JPS61252569A - Image forming device - Google Patents

Abstract

PURPOSE:To simplify constitution, and to maintain a prescribed developing bias voltage by connecting a voltage dividing circuit for applying a developing bias voltage to a developing sleeve, to after a connecting point of a grid electrode for constituting an electrifying device, and a non-linear resistance element. CONSTITUTION:A connecting point (a) of a varistor 10a and a grid electrode 9 is grounded through a voltage dividing circuit J consisting of two resistances 13a, 13b which have been connected in series, and a connecting point (b) of both the resistances 13a, 13b is connected to a developing sleeve 14 of a developing device 4. In the developing device 4, a voltage whose potential is lower than the surface potential of a photosensitive drum 1 electrified by an electrifying device 2 is applied to the developing sleeve 14 for carrying a developer consisting of a toner and a carrier for holding this toner. As for a developing bias voltage, that which has divided a voltage of the grid electrode 9 whose potential is stable by an operation of the varistor 10a, by a voltage dividing circuit J is used, therefore, it is unnecessary to provide other power source, and a stable developing bias voltage is always obtained. In this way, the constitution can be made compact and the cost is reduced.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention is directed to a charging device that uniformly charges the surface of a photoreceptor using a charging wire and a grid electrode, and a charging device that uniformly charges the surface of a photoreceptor using a developing sleeve. The present invention relates to an image forming apparatus that includes a developing device that visualizes a formed electrostatic latent image, and that has a grid electrode grounded via a nonlinear resistance element.

[Conventional technology]

In image-forming devices such as copying machines and printers, so-called electrostatic latent images are visualized by selectively adsorbing a developer onto an electrostatic latent image, for reasons such as high-speed processing and the ability to obtain high-quality images. In such image forming devices that often use electrophotography, a developing bias voltage is applied to the developing sleeve that constitutes the developing device to prevent excess developer from adhering to areas other than the image forming area. Prevention is being done.

Conventionally, known methods for applying a developing bias voltage include a method using a developing bias power supply connected to the developing sleeve, and a so-called self-bias method in which the developing sleeve is grounded via an impedance device. (For example, see Japanese Patent Publication No. 48-35501).

[Problem that the invention seeks to solve]

However, the conventional structure described above has the following problems and there is room for improvement.

First, in those using a developing bias power supply, the provision of this power supply tends to make the apparatus large-scale, which also leads to an increase in cost. In addition, the self-bias method utilizes the developing current generated when the charged developer moves from the developing sleeve side to the photoreceptor side that carries the electrostatic latent image. When the amount of agent movement is small, a situation may occur in which the development pressure does not reach a predetermined potential.

In view of the above-mentioned circumstances, an object of the present invention is to provide a simple structure for applying a developing bias voltage, and to always maintain a predetermined developing bias voltage.

[Means for solving problems]

A characteristic configuration of the image forming device according to the present invention is that a developing bias voltage is applied to the developing sleeve after the connection point between the grid electrode constituting the charging device and the nonlinear resistance element connected to the ground side of this grid node electrode. This is because a voltage divider circuit is connected.

[For production]

In other words, this nonlinear resistance element generates a current from the grid electrode to the ground side only when the potential exceeds a predetermined potential, thereby maintaining the grid electrode at a predetermined potential and reducing the surface of the photoreceptor. This is to stabilize the charging potential when charging. Therefore, by effectively utilizing the fact that the potential of this grid electrode is stable, the developing bias voltage applied to the developing sleeve is divided from this grid electrode portion.

〔Effect of the invention〕

As a result, there is no need to provide a separate power source to apply a developing bias voltage to the developing sleeve, making it possible to achieve a compact configuration and reduce costs. Furthermore, since the grid electrode itself is maintained at a predetermined potential, the developing bias voltage is also always maintained at a predetermined potential.
It is no longer affected by the amount of developer movement.

Therefore, as a whole, it has become possible to provide a development bias voltage application configuration that is excellent in performance and advantageous in terms of cost.

〔Example〕

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

(First Embodiment) FIG. 1 shows a schematic configuration of a copying machine as an example of an image forming apparatus according to the present invention.

Although not shown in the drawings, in this copying machine, a document on a document table is scanned by a scanning device, and an image of the scanned document is projected onto a photoreceptor drum (1) by an imaging device and becomes a static image. The device is configured to form an electrolatent image.

The photoreceptor drum (1) is rotated in the direction A in the figure by a drive mechanism (not shown), and around it are a charging device (2), an exposure section (3), and a developing device (4). ), a transfer device (5), etc. are arranged along the rotation direction. The photosensitive drum (1), whose surface is uniformly charged by the charging device (2'), is exposed to projection light (L) from an imaging device (not shown) in the exposure section (3). As mentioned earlier, an electrostatic latent image is formed on the surface.

Thereafter, the photosensitive drum (1) is processed by the developing device (4).
Charged toner is selectively attached to the upper electrostatic latent image and visualized, and the attached toner is further transferred onto copy paper (not shown) by a transfer device (5). Although not shown, the copy paper separated from the photoreceptor drum (1) is ejected from the copying machine after the transferred toner is fixed by a fixing device (not shown). ing. On the other hand, the photoreceptor drum (1) has its surface charge erased by a main eraser (not shown), excess toner is removed by a cleaner (not shown), and then reaches the charging device (2). Then, a new copying process is started.

As shown in Figure 1, the charging device (2) consists of a charging wire (7) connected to a high-voltage power supply unit (6), a grounded holder (8), a grid electrode (9), etc. ing. The grid electrode (9) is grounded via one varistor (10a), which is an example of a non-linear resistance element (B). This varistor (10a) has a non-linear voltage-current characteristic that allows current to flow only when a predetermined voltage is exceeded, and maintains the potential of the grid electrode (9) at a predetermined value. This makes it possible to stabilize the charged potential on the surface of the drum (1).

Note that the voltage applied to the transfer wire (11) constituting the transfer device (5) is obtained by connecting the transfer wire (11) to the high voltage power supply unit (6) via a resistor (12).

And this varistor (10a) and grid electrode (9)
Connect the connection point (a) with two resistors (13a) connected in series.
) and (13b), and the connection point (b) between both resistors (13a) and (13b).
) is connected to the developing sleeve (14) of the developing device (4). That is, in the developing device (4), the surface of the photoreceptor drum (1), which is charged by the charging device (2), is placed on the developing sleeve (14) that conveys a developer consisting of toner and a carrier that holds this toner. A voltage lower than the potential (for example, when using the regular development method, the photoreceptor drum (
[-100V] compared to the surface potential [-600V] of 1)
degree). This is called a developing bias voltage, and it prevents excess developer from adhering to areas other than the image forming area. In other words, by using the voltage of the grid electrode (9), whose potential is stabilized by the action of the varistor (10a), as the developing bias voltage, divided by the voltage dividing circuit (J), a separate power source can be used. It is designed so that a stable developing bias voltage can always be obtained.

(Second Example) From this example onwards, the configurations of the charging device (2), exposure section (3), developing device (4), and transfer device (5) are as follows until losing to (Fifth Example). , (first embodiment), so the explanation of the same parts will be omitted.

As shown in FIG. 2, in this embodiment, the charging device (2)
The grid electrode (9) is an example of three nonlinear resistance elements (B) connected in series, varistors (10b) to (10).
d) is grounded via. Then, the connection point (c) between the second varistor (10c) and the third varistor (10d)
) and a developing sleeve (14) are connected.

In other words, in the case of the first embodiment, a voltage divider circuit U) consisting of two resistors (13a) and (13b) was used, but since the potential of the grid electrode (9) is quite high, Those two resistors (13a), (13b)
must have a large resistance value.

However, resistors with high resistance values are quite expensive and do not necessarily have stable performance. Therefore,
In this embodiment, the voltage of the grid electrode (9) is divided into the developing bias voltage by the three varistors (10b) to (10d) that act to stabilize the potential, thereby making the developing bias voltage more stable. We are able to provide it at a low cost.

In this example, 3 is an example of the nonlinear resistance element (B).
Since the voltage divided by the three varistors (10b) to (10d) themselves is used as the developing bias voltage, the circuit consisting of these three varistors (10b) to (10d) is called a voltage dividing circuit (J).

(Third Embodiment) As shown in FIG. 3, in this embodiment, the charging device (2)
The grid electrode (9) is grounded via two varistors (10e) and (10f), which are examples of series-connected nonlinear resistance elements (B), in the same way as in the first embodiment. There is. And both baristas (10e).

The connection point (d) of (10f) is connected to the developing sleeve (14), and furthermore, the capacitor (15a) is connected in parallel with the varistor (10f) on the ground side.

In other words, in the case of (first example) and (second example),
In order to reduce power consumption, if voltage is applied intermittently to the charging device (2), the developing bias voltage will not be applied when no voltage is being applied to the charging device (2). I end up. Therefore, in this embodiment, by accumulating electric charge in the capacitor (15a),
Even when no voltage is applied to the charging device (2), a developing bias voltage of a predetermined potential is always applied.

In this example, two varistors (10e), (1
0f) and a capacitor (15a) is called a voltage dividing circuit (J).

(Fourth embodiment) As shown in Fig. 4, the configuration is almost the same as that of the (first embodiment), but the capacitor (15b) is
are connected in parallel. The operation is almost the same as in the third embodiment. In this example there are two resistors (13c)
, (13d), and the capacitor (15b) are collectively referred to as a voltage dividing circuit (J).

(Fifth embodiment) As shown in Fig. 5, it has almost the same configuration as the (first embodiment), but the capacitor (15c) is replaced with two resistors (13e) and (13f) for voltage division. It is connected in parallel with the one on the ground side (13f).

The operation is almost the same as in the third embodiment. Also in this embodiment, the two resistors (13e) and (13f) and the capacitor (15c) are collectively referred to as a voltage dividing circuit (J).

(Other Embodiments) Although not shown in the drawings, the following modifications or application to other devices are possible.

H>A variable resistor is used as the voltage dividing circuit (J).

(2) The number, combination, etc. of elements constituting the nonlinear resistance element (B) or the number, combination, etc. of elements constituting the voltage dividing circuit (J) can be changed as necessary.

(3) The capacitances of the capacitors (15a) to (15c) in the third to fifth embodiments can be changed as appropriate depending on the required development bias voltage application time and the like.

4> Instead of the photoreceptor drum (1), a band-shaped photoreceptor stretched between a pair of rollers may be used, and these are collectively referred to as the photoreceptor (1).

5) In addition to copying machines, the present invention can also be applied to printers that apply electrophotography, such as laser beam printers and microfilm printers.

[Brief explanation of drawings]

The drawings show embodiments of an image forming apparatus according to the present invention, FIG. 1 is a schematic partial configuration diagram of a copying machine showing a first embodiment, and FIG. 2 is a schematic partial configuration diagram of a copying machine showing a second embodiment. , Figure 3 is the third
FIG. 4 is a schematic partial configuration diagram of a copying machine showing a fourth embodiment, and FIG. 5 is a schematic partial configuration diagram of a copying machine showing a fifth embodiment. (1)...Photoreceptor, (2)...Charging device, (4)...Developing device, (7)...
Charging wire, (9)... Grid electrode, (14
)...Developing sleeve, (B)...Nonlinear resistance element, (J)...Voltage dividing circuit, (a)...
...Connection point between the nonlinear resistance element and the grid electrode.

Claims (1)

[Claims] A charging device that uniformly charges the surface of a photoreceptor using a charging wire and a grid electrode, and a developing device that uses a developing sleeve to visualize an electrostatic latent image formed on the surface of the photoreceptor. In an image forming apparatus in which a grid electrode is grounded via a nonlinear resistance element, a voltage dividing circuit for applying a development bias voltage to the development sleeve is connected after a connection point between the nonlinear resistance element and the grid electrode. Imaging device.