Patent Application
20120070203
The present exemplary embodiments broadly relate to a transfer assist blade (TAB) assembly for a marking device. However, it is to be appreciated that the present exemplary embodiments are also amenable to other devices and other applications.
The process of transferring charged toner particles from an image bearing member marking device (e.g. photoreceptor) to an image support substrate (e.g., sheet) involves overcoming cohesive forces holding the toner particles to the image bearing member. The interface between the photoreceptor surface and image support substrate is not always optimal. Thus, problems may be caused in the transfer process when spaces or gaps exist between the developed image and the image support substrate. A critical aspect of the transfer process is focused on the application and maintenance of high intensity electrostatic fields in the transfer region for overcoming the cohesive forces acting on the toner particles as they rest on the photoreceptive member. Careful control of these electrostatic fields and other forces is required to induce the physical detachment and transfer-over of the charged toner particles without scattering or smearing the developer material. Mechanical devices that force the image support substrate into intimate and substantially uniform contact with the image bearing surface have been incorporated into transfer systems. Various contact blade arrangements have been proposed for sweeping the backside of the image support substrate, with a constant force, at the entrance to the transfer region.
Today, field replacement of a TAB assembly needs to be done in a manner that is very robust and practical, and that meets the specific requirements of the conventional assembly. The TAB assembly has to translate extremely quickly in order to achieve the high speed (e.g., 7 msec) motion necessary to avoid sweeping into the inter-document zone process patches. Therefore, low mass is desirable to prevent the stepper motor from an over torque condition, which leads to skipped “steps”, causing a fault. However, in conventional TAB assemblies, the clamp/post assembly is thick and has an undesirably high mass in order to be rigid enough to support the translation speeds required.
Some spring-type clamps have been attempted but are not practical given that the clamp needs to be structurally supportive (for both the blade and posts), and electrically conductive to the lower semi conductive blade layer. Additionally, such “springs” are typically a thick (˜2.5 mm) sheet metal feature that is sectioned to allow flexure. As such, these springs cannot be compressed enough to provide a biasing force against the blade after riding past the ramp detent (the force is undesirably large and causes a non parallel point contact). In addition, in classical assemblies the upper section of the clamp that biases the blade into the extrusion does not provide a substantially secure and controlled position to maintain a proper 90 degree blade angle.
One known TAB assembly is a high frequency service interval (HFSI) part that has a HFSI replacement life of one million prints. The feature within the TAB assembly that fails or wears out is often a compliant blade subassembly that rides against the backside of the sheet during the Transfer process. This action, over time, even though the blade incorporates an UHMW (ultra high molecular weight) wear layer, eventually renders the blade out of specification for critical design dimensions, ultimately leading to image quality (IQ) defects. The common approach is to replace the entire TAB assembly at one million prints with a new part at a cost of about $80 each.
There is an unmet need in the art for a TAB assembly with a replaceable blade subassembly that can be replaced while the rest of the TAB assembly is retained, thereby reducing replacement costs and waste.
In one aspect, a transfer assist blade (TAB) assembly comprises a replaceable blade assembly, an extruded portion against which the replaceable blade assembly is biased, and a clamping assembly comprising a plurality of spring tabs that releasably interlock with the extruded portion to secure the replaceable blade assembly in an operational position between the extruded portion and the clamping assembly.
In another aspect, a replaceable blade assembly for a transfer assist blade (TAB) assembly comprises a blade proper that applies pressure on a passing print medium during printing, and a mounted blade portion with apertures therein through which spring tabs on a clamp assembly pass, and which is removably mounted between the clamp assembly and an extruded portion of the TAB assembly. The replaceable blade assembly further comprises a perforated portion between the mounted blade portion and the blade proper, the perforated portion being flexible to create an approximately 90° angle between the mounted blade portion and the blade proper when biased against an inner face of the extruded portion.
In yet another aspect, a method of replacing a blade assembly while reusing a transfer assist blade (TAB) assembly in which the TAB is mounted comprises monitoring wear of a blade proper on the blade assembly, determining that the blade assembly requires replacement, biasing a plurality of spring tabs on a clamp assembly upward to disengage the spring tabs from a corresponding plurality of interlocking features on an extruded portion of the TAB assembly, and rotating the clamp assembly away from the extruded portion about one or more clamp pockets at a top of the extruded portion. The method further comprises removing the blade assembly requiring replacement, positioning a replacement blade assembly on the clamp assembly, and inserting a plurality of clamp tabs on the clamp assembly into the plurality of clamp pockets on the extruded portion. Additionally, the method comprises rotating the clamp assembly toward from the extruded portion about the one or more clamp pockets at the top of the extruded portion, and snapping the spring tabs into the interlocking features to lock the replacement blade assembly in position between the clamp assembly and the extruded portion.
The systems and methods described herein can be utilized to reduce transfer assist blade replacement costs. With the described TAB assembly, users can reuse all of the components within the top level TAB assembly, less the replaceable compliant blade subassembly, which has a part cost of less than 9% of the current total price of the entire TAB assembly. The design of this reusable assembly incorporates simple yet robust features that allow for quick field replacement, saving considerable cost and landfill waste.
During removal of the blade assembly 12, the spring tabs 16 are biased upward and released from the extruded portion 18, and the clamp assembly 14 is free to pivot or rotate about clamp pocket(s) 26, which in turn allows one or more respective clamp tabs 28 to disengage from the clamp pocket(s) 26.
Various features of the TAB assembly 10 contribute to cost savings and improved operation of the TAB assembly 10. For instance, the bull nose block 24 prevents blade distortion as it maintains the blade assembly 12 in a 90° configuration. The mitigated distortion in turn reduces dirt or other contamination on the blade proper 21. The spring tabs 16 replace conventional rivets, which can come loose, causing the blade proper 21 to increase substantially above the 90° blade angle, contaminating the blade proper 21, resulting in backside streaks on successive prints. The spring tabs 16 additionally facilitate replacement of the blade assembly 21 and reuse of the extruded portion 18 and clamp assembly 14, which are expensive parts of the TAB assembly 10 and are not reusable when the blade assembly 12 is riveted thereto.
The reusable TAB assembly 10, whereby the only component being replaced is the compliant blade assembly 12, reduces costs compared to a conventional assembly in which the entire high precision alignment/mounting structure requires replacement. That is, both the extruded portion 18 and the clamp assembly 14 are reusable, since these are relatively expensive parts due to high tolerance machining and since these components do not wear out over the life of the machine, as does the blade assembly. Therefore, the described TAB assembly includes features that allow for meeting the critical parameters as described above, such as maintaining the space constraint, reducing mass and providing a simple means for field replacement. Additionally, the extruded portion 18 includes both interlock features 20 and clamp pockets 26 that, through mechanically advantaged leverage, precisely nest the blade 12 into the proper position. The clamp assembly 14 includes the clamp tabs 28, the block 24, and a plurality of spring tabs 16 to further assist in maintaining the proper blade position. The spring design affords ease of assembly/disassembly. Additionally, the TAB assembly 10 provides significant cost savings over current design via single item replacement, in addition to ease of serviceability.
When the replaceable blade assembly 12 reaches its HFSI end of life (e.g., one million prints or some other predefined number of prints), a field service representative or other technician may replace the blade assembly. To do so, the spring tabs 16 are biased upwards, using a straight edge such as a ruler or the like, while pressing the back edge of the springs sideways. Alternatively, a ruler or other straight edge may be wedged between the extrusion 18 and the spring tabs 16, thereby concurrently unlocking and removing the clamp assembly 14. The lower edge of the clamp assembly 14 is now free to rotate about the clamp pockets until the spring(s) clear the interlock features, allowing the clamp tab(s) 28 to disengage from the clamp pocket(s) 26. The blade assembly 12 can now be removed and recycled as waste plastic. A replacement blade assembly is inserted into the extrusion 18 using the clamp assembly 14 as a guide, folding the blade assembly 12 along the perforated portion 22 coincident to a 90° upper edge of the extrusion. The clamp tab(s) 28 insert into the clamp pocket(s) 26, nesting the blade assembly against the extrusion. The clamp assembly 14 then pivots about this engagement until the spring tabs 16 snap into the extrusion/spring tab interlock feature(s) 20. The plurality of spring tabs 16 on the clamp assembly 14 lock the blade assembly in place, while the block or bull nose 24 biases the blade 21 against the 90° upper edge of the extrusion 18, thus maintaining the proper blade profile.
At 72, the spring tabs on the TAB assembly are biased upwards, using a straight edge ruler or other straight edged tool, while pressing the back edge of the springs to sideways (e.g., to the right or left) relative to the top of the assembly shown in
The exemplary embodiments have been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiments be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
