JPH0479761A - Image forming apparatus - Google Patents

Abstract

PURPOSE:To improve an A-V efficiency synthetically by a method wherein, when a relatively large power intermittent load is in an off-state, a bypass switching device is turned on by a switch control means to short-circuit both the terminals of a choking coil and, when the intermittent load is in an on-state, the bypass switching device is turned off by the switch control means to provide a choking coil input operation. CONSTITUTION:A control circuit 5 receives a temperature signal from a thermosensor 40 and performs on-off control of a fixed heater(H) 6. As a NOT signal opposite to a signal applied to the light emitting part 35a of a photocoupler 35 is applied to the light emitting part 36a of a photocoupler 36, a TRIAC 4 is in an off-state when the H6 is in an on-state and a choking coil 3 is effective and, when the H6 is in an off-state, the TRIAC 4 is in an on-state and the choking coil 3 is short-circuited. When the H6, which is a relatively large capacity intermittent load, is in an off-state, a peak current does not exceed a specified value in the cases of both capacitor input type operation and choking coil input operation. In the case of the choking coil input type operation, the peak current does not exceed the specified value even if the H6 is in an on-state.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus, and particularly to an image forming apparatus equipped with various power loads.

[Conventional technology]

Image forming devices such as copying machines, printers, and facsimiles are equipped with commercial power sources, in addition to DC power supplies that supply DC power for controlling microcomputers and other mechanical components, as well as commercial power supply units, which vary depending on the model. Motors and exposure lamps (copying machines) that are used directly or with voltage transformation, as well as static elimination lamps and fixing heaters for equipment that uses the electrostatic latent image method.

Various power loads are provided, such as various high-voltage power supplies.

As a power supply circuit that supplies power to these loads, for example, as in the example of a copying machine shown in Japanese Patent Application Laid-open No. 58-220168, a power supply for control or a power supply for driving clutches, solenoids, etc. is provided, respectively. A power transformer steps down the voltage, rectifies and smoothes it, and then supplies stabilized DC power using a dropper. Other AC loads such as the main motor, exposure lamp, high-voltage power supply, fixing heater, and other AC loads are directly connected to the commercial power supply. Ta.

Dropper-type DC stabilized power supplies like this have the drawbacks of low efficiency, around 50% at most, and the need for large power transformers, but since their output is only a few tens of watts and less than 100W, this is not much of a problem. That never happened.

However, the development of OA equipment is remarkable, and in particular, image forming devices that form images on plain paper using an electrostatic latent image method have become faster, have higher image quality, and have more functions, and the capacity of their DC power supplies has increased significantly. .

For example, motors, which are a source of damage, have changed from AC motors to DC motors in order to accurately control their rotational speed, and high-voltage power supplies have also changed to converter systems from constant-voltage DC power supplies in response to these strict requirements.

In addition, from the viewpoint of workability, the number of peripheral devices such as high-speed automatic document feeders has increased, and in order to supply power for them, the capacity of the DC power supply, which was previously around 100VA, has increased from 400VA to 500V.
It has become A class, and some models have appeared with over 600 VA.
Moreover, strict voltage stability is required.

When the output capacity increases in this way, the dropper type power supply becomes a big problem in that it increases in size and generates a large amount of heat due to power loss.

Therefore, in recent years, instead of the dropper type, for example,
As shown in Japanese Patent No. 4-40849, a switching regulator that combines a primary rectifying and smoothing circuit and a switching DC-DC converter has come into use.

Switching regulators have an efficiency of 80% to 85%, which is much higher than the dropper type, and because they switch at high frequencies, they are smaller and lighter, including the transformer and choke, but the primary rectifier and smoothing circuit is a capacitor input type, so Since the capacitance is large, the power factor deteriorates, the peak value of the input current becomes high, and troubles due to high frequencies are likely to occur.

Therefore, although the (power) efficiency is good, the VA efficiency (output VAO ratio to input VA) is about 50%. Therefore, if the output of the DC power supply is 400VA, the input is 800VA.
, that is, the input current reaches 8A.

If the fixing heater is soow and the efficiency of the DC power supply is 80%, the input power is 400W10.8 +800W=1.3
KW, but the input VA is 800VA+800VA=
Since it is 1.6KVA, that is, the input current is 16A,
Outlets commonly used in offices, etc. (100V
, 15A), and it cannot be safely used as it is even with a switching regulator.

In order to improve this power factor or VA efficiency, for example, a buck-boost chopper circuit (see Japanese Patent Laid-Open No. 63-23561)
There are two methods: inserting an active filter consisting of the following in place of the smoothing capacitor in the primary rectifying and smoothing circuit of the switching regulator, and inserting a choke coil in front of the switching regulator.

[Problem to be solved by the invention]

The former method using a chopper circuit is desirable in terms of VA efficiency because it can improve the power factor to nearly 100%, but the circuit is complicated because the switching of the chopper circuit and DC-DC converter must be controlled independently. The problem was that the number of parts increased and the cost increased significantly.

In addition, in the latter method using a choke coil, this choke coil operates at a commercial frequency (50Hz).

Because it operates at a frequency of 60Hz), it is inevitably larger and heavier than the choke coil of a secondary rectifier and smoothing circuit that operates at a DC-DC converter switching frequency (50kHz to 200kHz), so it does not meet the goal of reducing size and weight. There was a problem.

This invention was made in view of the above points, and it suppresses the charging peak current in the primary rectifying and smoothing circuit of the DC power supply section when the load is large, improves the power factor, and improves the overall VA efficiency. The object of the present invention is to provide an image forming apparatus with improved performance.

[Means to solve the problem]

In order to achieve the above object, the present invention provides an image forming apparatus that inputs commercial power and supplies it to a DC power supply unit that converts it into DC power and an intermittent load that repeatedly turns on and off a relatively large amount of power. A parallel circuit of a choke coil and a bypass switch element inserted in series between a smoothing capacitor at the first stage of the section and a commercial power supply, and a switch control means for controlling on/off of the bypass switch element in response to on/off of an intermittent load. It was established.

[For production]

In the image forming apparatus configured as described above, the switch control means turns on the bypass switch element to short-circuit both terminals of the choke coil when the intermittent load of relatively high power is off, and causes the choke coil to function as a capacitor input type. However, when an intermittent load is on, the bypass switch element is turned off and acts as a choke input type.

Therefore, the power factor during heavy loads is improved and the charging peak current of the DC power supply section is suppressed, so that the VA efficiency is improved overall.

Furthermore, since the choke coil is not in constant operation, it can be relatively small and lightweight.

〔Example〕

Hereinafter, one embodiment of the present invention will be specifically described with reference to the drawings.

FIG. 2 is a schematic diagram showing the internal mechanism of a laser printer that is an embodiment of the present invention.

Around the photosensitive drum 10 rotating clockwise as shown by the arrow, chargers 11 . Optical writing unit 12. Phenomenon unit 13, transfer charger 1
4. Cleaning units 15 are arranged respectively.

The surface of the photosensitive drum 10 is first uniformly charged by a charging charger 11, and then the photosensitive drum 10 is scanned in the main scanning direction by a spot on which a beam modulated by image data from the optical writing unit 12 and deflected in the main scanning direction forms an image. to form an electrostatic latent image.

The electrostatic latent image is developed by the developing unit 13 and converted into a visualized toner image, and then the toner image is transferred by the transfer charger 14 onto a sheet of paper conveyed along the route shown by the dashed line. be done.

The toner and charge remaining on the photosensitive drum 10 are removed by the cleaning unit 15, and the removed toner is collected by the cleaning unit 15.

The paper is fed by a paper feed roller 19 from a paper stack 18 on a paper feed cassette 17, and is fed by a pair of registration rollers 2.
0, the toner image is conveyed to the position of the transfer charger 14 by a pair of registration rollers 20 at a timing that matches the image written on the photoreceptor drum 10 by the optical writing unit 12. is transcribed.

The paper onto which the toner image has been transferred is conveyed to a fixing unit (21), is pressed against a heated fixing roller 21a by a pressure roller 21b, is fixed by the heat and pressure, and is then transferred to a paper ejection roller 22. The paper is transported and discharged from the paper discharge port 23 onto the paper discharge tray 24 .

A fixing heater 6 arranged concentrically inside the fixing roller 21a heats the fixing roller 21a, and during operation, the surface temperature is high enough to instantaneously melt the toner on the paper passing at a predetermined conveyance speed. It is maintained at the operating temperature and at a lower holding temperature during standby.

Since the fixing heater 6 is set to have a sufficient amount of heat generation, that is, power capacity, to quickly reach the operating temperature when transitioning from standby to the operating state, the surface temperature of the fixing roller 21a is always controlled by a thermistor (not shown). After reaching the operating temperature, it is intermittently controlled on and off while the temperature is maintained, and when the temperature is maintained at the standby temperature, the duty ratio is controlled at an even lower duty ratio.

FIG. 1 is a circuit diagram showing an example of the power system of this laser printer.

AC power input from the commercial power supply 1 is supplied to the noise filter 26, which is composed of a high frequency choke and two bypass capacitors and prevents external noise from entering and internal noise from leaking, a power switch 27, and a no-use breaker 28. After passing through a power input section, the power is supplied to the DC power supply section 2 and the fixing heater 6.

The DC power supply section 2 includes a bidirectional 3 which is a bypass switch element.
A primary rectifying and smoothing circuit consisting of a parallel circuit of a terminal thyristor, a so-called triac 4, and a choke coil 3, a rectifier 29 consisting of a diode bridge, and a large-capacity capacitor CP that is the first stage smoothing capacitor, and a transformer 3o. It consists of a DC-DC converter configured as

The input AC power is supplied to the AC terminal of the rectifier 29 through the parallel circuit of the choke coil 3 and the triac 4, and the rectified DC power including ripple output from the DC terminal charges the capacitor CP. Smoothed.

The DC-DC converter has a primary winding NP and three secondary windings NSL, NS2. a transformer 3o having NS3;
It is a switching element that forms a series circuit with the primary winding NP and turns on and off the primary DC power input from the capacitor CP in accordance with a control signal from the constant voltage control circuit 34.
A transistor Q consisting of ET and three secondary windings NSI, NS2 . It is composed of rectifying and smoothing circuits 31 and 32 and a rectifying circuit 33 connected to NS3, respectively.

The rectifying and smoothing circuits 31 and 32 each include rectifying/current diodes Di, D2 and commutating diodes CD1. CD2 and small capacity choke coil Ll, L2 and large capacity capacitor C1,
It is composed of C2.

The rectifying and smoothing circuit 31 uses the DC power charged in the capacitor C1 as a DC 5V control power source, and supplies it to the control circuit 5.

The rectifying and smoothing circuit 32 uses the DC power charged in the capacitor C2 as a 24V DC instant power source to supply various loads 4.
5 to 50.

Either one of the rectifying and smoothing circuits 31 and 32, for example, the output voltage (DC5V) of the rectifying and smoothing circuit 31 which is a control power supply,
It is fed back to the constant voltage control circuit 34.

The constant voltage control circuit 34 outputs a control signal with a different duty ratio to the transistor Q according to the fed-back output voltage signal, so that the control power supply can be maintained even if the voltage of the commercial power supply 1 or the load power fluctuates. The output voltage of is stabilized to 5V.

When a current that is interrupted by turning on and off the transistor Q flows through the primary winding NP of the transformer 30, the secondary winding N S
1, NS2, NS3 have primary winding NP
A voltage power corresponding to each turns ratio is induced.

The rectifying and smoothing circuit 31 rectifies the power induced in the secondary winding NSL when the transistor Q is on, using a rectifying diode D1, and charges a capacitor C1 through a choke coil L1 forming a choke input type.

At this time, the energy stored in the choke coil L1 in magnetic form by smoothing the pulsating current is reconverted into a current when the transistor Q is off, and charges the capacitor C1 through the free-wheeling diode CDI.

The rectifying and smoothing circuit 32 is also completely similar, so its explanation will be omitted.

The rectifier circuit 33 includes a rectifier diode D3 and a limiter resistor R3.
The direct current (gate current) rectified by the rectifier diode D3 is connected to the limiter resistor R3 and the photocoupler 3.
It is connected to the gate electrode of the triac 4 through a light receiving section 36b consisting of a phototransistor 6, and while the light emitting section 36a of the photocoupler 36 is lit, the light receiving section 36b is turned on and the light is not turned on. 1 ~ Current flows,
The triac 4 is triggered and both terminals of the choke coil 3 are short-circuited, and the choke coil 3 does not operate.

AC that has passed through the no-use breaker 28 in the power input section
The power is also connected to a series circuit of the fixing heater 6 and the triac 38, which is an intermittent load of relatively high power (for example, soow).

The gate electrode of the triac 38 is connected to the circuit 39 to the gate 1 including the light receiving part 35b of the photocoupler 35, and while the light emitting part 35a of the photocoupler 35 is lit and the light receiving part 35b is on, the gate circuit 39 is connected to the triac. 38 is triggered to turn on the fixing heater 6, and if the light emitting section 35a is not lit, the fixing heater 6 is turned off.

The control circuit 5, which is powered by the constant voltage DC5V for control outputted by the rectifying and smoothing circuit 31, processes the input image data as video data in response to commands input to the laser printer from a host machine (not shown). In addition to sending the image to the optical writing unit 12 (FIG. 2) and writing the image thereon,
Sequential control of each mechanical part of the laser printer,
A series of operations is executed to develop the written image, transfer it onto the paper, fix it, and discharge it.

For this purpose, for example, a high-voltage power source 45. Motor 46. Solenoid 47. Clutch 48, static elimination lamp 49
A control signal is outputted as needed to each driver 45a, 46a, 50a (consisting of transistors) of the 9 display lamp 50, etc.

The control circuit 5 also inputs a temperature signal from a temperature sensor 4o consisting of a thermistor that detects the surface temperature of the fixing roller 21a heated by the fixing heater 6 in contact with the fixing roller 21a.
The fixing heater 6 is controlled on/off by turning on the light emitting part 35a of the photocoupler 35 when the temperature drops and turning it off when the temperature rises so that the holding temperature and the operating temperature become the holding temperature and the operating temperature depending on the standby and operating modes, respectively. .

Since a knot signal opposite to the signal applied to the light emitting part 35a is applied to the light emitting part 36a of the photocoupler 36,
When the fixing heater 6 is on, the triac 4 is turned off and the choke coil 3 operates effectively, and when the fixing heater 6 is off, the triac 1 is turned on and the choke coil 3 is short-circuited.

FIG. 3 is a waveform diagram showing an example of AC power input to the DC power supply section 2, where (A) is an input voltage waveform, and (B)
) and (C) respectively show the input power waveforms when the triac 4 is on and off, that is, when the choke coil 3 is short-circuited and when it is operating effectively.

Since the input current waveform shown in Figure 3 (B) is a capacitor input type waveform, during the period when the instantaneous value of the input voltage shown in Figure 3 (A) exceeds the voltage across the terminals of the capacitor CP, In order to charge the capacitor CP with the power required by the unit 2, the larger the capacitance of the capacitor CP, the higher the voltage between its terminals, and the shorter the charging time, so the peak value of the current increases.

By reducing the capacitance of capacitor CP, the terminal voltage (D
C) decreases, the charging time increases, and the peak value of the current decreases, but the fluctuation rate of the DC voltage between the terminals, that is, the input voltage of the DC-DC converter increases, and therefore the duty ratio (drive pulse width) of the transistor Q increases. ) will also increase, and there is a risk that the constant voltage property will not be maintained, especially depending on changes in the DC load of the traversing current.

Since the input current waveform shown in Figure 3 (C) is a choke input type waveform, the voltage between the terminals of capacitor CP will drop slightly and the charging time will also be slightly longer, resulting in the current waveform shown in Figure 3 (B). Compared to this, the change becomes gentler and the peak value of the current decreases significantly.

As the inductance of the choke coil 3 increases,
This tendency is increasing, and although this is desirable in terms of the current waveform, the size of the choke coil 3, which is difficult to miniaturize to begin with, is becoming larger and larger, so it is difficult to expect an excessively large inductance.

The current waveforms shown in FIGS. 3(B) and 3(C) indicate the input current of the DC power supply unit 2, and also the total input current of the laser printer when the fixing heater 6 is off.

FIG. 4 is a waveform diagram showing an example of the input current when the fixing heater 6 is turned on, and (A) in the same figure is a waveform diagram showing an example of the input current when the fixing heater 6 is turned on.
The input current waveform is shown in the same figure (B).

3(C) shows a total input waveform in which the currents shown in FIGS. 3(B) and 3(C) are superimposed on FIG. 3(A).

As is clear from both figures, if the fixing heater 6, which has a relatively large capacity intermittent load, is turned off,
In any case shown in , the peak current never exceeds 15A.

However, when the fixing heater 6 is on and the DC power supply section 2 is of the capacitor input type shown in FIG. 4(B), the peak current may exceed 15 A.
Image forming apparatuses with high performance and therefore high power consumption require a dedicated power outlet or need to be connected to two separate outlets, which is not practical.

Even if the image forming apparatus is the same, if the choke input type shown in FIG. can be connected to.

Even in an image forming apparatus in which the DC power supply device 2 is of a capacitor input type and the peak current does not exceed 15A even when the fixing heater 6 is on, a peak current of nearly 15A flows.
Wiring loss increases due to reactive current flowing,
It is desirable to use a choke input type to improve the power factor.

As the inductance of the choke coil 3 increases, the power factor and VA'J factor are improved and the peak current value is suppressed, but since the size increases, it is difficult to use a large inductance.

The above advantages and disadvantages are the same as the conventional example in which a choke coil is installed in front of the DC power supply, but even if the power factor is improved during standby, where power consumption is extremely low, and during stability, where power consumption is relatively low, the power factor remains unchanged. VA efficiency, which is the product of power efficiency, does not have much effect on improving the overall VA efficiency, which takes into account power consumption and its time integration. 'It is very effective to improve the power factor during large current output when the V4 power consumption peaks.

Additionally, if you try to downsize the choke coil without changing its inductance and current capacity, there is a tendency for loss to increase and heat generation to increase, so a heat sink or, in some cases, a cooling fan will be required to reduce the size. It is no longer fit for purpose.

However, it is relatively easy to downsize the choke coil even if it generates a little more heat by bypassing the choke coil instead of letting current flow through it all the time, and activating the choke coil only during short-term power peaks. It can be made lighter.

Since the switching frequency of the DC-DC converter is high, from tens to hundreds of KHz, the transformer 30 and the choke coils LL and L2 provided on its secondary side are extremely small considering the amount of power. The choke coil 3 intended for AC power is large, heavy, and expensive.

The effect of miniaturizing the choke coil 3 and the reduction in peak current due to improving the power factor during large currents reduce the burden on the commercial power supply side and the rectifier 29 on the image forming apparatus side.
The withstand voltage and maximum allowable forward current of 4) are reduced, and the reactive power flowing to the capacitor CP is reduced, which has a great effect of suppressing heat generation.

Furthermore, since the triac 4 is off when the power switch 27 is turned on, there is also an inrush current suppressing effect that suppresses the surge current during the initial charging of the capacitor CP.

Instead of providing a parallel circuit consisting of the choke coil 3 and the triac 4 between the commercial power supply 1 and the rectifier 29 (the AC input terminal thereof), it may also be provided between the rectifier 29 (the DC output terminal thereof) and the capacitor CP. .

The effect is exactly the same.

That is, it is sufficient to provide a parallel circuit consisting of a choke coil and its bypass switch element between the AC power supply 1 and the capacitor CP, and it does not matter whether it is before or after the rectifier 29.

However, since the part before the rectifier 29 is on the AC circuit side, the bidirectional triac 4 is used as a bypass switch element.
After the rectifier 29 is the DC circuit side (unidirectional)
Each transistor can be used.

The above description has been made using a laser printer as an example, but image forming apparatuses that form images on plain paper using electrostatic latent image technology, that is, copying machines, digital copying machines, and optical printers such as LED and LCA (liquid crystal) printers, etc.

Needless to say, the present invention can also be applied to power supplies for high-speed facsimile machines and the like.

Furthermore, although we have explained the fuser heater as an example of an intermittent load, in a copying machine, the exposure lamp that illuminates the document can also be considered as a relatively high-power intermittent load, and it can also be used to respond to the on/off status of multiple intermittent loads. The triac 4 may be controlled to turn on and off.

〔Effect of the invention〕

As explained above, the image forming apparatus according to the present invention has
When the load is large, the charging peak current in the primary rectifier and smoothing circuit of the DC power supply is suppressed to improve the power factor and reduce the overall V
A. Efficiency can be improved.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of the power system of a laser printer which is an embodiment of the present invention, Fig. 2 is a schematic configuration diagram showing its internal mechanism, and Figs. 3 and 4 are its inputs. FIG. 3 is a waveform chart showing an example of voltage and current. 1.Commercial power supply 2.DC power supply section 3.Choke coil 4..Triac (bypass switch element) 5..
Control circuit (switch control means) 6... Fixing heater (intermittent load) CP... Capacitor (first stage smoothing capacitor) 3rd
Figure 4

Claims (1)

[Claims] 1. In an image forming apparatus that inputs commercial power and supplies it to a DC power supply unit that converts it into DC power and a relatively large intermittent load that repeatedly turns on and off at any time, the smoothing capacitor at the first stage of the DC power supply unit and the commercial A parallel circuit including a choke coil and a bypass switch element inserted in series between a power source and a switch control means for controlling on/off of the bypass switch element in accordance with on/off of the intermittent load. image forming device.