US2931093A - Electrical mat switch and method of making the same - Google Patents

Description

April 5 1950. J. A. LucKEY 2,931,093 ELEcTRIcAL un' smcn AND muon oF MAKING THE SAME Filed April 24. 1957 2 sheets-sheet z v JNVENTOR. I falo @fcvce/ ELECTRICAL MAT SWITCH AND METHOD F MAKING THE SAME John A. Lachey, Chicago, Application April 24, 1957, Serial No.'554,869

i Claim. (Cl. 29-155.5)

This invention relates to an electrical mat switch of the type used for actuating electrically operated equipment or the like, and more particularly it relates to improvements in such switches wherein said mats are made with removable electrode assembly cores enabling replacement of the same; and to improved methods for con- Vstructing and assembling the same. Specifically the invention comprises an improvement of the mat swiches disclosed in my Patent No. 2,783,327, issued February 26, 1957, and entitled Molded Metal-Backed Electrical Mat Switch and Method of Making Same. v

The improved metal-backed mat switch comprising the lsubject matter of the aforementioned patent has materially increased the over-all life of such lswitches and thereby decreased the frequency of replacement of the same. However, notwithstanding such improvements, under continual use the electrical components, primarily .the electrodes, from time-to-time became inoperative for Various reasons, and finally necessitated the replacement of the mat switch. Heretofore when this occurred it was necessary to replace the entire switch resulting iu replacement costs equivalent to the original installation costs. Moreover, although only the electrode assembly or core was worn out or inoperative, it was necessary to replace the entire mat switch including the metalbacked, plastic bonded housing, which invariably was still in good condition at the time of replacement.

In view of the foregoing, it is an important object of this invention to provide an electrical mat switch which will overcome the disadvantages described hereinabove.

Another object of this invention is to afford an electrical mat switch comprising a housing or casing with a self-contained electrode assembly core, said core removable from the casing and replaceable by another such core.

A further object is to provide a self-contained, completely sealed mat switch electrode assembly which may be used for replacement purposes in a mat switch or may be used, after simple modification, as a switch yin and of itself under certain conditions.

Still another object is to afford a mat switch casing having means incorporated therein for readily connecting a replaceable electrode assembly core Within the circuit of the switch.

Still a further object is to provide a greatly simplified and improved method for making electrode assembly cores intended either .for use as replacement parts in electrical mat switches of the character described hereinabove, or by carrying the process a few steps further, adapting the electrode assembly core for use independently as a mat switch under conditions Where the switch is not subjected to excessive loads or wear.

Yet another object is to afford a .mat switch having a replaceable electrode assembly core, but yet designed to switch of the character described in which the replace- @attentati Apr. 5, i960 'able fcore is fully protected from vthe elements as well as from abrasion and wear yand tear. An object relating thereto `is to provide `a metal backed casing having :a metal edging or molding surrounding the core. A further related object is to so design said molding strips that the same may be utilized to assemble and maintain .in proper operative position the plastic portions of the switch mat casing while also permitting ready partial `removal of the same to afford access for replacing the core.

Another important object is to provide a simplified assembly line method of making either switch mats or electrode assembly cores which will insure maximum water-proofing lof the product and a much of uniformity in the same.

A further object is to provide a molded electrical metalbacked mat switch with a replaceable self-contained electrode assemblycore of simple, inexpensive construction, yet highly durable, effective, and resistant to wear, dust, oils, acids, weathering elements, and most chemicals vincluding sweeping or cleaning compounds.

Another important object is to provide an electrical `mat switch which is highly sensitive and immediately responsive to minimum pressure over a wide actuatingarea.

With the foregoing and other objects in view which will appear as the description proceeds, the invention cousists of certain novel features of construction, arrangement and a combination of parts hereinafter fully described, illustrated in the acocmpanying drawings, and vparticularly pointed out in the appended claim, it being understood that various changes in the form, proportion, size and minor details of the structure may be made without departing .from the :spirit or `sacrificing any iof .the advantages of the invention. y

4For the purpose of facilitating an understanding of vmy invention, I have illustrated in the accompanying drawings a preferred embodiment thereof, from an inspection of which, when considered in connection `with the following description, my invention, its mode of construction, assembly and operation, and many of its advantages should be readily understood and appreciated.

Referring to the drawings in which the same characters of reference are employed to indicate corresponding or similar parts throughout the several figures ofthe drawings:

Fig. 1 is atop plan view of an assembly of two switches embodying lthe principles of my invention, a portion `of the top covering broken away 'to reveal details ol construction of the interior thereof; said switches positioned on the threshhold of a doorway and connected in an electrical circuit to automatically open the door upon closing of the circuit;

Fig. 2 is an enlarged fragmentary `sectional view taken on the plane of line 2-2 in Fig. 1 of the drawings and viewed in the direction indicated;

Fig. 3 is a view in perspective of the switch mat with la portion of the top cover open to illustrate how 'the electrode assembly core may be removed and replaced therein;

Fig. 4 is a fragmentary exploded sectional view showing details of construction of the removable electrica terminal contact elements; Fig. 5 is an enlarged fragmentary top plan view ofa lfragment of the rmat switch with the electrical terminal 'elements and with portions of the cover and electrodes broken away to better illustrate the details of construction;

Fig. 6 is a fragmentary View illustrating Iother details of construction; and

Fig. 7 is a perspective view of the replaceable elecf trode assembly. v Referring rst to Fig. 1 of the drawings, .reference greater degree numeral indicates generally a mat switch assembly of..

two mat switches 12 and 14 positioned on both sides of the threshhold of a doorway D with both mats connected in an electrical circuit indicated generally by reference numeral 16. The mats are positioned, and in the present case connected, in the circuit so that upon closing of the circuit through either mat switch 12 or 14, the door (not shown in the drawings) closing the doorway D, will open. It will be recognized that the above-described mat switch assembly is presently popularly utilized in various installations including shops and stores so that a customer entering or leaving the store with his arms full of bundles may gain ready access or egress without necessitating the use of the hands in opening the door.

As will be noted in Figs. 1, 2 and 3 of the drawings, each of the mat switches 12 or 14 may comprise an outer casing indicated generally by reference numeral 18, and a removable, electrode assembly core indicated generally by reference numeral 20. The core 20 is positioned within a central cavity 22. The central cavity 22 is defined by a molded plastic top layer 24 and a bottom metal sheet, 26. The molded top layer 24 may be formed with spaced top ridges such as 28, the function of which is to aord a corrugated friction surface similar to the surface provided in the mat switch disclosed in the aforementioned Patent No. 2,783,327.

Encircling the central cavity 22, at least along three edges of the same, may be an internal molding strip preferably made of metal and indicated by reference numeral 30. This molding strip may be made of extruded aluminum and may be formed with a plurality of upwardly projecting protuberances such as 32, the function of which will become apparent as the description proceeds. It will further be noted that the molding strip 30 is permanently affixed to the top surface of the metal plate 26 by any suitable means such as welding as at 34, and it will also further be noted that the inner surface 36 of the molding strip 30 is positioned in spaced relationship with the outer edge 38 of the central cavity 22. Again the reason therefor will become apparent as the description proceeds.

The molded plastic top layer 24 is molded so that a portion 40 thereof extends beyond the outer edge 38 of the central cavity 22. It is further molded with that portion thereof positioned above the extruded aluminum molding strip 30 of complementary shape to the shape of the top surface of the molding strip including the protuberances 32. Thus .the elastic compressible plastic material is designed to tightly tit over and around the molding strip 30 in such a manner as to firmly retain the outer edges of the plastic-molded layer 24 in tight-fitting relationship. Nothwithstanding the same, the plastic layer 24 can with little effort be disassociated or removed by merely peeling the same off of the molding strip 30. A more detailed description of this feature of the invention will be disclosed as the description proceeds. v It will be noted that the plastic layer 24 is formed with a beveled outer edge surface 42 terminating in a short straight vertical surface 44, said vertical surface or outer edge 44 being spaced inwardly from the outer edge of the plate 26. Thus to complete the mold an outer molding strip 46 is provided which encircles again the mat switch along at least three edges thereof. The molding strip 46 may be formed with an inclined surface 48 complementing the surface 42 of the plastic molded layer 24 and thereby affording a further tight-fitting protective device which insures against admission of water and other extraneous materials into the mat switch itself. The molding strip 46 may also be formed with an outer beveled edge portion 50 especially designed for associa-tion with the mat switch when said mat switch is positioned on a dat surface. Obviously when the mat switch is positioned in a revetment or recess the outer beveled edge molding 46 may be dispensed with. As in the previously described molding 30, the molding strip 46 may be an 'aluminum extrusion.

For the purpose of securely attaching the outer molding strip 46 to the assembled mat switch, the strip is formed with a shaped depending segment 52. This segment 52 is formed with a number of protuberances such as 54 and the entire segment 52 is adapted to t securely into another preferable extruded aluminum molding strip 56 the shape of which complements the shape of the segment 52. The strip 56 again may be attached to the metal plate 26 by any suitable means such as welding at 53. It will be noted that due to the design of the molding strips a plurality of spaces such as 60 are provided between the outer molding strip 50 and the bottom plate 26.

Directing attention to Figs. 2 and 3 it will be noted that molded directly into the top plastic layer 24 is a cable 62 containing therein leads 64 and 66 of the circuit 16. This structure insures complete Waterproofing of said leads.

Attention is now directed to the electrode assembly core 20 which will now be described in some detail. The core comprises a pair of thin sheets of conducting material 68 and 70 separated by a sheet of non-conducting dielectric material 72. The non-conductor 72 may comprise a sheet of perforated sponge rubber formed with a plurality of spaced openings such as 74, the dimensions of said opening 74 being such that the application of pressure by one Walking over the mat switch will be sufficient to deforrn the top electrode 63 through the opening 74 so that contact is made with the bottom electrode 70. However, preferably small individual pieces of sponge rubber spaced apart one from the other may be used in lieu of a sheet thereof. Aside from the economics thereof, the latter-mentioned structure insures proper contact.

The outer surfaces of the electrode plates may be covered with a layer of primer material 7S andthe entire electrode assembly may then be encased by a coating or layer 76 of plastic material such as plastisch This layer of plastic material 76 completely encases the electrode assembly in fully waterproof relationship, and as will be disclosed subsequently may be applied by a novel dipping method.

Since the electrode assembly core 20 is removable from and replaceable in the mat switch, it is readily apparent that the electrical leads 64 and 66 cannot be permanently aixed thereto but must be so designed that the same may be readily disengaged from the core 2i) and as readily attached thereto. For this purpose I have designed a novel structure which now will be described in some detail. Attention is therefore directed to Figures 4 and 5 of the drawings.

It will be noted in Fig. 4 of the drawings that I have provided a pair of two-piece, snap-fastener, electrical terminal members such as 80. Each of said terminal members Si) comprises a male member 82 which in turn comprises a strip of conducting material 84, one end of which is embedded in the plastic layers 76 and in contact with either the top electrode 68 or the bottom electrode 70v as at 86. Mounted on the outer end of the strip S4 is an outwardly protruding button such as 88. The other member of the electrical contact terminal 86 comprises an arm 90 having clasps 92 adapted to embrace and secure thereto one end of one of the leads 64 or 66 `respectively. The inner end of the arm 90 is integrally formed with a cap 94 having an open or cavity 96 cornplementing the shape of the button 88 and adapted to receive in snap-fastening relationship the button 88 therein. Thus it can be readily perceived that the mat switch electrode assembly core 20 may be easily `connected within an electrical circuit and as easily disasseciated therefrom.

It will be noted in Fig. 3 of the drawings that a 'portion of the top layer 24 is lifted or peeled awayv from the balance of the mat switch revealing the core 29. Actually the portion of the layer 24 which remains in contact with the other portions of the mat switch is permanently bonded thereto by means of the primer to insure maximum resistivity to the admission of water therein. Thus, only approximately half of the molded plastic top layer 24 may be disengaged from the molding strip 30. However, this is sufficient to permit the removal and replacement of the electrode assembly core 2i) within the cavity 22. Obviously before lifting or peel ing back the top layer 24 is is necessary to rst remove the outer beveled edge molding strip 50. 1t will further be noted that the edges of the switch mats 12 and 14 which are adjacent each other need not be provided with molding strips, but instead the top layers are bonded directly to the bottom plate 26.

Attention is now directed to the novel method for making electrode assembly cores. As was previously stated the electrode assembly is completely encased in a layer of waterproof plastic material which insures a completely watertight structure. This watertight structure is achieved by means of a novel process carried out in the following steps:

(1) The electrode plates 68 and 70 are assembled together with the insulating dielectric sheet 72 positioned therebetween. (2) Leads such as 64 and 66 or in the alternative terminals such as 80 are affixed as by welding or soldering to the electrodes 68 and 70. (3) The outer surfaces of the electrodes are sprayed with the primer material 75. (4) The electrode assembly is hung from a conveyor and passed through a curing oven, the temperature of which is approximately 400 degrees F., to semi-cure the primer and to heat the assembly to a temperature which will insure satisfactory subsequent coating with the plastic material, plastisol. Depending on the thickness of plastic coating desired, the time for passing the assembly through the oven is approximately minutes. (5) The primer-coated electrode assembly is transported by means of the overhead conveyor to a dipping tank of plastisol and automatically plunged into the same. (6) After remaining in the tank of plastisol for approximately 2 minutes the electrode assembly is slowly and automatically raised out of the tank at a rate which insures uniform thickness of coating and permits the excess plastic to drop olf evenly. (7) The plasticcoated electrode assembly is then passed through an infrared oven at approximately one foot per minute so that it takes approximately 4 minutes to pass through the oven where it is heated to a temperature of approximately 350 F. and whereby the plastisol coating is cured. (8) The cured plastic-coated electrode assembly is then cooled and if desired the surface may be embossed so that the assembly may be utilized as an independent mat switch. If the same is to be used merely as a core, then of course the surface is left plain and not embossed. (9) Air or inert gas may be inserted into the mat by means of a hypodermic needle if desired.

Although the replaceable electrode assembly core has been described hereinabove as being encased in a watertight layer of plastisoL it should be obvious that any suitable impervious material may be substituted for the same. It should also be noted that if desired no coating whatsoever need be applied to the electrode assembly. Since the cavity 22 within the mat switch 12 or 14 is substantially watertight by virtue of the structure, namely, the cooperating molding strip 36 and plastic portion 40, the coating 76 on the electrode assembly core may be dispensed with if desired.

The specific details of construction illustrated in Fig. 2 of the drawings wherein the outer edge of the dielectric sheet '72 is spaced inwardly from the outer edges of the electrodes 68 and 70 insures reinforced and watertight sealing of the core edges since in dipping, the plastic material penetrates into the marginal space 98 aiforded thereby.

it is believed that my invention, its mode of construction and assembly, and many of its advantages should be readily understood from the foregoing without further description, and it should also be manifest that while a preferred embodiment of the invention has been shown and described for illustrative purposes, the structural details are nevertheless capable of wide variation within the purview of my invention as defined in the appended claim.

What I claim and desire to secure by Letters Patent of the United States is:

The method of making replaceable electrode assembly cores comprising, in combination, the steps of assembly of a pair of juxtaposed electrode plates with pieces of resiliently compressible insulating material there-between, spacing said insulating material inwardly of the edges of said plates, axing in electrical conductive relationship terminal contact members one to each of said electrode plates, spraying primer material on the outer surfaces and inner marginal edges of said electrode plates, semicuring said primer material, dipping said primer-coated assembly in liquid plastic to lill the space between the marginal edges and to form a thick coating on the assembly, and nally curing said plastic.

References Cited in the le of this patent UNITED STATES PATENTS 1,950,490 Greer et al. Mar. 13, 1934 2,165,227 Cooper July 11, 1939 2,251,351 Cooper Aug. 5, 1941 2,414,525 Y Hill et al. Jan. 21, 1947 2,459,018 De Monte et al. Jan. 11, 1949 2,496,948 Lutz Feb. 7, 1950 2,586,609 Burke Feb. 19, 1952 2,713,700 Fisher July 26, 1955 2,724,869 Merrill et al Nov. 29, 1955 2,743,308 Bardsley Apr. 24, 1956 2,785,383 Foster Mar. 12, 1957

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