US 3693129 A
Description (OCR text may contain errors)
United States Patent Shimizu [451 Sept. 19,1972
 Assignee: Alps Electric Co., Ltd., Tokyo,
Japan  Filed: April 12, 1971  Appl.No.: 133,211
 Foreign Application Priority Data July 31, 1970 Japan ..45/76556 Oct. 29, 1970 Japan ..45/107597  US. Cl. ..338/183  Int. Cl. ..H0lc 9/02  Field of Search ..338/183, 176
 References Cited UNITED STATES PATENTS 2,706,230 4/1955 Boums et a1 ..338/183 X 3,594,678 7/1971 Nomura ..338/183 3,566,330 2/1971 lchikawa et a1 ..338/183 Primary Examiner-Lewis l-l. Myers Assistant Examiner-D. A. Tone Attorney-James & Franklin [5 7] ABSTRACT A variable resistor includes an elongated housing, a dielectric base which supports elongated resistive and conductive strips, and a cover member. An elongated guide rail is mounted on the dielectric base and extends parallel to the resistive and conductive strips. A slider or carrier is provided with a groove at the lower surface thereof for slidably engaging the upper surface of the guide rail of the base. A control member is connected to the upper end of the slider and projects through an elongated slot in the cover member. A resilient member is so positioned between an upper surface of the slider and the inner surface of the top wall of the cover member that the slider is pushed evenly onto the guide rail. Thus, when the position of the slider is altered by the control member, the sliding contacts are moved evenly along the resistive and conductive elements without skipping, jumping or derailing therefrom.
10 Claims, 8 Drawing Figures PATENTEDSEFIQISYZ SHEUIUFZ INVENTOR YUTAKA JH/M/ZY/ g) /f ATTORNEY PATENTEDSEPIQ m2 3.693 129 F765 F/G6 FIG? v +768 VARIABLE RESISTOR The present invention relates to a variable resistor and control device therefor and particularly to a variable resistor of the type having a slider movable rectilinearly in the housing.
Variable resistors of the type herein described provide for a contact adapted to slidingly engage elongated resistive and conductive strips mounted on an elongated insulating base. Typically the slider mechanism is supported in a housing having side walls and a slotted top through which the slider control member extends. Resistors of this type are particularly well adapted for use in adjustable volume control mechanisms and communication receivers, but its use is not so limited. It is imperative for successful operation of such variable resistor devices that the slider contacts have a smooth sliding engagement with the conductive and resistive strips along the entire length thereof. In currently available devices of this type the path of the slider mechanism is defined by the inner side walls of the housing within which it is confined. Because of the limitations on the manufacturing process and the possibility of deformation during assembly, a tight sliding fit between the slider and the housing is not commercially feasible. As a result the device is generally designed and produced with substantial clearance between the housing side walls and the slider. As a consequence of this clearance and of such deformation or imperfection in the housing side walls as may result from the manufacturing or assembling process, the slider movement may be erratic to the extent that the contacts may run off the resistive and conductive strips.
A second problem usually encountered in the design of devices of this type is maintaining the contacts in firm electrical engagement. Normally the operative slider contacts are forced into engagement with the resistive and conductive strips by the top wall of the housing. Again, however, any deformation or imperfection in the top wall, the insulating base or the operative strips themselves may result in skipping or jumping of the slider contacts as they move along their respective strips. Conventional methods of dealing with this problem have generally been unsatisfactory. Thus, if the slider is sandwiched relatively tightly between the top wall of the housing and the base, the slider becomes difficult to move and slight imperfections in the various parts may result in sticking and severe wear on the sliding surfaces of the various parts. If, on the other hand, a substantial vertical clearance is provided and electrical contact is maintained by sufficient pressure on the vertically extending control member, the slider tends to rock to and fro as pressure is exerted on the control member in the longitudinal direction. While the foregoing difficulties could, to a large extent, be eliminated by the manufacture of the various parts to rather close tolerances, this alternative is generally not commercially feasible in view of the greatly increased manufacturing costs involved.
Accordingly, it is a primary object of the present invention to design a new and improved variable resistor of the type described which effectively eliminates the foregoing difficulties with no substantial increase in manufacturing costs.
It is another object of the present invention to design a variable resistor device having an improved slider mechanism which insures adequate sliding electrical contact along the entire length of the device regardless of deformities or imperfections in the housing or base members.
It is yet another object of the present invention to provide an improved variable resistor device of the sliding contact type which provides smooth and uniform slider movement without skipping, jumping or derailment of the sliding contacts on the operative conductive and resistive strips.
It isstill a further object of the present invention to provide a variable resistor device with improved operating characteristics and reliability even under adverse conditions such as rough or careless handling and/or assembly.
To these ends, in accordance with a preferred embodiment of the invention, there is provided an inverted U-shaped housing having a top wall provided with an elongated slot. The housing is operatively connected to an insulating base at its open face to thereby form an elongated enclosure adapted to slidingly receive a slide or carrier. The base includes one or more resistance elements printed on a surface thereof and extending lengthwise thereof, and a corresponding number of elongated conductive elements secured on the base surface and extending parallel to and spaced from the resistance elements.
An elongated guide rail is mounted on the surface of the base and extends parallel to the resistive and conductive elements. The slider or carrier is made of an in sulating material and is provided with a groove at its lower surface adapted to slidingly engage the guide rail. A pair of resilient contactors are secured to the aforesaid lower surface and include contacts wipably engaging the resistive and conductive elements. The device is adapted to be actuated by a control member having one end secured to the slider and the other end projecting through the elongated slot in the top of the housing. A resilient member is provided between an upper surface of the slider and the inner surface of the top wall of housing for maintaining the slider mounted on the guide rail and providing a smooth even sliding engagement between the contacts and the conductive and resistive elements.
To the accomplishment of the above and to such other objects as may hereinafter appear, the present invention relates to a variable resistor as defined in the appended claims and as described in this specification taken in connection with the accompanying drawings in which:
FIG. 1 is an exploded perspective view of a variable resistor in accordance with this invention;
FIG. 2 is a cross sectional view of the variable resistor taken generally along the line 2-2 of FIG. 1;
FIG. 3 is a cross sectional view, partly broken away, of a variable resistor taken along the line 3-3 of FIG.
FIG. 4 is a cross sectional view of another embodiment of a guide rail in accordance with the invention; and
FIGS. 5, 6, 7 and 8 show cross sectional views, partly broken away, of further embodiments in accordance with the invention.
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the views, and more particularly to FIG. 1 thereof, the variable resistor generally designated comprises a housing or cover member generally designated 11 having a top wall 13, elongated side walls 14 and end walls 16. The top wall 13 of housing 11 is provided with an elongated slot 18 and a plurality of tabs 20 extend downwardly from a lower edge of side walls 14, the purpose of which will become apparent hereinafter. The entire housing 11 may be fabricated from a single blank of sheet metal by a suitable punching operation, side walls 14 and end walls 16 being thereafter bent downwardly as shown.
A thin sheet 22 of any suitable insulating material is provided forelectrically insulating the remaining parts from metallic housing 11 as described hereinbelow. Insulating sheet 22 is provided with an elongated slot 24 of approximately the same length as slot 18 in housing 11, the sheet positioned within housing 11 against the inner surface of top wall 13, slot 24 being in registration with slot 18.
Housing 11 is adapted to be disposed over a base member made of an insulating material such, for example, as bakelite, these members cooperating to provide an enclosure for the slider mechanism to be described hereinafter. The base 26 includes a plurality of notches 28 at side edge portions thereof for receiving tabs 20 of the housing 11, the tabs 20 being folded under base 26 to secure the structure. An elongated resistive element or strip (here shown as two strips) 30 and 32 are deposited on the upper surface of base 26 by a conventional resistive printed process and extend longitudinally therealong. Electrical terminals 34 and 36 are secured at one of their ends to opposite ends of the resistive elements 30 and 32, respectively, the other ends of the terminals extending downwardly through slots 38 provided in the base 26 for that purpose. Similarly, a pair of elongated conductive elements 40 and 42 are mounted on base 26 parallel to resistive elements 30 and 32 and spaced inwardly thereof. The opposite end portions of the conductive elements 40 and 42 are likewise bent downwardly through slots 44 provided in base 26 for that purpose and are slightly twisted around a vertical axis to secure the elements 40 and 42 to the base 26. Like housing 11, base 26 is preferably formed from a single blank of insulating material by a simple stamping operation.
The base 26 is provided with a plurality of openings 46 spaced along a center line thereof (three openings are shown for purposes of illustration). An elongated guide rail member generally designated 48 is adapted to be secured on base 26. Guide rail 48 is provided with an upper rounded guide surface 50 and a flat lower surface from which a plurality of stem-like projections 52 depend. The guide rail 48 is secured to the base 26 by insertion of the projections 52 through the openings 46 of base 26, openings 46 being of a size adapted to receive projections 52 with a relatively tight fit.
A slider generally designated 54 is adapted to slide within the channel-like enclosure formed by housing 1 1 and base 26 and includes a main body portion or carrier 56 made of an insulating material, a control member 58 having one end secured to body 56 and its other end extending outwardly of housing 11 through slit 24 in sheet 27 and slot 18 in housing 11. A groove 60 having a rounded cross section is provided on the lower surface 62 of the sliding body 56, groove 60 being adapted to receive the rounded upper surface of rail 48 and ride thereon. A resilient member 64 having an opening or slot 68 is mounted centrally on the top surface 70 of body 56, control member 58 being received through slot 68. Resilient member 64 is fabricated from a suitable resilient material such as sheet metal and is in the shape of an H, having two pairs of arms 72 extending outwardly in opposite directions from its central portion 74 in the longitudinal direction (the direction of sliding). Portion 74 lies flat on the upper surface of slider body 56 and arms 72 are bent slightly upwardly from the plane of portion 74. Each arm 72 is provided with a rounded contact 75 mounted on the end thereof and projecting upwardly therefrom.
To insure smooth sliding movement of the slider 54 in the housing 11, a thin sheet of low friction insulating material 76 is mounted on resilient member 74 of slider 54 for sliding movement therewith. Sheet 76 is provided with an opening or slot 78 through which control member 56 extends, sheet 76 being sandwiched between sheet 22 and contacts 75. This arrangement effectively eliminates the friction losses which might otherwise result between the lower surface of thin sheet 22 and the contacts 75 of arms 72 mounted on sliding body 56 upon sliding movement of the slider.
The operative electrical connections are made by a pair of contactors generally designated 80 and 82. Contactors 80 and 82 are formed of a resilient conductive material such as sheet metal and each comprise a base portion 84 and 86 and three contactor arms 88, 90, 92 and 94, 96, 98, respectively, extending therefrom in parallel relationship in the direction of slider movement. Contactors 80 and 82 are adapted to be secured to the lower surface 62 of body 56. To this end, studs and 102 are formed integral with body 56, project downwardly from the lower surface 62 thereof and are received in openings 104 and 106 in the base portions 84 and 86 of contactors 80 and 82, the head portions of the studs 100 and 102 then being rounded by heating thereof to securely hold the contactors to the body. Arms 88-98 are bent slightly downwardly and are provided at their ends removed from base portions 84 and 86 with contacts 108, 110, 112 and 114, 116, 118 respectively. Contacts 108 and 110 are adapted to wipingly engage the resistive element 30 while contacts 116 and 118 are adapted to wipingly engage resistive element 32. Contacts 112 and 114 are adapted to wipingly engage conductive elements 40 and 42, respectively.
The manner of assembly and operation of the improved variable resistor mechanism described above will now be apparent from a consideration of FIGS. l-3. After rail 48 is mounted on base 26 and contactors 80 and 82 are mounted on slider body 53 in the manner previously described, the slider body is placed on base 26 with the rounded upper surface 50 of rail 48 being received in rounded groove 60 on the under surface of slider body 56. Arms 88-98 of contactors 80 and 82 are preferably bent downwardly a distance greater than the spacing between the bottom surface 62 of slider body 56 and the upper surface of base 26 when rail 48 is fully received in groove 60. Accordingly, the slider body is initially tilted counterclockwise as viewed in FIG. 1 and is supported at its lefthand side by the engagement of rail 48 in groove 60 and at its righthand side by the engagement of contact arms 108-118 with the upper surface of base 26. Insulating sheets 76 and 22 are then mounted on slider mechanism 54 with their slots 78 and 24 respectively receiving control member 58. The housing or cover member 11 is then placed over the entire assembly and tabs are received in cutouts 28 and are bent under base 26. It will be apparent that the top surface 13 of housing member 11 will exert a downward pressure upon slider mechanism 54 through insulating sheets 22 and 76 and resilient member 74. This pressure is effective to force the righthand side of slider body 56 onto firm engagement onto rail 48, groove 60 now receiving the upper surface 50 of rail 48 in contiguous sliding engagement along substantially its entire length. At the same time resilient contact arms 88-98 are flexed to press more firmly into engagement with their respective conductive and resistive elements on base 26.
In operation, the control member 58 of this sliding variable resistor is moved in either direction along the slot 24 in insulating plate 22. Accordingly, the slider body 56 will be moved longitudinally within the enclosure formed by housing 11 and base plate 26, being guided therein along guide rail 48 received in groove 60 in its lower surface, movable insulating plate 76 will slide along the lower surface of fixed insulating plate 22, and the contacts 108-118 of contactors 80 and 82 will be moved slidingly along the upper surface of resistive elements 30 and 32 and conductive elements 40 and 42, whereby the resistance value of the utilized portion thereof may be varied in accordance with the movement of the control member.
Several operating advantages result from the novel construction herein described. Thus, because the slider body is designed with large'clearances on either side between it and the housing member 11, the movement of the slider body 56 within the enclosure will be unaffected by deformations or imperfections in the housing side walls 14, the slider body 56 being guided solely along guide rail 48. Consequently, rough handling of the device during assembly or installment in a complete circuit, which might otherwise affect operation of the slider, may be tolerated even to the extent of sizable dents in the housing walls 14 without affecting smooth slider operation.
Since the variable resistance device in accordance with the present invention is so constructed that the slider body is resiliently biased away from both the upper top wall 13 of the housing 11 and the insulating base plate 26 by resilient arms 72 and resilient contacts 80 and 82, respectively, undesirable vertical play during sliding movement in either direction is substantially eliminated and an even and smooth movement of the sliding parts is assured. Moreover, the provision of a movable insulating plate 76 between the resilient member 54 and the fixed insulating plate 22 results in a smoother frictional engagement of these members.
Furthermore, rolling and pitching torques on sliding body 56 which inevitably result from the movement of control member 56 are effectively reduced and may even be eliminated by the counteracting resilient forces of arms 72 on resilient member 74, which render the movement of sliding body 54 extremely stable.
In addition the sliding motion of the device of this invention, because it utilizes primarily insulating members far softer than metal, exhibits a feel or touch substantially smoother than conventional devices, a particular advantage when used as a manually adjustable volume control for a communication receiver.
Various other configurations of guide rail 48 are possible in accordance with the present invention. For example, FIG. 4 illustrates a second embodiment of the invention utilizing a guide rail having an upper rounded surface 122 formed integral on an insulating base plate 124. This construction eliminates the step of mounting the guide rail on the base plate, and facilitates the deposition of the resistive elements on the upper surface of the base plate in precise parallel relationship with the guide rail 120.
FIG. 5 shows a guide rail 126 having a generally rectangular cross section with a flat upper surface 128 in sliding engagement with the flat recessed surface 130 of a correspondingly rectangular groove 132 in the lower surface of sliding body 56.
FIG. 6 shows a guide rail 134 with an inverted V- shaped upper surface 136 received in a correspondingly shaped groove 138 in the lower surface of sliding body 56.
The embodiment of FIG. 7 utilizes a generally U- shaped guide rail 140 having two generally rectangular spaced projections 142 received in two corresponding shaped parallel grooves 144 in the lower surface of body 56.
FIG. 8 shows two parallel spaced guide rails 50a similar to guide rail 50 received in two correspondingly shaped grooves 60a in body 56. Additional configurations will be apparent.
While only a limited number of embodiments of the present invention have been here specifically described, it will be apparent that many variations may be made therein, all within the scope of the present invention as defined in the following claims.
l. A variable resistor comprising an elongated housing comprising a base plate and a cover member operatively connected together to form an elongated enclosure, resistive material deposited in an elongated strip longitudinally along said base plate, a contact slidable over said resistive strip, a carrier to which said contact is secured, a guide rail mounted substantially along its entire length on said base plate parallel to said elongated resistive strip and operatively sliding engaging said carrier, said carrier being spaced from at least two opposite walls of said housing, and means for moving said carrier within said housing along said guide rail, whereby said contact slidably engages said resistive strip.
2. The variable resistor of claim I, wherein said cover member is provided with an elongated opening in the wall opposite said base plate and said carrier moving means comprises a control member secured to said carrier and extending through said elongated opening in said housing wall.
3. The variable resistor of claim 1, wherein said contact is resilient and is flexed into sliding engagement with said resistive strip.
4. The variable resistor of claim 1, further comprising means to bias said carrier away from at least one housing wall and into engagement with said guide rail.
5. The variable resistor of claim 4, wherein said carrier biasing means comprises a resilient member secured to said carrier and operatively engaging said at least one wall of said housing.
6. The variable resistor of claim 5, further comprising an insulating plate disposed between said at least one housing wall and said resilient member, said insulating plate being movable with said carrier.
7. The variable resistor of claim 6, further comprising a fixed insulating plate interposed between said at least one wall of said housing and said movable insulating plate whereby said movable insulating plate is urged into sliding contact with said fixed insulating plate.
8. The variable resistor of claim 5, wherein said resilient member comprises a main body portion secured to said carrier in the region of said control member and a plurality of resilient arms extending outwardly from said control member and upwardly from said carrier towards said at least one housing wall, whereby rolling or pitching torques on said carrier resulting from forces applied to said control member are resisted by said resilient arms.
9. The variable resistor of claim 8, further comprising an insulating plate disposed between said at least one housing wall and said resilient member, said insulating plate being movable with said carrier.
10. The variable resistor of claim 9, further comprising a fixed insulating plate interposed between said at least one wall of said housing and said movable insulating plate whereby said movable insulating plate is urged into sliding contact with said fixed insulating plate.