US3603854A

US3603854A - Variable resistor with tilted contact

Info

Publication number: US3603854A
Application number: US65133A
Authority: US
Inventors: Mogens W Bang
Original assignee: Stackpole Carbon Co
Current assignee: Stackpole Carbon Co
Priority date: 1970-08-09
Filing date: 1970-08-09
Publication date: 1971-09-07
Anticipated expiration: 1988-09-07

Abstract

A slide is movable lengthwise between spaced parallel collector and resistance strips. Extending across the space between the strips is a carbon block that is connected to the slide by spring means urging the block to turn on an axis parallel to the strips to press two diagonally opposite areas of the block against the strips so that the block forms a bridging contact between them.

Description

I Umted States Patent 1111 3,603,854

[72] Inventor Mogens W. Bang [56] References Cited g y UNITED STATES PATENTS P 65333 2,976,507 3/1961 Di Girolamo et al. 338/180 1221 Med 3 465 277 9/1969 Ban 338/183 Patented sept- 7,1971 g A st k l C b0 Com an 3,510,821 5/1970 Eberwem et al. 338/183 [73] ssgnee e P 3,551,871 12 1970 Eberwein et a1. 338/183 x St. Marys, Pa.

Primary Examiner-Lewis H. Myers Assistant Examiner-D. A. Tone Attorney-Brown, Murray, Flick 8:. Peckham ABSTRACT: A slide is movable lengthwise between s aced [54] VARIQBLE RESISTOR W TILTED CONTACT parallel collector and resistance strips. Extending acro s s the 11 Clams! 12 D'awmg space between the strips is a carbon block that is connected to [52] US. Cl... 338/183 the slide by spring means urging the block to turn on an axis [51] Int. Cl H01c 9/02 parallel to the strips to press two diagonally opposite areas of [50] Field of Search 338/ l 83, the block against the strips so that the block forms a bridging contact between them.

PATENTED SEP 71am sum 1 OF 2 PATENTEU SEP 719m SHEET 2 OF 2 VARIABLE RESISTOR WITI-I TILTED CONTACT It is among the objects of this invention to provide a variable resistor, in which there is a bridging contact formed from a carbon block making substantially line contact with both a resistance element and a parallel collector.

The invention is illustrated in the accompanying drawings, in which:

FIG. 1 is a side view, partly broken away, of a linear motion potentiometer;

FIG. 2 is a fragmentary plan view and section taken on the line Il-ll of FIG. 1;

FIG. 3 is an enlarged cross section taken on the line Illlll of FIG. 1;

FIG. 4 is a fragmentary side view of a slide with its bridging contact, showing a modification;

FIG. 5 is a cross section taken on the line VV of FIG. 4;

FIGS. 6 to 11 are views similar to FIGS. 4 and 5 of three further embodiments of the invention; and

FIG. 12 is a perspective view of another carbon block.

Referring to FIGS. 1 to 3 of the drawings, the long rectangular housing 1 of a variable resistor, such as a potentiometer, is provided along its front or top with a central slot 2 extending lengthwise of the housing for nearly its full length. Slidably mounted inthe slot for movement lengthwise of the housing is a rectangular slide 3 that has laterally opening grooves 4 in its opposite sides receiving the sidewalls of the housing slot to hold and guide the slide. The slide may be moved in any suitable manner, such as by a projection or knob 5.

Inside the housing a metal collector strip 6 and an electrical resistance strip 7 are mounted against its opposite sides in parallel relation to each other. The collector strip is provided with an integral terminal 8 that extends through the back or bottom of the housing, and each end of the resistance strip is connected to another terminal 9 likewise extending through the back. The slide 3 has a portion extending between these two strips, from which it is spaced. This portion of the slide is an open frame 10 that is parallel, or nearly so, to the collector and resistance strips. The frame preferably is rectangular.

Disposed inside the slide frame, but projecting from its opposite sides, is a carbon block 12. Carbon as used herein is intended to cover graphite also. The block is narrower than the space between the two strips and is considerably longer, lengthwise of the strips, than it is wide. It may take various shapes in cross section, such as elliptical or diamond shape,

but the simplest shape is rectangular, although the ends of the block may be curved transversely so that the block can fit more snugly in the frame and yet turn in it on an axis extending through the housing slot. The block may substantially engage the surrounding sidewalls of the frame to prevent loose play between the block and slide, but friction between them can be reduced by providing those walls with inwardly projecting transverse ribs 13 that substantially engage the block.

It is a feature of this invention that two diagonally opposite areas, such as edges, of the block are pressed against the two parallel strips by spring means, so that the block fonns a carbon bridging contact between the collector and the resistance element and remains pressed against them even as it wears, as

shown in FIG. 2. One way of applying the spring pressure to the block is to provide it with a central passage 15 that extends through it parallel to the strips. For best results, the central portion of the passage is smaller than the end portions. A coil spring 16 extends through this passage in tight engagement with the block and has projecting ends held by the sidewalls of the slide frame. The ends of the coil are straight and extend diametrically across it and fit in slots 17 in the slide. The spring is originally positioned in the block in such a manner that the block will have to be twisted or turned in the slide frame to a position more nearly parallel to the strips in order for the block to be inserted between them. When the block is released, the tendency of the spring to untwist will cause the diagonally opposite edges of the block to be pressed against the two strips. As the edges of the block wear away, the spring will continue to press the block against the strips.

Instead of a coil spring, a flat spring 20 can be used, as

shownin FIGS. 4 and 5. In this case the central portion of the passage 21 through the carbon block 22 there is a slot of substantially the same thickness as the spring. The spring fits snugly in the passage slot and projects from the oppositesides of. the block into slots 23 in the slide frame 24. The passage slot in the block is inclined to the side faces of the block so that when the block is inserted in the slide frame it will be tilted or inclined to the frame and require slight rotation before it can be inserted in the potentiometer housing.

A solid carbon block, without a passage through it, also can be used as the bridging contact, as shown in FIGS. 6 and 7. In this case the block 26 is held in its tilted position in a slide frame 27 by means of leaf springs 28 secured to opposite ends of the frame and extending inwardly into overlapping engagement with the diagonally opposite portions of the side faces of the block that are spaced from the resistance strip 29 and collector strip 30. These springs may be integral with the slide frame as shown, or they may be snapped or clamped onto it. They press the free diagonally opposite edges of the block against the strips.

A different arrangement is shown in the remaining figures of the drawings, where the slide 32 is not provided with a frame, but with a post 33 that extends between and across the collector and resistance strips 34 and 35. This post supports a leaf spring 36 that is fastened to a carbon block 37. One end of the spring is clamped onto the post, while the opposite end extends through a central slot 38 in the block. The projecting end of the spring is formed with reversely bent ears 39 that hold the block on the spring, while at the opposite side of the block there is a bend in the spring that prevents the block from moving inwardly along the spring. In order to insert the block between the resistance and collector strips, the block must be turned into a position more nearly parallel to the strips. This will bend the spring more. When the block is released, the spring will tend to straighten and thereby press the diagonally opposite edges of the block against the strips. The central portion of the spring may be reduced in width to limit flexing mainly to that area.

If desired, as shown in FIGS. 10 and 11, the post 41 can be provided with'a transverse slot 42 in which one end of a leaf spring 43 fits snugly. The opposite end extends through a slot 44 in a carbon block 45. The slot is inclined to the side faces of the block. Between the block and the post the spring has a laterally projecting U-shape portion which gives the spring its flexibility. The tendency of this portion to open wider causes the spring to press diagonally opposite edges of the block against the collector and resistance strips 47 and 48.

The carbon contact block 50 shown in FIG. 12 is similar to the one shown in FIGS. 8 and 9 and is provided with a central slot 51 so that it can be mounted in place in the same way. The difference is that block 50 has three points of contact, one at one side and two at the opposite side. For this purpose one side of the block has a central projection 52 and the opposite side has a central notch 53. Like a three-legged stool, this con tact will seat firmly against adjoining collector and resistance strips.

Since each of the contacts disclosed herein is a carbon block that engages both strips, there is only one type of material in the bridging contact. This avoids an interface between dissimilar materials, such as carbon and metal, which could cause chemical action and thus higher contact resistance.

According to the provisions of the patent statutes, l have explained the principle of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

l. A variable resistor comprising spaced parallel collector and resistance strips, a slide between said strips movable lengthwise thereof, a carbon block disposed in the space between the strips, the block being narrower than said space,

and spring means connecting the slide and block and urging the block to turn on an axis parallel to the strips to press two diagonally opposite areas of the block against the strips, whereby the block forms a bridging contact.

2. A variable resistor according to claim 1, in which said slide includes a frame spaced from said strips and containing said carbon block.

3. A variable resistor according to claim 2, in which said spring means are leaf springs having outer ends secured to opposite sides of said frame and having inner ends overlapping and pressing against diagonally opposite side portions of the carbon block to twist the block in the frame.

4. A variable resistor according to claim 2, in which the carbon block is provided with a central passage through it extending across said strips, and said spring means extends through said passage in tight engagement with the block, the ends of the spring means projecting from the block and being secured 7. A variable resistor according to claim 1, in which said block is generally rectangular and said areas of the block are diagonally opposite edges thereof.

8. A variable resistor according to claim 1, in which said slide includes apost extending across said strips beside the carbon block, and said spring means is a leaf spring having one end secured to said post and having its other end secured to the central portion of said block.

9. A variable resistor according to claim 8, in which said one end of the spring is wrapped around the post, and said block is provided with a central opening receiving the other end of the spring.

10. A variable resistor according to claim 8, in which said post is provided with a passage receiving one end of the spring, said block is provided with a passage substantially in line with the post passage and receiving the other end of the spring, and the spring between the post and block is provided with a laterally projecting U-shape portion.

11. A variable resistor according to claim 1, in which said contact block is provided at one side with a central projection engaging the collector strip and at the opposite side with a central notch to form two spaced points of contact with the resistance strip.

Claims

1. A variable resistor comprising spaced parallel collector and resistance strips, a slide between said strips movable lengthwise thereof, a carbon block disposed in the space between the strips, the block being narrower than said space, and spring means connecting the slide and block and urging the block to turn on an axis parallel to the strips to press two diagonally opposite areas of the block against the strips, whereby the block forms a bridging contact.

4. A variable resistor according to claim 2, in which the carbon block is provided with a central passage through it extending across said strips, and said spring means extends through said passage in tight engagement with the block, the ends of the spring means projecting from the block and being secured to opposite sides of said frame, and the spring means being twisted around its axis to exert pressure against the block.

5. A variable resistor according to claim 2, in which said spring means is a coil spring and said frame is provided with slots receiving the ends of the spring.

6. A variable resistor according to claim 2, in which said spring means is a flat spring and said frame is provided with slots receiving the ends of the spring.

7. A variable resistor according to claim 1, in which said block is generally rectangular and said areas of the block are diagonally opposite edges thereof.

8. A variable resistor according to claim 1, in which said slide includes a post extending across said strips beside the carbon block, and said spring means is a leaf spring having one end secured to said post and having its other end secured to the central portion of said block.