EP1013585A1

EP1013585A1 - Device for supplying web material

Info

Publication number: EP1013585A1
Application number: EP98830783A
Authority: EP
Inventors: Paolo Pasqualoni
Original assignee: Fameccanica Data SpA
Current assignee: Fameccanica Data SpA
Priority date: 1998-12-24
Filing date: 1998-12-24
Publication date: 2000-06-28

Abstract

The device includes a storage unit (5 to 8) and accommodates a reserve length of the web material (W) to be supplied. A first (17) and second (9) driving means make it possible to selectively control both the speed of the web material at the intake side (2) and the speed with which the stored reserve length of web material (W) is paid out, so that the speed at which the web material (W) is supplied at the output side (3) of the device can be kept constant independently of the fact that the supply of web material (W) to the intake side (2) is either slowed down or brought to a complete halt to permit, for example, the replacement of a roll from which the web material is supplied and/or to splice two lengths of the web material (W). The operation of the driving means (9, 17) is enslaved to a control signal generated by a sensor (19 to 23) that is preferably located at the output side (3) of the device and includes a return means (19) around which there passes a loop of the web material (W) that is being supplied. The control signal is generated as a function of the slackening and the shortening of the said loop in substantial absence of longitudinal tensile stresses applied to the web material (W).

Description

The present invention relates to systems for supplying moving web material in accordance with the preamble of Claim 1 hereinbelow.
A system of this type is known - for example - from US-A 3 995 791. This document describes a system for the continuous supply of moving web material, the system in question consisting, inter alia, of two stations intended to accommodate the rolls from which the web material is to be paid out. The web is taken alternatively from one or the other of the said stations, matters being arranged in such a manner that the expiring end of the web from a dispensing roll in one station is spliced to the beginning of the web from a ready roll carried in the other station, thus avoiding solutions of continuity in the supply (payout) of the web. The system in question includes a web storage device in the form of a so-called web festooner. When web supply is to be switched from one roll-carrying station to the other and the two web ends have to be spliced together, the said web storage device is brought into action in a positive manner by mechanical means in synchrony and in phase with a set of rollers that feed the web material towards the utilization station. The speed at which the web material is paid out on the output side of the system therefore stands in a fixed mechanical relationship with the speed at which the web is utilized, and this makes it possible to bring the motion of the web to a halt upstream of the web storage device, so that the two web sections can be spliced in what are to all intents and purposes conditions of standstill. As soon as the splicing operation has been completed, the system is set in motion again and the web storage device begins to reconstitute a certain web reserve contained in its interior, thus making possible a subsequent roll switching and web splicing operation in exactly the same conditions as have just been described.
More particularly, in the solution described in US-A-3 995 791 matters are arranged in such a way that the web storage device is inserted in a position directly between a web splicer and the unit that feeds the web towards a utilization station situated at the downstream end of the system. The system is controlled as a function of the operating speed of the said unit feeding the downstream station. When it becomes necessary to switch the rolls and splice the web, a signal provided by a sensor unit associated with the dispensing roll that is about to run out triggers the intervention of a cam mechanism that is operated by the shaft of the traction unit moving the web in the downstream station. The said mechanism not only causes a gradual slowdown of the speed with which the web is moved in the splicer (bringing it to a complete standstill), but also brings into action the driving means associated with the web storage unit. This is done in such a manner that, even during the period of time needed to complete the splicing of the web, the supply needs of the utilization station at the downstream end are satisfied by a length of web material taken from the storage device. As soon as the splicing has been completed, the web material in the splicer is gradually re-accelerated, while the driving means of the web storage device are gradually slowed down, these processes being continued until the re-establishment of the normal operating conditions in which the supply needs of the downstream utilization station can be satisfied directly by web material passing through the splicer. Subsequently, the driving means of the web storage device are activated again, but this time in the direction opposite to the previous one, so that the web storage unit can gradually build up a new web reserve.
This solution in accordance with the state of the art is however associated with some basic problems and difficulties.
Firstly, the deceleration/acceleration of the web motion at the splicer, as also the complementary motion of the driving means of the web storage unit, are piloted in a rigid manner via a cam mechanism, so that - for example - it is not readily possible to modify the applied acceleration and deceleration laws to take account of possible variations of the operating parameters (size and moment of inertia of the web rolls, etc.).
Secondly, the fundamental parameter for controlling the operation of the system is the rate (speed) at which the utilization station situated downstream of the web storage device absorbs the web. Both the speed of the web in the splicer and the speed of the driving means of the web storage device are controlled as functions of this absorption rate, though always in the previously described rigid manner.
Another drawback - and one that is extremely penalizing whenever the web material in use is of a delicate nature - is constituted by the fact that the part of the web comprised between the splicer and the unit that feeds the web to the downstream station has to be dragged in a positive manner between these two points and also in the web storage unit. Any instantaneous difference of speed between the various moving parts will therefore inevitably become translated into a longitudinal tensile stress acting on the web.
A solution of the previously described type can therefore prove to be generally satisfactory from the functional point of view only for as long as one is concerned with relatively low web payout speeds at the output side (generally less than 150 m/s) and web materials of relatively good tensile strength characteristics to enable them to withstand the traction forces, polyethylene and nonwoven tissue being two cases in point.
However, the present trend, especially in the sector of the production sanitary and hygienic products (for example, disposable hygienic products as sanitary towels for ladies, nappies and nappy pants babies, and the so-called nappies for enuresis), is to operate with much higher payout speeds (typically of the order of 300 - 500 m/s) even when such relatively fragile materials as cellulose wadding (the so-called "tissues") are involved.
When the operations are carried out at such high speeds and involve relatively fragile materials, it becomes imperative, especially in the transitory phases associated with the switchover of the web supply stations and the subsequent splicing of the two lengths of web material, to avoid the possibility of the materials becoming subjected to stresses. This is particularly true as regards longitudinal tensile stresses, which are liable to compromise the very integrity of the web material.
More generally, there also exists the need of providing devices of the type specified above and having operating characteristics that are either substantially or even completely independent of any equipment situated upstream and/or downstream thereof.
For example, the system described in the previously cited US-A-3 995 791 is intrinsically bound up with the possibility of having to function in combination with a splicer intended to operate in standstill conditions (that is to say, in accordance with what are nowadays known as "zero speed" modalities). The state-of-the-art system as previously described does not therefore constitute a self-contained unit capable of performing its function of supplying web material in a controlled manner, complete with storage capacity, in an autonomous manner. In particular, the said system is de facto designed and realized as a function of the processing stations situated upstream (splicer) and downstream (utilization station) of it. Such a device, conceived to operate with a splicer that works in "zero speed" conditions, cannot be adapted to enable it to function also with a splicing system capable of working in dynamic conditions, i.e. without bringing the web to a standstill, except on the basis of a complete reconfiguration. The previously examined state-of-the-art system does not therefore lend itself to being used for retrofitting operations involving already existing installations.
It is nevertheless very important to have at one's disposal systems or devices that can be combined with any type of web supply and switchover device and therefore offer the possibility of carrying out modernization operations on existing plant with a view to improving the performance of such installations in terms of operating speed.
Yet another need that is being felt to an ever greater extent is that of being able to use as web supply sources also very unstable raw material rolls (i.e. rolls having a very high ratio between the diameter and the width of the material) and rolls of web material having a very high moment of inertia (direct consequence of a large roll diameter or roll weight), at the same time avoiding the roll damage phenomena of the type generally known as "decoring", i.e. the phenomenon arising when the core on which the web material is wrapped becomes removed from the roll in an undesirable manner.
The present invention sets out to provide a device of the type specified hereinabove such as to overcome the drawbacks associated with the state-of-the-art systems and thus to provide a wholly satisfactory answer to the various needs just discussed.
According to the present invention, this scope can be attained by a device for the continuous supply of web materials having the additional characteristics set out in the claims hereinbelow.
The invention will now be described, though solely by way of an example not to be considered as limitative in any manner or wise, by reference to the drawings attached hereto, where:

Figure 1 is a general view in elevation of a device according to the invention,
Figure 2 is a perspective view of the said device, and
Figures 3 to 5 are three diagrammes that illustrate the behaviour of the device in accordance with the invention.

The reference number 1 in the figures and drawings attached hereto indicates the whole of a device capable of being used for supplying web material in a controlled manner and with storage capacity.
The web material, which is indicated by the letter W, may be - inter alia - a web material (sometimes also referred to as "fabric") to be used for the production of sanitary and hygienic products, including those of the previously mentioned type. In particular, the web material W may be constituted by a material such as cellulose wadding ("tissue") that has very limited resistance to mechanical stresses, especially tensile stresses in the longitudinal direction. It is however quite evident that the specific reference to the manufacture of sanitary and hygienic products is not to be interpreted as in any way limiting the scope of the present invention, which has a particularly wide range of possible uses.
In the embodiment example here illustrated - which, be it said once more, is no more than such - the device 1 is essentially configured as a module intended to be inserted between processing stations on its upstream and downstream side in the general context of a plant for the processing and/or handling of web material.
In the example explicitly illustrated by Figure 2 the device 1 may be located on the downstream side of a supply unit made up of a pair of stations intended to carry the respective rolls B1, B2 of web material, the said stations being associated with a splicer S to be used for making the joints between successive lengths of web material, which is taken in alternating sequence from the said two rolls. To all intents and purposes, the arrangement of the said supply unit may be substantially analogous to the one illustrated in US-A-3 995 791, a document already repeatedly referred to hereinabove.
Any type of utilization station employing the web material W may be situated on the downstream side of the device 1. For example, the said station (which is not illustrated here) may employ a typical "in line" process to pair the web material W with other web materials to form a chain of hygienic and sanitary products intended to be separated by means of a subsequent chain segmentation operation, thus giving rise to individual products.
It will nevertheless be appreciated that the characteristics and the nature of the processing stations situated upstream and downstream of the device 1 are not in themselves particularly relevant as far as a proper understanding of the embodiment of the present invention is concerned. In general terms, in fact, the invention aims at realizing a device capable of receiving at its intake side (i.e. the position generically indicated by the reference number 2 on the drawings annexed hereto) a web material W that is being supplied to it at a given input speed. This input speed may be selectively varied, this even to the point of completely zeroing the said speed and thus bringing the incoming supply of the web W temporarily to a standstill. The device 1 seeks to make the web material W available at its output side (i.e. the position generically indicated by the reference number 3 on the drawings annexed hereto) at a speed that within reasonably brief intervals of time (such as those necessary for making a splice between two successive lengths of a web material W) will be substantially independent - and to all intents and purposes wholly independent - of the speed at which the said material is supplied to its intake side. And this while yet making sure that the part of the web material W actually contained within the device 1 will not become subjected to forces capable of producing tensile stresses in the longitudinal direction.
In the embodiment example here illustrated, the device 1 consists of a vertical supporting panel 4 that may be constituted either by a frame or a single member of solid structure, usually realized as steelwork. Fixed to the supporting panel 4, in the solution here illustrated more or less in a central or midway position, there is a solid cage 5 that carries, likewise in a fixed position with respect to the support 4, a first set of rollers 6 (the set consisting of five such rollers in the particular embodiment here illustrated). The rollers 6 are here represented as capable of rotating freely around a horizontal axis.
In the embodiment example here illustrated the cage 5 projects from the supporting panel 4 in a horizontal direction, the general arrangement being that of a bracket (or shelf). Likewise mounted on the said supporting panel 4 there is a series of vertical guide rails 4a on which there is mounted a sliding trolley 7 that in the vertical direction extends to above the cage 5. On the trolley 7, in turn, there is mounted a certain number of rollers 8 (there being four such rollers in the particular embodiment here illustrated), which can once again rotate freely on a horizontal axis and are located above the rollers 6 carried by the cage 5.
As can be seen more readily from the side elevation shown in Figure 1, the rollers 8 are arranged in such a manner that, as seen in plan, each one of them is positioned midway between two of the rollers 6 carried by the cage 5. In particular, it can readily be appreciated in this connection that the number of rollers 8 will always be one less than the number of rollers 6. This makes it possible to arrange matters in such a way that the web material W will follow a general zig-zag course between the rollers 6 and 8 (as can be seen more readily from the perspective view reproduced in Figure 2), thus giving rise to a "festoon" of web material, i.e. a zig-zag section of web wrapped round the rollers 6 and 8 that has a very considerable overall length as compared with the space effectively occupied by the festoon.
The trolley 7 (and therefore also the rollers 8 mounted on it) can move along the guide rails 4a under the action of the driving means 9, which - just like the other driving and sensor organs subsequently to be described herein - are controlled by a central processing unit 10, for example, a so-called PLC (acronym for "Programmable Logic Controller"). The driving means 9, for example, can be an electric motor (of known type and characteristics) that acts via an appropriate reduction gear 11 on an endless screw 12 that engages with a female thread (not shown) provided on the trolley 7.
By appropriately controlling the operation of the driving means 9 (in either one or the other of the possible directions of rotation), the trolley 7 can therefore be selectively lowered or raised (and therefore be brought either closer to the cage 5 or moved further away therefrom), which has the effect of varying the distance that separates the set of rollers 6 mounted on the cage 5 from the set of rollers 8 carried on the trolley 7. The said translatory movement of the trolley 7 thus makes possible a selective variation of the length of the individual branches of the web festoon formed between the rollers 6 and 8 and therefore also the overall length of web material accumulated in the storage unit defined by the rollers 6 and 8.
With a view to clarifying ideas (though, naturally, without this being interpreted as limiting the range of the invention), in the case of the storage unit here illustrated, in which the web festoon consists of eight individual branches, a translatory movement of the trolley 7 of the order of - for example - 1.5 m (or, to be more precise, 1.5625 m) will make it possible to vary the overall length of the stored web material by 1.5625 x 8 = 12.5 m. And this, be it noted, without thereby interfering in any way with the actual mechanism that moves the web W from the intake side 2 to the output side 3. Moreover, it will be readily appreciated that even when the web W at the intake side 2 is brought ideally to a complete standstill, a lowering of the trolley 7 will still ensure that a corresponding length of web material will issue from the output side 3. The rate at which the web is paid out is determined by the translation speed of the trolley 7 and therefore by the speed of rotation of the driving means.
Preferably, the driving means 9 - and therefore also the appropriate control commands - are configured in such a way as to make it possible for the rollers 8 to descend below the level of the rollers 6. Placing the trolley in this position at the moment when the device 1 is initially prepared for operation, the web W can be made to pass horizontally between the rollers 6 and the rollers 8, which in that position will be situated, respectively, just above and just below the web. When the driving means 9 subsequently determine an upward movement of the rollers 8 to rise, this will automatically cause the web to become disposed in the manner of a festoon.
Still referring to the perspective view in elevation reproduced as Figure 2, it will be noted that the web material W enters the device 1 by passing over a series of rollers that are here jointly indicated by the reference number 13. The said series of rollers 13 comprises at least one motor-operated roller 14 over which the web W has to pass before it arrives, passing over one or more deflection rollers (such as the one here indicated by reference number 15), at the intake side of the previously described storage unit.
The roller 14 is operated, once again preferably via an appropriate reduction gear 16, by other driving means 17 substantially similar to the previously described driving means 9 and likewise slave to the control unit 10.
On leaving the storage device 6, 8, the web W passes over one or more deflection rollers 18, which must comprise at least one roller 19 performing the function of a so-called "floating" or "jockey" roller. More particularly, the roller 19 in question is mounted on a lever arm 20 capable of oscillating around a horizontal hinge pin 21 projecting from the supporting panel 4. The oscillating lever arm 20 should preferably be subject to the balancing action of a counterweight or some similar return device here indicated by the reference number 22. The latter should preferably act in the sense of inducing the lever arm 20 to swing in the direction that will cause a slackening of the loop of web material W that passes round the roller 19.
The reference number 23 indicates a position sensor (of a known type, which could be - for example - a linear potentiometer or some similar device) capable of providing the control unit 10 with a finely sensitive feedback signal that will enable the said control unit to detect with considerable accuracy any difference between the speed with which the web material W is fed into the intake side 3 of the device 1 and the speed with which the said web is paid out after leaving the storage unit defined by the rollers 6, 8.
It will therefore be appreciated that in the embodiment example here illustrated:

the supporting panel 4 is on the whole of an elongated shape and carries the first set of transmission means (the rollers 6) in the vicinity of the driving means 17 and the sensor means 19 to 23,
the driving means 9 are situated at the opposite end of the supporting panel 4, and
the second set of transmission means (the rollers 8) is mobile and arranged generically in a position between the first set of transmission means (the rollers 6) and the driving means 9.

The manner in which the device in accordance with the invention operates can be described by supposing the starting condition of the system to be its normal steady operating condition, which in the three diagrammes reproduced as Figures 3 to 5, where the time scale is always indicated on the abscissa, is represented by the condition prevailing immediately prior to the time t₁.
It will also be noted that in the said diagrammes the speed v₁ shown in Figure 3 corresponds to the speed at which the web material W passes over the set of rollers 13 at the intake side 2 of the device 1 and, more particularly, the motor-driven roller 14. In practical terms, this speed is determined by the speed of rotation that the control unit 10 imposes on the driving means 17.
The diagramme reproduced as Figure 4, on the other hand, identifies the operating speed that the said control unit 10 imposes on the driving means 9, i.e. the driving means that move the trolley 7 up and down. More precisely, the speed v₂ shown in Figure 4 represents the speed with which, following operation of the driving means 9, the web W is effectively paid out at the output side 3 of the device when the intake speed v₁ is reduced to zero. In particular, it has here been assumed that immediately prior to the time t₁ the trolley 7 is to be found in a position at some distance from the cage 5 (to be quite clear: in the position indicated schematically by means of broken lines in Figure 1). In practice we here have a condition in which the storage unit defined by the rollers 6 and 8 contains a rather substantial reserve of web material W. Naturally, when the trolley 7 is kept in a fixed position, the driving means 9 are necessarily at a standstill and its speed of rotation is zero (always refer to the part of Figure 4 immediately preceding the time t₁).
Lastly, the diagramme reproduced as Figure 5 represents the speed v_L at which the web material is paid out at the output side 3 of the device 1. The same value of the ordinate is indicated by the chain-dotted line in Figures 3 and 4, thus providing an immediate reference.
In the steady operating conditions just described, the driving means 9 are not running and the speed v_L, at which the web issues from the output side of the device 1 depends solely on the driving means 17. Naturally (and in a manner that is in itself known), the feedback signal provided by the sensor 23 and generated by the so-called "jockey" roller 19 will make it possible to absorb any instantaneous speed fluctuations, since these will become translated into a momentary variation of the position and orientation of the lever arm 20.
In actual practice, whenever the feed rate of the material on the intake side of the device drops accidentally below the speed at which it is paid out on the output side, the roller 19 will rise, the lever arm 20 will rotate (in a clockwise direction as seen when viewing the drawing) and this rotatory movement will be detected by the control unit 10 via the feedback signal it receives from the sensor 23. The control unit 10 will therefore arrange to step up the speed of the driving means 17 by such small amount as may be required to absorb the displacement just described. A complementary but functionally analogous operating sequence will take place whenever there occurs a momentary deflection in the other direction (i.e. whenever the web feed rate on the intake side exceeds the speed at which the material issues from the output side).
Put in other words, the described feedback mechanism aims at compensating accidental differences between the input speed and the output speed, this in the sense of seeking to keep the lever arm 20 always pointing in the same direction.
Let us now suppose that on account of some specific event (for example, because the two rolls furnishing the web material have to be switched at the upstream station and the two separate web lengths have therefore to be spliced while they are standing still or moving at practically zero speed) the speed v₁ at which the web material is fed to the intake side of the device has to be reduced, possibly to the point where it will momentarily be equal to zero. With this end in view, the control unit 10 will impose a gradual slowdown of the speed of the driving means 17, causing this speed to diminish very gradually, preferably in the manner of a flat ramp, until it attains a minimum value (virtually equal to zero) at the instant of time indicated by t₂.
In order to avoid this slowdown of the feed rate having repercussions on the payout to the downstream station, the control unit 10 immediately activates the driving means 9 and thus causes the trolley 7 to move downwards and come closer to the cage 5. The result of this movement is a gradual reduction of the length of web contained in the storage device. This becomes necessarily translated into the stored web being paid out to the output side 3 at a speed v₂, which can be selectively controlled (in a known manner, via the geometry of the storage unit 6, 8) by the control unit 10 and in accordance with a ramp pattern that is the exact counterpart (complement) of the ramp pattern in accordance with which the feed rate on the intake side is being reduced.
The process just described is therefore such as to assure that the relationship v1 + v2 = vL is always complied with.
More particularly, this is as true for the interval of time between t₁ and t₂ in which the driving means 17 are slowed down and the driving means 9 correspondingly accelerated as it is for the interval of time between t₂ and t₃ when the driving means 17 are maintained at a constant (and possibly zero) speed while the feed of web material W to the downstream station is de facto assured to a very substantial (and possibly complete) extent by the gradual reduction of the length of web stored between the rollers 6 and the rollers 8.
This operating mode is continued for the entire period of time in which the feed of web material to the intake side of the device has to be minimized or completely suspended (for example, to permit the two lengths of web material to be spliced in standstill or substantial standstill conditions), that is to say, until the instant of time indicated by t₃. At that moment of time (following a signal sent to the control unit 10, for example, by the splicer S, along a line generically indicated in Figure 1 by L), the control unit 10 will act on the two driving means 9 and 17 in accordance with the complementary modalities described hereinabove and schematically illustrated in Figures 3 and 4 for the time intervals between t₃ and t₄. The speed v₁ at which web material is fed to the device (driving means 17) will thus be gradually increased, so that it will be gradually brought up to its normal operating value (which de facto corresponds to v_L), while the speed at which the trolley 7 is lowered will be gradually and complementarily reduced until the trolley 7 (at the time t₄) is brought to a complete standstill in its lowermost position, at which point the driving means 9 are also brought to a halt. The entire operation is performed while complying with the previously cited relationship v₁ + v₂ = v_L.
At this point the system re-establishes the previously described steady operating conditions (as prevailing immediately prior to the time t₁).
The previously described operating cycle can thus be repeated at any time thereafter and whenever the need therefor arises.
Naturally, as soon as the steady operating conditions have been re-established, the control unit 10 again acts on the driving means 9, causing them to rotate (but now in the direction opposite to the one in which it rotated during the phase in which the stored length of web material was paid out to the output side of the device), so that the trolley 7 will now be gradually raised to its uppermost position, shown by the dotted line in Figure 1, which has the effect of creating a new reserve of web material within the storage device.
This operation of reconstituting the reserve can generally be carried out by operating in a gradual manner and therefore at a slow speed, always preserving (just as in all the other operating conditions of the storage device) the possibility of exercising fine control over the web supply rate assured by the supply speed sensor, which (in the embodiment here illustrated) is represented by the so-called "jockey" roller 19 mounted on the lever arm 20 and the various organs associated therewith. Any technician skilled in the art will in any case realize that a wholly analogous feedback function - based on the detection of a slackening or a shortening of a loop of web material W - can also be obtained with equivalent devices (for example, a speed sensor of the encoder type or similar devices).
The above description makes it clear that the various control phases that have just been described - by reference to both the diagrammes reproduced in Figures 3 to 5 and the reconstitution of the reserve of web material W in the storage unit constituted by the rollers 6 and 8 - can be realized by the control unit 10 on the basis of intervention laws that can be selectively varied, especially between one phase and the next.
Furthermore, the device 1 in accordance with the invention is a completely self-contained piece of equipment and can therefore perform its function no matter what type of web handling and/or processing stations may be situated upstream and downstream of it.
In particular, the device in accordance with the invention can be combined with any type of unwinding station and any type of splicer, quite irrespective of whether the latter operates at zero speed or at full speed. As far as splicers of the zero speed type are concerned, the device in accordance with the invention can be used both with tape splicing systems and with splicing systems of the hot wire type. Moreover, the device in accordance with the invention not only completely avoids tensile forces acting on the web W, but also drastically reduces the accelerations to which the various mechanical components of the system are subjected, including the set of parts (rollers 6 and 8 and the elements associated with them) that form the web reserve festoon.
Then located downstream of a web unwinding and splicing system, the device in accordance with the invention can be used to dilate the braking and acceleration times of the web rolls as compared with the corresponding times of the line they serve, and this quite independently of the switchover phase. This may become necessary with unstable rolls of raw material (for example, rolls having a very high ratio between diameter and web width) or rolls having an extremely high moment of inertia.
More particularly, the device in accordance with the invention makes it possible to modulate the deceleration, switchover and acceleration "ramps" to take due account of the various parameters in play. In this connection it should be noted that the straight-line pattern of the acceleration and deceleration ramps shown in Figures 3 and 4 are to be considered as purely exemplifying and can therefore be replaced by any other pattern capable of being used for that purpose (for example, acceleration and deceleration ramps of what is currently known as the "cos²" type).
When the raw material to be handled is of considerable inertia (i.e. rolls of large diameter and/or heavy material), the time of the deceleration ramp used to slow down a dispensing roll about to become exhausted can be cut down, subsequently extending the time of the acceleration ramp of the ready roll inserted to serve as the new source of web material, so that the motors to be installed can be of more limited power and reducing the probability of such harmful phenomena as roll decoring.
When it is desired to use a splicer S with a splicing system of the hot wire type, it becomes more or less imperative to extend the duration of the switchover time (i.e. the time during which the web material W at the intake side of the device 1 remains standing still) to enable the splicer to cool the splicing area.
Furthermore, the device in accordance with the invention is particularly and almost ideally suitable for retrofitting operations on existing installations, i.e. when it is desired to improve the performance of an existing plant without extensive reconfiguration interventions.
Without prejudice to the principle of the invention, of course, the design details and the embodiment forms of the invention can be widely varied as compared with what has here been described and illustrated without in any way going beyond the scope of the invention as defined by the claims attached hereto. In this connection it will readily be appreciated that the roller 19 (hereinabove referred to as "jockey" roller), together with the other elements associated with it, could also be situated upstream of the storage unit constituted by the rollers 6 and 8 and, more precisely, in a position between the roller set 13 inclusive of the motor-driven roller 14 and the said storage unit. This would still preserve the advantage deriving from the fact that the action of detecting the web speed is based on the slackening or the shortening of a loop formed by the web itself in substantial absence of tensile stresses applied to the web material W.

Claims

A device for supplying web material (W), including:

a storage unit (5 to 8) capable of accommodating a reserve length of the web material (W) passing between an intake side (2) and an output side (3) of the device,

first driving means (17) to control the speed of the web material (W) at the said intake side (2),

second driving means (9) acting on the said storage unit (5 to 8) to selectively vary the said reserve length of the web material (W), the variation of the said reserve length of the web material during the supply of this web material (W) producing a variation of the speed of the web material (W) at the said output side (3) even when the speed of the web material (W) at the intake side (2) remains unchanged,

sensor means (19 to 23) capable of detecting the speed of the web material (W) and generating an appropriate control signal, and

control means (10) sensitive to the said signal and capable of acting on the said first (17) and second (9) driving means in such a manner as to maintain the speed of the web material (W) at the said output side at a predetermined level independently of the speed of the web material (W) at the said intake side (2),

characterized in that the said sensor means (19 to 23) are capable of cooperating in a winding relationship with a loop of the said web material (W) and generating the said control signal as a function of the slackening or the shortening of the said loop in substantial absence of tensile stresses applied to the said web material (W).
A device in accordance with Claim 1, characterized in that the said sensor means (19 to 23) are sensitive to the speed of the web material (W) at the said output side (3) and the said control means (10) are configured for selectively controlling the said second driving means (9) as a function of the speed imposed by the said first driving means (17) on the said web material (W) at the said intake side (2).
A device in accordance with Claim 1 or Claim 2, characterized in that the said sensor means include:

a rotating lever arm (20) carrying a return means (19) for the said loop of web material (W), so that both a slackening and a shortening of the said loop of web material (W) will produce a rotation of the said lever arm (20), and

detection means (23) sensitive to the rotation of the said lever arm (20) and capable of generating the said control signal corresponding to the rotation of the said lever arm (20).
A device in accordance with any one of Claims 1 to 3, characterized in that the said sensor means (19 to 23) include an element (22) acting in the direction that induces a slackening of the said loop of web material (W).
A device in accordance with any of the preceding claims, characterized in that the said sensor means include a return means for the said loop of web material in the form of a roller (19).
A device in accordance with any one of the preceding claims, characterized in that it includes a supporting panel (4) that carries the said storage unit (5 to 8) as a self-contained unit, together with the said first (17) and second (9) driving means.
A device in accordance with any one of the preceding claims, characterized in that the said storage unit (5 to 8) includes a first (6) and a second (8) set of return means on which the said web material (W) is wound in the general configuration of a festoon, the said second driving means (9) acting in such a manner as to vary the distance between the said first (6) and the said second (8) return means.
A device in accordance with Claim 7, characterized in that the said first (6) and the said second (8) set consist of return means in the form of rollers.
A device in accordance with Claim 7 or Claim 8, characterized in that the return means of the said second set (8) are mounted on an appropriate mobile trolley (7) and that the said driving means (9) control the movement of the said mobile trolley (7).
A device in accordance with Claim 9, characterized in that it includes a supporting panel (4) provided with means (4a) for guiding the movement of the trolley (7).
A device in accordance with Claim 10, characterized in that the said supporting panel (4) is of an elongated shape, with the said first set of return means (6) positioned in the vicinity of the said first driving means (17) and the said sensor means (19 to 23), that the said second driving means (9) is situated at the opposite end of the supporting panel (4) and that the said second set of return means (8) is mobile in a position generically intermediate between the said first return means (6) and the said second driving means (9).
A device according to any one of the preceding claims, characterized in that the said first (17) and second (9) driving means are electric motors.
A device according to any one of the preceding claims, characterized in that the said control means (10) are configured to control the said first (17) and second (9) driving means in at least one of the following operating phases:

slowing down of the said first driving means (17), with a corresponding reduction of the speed (v₁) of the web material (W) at the said intake side (2) and activation of the said second driving means (9) in the direction of rotation that produces a reduction of the length of the web material (W) at a speed (v₂) such as to maintain the speed of the web material (W) at the said output side (3) at a substantially constant value (v_L) independently of the speed reduction at the said intake side (2),

acceleration of the said first driving means (17), with a corresponding increase of the speed (v₁) of the web material (W) at the said intake side (2) and activation of the said second driving means (9) in the direction of rotation that produces a reduction of the said length of web material (W) at a gradually decreasing speed (v₂), so that the speed of the web material (W) at the said output side (3) is maintained at a substantially constant value (v_L) independently of the increase of the speed of the web material (W) at the said intake side (2), and

activation of the said second driving means (9) in the direction that will produce an increase of the said length of web material (W) with a corresponding increase of the speed of the said first driving means (17), so that the speed of the web material (W) at the said output side (3) will be maintained constant and the reserve of web material (W) contained in the said storage unit (5 to 8) will be reconstituted.
A device in accordance with Claim 13, characterized in that the said control means (10) is configured in such a way as to realize the said phases, intervening on the said first (17) and second (9) driving means in accordance with selectively variable control laws.