JPH0415945B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image recording device, and more particularly to an image recording device that can be used for electrophotographic potential control in which the potential of a latent image forming body such as a photoreceptor is controlled to be constant. It is.

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 pattern of charges that follows the image pattern. A developer is applied and visualized.

Methods for forming a latent image include a method in which the photoconductor is uniformly charged and then exposed to light, or a method in which the photoconductor is uniformly primarily charged and then charged with AC or a polarity opposite to the primary charging. There are various methods, such as a method in which the entire surface is exposed after performing optical image exposure.

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 value in relation to matching with development.

That is, for development under certain conditions, unless the latent image falls within a predetermined range, the image density will be unstable and background 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, and (3) differences between each photosensitive drum. Examples include variations in characteristics.

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 conventional potential control methods, although the initial image is good, the potential changes from the initial value while recording a large number of sheets in a row, resulting in the image not being as good as the initial value. It may become impossible to maintain the quality of the product.

For example, as a general tendency, even if the photoreceptor is under the same corona charging conditions, if corona charging continues many times, the potential will gradually shift and become higher.
It often decreases or fluctuates. Especially when recording after the device has been stopped for a long time.
This trend is even greater.

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.

Further, 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.

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.

Recently, electrophotographic copying machines,
As computer output terminal devices become faster and the amount of data that can be recorded continuously increases, there is an increasing need to obtain stable images without slowing down the 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 may cause this to be inconsistent, such as the number of photoreceptors and changes in the environment.

The present invention has been made in order to eliminate the above-mentioned conventional drawbacks, and provides an image recording device that can be used for electrophotographic potential control that can always perform stable potential control without reducing throughput. The purpose is to

In order to achieve the above object, the present invention includes a latent image forming body on which a latent image is formed, a charging means for charging the latent image forming body, and a plurality of page images spaced apart on the latent image forming body. an exposure means for continuously forming images; a developing means for developing the area exposed by the exposure means; and a non-image area between the plurality of page images on the latent image forming body during continuous image recording. a detection means for repeatedly detecting a potential; and a control means for controlling a charging output of the charging means according to an average value of a plurality of detection outputs of the detection means; Then, during image recording, a configuration is adopted in which the charging output of the charging means is varied to keep the potential of the latent image forming body within an appropriate range.

Hereinafter, details of the present invention will be explained with reference to the drawings.

FIG. 1 shows a schematic configuration of a laser beam printer 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 which is also not shown. After being modulated according to the input signal to the modulator, it is scanned by the rotating polygon mirror 2, and the imaging lens 4
A light image is exposed onto the photoreceptor 3 through.

It is of course possible to use other means such as a cathode ray tube, plasma display, LED array, etc. for optical image exposure.

As is well known, the photoreceptor 3 basically has a conductive support, a photoconductive layer, and an insulating layer.
It is uniformly charged in advance by a primary corona charger 5, then subjected to an AC corona discharge by a secondary corona charger 6 that performs AC corona discharge while receiving photoimage exposure, and then uniformly charged over the entire surface by an entire surface exposure lamp 7. 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 light image, that is, a dark portion.

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

The toner image thus obtained is transferred to the tractor 9, 1
0, the toner image is transferred onto the fan-hold paper 13 that is transported along the transport guides 11 and 12 using the electric field of the transfer corona charger 14, and the toner image transferred onto the fan-hold paper 13 is transferred to the fan-hold paper 13 by the fixing device 15. After the image is fixed, the paper is ejected.

On the other hand, the photoreceptor 3 that has passed through the transfer section is cleaned by a cleaning device 16 to remove the developer remaining on its surface, and is further uniformly exposed to light by a lamp 17 and neutralized by an AC or DC corona discharger 18 to remove residual charges. Then, preparation for the next image forming process is performed.

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

FIG. 2 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 then converted into a digital value by an A/D converter 21. After being converted to CPU (Central Processing Unit) 22
be taken in.

The CPU 22 calculates how much the read surface potential values in 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 difference according to a predetermined algorithm. D/A conversion circuits 23 and 2 that calculate new primary high voltage values and secondary high voltage values that should make the surface potential an appropriate value, and convert digital quantities to analog quantities.
Command 4.

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

The surface potential of the photoreceptor formed by the corrected high voltage is read again by the potential sensor 19 and printing is started after it is confirmed that the potential has reached a proper value.

Incidentally, in a printer that records on fan-hold paper as in this embodiment, it is customary to avoid recording information on the perforations of the fold in order to avoid image omission due to poor transfer at the perforations. FIG. 3 is a diagram showing such a system, in which the shaded area 28
becomes the copy part. In this way, despite continuous recording, there are areas between pages where there is no optical image pattern depending on information.

In the present invention, the latent image potential of the photoreceptor is kept constant by detecting the surface potential of the photoreceptor corresponding to the page interval and controlling the high voltage power supply.

That is, in FIG. 2, the potential of the photoreceptor read by the potential sensor 19 during continuous printing is latched at a timing corresponding to the interval between pages and read by the CPU. The timing reference may be a mechanical pulse generator such as a rotary encoder, or a signal generated from a controller that sends optical information.

In addition, when reading the potential with reference to the top of the page of optical information to be recorded, if the potential is read after a delay of time for the photoconductor to rotate from the exposure position to the potential sensor section, it is possible to read the potential between the pages. The potential is read.

In this embodiment, since the information is a toner image in the area irradiated with the laser beam, the area between pages is the background, and in terms of potential, it is the dark area potential. The dark potential between pages read in this way is stored in the memory 27.

As described above, the potentials between pages are read sequentially, but the CPU, including the potential between the pages read last,
It is determined whether the potential is appropriate based on the average value of the past five times. This is to avoid local unevenness and noise of the photosensitive drum. The moving average value of the potential between pages is compared with the proper potential, and if it is about to deviate from the proper range, the CPU 22 controls the current high voltage output to a value that will bring the potential to the proper potential. In this embodiment, only the primary high voltage power supply 25 is controlled.

Next, the algorithm employed in the method of the present invention will be explained with reference to the flowchart shown in FIG.
FIG. 4 shows a case where the surface potential is read at a timing corresponding to between pages.

That is, first, control of the CPU is started in step _S1 , and all registers are cleared to 0 in step _S2 .

Then, in determination step _S3 , it is determined whether or not to continue printing. If printing is not to be continued, potential control ends in step _S4 .

In the case of continuing copying, it is determined in step _S5 whether the timing corresponding to the page interval is correct, and YES is selected.
Then, in step _S6 , the surface potential of the latent image forming member is
V _S is read, and the average value of the potentials corresponding to the past five pages is calculated in step _S7 . This average value V is compared with the permissible limit potential Vlimit.
Vlimit is a limit value that the potential increase Vshift allows within a range in which contamination due to developer carrier adhesion, toner adhesion, etc. does not occur, and is the value obtained by adding Vshift to the initial setting value Vi.

Step S ₈ in which the surface potential V _S continues to be detected until the moving average value of the past five times reaches Vlimit.
Then, when reaches the limit value Vlimit, the primary high voltage E ₁ is lowered by α volts and the output step is
Sa. As a result, the surface potential is set to the initial value Vdi
approach. Therefore, 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 value Vdi by lowering it by α; it is sufficient that the potential is within the allowable potential range Vshift, and α is determined within that range.

In FIG. 4, a method has been described in which the background potential is read at the same timing between pages, but there may be some inconveniences in this case.

That is, a reading delay time occurs depending on the potential sensor or 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, a processing method using an algorithm as shown in FIG. 5 is adopted.

That is, first, control of the CPU is started in step _S1 , and all registers are cleared to 0 in step _S2 .

Then, in step _S3 , the timer is set to 0, and in judgment step _S4 , it is determined whether or not printing is to be continued. If printing is not to be continued, potential control ends in step _S5 .

If printing is to be continued, the surface potential V _S of the latent image forming member is read repeatedly at intervals of T ₁ in step S ₆ . It is desirable that this interval T ₁ be 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 V _S is stored in the memory 27 in step _S7 .

Next, in judgment step _S8 , the surface potential V _S read at a period of _T1 exceeds the page length for a time _T2.
It is determined whether the time has elapsed or not, and when _T2 hours or more have elapsed, the maximum value Vms of the surface potential during the time _T2 is selected in step _S9 .

If T ₂ hours have not elapsed, wait for T ₁ hour and then return to step _S4 .

The fact that the maximum value Vms was extracted in step _S9 is
T means that the inter-page, ie, background potential was always read during _{the 2} hours. When the maximum potential Vms of the background between pages or within a page is read, the average value V of Vms of a plurality of times in the past (in this embodiment, five times in the past) is calculated in step _S10 .

As mentioned above, this is to minimize false detections due to noise or local unevenness of the photosensitive drum. If this is not done, the potential will be mistakenly judged to be incorrect even though it is correct. This is to prevent the potential from being controlled to an abnormal potential instead.

Once this average value V is calculated, it is compared with the permissible limit potential Vlimit in a judgment step _S11 .

Vlimit is indicated by the value obtained by adding the potential increase value Vshift within the good image range to the initial setting potential Vdi.

If the aforementioned average value V exceeds Vlimit, the primary high voltage _E1 is lowered by α volts and output in step _S12 . As a result, the surface potential approaches the initially set value Vdi, and 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 necessarily 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. The amount of α is the same as described in FIG. In this way, the surface potential of the latent image forming member can be stably kept within a certain range, and good printing can be continued.

In addition, in the above embodiment, the part with image information is described as a bright part and the background as a dark part, but even if the background is exposed to light and becomes a bright part, the present invention can be implemented. It is possible.

Further, although this embodiment has been shown 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 example, 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 means that the permissible limit potential Vlimit
The same applies to

By controlling the potential between pages during continuous recording in this way, it is possible to obtain stable images with no background fog and a constant density even when a large number of sheets are printed continuously.

FIG. 6 shows this potential control effect.
Figure 6 is a diagram recording the surface potential of the latent image forming body.The latent image forming body starts rotating at time _t0 , and the initial potential is set between _t1 and bright areas are set to Vli and dark areas. is set to be controlled by the value of Vdi. Conventionally, when copying is performed in this state, the dark area, or background potential, shifts and deviates from the permissible potential, resulting in image stains and decreased density, as shown by symbol A.
By implementing the present invention, the primary high voltage was corrected at times t ₂ and t ₃ so that the potential of the latent image forming member was maintained at a stable potential.

In addition, in Fig. 6, the bright area potential during copying is Vli
However, this depends on the resolution of the sensor and the responsiveness of the recorder. Microscopically, it is Vli, and in the case of continuous copying, the A of the background potential
There is a potential shift in the same way as in , but it is not shown in the recorder record.

As is clear from the above description, according to the present invention, by repeatedly detecting the potential of the non-image area between pages, it is possible to detect the charging output during continuous recording without reducing the throughput of continuous recording. possible,
Moreover, by controlling the charging output using the average value of the detection output, it has become possible to control with high reliability.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram of a laser beam printer to which the present invention is applied, Fig. 2 and the following are illustrations of an embodiment of the present invention, Fig. 2 is a block diagram of a control circuit, and Fig. 3 is a copy. FIGS. 4 and 5 are flowcharts explaining the operation, and FIG. 6 is a line showing the control state of the surface potential of the latent image forming body when the present invention is applied. It is a diagram. 1...Laser beam, 3...Photoreceptor, 5...1
Secondary corona charger, 6... Secondary corona charger,
13... Fan hold paper, 19... Potential sensor, 22... CPU, 25... Primary high voltage power supply, 26
...Secondary high voltage power supply.

Claims (1)

[Scope of Claims] 1. A latent image forming body on which a latent image is formed, a charging means for charging the latent image forming body, and a plurality of page images separated from each other and continuously forming images on the latent image forming body. an exposing means for developing the area exposed by the exposing means; a developing means for developing the area exposed by the exposing means; repeatedly detecting a potential of a non-image area between the plurality of page images on the latent image forming member during continuous image recording; a detection means, a control means for controlling the charging output of the charging means according to an average value of a plurality of detection outputs of the detection means, and the control means controls the charging output of the charging means when the average value is out of a proper range, the control means stops the image recording. An image recording apparatus characterized in that the charging output of the charging means is varied so that the potential of the latent image forming body is within an appropriate range.