US3701070A

US3701070A - Wormgear actuated potentiometer

Info

Publication number: US3701070A
Application number: US190012A
Authority: US
Inventors: Kenneth B Baldwin; Ronald D Sullivan
Original assignee: Bourns Inc
Current assignee: Bourns Inc
Priority date: 1971-10-18
Filing date: 1971-10-18
Publication date: 1972-10-24
Anticipated expiration: 1989-10-24
Also published as: FR2156524A1; JPS4862470A; DE2159399A1

Abstract

An exceptionally efficient inexpensive miniature wormscrew potentiometer in which three dual-purpose conductors are embedded intermediate their ends in one of two housing members, and positioned to brush respectively upon arcuate or circular conductors and an arcuate resistance element that are carried upon a rotor interlocked with a drive plate which is driven by a wormwheel whose teeth are engaged with a wormscrew that is seated, with the rotor, in a second housing member.

Description

United States Patent Baldwin et al. 1 Oct. 24, 1972 [541 WORMGEAR ACTUATED 3,596,223 7/1971 Stuckey et al. ..338/174 POTENTIOMETER 3,531,755 9/1970 Michik ..338/ 162 [72] Inventors: Kenneth Baldwin, Corona; 2,886,681 5/1959 Boums et a1 ..338/ 180 3,599,141 8/1971 Hildreth et a1 ..338/180 Ronald D. Sullivan, Riverside, both 3,626,351 12/1971 Schoettly ..338/162 of Calif.

[ Assigneel 39111115, 1119- Primary Examiner-Richard B. Wilkinson [22] Filed: Oct 18, 1971 Assistant Examiner-Stanley J. Witkowski Att0rney-William G. Becker [211 Appl. No.: 190,012

[57] ABSTRACT [52] U.S. Cl. ..338/162, 338/174, 338/180, 1 An exceptionally efficiem inexpensive miniature [51] I t Cl 3 worrnscrew potentiometer in which three dual-purn c pose conductors are embedded intermediate their of 1, I ends in one of two housing members and positioned 338/150 to brush respectively upon arcuate or circular conduc- 6 R f ed tors and an arcuate resistance element that are carried 1 e erences upon a rotor interlocked with a drive plate which is UNITED STATES PATENTS driven by a wormwheel whose teeth are engaged with a wormscrew that isseated, with the rotor, in a second 2,887,554 5/1959 Smith et a1 ..338/DIG. 1 housing member r 3,522,572 8/1970 Michik et a1 ..338/D1G. 1 3,576,510 4/1971 Bruder ..'..338/150 5 Claims, 13 Drawing Figures PATENTEDncI 24 1912 SHEET 1 [IF 2 CROSS-REFERENCE TO ANOTHER DISCLOSURE BRIEF SUMMARY OF THE INVENTION a. The Prior Art Wormgear actuated potentiometers, commonly referred to by the acronym WGAPs, are well known in the potentiometer art. Typical examples are illustrated in US. Pat. Nos.' 2,880,293; Re 25,412; 3,054,077; 3,059,200; 3,096,498; 3,099,810; 3,108,245; 3,124,778; 3,127,583; 3,242,450; 3,242,451; and 3,235,827. In general, such prior art potentiometers comprise a base upon which is mounted a resistance element, first and second elementterminals secured in the base and the inner ends of which are electrically connected to the element; a wormwheel; a rotary contact device with a resilient contact disposed to wipe along the extent of the element; a third terminal and means connecting the third terminal to the rotary. contact device; and a .wormscrew arranged to rotate the wormwheel to move the contact along the element. The operating instrumentalities are enclosed in a cavity formed by thebase and one or more other housing members such as a cover. Such prior art WGAPs are characterized by requiring considerable manual manipulation of parts during assembly, including generally, delicate welding of terminal connections to the element ends, and delicate adjustment of the tension in the cantilever spring arm of the contact to achieve good electrical contact with minimum wearing of the element.

b. The Present Invention Herein is disclosed a WGAP which greatly minimizes delicate assembly operations such as the noted welding operations and adjustment of contact tension to accommodate dimensional differences inherent in parts made with allowable tolerances. The potentiometer comprises an insulation cover member which has molded therein intermediate portions of three spaced apart conductive members whose exterior ends form respective electric terminals and whose interior ends form respective contacts disposed for automatic engagement with respective elements carried by an insulation rotor. The contacts are mechanically positioned for attainment of a selected desired contact pressure on the rotor-carried elements, and such pressure is assured by engagement of the element-carrying surface of the rotor with a bearing surface on the cover member that is precisely located relative to the contacts. By use of integral contact-and-terrninal members that are precisely embedded in the cover during formation of the latter by molding, all necessity for welding, soldering or brazing of internal connections is obviated, and considerable improvement in uniformity of potentiometers is attained. A flat-surface arcuate resistance element, such as one of the cermet type or of composition, it utilized; and since metallic-film terminations are conventional with such elements, the arcuate or circular conductors'on the rotor make no significant difference in cost of the instrument, being naught more than extensions of the conductive terminations of the resistance element.

The element-carrying rotor is held against or in con tact with the bearing surface of the housing cover, and against the three cover'carried contacts, by a resilient driving plate which concurrently serves also as a means for transferring rotational torque to the rotor from a wormwheel. The driving plate, while effecting a posi tive driving action upon the rotor, is provided with means permitting slippage in event the rotor is stopped at either end of its normal travel. The driving plate is keyed to the rotor, and is supported along its periphery by a wormwheel. The latter rotates about a gudgeon formed as an integral part of the floor of the principal housing member, herein called the base. The base is molded of thermoplastic material, and comprises walls forming a generally circular cavity in which the rotor, driving plate and wormwheel are disposed, and from an inner wall of which a stop abutment protrudes. The stop abutment limits rotational travel of the rotor, the latter being formed with a complementary stop that incident to continued rotation in either direction comes into collision with the stop abutment. The thermoplastic base is formed with energy-concentrating sharp-edged ridge means which under influence of pressure and ultrasonic vibration melt and fuse with the contacting surface of the housing cover to thereby concurrently unite the housing base and cover into a unitary integral housing, and seal the housing against ingress of foreign material.

The wormwheel is engaged with and driven by a wormscrew that is rotatably seated at its inner end in a recess-bore in the base, and adjacent its outer end in a larger coaxial bore, with a head or driving end exposed outside the base for engagement by a driving tool. Adjacent the head, and within the larger bore, the wormscrew is formed with a tapered section, preferably of conic-section configuration, terminating in a sharply defined shoulder. The disposition and arrangement is such that the wormscrew is forcibly pressed into place in the coaxial bores, with its threaded central section exposed in the housing cavity for coaction with the wormwheel. The conical section is of slightly larger diameter than the bore into which it is pressed, and thus the material of the housing base is expanded and closely grips the wormscrew adjacent the shoulder of the latter. Hence the bore is effectively sealed, and the shoulder strongly resists any possible forces tending to expel or withdraw the screw from the bores. Thus the screwshaft is effectively locked in position in the potentiometer housing without the necessity for the conventional pin or clip means of prior art constructions.

The preceding brief summary of the invention makes it evident that a principal object of the invention is to provide general improvements in construction of WGAPs whereby the cost thereof is reduced. Another object is to provide a WGAP of improved performance. Another object is to provide means in a WGAP for concurrently sealing and locking the wormscrew in place, without use of O-ring of like seals and without the use of clips or pins. Another object of the invention is to reduce the number of parts comprised in WGAP. Another object is to simplify the construction of a WGAP. Another object of the invention is to eliminate soldered or like electrical connections in a WGAP. Other objects and advantages of the invention are set references to the appended drawings forming part of this specification.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a pictorial representation of an exemplary preferred potentiometer according to the invention, with portions broken away to show details, the drawing being to no particular scale;

FIG. 2 is a bottom view, to reduced scale, of the potentiometerdepicted in FIG. 1;

FIG. 3 is'a sectional viewof structure depicted in FIGS. 1 and 2, to an arbitrary scale, the sectioning being as indicated by directors 3-3 in FIG. 2;

FIG. 4 is a view of the housing base shown in FIG. 1, with a portion broken away and with the self-sealing and self-locking wormscrew in operative position;

FIG. 4a is a fragmentary sectional view showing a structural detail;

FIG. 5 is a plan view of the preferred wormscrew of the exemplary potentiometer;

FIG. 6 is a view of the housing cap or cover as molded and prior to separation of terminals and deflection or bending of contact limbs;

FIG. 7 is a plan view of the wormwheel of the potentiometer shown in FIG. 1 with a portion broken away;

FIG. 8 is a plan view of the element-bearing rotor of the potentiometer depicted in FIG. 1;

FIG. 9 is a side view of the rotor depicted in ,FIG. 8; FIG. 10 is a bottom view of the rotor depicted in FIG.

FIG. 1 l is a plan view of a resilient driving plate used 'in the potentiometer shown in FIG. 1; and

FIG. 12 is a sectional viewof the driving plate, the sectioning being as indicated by indicators 12-12 in FIG. 11. v

DETAILED DESCRIPTION OF THE INVENTION In FIG. 1 the assembled complete exemplary potentiometer is denoted by number 20. Portions of components are broken away to show details of construction and arrangement of components. Principal components comprise a housing which is composed of a base 22 and a cover 24, a specially formed wormscrew 26, rotary means which comprise a wormwheel 28, a driving plate 30 and a flat-surfaced rotor 32, and a set of electric conductors which are embedded at their mid portions in cover 24 and the exterior ends of which serve as terminals T1, T2 and T3 and the interior ends of which form contact means comprising contacts C1, C2 and C3.

The base 22 is molded of thermoplastic insulative material such as nylon or other synthetic resin, and is formed as a generally square block presenting a cuplike cavity 34 (FIG. 3) with an upstanding cylindrical boss 22b at the bottom of the cavity, and with a bore 220 extending from the cavity to the exterior of the base. The base is further molded with upstanding sharp-edge ridges 22r and 22s (FIG. 4), the former of which is circular and is disposed on the upper face of the base around the cavity 34. The ridges are adapted to absorb ultrasonic-vibration energy applied through the cover 24 by an ultrasonic vibratory tool, and to thereby melt and fuse the base and cover into a unitary housing in which the cavity 34 becomes a closed chamber in which the wormwheel, driving plate and rotor are housed.

The wormscrew 26 (FIG. 5) is formed with a cylindrical inner end portion 26a dimensioned to be received for rotation in a blind recess 22y (FIG. 4) formed as a coaxial extension of bore 220 in base 22. Further the wormscrew is formed intermediate its ends with a screw thread 26t, and at its outer end with a head 26h adapted for coaction with a driving tool, e.g., a screwdriver. Between the screw thread and the head, the screw is produced with a cylindrical portion 260 that is interrupted intermediate its ends by a tapered section 26c, the smaller end of which merges gently with the inner end of the cylindrical portion and the larger end of which terminates abruptly to provide a sharply defined shoulder 26s that is spaced inwardly from the inner annular face 26f of the wormscrew. The cylindrical portion 260 adjacent the screw thread is produced to be of the same diameter as bore 22c in base 22. Thus the wormscrew 26 must be forcefully pressed or driven into operative position in base 22, with the slightly elastic material of the base yielding to the increasing diameter of the tapered portion 260' and 1 elastically closing behind should 26s as the latter moves into the bore, as indicated in FIG. 4. Thus the shoulder 26s serves as a catch, the material of the base closing around the outer cylindrical portion of the wormscrew adjacent head 26h and pressing against the end face of the shoulder and restraining the wormscrew from outward movement. Thus the wormscrew concurrently seals the bore and is firmly retained in operative position without use of retainer pin or clip means.

A wormwheel 2b (FIG. 7) has a central bore 28b dimensioned for a bearing fit on boss 2212 (FIG. 3) of base 22, and is dimensioned for gearing engagement with wormscrew 26 as indicated in FIG. I. The wormwheel is provided with a serrated upper face, the serrations or teeth 28: being spaced for coaction with a -set of radial deformations 30d (FIGS. 11 and 12) formed on a resilient driving plate 30. As is indicated in the latter figures, the driving plate is formed with a convex outer flange 30f in which the deformations are formed; and 'a measure of axial (up and down) resilience is provided by a series of radial slots 30s. A shaped central aperture 300 is formed in the driving plate whereby torque transmitted from wormwheel 28 to the plate via serrations 282 and deformations 30d may be transmitted to the rotor 32.

As is indicated in FIGS. 9 and 10, rotor 32 is provided with a shaped boss or key 32k that is dimensioned to be received in aperture 30a of the driving plate with a driving fit. In this particular exemplary embodiment the aperture and key are of square configuration, but it is evident that other complementary configurations may be used. The flat upper face of rotor 32 is adapted for bearing engagement on complementary arcuate bearing surfaces 24b (FIG. 6) formed on the inner face of cover 24, as indicated in FIG. 3. The dimensions and arrangement are such that driving plate 30 is slightly stressed whereby the rotor face is maintained in contact with the bearing surfaces.

formed, and they are further interconnected by webs Tx and Ty,

(FIG. 6) that are sheared away during final assembly procedures. Further, during the molding of cover 24, the protruding limbs or arms of the contacts stand upright from the inner surface of the cover, as indicated in FIG. 6, and are bent down at an acute angle to the plane of the terminals as indicated in FIG. 3. The bending is accurately performed by die means, with the consequence that when the cover is inverted and as sembled onto base 22 the resilient arms of the contacts urge the latter onto respective rotor-carried electrical elements with a predetermined force that is the same for the contacts of all of a large number of potentiometers serially manufactured by the same machinery. The mode of manufacture, in respect of formation of the embedded terminal-contact members and assembly of the cover 24 to base 22 maybe substantially the same as that described in the aforementioned co-pending disclosure, to which reference may. be had as may be necessary.

The rotor 32, of general configuration illustrated in FIGS. 8, 9 and 10, is provided on its upper flat face with generally arcuate resistive and conductive elements including an outer termination conductor 32a, an inner termination conductor 32b, and a resistance element 32r that may be of the-type termed cermet or may be of conductive plastic or of similar character. The resistive member, element 32r, is accurately electrically terminated at its first and second electrical ends by respective

radially extending continuations

32a and 32b of the

arcuate conductors

32a and 32b as indicated in FIG. 8, by having its physical ends overlaid or underlaid by the radially extending portions of the conductors, as will be understood by artisans in the resistor art. Thearcuate resistive element 32r extends over an arc of less than 360, whereas for convenience the arcuate conductive elements 32a and 3212 are formed to extend over arcs of 360 and the latter is for convenience extended over the entire central area of the upper face of the rotor. The resistive element 32)" is accurately spaced, as are the termination tabs formed by

continuations

32a and 32b, relative to a stop member 32s (FIGS. 9 and 10) that preferably is produced as an integral part of the insulative rotor 32. The stop member coacts with a stop abutment 22q (FIGS. 4 and 40) formed along the inner wall of base 22, to restrict rotation of the rotor to an angular traverse equal to or slightly greater than the larger arc angle between the electrical ends of element 32r.

The arrangement and nature of the parts forming the drive train including wormscrew 26, wormwheel 28, driving plate 30 and rotor 32 is such that the rotor receives torque from the driving plate 30 to which it is keyed, and similarly torque applied to the wormscrew is positively transmitted to the wormwheel. The wormwheel and driving plate are normally positively interengaged by way of serrations 28: and deformations 30d for positive transmission of torque exerted by the wormwheel. Thus the rotor is normally rotated in response to rotation of the wormscrew, to cause the resistance element to traverse past contact C2 and thereby vary the resistance exhibited between terminal T2 and either of the other two terminals. However, if wormscrew 26 is overdriven, stop 32s on the rotor collides with stop abutment 22q and the rotor is arrested. If overdriving continues, deformations 30d on the driving plate act as cams and ride over the teeth or ridges of serrations 282; thus stripping of gear teeth or other breaking of parts is avoided. It is evident, as illustrated in FIG. 1, that contact C1 engages inner arcuate conductor 32b, contact C2 engages arcuate resistance element 32r, and contact C3 engages outer arcuate conductor 32a. In the exemplary embodiment illustrated, contact C2 is formed as three independently movable contacts and arms all integral with terminal T2, whereby contact-resistance variation (CRV) is minimized as is well understood in the art. As is evident considerable improvement in uniformity of product and in reduction of cost of parts and of assembly are attained by virtue of the construction of the wormscrew and rotor 32 with the three elements mounted thereon,

and by the integral contact-terminal members and the positive and uniform spacing of the rotor-carried elements relative to the free ends of the several contacts. Thus it is clear that the aforementioned objects of the invention have been fully attained.

Having described in detail a preferred by exemplary embodiment of the invention, we claim:

1. A wormgear actuated potentiometer comprising:

housing means providing a closed chamber and having a bore extending from the exterior of the chamber to the interior of the housing means;

a plurality of electrical conductors extending into said chamber and forming at the inner free ends thereof respective contacts, and respective terminals outside said housing means and each electrically connected to a respective one of said contacts;

a wormscrew rotatable in said housing means in said bore and having a thread exposed in said chamber;

rotary means supported for rotation in said housing means in said chamber and including a rotor;

an arcuate resistance element and first and second arcuate film conductors on said rotor, said conductors being electrically connected with respective ends of said resistance element, and each of said film conductors and said resistance element engaged by a respective one of said contacts; a wormwheel engaging said wormscrew; and a resilient driving plate keyed to said rotor and frictionally engaging said wormwheel to transmit driving torque from the wormwheel to the rotor, whereby resistance exhibited between the contact engaging said element and either of the other contact is varied in response to rotation of said wormscrew.

2. A potentiometer as defined in claim 1, in which said plurality of conductors includes three conductive members each having an intermediate portion embedded in said housing means and mutually insulated thereby.

3. A potentiometer as defined in claim 1, in which said housing means comprises a base and a cover and in which each of said electrical conductors is an integral terminal-and-contact member having a portion intermediate its ends embedded in said cover with its outer end protruding from said cover to form a terminal and its inner end extending into said chamber and terminating in one of said contacts, said contacts being so arranged as to be brought into contact with a respective one of said arcuate film conductors and element incident to placement of said cover on said base, whereby to facilitate construction of said potentiometer and minimize the cost thereof.

4. A potentiometer as defined in claim 1, in which said cover presents in said chamber an arcuate bearing surface and in which said rotor and arcuate film conductors present a surface complementary to said bearing surface and engaged therewith, whereby said con tacts engage said element and film conductors with uniform determined force.

5, A potentiometer as defined in claim 1 wherein said 8 housing means is of a material which is somewhat elastic and deformable and said wormscrew includes a cylindrical section and a tapered section both disposed in said bore, the largest diameter of said tapered section being larger than the diameter of said bore and forming an abrupt shoulder, whereby material of said housing means around said shoulder is elastically expanded and deformed to form a complementary formation abutting and pressing against said shoulder to concurrently restrain said wormscrew against actual movement out of said bore and seal said bore against ingress of foreign material into said chamber.

Claims

1. A wormgear actuated potentiometer comprising: housing means providing a closed chamber and having a bore extending from the exterior of the chamber to the interior of the housing means; a plurality of electrical conductors extending into said chamber and forming at the inner free ends thereof respective contacts, and respective terminals outside said housing means and each electrically connected to a respective one of said contacts; a wormscrew rotatable in said housiNg means in said bore and having a thread exposed in said chamber; rotary means supported for rotation in said housing means in said chamber and including a rotor; an arcuate resistance element and first and second arcuate film conductors on said rotor, said conductors being electrically connected with respective ends of said resistance element, and each of said film conductors and said resistance element engaged by a respective one of said contacts; a wormwheel engaging said wormscrew; and a resilient driving plate keyed to said rotor and frictionally engaging said wormwheel to transmit driving torque from the wormwheel to the rotor, whereby resistance exhibited between the contact engaging said element and either of the other contact is varied in response to rotation of said wormscrew.

4. A potentiometer as defined in claim 1, in which said cover presents in said chamber an arcuate bearing surface and in which said rotor and arcuate film conductors present a surface complementary to said bearing surface and engaged therewith, whereby said contacts engage said element and film conductors with uniform determined force.

5. A potentiometer as defined in claim 1 wherein said housing means is of a material which is somewhat elastic and deformable and said wormscrew includes a cylindrical section and a tapered section both disposed in said bore, the largest diameter of said tapered section being larger than the diameter of said bore and forming an abrupt shoulder, whereby material of said housing means around said shoulder is elastically expanded and deformed to form a complementary formation abutting and pressing against said shoulder to concurrently restrain said wormscrew against actual movement out of said bore and seal said bore against ingress of foreign material into said chamber.