US2368710A - Adjustable resistance - Google Patents

Description

F. E. HESSEY 2,368,710

ADJUSTABLE RES I STANCE Feb. 6, 1945.

Filed Sept. 19, 1942 I6 INVENTOR.

FREDERIC E. HESSEY.

ATTORNEY.

Patented Feb. 6,; 1945 ADJUSTABLE RESISTANCE Frederic E. Hessey, Manoa, Pa., assignor to The Brown Instrument Company, Philadelphia, Pa., a corporation of Pennsylvania P Application September 19, 1942, Serial No. 458,985

v 12 Claims. This invention relates to adjustable resistances in general and more particularly to adjustable potentiometer resistances such as disclosed in T. R. Harrison et a1. Patent No. 2,150,502, granted March 14, 1939, or in W. P. Wills application Ser. No. 421,173, filed December 1, 1941.

Adjustable potentiometer resistances are utilized in potentiometer measuring instruments for accurately measuring small electromotive forces and successful operation of such potentiometer measuring instruments is directly dependent upon the construction and accurate operation of the adjustable potentiometer resistances. Small changes in contact resistance or wear due to prolonged use ma produce greater effects than the small electromotive forces being measured and it is desirable to maintain these effects at a minimum.

Accordingly, the prime object of this invention is to provide an improved adjustable resistance, and more particularly an improved adjustable potentiometer resistance, wherein changes in contact resistance and the effects due to wear are reduced to a minimum, accuracy and uniformity of operation is enhanced and wherein the cost of manufacture is materially reduced.

In accordance with.- this invention the improved adjustable resistance may comprise an elongated resistance element and collector, a contact carrier movable lengthwise with respect to the resistance element and collector but-at an angle with-respect thereto and including a slot substantially transverse with respect to the direction of movement, and a contact having sloping ends carried between the contact carrier member and the resistance element and collector with the contact slidably engaging the resistance element and collector and the sloping ends rotatable engaging the edges of the/slot. As the contact carrier member is moved,a new contacting surface of the contact i continuously and uniformly presented to the resistance element thereby decreasing the contact resistance, and affording accurate and uniform operation. The contact may take the form of a sphere, a cylinder with conical ends, a barrel with conical ends or anyother' similar shape. The contact may be made of softer material than the resistance element so that wear takes place on the readily replaceable contact and not on the resistance element and collector. The contact my be provided with a handle to facili te insertion of the contact between the contact carrier member and the resistance element and collector. The contact may be made of softer material than of the invention.

the contact carrier member whereby the edges of the slot automatically form an axle on the sloping surfaces of the contact for free rolling contact therewith. This obviates the necessity of accurately machining the contact to obtain the desired fit with respect to the slot and thereby greatly decreases the cost of manufacture thereof. To provide these aforementioned improved features also form. specific objects of this invention.

The various features of novelty which characterize this invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, its ad-- vantages and specific objects obtained with its use, reference should be had to theaccompanying drawing and descriptive matter in which is preferred embodiment illust ated and described a Figs. 5 and 6 are views similar to Figs. 2 and 4, respectively, of a. modified form of apparatus;

and

comprises a cylindrical base ll formed of in-.

sulating material, such as ceramic, and suitably secured to a bracket I2 which is utilized for mounting purposes. The cylindrical base II is provided with helical grooves l3 and I4, the grooves being uniformly and closely spaced with respect to each other and extending in a helix around the cylindrical base II. A collector II and a resistance element I6 are mounted in the grooves l3 and M, respectively. The collector l5 may be formed by helically winding a wire about another wire, the two wires forming the collector I5 preferably being in electrical contact throughout the length of the collector. The rewound about an insulated wire. Preferably the collector II and the resistance element It are of the same diameter and are formed of the same material, such as manganin. The bracket l2 may carry a terminal block I! provided with terminals II, I! and 20 to which are electrically connected the collector i and the resistance element II.

An arm II is adjustably secured to one end of a shaft 26 which extends coaxially through the cylindrical base II and is provided with a driving means, such as a cable operated drum 2! at the other end. Rotation of the drum 21 causes rotation of the shaft 28 and rotation of the arm 25 about the cylindrical base H. A contact-carrier member in the form of a spring arm 28 is secured to the arm 25 by means of rivets II and is suitably insulated from the arm 25 by insulating pads 29. The contact carrier member or spring arm 28 is preferably made of hardened beryllium copper and is provided with a slot 38 which is substantially transverse with respect to the direction of movement of the spring arm 20. A contact 38, which is made of a softer material than the collector l5, resistance element It and spring arm 28, is interposed between the spring arm 28 and the collector and resistance element and is held in place by the resilient force of the spring arm 28. The contact 38 operates in the slot 38 in a manner to be pointed out more fully hereafter. The contact 36 may be made of sterling silver or like material. Since the collector l5 and resistance element ii are helically wound on the cylindrical base ii, the spring arm 28 moves along the length of the collector and resistance element but also moves at an angle with respect thereto so that as the contact I! is moved around the cylindrical base II it must necessarily move upwardly and downwardly in the slot 35.

Figures 2 and 3 illustrate more clearly the construction and mode of operation of contact 3! with respect to the collector i5, resistance element II and the slot I5 in the spring arm 28. The contact 38 rotates about an axis as it is bodily moved and the contact is provided at the ends of the axis with sloping surfaces, which may be substantially conical surfaces 31 shown in Fig. 2. The periphery of the contact 88 engages the c0llector I! and resistance element It for-longitudi nal and rotational sliding movement with respect thereto and the conical surfaces 31 engage the edges of the slot 35 for rolling movement with respect thereto.

When the spring arm 28 moves to the left as shown by the arrow A in Fig. 2 it moves upwardly away from the plane of the drawing in Fig. 3 as designated at 8.. Such movement causes movement of the contact N to the left in Fig. 3 as illustrated by the arrow C since the helical winding of the collector II and resistance element It extends in that general direction, as illustrated. As a result of such movement and due to the forces present and the friction effects where the edges of the slot 35 engage the conical surfaces provides a wiping action which maintains contact resistance at a minimum.- When the adjustable resistance assembly is first operated there is an appreciable wedging action between the edges of the slot 35 and the conical surfaces 11 which produces a large force at these points of contact. This force insures rolling of the conical surfaces 31 along the edgesof the slot 35 and also causes the edges of the slot to form slight grooves or tracks in the conical surfaces 31 as illustrated at 39 in Fig. 3. These grooves or tracks 39, being formed during actual operation of the contact 38.

with respect to the slot Q5, form an accurate and true surface for rolling. contact between the contact 36 and the edges of the slot 35. Too close a fit which would cause binding or too wide a fit which would cause lost motion and cooking of the contact are thereby automatically eliminated. It is found that after a long period of operation this groove or track enlarges to form a pronounced axle as illustrated at M) in Fig. 4 which axle continues to guide rotatably and freely the contact 36 in the slot 35.

' This type of contact, which wears itself in to fit the slot 35, does not require hand fittingin order to eliminate lost motion or binding. It is not necessary to finish the wearing surfaces of the contact 35 other than roughly forming the such a contact. Since the contact 35 is of softer material than the collector 15' and the resistance element It, any wear that takes place takes place on the contact 38 and not on the collector I5 and resistance element l6, and since the con tact 36 is continuously rotated by its rolling contact with the edges of the slot 35, a new contacting surface is always presented to the collector i5 and resistance element i6 whereby the wear on the contact 36 is evenly distributed about the periphery thereof. Since the contact (it is of softer material than the spring arm any wear due to rolling action between the c 38 and the edges of the slot 35 is taken the contact 3! which is readily replaceable. litter the contact has performed its operation over a long period of time it may be readily r ced by a new contact for another long period of serviceable opera tion. In order to facilitate insertion of the contact in the slot 35 the contact may be provided with a handle 38 to provide a place to grip the contact with a pair of tweezers or long nose Figures 2, 3 and 4. The arrangementof Fig- I1 and where the periphery of the contact 38 engages the collector Ii andresistance I 8, the .contact rolls along the edges of slot and rotates in a clockwise direction in Fig. 3 as indicated by the arrow D. This clockwise rotation and rolling of the contact 38 as it'is moving to the left continuously presents a new contact surface to the collector II and resistance element II as it is moved bodily therealong and it also is ure 7 operates in identically the same manner as the arrangement of Figures 2, 3, and 4 and, therefore, a further description of this arrangement is not considered necessary.

While the contacts 38; 38' and 38" have generally different configurations, they all are, circular in cross section about their axes of rotation for contacting the collector I! and resistance element It and have sloping surfaces at the ends of the axes for rolling engagement with the edges of the slot 35. While the collector l5 andresist ance element It areshowninl 'ig. 1 tobehelically wound .about a cylindrical base H, they may be spirally wound on a flat base or longitudinally located on an elongated flat base and the same mode of operation is accomplished. In each of these instances, the contact carrier member 28 while moving longitudinally of the collector l and resistance It also moves at an angle with respect thereto so that the contact 36 will roll in the slot 35.

While in .accordance with the provisions of the statutes, I have illustrated and described the best form of this invention now known to me, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit of this invention as set forth in the appended claims, and that in some cases certain features of this invention may sometimes be used to advantage without a corresponding use of other features.

Having .now described this invention, what I claim as new and desire to secure by Letters Patent is:

- 1. In an adjustable resistance, the combination of, a resistance including a plurality of elongated resistance elements uniformly and closely spaced with respect to each other, a contact carrier wise with respect to the elongated elements but at an angle with respect thereto and including ber movable lengthwise with respect to the elongated elements but at an angle with respect thereto and including a slot substantially transverse with respect to the direction of movement, and a spherical contact carried between the contact carrier member and the pair of elongated resistance'eleinents with a portion thereof engaging each of the elongated resistance elements for sliding contact therewith and with portions thereof engaging. the edges of the slot for rolling contact I therewith.

member movable lengthwise with respect tothe elongated elements but at an angle with respect thereto and including a slot substantially transverse with respect to the direction of movement,

and a contact, circular in cross section about an axis and sloping at the ends of the axis, carried between the contact carrier member and the pair of elongated resistance elements with the circumference thereof engaging each of. the elongated resistance elements for sliding contact therewith and with the sloping surfaces thereof engaging the edges of the slot for rolling contact therewith.

2. In an adjustable resistance, the combination of, a resistance including elongated elements uniformly and closely spaced with respect to each other, a contact carrier member movable length- 6.. In an adjustable resistance, the combination of, a resistance including elongated elements uni;- formly and closely spaced with respect to each other, a contact carrier member movable lengthwise with respect to the elongated elements but at an angle with respect thereto and including a slot substantially transverse with respect to the direction of movement, and a contact, circular in cross section about an axis and sloping at the ends of the axis, carried between the contact car-' rier member and the elongated elements with wise with respect to the elongated elements but at an angle with respect thereto and including a slot substantially transverse with respect to the direction of movement, and a contact, circular in cross section about an axis and substantiallyv conical at the ends of the axis, carried between the contact carrier member and the elongated elements with the circumference thereof engaging the elongated elements for sliding contact therewith and with the substantially conical surfaces thereof engaging the edges of the slot for rolling contact therewith.

3. In an adjustable resistance, the combination of, a resistance including. elongated elements uniformly and closely spaced with respect to each other, a contact carrier member movable lengthwise with. respect to the elongated elements and collector but at an angle with respect thereto and including a slot substantially transverse with respect to the direction of movement, and a substantially cylindrical contact with substantially conical ends carried between the contact carrier member and the elongated elements with the substantially cylindrical surface thereof engaging V the elongated elements for sliding contact therewith and with the substantially conical ends thereof engaging the edges of the slot for rolling contact therewith. v

4. In an adjustable resistance, the combination of, a'resistance including elongated elements uniformly and closely spaced with respect to each other, a contact carrier member movable lengththe circumference thereof engaging the elongated elements for sliding contact therewith and with the sloping surfaces thereof engaging the edges of the slot for rolling contact therewith, said contact being formed of softer material than the elongated elements whereby wear due to sliding contact is taken by the contact.

7. In an adjustable resistance, the combination of, a resistance including elements uniformly and closely spaced with respect to each other, a contact carrier member-movable lengthwise with respect to the elongated elements but at an angle with respect thereto and including a slot substantially transverse with respect to the direction of movement, and a contact, circular in cross section about an axis and sloping at "the ends of the axis, carried between the contact carrier member and the elongated elements with the circumference thereof engaging the elongated elements for sliding contact therewith and with the sloping surfaces thereof engaging the edges of the slot for rolling contact therewith, said contact being formed of softer material than the contact carrier member whereby the edges of the slot form an axle on the sloping surfaces of the contact for rolling contact therewith.

8. In an adjustable resistance, the combination of, a resistance including elongated elements uniformly and closely spaced with respect to each other, a contact carrier member movable lengthends of the axis, carried between the contact carrier member and the elongated elements with the circumference thereof engaging the elongated elements for sliding contact therewith and with the sloping surfaces thereof engaging the edges of the slot for rolling contact therewith, and a handle formed on said contact to facilitate insertion of the contact between the contact carrier member and the elongated elements. 9. In an adjustable resistance, the combina-' tion of, a resistance including elongated elements uniformly and closely spaced with respect to each other, a contact carrier member movable lengthwise with respect to the elongated elements but at an angle with respect thereto and including a slot substantially transverse with respect to the direction-of movement, a contact, circular in cross section about an axis and sloping at the ends of the axis, carried between the contact carrier member and the elongated elements with the circumference thereof engaging the elongated elements for sliding contact therewith and with the sloping surfaces thereof engaging the edges of the slot for rolling contact therewith, said contact being formed of softer'material the elongated elements whereby wear due v to sliding contact is taken by the contact, and a handle formed on said contact to facilitate insertion of the contact between the contact carrier member and the elongated elements.

10. In an adjustable resistance, the combination of, a resistance including elongated elements uniformly and closely spaced with respect to each other, a contact carrier member movable lengthwise with respect to the elongated elements but at an angle with respect thereto and including a slot substantially transverse with respect to the direction of movement, and a contact, circular in cross section about an axis and sloping at the ends of the axis, carried between the contact carrier member and the elongated elements with the circumference thereof engaging the elongated elements for sliding contact therewith andwith the sloping surfaces thereof engaging the edges of the slot for rolling contact therewith, said contact being formed of softer material than the elongated elements whereby wear due to sliding contact is taken by the contact, and said contact being formed of softer material than the contact carrier member whereby the edges of the slot form an axle on the sloping surfaces of the contact for rolling contact therewith.

11. In an adjustable resistance, the combination of, a resistance including elongated elements uniformly and closely spaced with respect to each other, a contact carrier member movable lengthwise with respect to the elongated elements but at an angle with respect thereto and including a slot substantially transverse with respect to the direction of movement, a contact, circular in cross section about an axis and sloping at the ends of the axis, carried between the contact carrier member and the elongated elements with the circumference thereof engaging the elongated elementsfor sliding contact therewith and with the sloping surfaces thereof engaging the edges of the slot for,rollin'g contact therewith, said contact being formed of softer material than, the contact carrier member whereby the edges of the slot form an axle on the sloping surfaces of the contact for rolling contact therewith, and a handle formed on said contact to facilitate'insertion of the contact between the contact carrier member and the elongated ele-- ments.

12. In an adjustable resistance, the combination of, a resistance including elongated elements uniformly and closely spaced with respect to each other, a contact carrier member movable lengthwise with respect to the elongated elements but at an angle with respect thereto and including a slot substantially transverse with respect to the direction of movement, a contact, circular in cross section about an axis and sloping at the ends of the axis, carried between the contact carrier member and the elongated elements with the circumference thereof engaging the elongated elements for sliding contact therewith I and with the sloping surfaces thereof engaging the edges of the slot for rolling contact therewith, said contact being formed of softer material than the elongated elements whereby wear due to sliding contact is taken by the contact, said contact being formed of softer material than the contact carrier member whereby the edges of the slot form an-axle on the sloping surfaces of the contact for rolling contact therewith, and a handle formed on said contact to facilitate insertion of the contact between the contact carrier member and the elongated elements.

FREDERIC E. HESSE'Y.

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