Winding – tensioning – or guiding – Reeling device – With spring motor
Patent
1996-09-09
1998-03-03
Lorence, Richard M.
Winding, tensioning, or guiding
Reeling device
With spring motor
192 7, 192103C, A62B 3504
Patent
active
057226121
DESCRIPTION:
BRIEF SUMMARY
This invention relates to safety apparatus for use by persons working at height. Such apparatus is of the kind which is attachable to a fixture and incorporates a safety line drum holding a safety line for attachment to a worker's safety harness. The safety line can be drawn from the drum in response to pulling force on the line exerted by the user in the course of his work but the apparatus has arresting means which functions automatically if the unwinding speed of the drum becomes excessive as it does in the event of the worker falling.
The arresting means functions to decelerate the drum, usually to rest. Thus, the clutch mechanism may operate to stop drum rotation almost immediately, in the event of acceleration reaching a predetermined speed such as occurs in the event of a fall. Or, the line drum may be permitted to continue to rotate so that the safety line may continue to pay out, but at a limited, controlled speed.
Conventionally, the arresting means incorporates a centrifugal clutch device designed so that centrifugal force is relied upon for causing drive-transmitting coupling elements of the clutch to move into driving engagement with a fixed abutment to stop drum rotation; or, the drive-transmitting coupling elements of the clutch are moved into driving engagement with a rotatable component of a braking device, the consequential rotation of this brake component being opposed by friction which brings about the deceleration of the drum.
The conventional centrifugal clutch means hereinbefore referred to has been found to be unsuitable for reliably achieving the rotational speed-sensitivity which some use situations require. In particular, for certain work situations in which workers are working at a very modest height above the ground, a worker who falls may hit the ground before the clutch brings into play means capable to retarding or arresting the fall, or at least before the descent speed has been reduced sufficiently to prevent serious injury to the worker on such impact. In other words, too much time elapses between the commencement of rapid acceleration of the drum and engagement of the centrifugal clutch. Attempts to design the clutch so that the centrifuging elements are actuatable by centrifugal forces of smaller magnitude have resulted in the clutch being too sensitive in the sense that it is liable to be engaged by accelerations of the drum such as may result from ordinary movements of the worker. This could create an additional accident hazard.
The performance of the fall-arrest or fall retard mechanism is critically dependent on the sensitivity of the device clutch to the speed of drum rotation and the reliability and efficiency of its operation. The present invention has emerged in the course of research carried out with a view to achieving reliability standards and speed-sensitivity characteristics which are not attainable by apparatus incorporating a conventional form of centrifugal clutch.
Broadly stated, fall-arrest or fall-retard apparatus according to the present invention is characterised in that the speed-sensitive clutch for coupling the safety line drum to another component, thereby to effect retardation of the drum, incorporates (i) at least one drive-transmitting coupling element which is connected to the safety line drum so that it bodily rotates with the drum, about the axis of rotation of the drum, and is displaceable from an inactive position into a drive-transmitting position in which it transmits drive to said other component and (ii) an inertia member which is freely rotatable about said axis and relative to the drum itself; and in that said inertia member is formed and disposed so that in a normal operation it rotates together with the coupling element, while on the occurrence of rapid acceleration of the drum in consequence of a fall, the inertia member exerts pressure, due to its inertia, against said coupling element in such occurrances to cause or assist movement of the coupling member into its drive-transmitting position.
The invention enables a fall to be
REFERENCES:
patent: 2990131 (1961-06-01), Carlsson
patent: 4846313 (1989-07-01), Sharp
patent: 5351906 (1994-10-01), Feathers
patent: 5447280 (1995-09-01), Feathers
Barrow Hepburn Sala Ltd.
Lorence Richard M.
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