JPH0723799Y2 - Image forming device - Google Patents

Description

Description: TECHNICAL FIELD The present invention is an endless flexible device that is stretched around a plurality of rollers including a driving roller, is driven to rotate by the rotation of the driving roller, and has an electrostatic latent image formed on the surface side. A belt-shaped image carrier having flexibility, and a rotary developing device which is provided so as to face the belt-shaped image carrier and visualizes the electrostatic latent image formed on the carrier as a toner image. The rotary developing device has a circular developing casing, a plurality of developer chambers partitioned inside the casing, and the developer chambers provided in the developer chambers. By rotating about the center of the rotation axis as a rotation axis, the belt-shaped image carrier is selectively positioned at the developing position facing the belt-shaped image carrier, and at that position, the belt-shaped image carrier is pressed against its back surface side to bend it. Belt-shaped image carrier An image forming apparatus and a plurality of developer bearing member for pressing while the developing operation.

2. Description of the Related Art An image forming apparatus of the above type configured as a copying machine, a facsimile, a printer, etc. has been conventionally known.

In each developer chamber of the rotary developing device used in such an image forming apparatus, for example, developers having different colors are accommodated, and the developers are carried on the developer carrying member brought to the developing position. The electrostatic latent image formed on the belt-shaped image carrier is visualized as a toner image by the developer.

After the developing operation is carried out by a certain developer carrying member in this way, the developing casing is rotated to bring another developer carrying member to the developing position to carry out the developing operation.

However, the developer carrying member located at the developing position is pressed against the belt-shaped image carrier through the developer, and the belt-shaped image carrier is pressed against the back surface side of the belt-shaped image carrier to bend it. Since the carrier has flexibility, when the developing casing is rotated as described above and the developer carrying member that has occupied the developing position until that time is withdrawn from the developing position, the rotary developing device is The opposing belt-shaped image carrier portions sway when the pressing force of the developer carrying member is released. Therefore, the belt-shaped image carrier portion may come into contact with the outer peripheral surface of the developing casing, and the belt-shaped image carrier portion may be damaged.

In order to prevent such a problem, the belt-shaped image bearing member may be tensioned strongly. However, in this case, the driving torque increases and the bearing portion of each roller around which the belt-shaped image bearing member is wound. Is inevitably abraded and the life of the belt-shaped image carrier is shortened.

OBJECT The object of the present invention is to provide an image forming apparatus which eliminates the above-mentioned conventional drawbacks.

In order to achieve the above object, the present invention is directed to an image forming apparatus of the type described at the beginning, which is a plane portion of a belt-shaped image carrier between a driving roller and another roller, and a moving direction of the carrier. With respect to, the relative position between the rotary developing device and the belt-shaped image bearing member is set so that the developer holding member positioned at the developing position faces the tension side portion which is the flat surface portion on the downstream side of the drive roller. Each developer carrying member is set such that when the set and selected developer carrying member is positioned at the developing position, the tension side portion of the belt-shaped image carrying body and the outer peripheral surface of the developing casing are separated from each other. A part of the surface of the developing casing is projected outward from the outer peripheral surface of the developing casing.

Embodiment Hereinafter, the present invention will be described based on an embodiment.

In FIG. 1 showing an image forming apparatus according to an embodiment of the present invention, a color document (not shown) is placed on a document table 1.
In this state, the document table 1 moves in the direction of the arrow. At this time, the document is illuminated by the light source, the document image is slit-scanned by this, and the flexible belt photoconductor 2 driven to run in the direction of the arrow is exposed. The image is projected by the optical system 10. The belt photosensitive member 2 constitutes one example of the constitution of the belt-shaped image carrier.

A filter device 3 having a blue filter, a green filter, and a red filter (not shown) is provided in the image forming optical path between the document table 1 and the belt photosensitive member 2, and each filter is selectively used. As a result, electrostatic latent images corresponding to the color-separated images of the original are formed on the surface side of the belt photoconductor 2.

A rotary developing device 4 that faces the belt photoconductor 2 and visualizes the electrostatic latent image formed on the belt photoconductor 2 as a toner image is provided. As shown in FIGS. 2 and 3, this rotary developing device has a circular developing casing 104.
And a plurality of developer chambers partitioned inside the casing 104, and a plurality of (three in the illustrated example) developing rollers 5 provided in each developer chamber. These developing rollers 5 constitute an example of a developer carrying member, and are arranged on concentric circles in the circumferential direction of the developing casing 104. Each developer chamber contains a different color developer, for example, a powdery developer (not shown) of yellow, magenta, or cyan, and each developing roller 5 contains the developer. Carried.

By rotating the developing device 4 by 120 ° with the center of the developing casing 104 as the rotation axis O, each developing roller 5 is selectively positioned together with the developing roller to a developing position facing the belt photosensitive member 2. It Then, each time the electrostatic latent image is formed, the electrostatic latent image is developed by the developer carried on the developing roller which is brought to the developing position and rotationally driven. In this way, the developing roller 5 positioned at the developing position performs the developing operation at that position. At that time, the developing roller 5 located at the developing position is the belt photoreceptor 2
Is pressed against the back surface side of the belt-shaped photoconductor 2 while being bent, and the belt-shaped photoconductor 2 is pressure-contacted via the developer, and the developing operation is executed in the pressure-contacted state.

In FIG. 1, a transfer paper is fed from a paper feed cassette 6 by a paper feed roller 7, and the transfer paper passes through a registration roller 12 and is held on a transfer belt 8 made of an endless polyester film or the like. The transfer belt 8 is rotatable in the forward and reverse directions, and the transfer paper held on the belt 8 reciprocates together with the belt 8.

When the transfer paper held on the transfer belt 8 travels on the outward path in the same direction as the rotation direction of the belt photoconductor 2 and passes by the belt photoconductor 2, the toner of a certain color on the photoconductor 2 is transferred. The image is transferred onto the transfer paper by corona discharge by the transfer paper charger 9.

The transfer belt 8 can be swung in the direction of arrow A as a belt unit by the rotation of the eccentric roller 11. After the transfer of the toner image, the transfer belt 8 is swung to the broken line position and separated from the belt photoconductor 2. In this state, the transfer belt 8 is rotated in the reverse direction, and the transfer sheet advances in the return path in the direction opposite to the rotation direction of the photoconductor 2 and is returned to the original position. At this time, the registration roller 12
Is retracted upward so as not to disturb the unfixed toner image on the transfer paper.

After the transfer paper returns to its original position, it is passed again at the belt photoreceptor 2 so that the toner image of the next different color is superimposed on the previous transfer image. Is transcribed to. At the same time that the transfer of the first color is performed, the transfer paper is electrostatically attracted to the transfer belt 8 and repeats reciprocating movement integrally with the transfer belt 8.

When the transfer of the third color is completed, the transfer sheet 8 and the transfer belt 8 are discharged by the charge removing charger 13, and then discharged through the fixing device 14 as a color copy.

The belt photosensitive member 2 has a pair of supporting side plates 15 as shown in FIG.
Drive roller 1 rotatably supported on one side (not shown)
It is stretched between 7, driven roller 18 and tension roller 19. In this way, the endless belt photoreceptor 2 is driven by the drive roller.
Driven by multiple rollers, including 17
Is rotated and driven, and as described above, an electrostatic latent image is formed on the surface side of the belt photoreceptor 2.

When the belt photoconductor unit 16 configured as described above is set in the process case 21 shown in FIG. 2, the cleaning blade 22 is pressed against the belt portion wound around the tension roller 19 under the action of the spring 23. .

With the belt photoconductor unit 16 set in the process case 21, the belt photoconductor 2 and the rotary developing device 4 are positioned so as to face each other as shown in the drawing.

Here, as described above, in order to bring each developing roller 5 to the developing position, the developing casing 104 is rotated around its rotation axis.
When 4 is rotated and the developing roller that has been in the developing position until that time is withdrawn from this developing position, in the conventional image forming apparatus, the flexible belt photosensitive member wobbles during this withdrawal, which causes the developing casing 104 to move. Outer peripheral surface 4a (second
(Fig.), There is a risk that the photoconductor portion may be scratched. As described above, the developing roller located at the developing position presses the belt photosensitive member against the belt photosensitive member, presses the belt photosensitive member toward the back surface thereof, and bends the belt photosensitive member. When the sheet exited from the developing position, the belt photosensitive member part where the pressing force by the developing roller was released was largely wobbled.

Therefore, in the image forming apparatus of the present example, the rotary developing device 4 and the belt photosensitive member 2 are arranged so that the developing roller 5 positioned at the developing position is opposed to the tension side portion of the belt photosensitive member 2. The relative position is set.

When the belt photosensitive member 2 is wound around a plurality of rollers including the driving roller 17, and the driving roller 17 is rotationally driven to drive the belt photosensitive member 2 to travel, the photosensitive member has a tension side portion and a slack side portion. That is, the flat surface portion of the belt photosensitive member between the drive roller and the other roller, and the flat surface portion on the downstream side of the drive roller in the moving direction of the photosensitive member is the tension side portion. In the example shown in FIG. 2, the belt photosensitive member portion connecting the driving roller 17 and the driven roller 18 is the tension side portion, and the developing roller 5 occupying the developing position is opposed to this portion.

Moreover, as shown in FIG. 2, when the selected developing roller 5 is positioned at the developing position, the above-mentioned tension side portion of the belt photosensitive member 2 and the outer peripheral surface 4a of the developing casing 104 are separated from each other, Part of the surface of each developing roller 5 projects outwardly from the outer peripheral surface 4a of the developing casing 104.

In the example of FIG. 2, each developing roller 5 is a developing casing 104.
And slightly protrude by l ₁ from the outer peripheral surface 4a of and the line L connecting the drive roller 17 and the driven roller 18, as between the developing casing outer peripheral surface 4a becomes the gap l _2, the photoreceptor belt 2 The rotary developing device 4 is positioned.

For example, in a developing device using a one-component developer as the developer, the difference (l ₁ −l ₂ ) between the protrusion amount l ₁ and the gap amount l ₂ is 0.5 to
L ₁ and l ₂ are set so as to be about 1.5 mm, and the developing roller 5 occupying the developing position is brought into pressure contact with the surface of the belt photosensitive member 2 and pressed against the back surface side thereof to bend it.

According to the above configuration, the developing roller 5 occupying the developing position
Is located on the tight side of the belt photosensitive member 2, so that the developing casing can be operated while the belt photosensitive member 2 is being driven.
When the developing roller 5 is retracted from the developing position by rotating the developing roller 5, the tension side portion is originally tense, so that the tension side portion does not largely sway, and the belt photosensitive member 2 is provided on the outer periphery of the development casing 104. It is possible to prevent contact with the surface 4a. Moreover, when the developing roller 5 is at the developing position,
Since the tension side portion of the belt photosensitive member and the outer peripheral surface 4a of the developing casing 104 are separated from each other, even when the tension side portion of the belt photosensitive member 2 slightly fluctuates when the developing roller 5 moves out of the developing position, the development It is possible to prevent contact with the outer peripheral surface of the casing 104, and it is possible to completely prevent the defect that the belt photosensitive member is damaged.

Here, in the example shown in FIG. 5, the belt portion connecting the driving roller 17 and the driven roller 18 to the belt photosensitive member 2 is the tension side portion, and the driving roller 17 and the tension roller 19 are connected.
The belt portion connecting to and becomes the slack side portion, but conventionally, the rotary developing device 4 was provided in such a slack side portion.

Also in FIG. 5, when the developing roller 5 is positioned at the developing position, the belt portion on the slack side is covered by the roller with respect to the line L indicating the belt portion in the stretched state. However, in this state, when the developing roller 5 is retracted and another developing roller is positioned at the developing position in this state, the belt portion fluctuates as shown in FIG. 6 in this process. The bulging of the belt contacts the outer peripheral surface (outer wall surface) 4a of the developing casing 104, and the belt photoreceptor 2 is damaged. Such a problem occurs due to the developing roller 5 located at the developing position being opposed to the slack side belt portion that tends to wobble during rotation.

Therefore, if the protrusion amount l ₁ of the developing roller 5 is increased, it becomes difficult for the belt portion to contact the outer peripheral surface 4a of the developing casing.
If the amount of protrusion is too large, the exposed roller portion increases, and the developer easily scatters, which is not preferable.

Therefore, in order to make the belt portion less likely to bulge, the belt photosensitive member 2 can be strongly stretched. However, in this case, the driving torque is increased and the roller bearing portion is easily worn. , The life of the belt photoreceptor becomes short.

According to the configuration of the embodiment of the present invention, as described above, when the developing roller 5 retreats from the developing position, the tension side portion is
Since the bulge is less likely to occur, the belt portion is less likely to contact the outer peripheral surface 4a of the developing casing.

Further, in this embodiment, the cleaning blade 22 is pressed against the belt portion around the roller 19 under the action of the spring 23, and the braking force is applied to the belt photosensitive member 2. The belt portion between the 17 and the driven roller 18 tends to be further stretched, and the belt portion is more difficult to contact the outer peripheral surface 4a of the developing casing 104.

Further, since it is not necessary to stretch the belt photosensitive member 2 more than necessary, driving torque does not increase, and it is possible to prevent problems such as early wear of the bearing portion and shortening of the life of the belt photosensitive member.

Further, since it is not necessary to set the protrusion amount l ₁ too large, the scattering of the developer can be prevented as much as possible, and at the same time, the degree of freedom in designing the developing device can be increased.

The specific example in which the present invention is applied to an image forming apparatus for obtaining a full-color image has been described above. However, a so-called multi-color image can be obtained by accommodating, for example, red, blue, and black color developers in a rotary developing apparatus. Alternatively, the present invention can be applied to an image forming apparatus in which developers of the same color are contained to obtain a monochromatic image. Further, a belt dielectric is used as the belt-shaped image bearing member instead of the belt photosensitive member,
The same applies to an image forming apparatus using a belt or a sleeve that does not rotate as a developer carrying member.

As described above, according to the present invention, in the image forming apparatus that performs the development by the rotary developing device, the belt-shaped image carrier comes into contact with the outer peripheral surface of the developing casing when the developing casing rotates about the rotation axis. It is possible to prevent the defect that the carrier is scratched. Moreover, without shortening the life of the belt-shaped image carrier or increasing the cost of the image forming apparatus,
The function as a belt-shaped image carrier can be maintained for a long time.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, FIG. 2 is a diagram showing a main part thereof, FIG. 3 is a sectional view of a rotary developing device, FIG. 4 is a unit configuration diagram of a belt photosensitive member, and FIG. 6 and 6 are explanatory views used to explain conventional problems. 4 ... Rotary developing device, 4a ... Outer peripheral surface 17 ... Drive roller, 18,19 ... Roller 104 ... Developing casing, O ... Rotation axis

Claims (1)

[Scope of utility model registration request] 1. A belt-shaped image carrier having endless flexibility, which is stretched around a plurality of rollers including a drive roller, is driven to rotate by the rotation of the drive roller, and has an electrostatic latent image formed on the front surface side. And a rotary developing device which is provided so as to face the belt-shaped image carrier and visualizes the electrostatic latent image formed on the carrier as a toner image. The apparatus is provided in a circular developing casing, a plurality of developer chambers partitioned inside the casing, and each developer chamber, and the rotary developing device rotates about the center of the developing casing as a rotation axis. Thus, the belt-shaped image bearing member is selectively positioned at the developing position facing the belt-shaped image bearing member, and at that position, the belt-shaped image bearing member is pressed against the back surface side of the belt-shaped image bearing member to bend the belt-shaped image bearing member. Perform development operation while pressing it against the body In an image forming apparatus having a plurality of developer carrying members, a flat portion of the belt-shaped image carrying body between the driving roller and another roller, the driving roller of the driving roller in the moving direction of the carrying body. The relative position between the rotary developing device and the belt-shaped image carrier is set and selected so that the developer carrying member positioned at the developing position faces the tension side part which is the downstream flat part. When the developed developer carrying member is positioned at the developing position, one surface of each developer carrying member is arranged such that the tension side portion of the belt-shaped image carrying body and the outer peripheral surface of the developing casing are separated from each other. The image forming apparatus is characterized in that the portion projects outwardly from the outer peripheral surface of the developing casing.