Traversing hoists – Boom or mast – Extensible by sliding sections
Patent
1995-10-24
1997-10-21
Brahan, Thomas J.
Traversing hoists
Boom or mast
Extensible by sliding sections
152118, 212230, B66C 23693
Patent
active
056787081
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION
This invention relates to an extendible crane boom, e.g. an outer boom, of the type comprising, in addition to a tubular base boom section, at least three or four boom sections telescopically arranged within the base boom section and each composed of a tube and a holder mounted at an outer end of the tube for connecting it to a double-acting hydraulic cylinder which has a cylinder part and a piston rod, is located outside the associated tubular boom section and serves to displace each boom section out of and into an immediately preceding boom section so as to lengthen and shorten, respectively, the crane boom in its entirety.
BACKGROUND ART
In prior-art crane booms of %he above type, the hydraulic cylinders required for extending and shortening the boom are positioned so that the extension units, consisting of a boom section and an associated exterior hydraulic cylinder, will have an increasing overall height in the direction of the free end or tip of the crane boom. For example, in a crane having four extension units, the two cylinders of the first and the second boom section are disposed in a common plane which is parallel to the longitudinal extent of the boom and located comparatively close to the upper Side Of the base boom section, while the cylinders of the third and fourth boom sections are located in a common plane above or outside the two first-mentioned cylinders. In this manner, the overall height, counted as the centre distance between the individual boom section and the associated hydraulic cylinder, becomes greater at the outer two extension units than at the inner ones. This difference in overall height is further pronounced if, for lack of space, the first and second cylinders and the third and fourth cylinders, respectively, cannot be arranged side by side in common planes but must be arranged in the same vertical plane through the crane boom. In those cases, the difference in overall height becomes excessive. The fact that the different extension units will have an increasing overall height towards the boom tip entails a number of inconveniences in actual practice. Besides the crane boom having a structurally/aesthetically less attractive appearance when in the extended or maximally lengthened state, the fact that %he outermost extension unit has the largest overall height causes difficulties in operating the crane in certain situations. One example of such a situation is the case when a load suspended from the tip of the crane boom is to be passed through an opening of limited size, such at a window opening in a building. The large overall height of the outermost extension unit makes this unit difficult to maneuver through the opening. In addition, the crane boom will never be exactly straight when in the extended, loaded state, but will instead have a more or less pronounced bow shape (banana shape). When, therefore, a load at the tip of a crane boom introduced through such an opening is released from the tip, the bow-shaped crane boom will spring back towards a more rectilinear shape. There is then a manifest risk that the piston rod of the outermost, third or fourth cylinder will bump against the frame of the opening and be damaged. Another drawback resulting from the overall height of the different extension units increasing towards the crane tip is that the cylinder holders (or "noses") of the outer unit or units become large-sized, unwieldy and expensive.
OBJECTS AND FEATURES OF THE INVENTION
The present invention aims to overcome the above-mentioned drawbacks and provide an extendible crane boom which is easy to operate also in cramped spaces and which, additionally, has an aesthetically attractive appearance. According to the invention, this object it achieved by means of the features recited in the characterising clause of appended claim 1.
Other preferred features of the inventive crane boom will appear from the dependent claims.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
In the drawings,
FIG. 1 is a partially cut and partially si
REFERENCES:
patent: 3445004 (1969-05-01), Grider et al.
patent: 3721054 (1973-03-01), Hornagold
patent: 3804262 (1974-04-01), Wiencek et al.
patent: 4575976 (1986-03-01), McDermott et al.
patent: 5501346 (1996-03-01), Wimmer
Forsberg Lars
Ljungberg Kenneth
Sjostrom Tommy
Stolpe Jens
Brahan Thomas J.
Hiab AB
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