JPS61248068A - Developing density control device - Google Patents

Abstract

PURPOSE:To hold it hue effective by forming a control means for changing the density of other colors in accordance with the density change of a certain color. CONSTITUTION:An electrostatic latent image having a density detecting pattern recorded on a non-picture part of a photosensitive drum 7 by a laser optical system 6 is developed by cyanogen in a developing machine 9a to which a prescribed bias is applied on the basis of a value stored in a storage circuit 23. The developed pattern is detected by a density sensor 5 and its density signal is compared with the reference signal of a reference voltage generating circuit 20 by a comparator 21 through a detecting circuit 19. When the difference between two signals exceeds a control enabled range, the best compensation value within the control range for the color is stored in the storage circuit 23. Then, a compensation value for supplying a bias setting the density ratio of three colors to (a:b:c) previously determined on the basis of the fine hue is calculated. Although the whole density is reduced, a picture having the fine hue can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developer density control device for controlling the developer density of a color printer or a color copying machine.

BACKGROUND OF THE INVENTION Conventional development density control devices used in conventional printers or copying machines include, for example, creating a batch of solid images as a reference electrostatic latent image on a non-image area of a photoreceptor, and developing this batch with a developing machine. After that, the developed toner density is detected by an optical sensor, the deviation between the detection standard toner density and the target value is calculated, and the resulting correction value is fed back to the developing bias applied to the developing roll, thereby maintaining stable density for a long time. There are some that are intended to be retained for a period of time (Japanese Patent Laid-Open No. 55-1119
No. 70).

The process control device of a color copying machine detects the potential of the background formed on the surface of the photoreceptor, compares this detected potential with a reference potential, and adjusts the amount of exposure light in the next color development process according to the comparison value. The present applicant has proposed a control method (Japanese Patent Application No. 59-184996).

However, with conventional developer density control devices, there is a certain limit to the variation of the developing bias when controlling the amount of toner supplied from the developing machine to the photoreceptor, and the detected toner If the difference between the density value and the target value is large, it becomes impossible to control the amount of toner, resulting in a significant change in toner density.

If such a developer density control device is applied to a color printer or a color copying machine, for example, by changing the density of one of the three colors cyan (C), magenta (M), and yellow (Y), three colors can be overlapped. When the images are combined, a difference in color tone occurs, and therefore it becomes impossible to obtain accurate and clear colors corresponding to the original.

According to the present invention, when at least one of the plurality of developing machines for, for example, three colors as described above becomes uncontrollable, the toner density of the other color is controlled by another controllable developing machine. Accordingly, it is an object of the present invention to provide a density control device that can obtain an image with the same tone when three color toners are superimposed, although the toner density varies.

Means for Solving the Problems In order to solve the conventional problems, the development density control device of the present invention visualizes the reference electrostatic latent image formed on the photoreceptor using toner supplied from the developing machine, and The toner density of the visualized toner image is detected by a density sensor to obtain the reference toner density, the detected reference toner density signal is compared with a target value installed in a control circuit, and the voltage is applied to each developing roll based on this comparison signal. A first developing bias control means is provided for controlling the developing bias applied to the first developing roll according to the difference between the detection reference toner density value and the target value, and the developing bias is controlled by the first developing machine. and a second developing bias control means for controlling the toner density by a second developing device in accordance with the detected reference toner density value when the reference toner density value to be detected deviates from the developing bias variable range of the first developing bias control means. be done.

According to the present invention, the reference toner density formed on the photoreceptor in the developing process is detected by the density sensor, and the toner is applied to the first developing roll, for example, cyan, in accordance with the difference between the detected toner density and the target value. The developing bias is controlled by a first developing bias control means.

When this control range deviates from the developing bias variable range of the first developing bias control means, the developing bias applied to the next second developing roll, for example, magenta, is corrected by the second developing bias controlling means, and further, for example, If sufficient correction cannot be made due to the development bias of cyan and magenta, by correcting the development bias applied to the third yellow development roll, the entire three-color toner of cyan, magenta, and yellow can be overlapped. In combination, images on paper obtained through transfer and fixing can be formed to have the same color tone according to the input signal.

Embodiments Hereinafter, embodiments of the present invention will be described based on the drawings. 1st
The figure shows an embodiment of a color printer to which the present invention is applied.

This color printer basically consists of a laser optical system 6 that scans a 0N10FF laser beam based on a given image signal, a photosensitive drum 7 that is exposed to the beam, and a surface of the photosensitive drum 7 that is exposed to light before being exposed. A charger 8 that charges the photosensitive drum 7 uniformly, a developer 1!9a19b, 9c that sequentially develops an electrostatic latent image formed by exposure on the surface of the photosensitive drum 7 with toner every time the photosensitive drum 7 rotates once, and a developing machine 9c. (7
) A density detection sensor (optical sensor) 5 that detects the toner image once in the vicinity, a paper feed tray 11 into which the required number of sheets of paper is set, and a sheet of paper that is fed from the paper feed tray 11 at a predetermined timing. A paper feed roll 12 that transfers paper, a transport mechanism 13 that transports paper fed from the paper feed roll 12 to a transfer position, a transfer drum 14 that rotates each time the fed paper is wrapped and transferred, and A transfer charger 15 that is installed inside the drum and performs transfer by applying a high voltage, a fixing device 16 that fixes the color transferred image on the paper surface after transfer, and a paper discharge tray that stores the paper after fixing. 17, and a cleaner 18 that cleans the surface of the photosensitive drum 7 every time the transfer corresponding to each of the developing machines 9a to 9C is completed.

To explain the basic operation of the color printer shown in Figure 1,
First, the photosensitive drum 7 is uniformly charged by the charging device 8,
0N10 by laser optical system 6 according to the image signal of each color
The FF laser beam scans and exposes the photosensitive drum 7 rotating clockwise in the figure, thereby forming an electrostatic latent image on the photosensitive drum 7 corresponding to an image signal. Each time the photosensitive drum 7 rotates once, each color developer, for example, cyan (C), magenta (M), and yellow (Y), is supplied to the developing device 9a.
~9C is supplied onto the surface of the photosensitive drum to develop the electrostatic latent image described above.

On the other hand, a transfer sheet for transferring the developed image is supplied from the paper feed tray 11 by a paper feed roll 12, passes through a conveyance mechanism 13, and is conveyed to a transfer drum 14. The conveyed paper is wound around the transfer drum 14 by a gripper (not shown), and when corona discharge is performed from the back side of the paper by the transfer charger 15 in the transfer drum 14, the developed image on the photosensitive drum 7 is The image (toner image) is transferred. When the development and transfer of a predetermined number of colors is completed by multiple rotations of the photosensitive drum 7 and the transfer drum 14, the transferred paper is separated from the transfer drum 14 and sent to the fixing device 16 via the conveyor belt 25. After that, it is heated and compressed to fix the transferred toner image. When the transferred toner image is fixed on the paper, the paper is stored in the paper discharge tray 17, where the entire process of color printing is completed.

In the developing process, the toner density of the solid image formed on the photoreceptor is detected by a density sensor 5, and as shown in FIG. 2, the toner density is detected by a detection circuit 19 based on the output signal of this density sensor 5. Then, a comparison circuit 2 compares the output voltage of the detection circuit 19 and the reference voltage from the reference voltage generation circuit 20.
Compare with 1.

The arithmetic control circuit 22 inputting the output signal of the comparator circuit 21 performs arithmetic processing and outputs the control signal to the bias power supply 2 based on the arithmetic result.
A storage circuit 23 outputted to 4a to 24C and connected to the arithmetic control circuit 22 stores the arithmetic data obtained by the arithmetic control circuit 22. When the control signal of the arithmetic control circuit 22 is output to the developing bias I [24a to 24G, the developing machine 9 of each color
The voltage supplied to the developing rolls a to 9C is controlled as a predetermined developing bias.

The density detection pattern necessary to operate the control circuit 25 shown in FIG. 2 forms a reference electrostatic latent image on a non-image area on the photosensitive drum 7 by exposure of the laser optical system 6 using a signal prepared in advance. After developing the toner, the density sensor 5 detects the toner density. To explain the operation of the control circuit 25, the electrostatic latent image of the density detection pattern recorded on the non-image area of the photosensitive drum 7 by the laser optical system 6 is biased at a predetermined bias based on the value stored in the storage circuit 23. The image is developed in cyan by the developing device 9a to which the image is applied. This developed pattern is detected by the density sensor 5, and the density signal is passed through the detection circuit 19 and sent to the reference voltage generation circuit 20.
It is compared with the reference signal in the comparison circuit 21.

The difference ■. is within the controllable range, the arithmetic and control circuit 22 performs a correction calculation for bias (8) to correct the voltage value of the bias power supply 24a, and this information is stored in the storage circuit 23 and used in the developing device 9a for the next copying. This is the source of the bias value when developing a cyan image. Here, ■, and V
. The following relational expression 6% (1) (Δ■B: bias correction value, α: coefficient, ■o: difference between detected value and reference value) holds, and ■ is true for both yellow and magenta. When the value is within the controllable range, a correction is made in the same way, and the bias value is corrected at the time of the next copy.

V in one of three colors: cyan, magenta, and yellow. When the color is outside the controllable range, first, the best correction value within the control range for that color is stored in the storage circuit 23. Subsequently, a correction value that can supply a bias such that the density ratio of the three colors becomes a value a:b:c: determined in advance based on the quality of the color tone is calculated.

For example, bias and density have the relationship shown in Figure 3, and in terms of image quality, cyan (C), magenta (M), yellow (Y)
When the density standards of the three colors are 1.7.1.7.1.3, the biases are set to be 250, 250.300, respectively. When the cyan density decreased from 1.7 to 1.5 (see dotted line B in the graph), the bias was changed to 2.
00■ must be lowered to 50V, but since the bias can only take values between 100 and 600V, it is set to 100■ at this time, and the cyan density becomes 1665. Along with this cyan density, new density standards for magenta and yellow are calculated.

Here 1.65:L) (Magenta density):D~(
yellow density) -1,7:1.721.3, -1,
65, D, -1, 26. A bias correction value to achieve this density is calculated, and development is performed with a magenta bias of 300V and a yellow bias of 380V during the next copying. This will lower the overall density, but it is possible to obtain an image with good color tone.

In the above embodiment, the case of three-color development using development 1198 to 9C was explained, but the present invention only needs to mutually correct the development bias control of a plurality of developing machines, and the case of two-color or four-color development is described. Of course, the present invention is also applicable to those equipped with a developing machine. Further, the present invention can also be applied to a tandem type color development density control system having a process for each color. Furthermore, the present invention can also be applied to control based on the amount of toner supplied. In FIG. 1, an electrostatic latent image is formed on the photosensitive drum 7 by the laser optical system 6, but in the present invention, a lamp is used to irradiate the original on the platen, and the irradiated light is applied to the photosensitive drum. It can also be applied to copying machines that form electrostatic latent images.

According to the present invention, when a change in the density of a certain color occurs, a control means is provided that changes the density of other colors correspondingly, so that it is possible to prevent the density of a certain color from changing significantly. When a developing machine becomes uncontrollable, by correcting the density using another developing machine, the overall toner density will change, but the color tone will be maintained well, and an excellent image quality will be obtained based on a comprehensive evaluation. I can do it.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram showing an embodiment of a color printer to which the present invention is applied, Fig. 2 is a block diagram showing an embodiment of the present invention, and Fig. 3 shows the bias value applied to the developing roll and the solid density. It is a graph showing the relationship. 5: 81 degree sensor 6: Laser optical system 7: Photosensitive drum 8: Charger 9a19b, 9c: Developing device 11: Paper feed tray 14: Transfer drum 15: Transfer corotron

Claims (1)

[Claims] The reference electrostatic latent image formed on the photoconductor is visualized using toner supplied from a developing machine, the toner density of this visualized toner image is detected by a density sensor to obtain a reference toner density, and the detected reference toner density is transferred to a control circuit. In a color development density control device that controls the development bias applied to each development roll based on this comparison signal, the toner density control device compares the development bias with a target value set in A first developing bias control means is provided for controlling the developing bias applied to the first developing roll, and when the reference toner density value to be developed by the first developing device deviates from the developing bias variable range of the first developing bias control means, A developing density control device comprising a second developing bias control means for controlling toner density by a second developing device in accordance with a detection reference toner density value.