JPH07120102B2 - Image forming device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image forming apparatus for developing an electrostatic latent image formed on a photoconductor as a toner image by a contact type reversal development process.

Prior Art Fourth example of a schematic mechanism of a conventional image forming unit of an image forming apparatus such as a laser beam printer or a facsimile, in which development is carried out by a contact type reversal development process using high resistance toner.
Shown in the figure.

Around the photoconductor drum 1, a charging charger 2, an exposure system 3, a developing device 4, in the order of the rotation direction shown by an arrow,
The transfer charger 5 is provided, and the charging charger 2 is provided.
Is formed as a scorotron, a grid potential is applied to the grid electrode 6 by a grid potential control power source 7, and a scorotron casing electrode 8 is grounded.
A high voltage is applied to the scorotron charger wire 9 from a high voltage power source 10 for charging.

The base conductor 11 of the photosensitive drum 1 is armed.
The developing roller center conductor 12 of the developing device 4 can apply a developing bias to the developing bias power source 13.
The transfer charger 5 is configured as a corotron, its casing electrode 18 is grounded, and high voltage is applied to the charger wire 14 by the transfer high voltage power supply 15.

In the image forming apparatus having the above structure, when the photosensitive drum 1 starts moving in the direction of the arrow for image formation, the surface 16 of the photosensitive drum 1
The surface potential of the photosensitive member in the area A between the portion facing the charger 2 and the portion facing the developing roller 17 of the developing device 4 is approximately zero volt.

By the way, in the reversal development process, the polarity of the developing roller bias voltage is set in such a direction as to promote development during development. Therefore, the bias power source 13 is provided until the area A passes through the developing area at the contact portion with the toner layer on the developing roller 17 and the surface of the photoconductor (image forming area) charged by the charging charger 2 reaches the developing area. Therefore, it is necessary to prevent the toner from adhering to the area A on the photoconductor and being developed into a solid black image by causing the developing roller bias voltage to have a reverse polarity so that the toner is unnecessarily consumed. FIG. 5 shows the relationship between the developing bias output voltage and the toner adhesion amount to the area A in that case. In the figure, the voltage of 50 V at the point where the curve intersects the horizontal axis corresponds to the development start voltage as a process. As described above, while the area A on the photoconductor passes through the developing area, the developing roller bias voltage is set to the opposite polarity to suppress the toner consumption, increase the number of toner replenishment, transfer unit 5 and cleaning unit ( Although problems such as shortening the life of (not shown) can be avoided, in order to switch the polarity of the developing roller bias between normal and reverse, the bias power supply 13 shown in FIG. A timing circuit is required to switch the bias voltage to the opposite polarity when the area A on the photoconductor has finished passing through the development area from the start of movement of the body, which has a drawback that the configuration becomes complicated and the cost becomes high. .

SUMMARY OF THE INVENTION In view of the above-mentioned drawbacks of the conventional image forming apparatus using the contact reversal developing process, the present invention has a simple structure and after the photoreceptor starts moving for image formation, the image forming area reaches the developing area. SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of avoiding the above-mentioned inconvenience caused by the area A of FIG.

To achieve the above object, the present invention provides a potential shift voltage generator between a photoreceptor base conductor and an image forming apparatus main body grounding section in an image forming apparatus using a contact reversal process. And the potential shift voltage generator is capable of applying a voltage to the photoreceptor base conductor potential in the development blocking direction with respect to the apparatus main body ground potential.

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a drawing in which the present invention is applied to the image forming apparatus described in FIG. Therefore, the same members as those in the apparatus shown in FIG. 4 will be described with the same reference numerals.

The difference from the conventional device of this embodiment is that at least the conductive base conductor 11 of the photoconductor 1 and the ground of the entire device are
In addition to providing the potential shift voltage generating section 20, the developing bias power source 13 is provided with both polarities and is not provided with a forward / reverse switching and timing circuit, but is simply configured to have an on / off switching circuit. There is no difference from the device.

The potential shift voltage generation unit 20 is a high-voltage power supply system 10, 15
And the photosensitive system 1 from the apparatus main body grounding portion to the voltage generating portion 20
The generated voltage is shifted by the generated voltage. In the apparatus of this embodiment, in order to make the developing conditions the same as those in FIG. 4,
The output value of the developing bias power supply 13 is used as a potential shift voltage generator.
You only have to shift 20 outputs. The reason is that there is no change in the potential of the charger system based on the photoconductor base conductor 11. Therefore, it suffices to turn off the developing bias (zero volt) until the photosensitive member 1 starts moving, the area A passes through the developing area, and the image forming area arrives. There is no need to attach it.

FIG. 2 is a curve showing the toner adhesion amount to the area A with the output voltage of the potential shift voltage generator 20 as the horizontal axis and the toner adhesion amount on the developing roller 17 as a parameter. The three curves show that the toner adhesion amount on the developing roller is larger in the upper right portion. From these curves, it is understood that the output value of the potential shift voltage generator 20 may be set to a value larger than the value at which the toner adhesion amount to the area A becomes zero.

In another embodiment shown in FIG. 3, a voltage generating source for potential shift is used.
20 is a Zener diode, and most of the output of the charging charger 2 flows through the Zener diode to shift the potential. At the same time that the photoconductor 1 starts moving in the direction of the arrow, the charging high-voltage power supply 10 is turned on, and the charger casing 8, the grid 6,
The current to the photoconductor 1 flows into the Zener diode. In this embodiment, the output current of the charging high-voltage power supply 10 is -200μ.
A, the Zener voltage of the Zener diode 20 is 100V (for example, Ishizuka Denshi Z1100 is used), and the photoconductor base conductor potential is −100V with respect to the apparatus main body ground portion. Along with this, the photoconductor potential shifts by -100 V both in the exposed portion and the non-exposed portion compared with the case of the conventional apparatus shown in FIG.
As can be seen from the graph of FIG. 2, this value is a sufficient value to prevent the toner adhesion in the area A, and the toner adhesion amount to the area A of the photoconductor cannot be measured even in the result of the actual experiment ( 0.01 mg / cm ^{2 or} less).

In the embodiment shown in FIG. 3, since the power supply 15 of the charge wire 14 of the transfer charger 5 is grounded to the grounded portion of the main body, it is necessary to adjust the transfer current, but in the case of the embodiment shown in FIG. The isolated high-voltage power supply is unnecessary and safe. In the embodiment of FIG. 3 as well, as in the case of the embodiment of FIG. 1, it is necessary to shift the developing bias value by the output of the potential shift voltage generator 20 (-100V in this case).

In addition to the Zener diode, a varistor and a voltage generation circuit consisting of multiple parts can be considered as the configuration of the voltage generator for potential shift, but the shape, size, price, stability of characteristics, and low operational differential resistance. Therefore, the Zener diode is the best.

Further, since the surface potential of the photoconductor rises from the grounded part of the apparatus main body by the output of the voltage shift generation part, the cleaning performance against repulsion between the toner and the photoconductor is improved, and the transfer paper is suctioned and adhered to the photoconductor. As a result, secondary effects such as improvement in transfer performance can be obtained.

As described above, according to the present invention, in the image forming apparatus using the reversal development process, by applying the voltage of the same polarity as the toner polarity to the photoconductor, it is possible to generate the potential difference in the direction in which the development is blocked. Therefore, it is possible to suppress the toner adhesion to the portion in front of the image forming area at the start of movement of the photoconductor, without the need for a configuration for switching the polarity of the developing bias between normal and reverse.
This is effective in reducing the toner consumption.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the present invention, and FIG. 2 is a curve diagram showing the relationship between the output voltage of the potential shifting voltage generator and the toner adhesion amount to the front area of the image forming area of the photoconductor. 3 is a schematic diagram showing another embodiment of the present invention, FIG. 4 is a schematic diagram showing an example of a conventional image forming apparatus using a contact reversal development process, and FIG. 5 is a development bias in the development blocking direction. FIG. 5 is a curve diagram showing a relationship between an output voltage and a toner adhesion amount to a front area of a photoreceptor image forming area. 1 ... Photosensitive member 2 ... Charging charger 3 ... Exposure system 4 ... Developing device 5 ... Transfer charger 6 ... Charging charger grid electrode 7 ... Grid potential control power supply 8 ... Charging charger casing electrode 9 …… Charging charger wire 10 …… Charging high voltage power supply 11 …… Photoconductor base conductor 12 …… Developing roller center conductor 13 …… Development bias power supply 14 …… Transfer charger wire 15 …… Transfer high voltage power supply 17 …… Development roller 18 Transfer charger casing electrode 20 Potential shift voltage generator

Claims (5)

[Claims] 1. An image forming apparatus for obtaining a toner image by developing an electrostatic latent image formed on a photoconductor by a contact type reversal development process, wherein a potential shift voltage generating section and a photoconductor base conductor are formed. It is characterized in that it is provided between the apparatus main body grounding section and this potential shift voltage generating section can apply a voltage to the photoreceptor base conductor potential in the development blocking direction with respect to the apparatus main body grounding section. Image forming device. 2. The potential shift voltage generating section can set the photoreceptor base conductor potential to a value not lower than the development start voltage in the development process in the development blocking direction with respect to the apparatus main body ground potential. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. 3. The image forming apparatus according to claim 1 or 2, wherein the operation of the potential shift voltage generating section is performed in synchronization with the start of movement of the photosensitive member. 4. The invention according to claim 1, wherein at least a part of the output current of the high voltage power source for charging the photoconductor is used as the power source of the potential shift voltage generating section. The image forming apparatus according to item 1. 5. The output of the high voltage power source for charging the photoconductor,
The image forming apparatus according to claim 4, wherein at least a current flowing from the grid through the constant voltage element is used as a power source of the potential shift voltage generating section.