Electricity: electrical systems and devices – Control circuits for electromagnetic devices – For relays or solenoids
Reexamination Certificate
1999-08-09
2001-08-07
Jackson, Stephen W. (Department: 2836)
Electricity: electrical systems and devices
Control circuits for electromagnetic devices
For relays or solenoids
C361S115000
Reexamination Certificate
active
06272001
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an emergency stop switch and to an emergency stop switch circuit provided for shutting off the operation output from machinery at the time of an emergency to thereby ensure the safety of an operator.
BACKGROUND ART
In factories and the like where industrial machinery is installed, in order to ensure the safety of an operator in cases such as where a fault occurs during operation of machinery, an emergency stop switch for emergency stop of the machinery is necessarily provided.
Heretofore, such an emergency stop switch incorporates; a first switch section provided with normally closed contact points which are normally on and which are switched off by push button operation at the time of an emergency, and a second switch section provided with normally open contact points which are normally off and which are switched on by operation of the push button at the time of an emergency, and the first and second switch sections are operated linked together. At normal times, the normally closed contact points of the first switch section are switched on by spring force, and the normally open contact points of the second switch section are switched off by spring force. The construction is such that when at the time of an emergency the push button is operated, the normally closed contact points of the first switch section go off, and the normally open contact points of the second switch section come on.
Here, the normally closed contact points output from the first switch section is generally used as a reset input to a self hold circuit provided in the operating control circuit for the machinery. That is to say, if the normally closed contact points are once switched off, the self hold circuit is reset, so that after this, provided that a trigger input signal is not input to the self hold circuit by some other separate means, then, even if the normally closed contact points of the first switch section are again switched on by spring force, an output from the self hold circuit is not produced. Recently, there is also the case where this is managed by simply inputting to a monitor.
This type of emergency stop switch is installed at each work site in a factory, and has heretofore been wired as shown in FIG.
1
.
That is to say, respective first switch portions
2
1
~
2
n of a plurality of emergency stop switches
1
1
~
1
n
are connected in series to a machinery operation control circuit
6
via a relay terminal assembly
4
. Furthermore, respective second switch sections
3
1
~
3
n
are separately connected to a monitor
5
via the relay terminal assembly
4
. These emergency stop switches
1
1
~
n
are installed at each respective work site in a factory.
Consequently, in the case where none of the emergency stop switches
1
1
~
1
n
are operated, the operation control circuit
6
generates an operation output for the machinery as normal. However if any one of the emergency stop switches
1
1
~
1
n
is operated, then the relevant first switch section switches off so that the operation output from the operation control circuit
6
stops. At the same time, the second switch section of the operated emergency stop switch switches on so that the work site where the emergency stop switch is operated is shown on the monitor
5
, enabling the work site where the emergency situation occurred to be made known.
However, with the conventional emergency stop switch, due to the construction using electric contact points, there is the possibility of a contact point fusion fault occurring. Since the emergency stop switch is only used in the case where an emergency situation arises, and is thus not frequently operated, monitoring to determine if it will operate normally is difficult. Moreover, even if inspected individually, since there is a large number disposed within a factory, then the time taken is considerable. Therefore, there is the danger that contact point fusion faults can be overlooked, and if the normally closed contact points of the first switch section have a fusion fault, then even if the push button is operated, the operation output for the machinery cannot be stopped, thus posing a problem from the point of ensuring operator safety.
Moreover, the work site where the emergency stop switch circuit as shown in
FIG. 1
with emergency stop switches severally connected is installed, and the machinery operation control side where the operation control circuit
6
, the relay terminal assembly
4
and the monitor
5
and so on are installed, are detached from each other. Hence in the case of a switch circuit which utilizes emergency stop switches using conventional electrical contact points, then as shown in
FIG. 1
, it is necessary for the respective emergency stop switches
1
1
~
1
n
installed at the respective work sites to be connected in series via the relay terminal assembly
4
, and also the location of all of the emergency stop switches
1
1 ~1
n
must be notified individually to the monitor
5
via the relay terminal assembly
4
. Therefore, there is the problem that the number of wires for connecting between the emergency stop switches
1
1
~
1
n
and the relay terminal assembly
4
is considerable.
The present invention takes into consideration the above situation, with the object of providing an emergency stop switch having no contact points so that there is no possibility of contact point fusion faults. Moreover, it is an object to provide an emergency stop switch circuit which does not incur an increase in wiring even in the case where a switch circuit connected to a plurality of emergency stop switches is installed. Furthermore, it is an object to provide an emergency stop switch circuit wherein monitoring for normalcy of the respective emergency stop switches is facilitated.
DISCLOSURE OF THE INVENTION
According to the present invention, an emergency stop switch comprises: a first core member secured to a fixed body and wound with a primary winding and a secondary winding; a second core member provided so as to be movable towards and away from the first core member; and a moving device for moving the second core member, the construction being such that when the second core member is made to approach the first core member by the moving device, a transformer is formed by the first and second core members so that an AC signal from an AC signal generating source connected to the primary winding side is transmitted to the secondary winding side, and when the second core member is separated from the first core member by the moving device, the AC signal is not transmitted to the secondary winding side.
With such a construction, at normal times where a push button is not pushed, the second core member is made to approach the first core member by a resilient member, so that a closed magnetic circuit is created by the first and second core members to thus form a transformer. Consequently, the AC signal applied to the primary winding from the AC signal generating source is transmitted to the secondary winding side. On the other hand, if an emergency situation arises and the push button is pushed, then the second core member is separated from the first core member against the resilient urging force of the resilient member, and hence the magnetic path is no longer formed and the output level from the second winding side drops considerably or becomes zero, and the operation output to the machinery is shut off. Moreover, since there are no electrical contact points, the possibility of a contact point fusion fault does not arise.
More specifically, the moving device comprises; a push button with one end fixed to the second core member, and a resilient member for resiliently urging the second core member in an opposite direction to the push operation direction of the push button, the construction being such that at normal times, the second core member is made to approach the first core member by the resilient urging force of the resilient member to form a transformer, and when the push button is pushed, the second core member separates from the first
Jackson Stephen W.
McDermott & Will & Emery
The Nippon Signal Co. Ltd.
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