US 3392247 A
Description (OCR text may contain errors)
July 9, 1968 M. M. CHECK ELECTRIC C ONTRQL MAT Filed Sept. 15, 1966 IIIIIIIIIII IIIIIIIIII- INVENTOR M. M. CHECK ATTORNEY 3 United States Patent 3,392,247 ELECTRIC CONTROL MAT Mathias M. Check, Greenwich, Conn., assignor to Eaton Yale & Towne Inc., Cleveland, Ohio, a corporation of Ohio v Filed Sept. 15, 1966, Ser. No. 579,603
7 Claims. (Cl. 200-86) This invention relates to electric mat switches, and more particularly to a novel mat of the class having a pair of electricity conducting plates that will be pressed into contact with one another so as to close a circuit when trafiic enters upon the mat. For very many years, mats of the particular class have been utilized in control circuits for various mechanisms, and frequently are used for con-trolling a motor that operates a door, all as those skilled in the art will appreciate.
- The mats generally are manufactured through the placing of two metal plates in spaced parallel position, in which position they are maintained by a series of spacers. It has been thought the best practice to place one of these spacers at the peripheral edges of the two plates, supporting the edges in separate relation. With the plates placed as indicated, a plastic body is cast about the metal plates so as to protect the plates and to insulate them from weather. During the casting process, the edge spacer excludes the plastic from the space between the plates so that portions of the plates may flex into contact with one another, as is necessary.
Mat switches constructed in that way can be made at reasonable cost and have features that are much to be desired. Nevertheless, there have been frequent failures among the mats that are installed. I have found that this is due to the fact that parts of the mat become damaged at the edges of the metal plates. The plate edges are very vulnerable to injury by heels, and particularly the sharp heels worn by women. These heels will break down the plastic at the edges of the plates, allowing Water and dirt to enter and bringing about a short circuiting of the plates, so that the mat no longer will be etfective to control a circuit.
Attempts have been made to obviate this difficulty, but so far as I know, none have been successful heretofore.
I have found that the concept of my invention is most effective in preventing a failure of a mat of the class described. In brief, I place a peripheral spacing member between the plates and inwardly of the periphery of the plates. This leaves a space that is open between the peripheral edges of the plates, and that is defined at one side by the spacer.
Now, upon the casting of the plastic material about the plates, this plastic enters the space between the plates at the periphery, being limited only by the presence of the spacing member lying inwardly of the periphery. The end result is a mat in which the edges of the plates are maintained separated by a yielding plastic material so that if pressure is applied to the upper plate in a downward direction, there will be a slight flexing of this plate, a slight flexing of the plastic material between the edges of the plates, and perhaps a flexing of the plastic beneath the lower plate. The portion of the material which is between the plates naturally will be integral with that which is cast about the plates, and the plastic will have no line of cleavage at the plate edges. in other words, there will be a full yielding action. At the same time, the plates will be well reinforced so that they need not accept excessive bending pressure at their edges.
I have thus outlined rather broadly the more important features of my invention in order that the detailed description thereof that follows may be better understood, and in order that my contribution to the art may be better appreciated. There are, of course, additional fea- "ice tures of my invention that will be described hereinafter and which will form the subject of the claims appended hereto. Those skilled in the art will appreciate that the conception on which my disclosure is based may readily be utilized as a basis for the designing of other structures for carrying out the several purposes of my inventionflt is important, therefore, that the claims be regarded as including such equivalent constructions as do not depart from the spirit and scope of my invention, in order to prevent the appropriation of my invention by those skilled in the art.
In the drawings:
FIGURE 1 shows a perspective view of my novel mat switch.
FIGURE 2 shows a plan view partly broken away to illustrate parts of my mat switch.
FIGURE 3 is a partial section showing the plates of my switch in assembled relation.
FIGURE 4 shows a partial section on the line 44 in FIGURE 2.
Referring now more particularly to the drawings, 1 indicate my novel mat switch generally by the numeral 10, and I show a rather usual pair of upper and lower plates 11, 12 forming parts of the switch. I prefer to arrange the plates 11, 12 so that their peripheral edges 13, 14 will be in vertically aligned relation, as clearly shown in FIGS. 3 and 4. The material of plates 11, 12 may be a metal such as aluminum, but the particular material is not important to an understanding of my invention. It is merely necessary to know that each plate 11, 12 is electrically conducting, and that there may be some yielding, at least by the upper plate 11, so that it may flex into contact with lower plate 12, as will be understood by those skilled in the art.
In my invention, the plates 11, 12 normally will be held in spaced relation by a series of insulating spacers including members v1S that are arranged at intervals between the plates and a spacer strip 16 near the plate edges 13, 14. I particularly arrange the spacer strip 16 in position inwardly from the edges 13, 14, as well shown in FIG. 3, so as to leave a space 17 open between peripheral portions of the plates 11, 12. The open space 17 extends for a substantial linear distance along the plate edges, and is defined at one side by a surface of a spacer strip 16. I have found that my invention will contribute excellent results when the space 17 is formed to extend from the plate edges '13, 1'4 inwardly a distance that is at least equal to the spacing between those edges, but I naturally do not wish to be limited to particular proportions of the space 17.
I then cast a plastic material about plates 11, 12 so as to enclose the plates in a casing 18, while causing the material to enter into the space 17. Thereby the casing 18 will have an integral portion 19 extending past the peripheral edges 13, 14 of plates 11, 12, and bonded to inner surface portions of the plates. As to the material for casing 18, I prefer to utilize polyvinyl plastic.
Constructed in that way, my novel mat switch will very effectively resist damage by concentrated pressures such as are applied by sharp heels. Those pressures naturally may be applied in different ways and in different directions, and it is difficult to analyze exactly the manner in which those pressures may act. However, it is known that the pressures have been particularly damaging when applied near the edges of the metal plates. -It is believed that the success of my invention actually resides in the fact that an integral part of the plastic casing of my mat extends past the edges of the metal plates, together with the fact that the plastic is bonded to the inner surfaces of the plates for a considerable distance inwardly from the edges. That integnal portion, while able to yield,
nevertheless will very effectively support the plate edges so'that they will not be deformed. Also, because the plastic material is bonded to a considerable area on the inner surface of each plate, the plastic of the mat cannot easily be forced away from the edge of either plate.
I am aware that the prior art has suggested that a spacer formed of a porous material be applied between the peripheral edges of upper and lower plates of a mat switch. Upon the pouring or casting of a plastic casing about the plates, the plastic material will enter somewhat into the interstices of the porous spacer. Then, however, there will be at the periphery of the plates a spacer that actually is formed partially of the plastic and partially of the porous material. In my construction, the plastic material cannot enter beyond the spacer, which is of solid material, and the end result is a mat in which the plastic is fully bonded to the edges of the plates, and effectively holds them in separated relation. Also, the plate edges are well insulated from one another, and yet adapted to yield somewhat while still being reinforced.
I believe that the construction of my novel mat switch will now be understood, and that the very considerable merits of my invention will be fully appreciated by those skilled in the art.
I now claim:
1. A mat switch of the class described, comprising a pair of electricity conducting upper and lower flexible plates adapted to close an electric circuit upon contact with one another, spacers arranged at intervals between said plates for holding said plates in spaced planes so that pressure applied to one of said plates may flex a portion of that plate against the other plate for closing a circuit, a strip forming one of said spacers and positioned between the plates inwardly of at least a portion of the corresponding peripheries of both of said plates so as to leave between the plates an open space extending for a substantial linear distance along the peripheries of said plates, an edge of said strip defining one side of said space, a plastic insulating material cast in enclosing relation to said plates in the manner of a protective yielding casing, a filler strip of plastic material integral with said casing and positioned in said open space at the peripheries of said plates, said filler strip forming a sole spacer for said plates in said open space and reinforcing the plate peripheries, and said filler strip lying in contact with said edge of the spacer strip 2. A mat switch as set forth in claim 1, in which a surface on said integral filler strip is substantially bonded throughout its extent to the inner surface of each plate.
3. A mat switch as set forth in claim 1, in which the plate peripheries along which said open space extends are in vertically aligned relation to one another, and said integral filler strip of plastic material is substantially bonded to a surface extending from the peripheral edge of each plate on that plate.
4. A mat switch as set forth in claim 1, and including said spacer strip positioned inwardly that distance whereby the depth of said open space will be at least the spaced distance of the two upper and lower plates.
5. A mat switch of the class described, comprising a pair of electricity conducting upper and lower flexible plates adapted to close an electric circuit upon contact with one another, spacers arranged between medial portions of said plates for holding said plates inspaced planes so that pressure applied to one of said plates may flex a plate portion against the other plate to close a circuit, a plastic insulating material cast in enclosing relation to said plates in the manner of a protective yielding casing, an integral portion of said plastic material flowing during said casting between peripheral portions of said plates and bonding to the inner surfaces of those portions whereby to reinforce edges of the plates while holding said edges in spaced relation, a strip arranged in position between the plates and displaced a substantial distance inwardly from the edges of said peripheral plate portions, and an outer surface of said strip limiting the entrance of said plastic material between the plates during the casting operation.
6. A mat switch as set forth in claim 5, in which the limiting surface of said strip is displaced from said edges of the peripheral plate portions a distance which'is at least the distance that those plate portions are spaced from one another.
7. A mat switch as set forth in claim 6, and including said integral portion of the plastic material forming a sole spacer between said peripheral plate portions, and said strip forming a spacer for parts of the plates inwardly of their peripheral portions.
References Cited UNITED STATES PATENTS 1,725,963 5/1927 Morris 200-86 1,915,292 6/1933 Conklin ZOO-86 2,896,042 3/1958 Koenig 200-86 BERNARD A. GILHEANY, Primary Examiner. F. E. BELL, Assistant Examiner.