JP2005092135A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which loss of electric power can be reduced by suppressing overshooting of fixation temperature. <P>SOLUTION: Provided is an overshoot reduction mode wherein the overshooting of fixation temperature of a heating means 3 that a fixing device A has is suppressed and once the mode is set, the output voltage of a DC generating means 10 which rectifies and converts an AC input into a direct current is shifted to a specified value to suppress the overshooting of the fixation temperature of the heating means 3. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrophotographic image forming apparatus, and more particularly to a heat fixing control technique.

In an electrophotographic image forming apparatus, an unfixed toner image carried on a transfer sheet needs to be fixed by a fixing device. As the fixing device, a heating and pressure fixing method is generally used. This is done by pressing the fixing roller and the pressure roller. A heater is built in either or both rollers, and the unfixed toner image is melted on the transfer paper while the transfer paper passes through the nip between both rollers. , To be fixed.
In relation to the fixing control, for example, Patent Document 1 proposes a technique for performing an advance prediction of the energization state of the heating time by calculating and predicting the sheet passing timing and the amount of heat required for fixing. Patent Document 2 proposes a technique for rectifying and smoothing and supplying power only to the necessary portions when starting up the IH heater to shorten the startup.
JP 2002-116658 A Japanese Patent Laid-Open No. 2001-22234

Conventionally, in a fixing device that supplies an AC input to a heating unit, it has been impossible to control the fixing temperature so that the commercial power supply frequency is basically finer than a few ms. For example, even if it is desired to reduce the temperature ripple, the power supply means that supplies power to the heating means is not a direct current generating means that rectifies the alternating current input by the rectifying means and converts it into direct current, so fine control cannot be performed, There is a limit that cannot further reduce the ripple, and there is a limit even if it is desired to suppress the overshoot of the fixing temperature, and even if the transfer paper comes off, there is still a loss of power due to the addition of heat.
An object of the present invention is to provide an image forming apparatus capable of reducing power loss by suppressing overshoot of the fixing temperature.

In order to achieve the above object, the invention according to claim 1 is provided with an overshoot reduction mode for suppressing overshoot of the fixing temperature in the heating means provided in the fixing device, and when the mode is set, the AC input is rectified. And a means for shifting the output voltage of the direct current generating means for converting to direct current to a predetermined value to suppress overshooting of the fixing temperature of the heating means.
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the timing at which the output voltage of the direct current generating means decreases to a predetermined value is set for each image forming mode, and is switched correspondingly. Is the main feature.
According to a third aspect of the present invention, the image forming apparatus according to the first aspect is characterized in that the overshoot reduction mode can be canceled.

  In the present invention, there is an overshoot reduction mode for suppressing overshoot of the fixing temperature in the heating means of the fixing device, and when this mode is set, the output voltage of the direct current generating means that rectifies the alternating current input and converts it into direct current Is controlled to shift to a predetermined value, it is possible to suppress overshooting of the fixing temperature of the heating means, and power loss can be reduced.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram of the fixing device. The fixing device A is configured by press-contacting a fixing roller 1 and a pressure roller 2, and the fixing roller 1 includes a heating unit (heater) 3 therein. The heating means (heater) 3 may be provided on the pressure roller 2. The transfer paper P is fixed in the process of passing through the nip portions of both rollers 1 and 2.

FIG. 2 is a configuration diagram of the fixing control device in the image forming apparatus of the present invention. The configuration will be described together with the operation.
A temperature detecting means 4 for detecting the temperature of the heating means 3 is provided in the vicinity of the heating means 3, and the control means 5 controls the power supplied to the heating means 3 according to the difference between the target temperature and the detected temperature, and detects the detected roller. The surface temperature is kept constant to a predetermined value. More specifically, the temperature rise and fall predicted based on the sheet passing timing and the amount of heat required for fixing are calculated and predicted so that the predetermined roller surface temperature is maintained constant. Note that the power supplied to the heating means 3 for enabling this is a direct current that can be controlled with a minute value that can be kept constant, and can be kept constant in response to rapid temperature rise and fall. I am doing so. Furthermore, when the “overshoot reduction mode” is set, power is not supplied to the heating means even if the transfer paper passes through the fixing means for each image forming mode, and overshoot is suppressed. In anticipation of this, the voltage drops to a predetermined value and turns off in advance.

In the present embodiment, the heating means 3 is, for example, an infrared heater, and the temperature detection means 4 is a thermistor.
A thermal fuse 6 is provided in the vicinity of the heating unit 3 to prevent abnormal heating due to a failure of the control unit 5 or the like, and smoke and ignition. Further, when the control means 5 determines that the information from the temperature detection means 3 is abnormal, the control means 5 turns off the relay 8 provided in the input stage of the AC power supply 7 and cuts off the power supply to the heating means 3.
The AC power supply 7 is provided with a filter circuit 9 so that noise from the DC power generation circuit 10 does not affect the AC power supply 7. The output of the filter circuit 9 passes through the relay 8 and is full-wave rectified by a full-wave rectifier circuit 11 which is a rectifier. FIG. 3 shows the input AC voltage waveform, and FIG. 4 shows the full-wave rectified voltage waveform.
The positive side of the full-wave rectifier circuit 11 is connected to a noise absorbing capacitor 13, an input voltage detection circuit 14, and a choke coil 15 through a transistor 12 that is a switching means. In addition to the noise absorbing capacitor 13 and the input voltage detection circuit 14, The end is connected to the negative electrode side of the full-wave rectifier circuit 11. The other end of the choke coil 15 is connected to the collector or drain of the transistor 16 as a switch means and the anode of a diode 17 as a second rectifier means.
The emitter or source of the transistor 16 is connected to the negative side of the full-wave rectifier circuit 11. The cathode of the diode 17 is connected to the smoothing capacitor 18, the output voltage detection means 19, and the heating means 3, and the other ends of the smoothing condenser 18 and the output voltage detection means 19 are connected to the negative electrode side of the full-wave rectifier circuit 11. . The other end of the heating means 3 is connected to the negative electrode side of the full-wave rectifier circuit 11 via the temperature fuse 6. Here, the rectifying means may be a transistor.
Current detection means 20 is provided between the emitter side of the transistor 16 which is a switch means and the negative side of the full-wave rectifier circuit 11. The current detection means 20 uses a resistance of 0.1Ω or less or a current detection coil. The input voltage detection means 14 and the output voltage detection means 19 apply the voltage stepped down by resistance division to the control means 5, or temporarily insulate it with a photocoupler and apply it to the control means 5.

The DC power generation circuit 10 is a step-up chopper, stores energy in the choke coil 15 when the transistor 16 is on, and charges the capacitor 18 via the diode 17 when the transistor 16 is off. If the switching period of the transistor 16 is T, the off time is Toff, the average voltage E of the capacitor 18 and the input voltage Vin, E = k (T / Toff) × Vin × √2.
k is a coefficient determined by the impedance of the circuit, the resistance value of the heating means 3 serving as a load, and the like. When T = 5 μS and Vin = 100 V, E is 282 V when Toff = 2.5 μS. If Toff is reduced, E is likely to be increased as much as possible, but the actual boost ratio is about 5 times. Thus, by controlling Toff, for example, the output voltage can be arbitrarily changed to the rated voltage value of the heating means 3.

A case where there is no smoothing capacitor 18 will be described. In this case, the output of the diode 17 flows directly to the heating means 3, and a voltage waveform having a large ripple with a switching period of 5 μS (20 KHz) is applied to the heating means 3, but the heating means 3 is intended to generate heat, This ripple is not a problem because the constant is greater than the period of the alternating voltage. In this case, the temperature of the heating means 3 is viewed by the temperature detecting means 4, and the Toff is increased or decreased from the difference between the target temperature and the detected temperature, and controlled to reach the target temperature. Since there is no capacitor, cost reduction and size reduction can be achieved.
When the smoothing capacitor 18 is provided, the function is enhanced by flexible control using information on both the temperature and the output voltage of the heating means 3. In this step-up type chopper circuit, Emin = Vin × √2 when T / Toff = 1, so that Emin is applied to the heating means 3 as it is. Therefore, a transistor 12 is provided at the output of the full-wave rectifier circuit 11, and the transistor 12 is turned off when the temperature of the heating means 3 becomes a predetermined value or higher.

Conventionally, for example, when the input voltage is 100 V, the heater has a voltage rating of 100 V (AC), and an infrared heater having the maximum power required by the fixing device has been used. In addition, for example, a 650 W heater and a 350 W heater are provided. When the fixing device is started up, two lights are turned on simultaneously, and only one or two are controlled during the fixing operation. Even when the fixing operation is not being performed, there is heat loss, so the heater is blinked to control the heat.
In addition, the allowable input power is determined by the Electrical Safety Act etc. for electronic devices, and the domestic power outlets of domestic general offices and homes have a maximum rating of 15A at 100V. When the AC input is directly supplied to the heater, the maximum power that can be supplied to the heater is 1500 W even if the power other than the heater is zero. Since the output stage of the step-up chopper is provided with a capacitor, the power of 1500 W or more can be instantaneously supplied to the heating means 3.

It is a block diagram of a fixing device. 1 is a configuration diagram of a fixing control device in an image forming apparatus of the present invention. It is a figure which shows an input alternating voltage waveform. It is a figure which shows the voltage waveform by which the full wave rectification was carried out.

Explanation of symbols

  A fixing device, 3 heating means, 10 DC power generation circuit (DC generation means)

Claims (3)

  An overshoot reduction mode that suppresses overshoot of the fixing temperature in the heating unit provided in the fixing device is provided, and when this mode is set, the output voltage of the DC generation unit that rectifies the AC input and converts it into DC is set to a predetermined value. And an image forming apparatus characterized by suppressing overshooting of the fixing temperature of the heating means.   2. The image forming apparatus according to claim 1, wherein a timing at which the output voltage of the direct current generating means is lowered to a predetermined value is set for each image forming mode and is switched correspondingly.   2. The image forming apparatus according to claim 1, wherein the overshoot reduction mode can be canceled.

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