US3827800A

US3827800A - Apparatus for transferring electrostatic latent images in electrophotographic copiers of image transfer type

Info

Publication number: US3827800A
Application number: US00338784A
Authority: US
Inventors: T Fujiwara; S Tanaka; Y Enoguchi
Original assignee: Minolta Co Ltd
Current assignee: Minolta Co Ltd
Priority date: 1972-03-15
Filing date: 1973-03-07
Publication date: 1974-08-06
Anticipated expiration: 1991-08-06
Also published as: DE2312393A1; JPS547215B2; JPS4895241A; DE2312393B2; DE2312393C3

Abstract

An apparatus comprising a photosensitive element to be driven for charging and exposure to form an electrostatic latent image on its surface and having a grounded electroconductive backing on its rear face, a transfer roller adapted to bring the dielectric surface of copy paper into intimate contact with the surface of the photosensitive element and to ground the electroconductive backing of the paper for electrical connection with the conductive backing of the photosensitive element, disconnecting means for breaking electrical connection between the roller and the conductive backing of the element through grounding while the paper is not positioned between the element and the roller, and means for grounding the conductive backing of the paper after the paper has passed through a transfer station, so as to prevent discharge due to the breakdown of air gap between the transfer roller and the photosensitive element for the protection of the charge retaining surface of the element. The transfer roller has means for selectively breaking the electrical connection between the two backings for use with copy papers of varying sizes.

Description

United States Patent [191 Tanaka et al.

[ Aug. 6, 1974 [75] Inventors: Susumu Tanaka, Sakai; Yuji Enoguchi, Higashi-Osaka; Takao Fujiwara, Sakai, all of Japan [73] Assignee: Minolta Camera Kabushiki Kaisha,

Osaka, Japan [22] Filed: Mar. 7, 1973 [21] Appl. No.: 338,784

[30] Foreign Application Priority Data OTHER PUBLICATIONS Oldeboom, Electromechanical Transfer Mechanism, IBM Technical Disclosure Bulletin, Vol. 1, No. 3, DP. 4 & 5.

Primary Examiner-Samuel S. Matthews Assistant Examiner-Kenneth C. Hutchinson Attorney, Agent, or Firm-Wolder & Gross [5 7] ABSTRACT An apparatus comprising a photosensitive element to be driven for charging and exposure to form an electrostatic latent image on its surface and having a grounded electroconductive backing on its rear face, a transfer roller adapted to bring the dielectric surface of copy paper into intimate contact with the surface of the photosensitive element and to ground the electroconductive backing of the paper for electrical connection with the conductive backing of the photosensitive element, disconnecting means for breaking electrical connection between the roller and the conductive backing of the element through grounding while the paper is not positioned between the element and the roller, and means for grounding the conductive backing of the paper after the paper has passed through a transfer station, so as to prevent discharge due to the breakdown of air gap between the transfer roller and the photosensitive element for the protection of the charge retaining surface of the element. The transfer roller has means for selectively breaking the electrical connection between the two backings for use with copy papers of varying sizes.

8 Claims, 10 Drawing Figures PAIENIEDMIB 61914 3.827. 800

SHEET 1 [IF 2 Fig.7 PRIOR ART. (b

BACKGROUND OF THE INVENTION The present invention relates to an apparatus for transferring electrostatic latent images in electrophotographic copiers of the electrostatic latent image transfer type, more particularly to an apparatus for transferring electrostatic latent images which comprises a photosensitive element to be subjected to charging and exposure to form an electrostatic latent image on its dielectric surface layer and an electroconductive transfer roller for bringing the dielectric surface layer of an electrostatic image receptor such as copy paper into intimate contact with the dielectric layer of the photosensitive element and in which a support member supporting the rear face of the photosensitive element and the transfer roller are grounded respectively to electrically connect the electroconductive backing of the photosensitive element to the electroconductive backing of the copy paper and to thereby transfer the electrostatic latent image on the photosensitive element to the copy paper at an area where the dielectric layer of the paper comes into intimate contact with the dielectric layer of the photosensitive element. Thereafter, in accordance with the general practice, a toner powder is applied to the electrostatic image bearing face of the copy paper which is then heated to fuse the toner powder and form a permanent image.

With the electrophotographic copiers of the type described, the photosensitive element has a charge retaining area which is somewhat larger than the area of copy paper of a maximum size usable. Accordingly, in the case where a sheet of copy paper is used which has been previously cut to a specified size, part of the charged surface of the photosensitive element will be left uncovered by the paper during the transfer of image.

As indicated by hatching in FIG. 1 (a), the charged surface, namely the charge retaining surface A of a photosensitive element 2, is larger than a sheet of copy paper 1 of a maximum size. Even if the length of a grounded electroconductive transfer roller 3 is equal to the width of copy paper I, the roller 3 will come into direct contact with the charge retaining surface A of the photosensitive element twice when the paper 1 advances as shown in FIG. 1 (b), namely when the front end of the paper almost reaches the position of the roller 3 (see the phantom line) and when the rear end of the paper has passed the position of the roller 3 (see the solid line), breaking the insulation of the air gap upon contact to cause a very intense discharge, since the charge retained on the photosensitive element 2 is at a high voltage level whereas the roller 3 is grounded. Moreover, inasmuch as the impedance due to the electrical connection between the transfer roller 3 and the backing of the photosensitive element 2 is low, the abovementioned discharge takes place within a very short period of time at an extremely high current density.

Consequently, the dielectric layer of the photosensitive element 2 will be damaged by ion bombardment or chemically affected by ions. Further if it locally includes a point of low insulation, ions will concentrate at that point to damage the dielectric surface. When thus damaged, the dielectric layer locally fails to retain charges thereafter placed thereon, rendering the developed image defective and no longer assuring a satisfactory copying operation.

The same problem will be also experienced with the use of copy paper 1 of a smaller size. In this case, the

detrimental phenomena are not restricted to the vicinities of the front and rear ends of advancing paper 1'. As illustrated in FIGS. 2 (a) and 2 (b), the opposite ends of the roller 3 extend beyond the opposite edges of the paper 1 during the transfer operation and face the charge retaining surface A of the photosensitive element 2. Since the thickness of the copy paper 1' is up to a maximum of to microns, dielectric breakdown will take place across an air gap S on the opposite sides of the paper 1, causing a discharge at high current density to damage and destroy the dielectric surface layer of the photosensitive element 2. Such damage and destruction of the photosensitive surface seriously deteriorate the photosensitive element 2 and exert an adverse effect over an area including more or less inner portions of the surface of a large sheet of copy paper.

SUMMARY OF THE INVENTION An object of this invention is to eliminate any dis charge of large current due to the dielectric breakdown of a small air gap between the surface of a photosensitive element and an electroconductive transfer roller when copy paper is not positioned therebetween, the roller being positioned in proximity to the surface with the air gap interposed therebetween and also adapted for contact with the photosensitive surface for the transfer of an electrostatic latent image, so as to render the photosensitive surface free from damage and destruction and to thereby permit the photosensitive element to function as intended over a long period.

Another object of this invention is to prevent discharges due to the breakdown of an air gap produced between the copy paper and the photosensitive surface under the influence of a residual electric field possessed by the electroconductive backing of the copy paper when the rear end of the paper is peeled off the photosensitive surface after the transfer of the electrostatic latent image so as to protect the photosensitive surface from damage and destruction due to the discharges.

Another object of this invention is to prevent the above-mentioned discharge irrespective of the size of the copy paper.

According to this invention there is provided disconnecting means for isolating a circuit electrically connecting the electroconductive backing of a photosensitive element to an electroconductive transfer roller and operable to break the electrical connection while copy paper is not positioned between the photosensitive element and the transfer roller.

The disconnecting means mechanically moves the transfer roller toward or away from the photosensitive element in operative relation to the advance of the copy paper or of the photosensitive element so as to keep the transfer roller retracted, while the paper is not positioned between the photosensitive element and the transfer roller, at a safe position such that the dielectric breakdown of an air gap therebetween will not take place.

According to another embodiment of the disconnecting means, the circuit electrically connecting the backing of the photosensitive element to the transfer roller includes a switch for opening and closing the circuit in operative relation to the advance of the transfer paper or of the photosensitive element, so that while the paper is not positioned between the photosensitive element and the transfer roller the switch will be opened to electrically disconnect the transfer roller from the ground. In this case, there is no need to advance or retract the transfer roller mechanically.

In this way, the dielectric breakdown of the air gap is completely eliminated between the photosensitive element and the transfer roller by virtue of the presence of paper therebetween and by the disconnecting means while the paper is not positioned therebetween.

However, the grounding of the transfer roller serves to discharge the charge on the electroconductive backing of the copy paper to the earth, thereby preventing the paper from being attracted to the photosensitive surface by the electrostatic attraction. If the transfer roller is retracted to a safe position permitting no discharge or is electrically disconnected from the earth upon completion of charge transfer, the electroconductive backing la (see FIG. 3) of the paper 1 will have in the vicinity of its rear end a residual charge of polarity opposite to that of the charge on the photosensitive surface, with its dielectric layer lb still attracted to the photosensitive surface. Subsequently, the moment when the advancing paper 1 is separated from the photosensitive surface, the resulting small air gap will be subjected to dielectric breakdown by the field of the residual charge to permit discharge.

The present invention further provides means for eliminating such discharge. Thus there is provided electroconductive grounding means spaced apart from the transfer roller by a suitable distance in parallel thereto to ground the electroconductive backing of the copy paper after it has passed over the transfer roller and to thereby discharge the residual charge thereon to the earth. If the conductive backing has an electric resistivity of the order of 10 to 10 ohms as is usally the case with copy papers for the transfer of electrostatic latent images, the residual charge on the backing of the paper at its rear end will be satisfactorily returned to the earth by the grounding means asthe paper is out of contact with the grounded transfer roller. The grounding means serves also as a guide for the paper after it has passed over the roller.

According to this invention, the transfer roller further comprises an assembly of a center portionand opposite end portions electrically insulated from the center portion, the roller thus being adapted for use with copy papers of varying widths. The center portion and the opposite end portions are grounded by individual means, respectively, each of which has disconnecting means. If the copy paper is of a small width, the center portion alone of the transfer roller will be grounded only while the paper is positioned between the transfer roller and photosensitive element, the other portions of the roller being disconnected from earth electrically. For papers of large widths, the center portion and opposite end portions are all grounded only during the transfer operation.

The construction comprising the center portion and the end portions electrically insulated therefrom may BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 (a), (b) and FIGS. 2 (a), (b) are views illus- -trating only the transfer station of an electrophotographic copier of the electrostatic latent image transfer type, FIG. 1 (b) and FIG. 2 (b) being side elevations of FIG. 1 (a) and FIG. 2 (a) respectively;

FIG. 3 is a view illustrating copy paper at the transfer station as the paper isabout to be released;

FIG. 4 is a view illustrating only the transfer stationof an embodiment of this invention;

FIG. 5 is a view illustrating another embodiment of this invention and corresponding to FIG. 4;

FIG. 6 is a similar view illustrating another embodiment of this invention;

FIG. 7 is a view illustrating the transfer station of another embodiment of this invention which includes means for grounding the back of the copy paper;

FIG. 8 is a view illustrating another embodiment of the present invention and corresponding to FIG. 7;

FIG. 9 is a front view partly in section showing the construction of the principal part of a transfer roller employed in the embodiment of FIG. 8; and

FIG. l0 is a front view of a grounding roller.

DESCRIPTION OF THE PREFERRED 1 EMBODIMENTS FIG. 4 shows an embodiment in which a transfer roller 3 is adapted to be mechanically retracted from the surface of a photosensitive element 2 so that from the moment a sheet of copy paper 1 passes between the roller 3 and the photosensitive element-2 until the next sheet of paper is sent in between the roller 3 and the photosensitive element 2, the air gap between the roller 3 and the photosensitive element 2 will remain large to prevent dielectric breakdown notwithstanding the high voltage on the surface of photosensitive element 2 and the grounding of the transfer roller 3.

The photosensitive element 2 is supported on a drumlike support 2a which is grounded to ground the electroconductive backing of the photosensitive element. Similarly, the transfer roller 3 has its shaft grounded and is pressed against the rear face of copy paper 1 by a spring 4 during a transfer operation, whereby the dielectric surface of the copy paper 1 is brought into intimate contact with the charged surface of the photosensitive element 2 to provide an air gap therebetween which will permit latent image transfer. At the same time, the roller grounds the conductive backing of the copy paper 1. Consequently, the conductive backings of the photosensitive element 2 and the paper 1 are electrically connected to each other by the above-mentioned grounding. The intimate contact of the dielectric surface of the paper 1 with the charge surface of the element 2 permits an electrostatic latent image on the photosensitive element 2 to be transferred to the paper 1. which may then be treated in the usual manner such as by applying a powdered toner to the image bearing face of the paper 1 and heat fusing the toner to form a permanent image corresponding to the electrostatic latent image.

A cam 5 fixed to the support 2a is in itself made of an electrically highly insulating material or has a construction having high insulating properties. The cam has a circumferential length such that while the paper 1 is not positioned between the photosensitive element 2 and the transfer roller 3 during the rotation of the photosensitive element 2 and the advance of the paper 1 in timed relation thereto, the cam will shift the transfer roller 3 away from the influence of the element 2 against the spring 4 and retain the same at a retracted position to render the air gap free from dielectric breakdown as already described. Thus discharges which would otherwise result from the proximity of the transfer roller 3 to thephotosensitive surface are precluded in the copier for use with copy paper of a definite size.

FIG. 5 shows an embodiment comprising a photosensitive element 2 in the form of a belt, a drive roller 7 supporting the element 2, a transfer roller 3 biased by a spring 4 for bringing copy paper 1 into intimate contact with the element 2, and reciprocally driving means such as a plunger 6. While the paper 1 is not positioned between the photosensitive element 2 and the transfer roller 3, the plunger 6 keeps the transfer roller 3 away from the surface of the element 2 to provide a sufficient air gap therebetween to prevent the aforementioned dielectric breakdown.

The plunger 6 may be operated by electromagnetic, hydraulic or any other suitable means to be controlled by detectors such as microswitches for detecting the front and rear ends of paper 1 during its advancing movement. The transfer roller 3 and the drive roller 7 are of course electrically grounded.

The embodiment shown in FIG. 6 has a switch 9 included in a grounding circuit 8 for an electroconductive transfer roller 3. The switch 9 is open during the absence of paper 1 between the transfer roller 3 and a photosensitive element 2 to disconnect the transfer roller 3 from the ground and to thereby substantially prevent the injection of a charge for transfer.

According to this embodiment, the transfer roller 3 is always urged toward the element 2 by unillustrated means to bring the dielectric surface of copy paper 1 close to the charged surface of the element 2 to provide an air gap therebetween required for the image transfer. While the paper 1 is not positioned between the roller 3 and the element 2, the roller 3 is in rolling contact with the photosensitive surface. The support for the transfer roller 3 is of course insulated electrically. The operation of the switch 9 is controlled electromagnetically or mechanically in the same manner as above.

It will be apparent from the above that the mechanical or electrical disconnecting means 0 (specifically indicated at 5, 6 or 9) for retracting or ungrounding the conductive transfer roller 3 eliminates the electrical condition which permits a discharge between the transfer roller 3 and the photosensitive element 2 while the paper 1 is not located at the transfer station, i.e. between the element and the roller. More specifically, such effect is achieved by the mechanical means which forms a greater gap between the roller 3 and the element 2, or by the electrical means which disconnects the roller 3 from the ground. Therefore despite the presence of charged surface of the photosensitive element 2 which is not covered with the paper 1, the exposed area will be renderedfree from any discharge.

Due to the elimination of the electrical action between the roller 3 and the photosensitive element 2 achieved by the disconnecting means 0, the rearv end of the paper 1 passing through the transfer station carries a residual charge induced by the electrostatic latent image on the photosensitive element 2 as already described with reference to FIG. 3, with the result that the electric field of the residual potential gives rise to dielectric breakdown of the gap to cause discharge again when the rear end separates from the photosensitive surface. This results in fogging of the developed image. FIG. 7 shows means for eliminating such detrimental result.

With reference to FIG. 7, an electroconductive roller 10 is disposed beside the path of travel of copy paper 1 in contact with the conductive backing 1a of the paper 1, the roller 10 thus serving as grounding means E for the backing la. FIG. 7 does not illustrate disconnecting means 0 for retracting a transfer roller 3 or disconnecting the same from the earth when the rear end of the paper 1 passes through the transfer station.

Since the grounding means E serves to ground the conductive backing la of the paper 1 when the paper 1 separates from the photosensitive element 2, the means may be in the form of a conductive roller as described or in the form of an elastic tonguelike member, or it may be any other grounding member which is positioned beside the path of advance of the paper 1 passing through the transfer station and which is capable of grounding the backing la. As already described, the grounding means E serves also as a guide for the paper 1.

As illustrated in FIG. 7, the grounding means E grounds the conductive backing la of the paper 1 when the paper 1 is to be separated from the photosensitive element 2, with the transfer roller 3 retracted to a safe position to prevent the dielectric breakdown of the air gap between the roller 3 and the element 2, so that the foregoing operation of the disconnecting means 0 permits the residual charge (indicated as symbols in the drawing) on the conductive backing of the paper 1 to be returned to the earth by way of the grounding means E such as the conductive roller 10. As a result, the field of residual charge will be nullified when the paper 1 is separated from the photosensitive element 2 and the aforementioned discharge will not take place, consequently rendering the developed image free from fogging attributable to such discharge.

The distance between the transfer station and the position where the grounding means E contacts the conductive backing la of the copy paper 1 is so determined that the foregoing function can be fully performed with the electric resistivity of the element 1a taken into consideration. If the electric resistivity of the backing element la is of the order of 10 to 10 ohms as is generally the case with this type of paper, it is perfectly possible to return the residual charge from the rear end of the conductive backing la to the earth when the paper 1 is separated, without permitting the discharge to take lace.

p FIGS. 8 to 10 show another embodiment of this invention adapted for use with copy papers of different widths. In the case where paper 1 of a small width is used for copying, this embodiment eliminates dielectric breakdown that would otherwise occur between a transfer roller 3 and a photosensitive element 2 at the opposite sides of the paper.

The electroconductive transfer roller 3 comprises a center portion 3a having alength corresponding to the width of paper of a small size and other portions 3b electrically insulated from the center portion. The

respective portions

3a and 3b are grounded by way of separate circuits l1 and 12 for electrical connection with the conductive backing of the photosensitive element 2 individually. The circuits 1] and 12 include

switches

13 and 14, respectively, which serve as disconnecting means for opening and closing the circuits individually. Opening of the

switches

13 and 14 disconnects the

portions

3a and 3b from the earth electrically. FIG. 9 shows that the center portion 3a of the transfer roller 3 is connected to the circuit 11 at its shaft 3a.

The opposite end portions 3b are secured to and shortly spaced from the center portion 3a by electrical insulators interposed therebetween and are connected to the circuit 12 by way of contact members 3b. In cooperation with an auxiliary roller 16 made of an electrical insulator, a conductive roller 10 serving as grounding means E guides the paper 1 discharged from the transfer station.

If copy paper 1 of a small size is used, the switch 13 for grounding the center portion 3a only is held closed while the paper 1 is positioned in the transfer station, with the switch 14 left open to keep the opposite end portions 3b out of connection with the ground (see FIG. 8) whereby the injection of charge to transfer an electrostatic latent image will be achieved only through the center portion 3a. Since the end portions 3b are out of connection with the ground, there is no possibility of a discharge taking place across the air gap between the portions 3b and the charged surface of the photosensitive'element 2.

If copy paper 1 of a large size is used, both

switches

13 and 14 are held closed while the paper 1 is positioned in the transfer station, with the result that the image will be transferred onto the entire surface of the paper 1.

The transfer roller 3 may comprise a greater number of segments than in the foregoing embodiment for use with copy papers of varying widths, the segments being joined together in electrically insulated fashion and provided with grounding circuits, respectively, which are opened and closed individually.

Although the disconnecting means 0 described above for preventing discharges has such construction that the

switches

13 and 14 are opened and closed, the respective portions may alternatively be separated and adapted for forward and backward movement individually so as to prevent the abovementioned discharges mechanically.

The disconnecting means 0 can be operated, without any difficulty, in timed relation to the rotation of the photosensitive element and to the advance of the copy paper, for example, by providing a detector for sensing the rear end of the paper or by any other means generally known.

What is claimed is:

1. An apparatus in an electrostatic copying machine for transferring an electrostatic latent image to a receptor member having a dielectric layer and a conductive layer comprising:

a photosensitive element having a chargeable surface exposable to a light image to form thereon an electrostatic latent image and including a grounded conductive backing element,

a conductive transfer roller for transferring the electrostatic latent image to the dielectric face of said receptor member by bringing the dielectric layer into intimate contact with the surface of the photosensitive element,

said transfer roller being in contact with said conductive layer of the receptor member during the transfer of the electrostatic latent image and being grounded so as to electrically connect the conductive backing element with the transfer roller through said conductive layer,

disconnecting means for breaking the electrical connection between said transfer roller and said conductive backing element in the absence of a receptor member between said transfer member and said photosensitive element for preventing dielectric breakdown, and

means following the transfer roller for grounding the conductive layer of the receptor member bearing a transferred electrostatic latent image so as to dissipate the remaining charges.

2. The apparatus as set forth in claim 1 wherein the disconnecting means comprises mechanically operative means for holding the transfer roller away from the photosensitive element while a receptor is not positioned between the photosensitive element and the transfer roller so as to keep an air gap between the element and the roller sufficiently wide to prevent a dis charge due to the dielectric breakdown of the gap.

3. The apparatus as set forth in claim 2 wherein the operative means comprises a member for biasing the transfer roller toward the photosensitive element and a cam for keepingthe transfer roller retracted from the photosensitive element against the action ofthe biasing member while a receptor is not positioned'between the photosensitive element and the transfer roller."'

4. The apparatus as set forth in claim 2 wherein the operative means comprises a member for biasing the} transfer roller toward the photosensitive element and a reciprocating mechanism for keeping the transfer roller retracted from the photosensitive element while a receptor is not positioned between the photosensitive element and the transfer roller upon detecting the absence of the receptor therebetween.

5. The apparatus as set forth in claim 1 wherein the disconnecting means includes a switch for opening a grounding circuit of the transfer roller in the absence of a receptor between the photosensitive element and the transfer roller upon detecting the absence of the receptor therebetween.

6. The apparatus as set forth in claim 1 wherein the grounding means comprises an electroconductive grounding roller to be brought into rolling contact with the conductive backing of the receptor after the receptor has passed from between the transfer roller and photosensitive element.

7. The apparatus as set forth in claim 1 wherein the conductive transfer roller comprises an assembly of a plurality of coaxial end to end sections so as to be usable for copy papers of varying widths, the sections being insulated from one another and grounded individually for connection with the conductive backing of the photosensitive element, the sections being selectively disconnectable from the ground to selectively break their electrical connection with the conductive backing of the photosensitive element.

8. In an electrostatic copying machine a mechanism for producing an electrostatic latent image on the dielectric front face of an image receptor having an electrically conductive rear substrate comprising a photosensitive element having an electrically conductive backing, said photosensitive element being electrically chargeable and exposable to a light image to produce on the surface thereof a latent electrostatic image, a transfer member having an electrically conducting face and urged toward engagement with said photosensitive element, said image receptor being advanceable along a path between said photosensitive element and said transfer member with its front face engaging said photosensitive element and its rear substrate engaging said transfer member, means responsive to the presence of member to said photosensitive element backing.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION- PATENT NO. 3,827, 800 A DATED August 6, 1974 INVIENTOR(S) SUSUMO TANAKA, et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

"[75] Inventors: Susumu Tanaka, Sakai; Yuji Enoguchi, Higashi-Osaka; Takao Fujiwara, Sakai; Isao Iizaka, Toyokawa; Toshio Yamamoto, Toyokawa, all of Japan-- Signed and Sealed this T wenty-eighth D a) of February I 978 [SEA L] Attest:

RUTH C. MASON LUTRELLE F. PARKER Arresting Oflicer Acting Commissioner of Patents and Trademarks UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION 9 PATENT N0. 3 827 800 DATED August 6 1974 INV ENTOR(S) SUSUMO TANAKA, et a1 It is certified that error appears in the above-identified patent and that said Letters Patent Q are hereby corrected as shown below:

"[75] Inventors: Susumu Tanaka, Sakai; Yuji Enoguchi, Higashi-Osaka; Takao Fujiwara, Sakai; Isao Iizaka, Toyokawa; Toshio Yamamoto,

Q Toyokawa, all of Japan-- Signed and Scaled this Twenty-eighth of February I 978 [SEAL a 1 Arrest:

RUTH C. MASON LUTRELLE F. PARKER Arresting Officer Acting Commissioner of Patents and Trademarks O

Claims

1. An apparatus in an electrostatic copying machine for transferring an electrostatic latent image to a receptor member having a dielectric layer and a conductive layer comprising: a photosensitive element having a chargeable surface exposable to a light image to form thereon an electrostatic latent image and including a grounded conductive backing element, a conductive transfer roller for transferring the electrostatic latent image to the dielectric face of said receptor member by bringing the dielectric layer into intimate contact with the surface of the photosensitive element, said transfer roller being in contact with said conductive layer of the receptor member during the transfer of the electrostatic latent image and being grounded so as to electrically connect the conductive backing element with the transfer roller through said conductive layer, disconnecting means for breaking the electrical connection between said transfer roller and said conductive backing element in the absence of a receptor member between said transfer member and said photosensitive element for preventing dielectric breakdown, and means following the transfer roller for grounding the conductive layer of the receptor member bearing a transferred electrostatic latent image so as to dissipate the remaining charges.

2. The apparatus as set forth in claim 1 wherein the disconnecting means comprises mechanically operative means for holding the transfer roller away from the photosensitive element while a receptor is not positioned between the photosensitive element and the transfer roller so as to keep an air gap between the element and the roller sufficiently wide to prevent a discharge due to the dielectric breakdown of the gap.

3. The apparatus as set forth in claim 2 wherein the operative means comprises a member for biasing the transfer roller toward the photosensitive element and a cam for keeping the transfer roller retracted from the photosensitive element against the action of the biasing member while a receptor is not positioned between the photosensitive element and the transfer roller.

4. The apparatus as set forth in claim 2 wherein the operative means comprises a member for biasing the transfer roller toward the photosensitive element and a reciprocating mechanism for keeping the transfer roller retracted from the photosensitive element while a receptor is not positioned between the photosensitive element and the transfer Roller upon detecting the absence of the receptor therebetween.

8. In an electrostatic copying machine a mechanism for producing an electrostatic latent image on the dielectric front face of an image receptor having an electrically conductive rear substrate comprising a photosensitive element having an electrically conductive backing, said photosensitive element being electrically chargeable and exposable to a light image to produce on the surface thereof a latent electrostatic image, a transfer member having an electrically conducting face and urged toward engagement with said photosensitive element, said image receptor being advanceable along a path between said photosensitive element and said transfer member with its front face engaging said photosensitive element and its rear substrate engaging said transfer member, means responsive to the presence of said receptor between said transfer member and said photosensitive element for electrically connecting said rear substrate through said transfer member to said backing and responsive to the absence of a receptor between said photosensitive element and transfer member for electrically isolating the front face of said photosensitive element from said backing by way of said transfer member and means for electrically connecting the rear conductive face of a receptor advancing from between said photosensitive element and said transfer member to said photosensitive element backing.