Note: Descriptions are shown in the official language in which they were submitted.
I
"ELECTRIC SWITCH"
This invention relates to electric switches, particularly, but not
exclusively, strip switches.
British Patent specification 13519~1 of PUP. Engineering, Published
May 1, 197~, describes a mat-type switch having a wide variety of uses, in-
eluding security and safety applications. The described switch basically
comprises a pair of thin metal, for example stainless steel, sheets between
which is sandwiched a sheet of insulating material which separates and thus
electrically isolates the sheets from one another. Apertures are formed in
the insulating material whereby pressure in the area of an aperture causes
electrical contact between the sheets to be made through the aperture. The
present invention is related to this general mat-type of switch but has the
advantage over the earlier type that it can be actuated from several differ-
en angles, using a suitable actuator, making it particularly suitable in
safety applications. However, a variety of other uses for the switch will
become apparent.
According to the invention there is provided an electric switch
made up of a laminate comprising two strips of conducting material and, sand-
wicked between the strips to normally electrically isolate the strips from
one another, an elongate layer of electrically insulating material, said
layer extending lengthwise of the strips in the approximate geometric center
thereof such that the elongate edges of the strips overhang the layer, and
an actuator comprising a U-section strip of resilient material, whose legs
are positioned in such a way as to overlay said overhanging edges of the strips.
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Various arrangements are possible for example the sheets could
be of rectangular or square shape and overlay one another in registry, with
said resilient layer positioned centrally so that the edges of the sheets
overhang all around. Alternatively, the resilient layer could extend across
the sheets from the central part of one straight side to the central part
of the opposite straight side, with opposite edges of the two sheets over-
hanging. in the preferred embodiment, the sheets are in strip form, the
layer of resilient material taking the form of a foam tape extending length-
wise along the strips in the geometric center thereof, thus
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leaving the elongate edges of the strip sheets overhanging.
The overhanging edges could be covered in self-adhesive
insulating tape to prevent ingress of moisture and dirt. Alter-
natively, the whole assembly could be fitted in a suitably-shaped
sleeve of flexible plastics material.
With a suitable actuator, the switch of this invention
can be actuated from several angles, thus making it very suitable
for use in safety cushion switches found around potentially dangerous
machinery. Thus in an embodiment, the switch further includes
an actuator comprising a sel~-supporting U-section strip of
resilient material, for example foam rubber or plastics material
whose legs are fitted in positioned in such a way as to overlay
said overhanging edges of the laminate. In a preferred embodiment,
the legs are fitted into an open channel-section housing in the
bottom of which is situated said laminate. The switch is
operated by applying pressure to that part of the strip which
protrudes from eke housing and which forms a self-supporting
resilient cushion. Pressure may be applied either directly down-
wards - i.e. in a direction towards the channel - or to one or the
other side of the cushion. In all three of these instances either
one or both legs of the U-section strip will move towards the bottom
of the channel to actuate the switch by pressing one or both of said
overhanging edges together. It will be understood that the switch
of this invention could be used in any orientation and references to
"downwards" and "bottom" should be construed accordingly.
In a preferred embodiment of the invention, a bridge
member, being a block of, preferably, resilient material is
attached between the legs of the U-section strip near the bottom
thereof.
In order what the invention may be better understood,
an embodiment thereof will now be described by way of example
only and with reference to the accompanying drawings in which-
Figure I is a transverse cross sectional view of a strip
switch made in accordance with the invention;
Figure 2 is a diagrammatic transverse sectional view
of an actuator suitable for the switch of Figure l; and
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Figure 3 is a diagrammatic transverse section of
another actuator suitable for the switch of Figure 1.
Referring to Figure I the switch comprises a laminate
made up of two strips 1, 2 of metal for example stainless steel,
5 beryllium copper or phosphor bronze between which is sandwiched
a layer 3 of resilient insulating material in the form of a double
adhesive foam tape. The strips l, 2 are aligned in resist rye
with one another and are typically 1 in. to 3 in. wide and of
indefinite length. Typically the strips are of I thou to 15 thou
10 thickness, the foam strip of 1/16 inch thickness. Electrical
connections (not shown) are made to the respective strips 1. 2
and are taken away via conventional means to the device being
switched.
The foam material is positioned down the center of the
15 two strips to leave overhanging areas 4, 5 at each side. As is
clear from Figure 11 the sheets 1, 2 are normally electrically
isolated from one another by virtue of the layer 3, but pressure on
either side, as illustrated by the arrows Pi, Pi will cause contact
to be made due to movement of one strip with respect to the
20 other. Obviously contact could equally well` be effected by
upwards pressure. if the switch were to be restrained in the
upwards direction, or by a squeezing action near one of the edges.
The free edges of the switch are lightly bound with
tape 6 to prevent ingress of moisture and dirt between the over-
25 hanging edges.
A switch such as that shown in Figure I could be used directly by being mounted on a surface against which pressure may
be applied to actuate the switch, possibly providing only a simple
cover to protect and insulate the mechanism. Direct uses include
30 safety equipment and security applications and vehicle detection -
in this latter connection it will be noted that the passage of a
vehicle across the switch in a direction across the page in
Figure I will result in the switch being actuated twice. with an
interval between successive actuations governed by the speed of
35 the vehicle.
The switch may also comprise a suitable actuator, for
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example those shown with reference to Figures 2 and 3. In
Figures 2 and 3, the same reference numerals have been used where
appropriate. The switch shown in Figure 2 is protected not by
tape 6 along its edges, but by being totally enclosed in a sleeve 7
of plastics material.
Referring to Figure 2. the actuator comprises an
elongate actuator bar 8, for example of nylon. The bar 8, which
is seen in section in the drawings has an actuator portion 9 and
splayed-apart legs 10 which extend downwards as shown. The bar 8
is attached to the top of the switch by means of a strip 11 of foam
material. Protection of the mechanism is afforded by a housing 12,
for example of nylon, comprising a base portion 13 attached by
means of screws 14 to a suitable surface, and a shroud portion IS
which has free ends which bear against the bar 8 to seal the
assembly.
The switch is operated by moving the bar 8, any one or
more of three motions in different directions causing the switch
contacts, as represented by strips 1, 2, to close. Pressure in
direction Pi or Pi will cause the bar to locally tip over in the
appropriate direction about an axis approximately in the area of
the strip 11. As a result the appropriate leg 10 will bear against
and close the overhanging edge of the strips I and 2, thus
effecting an electrical connection. Pressure in a vertical direction.
as represented by the arrow Pi will cause the bar to move down-
warmly, thus causing both legs 10 to likewise move downwardly,
eventually causing contact, as before.
Although the illustrated switch has a "dead zone"
before contact takes place, it will be clear that the switch can
be made very sensitive, should this be desired.
The switch as described with reference to Figure 2
may be attached around dangerous machinery to protect the
operator by de-activating the machinery if the operator places
himself in a hazardous position. The switch is actable over a
wide range of angles, and is thus particularly advantageous in
safety applications where the switch is probably only actuated in
accidental or panic conditions.
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Referring now to Figure 3, it will be seen that the
laminate making up the switch is seated in the bottom of a
channel section housing 16 of rigid material, for example hard
plastics or, with suitable insulation, metal. The switch actuating
S member takes the form of a self-supporting Section strip 17 of
resilient material - for example foam plastics or rubber material.
The shape of the U-section may be achieved in practice by
folding a length of suitable foam material about an axis extending
centrally in a direction parallel to its elongate axis and then heat
forming the top portion 18 so that it retains the U-section shape.
The legs 19, 20 of the section extend downwards into the housing 16
and rest on, or possibly just above, the switch laminate. The
ends of the legs 19, 20 are chamfered at 21, 22 respectively so that
the area of contact between the switch laminate and the bottom
of the legs is reduced and moved as near to the edge of the
laminate as possible. This improves the operation of the switch
since, if the whole width of each leg were to be continued down
into contact with the laminate. it would be more difficult to
operate the switch because the effective mechanical leverage
I would be reduced. The spacing of the legs is maintained by a
bridging member I which may take the form of a strip of foam
material, similar to that used for the strip 17, which is glued or
otherwise adhered to the strip along the abutting edges.
A protective cover 24 of flexible rubber or plastics
sheet material completes the assembly. The cover 24 is attached
to the edges of the housing 16 and extends loosely over the
strip 17 in approximate contact therewith. Some care must be
taken in attaching the cover since, if it is too tight it will cause
the switch to be continuously actuated. If carefully applied, the
cover 24 can be used to retain the strip 17 and so ah element in
place in relation to the housing 16 as shown in Figure 3. It is
not though necessary to separately attach the strip 17 within the
housing.
In order to mount the switch, a base plate 25 may be
attached to the underside of the channel section. The base plate
extends beyond the channel section to define flanges 26 which may
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be attached by any suitable means to an appropriate surface.
The actuator described with reference to Figure 3
will permit actuation of the switch due to pressure applied in any
one or more of three directions. Lateral pressure in directions
S Pi or Pi will cause the leg 20 or 19 respectively to move down-
wards to press the overhanging edge of sheets I and 2 into contact
with one another. Downwards pressure in direction Pi will cause
both legs 19 and 20 to move downwards thus similarly resulting in
contact being effected between the two sheets I 2. For safety
applications, the material of the strip 17 must be chosen carefully
since it should be sufficiently rigid to transmit pressure to the
switch laminate almost instantaneously but must be capable of
collapsing easily if additional pressure is applied such as may occur
in safety applications due to overrun of a protected machine.
Foam polyethylene has been found to be suitable.
The switch of the invention could also be actuated over
a full 360 range by means of a joystick type control.
