Patent Publication Number: US-6223012-B1

Title: Developer unit with a replenish port

Description:
FIELD OF THE DISCLOSURE 
     This disclosure relates generally to developer units and, in particular, to an improved replenishable developer unit. 
     BACKGROUND OF THE INVENTION 
     Developer units, also known as customer replaceable units or “CRU&#39;s”, are known. Typically, developer units are arranged for mounting in a host printing machine to develop a latent image present on a photosensitive member. A typical developer unit comprises a donor roll (also known as a “mag roll”) and contains a supply of developer compound, also known as “toner”. The developer unit is arranged for supplying developer compound to the donor roll. The donor roll, in turn, is arranged to provide developer compound to the photosensitive member. Ultimately, the host printing machine produces copies of the developed latent image. 
     It is desirable for a developer unit to be capable of producing a large number of copies before its supply of developer compound becomes exhausted. As a result, it is thus advantageous for a developer unit to be capable of storing a large quantity of developer compound. 
     Once a developer unit&#39;s supply of developer compound is exhausted, the developer unit must be refilled or replenished with additional developer compound. Some developer units include a replenish port for purposes of replenishing by the user. With this arrangement, the user adds developer compound to the replenish port in order to replenish the developer unit with additional developer compound. 
     Typical developer units comprise internal agitators arranged to push or propel the developer compound to the donor roll. In large-capacity developer units, typically two (2) or more agitators are used in tandem. With a two-agitator developer unit design, for example, a first agitator is arranged for propelling developer compound to a second agitator. The second agitator, in turn, is arranged for propelling developer compound to the donor roll. 
     It is known that the developer unit business (industry) is very competitive. To gain competitive advantage, therefore, it is desirable to minimize the unit manufacturing cost of a developer unit. A developer unit&#39;s manufacturing cost is based on many cost factors, one key cost factor being the total number of components comprised by the developer unit. As a result, reducing the developer unit&#39;s total component count generally also will reduce the developer unit&#39;s manufacturing cost. 
     One cost limitation of a developer unit comprising multiple agitators, therefore, is the cost of the multiple agitator components. Thus, it would be desirable to provide a replenishable developer unit with one (1) agitator. 
     The problem, therefore, is how to reduce the number of agitators required in a replenishable developer unit, hopefully to a single (1) agitator. 
     As a result, there is a need for an improved replenishable developer unit. 
     SUMMARY OF THE INVENTION 
     In one aspect of the invention, a developer unit comprises a donor roll and a lower housing. The lower housing comprises a developer pan for containing developer compound. The developer pan has a first end near the donor roll and a second end opposite the donor roll. The developer pan further comprises a ramp inclined downwards at a substantially fixed angle from the second end towards the first end, with the fixed angle exceeding the angle of repose of the developer compound. 
     In another aspect of the invention, a printing machine comprises a developer unit. The developer unit comprises a donor roll and a lower housing. The lower housing comprises a developer pan for containing developer compound. The developer pan has a first end near the donor roll and a second end opposite the donor roll. The developer pan further comprises a ramp inclined downwards at a substantially fixed angle from the second end towards the first end, with the fixed angle exceeding the angle of repose of the developer compound. 
    
    
     DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     FIG. 1 shows an improved replenishable developer unit, in accordance with the present invention; and 
     FIG. 2 shows a printing machine having the FIG. 1 improved replenishable developer unit therein. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Briefly, a developer unit comprises a donor roll, a developer pan for containing developer compound, and a single agitator. The developer unit also comprises a replenish port for adding developer compound to the developer pan. The replenish port is arranged so that developer compound added to the replenish port falls through the port to an inclined ramp at one end of the developer pan. Further, the inclined ramp&#39;s angle of incline is arranged to exceed the angle of repose of the developer compound. As a result, the added developer compound flows down the ramp and towards the agitator. The agitator, in turn, is arranged to propel the developer compound towards the donor roll. 
     Referring now to FIG. 1, there is shown an improved replenishable developer unit  1   00 , in accordance with the present invention. The developer unit  100  comprises a donor roll  10  and a lower housing  120 . The lower housing  120  comprises a developer pan  13  arranged for containing a quantity of developer compound  17 . The developer pan  13  comprises a first end  131  near the donor roll  10  and a second end  139  opposite the donor roll  10 . 
     The developer unit  100  further comprises a single agitator  11  positioned between the first end  131  and the second end  139 . As shown, the agitator  11  comprises a paddle  110  arranged to rotate  113  around an axle  115 . It will be appreciated that the axle  1   15  is arranged to be rotatably powered by a gear train (not shown). The gear train, in turn, is powered by torque provided by a host printing machine. 
     Still referring to FIG. 1, the developer pan  13  comprises a ramp  135  located near the second end  139 . As shown, the ramp  135  is inclined downwards towards the agitator  11  and the first end  131  at a substantially fixed angle  15  with respect to the horizon  16 . The fixed angle  15  of the ramp  135  is selected to exceed the angle of repose of the developer compound  17 . 
     The developer unit  100  further comprises an upper housing  14  enclosing the developer pan  13 . The upper housing  14  comprises a replenish port  140  for adding developer compound  17  to the developer pan  13 . 
     The replenish port  140  is aligned with the ramp  135 . As a result of such alignment, developer compound  17  added  190  to the replenish port  140  falls  191  by means of gravity to the ramp  135 . 
     As mentioned above, the ramp  135  is arranged so its fixed angle  15  exceeds the angle of repose of the developer compound  17 . As a result, the force of gravity causes any developer compound  17  present on the ramp  135  to flow  195  towards the agitator  11 . In turn, the agitator  11  is arranged to propel the developer compound  17  towards the first end  131  and the donor roll  10 . 
     As shown, the developer unit  100  exclusively comprises only one (1) agitator, namely, the single agitator  11 . 
     In one embodiment, the fixed angle  15  of incline of the ramp  135  comprises about fifty (50) degrees. 
     Also in one embodiment, the developer compound  17  comprises SCD toner (known as “EMT-700”), with a corresponding angle of repose  15  comprising about thirty-five (35) degrees. 
     It will be appreciated that a printing machine may be arranged with an improved replenishable developer unit, in accordance with the present invention. Referring to FIG. 2, for example, there is shown an exemplary printing machine  200  arranged with developer unit  100 . It will be appreciated that developer unit  100  depicted in FIG. 2 corresponds to the developer unit  100  depicted in FIG.  1  and described herein. 
     In one embodiment, the printing machine  200  comprises a compact desktop multi-function digital machine. 
     Some advantages of an improved replenishable developer unit, in accordance with the present invention, now will be discussed. 
     To begin, the improved replenishable developer unit  100  comprises only a single (1) agitator, instead of multiple agitator components. As a direct result of reducing the number of required agitators, the total component count of developer unit  100  is advantageously reduced. Moreover, as a result of reducing the total component count, the corresponding unit manufacturing cost of developer unit  100  is thereby advantageously reduced. 
     As a further advantage of the improved replenishable developer unit  100 &#39;s single-agitator design, the corresponding gear train required to drive the single agitator  11  is simplified. This simplified gear train, in turn, results in a further advantageous reduction in manufacturing cost of developer unit  100 . 
     A further advantage of the improved replenishable developer unit  100 &#39;s single-agitator design is related to the fact that the torque required to drive the unit  100 &#39;s agitator  11  and corresponding gear train ultimately must be provided by the host printing machine  200 . Thus, as a result of developer unit  100  comprising a single (1) agitator  11  and corresponding simplified gear train, the total torque required by host printing machine  200  to drive these elements is now also reduced. This reduction of required drive torque, in turn, reduces power consumption by the host printing machine  200 . 
     Moreover, this reduction in power consumption by printing machine  200  comprises a further competitive advantage for the developer unit  100  itself. This is because the printing machine user generally will prefer to use a developer unit that reduces power consumption by the printing machine. 
     While various embodiments of an improved replenishable developer unit, in accordance with the present invention, have been described above, the scope of the invention is defined by the following claims.