US3684363A

US3684363A - Device for separating recording medium for use in electrophotographic copying machines

Info

Publication number: US3684363A
Application number: US67049A
Authority: US
Inventors: Yoshio Ito; Hajime Katayama; Masaru Yamaguchi; Hiroshi Nitanda
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1969-08-30
Filing date: 1970-08-26
Publication date: 1972-08-15
Anticipated expiration: 1989-08-15
Also published as: DE2042863B2; FR2059765A1; DE2042863A1; FR2059765B1; GB1326076A; NL7012781A; NL166804C; NL166804B

Abstract

A separating device for an electrophotographic copying machine consisting of a stationary or running belt and guide members for the belt. The belt extends through the nip between the photosensitive drum and the transfer roller of the copying machine. After the recording medium passes between the drum and the transfer roller, the medium is separated from the drum by the belt and subsequently separated from the belt by at least one of the guide members.

Description

United States Patent Ito et al.

DEVICE FOR SEPARATING RECORDING MEDIUM FOR USE IN ELECTROPHOTOGRAPHIC COPYING MACHINES Inventors: Yoshio Katayama, Kawasaki; Masaru Yamaguchi; Hiroshi Nitanda, both of Tokyo, all of Japan Assignee: Canon Kabushiki Kaisha, Tokyo,

Japan Filed: Aug. 26, 1970 Appl. No.: 67,049

Foreign Application Priority Data Aug. 30, 1969 Japan ..44/68790 Dec. 12, 1969 Japan ..44/l002l7 Dec. 12, 1969 Japan ..44/26l62 US. Cl ..355/3, 271/DIG. 2 Int. Cl. ..G03g 15/14 Field of Search ..355/3, 10, 12, l5, 16, 104, 355/106, 117; 27l/DlG. 2

Ito, Tokyo; Haiini'e 51 Aug. 15, 1972 [56] References Cited UNITED STATES PATENTS- 3,450,402 6/1969 Weiler ..27l/DlG. 2 3,386,730 6/1968 Hyosaka ..355/1 10 X 3,139,013 6/1964 Graves ..355/3 3,506,259 4/1970 Caldwell et al. ..355/3 X Primary Examiner-Samuel S. Matthews Assistant Examiner-Fred L. Braun AttorneyWard, McElhannon, Brooks & Fitzpatrick [5 7] ABSTRACT A separating device for an electrophotographic copying machine consisting of a stationary or running belt and guide members for the belt. The belt extends through the nip between the photosensitive drum and the transfer roller of the copying machine. After the recording medium passes between the drum and the transfer roller, the medium is separated from the drum by the belt and subsequently separated from the belt by at least one of the guide members.

8 Claims, 7 Drawing Figures DEVICE FOR SEPARATING RECORDING MEDIUM FOR USE IN ELECTROPHOTOGRAPIIIC COPYING MACHINES BACKGROUND OF THE INVENTION 1. Field of Invention The present invention relates to a novel device for separating a recording medium electrostatically attached to an electrophotographic photosensitive member of an electrophotographic copying machine.

2. Description of Prior Art In general, an electrophotographic copying machine comprises a rotary drum having a photosensitive layer which is charged and exposed with a light image, the electrostatic image being developed and transferred to a recording medium. In the image transfer step, the recording medium must be pressed against the photosensitive drum, but after the image transfer, it must be separated from the drum, which is cleaned for the next copying step. Because the recording medium is in general a paper, it tends to be electrostatically attached to the drum so that it is not separated with ease. Therefore, a suitable device for separating the recording medium from the drum after image transfer must be provided.

There have been proposed various means for separating the recording medium from the photosensitive drum. For example, one device utilizes vacuum to suck the recording medium away from the photosensitive drum. In another device, air under high pressure is blown against the leading edge of the recording medium along the peripheral surface of the photosensitive drum. However, both of the separating devices must operate in synchronism with the transport of the recording medium. Furthermore, both of the devices employ compressors or pumps so that they are expensive and the problem of noise occurs. In the latter device, the toner is blown by the air from the blower into the machine so that the components are contaminated.

SUMMARY OF THE INVENTION It is therefore one of the objects of the present invention to provide a device for separating from a photosensitive drum a recording medium which eliminates the defects described above and is economical and simple in construction.

It is another object of the present invention to provide a device for separating a recording medium from a photosensitive drum in which a recording medium separating member is held stationary so that the driving means and synchronizing means are not required, and whose function is positive and reliable.

It is another object of the present invention to provide a device for separating a recording medium from a photosensitive drum in which a separating member in the form of an endless belt rotates together with a separating roller so that no driving means and synchronizing means are required. The separating device always has a function of separating a recording medium from a photosensitive drum so that the recording medium may be always positively separated.

In brief, the present invention is characterized in that in an electrophotographic copying machine comprising a rotary drum having a photosensitive layer, charging means, exposure means, developing means, image present invention;

transfer means and cleaning means arranged around the photosensitive drum, a recording medium is so guided by a separating belt as to be moved away from the photosensitive drum.

BRIEF DESCRIPTION OF THE DRAWING FIG. .I is a perspective view illustrating an electrophotographic copying machine to which is applied FIG. 2 is a diagrammatic front view thereof illustrating the major component members;

FIG. 3 is a side view on enlarged scale illustrating a first embodiment of the present.invention;

FIG. 4 is a perspective view thereof;

FIG. 5 is a side view on enlarged scale illustrating a second embodiment of the present invention;

FIG. 6 is a side view illustrating a third embodiment of the present invention; and

FIG. 7 is a fragmentary front view thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT Various component members of an electrophotographic copying machine embodying the present invention are shown in FIG. 2. Around a photosensitive drum 1 having a photosensitive layer 2 are disposed a charger 4, an exposure station 5, a developing station 7, an image transfer station 9 and a cleaning station 10 in the order named in the direction of rotation of the drum 1 as shown by the arrow.

A separatingdevice in accordance with the present invention is illustrated in FIG. 3 together with the major component members in the image transfer station. A recording medium to which is transferred a toner image formed upon the drum 1 is fed between a transfer roller 13 and the drum 1 through a pair of feed rollers 28 and a pair of guides 29in the direction indicated by the tangent AA passing through the point of contact between the transfer roller 13 and drum 1.

The transfer roller 13 whose axis is substantially in parallel with that of the drum 1 is made of a resilient electric conductor having a length slightly longer than that of the width of the largest copy reproduced by the electrophotographic copying machine. The transfer roller 13 is pressed against the drum 1 by means of a spring or the like and electrically biased if required. When the toner image upon the drum 1 is transferred to the recording medium P, the latter is electrostatically attracted toward the drum 1 so that the device for separating the recording medium P from the drum 1 must be provided.

For this purpose, a separating belt 14 is extended from the front of the roller 13 along the tangent AA and wrapped around a driven roller 18, a drive roller 16, a tension roller 17 and a separating roller 15. The separating roller 15 rotates at a peripheral speed V equal to or slightly faster than the peripheral speed v of the drum 1 and is adapted to move the separating belt 14 away from the drum 1 since the belt 14 is wrapped around the arc of the separating roller 15 subtended by a central angle ofa (between 0 and That is, the recording medium P is transported in such a manner that one side edge of the recording medium P may be separated from the drum 1 during the time the toner image is being transferred from the drum 1 to the recording medium P. After passing over the transfer medium P. The width of the transfer roller 13 may be reduced by the width of the separating belt 14 in order to eliminate the friction between them and the wrinkles of the recording medium P. The width of the drum 1 must be wider than that of the recording medium because when the former is shorter than the latter, the recording medium is stained by the side edges of the drum 1.

The separating belt 14 is normally under tension by means of the tension roller 17 which is loaded with a spring 30. The separating belt 14 which is transported in the direction indicated by the arrow at a speed substantially equal to that of the recording medium makes frictional contact with the drum 1 so that the separating belt 14 may be preferably made of a material having a small coefficient of friction such as Myler, Teflon' (Trade Name) interwoven with glass fibers. Preferably the thickness is 50 to 15 p. and the width is to 20 In order to prevent slippage between the separating belt 14 and the drive roller 16, the latter is preferably made of a material having a greater coefficient of friction. For example, the drive roller may be covered with rubber. The recording medium P discharged from the image transfer station is transported into the fixing station by means of a guide 21 between a belt 12 and the separating roller 15. The function of a blower 31 for blowing weak air upon the recording medium P may be described in more detail hereinafter.

As explained above, the recording medium P contacts the drum 1 during the time the toner image formed upon it is being transferred to the recording mediumP which is transported into the nip between the drum 1 and the transfer roller 13 by means of the feed rollers 28 and the guides 29, but the side edge portion of the recording medium P is interposed between the separating belt 14 and roller 15 so as to be moved away from the drum 1 immediately after passing over the transfer roller 13. Therefore, the recording medium P may be gradually separated from the drum 1 from the side edge portion around the separating roller 15 with the contact angle or toward the opposite side edge.

The contact angle a between the belt 14 and the roller 15 should better be increased and the position of the separating roller 15 should preferably be nearer to the transfer roller 13 to improve the separation function. When the recording medium P is separated from the drum 1, it lies on the guide 21 and by the frictional force between the drive roller 16 and the guide 21 the medium P is fed to the belt 12'. In order to facilitate the separation of the recording medium P from the drum 1 by means of the separating belt 14 and roller 15, the present invention further provides the blower 31 so as to blow weak air upon the recording medium P separated from the drum 1 in the direction of the wedge-shaped space between the drive roller 16 and the recording medium P. Therefore the air from the blower 31 not only serves to separate the recording medium P from the drive roller 16 but also presses the recording medium against the guide 21 and the belt 12' so as to securely transport the recording medium into the fixing station. I

-The advantages of the above explained invention are as follows:

1. Since the recording medium separating device is always in operation, the recording medium can be positively and securely separated from the photosensitive drum; I

2-. Since the recording medium separating device is not required to be operated in synchronism with the transportation of a recording medium, the

. device becomes simple in construction and relatively low in cost;

3. Since the endless separating belt is always driven while the separating roller is rotated, there is no friction between the separating roller and belt so that wear of separating belt may be minimized;

4. The endless separating belt is always in contact with the separating roller under tension, so that the recording medium interposed therebetween may be always positively separated from the photosensitive drum in a stabilized manner;

5. The endless separating belt may be arranged within the width of the photosensitive drum so that it may not extend beyond the side edge of the drum; and

6. Since the width of the photosensitive drum may be made greater than that of the recording medium, the latter may be prevented from being stained by the edges of the drum. It is seen that the present invention may be also applied to -a -plate-shaped photosensitive member.

Next referring to FIG. 5, the second embodiment of the present invention will be described, but the description is limited to those features different from the first embodiment. Opposed to the first embodiment. the separating belt 14 in the second embodiment is stationary. One end of the separating belt 14 is fixed to a pin 18' while the other end is fixed to a hook-like member 33 which in turn is fixed to a spring 30 so as to impart a suitable tension to the separating belt 14. A guideroller32 is provided for bending the separating belt 14 as shown. As in case of the first'embodiment, the separating belt is preferably made of a material having a smaller coefficient of friction.

The toner image is transferred from the drum 1 to the recording medium P which is fed through the feed rollers 28 and the guides 29 into the nip between the drum '1 and the transfer roller 13 which presses the recording medium against the drum 1. In this case, the recording medium P is transported along the undersurface of the separating roller 13 toward the separating roller 15 which is rotating at the speed V at least as fast as or faster than the peripheral speed v of the drum 1 as in the case of the first embodiment. Furthermore, the separating belt 14 is wrapped around the arc of the separating roller 15 subtended by the central angle a as in the case of the first embodiment. In consequence, the tension is applied to the recording medium P between the transfer and separating

rollers

13 and 15 and is moved away from the drum 1 along the separating roller 15. Thus, the side edge portion of the recording medium is separated from the drum 1 immediately passing over the transfer roller 13 so that as the recording medium is transported, it may beseparated gradually from its side edge on the side of the separating belt toward its opposing side edge. The greater the angle of contact a between the separating belt and

roller

14 and 15 and the nearer the separating roller 15 is located toward the transfer roller 13, the more the separation may be facilitated. Furthermore, the greater the peripheral speed V of the separating roller 15 than the peripheral speed v of the drum 1, the greater the tension applied to the recording medium between the transfer and separating

rollers

13 and 15 so that the separation of the recording medium P from the drum 1 may be facilitated. The recording medium P emerging from the separating roller 15 is dropped upon the guide 21 and is advanced toward the belt 12. The second embodiment is also provided with the blower 31 and may be applied to an electrophotographic copying machine employing a plate-like photosensitive member. The other modification is characterized in that the diameter of one or both side edge portions of the transfer roller is reduced to such an extent that they will not make contact with the photosensitive drum through the recording medium and the separating belt and the reduceddiameter-side-edge-portion or portions rotates together with the transfer roller so that the recording medium may be so guided by the separating belt as to be moved away from the drum. Alternatively, the reduced-diameter-side-edge-portion or portions may be held stationary. Other arrangements are similar to those of the first and second embodiments. The third embodiment will be described with reference to FIGS. 6 and 7. Opposed to the first and second embodiment, the third embodiment eliminates the separating roller, but the transfer roller also serves as a separating roller. A transfer roller 113 made of an electrically conductive rubber is always pressed against the photosensitive drum 1 under the force of a spring, not shown, and is rotated as the drum 1 rotates. Since the recording medium P is electrostatically attracted by the drum 1, it tends it be transported together with the drum 1. A ring 114 made of a metal for guiding the recording medium P is coaxially carried by the shaft of the transfer roller 113, but is prevented from rotating by a pin 120 fitted into a notch 120' of the guide ring 114. In order to prevent the ring 114 from causing the damage to drum 1 because the recording medium is deformed due to the contact of the transfer roller with the drum 1, the ring is provided with a cut-away portion A.

One end ofa wear resistant belt 115 having a smooth surface made of for example a fluoro-resin film is fixed to a pin 118 located forwardly of the transfer roller 113, and the other end is joined to the belt 115 at B after it is wrapped around the

pins

116 and 1 17 and the drum 1. Thus, the separating device is constituted by the ring 114 and the belt 115. The device is preferably provided along one side edge of the drum 1, but if required, the devices may be provided along both side edges of the drum 1. Furthermore, the belt 115 may be an endless belt wrapped around the

pins

116, 117 and 1 18.

When the recording medium P is fed into the nip between the drum 1 and the transfer roller 113 from the guide 119, the side edge portion of the recording medium P is interposed between the belt 115 and the ring 114. Preferably, the joint B is so selected that a suitable gap may be formed between the belt and the ring 114, whereby the recording medium fed into the nip between the drum 1 and the ring 114 may not be stopped. Since the side edge portion, which is generally 10 mm in width, is sandwiched between the belt 115 and the ring 114, the side edge portion of recording medium may be forced to be separated from the drum 1 as it is advanced along the drum so that the recording medium is gradually separated from the drum 1 as soon as the image transfer is completed. No wrinkles are formed because the recording medium is transported between the belt 115 and the ring 114. The recording medium wrapped around the transfer roller 113 or the ring 114 may be separated by a separator guide 121 and transported toward the fixing station.

What is claimed is:

1. In an electrophotographic copying machine including a housing, a photosensitive drum in said housing, charging means, exposure means, developing means, image transfer means having a transfer roller adjacent the drum, and recording medium separating means arranged around said photosensitive drum; the recording medium separating means comprising, a separating belt extending through the nip between said photosensitive drum and said transfer roller and adapted to contact at least one end portion of said recording medium, means for guiding said separating belt and for separating the recording medium from the separating belt after said medium has been separated from the photosensitive drum, and means for transporting the recording medium so as to press it against said photosensitive drum through said separating belt.

2. The copying machine according to claim 1. wherein said separating belt is an endless belt, and said guide means comprise a separating roller disposed immediately after said transfer roller and out of contact with said photosensitive drum when the recording medium and said separating belt pass therebetween, a drive roller disposed in a position for redirecting the recording medium passed over said separating roller in a direction away from said photosensitive drum, and a guide roller for imparting tension to said separating belt.

3. The copying machine according to claim 2, wherein said separating roller rotates at a peripheral speed substantially equal to or faster than that of said photosensitive drum.

4. The copying machine according to claim 2, wherein blower means is provided for blowing air against the recording medium separated from said photosensitive drum by said separating belt.

5. The copying machine according to claim 2, wherein said drive roller is disposed in a position for directing the separated recording medium in a direction away from the photosensitive drum and keeping a contact angle of less than between said drive roller and the recording medium.

6. The copying machine according to claim 1, wherein the side edge portion of said transfer roller has a diameter smaller than that of themajor portion of said transfer roller whereby said side edge portion of said transfer roller is out of contact with said photosensitive drum even when said separating belt and the recording medium pass therebetween.

8. The copying .machine according to claim 1,

wherein said guide means comprises pins to which are securely fixed the leading and the trailing ends of said separating belt, and guide pins for moving the recording medium away from said photosensitive drum after image-transfer. I

Claims

2. The copying machine according to claim 1, wherein said separating belt is an endless belt, and said guide means comprise a separating roller disposed immediately after said transfer roller and out of contact with said photosensitive drum when the recording medium and said separating belt pass therebetween, a drive roller disposed in a position for redirecting the recording medium passed over said separating roller in a direction away from said photosensitive drum, and a guide roller for imparting tension to said separating belt.

5. The copying machine according to claim 2, wherein said drive roller is disposed in a position for directing the separated recording medium in a direction away from the photosensitive drum and keeping a contact angle of less than 180* between said drive roller and the recording medium.

6. The copying machine according to claim 1, wherein the side edge portion of said transfer roller has a diameter smaller than that of the major portion of said transfer roller whereby said side edge portion of said transfer roller is out of contact with said photosensitive drum even when said separating belt and the recording medium pass therebetween.

7. The copying machine according to claim 6, wherein a stationary ring is loosely fitted near to the side edge of said transfer roller, the diameter of said ring being selected in order that said ring is out of contact with said photosensitive drum even when the recording medium and said separating belt pass therebetween.

8. The copying machine according to claim 1, wherein said guide means comprises pins to which are securely fixed the leading and the trailing ends of said separating belt, and guide pins for moving the recording medium away from said photosensitive drum after image-transfer.