Implements or apparatus for applying pushing or pulling force – Hoisting truck – Single throw lever
Patent
1993-12-01
1995-05-30
Watson, Robert C.
Implements or apparatus for applying pushing or pulling force
Hoisting truck
Single throw lever
254122, 254 93HP, B60P 148
Patent
active
054195349
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a device for opening, in particular, scissor-type jack mechanism of variable length which is usually located in the space between opening bars of the hoisting mechanisms, for example a scissor-type mechanisms of jacks and lifting platforms, and which consists of a variable volume chamber connected to a controlled inlet and outlet of a fluid medium. A change of chamber volume produces a change of length of the opening device whose ends associated with arms of the cross-bars mechanism effectuate opening of the arms and thus the elevation of a platform situated on the top of a cross-bar mechanism.
DESCRIPTION OF THE PRIOR ART
Generally known are expansion members of lever hoisting mechanisms, for example the scissors mechanisms, constituted by a hydraulic cylinder, closed by a fixed bottom at its one end and comprising inside an axially movable piston whose piston rod projects from the other end of the hydraulical cylinder.
The space defined by the fixed bottom of the hydraulic cylinder, its jacket and the axially movable piston constitutes a variable volume chamber which is connected to a controlled inlet and outlet of a pressure medium. At its fixed bottom end the hydraulical cylinder is by means of a pivot or an eye rotatably attached to one arm of the first lever of the hoisting mechanism while the end of the piston rod is similary, by means of a pivot or an eye rotatably attached to the other arm of the second lever of the hoisting mechanism.
Both said arms of the two levers are mutually rotatably connected and the change of the length of the expansion member causes opening and closing motion of the arms. Maximum opening angle of both levers is defined by the length of the lever arms which are attached to the ends of the hydromotor and by the maximum of the distance between the attachment spots at both ends of the hydromotor. Minimum opening angle is similary, besides the lengths of the arms and levers, defined by the minimum distance between the attachment spots of the hydromotot.
Minimum opening angle of the levers affects proportionally the height of the hoisting mechanism in its collapsed position, i.e. the minimum height of a lifting platform above the base. The effort to achieve the lowest possible height of the hoisting mechanism in its collapsed position is appearent mainly by the motor-car jacks, lifting platforms for raising burdens from the base and lifting platforms whose levers consist of several sets of mutually interconnected hoisting mechanisms. With the recent devices this effort has resulted in a "bias" location of the hydromotor what means that the hydromotor is at its one end attached to a longer arm of the first lever while at its other end is attached to a shorter arm of the second level. By this way, with the same length of the hydromotor a smaller angle included by the levers in their collapsed position is attained, however at the price of greater stress to which the hoisting mechanism is exposed when raising a burden of the same weight and the necessity of gemerating by the hydromotor of greater force than it should be necessary with the vertical location of the hydromotor, i.e by attachment of its both ends to the lever arms of the same length.
Even the above said arrangement does not result in attaining minimum opening angles of the levers and moreover it is quite impossible to attain a zero angle included by the levers i.e. to reach such a position where both levers are in alignment.
Furthermore the EP No. 0136986 discloses hoisting mechanisms having at least two pairs of scissors assembly levers where the axially extending expansion member, for example a hydraulical cylinder, is rotatably mounted by its lower end upon the base of the hoisting mechanism approximately in the axis of rotation of the first pair of the scissors-type levers while to its upper end a cross joint projecting transversely through oblong holes in the upper arms of the second pair of the scissors assembly levers. The cross pivot is at its both ends
REFERENCES:
patent: 1986273 (1935-01-01), Leffingwell
patent: 2070960 (1937-02-01), Phillips
patent: 3174722 (1965-03-01), Alm
patent: 4149469 (1979-04-01), Bigler
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