JPS60220381A - Destaticizing device - Google Patents

Abstract

PURPOSE:To flow a large current without causing the falling of a thundervolt to attain a desirable separating capacity by shaping the waveform of an AC voltage impressed to a conductor so that the period when the voltage is equal to a maximum voltage and a minimum voltage practically exceeds 20% of each period of this AC voltage. CONSTITUTION:A prescribed DC high voltage is impressed to a transfer charger 14, and a toner image is transferred from a photosensitive drum 3 to a recording paper. A voltage where an AC voltage and a DC voltage are superposed is impressed to a wire 15a of a separating charger 15. When the recording paper passes this separating charger 15, corona discharging is generated between the wire 15a and the recording paper, and the electric charge on the recording paper is destaticized by the current of this corona discharging, and the attracton between the recording paper and the photosensitive drum 3 disappears, and therefore, the recording paper is separated from the photosensitive drum 3 naturally. High voltages impressed to an electrostatic charging charger 10, a developing device, the transfer charger 14, and the separating charger are outputted from a high voltage power supply unit 200. These voltages are impressed at prescribed timings respectively in accordance with indications from a copying process control unit 100.

Description

DETAILED DESCRIPTION OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for eliminating static electricity from a recording sheet or the like using an AC corona generator, such as in a separating section in a plain paper copying machine using an electrostatic recording method.

■Conventional technology In plain paper copying machines using electrostatic recording, an electrostatic latent image is formed on a photoreceptor, it is developed into a visible image using toner, and a recording sheet is fed onto the photoreceptor to make it visible. The visible image on the photoreceptor is transferred to the recording sheet by bringing the image and the recording sheet into close contact and performing a predetermined electrical process there, and then by performing a predetermined electrical process at a separating section. , the charge on the recording sheet is removed to eliminate the adhesion between the photoreceptor and the recording sheet, and the recording sheet to which the visible image has been transferred is separated from the photoreceptor.

Conventionally, in the static elimination process to separate the recording sheet from the photoconductor, a wire to which a sinusoidal AC high voltage is applied is placed close to the recording sheet to generate a corona discharge between the wire and the recording sheet. The static electricity is removed.

In order to improve separation performance, it is necessary to increase the amplitude of the AC high voltage applied to the wire to flow a corona current sufficient for static elimination. However, if the amplitude of the AC high voltage is increased too much, damage called lightning strikes will occur on the surface of the photoreceptor. This is a dielectric breakdown phenomenon caused by a temporarily applied high voltage (sine wave peak voltage). When lightning strikes, normal copying cannot occur in that area. Therefore, in conventional separation devices, separation is performed by applying a sinusoidal voltage of as large an amplitude as possible to prevent lightning strikes from occurring. However, if the amplitude of the AC voltage is reduced to prevent lightning strikes, the separation performance will deteriorate.

■Object of the Invention The object of the present invention is to sufficiently eliminate static electricity without causing lightning strikes, and to obtain preferable separation performance.

■Construction In order to perform sufficient static elimination, it is necessary to flow a substantially large corona current. Generally, the electrodes of this type of static eliminator have capacitive electrical characteristics. Therefore, the current begins to flow rapidly near the peak value of the AC voltage applied to the electrode, and then immediately decreases in an exponential curve. The effective value of the current in this case largely depends on the period during which the current flows.

Therefore, by lengthening the period during which the current flows, the effective value of the current can be increased. In the case of a conventional sine wave, the voltage begins to drop immediately after reaching its maximum value, so the period during which the current flows is relatively short. Therefore, for example, if the alternating current voltage applied to the electrodes is made into a rectangular waveform, the period during which the voltage is at its maximum value is longer, so the period during which the current flows is longer than when it is a sine wave. In this way, sufficient current can flow without increasing the amplitude of the alternating current voltage, so lightning strikes will not occur.

■Example Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1a shows the structure of one type of copying machine embodying the present invention, and FIG. 1b shows the structure of the drive system seen from the rear side of the apparatus shown in FIG. 1a.

The configuration of the apparatus will be explained with reference to FIG. 1a. 1 is a contact glass on which the original is placed. An optical scanning system 2 is provided below the contact glass 1, and an image of light reflected from the original is formed on the photoreceptor drum 3 via the optical scanning system 2.

The photoreceptor drum 3 rotates clockwise in FIG. 1a.

On the other hand, the paper feed system has two stages, with 4.5 paper cassettes.
The recording paper is fed by the paper feed roller 6 or 7 from the selected one. The fed paper passes between a registration roller 8 and a leading end bending roller 9 and is guided to the photosensitive drum 3.

As shown in FIG. 2, around the photoreceptor drum 3, there is a charger lO, an eraser 11. Developing device 12° Pre-transfer static elimination lamp 13. Transfer charger 142 Separation charger 1
51 separation claw 16. A fur brush I7, a static elimination lamp 18, etc. are arranged.

Explain the general copy process. The photosensitive drum 3 is
The surface is charged to a uniform high potential by the charger 10. When the photoreceptor drum 3 is irradiated with reflected light from the original, the surface potential changes depending on the intensity of the light, thereby forming an electrostatic latent image on the surface of the photoreceptor drum 3. When this electrostatic latent image passes through the developing device 12, toner adheres thereto according to its potential distribution and becomes visible. The fed recording paper is sent by registration rollers 8 at a predetermined timing according to the rotation of the photoreceptor drum 3, and overlaps the surface of the photoreceptor drum 3 on which the toner image is formed.

Thereafter, a predetermined DC high voltage is applied to the transfer charger 14, whereby the toner image is transferred from the photosensitive drum 3 to the recording paper side. In this state, the charges on the photoreceptor drum 3 and the charges on the recording paper attract each other, so that the recording paper is in close contact with the photoreceptor drum 3. A voltage obtained by superimposing an alternating current voltage and a direct current voltage, which will be described later, is applied to the wire 1.5a of the separate charger I5. When the recording paper passes through the separation charger 15, a corona discharge occurs between the wire 15a and the recording paper, and the charge on the recording paper is eliminated by this current.

When the charge on the recording paper is removed, the attraction force between the recording paper and the photoreceptor drum 3 disappears, so that the recording paper is naturally separated from the photoreceptor drum 3. The separated recording paper heads toward the conveyor belt I9. Then, the recording paper passes through a fixing roller 20 having a built-in heater and has the toner image fixed thereon, and then passes through a paper discharge roller 21 and heads toward a copy tray 22 .

Electric charger 10. Developing device 12. Transfer charger 14
The high voltage applied to the separate charger is output from the high voltage power supply unit 200. These voltages are applied at predetermined timings according to instructions from the copying process control unit 100.

Figure 3 shows 1 included in the high voltage power supply unit shown in Figure 2.
The configuration of the separate power supply unit is shown. This will be explained with reference to FIG. This separate power supply device is roughly divided into an AC power supply unit PWI and a DC power supply unit hPW2. First, the AC power supply unit PWI will be explained. Simply put, this unit is a DC/AC converter, and specifically, it is supplied with a DC voltage of 24V and outputs a rectangular wave-shaped AC high voltage having a peak value of about 5KV.

The oscillator OSCI outputs a short i-wave signal with a duty of 50% and a period of 2 m5 ec in this example. Therefore, the transistor Q3 constantly repeats on/off with a period of 2m5ec. Here, when the control signal 0N10FF is at a high level H, the transistor Q4 is turned on, and the DC power supply (
A current from T)C24V) flows to the primary side of the step-up transformer T1 via the transistor Q1.

This current has a rectangular waveform that turns on and off at a cycle of 2 m5ec. Therefore, a rectangular waveform AC voltage is generated in the two secondary windings of the transformer TI, which is boosted according to the winding ratio. A high voltage is developed in one secondary winding and a relatively low voltage is developed in the other secondary winding. The low voltage is applied to the amplifier AMP I after being rectified by the bridge diode BDI and smoothed to direct current.

The output signal from the amplifier @AMPI is transferred to transistor Q2.
is applied to When the voltage appearing on the secondary winding of the step-up transformer T1 is lower than a predetermined value, the voltage output from the amplifier AMPI becomes lower than the predetermined value, and the on-resistance of the transistor Q2 increases, thereby increasing the base potential of the transistor Q1. Therefore, the voltage drop within the transistor Ql becomes smaller, the voltage applied to the primary winding of the transformer T1 becomes higher, and the voltage on the secondary side rises to -. Also, if the voltage cursed on the secondary winding is higher than the specified value, the amplifier AMP]
The voltage output from the transistor Q2 becomes higher than a predetermined value, and the on-resistance of the transistor Q2 becomes smaller than a predetermined value. This lowers the base potential of the transistor Ql, so the voltage drop in the transistor Ql increases, and the primary winding of the transformer TI The voltage applied to the line decreases and the voltage on the secondary side decreases. In other words, the voltage (amplitude) applied to the secondary side of the transformer TI, that is, the output terminal, is automatically adjusted to a predetermined value.

The configuration and operation of DC power supply unit PW2 are mostly similar to AC power supply unit PW1, but differ in the following parts. Oscillator 03C2 outputs a sine wave signal.

Therefore, the voltage appearing on the secondary winding of transformer T2 is also a sine wave. Also, this sine wave voltage is applied to the diode DI,
It is full-wave rectified by D2 and output as a DC voltage.

This voltage is approximately 300v. This DC voltage and the AC voltage output from the AC power supply unit PWI are superimposed and applied to the wire 15a of the separate charger. The DC power supply unit PW2 uses an analog comparator OPI, but this operation is performed by the transistor Q2. of the AC power supply unit PWI. This is similar to a circuit made of a Zener diode ZDI or the like.

FIG. 4 shows the voltage vou7 applied to the wire 15a of the separate charger and the current IouL flowing therein.

Referring to FIG. 4, the current 1 ouL is equal to the voltage vout
It suddenly increases at the phase corresponding to the peak value of . Note that since the separate charger is capacitive, the current leads the voltage in phase. This peak current (region of γ) tends to increase as the period α during which the voltage Vout reaches its maximum value increases.

In other words, by increasing the ratio of the period α during which the voltage reaches its maximum value to the period β of the AC voltage, the current flowing through the separate charger I5 can be increased without increasing the amplitude, that is, without increasing the peak voltage. can do.

FIG. 5 shows the relationship between separation performance ΔIdc and α/β.

This is done while maintaining the quality of the copy image within an acceptable range.
It shows the current (voltage is constant) that can flow. In other words, when the applied AC voltage waveform is a rectangular wave, and in particular, as seen in FIG. 5, when α/β is greater than 0.2, a large current can flow, so that preferable separation can be achieved.

In the case of a sine wave, the separation performance is low because α/β is close to 0.

It should be noted that there are two main reasons why the separating section degrades the quality of the copied image. One is a phenomenon in which marks of the separation claw 16 are left on the recording paper due to poor separation. The other is a so-called print image phenomenon, which is a transfer failure caused when toner transferred to the recording paper is retransferred to the photoreceptor drum due to excessive charge removal.

In the above embodiments, a rectangular wave is used as the AC power waveform, but the waveform may be converted by clipping the peak voltage portion of a sinusoidal waveform, for example.

(2) Effects of the Invention As described above, according to the present invention, a large current can be passed without causing a lightning strike and favorable separation performance can be obtained.

[Brief explanation of the drawing]

FIG. 1a is a front view showing the main parts of one type of copying machine embodying the present invention, and FIG. 1b is a rear view showing the drive system of the copying machine shown in FIG. 1a. FIG. 2 is a block diagram showing the vicinity of the photosensitive drum shown in FIG. 1a. FIG. 3 is a block diagram showing an electric circuit of a separate power supply device included in the high voltage power supply unit 200. FIG. 4 is a waveform diagram showing the output voltage and output current of the circuit shown in FIG. 3. FIG. 5 is a graph showing the relationship between the waveform of the voltage applied to the separation charger and separation performance. 3: Photosensitive drum IO: Charger 12: Developing device 14: Transfer charger I5: Separation charger 15a: Wire 16: Separation claw 200: High voltage power supply unit pwl: AC power supply unit PW2: DC power supply unit Patent applicant Ricoh Co., Ltd. 3A 4th■ 5th A%

Claims (2)

[Claims] (1) A conductor is placed close to the member to be neutralized, an AC voltage is applied to the conductor, and the difference between the conductor and the target Ml is removed. In a static eliminator that generates a discharge between the conductor and the conductor; the AC voltage applied to the conductor has a maximum voltage and a period where the voltage is substantially the same as the maximum voltage is 20 out of each cycle of the AC voltage.
A static eliminator characterized by having a waveform exceeding %. (2) The static eliminator according to claim 1, wherein the AC voltage applied to the conductor is a rectangular wave.