US3026493A - Rectilinear potentiometer - Google Patents

Description

March 20, 1962 E. H. TREFF RECTILINEAR POTENTIOMETER Filed March 22, 1960 NUCH 5 Wm ATTORNEY I United States Patent 3,026,493 RECTILINEAR POTENTIOMETER Ernest H. Trelf, 166--25 12th Ave., Whitestone, N.Y. Filed Mar. 22, 1960, Ser. No. 16,745 2 Claims. (Cl. 338-183) This invention relates to potentiometers, and, more particularly, to improvements in rectilinear potentiometers.

Potentiometers are not new, and the recent develop ments in the electronics field, particularly developments in computer and automatic control systems, have greatly en larged the uses of potentiometers. Potentiometers are now used in many places where, at one time, the signals were too small to permit accurate control by sliding contact means. In such systems contact and thermal noise often reached the amplitude of the information signals themselves. For this reason, the search for improved potentiometer systems and circuits has continued at an ever increasing pace.

In many applications, the familiar disk-shaped potentiometer in which the brush contact is positioned on a circular resistance member by rotary motion is used. However, in some installations, such as in many hydraulic systems, the size and shape of the system elements dictate the use of elongated potentiometers having comparatively small transverse dimensions. In such units, the brush contact is moved by linear or straight line motion. Such potentiometers, as disclosed in United States Patent 2,863,- 031 of Gottschall et al., are called rectilinear potentiometers and comprise resistance elements and movable brush members for contacting various portions of the resistance elements. The brush members may bemounted upon a sliding block which moves along the longitudinal axis of the potentiometer. Such elongated potentiometers may have a section geometry which is rectangular, elliptical,

or circular, as desired, but, because it is easier to manufacture, and in the absence of other considerations, an elongated cylinder having a circular cross-section is generally used as the housing.

One of the basic problems involved in such potentiometer devices has been the noise introduced by uneven motion of the brush member over the resistive element due to sticking and sliding motion. Many rotary motion potentiometers incorporate ball bearings to achieve smooth rotary motion of the slide member, but the elongated linear movement potentiometers normally use sleeve bearings, and slow motion of the shaft member in the sleeve bearings may produce vibrations which are, in turn, transmitted to the slide contact and modulate the signal passing through the system.

Another problem in the design of rectilinear potentiometers has been the limitations placed upon the transverse dimension of the potentiometer by the devices, such as hydraulic actuators, in which it is to be used. The reduction in the diameter of the potentiometer has resulted in an increase in its length which has, in turn, presented problems in the mounting of the movable elements. In prior art rectilinear otentiometers, such as that shown in the aforesaid United States Patent 2,863,031, the brush block, that portion of the movable system which supports the brush members, has been purposely made completely free of the inside of the housing, This has been done because it was assumed that sliding contact between the brush block and the housing would produce undesired sticking, with the consequent modulation of the potentiometer output signals. As a result, the moving system within the prior art rectilinear potentiometers has been supported by a single bearing and by the brush members themselves. This placed an unnecessary load on the brush and resistance members, and its elimination is desirable.

3,026,493 Patented Mar. 20, 1962 It is an object of this invention to provide a new and improved rectilinear potentiometer.

It is a further object of this invention to provide new and improved potentiometersin which a novel construction greatly reduces noise introduced by the motion of the slide member over the resistive elements.

Other objects and advantages of this invention will become apparent as the following description proceeds, which description should be taken with the accompanying drawings, in which:

FIG. 1 is a perspective view of the outside casing of an elongated potentiometer;

FIG. 2 is a sectional view of the potentiometer of FIG. 1 taken along the lines 2-2;

FIG. 3 is a sectional view of the potentiometer of FIGS. 1 and 2 taken along the line 3-3; and

FIG. 4 is a sectional view of the potentiometer of FIG. 2 taken along the line 4--4.

Referring now to the drawings in detail, a generally elongated cylindrical housing 11 has a cap 13 at one end thereof and a perforate cap 15 at its other end. The

' cap 15 is held in place by a retaining ring 21 and supgenerally cylindrical brush block 23 is snugly fitted within the housing 11 and is mounted on the other end of the shaft 17 by means of threaded nuts 25 or other suitable engaging means so that shaft 17 is free to rotate. Better shown in FIG. 3 is the configuration of the brush block 23 which has, along its lower edge, a generally rectangular keyway 26 into which a key 27, provided on the lower portion of the housing 11 to restrain rotation of the block 23 within the housing 11, fits. The brush block 23 has an elongated support member 29 which carries at its outer end a pair of spring brush members 31 embedded in its upper surface. A resistance element comprises a track or ridge 35 of resistance material comolded with a base 33 with which the brush members 31 make contact. A third spring brush member 37 is carried by the support 29 and bears against the inner surface of the housing 11. Connection is made to the two ends of the resistance track 35 and to the contact member 31 by means of cable and wires 41 which enter the housing 11 through an opening 43 therein. In FIG. 4, the base 33 is shown having a pair of tracks 35. If de sired, both tracks may be formed of a high resistance material, or one track may be made of a good conductor and provided merely as a suitable means for making connection with the resistance track.

The base 33 may be formed of an insulating material having a resistive element on its upper surface on at least one of the ridges 35, or it may be formed of any suitable resistance material such as a conductive synthetic resin. The slide members 31, carried on the support 29, contact the upper surfaces of the ridges 35 and serve to determine the amount of resistance between the point of contact of the brush member 31 on the ridge 35 and the ends of the resistance element. Motion is imparted to the slide member 31 by the shaft 17 (toward the left as shown in FIG. 2) which may be positioned manually or by means of a solenoid, servo motor, or other drive means attached to the handle 18,. The brush block 23, which rides on the key 27, supports one end of the shaft 17 within the housing 11, and the other portion of the shaft 17 is supported in the bearing member 19 and the plug 15. The plug 15, or the bearing member 19, may be formed of a lubricating bearing material to reduce the amount of friction with the shaft 17. The motion of the shaft 17 produces sliding friction between the block 23 and the housing 11, and between the shaft 17 and its bearingv 19 inaddition. to the sliding motion of the three brush members 31 and 37.

The described construction including the brush block 23 and. the overhangingbrush support 29'; was found to greatly reduce the noise produced by'the sliding motion of the brushes and the block within the housing 11. In addition, the support of the shaft 17 at two point, by the bearing 19 and by the brush block 23-, tends to stabilize the forces on the slide; contact members and to reduce the Wear of the movable elements. Therefore, the devices described herein may comprise a precision instrument for use in servo and telemetering systems where small units are important and which inherently utilize small amplitude signals. As shown in the drawings, the housing 11 is preferably constructed on a metal, such as stainless steel, which resists corrosion, as is the plug member. 15 also. The brush members 31 and 37 may be formed of suitable contact materials, such as-berryllium copper, having precious metal contact points. The; brush block 23' may also berstainless steel, or, together with the'resistance 7 element 33 and the support 29, may be satisfactorily formed of suitable synthetic resins Which may have the desired characteristics. However, it should be borne in mind that although the materials mentioned herein are the preferred materials, any suitable structural material may be used without departing from. the spirit of this invention; Since it is anticipated that the above specificationmay suggestto those skilledinthe art other forms which theinvention may take,.it'is intended thatthis invention be limited only by the scope of the appended claims. What. is. claimed: is;

. 1. A rectilinear potentiometer. in which linear motion its other end extending into said housing, a piston slidably contained within said housing, said piston rotatably supporting the other end of. said operator shaft, a first spring member carried by said piston, an electrical resistance element mounted in said housing and extending longitudinally therein, an electrical contact mounted on said first spring member and sl-idably engaging the surface of said resistance element, said first spring member maintaining said contact is engagement with said resistance element, and means carried'by said piston for counteracting the force exerted by said first spring member.

2. A potentiometer comprising an elongated housing having a comparatively small transverse dimension, a resistance element contained within said housing and extending longitudinally therein, a brush block conforming closely'to the internal configuration of said housing and being dimensioned to closely fit therein, a key supported longitudinally by an internal wall of said housing, said brush block having a keyway adapted to fit said key to restrain said block from rotation with respect to said housing, a first spring member attached at one end to said brush block, an electrical contact brush mounted on the other end of said first spring and forced thereby into sliding contact with the surface of said resistance element, a second spring member carriedby said brush block and bearing against said housing to oppose the force exerted by said first spring member, an operator shaft'rotatably supported at one end by said'brush block, and a bearing mounted in an end wall of said" housing for slidably supporting said shaft at a location which isspaced'from said one end.

References Cited in the file of this patent UNITED STATES PATENTS 2,863,031 Gott'schall et a1. Dec. 2-, 1958

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