US3612677A

US3612677A - Electrostatic transfer apparatus

Info

Publication number: US3612677A
Application number: US830381A
Authority: US
Inventors: Michael J Langdon; Alan F Mccarroll
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1969-06-04
Filing date: 1969-06-04
Publication date: 1971-10-12
Anticipated expiration: 1988-10-12
Also published as: DE2027550A1; CA923961A; GB1296742A

Abstract

An electrically biased transfer drum for use as a transfer mechanism in an electrostatic reproduction machine and having gripping devices for maintaining a sheet of paper on the drum during one or multiple transfer operations and other means for effecting stripout of the sheet.

Description

United States Patent Michael J. Langdon Webster;

Alan F. McCarroll, Rochester, both of N.Y. 830,381

June 4, 1969 Oct. 12, 1971 Xerox Corporation Rochester, N.Y.

[72] Inventors [21 Appl. No. [22] Filed [45] Patented [73] Assignee [54] ELECTROSTATIC TRANSFER APPARATUS 5 Claims, 7 Drawing Figs.

[52] US. Cl. 355/4, 101/409, 101/177, 101/246 [51] Int. Cl G03g 15/16 [50] Field of Search... 355/4- [56] References Cited UNITED STATES PATENTS 2,118,238 5/1938 Smith 101/177 2,865,289 12/1958 Fowlie et a1. 101/409 3,520,603 7/1970 Gnage 355/4 Primary ExaminerSamuel S. Matthews Assistant ExaminerE. M. Bero Attorneys-Norman E. Schrader, James J. Ralabate and Bernard A. Chiama ABSTRACT: An electrically biased transfer drum for use as a transfer mechanism in an electrostatic reproduction machine and having gripping devices for maintaining a sheet of paper on the drum during one or multiple transfer operations and other means for efiecting stripout of the sheet.

PATENTEDum 12 Ian 6 1 2 SHEET 10F 4 INVENTOR. MICHAEL J. LANGDON ALAN Ff MC CARROLL ATTORNEY PATENTEDUET 12 Ian SHEET 30F 4 1 ELECTROSTATIC TRANSFER APPARATUS This invention relates to an electrostatic printing machine and in particular to a transfer mechanism for use in supporting a sheet of transfer material during the transfer of developed images in multiple-image-recirculating programming.

With the advent of electrostatic color reproduction involving the use of processing components which will produce a series of electrostatic images of an original wherein each image is representative of a particular color in the original and there is the need to superimpose corresponding series of developed images upon a sheet of transfer material, it is necessary that the images being superimposed be accomplished with extreme accuracy of registration. In addition, for high-speed automatic machine operation, and for flexibility in the event that one or more images of a series is possible, it is necessary that the transfer mechanism be adapted for programming for single transfer as well as multiple superimposed transfers.

Therefore, it is a principal object of the present invention to incorporate a transfer mechanism in an electrostatic printing machine which will render the machine capable of effecting one or more transfers of developed images upon a sheet of transfer material.

Another object of the invention is to utilize registration devices and sheet-edge-gripping devices in a transfer mechanism for accurately positioning the sheet to insure that successiveimages being transferred will be registered with a previously transferred image.

Another object of the invention is to control and effect the registration, supporting and stripout of a sheet of transfer material in accordance with desired requirements.

The foregoing objects are acquired by a transfer drum serving as a biased electrode which is arranged to support a sheet of paper, and to move the same in recirculating fashion into contact with a photoconductive surface bearing a developed image. Registration devices are mounted with the drum along with control mechanisms for controlling the actuation of the device in timed sequence relative to developed images moving into contact with the drum.

For a better understanding of the invention as well as other objects and further features thereof, reference is had to the following detailed description of the invention to be read in conjunction with the accompanying drawings wherein:

FIG. I is a schematic view of a reproduction machine showing various electrostatic processing components;

FIG. 2 is an enlarged view with parts broken away of the transfer drum utilized in the present invention in one condition of operation;

FIG. 3 is a longitudinal cross-sectional view of the transfer drum and supporting structure;

FIG. 4'is a cross-sectional view of the drum showing some parts in another condition of operation;

FIG. 5 is a cross-sectional view of the drum showing registration of a sheet of transfer material;

FIG. 6 is a cross-sectional view of the drum showing the sheet-gripping mechanism in a gripping condition; and

FIG. 7 is a cross section of a detail of the drum just prior to stripout of the sheet.

For a general understanding of the illustrated copier/reproduction machine, in which the invention may be incorporated, reference is had to FIG. 1 inwhich the various components for the machine are schematically illustrated. As in all electrostatic systems as well as a xerographic machine of the type illustrated, a light image of a document to be reproduced is projected onto the sensitized surface of a xerographic plate to form an electrostatic latent image thereon. Thereafter, the latent image is developed to form a xerographic powder image, corresponding to the latent image on the plate surface. The powder image is then electrostatically transferred to a support surface to which it may be fixed by a fusing device whereby the powder image is caused permanently to adhere to the support surface.

In the illustrated machine, an original D to be copied is placed upon a transparent support platen fixedly arranged relative to an illumination lamp assembly 10 positioned at the upper end of the machine as viewed in FIG. 1. While upon the platen, a programming system for the machine introduces a lamp control circuit to cause successive energization of the lamps in the lamp assembly 10 for impinging light rays upon the original thereby producing image rays which when acted upon by separation filters correspond to the color informational areas on the original. The image rays are projected by means of an optical lens system II for exposing the photosensitive surface of a xerographic plate at the exposure section A, the plate being in the form of a flexible photoconductive belt 12 arranged on a belt assembly generally indicated by the reverence numeral 13.

The photoconductive belt assembly 13 may be mounted upon the frame of the machine and is adapted. to drive the selenium belt 12 at a constant rate in the direction of the arrow as shown in FIG. 1. During this movement of the belt, the light-imaging rays of an original are successively flashed full frame upon the surface of the belt. The belt structure utilized comprises a layer of photoconductive insulating material such as selenium on a conductive backing that is sensitized prior to exposure by means of a suitable charging corona generator device 14.

The flash exposure of the belt surface to the light image discharges the photoconductive layer in the areas struck by light, whereby there remains on the belt an electrostatic latent image for each exposure, each being in image configuration corresponding to the light image projected from the original D on the supporting platen through the corresponding sepai'ation filters. As the belt surface continues its movement, the latent electrostatic images pass through a developing station B at which there is positioned a developer assembly generally indicated by the reference numeral 15 and where the belt is maintained in a fiat condition. The developer assembly '15 comprises a plurality of developing devices l6, l7, l8 and 19 each of which contains a different color-developing material to provide individual development of the electrostatic images. The successively developed electrostatic images are transported by the belt to a transfer station C whereat a sheet of copy paper is moved at a speed in synchronism with the moving belt in order to accomplish transfer of the developed images. There is provided at this station a sheet transport mechanism inthe form of a transfer drum 20 adapted to support a sheet of paper and to carry the same into, image transfer relationship with the belt 12 once for each image transfer operation. A sheet of paper S from a paper-handling mechanism, generally indicated by the reference numeral 21 is transported into position upon the drum 20 where it is supported during the image transfer function. The transfer of the developed image from the selenium belt surface to sheet material is effected by means of an electrical bias of the op posite polarity as the triboelectric charge on the developing particles utilized in image development being applied to the transfer drum 20 at the point of contact between the sheet and selenium belt as the sheet passes the transfer station C. a

After the sheet is stripped from the transfer drum 20, it is conveyed by conveyor 22 into a fuser assembly generally indicated by the reference numeral 23 wherein the developed and transferred powder image on the sheet material is permanently affixed thereto. After fusing, the finished copy is white-light-exposed images is moved out of the development.

station B and carried to the transfer station C. In this station, the belt 12 is carried around a roller 70 which forms one of the three rollers of the belt assembly 13. Transfer occurs at the line on the belt 12 resulting when the transfer drum 20, which serves as a biased electrode, is in contactwith the adjacent surface thereof as it is moved about the roller 70.

The transfer drum is normally held away from the selenium belt 12 by means of a spring retaining force and upon a control signal from the programming system for the machine, will energize a solenoid for overcoming the spring force and to force the drum against the belt. In this manner, the operation of the transfer drum is fail-safe; that is, in the event of power failure or machine malfunctions, the drum will be normally moved into position of safety relative to the more delicate structure of the selenium belt.

The drum 20 comprises a metallic cylinder mounted on two independently swinging arms and having an electrically conductive rubber blanket fixed therearound and connected to a suitable source of electrical current for image transfer purposes. As shown in FIGS. 2 and 3, a rubber-coating blanket 71 is applied to a metallic cylinder 72 and is preferably made of rubber having a resiliency such that with light pressure being applied thereto while in contact with the belt 12, there will be a very slight flattening of or indentation into the rubber for enhancing image transfer.

One end of the metal cylinder 72 is closed by an end cap 73 having a drive shaft 74 mounted centrally thereof. The other end of the cylinder 72 is also closed by a cap 75 which includes a centrally positioned hollow shaft 76. Means are pro vided for supporting the drum 20 by way of its supporting

shafts

74, 76, which will pennit movement of the drum into its two controlling positions. For this goal, the shaft 74 is suitably joumaled on one end of an arm 77 which is rotatably supported at its other end on a shaft 78 secured to the frame 80 of the machine with its axis parallel to the axis of the drum. Similarly, the shaft 76 extends through and is joumaled on one end of an arm 81 which is similar to the arm 77 and which is also joumaled upon the shaft 78. The machine frame 80 is provided with vertically extending plates 82 for supporting a shaft 83 in a position parallel to the axis of the drum and the shaft 78 and to one side of one edge of each of the arms 77, 81.

At each end of the shaft 83 there is formed a cam 85, only one of which is shown in the drawings, and at one end of the shaft adjacent the cam there is also provided an integral lever 86. Both earns 85 are adapted to engage the adjacent edges 87 of the arms 77, 81 for forcing these arms to rotate about their common shaft 78 during slight rotation of the shaft 83. With the cams 85 having slight camming surfaces, this rocking movement of the arms is slight, being sufiicient to disengage contact between he roller 20 and the belt 12. A coil spring 88 is held in tension between one end of the lever 86 and the machine frame 80 for normally tending to rotate the earns 85 against the arms in a direction to force the drum 20 away from the belt 12 (clockwise rotation of the arm 77, 81 in FIG. 2).

in order to overcome the spring force of spring 88, and to enable the drum 20 to contact the belt 12 for the image transfer function, there is provided a solenoid SOL-2 for rotating the shaft 83 in a direction opposite that produced by the spring 88. The solenoid SOL-2 is secured to the machine frame 80 and includes a plunger 90 pivotally connected to a link arm 91 secured to the shaft 83. As shown in FIG. 4, the link arm 91 is on the other side of the shaft 83 from the lever 86 so that upon energization of solenoid SOL-2, which results in the pull-in drive motion of the plunger 90, will overcome the spring force and cause rotation of the shaft 83 in a direction opposed to the spring action. This energization in effect will cause the arms 81, 77 to rotate in a counterclockwise direction and allow the drum 20 to engage the belt 12.

The transfer drum 20, in serving as an image transfer arrangement, is capable of registering and supporting a sheet of transfer material for either one transfer cycle or for recirculating the sheet through a plurality of transfer cycles. As previously described, the original D is exposed three times in order to produce a series of three latent electrostatic images each of which is developed in sequence and made ready for transfer.

In order to make a single color reproduction of the original, the three developed images are transferred individually and to the same sheet of transfer material.

In order to effect precise registration and positioning of sheets of transfer material upon the drum 20, there is provided a plurality of registration elements 95 mounted within and for movement radially of the drum. To permit registration, the elements extend through openings 96 formed in the periphery of the drum surface, the openings being in a line parallel to the axis of the drum. Each of the elements 95 has a flat rectangular configuration and is fonned with a outward-extending projection 97 which is movable radially with the elements from a position within the periphery surface of the drum to two positions slightly outwardly of the periphery of the drum. When in use, the leading edge of a sheet S engages the elements 95 immediately outwardly of the projections 97 upon which the edge will be held during recirculation of the sheet (see FIG. 5).

Radial movement of the elements 95 is provided by means of a shaft 98 mounted for rotation within the drum working in conjunction with drive rods 100 secured to the shaft and which are adapted to be slidably held within apertures 101 formed at the innermost ends of the element. The shaft 98 is supported and joumaled upon the inner surface of the cylinder 72 by means of bearing blocks 102, and upon rotation of the shaft 98 the rods 100 will be swung therewith for causing the elements 95 to move outwardly or inwardly as the case may be, relative to the axis of the drum 20. In operation, the elements 95 are adapted to assume three positions: the first, when no sheet is being transported, the elements occupy their innermost position, the second in a slightly outward position so that the projections 97 are positioned slightly away from the peripheral surface of the drum when a sheet has been registered as shown in FIG. 5 and third, with the projections 97 at a slightly greater distance from the periphery so as to move the leading edge of the sheet away from the drum periphery just prior to stripout of the sheet as shown in FIG. 6.

Operating in close conjunction with the registration elements 95 are a plurality of gripper fingers 105 which are secured to the shaft 98 by means of clamps 106 and which extend through openings 107 formed in the periphery of the drum 20 in alignment with the openings 96 for the elements 95. As shown in FIG. 6, when viewing the drum 20 axially, the fingers 105 and the elements 95 are in alignment parallel to the axis of the drum. A spring 108 is held in tension between an anchor fixed to the interior of the cylinder 72 and a link 109 secured to the shaft 98 for normally biasing the elements 95 in their retracted or innermost position and the fingers 105 in their paper-clamping position.

One end of the shaft 98 has a'crank arm 110 secured thereto adjacent to and inwardly of the end cap 75. A connecting rod 111 secured to one end of the am 110 projects through an opening 112 in the end cap 75, and is connected externally of the drum to a linkage system which will control the operation of the registration elements 95 and the gripper fingers 105.

The linkage system comprises a link member 113 pivotally mounted at one end by a pivot pin 114 to the upper end of the arm 81; a second link member 115 pivotally connected at one end to the free end of the link member 113; and a third link member 116 pivotally connected at one end to the free end of the link member 115. The link member 116 is secured intermediate its ends to a shaft 117 of a rotary solenoid SOL3 mounted on the arm 81. When the solenoid SOL-3 is not energized, a spring (not shown) built into the solenoid will normally maintain the linkage in the position shown in FIG. 3. When the solenoid is energized, clockwise rotation is imparted to the link 116 thereby forcing the link member 115 downwardly and to the left causing clockwise rotation of the link 113 about the pivot pin 114. This position of the linkage system is shown at FIG. 2, with the solenoid energized. In effeet, the pivot pin 114 and the solenoid shaft 117 supports the linkage system.

A cam lobe in the form of a detent 120 is formed on the inner edge of the link 113, and similarly the inner edge of the link 1 16 is formed with a cam lobe in the form of a detent 121. Actually, the inner edges of the

links

113, 116 are camming surfaces as will be presently described, and the detent curves mainly control the camming effect of these edges. Each of the detents 120, 121 is adapted to cooperate for specific operation with a cam follower 122 in the form of a bearing race secured to the exterior end of the rod 111. During rotation of the transfer drum 20, the connecting rod 111 revolves about the axis of the drum since the shaft 98 and the opening 1 12 for the rod 111 move in a revolving motion about the axis. As the rod 111 revolves, it carries the cam follower 122 therewith in a circulating path having a predetermined radius with its center coincident with the axis of the drum as illustrated by the letter P in FIGS. 2 and 4.

In the condition of operation for effecting either single or multiple image transfer with the solenoid SOL-3 energized to move the linkage to its position shown in FIG. 2, the cam follower 122 (see dotted position) in its revolution along the path P will engage the inner edge of the link 116 at a point to the left of the shaft 117 which is in the path of movement of the follower for forcing the rod 1 11 inwardly. The follower makes contact with the adjacent end of the detent 121 which slows down radial movement of the rod 111 as it slides along the curve of the detent. Without this detent upon striking the edge of the link 116, the rod 111 would be propelled inwardly at too great a speed for the structural parts of the drum. The resultant movement of the rod 111 toward the axis of the drum is in opposition to the force provided by the spring 108 upon the shaft 98. The opening 112 is of a size sufiicient to permit this limited movement of the rod 111 relative thereto. This slight inward movement of the rod 111 will produce slight rotation of the shaft 98 and consequently will produce slight onward radial movement of the registration elements 95 at the same time that the leading edge of a sheet of paper reaches these elements for registration thereby (see FIG. 5). At the same time, the gripper fingers 105 are rotated slightly out of the way to pen'nit sheet registration. Immediately after registration, the solenoid SOL-3 is deenergized for multiple image transfer to allow the linkage to assume the position shown in FIG. 4 by virtue of the solenoid spring, and to allow the spring 108 to rotate the shaft 98 back to its original position. This movement produces outward movement of the rod 111 as it continues its revolving motion and out of the inner edge of the link I 16. With the shaft 98 moved to its original position, it allows the registration elements 95 to assume their initial inactive condition and the fingers 105 to grip the leading edge of the sheet material thereby permitting transport and support of the sheet around the drum 20 (see FIG. 6 for this completed action). As the drum 20 rotates, it carries the leading edge of the sheet and the remaining portion thereof into the transfer station C to effect developed image transfer thereon. As the cam follower 122 continues its revolving movement and with the solenoid SOL-3 energized for single transfer, the follower engages the inner edge of the link 113 at the leading end of the detent 120 and the rod 111 is driven inwardly again in a softened action as provided by the detent. The position of the link 113 is such that this inward movement of the rod 111 is greater than its inward movement provided by the detent 121. This action again rotates the shaft 98 against the spring force of the spring 108 except that the rotation is slightly larger than the initial rotation when the leading edge of a sheet was being registered. This additional rotation causes movement of the gripper fingers 105 out of contact with the leading edge of the sheet and additional clearance therefrom, and permits the projections 97 of the registration elements 95 to move the leading edge away from the periphery of the drum. A slight additional rotation of the drum will transport the leading edge of a sheet over the leading points of fixed stripout fingers 130 (see FIG. 7) and thereby remove the sheet from the drum as continued rotation thereof is made. As shown in FIG. 7, when the projections 97 have been moved to their outermost .position for the stripout mode of operation to separate the leading edge of thesheet S from the drum, the leading points of the stripout fingers 130 are adapted to enter slightly below the surface of tee projections upon which the leading edge of the sheet S is placed.

1 In operation just prior to a sheet being fed to the drum 20, the linkage system comprising the

links

113, and 116 are arranged as shown in FIG. 4 wherein the detents 1 20 and 121 are positioned so that the cam follower 122 will not coact with either during a complete revolution. In the event that only one transfer is to be made per copy, say when black and white copies are being made, upon a sheet S being fed by the feeder 21, the solenoid SOL-3 is energized to bring the inner edge of the link 116 into the path of the follower 122. After the leading edge of the sheet is registered and gripped, the solenoid remains energized so that the follower may engage the detent in order to produce sheet stripout. In the event a threecolor series of images have been produced and three transfers on the same sheet are to be accomplished, after the solenoid is energized to register and grip a sheet of support material, it is quickly deenergized, before the follower 122 can reach the link 113. In this event, the sheet cannot be stripped off the drum 20 as the camming surface of the detent 120 is held away from the path of movement of the follower and the sheet will remain on the drum until three image transfers have been completed. After the last transfer and when the follower 122 has passed the detent 121, the solenoid SOL-3 is again energized to position the linkage as shown in FIG. 2 in order to permit the follower to engage the inner edge of the link 113. As previously described, upon this occurrence, the sheet S will be stripped off the transfer drum as it continues its rotation. In summary, when the solenoid SOL-3 is energized. both camming detents 120, 121 are actuated into the path of movement P of the follower 122. When deenergized both detents are actuated out of the path of the follower. For single image transfer copies, after registration, the solenoid remains energized. For multiple image transfer copies, after registration, the solenoid is deenergized and remains so until stripout.

For automatic operation, another sheet S of paper fed toward the drum by the paper sheet feed mechanism 21 will be registered and gripped by the

elements

95 and 105 as these elements continue around to the paper register position of the drum 20. The paper feed mechanism working in automatic conjunction with the transfer drum registration and gripping mechanisms feed individual sheets of paper into pinch rollers (see FIG. 1) which are arranged to feed the leading edge of the sheet at a greater speed than the circumferential speed of the drum 20 in order to permit the leading edge to contact the registration elements 95.

While the invention has been described with reference to the structure disclosed herein, it is not confined to the details set forth; but is intended to cover such modifications, or changes as may come within the scope of the following claims.

What is claimed is:

l. A transfer apparatus for use in a multicolor printing machine having means for producing a series of one or a plurality of transferable images of an original to be copied onto a printing member,

support means for supporting a sheet of transfer material and moving the same in a recirculating path into contact with the member, said support means including means for holding the sheet thereon and releasing the same to permit removal therefrom, and

means associated with the support means for controlling the releasing in accordance with a predetermined number of images of the original being produced.

2. A transfer apparatus for use in a multicolor printing machine having means for producing a series of one or a plurality of transferable images of an original to be copied onto a printing member,

support means for supporting a sheet of transfer material and'moving the. same in a recirculating path into contact with the member, said support means including means for gripping the transfer material for holding the same thereon and means for releasing the sheet to permit removal therefrom, and

means associated with the support means for controlling activation of the releasing means in accordance with a predetermined number of images of the original being produced. 3. A transfer apparatus for use in a multicolor printing machine having means for producing a series of one or a plurality of transferable images of an original to be copied onto a printing member,

support means for supporting a sheet of transfer material and moving the same in a recirculating path into contact with the member, said support means including means for registering and gripping the transfer material for holding the same thereon in one mode of operation and means for releasing the sheet to pen-nit removal therefrom in another mode of operation, and 7 means associated with the support means for placing said registering and gripping means in said one mode of operation in accordance with the time sequence of production of the first transferable image of the original.

4. A transfer apparatus for use in a multicolor printing machine having means for producing a series of one or a plurality of transferable images of an original to be copied onto a printing member,

support means for supporting a sheet of transfer material and moving the same in a recirculating path into contact with the member, said support means including means for registering and gripping the transfer material for holding the same thereon in one mode of operation and means for releasing the sheet to permit removal therefrom in another mode of operation, and

means associated with the support means for placing said registering and gripping means in said one mode of operation in accordance with the time sequence of production of the first transferable image of the original and to place said release means in said other mode of operation in accordance with a predetermined number of images of the original being produced.

5. A transfer apparatus operable in a multicolor printing machine having means for producing a series of one of a plurality of transferable images of an original to be copied onto a printing member,

a rotatable drum for supporting a sheet of transfer material and moving the same in a recirculating path into contact with the member, said drum including means for registering and holding the transfer material thereon,

means for normally maintaining said drum out of contact with the printing means,

force-generating means associated with said last-named means for overcoming its nonnal effect on the drum when said force means is activated, and

means associated with the force-generating means for ac-

Claims

1. A transfer apparatus for use in a multicolor printing machine having means for producing a series of one or a plurality of transferable images of an original to be copied onto a printing member, support means for supporting a sheet of transfer material and moving the same in a recirculating path into contact with the member, said support means including means for holding the sheet thereon and releasing the same to permit removal therefrom, and means associated with the support means for controlling the releasing in accordance with a predetermined number of images of the original being produced.

2. A transfer apparatus for use in a multicolor printing machine having means for producing a series of one or a plurality of transferable images of an original to be copied onto a printing member, support means for supporting a sheet of transfer material and moving the same in a recirculating path into contact with the member, said support means including means for gripping the transfer material for holding the same thereon and means for releasing the sheet to permit removal therefrom, and means associated with the support means for controlling activation of the releasing means in accordance with a predetermined number of images of the original being produced.

3. A transfer apparatus for use in a multicolor printing machine having means for producing a series of one or a plurality of transferable images of an original to be copied onto a printing member, support means for supporting a sheet of transfer material and moving the same in a recirculating path into contact with the member, said support means including means for registering and gripping the transfer material for holding the same thereon in one mode of operation and means for releasing the sheet to permit removal therefrom in another mode of operation, and means associated with the support means for placing said registering and gripping means in said one mode of operation in accordance with the time sequence of production of the first transferable image of the original.

4. A transfer apparatus for use in a multicolor printing machine having means for producing a series of one or a plurality of transferable images of an original to be copied onto a printing member, support means for supporting a sheet of transfer material and moving the same in a recirculating path into contact with the member, said support means including means for registering and gripping the transfer material for holding tHe same thereon in one mode of operation and means for releasing the sheet to permit removal therefrom in another mode of operation, and means associated with the support means for placing said registering and gripping means in said one mode of operation in accordance with the time sequence of production of the first transferable image of the original and to place said release means in said other mode of operation in accordance with a predetermined number of images of the original being produced.

5. A transfer apparatus operable in a multicolor printing machine having means for producing a series of one of a plurality of transferable images of an original to be copied onto a printing member, a rotatable drum for supporting a sheet of transfer material and moving the same in a recirculating path into contact with the member, said drum including means for registering and holding the transfer material thereon, means for normally maintaining said drum out of contact with the printing means, force-generating means associated with said last-named means for overcoming its normal effect on the drum when said force means is activated, and means associated with the force-generating means for activating the same when the latter is in condition for operation in the machine.