US2740025A

US2740025A - Miniature variable resistor

Info

Publication number: US2740025A
Application number: US362916A
Authority: US
Inventors: William R Polye; Andre P Viret
Original assignee: Bendix Aviation Corp
Current assignee: Bendix Aviation Corp
Priority date: 1953-06-19
Filing date: 1953-06-19
Publication date: 1956-03-27
Anticipated expiration: 1973-03-27

Description

March 27, 1956 w POLYE ETAL 2,740,025

MINIATURE VARIABLE RESISTOR Filed June 19, 1953 FIG. 1

4 |Q 27 5 a a k I i ii 23 4-| I ll \6 IIIEII III IN VEN TORS W/LL/AM R. POLVE United States Patent MINIATURE VARIABLE RESISTOR William R. Polye, River Edge, and Andre P. Viret,

Tenafly, N. L, assignors to Bendix Aviation Corporation, Teterboro, J., a corporation of Delaware Application June 19, 1953, Serial No. 362,916 Claims. (Cl. 201-48) This invention relates to electrical miniature variable resistors, such as potentiometers and rheostats, and especially to a construction for instruments of this type adapted for effective use in extremely small sizes. Such miniature instruments are desirable for incorporation in small electrical units, such as indicating instruments, where only a very small amount of space is available in the housing.

A feature of the invention is the provision of a variable resistor construction whose parts may be readily assembled in sizes so small that the usual arrangements are impractical or undesirable. More particularly, the casing is designed for assembly without screws, and the connection to the contact arm is planned so as to eliminate the usual devices located within the casing, thereby permitting a reduction in casing size. A further feature is the provision of an advantageous arrangement for adjusting the position of the contact arm including a simple structure which insulates the arm from the adjusting element. Another feature is an improved stop arrangement for limiting the travel of the arm.

These and other features of the invention will appear from the following description in conjunction with the accompanying drawings, in which:

Figure l is a vertical central section through an instrument embodying the invention;

Figure 2 is a plan view with the cover and adjusting arrangement removed; and

Figure 3 is a fragmentary vertical section on line 3-3 of Figure 2.

In the illustrated embodiment a housing 1 made of suitable plastic such as Bakelite or similar insulating material, is provided with a bottom 2, an integral cylindrical side wall 3 and a separable cover 4 tightly fitting said wall, and advantageously rabbeted at 5, arranged for secure engagement on the wall, as by cementing. A fiat resistance element 6 extends around the inner face of wall 3 and is suitably held in place, as by cement. Said element preferably consists of a wire resistance wound on a strip of fishpaper or other suitable sheet insulating material, when a substantial current is to pass through the instrument, though a strip or layer of carbon or other resistance material may be used where conditions permit. At least one end of the resistance element is electrically connected to a terminal mounted on the casing. In the form shown, the terminal 7 is in the form of a metal rivet extending through and flanged on both sides of the bottom 2, to which an end of the wire 8 of resistance 7 is at tached. Where the instrument is adapted for use as a potentiometer, as shown, the other end of wire 8 is also connected to a second similar terminal 7. Said wire ends are preferably cemented to the housing 1 so that they will not become loose.

A contact arm assembly 9 is rotatably mounted in the housing 1. It includes a metal spindle 10 having a lower cylindrical reduced end portion 11 extending through a bearing opening in the bottom 2 and having a slightly concave end bearing against a convex contact stud 12 fixed to a spring arm 13 fastened to the bottom 2, as by riveted terminal 14. The upper reduced cylindrical end 15 of spindle 10 extends through a bearing opening in housing cover 4 and is fixed to an insulating block 15 arranged for use in manual rotation of spindle 10. in the form shown, the spindle end 15 is cemented in a socket in block 16, and is further held in place by pin 17, the ends of which are inwardly spaced from the outer face of the block.

Block 16 advantageously includes an arrangement which facilitates manual operation of the contact arm assembly 9, such as a screw driver slo In the form shown, a short rod 18 coaxial with spindle 10 is mounted on block 16 as by cementing said rod in a socket in the block, and it may also be held in place by a short pin 19. The upper projecting end of rod 18 is provided with a screw driver slot 20.

The spindle 10 carries a spring contact arm 21 within housing 1, slidably engaging resistance element 6. In the illustrated embodiment, arm 21 comprises a metal spring strip having an end mounted in a flat-faced recess 22 in spindle 10 by screw 23; and arm 21 may be annular in form with both ends held in recess 22 by screw 23 as shown. A convex contact stud 24 fixed to spring arm 21 bears against the inner face of resistance element 6.

An arrangement for limiting the rotation of the contact arm assembly 9 may be provided. As shown, a laterally extending stop arm 25 is mounted on spindle 10, and has an upward extension 26 which engages a suitable stop on cover 4, such as stop stud 27 fitting tightly in an aperture in said cover and projecting into the path of arm 25.

The disclosed arrangement may be used as either a rheostat or a potentiometer. For rheostat use the power circuit lines are soldered to the external ends of terminal 14 and a terminal 7, the current passing through resistance 6, contact arm 21, spindle 10 and arm 13. When used as a potentiometer, the power circuit lines are of course soldered to terminals 7, and the voltage take-off line to terminal 14. Since in both cases spindle 10 is in the circuit, the insulating block 16 is arranged to prevent contact by a screw driver or other object with spindle 10 or pin 17.

The disclosed construction eliminates any structure for making take-off connections with the rotating contact arm assembly 9 inside the housing 1, providing a compact simple construction suitable for practical service in very small sizes, rheostats of this type having an overall diameter of only half an inch having been found satisfactory in use. The construction also eliminates the use of screws engaging the plastic housing parts, such screws being objectionable and often impractical in very small sizes.

While a preferred embodiment of the invention has been shown and described, modification thereof may be made without departing from the invention.

We claim:

I. A variable resistor comprising a housing, a resistance element in the housing, a rotatable contact unit slidably engaging the resistance element and including pivots extending through the housing at opposite sides, a terminal connected to the resistance element, and an external terminal device frictionally engaging a pivot.

2. A variable resistor comprising a housing of insulating material, an arcuate resistance element in the housing, an external terminal connected to an end of the resistance element mounted on the housing, a metal spindle in the housing having end portions extending through and rotatably engaging the housing, a contact arm on the spindle slidably engaging the resistance element, a contact element mounted externally on the housing and engaging an end of the spindle, and a spindle rotating device at the other end of the spindle.

3. A variable resistor as claimed in claim 2 in which the externally mounted contact element comprises a spring member having frictional endwise engagement with the spindle end.

4. A variable resistor as claimed in claim 2 in which the resistance element is mounted on a side wall of the housing, and the contact arm comprises a curved spring arm laterally mounted on the spindle.

5. A variable resistor as claimed in claim 2 in which the spindle rotating device comprises a drive member of insulating material engaging an end of the spindle projecting from the housing.

6. A variable resistor as claimed in claim 2 in which the spindle rotating device comprises a connector block of insulating material engaging an end of the spindleprojecting from the housing, and a metallic drive element fixed to the block and provided with a drive slot aligned with the spindle axis.

7. A variable resistor as claimed in claim 2 including a second terminal connected to the other end of the resistance element, mounted on and extending through the housing.

8. A variable resistor as claimed in claim 2 including a stop arm mounted on the spindle, and a stop projecting inwardly from the housing in the path of the stop arm.

9. A variable resistor as claimed in claim 2 including a stop arm mounted on the spindle, a stop projecting inwardly from the housing in the path of the stop arm, and a common mounting screw threaded into the spindle and engaging the contact arm and stop arm.

10. A miniature variable resistor comprising a housing of insulating material having a body and a cover held in place on the body by surface engagement therewith, an arcuate resistance element in the housing, an external terminal mounted on the housing and connected to the resistance element, a metal spindle in the housing having reduced cylindrical end portions rotatably fitting in openings in the housing, a spring contact arm mounted on the spindle and slidably engaging the resistance element, a spring contact arm mounted on the housing and frictionally engaging one end of the spindle, and a spindle rotating device at the other end of the spindle.

References Cited in the file of this patent UNITED STATES PATENTS