JP2006215061A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct the deviation of the magnification of an image caused by load on the movent of a body to be printed. <P>SOLUTION: When the rotational speeds of photoreceptor drums 152Y, 152M, 152C and 152K are respectively lower than the rotational speed of an intermediate transfer belt 160, an image magnification control part 220 corrects the magnification in a subscanning direction of developer images respectively transferred by the photoreceptor drums 152Y, 152M, 152C and 152K so that the magnification in the subscanning direction of the developer image transferred on a downstream side in the moving direction of the intermediate transfer belt 160 may be larger than the magnification of the developer image transferred on an upstream side in the moving direction, thereby making the magnification of the respective color developer images transferred to a recording medium nearly the same. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as an electrophotographic printer or an ink jet printer, a copying machine, or a facsimile.

There is known an image forming apparatus that forms a color image by superimposing developer images of a plurality of colors on a recording medium transported by a transport belt or on an intermediate transfer belt.
In this type of image forming apparatus, for example, in the case of double-sided printing, the image formed on the front surface of the paper is fixed to the paper by heat and pressure, so that the paper shrinks and is formed on the back surface of the shrunken paper. There was a problem that the image became larger as the paper stretched. Therefore, it is known to correct an image magnification error that occurs during double-sided printing by detecting the amount of shrinkage of the paper that has shrunk due to heat (see Patent Document 1).

Japanese Patent No. 3089039

  However, the conventional example has a problem that it is not possible to correct an image magnification shift caused by a load with respect to the movement of the printing medium.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of correcting an image magnification shift caused by a load with respect to movement of a printing medium.

In order to achieve the above object, the present invention is characterized in that a printing medium to be moved, a plurality of printing units provided in a moving direction of the printing medium, and printing images on the printing medium; The image forming apparatus includes a magnification correction unit that corrects the magnification in the moving direction of the image printed by each of the printing units in accordance with a load from the plurality of printing units with respect to the movement of the printing medium. That is, even if a load is applied from each of the plurality of printing units to the movement of the printing target, the magnification in the moving direction of the image printed by each of the plurality of printing units is corrected according to the load applied to the moving printing target. can do.
In this specification, printing includes forming a character or an image.

  Preferably, the magnification correction means has a magnification in the moving direction of an image printed upstream in the moving direction of the printing medium, rather than a magnification in the moving direction of the image printed downstream in the moving direction of the printing medium. The magnification in the moving direction of the image printed by each of the plurality of printing units is corrected so as to increase. Preferably, each of the plurality of printing units includes a rotating body that contacts the printing body, and the printing body is moved faster than a rotation speed of each of the plurality of printing units. Is slow. Therefore, for example, when the moving speed of the printing medium is slower than the rotating speed of each rotating body of the printing unit, the magnification in the moving direction of the image printed upstream in the moving direction of the printing medium is the load on the printing medium. Thus, even if the printing medium is reduced downstream in the moving direction, the magnification of the image can be corrected according to the load on the printing medium.

  Preferably, the magnification correction means is configured to move the image printed in the moving direction downstream of the printing medium rather than the magnification in the moving direction of the image printed upstream of the printing medium. The magnification in the moving direction of the image printed by each of the plurality of printing units is corrected so that the magnification is increased. Preferably, each of the plurality of printing units includes a rotating body that comes into contact with the printing body, and the printing body is moved faster than a rotation speed of each of the plurality of printing units. Is fast. Therefore, for example, when the moving speed of the printing medium is faster than the rotating speed of each of the plurality of printing units, the magnification in the moving direction of the image printed upstream in the moving direction of the printing medium is the printing medium. The image magnification can be corrected in accordance with the load on the print medium even when the print medium increases in the downstream direction in the moving direction due to the load on the print medium.

  Preferably, the printing medium is an intermediate transfer body that carries an image transferred from each of the plurality of printing units. Preferably, the printing medium is a recording medium conveyed by a recording medium conveying unit. Preferably, the printing medium is a band-shaped recording medium that contacts the plurality of printing units simultaneously.

  Preferably, the image forming apparatus further includes a magnification detection unit that detects a magnification in a moving direction of each image printed by each of the plurality of printing units, and the magnification correction unit is configured according to a detection result of the magnification detection unit. The magnification in the moving direction of the image printed by each of the plurality of printing sections is corrected. In other words, since the magnification in the moving direction of each image can be detected by the magnification detecting means, the magnification in the moving direction of the image can be corrected even if the magnification in the moving direction of each image changes.

  Preferably, the magnification correction unit corrects the magnification in the moving direction of the image by changing a rotation speed of a motor that moves the printing medium. Preferably, each of the plurality of printing units is provided with an image carrier that rotates by carrying an image, an optical writing unit that writes an electrostatic latent image on the image carrier, and a writing by the optical writing unit. Development means for visualizing each electrostatic latent image that has been incorporated, and the magnification correction means moves the image by changing the timing at which the optical writing means writes the electrostatic latent image on the image carrier. Correct each direction magnification. Preferably, the magnification correction unit corrects the magnification in the moving direction of the image by changing the rotation speed of the image carrier. Preferably, the magnification correction unit corrects the magnification in the moving direction of the image by changing image data serving as a basis for each image printed on the print medium.

  According to the present invention, it is possible to correct an image magnification shift caused by a load with respect to movement of a printing medium.

Next, a first embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows an outline of an image forming apparatus 10 according to the first embodiment of the present invention. The image forming apparatus 10 includes an image reading unit 12, an image forming unit 14, an intermediate transfer device 16, a plurality of trays 17, a conveyance path 18, a fixing device 19, a controller 20, and an image processing device 22. The image forming apparatus 10 has a function as a full-color copying machine using the image reading device 12 and a function as a facsimile in addition to a printer function for printing image data received from a personal computer (not shown). It may be a combined machine.

  First, the outline of the image forming apparatus 10 will be described. In the upper part of the image forming apparatus 10, an image reading apparatus 12, a controller 20, and an image processing apparatus 22 are arranged. The image reading device 12 reads an image displayed on the document and outputs it to the controller 20. The controller 20 receives image data input from the image reading device 12 or image data input from a personal computer (not shown) via a network line such as a LAN, and a user interface device (not shown). Settings for each component included in the image forming apparatus 10 are performed on the basis of the user setting information input via the user interface. Further, the controller 20 outputs the input image data to the image processing device 22. The image processing device 22 performs image processing such as gradation correction and resolution correction on the input image data, and outputs the processed image data to the image forming unit 14. Further, the image processing apparatus 22 receives a detection result of a sensor 163 described later, and transmits and receives signals necessary for image magnification correction to and from each component included in the image forming apparatus 10.

  Below the image reading device 12, a plurality of image forming units 14 are arranged corresponding to the colors constituting the color image. In this example, the first image forming unit 14Y, the second image forming unit 14M, and the third image forming corresponding to each color of yellow (Y), magenta (M), cyan (C), and black (K). The unit 14C and the fourth image forming unit 14K are horizontally arranged along the intermediate transfer device 16 with a predetermined interval. The intermediate transfer device 16 rotates an intermediate transfer belt 160 as an intermediate transfer member in the direction of an arrow A in the drawing, and these four image forming units 14Y, 14M, 14C, and 14K receive images input from the image processing device 22. Developer images of each color are sequentially formed based on the data, and the plurality of developer images are transferred (primary transfer) to the intermediate transfer belt 160 at a timing when they are superimposed on each other. The order of the colors of the image forming units 14Y, 14M, 14C, and 14K is not limited to the order of yellow (Y), magenta (M), cyan (C), and black (K). ), Yellow (Y), magenta (M), and cyan (C).

  The conveyance path 18 is disposed below the intermediate transfer device 16. The first tray 17a accommodates, for example, an A4 size recording medium 32a, and the second tray 17b accommodates, for example, an A3 size recording medium 32b. The recording medium 32a or 32b supplied from the first tray 17a or the second tray 17b is transported on the transport path 18, and the developer images of the respective colors transferred in multiple onto the intermediate transfer belt 160 are collectively displayed. Then, the transferred developer image is transferred (secondary transfer), and the transferred developer image is fixed by the fixing device 19 and discharged to the outside.

Next, each configuration of the image forming apparatus 10 will be described in detail.
As shown in FIG. 1, the image reading unit 12 reads a platen glass 124 on which a document is placed, a platen cover 122 that presses the document onto the platen glass 124, and an image of the document placed on the platen glass 124. And an image reading device 130. The image reading apparatus 130 illuminates a document placed on the platen glass 124 with a light source 132, and reflects a reflected light image from the document into a full-rate mirror 134, a first half-rate mirror 135, and a second half-rate mirror. Scanning exposure is performed on an image reading element 138 made of a CCD or the like via a reduction optical system consisting of 136 and an imaging lens 137, and the color material reflected light image of the original is made to have a predetermined dot density (for example, , 16 dots / mm).

The controller 20 performs predetermined image processing such as lightness / color space conversion, gamma correction, and frame removal on the image data read by the image reading unit 12. The color material reflected light image of the original read by the image reading unit 12 is, for example, three colors of red (R), green (G), and blue (B) (8 bits each) expressed in the RGB color system. Original color reflectance data of four colors of yellow (Y), magenta (M), cyan (C), and black (K) (8 bits each) by color space conversion processing by the controller 20. Converted into (raster data).
The image processing device 22 performs image processing such as gradation correction, density adjustment, sharpness correction, and screen processing on the image data input from the controller 20 to obtain binary image data suitable for printing. Are output to the corresponding image forming unit 14. Further, the image processing device 22 includes an image magnification control unit 220 described later, and is capable of changing the magnification of the image by adjusting the image data, and transmitting and receiving signals necessary for correcting the magnification of the image. Is performed with each component included in the image forming apparatus 10.

The first image forming unit 14Y, the second image forming unit 14M, the third image forming unit 14C, and the fourth image forming unit 14K are arranged in a line at a predetermined interval in the horizontal direction and are formed. Except for the difference in color, the configuration is almost the same. Accordingly, the first image forming unit 14Y will be described below. The configuration of each image forming unit 14 is distinguished by attaching Y, M, C, or K.
The image forming unit 14Y includes an optical scanning device 140Y that scans laser light in accordance with image data (binary) input from the image processing device 22, and an electrostatic latent image using the laser light scanned by the optical scanning device 140Y. Is formed.

  The optical scanning device 140Y modulates the semiconductor laser 142Y according to the yellow (Y) image data, and emits the laser light LB (Y) from the semiconductor laser 142Y according to the image data. The laser beam LB (Y) emitted from the semiconductor laser 142Y passes through the first reflecting mirror 143Y and the second reflecting mirror 144Y to the rotating polygon mirror 146Y driven by a motor 40Y (not shown) described later. Irradiated, deflected and scanned by the rotating polygon mirror 146Y, and irradiated onto the photosensitive drum 152Y of the image forming apparatus 150Y via the second reflecting mirror 144Y, the third reflecting mirror 148Y, and the fourth reflecting mirror 149Y. The The optical scanning device 140Y is provided with a light amount balance correction device that adjusts the light amount of the laser light in accordance with an instruction from the user interface device and the like, and an automatic output control device that keeps the output of the laser light constant. The laser beam LB (Y) emitted from the semiconductor laser 142Y is adjusted to a desired output level.

The image forming apparatus 150Y includes a photosensitive drum 152Y as an image carrier that rotates at a predetermined rotation speed in the direction of arrow A, and primary charging as a charging unit that uniformly charges the surface of the photosensitive drum 152Y. For example, a developing device 156Y for developing an electrostatic latent image formed on the photosensitive drum 154Y, and a cleaning device 158Y. The photosensitive drum 152Y is uniformly charged by the scorotron 154Y, and an electrostatic latent image is formed by the laser beam LB (Y) irradiated by the optical scanning device 140Y. The electrostatic latent image formed on the photosensitive drum 152Y is developed with a yellow (Y) developer by the developing unit 156Y and transferred to the intermediate transfer device 16. Note that residual developer, paper dust, and the like adhering to the photoreceptor drum 152Y after the developer image transfer step are removed by the cleaning device 158Y. Further, a potential sensor (not shown) for measuring the charge amount on the surface of the photosensitive drum 152Y is provided in the vicinity of the photosensitive drum 152Y, and is applied to the scorotron 154Y according to the output of the potential sensor. The charging bias voltage is controlled.
The other image forming units 14M, 14C, and 14K also form magenta (M), cyan (C), and black (K) developer images in the same manner as described above, and the formed developer images of the respective colors. Transfer to the intermediate transfer device 16.

  The intermediate transfer device 16 is wound around the drive roll 164, the first idle roll 165, the tension roll 166, the second idle roll 167, the backup roll 168, and the third idle roll 169 with a predetermined tension. An intermediate transfer belt 160 is included. The intermediate transfer belt 160 is formed into an endless belt shape by, for example, forming a flexible synthetic resin film such as polyimide in a band shape and connecting both ends of the synthetic resin film formed in the band shape by welding or the like. This is an image forming member on which a plurality of developer images are superposed with a predetermined tension applied by a tension roll 166. The drive roll 164 is driven to rotate by a motor 42 (not shown), which will be described later, thereby conveying and rotating the intermediate transfer belt 160 in the direction of arrow A at a predetermined speed. A belt home sensor 161 is provided in the vicinity of the drive roll 164. The belt home sensor 161 detects a rotation reference position (home position) of the intermediate transfer belt 160 by detecting a reference position display formed on the inner surface of the intermediate transfer belt 160.

Further, the intermediate transfer device 16 has a first primary transfer roll 162Y, a second primary transfer roll 162M, a third primary transfer roll 162C, and a first primary transfer roll 162Y at positions facing the image forming units 14Y, 14M, 14C, and 14K, respectively. 4 primary transfer rolls 162K, and developer images of respective colors formed on the photosensitive drums 152Y, 152M, 152C, and 152K are transferred onto the intermediate transfer belt 160 by the transfer electric field using these primary transfer rolls 162. Multiple transcription. Here, on the intermediate transfer belt 160, the photosensitive drums 152Y, 152M, 152C, and 152K, the first primary transfer roll 162Y, the second primary transfer roll 162M, the third primary transfer roll 162C, and the fourth primary transfer. The rolls 162K are in contact with each other. Residual developer adhering to the intermediate transfer belt 160 is removed by a cleaning blade or a brush of a belt cleaning device provided downstream of the secondary transfer position.
A sensor 163 is provided in the vicinity of the intermediate transfer belt 160. The sensor 163 detects, for example, a positional shift (color shift) and a developer density in the main scanning direction and the sub-scanning direction of each color developer image transferred to the intermediate transfer belt 160, and the detection result is sent to the image processing device 22. Output.

The transport path 18 includes a first pickup roller 181a and a second pickup roller 181b for taking out the first recording medium 32a or the second recording medium 32b from the first tray 17a or the second tray 17b, and the recording medium. A pair of conveyance rollers 182 and a registration roll 183 that conveys the recording media 32a and 32b to a secondary transfer position at a predetermined timing are disposed.
Further, a secondary transfer roll 185 that rotates in contact with the backup roll 168 via the intermediate transfer belt 160 is disposed at the secondary transfer position on the conveyance path 18, and is multiplexed on the intermediate transfer belt 160. The transferred developer images of the respective colors are secondarily transferred onto the recording medium 32a or 32b by the pressing force and electrostatic force of the secondary transfer roll 185. The recording medium 32 a or 32 b on which the developer images of the respective colors are transferred is conveyed to the fixing device 19 by the two conveying belts 186.

The fixing device 19 includes a heating roll 192 and a pressure roll 194, and records the developer by performing heat treatment and pressure treatment on the recording medium 32a or 32b onto which the developer image of each color is transferred. It is melt-fixed to the medium 32a or 32b.
A carry-out path 187 is provided as a part of the conveyance path 18 at the subsequent stage of the fixing device 19, and the recording medium 32 a or 32 b subjected to the fixing process (heating and pressurization) passes through the carry-out path 187 and passes through the image. The sheet is discharged to the outside of the forming apparatus 10 and stacked on a discharge tray. Further, a colorimetric sensor 189 is provided in the carry-out path 187.

Next, the magnification correction in the sub-scanning direction of the image formed by the image forming apparatus 10 will be described in detail.
FIG. 2 is a diagram showing a first example of the relationship between the force applied to the intermediate transfer belt 160 by each of the photosensitive drums 152Y, 152M, 152C, and 152K and the tension of the intermediate transfer belt 160. FIG. FIG. 6 is a schematic diagram showing a positional relationship between the body drums 152Y, 152M, 152C, and 152K and the intermediate transfer belt 160, and (B) is a graph showing a relationship between force and tension.
As shown in FIG. 2, each of the photosensitive drums 152Y, 152M, 152C, and 152K has, for example, a rotational speed (peripheral speed) of the intermediate transfer belt 160 in order to improve the transfer performance of the developer image to the intermediate transfer belt 160. Each is slower than the rotation speed (movement speed). A difference in rotational speed between the photosensitive drums 152Y, 152M, 152C, and 152K and the intermediate transfer belt 160 is, for example, about 0.5 to 3%.
Hereinafter, each of the photosensitive drums 152Y, 152M, 152C, and 152K may be simply abbreviated as the photosensitive drum 152.

The photosensitive drum 152 is in contact with or pressed against the intermediate transfer belt 160, and a frictional force and an electrostatic force due to a transfer electric field are generated between the photosensitive drum 152 and the intermediate transfer belt 160. Further, since there is a speed difference between the photosensitive drum 152 and the intermediate transfer belt 160, the direction from which the intermediate transfer belt 160 is prevented from rotating from the photosensitive drum 152 to the intermediate transfer belt 160 (the anti-rotation direction with respect to the rotation direction A). Loads F1, F2, F3, and F4 are added to. Since the photosensitive drums 152Y, 152M, 152C, and 152K are arranged in a line in the rotational direction of the intermediate transfer belt 160, for example, a tension T0 is applied to the intermediate transfer belt 160 between the tension roll 166 and the photosensitive drum 152K. Even between the photosensitive drums 152K and 152C, the tension T4 between the photosensitive drums 152C and 152M, the tension T2 between the photosensitive drums 152M and 152A, and the tension T2 between the photosensitive drums 152M and 152A. The tension is T1. Each of the tensions T4, T3, T2, and T1 has a relationship represented by the following formulas 1 to 4.
T4 = T0−F4 (1)
T3 = T0− (F4 + F3) (2)
T2 = T0− (F4 + F3 + F2) (3)
T1 = T0− (F4 + F3 + F2 + F1) (4)

  Here, as shown in FIG. 3, when the width of the intermediate transfer belt 160 is W, the thickness is t, the length is L, the longitudinal elastic modulus is E, the tension is T, and the elongation is ΔL, Holds.

  Further, when the distortion (deformation) of the intermediate transfer belt 160 is ε, the following expression 6 is obtained.

  That is, the strain ε of the intermediate transfer belt 160 is proportional to the tension T of the intermediate transfer belt 160.

Here, the distortion (deformation) of the intermediate transfer belt 160 to which the tensions T0, T1, T2, T3, and T4 are respectively applied are ε0, ε1, ε2, ε3, and ε4, respectively, and the photosensitive drums 152Y, 152M, and 152C , 152K, the length in the sub-scanning direction (the length of the image to be formed on the recording medium) of the developer image transferred onto the intermediate transfer belt 160 corresponding to the image data is X.
Further, the length of the yellow developer image transferred to the intermediate transfer belt 160 by the photosensitive drum 152Y between the photosensitive drums 152M and 152Y (a position where the tension T2 is applied to the intermediate transfer belt 160) is set to IY1. Then, the length IY1 of the developer image is expressed by the following formula 7.

  IY1 = X × (1 + ε2−ε1) = X × (1 + F1 / (WtE)) (7)

  Similarly, when the length in the sub-scanning direction of the magenta developer image transferred to the intermediate transfer belt 160 by the photosensitive drum 152M at the position where the tension T3 is applied to the intermediate transfer belt 160 is IM2, the length of the developer image The length IM2 is expressed as the following Expression 8.

  IM2 = X × (1 + ε3-ε2) = X × (1 + F2 / (WtE)) (8)

  Between the photosensitive drums 152C and 152M (a position where the tension T3 is applied to the intermediate transfer belt 160), the length of the yellow developer image in the sub-scanning direction expands and contracts according to the distortion of the intermediate transfer belt 160. Assuming that the length of the yellow developer image in the sub-scanning direction at the position where the tension T3 is applied to the intermediate transfer belt 160 is IY2, the length IY2 of the developer image is expressed by the following Expression 9.

IY2 = IY1 × (1 + ε3-ε2)
= X × (1 + F1 / (WtE)) × (1 + F2 / (WtE))
= X × (1+ (F1 + F2) / (WtE)) (9)
However, it approximates to (F1 × F2) / (WtE) ² = 0.

  Similarly, yellow between the photosensitive drums 152K and 152C (position where the tension T4 is applied to the intermediate transfer belt 160) and between the tension roll 166 and the photosensitive drum 152K (position where the tension T0 is applied to the intermediate transfer belt 160). The length of the developer image in the sub-scanning direction can be calculated. The length of the yellow developer image transferred onto the intermediate transfer belt 160 after the four color developer images have been transferred is IY4, and the length of the magenta developer image in the subscan direction is IM4. When the length of the cyan developer image in the sub-scanning direction is IC4 and the length of the black developer image in the sub-scanning direction is IK4, the developer image lengths IY4, IM4, IC4, and IK4 are It represents like Formula 10-13.

IY4 = X × (1+ (F1 + F2 + F3 + F4) / (WtE)) (10)
IM4 = X × (1+ (F2 + F3 + F4) / (WtE)) (11)
IC4 = X × (1+ (F3 + F4) / (WtE)) (12)
IK4 = X × (1 + F4) / (WtE)) (13)

  That is, when the loads F1, F2, F3, and F4 by the photosensitive drums 152Y, 152M, 152C, and 152K are applied to the intermediate transfer belt 160, and the magnification in the sub-scanning direction of the developer image is not corrected, The lengths (magnifications) of the developer images of yellow, magenta, cyan, and black differ in the sub-scanning direction, resulting in a color registration error (color shift), resulting in a reduction in image quality.

  For example, when the intermediate transfer belt 160 is a member using polyimide, polycarbonate, ETFE (Ethylene Tetrafluoroethylene), PVdF (Poly Vinylidene fluoride), or the like, the longitudinal elastic modulus E is 1 to 2.5 GPa. On the other hand, when the intermediate transfer belt 160 is a rubber member such as EPDM (Ethylene Propylene Diene Methylene Linkage) in order to improve transfer properties and reduce costs, the longitudinal elastic modulus E is a small value of about 100 MPa. And distortion is likely to occur.

  For example, the width W of the intermediate transfer belt 160 is 350 mm, the thickness t is 300 μm, the longitudinal elastic modulus E is 100 MPa, the load F is F1 = F2 = F3 = F4 = 2N, and the length X of the developer image in the sub-scanning direction is set. In the case of 420 mm (A3 size), the length IY4 of the developer image is expressed by the following formula 14.

IY4 = 420 mm × (1 + 4 × 2 N / (0.35 m × 0.3 × 10 ⁻³ m × 100 × 10 ⁶ Pa)) = 420.32 mm (14)

  Further, the developer image lengths IM4, IC4, and IK4 are 420.24 mm, 420.16 mm, and 420.08 mm, respectively. Therefore, the color shift between the yellow developer image and the black developer image is 0.24 mm at the maximum. If the color misregistration is, for example, about 0.1 mm, it is determined that the image quality is visually lowered.

  FIG. 4 is a diagram showing a deviation of each uncorrected developer image in the sub-scanning direction when the rotation speed of the photosensitive drum 152 is slower than the rotation speed of the intermediate transfer belt 160. FIG. FIG. 4 is a schematic diagram showing color misregistration due to a difference in the length of a developer image, and FIG. 5B is a graph showing positional deviation (magnification) with respect to the distance from the front end of the recording medium. As shown in FIG. 4, when the rotational speed of the photosensitive drum 152 is slower than the rotational speed of the intermediate transfer belt 160, the magnification in the sub-scanning direction of each developer image that has not been corrected is yellow, magenta, cyan, It becomes larger in the order of black. The magnification in the sub-scanning direction of each developer image is substantially proportional to the distance from the front end of the recording medium with respect to the length X in the sub-scanning direction of the developer image transferred corresponding to the image data. It has become.

FIG. 5 is a diagram showing a second example of the relationship between the force applied to the intermediate transfer belt 160 by each of the photosensitive drums 152Y, 152M, 152C, and 152K and the tension of the intermediate transfer belt 160. FIG. FIG. 6 is a schematic diagram showing a positional relationship between the body drums 152Y, 152M, 152C, and 152K and the intermediate transfer belt 160, and (B) is a graph showing a relationship between force and tension.
As shown in FIG. 5, each of the photosensitive drums 152Y, 152M, 152C, and 152K has a rotational speed (peripheral speed) of, for example, that of the intermediate transfer belt 160 in order to improve the transfer performance of the developer image to the intermediate transfer belt 160. Each is faster than the rotation speed.

Since there is a speed difference between the photosensitive drum 152 and the intermediate transfer belt 160, a load F1 is applied in the direction in which the rotation of the intermediate transfer belt 160 is pushed from the photosensitive drum 152 to the intermediate transfer belt 160 (the same direction as the rotation direction A). , F2, F3, F4 are added. Since the photosensitive drums 152Y, 152M, 152C, and 152K are arranged in a line in the rotational direction of the intermediate transfer belt 160, for example, a tension T0 is applied to the intermediate transfer belt 160 between the tension roll 166 and the photosensitive drum 152K. Even between the photosensitive drums 152K and 152C, the tension T4 between the photosensitive drums 152C and 152M, the tension T2 between the photosensitive drums 152M and 152A, and the tension T2 between the photosensitive drums 152M and 152A. The tension is T1.
In the second example of the relationship between the force applied by the photosensitive drum 152 to the intermediate transfer belt 160 and the tension of the intermediate transfer belt 160, the loads F1, F2, F3, and F4 are negative values. 13 holds.

  FIG. 6 is a diagram showing a deviation in the sub-scanning direction of each developer image that has not been corrected when the rotational speed of the photosensitive drum 152 is higher than the rotational speed of the intermediate transfer belt 160. FIG. 4 is a schematic diagram showing color misregistration due to a difference in the length of a developer image, and FIG. 5B is a graph showing positional deviation (magnification) with respect to the distance from the front end of the recording medium. As shown in FIG. 6, when the rotation speed of the photosensitive drum 152 is higher than the rotation speed of the intermediate transfer belt 160, the magnification in the sub-scanning direction of each uncorrected developer image is black, cyan, magenta, It becomes smaller in order of yellow. Further, the magnification of each developer image in the sub-scanning direction is small in proportion to the distance from the front end of the recording medium with respect to the length X in the sub-scanning direction of the developer image transferred corresponding to the image data. It has become.

In FIG. 7, an image magnification control unit 220 included in the image processing device 22 and its periphery are shown.
The image magnification control unit 220 includes a memory 222, a semiconductor laser control unit 224, a first motor control unit 226, a second motor control unit 228, and a correction processing unit 230. The image magnification control unit 220 in the sub-scanning direction of each color developer image. Control to correct the magnification is performed.
The memory 222 stores setting values for correcting the magnification in the sub-scanning direction of developer images of four colors, for example, yellow, magenta, cyan, and black. Note that the setting value for correcting the magnification stored in the memory 222 may be calculated by measuring the difference in the magnification of the developer image of each color in advance by an experiment using a test pattern (test image), for example. It may be a preset value set in advance using a calculation method described later.

  The correction processing unit 230 is, for example, a setting value for correcting the magnification input from the memory 222 or a position shift in the sub-scanning direction input from the sensor 163 (in accordance with a setting input (not shown) by the user). Color misregistration) or developer density detection result is selected. Further, the correction processing unit 230 is configured so that the magnifications in the sub-scanning direction of the developer images of the respective colors corresponding to the image data input from the controller 20 are substantially the same in accordance with the selected setting value or detection result. It controls at least one of the laser control unit 224, the first motor control unit 226, and the second motor control unit 228.

  The semiconductor laser control unit 224 changes the timing at which the semiconductor lasers 142Y, 142M, 142C, and 142K write electrostatic latent images on the photosensitive drums 152Y, 152M, 152C, and 152K, respectively. The first motor control unit 226 controls the rotation of the motors 40Y, 40M, 40C, and 40K that drive the rotary polygon mirrors 146Y, 146M, 146C, and 146K, respectively. The second motor control unit 228 controls the rotation of the motor 42 that drives the intermediate transfer belt 160.

  For example, when the rotational speeds of the photosensitive drums 152Y, 152M, 152C, and 152K are slower than the rotational speed of the intermediate transfer belt 160, the image magnification control unit 220 is transferred by the photosensitive drums 152Y, 152M, 152C, and 152K, respectively. The magnification of the developer image transferred downstream in the movement direction is smaller than the magnification of the developer image transferred upstream in the movement direction of the intermediate transfer belt 160 with respect to the magnification of the developer image in the sub-scanning direction. The correction is made so that the magnification is increased so that the magnifications of the developer images of the respective colors transferred to the recording medium are substantially the same.

  When the rotational speeds of the photosensitive drums 152Y, 152M, 152C, and 152K are higher than the rotational speed of the intermediate transfer belt 160, the image magnification control unit 220 is transferred by the photosensitive drums 152Y, 152M, 152C, and 152K, respectively. The magnification of the developer image transferred downstream in the movement direction is smaller than the magnification of the developer image transferred upstream in the movement direction of the intermediate transfer belt 160 with respect to the magnification of the developer image in the sub-scanning direction. The correction is made so that the magnification is reduced so that the magnifications of the developer images of the respective colors transferred to the recording medium become substantially the same.

  The image magnification control unit 220 adjusts the writing timing of the electrostatic latent image by the semiconductor lasers 142Y, 142M, 142C, 142K, for example, by the semiconductor laser control unit 224 in order to correct the magnification of the developer image in the sub-scanning direction. The rotation speeds of the rotary polygon mirrors 146Y, 146M, 146C, and 146K are adjusted by the first motor control unit 226, and the rotation speed of the intermediate transfer belt 160 is adjusted by the second motor control unit 228. Further, the image magnification control unit 220 may perform processing such as pixel insertion or thinning on the image data input from the controller 20 to correct the magnification in the sub-scanning direction of the developer image.

  Further, the load applied to the intermediate transfer belt 160 by the photosensitive drum 152 varies depending on the density (developer amount) of the developer image transferred from the photosensitive drum 152 to the intermediate transfer belt 160 and the transfer electric field. The magnification in the sub-scanning direction also changes depending on the density of the developer image. Therefore, the image magnification control unit 220 may correct the magnification of the developer image in the sub-scanning direction according to the developer concentration detected by the sensor 163.

Next, an example of setting values stored in the memory 222 in order to correct the magnification of the developer image in the sub-scanning direction will be described.
For example, the rotational speed of the photosensitive drum 152 is slower than the rotational speed of the intermediate transfer belt 160, the width W of the intermediate transfer belt 160 is 350 mm, the thickness t is 300 μm, the longitudinal elastic modulus E is 100 MPa, and the load F is F1 = When F2 = F3 = F4 = 10N and the length X of the developer image in the sub-scanning direction is 420 mm (A3 size), the length IY4 of the developer image is expressed by the following Expression 15.

IY4 = 420 mm × (1 + 4 × 10 N / (0.35 m × 0.3 × 10 ⁻³ m × 100 × 10 ⁶ Pa)) = 421.6 mm (15)

The developer image lengths IM4, IC4, and IK4 are 421.2 mm, 420.8 mm, and 420.4 mm, respectively.
Here, by setting the setting magnification MY of the yellow developer image transferred to the intermediate transfer belt 160 in the sub-scanning direction to a value calculated by the following equation 16, for example, the image magnification control unit 220 develops yellow. The magnification of the agent image in the sub-scanning direction can be set to the length X (100% magnification) of the image to be formed on the recording medium.

MY = 1 / (1 + 4 × 10N (0.35 m × 0.3 × 10 ⁻³ m × 100 × 10 ⁶ Pa)) × 100% = 99.62% (16)

Similarly, by setting the setting magnifications MM, MC, and MK in the sub-scanning direction of the magenta, cyan, and black developer images to 99.72%, 99.81%, and 99.90%, respectively, the sub-scanning direction Can be set to the length X (100% magnification) of the image to be formed on the recording medium.
That is, correction processing is performed so that the magnification in the sub-scanning direction of each color developer image corresponding to the image data input from the controller 20 to the image magnification control unit 220 becomes the length X of the image to be formed on the recording medium. The unit 230 controls at least one of the semiconductor laser control unit 224, the first motor control unit 226, and the second motor control unit 228. Further, the image magnification control unit 220 may perform processing such as pixel insertion or thinning on the image data input from the controller 20 to correct the magnification in the sub-scanning direction of the developer image.

  Similarly, when the rotational speed of the photosensitive drum 152 is higher than the rotational speed of the intermediate transfer belt 160, similarly, the set magnifications MY, MM, MC, and yellow, magenta, cyan, and black are set in the sub-scanning direction. By setting the MK, the image magnification control unit 220 can set the magnification in the sub-scanning direction of each developer image to the length X (100% magnification) of the image to be formed on the recording medium.

  Next, magnification correction in the sub-scanning direction when the load applied to the intermediate transfer belt 160 varies by the photosensitive drum 152 will be described. As described above, the load applied to the intermediate transfer belt 160 by the photosensitive drum 152 varies depending on the density (developer amount) of the developer image transferred from the photosensitive drum 152 to the intermediate transfer belt 160 and the transfer electric field. Therefore, for example, the density differs in the relationship between the density (developer amount) of the developer image and the load applied to the intermediate transfer belt 160 and the relationship between the load applied to the intermediate transfer belt 160 and the magnification of the developer image in the sub-scanning direction. A magnification in the sub-scanning direction of the developer image with respect to the density of the developer image is set by measuring in advance using a test pattern. The density of the developer image may be calculated based on the image data or may be detected by the sensor 163. Further, the magnification in the sub-scanning direction of the developer image may be calculated based on, for example, the developer image position shift detected by the sensor 163.

FIG. 8 shows an example of division in which one image (developer image) is divided in the sub-scanning direction in order to correct the magnification in the sub-scanning direction according to the density of the developer image. For example, the correction processing unit 230 first calculates a developer image of each color in each of the divided images 50a to 50d obtained by dividing the image 5 corresponding to the image data input from the controller 20 into four in the sub-scanning direction. Next, the correction processing unit 230 calculates, for example, a density difference between the average developer density of the divided image 50a and the average developer density of the divided image 50c, and the divided image 50c with respect to the divided image 50a according to the calculated density difference. At least one of the semiconductor laser control unit 224, the first motor control unit 226, and the second motor control unit 228 calculates the magnification change in the sub-scanning direction and reduces the magnification change in the sub-scanning direction of the divided image 50c. To control. Further, by reducing the interval at which the image is divided in the sub-scanning direction, the magnification of the image in the sub-scanning direction can be finely controlled.
In order to prevent a large difference in the load applied to the intermediate transfer belt 160 at the boundary between a portion where an image formed with the developer is formed and a portion where an image formed with the developer is not formed in the image 5, You may make it form a developer image also in the part in which the image by a developer is not formed.

Next, another embodiment of the present invention will be described.
FIG. 9 is a view showing the periphery of a transfer unit of an image forming apparatus according to another embodiment of the present invention. FIG. 9A shows the periphery of the transfer unit of the image forming apparatus 100 according to the second embodiment of the present invention. FIG. 8B is a schematic diagram illustrating the periphery of the transfer unit of the image forming apparatus 102 according to the third exemplary embodiment of the present invention. In FIG. 9, the same reference numerals are assigned to substantially the same components as those of the image forming apparatus 10 according to the first embodiment shown in FIG.
The photosensitive drums 152Y, 152M, 152C, and 152K are configured to superimpose and transfer developer images, for example, by pressing and rotating the recording medium 32a conveyed by the conveyance belt 46, respectively. In the image forming apparatus 100, the recording medium 32a moves and deforms in accordance with the movement and deformation of the image conveying belt 46.
As shown in FIG. 9A, the image forming apparatus 100 is an LED (Light Emitting Diode) that writes an electrostatic latent image to each of the photosensitive drums 152Y, 152M, 152C, and 152K, for example, in synchronization with a clock. 44Y, 44M, 44C, and 44K are provided, and the magnification in the sub-scanning direction of each color developer image is corrected by changing each clock frequency.

Further, as shown in FIG. 9B, the image forming apparatus 102 supplies the continuous belt 34 in the form of a belt from the continuous paper supply roll 47 toward the photosensitive drums 152Y, 152M, 152C, and 152K, and the continuous paper collection roll. 48 is collected. The continuous paper 34 moving from the continuous paper supply roll 47 to the continuous paper collection roll 48 is given a predetermined tension by tension rolls 49a and 49b, and the photosensitive drums 152Y, 152M, 152C, and 152K are continuous paper. 34 is simultaneously pressed and rotated. Further, the developer images of the respective colors are transferred onto the continuous paper 34 by the photosensitive drums 152Y, 152M, 152C, and 152K.
In the image forming apparatus 102, the magnification in the sub-scanning direction of each color developer image is corrected in accordance with the rotational speed of each of the photosensitive drums 152Y, 152M, 152C, and 152K with respect to the moving speed of the continuous paper 34. It has become. In the image forming apparatus 102, the magnification of the developer image in the sub-scanning direction may be corrected by changing the rotation speed of the photosensitive drums 152Y, 152M, 152C, and 152K.

FIG. 10 is a schematic view showing the periphery of the transfer unit of the image forming apparatus 104 according to the fourth embodiment of the present invention. 10 is substantially the same as the image forming apparatus 10 according to the first embodiment shown in FIG. 1 or the image forming apparatus 102 according to the second embodiment shown in FIG. Are denoted by the same reference numerals.
The image forming apparatus 104 is, for example, an ink jet printer, and a plurality of image forming units 60 that form images with ink under the control of a print control unit 240 included in the image processing apparatus 22 are disposed. In this example, the first image forming unit 60K, the second image forming unit 60C, and the third image forming corresponding to each color of black (K), cyan (C), magenta (M), and yellow (Y). The unit 60M and the fourth image forming unit 60Y are arranged horizontally at a predetermined interval. The first image forming unit 60K, the second image forming unit 60C, the third image forming unit 60M, and the fourth image forming unit 60Y are configured in substantially the same manner except that the color of the image to be formed is different. . Accordingly, the first image forming unit 60K will be described below.

  The first image forming unit 60K includes, for example, an ink ejection unit 600K that ejects ink in synchronization with a clock by an inkjet method on a recording medium conveyed by the conveyance belt 46, and a recording medium conveyed by the conveyance belt 46. A platen roll 602K disposed to maintain the flatness of the printing surface. The platen roll 602K is in contact with the conveyor belt 46 from below while rotating in the moving direction of the conveyor belt 46, for example. The platen roll 602K may be replaced with a guide formed in a plate shape, for example.

  The image forming apparatus 104 guides the recording medium picked up by the first pick-up roller 181a between the driving roll 164 and the transporting roll 62 at a timing by the registration roll 183, and the first image forming unit by the transporting belt 46. Transport toward 60K. The first image forming unit 60K, the second image forming unit 60C, the third image forming unit 60M, and the fourth image forming unit 60Y each form an image on the recording medium conveyed by the conveying belt 46. A full-color image is formed on the recording medium. Here, each platen roll 602 of each image forming unit 60 is in contact with the conveyance belt 46 from below, thereby placing a load on the movement of the conveyance belt 46 and causing the conveyance belt 46 to be deformed. Yes.

  Therefore, the print control unit 240 applies the ink ejection unit 600 to each of the first image forming unit 60K, the second image forming unit 60C, the third image forming unit 60M, and the fourth image forming unit 60Y. The magnification in the sub-scanning direction of each color image is corrected by changing the clock frequency. In addition, the print control unit 240 changes the rotation speed of each platen roll 602 of each image forming unit 60, changes the rotation speed of the drive roll 164, or an image that is the basis of an image formed on a recording medium. You may make it correct | amend the magnification of the subscanning direction of each image of each color by changing data.

1 is a side view showing an outline of an image forming apparatus according to a first embodiment of the present invention. FIG. 6 is a diagram illustrating a first example of a relationship between a force applied to the intermediate transfer belt by each of the photosensitive drums and a tension of the intermediate transfer belt, and (A) is a schematic diagram illustrating a positional relationship between the photosensitive drum and the intermediate transfer belt. (B) is a graph showing the relationship between force and tension. FIG. 6 is a partial view showing a size and the like of an intermediate transfer belt. FIG. 7A is a diagram showing a deviation of each uncorrected developer image in the sub-scanning direction when the rotational speed of the photosensitive drum is slower than the rotational speed of the intermediate transfer belt, and FIG. FIG. 5B is a schematic diagram illustrating color misregistration due to a difference in height, and FIG. 9B is a graph illustrating positional deviation (magnification) with respect to the distance from the front end of the recording medium. FIG. 6 is a diagram illustrating a second example of the relationship between the force applied to the intermediate transfer belt by each of the photosensitive drums and the tension of the intermediate transfer belt, and (A) is a schematic diagram illustrating the positional relationship between the photosensitive drum and the intermediate transfer belt. (B) is a graph showing the relationship between force and tension. FIG. 7A is a diagram showing a deviation of each uncorrected developer image in the sub-scanning direction when the rotation speed of the photosensitive drum is higher than the rotation speed of the intermediate transfer belt, and FIG. FIG. 5B is a schematic diagram illustrating color misregistration due to a difference in height, and FIG. 9B is a graph illustrating positional deviation (magnification) with respect to the distance from the front end of the recording medium. It is a block diagram which shows the image magnification control part contained in an image processing apparatus, and its periphery. In this example, one image (developer image) is divided in the sub-scanning direction in order to correct the magnification in the sub-scanning direction according to the density of the developer image. 6A and 6B are diagrams illustrating the periphery of a transfer unit of an image forming apparatus according to another embodiment of the present invention, wherein FIG. 5A illustrates the periphery of the transfer unit of the image forming apparatus according to the second embodiment of the present invention, and FIG. FIG. 6 is a schematic view showing the periphery of a transfer unit of an image forming apparatus according to a third embodiment of the present invention. FIG. 10 is a schematic diagram illustrating the periphery of a transfer unit of an image forming apparatus according to a fourth embodiment of the present invention.

Explanation of symbols

10, 100, 02 Image forming apparatuses 14Y, 14M, 14C, 14K Image forming units 142Y, 142M, 142C, 142K Semiconductor lasers 146Y, 146M, 146C, 146K Rotating polygon mirrors 152Y, 152M, 152C, 152K Photosensitive drum 160 Intermediate transfer Belt 164 Driving roll 166 Tension roll 20 Controller 22 Image processing device 220 Image magnification control unit 222 Memory 224 Semiconductor laser control unit 226 First motor control unit 228 Second motor control unit 230 Correction processing unit 240 Print control unit 34 Continuous paper 40Y, 40M, 40C, 40K Motor 42 Motor 44 LED
46 Conveying belt 60K First image forming unit 60C Second image forming unit 60M Third image forming unit 60Y Fourth image forming unit 600K, 600C, 600M, 600Y Ink ejection unit 602K, 602C, 602M, 602Y Platen roll

Claims (13)

  A plurality of print bodies to be moved, a plurality of print sections provided in the movement direction of the print bodies, and images printed on the print bodies, and magnifications in the movement directions of the images printed by the plurality of print sections, An image forming apparatus comprising: a magnification correction unit configured to perform correction according to a load from the plurality of printing units with respect to movement of a printing medium.   The magnification correction unit is configured so that the magnification in the moving direction of the image printed upstream in the moving direction of the printing medium is larger than the magnification in the moving direction of the image printed downstream in the moving direction of the printing medium. 2. The image forming apparatus according to claim 1, wherein each of the plurality of printing units corrects a magnification in a moving direction of an image to be printed.   Each of the plurality of printing units includes a rotating body that contacts the printing body, and the printing body has a moving speed slower than a rotation speed of a rotating body included in each of the plurality of printing units. The image forming apparatus according to claim 2.   The magnification correction unit is configured so that the magnification in the moving direction of the image printed downstream in the moving direction of the printing medium is larger than the magnification in the moving direction of the image printed upstream in the moving direction of the printing medium. 2. The image forming apparatus according to claim 1, wherein each of the plurality of printing units corrects a magnification in a moving direction of an image to be printed.   Each of the plurality of printing units includes a rotating body that contacts the printing body, and the printing body has a moving speed faster than the rotation speed of the rotating body included in each of the plurality of printing units. The image forming apparatus according to claim 4.   The image forming apparatus according to claim 1, wherein the printing medium is an intermediate transfer body that carries an image transferred from each of the plurality of printing units.   The image forming apparatus according to claim 1, wherein the printing medium is a recording medium conveyed by a recording medium conveying unit.   6. The image forming apparatus according to claim 1, wherein the printing medium is a band-shaped recording medium that contacts the plurality of printing units simultaneously.   Each of the plurality of printing units further includes a magnification detection unit that detects a magnification in a moving direction of each image printed, and the magnification correction unit is configured to detect each of the plurality of printing units according to a detection result of the magnification detection unit. The image forming apparatus according to claim 1, wherein the magnification in the moving direction of an image to be printed is corrected.   The image forming apparatus according to claim 1, wherein the magnification correction unit corrects a magnification in an image moving direction by changing a rotation speed of a motor that moves the printing medium. .   An image carrier that is provided in each of the plurality of printing units and carries and rotates an image; an optical writing unit that writes an electrostatic latent image on the image carrier; and an electrostatic latent image written by the optical writing unit. Developing means for visualizing each image, and the magnification correction means corrects the magnification in the moving direction of the image by changing the timing at which the light writing means writes the electrostatic latent image on the image carrier. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   12. The image forming apparatus according to claim 11, wherein the magnification correction unit corrects the magnification in the moving direction of the image by changing the rotation speed of the image carrier.   13. The magnification correction unit corrects the magnification in the moving direction of an image by changing image data that is a basis of each image printed on the print medium. The image forming apparatus described.

Images