Patent Application
20060280531
The present disclosure relates to a transfer-detack apparatus as is known in electrostatography or xerography.
The basic principles of electrostatographic printing with dry marking material (hereinafter generally referred to as xerography) are well known: an electrostatic latent image is created on a charge-retentive surface, such as a photoreceptor or other charge receptor, and the latent image is developed by exposing it to a supply of toner particles, which are attracted as needed to appropriately-charged areas of the latent image. The toner particles are then transferred in imagewise fashion from the photoreceptor to a print sheet, the print sheet being subsequently heated to permanently fuse the toner particles thereto to form a durable image.
The suitably charged areas on the photoreceptor surface are developed with fine toner particles, creating an image with the toner which is transferred to a print sheet, which is typically a sheet of paper but which could conceivably be any kind of substrate. This transfer is typically carried out by the creation of a “transfer-detack zone” (often abbreviated to just “transfer zone”) of AC and DC biases where the print sheet is in contact with, or otherwise proximate to, the photoreceptor. A DC bias applied to the back (i.e. on the face away from the photoreceptor) of the paper or other substrate in the transfer zone electrostatically transfers the toner from the photoreceptor to the paper or other substrate presented to the transfer zone.
The present disclosure relates to overcoming a problem with stray toner particles spreading through a xerographic printing module or machine, causing undesired marking on a print sheet passing through the transfer zone.
According to one aspect, there is provided an apparatus for applying a charge to an imaging member, the imaging member being rotatable along a process direction. At least one corona member extends perpendicular to the process direction. A shield is disposed to be operatively interposed between a non-imaging portion of the imaging member and a portion of the corona member, the shield being at least partially conductive.
According to another aspect, there is provided a printing apparatus, comprising an imaging member, rotatable along a process direction. At least one corona member extends perpendicular to the process direction. A shield is interposed between a non-imaging portion of the imaging member and a portion of the corona member, the shield being at least partially conductive.
At the transfer zone, the print sheet is brought into contact or at least proximity with a surface of photoreceptor 10, which at this point is carrying toner particles thereon. A corotron or other charge source in assembly 14 causes the toner on photoreceptor 10 to be electrically transferred to the print sheet. The print sheet is then sent to subsequent stations, as is familiar in the art, such as a fuser and finishing devices (not shown).
Following transfer of most of the toner particles to the print sheet in the transfer zone, any residual toner particles remaining on the surface of photoreceptor 10 are removed at a cleaning station, which is generally indicated as 20. A cleaning blade 22 is urged against the surface of photoreceptor 10 and scrapes the residual toner off the surface. The toner which is thus removed falls downward into a hopper 24 formed in housing 100 for accumulating the toner. A flexible flap seal 26, extending the length of the photoreceptor 10, prevents loose toner from escaping the hopper.
At the bottom of the hopper is an auger 28, shown end-on in the view of
Covering the end mountings of the wires 40, 42, 44 and the enclosure 46 is a cover 50. The cover 50 is disposed relative to photoreceptor 10 in the complete module so that one edge of photoreceptor 10 crosses the cover, such as shown by edge line E in
By grounding the cover 50, stray charged toner particles from the development of an electrostatic latent image on photoreceptor 10 will not accumulate at the edge of photoreceptor 10, and possibly attach to sheets passing through the transfer zone. Effectively the cover 50 works to shield the fields created by the transfer wires below the cover 50 from the overlapping portion of the photoreceptor 10 above the cover 50. The cover 50 is particularly useful if the transfer assembly is disposed substantially near the bottom of the rotating image member, where stray particles are likely to fall, particularly if the area around the cover 50 is exposed during jam clearance or other maintenance, or when a module such as 100 is removed for replacement.
In one practical embodiment of a printer without the cover such as 50, a positive charging of the photoreceptor can occur in the area near the ends of wires 42, 44, 46; this positive-charged “band” at the end of photoreceptor 10 can then attract negatively-charged toner particles elsewhere in the printing process with each rotation of photoreceptor 10, leading to a defect in resulting prints. The conductive or grounded cover 50 prevents any positive charging of the photoreceptor in the overlapping area, and thus obviates this type of print defect.
In the embodiment, the cover 50 is grounded as shown, but it is also possible that the cover 50 be biased to some predetermined polarity and potential. The bias would typically be supplied through a contact in the machine in which the module 100 is installed. Such a bias can be selected for most effective use in a particular machine design.
Although the illustrated embodiment is shown in the transfer zone of a xerographic printing apparatus, the shield or cover such as 50 can be employed at any location where a charge is applied to an imaging member, such as a charging or cleaning station. Also, although the illustrated embodiment is shown with a photoreceptor of a xerographic printing apparatus, the shield or cover such as 50 can be employed with other types of imaging member, such as an intermediate transfer belt, as would be used in color xerography.
The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
