US 3576512 A
Description (OCR text may contain errors)
United States Patent lnventor Robert D. Michik Walnut, Calif. Appl. No. 879,050 Filed Nov. 24, 1969 Patented Apr. 27, 1971 Assignee Bourns, Inc.
POTENTIOMETER 5 Claims, 11 Drawing Figs.
US. Cl 338/174, 338/ 162 Int. Cl 1101c 9/00 FieldofSearch 338/162, 164,171,174,175,166,167,168,169,170,172, 173
 References Cited UNITED STATES PATENTS 3,235,827 2/1966 Baker 338/162 3,235,828 2/1966 Baker 338/174 I 3,378,802 4/1968 Mishler et a1. 338/174 Primary Examiner-Lewis H. Myers Assistant Examiner-D. A. Tone Attorney-Fritz B. Peterson ABSTRACT: Ratcheting geared-drive simple potentiometer characterized by minimum number of parts of inexpensive materials and ease of assembly, the housing having a keyhole slot for insertion of a driving bevel pinion which is held in position by a contact-carrying driven bevel gear which is normally constrained to operational rotation about an operating axis defined by a tapered gudgeon which permits gear deflection and disengagement or slipping of gear teeth at the end of traverse of the potentiometer contact.
POTEN'I'IOMETER BRIEF SUMMARY OF THE INVENTION The potentiometer is of very small dimensions, optionally rectangular or cylindrical in configuration, but employs reduction gearing to'facilitate and improve precise setting and improve resolution while permitting ratcheting of the driving means. The potentiometer housing, comprising a molded housing body and a cover upon which resistive and currentretum elements are formed, provides an integral tapered gudgeon upon which a contact-carrying driven bevel gear is rotatably mounted. The driving means is in the form of a key or rotor whose outer end is arranged to be manually rotated and whose shank is confined in a keyhole slot and whose inner end comprises a driving bevel pinion which is effectively restrained by the driven gear to prevent exit of the shank from the confining slot. The bevels of the gears permit and induce axial translation or tilting of the driven gear on the gudgeon when the latter gear is arrested by engagement of stops incident to completion of a traverse of the contact along the arcuate resistance element. The resulting separation of the gears permits harmless slipping or ratcheting" of the pinion relative to the gear when attempt is made to overdrive the rotor. Thus damage to parts is avoided when the potentiometer is overdriven.
The driven gear may be stamped from a blank of conductive metal or alloy sheet and have integral lanced contact limbs and contacts, and an integral stop member. Alternatively, the driven gear may be of molded insulation to a face of which a conductive contact member is secured. In either case, it
plate of insulation such as ceramic, in which are provided electric terminals connected to respective ends of the resistive element and the conductive collector. The resistive and return conductor elements are formed from cerrnet and conductive inks by firing, in known manner. The cover is disposed against some of the aforementioned surfaces, or ledges; and it is retained in place by adhesive sealant which effects sealing of the principal opening in the housing. The other opening in the housing, the aforementioned keyhole slot, is preferably sealed by means of an O-ring seal disposed between the driving head of the driving rotor and a face of the housing body.
The preferred exemplary embodiment of the novel potentiometer is illustrated in the accompanying drawings forming a part of this specification, together with modified forms of housings and driven bevel gears.
DESCRIPTION OF THE DRAWINGS FIG. 1 is a pictorial view, on a grossly enlarged scale, of a potentiometer according to the invention;
FIG. 2 is a top view of the potentiometer depicted in FIG. I, on a larger scale, with portions including a rotor head removed or broken away to show details of the keyhole opening and the O-ring seal;
FIG. 3 is a sectional view through the potentiometer depicted in FIGS. 1 and 2, the section being taken as indicated by indicators 3-3 in FIG. 2;
FIG. 4 is a pictorial view of an exemplary driving key or I rotor of potentiometers according to the invention, to no particular dimensional scale; FIG. 5 is a pictorial view of a driven contact-carrying bevel gear shown in section in FIG. 3, to a different scale;
FIGS. 6 and 7 are pictorial views of potentiometers according to the invention, using modified forms or shapes of housings;
FIG. 8 is a sectional view similar to FIG. 3, but illustrating a modified form of driven bevel'gear produced from conductive sheet metal and having integral contact members, and the housing having a modified form of gear-bearing gudgeon;
FIG. 9 is a sectional view of the potentiometer depicted in section in FIG. 8, the section being taken as indicated by indicators 9-9 in the latter drawing; and
FIGS. I0 and 11 are top and face views, respectively, of the driven bevel gear and integral contacts, shown in section in FIG. 8 and in plan in FIG. 9.
DETAILED DESCRIPTION In FIGS. 1 through 5, the exemplary potentiometer 20 is shown to comprise parts including: a housing body 22 of boxlike fonn of molded insulation; a cover 24 in which are secured first, second and third terminals 26a, 26b and 26c, respectively, and which cover carries an arcuate resistance element 28 and a platelike conductor 30, both arranged around an imaginary axis A; a driving key or rotor 32; and a driven contact-supporting gear member 34. The housing body 22 provides a shaped interior or chamber 22c into which extends a tapered gudgeon 223 that preferably is formed as an integral part of the body 22. Also extending into cavity 220 through akeyhole-shaped opening or aperture 22k in the floor or base of body 22 is the shank 32s (FIG. 3) and pinion 32p of the driving key or rotor 32. The disclike head 32h of the rotor is disposed in an open recess 22r (FIG. 1 and 3) formed in the upper (as shown) face of housing body 22. In the initial steps or stages of assembly of the potentiometer, the pinion 32p and shank 32s of the rotor 32 are inserted through the larger portion of the keyholeshaped aperture 22k, and the rotor is slid laterally to bring the shank 32s into the narrow slot of the aperture whereat the pinion cannot move axially out of the cavity and slot and the shank is provided with a bearing at the end of the slot. While the rotor is in that position, the driven gear 34 is moved into the cavity and seated on gudgeon 22g, thereby bringing the pinion into operative engagement with the internal teeth 342 of the driven gear and barring lateral movement or escape of the pinion and rotor. Thus the gear 34 serves to retain the rotor in the potentiometer without other or auxiliary retainer means, as long as the two gears are engaged.
The housing body 22 is further provided with an O-ring receiving groove formed in its exposed face in recess 22r, encircling the keyhole-shaped aperture and dimensioned for reception of an O-ring 36. Thus with the operating gearing FIGS. 3 and 5, has a gudgeon-receiving hole providing a bearing surface 34b of taper complementary to that of gudgeon 22g. The gear 34 also is provided with a stop 34s (FIG. 5) which is accommodated in an arcuate recess 22t (FIG. 3) formed in the housing body and coaxial with gudgeon 223. The arcuate recess terminates at an end wall, as at 22s (FIG. 2), to provide stop abutments effective to restrict rotational travel of the gear to an extent conforming to the arcuate extent of a resistive element presently described. As shown in FIG. 3, the gear further has affixed to its lower (as shown) face, as by adhesive or other conventional means, a resilient-limbed conductive contact device 38, an outer limb 38a of which has a contact or end that is disposed for brushing traverse along the thin arcuate filmlike resistive element 28. The other, .or inner, limb of the contact device comprises a contact or end that is disposed to resiliently wipe on the circular conductive return film or member 30.
The resistive element 28 and conductive return member 30 are supported upon a rigid plate that forms the cover 24, which is preferably of fired ceramic as previously noted. The assembly composed of members 24, 28, 30 and terminals 26a,
26b and 26c is commonly referred to as a terminated against, and be positioned by, one-or more ledges such as 22;:
(FIG. 3). When the cover is pressed into place against the ledges in the housing chamber, the resistive and conductive elements 28 and 30 are brought into engagement with, and resiliently stress, respective ones of the limbs of contact device 38. The cover is retained in place at the position depicted by means of adhesive applied to the outer faces of the ledges and/or by a sealant potting compound 40 applied over the exposed exterior of the cover as indicated in FIG. 3.
The driven bevel gear 34 is preferably also provided with a protruding pedestal 34p which is dimensioned to brush on an idle or otherwise unused portion of the surface of the cover between elements 28 and 30 as the gear rotates, whereby a positive limit oncompressive deformation of the resilient limbs of the contact member 38 is provided. The pedestal may be formed as a part of the gear structure by means of which the contact member 38 is secured to gear 34.
When the rotor 32 is rotated, the pinion 32p is effective to rotate gear 34 through a lesser angular extent of rotation, and to thereby cause the outer contact limb 38a to sweep over or brush along an extent of the arcuate resistive element 28. Thus the value of resistance exhibited between terminals 26a and 26b is varied. When the rotation is continued sufficiently, the stop 34s on the periphery of gear 34 is brought into contact with the end of slot or groove 22!, as at 22s (FIG. 2), and thus rotation of the driven gear is arrested. The dimensional arrangement of the parts is such that at the point of arrestment of the gear 34, the contact of limb 38a is at one or the other of the two ends of resistive element 28. At the other extreme of travel of stop 34s in groove 22t, the contact of limb 38a is at the other end of the resistive element. If rotation of the rotor is continued after rotation of the driven gear 34 is arrested, abnormal axial forces are generated between teeth of the pinion and those of gear 34, which forces cause slight tilting and/or deformation and axial movement of that portion of the gear diametrically opposite the pedestal 34p and displacement of the gear 34 on gudgeon 22g. As the gear moves in a generally axial direction away from the base of the gudgeon, the teeth of gear 34 in contact with pinion 32p are permitted to move away from the pinion to an extent permitting slipping of pinion teeth past teeth of the gear. That slipping or ratcheting action continues until overdriving of the rotor and pinion ceases. If the rotor is manually rotated, as by means of a screwdriver or like device engaged in the slot 32d in the face of the rotor, such overdriving will result in a sense-perceptible signal being produced which may warn the operator of the excessive and needles rotation. The described slipping of the gears occurs without damage to the parts due to the resilience of the gear 34 and due to the taper of the gudgeon and bearing 34b, which taper permits lateral shifting of gear 34 coincident with slight axial shift of the latter gear. Following any such overdrive of the rotor, rotation thereof in the opposite direction causes resumption of normal positions and operations of the moving parts.
In FIGS. 6 and 7 there are illustrated modified forms of the potentiometer construction previously described and wherein the movable parts are or may be substantially identical to or immaterially different from those of the previously described parts, but wherein the housings are of different shape. In FIG. 6, the potentiometer comprises a square boxlike housing body 22 with a keyholeshaped rotorreceiving aperture adjacent one corner thereof. The rotor 32' and other operating components are like their counterparts in potentiometer 20, but the spatial arrangement or placement of the pin terminals is slightly different. Similarly, in FIG. 7, the
'housing body is of cylindrical form and accommodates a 120 very similar to that described in connection with FIGS. I
through 5, but utilizing a slightly different gudgeon 122g and a metal driven bevel gear 134 having integral contact limbs. The
housing body 122 is'formed to provide a gudgeon surface 122s of nearly hemispherical configuration which is adapted to receive a complementary depression l34b (FIG. 10) formed in the center of the web of the cup-shaped bevel gear 134. The latter gear is fonned from a flat sheet of' ductile metal by stamping and lancing operations. It is formed with a bevel rim 134r of corrugated configuration, to provide teeth of an internal bevel gear. The teeth, such as 1341, are complementary to those of the bevel pinion 132p, as indicated in FIG. 9. The bevel pinion is formed on the lower or inner end of a key or rotor 132 that is otherwise substantially identical to previously described rotor 32. Rotor 132 is mounted for rotation in the slot end of a keyhole aperture 122k formed in the housing body 122 of the potentiometer, and is retained in place therein by gear 134. The gear 134 is formed with an upwardly protruding stop 134s which travels in an arcuate slot in the interior of the body 122 in a manner and for a purpose similar to those described in connection with stop 34s and slot 22! in potentiometer 26. The gear has lanced therefrom two sets of contact limbs, 134v and 134w which are disposed to contact with respective ones of the resistive element and return conductor provided on the inner face of the cover 124. In other respects, the construction is like that of potentiometer 22. When the rotor is overdriven, the abnormal forces generated by the teeth of pinion 132p on the teeth of gear I34 cause resilient deformation of contact limbs and concurrent deflection of the gear downwardly and laterally to relieve the gear teeth and permit the pinion teeth to slip past teeth of gear 134. Otherwise the action is the same as that previously described in connection with the principal embodiment of the potentiometer. The advantage of the embodiment depicted in FIGS. 8-11 is that the driven bevel gear and contacts may be of one-piece, integral construction which is'not only economical in very small potentiometers but also avoids necessity of assembling extremely small contact devices to a very small gear.
As is made evident by the preceding description, the invention 'is susceptible of variation as to physical form, and hence it is not restricted to the exact details of the illustrated presently preferred embodiment except as required by the appended claims.
l. A potentiometer comprising:
first means, including a housing providing an enclosed chamber, said first means providing a tapered gudgeon protruding into said chamber, said gudgeon providing a bearing surface and defining an axis of rotation;
second means, including a resistance element having an arcuate surface exposed in said chamber;
third means, including a bevel gear having a gear axis and a series of gear teeth arranged equidistant from the gear axis, and contact means including a contact movable along said arcuate surface by the gear, said contact means tending to urge said gear into coaxial bearing relation on said gudgeon, said gear, disposed on said gudgeon for rotation thereon with its gear axis coincident with said axis of rotation defined by the gudgeon; and
fourth means, including rotary driving means comprising a bevel pinion engaged with said bevel gear and arranged to exert abnormal axial and radial forces on said gear incident to arrestment of rotation of said gear while being driven by said pinion, whereby said gear is thereby displaced out of coaxial relationship with said gudgeon to permit slipping of teeth of the pinion past teeth of the gear to avoid damage to any of said means.
2. A potentiometer as defined in claim 1, in which said housing provides a keyhole opening into said chamber, and in which potentiometer said rotary driving means is in the form of a key having said pinion at one end, a driving head at the 3. A potentiometer as defined in claim 1, in which said bevel gear and said contact means are comprised in a single member of sheet metal.
and third means further including means restricting rotary movement of said gear in either direction to arcuate traverse less than 360 of rotation and to effect arresting of said gear at either extremity of said traverse as rotation of said pinion is continued, whereby movement of said contact off either end of said arcuate element is prevented.