US3448426A - Infinitely adjustable potentiometer - Google Patents

Description

June 3, 1969 E. H. TUMBUSCH INFINITELY ADJUSTABLE POTENTIOMETER Sheet Filed May 4, 1966 g E TN. mm

Q SQK m M m June 3, 1969 H, TUMBUSCH 3,448,426

INFINITELY ADJUSTABLE POTENTIOMETER Filed May 4, 1966 Sheet 2 of 2 J1 l f- United States Patent INFINITELY ADJUSTABLE POTENTIOMETER Edward H. Tumbusch, Sepulveda, 'Calif., assignor to Techno-Components Corporation, Van Nuys,

Calif., a corporation of California Filed May 4, 1966, Ser. No. 547,652 Int. Cl. H01c 5/02 US. Cl. 338-143 5 Claims ABSTRACT OF THE DISCLOSURE The present invention is an infinitely adjustable potentiometer which includes a coarsely threaded armature mounted within a housing and rotatable from the exterior thereof. A wire resistance element is wound around the armature such that the resistance wire lies between the adjacent sides of each thread turn to form a helix having a number of turns equal to the number of threads along the length of the armature. A contactor is mounted with-' This invention relates to an electrical potentiometer and, more particularly, to miniaturized potentiometers of the type known as turn potentiometers.

A potentiometer is basically a variable voltage divider device or, stated differently, it is a resistor which has a variable contact arm so that any portion of the potential applied between its ends may be selected. An almost infinite variety of applications exist for potentiometer devices in the electronics field such as, for example, radio, instrumentation, controls, etc. In radio, for example, potentiometer devices are oftentimes used to intercouple succeeding stages and also used in circuitry for volume control. Again by way of example, in the instrumentation art a potentiometer will oftentimes be used as one of the arms in a bridge circuit of a meter.

A particular type of potentiometer is that known in the art as a 10 turn potentiometer. The term 10 turn signifies that ten turns of the adjusting knob will cause the wiper contact of the potentiometer to traverse the entire resistance range of the potentiometer. The term has come to be known in the art at the present time to apply to those potentiometers where great resolution is obtained because of a particular construction utilizing a long resistance element usually coiled and having the required adjustability by means of a contact which traverses continuously over the resistance element length rather than discretely going from one turn of resistance element to another as is the case with the typical potentiometer. Great resolution is obtained together with high resistance ranges by using a resistance element which is coiled and then wound again in a coil for compactness. 10 turn is somewhat of a misnomer since any potentiometer constructetd in such a manner will be a 10 turn type although more or less than ten turns are utilized.

Space and missile programs of today require eificient packaging of electronics. It is required in most systems that the electronic packaging be as small as achievable in the state of the art consistent with the high degree of reliability required in stringent environments encountered by missiles. The advent of solid state components and ice printed circuitry has advanced the electronic packaging art to the point where complex electronic circuitry in general can be packaged in incredibly small spaces. One of the major problems to date has been to achieve potentiometer constructions which are sufficiently small to meet the growing need for miniaturization and yet retain the high degree of reliability required in missile and space programs. The potentiometers must be able to withstand the particularly high levels of vibration and shock encountered in missile flight. Ultra-miniaturized potentiometers are also desirable for use in modern radio equipment where an entire radio may be installed in a pair of spectacles.

Compact 10 turn type potentiometers in miniaturized versions are particularly useful and needed. Because of their high resolution and, therefore, high accuracy, this type of potentiometer is used in great numbers in instrumentation systems and guidance networks. Typically, such potentiometers are capable of being either manually or automatically adjustable.

Presently available 10 turn potentiometers, although they provide high resolution, are not sufficiently compact or reliable under stringent environmental conditions. That is, although accurate adjustment can be attained, it cannot be maintained within the presently available 10 turn type potentiometer.

Accordingly, it is an object of the present invention to provide an ultra-miniature potentiometer.

It is another object of the present invention to provide a potentiometer that is extremely reliable both mechanically and electrically.

It is a further object of the invention to provide a potentiometer which is accurately adjustable.

A further object of this invention is to provide a potentiometer in which the wiper actuation mechanism is precise and durable.

It is another object of this invention to provide a potentiometer which is economical to manufacture.

Yet another object of this invention is to provide a potentiometer in which the adjustment is maintained under stringent environmental conditions.

Another object of this invention is to provide a potentiometer that is easily made moisture and dustproof.

The invention herein comprises a potentiometer having a housing. Within the housing and along its longitudinal axis is a drive member or armature which is rotated by a shaft extending beyond the end of the housing. The armature is coarsely threaded. A resistance element is wound around the threading so that the wire lies between successive threads. A spring biased contactor contacts the resistance element at two diametrically opposed points. The contactor is constrained by a guide rod so that it does not rotate during rotation of the drive member but travels along the guide member and, thus, the resistance element as the armature is rotated. Electrically shorting means are provided at the limits of the rotation of the armature rotation so that the resistance setting does not change after the contactor reaches the limits of its travel. The end part of the housing has recesses provided therein so that all Wires exit from the housing at a single point to simplify and make more reliable the sealing of the potentiometer. The housing has a single removable end section so that sealing of the unit can be accomplished at a single small area. The contactor and armature are constructed so that at the end of the travel of the contactor, the contactor contacts the peaks of the threads of the armature thus providing an automatic clutching action.

The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof will be better understood from the following description considered in connection with the accompanying drawing in which a presently preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawing is for the purpose of illustration and description only, and is not intended as a definition of the limits of the invention.

In the drawing:

FIG. 1 is a perspective view of a potentiometer constructed in accordance with this invention;

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is an end view taken along line 3-3 of FIG. 2;

FIG. 4 is a sectional view taken along line 44 of FIG. 2;

FIG. 5 is a sectional view taken along line 5--5 of FIG. 2;

FIG. 6 is a sectional view taken along line 6-6 of FIG. 2;

FIG. 7 is a sectional view partially broken away along line 7--7 of FIG. 4;

FIG. 8 is a top view of the contactor used in the potentiometer of FIG. 1;

FIG. 9 is a front view of the contactor shown in FIG.

FIG. 10 is a side view partially broken away of the contactor shown in FIG. 8;

FIG. 11 is a sectional view partially broken away taken along line 11--11 of FIG. '5; and,

FIG. 12 is a sectional view partially broken away taken along line 12--12 of FIG. 5.

Referring now to the drawing, the potentiometer 10 comprises generally a housing 11. The housing 11 has a main section 12 and an end section 13. The housing 11 has a rectangular cross section; however, it is to be noted that any convenient cross sectional shape can be utilized Without detracting from the invention.

At one end 15 of the housing and connected fixedly thereto is a bushing 20. The bushing has threads 21 for mounting the potentiometer 10' to a panel or chassis, however, any suitable mounting means other than threads could also be utilized. The bushing 20 is molded into housing 11 and is rigidly held thereto by flanges 24 and 25. At the other end of housing section 12, an end bell 27 is installed. Centrally located therein and facing inwardly of the interior of housing 10- is a cylindrical cavity 28 provided to journal a shaft 30 therein. The shaft 30 is thus journalled at one end in the cavity 28 and extends beyond housing 11 at the other end through bushing 20. The end of the shaft 30 is slotted by slot so that shaft 30 may easily be rotated with a screwdriver. The shaft 30 can also be easily turned by affixing a setscrew knob on shaft 30.

Molded around shaft 30 is a threaded armature 40. The armature is made of plastic because of its electrical insulating qualities, however, many other suitable materials such as glass, for example, could also be used. The shaft 30 has thereon a central ribbed portion 42 to more rigidly hold the armature 40 to the shaft 30. For the same purpose shoulders 43a and 43b are provided as shaft 30. The end threads 4411 and 44b of armature 40 are of smaller diameter than other threads to accommodate slip rings 45a and 45b as will be described hereinafter. The slip rings 45 are disk-like structures having a substantially vertical peripheral wall 47. Each ring 45 has a central opening 49 which has a diameter substantially equal to but greater than the diameter of the shank of armature 40; thus, the slip rings are press fitted to the armature 40. The walls 47 of the rings 45 face each other. The inside diameter of walls 47 are substantially equal to but greater than the diameter of threaded portions 44 such that the walls 47 are press fitted to the innermost portion of threads 44.

Wound between the threads of armature 40 is a resistance element 50. The wire of the resistance element 50 extends between the threads of the armature 40 to the slip rings 45 at the ends of the armature 40*. The diameter of the wire forming element 50 is of sufllcient-ly great diameter so that the outermost point protrudes slightly beyond threaded portions 44. Thus, it is readily seen that the resistance element 50 Will be contacted rigidly at its ends by slip rings 4'5. The rings 45 are made of any conductive material such as copper or for better wear any of several well-known conductive alloys used for electrical devices. The rings 45 will, as described hereinafter, provide an electrical path from the potentiometer terminals to the ends of the element 50. In operation, it is clear that when shaft 30 is rotated, so are armature 40, resistance element 50, and slip rings 45.

Spaced above armature 40 is a contactor guide rod 60. Rod 60 is parallel to the longitudinal axis of shaft 30. The rod 60 is anchored to housing 11 by means of recess 62. in section 12 and recess 63 provided in end section 13.

A novel contactor 70 acts as the resistance element wiper. The contactor 70 can best be described by reference to FIGS. 5 through 12. Contactor 70 is generally arcuate with parallel sides 72. Provided in the upper portion of contactor 70 is a substantially semicircular keyway 73. The sides 72 have grooves 75 dimpled into the contactor. The grooves 75 have a lead angle and pitch which are substantially equivalent to the lead angle and pitch of the armature 50. As can be best seen in FIGS. 8-10, resistance element contacting members 76a and 76b are cut and formed in the contactor 70. On each of the members 76 are depending contact fingers 77a and 77b. The members 76 are curved downwardly and towards center of the contactor 70 so that the fingers 77 will firmly contact the resistance element 50 as will be described hereinafter. In the assembly of the potentiometer, keyway 73 of contactor 70 is riding on guide rod 60 and dimples 75 are riding on the threads of armature 40 since as stated hereinabove, the lead angles and pitches of the armature 40 and the dimples 75 are equivalent. The engagement of a thread of armature 40 and a dimple 75 can be seen readily in FIG. 11. The contactor 70 is made of spring metal, such as an alloy of precious metal so that dimples 75 contact the armature threads firmly. Also, as can be seen best in FIG. 5, the contact fingers 77 because of their springiness also hear firmly on the resistance element 50. A particularly simple and reliable structure is achieved because of the one piece contactor 70 having wiper means and guide means formed out of the single piece of spring metal.

As can now be readily understood, as the shaft 30 is rotated, the armature 40 also rotates and, thus, drives contactor 70 along guide rod 60. The rod 60 is conductive and thus serves as the electrical pickoif lead for the contactor 7 0. As the contactor 70 reaches the end of the armature 40, the contactor 70 butts against the inside ends of the housing 10 and the contactor 70 can thus not proceed further. As the armature 40 continues to rotate, the thread peaks cause the contactor dimples 75 to ride oif the threads and, thus, an automatic clutching action is achieved.

As discussed hereinabove, the end thread peaks 44 are turned down, thus, during the clutching action, contact 70 is relaxed so that deformation does not occur. The wiper fingers 77 are lifted by the slip rings 45 and, thus, no deformation occurs on these elements. The slip rings 45 are contacted by spring loaded contacts 83 and 84. The spring loading is achieved by making the contacts and their depending strips 83a and 84a of a spring metal such as an alloy of precious metal. Depending to and integral with contact 83 is a metal lead strip 83a. The strip 83a is bent at point 87 towards the ring 45a to provide the necessary spring loading for contact 83. The strip 83a is flat and follows the wall 89 of housing 12 to contact by suitable 5 means the electrical pin 80!). In a similar fashion strip 84a is also flat and contacts electrical pin 800.

Electrical contact with the resistance element 50 is achieved through contactor 70, and the slip rings 45. As stated hereinabove, the guide rod 60 and provides the electrical lead from contactor 70. The end of the rod 60 is connected to potentiometer pin by a bent over portion 81 of rod 60 which is retained by suitable means pro vided in the housing.

Thus, there has been described a novel turn potentiometer having several advantages not found in devices of the prior art. The threaded armature provides a simple but highly reliable manner of affixing the resistance element 50. Each turn of the element 50 is separated by the threads of armature 50. The peaks of the threads drive the contactor 70 which does not rotate because constrained by guide rod 60. An automatic clutching action is provided by the interaction of the contactor 70 with the peripheral wall of slip rings,45 at the end of wiper travel of contactor 70. Finger contacting members 77 are disengaged from element '50 during clutching by rings so that no variation of output occurs because of clutching, i.e., the peripheral walls of rings 45. provide efiiective shorting bars at the ends of the wiper travel. The contactor 70 being made of spring metal and constrained provides firm contact by contacting the armature 40 and the element in two places, the element 50 being contacted by fingers 77 which are spring loaded and offset to provide excellent contact without attendant backlash. The fingers 77 as can best be seen in FIG. 8 are oppositely disposed and offset. Thus, as can be readily seen, when one finger 77a is forced out of contact with resistance element 50, the other finger 77b will be in firm contact with the element 50. The electrical connections to the ends of element 50 and to the contactor are accomplished by metal strips secured to the housing 12 of the potentiometer and, thus, do not cause the problems which occur with soldered wiring and also provide for simple assembly of the entire unit. The lead and contact configuration permits a package which is sealed at one end only and, thus, eliminates the problems of multiple sealing points and sealing large areas.

Although this invention has been disclosed and illustrated with reference to particular applications, the principles involved are susceptible of numerous other applications which will be apparent to persons skilled in the art.

What is claimed is:

1. A potentiometer comprising:

(a) a housing;

(b) a threaded armature having end threads of a smaller diameter than the other threads on said armature and having a longitudinal axis within said housing and means for rotating said armature, said rotating means being actuable outside of said housing;

(0) a resistance element wound between each of the threads of said armature;

(d) slip ring means at the ends of said armature, said slip ring means contacting electrically the ends of said resistance element;

(e) a contactor, said contactor comprising finger means for contacting said resistance element and dimple means for engaging threads of said armature;

(f) guide means for guiding said contactor along a line parallel to said longitudinal axis when said armature is rotated;

(g) electrical lead means for electrically contacting said contactor and said slip ring means and, said contactor and slip ring being cooperatively arranged such that at each end of said contactors travel along said armature said contactor is short circuited between said lead means through said slip ring and said dimples are disengaged from said threads.

2. A potentiometer as claimed in claim 1, wherein said contactor is made of spring metal and said dimple means are adapted to be fixed away from said armature when said contactor reaches the end of its travel.

3. A potentiometer as claimed in claim 2, wherein said guide means comprises a rod extended longitudinally through said housing parallel to said armature and a keyway in said contactor, said keyway adapted to bear upon and ride upon said rod.

'4. A potentiometer as claimed in claim 3, wherein said finger means comprises two oppositely disposed and oifset contact fingers.

5. A potentiometer as claimed in claim 4, wherein said contactor is a single integral member made of spring metal.

References Cited UNITED STATES PATENTS ROBERT K. SCHAEFER, Primary Examiner. H. I. HOHAUSER, Assistant Examiner.

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