JPH0572864A - Printing density control system for laser printer - Google Patents

Abstract

PURPOSE:To provide printing with a stable printing density even the when the number of printing colors is changed, on the printing density control system for a laser printer capable of multicolor printing. CONSTITUTION:Basically, a constitution is adopted so that the quantity of toner attracted to the photosensitive surface 1a of the photosensitive drum 1 on each of plural developing units 2, is increased according to the number of the developing units 2 of the rear steps of the developing units 2. The increase of the quantity of the toner attracted to the photosensitive surface 1a, such that, is executed by making the laser power of a laser beam 4 high by a laser power control means 5 controlling a voltage applied to a laser light source 3, and a constitution that the quantity of the toner attracted to the photosensitive surface 1a is increased, by making a developing bias high by a developing bias control means 6 controlling the developing bias applied to the developing unit 2, can be adopted. Therefore, even when the toner attracted to the photosensitive surface by the developing unit of the front step, is scratched off by the developing unit of the rear step, a constant toner quantity is obtained at the time of completing development, so that the printing is executed with the stable printing density.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a plurality of developing devices arranged in parallel along the photosensitive surface of a photosensitive drum corresponding to a printing color, and printing each color in the process of one rotation of the photosensitive drum. Based on the data, the photosensitive surface of the photosensitive drum is scanned by a laser beam emitted from a laser light source to form an electrostatic latent image corresponding to the color, and then the electrostatic latent image is transferred to a toner in a developing device corresponding to the color. The present invention relates to a print density control method for a laser printer that forms toner images of a plurality of colors on the photosensitive surface of the photosensitive drum by sequentially repeating the formation of an image.

[0002]

In the case of multicolor printing in a laser printer which forms an electrostatic latent image on a photosensitive surface of a photosensitive drum by irradiating a laser beam based on print data and develops the electrostatic latent image into a toner image. Has a developing device of the same number as the number of colors and adopts a soft touch method as a developing method. The main part of an example of such a laser printer is shown in FIG. As shown in FIG. 5, in the soft touch method, the developing device 71 is brought close to the photosensitive drum 70, and a carrier 72, which is a magnetic material, and a toner 73, which is a non-magnetic material, are disposed in the developing device 71. By agitating the component type developer, the toner 73 is provided with an electric charge to adhere the toner 73 to the surface of the carrier 72, and the carrier 72 is moved along the magnetic flux between the magnetic poles of the magnet roller 74 in the developing device 71. It is connected in a spike shape by magnetic force. The spike-shaped carrier 7 flutters in the opposite direction of the rotation of the magnet roller 74 as the magnet roller 74 rotates.
2 is rubbed against the photosensitive surface 70a of the photosensitive drum 70, and the toner 73 adhering to the carrier 72 is removed from the photosensitive surface 70a.
The toner image is formed by adsorbing to the portion of the electrostatic latent image of a.

In such a laser printer capable of multicolor printing which develops by the soft touch method, a color used for printing is selected from the printable colors, and the unused developing device is retracted from the photosensitive drum. However, the developing device for the color used is always close to the photosensitive drum during printing. For example, in a black-red two-color printing laser printer, in the case of black single-color printing, only the black developing device approaches the photosensitive drum, and the red developing device is retracted to avoid color mixing. In the case of color printing, the two developing devices are always close to the photosensitive drum during printing.

[0004]

However, in the case of the soft touch multicolor printing as described above, as shown in FIG. 5, the toner 75 adsorbed on the photosensitive drum by the developing device in the preceding stage is A part is scraped off by rubbing the carrier 72 of the developing device 70 in the subsequent stage as shown by the dotted line. Moreover, since the amount of such scraped toner varies depending on the number of developing devices (the number of printing colors) in the subsequent stage that is close to the photosensitive drum, there is a problem in that the print density varies even when printing is performed with the same developing device. There is. SUMMARY OF THE INVENTION The present invention aims to solve the above problems by providing a print density control method for a laser printer capable of printing with a stable print density even when the number of print colors changes in a multicolor laser printer. To do.

[0005]

The print density control method for a laser printer according to the present invention is basically configured as shown in the block diagram of the principle of the invention of FIG. 1 in order to achieve the above-mentioned object. , Photosensitive drum corresponding to print color (1)
Has a plurality of developing devices (2) juxtaposed along the photosensitive surface (1a) of the photosensitive drum (1a), and in the process of rotating the photosensitive drum (1) once, the photosensitive drum (1) is printed based on print data of each color. Laser light source (3) on photosensitive surface (1a)
To form an electrostatic latent image corresponding to the color by scanning with a laser beam (4) emitted from the laser beam (4), and then form a toner image in the developing device (2) corresponding to the color. In a printing density control system of a laser printer in which toner images of a plurality of colors are formed on the photosensitive surface (1a) of the photosensitive drum (1) by repeating it sequentially, each developing device (2) of the plurality of developing devices (2) The amount of toner adsorbed on the photosensitive surface (1a) of the photosensitive drum (1) in (1) is increased according to the number of developing devices in the subsequent stage of the developing device (2).

The increase in the amount of toner adsorbed on the photosensitive surface (1a) of the photosensitive drum (1) in each developing device (2) is controlled by a laser power control for controlling the voltage applied to the laser light source (3). Laser beam (4) by means (5)
Is preferably performed by increasing the laser power, or by increasing the developing bias by the developing bias control means (6) for controlling the developing bias applied to the developing device (2).

[0007]

In the process of having a plurality of developing devices (2) arranged in parallel along the photosensitive surface (1a) of the photosensitive drum (1) corresponding to the printing color, the photosensitive drum (1) makes one rotation. , An electrostatic latent image corresponding to the color is formed by scanning the laser beam (4) emitted from the laser light source (3) on the photosensitive surface (1a) of the photosensitive drum (1) based on the print data of each color, Then, the electrostatic latent image is formed on the photosensitive surface (1a) of the photosensitive drum (1) by sequentially repeating the formation of the toner image in the developing device (2) corresponding to that color, thereby forming a plurality of color toner images. In the multi-color printable laser printer described above, the toner attached to the photosensitive surface by the developing device in the preceding stage is scraped off by the developing device in the subsequent stage, and the amount of toner scraped off varies depending on the number of developing devices in the subsequent stage. Therefore, the photosensitive surface (1) of the photosensitive drum (1) in each developing device (2) of the plurality of developing devices (2) is
If the amount of toner adsorbed to a) is increased in consideration of the amount of toner scraped off by the developing device of the latter stage in accordance with the number of developing devices of the latter stage of the developing device (2), the photosensitive drum (1) will be 1 When the rotation and the development of the previous color are completed, a certain amount of toner is attached to the photosensitive surface (1a) for each color.

The amount of toner adsorbed on the photosensitive surface (1a) is obtained by increasing the laser power of the laser beam (4) by the laser power control means (5) for controlling the voltage applied to the laser light source (3). , The potential difference between the electrostatic latent image formed on the photosensitive surface and the magnet roller increases, and the attraction force of the toner to the electrostatic latent image increases, which increases. Further, even if the developing bias is increased by the developing bias control means (6) for controlling the developing bias applied to the developing device (2), the potential difference between the electrostatic latent image and the magnet roller becomes large, and the electrostatic latent image is detected. Since the attracting force of toner increases, the amount of toner adsorbed on the photosensitive surface (1a) increases.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A concrete embodiment of a print density control system for a laser printer according to the present invention will be described with reference to the drawings. In the first and second embodiments described below, the laser printer to which the print density control method of the laser printer according to the present invention is applied is capable of two-color printing as shown in FIG. Laser printer 20
Is. In such a laser printer 20, first, in order to develop the first color, print data input from an external information processing device (not shown) to the photosensitive surface 22a of the photosensitive drum 22 charged by the charger 21. Based on this, an electrostatic latent image is formed by scanning the laser beam L emitted from the optical unit 23. Further, in the developing device 24 containing the developer composed of the toner of the first color and the carrier, the toner is adsorbed to the electrostatic latent image to form the toner image of the first color. Then, in order to form a toner image of the second color, the charger 25, the optical unit 26, and the developing device 27.
Is used to perform the same process as the first color. The two color toner images thus formed on the photosensitive surface 22a are transferred onto the paper 29 by the transfer device 28 and printed. The photosensitive surface 2
The toner remaining on 2a is scraped off by the cleaner 30 and collected. Further, when performing monochrome printing, the developing devices 24 and 27 for the colors that are not to be printed are retracted from the photosensitive drum 22 as indicated by the dotted line.

(First Embodiment) In this embodiment, in the laser printer 20 capable of two-color printing as shown in FIG. 2, the laser power is changed among the print density control methods of the laser printer according to the present invention. By doing so, the print density is controlled. In FIG. 3, which shows an optical system and a control system of the laser printer 20 to which the print density control method of the laser printer according to the present invention is applied, data relating to printing input to the print data storage unit 40 from an information processing device (not shown). Among them, video data representing characters, figures, etc. is stored in the video data storage area 41, and the developing device 2 used for printing those video data.
Information relating to Nos. 4 and 27 (such information is hereinafter referred to as "printing style"), in other words, a developing device that is retracted in single-color printing is input to the printing style register 42.
In the controller unit 45 configured by the microprocessor 43 (hereinafter, abbreviated as “MPU”) and the memory 44 to control the printing process, the laser power conversion table 46 of the memory 44 stores the printing mode register 42. Data for setting the laser beam L in the optical units 23 and 24 (only the optical unit 23 is shown) to a predetermined laser power is stored corresponding to the printing mode, and these data are stored in the control program of the memory 44. It is given to the output intensity switching register 49 of the laser beam output switching unit 48 under the control of the MPU 43 based on the control program stored in the area 47. Further, in the laser beam output switching section 48, based on the data given to the output intensity switching register 49, the analog switch 50 is switched to select a predetermined voltage obtained by voltage division by the resistance and select the laser driver section 51. It is applied to the laser diode 52.

As shown in FIGS. 2 and 3, the laser beam L thus switched to the predetermined laser power has a polygon mirror 53 based on the video data stored in the video data storage area 41. The photosensitive surface 22a of the photosensitive drum 22 is scanned via the fθ lens 54 in accordance with the rotation of the electrostatic latent image to form an electrostatic latent image. The electrostatic latent image on the photosensitive surface 22a is developed into a toner image by the developing device 24, transferred to the paper 29 by the transfer device 28, and printed.

In the above laser printer 20, as the laser power of the laser beam L for scanning the photosensitive surface 22a becomes higher, the potential difference between the electrostatic latent image formed on the photosensitive surface 22a and the developing bias applied to the magnet roller is increased. Becomes larger, the toner attracting force increases, the amount of toner attracted to the photosensitive surface 22a increases, and the print density becomes darker. Therefore, in the case of performing two-color printing, the amount of toner scraped off by the developing device 27 in the subsequent stage according to the printing style stored in the printing style register 42 is taken into consideration, and the laser power in the optical unit 23 in the preceding stage is higher than that in monochromatic printing. If the voltage applied to the laser diode 52 in the laser beam output switching unit 48 is selectively switched so that the amount of toner adsorbed by the developing device 24 in the preceding stage increases, the developing device 27 in the subsequent stage scratches the toner of the first color. Even if the toner is dropped, the amount of toner adsorbed becomes a predetermined amount when the development of two colors is completed, and the print density becomes stable. That is, the print density of the first color in the two-color printing is the same as that of the first color in the single-color printing.
The first and second colors during color printing have the same print density.

(Second Embodiment) In this embodiment, in the laser printer 20 capable of two-color printing as shown in FIG. 2, the developing bias is switched among the print density control methods of the laser printer according to the present invention. The print density is controlled by. In FIG. 4, which shows the control system of the laser printer 20 to which the print density control system of the laser printer according to the present invention is applied, the same reference numerals as those in FIG. 3 and the first embodiment indicate the same functions. The description will be omitted.

A controller section 45 'for controlling the printing process
At the developing bias conversion table 55 of the memory 44.
Stores data for setting the developing bias in each of the developing devices 24 and 27 to a predetermined value in accordance with the printing style stored in the printing style register 42, and these data are stored in the control program of the memory 44. MPU based on the control program stored in the storage area 47
By the control of 43, it is given to the first developing bias controller 56 and the second developing bias controller 57. further,
In the first development bias control device 56 and the second development bias control device 57, the predetermined development converted into analog values by the D / A converters 58 and 59 based on the respective data given from the development bias conversion table 55. A bias is applied to the magnet rollers of the developing devices 24 and 27.

In the laser printer 20 as described above, the larger the developing bias applied to the developing units 24 and 27, the larger the amount of toner adsorbed and the darker the print density as described in the prior art. Therefore, in the case of performing two-color printing, the developing bias in the developing device 24 in the preceding stage is higher than that in the monochromatic printing in consideration of the amount of toner scraped off by the developing device 27 in the succeeding stage according to the printing mode stored in the printing mode register 42. If the data of the developing bias conversion table 55 is set so that
As in the embodiment, the amount of toner adsorbed by the developing device 24 in the preceding stage is increased, and the developing device 27 in the subsequent stage scrapes off the toner of the first color to obtain the same print density as when the first color is printed in a single color. Be done. Also, the same print density can be obtained for the first color and the second color.

In the above-described first and second embodiments, the print density control method of the laser printer according to the present invention has been described by taking a laser printer capable of two-color printing as an example. In multicolor printing as well, the same method as in this embodiment can be applied to control the print density of the laser printer.

In the present embodiment, the photosensitive drum 22 is the photosensitive drum 1 of the present invention, the photosensitive surface 22a is the photosensitive surface 1a of the present invention, the developing devices 24 and 27 are the developing device 2, and the laser diode 52 is the laser light source 3. , The laser beam L is the laser beam 4, the print data storage unit 40, the control unit 45, and the laser beam output switching unit 48 are the laser power control means 5, the print data storage unit 40, the control unit 45 ′, and the first developing unit. Bias controller 56 or second
The developing bias control device 57 is the developing bias control means 6
It corresponds to each.

[0018]

According to the print density control method of the laser printer of the present invention, the number of printing colors changes in a multicolor laser printer, and the toner adsorbed on the photosensitive surface by the developing device in the preceding stage is changed by the developing device in the succeeding stage. Even if the toner is scraped off, the toner amount becomes constant after the development is completed, so that it is possible to print with a stable print density.

[Brief description of drawings]

FIG. 1 is a block diagram of an invention principle showing a principle configuration of a print density control system of a laser printer according to the present invention.

FIG. 2 is a schematic view of a main part of a laser printer in an embodiment to which a print density control method for a laser printer according to the present invention is applied.

FIG. 3 is a block diagram illustrating a first embodiment of a print density control method for a laser printer according to the present invention.

FIG. 4 is a block diagram illustrating a second embodiment of a print density control method for a laser printer according to the present invention.

FIG. 5 is an explanatory diagram of toner development by a soft touch method.

[Explanation of symbols]

 1, 22, 70 Photosensitive drums 1a, 22a, 70a Photosensitive surfaces 2, 24, 27, 71 Developing device 3 Laser light source 4 Laser beam 5 Laser power control means 6 Development bias control means 20 Laser printer 21, 25 Charger 23, 26 Optical unit 28 Transfer device 29 Paper 30 Cleaner 40 Print data storage unit 41 Video data storage area 42 Printing style register 43 Microprocessor (MPU) 44 Memory 45, 45 'Control unit 46 Laser power conversion table 47 Control program storage area 48 Laser beam Output switching unit 49 Output intensity switching register 50 Analog switch 51 Laser driver unit 52 Laser diode 53 Polygon mirror 54 fθ lens 55 Development bias conversion table 56 First development bias control device 57 Second development Toner adsorbed to the photosensitive drum with bias control device 58, 59 D / A converter 72 carrier 73 Toner 74 magnet roll 75 preceding the developing device

Claims (3)

[Claims] 1. A plurality of developing devices (2) are arranged in parallel along a photosensitive surface (1a) of a photosensitive drum (1) corresponding to a printing color, and the photosensitive drum (1) rotates once. In the process, a laser beam (4) emitted from a laser light source (3) scans the photosensitive surface (1a) of the photosensitive drum (1) based on print data of each color to form an electrostatic latent image corresponding to that color. Then, the electrostatic latent image is formed on the photosensitive surface (1a) of the photosensitive drum (1) by sequentially repeating the formation of the toner image in the developing device (2) corresponding to that color. In the printing density control method of a laser printer for forming a photo printer, the photosensitive drum (1) in each developing device (2) of the plurality of developing devices (2)
The printing density control method for a laser printer, wherein the amount of toner adsorbed on the photosensitive surface (1a) of the above is increased according to the number of developing devices in the subsequent stage of the developing device (2). 2. A laser power control for controlling a voltage applied to the laser light source (3) for increasing the amount of toner adsorbed on the photosensitive surface (1a) of the photosensitive drum (1) in each of the developing devices (2). 2. The printing density control system for a laser printer according to claim 1, wherein the method is performed by increasing the laser power of the laser beam (4) by means (5). 3. An increase in the amount of toner adsorbed on the photosensitive surface (1a) of the photosensitive drum (1) in each of the developing devices (2) increases the developing bias for controlling the developing bias applied to the developing device (2). The control is performed by increasing the developing bias by the control means (6).
The printing density control method of the laser printer described in.