US2979684A

US2979684A - Rectilinear potentiometers

Info

Publication number: US2979684A
Application number: US671861A
Authority: US
Inventors: Jr Joseph M Looney; Fraser Alton; Robert M Martin
Original assignee: Technology Instrument Corp of Acton
Current assignee: Technology Instrument Corp of Acton
Priority date: 1957-07-15
Filing date: 1957-07-15
Publication date: 1961-04-11
Anticipated expiration: 1978-04-11

Description

J. M. LOONEY, JR., ET AL April 11, 1961 RECTILINEAR POTENTIOMETERS 2 Sheets-Sheet 1 Filed July l5, 1957 RECTILINEAR POTENTIOMETERS Filed July l5, 1957 2 Sheets-Sheet 2 FIG. 5 I FIGS ,276 /30 3/4 20a, /2/2 ,240 2264`V9 564)(4 2792 2f?? SM2/302 f y f/IEZ/ f W. 204 /W 1 JOSEPH M. LOONEY, JR- ROBERT M. MARTIN ALTON FRASER United States Patent C RECTILINEAR POTENTIOMETERS Joseph M. Looney, Jr., Tarzana, and Alton Fraser and Robert M. Martin, Van Nuys, Calif., assignors to Technology Instrument Corporation of Acton, a corporation of Massachusetts Filed July 15, 1957, Ser. No. 671,861

3 Claims. (Cl. SSS-183) This invention relates to variable resistors or potentiometers and more particularly to new and improved rectilinear potentiometers.

The primary object of this invention is to provide a new and improved recilinear potentiometer characterized by a unique coniiguration and mode of assembly that prevents relative motion between the resistance winding and the contact-carrying member except for the normal desired rectilinear movement of the contact-carrying member along the length of the resistance element, thereby resulting in improved noise characteristics under conditions of shock or vibration, as well as reduction in backlash or hysteresis.

Another object of this invention is to provide a rectilinear potentiometer comprising a, resistance element, a carriage provided with a brush or contact member engaging the resistance element, and parallel guide ways supporting the carriage for rectilinear motion relative to the resistance element, the carriage being so constructed and mounted on the guide ways that it has freedom of movement onlyin the direction in which signal motion is introduced. y,

A further object of this invention is to provide a rectilinear potentiometer adapted to be enclosed in a case which is so constructed that the case is the last item to be attached, thereby permitting the unit to be tested before assembly is complete.

An additional object of this invention is to provide a rectilinear potentiometer wherein the resistance element or elements can be shifted longitudinally, parallel to the wiper motion, for the purpose of phasing the resistance elements toy any desired characteristic within the limitations imposedby design. n f i v f Still another object is to provide a potentiometer characterized by ease of assembly and a novel mode of securing the resistance element in place.

yOther objects and` many of the attendant advantages of the present invention will become readily apparent as reference is had to the following detailed specification when considered together with the accompanying drawings, wherein: D

Fig. lisa sectional view in side elevation ytaken along line 1-1 of Fig. 3'of a preferred form of the present invention;`

y Fig.k2 is a sectional plan view of the same embodiment taken along line.2,-2dof' 1 iig. 3;

Fig. 3`is an end view looking from left to right in Figl; n

Fig. 4is a viewin elevation of the opposite end of the samepdevice; d i

kFig. 5 ,is` a'scctional `view taken along line 5-5 of pighww :7,

Fig. 6 is a cross-sectional view of the brush carriage employed inlthe embodiment ofFig. 1;

f Fig.V 7 is'fa sectional planview likefFig; 2 of a second form of the present invention; t l Fig. Adinan end view looking` fromright to 'leftin Fig. 7i

Fig. 9 is a sectional view taken along 9-9 of Fig. 7; and

Fig. 10 is a cross-sectional view illustrating how the supports for the resistance element and the take-oli rod are flexed in order to be inserted in the potentiometer housing.

Referring now to Figs. l, 2 and 5, the rst form of the invention comprises two

opposed support members

4 and 6, two opposed

guide members

8 and 10, and two

circular end pieces

12 and 14. The support members, the guide members and the end pieces are all formed from aluminum.

Support members

4 and 6 have been hard anodized to provide hard non-conducting surfaces. It is to be understood that these members, particularly the

support members

4 and 6, may be fabricated from other varieties of insulating material, such as a phenolic resin or other plastics. As best seen in Fig. 5, the

supports

4 and 6 correspond in cross-section to a segment on a chord of a circle and the

guides

8 and 10 correspond in cross-section to sectors of a circle. The opposite ends of each of the

supports

4 and 6 are notched so as to fit into grooves 16 and 18 cut into the inner surfaces oi the

end pieces

12 and 14. The opposite ends of

guides

8 and 10 abut the inner surfaces of

end pieces

12 and 14. The

end pieces

12 and 14 are secured to the

guides

8 and 10 by means of

screws

20 and 22. The grooves 16 and 18 cut in the

end pieces

12 and 14 are suiciently deep so as to permit the

supports

4 and 6 to be moved longitudinally a predetermined amount. However, the

end pieces

12 and 14 are provided with tapped

openings

24 and 26 respectively in which are screwed set

screws

28 and 30. The

set screws

28 and 30 prevent the

supports

4 and 6 from moving. However, by turn ing'the

screws

28 and 30 it is possible to adjust the positions of the

supports

4 and 6 relative to each other and also relative to the

end pieces

12 and 14. In so far as already described, the assembly is self-supporting.

The

supports

4 and 6 are provided with pairs of

circular grooves

32 and 34 respectively. Secured in one ofthe grooves 32 is a resistance element A comprising a cylindrical core 38 on vwhich is wound a resistance wire 40 formed of a suitable alloy A second resistance element B identical in construction is secured in one of the grooves 34. Secured in the

other grooves

32 and 34 are cylindrical take-oit bars C and D formed of silver.) or any other suitable conductor, as, for example, silver platinum, palladium, gold, etc.' The resistance elements are secured to supports 4 and 6 by any suitable means, as for example, a cement.

The electrical connections to the resistance elements and the take-off bars may be made in various ways. The preferred mode is described hereafter.

Secured to the opposite yends of resistance elements A and B in surrounding engaging relation thereto are

conductive terminals

46, 48,.y 50 and 52. Secured to

terminalsY

46 and 48 aretwo insulated leads 54 and 56 which pass through suitable insulator bushings 58 provided in openings in support member 4 and pass along a groove 60 cut in the outer surface of support member 4. The leads 54 and 56 run toward end piece 12. The other support member 6 is provided with corresponding insulator bushings 62 through which pass insulated leads 64 and 66 connected to terminals V50 and 52. Two additional wire leads and 72 are vconductively secured tothe take-off bars C and D at the ends nearest the end piece V12.

The end piece 12 is provided with a cylindrical centrally located bore in which is secured a terminal header 76 formed of glass or other suitable material. imbedded in header 76 are three insulated terminal leads 78,` 80 ,and 82. Y The wire cores of these terminal leads extend through the header 76 into the open space defined by the acuosa supports 4 and 6 and the guides S and 10. The leads 54, 56, 64 and 66 enter the same space through openings 54- and 86 provided in

supports

4 and 6. Leads 54 and 64 are conducti-vely connected to terminal lead 78. Leads S6 and 66 are similarly secured to terminal lead 82. The leads 70 and 72 running from the take-off rods C and D are connected to the terminal lead 80.

As illustrated in Fig. 5, the guide ways and 10 are V-shaped and are so positioned that their center lines reside in a common plane passing through the longitudinal `axis of the potentiometer.

The opposite end piece 14 also is provided with a centrally located bore in which is secured a bushing 88. Bushing 8S is fabricated from bearing bronze or other suitable mater-ial and serves to supply a `hearing support for a shaft 90. Shaft 90 is formed of stainless steel or other suitable material and is provided at its inner end with a brush carriage block 92. Atiixed to shaft 92 is a retaining ring 94 which prevents the shaft from being pushed too far into the potentiometer body by limiting motion to the point at which the ring contacts the bushing 88. The inner end of bushing 8S is counter-bored to receive a seal 96 formed of Telion or other suitable material such as nylon or rubber. The Teflon seal 96 protects the inside of the potentiometer from external environmental influences.

In the preferred form of this invention it is preferred that the brush carriage block 92 be made of a suitable plactic such as Kel-F, a plastic belonging to the general family of triiluoro-chloroethylene plastics. This material is preferred since it has excellent mechanical characteristics in terms of tensile strength, low cold-dow characteristics, and high heat resistance characteristics, as well as being an insulator.

As seen in Figs. l, 2 and 5, the inner end of the shaft 90 is reduced in diameter so as to accommodate the brush block 92 and also to form a shoulder at 100 which engages one end of the block and prevents it from moving up along the shaft toward end piece 14. The diameter of the end of the shaft on which the brush block is supported is sutciently small to permit the shaft to rotate relative to the brush block. A bowed retaining ring 102 is secured to the inner end of the shaft and prevents the block from moving away from the shoulder at 100 while still permitting relative rotation of the shaft.

As is quite clear from Figs. and 6, the brush block is H-shaped in cross-section. The legs of the block are identified by

numerals

106, 108, 110, and 112.Y Secured to opposite sides of the brush block are two

conductive members

114 and 116 formed of beryllium copper or other suitable material. These members are provided with pairs of tabs 11% and 120 respectively which pass through small openings in the legs-of the block and are secured thereto by a suitable cement. Secured between

members

114 and 116 and the brush block are two pairs of precious metal brushes or

contacts

122 and 124. The brush members are conductively secured to

members

114 and 116. Brushes 122 extend up away from the brush block and lightly engage resistance element A and takeoff bar C. Brushes 124 contact resistance elementgB and take-off bar D. Thus when shaft 90 is moved, the brushesl move along the resistance elements and the take-off bars in the same direction. Y Y

Looking in particular to Figs. 5 and 6, it is apparent that the legs of the brush block, 106, 108, 110 and 112, yare relatively straight extensions of the brush block but have bevelled ends as at 130 for engaging the sloping sides of the V guides 8 and 10. Due to the lengthof these legs and the angles of their bevelled end surfaces 130 (as well as the geometrical configuration and positions of the guides), when they are brought into engagement with the guides, they are stressed apart in the direction shown by the arrows. For purposes of explanation, the amount bywhich the-legs are bent apart is slightly exaggerated in Fig. 5. In practice the distortion is barely perceptible to the naked eye, being sufcient to prevent lateral shifting of the brush block. At the same time, due to the tendency of the legs to return to unflexed position, their bevelled ends contact the guides with just enough friction to prevent the brush block and the shaft to which it is aixed from sliding axially of their own weight when the potentiometer is held on end. Thus only a slight force is required to move the shaft. Because of the preloading brought about by forcing the arms in the direction indicated by the arrows, only one degree of freedom of motion is possible, that is, motion parallel to and along the guides. Motion in either of the other two planes is restricted, since the configuration in which the ends of the brush carriage block are stressed eliminates all play and consequently all lateral motion.

After the unit has been assembled and tested, a cylindrical housing 140 is slipped over the assembly. This housing is also formed of anodized aluminum or other suitable material. The housing has an inside diameter just suicient to clear the outer surfaces of the support members `4 and 6 and the

guides

8 and 10 as well as the end piece 12. The end piece 14 is provided with a peripheral ange 142 which acts as a stop for the housing. The housing 140 is secured in place by screws 144 and 146 `which are received in threaded openings provided in the

guides

8 and 10. An aluminum alloy mounting plate 148 is fastened to the potentiometer housing by means of screws 1146.

In the second form of the invention illustrated in Figs. 7, 8 and 9, the basic concept of a pre-loaded brush car riage running on parallel V ways is still inherent. However, in this form of the invention the parallel V ways are an integral part of the outside case or housing.

In this formV of the invention the outside case 200 is formed of aluminum which has been anodized on its inside and outside surfaces. As seen in Fig. 7, the housing consists of several portions of different inside diameters and configurations. Commencing at the left of Fig. 7, the housing 200 is provided with an axial bore 204 in which is received a bearing 206. A set screw 208 screwed into a tapped radial opening in housing 200 permits the position of the bearing to be adjusted. A shaft 210 formed of stainless steel extends through the bearing 206. An 0ring 212 makes a slip tit seal with the shaft 210. Positioned on the inner end of the shaft 210 is a brush carriage block 214 which is of substantially the same cross-sectional configuration as the brush carriage block or" the embodiment previously described. The end of the shaft is reduced in diameter to accommodate the brush block and also to form a shoulder 216 which abuts the brush block and prevents it from moving back along the shaft. A retaining ring 218 prevents movement of theV brush block in the opposite direction. As in the preferred embodiment, the shaft is rotatable relative to the brush block. Attached to the brush block is a sleeve 220 which limits retraction of the shaft upon engagement with the bearing 206.` It is believed apparent that the stroke of the shaft in one direction can be adjusted by changing the position of bearing 206. Attached to the brush block 214 by means of beryllium copper conducting strips 222 and 224V similar to the conducting strips 114 and 116 of Fig. 6 are twoprecious metal brushes 226 and 228, one on each sdeof the brush block. A copper shorting strip 230 is connected to the

strips

222 and 224.

Beyond the bore 204, housing 200 has an internal configuration as illustratedk in Fig. 9. This internal configuration is characterized by a pair of longitudinally-extendedsubstantially V-shaped

ribs

2,32 andr234 opposed to each other and a pair of

curvedsurfaces

236 and 238 havinga larger radius, of curvature than bore 204, thereare two identical

e1ongated support members

244 and 246 fabricated from a Teflon or Kel-F extrusion. These support members have a main body portion 248 defining a circular groove 250 and oppositely extending

arms

252 and 254 whose ends are bevelled to conform to the curvature of

surfaces

236 and 238 of the housing. The outer surface 256 of the body portion 248`of the two support members also is curved to coincide with the curved inside

surfaces

236 and 238 of the housing. The walls defining grooves 250 extend through an arc in excess of 180. The configuration of the support members is such as to provide pairs of

grooves

260 and 262 between the body portions and the arms 252and 254.

The function of

members

244 and 246 is to clamp and support in position a resistance element 264 and a takeott` rod 266 constructed like the resistance elements of the embodiment of Fig. 1.

When the support members are formed their

arms

252 and 254 extend outwardly too far to be received by the housing 200. In order to be placed in the position shown in Figs. 7 and 9, it is necessary iirst to squeeze the supports so as to liex their arms inwardly to the position illustrated in broken lines in Fig. 10. When the supports are in their unexed positions the grooves 250' are just large enough to receive the resistance element and the take-olf rod. When the arms of the supports are bent toward each other, the body portion also bends so as to constrict the groove 250' and clamp in place the resistance element and the take-off rod.

The support for the resistance element is provided with two lateral openings, one at each end of the resistance element, that run from groove 250 to

grooves

260 and 262. The opening that leads to groove 260 is shown in dotted lines at 270 in Fig. 9. The other opening is not shown but it is to be understood that it communicates with groove 262 at the right hand end of the resistance element as seen in Fig. 7. The purpose of these lateral openings is to permit leads 272 and 274 which run along

grooves

260 and 262 to be connected to the opposite ends of the resistance element. The connection with the resistance element is made before the support 244 is inserted in the housing.

Immediately in front of the resistance element at the end nearest bore 242, support 244 is provided with two openings which connect

grooves

260 and 262 with the interior of the housing. One of these openings is illustrated at 276 in Fig. 7. Insulated leads 272 and 274 pass through these openings into the interior of the housings. These leads are pulled through openings 276 and its counterpart before the support 274 is inserted in the housing.

The take-olf rod 266 is connected at one end to an insulated lead 280. This also is done before support 246 and rod 266 are inserted in the housing.

Assuming that the two supports carrying the resistance element and the take-olf rod have been flexed and inserted while llexed into the housing, the

karms

252 and 254 will tend to unex, but will be restrained from doing so by the

curved surfaces

236 and 238 of the housing in cooperation with ribs 232and 234 which hold the supports against the curvedsurfaces. In their restrained position the supports clamp the resistance element and the takeoff rod so as to prevent any relative movement by the latter.

The supports engage the shoulder 240 and are prevented thereby from moving` toward bore 204. Movement in the opposite direction is prevented by a circular header 282 which is securely positioned in bore 242 in abutting relation with the opposite end of the two supports. The header 282 is formed of anodized aluminum which is provided with three equiangularly positioned openings in which are secured glass tubes 284, each of which surroundsl and secures metal contact tubes 286 through which extend leads 2,72, 274 and 280. Alternatively leads 272, 274 and 288 may be conductively se cured to contact tubes 286 and/or tubes 286 may be replaced by solid metal contact wires embedded in the glass sections 284. These tubes are in the 3, 6 and 10 oclock positions about the center of the header. Due to the way Fig. 7 is taken, only two of the tubes 286 are shown. The header 282 also is provided with a tapped opening at its center in which is screwed a set screw 290. The latter functions as an adjustable stop for the shaft 210. A retaining tube 292 holds the header in place. Potting 294 is positioned behind header 280 and around tubes 286. The potting does not interfere with the set screw 290.

Engaging the rear edge of the retaining tube 292 is an end piece 296 which is held in place by a narrow retaining ring 298 positioned in a groove 300 in the housing. The inner surface of the end piece 296 is provided with a tapered bore 302 which communicates with three deeply angularly placed bores 304, 306 and 308. Fitting in the tapered bore is a frusto-conical plug 310 which is secured to the end piece 296 by means of a screw 312. The diameter of the conical portion of the plug is smaller than the surrounding surface of the bore, leaving an annular space therebetween to receive three insulated terminal leads 314 which are conductively connected to the 4 three

leads

272, 274 and 280 and pass through end bores 304, 306 and 308. It is to be noted that if leads 272, 274 and 280 are conductively secured to the inner ends of the metal contact tubes 286, terminal leads 314 may be conductively secured to the opposite ends of the same contact tubes. When the screw 312 is tightened, the three leads 314 are compressed between the plug and the end piece, thereby holding them tixed. Thus any strain on the three terminal leads cannot bertransmitted to the interior of the potentiometer assembly, and particularly not to the resistance element or to the take-off rod.

The advantages of the construction of Figs. 7, 8 and 9 are many. Among the more important advantages are the following:

(l) By utilizing a housing within which the V ways are an integral portion, it is possible to reduce the diameter of the potentiometer by a considerable amount,

(2) The element supports, which are fabricated from Teflon or Kel-F, not only serve to support the resistance element and the take-off rod, but they also serve as a clamp. This eliminates the need for securing the takeoff rod and the resistance element to the supporting member by means of a cement or some other material.

(3) The third advantage resides in the unique mode of clamping the terminal leads. VIt permits the internal leads of the potentiometer to be brought out axially with the longitudinal axis of the potentiometer case and yet be easily clamped so as to prevent any strain from being transmitted to the interior of the potentiometer assembly.

It is to be understood that the brush carriage block in both embodiments may be made of metal, e.g., stainless steel. This would permit the potentiometer to function at temperatures as high as 600-700 degrees F. In the event that the brush block is made of metal, it would be necessary to insert glass insulators into the block to which metal posts could be molded, to which the

conductive members

114 or 222 could be welded in order tcl irlizsulate them from the shaft and the brush carriage b oc .f

It is to be understood that the resistance elements may be linear or non-linear and may take the form of a fiat card secured to suitable supports in a conventional manner. The resistance elements also may have addin tional taps. Where two resistance elements are employed,

they need not be connected in parallel, in which case additional terminal leads will be provided. Similarly the cross-section of the housing may be square or rectangular or have some other suitable configuration and the end pieces could be secured to the housing in a suitable manner other` than as illustrated and described.

The form of header may also be varied without departing from the principles of the invention. Moreover, as indicated previously, difierent materials may be used to fashion the various elements of potentiometers constructed according to the present invention.

Obviously other modifications and variations of the present invention are possible in the light of the above teachings. Therefore, it is to be understood that the invention is not limited in its application to the details o 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.

We claim:

l. In a potentiometer having a housing, a shaft extending longitudinally of said housing, and means attached to said housing supporting said shaft for rectilinear motion relative to said housing, the combination comprising a brush carriage attached to said shaft having an H-shaped cross-section, and comprising a body, a iirst pair of legs, and a second pair of legs; the ends of said legs being beveled, and a pair of guides having sloping sides iisedly positioned within said housing and supporting said carriage, said iirst and second pairs of legs each having their ends in engagement with the sides of a guide and being iiexed apart by said sides, whereby said carriage is movable back and forth along said guides and is held by said guides against lateral movement within said housing.

2. A potentiometer comprising a tubular housing having opposite end walls, each end wall having a groove in its inside surface, a resistance element consisting of a core and a resistance Wire wound about said core, an elongated resistance element support to which said resistance element is secured, said resistance element support located Within and extending longitudinally of said housing, said resistance support having its opposite ends disposed in said grooves in said end walls, and set screwsA projecting into said grooves and bearing against said opposite ends for selectively positioning said support and locking said support against longitudinal movement out of a selected position.

3. In a potentiometer the combination comprising a cylindrical housing, a resistance element and an elongated support for said resistance element disposed within said housing, said resistance element comprising a cylindrical core and a resistance wire Wound about said core, said support comprising in cross-section a body portion and a pair of oppositely extending arms, said support having a longitudinal groove in said body portion, said groove having a size suiiicient to receive said resistance element when said support is outside of said housing, the normal distance between the ends of said arms when said support is outside of said housing being too great for insertion of said support in said housing without inward exing of said arms, said arms exed inward by said housing with said longitudinal groove constricted to clamp said resistance element to said support.

References Cited in the le of this patent UNITED STATES PATENTS 2,273,760 Nelson Feb. 17, 1942 2,339,721 Wilson Jan. 18, 1944 2,790,052 Armstrong Apr. 23, 1957 2,813,183 Gearheart Nov. 12, 1957 2,850,607 Bourns Sept. 2, 1958 2,857,497 Bourns Oct. 21, 1958 FOREIGN PATENTS 397,935 Great Britain Sept. 7, 1933 741,391 Great Britain Nov. 30,A 1955