Electricity: circuit makers and breakers – Switch activation inhibitor – Removable actuator
Patent
1996-10-21
1998-07-07
Gellner, Michael L.
Electricity: circuit makers and breakers
Switch activation inhibitor
Removable actuator
200 6162, 200318, H01H 2700, H01H 152
Patent
active
057772843
DESCRIPTION:
BRIEF SUMMARY
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.
Known safety switches comprise a housing within which are mounted normally-open sets of contacts, one set of contacts being fixed, and the other being movable and carried by an axially-movable push rod. The push rod is spring-loaded to maintain the sets of contacts apart and the power supply consequently OFF.
The axially-movable rod is moveable by a rotatable cam of a cam arrangement normally disposed to prevent cam rotation and consequently to secure the 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.
It is known to supplement safety switch assemblies with a locking mechanism that locks the actuator in engagement with the safety switch. The objective is to provide an extra level of safety which positively prevents opening of the enclosure except in predetermined controlled conditions, for example actuation of a control which turns off machinery within the enclosure. In one known arrangement, the actuator is engaged by locking members that are pivotally supported by the housing and jammed in a locking position by a solenoid controlled member. This known arrangement requires relatively large locking components that occupy much valuable space and require a relatively powerful operating solenoid.
It is an object of the present invention to provide an improved safety switch assembly incorporating a locking mechanism.
According to the present invention there is provided a safety switch comprising electrical contacts movable from a power supply OFF position to a power supply ON position, an actuating cam adapted to be rotated about a predetermined axis by an actuator of a predetermined condition, rotation of the cam causing movement of a cam plunger which moves, the electrical contacts between the ON and OFF positions, and at least one locking member actuable between a locking position in which it engages the plunger such that when an attempt is made to withdraw the actuator from the switch movement of the cam plunger and consequent cam rotation is prevented and an unlocked position in which the cam plunger is released and the cam is free to rotate to allow withdrawal of the actuator.
Preferably the locking member is in the form of a pivotally mounted lever which has a locking end engageable with a locking surface of the cam plunger, and a tail end which is operable to pivot the lever into and out of the locking position.
There may be provided means for moving the locking member between the locked and unlocked positions which means may be for example a solenoid.
In a preferred embodiment the locking members co-operate with a sliding member which is operated by said means for moving, the locking members engaging in guide slots in the sliding member. The sliding member may be connected to the solenoid by a pivotal arm such that when the solenoid plunger is in an extended position the sliding member is moved to a first position in which the cam plunger is free to move and when the solenoid plunger is in a retracted position the sliding member is moved to a second position in which the cam plunger is locked.
The guide slots may engage with the tail ends of the locking members and may be formed such that the sliding movement of the plate causes the tail ends of the locking members to move in the slots so as to pivot the levers such that the locking ends move into and out of engagement with the plunger.
Preferably the locking surface of the plunger is formed by a set of flats.
The solenoid may be provided with circuit which indicates the status of the
REFERENCES:
patent: 3731174 (1973-05-01), Harris
patent: 4524251 (1985-06-01), Schulz
patent: 4593545 (1986-06-01), Terry et al.
patent: 4904829 (1990-02-01), Berthaud et al.
patent: 5488207 (1996-01-01), Niwa et al.
patent: 5587569 (1996-12-01), Mohtasham
E.J.A. Engineering plc
Gellner Michael L.
Hayes Michael J.
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