JP3240684B2 - Development bias power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing bias power supply for applying a bias voltage to a developing sleeve which faces a photosensitive member and supplies toner to the photosensitive member in an electrophotographic image forming apparatus such as a copying machine or a printer. About.

[0002]

2. Description of the Related Art Conventionally, as shown in FIGS. 6 and 7, in an image forming apparatus 100 of a reversal developing system, an outer peripheral surface of a photosensitive member 101 is charged to a predetermined voltage Vo, and an image forming area A on the photosensitive member 101 is charged. Between the image forming area A ′ of the next page and the image forming area A ′ of the next page, and the surface voltage of the image forming section B is Vo ′.
Has been lowered.

On the other hand, in a developing device 102 for supplying toner to the photosensitive member 101, a developing sleeve 103 facing the photosensitive member 101 is connected to a developing bias power supply 104, and the developing sleeve 103 is connected to image forming areas A and A '. When opposed, the developing sleeve 10 is
3 by applying a predetermined developing bias voltage V _B to prevent the toner adhesion to the image background section, when the developing sleeve 103 is opposed to the image between the portion B is off the output of the development bias power source 104 (developing bias voltage V _B ′ = OV) to prevent toner from adhering to the inter-image portion B.

[0004]

However, when the developing bias voltage V _B ′ is switched to OV only when the developing sleeve 103 faces the inter-image portion B, the photoreceptor 101 cannot be used.
The difference between the voltage of the developing sleeve 103 and that of the developing sleeve 103 was only Vo ′, which was insufficient to prevent toner from adhering to the inter-image portion B.

In particular, in a so-called contact transfer type image forming apparatus in which toner is transferred while nipping and transporting a transfer material between the photosensitive member 101 and a transfer roller pressed against the photosensitive member 101, when the toner adheres to the inter-image portion B, the toner is removed. Transferred to the transfer roller,
There has been a problem that the toner adhered to the transfer roller is transferred to the back surface of the transfer material and soils the transfer material.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and a method of adjusting the amount of toner supplied from a developing sleeve to a photoreceptor to a developing sleeve for supplying toner to the photoreceptor. In the developing bias power supply device for applying a bias voltage, a DC power supply is connected to a first voltage dividing resistor and a second
Grounding via a voltage-dividing resistor, connecting the output of the first voltage-dividing resistor to the developing sleeve, connecting a capacitor in parallel with the first voltage-dividing resistor, and connecting at least one of the photoconductor and the developing sleeve The control device turns on the output of the DC power supply for a predetermined time before one of them starts driving.

[0007]

In the above-described developing bias power supply device, the output of the DC power supply is turned on by the control device for a predetermined time before the photosensitive member or the developing sleeve starts rotating, and the developing sleeve is charged with the first power.
A developing bias voltage having a predetermined potential lowered by the voltage dividing resistor is applied, and the capacitor is charged with electric charge. When the DC power supply is turned off, a developing bias voltage of the opposite polarity is applied to the developing sleeve by the electric charge charged in the capacitor. Therefore, even when the photosensitive member or the developing sleeve rotates, a sufficient developing bias voltage is secured between the developing sleeve and the uncharged region on the photosensitive member, that is, the region from the charged position to the developing position, and the uncharged region No toner adheres to the surface.

[0008]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a schematic configuration of an image forming unit in the image forming apparatus. The photoconductor 1 has a photoconductor layer on the outer periphery, and is driven to rotate in a direction of an arrow a by a main motor 20. The charging device 2 charges the outer peripheral photoconductor layer of the photoconductor 1 to a predetermined voltage (Vo) at a charging position X. The laser optical unit 3 exposes the charged photoreceptor 1 to a laser beam to form an electrostatic latent image in the image forming areas A and A 'and attenuates the voltage of the inter-image portion B. The developing device 4 is to supply toner to the electrostatic latent image on the photosensitive member 1 at the developing position Y, the developing sleeve 4a opposed to the photosensitive member 1 is a predetermined developing bias voltage V _B from the developing bias power supply 10 Is applied. The transfer roller 5 is in pressure contact with the photoconductor 1 at the transfer position Z, and is rotated by the rotation of the photoconductor 1. The cleaning device 6 collects untransferred toner and the like from the photoconductor 1.

The developing bias power supply device 10 has a DC bias power supply 11 as shown in FIG. 2, and an output section T ₁ of the DC bias power supply 11 has a Zener diode 12, a diode 13, and a first voltage dividing resistor. and through the second minute resistor 14 is pressure resistance is grounded to the earth 15, the output portion T ₂ of the Zener diode 12 is connected to the developing sleeve 4a. A capacitor 16 is connected in parallel with the Zener diode 12.

In the image forming apparatus having the above-described configuration, the photosensitive member 1 rotates in the direction of the arrow a based on the driving of the main motor 20, and the outer peripheral photosensitive member layer is charged by the charging device 2 at the charging position X with a predetermined voltage (Vo = After being charged to (−500 V), an electrostatic latent image is formed in the image forming areas A and A ′ by laser exposure of the laser optical unit 3, and the voltage of the inter-image part B is attenuated to a predetermined voltage. The electrostatic latent image is visualized as a toner image by supplying toner having a negative charge from the developing sleeve 4a of the developing device 4 at the developing position Y. The toner image is transferred to a transfer material (not shown) which is nipped and conveyed by the photoconductor 1 and the transfer roller 5 at a transfer position Z. The transfer material to which the toner image has been transferred is discharged to a predetermined paper discharge unit (not shown) after the toner is fixed by a fixing device (not shown). On the other hand, the cleaning device 6 removes residual toner and the like from the photoconductor 1 that has passed the transfer position Z.

In the developing bias power supply 10, when a print start signal is input, as shown in FIG.
The controller supplies a developing bias remote signal to the developing bias power supply 11. When the development bias power source 11 is subjected to the developing bias remote signal, from the output portion T ₁ -
Outputs 450V DC. The output voltage (−450
V) is dropped by the Zener diode 12, and a developing bias voltage V _B1 of −300 V is applied to the developing sleeve 4a. The capacitor 16 is charged with electric charge until a voltage equal to the potential difference 150 V across the Zener diode 12 is obtained.

When the developing bias remote signal is turned off, a +150 V reverse polarity developing bias voltage V _B1 ′ is applied to the developing sleeve 4a by the electric charge charged in the capacitor 16. The developing bias remote signal may be turned off before the driving of the main motor 20 starts, or may be turned off at the same timing as when the driving of the main motor 20 starts.

Next, the charging bias remote signal is turned on at the same time when the main motor 20 is turned on, and the charging position X
Is charged to Vo = −500V.
However, the region from the charging position X to the developing position Y (uncharged portion C) is not charged. Therefore, the uncharged portion C, that is, the region of the voltage OV first advances to the developing position Y. However, the reverse polarity developing bias voltage V _B1 ′ = + 150 V is applied to the developing sleeve 4a, and the photosensitive member 1 in the uncharged portion C is-with respect to the developing sleeve 4a.
It is 150 V low potential. Therefore, the negatively charged toner held on the developing sleeve 4 a is electrically repelled from the photoconductor 1 and does not adhere to the uncharged portion of the photoconductor 1.

The charge stored in the capacitor 16 is prevented from leaking by the Zener diode 12 and the diode 13. When the developing bias power supply 11 is turned off, the voltage of the developing sleeve 4a gradually decreases, but its time constant is sufficiently long. Therefore, in preventing the toner from adhering to the photoreceptor 1, the leakage or attenuation of the electric charge does not matter.

When the uncharged portion C of the photosensitive member 1 passes through the developing position Y, and the charged portion (image forming area) A newly charged to Vo = -500 V by the charging device 2 reaches the developing position Y, The developing bias remote signal is turned on, and a developing bias voltage V _B2 = −300 V is applied to the developing sleeve 4a. As a result, the toner adheres to the image printing portion and prevents the toner from adhering to the image background portion. While the developing bias remote signal is on, the capacitor 16 is charged.

When the image forming area A passes the developing position Y and the inter-image portion B between the image forming area A and the image forming area A 'of the next page reaches the developing position Y, the developing bias remote signal is turned off. Is done. As a result, the charge stored in the capacitor 16 causes V _B2 ′ = +
A developing bias voltage of 150 V is applied. On the other hand, the inter-image portion B of the photoreceptor 1 has Vo ′ = − 100 V by laser exposure.
Has declined. Therefore, the inter-image portion B of the photoconductor 1 has a lower potential of -250 V relative to the developing sleeve 4a, and the negatively charged toner held on the developing sleeve 4a does not adhere to the photoconductor inter-image portion B. Absent.

When the inter-image portion B passes the developing position Y and the image forming area A 'of the next page reaches the developing position Y, the developing bias remote signal is turned on as in the case of the image forming area A. Then, the developing bias voltage _VB2 is switched to -300 V, so that toner adheres to the image printing portion and toner adherence to the image background portion is prevented.

In the above embodiment, the case where the Zener diode 12 is used as the first voltage dividing resistor has been described. However, as shown in FIG. 4, a resistor 17 may be provided instead of the Zener diode 12, or a diode 17 may be provided. 13 is not always necessary. In this case, as in the above-described embodiment, while the developing bias remote signal is on, predetermined developing biases V _B1 and V _B2 are applied to the developing sleeve 4a. While the developing bias remote signal is off, the developing sleeve 4a has a developing bias voltage V of the opposite polarity.
_B1 'and _VB2 ' are applied. Further, the time constant is sufficiently long, and the attenuation of the developing bias voltages V _B1 ′ and V _B2 ′ when the developing bias signal is off does not matter.

Although the developing bias voltages V _B1 and V _B2 before and after the main motor 20 is turned on are set to be the same, they need not be the same. However, the developing bias voltage V _B1
Is too high compared to V _B2 , the toner flies to and adheres to the photosensitive member 1 before and after the contact portion between the developer and the photosensitive member 1, and conversely, the developing bias voltage V _B1 is too low compared to V _B2 . Thus, there is a disadvantage that charging of the capacitor 16 takes a long time, and the charging standby time becomes long. Therefore, it is necessary to determine the developing bias voltage V _B1 in consideration of these points.

In order to make the developing bias voltages V _B1 and V _B2 different, a D / A converter 19 is provided between the control device 18 and the developing bias power supply 11 as shown in FIG. An output voltage adjustment signal is output to the / A converter 19, and the output of the power supply 11 is changed based on this signal.

Further, the off timing of the developing bias remote signal is determined based on the start of driving of the main motor 20. However, based on the start of driving of the developing sleeve 4a, at this time or before this time. The developing bias remote signal may be turned off. However, it is necessary to turn off the remote signal of the developing bias voltage V _B1 before the toner on the developing sleeve 4a relatively moves with respect to the photoconductor 1 due to the rotation of the photoconductor 1 or the developing sleeve 4a.

[0022]

As is apparent from the above description, according to the developing bias power supply of the present invention, the capacitor is charged before the developing sleeve or the photosensitive member starts rotating, and the developing sleeve or the photosensitive member is charged. Since the developing bias voltage of the opposite polarity has already been applied to the developing sleeve at the start of the rotation of the developing roller, even if the uncharged photoconductor from the charging position to the developing position passes through the developing device, the developing of the opposite polarity is performed. The toner does not adhere to the uncharged portion due to the bias.

Also, when the inter-image portion on the photoreceptor passes the developing position, if the developing bias power supply is turned off, a developing bias voltage of the opposite polarity is applied to the developing sleeve from the capacitor. A sufficient voltage is ensured between the sleeve and the sleeve, and toner adhesion to the inter-image portion is reliably prevented.

Further, there is no need for a developing bias power supply capable of outputting positive and negative polarities and a mechanism for switching the output.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image creating unit in an image forming apparatus.

FIG. 2 is a circuit diagram of a developing bias power supply device.

FIG. 3 is a diagram showing a relationship between a time chart of a developing bias remote signal and the like, a photosensitive member surface voltage passing through a developing position, and a developing bias voltage.

FIG. 4 is a circuit diagram of another embodiment of the developing bias power supply device.

FIG. 5 is a partial circuit diagram of another embodiment of the developing bias power supply device.

FIG. 6 is a circuit diagram of a conventional developing bias power supply device.

FIG. 7 is a diagram showing a relationship between a photosensitive member surface voltage and a developing bias voltage by a conventional developing bias power supply device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photoreceptor, 2 ... Charging device, 4 ... Developing device, 4a ... Developing sleeve, 5 ... Transfer roller, 10 ... Developing bias power supply, 11 ... Developing bias power supply, 12 ... Zener diode (first voltage dividing resistor), 14: resistance (second voltage dividing resistance), 16
... capacitors.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hitoshi Saito Osaka International Building Minolta Camera Co., Ltd. 2-3-13 Azuchicho, Chuo-ku, Osaka-shi, Osaka (72) Inventor Koji Uno Azuchi, Chuo-ku, Osaka-shi, Osaka 2-3-3, Osaka-cho, Osaka International Building Minolta Camera Co., Ltd. In-house (56) References JP-A-54-37742 (JP, A) JP-A-62-148982 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) G03G 15/06 101 G03G 21/14 G03G 15/00 303

Claims (1)

(57) [Claims] 1. A developing bias power supply device for applying a bias voltage to a developing sleeve for supplying toner to a photoconductor to adjust a toner supply amount from the developing sleeve to the photoconductor. , Grounding via a second voltage-dividing resistor, connecting the output of the first voltage-dividing resistor to the developing sleeve, connecting a capacitor in parallel with the first voltage-dividing resistor, A developing bias power supply device wherein an output of the DC power supply is turned on by a control device for a predetermined time before at least one of the driving starts.