Supports: racks – Special article – Electrically powered
Reexamination Certificate
2001-05-01
2003-10-07
Gibson, Jr., Robert W. (Department: 3634)
Supports: racks
Special article
Electrically powered
C312S223100, C312S265100
Reexamination Certificate
active
06629614
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to systems for mounting equipment on racks, and in particular to the mounting of telecommunications equipment shelves or sub-racks on rack systems.
BACKGROUND OF THE INVENTION
Telecommunications equipment such as switching circuits on cards are typically held in parallel slots within shelves or sub-racks. These shelves are in turn mounted within rack structures by mounting bolts or similar connectors.
My earlier U.S. Pat. No. 5,975,315 (the entire contents of which are incorporated herein by reference) describes an equipment rack of this type for holding telecommunications equipment within shelves mounted in the equipment rack.
The rack of U.S. Pat. No. 5,975,315 comprises a base member, a pair of parallel side members extending vertically upwards from the base member and a top member coupling the free ends of the side members. Means are provided for securing the base member to a floor (or other support surface).
Rack systems such as those of U.S. Pat. No. 5,975,315 are required to conform to industry standards such as the standard “ETS 300-Pt3: Engineering Requirements for Miscellaneous Racks & Cabinets” set by the European Telecommunications Standards Institute (ETSI), or the “23 inch” standard (“ANSI/EIA-310-D-1992: Cabinets, Racks, Panels, & Associated Equipment” set by the American National Standards Institute and the Electronic Industries Association). In an ETSI rack conforming to ETS 300 a plurality of mounting holes are provided down the front surfaces of the two side members.
The shelves are provided with mounting means such as a pair of L-shaped brackets affixed to the front part of the sidewalls of the shelves and extending outwards from the front surface of the shelves on either side. In this way, when a shelf is inserted into the rack between the side members, a portion of the L shaped bracket overlaps the mounting holes of the respective side member, allowing a bolt or screw to affix the bracket (and thus the shelf) to the rack.
The L-shaped brackets serve a further purpose in earthing the shelves and the equipment in the shelves, by making a good electrical connection between the shelf housing and the rack structure which is itself earthed.
In a rack conforming to the 23 inch EIA standard the mounting method is similar but the support is located more deeply within the rack, i.e. at a point between the front and back of the shelves.
The susceptibility of a geographical location to severe earthquake damage is classified, with any given location being rated from Zone
1
to Zone
4
(with Zone
4
denoting the greatest risk). In Zone
4
locations, telecommunications equipment contained in standard rack systems is likely to suffer vibration- or shock-induced damage due to the potential severity of an earthquake in such a zone.
The rack of U.S. Pat. No. 5,975,315 addresses earthquake induced vibrations by providing a number of bolts for mounting the base member to the floor. When these bolts are overtightened or overtorqued (as they are designed to be), the base member is pre-stressed, and this stress is transmitted to the side members. This has the effect of increasing the frequency response of the rack. Since earthquake induced vibrations are typically low frequency vibrations (e.g. most of the energy is at frequencies of not more than about 10 Hz), many of the effects of earthquake induced vibration can be greatly reduced by this method.
Other methods of earthquake proofing telecommunications equipment racks have been proposed such as in U.S. Pat. No. 5,004,107, which discloses a rack having a heavily reinforced base portion which braces the rack against applied forces. The disadvantage of this is that the box-like base portion is bulky and limits the volume of equipment which can be housed in the rack. Since racks will typically have standard outer dimensions (e.g. 2200 mm×600 mm×300 mm for an ETSI rack), a reduction in available volume will result in more racks being needed to house the same amount of equipment, which is a severe problem in installations where space is at a premium.
In order to be certified for Zone
4
earthquake resistance, telecommunications equipment is required to undergo a vibration test which involves vibrational accelerations of up to 5 g. The equipment, which could, in use, be carrying emergency traffic, such as 911 calls, must be operational after the test is conducted without manual resetting or adjustment (so that in an earthquake scenario it would not require an operator to enter a potentially dangerous building to reset or repair the equipment.
It is therefore an object of the present invention to provide an improved method of mounting telecommunications equipment, and in particular to provide a rack and a shelf providing greater earthquake resistance to telecommunications equipment stored therein.
Due to the large amount of telecommunications equipment already deployed in rack structures, it is a further object of the invention to provide improved earthquake resistance, and preferably Zone
4
compliance, to existing racks and shelves which can be easily retrofitted in current installations with minimal modification of the shelves. Because existing shelves have been certified for structural strength and EM shielding, any significant modifications to shelf structure will require the modified design to be reassessed.
SUMMARY OF THE INVENTION
The invention provides a mounting bracket for mounting an equipment housing to a rack. The mounting bracket has a bracket body for rigid attachment to the housing, a fastener for rigid attachment to the rack, and a damping member coupling the fastener and the bracket body.
The damping member isolates the housing and bracket body from the rack and fastener, so that vibrations carried by the housing can only be transmitted to the housing via the damping member.
The conventional way of increasing earthquake resistance for telecommunications racks is to overengineer the rack structure itself and thereby prevent damage to the rack and preventing the equipment from e.g. breaking loose. The present invention takes a different approach by recognising that not all vibrations can be eliminated from the rack, even when the resonant frequency of the rack is increased it thus provides a bracket which isolates the loaded rack into a number of distinct sub-systems, each mechanically connected only via damping members.
The damping member is preferably an elastomeric material such as a silicone. Particularly preferred is very high density silicone, having a modulus of 10-15 daN/cm
2.
In the preferred embodiment, the bracket body is in the form of a plate which engages with a side panel of the housing, extending from the front to the rear. A flange which is perpendicular to the plate and depends from the front edge carries the damping member.
Such a bracket is particularly suited for fitting to equipment housing to be carried in ETSI-compliant racks, where the mounting is at the front.
In preferred embodiments a rear mounting is located adjacent the rear edge of the plate. This rear mounting also has a fastener for rigid attachment to the rack, and a rear damping member coupling the rear fastener to the bracket body.
It has been found that conventional ETSI or front-mounted shelves can be damaged by the fact that whereas the support is at the two front side edges, the centre of gravity is towards the centre of the shelf. By providing a further mounting at the rear of each side, the housing is dramatically stabilised during earthquake tests.
In one embodiment to be described below, the rear damping member takes the form of a solid cylinder of elastomeric material, and the bracket body and the fastener are coupled to the opposite faces of the cylinder.
This cylinder is preferably carried with its axis running vertically to absorb vertical vibrations, since the damping member between the front flange and the rack mounting rail will absorb horizontal vibrations.
In another embodiment the rear damping member and the front damping member each take the
Barnes & Thornburg
Gibson , Jr. Robert W.
Nortel Networks Limited
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