US 3828154 A
In a variable network loudness and/or tone control, a mechanism is disclosed for use as an "off-on" switch. The switch is actuated by rotating the same shaft that controls the loudness or volume.
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Description (OCR text may contain errors)
Unite States atent [191 Fabricius et al.
[451 Aug. 6, 1974 VARIABLE ELECTRONIC COMPONENT SWITCH Inventors: John H. Fahricius, Stamford; John P. Maher, North Adams, both of Mass.
Assignee: Sprague Electric Company, North Adams, Mass.
Filed: Feb. 26, 1973 Appl. No.: 335,617
Related US. Application Data Continuation-impart of Ser. No. 260,293 June 6,
1972, Pat. No. 3,760,321.
US. Cl. 200/153 LB, 200/6 BB, 200/166 Int. Cl. H0lh 21/82 Field of Search 200/153 LB, 166 CT, 6 B, 200/6 BA,'6 BB, 6 C, 166 K, 153 L  References Cited UNITED STATES PATENTS 2,855,490 10/1958 Arisman et a1. 200/153 LB X 2,932,709 4/1960 Budd et a1 200/153 L 2,957,970 10/1960 Taylor 200/153 LB X Primary Examiner-Robert K.- Schaefer Assistant ExaminerWilliam .1. Smith Attorney, Agent, or Firm-Connolly and l-lutz  ABSTRACT In a variable network loudness and/or tone control, a mechanism is disclosed for use as an off-on switch. The switch is actuated by rotating the same shaft that controls the loudness or volume.
1 Claim, 4 Drawing Figures CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of application Ser. No. 260,293 filed June 6, 1972 now US. Pat.
No. 3,760,321 issued Sept. 18, 1973 by John H. Fabricius and John P. Maher.
BACKGROUND OF THE INVENTION which are simultaneously varied. It is thereby possible,
for example, to change the shape of the frequency response as a function of overall gain in a prescribed manner. For example, thefrequency response of the variable network as a function of gain setting may be designed to match the standard loudness curves (Fletcher-Munson curve).
Such variable network components normally employ a shaft, one end of which protrudes through an aperture in the back cover of the component housing, the shaft thus being physically stabilized. The shaft thereby preempts a central space in the rear of the housing that could otherwise house a conventional off-on switch.
In such a variable network as described in detail in the referenced application Ser. No. 260,293 now US. Pat. No. 3,760,321 of which the present invention is a continuation-in-part, the housing, the back cover, and the shaft may all be of a plastic material and more particularly a thermoplastic such as nylon or Delrin (a Du- Pont trademark for a crystalline form of a polymerized formaldehyde). The cover and housing may thus be ultrasonically welded together, advantageously forming a sealed protective shell around the components and further permitting low cost injection molding fabrication of the parts. The physical integrity and ruggedness of the finished assembly is thus assured. The use of thermoplastic material for the cover has the additional attractive feature that it is significantly more elongatable or pliable compared with thermosetting plastics, phenolics or metal. Thus in the cover, the centrally located hole made to receive the knurled end of the shaft, elongates and widens while the knurl is pressed through it, and subsequently snaps back to its original dimensions. The shaft is thereby locked into the hole providing the assurance that it will not inadvertently withdraw when rotated or operated.
Some switch structures are known which are designed around a centrally located shaft in the back of a variable component, namely a potentiometer. However none are known to employ a thermoplastic cover, the multiple advantages of which have been noted. A disadvantage for so doing is the tendency for the thermoplastic to melt and flow or at least distort upon soldering to the switch terminals that protrude through the back cover.
It is therefore an object of the present invention to provide a switch that is integral with a variable network component.
It is a further object of this invention to provide a switch, with terminals protruding through a thermoplastic cover, such that the thermoplastic does not distort when soldering to the terminals.
It is a further object of this invention to provide a switch that is operable by and built around a shaft in a variable network component.
SUMMARY OF THE INVENTION This invention comprises a switch mounted integrally with a variable component such that a common shaft actuates the switch and varies the electronic network ofthe component. The switch is constructed around the shaft, which extends through and is rotatable in a metal bushing at one end and an aperture in the thermoplastic cover at the other end of the variable component. The switch terminals protrude through the cover and are thermally intimate with large metal strips that act to distribute the heat and prevent cover distortion while soldering. The same strips also serve as the switch contacts.
BRIEF DESCRIPTION OF THE DRAWING FIG. 4 shows a washer for actuating the switch of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows an inside face view and FIG. 2 shows a side view of a rear molded plastic cover 10 to the insulative housing of a variable network component (not shown). Mounted inside the cover 10 are two metal strips 11 and 12. The relatively rigid metal strip 11 is mounted in the cover 10 by force fitting or snapping it into the slots formed by three pairs of cover projections 31 and 32, 33 and 34, and 35 and 36. The relatively flexible metal strip 12 is mounted in the cover by snapping it into the slots formed by two pairs of projections 23 and 24, and 25 and 26. The second strip 12 is formed so as to be spring loaded against one end of the first strip 11 and thus they are normally in firm physical and electrical contact with each other. The switch is seen normally closed. Each strip has a terminal portion extending through a rectangular hole in the cover. Referring to FIGS. 2 and 3, the terminal 14 of strip 11 is not seen but is hidden in the side view by the terminal 17 of strip' 12.
Both strips are made much longer and have much more bulk than would be necessary for secure mounting and proper mechanical operation. Thus they each represent a relatively large heat sinking capacity such that when the terminals are heated for soldering connective wires thereto, the heat is absorbed in the large heat capacity of the metal strips. The temperature of a strip during soldering is thus reduced and controlled so that the thermoplastic case does not distort.
The strips are also seen to be in good physical and thermal contact with the cover, providing an even greater heat distribution and heat sinking capability. The intimacy between the cover and the strips may be further enhanced by providing short tabs or metal extensions from the strip that press into but not through notches molded into the cover therefor. Such a feature is not shown in the drawings.
The cover can be seen in perspective in FIG. 3. In FIG. 4, a washer 40 is shown in perspective view lying in a plane that is beneath and parallel tothe plane of the cover.
A shaft of the variable component (not shown) normally projects through hole 41 and is fix mounted or keyed to the washer 40. The shaft also projects through the hole 16 in the cover and is stabilized and rotates therein. Thus, when the shaft is rotated, the washer 40 rotates in relation to the cover 10.
The washer 40 features a projection that acts as a cam 42, that rotates into contact with the topmost portion (as shown crosshatched in FIG. 1) of strip 12. As shown in FIG. 1, the stripsll and 12 are bent and positioned to partially encircle the shaft. When the cam 42 presses strip 12,-the strip deflects down and to the right so as to separate from strip 11 and thus open the switch. Another projection 43 of the washer 40 is designedto contact a stop 13 of the cover 10. The flexible second strip 12 is extra wide at one end, namely the (crosshatched) topmost portion, so as to insure engagement with the cam 42. This extra wide portion of strip 12 is seen in the side view of FIG. 2 extending to the left from the face of the cover.
' Another projection 21 of the cover serves as a guide to the movable end of strip 12. Another part of cover 10 is made to guide and secure the cover into the open end of the component housing. The housing and variable network assembly with which the switch of this invention is associated, is not depicted in the drawings. The housing has a metal bushing extending out of a face that opposes the cover. The aforementioned shaft or concentric shafts rotate in Switch Element and Number Linear Dimension (inches) strip l I We strip 12 1% projections 23, 24
- do. 25, 26 3/16 do. 3i, 32 3/16 do. 33, 34 7/16 do. 36, 35 A;
The glass filled square nylon cover measures 1 l/l6 inches on a side and is 0.050 inches thick in its thinnest central regions. The strips are press fitted between projection pairs such as strip 12 in pair, 23 and 24. The
the bushing. Fixed in the housing is a substrate having variable and fixed resistors and capacitors on one or both major surfaces. One or more contactors mounted to a shaft makes pressurized contact with the variable elements.
The variable network is advantageously that described in U.S. Letters Pat. No. 3,668,478. A suitable structure for the substrate and contactor assembly is described in pending application Ser. No. 260,293.
In a prototype model of the switch of this invention, the washer is made of Delrin. The housing and cover of the prototype were injection molded pieces of glass fiber filled nylon. Other thermoplastic materials may be suitable. The washer may be mounted on the shaft by keying both, for example by flats, such that they rotate together. The shaft or concentric shafts may be of plastic or if greater strength is desired, of metal. The rigid first strip was made of 0.032 inches thick brass. The flexible second strip was made of 0.015 inches thick phosphor bronze. Both pieces had, in addition to terminal tabs, short tabs that pressed into grooves formed in the cover therefor. These extra tabs provided additional holding power between the cover and the strips. The width of both strips in areas not having tabs was 0.060 inches.
mechanical holding power of these intimate connections is much greater than is required to give the switch members, namely the stubs, mechanical rigidity. This intimate and extensive connection means provides good thermal conductivity between the strips. and the cover helping to distribute the heat from soldering and thus keeping the temperature of the cover low except in the immediate vicinity of the terminal being soldered'Even if a small region of the thermoplastic cover, around a terminal being soldered, is softened, it experiences no stress due'to the extensive connection of all the elements, and it freezes without distortion after the soldering has been completed.
In the prototype, the strips are provided with tabextensions, heretofore mentioned, which press into slots between the projection pairs, thus even further enhancing the thermal and mechanical connection between cover and strips.
It should be noted that the seemingly over long strips provide not only a means for distributing the heat over the cover, but also provide alarge heat capacity tending to limit and regulate the strip and cover temperature.
Prototypes were tested for cover distortion due to soldering. Using a 40 watt soldering iron having a temperature of 760 F, no distortion occurs for at least the first 30 seconds. Other tests to date on the switch indicate that it is capable of greater than 50,000 ON-OFF operations without failure.
The above-described embodiment of the invention has been set forth for purposes of illustration. It is not intended that the invention be limited other than by the scope of the appended claim.
What is claimed is:
1. A variable electronic component comprising a housing of thermoplastic material having a metal bushing extending out therefrom; a cover of thermoplastic material disposed over an open end of said housing, said cover having an aperture therein; and a rotatable shaft having one end thereof knurled and positioned in said aperture of said cover and the other end thereof extended out from said housing through said bushing; wherein the improvement comprises a. a first and a second metal strip each being snap pressed between two or more pairs of projections that are provided therefor on the inside face of said cover, each said strip having a length that is greater c. a cam fixedly connected to said shaft and being rotatable therewith, said cam being capable of contacting and deflecting said other strip generally toward said shaft and out of contact with said one strip, thus forming around said shaft a switch made operable by rotating said shaft.