Electricity: circuit makers and breakers – Multiple circuit control – Operating means
Patent
1994-06-24
1996-12-24
Brown, Brian W.
Electricity: circuit makers and breakers
Multiple circuit control
Operating means
200 6162, 200 4307, H01H 316
Patent
active
055875696
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to safety switch assemblies used especially but not exclusively in machinery guards enclosing kinetic machinery.
Known safety switch assemblies comprise a safety switch adapted to be fitted to an enclosure and an actuator adapted to be fitted to a door, gate or protective cover of the enclosure and insertable into the safety switch to turn ON the electrical power supply when the enclosure is closed by the door, gate or protective cover.
2. Description of the Prior Art
Known safety switches comprise within a housing normally-open contacts, one set fixed, and the other movable and carried by an axially-movable push rod spring-loaded to maintain the sets of contacts apart and the power supply consequently OFF.
The axially-movable push rod is connected to a rotatable cam of a cam arrangement normally disposed to prevent cam rotation and consequently to secure the push rod in a power supply OFF position but which is operable by the actuator to cause cam rotation and axial movement of the push rod to a power supply ON position.
Cam arrangements are known in which the rotatable cam prevented from rotating by a releasable connection between the cam and a non-rotatable locking element, rotation of the cam and consequent axial movement of the push rod from the OFF position to the ON position being effected by the actuator engaging the rotatable cam either to move the cam axially along its axis of rotation to release the connection between the rotatable cam and non-rotatable locking element, or to move the latter axially along a shaft defining the axis of rotation of the cam to release the connection with the cam.
These known cam arrangements are vulnerable to loss of free axial movement of the cam or the locking element along the cam shaft due to the accumulation of dust and grease between the latter and the cam or the locking element which may inhibit their axial displacement by the actuator or their return to the locked position upon withdrawal of the actuator.
It is an object of the present invention to provide an improved switch assembly.
SUMMARY OF THE INVENTION
According to the present invention there is provided a safety switch comprising a housing containing electrical contacts movable from a power supply OFF position to a power supply ON position by rotation of an actuating cam also contained within the housing and adapted to be rotated about a predetermined axis by an actuator of a predetermined shape insertable into the housing, wherein at least one locking member is mounted within the housing for movement in a direction perpendicular to the axis of rotation of the actuating cam, and the or each locking member is resiliently urged towards engagement with the actuating cam to prevent rotation thereof and consequent movement of the electrical contacts to the power supply ON position, the actuator being shaped such that when inserted into the housing it engages and displaces the or each locking member away from the path of movement of the actuator and out engagement with the actuating cam, and engages and rotates the cam to cause movement of the electrical contacts to the power supply ON position.
Preferably there are two locking members each slidably mounted on tracks defined by the housing. The housing may define two apertures through which the actuator is insertable to contact the locking members and the actuating cam, the two apertures opening in mutually perpendicular directions.
The actuating cam is preferably arranged so as to rotate in the same direction as the result of insertion of the actuator through either aperture. Preferably each locking member comprises a first component slidably mounted on the housing and a second component slidably mounted on the first, the first and second components being arranged such that insertion of the actuator through one aperture causes it to contact one component whereas insertion of the actuator through the other aperture causes it to contact the other component. Each locking member
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patent: 3205320 (1965-09-01), Soscia
patent: 4395608 (1983-07-01), Eicker et al.
patent: 4524251 (1985-06-01), Schulz
patent: 4658102 (1987-04-01), Seim et al.
patent: 4963706 (1990-10-01), Mohtasham
German Patent Search Report, Appl. No. G 93 08 260.6.
Search report dated Aug. 25, 1994, PCT application Ser. No. PCT/GB93/01135, filed May 28, 1993.
Brown Brian W.
E. J. A. Engineering PLC
Friedhofer Michael A.
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