JPH0326390B2 - - Google Patents

Description

[Detailed description of the invention]

In this invention, a reference target is exposed on a photoreceptor in advance and then developed, the density and potential of the toner image are detected, and the obtained detection signal is used to determine whether the copy density or white background density falls within a certain specified value range. The present invention relates to a control method for an electronic copying machine in which a toner supply device, developing bias voltage, charger, exposure system, etc. are comprehensively controlled according to a preset mode. Conventionally, this type of copying machine has been equipped with a device that automatically controls the amount of toner supplied and a device that controls the developing bias voltage in order to maintain the image quality of the resulting copies, especially the density of the copied image, at a constant level. etc. are being adopted. These devices improve the stability of image quality by detecting changes in the amount of transmitted light, electrical resistance, magnetic resistance, etc. of the developer and automatically maintaining the toner content in the developer at a constant level. . However, these devices require control so that the toner content remains constant even when the developer or exposure lamp deteriorates or when humidity increases.
On the other hand, the quality of the resulting copy deteriorates. In particular, copying machines using magnetic brush developing devices have the drawback of being susceptible to these effects. For example, the method disclosed in Japanese Patent Application Laid-Open No. 55-55349 has been proposed to improve this drawback, but since this method uses only the toner density as a signal, even if the developed density is constant, Since it is unclear whether the toner charge has the amount of charge necessary for transfer, the following two
There is a problem that causes a secondary failure. That is, in general, development in this type of copying machine is performed using electrical force due to charging and mechanical force due to friction. When the amount of charge is large, development is mostly performed by electric force, but when the amount of charge is small, mechanical force becomes larger than electric force. However, the toner mechanically attached to the photoreceptor hardly contributes to transfer to paper.
Therefore, even if the amount of toner adhering to the photoconductor is constant, for example, if the amount of charge on the toner decreases, the amount of toner transferred to the paper will decrease, resulting in a decrease in image density. The toner remaining on the surface adheres to the non-image areas of the paper, resulting in copies with low density and high fog. Simply controlling the toner density on the photoreceptor surface to a constant level will not produce copies with stable image density and no fog. There are no drawbacks. The present invention was made with the aim of improving the drawbacks of such conventional control devices. It is an object of the present invention to provide a control method for an electronic copying machine that allows copies of stable image quality to be obtained at all times by controlling the electronic copying machine using a value obtained by comparing the present invention with a reference value. An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows an electronic copying machine employing the control method and control device of the present invention, in which an original table 2 (not shown) is provided on the upper part of a main body 1 of the copying machine. Below the document table 2, there is a reference target 3 and an exposure lamp 4 that moves along the document table 2.
An exposure lamp 4 is provided so that the original and the reference target can be exposed. The reflected light from the original or the reference target 3 passes through the optical system 5 and reaches the photoconductor 6 in the copying machine main body 1.
forms an electrostatic latent image on the peripheral surface of the The electrostatic latent image on the photoreceptor 6 is developed into a toner image by the next developing device 7.
The developing device 7 has a developing electrode 8 to which a high voltage is applied along the circumferential surface of the photoreceptor 6, and the electrostatic charge on the photoreceptor 6 is removed by a developer containing toner supplied from a toner supply device 9. A detector 10 is provided above the developing device 7 to detect the density of the toner image of the reference target 3 formed on the photoreceptor 6. The detector 10 is a combination of a reflection type densitometer 10 ₁ consisting of a light emitting diode and a photodiode, and a surface electrometer 10 ₂ , and detects the toner image of the reference target 3 formed on the non-image area of the photoreceptor 6. The concentration signal and potential signal detected by these detectors 10 are input to the microcomputer device 16 via the input circuit 12 which is sequence-controlled by the processor 13, and are processed as follows. A control signal is calculated. When the surface of the photoreceptor 6 is uniformly charged by the charger 25 when copying is started, the surface potential of the photoreceptor 6 becomes Vs as shown in FIG. 4, and after charging, it attenuates with time (see FIG. 4). ). Next, the reference target image is exposed and developed into a toner image by the developing device 7, and when the surface potential of the developed area is measured from above the toner image, it becomes Vd (V). When the photoconductor 6 is further rotated and the unnecessary image erasing light source 11 is irradiated onto the surface of the photoconductor 6, the potential of the toner adhesion part disappears, and when the potential is measured with a surface potentiometer ₁₀₂ , Vt as shown in FIG.
(V). Since it is known in advance that the following relational expression holds between the toner charge Qt and the above-mentioned Vt (V), the toner charge Qt value is stored in the microcomputer device 16 in advance and newly measured with the surface electrometer _102. The amount of charge of the developed toner is calculated from the value Vt using the following formula. Vt=AQ ² t...(1) Yotsute

[Formula] A is determined by the toner used. On the other hand, at the same time as measuring the amount of electric charge, the reflection type densitometer 10 ₁
The weight per unit area of the toner used in development is calculated from the value Vi (V) measured in . That is, since the relationship between the value Vi (V) measured by the reflection type densitometer 10 ₁ and the toner weight Mmg/cm ² can be expressed by the following equation (3), this is stored in the microcomputer device 16 in advance. M=Blog(1/Vi) mg/cm ² ......(3) Note that B is a constant. Also, the charge amount Qt of the developer can usually be expressed in μq/g, and from the above values Qt and M, it can be expressed as follows. It can be calculated as follows. Q _T =QtμC/cm ² /Mmg/cm ² =Qt/MμC/mg≡Qt×10 ₃ /MμC/g ……(4) Therefore, the above formula can be expressed as
By executing this, it is possible to calculate the amount of charge of the developer as a tribo value which is normally handled. The values calculated by the microcomputer device 16 are outputted to various control circuits 15 via the output circuit 14. Various control circuits 15 include, for example, a development control circuit 15
₁ , exposure control circuit 15 ₂ , toner supply amount control circuit 1
5 ₃ , developer agitator control circuit 15 ₄ , exposure charge control circuit 15 ₅ , etc., when the density or surface potential detected by the reflective densitometer 10 ₁ or the surface electrometer 10 ₂ deviates from the reference value. , the charging current 15a of the charger 25, the developing bias voltage 15b of the developing device 7, and the exposure lamp 4 so that these control circuits 15 have appropriate values.
The amount of light 15c, the amount of toner supplied by the toner supply device 9, 15d, the number of rotations and speed 15e of a stirring mechanism (not shown) provided in the developing device 7, and the charging current 15f of the exposure charger 12 are controlled. That is, FIG. 6 is a flowchart showing the control operation of the toner supply device 9 and the exposure charger 12.An example of the control operation will be explained using this flowchart below.The surface potential Vt and the density Vi are detected by the detector 10. Then, the amount of charge Qt and the weight M of the developer are calculated from these values through the operations described above, and further, the tribovalue Q _T is calculated from these values. The obtained tribo value is displayed on a suitable display, and at the same time it is displayed on the microcomputer device 1.
The charge amount is compared with a preset amount of charge in 6. The relationship between the charge amount of the toner image and the transfer efficiency is the seventh
As shown in the figure, when the transfer current is the same, the lower the tribo value (indicated by T/V in FIG. 7), the lower the transfer efficiency. Further, FIG. 8 shows the relationship between the DC bias and the amount of charged charge when the AC current is kept constant, and it can be seen that by controlling the DC bias, it is possible to control the amount of charge on the toner image to an appropriate value. Therefore, when the tribo value is higher than a preset reference value, the charging current 15f is controlled so that the DC bias of the exposure charger 12 is decreased, and when it is low, the charging current 15f is controlled so that the DC bias is increased. As a result, the amount of charge on the toner image becomes an appropriate value. That is, the exposure charger 12 is located between the developing device 7 and a transfer device (not shown), and includes an AC corotron 12a and a static elimination lamp 12b, and a DC bias 12c is applied to the AC corotron 12a. The toner image now developed by the developing device 7 is transferred to the exposure charger 12.
When the voltage reaches 1, the surface potential of the toner image and the photoreceptor 6 is removed by the AC corotron 12a and the electricity removal lamp 12b, and at the same time, the surface potential of the toner image and the photoreceptor 6 is charged by the DC bias 12c. Since the DC bias 12c is controlled to have an appropriate value as described above, the amount of charge charged on the toner image by the exposure charger 12 is optimal. The above is the control operation of the exposure charger 12, but the control operation of the toner supply device is as follows. When the development weight M is calculated from the toner image density signal Vi,
This value is displayed on an appropriate display and at the same time is compared with a preset reference value in the microcomputer device 16. If it is lower than the reference value, the toner supply device 9 is turned on and toner is supplied, and If it is high, the toner supply device 9 is turned off and the supply of toner is stopped. As described in detail above, the present invention detects the toner density and toner charge amount from the toner image of the reference target exposed and developed on a part of the photoreceptor during copying, and compares and calculates this with a reference value stored in advance. The obtained control signal controls various control circuits simultaneously or individually according to a preset mode, and at the same time controls the DC bias current of the exposure charger installed between the developing device and the transfer device. Since the toner image has the optimum amount of charge,
A stable copy image can always be obtained without being affected by the environment in which the copying machine is installed or changes over time in each part of the copying machine, and the transfer efficiency is also significantly improved.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention, and Fig. 1 is an overall configuration diagram of the copying machine, Fig. 2 is an enlarged view of the area around the photoconductor, Fig. 3 is a block diagram of the control system, and Fig. 4 is the photoconductor. A diagram showing the transition of the body surface potential, Figure 5 is a diagram showing the relationship between the amount of toner adhesion and the output voltage of the reflection type densitometer that detects it, Figure 6 is a flowchart showing the operation, and Figure 7 8 is a diagram showing the relationship between the amount of charge of a toner image and transfer efficiency, and FIG. 8 is a diagram showing the relationship between the DC bias and the amount of charged charge. 3 is a reference target, 6 is a photoreceptor, 7 is a developer, 12 is an exposure charger, 12a is an AC corotron, and 12b is a static elimination lamp.

Claims (1)

[Scope of Claims] 1. Detecting the toner concentration and surface potential from the toner image of the reference target 3 formed on the surface of the photoreceptor 6, and comparing the calculation result of this detected value with a preset reference value, In a copying machine that controls each control section of the copying machine simultaneously or individually according to a preset mode using the obtained control signal, exposure charging is performed by applying a DC bias between the developing unit 7 and the transfer unit of the copying machine. The DC bias current of the exposure charger 12 is calculated from the toner concentration Vi detected from the toner image and the surface potential Vt using the following formula: Q _T =√Vt/A/Blog(1/Vi)μC/ g However, A and B are characterized in that a tribo value Q _T is calculated using a constant, this tribo value Q _T is compared with a preset reference value, and control is performed using the obtained value. How to control an electronic copying machine.