CLEANING UNIT FOR CLEANING THE RECORDING MEDIUM OF AN ELECTROPHOTOGRAPHIC APPARATUS

Abstract: A recording apparatus of toner image transfer type, having an improved cleaning device for removing residu­ al contaminants on the surface of a rotating recording drum after toner image transfer. The cleaning unit includes a blade of counter type engaging with down­ wardly moving surface of the drum, a rotatable cleaning brush disposed immediately upstream from the blade, and a housing structure shielding the blade and the rotata­ ble fur brush. The housing is evacuated by an air pump, and external air is introduced from an opening of the housing, where the fur brush and the blade engage with the surface of the drum. Thereby, the contaminants removed by the blade and the fur brush from the surface of the drum is efficiently discharged by the aid of air flow having velocity enhanced by the above-described pneumatic structure. The air velocity is further enhanced by forming an air passage passing through the fur brush.

Description: The present invention relates to a recording apparatus of toner image transfer type, namely electrostatographic apparatus, such as an electrophotographic apparatus and an electrostatic electrographic apparatus. In particular, it relates to an improved cleaning device to remove residual contaminants from the surface of recording medium of the recording apparatus after toner image transfer operation. As well known, in a recording apparatus of toner image transfer type, such as an electrophotographic printer or copying machine, or an electrographic printing machine or copying machine, an electrostatic latent image is formed on a recording medium such as a photoconductive drum or a dielectric drum. The latent image is developed as a toner image formed on the surface of the drum. Thereafter, the toner image is adhesively transferred onto a printing medium such as cut sheet or web at an image transfer station of the apparatus where the surface of the recording medium and that of the printing medium are set in contact with each other. The present invention is applicable to both the electrophotographic recording apparatus and the electrographic recording apparatus. However, for clarity and simplicity of description, the description of the present invention will be limited to an electrophotographic recording apparatus having a photoconductive drum and employing cut sheet as a printing medium. Since the image transfer usually does not remove all the toner particles from the surface of the recording medium, leaving small amounts of toner particles thereon, and since it is necessary to keep the surface of the recording medium clean for the subsequent image formation thereon, the surface must be cleaned completely immediately after the image transfer. Accordingly, at the next cleaning station, contaminants remained on the surface of the photoconductive drum, including residual toner particles, toner carriers, and paper lints are removed. A cleaning device. therefore. is disposed downstream from the image transfer station with respect to the rotation of the drum. Hereinafter, the terms "downstream" and "upstream" are used with respect to the rotating movement of the photoconductive drum. In conventional cleaning devices, there have been two types. The one is a type having a rotatable cleaning means such as a rotatable brush including a number of hairs made of plastic wire, planted around a rotatable shaft, or a rotatable cylinder of sponge-like material formed around a shaft. The cleaning means is extended in the axial direction of the photoconductive drum. The other is a blade type using a blade of elastic material such as polyurethane rubber. The blade is extended in the axial direction of the photoconductive drum, and disposed such that the edge of the blade engages with a rotating surface of the relevant photoconductive drum in contact under pressure. Cleaning capability of a cleaning device of the former type is not sufficient, and there is a tendency to cause a contaminated toner image on a cut sheet or to cause fluctuated electric discharge of the relevant electric discharger due to the residual toner particles scattered by brushing. A cleaning device of the blade type can clean the surface of the photoconductive drum with a favorable completeness. However, there is a problem of abrasion of the edge of the blade caused by contaminants of large size such as toner carriers and paper lints accumulated on the edge. The problem is described in detail. When a feed passage of the cut sheet is selectively disposed in an upper portion of the recording apparatus, the image transfer station must be set at the top portion of the photoconductive drum. This configuration of the arrangement of the photoconductive drum to the printing medium is essentially beneficial for an operator of the apparatus, because removal of jammed sheets and replacement of the photoconductive drum can be performed very easily and safely from the top side of the apparatus without damaging the surface of the photoconductive drum. The sheet jamming tends to occur at a portion of the sheet feed passage in the vicinity of the image transfer station. Consequently, approach to the jammed cut sheet and the photoconductive drum by the operator can be done easily only by opening the upper portion of the recording apparatus. With respect to the above-described configuration of the arrangement of the photoconductive drum and the feed passage for the cut sheet, the blade must be naturally disposed such that the edge of the blade engages along a substantially downwardly moving surface of the photoconductive drum in contact under pressure, and the edge thereof is directed upstream, usually upwardly. When the edge scrapes the surface of the photoconductive drum to remove the contaminants attached thereon, the scraped contaminants might accumulate on the edge of the blade. The accumulated contaminants contain toner particles, toner carriers and paper lints. The toner particles are fine particles having a diameter of micromillimeter order. The toner carriers contained in two-components develop material have diameters of ten micrometer order. When the two-components develop material is employed, the toner carriers tend to be scattered inside the apparatus by centrifugal force of a rotating magnetic brush which is formed of the develop material. The paper lints have large size ranging from 50 to 100 micrometers, being generated by friction between the advancing printing medium and the sheet feed passages, particularly between the side edge of the printing medium and the passage. The accumulated contaminants tend to stick to the edge of the blade, forming a layer stuck to a leading surface portion of the blade which is directly in contact with the surface of the photoconductive drum. This phenomenon is referred to as "filming" in the field of art. As a result, the surface of the photoconductive drum is scratched and damaged by the toner carriers and the paper lints after some duration of recording operation. To avoid the damage, the used blade must be replaced by a new one occasionally, leading to a short life of the blade causing a costly running expense. In contrast, fine toner particles appear to have lubricant function, thus a layer of toner particles having a certain thickness is allowed to accumulate on the edge of the blade. However, particularly in a case where the top surface of the blade is formed to be perpendicular to the surface of the drum, forming a step there, toner particles accumulate on the step excessively, forming a pile on the top surface of the blade and the portion of the surface of the drum adjacent to the cleaning edge. This is not desirable because such piled toner particles tend to be scattering within the recording apparatus, causing various problems. Further, some toner particles may pass underneath the cleaning edge, leaving a film on the periphery surface of the drum. The film of the toner particles may produce an unclear toner image at the subsequent toner image formation. The above-described problem has been expected to be solved. As one of the countermeasures to solve the above-described problem, in a prior art recording apparatus, the edge of the blade is sharpened to be formed in a wedge-like shape, providing the blade with a slant top surface over which scraped toner particles can easily fall down, and thus the accumulation of the contaminants on the edge is reduced. However, the sharpening of the edge is rather difficult and costly, and the edge tends to be easily abraded by repeated recording operations. DE-A-30 26 025 discloses a recording apparatus of image transfer type according to the pre-characterizing part of claim 1. JP-A-62-163 082 discloses an elastic cleaning roller arranged on the upstream side of a cleaning blade and sliding on the surface of the photosensitive body to remove foreign substances therefrom. Summary of the Invention The object of the present invention is to provide a recording apparatus of toner image transfer type capable of transferring clear images from a drum of recording medium onto a cut sheet. Another object of the present invention is to provide a recording apparatus of toner image transfer type having an image transfer station on the top side of the relevant drum of recording medium with a suitable cleaning unit. Still another object of the present invention is to provide an improved cleaning device having a cleaning blade for cleaning the surface of the drum of recording medium, wherein the blade is free from "filming" of contaminants stuck thereon, achieving an extended long life. The above-described recording medium, hereinafter, is limited to photoconductive material for description. The objects can be realized by an electrophotographic recording apparatus having a cleaning unit according to the present invention. In the apparatus, a cut sheet is advanced approximately horizontally, contacting with a photoconductive drum at an image transfer station located at the top portion of the photoconductive drum. The cleaning unit has a cleaning blade, a rotatable fur brush and a suction means working in cooperation. The cleaning blade is disposed such that the edge thereof can engage with the downwardly moving surface of the photoconductive drum at a portion downstream from the image transfer station, and is directed upwardly. Such a blade is referred to as a blade of counter type. The rotatable fur brush having elastic hairs is disposed immediately upstream from the cleaning blade forming a mutual contacting zone on the surface of the drum. The rotatable fur brush is disposed such that the hairs of the brush do not contact with the edge of the blade, leaving a narrow non-contact portion between the edge of the blade and the contacting zone. Contaminants of relatively large size such as paper lints and toner carriers, if any, remained on a portion of the surface of the photoconductive drum, are preliminarily removed by the rotatable fur brush at the upstream portion of the contacting zone. The toner particles accumulated on the top surface of the cleaning edge, and other particles of large size escaping from the rotatable cleaning brush and being mixed with the toner particles, are scraped off the surface of the drum by the edge of the blade. Almost all of the contaminants brushed by the brush and scraped by the cleaning edge from the surface of the drum, are removed efficiently by the aid of an air flow caused by the suction means, and collected to toner collecting means. Hereby, a cleaning housing of the suction means encloses the fur brush and the blade except for an opening through which the blade and the fur brush contact with the surface of the recording medium in order to guide the suctioned air to form an effective air flow having a speed sufficient to blow off the scraped and brushed contaminants and transfer to the collecting means. To enhance the air speed of the air flow, an air intake passage is formed within the rotatable brush with a substantial effect. The features and the advantages of the present invention as claimed will be apparent from the following description with reference to the following drawings wherein like reference numerals represent like parts. Brief Description of the Drawings Fig. 1 is a cross-sectional view of an electrophotographic recording apparatus, illustrating the structural configuration; Fig. 2 is a cross-sectional view of the cleaning unit, illustrating the structure in more detail; Fig. 3 is a perspective view of the cleaning unit, illustrating the structure in more detail; Fig. 4 is a schematic cross-sectional view of the blade and the associated members, illustrating the set angle of the blade set to the surface of the photoconductive drum; Fig. 5 is a perspective view of an improved rotatable cleaning fur brush; Fig. 6(a) and Fig. 6(b) are respectively cross-sectional front view and side view of another improved rotating cleaning fur brush; Fig. 7(a) and Fig. 7(b) are respectively cross-sectional front view and side view of a rotatable cleaning cylinder made of sponge like material, having a hollow shaft; and Fig. 8 is a perspective view of a rotatable cleaning cylinder having a cylindrical layer made of sponge-like material. Fig. 1 is a cross-sectional view of an electrophotographic recording apparatus, illustrating the structural configuration. The apparatus is composed of a sheet feed unit 11, an electrophotographic processing section 12, a sheet stacker unit 13, and a sheet reversing unit 14. These apparatus elements are enclosed and mounted within an apparatus housing 100. Hereby, the apparatus housing 100 includes various frame structures for supporting the elements of the apparatus and housing plates. The sheet feed unit 11 comprises two conventional sheet hoppers 15 and 16, and a sheet cassette 17. A number of cut sheets having the same sheet size and the same sheet quality are stacked in alignment in one of the hoppers 15 and 16, and the sheet cassette 17. Pick rollers 18, 19 and 20 are disposed corresponding to the sheet hoppers 15 and 16, and the sheet cassette 17, to separate a sheet from the stack of sheets one by one and selectively transfer the sheet to the electrophotographic processing section 12. With the above-described configuration, the apparatus can hold sheets of three types at the same time. The electrophotographic processing section 12 comprises a photoconductive drum 21, a precharger 22, an optical exposer 23 for forming a latent image on the surface of the photoconductive drum 21, a developer 24, an image transfer means 25, a sheet transfer means 26, an image fixer 27, a discharger 28, and a cleaning unit 29. The above-described elements of the apparatus except for the cleaning unit 29 are the conventional ones which are widely used in the field. The photoconductive drum 21 includes an organic photoconductive layer or an amorphous silicon photosensitive layer, and is clockwisely rotatable as shown by an arrow X around a shaft 21a which is horizontally supported at both ends by supporting members (not shown) fixed to the apparatus housing 100. A sheet guide 30 is disposed in the vicinity of the upper portion of the photoconductive drum 21 and fixed to the housing 100 to introduce a cut sheet delivered from one of the sheet hoppers 15 and 16 and the sheet cassette 17. The image transfer means 25 is disposed facing the top portion of the photoconductive drum 21. The cut sheet is fed along a sheet feed passage 99 by the aid of feed roller pairs 57 and 58 and introduced between the photoconductive drum 21 and the image transfer means 25 through the sheet guide 30. Thus an image transfer station C is formed at the top portion of the photoconductive drum 21 as indicated in Fig. 1, and the sheet is transferred almost horizontally. A part of the apparatus housing 100 can be opened from the upper side of the housing 100, facilitating the dismantling of the photoconductive drum 21 for exchange with a new one and removal of sheet jamming which tends to occur in the vicinity of the sheet guide 30. This is an essential advantage of the structural configuration shown in Fig. 1. The optical exposer 23 comprises a rotating mirror 31, reflecting mirrors 32 and 33, a cover housing 34 strengthened by a frame (not shown) to which the above-described elements are secured. The rotating mirror 31 rotates at a high speed by a drive motor (not shown) and deflects a laser beam 35 injected thereto. The laser beam 35 is projected on the surface of the photoconductive drum 21 at an exposing station indicated as A by the aid of the mirrors 32 and 33, and an f-ϑlens (not shown), forming an electrostatic latent image in the photoconductive drum 21. The cover housing 34 encloses the elements of the optical exposer 23 to shield the elements from toner particles scattering inside the apparatus housing 100, having a glass window 36 to allow the passage of the laser beam 35 toward the photoconductive drum 21. The developer 24 comprises: a toner reservoir 37 to hold two-components developing material containing toner particles and toner carriers, develop roller 38 to form magnetic brush thereon, a toner density sensor 39 for sensing the density of the toner particles contained in the two-components developing material, stirring rollers 40a and 40b to stir the developing material held in the toner reservoir 37, a doctor blade 41 to control the height of the magnetic brush formed on the develop roller 38, a flow restricter 42 to control the flow of the developing material in the toner reservoir 37, and a toner recovery box 43 to collect and deposit used toner particles therein. In the bottom portion of the toner reservoir 37, a hinged releasing door 44 is disposed to release the used toner particles deposited in the bottom of the toner reservoir 37 into the toner recovery box 43. Toner supply hopper 45 comprising a toner cartridge receiver 46 and a supply roller 47 is disposed adjacent to the toner reservoir 37 forming one body with the toner reservoir 37. The toner particles supplied from a toner cartridge which is accomodated in the toner cartridge receiver 46, is transferred to the toner hopper 45 by the supply roller 47. The develop roller 38 is composed of a magnet roller and an outer sleeve being made of non-magnetic material and rotatable around the magnet roller. A sheet transfer means 26 includes a belt 50 extended between belt rollers 49a and 49b. An electric charger (not shown) for electrically charging up the belt 50 is attached. Fig. 2 and Fig. 3 are respectively a cross-sectional view and a partially broken perspective view of the cleaning unit 29, illustrating the structure thereof in detail. The cleaning unit 29 comprises a blade 51, a rotatable cleaning means 52, a suction means 53 and a cleaning housing 54. The blade 51 is detachably disposed on the bottom member 54a which is air-tightly connected to the bottom portion of the cleaning housing 54 through a supporting member 55. Fig. 4 is a magnified schematic cross-sectional view of the blade 51 and the associated members, cut in a plane perpendicular to the longitudinal direction, illustrating the mutual positional relationship. The blade 51 is extended in a direction parallel with the axis of the photoconductive drum 21 such that an edge 51a contacting with the surface of the photoconductive drum 21 (hereinafter the edge 51a is referred to as a cleaning edge) can scrape the surface along the whole axial length of the drum 21. The blade 51 has an extended rectangular cross-section having a top surface 51b almost perpendicular to the side surface 51c of the blade 51 near the cleaning edge 51a. The blade 51 is made of polyurethane rubber (product of Bandou Kogaku Co.) having a Young's module of 45 kg/square centimeter, a hardness of HS 60 degree (defined in Japanese Industrial Standard), a thickness of 1,5 mm (indicated by t) and a height of a cantilever portion of 6 mm (indicated by h). The straightness of the cleaning edge 51a lies within 10 micrometer, and the corner round is limited below 10 micrometer. The blade 51 is secured to the supporting member 55 with thermoplastic adhesive material as shown in the left portion of Fig. 3. The cross-section of the supporting member 55 perpendicular to the longitudinal direction has a shape of inverted U letter, and is engageable with the bottom member 54a which has a cross-section of the same shape as that of the supporting member 55 such that the supporting member 55 is received by the bottom member 54 slidable in the longitudinal direction over the bottom member 54a as shown by an arrow Z in Fig. 3. Consequently, the bottom member 54a is a rail member. Both members 54a and 55 are fixed to each other by clamping a clamping structure (not shown) when the blade 51 is set at a predetermined position. Since the cleaning edge 51a of the blade 51 may be abraded during a long operating period, the blade 51 must be exchanged with a new one. With the above-described sliding structure, mounting and dismounting of the blade 51 is easily and promptly conducted by an operator. The supporting member 55, hereby, is extended along the blade 51, closing the space between the blade 51 and the bottom member 54a. Thus, the supporting member 55 is designed to act as one member of a shielding means of the cleaning unit 29. In Fig. 4, set angle of the blade 51 set to the surface of the photoconductive drum 21 is illustrated. The cross-section of the drum 21 is represented by a circle R. The set angle is defined as an angle between a tangential line T of the circle R at a point Q where the cleaning edge 51a contacts with the drum 21, and a tangential line S of the side surface 51c of the blade 51 at the blade edge 51a. The set angle is selected to be an acute angle as shown in Fig. 4, and 30 degree is most desirable according to the experience of the inventor. A cleaning blade engaging with a rotating drum with an acute set angle like the above-described one is referred to as a blade of counter type in the art. The rotatable cleaning means 52 is a cylindrical, rotatable, fur brush, or a roller having a surface layer made of sponge-like material, such as polyurethane foam, and is disposed in the cleaning housing 54 such that the axis of the rotatable cleaning means 52 becomes horizontal and in parallel with the axis of the photoconductive drum 21. In the following description, the rotatable cleaning means is referred to as rotatable fur brush. In practice, the rotatable fur brush 52 has elastic brush hairs (bristles) made of rayon fibers of 12,5 Denier thick, planted on a shaft with a density of 25000 pieces per square inch. The rotatable fur brush 52 is disposed such that the tips of the brush hairs (bristles) are pressed against the surface of the drum 21 to form a contacting zone G on the surface of the drum 21. The zone G has a width and extends in the axial direction of the drum 21. The rotatable fur brush 52 is also disposed such that the tips of the brush hairs can be free from the edge of the blade 51, to leave a narrow space between the cleaning egde 51a and the contacting zone G. Otherwise, the tips of the hairs may be damaged by the blade 51 contacting the tips. The cleaning housing 54 encloses the rotatable fur brush 52 closely with a small space distance therebetween except for an opened portion 54b of the cleaning housing 54 through which the blade 51 and the rotatable fur brush 52 can engage the surface of the photoconductive drum 21. The bottom portion of the cleaning housing 54 has a connecting opening 54c opened downwardly to be connected to a duct 56 of the suction means 53. The cleaning housing 54 is fixed to the apparatus housing 100 in a position located at the left side of the photoconductive drum 21, and a lower portion from the center of the photoconductive drum 21 as shown in Fig. 1 and Fig. 2. The fixing position of the cleaning housing 54 is carefully selected such that, during a cleaning operation, the upwardly directed cleaning edge 51a of the blade 51 contacts a downwardly moving portion of the rotating photoconductive drum 21 with a predetermined pressure, 15.8 gr./cm in the embodiment, and the rotatable fur brush 52 is pressed against a portion of the photoconductive drum 21, located at immediate upstream portion from the cleaning edge 51a under pressure forming the contacting zone G. A flicker blade 69 is disposed to engage the hairs of the rotatable fur brush 52 to remove particles attached to the hairs. The suction means 53 includes the duct 56, a toner recovering box 71, an air pipe 97 (shown by chain lines) and an air suction fan or an air pump 98 (shown by chain lines). The duct 56 is connected to the cleaning housing 54 through the connecting opening 54c, and to the toner recovering box 71 at the bottom portion 56a of the duct 56 by flange coupling. The toner recovering box 71 has a conventional air filter 71a like a filter used for a vacuum cleaner for home use, to collect the toner particles and other contaminants scraped off the surface of the photoconductive drum 21 by the blade 51 and the rotatable fur brush 52. The air pump 98 is connected to the duct 56 through the air pipe 97 and the toner recovery box 71. The contaminants deposited in the filter 71a are removed by decoupling the toner recovery box 71 occasionally. With the above-described structural configuration of the suction means 53, the space inside the cleaning housing 54 is evacuated to a low pressure of approximately 200 mm Aq. As a result, air is introduced within the cleaning housing 54 through the opening 54b which is partially closed by the blade 51, the supporting member 55, and the rotatable fur brush 52. The introduced air flows around the surface of the rotatable fur brush 52, and finally is discharged from the opening 54c. The removal efficiency of toner particles and other contaminants which are scraped by the blade 51 and taken off by the rotatable fur brush, substantially depends on the air flow velocity in a space adjacent to the cleaning edge 51a of the blade 51. While the cleaning unit 29 except for the opening 54b is enclosed air-tightly on the whole, otherwise contaminants, in particular toner particles may be scattered within the apparatus housing 100, causing various problems in the recording apparatus. This enclosing structure serves to create an air flow within the cleaning housing 54 as described later. The recording operation of the above-described electrophotographic recording apparatus is described in the following. A cut sheet is selectively delivered from one of the sheet hoppers 15 and 16 and the sheet cassette 17, being advanced by the aid of the feed roller pairs 57 and 58 along the sheet feed passage 99, being introduced into the electrophotographic processing section 12 through the sheet guide means 30, and reaching the toner image transfer station A. A latent image is formed on the surface of the photoconductive drum 21 which is previously electrically uniformly charged by the precharger 22 and exposed to the irradiation of the laser beam 35 at the exposing station A. The latent image is moved to the developing station B in contact with the magnetic brush of the developing material formed on the develop roller 38, and developed to form a toner image on the surface of the photoconductive drum 21. The cut sheet and the toner image formed on the surface of the photoconductive drum 21 are advanced in synchronized movement, and the toner image is transferred adhesively onto the cut sheet at the image transfer station C. Then, the sheet is attracted electrostatically by the electrically charged belt 50 to be peeled off the photoconductive drum 21, and transferred to the image fix station E by the belt 50 of the sheet transfer means 26 under which the sheet is attracted. The sheet is pinched by a heat roller 59 and a press roller 60 of the image fixer 27, thereby the toner image is heated and pressed against the sheet and permanently fixed on the surface of the sheet. Thereafter, the sheet is separated off the rollers 59 and 60 by roller separators 59a and 60a, advanced by feed roller pairs 61a, 61b and 62a, 62b to the sheet stacker unit 13 (shown by chain lines) and is discharged therein. When both sides printing on the sheet is required, the leading edge of the sheet delivered from the feed rollers 61a, 61b is picked up by a switching member 63 to change the feed direction upwardly, and the sheet is transferred into the sheet reversing unit 14 through a guide member 64. The sheet is reversed by a conventional reversing mechanism 65 (simply represented by a chain line rectangular) and fed back through a guide passage 66 to the image transfer station C again by the aid of feed roller pairs 67 and 68. While the portion of the surface of the photoconductive drum 21, from where the toner image is removed by the image transfer, is discharged by the discharger 28 and moved to the cleaning station D to clean the portion. The portion of the surface of the photoconductive drum 21 to be cleaned comes first in contact with the rotatable fur brush 52. The rotatable fur brush 52 is rotated in the clockwise direction as indicated by an arrow Y. As a result, the surface of the photoconductive drum 21 which rotates in anti-clockwise direction and that of the fur brush 52 move in the same moving direction, namely in downwardly moving direction, at the contacting zone G. The surface velocity of the rotatable fur brush 52 is from two to three times that of the photoconductive drum 21. Consequently, the rotatable fur brush 52 rubs the surface of the photoconductive drum 21 with a speed of from one to two times of the surface speed of the photoconductive drum 21. The residual contaminants having relatively large size compared with those toner particles such as toner carriers and paper lints are removed by the rotatable fur brush 52 preliminary at the upstream portion of the contacting zone G. The contaminants of small size, mainly toner particles, and some of the contaminants of large size may escape from the cleaning brush 52. These escaped contaminants are scraped by the cleaning edge 51a of the blade 51 which is in contact with the surface of the photoconductive drum 21 under pressure. Mainly the fine toner particles and some toner carriers and paper lints are together accumulated on the cleaning edge 51a and along the surface of the photoconductive drum 21 adjacent to the cleaning edge 51a, forming a pile 99 of contaminants (refer to Fig. 4). The upper part of the pile 99 is taken off by the rotatable cleaning brush 52 at the downstream portion of the contacting zone G As a result, the cleaning edge 51a can be free from undesirable contaminants of large size such as toner carrier particles and paper lints, resulting in the reduction of the cleaning edge leading to an extension of the life of the blade 52. This is one of the features of the cleaning unit 29 according to the present invention. Herein, the reason that the cleaning brush 52 engages with the surface of the drum 21 in coming down movement is described briefly. If the fur brush 52 is rotated in the opposite direction, namely counter-clockwise direction, the surface of the fur brush, namely the tips of the hairs of the brush, would move upwardly at the contacting zone G. By this movement of the brush hair tips, the residual contaminants on the surface of the photoconductive drum could be removed. However, the removed contaminants would be ejected upwardly and ejected outside the cleaning housing 54 from the opening 54b, scattering inside the recording apparatus and causing various problem. Thus, the upwardly moving surface of hair tips is not suitable for removing the residual contaminants scraped by the blade 51. The contaminants of large size which are brushed away by the rotatable fur brush 52 and the contaminants of small size which are scraped off by the blade 51, are carried by the flow of air which is generated by air suctioned into the cleaning housing 54 through the opening 54b of the cleaning housing 54. The contaminants carried by the air flow are transferred and introduced into the toner recovering box 71 through the duct 56. The thus cleaned portion of the photoconductive drum 21 is moved to the optical exposing station A again for subsequent forming operation of a latent image. Since the structure and the function of the cleaning unit 29 is the focusing point of the present invention, more detailed additional description of features and advantages thereof is provided. In the cleaning unit 29, the blade 51, the rotatable fur brush 52 and the suction means 53 work in cooperation by the aid of the cleaning housing 54. Firstly, the rotatable fur brush 52 preliminarily removes the toner carriers and paper lints having large size compared with toner particles before the cleaning edge 51a starts to scrape contaminants attached to the surface of the photoconductive drum 51 as described above. As a result, the probability of contacts between contaminant particles of large size and the cleaning edge 51a is substantially reduced, since abrasion of the cleaning edge 51a is caused mainly by the contaminants of large size in contact with the cleaning edge 51a. Therefore, direct contact of the contaminants of large size to the cleaning edge 51a should be substantially avoided. Thus, the life of the blade 51 is prolonged and longer than that with the absence of the rotatable fur brush 52. Secondly, the rotatable fur brush 52 takes off the upper part of the pile 99 of the contaminants accumulated on the cleaning blade and on the vicinity thereof. Major part of the pile 99 is composed of fine toner particles since such fine particles can pass through the hairs, and a minor part of the pile 99 is composed of large particles such as toner carriers and paper lints which tend to be concentrated at the upper portion of the pile 99, due to the associated small vibration of the relevant elements of the apparatus. Accordingly, the large sized particles escaping from the brush hairs may be captured again by the brush hairs at the top of the pile 99 and are removed. Meanwhile, toner particles appears to act as lubricant to reduce the friction between the blade 51 and the surface of the photoconductive drum 21, suppressing scratching of the surface caused by the blade 51. However, an excessive amount of piled toner particles tends to scatter inside the recording apparatus with undesirable results. The above described contaminant particles of large size in minority and a part of excessive toner particles both of which exist in the upper part of the pile 99 are now taken off at the downstream portion of the contacting zone G. This serves to prolong the life of the blade 51 and prevent the inside of the apparatus from contamination by attached fine toner particles. Thirdly, as described before, the air-tight enclosing structure of the cleaning unit 29, except for the opening 54b, serves to create air flow. As shown in Fig. 2, narrow space 90a is formed between the cleaning housing 54 and the fur brush 52 along the upper portion of the surface of the fur brush 52, allowing air flow Wa to pass, and another narrow space 90b is formed along the lower portion of the fur brush 52, allowing air flow Wb to pass. The space 90b is surrounded by the photoconductive drum 21, the blade 51 and the hairs (bristles) of the rotatable cleaning brush 52, and external air is sucked through the small clearances of the hairs densely planted. The air flow Wb is effective to remove contaminants scraped by the blade 51 and prevent the contaminants from attaching to the surfaces adjacent to the cleaning edge 51a; while, the air flow Wa may serve to remove the contaminants attached to the fur brush hairs. However, the velocity of the air flow Wb may be much lower than that of the air flow Wa, since pneumatic resistance to the air flow Wb is high because the air flow Wb must run through the densely planted hairs of the fur brushes 52, while the air flow Wa may run through the space 90a without remarkable pneumatic resistance. In order to enhance the velocity of the air flow Wb, an improved rotatable cleaning brush has an air flow passage through which external air is introduced. Fig. 5 is a perspective view of the improved fur brush 70, having a single spiral groove-like space 71 which is formed by the selective absence of the brush hairs 71a planted on a rotatable solid shaft 72. External air may be sucked and flows through the spiral space 71 during the rotation of the fur brush 70. As for the dimension of the groove-like space 71, there is provided an example in which, the width H of the space groove 71 is 2 millimeter and the spiral pitch is 50 millimeter when the diameter of the fur brush 70 is 52 millimeter and the length thereof is 340 millimeter. Although, the spiral shown in Fig. 5 is a single spiral, a multiple spiral such as double spiral is also applicable. Fig. 6(a) and Fig. 6(b) are respectively front and side cross-sectional views of another improved fur brush 73 having a shaft 74 of hollow cylinder having an inner space 74a. The shaft 74 has an opening 75 at the end surface to suck in external air. The hollow shaft 74 has a plurality of small holes 76 in the cylindrical side-wall, distributed in the axial direction of the shaft 74. The small holes 76 are opened radially, and the angular positions with respect to the axis of the holes 76 are distanced by several phase angle such as four radial directions mutually spaced by 90 degrees. Naturally, the brush hairs 78 (bristles) are absent on the holes 76, resulting in cylindrical spaces 77. The air sucked in through the opening 75 as indicated by arrows M flows through the inner space 74a of the shaft, and is radially ejected as indicated by arrows N through the spaces 77 when the spaces 77 are opened toward the space 90b (refer to Fig.2) depending on the angular position of the fur brush 73. Other modified air flow passages formed in the fur brush are not described. Employing an electrophotographic recording apparatus having the above-described structural configuration including a rotatable cleaning brush 70 of Fig. 5, a repeated printing operation test was conducted for long duration in order to confirm the effect of the invention. The surface velocity of the photoconductive drum 21 was 265 mm/sec. and that of the fur brush 52 was selected from 530 to 790 mm/sec. As the result, the abrasion life of the blade 51 was extended from 75.000 sheets of A4 size (210 mm x 297 mm) in average with respect to a prior art apparatus to approximately 250.000 sheets of the same size, by approximately 3,5 times. Fig. 7(a) and Fig. 7(b) are respectively front and side cross-sectional views of the rotatable cleaning cylinder 83 having a shaft 84 of hollow cylinder having an inner space 84a. The above-described cleaning brushes 52 of Fig. 5 and Fig. 6 can be replaced by a rotatable cleaning cylinder 83 having a cleaning layer 88 made of sponge-like material such as plastic foam formed around a shaft 84 with a cylindrical surface. The shaft 84 has an opening 85 at the end surface to suck in external air. The hollow shaft 84 has a plurality of small holes 86 in the cylindrical side-wall, distributed in the axial direction of the shaft 84. The small holes 86 are opened radially, and the angular positions with respect to the axis of the holes 86 are distanced by several phase angles such as four radial directions mutually spaced by 90 degrees. Naturally, the cleaning layer 88 is absent on the holes 86, resulting in cylindrical spaces 87. The air sucked in through the opening 85 as indicated by arrows M, flows through the inner space 84a of the shaft, and is radially ejected as indicated by arrows N, through the spaces 87 when the spaces 87 are opened toward the space 90b depending on the angular position of the fur brush 83. Other modified air flow passages formed in the cleaning layer are not described. In the cleaning layer 88 a groove-like air passage space is formed in the layer. Fig. 8 is a perspective view of a cleaning cylinder 93 corresponding to the cleaning brush shown in Fig. 5(a). In the same manner, a groove-like spiral air passage 92 is formed in a rotatable cleaning layer 91 made of sponge-like polymer material, formed around a solid shaft 94. External air can be sucked inside the cleaning housing 54 in the same manner as the cleaning brush 70 of Fig. 5. In addition, as described above, with respect to the recording apparatus of Fig. 1, there is an additional advantage that the structure for holding the blade is very simple. This is because cleaning capability of the cleaning unit 29 according to the present invention is favorably high with the result that the blade 51 may always engage the surface of the photoconductive drum 21 regardless the operation steps of the recording apparatus. If a blade engages the surface of a drum during cleaning operation only, and is disengaged during other operations of the apparatus, in order to protect the blade and the surface of the drum, this results in the requirement for a complicated structure of the supporting means of the blade, raising the cost of the recording apparatus. The present invention has been described by referring to several embodiments, however, modification of the present invention within the scope of the subject matter of the present invention as claimed is possible. Since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact methods and applications shown and described, all suitable modifications and equivalents which may be resorted to fall within the scope of the invention as claimed are considered to be embraced.

Claims: A recording apparatus of image transfer type comprising: a rotatable image bearing means (21) having a recording medium layer formed thereon for forming a toner image on the surface of said recording medium layer; a toner image transfer means (26) for transferring said toner image to a printing medium; and a cleaning unit (29) disposed downstream of said toner image transfer means with respect to the rotation of said image bearing means (21), for cleaning the surface of said image bearing means (21) after image transfer, said cleaning unit comprising: a blade (51) extending in parallel with the axis of rotation of said image bearing means and whose cleaning edge (51a) is in line contact with the downwardly moving surface of said recording medium layer under a predetermined pressure for scraping said surface to remove contaminants remained on said surface; rotatable cleaning means (52) extending in parallel with the axis of rotation of said image bearing means (21), disposed immediately upstream of said blade (51), engaging with said surface of said recording medium layer for removing contaminants remained on said surface; characterised by said toner image transfer means (26) being disposed adjacent to the top portion of said image bearing means (21), by shielding means (54) closely enclosing said blade (51) and said rotatable cleaning means (52), having an opening (54b) for sucking external air and for allowing the contact of said blade (51) and said rotatable cleaning means (52) with said surface of said recording medium layer, and a connecting outlet (54c); and by suction means (53) air-tightly connected to said connecting outlet (54c) of said shielding means for evacuating the space inside said shielding means. A recording apparatus according to claim 1 wherein said image bearing means (21) is a drum. A recording apparatus of claim 1 or 2, wherein said recording medium layer contains photosensitive material, preferably photoconductive material. A recording apparatus of claim 1 or 2, wherein said recording medium layer contains a dielectric insulating material. A recording apparatus of any preceding claim, wherein said image bearing means (21) and said rotatable cleaning means (52) are rotated in the opposite angular directions to each other, and the circumferential velocity of said rotatable cleaning means is higher than that of said image bearing means. A recording apparatus of any preceding claim, wherein said rotatable cleaning means (52) has an air passage capable of sucking external air into a space which is surrounded by surfaces of said rotatable cleaning means, said blade, and said image bearing means (21) and connected to said suction means, whereby the velocity of the air flow generated in said space is enhanced with the result that said contaminants removed from the surface of said image bearing means (21) by said blade (51) and said rotatable cleaning means are enhanced. A recording apparatus of any preceding claim, wherein said rotatable cleaning means is a rotatable brush having a shaft supported rotatably around the axis thereof. A recording apparatus of claim 7, wherein said rotatable cleaning brush has hairs (71a) radially planted on said shaft, and, as air passage, a groove-like space (71) is formed among said hairs, said space extending along said shaft (72) in a spiral. A recording apparatus of claim 7 or 8, wherein said shaft (74) is a hollow shaft which has a perforated cylinder wall and an opening (75) provided in at least one of the ends of said shaft and directed toward external air space. A recording apparatus of claim 6, wherein said rotatable cleaning means is a rotatable cylinder (83), having a shaft (84) rotatably supported around the axis thereof, and a layer (88) made of sponge-like material formed around said shaft with a cylindrical surface. A recording apparatus of claim 10, wherein said air passage is a groove-like space (92) formed in said layer (91) of sponge-like material, said space extending along said shaft in spiral. A recording apparatus of claim 10 or 11, wherein said shaft is a hollow shaft (84) having an inner space (84a) and at least one end (85) opened toward external air space, and said rotatable cleaning cylinder has a plurality of holes (86, 87) which pass through said cylinder wall of said shaft and said layer of sponge-like material connecting said inner space of said shaft to external air space. A recording apparatus of any preceding claim, wherein said shielding means further comprises a rail member (54a) extending in a direction parallel to the axis of said image bearing means (21), and said blade (51) is supported by a supporting member (55) such that said blade (51) is mountable and dismountable by sliding movement along said rail member by the aid of said supporting member which is formed to have a fitting groove slidable over said rail member. An electrophotographic recording apparatus comprising: a photoconductive drum (21) rotatable around the axis thereof for forming a toner image on the cylindrical surface of said photoconductive drum, the axis being approximately horizontally positioned; a toner image transfer means (26) disposed adjacent to the top portion of said photoconductive drum (21) for transferring said toner image to a printing medium; and a cleaning unit (29) disposed downstream of said toner image transfer means with respect to the rotation of said photoconductive drum, for cleaning said cylindrical surface of said photoconductive drum (21) after image transfer, said cleaning unit comprising: a blade (51) extending in parallel with said axis of said photoconductive drum, being directed upwardly, having a cleaning edge (51a) in line contact with the downwardly moving cylindrical surface of said photoconductive drum (21) under predetermined pressure for scraping said cylindrical surface to remove contaminants remained on said cylindrical surface; and rotatable cleaning means (52) made of elastic material extending in the direction of said axis of said photoconductive drum, disposed immediately upstream of said blade without contacting said blade, engaging with said cylindrical surface for removing contaminants accumulated on the cleaning edge of said blade (51) and in a space in the vicinity of the cleaning edge, whereby larger particles of said contaminants are removed and smaller remaining particles of contaminants serve to lubricate said blade edge (51a) at the drum (21) surface. An electrophotographic recording apparatus according to claim 14, wherein the rotatable cleaning means is a brush (52), and at the contact of the drum (21) and the brush, their suface velocities are directed downwards and the surface velocity of the brush is higher than that of the drum. An electrophotographic recording apparatus according to claim 15, wherein the surface velocity of the brush is from two to three times that of the drum.

Inventors: TONOMOTO, YOSHIHIRO
Applicants: FUJITSU LIMITED
Application year: 1988
Main classification: G03G21
IPC codes: G03G21