JPH04195172A - Image forming device - Google Patents

Abstract

PURPOSE:To control the density of an image without receiving an effect caused by the dispersion of the individual difference of a photosensitive body or the like by storing electrostatic charging ability detected after the photosensitive body is loaded, comparing it with the electrostatic charging ability detected thereafter by regarding it as a reference value and controlling the density of the image according to the compared result. CONSTITUTION:When the photosensitive body 2 is loaded, the electrostatic charging ability thereof is detected by an electrostatic charging ability detection means 37 and stored in a storage means 101. Then, the electrostatic charging ability detected thereafter is compared with the stored electrostatic charging ability and the density of the image is controlled by changing exposure or a developing bias voltage or the like according to the compared result. That means, the value initially detected and the value detected thereafter are compared. Thus, even when the body 2 is exchanged, the density of the image can be controlled according to the individual difference thereof. Simultaneously, even when the body 2 is deteriorated, image quality can be maintained and the excellent image is obtained.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an image forming apparatus such as a copying machine or a laser beam printer, and more particularly to an image forming apparatus that prevents a decrease in image density due to deterioration of the charging ability of a photoreceptor. .

[Conventional technology]

A photoreceptor drum used in this type of image forming apparatus such as a copying machine has a photoreceptor whose surface is coated or laminated with a photoconductive film made of an organic or inorganic material. The charging ability of such a photoreceptor is affected by its film thickness. As the film thickness of the photoreceptor changes and becomes thinner over time, the charging ability of the photoreceptor also deteriorates accordingly. Furthermore, since charging, exposure, and erasing are repeated each time an image is formed, the charging ability thereof also deteriorates. When the charging ability of the photoreceptor deteriorates, it becomes difficult for toner to adhere to the photoreceptor in the case of a two-component developer, or for developer to adhere to the photoreceptor in the case of a one-component developer, resulting in a decrease in image density and image quality. occurs.

With regular copying machines, service personnel adjust the exposure curve of the exposure device using the volume every time they perform periodic maintenance and inspection.
Corrects for deterioration in the charging ability of the photoreceptor.

However, as the cost of copying machines continues to fall and many copying machines become widespread in the market, there is a shortage of service personnel to carry out such maintenance and inspections, and there are many opportunities for machines to be used without adequate maintenance and inspections. In particular, low-cost copying machines are increasingly being used with low image quality.

In order to solve this problem, an image adjustment method in which the exposure amount or developing bias voltage is controlled by the potential of a latent image formed on a photoreceptor is known from Japanese Patent Laid-Open No. 53-63020. This method forms a standard latent image with an appropriate density on the surface of the photoreceptor, measures the potential of the formed latent image with an electrometer, and controls the exposure amount or developing bias voltage based on the measurement results. be.

[Problem to be solved by the invention]

However, in the prior art disclosed in the above publication, the potential of the latent image is compared with a fixed dark value, and the exposure amount or developing bias voltage is controlled based on the comparison result. It is not possible to correct for various variations such as variations in the exposure amount, variations in the sensitivity of sensors such as electrometers, and errors in mounting the sensors, and there is a problem in that the image quality differs slightly from copying machine to copying machine. In particular, since the photoreceptor is a consumable item, it is removable and has to be replaced frequently, but when it is replaced, there is a problem that the image density under the above-mentioned control will differ from photoreceptor to photoreceptor due to individual differences. .

The present invention has been developed in view of the above circumstances, and it stores the charging ability detected after attaching the removable photoreceptor, uses it as a reference value, and compares it with the charging ability detected thereafter. By controlling the image density according to the comparison results, it is possible to control the image density without being affected by various variations such as individual differences in photoreceptors, and it is possible to obtain good image quality and to avoid replacing the photoreceptor. An object of the present invention is to provide an image forming apparatus that can control image density according to individual differences even when the image density is changed.

[Means to solve the problem]

The image forming apparatus according to the present invention charges a detachable photoconductor, exposes the charged photoconductor to form an electrostatic latent image, and develops the formed electrostatic latent image to form an image. In the image forming apparatus, a charging ability detection means for sequentially detecting the charging ability of the photoreceptor, a means for storing the charging ability detected by the charging ability detection means after the photoreceptor is mounted, and a stored charging ability. It is characterized by comprising a comparison means for comparing the charging ability detected after storage, and a means for controlling the image density according to the comparison result of the comparison means.

[Effect]

In the present invention, when the photoreceptor is mounted, its charging ability is detected by the charging ability detection means, which is stored in the storage means, and then the detected charging ability is compared with the stored charging ability, Depending on the comparison result, the image density is controlled by, for example, changing the exposure amount, changing the developing bias voltage, etc. Therefore, since the initially detected value and the subsequent detected value are compared, even if the photoreceptor is replaced, the image density can be controlled according to individual differences, and other variations can also be absorbed.

〔Example〕

The present invention will be described in detail below based on the drawings showing one embodiment thereof.

FIG. 1 is a schematic vertical sectional view showing the internal structure of a copying machine (hereinafter referred to as the apparatus of the present invention) which is an image forming apparatus according to the present invention. In the figure, l is a main body of the copying machine, and a glass document table 15 is provided on the upper surface of the main body 1. Original table 15
The document placed thereon is scanned by an optical scanning device 10 driven by a scan motor (not shown), and its image is formed on the photosensitive drum 2 as an electrostatic latent image.

The optical scanning device 10 includes an exposure lamp 9 and a movable mirror 17°1.
8a, 18b, lens 8 and fixed mirror 19a, 1
The photoreceptor drum 2 is exposed to light at a predetermined exposure position E by the reflected light from the document that is reflected or transmitted in this order. Also, a first slider to which an exposure lamp 9 and a movable mirror 17 are attached, and movable mirrors 18a and 18b.
The second slider to which is attached is moved in the direction indicated by the arrow by the scan motor. At this time, the first slider moves at twice the speed of the second slider to scan the document. In addition, the first
The figure shows the positions of the first slider and the second slider when they scan to the maximum.

A cover 16 is pivotally supported on the document table 15 so that it can move up and down on the back side, and the document table 15 is opened and closed by moving the front end up and down. The cover 16 is opened to place a single sheet or bound book original on the original platen 15 with the image facing downward, and then closed to allow copying of the original.

Further, on the front side of the main body 1, a front cover (not shown) is pivotally supported on its lower surface side so as to be rotatable back and forth, and by moving the front upper part back and forth, the main body 1 is opened and closed, and an imaging unit, which will be described later, is 40 attachment/detachment operations are performed.

The photosensitive drum 2 has a photoconductive layer made of an organic photosensitive material with a film thickness of about 60 μl laminated on its outer peripheral surface, and can be driven to rotate in the counterclockwise direction indicated by the arrow.

A charger 5 is arranged above the photoreceptor drum 2, and applies a constant electric charge to the surface of the photoreceptor drum 2.

Further, near the charger 5, LEDs are arranged in parallel in the width direction of the photoreceptor drum 2, and an AIDC (Automatic I IIlage Densi) for detecting charging ability is installed.
ty Control) An editing eraser 36 is provided for creating patterns and erasing areas between images.

The circumferential speed (2) of the photosensitive drum 2 is constant, and the moving speeds of the first slider and the second slider of the optical scanning device 10 are (2) and V/2, respectively.

A developing device 4 is provided downstream of the exposed position E of the photosensitive drum 2 in the rotational direction. The developing device 4 uses a magnetic brush method to develop an electrostatic latent image formed on the surface of the photoreceptor drum 2 into a toner image. On the downstream side in the rotation direction of the developing device 40, there is an AI which is a charging ability detection means for reading the image density of the AIDC pattern created by the editing eraser 36.
A DC sensor 37 is provided. AIDC sensor 37
has a light emitting section and a light receiving section, and measures image density based on the reflectance of the AIDC pattern. The image density of this AIDC pattern gradually decreases as the thickness of the photoconductive layer of the photoconductor drum 2 becomes thinner and the charging ability deteriorates.

Therefore, the charging ability can be detected based on the detection result of the AIDC sensor 37.

A transfer charger 6 is provided below the photosensitive drum 2, and this transfer charger 6 is connected to a cassette 1, which will be described later.
An electric field is applied to the paper P conveyed from 20 from the back side thereof, and the toner image formed on the surface of the photosensitive drum 2 is transferred onto the paper P by the developing device 4.

A cleaning device 3 is provided in the rotation direction of the photosensitive drum 20 of the transfer charger 6 . Cleaning device 3
The toner remaining on the surface of the photoreceptor drum 2 is removed using a blade method. An eraser lamp 7 is provided between the cleaning device 3 and the charger 5. The eraser lamp 7 uses light irradiation to remove charges remaining on the surface of the photosensitive drum 2 in preparation for the next copying process.

Further, the photosensitive drum 2. Eraser lamp7. Developing device 4
．． Cleaning device8. Electrostatic charger 5, [collection eraser 36. AIDc sensor 37 high-massing unit 4
0, and the imaging unit 1-4
0 can be attached to and detached from the main body l. Further, a conveyor I2 that conveys the developer is disposed opposite to the photosensitive drum 2 of the developing device 4 in the imaging unit 40. The conveyor 12 uses conveyor blades, and its rotation agitates the developer and supplies it to the magnetic brush type developing device 4 .

At the top of the imaging unit 40 is a toner supply device I.
f is provided. The toner supply device ll will be described later.
Toner is replenished in a fixed quantity based on a toner replenishment signal from the PU 100.

The imaging unit 40 also has an E"PR that stores information such as toner empty, the number of times of image formation, the image density and exposure step of the initial AIDC pattern, and exposure voltage characteristics.
OM (Electrically Erasable
A PROgra-wable RUM) 101 is provided.

Figure 2 shows the memory map of E”FROM.
"FROM 101 includes a total counter that indicates the number of image formations, a counter area that stores the values of various counters including an interval counter that counts 1000 image formations, density data of the initial AIDC pattern, and lamps for each of the nine exposure steps. An exposure data area for storing voltage control data, a flag area for storing various flags such as a toner empty flag, and other areas are provided.

On the other hand, in FIG. 1, 120 is a cassette for storing paper P, which is detachable from the main body 1, and is provided with a paper feed roller 31 for feeding the paper. . Further, the paper feed roller 31 is connected to a motor (not shown) provided inside the paper feed roller 31 and driven to rotate. The paper P sent out from the cassette 120 is sent to the timing roller 33 via the intermediate roller 32, and is sent out between the photosensitive drum 2 and the transfer charger 6 at the timing by the timing roller 33.

Here, the paper P onto which the toner image has been transferred is sent to the fixing device 34 via the conveyance path 22. The fixing device 34 fuses and fixes the toner image onto the paper P using heat. The paper P on which the image has been fixed is discharged to the paper discharge tray 121.

FIG. 3 is a block diagram showing the configuration of the control system of the device of the present invention, and the control system mainly consists of a microcomputer (hereinafter referred to as CPU).
) 100, and the CPU 100 is supplied with manual input from each key on the operation panel 200 and various sensor inputs, as well as a toner concentration sensor 1 in the imaging unit 40.
3 toner concentration signal and AI from AIDC sensor 37
A DC pattern density signal is given, and E”PROMl0I
The data within is applied to the serial data input port.

Further, from CP[+100, signals for displaying the operation panel 200 and signals for controlling various loads such as the main motor and scan motor are output. Further, the CPU 100 outputs a developing bias control signal to a developing bias control circuit 103 that controls the developing bias voltage of the developing device 4, and a lamp voltage control signal to a lamp regulator 102 that controls the light amount of the exposure lamp 9. . In addition, the E"PROM 101 in the imaging unit 40 contains E"PROM10 for chip selection, clock, various counter values, etc.
Serial data to be stored in I is output, and a signal for controlling the toner supply motor 14 of the toner supply device 11 is output. Furthermore, the CPU 100 inputs and outputs data to and from a RAM 104 that temporarily stores the control program for the main body 1 and various flags and counter values indicating the status of the main body 1.

In the present invention, the CPU 100 is the imaging unit 40
AI according to the counter value in E”PROM 101
The density of the AIDC pattern is read by the DC sensor 37, the exposure curve is corrected according to the density of the read AIDC pattern, and the corrected data is converted to E"Pl?0M.
At the same time, a lamp voltage control signal is given to the lamp regulator 102 to control the exposure lamp 9.

Next, referring to the flowcharts in Figures 4 to 6, the CPU
The control procedure by 100 will be explained.

FIG. 4 is a flowchart showing the contents of the main routine controlled by the CPU 100. When the power is turned on,
Initial settings such as resetting the registers inside the CP[1100, RAM 104, etc.] are performed (step $401).
.

Then, an internal timer is started to repeat the processes from step 11402 to step 5409 at a fixed time (step 5402). Next, memory processing is performed to read and write data in E"PROMl0I in the imaging unit 40 (step #403),
Input processing is performed to detect key input from the operation panel 200 and input states of various sensors (step Jt404).
.

When the input processing is completed, it is determined whether or not copying is in progress based on whether the copy flag is 1 (step 11405). If copying is in progress, the process proceeds to step #406, where exposure correction processing, which is the gist of the present invention, is performed. When the exposure correction process is completed, a copy process is performed (step #407).

Here, we will discuss the charging and exposure necessary for copying.

Performs process control such as development, copying, fixing, paper feeding, and transportation. Next, other processes such as temperature control of the fixing device 34 and display processing of the operation panel 200 that are not directly related to the copying process are performed (step 5408), and after waiting for the internal timer to end (step 11409), the process returns to step #402.
Steps 11402 to #409 are repeated until the power is turned off.

Further, if the copy flag is not 1 in step 1405 and copying is not in progress, the process advances to step #408.

FIG. 5 is a flowchart showing the details of the exposure correction process at step 11406 in FIG.

First, it is detected whether the total counter value of the imaging unit 40 in use is 0, that is, the initial state (Step 1 $ 501), the imaging unit 4
If 0 is the initial state, proceed to step $1502 and AI
Create a DC pattern. Then, the image density of the created AIDC pattern is read by the AIDC sensor 37 (step 1503), and the read value is set as initial AIDC pattern density data (step 1504).
, - then returns to the main routine and sets the data write flag to 1 to execute step 114 of the next loop.
The initial AIDC pattern set in the E"FROM 101 is written in the memory processing of step 03. When a new imaging unit 40 is set, the AIDC pattern density in the initial state is memorized, and later the film of the photoreceptor drum 2 is written. This is to absorb various variations and estimate the appropriate amount of film scratching by comparing it with the AIDC pattern density when scratching occurs.This information is then used in the imaging unit 40 (photoreceptor drum 2). E” in the imaging unit 40 because it is unique information.
Write to PROM10I, and read if necessary. Thereby, even when the imaging unit 40 is installed in another copying machine, an appropriate amount of film shearing can be estimated.

On the other hand, if it is determined in step 5501 that the imaging unit 40 is not new, the process proceeds to step II 506, in which it is determined that copying has been completed, and when the copying is completed, the value of the interval counter is checked (step #507).
, 1000 or less, increment the interval counter and total counter in step 11508.
．． 1509), and writes those values to E''FROMlol in the next loop by setting the data write flag (step 5510).

When the interval counter reaches 1000, proceed to step #511, reset the interval counter, and create an AIDC pattern (step 11512).
, reading the density of the AIDC pattern (Step #5
13), proceed to the step board 514, and select the memorized A.
Compare the IDC pattern with the read AIDC pattern (step $1514) and read it earlier ^
IDC pattern image density 10 and E”PROM 101
The exposure voltage is set from Table 1 according to the ratio (rD/IDo) of the initial AIDC pattern to the image density rho stored in the memory (step 11515). The relationship shown in Table 1 is, for example, ROM connected to CPIJ 100.
(not shown), and according to the ratio, So'
Select one from the five exposure curves of =34.

(Left below) For example, when l0 = 1.4, ID, = 1.6 -
=0.875 10°, so the exposure curve S2 is selected. Then, the exposure voltages for exposure steps 1 to 9 are determined from the selected exposure curve, and the determined exposure voltages are set as lamp voltage control data (step 11516), and the data write flag is set for memory processing in the next loop. The lamp voltage control data stored in the E"FROM 101 is memorized (step 1517). Based on the memorized lamp voltage control data, the stored lamp voltage control data is stored in step 540.
7, the CPU 100 outputs a lamp voltage control signal to the lamp regulator 102 to control the exposure amount.

FIG. 7 is a graph showing the relationship between the original density, the amount of exposure to the photoreceptor drum due to reflected light from the original, and the surface potential of the photoreceptor drum surface with respect to the amount of exposure. The negative direction represents the original density, and the vertical axis represents the amount of exposure to the photoreceptor drum. The higher the density of the original, the less reflected light there is, the lower the amount of exposure to the photosensitive drum 2, and the higher the surface potential. When the surface potential is high, a large amount of toner adheres to the toner, resulting in a high concentration.

Here, the solid line indicates the relationship between the exposure amount and the surface potential in condition B (new) where the photoreceptor has a thick film. In this state, when the original density is high, the surface potential is high, and when the original density is low, the surface potential is low.

As a result, the copy is reproduced in such a way that areas where the density of the original is low are light and areas where the original density is dark are dark, making it possible to faithfully reproduce an image.

As the number of copies increases, the film of the photoconductive layer on the photosensitive drum 2 becomes thinner, and the surface potential when unexposed, as shown by the broken line, is lower than when it was new, as shown by the solid line. At the same time, the sensitivity of the photoconductive layer of the photosensitive drum 2 decreases, so that the surface potential in a sufficiently exposed state becomes higher than in a new state.

As a result, areas where the original density is light become slightly darker, areas where the original density is higher become lighter, and the overall image becomes dim.
The result was an image with no sharpness. In order to eliminate this problem, it is necessary to increase the overall exposure amount and brighten the image. This is performed in the exposure voltage correction in step 11507 in FIG. 5, in which an exposure curve is selected according to the read value of the AIDC pattern, and an exposure lamp voltage for the exposure step is set.

Figure 8 shows the film thickness of the photoreceptor, the surface potential when not exposed, and the AJD.
This is a graph showing the relationship with the C pattern concentration, with the film thickness in the positive direction on the horizontal axis, the AIDC pattern concentration in the negative direction, and the surface potential on the vertical axis.

As copies continue to be made, the film thickness becomes thinner, so the surface potential when unexposed decreases, and the AIDC pattern density decreases. That is, by detecting the AIDC pattern density, it is possible to estimate the film thickness of the photoreceptor and correct the exposure step and exposure lamp voltage accordingly.

FIG. 9 is a graph specifically showing the relationship between the exposure step and the exposure lamp voltage when the density of the AIDC pattern changes, and Table 1 above shows this in a table format. Here, the vertical axis represents the lamp voltage, and the horizontal axis represents the exposure step. As the film thickness of the photoreceptor becomes thinner, the AI
The rate of change in DC pattern density decreases, S0→S1→S2
Follow the route →S, →S4. In other words, the exposure level gradually increases.

FIG. 6 is a flowchart showing the details of the memory processing at step #403 in FIG. First, it is determined whether the data write flag is set to 1 (step 11601).The data write flag is set as necessary in each subroutine, for example, E"F.
Set to write data to each area of ROM. When the data write flag is set to 1 and a data write request is made in each subroutine, an address for data writing is specified in step 11602.
), writes the data to the specified address (step 11603).

Then, check whether the data to be written matches the written data (step cloud 604).
, if they do not match, return to step 11602, specify the address again, and write. If they match, reset the data write flag to 0 in step 11609.
), the process ends.

On the other hand, if the data write flag has not been set yet in step $1601, it is determined whether the data read flag has been set, that is, whether there is a data read request (step 11605).

Like the write request, this is also set as necessary in each subroutine, but in most cases it is stored in the RAM 104 connected to the CPU 100 of the main unit 1 immediately after the power is turned on, so it is not executed once. .

Then, when the read flag is set to 1, set the address in the same way as for writing (step 606).
, read the data (step $607)
, step 160 to reset the Pt protrusion flag to O.
8) End the process. Further, when the read flag is reset to O, the process ends without processing anything.

In this embodiment, the E"FROM, which is a storage means for storing the talk counter, exposure data, etc., is provided within the imaging unit, but the present invention is not limited to this, and the storage means may be provided within the main body. .

When data is stored in the E"FROM in the imaging unit, which is detachable from the main body, rather than inside the main body, as in this example, the data will continue to be stored even if the imaging unit is installed in another copying machine. It can be used for
Image density can be easily controlled even though it is often shared among multiple parts.

Furthermore, although this embodiment has been described using a copying machine as an example of an image forming apparatus, it goes without saying that the present invention is not limited to this, and can also be applied to a laser beam printer or the like.

Furthermore, although the image density is controlled by the exposure amount in this embodiment, the present invention is not limited to this, and it goes without saying that it may be controlled by other means such as controlling the developing bias voltage. Further, the image density may be controlled by combining them.

Furthermore, in this example, the charging ability of the photoreceptor was changed to AIDC.
Although the detection is based on the pattern, the present invention is not limited to this, and it goes without saying that the charging ability may be detected by other means such as detecting the surface potential of the unexposed area or the exposed area, or detecting the film thickness. .

〔effect〕

As detailed above, in the present invention, the initial charging capacity is memorized and the image density is controlled based on the relationship between it and the detected charging capacity. Image density can be appropriately controlled without being affected by errors, sensitivity differences, etc., image quality can be maintained even if the photoreceptor deteriorates, good images can be obtained, and even if the photoreceptor is replaced. Even if the image density is controlled according to individual differences, the same effect can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a schematic vertical sectional view showing the internal structure of a copying machine which is an image forming apparatus according to the present invention, FIG. 2 is a diagram showing a memory map of E"FROM, and FIG. 3 is a block diagram showing the configuration of a control system. Fig. 4 is a flowchart showing the contents of the main routine of the CPU, Fig. 5 is a flowchart showing the contents of the exposure processing subroutine, Fig. 6 is a flowchart showing the contents of the memory processing subroutine, and Fig. 7 is a flowchart showing the contents of the original density and photoreceptor. Figure 8 is a graph showing the relationship between film thickness, surface potential when unexposed, and AIDC pattern density, Figure 9 is a graph showing the relationship between the exposure amount and the surface potential of the five exposure curves, and Figure 9 shows the exposure steps and lamps for the five exposure curves. It is a graph showing the relationship with voltage. 1... Copying machine main body 2... Photosensitive drum 5...
Charger 9...Exposure lamp 37...AI
DC sensor 100-CPU 101-E"FROM
102-Wrap Regulator Patent Applicant Minolta Camera Co., Ltd. Agent Patent Attorney Noboru Kono Figure 2 Figure 4

Claims (1)

[Claims] 1. An image in which a removable photoconductor is charged, an electrostatic latent image is formed by exposing the charged photoconductor, and the formed electrostatic latent image is developed to form an image. In the forming apparatus, a charging ability detecting means for sequentially detecting the charging ability of the photoreceptor, a means for storing the charging ability detected by the charging ability detecting means after the photoreceptor is mounted, and a storage for storing the stored charging ability. An image forming apparatus comprising: a comparison means for comparing the charging ability detected later; and a means for controlling image density according to the comparison result of the comparison means.