JPH05289477A - Electrophotographic device - Google Patents

Abstract

PURPOSE:To obtain stable image quality without sticking toner to the light emitting surface of a lens array, even in long-term use by adopting a constitution so that, at least, the light emitting surface of an exposing head can be electrostatically charged to the same polarity as that of a potential by electrification, at the time of forming an image. CONSTITUTION:An electrostatic charging unit 4 is composed of a corotron wire 41, and a metallic shielding case 43 on which an electrostatic charging grid 42 is formed. The exposing head 3 is provided with a SELFOC(R) lens array 31 and an LED chip array. The side of the light emitting surface 31a of the lens array 31 is arranged so as to face the electrostatic charging grid 42 in the adjacent relation. When a high electrostatic charging voltage is applied to the corotron wire 41, the grid voltage of the same polarity, lower than an electrostatic charging voltage is applied to the electrostatic charging grid 42 via the shielding case 43, to uniformly/electrostatically charge the side of a photosensitive drum. At this time, the side of the lens array 31 is exposed by a discharge current from the electrostatic charging grid 42, and the light emitting surface 31a of the lens array 31 is electrostatically charged to the same polarity as that of the potential by the electrification.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus applicable as a printer or a facsimile, and in particular, the reversal development method is effectively used to prevent toner contamination of LED heads and other exposure heads for a long period of time. The present invention relates to an electrophotographic apparatus capable of forming a clear image.

[0002]

2. Description of the Related Art Conventionally, an exposure image corresponding to image information is formed on a photosensitive drum that has been uniformly charged by using an LED head or other linear exposure head, and then toner is applied to the exposure image from the developing sleeve side. Printers and facsimiles are known in which the toner image is adhered, and then the toner image can be transferred to plain paper or other recording material guided to a transfer position via a resist roller. In the LED head constituting the exposure head, a selfoc lens array made of glass or resin is arranged on the front surface of a head array in which LED chips are arranged in a row, and these are integrally formed by a resin or metal support. It has a holding structure.

[0003]

In the above apparatus, since developing is performed while rotating the developing sleeve in the developing unit, floating toner or toner scattering is likely to occur, while the exposure head adjacent to the developing sleeve is In particular, since the SELFOC lens array located on the side facing the photosensitive drum is made of a material having a different charging series from that of the toner, the toner is apt to electrostatically adhere to the lens array. If toner adheres to the front surface (emission surface) of the lens array, it adversely affects the image quality.

Therefore, in the above-mentioned conventional apparatus, periodical cleaning of the exposure head is forced, and the maintenance work becomes complicated. For this reason, it is difficult to achieve free maintenance in the electrophotographic apparatus, which has been a major obstacle to the spread of the maintenance cost to individual users who presume free maintenance.

In view of the above drawbacks of the prior art, it is an object of the present invention to provide an electrophotographic printer capable of obtaining stable image quality without toner adhering to the exit surface of the lens array or the like even after long-term use. ..

[0006]

SUMMARY OF THE INVENTION The present invention is a charging unit including a corotron wire for uniformly charging a photosensitive drum,
The non-latent exposure head is formed by exposing the uniformly charged photosensitive drum to form a non-latent image portion corresponding to image information, and a developer into which a charge having the same polarity as the charging potential is injected. A developing unit for adhering a developer to an image portion, and the exposure head is disposed adjacent to and facing the charging unit without being grounded, and at least the emission surface of the exposure head is set to a charging potential at the time of image formation. It is characterized in that it can be charged to the same polarity.

In order to smoothly charge the same polarity as the charging unit during image formation, as shown in FIG. 3 (A),
An intersection X connecting the extension lines of the charging grid 42 forming surface of the shield case 43 and the emission surface 31a of the SELFOC lens 31 is located on the space between the exposure head 3 and the charging unit 4 or further on the shield case 43 side. By doing so, the surface of the charging grid 42 and the emission surface 31a or the lens side surface of the SELFOC lens 31 directly face each other, which facilitates smooth charging of the emission surface 31a and the lens side surface.

However, as shown in FIG. 3B, the fact that the intersection point X is located outside the lens means that the exit surface 31a of the SELFOC lens does not directly face the charging grid 42 but only the side surface of the shield case 43. Therefore, it becomes difficult to smoothly charge the emission surface 31a.

Further, the resin frame and the exposure head, which are adjacent to the shield case surrounding the corotron wire, are electrically connected to each other without or in combination with the above-mentioned structure, and both are charged to the same polarity. It may be configured as follows. The electrical conduction can be easily achieved by connecting the shield case or the frame supporting the case and the exposure head with a conductive wire.

[0010]

According to such a technical means, the exposure head is substantially in the floating electrode state, and the discharge current from the charging unit side causes the emission head, particularly the emission surface of the SELFOC lens facing the photosensitive drum, to have the same polarity as the toner. Therefore, even if the floating toner or the scattered toner repels each other even if they come close to the lens surface, the risk of toner adhesion is greatly reduced. In particular, in the present embodiment described later, it is possible to obtain an experimental result that the cleaning is unnecessary even after printing 300,000 sheets. As a result, stable image quality can be obtained without toner adhered to the exit surface of the lens array even after long-term use. Can be obtained.

If the exposure head is maintained at the same polarity as the charging unit side, noise or the like is less likely to occur in the signal current inside the LED head, and especially the LED head array and the SELFOC lens array in the exposure head are supported. By forming the supporting body with an insulating material, it is possible to completely prevent noise from being carried on the signal current flowing through the LED head array, which leads to prevention of image disturbance and the like. Further, since the present invention does not require a special member and can be achieved by a simple layout configuration, it is possible to avoid the complexity of the device configuration without increasing the cost.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described in detail below as an example with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, relative positions, etc. of the components described in this embodiment are not intended to limit the scope of the present invention thereto, but are merely illustrative examples. Not too much. Figure 1
Is a photosensitive drum unit incorporated in the image forming apparatus according to the exemplary embodiment of the present invention. The photosensitive drum 1 including the heater 2 is configured to be rotatable in the arrow direction, and the developing sleeve is arranged on the right side in the drawing along the rotational direction. A developing unit 10 having a transfer unit 8 disposed below the transfer unit 8 via a recording paper conveyance path, and a cleaning mechanism 5, an eraser 7 including an optical fiber, and a charger 4, which are arranged in the drum unit along the rotational direction. And the LED unit 3 are provided.

The cleaning mechanism 5 is provided with a cleaning roller 50 and a cleaning blade 51 on the side facing the peripheral surface of the photosensitive drum 1 along the rotation direction thereof, and the peripheral surface and the tip of the blade 51 can be pressed against the drum. In addition, the frame body 52 that supports or supports them is substantially
A screw 53, which is formed in a character shape and extends in parallel with the drum shaft together with the cleaning roller 50, is arranged on the inner side of the frame 52, and the residual toner scraped off by the cleaning roller 50 and the cleaning blade 51 is removed by the screw 53. It is conveyed to the collection container side (not shown). To do.

The charging unit 4 has a corotron wire 41 stretched between main body frames (more properly, drum unit frames) 10 on the drum shaft end side, and a side surrounding the corotron wire 41 and facing the photosensitive drum 1. A metal shield case 43 having a U-shaped cross section and having a charging grid 42 formed thereon is supported by the body frame 10 made of an insulating resin on both axial ends of the shield case 43.

On the other hand, the LED unit 3 has a selfoc lens array 31 on the side facing the photosensitive drum 1, an LED chip array 32 in which LED chips are arranged in a row on the incident surface side, and these are integrally supported. A support 33 made of an insulating resin and a lens support frame 34 made of metal for holding the lens array 31 in cooperation with the support 33. Then, the SELFOC lens array 31 and the SELFOC lens array 31 are formed on the surface on which the charging grid 42 is formed and the SELFOC lens array 31 in a cross section orthogonal to the axis of the photosensitive drum 1.
The length and the focal length are set so that the intersection X connecting the extension lines of the respective exit surfaces is located in the space between the lens 31 and the shield case 43.

As shown in FIG. 2, the support body 33 made of an insulating resin extends on both longitudinal ends, and a screw mounting hole 35a is screwed into the extending portion 35 to form the screw mounting hole 35a. LED frame 36 and L located on the upper surface side by utilizing
The LED mounting screws 37 fix the ED heads 3 to each other.
The LED mounting screw 37 has a coil spring 37a between the head 3 and the LED frame 36, and the tip of the mounting screw 37 has the housing frame 1 on both axial sides of the main body frame 10.
6 is abutted on the receiving surface 17 extending inward.

As a result, by adjusting the screw 37, the distance between the generatrix of the photosensitive drum pivotally supported on the main body frame 10 and the SELFOC lens array 31 can be adjusted.
The body frame 10 and the LED head 3 are electrically connected via the screw 37, and the LED head 3 and the shield case 43 are electrically connected via the body frame 10. In this embodiment, the support 33 and the shield case 4 are further added.
The main body frames 10 supporting 3 are connected via a conductive wire 39 to further secure electrical conduction.

On the other hand, the developing unit 10 carries on the developing sleeve 11 an insulating toner charged in the same polarity as the charging potential of the charging unit, in other words, the surface potential of the photosensitive drum, and obtains it by exposing the LED head 3. Toner can be attached to the formed non-latent image portion.

Next, the operation of this embodiment will be described. First, a high voltage + polarity charging voltage is applied to the corotron of the charging unit, and the charging grid 42 is passed through the shield case 43.
Is applied to the grid voltage of + polarity lower than the charging voltage, so that the photosensitive drum side is uniformly charged. At this time, L
Since the emission surface side of the SELFOC lens array 31 of the ED head is arranged facing the charging grid 42, the discharge current from the charging grid 42 is radiated to the lens array 31 side and is equal to the charging potential. It is charged with a positive polarity. On the other hand, also on the resin support 33 side, the main body frame 10 that supports the shield case 43 via the conductive wire 39.
Since it is electrically connected to the side, the SELFOC lens array 31 and the support 33 are also charged with +.

As a result, the entire LED head 3 is positively charged, and when an image is formed in this state, even if floating toner or toner scattering occurs due to rotation of the developing sleeve, the toner is still positively charged. Even if the toners approach the LED head 3, they repel each other, and the risk of toner adhesion is greatly reduced. In this embodiment, the image quality did not deteriorate due to toner adhesion even after printing 300,000 sheets. Further, since the LED head 3 is substantially in the floating electrode state, stable image quality can be obtained without toner adhesion even after the image forming operation is stopped.

[0021]

As described above, according to the present invention, it is possible to obtain stable image quality without toner adhered to the exit surface of the lens array or the like even after long-term use. And so on.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a main part of an image forming apparatus according to an exemplary embodiment of the present invention.

FIG. 2 is a perspective view of a main part of the LED head shown in FIG.

3 (A) and 3 (B) show the positional relationship of the intersections connecting the extension lines of the charging grid forming surface of the shield case and the emission surface of the SELFOC lens, respectively. FIG.
Shows a comparative example.

[Explanation of symbols]

1 Photosensitive Drum 3 LED Unit 4 Charging Unit 10 Developing Unit 41 Corotron Wire 42 Charging Grid 43 Shield Case 31 SELFOC Lens Array 32 LED Chip Array 33 Support 34 Support Frame

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location H04N 1/29 Z 9186-5C

Claims (4)

[Claims] 1. A charging unit including a corotron wire for uniformly charging the photosensitive drum, and a linear exposure for exposing the uniformly charged photosensitive drum to form a non-latent image portion corresponding to image information. A head and a developing unit for adhering the developer to the non-latent image portion by using a developer injected with a charge having the same polarity as the charging potential, and adjoining the charging unit without grounding the exposure head. And an electrophotographic apparatus characterized in that at least the emission surface of the exposure head can be charged to have the same polarity as the charging potential during image formation. 2. A charging unit having a shield case surrounding a corotron wire and having a charging grid formed on the side facing the photosensitive drum, and an exposure head having a SELFOC lens array (trade name) on the front surface. Claim 1
In the electrophotographic apparatus described above, in a cross section orthogonal to the axis of the photosensitive drum, an intersection between the extension lines of the charging grid forming surface and the emission surface of the SELFOC lens is at least a space sandwiched between the lens and the shield case. Electrophotographic device characterized by being located inside or on the shield case side 3. The electrophotographic apparatus according to claim 1, wherein a resin frame adjacent to a shield case surrounding the corotron wire and the exposure head are electrically connected to each other and are charged to the same polarity. 4. The electrophotographic apparatus according to claim 1, wherein a support for supporting the LED head array and the SELFOC lens array in the exposure head is formed of an insulating material.