JPH09222827A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a problem with image forming caused by meandering of a belt with simple constitution by calculating a belt meandering quantity according to edge position information, and correcting an image forming position in the belt width direction. SOLUTION: A belt meandering quantity in positions of image forming units K, Y, M and C is calculated by a meandering quantity calculating circuit 10 on the basis of the relative positional relationship between a belt position regulating edge guide 6, an edge detecting sensor 7 to detect the edge and the image forming units K, Y, M and C and edge position information obtained from the edge detecting sensor 7. An image forming position in the belt width direction in the image forming units K, Y, M and C is corrected by correcting means 11 and 15 on the basis of an obtained belt meandering quantity. Since the image forming position in the belt width direction in the image forming units is properly corrected according to the belt meandering quantity, inconvenience at image forming time caused by meandering of a belt can be eliminated without using the conventional complicated and large-scale device constitution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention spans, for example, a transfer material conveying belt, an intermediate transfer belt, and an endless belt used as a photoconductor belt between a plurality of rolls, and runs the endless belt in the circumferential direction. The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile, which performs an image forming process by an electrophotographic process.

[0002]

2. Description of the Related Art FIG. 11 is a schematic view showing the structure of a color copying machine as an example of this type of image forming apparatus. FIG.
The endless belt 5 as a transfer material transport belt.
1 is bridged between a plurality of rolls such as a drive roll 52, a peeling roll 53, a tension roll 54, and an idle roll 55. On the traveling path above the endless belt 51, black, yellow, magenta,
The image forming units K, Y, M, and C for cyan are arranged in parallel. Image forming units K, Y, M, C for each color
Includes a photosensitive drum 56, a charge corotron 57, an image writing device 58, a developing device 59, a transfer corotron 60, a cleaner 61, and the like.

In the vicinity of the drive roll 52, a transfer material suction roll 62 and a suction corotron 63 are arranged to face each other with the endless belt 51 interposed therebetween. On the other hand, the transfer material stored in the paper feed tray 64 is the same as the feed roll 6
5 and the pair of registration rollers 66 are supplied onto the endless belt 51, and the transfer material suction roll 62 and the suction corotron 63 suck the endless belt 51 there. On the other hand, a fixing device 67 is provided near the peeling roll 53, and the image forming units K of the respective colors are provided.
The transfer material on which the images are superimposedly transferred by Y, M, and C is subjected to image fixing processing by the fixing device 67, and then discharged to the outside of the machine.

In addition, a document table 69 on which a document 68 is placed
Below the exposure lamp 70, the reflection mirrors 71, 72,
An image reading unit 75 including an image forming lens 73 and a color CCD 74 is incorporated. The image reading unit 75 optically reads the image recorded on the document 68 while moving the optical system including the exposure lamp 70 and the reflection mirrors 71 and 72 in the horizontal direction in the drawing, that is, the sub-scanning direction. is there.

In the color copying machine having the above construction, the photosensitive drum 56 is uniformly charged by the charge corotron 57, and then the image writing device 58 is exposed according to the image reading information in the image reading unit 75. By the processing, an electrostatic latent image corresponding to the original image is formed on the photosensitive drum 56.
Formed on top. On the other hand, in the developing device 59, toner is supplied to the surface of the photoconductor drum 56, and thereby a toner image (visible image) is formed on the photoconductor drum 56. The toner image thus developed is transferred onto the transfer material on the endless belt 51 by the transfer corotron 60, and then the toner remaining on the photosensitive drum 56 is removed by the cleaner 61. Since such a series of image forming processes is performed for each image reading unit K, Y, M, C of each color, the transfer material conveyed to each image reading unit K, Y, M, C by the running of the endless belt 51. The toner images of the respective colors are sequentially transferred and superposed on each other to form one color image.

By the way, in this type of image forming apparatus, when the endless belt 51 is run in the circumferential direction by the rotation of the drive roll 52, the endless belt 51 moves in the belt width direction during running, a so-called meandering phenomenon. There was a problem that occurs. Such meandering of the belt causes image misregistration or the like during image formation, and in particular in a color copying machine or the like, color matching is not accurately performed, resulting in color misregistration. For example, in a color copying machine having a reading resolution of 400 spi, if there is a deviation of about 0.1 mm during image formation, a color deviation in a copied image will appear to be clearly recognizable. Become. Therefore, conventionally, various measures have been taken to prevent the meandering of the endless belt.

First, as a first conventional technique, Japanese Unexamined Patent Publication No.
In JP-A-190280, as shown in FIG. 12A, a detent member 76 is attached to both ends of the inner peripheral surface of the endless belt 51 over the entire circumference of the belt, and a roll for supporting the belt, for example, a tension roll 54 is provided. A technique is disclosed in which the stop member 76 is abutted against the end face to prevent the belt from meandering. Further, as a second conventional technique, Japanese Patent Laid-Open No. 58-
In Japanese Patent No. 177811, a plurality of slits 77 are provided in the roll longitudinal direction (axial direction) as shown in FIG.
Rubber roll 77 provided with a (LLF roll: Low La
There is disclosed a technique in which the endless belt 51 is supported by a teral force roll and one edge portion of the belt is abutted against the guide member 78 to prevent the belt from meandering. Further, as a third conventional technique, Japanese Patent Laid-Open No. 6-64773 discloses a method for improving the second conventional technique as shown in FIG.
As shown in (b), a technique is disclosed in which the guide member 78 is supported by a spring 79 in the longitudinal direction of the roll to control the meandering of the belt.

[0008]

However, the above-mentioned first to third prior arts have the following problems. That is, in the first prior art, the biasing member 76 receives the thrust force generated in the belt, so that the amount of meandering of the belt depends on the mounting accuracy of the biasing member 76. However, it is technically very difficult to attach the detent member 76 with high precision over the entire circumference of the belt, and even if the detent member 76 is attached as accurately as possible when manufacturing the belt, it is 0.5 to 1.0.
A meandering of about mm will occur. In addition, in the second conventional technique, since the rubber roll 77 exhibits elasticity in its axial direction, the force applied to the endless belt 51 in the roll axial direction (belt width direction) can be reduced, but the belt edge is set as the guide member 78. Since the method is abutting, the meandering amount of the belt depends on the shape of the belt edge. However, it is technically very difficult to actually process the belt edge with high precision as in the case of the attachment of the deviation preventing member 76, and therefore, meandering of about 0.5 mm is generated. Further, in the third conventional technique, the endless belt 5
If the spring constant of the spring 79 is appropriately set with respect to the rigidity in the width direction of 1, a sufficient meandering suppressing effect can be obtained. However, the rigidity in the width direction of the belt is dimensional accuracy of the roll or the belt, the roll alignment ( Parallelism between rolls, etc.)
Since it changes depending on various conditions such as
There is a problem that it is difficult to properly set the spring constant of 9.

Therefore, as another conventional technique, there is a technique in which a sensor detects a relative position in the width direction of a belt traveling according to rotation of a roll, and variably adjusts roll alignment by a motor or the like based on an output signal of the sensor. As disclosed in Japanese Patent Laid-Open No. 3-288167,
In this case as well, technical difficulties are involved, and the device configuration for adjusting the roll alignment becomes complicated and large-scaled, and there is a problem that the cost disadvantage is large.

The present invention has been made to solve the above problems, and an object of the present invention is to form an image capable of eliminating the inconvenience at the time of image formation due to the meandering of a belt without adopting a complicated and large-scale apparatus configuration. To provide a device.

[0011]

The present invention has been made to achieve the above object, and an endless belt is bridged between a plurality of rolls provided substantially parallel to each other, and any one of the plurality of rolls is provided. An image forming apparatus having an image forming unit for running an endless belt in a circumferential direction to form an image on an endless belt or a sheet carried by the endless belt by rotating one of them as a driving roll, Restriction means for restricting the movement of the endless belt in the belt width direction at a predetermined position on the running path of the belt.
Detecting means for detecting the edge position of the endless belt in the belt width direction at a position different from the restricting means, and the relative positional relationship between the restricting means, the detecting means and the image forming unit and the edge position obtained from the detecting means. The meandering amount calculating means for calculating the belt meandering amount at the image forming unit position based on the information, and the image forming in the belt width direction in the image forming unit based on the belt meandering amount obtained from the meandering amount calculating means. A configuration including a correction unit that corrects the position is adopted.

In the image forming apparatus having the above structure, when the endless belt is made to travel by the rotation of the driving roll, the movement of the endless belt in the belt width direction is restricted by the restriction means at a predetermined position on the running path. . At this time, the edge position of the endless belt in the belt width direction is detected by the detection unit at a position different from the regulation unit,
The detected edge position information is given to the meandering amount calculation means. The edge position information thus obtained corresponds to the meandering amount of the endless belt when passing through the predetermined position. Therefore, the meandering amount calculating means determines the relative amount of the regulating means, the detecting means, and the image forming unit. Based on the positional relationship and the edge position information, the belt meandering amount at the position of the image forming unit is calculated, and based on the belt meandering amount obtained by this, the correcting means produces an image in the belt width direction of the image forming unit. Correct the formation position. As a result, the image forming position in the belt width direction of the image forming unit is corrected according to the belt meandering amount at the image forming unit position.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 1A and 1B are diagrams illustrating an embodiment of an image forming apparatus according to the present invention, in which FIG. 1A is a block diagram showing a functional configuration thereof, and FIG. 1B is a schematic diagram showing a support mechanism for an endless belt. It is a figure.

First, in the image forming apparatus shown in FIG. 1, the endless belt 1 is adopted as the transfer material conveying belt for conveying the transfer material to the image forming units K, Y, M and C of the respective colors. The endless belt 1 includes a plurality of rolls provided substantially parallel to each other, that is, a drive roll 2, a peeling roll 3, a tension roll 4, and an idle roll 5.
It is configured to run in the circumferential direction indicated by the arrow in the figure by the rotation of the drive roll 2 when the drive roll 2 rotates.

Among them, the drive roll 2 has a structure in which the outer peripheral surface of a metal roll body is covered with a high friction material such as rubber in order to prevent slipping with the endless belt 1, and thereby the endless belt is formed. The frictional resistance with the belt 1 is set to be large. Also, the wrap angle (wrapping angle) of the endless belt 1 with respect to the drive roll 2 is set as large as possible (preferably 90 ° or more) mainly from the viewpoint of slip prevention. On the other hand, a small diameter LLF roll (roll with slit) is adopted as the peeling roll 3 in order to easily peel the transfer material from the endless belt 1.

On the other hand, the tension roll 4 arranged below the peeling roll 3 is supported by a spring (not shown),
At both ends of the tension roll 4, edge guides 6 having a disc structure having a diameter larger than the diameter of the roll are attached coaxially as a regulating means. The edge guide 6 regulates the movement of the endless belt 1 in the belt width direction on the traveling path of the endless belt 1. Further, on the tension roll 4, as opposed to the edge guide 6, as a means for permitting the movement of the endless belt 1 in the belt width direction, the LLF roll having a large number of slits formed in the roll axial direction as described above (Fig. 12 (b)) is adopted.

As described above, the edge guide 6 which is the regulating means.
By providing a means for allowing the movement of the belt in the belt width direction with respect to the roll located in the vicinity of, the tension roll 4 in this case, the belt edge of the endless belt 1 wound around the tension roll 4 is always The vehicle travels in a state of being abutted against one of the edge guides 6. In the present embodiment, the edge guides 6 are provided at both ends of the tension roll 4, but if the deviation direction of the endless belt 1 in the belt width direction is restricted to one direction by, for example, roll alignment, the The edge guide 6 may be provided only in the direction of deviation.

Further, in the above-mentioned structure, the edge guide 6 as the restricting means is attached to the end portion of the tension roll 4. However, even if the roll and the restricting means are not arranged at the same position in the belt width direction. Endless belt 1
It is possible to regulate the movement of the. However, considering the transferability of the image on the belt, the thickness of the endless belt 1 must be set as thin as possible, and the strength of the belt itself is extremely weak. Therefore, in order for the endless belt 1 to withstand the force acting in the belt width direction, it is preferable to regulate the movement of the endless belt 1 at the portion wound around the roll (lap portion) as described above.

Further, in the apparatus configuration shown in FIG. 1, the edge position of the endless belt 1 in the belt width direction is detected at a position different from the edge guide 6, that is, in the vicinity of the drive roll 2 separated from the tension roll 4 by a predetermined distance. An edge detection sensor (detection means) 7 is provided. The edge detection sensor 7 is composed of, for example, a light emitter 7a and a light receiver 7b which face each other via the edge portion of the endless belt 1 as shown in the figure, and in this case, one of the light emitted from the light emitter 7a. The edge portion of the endless belt 1 can be detected by blocking the portion with the belt edge and detecting the amount of light passing through the portion with the light receiver 7b.

By thus setting the detection point of the belt edge by the edge detection sensor 7 in the vicinity of the driving roll 2, the lateral displacement of the endless belt 1 on the driving roll 2 covered with the high friction material as described above. Therefore, the edge detection sensor 7 can accurately detect the edge shape of the endless belt 1, that is, the change in the edge position, over the entire circumference of the belt. The detection point of the belt edge by the edge detection sensor 7 can be set not only in the vicinity of the drive roll 2 as shown in the drawing but also on the drive roll 2 depending on the type of sensor adopted. When a roll having a high frictional resistance is interposed in addition to the drive roll 2, a belt edge detection point may be set on or near the roll. However, if the detection point of the belt edge by the detection means is set to an improper position, for example, on or near the roll where the lateral displacement of the belt occurs, or at an intermediate position between the two rolls, it is obtained from the edge detection sensor 7. Since the lateral deviation and the meandering of the belt are included in the edge position information as an error, it becomes impossible to accurately detect the change in the edge position corresponding to the belt edge shape.

Further, in the present embodiment, in order to recognize the reference position of the endless belt 1 when the belt is running, a mark or a hole (not shown) is provided near the edge of the endless belt 1. On the other hand, a home sensor 8 is provided at an arbitrary position on the belt traveling path, for example, on the upstream side of the idle roll 5 as shown in the figure,
The home sensor 8 senses a mark (or a hole) on the belt so that the reference position of the endless belt 1 can be recognized.

In addition, the detection signal output from the edge detection sensor 7 is amplified by the amplifier 9 and the meandering amount calculation circuit 1
0 is supplied. On the other hand, the detection signal output from the home sensor 8 is supplied to the meandering amount calculation circuit 10 and the timing calculation circuit 11, respectively. Here, the meandering amount calculation circuit 10 includes the edge guide 6 and the edge detection sensor 7 described above.
Based on the relative positional relationship between the image forming units K, Y, M, and C and the edge position information obtained from the edge detection sensor 7, the image forming units K, Y, and
The belt meandering amount at the M and C positions (in this case, the image transfer position) is calculated. Also, the timing calculation circuit 1
1 indicates each of the image forming units K, Y, M and C based on the belt meandering amount information obtained from the meandering amount calculating circuit 10.
The image writing timing in the main scanning direction is calculated.

The memory 12 is, for example, a RAM (random
Access memory), which stores the image writing timing calculated by the timing calculation circuit 11. The start signal generation circuit 13 is a reference start signal (SOS: start of signa) when setting the above-described image writing timing.
l) is generated. The video clock signal generation circuit 14 generates a clock pulse having a constant cycle.

The horizontal synchronizing signal generating circuit 15 generates a horizontal synchronizing signal according to the image writing timing calculated by the timing calculating circuit 11. The image data generation circuit 16 converts an analog image signal of a document image read by an image reading unit (not shown) into digital data, and performs predetermined processing on the digital data, for example, shading correction, filtering correction, reduction / enlargement, etc. Image data is generated by performing processing. The write data output circuit 17 includes a horizontal synchronization signal generation circuit 15
The image data received from the image data generation circuit 16 is output in synchronization with the horizontal synchronization signal output from the vertical synchronization signal generation circuit 18 and the vertical synchronization signal output from the vertical synchronization signal generation circuit 18. The image writing device 19 is composed of, for example, a laser writing device (ROS) using a laser, drives the laser according to the image data output from the writing data output circuit 17, and emits a laser beam from the image forming unit. To form an electrostatic latent image by irradiating the photoreceptor.

Next, the operating principle of the image forming apparatus according to the present invention will be described with reference to FIG. Note that FIG.
In the figure, for convenience of explanation, the structure in which the endless belt 1 is supported by the drive roll 2 and the tension roll 4 is schematically shown. In FIG. 2, the endless belt 1
In the traveling route of the above, the restriction point of the belt by the restriction means (edge guide 6) is "A", and the position of each image forming unit arranged between the rolls is from the downstream side (tension roll 4) to the upstream side (drive roll 2). ), “B, C, D, E”, and the detection point of the belt edge by the detection means is “F”. Further, the distance from the regulation point A by the regulation means to the belt edge detection point F is set to "L", and then the distance to each image forming unit is set to "L1, L2" with reference to the belt edge detection point F. , L3, L4 ". further,
The interval (pitch) between the image forming units is "P", and the circumferential length from the image writing position to the transfer position in each image forming unit is "m".

Here, when the endless belt 1 is run in the direction of the arrow (circumferential direction) in the figure by the rotation of the drive roll 2, at the restriction point A, the endless belt 1 is displaced in the belt width direction according to the edge shape of the belt. , Causes a so-called meandering phenomenon. That is, when the edge portion that is curved outward with respect to the ideal (straight) edge line passes the regulation point A, the entire belt is pushed back by the regulation means by that amount, and is curved inwardly. When the edge portion passes the regulation point A, the entire belt is moved closer to the regulation means by that amount. In other words, regulation point A
Then, the meandering of the belt occurs by reversing the edge shape of the endless belt 1 passing therethrough.

At this time, assuming that the belt meandering amount at the regulation point A is ΔA, the belt meandering amounts ΔB to ΔE in each image forming unit become smaller as approaching the drive roll 2,
At the belt edge detection point F, ΔF≈0 (zero). The belt meandering amount ΔA at each of these points
As shown in FIG. 3, ΔF gradually decreases with ΔA as a max value in a manner substantially proportional to the distance from point F.
This is because, as described above, the lateral displacement of the belt is prevented on the drive roll 2 side, while the tension roll 4
This is because lateral deviation of the belt is allowed on the side.

In consideration of these points, in the meandering amount calculating circuit 10 described above, each image forming unit position B is as follows.
Calculate the amount of belt meandering at ~ E. First, the detection timing of the edge detection sensor 7 is set to the same time interval as the sub-scanning interval at the time of image formation, and when n = 0, the home sensor 8 is set.
Is on, that is, it senses a mark or hole on the belt. In such a case, assuming that the position of the belt edge detected at the point F in FIG. 2 is E (n), the edge position EA (n) at the point A, which is the regulation point, is calculated by the following mathematical formula 1 It is expressed as an expression.

## EQU1 ## EA (n) = E (n-nL) In this equation 1, "nL" is a value obtained by dividing the distance (L) from the edge detection point F to the regulation point A by the sub-scanning interval. is there.

In this case, the belt meandering amount at the regulation point A is such that the fluctuation of the edge position (edge shape change) is reversed as described above, and therefore the belt meandering amount WA (n) at the regulation point A is as follows. Equation 2 is expressed as

## EQU2 ## WA (n) =-EA (n) =-E (n-nL) Further, the belt meandering amounts WB (n) to WE (n) at each image forming unit position at this time are the following numbers. It is expressed as in Equation 3.

[Formula 3] WB (n) = LB × WA (n) WC (n) = LC × WA (n) WD (n) = LD × WA (n) WE (n) = LE × WA (n) where By substituting WA (n) =-E (n-nL) into the above equation 3, the respective belt meandering amounts are represented by the following equation 4.

## EQU4 ## WB (n) =-LB * E (n-nL) WC (n) =-LC * E (n-nL) WD (n) =-LD * E (n-nL) WE (n) = −LE × E (n−nL) In this equation 4, “LB to LE” is the belt meandering amount at each image forming unit position with the belt meandering amount WA (n) at the regulation point A as the max value. Is a coefficient that determines, and can be expressed by the following equation 5 from the relationship shown in FIG. 2 and FIG.

[Formula 5] LB = L4 / L LC = L3 / L LD = L2 / L LE = L1 / L

In the meandering amount calculating circuit 10 according to the above equation, the belt meandering amounts WB (n) and WC (at each image forming unit position are based on the edge position information E (n) obtained from the edge detecting sensor 7. n), WD (n), WE
(N) is calculated and given to the timing calculation circuit 11.

Here, as shown in FIG. 4, the image writing start timing in the main scanning direction (belt width direction) (hereinafter referred to as the image writing timing) is the start signal output from the start signal generating circuit 13 ( SOS)
Is determined by the pulse number j of the video clock signal (clock pulse) from the falling edge of. That is, the image forming position in the belt width direction at each image forming unit position can be corrected by changing the count value j of the clock pulse up to the image writing timing based on the start signal.

Therefore, the timing calculation circuit 11 calculates the image writing timing in each image forming unit as follows. That is, assuming that the home sensor is turned on when n = 0 and the transfer of the image leading edge at the first point E is started at this point, the correction amount of the image writing timing at each image forming unit position: MB ( i), MC
(I), MD (i), and ME (i) are expressed by the following equation (6).

## EQU6 ## MB (i) = WB (n + 3np) MC (i) = WC (n + 2np) MD (i) = WD (n + np) ME (i) = WE (n) "i" in this equation 6 Is the distance from the leading edge of the image (the number of sub-scans), and "np" is the value obtained by dividing the pitch (P) between the image forming units by the sub-scanning interval.

In accordance with the above equation, the timing calculation circuit 11 corrects the image writing timing at each image forming unit position MB (i), based on the belt meandering amount information supplied from the meandering amount calculation circuit 10. MC (i), M
D (i) and ME (i) are calculated, and these values are stored in the memory 1
It is stored in 2.

The above points will be schematically described with reference to FIGS. 5 and 6. First, in FIG. 5A, the edge detection point F when the home sensor 8 is turned on at n = 0
The degree of fluctuation of the belt edge position E (n) in FIG. Here, since the time from when the home sensor 8 is turned on to when it is turned on again corresponds to the time when the endless belt 1 makes one full rotation, the edge position E (n) at the edge detection point F is the belt 1 It will repeatedly change in the rotation cycle (on cycle of the home sensor).

In this case, since the edge detection point F and the regulation point A have a time difference of nL represented by the above equation 1, the belt edge position EA (n) at the regulation point A Is expressed as shown in FIG. 5 (b) according to the equation (1), considering nL from the time axis of the edge position variation at the edge detection point F. At this time, the belt meandering amount WA (n) at the regulation point A is expressed as shown in FIG. 5C according to the equation 2 in the form of reversing the edge position fluctuation EA (n) at the regulation point A. .

Further, with respect to the belt meandering amount WA (n) at the regulation point A, the belt meandering amount at each of the image forming unit positions B to E is calculated from the edge detection position F in accordance with the formulas 3 and 4. Distance to each image forming unit position (LB = L4 / L, LC = L3 / L, LD = L2 / L,
It is expressed in a form proportional to LE = L1 / L). That is, the belt meandering amount WB (n) at the point B is L of WA (n).
5 (d) corresponding to B times, and the belt meandering amount WC (n) at point C is expressed as in FIG. 5 (e) corresponding to LC times WA (n). The belt meandering amount WD (n) at the point D corresponds to LD times WA (n) in FIG.
As shown in (f), the belt meandering amount WE at point E
(N) is represented as in FIG. 5 (g) corresponding to LE times WA (n).

Here, if n = 0 (the home sensor is on) and the transfer of the leading edge of the image is started at point E, as in the above, each image forming unit position B on the downstream side of that point will be described.
As the correction amount of the image writing timing at the points C, D, in consideration of the time shift (np, 2np, 3np) from the point E at the time of image formation, according to the above formula (6). expressed. That is, the correction amount MB (i) at point B
Is represented as shown in FIG. 6 (a) with the time lag of 3 np taken into account, and the correction amount MC (i) at point C is shown in FIG. 6 (b) with the time lag of 2 np taken into consideration. It is expressed as. Further, the correction amount MD (i) at the point D is expressed as shown in FIG. 6C in consideration of the time shift of nP, and the correction amount ME (i) at the point E is time shift. It is represented as shown in FIG.

The correction amount of the image writing timing calculated for each image forming unit is stored in the memory 12 for one rotation of the belt, and this is detected by the home sensor 8 when the actual image forming (on Signal) as a reference, and the horizontal synchronizing signal generating circuit 15 corrects the image writing timing in the belt width direction (main scanning direction) at each image forming unit position. By the way, the edge position at the edge detection point A will repeatedly change in a cycle of one rotation of the belt unless the edge shape changes due to belt replacement or the like.
The calculation of the correction amount based on the edge position information may be performed in the form-up cycle when the power is turned on. Further, in that case, the correction amount may be calculated based on the belt meandering amount calculated by rotating the endless belt 1 once, and more preferably, the endless belt 1 is rotated a plurality of times, and every one rotation of the belt. Alternatively, the correction amount may be calculated based on the average of the belt meandering amounts calculated in the above.

Further, in calculating the belt meandering amount, the edge detection point F to the regulation point A are not necessarily required to be based on the detection timing of the home sensor 8.
From the relation between the distance to the belt and the belt traveling speed, the timing at which the edge portion detected at the edge detection point F reaches the regulation point A is calculated, and the belt meandering amount at each image forming unit position is calculated at each timing. You may However, in most cases, the home sensor 8 is installed in the existing image forming apparatus in order to detect the joint portion of the endless belt 1, and simplification of data processing during image formation. In consideration of this, it is more preferable to calculate the belt meandering amount based on the detection timing of the home sensor 8 and store the correction amount for one rotation of the belt in the memory 12 as in the present embodiment.

The procedure of correcting the image forming position in the belt width direction in each image forming unit will be described below with reference to the timing chart of FIG. First, t = 0 (n
= 0), the home sensor 8 is turned on, and t = t1 (n =
When the transfer of the first image at the point E is started at the time of n1), each image forming unit shown in the following formula 7 is selected from the correction information for one rotation of the belt stored in the memory 12. Correction amount of image writing timing HB (i) to HE
(I) is called based on the detection signal from the home sensor 8 according to the distance (the number of sub-scanning lines) i from the leading edge of the image.

[Equation 7] H B (i) = MB (i + n1) HC (i) = MC (i + n1) HD (i) = MD (i + n1) HE (i) = ME (i + n1)

Based on the correction amount of the image writing timing thus called, the horizontal synchronizing signal generating circuit 15
The clock pulse from the video clock generation circuit 14 is counted based on the start signal output from the start signal generation circuit 13. Then, the count value of the clock pulse is a prescribed value, in this case, the count value (n ') corresponding to the time period from exposure to transfer is subtracted from the count value (n1) at which transfer starts ( n1-
When it becomes n '), the horizontal synchronizing signal for image writing is output. In response to this, the write data output circuit 17 outputs image data for laser writing at a timing synchronized with the horizontal synchronizing signal from the horizontal synchronizing signal generating circuit 15 and the vertical synchronizing signal from the vertical synchronizing signal generating circuit 18. In response to this, the image writing device 19 starts writing the image by driving the laser.

Thus, in the image forming unit at point E,
While correcting the image writing timing in the main scanning direction (belt width direction) from the time point n'back from the first image transfer start point n1 after the home sensor 8 is turned on, Write an image. Then D
The point image forming unit writes the image while correcting the image writing timing in the main scanning direction (belt width direction) from the time point when np minutes have elapsed from the image writing timing at the point E. After that, similarly, in the image forming units at the point C and the point B, the image writing timing in the main scanning direction (belt width direction) respectively from the time point when np minutes have elapsed from the image writing timing in the immediately previous image forming unit. While correcting the
Write an image. The correction of the image writing timing in the main scanning direction is repeated by the same procedure at the time of transferring the second image and the subsequent images, which is started after the time of n2 minutes has elapsed from the time point of n = 0.

As a result, the image forming position in the belt width direction of each image forming unit is previously determined by the meandering amount calculating circuit 10.
Since the correction is performed in real time based on the belt meandering amount calculated in step 1, even if the meandering phenomenon of the endless belt 1 occurs corresponding to the belt edge shape, the individual image forming units and the image forming units are formed. The transfer position of the image in the belt width direction between the units is controlled to a prescribed position for each page, which makes it possible to obtain a good color image without color shift in a color copying machine or the like.

In the above embodiment, the edge position sensor 7 composed of the light emitter 7a and the light receiver 7b has been described as an example of the detecting means for detecting the edge position of the endless belt 1 in the belt width direction. However, in addition to this, for example, as shown in FIG. 8A, the CCD sensor 20 is disposed so as to face the edge portion of the endless belt 1, and the output signal from the CCD sensor 20 is amplified by the amplifier 21. And to provide the above-mentioned meandering amount calculation circuit 10,
Alternatively, as shown in FIG. 8B, a contact-type position detection sensor 22 is arranged in the vicinity of the endless belt 1, and the movable contact 22a of the position detection sensor 22 contacts the edge portion of the endless belt 1. And the position detection sensor 22
It is also possible to have a configuration in which the output signal from is amplified by the amplifier 23 and is given to the meandering amount calculation circuit 10. In particular, in the former configuration, if there is a difference in surface reflectance between the endless belt 1 and the drive roll 2, the edge detection point can be set directly on the drive roll 2, which is more preferable.

Further, also in the structure of the tension roll 4 equipped with the regulation means (edge guide 6), in addition to the slit LLF roll described above, for example, as shown in FIG. A configuration in which the edge guides 25 are provided at both ends of may be adopted. However,
In the normal roll structure shown in FIG. 9A, it is feared that the force applied from the edge guide 25 to the edge portion of the endless belt 1 becomes too large and the endless belt 1 is damaged. Therefore, in consideration of damage to the endless belt 1, the tension roll 4 may be an LLF roll as in the above-described embodiment, or FIG.
As shown in FIG. 9, the roll main body 28 is slidably inserted into the roll rotary shaft 26 through the bearing 27, and both ends of the roll main body 28 are elastically supported by the springs 29 with the edge guides 30, and FIG. It is preferable to adopt a configuration in which the fixed baffle 31 with an edge guide (not shown) having a low friction coefficient is used to reduce the force received from the edge guide by sliding the endless belt 1, as shown in FIG. .

Further, as means for correcting the image forming position in the belt width direction in each image forming unit, in addition to correcting the image writing timing as described above, for example, a mirror (for reflecting a laser beam toward the photosensitive member ( It can also be realized by changing the position, angle, etc. of a polygonal mirror: polygon mirror) or by changing the position of an image writing LED rod array in which a plurality of light emitting elements are arranged at a predetermined pitch in the axial direction.

In addition, the configuration of the image forming apparatus to which the invention is applied is not limited to the one in which the endless belt 1 is adopted as the transfer material conveying belt as described above.
As shown in (a), each image forming unit K, Y, M, C
Image is transferred onto the endless belt 1 by means of, and the combined image is collectively transferred onto a transfer material by a transfer roll pair 32, which uses the endless belt 1 as a so-called intermediate transfer belt, and FIG. As shown in (b), each of the image forming units K, Y, M and C directly writes and develops an image on the endless belt 1, and the combined image is transferred by a transfer roll pair 33. For example, the one in which the endless belt 1 is adopted as a so-called photosensitive belt, which is collectively transferred to, and the one including an unillustrated single-color image forming unit are run by spanning the plurality of rolls. The present invention can be applied to all image forming apparatuses including a belt support mechanism.

[0048]

As described above, according to the image forming apparatus of the present invention, it is possible to obtain the relative positional relationship between the belt position regulating means, the edge detecting means and the image forming unit and the detecting means. Based on the edge position information
The belt meandering amount at the image forming unit position is calculated by the meandering amount calculating means, and the image forming position in the belt width direction of the image forming unit is corrected by the correcting means based on the belt meandering amount obtained thereby. By adopting the configuration,
Since the image forming position in the belt width direction of the image forming unit is appropriately corrected according to the belt meandering amount, the image accompanying the belt meandering can be obtained without adopting a complicated and large-scale device configuration as in the past. Inconvenience at the time of formation can be eliminated. As a result, a color type image forming apparatus can obtain a good color image without color shift, and a single color type image forming apparatus can also obtain a good image without line shift.

[Brief description of drawings]

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

FIG. 2 is a diagram illustrating an operation principle of the image forming apparatus according to the present invention.

FIG. 3 is a diagram showing a relationship between belt meandering amounts at respective points.

FIG. 4 is a diagram illustrating an example of a method of correcting an image forming position.

FIG. 5 is a schematic diagram illustrating a method of calculating a belt meandering amount at each image forming unit position in a meandering amount calculating circuit.

FIG. 6 is a schematic diagram illustrating a method of calculating the image writing timing at each image forming unit position in the timing calculation circuit.

FIG. 7 is a timing chart at the time of image formation in the embodiment.

FIG. 8 is a schematic diagram illustrating another form of detection means.

FIG. 9 is a diagram illustrating another form of the tension roll.

FIG. 10 is a schematic diagram illustrating another application mode of the image forming apparatus.

FIG. 11 is a schematic diagram illustrating an example of an image forming apparatus.

FIG. 12 is a diagram illustrating a conventional technique.

[Explanation of symbols]

 1 Endless Belt 2 Drive Roll 3 Peeling Roll 4 Tension Roll 5 Idle Roll 6 Edge Guide (Regulating Means) 7 Edge Detection Sensor (Detecting Means) 10 Meandering Amount Calculation Circuit (Meandering Amount Calculation Means) 11 Timing Calculation Circuit 15 Horizontal Sync Signal Generation circuit K, Y, M, C Image forming unit

Claims (3)

[Claims] 1. An endless belt is spanned between a plurality of rolls provided substantially parallel to each other, and any one of the plurality of rolls is rotated as a drive roll, whereby the endless belt is circumferentially moved. In an image forming apparatus having an image forming unit that runs to form an image on an endless belt or a sheet carried on the endless belt, the endless belt in a belt width direction at a predetermined position on a running path of the endless belt. Means for restricting the movement of the endless belt, a detecting means for detecting the edge position of the endless belt in the belt width direction at a position different from the restricting means, and the restricting means, the detecting means and the relative position of the image forming unit. The meandering amount of the belt at the position of the image forming unit based on the relative positional relationship and the edge position information obtained from the detecting means. And a correction unit that corrects an image forming position in the belt width direction of the image forming unit based on the belt meandering amount obtained from the meandering amount calculating unit. Image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the detection point of the belt edge by the detection means is set on or near the drive roll. 3. The image according to claim 1, wherein among the plurality of rolls, a roll located in the vicinity of the restricting means has means for allowing movement of the belt in the belt width direction. Forming equipment.