Process unit for image forming apparatus

Abstract: A process unit (10) for an image forming apparatus (20), the process unit (10) being loadable into and removable from the image forming apparatus (20) as a single integral unit, the unit (10) comprising a unit case (3) housing at least a photosensitive member (12), for example a drum or a belt, on a surface of which a latent image is formed when the process unit (10) is loaded into the image forming apparatus (20) and the apparatus put to use, and a conductive brush type charger (2, 2a, 2b), for electrostatically charging the latent image formation surface of the photosensitive member (12), the charger (2, 2a, 2b) comprising a plurality of conductive brush fibers (2a) having tips arranged for contacting the latent image formation surface substantially perpendicularly, for application of charging voltage through the fibers.

Description: The present invention relates to a process unit for image forming apparatus. A process unit includes units for carrying out image formation, when the process unit is loaded into image forming apparatus, and facilitates maintenance of the image forming apparatus, which can be effected by interchanging the process unit. An image forming apparatus such as an electrophotographic copying apparatus or printer comprises the following units for carrying out image formation: a photosensitive drum consisting of a cylindrical base body, rotatable around an axis of rotation, with a photosensitive layer around the outer wall surface of the cylindrical base body; a charging unit for charging the photosensitive layer; a light irradiating unit for forming an electrostatic latent image on the photosensitive layer by irradiating a scanning light beam on to that layer in accordance with an electrical image signal; a developing unit for developing the electrostatic latent image on the photosensitive layer so as to form a toner image on the surface of the photosensitive layer in accordance with the latent image; a transfer unit for transferring the toner image to an appropriate sheet of paper; an erasing unit for extinguishing the electrostatic latent image; and a cleaning unit for cleaning off toner left on the surface of the photosensitive layer. As time passes, these units involved in image formation become worn and dirty, so that their characteristics and performances are changed and subject to deterioration. Therefore, these units have to be cleaned or interchanged by an expert. Above all, the photosensitive unit and the charging unit are required to be interchanged (exchanged). It has been proposed that some of these units, for example, the photosensitive drum and the charging unit, be integrated into a unit called a "process unit", and that this process unit be interchanged. Sometimes, the developing unit and the cleaning unit might also be integrated into the process unit. The light irradiating unit, the transfer unit and the erasing unit are not so appropriate for integration into the process unit, because these units do not need to be interchanged so often, so that these units are installed in a main body of the image forming apparatus and apertures provided to give them access to the process unit. By the provision of such a process unit, the problems of cleaning and interchanging units and parts are mitigated. The need for an expert to carry out these tasks is eliminated, so that maintenance of the image forming apparatus can be performed by interchanging the process unit without the need to call in a maintenance expert. Usually, in a previously proposed process unit, a corona discharge type charger, which will be simply called a "corona charger" hereinafter, has been used as the charging unit. However, there has been a problem in that the corona charger requires a high voltage, for example several kilovolts (kV), for corona discharging, and ozone is generated during the corona discharging. Because of the need for high voltage, a high voltage power supply must be provided in the main body of the image forming apparatus, resulting in increased size, weight and cost of the image forming apparatus. Moreover, because of the ozone generation, the photosensitive drum tends to be damaged, resulting in a reduced life for the photosensitive drum and therefore a reduced life for the process unit. In a process unit using a corona charger, ozone protection means, such as an ozone filter and an ozone exhauster, for protecting the photosensitive drum from ozone damage may be provided for the process unit. Such ozone protection means are effective to prolong the life of the process unit; that is, employing ozone protection means, on average 5,000 sheets can be copied by one process unit. However, the provision of such means make the process unit complicated, the size and weight of the image forming apparatus large and heavy respectively, and the cost of the process unit high. Furthermore, these means pollute the air around the image forming apparatus due to exhausted ozone. Process units have been disclosed in the following patents:- US-A-4,538,896 (1985); US-A-4,575,221 (1986); and JP-A-59-26745 (1984). All of these process units include corona chargers. Fig. 1 is a schematic diagram illustrating a process unit 100 as disclosed in US-A-4,575,221. The process unit 100 is provided in image forming apparatus, and in the process unit a photosensitive drum 101, a corona charger 102, a developing unit 103 and a toner cleaner 104 are integrated together. The corona charger 102 is connected to a high voltage power supply 105 of the image forming apparatus, provided externally of the process unit 100. The process unit 100 is effective for facilitating operation and maintenance of the image forming apparatus, but, as mentioned above, the corona charger 102 produces ozone, resulting in damage to the photosensitive drum 101. The photosensitive drum 101 is composed of a cylindrical base body 1012 with a photosensitive layer 1011 provided around the outer wall surface of the cylindrical base body 1012. The photosensitive layer 1011 is made of inorganic sensitive material such as zinc oxide or a selenium compound. However, recently, organic photosensitive material, composed of organic compound, has been proposed for use for the photosensitive layer instead of an inorganic photosensitive material. This is because the inorganic photosensitive material is injurious to the human body, so that a process unit using inorganic photosensitive material for the photosensitive layer cannot be disposed of easily. The organic photosensitive material is not injurious, so that a process unit using organic photosensitive material for the photosensitive layer can be disposed of more readily and safely. Moreover, the cost of the organic photosensitive material is lower than that of the inorganic material. However, there is a problem in that the organic photosensitive material is susceptible to damage by ozone. Consequently, the previous process unit using a corona charger has suffered the following problems:- (1) because of ozone generation, the photosensitive layer is easily damaged; (2) because of ozone generation, the life of the photosensitive layer cannot be made so long, even when generated ozone is exhausted from the process unit, resulting in a reduced life for the process unit; (3) because of ozone generation, air around the image forming apparatus is polluted when the generated ozone is exhausted from the process unit; (4) because of ozone generation, economical, non-injurious and easily disposable organic photosensitive material cannot easily be used for the photosensitive layer; (5) because a high voltage power supply must be provided in the image forming apparatus, the size, weight and cost of the image forming apparatus cannot be reduced; and (6) because of the use of a corona charger in the process unit, it is difficult to charge the photosensitive layer uniformly because a clogging problem occurs with corona discharging as time passes, producing an irregular charge on the photosensitive layer. Patent Abstracts of Japan, Vol. 5, No. 191 (P-92) (863), 5th December 1981 (JP-A-56 114978) discloses an image forming apparatus including an assembly comprising a photosensitive member and a conductive brush charger having conductive brush fibers for electrostatically charging a surface of the photosensitive member by making the tips of the conductive brush fibers touch to the surface of said photosensitive member and applying a charging voltage to the surface of the photosensitive member through the conductive brush fibers. This assembly is not provided as a process unit loadable into the image forming apparatus. According to the present invention there is provided an assembly for use in an image forming apparatus, the assembly comprising:- a photosensitive member transferable in a first direction; and a conductive brush type charger comprising a plurality of conductive brush fibers, arranged in a second direction, perpendicular to the first direction, for electrostatically charging a surface of the photosensitive member uniformly by making the tips of the conductive brush fibers touch to the surface of said photosensitive member and applying a charging voltage to the surface of the photosensitive member through the conductive brush fibers; characterised in that the photosensitive member and the conductive brush type charger are comprised in a process unit which is loadable into the image forming apparatus, the process unit further comprises a unit case for housing the photosensitive member and the conductive brush type charger, and means for supporting the conductive brush type charger so as to position the tips of the conductive brush fibers out of contact with the surface of said photosensitive member whilst the process unit is not loaded into the image forming apparatus. According to the present invention there is also provided an image forming apparatus comprising:- a photosensitive member transferable in a first direction; a conductive brush type charger comprising a plurality of conductive brush fibers, arranged in a second direction, perpendicular to the first direction, for electrostatically charging a surface of the photosensitive member uniformly by making the tips of the conductive brush fibers touch to the surface of said photosensitive member and applying a charging voltage to the surface of the photosensitive member through the conductive brush fibers; and further including developing means for developing an electrostatic latent image so as to form a toner image on the surface of the photosensitive member; and transfer means for transferring said toner image on said photosensitive member to a medium; characterised in that the photosensitive member and the conductive brush type charger are comprised in a process unit which is loadable into the image forming apparatus, and the process unit further comprises a unit case for housing the photosensitive member and the conductive brush type charger, and in that means are provided for supporting the conductive brush type charger so as to position the tips of the conductive brush fibers out of contact with the surface of said photosensitive member whilst the process unit is not loaded into the image forming apparatus. An embodiment of the present invention can overcome problems associated with previously proposed process units, occurring due to the use of corona chargers. Use of an embodiment of the present invention can result in extension of the life of the photosensitive layer, resulting in extended life for a process unit. An embodiment of the present invention can provide a process unit which does not result in pollution of air around the image forming apparatus by ozone. Use of an embodiment of the present invention can facilitate disposal of a process unit since a photosensitive material can be used which presents lesser disposal problems. An embodiment of the present invention can provide an image forming apparatus small in size and light in weight, by excluding a high voltage power supply for a charging unit from the image forming apparatus. An embodiment of the present invention can provide a process unit with a simple construction, not including an ozone filter and exhauster. An embodiment of the present invention can provide for apparatus which can form a stable image at low cost. In an embodiment of the present invention a conductive brush type charger, which will be simply called a "brush charger" hereinafter, is used in a charging unit in a process unit, instead of a corona charger. An organic photosensitive material is used for the photosensitive layer in the process unit, instead of inorganic photosensitive material. The brush of the brush charger is made of conductive material, and the photosensitive layer can be charged by making the brush touch the surface of the photosensitive layer and by applying 500 V to 1,500 V to the surface through the brush. Accordingly, the brush charger does not require as high a voltage as a corona charger, and ozone is not generated (or is generated only in small amounts). Therefore organic photosensitive material can be used for the photosensitive layer. Potential benefits are: prolonged life of the photosensitive drum, and thus prolonged life of the process unit; keeping the air around the image forming apparatus clean; allowing the process unit to be more easily disposed of; simplification of the structure of the process unit; enabling the process unit and the image forming apparatus to be small in size and light in weight because ozone protection means are not necessary in the process unit and a high voltage power supply is not necessary in the main body of the image forming apparatus; reduction of cost of the process unit and the image forming apparatus respectively; and the photosensitive layer can be charged uniformly because the brush charger does not produce the clogging phenomenon. Reference is made, by way of example, to the accompanying drawings, in which:- Fig. 1 is a schematic cross-sectional view illustrating a prior art process unit; Fig. 2 is a cross-sectional view schematically illustrating a process unit for assistance in explaining embodiments of the invention; Fig. 3 is a perspective view of the process unit of Fig. 2; Fig. 4 is a side view schematically showing the internal structure of an electrophotographic printing apparatus using in a process unit according to Fig. 2, Fig. 5 is a side view schematically illustrating electric connection of a process unit according to Fig. 2 in an electrophotographic printing apparatus; Fig. 6 is a graph giving plots of variation of the concentration of ozone as time passes, comparing cases in which a brush charger is used as in an embodiment of the present invention and in which a corona charger is used as in the prior art; Fig. 7(a) is a graph giving a plot of charged potential distributed on a surface of a photosensitive drum along the axial direction of the photosensitive drum, obtained by a brush charger in a process unit as in an embodiment of the present invention; Fig. 7(b) is a plot of charged potential distributed on a surface of a photosensitive drum along the axial direction of the photosensitive drum in a prior art process unit having a corona charger; Figs. 8, 9, 10(a) and 10(b) are cross-sectional views illustrating process units for assistance in explaining embodiments of the invention, being modifications of the process unit of Fig. 2; Fig. 8 is a cross-sectional view of a process unit including a photosensitive drum, a brush charger and a developing unit; Fig. 9 is a cross-sectional view of a process unit including a photosensitive drum, a brush charger and a cleaner; Fig. 10(a) is a cross-sectional view of a process unit including a photosensitive drum, a brush charger, a developing unit and a blade cleaner; and Fig. 10(b) is a cross-sectional view of a process unit including a photosensitive drum, a brush charger, a developing unit and a brush cleaner; Fig. 11(a) is a cross-sectional view, schematically showing a process unit for assistance in explaining embodiments of the invention; Fig. 11(b) is a side view schematically showing electric connection of the process unit of Fig. 11(a) in an electrophotographic printing apparatus; Fig. 12 is a cross-sectional view, schematically showing a process unit for assistance in explaining embodiments of the invention; Fig. 13(a) is a schematic cross-sectional view of a process unit according to an embodiment of the invention, the process unit not being loaded in an electrophotographic printing apparatus; Fig. 13(b) is a schematic cross-sectional view of a process unit of Fig. 13(a) loaded into an electrophotographic printing apparatus; Fig. 14 is a side view schematically showing the internal structure of an electrophotographic printing apparatus using the process unit of Fig 13(a); Fig. 15(a) is a schematic cross-sectional view of a process unit according to another embodiment of the present invention; Fig. 15(b) is a side view schematically showing the internal structure of an electrophotographic printing apparatus using the process unit of Fig. 15(a); Fig. 16 is a side view schematically showing the internal structure of an electrophotographic printing apparatus using the process unit of Fig. 15(a); Fig. 17 is a schematic cross-sectional view of a process unit modified from that of Fig. 15(a), according to an embodiment of the present invention, including a developing unit besides a photosensitive drum and a brush charger; Fig. 18 is a schematic cross-sectional view of a process unit modified from that of Fig. 15(a), according to an embodiment of the present invention, including a developing unit and a cleaner besides a photosensitive drum and a brush charger; and Fig. 19 is a cross-sectional view schematically showing a further process unit for assistance in explaining embodiments of the invention, including a photosensitive belt instead of a photosensitive drum. Process units of image forming apparatus, such as electrophotographic printing apparatus, will be described below for assistance in explaining embodiments of the invention. Fig. 2 is a diagram illustrating a process unit. Fig. 3 is a perspective view of this process unit and Figs. 4 and 5 illustrate the process unit loaded into photographic printing apparatus, Fig. 4 being a cross-sectional view and Fig. 5 a side view. In Figs. 2, 3, 4 and 5, the same reference signs designate the same or similar units or parts. In Fig. 2, a process unit 10 comprises a unit case or housing 3, a conductive brush type charger (brush charger) 2 fixed to an inner surface of the unit case 3, and a photosensitive drum 1 housed in the unit case 3. The photosensitive drum 1 consists of a cylindrical base body 12 rotating in a direction 14 around an axis 13 and a photosensitive layer 11 mounted around the outer peripheral wall of the cylindrical base body 12. Details of the process unit 10 will be explained below with reference to Fig. 4. 3a to 3d are apertures in the case 3, providing access for other units to the process unit. The brush charger 2 consists of a conductive base 2b which will be simply called a "base 2b" hereinafter, and a conductive brush 2a which will be called a "brush 2a" hereinafter. The brush 2a consists of a plurality of brush fibers and the brush 2a is fixed to a curved surface of the base 2b so that each brush fiber stands approximately perpendicularly to the curved surface. The brush may be, for example, fabricated by weaving a cloth made of carbon-dispersed chemical fibers such as carbon-dispersed rayon, acrylic or nylon, and raising nap on the cloth, and the brush charger may be fabricated by bonding the cloth to the base by a conductive adhesive so that the nap, consisting of a plurality of carbon-dispersed chemical fibers, stands perpendicularly to the base. Thickness and length of each carbon-dispersed chemical fiber (simply called a brush fiber hereinafter) and density of the brush fibers are carefully selected for obtaining uniform charge on the photosensitive layer. Voltage applied to the brush and current flowing through each brush fiber, in other words the resistance of each brush fiber, are also selected for obtaining uniform charge on the photosensitive layer. For a brush charger the length and the thickness of the brush fibers and the density of the brush fibers are important. Particularly, maintenance of an appropriate distance between the surface of the base of the brush charger and the surface of the photosensitive drum is important for obtaining stable and uniform charge on the surface of the photosensitive drum. Therefore, the usage of a brush charger in a process unit is more effective for realizing uniform charge on the surface of a photosensitive drum, as compared with the use of an individually interchangeable brush charger. Since the brush charger is, in embodiments of this invention, packed in the process unit, the appropriate distance can be determined in advance and fixed in the course of fabrication of the process unit. In Fig. 3, the photosensitive drum 1 is fixed to the unit case 3 at the axis 13 of the drum 1 so as to be rotatable around the axis 13. A driving unit 32, provided in the main body of the electrophotographic printing apparatus and shown in Fig. 5, drives the photosensitive drum 1 through a gear train consisting of gears 14 and 33. Fig. 4 is a schematic side view of the internal structure of an electrophotographic copying or printing apparatus 20 in which the process unit is loaded. The electrophotographic copying apparatus 20 has a light emitting diode (LED) array 24 for light irradiation, rod lens array 25 for focusing the light on to the surface of the photosensitive drum 1, a developing unit 26 for developing an electrostatic latent image on the surface of the photosensitive drum 1 so as to produce a toner image thereon, a transfer belt 27 for transcribing the toner image on to an appropriate sheet 50, of paper for example, a fixing device 28 to fix the toner image by heating the sheet 50, a cleaner 29 for removing toner left on the surface of the photosensitive drum 1 and an angle structure 30 and 31 is for sliding and positioning the process unit 10 in the electrophotographic printing apparatus 20. The process unit 10 is loaded in the electrophotographic printing apparatus 20 so that the process unit 10 is set on the angle structure 30 and 31 which is used as a guide rail placed in parallel with the axis 13 of the photosensitive drum 1. Fig. 5 is a side view schematically illustrating the electrophotographic printing apparatus 20 in which the process unit 10 is loaded, in which electric connection of the process unit 10 to the electrophotographic printing apparatus 20 is indicated. When the process unit 10 is loaded, an electrical contact 45 attached to the process unit 10 (see also Fig. 3) is connected to a spring contact 61 provided to the side of the electrophotographic printing apparatus 20, so that the conductive base 2b of the brush charger 2 is connected to a power supply 60 generating 500 V to 1,500 V and the surface of the photosensitive layer 11 can be charged. Thus, using lower than 1,500 V for the charging voltage, there is no real possibility of ozone being generated significantly. In Fig. 5, the photosensitive drum 1 is rotated by a driving unit 32 through a gear train consisting of gears 33 and 14. After removing a cover 34 of the electrophotographic printing apparatus 20, the process unit 10 is loaded into the main body of the electrophotographic printing apparatus so as to be slid on the angle structure 30 and 31 in a direction 80. Variation of the concentration of ozone with time is illustrated in Fig. 6, comparing electrophotographic apparatus using a brush charger as in an embodiment of the present invention with a prior art apparatus using a corona charger. In Fig. 6 the plotted line giving lower ozone concentration levels relates to the brush charger, the plotted line giving higher ozone concentration levels relates to the prior art apparatus. As indicated in Fig. 6, the concentration of ozone in the case of an apparatus with a brush charger is sufficiently less than an acceptable limit 0.1 ppm. Before the charging characteristic of the photosensitive drum 1 suffers deterioration because of toner adhering to brush fibers and because of weakened brush fibers due to the compression of the brush fibers so that they touch the surface of the photosensitive drum, the process unit 10 is interchanged with a new one. The interchange is performed after printing several thousands to several tens of thousands of sheets 50. Distribution of charged potential provided by the brush charger as used in an embodiment of the invention is illustrated in Fig. 7(a), whilst that provided by a corona charger is illustrated in Fig. 7(b). In Figs. 7(a) and 7(b), the charged potential is plotted against distance across the surface of photosensitive drum 1 measured from an appropriate point along the axial direction of the photosensitive drum 1. As seen in Figs. 7(a) and 7(b), the charge distribution provided by the brush charger is more uniform than that provided by the corona charger. The process unit of Fig. 2 includes the photosensitive drum 1 and the brush charger 2, but a developing unit and a cleaner can be included in the process unit, as illustrated in Figs. 8, 9, 10(a) and 10(b). In Figs. 8, 9, 10(a) and 10(b), the same reference signs as are used in Fig. 2 designate the same or similar units or parts. A process unit, modified from the process unit of Fig. 2, including the photosensitive drum 1, the brush charger 2 and a developing unit 5 in the unit case 3 is shown in Fig. 8; a modified process unit, including the photosensitive drum 1, the brush charger 2 and a blade cleaner 6 in the unit case 3 is shown in Fig. 9; a process unit, including the photosensitive drum 1, the brush charger 2, the developing unit 5 and the blade cleaner 6 in the unit case 3 is shown in Fig. 10(a); and a process unit, including the photosensitive drum 1, the brush charger 2, the developing unit 5 and a brush cleaner 6' in the unit case 3 is shown in Fig. 10(b). A cross-sectional view of a further process unit is shown in Fig. 11(a), and a side view of this process unit is illustrated in Fig. 11(b). Electric connection of the process unit to electrophotographic printing apparatus in which it is installed is shown in Fig. 11(b). In Fig. 11(a), the same reference signs as in Fig. 2 designate the same or similar units or parts, and in Fig. 11(b), the same reference signs as in Fig. 5 designate the same or similar units or parts. In the process unit of Figs. 11, the brush charger 2 is rotated around an axis 2d placed in parallel with the axis 13 of the photosensitive drum 1. This rotating type brush charger 2, has a feature that the fibers of the brush 2a are not contaminated by toner left on the surface of the photosensitive drum 1 and not weakened by strong compression during long operation. Fig. 12 shows a schematic cross-sectional view of another process unit. In Fig. 12, the same reference signs as in Fig. 2 designates the same or similar units or parts. In the process unit of Fig. 12, the charging unit 2 consists of a conductive layer 2c made of a conductive paint painted on the inner surface of the unit case 3 and the conductive brush 2a provided on the conductive layer 2c so that the brush fibers stand approximately perpendicularly to the conductive layer 2c and the tips of the brush fibers touch to the surface of the photosensitive drum 1. In this instance, as in others, the unit case may be electrically non-conductive. The process unit of Fig. 12 may be modified in several respects, in the same way as the process unit of Fig. 2 can be modified, for example as shown in Figs. 8 to 10(b). The process unit of Fig. 12 has the advantages of low cost and small size because the brush charger 2 does not have the conductive base 2b. Fig. 13(a) is a schematic cross-sectional view of a process unit in accordance with an embodiment of the present invention. In Fig. 13(a), the same reference signs as in Fig. 2 designate the same or similar units or parts. In Fig. 13(a), the brush charger 2 is sustained by a spring 47 fixed to the inner surface of the unit case 3. Whilst the process unit 10 is not loaded in imaging apparatus, for instance whilst it is in stock, the brush charger 2 is fixed to the unit case 3 by inserting a spacer 44, compressing the brush charger 2 toward the inner surface of the unit case 3 against the elastic force of the spring 47, for separating the tips of the brush fibers of the brush 2a from the surface of the photosensitive drum 1. This avoids the brush fibers being weakened by a long period with the tips contacting the surface of the photosensitive drum 1. When the process unit 10 of Figs. 13 is loaded in the electrophotographic printing apparatus, the spacer 44 is manually removed from the electrophotographic printing apparatus after the process unit 10 has been loaded, so that the brush charger 2 is automatically pushed toward the photosensitive drum 1 by the elastic force of the spring 47 until the base 2b is stopped by a stopper 49 provided internally of the unit case 3. The brush charger 2 is positioned by the stopper 49 so that the tips of the brush fibers are uniformly touched to (in uniform contact with) the surface of the photosensitive drum 1 (Fig. 13(b)). Fig. 14 is a side view schematically showing the internal structure of electrophotographic printing apparatus into which the process unit 10 of Figs. 13 is loaded. In Fig. 14, the same reference signs as in Fig. 11(b) designate the same or similar units or parts. With the process unit 10 of Figs. 13, the life of the brush charger 2 is sufficiently long because the tips of the brush fibers do not touch to the surface of the photosensitive drum 1 whilst the process unit 10 is in stock. Fig. 15(a) is a schematic cross-sectional view of another process unit in accordance with an embodiment of the present invention. Fig. 15(b) is a side view schematically showing the internal structure of an electrophotographic printing apparatus into which the process unit of Fig. 15(a) is loaded. In Fig. 15(a), the same reference signs as in Fig. 2 designate the same or similar units or parts. In the process unit 10 of Fig. 15a, the base 2b is pulled toward the inner surface of the unit case 3 by springs 41 and 42 fixed to the inner surface of the unit case 3. So, before the process unit 10 is loaded into electrophotographic copying apparatus, the tips of the conductive brush fibers of the brush charger 2 are kept away from the surface of the photosensitive drum 1. The unit case 3 of the process unit has an aperture 3e at the location where base bar 2b is provided. A cross-sectional view illustrating the internal constitution of the process unit 10 is shown in Fig. 15(b). In Fig. 15(b), the same reference signs as in Fig. 4 designate the same or similar units or parts. In Fig. 15(b), LEDs 24 and rod lens array 25, the developing unit 26, transfer belt 27 and cleaner 29 are provided in the main body of electrophotographic printing apparatus 20, in correspondence to apertures 3a, 3b, 3c and 3d respectively. Meanwhile, the electrophotographic printing apparatus 20 has a protruding portion 43 which makes the tips of the conductive brush fibers of the conductive brush 2a touch the surface of the photosensitive drum 1, when the process unit is loaded into the electrophotographic printing apparatus 20. Fig. 16 is a side view schematically showing the internal structure of electrophotographic printing apparatus into which the process unit 10 of Fig. 15(a) is loaded. In Fig. 16, the same reference signs as in Fig. 5 designate the same or similar units or parts. When the process unit is loaded into the electrophotographic printing apparatus 20, the protruding portion 43 is relatively slid into the process unit 10, contacting the base bar 2b through the aperture 3e and pushing the bar 2b toward the photosensitive drum 1 against the elastic force of the springs 41 and 42. This makes the tips of the conductive brush fibers of the conductive brush 2a uniformly touch to the surface of the photosensitive drum 1. The protruding portion 43 is beveled at an inlet side looking from the loading process unit 10 so as to make the insertion of the process unit smooth. The process unit of Fig. 15(a) has advantage over the process unit of Fig. 13(a) because the former process unit can be loaded simply by inserting the process unit into the electrophotographic printing apparatus; it is not necessary to remove a spacer. The process unit 10 of Fig. 15(a) includes the photosensitive drum 1 and the brush charger 2. However, it is possible to include other processing units, such as the developing unit and the cleaner, in the process unit. A schematic cross-sectional view illustrating such a process unit including developing unit 5 together with the photosensitive drum 1 and the brush charger 2 is shown in Fig. 17. In Fig. 17, the same reference signs as in Fig. 8 designate the same or similar units or parts. A schematic cross-sectional view of such a process unit including a developing unit 5 and a cleaner 6 together with the photosensitive drum 1 and the brush charger 2 is shown in Fig. 18. In Fig. 18, the same reference signs as in Fig. 9 designate the same or similar units or parts. In the above embodiments of the present invention, a photosensitive drum 1 is employed in the process units. However, embodiments of the present invention can be applied not only to process units using photosensitive drums but also, for example, to process units using photosensitive belts as photosensitive members, as shown in Fig. 19. In Fig. 19, the same reference signs as in Fig. 2 designate the same or similar units or parts. In Fig. 19, a photosensitive belt 90 is driven by a driving roller 72 so as to go round, passing through guide rollers 73, and the brush 2a is touched to the surface of the photosensitive belt 90 passing over the surface of a sustainer 71 made of conductive material such as stainless steel. The photosensitive belt 90 is, for example, made of polyethylene terephthalate on which aluminum is evaporated, forming an aluminum layer on which organic photosensitive material is painted by a dipping method. The embodiments of Figs. 11, 13 and 15 may, for example, be adopted to use other photosensitive members, such as belts. An embodiment of the present invention provides a process unit to be loaded into an image forming apparatus, including at least a photosensitive member, for example a drum or belt to be rotated, and a conductive brush type charger for uniformly charging a surface of the photosensitive member by making tips of conductive brush fibers of the charger touch to the surface of the photosensitive member and applying a charge voltage of 500 V to 1,500 V to the surface of the photosensitive member through the conductive brush fibers for uniformly charging the surface of the photosensitive member. The present invention provides a process unit for an image forming apparatus, the process unit being loadable into and removable from the image forming apparatus as a single integral unit, the unit comprising a unit case housing at least a photosensitive member, for example a drum or a belt, on a surface of which a latent image is formed when the process unit is loaded into the image forming apparatus and the apparatus put to use, and a conductive brush type charger, for electrostatically charging the latent image formation surface of the photosensitive member, the charger comprising a plurality of conductive brush fibers having tips arranged for contacting the latent image formation surface substantially perpendicularly, for application of charging voltage through the fibers.

Claims: An assembly for use in an image forming apparatus, the assembly comprising:- a photosensitive member (1, 90) transferable in a first direction; and a conductive brush type charger (2) comprising a plurality of conductive brush fibers (2a), arranged in a second direction, perpendicular to the first direction, for electrostatically charging a surface of the photosensitive member (1, 90) uniformly by making the tips of the conductive brush fibers (2a) touch to the surface of said photosensitive member (1, 90) and applying a charging voltage to the surface of the photosensitive member (1, 90) through the conductive brush fibers (2a); characterised in that the photosensitive member (1, 90) and the conductive brush type charger (2) are comprised in a process unit (10) which is loadable into the image forming apparatus, the process unit (10) further comprises a unit case (3) for housing the photosensitive member (1, 90) and the conductive brush type charger (2), and means (44, 47, 49; 41, 42) for supporting the conductive brush type charger (2) so as to position the tips of the conductive brush fibers (2a) out of contact with the surface of said photosensitive member (1, 90) whilst the process unit (10) is not loaded into the image forming apparatus. An assembly as claimed in claim 1, wherein the conductive brush type charger (2) further comprises:- a conductive base bar (2b) on which the conductive brush fibers (2a) are provided, the base bar being placed perpendicularly to the first direction; thrust means (47) for urging the base bar towards the surface of the photosensitive member (1, 90); and stopper means (49) for retaining the bar against the thrust force of the thrust means (47) so that the tips of the conductive brush fibers (2a) uniformly touch to the surface of the photosensitive member (1, 90); and the base bar (2b) and stopper means (49) being such that spacer means (44) can be inserted between the base bar (2b) and the stopper means (49), for providing a space between the tips of the conductive brush fibers (2a) and the surface of the photosensitive member (1, 90), the spacer means (44) being insertable when the process unit (10) is not loaded into the image forming apparatus and removable for loading of the process unit into the image forming apparatus.. An assembly as claimed in claim 1, the conductive brush type charger further comprising:- a conductive base bar (2b) on which the conductive brush fibers (2a) are provided so that the conductive brush fibers (2a) are directed towards the surface of the photosensitive member (1, 90), the conductive base bar (2b) being arranged in the second direction and placed in parallel with the surface of the photosensitive member (1, 90), conductive base bar (2b) comprising a first sliding surface parallel to the surface of said photosensitive member (1, 90) for positioning the conductive base bar (2b) so that the tips of the conductive brush fibers (2a) uniformly touch to the surface of the photosensitive member (1, 90) when the first sliding surface is contacted by an appropriate second sliding surface when the process unit is loaded into image forming apparatus, the second sliding surface being provided on a bar (43) protruded from the image forming apparatus; and means (41, 42) for urging the conductive base bar (2b) away from the surface of the photosensitive member (1, 90) providing a space between the tips of the conductive brush fibers (2a) and the surface of said photosensitive member (1, 90) when the process unit (10) is not loaded in image forming apparatus, and providing firm contact between the first and second sliding surfaces when said process unit (10) is loaded into the image forming apparatus. An assembly as claimed in any preceding claim, further comprising, housed in the unit case (3), developing means (5) for developing an electrostatic latent image so as to form a toner image on the surface of the photosensitive member (1, 90); cleaner means (6) for cleaning toner left on the surface of the photosensitive member after transcription of the toner image from the photosensitive member (1, 90). An assembly as claimed in any preceding claim, wherein the photosensitive member is a photosensitive drum (1) comprising a conductive rotatable drum, rotatable in the first direction, and a photosensitive layer provided around a wall surface of the drum. An assembly as claimed in any one of claims 1 to 4, wherein the photosensitive member is a photosensitive belt (90) transferable in the first direction, the photosensitive belt comprising a belt body on which conductive material is coated, and a photosensitive layer provided on the conductive material. An assembly as claimed in any preceding claim, wherein the conductive brush fibers (2a) are carbon-dispersed chemical fibers. Image forming apparatus comprising:- a photosensitive member (1, 90) transferable in a first direction; a conductive brush type charger (2) comprising a plurality of conductive brush fibers (2a), arranged in a second direction, perpendicular to the first direction, for electrostatically charging a surface of the photosensitive member (1, 90) uniformly by making the tips of the conductive brush fibers (2a) touch to the surface of said photosensitive member (1, 90) and applying a charging voltage to the surface of the photosensitive member (1, 90) through the conductive brush fibers (2a); and further including developing means (26, 5) for developing an electrostatic latent image so as to form a toner image on the surface of the photosensitive member (1, 90); and transfer means (27) for transferring said toner image on said photosensitive member (1, 90) to a medium (50); characterised in that the photosensitive member (1, 90) and the conductive brush type charger (2) are comprised in a process unit (10) which is loadable into the image forming apparatus, and the process unit (10) further comprises a unit case (3) for housing the photosensitive member (1, 90) and the conductive brush type charger (2), and in that means (44, 47, 49; 41, 42) are provided for supporting the conductive brush type charger (2) so as to position the tips of the conductive brush fibers (2a) out of contact with the surface of said photosensitive member (1, 90) whilst the process unit (10) is not loaded into the image forming apparatus.

Inventors: KIMURA MASATOSHI FUJITSU LIMIT, NAKAJIMA JUNZO FUJITSU LIMITED, SATO KUNIHIKO FUJITSU LIMITED, WANOU MASAHIRO FUJITSU LIMITED, KIMURA, MASATOSHI FUJITSU LIMITED, NAKAJIMA, JUNZO FUJITSU LIMITED, SATO, KUNIHIKO FUJITSU LIMITED, WANOU, MASAHIRO FUJITSU LIMITED
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1988
Main classification: G03G15
IPC codes: G03G15, G03G21