Patent Application
20120288307
This disclosure relates generally to ionographic or electrophotographic imaging and printing apparatuses or reproduction machines, and more particularly is directed to a constrained transfer assist blade assembly for contacting a printing media.
Electrostatographic printing includes the well-known process of transfer. In transfer, charged toner particles from an image-bearing photoreceptor member are transferred to an image support substrate or print media, such as a copy sheet. Transfer is accomplished at a transfer station, wherein the transfer occurs by electro-statically overcoming adhesive forces holding the toner particles to the image-bearing member, thus transferring the developed toner image to the substrate.
In conventional electrostatographic machines, transfer is achieved by transporting the image support substrate into the area of the transfer station. The transfer station applies electrostatic force fields sufficient to overcome the adhesive forces holding the toner to the photoreceptor surface in order to attract and transfer the toner particles onto the image support substrate. In general, such electrostatic force fields are generated by means of electrostatic induction using a corona-generating device such as, for example, a dicorotron. The copy sheet is placed in direct contact with the developed toner image on the photoreceptor surface while the reverse side of the copy sheet is exposed to a corona discharge. This corona discharge generates ions having a polarity opposite to that of the toner particles, thereby electro-statically attracting and transferring the toner particles from the photoreceptive member to the image support substrate.
During electrostatic transfer of a toner image to a copy sheet, it is important for the copy sheet to be held in direct, uniform and intimate contact with the photoconductive surface and the toner image developed thereon. Unfortunately, however, the interface between the photoreceptive surface and the copy substrate is not always optimal. Various substrate conditions such as copy sheets being mishandled, wrinkled, creased, left exposed to the environment, or previously processed by a heat and pressure fusing or fixing operation, result in insufficient substrate contact with the photoreceptor surface during transfer. This substrate condition creates spaces or air gaps between the developed image on the photoreceptor surface and the copy sheet. The air gaps, in turn, impair transfer of the toner image, thus causing copy defects.
It is known to use a transfer assist blade (TAB) in the transfer process. Such transfer assist blades mechanically press the print media into substantially uniform intimate contact with the image-bearing surface, just prior to the build-up of the transfer electrostatic field. However, an electrostatic interaction may occur between the TAB member and the copy substrate. This is because the transfer-assist pressure blade is located in the transfer zone between the transfer corona-generating device, such as a dicorotron, and the photoreceptor. As a result, a measurable electrostatic charge is imparted on the blade member by the transfer dicorotron. In particular, the TAB tends to delaminate at higher actuation speeds that lead to print defects and backside sheet contamination. Once the TAB tip becomes charged, for example, the blades can splay from one another in a fan pattern. This type of delamination is undesirable since the blade tips are moved from their original positioning closer to the photoreceptor. This change in positioning means that the blades can either swipe through process control patches along the photoreceptor or can be close enough that they electro-statically attract the toner and contaminate the backside lead edge of the next print media or sheet.
As a result, to solve the problem of delamination at high speed printing, there is a need for an improved TAB that substantially eliminates the unwanted delamination of the TAB.
The following references, the disclosures of which are incorporated in their entireties by reference herein, are mentioned:
An imaging system and a constrained transfer assist blade (CTAB) assembly are disclosed that includes an upper blade with biasing features configured to constrain primary pressure blades against a lifter assembly (i.e., a fulcrum point), in which they articulate about. As a result, the primary pressure blades are kept from delaminating. The CTAB assembly is adapted to bias media (e.g., a paper sheet or like medium) toward a photoreceptor device of a printing machine. For example, the CTAB assembly comprises a blade member having at least one blade segment that includes pressure blades movable toward the photoreceptor device for biasing media toward the photoreceptor device. One or more biasing features constrain the pressure blades from splaying toward the photoreceptor device. Splaying occurs as a result of delamination or separation of the blades from one another, such as in an electrostatic field that may repel the pressure blades from one another.
In another embodiment, a CTAB assembly has a first blade segment that includes one or more first pressure blades that are movable toward the photoreceptor device and a first biasing feature. The first blade segment also includes a first wear layer overlaying an outer portion of the first blade segment that contacts the backside of the media for directing the media toward the photoreceptor device. A second blade segment further includes one or more second pressure blades, a second biasing feature, and a second wear layer overlaying an outer portion of the second blade segment that contacts the backside of the media for directing the media toward the photoreceptor device. In certain embodiments, the first and second blade segments partially overlap one another to eliminate gaps therebetween.
An imaging system and apparatus are disclosed that provide for an improved transfer assist blade (TAB) that is constrained from delaminating and decreases the amount of blade levitation that is experienced by the TAB assembly. Blade levitation includes distances caused by the blades of the TAB splaying from one another as well as separation distances from a fulcrum point where a lifter assembly contacts the blades to lift them to a printing media, such as a copy sheet. For example, a constrained transfer assist blade (CTAB) is disclosed that substantially eliminates the delamination, which is particularly pronounced when printing is performed at increased speeds.
The printing machine shown in
A controller 18 receives signals from various sensors in a feedback loop 21 at a feedback input 19 and is configured to store into memory data received. Initially, a portion of belt 11 passes through a charging station A. At charging station A, a corona generation device 22 charges the SZ portion of the photoconductive surface of belt 11 to a charge, for example, a relatively high, substantially uniform negative potential. Next, the charged portion of the photoconductive surface is advanced through an exposure station B. At exposure station B, after the exterior surface of photoconductive belt 11 is charged, the charged portion thereof advances to an exposure device 28. The exposure device includes a raster output scanner (ROS), which illuminates the charged portion of the exterior surface of photoconductive belt 11 to record a first electrostatic latent image thereon. Alternatively, a light emitting diode (LED) may be used or any other suitable exposure devices as one of ordinary skill in the art will appreciate. The exposure device 28 selectively illuminates the photoreceptor in areas requiring image development. As a result of light exposure in these areas, the photoreceptor 11 is selectively discharged resulting in an electrostatic latent image corresponding to the desired print image. The photoreceptor 11 then advances the electrostatic latent image to a development station C.
At development station C, a development apparatus indicated generally by the reference numeral 32, transports toner particles to develop the electrostatic latent image recorded on the photoconductive surface. Toner particles are transferred from the development apparatus to the latent image on the belt, forming a toner powder image on the belt, which is advanced to transfer station D.
At transfer station D, a sheet of support material or print media 38 is moved into contact with a toner powder image, which is developed on the photoreceptor and contacts a support material or print media 38 with the transfer station D, which includes a dicorotron 48 with a constrained transfer assist blade (CTAB) 49, for example, that provides for electrostatic and mechanical image transfer thereat.
The print media 38 is advanced to transfer station D by a sheet feeding apparatus 40, which could include a feed roll 42 that contacts the uppermost sheet of a stack of sheets 44. Feed roll 42 rotates to advance the uppermost sheet from stack 44 into chute 46. Chute 46 directs the advancing sheet of support material 38 into contact with the photoconductive surface of photoreceptor 11 in a timed sequence so that the toner powder image developed thereon contacts the advancing sheet of support material at transfer station D at a print zone. After transfer, the sheet continues to move in the direction of arrow 50 into a conveyor (not shown) which advances the sheet to fusing station E.
In one embodiment, the CTAB 49 actuates by engaging the backside of the print media or sheet 38 and disengages quickly in order to apply uniform pressure to the entire backside and to not touch toner particulate at an inter document zone area. For example, an increased speed from 110 pages per minutes speed to 137 pages per minute is achieved with a three millimeter image to edge border also being improved to a smaller allotted amount.
Further along, fusing station E includes a fusing device 52, which permanently affixes the transferred powder image to sheet 38. Sheet 38 passes between a fuser roller 54 and a back-up roller 56 with the toner powder image contacting fuser roller 54, and thus, making the toner powder image permanently affixed to sheet 38. Chute 58 then advances the sheet to catch tray 60. Residual particles are removed from the photoconductive surface at cleaning station F, which can include a brush 62 for example. An erase station 64 is also included for an erase step that may be provided before or after the cleaning station F. The erase station 64 brings the photoreceptor voltage to a uniform low voltage level before the next charging cycle, effectively “erasing” residual negative charge therefrom.
Referring now to
The blade member 202 includes two layers, an underlying layer 206 and an upper layer 208. Both layers form together to form part of a flexible blade member that actuates by a lifter assembly (not shown) to bias a print media toward a photoreceptor. The underlying layer 206 includes one or more pressure layers, which may include biaxially-oriented polyethylene terephthalate, such as Mylar or other like polyester film material that provides flexibility and high tensile strength.
The upper layer 208 includes two separate features overlaying the underlying layer 206 of the blade member 202 and residing within the same plain above a top surface of the underlying layer 206. One such feature is a wear layer 210 that extends over and above an outer portion 212 of the one or more blade segments 204. For example, the wear layer 210 can extend over a tip of each blade segment 204 and overlaps the underlying layer 206 from the tip of an outer edge of the blade member 202 that protrudes outward at a right angle with respect to a lower section 214 for support.
In addition, the upper layer 208 further includes a bias feature 216 or a constraining blade section, which operates as a constraining blade overlapping the underlying layer 206 in order to constrain the one or more underlying layers 206 from delaminating upward. Delamination of the underlying layer 206 occurs by the one or more layers splaying upward within an electrostatic charge field, which causes decreasing distance between the photoreceptor and the CTAB 200. Consequently, the blade member 202 separates from a lifter assembly and the blade tips can either swipe through process control patches as the photoreceptor rotates and/or electrostatically attract toner that can contaminate the backside lead edge of a subsequent print sheet.
The bias feature 216 overlays an inner portion 218 or inner edge of a top surface 220 of the underlying layer 206. This inner portion 218, in which the bias feature 216 spans, extends from the lower section 214 up to a lifter contact region 220, which is between the bias feature 216 and the wear layer 210. In one embodiment, the constraining blades or bias features 216 are trapezoidal in shape in order to facilitate efficient and easy cleaning of the CTAB 200. Although, other shapes in which the bias features 216 are formed also envisioned as within the scope of the present disclosure.
The upper layer 208 of the blade member 202 thus includes two different features separate from one another and on the same directional plane that laterally extends along the top surface of the one or more underlying layers 206. In one embodiment, the bias feature 216 and the wear layer 210 comprises different materials from one another. For example, the wear layer 210 includes an ultra-high molecular weight material that is different from the bias feature 216, which may include a biaxially-oriented polyethylene terephthalate, such as Mylar or other type polyester film material. The wear layer 216 functions to provide a material at the outer portion 212 of the blade member 202 and/or each segment 204 that protects from wear and improves blade life. The outer portion 212 especially operates as a contact region of the blade member 202 that repeatedly comes into contact with the backside of the printing sheets. Rather than covering the entire top surface of the underlying layer 206 with the wear layer 210, the outer portions of the blade and any segments is covered with the wear layer 210. This allows for the additional bias feature 216 to also reside on the top surface as part of the upper layer 208 and maintains wear resistance to the blade member 202 while improving response times of the CTAB 200, which is further explained below.
Referring now to
The underlying layers 308 for pressure blades include at least one layer 312 forming a backside of the blade member 300 and a top layer 314 that provides top surface. In addition, the top layer 314 provides an overlapping portion 316 that is delineated by segmented curved lines of
The upper layer 310 spans portions of the top surface of the underlying layers 308. For example, the upper layer 310 includes a wear layer 318 and a constraining layer 320, which forms biasing features at each blade segment for constraining the underlying layers 310. The wear layer 318 and the constraining layer 320 both reside on the top surface of the top layer 314 and are opposite from one another with a gap therebetween, which forms a lifter contact region 322 at each blade segment. The region 322 separates the wear layer 318 and the constraining layer 320 and allows for different features thereat to be formed with different materials. For example, although the wear layer 318 and the constraining layer 320 are adjacent to one another on the top surface, each form separate features that are opposite from one another. The wear layer 318 extends past an outer edge of the blade member (e.g., two or three millimeters) and up to the lifter contact region 322. Further, the constraining layer 320 of each segment laterally extends from an inner edge to the contact region 322, which is a region where a lifter assembly (not shown) contacts the blade member 300 underneath the underlying layers 308 as a fulcrum point.
An advantage of the present blade assembly disclosed herein is that the delamination distance is eliminated and blade levitation distances are within acceptable levels even when printing at a high speed (e.g., 137 pages per minute or higher). In addition, image to edge borders of three millimeter or less can be provided without decreasing the inter document zone between images on the photoreceptor 502, where control patches or different sensors are often employed.
In general, a three millimeter image-to-edge border is an allotted specification for printing images and a pressure profile for this border is illustrated as a required curve 704. This represents a drop in the pressure forces to zero within three millimeters of the leading edge (LE) and from the trailing edge (TE) of each sheet in order to obtain a three millimeter image-to-edge border on a printed sheet and not interfere with the IDZ area. In order to meet this specification, an actual curve 706 is shown where the transfer blade releases pressure within three to fifteen millimeters within each leading and trailing edges of the sheet zones. This, in turn, enables each printed sheet to be actuated and de-actuated from the photoreceptor PR with transfer blades and meet specifications. A relative ideal curve 708 illustrates an impractical situation where the printed sheet is fully actuated up to an exact point where each sheet zone begins and ends during transfer of the images from the photoreceptor PR to a printed sheet. An intermediate curve 710 illustrates an improved pressure force profile that approaches the shape of the ideal curve 708. However, the CTAB assembly discussed provides a CTAB curve 712 that is an even larger improvement that allows for an increased pressure force, shown as twenty steps as opposed to seventeen steps of a step motor with curve 704. One advantage that the present CTAB assembly disclosed herein allows is an improved image-to-edge border profile so that printing can be performed closer to the edges of a printed sheet or media acquiring the transferred images. This is caused by improved blade response times as shown in
It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.
