JPH049076A - Electrophotographic device - Google Patents

Abstract

PURPOSE:To prevent transfer of toner to a drum when abnormality is generated in a main electrifying device by changing over the potential impressed to a developing means from a specified developing bias to a non developing bias when current value fed to a grid is below a specified value. CONSTITUTION:Negative ion generated in a vicinity of a wire of the main charger 12 is captured by a grid 14, fed to the ground through a Zener diode 16 and a resistor R, and the potential between the diode 16 and the resistor R is compared with a specified reference potential EREF by a comparator 18. Then, a changeover switch 24 is controlled by the output of the comparator 18, when the main charger 12 is normally activated, the bias of a developing roll 22 is made EDEU, but when the current i fed to the grid 14 is smaller than the specified value fixed by the reference potential EREF, it is changed over to ENON side which is positive potential in a reverse direction. Thus, the negatively electrified toner is retained on the developing roll 22, and transfer of needless toner to the drum 20 can be prevented.

Description

[Detailed description of the invention] FIELD OF THE INVENTION The present invention relates to a device for dealing with an abnormality in a charger of an electrophotographic apparatus.

] Etc. lambda reform - In an electrophotographic device using a two-component reversal development method, the charger's 0N
The developing bias potential is switched between two states in synchronization with 10FF. That is, to explain the specific numerical value of the potential as an example, when the charger is turned on (at this time, the potential of the drum is -700V), the developing bias is set to -1500V.
(2) When the charger is set to FF (at this time, the potential of the drum is O), the developing bias is set to +100■ to prevent negatively charged toner from adhering to the drum during non-development.

Conventionally, as long as the main charger is in the ON state, the developing bias always remains at the value at the time of developing (in the above example, =500V).
). Therefore, if a problem occurs during the developing process, such as a charging device not being properly installed, a wire being disconnected, or a leak, toner may be transferred from the developing roller to the entire area of the drum, resulting in wasted toner, contamination inside the machine, or damage to the drum. Problems such as poor cleaning occurred.

The present invention solves these problems in an electrophotographic apparatus equipped with a scorotron charger, and provides an electrophotographic apparatus that can prevent toner from being transferred to the drum if an abnormality occurs in the main charger during development. The purpose is to provide.

In order to achieve the above object, the present invention provides a scorotron charger having a grid for controlling the surface potential of a photoreceptor, and a developer to which a predetermined development bias is applied for transferring toner to the photoreceptor. means for detecting a current flowing through the grid; means for generating a non-developing bias potential in the opposite direction to the toner charging potential; and when the current value is below a predetermined value, the developing It is characterized by comprising means for switching the potential applied to the means from the predetermined developing bias to a non-developing bias.

In an electrophotographic device, the photoreceptor is charged by applying a predetermined potential to the main charger during development, but in a scorotron developer, ions moving from the main charger to the photoreceptor are captured by a grid. This controls the charging potential. Conversely, while the photoreceptor is actually charged,
A certain amount of current should flow through the grid. Therefore,
The fact that the current flowing through the grid is less than a predetermined value (normal value) is considered to indicate that some abnormality has occurred in the main charger and the photoreceptor is not being charged normally. At this time, in order to prevent the wasteful transfer of toner to the photoreceptor as described above, the bias of the developing device is switched to a non-developing bias. As a result, when the main charger is abnormal, the toner is retained in the developing means and is not transferred to the photoreceptor.

Example 1 - FIG. 1 shows the configuration of an embodiment of an electrophotographic apparatus according to the present invention. Further, FIG. 2 shows a timing chart of the states of each part during operation.

When the start button (copy start button in a copying machine) of the electrophotographic apparatus is pressed (tO), the main motor is turned on, and the main charger 12 is also turned on. The wire of the main charger 12 has a high voltage unit (
A predetermined potential (-5 kV) is applied by the HVU 10, and the ions generated thereby charge the photoreceptor of the drum 20. A grid 14 placed between the wire of the main charger 12 and the photoreceptor is used to control the charging potential of the photoreceptor. Negative ions generated near the wire are captured by this grid 14, and the electrons are It flows through Zener diode 16 and resistor R to ground. The grid 14 is held at a predetermined potential (-700 .ANG.) by the Zener diode 16, and therefore the charging potential of the photoreceptor is also controlled to a value close to that value.

In this embodiment, the current flowing through the grid 14 is checked by comparing the potential between the diode 16 and the resistor R with a predetermined reference potential EREF by the comparator 18. When the current flowing through the grid 14 when the main charger 12 is operating normally is i, the reference potential EREF
is set to a value smaller than R-i.

At the same time as the main motor and main charger 12 are turned on, the developing bias generator is also turned on, and two types of developing biases EDELI (500V) and ENON (+10V) are turned on.
0V) is generated. E DELI is a bias used for normal development, and this bias causes negatively charged toner to be transferred from the developing roller 22 to the drum 20.

E NON is a bias for preventing toner from being transferred to the drum 20, and is set to a positive value to retain negatively charged toner. At the time (tl) when the exposed portion of the drum 20 reaches the developing roller 22, a developing bias EIII is applied to the developing roller 22. This results in
The toner on the developing roller 22 is transferred to the drum 20, and development is performed.

While developing in this way, main charger 1
2 (or HV U 10) and the normal potential (-5kV) is no longer applied to that wire, the amount of ions generated around the wire will decrease (or no ions will be generated), The current i flowing through the grid 14 becomes smaller (or becomes O) (t2)
. As a result, when the voltage R-1 decreases to below the reference potential E3, the output of the comparator 18 is inverted. The output of the comparator 18 controls the changeover switch 24, and when the main charger 12 is operating normally, the bias of the developing roller 22 is set to EocJ-500V), but the current i flowing through the grid 14 is set to the reference potential. E R
When I:F becomes smaller than a predetermined value (for example, 20 μA), the positive potential E N0N (+1
00V) side. As a result, the negatively charged toner is held on the developing roller 22'-, and wasteful transfer of toner to the drum 20 is prevented.

Note that the output of the comparator 16 may also be connected to an alarm device (lamp, buzzer, etc.) so that an alarm is issued to the user at the same time as the developing bias is switched.

Note that the values described in parentheses in the following explanation are merely examples, and the values may of course be different, or all signs may be reversed.

As explained above, according to the present invention, no matter what the cause is, such as improper installation of the main charger, disconnection, leakage, etc., the main charger (including the high voltage unit) is defective. If the photoreceptor is not charged normally, the bias applied to the developing means is switched to a non-developing bias (a bias that prevents toner from being transferred from the developing means to the photoreceptor). This eliminates unnecessary toner transfer to the photoreceptor, reducing toner waste and
Contamination inside the machine, poor cleaning, etc. can be prevented.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a timing chart of its operation.

Claims (1)

[Claims] (1) In an electrophotographic apparatus including a scorotron charger having a grid for controlling the surface potential of the photoreceptor, and a developing means to which a predetermined developing bias potential is applied for transferring toner to the photoreceptor, means for detecting a current flowing through the grid; means for generating a non-developing bias potential in a direction opposite to the charging potential of the toner; An electrophotographic apparatus comprising: means for switching from to non-developing bias to non-developing bias.