Electricity: circuit makers and breakers – Limit switch
Reexamination Certificate
2002-06-24
2003-12-16
Friedhofer, Michael (Department: 2832)
Electricity: circuit makers and breakers
Limit switch
Reexamination Certificate
active
06664487
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to limit switches used for detection of objects or the like such as safety limit switches which have passed certain safety standard tests including the dielectric strength test, the electrical endurance test and the cable strength test.
FIG. 29A
shows an example of prior art limit switch S-
1
, comprising a switch unit
190
and a head unit
191
. The switch unit
190
includes a case
192
and a plunger
193
and also contains an inner switch
194
with a mobile switch plunger
195
. The switch plunger
195
supports two mobile members (not shown) and is contained inside a switch plunger holder (not shown) by means of a returning spring (not shown). Mobile contact points (not shown) on the mobile members and fixed points of a fixed terminal (not shown) form a contact point part. The head unit
191
includes a rotary shaft
197
rotatably supported by a head case
196
. A roller lever
199
with a roller
198
is attached to an end part of this rotary shaft
197
, and a cam
200
is provided to the rotary shaft
197
. The limit switch is formed by attaching the head unit
191
to the switch unit
190
such that the plunger
193
is pushed against the cam
200
of the rotary shaft
197
. The head unit
191
is attached to the switch unit
190
by placing the head unit
191
on top of the switch unit
190
, pushing in screws (not shown) into holes formed in the head case
196
of the head unit
191
and engaging these screws in threaded holes (not shown) formed in the case
192
of the switch unit
190
. This method of attachment, however, did not provide enough rigidity.
The limit switch is operated by moving a so-called dog (not shown) to cause the roller
198
of the limit switch to contact the dog and to tilt the roller lever
199
. As the roller lever
199
is tilted, the rotary shaft
197
is rotated to push the plunger
193
such that the switch plunger
195
of the inner switch
194
is pressed and the inner switch carries out a switching operation.
With a prior art limit switch, if the number of circuits for the inner switch
194
is increased, the total number of components increases and the inner switch
194
becomes too large, causing the limit switch as a whole to become also too large. If each constituent parts is made small so as to prevent the limit switch from becoming too large, however, it becomes difficult to produce a switch which can pass safety tests.
For attaching the limit switch to a target structure
201
(such as a wall), as shown in
FIG. 29B
, a screw
202
is passed through a screw hole
192
A in the case
192
of the switch unit
190
and is screwed into the target structure
201
. With a prior art limit switch, the attachment between the head unit
191
to the switch unit
190
was not sufficiently rigid, as explained above. If an object
203
is unexpectedly inserted or falls into the space between the head unit
191
and the target structure
201
to which the limit switch is to be attached, as shown in
FIG. 29B
, the head unit
191
may tilt forward as the screw
202
is tightened, causing the limit switch be deformed or otherwise damaged. If the limit switch is provided with an attachment member for attaching it to a target structure (such as shown at
201
) and if there is a gap provided between the attachment member and the target structure, furthermore, it is necessary to fill the gap with a spacer or the like for preventing deformation and breakage.
Another problem with prior art limit switches was that any attempt to improve their sensitivity in response to the market demand had adverse effects on resistance against vibrations, shocks and telegraphing.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a limit switch which need not be increased in size to satisfy the safety requirements of regulations although the total number of circuits is increased.
It is another object of the invention to provide a limit switch which is sufficiently strong and hence does not become deformed or damaged at the time of attachment and hence does not require extra components for preventing deformation and breakage or damage easily even if an unwanted object is inserted between the head unit and the target structure on which it is to be attached.
A limit switch embodying this invention may be characterized not only as comprising an inner switch having a plurality (say, more than four) of switch element units and an inner case, the inner case containing the inner switch and having covers and a switch case, a partition wall being provided such that independently provided switch areas sandwich the partition wall in between, and the switch element units being distributed individually into these switch areas, and the covers each sealing a corresponding one of the switch areas such that insulation characteristics can be improved. Screening members may be further provided for separating the switch element units when they are contained in the switch areas.
Each switch element unit comprises a fixed terminal having two (first and second) fixed contact points, a mobile member having two (first and second) mobile contact points and a switch plunger. The first fixed contact point and the first mobile contact point together form a first contact unit, and the second fixed contact point and the second mobile contact point together form a second contact unit. The switch plunger serves to open and close these contact units.
The switch areas include a part for containing the switch plunger (“switch plunger containing part”), parts for attaching the fixed terminals (“fixed terminal attachment parts”) sandwiching the switch plunger containing part from both sides, and lead line areas for keeping lead lines disposed along the fixed terminal installation parts and connected to the fixed terminals. With the switch areas thus structured, the number of switch element units may be increased without increasing the size of the limit switch without adversely affecting the safety characteristics.
The fixed terminal attachment parts include a plurality of fixed terminal installation parts for detachably installing the fixed terminals along the direction in which the switch plunger moves. The switch plunger comprises a switch plunger main body having a plurality of mobile members detachably attached and an elastic holder for holding and applying a biasing force on the mobile members. The fixed terminals are detachably set to the fixed terminal installation parts, and the switch plunger is biased by a returning spring when contained movably inside the switch plunger containing part. With a limit switch thus structured, the structure of contact units can be modified without using different components and only by changing the position of the mobile member, making it possible to develop an increased number of variations. Moreover, since common components will be used, it does not incur any extra cost to develop such variations in the structure of the contact units.
A limit switch of this invention may comprise plunger means for operating inner switches, including a link plunger for operating switch plungers of a plurality of inner switches. With such a structure, a link plunger as a different component can operate the switch plunger s of a plurality of inner switches and since this does not depend on the shape of the actuator, it becomes easier to develop variations.
The main body of the case may be provided with a hole part for the link plunger to pass through and a seal cap holder at this hole part for holding a seal cap. The link plunger has a plunger engaging part. The seal cap comprises a cap main body made of an elastic material with two (first and second) engaging parts at end parts of the cap main body, one of them formed as an O-ring. The link plunger is attached to the seal cap by engaging the first engaging part with the plunger engaging part and the second engaging part with the seal cap holder. Since the seal cap has the function of an O-ring, a more reliable sealing can be effected and the link p
Kaijo Hiroyuki
Miyoshi Tetsuhiko
Takenaka Hidemitsu
Beyer Weaver & Thomas LLP
Friedhofer Michael
Omron Corporation
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