JPS63265253A - Electrophotographic device - Google Patents

Abstract

PURPOSE:To prevent scattering of a developer so that output of high printing quality is obtd. by setting a switching means at a connected state and starting development at the point of the time when the electrostatically charged part on a body to be electrostatically charged arrives at a developing device after the impression of a voltage to an electrostatic charge is started. CONSTITUTION:The voltage is impressed to a TTLIC 20 and the TTLIC 20 outputs an H level when the body 12 to be charged rotates in the direction shown by an arrow B and the charged part on the body 12 arrives at the developing device. A transistor 17 is, therefore, disconnected and a transistor 12 is decreased in the base current, by which the potential difference between the collector and the emitter is increased and the developing bias voltage is impressed to a sleeve electrode 11. The splashing of the developer is thereby prevented and the output of the high printing image is obtd.

Description

[Detailed description of the invention] Industrial applications The present invention relates to an electrophotographic apparatus.

Conventional technology There have been remarkable advances in electrophotographic equipment in recent years, but
Among these, a charged member is charged by corona discharge, and an electrostatic latent image is formed by scanning the charged member with a laser beam.
Particularly remarkable progress has been made in developing the electrostatic latent image by attaching a charged developer to it.

These types of electrophotographic devices require high voltage power supplies that generate several types of high voltages.

A high-voltage power supply device used in a conventional electrophotographic apparatus will be described below.

FIG. 2 is a circuit diagram of a main part of a conventional electrophotographic device, and 1
is an oscillator whose oscillation output current changes depending on the input voltage; 2 is a step-up transformer; 3 is a rectifier; 4 is a resistor that adjusts the output voltage of step-up transformer 2; 7 is a resistor that outputs the current used for corona discharge in the form of a voltage drop. 8 is a resistor that outputs the current used for corona discharge in the form of a voltage drop. The voltage drop obtained by the voltage drop of resistor 7 is compared with the reference voltage, and An amplifier that feeds back the output according to the difference to the oscillator 1, 9 is a discharge electrode, 1
0 is a shield plate surrounding the discharge electrode 9, and the discharge electrode 9 and the shield plate 10 constitute a charger. 11 is a sleeve electrode to which the developing bias voltage obtained by resistors 5 and 6 is applied, and the sleeve electrode 11 is connected to the developing device (
It is omitted in the figure. ). 12 is an object to be charged.

Regarding the conventional electrophotographic device configured as described above,
The operation will be explained below.

The current generated by the oscillator 1 is boosted by a step-up transformer 2 and rectified by a rectifier 3. Here, the voltage generated by the voltage drop across the resistor 7 is amplified by the amplifier 8 and fed back to the oscillator 1, and the current applied to the discharge electrode 9 is controlled to be constant.

By applying a high voltage to the discharge electrode 9, corona discharge occurs, and the object to be charged 12 is charged. Charged object 1
2 rotates in the direction shown by arrow A, and before the charged portion reaches the sleeve electrode 11, the charged member 12 is scanned with a laser beam and an electrostatic latent image is formed. Next, the charged object 1
When the portion where the electrostatic latent image No. 2 is formed reaches the position of the sleeve electrode 11, the developer is charged by the developing bias voltage of the sleeve electrode 11 (not shown in the figure). ) adheres to the electrostatic latent image, thereby performing development.

Problems to be Solved by the Invention However, in the conventional configuration described above, the voltage applied to the discharge electrode 9 and the developing sleeve voltage applied to the sleeve electrode 11 are generated simultaneously, so immediately after both voltages are generated simultaneously, Since the developing unit develops the areas on which the electrostatic latent image has not yet been formed, developer scatters and adheres to the paper, which is fixed and causes the paper to become dirty. This poses a problem in that the quality of the image is significantly degraded.

Means for Solving the Problems The present invention provides a voltage generating means for generating two types of constant voltages, a charger having a discharge electrode to which a first voltage is applied,
The developing device includes a developing device having a developing sleeve to which a second voltage is applied, and a switching means for applying the second voltage to the developing sleeve after the first voltage is applied to the discharge electrode.

Operation With the above configuration, after starting the application of voltage to the charger, when the charged portion on the object to be charged reaches the developing device, the switching means is connected to start development.

Embodiment FIG. 1 is a circuit diagram of main parts of an electrophotographic apparatus in an embodiment of the present invention, in which 1 is an oscillator, 2 is a booster, 3 is a rectifier,
4.5.6 and 7 are resistors, 8 is an amplifier, 9 is a discharge electrode,
Reference numeral 10 denotes a shield plate, 11 a sleeve electrode, and 12 a charged body.Since these have the same structure as the conventional example, they are given the same numbers and their explanation will be omitted. 13 is a PNP transistor that is mainly used in the active region and is used to open and short between the sleeve electrode 11 and the ground; 14, 15 and 16 are resistors that determine the voltage applied to the base of the transistor 13; 17 is a saturation region transistor 13
18.19 is a resistor that determines the bias voltage applied to the base of the transistor 17, and 20 is an oven collector type TTLIC (e.g. manufactured by Texas Instruments). 5N7407 etc.), TTL IC2
0, the output of the developing bias voltage is intermittent.

The operation of the electrophotographic apparatus of this embodiment configured as described above will be described below.

When oscillator 1 starts oscillating, oscillator 1 starts oscillating as in the conventional example.
The current generated is boosted by a step-up transformer 2 and rectified by a rectifier 3. A voltage is applied to the discharge electrode 9. At this time, OV (hereinafter referred to as L level) is applied to TTL IC20, TTL IC20 outputs L level, transistor 17 is in a connected state, and transistor 13 has a large base current. It is flowing,
The potential difference between the collector and emitter is small, and the sleeve electrode 1
1, no developing bias voltage is applied.

Next, the charged member 12 rotates in the direction shown by arrow B, and when the charged portion on the charged member 12 reaches the developing device, the TTL
IC201=+5V (hereinafter abbreviated as H level voltage).

) is applied, and the TTLIC 20 outputs an I (signal). Therefore, the transistor 17 becomes disconnected, the base current of the transistor 13 decreases, the potential difference between the collector and emitter increases, and the developing bias voltage is applied to the sleeve electrode 11. applied.

As explained above, according to this embodiment, after the charging is started, the developing sleeve voltage can be applied at the time when the charged portion on the charged object 12 reaches the developing device, so that the developer is scattered. This makes it possible to prevent paper from becoming smudged and to obtain output with high print quality.

Effects of the Invention The present invention includes a voltage generating means for generating two types of constant voltages, a charger having a discharge electrode to which a first voltage is applied,
The developing device includes a developing sleeve to which a second voltage is applied, and a switching means for applying the second voltage to the developing sleeve after the first voltage is applied to the discharge electrode. After starting the application of voltage to the object, when the charged portion on the object to be charged reaches the developing device, the switching means can be connected and development can be started, thereby preventing the developer from scattering. This allows for high print quality output without staining the paper.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a main part of an electrophotographic apparatus according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of a main part of a conventional electrophotographic apparatus. 1... Oscillator, 2... Step-up transformer, 3...
Rectifier, 4.5.6.7... Resistor, 8... Amplifier, 9... Discharge electrode, 10... Shield plate,
11...Sleeve electrode, 12...Charged object,
13...Transistor, 14.15.16...Resistor, 17...Transistor, 18.19...Resistor,
20...TTL I C.

Claims (1)

[Claims] a voltage generating means for generating two types of constant voltage; a charger having a discharge electrode connected to the voltage generating means and applying a first voltage to charge a charged object; and a charger connected to the voltage generating means. a developing device having a developing sleeve to which a second voltage is applied; and a switching means for applying the second voltage to the developing sleeve after the first voltage is applied to the discharge electrode. An electrophotographic device characterized by: