Implements or apparatus for applying pushing or pulling force – Apparatus for hauling or hoisting load – including driven... – Device includes rotatably driven – cable contacting drum
Reexamination Certificate
1999-10-21
2001-09-11
Marcelo, Emmanuel M. (Department: 3653)
Implements or apparatus for applying pushing or pulling force
Apparatus for hauling or hoisting load, including driven...
Device includes rotatably driven, cable contacting drum
C254S372000, C254S382000, C254S397000
Reexamination Certificate
active
06286816
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
This application claims the priority of German Patent Application Serial No. 198 52 538.9, filed Nov. 5, 1998, the subject matter of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates, in general, to a chain hoist, and more particularly to a compact chain hoist of a type including a chain which is guided via at least one sprocket for connection to a load-bearing member, and a drive unit having a housing which accommodates a driveshaft for support of a sprocket to drive the chain.
It is generally known in the field of chain hoists or chain blocks that chain vibrations in longitudinal and transverse directions are generated as a consequence of the so-called “polygon effect”. The degree of vibration existing in a chain hoist is related to the natural frequency of the chain and the frequencies being imposed on the chain during operation of the chain hoist. The oscillation frequency is thereby dependent on the lift velocity and the chain pitch, whereas the degree of encountered accelerations depends on the lift velocity as well as on the number of teeth of the sprockets. It is also known that accelerations upon several deflections cumulate longitudinally in the direction of the chain substantially at the individual sprockets.
German Pat. No. DE 93 17 630 U1 discloses a chain drive provided with a polygon damping device which includes a resiliently mounted and rotatable carrier roller by which the return strand of the chain is supported. The carrier roller is provided with elastic material so as to realize a damping of oscillations, whereas the resilient support of the carrier roller is implemented by a hydraulic unit.
German Pat. No. DE 197 16 411 C1 describes a chain drive, in particular for an auxiliary drive of internal combustion engines, by which excitations of the endless chain as a consequence of the polygon effect are substantially reduced by using a mass damper in the form of a flywheel in one of both sprockets. The mass damper is shiftable essentially radially elastically and swingably mounted in the direction of the connecting line of both sprocket shafts linked together by the chain, for damping of oscillation.
These types of chain drives, described in German Pat. Nos. DE 93 17 630 U1 and 197 16 411 C1 are concerned with endless chains with a pulling chain strand and a returning idle strand, and are unsuitable for incorporation in a chain hoist having a chain which is fixed at one end to the chain hoist.
SUMMARY OF THE INVENTION
It is thus an object of the present invention to provide an improved chain hoist, obviating the afore-stated drawbacks.
In particular, it is an object of the present invention to provide an improved chain hoist which effectively eliminates chain oscillations as a result of the polygon effect, in particular in conjunction with compact chain hoists having several chain deflections.
These objects, and others which will become apparent hereinafter, are attained in accordance with the present invention by training a chain over first and second sprockets for defining a movement path for the chain, with one of the sprockets being connected to a load-bearing member, and the other one of the sprockets being part of a drive unit for operating the chain, and by providing a damping unit which is positioned in the movement path of the chain for damping vibration.
In the practice of the invention, the damping unit can be incorporated in the chain hoist in a variety of ways and locations. According to one embodiment of the present invention, the damping unit is so incorporated in the movement path of the chain as to support at least one of the first and second sprockets on the chain hoist. This configuration of the chain hoist can be realized in a simple manner to effect a damping of vibrations and/or prevention of a chain with continuously alter nating loads, in particular a damping of vibrations in longitudinal direction of the chain as a consequence of dilatation. Resonance is prevented, without need for changing the excitation frequency based on the lift velocity, by simply lowering the natural frequency of the entire system Thus, the chain hoist can be operated in the supercritical range, i.e. above the natural frequency of the chain hoist because through these measures the natural frequency is reduced. As a result, undesired noise generation caused by strong vibrations in case of resonance are eliminated.
According to another feature of the present invention, the guidance of the components interconnected via the damping unit can be realized in a simple and mechanically very stable manner by providing a rocker which supports the at least one of the sprockets, with t he rocker having one end, which is swingably mounted, and another end supported by the chain hoist via the damping unit.
A very compact configuration is realized when securing the rocker to the housing of the drive unit at a location underneath the driveshaft. In this manner, the typically stable housing is used as support frame for the rocker. Moreover, the chain hoist can be retrofitted with such a rocker for damping vibrations, without significantly complicating the overall construction.
Overload of the damping unit at great oscillation amplitudes can be prevented by providing the housing with a stop member to thereby limit the pivot angle of the rocker.
A very compact configuration can further be realized by positioning the pivot axle of the rocker vertically underneath the driveshaft in parallel relationship thereto and in parallel disposition to the axis of the driving sprocket. Thus, the movement path of the chain is directed vertically downwards in this area and advances upwardly following a deflection of the chain by the sprocket of the rocker in a direction away from the pivot axle.
According to another feature of the present invention, the damping unit includes a damper which is securely fixed to the rocker and the housing. Suitably, the rocker is mounted via the damper to the housing and the pivot axle is swingably secured to the housing, to thereby exploit the stability of the housing.
According to another embodiment of the present invention, the housing and the sprocket which is mounted on the driveshaft, and a further sprocket which is positioned downstream in load direction of the chain, may form a structural unit whereby the damping unit is so incorporated in the movement path that the structural unit is supported via the damping unit by a carrier. Thus, the entire drive unit, including the first sprocket, is secured as a whole via the damping unit to the carrier. This is possible because sufficient space is available in this area. Suitably, the carrier is track-bound so that the chain hoist is universally useable.
A stable configuration of this embodiment of the chain hoist, which can be subjected to high loads, is implemented when the structural unit of drive unit and downstream sprocket is supported by a rocker which has one end swingably mounted on the carrier and another end supported by the carrier via the damping unit, whereby the chain, which is guided downwardly via a further sprocket and returned by the sprocket of the load-bearing member, is also secured to the carrier.
According to still another embodiment of the present invention, the damping unit is incorporated in the movement path of the chain such that one end of the chain may be fixed to the chain hoist via the damping unit. This configuration can easily be realized in already constructed chain hoists.
Another embodiment of a chain hoist according to the invention includes the securement of one end of the chain to the load-bearing member via the damping unit. This solution is independent from the configuration of the chain hoist per se. Thus, the load-bearing member is capable to accomplish an effective damping of vibration in a widest variety of chain hoists (preferably at 1/1 fold)
Another embodiment of a chain hoist according to the invention is advantageously employed at 2/1 folds, and involves a chain which is gui
Liebig Karl
Moll Oliver
Schubert Michael
Feiereisen Henry M.
Mannesmann AG
Marcelo Emmanuel M.
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