JPS6250818B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a print density control method for an electrostatic printing device, typified by an electrophotographic device.

Generally, this type of device includes a latent image forming medium for forming an electrostatic latent image, an initial charger for forming the electrostatic latent image on the latent image forming medium, a laser light source, a laser light modulator, and a laser. A latent image forming means consisting of a light deflector, etc., a developing device that visualizes the electrostatic latent image formed on the latent image forming medium by supplying toner, and a device for transferring the obtained visible image onto recording paper. It consists of a transfer device and a fixing device that fixes the transferred image on the recording paper.

A latent image of information is developed on a drum-shaped or endless belt-shaped latent image developing medium, such as a photosensitive drum, and then this latent image is made into a visible image by a developing device, and then a recording paper is transferred to the photosensitive drum. Press the
2. Description of the Related Art Electrostatic printing apparatuses are known that transfer a visible image onto recording paper and heat and fix the transferred visible image.

Such a printing device can repeatedly form a latent image on a photosensitive drum, there is no need to replace the photosensitive drum until a considerable lifespan has passed, plain paper can be used as the recording paper, and there is freedom in size and thickness. It has various advantages such as being able to use foldable form paper that is flexible and easy to handle, printing speed is fast, print quality is good, there is flexibility in character size and orientation, and it is easy to overlay K-line form. It is extremely useful and can be applied to all printing fields such as newspaper printing, general EDP printing, and receipt printing.

FIG. 1 is a schematic explanatory diagram of the principle of an electrophotographic recording device using a photosensitive drum, in which 1 is a photosensitive drum whose surface is coated with a photoconductor, and 2 is a photosensitive drum 1 that has a positive or negative polarity by corona discharge or the like. 3 is a latent image forming unit comprising the above-mentioned laser light source, etc., for forming a desired electrostatic latent image on the photosensitive drum 1; 4 is a latent image forming unit that forms a desired electrostatic latent image on the photosensitive drum 1 with toner; 5 is a transfer device that transfers toner onto recording paper 6; 7 is a cleaner that removes residual toner on photosensitive drum 1; 8 is photosensitive drum 1;
A static eliminator 9 is used to discharge the afterimage charge on the recording paper 6, and a heating fixing device 9 includes a flash lamp or the like that heats and fixes the toner on the recording paper 6 onto the recording paper 6.

The latent image forming method involves irradiating an image on an optical fiber tube (referred to as OFT) onto the photosensitive drum 1 through a lens system, and then applying a charge on the entire surface of the photosensitive drum 1, which is positively or negatively charged by a corona discharger 2. A method for extracting the charge on the photosensitive drum 1 according to the image pattern on the OFT, a method for turning the laser beam on and off according to the information pattern to be recorded by an optical modulator, and extracting the charge on the photosensitive drum 1 along the pattern. Electrodes are provided linearly in the direction of the rotation axis of the photosensitive drum 1 and facing the surface of the photosensitive drum 1, and a high voltage is applied to desired pin electrodes according to the information pattern to be recorded to generate charges along the pattern. There are ways to remove it.

By the way, in this type of conventional printing apparatus, a density detector is provided for monitoring the density of the visible image formed on the surface of the photosensitive drum 1 and always maintaining a constant print density. This density sensor is arranged at a position close to the surface of the photosensitive drum 1 between the developing device 4 and the transfer device 5, as shown by 10 in FIG.

Alternatively, as shown by 10' in the figure, it is arranged near the recording paper conveyance path between the transfer device 5 and the heat fixing device 9.

The density detector 10 or 10' optically detects the density of the visible image on the surface of the photosensitive drum 1 or the recording paper 6, and inputs the detection output to the control section of the developing device 4 to detect the density of the visible image on the photosensitive drum 1. Controls the amount of developer powder (hereinafter referred to as toner) supplied.

As a result, the visible image density is controlled to always be maintained at a constant, appropriate level.

The density detector 10 or 10' is disposed at the end of the photosensitive drum 1 or the end of the recording paper 6, and detects a density mark formed on the surface of the photosensitive drum 1 or on the recording paper 6 in the same manner as an information latent image. The density is optically read, and a toner supply shaft (not shown) at the lower end of the toner hopper is controlled to rotate in accordance with the detection result to keep the amount of toner in the developing device 4 constant. That is, in the above-described printing apparatus, the image density tends to fluctuate due to deterioration of the developer carrier, image density, and variations in the amount of toner fed from the toner hopper into the developer carrier. For this purpose, various concentration control methods have been studied and put into practical use.

Laser printers generally print a density mark on the edge of the paper and detect it with a density detector.
Compare with the preset concentration control level,
This determines whether the image density is "dark" or "light" and controls the amount of toner supplied into the developer.

Therefore, the printed density mark must sufficiently reflect the image density of other text information printed at the same time. Further, it is necessary that the output of the density detector for detecting this is stable and that a sufficient difference in output can be obtained for the density of the image density of the text information.

Generally, with this type of device, when character information is printed from a blank sheet, the image density of the first line is darker than the image density of the characters printed continuously after that, and the image density is particularly light. In some cases, the difference can be large. In other words, the image density of the first row is
The difference in shading is small compared to the subsequent image densities.

Density marks are generally printed isolated on the edge of the paper as shown in FIG. 2A, so they are susceptible to the above-mentioned effects. The mark shown in FIG. 1A is of a type with a length of 1 mm and a width of 3 mm, but it has the disadvantage that it does not sufficiently reflect the shading of the actual characters printed on the paper. For this reason, the difference in the outputs of the concentration detectors is small, and it is therefore substantially difficult to provide multiple concentration control levels. In addition, the mark shown in Figure C is a square or vertical type with a length of about 3 to 4 mm and a width of 3 mm, but in this case too, especially at low concentrations, the mark shown in Figure C shows the mark shown in Figure D. The printed image becomes a printed image, and the output waveform of the density detector becomes as shown in figure d. Here, when comparing the output of the concentration detector with a preset concentration control level, if the peak value P of the output of the concentration detector is adopted, the same drawback as in the case of the mark A in the figure will occur. It is also possible to avoid the peak value P and adopt the range B in the figure, but since the level in this part is relatively unstable, it is still difficult to accurately detect the concentration.

In addition, we have also investigated the use of white marks as shown in Figures 3A and 3B, but this did not cover the above-mentioned drawbacks.

Next, the density mark according to the present invention will be explained using FIG. 4.

As can be seen from A to D in the same figure, according to the present invention,
The density mark is composed of a density control mark 12-2 and an auxiliary mark 12-1, and the density control mark 12-
The above-mentioned drawbacks are solved by printing the auxiliary mark 12-1 in front of the mark 2.

In the figures A, B and D, an auxiliary mark 12-1 having a smaller black area is printed near the front stage of the density control mark 12-2, respectively.
Further, as shown in FIG. 3C, a line extending both ends of the width of the density control mark 12-2 in the direction perpendicular to the direction in which the density mark moves in the direction in which the density mark moves;
Auxiliary mark 12-1 in the direction in which the density mark moves
The pixel area of the auxiliary mark 12-1 surrounded by both ends of the width or its extension line (area of the shaded area in the figure) is set within a range that does not exceed the pixel area of the density mark 12-2. A similar effect can be obtained by using a density mark that has been set.

In this way, the density mark is composed of a density control mark and auxiliary marks formed before and after the density control mark, and by setting the pixel area of the auxiliary mark to be smaller than that of the density control mark, the influence of edge effects is reduced and the paper surface is This sufficiently reflects the image density of other characters printed on the image, and since the output difference of the density detector can be made sufficiently large, many density control levels can be provided.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram of an electrophotographic device, and FIG.
FIG. 3 is a diagram for explaining a conventional density mark, and FIG. 4 is an embodiment showing a density mark according to the present invention. In the figure, 10 is a concentration detector, 12 is a concentration mark, 12-1 is an auxiliary mark, 12-2
is a density control mark.

Claims (1)

[Claims] 1 A means for forming an electrostatic latent image according to the shape of a mark for detecting information to be printed and print image density on an electrostatic latent image forming medium, and a means for forming an electrostatic latent image on the electrostatic latent image forming medium. means for developing an image with toner powder to generate an information image and density mark to be printed out consisting of a toner image; means for transferring the toner image onto a recording medium; and a toner image transferred onto the recording medium. an electrostatic printing device, comprising: means for fixing the mark on the recording medium; and means for detecting the density state of the density mark; and means for controlling the appropriate printing density according to the output of the detecting means. The density mark formed on the medium is composed of a density control mark and an auxiliary mark, and the auxiliary mark is provided at a stage preceding the density control mark in the moving direction.
In addition, after the pixel area of the region sandwiched by the extension line of the width of the density control mark is formed to be smaller than the pixel area of the density control mark, the density control mark is formed in accordance with the density state information of the density control mark from the detection means. 1. A method for controlling print density of an electrostatic printing device, characterized in that the print density is controlled by