Patent Publication Number: US-7912387-B2

Title: Screen configuration for use in a toner concentration field measurement tool

Description:
Cross-reference is hereby made to commonly assigned and copending U.S. application Ser. No. 12/028,022, filed Feb. 8, 2008, and entitled “Toner Concentration Field Measurement Tool” by Mark Alan Scheuer, et al. The disclosure of the heretofore-mentioned application is incorporated herein by reference in its entirety. 
     The present disclosure is related to a toner concentration (TC) measurement device and method that measures the concentration of toner used in electrostatic printing machines, and more particularly, to an improved screen to be used in the TC measurement device. 
     Electrostatographic machines including printers and copiers form a latent image on the surface of photosensitive material which is identical with an original image, brings toner-dispersed developer into contact with the surface of the photosensitive material, and sticks toner particles only onto the latent image with electrostatic force to form a copied image on a copy sheet. In order to maintain the copy quality of the image transferred to the copy sheet, there are several types of toner concentration measuring devices. 
     One such device is in U.S. Pat. No. 6,377,760 where a toner concentration apparatus is shown that measures TC by providing first and second light guiding devices whose end surfaces project into a duct traversed by developer fluid and a light receiving device for receiving light transmitted from the first light guiding device to the second light guiding device. In U.S. Pat. No. 6,931,219 an apparatus and method is disclosed for determining TC of a sample comprised of toner and carrier that includes exposing the sample to light; the exposing includes emitting light at a predefined wavelength based upon the color of the toner; detecting the light reflected off the sample with an optical sensor and determining the TC of the sample base upon the light reflected off the sample. These techniques are directed to in-machine TC testing and do not answer problems encountered when measuring TC in the field and separate and apart from a machine. The heretofore mentioned references are included herein by reference to the extent necessary to practice the present disclosure. 
     The measurement of TC in the field by a technical representative is presently done by indirect means, for example, as shown in U.S. Pat. No. 5,166,729, and with limited results since measurement of clear and shades of gray toner are difficult, if not impossible, to sense relative to gray carrier. 
     Heretofore, TC has been measured in the laboratory by blowing toner off of carrier which, in turn, is kept captive in a metal cage. By measuring the weight of the cage, the cage with developer, and the cage with carrier only, the TC is easily calculated. Putting the laboratory measurement into the field has proven to be very difficult because the laboratory measurement device is too large, cumbersome and expensive to be used by each technical representative in the field. For example, laboratory scales cost over $1000.00 and are not meant for travel. Removing the toner from the carrier is non-trivial, and proper handling of materials in customer sites has been troublesome. Hence, there is still a need for an efficient, low cost method and apparatus that can be used to measure TC in the field. 
     The TC method and apparatus in copending U.S. application Ser. No. 12/028,022 for direct gravimetric measurement of TC in the field is simple, cost effective and compact and includes a molded conductive plastic developer container with an entry nozzle for air and a series of screens strategically positioned therein to cover an open portion in the bottom thereof. A portable vacuum cleaner is adapted to fit around the bottom portion of the container. The developer container is configured to take advantage of cyclone separator functionality with multiple screen filtration creating a vortex with applied pressures from the vacuum cleaner to assist in separation of the fine toner from the coarser, high density carrier particles. The multiple screens are cleaned periodically by reversing the air flow. A problem has been encountered because presently there is no feature that prevents a small percentage of the carrier bead population from being trapped between screens during screen filtration and resist cleaning when airflow in the device is reversed and thereby ultimately requiring the container to be replaced. 
     Hence, in answer to the above-mentioned problem and in accordance with the present disclosure, a sandwich of 3 screens is shown for filtration use in the above-mentioned system with a lower 20 mesh screen for strength, a middle 500 mesh screen to contain the beads inside the container and an upper 400 mesh screen to break the momentum of the agitated beads and keep them from damaging the middle screen. The upper screen has die-cut holes around its edges to allow removal of any trapped beads between the upper screen and the middle screen. When the air is turned ON, the beads approach the screens in the center of the container. Recirculating airflow within the container carries the beads away from the upper screen at the edges. Thus, with the upper screen being die-cut with openings around its edges, the openings allow the trapped beads to return to the inner chamber of the container for removal during cleaning. 
    
    
     
       Various of the above-mentioned and further features and advantages will be apparent to those skilled in the art from the specific apparatus and its operation or methods described in the example(s) below, and the claims. Thus, they will be better understood from this description of these specific embodiment(s), including the drawing figures (which are approximately to scale) wherein: 
         FIG. 1  is a frontal view of an exemplary weighing cage that includes the improved filtration screen design of the present disclosure; 
         FIG. 2  is an exploded, isometric view of the improved composite filter of the present disclosure and a seal that filter toner from carrier as it is evacuated from the cage of  FIG. 1 ; 
         FIG. 3  is a plan view of an improved screen embodiment in accordance with the present disclosure; 
         FIG. 4  is a plan view of an alternative improved screen embodiment in accordance with the present disclosure; and 
         FIG. 5  is a frontal view of the weighing cage of  FIG. 1  connected to a vacuum source. 
     
    
    
     While the disclosure will be described hereinafter in connection with a preferred embodiment thereof, it will be understood that limiting the disclosure to that embodiment is not intended. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the disclosure as defined by the appended claims. 
     The disclosure will now be described by reference to a preferred embodiment xerographic printing apparatus that includes a method of loading multiple types of paper in a feed tray to allow printing of multiple jobs without operator intervention. 
     For a general understanding of the features of the disclosure, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to identify identical elements. 
     Referring now to  FIGS. 1-5 , parts of a field measurement kit are disclosed for measuring TC in the field. In  FIG. 1 , cage  112  is a molded conductive plastic unit. The cage has an open upper funnel end that narrows to a throat area of about 5 mm located between arrows  114  that widens out to a straight cylindrical detone chamber. The throat area of the venturi shaped cage is structured to accelerate airflow therethrough which will strip toner off the carrier beads as air is drawn through the open end of the cage. The venturi shape is critical. The streamlined shape keeps the sides free of toner. Any stagnation point in the interior will provide a surface for toner to collect. Carrier beads  115  are airborne during the toner removal stage and will scrape toner that lands on the sides, which can occur when the vacuum is turned ON. The beads form a tornado shape inside the cage and rise to the neck of the venturi as shown by the arrows. The cage has a partially open end at the bottom thereof that is covered by an improved set or sandwich of screens  119  as shown in  FIG. 2  in accordance with the present disclosure. The set of metal or fabric screens at the base of the cage contain the carrier beads and allow the toner to pass out of the cage and prevent bead leakage. The sandwiched set of screens consists of a bottom screen of rectangular weave of coarse 20 mesh material (20 openings per inch)  126  for strength to support the other screens, a center 500 mesh screen  124  with 25 micron openings and 0.0009 inch wire to contain the beads inside the cage, and a top 400 mesh screen  122  with 38 micron openings and 0.0011 inch wire to break the momentum of the agitated carrier beads and absorb most of the impact of the carrier beads (and protect the 500 mesh screen from damage). A flat latex gasket seal  120  which could be rubber, if desired, is placed on top of the sandwich of screens to seal the cage. The choice of a 400 mesh coarse screen and a 500 mesh filter screen, while preferred, is dependent on the carrier size distribution and the toner size distribution, it should be understood that larger or smaller particles of both toner and carrier will affect the choice of the screen sizes. Also, while the preference of steel wire screens over nylon, polyester, fabric, etc., is based on the percent of open area, the efficiency of the toner removal and a desire to limit the amount of filter screen area to which the free toner could stick (and effect measurement), any of the aforementioned screens will produce usable results. 
     It is possible for a small percentage of the carrier beads to become trapped between the 400 and 500 mesh screens and resist cleaning when air flow is reversed in the system disclosed in  FIG. 5  and will eventually require replacement of the screens. These beads become trapped between the 400 and 500 mesh screens, particularly since they have large initial velocity when hitting the 400 mesh screen from above. In some cases, only about 25% of these beads can be removed by back vacuuming cage  112 . The trapped beads will eventually clog the screens, cutting off the vacuum air flow, and the cage will cease to function, thus causing a replacement expense. The 400 and 500 mesh screens and a coarse support screen are die-cut from large sheets and spot welded together at their edges. The weld holes are covered with a latex gasket and encapsulated in the plastic housing of the cage so no carrier loss occurs through the weld holes. In order to eliminate the possibility of carrier beads becoming trapped during the cleaning process, and in accordance with the present disclosure, one of die-cut hole patterns  141  and  148  as shown in screens  140  and  145  in  FIGS. 3 and 4 , respectively, is placed into the 400 mesh screen around its edges to allow any trapped beads to escape while simultaneously providing protection to the 500 mesh screen in the center of the cage. The 400 mesh material must still extend to the edges of the cage to provide mechanical integrity to the screen, which is solely supported on the edges by the welds and the plastic housing. When the air is turned ON, the beads approach the screens in the center of the cage as shown by the arrows and beads in  FIG. 1 . The recirculating airflow carries the beads away from the screen at the edges. Therefore, sections of the 400 mesh can be removed from the edges without affecting the capacity of the 400 mesh screen to protect the 500 mesh screen. These openings,  141  and  148 , allow the trapped beads to return to the inner chamber for removal. Preferred openings or hole patterns  141  and  148  for the 400 mesh screen are shown in  FIGS. 3 and 4 , but other hole patterns could be employed, if desired. The 400 mesh screen is preferably circular and with or without the openings is die-cut in either case so the added openings do not affect the cost of manufacturing the cage assembly. 
     In  FIG. 5 , a portable vacuum source  130  that is part of the heretofore mentioned field measurement kit is shown connected to the bottom end of conductive plastic cage  112  through a hose  132  with the bottom of cage  112  resting on a grounded conductive pin  134  to ensure complete removal of toner. 
     Over time, as the beads become trapped in the center section of the 400 mesh screen cleaning of the screen necessary, however, simply inverting cage  112  and reversing the air flow is not sufficient to remove the beads caught in the screen. In addition, the user must strike the cage on the side to mechanically move the beads from the closed areas in  FIG. 4  to the open areas so the reversed flow can dislodge them from the screen. Now inverting the cage in the vacuum cleaner hose and turning on the vacuum will supply sufficient force to release the beads from the 400 mesh screen and cause them to exit the cage via the throat section of the cage. 
     In practicing field measuring of TC, a sample of toner/carrier of approximately 3 grams is obtained from a developer housing of a machine and placed into cage  112  which is connected to vacuum source  130  to vacuum the toner off the carrier. The field measurement kit also contains a conventional digital portable scale that has a 1 mg resolution. The digital scale will allow the technical representative to measure the weight of the empty cage, the developer sample in the cage, and the detoned carrier in the cage. Then, using a look-up table, a toner concentration value is determined and used to adjust the calibration of an in-situ toner concentration sensor in software or to validate the current reading from the sensor. 
     It should now be understood that a method and apparatus that assures a long useful life of a TC measurement device at minimal cost is disclosed that includes a filtration screen that has a die-cut pattern of holes around the periphery thereof that facilitate removal of carrier beads trapped between the filtration screen and a second screen. 
     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. Unless specifically recited in a claim, steps or components of claims should not be implied or imported from the specification or any other claims as to any particular order, number, position, size, shape, angle, color, or material.