JP2011008009A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct the misregistration of an image in a direction crossing the conveying direction of a recording medium.SOLUTION: A control unit 103 calculates ΔT=T2-T1. In accordance with the value of ΔT, the control unit 103 calculates a variation showing a positional change of a patch image pt in a period where the patch image pt moves from a primary transfer position to the position of a patch image detection sensor 20. Next, based on the calculated variation, the control unit 103 predicts a value showing in which direction and how far a normal image 22 is deviated in a period where the normal image 22 moves from the primary transfer position to a secondary transfer position, and then calculates a correction amount for the skew of an intermediate transfer belt 2 in accordance with the predicted value. Based on the calculated correction amount, the control unit 103 controls the posture of an adjusting mechanism 104 so that the conveying direction of the intermediate transfer belt 2 becomes close to the original conveying direction of that at the secondary transfer position.

Description

  The present invention relates to an image forming apparatus.

  An image forming apparatus using an electrophotographic system forms an electrostatic latent image corresponding to an image signal on a photoreceptor, and transfers an image obtained by developing the image onto a recording medium such as paper. Some image forming apparatuses of this type adopt a conveyance form in which a sheet is fed by a registration roll to a transfer position where an image is transferred to the sheet. In Patent Documents 1 and 2, for the purpose of correcting a shift in the position of the image in the sub-scanning direction (that is, the conveyance direction of the sheet), the image is conveyed on the image carrier belt rather than the image transferred to the sheet. A technique is disclosed in which a patch image is formed on the downstream side in the direction, the position of the patch image is detected, and the timing for feeding the paper to the transfer position is controlled.

Japanese Patent No. 3978837 JP 2007-225818 A

  An image transferred to a recording medium such as paper may not only shift in the conveyance direction of the recording medium but also shift in a direction crossing the conveyance direction of the recording medium. An object of the present invention is to correct a shift in the position of an image in a direction that intersects the conveyance direction of a recording medium.

According to the first aspect of the present invention, the first image is formed on the belt-shaped member transported by the transporting means at the first position in the transporting path of the belt-shaped member and the belt-shaped member that is a belt-shaped member. , And after the transfer, the first transfer means for transferring a second image different from the first image, and the first image is transferred to the first image as the belt-shaped member is conveyed. The position of the first image is in a direction intersecting the transport direction of the belt-shaped member from the position of 1 to the second position downstream of the first member in the transport direction of the belt-shaped member. With the detection means for detecting the changed amount of change, and the conveyance of the belt-shaped member, the second image is moved to the third position on the downstream side in the conveyance direction of the belt-shaped member with respect to the second position. The recording medium is placed at the third position according to the time when it is conveyed. Supply means for supplying, second transfer means for transferring the second image from the belt-like member to the recording medium supplied by the supply means at the third position, and the supply means for the third position. When the recording medium is supplied to the position, the relative position between the strip member and the recording medium in the direction intersecting the transport direction of the strip member is the amount of change detected by the detection means. An image forming apparatus including an adjusting unit that adjusts accordingly.
According to a second aspect of the present invention, in the configuration according to the first aspect, the first image has a direction component parallel to the transport direction of the belt-shaped member and a direction parallel to a direction intersecting the transport direction of the belt-shaped member. A first segmental image extending in a direction having a component and a second partial image symmetrical to the first image in a direction intersecting the conveying direction of the belt-shaped member, and the detecting means , The reading means for reading the first partial image and the second partial image, and the amount of change based on the difference between the time when the first partial image is read and the time when the second partial image is read. Calculating means for calculating.

According to the first aspect of the present invention, it is possible to correct an image position shift in a direction crossing the recording medium conveyance direction.
According to the second aspect of the present invention, it is possible to obtain the image shift amount in the direction intersecting the recording medium conveyance direction from the result of reading the single first image.

1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a diagram illustrating a configuration of a main part of an image forming apparatus. It is a figure which shows a mode that the position of the normal image has shifted | deviated. It is a figure which shows the shape of a patch image. It is a figure which shows the shape of a patch image detection sensor. It is a figure which shows a mode that the position of a patch image has shifted | deviated. It is a figure which shows the output signal from a patch image detection sensor. It is a figure which shows a mode that the position of the normal image has shifted | deviated. It is a figure which shows the relationship between a patch image and a patch image detection sensor.

(1) Embodiment The best mode for carrying out the present invention will be described.
FIG. 1 is a diagram showing the structure of an image forming apparatus 100 according to an embodiment of the present invention.
The image forming apparatus 100 incorporates a control unit 103 including an arithmetic device such as a CPU (Central Processing Unit) and various memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory). The control unit 103 controls the operation of the image forming apparatus 100. The image forming units 1Y, 1M, 1C, and 1K form images of yellow (Y), magenta (M), cyan (C), and black (K) colors, respectively. Hereinafter, unless there is a particular need for distinction, these are collectively referred to as “image forming unit 1”. Each image forming unit 1 includes a photoconductor that is an image holding member, a charging device that charges the photoconductor, an exposure device that irradiates the photoconductor with light according to image data to form an electrostatic latent image, and a static device. A developing device that supplies toner to the electrostatic latent image to form an image on the surface of the photoreceptor, a primary transfer roll that primarily transfers the image to the intermediate transfer belt 2 that is an intermediate transfer body, and the surface of the photoreceptor after the primary transfer And a cleaning device for removing the toner remaining on the toner.

  The intermediate transfer belt 2 is a band-shaped member (band-shaped member) that is stretched over a plurality of rolls, and one or a plurality of driving rolls included in these roll groups are rotated under the control of the control unit 103. Is conveyed in the direction of arrow A. The intermediate transfer belt 2 is primarily transferred so that the images of the respective colors formed by the image forming unit 1 are superimposed. The control unit 103 and the drive roll function as an example of a transport unit that transports the intermediate transfer belt 2. The image forming apparatus 100 adjusts the axial direction of the rotating shaft by changing the attitude of the supporting mechanism that supports the rotating shaft of at least one of the plurality of rolls. It has. The operation of the adjustment mechanism 104 is controlled by the control unit 103. In the storage trays 3a, 3b, 3c, and 3d, sheets P of different sizes are stored. The sheet P of the designated size is sent out from any of the storage trays 3a, 3b, 3c, 3d (hereinafter, when there is no need for distinction, these are collectively referred to as “storage tray 3”), A plurality of transport rolls transport the transport path Path in the direction of arrow B or arrow C.

  The transfer device 61 secondarily transfers the image primarily transferred to the intermediate transfer belt 2 onto the paper P conveyed on the conveyance path Path. The fixing device 7 fixes the image secondarily transferred to the paper P to the paper P by heating and pressurizing. The sheet P on which the image has been fixed is discharged to one of the discharge trays 8a, 8b, and 8c along the direction of the arrow C. A display unit 101 and an operation unit 102 are provided on the upper surface of the casing of the image forming apparatus 100. The display unit 101 includes a liquid crystal panel, and displays various information by driving the panel. The liquid crystal panel of the display unit 101 also functions as a touch panel, and the operator performs various operations using the liquid crystal panel in addition to the operation unit 102.

FIG. 2 is a diagram illustrating a configuration of a main part of the image forming apparatus 100.
On the outer peripheral side of the intermediate transfer belt 2, the image forming units 1 are arranged in the order of the image forming units 1K, 1C, 1M, and 1Y from the upstream side in the arrow A direction to the downstream side. The image forming units 1K, 1C, 1M, and 1Y are arranged at the first position where the photosensitive drums and the intermediate transfer belt 2 are in contact with each other. The image is primarily transferred. More specifically, on the outer peripheral surface of the intermediate transfer belt 2, the patch image pt is primarily transferred downstream in the transport direction, and the normal image 22 is primarily transferred upstream in the transport direction. The normal image 22 is an image corresponding to the image information designated by the user, and the patch image pt is an image used for correcting the positional deviation of the normal image 22 with respect to the paper P. is there. That is, the image forming units 1K, 1C, 1M, and 1Y apply the patch image pt, which is an example of the first image, to the intermediate transfer belt 2 that is conveyed at the first position in the conveyance path of the intermediate transfer belt 2. This is an example of a first transfer unit that transfers and, after the transfer, a normal image 22 that is a second image different from the patch image pt.

  The transfer device 61 includes a secondary transfer backup roll 611 and a transfer roll 612. The secondary transfer backup roll 611 is a roll that transports the intermediate transfer belt 2 in the direction of arrow A, and the transfer roll 612 transports the paper P that has been sent out from the storage tray 3 in the direction of arrow B along the transport path Path. It is a transport roll. The transfer device 61 is disposed downstream of the image forming unit 1 in the direction of arrow A, and presses the intermediate transfer belt 2 between the secondary transfer backup roll 611 and the transfer roll 612. When the sheet P is conveyed from the storage tray 3, the transfer device 61 presses the sheet P together with the intermediate transfer belt 2, and transfers the image formed on the outer peripheral surface of the intermediate transfer belt 2 to the sheet P. Transcription. However, the secondary transfer backup roll 611 and the transfer roll 612 are controlled by the control unit 103 so as to be separated from each other when the patch image pt passes between them and to contact each other when the normal image 22 passes between them. The In other words, the transfer device 61 applies the normal image 22 from the intermediate transfer belt 2 to the paper P supplied along the transport path Path at the third position where the secondary transfer backup roll 611 and the transfer roll 612 are in contact with each other. It functions as an example of a second transfer means for transferring.

  A patch image detection sensor 20 is provided at a second position downstream of the image forming unit 1 in the direction of arrow A and at a distance L from the transfer device 61 upstream. That is, the second position where the patch image detection sensor 20 is provided is on the downstream side in the transport direction of the intermediate transfer belt 2 with respect to the first position and on the upstream side with respect to the third position. It is. The patch image detection sensor 20 reads the patch image pt formed on the intermediate transfer belt 2.

  The registration roll 31 is located at a position where the transfer device 61 presses the paper P together with the intermediate transfer belt 2 among a plurality of transport roll groups that transport the paper P sent out from the storage tray 3 in the direction of arrow B along the transport path Path. It is a transport roll just before. When the registration roll 31 rotates under the control of the control unit 103, the timing at which the paper P is conveyed to the third position pressed against the transfer device 61 is adjusted. That is, the sheet P is supplied to the third position in accordance with the time when the normal image 22 is conveyed to the third position as the intermediate transfer belt 2 is conveyed. That is, the control unit 103 and the registration roll 31 function as an example of a supply unit that supplies the paper P to the secondary transfer position in accordance with the time when the image on the intermediate transfer belt 2 is conveyed to the secondary transfer position. To do.

  Between the transfer roll 612 and the registration roll 31, a paper passage detection sensor 23 for detecting the passage of the paper P is provided. The paper passage detection sensor 23 is an optical sensor that combines, for example, a light emitting element and a light receiving element. Since the light emitted by the light emitting element is shielded by the conveyed paper P, the amount of light received by the light receiving element changes according to the presence or absence of the paper P at the detection position. When the arrival of the paper P is detected, the detection signal of the paper passage detection sensor 23 switches from the off state to the on state, and when it is detected that the paper P has passed and left the detection position, the detection signal is changed from the on state. It is designed to switch to the off state. In this way, the paper passage detection sensor 23 detects the arrival and passage of the paper P.

  Meanwhile, during the conveyance of the intermediate transfer belt 2, the intermediate transfer belt 2 may travel in a direction different from the original conveyance direction between the primary transfer roll of the image forming unit 1 and the secondary transfer backup roll 611 of the transfer device 61. . This phenomenon is called “belt skew”. When such a belt skew occurs, a position A2 where the normal image 22 is actually formed on the paper P is actually a position A2 where the normal image 22 is to be formed on the paper P, as shown in FIG. The sheet P is shifted in the direction (referred to as direction n) intersecting the transport direction (referred to as direction m) of the paper P. The direction m is a so-called sub-scanning direction, and the direction n is a so-called main scanning direction. The control unit 103 moves the patch image pt from the primary transfer position (first position) to the position (second position) of the patch image detection sensor 20 as the intermediate transfer belt 2 is conveyed. Then, a change amount in which the position of the patch image pt is changed in a direction crossing the conveyance direction of the intermediate transfer belt 2 is obtained. The control unit 103 controls the posture of the adjustment mechanism 104 according to the amount of change, so that when the paper P is supplied to the secondary transfer position (third position), the intermediate transfer belt 2 and the paper P The relative position in the direction n is adjusted, and the shift amount of the normal image 22 due to the belt skew is reduced.

FIG. 4 is a plan view showing an example of the patch image pt formed on the intermediate transfer belt 2.
The patch image pt includes a line segment image pt1 (first partial image) and a line segment image pt2 (second partial image) extending in different directions. These line segment images pt1 and pt2 each have a direction component parallel to the direction m and a direction component parallel to the direction n. The line segment images pt1 and pt2 are respectively inclined by 45 degrees with respect to the direction m, and the angle formed by the line segment image pt1 and the line segment image pt2 is 90 degrees. The line segment image pt <b> 1 and the line segment image pt <b> 2 are symmetrical with each other in the direction intersecting the conveyance direction of the intermediate transfer belt 2.

Next, FIG. 5 is a plan view showing an example of the patch image detection sensor 20.
The patch image detection sensor 20 includes two sensors, sensors D1 and D2. The sensor D1 is composed of a photodiode D11 and a photodiode D12, and the sensor D2 is composed of a photodiode D21 and a photodiode D22. The photodiodes D11, D12, D21, and D22 are provided symmetrically with respect to the direction m so as to be inclined by an angle of 45 degrees similarly to the line segment images pt1 and pt2.

  When the belt skew occurs, as shown in FIG. 6, the position of the patch image pt formed on the intermediate transfer belt 2 is changed from the primary transfer position (first position) to the position of the patch image detection sensor 20 (second position). Until it is conveyed to the position B), it shifts from the original position B1 to the position B2 in a direction parallel to the direction n. Note that FIG. 6 shows an example in which the patch image pt is shifted from the position B1 to the position B2 in the positive direction of the direction n (the direction from the left to the right in the figure). It may be shifted in the reverse direction (the negative direction of the direction n, that is, the direction from right to left in the figure).

FIG. 7 is a diagram illustrating a waveform of a signal output from the patch image detection sensor 20. The waveform shown in the figure represents the direction from the top to the bottom in the figure as a time axis.
A waveform w11 corresponds to a signal output from the photodiode D11, and a waveform w12 corresponds to a signal output from the photodiode D12. The waveform w21 corresponds to the signal output from the photodiode D21, and the waveform w22 corresponds to the signal output from the photodiode D22. The waveform d1 is a digital waveform obtained by A / D converting the waveform w12 output after the waveform w11 is output, and the waveform d2 is A / D converted by the waveform w22 output after the waveform w21 is output. It is a digital waveform. These digital waveforms are output from the patch image detection sensor 20. As shown in FIG. 6, when the position of the patch image pt is shifted from the original position B1 to the position B2, the photodiode D21 and the photodiode D22 detect the line segment image pt2 constituting the patch image pt. The timing is earlier than the timing when the photodiode D11 and the photodiode D12 detect the line segment image pt1 constituting the patch image pt. Therefore, the output timing T2 of the waveform d2 output from the patch image detection sensor 20 is earlier than the output timing T1 of the waveform d1, and ΔT = T2−T1, which is the difference between the two, corresponds to the amount of deviation of the patch image pt. Value.

The control unit 103 performs the following control based on T1 and T2 measured based on the waveform output from the patch image detection sensor 20.
First, when T1 = T2, it means that no belt skew has occurred, and the control unit 103 adjusts the position of the normal image 22 with respect to the paper P in the direction m. More specifically, the control unit 103 starts the conveyance of the paper P prior to the secondary transfer, and stops the conveyance of the paper P when the paper passage detection sensor 23 detects the paper P. . Next, the control unit 103 determines either T1 or T2, the distance L from the position of the patch image detection sensor 20 (second position) to the secondary transfer position (third position), and the intermediate transfer belt 2. Based on the conveyance speed, the time when the normal image 22 is conveyed to the secondary transfer position is calculated. Then, the control unit 103 resumes the conveyance of the sheet P immediately before the time when the normal image 22 is conveyed to the secondary transfer position, and the sheet P is transferred at a timing at which the normal image 22 is transferred to the sheet P. Send to secondary transfer position. The distance L and the conveyance speed of the intermediate transfer belt 2 are stored in advance in the control unit 103, and the control unit 103 may perform the above calculation using values stored in itself.

Next, when T1 ≠ T2, it means that belt skew has occurred. In this case, the control unit 103 calculates ΔT = T2−T1 which is the difference between them. If ΔT is positive, it means that the patch image pt is shifted in the positive direction of the direction n as shown in FIG. 6, and if ΔT is negative, the patch image pt is shifted in the negative direction of the direction n. I mean. The control unit 103 determines the direction D and the amount of change C in which the position of the patch image pt has changed between the primary transfer position and the position of the patch image detection sensor 20 according to the value of ΔT. Is calculated. That is, the patch image detection sensor 20 and the control unit 103 function as an example of a detection unit that detects the amount of change in the position of the patch image pt. Next, the control unit 103 predicts how much the normal image 22 is shifted in which direction from the primary transfer position to the secondary transfer position based on the direction D and the change amount C. Specifically, when the distance from the primary transfer position to the position of the patch image detection sensor 20 is X, the amount of shift of the normal image 22 from the primary transfer position to the secondary transfer position is as described above. Using the distance L, it is calculated by the formula (X + L) * C / X. Since the primary transfer positions are actually four positions corresponding to the image forming units 1Y, 1M, 1C, and 1K, the control unit 103, for example, each image forming unit 1Y, 1M, 1C, and 1K. A value obtained by averaging the distances from the primary transfer position to the position of the patch image detection sensor 20 is used as X. Then, the controller 103 determines that the intermediate transfer belt is (X + L) * C / X until the normal image 22 on the intermediate transfer belt 2 reaches the secondary transfer position from the position of the patch image detection sensor 20. A control amount for the attitude of the adjustment mechanism 104 is calculated so as to move while moving obliquely in a direction opposite to the direction D. Then, the control unit 103 controls the attitude of the adjustment mechanism 104 based on the control amount. That is, the control unit 103 and the adjustment mechanism 104 adjust the relative position between the intermediate transfer belt 2 and the paper P when the paper P is supplied to the secondary transfer position according to the change amount C. Functions as an example of adjusting means. At the same time, the control unit 103 adjusts the position of the normal image 22 with respect to the paper P in the direction m as in the case of T1 = T2. Specifically, the control unit 103 sets the normal image 22 at the secondary transfer position based on (T1 + T2) / 2, which is the average value of T1 and T2, the distance L, and the conveyance speed of the intermediate transfer belt 2. The conveyance timing is specified, and conveyance control is performed so that the sheet P reaches the secondary transfer position at that timing.
With the above processing, the image forming apparatus 100 reduces the amount of displacement of the normal image 22 due to the occurrence of the belt skew.

(2) Modification (Modification 1)
The embodiment described above may be modified as follows.
As shown in FIG. 8, the normal image 22 on the paper P may be shifted so as to be inclined with respect to both the direction m and the direction n. This is called skew deviation.
In order to eliminate such skew deviation, as shown in FIG. 9, two patch image detection sensors 20R and 20L are provided at different positions in the direction n, and two patch images ptR and ptL are provided in the direction n. Each is formed at a different position. The installation position of the patch image detection sensor 20R corresponds to the formation position of the patch image ptR, and the installation position of the patch image detection sensor 20L corresponds to the formation position of the patch image ptL. The patch image ptR and the patch image ptL have the same shape as the patch image pt shown in FIG. The patch image detection sensor 20R and the patch image detection sensor 20L have the same structure as the patch image detection sensor 20 shown in FIG. The patch image detection sensor 20R and the patch image detection sensor 20L detect the patch image ptR and the patch image ptL on the intermediate transfer belt 2, respectively. Here, the detection timing of the patch image ptR detected by the patch image detection sensor 20R is T3, and the detection timing of the patch image ptL detected by the patch image detection sensor 20L is T4. Based on the difference between T3 and T4, the control unit 103 calculates how much the normal image 22 is inclined, and in order to reduce the inclination, in which direction the conveyance direction of the intermediate transfer belt 2 is set. Specify how much to change. And the control part 103 controls the attitude | position of the adjustment mechanism 104 based on the specified content.

(Modification 2)
An adjustment mechanism that adjusts the relative position between the intermediate transfer belt 2 and the paper P in the direction n when the paper P is supplied to the secondary transfer position is an adjustment mechanism that adjusts the conveyance direction of the intermediate transfer belt 2. For example, the position of the paper P may be adjusted using a guide member that guides the conveyance direction of the paper P. In short, what is necessary is just to adjust the relative position between the intermediate transfer belt 2 and the paper P in the direction n.

(Modification 3)
The image forming apparatus 100 may include various sensors that read an image, such as a sensor that detects a shift between images of a plurality of colors. These sensors may also be used as the patch image detection sensor 20 described above.

(Modification 4)
The shape of the patch image pt is not limited to the example of the embodiment. In short, a line-shaped first partial image extending in a direction having a direction component parallel to the conveyance direction of the intermediate transfer belt 2 and a direction component parallel to a direction intersecting the conveyance direction of the intermediate transfer belt 2; What is necessary is just to be comprised by the 2nd partial image which is symmetrical with a 1st image in the direction which cross | intersects the conveyance direction of the intermediate transfer belt 2. FIG. The patch image detection sensor 20 has a structure corresponding to the shape of the patch image pt.
In addition, the detection unit that detects the amount of change that occurs between the position of the patch image pt with respect to the paper P and the position of the patch image detection sensor 20 from the primary transfer position is not limited to the example of the embodiment. For example, a sensor for detecting the position of the patch image pt in the direction m is provided on each of the upstream side and the downstream side in the conveyance direction of the intermediate transfer belt 2, and the amount of change described above is calculated based on the difference between the detection positions of these sensors. You may ask for it.

1Y, 1M, 1C, 1K ... image forming unit, 100 ... image forming apparatus, 20, 20L, 20R ... patch image detection sensor, pt, ptR, ptL ... patch image, 22 ... normal image, 23 ... paper passage detection sensor, 2 ... Intermediate transfer belt, 61 ... Transfer device

Claims (2)

Transport means for transporting a belt-shaped member which is a belt-shaped member;
The first image is transferred to the belt-shaped member transported by the transport means at a first position in the transport path of the belt-shaped member, and after the transfer, a second image different from the first image is transferred. A first transfer means for transferring;
As the belt-shaped member is transported, the first image reaches from the first position to a second position downstream of the belt-shaped member in the transport direction from the first position. Detecting means for detecting a change amount in which the position of the first image has changed in a direction intersecting the transport direction of the belt-shaped member;
As the belt-shaped member is transported, the second image is moved to a third position that is downstream of the belt-shaped member in the transport direction with respect to the second position. Supply means for supplying a recording medium to position 3,
Second transfer means for transferring the second image from the belt-like member to the recording medium supplied by the supply means at the third position;
When the supply means supplies the recording medium to the third position, the relative position between the strip member and the recording medium in the direction intersecting the transport direction of the strip member is detected. An image forming apparatus comprising: an adjusting unit that adjusts the amount of change detected by the unit. The first image is
A line-shaped first partial image extending in a direction having a direction component parallel to the transport direction of the strip member and a direction component parallel to a direction intersecting the transport direction of the strip member;
It consists of a second partial image that is symmetrical to the first image in a direction that intersects the transport direction of the belt-shaped member,
The detection means includes
Reading means for reading the first partial image and the second partial image;
2. The image according to claim 1, further comprising a calculation unit that calculates the amount of change based on a difference between a time when the first partial image is read and a time when the second partial image is read. Forming equipment.

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