Electricity: circuit makers and breakers – Electric switch details – Actuators
Patent
1997-09-22
1999-02-09
Friedhofer, Michael A.
Electricity: circuit makers and breakers
Electric switch details
Actuators
200 17R, 200 6162, 200 4307, H01H 2700
Patent
active
058682430
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a safety switch for a guard device associated with a machine or device.
Guard devices of this type prevent persons from being able to get within the danger range of a machine or device as long as the machine or device is in operation. To that end, the door or the like that allows access is monitored by a safety switch, which allows the machine or device to be turned on only if the door or the like is closed, and which stops the machine or device if the door or the like is opened.
The known safety switches of the type referred to at the outset are actuated by means of a key, which can be introduced into a channel provided in the head of the switch and removed from it again. Both when the key is inserted into the switch head and when it is removed, a switchover of the switch takes place, in the one case preferably by compulsion, because of the force exerted on the key.
The known safety switches have the serious disadvantage that whenever the switch head comes loose from the switch housing, especially in response to externally exerted force, breakage occurs that causes disconnection; the tappet of the safety switch, because of the restoring force exerted on it, changes over to the switching state in which the machine or device can either be turned on or stays on. If the disconnection of the switch head from the switch housing occurs when the door or the like of the guard device is open or is being opened, then the protection sought by means of the guard device and the safety switch is entirely lacking.
SUMMARY OF THE INVENTION
It is therefore the object of the invention to create a safety switch of the type referred to at the outset that does not lose its safety function even if the switch head is disconnected from the switch housing. In accordance with the invention a sensor that detects the presence and absence of the switch head is provided, and an actuator is arranged in the switch housing under the control of the sensor and, in the event of loosening of the switch head from the switch housing, exerts a force on the switch actuating device in direction of motion counter to the restoring force, that is equal to or greater than the restoring force, depending on whether the switch actuating device is to be held in its previously assumed position or is to be returned thereto.
Thanks to the sensor that detects the presence and/or absence of the safety switch and to the actuator, disposed in the switch housing and controlled by this sensor, it is possible, if the switch head is disconnected from the switch housing, for the actuator to exert a force on the switch actuating device, on whose position the switching position of the switch depends, that either puts the switch in the OFF position or prevents the switch from changing over to the position in which the machine or device is, or can be, put into operation.
In a preferred embodiment, the sensor has at least one mechanical feeler member. It is understood that other sensors, such as optical or electrical sensors, can also be considered.
In the case of the actuator as well, a mechanical version is advantageous, for reasons of both cost and reliability; it is expedient for the actuating force to be made available by a spring loader. However, the actuator may also have or comprise other components, such as electromagnetic components.
In a mechanical version of the actuator, an embodiment of the force transmitting member as a pivot lever, in whose pivot path a stop face of the switch actuating device is located, is especially advantageous.
In the case of a mechanical feeler member, this member is preferably embodied as a barrier element that, when there is a switch head, keeps the force transmitting member in its inactivated state and does not enable it until the feeler member ascertains the separation of the switch head from the switch housing.
The actuator is especially simple and space-saving if the feeler member is formed by one arm, and the force transmitting member by the other arm, of a double-armed
REFERENCES:
patent: 4963706 (1990-10-01), Mohtasham
patent: 5464954 (1995-11-01), Kimura et al.
patent: 5516993 (1996-05-01), Wecke et al.
patent: 5587569 (1996-12-01), Mohtasham
Euchner & Co.
Friedhofer Michael A.
Striker Michael J.
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