US2807233A

US2807233A - Electrophotographic printing machine

Info

Publication number: US2807233A
Application number: US419314A
Authority: US
Inventors: Clyde J Fitch
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1954-03-29
Filing date: 1954-03-29
Publication date: 1957-09-24
Anticipated expiration: 1974-09-24
Also published as: CH333952A; BE536878A; BE536877A; NL195972A; CH333951A; GB768020A; US2859673A; GB766426A; FR1141378A

Description

P 24, 7 c. J. FITCH ELECTROPHOTOGRAPHIC PRINTING MACHINE 3 Sheets-Sheet 1 Filed March 29, 1954 PIC-Ll INVENTOR. CLYDE J. FITCH Ji v.71

AT-roR NEY Sept. 24, 1957 c.- J. FITCH ELECTROPHOTOGRAPHIC PRINTING MACHINE 3 Sheets-Sheet 2 Filed March 29, 1954 INVENTOR. CLYDE J. FITCH f I ATTORNEY Sept. 24, 1957 Filed March 29, 1954 c. J. FITCH 2,807,233

ELECTROPHOTOGRAPHIC PRINTING MACHINE 3 Sheets-Sheet 3 PI 6 5 INVENTOR.

CLYDE J. FITCH BY j JM JV.

ATTORNEY United States Patent 2,807,233 ELECTROPHOTOGRAPHIC PRINTING MACHINE Clyde J. Fitch, Endicott, N. Y., assignor to International Business Machines Corporation, New York, N. Y., a corporation of New York Application March 29, 1954, Serial No. 419,314 13 Claims. (Cl. 118-637) This invention relates to electric printers in general, and to the print transfer apparatus thereof in particular.

In keeping with electric printers in general, and with electrophotographic printers in particular, the embodiment of this invention pertains to apparatus for elfecting a transfer of a visible image from an image carrying member, to a print receiving material, such as a web of paper for example, and has for its purpose to provide an improved image, or print, transfer apparatus by which selective electric printing may be effected.

To amplify the foregoing, the embodiment of this invention pertains to so'called xerographic machines capable of making a duplicate of information appearing on source records, such as record cards for example, on a print receiving strip by means of a transfer or printing process. As is well known to persons familiar with the electrophotographic printing art, xerography is a term applied to a printing process in which electrostatic latent images are rendered visible by a suitable electrically charged toner powder, the resulting powder image thereafter being transferred and fixed to a print receiving material.

Another broad object of this invention is to provide a selective printing electric printer whereby only selected information appearing at a certain place, or places, on a source record, is transferred from the source record onto a copy record.

Another object of this invention is to provide an electrophotographic printer having an improved image transfer apparatus associated therewith for transferring by electric power only select electrically charged powder images. i

More specifically, another object of this invention is to provide a xerographic printer having an image transfer'apparatus associated therewith which is capable of selectively effecting or disabling the image transfer or printing process 9 In line with the foregoing, a still another object of this invention is to provide an electrophotographic printer having an image transfer apparatus which requires lower voltages than used heretofore.

Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawingsywhich disclose, by way of example, the principle of the invention and the best mode, which has been contemplated, of applying that principle.

In the drawings:

Fig. l is a somewhat diagrammatic view of an electrophotographic printer utilizing alshifting transfer roller apparatus at the image transfer station.

Fig. 2 is'a somewhat diagrammaticview of an electrophotographic printer utilizing an electric pulse controlled transfer apparatus at the image transfer station.

Fig. 3 is a flow diagram depicting generally the operations required in order to place the image of source record information upon a print receiving a copy record.

Fig. 4 is a somewhat diagrammatic view of the transfer apparatus and associated mechanism taken along the plane 4-4 of Fig. l.

Fig. 5 is a somewhat diagrammatic view of the transfer apparatus and associated mechanism taken along the plane 5-5 of Fig. 2.

Referring to Fig. 1, record cards 20 to be operated on are stacked in hopper 21, and are fed, one by one, by a conventional picker (not shown) of the type in Patent No. 2,448,830 issued to J. J. Robbins et al., each card cycle out of card hopper 21 to stacker 22. Successive pairs of

feed rolls

23 and 24 cause cards 20 to be advanced during successive card cycles past the optical projector apparatus 25.

Apparatus 25 includes a single light ray projector 26. which throws a concentrated band of parallel light rays upon the constricted center of the aperture in member 27. Inasmuch as the reflecting surface of a mirror 28 is over the aperture of member 27, the light band is caused to impinge upon the surface of xerographic drum 29 when there are no cards present between member 27 and mirror 28.

As is shown in Fig. 3, each of the record cards 20 is shown to include printed information which is represented and identified by block 30. Due to the fact that the surface of each card 20 has a light reflecting property," as the cards are fed past projector 25 (see also Fig. 1), and between member 27 and mirror 28, light rays are directed onto the surface of drum 29 except when the symbols included within the printed information identified by the reference numeral 30, are not brought into alignment with the aperture of member 27. It may be-seen then that apparatus 25 includes a conventional light scanning means for transferring the image of the aforesaid printed information onto the surface of the xerographic drum 29.

The drum 29 is mountedon a shaft 31 which is suitably supported in frame members (not shown) for rotation in a counterclockwise direction, said shaft 31 being driven by an electric motor 34 (see also Fig. 4). Xerographic drum 29 includes an electrically conducting cylinder 35 and a printing element, or plate, 36 in the form of an electrically insulating or non-conducting image layer. This layer is carried by a sheet of any flexible metal or other conductive material 37 that enables its being flexed around and attached to the cylinder 35, the sheet 37 being secured to the cylinder in any of the conventional ways of attaching a printing plate to a supporting cylinder, as by means of suitable clamping devices. It is necessary, however, that the backing sheet 37 of the 7 image layer plate 36 is in good electrical contact with thereon by-electrostatic charging,

the electrically grounded drum shaft 31. The electrically conductive backing sheet 37 is preferably coated with a light sensitive photoconductive insulating-material, such as plate 36, which may have a powder image produced exposure and powder development, after which the powder image can be made into a permanent print image by transferring and fixing the developed powder image onto a print receiving material such as paper strip, or web, 38.

With the feeding of record cards 20 from hopper 21 to stacker 22, xerographic drum 29 is caused to rotate at a speed which is correlated to the record card feed speed, by means of drive shaft 31. As successive incremental areas of the light sensitive photoconductive plate 36 are moved past ion-producing unit 32, the aforesaid plate is electrostatically charged by the ion-producing source. Carlson Patent No. 2,588,699 may be referred to for a complete showing and description of the afore-mentioned electrophotographic charging apparatus.

consequent upon the exposure of the surface of plate 36 to the image of a record card 20, said image being caused by the light rays which are directed from projector apparatus 25, those electrically charged incremental areas of plate 36 onto which light rays are directed, are discharged, and those areas not illuminated by light rays remain charged. This, of course, is for the reason that plate 36 is a photoconductive insulating material which is in electrical contact with conductive backing sheet 37, said sheet 37 being electrically connected to grounded shaft 31. Hence, after photoconductive plate 36 is exposed to the light image of a record card, an electrostatic latent image of the record card will remain on plate 36, this electrostatic latent image being one wherein the dark characters within printed information image areas identified by reference numeral 30 (Fig. 3) cause charged characters within image areas identified by reference numeral 30a which correspond to the afore-mentioned dark characters, and wherein the light image areas corresponding to the record card surface are no longer charged.

Continued rotation of the xerographic drum in a counterclockwise direction causes the image portions 30a of plate 36 (Fig. 3) to be moved into developing chamber 39. A similar chamber is utilized in the apparatus of Schatfert Patent No. 2,576,047. The electrically charged toner powder in chamber 39 will flow onto plate 36 and over the electrostatic latent image, and will move downwardly thereover due to gravity in a continuous stream, thus being evenly distributed over the image layer. The surplus toner powder which does not adhere to the electrostatic latent image formed on plate 36, falls into a receiving receptacle within chamber 39 so as to cause the powder to be completely retained within the chamber housing. The powder image that is formed on the image plate 36 visibly defines the electrostatic latent image, i. e., the powder will cling only to the dark printed information image areas having an electric charge there- The powder in chamber 39 may be a finely powdered dye, pigment, carbon or other black or colored substance, or in some cases a white powder such as zinc oxide. A suitable electroscopic developer powder, or toner, is described in Copley Patent No. 2,659,670

Continued rotation of drum 29 causes the powder image on plate 36 to move out of chamber 39 and into the transfer, or printing, station having transfer roller 40 thereat. The transfer roller comprises an inner-metallic portion 41 and an outer portion 42 of very resilient or yielding material having a high electrical resistance, as for example, a layer of soft semi-conducting rubber. The transfer roller requires a resilient outer portion so as to compensate for mechanical irregularities of the xerographic drum surface, and to prevent mechanical damage to the photoconductive surface thereof. The conductive rubber is preferably a very poor conductor of electricity, and may have an electrical resistivity of approximately ohms per cubic centimeter. The resistance value is not too critical and it may be greater than the aforementioned value. However, the resistance value is preferably not less than 10 ohms per cubic centimeter.

Transfer roller 40 is biased by springs 43 (see also Fig. 4) in the direction of photoconductive plate 36 so that web 38 is sandwiched therebetween. The transfer roller is supported by the shaft is journaled in arms 45. The latter arms are each at- 44 thereof which, in turn,

tached to cam follower arms 46 which are also fixed to shaft 47 whereon cam follower roller 48 is mounted. Web feed control arms 49 having feed roller 50 attached thereto are also fixed to shaft 47 so that

arms

45, 46 and 49 act in unison. The afore-mentioned arms are pivotally mounted upon shaft 54, the said shaft having idler roller rotatably mounted thereon, and being fixed in printing machine support frames, such as frame 53 for example. As is shown in Fig. 1, web 38 is fed from reel 56 past drag rollers 57, around idler roller 55 and transfer roller 40, between fixing rollers 58,

feed rollers

50 and 59, and rollers 60, to reel 61.

In order to produce a permanent image, it is necessary to fix onto the print receiving material, such as web 38 for example, those powder images that are transferred thereto. One means for fixing powder images utilizes a line pressure such as is afforded by the pressure fixing rolls 58 (Fig. 1) and 158 ('Fig. 2). A sufficient line pressure for example 500 pounds per lineal inch of contact, will cause the toner powder to flow into the fibers of the web material. An oil pad 68 (Fig. 1) and 168 (Fig. 2) is provided to remove any excess powder which will cling to the upper fixing roller.

As long as powder images are plate 36 onto web 38,

to be transferred from the generally T-shaped unit comprised of

arms

45, 46 and 49, will be positioned under the urging of springs 43 so that transfer roller 40 causes Web 38 to engage plate 36. In addition, this generally T-shaped unit is positioned so that roller 50 maintains the web in contact with continuously rotating drive roller 59 in order to cause the web to advance. It is necessary to point out that roller 59 is spring-biased in an upward direction so that there is assurance of good contact between transfer roller 40 and drum 29 during the periods that

rollers

50 and 59 are in contact. In order to disable printing, i. e., to prevent the transfer of charged powder images, cam 62 is rotated so as to engage roller 48 which, in turn, causes

arms

45, 46 and 49 to pivot in a. counterclockwise direction. Hence, transfer roller 40 will be moved away from drum 29, and web feed roller 50 will be moved away from drive roller 59, to thereby disable the friction-drive applied to web 38 by

rollers

50 and 59. In addition, transfer roller 40 is moved a sufficient distance to carry the web into engagement with braking member 65 whereby web 38 is stopped immediately by the braking action.

In order to remove any toner powder which remains on the surface of plate 36 prior to the incremental areas thereof becoming charged again by ion-source unit 32, a rotating plush roller 66 is provided. This roller is po sitioned within a housing 67 for retaining the powder removed by the counterclockwise rotating action of the roller, from the xerographic drum plate 36.

A comparison of the electrophotographic printers shown in Figs. 1 and 2 will reveal a similarity between many elements thereof. Hence, for purposes of clarity and simplicity, those elements in the printer of Fig. 2 which are similar to corresponding elements in the printer shown in Fig. 1, will be identified by a series reference numeral corresponding to the reference numeral used in Fig. 1. That is, for example, the xerograph'ic drum of the printer shown in Fig. l, is identified by the reference numeral 29, and the xerographic drum of the printer shown in Fig. 2 is identified by the reference numeral 129.

Referring to Fig. 2, record cards to be operated on are stacked in hopper 121, and are fed, one by one, each card cycle out of card hopper 121 to stacker 122. Successive pairs of feed rolls 123 and 124 cause the record cards to be advanced during successive card cycles past the optical projector apparatus 125.

Apparatus 125 includes a single light ray projector 126 for directing a band of light rays upon the constricted center of the aperture in member 127, to thereby effect a conventional light scanning operation whereby the image of the printed information on the record card is trans- 75 ferred to the surface of the xerographic drum 129.

Xerographic drum 129 is mounted on a shaft 131 which is driven by an electric motor 134 (see also Fig. in a counterclockwise direction. The aforesaid drum includes an electrically conducting cylinder 135 and a light sensitive photoconductive insulating printing plate 136. This plate is carried by a sheet of any flexible metal or other conductive material 137 that enables its being flexed around and attached to the cylinder 135.

With the feeding of record cards from hopper 121 to stacker 122, the xerographic drum is caused to rotate by shaft 31 at a speed which is correlated to the record card feed speed. As successive incremental areas of the light sensitive photoconductive plate 136 are moved past charging roller 170, the aforesaid plate is caused to have an electrical charge placed thereon. The charging roller includes an inner-metallic portion 171 and an outer portion 172 of very resilient or yielding material having a high electrical resistance, as for example, a layer of soft conducting rubber. Inasmuch as this charging roller is substantially similar to the upper cylindrical member or roll used in the electrical printing apparatus described in Hooper Patent No. 2,520,504, reference may be had to this patent for more detailed information.

Consequent upon the exposure of the surface of plate 136 to the image of a record card 120, an electrostatic latent image is caused to remain thereon in the manner, and for the reasons, mentioned hereinbefore. Continued rotation of the xerographic drum 129 in a counterclockwise direction causes the electrostatic latent image-exposed portions of plate 136 to be moved into developing chamber 139 wherein the electrically charged toner powder is permitted to flow onto plate 136 and over the electrostatic latent image. As a result thereof, a powder image which visibly defines the electrostatic latent image is formed on the surface of plate 136. Further rotation of the ,xerographic drum causes the powder image on plate 136 tomove out of chamber 139 and into the transfer, or printing, station having transfer cylinder 175 thereat.

Transfer cylinder 175 includes end wheels 176 (see also Fig. 5) and 177, and a conductive roller 178. The diameter of roller 178 is smaller than the diameters of

end wheels

176 and 177 by an amount such that a gap of approximately 0.002 inches exists between plate 136 and web 138. In order that the web does not rub against the drum surface during print suppress time, it is necessary that the diameter of roller 178 is smaller than the diameter of the end wheels by an amount greater than twice the thickness of the web. Roller 178 is rotatably mounted on cylinder shaft 179 in order that feeding of web 138 may be stopped during non-print periods even though the Xerographic drum is caused to continue rotating. The

wheels

176 and 177 are journaled and arranged in such a manner as to be electrically separated from shaft 179 which, as shown in Fig. 2, is used to supply electric power to conductive roller 178, and the cylinder shaft is biased in a direction towards drum 129 by conventional means so that the end wheels ride on the peripheral surface of the drum. As is shown, web 138 is fed from reel 156 past drag rollers 157, around

rollers

160 and 178, between fixing rollers 158, feed

rollers

150 and 159, to reel 161. In order to remove any toner powder which remains on the surface of plate 136, prior to the incremental areas thereof becoming charged again by charging cylinder 170, there is provided a rotating plush roller 166. This roller is positioned within a housing 167 for retaining the powder removed by the counterclockwise rotating action of. the roller, from the xerographic drum plate 136.

Image transfer apparatus Referring to Fig. 1, transfer roller 40 is connected to a source of positive potential, e. g., 1000 volts, via wire 70 and manually operated switch 71 and/ or cam contacts C1. The insulating image plate 36, carried by the conductive supporting plate 37, is charged negatively, whereas the toner powder which produces the image by adherence to the plate 36, is charged positively by triboelectric action of the carrier material to which the electroscopic powder particles adhere until separated therefrom by the stronger attractive force of the negatively charged insulating image plate 36. Inasmuch as backing sheet 37 is electrically connected to grounded shaft 31, an effective condenser is obtained at the transfer station wherein backing sheet 37 and transfer roller 40 serve as plates thereof, and insulating plate 36 along with web 38 act as the dielectric thereof. The aforementioned positive potential applied to transfer roller 40 is sulficient to cause an electric field to exist between the transfer roller 40 to backing plate 37. This electrostatic field or potential gradient causes the powder adhering to plate 36 to transfer onto web 38, Whereafter the transferred powder on web 38 is fixed thereto by pressure rollers 58. In order to disable printing, i. e., to prevent the transfer of charged powder images, cam 62 is rotated so as to engage cam follower roller 48 which, in turn, causes

arms

45, 46 and 49 to pivot in a counterclockwise direction. This, as stated previously, causes transfer roller 40 to be moved away from xerographic drum 29, and web feed roller 50 to be moved away from drive roller 59. The resulting air space defined by the outer peripheries of plate 36 and transfer roller 40 is sufiicient to preclude a transfer of the powder from xerographic drum 29 onto web 38. Inasmuch as the generally upward movement of roller 50 disables the friction-drive that is applied to web 38 by

rollers

50 and 59, and since the shifting of transfer roller 40 is of such a nature as to brake web 38 by means of braking member 65, web 38 is stopped immediately.

Referring to Fig. 2, a suitable positive potential, e. g., +2000 volts, is applied to the conductive roller 178 of transfer cylinder 175 via line 177. Hence, roller 178 is electrified so that a resulting ion-stream transfers the toner powder adhering to plate 136 onto web 138, and the transfer of power is effective so long as cam contacts C2. are closed. In order to disable the printing operation, i. e., the transfer of powder images, cam contacts C2 are caused to open. Concurrently therewith, web feed drive roller 159 is stopped so as to stop the feeding of web 138. The drag load applied to web 138 by

rollers

157, 158, 160, and 159, is sutficient to prevent any creep thereof. Inasmuch as roller 178 (see also Fig. 5) has a diameter which is smaller than that of

end wheels

176 and 177, cylinder need not be shifted away from xerographic drum 129 during the periods when web 138 is not being moved.

It is necessary to point out at this time that the description thus far pertains to a positive-to-positive printer. However, a reverse image printer may be had simply by employing a reversal developer powder so that the charge on the powder image is reversed, and by connecting the transfer roller or cylinder to a voltage that is negative with respect to the Xerographic drum. A suitable voltage may range from negative 1000 volts to negative 2000 volts.

In order to avoid undue complexity and prolixity, a positive-to-positive printer will be described for illustrative purposes only. This is not to be construed as a limitation, however, but is to be accepted as a preferred embodiment.

Operation The printed information which is to be transferred to the print receiving web is identified in the illustrated embodiments by reference numeral 30 (Fig. 3) and is typed, for instance, onthe source records. The information to be transferred need not be in reversed order on the source records because the double reversal effected by the projection of the image onto plate 36 (Fig. 1), for example, and the subsequent transfer of the powdered image onto web 38, causes the information transferred to the web to be arranged in the same order as is the information on the source records.

Referring to Figs. 1 and 4, xerographic drum 29 is shown to be operated by motor 34 through a speed reduction unit 80 having gears, or the like, therein, and which is also connected to drive unit 81 so as to cause cam 62 and cam contacts CI to operate in step with the drum. The rotational speed of drum 2% and cam 62 is so correlated that whenever the image-portion 30a of the card provided with the information to be transferred, is disposed between drum 29 and transfer roller 40, cam 62 is in a position whereat springs 43 are free to move web 33 into simultaneous contact with plate 36 and transfer roller 40. As mentioned hereinbefore, the information is thereby transferred from the xerographic drum to the paper strip 38. A further movement of the xerographic drum and cam 62 will cause transfer roller 49 to be shifted from an effective print position to a non-print position only after the desired information 3001 has been transferred to web 38. The transfer roller will remain in the latter non-print position until a succeeding image 300 is moved into the transfer station. Inasmuch as feed roller 50 is moved away from drive roller 59 during nonprint time, web 38 is not advanced during this time.

It is apparent that cam 62 may be adjustable, or interchangeable with another cam so that the height of the information to be transferred to the web can be varied according to a predetermined requirement. It is apparent too that cam 62. may be provided with a number of cams, and in this event, a number of horizontal strips can be transferred to the web from several card sections. In addition, the length of transfer roller 40 can be varied so as to be effective to transfer to web 38 only predetermined information. The arrangement may be such, for example, that the length of roller 4% corresponds to the vertical width of the information on the card. Furthermore, roller 49 may be laterally adjustable so that the same presses onto xerographic drum 2 9 only when a certain part of the powder image is moved into the transfer station. Transfer roller 4'0 may also be subdivided so that a number of vertical portions are printed from a single card section. Thus, by the above arrangements any printed information from a source record can be transferred to a print receiving material by merely varying the two transfer control members; namely the cam 62 and the transfer roller 40.

As stated previously, printing at the transfer station may be disabled by simply shifting transfer roller 40 away from xerographic drum 29. However, in some cases it may also be desirable to disrupt the power applied to transfer roller 46 whenever the transfer roller is shifted away from the xerographic drum. This type of operation may be had by opening manually operated switch 71 and permitting the electric power that is applied to transfer roller 40 to be under control of cam contacts C1. The cam contacts may be timed so that a circuit is completed to roller whenever the said roller is shifted to a printing position, and opened whenever roller 40 is shifted to a non-printing position.

Referring to Figs. 2 and 5, Xerographic drum 129 is operated by motor 134 through a suitable gear unit 180 which is also connected to a driven unit 181 for operating paper feed roller 159 and cam contacts C2. Unit 181 includes a gear sector for operating roller 159 intermittently so that roller 159 is operated to advance web 138 whenever the image lfitla to be transferred is moved to the printing, or transfer, station. Cam contacts C2 are timed to be in step with the movement of feed roller 159; i. e., the contacts are closed so as to apply a positive potential to conductive roller 178 during the time that image 130a is at the transfer station, and open during all other periods. As described previously, the diameter of roller 173 is smaller than that of

end wheels

176 and 177 and, as a result thereof, web 138 may be stopped during non-print time even though Xerographic drum 12f continues to rotate. That is, there is a sufficient clearance between the outer surface of web 138 and the outer surface of plate 136 so that either the web or the plate may be stopped during a movement of the other Without creating a rubbing action therebetween.

In summation, apparatus have been shown and described whereby selective electrophotographic printing is effected in order to transfer onto a print receiving material only select information in a predetermined place, or places, of a source record. And while there have been shown and described and pointed out the fundamental novel features of the invention as applied to preferred embodiments, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated and in their operation may be made by those skilled in the art, without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. In an electric printer comprising a rotatable printing drum having an inner electrically conducting member and an outer dielectric surface portion adapted to support transferable images thereon for transfer at a printing zone to a Web, a conductive cylinder for supporting the web in a position at the printing zone intermediate said printing drum and said cylinder, a source of electric power, electric circuit means for connecting said conducting member and said cylinder to said power source, means for rotating said printing drum, means for moving said web at a lineal speed correlated to the peripheral speed of said printing drum, and circuit interrupter means operable synchronously with said drum rotating means for governing said electric circuit means so that electric power is applied to said member and said cylinder as said transferable images are moved through the printing zone, to thereby effect a transfer of said images from said printing drum to said web.

2. In an electrophotographic printer comprising a printing member, shiftable means normally at: one limit of movement nearest said printing member for applying an electric force at a printing zone, means for moving said printing member relative to said electric force applying means, means for feeding a print receiving material between said member and said electric force applying means in a timed relation to the movement of said member, and means operable synchronously with said printing member moving means for shifting said electric force applying means from said one limit whereat said electric force applying means is effective to cause printing, to another limit of movement away from said printing member whereat said electric force applying means is ineffective to cause printing.

3. In a printer of the class described having a printing member, means including a shiftable conductive cylinder for producing a print effecting electric force at a printing Zone, means for moving said printing member relative to said cylinder in a direction substantially parallel to the axis of said cylinder, means for feeding a print receiving material between said member and said cylinder in a timed relation to the movement of said member, and means operable synchronously with said member moving means for normally maintaining said conductive cylinder in pressure engagement with said web and said printing member and for shifting said conductive cylinder away from, said printing member to thereby effect selective printing at the printing zone.

4. In a printer according to claim 3, means operable synchronously with said cylinder shifting means to control said print receiving material feeding means so that said material is advanced only when said cylinder is maintained in pressure engagement with said web and said printing member.

5. In an electrophotographic printer having a rotatable printing drum including an inner electrically conducting member and an outer dielectric surface portion adapted to support electrically charged powder images thereon for transfer to a web, a shiftable conductive cylinder for supporting the web between opposing surfaces of said cylinder and said drum, a source of electric energy, electric circuit means for connecting said conducting member and said cylinder to said source, means for continuously rotating said drum, whereby said web is fed in a path adjacent to a portion of the periphery of said drum and at a lineal speed correlated to the peripheral speed of said drum, a stationary web braking member, and means operable synchronously with said drum rotating means for shifting said cylinder from a printing position whereat said web engages said drum and said cylinder simultaneously, to a non-printing position whereat said web engages said braking member and said cylinder.

6. In an electrophotographic printer, the combination of apparatus at a printing zone for transferring electrically charged powder images to a web comprising an electrostatically charged printing drum adapted to support said charged powder images thereon, radially shiftable means for normally supporting said web in contact with said printing drum at one limit of movement of said shiftable means and out of contact with said drum at the other limit of movement thereof, said web supporting means including a rotatable cylinder having a surface layer of conducting resilient material for producing by electric current an electrostatic field of force at the region of contact of said web and said printing drum, said lines of force thereof acting in a direction to transfer said charged powder images from said drum to said web, means for rotating said printing drum whereby said web is normally moved at a lineal speed correlated to the peripheral speed of said drum, and means for shifting said web supporting means radially with respect to the axis of said drum from said one limit of movement to said other limit of movement so that the strength of said electrostatic field of force at the printing zone is changed respectively from one effective to cause printing onto said web moving with said drum and to one non-effective to cause printing onto said web now stationary and supported only by said cylinder.

7. The combination in an electric printer having a printing drum adapted to support successively arranged transferable information thereon, of drive means for rotating said drum at a speed correlated to the lineal speed of a paper strip, a shiftable conductive cylinder at a printing zone for supporting said paper strip between opposing surfaces of said cylinder and said drum, a power source, electrical circuit means connecting said power source to said cylinder and said drum, and a cam device operable synchronously with the drum drive means for shifting said cylinder relative said drum in one direction so as to produce an electric force at the printing zone to effect printing only whenever said transferable information is moved through the printing zone, and in another direction so as to stop movement of said paper strip only whenever said transferable information is outside the printing zone.

8. In a printer of the class described having a printing member, means including a conductive cylinder having a resistivity of at least ohms per cubic centimeter for producing an electric force at a printing zone, means for moving said printing member relative to said cylinder in a direction substantially parallel to the axis of said cylinder, means for feeding a print receiving material between opposing surfaces of said member and said cylinder in a timed relation to the surface movement of said member, and means operable synchronously with said member moving means for shifting said conductive cylinder towards and away from said printing member to thereby control printing at the printing zone.

9. The combination in an electric printer having a rotatable printing drum adapted to support successively arranged items of transferable information thereon, of drive means for rotating said printing drum at a speed correlated to the lineal speed of a paper strip, a conductive cylinder having a resistivity of at least 10.ohms per cubic centimeter positioned at a printing zone for supporting the paper strip between said cylinder and said drum, and

wards said drum so as to produce an electric force'at the printing zone to effect printing whenever each one of said items oftransferable information is moved through the printing zone and in a direction away from said drum so as to stop movement of said paper strip whenever said items of information are outside of said printing zone.

10. An electrophotographic printer transfer station comprising a photoconductive member adapted to support charged powder images thereon, an electrically conducting transfer roller, means for feeding a powder receiving web between opposing surfaces of said photoconductive member and said transfer roller, yielding means urging said photoconductive member and said transfer roller into engagement, and means associated with said web feeding means to cause said yielding means to be out of engagement with said member when the advancing movement of said Web is stopped.

11. Apparatus for transferring select ones of a plurality of electrically charged powder images to the surface of a sheet material, comprising a printing member adapted to support a plurality of said charged powder images arranged successively thereon, means including a conductive rotatable cylinder for applying an electric force at a printing zone, means for normally feeding said sheet material through said printing zone defined by the opposing surfaces of said printing member and said conductive cylinder so that said cylinder is rotated thereby, drive means for moving said printing member in a direction substantially parallel to the axis of said conductive cyl inder and in a timed relation to the feeding movement of said sheet material, means for controlling said electric field of force from one limit whereby said charged powder images may be transferred from said printing member to said sheet material, to another limit whereat said charged powder images may not be transferred from said printing member to said sheet material, and means effective concurrently and conjointly with said electric force applying means to render said sheet material feeding means disabled when the strength of the electric field of force is altered to said another limit.

12. In a machine of the class described, a printing member, means including .a conductive cylinder for applying an electric force at a printing zone, means for moving said printing member relative to said cylinder in a direction substantially parallel to the axis of said cylinder, means for feeding a print receiving material through said printing zone defined by opposing surfaces of said member and said cylinder in a timed relation to the movement of said member, means operable simultaneously with said member moving means for controlling said electric force applying means so that the electric force at said printing zone is effective for printing, and means including said cylinder for preventing feeding of said print receiving material when the electric force at said printing zone is ineifective for printing.

13. In a printing machine of the class described having a printing drum, a web feeding roller, and means for continuously rotating said drum and said roller; a transfer apparatus comprising a web idler roller; a conductive cylinder; a pivotally mounted member adapted to support said web idler roller and said conductive cylinder; a stationary web braking element; resilient means (a) for normally maintaining said web idler roller in a web feeding position relative said web feeding roller whereby said web is in pressure contact with both of said rollers so that said web is advanced through a printing zone defined by the opposing surfaces of said printing drum and said cylinder, and through a web braking zone defined by the opposing surfaces of said cylinder and said stationary braking element, and (b) for normally maintaining said cylinder in a print efiecting position relative said printing drum whereby said web is in pressure contact with said printing drum and said cylinder; and means for pivoting said pivotally mounted member so that said web idler roller is moved relative said web feeding roller and out of the web feeding position, and said cylinder is moved concurrently therewith relative said printing drum and out of the print effecting position to a web braking position relative said braking element whereby said web is in pressure contact With said cylinder and said stationary l0 braking element so that said Web is stopped.

UNITED STATES PATENTS Schwarzschild Nov. 29, 1898 Vannote June 19, 1928 Carlson Sept. 12, 1944 Walkup et a1. Nov. 6, 1951 Carlson Jan. 6, 1953 Pethick Apr. 7, 1953 Butterfield et a1. June 16, 1953