GB2264106A

GB2264106A - Regulating tension in a running web.

Info

Publication number: GB2264106A
Application number: GB9303021A
Authority: GB
Inventors: Milan Andjelic; Jens Punner; E C H Will Gmbh
Original assignee: ECH Will GmbH and Co
Current assignee: ECH Will GmbH and Co
Priority date: 1992-02-15
Filing date: 1993-02-15
Publication date: 1993-08-18
Also published as: ITMI930145A1; GB9303021D0; DE4204550A1; IT1263987B; JPH061503A; ITMI930145A0

Description

2264106 1 - 11 -:IEBTHOD OF ATIND APPARATUS FOlft REGULATING THE TENSIONAL

STRESS UPON A RUNNING 0B The invention relates to t-he processing of webs o'-F paper, nvetal, plastic and/or other sheet materials. More particularly, the invention relates to improvements in methods of and in apparatus for regulating the tensional stresses upon running webs. Still more particularly, the invention relates to improvements in methods of and in apparatus for regulating the tensional stresses upon webs which are drawn from a source of supply, such as a roll of convoluted web, and are being advanced to a subdividing, imprinting, stitching, stapling, perforating and/or other treating or processing station.

As a rule, or at least in many instances, a web of paper, metallic foil, plastic foil and/or other sheet material is advanced from a source of supply to a treating or processing station by pulling it through a magazine wherein the web is trained over idler pulleys and/or driven pulleys. The actual advancing action is carried out by driven rolls which are installed at the treating or processing station and draw or pull the web from the source (e.g., off a roll of convoluted web), through the aforementioned magazine and toward and into the treating or processing station. It is of ten desirable, and in many instances hecessary, that the tensional stress upon t-he. running web remain at least substantially constant, especially if the web is relatively thin and/or its tensile strength is low, or relatively low, for any other reason. For example, a paper web which is produced with a view to satisfy various rules and regulations adopted for ecological reasons is highly likely to exhibit a relatively low tensile strength. In other words, it is desirable and advantageous to select the optimal tensional stress upon a running web of paper or the like and to thereupon maintain the selected tanslonal stress t1ncha-_nrj-:.-_,d or at Itaasl' subs-'Clantially unchanged.

2_ it is already known to equip machines which are - or process webs of paper or the like with used to treat suitable means for regulating the tensional stress uDon a running web with a view to ensure that the tensional stress will be changed as soon as it departs from a preseleclCed optimal value. Presently known regulating devices and apparatus operate satisfactorily as long as the tensional stress fluctuates within a relatively narrow range and as long as the departure above or below a selected optimal tensional stress is gradual. However, the situation is entirely different if the tensional stress upon a running web is changed abruptly and to a considerable extent, for example, when the tensional stress is abruptly reduced to zero due to a failure of the web pulling device or devices at the treating or processing station and/or for any other reasons. As a rule, the inertia of heretofore known means for regulating the tensional stress upon a running web of paper or the like is too pronounced to permit instantaneous reaction in the event of an abrupt and pronounced change of tensional stress. For example, if the means for regulating the tensional stress includes the aforediscussed pulleys in a magazine which defines a portion of or the entire path for a web between the source and the treating or processing station, one or more pulleys are movable toward and away f rom the other pulleys to thus alter the length of the path with attendant changes of tensional stress upon the running web. The movable pulley or pulleys are located beneath the other pulleys and are disposed in the bights of loops which are def ined by the web because the web is alternatingly trained over stationary and vertically movable pulleys. If the tensional stress upon the web is abruptly reduced, the size or sizes of the loop or loops increase practically instantaneously but the inertia of the vertically movable pulley or pulleys is --oc high to ensure that the vertically movable pulley or pi-ileys will remain in contact with and 1 11 S 3.

will tension the respective loop or loops of the web solely under the action of gravity. The means for ascertaining variations of tensional stress upon the running web normally includes one or more devices which monitor the changes of the level of the vertically movable pulley or pulleys, i.e., which monitor the fluctuations of the distance between the stationary and vertically movable pulleys.

4.

One feature of the present invention resides in the provision for a method of regulating the tensioning of a web which can consist of paper, metallic or plastic foil or other sheet material and is advanced in a predeternined direction along an elongated path from a source of supply to a processing station. The improved method comprises the steps of normally applying to the web a pulling force to advance the web along the elongated path and to impart to the web a f irst tensional stress, abruptly reducing the pulling force with attendant abrupt reduction of tensional stress upon the advancing web, and exerting upon the advancing web a second tensional stress which at least approximates the first tensional stress.

The exerting step can include varying the length of the elongated path. The path is preferably defined, at least in part, by a set of pulleys including a plurality of f irst pulleys and at least one second pulley which is movable toward and away from the f ir-st pulleys. The web is alternatingly trained over the f irst and second pulleys, and the step of varying the length of the elongated path includes moving the at least one second pulley relative to the first pulleys.

The web is advanced from a source of supply preferably including a roll of convoluted web, and the method preferably further comprises the step of braking the roll in the course of the exerting step.

The step of abruptly reducing the pulling force normally or invariably entails a pronounced first change of the tensional stress, and the method can further comprise the steps of randomly varying the pulling force within a range which entails less pronounced second changes of the tensional stress, and continuously compensating for the less p-ronounced second changes of tensional stress so that, in the absence of the step of abruptly reducing the pulling i -i 5.

f orce, the first -14--ensional stress remains at least substantially unchanged. The compensating step can include moving the at least one second pulley with reference to the first pulleys, and the exerting step preferably includes moving the at least one second pulley away from the first pulleys. The web f orms at least one loop having a bight which receives the at least one second pulley. The step of abruptly reducing the pulling force entails an enlargement of the at least one loop and the tendency of the bight to become disengaged from the at least one second pulley. The aforementioned moving step preferably includes maintaining the, at least one second pulley in at least substantially uninterrupted contact with the bight of the at least one loop.

The applying step is carried out in a f irst portion of the elongated path, and the exerting step is carried out in a second portion of the path upstream of the first portion. The second portion of the path can have a meandering shape so that the web is looped during advancement along such second portion of the path.

The method can further comprise the step of opposing the advancement of the web through the second portion and toward the first portion of the path with a force which varies as a function of variations of the pulling force. This step can be carried out by braking the roll of convoluted web with a variable force which Ls abruptly increased in response to each abrupt reduction of the pulling force and which is increased or reduced in dependency on variations of the pulling force in normal operation, i.e. , not when the pulling force is abruptly reduced at the first portion of the elongated path.

Another feature of the invention resides in the provision of an apparatus for regulating the tensioning of a web of paper and/or other material. The improved apparatus comprises means for advancing the web from a 6.

source in a predetermined direction along an elongated path including a device serving as a means for normally applying to the web a f irst pulling f orce to impart to the web a f irst tensional stress and further including means for abruptly reducing the first pulling force at randomly occurring intervals (or not at all in the absence of any need f or an abrupt reduction of the f irst pulling f orce) with attendant reduction of tensional stress upon the advancing web, and means f or exerting upon the advancing web a second pulling f orce in response to each abrupt reduction of the first pulling force to impart to the web a second tensional stress which at least approximates the first tensional stress. The apparatus preferably further comprises guide means which defines at least a portion.of the elongated Dath; such guide means preferably includes a portion forming part of the means for exerting the second pulling force. Still further, the improved apparatus preferably comprises means for monitoring the tensional stress upon the advancing web and for operating the means for exerting the second pulling force in response to abrupt reduction of the first pulling force.

The guide means can comprise a magazine having preferably stationary first pulleys and at least one second pulley which constitutes the aforementioned portion of the guide means, i.e., an element of the means for exerting the second pulling force. The web is alternatingly trained over the first and second pulleys, and the means for exerting the second pulling force further comprises means (e.g., a reciprocable carriage) for moving the at least one second pulley away from the first pulleys to thereby lengthen the path of the advancing web.

The first pulleys are normally disposed at a first level and the at least one second pulley is normally disposed at a second level, as a rule below ithe- first 1. is alternatingly trained level. The advancing web whic.1 over the first and second pulleys includes a loop having a bight for the at least one second pulley. The aforementioned carriage or other suitable moving -means is then operable to move the at least one second pulley away from the first pulleys (downwardly) in response Ito each abrupt reduction of the first pulling force.

The means for exerting the second pulling force is preferably adjustable, and the monitoring means preferably includes means for adjusting the means for exerting the second pulling force so as to vary the second tensional stress.

The aforementioned device can include means for subdividing, perforating, folding, slitting and/or otherwise manipulating or processing the advancing web.

The at least one second pulley is movable relative to the first pulleys not only in response to an abrupt reduction of the first pulling force but also in response to variations of the first pulling force other than (i.e., in addition to) abrupt reductions of the first pulling force.

The means for exerting the second pulling force can include a f luidoperated motor and means for connecting a movable part of the motor with the aforementioned portion -of the guide means, for example through the carriage for the at least one second pulley. The operating means preferably includes means for effecting a movement of the af orementioned part of the motor in a direction to move the at least one second pulley away from the first pulleys in response to each abrupt reduction of the first pulling force. The motor can include a cylinder and piston unit, can constitute the piston of such and the -movable part unit. The motor can also constitute or comprise a compressed-gas motor, particularly a motor which is operated by compressed air.

The operating means of the improved apparatus can include an emergency actuator (e.g., a switch, particularly an electric switch) for the means for exerting the second pulling force. Such operating means can further comprise a nornally disengaged coupling or clutch which is installed between the at least one second pulley and the remaining parts of the means for exerting the second pulling force, and means for engaging the clutch or coupling in response to a signal from the actuator.

The means for abruptly reducing the first pulling force can include an emergency switch which is actuatable (e.g., by hand) to initiate an abrupt reduction of the first pulling force and to actuate the operating means.

As already mentioned above, the apparatus can also comprise means for compensating for minor variations or fluctuations of the first pulling force which is normally applied to the web by the afore-mentioned device.

If the source includes at least one roll of convoluted web, the apparatus can further comprise means for applying to the at least one roll braking force which varies as a function of variations of tensional stress upon the advancing web. The means for applying variable braking force can include means for maintaining the tensional stress upon the advancing web at a substantially constant value or within a selected range of values. Such means, for applying variable braking force preferably includes means for abruptly increasing the braking force upon the at least one roll in response to any and each abrupt reduction of the first pulling force.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved apparatus itself, however, both as to its construction and the mode of manipulating the sane, together with additional features -dvan'La,-:;es thereof, will be best understood upon perusa' of the following detailed description of certain

51 1 9.

presently Preferred specific embodiments with reference -to the accompanying drawings.

10.

FIG. 1 is a schematic elevational view of an apparatus which embodies one form of the invention and employs a cylinder and piston unit as a part of means for exerting upon the advancing web a second tensional stress when the first pulling force is abruptly reduced; and FIG. 2 is a schematic elevational view of a portion of a modified apparatus wherein the means for exerting a second tensional stress includes a compressedgas motor.

11.

FIG. I shows an apparatus wherein a flexible web 4 of paper and/or other suitable material is transported from a source of supply 1 to a treating or processing station accommodating a processing device 6 having a pair of driven advancing rolls 5 or other suitable means for drawing the web off a roll 3. The source 1 further includes a bearing 2 for the core of the roll 3, and the path for the web 4 between the roll 3 and the processing device 6 is defined, at least in part, by a guide 7 which constitutes a magazine and defines a meandering portion of the path. The illustrated guide 7 includes three stationary idler pulleys or rollers 8 and two vertically movable idler pulleys or rollers 9 extending into the bights of loops 11 forming part of the web 4. The directions in which the mobile pulleys 9 are movable toward and away from the stationary pulleys 8 (to thereby shorten or lengthen the path between the roll 3 and the device 6) are indicated by a double-headed arrow 13.

The means for moving the pulleys 9 relative to the pulleys 8 (or to be moved by the pulleys 9) includes a carriage 14 which is movable up and down along upright posts 12. In normal operation of the improved apparatus, the carriage 14 rises and falls with the pulleys 9, depending on minor or relatively minor fluctuations of tensional stress upon the running web 4. If the stress slackens, the pulleys 9 descend; the pulleys 9 rise if the stress upon the web increases. The advancing rolls 5 and/or other suitable advancing means of the device 6 are designed to normally exert upon the web 4 a constant (first) pulling force which entails the application of a predetermined tensional stress. Such stress is selected in dependency on the ability of the web 4 to resist breaking or tearing dur-ing movement along the path extending from t -he device 6.

-he roll 3 to t 12.

The. carriage 14 is attached to a portion of a belt or chain 16 (hereinafter called chain) which is L-rained over pulleys or sprocket wheels 17, 18. The shaft for the lower sprocket wheel 18 is connected with a first gear 19---matingwith a second gear 22 which is coaxial with disc cam 21. The periphery of the cam 21 is tracked by follower 26 on a first arm of a two-armed lever 24 which is fulcrumed at 23. The second arm of the lever 24 is coupled to a piston rod 271 forming part of a brake regulating device further including a cylinder 28 having a chamber containing a supply of pressurized fluid. The chamber is connected to an adjustable brake 31 for the roll 3 by a conduit 29.

As already mentioned above, the carriage 14 follows the movements of the mobile pulleys 9 in response to departure of tensional stress upon the running web 4 from a predetermined value. This entails a movement of the chain 16 whereby the lower sprocket wheel 18 turns the gear 19 which, in turn, changes the angular position of the gear 22 and cam 21. The latter pivots the lever 24 by way of the follower 26, and the lever causes the cylinder 28 to actuate the brake 31, i.e., to increase or reduce the braking force upon the roll 3 for the purpose of maintaining the tensional stress upon the running web 4 at least close to a preselected value.

In accordance with a feature of the invention, the apparatus of FIG. 1 further comprises an adjustable unit or assembly 32 (hereinafter called unit for short) which is designed to exert upon the web 4 a second pulling force (other than that normally applied by the advancing rolls 5 of the device 6) in order to rapidly compensate f or any abrupt and appreciable reduction of the pulling force normally exer4Ced by the device 6. The unit 32 includes a fluid-operated moto-l- 33 in the form of a so-called band cylinder having a piston 38 but no piston rod. Such motors 13.

are available on the market and are distributed, for example, by Robert Bosch GmbH, Stuttgart, Federal Republic Germany. As shown in FIG. 1, the piston 38 in the cylinder of the motor 33 is connected with both ends of a band 36 which is trained over pulleys 39. That reach or stretch of the band 36 which is located outside of the cylinder of the motor 33 is connected with a holder 37 for a motion transmitting rod 34 coupling the belt 36 to the chain 16.

The lower chamber 51 of the cylinder forming part of the motor 33 is free to communicate with the atmosphere. The upper chamber 49 of this cylinder can receive a pressurized fluid from a source 43 through a pressure regulating or adjusting element 42 and a regulatable valve 41. The valve 41 can be actuated by a servomotor 44 which receives signals from the control circuit 46 for the web treating or processing device 6. The control circuit 46 comprises or is combined with an emergency actuator 47, such as an electric switch, which can be actuated to abruptly reduce the pulling force of the device 6 (e.g., to arrest the device 6 and its advancing rolls 5) when the need arises. The parts 41-44 and 46-47 together constitute a monitoring system 48 which monitors the tensional stress upon the web 4 and adjusts the unit 32 when necessary for the purpose of counteracting a pronounced reduction of tensional stress upon the web when the roll 3 continues to pay out the web due to its inertia while the advancing rolls 5 oil the device 6 cease to pull the web in the direction of arrow A.

The operation of the apparatus of FIG. 1 is as -1"01lows:

The advancing rolls 5 of the device 6are normally driven to pull the web 4 in the direction of arrow A, i. e, the web is drawn of f the roll 3 and advances al' ong the in part meendering path which is defined pullc:ys 8, 9 of the guide 7. The web 4 is alternat-:.,c.-.,.L-.,, trained 14.

over the pulleys 8 and 9 so that it f orms the aforementioned loops 11, and the bight of each of these loops normally contacts the adjacent portion of 'the respective pulley 9. Mhen the pulling force upon the web is constant and the roll 3 offers a constant resistance to unwinding, the web 4 is subjected to a selected optimum tensional stress which is sufficiently low to avoid tearing in normal operation of the improved apparatus. At such time, the distance of the mobile pulleys 9 from the stationary pulleys 8 is constant.

If the pull upon the web 4 changes, the pulleys 9 move toward or away from the stationary pulleys 8, depending upon whether the pull increases or decreases. Thus, the pulleys 9 move in one of the directions indicated by the double-headed arrow 13. If the pulleys 9 rise in response to an increasing tensional stress upon the web 4, the carriage 14 rises with the pulleys 9 whereby the carriage transmits motion to the chain 16 which turns the lower sprocket wheel 18 in a counterclockwise direction. The gears 19 and 22 cooperate to turn the cam 21 in a clockwise direction whereby the lever 24 pulls the piston rod 27 in a direction to the left and the pressure in the conduit 29 decreases. The brake 31 then reduces the force which opposes rotation of the roll 3 in a direction to pay out the web 4, i.e., the tensional stress upon the web 4 decreases and the pulleys 9 descend to remain in contact with the bights of the respective loops 11. The carriage 14 descends with the pulleys 9 and causes the chain 16, the sprocket wheel 19, the gears 19, 22, the cam 21, the follower 26, the lever 24 and the brake regulating device including the parts 27-29 to adjust the brake 31 so that the roll 3 begins to offer greater resistance to rotation and the tensional stress upon the web 4 increases to -the.normal or oDti'mal value. The situation is analogous when the tensional stress upon -the web 4 increases so that the 15.

carriage 14 rises with the pulleys 9; the brake -) 1 1Chen initially reduces the resistance to rotation Of the roll 3 and such resIstance increases again when the carriage 114 descends. In this manner, relatively small fluctuations of tensional stress upon the web 4 are automatically compensated f or by the pulleys 9 (which can be said to form part of the unit 32) in cooperation with the carriage 14, chain 16, cam and follower means 21, 26, lever 24, brake regulating device 27-29 and brake 31.

If the tensional stress upon the web 4 is abruptly reduced to a considerable extent (e.g., to zero), the tensional stress is automatically and immediately increased by the unit 32. Abrupt reduction of tensional stress upon the web 4 can take place in response to f ailure of the device 6 or in response to automatic stoppage of the device 6 as a result of actuation of the emergency switch 47. Stoppage of the device 6 and of its advancing rolls 5 initially entails a complete collapse of tensional stress upon the web 4. Thus, the inertia of the roll 3 suffices to prevent immediate stoppage of such roll when the rolls 5 of the device 6 abruptly cease to pull the web 4 in the direction of arrow A. The pulleys 8 also continue to rotate due to inertia so that the length of the loops 11 increases.within an interval of time which is too short to ensure that the pulleys 9 will continue to contact the bights of the respective loops 11 without the exertion of a force which serves to abruptly lower the pulleys 9 so that they remain in contact (or immediately return into contact) with the bights of the respective loops 11. In other words, the ability of the pulleys 9 and carriage 14 to descend by gravity and to thus maintain the pulleys 9 in contact with the bights of the respective loops 11 will normally suffice when the changes of tensional stress upon the web t are aradual; however, such abi-lit-y of the pulleys 01 and carriage 14 cannot prevent diseagagement of 16- loops 11 from the respective pulleys 9 T--Then the tensional stress upon the web 4 is abruptly reduced to a considerable extent, such as all 'he way to zero. Tn the absence of the unit 32 and monitoring system 48, it could Itake a certain period of time before the pulleys 9 would descend by gravity to reengage the bights of the respective loops 11 subsequent to an abrupt and pronounced reduction of tensional stress upon the web. The combined weight of the pulleys 9 and carriage 14 would suffice to damage (particularly tear or break) the web 4 in response to abrupt gravitational descent of pulleys 9 into contact with the respective loops 11 following an abrupt drop of tensional stress to zero or close to zero. As a rule, a paper web which has been produced with a view to satisfy the regulations of environmental protection agencies does not exhibit a pronounced resistance to tearing stresses so that such paper web would be likely to break or tear under the above outlined circumstances.

The unit 32 automatically ensures that the tensional stress upon the web 4 remains at least substantially constant (even if the device 6 is arrested by the switch 48 or comes to an abrupt halt f or any other reason so that its advancing rolls 5 cease to pull the web in the direction of arrow A) in the following way: Let ilt be assumed that an operator has decided to actuate the emergency switch 47 which has caused the control circuit 47 to abruptly arrest the device 6 and its advancing rolls 5. The control circuit 46 transmits a signal to the servomotor 44 which changes the setting of the valve 41. The valve 41 -s a pressurized fluid to flow from the source 43 then permit and into the upper chamber 49 of the cylinder forming partof the motor -13 at a pressure which is determined by the setting of the regulator 42. The source 43 can contain a suDDlY of oressurized gaseous fluid, such as ai-r- Since the lower chamber 51 of the cylinder of the mot'-or 33 is k.

17- free to communicate with the atmosphere, the piston 38 is free to rapidly descend at a speed which is determined by the selected pressure of fluid flowing from the source 43 into the chamber 49. The descending piston 38 causes the belt 36 to lift the coupling member 34 so that the chain 16 is caused to abruptly lower the carriage 14 and the pulleys 9. The regulator 42 can be actuated to select the pressure of fluid flowing from the source 43 into the chamber 49, and hence the speed of downward movement of the carriage 14, in such a way that the pulleys 9 remain in contact with the bights of the respective loops 11 even when the switch 47 is actuated to abruptly arrest the device 6 and its advancing rolls 5. Thus, the pulleys 9 apply to the web 4 a second pulling force which at least substantially compensates for (i.e., replaces) the pulling force of the device 6. In other words, the tensional stress upon the running web 4 remains at least substantially unchanged because the regulator 42 can ensure that the second pulling force which is applied by the output element (pulleys 9) of the unit 32 closely approximates or matches the pulling force of advancing rolls 5 forming part of the device 6 as well as that the second pulling force is applied practically simultaneously with cessation of application of the first-pulling force by the device 6.

In order to even further reduce the likelihood of prolonged interruption of the application of a required pulling force and to immediately ensure that the web remains subjected to a practically uninterrupted optimal tensional stress, the abruptly descending carriage 14 causes the chain 16, the sprocket wheel 18 and the gears 19, 22 to turn the cam 21 with the result that the braking action upon the roll 3 is abruRtly increased so that the the web 4.

roll 3 increases its resistance to unwinding a-f Suc'-rl -res ilstance, coupled with 'the lengthening of the path for the web 4 by the rapidly descending pulleys 9, even 18.

further reduces the likelihood of prolonged reduction of tensional stress upon the web 4 below the optimum value. it has been found that this holds true even if the device 6 is abruptly arrested by the emergency switch 47 or comes to an abrupt halt du e to failure or for any other reason which warrants activation of the unit 32 by the monitoring arrangement 48. When the device 6 is restarted, its rolls 5 begin to pull the web 4 with

the prescribed force. This causes an increase of tensional stress upon the web 4 because the roll 3 continues to be braked in a manner as required when the device 6 is idle. The web 4 then lifts the pulleys 9 and the carriage 14, and such lifting takes place simultaneously with outflow of pressurized fluid from the chamber 49 via valve 41. The reason is that, when the device 6 is restarted, the control circuit 46 actuates the servomotor 44 which resets the valve 41 so that the latter connects the chamber 49 with the atmosphere. The piston 38 then offers minimal resistance to abrupt lifting by the carriage 14 (the carriage then transmits motion via chain 16, coupling member 34 and belt 36) which is being lifted by the web 4 as a result of increased tensional stress upon the web while the brake 31 is still applied in a manner as required when the device 6 is idle. The ascending carriage 14 causes the chain 16 to turn the sprocket wheel 18 in a direction to reduce the braking f orce upon the roll 3 via gears 19, 22, cam 21, follower 26, lever 24 and brake operating means 27-29. This causes the operation of the apparatus to return to normal and any minor fluctuations of tensional stress upon the running web 4 are thereupon compensated for by the pulleys 9 in cooperation with the brake 31.

The reference character 56 denotes a compression spring which serves to resist, with a progressively -che increasing force, cer-tain stages of upward movement of 19.

carriage 14 and pulleys 9, namely tliose stages which would L.ake place in response to excessive tensional stressing of the web 4. The upper portion of the spring 56 is located in the path of downward movement of the coupling member 34 (-'this member moves downwardly in response to upward movement of the carriage 14), i.e., the member 34 encounters a progressively increasing resistance to further downward movement when the spring 56 begins to store energy, and the downward movement of 'the coupling member 34 (and hence the upward movement of the carriage 14 and pulleys 9) is terminated when the stressed spring 56 stops the member 34.

FIG. 2 shows a portion of a modified apparatus wherein all such parts which are identical with or clearly analogous to corresponding parts of the apparatus of FIG. 1 are denoted by similar reference characters. The main difference between the two apparatus is that the motor 33 of the unit 32 shown in FIG. 1 is replaced with a compressed-gas motor 52 having a movable part (shaft 52a) which drives a transmission having an endless belt or chain 53 for a pulley or sprocket wheel 54 on the shaft of the lower sprocket wheel 18. The motor 52 is started'to set 4- in motion and to abruptly lower the carriage the chain 16 14 (not shown in FIG. 2) as soon as the emergency switch 47 actuates the control system 46 for the device 6. At such time, the control system 46 starts the servo 44 which resets the valve 41 so that the latter opens a path f or the flow of a preferably gaseous fluid (such as compressed air) from the source 43 to the motor 52 at a pressure which is determined by the setting of the regulator 42. 'The output element 52a of the motor 52 then abruptly starts the chain 16 which abruptly lowers the carriage 14 and the pulleys 9 for the same purpose as described in connection with the operatiLon of the unit 32 shown in FIG, 1. A clutch 60 is installed het-ween the pulley or sproc'p-e:: wheel. 54 and t1nee 20.

sprocket wheel 18 to nor-mally interrupt the power flow between the motor 52 and the sprocket w1rieel 18, This ensures thLt the pulleys 9 can move up and down in response to relatively small and gradual changes of tensional stress u-oon the web 4, i.e., that the chain 16 need not transmit motion to the transmission including the endless belt or chain 53 and the pulley or sprocket wheel 54 when the pulling force which is being applied by the advancing rolls 5 of the device 6 fluctuates within a rather narrow range such as can be eliminated by the brake 31 alone. The arrow 61 indicates an operative connection which is established between the control system 46 and the clutch 60 so that the clutch is engaged in automatic response to stoppage of the device 6, e.g., by the emergency switch 47.

The feature that the carriage 14 need not transmit motion to the transmission including the belt or chain 53 and to the motor 52 when the device 6 is operative to pull the web 4 with a prescribed force or with a force at least approximating the prescribed force brings about the advantage that the unit 32 of FIG. 2 is more sensitive and can even more rapidly and more accurately respond to abrupt changes of first pulling force which is normally applied by the device 6. On the other hand, the servo 44 reacts in-immediate response to stoppage of the device 6, e.g., in response to actuation of the switch 47, to start the motor 52 by resetting the valve 41 so that the motor 52 immediately begins to move the carriage J,A and the pulleys 9 in a downward direction in order to maintain the pulleys 9 in uninterrupted contact with the bights of the respective loops 11. Thus, the carriage 14 and the chain 16 control the brake 31 (and hence the tensional stress upon the running web 4) when the device 6 is on, and the motor 52 lowers the carriage 14 and the pulleys 9 when the device 6 is arrested.

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->3, Without further analysis, the foregoing will so fully reveal the gist of the present invention that others Eor can, by applying current knowledge, readily adapt it f various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic and specific aspects of our contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the appended claims.

2 't.

Claims

CLAI'LIS:

1. A method of regulating the tensioning oz a web -v',',-,-ch is advanced in a predetermined direction along an elongated path from a source of supply to a processing station, comprising the steps of normally applying to the web a f irst pulling force to advance the web along said path and to impart to the web a first tensional stress; abruptly reducing the f irst pulling force with attendant reduction of the tensional stress -upon the advancing web; and exerting upon the advancing web a second pulling force to impart to the web a second tensional stress at least approximating the f irst tensional stress.

1 L 'S 2. The method of claim 1, wherein said exert-!r,,j step includes varying the length of said path.

3. The method of claim 2 of regulating the tensioning of a web which is advanced along an elongated path defined at least in part by a set of pulleys including a plurality of first pulleys and at least one second pulley movable toward and away from the first pulleys, wherein said step of varying the length of said path includes movinj the at least one second pulley relative to the first pulleys.

4. The method of claim 1 of regulating the tensioning of a web which is advanced from a source including a roll of convoluted web, further comprising the step of braking the roll in the course of said exerting step.

7-16 5. The method of claiin 1,.,ibere-in said step of abruptly reducing the first pulling force entails a pronounced f irst change of the tensional stress upon the web, and further comprising the steps of randomly varying the first pulling force within a range which entails less pronounced second changes of the tensional stress, and continuously compensating f or the less pronounced second changes so that, in the absence of said step of abruptly reducinq the f irst pulling f orce, the f irst tensional str'ess remains at least substantially unchanged.

6. The method of claim 5 of regulating the tensioning of a web in -- a path which is defined at least'in part by a set of pulleys including a plurality of first pulleys and at least one second pulley movable toward and away from the first pulleys, said compensating step including moving the at least one second pulley with reference to the first pulleys and said exerting step including moving the at least one second pulley away from the first pulleys.

1 2---7 7. The nethod of clalim 6 of regulating the tensioning of a web which is alternatingly trained over -the first and second pulleys and for,-is at least one loop having a bight receiving the at least one second pulley, wherein said step of abruptly reducing the first pulling ILorce entails an enlargement of the at least one loop and the tendency of the bight to become disengaged from the at least one second pulley, said moving step including maintaining the at least one second pulley in at least substantially uninterrupted contact with the bight.

8. The method of claim 1, wherein said applying step is carried out in a f irst portion of said path and said exerting step is carried out in a second portion of said path upstream of said first portion.

2-5 9. The inathod of claim 'S, where-in- the second portion of said path has a meandering shape and the web is looped during advancement along said second portion of said path.

10. The method of claim 1, further comprising the steps of opposing the advancement of the web from the source with a force which varies as a function of variations of the first pulling force.

t 1 11. Apparatus for regulating the tensioning of a web, comprising means for advancing the web from a source in a predetermined direction along an elongated path including a device for normally applying -to the web a first pulling force to impart to the web a first tensional stress, said device including means for abruptly reducing the first pulling force at random intervals with attendant reduction of the tensional stress upon the advancing web; and means for exerting upon the advancing web a second pulling force in response to abrupt reduction of the first pulling force to impart to the web a second tensional stress at least approximating the first tensional s-tress.

-> 0 12. The apparatus of claim 11, further comprising guide means defining at- least a portion of sa--d elongated path, said guide means including a portion forming part of said means for exerting said second pulling force.

13. The apparatus of claim 12, further comprising means for monitoring the tensional stress upon the advancing web and for operating said means for exerting said second pulling force in response to abrupt reduction of the first pulling force.

3 14. The apparatus of claim 13, wherein said guide means comprises first pulleys and at least one seconCIL pulley constituting said -portion of said guide means, the web being alternalLingly trained over said first and second pulleys and said means for exerting said second pullIng force further comprising means for -moving said at least one second pulley away from said first pulleys.

15. The apparatus of claim 14, wherein said first pulleys are stationary and said moving -means comprises means for moving said at least one second pulley toward and away from said first pulleys.

D,- 16. The apparatus of clai--,-.i 13, wherein said guide ineans comprises a magazine including first pulleys disposed at a first level and at least one second pulley disposed at a second level and constituting said portion of said means for exerting said second pulling force, the web being alternatingly trained over said first and second pulleys and including a loop having a bight for said at least one second pulley, said means for exerting said second pulling force further comprising means for moving said at least one second pulley away from said first pulleys in response to said abrupt reduction of the first pulling force.

17. The apparatus of claim 13, wherein said means for exerting said second pulling force is adjustable and said monitoring means comprises means for adjusting said means for exerting said second pulling force so as to vary said second tensional stress.

33 18. The a-z),.,aratus of claim 13, wherein said device includes neans Ear. processing the web.

19. The apparatus of claim 13, wherein said guide means includes first pulleys and at least one second pulley movable toward and away from said first pulleys in response to variations of said first pulling force in addition to abrupt reductions of such first pulling force, the web being alternatingly trained over said first and second pulleys.

20. The apparatus of claim 19, wherein said at least one second pulley constitutes said portion of said guide means.

) 1 '.:) -1 21. The apparatus Df claim 13, wherein said means for exerting said second pulling force includes a fluid-oDerated motor and means for connecting a movable part of said motor with said portion of said guide means.

22. The apparatus of claim 21, wherein said guide means comprises a plurality of first pulleys and at least one second pulley constituting said portion of said guide means, the web being alternatingly trained over said first and second pulleys and said second pulley being movable toward "and away from said first pulleys to compensate for variations of said first pulling force in addition to abrupt reductions of such first pulling force, said operating means including means for effecting a movement of said part of said motor in a direction to move said at least one second pulley away from said first pulleys in response to abrupt reduction of the first pulling force.

1 -) 'I 23. The apparatus of claim 22, whereln said motor includes a cylinder and piston unit and said novable park'- includes said piston.

24. The apparatus of claim 22, wherein said motor is a compressedgas motor.

25. The apparatus of claim 13, wherein said operating means includes an emergency actuator for said means for exerting said second pulling force.

3(.0 26. The apparatus of claim 25, said act-uator includes a switch.

27. The apparatus of clain 25, wherein said operating means further comprises a normally disengaged clutch between said portion of said guide means and said means for exerting said second pulling force, and means for engaging said clutch in response to a signal fron, said actuator.

28. The apparatus of claim 13, wherein said means for abruptly reducing comprises an emergency switch which is actuatable to initiate an abrupt reduction of said first pulling force and to actuate said operating means.

D 29. C The apparatus O.L claim 12, further comprising neans for compensating for minor variations of first pulling force which is normally applied to the web by said device.

30. The apparatus of claim 11, wherein said source includes a roll of convoluted web and further comprising means for applying to said roll a variable braking force as a function of variations of tensional stress upon the web.

31. The apparatus of claim 30, wherein said means for applying said variable braking force includes means for maintaining the tensional stress upon the web at a substantially constant value.

32. The apparatus of claim 30, wherein said means for applying said variable braking force includes means for abruptly increasing the braking force upon the roll in response to each abrupt reduction of the first pulling force.

33. A -inethod of regulating the tension of a web, substantially as herein described with reference to the accompanying drawings.

34. Apparatus for regulating the tensioning of a web, substantially as herein described with reference to the accompanying drawings.