JPS6389877A - Imaging device - Google Patents

Abstract

PURPOSE:To prevent the area of a photosensitive body from being developed in flat black during the period from the start of movement of a photosensitive body due to imaging up to the arrival of the area at a developing area through an imaging area by arranging a potential shifting voltage generating part for setting up the potential of a base part electric conductor of the photosensitive body to a value different from that of an earth part of an imaging device between a base part electric conductor and a earth part. CONSTITUTION:The potential shifting voltage generating part 20 is provided between the electric conductive base part conductor 11 of the photosensitive body 1 and the earth of the whole device and a developing bias power supply 13 is formed by a simple constitution having only an ON/OFF switching circuit. The voltage generating part 20 shifts high voltage source systems 10, 15 and the photosensitive body 1 from the earth part of the device body by the voltage generated from itself. Since the developing bias is simple kept at OFF during the period from the start of movement of the photosensitive body up to the arrival of an area A at the imaging area through the developing area, it is unnecessary to propose a bipolar switching circuit. The output value of the voltage generating part 20 may be set up to a value larger than a value setting up the quantity of toner sticking to the area A to zero.

Description

TECHNICAL FIELD The present invention relates to an image forming apparatus that develops an electrostatic latent image formed on a photoreceptor into a toner image by a contact type reversal development process.

Prior Art FIG. 4 shows an example of a schematic configuration of a conventional image forming section of an image forming apparatus such as a laser beam printer or a facsimile machine in which development is performed by a contact type reversal development process using high-resistance toner.

Around the photoreceptor drum 1, IF electric chargers 2. Exposure system 3, developing device 4
, a transfer charger 5 is provided.

The charger 2 is formed as a scorotron.

A grid potential is applied to the grid electrode 6 by a grid potential control power source 7, and the scorotron casing electrode 8
is grounded. Further, high voltage is applied to the scorotron charger wire 9 by an f-heavy high voltage power source 10.

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

In the image forming apparatus having the above configuration, when the photoreceptor drum 1 starts moving in the direction of the arrow for image formation, the surface 1 of the photoreceptor drum 1
The surface potential of the photoreceptor in area A between the portion facing the charger 2 of 6 and the portion facing the developing roller 17 of the developing device 4 is 0 volts.

Now, in the reversal development process, the polarity of the developing roller bias voltage is set in a direction that promotes development during development. Therefore, until the area A passes through the developing area of the contact portion with the toner layer on the developing roller 17 and the photoreceptor surface (image forming area) charged by 11F by the charging charger 2 approaches the developing area, the bias power source is 13, the developing roller bias voltage is set to the opposite polarity so that the toner is transferred to area A on the photoreceptor.
It is necessary to prevent the toner from being wasted by adhering to the toner and being developed as a solid black image. The relationship between the developing bias output voltage and the amount of toner adhering to area A in that case is shown in FIG. Voltage 5 at the point where the curve intersects the horizontal axis in the figure
0V corresponds to the development start voltage as a process. As mentioned above, by setting the developing roller bias voltage to the opposite polarity while the area A on the photoreceptor passes through the developing area, toner consumption is suppressed, the number of times of toner replenishment is increased, and transfer unit 5 and cleaning unit ( However, in order to switch the polarity of the developing roller bias between forward 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 finishes passing through the development area after the body starts moving, which has the disadvantage of complicating the configuration and increasing cost. .

In view of the above-mentioned drawbacks of the conventional image forming apparatus using a contact type reversal development process, the present invention has a simple structure, and after the photoreceptor starts moving for image formation, the image forming area is the developing area. It is an object of the present invention to provide an image forming apparatus that prevents the A area from being developed into a solid black image until reaching the image forming area and avoids the above-mentioned problems associated with this.

In order to achieve the above object, the present invention makes it possible to set the conductor potential at the base of the photoconductor to a value different from the potential at the ground portion of the main body of the image forming apparatus in an image forming apparatus using a contact type inversion process. The present invention is characterized in that a voltage generating section for potential shifting is provided between the photoconductor base conductor and the ground section.

Embodiments of the present invention will be described in detail below based on the drawings.

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

The difference between this embodiment and the conventional apparatus is that a voltage generating section 20 for potential shift is provided at least between the conductive base conductor 11 of the photoreceptor 1 and the ground of the entire apparatus, and a bias power source for development is provided. There is no difference from the conventional device except that 13 has a bipolar polarity and has a simple structure having only an on/off switching circuit without a forward/reverse switching or timing circuit.

The potential shift voltage generation section 20 described above is a high voltage power supply system 10.
．． 15 and the photoreceptor system 1 are shifted from the grounding part of the apparatus main body by the voltage generated by the voltage generating section 20. In the apparatus of this embodiment, in order to make the developing conditions the same as those in FIG. It is only necessary to shift the output value of the developing bias power supply 13 by the output value of the voltage generation section 20 for potential shift. The reason is that there is no change in the potential of the charger system with respect to the photoreceptor base conductor 11. Therefore, it is only necessary to keep the developing bias off (zero volts) until the photoreceptor 1 starts moving, 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 amount of toner adhering to area A with the horizontal axis representing the output voltage of the potential shift voltage generating section 20 and the amount of toner adhering on the developing roller 17 as a parameter.

The upper right of the three curves indicates a larger amount of toner adhesion on the developing roller.From these curves, the output value of the potential shift voltage generating section 2o is a value at which the amount of toner adhesion for area A is zero. It turns out that a larger value is sufficient.

In another embodiment shown in FIG. 3, the potential shifting voltage generation source 2o is a Zener diode, and most of the output of the charger 2 flows through the Zener diode to shift the potential. At the same time that the photoreceptor 1 starts moving in the direction of the arrow, a high-voltage charging electric current 'g' is applied.
10 is turned on and the charger casing 8. The current to the grid 6 and photoreceptor 1 flows into the Zener diode.

In this embodiment, the output current of the charging high voltage power supply 1o is -20
0 μA, Zener voltage of Zener diode 20 is 10
0V (for example, use Ishizuka Denshi's 21100),
The potential of the conductor at the base of the photoreceptor is -10 with respect to the grounding section of the main body of the device.
It becomes 0v. As a result, the potential of the photoreceptor in both the exposed and non-exposed areas is - compared to the case of the conventional device shown in FIG.
Shift by 100V. As can be seen from the graph in Figure 2, this value is sufficient to prevent toner from adhering to area A, and even in actual experiments, the amount of toner adhering to area A of the photoconductor cannot be measured. (0,01■/d
within).

In the embodiment shown in FIG. 3, the power source 15 of the charge wire 14 of the transfer charger 5 is grounded to the grounding part of the main body, so adjustment of the transfer current is required, but this is not necessary in the embodiment shown in FIG. An isolated high-voltage power supply is unnecessary and safe. In the embodiment shown in FIG. 3, as in the embodiment shown in FIG.
It is necessary to shift the output by the amount of output (-100V in this case).

In addition to Zener diodes, varistors and voltage generation circuits made up of multiple components are conceivable as the configuration of the voltage generation section for potential shifting. For these reasons, Zener diodes are the best.

In addition, since the surface potential of the photoreceptor increases from the grounding part of the device main body by the output of the voltage generation part for potential shift, the cleaning performance is improved due to the repulsion between the toner and the photoreceptor, and the transfer paper is attracted to the photoreceptor. Secondary effects such as improved transfer performance can be obtained.

Effects As described above, according to the present invention, in an image forming apparatus using a contact type reversal development process, solid black development does not occur in the area in front of the image forming area when the photoreceptor starts moving, and toner consumption is reduced. , cleaning unit, and transfer charger.

[Brief explanation of the drawing]

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 shift mold pressure generating section and the amount of toner adhering to the front area of the photoreceptor image forming area. FIG. 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 type reversal development process, and FIG. 5 is a diagram showing the development in the development blocking direction. FIG. 3 is a curve diagram showing the relationship between the bias output voltage and the amount of toner adhering to the front area of the photoreceptor image forming area. 1... Photoreceptor 2... Charger 3... Exposure optical system 4... Developing device 5... Transfer charger 6... Charger grid electrode 7... Grid potential control power source 8 ... Charger casing electrode 9 ... Charger wire 10 ... High voltage power supply for charging 11 ... Photoreceptor base conductor 12 ... Development roller center conductor 13 ... Bias power supply for development 14. ...Transfer charger wire 15...High voltage power supply for transfer 17...Developing roller

Claims (5)

[Claims] (1) In an image forming device that develops an electrostatic latent image formed on a photoreceptor by a contact-type reversal development process to obtain a toner image, the potential of the conductor at the base of the photoreceptor is set to a value different from the potential of the ground portion of the main body of the image forming device. An image forming apparatus characterized in that a voltage generating section for potential shifting is provided between a photoreceptor base conductor and a grounding section of the main body of the apparatus. (2) The above-mentioned potential shift voltage generation section is capable of setting the photoconductor base conductor potential to a value that is different from the potential of the grounding section of the apparatus main body in the development prevention direction by more than the development start voltage in the above-mentioned development process. An image forming apparatus according to claim 1, characterized in that: (3) The image forming apparatus according to claim 1 or 2, wherein the operation of the voltage generating section for potential shift is performed in synchronization with the start of movement of the photoreceptor. (4) Any one of claims 1 to 3, characterized in that at least a part of the output current of the high-voltage power supply for charging the photoconductor is used as a power source for the voltage generating section for potential shifting. The imaging device described in Section 1. (5) A claim characterized in that, of the output of the high-voltage power supply for charging the photoreceptor, at least the current flowing from the grid via the constant voltage element is used as a power source for the voltage generation section for potential shifting. The imaging device according to item 4.