US3377604A - Electrical devices with frictionless flexible contacts - Google Patents

Description

April 1968 J. w. FORREST 3,

ELECTRICAL DEVICES WITH FRICTIONLESS FLEXIBLE CONTACTS Filed April 26, 1967 I 2 Sheets-Sheet L INVENTOR. JOHN W FORREST BY @ZflflW ATTORNEY A ril 9, 1968 J. w. FORREST ELECTRICAL DEVICES WITH FRICTIONLESS FLEXIBLE CONTACTS Filed April 26, 1967 2 Sheets-Sheet FIG. 4

INVENTOR. JOHN W. FORREST ATTORNEY United States Patent 3,377,604 ELECTRICAL DEVICES WITH FRICTIONLESS FLEXIBLE CONTACTS John W. Forrest, West Acton, Mass., assignor to Acton Laboratories, Inc., Acton, Mass, a corporation of Massachusetts Filed Apr. 26, 1967, Ser. No. 633,999 14 Claims. (Cl. 338154) ABSTRACT OF THE DISCLOSURE This patent specification describes improvements in devices of the type shown in US. Patents 2,862,088, 3,070,- 768, 3,170,047 and 3,274,350 which essentially comprise a rotating depressor which runs over a flexural contact diaphragm and urges the latter to successively engage a series of switch contacts or successive portions of an electrical resistor. The invention involves changes in how the diaphragm is supported and how the depressor is disposed with respect to the diaphragm, as well as an improved mode of assembling the various parts so as to maximize diaphragm life, stabilize the output signal, and facilitate disassembly for inspection and repair.

This invention relates to encapsulated rotary electrical control devices and more particularly to encapsulated rota-ry switches and potentiometers.

Field of invention Prior art The most pertinent prior art known to applicant consists of US. Patents 2,862,088, 3,070,768, 3,170,047 and 3,274,350, and the references cited therein. The chief limitation of prior encapsulated switches and potentiometers is the difficulty of maintaining quality and meeting operational specifications when manufacturing units in production quantities. Although it has been possible to build units that perform satisfactorily over a large number of operating cycles, such success has been sporadic and unpredictable. The chief problem that has persisted is inconsistent performance of the diaphragm, with some diaphragms functioning satisfactorily for as much as 30 million operating cycles of the depressor but more failing to perform to specifications after 10-15 million cycles. In some cases the deterioration in performance has involved rupture or cracking of the diaphragm along the line of contact by the depressor, but in other cases the deterioration has been manifested by marked decreases in the signal to noise ratio and variations in output signal quality with changes in ambient temperature. It has been discovered that this problem of diaphragm performance is attributable to a variety of factors, including the way in which the diaphragm is mounted, misalignment of parts and differences between the thermal coefficient of expansion of the metal layer of the diaphragm and that of the disc carrying the switch segments or resistor element. Another problem is that the amount of torque required to rotate the depressor tends to change during extended operation. Other problems are improper positioning and clamping of the dis-c carrying the switch segments or resistor element. If the disc is 3,377,604 Patented Apr. 9, 1968 not secured tight enough and hence can move, noise will occur in the output signal. On the other hand if the disc is secured so tightly as to be distorted, the contact made by the diaphragm with the switch segments or the resistor element may vary sufficiently to produce undesired variation in the output signal. These and other problems have been complicated by the fact that prior designs were not adapted to production control permitting detection of defects and replacement of defective parts at different stages of assembly.

Summary of invention The general object of this invention is to provide new and improved devices of the character described that overcome the problems previously existent in the prior art. More specific objects of the invention are to provide modifications over the prior art that minimize the contact area and diaphragm stress, reduce contact laminate wear, assure constant torque over extended use, facilitate rnounting of the switch and resistor discs without'physically distorting them, simplify shaft alignment and loading of bearings, minimize noise and fluctuation in the output signal, and permit detection of defects at different stages of assembly.

These and other objects are achieved by providing an electrical control device consisting of an annular disc carrying a circular array of spaced switch segments or a circular resistor element, an annular laminated contact diaphragm consisting of an outer layer of a hard fatigue resistant spring alloy and an inner layer of a low electrical resistance metal, a pair of standoff rings separating the disc and diaphragm at their inner and outer edges with only one of said standoff rings secured to both the disc and diaphragm, an insulated depressor mounted on a rotatable shaft and positioned to slide on and press the diaphragm against the switch segments or resistor element, and bearing means for rotatably supporting the shaft. The device also includes means for clamping the disc under controlled pressure, and means for adjustably loading the bearings. The standoff rings are made of a resilient material that provides dimensional stability yet yields sufficiently to minimize diaphragm strain.

Other objects and advantages of the invention are believed to be readily apparent from the following detailed description which is to be considered together with the accompanying drawings, wherein:

FIG. 1 is a longitudinal sectional view of a commutator switch embodying the invention;

FIG. 2 is an end view of the same device looking from right to left in FIG. 1;

FIG. 3 is a fragmentary top view of the switch disc and contact diaphragm, with certain parts broken away for convenience of illustration; and

FIG. 4 is a sectional view taken along line 4-4 of FIG. 3.

Turning now to FIG. 1, there is a commutator switch comprising a cylindrical housing 2 having an end wall 4 provided with a centrally located hole 6 to accommodate a shaft 8 on which is mounted a depressor assembly indicated generally at 10 that coacts with a switch assembly indicated generally at 12. The opposite end of housing 2 is formed without an end wall but is closed off by a cover 14.

Referring now'to FIGS. 3 and 4, the switch assembly comprises (a) a rigid annular non-conductive switch disc 16 preferably made of epoxy resin reinforced with glass fibers and having a circular array of spaced switch segments 18 on one face thereof, (b) a flexural annular contact diaphragm identified generally at 20 that overlies the said one face of the switch disc, and (c) a pair of concentric standoff rings 22 and 24 disposed between the 3 switch disc and the contact diaphragm and functioning to support the latter in spaced relation to the switch segments 13. The switch segments are plated onto the disc 16. and are made of a conductive metal or metal alloy. This preferred embodiment is adapted for multiplexing digital information emanating from three different sources. Accordingly the switch segments 18 are coupled together in three discrete groups 18A, 18B and 18C, with successive members of one group separated by a member of each of the other groups. More specifically, switch segments 18A are connected by a continuous ribbon 26 of conductive metal that encircles and is coplanar with the array of switch segments, switch segments 18B are connected by asecond ribbon of conductive metal 28 that is coplanar with and runs along the inside of the array, and switch segments 18C are connected by a third ribbon 30 that is concealed within switch disc 16 and follows a zig-zag pattern between segments. Ribbon 30 is connected to switch segments 18C by short vertical conductive members 32. Four different conductive metal eyelets 34, 36, 38 and 40 are attached to the switch disc near its center. Switch segments 18A are electrically connected to eyelet 34 by a short plated metal strip 42, switch segments 18B are connected to eyelet 36 by a second plated metal strip 44, and switch segments 18C are connected to eyelet 38 by a third plated metal strip 46. The fourth eyelet 40 is reserved for connection to the contact diaphragm.

The flexural contact diaphragm is of laminated metal construction and comprises an outer layer 50 formed of a hard, fatigue resistant spring metal alloy whose physical properties are retained to a satisfactory degree over a wide temperature range, e.g., from sub-zero temperatures up to about 500 F. A number of cobalt-based alloys meet these requirements, but I prefer to employ the alloy Havar manufactured by Hamilton Watch Company, Precision Metals Division, Lancaster, Pa., or Elgiloy sold by the Elgin National Watch Co. The contact diaphragm also comprises an inner layer 52 of a conductive metal, preferably gold, which is secured to the outer layer by an intermediate layer 54 of a metal such as nickel which can bond readily to the inner and outer layers. The outer spring metal layer preferably has a thickness in the range of from about .0008 to about .001 inch, while the nickel and gold each are plated on in layers measuring about 50 10 inch. The laminate is formed free of wrinkles, depressions and scratches. The foregoing laminated construction is not novel with me but is taught by U.S. Patent No. 3,274,350 issued Sept. 20, 1966, 'to E. H. Mongeau for Frictionless Contact Construction for Electrical Devices. However it is to be noted that the Mongeau patent teaches the use of a flexible depressor tracking ring made of Mylar or similar material that is attached to the outer surface of the cobalt alloy layer and serves to insulate the depressor from the contact diaphragm. In the practice of my invention as herein described and illustrated I deliberately omit the flexible insulating tracking ring and instead permit the depressor to directly engage the contact diaphragm. The purpose of this departure from the teaching of Mongeau is explained below.

I have determined that the standoff rings 22 and 24 must have dimensional stability yet be resilient. I also have found that improved results are achieved if the inner standoff ring 22 is secured to both the contact diaphragm and the switch disc while the outer standoff ring 24 is secured to only the contact diaphragm. This arrangement appears to be particularly advantageous for small diameter commutators, e.g., commutators having an outside diameter of 1-l' /2 inches. I have further determined that best results are obtained if the inner standoff ring is made of a material having a durometer of about 40-50 and if the outer standoff ring is made of kraft paper. The requirements for the inner standoff ring are met if it is made of single ply Scotchweld #583 adhesive tape (a product of Minnesota Mining and Manufacturing Co.) measuring about 2 l0 inch thick. This tape is a flexible solids dry film adhesive composed of a synthetic elastomer and a combination of thermosetting and thermoplastic resins. In its uncured state, i.e., before heat is applied, the tape has a tensile strength of 3.2 lbs. per inch of width and is capable of minimum elongation of 300%. This tape is adapted to adhere to a variety of materials when subjected to heat and pressure.

In practice the inner standoff ring 22 is secured to the contact diaphragm by application of heat and pressure. Then the kraft ring 24 (measuring about 0.002 inch thick) is cemented to the diaphragm using Phiobond cement. Then the diaphragm is placed over the switch disc with the standoff rings located concentrically with the circular array of switch segments and the inner standoff ring is secured to the switch disc by use of heat and pressure. Firm adherence of the Scotchweld ring 22 to switch disc 16 and/or diaphragm 20 is achieved by applying pressure of about 100 psi. at a temperature of about220- 240 F. for about one hour.

The diaphragm is formed with a tab 58 on its inner edge. After the diaphragm is secured to the switch disc, a flexible lead 60 is soldered to tab 58 and also to the fourth eyelet 40. The encapsulated switch assembly 12 is completed by four insulated flexible wire leads 62 which are inserted into and soldered to the eyelets 3640.

Referring now to FIG. 1, the shaft 8 is supported by a roller bearing 66 whose inner race is secured to the shaft and whose outer race is sized to make a snug fit in the hole 6 provided in the end wall 4 of the housing, The outer race of the bearing is provided with a flange 68 that engages the inner surface of the end wall 4 and shaft 8 is formed with an annular flange 70 that engages the inner race of the bearing.

The depressor assembly 10 comprises two metal plates 72 and 74 between which is sandwiched a flat spring metal arm 76 (preferably formed of spring steel or beryllium copper). Plates 72 and 74 and arm 76 are formed with holes of identical size to accommodate a sleeve 78 formed of a sturdy insulating material, preferably a plastic such as Delrin or nylon. Sleeve 78 is cemented to shaft 8 and, although not shown, it is to be understood that arm 76 and plates '72 and 74 are interlocked with sleeve 78 so as to rotate therewith. Such interlocking may be achieved by a keying or tongue and groove arrangement. The two plates and arm 76 are clamped together by one or more rivets 80. Arm 76 projects radially of shaft 8 and attached to one projecting end thereof is a small shaft 82 carrying a miniature roller bearing 84 which functions as a depressor for the contact diaphragm. The outer race of bearing 84 is beveled so to provide a rounded surface as shown at 86. It is to be noted that the arm has a length such that the roller bearing depressor 84 is not located midway between the two standoff rings but instead is positioned so that its circular line of contact with the diaphragm subdivides the latter into two concentric annular portions of approximately equal area. In effect the depressor tracks along a line of minimum strain.

Referring again to FIGS. 1 and 2, the cover 14 has four evenly spaced threaded holes into which are screwed four insulated terminals 90, 92, 94 and 96 of conventional construction. The four flexible leads 62 which are attached to the eyelets in the switch disc are connected to these terminals. The cover also has a centrally located hole 98 in which is positioned a roller bearing 100, The outer race of bearing 100 is sized to fit snugly in hole 98 while its inner race is secured to shaft 8. The latter is provided with a circumferential groove into which is snapped a C-shaped retaining ring 102 which engages the inner race of hearing 100. The outer race of the bearing is engaged by a cup-shaped metal spacer 104 which in turn is engaged by a Belleville spring washer 106 and one or more shims or spacers 108. The latter are captivated by another C-shaped retaining ring 110 that snaps into a suitable groove formed in the cover around hole 98. The encapsulated switch assembly 12 is held against shoulder 64 by the cover acting through a resilient O-ring 112. The cover is secured to the housing by one or more screws 114.

Operation of the illustrated commutator is straightforward. Assume that (a) terminals 90, 92 and 94 are connected internally to the three groups of switch segments 18A, 18B and 18C and terminal 96 is connected internally to contact diaphragm 20 in the manner described above; (b) terminals 90, 92 and 94- are connected externally to three different signal channels, e.g. channels generating information signals, and terminal 96 is connected externally to a signal processing system, e.g. a telemetering transmitter; and (c) shaft 8 is connected to and driven by an electric motor. The depressor assembly 10 will rotate with respect to switch assembly 12 and as it does, the depressor roller 84 will press successive portions of the contact diaphragm into contact with successive switch segments, with the result that the three signal channels are alternately switched into and out of connection with the H signal processing system that is connected to terminal 96.

Although not illustrated, it is to be understood that the invention also is applicable to rotary potentiometers, as is the case with the invention described and claimed in US. Patent No. 3,274,350 mentioned above. This alternative mode of practicing the invention is not illustrated for the purposes of brevity of this specification and also because it is believed to be clear to persons skilled in the art. Suffice it to say that in making potentiometers the switch segments are supplanted by a resistor element as described in the aforementioned Patent 3,274,350 and also in US. Patent No. 2,862,089. Of course, in the case of a potentiometer, only three eyelets like those shown at 3440 in FIG. 3 (and also only three insulated terminals like those shown at 9096) are required, two connected to the ends of the resistor element and the third connected to the contact diaphragm.

Commutators and potentiometers embodying the invention herein exemplified and described offer many important advantages. For example, assembly is facilitated. Except as explained below, the various components are assembled in the order in which they occur looking from left to right in FIG. 1. The bearing 62 and the depressor assembly are mounted on shaft 8 before it is inserted into the case. The leads 62 are suificiently long to permit them to be connected to the terminals 90-96 before or after the switch assembly is inserted. This mode of assembly also facilitates disassembly of the device to the extent necessary to check for malfunctioning, electrical shorts, etc.

Another important advantage is the manner in which the switch assembly 12 is held in place. The clamping force exerted by shoulder 64 and the cover 14 acting through the resilient O-ring 112 is sufliciently positive to prevent movement of the switch assembly, yet is limited suificiently by virtue of compression of the O-ring to avoid distortion of the switch assembly.

A further advantage results from the mode of mounting the shaft 8. Unlike previous designs, it is a relatively easy task to adjust the loading on the shaft bearings. This involves varying the number and/or thicknesses of the shims 108, and may be accomplished without removing the cover. It is to be noted also that the use of through bearing holes 6 and 98 also facilitates checking for shaft alignment.

Still another advantage results from the fact that the depressor directly engages the spring metal layer 50 of the contact diaphragm instead of running on a tracking ring made of Mylar or similar material which is softer than layer 50. I discovered that relatively soft materials such as Mylar tend to undergo physical changes, e.g. cold flow, even under the realtively light pressure required to be exerted by the depressor to press the contact diaphragm against the switch segments. These physical changes are felt as variations in the torque required to rotate the depressor. No such result occurs when the tracking ring is III eliminated and the depressor made to engage the metal laminate in the manner described herein. Of course this modification involves insulating the depressor assembly from the shaft to avoid short circuiting.

The most notable advantages of the invention are substantial reducton in noise, extended diaphragm life (between 30 and million cycles), and elimination of fluctuations in the output signal throughout the duty cycle over a wide temperature range. The reduction in noise is attributable to the combination of diaphragm flexing and yielding of the standoff ringsv The extended life is attributable to the distortion-free clamping arrangement, the resilient standoff rings (including the fact that only one ring is secured to the rigid switch disc), and the position of the depressor with respect to the diaphragmf The resiliency of the standoff rings (together with the fact that only one ring is secured to the switch disc) stabilizes the output signal despite disproportionate expansion or contraction of the diaphragm and the switch disc due to changes in ambient temperature. The standoff rings compress to the extent desired to permit pressing the diaphragm against the switch disc, yet are dimensionally stable to the degree necessary to maintain a minimum gap between the two where relieved of the depressor pressure. The standoff rings have no tendency to set in compressed condition at elevated temperatures e.g., 96 C. and remain resilient even at temperature as low as C.

A further incidental advantage resides in the fact that the tab 58 of the contact diaphragm is not directly secured to the eyelet 40 but instead is connected thereto by the flexible service lead 60. I discovered that cementing the tab to the switch disc (as is shown in US. Patent No. 3,274,350) has a limiting effect on the flexibility of the contact diaphragm. This effect is avoided by using the service lead 60 since this arrangement allows the tab freedom to move up and down as the diaphragm is flexed.

It is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts specifically described or illustrated, and that within the scope of the appended claims, it may be practiced otherwise than as specifically described or illustrated.

I claim:

1. An electrical device comprising a housing; a contact assembly mounted within said housing, said contact assembly comprising (1) a rigid annular disc having at least one electrically conductive element on one face thereof, (2) a flexural annular conductive contact diaphragm overlying said disc in parallel relation to said conductive element, (3) a first resilient standoff ring disposed between said disc and said diaphragm adjacent the inner edges thereof, said first ring secured to said disc and also to said diaphragm, and (4) a second resilient standoff ring disposed between said disc and said diaphragm adjacent the outer edges thereof, said second ring secured only to said diaphragm, said rings supporting said diaphragm in spaced relation to said disc; depressor means pressing a portion of said diaphragm into contact with said at least one conductive element, and drive means for moving said depressor means along said diaphragm so as to cause said depressor means to press successive portions of said diaphragm into contact with successive portions of said conductive element.

2. An electrical device as defined by claim 1 wherein said last mentioned drive means is adapted to move said depressor means in a circular path along said contact diaphragm, and further wherein said depressor means is dis posed so as to contact said diaphragm along a line that is closer to said second ring than said first ring.

3. An electrical device as defined by claim 1 wherein said diaphragm is provided with a tab on its inner edge and said disc is provided with at least two conductive terminal members, and further including means coupling one of said terminal members to said at least one conductive element and a flexible insulated lead attached at one end 7 to said tab and at the other end to another of said terminal members.

4. An, electrical device as defined by claim 1 wherein said depressor comprises a roller whose peripheral surface is bevelled to reduce the area of its contact with ;he diaphragm.

5. An electrical device as defined by claim 1 wherein said diaphragm is of laminated construction and comprises a thin conductive inner layer facing said disc and an outer layer made of a conductive resilient hard alloy, and further wherein said depressor means is insulated so as to prevent electrical shorting through said drive means.

6. A device as defined by claim 1 wherein said disc has a plurality of spaced conductive elements disposed in a circular array on said one face thereof, and said drive means is adapted to move said depressor means in a circular path along said contact diaphragm so as to cause successive portions of said diaphragm to be flexed into and out of contact with successive ones of said conductive elements.

7. A device as defined by claim 1 wherein said housing is formed with an open end and also an interior annular shoulder which is engaged by the outer edge portion of said one face of said disc, and further wherein said device includes a resilient member engaging the opposite face of said disc and a cover member secured in said open end and pressing said resilient member against said disc so that said contact assembly is clamped between said shoulder and said resilient member.

8. A device as defined by claim "7 wherein said resilient member is an O-ring.

' '9. An electrical device comprising a housing; a contact assembly mounted within said housing, said contact assembly comprising (1) a stiff annular disc having at least one electrically conductive element on one face thereof, (2) a flexural annular'contact diaphragm overlying said disc in parallel relation thereto, and (3) first and second standoff rings interposed between said diaphragm and said disc at the inner and outer edges respectively thereof, said standoff rings supporting said diaphragm in close spaced relation to said disc; a shaft extending axially through the open center of said contact assembly; means rotatably supporting said'shaft; and a depressor assembly secured to said shaft, said depressor assembly including a depressor member spaced radially of said shaft and adapted to press successive portions of said diaphragm into contact with successive portions of said at least one conductive element as said shaft is rotated, said depressor member located so that its movement along said diaphragm follows a circular path that is located closer to said sec-nd standoff ring than said first standoff ring.

10. An electrical device as defined by claim 9 wherein the unsupported surface area of said diaphragm between said first standoff ring and said circular path is approximately equal to the unsupported area of said diaphragm between said second standoff ring and said circular path.

11. An electrical device comprising a housing open at one end and provided with an end wall at its opposite end, said housing having an interior annular shoulder located intermediate its ends; a contact assembly within said housing, said contact assembly comprising a stiff annular disc having the 'outermarginal portion of one face thereof in engagement with said shoulder, at least one electrically conductive element on said one face, and a flexural annular contact diaphragm secured to said one face in overlying parallel spaced relation to said at least one conductive element; a shaft; first bearing means mounted in said end wall; a first portion of said shaft rotatably supported by said first bearing means; a cover member secured in and closing off said open end of said housing, said cover member having a hole therein; resilient means interposed between said cover member and the opposite face of said disc, said resilient member being pressed against said disc by said cover so that said disc is clamped between said shoulder and said resilient member; second bearing means mounted in said hole, a second portion of said shaft rotatably supported *by said second bearing means; means mounted within said hole for loading said second bearing means and urging said shaft towards said first bearing means so as to also load said first bearing means; and a depressor assembly secured to said shaft and including a depressor member spaced radially away from said shaft, said depressor member disposed so as to press successive portions of said diaphragm into contact with successive portions of said at least one conductive element as said shaft is rotated relative to said housing.

12. An electrical device as defined by claim 11 wherein said end wall has an opening located in alignment with said hole, and further wherein said first bearing means is mounted in said opening.

13. An electrical device as defined by claim 12 wherein said shaft projects out of said end wall.

14. An electrical device as defined by claim 11 wherein said cover member includes terminal means for said diaphragm and also said at least one electrically conductive element, and flexible conductive means connecting said terminal means with said diaphragm and said at least one electrically conductive element.

References Cited UNITED STATES PATENTS 2,862,088 11/1958 Mairs 338-154 2,916,717 12/1959 Hartman et al. 338-154 2,917,720 12/1959 Budd et al. 338-454 3,070,768 12/1962 Mairs 338154 3,102,989 9/1963 Sielsch 338l54 3,198,895 8/1965 Richman ZOO-11 X 3,274,350 9/1966 Mongeau 200-11 ROBERT K. SCI-IAEFER, Primary Examiner.

H. J. HOHAUSER, Assistant Examiner.

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