Electricity: circuit makers and breakers – Special application – Feeler moves into detecting contact with object
Reexamination Certificate
2002-08-15
2004-05-25
Luebke, Renee (Department: 2833)
Electricity: circuit makers and breakers
Special application
Feeler moves into detecting contact with object
C200S061810
Reexamination Certificate
active
06740826
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
2. Description of the Related Art
The invention relates to a safety contact strip having at least two conducting switching layers in a non-conducting, closed switching chamber within a profile forming an outer jacket.
Safety contact strips are often used as closing edge safety devices at pinching and shearing points. Fitted on gates, machines and handling equipment, persons and material are protected by such safety contact strips. For this purpose, the known safety contact strips are usually held on a respective fastening side in an aluminum carrier profile.
A safety contact strip of the generic type has a contact-maker profile which is held in a carrier profile and in which a separately formed safety contact strip is accommodated in a switching chamber within the outer jacket of the profile. The special shaping of the contact-maker profiles, consisting in particular of an EPDM or an NBR rubber, protects the safety contact strip lying in the switching chamber from damage and permits not only switching loads for switching the contact-maker profile that are perpendicular to the oppositely lying switching layers of the contact-maker profile.
The advantage of the separate formation of a safety contact strip is firstly to be seen in that it can be accommodated in extremely different contact-maker profiles, in which only the switching chamber is to be formed in cross section in a way corresponding to the safety contact strip. Further advantages are offered by the choice of material components with regard to a highly insulating outer jacket of EPDM with two conductive switching layers lying opposite each other on the inside. These switching layers may also consist of an EPDM material, which is often a comparatively poor electrical conductor. Therefore, metallic conductors, for example stranded copper wires or special metal meshes, which bond well in the conducting layers, are often used in these conducting layers to reduce the ohmic resistance.
DE G 93 08 344.0, DE 94 22 030 U1, DE 93 21 338 U1 or EP 0 654 575 disclose safety contact strips of another type, in which a profile is provided with a single hollow chamber, which has on the inside at least two switching layers lying opposite each other. Although in the case of safety contact strips of this type only a low switching load is necessary, there is the great risk of soiling of the switching layers, for example in the event of breakage of the profile. Since these safety contact strips can be produced from a conductive material and a non-conducting EPDM material, which materials can also be coextruded to form these safety contact strips, there is the great risk of the comparatively thin, outer protective layer of the non-conducting EPDM material not being correctly formed and the conductive layer remaining outwardly uninsulated and easily liable to damage.
SUMMARY OF THE INVENTION
Against this technical background, the invention has the object of providing a safety contact strip of the type in question of high quality, but at the same time of comparatively simple construction, which switches reliably, in particular even under low switching loads, not only from the direction which is actually to be expected.
According to the invention, the profile, the switching chamber and the switching areas, each with at least one embedded conductor, are formed in one piece. As compared with a two-part formation, with a contact-maker profile and a pushed-in safety contact strip, a one-piece formation is advantageous from technical production-related aspects. In particular, the measures of the one-piece formation also allow the thickness of the walls of the switching chamber to be kept relatively small, without there being the risk of soiling in the event of breakage of the outer jacket. The measure of a thinner wall of the switching chamber also significantly improves the response of the safety contact strip under a switching load. In particular, the omission of a separately formed enclosure of the switching layers produces a significant saving of material.
Alternatively and in particular in combination with the aforementioned features, a better switching performance can also be achieved by an embodiment wherein the switching chamber is kept free in a cross section by webs formed in the manner of spokes. At least two webs, preferably three or four webs, of a material thickness which are often within the range of the wall thickness of the profile in the region of the loads to be expected, hold the switching chamber, the wall of which is made much thinner. In this way, a reliable application of force under a switching load of the outer jacket on the switching layers within the switching chamber is ensured. In particular, this measure permits force to be introduced not only in a preferred direction but additionally also from directions which are significantly inclined onto the switching areas of the switching layers.
In this respect, consideration has been given to the fact that an outer jacket of a profile, webs within a profile and a switching chamber form a plurality of chambers that are separate from one another within the profile.
In a particularly advantageous way, it may be provided that the safety contact strip according to the invention is a coextrudate. This produces a simple, one-piece formation of this safety contact strip, which additionally ensures a reliable function. Obtained as a coextrudate of one or more of the preferred materials, silicon, EPDM, NBR, PVC, TPE and further known, expediently elastic, at the same time resistant materials, is a safety contact strip that is formed in one piece and can be optimally adapted to specified mechanical and electrical requirements by the selection of the materials used. In particular in the case of such a coextrudate, it is preferred that the profile is formed from a TPE, that the switching layers are formed from a conducting EPDM and that the conductors are formed from a metal. Consequently, significantly different materials are used here, to be specific non-conducting, thermoplastic elastomers and ethylene/propylene-diene terpolymers and also incorporated metal conductors, for example copper wires, stranded copper wires, metal meshes or the like, whereby much improved switching characteristics can also be achieved. In particular, the outer jacket of the profile of TPE can be adapted comparatively easily to the degree of switching load. TPE is also much more resistant than many chemical compounds such as are also used, for example, in the automotive industry, where safety contact strips of this type are used for example in the case of electric window lifting mechanisms. It is also possible to form the conducting EPDM switching layers specifically with regard to their ohmic resistance, without having to make allowance for an outer, non-conducting EPDM enclosure.
Alternatively and nevertheless expediently against the background of disposal, the profile and the switching layers may consist of a single-grade plastic and the conductors may consist of a metal. For this purpose, the plastics presented above can be used. In this case, only the electrical conductivity of a plastics material has to be differently set, although this has no bearing on joint disposal. The metal may in this case be disposed of in a way known per se or by means of magnetic separators.
If the material, for example a TPE, of the profile has a Shore hardness of 50 to 70, in particular of 60, this produces a balance between a force of resistance against a switching load and a necessary softness for elastic deformation, the elastic deformation having the effect of exerting a pressure via the webs on the switching chamber, by which the switching layers come for example into touching electrical contact.
In particular, if it is used as the material for the outer jacket of the profile, the TPE material, as a non-conductor, should also have an electrical resistance of over 30 M&OHgr;.
In a preferred embodiment of the safety contact strip according to the invention, a sealing lip
Friedrich Helmut
Meyer Paul
ASO GmbH Antriebs-und Stenerungstechnik
Cohen & Pontani, Lieberman & Pavane
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