US 3132321 A
Description (OCR text may contain errors)
May 5, 1964 o. F. KUHLMAN MICRO POTENTIOMETER Filed Sept. l, 1960 /QA Iii ,4M/fa MAM,
IN VEN TOR. IgM/4% Aram/551s United States Patent O 3,132,321 MICRO PTENTIOMETER f Ora F. Kulrlrnan, Portuguese Bend, Calif., assigner to Key Resistor Corp., Gardena, Calif., a corporation of Delaware Filed Sept. 1, 1960, Ser. No. 53,502 3 Claims. (Cl. SSS- 174) This `invention relates to potentiometers or variable resistors and more particularly, to an improved type of potentiometer which is particularly adapted to construction in extremely miniaturized size.
The increased use of miniaturized electrical components and electronic circuitry in applications such as servo mechanisms, computor apparatus, missiles and the like, have made necessary potentiometers which are extremely compact but which have precision accuracy and extreme reliability. Since such potentiometers are exposed to extreme ranges of environmental conditions and shock and vibration, the potentiometer, in addition to being of extremely small size, rnust be rugged in construction and capable of withstanding large variations in. temperature and other ambient conditions. Prior art potentiometers have been reduced somewhat in size but the construction of such potentiometers is relatively complicated making them expensive to manufacture and more susceptible to failure in use. Additionally, complexity of construction places a limit on the size to which they can be reduced.
Accordingly, it is a primary object of the present invention to provide an improved potentiometer construction which is particularly adaptable to extreme miniaturization of such potentiometer-s or variable resistors.
It is another object of the present invention to provide an improved potentiometer construction which is simple and inexpensive of manufacture but which is rugged and reliable in use.
It is a further object of the present invention to provide such a potentiometer which is extremely accurate and subject to precision adjustment.y
Yet another object of the present invention is to provide a potentiometer which is accurate and reliable and easily adjustable to ne degree.
The novel features which are believed to be characteristie of the invention together with further objects and advantages thereof Will be better understood from the following description considered in connection with the accompanying drawing in which the invention is illustrated by way of example. It is to `be expressly understood, however, that the description and drawing are for the purposeof illustration only and are not intended to be definitive of the invention.
The present invention comprises in general kterms a sub-miniature potentiometer which includes a body wafer of insulating material upon which there is formed an arcuate band of electrically conductive material having a predetermined resistance. Means are provided for afixing electrical contacts to opposed ends of the arcuate f band. A cover plate is aihxed to the body wafer and includes a side wall surrounding the resistanceband and an outer Wall spaced from and substantially parallel to the body wafer. ,A hub portion is rotatably mounted within the cover. The hub element has a wiper arm in` adjustable contact with the arcuate resistance band and in electrical contact with the cover. A lead element is alixed to the device in electrical contact with the cover. Thus, an electrical circuit is provided between the rotative hub element and the resistance band formed on the base and between the hub element and the cover element of the device.
In the drawing:
FIGURE l is a view in perspective of a finished device assembled in accordance with the present invention;
Patented May 5, 1964 FIGURE 2 is an exploded view showing the various elements of the presently preferred embodiment of the present invention;
FIGURES is a View in section taken along line 3 3 of FIGURE l;
FIGURE 4 is a view of the hub assembly in an alternative embodiment of the present invention; and,
FIGURE 5 is a View in elevation taken along line 5--5 of FIGURE 4. v
Referring now to the drawing and particularly to FIG- URES l, 2 and 3, there is shown a presently preferred embodiment of this invention which includes in general, a body wafer A, a hub and contact assembly B, and a cover element C. It should be noted that the figures in the drawingare greatly increased in size in order to describe and show the invention with clarity.` In actual size for example,4 the-presently preferred potentiometer in accordance with this invention is approximately 0.3 inch across the edge of the body which is the maximum dimension of the device. The over-all thickness of the l device is approximately 0.025 inch.
wafer of the type which is commercially available and extensively used in micro-module and micro-circuitry applications. Such wafers are of high alumina ceramic and are good electrical insulators. Upon the upper surface 10 of the body wafer A, there are formed two concentric arcuate bands of metal. The first, or inner, band 12 is the resistance element of the potentiometer by means of which the resistance of the device is varied. The second band 14 is a band of solderable metal by means of which the cover element C is athxed to the body water A. The inner band 12 can be formed of any suitable electrically conductive metal, metal alloy, or material such as carbon iilm. In the presently preferred embodi` ment, an nickel-20 chromium alloy is utilized. The composition of the metal can be varied, of course, to vary the resistance per length of the resistance band 12. In addition, the thickness of the resistance band and the cross-sectional area thereof can be varied to achieve a predetermined resistance per degree of length around the band. In the embodiment shown the arcuate extent of the band is approximately 330. At each end of the resistance band 12 there are provided conducting legs 15 and 16 which extendfrom the respective ends of the arcuate band 12 to the edge of the body wafer A. The band 12 and legs 15 and 1d are integrally formed upon the surface 10 of the wafer A and are deposited thereon by suitable means well-known to the art, such as the wellknown vacuum evaporation method. In the embodiment shown, the 80-20 nickel-chrome alloy is deposited at a width of approximately 10 mils and a thickness of 4000 to 5000 angstroms to obtain a resistance of 200 ohms to 6000 ohms in a device rated at 0.1 watt. Contact regions 18 and 20 are formed at the edge of the wafer in electrical contact with the legs 15 and 16 respectively of the resistance band. The Contact regions 18 and 20 are formed of material to which electrical leads Z2 and 24 can be soldered upon completion of the device. contact regions 18 and 20 are thus of electrically conductive solderable material such as solderable silver or gold alloys. These contact regions 18 and 20 can be deposited on the water by conventional means well-known to the art. For example, by silk screening and direct tiring when the outer band 14 is formed as more fully described hereinafter. Thus, with an electrical lead 24 soldered to the contact region 20 and a second electrical lead soldered to the contact region 18, an electrical circuit exists between the leads through the resistance band.
The outer band 14 is also arcuate and is concentric with respect to the inner band 12. The outer band 14 is.
The f 3 however, of less arcuate extent and is spaced from the leg 15 and the leg 16 of the inner resistance band as shown particularly in FIGURE 2. Thus, the arcuate extent of the outer band 14 is approximately 326 in the illustrative embodiment. The outer band is a band of solderable material such as silver or gold solderable alloy. In the illustrative embodiment, gold-platinum is used and is silk screened and directly tired upon the surface of the wafer in the arcuate configuration. During forniation of the outer band 14, and extending contact leg 30 is also formed which extends from the band to the edge of the body wafer A opposed to the contact regions 18 and Ztl. There is also formed a third Contact region 31 in electrical contact with the contact leg 30. The region 31 is adapted to receive the third lead 32 of the device which is soldered or otherwise affixed thereto. A circular opening 34 is provided through the wafer along the axis thereof. That is, concentrically about the center point of the bands 12 and 14. The opening 34 is substantially equal to the diameter of the adjusting shaft of the hub as described more fully hereinafter.
The hub and contact assembly is a circular plate-like member which includes a contact plate 36, a raised shoulder portion 37 and the hub shaft 38, all of which are circular and symmetrical with respect to the axis through the hub and contact assembly. The hub and contact are formed as an integral unit of electrically conductive material such as 302 stainless steel which is rodium plated for good wearing characteristics and sliding contact as described hereinafter. The hub shaft 38 is substantially equal in diameter to the inside diameter of the opening 34 through the body wafer A. The thickness or length of the hub shaft 38 is substantially equal to or greater than the thickness of the body wafer and an adjusting slot 33 is provided for the insertion of a small screw driver or other means for rotating. The diameter of the shoulder plate 37 is less than the inside diameter of the resistance band 12 such that when the elements are mated, the shoulder plate 37 has its surface 37a in sliding rotating contact with the surface 10 of the body wafer within the region defined by the resistance band but not in contact therewith. The hub plate 36 is of less diameter than the inside diameter of the outer band 14 on the body wafer. A commutator, or wiper arm 40, is afxed to the inner surface 39 of the hub plate and has a wiping contact point 41 at the radius of the resistance band 12. The wiper arm 40 is axed to the inner surface 39 and is formed with a spring action such that when the hub and contact element B is assembled with the body wafer A, with the hub shaft 38 extending through the opening 34, the wiper point 41 is urged into spring contact with the resistance band 12.
The cover element C is substantially cylindrical with an upstanding circular wall 42 and a surface plate 43. The coverelement C is again formed of suitable electrically conductive material such as 302 stainless steel which is palladium plated on the inner sulface for sliding contact with the hub and contact element B. As shown particularly in FIGURE 2 the cylindrical side wall 42 has an arcuate segment removed therefrom which segment spans an arcuate distance greater than the arcuate spacing of the legs and 16 on the body wafer A. That is, the arcuate extent of the cylindrical side wall is approximately equal to the arcuate extent of the outer affixing band 14 on the body wafer, of 326 in the illustrative embodiment. The inner edge 44 of the cylindrical side Wall is planar and is thinner than the radial width of the outer band 14 such that when the cover element C is positioned on the body wafer A, the inner edge 44 of the cover element is in contact with the aifixing band 14. The depth of the side wall 42 is such that the inner surface 43 of the cover element C is spaced above the Wafer at a distance substantially equal to the combined thickness of a shoulder plate and the hub plate 36 of the hub and concontact element B.
Accordingly, it can be seen by reference to FIGURES 2 and 3, that the device in accordance with the present invention is assembled by positioning the hub and contact element B in position upon the body wafer A by inserting the hub shaft 38 through the opening 34. When assembled, the Wiper point 41 of the wiper arm 40, is in sliding electrical contact with the resistance band 12 of the body wafer. The cover plate can then be placed over the hub and contact element and affixed to the body Wafer by soldering or high temperature brazing the inner edge 44 of the cover element to the aixing band 14. The cover element C is aligned such that the arcuate sector removed from the side wall 42 of the cover element C is aligned with the arcuate space between the ends of the afxing band. That is, the side wall 42 of the cover element C is spaced from the contact legs 15 and 16 of the resistance band 12. Since the wiper arm 40 is spring loaded, or spaced from the surface 39 of the hub plate 36 by a distance greater than the thickness of the shoulder plate 37, it is in'sliding electrical Contact with the resistance band 12. Similarly, the hub plate 36 is in electrical contact with the inner surface 43 of the cover element C. The manufacturing tolerances of the hubl and contact element and the cover element are such that the hub and contact element remains in electrical contact with the cover element C. In order to assure such electrical contact, particularly when the device is subjectedv to shock and vibration, it is preferable to form the surface 43 of the cover element C to exert a pressure on the hub and Contact element B. In the presently preferred embodiment the surface 43 is formed with a central concavity toward the hub element to exert a spring force downwardly on the hub element such that the hub element exerts a force at the surface 37a against the body surface 10. The compressive forces between the elements thus prevents a change of relative position or break in the electrical contacts when the device is subjected to shock and vibration. In addition, this contact is assured by the spring action of the wiper arm 40 against the resistance band 12. The leads 24, 22 and 32 of the potentiometer or the variable resistance device are aixed at the contact regions 18, 20 and 31 as described previously. An electrical circuit then exists between the leads 22 and 24 through the resistance band 12 and a second circuit exists between the resistance band 12 through the wiper arm 4t) and through the cover element C to the lead 32. Thus, it can be seen that the resistance of the device can be varied by rotating the entire hub and contact assembly by rotation of the hub shaft 38 to vary the position of the wiper contact point 41 upon the resistance band 12 to vary the resistance of the circuit through the resistance band 12, the wiper arm 40, and the cover plate C and thence to the lead 32. In order to hermetically seal the interior of the device, a plug 44 of epoxy or similar potting material can be placed in the arcuate opening through the side wall 42.
Referring now to FIGURES 4 and 5, there is shown a hub and contact element of an alternative embodiment of the present invention. The body wafer and cover element are similar to those previously shown and described in connection with the illustrative preferred embodiment. In the embodiment of FIGURES l through 3, the hub and contact element B was formed of electrically conductive metal and the hub shaft has a voltage thereon when a voltage isimpressed across the device. In the alternative embodiment shown in FIGURES 4 and 5, the hub and contact element is formed of two sections. The hub plate 36' and the shoulder 37 are formed of electrically insulating material such as resin or plastic. The hub shaft 38 is separately formed and is extended into the hub plate and shoulder plate and aflixed thereto as shown particularly in FIGURE 5. The hub shaft is formed of metal and includes an adjusting slot. Opposed Wiper arms 50 and 51 are aixed at opposite surfaces of the hub plate 36. The lower arm 51 is positioned as previously de'- scribed such that the wiping point 52 is in contact with the resistance band 12 of the body wafer. The upper arm 50 is positioned in opposed relationship to the lower arm and is electrically connected thereto. In the embodiment shown, a connecting pin 54 extends through the hub plate 36 to electrically connect the upper and lower arm 50 and 51. Thus, in this embodiment, the lower arm 51 is in sliding contact with the resistance band 12 while the upper arm 50 is in sliding contact with the underside 43 of the cover element C. lt can thus be seen that the electrical circuitry is similar to the preferred illustration embodiment since the electrical path is from the lower arm 51 to the upper arm 50 and thence to the cover element C and outwardly to the lead element 32. By means of the alternative embodiment, the adjusting shaft 38 is electrically insulated.
It can be seen from the foregoing that the cover element C and the device proper can be potted or electrically insulated. In one embodiment a mass of insulating material suchfas epoxy resin is utilized to seal the arcuate segment removed from the side wall 42 of the cover element C to thus hermetically seal the device when the hub screw is also hermetically sealed. The cover element C which is electrically charged can also be insulated by covering its outer surface with a layer of insulating material such as epoxy resin. From the foregoing, it can also be seen that the variable resistance of the device can be altered by various variable factors. Namely, the resistance of the resistance band 12 can be varied by varying the thickness or cross-sectional area of the band or by varying the material from which the band is formed.
Thus, what has been described, is an improved miniaturized potentiometer or variable resistor which is rugged and simple in construction but which is nevertheless, eX- tremely accurate and reliable in use,
What is claimed is:
1. A miniaturized potentiometer or variable resistor which includes: a body wafer of electrically insulating material; a resistance band of electrically conductive material formed upon a surface of said body wafer, said band being formed along a first radius through a length of less than 360 such that the ends thereof are spaced apart; first and second electrical lead elements electrically connected to opposed ends of said resistance band; a hub element of electrically insulative material rotatably mounted upon said body wafer, said hub element including a hub plate of electrically insulative material positioned parallel to but spaced from said body wafer; a irst wiper arm afxed to said hub plate at the side thereof prbximate said body wafer in sliding electrical contact with said resistance band, a second wiper arm allixed to said hub plate at the opposite side thereof, said lirst and second wiper arms being electrically connected; a cylindrical cover element having a closed outer end, said cover element being aflixedto said body wafer surrounding said resistance band, said second wiper arm being in electrical sliding contact with said outer end of said cover element, an electrical lead electrically connected to said cover element whereby rotation of the hub element varies the resistance of a circuit extending from one end of said resistance band through said wiper arm to said cover and from said cover to said second electrical lead.
2. A miniaturized potentiometer or variable resistor which includes: a body wafer of electrically insulating material, said body wafer having a substantially planar surface thereon, a rst band of electrically conductive material formed upon said planar surface, said lirst band being formed along a lirst radius through a length of less than 360 suchthat the ends thereof are spaced apart; lirst and second electrical lead elements electrically connected to opposed ends of said first band; a second arcu-y ate band formed on said planar surface at a second radius greater than said rst radius; a cover element aixed to said body wafer along said second band, said cover element being formed of electrically conductive material and having a closed upper end; a third electrical lead electrically connected to said second band; a hub element positioned between said cover element and said surface, said hub element being formed of electrically conductive material, said hub element being in electrical contact with said cover element and spaced from said first band, a wiper arm ailixed to said hub element in electrical Contact with said rst band,y said hub element being rotatable within said cover element to vary the contact position of said wiper arm along said first band.
3. A miniaturized potentiometer or variable resistor comprising: a body wafer of electrically insulating material, said body wafer having a substantially planar surface, said wafer dening a circular opening therethrough; a lirst metallic resistance band formed on said surface at a first radius substantially greater than the radius of said opening and concentric with respect to said opening, said first band having a length less than 360 such that the ends thereof are spaced apart, rst and second electrically conductive paths on said surface extending from the respective ends of said first band to anedge of saidbody wafer; a second metallic aixing band formed on said surface spaced from and concentric with said iirst band, said second band being of less circumferential extent than said first band with opposite ends of said second f band spaced from said conductive paths, a third electricallyconductive path extending from said second band to another edge of said body wafer; a cover element of electrically conductive material, said cover element being substantially cylindrical with an upstanding arcuate side wall of substantially equal circumferential extent as said second band aiiixed to said second band, said cover element having a closed end wall substantially parallel to said planar surface; a hub element of electrically conductive material positioned between said cover element end wall and said planar surface, said hub element having a shaft portion extending into and rotatable within said opening through said body wafer, a rst bearing surface on said hub element in bearing contact with said planar surface, said first bearing surface having a radius less than the inside radius of said iirst band, saidy hub element including a hub plate extending outwardly to a radius substantially less than the inside radius of said cover element and substantially greater than the radius of said rst band, said hub plate having an inner surface spaced from and substantially parallel to said rst band, the opposite surface of said hub plate of said hub element being in electrical contact with said closed end of said cover element; and a wiper arm connected to said hub plate in electrical sliding contact with said first band, said hub element being rotatable within said cover element to Vary the contact point of said wiper arm along said first band.
References Cited in the file of this patent UNITED STATES PATENTS