US2938186A

US2938186A - Trimming potentiometer

Info

Publication number: US2938186A
Application number: US619312A
Authority: US
Inventors: John L Kassay; Fave Gene M Le; Alfred W Stewart; Albert J Baranoff
Original assignee: YUCAIPA INSTR Ltd Inc
Current assignee: YUCAIPA INSTR Ltd Inc; YUCAIPA INSTRUMENTS Ltd Inc
Priority date: 1956-10-30
Filing date: 1956-10-30
Publication date: 1960-05-24
Anticipated expiration: 1977-05-24

Description

May 24, 1960 J. l.. KAssAY ETAL 2,938,186

TRIMMING POTENTIOMETER Filed Oct. 30, 1956 John L. Kassay, Gene M. LeFave, Alfred Mt. Stewart E Albert J. Barano tf.

Inventors.

A TTORNE Y.

United States Patent() TRn/IMING PornNrroMETER John L. Kassay, Yucaipa, Gene M. Le Fave and Alfred W. Stewart, Riverside, and Albert J. Baranotf, Santa Ana, Calif.; said Kassay assignor to Yucaipa Instruments Ltd., Inc., Yucaipa, Calif., a corporation of California Filed Oct. 30, 1956, Ser. No. 619,312

12 Claims. (Cl. 338-180) This invention relates to a trimming potentiometer and more particularly to a trimming potentiometer which can be fabricated in miniature sizes and easily assembled and which is also easily convertible to a trimming resistor.

Trimming potentiometers of this type now in use require'that the resistance element and the leads be imbedded in a plastic material, such as Bakelite, in order to be properly insulated. Such a construction necessitates the molding of the resistance element and leads into the small plastic body and and considerable diiiculty is encountered in properly locating these components. Further, the wiper mounting must be constructed of a plastic material, such as Bakelite, having a threaded opening to receive a threaded shaft and t-he threads are subject to being stripped at either end of the travel of the wiper if continued pressure is exerted on the shaft. In addition, the mounting shaft is` provided with bearing surfaces in the Bakelite body which do not provide a moisture seal for the instrument. Further, the resistance element of such prior devices cannot be readily modified to utilize different material to obtain different lranges of resistance while utilizing the same body construction.

By the present invention, a trimming potentiometer is provided in which the components can be assembled simply by dropping one after another into place in the potentiometer body. The potentiometer body can be constructed of anodized aluminum which provides increased mechanical strength and a hard ceramic insulation surface for insulation purposes. The aluminum body also has the characteristic of good heat dissipation which allows operation at much higher temperatures and power rating. The body can be constructed in body portions which are identical in construction and interchangeable so that only one body portion need be produced to construct the complete potentiometer. The body portions are held together by humidity resistant adhesive which provides both a mechanical and moisture seal and moisture sealing means are provided for the shaft. The sealing means for the shaft is preferably fabricated of nylon which expands with increase in moisture content and still retains good lubricating properties.

The resistance unit of the present invention comprises a mounting board which is received within one of the body portions land carries the resistance element. The use of the mounting board permits the use of various types of resistance material with the same instrument components. For instance, the mounting board can be wire wound or strips of carbon coated tape or thin, highly resistance metal can be mounted on the board. The wiper assembly has two notched elements which engage a threaded shaft and at either end of the travel vof the wiper assembly, one element will skip the threads during continued rotation of the shaft, thus preventing stripping of the threads and jamming of the wiper assembly. Also, because of the fact that the notched elements serve as the threads for the wiper assembly, the

r2,."l38,'l86 Patented May 24, 1960 wiper assembly can be incorporated in the instrument by simply placing the assembly on the shaft.

'Ihe leads for the potentiometer are located Ain grooves within the body portions which are so located that the body portions are interchangeable and the leads can extend from either side of the instrument. Leads of at strip material are utilized and thus, the leads can be easily replaced by printed circuitry attached by adhesive to the resistance unit. Since the output lead of the potentiometer extends the length of the resistance element, it is possible to utilize the instrument as a trimming resistor by simply placing one of the terminal leads and the' output lead in any given circuit and thereafter, the wiper assembly can be adjusted to incorporate into the circuit the precise resistance desired. Since the body portions are held together by a humidity resistant adhesive and the shaft is sealed against moisture, it is possible to fill the interior of the instrument with a viscose, heat resistant oil so that the potentiometer is highly resistant to wear, noise, etc.

It is therefore an object of the present invention to provide a trimming potentiometer constructed of interchangeable body portions into which the elements can be simply dropped one after another and thereafter, the body portions sealed together to provide the complete instrument.

Another object of the present invention is to provide an instrument housing formed of rigid material, such as aluminum, having good heat dissipation qualities and having a hard ceramic surface for insulation purposes.

A further object of the present invention is to provide electrical connections for a potentiometer so that the potentiometer can be easily converted to a trimming resistor.

Another object of the present invention is to provide a mounting member for the resistance element which can support a variety of resistance material, such as wire or strips of resistant material, without changing the construction of the instrument.

A further object of the invention is to provide a wiper assembly having notched elements for engaging the threads on the shaft so that the wiper elements can be dropped onto the shaft and will skip the threads at either end of the wiper assembly travel.

A further object of the invention is to provide a bearing and moisture sealing shaft head constructed of nylon or other suitable plastic material which has inherent lubricating qualities.

These and other objects of the invention not specifically set forth above will become readily apparent from the accompanying description and drawings in which:

Figure 1 is a horizontal section of the trimming po tentiometer of this invention with the top body portion removed to illustrate the resistance unit and the wiper assembly.

Figure 2 is a vertical section along line 2f-2 of Figure l showing the notched elements of the wiper assembly positioned on the shaft and illustrating the sealing means for the shaft.

Figure 3 is a transverse vertical section along line 3--3 of Figure 2 showing the Wiper contacts riding on the resistance element and the terminal leads positioned on the opposite side of the resistance element.

Figure 4 is a perspective view of the wiper assembly showing the spring arm, the wiper contacts and the notched elements which engage the shaft.

Figure 5 is a partial vertical section similar to Figure 2 illustrating a modification of the sealing means for the shaft.

Figure 6 is a perspective view of a modification of the resistance unit wherein two strips of resistant material `are attached to the mounting board and are connected to the' terminal leads by silver clips positioned over the ends of the mounting board.

Figure 7 is a perspective View of another modilication of the resistance unit wherein two strips are positioned on the mounting board and are connected in series with the terminal leads.

Referring to Figures l and 2, the instrument housing comprises two

body portions

10, 11 which are identical in construction. One end of each body portion has a semicircular cutout 12 having a larger semi-circular cutout 13 positioned intermediate its ends. When the body portions and 11 are placed together, the

cutouts

12 and 13 receive a cylindrical head member 14 which has an enlarged rib 15 positioned in the circular space formed by the cutouts 13. The member 14 also has a circular opening 16 into which knurled end 17 of shaft 18 is pressed. The member 14 also has a notch 19 located exteriorly of the housing to provide for connecting the shaft to any suitable type of rotating mechanism. The other end of each of the body elements contains a rectangular cutout 20 which connects with a semi-circular cutout 21, so that when the

body portions

10 and 11 are placed together, the semi-circular cutouts 21 form a circular opening for the Unthreaded end 22 of shaft 18. T he end 22 contains a groove 23 and has a rounded end portion 24, both of which are located in the closed space formed by the cutouts Ztl when the body portions are placed together. This space also receives a channel shaped member 25 constructed of spring metal and having a slot 26 for receiving the groove 23 when the member is flexed inwardly. After the member 25 is released, the pressure of the member upon the end 24 serves to continually force the end 24 against the side of the opening formed by the spaces 2t). Thus, the shaft 18 is held in fixed position within the housing and the force on end 24 places a desirable drag upon shaft 18. The circular opening formed by the cutouts 13 is somewhat wider than the rib 15 so that the member 14 does not have to be accurately located on the end of the shaft.

Each

body portion

10, 11 contains a rectangular cavity 27 so that when thel body portions are placed together, a closed, interior, rectangular cavity is formed. The cavity portion 27 of lower body member 11 receives the resistance unit 28 which comprises a rectangularly shaped mounting board 29having a wire element 30 wound therearound. A wiper assembly 31 is illustrated in Figure 4 and comprises a flat member 32 from which is cut a spring arm 33 terminating in a contact member 34. Wiper arms 35 and 36 extend'from opposite sides of the member 32fand terminate in `flat

sections carrying contacts

37 and 38, respectively. The ends 39 and 4t) of member 32 are bent downward and contain V-shaped notches 41 and 42, respectively. Thus, it is only necessary to drop the notches 41 and 42 onto the threads of the shaft 18 in order to connect the wiper assembly to the shaft 18. Upon the rotation of the shaft, the threads will engage the

notched ends

39 and 40 and cause the wiper assembly 31 to move along the shaft in a direction corresponding to the direction of rotation of the shaft.

The surface of each of the cavities 27 contains a rectangular center groove or slot 43 which extends the full length of the cavity 2.7 and each slot 43 is crossed by grooves or

slots

44, 45 and 46 which extendgacross the cavity and connect, respectively, with

slots

47, 48 and 49 at one side of the cavity and with

slots

47, 48 and 49 atV the other side of the cavity. Since the slot `45 `is located centrally of the body portions and the slots 44 and 46 are located equal distances from the ends of the body portions, it is apparent that both the body portions can be constructed from the same tooling and placed together to provide slots for leads which can extend to either side of the housing. One end of the winding 30 is connected to terminal lead 50 which is bent downward to form a leg 51 and then outward to form a leg 52 and then inwardly, to form a leg 53. The leg 51 is located in the slot 49 of the body portion 11, the leg 52 is located in the slot 46 of portion 11 and the leg 53 is located in slot 43 of portion 11. A contact bead 54 is located at the junction of

legs

52 and 53 and bears aginst the wire element 30. A second terminal lead 55 is located at the opposite end of the housing and is formed with legs 51', 52' and 53 which are received inthe

slots

47, 44 and 43, respectively, of the body portion 11. A contact bead 56 is located at the junction of legs 52' and 53' and engages the opposite end of the winding '30 to complete the circuit through the winding 30 and terminal leads 50 and 55. As illustrated in Figure 2, the

legs

53 and 53 do not extend far enough to contact each other in slot 43.

An output lead 57 is located centrally of the body portion and has a leg 58 extending upwardly in slot 48 in the upper body portion 10 and has a leg extending through groove 45 of the upper body portion to connect with strip 59 which extends the complete length of slot 43 of the body portion 10. As illustrated in 'Figure' 2, the contact 34 on spring arm 33 moves along the strip 59 to continually connect the wiper assembly with the' output lead 57 so that the output of this lead will vary with the location of the wiper assembly on shaft 18.

The construction of the various components described above form an important part of the present invention. The body portions 1i) and 11 are preferably constructed of aluminum which has been anodized with a hard ceramic surface to insulate the body portions. By constructing the body portions of aluminum or some similar metal, advantage can be talren of the mechanical strength of the metal and of the good heat dissipation characteristics of the metal so that much higher operating temperatures and power ratings can be obtained. Of course,v

other materials, such as plastics, can be utilized for the body portions if so desired. The leads 50, 55 and 57 and the wiper assembly 31 are preferably constructed of half hard beryllium copper having a gold flash on all surfaces so that these components incorporate very little resistance in their circuits and resist corrosion. The member 25 can also be constructed of beryllium copper, heat treated to full hardness, in order to have suicient spring properties to hold the end 24, of shaft 18. As previously mentioned, the member 14 is constructed of nylon or other similar plastic material which retains good lubricating properties.

Themounting board 29 can be constructed of anodized aluminum or a suitable plastic and the surfaces of the wire are sprayed with an insulating varnish so that long lengths of board can be wound and then cut to the desired siZ'e of the resistance unit. The wire 30 is buffed along the path of the

contacts

37 and 38 to remove the varnish and provide good electrical connection and the lower surface of the wire is bulfed at locations to provide good connections with

contacts

54 and 56. The

body portions

10 and 11 are held together by adhesive 60 located at their adjacent edges around the cavities 27 and this adhesive accomplishes the dual purpose of a mechanical connection and a humidity Seal. The adhesive 60 and the nylon member 14 seal all openings into the interior of the potentiometer housing and thus, a low moisture condition can be maintained within the interior of the housing. The adhesive 60 can `be subjected to induction heating in order to obtain a very strong bond between the body portions.

The manner in which the trimming potentiometer of the present invention can be assembled by simply placing one component after another together, will now be deh scribed. Starting with the body portion 11, the terminal leads 50 and 55 are first dropped into the slots in this portion and can be held therein by adhesive if so desired. Thereafter, the resistance unit 28 can be droppedinto the cavity `27 of the body portion 11 and the spring' member 25 can be inserted into the cutout 20 of the body portion 11. Next, the shaft 18 is dropped onto the body portion 11 lSo that member 14 is located in

cutoutsv

12 and 13 and spring member 25 is sprung to receive slot 23 so that shaft end 22 can be located in cutout 21. 'Ihe wiper assembly 31 can now be assembled on the shaft by simply dropping the notches 41 and 42 of the assembly onto the threads on the shaft 18. Thereafter, the output lead 57 can be assembled with the strip 59 in the slot 43 of the body member 10 and adhesive 60 is applied around the edges of the two body members. After the portions and 11 are placed together and secured by the adhesive, contact 34 will engage strip 59 to provide an output reading from the potentiometer and the spring arm 33 will be flexed to hold the Wiper assembly on the threads of shaft 18.

In operation of the device, the head member 14 can be rotated by any suitable instrument or manually in order to vary the output signal. The wiper assembly will be held in any set position because of the force of spring arm 33 acting between the strip 59 and the notches 41 and 42. Also, when the wiper assembly abuts either end of the housing, one of the notched ends will be off the threads of shaft 18 (see dotted line position of Fig. 2) and the other notched end will skip over the threads since the wiper assembly can move away from the threads by flexing spring arm 33. The spring member 25 serves to hold the shaft 18 in any fixed position against vibrations and jiggling. In normal use, the terminal leads 50 and 55 will be connected in series with the winding element 30 and the output lead 57 will carry an electrical signal corresponding to the position of the wiper assembly 31. However, by simply placing one of the terminal leads and the output lead 57 in series with the winding 30, rotating of shaft 18 will select any desired resistance for the circuit so that the instrument is easily convertible into a trimming resistor.

Referring to Figure 5, a modified element 14', constructed of suitablev plastic material, has an opening at one end for receiving the knurled end 17 of shaft 18 and the other end has a slot 19. A circular groove 61 in the side of element 14 receives an O-ring 62 which bears againstV a uniform` circular opening 12. 'I'he O-ring can be constructed of neoprene or nylon to seal the opening 12. In the assembly of this modification, the O-ring 62 will first be assembled in the groove 61 prior to placing the shaft 18 onto the body portion 11.

The resistance' unit 28 is particularly adapted for the use of a variety of resistance materials. In Figure 6 two

strips

63 and 64 are shown attached along the length of the mounting board 29 and secured thereto by suitable adhesive. The

elements

63 and 64 are located along the pathof the contacts 37 and 3S as they move along the resistance unit upon rotation of the member 14. In order to place these strips in the electrical circuit of

leads

50 and 55, silver clips 65 and 66 areplaced around opposite ends of theboard 29 so that the upper sides of the clips contact opposite ends of

thestrips

63 and 64 and the lower surfaces of the clips extend inwardly sufficient so that clip 65 connects with contact 54 and clip 66 connects with contact 56. Thus, the

strips

63 and 64 are connected in parallel with the

leads

50 and 55. The versatility A.of the resistanceunit is demonstrated by the fact that the

strips

63 and 64 can be formed of very thin strips of a high resistance metal, such as a nickel chrome alloy, which hashigh resistance properties and theresistance rangewill vary-with the thickness of the strips. Also, the

strips

63 and 64 can comprise a pressure sensitive tape impregnated with thin flakes of carbon, such as carbon black, in order to produce a resistance. It is understood that the distance between the particles of the carbon on the tape can be varied to vary the resistance of the tape per unit length. Thus, the mounting board 29 forms a convenient support for any suitable type of resistance material and if so desired, only one strip of any desired width can be utilized. lt is apparent that the various forms of resistances can be used with any change in the components of the instrument. Also, the silver clips 65 and 66 can be replaced by beryllium copper clips with gold ash or with a silver paint composition which is conductive.

Referring to Figure 7, the mounting board 29 has mounted thereon the

strips

63 and 64 which can be constructed of the various materials previously described. In this embodiment of the invention, the

strips

63 and 64 are placed in series rather than in parallel with the terminal leads. The lead 50 has a short leg 52 in the slot 46 of body portion 11 and this leg 52 is connected with one end of strip 64 by a layer of conductive silver paint 67 which passes around to the end of the mounting board 29. The opposite end of strip 64 is connected to the adjacent end of strip 63 by another layer 68 of conductive silver paint. The end of strip l63 opposite layer 68 connects with a layer of silver paint 69 which passes over the end of the mounting board 29 and along the bottom of the mounting board to contact extended leg 52" of lead 55. It is understood that leg 52 will extend completely across the cavity 27 in groove 44 and since the

strips

63 and 64 are placed in series, a longer resistance is provided to give a greater potential drop. Because the

contacts

37 and 38 on

strips

63 and 64, respectively, will sense different potentials, the output lead 59 will provide a signal which is a function of these two different potentials.

By the present invention a novel trimming potentiometer is provided which can be easily constructed in miniature size at minimum cost since all of the components are simply placed together one after another and the hous ing is thereafter sealed to provide both a mechanical seal and a humidity seal. The potentiometer can be easily and quickly converted into a trimming resistor by placing either of the terminal leads in series with the output lead through the winding element. The potentiometer has the feature that it is completely humidity tight so that the resistance element is not affected by changes in the humidity. One important advantage of the invention is that the resistance elements are assembled on a mounting board which is fabricated prior to assembly and thus, a wide variety and assembly of the resistance elements can be utilized without changing the over-all construction of the potentiometer. r[The novel assembly can be accomplished because of the manner in which the wiper assembly is connected with the shaft 18 and because of the manner in which the member 14 is constructed to automatically compensate for moisture changes. Various modifications are contemplated by those skilled in the art without departing from the spirit and scope of the invention as hereinafter `deined by the appended claims.

What is claimed is:

1. A potentiometer comprising a housing constructed of two body portions of -identical construction, a cavity in each of said body portions lfor forming a closed space within said housing when said body portions are placed together, a plurality of grooves in the surface of each cavity for receiving the leads for said potentiometer, each cavity having three grooves leading to both sides of the cavity so that the body portions are interchangeable and the lead located in each groove can be positioned at either side of the housing.

2. A potentiometer as defined in claim l wherein each body portion has a semi-circular cutout at each end, said cutouts forming circular shaft supporting openings at each end of said housing when said body portions are placed together.

3. A potentiometer as defined in claim 2 having two terminal leads of a configuration substantially similar t0 said grooves in one body portion, resistance means carried by a mounting member of a configuration substantially similar to the cavity and positionable within the cavity of said one body portion over said two leads, a shaft having portions at opposite ends to be dropped into the semicircular cutouts of said one body portion, a wiper assernbly movably carried on the shaft and having notched ends receivable onto thev threads of said shaft, and an' output lead receivable into one of the grooves of the other body portion cooperating with said one body portion' to form said closed space.

4. A potentiometer as defined in claim 3l wherein each body portion contains an'opening` at one end -t'oI form a second closed space in cooperation with isaid? body portions, spring means received by said opening in saidv one body portion, a notch in saidA spring means -to receive one end of said shaft as. said shaft is positioned inthe cutouts of said one body portion, said spring means being exed to receive said one end of said shaft toliold the end of said shaft against a surface of said second space.

5. A potentiometer as deiined in claim 3l having seal` ing and supporting means attached to one end of said shaft, said sealing means being located in one of said circular openings and extending exteriorly of saidV housing.

6. A potentiometer comprising a housing constructed of twobody portions, a cavity in each ofsaid body portions dening a closed space within lsaid housing-'when' said bodyp'ortio'ns are placed together, v"tv'voi-groov`es`A in the'cavity of one body portion and a thirdgr'oove infthe cavity of the other.bodyportion,,semicircula-cutouts at both ends of each body'memberlfor'ming a circular shaft supporting opening'at each end of' said housing, two terminal leads having a similar coniiguration` to and receivable into the two grooves in saidl one body portion, resistance means carried by amounting member of similarconfiguration to the cavityandreceivable into the cavity' of said one body portion over said two terminal leadsya'` shaft having portions at opposite ends -to bedropped into the cutouts of said one body portion, ay wiperassembly having notched ends mounted onto` the threads of said shaft, and an output leadreceivable intosaidthird groove of said other body portion cooperating with said one body portion to form saidclosed space.

7. A potentiometer comprising a housing having an internal cavity, a resistance unit located within said cavity and connected at its ends with terminal leads extending exteriorly of said'housing, said resistance unit comprising a flat mounting member extending along said cavity for supporting a resistance means, movable means extending' into said cavity, a wiper assembly carried by said mov#v able means for movement along said resistance'means',l

andan output lead connected with said wiper assembly and extending exteriorly of said housing, said resistance means comprisinga strip'of resistance material attachedv along each edge of said mounting member, said wiper assembly having two contacts located at opposite sidesfof ing along said oppositel side `for connecting the other strip to the other terminal lead, and third conductive means connecting said strips together at the other end of said member' so that said strips are in Series with said terminal leads. 10.-A Ipotentiometer. comprising a housing having an internal cavity, a resistance unit located -within said cav` ity, a'threaded `'shaft extending through said cavity, and a wiper assembly `carried `by said shaft for movement along said resistance unit pon'rotation of said shaft, said wiper assembly comprising a body having two notched elements spaced apart to be received by the threads on said shaft and a Aspring arm carrying-a contact, said contact bearing against av lead extending along said cavity in order to bias said elements against said threads and said spring armvbeing ielribleto` permit either notched element to skip from thread to-'thread after the other element has run off the threads at' one end of the shaft and into engagement with an end ofy said cavity.

11. A potentiometer comprising -a housing-having an internal cavity, a resistancev unit located withinsaid c'av ity and connected at its ends with terminal leads vembedded in one side of said cavity, a threaded 'shaft extending throu'gh said cavity, means attached to one endy of said shaft and extending through an opening at one end of said housing to` provide a bearing support and moisture seal, spring means attached to the other end of lsaidshaft to hold vsaid other end in lixed position against said housing and provide a dragon said` shaft, a wiper assembly carried vb'ysaid shaft for movement along said resistance unit, said wiper assembly comprising a body having two notched elements spaced apart to be received by the threads on said shaft and a spring arm carrying a contact, and an output lead embedded in the other side of said cavity and extending along said cavity to continually engage said contactduring movement of said contact by rotation of said shaft, said spring arm being exible to permitA either notchedjelement to skip from thread to thread after the other element has saidvmountng member so that each contact will move along one of said strips. y

8. A potentiometer as defined in claim 7 wherein said terminal leads are vlocated onv the opposite side of said mounting member from said strips, and conductive means passing around each end of said'niounting :member to connect said strips inparallel `with "said terminal leads.

9. A potentiometer as defined vin claim 7 wherein said terminal leads arel located lon the opposite side of saidv mounting member from said strips, irstconductive means, passing around one endv` of said member for connecting one strip to one terminal lead, second conductive means passing around'said one end of said member and extend.-I

run off the threads at one end of the shaft and into engagement with an end of said cavity.

12. A potentiometer as defined in claim 11 wherein said resistance unit comprises resistance means carried by a` at mounting member extending along said cavity.

lReferences Cited in the le of this patent i UNITED STATES PATENTS 1,371,049

OTHER REFERENCES Westinghouse Engineer, .lanuary 1947, pages 9 to 13.