JPH0812531B2 - Image forming device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus having a control unit that controls a bias applied to a charger that charges a body to be charged.

[Prior Art] The above configuration is widely used in laser beam printers and copying machines at present. In this type of apparatus, a charger is used to uniformly charge the photoreceptor or transfer toner before exposure.

2. Description of the Related Art Conventionally, a method of making a charging current constant has been widely used in order to prevent image deterioration due to contamination with toner, etc., on a wire, a grid of a charger, or a shield casing, and a deterioration with time.

On the other hand, in the past, the life of the photosensitive drum was short, and maintenance had to be performed regularly in a relatively short cycle.
In recent years, the number of maintenances has tended to be reduced due to improvement of the photosensitive drum itself and extension of the life of the drum due to surface potential control, and the problem of dirt on the charger has been attracting attention. That is, although the charger can be frequently cleaned in the conventional short maintenance cycle, as the maintenance cycle becomes longer, the image deterioration due to the stain remaining on the charger is accompanied by the speeding up of the image processing.

[Problems to be Solved by the Invention] Conventionally, in order to reduce the influence of the image deterioration due to the dirt of the charger, no measures have been found other than increasing the charging current. This is because when the charging current is increased and the discharge corona amount is increased, the speed at which foreign matter adheres to the discharge electrode (wire) grid of the charger is increased, but the influence of dirt on discharge can be reduced.

However, according to such a method, a large charging current only promotes the contamination of the charging device in a state where there is no pollution immediately after the start of use, and the capacity of the high voltage power source must be increased due to the increase in the current, so that the device is It had the drawbacks of large size and easy cost increase.

Furthermore, in general, when the current flowing from the charger to the image carrier is controlled with a constant current, the potential of the image carrier fluctuates due to deterioration of the image carrier. Further, when the current flowing from the charger to the image carrier is controlled by constant current, it is necessary to detect the current flowing through the image carrier, but the current flowing through the image carrier from other members may be erroneously detected. Accurate control may not be possible.

In order to improve these, it is desirable that the charger is provided with a grid and the grid bias is controlled based on the surface potential of the image carrier. As described above, if the grid bias is controlled based on the surface potential of the image carrier, the potential of the image carrier can be directly known, and accurate potential control can be performed regardless of deterioration of the image carrier.

However, when performing such control, if the current given to the charger is a preset fixed value, the current given to the charger must be set to a large value in advance in consideration of deterioration characteristics due to dirt on the charger. . If the current supplied to the charging device is set to a large value, the charging device will be further soiled, and the life of the charging device will be shortened.

Therefore, in order to prevent the image deterioration due to the deterioration of the image carrier and prevent the charging failure due to the dirt of the charger, the present invention (1) shows the surface potential of the image carrier charged when a predetermined amount of power is supplied to the charger. An object of the present invention is to provide an image forming apparatus that controls a bias applied to a grid based on a detection result, and (2) determines a predetermined power supply amount to be supplied to a charger according to a physical quantity corresponding to the number of image forming times of the apparatus. And

[Means for Solving the Problems] In order to solve the above problems, in the present invention, a charger having a grid for charging an image carrier, and a charging device when a predetermined power supply amount is applied to the charger In the image forming apparatus, a detection unit that detects the surface potential of the image carrier charged by the charger, and a control unit that controls the bias applied to the grid of the charger based on the detection result of the detection unit, A configuration is adopted in which the predetermined power supply amount is determined according to a physical quantity corresponding to the number of image forming times of the apparatus.

[Operation] With the configuration described above, the charger current is increased according to the number of image formations, which is a guideline for stains on the charger. Therefore, the stain is not increased, and the surface potential of the photoconductor is not increased excessively. An image can be formed with good image quality.

[Examples] Hereinafter, the present invention will be described in detail based on examples shown in the drawings.

First Embodiment FIG. 1 shows the structure of a copying machine as an example of the image forming apparatus of the present invention. In the drawing, reference numeral 1 is a photosensitive drum having a photosensitive member such as Cds on its circumference. A primary charger 2, a surface potential sensor 3 for detecting a charge amount, a developing roller 5 for toner development, and a transfer charger 4 are arranged along the circumferential surface of the photosensitive drum 1.

These members are connected to a control unit 9 including a microcomputer for controlling the operation of the entire apparatus. High-voltage power supply control for each member is performed by reference numerals 81, 82, 83 and
This is done via a D / A converter indicated at 84 and a high voltage output unit indicated at 61, 62, 63 and 64. Further, the detection amount of the surface potential sensor 3 is sent to the control unit 9 via the A / D converter 72.

In particular, the electric power applied to the discharge electrode of the primary charger 2 and the grid 21 is controlled by the two D / A converters 81 and 82 and the high voltage output units 61 and 62, respectively.

To form an image, first, the photosensitive drum 1 is uniformly charged by the primary charger 2, and then the reflected light 10 of the document is applied to the drum to form an electrostatic latent image. The development is performed, and the toner on the photosensitive drum 1 is transferred by the transfer charger 4.

FIG. 2 shows the structure of the high-voltage output unit 61 for the discharge electrode of the primary charger 2. In the figure, reference numeral T1 is a boosting transformer, and one end of its primary winding has a low-voltage power supply voltage via a low-pass filter composed of a resistor R1 and a capacitor C1
It is connected to Vcc and the other end is turned on / off by the switching transistor Tr1 to obtain a high voltage alternating current boosted to the two windings. A resonance capacitor C2 and a protection diode D2 are connected to the collector-emitter of a transistor Tr1 having a grounded emitter. The ON / OFF of the switching transistor Tr1 is controlled by the oscillator Q4.

The secondary side output is converted into direct current by the rectifying / smoothing diode D1 and the capacitor C3, and applied to the discharge electrode of the primary charger 2 from the terminal P1 via the spark preventing resistor R4.

The charging current i _C is the ground potential terminals P2 and 2 for the charger.
It is taken out as the terminal voltage change of the resistor R5 connected to the low voltage side of the next winding. Capacitor C5 in parallel with resistor R5
Is a decoupling capacitor. The detection voltage is input to the error amplifier Q2, and the error amplifier with the voltage value corresponding to the predetermined charging current input from the control unit 9 via the terminal P3 is input to the pulse width modulator (hereinafter referred to as PWM) Q3. .

PWM Q3 controls the duty ratio of the output pulse to the base of the transistor Tr1 of the oscillator Q4 according to the input value,
As a result, the charging current i _C is subjected to constant current control to the target value input by the controller 9.

FIG. 3 shows the structure of the high-voltage output unit 62 connected to the bias grid 21 of the primary charger 2. This unit is composed of a switching regulator similar to that shown in FIG. The difference is that the error amplifier Q6 detects the applied voltage V _G to the grid 21 by the resistors R7 and R8, and directly controls the input voltage on the primary side of the boosting transformer T2 instead of the oscillator Q5. That is the point. The error amplifier Q6 controls the voltage applied to the grid 21 in response to a predetermined bias voltage input from the control unit 9 via the terminal P7.

Next, the operation of the above configuration will be described in detail with reference to the flowchart of FIG. FIG. 4 shows the control unit 9
It is a flowchart figure which showed the procedure of the control of the primary charger 2 which this performs.

The control section 9 is provided with a counter means which can be manually reset by hardware or software, and this counter is incremented according to the number of times of copying the original.
Further, the coefficient value of the counter is maintained by the backup power supply even when the main power supply is off.

From the control system (not shown), the primary charger 2
When a command to change the applied current is input, the control section 9 first inputs the number of copying times N from the counter in step S1 of FIG.

Subsequently, in step S2, the control unit 9 obtains the primary charging current I ₁ by the following control formula.

I ₁ = I _O + KN (1) where I _O is the initial value of the primary charging current (previous value), K
Is a correction coefficient.

Next, in step S3, the determined primary charging current I ₁
To the primary charger 2, and the surface potential sensor 3 measures the dark portion potential v _D of the photosensitive drum 1. That is, the anti-light shield 10 of the original is cut off, and the surface potential of the unexposed photoreceptor is measured.
This measured quantity is digitally converted via the A / D converter 72,
It is input to the control unit 9.

Next, in step S4, the control unit 9 obtains the correction value of the grid voltage V _G of the primary charger 2 by the following control formula.

ΔV _G = α (v _D + V _DO ) ... (2) where α is a predetermined control coefficient and V _D0 is the target dark area potential.

According to the above configuration, the number of times of copying, which is a measure of dirt on the charger, is reflected in determining the primary charging current, and the charging current is gradually increased according to the number of times of copying. It is not necessary to feed unnecessary current more than 10 times the current to the grid and charger housing, the amount of dirt at the start of use can be reduced, and the charger life can be extended. In addition, the surface potential control can be started from the charging current value necessary to obtain the minimum required latent image potential, so that the life of the charger electrode can be extended, the power source can be downsized, the power consumption can be reduced, and the ozone generation amount can be reduced. This can be achieved, and it can greatly contribute to high performance, high reliability, and low cost of the device.

The control coefficient K of the control equation (1) in step S2 may be appropriately determined according to the characteristics of the charger of the apparatus and the image control characteristics. A counter for measuring the number of times N of copying is configured to be reset by a service person when the charger is replaced or cleaned.

In the above, the charging current is corrected by the cumulative value of the number of times of copying, but it is also possible to measure a physical quantity according to the number of times of image formation such as accumulation of the rotation time of the photosensitive drum and reflect it in the determination of the charging current. The above configuration is not limited to a copying machine, but can be applied to an apparatus having a similar configuration such as a laser beam printer.

Second Embodiment In the above embodiment, the grid voltage of the charger is determined by using the surface potential sensor. However, in the embodiments shown in FIGS. 5 and 6, the drum applied to the photosensitive drum out of the current applied to the charger. Only the current is measured, and the surface potential is stabilized by controlling this constant current. That is, when the charging current is increased according to the number of copies, the drum current also increases. Therefore, the surface potential of the photosensitive drum may become excessively high in the same potential control as the conventional one.

Therefore, in addition to the gradual increase of the charging current according to the number of times of copying in the first embodiment, the power supply control to the charger electrode and the grid is performed based on the drum current using the circuits of FIGS. 5 and 6.

The discharge electrode 22 and the grid 21 of the charger 2 shown in FIG. 5 are controlled by the controller 9 through the D / A converters 81 and 82 and the high voltage output units 61 'and 62' which are substantially the same as those described above. Charger 2
Of the housing 23 and the negative side terminals of the high voltage output units 61 'and 62' are commonly connected, and a current detection circuit by a capacitor C11 and a resistor R11 is connected between this connection point and the ground potential of the drum 1. . The drum current i _D detected by this is A /
It is fed back to the control unit 9 via the D converter 73.

Each block in FIG. 5 is constructed as shown in FIG. The difference from the first embodiment is that the high voltage output unit
At 61 ', the total applied current i ₁ to the discharge electrode 22 is the resistance R13,
It is detected through the error amplifier Q11 for impedance conversion, and based on this, the transformer T is transmitted through the PWMQ14 and the oscillator Q13.
11 output current is to be controlled. In the high voltage output unit 62 ', the grid 21 is formed by the resistors R16 and R17 as described above.
The applied voltage to the control circuit is detected, but the control loop by the error amplifier Q15, the PWM, and the oscillator Q16 controls the base of the switching transistor Tr12.

In the above configuration, the total current i ₁ supplied to the charger is divided into the shield current i _S flowing to the charger housing 23, the grid current i _G flowing to the grid 21, and the drum current i _D flowing to the photosensitive drum 1. To be done. When the total current i ₁ is gradually increased depending on the number of times of copying as in the above embodiment, the drum current i _D also increases accordingly, and the surface potential tends to be excessive.

Therefore, the drum current i _D detected by the resistor R11 and the capacitor C11 is sent to the control unit 9 via the A / D converter 73, and the control unit 9 sets the drum current i _D to a predetermined value suitable for obtaining the target surface potential. The grid voltage of the high voltage output unit 62 'is controlled via the D / A converter 82 so as to approach them.

That is, the reference voltage of the D / A converter Q15 is changed and the grid voltage is controlled so as to increase the grid i _G.

By repeating this operation a predetermined number of times, the drum current i _D can be controlled to a desired value with high accuracy.

As described above, the charging current can be increased in accordance with the dirt on the charger and the surface potential of the photosensitive drum can be stabilized, and image formation can be performed without degrading image quality.

The above drum current measurement → grid voltage control is performed at a predetermined timing in the non-image portion (dark portion) of the photosensitive drum 1. This control may be performed each time image formation is performed, but the determined grid voltage value may be stored in the memory of the control unit 9 and used.

In the two embodiments described above, the number of copies is adopted as the physical quantity corresponding to the number of times of image formation, which is an index of the contamination of the charger. However, the rotation time of the photosensitive drum may be used in a laser beam printer or the like. Further, the dirt on the charger may be determined by calculating the equivalent impedance from the current and voltage applied to the discharge electrode and using this value.

Furthermore, when using a charger having no grid electrode, the same effect as described above can be obtained by insulating the charger housing from the ground potential and controlling the voltage applied to the housing.

[Effect] As is apparent from the above description, according to the present invention, a charger having a grid for charging the image carrier, and a charger for charging a predetermined amount of electricity, the charger is charged. In the image forming apparatus having a detection unit that detects the surface potential of the image carrier and a control unit that controls the bias applied to the grid of the charger based on the detection result of the detection unit, the predetermined power supply amount is Since the configuration determined according to the physical quantity corresponding to the number of times of image formation of the apparatus is adopted, appropriate charging control can be performed according to changes in charging conditions due to dirt on the charger. For example, immediately after the start of use of the device, a large current is not applied to the charger when the charger is clean, so that it is possible to prevent the contamination of the charger from being promoted, and thus the current applied to the charger is not so much. There is an effect that the charged body can be charged to a desired potential without increasing the size, and it is possible to achieve high performance and high reliability of the device such as downsizing of the power supply, long life of the charger, and stable operation. Further, it is possible to provide an excellent power supply device capable of forming a high quality image based on the surface potential control of the photoconductor.

[Brief description of drawings]

1 is a block diagram showing the structure of a first embodiment of an image forming apparatus according to the present invention, FIG. 2 and FIG. 3 are circuit diagrams showing the structure of the high voltage output unit of FIG. 1, respectively. The figure is a flow chart showing the control procedure of the control unit in FIG. 5 and 6 show a second embodiment of the present invention. FIG. 5 is a block diagram of the main part of the apparatus, and FIG. 6 is a more detailed circuit diagram of FIG. 1 ... Photosensitive drum, 2 ... Primary charger 3 ... Surface potential sensor, 4 ... Transfer charger 5 ... Developing roller, 9 ... Control section 21 ... Grid, 22 ... Discharge electrode 23 ... ... Casing 61 to 64, 61 ', 62' ... High-voltage output unit

Claims (1)

[Claims] 1. A charger provided with a grid for charging an image carrier, and a detecting means for detecting the surface potential of the image carrier charged by the charger when a predetermined amount of power is supplied to the charger. An image forming apparatus having: a control unit configured to control a bias applied to the grid of the charger based on a detection result of a detection unit; wherein the predetermined power supply amount is determined according to a physical amount corresponding to the number of image forming times of the device. An image forming apparatus characterized by the following.