Electric heating – Heating devices – With power supply and voltage or current regulation or...
Reexamination Certificate
2003-01-16
2004-09-21
Paschall, Mark (Department: 3742)
Electric heating
Heating devices
With power supply and voltage or current regulation or...
C219S497000, C219S216000, C219S505000, C323S908000, C323S238000, C399S069000
Reexamination Certificate
active
06794619
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as a facsimile machine with a copying function (hereinafter referred to as a Multi-Function Peripheral (MFP)), which prints an image on a recording paper by using an electro-photographic method. In particular, the present invention relates to a heater energization control circuit for controlling an energization to a heater of a heat fuser that heats and fuses a toner image on a recording paper.
DESCRIPTION OF THE RELATED ART
Recently, the MFP, which prints an image on a recording paper by using an electro-photographic method, is being distributed widely throughout the market. The MFP generally includes a charger that charges a surface of a photoconductor uniformly, an exposure unit that forms an electrostatic latent image by exposing the surface of the photoconductor, a developer that forms a toner image by adhering toner supplied from a toner case to the electrostatic latent image, a transfer unit that transfers the toner image to a recording paper, and a heat fuser that heats and fuses the transferred toner image on the recording paper. A series of processes from charging, exposing, developing, and transferring, heat fusing is one unit of the recording process in the electro-photographic method.
The heat fuser includes a heater, and an alternating current is supplied to the heater. As a result, the toner image transferred to the recording paper is fused as a permanent image on a recording paper by heat that generates according to the alternating current supplied to the heater.
In general, the heater is dependent on temperature, and a resistance value of the heater changes greatly according to the temperature of the heater. In other words, when the temperature of the heater is low, the resistance value is extremely small comparing to a case when the temperature of the heater is high. As a result, when the temperature of the heater is low, an extremely large incoming electric current flows through the heater, a power supply voltage of the MFP decreases, and a flicker generates on the exposure unit. When the flicker generates, light intensity of the exposure unit becomes uneven, and there is a possibility for an image quality on the recording paper to deteriorate.
SUMMARY OF THE INVENTION
Therefore, an advantage of the present invention is to provide a heater energization control circuit and method, and an image forming apparatus that can prevent an incoming electric current flowing through a heater of a heat fuser.
The present invention relates to an image forming apparatus using an electro-photographic method. The image forming apparatus includes a heat fuser having a heater, and a supply unit for supplying an alternating current to the heater. In addition, the image forming apparatus includes a first capacitor that charges and discharges in accordance with a first time constant determined by an electrostatic capacitance of the first capacitor and a resistance value of a first resistor. The image forming apparatus also includes a second capacitor that charges and discharges in accordance with a second time constant determined by an electrostatic capacitance of the second capacitor and a resistance value of a second resistor. Furthermore, the image forming apparatus includes a determining unit for determining a time to start energization to the heater in accordance with a size relationship between the voltage of the first capacitor and the voltage of the second capacitor, and starting to supply the alternating current to the heater by the supply unit under this timing.
The determining unit starts the energization to the heater when the voltage of the second capacitor becomes larger than the voltage of the first capacitor.
The determining unit determines a period when energizing the heater in accordance with a size relationship between the voltage of the first capacitor and the voltage of the second capacitor.
The determining unit energizes the heater during a period when the voltage of the second capacitor is larger than the voltage of the first capacitor.
The determining unit is a comparator, and the voltage of the first capacitor is input to a non-inverting input terminal of the comparator, and the voltage of the second capacitor is input to an inverting input terminal.
Furthermore, the image forming apparatus of the present invention includes a zero crossing detecting unit for detecting a zero crossing of the alternating current, and discharges the first capacitor during a period of the zero crossing, and charges the first capacitor during a period of the non-zero crossing.
In addition, the image forming apparatus of the present invention includes a power switch, and charges the second capacitor when the power switched is ON, and discharges the second capacitor when the power switch is OFF.
At least one of the first capacitor and the second capacitor is a variable capacitor.
At least one of the first resistor and the second resistor is a variable resistor.
According to the above-described present invention, an incoming electric current flowing through the heater of the heat fuser can be prevented. In particular, the incoming electric current flowing through the heater can be suppressed as much as possible.
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Hogan & Hartson LLP
Murata Kikai Kabushiki Kaisha
Paschall Mark
LandOfFree
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