Electricity: circuit makers and breakers – Weight – Treads
Reexamination Certificate
2000-05-16
2002-09-24
Scott, J. R. (Department: 2832)
Electricity: circuit makers and breakers
Weight
Treads
Reexamination Certificate
active
06455793
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a continuous-length switch which is operated under the load of a human being, an animal, a substance or the like to electrically detect the existence thereof.
The present invention also relates to a continuous-length switch which is to be used for detecting contact of a substance or the like and is excellent in durability.
The present invention also relates to a method for manufacturing the switch as described above.
2. Prior Art
Conventional continuous-length switches generally have a construction in which both ends of a pair of opposed electrode plates are insulated, and one of the electrode plates, i.e. an upper electrode plate
151
, for example, has been worked to have an odd-shaped geometry such that a linear portion of the electrode plate
151
is interrupted, as shown in
FIG. 14
, to increase sensitivity of the switch. With such a geometry of the upper electrode plate
151
, the edges are not linear, but rather are interrupted, which presents the following problems.
A part of the upper electrode plate
151
may get beneath the end insulating material when heavily deformed by an external force, which results in short-circuiting of the switch, which is a fatal fault.
When a lead wire is to be drawn out, the geometry in the direction along the breadth of the switch may be varied, and drawing the lead wire out may cause the switch to be stretched like a spring, depending upon a cutting location. Therefore, a precision end working as a secondary working for prevention of this stretching may have to be provided at the drawing-out location.
With a machine tool or the like, a safety mat M which has a continuous-length switch connected in series is used to assure operator safety. In this case, a four-wire type disconnection detection circuit which uses a power supply
160
, a current limiting resistor R, and a relay
161
for detecting disconnection between the upper electrode plate
151
and a lower electrode plate
152
that is opposed to the upper electrode plate, as shown in
FIG. 15
, is employed.
Because the upper electrode plate
151
through which a current flows is odd-shaped as shown in
FIG. 15
, its line length is approximately two times as long as that which would be obtained if the electrode plate were linear. Therefore, when this four-wire type disconnection detection circuit is used for carrying out disconnection detection, the electrical resistance is increased, which results in an increased power loss.
When the operator arrives on the safety mat M, a wire is disconnected, the power supply
160
fails or a coil
162
is deenergized, resulting in contacts
161
a
for the relay
161
being opened, which allows the power fed to the machine tool or the like to be shut off.
However, in this case, the four-wire type disconnection detection circuit must always be supplied with a current to energize the coil
162
for the relay
161
, and therefore, a problem is presented in that the power loss due to the circuit resistance cannot be avoided.
Another conventional continuous-length switch
250
generally has a construction with which both ends of an opposed upper electrode plate
251
and lower electrode plate
252
are insulated with an insulator
255
as shown in
FIG. 33
to FIG.
35
. As the geometry of either one of the upper electrode plate
251
and lower electrode plate
252
, i.e., the upper electrode plate
251
for example, a concave and convex geometry as shown in
FIG. 36
has been adopted to enhance the sensitivity associated with some switches.
The geometry of this upper electrode plate
251
can be easily deformed if a force “f” in the direction of a tensile load is applied to the upper electrode plate. Therefore, a method which winds a string
253
around the circumferences of the upper electrode plate
251
and lower electrode plate
252
, and fixes the string
253
thereto with an adhesive tape has been adopted.
However, such a continuous-length switch
250
presents problems, such as an increase in the number of manufacturing processes required, and the upper electrode plate
251
getting beneath the insulator
255
which results in a short-circuit.
Although it is not shown, an upper electrode plate with which polygonal holes are arranged at fixed intervals along a center line in the longitudinal direction of the electrode plate has been adopted.
If such an upper electrode plate is used, the need for steps of winding a string around the upper electrode plate and the lower electrode plate, and fixing the string to the electrode plates with an adhesive tape is eliminated, thereby resulting in the manufacturing process being simplified.
However, with the upper electrode plate having such a configuration, a problem is that the electrode plate can be stretched and contracted only within a small range based on its metallic elasticity when a force in the longitudinal direction is applied.
As a result of this, when this continuous-length switch is wound up for manufacturing, transporting, construction, storing, or the like, one electrode plate may be buckled and plastically deformed, resulting from the difference between the inside and outside diameters of the upper electrode plate and the lower electrode plate. Therefore, for a continuous-length switch having a long overall length, there sometimes arose the need for handling the switch without winding it up, which was inconvenient especially with regard to transporting, storing, and the like.
An example of another conventional continuous-length switch will be explained with reference to FIG.
43
and FIG.
44
.
A conventional continuous-length switch as shown in FIG.
43
and
FIG. 44
comprises a lower electrode plate
321
made of a continuous-length plate-like conductive material; an upper electrode plate
322
made of a continuous-length plate-like conductive material; and a jacket
324
made of a continuous-length insulating material which has a pair of symmetrical protrusions
324
a
and
324
b
on the inner walls of both sides thereof to form a space portion
323
between the lower electrode plate
321
and the upper electrode plate
322
, and is open on its bottom side; two strings
325
, for example, which are wound around the circumference of the jacket
324
in a crossed configuration to integrate the lower electrode plate
321
with the upper electrode plate
322
; and a continuous-length adhesive tape
326
which is bonded to the strings
325
on the bottom side of the lower electrode plate
321
along the longitudinal direction of the lower electrode plate
321
.
In other words, the upper electrode plate
322
is held between the pair of protrusions
324
a
and
324
b
inside the jacket
324
and an inner wall ceiling
324
c
of the jacket
324
; and the lower electrode plate
321
is attached to the lower surfaces of the pair of protrusions
324
a
and
324
b
.Then, the process of cross-winding the two strings
325
is carried out to integrate the lower electrode plate
321
with the upper electrode plate
322
.
At the middle of the top of the jacket
324
, a protrusion
324
d
is provided, and by pressing this protrusion
324
d
with a foot or the like, the upper electrode plate
322
is deformed through the protrusion
324
d
in the region of the space portion
323
, resulting in a switching operation being performed by the lower electrode plate
321
and the upper electrode plate
322
.
As stated above, conventional continuous-length switches are easy to be short-circuited, thereby presenting problems of safety and reliability, and requiring cumbersome secondary working. In addition, they have presented a problem in that power requirement is high.
The present invention has been developed in consideration of the above situation, being intended to offer a continuous-length switch which is excellent in safety and reliability, eliminates the need for a cumbersome secondary working, allows improvement of the operational efficiency during manufacturing, and can minimize the power requirement.
As stated above
Arakawa Uhei
Horikoshi Toshiaki
Kasahara Takeshi
Natsugiri Takaki
Scott J. R.
Tokyo Sensor Co., Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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