JPS58120271A - Controlling method of electrophotography - Google Patents

Abstract

PURPOSE:To obtain a stable picture, by controlling a corona potential in the direction, where the potential of a latent image forming material is approximated to the initial value, when the surface potential of the latent image forming material detected during continuous recording is deviated from an initial potential over a certain range. CONSTITUTION:The surface potential of a photoreceptor is read by a potential sensor 19 and is read by an amplifying circuit 20 and is amplified by the amplifying circuit 20 and is converted to a digital quantity by an A/D converter 21 and is taken into a CPU 22. The CPU 22 operates degrees of deviation of surface potential values of bright and dark parts of a photoreceptor 3 from proper values by comparing these surface potential values with values stored in a memory 27 and controls surface potentials in accordance with a prescribed algorithm in the direction where they are approximated to initial values. Thus, a stable picture is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of controlling electrophotography, and more particularly, to a potential control method of electrophotography that controls the potential of a latent image forming body such as a photoreceptor to a constant value.

Generally, in electrophotographic image formation, a photoreceptor is uniformly charged by corona charging, and then exposed to light to form a so-called latent image, which is a charge pattern according to the image pattern, and then a developer called toner is applied. It is attached and visualized.

Methods for forming latent images include a method in which the photoreceptor is uniformly charged and then exposed to a light image, and a method in which the photoreceptor is uniformly charged in a primary manner and then subjected to AC
Alternatively, there are various methods, such as a method in which charging is performed with a polarity opposite to that of the -order charging, and at the same time, after performing optical image exposure, the entire surface is exposed.

Further, there are cases in which a latent image once formed on a photoreceptor is transferred to another latent image forming member, that is, development is performed after performing latent image transfer.

Regardless of which of the above-mentioned methods is employed, the latent image must maintain an appropriate potential in relation to matching with development.

That is, for development under certain conditions, if the latent image is not within a predetermined range, the surface image density will be unstable, and bank ground stains, so-called fog, will occur.

Factors that prevent a constant latent image, that is, a constant potential, include (1) differences in corona generation depending on temperature and humidity conditions, (2) temperature and humidity characteristics of the photosensitive drum,
(3) There are variations in characteristics among photosensitive drums.

As a method to solve the above-mentioned factors that prevent the potential from being maintained at a constant level, the potential of the dark or bright areas of the photoreceptor is detected by a potential sensor before recording starts, and the detected potential is converged to a desired potential. An electrophotographic recording device that adopted a method of controlling high corona pressure was proposed, and this device was confirmed to be somewhat effective.

However, with the conventional potential control method, although the initial image is good, while recording a large number of sheets in succession (because the two potentials differ from the initial value,
Images may no longer maintain their initial quality.

For example, as a general tendency, even if the photoreceptor is under the same corona charging conditions, if corona charging is continued many times, the potential often shifts gradually and fluctuates, increasing or decreasing. In particular, this tendency is even greater when C2 recording is performed after the device has been opened and stopped for a long time.

If the cause is on the photoconductor side, such as the charging history, it may be possible to solve the problem by changing the material of the photoconductor or its manufacturing method, but research and development for this purpose not only takes time but also costs money. However, the resulting photoreceptor is extremely expensive.

Furthermore, even if the potential fluctuates due to changes in temperature or humidity, it is not possible to obtain continuously stable images by controlling the potential only before starting recording.

Figures 1 (A) and [F]) are diagrams to explain the shortcomings of the conventional method. They record images of only dark areas when a toner latent image is formed against a background that has already been exposed to light. It shows the dark potential when

FIG. 1 (Alj2) shows the case where the dark potential increases as recording is continued.

In this case, no matter how optimal the initial dark potential Vdi is set for 1'-, if recording is performed continuously, the potential will exceed the appropriate image permissible upper limit potential Vul.

FIG. 1(B) shows a case in which the potential decreases, and in this case, it falls below the appropriate lower limit potential Vll.

The above-mentioned upper and lower allowable limit potentials Vd and Vll are determined by matching the developing device and the potential. For example, the bright area potential is a negative potential lower than the dark area potential, and the developer is mixed with a carrier such as iron powder. In the case of a toner made of carbon resin and a so-called two-component developer, v- is the limit potential at which carrier adhesion does not occur, and Vll is the limit potential at which toner fog does not occur.

Therefore, good images can only be obtained continuously up to time t in the case of FIG. 1(A) and only up to time t2 in the case of FIG. 1(B).

In order to eliminate such defects, it is necessary to control the potential during continuous recording.

When image formation is performed intermittently, it is possible to control the potential for each page of the recorded image so that the potential is always at an appropriate level, but this inevitably reduces the throughput of image formation.

In recent years, electrophotographic copying machines and computer output terminal devices have become faster, and the amount of data that can be recorded continuously has increased, making it increasingly necessary to obtain stable images without reducing throughput.

Furthermore, if the tendency of the potential shift of the photoreceptor is constant, it is possible to control the high voltage of corona discharge to match the characteristics, but there are many factors that are not constant, such as changes in the lot of the photoreceptor and the environment.

The present invention has been made in order to eliminate the above-mentioned drawbacks of the conventional method, and it is an object of the present invention to provide a potential control method for electrophotography that can always perform stable potential control without reducing throughput. The purpose is

In order to achieve the above object, the present invention controls and sets the potential of the latent image forming body to a desired initial potential before the start of recording, and furthermore, the surface potential of the latent image forming body detected during continuous recording is A method is adopted in which the corona potential is controlled in such a way that the potential of the latent image forming body approaches the initial value when the potential deviates from the initial potential by more than a certain range, and the corona voltage is gradually varied until the potential deviates from the initial potential by more than a certain range. .

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 2 shows a schematic configuration of a laser beam printer device to which the method of the present invention is applied. In the figure, the reference numeral 1 indicates a laser beam, which is oscillated from a laser oscillator (not shown) and modulated (also not shown). After being modulated in accordance with the input signal to the device, it is scanned by a rotating polygon mirror 2, and a light image is exposed onto a photoreceptor 3 through an imaging lens 4.

Cathode ray tube or plasma display to expose the light image,
It is of course possible to use other means such as an LED array.

As is well known, the photoreceptor 3 basically has a conductive support, a photoconductive layer, and an insulating layer, and is uniformly charged in advance by a primary corona charger 5, and then subjected to photoimage exposure. Secondary corona charger 6 that performs AC corona discharge while receiving
The entire surface is uniformly exposed to light by a full-surface exposure lamp 7, and an electrostatic latent image is formed on the surface of the photoreceptor according to the light image.

This electrostatic latent image is developed as a toner image by a developing device 8.

A toner image may be formed in a portion that has been exposed to light image, that is, a bright portion, or conversely, a toner image may be formed in a portion that has not been exposed to image light, that is, a dark portion.

In this embodiment, the explanation will be given assuming that the former method is adopted.

The toner image thus obtained is transferred by the tractors 9 and 10 onto the fan-hold paper 13, which is being transported along the transport guide 11.12, using the electric field produced by the transfer corona charger 14, and is further transferred to the fan-hold paper 13, which is transported along the transport guide 11.12. The toner image transferred onto the sheet 13 is fixed by a fixing device 15 and then discharged.

On the other hand, the photoreceptor 3 that has passed through the transfer section is cleaned by a cleaning device 1.
6, the developer remaining on the surface is removed, and the remaining charge is removed by uniform exposure using a lamp 17 and charge removal using an alternating current or direct current corona discharger 18, thereby preparing for the next image forming process.

Note that before printing starts, bright and dark areas are formed on the photoreceptor 3 by a laser beam image, and the bright area potential and the dark area potential are read by the potential sensor 19.

FIG. 3 is a block circuit diagram of a system for controlling high-voltage corona voltage, in which the potential on the surface of the photoreceptor is read by a potential sensor 19, amplified by an amplifier circuit 20, and converted into a digital quantity by a Φ converter 21. After that, the data is taken into a CPU (central processing unit) 22.

The CPU 22 calculates how much the read surface potential values of the bright and dark areas of the photoreceptor 3 deviate from the appropriate values by comparing them with the values stored in the memory 27, and calculates the surface potential according to a predetermined algorithm. D/A conversion circuits 23 and 24 that calculate new primary high voltage values and secondary high voltage values that should be adjusted to the appropriate values, respectively, and convert digital quantities to analog quantities.
command.

The primary high voltage and secondary high voltage values that should bring the potential of the photoreceptor to an appropriate value are transmitted via the D/A conversion circuits 23 and 24 to the primary high voltage power source 25,
This is transmitted to the secondary high-voltage power supply 26, and as a result, a new value of high voltage is applied to the primary corona discharger 5 and the secondary corona discharger 6.

The photoreceptor surface potential formed by the corrected high voltage is read again by the potential sensor 19, and after it is confirmed that it has become an appropriate value, recording is started.

By the way, in a printer that records on fan-hold paper as in the present embodiment, it is customary to avoid recording information on the perforations in order to avoid image omission due to poor transfer at the perforations of the fold. FIG. 4 is a diagram showing such a system, and the shaded area 28 is the recording area. In this way, despite continuous recording, there are areas between pages where there is no optical image pattern depending on information. Furthermore, the fourth
A solid image in which the entire page of the fan-hold paper 13 shown in the figure is an image is rare, and it is more usual that there are many pack grounds without a light image pattern within the page.

In the present invention, the latent image potential of the photoreceptor is kept constant by detecting the surface of the photoreceptor corresponding to the background area between pages or within a page and controlling the high voltage power supply.

Furthermore, in order to compensate for the drawbacks explained with reference to FIG. 1, by increasing the primary high voltage little by little, it becomes possible to maintain the potential within a certain range even when the potential rises or falls. Note that when reading the potential between pages, there is a method of reading the back ground potential in timing with the position between pages, but this method may have some inconveniences.

That is, a reading delay time occurs depending on the potential sensor and detection system used. In order to avoid this, it may be possible to select potential sensors and detection systems that have the same response time, or to determine the timing for each system separately, but this would be disadvantageous in terms of cost and labor. Therefore, in the present invention, in order to avoid such disadvantages, an algorithm-based processing method is adopted.

Next, the algorithm employed in the method of the present invention will be explained with reference to the flowchart shown in FIG.

That is, first, control of the CPU is started in step S, and the registers are all cleared to 0 in step S2. Then, the timer is set to O in step S3, and it is determined in judgment step S4 whether printing is to be continued. If printing is not continued, step S
The potential control ends at .

If printing is to be continued, the surface potential Vs of the latent image forming member is read repeatedly at intervals of T1 in step S6. This interval T□ is preferably sufficiently shorter than the time it takes for the space between the pages to pass through the potential sensor 19 shown in FIG. The read potential Vs is stored in the memory 27 in step S7.

Next, in judgment step S8, it is determined whether or not 12 hours have elapsed for the surface potential ■8 read at a cycle of T, which exceeds the page length. If 12 hours or more have elapsed, in step S9 The maximum potential value Vms is selected.

If 12 hours have not elapsed, the process returns to step S3 after waiting for T1 hours.

The fact that the maximum value vms was extracted in step S means that the inter-page, ie, background potential was always read during the 12 hours. When the maximum potential vms of pack ground between pages or within a page is read, multiple times in the past,
In this embodiment, the average value V of the past five Vms is calculated in step SIO.

This is to minimize false detections caused by noise or local unevenness of the photosensitive drum. If this is not done, the potential may be incorrectly determined to be incorrect even though it is correct. This is to prevent the potential from being controlled to an abnormal potential.

When the average value ■ is calculated, the value is determined at the judgment step So.
is compared with the allowable limit potential Vtl1mlt at 27
! . This Vlimit corresponds to Vul explained in FIG.

VJimit is represented by a value obtained by adding the potential increase value Vshift within the good image range to the initial setting potential Vdi.

If the above-mentioned average value V exceeds Vlimit, the primary high voltage E is lowered by α volts and output in step S12. As a result, the surface potential approaches the initially set value Vdi. Therefore, the value of α is determined by the amount that a change in the primary high voltage affects the surface potential. Furthermore, it is not necessary to lower the surface potential to the initial setting potential Vdi by lowering it by α; it is sufficient that the potential falls within the allowable range Vshift, and α is determined within that range.

On the other hand, if α has reached the allowable limit Vlimit, the process returns to step S2, but if it has not reached the allowable limit, then step S
At step 13, the primary high pressure E1 is raised by β. This β
The amount is a value that can be known empirically as explained in (Bl) in Fig. 1, and it can be set as the amount of change β in the primary high pressure E1 by adding some margin to this value.If Fig. 1 (5
), even if you raise the primary high voltage E, it will be suppressed by VJimit and the potential will be VJi.
It will not go much beyond the mit.

After the operation of increasing the primary high pressure E by β is performed, the process returns to step S3 and the same operation is repeated.

In this way, the surface potential of the latent image forming member can be stably kept within a certain range, and good copying can be continued.

In addition, in the above embodiment, the part with image information was described as a bright part, and the background was described as a dark part.
On the contrary, the present invention can be practiced even when the back ground is exposed to light and becomes a bright area.

Furthermore, although this embodiment has been described as an example in which the present invention is applied to a laser beam printer, it is of course applicable to various types of copying apparatuses that obtain copied images from original documents.

Furthermore, in the above embodiment, the background potential was explained on the positive side, so the maximum value of the potential is large on the positive side, but when the background potential is on the negative side and the image potential is on the positive side, The maximum potential has a large value on the negative electrode side. This also applies to the allowable limit potential Vlimit.

As is clear from the above description, according to the present invention, by controlling the potential of the background during continuous recording, there is no background fog and the density is stable even when a large number of sheets are continuously copied. An electrophotographic potential control method that can obtain images can be provided.

[Brief explanation of the drawing]

FIG. 1 (Al, Q3) is a diagram showing the change over time in the surface potential of the latent image forming body, which explains the drawbacks of the conventional method, respectively.
@2 The figures below explain one embodiment of the present invention.
3 is a block diagram of a control circuit, FIG. 4 is an illustration of a continuous copying state, and FIG. 5 is a flow chart explaining the control method. be. 1...Laser beam 3...Photoconductor 5...1
Secondary corona charger 6...Secondary corona charger 7...Full exposure lamp 8...Developing device 13...Fan hold paper 16...Cleaning device 17...Lamp 18...DC corona Discharger 1901.
Potential sensor 22... CPU25... Primary high voltage power supply 2B... Secondary high voltage power supply. Figure 3 27 Figure 4 Figure 5 1

Claims (1)

[Claims] When controlling the potential of the latent image forming body of an electrophotographic apparatus equipped with means for detecting the potential on the surface of the latent image forming body and means for controlling corona voltage, if the potential deviates from the initial potential on the recording side by more than a certain range. Further, the surface potential is controlled by controlling the corona potential in a direction to bring the potential of the latent image forming body closer to the initial value, and by gradually changing the corona voltage until it deviates from the initial potential by more than a certain value. An electrophotographic potential control method characterized by: