Multi layer toner filtration trap

Abstract: An apparatus (90) for trapping and removing a contaminant from particulate material, such as for example, toner or developer, includes a first member (134) having a plurality of apertures (136) in the first member and at least a second member (140) having a plurality of apertures in the second member. The second member is in juxtaposition with the first member. A space (138) between the first member and the second member is smaller than a maximum length of the contaminant, and the apertures of first and second members are not in alignment. A vibration driving device (112) vibrates the first and second member to assist in directing the particle material therethrough while trapping the contaminant therein.

Description: The present invention relates to an apparatus for removing contaminants from particulate matter, and more specifically, relates to a filter for filtering toner in a developer apparatus for electrophotographic printing. In more recent copy machines and printers, toner used in the developer unit is replenished by exchanging an empty toner resupply cartridge with a new, full cartridge. Many devices have been used to seal the cartridge prior to installation in the machine. These devices and others have been used to maintain the sealed integrity of the copy cartridge during the exchange of an empty cartridge for a full cartridge. The use of cartridges has reduced the problems with spilled and settled toner as well as contamination problems during toner replenishing. To provide for a small compact toner cartridge and to provide for a toner cartridge in which the opening to the cartridge may be easily opened and closed or removed, the toner cartridge typically has a compact shape with a small opening from which the toner is dispensed. While the use of cartridges for the storage and refilling of toner within a machine reduces the contamination encountered during filling, even in the most stringently controlled manufacturing environments, contaminants may enter the toner itself during its manufacture and/or could enter the cartridge during filling at the factory and later progress into the developer housing causing copy quality problems. The development system, the area of an electrophotographic printer where the developer material is transferred to the photoreceptor, typically includes a wide area extending across the full width of the photoreceptor in order that a full image width may be developed. The toner must progress from the toner container into the developer housing and progress along the full width of the developer housing in order that the full width of the latent image may be developed. Furthermore, in attempts to make inexpensive and compact electrophotographic printers and to minimize space and related costs, the location of the toner cartridge and the developer housing may be far apart. If the contamination, particularly in the form of clothing and paper fibers, reaches the developer housing, copy quality and machine reliability suffer. Toner particles also have a tendency to adhere together into large scale clumps which ride on the top of the developer material in the developer housing negatively effecting the blending and admixing of the incoming toner. The use of smaller carrier and toner particles, which are typical when using colored toners for color electrophotography compounds problems associated with contamination. Imperfections in color copies, such as those caused by contamination, are much more noticeable to the human eye than imperfections in monochromic copies. The presence of contamination in development systems utilizing hybrid scavengeless development is particularly a concern. The purpose and function of scavengeless development are described more fully in, for example, US-A-4,868,600; US-A-4,984,019; US-A-5,010,367 or US-A-5,063,875. In a scavengeless development system, toner is detached from the donor roll by applying AC electric field to self-spaced electrode structures, commonly in the form of wires positioned in the nip between a donor roll and photoreceptor. This forms a toner powder cloud in the nip and the latent image attracts toner from the powder cloud thereto. Because there is no physical contact between the development apparatus and the photoreceptor, scavengeless development is useful for devices in which different types of toner are supplied onto the same photoreceptor, such as, for example, in color xerography. The small color toner and related carrier particles used for color reproducing devices and the greater visual scrutiny given to color copies compound contamination problems. Furthermore, the electrode wires utilized to form the toner powder cloud are particularly susceptible to contamination in general and, in particular, to long slender fibers such as clothing and paper fibers. Filters have been used to trap these fibers, but long slender fibers are particularly difficult to remove. Screens with large apertures permit the passage of fibers as well as toner,while filters with small apertures either prohibit the passage of fibers and toner or greatly inhibit the flow of toner therethrough. US-A-5,200,788 discloses a brush auger reclaim filtration assembly incorporated into an open ended chamber. The brush auger is a toner reclaim filtration device that is rotatably mounted, in the chamber, to move toner and debris along a separating screen. Also contained in the housing is a mounted transport auger that rotates as it moves the reclaimed toner to the development housing. US-A-4,752,805 discloses a device for recycling residual developer particles which are removed from a photoconductive element by a cleaning unit in an electrographic copier or printer. The device comprises a first tube connected to the cleaning unit and a second tube which is connected to the first tube and leads to the developer unit. The second tube is disposed along the developer unit. The residual particles are transferred from the cleaning device through the first tube and into the second tube. The second tube is provided with holes spaced at predetermined distances from each other. The residual particles fall through those holes and co-mingle with developer material stored in the developer unit. A second auger is disposed within the second tube to move the residual particles to the first tube. US-A-4,561,759 discloses a device for filling and filtering toner from a supply container which is placed by an operator in communication with a feed container in a photocopier. The device has a cylindrical filling opening for the feed container with a cross section such that the supply container can be inverted. The device has a filter basket disposed in the region of the filling opening which is closed from the feed container by a filter mesh. An electric vibrator is connected to the device. US-A-4,389,968 discloses a toner regenerating device with a mesh disposed in the route of the toner collected from an image bearing member. The device includes an apparatus for imparting to the collected toner through the mesh a force causing the collected toner to move along the mesh. The collected toner on the mesh containing foreign material and solidified toner is loosened so that the solidified toner is divided into fine particles. The foreign matter is caused to float up over the collected toner and prevented from passing through the mesh. US-A-4,054,381 discloses a toner filter arrangement adepted for use in a cleaning station of a xerographic reproduction machine. Foreign material and other contaminants are removed from residual toner prior to its collection in a disposable or reuse container or return to the developer station. The filter arrangement comprises a housing having an input opening through which removed toner enters and an output opening through which filtered toner exits. The housing includes a spiral brush mounted for rotation on a shaft centrally located within the housing and a stationary open mesh screen coaxially located with respect to the shaft. Rotation of the brush operates to sift toner through the screen to the outlet of the filter housing. US-A-4188197 discloses a filler bag for toner comprising three parallel filters having decreasing pore diameter to remove contaminants without clogging. According to the present invention, there is provided an apparatus for trapping a contaminant. The apparatus includes a screen member defining a plurality of apertures therein and a second member defining a plurality of apertures therein, the second member in juxtaposition with the first member and defining a distance between the first member and the second member smaller than a maximum length of the contaminant, wherein at least a portion of the apertures in said screen member are offset from the apertures in said second member. According to another aspect of the present invention there is provided a printing machine of the type having a developer unit adapted to develop a latent image with marking particles. The machine includes a conduit having marking particles and contaminants moving through the conduit. The machine further includes a screen member defining a plurality of apertures therein and positioned at least partially in the conduit. The machine further includes a second member defining a plurality of apertures therein. The second member is positioned in juxtaposition with the first member and defines a distance between the members smaller than a maximum length of the contaminants. The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a multi layer screen filter according to the present invention; Figure 2 is an exploded perspective view of the filter of Figure 1; Figure 3 is a perspective view of the the plates and spacers of the filter of Figure 1; Figure 4 is a partial sectional view of the the plates and spacers of the filter of Figure 1 showing the position of the apertures; and Figure 5 is a schematic elevational view of an illustrative electrophotographic printing machine incorporating the multi layer screen filter of the development apparatus of the present invention therein. Referring initially to Figure 5, there is shown an illustrative electrophotographic printing machine incorporating the apparatus of the present invention therein. The various processing stations employed in the machine of Fig.5 are described in detail in U.S. application S.N. 08/474,861, a copy of which was filed with the present application. For conciseness, a detailed discussion thereof has been omitted from the present disclosure. After an electrostatic latent image has been recorded on photoconductive surface 12, the motion of the belt 10 advances the latent image to development station C. At development station C, a development system 38, develops the latent image recorded on the photoconductive surface. A chamber or sump 82 in developer housing 44 stores a supply of developer material 47. The developer material 47 may be a two component developer material of at least magnetic carrier granules 48 having toner particles 50 adhering triboelectrically thereto. It should be appreciated that the developer material may likewise comprise a one component developer material consisting primarily of toner particles. In order to provide a constant supply of at least toner 50 to replace that consumed in the developing of the latent image, the development system 38 includes a cartridge 80 for storing a replaceable supply of replenisher 76 including at least toner 50. The replenisher 76 may contain carrier granules 48 as well as toner particles 50 in order to replace worn and broken carrier granules 48. As the typical usage of toner is larger than the typical usage of carrier granules (on a weight basis) whether on a per copy or per hour basis, the ratio of toner to carrier in the cartridge is much larger than the ratio of toner to carrier in the housing. The use of replenisher containing carrier particles as well as toner is disclosed in US-A-4,614,165. The cartridge 80 is a replaceable item that can be made of any suitable durable material. It may be vertically oriented with its opening pointed downward whereby it may be emptied by gravity. Where, however, space constraints become a problem, the cartridge 80 may include a device (not shown) for extracting the developer material from the cartridge 80. Particles in the toner cartridge 80 progress to a toner sump or developer sump 82 as shown in Figure 5. While the sump 82 may ideally be located above the developer housing 44 whereby gravity may feed the replenisher 76 from the sump 82, where, as earlier stated, space constraints for the toner cartridge 80, sump 82, and developer housing 44 become a concern, the sump 82 may not be located above the developer housing 44. Referring again to Figure 5, according to the present invention, an apparatus 90 for filtering contaminants is shown as part of development system 38. It should be appreciated that the use of apparatus or filter 90 is adaptable to development systems utilizing primarily toner or toner and carrier (developer). The development system 38 as shown in Figure 5 represents a typical development system providing toner from toner cartridge 80 to the photoreceptor belt 10. It should also be appreciated that the copy machine may also include a cleaning system (not shown) as part of the cleaning station F in which toner not used in the development process may be recycled for use in the developer system 38. It should be appreciated that the toner supplied by the cleaning system may alternatively or additionally be filtered by the multi layer filter 90. It should further be appreciated that in the manufacture of toner particles, contamination which may include fibers may need be filtered from the manufactured toner and that the multi layered toner filter 90 may be adapted to the manufacture of toner. The development system 38 includes the developer housing 44 which supports the remainder of the developer system 38. The cartridge 80 may be interconnected in any suitable fashion to the developer housing 44. Preferably, where space is available, the cartridge 80 is located above the developer housing 44 to take advantage of the effects of gravity. Also, the cartridge 80 may preferably be at a location near the periphery of the copy machine to facilitate the replacement of the cartridge 80. Although preferably the replenisher 76 is moved from the cartridge 80 to the developer housing 44 solely by means of gravity, when required, a toner mover in the form, for example, of an auger 92 is located in an inlet conduit or supply pipe 94 between the cartridge 80 and the apparatus 90. An outlet conduit 96 interconnects the apparatus 90 to the developer housing 44. The replenisher 76 thus travels from the cartridge 80 through the inlet conduit 94, through the apparatus 90, out the outlet conduit 96 and finally into developer housing 44. Referring now to Figures 1 and 2, the apparatus 90 is shown in greater detail. The apparatus 90 includes mounting bracket 100 which is connected to copier frame 102 by any suitable means. For example, the mounting bracket may be connected to the frame 102 by fasteners in the form of screws 104 which fit through openings 106 of the mounting brackets 100 and are threadedly secured to the copier frame 102. A filter housing assembly 107 is secured to mounting bracket 100 in any suitable fashion such as by fasteners or adhesives. The filter housing assembly 107 is composed of an upper filter housing body 108 and a lower filter housing body 110. Inside the filter housing assembly 107 is a filter screen assembly 111 which is connected to a vibration driving device 112. The vibration driving device 112 preferably is in the form of a mechanical vibrator. The mechanical vibrator 112 may be any suitable vibrator such as those commercially available. The vibrator 112 induces vibration into the filter screen assembly 111 (Figure 3). In Figure 1, the apparatus 90 is shown with the components of the apparatus separated in an exploded view. The mechanical vibrator 112 is secured by vibrator mounting bracket assembly 114 to the mounting bracket 100 (see Figure 2). It is desirable that the vibrator mounting bracket assembly 114 include some means for isolating the mechanical vibration of the vibration driver 112 and the filter screen assembly 111 from the mounting bracket 100. Thus, while the mounting bracket is illustrated as a single piece, in practice it will most likely be a combination of materials suitable to provide both the mounting and vibration isolation functions. The vibrator mounting bracket assembly 114 may be made of any combination of suitable durable material such as steel stampings or plastics. Extending from mechanical vibrator 112 is a mounting stem 120. The vibrator 112 and the stem 120 vibrate when the vibrator 112 is engaged. Mounting stem 120 is connected to an upper screen mounting plate 122 by any suitable means such as adaptor 124. The upper screen mounting plate 122 and the adaptor 124 are made of any suitable durable rigid material such as plastic or a metal. The adaptor 124 includes an opening 126 to which stem 120 matingly fits and a flat surface 130 to which protruding tab 132 of the upper screen mounting plate 122 matingly fits. A first filter screen plate 134 is placed below the upper screen mounting plate 122. The filter screen plate 134 is made of a thin durable material with numerous small openings 136. This screen 134 may be fabricated from a thin metal foil or plastic film with the openings formed by any suitable means such as chemical etching, laser machining, or punching. Alternatively, this screen may be fabricated from a woven plastic or metal wire mesh. Yet another method for formation of this screen is the process of electrodeposition of metals. Placed below the first filter screen plate 134 is a screen spacer 138. The spacer 138 may be made of any suitable material but preferably is made of a non compressible material. The screen spacer 138 may be made of any suitable durable material such as metal or plastic. A second filter screen plate 140 is placed below the first screen spacer 138. A second screen spacer 142 is placed below the second filter screen plate 140. While this invention may be practiced with only two screens, the apparatus 90 preferably includes a third filter screen plate 144 which is placed below the second screen spacer 142. A lower screen mounting plate 146 is next located below the third filter screen plate 144. The lower screen mounting plate 146 is made of any suitable durable rigid material such as plastic or a metal. Located on top of the upper screen mounting plate 122 are a gasket 150 and a replenisher containment housing 152. The gasket 150 can be fabricated from any suitable material such as a foam rubber. The replenisher containment housing 152 is typically fabricated from a plastic material. When the apparatus is assembled, the toner inlet conduit supply pipe 94 passes through and is sealed to an opening 154 in the upper filter housing body 108. The toner inlet conduit supply pipe 94 passes through an opening 156 in the replenisher containment housing 152 without touching the housing 152. There can optionally be a thin elastomeric diaphragm seal (not shown) between the toner inlet supply pipe 94 and the replenisher containment housing 152. If such a diaphragm seal is implemented, it should be designed so as not to impede the vibration of the filter screen assembly 111. Additionally, there is a tubular membrane seal (not shown) between the filter housing assembly 107 and the adapter 124. Referring to Figure 3, the filter screen assembly 111 is shown. The filter screen assembly 111 includes the filter screen plates 134, 140, and 144 and the screen spacers 138 and 142. The filter screen assembly 111 also includes the upper screen mounting plate 122 and the lower screen mounting plate 146. The filter screen assembly 111 further includes the gasket 150 and the replenisher containment housing 152 (not shown in Figure 3). It should be appreciated that all components of the filter screen assembly 111 should be mechanically locked together. This can be done by any suitable means such as a mechanical fastener located through holes 160 in the plates and spacers. Preferably only a minimal mass should be vibrated. This is done to minimize the required strength of the mechanical vibrator 112 (see Figure 2) and to minimize the vibration induced into the rest of the copy machine. Thus, it is desirable to minimize the thickness of the mounting plates 122 and 146, solid or plate area 170 the screen plates, and the wall thickness of the replenisher containment housing 152. The screen plate 122 includes the solid or plate area 170 and at least one screen area 171. The filter screen assembly 111 as shown in Figure 3, includes also a second screen area 172 similar to first screen area 171. The size and quantity of screen areas is determined by the amount of toner which must flow through the filter 111. The screen areas 171 and 172 include a plurality of openings or apertures 136. A sufficient number of apertures 136 exist to provide for approximately 20 to 50 percent of the screen area 171 and 172 to be open. The filter 111 as shown in Figure 3, includes a sandwich of filter screen plates 134, 140, 144, and screen spacers 138,142, with one spacer being placed between adjacent screen plates. Four screen mounting plates and spacers are separated by three filter screen plates. The upper screen mounting plates 122 includes openings 176 to which fasteners (not shown) are used to interconnect the tab 132 of the upper screen mounting plate 122 with the adaptor 124 (see Figure 1). While the screen plates and spacers, as shown in Figure 3, have a generally planar shape, to simplify manufacturing and to minimize their mass, it should be appreciated that the invention can be practiced with screen plates of different shapes such as arcuate discs or rings or any other suitable shape with which layers of screens may be separated by spacers. Referring to Figure 4, the apertures of adjoining screen plates are shown in greater detail. The first plate 134 is separated from the second plate 140 by spacer 138 (not shown) and the second plate 140 is separated from the third plate 144 by spacer 142 (not shown). The first second and third plates 134, 140 and 144 preferably have a generally uniform thickness T m of approximately 50 µm. In order to trap contaminants with a length greater than 1000 µm, the spacers 138 and 142 have a generally uniform thickness T s less than the length of the contaminant, for example of approximately 250 µm. The apertures 136 of the screen plate areas 171 and 172 (Figure 3) have a diameter D a of approximately 325 µm with an acceptable range for the filtering of toner of from about 200 µm to 750 µm. Centerlines 182 of the apertures 136 of the first screen plate 134 are preferably non-coincident with centerlines 184 of the apertures 136 of the second screen plate 140. Centerlines 184 of the second screen plate 140 are preferably non-coincident with centerline 186 of the third screen plate 144. Either by design or fabrication or both the apertures in the multiple filter screen plates do not line up in a straight line. Adjoining apertures 136 have a distance between their respective centerlines of approximately 0.025 inches (625 µm). In the operation of the apparatus 90, one end of a fibrous contaminant, for example in the form of a fiber 187, 188, or 190, to be filtered from the replenisher 76 enters an aperture 136 in the first screen plate 134. Since the diameter D f of the fiber 187, 188 or 190 is smaller than the diameter D a of the aperture, the fiber passes through the aperture 136 of the first screen plate 134. At this point the end of the fiber will either encounter the structure of the second filter screen plate 140 or it will encounter an aperture in the second filter screen plate. For example, the fiber 187 encounters the structure of the second filter screen plate 140 and can continue to progress into the space between the first and the second filter screen plates, 134 and 140, respectively. The fiber 187, has a length greater than the distance T s between the plates 134 and 140, the fiber 187 can not reorient itself in a favorable attitude so as to enter an opening in the second screen plate 140. The fiber 187 is thus trapped between the first and second screen plates 134 and 140 and may not travel further. For example, the leading end of the fibers 188 and 190 encounter an aperture 136 in the second filter screen plate 140. The fiber 188 will continue to progress into the space between the filter screen plates 140 and 144. Here again the fiber can encounter the structure of the third filter screen plate 144 or it can encounter an aperture 136 in the third filter screen plate. For example, the fiber 188 encounters the structure of the third filter screen plate 144, the fiber can, in a fashion similar to that described above, proceed into the region between the second and third filter screen plates 140 and 144. Here because of the inability of the fiber 188 to reorient itself, the fiber 188 will become trapped. For example, the fiber 190 encounters the an aperture 136 in the third filter screen plate 144. The fiber 190 will also most likely become mechanically trapped if it is sufficiently long. Since, by design / fabrication, the apertures in the multiple filter screen plates do not line up in a straight line, only curved fibers will be able to enter an aperture in the third filter screen plate 144. Thus, only longer fibers with a smooth and constant curvature will be able to progress simultaneously through the apertures 136 in the three filter screen plates 134, 140, and 144. If the fiber is sufficiently long and does not have a uniform curvature, at some point during passage through the apertures, the fiber will become mechanically bound by the plurality of screens. The replenisher 76 to be filtered includes, on the other hand, toner particles 50 having a size of approximately 7 µm as well as carrier granules 48 having a particle size of approximately 50 µm which are much smaller than the aperture diameter D a . Also, the carrier granules 48 and toner 50 particles are significantly smaller than the spacing between the filter screen plates. This spacing is determined by the thickness of the filter screen spacers. Thus, the carrier granules 48 and toner 50 particles move freely through apertures 136 in both the first screen plate 134 and the second screen plate 140. The filter 140 thereby traps fibers 187, 188, and 190 while permitting toner 50 and carrier particles 48 to freely flow therethrough. It has found that while the invention may be practiced with as few as two screen plates 134 and 140, filtering efficiency increases if three or more plates are utilized. Referring again to Figure 2, the mechanical vibrator 112 preferably has a frequency from 30 to 120 Hz. Applicant has found that the amplitude of vibration of the mechanical vibrator 112 is important and needs to be tuned with the characteristics of the replenishers 76. The use of a screen type filter including a plurality of filters serves to trap filter fibers between adjacent screens permitting the free flow of carrier granules and toner particles while trapping fibers. The use of a vibrator secured to a plurality of spaced apart screens permits the free flow of carrier granules and toner particles while trapping fibers within the several screens and in the spaces therebetween.

Claims: An apparatus (90) for trapping a contaminant, comprising: a screen member (134) defining a plurality of apertures (136) therein; and a second member (140) defining a plurality of apertures (136) therein, said second member in juxtaposition with said screen member and defining a distance (T s ) therebetween smaller than a maximum length of the contaminant (187,188,190); wherein at least a portion of the apertures in said screen member are offset from the apertures in said second member. An apparatus according to claim 1, further comprising means (112) for inducing vibrations into at least one of said screen member and said second member. An apparatus according to claim 1 or 2, wherein at least one of said screen member and said second member comprise a plate. An apparatus according to any of the preceding claims, wherein said screen member and said second member are substantially parallel to each other. An apparatus according to any of the preceding claims, wherein said screen member and said second member define a plurality of randomly distributed apertures. An apparatus according to any of claims 2 to 5, wherein said inducing means comprises a mechanical vibrator. A printing machine having a developer unit (38) adapted to develop a latent image on a photoreceptor (10) with marking particles (50), comprising: a conduit (94,96) having marking particles (50) and contaminants (187,188,190) moving therethrough; and an apparatus according to any of the preceding claims, said screen member being positioned at least partially in said conduit. A printing machine having movable photoreceptor (10) and a developer unit (38) adapted to develop latent images on said photoreceptor with marking particles (50), comprising: a cartridge (80) containing replacement marking particles for the developer unit, the cartridge also containing contaminants (1878,188,190) mixed with said marking particles; and a conduit (94,96) connecting the cartridge to the developer unit; characterised by : the trapping apparatus of claims 1 to 6 being positioned in said conduit.

Inventors: HART STEVEN C, HART, STEVEN C.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1996
Main classification: G03G15
IPC codes: G03G21, G03G15