Patent Publication Number: US-6670817-B2

Title: Capacitive toner level detection

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to an apparatus for the detection of toner levels in an electrophotographic printing machine. 
     BACKGROUND OF THE INVENTION 
     Generally, the process of electrophotographic printing and/or copying includes charging a photoconductive surface to a substantially uniform potential or voltage. The charged photoconductive surface is then exposed to record an electrostatic latent image corresponding to an original document to be copied. Thereafter, a developer material is brought into contact with the latent image. The developer material attracts toner particles onto the latent image. The resultant image is then transferred from the charged photoconductive surface onto a copy sheet, to which it is subsequently bonded. 
     Contaminants, such as paper fragments, developer material, toner and other residue, remain on the photoconductive surface after the image has been transferred to the copy sheet. This residue must be removed from the photoconductive surface prior to the next charging thereof. Typically, a cleaning station is provided within the electrophotographic printing and/or copying machine to remove the residue from the photoconductive surface. The cleaning station generally includes cleaning brushes and a vacuum system. The cleaning brushes dislodge the residue from the photoconductive surface into an air stream created by the vacuum system. The residue is deposited by the air stream into a waste container. The waste container must be emptied when full or nearly full, in order to prevent residual toner particles from being catastrophically distributed throughout the machine. Thus, the level of residual toner within the waste container must be monitored in some way in order to detect when the container is full or nearly full. 
     One method by which the level of residual toner is conventionally monitored is through the use of an optical monitoring device. Optical devices, however, require frequent cleaning to remove stray contaminants, such as dust and other particles, from the device to ensure proper operation. Further, such optical devices can yield premature or inaccurate indications of a full waste container due to toner dust clinging to the sides of an otherwise empty or only partially full waste container. Such false indications of a full waste container can result in increased machine downtime due to the required operator intervention to clear such a false indication. 
     Another method by which the level of residual toner is conventionally monitored is through the use of a weighing device which measures the weight of the waste container to thereby indicate when the container is full or nearly full. Such weighing devices require frequent calibration. Furthermore, different types of toner will have different densities. When, for example, a lower density toner is in use, a weight-based monitoring system can result in the waste container being filled with residual toner before the system indicates a full waste container. Such a failure to detect a full waste container results in toner particles being catastrophically distributed throughout the machine, increased machine downtime, and is likely to require a lengthy servicing of the machine. 
     Yet another method by which the level of residual toner is conventionally monitored is through the use of a capacitive sensor disposed on the outside of and adjacent to the waste container. Such external capacitive sensors are susceptible to electrostatic discharge and other forms of electrical interference which can contribute to an erroneous indication of container status. Further, and similar to optical systems, particles, such as stray toner and other particles, may become lodged between the waste toner bottle and one or more of the electrodes or plates thereby interfering with the operation of the sensor. Moreover, such external capacitive sensors may be bumped and damaged during changing and/or emptying of the waste toner bottle. 
     Therefore, what is needed in the art is a toner level sensing device that is less affected by stray toner particles and other contaminants. 
     Furthermore, what is needed in the art is a toner level sensing device that is less sensitive to variations in toner density. 
     Still further, what is needed in the art is a toner level sensing device that is less susceptible to electrical noise and has a high signal-to-noise ratio. 
     Moreover, what is needed in the art is a toner level sensing device that is less susceptible to erroneous operation due to electrostatic discharge and other forms of electrical interference, and can be used with a conductive bottle. 
     SUMMARY OF THE INVENTION 
     The present invention provides an apparatus for detecting the level of material within a container. 
     The invention comprises, in one form thereof, a container having an electrically conductive container body. The container body defines a container cavity. A sensor assembly is disposed within said container cavity. The sensor assembly is electrically isolated from the container body, and is configured for sensing a level of material within the container cavity. 
     An advantage of the present invention is that the sensor is disposed within the container, and thus is less effected by electrical noise, large objects and other contaminant particles. 
     Another advantage of the present invention is that it less sensitive to variations in toner density. 
     Yet another advantage of the present invention is that toner particles are less likely to cling or stick to the sensor or to the sides of the waste container, or become lodged between the sensor plates, and therefore it is less susceptible to erroneous operation. 
     A still further advantage of the present invention is that it is less susceptible to erroneous operation due to electrostatic discharge and other forms of electrical interference. 
     An even further advantage of the present invention is that it has a high signal-to-noise ratio. 
     Other advantages of the present invention will be obvious to one skilled in the art and/or appear hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become appreciated and be more readily understood by reference to the following detailed description of one embodiment of the invention in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a schematic elevational view of portions of an electrophotographic printing machine incorporating one embodiment of a capacitive toner level detector of the present invention; and 
     FIG. 2 is an elevational view of the container and capacitive toner level detector of FIG.  1 . 
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Referring now to the drawings, and particularly to FIG. 1, there is shown an electrophotographic printing and/or copying machine incorporating one embodiment of a capacitive toner level detector of the present invention. 
     Electrophotographic printer or copying machine  10  generally includes main belt  12  that rotates through the various functional areas or stations of machine  10 . Belt  12  is typically constructed of an electrically conductive material, and has a photoconductive surface deposited thereon or otherwise affixed thereto. Belt  12  is driven in the direction of arrow  14  by drive roller  16 , which is driven by a motor (not shown), and is tensioned by tensioning roller  18 . A portion of belt  12  is first passed through charging station  20 , such as a corona generating device, which charges belt  12  to a predetermined electrical potential that is typically negative. Belt  12  is then rotated to exposure station  22 , which selectively discharges the photoconductive surface of belt  12  to thereby form an electrostatic latent image that corresponds to an original to be printed or copied. 
     The latent image now on the surface of belt  12  is rotated to development station  24 , wherein toner particles are brought into contact with the latent image by, for example, magnetic brush rollers to thereby form a toner image on belt  12 . Belt  12  is then rotated to place the toner image within transfer station  26 , and an image substrate  28 , such as a piece of paper or transparency, is brought into contact with the toner image. Transfer station  26  ionizes or otherwise charges, typically through a corona generating device, image substrate  28  and thereby attracts the toner image to image substrate  28 . Image substrate  28  is then passed in the direction of arrow  29  to fusing station  30  wherein the toner image is fused, typically by fusing rollers, to image substrate  28 . Image substrate  28  is then separated from belt  12  and is guided to a paper tray for removal from machine  10  by an operator. 
     Belt  12  is then cleaned of residual toner particles at cleaning station  32 . Cleaning station  32  typically includes a charging station that charges to a suitable electrical potential and polarity the residual toner particles remaining on the photoconductive surface of belt  12 . Cleaning station  32  further typically includes at least one vacuum-assisted electrostatic cleaning brush. The cleaning brush rotates at relatively high speed to create sufficient mechanical force to remove the residual toner from belt  12 . The dislodged residual toner particles are drawn into an air stream created by a vacuum device, also typically included within cleaning station  32 , which deposits the residual toner particles into conductive container  40 . 
     Conductive container  40 , referring now to FIG. 2, includes container body  40   a  which defines container cavity  40   b . Conductive container  40  is installed within machine  10  such that the residual toner particles carried by the air stream are deposited in container cavity  40   b . More particularly, conductive container  40  is suspended by neck  42  from brackets  44  of machine  10 . Brackets  44  are attached to or integral with frame  46  of machine  10 . Conductive container  40  is constructed of an electrically conductive material, such as, for example, aluminum or other suitable material. Conductive container  40  further includes electrical cable  52 , connector  54 , grounding wire attachment  56 , orifice  58  and sensor assembly  60 . 
     Electrical cable  52  electrically interconnects sensing circuit  70  with sensor assembly  60 . Electrical cable  52 , includes electrical conductors or wires  52   a ,  52   b  and an insulative cover  52   c . Electrical cable  52  is terminated at one end thereof by connector  54 . Connector  54  is, for example, a standard electrical connector which mates with a corresponding connector (not referenced) associated with circuit  70  to thereby electrically interconnect sensing circuit  70  and sensor assembly  60 . Electrical cable  52  passes through orifice  58  defined by conductive container  40  and into the interior of conductive container  40 . Sealing member  58   a , such as, for example, a gasket or seal, is disposed in association with orifice  58  to thereby seal the interface of insulative cover  52   c  and conductive container  40  in a fluid and liquid tight manner to thereby prevent the escape of residual toner particles from conductive container  40 . 
     Ground wire attachment  56 , such as, for example, a quick connect device or terminal, is affixed to or integral with conductive container  40 . A first end of ground wire  72  is received within or affixed to ground wire attachment  56  to thereby electrically interconnect ground wire  72  and conductive container  40 . A second end of ground wire  72  is electrically connected, such as, for example, soldered or through an electrical connecter, to frame  46  of machine  10 . Frame  46  of machine  10  is held at ground potential. Thus, ground wire  72  electrically interconnects conductive container  40  to frame  46  and thereby holds conductive container  40  at ground potential. 
     Sensor assembly  60  senses the level of waste or residual toner particles disposed within conductive container  40 . Sensor assembly  60  includes a first electrode or plate  76  and a second electrode or plate  78 . Each of plates  76  and  78  is coated with a non-stick coating  79 , such as, for example, polytetrofluroethylene or other suitable non-stick coatings. Each of plates  76 ,  78  are disposed within and mechanically secured to conductive container  40 , and are electrically isolated from conductive container  40 . More particularly, plates  76 ,  78  are mechanically secured to and electrically isolated from conductive container  40  by electrically non-conductive fasteners  80   a ,  80   b , respectively, such as, for example, plastic brackets or snap-fit tabs or projections, which are in turn affixed to an inside surface of conductive container  40 . Plates  76 ,  78  are disposed within conductive container  40  at approximately the same distance d from the bottom thereof, are spaced a predetermined distance apart from each other, and are disposed at generally diametrically-opposed points of conductive container  40 . Each of plates  76 ,  78  is electrically connected to a respective one of wires  52   a ,  52   b  of electrical cable  52 , to thereby connect plates  76 ,  78  to circuit  70 . 
     More particularly, wire  52   a  interconnects plate  76  to a node (not shown) of circuit  70  that is held at ground or nearly ground potential, such as, for example, by a virtual ground amplifier (not shown) having a low input impedance. Wire  52   b  interconnects plate  78  to a voltage signal source, such as, for example, an oscillating circuit or alternating current sine wave generator (neither of which is shown), included within circuit  70 , or to a suitable voltage signal source within machine  10 . Thus, plate  78  carries a voltage signal source whereas plate  76  is held at ground or nearly ground potential. The voltage signal source applied to plate  78  induces a corresponding current on plate  76 . The magnitude of the current induced in plate  76  will vary dependent upon the amount of waste or residual toner that is disposed between plates  76  and  78 . If a substantial amount of residual toner is disposed within conductive container  40  between plates  76  and  78 , the magnitude of the current induced in plate  76  will be relatively high compared to the current induced in plate  76  when no or only a small amount of residual toner is disposed within conductive container  40  between plates  76  and  78 . 
     The current induced in plate  76  is carried by wire  52   a  to circuit  70 . Circuit  70  converts the induced current, such as, for example, by a rectifier, to an indicating direct current (DC) voltage which is then compared, such as, for example, by a comparator, to a reference DC voltage. The reference DC voltage corresponds to a predetermined DC voltage level that is indicative of conductive container  40  being full or nearly full of residual toner particles. If the indicating voltage is greater than the reference voltage, conductive container  40  is full and bottle fall signal  82  is issued by circuit  70 . In response to bottle full signal  82  associated control circuitry (not shown) of machine  10  suspends the operation thereof until conductive container  40  is emptied to thereby reset full signal  82 . If the indicating voltage is less than the reference voltage, conductive container  40  is not full and bottle empty signal  84  is issued by circuit  70 . 
     In use, and as stated above, residual and waste toner particles are dislodged from belt  12  and deposited into conductive container  40  by cleaning station  32 . This process continues until the level of waste toner particles contained within conductive container  40  reaches approximately depth d, whereupon the induced current in plate  76  increases to a level which results in bottle full signal  82  being issued and the operation of machine  10  being suspended as described above. 
     In conventional nonconductive toner waste containers toner particles tend to cling to and accumulate first upon the sides of the container due to electrostatic forces. Such a condition can result in a premature indication that the nonconductive container is full due to the sides of the container being completely covered with toner particles. Due to the tendency of the toner particles to cling to accumulate first upon the sides of the container, a large area or volume in the middle portion of the container is often virtually empty and the full capacity of the nonconductive container is not utilized. In contrast, conductive container  40  is held at ground potential by ground wire  72 . As particles of waste toner drop into conductive container  40  and accumulate therein, any electrostatic charge on conductive container  40  and/or the toner particles is dissipated by virtue of conductive container  40  being held at ground potential. The toner particles are therefore less likely to cling to and accumulate on the sides of conductive container  40  due to electrostatic force. The toner particles are more likely to settle into and utilize the entire volume of conductive container  40 , and the likelihood of a premature indication of a full condition of conductive container  40  is thereby reduced. 
     Any electrostatic charges that would build up on an otherwise nonconductive waste container are dissipated by virtue of conductive container  40  being constructed of an electrically conductive material and being held at ground potential via ground wire  72 . Since any electrostatic charge on conductive container  40  is dissipated, sensor assembly  60  is less susceptible to electrostatic charge on conductive container  40 . Furthermore, the grounding of conductive container  40  reduces the susceptibility of sensor assembly  60  to various other forms of electrical interference, such as random electrostatic discharges which occur in the electrically noisy environment of machine  10 . Moreover, the positioning of sensor assembly  60  within conductive container  40  reduces the exposure of sensor assembly  60  to electrostatic discharges and other forms of electrical interference. Thus, an erroneous indication of a full, or a faulty indication of an empty, conductive container  40  is less likely to occur. 
     Sensor plates  76 ,  78  are each covered with non-stick coating  79 . Non-stick coating  79  inhibits toner particles that enter and accumulate within conductive container  40  from adhering to sensor plates  76 ,  78 . Toner particles which adhere to plates  76 ,  78  affect, i.e., increase, the magnitude of the current induced in plate  76  and can therefore lead to an erroneous full bottle indication. Thus, non-stick coating  79  of plates  76 ,  78 , by making toner particles less likely to adhere thereto, reduces the likelihood that sensor assembly  60  will yield false bottle fall indications. 
     In the embodiment shown, sensor assembly  60  includes two plates or electrodes  76 ,  78 . However, it is to be understood that the sensor assembly of the present invention can be alternately configured, such as, for example, with four or more plates or electrodes Furthermore, plates  76 ,  78  are shown as being generally diametrically-opposed within container  40 . However, it is to be understood that the electrode plates can be alternately configured, such as, for example, variously spaced apart and/or positioned within the conductive container. 
     In the embodiment shown, container  40  includes ground wire attachment  56  disposed on the exterior of the container. However, it is to be understood that the container of the present invention can be alternately configured, such as, for example, with a ground wire attachment disposed on the inside of the container. 
     In the embodiment shown, a separate ground wire  72  electrically connects ground wire attachment  56  of container  40  to frame  46  of machine  10 . However, it is to be understood that a ground wire can be incorporated into electrical cable  52 , and be similarly connected between frame  46  and ground wire attachment  56 . 
     While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the present invention using the general principles disclosed herein. Further, this application is intended to cover such departures from the present disclosure as come within the known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.