JP2010044133A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image forming apparatus that can correct shift of an image caused by variation of bending of a photoreceptor drum with simple constitution, and then obtain a high-quality image whose color shift is inconspicuous. <P>SOLUTION: In the image forming apparatus, photoreceptor drums 10y, 10m and 10c having a comparatively small outside diameter, and a photoreceptor drum 10k having a comparatively large outside diameter are juxtaposed. By scanning an outer circumferential surface of each photoreceptor drum with a light beam by a light beam scanning device 30, an image is plotted. Thickness (outside diameter and inside diameter) of a cylindrical base material of each photoreceptor drum is set so that bending caused in each photoreceptor drum may be nearly constant according to a press-contact condition of a cleaning blade 13. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus such as a tandem color printer or a copier in which a plurality of photosensitive drums are juxtaposed.

  Conventionally, in a tandem image forming apparatus, as shown in FIG. 3, a photosensitive drum 10y for forming images of Y (yellow), M (magenta), C (cyan), K (black), 10m, 10c, and 10k are juxtaposed to form an electrostatic latent image on the outer peripheral surface of each photosensitive drum by scanning in the main scanning direction with the light beams By, Bm, Bc, and Bk. Thereafter, the toner image was primarily transferred / synthesized onto the intermediate transfer belt 20 by the electric field applied from each transfer roller 15. The toner image synthesized on the intermediate transfer belt 20 is secondarily transferred onto a transfer material (not shown).

  By the way, in the tandem type image forming apparatus, the photosensitive drum tends to be reduced in diameter due to a demand for downsizing the apparatus. However, the photosensitive drum 10k for forming a black image has a larger diameter than the other drums 10y, 10m, and 10c in order to ensure durability because of the high frequency of use.

  When the diameter of the photosensitive drum is reduced, the moment of inertia is reduced, so that bending (bending) occurs in the drum itself due to the pressing force of the residual toner being pressed from the cleaning blade 13. As shown in FIG. 4A, due to bending, when the line L1 scanned in a straight line in the exposure portion A is rotated by approximately 180 degrees and reaches the transfer portion B, the line L1 ′ is distorted. . On the other hand, the large-diameter photosensitive drum 10k has a large moment of inertia, so that bending does not occur, and the linear line L1 is maintained in the transfer portion B as shown in FIG. Therefore, the synthesized image has a color shift as shown in FIG.

In order to solve such a problem of color misregistration, image forming apparatuses described in Patent Documents 1 and 2 have been proposed. In Patent Document 1, color misregistration caused by bending of a photosensitive drum is detected by three sensors, and image data is corrected. In Patent Document 2, the rotational unevenness is measured from the color misregistration pattern on the intermediate transfer belt, and the rotational speed of each photosensitive drum is controlled so as to cancel the periodic rotational fluctuation. However, in both cases, it is necessary to dispose detection means and measurement means, which leads to complication of the apparatus.
JP 2000-103121 A JP 2006-047920 A

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of eliminating image misalignment caused by variation in bending of a photosensitive drum with a simple configuration and obtaining a high-quality image with no noticeable color misregistration. It is to provide.

In order to achieve the above object, an image forming apparatus according to an aspect of the present invention includes:
A plurality of photosensitive drums including at least one photosensitive drum having an outer diameter larger than that of the other photosensitive drums;
A light beam scanning unit that draws an image in the main scanning direction with a light beam on the outer peripheral surface of each of the photosensitive drums that is rotationally driven at a predetermined peripheral speed to form an electrostatic latent image;
Developing means for using the electrostatic latent image formed on each photosensitive drum as a toner image;
A cleaning blade that presses against the outer peripheral surface of the photosensitive drum and wipes off residual toner;
Transfer means for transferring and synthesizing the toner image from each photosensitive drum to a transfer member;
With
The thickness of the cylindrical base material of each photosensitive drum is set so that the bending generated in each photosensitive drum according to the pressure contact condition of the cleaning blade is substantially constant,
It is characterized by.

  The bending amount of each photosensitive drum is determined based on the material of the cylindrical base material, the thickness (difference between the outer diameter and inner diameter), the length of the beam, the pressure contact force of the cleaning blade, and the like, and can be obtained by calculation. . In the image forming apparatus, by selecting a preferable value for the thickness (outer diameter and inner diameter) of the cylindrical base material of each photosensitive drum, the bending generated in each photosensitive drum becomes substantially constant, and image distortion is detected. It is possible to eliminate the image shift caused by the variation in the bending of the photosensitive drum without providing a sensor or uneven rotation measuring means.

  Embodiments of an image forming apparatus according to the present invention will be described below with reference to the accompanying drawings.

  As shown in FIG. 1, an image forming apparatus according to an embodiment of the present invention forms a color image by a tandem method, and forms Y (yellow), M (magenta), and C (cyan) images. The photosensitive drums 10y, 10m, and 10c having relatively small diameters for this purpose and the photosensitive drum 10k having a relatively large diameter for forming a K (black) image are juxtaposed. Around each photosensitive drum, a charger 11, a developing device 12, a transfer roller 15, a residual toner cleaning blade 13, and the like are arranged.

  Immediately above the photosensitive drums 10y, 10m, 10c, and 10k, an intermediate transfer belt 20 is stretched endlessly on a drive roller 21, a support roller 22, and a tension roller 23, and is installed to be rotatable counterclockwise. .

  The image is drawn in the main scanning direction (direction parallel to the axial direction of the photosensitive drum) on the outer peripheral surface of each photosensitive drum in the exposure unit A by the light beam scanning device 30. The light beam scanning device 30 includes a light source unit (not shown), a single polygon mirror 31, first and second scanning lenses 32 and 33, and a plurality of folding mirrors 35y, 35m, 35c, 35k, 36y, 36m, and 36c. , 37c and third scanning lenses 34y, 34m, 34c, 34k.

  The light beams By, Bm, Bc and Bk are deflected by a single polygon mirror 31 and then pass through the first and second scanning lenses 32 and 33. Thereafter, the light beam By exposes the photosensitive drum 10y through the folding mirror 35y, the third scanning lens 34y, and the folding mirror 36y. The light beam Bm exposes the photosensitive drum 10m through the folding mirror 35m, the third scanning lens 34m, and the folding mirror 36m. The light beam Bc exposes the photosensitive drum 10c through the folding mirrors 35c and 36c, the third scanning lens 34c, and the folding mirror 37c. The light beam Bk passes through the third scanning lens 34k and the folding mirror 35k and exposes the photosensitive drum 10k. The first, second, and third scanning lenses 32, 33, and 34 each have a function of correcting fθ characteristics, field curvature, scan line inclination, bow (bow-like curvature on the image plane), and the like in the optical system. Have.

  In the above configuration, in the exposure unit A, an electrostatic latent image is formed on the outer peripheral surface of each photosensitive drum that is rotationally driven at a predetermined peripheral speed by exposure in the main scanning direction with a light beam. After the image is formed, the toner image is primarily transferred / synthesized onto the intermediate transfer belt 20 by the electric field applied from each transfer roller 15 in the transfer portion B. The toner image synthesized on the intermediate transfer belt 20 is secondarily transferred onto a transfer material (not shown) in the secondary transfer portion C.

  Incidentally, as shown in FIG. 4, in the small-diameter photosensitive drums 10y, 10m, and 10c, bending occurs due to the pressing force of the cleaning blade 13, and an image drawn linearly in the exposure portion A is transferred to the transfer portion B. In this case, distortion (bow) occurs and color shift occurs. In the light beam scanning device 30, each optical element is corrected so that image distortion does not occur. However, distortion due to bending of the photosensitive drums 10y, 10m, and 10c is uniquely generated due to a cause different from the optical element built in the light beam scanning device 30.

  Therefore, in this embodiment, each photoconductor is set so that the bending generated in each photoconductor drum is almost constant so that the bend generated in each photoconductor drum is constant according to the pressure contact condition of the cleaning blade 13. The thickness of the cylindrical base material of the drum was set. The photosensitive drums 10y, 10m, and 10c for color image formation have a relatively small diameter, and the cylindrical base material 10A has a common inner diameter d1 and outer diameter d2 as shown in FIG. The photosensitive drum 10k for forming a black image has a relatively large diameter, and the cylindrical substrate 10B has a predetermined inner diameter d3 and outer diameter d4.

The bending amount of the cylindrical base materials 10A and 10B due to the pressure contact of the cleaning blade 13 can be calculated by a formula for obtaining the maximum deflection δ of the stationary beam due to material mechanics. This formula is (5wl ⁴ ) / (384EI). By changing the value of E and / or I in the formula, the maximum deflection (bending amount) δ in the central portion can be set to a constant value in both the cylindrical base materials 10A and 10B.

  The official moment of inertia I is determined based on the material and the difference between the outer diameter and the inner diameter. Therefore, in the cylindrical base materials 10A and 10B, the bending amount of the cylindrical base materials 10A and 10B is set by satisfying the relationship of π (d2−d1) / 64 = π (d4−d3) / 64. Can be made constant. Specific numerical value combination examples are as shown in Tables 1 and 2 below.

  In the combination examples in Table 1, both the cylindrical base materials 10A and 10B are made of aluminum. The small-diameter cylindrical base material 10A has an outer diameter d2 of 30 mm and an inner diameter d1 of 26 mm. The large-diameter cylindrical base material 10B has an outer diameter d4 of 40 mm and an inner diameter d3 of 38.54 mm. In any of the cylindrical substrates 10A and 10B, the bending amount δ is 0.014 mm.

  In the combination example of Table 2, the small-diameter cylindrical base material 10A is made of steel, and the large-diameter cylindrical base material 10B is made of aluminum. The small diameter cylindrical base material 10A has an outer diameter d2 of 30 mm and an inner diameter d1 of 25 mm. The large diameter cylindrical base material 10B has an outer diameter d4 of 60 mm and an inner diameter d3 of 58.50 mm. In any of the cylindrical base materials 10A and 10B, the bending amount δ is 0.004 mm.

  As described above, in this embodiment, since the bending generated in each photosensitive drum is constant, the image distortion caused by the variation in the bending of the photosensitive drum is not provided without providing an image distortion detection sensor or a rotation unevenness measuring unit. The deviation can be eliminated.

(Other examples)
The image forming apparatus according to the present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the gist thereof.

  For example, it is needless to say that the numerical values shown in the above embodiments are merely examples. Further, the configuration of various units for image formation is arbitrary.

1 is a schematic configuration diagram illustrating an embodiment of an image forming apparatus according to the present invention. It is sectional drawing which shows the cylindrical base material of a photoreceptor drum. It is a schematic block diagram which shows the conventional image forming apparatus. It is explanatory drawing which shows the distortion and color shift of an image.

Explanation of symbols

10y, 10m, 10c, 10k ... photosensitive drums 10A, 10B ... cylindrical base material 12 ... developer 13 ... cleaning blade 20 ... intermediate transfer belt 30 ... light beam scanning device By, Bm, Bc, Bk ... light beam

Claims (2)

A plurality of photosensitive drums including at least one photosensitive drum having an outer diameter larger than that of the other photosensitive drums;
A light beam scanning unit that draws an image in the main scanning direction with a light beam on the outer peripheral surface of each of the photosensitive drums that is rotationally driven at a predetermined peripheral speed to form an electrostatic latent image;
Developing means for using the electrostatic latent image formed on each photosensitive drum as a toner image;
A cleaning blade that presses against the outer peripheral surface of each of the photosensitive drums to wipe off residual toner;
Transfer means for transferring and synthesizing the toner image from each photosensitive drum to a transfer member;
With
The thickness of the cylindrical base material of each photosensitive drum is set so that the bending generated in each photosensitive drum according to the pressure contact condition of the cleaning blade is substantially constant,
An image forming apparatus.   The relationship between the outer diameter d2 and the inner diameter d1 of the cylindrical substrate of the photosensitive drum having the first outer diameter, and the outer diameter d4 and the inner diameter d3 of the cylindrical substrate of the photosensitive drum having the second outer diameter. The image forming apparatus according to claim 1, wherein a relationship of π (d2−d1) / 64 = π (d4−d3) / 64 is established.

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