JPH07319295A - Image forming device - Google Patents

Abstract

(57) [Summary] [Object] To provide a separation device capable of enlarging the separation region and stabilizing the separation property without increasing the size of the device body. The separating device 50 is composed of two rotatable separating rollers 14a and 14b, and the gap between the photosensitive drum 1 and the separating rollers 14a and 14b is separated by the separating rollers 14a and 14b.
It is kept constant by the butting roller 24 provided at the end of the roller shaft 40. This enlarges the separation area without increasing the size of the separation device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine or a laser beam printer, which is characterized by a separating device which is a charge eliminating means for a transfer material.

[0002]

2. Description of the Related Art Conventionally, corona dischargers such as corotrons and scotrons, which have good charge removal property, have been widely used as means for removing charges of charge-removed objects such as image carriers and transfer papers. However, the corona discharger requires an expensive high-voltage power supply, and also requires space such as itself and a shield space for the high-voltage power supply. Furthermore, since a large amount of corona products such as ozone is generated, additional means / mechanisms for coping with the large amount are required, which have been factors for increasing the size and cost of the apparatus.

Therefore, in recent years, a contact neutralization type separator has been proposed in place of the corona discharger. In the contact static elimination method, a static elimination member to which a voltage (for example, a DC voltage of about +1 to +5 KV or an alternating voltage of direct current and alternating current) is applied is brought into contact with an object to be neutralized such as an image carrier with a predetermined pressing force. The charge of the object to be removed is removed. However,
Since the static elimination member is in contact with the static elimination target, the contact static elimination method has disadvantages such as vibration noise of the static elimination member and shortening of the life of the static elimination member.

On the other hand, a separating device for eliminating static electricity by providing a gap between the static eliminating member and the object to be neutralized is US Pat. No. 5,146.
Proposed in No. 280, etc.

[0005]

The inventor of the present invention has made trial productions of the above-described two types of separation devices and has made repeated studies. Hereinafter, the background of the study for pointing out the problems of the conventional example will be described.

The graph of FIG. 7 is data when transfer / separation is performed by contact transfer and contact separation on a photosensitive drum having a diameter of 108 mm using a copying machine of 60 sheets / min.

In the graph of FIG. 7, the horizontal axis shows the static elimination voltage applied to the separation roller, and the vertical axis shows the static elimination current value flowing toward the photosensitive drum due to the applied voltage. At each static elimination voltage, 20 sheets of domestic A4 size transfer paper were passed, and the state where all 20 transfer paper tips were completely separated was evaluated as separation ○, and even one sheet floated. The state of being separated is evaluated as separation ×. Further, all 20 transfer papers were subjected to image evaluation, and the state where retransfer (image defect due to low density) occurred even on 1 sheet was designated as retransfer x, and the state where retransfer did not occur was retransferred. The area is indicated by the arrow shown in FIG.

The primary charging has a resistance value of about 2 kΩ and a diameter of 16
Two charging rollers having a conductive rubber layer of mm are arranged in parallel, and a DC voltage of +970 V is applied to charge the photosensitive drum. In the transfer, a DC voltage of +4 KV is applied to a transfer roller having a conductive rubber layer having a resistance value of about 10 MΩ and a diameter of 16 mm to transfer the transfer roller onto a transfer paper. Separation is performed by bringing one separation roller having a conductive rubber layer having a resistance value of about 10 MΩ and a diameter of 16 mm into contact with the photosensitive drum and applying a DC voltage to the separation roller. The examination environment was temperature and humidity of 20 ° C. and 20%.

As can be seen from the data shown in FIG. 7, in the static elimination method in which the separation roller is brought into contact with the photosensitive drum, there is no region that simultaneously satisfies separation and retransfer.

Next, the present inventor considers that the reason why there is no region that satisfies the separation in the case of the static elimination method of contacting the separation roller is that the transfer paper and the separation roller are in contact at the time of separation, and both ends of the separation roller are considered. Further, a distance assurance means for keeping a constant distance from the photosensitive drum is provided, the separation roller is arranged apart from the drum, and a DC bias is applied to the separation roller to examine the separation device.

The graph in FIG. 8 is data with the above configuration. Separation was performed by disposing one separation roller (the same separation roller as that used for contact charge removal) at a distance of 1 mm from the photosensitive drum, and rotating the same at the same peripheral speed as the drum. The study conditions for the primary charger and the transfer charger are the same as the study conditions for the contact static elimination described above. The evaluation method is also the same as described above. From this data, it can be seen that in the non-contact roller separation (single roller) system, there is no area that simultaneously satisfies separation and retransfer.
However, although it cannot be judged from the graph, the level of separation is shown in FIG.
It was visually confirmed that it was better than the contact static elimination.

Therefore, a non-contact roller separation system (roller 1
In this book, the reason why a satisfactory separation area does not appear is that the separation roller removes the charge on the surface of the drum in a small area, and in order to obtain a satisfactory separation area, the discharge area is widened. In particular, in a high-speed machine having a high transfer paper conveyance speed, the static elimination time is shorter than in a low-speed machine having a slow speed, and thus the static elimination area needs to be further widened.

As a method for widening the charge removal area, a plate charge removal method has been known, which has been conventionally proposed to remove charge by a non-contact plate-shaped member. This static elimination method is very inconvenient because the static elimination member is stationary, so that the static elimination member is liable to be contaminated and it is necessary to take it out to clean the stain. As a result, it is easy to neglect the cleaning, and in that case, poor separation occurs and it is impossible to use the apparatus.

If the diameter of the separation roller is increased in order to widen the charge removal area, the size of the separation device becomes large and, as a result, the size of the entire image forming apparatus also becomes large. Further, there is a problem in that it is difficult to keep the resistance value of the roller surface constant because the cost is increased due to the enlargement of the roller and the surface area of one roller is large, and as a result, the static elimination characteristics are not stable.

Therefore, a main object of the present invention is to provide an image forming apparatus equipped with a separation device which can enlarge the separation region without increasing the size of the main body of the device.

Another object of the present invention is to provide an image forming apparatus provided with a separating device having a stable separating property.

[0017]

The above object can be achieved by an image forming apparatus according to the present invention. In summary, the present invention is
In an image forming apparatus provided with a charge removing unit for supplying electric power, which removes electric charges of an image carrier or a transfer material, the charge removing unit has a conductive core material and an elastic body covering the conductive core material. At least one roller-shaped rotating body and the image-bearing member are arranged so as to have at least one roller-shaped rotating member rotated by a driving unit about the rotation axis thereof, and the static eliminating unit and the image-bearing member are not in contact with each other. The image forming apparatus is characterized by having a distance assurance means for keeping a constant gap with the body.

It is preferable to dispose the action area of the charge eliminating means on the upstream side in the moving direction of the image carrier relative to the contact point between the straight line parallel to the conveying direction after the transfer material separation and the image carrier.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Embodiment 1 FIG. 6 is a block diagram showing Embodiment 1 of the image forming apparatus according to the present invention. In FIG. 6, a charging roller 2 of the charging device 20 having a high-resistance conductive rubber layer is brought into contact with the photosensitive drum 1, and a direct current voltage is applied to the charging roller 2 to uniformly charge the photosensitive drum 1. Then, by exposing the charged photosensitive drum 1 by the exposure device 3, the potential of the exposed portion is attenuated and a latent image is formed. The latent image is developed by the developing device 4 into a toner image. Next, the transfer device 5 transfers the toner image onto the transfer paper supplied by the paper supply device. The transfer device 5 is composed of a transfer roller 5a having a high-resistance conductive rubber layer, which is brought into contact with the photosensitive drum 1 and a DC voltage is applied to perform transfer.

The transfer paper on which the toner image has been transferred is separated from the photosensitive drum 1 by removing the charges on the photosensitive drum 1 by a separating device 50 which is a charge eliminating means. The toner remaining on the photosensitive drum 1 is removed by the cleaning device 6. Further, the transfer paper is sent to a predetermined position of the fixing roller 8 by the paper conveying device 7 and the paper guide 10. Next, the transfer sheet is heated by the heater 12 and the thermistor 11 to a constant temperature, and the transfer sheet is held by the fixing roller 8 connected to a rotation driving device (not shown) and the pressure roller 9 that is rotated by being pressed against the fixing roller 8. The toner image is conveyed and, during this time, the toner image is permanently fixed on the transfer paper. The transfer paper that has passed between the fixing roller 8 and the pressure roller 9 is ejected to the outside of the machine by the paper ejection roller pair 13.

Next, a separating device 50 which is a characteristic part of the present invention.
This will be described in detail with reference to FIGS. 1 is a perspective view showing a separating device 50, FIG. 2 is a partial cross-sectional view of the photosensitive drum 1 of the separating device 50 of FIG. 1 in the direction of the rotation axis, FIG. FIG. 4 is an electrical system diagram of the separation device 50.

1 and 2, the separation roller 14a,
Reference numeral 14b includes a conductive core material, for example, a roller shaft 40 which is a conductive core material made of SUS, and a conductive rubber layer 42 which is a ring-shaped elastic body and is covered with the roller shaft 40. Both ends of the roller shaft are in contact with the outer peripheral surface of the roller shaft, and
conductive bearings 15a, 15 for supporting a, 14b
b is provided. The bearings 15a and 15b are configured to be pressed against the photosensitive drum 1 side by a roller spring 16 which is a compression coil spring, but have a retaining structure described later so as not to contact the photosensitive drum 1.

Further, along the inner wall of the casing 25 for accommodating the separation rollers 14a and 14b, conductive members 18 and 19 are continuously arranged near one bearing 15b.
The conductive member 19 arranged inside in FIG. 2 is electrically connected to the roller spring 16, and the conductive member 18 arranged outside is a contact held inside the projecting portion 25 c of the casing 25. It is electrically connected to 17. As a result, the voltage output from the voltage generation / control device 20 shown in FIG. 4 is transmitted to the separation rollers 14a and 14b via the contact 17, the conductive members 18 and 19, and the roller spring 16.

The voltage generation / control device 20 shown in FIG. 4 is a device for outputting a DC voltage or an AC voltage, and is a drum driving device 21.
It can be switched on and off by a signal from. That is, when the drum drive is on, the voltage applied to the separation rollers 14a and 14b is also on, and when the drum drive is off, the voltage is off.

In FIG. 2, a roller gear 22 is fixed to the end of the separation roller 14b, and a drum gear 23 is fixed to the end of the photosensitive drum 1. This roller gear 22
And the drum gear 23 are meshed with each other, the drive of the photosensitive drum 1 is transmitted to the separation roller 14b, and the photosensitive drum 1 and the separation roller 14b are driven so that the peripheral speeds of both are the same. Then, as is apparent from FIG. 1, the separation rollers 14a and 14b rotate in the same direction and at the same speed by the belt 32 stretched between the pulleys 31a and 31b fixed to the separation rollers 14a and 14b, respectively.

The roller gear 22 and the drum gear 23 are preferably helical gears having high transmission efficiency so as not to transmit the vibration of the photosensitive drum 1 to the separation roller 14b. Further, either or both of them must be made of a non-conductive material so as not to be electrically connected between the gears. In addition to the gear driving, the gear may be replaced with rubber having a high friction coefficient, for example, non-conductive silicone rubber to perform the drive transmission.

Bearings 15a and 15b and separating roller 14a,
Abutting rollers 24, which are, for example, POM or a resin member obtained by applying fluorine coating to POM, are arranged between 14b. The abutment roller 24 is configured to ensure a proper gap between the photosensitive drum 1 and the separation rollers 14a and 14b.

The bearings 15a and 15b are held by a part of a casing 25 made of a non-conductive resin and slidable toward the photosensitive drum 1. The separation rollers 14a and 14b are shielded by a casing 25 to prevent voltage leakage to other parts.

As shown in FIG. 2, the position of the separating device 50 with respect to the photosensitive drum 1 is formed integrally with the casing 25 by a leaf spring 26 which is an urging means provided on the bottom rear surface of the casing 25. Two convex portions 25a, 25
b and the cylindrical projection 25c (FIG. 1) are positioned by hitting the non-rotating members 27, 28 (FIG. 2) held on the photosensitive drum 1. The non-rotating members 27, 28 are arranged coaxially with the cylindrical photosensitive drum 1, and guarantee the positional accuracy with the photosensitive drum 1.

Therefore, in the modified example of the first embodiment shown in FIG. 3, the abutting roller 24 is provided only on the separating roller 14a, and the separating roller 14b includes the drum 1 and the casing 25 as described with reference to FIG. The non-rotating members 27 and 28 come into contact with each other to uniquely determine the position.

Next, the transfer / separation process of this embodiment will be described with reference to FIG. The post-charger 29 applies an electric charge to the negatively charged toner on the photosensitive drum 1, and the electric charge of the toner on the paper is pulled up, so that retransfer (defective image with low density) is less likely to occur. Next, by applying a positive DC voltage to the above-mentioned transfer roller 5a on the transfer paper fed through the transfer guide 30, the toner is electrostatically transferred to the transfer paper. Thereafter, the transfer paper is neutralized and removed by applying a negative DC voltage to the separation rollers 14a and 14b, and the transfer paper is separated from the photosensitive drum 1.

FIG. 9 is a graph showing the examination result of the separation apparatus of this embodiment. Separation rollers 14a, 14b (Fig. 3)
The separation roller 14a has a gap of 6 m from the photosensitive drum 1.
In m, the separation roller 14b is 1 mm. The two separation rollers 14a and 14b are rotationally driven at the same peripheral speed as the photosensitive drum 1. The other examination conditions are the same as the examination conditions of the separation device in the above-mentioned conventional technique.

From the graph shown in FIG. 9, it is understood that a region that simultaneously satisfies separation and retransfer appears.

As described above, the separating device is provided with the two separating rollers, and the distance assurance means for keeping the gap between the at least one separating roller and the photosensitive drum constant is provided.
The separation area can be expanded without increasing the size of the separation device and the device main body.

Second Embodiment Next, a second embodiment of the separation device according to the present invention will be described.

First, in order to facilitate understanding of the present embodiment, FIG.
The operation of the transfer / separation unit of the first embodiment and its problematic problems will be described with reference to FIGS.

As shown in FIG. 12, the separating apparatus of the first embodiment has the working regions of the separating rollers 14a and 14b (in the figure, the shaded portions).
Is located on the downstream side in the rotation direction of the photosensitive drum 1 with respect to the contact point C _p between the straight line L parallel to the paper transport direction and the photosensitive drum 1, and therefore the gap between the separation roller 14a and the photosensitive drum 1 is about 6 m.
had to spread to m. As shown in FIG. 10, if the gap is set to 1 mm, which is the same as the gap of the separation roller 14a, when a thick paper P _a such as 128 g / m ² paper is passed, the photosensitive drum 1 due to the weight of the paper passes through the separation roller 14b. Separate from. However, since the action area of the separation roller 14a is located above the action area of the separation roller 14b, the thick paper p _a enters between the separation rollers 14a and 14b, and as a result, a jam occurs.

In FIG. 11, when domestic paper P _b such as 64 g / m ² paper is passed, it is not separated by the separation roller 14b and is separated from the photosensitive drum 1 by the separation roller 14a, but the paper at the separation point is Since the force F is applied to the clockwise direction with respect to the carrying direction of the paper carrying device 7 after separation, the domestic paper p _b is carried while forming a loop as shown in the figure. Therefore, the transfer side of the transfer paper comes into contact with other parts, and as a result, toner is scattered and an image defect occurs. Therefore, FIG.
As shown in, the gap between the separation roller 14a and the photosensitive drum 1 had to be widened to 6 mm.

However, when the separation roller 14b is moved away from the photosensitive drum 1 as shown in FIG. 12, the operation area B of the separation roller 14b becomes narrower than the discharge area A (FIG. 11) when the gap is 1 mm, and the separation performance deteriorates. Further, since the discharge start voltage also rises, the voltage value applied to the separation roller 14b must be raised, and as a result, the power consumption also rises. Further, in the action area B, the gap with the photosensitive drum 1 is as long as 6 mm, so that the combined amount of oxygen is large, and as a result, the amount of ozone generated is larger than the gap of 1 mm.

Therefore, in this embodiment, as shown in FIG. 13, a transfer / separation device, a transfer guide 30, a post charger 2 are provided.
9 and the like were moved to the upstream side in the rotation direction of the photosensitive drum 1.
As a result, the gap between the separation roller 14a and the photosensitive drum 1 can be narrowed, and in this experiment, it could be 1 mm.

In FIG. 13, when the thick paper P is passed,
As described above, when the sheet passes through the separation roller 14a, it is separated from the photosensitive drum 1 by the waist of the paper or its own weight. However, since the operation area of the separation roller 14a is located below the operation area of the separation roller 14b, the separation roller 14a is separated. There is no occurrence of jamming between the rollers 14b. Also, the separation roller 1
Since the separation action areas of 4a and 14b are located on the upstream side in the rotation direction of the photosensitive drum 1 with respect to the contact point C _p between the straight line parallel to the conveying direction of the separated paper and the photosensitive drum 1, the separation point of the paper P is detected. At the same time, the force F ′ applied to the paper P is applied in the same direction as the conveyance direction of the paper conveyance device 7 or in the counterclockwise direction with respect to the conveyance direction, so that the paper does not form a loop as in the first embodiment (FIG. 11). Paper can be transported smoothly.

As described above, as a peculiar effect of the second embodiment, by setting the gap of the separation roller 14a to 1 mm, the separation action area is expanded and the separation performance can be improved as compared with the first embodiment. Further, by shortening the gap, it is possible to reduce the amount of ozone generated and to stably carry the paper.

[0044]

As is apparent from the above description, in the image forming apparatus according to the present invention, the charge eliminating means has two or more rollers having a conductive core material and an elastic body covering the conductive core material. A rotating body, which is rotated about its rotation axis by a driving means, the static eliminating means and the image carrier are arranged in non-contact with each other, and a gap between at least one of the roller-like rotating body and the image carrier. The following effects can be obtained by having the distance guaranteeing means for keeping constant.

1. By widening the charge removal area of the charge removal means, the separation area is expanded and stable separation performance is obtained.
Particularly in a high-speed copying machine, since the process speed is fast, the static elimination time becomes short, and this effect is particularly advantageous.

2. It is possible to widen the separation area without increasing the diameter of the roller-shaped rotating body of the static eliminator. As a result, cost reduction due to downsizing of the static elimination means can be achieved, and the miniaturized static elimination means can keep its surface resistance constant, so that the separability can be stabilized. By reducing the size of the roller-shaped rotating body, the charge removing unit can be reduced in size, and as a result, the size of the entire image forming apparatus can be reduced.

Further, by arranging the action area of the static eliminator on the upstream side in the moving direction of the image carrier relative to the contact point between the straight line parallel to the conveying direction after the transfer material separation and the image carrier, The following additional effects can be obtained.

3. Separability is further improved, the amount of ozone generated is reduced, and stable paper conveyance is possible.

4. Since the static elimination means rotates in a non-contact manner, the amount of wear of the roller-shaped rotating body is reduced and the life of the roller-shaped rotating body can be extended. Further, even if the cleaning member is brought into contact with the roller-shaped rotating body, it is possible to prevent the occurrence of an image defect caused by a part of the cleaning member being transferred to the image carrier.

[Brief description of drawings]

FIG. 1 is a perspective view showing a separation device according to a first embodiment.

FIG. 2 is a partial cross-sectional view of the separating device of FIG. 1 in the direction of the photosensitive drum rotation axis.

3 is a cross-sectional view of the separation device of FIG. 1 in a transfer paper conveyance direction.

FIG. 4 is a schematic electric system diagram of the separation device.

FIG. 5 is a cross-sectional view of a separating device according to a second embodiment in a transfer paper conveyance direction.

FIG. 6 is an overall configuration diagram of an image forming apparatus in which the separation devices of the first and second embodiments are implemented.

FIG. 7 is a graph showing examination results of separation / retransfer in a conventional separation device.

FIG. 8 is a graph showing examination results of separation / retransfer in another conventional separation device.

9 is a graph showing the examination results of separation / retransfer with the separation device of Example 1. FIG.

FIG. 10 is an enlarged explanatory diagram illustrating a state in which thick paper is passed through the transfer / separation unit according to the first exemplary embodiment.

11 is an enlarged explanatory diagram showing a state in which domestic paper is passed through the transfer / separation unit in FIG.

FIG. 12 is an enlarged explanatory diagram illustrating another aspect of the transfer / separation unit according to the first embodiment.

FIG. 13 is an enlarged explanatory diagram of a transfer / separation unit according to the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image carrier (photosensitive drum) 5 Transfer devices 14a, 14b Roller-shaped rotating body (separation roller) 20 Charging device 24 Distance assurance means (abutting roller) 40 Conductive core material (roller shaft) 42 Elastic body (conductive rubber) Layer) 50 static eliminator (separator)

Claims (2)

[Claims] 1. A charge of an image carrier or a transfer material is removed.
In an image forming apparatus provided with an electricity removing means for supplying electric power, the electricity removing means includes two or more roller-shaped rotating bodies each having a conductive core material and an elastic body covering the conductive core material, and a driving means. Is rotated about its rotation axis, and the static eliminator and the image carrier are arranged in non-contact with each other, and a distance assurance device for maintaining a constant gap between at least one of the roller-shaped rotor and the image carrier is provided. An image forming apparatus having. 2. The action area of the static eliminator is arranged on the upstream side in the moving direction of the image carrier relative to the contact point between the straight line parallel to the conveying direction after the transfer material separation and the image carrier. The image forming apparatus according to claim 1.