JPH09146422A - Image forming device - Google Patents

Abstract

(57) [Summary] (Correction) [Problem] To provide an image forming apparatus capable of suppressing an inrush current and a harmonic component of the current. SOLUTION: The fixing heater 3 and the exposure lamp 5, which are respectively resistive AC loads, the fixing heater drive circuit 4, the exposure lamp drive circuit 6, the zero cross detection circuit 2 for detecting the zero cross timing in the AC power source 1, and the zero cross timing. The control circuit 7 outputs a trigger for controlling the phase angle to the fixing heater drive circuit 4 and the exposure lamp drive circuit 6 based on the above. The control circuit 7 performs a soft start for gradually increasing the firing angle when the fixing heater 3 and the exposure lamp 5 are turned on, and also performs a soft start for the fixing heater 3 when the exposure lamp 5 is on.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine.

[0002]

2. Description of the Related Art As a conventional technique relating to an image forming apparatus,
For example, Japanese Unexamined Patent Application Publication No. 6-1 entitled "Harmonic Suppression Circuit for Equipment in Which Phase Control Circuit and DC Stabilized Power Supply Circuit are Installed in Parallel".
There is 21523 issue.

This prior art is intended to reduce various obstacles to the electric power system due to harmonic currents of equipment in which a phase control circuit and a stabilized DC power supply circuit are arranged in parallel. A phase control circuit that controls the phase angle of the AC power supply by the output phase angle control signal to adjust the power supplied to the AC load, and a DC power supply that rectifies the AC from the AC power supply and supplies it to the DC load A harmonic suppression circuit of a device in which a DC stabilized power supply circuit is installed in parallel, wherein the phase control circuit supplies a current from the AC power supply to the DC stabilized power supply during a main period of supplying a current to the AC load. A configuration is disclosed in which a suppressing phase control circuit and a DC stabilizing circuit are arranged in parallel. Here, the AC load as described above is specifically the fixing heater (halogen heater) of the thermal fixing unit or the exposure lamp (halogen lamp) of the document reading unit. For these AC loads, zero-cross control is performed in which the AC power is triggered and turned on at the zero-cross timing.

[0004]

The AC load such as the fixing heater and the exposure lamp described above is a resistive AC load, but the resistance value of the internal filament has temperature dependency and the resistance at room temperature is low. The value is, for example, 1/10 or less of the resistance value in the lighting state. For this reason, when the control is started at the zero-cross timing as described above, an inrush current that exceeds, for example, 10 times that in the steady state will flow after turning on.
An example of such an inrush current is shown in FIG. In FIG. 8, (a) is a voltage waveform of the AC power supply, (b) is a trigger waveform, and (c) is a current waveform of the AC power supply.

Since the power supply voltage drops (fluctuates) due to the inrush current as described above, for example, when the fixing heater is turned on while the original is being read by turning on the exposure lamp, the exposure lamp flickers. There is. Further, due to this rush current, the capacity of the electric element forming the drive circuit of the AC load in the image forming apparatus has to be increased, and as a result, there is a problem that the drive circuit costs higher.

Here, as a means for suppressing the inrush current to be low, a method of performing soft start control on the AC load can be considered. In this case, the zero-cross timing of the AC voltage waveform shown in FIG. 9A is detected, and the trigger timing is set when the AC load is turned on as shown in the trigger waveform of FIG. 9B at this zero-cross timing. Control to gradually widen the arc angle. The AC voltage waveform applied to the AC load in this case is as shown in FIG. As a result, the AC load is turned on at a low applied voltage, and the applied voltage is gradually increased.
Since the current is increased while gradually raising the temperature of the filament of the AC load, the inrush current can be suppressed.

In the AC load, the exposure lamp is generally used with the phase angle lighting instead of the full wave lighting, so that the phase angle lighting is usually performed after the soft start as shown in FIG. The fixing heater may be used in full-wave lighting or in phase angle lighting. In the former case, zero-cross start is often performed as shown in FIG. 8 without soft start. In the latter case, the phase angle lighting is performed after the soft start as in the exposure lamp.

However, although the inrush current can be lowered and the drop of the power supply voltage can be reduced by performing the soft start as described above, there is a drawback that the harmonic component of the current increases.

Therefore, the present invention provides an image forming apparatus equipped with a control system capable of suppressing the inrush current to suppress the fluctuation of the power supply and also suppressing the harmonic component of the current to a low level. To aim.

[0010]

An image forming apparatus of the present invention according to claim 1 detects two resistive AC loads, a drive unit of the two AC loads, and a zero-cross timing in an AC power source of the drive unit. In the image forming apparatus having the zero-cross detection circuit, the drive unit controls the phase angle from the zero-cross timing detected by the zero-cross detection circuit, and when the two AC loads are turned on during image formation, In addition to performing a soft start for gradually increasing the firing angle, a soft start for one of the two AC loads is performed when the other AC load is on.

The image forming apparatus of the present invention according to claim 2 is
The soft start of the one AC load is performed when the other AC load is on with full-wave lighting.

The image forming apparatus of the present invention according to claim 3 is
The one AC load is the fixing heater of the thermal fixing unit, the other AC load is the exposure lamp of the document reading unit, and the drive unit is the fixing heater after the exposure lamp finishes the irradiation of the rear end of the document. It is characterized by starting the soft start of.

The image forming apparatus of the present invention according to claim 4 is
When the one AC load is the fixing heater of the thermal fixing unit, the other AC load is the exposure lamp of the document reading unit, and the driving unit turns on the fixing heater in a standby state in which image formation is not performed. It is characterized by performing zero-cross control that turns on near zero-cross instead of soft start.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment in which the present invention is applied to a copying machine as an example of an image forming apparatus will be described below.

FIG. 1 shows the drive unit of the exposure lamp and the fixing heater in the copying machine of the above embodiment. This drive unit drives an AC power supply 1 such as a commercial power supply, a zero-cross detection circuit 2 for detecting the zero-cross timing in the AC power supply 1, a fixing heater drive circuit 4 for driving the fixing heater 3, and an exposure lamp 5. Exposure lamp drive circuit 6 and zero-cross detection circuit 2 for
The control circuit 7 outputs a trigger signal (drive signal) to the fixing heater drive circuit 4 and the exposure lamp drive circuit 6 based on the zero-cross timing detected by. The zero-cross detection circuit 2 specifically detects the timing at which the AC voltage in the AC power supply 1 crosses zero volts.

In addition to the above-mentioned structure, this copying machine has, for example, a contact glass on which a copy original is placed, an original pressing plate for sandwiching the original with the contact glass, and reflection of an image from the original. Originals such as an optical scanning system composed of a mirror and a variable magnification lens for enlargement / reduction, a photosensitive drum which is an electrophotosensitive body, a heat fixing unit composed of a fixing heater, a developing roller, a transfer device, or a fixing roller. It is composed of various known components necessary for copying, and performs a copying operation in a known manner. The exposure lamp 5 and the fixing heater 3 are respectively composed of a halogen heater and a resistive AC load of the halogen lamp.

2 to 4 exemplify a specific circuit configuration of the zero-cross detection circuit 2. In the zero-cross detection circuit of FIG. 2, the primary side to which the AC voltage VAC is applied by the bidirectional photocoupler 11 and the secondary side from which the zero-cross timing detection signal S is output are insulated. Then, in the vicinity of the AC voltage VAC becoming zero volt, the photo coupler 11
The zero-cross timing is detected by turning off the LED constituting the.

Further, in the zero-cross detection circuit of FIG. 3, the zero-cross timing detection signal S is detected by detecting the zero-cross in the voltage after the full-wave rectification of the AC voltage VAC by the diode bridge 12 in the previous stage by the photo coupler 13 provided in the subsequent stage. It is outputting. Further, in the case of the zero-cross detection circuit of FIG. 4, a zero-cross in the voltage after full-wave rectifying the AC voltage VAC by the diode bridge 12 via the insulating transformer 14 is provided in the subsequent stage.
5 and outputs the zero-cross timing detection signal S.

On the other hand, specific circuit configurations of the fixing heater drive circuit 4 and the exposure lamp drive circuit 6 are shown in FIG. This circuit is configured to have a photo triac 23 which is a non-zero cross control element and a triac 22. Then, when the trigger signal S becomes low, the phototriac 23 becomes conductive, a voltage is applied to the gate G of the triac 22, the triac 22 is turned on, and the AC load 2
An alternating current flows through 1. As shown in FIG. 6, it is conceivable to use the phototriac 24 configured by using the zero-cross control element ZC, but in this case, regardless of the trigger signal T, the phototriac 24 is always zero-crossed. Since the triac is turned on, it is not suitable for the application of the present invention.

Next, the drive timing of the exposure lamp 5 and the fixing heater 3 which are two AC loads in the copying machine according to the embodiment of the present invention will be described with reference to FIG. In FIG. 7, A is a period during which a soft start gradually increases the firing angle, B is a period during lighting by phase angle control, and C is
Is the period during which full-wave lighting is performed. Further, in the figure, the arrow indicates a section during document exposure by the exposure lamp 5 in the copying machine. Further, in FIGS. 7A to 7C, the upper stage shows the drive timing of the exposure lamp 1 and the lower stage shows the drive timing of the fixing heater 3, respectively.

Here, during the image formation, that is, during the copying operation, the exposure lamp needs to be turned on / off at a constant interval of 5. Further, the fixing heater 3 needs to be controlled so that the temperature of the fixing roller is always within the target control temperature range, although the on / off timing is not constant. Therefore, in the present embodiment, as shown in FIG. 7A, the timing at which the fixing heater 3 is turned on is set immediately before the exposure lamp 1 is turned off. Further, the timing for turning off the fixing heater 3 is set after the soft start of the exposure lamp 5 is completed. As a result, the soft start of the fixing heater 3 and the soft start of the exposure lamp 5 can be performed while the load of the other party is lit. And
As a result, the current amount of the harmonic current is the same as when it is turned on independently, but the ratio of the harmonic current can be reduced by increasing the total current amount.

Further, when the fixing heater 3 is turned on, the power supply voltage may drop due to the inrush current even when the soft start is performed, and the drive voltage of the exposure lamp 1 may drop and the light amount may drop. In such a case, FIG.
As described above, the fixing heater 3 may be turned on after the exposure lamp 5 is turned on after the trailing edge of the original has passed. As a result, the light amount of the exposure lamp 5 during irradiation of the document can be stabilized. In this case, the lighting time of the exposure lamp 5 is extended by the soft start time of the fixing heater 3.

Further, the exposure lamp 5 is normally used by controlling the phase angle without being turned on, but as shown in FIG.
When all the exposure lamps 5 are turned on while the fixing heater 3 is soft starting, the proportion of the harmonic current can be further reduced.

When the copying machine is on standby, the exposure lamp 5 is always off, only the fixing heater 3 is on / off, and the fixing heater 3 is turned on / off independently. Therefore, in this case, when the fixing heater 3 is soft-started, the proportion of higher harmonics increases. Therefore, when only one of the AC loads is turned on / off independently, it is sufficient to control at zero cross timing.
This can suppress the generation of harmonic components. Further, in this case, since the exposure lamp 5 is not turned on / off, the fluctuation of the power supply voltage in the AC power supply 1 can be suppressed to be lower than that during the copy operation.

Although the exposure lamp and the fixing heater have been described as an example of the two resistive AC loads, the present invention is similarly applicable to other resistive AC loads used at the same time. It goes without saying that you can do it.

[0026]

According to the inventions of claims 1 and 3, it is possible to realize the soft start control in which the inrush current at the time of copying is low, the fluctuation of the power supply voltage is small, and the ratio of the harmonic current is low. .

According to the invention of claim 2, further,
The light quantity of the exposure lamp can be stabilized.

According to the fourth aspect of the present invention, it is possible to further reduce the proportion of the harmonic current during standby.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a driving unit of an exposure lamp and a fixing heater in a copying machine according to an embodiment of the present invention.

FIG. 2 is a circuit diagram illustrating the configuration of a zero-cross detection circuit in the drive section of FIG.

FIG. 3 is a circuit diagram illustrating the configuration of a zero-cross detection circuit in the drive section of FIG.

FIG. 4 is a circuit diagram showing a configuration of a zero-cross detection circuit in the drive section of FIG.

5 is a circuit diagram showing a configuration of a fixing heater drive circuit and an exposure lamp drive circuit in the drive unit of FIG.

FIG. 6 is a circuit diagram showing a configuration example of a fixing heater drive circuit and an exposure lamp drive circuit.

7A to 7C are explanatory diagrams showing driving timings of a fixing heater and an exposure lamp in the embodiment, respectively.

FIG. 8 is an explanatory diagram showing an example of inrush current when an AC load is turned on.

FIG. 9 shows an example of soft starting an AC load,
(A) is an alternating current waveform, (b) is a trigger waveform,
(C) is a waveform diagram showing an AC voltage waveform.

FIG. 10 is a waveform diagram of an AC voltage when the exposure lamp is turned on at a phase angle.

[Explanation of symbols]

 1 AC power supply 2 Zero cross detection circuit 3 Fixing heater 4 Fixing heater drive circuit 5 Exposure lamp 6 Exposure lamp drive circuit 7 Control circuit

Claims (4)

[Claims] 1. An image forming apparatus having two resistive AC loads, a drive unit for the two AC loads, and a zero-cross detection circuit for detecting a zero-cross timing in an AC power source of the drive unit, wherein the drive unit is It controls the phase angle from the zero-cross timing detected by the zero-cross detection circuit.
When the two AC loads are turned on during image formation, the ignition angle is gradually increased and the soft start is performed.
An image forming apparatus, wherein a soft start of one of the two AC loads is performed when the other AC load is on. 2. The image forming apparatus according to claim 1, wherein the soft start of the one AC load is performed when the other AC load is turned on by full-wave lighting. 3. The one AC load is a fixing heater of a thermal fixing unit, the other AC load is an exposure lamp of a document reading unit, and the driving unit of the driving unit ends the exposure of the rear end of the document. The image forming apparatus according to claim 1 or 2, wherein the soft start of the fixing heater is started after heating. 4. The one AC load is a fixing heater of a thermal fixing unit, the other AC load is an exposure lamp of a document reading unit, and the drive unit is the fixing heater in a standby state where image formation is not performed. 3. When turning on, the zero cross control for turning on near the zero cross is performed instead of the soft start.
Or the image forming apparatus according to 3.