Electrophotography – Control of electrophotography process – Control of fixing
Reexamination Certificate
2000-05-25
2001-11-13
Braun, Fred L (Department: 2852)
Electrophotography
Control of electrophotography process
Control of fixing
C399S088000
Reexamination Certificate
active
06317571
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to printers and copiers having heater controllers. In particular, it relates to improving machine power factors using pulse-width-modulation heater controllers.
BACKGROUND OF THE INVENTION
Business machines are often powered by alternating current (AC) supplied via standard power lines. With some machines the required power line AC input varies widely over time. For example, electrophotographic marking machines usually include fusers that produce permanent images by using heat and pressure to fuse toner with substrates, such paper. Such fusers generally use temperature-controlled, AC powered fuser heaters that require large amounts of electrical power when initially heating a pressure roller to a using temperature, less power when actually fusing, and even less power when in stand-by. The fuser heater temperature depends on, among other factors, the electrical power applied to the fuser heater. Other alternating current (AC) business machines also have widely varying electrical power requirements. For example, high volume ink jet printers frequently include AC powered heaters that remove moisture from inked paper to prevent ink smearing. Again, the AC electrical power applied to a heater is usually controlled such that the proper drying temperature is achieved. It should be noted that the AC heaters discussed above are frequently high-power devices that require substantial currents.
Heater temperature regulation is usually performed by a heater controller that limits the electrical power to the heater such that the heater does not overheat (which wastes energy, reduces operating lifetimes, and presents a fire and burn hazard). Prior art heater controllers include simple ON/FF switching devices, cycle stealing, and AC phase control devices. While generally successful, such prior art heater controllers have problems. ON/OFF power switching and cycle stealing lead to low apparent power factors and voltage fluctuations that can cause loss of data while phase control can produce high harmonic content signals, low apparent power factors, and interference with other devices. Indeed, European standards can be difficult to meet using any prior art heater controller.
Low apparent power factors are a significant problem. Consider a machine designed to draw less than 1380 volt-amps. This power rating can be achieved using a 15-ampere service connection. However, a low apparent power factor can cause the instantaneous line current to greatly exceed 15-ampere, even though the time-averaged current may be well below 15-ampere.
In addition to a high power heater, most AC powered business machines also have other electrical power requirements. For example, electrophotographic marking machines have photoreceptor chargers that require high voltages at low currents and electronic subsystems that require low voltages at high currents. Implementing multiple power requirements can be difficult. For example, voltage fluctuations caused by switching power to and from AC heaters can cause lamps to flicker and potential loss of valuable system information.
In view of the foregoing, a new technique of controlling AC heater loads in business machines having multiple power requirements would be useful.
SUMMARY OF THE INVENTION
The principles of the present invention provide for power factor control in machines having multiple electrical power requirements. A machine according to the principles of the present invention receives AC input power, powers at least one relatively low input-current device with the AC input power, and selectively applies relatively high current, high frequency pulse modulated AC power to another AC load. The high frequency pulse modulated AC power is controlled so as to be proportional to the input AC line voltage and to the input AC line current. If the AC load is a heater the high frequency pulse modulated AC power is also controlled to depend on the heater's temperature. The high frequency pulse modulated AC power is further controlled such that the total AC input power remains less than a design limit.
Beneficially, if the AC load is a printer heater, and if the high frequency pulse modulated AC power cannot maintain the heater's temperature while maintaining the total AC input power below a predetermined value, the printer's operation slows down until both the heater temperature and the total AC input power are within design limits.
REFERENCES:
patent: 5627628 (1997-05-01), Soda et al.
patent: 5942882 (1999-08-01), Ohta
patent: 6018151 (2000-01-01), Hirst
patent: 6111230 (2000-08-01), Cao et al.
patent: 6177739 (2001-01-01), Matsudaira et al.
patent: 9-218720 (1997-08-01), None
Integrated Circuits UNITRODE, 5/93, pp. 5-226-5-228, “Enhanced High Power Factor Preregulator”.
Integrated Circuits UNITRODE, 2/93A, pp. 5-218-5-225, “High Power Factor Preregulator”.
Braun Fred L
Henn David E.
Kelly John M.
Xerox Corporation
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