EP1043259A2

EP1043259A2 - Self-centring expanding shaft

Info

Publication number: EP1043259A2
Application number: EP99119660A
Authority: EP
Inventors: Paolo Garella
Original assignee: Finsid Srl
Current assignee: Finsid Srl
Priority date: 1999-03-29
Filing date: 1999-10-04
Publication date: 2000-10-11
Also published as: IT1312239B1; EP1043259A3; ITMI990647A1

Abstract

A composite expanding shaft comprising a pneumatic expanding blocking system of a bobbin and a pneumechanic centering system is disclosed, wherein the pneumechanic system comprises at least a movable thrust element operated by a fluid under pressure supplied into an expansion chamber, a first passage way being apt to connect said expansion chamber to an inflation duct of the pneumatic system, and comprising further an obstructing means of said firts passage way, jointly movable with said thrust element of the centering system, apt to keep closed said first passage way for at least a predetermined portion of the thrust element stroke.

Description

The present invention concerns a self-centering pneumatic expanding shaft. In particular, a self-centering pneumatic expanding shaft with a composite system allowing sequential operation.
As known, expanding shafts are used in a large number of industrial applications for the rotating support of bobbins. For this purpose, expanding shafts generally consist of a hollow framing 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 a bobbin core and dragging it in rotation.
In particular, in the pneumatic type expanding shafts the movable gripping elements are in the form of extended expanding pads, which are housed into a plurality of longitudinal seats formed in the surface of the hollow cylinder. As it appears evident, operation of the pneumatic expanding shaft provides that the bobbin is fitted thereon with the expanding pads at rest and is blocked by said pads which, being expanded through the introduction of compressed air, press on the inner surface of the bobbin core, gripping the same.
Such expanding shafts, though providing various advantages in many applications - which are not reported herein but are perfectly known to a skilled of the field - particularly suffer from a drawback which, amongst others, turns out to be the most macroscopic one and shows up while the bobbin is being loaded on the shaft. Since the pads are normally inflated with compressed air, they tend to deform to a different extent according to the local loading conditions to which they are subjected. In particular, in the static loading conditions of the bobbin, the pads on the upper side surface of the expanding shaft - where the whole weight of the bobbin is insisting - tend to expand lesser than the pads in the underlying side of the shaft - where the load being applied is insignificant. As it appears evident, this causes a misalignment of the bobbin in respect of the shaft rotation axis.
While for the bobbins of reduced weight said misalignment effect can be disregarded, for the heavy bobbins (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 which 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 bobbin - but also in dynamic conditions, is to combine, on the same shaft, a merely pneumatic expanding system with an additional expanding system of different type, which may be apt to symmetrically expand in respect of the rotation axis, independently from the loading conditions.
Said additional system is normally of the mechanic or, rather, of the pneumechanic type. This system allows to establish a mechanic 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, project in unison from the surface of the shaft, thereby ensuring a mechanical centering of the bobbin core.
In prior art, there are different types of such self-centering expanding shafts provided with a composite system.
A solution - which will be defined as a "single-effect" solution - provides to combine a conventional pneumatic system with a cone system for extracting mechanic gripping elements, such as keys, having an inclined plane apt to engage with said cones. Normally, the extraction of the gripping elements, and thus the centering of the bobbin, is obtained by "shooting" thereon the mechanic cones by means of compressed air. Nonetheless the cones thus shot, in a static condition of the shaft, tend to loosen and gain some slack during rotation of the shaft: this leads the weight of the bobbin to progressively load exclusively on the pneumatic system, whereby the centering of the bobbin comes to fail.
Another very common typology provides for the centering system not to be a purely mechanic type, but to comprise a set of independent pneumechanic modules. That means a system where gripping elements of the centering system, thought mechanically connected each other, for instance being engaged on the same traslable thrust element with inclined planes, are extracted, in a reversible way, through the introduction of compressed air into an expansion chamber defined, at least in part, by the thrust element itself.
A manufacturing technique recently offered on the market, provides to adopt one or more pneumechanic modules - each comprising a gripping element group engaged to a single thrust element with inclined plans - coupled one to the other. The head module comprises a thrust element working as a piston for the whole series of the modules coupled to it. The expansion chamber of the head module is fed by compressed air through an inlet duct. From the same inlet duct starts an inflation duct which communicates with the inflating pads belonging to the pneumatic expanding system.
Nevertheless, this type of solution has some drawbacks, among which, the main one is the difficulty of obtaining a precise centering. In fact, compressed air in the inlet duct tends to run towards the system with the lesser resistance, which system could not be the most convenient to be fed in the specific condition. What happens, normally, is that compressed air inflates, at the beginning, the pneumatic system (blocking system) and, just afterwards, the pneumechanic one (centering system): this is exactly the contrary of what should happen. In fact, when the pneumatic system has already started to grip the bobbin core, it is very hard for a centering system to overcome the friction forces between the bobbin core and the expanding pads to reset the centering. After all, this system results, in many occasions, a not very functional one.
A possible way to overcome this drawback, is to provide separate ducts for the centering system and for the blocking system, separately controlled in different times and ways: this solution, even if possible, is uneconomic and leads to an expanding shaft which is complicated and uncomfortable for users.
Another drawback troubling the prior art is represented by the impossibility of removing the risk related to the wrong choices about the bobbin to be loaded on the shaft. In fact, if an operator loads on the shaft a bobbin which has a slightly bigger diameter than the one provided for the specific shaft used, the pneumatic blocking system could, anyway, succeed in engaging the bobbin, although not very strongly and in a defective way. The operator, not realising the mistake, could start the rotation of the bobbin with all the risks it takes. Since now, there isn't any system apt to avoid this event, the expanding shafts of the prior art being able to accomplish only its normal functionality while being unable to face with abnormal conditions.
The object of present invention is, then, to overcome the mentioned drawbacks, supplying an expanding shaft with a composite system, where the centering and blocking operations automatically occur sequentially, that is, in which the pneumechanic centering system accomplishes the centering always before the pneumatic blocking system starts to work.
A second object is to supply an expanding shaft which is apt to "recognize" the bobbin core, in which the blocking system is inherently unable to grip a wider core than the expected specific one.
These objects are achieved by a pneumatic expanding shaft as described in the enclosed claims.
Further characteristics and advantages of the expanding shaft according to present invention will be more evident in the following detailed description of a preferred embodiment thereof given by way of example and illustrated in the enclosed drawings, in which:
Fig. 1 is an interrupted longitudinal section view of an expanding shaft according to the present invention, at rest; and
Fig.2 is an interrupted longitudinal section view similar to that of Fig.1, in gripping condition;
A generic hollow framing cylinder 1 for an expanding shaft is equipped with a pneumatic blocking system for a bobbin (not shown) and a pneumechanic centering system.
The pneumatic blocking system comprises a series of rubber short splines 2a, apt to grip the bobbin core to drag it in rotation, integral to expanding pads 2b housed in longitudinal seats in the framing cylinder 1.
The pneumechanic centering system comprises one or more thrust elements 3ai, slideable within the hollow framing cylinder 1, each thrust element engaging, through inclined plane 3a', a plurality of gripping elements 3b, such as keys, apt to be radially extended from the framing cylinder 1 itself.
One of said thrust elements 3ai, for example the head element 3a1 entirely illustrated in the drawings, ends with a thrust surface 4a faced to an expansion chamber 4.
According to a preferred embodiment of the invention, a selecting rod 5 protrudes, lenghtwise to the sliding axis of element 3a1, from the thrust surface 4a of the head element 3a1, in which rod a distribution duct 6 for a fluid under pressure, preferably compressed air, is provided.
The distribution duct 6 communicates with the expansion chamber 4 and with further(not visible)chambers.
The selecting rod 5 slides inside a coupling cylinder 7. In the coupling cylinder 7 a vent duct 10 is provided, apt to allow the compressed air to flow out of the framing cylinder 1, and also an inflation duct 11, apt to distribute compressed air towards the expanding pads 2b.
Between the outer surface of the selecting rod 5 and the inner surface of the coupling cylinder 7 there is a slight slack or gap which is sufficient to define a passage way to connect the expansion chamber 4 to the inflation duct 11 and to the vent duct 10. In such a gap, between the rod 5 and the cylinder 7, there are also provided circular gaskets, such as O- rings 9a, 9b, 9c.
The position of ducts 10 and 11 and of gaskets 9 in the sliding direction of the selecting rod 5, that is in the longitudinal direction, is properly defined on the basis of the following considerations concerning the operation of the device of the invention.
At rest, as illustrated in Fig. 1 - when both the centering system and the blocking system are retracted - the inflation duct 11 communicates, through a communication chamber 8a defined between the two gaskets 9a and 9b, with the vent duct 10: therefore, the expanding pad 2b is at ambient pressure and remains deflated.
Compressed air supplied into the distribution duct 6 is delivered only towards the expansion chamber 4, which is tightly closed by the engagement of gasket 9a with the coupling cylinder 7 walls. Therefore, at the beginning, only the thrust head element 3a1 is operated, and as a result, the pneumechanic centering system is activated.
After the thrust element 3a1 has covered a certain stroke, sufficient to achieve the centering of the bobbin, gasket 9a disengages from the coupling cylinder 7 walls and opens the passage way between the expansion chamber 4 and the inflation duct 11. In the meantime, gasket 9b has been shifted between the inflation duct 11 and the vent duct 10: therefore, distribution chamber 8a doesn't communicate any longer with the outside. Only in this state (Fig. 2), compressed air can also operate the pneumatic blocking system.
A check valve 12 is then provided at the external end of the distribution duct 6, in order to keep the working pressure inside both the centering and blocking systems without keeping on feeding them with compressed air.
As it is shown, the device of the present invention is apt to achieve a sequential operation according to the desired order, obtaining, in this way, one of the purposes mentioned above.
In the act of deflating is sufficient to cause the opening of the check valve 12 to allow, for a first stroke, the ejection of compressed air simultaneously from the expansion chamber 4 and from the expanding pad 2b through the check valve 12 and then, for a second stroke, the complete deflating of the expansion chamber 4, still through the check valve 12, and of the expanding pad 2b through the vent duct 10.
According to another aspect of the present invention, in the case the stroke of thrust element 3a1 should result too long due to the loading of a wrong bobbin, i.e. with a too large core, the condition illustrated in Fig.2 is exceeded and the gasket 9b is shifted behind the inflation duct 11 towards the right(in the drawings): this latter thus is connected again to the vent duct 10 through a second distribution chamber 8b, defined between the gasket 9b and the gasket 9c.
In this "unusual" state, pressure in the expanding pads is set again at ambient pressure. It is not possible, thus, to obtain any positive engagement between the rubber short splines 2a and the bobbin core and, as a result, the undesired false blocking of the bobbin doesn't occur.
In this way, it has been provided an expanding shaft with a composite system apt to "recognize" the correctness of the bobbin being loaded on it, reaching also another object of the invention.
It is to be noted that the invention is not limited by the embodiment illustrated above, which is just an example of the invention, and that many modifications, within the reach of a skilled of the field, could be adopted without departing from the scope of the invention.
For example, the coupling cylinder 7, which has been illustrated as a separate element for manufactural requirements, can also be integral with the framing cylinder 1 itself appropriately shaped and drilled.
Moreover, apart from the illustrated preferred solution, other equivalent solutions, more simple and essential, can be conceived, wherein the passage way between the expansion chamber and the inflation duct can be occluded and opened in the right sequence in many other ways, without deviating from the main teaching of the present invention.

Claims

Composite expanding shaft of the type comprising a pneumatic expanding blocking system and a pneumechanic centering system for a bobbin, wherein the pneumechanic system comprises at least a movable thrust element operable by a fluid under pressure supplied into an expansion chamber, a first passage way connecting said expansion chamber to an inflation duct of the pneumatic system, characterized in that it also includes obstructing means of said first passage way, jointly movable with said thrust element of the centering system, apt to keep closed said first passage way at least for a predetermined portion of the thrust element stroke.
Expanding shaft as in claim 1), wherein said obstructing means is a first gasket.
Expanding shaft as in claim 2), wherein said thrust element is integral with a selecting rod on which said first gasket is housed.
Expanding shaft as in claim 3), wherein said first passage way is defined between said selecting rod and a coupling cylinder in which said rod is slidable.
Expanding shaft as in any one of the previous claims, wherein a second obstructing means is provided, jointly movable with said thrust element, apt to obstruct and open a second passage way to communicate said pneumatic system to a vent duct, said second passage way being open with said thrust element exceeding a normal working position.
Expanding shaft as in claim 5), wherein said second passage way is open also in a condition in which said first obstructing means obstructs said first passage way.
Expanding shaft as in claims 5) or 6), wherein said second passage way is arranged on said selecting rod.
Expanding shaft as in claim 7), wherein said second passage way is defined between the selecting rod and the coupling cylinder towards which said inflation and vent ducts communicate, said ducts being longitudinally offset each other and said second obstructing means being a second gasket housed on said rod.
Expanding shaft as in any one of claims 3) to 8), wherein said selecting rod comprises a distribution duct for supplying fluid into the expansion chamber.
Expanding shaft as in claims 8) and 9), wherein at the end of said rod, a third gasket tightly engaging the coupling cylinder is provided.
Method for blocking a bobbin on an expanding shaft, wherein, after the bobbin has been loaded on the expanding shaft,

a) at least a thrust element with inclined plans of a pneumechanic system is caused to translate through the introduction of compressed air into an expansion chamber so as to radially extend gripping elements apt to center the bobbin on the rotation axis of the shaft;

b)expanding pads of a pneumatic system are inflated, through the introduction of compressed air, to perform blocking of the bobbin, characterized by that said step b) is carried out only after the thrust element has covered a first predetermined stroke during phase a), opening a first passage way which allows the compressed air to flow from the expansion chamber to said pneumatic system.
Method as in claim 11), wherein said thrust element, upon exceeding a second predetermined stroke, opens a second passage way which allows the air to flow from the pneumatic system to a vent duct.