JPH04178171A - Imaging apparatus - Google Patents

Abstract

PURPOSE:To improve power factor of a DC power supply to reduce an input current by providing a voltage boosting means consisting of an auto transformer between a commercial AC power supply and a DC power supply. CONSTITUTION:An auto transformer 9 for boosting a voltage is provided between an AC power supply 1 and a SW regulator 2. Here, the auto transformer 9 is formed by a choke coil having an intermediate tap 9c, an output of the AC power supply 1 is connected between the intermediate tap 9c and the one end 9a to obtain boosted voltage from both ends 9a, 9c of the choke coil. It means that an inductance between the terminal 9b and the intermediate tap 9c is inserted between the input AC power supply and SW regulator 2. Thereby, a power factor can be improved and drop of input voltage into DC-DC converter 4 can be compensated by its boosting effect.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus that is equipped with a DC power supply and an AC load such as a fixing heater and forms an image using electrostatic latent image technology.

[Conventional technology]

A charged photoconductor is exposed to light to form an electrostatic latent image, and the electrostatic latent image is converted into a toner image by development and printed on paper (plain paper).
An image forming device using electrostatic latent image technology that heats and pressurizes the transferred toner image to fix it on the paper after the toner image is transferred onto the paper;
Examples include copying machines, laser printers, electronic copying machines, and high-speed facsimile machines.

The power supply circuit of these image forming apparatuses is disclosed in, for example, Japanese Patent Application Laid-Open No. 58
As disclosed in Japanese Patent No. 220168, the AC load includes a main motor, an exposure lamp, a high-voltage power supply for charge removal, a fixing heater, etc., and a DC power supply. A clutch serves as a load for a DC power supply.

There are driving loads such as solenoids and control circuits that control them, and their output is at most several tens of watts, and most of them are 100 watts.
It was less than W.

However, recently, image forming devices have become faster.

Multi-functionality is required, and what used to be AC loads is being replaced by DC loads.

For example, in the case of a motor, a single AC main motor can be used to drive a photoreceptor drum using a clutch, solenoid, etc.

In contrast to the exposure scanner, paper conveyance, and development unit drive, all of the drives had to be driven by a separate DC motor to meet the demands. Peripheral devices such as an automatic document feeder are also essential, and their drive also requires high precision, so many DC motors are used independently of the device itself.

Therefore, the output capacity of DC power supplies that supply power to these DC loads has increased significantly, from 400W to 600W.
It has become quite large.

If such a high-output DC power supply is configured with a conventional dropper, it will be large and heavy, and its efficiency is at most 50%, so it generates a large amount of heat.

Therefore, instead of the dropper method, for example,
Switching regulators such as those disclosed in Japanese Patent No. 40849 have come into use.

The efficiency of a switching regulator is 80% to 85%, which is significantly higher than that of a dropper, and it is very effective because it is small and lightweight, but the primary smoothing capacitor on the input side requires a large capacity, so the input The current waveform becomes peak-like, distortion increases, the power factor worsens, the input current flows in excess of the active power, and since it contains many harmonic components, there is a risk of noise-induced failures.

Therefore, although the efficiency is high, the power factor is poor, and the VA efficiency (output VA relative to input VA) of the switching regulator is approximately 50%, so the DC average load is 400%.
W, even if the input power is about 500W, the input VA
is 800VA, and the input current at 100V input is 8
A will flow.

The capacity of the fixing heater also increases as the speed increases, and a high-speed copying machine requires at least 800W, and the input current combined with the DC power supply device consumes 1.3KW.
Despite this, the current is 16A, making it impossible to use a regular outlet (100V/15A) for safety reasons.

In order to solve this problem, for example, Japanese Patent Application Laid-Open No. 63-2356
As shown in Publication No. 1, there is a proposal to provide an active filter circuit consisting of a step-up chopper etc. in the front stage of the DC-DC converter of the switching regulator, which can improve the power factor to almost 100%, so the above No such problems will occur.

[Problem to be solved by the invention]

However, this proposal requires a large number of components and is complicated to control, and since the input voltage to the DC-DC converter of the switching regulator increases to a certain degree, a high withstand voltage element is required, resulting in high cost and poor reliability. A new problem arises:

Furthermore, as an alternative to this, the present applicant has already inserted a choke coil LO between the AC power supply unit 1 and the smoothing capacitor CO of the primary rectifying and smoothing circuit 3, as shown in FIG. We have filed a proposal to improve the power factor and reduce input current by suppressing charging peak current and reducing input current waveform distortion.

However, in the case of this method, a voltage drop occurs due to the insertion of the choke coil LO, and the charging voltage of the capacitor CO, that is, the input voltage of the DC-DC converter 4 decreases.
If excessive stress is applied to O and the voltage of the commercial AC power source decreases, the reliability of the DC power source may be impaired and a predetermined output may not be obtained.

This invention was made in view of the above points, and by improving the power factor of a DC power supply and reducing the input current, it provides highly reliable, high-speed, multifunctional image formation that can be used even in a general outlet. The purpose is to provide equipment.

[Means for Solving the Problems] In order to achieve the above object, the present invention connects a commercial AC power source to a DC power supply and other AC loads in the main body, and generates an image using electrostatic latent image technology. In this image forming apparatus, a voltage boosting means consisting of a single-turn transformer is provided between a commercial AC power supply and a DC power supply.

Further, it is preferable to provide an inductance element between the commercial AC power supply and the boosting means, or between the boosting means and the DC power supply device.

[Function] In the image forming apparatus configured as described above, by providing a boosting means consisting of a single-turn transformer, its inductance acts as a choke input type, suppressing the peak of the input current and reducing the power factor. As the voltage increases, it is possible to compensate for a drop in the charging voltage of the capacitor CO.

In addition, if the inductance of the boosting means is insufficient, a separate inductance element may be provided.
You can easily obtain the highest VA efficiency.

[Example] Hereinafter, an example of the present invention will be specifically described with reference to the drawings.

FIG. 4 is a schematic diagram showing the internal mechanism of a laser printer which is an embodiment of the image forming apparatus according to 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 the registration roller pair 2o 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 the fixing unit 21, and the pressure roller 2 is applied to the heated fixing roller 21a.
1b and is fixed by the heat and pressure, the paper is conveyed to the paper ejection roller 22 and ejected from the paper ejection port 23 onto the paper ejection tray 24.

The fixing heater 7 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 7 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 an AC power system in which a booster is provided before the DC power supply of this laser printer. The same parts as in the conventional example shown in FIG. ing.

FIG. 2 is a circuit diagram showing an example of an AC load and a DC-DC converter connected to the primary DC output in the AC power system and the DC power supply, and a DC load connected to the DC-DC converter. It is.

The AC power system shown in FIG. 1 consists of an AC power supply section 1 that distributes AC power input from a commercial AC power source (not shown) to each load.
It consists of a two-output switching regulator (hereinafter referred to as "rSW regulator") 2, which is a DC power supply, a fixing heater 7, which is the main AC load, and other AC loads 8, and a single-turn transformer 9, which is a step-up means. ing.

The AC power supply unit 1 includes a power plug 25 that is detachably connected to a commercial AC power outlet, a noise filter 26 consisting of a capacitor and a choke coil, and a power switch 2.
7 and a non-fuse breaker 28, and when the power switch 27 is on, noise is removed from the AC power input via the power plug 25 by a noise filter 26 and output to each load.

A negative part of the AC power output from the AC power supply unit 1 is input to the SW regulator 2 via the autotransformer 9, and the other part is supplied to the fixing heater 7 and other AC loads 8.

The SW regulator 2 has a primary rectifier smoothing circuit 3 and a 2-output D
The primary rectifying and smoothing circuit 3 performs full-wave rectification of input AC power using a diode bridge DB, and converts the primary DC power smoothed by a large-capacity smoothing capacitor CO into a DC-DC converter. Output to 4.

As shown in FIG. 2, the DC-DC converter 4 has 1
Secondary coil NP and two secondary coils NSI.

A primary side circuit consisting of a transformer T equipped with NS2, a series circuit of its primary coil NP and a transistor QO which is a switching element, and rectifying diodes Di and D2 connected to the secondary coils NS1 and NS2, respectively. , commutation diodes DTI, DT2, and choke coils LL, L
2, and two mutually independent secondary rectifying and smoothing circuits consisting of large-capacity smoothing capacitors CI and C2. drive unit 6 as a driving power source.
Output to.

The primary DC power input from the primary rectifier smoothing circuit 3 to the primary side circuit of the transformer T is turned on and off by the transistor QO driven by the pulse width modulated drive signal input from the driver 30, and the primary side When the current in the primary coil NP of the circuit is on, the power induced in the secondary coil NSI passes through the diode DI and the choke coil L1 to charge the capacitor C1.

At this time, the power stored as magnetic energy in the choke coil L1 due to the smoothing effect of the choke coil L1 is 1
When the current in the next coil NP is off, it is reconverted into a current, which passes through the free-wheeling diode DTI and the choke coil Ll to further charge the capacitor C1.

Similarly, the power induced in the secondary coil NS2 charges the capacitor C2.

Although not shown, the terminal voltage of either capacitor C1 or c2 is fed back to the driver 30.
By controlling the duty ratio of the drive signal according to the voltage to which 0 is fed back, the fed-back terminal voltage is stabilized, and the other terminal voltages are made quasi-stable.

The control section 5 performs sequence control by outputting signals according to timing to each section of this laser printer, and
The condition of each part is inspected using sensors, etc., and controlled to maintain optimal conditions.

For example, the high voltage power supply 31 configuring the drive unit 6. motor 32
．． Lamp 33. Solenoid 34. The control unit 5 operates the loads by outputting signals according to timing to the bases of transistors Q1 to Q5, which are switches that are connected in series to loads such as the clutch 35 and control their on/off states. .

For example, the surface temperature of the fixing roller 21a (FIG. 4) heated by the fixing heater 7 is detected by the thermistor TH, and the triac TR, which is a bidirectional switch connected in series with the fixing heater 7, is turned on/off. As a result, the surface temperature of the fixing roller 21a is controlled to be constant.

Looking at each load from the power source side, the fixing heater 7, which is an AC load, has a large power capacity and is an intermittent load, so the load fluctuations are large. Other AC loads 8 are generally smaller than the fixing heater 7.

The control unit 5, which is one of the DC loads, has strict requirements for constant voltage performance, but has a relatively small power capacity and almost no load fluctuations.

As already explained, the drive unit 6, which is another DC load,
As image forming apparatuses become faster and more sophisticated, their power capacities continue to increase, and since each image forming apparatus operates according to timing from the control unit 5, load fluctuations are also large.

The example shown in Figure 2 is only a part of this, and in reality there are many types of loads, and the number of outputs of the SW regulator 2 is two, one for control and one for drive. As the number of devices increases, the number of devices increases, and in some cases there are six or more outputs, so a single DC-DC converter may not have enough capacity, and it may be configured with multiple DC-DC converters, so the load on the DC power supply The capacity may be around 600W.

In order to operate such a large capacity SW regulator stably, the capacitance of the primary smoothing capacitor CO must be extremely large, and with the capacitor input method, the power factor decreases and the AC input current increases, causing 15 when combined with heater 7
If it exceeds A, there is a risk that you will not be able to use a regular electrical outlet.

Therefore, a step-up autotransformer 9 is provided between the AC II power supply section and the SW regulator 2.

The autotransformer 9 is composed of a choke coil having an intermediate tap 9C, and the output of the AC power supply unit 1 is connected between the intermediate tap 9C and a portion 9a, and both ends 9a of the choke coil are connected to each other.
A boosted output is obtained from between 9c.

At the same time, the inductance between the terminal 9b and the intermediate tap 90 is inserted between the input AC power supply and the SW regulator 2, which improves the power factor and increases the voltage to the DC-DC converter 4 due to its boosting effect. The drop in input voltage is compensated.

FIG. 3 is a circuit diagram showing an example of an AC power system in which a choke coil LO, which is an inductance element, is further provided in the AC power system shown in FIG. , SW regulator 2. The DC load and AC load are the same as in the example shown in FIG.

In this embodiment, when a sufficient power factor improvement effect cannot be obtained with the inductance between 9b and 9c of the single-turn transformer 9, another choke coil LO is inserted.

Since the inductance of the autotransformer 9 is also present in series, the same power factor improvement effect can be obtained even if the value of the choke coil LO is smaller than that of a conventional autotransformer without an autotransformer, and the boosting effect of the autotransformer 9 Similarly to the example shown in FIG. 1, the problem that the input voltage to the DC-DC converter 4 decreases can also be solved.

In the example shown in FIG. 3, the AC power supply section l and the autotransformer 9
A choke coil LO was inserted between the autotransformer 9 and the diode bridge DB of the primary rectifier and smoothing circuit 3, or between the diode bridge DB and the capacitor CO.
It is clear that exactly the same effect can be obtained by inserting choke coils between the two or in separate locations.

〔Effect of the invention〕

As described above, according to the present invention, by improving the power factor of the DC power supply and reducing the input current, a highly reliable, high-speed, multifunctional image forming apparatus that can be used even with a general outlet is provided. You can.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of an AC power system of an image forming apparatus according to the present invention, FIG. 2 is a circuit diagram showing an example of the DC power supply, its DC load, and AC load, and FIG. 3 is the same. FIG. 4 is a circuit diagram showing another example of the AC power system; FIG. 4 is a schematic configuration diagram showing the internal mechanism of a laser printer, which is also an example of the AC power system; FIG. 5 is a circuit diagram showing a conventional example of the AC power system. be. 1... AC power supply section 2... SW (switching) regulator (DC power supply) 3... Primary rectifier smoothing circuit 4... DC-DC converter 7... Fixing heater (AC load) 9. ...Single-turn transformer (step-up means) LO...Choke coil (inductance element) Applicant Rico Co., Ltd. m m U] 1--------J Fig. 2 1-- - ++ ++ +--" +
1+1t. -----J

Claims (1)

[Scope of Claims] 1. An image forming apparatus that inputs a commercial AC power source and connects it to a DC power supply device and an AC load in the main body to form an image using electrostatic latent image technology, comprising: the commercial AC power source and the DC power source; An image forming apparatus characterized in that a step-up means consisting of a single-turn transformer is provided between the image forming apparatus and the apparatus. 2. The image forming apparatus according to claim 1, further comprising an inductance element provided between the commercial AC power supply and the boosting means, or between the boosting means and the DC power supply. 3. The image forming apparatus according to claim 1 or 2, wherein the DC power supply device is a switching regulator that rectifies and smooths its AC input, converts it to DC, and then outputs a predetermined DC output using a DC-DC converter. . 4. The image forming apparatus according to claim 1, wherein the AC load includes a fixing heater.