JP2644229B2 - Image control method for image forming apparatus - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image control method for an image forming apparatus, and more particularly, to forming a reference pattern latent image for density detection on a latent image carrier, and changing the developed density to a density. The present invention relates to an image control method for an image forming apparatus configured to control an image forming condition by detecting with a sensor.

(Prior Art) Generally, in an image forming apparatus such as an electrophotographic copying machine, in order to keep the image density constant at all times, the toner density in a developing device, a developing bias value, a charging condition of a latent image carrier, a transfer condition, and the like. Must be suitably controlled. For this reason, conventionally, a detection reference plate having a constant density has been installed near the document placing surface, and the light image of the detection reference plate is exposed to a non-image area of the latent image carrier to obtain a reference for density detection. A pattern latent image is formed, the development density of the reference pattern latent image is optically detected by a density sensor, and the various image forming conditions are controlled based on the detection signal.

In this case, as in an electrophotographic copying machine described in, for example, JP-A-58-190966, a developing bias voltage for developing an electrostatic latent image corresponding to a document image and a reference pattern latent image are generated. And the developing bias voltage at this time is switched in two stages. This is because, when developing the reference pattern latent image, the toner in the developer is adjusted by adjusting the developing bias voltage so that the toner particles are attracted to the developer carrier side more than when the image latent image of the document is developed. When the density is at the set value, the image density of the developed image obtained by developing the latent image of the reference pattern is set to a medium level, that is, a halftone image, and the detection accuracy of the toner density in the developer is improved. Is made possible.

However, in such an image control method, when the reference pattern latent image is developed, the toner particles are attracted to the developer carrier, so that the surface of the developer carrier tends to be stained with toner. Such toner stains occur in layers on the surface of the developer carrying member, and the toner layer results in the weakening of the effective force of the developing bias applied to the developer carrying member, resulting in a high actual copy density. There is a problem that the detection accuracy of the image density becomes unstable with the eyes.

FIG. 3 shows the toner adhesion amount on the developer carrier (vertical axis) with respect to the development potential (horizontal axis) which is the difference between the surface potential of the latent image carrier and the developing bias potential applied to the developer carrier. Is expressed. In the case of a new developer, toner contamination on the developer carrier tends not to occur, but in the case of a developer that has been used continuously, toner contamination on the developer carrier occurs. Then, when a bias potential of 300 V or more is applied to the non-image area (photoconductor potential is approximately 0 V), toner contamination on the developer carrier starts to occur, and the image area (photoconductor background potential is 50 to 150 V) It can be seen that when a high bias voltage of about 400 to 500 V is applied continuously, considerable toner contamination occurs on the developer carrying member.

(Object) In view of the above, the present invention relates to a developing method in which a developing bias electric field is adjusted so that toner is attracted to a developer carrier side in developing a reference pattern latent image more than in developing an original image latent image. It is an object of the present invention to provide an image control method for an image forming apparatus that prevents toner contamination on an agent carrier and enables stable image density detection.

(Structure) In order to achieve the above object, the present invention provides a method for forming an image latent image of a document in an image area of a latent image carrier, and a method for forming a latent image on a non-image area of the latent image carrier not forming an image latent image of a document. A reference pattern latent image for image density detection is formed, and the image latent image and the reference pattern latent image are respectively developed with toner held on a developer carrier under a predetermined developing bias electric field. In the image control method of the image forming apparatus, wherein the density of the visualized image of the obtained reference pattern latent image is optically detected by a density sensor to control image forming conditions, The developing bias voltage applied to the developer carrier,
While adjusting the developing bias voltage applied to the developer carrier when developing the image latent image of the document, the toner particles are adjusted so as to be attracted more toward the developer carrier,
A developing bias voltage applied to the developer carrier at a predetermined timing immediately before developing the reference pattern latent image,
A developing bias voltage for attracting toner particles to the developer carrier side with respect to a developing bias voltage applied to the developer carrier when developing the reference pattern latent image; The developing bias voltage is adjusted to such an extent that toner is released from above.

In the image control method of the image forming apparatus having such a configuration, at a predetermined timing immediately before developing the reference turn latent image, the developing bias electric field is adjusted to such an extent that the toner is released from the developer carrier. When developing the reference pattern latent image, the developing bias is adjusted to attract the toner to the developer carrier side, so that a so-called halftone visible image is obtained. Is prevented, and the developing bias always works well.

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

FIG. 2 schematically shows an embodiment of a copying machine configured to carry out the present invention. In this embodiment, the photosensitive drum 1 as the latent image carrier has an outer diameter of 80 mm.
Peripheral speed 180mm / sec in the direction of the arrow by the drive unit not shown
Is driven to rotate. In the vicinity of the photosensitive drum 1, a charging charger 2 for uniformly charging the surface of the photosensitive drum 1 is provided. In the present embodiment, the surface potential of the photosensitive drum 1 which was originally about 0 V is uniformly charged to 50 to 150 V by the charging charger 2. Above the charging charger 2, a reference pattern 5 having a predetermined reflectance provided below the transparent platen 4 and a document on the platen 4 are illuminated by a light source to expose the reflected light. An exposure device 3 including exposure optical systems 6 to 9 for slit exposure on the body drum 1 is arranged. The light source and the exposure optical system 6 of the slit exposure device 3
8 or the document table 4 is reciprocated, whereby the reference pattern 5 and the light image of the document are sequentially projected on the photosensitive drum 1 to form corresponding reference pattern latent images and image latent images. It has become. The reference pattern 5 is provided outside the document placement area of the document table 4 and is formed of, for example, a black portion pattern having a density of 1.80.

Further, around the photosensitive drum 1, there is an eraser (not shown) for removing electricity outside the latent image forming area after exposure, and a developing device 1 for visualizing the latent image with color toner or black toner.
0, a photosensor 11 for detecting the density of the developed image of the reference pattern 5 (the degree of toner adhesion), a transfer unit 12 for transferring the developed image of the document to transfer paper, a cleaning unit 13 for cleaning and removing static electricity from the residual toner, and a charge removing unit 14 are arranged in order.

The developing device 10 includes a developing roller 10b serving as a developer carrying member and a dry type two-component developer including a single color toner (black toner or color toner) and a carrier in a developing container 10a.
To perform development of a single color by supplying to the photosensitive drum 1 side. In the present embodiment, the developing roller 10b has an outer diameter of 40 mm, and is driven to rotate at a peripheral speed of 540 mm / sec in the direction of the arrow. A predetermined amount of toner is accumulated in the toner storage unit 10c, and a supply roller 10d that supplies an appropriate amount of toner to the developing container 10a is provided at an outlet of the toner storage unit 10c. Such a developing device 10 can be replaced with a toner having a different toner color, and by this replacement, a color of a mono-color copy can be selected.

The CPU (microcomputer) 15 receives the output signal of the photosensor 11, determines whether toner is to be replenished at different toner density control levels for the black toner and the color toner, and operates the driving unit 16 to replenish the supply roller. It has a function to supply toner by rotating 10d. That is, if the value detected by the photosensor 11 is lower than the reference value, the supply roller 10d is driven to rotate to supply toner, and if the value is higher, the rotation drive of the supply roller 10d is stopped to stop toner supply. ing. In this case, the CPU 15 determines whether the used toner is the black toner or the color toner based on a signal given by whether or not the harness and the pin in the harness of the main body of the copying apparatus are fitted.

The CPU 15 has a function of adjusting an output value of a bias power supply 17 for applying a predetermined developing bias voltage to the developing roller 10b. The output value of the bias power supply 17 is switched according to the development stage. That is, in a non-image area between images where the latent image on the photosensitive drum 1 is not formed, the developing bias voltage is set to 200 to 300 V or more so as to prevent wasteful toner consumption, and the development of the reference pattern latent image is performed. At a timing before the start timing by one rotation of the developing roller 10b or more, the developing bias voltage is adjusted to drop to 0 to 200V, which is a level at which the toner is released from the developer carrier. As a result, the non-image portion potential of the photosensitive drum 1 (approximately 0
The developing potential for V) was -200 to -300 V in a non-image area where a latent image was not formed.
Corrected to -200V, the negative polarity toner particles are
It is made free from the surface of 10b and adhered.

Further, the developing bias voltage when developing the reference pattern latent image is switched and adjusted to a voltage 400 to 600 V higher than the developing bias voltage 150 to 500 V applied when developing the image latent image of the document, and the toner particles are reduced. The developing roller 10b is attracted by the developing roller 10b as compared with developing the latent image. That is, the developing potential of the image portion of the photosensitive drum 1 with respect to the background potential (50 to 150 V) is:
In developing the reference turn latent image, the toner image is modified to be smaller, and the negative polarity toner particles are
b tends to be adsorbed on the surface side. Therefore,
The reference pattern latent image is developed into a so-called halftone image.

Further, the CPU 15 has a function of detecting the toner end of the toner storage unit 10c and displaying the toner end on the display unit of the operation unit.

An embodiment of the present invention using such an apparatus will be described with reference to FIG. When the print key is turned on, the photoconductor drum 1 is uniformly charged by the charging charger 2 at the same time when the main motor is started, and is then exposed by the slit exposure device 3 to form a latent image. This latent image is
It comprises a reference pattern latent image, which is a light image of a reference pattern 5 having a predetermined reflectance provided on the lower side of the transparent document table 4, and an image latent image, which is a light image of a document on the document table 4. ,
The reference pattern latent image is formed first. Photoconductor drum 1
After the exposure, the eraser removes the electric charge outside the latent image forming area by the eraser, and the latent image of the reference pattern 5 is erased at times other than 10 + 1 (n is a positive integer) copy cycles after the main switch is turned on.

Further, the latent image of the photosensitive drum 1 is visualized with the color toner or the black toner by the developing device 10 after the neutralization by the eraser, and the density (toner adhesion condition) of the visualized image of the reference pattern 5 is detected by the photo sensor 11. At the same time, after the visual image of the document is transferred to the transfer paper by the transfer unit 12, the cleaning unit 13 and the charge removing unit 14 clean and remove the residual toner to prepare for the next copy cycle.

Further, the developing bias applied to the developing roller 10b is set to a high voltage of 200 to 300 V or more during a period in which a developing operation is not performed, that is, in a non-image area between images. Is prevented. Further, at a predetermined timing at least one rotation of the developing roller 10b from the timing when the development of the reference turn latent image is started, the developing bias voltage is 0 to 200 V, which is a degree at which toner particles are released from the developing roller 10b. The developing potential of the photosensitive drum 1 with respect to the non-image portion potential (approximately 0 V) is adjusted to 0 to -200 V. As a result, the surface of the developing roller 10b is brought into a state in which the toner is not attached, and the developing roller 10b is cleaned.
This is the mechanical rubbing force called scavenging force,
The charge of the toner, the cloning force (image force) applied between the carrier particles, and the like are used, and the toner particles are confined in the developer. As a result, in the subsequent development of the latent image, the development bias is directly and stably applied without the intervention of the toner layer. If the adjustment of the lowering of the developing bias is excessive,
The toner particles are carried to the surface of the photoreceptor, and wasteful toner consumption occurs.

Further, the developing bias voltage when developing the reference pattern latent image is switched and adjusted to a voltage of 400 to 600 V higher than the developing bias voltage of 150 to 500 V applied when developing the image latent image of the document. As a result, the developing potential for the negative toner particles is reduced as compared with the case of developing the image latent image of the original, and the toner particles are
Will be attracted by the side. As a result, the reference pattern latent image is developed into a so-called halftone image.
With such a halftone image, the density detection accuracy can be improved.

The detection signal from the photo sensor 11 is received by the CPU 15 to determine the image density. If the detected image density value of the visualized reference pattern latent image is lower than the reference value, the replenishing roller 10d is driven to rotate and the toner is discharged. When the replenishment is high, if the replenishment is high, the rotation drive of the replenishment roller 10d is stopped, and the toner replenishment is stopped.

In the present invention, not only the normal rotation developing device as in the above embodiment, but also the charging potential of the photosensitive drum is set to a negative polarity (for example,-
800 V) and a reversal developing device in which the developing bias potential is negative (for example, -600 V in the image area). In addition, the present invention relates to
The present invention is not limited to the component developing device, and can be similarly applied to a one-component developing device. The present invention is not limited to the above-described toner concentration control method, but can be naturally applied to a method for controlling charging conditions, development conditions, and the like.

(Effects) As described above, according to the present invention, an image latent image of a document is formed in the image area of the latent image carrier, and the non-image area of the latent image carrier not forming the image latent image of the document is formed. Forming a reference pattern latent image for image density detection, and developing the image latent image and the reference pattern latent image with toner held on a developer carrier under a predetermined latent image bias electric field. In an image control method of an image forming apparatus, the density of a visible image of the reference pattern latent image obtained by development is optically detected by a density sensor to control image forming conditions. The developing bias voltage applied to the developer carrier when
While adjusting the developing bias voltage applied to the developer carrier when developing the image latent image of the document, the toner particles are adjusted so as to be attracted more toward the developer carrier,
A developing bias voltage applied to the developer carrier at a predetermined timing immediately before developing the reference pattern latent image,
A developing bias voltage for attracting toner particles to the developer carrier side with respect to a developing bias voltage applied to the developer carrier when developing the reference pattern latent image; Since the developing bias voltage is adjusted to such an extent that the toner is released from above, the toner on the developer carrier can be cleaned in advance when the reference pattern latent image is developed, and this is caused by toner contamination. The weakening of the effective force of the developing bias can be avoided, and the visible image density of the pattern latent image can be detected stably and accurately.

[Brief description of the drawings]

FIG. 1 is a time chart showing an image control process according to an embodiment of the present invention. FIG. 2 is a schematic explanatory view showing an embodiment of a copying machine configured to carry out the present invention. The figure is a diagram showing the toner contamination state of the developer carrying member. 1 photosensitive drum, 5 reference pattern, 10 developing device, 10b developing roller, 11 photosensor, 15 C
PU, 17 ... Bias power supply.

Claims (1)

(57) [Claims] An image latent image of a document is formed in an image area of the latent image carrier, and a reference pattern latent image for image density detection is formed in a non-image area of the latent image carrier which does not form an image latent image of the document. Is formed, and the image latent image and the reference pattern latent image are respectively developed with a toner held on a developer carrier under a predetermined developing bias electric field, and the reference pattern latent image obtained by the development is developed. When the reference pattern latent image is developed in the image control method of the image forming apparatus in which the density of the visible image is optically detected by a density sensor to control image forming conditions, the image is applied to the developer carrier. When the developing bias voltage is adjusted with respect to the developing bias voltage applied to the developer carrier when the image latent image of the document is developed, the toner particles are more attracted toward the developer carrier. A developing bias voltage applied to the developer carrier at a predetermined timing immediately before developing the reference pattern latent image is changed to a developing bias applied to the developer carrier when the reference pattern latent image is developed. An image forming method, wherein the voltage is adjusted to a developing bias voltage that attracts toner particles to the developer carrier side with respect to the voltage, and is adjusted to such an extent that toner is released from the developer carrier. An image control method for a device.