Electricity: circuit makers and breakers – Liquid contact – Contact dips into the conductive liquid
Reexamination Certificate
2002-06-17
2004-04-13
Lee, K. (Department: 2832)
Electricity: circuit makers and breakers
Liquid contact
Contact dips into the conductive liquid
C200S043040, C200S061620
Reexamination Certificate
active
06720508
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to switches such as limit switches and key switches usable for doors that are electromagnetically locked.
A key switch is often used on a door to a work area with power machine tools for switching power on and off by detecting the opening and closing of the door. A key is usually operated on the door while the main part of the door switch is set on a fixed frame at the doorway such that the power source for the machine tools is switched on when the door is closed and the key is inserted into a keyhole provided to the main part of the switch and switched off when the door is opened and the key is pulled out from the main part.
FIG.
15
A and
FIG. 15B
show such a key switch with a main case
71
containing a plunger
70
which is upwardly biased by way of a spring (not shown) and a head case
73
provided with a key hole
74
, and a rotary cam
72
contacting the upper end of the plunger
70
connected to the main case
71
. As the cam is rotated to displace the plunger
70
, a mobile terminal (not shown) associated with the plunger
70
contacts or moves away from a fixed terminal, thereby switching on and off the switch mechanism.
FIG. 15A
shows a key
75
not yet inserted into the keyhole
74
and the plunger
70
remaining in the pushed-in condition against the biasing force thereon such that the switch is in the switched-off condition. When the key
75
is inserted into the keyhole
74
and the door is closed, the cam
72
has rotated and the plunger
70
is released from the pushed-in condition, thereby allowing the mobile terminal to contact the fixed terminal to bring the switch into the switched-on condition.
A key switch thus structured remains in the switched-off condition unless the key
75
is inserted because the cam
72
inside the head case
73
keeps the plunger
70
pushed in. If the head case
73
is removed for a maintenance work or happens to be knocked away accidentally from the main case
71
by an external force, the force pushing in the plunger
70
may be diminished, allowing the plunger
70
to be moved by the biasing force thereon and to bring about the switched-on condition.
Thus, at the time of a maintenance work when the head case
73
is removed from the main case
71
, say, for replacing a damaged head case with a new one or changing the direction of insertion of the key, the machine tools under the control of the switch may be inadvertently switched on. A similar situation may come about when wires are being connected to the main case
71
while the head case
73
is disconnected from the main case
71
. Thus, it has been a common practice to switch off a source switch situated somewhere else before such work is carried out and to switch on the source switch after the work has been completed.
If an excessive force is applied to the head case
73
as the door is opened or closed and the head case
73
becomes removed from the main case
71
, the door may open while the machine tools remain switched on. This may happen, for example, when the door is not provided with a door stopper and is closed with a bang such that the impulsive force of the closing is directly communicated to the head case
73
. If the door is sufficiently heavy, the impulse may be sufficiently large to displace the head case
73
. Moreover, when the door is closed while the key is deformed, the key
75
may hit the head case
73
without being inserted into the keyhole
74
, causing the head case
73
to fly off the main case
71
.
In the case of a key switch with an electromagnetic interlocking mechanism, adapted to lock its switching mechanism when the door is closed, if the electromagnetic lock is used as a lock for the door without using a hook or a latch, the head case
73
may become removed from the main case
71
when the door is forcibly opened without releasing the electromagnetic lock because the cam inside the main body is not allowed to rotate by the switching mechanism and the key is being forcibly pulled with the door while being hooked to the cam.
There are two kinds door switches for electromagnetically locking. With the mechanical lock type, the door becomes automatically locked when it is closed by a locking mechanism by a biasing force and the door is released from the locked condition by passing a current through a solenoid. With the solenoid lock type, the door is not immediately locked when it is closed and its locked condition continues only while a current passes through a solenoid to overcome the biasing force which keeps the locking mechanism in an open condition, the opening of the door becoming allowed by stopping the current through the solenoid.
With either kind, if the door is forcibly opened without carrying out the proper unlocking process while the door remains locked, the cam inside is forcibly rotated with the key pulled. As a result, the cam or the plunger operated thereby may be damaged and the cam may rotate to open the door. Thus, the power circuit may remain switched on although the door is open, the machine tools in the work area being kept running.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a switch capable of operating correctly even if the head case is inadvertently removed from the main body without causing the switching mechanism to operate erratically.
It is another object of this invention to provide a switch capable of operating correctly even if the key is forcibly pulled out while the switch is locked.
In one aspect, the invention relates to a switch characterized as comprising a main case including a switching mechanism and a forcing means and a head case containing an operating mechanism for the switching mechanism, wherein the head case is normally attached to the main case, the switching mechanism is subjected to a biasing force, the switching mechanism and the operating mechanism are correlated such that the switching means is kept in a first switched condition (or the switched-off condition) by opposing against the biasing force when no external operation is being effected on the operating mechanism, the switching mechanism is displaced by the biasing force and is set in a second switched condition (or the switched-on condition) when an external operation is effected on the operating mechanism, the forcing means serves to set the switching mechanism in the first switched condition by a forced displacement operation on the switching mechanism, the forcing means is released from the forced displacement operation when the head case is properly connected to the main case, and the forcing means carries out the forced displacement operation when the head case is not properly connected to the main case.
In the above, “no external operation being effected on the operating mechanism” means that nothing is being done to operate the switch, for example, by inserting a key if the switch is a key switch. The condition that the head case and the main case are not properly connected may occur when at least a portion of the head case is separated from the main case. Thus, according to this aspect of the invention, the forcing means does not operate when the head case and the main case are normally attached but when they become separated either intentionally or accidentally, this function is activated and the switching mechanism is forcibly maintained in the first switched condition in spite of the biasing force thereon to switch it to the second switched condition.
According to a preferred embodiment of the invention, the aforementioned switching mechanism includes fixed terminals, mobile terminals, a mobile member supporting these mobile terminals and a returning spring applying a force on the mobile member so as to bring about the second switched condition (or the switched-on condition) where the mobile terminals contact the fixed terminals. The first switched condition (or the switched-off condition) is where the fixed terminals and the mobile terminals are separated and is realized by displacing the mobile member against the biasing force
Akiyama Shingo
Honda Sueaki
Kajio Hiroyuki
Kawata Kazuki
Miyoshi Tetsuhiko
Beyer Weaver & Thomas LLP
Lee K.
Omron Corporation
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