US 3308253 A
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March 7, 1967 M. KRAKlNOWSKl 3,308,253
DIAPHRAGM SWITCH HAVING A DIAPHRAGM SUPPORTED ON AN INCOMPRESSIBLE LAYER AND AN ELASTOMER OVERLAYING THE DIAPHRAGM Filed March 25, 1965 FIG 1 A I fIIIIIl/IIIIA 22 d 1 Pr 24 INVENTOR. MORRIS KRAKINOWSK I' FIG.3
United States Patent 3 308,253 DIAPHRAGM SWITCH HAVING A DIAPHRAGM SUPPORTED ON AN INCOMPRESSIBLE LAY- ER AND AN ELASTOMER OVERLAYING THE DIAPHRAGM Morris Krakinowski, Ossining, N.Y., assignor to International Business Machines Corporation, Armouk, N.Y., a corporation of New York Filed Mar. 25, 1965, Ser. No. 442,758 8 Claims. (Cl. 200 -46) This invention relates to electrical switching elements and more particularly to pressure-sensitive diaphragm switching elements.
While pressure-sensitive switches have been in existence for some time, their field of application has been limited by such factors as their size, cost, and lack of sensitivity to very slight pressures. One way in which such limitations have been overcome is to form the switch by use of thin film techniques. In doing this, a first conducting segment or strip is laid down on a substrate, a non-conductive spacer layer placed over this with an opening over the conducting segment, and a diaphragm hav-' ing a conducting segment positioned adjacent to the conducting segment on the substrate positioned over the spacer layer. With such an arrangement, the conducting segments are brought into contact with each other by applying pressure to deform the diaphragm.
Since thin film techniques are employed in constructing these switches, the size of the switch may be made quite small and their cost kept low. However, there are still practical limitations on their usefulness. One disadvantage is that if a fairly pointed stylus such as a pencil ora pen is being used as the actuating element, as would often be the case in many applications of such switches, a thin diaphragm tends to puncture or to at least sustain permanent deformation on the point where pressure is applied due to the high stress concentration. The deformation may occur in the diaphragm itself and/or in the conducting segment attached to the diaphragm, and may occur after only a short number of switching cycles. This problem may be overcome to some extent by using a thicker diaphragm. However, when this is done, the permissible switch density (i.e. switches per unit area) is severely restricted. In applications of such switches, such as in a punched card reader, an embossed card reader, or a constrained handwriting recording device, the limitation on the switch density becomes a serious problem. Also, with a thick diaphragm, the amount of force required to energize the switch is increased.
In addition to the shortcomings mentioned above, most diaphragm switches have a limited contact area which is largely determined by the surface area of the actuating device and its alignment with the plane of the switch. The contact resistance and the current density at the point of contact between the two conducting segments is inversely proportional to the area of contact between these two segments. Heating at this junction is directly proportional to both the current density and the resistance, and therefore the smaller the contact area, the greater the heating at the junction. This causes evaporation of contact material and material transfer, which ultimately results in a failure of the switch. The limited contact area and the resulting heating problem therefore seriously reduces the current carrying capacity of the switch.
Another problem with diaphragm switches is contamination of the conducting surfaces by organic molecules and other dirt in the atmosphere which causes a thin film to form over the contacts. Such a film, unless broken, prevents good contact from being made, lead- 3,308,253 Patented Mar. 7, 1967 ing to erroneous indications from the switch. It is therefore important that the switch be designed to prevent contamination of the contacts as much as possible and to pierce such film as may exist in order to establish good contact in every instance.
A diaphragm switch should also be designed to have a minimum stroke so as to have a short response time and to be capable of being stacked so as to provide multi-pole isolated switching elements that can be activated by a single actuator.
It is therefore a primary object of this invention to provide an improved pressure responsive electrical switching element.
A more specific object of this invention is to provide an improved diaphragm, pressure-responsive switching element.
Another object of this invention is to provide a diaphragm switching element which is capable of operating for a very large number of switching cycles, even with a relatively pointed actuating element, without having the diaphragm puncture or become permanently deformed.
A further object of this invention is to provide a diaphragm switching element which provides a larger contact area at the terminals than the area of the pressureapplying element.
Still another object of this invention is to provide a pressure-responsive diaphragm switch which is capable of switching relatively large currents.
A still further object of this invention is to provide a pressure-responsive diaphragm switch which allows a very dense array of switching points to be constructed.
Another object of this invention is to provide a pressure-responsive diaphragm switch which requires a minimum actuating force to cause contact closure.
Another object of this invention is to provide a pressure-responsive diaphragm switching element, several of which may be stacked together to provide multi-pole isolated switching elements that can be activated by a single actuator.
Still another object of this invention is to provide a pressure-responsive diaphragm switch with a very small stroke and therefore very short response time.
A still further object of this invention is to provide a pressure-responsive diaphragm switch which is easy and inexpensive to fabricate.
Another object of this invention is to provide a pressure-responsive diaphragm switch which is nearly maintenance free and therefore extremely inexpensive to operate.
A feature of this invention is the provision of a pressure-responsive diaphragm switch, the terminals of which open and close with an inherent rolling action which helps penetrate any contaminant film on the contacting surfaces.
Another feature of this invention is the provision of a pressure-responsive diaphragm switch which is inherently sealed and which may easily be hermetically sealed so as to be capable of operating under adverse environmental conditions.
In accordance with these objects, this invention provides a switching element which includes a first terminal which is fixed on a substrate, a' diaphragm-carried second terminal which is adjacent to the first terminal, a spacer for normally separating the terminals, and a layer of elastomeric material over the diaphragm. The spacer has an opening in it so that when pressure is applied to the elastomeric material, the elastomeric material and the diaphragm are deformed to bring the terminals into contact with each other. The individual switching element of the invention, as illustrated in the accompanying drawings.
' In the drawings:
I FIGJI is a sectional side view of a single switching element of this invention in its open condition.
FIG. 2 is a sectional side view of the switching elemerit shown in FIG. 1 in its closed condition.
FIG. 3 is a partially cutaway perspective view of an array of switching elements of the type shown in FIGS. 1 and 2.
Referring now to FIGS. 1 and 2, it is seen that the preferred embodiment of the switching element of this invention has a laminar structure. The individual lamina of this structure are 1) a substrate 10, having a segment of conductive material 12 plated on its upper surface; (2) a layer of insulating material 14 overlay ng or plated on substrate 10, the insulating material being incompressible and having an opening 16 in it in the area of conducting segment 12; (3) a diaphragm 18 positioned on top of the insulating material 14; (4) a segment 20 of conducting material fixed to the underside of diaphragm 18 in the area of opening 16; (5) a layer 22 of elastomeric material resting on diaphragm 18; and (6) a layer of lubricant 24 between diaphragm 18 and elastomeric material 22. While the particular materials employed for the various layers shown in FIGS. 1 and 2 and the relative thicknesses of these layers are a matter of choice and will vary with the application to which the switch is being put, the following materials and relative dimensions have been found to give satisfactory results:
The substrate is of copper-clad glass or paper-filled epoxy laminate and is 0.060" thick, with 1 oz. copper. Separator 14 is of Mylar 1 and is 0.001 to 0.005" thick. Diaphragm 18 is of a Mylar-copper laminate and is 0.003 to 0.006 thick with one-half to 1 02. copper. Contacts 12 and 20 are of gold and are to 10* thick. Cover sheet 22 is of neoprene, Hypalon, Viton film rubber, a urethane synthetic rubber, or of any other elastomer and ;may vary in; thickness from 0.005510 0.030", depending on the application to which the switch is beingput: 22 will be referred to as being made of either an elastomer or an elastomeric material. Lubricant 24 is a silicone grease.
Referring now to FIG. 2, it is seen that when pressure is applied to the upper surface of elastomer cover sheet 22, the single component of pressure P in the downward direction is converted by the elastomer into a component of' pressure Pd in the downward direction and components of pressure Pr which radiate out in all directions in a'plane parallel to that of substrate 10. This effec;
tively widens the area over which pressure is applied to diaphragm 18, causing a larger area, D, of conductive segment 20 to be brought in contact with conductive segment 12, then the area, d, of actuating stylus 26. The relatively large contact area, D, reduces the contact resistance and the current density so that the switch is capable of handling relatively large currents of a magnitude approaching 1 amp.'withoutoverheating. With lower currents of a magnitude in the milliamp range, the switch iscapable of operating for an almost unlimitednumber of cycles without breakdown. tact-making ability of the switch is further enhanced by the inherent rolling action which occurs as the center of segment 20 first touches segment 12 followed by adjacent sections of this segment making contact until contact is made over the entire area D. A reverse unrolling action 1 A trademark of the Du Pont Corporation.
In" the discussion to' follow, cover sheet The conoccurs when contact is broken. The initial point contact causes a high pressure to" be momentarily applied over a small area to physically puncture any contaminant film which may have accumulated on the conducting segment surfaces and also causes a high contact resistance and current density to exist for a short period of time. This latter condition exists long enough for any contaminant film to be burned away but not long enough to do any damage to the conducting surfaces.
From FIG. 1, it can be seen also that the stroke(s) of the switch is very small (0.003 to'0.030" with the illustrative dimensions previously stated) so that the re sponse time of the switch is good and the force required to activate it low. The silicone grease 24 between diaphragm 18 and cover sheet 22 reduces the friction which would otherwise occur as these two sheets move relative to each other, thereby further reducing the energizing.
force required and improving the response time of the switch. 'The fact that only the relatively thin diaphragm 18 must move into opening 16 permits opening 16 to be relatively' small and therefore allows a relatively dense array of switching points to be constructed.
In order to'provide a fuller understanding of the invention, the physical sequence of events which occurs when pressure is applied to a small area, having a diameter d, near the center of the switch will now be described in detail. The pressure P applied to the elastomeric layer 22 is initially transmitted through the elastomeric layer to deform the diaphragm with a very small radius of curvature, resulting in a point contact between conducting segments 12 and 20. The small radius of-curvature of the diaphragm results from the fact that it is being rigidly supported at the walls of the opening as it is being poked and stretched into theopening by the pressure apapplied to'the diaphragm which furtherdeform the diaphragm toward the walls of the opening. This further deformation of the diaphragm increases the radius of curvature thereof, and therefore increases the contact area betweensegments 12 and 20. The rolling action described above is in this manner achieved. 7
FIG. 3 is a partially cutaway view of an array of the pressure-responsive diaphragm switches of this invention. This array may, for example, be used as part of a punched card reader'orto give a series of x-y coordinates when used as part of a curve or character reading device. In this array, the layers 10, 12, 14, 18,20 and 22 are clamped in aframe 28 to avoidfgrossrelative shift of the separate layers. For purpose of illustration, segments 12 have been shown as being continuous strips oriented in one direction, and segments 20 have been shown as continuous strips oriented in a direction perpendicular to that of the strip 12. A line 30 is connected to each of the strips 12 and a line 32 to each of the strips 20.
As an example of how the array shown in FIG. 3 may beoperated, assume that a stylus is moved across the top of sheet 22. As the stylus comes over each opening 16, diaphragm 18 and an associate strip 20 are forced through the opening into contact with a strip 12. By succeedingly applying a signal to the lines 30 and sensing on which of the lines 32 an output occurs, it is possible to determine which of the openings 16 the stylus is positioned over at any given time.
It can be seen that the array shown in FIG. 3 may be easily fabricated by use of known thin film techniques However, since an elastomer is substantially such as photo-etching and that the cost per switching point for a switching array may be made extremely low by use of such techniques. Such techniques also provide an extremely thin switching array as may be observed from the illustrative layer thickness previously stated. Further, the frame 28 forcing the various layers together, provides an inherent sealing action which enables the array to operate under adverse conditions of temperature, humidity and contamination without ill effect. Should further security against adverse environmental conditions be desired, the entire array may be hermetically sealed. Any contamination of the contacts which still exists is taken care of by the inherent rolling action previously described. It should also be noted that a sheet of paper or similar material may be placed over layer 22 and written on without in any way hampering the switching action of the array so that a visual record of what is being recorded may be obtained at the same time that it is being electrically recorded.
While in FIG. 3, segments 12 and 20 have been shown as being strips of conducting material oriented perpendicular to each other and the switching points oriented in a matrix array, the array may also be constructed by, for example, coating the entire underside of diaphragm 18 with conducting material or using a diaphragm of conducting material and providing an individual conducting segment 12 for each index position. A single lead would be connected to the conducting layer under the diaphragm and an individual output lead would be provided for each of the segments 12. The array could then be laid out in any desired fashion.
Where it is desired to provide a multi-pole isolated switching element which may be activated by a single actuator, segment 12 is mounted on the upper surface of a second diaphragm with the underside of the diaphragm having a conducting segment 20. This second conducting segment 20 has a separator layer 14, a conductor segment 12, and a substrate associated with it, thereby providing a two-layer stacked diaphragm switch, the upper layer of which closes first and opens last when pressure is applied to cover sheet 22. A third and possibly a fourth layer of stacked switch could likewise be provided in this manner.
While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and detail may be made therein without departing from the spirit and scope of the invention.
What is claimed is:
1. A switch which is activated by pressure applied to a small area near the center thereof comprising:
a base assembly having a first conductive contact element;
a substantially incompressible insulating layer overlaying said base assembly, said insulating layer having an opening therethrough which is aligned with said first conductive contact element;
a diaphragm assembly overlaying said insulating layer, said diaphragm assembly having a second conductive contact element which is aligned with said first conductive contact element but is normally separated therefrom by a gap formed by said opening;
and an elastomer layer in contact with the upper surface of said diaphragm assembly and having a low coefficient of friction therewith, said elastomer layer coacting with the walls of said opening to deform said diaphragm assembly into said opening with a small radius of curvature as pressure is initially applied to said small area to cause an initial point contact to be established between said contact elements, and further coacting with the walls of said opening to further deform said diaphragm assembly to increase the radius of curvature of the lower surface thereof, as the pressure applied to said small area is increased,
3 to cause the area of contact between said contact elements to be increased.
2. A switch of the type described in claim 1 including a layer of lubricant between said elastomer layer and said diaphragm which provides said low coefficient of friction.
3. A switch of the type described in claim 1 wherein said first and second conductive contact elements are plated onto said base and diaphragm assemblies respectively;
and wherein said insulating layer is plated on said base assembly.
4. A switching array, each element of which is activated by pressure applied to a small area of the array near the center of the element, comprising:
a base assembly having at least one first conductive contact element, and a diaphragm assembly having at least one second conductive contact element, Where at least one of said assemblies has a plurality of conductive contact elements which are electrically isolated from each other;
a substantially incompressible insulating layer separating said base and diaphragm assemblies from each other, said insulating layer having an opening therethrough at each point which is between a first contact element, or a portion thereof, and a second contact element, or a portion thereof, which contact elements it is desired to have make switching contact with each other;
an elastomer layer in contact with the upper surface of said diaphragm assembly and having a low coefificient of friction therewith, said elastomer layer coacting with the walls of said opening, when pressure is applied to a small area of said switch above a point near the center of one of said openings, to deform said diaphragm assembly int-o said opening with a small radius of curvature to cause a point contact to be established between the conductive contact elements on either, side of said opening, and coacting with the Walls of said opening, as the pressure applied to said small area of the switch is increased, to further deform said diaphragm assembly to increase the radius of curvature of the lower surface thereof to cause the area of cont-act between said conductive contact elements to be increased;
and means adapted to indicate which two of said conductive contact elements have been brought into contact with each other.
5. A switching array of the type described in claim 4 including a layer of lubricating material between said elastomer layer and said diaphragm assembly to provide said low coetficient of friction.
6. A switching array of the type described in claim 4 wherein said based assembly includes a substrate having conductive material selectively plated thereon to form said first conductive contact elements;
wherein said diaphragm assembly includes an elastic sheet having conducting material selectively plated thereon to form said second conductive contact elements;
and wherein said insulating layer is plated onto said base assembly.
7. A switching array of the type described in claim 4 including a frame holding said base and diaphragm assemblies, said insulating layer, and said layer of elasmeric material together.
8. A switching array of the type described in claim 4 wherein said first conductive contact elements are parallel strips;
wherein said second conductive contact elements are parallel strips oriented at right angles to the strips forming said first conductive contact elements;
and wherein the openings in said separating means are at each intersection of a first and second conductive contact element.
(References on following page) References Cited by the Examiner References Cited bythe Applicant UNITED STATES PATENTS 2/1956 Kidd.
OTHER REFERENCES Electro Mechanical Design, November 1962, pages 40-41.
UNITED STATES PATENTS 7/1958 Osuch et a1 20086 9/1962 Larson 20096 5 1/1965 Parkinson 2()086 X FOREIGN PATENTS 1/ 1931 Great Britain. 2/ 1934 Great Britain. 11/1916 Norway.
BERNARD A. GILHEANY, Primary Examiner. 10 H. A. LEWITTER, Assistant Examiner.