JPS6236229B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a static eliminator for an electrophotographic copying machine.

When cleaning the toner remaining after the development and transfer of an electrophotographic copying machine that has each process of charging, exposure, development, transfer, and cleaning, the residual electrostatic charge on the drum is removed to improve the effectiveness of this toner cleaning. There is a need to. For this purpose, neutralization is carried out by applying a charge having a polarity opposite to that of the residual charge.

Conventionally, static elimination in this type of device has been performed using AC current.

FIGS. 1 and 2 show equivalent circuits when the residual charge is positive and when the instantaneous value of the static eliminating AC voltage is positive and negative, respectively. E _r is the potential due to residual charge on the drum surface (residual potential),
Z _g is the impedance due to the gap between the discharge electrode and the drum surface, and E is the high voltage for static elimination.

FIG. 3 shows the static elimination current flowing to the drum when there are relatively many positive residual charges and the residual potential is high, and FIG. 4 shows the static elimination current when the positive residual potential is low.

As is clear from these figures, when the residual potential is positive, the larger the residual charge, the larger the negative drum current i, and the smaller the residual charge, the smaller the negative drum current i. In other words, by passing the static eliminating AC current, charges are applied depending on the magnitude of the charges on the drum, and are immediately neutralized.

In this case, in order to completely eliminate static electricity even in the worst case, for example, when the drum is not exposed to light after being charged, a sufficient current for neutralizing the static electricity must flow during the static elimination process to neutralize the highest possible residual potential. The static elimination voltage must be determined so as to obtain the desired voltage. For example, when the maximum residual potential is 1500V, the specified static electricity removal time is
If it is 350ms, the effective value of current for current removal is 200μ
A is selected, and its static elimination curve is as shown in FIG.

As mentioned above, if the static electricity removal current is set to match the worst-case situation, static electricity will be removed reliably, but when normal exposure is performed and there is little residual charge, the static electricity removal current will become larger than necessary. , resulting in the disadvantage of accelerating drum deterioration.

To avoid this, conventionally the highest residual potential was
Even when approximately 1500V was expected, it was common to set the static elimination voltage to 5 to 600V from a practical standpoint. Therefore, it is clear that if the residual potential exceeds this value, it is not possible to completely eliminate static electricity, which causes new drawbacks such as fogging and staining on the reproduced image and requiring frequent maintenance services. It was happening.

By the way, if we consider the magnitude of the static elimination current in the positive and negative directions when the static elimination voltage is constant, (1) If there is no residual charge on the drum, the current will gradually flow in the same way in both the positive and negative directions. , (2) It can be seen that as the positive residual charge on the drum increases, the positive direction current during charge removal decreases and the negative direction current increases.
Furthermore, from this, (3) if the static electricity removal current is changed so that the magnitude of the static electricity removal current in the positive direction is constant, the more the residual charge on the drum increases (that is, the higher the residual potential) It can be seen that the static elimination current in the negative direction increases, and the static elimination ability increases.

The present invention has been made based on the above consideration, and detects only the half wave of the drum current during static elimination, i.e., i _p in Figs. It was designed to be supplied as a.

FIG. 6 is a block diagram of one embodiment of the present invention.
2 is a drum of an electrophotographic copying machine, 2 is a corotron for static elimination, 3 is a high voltage source that applies an AC high voltage to the corotron, and 4 is a drum that applies only the half-wave component (forward current in the illustrated example) of the drum current during static elimination. A half-wave current detection section 5 is a control section that controls the output voltage of the high voltage source 3 according to the output of the detection section 4.
When the residual charge on the drum 1 is zero, the control section 5 causes a specified current to be removed, and even when the residual charge increases, the value of the half-wave current component detected by the half-wave current detection section 4 (for example, the effective The output voltage of the high voltage source 3 is controlled so that the current value) is maintained at a substantially constant value (specified static elimination current value).

With the above structure, according to the present invention, the more residual charges on the drum 1, the higher the static elimination current becomes, and accordingly, the negative direction current eliminates the current. The static elimination ability around the area is increased. In other words, the amount of static electricity removed at the beginning of the static elimination process increases, and the static elimination curve becomes as shown in Figure 7.Even if the residual voltage fluctuates, complete static elimination can always be achieved, and the drum deteriorates due to excessive voltage application. can also be prevented. As is clear from this figure, according to the present invention, when the specified static elimination current is kept constant, the time required for static elimination is shortened, so the rotation of the drum can be accelerated; By doing so, it is possible to reduce the current for removing static electricity and prevent deterioration of the drum.

According to the inventor's experiments, when the static electricity removal time is constant, the static electricity removal current is 100 to 150 μA, compared to the conventional 200 μA.
Even if the current was reduced to 1/2 to 1/3 μA, sufficient static electricity removal could be achieved. Further, in the present invention, since a positive half-wave current is detected, there is an advantage that the control circuit is stable and resistant to disturbances.

FIG. 8 is an example of a circuit embodying the present invention, in which L _h is a high voltage coil, L _c is a control coil, I _d is a drum current, I _s is a shield current, and V _h
is a high voltage output. The current flowing into the drum side due to high voltage becomes drum current _Id and enters the detection section.
It is smoothed and converted into DC. The difference between the detected voltage and the reference voltage _Vz is amplified and applied to the control transistor _Tr1 . This detected amount defines the current flowing through the control coil L _c and controls the output of the high voltage coil L _h . The transformer used here is called a constant voltage/constant current transformer, and the control amount and high voltage output amount operate in opposition to each other.

In the above, an example has been shown in which the drum is positively charged and the positive half-wave of the static elimination current is detected and controlled, but it is clear that the present invention can also be applied when the polarity is reversed. .

[Brief explanation of the drawing]

Figures 1 and 2 are equivalent circuit diagrams for static eliminator, Figures 3 and 4
The figure shows their waveforms, Figure 5 shows an example of a static elimination curve by a conventional device, Figure 6 is a block diagram of an embodiment of the present invention, and Figure 7 shows an example of a static elimination curve by the present invention. The figure shown in FIG. 8 is a diagram of an example of a circuit that further embodies the present invention. DESCRIPTION OF SYMBOLS 1... Drum, 2... Corotron for static elimination, 3... High voltage source, 4... Half-wave current detection part, 5... Control part.

Claims (1)

[Scope of Claims] 1. In a static eliminator for an electronic copying machine having each of the steps of charging, exposure, development, transfer, and cleaning, means for applying an AC high voltage to a static eliminator disposed opposite to a photosensitive drum; means for detecting only a predetermined half-wave component of the AC drum current during static neutralization; A static eliminator for an electronic copying machine, comprising correspondingly means for controlling the amplitude of the AC high voltage.