US2708729A - Shakeproof variable condenser - Google Patents

Description

May 17, 1955 c. L. SHULL SHAKE PROOF VARIABLE CONDENSER Filed Dec. 27, 1951 INVENTOR. (Adfl68 0C kwfi BY W A ORA/E1 WI TNESS United States Patent- SHAKEPRGOF VARIABLE CONDENSER Qharies L. Shull, Horseheads, N. Y. Application December 27, 1951, Serial No. 263,540 4 Claims. (Cl. 317249) The present invention relates to a shakeproof variable electrical condenser and more particularly to a trimmer condenser for high frequency electric circuits which is adapted for use under conditions of extreme vibration.

Trimmer condensers as heretofore constructed have been more or less subject to the production of microphonic variations of resistance and to loss of adjustment when subjected to violent shocks or vibrations such as sometimes encountered more particularly in military equipment. Such microphonic and/or reduction in effectiveness may even reach the point where satisfactory operation of a piece of electronic equipment becomes difficult or even impossible in certain situations.

it is an object of the present invention to provide a novel trimmer condenser in which the capacity of the condenser, when once adjusted, is maintained substantially constant irrespective of shock or vibration below the level of destructiveness.

It is another object to provide such a device in which the electrical conductivity of the device is maintained constant, and more particularly the resistance of the joints between the adjustable parts is very low and is unaffected by any vibration of the instrument encountered in its intended use.

Further objects and advantages will be apparent from the following description taken in connection with the accompanying drawing, in which:

Fig. l is a side elevation, partly broken away and in section, of a preferred embodiment of the invention;

Fig. 2 is a detail in elevation of the spring member for immobilizing the inner electrode in its adjusted position;

Fig. 3 is a mid-sectional view of the spring ring illustrated in Fig. 2; and

Fig. 4 is a section taken substantially on the line 44 of Fig. 1.

In Fig. 1 of the drawing there is illustrated a sleeve 1 of suitable electrically conductive material such as brass having a fiange 2, and threaded for the reception of a nut 3 which serves to clamp the sleeve in a panel 4. When, as is frequently the case, the inner electrode of the condenser is to be grounded, the panel is made of conductive material such as aluminum, and the clamping action of the nut 3 against the shoulder 2 makes a firm electrical connection. In other cases, the panel may be of a dielectric material and the sleeve 2 connected in its circuit in any suitable manner as by a soldered terminal.

A hollow cylinder or tube 5 of dielectric material such as glass is rigidly mounted at one end on a reduced terminal portion 6 of the sleeve 1, coaxially therewith. This connection is most conveniently made as illustrated by metallizing the exterior surface of the glass cylinder and then soldering it to the sleeve as indicated at 7.

An outer cylindrical electrode 8 is mounted on the dielectric cylinder 5, extending somewhat less than half the length of the cylinder from its outer end. This electrode is conveniently formed by metallizing the surface of the cylinder, and an electrical conductor 9 is soldered to the end of the cylinder as indicated at 11 for connection in the circuit to be tuned in a convenient manner.

A threaded shaft 12 of electrically conductive material such as brass is slidably mounted in the sleeve 1 and extends into the dielectric cylinder 5 coaxially therewith. An inner electrode 13 having a sliding fit in the cylinder 5 is fixedly mounted on the end of the screw shaft 12 as by means of a press fit on a smooth terminal portion of the shaft. The shaft 12 is formed from stock having a polygonal cross-section; preferably square as best shown in Fig. 4, the corners being threaded so as to leave flat surfaces 10 between the threaded portions. The sleeve 1 is provided with an opening 14 conforming to and slidably receiving the square shaft; and means for adjusting'the shaft longitudinally is provided in the form of a nut 15 rotatably mounted in the sleeve 1 and having a portion 16 of reduced diameter extending out from the sleeve. The end of the sleeve is spun inwardly as shown at 17 so as to embrace the reduced portion of the nut and retain it'inthe sleeve, thus providing a swivel connection between the sleeve and nut. The end of the nut is provided with a flatted portion 18 arranged to receive a spanner to conveniently effect its rotation.

Means are provided for yieldably pressing the nut against the constricted portion 17 of the sleeve, and at the same time providing a positive electrical connection between the shaft and sleeve forming in effect an electrical bond therebetween. This is accomplished by forming an inwardly tapered wall 19 in the sleeve 1 adjacent the opening 14 and placing a plurality of balls 21, in this case four, of comparatively soft electrically conductive material such as lead or copper in the sleeve in position to bear on the tapered wall 19 of the sleeve and the flat surfaces 10 of the shaft 12. The balls are wedged between these converging surfaces by means of a spring 22 which bears at one end against a washer 23 in contact with said balls and its other end bears against the nut 15 pressing it against the constricted portion 17 of the sleeve. The shaft and sleeve are thus electrically bonded together so as to prevent any microphonic action, although longitudinal adjustment of the shaft 12 and electrode 13 is permitted.

Means for immobilizing the inner electrode 13 in adjusted position is provided in the form of a spring ring 24 rigidly mounted on a reduced terminal portion 25 of the electrode as by means of a spinning operation as indicated at 26. The electrode 13 is provided with a tapered portion 27 adjacent the reduced portion 25, and spring 24 is provided with a plurality of diverging arms 28 embracing said tapered portion when compressed by introduction of the electrode into the dielectric cylinder 5.

In the operation of the device, the parts being assembled and the electrical connections completed, rotation of the nut 15 by means of a spanner acting on the portion 18 thereof causes longitudinal movement of the shaft 12 and electrode 13 since rotation of the shaft is prevented by its non-circular bearing in the sleeve 1. During this adjustment, the positive electrical connection between the shaft and sleeve is maintained by the wedging engagement of the conductive balls 21 between the surfaces 10 and 19 thereof so that adjustment is accomplished in the most effective manner. Thereafter this adjustment is maintained by the firm engagement of the arms 28 of the spring 24 against the interior of the dielectric tube 5, which spring, by its riveted connection to the inner elec trode 13, maintains it perfectly stationary in spite of shock or vibration.

Although but one embodiment of the invention has been shown and described in detail, it will be understood that other embodiments are possible and that changes may be made in the precise design and arrangement of the parts without departing from the spirit of the invention.

What is claimed is:

1. In a trimmer condenser for high frequency electronic circuits having a dielectric tube and a cylindrical electrode axially movable therein, means for mounting and adjusting said electrode including an electrically conductive threaded shaft fixed thereto having a plurality of longitudinally extending plane surfaces, an electrically conductive sleeve slidably but non-rotatably supporting the shaft having an internal surface in converging relation to the plane surfaces of the shaft, a nut threaded on the shaft and swivelled in the sleeve, a plurality of balls of electrically conductive material on the sleeve bearing simultaneously on the plane surfaces of the shaft and the converging surface of the sleeve, and a spring pressing the balls into wedging engagement between said surfaces to thereby form a self-centering pressurized electrical bond between the shaft and sleeve shunted across the threaded connection.

2. Mounting and adjusting means for a trimmer condenser as set forth in claim 1 in which the spring which maintains the electrically conductive balls in operative position bears against said nut and frictionally maintains i it in adjusted position.

3. Mounting and adjusting means for a trimmer condenser as set forth in claim 1 including further elastic means for holding the electrode centered and aligned in Cit the dielectric tube in adjusted position in the form of a ring of elastic material fixedly mounted on the electrode having a plurality of equally spaced divergent arms bearing frictionally on the interior of the tube.

4. Mounting and adjusting means for a trimmer condenser as set forth in claim 3 in which the electrode is formed with a tapered terminal portion on which the elastic ring is mounted, and the divergent arms of said ring loosely embrace said tapered portion and press outwardly against the inner surface of the dielectric cylinder.

References Cited in the file of this patent UNITED STATES PATENTS 2,149,702 Maris Mar. 7, 1939 2,314,208 Gurewitsch Mar. 16, 1943 2,385,194 Carroll Sept. 18, 1945 2,578,608 Shull Dec. 11, 1951 2,591,644 Wadsworth Apr. 1, 1952 FOREIGN PATENTS 600,033 Great Britain Mar. 20, 1948 602,270 Germany Sept. 5, 1934

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