JPH04261560A - Image forming device - Google Patents

Abstract

PURPOSE:To form an image excellent in tone reproduction without causing surface staining even in the case of consecutively forming the image. CONSTITUTION:In the case of consecutively forming the image, a reference pattern arranging means 1 issues a command for forming a reference pattern in timing among the respective images, and a reference pattern forming means 2 forms a reference pattern latent image 4 on a photosensitive body 3 on a photosensitive drum 10 according to the command. A potential sensor 13 detects the surface potential of the photosensitive body and an image forming condition setting means 5 sets an image forming condition such as bias voltage Vb for a developing unit 14, an exposure control signal Ve, an impressed current Ic or the voltage Vc for an electrostatic charger 11 according to the signal V1 of the sensor 13.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus equipped with a photoreceptor surface potential detection means and using electrostatic latent image technology.

0002

2. Description of the Related Art There are image forming apparatuses, such as copying machines, laser (beam) printers, digital copying machines, color copying machines, and high-speed facsimile machines, which form images on plain paper using electrostatic latent image technology.

[0003] These image forming apparatuses often use SeAs (selenium arsenic) photoreceptors, which have excellent sensitivity, but this type of photoreceptor is relatively easily scratched, and is particularly prone to problems such as poor paper feeding. If a paper jam occurs due to paper jams, the photoreceptor drum or photoreceptor belt will end up being defective, so the surface is coated with an insulating resin to prevent scratches.

However, surface-coated SeA
When an S-type photoreceptor is used to continuously form images, it is unstable for the first 20 to 30 sheets, depending on the surrounding conditions, and the surface potential changes significantly, and after that, it becomes relatively unstable. It has the property of being stable. That is, even if the image forming conditions are set according to the surrounding conditions and a good image is obtained on the first sheet, the image quality gradually deteriorates as the number of sheets increases.

[0005] For this reason, there have been methods that set average image forming conditions depending on the specified number of sheets, for example. However, it is good when making a specified number of copies from one original using a copying machine, but the ADF (Automatic Document Feeder)
This cannot be applied in cases where the total number of consecutive copies is unknown, such as with a copier or laser printer that makes copies using There was a problem in that it was too large and it was difficult to set average image forming conditions.

[0006] Therefore, an image forming apparatus is provided with a surface electrometer, and several images detected by the surface electrometer, for example, 8
There is a copying machine that controls image forming conditions according to the average value of the surface potential of each sheet. Or, JP-A-61-1897
As shown in Publication No. 5, the surface potential Da on the photoreceptor is detected and stored between the formation of the first and second images, and the surface potential Db detected immediately before copying the second sheet is detected and stored. There was a proposal to modify the conditions for forming the second image according to the difference.

[0007]

[Problem to be Solved by the Invention] However, when controlling according to the average value of the surface potential of several sheets, depending on the surrounding conditions, it may not be possible to follow the initial change, for example, the surface potential may increase. There were problems such as background smearing.

[0008] Furthermore, a proposal disclosed in Japanese Patent Application Laid-Open No. 18975/1983 is to automatically maintain the background density of copies at a constant level when the background density of multiple originals placed on the ADF changes. Because of the control, it works effectively when copying binary images such as documents, but when copying something such as a photographic original where the background density changes significantly, the overall tone changes significantly and good reproducibility is affected. The problem was that it was not possible to obtain

The present invention has been made in view of the above points, and it is possible to form images with excellent tone reproducibility without causing background smearing even when images are formed continuously. The purpose is to

0010

[Means for Solving the Problems] In order to achieve the above objects, the present invention provides a reference pattern forming means for forming a reference pattern latent image on a photoreceptor, and a reference pattern latent image formed by the reference pattern forming means. In an image forming apparatus that forms images using electrostatic latent image technology, the reference pattern forming means creates a reference pattern between each image when forming a plurality of images in succession. A reference pattern arrangement means for forming a latent image, and an image for setting image forming conditions for the next image of the reference pattern latent image according to the surface potential of the reference pattern latent image between each image detected by the potential detection means. A forming condition setting means is provided.

The above-mentioned image forming condition may be a developing bias voltage applied to a developing device, an exposure amount for exposing an image on a photoreceptor, or a charger for uniformly charging the photoreceptor. It may be a current or voltage applied to.

0012

[Operation] In the image forming apparatus configured as described above, when a plurality of images are successively formed, the reference pattern placement means places a reference pattern between each image formed on the photoreceptor by the reference pattern forming means. A latent image is formed, and the image forming condition setting means sets image forming conditions according to the surface potential of the reference pattern latent image detected by the potential detecting means.

That is, the characteristics of the photoreceptor change over time by setting the image forming conditions such as the developing bias voltage, exposure amount, or the applied current or voltage of the charger according to the surface potential of the reference pattern latent image. Excellent tone reproducibility can be obtained without causing background smudges on each image.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be specifically described below with reference to the drawings.

FIG. 2 is a schematic diagram showing an example of a development transfer mechanism in a copying machine which is an embodiment of the present invention. Photosensitive drum 10 rotating counterclockwise as shown by the arrow
Around the , in order of rotational direction, are a charging charger 11, an eraser 12, a potential sensor 13 as a potential detection means, a developing unit 14 as a developing device, a pre-transfer charger 15, a transfer charger 16, a separation charger 17, a cleaning unit 18, A pair of registration rollers 21 and a conveyance belt 22 are disposed along the conveyance path shown by the broken line of the paper 20 which is conveyed between the photoreceptor drum 10 and the transfer charger 16 to which the toner image is transferred. , a fixing roller 23, and a pressure roller 24 are arranged, respectively.

The surface of the rotating photosensitive drum 10 is uniformly charged by the charger 11, and the eraser 1
After static electricity is removed from areas other than the effective image area by the irradiation in step 2, an electrostatic latent image is formed by exposure to imaging light IM from a copying optical system (not shown), and the electrostatic latent image is transferred to the developing unit 14.
is converted into a visible toner image by On the other hand, the paper 20 fed from a paper feeder (not shown) comes into contact with a pair of registration rollers 21 and stops once, and then is conveyed by the pair of registration rollers 21 in time with the toner image, and the transfer charger 16 transfers the toner. The image is transferred.

After the transfer, the toner and charge remaining on the photoreceptor drum 10 are first removed by the cleaning unit 18, then the charge is discharged by irradiation with the static elimination lamp 19, and then charged again by the charger 11. The next cycle begins. On the other hand, the paper 20 onto which the toner image has been transferred is transferred to the photosensitive drum 10 by the separation charger 17.
The toner image is separated from the toner image and transported to the fixing unit by the transport belt 22, where the toner image is fixed by the heat of the heated fixing roller 23 and the pressure of the pressure roller 24, and then discharged outside the machine.

The imaging light IM is not shown because it is well known, but if the original table is of a fixed type, a scanner in which a mirror and an original irradiation lamp are integrated is used to adjust the circumferential speed of the photosensitive drum 10. The document surface is scanned at a speed synchronized with the document surface, and a correction optical system consisting of two mutually orthogonal mirrors follows at 1/2 the speed, keeping the distance between the fixed imaging lens and the document surface constant. A scanned image of the document is exposed onto the photoreceptor drum 10 by the imaging lens while maintaining the original image. In addition, if the document placing table is of a movable type, the document placing table moves in synchronization with the circumferential speed of the photoreceptor drum 10 with the original placed thereon, and the imaging lens similarly moves the photoreceptor drum 10 by the imaging lens. A scanned image of the original document is exposed onto the image forming apparatus 10 .

The background smear in the white part and the density of the black part (and in some cases, the density of the intermediate part) of the image fixed on the paper 20 are determined by the ambient conditions such as temperature and humidity, and the cumulative number of continuous processes (number of sheets). In addition to the working conditions such as these, the current (in the case of a corotron charger) and voltage (grid voltage in the case of a scorotron charger) applied to the charger 11 are determined, and the brightness of a lamp (not shown) that illuminates the original is determined. It is influenced by image forming conditions such as the exposure amount and the developing bias voltage applied to the developing sleeve 14a of the developing unit 14.

Therefore, variations due to ambient conditions or work conditions can be corrected by changing one of the image forming conditions or by controlling a combination of them to produce images of uniform quality without background smudges. can be formed.

FIG. 1 is a functional block diagram for explaining the functions of this embodiment. The reference pattern placement means 1 is
A command is output to the reference pattern forming means 2 at a timing between the electrostatic latent images on the photoreceptor drum 10 that are continuously formed (immediately before the first image), and the reference pattern forming means 2 In response to the command, a pattern image is formed on the photoconductor 3 on the surface of the photoconductor drum 10 with an optical density slightly higher than the background of a typical original (for example, OD=0.15, reflectance of about 71%). Exposure is performed to form a reference pattern latent image 4 (hereinafter referred to as "reference pattern image") indicated by an x mark.

The potential sensor 13, which is potential detection means, detects the potential Vl of the formed reference pattern image 4, and detects the potential Vl of the formed reference pattern image 4.
A signal corresponding to l is output to the image forming condition setting means 5.

The central control means 6, which is made up of, for example, a microcomputer, performs sequence control that instructs each part of the copying machine to operate in a timely manner, and sets target values or operating conditions of each part based on information from various sensors. Process control is performed to control the process so that the value is the same. The reference pattern placement means 1 is an example of the sequence control of the central control means 6, and the image forming condition setting means 5 is also an example of the process control.

Therefore, the image forming condition setting means 5
The developing unit 14, which is the image forming condition, according to the signal corresponding to the potential Vl input from the potential sensor 13,
a developing bias voltage Vb to be applied to a signal Ve for controlling an exposure amount setting means 7 such as the brightness of an original irradiation lamp;
By modifying one or more (simultaneously) of the current Ic or voltage Vc applied to the charger 11, the density of each part (including the white part) of the toner image forming the next image is adjusted to the desired density. Control the concentration.

FIG. 3 is a flowchart showing an example of a routine for controlling the developing bias voltage Vb among the image forming conditions. When this routine starts, it waits until an operator on a control panel (not shown) turns on a print key instructing to start copying.

When the print key is turned on, first a reference pattern image is formed on the photosensitive drum 10, and the potential sensor 1
3 to detect the surface potential Vl. Next, depending on the surface potential Vl, the developing bias voltage Vb is set to, for example, V
Control to l+α. α varies depending on the copying machine, but in this example it is set to 150V, so the developing bias voltage Vb=Vl+150V. After copying one sheet under the development conditions, it is determined whether or not continuous copying has ended.

[0027] If the original is set manually, the judgment is whether the specified number of copies has been reached or not, and the ADF
If you are copying with multiple originals set on the ADF, when the specified number of copies is reached, the ADF will check whether there is another original on the ADF, and if there is, it will set the next original, and if there is not, it will continue copying. It's over. Based on this determination, if the continuous copying is completed, the process returns to the end, and if not, the process returns to the reference pattern image formation.

An example of the routine for controlling the developing bias voltage Vb has been described above.
In the case of c, it is possible to control in the same way.

The reference pattern forming means 2 is provided, for example, on one side of the document mounting table orthogonal to the image scanning direction as described above, and controls the position of the document by abutting the document on the back side of the document position reference side, that is, the imaging lens. On the side, optical density O
A reference pattern of D=0.15 is provided. Therefore, before the scanner (fixed document table type) or document table (movable type) starts image scanning, or after it returns after completing image scanning, the image of the reference pattern is always displayed on the photoreceptor drum 10. Since the image is formed, if the original irradiation lamp is turned on for a predetermined period of time in response to a command from the reference pattern placement means 1, the rotating photoreceptor drum 10 will not overlap with the image of the original. A reference pattern image can be formed thereon.

Although the present invention has been described above as an example of implementing it in a copying machine, it can also be implemented in exactly the same way with a laser printer. That is, the development and transfer mechanism of the laser printer is similar to that of the copying machine shown in FIG. The only difference is that it is a pulse-modulated beam spot that scans the 10 plane orthogonally to its rotation direction.

Therefore, the reference pattern forming means 2 is
For example, an optical writing unit (not shown) that generates a scanning beam spot, and a beam that is finely modulated in area at a predetermined ratio with an amount of light that forms a white background, or an unmodulated beam with a predetermined amount of light that is slightly lower than that. It may be configured by a means for instructing to output.

The process after the potential sensor 13 detects the surface potential of the reference pattern image thus formed is exactly the same as in the case of a copying machine.

In the case of one-sheet printing, it has been conventional practice to not only set the image forming conditions from the surrounding conditions, but also to set the image forming conditions by detecting the surface potential of the reference pattern image. As explained above, in the case of continuous printing, the invention forms a reference pattern image between that image and the previous image for the second and subsequent prints, detects the surface potential of the reference pattern image, and adjusts the image forming conditions. Because of the setting, even if the characteristics of the photoconductor change due to changes in the temperature of the photoconductor drum 10 or the total number of prints, images of the best quality can always be obtained, and even if the background of the document changes, such as a photograph, Also provides excellent tone reproduction.

[0034]

[Effects of the Invention] As explained above, the image forming apparatus according to the present invention can form images with excellent tone reproducibility without causing background smearing even when images are formed continuously. You can.

[Brief explanation of the drawing]

FIG. 1 is a functional block diagram showing an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a schematic configuration diagram showing an example of the development transfer mechanism of this embodiment.

FIG. 3 is a flow diagram showing an example of a routine for setting image forming conditions.

[Explanation of symbols]

1 Reference pattern arrangement means
2 Reference pattern forming means 4 Reference pattern image (reference pattern latent image) 5
Image forming condition setting means 7 Exposure amount setting means
10 Photosensitive drum 11 Electrostatic charger
13 Potential sensor (potential detection means) 14 Developing unit (developing device)

Claims (4)

[Claims] 1. A reference pattern forming means for forming a reference pattern latent image on a photoreceptor, and a potential detecting means for detecting the surface potential of the reference pattern latent image formed by the reference pattern forming means, In an image forming apparatus that forms images using latent image technology, when a plurality of images are continuously formed, the reference pattern forming means forms the reference pattern latent image between each successively formed image. image forming conditions for setting image forming conditions for the next image of the reference pattern latent image according to the surface potential of the reference pattern latent image between the reference pattern placement means and each image detected by the potential detection means; An image forming apparatus comprising: a setting means. 2. The image forming apparatus according to claim 1, wherein the image forming condition is a developing bias voltage applied to a developing device. 3. The image forming apparatus according to claim 1, wherein the image forming condition is an exposure amount for exposing an image on the photoreceptor. 4. The image forming apparatus according to claim 1, wherein the image forming condition is a current or voltage applied to a charger that uniformly charges the photoreceptor.