US2901719A - Adjustable tap means for variable resistance device - Google Patents

Description

1959 P. c. SMITH 2,

ADJUSTABLE TAP MEANS FOR VARIABLE RESISTANCE DEVICE Filed Jan. 23, 1956 I r K 4 i 40 26 I6 I 427%; 44 22 Q r ,M Q

Fig. 4

INVENTOR.

' Paul O. Smith AGENT.

United States Patent ADJUSTABLE TAP MEANS FOR VARIABLE RESISTANCE DEVICE Paul C. Smith, Far Rockaway, N.Y., assignor to Micro MachineWorks, Inc., a corporation of New York Application January 23, 1956, Serial No. 560,729 3 Claims. 01. 338-135) with respect to the associated resistance winding and additionally, similar taps of similar potentiometers must be individually set to compensate for unavoidable differences in the various resistors. To obviate these inaccuracies, it is necessary that these taps are individually adjustable during the assembly of the potentiometer and capable of retaining this setting when being locked in place.

At the present time, it is the practice to form a tap of a spring strip having a slotted ear, the slot having a screw passing therethrough and clamping the ear to a non-conductive element to lock the tap in place. It has been found, that with the most accurate setting of the tap, when the locking screw is tightened, it is impossible to prevent the tap from moving slightly. Additionally, because of the width of the tap arm and the extending ears of the standard type taps, it is impossible to group more than two taps in close proximity to one another.

Therefore, it is an object of this invention to provide wire-form taps for potentiometers which are easily and positively adjustable with respect to the associated resistance winding and adaptable to retain the precise setting while being locked in position.

Another object of this invention is to provide a wireform tap contact for variable resistance units which are not deformed during adjustment relative the associated resistance winding which may remain in a sprung condition until after being locked in the desired position.

Still another object of this invention is to provide formed wire taps for precision type potentiometers which may be ganged in close proximity to one another and not being limited in number due to the physical charac= teristics of the taps.

These and other objects and advantages will become more apparent by reference to the following description and the accompanying drawings wherein:

Figure 1 is a plan view of a variable resistor or potentiometer with the rotor element removed and incorporating the present invention,

Figure 2 is a sectional view of a potentiometer taken on line 22 of Figure 1,

Figure 3 is an enlarged view of the tap contact, and

Figure 4 is an end view of the tap contact taken on the plane 4-4 of Figure 3 and indicating the path of the tap contact point as the tap is pivotally positioned. Now referring to the drawings, the potentiometer has 2,901,719 C6 Patented Aug. 25, 1959 a cylindrical shell or case 10 which is normally metallic and fixed thereto is a terminal board 12 which mounts the terminals 14. These terminals 14 are electrically joined to the commutator (not shown) and the various taps or tap contacts 32 by lead wires 16. Lining the shell 10 is an insulation 18, in this instance, being com prised of a synthetic, non-conductive ring or coil form 20 and a flanged, cup-shaped member or tap disc 22 which is also made of a non-conductive synthetic. This insulation, lining the shell, not only segregates the electrical components within the potentiometer but also is the mounting stmcture for the taps 32, the resistance coil winding 40 and the commutator (not shown). When synthetic material is used, the two piece construction of the insulation 18 is preferred inasmuch as closer tolerances can be held to a greater degree than if the insulat-. ing member is formed in a single unit. It should be understood, that while this is merely a preferred form, this does not preclude the use of a single unit construction of the insulating member. The tap disc 22 has a hub portion 26 which surrounds the enlarged portion of the shell 10 which mounts a rotor assembly (not shown) and is spaced therefrom to provide a circular passageway for the lead wires 16. Although the path of the lead wires is not critical, the wires are coursed through the provided passageway within the hub portion 26 instead of around the outside of the hub to pervent fouling and as an added precaution against shorting. There is a slot 28 in the flange portion 24 of the tap disc 22 which extends through the base of the wall of the hub portion to provide an access for the lead wires to permit their entrance into the passageway within the hub where they attach to the individual tap contacts. This slot 28 is located directly opposite a bridge 44 through which the lead wires pass as they enter the confines of the potentiometer. The bridge 44 serves as a track for carrying a resistance coil contact (not shown) which is carried by and forms a part of a rotor assembly (not shown) over the breach between the ends of the resistance coil 49 which is wound on a winding card 42. A series of small holes or openings 30 are located in the wall of the hub 26 for mounting the tap contacts 32. It is Well to note, that although the hub portion 26 is shown as being of a cylindrical, inverted cup shape with an opening in the end wall thereof, this portion could also be merely an upstanding cylindrical flange.

Each of the taps 32 (see particularly Figures 3 and 4) has a body of mounting portion 34 which extends through a hole or opening 30 in the wall of the hub 26 on the axis AA and a spring arm portion 36 on an axis BB, the axes AA and BB forming an external angle x which is variable as to degree and as the extent of the angle increases, the possible adjustment sweep of the tap increases. At the free end of the spring arm 36 is a contact portion 38 which electrically engages the side face of the resistance coil 40. These taps 32 are preferably made of a precious metal wire and treated so as to have a degree of resiliency. This wire-form tap 32, in being set relative to the resistance winding 40, pivots about the axis AA, the contact point 38 traveling in an arcuate path C which crosses successive windings of the resistance coil, as may be seen in Figure 4. When the tap 32 is set at the desired location, the spring tension of the arm 36 will hold the contact portion 38 firmly against the resistance winding 40 and the application of a small amount of a homogeneous adhesive 46 at the point where the tap 32 emerges from the hub portion 26 of the tap disc 22 will positively lock the tap in the desired setting. As an alternate method of locking these taps in place, the contact portion 38 may be joined to the resistance winding 40 by the application of silver solder or any of the other acceptable materials.

In addition to utilizing this tap construction and installation for intermediate contacts, because of the ease and accuracy of installing, they have been found more suitable for resistance coil terminal contacts than those in use at the present time.

Having thus described my invention in the preferred form, I claim:

1. A Wire-wound variable electrical resistance unit that comprises, a cylindrical casing, a non-conductive liner mounted within said casing and consisting of a circular bottom piece, an upright central hub portion and, an upright cylindrical wall portion adapted to be received against the inner Wall of said casing, said hub portion and wall portion being spaced from each other to define an annular cavity therebetween and closed across one end by said circular bottom piece, a wire-wound resistance element mounted within said annular cavity against the upright cylindrical Wall and extending around substantially the entire circumference of said wall, said central hub portion being adapted to be undercut adjacent said bottom piece at any point around its periphery such as to define tap element mounting means, at least one such tap element mounting means, at least one pretensioned resilient wire tap element having a pivot arm pivotally mounted within said mounting means for adjustable movement with respect to said wire-wound resistance element and having a contact arm adapted to engage the wire-wound resistance element in pressure relationship when the pivot arm thereof is inserted within said undercut mounting means, and means for connecting said wire tap element into an electrical circuit exteriorly of said casing.

2. The wire-wound variable electrical resistance unit as claimed in claim 1, that further comprises means for forming a semi-permanent bond between the pivot arm of said wire tap element and said tap element mounting means after said contact arm has been positioned at a predetermined point on the wire-wound resistance element.

3. The wire-wound variable electrical resistance unit as claimed in claim 2, that further comprises means for forming a semi-permanent bond between the contact arm of said wire tap element and said wire-Wound resistance element.

References Cited in the file of this patent UNITED STATES PATENTS 1,783,542 Merle Dec. 2, 1930 2,448,783 De Giers et -al. Sept. 7, 1948 2,551,989 Wilson May 8, 1951 2,619,570 Takats Nov. 25, 1952 2,782,288 Weld Feb. 19, 1957 2,806,928 Woods et al. Sept. 17, 1957

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