Brakes – Wheel – Continuous
Patent
1992-11-17
1994-02-22
Oberleitner, Robert J.
Brakes
Wheel
Continuous
188 8277, 188187, 192 8R, 254376, A62B 3504
Patent
active
052879500
DESCRIPTION:
BRIEF SUMMARY
This invention relates to fall-arrest apparatus for attachment to a fixed anchorage, which apparatus comprises a drum for holding a cable or other extendable anchorage line and a drum brake which functions automatically to brake the drum if it exceeds a given unwinding speed.
Apparatus of this kind have long been used for protecting workers who are exposed to the risk of falling from an elevated work site. Examples of such apparatus are described in UK Patents 851981 and 1552667.
The drum brake employed in apparatus of the kind referred to may be of centrifugal type, comprising braking elements which bodily rotate with the drum. The drum is biased by torsion spring means in the winding direction so as automatically to take up any slack in the anchorage line. The said drum braking elements are normally held retracted by springs but if the drum should reach an unwinding speed above a certain value they move against the action of their springs into positions in which they cause deceleration of the drum to rest.
It is known (see e.g. U.S. Pat. Nos 4,489,919 and 4,846,313) to provide apparatus of the kind referred to with a winch mechanism by which the drum can be manually re-wound to raise a fallen suspended load. The winch handle drives the drum via a reduction gearing affording a substantial mechanical advantage. As the drum begins to be rotated, the centrifugal drum brake mechanism disengages. In order to prevent the load from descending under its own weight as soon as winding force on the winch handle is relaxed, a ratchet operates between the winch handle and the drum housing to prevent any reverse movement of the winch handle. It follows that the winch mechanism cannot be used for lowering a suspended load unless the ratchet is rendered inoperative with consequent risks of the load sustaining an arrested fall due to loss of control of the winch handle by the operator. That is a disadvantage. For example, in the case of the fall of a worker using the fall-arrest apparatus, circumstances may be such that recovery and care of the worker could be more speedily effected if the worker could be lowered to the ground in a controlled manner with complete safety.
U.S. Pat. No. 4,589,523 and European Patent 152041 describe fall-arrest apparatus having a winch mechanism which can be selectively operated in winding or unwinding mode for raising or lowering a fallen load suspended from the anchorage line. This is made possible by a progressively acting screw-type friction clutch incorporated in the transmission between the winch handle and the anchorage line drum. Operation of the winch handle in winding or unwinding mode cause clockwise or anti-clockwise movement of a clutch clamping nut which is in screw engagement with the winch shaft and consequently causes approach or separating movement of friction rings of the clutch. Turning of the winch handle in the winding mode causes the clutch rings to become clamped together so that winding torque is transmitted to the drum, in consequence of which the centrifugal drum brake becomes released. Continued turning of the winch handle in the winding mode causes the load to be winched up. The frictional resistance of the clutch, together with the operation of a pawl and ratchet lock associated with the winch shaft, prevents the drum from unwinding under the suspended load whenever the winding force on the winch handle is relaxed. For lowering the suspended load the winch is operated in either of two ways. In one way, the winch handle is first turned in the winding mode sufficiently to cause release of the centrifugal drum brake as aforesaid and is then turned in the reverse direction until the clamping force on the clutch rings becomes so reduced that the clutch slips under the torque applied by the suspended load. Thereafter a very nice control of the winch handle is necessary if the lowering of the load is to proceed reasonably smoothly. In practice this is difficult. Unwinding motion of the drum in consequence of the clutch slippage tends to tighten the clutch rings again a
REFERENCES:
patent: 1807690 (1931-06-01), Ehemann et al.
patent: 2134405 (1938-10-01), Hulshizer
patent: 2515434 (1950-07-01), Zwald
patent: 4325522 (1982-04-01), Sauber
patent: 4456227 (1984-06-01), Notenboom
patent: 4489919 (1984-12-01), Ostrobrod
patent: 4589523 (1986-05-01), Olson et al.
patent: 4846313 (1989-07-01), Sharp
Feathers Leonard J.
Hartley Ian L.
Murphy Gerald P.
Ballato Josie A.
Barrow Hepburn Sala Ltd.
Oberleitner Robert J.
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