US2681004A

US2681004A - Feeder for printing machines

Info

Publication number: US2681004A
Application number: US184942A
Authority: US
Inventors: Frecborn James Edward
Original assignee: SCREEN PRINTING MACHINERY Ltd
Current assignee: SCREEN PRINTING MACHINERY Ltd
Priority date: 1949-09-07
Filing date: 1950-09-06
Publication date: 1954-06-15
Anticipated expiration: 1971-06-15

Description

June 15, 1954 .J. E. FREEBORN FEEDER FOR PRINTING MACHINES 5 Sheets-Sheet 1 Filed Sept. 6, 1950 Inventor Jinn f. Zaasae/v Attorney June 15, 1954 J. E. FREEBORN FEEDER FOR PRINTING MACHINES 5 Sheets-Sheet 2 Filed Sept. 6, 1950 III 28 Inventor Jamesi l-kzfaom By m M Attorney ouaooebaooooocono9a June 15, 1954 J. E. FREEBORN 2,681,004

FEEDER FOR PRINTING MACHINES Filed Sept. 6, 1950 5 Sheets-Sheet 3 v mom mm I June 15, 1954 J. E. FREEBORN FEEDER FOR PRINTING MACHINES 5 Sheets-Sheet 5 Filed Sept. 6, 1950 In ventor J4me: l 525550 A Home y Patented June 15, 1954 UNITED STATES PATENT OFFICE James Edward Freeborn, Broxbourne, England, assignor to Screen Printing Machinery Limited,

London, England Application September 6, 1950, Serial No. 184,942

Claims priority, application Great Britain September 7, 1949 16 Claims.

This invention relates to printing machines of the type which comprise a printing table and printing mechanism for printing on a sheet placed on the table.

With such machines it is desirable to provide mechanical means for feeding the sheets to be printed into position on the printing table. In the case particularly of multi-colour printing it is important that each sheet should be correctly registered in the printing position in order to ensure that the impressions are printed in the correct positions on the sheet and that successive impressions on the same sheet are printed in correct register.

It is one of the principal objects of the present invention to provide a novel and improved feed mechanism for this purpose, while the invention is also concerned with the provision of mechanism for delivering the printed sheets from the printing table.

The invention is more particularly concerned with screen or stencil printing machines, although it is also applicable to other forms of printing machine.

According to the invention a printing machine is provided com-prising a printing table, printing mechanism for printing on a sheet resting on the table and feed mechanism for feeding the sheet to be printed into position on the table, wherein the feed mechanism comprises a feed table having register elements against which a sheet to be fed to the printing table can be placed in an accurately defined position and a feed member having at least one gripping element adapted to grip the said sheet, the feed member being movable through a predetermined distance away from the feed table to cause it to feed the sheet into the correct position on the printing table.

For removing the printed sheet from the printing table the machine is preferably provided with a delivery mechanism which comprises a delivery table located adjacent the printing table and a delivery member having a clamping element adapted to engage a sheet in the printing position on the printing table, the delivery member being movable away from the printing table to draw the sheet off it on to the delivery table.

The feed member and the delivery member, the operations of which are synchronised with the printing operations of the machine, are preferably so arranged that when the feed member is making a forward stroke to feed a sheet on to the printing table the delivery member is making a return stroke to bring its clamping element into position to engage this sheet and to hold the leading edge of the latter while printing is actually taking place.

The invention will now be more fully described, by way of example, with reference to the accompanying drawings. In the drawings:

Figure 1 is a diagrammatic side elevational view showing one form of feed and delivery mechanism according to the invention, which mechanism is included in a stencil printing machine;

Figure 2 is a detail view, taken in the direction of the arrow II of Figure 1, showing part of the drive to the feed and delivery mechanism;

Figure 3 is a detail sectional View, to a larger scale, showing another part of the feed and delivery mechanism of Figure 1;

Figure 4 is a section taken on the line IVIV of Figure 3;

Figure 5 is a section taken on the line V-V of Figure 4;

Figure 6 is a partly cut-away sectional view, taken on the line VIVI of Figure 8, showing the feed trolley which is used for feeding the sheet to be printed from the feed table to the printing table;

Figure '1 is a similar view, but taken on the line VII-VII of Figure 9, showing particularly the means provided for arresting the movement of the feed trolley at the limits of its travel;

Figure 8 is a transverse sectional View through the feed trolley, taken on the line VIII-VIII of Figure 6;

Figure 9 is a sectional view similar to Figure 8 but showing the elements used for gripping the sheets in their retracted positions;

Figure 10 is a sectional view taken on the line X-X of Figure 6, showing the mechanism provided for retracting the gripping elements at one end of the travel of the feed trolley;

Figure 11 is a view similar to Figure 10 but showing the mechanism after it has been operated to retract the gripping elements;

Figure 12 is a detail plan view, taken in the direction of the arrow XII of Figure 6, showing part of the mechanism used for locking the gripping elements in their retracted positions;

Figure 13 is a detail sectional view, taken on the line XIIIXIII of Figure 14, showing the delivery trolley which effects the delivery of the sheet from the printing table, the sheet-clamping element of the trolley being shown in its retracted position;

Figure 14 is a detail sectional view similar to Figure 13 but showing the trolley at the opposite end of its travel and the sheet clamping element in its operative position;

Figure 15 is a transverse sectional View of the delivery trolley in the position in which it is shown in Figure 14,-

Figure 16 is a view similar to Figure 1 but showing a stencil printing machine having a modified form of sheet feed and delivery mechanism;

Figure 17 is a detail plan view showing part of the machine of Figure 16;

Figure 18 is a section taken on the lineXVIII- XVIII of Figure 17;

Figure 19 is a detail sectional view showing the gripping element which is used for gripping the sheet, this gripping element being shown in its operative position;

Figure 20 is a view similar to Figure 19 but showing the gripping element retracted;

Figure 21 is a section, taken on the line XXI- XXI of Figure 19;

Figures 22 and 23 are partly diagrammatic detail views, corresponding to Figures 19 and 20 respectively, but showing part of the mechanism for operating the gripping element;

Figure 2ais a detail sectional view showing a side guide member which is used for the initial positioning of the sheet and for guiding it during its travel into position on the printing table;

Figure 25 is a view similar to Figure 24 but showing the guide member depressed below the plane of the table.

Referring first to the construction shown in Figures 1 to 15, the machine comprises a frame of any suitable construction which supports a printing table 2, a feed table 3 and a delivery table i. The positions of these tables, when viewed in plan, correspond to those of the tables 252, 2% and 23 3 respectively of the modified form of machine as shown in Figure 17. In both cases the delivery table provides in effect a continuation of the printing table surface, as does a side portion 265 of the feed table, but the main part of the feed-table is arranged to be adjustable in height, any suitable mechanism being provided for raising and lowering it. In use a stack of sheets to be printed is placed on the adjustable part of the feed table, which is progressively raised as printing proceeds so that the top sheet is always level with or a little above the level of the printing table. It is the duty of one of the operators to slide each sheet in turn from the top of the stack into position to be engaged by the feed mechanism. As will appear this position is accurately defined by register elements provided at the side of and at the front of the feed table.

The printing table 2, like the table 252, is

' formed with a series of perforations opening from its printing surface and leading into a vacuum chamber located beneath the table. Such perforations in the table 2&2 are indicated at 286 in Figure 17 Suitable means are provided for intermittently creating a partial vacuum in the vacuum chamber in order to provide a suction which, by acting through the perforations in the printing table, will hold the sheet in position after it has been fed onto the table and during the printing operation.

For printing on a sheet placed on the printing table 2 screen frame carrier is provided, which is hinged at 8 to suitabie bearings provided on the frame of the machine at opposite sides thereof. These bearings are located slightly in front of the rear or feed end of the printing table 2.

The carrier 2 carries a screen frame 9 which includes a stencil screen, made of silk, organdie, wire mesh or any other suitable material. The necessary stencil pattern may be applied to this screen in any of a number of ways. The stencil may, for example, be of any one of the types known as block out, resist, paper or film or it may be prepared photographically by the gelatine-bichromate process. The present invention is not concerned with the particular form of screen used or with the process employed for applying the stencil pattern to it.

It may be noted here that the side members Iii of the screen frame carrier '1 at the rear or feed table end of the latter project considerably beyond the rear edge I i of the screen frame and the corresponding edge of the printing table. This ensures that sumcient clearance is obtained between the rear portion of the screen Q and the table when the screen is raised as shown in Figure 1.

The screen frame carrier I is raised and lowered by means of a suitable mechanism which may comprise a slidably mounted rod 52, the upper end of which carries a roller it which bears on a suitable plate provided on the side of the screen frame carrier 1. The rod 52 is raised and lowered by means of an appropriate mechanism operated from the main cam shaft of the machine, which is indicated at it. This mechanism may comprise a cam mounted on the end of the shaft i l and a cam follower which is operativeiy connected with the rod i2 through a lever or other suitable form of linkage. The rod it with its cam operating mechanism is preferably duplicated on the opposite sides of the machine.

The shaft ll'is driven by an electric motor i5 through a belt if"; and through a suitable speed-reducing gear which may be contained within the supporting structure or casing ll. If desired, means may be provided for varying the speed of the shaft is in order that the working speed of the machine may be adjusted to suit particular requirements.

In order to force the printing ink or colour through the screen to effect a printing operation, an inking carriage i8, is provided, which is mounted for reciprocating movement along the screen frame carrier 8. This inking carriage is reciprocated along the carrier by means of suitable mechanism which may be driven from the shaft it. The operation of the carriage is synchronised with the raising and lowering of the screen frame carrier so that each time the'screen is lowered into contact with a sheet on the printing table '2 the inking carriage it makes a printing stroke. It then remains at the end of the screen while the latter is raised and lowered, during which time the printed sheet is delivered from the printing table and a fresh sheet is fed into place on the table. The screen is then lowered on to this fresh sheet and the inking carriage !8 makes a printing stroke in the reverse direction.

As will be understood by those skilled in the art, the inking carriage will require to have either a single reversible squeegee or a pair of oppositely-arranged squeegees and means must be provided which operate when the carriage reaches the end of its travel for bringing the squeegee (or the appropriate one of the squeegees) into the correct trailing position in readiness for the next printing stroke. Such mechanism, which may be of any suitable type, forms no part of the present invention.

The mechanism for feeding the sheets into position on the printing table 2 and for deliver ing them after printing from this table on to the delivery table is will now be described.

The mechanism for feeding the sheets comprises a feed trolley 28 which is re'ciprocated in a trough 2i extending along one side of the feed table 3 and the delivery table 2. This feed trolley is connected to the upper lap of a feed drive chain 22, which is trained around a driving sprocket 23 and an idler sprocket 24.

The sheet delivery mechanism comprises a delivery trolley 25 which is reciprocatably mounted below a longitudinal slot formed centrally in the delivery table ll. The end of this slot extends a short distance into the delivery end of the printing table so that a clamp carried by the trolley can engage and grip the edge of a sheet while the latter is in its printing position on the printing table.

The delivery trolley 25 is connected to the lower lap of a delively drive chain 25 which is trained about a driving sprocket 2i and an idler sprocket 2B.

As is best shown in Figure 4, the driving

sprockets

23 and 2? are mounted on a transverse shaft 29 which is journalled in suitable bearings (not shown) provided on the frame of the machine.

The delivery drive sprocket 2'! is keyed to the shaft '29 but the feed drive sprocket 23 is rctatably mounted on this shaft, being retained in position on it by means of a collar 30. The sprocket 23 is driven from the shaft 29 through a resilient, lost motion coupling which is best shown in Figures 4 and 5. This coupling comprises a disc 3i which is keyed to the shaft 29 and which carries a drive pin 32. The end of this pin engages between two levers 33 which pass on opposite sides of the shaft 29 and the ends of which are pivoted at 34 to the sprocket 23. The opposite ends of the levers 33 are urged into engagement with the drive pin 32 by means of compression springs 35 mounted on a rod 3% which passes through the levers 33 and through fixed bosses 37 mounted on the face of the sprocket 23. The springs 35 are under compression between these bosses and the ends of the levers 33 and thus maintain the latter in their normal position in which they are in contact with the pin 32. Arcuate stop elements 33 provided on the levers 33 define this position of the latter by their engagement with the shaft 29.

It will be understood that the coupling which has been described normally provides a direct driving connection between the shaft 29 and the sprocket 23, but when the movement of the sprocket is arrested by the feed trolley reaching the limit of its possible movement in one direction or the other the shaft 29 is able to rotate a small amount further, which movement is absorbed by one or other of the springs 35. The shaft 29 is arranged to be driven first in one direction and then in the other by mechanism which will be described. The amount of this movement is arranged to be very slightly more than is required to cause the feed trolley 25* to make a complete stroke from one limit stop to another.

The mechanism for driving the shaft 29 is operated from the main cam shaft M and. comprises a pair of cams 4| and 42 (Figures 1 and 2) which are mounted on the shaft 5 4 and which engage rollers i3 and 44 respectively mounted on the two arms of a bell crank lever 45. This lever 45 is journalled on a cross shaft 46 and its longer arm 4! is connected to two

link arms

48 and 49 which are coupled to an epicyclic speed-multiplying mechanism which is indicated at 50.

The two cams 4| and 42 are so shaped that the

rollers

43 and 44 are maintained in contact with them during the entire rotation of the shaft i4,

the cam 4! providing a positive drive to turn the bell crank lever in a clockwise direction (Figure 1) and the cam 42 providing a positive drive to turn this lever in an anti-clockwise direction. Furthermore, the shapes of these cams are such that the lever 45 is given a substantially harmonic motion.

The fact that the bell crank lever 45 can only turn through a small fraction of a complete revolution whereas, the shaft 29 must rotate through several complete revolutions in each di rection, makes it necessary to provide the speed multiplying mechanism 50. This mechanism, which is best shown in Figures 3 and 4, comprises an annulus which is internally toothed at 55, a planet carrier 5?, which carries a pair of planet wheels 5% meshing with the teeth 56, and a sun wheel 59 which is also engaged by the planets 53. The sun wheel 59 is keyed to the shaft 29, whereas the annulus 55 and the planet carrier 5i are freely rotatable on this shaft. The upper end of the link arm 48 is pivotably connected at it to a projected portion 51 of the annulus 55, while the link arm 32 is pivotably connected at 62 to an arm 53 which extends from the planet carrier 5?.

Referring more particularly to Figure 4 it will be seen that when the

link arms

48 and 42 are moved upwardly by an anti-clockwise rotation of the bell crank lever 45 the annulus 55 will be rotated in a clockwise direction and the planet carrier 5? will be rotated in an anti-clockwise direction. Owing to the effect of the planet wheels 58 which mesh both with the annulus and with the sun wheel 59, this latter wheel and with it the shaft 29, will be rotated in an anti-clockwise direction by an amount which is very much greater than the amount of the rotation of either the annulus or of the planet carrier. In this way the shaft 29 is rotated through several revolutions sufficient to drive the feed and delivery trolleys the complete lengths of their strokes. Owing to the use of the two cams 4| and 42 the drive of the trolleys is positive in both directions, apart from the small amount of lost motion which is provided for in the drive to the sprocket 23.

It may be noted here that owing to the fact that the feed trolley 20 is connected to the upper lap of the chain 22, while the delivery trolley 25 is connected to the lower lap of the chain 26, the two trolleys move in opposite directions to each other. Thus, when the feed trolley 20 is moving to the left (Figure 1) to feed a sheet to the printing table 2, the delivery trolley 25 is moving to the right in order to come into position to engage this same sheet as soon as it reaches its correct position on the printing table. On the other hand, when the delivery trolley 25 moves to the left to withdraw the printed sheet from the printing table, the feed trolley 26 makes a return stroke to the right to bring it into position to engage a fresh sheet on the feed table. The shapes of the cams 4| and 42 are such that the required pauses or dwell times are provided to permit of the screen being lowered on to and subsequently raised from the printing table and for the inking carriage E8 to make its printing stroke, during which operation the

trolleys

20 and 25 remain stationary.

The construction and operation of the feed trolley 22 will now be described in greater detail, with particular reference to Figures 6 to 12. The trolley comprises a pair of side plates 10 and l! which are secured on opposite sides of a bottom bar 12. The trolley is provided with two pairs of wheel 13 which are mounted on axles M and which run in guide channels '35 formed in the base "55 of the guide trough 2!. This trough is mounted below and at one side of the feed and printing tables 2 and 3.

The guide trough 2| is also provided with a register bar I? which is supported at its ends and which extends the length of the trough. side plates 59 and H of the feed trolley 21! run on opposite sides of this register bar.

Where the register bar i1 extends alongside the feed table 3 its upper edge (8 is extended so as to project above the top surface of the food table. It can thus act as a register element and guide for positioning the sheet which is to be fed to the printing table.

A front register stop 80 (Figures 6 and '7) is provided at the front of the feed table a short distance inside the line or" the side register bar ll. This stop 80 takes the form of a short rod which is slidably mounted in the table and the lower end of which is supported on one end of a transverse lever (not shown). The other end of this lever, which is mounted in a pivot bearing in the neighbourhood of the centre line of the machine, supports an operating plunger 86 (Figure 1) which is located near the opposite side of the achine. When the stop Bil is in its lower position below the surface of the table, the upper end of the plunger 8! projects above the table. When, however, the frame 4 descends, an element on one of its side frame members is engages and depresses the plunger 8!. This rocks the transverse lever and causes the register stop to be raised into its operative position.

The feed carriage 2c is provided with four gripping elements which are rotatabl mounted on a rod 85 running longitudinally along the carriage 21: above the outer side plate ll). Each the gripe-er elements 85 is prov ed with a coil spring 8? which tends to urge it into its operative position as shown Figure 8.

The grip ng elements till are adapted to be moved away from their operative positions to the retr cted positions (as shown in Figure 9) by rota ing the shaft For this purpose collars 33 are to the shaft 86 adjacent to the ing elements each collar having a protooth 8% which is adapted to engage a rcvided on one side of the corresponding element As a result of this arrangement, the shaft 36 is rotated in one direction the ping elements are turned by it away from their operative positions against the force of the springs 81, whereas when the shaft is rotated in the opposite direction the springs can turn the gripping elements back until their ends engage the top of the side plate H (or a sheet of paper such as iii the of which overlaps the top of this plate). Thus the gripping elements grip the paper individually under the action of the springs In order to improve the effectiveness of the gripping elements rubber inserts t2 (Figure 7) be provided along the edge of the plate l' itions corresponding to the ends of the gri ping elements.

T e mechanism by means of which the gripping elements are operated to cause them to be raised grip a sheet when the feed trolley 26 is adjacent to the feed table and to cause them to be depressed below the level or the printing table after my have fed th sheet into the correctl registered position on the latter will now be described.

The shaft 86 is provided at its forward end with a dog-clutch element 92 having a project bar 93 which is adapted to engage in a slot formed in a cooperating clutch element This latter element is mounted on the end of a shaft 8" which is journalled in a fixed bearing member Ql, The clutch element 55 is formed with teeth 48 which are engaged by a rack bar This bar is slidably mounted in the sides of the trough 2i and carries a compression spring Hill which is fitted on a reduced portion llll of the bar Q9. It thus urges this bar to the left as shown P1: ares l0 and 11, its movement being limited by a nut 32 provided on the end of the bar.

Th rack bar $39 is adapted to be forced inwardly against the force of the spring we by means of a lever ass which is pivoted at ms. and

which is operated by means of a rod M55. The mechanism for operating this rod Hi5 is not shown in the drawings but it may comprise a cam mounted on the shaft ill and a cam follower w ich is operated by this cam and which is connected with rod 595 by means of any suite form of linkage. The arrangement is such that, after the fee trolley 22} has moved to the left to feed a sheet into the correct position on the printing table, lever 583 is actuated to move the rack bar so inwardly and thus to rotate the shaft 8% in the appropriate direction to retract the gripping elements into the position shown in Figure 9, in which they are below the level of the printing table. This is done after the trolley has reached th end of its travel to engage the

clutch elements

92 and 95 but before the screen frame descends. It is thus ensured that the gripping elements are not caught by th descending frame. This makes it possible for the screen to overlap the side edges of the sheet so that printing can be effected right up to the edges if required.

At its other end the shaft 86 is provided with a collar B ll which is formed with a transverse slot tell. The position of this slot in the collar is such that it is vertical when the rod 86 has been rotated to retract the gripping elements 85. As soon as the shaft reaches this position the upper end of a locking lever Hill, which is pivoted at ill? to the side of the trolley 25 is caused to enter the slot its under the action of a compression spring Hi. It thus locks the shaft 8% against rotation.

After the feed trolley so has fed a sheet on to the printing table the gripping elements are retracted and locked in their retracted position, as described above, after which the trolley is returned to its initial position ready to receive another sheet. This movement or the trolley at once disengages the clutch element 92 from the clutch element 2E5, but the shaft 86 and consecuently the gripping elements t5 are prevented from being rotated under the action of the springs El by the engagement of the locking lever 585' in the slot its, When, however, the trolley reaches the limit of its movement in the return direction, the lower end of the lever its engages a stop iii provided at the end of the trough 2i, aiter which the continued movement of the trolley causes the lever it!) to be disengaged from the slot 453. This allows the springs ill to reassert themselves so as to rotate the gripping elements 85 with the shaft 36 and causes the gripping elements to engage and grip the edge of a fresh sheet of paper, which has in the meantim been positioned by the operator against the side and front register stops it and 88. When the trolley makes its next forward movement, therefore, it will feed the sheet from the feed table on to the printing table, the front stop M having in the meantime been retracted as a result of the raising of the screen frame away from the plunger at.

As has been explained, the drive to the feed trolley 29 is arranged so that it tends to drive the trolley very slightly beyond the limits of its travel, which are defined by stops. Also the movement of the trolley is arranged to be of a generally harmonic nature owing to the par ticular shape of the cams 4| and 42. In other words, the trolley is arranged to gather speed progressively as it moves away from one end stop and to decelerate as it approaches the other end stop.

It has been found that there is a tendency for the trolley to rebound slightly when it strikes the end stops and in order to avoid the risk of it doing this, which would prevent correct reg-- ister from being obtained, frictional means are provided for assisting in the retardation of the trolley as it nears the end of its travel and also for resisting any tendency of the trolley to rebound from its end stops. The mechanisms for doing this are shown in Figure 7.

The two mechanisms which are provided at opposite ends of the trough 2| are generally similar to each other. Each comprises a pair or" levers H3 which are pivoted to the sides of the trough at H4 and the rear ends of which are urged towards each other by means of compression springs H5. The effect of these springs is thus to urge the inner ends MB of the levers away from each other, this movement being limited by means of a stop I I! provided between the levers.

The side plate ll of the trolley is formed in its opposite ends with recesses H8 which are of approximately key-hole shape, having flared or tapered mouths and enlarged, rounded inner ends H9. As the trolley 28 nears the end of its travel, the ends N6 of the levers H3 enter the corresponding recess H8 and during the final movement of the trolley the levers H3 are forced towards each other against the force of the springs H5. This provides a resistance to the movement of the trolley, which movement is finally arrested by the engagement of the end of the plate 7! against stop shoulders 120 formed on the levers H3.

The final movement of the trolley 20 allows the enlarged ends MS of the levers M3 to enter the enlarged end portion H9 of the recess H8, with the result that the levers prevent any tendency for the trolley to rebound from the stops 525.

The sheet delivery mechanism will now be described with more particular reference to Figures 13 to 15.

The delivery trolley comprises a frame plate 936, the sides 53! of which are bent upwardly. The trolley is provided with two pairs of wheels I32 which run on a guide plate E33. extends along beneath the aforesaid slot in the delivery table t. A stirrup-shaped bracket E34 is rigidly secured to the sides of the trolley 25 and it is also attached at M5 to the lower lap of the delivery drive chain 26. The side arms of the bracket 536 pass on opposite sides of the guide plate 33 and serve to guide the trolley 25 during its movement.

A pair of upstanding support arms 535 are provided on opposite sides of the trolley 25, the

This plate lower ends of these arms being clamped between the ends of the bracket I34 and the sides 13! of the trolley frame. The arms I36 carry a rotatable anvil member I38 which is supported by means of end pins I39 which are journalled in the arms 536. This anvil member i38 supports a movable clamping plate Hill which is provided with downwardly projecting pins Ml. These pins pass slidably through suitable bores formed through the anvil member.

The lower ends of the pins i4! bear on a stirrup member Hi2, which is pivotably connected at Hi3 with a pair of links M4. The other ends of these links are secured to a transverse operating shaft M5 which is rotatably mounted in the arms I36. Operating cams I46 are secured to the outer projecting ends of the shaft M5.

Compression springs M1 interposed between the bottom of the anvil i558 and the stirrup member Hi2 tend to hold the clamping plate MB' against the top surface of the anvil.

As will be understood from a comparison of Figures 13 and 14 the mechanism provides a toggle action by means of which the anvil I38 and the clamping plate it are retained either in their operative position, as shown in Figure A, or in their retracted position as shown in Figure 13. These parts can, however, be moved from one position to the other by rotating the shaft M5; and during this movement the effect of the toggle action is such that the clamping plate its is forced upwardly away from the anvil 535.3, to which it is allowed to return under the action of the springs M! as the anvil completes its movement.

During the return stroke of the delivery carriage 25 the clamping plate and anvil are in the retracted position shown in Figure 13. When, however, the trolley reaches the limit of its movement in the direction of the feed table 2 (as shown in Figure 14) the operating cam M6 is engaged and turned by a lever EM (see also Figure 15). been turned by this lever past its dead centre position the action of the springs 147 causes the mechanism to snap over to the operative position shown in Figure 14. This causes the clamping plate see to grip the leading edge of a sheet i413 resting on the printing table 2. This sheet is in its actual printing position to which it has been brought by the movement of the feed trolley, which movement takes place while the delivery trolley 25 is making its return stroke. The clamping plate M53 maintains its grip on the sheet hi6 during the printing operation and subsequently during the delivery stroke of the trolley 25.

It may be noted here that the upper surface of the clamping plate Md is substantiall flush with the surface of the sheet M8. This makes it possible for the screen 9 to overlap the clamping plate and for the squeegee to make a stroke up to and over the clamping plate. Thus printing can be effected almost to the edge of the sheet M8.

The mechanism for operating the lever M1 is not shown in the drawings, but it may conveniently comprise a cam mounted on the main cam shaft M. This cam is provided with a follower which is coupled with the lever M! through a suitable linkage.

When the delivery trolley 25 reaches the end of its delivery stroke, during which stroke it draws the sheet i 38 away from the printing table 2 on to the delivery table i, the operating cam Once the toggle mechanism has I46 engages a stop rod I49 which is mounted at the end of the guide plate 533. The action of this stop is to tilt the cam Hi8 and thus to move the clamping plate and anvil into their retracted position, as shovm in Figure 13. The sheet M8 is thus released and can be removed from the delivery table by the operator.

The sequence of the various operations which takes place during the working of the machine will now be described. It will be assumed that a sheet on the printing table has just been printed and that the frame carrier 1 is in its lower position. The feed trolley as will be in its forward position alongside the printing table 2, the gripping elements as being retracted, while the delivery trolley 25 will be in its rearward position, nearest the feed table, with the clamping plate to gripping the edge of a sheet which has just been printed. This sheet will also be held down on the printing table by the suction acting through the perforations in the table.

During the time that the printing was taking place one operator will have drawn a fresh sheet from the top of the stack on the movable portion of the feed table and will have positioned it with its front edge engaging the front register stop 8% (which is raised owing to the frame carrier being in its lower position) and with its side edge against the side register guide 18. Another operator will have removed the previously printed sheet from the delivery table 4.

As soon as the inking carriage [3 has completed its printing stroke the frame carrier 1 will begin to rise, whiie the vacuum acting through the printing table is released. As the frame carrier rises the delivery trolley 25 starts its delivery stroke. Owing largely to the fact that the frame carrier is hinged at the feed table end of the machine the movement of the screen frame and of the delivery trolley produce a progressive peeling of the printed sheet away from the screen. This peeling action is of the greatest importance since it is only in this Way that the sheet can be quickly and cleanly removed from the screen, which is necessary if a rapid operation of the machine is to be obtained without smudging of the impression on the sheet.

After the printed sheet has been peeled off the screen the delivery trolley continues to move away at a progressively increasing speed until it reaches the mid-point in its travel, when it begins to decelerate until it finally comes to rest at the end of its stroke. During the last part of the movement of the trolley the engagement of the operating cam 46 against the stop rod I 39 disengages the clamping plate from the printed sheet and depresses the clamping plate and anvil into their retracted position. This enables the trolley to make its return stroke without waiting for the operator to remove the printed sheet from the delivery table. The operator can do this at any time before the next printed sheet is delivered from the printing table.

During the delivery stroke of the trolley 25 the feed trolley 20 makes its return stroke, at the end of which the gripping elements 85 are operated, as previously described, to grip the sheet which has been positioned against the side and front register elements l8 and 80 respectively. The raising of the frame carrier '1 will have retracted the front register stop 8%, but this does not occur until after the operator'has had plenty of time to position the sheet in the correct position against the stop.

Almost immediately after the trolleys 2e and 25 have completed their return and delivery strokes respectively their motion is reversed. The feed trolley thus feeds a fresh sheet into the correct position on the printing table, after which the gripping elements 85 are immediately retracted. At the same time the delivery trolley 25 makes its return stroke, at the end of which the clamping plate 2st is operated to grip the leading edge of the sheet, as is shown in Figure 14. A partial vacuum is re-created in the vacuum chamber so as to produce suction to hold the sheet on the printing table and the frame carrier 1 descends. When the screen is in contact with the sheet on the printing table the inking carriage makes a printing stroke along the frame carrier, after which the above sequence of operations is repeated.

It may be found that, owing to the fact that the feed trolley only grips the sheet along one side edge, there is sometimes a tendency for the other side of the sheet to rise or be blown up during its travel on to the feed table. In order to avoid this, an air nozzle 553 may be provided, mounted above the delivery table in front of the end of the frame carrier. This nozzle is directed laterally away from the feed trolley and also forwardly and downwardly, and air is blown through this nozzle during the operation of the machine. The pressure of this air keeps the sheet flat on the table while it is being fed from the feed table to the printing table.

The modified form of feed and delivery mechanism which is shown in Figures 16 to 25 will now be described.

The drawings show a stencil printing machine having a frame 20!, a printing table 282, a feed table 283, a delivery table 2% and a screen frame carrier 2537, which is provided with a screen frame 2&9 and with an inking carriage 2533. All of these parts are of a generally similar construction to the corresponding parts of the machine already described and are operated in an equivalent manner from an electric motor 215. The drive from this motor is taken by means of a belt 2H5 to a reduction gear box 2%? which is provided with one or more output shafts for driving the various parts of the machine at the required speeds and in correct synchronism with each other.

The feed and delivery mechanism of the machine shown in Figures 16 to 25 comprises a feed bar 390 and a delivery bar Sill, which bars are mounted beneath

slots

362 and 303 formed in the side portion 285 of the feed table and in the printing and delivery tables as shown in Figure 17. Ihe feed bar 330 is slidably mounted in a guide-way or trough 354, while the delivery bar, which is of T-section, is mounted on rollers 395.

The feed bar 368 is formed with teeth along its under side and meshes with a feed drive pinion 385. The delivery bar 35;! is toothed along its upper edge and meshes with the under side of a similar delivery drive pinion 3 3?, which pinion is similar to and is rigidly connected with the pinion 336. The unit which includes these two pinions is rotatably mounted on a drive shaft 3%, which shaft is mounted in suitable bearings beneath the printing table 2ii2. The drive from this shaft to the pinion unit is transmitted through a slipping clutch 3% which acts as a lost motion connection. It thus permits the shaft 388 to continue to rotate after the rotation of the pinion unit has been arrested by the engagement of the feed bar 386 against one or other of its limit stops (not shown) As in the case of the shaft oi the previous construction, the shaft 308 must be rotated through a number of revolutions, first in one direction and then in the other. In order that this movement may be harmonic in character, a drive is provided for the shaft 303 comprising a reciprocating member and a speed multiplying gear which fulfil the functions of the bell crank 45 and the speed multiplying gear of Figures 1 and 2.

The drive accordingly includes a crank disc 3H mounted on the end of a main driving shaft which projects from the casing 2!! and which is continuously rotated by the reduction gear therein at a suitable speed. This crank disc set is provided with a crank pin ti! on which is mounted a slide block 312. This block 3E2 is a sliding fit in a horizontal slot 3H3 formed in a slide plate 3 l The plate 3 i d is slidably mounted between vertical guides 3E5. It will thus be seen that roation of the crank disc 3H3 will cause the slide plate 314'; to reciprocate with a sinusoidal or harmonic motion.

The slide plate 3M is connected by means of a connecting link 318 with an arm 3!? which is rigidly secured to the hub of a gear wheel 3%. This gear wheel is freely rotatable on the shaft 388 within a casing 3E9, this casing also being rotatable on the shaft 368. The casing SIB is provided with an extension element 320 which is connected with the slide plate Bit by means of a connecting link 32! similar to the link 3E5. It will thus be seen that as the slide plate 3 i l moves upwardly the gear wheel BIS is rotated in one direction about the shaft 3%, while the casing M9 is rotated in the opposite direction about this same shaft.

The casing SIS carries a countershaft 322 on which are rigidly mounted a pinion i323 and a gear wheel 325. The pinion 323 meshes with the gear wheel 3|8, while the gear Wheel 32 3 meshes with a further pinion 325 which is rigidly secured to the shaft 393. The arrangement is such that when the pinion M3 is rotated in one direction and the casing SIB is rotated in the opposite direction, as a result of the movement of the slide M4, the rotations of these parts are added together as well as being multiplied by the gears 3H3, 323, 32s and 325, with the result that the shaft 383 is rotated through the necessary amount to cause the feed and delivery bars 3% and 3635 to carry out the required strokes.

The feed bar 300 is provided with a single gripping element 336 the construction of which is best shown in Figures 19 to 23. This gripping element, which is housed in a recess 33! formed in the feed bar, comprises a radial arm 332 from which an arcuate tongue 333 extends. The shape of this tongue is such that when the gripping element is rotated to the position shown in Figure 19 the tongue 3-33 emerges through a hole 334 in the top of the feed bar so that its end bears down on a rubber insert 335 provided in the upper surface of the feed bar. The sheet which is to be fed to the printing table is clamped between the end of the tongue 333 and this insert.

The gripping element 338 is biased away from a central dead-centre position towards either its operative position (shown in Figure 19) or its retracted position (shown in Figure 20) by the action of a spring-urged plate 336. This plate 336 is mounted on the upper ends of pins 33'? which engage slidably in holes formed through the bottom of the feed bar. Compression springs 33B press the plate 336 upwardly and this plate, by engaging a roller 339 provided on the gripping element 330, urges the latter into one or other of its positions as shown in Figures 19 and 20.

The gripping element 331! is operated with a snap action by means of a slotted operating member S te which is pivotably mounted on the pin 34! which also supports the element 339.

This operating arm 349 is formed with an arcuate slot 342 in which a pin 343 on the element are engages. At its outer end the arm 3% is provided with a pin 344 which projects through an arcuate slot formed in the side of the feed bar.

The delivery bar 38!, the outer end portion of which is extended upwardly as shown at 35c, is provided with a gripping element 35!, the con struction and operation of which are similar to those of the feed gripping element 330.

The

gripping elements

330 and 35! may be operated by any suitable mechanism when the feed and delivery bars are at the limits of their travel. Thus small operating levers may be provided positions to engage the pin 34 of the feed gripping element and the corresponding pin of the delivery gripping element when the feed and de livery bars are at the ends of their strokes. levers may be operated from the gear box 23'? by means of cams or other suitable means.

For positioning the sheet on the feed table the correct position for it to be engaged by the gripping element 33%, a side register bar 3% is provided along the side of the feed table and front register stop 365 is provided at the front of the feed table close to the feed bar slot. The side register bar 360 is fixed but the front register stop 355 is retractable in order that the sheet may pass over it when being fed to the printing table.

The front stop 365 may consist of a vertically slidable rod which normally remains with its upper end flush with the top of the table, but which is raised into its operative position at the appropriate time by means of suitable mech anism. Thus it may be operated by means of a cam provided on the delivery bar 3m.

Since the sheet is only held at one corner while it is being fed to the printing table it is necessary that a side guide should be provided along the side of the printing table, in line with the side register element 360, in order to ensure that the sheet does not twist about the point where'it is held by the gripping element. Furthermore, if printing is to be effected up to the edge of the sheet, this side guide must be retractable in order to allow the screen to descend on to the sheet.

One form of retractable side guide is shown at 36L This consists of a plate which is pivotably mounted adjacent its lower edge by means of hinged pins 352 and which is urged into its upper operative position, as shown in Figure 24, by means of a spring 363. The guide 35! is provided with a laterally-inclined arm 36 which is adapted to be engaged by a part of the screen frame 209 when the latter descends. In this way the guide 35! is automatically depressed shown in Figure 25) when the screen comes down on to the paper.

The stops which are provided for arresting the movement of the feed bar at the ends of its travel are not shown in the drawings but they may be similar to those provided for the feed troiley 20 of the previous construction.

The sequence of operations of the machine 15 shown in Figures 16 and 25 corresponds substantially to that which has been described in connection with the machine of Figures 1 to 15 and it will be clearly understood from the foregoing description.

It may be mentioned that various parts of the machine shown in Figures 1 to .5 can be terchanged with the corresponding parts of the machine shown in Figures 16 to 25. Thus the speed multiplying gear of the first machine be incorporated in the second machine and vice versa, while the same is true of mechanisms used for driving these gears.

A point which may be mentioned here, in connection particularly with the construction of Figures 1 to 15, is that the axis about which the screen frame carrier '1 hinges is arranged to be a short distance above the surface of the prin ing table. The result of this is that when the screen frame is pivoted upwardly away from the table the screen and the printed sheet adhering to it tend to move very slightly away from. the delivery clamping plate. This action assists in the peeling of the sheet away from the surface of the screen, which starts immediately the screen begins to lift. Subsequently the rapid rise of the portions of the screen furthest from the hinge. and nearest to the delivery clamp, serves to pull the sheet rapidly away from the screen, the two surfaces forming an appreciable angle with each other during this peeling operation.

Furthermore, as has been stated, the delivery trolley may commence its movement away from the printing table before the sheet has been fully separated from the screen, since this movement away from the screen, the slope of which latter is continuously increasing, accentuates the peeling action and thus permits of the speed of printing being considerably increased.

I claim:

1. In a printing machine comprising a printing table, printing mechanism for printing on a sheet resting on the table and feed mechanism for feeding the sheet to be printed into position on the table, the improved feed mechanism which comprises a feed table having a front register member and a side register member, against which front and side edges of the sheet can be placed in order to locate the sheet in an accurately determined position on the feed table, and a feed member having at least one gripping memher for the sheet, which feed member movable through a predetermined distance to feed the sheet from the feed table into an accurately registered position on the printing table, and the front register member being retractable from an operative position, in which it is engaged by the sheet on the feed table, into an inoperative position in which it allows the sheet to be fed past on to the printing table, means for reciprocating the feed member comprising a rotary driving shaft, a reciprocable drive member, means connecting the driving shaft to the drive member to reciprocate the latter, a driven shaft opera tively connected to the feed member, a pair of angularly-movable members turnable relatively to the driven shaft, a pair of links connecting the drive member with the respective angularly movable members so that the drive member rotates the angularly-movable members simultaneously and in opposite directions about the driven shaft and gearing connecting one of the singularly-movable members with the other angularly-movable member and with the driven shaft to convert the angular movements of the 16' said angularly-movable members into added and amplified movements of the driven shaft.

2. A printing machine as claimed in claim 1, characterised in that said drive member is a pivoted bell crank lever having its arms directed on opposite sides of the driving shaft and in that the said mechanism connecting the driving shaft with the bell crank lever includes a pair of cams mounted on said driving shaft, a first cam follower mounted on one of the arms of said bell crank lever and engaging one of said cams and a second cam follower mounted on the other of the arms the bell crank lever and engaging the other of said cams.

3. A printing machine as claimed in claim 1, characterised in that the mechanism connecting the driving member to the drive member in-- cludes a crank pin mounted on the driving member and engaging in a slot formed in the drive member.

4. A printing machine as claimed in claim 1, characterised in that one of said angularly-movable members is a planet carrier carrying at least one planet wheel which meshes with a set of teeth on the other of said angularly movable members, said driven shaft also having a toothed wheel mounted thereon meshing with said driven shaft.

5. A printing machine as claimed in claim 1, characterised in that one of the angularly-movable members is a planet carrier carrying at least one planet wheel which meshes with a set of internal teeth on the other angularly-movable member and with a sun wheel mounted on the driven shaft concentrically within the said internal teeth.

6. A printing machine as claimed in claim 1, characterised in that one of the angularly-movable members is a planet carrier, a set of operatively-coupled planet wheels on said planet carrier, the other angularly-movable member.

having a toothed gear meshing with said planet wheels, a gear wheel mounted on said driven shaft, said last named gear wheel meshing with another of said planet wheels.

7. In a printing machine comprising a printing table, printing mechanism for printing on a sheet resting on the table and feed mechanism for feeding the sheet to be printed into position on the table, the improved feed mechanism which comprises a feed table having a front register member and a side register member, against which front and side edges of the sheet can be placed in order to locate the sheet in an accurately determined position on the feed table, and a feed member having at least one gripping member for the sheet, which feed member is movable through a predetermined distance to feed the sheet from the feed table into an accurately registered position on the printing table, and the front register member being retractable from an operative position, in which it is engaged by the sheet on the feed table, into an inoperative position in which it allows the sheet to be fed past it on to the printing table, a

sheet delivery mechanism for removing the printed sheet from the printing table, said sheet deiivery mechanism comprising a delivery table located adjacent the printing table at the end thereof remote from the feed table, a delivery member having a clamping element adapted to grip a sheet on the printing table, said delivery member being adapted to remove the printed sheet from the printing table to the delivery table, means for operating the sheet delivery member and the feed member from the same driven shaft, said driver shaft being so synchronised with the operation of the feed member that the delivery member makes a delivery stroke when the feed member is making a return stroke towards the feed table.

8. A printing machine as claimed in claim 7, characterised, in that the feed and delivery members comprise trolleys which are operated by feed and delivery sprocket chains respectively, said chains passing around drive sprockets mounted on the driven shaft.

9. A printing machine as claimed in claim 7, characterised in that the feed and delivery mem-- bers comprise rack bars which are engaged and driven by gear wheels mounted on the driven shaft.

10. In a printing machine comprising a printing table, printing mechanism for printing on a sheet resting on the table and feed mechanism for feeding the sheet to be printed into position on the table, the improved feed mechanism which comprises a feed table having a front register member and a side register member, against which front and side edges of the sheet can be placed in order to locate the sheet in an accurately determined position on the feed table, and a feed member having at least one gripping member for the sheet, which feed member is movable through a predetermined distance to feed the sheet from the feed table into an accurately registered position on the printing table, and the front register member being retractable from an operative position, in which it is engaged by the sheet on the feed table, into an inoperative position in which it allows the sheet to be fed past it on to the printing table, said feed member comprising a side plate mounted parallel to the direction of movement thereof, brake parts at each end of said side plate, and cooperating brake parts mounted on the machine adjacent the limits of movement of the feed member.

11. A printing machine as claimed in claim 10, characterised in that the said brake parts comprise resilient catch elements adapted to prevent the said feed member from rebounding therefrom.

12. In a printing machine comprising a printing table, printing mechanism for printing on a sheet resting on the table and feed mechanism for feeding the sheet to be printed into position on the table, the improved feed mechanism which comprises a feed table having a front register member and a side register member, against which front and side edges of the sheet can be placed in order to locate the sheet in an accurately determined position on the feed table, and a feed member having at least one gripping member for the sheet, which feed member is movable through a predetermined distance to feed the sheet from the feed table into an accurately registered position on the printing table, and the front register member being retractable from an operative position, in which it is engaged by the sheet on the feed table, into an inoperative position in which it allows the sheet to be fed past it on to the printing table, means for automatically retracting each of said gripping members into a position below the level of the 18 feed and printing tables as the sheet is positioned on said printing table.

13. A printing machine as claimed in claim 12, characterised in that each gripping member is spring-loaded into its operative position and means for actuating each gripping member, said actuating mechanism comprises a first actuating member mounted on the feed member for retracting the gripping member against the spring force, a second actuating member mounted on the machine in a position to be engaged by the first actuating member when the feed member reaches the end of its feed stroke, and means for operating the second actuating member to cause the first actuating member to retract the gripping member or members, a locking member carried by the feed member for retaining the gripping member or members retracted after the disengagement of the first actuating member from the second actuating member and means for releasing the locking member to release the gripping members when the feed member reaches the end of its return stroke.

14. The device as set forth in claim 12 comprising, in combination a stencil screen frame carrier carrying an inking carriage, said frame carrier being movable towards and away from the printing table and means for moving the front register member into its operative position comprising a member which is engaged by the screen frame when the latter is moved towards its printing position on the printing table.

15. A printing machine as claimed in claim 12 comprising in addition a plurality of stops adapted to be engaged by the feed member to arrest the movement thereof and to define accurately the limits of its travel, and a mechanism for reciprocating the feed member, which mechanism includes a lost motion coupling comprising a driving member, a driven member and a resilient connection between the said members, whereby said coupling absorbs any further movement of the driving member after the movement of the driven member has been arrested by the engagement of the feed member against one of the stops.

16. A printing machine as claimed in claim 12, the additional structure comprising a stop to arrest the movement of said feed member, a mechanism for reciprocating the feed member, said mechanism including a slipping clutch comprising a driving member and a driven member, said driven member being frictionally coupled to the driving member so as to permit of further movement of the driving member after the movement of the driven member has been arrested by the engagement of the feed member of said stop.

References Cited in the file Of thi patent UNITED STATES PATENTS Number Name Date 1,46,379 Bornschein Feb. 20, 1923 1,470,588 Kirkland Oct. 9, 1923 1,743,158 Morse Jan. 14, 1930 1,811,618 Dudley June 23, 1931 1,922,710 Owens Aug. 15, 1933 2,510,559 Daly June 6, 1950