JP4386622B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus having a developing device that performs development by pressing a developing roller against a photosensitive drum.
[0002]
[Prior art]
An example of this type of image forming apparatus is shown in FIGS. The image forming apparatus 40 shown in the figure is configured to read the original data read by the primary corona charger 3, the scanner or the like that uniformly charges the surface of the photosensitive drum 41 around the photosensitive drum 41 as an image carrier. The optical projection device 4 that forms an electrostatic latent image on the photosensitive drum 41 by projecting by the like, the developing device 42 that develops the electrostatic latent image, the transfer belt 10 stretched between the three rollers 9 and the transfer roller 11 A transfer unit 6 for transferring the developed toner image onto a transfer material (not shown) such as paper, and a static eliminator 8 for uniformly eliminating the electric potential charged on the surface of the photosensitive drum 41. These are arranged so as to act on the photosensitive drum 41 sequentially.
[0003]
In the image forming apparatus 40, the developing device 42 for developing the electrostatic latent image formed by the optical projection device 4 has the following configuration.
[0004]
That is, the developing device 42 has a housing 14 having an opening 13 formed facing the photosensitive drum 41, and a part of the peripheral surface is exposed from the opening 13 in the housing 14. A developing roller 43 that presses against the photosensitive drum 41 and supplies toner to the surface of the photosensitive drum 41, a supply roller 16 that is provided in contact with the developing roller 43 and supplies toner to the developing roller 43, and the supply roller 16 The agitation roller 17 for supplying toner to the developing roller 43 and the layer thickness regulating roller 18 provided in pressure contact with the developing roller 43 to regulate the thickness of the toner layer formed on the developing roller 43 are accommodated.
[0005]
[Problems to be solved by the invention]
In such a developing device 42, the developing roller 43 is pressed against the photosensitive drum 41 and rotated for development, so that the developing roller 43 and the photosensitive drum 41 are in contact as shown in FIG. The toner 26 on the surface 44 protrudes from the contact end portion (end portion of the contact surface) 45 between the developing roller 43 and the photosensitive drum 41 when the developing roller 43 presses the photosensitive drum 41. The protruding toner 26 moves to the surface of the photosensitive drum 41 (arrow A in FIG. 4) to form a ring-shaped toner layer on the peripheral surface of both ends of the photosensitive drum 41 or the end surface 46 of the developing roller 43. (Arrow B in FIG. 4) or fall as it is (arrow C in FIG. 4).
[0006]
If the development is continued in such a state, the toner 26 moves to the surface of the photosensitive drum 41 (arrow A in FIG. 4) and forms a ring-shaped toner layer on the peripheral surface of both ends of the photosensitive drum 41. The toner is scattered by the rotation of the photosensitive drum 41 and the toner is in the image forming apparatus 40. In such a state, there is a possibility that toner adheres to the peripheral portion of the process such as the optical projector 4 and a good image cannot be formed. Further, the ring-shaped toner layers formed on the peripheral surfaces of both end portions of the photosensitive drum 41 adhere to the transfer belt 10 or dust on the transfer unit 6, and the transfer material is soiled. Furthermore, it enters into the transfer unit 6 and leads to failure of the transfer unit 6.
[0007]
Further, the toner 26 that has moved to the end surface 46 of the developing roller 43 (arrow B in FIG. 4) and adhered to the end surface 46 scatters due to the rotation of the developing roller 43 and stains the inner wall surface of the housing 14 of the developing device 5. Then, it falls to the bottom of the casing 14. Further, the toner 26 that protrudes from the contact end portion (end portion of the contact surface) 45 between the developing roller 43 and the photosensitive drum 41 and falls as it is (arrow C in FIG. 4) falls to the bottom portion of the casing 14 (FIG. 4 shows this case). When the toner 26 falls to the bottom of the casing 14 in this manner and the toner 26 is left as it is, the toner 26 gradually accumulates at the bottom of the casing 14 and the toner overflows from the opening 13. Then, the overflowing toner 26 may drop and adhere to a transfer material (not shown) or the transfer unit 6 to contaminate the transfer material.
The above phenomenon is particularly remarkable in a high-speed machine having a process speed of 150 mm / sec or more.
[0008]
An object of the present invention is to provide an image forming apparatus having a developing device that does not fall even if it protrudes from the contact end portion of the developing roller and the photosensitive drum when developing by pressing the developing roller to which the toner is attached to the photosensitive drum. It is to provide.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, an image forming apparatus according to the first aspect of the present invention is an image forming apparatus having a developing device that performs development by pressing and rotating a developing roller against a photosensitive drum.
The photosensitive drum is formed longer in the longitudinal direction than the developing roller, and forms a tapered stepped portion that gradually decreases in diameter from both ends of the large diameter portion of the photosensitive drum contacting the developing roller toward the rotation axis. and the small diameter portion is formed continuing from the end of the step portion, the gap portion is provided toward the front Symbol developing roller and an end portion or et outside side of the contact surface of the photosensitive drum,
The photosensitive drum and the developing roller are formed longer in the longitudinal direction than the large-diameter portion of the photosensitive drum, and a tapered step portion that gradually decreases in diameter toward the rotation axis of the photosensitive drum and the photosensitive drum The gap portion is formed by a portion protruding in the longitudinal direction from the large diameter portion of
The developing roller is formed of an elastic body, and is configured to press and contact the large diameter portion of the photosensitive drum with a rotation axis as a center,
The toner supplied by the developing roller is supplied to the large diameter portion of the photosensitive drum, and the large diameter portion becomes an image area.
The toner protruding from the contact end with the photosensitive drum is held on the developing roller near the gap and collected in the developing device.
With this configuration, even if the toner in the portion where the developing roller and the photosensitive drum are in contact protrudes from the contact end portion of the developing roller and the photosensitive drum due to the pressing against the photosensitive drum by the developing roller, the developing roller and the photosensitive drum Since the gap portion formed by providing a small diameter portion on the photosensitive drum from the end of the contact surface to the inside of the contact surface is provided, the protruding toner is held on the developing roller near the gap portion. The toner does not fall.
[0010]
With this configuration, even if the toner in the portion where the developing roller and the photosensitive drum are in contact protrudes from the contact end portion of the developing roller and the photosensitive drum due to the pressing against the photosensitive drum by the developing roller, the developing roller and the photosensitive drum Since the gap portion is provided from the end of the contact surface to the inside of the contact surface, the toner that protrudes on the developing roller near the gap portion is held on the developing roller, and the toner falls. do not do.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example of an embodiment of an image forming apparatus according to the present invention will be described.
1 and 2 show an embodiment of an image forming apparatus according to the present invention.
[0014]
The image forming apparatus 1 according to the present embodiment is an image forming apparatus having a developing device using a non-magnetic one-component developer that performs development by pressing a developing roller against a photosensitive drum. In addition, the image forming apparatus 1 according to the present embodiment includes a reversal development method in which toner is attached to a place exposed by an exposure device, and a normal development method in which toner is attached to a location not exposed by the exposure device. In this embodiment, an image forming apparatus using the reversal development method will be described as an example.
[0015]
In the figure, an image forming apparatus 1 uses an LED or the like to read document data read by a primary corona charger 3, a scanner or the like that uniformly charges the surface of the photosensitive drum 2 around a photosensitive drum 2 that is an image carrier. An optical projection device 4 for projecting to form an electrostatic latent image on the photosensitive drum 2; a developing device 5 for developing the electrostatic latent image; a transfer unit 6 for transferring the developed toner image to a transfer material such as paper; A static eliminator (specifically, an eraser lamp) 8 for uniformly eliminating the electric potential charged on the surface of the photosensitive drum 2, which is arranged so as to act on the photosensitive drum 2 in sequence. Yes.
[0016]
The primary corona charger 3 is for uniformly charging the surface of the photosensitive drum 2 by corona discharge to ensure a primary potential (for example, −700 V). The optical projection device 4 exposes an electrostatic latent image and irradiates the surface of the photosensitive drum 2 with the infrared light of the LED print head in accordance with the contents of the image data, thereby neutralizing the charge and thereby surface potential. To form an image.
[0017]
The transfer unit 6 includes a transfer belt 10 stretched around three rollers 9, a toner image formed on the photosensitive drum 2 to which a predetermined voltage is applied as a bias voltage, and a transfer material such as paper (not shown). A transfer material (not shown) is sent between the transfer roller 11 and the photosensitive drum 2 by the transfer belt 10, and the toner image formed on the photosensitive drum 2 by the developing device 5 is transferred to the transfer roller 11. 11 is transferred onto a transfer material.
[0018]
A red LED is used as a light source as the static eliminator 8, and the static eliminator 8 irradiates the surface of the photosensitive drum 2 and erases residual charges on the surface of the photosensitive drum 2 before performing primary charging. (In actuality, it may not be completely erased, and the actual surface potential of the photosensitive drum 2 is 0 to -150 V).
[0019]
The developing device 5 has a housing 14 having an opening 13 formed facing the photosensitive drum 2, and a part of the peripheral surface is exposed from the opening 13 in the housing 14. A developing roller 15 that presses and contacts the photosensitive drum 2 and supplies toner to the surface of the photosensitive drum 2, a supply roller 16 that is provided in contact with the developing roller 15 and supplies toner to the developing roller 15, and the supply roller 16 An agitation roller 17 that supplies toner and a layer thickness regulating roller 18 that is provided in pressure contact with the developing roller 15 and regulates the thickness of the toner layer formed on the developing roller 15 are accommodated.
[0020]
The developing roller 15 and the photosensitive drum 2 in the developing device 5 will be described in detail with reference to FIG.
[0021]
In the present embodiment, the photosensitive drum 2 has a configuration in which an electrophotographic photosensitive member is provided on the surface of a drum-shaped substrate such as aluminum. As the photoreceptor, a known photoreceptor such as an OPC photoreceptor or an amorphous silicon photoreceptor can be used.
[0022]
The photosensitive drum 2 is longer in the longitudinal direction than the developing roller 15, and includes a large diameter portion 19 and small diameter portions 21, 21 that continue from the large diameter portion 19 through the step portions 20, 20. have. And it rotates around the rotating shaft 22. A photoreceptor layer is formed on the large diameter portion 19 and the small diameter portion 21. The small diameter portion 21 is provided with an insulating layer in order to prevent leakage.
[0023]
The developing roller 15 rotates about the rotation shaft 23, is made of an elastic body, and is in pressure contact with the large diameter portion 19 of the photosensitive drum 2. Therefore, the toner supplied by the developing roller 15 is supplied to the large-diameter portion 19 of the photosensitive drum 2, and the large-diameter portion 19 is an image area.
[0024]
The developing roller 15 is shorter in the longitudinal direction than the photosensitive drum 2, but has a length that reaches the small diameter portion 21 of the photosensitive drum 2.
[0025]
A gap 25 is provided from the end of the developing roller 15 toward the contact end 24 of the developing roller 15 and the photosensitive drum 2. In the enlarged view of the vicinity of the end portion of the developing roller 15 in FIG. 2, the alternate long and short dash line 30 indicates a conventional photosensitive drum that does not have the step portion 20 and the small diameter portion 21. The gap portion 25 in the present invention is formed from the end portion (contact end portion) 45 of the contact surface between the conventional developing roller and the photosensitive drum toward the inside of the conventional contact surface between the developing roller and the photosensitive drum.
[0026]
In such a developing device 5, the toner layer formed by attaching toner to the surface of the developing roller 15 is regulated to a certain thickness by the layer thickness regulating roller 18, and lines and characters are drawn on the developing device 5. Since a voltage (−550 V) that is several tens to several hundreds V higher than the dark potential (−700 V) of the electrostatic latent image is applied as a bias voltage, an electrostatic latent image is formed on the surface of the developing roller 15. When the surface of the photosensitive drum 2 comes into contact, the toner is exposed to the bias voltage (−550 V) and the light portion potential (−) on which lines and characters on the surface of the photosensitive drum 2 are drawn by the electrostatic action of the toner itself. 200V), the development is performed.
[0027]
At this time, the toner in the portion where the developing roller 15 and the photosensitive drum 2 are in contact protrudes from the contact end 24 between the developing roller 15 and the photosensitive drum 2 due to the pressing of the developing roller 15 against the photosensitive drum 2 (FIG. 2 is the toner). However, since a gap 25 is provided from the end of the developing roller 15 toward the contact end 24 of the developing roller 15 and the photosensitive drum 2, the developing roller 15 is placed on the developing roller 15 near the gap 25. And the toner 26 protruding from the contact end 24 between the photosensitive drum 2 and the photosensitive drum 2 are held, and the toner 26 does not fall. The toner 26 is collected in the developing device 5, and toner adhesion is not accumulated on the surfaces of both end portions of the developing roller 15. For this reason, since toner does not collect at the bottom of the housing 14 of the developing device 5, it is not necessary to frequently clean the bottom of the housing, and maintenance is easy. Further, there is no case where a toner adheres to a peripheral portion of the process such as the optical projection device 4 and a good image cannot be formed. Further, the toner 26 does not adhere to the transfer material or the transfer unit 6 due to the fall of the toner 26, so that the transfer material can be prevented from being soiled. The present invention is particularly significant in that the toner can be prevented from dropping from the contact end portion 24 between the developing roller 15 and the photosensitive drum 2 even in a high-speed machine having a process speed of 150 mm / sec or more.
[0028]
Further, by providing a cleaning member (not shown) in the gap portion 25 of the photosensitive drum 2, it is possible to further prevent the toner from falling. Furthermore, only by extending the gap 25 in the longitudinal direction L, an appropriate region for preventing toner leakage from the end of the developing roller 15 can be set according to the process speed.
[0029]
【The invention's effect】
As described above, according to the present invention, the toner in the portion where the developing roller and the photosensitive drum are in contact may protrude from the contact end portion of the developing roller and the photosensitive drum due to the pressing of the developing roller against the photosensitive drum. Since the gap is provided from the end of the contact surface between the developing roller and the photosensitive drum toward the inside of the contact surface, the protruding toner is held on the developing roller near the gap. The toner does not fall.
[Brief description of the drawings]
FIG. 1 is a side view showing an embodiment of an image forming apparatus according to the present invention.
2 is a plan view showing portions of a photosensitive drum and a developing roller of the image forming apparatus shown in FIG.
FIG. 3 is a side view of a conventional image forming apparatus.
4 is a plan view showing portions of a photosensitive drum and a developing roller of the image forming apparatus shown in FIG. 3;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Photosensitive drum 3 Primary corona charger 4 Optical projection apparatus 5 Developing apparatus 6 Transfer unit 8 Static eliminator 9 Pulley 10 Transfer belt 11 Transfer roller 13 Opening part 14 Housing | casing 15 Developing roller 16 Supply roller 17 Stirring roller 18 Layer Thickness regulating roller 19 Large diameter portion 20 Step portion 21 Small diameter portion 22 Rotating shaft 23 Rotating shaft 24 Contact end portion 25 Gap portion 26 Toner

Claims (1)

In an image forming apparatus having a developing device for performing development by pressing and rotating a developing roller against a photosensitive drum,
The photosensitive drum is formed longer in the longitudinal direction than the developing roller, and forms a tapered step portion that gradually decreases in diameter from both ends of the large-diameter portion of the photosensitive drum that contacts the developing roller toward the rotation axis. and the small diameter portion is formed continuing from the end of the step portion, the gap portion is provided toward the front Symbol developing roller and an end portion or et outside side of the contact surface of the photosensitive drum,
The photosensitive drum and the developing roller are formed longer in the longitudinal direction than the large-diameter portion of the photosensitive drum, and a tapered step portion that gradually decreases in diameter toward the rotation axis of the photosensitive drum and the photosensitive drum The gap portion is formed by a portion protruding in the longitudinal direction from the large diameter portion of
The developing roller is formed of an elastic body and is configured to rotate while pressing against the large diameter portion of the photosensitive drum around a rotation axis.
The toner supplied by the developing roller is supplied to a large diameter portion of the photosensitive drum, and the large diameter portion becomes an image area.
An image forming apparatus, wherein toner protruding from a contact end with the photosensitive drum is held on the developing roller near the gap and collected in the developing device.

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