US 3629777 A
Description (OCR text may contain errors)
United States Patent lnventors Robert J. De Long Temple City; Paul I. Gerwitz, West Covlna, both of Calif.
App]. No. 89,192
Filed Nov; 13, 1970 Patented Dec. 21, 1971 Assignee Spectral Electronics Corporation City of Industry, Calif.
END CLOSURE ARRANGEMENT FOR VARlABLE RESISTOR 6 Claims, 4 Drawing Figs.
US. Cl. 338/149, 3 38/ l 84 Int. Cl 1101: 5/02 Field of Search 338/149,
References Cited UNITED STATES PATENTS ABSTRACT: A potentiometer is provided having a cylindrical housing with an internal helical resistor groove having a heli cal resistance element disposed in the forward portion thereof. A rotor member having a resistance wiper element is disposed within the housing for contact with resistance element. A
' cylindrical end closure member having a raised external helical ridge thereon is threaded into the end portion of the helical resistor groove in the housing member. A rotor terminal pin is threaded radially into the housing member and through a radial aperture in the closure member to secure the closure member in a predetermined rotational relationship with the housing member and to align a stop shoulder on the closure with the housing member. A plurality of radially extending compression pads are formed on a forwardly facing shoulder of the closure member and engage a rearwardly facing Simon Ct a]. shoulder on the housing member to enable the closure 3,021,494 2/1962 Perter et a1. 338/ 14 member to be rotated to a precise predetermined relationship Gach et a1 the housing compensating for manufacturing tolerances in the fabrication of the housing and closure members.
5O |8 1Y-|- l9 IO 42 a o a I7 44 r l6 32 23-1: 33 l 3| II PATENTED nEc21 i871 3829-??? FIGI INVENTOR.
ROBERT J DE LONG 4 PAUL F. GERWlTZ ATTORNEY END CLOSURE ARRANGEMENT FOR VARIABLE RESISTOR BACKGROUND OF THE INVENTION This invention relates to variable resistors and is especially adapted for use with multiturn potentiometers of the type having a helical resistance element'disposed in an internal helical groove in the potentiometer housing. It is desirable to provide a closure member for such resistors in order to inhibit the entrance of moisture and dirt into the resistor housing which might cause a malfunction. Previously it has been common to secure an end closure member by. means of a band clamp, set screws or by attaching the closure to the housing with headed screws. Such arrangements are undesirably expensive, require a multiplicity of parts, and often require special care to properly align the closure member with the housing particularly when a stop member is incorporated with the closure to limit rotation of the rotor in the completed resistor. It is, therefore, a principal feature of this invention to provide a variable resistor having an end closure member which is relatively inexpensive to manufacture and which is easily assembled in a predetermined relationship with the housing.
SUMMARY OF THE INVENTION In accordance with the preferred embodiment of this invention, a variable resistor is provided which includes a housing member, a rotor member disposed within the housing member, and a closure member. A helical resistor groove if formed in the interior of the housing member and a resistance element is disposed within the forward portion of the groove. A closure member is formed with an exterior screwthread which is threadably engaged with the rearward portion of the groove in the housing. A suitable means, such as a terminal pin extending radially through the housing into the closure member may be provided for securing the closure member in a predetermined rotational relation with the housing.
BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a cross-sectional view through. a variable resistor having a closure member secured therewith in accordance with this invention;
FIG. 2 is a perspective view of the end closure;
FIG. 3 is a perspective view of the housing member showing the rotor member assembled therewith; and
FIG. 4 is a fragmentary cross-sectional view taken on line lV-IV ofFlG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT Referring particularly to the drawings variable resistor 10, which in the preferred embodiment is a potentiometer, comprises a housing member 11, a rotor member 12, and a closure member 13. While the invention will be particularly described with reference to a multiturn potentiometer, of the wire wound type, it will be apparent that the invention is applicable to single or multiturn resistors and potentiometers of either the wire or nonwire wound type which utilize a resistance element disposed in a helical resistor groove.
Housing member 11 is hollow and has a generally cylindrical interior surface with a helical resistor groove 15 formed thereon. A helical wire wound resistance element 16 is disposed in one end of groove 15. The resistance element may comprise a helical core 17 having a fine resistance wire 16 wrapped about the core. A pair of terminal elements 18 and 19 extend radially through housing 11 for 'making electrical contact with the desired electrical ends of element 16 from the exterior of housing 11. Resistance element 16 occupies the forward portion of helical groove 15 leaving an unoccupied free end portion 20 of the groove adjacent the open rearward end of housing 11. The forward end of housing 11 is preferably closed by an integral radially extending end portion 21 having a cylindrically apertured bushing 22 therein which forms a bearing for rotor member 12. Housing member 11 is also provided with a rearwardly facing radially extending shoulder 25 which is recessed in the housing and may conveniently be located adjacent the free end of groove 15.
Rotor member 12 may be of any type which is arranged to provide electrical contact with the resistance element. As illustrated in the drawing, rotor member 12 may comprise a body securely mounted on an axially extending shaft 31 which projects through aperture 22 of housing 11 in bearing relation therewith. Body 30 is provided with an axially extending slot in which is mounted reciprocating slider element 32 carrying electrically conductive wiper element 33. A wiper element 33 is electrically connected by flexible conductor wire 34 to slip ring 35 mounted at the rear end of body 30. Preferably shaft 31 is made of metal and body 30 is made of a suitable insulating plastic which insulates slip ring 35 from the shaft. Wiper element 33 electrically contacts resistance element 16. Rotation of shaft 31 causes body 30, slider 32 and wiper element 33 to rotate with the shaft. Slider 32 is formed with an outwardly facing semicircular groove having ears which closely conform to the inner surface of resistance element 16 so that rotation of shaft 31 causes the slider to follow the helical path of the resistance element. It will be appreciated that slider 32 rotates with the rotor body and slides axially in the groove therein in order to enable wiper element 33 to make continuous electrical contact with the turns of the resistance element to provide a desired resistance by rotation of shaft 31.
A wiper terminal assembly 40 is provided for making electrical contact with the resistance element through wiper element 33 from the exterior of housing 11. Wiper terminal assembly 40 includes solder lug 41 secured under slotted head of a screw-threaded terminal pin 42. A wiper brush 43 extends from the shank of terminal pin 42 into electrical contact with slip ring 35 which in turn is connected to wiper element 33 by flexible wire 34. Terminal pin 42 is threaded into threaded radial aperture 45 adjacent the open rear end of housing 11. A frustoconical cam surface 44 is provided on terminal pin 42 between brush 43 and the unthreaded portion of the shank.
Closure member 13 is preferably cylindrical in shape and of an exterior diameter which closely conforms to the interior diameter of recess 24 in housing 11. A shoulder 55 extends radially inwardly from the outer surface of closure member 13 and is formed with a plurality of axially extending, resilient, radial compression ribs 56 shown in FIG. 2. Closure member 13 is also formed with a radially outwardly extending helical screw thread ridge 50 having the same pitch as that of helical resistor groove 15. The end of closure member 13 is provided with an axially extending, coaxially aligned, cylindrical recess 59 which is adapted to form a bearing journal for the rearward end of shaft 31. A radially inwardly extending stop shoulder 62 may be molded into the preferably synthetic resin material of closure member 13. Stop shoulder 62 is adapted to engage slider 32 of rotor member 12 to limit rotation of shaft 31 when the slider has reached the end of the last turn of the resistance element. A radially extending aperture 51 is formed in closure member 13 at a location relative to stop shoulder 62 such that when the closure member is assembled with housing 11 the stop shoulder is located at the desired angular position to prevent rotation of shaft 31 when wiper element 33 has reached the end of helical resistance element 16. Preferably, aperture 51 is axially elongated and has tapered axial walls. Preferably the entire closure member is molded from a synthetic resin material. The material of at least ribs 56 should have some resilience so that ribs 56 may deform to provide axial accommodation and thereby allow accurate rotational alignment of closure 13 with body 11 in spite of dimensional variations due to manufacturing tolerances.
In accordance with this invention, the resistor is assembled by securing helical resistance element 16 in the forward end of resistor groove 15, preferably with a suitable adhesive. Groove 15 is of such axial length that the free rearward end portion 20 has one turn left unoccupied by the resistance element. Terminals 18 and 19 are electrically connected to the desired ends of resistance element 16. Rotor member 12 is assembled with the forward portion of shaft 31 projecting from the forward portion 21 of housing 11. Care is taken to assure that wiper element 33 and slider 32 are properly positioned so that the wiper rides on the radially inner surface of resistance element l6 and the slider ears are captured so that they follow the resistor turns.
Closure member 13 is inserted into housing 11 and rotated until screw thread 50 on the forward end of the closure member engages the free end portion of resistor groove 15 on housing 11. By convention, clockwise rotation of shaft 31 causes wiper 33 to be advanced toward the forward end of housing 11 and consequently as viewed from the back of the housing closure member 13 is rotated in a counterclockwise direction to assemble it into the housing. Closure member 13 is threadably advanced into housing 11 until radial aperture 51 therein is visually aligned with the corresponding radial aperture 45 in housing 11'. Radial aperture 51 may be slightly axially elongated as shown in the drawings to form an axially extending slot which assures alignment with aperture 45 when the parts are in correct rotational alignment. The parts are so dimensioned that resilient compression ribs 56 are somewhat compressed throughout the range of manufacturing tolerances anticipated in the molded parts when the radial apertures are in alignment with each other. The compression of compression ribs 56 against rearwardly facing shoulder on housing 11 provides a relatively tight frictional fit between the cover member and the housing while allowing rotation of the closure member to the precise angular position desired in spite of dimensional variations in the parts.
Rotor terminal assembly 40 is then inserted through aligned radial apertures 45 and 51 so that brush 43 engages slip ring and makes electrical contact therewith. As shown in FIG. 4, the transverse dimension between the axially extending sides of radial aperture 51 is preferably sufficiently narrow to provide an interference fit with the sides of the smooth unthreaded shank portion of terminal pin 42. Axial slot 51 may be formed in either member and the other member threaded to receive terminal pin 40. As the terminal pin is screwed into the housing by means of a screwdriver engagement with a screwdriver slot in the head of the pin, conical cam surface 44 engages the narrowly spaced axial edges of radial aperture 51 and cams the closure member into precisely predetermined rotational position with respect to body 11 thereby precisely radially or angularly positioning stop shoulder 62 for engagement with wiper member 33 at the proper rotational position of shaft 31. The rear end of shaft 31 slides into recess 59 in closure member 13 to provide a rear bearing journal for rotor member 12.
While it is preferred to utilize terminal pin 42 as a means for securing the closure member with the housing to obtain precise alignment thereof in the final assembly, various other means may be alternately used. For example, notches may be heat formed in the closure member or the housing after assembly to prevent unscrewing of the closure member from the housing or other means may be provided to prevent unscrewing of the closure. The closure member could likewise be made as the forward end of the resistor housing or both ends may be closed by a closure member if desired. Furthen'nore, a number of ganged resistor housings can be assembled wherein the closure member of one resistor forms the housing member of a succeeding resistor.
A resistor made in accordance with this invention has the advantage of being relatively inexpensive to manufacture, requires few parts, and is easily assembled without requiring great skill.
After assembly, the members are securely maintained in precisely predetermined relation with each other and allowance is made for dimensional tolerances occasioned by molding ormachining of the parts.
While for purposes of illustration, a preferred embodiment of this invention has been described, the invention may be otherwise embodied within the scope of the following claims.
B. a rotor member assembled with said housing, said rotor member carrying a wiper element disposed in the housing for making electrical engagement with said resistance element, said rotor member including adjustment means for adjusting the position of the wiper element from the exterior of said housing; and wiper terminal means for making electrical connection with said wiper element from the exterior of said housing;
C. a closure member closing said open end of the housing, said closure member having a helical screw thread ridge formed thereon, the helical screw thread ridge being threadably engaged with the free end portion of the helical groove on said housing to retain the closure member on the housing member; and
D..said housing member having a radially extending aperture therein, said closure member having a radially extending aperture therein which is radially aligned with the aperture in said housing, said wiper terminal means extending through said radical apertures and into electrical contact with said wiper element for forming both an electrical terminal and a means for securing the closure member in fixed rotational engagement with said housing member.
2. A variable resistor as defined in claim 1, one of said radially extending apertures comprising an axially extending slot whereby said apertures are aligned with each other at a predetermined rotational relation between said members, the other of said members being threaded to receive a threaded terminal pin, said wiper terminal means comprising a threaded pin having a cam surface thereon engageable with the axially extending sides of said slot during assembly of the resistor, said terminal pin being threaded into said radially extending threaded aperture, said wiper terminal means extending through said radial apertures into electrical contact with said wiper element to form an electrical terminal for said wiper element and serving to cam the closure member into a predetermined rotational position during threading of said terminal pin into the threaded aperture by engagement of said cam surface with the axial sides of said slot.
3. A variable resistor as defined in claim 1, said aperture in the housing member being threaded, said wiper terminal means comprising a threaded terminal pin threadably engaged with the housing member and extending through the radial aperture in said closure member into the housing into engagement with the rotor member for making electrical contact with the wiper element, said terminal pin further having a conically tapered cam surface means thereon for camming the cover member into a predetermined rotational position with respect to the housing member by engagement with the edge of the radial aperture in the closure member during insertion of the terminal pin in the housing.
4. A variable resistor as defined in claim 1, said closure member having a stop shoulder formed thereon, said stop shoulder being engageable with a portion of said rotor member to limit rotation thereof at a predetermined desired point when said closure member is disposed in a predetermined relation with said housing member, and means for locating said closure member on said housing member in predetermined rotational alignment therewith.
5. A variable resistor as defined in claim 1, said housing member including a radially extending shoulder, said closure member including a radially extending shoulder facing the radially extending shoulder on the housing member, and one of said shoulders having formed thereon an axially extending eluding a radially extending shoulder, said closure member including a radially extending shoulder facing the radially extending shoulder on the housing member, and one of said shoulders having formed thereon a plurality of axially extending, resilient compression ribs extending from said one shoulder into engagement with the other shoulder to provide axial accommodation for accurate rotational alignment of said closure member and said body member.