Patent Application
20120262017
This application claims benefit of Ser. No. 1138207.9, filed 24, Mar. 2011 in Europe and which application is incorporated herein by reference. To the extent appropriate, a claim of priority is made to the above disclosed application.
The present invention relates to a hybrid magnetic clutch for the transmission of tightening torque, which combines the advantages and benefits of the hysteresis magnetic clutches and the magnetic synchronous clutches.
The present invention has been especially designed for its application in the industrial sector in general, being particularly appropriate in the packaging industry to close containers that use screw caps, and more generally for any application that requires tightening torque.
The magnetic clutches for the transmission of tightening torque are frequently used in the packaging industry, one of its more usual applications being its use for screwing caps on container necks.
Said clutches usually consist of a body, or casing, that is associated with a first shaft, which normally acts as a driving shaft on which an external rotation force is applied. In the interior of said casing there is a second shaft, coaxial to the first shaft, which is fixed to the casing by mechanical means that allow its free rotation movement relative thereto. The second shaft, or driven shaft, is drawn by magnetic attraction to finally generate tightening torque on one of its ends, on which there are clamping means for the cap to be screwed. The various ways of adjusting and regulating tightening torque have yielded several designs for this type of magnetic clutches.
Some of these solutions are based on the use of magnetic synchronous clutches. One example of these is seen in U.S. Pat. No. 6,941,724 corresponding to a clutch for screwing capping heads that use two concentric opposite rings of permanent magnets with alternating polarity (where “permanent magnets” refers to those magnets that present high resistance to demagnetization, also known as “hard magnets”). Each one of said magnets rings are associated with one of the driving and driven shafts, so that when the driving shaft rotates, the driven shaft is synchronically drawn due to the attraction force between the opposite pole magnets and the repulsion between equal poles. The attraction/repulsion force between the magnets could be adjusted according to the type of container to be used. This is achieved by screwing/unscrewing an adjustment neck associated with a lower part of the driven shaft. The movement of the adjustment neck generates an axial displacement, without rotation, of the magnet ring associated with the driven shaft. Thus the axial distance between both magnet rings is modified, allowing a decrease or increase of the facing surface between them in radial direction. When the resistance to the movement of the screw cap is greater than the drawing force on the driven shaft, this slips and stops following the movement of the driving shaft. When the driven shaft slips a hammering effect is produced, since the permanent magnets of both shafts look for stable positions, which are produced when the magnets of opposite poles face each other. The hammering helps to close the cap better, thanks to the intermittent force peaks that are generated during it, as it enables to unblock undesired positions between the cap and the container neck when these are jammed together. By contrast, the hammering may produce gripping failures of the elements that clamp the cap, making them slide on it and thus damaging it, as well as undesired vibrations that generate greater wear on the clutch components.
Other solutions used are based on the use of hysteresis magnetic clutches. An example of these can be seen in U.S. Pat. No. 5,996,311 corresponding to a device for screwing caps on containers, which uses a hysteresis ring facing a group of circular permanent magnets of alternating polarity. The hysteresis ring, formed by a low magnetic reluctance material (also known as “soft magnets”), is associated with the driving shaft, while the group of permanent magnets are associated with the driven shaft. When the driving shaft rotates, the permanent magnets associated with the driven shaft tend to continuously change the polarity of the ring and a drawing movement of said driven shaft is produced. When the resistance to the movement of the screw cap is greater than the drawing force on the driven shaft, this slips and stops following the movement of the driving shaft. The drawing force may be adjusted according to the type of container to be used, pre-setting some pre-established working positions in which the hysteresis ring and the permanent magnets are at different distances in axial direction, allowing a decrease or increase of the facing surface between them in radial direction.
In order to achieve this pre-adjustment, the casing, housing the hysteresis ring, may be arranged on a limited number of predetermined machined positions on the driving shaft that vary their relative position in axial direction relative to the driven shaft. Unlike magnetic synchronous clutches, when the driven shaft slips, a soft movement is produced. Hence, by avoiding the hammering, the damage on the cap and the wear of the components of the clutch are prevented. While by contrast, as no intermittent force peaks are produced, the cap may either remain improperly closed or be blocked in an undesired position of the container neck. Besides, the force density of a hysteresis clutch is always lower than that of a synchronous clutch. That is, for the same clutch size, the synchronous technology allows obtaining a tightening torque greater than the one obtained with the hysteresis technology.
The present invention comprises a hybrid magnetic clutch that uses both magnetic technologies described above, enabling to solve the problems presented by each one of them while obtaining all their advantages. In this sense, the hybrid magnetic clutch of the present invention enables to regulate the slip between the shafts, making this happen in a soft way with a slight hammering.
In order to solve the aforementioned problems, the magnetic clutch for the transmission of tightening torque of the present invention comprises a first shaft integral to a casing in whose interior there is a second shaft coaxial to the first shaft. Said second shaft is fixed to the casing by mechanical means that allow its free rotation movement relative thereto, being both shafts engaged together by magnetic attraction to transmit the tightening torque. The configuration described above maintains the symmetry principle, being it possible for each one of the shafts to independently act as a driving shaft or a driven shaft.
The magnetic clutch in turn comprises:
and:
where:
The magnetic coercivity represents the magnetic field value necessary to eliminate the magnetization of a ferromagnetic material, and therefore it also represents the resistance of a magnet to demagnetization. A high magnetic coercivity implies demagnetization values equal to or higher than 0.20 T, such as for example those offered by rare earth magnets such as Neodymium or Samarium, having coercivities of 1,20 T and 1 T respectively, or other ferrite magnets, having mean coercivities of 0.25 T. In turn, a low magnetic coercivity implies demagnetization values lower than 0.20 T, such as for example Alnico alloys, having a coercivity of approximately 0.07 T. Hard magnets are characterized by presenting high magnetic coercivity values, while soft magnets are characterized by presenting low magnetic coercivity values.
By means of the configuration described above, the present invention enables to place the first and second magnetic assembly in a desired position, according to the type of cap to be used and/or to the necessary tightening torque, type of container etc., in which some particular slipping conditions are produced. That is, the position between the first and second magnetic assembly is adjusted to offer a more or less soft slide and a more or less slight hammering. Although the adjustment principle is mainly based on varying the facing surface in radial direction between both assemblies.
In this sense, according to a first preferred embodiment of the present invention, both magnetic assemblies present a displacement movement relative to each other in axial direction, configured to progressively increase or decrease the facing surface between the magnets of both assemblies, progressively varying from a simple hysteresis magnetic clutch position to a mixed magnetic hysteresis clutch and magnetic synchronous clutch position, and vice versa. Thus, the simple position comprises the first group of high magnetic coercivity magnets facing only the low magnetic coercivity magnet, while the mixed position comprises the first group of high magnetic coercivity magnets facing both the low magnetic coercivity magnet and the second group of high magnetic coercivity magnets.
There exist various designs for placing each one of the magnetic assemblies on their corresponding shafts, thus linking the movements of each one of them. According to a first preferred embodiment of the present invention, the first magnetic assembly is arranged on the inner face of the casing, in a way that is concentric to the first shaft, while the second magnetic assembly is arranged on the outer face of the second shaft in a way that is concentric thereto. Preferably, the first magnetic assembly is arranged to slip axially on the inner face of the casing, while the second magnetic assembly is fixed on the outer face of the second shaft.
The mechanical means that allow for the free movement of one of the shafts relative to the other also offer various design variants. According to a first embodiment of the present invention, said mechanical means comprise the use of bearings that keep the second shaft and the casing joined.
There follows a very brief description of a series of drawings that will help understand the invention better relating to a preferred embodiment of said invention presented as a non-limiting example thereof.
In these figures it can be seen that the magnetic clutch (1) for the transmission of tightening torque of the present invention comprises a first shaft (2) integral to a casing (3) in whose interior there is a second shaft (4) coaxial to the first shaft (2). Said second shaft (4) is fixed to the casing (3) by mechanical means (5) that allow its free rotation movement relative thereto, being both shafts (2, 4) engaged together by magnetic attraction to transmit tightening torque.
The magnetic clutch (1) comprises in turn a first and a second magnetic assembly (6, 8). In the present embodiment example, the first magnetic assembly (6) is linked to the first shaft (2), which acts as a driving shaft, while the second magnetic assembly (8) is linked to the second shaft (4), which acts as a driven shaft.
As it can be seen the first magnetic assembly (6) is formed by a first group of magnets (7) of high magnetic coercivity, arranged with alternating polarities,
There exist various designs for placing each one of the magnetic assemblies (6, 8) on their corresponding shaft, thus linking the movements of each other. According to the present example, the first magnetic assembly (6) is arranged on the inner face of the casing (3), in a way that is concentric to the first shaft (2), while the second magnetic assembly (8) is arranged on the outer face of the second shaft (4) in a way that is concentric thereto.
In the present embodiment example both magnetic assemblies (6, 8) present an axial displacement relative movement with respect to each other. Specifically, the first magnetic assembly (6) is configured to axially slide on the inner face of the casing (3), while the second magnetic assembly (8) is fixed on the outer face of the second shaft (4). Said movement is configured to progressively increase or decrease the facing surface (F) between the magnets (7, 9, 10) of both assemblies (6, 8), switching from a simple hysteresis magnetic clutch position to a mixed hysteresis magnetic clutch and a magnetic synchronous clutch position, and vice versa.
The mechanical means (5) that enable the free movement of one of the shafts relative to the other, according to the present example, comprise the use of bearings (11) that keep the second shaft (4) and the casing (3) joined.
| Number | Date | Country | Kind |
|---|---|---|---|
| 11382079.9 | Mar 2011 | EP | regional |
