US2066415A - Web regulating mechanism - Google Patents

Description

Jan. 5, 1937. M. J. MILMOE WEB REGULATING MECHANISM Filed June 9, 1953v s Sheets-Sheet 1 RELAY IE VVENT0R :EIE- 3 I BY T 7% A TTORNEYS.

Jan. 5, 1937. M. J. MILMOE 2,066,415

WEB REGULA'I'ING, MECHANISM Filed June 9, 193:5 s Sheets-SheetE T :51 ATTORNEYS.

Jan. 5, 1937. M. J. MILMOE WEB REGULATING MECHANISM Filed June 9, 1935 I5 Sheets-Sheet 3 INVENTOR. WM 97% By W 071 ATTORNEYS.

Patented Jan. 5, 1937 2,066,415 WEB REGULATING MECHANISM Michael J. Milmoe, Glen Ellyn, Ill., assignor to F. B. Redington 00., Chicago, 111., a corporation of Illinois Application June 9, 1933, Serial No. 675,037

16 Claims.

The present invention relates to feeding mechanism for webs such as are used in packaging machines and which are generally cut into strips of predetermined length to form wrappers for packages. Usually such webs have printed matter thereon for indicating the contents of the package or the like and means must be provided for cutting the web into strips at predetermined points along the web between the various sections of printed matter so that the printed matter bears a certain relation to the article wrapped when the strip is cut and wrapped about the article.

Since it is very difiicult to provide a feeding means which will at all times feed the exact amount of 'web in timed relation to the rest of the wrapping mechanism and particularly the cut-oil knives, and due to the stretching of the web, slippage, etc., it is necessary to provide some means which cooperates to adjust the feed auto matically so that at all times the proper feeding of the web will take place and the web will be cut at the desired points. In high speed wrapping machines, it is almost impossible to regulate manually the position of the web and furthermore even if it were possible to adjust the same manually, it is extremely difiicult for the operator to tell when an adjustment is necessary.

Accordingly the present invention has for its object, the provision of means for adjusting the feed for the web in such a manner that the web is always out at predetermined points with respect to the printed matter thereon within certain small limits. The limits can be changed as desired.

The basic principle upon which my invention operates is the feeding of the web at a speed which varies from the actual desired feed for the web so as to insure a definite variation in one direction from that desired. As the feed of the web continues, the total variation becomes greater. In other words, the variation causes an accumulation of errors which finally results in a total variation which should not be exceeded.

At this point, an adjusting means operated by the web itself comes into operation and corrects for the variation and the accumulation of errors again begins.

More specifically my invention contemplates what is commonly known as an electric eye which is a lightsensitive cell which responds to variations in light intensities which it receives, the variation of the intensity of light received by 5 the cell actuating a corrective device which in the present instance is a variable drive which varies a definite amount on each actuation.

Another object of this invention resides in the provision of a drive to a web which drives the web at a greater rate of speed than would be 5 theoretically desired or necessary. Therefore there'is introduced into the web feed an error which accumulates which would soon cause an over feed which would position the printed matter improperly with respect to the cutting knives, 10 and the error would in time become so great that the web would be cut through the printed matter so that a part of the printed matter intended for one wrapper would appear on two wrappers. Therefore when the over feed becomes too great, 5 the driving mechanism for the web is changed preferably a definite amount to retard the feed temporarily and correct for the accumulated error. Thiscorrection is only introduced when the total error exceeds a certain amount so that if there is a slippage of the feeding mechanism with reference to the web which reduces the normal intended over feed for 'the web, the correcting mechanism does not come into operation. desired feed Whether it be in one foot of travel of the web or 100 feet of travel of the web, the correcting mechanism becomes operative and introduces a lag in the feeding mechanism in such a manner that the total error is reduced within 30 the permitted limits of tolerance.

Another object of this invention is to provide means whereby variationsin the feed of a web are automatically controlled by an electric eye'or similar device. 35

Another object of this invention resides in providing a device which is operative on opaque materials as well as on transparent materials.

Another object of this invention is to provide means whereby delicate webs of material are fed 0 along a predetermined path and any error in their feed compensated for without putting a strain on the material itself by holding it back positively against the feeding means which tends to pull the same forward. 5

Other objects of this invention will appear hereinafter as the description thereof proceeds, the novel features, arrangements and combinations being clearly set forth in the specification and claims appended hereto.

In the drawings:

Fig. 1 is a front elevation of a device embodying my invention with parts broken away for the sake of clearness;

. Fig. 2 is a detail view of the pawl and ratchet Whenever the total error exceeds the 25 mechanism for introducing a correction into the drive to the web, the same being shown in rear elevation;

Fig. 3'is a view similar to Fig. 2 showing the parts in diflerent positions of adjustment;

Fig. 4 is a plan view of the mechanism shown in Fig. 1;

Fig. 5 is a cross-section taken substantially along the line 55 of Fig. 1;

' Figs. 6 and 'l'show diflerent positions for the web shown in Fig. 5;

Fig. 8 is a cross-section taken substantially along the line 9-4 oi Fig. 1;

Fig. 9 is a section taken substantially along the line 9-9 of Fig. 1;

Fig. 10 is a plan view of the mechanism shown in Fig. 2; 1

Fig. 11 shows the schematic wiring diagram for operating the correcting mechanism; and

Fig. 12 is an enlarged plan view of the timer.

Referring now more particularly to Figs. 1 and 4, the reference character illustrates the base of the machine and on this base there is supported a bracket 2| secured thereto. 22 indicates the web which is to be fed and in the present instance is a piece of transparent material such as cellophane". The reference character 23 indicates the single web of material as it leaves the roll 22 and this is fed over a roll 24 along guides indicated generally at 25 past a casing 29 having a light sensitive cell 21 therein. The casing is provided with an opening 23 in the side of the casing adjacent the web 23. The web is fed downwardly to the feed rolls 29 which are geared together by gears 30 secured to the same shafts as the rolls 29 so that the rolls 29 operate in unison with each other. The material fe'd between the rolls 29 passes between a pair of rollers 3| carrying the cut-off knives 32 which in the present instance are such as to form a serrated edge on the strips 33 which are cut from the web by the knives 32. I have indicated the position at which light passes through the opening 23 to the cell 21 as position A and the position at which the web is cut as B. See also Figs. 5, 6, and "I. The distance between these two positions A and B is fixed.

The webs illustrated in Figs. 5, 6, and 7 are provided respectively with the markings C, C and C Usually there is other printed matter on the web and this is illustrated in the drawings by the letters XYZ, grouped together. It is desired to cut the web midway between adjacent groups oi printed matter on the web, or at predetermined points with respect to these groups of letters or other printed matter appearing on the web. In each of Figs. 5, 6, and 7 I have illustrated the webs at the positions which they occupy at a certain predetermined position of the parts oi the feeding and cut-ofl mechanism. To make the illustration of my invention rather simple, I have indicated the position of the web at the instant the knives 32 cut the web and at the same instant at A there comes into operation, a certain correcting device presently tobe described which will make a correction in the web feed if the feed of the web varies more than a predetermined amount from the desired feed therefor. Actually in operation, the device at A does not come into operation at the same time that the web is cut at B. All that is necessary is that the device at A operate in timed relation to the cut-ofl mechanism at B so that the adjustment will be with respect to the position at which the web is cut.

In Fig. 5, I have illustrated the position of the web at its initial adjustment by the operator. In

this adjustment, the markings C arrive at a position just short oi. the position, A so that they are not within the controlling beam of light which is projected through the film at the position A. In other words, the beam of light is not screened by the marking adjacent the position C. As will appear hereinafter, whenever the light passes uninterruptedly through the transparent web, no correction is introduced in the web feed, but however in the event that a marking such as C! in Fig. 6 arrives at the position A at the instant the correcting device becomes operative, the beam of light is cut oil and as a result, the correction is introduced for the mechanism is such that the correction is introduced whenever the beam of light is cut oil. This actuates the correcting mechanism which retards the feed of the web so that successive markings are justshort of the position A at the instant of operation of the correcting mechanism. such as is illustrated at (Pin Fig. '7. After the correction has been introduced, the rollers 29 which give an over feed to the web, feed the web with a slight over feed until the over feed again brings the markings at the position A at the time the correcting mechanism becomes operative, at which time another correction is introduced.

' I have stated that the correcting mechanism is such that it comes into operation when the beam oi light is cut. However, a difierent type of correcting means which operates on the reverse principle can be used. Thus the entire web can be dark so as to prevent the of the light normally through the web and the markings C, C and C can be transparent portions of the web. The device can also operate on opaque materials and when such materials are used instead of having the light beam projected through the material, the light is reflected oi! the material. The mechanism for actuating the correcting mechanism is illustrated in Fig. 11 and in this figure, the web 23 is indicated in the same position with respect to the position A at the instant of operathm asthewebin Fig.6bearstothepositionA. The reference character 23 in this figure represents the walls of the casing for the photo-electric cell 21. The beam of light projected through the web 23 is created by the source of light 34 and the condenser 35 which concentrates the rays of light on the photo-electric cell 21 through the web 23. If a portion of these light rays are screened as by the markings C thereon, the amount of light (alling on the photo-electric cell 21 is diminished and as a result a relay of any well known type such as indicated at 33 becomes operative to actuate the correcting mechanism.

The relay 33 may be of the type illustrated in Patent No. 1,273,627, granted July 23, 1918, to Irving Langmuir and includes a reversing switch for causing the same to operate when the photoelectric cell is shielded from the rays of light or when the rays are directed thereagainst as may be desired.

The photo-electric cell is connected to the relay by the leads 31. The power lines are indicated at 39 and lead into the relay 39. There also are leads 39 to the source of light 34. A separate timing circuit is connected to the relay and this circuit includes the leads 49, timer ll oscillating in timed relation to the movements of the feeding mechanism about the axis 42, and a solenoid 43 which is adapted to actuate the rod 44 in a vertical direction whenever the solenoid becomes operative. The relay is adapted to close the circuit within the relay by the ends or theleads ll and the timer 4| also closes the remaining break in the circuit at the opposite ends of the leads 40. Fig. 11 illustrates the position of the parts at the instant of closing of the timer 4|, the same being inoperative at all other times, and therefore it is impossible except when the timer is in the position shown in Fig. 11 to operate the solenoid 43. However, one more condition must be present before the solenoid will become operative and that condition is that the relay 36 must be closed to complete the circuit through the leads 40, timer 4| and solenoid 43. Normally, as already explained, the photo-electric cell will not operate the relay when it is receiving a suflicient amount of light, but when the amount of light is dimin ished, the relay becomes operative. Therefore, if the marking C appears opposite the position A when the timer 4| is closed, the light to the photoelectric cell 21 is diminished and the relay becomes operative. Since the timer 4| is also closed, the solenoid is operated and the rod 44 is moved vertically and actuates the means which introduces the correction into the feed.

If, however, the marking C does not appear at the position A when the timer is closed, the result is that the relay remains open and the solenoid will not become operative.

The feed rolls and timer shaft 60 both derive their movement from the same source of power as do also the knives 32 so that these parts are all operated in unison with each other. The source of light 34 is always operative to throw a beam of light toward the web. The main drive shaft is indicated at 45 and is connected by a chain 36 to a jack shaft 41 to drive the same. A chain 58 trained over a sprocket on the shaft 45 and a similar sprocket on the shaft 50 shown in Fig. 8 is used to drive the rolls 3| which carry the knives 32. fThe shaft 50 has the axis thereof co-incidental with the axis of the roll 3| carrying the cut-oh knife 32 shown at the right in Fig. 1.

The roll 3-|-shown at the left is rotated by means of the gears 5| meshing with each other and mounted on the shafts which carry the rolls 3|. See particularly Fig. 4.

The roll 29 at the left in Fig. 1 is positively driven by the chain 52 from a sprocket secured to the rear end of the shaft which carries one of the rolls 29 as is best illustrated in Fig. 8. The rolls as previously described have inter-meshing gears 30 which cause them to rotate in opposite directions to feed the. web. The chain 52 is trained over a sprocket 53 on the shaft 54 which shaft also carries a gear 55 which meshes with the gear 55 on the shaft 47 driven by the chain #16 from the main drive shaft 45. The gear 55 is not directly connected to the shaft 54 but is normally connected thereto by a pawl and ratchet mechanism which later will be described. When the position of the gear 55 with respect to the shaft 54 is altered by altering the adjustment of said pawl and ratchet mechanism, the drive to the feed rolls 29 will be changed to introduce the correction. The pawl and ratchet mechanism is so arranged that when the pawl is disconnected from the ratchet, the gear 55 continues to be actuated but the shaft 54 lags and moves relatively to the gear 55. A corresponding lag occurs in the rolls 29, the feed being continued immediately when the pawl again engages the ratchet. The main drive shaft is actuated in any suitable manner as by a belt trained over the pulley 51 secured rigidly to the shaft 45.

The shaft 41 carries a bevel gear 58 meshing with a similar bevel gear 59 on a vertically arranged shaft 60 which shaft forms a part of the timing mechanism as is more clearly illustrated in Fig. 12. In this figure, it will be noted that the shaft 60 is provided on one side thereof with a flat spot 6|. A fixed contact 62 and pivoted contact 4| are mounted on the boss 64 surrounding the shaft 60. A spring 65 normally urges the pivoted contact member 4| toward the contact member 62. Normally the shaft 60 holds the contacts out of engagement with each other but when the shaft 60 rotates to a position to bring the fiat spot 6| thereof opposite the follower 66 on the contact 4|, the contact 4| will move toward the contact 62 and close the gap therebetween completing the electrical circuit through the relay 36 and leads 40 in the manner previously described. As previously brought out, the correcting mechanism cannot be operated unless the contact member 4| is in engagement with the contact member 62. The pawl and ratchet mech-,

anism previously referred to to correct excessive over-feed of the web and the means for actuating said pawl and ratchet mechanism are best illustrated in Figs. 1, 2, 3, 8, and 9.

In Figs. 8 and 9, it will be noted that the gear 55 is secured to a sleeve 63 and the sleeve 63 also has a disk 61 secured thereto. Pivoted to the disk 61 are a pair of pawls 68 and 69 which are normally urged against the ratchet 10 secured to the shaft 54 by means 5 of the springs H and 12 respectively. It will be noted that normally the pawl 68 operatively engages the face of a tooth on the ratchet but the pawl 69 does not, the same being spaced somewhat from the operative face of an adjacent pawl 68 remains in engagement with the ratchet but whenever there is an excessive over feed, the same is moved out of engagement with the ratchet to introduce the aforesaid correction. In order to move the pawl 68 out of engagement with the ratchet, I provide a lever 13 pivoted at 14 to a bracket 15 mounted on the frame 20 and one end of this lever 13 is provided with an extension 16 which is normally in inoperative position as illustrated by dotted lines in Fig. 8. In this position, the same cannot move the pawl out of engagement with the ratchet. However, when the Q solenoid 43 is actuated to move the rod 45 upwardly to the position shown in Fig. 8, the rod 44 through the intermediacy oi the link 11 rocks the lever 13 into the full line position shown in Fig. 8. This results in the movement of the extension '16 into the path of movement of the cam 18 integral with the pawl 68. A similar cam 19 is integral with the pawl 69. The cam 18 riding over the extension 16 raises the pawl out of engagement with the ratchet and the disk 61 and ratchet 10 thereafter have a relative angular movement until the pawl 69 engages the operative face of the tooth on the ratchet. Means which will presently be described is provided for holding the extension 16 in operative position until the cam 79 on pawl 69 engages the extension 16 and is moved out of of engagement with the ratchet in the same manner as the pawl 68. By this time, however, the cam 18 on pawl 68 has passed the extension 18 and is free to move into engagement with the .ratchet. It is desired, however, to have the pawl 88 in position to engage the ratchet before the pawl 88 is moved out of ensuement therewith and for this purpose, I provide the rigid guide 88 which has a cam surface 8| for engaging the cams 18 and 18 on the pawls 88 and 88 respectively. When the cam 18 reaches the portion 88 of the cam 8i, this portion of the cam forces the pawl positively toward the. ratchet and insures that the pawl will be in a position to engage a tooth on said ratchet before the pawl 88 is released. The releasing of the pawl 88 permits the ratchet to lag again until the pawl 88 engages a tooth. After the pawl 88 is again operative, the extension 18 can be, and is released. During the rotation of the disk 81, the pawls 88 and 88 are positively held against movement away from the ratchet, except at their uppermost position illustrated in Fig. 2, and one pawl is always under the guide 88. This insures that there will always be a driving connection between the ratchet and disk. If the machine should be stopped suddenly the ratchet cannot overrun because the pawls cannot, while beneath guide 88, move away from the ratchet a distance suilicient to permit the ratchet to advance. Similarly if and when the operator backs of! the machine, the reversal of the movement of the parts will not cause relative rotation between the pawls and ratchet for the same reason. The result is that the parts always are kept in proper adjustment.

The link 11 is provided with teeth 88 to form a sort of rack bar. A pawl 84 pivoted on a shaft 85 is normally urged toward the link 11 by a spring 88. See Fig. 1. Therefore, if the link 11 is raised by the solenoid 48, the link is held against downward movement by the engagement of .the pawl-84 with the teeth 88 on the link until such time as the pawl 84 is released. In view of the fact that the contacts 88 and 4| are in engagement only for a short interval of time and the actuation of the bar 44 is therefore only for a very short period, it is necessary to provide such a mechanism as has been described for holding the link 11 in raised position for a predetermined time sufficient to enable the extension 18 to operate the pawls 88 and 88 in the manner described. After the pawl 88 has been raised out of engagement with the ratchet, the pawl 84 may be released to permit the link 11 to drop, thereby restoring the lever 18 to its inoperative position. The means for releasing the pawl 84 operates in timed relation with the drive to the shaft 41 and comprises a lever 81 pivoted on the shaft 88 and having a pin 88 extending into a position in front of the pawl 84. See Fig. l. The lower end of the lever 81 is normally urged against the pin 88' by the spring 81'. In order to move the lower end of the lever to the right and thereby release the pawl 84, I provide a pin 88 which engages the lower end 'of the lever 81 at each rotation of the gear 88. Therefore at each revolution of the gears 58, the pawl 84 isreleased and the extension 18 restored to an inoperative position. Rollfirmly in operative position.

In order to shield the photo-electric cell 21 1mm light which may be projected thereon, other than from the source of light 84. I provide a tubular shield 88 secured to the end of an arm 8| pivoted at 88 to the guide 88 or to any fixed support. The center of gravity of the shield 88 is to the left of the pivot 88 and therefore the shield tends to rotate to the right against the web 88 and casing 88. This not only holds the web firmly against the casing 88, but also forms a substantially light-tight housing for the beam of light for an appreciable distance away from the easing. A spring could be used to move the shield against the web if desired, but the pendulous action of the shield 88 acts as a yielding means for pressing the shield against the web and is very simple to construct. Furthermore, it permits the shield to be moved to an inoperative position, very readily in case it is desired to inspect the web when an adjustment of the webis desired. This means for shielding the web is important in view of the fact that if for instance at the time the beam is cut by one of the markings 0. some other source of light outside the machine such as the light of a match which the operator may be using, or of a light bulb may cause a sufficient intensity of light passing through the opening 88 to prevent the operation of the relay 88 by the photo-electric cell 81. The shield 88, however. substantially prevents any light from entering the opening 88 except that light which comes from the source of light 84.

The operation of the device which has been described is as follows: Before the machine is set in motion, the operator sets the web so that'it occupies with respect to the positions A and B, a position such as that shown in Pig. 5. The web is fedbymeansoftherolls88andthesameiscut by the knives 88 to form the strips 88. If the light from the source 84 is passing freely through the web as it would in Fig. 5, the photo-electric cell receives a. sufllcient amountof light to prevent operation of the relay 88. If, however, the over feed accumulates until the markings C arrive at the position A as in Fig. 6, a part of the light is screened from the photo-electric cell 81, and this operates the relay 88. If at the instant of presentation of the marking C opposite the opening 88,- the contacts 88 and 4| are closed, then the solenoid can be energized and the link 11 raised to the position shown in Figs. 1 and 8. The pawl 84 engages the teeth 88 and holds the link 11 upwardly a sufllcient length of time to permit the extension 18 to successively raise the pawls 88 and 88, and thereafter the lever 81 is rocked by the pin 88 to release the pawl 84, and this permits the link 11 to move downwardly by gravity and rock the extension 18 to an inoperative pomtion. The successive movements of the extension 18 out of and into operative position introduces a relative angular displacement between disk 81 and ratchet 18 as previously described, so that the feed for the rolls 88 lags and the markings drop back to a position such as illustrated in Fig. '1, it being understood that the position A not only indicates the position of the light source but also indicates the instant of closing of the contacts 4| and 88, for it is obvious that all of the markings at one time or another are covering the photo-electric cell 81. It is only when the markings screen the light at the instant the contacts 88 and 4| are closed that operation of the correcting mechanism becomes operative.

During the feeding of the web, the shield 88 opening 88 and cut of! the supply of light to the is yieldingly pressed into contact with the web due to its gravitational movement to the right about the pivot 88.

2,oee,415

Obviously those skilled in the art to which this invention pertains may make various changes in the particular arrangement and construction of parts shown in the drawings without departing from the spirit of this invention and therefore I do not wish to be limited except as hereinafter set forth in the appended claims.

Having thus fully described my invention, what I claim as new and desire to obtain by Letters Patent is:

1. A web feeding mechanism for feeding webs having indicia thereon at predetermined points along said web comprising feeding means for feeding said web along a predetermined path, a

rotatable driven element connected to said feeding means, a rotatable driving element rotatable on an axis coincidental with the axis of rotation of said driven element and actuated continuously, a releasable connection between said driving and driven lementfor connecting the same in driving relation witheach other comprising a plurality of pawls on one of said elements, a ratchet on the otherof said elements, means for urging said pawl's into engagement with said ratchet, said pawls being spaced from each other a. distance such that only one of said pawls is in engagement with the operative face of a tooth on said ratchet, means operable when the feed of said web varies more than apredetermined amount from that desired for moving said pawl which is in engagement with the tooth on said ratchet out of engagementvrith said tooth to thereby permit relative movement between said elements until the other of said pawls comes into engagement with a tooth on said ratchet and stops the relative rotation between said elements, whereby the total amountof actuation of said feeding means by said driven element is varied from that whichwould occur if said first pawl was in engagement with said ratchet and remained operative.

2. A device as set forth in claim 5 which mcludes means for releasing said second pawl from its operative engagement with its tooth on said ratchet and also includes means for moving said first pawl toward said ratchet to a position opposed to but not in engagement with the operative face of a-tooth prior to the release of said second pawl, whereby one pawl is always in operative position to engage a tooth on said ratchet to establish a driving connection between said elements.

3. A web feeding mechanism for feeding webs having indicia thereon at predetermined points along said web comprising feeding means for feeding a web along a predetermined path, a rotatable driven element connected to said feeding means for actuating the same, a rotatable driving element for driving said driven element, a

pawl on one of said elements, a ratchet on the other of said elements, detecting means cooperating with the indicia on said web for detecting when said web is being fed a total amount which varies from the desired total amount, means for releasing said pawl from its operative engagement with a tooth on said ratchet and means for thereafter engaging said pawl with said ratchet after a predetermined relative movement between said elements, said releasing means being operatively controlled by said detecting means.

4. A web feeding mechanism for feeding webs having indicia thereon at predetermined points along said web comprising feeding means for feeding a web along a predetermined path, a rotatable driven element connected to said feeding means, a rotatable driving element, a pair of pawls on one of said elements, a ratchet on the other of said elements engaged by said pawls,

said pawls being spaced with respect to said ratchet in such a manner that only one of said pawls can engage the operative face of a tooth thereon to establish driving connection between said elements, the other of said pawls being in a position to engage the operative face of a tooth when said first pawl is released, mechanism for positively preventing movement of said pawls away from the aforesaid operative position ex cept at a predetermined position in their path of movement, means located adjacent said position for moving said pawls successively in the order named away from said ratchet said movement preventing mechanism including a part operable for moving said first pawl into a position to engage a tooth on said ratchet prior to release of said second pawl, and means cooperating with the indicia on said web for actuating said means for moving said pawls successively out of engagement with said ratchet operable upon a variation in the feed of said web beyond predetermined limits, whereby the relative movement between said elements resulting from the release of said pawls and reestablishing of the connection between said first pawl and said ratchet results in a relative rotation between said elements to vary the drive to said feeding means.

5. A web feeding mechanism for feeding webs having indicia thereon comprising feeding means for feeding a web along a predetermined path, a pair of rotatable elements relatively movable with respect to each other, a pair of pawls on one of said elements, a ratchet on the other of said elements in a position to be engaged by said pawls, yielding means for urging said pawls toward 'said' ratchet, a fixed guide for'lengaging means on said pawls to hold them against movement away from said ratchet throughout all but a relatively small portion of their path of travel, means positioned adjacent said portion of said path of travel of said pawls movable when operated into a position to raise said pawls out of engagement with said ratchet successively, the pawls being spaced about said ratchet more than a multiple of. the distance between adjacent teeth, whereby only one pawl is operative at one time, said guide being operable for establishing connection between the first of the pawls moved out of engagement with the ratchet before the other of the pawls is moved out of engagement with the ratchet, and means cooperating with the indicia on said web for operating means which releases said pawls.

6. A web feeding mechanism for feeding webs having indicia thereon comprising feeding means for feeding a web along a predetermined path, a pair of rotatable elements, relatively movable with respect to each other, a pair of pawls on one of said elements, a ratchet on the other of said elements in a position to be engaged by said pawls, yielding means for urging said pawls to ward said ratchet, a fixed guide for engaging means on said pawls to hold them against movement away from said ratchet throughout all but a relatively small portion of their path of travel, means positioned adjacent said portion of said path of travel of said pawls movable when operated into a position to raise said pawls out of engagement with said ratchet successively, the pawls being spaced about said ratchet more than a multiple of the distance between adjacent teeth, whereby only one pawl is operative at one time, said guide being operable for establishing connection between the first of the pawls moved out of engagement with the ratchet before the other of the pawls is moved out of engagement with the ratchet, and means cooperating with the indicia on said web for operating the means which releases said pawls, said means which 00- operates with the indicia on said web comprising anelectric eye cooperating with said indicia and operable when said indicia arrives at a given position at a time which varies from the time the same should arrive at said position more than a predetermined amount. I

7. A device as set forth in claim 10 in which the means for moving the means for releasing said pawls into operative position comprises a solenoid, a rack bar movable in one direction by said solenoid, a pawl cooperating with the teeth on said rack bar for preventing reverse movement of said rack bar after the same has been moved by said solenoid, and means operable to release said pawl to permit movement of said rack bar in a direction opposite to the movement imparted thereto by said solenoid, whereby the means forreleasing said pawls is moved to an inoperative position.

8. A device of the class described comprising a source of light for cooperating with indicia on a web being fed, a photo-electric cell, a casing for said photo-electric cell having an opening adjacent said web, a shield mounted on the side of said web away from said casing, means engaging the shield and yieldingly pressing the shield against said web to hold said web against said casing in proper relation to said opening and prevent a portion of the light from other sources than from said light beam from reaching said photo-electric cell, said shield being pivotally mounted at a point to one side of a vertical plane through the center of gravity thereof in a direction more than a predetermined amount and for releasing said pawl to disconnect the drive to said feeding means, means for thereafter establishing driving connection between said pawl and ratchet after said pawl and ratchet have moved relatively to each other and said pawl is in a position to engage a different tooth on said ratchet, whereby to vary the feed to said web, the pawl being moved into engagement with said ratchet after the feed of said web is adjusted in the direction to more nearly approach the desired feed for the same and being held positively against movement away from said ratchet beyond the ends of the teeth on said ratchet except at selected time's, whereby even movement of said pawl relative to said ratchet in a direction opposite to the normal movement ofsaid pawl toward said ratchet will not enable the pawl to slip over a tooth and as a result upon the reestablishment of the normal movement of the parts, the same tooth on said ratchet will be engaged by said pawl.

10. A web feeding mechanism for feeding webs having indicia thereon comprising feeding means for feeding a web along a predetermined path, a pair of rotatable elements relatively movable with respect to each other, a pair of pawls on one of said elements, a ratchet on the other of said elements in a position to be engaged by said pawls, yielding means for urging said pawls toward said ratchet, a fixed guide for engaging means on said pawls to hold them positively against movement beyond the ends of the teeth on said ratchet throughout all but a relatively small portion of their path of travel, means positioned adjacent said portion of said path of travel of said pawls movable when operated into a position to raise said pawls out of engagement with said ratchet successively, the pawls being spaced about said ratchet more than a multiple of the distance between adiacent teeth; whereby only one pawl is operative at one time, said guide having provisions for establishing connection between the first of the pawls moved out of engagement with the ratchet before the other of the pawls is moved out of engagement with the ratchet, and means cooperating with the indicia on said web for operating the means which releases said pawls, one

of said pawls being acted on by said guide at all times.

11. In a web feeding device, means for feeding a web, said web having indicia thereon, driving means for said feeding means, connections between the driving means and feeding means, means for performing an operation on the web at spaced intervals thereon, means responsive to the relative position of the indicia on the web and the last named means, means acting in timed relationship with said last named means, and means operable when the last two means operate simultaneously for releasing the connections 'between the feeding means and the driving means, and means for re-establishing said connections after a predetermined relative movement between the web feeding means and the driving means.

12. In a web feeding device. means for feeding a web, said web having indicia thereon, driving connections for said feeding means, means for performing an operation on the web with spaced intervals thereon, photo-electric means responsive to the relative pomtion of the indicia on the web and the last named, a timer element making intermittent electrical contact, means operable only when the indicia is at a predetermined position and the timer is in aposition to make electrical contact for releasing the driving connections at a predetermined position of the feeding means, and means for re the connections after a predetermined movement of the feeding means.

13. In a web feeding mechanism, the combination with means forfeeding a web along a predetermined path including a pair of relatively movable elements, of means for releasably establishing a positive driving connection therebetween, means for releasing said last mentioned means to permit relative shifting of said relatively movable elements, sensing means, means operable in timed relationship with the movement of the web, means controlled jointly by said sensing means andby said last named means for operating said releasing means, means for re-establishing said positive driving'connection after said elements have moved relatively to each other a predetermined amount, and means for positively preventing the driving connection from being released except when desired and irrespective of the direction in which said elements have a tendency to move relative to each other.

14. In a device of the class described havin means for feeding a web and means for sensing indicia on the web including a light source and a photo-electric cell, the combination of a shield arranged. in the path of travel of the light and positioned to screen the light rays reaching the cell, said shield being pivotally mounted for movement from inoperative to operative positions about an axis eccentrically disposed with respect to the center of mass of the shield whereby when in operative position said shield will be yieldably urged by gravity into engagement with the web to tension the web and maintain-it in proper position.

15. In a device of the class described having means for feeding a web and means for sensing indicia on the web including a light source and a photo-electric cell, the combination of a shield arranged in the path of travel of the light and positioned to screen the light rays reaching the cell, said shield being eccentrically pivoted relative to its center of mass whereby to be yieldably urged by gravity against the web to tension the web and maintain it in proper position.

16. In a web sensing device, a light source, a photo-electric cell, a shield arranged between the light source and the cell in the path of the light rays, and means for feeding a web between said shield and said cell, said shield being mounted for movement from inoperative to operative positions about an axis eccentrically disposed with respect to the center of mass of the shield whereby when in operative position said shield

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