JPS63100484A - Transfer device for electrophotographic copying machine - Google Patents

Abstract

PURPOSE:To stabilize the carrying and holding of a sheet of transfer paper, by constituting a device so that the cylindrical intermediate part of a drum body is cut leaving an intermediate linking part that is a part of a peripheral plane being connected to both end parts, and it can be supported with a supporting a plate possible to be rocked and being brought into contact with the inner peripheral plane of the both end parts. CONSTITUTION:In the drum body 21, the intermediate part of a resin made cylinder is cut largely, leaving the both side parts 22 and 23, and a belt-shaped linking part 24 in parallel with an axial line that is a part of the peripheral plane being continued to the side parts. The above cut part is covered with an insulating transfer paper supporting sheet 25 having a width a little larger than that of the cut part by winding the sheet from the one side to the other side of the linking part 24. A transfer drum 41 is supported with three rollers 43-45 provided at a supporting lever 42, and brought into contact with the inner peripheral plane of the transfer drum. The lever 42 is extended to the outside of the transfer drum, and turns centering a shaft 46 provided on the way. The shaft 46 is supported with a stationary member.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transfer device for an electrophotographic copying machine, particularly a color electrophotographic copying machine.

In a color electrophotographic copying machine, each visible image formed on a photoreceptor is separately superimposed and transferred onto the same transfer paper to obtain a single copy.

A bias type transfer device is one of the transfer devices of such a color copying machine. This applies a bias voltage of opposite polarity to the toner image on the photoreceptor to a conductive transfer drum that rotates in pressure contact with the photoreceptor drum, thereby transferring this toner image onto the transfer paper on the transfer drum. It is. The advantages of this device are that the transfer paper is held securely on the transfer drum, the transfer drum is easy to control, the transfer paper has good transport performance, and the bias application during transfer is easy to control. etc. Disadvantages include that the first transfer drum lacks precision and material stability. In the case of this apparatus, conductive rubber is often used as the material of the transfer drum in order to bring the transfer drum into close contact with the photoreceptor and apply a bias voltage.

For this reason, it is difficult to increase precision due to its hardness and conductivity, and it also lacks material stability due to changes over time. Furthermore, with this device, abnormal discharge during transfer causes problems such as worm-eating and hollowing out in image quality. This occurs when the contact pressure of the transfer drum against the photoreceptor is increased in order to obtain sufficient adhesion. Furthermore, if a carrier such as iron powder is mixed into the toner image in order to bring the transfer drum into pressure contact with the photoreceptor, the surface of the photoreceptor or the transfer drum may be damaged by this hard carrier. Furthermore, since the surface resistance of the transfer drum easily changes due to environmental changes such as temperature and humidity, the transfer characteristics are sensitive to these changes.

Another type of transfer unit is a charge type transfer device. In this method, a portion of a loop-shaped flexible dielectric supported by several rotating bodies is brought into contact with the photoreceptor, and a corona charger with a charging polarity opposite to that of the toner image is placed on the inside of the loop-shaped flexible dielectric. be. The transfer paper is electrostatically brought into close contact with the dielectric sheet 1, and is conveyed, and the toner image is transferred to the transfer paper side by charges of opposite polarity applied from a corona charger.

Overall, this device has extremely stable image quality, but the positioning and conveyance of the transfer paper are unstable and color shift is likely to occur. In addition, the entire device becomes very complex, making it difficult to control and lacking in reliability.

As described above, bias type and charge type transfer devices each have advantages and disadvantages. The transfer device according to the invention eliminates the disadvantages of each and incorporates the advantages of each.

The features of this invention reside in the structure of the transfer drum and its supporting method. The basic structure of the transfer drum is a rigid body at both ends and a flexible sheet wound around the rigid body in the middle. A drum body for winding a flexible sheet is formed by cutting out a large part of the middle part of a cylinder, leaving an intermediate connecting part which is a part of a continuous curved surface at both ends. A transfer paper holding device is provided in the intermediate linking section.

The transfer drum is supported by a swingable support plate each having three rollers in contact with the inner circumferential surface of both ends thereof. The center of swing of the transfer drum support plate is located on the outside of the transfer drum, and by pulling its outer end with a tension coil spring, the transfer drum is brought into pressure contact with the photoreceptor.

By using this transfer drum and its support device in a transfer device, there are the following benefits.

I) Since the transfer paper is held and conveyed reliably, the color will not fade even when used in a color copying machine with overlapping transfer, and since the conveyance path can be simplified, the number of parts can be omitted, and the number of parts that come into contact with it can be simplified. The color will not fade due to

■) The structure of the transfer drum is rigid, making it easy to achieve precision and stable in terms of material.

■) The transfer drum is brought into pressure contact with the photoconductor, but the pressure contact is only at both ends of the transfer drum, and the contact pressure in the middle is low, so even if carrier is mixed in the toner image, it will cause damage to the photoconductor and transfer drum. There is no damage, and there is no hollowing out phenomenon caused by high contact pressure, so the image quality is good and stable.

■) It is easy to control the rotation, mounting position, contact pressure, etc. of the transfer drum.

(2) It is easy to manufacture the device because there is no need to consider the precise distance relationship between the photoreceptor and the transfer drum.

■) The structure of the transfer section is simple and compact, and the entire copying machine can be made small and simple.

(2) Since the transfer drum can be easily separated from the photoreceptor, it can be removed without damaging the photoreceptor.

(2) Since the contamination of the transfer drum caused by the developer is concentrated on the rigid structure of the transfer drum, the cleaning effect of the cleaning roller is improved.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an improved transfer device for an electrophotographic copying machine.

Other objects and effects will become clear from the following description with reference to the accompanying drawings.

First, an outline of a color electrophotographic copying machine equipped with a conventionally known bias type transfer device will be explained with reference to FIG. The photosensitive drum 1 rotates at a constant speed in a counterclockwise direction. A photoconductive layer is provided on the surface of the photosensitive drum 1, and this surface is uniformly charged to a predetermined polarity by a corona charger 2. When an original image is projected by the exposure optical system 3 onto the surface of the photoreceptor that holds charges, the charges are dissipated according to the density of the image area of the original image, and an electrostatic latent image is formed there. This electrostatic latent image is visualized by the developing device 4. In the case of a color copying machine, the developing devices include at least device 5 for yellow development and device 5 for magenta development! !
6, and the device 7 for cyan development are changed. Accordingly, the exposure optical system 3 includes blue, green,
It is equipped with color separation filters for each color of red.

The developing device may be equipped with a device for black development in order to adjust the image tone.

Development is performed for each color. That is, when a color original image is first projected onto the surface of a photoreceptor using a blue filter, an electrostatic latent image consisting of a yellow component, which is a complementary color to blue, is formed. This is visualized by the yellow developing device 5. The yellow developer bag rn5 contains a developer consisting of yellow toner and iron powder as a carrier, and the two are stirred and mixed to be frictionally charged, and the toner has a polarity opposite to that of the electrostatic latent image. charged. The toner and carrier are both attracted to the developing roller 5a and conveyed to a developing position close to the photoreceptor 1.

At the development position, only the toner charged to the opposite polarity is attracted to the electrostatic latent image and becomes a visible image.

Yellow developing bag! ! ! While the developing device 5 is being developed, the other developing devices 6 and 7 are moving away from the surface of the photoreceptor 1, and the yellow toner image on the photoreceptor moves toward the transfer position.

The transfer drum 8 has the same diameter as the photoreceptor drum 1, and rotates in the same direction and at the same speed at the contact point where it comes into pressure contact with the photoreceptor drum 1, that is, at the transfer position. The transfer drum 8 is electrically conductive, and a bias DC power source 9 is connected to it.

The DC current [9] is connected so that the transfer drum side has a polarity opposite to that of the toner charge. The transfer drum 8 is provided with a transfer paper gripping claw 10, and the paper feed cassette 1 is attached to this claw.
The leading edge of the transfer paper 12 sent from 1 is held in its mouth.

The transfer paper is wound onto the drum as the transfer drum rotates, and is brought into close contact with the drum surface by the electric charge on the drum surface. The timing of image formation on the photosensitive drum 1 and the timing of feeding the transfer paper 12 to the transfer drum 8 are synchronized, and the leading edge of the developed image and the leading edge of the transfer paper coincide at the transfer position.

The conductive support under the surface of the photosensitive drum 1 and one pole of the bias power supply 9 are both grounded.

Therefore, at the transfer position, an electric field is generated between the transfer drum 8 and the photoreceptor drum 1 via the transfer paper, and the transfer drum 8 applies an electric charge of opposite polarity to the toner to the transfer paper, and the toner on the photoreceptor drum The image is transferred to transfer paper.

After the yellow toner image is transferred to the transfer paper, the toner remaining on the photoreceptor drum is removed by a cleaning device 13, and the residual charge is similarly removed by a static eliminating corona charger 14. The surface of the photosensitive drum 1 is uniformly charged again by the charging corona charger 2, and exposed by the exposure optical system 3 using a green filter. Then, the electrostatic latent image becomes magenta developing device 6.
The image is developed and transferred to transfer paper.

On the other hand, after the yellow image has been transferred to the transfer drum, the charge on the transfer paper is removed by the action of the charge eliminating corona charger 15. The transfer drum continues to rotate and returns to the transfer position without being affected by the stripping claws 16 and the cleaning device 17.

Next is exposure using a red filter and cyan developing device! ! When the cyan image obtained by the development in step 7 is transferred to the transfer paper, the gripping claws 10 of the transfer drum come off and release the holding of the leading edge of the transfer paper. Next, the tip of the transfer paper is
The transfer paper is peeled off from the transfer drum 8 by a stripping claw 16 and directed to a fixing device 18, where the toner image on the transfer paper is permanently fixed. The transfer drum from which the transfer paper has been removed is cleaned by a cleaning device 17.

Next, the transfer drum used in the present invention will be explained with reference to FIG. The drum body 21 is basically made by cutting a large part of a resin cylinder into the middle part, leaving side parts 22 and 23 and a belt-like connecting part 24 parallel to the axis, which is a part of the circumferential surface continuous to these parts. Become. The width of the part to be cut out is slightly larger than the maximum width of the document to be used. This cut portion is covered by wrapping an insulating transfer paper support sheet 25 having a width slightly larger than the cut portion from one side of the connecting portion 24 to the other side. Sheet 25 is
Connecting part 2 with double-sided adhesive tape, etc. at the leading and trailing ends.
Fixed to 4. The connecting portion 24 is provided with a cutout groove 26 in the longitudinal direction for attaching a transfer paper holding device.

Here, the outline of the transfer paper holding device 27 will be explained with reference to FIG. 3. The groove 26 has an uneven shape on the transfer paper supply side 24a having several concave portions 26a and convex portions 26b. The opposite side 24b is straight. In addition,
The convex portion 26b is a slope. A shaft 29 is disposed in the groove and has both ends supported on both sides of the drum body.
A presser pawl 30 is fixed at a position facing the recess 26a of the groove 26. The presser claw 30 is attached to the lower sheet removing portion 30a.
has a width that fits in the recess 26a, and the upper sheet stopper 3
0b has the same width as the sheet removing portion and its tip is bent downward, and on the right side thereof, there is a sheet pressing portion 30c located above the convex portion 26b of the groove 26. An operating lever 31 is fixed to both ends of the shaft 29, and is controlled by an external cam or the like (not shown). The torsion coil spring 32 provided on the shaft 29 is connected to the presser portion 3Qc of the presser claw 30.
It is provided between the actuating lever 31 and the connecting portion 24b so that it can be rotated in a direction such that it comes into pressure contact with the convex portion 26b of the groove.

When the presser pawl 30 is activated, the presser portion 30c is separated from the convex portion 26b, as shown in FIG. When the transfer sheet S is inserted between the two, the leading edge of the sheet hits the stop portion 30b and stops.

Subsequently, when the lever 31 is actuated, the presser portion 30c comes into pressure contact with the convex portion 26b and presses the sheet S, as shown in FIG.

When the sheet is to be removed from the drum after a series of steps have been completed, the actuating lever 31 is rotated to the opposite side, and the removing portion 30a removes the sheet S from the convex portion 26b, as shown in FIG.

Next, an example of a device for supporting the transfer drum configured as described above will be explained with reference to FIG. The transfer drum 41 is supported by three rollers 43, 44, and 45 provided on the support lever 42 and in contact with the inner peripheral surface of both sides of the transfer drum. The lever 42 extends outside the transfer drum and rotates around a shaft 46 provided in the middle. The shaft 46 is supported by a stationary member (not shown). A tension coil spring 47 is provided at the lower end of the lever 42 to press the transfer drum 41 against the photosensitive drum 48.

The coil spring 47 ensures and controls the transfer pressure of the transfer drum 41. Therefore, compared to the conventional method of obtaining the necessary transfer pressure by accurately determining the distance between the axes between the transfer drum and the photosensitive drum in advance, it is possible to obtain the necessary transfer pressure much more easily and simply.

In addition, compared to the case where the distance between the axes is determined, there is no change in transfer pressure due to eccentricity of the drum, etc.Furthermore, by separating the transfer drum from the photoreceptor drum, it is easy to remove the transfer drum and the photoreceptor drum. .

FIG. 8 is a sectional view taken along line A-A in FIG. 7. The axial positioning of the transfer drum 41 is performed using rollers 45. (44, 43) This is done by engagement between the chevrons on the circumferential surface and the V-grooves 49 provided on the inner periphery of the side portions 22 and 23 of the transfer drum 41. Alternatively, this can be accomplished by using rollers with flanges on both sides, the flanges of which are in contact with both end faces of the drum. The transfer drum 41 is driven by meshing between a gear 51 fixed to a drive shaft 50 of the photosensitive drum 48 and a gear 52 fixed to the outer periphery of one side of the transfer drum. The transfer drum can also be driven by engagement with a friction wheel. In addition, the said roller can also be provided in contact with the drum side outer circumferential surface, end surface, etc.

FIG. 9 shows a charge-type transfer device according to the present invention, which is equipped with the above-described transfer drum and its support device. A 'M electric sheet is used for the transfer paper support sheet 25 of the transfer drum 41. The center portion of an L-shaped bar 62 is loosely fitted to the shaft 46, which is the center of rotation of the transfer drum support lever 42, and a squeezing roller 63 is fixed to one end thereof. The other end of the lever 62 is connected to a tension coil spring 64 from both sides.
65, and a solenoid (not shown) is connected to the other end of the spring 65.

The transfer corona charger 91 is attached to the transfer drum support lever 42 at a position opposite to the transfer position inside the transfer drum 41. The corona charger 91 is a normal DC corona charger, and has a guide member 91 attached to the support lever 42. The shield case 91b is removable.

In conventional charging type transfer devices that place a corona charger inside a dielectric sheet, although the positional relationship between the corona charger fixed at a predetermined position and the moving dielectric sheet is fixed, the movement of the dielectric sheet This may cause the positional relationship to shift, which may also change the transfer characteristics.

In this embodiment, since the transfer corona charger 91 is attached to the lever 42 supporting the transfer drum 41, the corona charger 91 and the dielectric sheet 2
Stable transfer characteristics can be obtained without shifting the positional relationship with 5. Further, by adjusting the mounting position of the corona charger 91, the positional relationship with the dielectric sheet 25 can be easily adjusted, and the mounting is simple, the operability is good, and the support is reliable.

Transfer sheets 68 and 69 of different sizes are stored in the paper feed cassettes 66 and 67, and one of them is selected and sent to the transfer drum 41 through the paper feed device 70 for transfer by the paper feed device 70. The paper feeding and the rotation of the transfer drum 41 are synchronized, and the leading edge of the fed transfer paper is held in the transfer paper holding device 27 of the transfer drum 41. The transfer paper held in the transfer drum 41 is wound onto the dielectric sheet 25 of the drum by rotation of the transfer drum.
It is brought into close contact with the sheet by a squeezing roller 63. When the leading edge of the transfer paper reaches the point of contact with the photosensitive drum 48, that is, the transfer position, a solenoid connected to the spring 65 is activated, and the squeezing roller 63 separates from the transfer drum.

- When the transfer of the image to the transfer paper is completed, the charge on the surface of the transfer paper is removed by the neutralizing AC corona charger 71. The stripping claw 72 and the cleaning device 73 are normally separated from the surface of the transfer drum. i When the final transfer is completed, transfer paper holding bag! ! 27 removes the leading edge of the transfer paper, and the transfer paper is peeled off from the transfer drum by a peeling claw 72 in contact with the drum and headed for a fixing device (not shown).Meanwhile, the surface of the transfer drum is cleaned by a cleaning group W173.

The cleaning device 1173 includes a conventionally known scraping roller 74 made of urethane or sponge, a scraping plate 75 in contact with this, a wiping roller 76 made of rubber or metal, and a cleaner pad in contact with the wiping roller float. 77, the entire device swings around a shaft 78, and the scraping roller 74 is configured to be able to approach and separate from the surface of the transfer drum. Cleaning group! ! 7
3 is usually remote from the transfer drum. The top of the transfer drum is cleaned when the transfer paper is not held on the transfer drum, that is, from the first transfer paper clamping step to the transfer step at the transfer position, and after the transfer paper is peeled off from the transfer drum.

However, even with such a conventional device, the cleaning effect can be greatly improved by combining it with the transfer drum according to the present invention. This is because, generally, the location where the transfer drum is contaminated by developer or the like is a location other than where the transfer paper is located on the transfer drum, and is within the length of the developing roller. In the transfer drum of the present invention, as shown by diagonal lines in FIG. 10, there are areas on the transfer paper support sheet 25 other than the transfer paper 68 and on the drum connecting portion 24. (
However, in this example, the length of the developing roller is the same as the width of the sheet 25. ) However, the transfer drum 4 of this invention
1 is rigid in both side parts 22 and 23 and the intermediate connecting part 24, and the rest is a flexible part made up of a thin sheet 25.

Therefore, when the elastic cleaning roller 74 is brought into pressure contact with the transfer drum 41 as shown in FIG. This will effectively wipe away any dirt that may be present. In addition, since the roller 74 does not come into strong pressure contact with the entire surface of the transfer drum,
Loss of torque during cleaning is small, and the efficiency of the device is reasonable and economical. Note that the same effect can be obtained by using a cleaning blade in place of the cleaning roller 74, or they may be used in combination.

The charge eliminating corona charger 92 is for removing charges on the dielectric sheet 25, and is applied with an alternating current or a voltage in which alternating current and direct current are superimposed. In order to effectively eliminate static electricity, a counter electrode plate 93 is attached to the transfer drum support lever 42 close to the inner side of the transfer drum facing the counter electrode plate 93. The static eliminating corona charger 92 is a cleaning device i.
! Similarly to 73, it operates when the transfer paper is not held on the transfer drum, that is, from the initial transfer paper clamping step to the transfer step at the transfer position, and after the transfer paper is peeled off from the transfer drum.

As mentioned above, well-known techniques can be adopted for parts that are not explained in detail in this specification, and regarding the examples,
Various modifications are possible within the spirit of the invention.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram showing an example of a color copying machine using a bias type transfer device, Fig. 2 is a schematic perspective view of a transfer drum used in the present invention, and Fig. 3 is a schematic diagram showing a color copying machine installed on the transfer drum. FIGS. 4 to 6 are diagrams for explaining the operation of the transfer paper holding device. FIG. 7 is a schematic perspective view of the transfer drum supporting device according to the present invention.
The figure is a sectional view taken along line A-A in Figure 7, and Figure 9.
The figure is a schematic configuration diagram of a charge type transfer device according to the present invention, Figure 1θ is an explanatory diagram showing a contaminated portion of the transfer drum, and Figure 11 is a front view for explaining cleaning Q by a cleaning roller. It is. 21...Drum body of transfer drum, 25...Transfer paper support sheet, 27...Transfer paper holding device, 41...
...Transfer drum, 42...Transfer drum support lever,
43.44.45...Transfer drum support roller, 48.
... Photoreceptor drum, 63 ... Irrigation roller. 1 Figure J

Claims (1)

[Scope of Claims] A drum body obtained by removing a cylinder, leaving a peripheral edge on both sides and a band-like connecting part that is continuous with the peripheral edge and is a part of the peripheral surface parallel to the axis; comprising a dielectric sheet wrapped around the drum body so as to cover the entire excised part of the body, and a rotating support body in contact with both peripheral edges of the drum body,
and a drum support having a center of rotation on the outside of the drum body; means for imparting rotational behavior to the drum support to press the drum body against the photoreceptor; and an inner portion of the drum body facing the photoreceptor. A transfer device for an electrophotographic copying machine, comprising: a charging device provided on the drum support close to the circumferential surface; and a transfer paper holding device provided on the band-like connecting portion of the drum body.