JPH0721670B2 - Charging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a charging device, and more particularly to a charging device for charging a body to be charged, and a charging device having a constant current control means for controlling a constant current applied to the charging device. It relates to the device.

[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 regularly performed in a relatively short cycle.In recent years, however, the number of maintenance operations has been reduced due to improvements in the photosensitive drum itself and extension of the drum life due to surface potential control. The problem of dirt on the charger has been attracting attention. That is, although the charger was able to be frequently cleaned in the conventional short maintenance cycle, as the maintenance cycle became longer, the image deterioration was caused by the stain remaining on the charger due to 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.

[Means for Solving the Problems] In order to solve the above problems, the present invention has a charging device that charges a body to be charged, and a charging device that has a constant current control device that controls the current applied to the charging device with a constant current. In the apparatus, a detection unit that detects the impedance of the charger that changes according to the dirt of the charger, and a constant current of a constant current control unit based on a change in the impedance of the charger that is detected by the detection unit. A structure having a control means for correcting the control value is adopted.

[Operation] With such a configuration, it is possible to apply a charging current according to the dirt on the charger, and prevent image deterioration due to the dirt on the charger.

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

FIG. 1 shows the structure of a copying machine as an example of the image forming apparatus of the present invention. In the figure, 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. The high-voltage power supply control of each member is 81, 82, 83 and 84.
And a high-voltage output unit 61, 62, 63 and 64. Further, the detection amount of the surface potential sensor 3 is controlled by the control unit 9 via the A / D converter 72.
Sent to.

Particularly, the electric power applied to the discharge electrode of the primary charger 2 and the grid 2 is controlled by the two D / A converters 81 and 82 and the high voltage output units 61 and 62, respectively. Further, the high voltage output unit 61 has a circuit for detecting the voltage Vp applied to the discharge electrode, and the detected output is transmitted to the control unit 9 via the A / D converter 71.

In image formation, first, the photosensitive drum 1 is uniformly charged by the primary charger 2, and then light 10 such as a reflected light of a document or a laser beam is applied to the drum to form an electrostatic latent image. Is developed by the developing roller 5 and the toner on the photosensitive drum 1 is transferred by the transfer charger 4.

FIG. 2 shows a high voltage output unit for the discharge electrode of the primary charger 2.
61 configuration is shown. In the figure, reference symbol T1 is a step-up transformer, and one end of its primary winding has a resistor R1 and a capacitor.
Low-voltage power supply voltage Vc via a low-pass filter consisting of C1
It is connected to c, and the other end is turned on / off by the switching transistor Tr1 to obtain a high-voltage alternating current boosted in the secondary winding. A resonance capacitor C2 and a protection diode D2 are connected between the collector and the emitter of the transistor Tr1 provided with an emitter. The ON / OFF of the switching transistor Tr1 is controlled by the oscillator Q4.

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

The charging current ip is taken out as a terminal voltage change of the terminal P2 of the ground potential for the charger and the resistance R5 connected to the low voltage side of the secondary winding. A capacitor C5 connected in parallel with the 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. .

The PWM Q3 controls the duty ratio of the output pulse with respect to the base of the transistor Tr1 of the oscillator Q4 according to the input value, and as a result, the charging current i _c is constant-current controlled to the target value input by the control unit 9.

Further, the applied voltage V _P to the charger is divided into a predetermined ratio by the resistors R2 and R6 and input to the error amplifier Q1. The detection voltage corresponding to the charging voltage V _P impedance-converted by the error amplifier Q1 is sent to the control unit 9 via the A / D converter 71.

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 the voltage of the transformer T2 for boosting is not 1
The point is that the input voltage on the secondary side is directly controlled. 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 is a flow chart showing the procedure of the control of the primary charger 2 performed by the controller 9. The charging device is controlled at power-on or at an appropriate timing after the formation of a predetermined number of images.

The control unit 9 first resets the applied current i _c of the primary charger 2 to a predetermined initial value I _o in step S1 of FIG. That is, a voltage value corresponding to the charging current I _o is applied to the terminal P3 of FIG. 2, and the charger P2 is supplied from the terminal P1 of the high voltage output unit 61.
The current I _o is controlled to flow between the discharge electrode and the ground of.

Next, in step S2, the controller 9 measures the applied voltage V _P of the primary charger 2 via the terminal P4 of the high voltage output unit 61.

Then, in step S3, the applied current I _O
The calculation of V _P / i _c (I _O ) is performed from the voltage V _P measured in step S1 and the equivalent impedance z _C of the primary charger at that time is calculated.

Next, in step S4, the following equation is calculated to obtain the correction value Δi _c of the primary charging current.

Δi _C = δ (z _c −Z _oo ) However, δ is a predetermined control coefficient and is determined from the voltage condition for performing desired image formation. In addition, _Zoo is the primary charger 2
Is the initial impedance of.

Next, in step S5, the primary charging current i _c is corrected to i _c + Δi _c via the terminal P3 of the high voltage output unit 61.

In step S6, the latent image potential V _s on the photosensitive drum 1 is measured by the surface potential sensor 31 and the applied voltage V _G of the grid 21 of the primary charger 2 is determined by the following equation. The grid voltage correction amount ΔV _G is determined by ΔV _G = (v _s −V _so ). Here, α is a predetermined control coefficient, and V _so is a target value of the latent image potential. The surface potential control in step S6 is repeatedly performed a predetermined number of times to obtain a predetermined latent image potential, and thereafter, image formation similar to the conventional one is performed.

Since the impedance of the charger fluctuates according to the dirt on the charger, according to the above-described embodiment, an appropriate charging current can be determined according to the degree of dirt. It is no longer necessary to apply unnecessary current of 10 times or more to the grid charger housing. In addition, the surface potential control in step S6 can be started from the charging current value required to obtain the minimum required latent image potential, so the life of the charger electrode can be extended, the power source can be made smaller, the power consumption can be reduced, and the amount of ozone generated can be increased. It is possible to achieve reductions and the like, which can greatly contribute to high performance, high reliability, and low cost of the device.

In the above embodiments, the impedance of the charger is used as a measure of the stain on the charger, but the number of image formations, the rotation time of the photosensitive drum, etc. can also be used as an index corresponding to the stain.

Further, when a charger having no grid electrode is used, the surface potential control similar to that described above can be performed by insulating the charger casing from the ground potential and controlling the applied voltage to the casing. .

[Effect] As is apparent from the above, according to the present invention, in a charging device having a charger for charging a body to be charged and a constant current control means for controlling a constant current applied to the charger,
Based on a change in the impedance of the charger, which is detected by the detecting unit that detects the impedance of the charger that changes according to the dirt of the charger,
Since the constitution having the control means for correcting the constant current control value of the constant current control means is adopted, even if the charger is dirty to some extent, the constant current control value of the charging current should be corrected according to the degree of the dirt. As a result, it is possible to provide an excellent image forming apparatus capable of performing appropriate charge control for a long period of time, extending the maintenance cycle, and preventing image deterioration.

[Brief description of drawings]

FIG. 1 is a block diagram showing the structure of an image forming apparatus according to the present invention, FIGS. 2 and 3 are circuit diagrams showing the structure of the high voltage output unit of FIG. 1, and FIG. 4 is of FIG. It is a flowchart figure which showed the control procedure of a control part. 1 ... Photosensitive drum, 2 ... Primary charging device 3 ... Surface potential sensor, 4 ... Transfer charging device 5 ... Developing roller, 9 ... Control unit 21 ... Brid 61 to 64 ... High voltage output unit

Claims (1)

[Claims] 1. A charging device comprising: a charging device for charging an object to be charged; and a constant current control means for controlling a constant current applied to the charging device, wherein the charging device changes according to contamination of the charging device. A charging device comprising: a detection unit that detects an impedance; and a control unit that corrects a constant current control value of the constant current control unit based on a change in the impedance of the charger detected by the detection unit.