Patent Application
20100142982
The exemplary embodiments are directed to an electrostatic image transfer apparatus. More specifically, the exemplary embodiments are directed to an apparatus, a method and a system for feedforward of sheet electrostatic tacking parameters to an image transfer assembly.
Electrostatic imaging and printing processes are comprised of several distinct stages. These stages may generally be described as (1) charging, (2) imaging, (3) exposing, (4) developing, (5) transferring, (6) fusing and (7) cleaning. In the charging stage, uniform electrical charges are deposited on a charge retentive surface, such as, for example, a surface of a photoreceptor, so as to electrostatically sensitize the surface. Imaging converts an original, or digital image into a projected image on the surface of the photoreceptor and the image is then exposed upon the sensitized photoreceptor surface. An electrostatic latent image is thus recorded on the photoreceptor surface corresponding to the original, or digital image.
Development of the electrostatic latent image occurs when charged toner particles are brought into contact with this electrostatic latent image. The charged toner particles are attracted to either the charged or discharged regions of the photoreceptor surface that correspond to the electrostatic latent image, depending on whether a charged area development (CAD) or a discharged area development (DAD, more common) is being employed.
In the case of a single step transfer process, the photoreceptor surface with the electrostatically attracted toner particles is then brought into contact with an image receiving surface, i.e., paper or other similar substrate; Toner particles are imparted to the image receiving surface by a transferring process wherein an electrostatic field attracts the toner particles toward the image receiving surface, causing the toner particles to adhere to the image receiving surface rather than to the photoreceptor. Toner particles then fuse into the image receiving surface by a process of melting and/or pressing. The process is completed when the remaining toner particles are removed or cleaned from the photoreceptor surface.
An objective of the transferring process is to ensure that all of the toner is removed from the photoreceptor surface onto the paper or other suitable media. To accomplish this objective, it is known in the art that an electric field, or transfer field, is built at the point at which the media passes the photoreceptor for transfer as it is carried by a belt through the image transfer apparatus. As the media enters the transfer nip, a roll that may be electrically biased applies pressure to the media in a direction opposite of pressure applied by the photoreceptor to the media to enhance toner transfer to the media. The transfer field assists in applying a net force on the toner particles that causes the toner particles to move from the photoreceptor to the paper.
It is increasingly difficult, however, to achieve optimal toner particle transfer at the transfer nip due to a widening variety of media types, each having unique dielectric properties. The dielectric properties of media may influence the shape and intensity of the transfer field.
It is known that transfer nip settings may be adjusted prior to the arrival of a specified media based upon system inputs including user supplied information about the media composition (thickness, media type), nominal media size, and environmental factors (temperature, relative humidity). These system inputs may then be used to determine transfer nip settings for the specified media. However, the specific media dielectric properties may vary substantially due to individual sheet moisture content variation, sheet size and thickness tolerances, variation in the sheet constituent materials, and user input error. A need therefore exists in the art for manipulating the electric field at the transfer nip, i.e. the transfer field, to compensate for the unique dielectric properties of varied media fed through an image transfer apparatus. Further, there is a need in the image transfer art for determining dielectric properties of media carried by a transfer belt before passage through the transfer nip so as to accommodate optimal toner particle transfer to media regardless of type by accounting for the dielectric properties of a particular sheet as it approaches the transfer nip, and adjusting the transfer field accordingly.
It would be advantageous to provide an image transfer apparatus that enhances or improves the quality of prints, reduces the number of components and therefore cost of manufacture, and expands the overall capability of the image transfer apparatus by accommodating varying media types. To address or accomplish these advantages, advantages described below and/or other advantages, the exemplary embodiments may include a toner image transfer apparatus having a tacking assembly, an image transfer assembly, and a media transfer assembly interposing the tacking assembly and the image transfer assembly. The image transfer assembly is capable of electrostatically transferring an image to a media. The media transfer assembly is constructed and arranged to accommodate the carriage of media from the tacking assembly to the image transfer assembly.
The tacking assembly is constructed to electrostatically tack media to e.g., a belt of the media transfer assembly. The tacking assembly may be constructed to sense critical electrical properties of the media. Specifically, a sheet may be first electrostatically tacked to a belt which then escorts the sheet to the image transfer assembly. The tacking assembly senses critical media electrical properties as the sheet is being tacked to the belt, prior to toner transfer. Data corresponding to the sensed electrical properties may be fed forward to the image transfer assembly before passage of the sheet through the image transfer assembly. The feedforward of electrostatic tacking parameters allows for fine-tuning of the transfer field at the transfer nip of the image transfer assembly during toner particle transfer from the photoreceptor to the sheet.
Exemplary embodiments are described herein with respect to architecture of graphic or electrophotographic print engines. However, it is envisioned that any imaging devices that may incorporate the features of the electrostatic imaging apparatus described herein are encompassed by the scope and spirit of the exemplary embodiments.
The exemplary embodiments are intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the devices, methods and systems as defined herein.
For an understanding of the apparatus, method and system for feedforward of sheet electrostatic tacking parameters, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to designate similar or identical elements. The drawings depict various embodiments of illustrative electrophotographic printing machines incorporating the features of the exemplary embodiments therein. As shown, the drawings schematically depict the various components of electrophotographic printing machines that have the various features. In as much as the art of electrophotographic printing is well known, the various processing stations employed in the printing machines will be schematically shown herein and their operation described with reference thereto.
Referring now to
Toner image transfer assembly 101 may include a photoreceptor 104 and a transfer nip roll 105 that together define a transfer nip 108. Photoreceptor 104 is illustrated in the shape of a roll. However, photoreceptor 104 may alternatively be a belt, in any shape, or constitute any known or later developed device that may be electrostatically charged so that it may carry and transfer a toner image or an electrostatic image. In the embodiment of
Media transfer assembly 103 may include a transfer belt 112 constructed to carry a media sheet 114. Transfer belt 112 may be supported by one or more transfer rolls 118. Transfer belt 112 may be constructed to carry a media sheet 114 from tacking assembly 102 through transfer nip 108 in the direction of arrow 115. Transfer nip roll 105 may be one of transfer rolls 118. Transfer belt 112 may be constructed to translate past transfer nip roll 105 to synchronously bring the media sheet 114 into contact with photoreceptor 104 at transfer nip 108 and the toner image retained thereon. In an exemplary embodiment, transfer nip roll 105 may be connected to a power supply. In such an embodiment, transfer roll 105 may be an electrostatic charge roll that may maintain an electrostatic field which would then attract the charged toner particles toward the media surface. The net downward force applied to the toner particles, which may be combined with pressure applied to the toner and media, effects transfer of toner particles from the photoreceptor 104 to the media sheet 114.
Although the embodiment of
The electrostatic field or transfer field at transfer nip 208 may be tailored in accordance with tacking parameters fed forward from a tacking assembly 202 to ensure substantially complete transfer of toner particles. Tacking assembly 202 may include a variable voltage power supply 206, and a bias nip charge roll 221. Media transfer assembly 203, which includes transfer belt 212, may further include one or more transfer rolls 218. Transfer belt 212 may define with charge roll 221 a bias nip 222. The power supply 206 may be operated in constant dynamic current mode to apply a current to bias charge roll 221, to which variable voltage power supply 206 may be connected. The bias nip 222 defined by bias charge roll 221 and transfer belt 212 may accommodate passage of media sheet 214, which is inserted in the direction of arrow 215 and is delivered to bias nip 222. Power supply 206 may be operated in constant dynamic current mode as soon as a lead edge of media sheet 214 arrives or has arrived at bias nip 222. During this period, media sheet 214 and adjacent transfer belt 212 received a net charge density to establish a substantially high electric field, for example, about 20 volts per micrometer, at a point between media sheet 214 and transfer belt 212. This field may result in electrostatic pressure that may attract media sheet 214 to transfer belt 212, effectively tacking the media sheet 214 to transfer belt 212.
If the tacking assembly 102 has no stored data related to a approaching media type, then a default current set point will be maintained. For example, a 20-32 uA range with corotron tacking an 11″ wide media is exemplary, but other set points are possible. If the tacking assembly 102 does have data characterizing the approaching media type, user intervention or data from previous measurements and/or lookup tables may be used to apply a current set point best suited for tacking that particular media type.
The voltage of the power supply can be monitored while the set point current is being delivered, and the voltage level may give the system controller an indication of how much voltage the power supply must supply to deliver the current to media sheet 114 and transfer belt 112. Because the electrical properties of the belt 112 are essentially constant over a short time period, it can be inferred that the differences in power supply voltages are caused by differences in media properties. For example, one such media property is the effective width of the sheet in the cross-process direction. Another such media property is the bulk resistivity of the sheet, which generally can vary as a function of the moisture content of the sheet. The specific differences may be sensed at the bias nip 122 of the tacking assembly 102, in advance of the media sheet 114 lead edge arriving at the toner image transfer assembly 101. It is therefore possible to feedforward the tacking power supply reaction to the media sheet 114 to toner image transfer assembly 101 in order to control the transfer field accordingly.
With reference to
Referring to
For purposes of explanation, in the above description, numerous specific details were set forth in order to provide a thorough understanding of the image transfer apparatus, method and system. It will be apparent, however, to one skilled in the art that image transfer as described above can be practiced without the specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid obscuring the image transfer method, system and apparatus described.
While image transfer has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, embodiments of the apparatus, method and system as set forth herein are intended to be illustrative, not limiting. There are changes that may be made without departing with the spirit and scope of the exemplary embodiments.
It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also, various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art, and are also intended to be encompassed by the following claims.
