Abstract:
A fuser assembly and associated method for an electrophotographic machine heats a first fuser roll with a first heating device. A second heating device heats a second fuser roll. It is determined whether a first temperature of the first fuser roll is below a first target temperature. It is also determined whether a second temperature of the second fluser roll is below a second target temperature. If both the first temperature is below the first target temperature and the second temperature is below the second target temperature, the first heating device is operated during a first time period and operation of the second heating device is inhibited throughout the first time period.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention. 
     The present invention relates to an electrophotographic machine, and, more particularly, to a fuser assembly in an electrophotographic machine. 
     2. Description of the Related Art. 
     A fuser assembly is used in an electrophotographic machine to fuse previously applied toner onto a surface of a print medium, such as paper. The fuser assembly includes a fuser roll which presses the toner into the print medium. The fuser roll is heated internally by a heating element, such as a fuser lamp, disposed therein. 
     The increase in function and speed of electrophotographic printers has driven a continuing increase in the amount of current drawn from the wall outlet to power the printing operation. The wattage of the system power supply continues to increase as more functions and higher speeds are demanded. The higher speeds, expressed in pages per minute, have led to the use of higher wattage fuser lamps and the use of multiple lamps to facilitate the toner fusing operation at these higher print speeds. 
     A problem is that the combination of the current drawn by the power supply and the fuser lamps can now exceed the amount of current available from a standard 15 ampere, 120 volt wall outlet. The high current draw can result in nuisance tripping of the circuit breaker. It is known to avoid such nuisance tripping by specifying the use of a dedicated, high current outlet. A problem is that such dedicated high current outlets require installation by a qualified electrician, which is both costly and time consuming. 
     What is needed in the art is a way of preventing the fuser assembly of an electrophotographic machine from causing nuisance tripping of the circuit breaker without having to install a dedicated high current outlet. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method and apparatus for preventing the combined load of a printing system power supply and multiple high wattage fuser lamps from exceeding the alternating current (AC) line current available from a standard 15 ampere, 120 volt wall outlet. 
     The invention comprises, in one form thereof, a method of operating a fuser assembly in an electrophotographic machine. A first heating device heats a first fuser roll. A second heating device heats a second fuser roll. It is determined whether a first temperature of the first fuser roll is below a first target temperature. It is also determined whether a second temperature of the second fuser roll is below a second target temperature. If both the first temperature is below the first target temperature and the second temperature is below the second target temperature, the first heating device is operated during a first time period and operation of the second heating device is inhibited throughout the first time period. 
     An advantage of the present invention is that both a primary fuser lamp and a back-up fuser lamp may be operated without exceeding the amount of current available from a standard 15 ampere, 120 volt wall outlet. 
     Another advantage is that installation of a dedicated high current outlet is not required. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a side, sectional view of one embodiment of a multicolor laser printer in which the present invention may be used; 
     FIG. 2 is a schematic diagram of one embodiment of a fuser lamp control circuit of the present invention; and 
     FIG. 3 is a schematic diagram of another embodiment of a fuser lamp control circuit of the present invention. 
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate preferred embodiments of the invention, but such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings and, more particularly, to FIG. 1, there is shown one embodiment of a multicolor laser printer  10  including laser print heads  12 ,  14 ,  16 ,  18 . a black toner cartridge  20 , a magenta toner cartridge  22 , a cyan toner cartridge  24 , a yellow toner cartridge  26 , photoconductive drums  28 ,  30 ,  32 ,  34 , and an intermediate transfer member belt  36 . 
     Each of laser print heads  12 ,  14 ,  16  and  18  scans a respective laser beam  38 ,  40 ,  42 ,  44  in a scan direction, perpendicular to the plane of FIG. 1, across a respective one of photoconductive drums  28 ,  30 ,  32  and  34 . Each of photoconductive drums  28 ,  30 .  32  and  34  is negatively charged to approximately −900 volts and is subsequently discharged to a level of approximately −200 volts in the areas of its peripheral surface that are impinged by a respective one of laser beams  38 ,  40 ,  42  and  44 . During each scan of a laser beam across a photoconductive drum, each of photoconductive drums At  28 ,  30 ,  32  and  34  is continuously rotated, clockwise in the embodiment shown, in a process direction indicated by direction arrow  46 . The scanning of laser beams  38 ,  40 ,  42  and  44  across the peripheral surfaces of the photoconductive drums is cyclically repeated, thereby discharging the areas of the peripheral surfaces on which the laser beams impinge. 
     The toner in each of toner cartridges  20 ,  22 ,  24  and  26  is negatively charged to approximately −600 volts. Thus, when the toner from cartridges  20 ,  22 ,  24  and  26  is brought into contact with a respective one of photoconductive drums  28 ,  30 ,  32  and  34 , the toner is attracted to and adheres to the portions of the peripheral surfaces of the drums that have been discharged to −200 volts by the laser beams. As belt  36  rotates in the direction indicated by arrow  48 , the toner from each of drums  28 ,  30 ,  32  and  34  is transferred to the outside surface of belt  36 . As a print medium, such as paper, travels along either path  50  or duplexing path  52 , the toner is transferred to the surface of the print medium in nip  54 . 
     After passing through nip  54 , the print medium then passes through another nip  56  defined between a primary fuser roll  58  and a back-up fuser roll  60 . As the print medium passes through nip  56 , primary fuser roll  58  contacts the toner and presses it into the top side of the print medium. In order to improve the quality of this fusing process, primary fuser roll  58  and back-up fuser roll  60  are heated by a primary fuser lamp  62  and a back-up fuser lamp  64 , respectively. Each of primary fuser roll  58  and back-up fuser roll  60  includes an internal cavity which receives a respective one of primary fuser lamp  62  and back-up fuser lamp  64 . 
     Each of primary fuser lamp  62  and back-up fuser lamp  64  is connected to a fuser lamp control circuit  66  (FIG. 2) which allocates the available current from an AC wall outlet having an input (hot)  68  and a return (neutral)  70  in such a way as to prevent the sum of the currents on current paths  72  and  74  from exceeding the rating of the outlet. This is accomplished by using a logic control circuit to allow only one of fuser lamps  62  and  64  to turn on at a given time. Further, lamps  62  and  64  are prioritized to insure that primary fuser lamp  62  receives power in the case where primary fuser roll temperature sensing circuit  76  and back-up fuser roll temperature sensing circuit  78  are attempting to turn on both lamps  62  and  64  at the same time. 
     Circuit  76  includes a sensor (not shown) for sensing the temperature of primary fuser roll  58 . When the temperature of fuser roll  58  is below a predetermined target temperature, sensing circuit  78  generates and supplies a signal on signal path  80  to control switch  82 . The signal on path  80  is a digital signal that has a signal level which is “high” when the temperature of primary fuser roll  58  is below the target temperature, and is “low” when the temperature of primary fuser roll  58  is at or above the target temperature. Upon receiving the “high” signal on path  80 , control switch  82  closes, thereby applying power to primary fuser lamp  62 . Conversely, when the signal on path  80  is “low,” control switch  82  opens, thereby disconnecting power from primary fuser lamp  62 . 
     Similarly to sensing circuit  76 , back-up fuser roll temperature sensing circuit  78  includes a sensor (not shown) which senses the temperature of back-up fuser roll  60 . When the temperature of back-up fuser roll  60  is below another predetermined target temperature, sensing circuit  78  generates and supplies a signal, on signal path  84 , having a digital signal level which is “high.” Conversely, when the temperature of back-up fuser roll  60  is at or above the second the target temperature, the signal on path  84  is “low.” 
     A switch control circuit  86  includes an inverter  88  and an AND gate  90 . One input  92  of AND gate  90  receives the digital signal supplied on signal path  84 . The other input  94  of AND gate  90  receives an inverted version of the digital signal supplied on signal path  80  by sensing circuit  76 . More particularly, an input  96  of inverter  88  receives the signal on path  80 . An output  98  of inverter  88  then sends the inverted version of this signal to input  94  of AND gate  90 . An output  100  of AND gate  90  supplies a digital signal on signal path  102  which is sent to a control switch  104 . 
     If the temperature of primary fuser roll  58  is at or above the first target temperature, and the temperature of back-up fuser roll  60  is below the second target temperature, then a “high” signal is generated and sent to control switch  104  on signal path  102 . Upon receiving this “high” signal, control switch  104  closes, thereby applying power to back-up fuser lamp  64 . Under other conditions, the most important of which being when primary fuser roll  58  is below the first target temperature and power is being applied to primary fuser lamp  62 , switch control circuit  86  prevents power from being applied to back-up fuser lamp  64 . That is, switch control circuit  86  allows power to be applied to back-up fuser lamp  64  only when power is not being applied to primary fuser lamp  62 . Even in this case, should the temperature of primary fuser roll  58  fall below the first target temperature, switch control circuit  86  will immediately shut off power from back-up fuser lamp  64  so that back-up fuser lamp  64  does not operate simultaneously with primary fuser lamp  62 . 
     In another embodiment (FIG. 3) switch control circuit  86  is replaced by a microcontroller  106 . Microcontroller  106  may pass unaltered the signal on path  80  to control switch  82 . Alternatively, microcontroller  106  may delay one or both of the turn on times of control switch  82  and control switch  104  in order to place, for example, a gap of a few milliseconds between the turn off time of one of primary fuser lamp  62  and back-up fuser lamp  64  and the turn on time of the other. This further insures that current in not simultaneously drawn by primary fuser lamp  62  and back-up fuser lamp  64 . 
     The present invention has been described herein in conjunction with fuser lamps. However, it is to be understood that the present invention can also be used with other types of heating elements, such as ceramic heating elements and resistive heating elements. 
     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 adaptions of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within know or customary practice in the art to which this invention pertains and which falls within the limits of the appended claims.