JPH04156470A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent damage of a photo-sensitive drum caused by external light or operator's hands or tool and the like, prevent a poor transfer and to reduce spacing in an image forming device and to provide a small-sized device by a method wherein when a protection cover is placed at its escaping position, a sheet transporting passage is formed by a protection cover. CONSTITUTION:When a main body device is closed toward a direction (a), a supporting member 1b is cooperatively operated to move a shutter member 1a to its escaping position. At this time, the shutter member 1a approaches a resist roller 10 to transport a sheet member 13 in synchronism with a rotation of a photo-sensitive drum 2 and a corona charger 6 so as to form a transporting passage for the sheet member 13. A transferring electric field restricting member 1d arranged along a longitudinal direction of a drum at a corona charger 6 of the shutter member 1a may restrict a transfer electric field in such a way as a transfer electric field from the corona charger 6 may not act against the developer agent forming the visual image upstream of its rotating direction than a transfer region on the photo-sensitive drum 2. With such an arrangement, it is possible to prevent damage of the photo-sensitive drum caused by the operator's hands, or tool and the like, to reduce a spacing in the device, to provide small-sized device and to prevent poor transferring operation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus, and particularly to an image forming apparatus having an image bearing member and a protective cover for protecting the image bearing member.

[Conventional technology]

2. Description of the Related Art Conventionally, electrophotographic systems and electrostatic recording systems have been widely used in image forming apparatuses such as copying machines and computer output terminals.

In these image forming apparatuses, as shown in FIG. 4(a), an image carrier is charged with an image corresponding to an optical signal emitted from a light emitter 4 such as a laser beam or an LED using a primary charger 3. An electrostatic latent image is written on a photosensitive drum 2 as a body, and after this electrostatic latent image is visualized by a developing device 5, it is transferred to a sheet material 13 by a transfer device 6, and then the image transferred to the sheet material 13 is transferred to a fixing device. Image formation is performed in which the image is fixed in step 14 to form a recorded image.

In such an image forming apparatus, in addition to regular maintenance work such as replenishing developer to the developing device 5 and collecting unnecessary developer removed in the cleaner 8, feeding of the sheet 1-4-A' ] 3 is performed. In the event that defects or other inconveniences occur, it is necessary to expose the inside of the main unit as shown in FIG. 4(b) in order to dispose of them. At this time, since the inside of the image forming apparatus is exposed to light, there is a risk that the photosensitive layer on the surface of the image carrier may deteriorate. This is particularly a problem in the transfer area of the image carrier (hereinafter also referred to as electrostatic latent image carrier) due to the structure of the apparatus.

Furthermore, in recent years, a so-called process unit has been developed that integrates a secondary charger 3, a developing device 5, a cleaner 8, etc. that act on the electrostatic latent image carrier 2, and can be removed from the main unit as a whole. This method is applied for the purpose of reducing the maintenance work mentioned above, and the photosensitive drum 2, which serves as an electrostatic latent image carrier, is increasingly exposed to light. In addition, in the transfer area of the electrostatic latent image carrier 2, there is a problem that the surface of the sheet material 13 may be damaged by hands or tools when handling a feeding failure of the sheet material 13.

Therefore, in order to protect the transfer area of the electrostatic latent image carrier 2 from outside light and stimulation from hands, tools, etc., a protective cover for the electrostatic latent image carrier that is linked to the opening/closing operation is installed when the inside of the main unit is exposed. It has been proposed to provide the photosensitive drum near the photosensitive drum as an electrostatic latent image carrier. The protective cover 1 for the electrostatic latent image carrier covers the photosensitive drum as the electrostatic latent image carrier when the main unit is opened, as shown in FIG. 5 (1), for example, and covers the photosensitive layer on the photosensitive drum surface. protect from the external stimuli mentioned above.

As shown in FIG. 5(a), when the main body is closed, the photosensitive drum 2 approaches the transfer charger 6 in conjunction with the opening/closing operation.
, and retreat to a position where the function of the sheet material conveyance path 9 is not obstructed. Therefore, by adding a protective cover for the electrostatic latent image carrier, even if the inside of the device is exposed during maintenance work, the photosensitive drum 2 will not be exposed to external light, and it will also be prevented from being damaged by hands or tools. can.

[Problem that the invention is trying to solve]

However, the protective cover 1 described in -1- requires a retracting area inside the device, which is unnecessary during image formation. There was a problem.

On the other hand, the transfer device 6 located near the retracted position of the protective cover 1 has the following problem in faithfully transferring the developer forming the visible image on the photosensitive drum 2-L onto the sheet material 13. As the transfer device 6 of the image forming apparatus, a sixth transfer device 6 is used.
A corona charger as shown in the figure is generally used to transfer the developer that forms a visible image on the photosensitive drum 2 onto the sheet material 13 using the electric field generated by the developer. A in the figure where material 13 is close to
This may affect not only the transfer area within the range, but also the area B in the figure upstream in the rotational direction of the photosensitive drum 2.

The force on the sheet material 13 due to the electric field applied to the developer in this area B is weaker than the force due to the electric field applied to the developer in the transfer area A described above, so normally the developer in area B is not transferred. Among the developers attached to the photosensitive drum 2, those whose adsorption force to the photosensitive drum 2 has weakened are in area B.
Even if the developer is present, the electric field causes the developer to be transferred onto the sheet material 13 in advance. The developer transferred in this process causes the image formed by the developer to shift slightly from the original position where it should be transferred, resulting in so-called developer wobbling, which greatly reduces the quality of the final recorded image. It causes disturbance.

Therefore, conventionally, a transfer electric field guide member 16, as shown in FIG. A separate space is provided between the photosensitive drums 2 and 2 to deal with the unevenness caused by the advance transfer of the developer onto the photosensitive drum 2. However, although it is a very small amount, developer scattered during jam processing and paper dust from paper as a sheet material adheres to the transfer electric field guide member 16. These deposits are
As the number of printed sheets increases, the electric field accumulates on the transfer electric field guide member 16, and eventually spills into the corona charger located below, staining the corona wire and causing transfer defects. Therefore, there is also a drawback that the transferred developer in the transfer electric field guide member 16'' has to be cleaned periodically.

In addition, in the transfer device 6, the transfer electric field acts on the developer on the photosensitive drum 2'' through the sheet material 13, so that the sheet material]
If 3 is a material such as paper whose resistance value decreases as the humidity increases, in high humidity, the transfer electric field from the transfer device 6 may not provide enough of the electric field necessary for transfer, resulting in good transfer. There is also the problem of not being able to do so.

In order to solve this problem, conventional techniques have been devised to evaporate the moisture in the sheet material 13 using a heat source such as a heater before the sheet material 13 is conveyed to the transfer area. As shown, since it is necessary to separately install the preheater 18 within the device, there is a drawback that the device becomes larger.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to completely protect an image carrier from outside light, hands, tools, and other external stimuli, and to waste space within the apparatus. An object of the present invention is to provide a protective cover for an image carrier that does not protect the image carrier.

[Failure to solve the problem]

That is, the protective cover of the present invention not only has the basic function of completely protecting the image carrier from external stimuli, but also has the secondary function of functioning as a means related to image formation during image formation.

According to the present invention, the protective cover during image formation is moved from the position where it protects the image carrier, and at the retracted position serves as a conveyance path for the sheet, and furthermore, as the transfer electric field guide member described in 01, It also functions as a heating section for the sheet.

〔Example〕

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

FIG. 1(a) shows the vicinity of a transfer section of an image forming apparatus that best represents the features of the present invention. In this figure, a drum shutter 1 serving as a protective cover includes a shutter member (a) serving as a cover function of the drum shutter;
It is composed of a support member 1b that movably supports it, a conveyance guide member 1c, and a transfer electric field regulating member 1d. This support member 1b moves the drum shutter 1 to the retracted position shown in FIG. 2 in conjunction with the closing operation of the main unit in the direction of arrow a in the figure as shown in the conventional example described above. let At this time, the drum shutter 1 comes close to a registration roller 10 that conveys the sheet material 3 in synchronization with the rotation of the photosensitive drum 2 and a corona charger 6 as a transfer device, thereby forming a conveyance path for the sheet material. A transfer electric field regulating member provided on the corona charger 6 side of the drum shutter 1 along the longitudinal direction of the tram] d is a developer that forms a visible image and is located upstream of the transfer area on the photosensitive drum 2 in the rotational direction. The transfer electric field is regulated so that the transfer electric field from the corona charger 6 does not act on the transfer electric field.

Although the regulating member 1d may be made of an insulator, it is preferably made of a conductive material such as metal in order to more effectively regulate the transfer electric field. Further, when the regulating member 1d is made of a conductive material, it is more effective to ground it or apply a bias voltage opposite to the transfer electric field.

Further, although the case where the transfer device 6 is configured with a corona charger is shown, the same structure as above can be used also when a so-called roller charger is used, which generates a transfer electric field by applying a transfer bias to a conductive rubber roller. It is possible to take.

In addition, the developer, paper dust, and other substances adhering to the regulating member 1d are removed by a cleaning pad 7a provided at the tip of the main body member or the frame 7 of the process unit, and removed from the tram on which the regulating member 1d is provided. It is cleaned when the shutter 1 is closed. Note that the process unit is provided with at least a drum and a protective cover.

As shown in "2" below, the drum shutter 1-1- serves as a movable image carrier protection cover for the transfer electric field regulating member 1d.
Since the foreign matter on the regulating member [d] is disposed of each time the device is opened for jam removal, etc., it is possible to prevent transfer failures due to deposits accumulating and falling into the transfer device 6. .

Further, as shown in FIG. 1(b), a storage section 71 for storing the regulating member 1d is provided in the main body member or the frame 7 of the process unit.
), and the above-mentioned cleaning pad 7a is provided inside the cleaning pad 7a.
By providing a regulating member every time the device is opened, it is possible to prevent the deposits from falling off due to vibrations from the cleaning pad 7a that has been treated with the deposits of dJ2 and contaminating the inside of the device again. It is also possible to prevent hands from getting dirty by touching the cleaning pad 7a during work.

In any case, since the drum shutter 1 serving as a protective cover forms a conveyance path for the sheet in its retracted position, there is no need to secure a special space.

FIG. 3 is another embodiment of the invention. The hatched area on the sheet material conveying surface of the drum shutter in the figure is
This is a preheater 1e that heats the sheet material 13 before being conveyed to the transfer area and evaporates moisture in the sheet material 13.

This preheater 1e is located in the same plane as the sheet material conveyance surface formed by the shutter member 1a, and the sheet material 13 is guided through the sheet material conveyance path formed by this and the conveyance guide member 1c.
When passing, the sheet material 13 is heated to evaporate the moisture in the sheet material]3. As a result, the amount of moisture contained in the sheet material 13 conveyed to the transfer area is appropriately adjusted, so that the resistance value is maintained at which the transfer electric field can appropriately act on the developer on the photosensitive drum 2.

1. The preheater 1e may be made of nichrome wire, heat-generating ceramic, etc., which are normally used as a heater part, but the sheet material cannot be heated at the boundary between the drum shutter part and the preheater part on the sheet material conveying surface. Lasdol Chemical Co., Ltd.'s product name MR allows material 13 to be transported smoothly and is easy to process.
It is also possible to use a heat-generating paint such as X-001.

In addition, in order to reduce the power load on the main unit, the operation of the preheater 1e may be controlled in synchronization with the movement of the registration rollers 10 or with sensors, such as a sheet material conveyance detection sensor, installed separately within the unit. It is desirable to turn it on and off. Furthermore, the operation of the preheater 1e may be controlled based on commands from a humidity center (not shown) built into the main body.

FIG. 9 shows a color image forming apparatus to which a drum shutter according to the present invention is applied. In the illustrated color image forming apparatus, after the photosensitive drum 2 is uniformly charged by the charger 3,
A colored electrostatic latent image is formed on the photosensitive drum 2'' by exposure 4a corresponding to the image signal of the first color, and a developing device 5a containing a color developer corresponding to the image signal of the first color, for example, with red toner, is used. After visualization, the visible image of the first color is transferred by the transfer device 6 onto the sheet material 13 held on the transfer drum 2.

Next, after the transfer residual developer on the photosensitive drum 2 is removed by the cleaner 8, the photosensitive drum 2 is uniformly charged again by the charger 3, and an electrostatic latent image corresponding to the image signal of the second color is formed. By exposure 4b, the photosensitive tram 2'' is formed into 2
A developing device 5 containing a color developer such as a black toner
After visualization by b, the first color visible image is transferred, and the second color visible image is superimposed and transferred onto the sheet material 13 held by the transfer drum 16 by the transfer device 6. Subsequently, the sheet material 13 onto which the two-color visible image has been transferred is separated from the transfer drum 16 and fixed by a fixing device to form a recorded image.

In these color image forming apparatuses, when transferring visible images of two or more colors, it is necessary to apply a stronger transfer electric field than when transferring the previous color image in order to cancel the electric charge held by the developer on the sheet material 13''. Therefore, image disturbances due to blurring are more likely to occur than in the above-mentioned one-time transfer image forming apparatus. Therefore, using the drum shutter 1 equipped with the transfer electric field regulating member described above in the color image forming apparatus has the following advantages:
Layers are effective.

Further, when using electrostatic adsorption force as a method of holding the sheet material 13 on the transfer drum 16, the resistance value of the sheet material 3 decreases at high temperatures as described above, so that it is not attracted to the electric field of the transfer drum 15. The electric charge on the sheet material 13 that comes off becomes easier to dissipate, and the adsorption force decreases.

Therefore, if the drum shutter 1 to which the above-mentioned preheater is added is used in the above-mentioned apparatus, it is useful not only for assisting transfer but also for holding the sheet material 13 by electrostatic adsorption force.

In the above description, a two-color image has been described, but the present invention can also be applied to a so-called full-color device having three or more sets of developing devices.

〔Effect of the invention〕

As described above, the protective member according to the present invention not only has its original functions, but also has secondary functions such as a transfer auxiliary device, a sheet material conveyance path, and a pre-transfer heater, so that these members can be installed in the device. This has the effect of eliminating the need for a separate provision and making the device more compact.

In addition, since the transfer electric field regulating member is cleaned by opening and closing the protective cover, there is no need to separately clean the developer, paper dust, etc. on the regulating member as described above, and when configured as a process unit. Since the photosensitive drum and the regulating member are integrated, the sheet material conveyance path can be precisely defined with respect to the photosensitive drum, which also has the effect of reducing changes in image quality due to cartridge replacement.

[Brief explanation of drawings]

FIGS. 1(a), (b) and 2 are cross-sectional views showing an embodiment of the drum shutter according to the present invention, FIG. 3 is a cross-sectional view showing another example of the drum shutter according to the present invention, and FIG. 8 are schematic diagrams showing a conventional example, and FIG. 9 is a schematic diagram in which the present invention is implemented in a color image forming apparatus. 1... Drum cover 2... Photosensitive drum] a... Shutter member 1b... Drum cover support member 1d... Electric field regulating member 1e... Heater member 7a... Cleaning pad 13... Sheet material lol 5 (necessary) (b)

Claims (1)

Scope of Claims: (1) An image forming apparatus including an image carrier and a protective cover that moves between a position covering an exposed portion of the image carrier and a position evacuated from the position, wherein the protective cover An image forming apparatus characterized in that when the protective cover is in a retracted position, the protective cover forms a sheet conveyance path. (2) A transfer means is provided opposite to the image carrier exposed when the protective cover moves to the retracted position, and the protective cover has a member for regulating the transfer electric field of the transfer means. Image forming device. (3) The image forming apparatus according to claim 1 or 2, wherein the protective cover includes a heating member that heats the sheet being conveyed. (4) Claim 1, wherein the image carrier and the protective cover are provided in a process unit that is detachably attached to the image forming apparatus.
3. The image forming apparatus according to item 3. (5) The image bearing member and the protective cover are provided in a process unit that is detachably attached to the image forming apparatus, and the process unit has a cleaning member that cleans the transfer electric field regulating member of the protective cover. Image forming device. (6) The image forming apparatus according to claim 5, wherein the transfer electric field regulating member is cleaned by moving the protective cover.