Electricity: conductors and insulators – With fluids or vacuum – Boxes and housings
Reexamination Certificate
1999-06-30
2001-01-16
Kincaid, Kristine (Department: 2831)
Electricity: conductors and insulators
With fluids or vacuum
Boxes and housings
C174S034000, C361S816000
Reexamination Certificate
active
06175076
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a casing gasket for providing a spatial contact and an electrical connection between first and second pieces of a casing for electronic equipment, particularly, but not exclusively, for computers.
BACKGROUND OF THE INVENTION
As is well known, electronic devices generate electromagnetic emissions. These emissions are undesirable for a number of reasons, in particular since they may interfere with other electronic devices, such as telephones, televisions and radios. In consequence, it is conventional to use a metallic casing to cover and shield many types of electronic apparatus.
Personal computers, being electronic devices, are no exception to this rule. Personal computers generate unwanted electromagnetic emissions and the faster the processor, the worse is the interference problem. Standards have been established by the Federal Communications Commissions (FCC) and other standard setting bodies which strictly limit the amount of EMI emitted from electronic devices. Meeting these standards in a cost-effective way is a significant technical challenge.
Whilst the use of a metallic casing can be effective in reducing unwanted emission of electromagnetic radiation, at high frequencies further measures are necessary to keep EMI emissions down to the required levels. Modern personal computers use clock speeds of 200 MHz or more. Digital circuits operating at this speed can cause electromagnetic radiation to be emitted at frequencies in excess of 1 GHz. At such high frequencies, the wavelength of the emitted radiation can be such that the joints between different pieces of a casing can be a weak point where small gaps can allow electromagnetic radiation to leak out.
To alleviate this problem, an EMI gasket or sealing strip can be used in order to provide a tight spatial contact and an electromagnetic connection between two mating pieces of a casing. Examples of this kind of gasket can be found in U.S. Pat. No. 4,659,869 and U.S. Pat. No. 5,015,802.
Many different types of such gaskets are commercially available for different applications. Whilst these are generally satisfactory, they do suffer from a number of drawbacks.
Typically, the gaskets that are used in personal computers are made of resilient beryllium copper and, commonly need to be fixed in place using some kind of adhesive. This material is relatively expensive and the very thin sheets of the material which are used can have sharp edges. These sharp edges can lead to safety problems both in manufacturing and in the use of the device concerned. The need to use an adhesive to fix the gasket complicates the manufacturing process and can lead to difficulties in disposing of or recycling the apparatus at the end of its useful life. Moreover, if the gasket is made from a different metal than the casing itself, problems can arise due to chemical reaction between the two different metals in the gasket and the casing.
Another problem with conventional gaskets is that it is often difficult to avoid stressing the resilient material of the gasket beyond its elastic limit. This can lead to an irreversible deformation or crushing of the gasket which reduces the effectiveness of the shielding once the casing has been opened and closed a few times. This latter problem is particularly acute in the case of personal computer casings, since these are usually designed so that option cards of various types can be mounted and removed by a user to the interior of the casing. In contrast to other types of electronic apparatus, such as video or audio equipment, a personal computer casing may need to be opened and closed many times during its life.
The object of this invention is to provide a simple reduced-cost casing gasket design which mitigates the above drawbacks.
SUMMARY OF THE INVENTION
In brief, this is achieved by a casing gasket for providing a spatial contact and an electrical connection between first and second pieces of a casing for electronic equipment, the gasket comprising an electrically conductive resilient body of substantially C-shaped cross-section for grasping opposite sides of a panel on said first piece of said casing. The body has a first limb for engaging one side of the panel and a second limb for engaging the other side of the panel. A contact portion is provided on the convex side of the body. The body is shaped so that a lateral contact force applied to said contact portion by said second piece of said casing being brought into overlapping relation with said panel causes the body to pivot with respect to said panel so that the movement of the contact portion is made up not only of the elastic deformation of the body, but also by the pivotal motion of the body with respect to the panel.
Since the motion of the contact portion is made up in part by the pivotal motion of the body with respect to the panel, the gasket can be manufactured from a much less resilient material than is usual, such as steel, and the sheet from which the gasket is formed can be made thicker. In the preferred embodiment, for instance, the gasket is formed from sheet steel of
0
.
4
mm thickness. Since the casing, at least for computers, is also usually made of steel, the chance of chemical reaction between different metals is reduced.
Suitably, the pivotal engagement of the first limb of the gasket and the panel can be provided by a hook portion on the first limb for engaging an opening in the panel. This provides a convenient way of allowing the gasket to clip onto the panel, thus avoiding the need for the use of adhesive.
In a preferred embodiment, the gasket includes a portion of generally concertina configuration for providing an elastic deformation. If this concertinaed portion is disposed so as to have a concavity opposite the hook portion, a structure is formed which guides the panel into position, thereby allowing easy and convenient assembly of the gasket onto the panel.
Conveniently the gasket can comprise locating means, suitably a tongue extending into the concave side of the body, for locating the body with respect to the panel.
REFERENCES:
patent: 3277230 (1966-10-01), Stickney et al.
patent: 4572921 (1986-02-01), May et al.
patent: 4659869 (1987-04-01), Busby
patent: 4761516 (1988-08-01), Reichert
patent: 5015802 (1991-05-01), Chi
patent: 5039825 (1991-08-01), Samarov
patent: 5897808 (1999-04-01), Kim
patent: 5981871 (1999-11-01), Trumble et al.
patent: 2257839 (1993-01-01), None
Hewlett--Packard Company
Kincaid Kristine
Patel Dhiru R
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