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A Aúg. v13, 1946. ' 2,405,890 w. H. KUNz ` -INDUCTIVE TUNER Filed May 5, 1944 ¿ '_ IN VEN TOR. Walden _ZZ £21112 BY i „from/Er 2,405,890 Patented Aug. 13, 1946 UNITED STATES PATENT OFFICE 2,405,890 ENDUCTIVE TUNER Walden H. Kunz, Jackson, Mich., assignor to P. R. Mallory & Co., Inc., Indianapolis, Ind., a cor poration of Delaware Application May 5, 1944, Serial No. 534,216 2 Claims. (Cl. YY1-242) l 2 This invention relates to continuously variable inductive tuning devices and has for its object to provide a device of this type having novel and im acteristic of the invention are set forth more in proved details of construction and features of detail in the claims appended hereto, the nature and scope of the invention may be better under stood by referring to the following description, taken in connection with the accompanying drawing forming a part thereof, in which a spe Another object of the invention is to provide an ciñc embodiment has been set forth for purposes inductive tuner of the above type having a new of illustration. and improved rotary contact member and asso In the drawing: ciated control elements which are particularly Fig. l is a side elevation of a continuously adapted for use with inductance coils of small 10 variable inductive tuning device embodying the diameter. invention; Various other objects and advantages will be opera-tion. apparent as the nature of the invention is more fully disclosed. Slide-wire variable inductance devices are used 15 Fig. 2 is a longitudinal section taken on the line 2--2 of Fig. l; Fig. 3 is a transverse section taken on the line for tuning radio receivers, oscillators and various 3-3 of Fig. 2; and other electric and electronic instruments and de vices. Generally, they comprise a bare wire coil of Fig. 2. trolley rod slides along the wire of the coil in electrical contact therewith as the coil is rotated. The mechanical and electrical requirements of however, are to be interpreted in accordance with the state of the art. The variable inductive tuning device shown in Fig. 4 is a transverse section taken on line ¿i-fl In the following description certain specific wound on a suitable insulating form which is mounted on a shaft so as to rotate about its axis, 20 terms are used for convenience in referring to the various details of the invention. These terms, and a sliding Contact tracking on a stationary such inductive tuning devices are severe, espe cially since positive and constant contact must be maintained for electrical reasons, while at the same time lightness of contact is required for ease of tuning and to keep down wear over long periods of use. The present invention provides a tuning device of the foregoing type in which the Wire coil is sta tionary and in which tuning is effected by rotat ing the sliding contact member over the convolu tions of the coil, The Contact itself comprises a si r~le piece of light spring material having con tacting nibs at its ends engaging the coil and a A the drawing comprises a support or end plate Iii carrying a coil form II of insulating material such as resin impregnated über. The form is shown as cylindrical but it is understood that it may be made conical or frusto-conical if desired. A bare wire coil I2 is wound on the surface of form II with adjacent turns spaced from each other. If desired, the form may be provided with a shallow groove in which the wire I2 is wound. ri‘he coil may suitably be made of hard drawn copper wire plated with silver, and, if desired, coated with a protective lubricant. One end I3 of the coil I2 is soldered to a central Contact portion in sliding engagement terminal I4 mounted on an insulating block l5 with an axially extending trolley rod which is adapted to be rotated around the coil. As the trolîey rod is rotated about the coil, as by means of a shaft extending axially through the coil, the which is secured to the end plate I0 by stud iii. The opposite end of the coil is soldered to a metal disc I'I fixed to the outer end of the coil form I i. spring contact slides along the convolutions of the wire and at the same time slides longitudinally on the trolley rod, insuring a positive and con stant contact with a minimum of friction and wear. Another feature of the invention resides in the provision of a novel stop mechanism for arresting the movement of the spring contact at either end of its travel without exerting any pressure on the Contact itself, thus eliminating any possibility of bending or otherwise damaging the contact or the associated electrical connections. Although the novel features which are char The disc I'I carries a bearing sleeve I8 within the bore I9 of the form II which is connected by a wire 2B to a second terminal similar to the ter minal I4. The wire 2€) extends through the bore I9 and radially through the form II at a point adjacent the second terminal. A second bearing sleeve 2| is positioned within the end of the bore I9 opposite the sleeve I8 and a rotatable control shaft 22 of insulating mate rial extends axially through both sleeves and through the coil form II, one end of said shaft projecting outwardly beyond end Plate Ill to re ceive a suitable control knob, while the opposite 2,405,890 3 4 end of the shaft extends outwardly of the coil form past the end disc Il. A hub 23 is >secured to the inner end of the shaft 22 by set screw 24; and an arm 25 secured to hub 23 carries a trolley rod 26 which extends axially along the side of coil form Il parallel to the cylindrical surface thereof. The arm 25 and trolley rod 25 are composed of suitable conduct ing material, and between them is secured a fork posed between the rod 26 and the coil, and my im proved construction enables this initial adjust ment to be maintained indefinitely under all con ditions of use. While the present invention has been described herein as carried out in a specific embodiment, it is not to be limited thereto, but is only to be restricted in accordance with the spirit and scope of the appended claims. l0 What is claimed is: tact brushes 28 which slide on the metal disc Il 1. A Variable. inductance device comprising in on the inner end of coil form Il, thereby provid combination a coil form of circular cross section. ing a slip ring connection to the end of the coil a bare helical conductive coil wound thereon, a rotatable shaft extending axially through said and to the contact to be desired. A stop member 29 is slidably mounted on trolley coil form, a trolley rod carried by said shaft ad jacent and parallel to said coil form and mounted rod 26. The stop member 23 is formed of Bake» lite, ceramic or other suitable insulating material to be rotated about said coil by said shaft, a con tact element integrally formed of a single piece and, in the embodiment illustrated, is of gener of sheet metal in a substantially symmetrical and ally tubularl shape with a substantially semi-cir cular opening intermediate its ends exposing the 20 dynamically balanced shape, the ends of said ele trolley rod 2t through said opening. ment being bent into smooth-surfaced grooved ' contact nibs engaging the wire of said coil in the A sliding contact member 3D, preferably grooves therein and the mid-portion of said ele stamped in a single piece from sheet spring metal, has its central portion bent to form a semi-circu~ ment being bent into a smooth-surfaced trans verse channel which is concave on the opposite lar channel 3l which fits within the opening of >:face of said element from said grooves and en stop member 29 and engages the trolley rod 25, gages the trolley rod, said contact element being while the outer ends of the contact member are biased to produce smoothly sliding and uniformly formed to provide narrow channel-shaped nibs distributed spring pressure against said coil at 32 conforming to and engaging the wire of coil l2. The nibs 32 rest on the same turn of coil I 2 at 30 said nibs and against said rod at said channel for movement along said rod when said shaft is ro spaced points thereon and one nib is slightly tated, a disc mounted on the inner end of said twisted or skewed with respect to the other to coil form, a spring contact arm attached to said allow for the pitch angle of the helical coil. trolley rod having sliding contact means with said It will be evident that as the shaft 22 is ro tated, «causing trolley rod 26 to rotate about'the 35 disc, and a terminal connected to said disc. 2; A variable inductance device comprising in cylindrical surface of coil form ll, the nibs 32 combination a coil form of circular cross section, of contact member 30 slide along the wire i2 and a bare helical conductive coil wound thereon, an move the member 3S and stop member 29 length axially disposed bearing sleeve at each end of said wise along the trolley rod. The contact member 30 is connected by the trolley rod 26, contact 40 coil form, a shaft extending axially through said coil form and rotatable in said bearing sleeves, a spring 2l', contacts 28, disc il and Wire 20 to the trolley rod carried by said shaft adjacent and par terminal I4. allel to said coil formv and mounted to be rotated In accordance with a feature of the invention, about said coil by said shaft, a contact element I provide stop members or lugs 34 and 35 on the integrally formed of a single piece of sheet metal cylindrical surface of coil form Il, adjacent op in a substantially symmetrical and dynamically posite ends thereof, for engagement with the slid balanced shape, the ends of said element being able stop member 29 whenever the trolley rod 25 bent into smooth-surfaced grooved contact nibs is rotated suiñciently to bring the contact mem engaging the wire of said coil in the grooves ber 3l) near either end of the coil l2. The lugs therein and the mid-portion of said element be 34 and 35 are so positioned that, when the »con ing bent into a smooth-surfaced transverse chan tact member 30 reaches a point adjacent the end nel which is concave on the opposite face of said of the coil, the leading side of stop member 29 will element from said grooves and engages the trol strike against the side of lug 34 or 35, as the case ley rod, said contact element being biased to pro may be, and thus prevent further rotation of the shaped contact spring 2l' having silver alloy con trolley rod. duce smoothly sliding and uniformly distributed A particular advantage of the foregoing con struction is that the impact of stop member 29 against lugs 34 and 35 is completely isolated from the delicate spring contact member 30 and there fore cannot injure said contact member, noi- can the nibs 32 of the contact member over-run the ends of the coil or strike against the soldered ends thereof. The contact member 353 is originally spring pressure against said coils at said nibs and against said rod at said channel for movement along said rod when said shaft is rotated, a disc integrally formed with the bearing sleeve at the bent just enough to provide the proper spring pressure on the nibs when the member is inter inner end of said coil form, a spring contact arm attached to said trolley rod having sliding con tact means with said disc, and a terminal con nected to said sleeve. WALDEN H. KUNZ.