US2190295A

US2190295A - Switching device

Info

Publication number: US2190295A
Application number: US169180A
Authority: US
Inventors: Robert A Miller; Harry C Rubly
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1937-10-15
Filing date: 1937-10-15
Publication date: 1940-02-13
Anticipated expiration: 1957-02-13
Also published as: BE430635A; FR844645A

Description

Feb. 13, 1940. R. A. MILLER ET AL SWITCHING DEVICE Filed Oct. 15, 1957 COPPER FIG. 3

FIG. 5

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RAMI'LLER 5 H. CRUBLV f fizgm M lNVE/VTORS! ATTORNEY Patented Feb. 13, 1940 UNITED STATES PATENT OFFICE SWITCHING DEVICE Application October 15, 1937, Serial No. 169,180

3 Claims.

: :p This invention relates to switching devices and more particularly to selective switching devices.

The object of this invention is to provide a 5 switching device adaptable for use in electrical sound translating systems in which signals generated by operation of a switching device must be eliminated or reduced to a comparatively low level.

A feature of the invention resides in matched contact means in the relatively movable electrical conducting portions of the structure.

Another feature resides in the particular combination of elements by means of which a comparatively noiseless se.-itching structure is obtained.

in the drawing, P. is a side elevaticnal view. section, or" the switching device;

Big. 2 rear view of the device, partly in 1213 section, t en on ai ne 2-2 in Fig. 1;

Fig. 3 front ve, partly in section, of a ortion or he device and taken on line 3-3 ii. Fig l ELisatopviewoi device shown in and in sound transiatiiig systems it is often devices and electricai therewith produce at e switching associated resulting rmpart of when a potenused corms sound translating apparatus, sound currents may be generated in the reiativeiy movable parts or" the potentiometer or in a resistance element or elements asociated with the electrical contacts in the potentiometer. The potentiometer switching structure and/or the element or elements associated therewith are therefore found to be, in effect, microphonic since sound cur rents are produced thereby. 'Such sound currents are objectionable since they interfere or combine with the desired sound currents produced by operation of the microphone per se.

We have found that in some cases thermocouple electrcmotive forces are developed in a potentiometer due to the existence in the structure of unlike materials in the contact making parts and that the thermocouple electromotive I force: produced are at such levels that audible sounds are produced from the thermocouple electromotive forces, when the electrical currents are retranslated into sound waves through a receiver. A potentiometer very often becomes quite microphonic after a comparatively 5 short period of service due to wearing away of the relatively fixed and movable contact making parts since the worn contact parts do not make suiiicient contact with other contact parts to prevent sparking.

When a wiper contact for instance is moved with a wiping action over a series of fixed segmental contacts or when segmental contacts are moved with a wiping action into successive engagement with a wiper contact the heat generated at the point of contact results in the development of thermo-electromotive forces suflicient to introduce in a sound translating system variations in current which cause the translating apparatus to produce undesired sounds when the currents therein are retranslated. When the segmental contacts are made f a metal quite diiferent to that of the wiper contact the thermoeeiectromotive forces produced are quite pronounced. We have found 25 that a considerable reduction in the thermoelectrcmotive forces can be eifected by making the respective fixed and movable contacts of same kind of material. For instance, should the respective fixed and movable contacts be 0 both made of silver the thermo-eiectromotive forces would be reduced to a very low level. This silver tosilver contact structure however does not have good wearing qualities since the silver wears away too fast. A copper to copper contact structure provides good conducting means and has only very ic-w thermo-electromc'cive force producing characteristics under increase of temperature produced by frictional engagement of the parts. To prevent wearing of the parts the contacting portions should be made substantially smooth. When a series of 7 contacts are successively brought into engagement with a wiper contact the temperature of the wiper contact is raised relative to the temperature of the series of contacts since the wiper contact is continually being rubbed by the series of contacts while each contact in the series is only intermittently engaged by the wiper contact. This relative diflerence in temperature results in the production of some slight thermoelectromotive forces.

To provide a switching device in which the development of thermo-electromotive forces is u reduced to a very low degree we do four things, that is:

In the first place we make the contacting parts of materials of about the same order.

Inv the second place we make the contacting parts smooth at the point of engagement and so match these parts that there will be very little wearing away of the parts.

In the third place we provide sufllclent spring pressure in one of the parts to keep the parts in sufllcient engagement to prevent sparking.

In the fourth place we so form the wiper contact that there will be sufficient heat dissipatlon' to prevent raising the temperature of this part appreciably above the. temperature of the series of contacts.

The switching device when used as a potentiometer is further prevented from being in efiect microphonic by providing a resistance structure which is substantially non-microphonic. 'To do this we provide a resistance structure comprising resistance elements having no loose particles of resistance material therein.

The invention provides a switching device which is almost entirely non-microphonic and has practically no thermocouple action and which will not change its characteristics over a comparatively long period of service. The switching device, therefore is suitable for use in a sound translating system.

The switching device as shown particularly in Figs. 1, 2 and 3 in the drawing comprises aset of fixed segmental contacts I and a wiper contact 2. The segmental contacts I are mounted on the outer surface of an annular support 3 of insulating material, the segmental contacts being arranged in spaced relation in the form of a ring of separated segmental contacts. a

The segmental contacts I are made of substantially dense metal so that there will be no appreciable pockets developed therein due to wearing away of the segmental contacts in service. Harddrawn copper serves well as a material for the segmental contacts.

The wiper contact 2 is madeof substantially hard metal, so that there will be no appreciable wearing away of the wiper. contact 2 when the wiper contact 2 passes in a wiping action over the segmental contacts I. The parts of the wiper contact 2 having engagement with the segmental contacts are made extremely smooth so that there will be no cutting of the segmental contacts by the wiper contact. The material in the wiper contact 2 must have an electrothermal characteristic about equal to that of the material of the segmental contacts I. contact 2 should also be such that suflicient spring pressure may be developed therein to continually urge a portion of the wiper contact 2 against the ring of segmental contacts I. The wiper contact 2 has a plurality of spring finger portions 4 which are slightly bowed in the direction of the ring of segmental contacts I ,so that spring tension is developed in the finger portions 4 and so that the outer surface of the bowed portion is presented to and presses against the segmental contacts adjacentv thereto. The spring finger formation in the wiper contact 2 provides'for dissipating of heat and keeps the wiper contact 2 at about the same temperature as the segmental contacts I.

The wiper contact. 2 is attached at one end to an L-shaped arm 5 which is made of the same kind of material as the wiper contact 2. The arm 5 has a comparatively large flat disc portion 6 on one of its leg portions. The other leg portion The material in the wiper supports the wiper contact 2. A comparatively large rectangular aperture 1 is provided in the central portion of the disc portion 6. Secured to one face of the disc portion 6 by means of rivets 8 is a ring 9 of insulating material. The ring 9 extends across the greater portion of the rectangular aperture I and has one straight edge portion I0 lying in spaced relation to one end of the rectangular aperture 1 in the disc portion 6. An L-shaped stop arm II apertured on one leg portion I2 to I3 is secured to the operating shaft I3, an end of the operating shaft l3 extending through the aperture in the leg portion I2 and being upset or spun over against the leg portion I2. The leg portion I2 01 the stop arm II is narrower than the width of the rectangular aperture 1 in the disc receive an end of an operating shaft portion 6 of the arm 5, and rests against one face of the ring 9 of insulating material and does not touch at any point the disc portion 6 of the arm 5. A free leg portion ll of the stop arm II extends over the straight edge portion II) of the ring 9 and inwardly toward the annular support 3 of I) insulating material.

The operating shaft I3 is journaled in a comparatively long bearing I5 externally threaded on an outer end and having lock-nuts l6, I1 and I8 supported thereon. The bearing I5 projects through a central aperture in a shallow cup mernber I9, and is secured therein by means of the lock-nuts I1 and I8. The bearing I5 also extends through the annular support 3 of insulating material which supports the segmental contacts I. An L-shaped bracket 20 is secured at one of its le I portions to an inner surface of the cup member I9 by suitable means such for instance as the rivets 2I and at a point oifset radially from the central aperture in the cup member IS. The unsecured leg portion of the bracket extends parallel with the inner surface of the side wall of the cup member I9.

A rectangular apertured strip 22 of insulating material is supported above the unsecured arm of the bracket 20 by means of a machine screw 23 and a spacer 24, the machine screw 23 extending through an aperture in the strip 22 of insulating material and then through the'spacer 24 and threading into an internally threaded aperture in the unsecured leg portion of the bracket 20

Spaced terminals

25 and 26 are secured to the strip 22 of insulating material and project upward from the upper surface of the strip 22. The strip 22 of insulating material is comparatively thick and is sufiiciently stiil to serve as part of a supporting means for the inner end of the bearing l5. To provide the supporting means abovementioned, an apertured arm 21 of insulating material is supported at one end of the strip 22 of insulating material by means of a corner bracket 28, the arm 21 being comparatively thick and rigid and extending downward at an angle of 90 degrees from the plane of the strip 22. One leg portion or the corner bracket 28 is secured against the lower surface of the strip 22 of insulating material, by means of the rivet 29. The other leg portion of the comer bracket 28 supportsa rivet 30 which extends through an aperture in the corner bracket 28 thence through an aperture in a terminal 3| and through an aperture in the arm 21, the rivet 30 serving to hold together the parts through which it extends. The lower end of the arm 21 is enlargedand apertured to permit extension therethrough of a portion of the bearing I5,

the portion extending through-the arm 21 being adjacent an annular flange 32 provided on the 15 2,190,595 inner end portion of the bearing ii. A washer 33 is supported on the shaft l3 between the flange 32 of the bearing li'and the inner face of the ring 9 of insulating material.

The arm 5 which as above-mentioned is made of the same material as the wiper 'contact 2 has the disc portion 6 at one end, the disc portion 6 being secured to the ring 9 of insulating material. The ring 3 of insulating material has a central aperture adapted to receive the shaft l3 and fits thereover. When the ring 9 is placed on the shaft l3 and the shaft i3 is extended through the aperture in the stop arm I! and the end of the shaft is upset or spun over against the stop arm H, the parts are held together so that rotation of the shaft i3 will cause the wiper contact 2 to successively engage the segmental contacts I. A stop pin 34 secured to the flange 32 and extending radially therefrom extends into the path of movement of the inwardly extending end I4 of the stop arm i I. Engagement of the end H of the stop arm H with the pin 34 limits the rotational movement of the wiper contact 2 over the segmental contacts I.

The terminal 3i has two rather widely separated leg portions 35 offset from the plane of the upper portion of the terminal and extending into frictional engagement with the disc portion 6 of the arm 5, the free ends of the leg portions 35 being curved to present a rounded surface against the disc portion 6.

As above-mentioned the wiper contact 2 and the arm 5 are made of the same kind of material and this material has about the same electrothermal characteristic as the material of the segmental contacts I. The terminal 3! is also made of the same kind of material as the wiper contact 2 and the arm 5. Since the wiper contact 2, the arm 5 and the terminal 3i have curved and bent portions and cannot well be formed from hard-drawn copper and since the parts make frictional contact with other parts some material having like electrothermal characteristics to that of hard-drawn copper but being more readily workable is desirable. We have found that beryllium copper has about the same electrothermal characteristics as hard-drawn copper, and that it may be annealed and worked to required shape and given a smooth surface and then hardened to provide a substantially hard smooth surfaced contact. The parts such as the wiper contact 2, the arm 5 and the terminal 3i requiring bending to form them into the required shapes may therefore be readily made of beryllium copper. These parts may then be hardened as required. When the segmental contacts i are made of hard drawn copper and the wiper contact 2, the arm 5 and the terminal 3| are made of beryllium copper and the beryllium copper parts are hardened, there is comparatively little wearing of the parts in service. The contact making parts throughout also possess about the same electrothermal characteristics as each other, the generation of thermo-electromotive forces between the parts, therefore, is reduced to such a low point as to be negligible. The switching device, therefore/is in effect comparatively non-microphonic and is suitable for use in connection with sound translating apparatus and will give long service.

Connected to the segmental contacts I are resistance devices 36. The 1' devices 33- comprise suitable lengthsof resistancewire or other like non-microphonic resistance material. The resistance devices 36 connected by means of comparatively stifi conductor wires 31 to predetermined segmental contacts-l which are slotted at 38 to receive the wires 31. With this arrangement the resistance devices 36 are supported by means of the conductor wires 31 in their required positions relative to the segmental contacts l and require no other means of support.

The resistance devices 33 may be connected in series and arranged as shown in Fig. 5 or in any other desired manner, and connected to the segmental contacts I by means of the conductor wires 31.

A cup-shaped cover 33 is applied over the switching parts and resistance devices above described. The open end of the cover 33 fits over the side walls of the cup-shaped member l9 and frictionally engages the outer surface of the side wall. An open ended slot 30 is provided in the open end portion of the cover 39 to accommodate the upper end portion of the arm 2i when the cover 33 is being applied or removed. When the cover 33 is applied the side edge portions defining the slot 40 pass under the rectangular strip 22 of insulating material and are overlapped thereby since the slot 40 is narrower than the strip 22 and the strip 22 is elevated by means of the spacer 24 a suflicient distance to permit passage of the wall of the cover under the strip 22.

What is claimed is:

1. In a switching device, in combination, a ring of spaced segmental contacts, a support for said contacts, an arm movable relative to said ring of contacts, a support for said arm, a fin-- gered wiper contact supported on said arm and slightly bowed into tangential engaging position relative to said segmental contacts and having only a central portion presented into engaging position relative to said segmental contacts and said segmental contacts, said arm and said wiper contact being made of metal of the same general kind to the development of electrothermocouple effects in the parts.

2. In a switching device, in combination, a ring of spaced segmental contacts of hard-drawn copper, a support for said contacts, an arm of beryllium copper movable relative to said ring of contacts, a support for said arm, a fingered wiper contact of beryllium copper supported on said arm and having finger portions slightly bowed into tangential frictional spring pressed engagement. with said ring of contacts'and so that only the central portion of the wiper contact is in engaging position relative to said segmental contacts, a terminal of beryllium copper and curved leg portions on said terminal bowed in long radius curved formation into spring pressed frictional engagement with said arm and having the long radius curved portion in engagement with said arm.

3. In an electrical switching device, in combination, a cup member, a tubular bearing extending through the diametrical center of said cup member and supported in said cup member, a ring of insulating material supported on said bearing, spaced segmental contacts supported in ring formation on said ring, a rotatable shaft journaled in said bearing and having a portion projecting beyond said bearing, an V-shaped arm supported on said shaft and extending in spaced relation over said segmental contacts, a wiper contact supported on said arm and extending tangentially of and into engaging position relative to said mental contacts, an insulating support supported on said cup member and ex- 4 mitoses tending in spaced parallel relation with said on said terminal in frictional engagement with bearing and'then downwardly to meet said bearsaid arm and said segmental contacts, said wiper ing, the portion meeting said bearing being apercontact, said arm and said terminal being all tured to receive said bearing and serving as a, made of metal of the same general kind. support for one end of said bearing, a bifurcated terminal supported on said insulating support ROBERT A. MILLER. and relatively long radius curved leg portions HARRY C. RUBLY.