JPH1172980A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the movement of an endless belt in the width direction and to form a high-quality recorded image faithful to image information without color slurring by detecting the displacement amount of the endless belt in the width direction caused by the rush-in of a recording sheet and perfectly making the carrying direction of the recording sheet coincide with the turning direction of the endless belt based on the detected result. SOLUTION: The meandering amount of an intermediate transfer belt due to the insertion of a recording sheet is calculated by comparing a belt position detection signal acutally outputted from a belt side edge part detection circuit 49 with a belt position detection signal stored in a belt shape storage memory 54 and arithmetically calculated by a belt meandering amount calculation circuit 51. Based on the calculated meandering amount, a direction correction amount calculation circuit 55 calculates to what a degree the carrying direction of the recording sheet is changed to suppress the meandering of the intermediate transfer belt and transmits a driving signal to a motor driver 56 of a resist roll correcting motor 35. Thus, the motor 35 changes the disposing angle of a resist roll.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for transferring a toner image onto a recording sheet using an endless belt wound around a plurality of transport rolls, and more particularly, to an image forming apparatus for transferring an endless belt. The present invention relates to an improvement for preventing displacement in the width direction during movement.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus for transferring a toner image to a recording sheet using a rotating endless belt, a toner image formed on a photosensitive drum is sequentially transferred to an endless intermediate transfer belt. A color image forming apparatus configured to transfer and superimpose a plurality of color toner images on the intermediate transfer belt, and then collectively transfer these toner images to a recording sheet, or an endless photosensitive belt. The color image forming apparatus is configured to repeat exposure and development for each rotation of the image forming apparatus, to form toner images of a plurality of colors on the photosensitive belt in a superimposed manner, and to transfer these toner images collectively to a recording sheet. Are known. Further, there is also a color image forming apparatus in which a recording sheet is attracted to a rotating endless belt, and a toner image is sequentially transferred from a plurality of photosensitive drums to the recording sheet conveyed by the endless belt in a multiplex manner. Are known.

In these image forming apparatuses,
In any of the apparatuses, since the toner images of a plurality of colors are superimposed on the endless belt, the endless belt is rotated to form a high-quality color recording image without color shift. It is important not to displace in the width direction inside.

However, in general, when an endless belt is wound around a plurality of transport rolls including a drive roll and a driven roll and rotated, an error in the formation of the endless belt and a diameter of the transport roll may occur. Due to the error and the mounting angle error, a biasing force acts on the endless belt in the axial direction of the transport roll, and the endless belt moves in the axial direction of the transport roll to obtain a stable rotation position. It will be displaced.

[0005] Therefore, various proposals have been made to stably rotate the endless belt along a fixed path. One of the proposals is to attach the endless belt to both side edges of the inner peripheral surface of the endless belt. Along with the ribs, the endless belt is wound around the transport roll so that the pair of ribs sandwich the transport roll from its axial direction. 2. Description of the Related Art An image forming apparatus in which movement of a belt is restricted is known (Japanese Patent Laid-Open No. 4-2)
57888, JP-A-5-35131, etc.).
In this image forming apparatus, it is not clear in which direction the endless belt is displaced until the belt is actually wrapped around the transport roll and rotated, but ribs are formed on both side edges of the endless belt. Since the belt is formed, when the endless belt is displaced, one of the ribs always interferes with the transport roll, and the belt can be rotated stably.

Another proposal is to finely adjust the arrangement angle of the transport rolls so that a slight biasing force in a constant direction always acts on the rotating endless belt.
At one end in the axial direction of the transport roll, an edge guide member is provided to lock the side edge of the endless belt against the biasing force, and the endless belt always contacts the side edge with the edge guide. An image forming apparatus configured to rotate is also known (Japanese Patent Application Laid-Open No. 5-319611).

[0007]

However, in these image forming apparatuses, when a recording sheet conveyed from a sheet tray or the like enters a transfer position of a toner image or a suction position on an endless belt, the recording sheet is not moved. If the direction of conveyance of the endless belt does not completely match the direction of rotation of the endless belt, a new biasing force is generated in the endless belt as the recording sheet enters, and until then the widthwise direction is reached. The endless belt, which has been stably rotated without moving, also attempts to move in the width direction in search of a new stable state each time the recording sheet enters.

At this time, if the direction in which the endless belt attempts to move is the same direction as before, that is, the same direction as the direction previously locked by the ribs or the edge guides, the endless belt is actually used. Depending on the magnitude and direction of the newly generated biasing force, the endless belt may be stopped in the opposite direction, that is, by the ribs and the edge guide. In some cases, the composite toner image formed on the endless belt has a color shift.

When the endless belt shifts from the previous stable state to the next stable state as described above, since the belt has a property of slowly moving in the axial direction on the transport roll, the belt is continuously operated. When a color image is formed on a large number of recording sheets, the endless belt cumulatively moves in one direction, and in the worst case, the side edge of the endless belt comes into contact with peripheral devices, and There is also a problem that the belt is broken.

Further, if the direction in which the endless belt is to move is the same as the direction previously locked by the ribs or the edge guide, the apparent endless belt may move in the width direction. However, in such a case, a large load is applied to the ribs and the side edges of the endless belt, causing problems such as peeling of the ribs and buckling of the side edges of the belt.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a recording medium in which, when a recording sheet comes into close contact with a rotating endless belt, the width of the endless belt is increased. An object of the present invention is to provide an image forming apparatus capable of forming a high-quality recorded image which is prevented from being displaced in the direction and is faithful to image information and has no color shift.

[0012]

In order to achieve the above object, an image forming apparatus according to the present invention comprises an endless belt which is wound around a plurality of transport rolls and rotates while carrying a toner image. Assume that the image forming apparatus includes a transfer unit that transfers the toner image from the endless belt to the recording sheet, and a conveyance unit that conveys the recording sheet to the transfer position of the toner image. Detecting means for detecting the amount of displacement of the endless belt in the width direction caused by the rush into the recording medium, and direction adjusting means for adjusting the conveying direction of the recording sheet in the conveying means based on the detection result of the detecting means. It is characterized by having been provided.

According to another image forming apparatus of the present invention, there is provided an endless belt which is wound around a plurality of conveying rolls and rotates while adsorbing a recording sheet, and a recording sheet conveyed by the endless belt. The image forming apparatus is provided with a plurality of image carriers for transferring a toner image to the endless belt, and conveying means for conveying the recording sheet to a position for adsorbing the recording sheet to the endless belt. Detecting means for detecting the amount of displacement of the endless belt in the width direction caused by the rush into the recording medium, and direction adjusting means for adjusting the conveying direction of the recording sheet in the conveying means based on the detection result of the detecting means. It is characterized by having been provided.

As described above, if the conveying direction of the recording sheet when the recording sheet comes into contact with the endless belt does not completely match the rotation direction of the endless belt, the biasing force is applied to the endless belt. Occurs, and the endless belt moves in the width direction. According to such technical means of the present invention, the detection means causes the endless belt to be displaced in the width direction caused by the entry of the recording sheet. Since the amount is detected, it is possible to grasp how much the recording sheet conveyance direction is displaced with respect to the conveyance direction of the endless belt based on the detection result. Therefore, if the direction of the recording sheet is adjusted by the direction adjusting means based on the detection result,
The direction in which the recording sheet is conveyed and the direction in which the endless belt rotates can be completely matched, and the endless belt can be prevented from moving in the width direction due to the entry of the recording sheet.

Here, as the detecting means, if it is possible to detect the amount of displacement in the width direction of the endless belt caused by the entry of the recording sheet, for example, a photo sensor or the like is used to detect the side edge of the endless belt. May be actually detected. However, if the movement of the endless belt in the width direction is locked by the edge guide members and the ribs described above, even if the endless belt acts on the endless belt in the width direction due to the entry of the recording sheet, the endless belt does not move. Does not move in the width direction, the photosensor cannot detect a mismatch between the recording sheet conveyance direction and the rotation direction of the endless belt.

Therefore, from this viewpoint, the detecting means is a biasing force detecting means such as a load cell which contacts the side edge of the endless belt and detects a biasing force in the width direction of the endless belt. Is preferred. According to such a deviation force detecting means, the deviation force in the width direction of the endless belt can be directly measured, so that the increase or decrease of the deviation force caused by the entry of the recording sheet can be grasped. It is possible to predict how much the recording sheet conveyance direction is displaced with respect to the rotation direction of the endless belt,
Even when the endless belt is not actually displaced in the width direction, the direction of the recording sheet can be matched with the rotation direction of the endless belt by the direction adjusting means.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows a schematic configuration of a color electrophotographic copying machine using the belt device of the present invention as an intermediate transfer member for a toner image. Reference numeral 1 denotes an image input unit for reading an image of the original, which is configured to receive reflected light of the original 12 scanned by the lamp 11 with the CCD sensor 13 and convert image information of the original 12 into an electric signal. .

Reference numeral 2 denotes an image output unit for forming an image on the recording sheet 3 based on the image information obtained in the image input unit 1. In the image output unit 2, reference numeral 21 denotes a photosensitive drum, and an electrostatic latent image corresponding to image information is formed on the surface of the photosensitive drum by a well-known electrophotographic process (not shown) with the rotation in the direction of arrow A. It is formed. That is, after the photosensitive drum 21 is charged to a predetermined dark potential by the charger 21a, exposure is performed by a light beam emitted from the laser beam scanner 22 according to image information. A rotary developing unit 23 having black (K), yellow (Y), magenta (M), and cyan (C) color developing units is provided next to the photosensitive drum 21.
Is provided, and the electrostatic latent image formed on the photosensitive drum 21 is developed by any one of the developing devices to form a toner image T. Therefore, if the electrostatic latent image written on the photosensitive drum 21 corresponds to the yellow image information, this electrostatic latent image is developed by a developing device containing yellow (Y) toner, and A yellow toner image is formed on the drum 21.

Reference numeral 4 denotes an endless intermediate transfer belt arranged so as to be in contact with the surface of the photosensitive drum 21. The intermediate transfer belt is stretched around a plurality of transport rolls 4a to 4c including a driving roll and a driven roll. And rotate. The unfixed toner image T formed on the photosensitive drum 21 is
1 is transferred from the photosensitive drum 21 to the surface of the intermediate transfer belt 4 at a primary transfer position where the intermediate transfer belt 1 contacts the intermediate transfer belt 4. At this primary transfer position, a primary transfer corotron 5 is disposed on the back side of the intermediate transfer belt 4. By applying a voltage having a polarity opposite to the charging polarity of the toner to the primary transfer corotron 5, The unfixed toner image T on 21 is electrostatically attracted to the intermediate transfer belt 4.

When a single-color image is formed, the unfixed toner image T primarily transferred to the intermediate transfer belt 4 is secondarily transferred to the recording sheet 3 immediately. In the case of forming, the formation of the toner image on the photosensitive drum 21 and the primary transfer process of this toner image are repeated for the number of colors. For example, when forming a full-color image in which four color toner images are superimposed,
An unfixed toner image T of black, yellow, magenta, and cyan is formed on the photosensitive drum 21 for each rotation thereof, and these unfixed toner images T are primarily transferred to the intermediate transfer belt 4 in order. On the other hand, the intermediate transfer belt 4 rotates at the same cycle as the photosensitive drum 21 while holding the black primary untransferred toner image T which has been firstly transferred, and the intermediate transfer belt 4 rotates yellow, magenta And the cyan unfixed toner image T is superimposed and transferred on the black unfixed toner image T.

The unfixed toner image T primarily transferred to the intermediate transfer belt 4 in this manner is conveyed to a secondary transfer position facing the conveyance path of the recording sheet 3 with the rotation of the intermediate transfer belt 4. You. At the secondary transfer position, a semiconductive secondary transfer roll 6 is in contact with the intermediate transfer belt 4, and the recording sheet 3 carried out of the tray 8 at a predetermined timing by a feed roll 7 is connected to the secondary transfer roll 6. It is sandwiched between the intermediate transfer belt 4. A transport roll 4c facing the secondary transfer roll 6 with the intermediate transfer belt 4 interposed therebetween forms a counter electrode of the secondary transfer roll 6.
When a voltage having a polarity opposite to the charge polarity of the toner is applied to the secondary transfer roll 6, the unfixed toner image T carried on the intermediate transfer belt 4 is electrostatically transferred to the recording sheet 3 at the secondary transfer position.

Then, the recording sheet 3 onto which the unfixed toner image has been transferred is peeled off from the intermediate transfer belt 4 and sent to a fixing device 9 where the fixing process of the unfixed toner image is performed. On the other hand, the residual toner is removed by the cleaner 10 from the intermediate transfer belt 4 on which the secondary transfer of the unfixed toner image has been completed.

In the above construction, the secondary transfer roll 6
The cleaner 10 is provided so as to be able to freely contact and separate from the intermediate transfer belt 4. When a color image is formed, these members are used until the final unfixed toner image is primarily transferred to the intermediate transfer belt 4. It is separated from the intermediate transfer belt 4.

Next, a configuration for stably rotating the intermediate transfer belt 4 along a fixed path without displacing the intermediate transfer belt 4 in the width direction will be described. As described above, when the endless belt is rotated, the endless belt is displaced in the axial direction of the transport roll due to a molding error of the endless belt, an error in the diameter of the transport roll, and an installation angle error. Therefore, in this embodiment, one of the transport rolls 4a to 4c around which the intermediate transfer belt 4 is wound is used as a steering roll, and the steering roll 4a is moved in accordance with the amount of displacement of the intermediate transfer belt 4 in the width direction. , The intermediate transfer belt 4 is configured to rotate stably along a fixed path.

As shown in FIG. 2, the rotation of the steering roll 4a is supported by bearings 41a and 41b, and one of the bearings 41b is pressed by an eccentric cam 43 by a spring 42.
When the eccentric cam 43 is rotated by 4, one end of the steering roll 4 a pressed by the eccentric cam 43 swings, and the arrangement angle of the steering roll 4 a with respect to the other transport rolls 4 b and 4 c changes to an unrestricted floor. It has become.

On the other hand, a photo sensor 45 for detecting the side edge of the belt is provided at one position of the rotation path of the intermediate transfer belt 4.
The belt side edge detection circuit detects the position of the side edge of the intermediate transfer belt 4 during rotation based on the detection signal of the sensor 45, and the eccentric cam 43 based on the detection result. It is configured to control the rotation angle of. As shown in FIG.
Is a so-called transmission type in which the light projecting unit 46 and the light receiving unit 47 are opposed to each other, and when the side edge of the intermediate transfer belt 4 is inserted between the light projecting unit 46 and the light receiving unit 47, the light projecting unit 46 Part of the emitted light is blocked by the intermediate transfer belt 4, whereby the position of the side edge of the intermediate transfer belt 4 is detected from the detection signal of the light receiving section 47.

Further, since it is impossible to form the side edge of the intermediate transfer belt 4 straight,
The detection value of No. 5 also includes a defect in the formation of the intermediate transfer belt 4, and if the steering roll 4a is operated so that the detection value of the photosensor 45 becomes constant, the intermediate transfer belt 4 will not Meandering. Therefore, in order to stabilize the rotation of the intermediate transfer belt 4, it is necessary to compare the value detected by the photosensor 45 with each rotation of the intermediate transfer belt 4. Is provided with a rotation position detection sensor 48 for detecting that the intermediate transfer belt 4 has reached a predetermined rotation position (see FIG. 1). This sensor 48
Is configured to detect a rotation reference mark (not shown) provided at one location on the intermediate transfer belt 4 and output a rotation reference signal of the belt 4 every one rotation of the intermediate transfer belt 4. I have.

FIG. 4 is a block diagram showing a control system for operating the steering roll 4a based on the detection value of the photo sensor 45. When the intermediate transfer belt 4 starts rotating, the detection signal of the photo sensor 45 is input to a belt side edge detection circuit 49, where the position of the side edge of the intermediate transfer belt 4 is determined by comparison with a predetermined threshold level. Is generated. The belt position signal is sequentially read into the belt meandering amount calculation circuit 51 together with the count value of the timer 50. On the other hand, the rotation position detection sensor 48 outputs a rotation reference signal when detecting a rotation reference mark provided on the intermediate transfer belt 4, and the count value of the timer 50 is cleared by the rotation reference signal. That is, the count value of the timer 50 indicates the circumferential coordinates of the intermediate transfer belt 4 with the rotation reference mark as the origin.

The belt meandering amount calculating circuit 51 compares a large number of belt position detection signals obtained for each rotation of the intermediate transfer belt 4 with those of the previous rotation by using the timer count value as an address. The meandering amount of the belt 4 is calculated. On the other hand, the steering amount calculating circuit 52 calculates, based on the meandering amount obtained by the belt meandering amount calculating circuit 51, how much the arrangement angle of the steering roll 4a is changed so that the meandering of the intermediate transfer belt 4 can be settled. A drive signal is sent to the motor driver 53 of the angle correcting motor 44 of the steering roll 4a. Thereby, the angle correcting motor 44 rotates the eccentric cam 43 described above, and the arrangement angle of the steering roll 4a is changed.

By appropriately changing the arrangement angle of the steering roll 4a based on the detection signal of the photo sensor 45, the meandering of the intermediate transfer belt 4 gradually converges, and finally some external force is applied. Intermediate transfer belt 4
, The intermediate transfer belt 4 rotates on a fixed path without meandering.

At this time, the belt position detection signal sent from the belt side edge detection circuit 49 does not include the meandering amount of the intermediate transfer belt 4, and the belt position detection signal is purely the side edge of the intermediate transfer belt 4. Only the shape of. Therefore, the belt position detection signal indicating the shape of the side edge portion of the intermediate transfer belt 4 is stored in the belt shape storage memory 54. Thereafter, the meandering of the intermediate transfer belt 4 occurs based on the stored belt position detection signal. Is checked.

On the other hand, a recording sheet 3 conveyed to a secondary transfer position of a toner image by a registration roll (hereinafter referred to as a registration roll) 31 disposed before the secondary transfer position.
When the transport direction A of the intermediate transfer belt 4 does not completely coincide with the rotation direction B of the intermediate transfer belt 4, as shown in FIG. Direction external force f acts. Therefore, the intermediate transfer belt 4 that has been stably rotated along a fixed path under the control of the steering roll 4a described above.
In addition, meandering occurs again as the recording sheet 3 enters the secondary transfer position.

Therefore, in the image forming apparatus of this embodiment, the meandering of the intermediate transfer belt 4 caused by the recording sheet 3 entering the secondary transfer position is detected by the photosensor 45 and the belt side edge detecting circuit 49. It is configured to detect and immediately correct the conveying direction of the recording sheet 3 by the registration roll 31 based on the detected value.

FIG. 6 shows a recording sheet 3 formed by the registration roll 31.
3 shows a mechanism for correcting the transport direction of the above. Like the above-described steering roll 4a, the registration roll 31 is supported by bearings 32a and 32b for rotation, and one of the bearings 32b is pressed by an eccentric cam 34 by a spring 33. When the cam 34 is rotated, the eccentric cam 34
As a result, one end of the registration roll 31 pressed swings, and the arrangement angle of the registration roll 31 changes to the floor without permission.

FIGS. 7 and 8 show the change over time of the belt position detection signal output from the above-described belt side edge detection circuit 49. In the former, the meandering of the intermediate transfer belt 4 is controlled by the control of the steering roll 4a. The latter shows the belt position detection signal when the recording sheet 3 is pushed into the secondary transfer position from such a state. In the state shown in FIG.
The belt position detection signal shown in FIG. 4 indicates the shape of the side edge of the intermediate transfer belt 4 and is a signal stored in the belt shape memory 54. is there. In order to facilitate understanding of the difference between FIGS. 7 and 8, assuming that the shape of the side edge of the intermediate transfer belt 4 is ideally straight, these figures are the same as those in FIGS.
Can be redrawn as shown in The broken line in FIG. 9 is the belt position detection signal corresponding to FIG. 7, the solid line is the belt position detection signal corresponding to FIG. 8, and the displacement of the solid line with respect to the broken line is the amount of displacement of the intermediate transfer belt 4 caused by the insertion of the recording sheet 3. The meandering amount is shown.

The meandering amount of the intermediate transfer belt 4 caused by the insertion of the recording sheet 3 is determined by the belt position detection signal actually output from the belt side edge detecting circuit 49 when the recording sheet 3 is inserted, and the belt position detection signal. It can be calculated by comparing with the belt position detection signal stored in the shape storage memory 54, and is calculated by the belt meandering amount calculation circuit 51 shown in FIG. Then, based on the calculated meandering amount, the direction correction amount calculating circuit 55 calculates how much the conveying direction of the recording sheet 3 should be changed before the meandering of the intermediate transfer belt 4 can be settled. A drive signal is transmitted to 56. As a result, the registration roll correction motor 35 is driven by the eccentric cam 34 described above.
Is rotated, and the arrangement angle of the registration roll 31 is changed.

As a result, the disposition angle of the registration roll 31 is changed so that the amount of displacement of the intermediate transfer belt 4 in the width direction during the insertion of the recording sheet 3 is zero, and the rotation direction of the intermediate transfer belt 4 and the registration roll 31 are changed. And the transport direction of the recording sheet 3 completely matches. As described above, it is possible to prevent the meandering of the intermediate transfer belt 4 from occurring even when the recording sheet 3 is pushed into the secondary transfer position, and to simultaneously perform the secondary transfer of the toner image onto the recording sheet 3 and the photosensitive drum 2.
Even when the toner image is primary-transferred from No. 1 to the intermediate transfer belt 4, it is possible to prevent the color shift of the toner image multi-transferred onto the intermediate transfer belt 4.

The correction of the conveying direction of the recording sheet 3 by the registration roll 31 may be performed every time the recording sheet 3 enters the secondary transfer position. When using the recording sheet 3 having a weak recording speed, the transport direction of the recording sheet 3 and the intermediate transfer belt 4
However, the external force f applied by the recording sheet 3 in the width direction of the intermediate transfer belt 4 is very small even if the rotation direction of The belt 4 does not have a large meandering amount. on the other hand,
When a strong recording sheet 3 such as thick paper or an OHP sheet is used, the external force f applied by the recording sheet 3 in the width direction of the intermediate transfer belt 4 becomes extremely large, so that the intermediate transfer is performed every time the recording sheet is inserted. It is expected that the belt meanders largely in the width direction.

Therefore, from this point of view, when a recording image is formed on a recording sheet 3 having a weak stiffness, the arrangement angle of the registration roll 31 is adjusted once per insertion of a plurality of recording sheets 3. On the other hand, a strong recording sheet 3
When a recording image is formed, it is preferable to adjust the arrangement angle of the registration roll 31 every time one recording sheet 3 is inserted.

In the above-described embodiment, the eccentric cam 34 is used to adjust the arrangement angle of the registration roll 31 so that the conveying direction of the recording sheet 3 matches the rotation direction of the intermediate transfer belt 4. As shown in FIG.
Can be divided in the axial direction, and the rolls 31a and 31b can be rotated by independent drive motors 35a and 35b, respectively, to adjust the transport direction of the recording sheet 3.

On the other hand, the present invention is not limited to the color image forming apparatus shown in FIG. 1, but is also applicable to the color image forming apparatuses shown in FIGS. In the color image forming apparatus shown in FIG. 11, an endless photoreceptor belt 61 is wrapped around a plurality of transport rolls 62, 63, and 64. An electrostatic latent image corresponding to the image information is formed by the process. That is, the photoreceptor belt 61 is charged to a predetermined potential by the charging roll 61a, and is then exposed to the laser light Bm modulated by image information. On one side of the photosensitive drum 61, black (K), yellow (Y),
Magenta (M) and cyan (C) color developing units 65 are provided to develop the electrostatic latent image formed on the photosensitive drum 61 to form a toner image T.

In this apparatus, the toner images of the respective colors are formed so as to be superimposed every one rotation of the photosensitive belt 61, and when the last toner image is formed on the photosensitive belt 61, these toner images T
Is transported to a transfer position facing the transport path of the recording sheet 3 with the rotation of the photosensitive belt 61, and the photosensitive belt 61
Is collectively transferred to the recording sheet 3 by the transfer roll 66 which comes into contact with the recording sheet 3. Then, the recording sheet 3 onto which the toner image has been transferred is peeled off from the photoreceptor belt 61, sent to the fixing device 67, and subjected to a fixing process of the unfixed toner image. on the other hand,
The residual toner is removed from the photoreceptor belt 61 to which the transfer of the toner image has been completed by the cleaner 68, and is used for forming the next toner image.

The image forming apparatus shown in FIG.
Also, an endless sheet conveying belt is wound around a plurality of conveying rolls. Specifically, the driving roll 74 and the driving roll 74 are provided on a conveying path of the recording sheet 3 connecting the recording sheet supply tray 71 and the fixing device 72. Driven rolls 75, 76, 7
At 7, the endless sheet conveying belt 78 is stretched,
Four image forming units 79 for forming toner images corresponding to the respective colors of yellow Y, magenta M, cyan C, and black K by an electrophotographic process are arranged on one side of the sheet conveying belt 78 at appropriate intervals. Things.

Each image forming unit 79 has a charging corotron 81, a laser beam scanning unit 82, a developing device 83, a transfer corotron 84, and a cleaner 85 arranged around a photosensitive drum 80, and each color is formed by a so-called reversal developing method. A toner image corresponding to the image information of the photosensitive drum 8
0. That is, the photosensitive drum 80 is uniformly negatively charged by the charging corotron 81, and a negative latent image is formed on the photosensitive drum 80 by exposure of the laser beam scanning unit 82. The toner is developed with negatively charged toner having the same polarity as the charge polarity of 80. Then, the transfer corotron 8
4 applies a toner and a charge having a polarity opposite to that of the photosensitive drum 80, that is, a positive charge to the back side of the sheet conveying belt 78, so that the toner image developed with the negatively charged toner is recorded by the sheet conveying belt 78. It is transferred to sheet 3.

In the color copying machine of the present embodiment thus configured, the recording sheet 3 carried out from the supply tray 71 is electrostatically attracted to the sheet conveying belt 78 at a predetermined timing, and the movement of the sheet conveying belt 78 is performed. Accordingly, the image forming units 79 and 7 are provided on the recording sheet 3.
The transfer of the toner image of each color is performed sequentially from 9,. Accordingly, a full-color toner image in which four color toner images are overlapped on the recording sheet 3 that has passed through the black BK image forming unit 79 is completed. Then, the recording sheet 3 on which the transfer of the toner image has been completed is peeled off from the sheet conveying belt 78, and then sent out onto the discharge tray 86 via the fixing device 72. Thus, the formation of the color recording image is completed.

Also in these image forming apparatuses, when the recording sheet 3 comes into contact with the photosensitive belt 61 or the sheet conveying belt 78 formed in an endless shape, the conveying direction of the recording sheet 3 and the endless belt 61, The endless belts 61 and 78 meandering in the width direction due to a slight shift from the rotation direction of 78 are the same as in the case of the intermediate transfer belt 4 described above. Therefore, the amount of displacement of the endless belts 61 and 78 in the width direction due to the contact of the recording sheet 3 is detected as in the above-described embodiment, and the conveying direction of the recording sheet 3 is finely adjusted based on the detected value. This prevents the photoreceptor belt 61 or the sheet conveying belt 78 from meandering, thereby obtaining a high-quality color image without color shift.

[0047]

As described above, according to the image forming apparatus of the present invention, when the recording sheet is brought into contact with the endless belt, the conveyance direction of the recording sheet completely matches the rotation direction of the endless belt. Even if it is not aligned, the amount of displacement of the endless belt in the width direction caused by the rush of the recording sheet is detected, and based on the detection result, the recording sheet conveyance direction is set to the rotation direction of the endless belt. Can be completely matched, so that the movement of the endless belt in the width direction due to the entry of the recording sheet can be prevented, and a high-quality recorded image that is faithful to image information and has no color shift can be formed. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of an image forming apparatus to which the present invention can be applied.

FIG. 2 is a schematic diagram illustrating a configuration of a steering roll around which an intermediate transfer member according to the first embodiment is wound.

FIG. 3 is a schematic diagram illustrating a configuration of a photosensor according to a first example.

FIG. 4 is a block diagram illustrating a configuration of a control system for controlling meandering of the intermediate transfer belt according to the first embodiment.

FIG. 5 is an explanatory diagram illustrating a state in which a recording sheet conveyance direction by a registration roll does not match a rotation direction of an intermediate transfer belt.

FIG. 6 is a schematic diagram illustrating a configuration for adjusting a conveyance direction of a recording sheet by a registration roll according to the first embodiment.

FIG. 7 is a graph illustrating an example of a belt position detection signal representing only a shape of a side edge of the intermediate transfer belt.

FIG. 8 is a graph illustrating an example of a belt position detection signal when a meandering occurs in the intermediate transfer belt due to entry of a recording sheet.

FIG. 9 is a graph showing a state where the belt position detection signals shown in FIGS. 7 and 8 are simplified and overlapped.

FIG. 10 is a schematic diagram illustrating a second configuration for adjusting the conveyance direction of a recording sheet.

FIG. 11 is a schematic configuration diagram showing a second embodiment of an image forming apparatus to which the present invention can be applied.

FIG. 12 is a schematic configuration diagram showing a third embodiment of the image forming apparatus to which the present invention can be applied.

[Explanation of symbols]

3 ... Recording sheet, 4 ... Intermediate transfer belt (endless belt), 4a ... Steering roll, 31 ... Registration roll,
45 photo sensor, 48 rotational position detection sensor,

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Norio Hokari, 2274 Hongo, Ebina-shi, Kanagawa Prefecture, inside Fuji Xerox Co., Ltd. (72) Inventor Susumu Kibayashi 2274, Hongo, Ebina-shi, Kanagawa Prefecture, inside Fuji Xerox Co., Ltd.

Claims (4)

[Claims] 1. An endless belt that is wound around a plurality of transport rolls and carries a toner image and rotates, a transfer unit that transfers the toner image from the endless belt to a recording sheet, and the toner image And a conveying means for conveying the recording sheet to the transfer position of the endless belt. A detecting means for detecting an amount of displacement of the endless belt in a width direction caused by the recording sheet entering the transfer position. When,
An image forming apparatus comprising: a direction adjusting unit that adjusts a conveying direction of a recording sheet in the conveying unit based on a detection result of the detecting unit. 2. An endless belt that is wound around a plurality of transport rolls and rotates while adsorbing a recording sheet, and a plurality of images that transfer toner images to the recording sheet transported by the endless belt. An image forming apparatus comprising: a carrier; and conveying means for conveying the recording sheet to a position where the recording sheet is attracted to the endless belt, wherein the width of the endless belt caused by the recording sheet entering the position where the recording sheet is attracted. Detecting means for detecting the amount of displacement in the direction;
An image forming apparatus comprising: a direction adjusting unit that adjusts a conveying direction of a recording sheet in the conveying unit based on a detection result of the detecting unit. 3. An image forming apparatus according to claim 1, wherein said detecting means detects a change in the position of a side edge of the endless belt. 4. An image forming apparatus according to claim 1, wherein said detecting means detects a biasing force in a width direction of the endless belt.