EP0968775A2 - Self-centering expanding shaft with a composite system - Google Patents

Abstract

The present invention relates to a self-centering expanding shaft with a composite system - of the type comprising a structural cylinder, equipped with a pneumatic expanding system to block a reel and housing at least one pneumomechanical module to center the reel, said pneumomechanical module comprising a pair of opposed slidable thrust elements (3), coupled with gripping elements (4) apt to be extracted from and withdrawn into said structural cylinder (1), and two pressure chambers (8a,8b) positioned at its ends, in which said two pressure chambers (8a,8b) are connected through a single pneumatic line (10) which crosses the two thrust elements (3), the extraction of said gripping elements (4) being obtained by supplying compressed air into said compression chambers (8a,8b), and in that, at least an elastic element (7) is provided to act on said thrust elements (3) so as to reset the conditions of rest.

Description

The present invention concerns a pneumatic expanding shaft and, in particular, a self-centering pneumatic expanding shaft with a composite system.

As known, expanding shafts are used in a large number of industrial applications for the rotating support of reels. For this purpose, expanding shafts generally consist of a hollow structural cylinder, apt to form the carrying structure of the expanding shaft, and of a set of movable elements, of different type, projecting from the contour of the cylinder so as to grip the reel core and keep it onto the shaft.

In particular, in the pneumatic type expanding shafts the movable gripping elements are in the form of alongated expanding pads, which are housed into a plurality of longitudinal slots formed onto the surface of the hollow cylinder. As it appears evident, the reel is fitted on the pneumatic expanding shaft with the pads at rest and is blocked by said pads which, being expanded by introducing compressed air, press onto the inner surface of the reel core and keep it blocked.

Such expanding shafts, though providing various advantages in many applications - which are not reported herein but are perfectly known to one skilled in the art (for example, the highly reliable gripping force that the pads are able to apply on the reel core) - particularly suffer from a drawback which, amongst others, turns out to be the most macroscopic and shows up while the reel is being loaded onto the shaft. Since the pads are normally inflated with compressed air, which is a compressible fluid, they tend to deform to a different extent according to the loading conditions to which they are subjected. In particular, in the static loading conditions of the reel, the pads on the upper side of the expanding shaft - where the whole weight of the reel is pressing - tend to expand less than the pads in the underlying part of the shaft - where the load being applied is practically inexistent. As it appears evident, this causes a misalignment of the reel in respect of the shaft rotation axis.

While for the reels of reduced weight said misalignment is neglectable, for the heavy reels (for example, rolls of aluminium foil) this condition produces high degrees of eccentricity on the shaft rotation axis, which can by no means be tolerated and must hence be eliminated by resorting to suitable expedients.

One of the systems mostly adopted to obtain the centering in static conditions - namely, before causing the rotation of the reel - but also in dynamic conditions, is to combine, on the same shaft, a merely pneumatic expanding system with an auxiliary expanding system of different type, which may be apt to symmetrically expand in respect of the shaft rotation axis, independently from the loading conditions.

Said auxiliary system is normally of the mechanical or, rather, of the pneumomechanical type. It allows to establish a mechanical coupling between the gripping elements belonging to the same section area, thereby producing a fully symmetrical radial displacement of the same: this means that the gripping elements - for instance in the form of keys - belonging to the same section area, simultaneously project from the surface of the shaft thereby ensuring a mechanical centering of the reel core.

In prior art, there are different types of such self-centering expanding shafts provided with a composite system.

A solution - which may be defined as a "single-acting" solution -provides to combine a conventional pneumatic system with a cone system for extracting mechanical gripping elements, such as keys, having an inclined plane apt to engage with the cones. Normally, the extraction of the gripping elements, and thus the centering of the reel, is obtained by "shooting" thereon the mechanical cones by means of compressed air. Nonetheless the cones thus shot, in a static condition of the shaft, tend to loosen and produce some slack during rotation of the shaft: this leads the load of the reel to progressively weigh exclusively on the pneumatic system, whereby the centering of the reel core comes to fail.

The technique mostly adopted at present provides for the centering system to be neither of the single-acting type, nor of a purely mechanical type, but to comprise a set of independent pneumomechanical modules. This structure allows, at least in theory, to obtain an improved centering of the reel also along the longitudinal axis - in that the single modules determine the centering of the reel core one independently from the other - so that it may be possible to perfectly center also a reel whose core is not perfectly cylindrical lengthwise.

A shaft of this type is, for example, disclosed in the Italian Patent application N. MI95A002504, in the name of RE GIANPIERO. It is disclosed a pneumatic expanding shaft equipped with an auxiliary centering device formed of two pneumomechanical modules, each comprising a thrust piston coupled with extractable keys connected to small bent tiles.

Although, in theory, this solution seems to provide a good result, in practice it has different drawbacks.

Operating exclusively with compressed air, both while extracting the keys and during withdrawal thereof, this shaft implies the presence of two compressed air distribution lines - with the structural complications involved - and does not provide an optimal performance.

In fact, according to a first embodiment, the two pneumomechanical modules are operatively independent - which allows a differentiated extraction of the two groups of keys, and thus a longitudinal adjustment of the tiles to the irregularities of the reel core - but the compressed air supplying path crosses the expanding pads, leading the pneumatic system to be operatively connected to the centering system, which is not always desirable. Moreover, the supplying of compressed air through the expanding pads can easily take place only in correspondence of the two ends of said pads, while it gets complicated to form other pressure intakes along the length of the pad for any further pneumomechanic modules, thereby positively hampering the production of an shaft with more than two pneumomechanical modules.

Whereas, according to a second embodiment, compressed air is fed to the pneumomechanic system, on one side, directly into a "head" compression chamber and, on the other side, into a "bottom" compression chamber, through a rigid pipe extending inside the pistons of the device. In this case, the pistons of the pneumomechanical modules can even be more than two but it is necessary for them to be operatively tied one to the other, whereby it is not possible to obtain a longitudinal adjustment of the tiles to the irregularities of the reel core.

This last drawback is particularly felt in all those cases wherein it is necessary to guarantee both a perfect centering of the reel in the radial sense and a uniform blocking thereof in the longitudinal sense -even in the presence of an irregular core - so as to make sure that, during reel rotation, no oscillation occurs. For example, a critical application field concerns the rolls of aluminium foil: in fact, in this case, rools are normally very heavy and, in addition, the aluminium foil is quite fragile and can stand only a very slight oscillation while being unwound at high speed.

The object of the present invention is to thus overcome the above mentioned drawbacks by supplying an expanding shaft provided with a composite system, wherein the expanding centering device is conceived so as to allow adopting any number of pneumomechanical modules, operatively independent one from the other and from the pneumatic expanding system, and a single compressed air supplying line.

Said objects are reached with a pneumatic expanding shaft according to one or more of the accompanying claims.

Further characteristics and advantages of the expanding shaft according to the present invention will anyhow be more evident from the following detailed description of a preferred embodiment thereof, given by way of example and illustrated on the accompanying drawings, in which:

Fig. 1 is a longitudinal section view of an expanding shaft according to the present invention;

Fig. 2 is a longitudinal section view of an shaft according to another embodiment of the invention; and

Fig. 3 is a cross section view of the expanding shaft of fig. 2.

A pneumatic expanding shaft - as shown in fig. 1 - comprises a structural cylinder 1, carrying at its ends support pins 2 fixed thereto, onto which there are formed a plurality of longitudinal slots 1a (fig. 3) apt to house pneumatic expanding pads 1b.

The structural cylinder 1 is hollow and it houses thrust elements in the form of sliding pistons 3, into which engage - in known manner -gripping elements or keys 4, apt to project from respective slits 5 formed into the wall of the cylinder 1. Preferably, a spline or bent tile 6 is fixed to the outer edge of the keys 4 which coincide lengthwise.

According to the present invention, the hollow cylinder 1 houses a modulus comprising two opposed thrusts element 3, coupled with gripping elements 4 which are extracted as a consequence of opposite translations of said thrust elements 3, an elastic element 7 - for example a spiral spring - extending between the adjacent ends of said elements 3. Pressure chambers 8a and 8b are positioned at the other ends of the thrust elements 3 (the volume of the pressure chambers shown in figs. 1 and 2 is very reduced, because the pistons 3 are at their top dead center). Two ducts 9 cross the pistons 3 lengthwise leading, at one end, into the respective pressure chambers 8a and 8b and being connected, at the other end, to a common connection pipeline 10.

To operate the centering device of the present invention, the compressed air is supplied directly into one of the two pressure chambers - for example, the chamber 8a shown in fig. 2 - while, in the other chamber 8b, it is supplied through the only distribution line consisting of the two ducts 9 and of the pipeline 10. The pressure increase in the two chambers 8a and 8b leads the two pistons 3 to perform a motion of translation one towards the other, in opposition to the spring 7, such as to cause the extraction of the keys 4, which thus press - either directly, or by way of the tiles 6 - onto the core 11 of the reel (not shown), thereby centering and blocking the same.

To allow the pistons 3 to perform the motion of translation, the stretch of pipeline between said two pistons is apt to be modified lenghtwise. In other words, the connection points of the pipeline 10 to the ducts 9 of the pistons 3 can be freely drawn close: this is obtained by adopting either a telescopic pipeline 10 (as shown in fig. 2) - namely, a small rigid tube fixed to one duct 9 and slidable into the opposite duct 9 through a sealing gasket 10a - or a flexible pipeline 10 (as shown in fig. 1). If adopting a flexible pipeline 10 it is also possible to avoid the use of sliding gaskets.

After the reel has been centered onto the shaft, or while being centered thereon, also the pneumatic expanding system is operated, thereby blocking and firmly retaining the reel thanks to the very efficient gripping of the pneumatic pads 1b (normally made of rubber) onto the reel core 11. Only after release of the pressure from the chambers 8a and 8b, the elastic action of the spring 7 is able to reset the pistons 3 in a position of rest.

The solution provided by the present invention fully achieves the objects set forth in the introductory part of the description. In particular, the invention supplies an expanding shaft provided with a composite system equipped with an independent centering device, the working of which is ensured by a single compressed air supplying line operated to extract the gripping elements 4, and by an elastic return element used to withdraw said gripping elements 4.

At the same time, the two thrust elements 3 have been kept totally free each other from mechanical ties, so as to allow adjusting the groups of keys to the specific local conditions of the reel core.

Finally, the possibility has been provided to increase the number of centering modules to the required extent. In fact, although the drawings always refer to an expanding shaft comprising a single module with two pistons, it can be easily understood that the expanding shaft could comprise a plurality of identical modules arranged in succession, each module being interconnected with the adjacent module (all the pressure chambers would be interconnected along the same supplying line).

It is anyhow understood that the invention is not limited to the particular embodiment described heretofore, but that any technically equivalent structural modifications can be introduced therein, without thereby departing from the scope of the present invention.

Claims (7)

1. Self-centering expanding shaft with a composite system - of the type comprising a structural cylinder, equipped with a pneumatic expanding system to block a reel and housing at least one pneumomechanical module to center the reel, said pneumomechanical module comprising a pair of opposed slidable thrust elements, coupled with gripping elements apt to be extracted from and withdrawn into said structural cylinder, and two pressure chambers positioned at its ends - characterized in that, said two pressure chambers are connected through a single pneumatic line which crosses the two thrust elements, the extraction of said gripping elements being obtained by supplying compressed air into said compression chambers, and in that, at least an elastic element is provided to act on said thrust elements so as to reset the conditions of rest.
2. Shaft as in claim 1), wherein said line comprises a lenghtwise variable stretch between said thrust elements and a duct crossing each of said thrust element.
3. Shaft as in claim 2), wherein said line comprises a lenghtwise variable stretch consists of a small flexible tube, connected to the ducts crossing the two thrust elements.
4. Shaft as in claim 2), wherein said line comprises a lenghtwise variable stretch consists of a small rigid telescopic tube.
5. Shaft as in claim 4), wherein said small rigid telescopic tube has one end fixed to the duct crossing one of the thrust elements, and the other end slidable into the duct crossing the other thrust element.
6. Shaft as in any one of the previous claims, wherein said elastic element is positioned between the adjacent ends of the two thrust elements.
7. Shaft as in any one of the previous claims, wherein said elastic element consists of a spiral spring, partially housed into guide seats formed into the thrust elements.

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