JP2000293072A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct the output voltage to be outputted to a driving system without wastefully consuming power by a dummy resistance. SOLUTION: In the midst of the standing-by of image forming (standby), an HI signal is transmitted from a controller 40 to an NPN transistor 41 so as to turn on the transistor 41. By making a heating element 37 for preheating a fixing device generate heat, a current is consumed in the heating element 37. By preheating the fixing device by the heating element 37, time (first printing time) taken till starting image forming operation after an image forming signal is inputted at the time of forming an image is shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus applied to a copying machine, a printer and the like, and more particularly to an image forming apparatus having a fixing means for thermally fixing a toner image to a transfer material by heating with a heating element. .

[0002]

2. Description of the Related Art FIG. 9 is a schematic diagram showing an example of a conventional electrophotographic image forming apparatus (laser printer in the figure).

When an image is formed by this image forming apparatus,
The photosensitive drum 117 disposed in the image forming unit 108 is driven to rotate, and the surface thereof is uniformly charged by a charging roller 119. Then, exposure is performed from an exposure device (laser scanner unit) 107 in accordance with image information, and an electrostatic latent image is formed. Form an image.

The exposure device (laser scanner unit) 107
A laser unit 113 that emits a laser beam modulated based on an image signal (image signal VDO) input from the engine controller 126;
A polygon mirror 114 for scanning the photosensitive drum 117 with the laser light from No. 3, an imaging lens 115, a return mirror 116, and the like.

[0005] An external device 131 such as a personal computer and a video controller 127 are connected to the engine controller 126 via general-purpose interfaces 130 and 128. The video controller 127 expands image information input from the external device 131 via the interface 130 into bit data, and sends the bit data as a VDO signal to the engine controller 126 via the interface 128.

Then, the electrostatic latent image formed on the photosensitive drum 117 is developed by the developing device 120 and is visualized as a toner image.

When the toner image on the photosensitive drum 117 reaches the transfer nip between the transfer roller 121 and the photosensitive drum 117, the cassette 1
02 is conveyed to the transfer nip by the feed roller 105 and the pair of registration rollers 106, and the toner image is transferred to the transfer material S by the transfer roller 121 to which a transfer bias is applied.

The cassette 102 includes a cassette presence / absence sensor 103 for detecting the presence / absence of the transfer material S in the cassette 102,
Cassette size sensor 10 for detecting the size of transfer material S
4 are installed. After the transfer, the photosensitive drum 117 is transferred.
The transfer residual toner remaining on the upper surface is removed by a cleaning device (cleaning blade) 122.

The transfer material S onto which the toner image has been transferred is conveyed between the fixing film 109a of the film heating type fixing device 109 and the pressure roller 109b. The fixing device 109
The fixing device includes a fixing film 109a, a pressure roller 109b, a ceramic heater 33 as a heating element provided inside the fixing film 109a, and a thermistor 34 for detecting the surface temperature of the ceramic heater 33. Then, the toner image is heated and fixed as a fixed image on the transfer material S by the pressure of the pressure roller 109b, and then discharged onto the stacking tray 112 via the discharge roller 111. Above the paper discharge roller 111, a paper discharge sensor 110 that detects the paper discharge state of the transfer material S is provided.

The main motor 123 applies a driving force to the sheet feeding roller 105 via a sheet feeding roller clutch 124 and a driving force to the registration roller pair 106 via a registration roller clutch 125.
17, each unit of the image forming unit 108, the fixing device 10
9. The driving force is also applied to the paper discharge roller 111. In addition,
129 is a cooling fan for cooling the inside of the apparatus main body 101.

FIG. 10 is a diagram showing a drive and control circuit of the ceramic heater 33 of the fixing device 109.

The ceramic heater 33 is connected to a commercial power supply (AC power supply) 1 via a triac 32 which is a switching control element, and is supplied with electric power by the commercial power supply 1 to generate heat. The power supply to the ceramic heater 33 is performed by turning on and off the triac 32.
The resistors 35 and 36 are bias resistors for the triac 32, and the triac 32 is the engine controller 1
It operates according to the ON signal from.

The commercial power supply 1 is connected to a zero-cross detection circuit (not shown).
The commercial power supply 1 notifies the engine controller 126 of a voltage lower than a certain threshold by a pulse signal. Hereinafter, this signal sent to the engine controller 126 is referred to as a ZEROX signal.

The engine controller 126 has the ZE
The edge of the pulse of the ROX signal is detected, and the triac 32 is turned on / off by phase control or wave number control.

A temperature detecting element 34 for detecting the temperature of the ceramic heater 33 such as a thermistor temperature sensing element is provided near the ceramic heater 33. Ceramic heater 33 detected by temperature detecting element 34
Is detected as a partial pressure between the resistor 31 and the temperature detection element 34, and is input to the engine controller 126 as an A / D signal as a TH signal.

The temperature of the ceramic heater 33 is set at the above-mentioned TH.
The power to be supplied to the ceramic heater 33 is calculated by monitoring the signal as a signal in the engine controller 126 and comparing the temperature with the set temperature of the ceramic heater 33 set in the engine controller 126. The engine controller 126 controls the triac 32 on / off by controlling the phase or the wave number of the commercial power supply 1 to thereby control the ceramic heater 33.
The power supply to the power supply is turned on / off, and the temperature is controlled so as to reach the set temperature.

FIG. 11 is a diagram showing a power supply circuit (in the figure, a separately-excited flyback switching power supply circuit) 200 of the above-described image forming apparatus.

Hereinafter, the operation of the power supply circuit 200 will be described.

First, an alternating current input from a commercial power supply (AC power supply) 1 is full-wave rectified to a DC voltage by a first rectifier circuit including a diode bridge 2 and an electrolytic capacitor 3.
This full-wave rectified DC voltage is supplied to a power MOS-FET (hereinafter, referred to as F
ET5), and is turned into a pulsed waveform by the on / off operation of the FET 5, and is transferred from the primary side to the secondary side via the transformer 4 and transmitted as a switched pulsed voltage waveform having the same cycle. Is done. FET
5 is turned on / off by a drive pulse of about 100 KHz inputted to the gate from the power supply control IC 6.

The pulsed voltage transmitted to the secondary side of the transformer 4 is rectified and smoothed by a second rectifier circuit composed of a diode 11 and an electrolytic capacitor 12, and thereafter,
The switching frequency component is removed by the LC filter including the inductor 13 and the electrolytic capacitor 14, and 3.3.
It is output as a DC voltage of V.

Similarly, the pulse-like voltage transmitted to the primary side of the transformer 4 is rectified and smoothed by a third rectifier circuit composed of a diode 7 and an electrolytic capacitor 8, and thereafter, from the inductor 9 and the electrolytic capacitor 10. The switching frequency component is removed by the LC filter
It is output as a DC voltage of V.

Since the power supply circuit 200 is of a flyback type, when the FET 5 is on, the diode 7
11 does not conduct, the diode 7 when the FET 5 is off,
11 conducts and energy is transferred from the primary side to the secondary side.

The output voltage of 3.3 V is controlled by a CPU (not shown) of a control system for controlling each driving system of the image forming apparatus (the image forming unit 108, the exposing device 107, the fixing device 109, etc. shown in FIG. 9). 24V of the above output voltage.
Are output to the motors (the main motor 123 shown in FIG. 9) of each drive system of the image forming apparatus.

Next, the power supply circuit 200 described in 3. above.
The operation of the 3 V output overcurrent protection circuit 201 will be described.

The overcurrent protection circuit 201 detects an output current of 3.3 V on the secondary side, and this current is supplied to the power supply circuit 2.
This circuit stops the driving pulse output from the power supply control IC 6 on the primary side to the gate of the FET 5 when the current exceeds the maximum rated current of 00.

Reference numeral 15 denotes a current detection resistor for detecting a current flowing through the 3.3V output as a voltage appearing at both ends thereof.
Usually, a cement resistance of about 22 mΩ is used. The 3.3 V output terminal of the voltage across the detection resistor 15 is connected to the V + terminal of a comparator 18 via a resistor 37, and the voltage obtained by dividing the other by two resistors 16 and 17 is It is connected to the V- terminal of the comparator 18 as a reference value.
The overcurrent protection circuit 201 includes a zener diode 1
9, a resistor 20, 22, an electrolytic capacitor 21, a PNP transistor 23, and a photocoupler 24.

Considering the resistance value of the detection resistor 15, the resistors 16 and 17 determine the V of the comparator 18 when the current flowing through the 3.3V output line becomes the maximum load current + α (a predetermined allowable value).
It is necessary to set so that the voltage of the − terminal becomes larger than that of the V + terminal.

During normal operation, V of comparator 18
Since the negative terminal voltage is lower than the V + terminal and the output of the comparator 18 is at the HI level, the PNP transistor 23 is off.

On the other hand, at the time of overcurrent protection, the V
The negative terminal voltage becomes higher than the V + terminal, and the output of the comparator 18 becomes LOW level.

When the power is turned on, the input voltage to the comparator 18 does not become a desired value, so that the overcurrent protection circuit becomes unstable. In order to prevent malfunction at startup, the values of the electrolytic capacitor 21 and the resistor 22 are selected to have a time constant equal to or longer than the startup time of the power supply.

When an overcurrent occurs, the output of the comparator 18 becomes L
When it becomes OW, the PNP transistor 23 is turned on, so that the phototransistor of the photocoupler 24 becomes conductive,
The voltage at the ON / OFF terminal of the power control IC 6 increases. When the ON / OFF terminal voltage exceeds a certain voltage, the operation of the power supply control IC 6 stops,
The output of the power supply circuit 200 stops.

Next, the accuracy of the output voltage in the power supply circuit 200 will be described.

In the power supply circuit 200 described above, the transformer 4
When two kinds of voltages (3.3 V and 24 V) are directly output from the, the voltage accuracy varies depending on the load current of the 3.3 V output or the load current of the 24 V output.

In general, an output with a small voltage (3.3 V) often requires more accurate accuracy.

For this reason, as shown in FIG.
When trying to stabilize the 3V output (3.3V ± 1%),
As shown in FIG. 12B, the load of 3.3 V is heavy,
When the load of V is light, the voltage accuracy of the 24V output jumps to point A (24V + 12%).

In order to improve the voltage accuracy of the 24 V, conventionally, a zener diode 26, resistors 27, 28, 29,
A dummy load circuit 202 including the NPN transistor 30 is connected to the power supply circuit 200. The dummy load circuit 202 is a circuit that consumes current by the dummy resistor 29 when the output voltage of 24 V jumps.

That is, when the output voltage of 24 V rises to a predetermined voltage (for example, 28 V) or more, the Zener diode 26 conducts and the NPN transistor 30 turns on.
Then, a current flows through the dummy resistor 29, and the voltage accuracy of the 24V output can be improved by slightly increasing the load of the 24V output.

It is to be noted that, as the larger current flows through the dummy resistor 29, the voltage accuracy of the 24V output is improved, but wasteful power is consumed accordingly. Therefore, it is necessary to select an appropriate resistance value.

[0039]

As described above, the power supply circuit 200 of the conventional image forming apparatus is provided with the dummy load circuit 202 for improving the voltage accuracy of 24V. When the forming operation is completed and a standby state (standby state) is established and each drive system is stopped, the load current of the 24 V system output to the motor or the like of the drive system is almost eliminated.

For this reason, when the load of 3.3 V becomes heavy in this state, there arises a problem that the voltage accuracy of the 24 V output deteriorates.

Conventionally, when the output voltage of 24 V rises to a predetermined voltage (for example, 28 V) or more as described above, useless power is consumed by the dummy resistor 29 of the dummy load circuit 202.

Accordingly, it is an object of the present invention to provide an image forming apparatus capable of correcting the voltage accuracy of an output voltage output to a drive system without wasting power by a dummy resistor.

[0043]

In order to achieve the above object, the present invention provides an image forming section for forming a toner image on a transfer material, and an unfixed image formed on the transfer material in the image forming section. Fixing means for thermally fixing the toner image on the transfer material by heating with a heating element,
A first power supply voltage section for outputting a first output voltage from a power supply to a control system for controlling each drive system of the image forming apparatus; and a power supply section for mainly supplying the drive system of the image forming apparatus to the drive system. A second power supply section for outputting a second output voltage; and a preheating section for preheating the fixing section, wherein the preheating section includes a second power supply section for supplying the second output voltage from the second power supply section. It is characterized in that heat is generated by the output voltage.

Further, the present invention is characterized in that the preheating means generates heat by the second output voltage when the image forming section waits for an image forming operation.

Further, the apparatus further comprises voltage value detecting means for detecting the voltage value of the second output voltage, and the voltage value of the second output voltage is set to a predetermined voltage value by the voltage value detection by the voltage value detecting means. Is exceeded, the preheating means is caused to generate heat by the second output voltage.

Further, the apparatus further comprises load current value detecting means for detecting a load current value of the first output voltage, and the load current value of the first output voltage is determined in advance by detecting the load current value by the load current value detecting means. When the load current value exceeds a set value, the preheating means generates heat by the second output voltage.

[0047]

Embodiments of the present invention will be described below with reference to the drawings.

<First Embodiment> FIG. 1 is a diagram showing a power supply circuit (in the figure, a separately excited flyback type switching power supply circuit) of an image forming apparatus according to the present embodiment, and FIG.
FIG. 3 is a diagram showing an output characteristic of a 24V output voltage of the power supply circuit. FIG. The same parts as those in the conventional example shown in FIG. 11 are denoted by the same reference numerals, and overlapping description will be omitted. Further, the image forming apparatus of the present embodiment is the same as the conventional image forming apparatus shown in FIG. 9 and includes a film heating type fixing device.

As described above, when the driving system such as the motor is stopped in the standby state (standby state) of the image forming operation of the image forming apparatus, the driving system is mainly used for the driving system.
The load current of the 4V output is a very small load of about 0.1A. In this state, when the load current of the 3.3 V output mainly used for the control system of the drive system increases to, for example, the maximum value, the voltage of 24 V is changed to the point A (24 V + 12
%).

Therefore, in the present invention, 2
As shown in FIG. 3, a heating element 37 is provided as a preheating means for preheating the fixing section around the ceramic heater 33 of the fixing device in order to correct the voltage rise of the 4V output. The other configuration is the same as the drive and control circuit of the ceramic heater of the fixing device shown in FIG.

As shown in FIG. 1, the power supply circuit 200 includes a heating element 37, an NPN transistor 41, and a control device (CP) for controlling ON / OFF of the NPN transistor 41.
U) 40 is connected. The power supply circuit 20 shown in FIG.
The configuration and operation of 0 and the overcurrent protection circuit 201 are the same as those of the conventional example shown in FIG. 11, and a description thereof will be omitted in the present embodiment. Also, the power supply circuit 200, the overcurrent protection circuit 201, the NPN transistor 41, and the control device (CP
U) 40 is provided in the engine controller 126 shown in FIG.

Hereinafter, the on / off operation of the heating element 37 in this embodiment will be described.

While the image forming apparatus is on standby for image formation (standby), the control device (CPU) 40
The HI signal is sent to the transistor 41 to turn it on, and the heating element 37 is heated (turned on). When the image forming apparatus shifts to the image forming operation, the control device (CP
U) The LOW signal is sent from the 40 to the NPN transistor 41 to turn it off to stop (turn off) the heat generation of the heating element 37.

As described above, image formation standby (standby)
When the heating element 37 is heated (turned on) during the operation, current is consumed by the heating element 37.
The correction is made from point (24V + 12%) to point B (24V + 8%). That is, the voltage accuracy of 24 V is apparently
Move to the point A (24V + 12
%) Has moved to the point A '(24 V + 8%).

As described above, in the present embodiment, during the image forming standby (standby), the heating element 37 is heated (turned on) to preheat the fixing section around the ceramic heater 33 and the surrounding area, thereby providing the heating element. Since the current is consumed at 37, the voltage accuracy of 24V can be corrected.

During image formation standby (standby),
The heating element 37 is heated (turned on), and the ceramic heater 33 is turned on.
By preheating the peripheral fixing unit and the periphery thereof, it is possible to reduce the time (first print time) from when an image forming signal is input at the time of image formation to when the image forming operation is started.

Embodiment 2 FIG. 4 is a diagram showing a power supply circuit (in the figure, a separately-excited flyback switching power supply circuit) of an image forming apparatus according to the present embodiment. The same parts as those in the conventional example and the first embodiment are denoted by the same reference numerals, and duplicate description will be omitted. Further, the image forming apparatus of the present embodiment is the same as the conventional image forming apparatus shown in FIG. 9 and includes a film heating type fixing device.

In the present embodiment, the heating element 37, the NPN transistor 41 for controlling on / off of the heating element 37, and the Zener diode 4 are provided in the power supply circuit 200.
4, resistors 42 and 43 are connected. Note that the configurations and operations of the power supply circuit 200 and the overcurrent protection circuit 201 in FIG. 4 are the same as those in the conventional example shown in FIG. 11, and a description thereof will be omitted in the present embodiment.

Hereinafter, the on / off operation of the heating element 37 in this embodiment will be described.

During an image forming standby (standby) of the image forming apparatus, the output voltage of 24 V is changed to a predetermined voltage (for example, 28
When the voltage rises above V), the Zener diode 44 as the voltage value detecting means is turned on and the NPN transistor 41 is turned on, so that a current flows through the heating element 37 and a predetermined current is consumed.

Thus, the output voltage of 24 V is corrected from point A (24 V + 12%) to point B (24 V + 8%) in FIG. That is, the voltage accuracy of 24V apparently moves as shown by the broken line in FIG.
%) Has moved to the point A '(24 V + 8%).

As described above, in the present embodiment, when the output voltage of 24 V rises to a predetermined voltage (for example, 28 V) or more during image formation standby (standby), the heating element 37 is heated (turned on). By preheating the fixing portion around the ceramic heater 33 and its periphery, current is consumed by the heating element 37, so that the voltage accuracy of 24V can be corrected.

During standby for image formation (standby),
When the output voltage of 24V rises to a predetermined voltage (for example, 28V) or more, the heating element 37 is heated (turned on) to preheat the fixing section around the ceramic heater 33 and the periphery thereof, thereby forming an image forming signal during image formation. (First print time) until the image forming operation is started after the input is input.

Third Embodiment FIG. 5 is a diagram showing a power supply circuit (in the figure, a separately-excited flyback switching power supply circuit) of an image forming apparatus according to the present embodiment. The same parts as those in the conventional example and the first and second embodiments are denoted by the same reference numerals, and overlapping description will be omitted. Further, the image forming apparatus of the present embodiment is the same as the conventional image forming apparatus shown in FIG. 9 and includes a film heating type fixing device.

In this embodiment, the output voltage of 3.3 V from the power supply circuit 200 is connected as a reference value to the V + terminal of a comparator (comparator with hysteresis) 47 via a resistor 48, and the output voltage of 24 V is Two resistors 51, 52
Is connected to the V- terminal of the comparator 47.
The heating element 37 is connected to a PNP transistor 45 for controlling on / off of the heating element 37, resistors 50 and 53, and a zener diode 49. Note that the configurations and operations of the power supply circuit 200 and the overcurrent protection circuit 201 in FIG. 5 are the same as those of the conventional example shown in FIG. 11, and a description thereof will be omitted in the present embodiment.

The comparator 47 has a hysteresis characteristic as shown in FIG. 6 so that the heating element 37 is not repeatedly turned on / off by repeated instantaneous current fluctuations.

Thus, when the V-terminal voltage of the comparator 47 becomes larger than the Vb voltage in FIG. 6, the output of the comparator 47 becomes LOW, and the V-terminal voltage of the comparator 47 becomes Va in FIG.
When the voltage becomes lower than the voltage, the output of the comparator 47 becomes HI.
And The voltage value of 24 V at which the heating element 37 operates (heats) is determined by taking into account the voltage accuracy of the 24 V output, and only when the output voltage of 3.3 V is near the maximum load current value, the V−V The resistors 46, 51, and 52 are set so that the terminal voltage becomes higher than the Vb voltage in FIG. At this time, it is necessary that the operating voltage be at least smaller than the operating voltage of an overvoltage protection circuit (not shown) having an output of 24 V.

Hereinafter, the ON / OFF operation of the heating element 37 in the present embodiment will be described.

During the image forming standby of the image forming apparatus, the output of the comparator 47 is normally at the HI level, so that the PNP transistor 45 is off. While the image forming apparatus is waiting for image formation (standby), the output voltage of 24 V is changed to a predetermined voltage (for example, 28 V).
V) or more, the V− terminal voltage of the comparator 47 as the voltage value detecting means becomes larger than the Vb voltage in FIG. 6 and the output of the comparator 47 becomes LOW, so that the PNP transistor 45 is turned on. The heating element 37 operates (heats). When the heating element 37 operates (heats), a preset current is consumed. Therefore, the output voltage of 24V shown in FIG. 2 is changed from the point A (24V + 12%) to the point B (24V + 8%).
It is corrected until. That is, the voltage accuracy of 24 V apparently moves as shown by the broken line in FIG.
12%) has moved to the point A '(24V + 8%).

On the other hand, when the output voltage value of 24 V decreases, the heating element 37 continues to operate (heat generation) until the V- terminal of the comparator 47 becomes lower than the Va voltage of FIG.

As described above, in the present embodiment, similarly to the second embodiment, during image formation standby (standby),
When the output voltage of 24V rises to a predetermined voltage (for example, 28V) or more, the heating element 37 is heated (turned on) to preheat the fixing section around the ceramic heater 33 and the surrounding area, so that the current is generated by the heating element 37. 24 to be consumed
The voltage accuracy of V can be corrected.

During image formation standby (standby),
When the output voltage of 24V rises to a predetermined voltage (for example, 28V) or more, the heating element 37 is heated (turned on) to preheat the fixing section around the ceramic heater 33 and the periphery thereof, thereby forming an image forming signal during image formation. (First print time) until the image forming operation is started after the input is input.

Fourth Embodiment FIG. 7 is a diagram showing a power supply circuit (in the figure, a separately-excited flyback switching power supply circuit) of an image forming apparatus according to the present embodiment. The same parts as in the conventional example and the first, second, and third embodiments are denoted by the same reference numerals, and overlapping description will be omitted. Further, the image forming apparatus of the present embodiment is the same as the conventional image forming apparatus shown in FIG. 9 and includes a film heating type fixing device.

In the present embodiment, of the voltages across the detection resistor 15, the 3.3 V output terminal is connected to the V + terminal of a comparator 47 via a resistor 56, and the other is connected to two resistors 55. , 58 are the voltages of the comparator 47
-Terminal is connected as a reference value. The detection resistor 15 is
It is also used as the 3.3 V output overcurrent protection circuit 201 side. The heating element 37 includes a PNP transistor 45 for controlling on / off of the heating element 37, resistors 50 and 53,
A zener diode 49 is connected.

The comparator 47 is connected via a resistor 57 to an NPN transistor 41 for turning off the heating element 37 and a control device (CPU) 40 for controlling ON / OFF of the NPN transistor 41. The configuration and operation of the power supply circuit 200 and the overcurrent protection circuit 201 in FIG.
Is the same as the conventional example shown in FIG.

The comparator 47 has a hysteresis characteristic as shown in FIG. 8 so that the heating element 37 is not repeatedly turned on / off by repeated instantaneous current fluctuations.

As a result, when the V + terminal voltage of the comparator 47 becomes smaller than the Va voltage of FIG. 8, the output of the comparator 47 becomes LOW, and the V + terminal voltage of the comparator 47 becomes Vb of FIG.
When the voltage exceeds the voltage, the output of the comparator 47 becomes HI
And Also, 3.3 V at which the heating element 37 operates (heats).
Is 3.3 V considering the voltage accuracy of the 24 V output.
8 is set by the resistors 54 and 58 so that the V + terminal voltage of the comparator 47 becomes larger than the Va voltage in FIG. 8 only when the output voltage of the comparator becomes near the maximum load current value. At this time, it is necessary to set the value to at least a value smaller than the operating current of the overcurrent protection circuit 201 of 3.3 V output.

Hereinafter, the on / off operation of the heating element 37 in the present embodiment will be described.

During an image forming standby (standby) of the image forming apparatus, the output of the comparator 47 is normally at the HI level, so that the PNP transistor 45 is off. When the 3.3V current value increases to a predetermined current value or more and becomes close to the maximum load current value during image formation standby (standby) of the image forming apparatus, the comparator 47 as load current detection means. V + terminal voltage becomes smaller than the Va voltage in FIG. 8, the output of the comparator 47 becomes LOW,
Since the NP transistor 45 is turned on, the heating element 37 operates (heats). When the heating element 37 operates (heats), a predetermined current is consumed. Therefore, the output voltage of 24 V shown in FIG. 2 is changed from the point A (24 V + 12%) to the point B (24 V + 8).
%). That is, the voltage accuracy of 24 V apparently moves as shown by the broken line in FIG.
V + 12%) has moved to the point A '(24V + 8%).

On the other hand, when the output voltage value of 3.3 V decreases, the heating element 37 continues to operate (heat generation) until the V + terminal of the comparator 47 becomes higher than the Vb voltage in FIG.

Then, when the image forming operation starts, the control device (CP) stops the operation (heat generation) of the heating element 37.
U) The heating element OFF signal is sent from the NPN transistor 4
Output to 1. As a result, the NPN transistor 41 is turned on, the output of the comparator 47 is forced to HI, and the operation (heating) of the heating element 37 is stopped.

As described above, in this embodiment, when the current value of 3.3 V increases to a predetermined current value or more and becomes close to the maximum load current value during image formation standby (standby),
The heating element 37 is heated (turned on), and the ceramic heater 33 is turned on.
By preheating the peripheral fixing unit and its periphery, current is consumed by the heating element 37, so that the voltage accuracy of 24V can be corrected.

Also, during image formation standby (standby),
When the current value of 3.3 V increases to a predetermined current value or more and becomes near the maximum load current value, the heating element 37 generates heat (ON).
By preheating the fixing portion around the ceramic heater 33 and the periphery thereof, the time (first print time) from when an image forming signal is input during image formation to when the image forming operation is started can be reduced.

[0084]

As described above, according to the present invention, the preheating means for preheating the fixing means under the condition that the second output voltage output to the drive system is expected to exceed a predetermined voltage is provided. By operating, the voltage correction of the power supply voltage of the driving system can be favorably performed without wasteful power consumption by the dummy resistor as in the related art.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a power supply circuit of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating output characteristics of a power supply circuit in Embodiment 1.

FIG. 3 is a diagram showing a driving circuit of the ceramic heater according to the first embodiment.

FIG. 4 illustrates a structure of a power supply circuit in Embodiment 2.

FIG. 5 illustrates a structure of a power supply circuit in Embodiment 3;

FIG. 6 is a diagram illustrating characteristics of a comparator of a power supply circuit according to Embodiment 3.

FIG. 7 illustrates a structure of a power supply circuit in Embodiment 4.

FIG. 8 is a diagram illustrating characteristics of a comparator of a power supply circuit according to Embodiment 4.

FIG. 9 is a diagram showing a configuration of an image forming apparatus in a conventional example.

FIG. 10 is a diagram showing a driving circuit of a ceramic heater in a conventional example.

FIG. 11 is a diagram illustrating a power supply circuit of an image forming apparatus in a conventional example.

12A and 12B are diagrams showing output characteristics of a power supply circuit in a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Commercial power supply 4 Transformer 6 Power supply control IC 18, 47 Comparator 33 Ceramic heater 37 Heating element 40 Controller 41 NPN transistor 44 Zener diode 45 PNP transistor 200 Power supply circuit

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 2H027 DA03 DA34 DA50 DE05 DE07 DE09 EA12 EA16 EC06 EC09 ED25 EE04 EE06 EJ18 EK13 ZA01 2H033 AA32 BA22 BA25 BA30 BA31 BB01 BB18 BB28 BB34 CA03 CA05 CA30 CA32 CA30

Claims (4)

[Claims] An image forming section for forming a toner image on a transfer material, and an unfixed toner image formed on the transfer material in the image forming section is thermally fixed on the transfer material by heating with a heating element. A first power supply voltage section for outputting a first output voltage from a power supply to a control system mainly for controlling each drive system of the image forming apparatus; A second power supply voltage unit that outputs a second output voltage from the power supply to each of the drive systems of the image forming apparatus; and a preheating unit that preheats the fixing unit. The second power supply voltage from the second power supply voltage unit;
An image forming apparatus, wherein heat is generated by the output voltage of the image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the preheating unit is configured to stop the image forming operation in the image forming unit when the driving system is stopped.
The image forming apparatus according to claim 1, wherein heat is generated by the output voltage. 3. A voltage value detecting means for detecting a voltage value of the second output voltage, wherein the voltage value of the second output voltage is set in advance by the voltage value detection by the voltage value detecting means. The image forming apparatus according to claim 1, wherein when the temperature exceeds a predetermined value, the preheating unit generates heat by the second output voltage. 4. A load current value detecting means for detecting a load current value of the first output voltage, wherein the load current value of the first output voltage is determined in advance by the load current value detection by the load current value detecting means. When the set load current value is exceeded,
The image forming apparatus according to claim 1, wherein the preheating unit generates heat by the second output voltage.