|Publication number||US2935714 A|
|Publication date||May 3, 1960|
|Filing date||Apr 25, 1958|
|Priority date||Apr 25, 1958|
|Publication number||US 2935714 A, US 2935714A, US-A-2935714, US2935714 A, US2935714A|
|Inventors||Mervin B Arisman, Wayne A Barden|
|Original Assignee||Chicago Telephone Supply Corp|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (5), Referenced by (15), Classifications (10)|
|External Links: USPTO, USPTO Assignment, Espacenet|
May 3, 1960 W. A. BARDEN ET AL VARIABLE RESISTOR WITH VERNIER CONTROL 2 Sheets-Sheet 1 Filed April 25, 1958 -l 2 27 3| H 7 IO J 24 9 9 I8 24 A 1/ 3P4, 228 25 /2 Z9 Z7 39 Wayne A..Evardan MEPVITLE.ATZETHETL y 3, 1960 w. A. BARDEN ETAL 2,935,714
O VARIABLE RESISTOR WITH VERNIER CONTROL Filed April 25, 1958 2 Sheets-Sheet 2 Wayne A. arden Mar-v21"; B. zsman as W AW United States Patent 2,935,714 VARIABLE RESISTOR wrrn VERNIER CONTROL Wayne A. Barden and Mervin B. Arisman, Elkhart, Ind., assignors to Chicago Telephone Supply Corporation, Elkhart, Ind., a corporation of Indiana Application April 25, 1958, Serial No. 730,965
4 Claims. (Cl. 338-157) This invention relates to variable resistors of the type used in radio and television apparatus, and has as its general purpose to provide a variable resistor or potentiometer which has an extremely fine adjustment.
In some of the more recent television receivers, the horizontal deflection circuits require very fine adjustments. Heretofore this requirement has been met through the use of two separate variable resistors, connected in series, one of which provided the usual relatively course adjustment of the controlled circuit and the other, which had a much narrower resistance range, provided the desired fine adjustment. Obviously, of course, if the first resistor were equipped with a fine enough mechanical adjustment, the second resistor would not be'required.
Means for efiecting fine or very close adjustment of the rotor of a control such as a variable resistor or condenser, are not broadly new. In the early days of radio, for instance, the knobs used to adjust the tuning condensers often incorporated gear reduction transmission means through which manual actuation of the knob was translated into much slower rotation of the condenser shaft.
In a very broad sense, the present invention follows this same approach in that it employs the principles of planetary gearing to obtain a ratio as high as 15 to 1 between the actuator of the control and its rotor, but where prior adaptations of the idea placed the gear reduction in the knob for the control or were otherwise extraneous to the control, this invention incorporates the transmission in the control itself and, moreover, does so in a way which is entirely consonant with the established requirements, both functional and structural, of variable resistors used in television and radio receivers. Among these, of course, is the need for keeping the control small, avoiding an excessive number of piece parts, and enabling mass production of the control to assure low cost. a
With this general objective in mind, it is specifically an object of-the present invention to provide a variable resistor embodying means within itself for producing very fine adjustment of the resistance it introduces into a circuit in which it is connected.
Another object of the invention is to provide a high ratio dilferential motion transmitting connection between the actuating shaft of a variable resistor and is rotor which, though reliably effective to produce the desired fine adjustment or traverse of the eontactor along the resistance path, nevertheless is impositive, so that despite the great mechanical advantage inherent in the transmission, continued turning'of the actuating shaft after the contractor has reached one of its limits of rotation will not damage the control.
Another specific object of this invention is to provide a variable resistor with a high ratio or vernier type drive transmission between its actuating shaft and eontactor which employs no gears, and which is so designed and constructed that essential elements thereof are Parts of 'ice the elements already present in the control, to thus hold the number of piece parts to a minimum.
With these and other Objects in view which will appear as the description proceeds, this invention resides in the novel construction, combination and arrangement of parts substantially as hereinafter described and more particularly defined by the appended claims, it being understood that such changes in the precise embodiment of the hereindisclosed invention may be made as come within the scope of the claims.
The accompanying drawings illustrate two complete examples of the physical embodiments of the invention constructed according to the best modes so far devised for the practical application of the principles thereof, and in which:
Figure 1 is a longitudinal sectional view through a variable resistor embodying this invention;
Figure 2 is a cross sectional view through Figure 1 on the plane of the line 2-2, but with a portion thereof broken away;
Figure 3 is a' perspective view of the cover of the control, viewing the same from the inside and ready for assembly with the base of the resistor;
Figure 4 is an exploded perspective view of the rotor assembly of the resistor; and 1 Figure 5 is a view similar to Figure 1, but on a somewhat smaller scale and illustrating a slightly modified form of the invention.
Referring now particularly to the accompanying drawings, the numeral 6 designates the base of a variable resistor of the type commonly used in radio and television receivers. As such, the base is made of suitable insulating material and, at its center, it has a mounting bushing 7 fixed thereto and projecting axially from the front face thereof. This bushing, in addition to providing means for mounting the entire control upon a suitable support, also'provides a hearing or journal for the actuating shaft 8 of the control. The shaft is thus constrained to rotate about an axis perpendicular to the base and, in the preferred embodiment of the invention illustrated in Figures 1 to 4, inclusive, is secured against axial displacement in either direction by a pair of conventional C-washers 9--9' mounted on the shaft, with the bearing portion 10 of the bushing received ,therebetween. Rearwardly of its bearing portion 10 the bushing is counterbored as at 11, for a'purpose to be hereinafter described.
The rear face of the base has a resistance path 12 thereon arranged concentrically about the axis of the shaft. Although this resistance path has been illustrated as an arcuate element separate from the base but fixed thereto by means of end terminals 13, it could be provided in any other suitable way.
Also overlying the rear face of the base is a metal collector ring 14 which is disposed concentrically within the arcuate resistance element and, like the element, is held in place by means of its terminal 15. Since the manner in which the resistance path and the collector ring are mounted or arranged on the base forms no part Of this invention, these features have not been illustrated in detail. If more specific information is desired respecting these details, reference may be had to Patent No. 2,632,832.
As is customary in variable resistors or Potentiometers, the resistance path and the collector ring have resilient contact fingers16 and 17 respectively bearing thereon. Both of these fingers are carried by or, more correctly, are an integral part of a eontactor 18 stamped and formed of metal possessing suitable resilience. The eontactor is mounted on a eontactor carrier 19, sometimes referred to as a drive arm, which is constrained to rotation about the axis of the shaft and is supported against rearward axial displacement in exactly the correct position with respect to the base to assure proper contact pressure between the resistance path and the contactor finger which rides thereon.
The manner in which the contactor carrier is mounted and supported against rearward axial displacement, and more particularly the way in which it is driven, are important and significant features of this invention. Contrary to the conventional practice wherein the carrier is fixed to the shaft, the contactor carrier 19 is freely slidably journalled upon the rear portion of the shaft, being preferably provided with a forwardly projecting hub portion 25) to provide a longer and more. stable bearing on the shaft.
Rotation of the shaft is differentially transmitted to the contactor carrier 19 through a transmission means on the order of a planetary system. This transmission means comprises a small diameter driving element 21 on the rear end of the shaft, the cylindrical outer surface of which provides an inner circular rotatable track 21a, a stationary circular outer track 22 concentrically encircling the inner track, and a plurality of balls 23-three in the illustrated embodiment of the invention-confined between these two tracks in frictional rolling engagement therewith. The outer stationary track 22 is formed by the inside surface of a frustoconical rearwardly projecting extrusion of the rear wall of a generally cup-shaped stamped metal cover 24 like those usually provided in variable resistors of this type and which, as is customary, is secured to the base 6 to coact therewith in providing a housing or enclosure for the instrumentalities of the resistor..
The balls 23 are held in place between the inner and outer tracks by the contactor carrier 19, the rear face25 of which bears against the side of the balls substantially opposite the side thereof in contact with the stationary track. The contactor carrier 1% not only coacts with the two tracks to hold the balls in place, but also provides means for applying the rearward axial thrust of a spring 26 upon the balls. This spring 26 is received in the counterbore 11 of the mounting bushing and is confined between the bottom of the counterbore and the front of the hub 26 on the contactor carrier.
Because of the truncated, conical shape of the stationary track 22, it follows that a substantial part of the rearward axial thrust imposed upon the balls 23 by the spring 26- is converted into a radially inward component so that the balls have good frictional engagement not only with the stationary outer track 22 but also with the rotatable inner track 21a.
Hence, upon rotation of the inner track 21a in consequence of adjustment'of the actuator shaft, the balls rotate about their points of tangency with the rear face 25 of the contactor carrier, and such rotation of the balls causes them to roll alongthe outer track 22 to thereby efiect orbital motion of the balls about the shaft. This orbital motion which is much slower than the rotation of the actuator shaft, is transmitted directly to the contactor carrier to effect the desired fine adjustment of the resistor.
While the frictional engagement between the balls and the contactor carrier of itself serves as a motion trans mitting connection between these parts, a more positive driving connection is desirable and, for this purpose, the contactor carrier has a generally circular wall 27 projecting from its rear surface 25, shaped on its inside to provide three pockets 28, one for each of the balls. The pockets are separated from one another by lugs 29 angularly spaced apart slightly more than necessary to accommodate the balls, so that the balls have a degree of freedom in their respective pockets to assure smooth operation. In effect, therefore, the contactor carrier forms a cage for the balls, so that the carrier must move with the balls as they orbit about the shaft.
' Through proper selection for the angle of'the truncated conical stationary track 22 and the strength of the spring 26, it is a simple matter to make the component of friction between the balls and the tracks sufficiently greater than the drag on the contactor resulting from the engagement of its fingers upon the resistance element and the collector ring, to assure the described operation of the device. Nevertheless, since friction between the balls and the tracks is depended upon to translate rotation of the actuator shaft into adjustment of the contactor, the transmission means of this invention has an important advantage over a positive driving connection such as would be provided by a gear train.
As in all variable resistors, the adjustment of the contactor is confined to less than 360 degrees. This is done by the engagement of stop abutments 3%) on the contactor carrier with a stationary stop 31 on the cover. Because of the substantial mechanical advantage resulting from the relatively high ratio between the driving and driven elements of the transmission, serious damage might be caused by continued rotation of the shaft after the contactor reached one of its limits of adjustment if torque were positively transmitted from the shaft to the contactor carrier.
The present construction eliminates this possibility, and does so without incurring other objections.
As explained hereinbefore, the rear face 25 of the contactor carrier bears against the balls 23 and is thereby supported against rearward displacement, as is also the contactor which is mounted on the carrier. The balls thus define the axial position of the contactor and determine the contact pressure on the resistance path.
Though it is preferable to have the actuator shaft positively secured against axial displacement in either direction in the manner described, the shaft can be held against forward displacement by giving its rear end portion which provides the inner track 21a a spool shaped configuration, as at 32 in Figure 5. In this case the rearmost flange 33 of the spool, being considerably larger in diameter than the inner track 21a would collide with the balls and prevent forward axial shifting of the shaft. In other respects, the modified embodiment of the invention shown in Figure 5 is the same as that described.
From the foregoing description, it will be readily apparent to those skilled in this art that this invention provides a variable resistor with an adjustment fine enough to obviate the need for separate fine tuning resistors as has been the practice in the past wherever the controlled circuit had to be very accurately and closely adjusted; and that because of the novel manner in which the invention incorporates the planetary principle into the driving connection between the actuating shaft of the control and its contactor, the device of this invention has the salutary attributes of small overall size, low cost and reliable performance.
What is claimed as our invention is:
1. In a variable resistor, the combination of: a housing having a front wall; variable resistance mechanism in the housing comprising stator means mounted on the front wall, rotor means adjacent to the front wall and cooperable with the stator means, and an actuating shaft carried by the housing for rotation on an axis perpendicular to the front wall, for imparting rotation to the rotor means, the shaft projecting through the front Wall and having a rear portion thereof disposed rearwardly of the rotor; means carried by the housing supporting the rotor for rotation coaxially'of but relative to the shaft and for axial motion lengthwise of the shaft; means on the housing providing a frusto-conical track spaced rearwardly of the rotor, and spaced radially from but coaxially encircling said rear portion of the shaft, the smaller diameter portion of said frusto-conical track being rearmost; a plurality of balls confined in the space between the rear of the rotor, the frusto conical track and the rear portion of the shaft; spring means carried by the housing and exerting a rearward axial force upon the balls through the rotor to maintain the balls substantially wedgingly confined in good frictional rolling engagement with the track and the rear portion of the shaft, whereby rotation is imparted to the balls by the shaft to cause the balls to roll along the track and travel orbitally relative to the shaft at a rate slower than'the rate of shaft rotation; and means on the rear of the rotor engaging over peripheral portions of each of the balls forwardly of the track to connect the rotor to the balls whereby the rotor rotates with the balls as they orbit.
2. The combination set forth in claim 1 further characterized by the fact that the rotor is provided with a hub by which it is journaled upon the actuating shaft for rotation relative thereto and for limited sliding motion lengthwise thereof.
3. The combination set forth in claim 2, further characterized by the fact that said spring means comprises a helically coiled spring loosely encircling the shaft at a location ahead of the rotor, and confined between the front of the rotor hub and a part fixed with respect to the housing.
4. In a variable resistor, the combination of: a housing having spaced front and rear walls; an actuating shaft supported by the housing for rotation on an axis normal to and substantially centered with respect to said walls, said shaft projecting through the front wall and having a rear portion adjacent to the rear wall of the housing; an arcuate resistance path on the rear of the front wall, concentric to the shaft axis; means on the rear wall of the housing defining an annular frusto conical track concentrically surrounding said rear portion of the shaft, the smaller diameter portion of said track being rearmost; a rotatable contact carrier in the housing having spring contact means on one face thereof; means carried by the housing mounting the carrier for rotation concentrically with and relative to the shaft and for axial motion along its axis, with said face of the carrier opposing the front wall of the housing and its spring contact means in engagement with the resistance path on said front wall to traverse the same during rotation of the carrier; 2. plurality of balls confined axially between said frusto conical track and the rear of the carrier, and confined radially between the track and said rear portion of the shaft; spring means exerting rearward axial force on said balls through the carrier to maintain the balls substantially wedgingly confined between and in good frictional rolling engagement with the track and said rear portion of the shaft, whereby rotation of the shaft causes the balls to roll orbitally along said track at a rate slower than the rate of shaft rotation, and whereby the balls define the rearmost position of the carrier in the housing and thus serve to hold the spring contact means on the carrier in pressure engagement with the resistance path; and means on the carrier projecting rearwardly therefrom and engaged between said balls to constrain the carrier to rotate with the balls as they orbit;
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|U.S. Classification||338/157, 475/196, 338/68|
|International Classification||H01C10/14, G05G1/00|
|Cooperative Classification||G05G23/00, G05G2700/02, H01C10/14|
|European Classification||G05G23/00, H01C10/14|