Electrophotographic apparatus

Abstract

 An electrophotographic apparatus, suitable for use in a printer, fax machine or photocopier for example, comprises a photoconductive drum 100 on which a toner image can be formed by means of a photo-exposing section 2 and a toner supply section 3. A recording medium 110, such as paper, is passed over the drum 100 and held in contact with the drum by a transferring rotary body 4 to transfer the image to the gravity-oriented lower face of the recording medium. Downstream of the drum, the recording medium enters a fixer 5, where the image on the recording medium is fixed.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] The present invention relates to an electrophotographic apparatus for use in electrophotographic printers, facsimile apparatuses or copying machines.

Description of the Related Art

[0002] In an electrophotographic apparatus, usually a toner image, after being formed on the surface of a photoconductive drum according to a latent electrostatic image, is transferred to recording paper or some other recording medium by a transfer charger. The transfer charger, known as a corotron, is often used for this transferring purpose. A corotron electrifier generates a strong electric field having a polarity reverse to that of the toner adhering to the photoconductive drum, and draws the toner on the photoconductive drum to the recording paper to accomplish transfer of the image. The peripheral speed of the photoconductive drum and the carriage speed of the recording paper are basically equal, and the paper, during the transferring process, should be pressed against the photoconductive drum with appropriate strength by the paper supply mechanism.

[0003] However, since the corotron electrifier has no mechanism to press the recording paper to transferring part, if the impact which is generated when the tip of the paper rushes into the fixing section is transmitted to the corotron electrifier via the recording paper, the toner image is susceptible to disturbance during transfer. For this purpose, there should be provided a long enough distance between the transferring part of the corotron electrifier and the fixing section to prevent the impact generated on the tip of the recording paper from reaching the transferring part. This distance should be no less than 10 cm according to the prior art, necessitating a space in which to secure the distance and thereby preventing electrophotographic apparatuses from being reduced in size.

[0004] On the other hand, some transfer chargers use a transferring rotary body (transcribing roller) which transfers the toner image to the recording paper while rotating in contact with the photoconductive drum. The transferring rotary body has its own capability to carry the recording paper to the fixer and accordingly the advantage of keeping the transferring part unaffected by the impact which arises when the tip of the recording paper rushes into the fixing section. This transferring rotary body is arranged underneath the photoconductive drum, and the recording paper onto which the toner image has been transferred is carried with its front face up and, after the image is fixed, stacked in a substantially horizontal state with its front face down in the upper part of the electrophotographic apparatus. This arrangement makes the order in which the sheets of recording paper are stacked conform to the sequence of page numbers, and thereby dispenses with the need to reorder the sheets after the recording. However, this configuration, since it requires 180° reversal of the carrying direction of the paper after transcription in the limited space, allows no such rigid recording medium as thick paper to be carried.

[0005] According to the prior art, there further are electrophotographic apparatuses in which a transfer charger using a corotron electrifier is arranged above the photoconductive drum. Such an electrophotographic apparatus, since the toner image is transferred onto the under face of the recording paper, the sheets of recording paper can be stacked in the same order as the sequence of page numbers if the sheets having gone through fixing are discharged without being turned over. In this case, however, the distance between the transferring and fixing sections is extended for the above-described reason with the result that the tip of the recording paper falls down by gravity and tends to come in touch with some part of the apparatus before the toner-adhering face of the recording paper after transcription reaches the fixing section. Therefore, a mechanism to prevent such contact is required.

[0006] As described above, electrophotographic apparatuses according to the prior art involve one or another of the problems that the limitation of size reduction by the extended distance between the transferring and fixing sections, incompatibility with rigid recording medium, and undesirable contact of the toner image transferred to the recording medium. No electrophotographic apparatus representing the solution of all these problems has been invented as yet.

SUMMARY OF THE INVENTION

[0007] In an electrophotographic apparatus according to a first aspect of the invention, a transferring rotary body transfers a toner image to a recording medium while contacting the recording medium to a photoconductive drum on whose surface the toner image is formed, and it is arranged above the photoconductive drum, thereby the toner image on the photoconductive drum is transferred onto the gravity-oriented face of the recording medium. The fixer is arranged in the moving direction of the recording medium fed from the transferring rotary body.

[0008] Since the transferring rotary body transfers the toner image to the recording medium while keeping the medium in contact with the photoconductive drum, the vibration which arises when the tip of the recording medium comes in touch with the fixer does not affect the transferring action. Therefore, the distance between the fixer and the transcribing rotary body can be shortened, and this contributes to reducing the size of the electrophotographic apparatus. Nor is there fear for the transferred image to come into contact with any other part of the electrophotographic apparatus.

[0009] Moreover, the recording medium is carried in a substantially straight shape without being significantly curved in the process from transcription to fixing, and the sheets of recording medium having been carried can be stacked in a bottom-to-top order.

[0010] According to a second aspect of the invention, there is provided an electrophotographic apparatus comprising a supply section for supplying sheets of recording medium; a photoconductive drum on whose surface a toner image is formed; a transferring rotary body, arranged above the photoconductive drum, for transferring the toner image on the recording medium while keeping the medium in contact with the photoconductive drum; a fixer for fixing said toner image transferred to the recording medium on said recording medium; and a discharge section for discharging the recording medium the toner image on which has been fixed by the fixer. Characteristically, the transferring rotary body transfers the toner image on the photoconductive drum onto the gravity-oriented face of the recording medium, and the fixer is arranged in the moving direction of the recording medium fed from the transferring rotary body.

[0011] This invention may thus advantageously provide an electrophotographic apparatus which not only permits the distance between the transferring and fixing sections to be reduced, preferably to 100 mm or less and particularly preferably to 80 mm or less, but also represents a solution to the problem of the undesirable contact of the toner image transferred to the recording medium.

[0012] Desirably, the supply section, the transferring rotary body, the fixer and the discharge section should carry the recording medium along a substantially straight path. This may advantageously allow printing on a rigid or thick recording medium.

[0013] The recording medium may be any appropriate medium, such as paper for example.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] 

FIG. 1 is a cross-sectional diagram-illustrating an electrophotographic apparatus, which is a preferred embodiment of the present invention, and

FIG. 2 is a cross-sectional diagram of a printer in which is used the electrophotographic apparatus illustrated in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0015] Next will be described in detail a preferred embodiment of the invention with reference to accompanying drawings.

[0016] FIG. 1 is a cross-sectional diagram illustrating an electrophotographic apparatus, which is a preferred embodiment of the invention. Referring to the diagram, the electrophotographic apparatus comprises a photoconductive drum 100 further comprising a plain aluminum tube and an organic photoconductive (OPC) film formed over the surface of the tube; a brush electrifier 1 in contact with the surface of the photoconductive drum 100; a photo-exposing section 2; a developing section 3 for supplying toner onto the surface of the photoconductive drum 100; a transferring rotary body 4; a fixing section 5; a cleaner 6; and a feed roller 21 for supplying recording media 110 to the transferring rotary body 4. This embodiment is characteristic in that the transferring rotary body 4 is arranged above the photoconductive drum 100, and the recording media 110 are carried in a substantially horizontal state.

[0017] A negative voltage is supplied to the brush electrifier 1, which negatively electrifies the surface of the photoconductive drum 100 through contact. Thus, the surface of the photoconductive drum 100 is evenly electrified negatively, though the external periphery of the photoconductive drum 100 is provided with an initial voltage lower in absolute level than the electrifying voltage.

[0018] The photo-exposing section 2 irradiates the electrified surface of the photoconductive drum with scanning rays corresponding to visual image data to form a latent electrostatic image. The photo-exposing section 2 uses a laser, LED or liquid crystal light source, which is driven according to the visual image data.

[0019] The developing section 3 has a toner supply chamber 30 including a toner carrier 31 and a supply roller 32, both rotating in the direction of the arrows in the diagram, and a toner hopper 33 for storing toner 10. The toner 10, which is the developer, is stored in the toner hopper 33 and, while being stirred by a stirring member 34, shifts to the toner supply chamber 30. The toner 10 having entered the toner supply chamber 30 is led to the roller-shaped toner carrier 31 by the rotation of the supply roller 32 consisting of such materials as foamed urethane or silicone either electroconducting or insulating, and aluminum. The toner carrier 31, consisting of a flexible member of silicon rubber, urethane rubber, nitrile butylene rubber or natural rubber, or foamed urethane or silicone or a surface-treated product of any of these materials, and rotates in the direction of the arrow in the diagram. The toner carrier 31 and the supply roller 32 rotate against each other where they come into contact, when the toner electrified by friction adheres to the toner carrier 31.

[0020] The quantity of the toner 10 adhering to the toner carrier 31 is regulated by a regulatory blade 35 consisting of an elastic plate, and restricted to about one layer of uniform film. One end of the regulatory blade 35 is fixed to the toner hopper 33, and its tip is in contact with the surface of the toner carrier 31. The toner carrier 31 is supplied with a voltage of the same polarity (negative) as that of the electrified photoconductive drum 100. Then, the electrified toner 10 on the surface of the toner carrier 31, when it comes opposite to the photoconductive drum 100, adheres to the latent electrostatic image on the photoconductive drum 100, whose polarity has been made positive by exposure to light, and develops the latent image to form a toner image 11.

[0021] The toner image 11 on the photoconductive drum 100 is transferred by the transferring rotary body 4 to a recording medium 100, which is ordinary paper or the like. After the toner transfer operation, the toner image is thermally fixed by the fixer 5 to the recording medium 110. The transferring rotary body 4, in contact with the photoconductive drum 100 via the recording medium 110, transfers the toner image to the recording medium 110 while rotating at the same peripheral speed as the photoconductive drum 100. The transfer is accomplished as the surface of the transferring rotary body 4 takes on a positive potential to attract the toner image 11 having a negative potential on the photoconductive drum 100 to the recording medium 110. At this time, the transfer takes place on the gravity-oriented face of the recording medium 110. When no transfer takes place, the transferring roller 4 is kept at the same potential as the photoconductive drum 100. The toner remaining on the photoconductive drum 100 after transfer is removed by the cleaner 6, which is fixed to a cleaner body 16 in which to deposit removed toner.

[0022] This embodiment has three characteristic features regarding the positional relationships among the photoconductive drum 100, the transferring rotary body 4 and the fixer 5. First, the transferring rotary body 4 is arranged above the photoconductive drum 100. Second, the roller of the fixer 5 is advantageously arranged at a horizontal distance of 65 mm or less from the transferring part, where the photoconductive drum 100 and the transferring rotary body 4 come into contact with each other. In a particularly preferred embodiment, the roller of the fixer 5 is at about 58 mm horizontal distance from the transferring part. Third, the fixer 5 is arranged in the moving direction of the recording medium 110 fed out of the transcribing part.

[0023] Since the transferring rotary body 4 transfers the toner image while keeping the recording medium 110 in contact with the photoconductive drum 100, the vibration which arises when the tip of the recording medium 110 comes in touch with the fixer 5 does not affect the transferring action. Therefore, the distance between the fixer 5 and the transcribing part can be shortened as the second characteristic feature indicates, and this contributes to reducing the size of the electrophotographic apparatus.

[0024] It is also important that the recording media 110, after being fed by the feed roller 21 to the transcribing part, are carried as nearly straight as possible without being significantly curved and, after being carried, can be stacked in a bottom-to-top order. Therefore, even if the recording media are thick, there is no trouble in carrying them.

[0025] FIG. 2 is a cross-sectional diagram of a printer in which is used the electrophotographic apparatus illustrated in FIG. 1. Referring to the diagram, a paper supply section 20 is fixed over a printer body 40, to one of whose sides is fixed a discharge tray 50. The paper supply section 20 has a hopper 22 fixed to the printer body with a 40° inclination upward from the horizontal plane, a hopper plate 23 mounting a plurality of recording media 110 and fixed at one end to an axis of rotation, a spring 24, and a paper supply roller 25. The hopper plate 23 is pressed against the paper supply roller 25 by the spring 24 all the time in order to bring the recording media 110 into contact with the paper supply roller 25.

[0026] As the paper feed roller 25 turns, the top sheet of the recording media 110 is fed, passing over a plate 26 and reaching the feed roller 21. The recording medium 110 is fed from the feed roller 21 to the transferring rotary body 4 and, after a toner image is transferred and fixed by the transferring rotary body 4 and the fixer 5, respectively, discharged by a discharge roller 60 to the discharge tray 50. Since the path of carriage of the recording media 110 from the paper supply section 20 to the discharge tray 50 is substantially straight, the paper supply is stable even where printing is to be done on thick recording media, with scarce jamming or forcible curling of paper if at all. Furthermore, the printed pages are stacked on the discharge tray in the same sequence as that of printing.

Claims

1. An electrophotographic apparatus comprising a photoconductive drum on whose surface a toner image is formed; a transferring rotary body for transferring the toner image to a recording medium while keeping the medium in contact with said photoconductive drum; and a fixer for fixing said toner image transferred to said recording medium on said recording medium, wherein:
   said transferring rotary body is arranged over said photoconductive drum and transfers. the toner image to said photoconductive drum onto the gravity-oriented face of said recording medium, and said fixer is arranged in the moving direction of said recording medium fed from said transferring rotary body.

2. An electrophotographic apparatus comprising a supply section for supplying sheets of recording medium; a photoconductive drum on whose surface a toner image is formed; a transferring rotary body, arranged above said photoconductive drum, for transferring said toner image to said recording medium supplied from said supply section while keeping the medium in contact with said photoconductive drum; a fixer for fixing said toner image transferred to said recording medium on said recording medium; and a discharge section for discharging said recording medium the toner image on which has been fixed by said fixer, wherein:
   said transferring rotary body transfers the toner image to said photoconductive drum onto the gravity-oriented face of said recording medium, and said fixer is arranged in the moving direction of said recording medium fed from said transferring rotary body.

3. An electrophotographic apparatus, as claimed in Claim 2, wherein said supply section, said transferring rotary body, said fixer and said discharge section feed out said recording medium along a substantially straight path of carriage.

Drawing