US2515981A - Adjustable resistor - Google Patents

Description

July18, 1950 Original Filed Feb. 20, 1948 M- E. BOURNS ADJUSTABLE RESISTOR 2 Sheets-Sheet 2 INVENTOR.

MARLAN E BOURNS ATTORNEY Patented July 18, 1950 V UNITED S TATES PATENT OFFICE ADliUSTABLE RESISTOR Marlan E. Bourns, Altadena, Calif. briginal application February 2i), 1948, Serial No.

issogsemino. 153,690

(Cl. cor-e2) 1 Claim.

This invention relates to adjustable resistors, and more particularly to adjustable resistors which must respond precisely and without an1- big'uityto the meanswhich actuates the inovable slider.. This is'a division of application curately, precise1y, and 'withou't'lag in response tothe condition to be observed.

, Itis an object of this invention'to provide an adjustable resistor suited to be actuated by a de tecting elementas described immediately above.

It is another object of this'invention to provide an adjustab1efresistorwhich will be rugged, reliable, simple in construction, and easilyand accurately assembled.

p It is another object of this invention to provide van adjustable resistor which may be subjected to accelerations up to g. without detrimental effect to the instrument, and without producing a false electric output.

It is another object of this invention to provide :fln lad lustable resistor in which the electrical 'd'etection"propertiesare very sensitive to the physical displacement of the mechanical arm and slider.

. It is a further object of this invention to pro- Videan adjustable resistor in which the actuating arm and slider may be moved by a very low acis subjected to high acceleration and to severe vibration. s

I Another object of this invention is to simplify adjustable resistor construction so that need for l special limit stops in the oscillatory path of the actuating arm is eliminated.

In accordance with these objects and with other objects which will become apparent in the iollbwing' specification, the instant invention is "embodied in a base, in which is movably mounted "an actuating member or arm. Resilient contact means inthe form of a' resilient'piece of conduct- Divided and this application April 3,

ing material is secured to the actuatingnieniber. A cover ineinber ismounted on the base. Simplicity of construction is enhanced by fabricating the cover member of non-conducting material, an mounting on'the inner face thereof a 'res nce element and a contact piece, theformer engaging (when the cover is in place) a portion of the resilient contact means, the latter engaging another portion of the contact means. Thus, when the cover member is secured in place to'the base, the resilient contact means is automatically engaged with the resistance elementand'with the contact piece at a proper, predetermined contact pressure.

Two embodiments of the invention described generally above have been illustrated in the dra 'ngs, wherein:

Figs. 1, 2, 3, and 4 illustrate apreferredembodiment, Fig. being a plan view of the adjustable resistor with the cover partially broken away, 2 being a sectional elevation taken along line 2-2 inF-ig. 1, Fig. B being a cross section taken along line 3 .3} in Fig. l, and Fig. being a fragmentary section'taken along line i in Fig. 2;

Fig. 5 is a diagrammatic sketch of the circuitry involved in the invention; and

Figs. 6, 7, 8, and 9 illustrate another embodiment of the instant invention, Fig.6 being an elevation partly sectionalized, Fig. 'Lbeing across section taken alcngline 7-1 in Fig. 6, Fig. 8 being a view looking at the underside of the cover along the line i 8 in Fig. '6, and Fig. Qbeing a n "pective view of one of the contact elements removed from the instrument.

First embodiment Referring to Figs. 1, 2, and 3, H designates a base having a recess 12 therein, partially closed by a wall it secured to the base I! by'screws l4, and accuratel positioned by dowel pins 15. EX- tending through the base ll, the'recess l2, and into the wall it ashaft it rotatably mounted therein by means of ball bearings ll. Secured to the shaft Hi by any suitable means, such as a diainetral pin it, is an arm is made of non-conducting material. The arm I 9 is thus oscillatable with respect to the base i I by means of the shaft it, the position of which is in turn controlled by a vane having formed on one end thereof a hub 22 bored at 23 to accept the externalend'of the shaft it. The seating of a diametral pin'24 protruding from the shaft '16 in a pair of diametrically disposed V notches 26 in the hub22 assures that the vane 21 will'always' be assembled in the proper predetermined relation with respect to the arm I9. A screw 2'! extending through the end of the hub and threaded into the end of the shaft l6 serves to anchor the vane 2| to the shaft l6.

Near the end of the arm l9 opposite the shaft I6 there is secured, by means of screws 28, a resilient contact strip 29 of conducting material. The strip 29 is disposed generally parallel to the arm 19, and the two ends of the strip face outwardly of the recess I2, being terminated by button contact members 3| and 32, respectively.

Both elements with which the contact strip 29 engages are attached to the inner face of a non-conducting cover 33, which, in the final assembly, is secured to the base H over the recess I2 by screws 3-4. One of these elements, a wire wound elongate resistance element 36, is disposed in an arcuate groove 3! formed on the inner face of the cover 33, and held thereto by means of terminal members 38, which extend through and are secured to the cover 33. The arcuate disposition of the groove 31 is adjacent the oscillatory path of the end 32 of the resilient strip 29, so that the strip 29 is constantly in contact with some portion of the resistance element 36 during all times that the cover 33 is in place. The element 36 is connected, both mechanically and electrically, at each end to the respective terminals 38, by means of metallic strips 39, which are attached to the inner ends of the terminals 39 by the peening of the latter at M, and hooked over the element 36 at each end thereof as shown at 42. The members 38 and 39 thus serve the double function of securing the element 36 to the inner face of the cover 33, and of providing electrical connections to each end thereof. The terminal members 39 are drilled and tapped externally of the cover 33 to accommodate terminal screws 43, to which may be connected lead wires for the resistor.

The contact member 3! on the other end of the resilient strip 29 is in constant contact with a conducting piece or plate 454 held to the inner face of the cover 33 by a terminal member 45,

passing through and secured in the cover 33. Like the terminal member 38, the member 56, which is peened over the surface of the plate 44 at 41, serves the double function of physically holding the plate 44 in place and of providing an electrical connection to the plate. The members 46 and 38 are splined, as exemplified at 48, to prevent turning. Member 43 is drilled and tapped externally of the cover 33 to accommodate a terminal screw 49. A small screw 59 passing thru the plate 44 into the cover 33 prevents the plate from turning about the terminal mem-- ber 46.

To minimize the effect of extraneous acceleration on the instrument and to further enhance its response characteristics, a counter-balance screw 51 is threaded into the arm l9 paralleling the strip 29. Screw has a knurled head 52 to aid in the balancing of the instrument while the arm I9 is mounted to the base H. A transverse set screw 53 threaded into the arm l9 serves to anchor the counter-balance screw 5| in place after adjustment.

Cross-balancing is effected by means of a screw .54 mounted in a tapped bore extending trans versely through the arm I9 at a right angle to the shaft l6. After adjustment, the screw 54, which is generally positioned fully within its bore, is anchored in place by a set screw 56.

Low density material is employed for the vane 2| to lower inertia, thereby reducing lag in response, and minimizing the undesirable eifects of acceleration. The instrument is of manifest simplicity, being directly actuated without the employment of gears, links, or similar mechanisms. The frictional torque which the vane 2| must overcome is minimized by pivoting the shaft H5 in the ball bearings H, by using low contact pressure at button contacts 3| and 32, and by disposing the contact 3| as near as feasible to the shaft l6, thereby minimizing the moment arm. The non-conducting cover member 33 serves the triple function of a cover, an insulator between elements, and means for securing the elements in position.

A vane actuated resistor constructed in accordance with the above description has been found to be rugged, reliable, precise, and to be electrically sensitive to an angular displacement of three minutes of arc on the part of the shaft [6.

Second embodiment In the embodiment shown in Figs. 6, '7, 8, and 9, Bl represents a base having a groove therein formed of two portions, a bore 62 and a slot 63 communicating with the top of the base 6!. A shaft 64 is reciprocably mounted in the bore 62, being prevented from rotation therein by a post 66 extending radially from the shaft 64 and through the groove 63 to a region above the base 6|. A contact plate 61 is secured to the top of the post 66 at a right angle thereto by a screw 69, and is insulated therefrom by a fiber washer assembly l0. Each side of the plate is slotted and the resulting strips are bent upwardly to form resilient contacts 69 and l l.

A cover 12 made of non-conducting material is secured to the base 6| over the groove 63, and carries an elongate resistance element 13 and an elongate conducting strip 14 seated in grooves 76 and ll, respectively, formed in the inner face of the cover l2. The element 13 is held in place by being secured at each end, as by soldering, to a pair of strips 8 l, the opposite ends of the strips 8| being held to the inner face of the cover 12 by the terminals 82 which are peened over the strips 9! at 93. In a similar manner, the elongate strip 74 is held to the cover '12 by the strip 84 and the terminal 86.

Each of the terminals 92 and 8B is drilled and tapped for reception of terminal screws 81.

The end of the base 6| opposite the mouth of the bore 92 is provided with a boss 88 through which extends a threaded mounting stud 89, by means of which the adjustable resistor may be pivotally mounted to follow swinging movement of whatever driving means may be actuating shaft 64.

It will be noted that the groove 63 terminates short of the ends of the base 6|, so that the post 66 abutting the ends of the groove 63 limits reciprocation of the shaft 64. Screws 9] serve to secure the cover 12 to the base 6|.

Like the first embodiment, shown in Figs. 1, 2, and 3, the embodiment just described is also rugged, reliable, and simple in construction. Like the first embodiment also the insulating cover member carries all the electrical terminals, yet is completely free of the actuating element, 1. e the shaft 64. Thus, the final assembly step, which is the simple placing of the cover 12 upon the base 6 I, automatically elfectuates engagement between the two pairs of contact elements at a predetermined proper contact pressure.

An adjustable resistor constructed as described above has been found to be able to electrically detect a movement as small as 0.002 of an inch on the part of the shaft 64.

What is claimed is:

An adjustable resistor comprising a base having a groove therein, a shaft reciprocably mounted in said groove, a post mounted transversely to said shaft and slidable back and forth in said groove, a resilient contact plate secured to said post, a cover mounted to said base over said groove, an elongate resistance element and an electrically conductive elongate strip disposed parallel and mounted to the inner face of said cover and engaging the ends of said resilient plate, a pair of terminals passing thru and secured in MARLAN E. BOURNS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,242,327 Rubinstein May 20, 1941 2,306,152 Batcheller Dec. 22, 1942

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