Electricity: circuit makers and breakers – Multiple circuit control – Reciprocating contact
Patent
1996-02-13
1998-04-07
Spyrou, Cassandra C.
Electricity: circuit makers and breakers
Multiple circuit control
Reciprocating contact
200 4, H01H 2184
Patent
active
057366985
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention is related to a manually operated switch for the control of electrical equipment.
For switches employed in electrical equipment, the switch position or the switch status must be secured so that an uncontrolled change of the switch state cannot readily occur. An inadvertent starting of an electrical apparatus due to, e.g., vibration or a strong shock, causing the movement of the switch to a wrong position, may produce a very dangerous and hazardous situation as a result of the unintentional starting of the equipment. The inadvertent switching-on of electric power in a circuit may also be hazardous during, e.g., maintenance operations. Correspondingly, unintentional toggling of a switch to the zero position, that is, the switching off of the current from an electric circuit may cause machinery damage due to uncontrolled stopping of actuators. Due to such risks, reliable latching of equipment switches in their ON and OFF positions using, e.g., spring-loaded means is very important.
Positive latching of a switch position can be implemented by means of, e.g., a cam attached to the switch operating shaft, whereby the cam is followed by a spring-loaded detent lever. The detent lever is provided with a guide slot suited to accommodate a guide pin fixed to the body structure of the switch. The loading spring of the detent lever is adapted about the detent lever and compressed between the guide pin and the meeting point of the detent lever with the cam. When the switch is in its ON position or in its OFF position, the spring positively latches the switch in its set position and prevents uncontrolled rotational movement of the switch operating shaft. As the shaft is rotated, the spring is compressed between the guide pin and the cam tip. After the cam tip is rotated to its top dead center position, the toggling point of the cam/detent system is attained and as the cam is further rotated over its TDC position, the spring pushes the cam and the attached switch operating shaft to its opposite position.
However, such a switch construction has some drawbacks. Although the spring can positively latch the switch in a correct position, at the ends of the shaft rotational travel, the operation of the switch is rather uncontrolled in the middle of the shaft rotational travel. In the TDC position of the cam/detent mechanism, the spring force is oriented perpendicular to the longitudinal axis of the cam/detent combination, thus being exerted onto the switch operating shaft and not exerting a rotational force on the switch operating shaft and the guide pin. Consequently, this sector of the rotational travel forms an undetermined position of the switch setting, in which the switch may remain after operation by a careless user. The mutual friction between the switch members makes such a position uncontrollable and relatively easily permits the switch to assume this intermediate position. As the intermediate position coincides with the TDC position of the cam/detent mechanism, the position is quite unstable. Therefore, a switch left in this intermediate position may readily toggle from this intermediate position due to, e.g., a small shock to either limit position. Consequentially, such an uncontrolled change of switch position can cause an inadvertent starting of the equipment or the switching-on of the power in an electric circuit which is supposed to be at zero voltage. Obviously, a hazardous situation occurs.
In addition to that discussed above, a conventional switch has the drawback that the operating speed of the switch is dependent on the operator action. This property degrades the electrical performance specifications of the switch. When the switch is operated using, e.g., too low a torque, the switching action does not take place at sufficient speed, whereby an arc will be formed between the contacts that can destroy the switch very quickly as the energy released by the arc obviously has the greater burning effect the longer the arc is maintained. In addition to
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Mattlar Harri
Pussinen Matti
ABB Control Oy
Friedhofer Michael A.
Spyrou Cassandra C.
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