JP4735326B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus such as a tandem electrophotographic copying machine or printer.

  In general, in the image forming apparatus, as shown in FIGS. 6A and 6B, the photosensitive drum 11 carrying the toner image rotates in the center hole 13 of the flange 12 fixed to both ends of the drum 11. The drive shaft 30 connected to the drive source is inserted, and the pin 31 provided on the drive shaft 30 is engaged with the groove portion 14 of the center hole 13 to transmit the rotational force.

  Further, there is a tolerance of about 30 μm in design between the rotary drive shaft 30 and the center hole 13 of the flange 12 and between the pin 31 and the groove portion 14. This tolerance is the minimum necessary in consideration of machining errors. By the way, there is a problem that the image exposure position is deviated depending on the engagement position between the pin 31 and the groove portion 14 due to the designed tolerance of about 30 μm.

  For example, FIG. 6A shows a state where the pin 31 is engaged with the groove portion 14 at a position facing downward, and FIG. 6B shows that the pin 31 is engaged with the groove portion 14 at a position facing upward. It shows the state. In both cases, the exposure position is shifted by about 30 μm due to the tolerance. Tandem system in which four photosensitive drums 11 are juxtaposed at predetermined intervals and rotated in one direction while charging, image exposure, development, and transfer are sequentially performed on the photosensitive drum 11. In such an image forming apparatus, if such a positional shift occurs for each of the four photosensitive drums 11, a color shift occurs in the composite image on the intermediate transfer body, resulting in a deterioration in image quality.

  Therefore, in order to correct the positional deviation of the photosensitive drum, Patent Document 1 describes a configuration in which the developing unit presses the photosensitive drum in the center direction by the driving force to the developing roller. However, in this configuration, the pressing force changes due to the difference in load from the developing device, and it is difficult to eliminate the change in position of the photosensitive drum.

Patent Document 2 describes that the direction of the resultant force applied from the peripheral member to the photosensitive drum is configured to match the exposure direction. However, even in this configuration, the resultant force direction is affected by the load difference from the peripheral members of the photosensitive drum, and it is difficult to eliminate the change in the position of the photosensitive drum.
Japanese Patent Application Laid-Open No. 10-282275 JP-A-10-186758

  Accordingly, an object of the present invention is to eliminate variations in image exposure positions on a plurality of respective image carriers, despite the existence of the minimum required tolerance between the flange member of the image carrier and the rotational drive shaft. An object of the present invention is to provide a tandem type image forming apparatus capable of minimizing image positional deviation and color misregistration and obtaining a good quality image.

  In order to achieve the above object, the present invention provides a plurality of image bearing members juxtaposed at predetermined intervals while rotating in one direction, and charging, image exposure, development, and transfer operations on the image bearing member. In the tandem type image forming apparatus that sequentially performs the image process, an engagement portion provided on a rotation drive shaft of each image carrier is engaged with a flange member provided on each image carrier, At the timing when the image carrier starts image exposure, the circumferential position where the flange member transmits the rotational driving force from the engaging portion is set to the same position in each image carrier, It is characterized by.

  According to the image forming apparatus of the present invention, at the timing when each image carrier starts image exposure, the circumferential position at which the flange member transmits the rotational force from the engaging portion of the rotation drive shaft is respectively set. Since the image bearing members of the image bearing members are set at the same position, the image exposure start position is fixed at each image bearing member regardless of the presence of tolerance between the flange member and the rotation drive shaft. Color misalignment hardly occurs when the images formed above are combined, and an image with good quality can be obtained.

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

(See schematic configuration of image forming apparatus, FIG. 1 and FIG. 2)
An image forming apparatus 1 shown in FIG. 1 is a color printer based on electrophotography, and is configured to synthesize four color images by a so-called tandem method. FIG. 2 shows an image forming portion of the image forming apparatus.

  The outline of the image forming unit 10 (10Y, 10Y, 10Y, 10Y, 10Y, YMCK) includes a photosensitive drum 11, a charging roller 15, a developing device 16, a residual toner cleaning device 17, and the like. 10M, 10C, 10K) are juxtaposed directly above the intermediate transfer belt 20. Further, a laser scanning unit 25 is disposed immediately above the image forming unit 10 so as to scan and expose each photosensitive drum 11 with laser light.

  The image data is transmitted to the image processing unit 27 as image data for each YMCK from an image reading device (scanner) or a computer (not shown), and the laser scanning unit 25 is driven based on these image data, and the direction of the arrow A (FIG. 2). A toner image is formed on each photosensitive drum 11 that is rotationally driven as shown in FIG. Such an electrophotographic process is well known and will not be described in detail.

  The intermediate transfer belt 20 is stretched endlessly by a driving roller 21, a support roller 22, and a tension roller 23, and is rotationally driven in the direction of arrow B, and is primarily transferred to each photosensitive drum 11 via the intermediate transfer belt 20. A secondary transfer roller 24 is disposed in a portion (secondary transfer portion) where the roller 19 is in pressure contact and the portion where the driving roller 21 is disposed is opposed to the intermediate transfer belt 20.

  In the lower part of the image forming apparatus 1, an automatic paper feeding unit 2 that feeds the stacked transfer materials one by one is installed. A fixing unit 3 is installed immediately above the secondary transfer portion.

  The toner images formed on the respective photosensitive drums 11 are sequentially primary-transferred onto the intermediate transfer belt 20 that is rotationally driven in the direction of arrow B by an electric field applied from the primary transfer roller 19, and four-color images are formed. Synthesized. On the other hand, the transfer materials are fed one by one from the sheet feeding unit 2 one by one, and the composite image is secondarily transferred from the intermediate transfer belt 20 by the electric field applied from the secondary transfer roller 24 in the secondary transfer unit. Thereafter, the transfer material is conveyed to the fixing unit 3 where the toner is heated and fixed, and is discharged from the discharge roller 4 onto the tray 5.

(Engagement of flange and drive shaft, see FIGS. 2 and 3)
In the image forming apparatus 1, as shown in FIG. 2, each photosensitive drum 11 (11 </ b> Y, 11 </ b> M, 11 </ b> C, 11 </ b> K) has flanges 12 fixed to both ends thereof. The rotary drive shaft 30 is engaged as described below. That is, the rotation drive shaft 30 is provided with a pin 31, and the pin 31 is engaged with a groove portion 14 formed in the center hole 13 of the flange 12. This engagement state has a tolerance of about 30 μm in design between the drive shaft 30 and the flange 12 as in the conventional example shown in FIGS. 6A and 6B. This is necessary for processing and is the same as the conventional one.

  At the timing when each photoconductor drum 11 starts image exposure, the circumferential position where the rotational driving force is transmitted from the pin 31 to the flange 12 is set to the same position in each photoconductor drum 11. Yes. Further, the image exposure start position on each photoconductive drum 11 is overlapped at the same position on the intermediate transfer belt 20 that is rotationally driven in the direction of arrow B, and the diameter of the photoconductive drum 11, the rotational peripheral speed, and the intermediate transfer belt 20. Rotational peripheral speed is set.

  Specifically, FIG. 2 shows the timing when image exposure is started on the photosensitive drum 11Y that forms a Y image. At this time, in the photosensitive drum 11Y, the angle θ between the straight line connecting the position where the pin 31 engages with the groove 14 and the rotation center and the horizontal straight line is set to 0 °. At this time, in the photosensitive drum 11M that forms the M image, the angle θ is set to be 30 °. Further, in the photosensitive drum 11C for forming the C image, the angle θ is set to 60 °. Similarly, in the photosensitive drum 11K that forms the K image, the angle θ is set to 90 °. Note that the angle θ shown here is merely an example because it varies depending on the intervals between the photosensitive drums 11Y, 11M, 11C, and 11K.

  FIG. 3 shows the timing when image exposure is started on the photosensitive drum 11M that forms the M image. At this time, the angle θ in the photosensitive drum 11M is 0 °. Although not shown, the angle θ at the photosensitive drum 11C is 0 ° at the timing when image exposure is started on the photosensitive drum 11C. Similarly, at the timing when image exposure is started on the photosensitive drum 11K, the angle θ on the photosensitive drum 11K is 0 °.

  As described above, the circumferential direction in which each flange 12 transmits the rotational force from the pin 31 of the rotary drive shaft 30 at the timing when the respective photosensitive drums 11 (11Y, 11M, 11C, and 11K) start image exposure. Is set at the same position in each photoconductor drum 11, the image exposure start position is constant in each photoconductor drum 11 regardless of the presence of tolerance between the flange 12 and the rotary drive shaft 30. Position, and color misalignment hardly occurs when the images formed on the respective photosensitive drums 11 are combined, and an image with good quality can be obtained.

(Setting the docking gear when assembling the device, see Fig. 4)
Here, a setting method for setting the engagement relationship between each photosensitive drum 11 and each drive shaft 30 to the relationship shown in FIG. 2 when assembling the apparatus will be described.

  As shown in FIG. 4, docking gears 35 (35Y, 35M, 35C, and 35K) are coupled to the drive shafts 30 (30Y, 30M, 30C, and 30K), respectively, and the rotational driving force is supplied from the docking gear 35, respectively. It is transmitted to the drive shaft 30 and also transmitted to the flange 12 and the photosensitive drum 11. Each of the docking gears 35 and each of the drive shafts 30 are engaged with each other at a certain circumferential position by engaging the concave portions 36 and the convex portions 32. Holes 37 are formed at corresponding circumferential positions.

  On the other hand, a rod 41 protrudes from the setting reference plate 40 at a position corresponding to the angle θ. When the holes 37 of the respective docking gears 35 are engaged with the rods 41, the respective docking gears 35 (rotary drive shafts 30) are set in the relationship of the angle θ.

(Setting when changing docking gear, see Fig. 5)
When it is necessary to replace the docking gear 35 due to damage or the like after the image forming apparatus 1 enters the market, for example, as shown in FIG. 5, when replacing the gear 35Y, a dedicated setting reference plate 45 is used. Is used to engage the hole 37 of the new docking gear 35Y with the rod 46.

  A hole (not shown) in the image forming apparatus 1 is provided with a hole for fixing the setting reference plate 45 corresponding to each docking gear 35, and the leg 47 of the setting reference plate 45 is fixed to the hole. Thus, the rod 46 positions the hole 37 of each docking gear 35 at a position corresponding to the predetermined angle θ.

(Other examples)
Note that 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, the engagement between the flange and the rotary drive shaft can employ various configurations other than the configuration using the groove and the pin shown in the above-described embodiment. Further, the image carrier may be a belt instead of a drum, or the intermediate transfer member may be a drum instead of a belt. The overall system configuration of the image forming apparatus is also arbitrary.

1 is a schematic configuration diagram illustrating an embodiment of an image forming apparatus according to the present invention. FIG. 6 is a front view showing an image forming portion of the image forming apparatus, showing a timing at which image exposure is started on the photosensitive drum 11Y. FIG. 6 is a front view showing an image forming portion of the image forming apparatus, showing a timing at which image exposure is started on the photosensitive drum 11M. FIG. 3 is a perspective view illustrating a setting state of a docking gear when the image forming apparatus is assembled. FIG. 3 is a perspective view illustrating a setting state when the docking gear is individually replaced in the image forming apparatus. It is a front view which shows the principal part of the conventional image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 11 ... Photosensitive drum 12 ... Flange 13 ... Center hole 14 ... Groove part 30 ... Drive shaft 31 ... Pin

Claims (1)

Tandem image formation in which a plurality of image carriers arranged in parallel at predetermined intervals are driven to rotate in one direction, and image formation processes of charging, image exposure, development, and transfer are sequentially performed on the image carrier. In the device
An engagement portion provided on a rotation drive shaft of each image carrier is engaged with a flange member provided on each image carrier,
At the timing when each image carrier starts image exposure, the circumferential position at which the flange member transmits the rotational driving force from the engaging portion is set to the same position on each image carrier. thing,
An image forming apparatus.

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