JPH07113801B2 - Electrophotographic recording device - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an electrophotographic recording apparatus of the type using a powder developer.

2. Description of the Related Art An electrophotographic recording apparatus has a photosensitive drum having a photosensitive layer on its surface, and a charging device, an exposing device, a developing device, a transfer device, a separator, a cleaning device, etc. arranged around the photosensitive drum. While the drum is rotating, the surface of the photosensitive drum is uniformly charged by the charging device, then exposed by the exposure device to form an electrostatic latent image. The latent image is supplied with the developer (toner) and is visible. Imaged,
This toner image is transferred onto recording paper, and then the recording paper is separated from the photosensitive drum and sent to a fixing device, where it is fixed and discharged, whereby image recording is performed. A developing roller is generally used for the developing device in such an electrophotographic recording apparatus. FIG. 4 shows a conventional photosensitive drum and developing roller. The photosensitive drum 1 is provided with a photosensitive layer 3 on the outer peripheral surface of a cylindrical conductive substrate 2 made of a conductive material such as aluminum except for both ends. The developing roller 4 is provided so as to maintain a constant gap (developing gap) with respect to the photosensitive drum 1, and the toner 5 held on the surface of the developing roller 4 is applied to the photosensitive drum 1. . Here, in order to keep the developing roller 4 at a constant gap with respect to the photosensitive layer 3 of the photosensitive drum 1, the shaft 6 supporting the developing roller 4 has an outer diameter larger by a predetermined size than the outer diameter of the developing roller. A spacer ring 7 is attached, and the spacer ring 7 is pressed against the outer peripheral surface of the conductive substrate 2 of the photosensitive drum 1 to maintain a predetermined gap between the photosensitive drum 1 and the developing roller 4. This spacer ring 7
Is a resin ring 8 generally made of resin such as Duracon
And the bearing 9 are combined.

SUMMARY OF THE INVENTION However, according to such a configuration, density unevenness is likely to occur in the image in the vertical direction (recording paper running direction), and this density unevenness is particularly large in a method using a one-component developer. was there.

The above problem occurs for the following reasons. That is, since the bearing and the resin ring are combined in the spacer ring, the runout of the outer circumference of each of the two constituent elements is accumulated and appears as the runout of the outer circumference of the spacer ring. In particular,
It is difficult to increase the processing accuracy of the resin ring used as the insulating portion, and finally the outer peripheral runout when it is attached to the shaft of the developing roller as the spacer ring is limited to about 0.05 mm. Further, since the deviation of the outer circumference of the developing roller with respect to the shafts at both ends of the developing roller to which the spacer ring is attached is added as a factor of the fluctuation of the developing gap, the final fluctuation of the developing gap becomes 0.07 to 0.10 mm.

This is a relatively small problem in the case where the development gap is several mm as in the method using a two-component developer, but the development gap is generally narrow in the method using the one-component developer, In many cases, it is 0.50 mm or the like, and the fluctuation of the development gap due to the fluctuation of the outer circumference directly appears as unevenness of the image density.

Further, even if the processing accuracy is increased, it will increase the cost. Of course, this also applies to bearings.

Therefore, the present applicant intends to solve this problem by
As shown in FIG. 5, a method has been developed in which an endless film 10 made of an electrically insulating material is mounted on both ends of the photosensitive drum as spacer members, and the developing roller 4 is pressed against the endless film 10.
In this method, the development gap is directly controlled by the endless film 10, so the only variation factor is the thickness unevenness of the endless film, which is easy to increase in accuracy and can also reduce the cost. Is to have.

However, when this method is used, since the photosensitive drum and the developing roller rotate while rubbing against each other with the endless film 10 interposed, the film may shift in the axial direction of the photosensitive drum during repeated use. However, it has been found that there is a problem that when the state becomes excessive, the film may shift to the recording sheet on the center side of the photosensitive drum, or conversely, the film may shift outward and the photosensitive drum may come off.

For such problems, it is possible to make the length of the film shorter than the outer peripheral length of the photosensitive drum and to attach it in a tightly bound state, but in that case a great amount of force is required at the time of attachment, which makes attachment difficult. turn into. Further, it is fully conceivable that the pressures of the photosensitive drum and the developing roller will be different at both ends during repeated use, and there is no guarantee that they will not shift. There is also a method of fixing the film using a mounting agent,
When it is used for such a sliding portion, it cannot be guaranteed permanently like the previous example.

The present invention has been made in view of the above problems, and is provided with a photosensitive drum and a developing roller that can set a developing gap easily, accurately, at low cost, and permanently and stably. It is an object to provide an electrophotographic recording device.

Means for Solving the Problems In order to achieve the above-mentioned object, the present invention has a photosensitive drum having a photosensitive layer on a substantially cylindrical outer peripheral surface, and an elastic member attached to both ends of the outer peripheral surface of the photosensitive drum. A ring-shaped spacer member made of an insulating material and a developing roller for applying a developer to the surface of the photosensitive drum are provided, and the diameter of the photosensitive drum, which is the mounting surface of the ring-shaped spacer member, is larger than the diameter other than the mounting surface. And the end edge of the developing roller that abuts on the ring-shaped spacer member is located in the middle of the ring-shaped spacer member.

Effect According to the present invention, since the spacer member is directly provided on the outer peripheral surface of the photosensitive drum with the above-described configuration, even if the photosensitive drum or the developing roller itself is shaken, the developing gap is hardly affected, and the fluctuation of the developing gap is small. Is caused only by the uneven thickness of the spacer member, and by making the thickness uniform, the developing gap can be made uniform. Further, the structure is simpler and the cost can be reduced as compared with the conventional spacer ring including the bearing and the resin ring. Moreover, since the end edge of the developing roller is always in contact with the outer peripheral surface of the spacer member in the middle in the width direction, a force outward in the axial direction of the photosensitive drum acts on the spacer member, and each spacer member Since the spacer member is always pressed against the large-diameter portion on the outer side, development in which the spacer member is displaced on the photosensitive drum during use is prevented.

Embodiment 1 FIG. 1 is a plan view showing a photosensitive drum and a developing roller used in an electrophotographic recording apparatus according to an embodiment of the present invention. In the figure, reference numeral 11 is a photosensitive drum, and a photosensitive layer 13 is provided on a conductive base 12 made of a conductive material such as aluminum, except for both ends of the base 12. This conductive substrate
12, on the outer peripheral surface located outside both ends of the photosensitive layer 13,
A ring-shaped spacer member 14 of an insulating material having a thickness equal to the desired development gap is provided. Further, a flange 15 having an outer diameter larger than the outer diameter of the mounting portion of the ring-shaped spacer member 14 is attached to the outer side thereof. on the other hand,
The developing roller 16 arranged to face the photosensitive drum 11 is formed longer than the width for supplying the toner 17, and the outer peripheral surface thereof is a ring-shaped spacer member 14 attached to the outer peripheral surface of the photosensitive drum 11.
The developing roller 16 is configured so that the end edges 16A at both ends thereof come into contact with the middle of the outer peripheral surface of the ring-shaped spacer member 14. Thus, during development, the outer circumference of the developing roller 16 is pressed against the ring-shaped spacer member 14, and the developing gap between the photosensitive layer 13 and the developing roller 16 is equal to the thickness of the ring-shaped spacer member 14. (Strictly speaking, the outer surface of the photosensitive layer is different from the outer surfaces of both ends of the conductive substrate by a dimensional difference), and the toner 17 on the outer peripheral surface is supplied to the photosensitive drum 11 by the rotation of the developing roller 16.

As the ring-shaped spacer member 14 used here, an endless resin film, for example, an endless polyester film is suitable. As this endless polyester film, one sold by Hokushin Kogyo Co., Ltd. under the product name "Polyester Belt (Material: Hytrel)" can be used. The thickness of the endless resin film can be easily made high in precision at the time of production. For example, in the above "polyester belt", the thickness precision is about ± 5 μm. Therefore, the fluctuation of the developing gap during the rotation of the photosensitive drum 11 and the developing roller 16 is extremely small, and the fluctuation of the developing gap that causes the uneven density of the image does not occur. Further, since the polyester film is sufficiently strong in abrasion resistance, when the photosensitive drum and the developing roller rotate in the same direction in the developing section, the rotational speed (peripheral speed) of the photosensitive drum 11 and the developing roller 16 is intentionally changed. There is no need to match the peripheral speed of the photosensitive drum 11.

When the ring-shaped spacer member 14 contacts the outer periphery of the photosensitive drum 11, it is not necessary to bond it with an adhesive or the like. That is,
As shown in FIG. 2, the endless resin film, which is simply the ring-shaped spacer member 14, is pulled and stretched to form a photosensitive drum.
It may be mounted on the conductive substrates at both ends of 11, and then the flanges 15 as shown in FIG. 1 may be mounted. Further, it is not necessary to bind the endless resin film to the photosensitive drum so strongly. In such a state, the ring-shaped spacer member
It is possible for 14 to move axially on the photosensitive drum 11.
However, as described above, the edge 16 of the developing roller 16 is
Since A is pressed in the middle of the width of the ring-shaped spacer member 14, the ring-shaped spacer member 14 is indicated by an arrow A when the developing roller 16 is pressed against the ring-shaped spacer member 14. As described above, the force outward in the axial direction of the photosensitive drum acts, and the spacer member 14 is constantly pressed against the outer flange 15 thereof. Therefore, even if recording is continued for a long period of time, the ring-shaped spacer portion 14 does not shift to the recording area on the photosensitive drum 11, and good recording is performed.

The edge 16 of the developing roller 16 to the ring-shaped spacer member 14
The pressing position of A may be between both ends in the width direction of the ring-shaped spacer member 14, and may be appropriately determined according to the materials of the ring-shaped spacer member 14 and the developing roller 16 and the pressing force. Normally, if the end edge 16A of the developing roller 16 is set at the center of the ring-shaped spacer member 14 in the width direction or inside of it (on the photosensitive drum center side), the shift of the ring-shaped spacer member 14 to the center side is surely performed. This is preferable because it can be prevented.

FIG. 3 is a sectional view showing a photosensitive drum according to another embodiment of the present invention. The photosensitive drum 11A of this embodiment also has a conductive base 12A and a photosensitive layer 13A, but a small diameter portion is formed at both ends of the conductive base 12A, and a ring-shaped spacer member 14A is attached to this small diameter portion, A flange 15A is attached to the outside. In this embodiment, the spacer member 14A
Are accommodated in the groove formed by the small-diameter portions on both ends of the conductive base 12A and the flange 15A.
There is an advantage that it is possible to more reliably prevent A from coming off or causing a positional shift.

In the above two embodiments, the structure in which the flanges are attached to both ends of the photosensitive drum is described, but the shape of the photosensitive drum according to the present invention is not limited to this. For example,
Even in the photosensitive drum integrated with the flange, the method of the embodiment shown in FIG. 1 can be adopted by incorporating a large diameter portion having a thickness of about 1 to 2 mm at both ends. Further, the large diameter portion may be formed by a ring-shaped member which is press-fitted or adhered to the photosensitive drum. Since the ring member itself does not rub against the developing roller, sufficient strength and reliability can be obtained even by such pressure bonding or adhesion. The advantage in this case is that it is not necessary to provide the large diameter portion on the photosensitive drum itself as in the previous example.

It goes without saying that the developer usable in the present invention may be magnetic or non-magnetic.

EFFECTS OF THE INVENTION As is apparent from the above description, the present invention provides a photosensitive drum having a photosensitive layer on a substantially cylindrical outer peripheral surface, and an elastic insulating material attached to both ends of the outer peripheral surface of the photosensitive drum. And a developing roller that applies a developer to the surface of the photosensitive drum, and the diameter of the photosensitive drum that is the mounting surface of the ring-shaped spacer member is smaller than the diameter of the surface other than the mounting surface. Since the end edge of the developing roller contacting the spacer member is located in the middle of the ring-shaped spacer member, the spacer member is directly provided on the outer peripheral surface of the photosensitive drum, so that even if the photosensitive drum or the developing roller itself shakes. The development gap is hardly affected by the fluctuation, and the variation of the development gap is caused only by the uneven thickness of the spacer member. As a result, the development gap can be made uniform, and the structure is simpler and the cost can be reduced as compared with the conventional spacer ring including a bearing and a resin ring. Further, since the edge of the developing roller is always in contact with the outer peripheral surface of the spacer member in the middle in the width direction, a force outward in the axial direction of the photosensitive drum acts on the spacer member, and each spacer member is Since the spacer member is always pressed against the large-diameter portion on the outer side of the photosensitive member, the spacer member has an effect of preventing development that is displaced on the photosensitive drum during use.

[Brief description of drawings]

1 is a partial sectional plan view showing a photosensitive drum and a developing roller of an electrophotographic recording apparatus according to an embodiment of the present invention, FIG. 2 is a perspective view of the photosensitive drum in the above embodiment, and FIG. 3 is a photosensitive drum. FIG. 4 is a cross-sectional view showing a modified example of FIG. 4, FIG. 4 is a perspective view showing a photosensitive drum and a developing roller of a conventional electrophotographic recording apparatus,
FIG. 5 is a partial cross-sectional plan view showing a photosensitive drum and a developing roller of an electrophotographic recording apparatus developed to solve the problems of the conventional apparatus. 1,11,11A ... Photosensitive drum, 2,12,12A ... Conductive substrate, 3,
13,13A Photosensitive layer, 4,16 Developing roller, 5,17 Toner, 14,14A Ring spacer member, 15 Flange

Claims (3)

[Claims] 1. A photosensitive drum having a photosensitive layer on a substantially cylindrical outer peripheral surface, ring-shaped spacer members made of an elastic insulating material and attached to both ends of the outer peripheral surface of the photosensitive drum, and the photosensitive drum. A developing roller for applying a developer to the surface of the developing roller, wherein the diameter of the photosensitive drum, which is the mounting surface of the ring-shaped spacer member, is smaller than the diameter other than the mounting surface, and the developing roller is in contact with the ring-shaped spacer member. The electrophotographic recording apparatus is characterized in that the end edge of is located in the middle of the ring-shaped spacer member. 2. The electrophotographic recording apparatus according to claim 1, wherein the ring-shaped spacer member is composed of an endless film. 3. The electrophotographic recording apparatus according to claim 2, wherein the endless film is made of polyester.