 10.

  Reference numeral 17 denotes a cleaning device for cleaning the intermediate transfer body 10 after transfer.

  A fixing device 23 fixes the color toner image to the recording material P.

  The image forming units Y, M, C, and K each include a drum-shaped photoconductor 1, a charging device 2, an exposure device 3, a developing device 4, a transfer device 5 that performs primary transfer, and a cleaning device 6. By electrostatic charging and exposure, an electrostatic latent image is formed on the photoconductor, developed by the developing device 4 to form a monochromatic toner image on the photoconductor 1, and the monochromatic toner image on the photoconductor 1 is intermediated by the transfer device 5. Primary transfer is performed on the transfer body 10. In the figure, only the image forming unit Y is provided with the reference numerals for the components constituting the image forming unit, but the other image forming units M, C, and K have the same configuration, and the above process is performed. A monochromatic toner image is formed on the photoreceptor 1.

  The single color toner images formed in the image forming portions Y, M, C, and K are transferred onto the intermediate transfer member by the transfer device 5, but the image formation in each of the image forming portions Y, M, C, and K is intermediate. A color toner is formed on the transfer body 10 so as to overlap, and a color toner image is formed on the intermediate transfer body 10.

  In the image forming process, the photosensitive member 1 and the intermediate transfer member 10 operate as indicated by arrows to form a single color toner image in each of the image forming portions Y, M, C, and K, and the formed single color toner The image is transferred to the intermediate transfer member 10 and a color toner image is formed on the intermediate transfer member 10.

  The color toner image on the intermediate transfer body 10 is transferred to the recording material P by the transfer device 16.

The recording material P carrying the color toner image passes through the fixing device 23, and the color toner image is fixed to the recording material P.
<Image position shift on recording material>
First, the displacement of the leading edge of the image on the recording material will be described with reference to FIGS. FIG. 2 is an enlarged view of the main part showing the path of the intermediate transfer member from the image forming position to the transfer position where the secondary transfer is performed and the path of the recording material from the conveying means to the transfer position.

  The toner image on the intermediate transfer member 10 is at a transfer position TR where the intermediate transfer member 10 supported by the backup roller 13 and the transfer roller of the transfer device 16 nip the recording material P. Although the image is transferred to the recording material P, the registration roller R2 transports the recording material P toward the transfer position TR under timing control so that the image on the intermediate transfer member 10 and the recording material P coincide with each other.

  The starting time of the registration roller R2 performed in the timing control of the registration roller R2 is the image formation start time in the image forming units Y, M, C, and K, specifically, in the sub-scanning direction in the digital scanning exposure dew of the exposure device 3. It is determined on the basis of the image writing start time.

  Since the registration roller R2 starts the registration roller R2 in synchronization with the start of image writing at the image writing position EX by the control means 30, in FIG. 2, the moving speed of the intermediate transfer member 10 and the recording material conveyance speed of the registration roller R2 Is constant, the moving distance L1 of the image from the image writing position EX as the exposure position to the transfer position TR and the moving distance of the recording material P from the start position of the recording material P to the transfer position TR in the registration roller R2. If L2 is constant, the leading edge position of the image coincides with the leading edge of the recording material P, and image displacement does not occur. In FIG. 2, the image writing position EX is the exposure position of the exposure apparatus 3 and indicates the exposure position EX of the image forming unit K. The image forming writing positions in the image forming units Y, M, and C are as follows. 2 are different from the image forming position EX in FIG. 2, but are at a fixed distance. Therefore, the movement of the moving distance L1 described below occurs in the same manner in the image forming units Y, M, and C, and the change from the image writing position EX to the secondary transfer position TR in the black image forming unit. The change in the movement distance of the color toner image is explained by the description of the movement of the movement distance L1.

  As will be described next, the moving distance L1 is not constant and varies, so that the leading edge of the image may be displaced from the leading edge of the recording material.

  The tension roller R1 is urged in the direction of the arrow A1 by the spring 18 and always applies a constant tension to the intermediate transfer member 10, but is displaced as indicated by arrows A1 and A2 when the intermediate transfer member 10 is traveling.

  For this reason, the movement locus of the intermediate transfer member 10 may change as 10A. As a result, the length of the intermediate transfer body 10 between the roller 12 and the transfer position TR may change from Y to Y + β, and the moving distance L1 of the image between the exposure position EX and the transfer position TR may be increased by β.

  FIG. 3 shows the timing of image formation and recording material conveyance in an ideal recording material conveyance, and FIG. 4 shows the timing of image formation and recording material conveyance when the above-described deviation occurs.

  In FIG. 3, image writing starts at time t1.

  The registration roller R2 is started at a time t2 when the time T1 has elapsed with reference to the image writing start time t1, and conveys the recording material at a speed V equal to the linear movement speed of the intermediate transfer member 10.

  The leading edge of the image and the leading edge of the recording material reach the transfer position TR at time t3 when T2 time has elapsed from the image writing start time t1, and the image is transferred to the recording material.

  In FIG. 4, image writing starts at time t1.

  The registration roller R2 starts at a time t2 after the lapse of time T1 with the image writing start time t1 as a reference, and conveys the recording material. When there is a fluctuation β of the image movement distance due to the tension control, the leading edge of the image reaches the transfer position TR at a time t4 that is delayed from the time t3 in FIG.

  Since the recording material has reached the transfer position at time t3, a shift of β occurs between the leading edge of the image and the leading edge of the recording material.

  FIG. 5A shows an image when there is no displacement, and FIG. 5B shows an image when there is a displacement. As shown in FIG. A white portion W is formed at the tip.

The white background portion W is inconspicuous in a text document or a framed image, but in the case of a rimless photographic image or pattern image, the white background portion W becomes conspicuous even if the width of the white background portion W is 1 mm or less, and the image quality is deteriorated. .
<Correction of misalignment (1)>
In the present embodiment, such image shift on the recording material is eliminated by using the mark sensor MS.

  FIG. 6 shows a support structure of the mark sensor MS.

  As shown in FIG. 6, the tension roller R1 is supported by a lever 24 that can rotate around the rotation axis of the backup roller 13, and can be displaced with a circular arc centered about the transfer position TR as a locus. Therefore, even if the tension roller R1 is displaced as indicated by arrows A1 and A2, the distance between the transfer position TR and the tension roller R1 hardly changes.

Since the mark sensor MS is fixed to the lever 24, the mark on the intermediate transfer body 10 is detected at a substantially constant distance from the transfer position TR.
The mark sensor MS is composed of a light emitting element and a light receiving element, projects light toward the detected object, receives reflected light, and detects the passage of the detected object.

  The mark sensor MS detects a delay in the passage time of the front end of the image corresponding to a change in the distance from the exposure position EX to the detection position.

  As described above, since the distance between the mark sensor MS and the transfer position TR is constant regardless of the position of the tension roller R1, the delay in the detection time detected by the mark sensor MS is the movement distance. A value β / V obtained by dividing the change amount β by the moving speed V, and this delay is a delay in the time for the image to reach the transfer position TR.

  FIG. 7 is a timing chart of recording material conveyance control performed using the mark sensor MS.

  Prior to the description of FIG. 7, the formation of timing control marks on the intermediate transfer member 10 will be described.

  Prior to image formation, a mark MK as shown in FIG. 8 is formed by any one of the image forming units Y, M, C, and K. In FIG. 8, R is a recording image transferred to the recording material, the mark MK is formed at a position that is off the leading edge of the image and is not transferred to the recording material, and the mark MK and the recording image R have a certain positional relationship. It is formed.

  By detecting the leading edge of the mark MK, the travel time of the intermediate transfer body 10 from the exposure position EX to the mark sensor MS is detected. This travel time includes a time variation corresponding to the travel distance variation β. Accordingly, as indicated by tma to tmb in FIG. 7, the time point detected by the mark sensor MS varies depending on the movement distance of the intermediate transfer body 10.

  The control means 30 controls the conveyance of the recording material by controlling the stepping motor MT that drives the registration roller R2 based on the detection signal of the mark sensor MS, that is, the detection signal Sm generated in the time interval tma to tmb. Do.

  As shown in FIG. 7, at the time point tn1, the recording material conveyance speed of the registration roller R2 is decreased from the initial value V1 to V2.

  Then, after the registration roller R2 is driven at the speed V2 for a time that can correct the positional deviation β between the leading edge of the image and the leading edge of the recording material, the speed is returned to the initial value V1 at the time tn2 based on the detection signal Sm.

  Thereby, the positional deviation between the leading edge of the image and the leading edge of the recording material is eliminated.

  The calculation formula or correspondence table of the time tn2-tn1 corresponding to the movement distance fluctuation β is stored in the storage means MR, and the control means 30 reads the data from the storage means 31 and determines the time tn2-tn1. .

  In this calculation, the delay of the detection time is equal to the delay from the arrival time of the image leading edge corresponding to the detection time to the transfer position TR as described above, so that the calculation of the time tn2-tn1 becomes very simple.

That is, the low speed conveyance time tn2-tn1 is calculated by the following equation.
(Tn2-tn1) = β / (V1-V2)... A1
By correcting that the recording material is conveyed by reducing the conveying speed from V1 to V2 during the time represented by the formula A, the leading edge of the image and the leading edge of the recording material simultaneously reach the transfer position TR at time t6, and the toner image is transferred. Is called.
<Correction of misalignment (2)>
FIG. 9 is a timing chart of image formation and recording material conveyance in another example in which the deviation of the image position on the recording material is corrected.

  The figure shows a case where two images are formed. In the first image formation, the recording material conveyance speed control similar to that shown in FIG. 7 and described above is performed.

  That is, based on the mark detection signal Sm1 from the mark sensor MS, the low-speed conveyance time tn2-tn1 in which the conveyance speed of the registration roller R2 is lowered from the initial value V1 to V2 is adjusted to adjust the leading edge of the image and the recording. Match the tip of the material.

  Writing of the second image starts at time t11.

  At time t12 when time T1a has elapsed from time t11, the registration roller R2 is activated and transports the recording material.

  The activation time t12 of the registration roller R2 is determined based on the mark detection signal Sm1.

  In continuous image formation in which a plurality of images are continuously formed, the running characteristics of the intermediate transfer member 10 are not likely to fluctuate greatly throughout the entire image formation process, and data is not obtained during previous image formation in the continuous image formation process. Effective correction is performed by controlling the subsequent image formation.

  Such a correction method is also effective for correcting the image position, and as shown in FIG. 7, the start point of the registration roller R2 is controlled using the detection signal Sm1 of the mark sensor MS in the first image formation. Thus, the recording material conveyance timing in the second image forming process is controlled, and the positional deviation of the image on the recording material is corrected satisfactorily.

Also in the image formation for the third sheet, correction using the detection signal Sm2 of the mark sensor MS in the previous image formation process is performed, and similar correction is performed for the fourth and subsequent sheets.
<Correction of misalignment (3)>
As described above, the registration roller R2 conveys the recording material in synchronization with the image formation, but the recording material conveyance timing by the registration roller R2 may include an error as described below.

  FIG. 10 shows the state of the recording material P at the start of conveyance of the registration roller R2, that is, when the registration roller R2 is activated.

  After the leading portion reaches the registration roller R2 after being conveyed from the paper feeding unit, the recording material conveyance is continued in a state where the leading edge of the recording material hits the stationary registration roller R2, and the recording material P is placed upstream of the registration roller R2. The conveyance control for forming the loop is performed.

  When the loop is formed, the leading edge of the recording material P may not accurately enter the nip between the rollers R2A and R2B that constitute the registration roller R2.

  In FIG. 10, PA is the case where the leading edge of the recording material P has entered the nip between the rollers R2A and R2B accurately, and the case where PB has not entered correctly.

  Since the leading end of PA and the leading end of PB have different phases separated by a distance α on the circumferential surface of the roller R2A, the recording material P at the leading end PA and the recording material P at the leading end PB differ when the registration roller R is activated. Therefore, the recording material P has a leading edge position shift α.

  In this example, the shift α is corrected using a recording material sensor PS that detects the leading edge of the recording material P immediately downstream of the registration roller R2.

  FIG. 11 is a timing chart of conveyance control for performing correction based on the leading edge detection signal Sp of the recording material sensor PS in addition to correction using the mark sensor MS.

  The time tn2-tn1 during which the recording material is transported by lowering the transport speed of the recording material P from the initial value V1 to V2 is determined based on the detection signal Sm of the mark sensor MS and the leading edge detection signal Sp of the recording material sensor PS. In the correction control shown in FIG. 11, the low speed conveyance time tn2-tn1 is the difference between the fluctuation β of the movement distance of the intermediate transfer member 10 by tension control and the deviation α of the start position of the recording material in the registration roller R2. , Β-α.

  In order to simplify this correction control, the movement distance X1 of the intermediate transfer body 10 from the detection position of the mark sensor MS to the transfer position TR is the recording material conveyance distance X2 from the detection position of the recording material sensor PS to the transfer position TR. The recording material sensor PS is arranged so as to be equal to.

By such an arrangement of the mark sensor MS and the recording material sensor PS, the correction for the deviation β-α can determine the low speed driving time tn2-tn1 of the registration roller R2 in FIG. 11 by the following equation A2.
(Tn2−tn1) = (β−α) / (V1−V2)... A2
With the correction shown in FIG. 11, the leading edge of the image and the leading edge of the recording material can be matched more accurately.

  The misregistration correction (3) is effective when an image is formed on a recording material such as thick paper that is liable to cause the positional deviation α in the registration roller R2.

  Needless to say, the correction (2) of the positional deviation described above can also be used to correct the positional deviation β-α.

1 is a diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 5 is an enlarged view of a main part showing a path of an intermediate transfer body from an image forming position to a transfer position where secondary transfer is performed and a path of a recording material from a conveying unit to the transfer position. FIG. 6 is a diagram illustrating timing of image formation and recording material conveyance in an ideal recording material conveyance. FIG. 10 is a diagram illustrating recording material conveyance timing when a change in the movement distance of the intermediate transfer member occurs. It is a figure which shows the shift | offset | difference of an image. It is a figure which shows the support structure of a mark sensor. 6 is a timing chart when recording material conveyance control is performed using a mark sensor. It is a figure which shows the positional relationship of a mark and a recording image. 10 is a timing chart of image formation and recording material conveyance in another example in which a deviation in image position on a recording material is corrected. FIG. 6 is a diagram illustrating a state of the recording material P at the start of conveyance of the registration roller R2, that is, when the registration roller R2 is activated. FIG. 10 is a timing chart of image formation and recording material conveyance in still another example for correcting a shift in image position on a recording material. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Intermediate transfer body 24 Lever 30 Control means 5, 16 Transfer apparatus EX Image writing position MS Mark sensor PS Recording material sensor

Claims (7)

A belt-shaped image carrier, an image forming unit that forms a toner image on the image carrier, a transfer unit that transfers a toner image formed on the image carrier to a recording material, and image formation in the image forming unit In an image forming apparatus having a conveying unit that conveys a recording material toward a transfer position formed by the transfer unit synchronously,
A tension control unit that is provided between the image forming unit and the transfer position and maintains a constant tension of the image carrier, and is supported by a support member that can rotate about the transfer position. Tension control means,
A mark sensor supported by the support member and displaced integrally with the tension control means for detecting a mark on the image carrier formed in a predetermined positional relationship with the toner image; and
An image forming apparatus comprising: a control unit that controls a conveyance speed of the conveyance unit based on an output of the mark sensor. The control means performs control to temporarily change the transport speed before the leading edge of the recording material reaches the transfer position, and outputs the length of the transport time by changing the transport speed. The image forming apparatus according to claim 1, wherein control is performed based on A recording material sensor for detecting a recording material between the conveying unit and the transfer position; and the control unit controls the conveying speed of the conveying unit based on a leading edge detection signal of the recording material sensor. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. A belt-shaped image carrier, an image forming unit that forms a toner image on the image carrier, a transfer unit that transfers a toner image formed on the image carrier to a recording material, and image formation in the image forming unit In an image forming apparatus having a conveying unit that conveys a recording material toward a transfer position formed by the transfer unit synchronously,
A tension control unit that is provided between the image forming unit and the transfer position and maintains a constant tension of the image carrier, and is supported by a support member that can rotate about the transfer position. Tension control means,
A mark sensor supported by the support member and displaced integrally with the tension control means for detecting a mark on the image carrier formed in a predetermined positional relationship with the toner image; and
An image forming apparatus comprising: a control unit that adjusts a starting point of the transport unit based on an output of the mark sensor. A recording material sensor for detecting a recording material between the conveying unit and the transfer position; and the control unit controls the start point of the conveying unit based on a leading edge detection signal of the recording material sensor. The image forming apparatus according to claim 4. The image forming apparatus according to claim 1, wherein the image forming unit forms the mark on the image carrier. The moving distance of the image carrier from the detection position of the mark sensor to the transfer position is substantially equal to the recording material conveyance distance from the detection position of the recording material sensor to the transfer position. The image forming apparatus according to claim 5.

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