US3271721A

US3271721A - Rectilinear potentiometer

Info

Publication number: US3271721A
Application number: US584088A
Authority: US
Inventors: James F Gordon
Original assignee: Beckman Instruments Inc
Current assignee: Beckman Coulter Inc
Priority date: 1956-05-10
Filing date: 1956-05-10
Publication date: 1966-09-06
Anticipated expiration: 1983-09-06

Description

Sept- 6, 1966 J. F. GGRDQN 3,271,721

RECTILINEAR POTENTIOMETER Filed May l0, 1956 United States Patent O 3,271,721 RECTILINEAR POTENTIGMETER James F. Gordon, San Marino, Calif., assigner to Beckman Instruments, Inc., Fullerton, Calif., a corporation of California Filed May 10, 1956, Ser. No. 584,088 7 claims. (C1. sas-iss) This invention relates to potentiometers or variable resistors for use in electrical circuits and in particular to potentiometers which are adapted for use in miniaturized equipment.

It is an object of the invention to provide a miniature poten-tiometer which is small in size and stable in operation under extremes of vibration, shock, atmospheric pressure, temperature and humidity. A further object of the invention is to provide such a potentiometer which is simple in design and inexpensive to produce and test and which is well adapted to automatic methods of manufacture.

It is another object of the invention to provide a miniature potentiometer which is completely assembled and tested before being placed in its case and which may be mounted with a plurality of similar potentiometers in horizontal and/or vertical rows, either with or without the cases for the individual potentiometers. Another object of the invention is to provide a miniature potentiometer in which the moving element is translated -by means of a rotating threaded shaft with the shaft being manually operable from the end of the potentiometer by a screw driver or the like.

It is a further object of the invention to provide .a miniature potentiometer which may be sealed in its case to minimize the entrance of dust and moisture with the openings for the electrical terminals being closed by solder and with the opening for the adjusting shaft being sealed by a labyrinth bearing structure. Another object of the invention is to provide a miniature potentiometer suitable for use with resistance elements which are fired or ceramic bases las well as with wound or molded resistance elements.

It is an object of the inventi-on to provide a method of manufacturing .a miniature potentiometer having a rotating adjustment shaft in which the adjustment shaft is positioned within the bearing area of the potentiometer body and in which the bearing is poured in molten condition iabout the shaft `and is adhered to the walls of the bearing area of the body, thus forming a rigidly connected `complete potentiometer.

It is another :object of the invention to provide a method of manufacturing a miniature potentiometer in which the conducting and resistance elements, the terminal connecting pins and the receptacles for the poured bearings are tired onto a ceramic body in a single operation. Another object vof the invention is to provide such a method in which the terminal connecting pins are electrically joined to the conducting and resistance elements by the firing step.

The invention also comprises novel details of construction and novel combinations yand arrangements of parts, which will more fully appear in the course of the following description. The drawing merely shows and the description merely describes preferred embodiments of the present invention which are given by way of illustration or example.

In the drawing:

FIG. 1 is an isometric view of a preferred embodiment of the invention, with a portion of the case broken away;

FIG. 2 is .an enlarged sectional view taken along the line 2 2 of FIG. 1;

FIG. 3 is a Sectional View taken along the line 3 3 of FIG. 2;

3,271,721 Patented Sept. 6, 1966 taken along the line 4 4 of y potentiometer at a subsequent step in the manufacturing process.

The preferred embodiment of the invention illustrated herein includes an elongated body 10 having a central portion 11 and

upstanding end portions

12 and 13, bearings 14 and 15 mounted in the

end portions

12 and 13 respectively, a rotating adjustment shaft 16 positioned in the bearings and a contact block 17 carried on the Iadjustment shaft.

An elongated resistance element 20 and an elongated electrical conducting element 21 are mounted side-by-side on the central lportion 11 of the body 10. The 'body 10 is preferably formed of a single piece of electrical insulating material, a ceramic such as steatite vbeing `a highly suitable material. The resistance element 20 may be 'a Wire wound resistor, a molded resistor, a deposited filmy resistor, or any other suitable type, the deposited film type of resistance element which is fired on a ceramic base being especially well adapted for use in this embodiment. Similarly, the electrical conducting element 21 may take various known forms, a lm of silver tired on ceramic being preferred.

Means are provided for manually rotating the adjustment shaft 16, one form of such means being a head22 having a screw driver slot 23 therein, the head extending through the bearing 14 to the exterior of the end of the potentiometer. A central portion 2-4 of the shaft 116 is threaded, the block 17 having a corresponding opening 25 so that rotation of the shaft translates the block `along the central portion of the body.

Means are carried on the contact block 17 for electrically connecting a point on the resistance element 20 with the conducting element 21. A preferred form for this connecting means which provides positive interconnection under extreme conditions of vibration and shock Without requiring a complicated structure or precision contact surfaces is illustrated in FIGS. 2 and 3. A plate 28 of electrical conducting material is clamped against the bottom surface of the contact block 17 by two

U-shaped pins

29, 30 which pass through four vertical openings 31 in the contact block and are bent over at the tops ofthe openings to secure the ends in place. The Contact block 17 is preferably made of a single piece of electrical insulating material such as nylon or Teflon in order to electrically insulate the resistance and conducting elements from the shaft. Such insulation cou-ld also be achieved when required by making the shaft of an electrical insulating material. The plate 28 is made of a resilient material and is provided with a plurality of fingers 32 at one end thereof, the fingers being bent substantially to the shape shown in FIG. 2 so that the resilient nature of the material urges the tinge-rs into contact with the resistance and conducting elements.

Downwardly extending

runners

33, 34 are provided at opposite edges of the contact block 17 with the lower edges of the runners being spaced very slightly above the resistance and conducting

elements

20, 21. When the shaft 16 is rotated to translate the contact block, one of the runners is engaged with one of the elements and prevents a corresponding rotation of the contact block. It is not essential that the runners engage the elements;

the relative positions of the runners and the elements could be such that the runners engage the body on which the elements are supported.

LConnections must be provided for coupling the resistance and conducting elements of the potentiometer into an electrical circuit. The structure described herein permits these electrical connections or leads to be brought out the end of the potentiometer, a very important feature when it is desired to stack a plurality of the potentiometers side-by-side or on top of each other in a minimum of space.

Openings

36, 37 and 38 are provided in the central portion 11 of the body 10 adjacent the ends of the resistance and conducting element-s, the openings communicating with the upper surface of the central portion 11 and a groove 39 which extend-s longitudinally along the bottom of the body 10. Connecting

pins

40, 41 and 42 are positioned in the

openings

36, 37 and 38 respectively, pin 40 being connected to the conducting element 21 by suitable means such las soldering and

pins

41 and 42 being connected to each end respectively of the resistance element by suitable means. Electrical'wires 43', 44 and 45 are connected to the other ends of the

pins

40, 41 and 42 respectively, after which the pins are bent at 90 as shown in FIG. 2 so that the wires will lie in the groove 39 and extend from the end of the potentiometer.

The

pins

40, 41, 42 may be held in place by the solder joints which connect them to the resistance and conducting elements. A preferred form of construction contemplates using pins which are coated with a material, such as silver, which can be adhered to the body 10. The coated pins are inserted into the

openings

36, 37, 38 and the unit is fired at an elevated temperature, thereby adhering the coating to the walls of the openings land to the pins and producing a long, sealed joint between each pin and the body.

The pins which have been fired in place may now be soldered to the resistance and conducting elements. When theresistance and/ or conducting elements are of the type which are deposited on the body and fired, as described above, these elements may be deposited over the ends of the pins before any firing is done. Then the elements and pins are fired in one operation, electrically joining the components and eliminating the soldered connections previously referred to.

An alternative form for making electrical connections tothe potentiometer is shown in FIG. 6, whe-rein the

pins

40, 41 and 42 are omitted, the bare ends of the

wires

43, 44 and 45 being passed upward through the

openings

36, 37 and 38 respectively and connected directly to the conducting element and the resistance element. When making solder connections between the wires and the conducting and resistance elements, the solder may be owed into the

openings

36, 37, 38 to seal them.

The

ends

12 and 13 of the body 10 have openings or

saddles

48 and 49 respectively for receiving the bearings 14 and 15. In the preferred method of manufacturing the potentiometer of the invention, the

bearing saddles

48 and 49 are lined with a layer 50 of metallic material such as silver or the like, which may be adhered to the body by well known means such as painting a film of the material on the body and then firing the unit at an elevated temperature. The layers v50 in the bearing saddles, the

pins

40, 41, 42 and the resistance and conducting

elements

20, 21 may be applied to the body and tired together,'thereby effecting a saving in time and cost of manufacturing. In FIG. 7, a body 10 is shown with the resistance and conducting

elements

20, 21, the

pins

40, 41, 42 and the bearing saddle layers 50 adhered thereto. The shaft 16 with the contact block 17 mounted thereon is positioned in the bearing saddles as shown in FIG. 8, by a suitable clamp 51. The open ends of the bearing saddles are blocked by removable .plates and a molten bearing material, such as a lead-tin alloy, is poured into the bearing saddles. The shaft 16 is made of a material having a relatively high melting point, such as stainless steel, so that the molten bearing material will not adhere to the shaft but will adhere to the layers 50 in the bearing saddles. After the bearing material has hardened, the removable end plates are removed, the clamp 51 is removed and the shaft 16 is rotated to free it from the bearings.

One end of the shaft 16 is provided with a plurality of grooves 54 and lands 55 which, after the bearing has been poured therearound, serve as a thrust bearing preventing axial movement of the shaft relative to the body. While a single groove would serve this purpose, it is preferred to use a plurality of grooves as shown in FIG. 2, the resulting labyrinth serving to reduce the possibility of dirt and moisture entering the interior of the potentiometer along the adjustment shaft. The other end of the shaft preferably is cylindrical and does not extend through the bearing 15. As the bearings are being poured, the metal shaft 16 expands more than the ceramic body 10, resulting in a small gap 56 between the bearing 15 and the end of the shaft when the unit has cooled. Thus clearance is provided for operation of the potentiometer at elevated temperatures without binding due to differential expansion of the various elements thereof. The use of the above described poured bearing construction in a miniature potentiometer enables one to produce a high quality, accurate and durable component in a minimum of space and at a minimum of cost.

Conventional bearings which are preformed may also be used in the potentiometer of the invention if desired. An example `of such construction is shown in FIG. 6, wherein a block 60 of bearing material is inserted in the saddle 49, the`block being held in place by

pins

61, 62. which engage the end 13 of the body. The block 60 is provided with an opening 63 for receiving the end of the shaft 16. A similar bearing may be used in the end 12 in place of the poured bearing 14.

It should be noted that the potentiometer consisting of the body, bearings, the shaft, t-he contact block, the resistance and conducting elements and the wires attached thereto comprises a complete unit ready for use. Since the leads leave from one end of the unit and adjustment is made at the other end of the unit, a plurality of the units may be mechanically assembled together side-by-side and/ or on top of each other to provide a compact installation providing for a plurality of electrical adjustments. One method of mounting the potentiometer is illustrated in the drawing, consisting of

parallel openings

66 and 67 in the

ends

12 and 13 respectively of the body, the openings lying transverse to the longitudinal axis of the body. A plurality of similar potentiometers may be aligned horizontally on two long screws passing through the openings 66 land 67. Similarly a plurality of the potentiometers may be stacked vertically with each potentiometer being clamped to a vertical mounting plate by two screws passing through the

openings

66 and 67.

In the embodiment illustrated herein, an open-ended case 68 is provided for sliding over the finished potentiometer, the case having a cross-sectional shape substantially corresponding to that of the

ends

12 and 13 of the body.

Four openings 69 are provided in the case correspond ing with the

openings

66 and 67 in the body so that screws 70 for fixing the case to the body and/or mounting the potentiometer as described above may be passed there.- through.

The case 68 is preferably made slightly longer than the body 10, as shown in FIG. 2, to provide a recessed area at each end of the encased potentiometer so that a potting tor sealing compound 71 may be placed in each end of the unit to act as a moisture and dust seal. A layer 72 of a sticky resilient tape is affixed to each inner Wall of the case containing the openings 69, or to the corresponding sides of the body 10, the tape being provided with openings corresponding to the openings 66,Y 67 andV 69, but preferably smaller in diameter, thereby enabling the tape to serve as a moisture and dust seal around the screws passing through the openings. This tape preferably is thin with good mechanical resilient and electrical insulating properties at both high and low extremes of temperature. One tape suitable for this application is currently known by the trade name Mylan Further moisture and dust sealing is provided by the labyrinth between the shaft 16 and bearing 14 previously referred to, and by the solder joints connecting the pins or leads to t-he resistance and conducting elements, the solder joints completely filling the

openings

36, 37 and 38 as seen in FIGS. 2, 5 and 6. If desired, a case similar to the case 68, but adapted to contain two or more of the potentiometers may be utilized and may be sealed against moisture and dust in the manner described above.

Thus it is seen that the objects of this invention are achieved by the potentiometer described in detail herein. Suitable potentiometers have been manufactured according to the teachings of this invention with over-all dimensions less than five sixteenths by five sixteenths by one and one quarter inches.

Although exemplary embodiments have been disclosed and discussed, it will be understood that other applications of the invention are possible and that the embodiments disclosed may be subjected to various changes, modifications and substitutions without necessarily departing from the spirit `of the invention.

I claim as my invention:

1. In a miniature potentiometer, the combination of: an elongated body having bearing saddles adjacent each end thereof; an elongated film of resistance material fired on said body between said saddles; an elongated film of conducting material fired on said body between said saddles substantially parallel to said resistance material; a film of metallic material fired on each of said bearing saddles; bearings fixed to each of said metallic films in said bearing saddles; a shaft rotatably mounted in said bearings, said shaft having a threaded section positioned between said bearings; and contact means for electrically connecting said resistance material and said conducting material, said contact means including means engaging the threaded section of said shaft and means preventing rotation of said contact means as said shaft is rotated so that rotation of said shaft advances said contact means along said resistance material.

2. In a potentiometer, the combination of: an elongated body having bearing openings adjacent each end thereof and having openings therethrough transverse to the longitudinal axis thereof and adjacent each of said bearing openings; a unitary bearing mounted in each of said bearing openings; a shaft rotatably mounted in said bearings, said shaft extending through one of said bearings and terminating within the other of said bearings, said shaft having a threaded section positioned between said bearings, that portion of said shaft positioned in said one of said bearings having a plurality of spaced sections of lesser diameter than the sections intermediate said spaced sections; said one bearing having a plurality of spaced sections of larger diameter than the sections intermediate said larger diameter spaced sections of said bearing, said larger diameter spaced section of said bearing being of a size to mate with and project into said lesser diameter spaced sections of said shaft to retain said shaft against axial movement; an elongated resistance element mounted on said body; an elongated conductor element mounted on said body substantially parallel to said resistance element; contact means for electrically connecting said resistance element and said conductor element, said contact means being carried by said threaded section of said shaft, said contact means including means engaging said threaded section of said shaft and means to prevent rotation of said contact means as said shaft is rotated so that rotation of said shaft advances said contact means along said resistance element; an elongated case open at each end thereof and slidable over said body, said ends of said body having substantially the same cross-sectional shape as said case, said case being longer than said body, defining recessed spaces at each end of the potentiometer, said case having opposed openings therein aligned with each of said openings in said body; screw means passing through each of said aligned openings; strips of resilient tape positioned between the sides of said body and the opposed inner walls of said case having said opposed openings for providing a seal around each of said screw means passing therethrough; and a mass of sealing material positioned in each of said recessed spaces.

3. In a miniature potentiometer, the combination of: an elongated body having bearing saddles on one side adjacent each end thereof and a channel in a side opposite said one side with a plurality of terminal openings in said body providing communication between said channel and said one side; an elongated film of resistance material fired on said one side between said saddles; an elongated film of conducting material fired on said one side between said saddles substantially parallel to said resistance material; a film of metallic material of relatively high melting temperature fired on each of said bearing saddles; bearings of relatively low mel-ting temperature fixed to each of said metallic films in said bearing saddles; a shaft rotatably mounted in said bearings, said shaft having a threaded section positioned between said bearings; contact means for electrically connecting said resistance material and said conducting material, said contact means being carried by the threaded section of said shaft, said contact means including means engaging said threaded section of said shaft and means preventing rotation of said contact means as said shaft is rotated so that rotation of said shaft advances said contact means along said resistance material; and a plurality of electrical conductors positioned in said channel and extending through said terminal openings for coupling said resistance and conducting films to an electrical circuit.

4. Ina miniature potentiometer, the `combination of: an elongated body having bearing saddles on one side adjacent each end thereof and a channel in a side opposite said one side with a plurality of terminal openings in said body providing communication between said channel and said one side; an elongated film of resistance material fired on said one side between said saddles; an elongated film of conducting material fired on said one side between said saddles substantially parallel to said resistance material; a film of metallic material of relatively high melting temperature fired on each of said bearing saddles; bearings of relatively low melting temperature fixed to each of said metallic films in said bearing saddles; a shaft rotatably mounted in said bearings, said shaft having a threaded section positioned between said bearings; contact means for electrically connecting said resistance material and said conducting material, said contact means being carried by the threaded section of said shaft and including means slideably engaging said threaded section of said shaft, said contact means including means preventing rotation of said contact means as said shaft is rotated so that rotation of said shaft advances said contact means along said resistance material; a plurality of electrical conductors positioned in said channel and extending through said terminal openings for coupling said resistance and conducting films to an electrical circuit; and an elongated case open at each end thereof and slidable over said body to close said channel, said ends of said body having substantially the same oros-sectional shape as said case with said electrical conductors passing outward through said channel and an open end of said case.

5. In a miniature potentiometer, the combination of: an elongated unitary body having a bearing mounted thereon adjacent each end thereof; a shaft rotatably mounted in said bearings, said shaft having a threaded section positioned between said bearings; an elongated resistance element mounted on said body; an elongated conductor element mounted on said body substantially parallel to said resistance element; a contact block carried by said threaded section of said shaft and including a thread mating with the thread of said threaded section of said shaft, means to prevent rotation of said contact block as said shaft is [rotated so that rotation of said shaft advances said contact block along said resistance element; electrical conducting means mounted on said contact block for engaging said resistance element and said conductor element; means positioned at one of said ends of said body for rotating said shaft; passage means including a channel in a side of said body opposite said conductor and resistance elements for communicating with said elements and with the other of said ends of said body; a plurality of electrical conductors positioned in said passage means for coupling said elements to an electrical circuit; and an elongated case open at each end thereof and slidable over said body for enclosing said channel, said ends of said body having substantially the same cross-sectional shape as said case with said conductors extending outward through said channel and an open end of said case. v 6. In a miniature potentiometer, the combination of: an elongated body having bearing saddles adjacent each end thereof and having a plurality of terminal openings; an elongated lm of resistance material fired on said body between said saddles; an elongated lrn of conducting material red on said body between said saddles substantially parallel to said resistance material; a terminal pin of conducting material fired in each of said terminal openings of said body, one of said terminal pins being electrically connected to said lm of conducting material and two of said terminal pins being electrically connected to spaced points on said ilm of resistance material; a lm of metallic material red on each of said bearing saddles; bearings xed to each of said metallic films in said bearing saddles; a shaft rotatably mounted in said bearings, said shaft having a threaded section positioned between said bearings; and contact means for electrically connecting said resistance material and said conducting material, saidcontact means being carried by the threaded section of said shaft, said contact means including means engaging `said threaded section of said shaft and means to prevent rotation of said contact means as said shaft is rotated so that rotation of said shaft advances said Contact means along said resistance material.

7. In a miniature potentiometer, the combination of: an elongated body having bearing saddles adjacent each e'nd thereof; an elongated resistance element mounted on said body between said saddles; an elongated conductor element mounted on said body substantially parallel to said resistance element; a lm of metallic material red on each of said bearing saddles; a nondeformable bearing xed to each of said metallic films in said bearing saddles; a shaft rotatably mounted in said bearing said shaft having a threaded section positioned between said bearings, that portion of said shaft positioned in one of said bearings having a plurality of spaced sections of lesser diameter than the sections adjacent said spaced sections for engaging mating, greater diameter, spaced sections of said one bearing; contact means for electrically connecting said resistance element and said conductor element, said contact means being carried by said threaded section of said shaft and including means slideably engaging said threaded section of said shaft, and means to prevent rotation of said contact means as said shaft is rotated so that rotation of said shaft advances said contact means along said resistance element.

References Cited by the Examiner UNITED STATES PATENTS 62,500 2/1867 Purdy.

563,134 6/1896 Campbell 308-162 1,515,266 11/ 1924 Mitchell 22- 203 1,516,914 11/1924 Croft 22-203 1,671,469 5/ 1928 Egly 338-327 1,939,444 12/1933 Geyer 308-237 X 2,069,781 2/ 1937 Skillman 308-26 X 2,333,622 11/ 1943 MCNab 22--202 2,596,503 5/1952 Newnham 338-202 X 2,625,633 1/1953 Warsher 338-183 X 2,706,230 4/1955 Bourns .338183 X 2,751,475 6/1956 Gottschall 338-183 X 2,759,080 8/1956 Bourns 338-183 2,777,926 l/l957 Bourns 338-183 X 2,831,949 4/1958 Bourns 338-180 2,860,216 11/1958 Hubbard et al. 338-183 X ANTHONY BARTIS, Acting Primary Examiner.

RICHARD M. WOOD, JOHN E. LADY, CLAUDE A.

LE ROY, RAY K. WINDHAM, Examiners.

B. M. MULLIN, D. B. REECE, I. A. HREN,

Assistant Examiners.

Claims

3. IN A MINIATURE POTENTIOMETER, THE COMBINATION OF: AN ELONGATED BODY HAVING BEARING SADDLES ON ONE SIDE ADJACENT EACH END THEREOF AND A CHANNEL IN A SIDE OPPOSITE SAID ONE SIDE WITH A PLURALITY OF TERMINAL OPENINGS IN SAID BODY PROVIDING COMMUNICATION BETWEEN SAID CHANNEL AND SAID ONE SIDE; AN ELONGATED FILM OF RESISTANCE MATERIAL FIRED ON SAID ONE SIDE BETWEEN SAID SADDLES; AN ELONGATED FILM OF CONDUCTING MATERIAL FIRED ON SAID ONE SIDE BETWEEN SAID SADDLES SUBSTANTIALLY PARALLEL TO SAID RESISTANCE MATERIAL; A FILM A METALLIC MATERIAL OF RELATIVELY HIGH MELTING TEMPERATURE FIRED ON EACH OF SAID BEARING SADDLES; BEARINGS OF RELATIVELY LOW MELTING TEMPERATURE FIXED TO EACH OF SAID METALLIC FILMS IN SAID BEARING SADDLES; A SHAFT ROTATABLY MOUNTED IN SAID BEARINGS, SAID SHAFT HAVING A THREADED SECTION POSITIONED BETWEEN SAID BEARINGS; CONTACT MEANS FOR ELECTRICALLY CONNECTING SAID RESISTANCE MATERIAL AND SAID CONDUCTING MATERIAL, SAID CONTACT MEANS BEING CARRIED BY THE THREADED SECTION OF SAID SHAFT, SAID CONTACT MEANS INCLUDING MEANS ENGAGING SAID THREADED SECTION OF SAID SHAFT AND MEANS PREVENTING ROTATION OF SAID CONTACT MEANS AS SAID SHAFT IS ROTATED SO THAT ROTATION OF SAID SHAFT ADVANCES SAID CONTACT MEANS ALONG SAID RESISTANCE MATERIAL; AND A PLURALITY AND EXTENDING CONDUCTORS POSITIONED IN SAID CHANNEL AND EXTENDING THROUGH SAID TERMINAL OPENINGS FOR COUPLING SAID RESISTANCE AND CONDUCTING FILMS TO AN ELECTRICAL CIRCUIT.