US2639340A - Cam device for controlling electric circuits - Google Patents

Description

M y 1953 H. D. GA lTE v 2,639,340

CAM DEVICE FOR CONTROLLING ELECTRIC cmcuns- Filed Aug. 29, 1951 Patented May 19, 1953 CAM DEVICE FOR CONTROLLING ELECTRIC CIRCUITS HaroldDodimead Gaite, Taplow, England, as-

signor to British Telecommunications Research Limited TapI W,England, a British company Application August 29, 1951, Serial N 0. 244,193 In GreatBritain September 6; 1950 (C1. ZOO-+46) Claims.

The present invention relates to cam devices and is more particularly concerned with cam devices arranged to control an electricalv circuit or circuits.

The object of the invention is to provide a cam device-in which the'mass of the moving parts is reduced to a minimum and in which the acceleration of the cam follower on operation is reduced to a reasonable figure by simple means.

Accordingto the invention, in a cam-operated switching-device, a thin sheetsupported by a base member having an electrical contact inset or insets is provided with one or more slots or cut-out portions aligned with said inset or insets and is arranged to co-operate with a cam follower for each slot and forming the other electrical -contact, relative movement between the sheet and-thecam follower or followers causing the latter to ride into and: out of the slot or slots to complete the electrical circuit or circuits between the cam follower or followers and the contact inset or insets.

In one embodiment of the invention the sheet is in the-form of a disc 'mountedaon a =rotatable spindle, a slot .or-slots being provided at the desired radius or radii from'the centre of the disc,-.while the cam followers are stationary. The base member by which the disc is supported is fixed relative tothedisc and carries contact pins of electric'conducting material with which thefollowers contact ,as they. drop into the corresponding slot.

Alternatively the'base member is mounted for rotation with the .disc. and carries a contact inset. or insets having substantially the :dimensions .of the slot or. slots in the disc.

Preferably the cam followers are made of spring wire, of circular cross-section, the free endsof the followers being bent to forman acute or an obtuse angle with the shank orare of narrow. U-shape or of V-shape. Alternatively the followers may consist of spring-pressed balls. It is also preferred to contourat least theleading. edges of the slot orslots or to make the leading edge flexible.

The invention will be better understood from the following description of several embodiments given by way of example only and taken in conjunction with the-accompanying drawings comprising Figs. 1 to 9.

In the drawings,

Fig. 1 shows ,a. plan view ,of 'oneembodiment,

-Fig. .2-shows a part-sectional side. elevationof the embodiment of Fig. 1,

Fig. 3 shows a plan view of a second embodiment Fig. 4 shows a part-sectional side elevation of the embodiment of Fig. 3, and

Figs. 5 to 9show various constructions of the cam-followers and the edges of the disc.

Referring firstto-Figs. 1 and 2, the device is shown as'mounted on both sides of a plate I and comprises a circular disc 2 provided withslots or-cut-out portionst. The disc is made of conducting material, for instance, shim steel and is mounted for rotation on the spindle t. The spindle 4 passes through the base or supporting member 5 which together with distance piece 6 is suitably secured by means not shown to abase l fittingwithin the circularzhousing 8 and suitably secured byscrews (not shown) to the plate I. The provision of the distance piece 6 enables terminals 9 to be secured to the underside of the base or supporting member, the terminals 9 beingconnected to the contact insets or pins ii} and to the controlled circuits. Asuitable cover (not shown) would normally be providedfor the housing 8. The cam followers H are made. of spring wire and as shown in Fig.2 the free ends are of narrow U-shape. The followers are threaded through holes in a mounting block [2 secured to the'supporting'member 5, the screws [3 enabling the position of the followersin the .blockto'be adjusted. A. terminal I4 is also secured tothe block to enable connection to be madewith one pole of the current source,.the other pole being connected to remote ends of the controlled circuits the near ends of which are connected to the terminals 9. It will thus be seen that asthe disc rotates contact'will be made between the cam-followers and the conducting insets only where a slot in the disc passes beneath the cam follower. Where the disc is of conducting material, the pins in the supporting member will be adjusted so that their top surface is slightly below the level of the supporting member so that contact between the pinsand the. disc is avoided. Alternatively, of course, the disc may be made of insulating material. but the advantage of using shim steel, namely that the disc may be made very thin and flexible, is thereby lost.

In the embodiment shown, the spindle 4 is continuously driven by means of an electric motor indicated at 15, the motor being secured by a reduction gear and a friction clutch but as.

these form no part of the invention they are not shown in detail but are indicated diagrammatically by IT.

In the embodiment, shown in Figs. 3 and 4, those parts which are shown in Figs. 1 and 2 are given the same reference numbers. In this embodiment the supporting member 20 and the disc 2 are;mounted for rotation on the spindle 4. The contact insets in this case will have substantially the same dimensions as those of the slots in the disc and electrical connection therewith will be effected, for instance-by means of suitable brushes 2i mounted in an insulating block 22. The mounting block His new secured to an individual support 23 :mounted :on' thebase I. This arrangement hasltheadvantage that there is no friction between the disc and the supporting member although, as will be seen from Fig. 1, friction is reduced to a minimum by recessing the supporting member at I85 "Iti's also pointed out that with the embodiment of Figs. 1- and'2 there is no axial load-onthe spindle and the flexibility of the disc allowsiof-aXial float at-all times. l 1

Referring now to Figs. '5"to 9, these show enlarged viewsof vvarious shapes .of cam-followers and the shaping of the edgesofthe slots. Inthe arrangement shown in Fig. 5 the-wire forming the cam-follower is of circular cross-section and the free end of the-follower-is bent at an-acute angle to the shank. ,Furtherthe edges-25 of the slot are vertical. In this case; the acceleration' imparted'to a cam-follower: upon engagement with a flankof a slot may be excessive. However, it is frequently found that continual operation of the device for ashort period wears down the sharp edges of the slots, thus reducing the acceleration of thefolloweriand theloading on the cam. These two effects cumulatively reducethe rate, of wear and. it isq-found that after a'short period of running, the contour of the cam andhence the timing will-remain substantially constant.v r .1.

I It may, however, be inconvenient to perform this initial running in operation in which case the follower of the edges. of thel slots; may: be specially shaped to reduce bothithe acceleration of the follower andtheloadingq, Forinstancaas shown.in Fig.. 5,:theleading edgelalofrthe slot may be inclined and the free: endzof' therfollower is1bent to form an obtuse angle with the shank or as shown in.Fig;.7, the free end of the follower may have a: ,v shapeqmAgain. ibothttheset iconstructions maybe included inva further embodiment. Another arrangement which n-avoids -this disadvantage is'shown in-Figs. 8 andy9 wheretthe leading and trailing edges of the slots are providedwitnflexible tongues 21-and.29.-: Intthis case, however, care mustbetaken oo-ensure that the base member or supporting member does not nullify these precautions. For instance, as shown in' Fig. -8, where the supporting memberrotates with the disc, the basemember shouldbe'pr'ovided with recesses such as 28 having the same width as the slots in the disc but slightly greater length; The flexible edges are'sh'own at 21. Where the supporting member is fixed" relative to the disc the recesses should extend in complete circles in the supporting member or; as shown in Fig. 9, an additional'i'disctfl"maybe inserted between-the'slotteddisc2"and the supporting I member 5, the additional disc having similar slots 3i of s1ightly'greater length than the slots inthe disc Itwill, of course, be understood that While the embodiments described are arranged" =to--controla plurality of circuits, there is no limitation to more than one. Further, other alternative arrangements are possible and, in particular, the cam-followers could consist of spring-pressed balls. In addition the height of the contact pins or insets may be made variable to enable accurate adjustments to be made of the instants of making and breaking contact between the follower and the pin and also to enable compensation to be made for wear of the cam follower.

Other arrangements than the slotted disc may also be used. For instance, the sheet may be arranged in the form of a tube mounted on a cylinder or. the sheet may be wrapped round a rotatable cylinder or cone. It may also be in the form of -a tape which may be continuous where repetitive'operation is required, the movement of the'sheet being linear in this case.

-The cam device of the invention has many applications. For instance, it may be employed for operating electric contacts which control the operation of flashing fluorescent lights It-may also be used for the generation of repetitive make and break signals which form, for example, the elements of a telegraphic code. Other applications will also be apparent to thoseskilled in the art. 4 1

Iclaim:

1. An electrical switching deyice comprising a shaft, means for rotating said shaft, a thin metallic disc secured to said shaft with its-plane normal thereto so as to be rotated therewith and provided with a plurality of rows of perforations at different radii, a plurality of contact-members located in a plane parallel to the plane of said disc and spaced apart so as to register with said rows of perforations respectively, an insulating support for said-disc located on the side thereof remote from said contact members, and metallic inserts in said support atradii corresponding to the contact-making ends of said contact members whereby as said disc is rotated said contact members make intermittent contact with said inserts.

2; An'electrical switching device comprising a shaft, means for rotating said shaft, a thin metallic disc'secured to said shaft with its plane normal thereto sov as to be rotatable therewith and provided with a plurality of concentric rows of perforations, a plurality ofcontact members 10- catedin aplane'parallel to the plane of said disc and spaced apart so as to register with said rowsof perforations respectively, 'a' fixed insulating support for said disc located on the side thereof remote from said contact members, and metallic inserts in said insulating support in positions'opposite the contact-making ends of said contact members. r a? '3. An electricalswitc'hing device comprising a shaft, means for rotating said shaft, a thin metallic disc secured to said sh aft wi'th its plane normal thereto so a to be ro'tatabletherewith and provided with a plurality of concentric rows of perforations, a plurality of contact members located in a plane parallel to the plane of said disc and spaced apart so that, their contact-making ends register with said rows of perforations, an insulating support for said disc located -.on the side thereof remotefrom said contact members and secured to said shaft so as ,to berotatable therewith, metallic inserts in said support in positions corresponding'to the perforations in said disc, slip rings on said shaft connected respectively-to said inserts and brushes cooperating 10 Number longer in the direction of movement of said first disc and flexible tongues on the edges of said per forations on said first disc extending into the perforations of said second disc.

HAROLD DODIMEAD GAITE.

References Cited in the file of this patent UNITED STATES PATENTS Name Date 2,055,031 Hutchings Sept. 22, 1936

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