JPS645300B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developer concentration control method, and more particularly, to a developer concentration control method that makes it possible to maintain a stable and good developer concentration.

Conventionally, as a developing method for developing an electrostatic latent image formed by electrophotography or the like, a magnetic brush method, a cascade method, etc. using a two-component developer having a toner and a carrier are widely known.

Toner is gradually consumed during development depending on the type and number of originals, and the toner concentration in the developer, that is, the developer concentration, gradually decreases, so it is necessary to replenish toner appropriately. If it is too dark,
This may cause the obtained image density to be too high or cause fogging. Therefore, in order to continuously obtain good images, the mixing ratio of toner and carrier must always be kept constant.

For this reason, conventionally, a fixed amount replenishment method was used in which a fixed amount of toner was replenished into the developing device each copy cycle if the density was insufficient, or the developer concentration in the developing device was detected and the toner replenishment amount was adjusted according to the change. It was an ad hoc replenishment system that adjusted and replenished the amount.

In the case of the former method, since toner consumption changes during the copy cycle, the concentration of supplied developer inevitably tends to fluctuate significantly. Particularly in the case of color reproduction, density changes disrupt color balance and are extremely inconvenient.

On the other hand, in the latter method, toner is replenished in accordance with the change in consumption amount, so that no large change in density occurs, but due to the delay in tracking, the developer density tends to remain constant at a low level.

The present invention has been made in view of the above points, and provides a new and excellent developer concentration control method.

The present invention provides a developer concentration control method for controlling the developer concentration in a developing device to a predetermined concentration, in which the amount K.(Cs -Cx) (K is proportionality constant)
and the predetermined reference amount B {B+K・
(Cs-Cx)} is supplied to a developing device.

Hereinafter, details of the present invention will be explained using specific examples with reference to the drawings.

First, in order to facilitate understanding of the present invention, specific examples will be used to explain density changes with respect to the number of copies in the two conventional methods.

Figure 1 a and b are for the case of fixed amount replenishment method.
This is a computer simulation.

As a condition, The developer concentration detection error is assumed to be 0.

There is a delay of 10 copies before the replenished developer is detected.

The toner consumption amount A per copy is set to 0 to 0.8 gr as a guideline for variation during color reproduction.

The standard density is 10%, and if it is darker than that, it is not replenished, and if it is lighter than that, a certain amount B (gr) is replenished for each copy.

The initial concentration of the developer matches the reference concentration, and the carrier amount V is 900 gr. Replenishment developer is toner
Set as 100%.

In Figure 1a, the supply amount per copy is 0.2gr.
FIG. 2 is a schematic diagram showing cases where the toner consumption amount A is 0.1gr, 0.2gr, 0.4gr, and 0.8gr.

At toner consumption A (0.1gr), there is a gradual increase, and at A (0.2gr), the toner remains balanced and constant, but beyond that, addition cannot catch up with consumption and the density decreases. In addition, Figure 1b shows the case where the supply amount per copy is 0.8gr, and it does not monotonically decrease, but when A = 0.1gr, the supply amount increases every time 10 copies are made.
It has changed by 0.8%. That is, in the quantitative replenishment method as in the above example, fluctuations in developer concentration are likely to occur.

FIGS. 2a and 2b show the case of an occasional replenishment method, in which an amount K (Cs-Cx) gr is replenished in proportion to the difference between the developer concentration (Cx%) and the reference concentration (Cs%). K is a proportionality constant and is the percent concentration in g/sheet. Also, K is the detection gain α (V/% concentration) of the detector.
Ratio of replenishment time to density difference S (V/sec) If the replenishment amount of developer per unit time is β (g/rec), then K=αβ/S.

Other simulation conditions are the same as in the first illustrated method. Figure 2 a is for K=0.4,
There is no up and down fluctuation in the density, but as the toner consumption increases, the developer density decreases and becomes balanced. FIG. 2b shows the case where K=2.0, and in this case, fluctuations of vertical fluctuation occur.

Such fluctuations are also inconvenient, especially in color reproduction.

In the case where Fig. 3 a and b are based on the method of the present invention, the predetermined amount B and the amount K (Cs - Cx) proportional to the concentration difference
It supplies the total amount of

Figure 3a shows the case where B=0.4, K=0.4, and the third
Figure b shows the case where B=0.6 and K=0.2. In either case, stable concentration control was achieved without large fluctuations.

FIG. 4 is an explanatory diagram of a developing device to which a specific example density control device based on the present invention is applied. Developing device 1
is a fixed magnet 2 using magnetic brush method.
The developer T is supplied onto the photoreceptor drum 4 by the sleeve 3 rotating around the sleeve 3, and the electrostatic latent image on the photoreceptor is developed and visualized. In the developer T, for example, the carrier is reduced iron powder, and the toner is a mixture of resin, dye and pigment, and the main component is a mixture pulverized to about 10 μm.

The developer concentration is detected by a reflection density detector 5 by receiving reflected light from a lamp 6 with a light receiving element 7 such as a photodiode. When receiving this light, it is preferable to use a near-infrared filter that transmits light with a wavelength longer than 740 nm. The detected concentration is converted into a predetermined control signal by the detection control circuit 8 and drives the replenishment motor 9. The motor 9 rotates a worm gear and drives a conveying screw provided at the bottom of the toner hopper 12 to supply a predetermined amount of toner into the developing device. FIG. 5 is a perspective view illustrating further details of the reflection density detector 5 portion.
A chopper 14 that opens and closes a bottom opening 13 ₁ of the detector casing 13 is locked by a support shaft 14 ₁ and controlled to open and close by an electromagnet 15 . That is, while the developing device is in operation, the electromagnet 15 is excited, attracts the chopper 14, and removes the chopper 14 from the opening. At this time, the light from the lamp 6 hits the developer through the aperture, is reflected, and enters the photodiode 7. On the other hand, when the developing device is not operating, the electromagnet 15
is de-energized and the chopper 14 covers the opening. The back surface of the chopper 14 is coated with a developer standard concentration, and this standard concentration light is incident on the light receiving element 7.

FIG. 6 is a specific example circuit diagram of the above-mentioned comparison control circuit 8 of the present invention. Light receiving element 7 such as a photodiode
The input light is photoelectrically converted and amplified by amplifiers 16 and 17. The output of amplifier 17 is divided into two parts, one of which is directly connected to the input terminal of amplifier 18. The other starts charging the capacitor C ₁ via VR ₃ and R ₃ diode D ₁ . The timers C ₂ and R ₂ are activated by the developing device operation signal S _D , and TR is turned on after a predetermined time delay. This allows the capacitor to
C ₁ discharges. FIG. 7 is a flowchart illustrating the operating state before and after the amplifier 18 of the control circuit. S _D is the signal from the developer S _A is on the A terminal side,
S _B is on the B terminal side. The B terminal side input is as described above.
Due to the timer action of C ₂ R ₂ , the transistor TR turns on after a delay of t ₁ , and the capacitor C ₁ starts discharging. In this way, until the thresholds of the B terminal and the A terminal match, the output signal remains on and toner is supplied to the developing device. And A, B
When the terminal voltages match, toner supply is turned off. Thus, the timer
The reference amount determined by C ₂ , R ₂ and the capacitor C ₁
This means that the toner can be supplied satisfactorily by the replenishment amount determined by the variable resistor _VR2 .

In a developing device that accommodates 1000 g of developer with a developer concentration of 10% (weight), B is 0.2≦B≦0.7, and K is
0.2≦K≦0.9 was suitable. Incidentally, if the carrier amount is V and the toner amount is Tx, the developer concentration Cx is as follows: Cx=tx/V+tx×100≒tx/V×100 =100/V×{t-A+B+K(Cs-C)} Therefore, any capacity can be converted sufficiently.

As described above in detail in the specific examples, the present invention is excellent in that the developer concentration can be easily maintained at a good level.

[Brief explanation of the drawing]

Figures 1a and b are schematic diagrams illustrating the conventional quantitative replenishment system, Figure 2 a and b are schematic diagrams illustrating the conventional occasional replenishment system, and Figure 3 a and b are diagrams based on the method of the present invention. 4 is an explanatory diagram of a developing device to which a specific example device of the present invention is applied, FIG. 5 is a perspective view of a reflection density detector, FIG. 6 is a comparative control circuit diagram of a specific example,
FIG. 7 is an explanatory diagram of amplifier operation. In the figure, 1...Developing device, 2...Fixed magnet, 3...Rotating sleeve, 4...Photosensitive drum (image carrier), 5...Reflection density detector, 6...Lamp, 7...Light receiving element.

Claims (1)

[Claims] 1. In a developer concentration control method for controlling the developer concentration in a developing device to a predetermined concentration, an amount proportional to the difference between a reference developer concentration Cs and a detected developer concentration Cx in the developing device. K・(Cs−Cx)(K
is a proportionality constant) and a predetermined reference amount B (B+K.(Cs-Cx)).