US2783327A - Molded metal-backed electrical mat switch and method of making the same - Google Patents

Description

J. A. LUCKEY MOLDED METAL-BACKED ELECTRICAL MAT SWITCH Feb. 26, 1957 2,783,327

AND METHOD OF MAKING THE SAME 2 Sheets-Sheet 1 Filed Jan. 17, 1955 2 4 N M j W M, H:.4.......H 2 45 y x Feb. 26, 1957 LUCKEY 2,783,327

MOLDED METAL-BACKED ELECTRICAL MAT SWITCH AND METHOD OF MAKING THE SAME Filed Jan. 17, 1955 2 Sheets-Sheet 2 United States Patent MOLDED METAL-BACKED ELECTRICAL MAT SWITCH AND METHOD OF MAKING THE SAME John A. Luckey, Chicago, Ill. Application January 17, 1955, Serial No. 482,116

3 Claims. (Cl. 200-86) This invention relates to an electrical mat switch of the type used for actuating electrically operated equip ment or the like and more particularly it relates to an improved mat switch construction affording a plurality of highly desirable advantages and to a simplified method for making the same.

Heretofore the use of electrical switches incorporated into floor mats has been well known. Such switches have been used in industrial plants, commercial establishments, and in homes. In industry they are often used as versatile foot switches for various types of industrial equipment, for example as actuators for automatic door operators, in interplant traffic controls, safety or protective devices for production machine operators, actuators or initiaters of mechanical operations, entry alarms, automatic lighting devices, in signs and advertising displays and in many other safety, production and convenience applications. In commerce they are often used in stores to open doors automatically, to operate bells, alarms and counters in stores and offices and to animate, light or to activate advertising displays. In the home they find many uses, for example in nurseries to sound remote alarms, actuate burglar alarms, as automatic switches to light dark Stairways, and similar uses.

Heretofore, such electrical mat switches have been constructed of laminated plastic or rubber or of other materials stitched together or in some other manner joined or assembled. All of these prior constructions have, however, been characterized by a number of objectionable features which, to a large extent, have limited the more universal use and application of these otherwise practical and highly functional mat switches. For example, it is necessary in many applications that the mats be held to a minimum thickness, especially when such mats are positioned underneath a floor covering. Furthermore, the thinner the mat the less apt the edges are to curl and the better it will hug the floor and remain in operational position. On the other hand, the function of the switches as floor limits the minimum thickness to one which will withstand to a practical degree the wear and tear to which floor mats are necessarily subjected.

It is therefore an important object of this invention to provide an electrical mat switch which will overcome all of the disadvantages mentioned hereinabove and particularly will permit the construction of a very thin mat without sacrificing any of the other highly desirable and necessary characteristics.

Heretofore most mat switches have been constructed of pliable, relatively soft materials such as plastics, rubber and the like, which material obviously was easily pierced as, for example, by a nail or other sharp, hard object which might work its way underneath the mat. When so pierced, it is obvious that water could readily be admitted to the inner electrical circuit, thereby causing shorts, etc.

It is therefore another important object of this invention to'provide an electrical switch mat having a hard metal bottom highly resistant to piercing.

2,783,327 Patented Feb. 26, 1957 As was set forth hereinabove, most of the prior mat constructions were laminated with the laminations adhered together by adhesives or the like. It is obvious that after continued use such laminations often separated one from the other, thereby again affording access to the electrodes for the admission of water to cause the shorting of he same. It is therefore another important object of this invention to afford an integrally formed or molded mat construction within which are permanently sealed the electrical components of the switch.

Another disadvantage of previous switch mat constructions was the fact that under repeated heavy loads, the bottom electrode was depressed or bent through the resilient soft bottom layer until it either was bent through the backing or lost its resistance and did not return to its normal position. This, of course, resulted again in p rcing of the bottom layer and also in the causing of shorts or inoperative switches.

It is therefore still another important object of the invention to provide a mat switch having a hard metal back which effectively limits the bending of the bottom electrode and actually reinforces the same against such bending or deformation.

Still another object is to provide a mat switch made of plastic or rubber with a metal backing in which the plastic or rubber is actually bonded or molded to the metal in such a manner that separation of the two elements is practically impossible.

"ince the top portion of the mat is obviously subjected to the greatest wear and abrasion, it is obvious that this portion requires the greatest amount of reinforcement or insulation. l-leretofore it was impossible to increase the thickness of the top covering without measurably increasing the overall thickness of the mat. However with my new switch mat construction, since the bottom is made of metal, it is obvious that this may be relatively thin thereby permitting the top covering to be made thicker without increasing the overall thickness of the mat.

Yet a further object is to afford a metal-backed mat in which the metal backing also serves as the bottom, fully grounded electrode of the switch.

Heretofore in the molding of mats or the like it was necessary to assemble all of the various component parts in a mold and then cover the same with a heavy cover during the molding process. Such a method, aside from the extra cost of the equipment, was also undesirable since it required additional labor and further interfered to some extent with the heat-transfer during the curing of the same. it is therefore another important object of this invention to provide an improved method of molding electrical mat switches in which the heavy cover may be entirely eliminated f om the process. An object relating thereto is to mold the mat wtih the metal back thereof positioned to serve as the cover for the mold.

Still a further object is to afford a method or process for molding metal-backed electrical switch mats in quantity production in which all of the electrical components are permanently covered and insulated wthin an integrally-formed housing.

Another important obiect is to provide an electrical e r tch which is highiy sensitive and immediately reto minimum pressure over a wide actuating area. i r object is to afford a molded electrical metalbacked mat switch of simple, inexpensive construction yet highly durable, eifective and resistant to wear, dust, oils, acids and most chemicals, including sweeping or cleaning compounds.

With the foregoing and other objects in view which appear the description proceeds, the invention con- .2 of certain novel features of construction, arrangement and a combination of parts hereinafter fully described, il-

lustrated in the accompanying drawings, and particularly pointed out in the appended claims, 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 of the advantages of the invention.

For the purpose of facilitating an understanding of my invention, I have illustrated in the accompanying drawlugs 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 of the drawingsz' Fig. 1 is' a fragmentary perspective View looking down on a mat switch embodying the principles of my invention;

Fig. 2 is a view in perspective showing my mat switch in operational position connected in an alarm system circuit and adjacent a door of a room or building wall;

Fig. 3 is an enlarged fragmentary sectional view taken on the plane of line 3-3 in Fig. 1 of the drawings and viewed in the direction indicated; Fig. 4 is a View similar to that of Fig. 3 but on a somewhat reduced scale and showing the switch in an operative circuit-closing position under the weight of the shoe-heel of a human foot;

Fig. 5 is a bottom plan view of the mat showing a detail of construction;

Fig. 6 is a fragmentary top plan view with a series of layers broken away to better illustrate the various components of the same;

Fig. 7 is an enlarged end elevational view partially in section to illustrate the detail of construction shown in Fig. 5 of the drawings;

Fig. 8 is an exploded perspective view with a portion of the top covering broken away to better illustrate the construction and assembly of the mat; and

Fig. 9 is a sectional view of a mold with the component parts assembled therein during the process or method of making the same.

7 Referring to the several figures of the drawings, especiallyFigs. 1 and 2, reference numeral iii indicates generally my electrical mat switch connected by suitable leads such as 12 and 14 to an alarm mechanism such as 16 in front of a door D positioned in a wall W of a room or building. In this application it should be obvious that the alarm will be actuated by any person stepplug on the mat as he enters or leaves the room through the door D.

Directing attention now to Figs. 3 and 7 of the drawings, it will be noted that the mat comprises a metal sheet 18 coated with a border of primer material 2%), the purpose of which will become apparent as the description proceeds. The plate itself may be made of any suitable metal conductor including steel and the like.

Positioned on top of the metal plate 13 may be a sheet of perforated sponge rubber material 22 formed with a plurality of spaced openings such as therethrough. This sheet is dimensioned so that it does not cover the primer-coated border 2% when placed in operatiouaiposition on the sheet 18 but is instead encircled thereby. The reason therefor will become apparent as the description proceeds. If desired a plurality of strips of sponge rubber spaced one from the other may be substituted for the perforated sheet 22. it should further be noted that any suitable non-conductor may be substituted for the sponge rubber material.

Positioned on the non-conducting sheet may be a thin sheet of conducting material such as 2.5 which comprises the second or top electrode of the switch. Again, if desired, any suitable conductor electrode may be used as, for example, a copper screen or grid. Preferably the material used should be ilexible enough to return to its position between actuations of the switch.

lne electrical leads 12 and 14 are connected by any suitable means as, for example, by soldering 27, one to each of the electrodes 18 and 26 respectively.

Finally all of the electrical components with the exception of the bottom plate, are protectively encased in a layer 28 of molded plastic material. The plastic layer 28 be formed with spaced top ridges such as St, for the ose oi a fording a better friction surface. The marginal edges of the plastic layer 23 are thickened as at 3 so that the same is bonded to the primer border 20 completely encases the electrical components of the r 2 pl 0 overlay the edge 34 of the metal plate 18. The bottom f this extended portion 33 is formed with a laterally exa ing groove 3-6 communicating with a central longin diually extending short groove 38 connecting the groove .3 to the leading edge 34 of the plate 13. These grooves are provided to accommodate therein the electrical leads l2 and 14 in either a right hand or left hand position. The leads are fully protected within the groove and need not extend under the plate itself where it would cause a bump or prevent the mat from lying flat on the floor.

in operation the electrodes 18 and 26 are normally spaced and insulated from each other by means of the non-conducting sheet 22. However, when pressure is applied to the top surface of the mat, as for example, by the heel H of the shoe of a human being, the electrode as is depressed so that a portion of the same abuts or contacts the top of the electrode 18 through one or more openings 24, substantially as shown in Fig. 4 of the drawings. This closes the circuit and permits the actuation of the electrically operated equipment, alarm, or any other device in whose circuit the mat switch is connected.

Attention is now directed to the unique and novel molding process by means of which the above-described electrical mat switch is made. The process is carried out in the following steps: (1) The backing plate electrode 13 is selected and the primer material 20 is painted on the border edges of the same; (2) The primer is partially cured by allowing the same to dry in the air until it loses its tackiness at which time the coated plate is inserted in an oven and baked at a temperature of approximately 350 Fahrenheit for a period of approximately 20 minutes; the plate is then removed and allowed to cool in the atmosphere; (3) The insulator sheet 22 is then assembled to the bottom of the top electrode 26 and ad-' hered thereto with any suitable adhesive, as for example, with a pressure sensitive cement; (4) The leads 12 and Eldare then aihxed as by soldering each to its respective electrode 18 and 26; (5) The assembled top electrode and insulator is then placed on the bottom plate electrode 13 within the primer border and the entire assembly is then clamped together, inverted and placed into the cavity it) of a mold 42. It will be noted that the plate then becomes the cover for the cavity 40 of the mold 42. It should further be noted that the assembled electrical components of the mat are spaced from the bottom 44 of the mold cavity 42. It should also be further noted that the mold 42 is formed with a hollow tube 46 extending from the side thereof and communicating by means of a passage 48 with the cavity 46; (6) Liquid plastic is then pumped intothe cavity 40 until the same is filled. If desired the plastic may be admitted into the cavity through a hole in'the metal plate or the 'mold cavity may be first filled with the liquid plastisol before positioning the assembled electrodes therein; (7) The filled mold is then cured in an oven at a temperature ranging from 350 F. to 375 F. for'a period of approximately fifty minutes; (8) Finally the mold is removed from the oven and the finished mat is stripped from the same.

It should be noted although any suitable thermosetting or thermo-plastic plastic may be used, I prefer to use the type of plastic which is commonly known as plastisol. Moreover, where the electrode 26 is a solid sheet, the top surface may be coated with primer and the plastisol 28 bonded thereto to insure better protection. It should further be noted that the plate 18 may be made oversize so that the marginal edges overlap the edges of the cavity 40 during the molding operation.

This process affords a mat in which the bonded border edge 32 of the plastic cover 28 is permanently and intimately bonded to the metal back 18 with the inner electrode 26 encased therein in a totally dust-proof and leakproof condition. The metal back serves as one of the electrodes of the switch but of even more importance is the greatly improved physical properties which characterize the resultant mat switch. The process itself greatly simplifies the manufacture of such mats by cleverly substituting one of the mat switch elements for one of the mold parts. By so doing, the problem of heattransfer during the curing phase of the process is materially reduced. At the same time equipment cost, handling and labour costs and time are all markedly reduced.

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 claims.

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

1. A unitary molded electrical mat switch comprising a flat sheet of metal having the border edges of the upper surface thereof coated with a primer material, a perforated sheet of sponge rubber positioned on said sheet within the area defined by said primer coated border edges, a flexible metal sheet positioned on said sheet of sponge rubber, a layer of plastic molded over said flexible metal sheet with the marginal edges of said layer molded to the primer coated border edge of said metal sheet, one end of said layer of plastic extending beyond the adjacent edge of said metal plate with a laterally extending groove formed in the lower surface thereof, a mid-portion of said extended plastic layer formed with a longitudinally extending groove connecting said lateral groove with said metal sheets, a pair of electrical leads posi- 6 tioned in said grooves with the inner ends thereof electrically joined one to each of said metal sheets.

2. A process for making molded metal-backed elec trical mat switches comprising in combination the steps of: coating the border edges of a steel sheet with primer material; partially curing the primer material by drying the same in air until the coating is no longer tacky, finishing the curing by baking the coated sheet at a temperature of approximately 350 Fahrenheit for a period of approximately 20 minutes and then cooling in the atmosphere to room temperature; adhering an insulator sheet to the bottom of a flexible electrode sheet; soldering the ends of a pair of electric leads one to said electrode sheet and the other to said steel sheet; assembling and clamping said electrode sheet and insulator assembly within the coated border of said steel sheet; placing said assembly within the cavity of a mold with said steel sheet covering said cavity; pumping liquid plastic into said cavity until the same is filled; and curing said plastc by bakng in an oven for approximately fifty minutes at a temperature of not less than 350 Fahrenheit nor more than 375 Fahrenheit.

3. A unitary electrical mat switch comprising a flat metal sheet, a non-conducting layer of material of smaller size then said metal sheet positioned thereon with the marginal edges of said metal sheet encircling the nonconducting layer, a flexible metal member positioned on said non-conducting layer, said latter-mentioned mem ber likewise encircled by the marginal edges of the metal sheet, a plastic layer molded over said flexible metal member, said plastic layer having unitary thickened marginal edges aligned with the marginal edges of said metal sheet and bonded thereto, said metal sheet and plastic layer completely encasing said non-conducting layer and said flexible metal member, and suitable electrical leads connected one to said metal sheet and another to said flexible metal member.

References Cited in the file of this patent UNITED STATES PATENTS 1,776,992 Brockman Sept. 30, 1930 1,915,292 Conklin June 27, 1933 1,928,472 Wilcox Sept. 26, 1933 2,040,919 Caldwell May 19, 1936 2,060,890 Olafson Nov. 17, 1936 2,367,441 Schwinn Jan. 16, 1945 2,583,813 Burke Ian. 29, 1952 2,667,553 Moorhead et al. Jan. 26, 1954 2,683,784 Rector July 13, 1954 FOREIGN PATENTS 274,148 Great Britain June 18, 1927 392,936 Great Britain May 25, 1933

Images