US2211765A

US2211765A - Stripping mechanism for printing presses

Info

Publication number: US2211765A
Application number: US227857A
Authority: US
Inventors: Davidson William Ward
Original assignee: DAVIDSON Manufacturing CORP
Current assignee: DAVIDSON Manufacturing CORP
Priority date: 1938-08-31
Filing date: 1938-08-31
Publication date: 1940-08-20
Anticipated expiration: 1957-08-20

Description

20, 1940- w. w. DAVIDSON STRIPPING' MECHANISM FOR PRINTING PRESSES 4 Sheets-Sheet 1 Filed Aug. 31, 1938 Aug. 20, 1940. w. w. DAVIDSON STRIPPING MECHANISM FOR PRINTING PRESSES Filed Aug. 31, 1938 4 Sheets-Sheet 2 20, 1940- w. w. DAVIDSON STRIPPING MECHANISM FOR PRINTING PRESSES,

Filed Aug. 31, 1938 4 Sheets-Sheet 5 flan/$07 K MmWaxxifiawdsom g 1940. w. w. DAVIDSON STRIPPING MECHANISM FOR PRINTING PRESSES Filed Aug. 31, 1938 4 Sheets-Sheet 4 WFQ.

WW NW Wilda/77, Vafidficuwdson Patented Aug. 20, 1940 PATENT OFFICE STRIPPING MECHANISM FOR PRINTING PRESSES William Ward Davidson, Evanston, 111., assignor to Davidson Manufacturing Corporation, a corporation of Illinois Application August 31,

19 Claims.-

With high speed printing, such as that which may be provided with a continuously rotating printing drum, it is very diflicult to obtain the accurate registry of the sheets on the printing drum which is vital for some types of printing and always highly desirable.

The most successful commercial feeding devices heretofore have been of the type in which the sheets were fed against a stationary gaugestop and then advanced against a final gauge on one of the cooperating printing rolls at which time the sheets were seized by gripping fingers also carried by one of the printing rolls of the press. Such gauge and gripping fingers on the printing rolls have been considered necessary because of the unreliability of the registry which could be obtained in practice with the external feeding mechanism if the final gauge and grip fingers were not used.

However, the use of gauge and grip fingers has been objectionable for several reasons. For example, they have necessitated the use of a platen roll having the same diameter as the impression roll in order that the grip fingers register with the opening provided in the other roll. Furthermore, they are relatively complicated mechanical structures which add substantially to the cost of the printing machine.

According to the illustrated form of the invention the feeding means feeds the sheets so accurately and uniformly that their registration with the printing rolls will be satisfactory without the provision of gripping fingers on either of the printing rolls, thus enabling the gripping fingers to be omitted. As a result, the platen roll can be of any suitable diameter and have an unbroken periphery with obvious advantages.

However, in addition to their registration function the gripping fingers have also served to pull the leading ends of the sheets away from the printing drum to facilitate stripping the sheets from this drum, to which they tend to stick. This tendency is most pronounced when the ink coverage at the leading end of the sheet is relatively heavy.

An object of the invention is to provide a simple type of stripping mechanism which is capable of stripping sheets from the printing drum of a printing press without the aid of grip fingers or other mechanism mounted on and rotating with either of the printing rolls. The invention is particularly useful in offset printing 1938, Serial No. 227,857

ping is required. Since its chief use is on printing presses, it will be described only with reference to such use. The term printing presses should be understood as including duplicators known more commonly under other names.

An additional object of the invention is to provide a printing press in which sheets are accurately registered and reliably stripped without the use of grip fingers of any kind.

Additional objects and advantages of the invention will be apparent from the following description and from the drawings, in which:

Fig. 1 is a perspective and somewhat diagrammatic view of the printing press chosen for illustration, portions thereof being broken away for the sake of clarity.

Fig. 2 is a fragmentary longitudinal vertical section showing particularly the relationship of the feeding and stripping mechanism to the printing rolls.

Fig. 3 is a fragmentary perspective view of one form of the stripping fingers which may be used in the structure of Figs. 1 and 2.

Fig. 4 is a similar view of a modified form of stripping fingers.

Fig. 5 is a horizontal sectional view taken approximately on the line 5-5 of Fig. 2.

Figs. 6, 7 and 8 are fragmentary and somewhat diagrammatic views illustrating the operation of the stripping mechanism. Fig. 6 is a sectional view taken on the line 6-6 of Fig. 5 but partly broken away and showing the blanket roll and associated cam angularly foreshortened. Figs. 7 and 8 are sectional views taken on line 11 of Fig. 5.

Preferred embodiments of the invention have been shown in the drawings and will hereinafter be described all as required by section 4888 of the Revised Statutes but the appended claims are not to be limited by the disclosure except as required by the prior art.

In Fig. 1 a printing press is indicated diagrammatically by the reference character l0 and it comprises a printing drum II (also called the transfer cylinder) and a platen l2. The printing drum H has been illustrated as the blanket roll of an offset printing press. The drum II and the platen l2 may jointly be called the printing couple or the printing press, though the latter term may also be used for the entire mechanism. Sheets of paper are fed to the printing couple at timed intervals by preliminary feeding mechanism generally designated l3 and including feed board it, separator roll generally designated [5, pull-out roll generally designated I6, and a conveyor table generally designated I1. The delivery end of the conveyor table has associated with it a sheet-registering device generally designated I8, which receives the sheets from the table 11 and delivers them with extreme accuracy into the bite of the printing rolls H and I2.

The sheet-registering device I8 operates in synchronism with the press II), and the speed at which the press can operate is partially determined by the ability of the feeding mechanism to deliver sheets to the registering mechanism I8 in sufficiently correct timing relationship with the operation of the registering mechanism [8 that the latter is given an opportunity to properly perform its function.

The sheet-registering mechanism functions by 7 having stop fingers l9, associated with the lower feed roll 20, moved to an upright position for a given portion of a cycle of press operation to receive and end-register a sheet delivered to them by the conveyor l1. As soon as this registry has been accomplished the upper feed roll 2| of the registering mechanism l8 descends to make contact with the lower roll 20, and after the bite has been made the lower roll is automatically rotated to deliver the sheets into the bite of the printing drum II and platen l2. Since this action takes place for each revolution of the printing drum I I, it can readily be understood Why it is necessary to have the feeder l3 deliver the sheets to the registering mechanism IS in reasonably correct timed relationship.

Preliminary feed mechanism The feed table i4 is suitalbly mounted on the feeder frame 22, and it is provided with laterally adjustable magazine side walls 23 and 24 so that the pile 25 of fanned-out sheets may be centrally positioned with respect to the feeder mechanism.

The separator rolls l5 comprise a feed roll 26, and a retard roll 21, the former being intermittently driven by a pitman 28, or equivalent means, from the press It), with an overrunning clutch 29 being interposed in the drive so that the pull-out rolls l6 may draw the sheet being fed by the separator rolls [5 through these rolls, even though the intermittent drive through the pitman has ceased. The roll 26 is mounted on a shaft 30, to rotate about its own axis, and a clutch 3i, actuated by a rod 32, operating through a clutch arm 33, is provided to disengage the feed roll 26 from the drive through the pitman 28.

The retard roll 21 is rigidly mounted on a shaft 34, provided with eccentric trunnion bearings journaled in the side frames 22 of the feeder. The bearings for the trunnions 35 are so located with respect to the shaft 39 carrying the feed roll 26 that when the retard roll 21 is in substantial tangential contact with the feed roll 26 the axis of the trunnions 35 is so positioned that rotation of the retard roll 21 in the direction in which the sheets are advancing causes the roll to move forward slightly and away from the feed roll 26.

The shaft 34 is constantly urged in the opposite direction (that is, in a clockwise direction when viewing the separator rolls as in Fig. 1) by a spring 31, which acts upon the end of an arm 38 rigidly attached to the shaft 34 and a flange 39 integral with the side frame 22. Rotation of the shaft, however, in the direction in which it is urged by the spring 31 is limited by an adjustable stop 40, against which the arm 38 may come to rest, the stop consisting of a threaded rod passing through the flange 39 on the frame 22, and a similar flange 42, also integral with the frame 22, adjusting nuts 43 being provided to fix the position of the threaded rod with respect to the flanges 39 and 42.

The stop is preferably adjusted so that the gap between the feed roll 26 and retard roll 21 is slightly less than the thickness of a single sheet of the paper or material being fed to the press. The feed roll 26, being the driven member, makes contact with the top sheet and tries to drive it through the gap, and normally it accomplishes this function without drawing with it the lower sheet. If, however, the lower sheet for some reason sticks to the top sheet, it will enter the bite of the separator rolls, and the retard roll 31, being free to rotate on its eccentric axis, will move slightly to the left and its center will move a corresponding distance from the center of the feed roll 26. As soon as this movement takes place, the arm 38 is moved away from the stop ll], and the spring 31 continuously urges it back to its normal position, with the result that roll 21 has a clockwise force applied to it while the feed roll 26 continues its rotation to advance the upper sheet.

It has been found in practice that this ability of the retard roll 21 to yield whenever more than one sheet enters the bite of the separator rolls, and then exert a rotative force which opposes the movement of the second sheet, effectively pre vents more than one sheet from being fed to the pull-cut rolls H3 at a time, and this is so even when the thickness of the paper stock in the pile 25 varies within wide limits. In this respect the performance of the feeder is exceptional, because heretofore it has always been necessary to make accurate adjustments for different stocks of paper.

Although the sheet is restrained from going along with the upper sheet as the latter moves toward the pull-out rolls l6, it may, and usually does, remain in the bite of the separator rolls after the upper sheet has been pulled from those rolls, and it is therefore important that the roll 26 be stopped immediately after the sheet passing to the pull-out rolls has left the separator rolls. This is accomplished in the present invention by continuously urging the shaft 30 axially in a direction to cause the face of the hub 46 of the clutch 29 to frictionally engage a friction face of bearing 4']. The axial thrust of the shaft 30 may be conveniently accomplished by means of a spring 48, telescoped over the shaft 30 and hearing at one end against the side frame 22 and at the other end against a collar 49 which may be adjustablypositioned on the shaft 39 to obtain the desired thrust. Experience has shown that this friction brake is capable of stopping the feed roll 26 substantially instantaneously when the sheet being moved by the pull-out rolls l6 leaves the bite of the separator rolls, positive drive by pitman 28 having ceased previously.

Preferably the feed roll 26 is made of relatively soft rubber, pure Gum Anemone stock having a durometer reading of 40 having been found satisfactory. The retard roll 21 is preferably made of somewhat harder rubber, Grey Commercial Compound Rubber, 78 durometer, having been found satisfactory.

It is obvious that the retard roll 21 may take various forms, and may be mounted in numerother shape, as long as the roll (used in its broadest sense) retains its characteristic function of retarding the extra sheet with which it is,

in contact.

The conveyor I1 comprises parallel belt rolls and 5I, fixed in the side frames 22 at a slight angle with respect to the transverse axis of the feeder, so that the conveyor belts 52, which are mounted on the rolls 5'0 and 5|, are biased toward the side guide 53. The guide 53 is adjustable laterally with respect to the conveyor, as are also the belts 52, so that the sheets may be fed to the printing drum I I in any desired lateral registry.

The pull-out rolls IE comprise upper and

lower rolls

55 and 55, the latter preferably being formed as a rubber facing of suitable hardness in a shallow groove in roll 5| which is preferably wooden. The upper roll 55 is preferably a steel roller, and it is carried by a jaw 58, fixed to a rod 59 journaled in the side frames 22. The rod 55 is provided at each end with an arm Bil, the end of which is connected to a stud BI on the side frame by a spring 52. The jaw 58 may be fixed to the rod 59 at any desired angular position of the rod 59,'by means of a setscrew 55, so that the pressure of the roll 55 on the roll 55 may be conveniently adjusted.

The pressure of the upper roll 55 on the lower roll 55 should be sufficient so that the pull-out rolls I6, which are continuously driven by a belt through the conveyor belts 52, will draw the sheets of material delivered to them through the separator rolls I5, against the action of the friction brake at the contacting surfaces of members 415 and ll, associated with the shaft 30. This relationship is necessary so that when the trailing edge of a sheet has left the separator rolls I5 the shaft 30 will immediately stop rotating.

It is important to note that the feeder mechanism is extremely simple and inexpensive to manufacture as compared with most friction feeders, and one reason for this economy in materials and cost of manufacture is that the sheets are delivered to the press I0 along the center line of the feed mechanism. Heretofore it has been the common practice to guide the sheets along one side or the other of the conveyor, and to have the separator rolls and pull-out rolls adjustable laterally to accommodate different sizes of paper stock. In the illustrated structure the magazine sides 23 and 24 are adjustable so as to initially position the pile 25 in the center of the feed board I l, and the only additional adjustment for lateral registry which is necessary is to properly position the side guide 53. No lateral adjustment of the separator rolls I5 or the pullout rolls I5 is necessary or desirable, and because of this fact the lower pull-out roll 55 may be made a part of the belt roll 5!.

Sheet-registering mecahnism As previously stated, the sheets are delivered by the conveyor table II against the stop fingers I9, the upper feed roll 2i being raised at this time. The roll 2I is then lowered to grip the sheets firmly, after which the lower roll 20 is driven to advance the sheets to the bite of the printing rolls I I and I2. The speed of the roll 25' is accelerated smoothly but quickly so as to prevent slippage between it and the sheets and so that at the time the sheets reach the bite they will be moving atapproximately the peripheral speed of the printing rolls I I and I2 so that there,

will be no slippage between the sheets and the printing rolls. It will be observed that since the printing rolls II and I2 are rotating continually the time allowance for stopping the sheets, then starting them and speeding them upto the speed of the printing rolls is veryshort, and, accordingly, there cannot be much lost time and the various parts must be timed with great accuracy. Furthermore, the utmost uniformity is necessary to obtain accurate registry.

One of the vital considerations in obtaining uniformity is the action of the pressure feed roll 2i. As seen best in Fig; 5, this feed roll is rotatably carried by brackets 5I formed on a pivoted cross bar 52 which is rigidly connected to an upstanding arm 63 carrying a cam follower roller 65 which bears on a cam 65 which is mounted on and rotates with the shaft of printing drum or cylinder II. The arm 63 is urged in a direction to press the cam follower 55 against the cam 65 by means of a spring 66. The cam 65 is so shaped and positioned that its high portion rides out from under the roller 65 and permits the spring 56 to urge the roll 2i against the roll 2!! while each sheet is being pressedby the belts 52 against the stationary stops I9. It is important that the gripping of each sheet by the rolls 20 and 2| become fully effective before the roll 20 starts to rotate so that there will be no variations in the timing of the forward movement of the sheet. 1 In order that the movement of the sheets maypinion 12 (Fig. 5). The pinion I2 is driven by a gear segment I3 which is carried by a bell crank lever 75, the other end of which carries a cam follower roller I5 bearing on a cam 16 mounted on and rotating with the shaft of printing drum II. The cam 75 is shaped to accelerate the roll 20, and hence the sheets, smoothly but to deliver the sheets to the bite of rolls I I and I2 at a speed corresponding to the peripheral speed of these rolls. This prevents any variations in registration due either to slippage between the printing rolls and the sheets or to differences in thicknesses of the sheets. The pressure on advancing rolls 20 and 2! should not be so great as to mar the sheet or prevent its being slid therefrom by the printing rolls if the speeds are not quite equal.

As each sheet is seized in the bite between the rolls II and I2, the high portion of the cam strikes cam follower 55 to raise the pressure roll 2| and release the sheet. Immediately thereafter the largest portion of cam 16 may reach cam follower roller 15 so that the forward rotation of feed roll 25 will cease. While the sheet is being drawn from between the rolls 25 and ZI, the roll 20 may be held stationary. As the rear end of the sheet approaches the roll 20, however, the diminishing portion of the cam 15 reaches cam follower I5 so that the feed roll 20 is permitted to rotate in reverse direction and return to its original position. The return is accomplished by means of a spring 18 (Fig. 5). It is important that this spring act on the shaft II rather than directly on the bell crank I4 so that it will prevent the appearance of any backlash between the pinion I2 and the gear segment l3.

The stop fingers I9 are rigidly mounted on the shaft II so that they rotate with the feed rolls 28. Thus, there is no chance of their lagging behind and obstructing the advancing of the sheets nor is there any necessity for delaying the forward movement of the rolls 28 to be sure that the stop fingers I9 are out of the way. It is desirable, however, that the final portion of the return movement of the roll 28 be delayed until the sheet being printed has passed therebeyond so that the stop fingers I9 will-not strike this sheet.

Stripping mechanism Because of the accurate registry of the sheets with the printing drum II, no grip fingers are provided on this drum II or on the platen I2. The omission of these fingers is of course a con siderable saving in itself. It also permits the use of a platen I2 of a size much smaller than the size of the drum II since there is no need for the platen I2 to rotate at a one to one ratio with the drum II. If gripping fingers were provided on platen I2, they would continue to grip each sheet until its leading edge had been pulled away from the printing cylinder II and drawn perhaps half a revolution around the platen I2. Since such gripping fingers are not provided, it is desirable to make other provision for insuring that the sheets will always be satisfactorily stripped from the printing drum II. This is particularly important in the case of offset printing. In offset printing a plate roll 8| (Fig. 2), which is suitably inked by means not shown, engages the printing cylinder II, which in this case is a blanket roll, so that ink from the plate cylinder 8| is transferred to the blanket 82 of the blanket roll II, which in turn applies the ink to the sheet being printed. Because the blanket 82 is commonly made of rubber, there is a great tendency for the sheets to stick to such blanket, although'they would have some tendency to stick to any printing drum because of the somewhat adhesive nature of the ink. Accordingly, there is a tendency for the sheets to follow around with the printing drum and a principal object of the present invention is to provide satisfactory and dependable means for stripping the sheets from the printing drum. The srtpping mechanism includes the stripper 84 which preferably includes a plurality of stripping fingers which may be formed as corrugations 85 in a corrugated plate 88 (Fig. 31 or as separate fingers 81 (Fig. 4) A fiat stripping blade could be used but the fingers 85 or 8! are preferred since a fiat blade tends to collect ink and smear it on the printed sheets. The fingers 85 or 81 are preferably V-shaped in cross section and somewhat pointed at their forward ends although they may be narrow and rectangular in cross section as seen in Fig. 4. In other words, they are preferably provided with sheet-engaging points 88 and line-like sheet-engaging surfaces 89 extending from the points 88 in the directions of movement of the sheets. The line-like sheet-engaging surfaces 89 and the points 88 do no collect ink and hence do not smear the printed sheets. A large number of them should be provided since, if only a few are provided, the stripping action may not always be satisfactory. For the purpose of furnishing a large number of stripping fingers economically, the corrugated plate 86 is preferred. The stripping fingers, Whether formed by the corrugated plate 86 or by separate members 81, are secured to a cross bar 98 as by welding or by screws 9| passing through slots in the cross bar 98 to permit adjustment. The screws may screw into blocks welded to the stripper 84 or positioned below it, or threaded studs may be welded to the stripper 84 to pass upwardly through the bar 98 and have nuts applied thereto. The cross bar 98 is carried by arms 92 which may be bent therefrom and which are pivoted to the press frame 93 as by screws 94. The cross bar also carries an arm 95 adjustably positioned thereon by means of a screw 98. The arm 95 carries at its end a cam follower roller 91 which engages a cam 98 mounted on and rotating with the shaft of printing drum II. The cam 98 is shaped so that it normally holds the stripper 84 in the position shown in Fig. 2. However, as each sheet reaches or approaches the bite between the printing rolls II and I2, a reduced portion of the cam 98 reaches the follower 91 so that the stripper 84 under the influence of a spring 99 is tilted to the position shown in Fig. 6. In this position the points 88 extend within the periphery of the blanket 82 extending into an opening I8I which is commonly provided in blanket rolls for the purpose of securing the blanket to the drum II and tightening it. When the opening I8I would not otherwise be provided, a shallow recess or a series of shallow recesses across the printing drum may be provided especially for the purpose of receiving the points 88. On a type drum, the area where the type or plates are omitted may serve as such a recess. The cam 98 is so shaped that it will tilt the stripper 84 back to its normal position shown in Fig. 8 just before the blanket 82 reaches the points 88. In this way the stripper 84 will in effect pass downwardly immediately adjacent the leading corner or edge I82 of the blanket. It will therefore strike a projecting portion I83 of the sheet, the sheet being purposely fed to the drum II in such position as to project slightly beyond the corner I82. Since the sheet is accurately and uniformly registered with the drum II, this overlap I83 or extension will be very uniform and may be made any length desired. A length of approximately or of an inch has been found quite satisfactory. The extension I83 should not be too short, or the points 88 might tear through and nick the edge of the sheet.

The positioning of the stripper 84 is very important. In its normal position it should extend as close to the printing drum as practical, so that any tendency of the sheet to buckle and pass between the printing drum and the stripper will be minimized. It is also desirable that the active or sheet-engaging surface of the stripper lie approximately in a plane tangent to the printing drum, although it may be slightly inside of such a plane, 1. e., between the plane and the printing drum. If the rear end of the stripper is too far outside of a tangent plane passing through the point of the stripper, the stripper will tend to double the sheet and permit it to buckle and pass between the stripper and the printing roll. 0n the other hand, if the rear end of the stripper is too far within the tangent plane passing through the points of the stripper the entire stripping force will be applied to each sheet by the points with the result that the points will be likely to scar or even puncture the sheets. As a further safeguard against puncturing, the points are slightly dulled or rounded as seen from above.

The stripper 84 is mounted with its rear end in a suitable position and in all other respects its positioning is adjustable. Thus, by loosening the screws 9| the stripper can be made true or square with respect to the printing drum H and can also be adjusted regarding the distance that it extends toward the bite or the closeness with which it will pass the leading edge I02 of the blanket when the printing drum is in a predetermined position. In addition, the normal angular position of the stripper and its proximity to the circumference of the printing drum H can be adjusted by turning an eccentric bearing pin I06 which carries the cam follower roller 91 and which may be locked in any position by tightening a nut I01. The length of the arm 96 on which the roller is carried may also be adjusted, chiefly for the purpose of varying the timing of the movement of the stripper 84 with respect to the leading edge I02 of the blanket.

I claim:

1. A printing press including a printing drum and a platen roll rotatably mounted to form a bite there'between, feeding means for feeding a sheet to the bite in accurate registry with the printing drum and at approximately the speed of the periphery thereof, and stripping mechanism including means pivotally mounted outside the drum and positioned to engage the leading edge of the sheet at spaced points and strip the sheet from the printing drum, and means for pivoting the sheet-engaging means to position its forward end within a recess of the printing drum to prevent the sheet from passing between the printing drum and the sheet-engaging means.

2. A printing press including a printing drum having a recess therein, sheet-feeding means for feeding a sheet in accurate registry with the printing drum with the leading edge portion of the sheet extending partially over the recess, stripping means including a planar surface mounted outside the drum and normally positioned close to the surface of the printing drum to strip the sheet therefrom, and means for moving the stripping means into the recess ahead of the leading edge of the sheet and then out of the recess in a path passing through the original position assumed by the leading edge portion of the sheet with respect to the printing drum to engage and deflect the leading edge of the sheet and prevent passage of the sheet between the printing drum and the stripping means.

3. A printing press including a printing drum having a recess therein, sheet-feeding means for feeding a sheet to the printing drum with the leading edge portion of the sheet extending partially over the recess, stripping means mounted outside the drum and having sliding spaced line contact with the sheet normally positioned close to the surface of the printing drum to strip the sheet therefrom, and means for moving the stripping means into the recess ahead of theleading edge of the sheet and then out of the recess in a path passing through the original position assumed by the leading edge portion of the sheet with respect to the printing drum to prevent passage of the sheet between the printing drum and the strip-ping means.

4. A printing press including a printing drum having a recess therein, sheet-feeding means for feeding a sheet to the printing drum with the leading edge portion of the sheet extending partially over the recess, stripping means normally positioned close to the surface of the printing drum to strip the sheet therefrom along a plane substantially tangential to the drum, and

means for moving the stripping means into the recess ahead of the leading edge of the sheet and then out of the recess in a path passingv through the original position assumed by the leading edge to engage same and deflect it from the peripheral path of the printing drum to prevent passage of the sheet between the printing drum and the stripping means, the portion of the stripping means engaging the sheet lying approximately in alinement with the surface of the sheet facing the printing drum as it approaches the drum.

5. A printing press including a printing drum having a recess therein, sheet-feeding means for feeding a sheet to the printing drum with the leading edge portion of the sheet extending partially over the recess, stripping means normally positioned close to the surface of the printing drum to strip the sheet therefrom, and means for moving the stripping means into the recess ahead of the leading edge of the sheet and then out of the recess in a path passing through the original position assumed by the leading edge portion of the sheet with respect to the printing drum to prevent passage of the sheet between the printing drum and the stripping means, the portion of the stripping means engaging the sheet lying approximately in alinement with the surface of the sheet facing the printing drum as it approaches the drum and the stripping means wherever it, engages the sheet having free sliding engagement therewith entirely on the printing drum side of the plane of said surface.

6. A. printing press including a printing drum having a recess therein, sheet-feeding means for feeding a sheet to the printing drum with the leading edge portion of the sheet extending partially over the recess, stripping means normally positioned close to the surface of the printing drum to strip the sheet therefrom, and means for moving the stripping means into the recess ahead of the leading edge of the sheet and then out of the recess in a path passing through the original position assumed by the leading edge portion of the sheet with respect to the printingdrum to prevent passage of the sheet between the printing drum and the stripping means, the stripping means including a plurality of sheet-engaging fingers each of which is provided with a point adjacent the printing drum and engages the sheet along a narrow surface extending away from the point approximately in the direction of movement of the sheet.

7. A printing press including a printing drum having a recess therein, sheet-feeding means for feeding a sheet to the printing drum with the leading edge portion of the sheet extending partially over the recess, stripping means normally positioned close to the surface of the printing drum and constructed to strip the sheet therefrom. with a free sliding relationship Wherever the stripping means engages the sheet, and means for moving the stripping means into the recess ahead of the leading edge of the sheet and then out of the recess in a path passing through the original position assumed by the leading edge portion of the sheet with respect to the printing drum to prevent passage of the sheet between the printing drum and the stripping means, the sheet-engaging surface of the stripping means in the vicinity of the printing drum. being positioned entirely on the printing drum side of the plane of the sheet as it approaches the drum and being sufliciently nearly parallel with said plane to prevent buckling the sheet or piercing it with said stripping means.

8. A printing press including a printing drum having a recess therein, sheet-feeding means for feeding a sheet to the printing drum with the leading edge portion of the sheet extending partially over the recess, stripping means normally positioned close to the surface of the printing drum to strip the sheet therefrom, and means for moving the stripping means into the recess ahead of the leading edge of the sheet and then out of the recess in a path passing through the original position assumed by the leading edge portion of the sheet with respect to the printing drum to prevent passage of the sheet between the printing drum and the stripping means, the sheet-engaging surface of the stripping means in the vicinity of the printing drum lying on the printing drum side of and approximately parallel to a plane tangent to the drum and passing adjacent said surface.

9. A printing press including a printing drum having a recess therein, sheet-feeding means for feeding a sheet to the printing drum with the leading edge portion of the sheet extending partially over the recess, stripping means normally positioned close to the surface of the printing drum to strip the sheet therefrom, and means for moving the stripping means into the recess ahead of the leading edge of the sheet and then out of the recess in a path passing through the original position assumed by the leading edge portion of the sheet with respect to the printing drum to prevent passage of the sheet between the printing drum and the stripping means, the stripping means including a plurality of sheet-engaging fingers each of which comes to a point adjacent the printing drum and engages the sheet along a narrow surface extending away from the point approximately in the direction of movement of the sheet and sufficiently close to a plane passing through the points and tangent to the printing drum to avoid buckling or marring the sheets.

10. Stripping mechanism for stripping a sheet from a rotating roll having a recess therein extending on both sides of the leading edge of the sheet, including stripping means having planar elongated sheet-engaging portions spaced one from another and normally positioned with the forward ends thereof disposed adjacent the surface of the roll, and means for moving said stripping means between a position tangent to the roll and a position intersecting the surface of the roll to cause the forward end of the stripping means to pass into said recess ahead of the leading edge of the sheet and out therefrom behind the leading edge of the sheet to remove the sheet from the roll in a plane tangent to the roll.

11. Stripping mechanism for stripping a sheet from a rotating roll, including stripping means normally positioned stationarily with its forward end presenting a leading edge adjacent the surface of the roll adapted to engage the sheet at spaced points of limited contact, and means for causing the forward end of the stripping means to approach relatively closer to the axis of the roll as the leading edge of the sheet approaches the stripping means to prevent the sheet from passing between the stripping means and the roll,

12. An offset printing press including a blanket roll having a blanket thereon and a blanket-securing recess therein, means for applying ink in the form of matter to be printed to the blanket roll, means for feeding a sheet to the blanket roll with its leading end extending over the recess, a platen roll for pressing the sheet firmly against the blanket to cause the ink to be printed on the sheet, stripping means having a plurality of transversely spaced edges defining a plane surface normally stationary and positioned close to the surface of the blanket to strip the sheet therefrom, and means for moving the stripping means into the recess ahead of the leading edge of the sheet and out of the recess behind the position over the recess originally assumed by the leading edge of the sheet to engage the leading edge and carry the sheet tangentially from the blanket.

13. A printing press including a printing drum having a recess therein, sheet-feeding means for feeding a sheet in accurate registry with the printing drum with the leading edge portion of the sheet extending partially over the recess, stripping means normally positioned close to the surface of the printing drum to strip the sheet therefrom, and means for moving the stripping means into the recess ahead of the leading edge of the sheet and then out of the recess in a path passing through the original position assumed by the leading edge portion of the sheet with respect to the printing drum to prevent passage of the sheet between the printing drum and the stripping means, said stripping means and means for moving it being adjustable to control independently the normal proximity of the stripping means to the printing drum and the proximity of the stripping means to the edge of the'recess as it is moved out of the recess.

14. A printing press including a printing dru having a recess therein, sheet-feeding means for feeding a sheet in accurate registry with the printing drum with the leading edge portion of the sheet extending partially over the recess, stripping means normally positioned close to the surface of the printing drum to strip the sheet therefrom, and means for moving the stripping means into the recess ahead of the leading edge of the sheet and then out of the'recess in a path passing through the original position assumed by the leading edge portion of the sheet with respect to the printing drum to prevent passage of the sheet between the printing drum and the stripping means, said stripping means being supported by a pivoted bar and being adjustable with respect to said bar toward and from the printing drum, and the means for moving the stripping means including a cam carried by and rotating with the printing drum, and a cam follower adjustably carried by said bar.

15. A printing press including a printing drum having a recess therein, sheet-feeding means for feeding a sheet in accurate registry with the printing drum with the leading edge portion of the sheet extending partially over the recess, stripping means normally positioned close to the surface of the printing drum to strip the sheet therefrom, and means for moving the stripping means into the recess ahead of the leading edge of the sheet and then out of the recess in a path passing through the original position assumed by the leading edge portion of the sheet with respect to the printing drum to prevent passage of the sheet between the printing drum and the stripping means, said stripping means being supported by a pivoted bar and being adjustable with respect to said bar toward and from the printing drum, and the means for moving the stripping means including a cam carried by and rotating with the printing drum, and a cam follower including a roller eccentrically carried by an elongated arm carried by and longitudinally adjustable with respect to said bar.

16. In a printing press having a rotatable cylinder provided with a gap and defining a surface of revolution when in operation, and means for feeding sheets to the cylinder with the leading edge thereof overlapping the gap, a stripper comprising means having spaced line contacts with the sheet lying normally in a plane substantially tangential to said surface of revolution, and terminating short of contact with the cylinder, means for tilting the stripper means to move a limited portion of the stripper means into the gap whereby the stripper means is located in a position intersecting said surface .of revolution ahead of said leading edge and withdrawing said portion when the leading edge has contacted said portion.

17. In a printing press having a rotatable cylinder provided with a gap and defining a surface of revolution when in operation, and means for feeding sheets to the cylinder with the leading edge thereof overlapping the gap, a stripper comprising means having sliding line contact at spaced points with the sheet over a substantial portion of the sheet as the sheet moves between the cylinder and a place of deposit, said stripper means lying in a plane substantially tangential to said surface of revolution and terminating along a line short of contact with the cylinder, means for moving the stripper means and the leading edge of the sheet relative to each other as said leading edge approaches the stripper means.

18. In a printing press having a frame and a rotatable printing drum provided with a relieved portion, the combination of means for feeding a sheet into printing position with the printing member to have the leading edge of the sheet overlap said relieved portion, stripping means lying in a plane and mounted outside of the printing drum, said stripping means being movable through a path between a position in which the stripping means is partially within the relieved portion of the printing member and one in which the stripping means lies completely outside of the drum periphery, and means operated in cooperation with the printing drum for synchronizing the movement of said stripping means to cause said stripping means to move into the relieved portion at the time that the relieved portion of the printing drum is adjacent to the stripping means.

19. In a printing press having a frame and a movable printing member provided with a relieved portion, the combination of means for feeding a sheet into printing position with the printing member to have the leading edge of the sheet overlap said relieved portion, stripping means lying in a plane and mounted on a relatively fixed part of the frame, said stripping means being movable through a path between a position in which the stripping means is partially within the relieved portion of the printing member and one in which the stripping means lies outside of the printing surface of the printing member, and means operated in cooperation with the printing member for synchronizing the movement of'said stripping means to cause said stripping means to move into the relieved portion at the time the relieved portion on the printing member is adjacent to the stripping means.

WILLIAM WARD DAVIDSON.