Electricity: circuit makers and breakers – Special application – Liquid or moisture responsive
Patent
1986-03-27
1988-07-19
Luebke, Renee S.
Electricity: circuit makers and breakers
Special application
Liquid or moisture responsive
200 76, H01H 1518
Patent
active
047586982
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to electrical engineering, and more particularly to microswitches.
2. Description of the Prior Art
The process of contact switching in limit switches is normally induced by the action of a movable cam on the drive element of the switch. At low speeds of operation of the machine cam member and at a speed of contact switching dependent on the speed of travel of the cam, as is the case with direct action switches, the interval between the initial engagement of contacts under load and the point when a suffient contact pressure is developed between the contacts is relatively lengthy. The prolonged closed position of the contacts under electric load accompanied by insufficient contact pressure, as well as slow switching action of the contacts may cause numerous emergencies, such as fusing, burning and welding of contacts.
In order to obviate the aforedescribed contact damage at low speeds of travel of the movable cam, use is generally made of microswitches provided with means for accelerating the speed of contact switching.
There is known a microswitch (cf., e.g. U.S. Pat. No. 2,791,656) comprising a base, fixed contacts secured on the base, and movable contacts connectable with the fixed contacts. Connected to the movable contacts is a drive member, this connection being executed by means of a mechanism for switching the movable contacts in the form of a resilient strip. Immediately in the central portion of the resilient strip there are arranged the movable contacts. At the portions between the attachment points of the movable contacts and their outer ends connected to the drive member the resilient strip has two resilient elements disposed symmetrically relative to the axis of the drive member at an angle to each other for swinging angularly relative to each other. This microswitch is simple to construct and has relatively small dimensions.
Operation of this microswitch is characterized in that during the movement of the drive member the ends of the resilient elements of the mechanism for switching the movable contacts connected therewith tend to be displaced. Therewith, the resilient elements change their position relative to the movable contacts, whereas the contact pressure varies depending on the speed of travel of the drive member from its nominal value to the minimum. Upon the drive member reaching the movable contacts the resilient elements assume substantially horizontal position, while the contact pressure drops practically to zero. A slow or reverse movement of the drive member may result in that the contact pressure may be close to zero for a considerable length of time, which in turn may cause failure of the microswitch.
When operation of the aforedescribed microswitch is accompanied by vibrations or impacts, even negligeable displacements of the drive member and movable contacts upset the position of the spring elements relative to the movable contacts and lead, accordingly, to minimized contact pressure.
When the drive member assumes a position close to contact making or breaking, the fully deformed resilient strip is almost horizontal, whereas its central portion is pressed by the movable contacts to the fixed contacts with a minimal force to result in unstable position of the resilient strip. Even small vibrations or impact forces acting on the microswitch in this position of the drive member may cause accidental switching of the movable contacts when the drive member is short of the position for contact making or breaking, or triggering. For this reason, the above microswitch fails to provide a reliable triggering accuracy (repeatability of triggering points) when the drive member moves slowly or reversed, or when the microswitch is subjected to vibrations and shocks.
Such a low accuracy of the microswitch and insufficiently reliable operation thereof during slow or reversed movement of the drive member accompanied by vibrations and impacts exerted on the microswitch limits the field of its application.
Th
REFERENCES:
patent: 2125432 (1938-08-01), Du Brie
patent: 2791656 (1957-05-01), Dehn et al.
patent: 3764761 (1973-10-01), Poltorak et al.
patent: 4086455 (1978-04-01), Takahashi
Chaly Fedor P.
Filatov Nikolai I.
Kosovtsev Vladimir A.
Mironenko Vyacheslav G.
Poltorak Alexandr P.
Luebke Renee S.
Vsesojuzny nauchno-issledovatelsky, proektno-konstruktorsky i
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