Energy absorbing device

Details Energy absorbing device Energy absorbing device

1996-10-10

1998-09-01

Butler, Douglas C.

Brakes

Plastic deformation or breakage of retarder element

267155, 182 3, A62B 3504, F16F 712

Patent

active

057997608

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The invention relates to the field of safety equipment, more particularly to a novel energy absorbing device for arresting the motion of moving bodies. The energy absorbing device finds applications in personal fall protecting systems that protect workers against accidental falls. The invention also extends to a fall protection system incorporating the novel energy absorbing device.


BACKGROUND OF THE INVENTION

To prevent fatal injuries as a result of accidental falls, labour legislation codes require workers that perform a task on an elevated structure to wear a safety harness firmly attached to a fixture. In the event of an accidental fall, the safety harness is intended to arrest the falling movement at a safe distance above ground.
For an increased manoeuvrability it is common practice to tether the safety harness to a horizontal or a vertical safety track, such as a steel cable or a synthetic rope, among others, anchored to the structure on which the work is performed. The safety harness is freely displaceable along the track allowing the individual to walk around the work site without impairing the level of fall protection. In the event that a fall takes place the track anchors must generate the reaction force necessary to decelerate the human body to a stop.
The loading imposed on the various components of a fall protection system can be extremely severe especially in the case where several workers collectively fall. In order to buffer the loading, it is known to provide the fall protection system with an energy absorbing device that progressively dissipates the kinetic energy of the falling body.
The prior art discloses a variety of energy absorbers specifically designed for use in personal fall protection systems. The following patents are representative of state-of-the-art in this field.


______________________________________ PATENT NUMBER AND COUNTRY PUBLICATION DATE ______________________________________ U.S. 4,100,996 July 18, 1978 U.S. 4,446,944 May 8, 1984 U.S. 4,538,702 September 3, 1985 U.S. 5,174,410 December 29, 1992 U.S. 5,224,427 July 6, 1993 CANADA 2,039,004 March 25, 1991 ______________________________________
Most of the energy absorbers described in the prior art noted above, dissipate energy by inducing a controlled rupturing of a fibrous network. One approach consists of folding several times upon itself a strip made of non-stretchable woven fibers. The various plies of the strip are attached to one another by sacrificial links. The sudden tensile loading developed in a fall progressively breaks the links that provide a shock absorbing action. In a somewhat different approach, a pin is forced longitudinally through a strip of woven fibers to provide energy dissipation by producing a long and continuous rupture line in the fibrous material. The prior art also contemplates a non-destructive design that absorbs energy through frictional force developed when a length of synthetic webbing is pulled through a buckle.
The prior art energy absorbers noted above suffer from a variety of drawbacks. The designs utilizing sacrificial links provide merely an intermittent energy absorption effect. The force/deployment characteristics of this style of energy absorbers give rise to force spikes each time a link ruptures, followed by a relatively unimpeded deployment until the next link becomes loaded. The shock absorbers that use a pin destructively tearing synthetic webbing are efficient energy dissipators, however, their behaviour is largely dependent upon environmental conditions. For instance, the force necessary to induce deployment significantly varies between a dry webbing and a wet frozen webbing. Synthetic materials also have a limited lifespan when subjected to ultraviolet radiation such as sunlight. The same observations can also be made with regard to the energy absorbers based on frictional forces. Here, the behaviour of the device also depends upon the frictional/thickness properties of the webbing. A minor change in the friction prop

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