US2611847A - Cam-actuated device - Google Patents

Description

Sept. 23, 1952 sco'r'r CAM-ACTUATED DEVICE Filed Dec. 14, 1950 INVENTOR BENJAMIN B. SCOTT ATTORNEY Patented Sept. 23, 1952 Benjamin B. Scott,

Schenectady, N. Y'., assignor,

by mesne assignments, to the United States of America as represented bythe Secretary of the Navy Application December 14, 1950; sereu No. 200,859

"The invention relates to improvements in carnactuated devices such as electrical brushes for variable resistors.

An important object of the invention is to provide a cam-actuated electrical brush support so constructed and arranged as to minimize its frictional resistance to camactuated movement whereby the use of a cam having the theoretical'- ly maximum usable slope of cam approach angle is made practicable.

Another object is the provision of a cam-actuated electrical brush carriage movable along a guide rail on antifrictionrollers adapted to grip opposite sides of the guide rail with a minimum of lost motion.

Other objects and advantages of the invention will become apparent during the course of the following detail description taken in connection with the accompanying drawing forming a part of this specification and in which drawing:

Fig. 1 is a side elevational view of a cam-am tuated brush carriage and vectors diagrammatically illustrating the cam forces; 1

Fig. 2 is, an enlarged fragmentary view in side elevation of the assembly shown in Fig. 1; and

Fig. 3 is a horizontal sectional view substantially on the line 3-3 of Fig. 2. I

In the drawing, which for. the purpose of illustration shows only apreferred embodiment of the invention, and wherein similar reference characters denote corresponding parts throughout'the several views, the numeral in Fig. .1 designates a plate cam rotatable about .an axis II to exert a force [2 against an antifriction roller-type follower l3 attached to a'jbrush carriage l4 as by a bifurcated bracket'lt. This brush carriage l4 rolls along a vertical rail It so aligned that its longitudinal axis extends normal to the cam axis ll whereby the entire path of travel of the follower I3 is radial to the cam axis ll. Insulatively attached to the carriage I4 is a brush l1 adapted to slide along the edge 18 of a wire-wound linear master card l9.upon movement of the carriage. Inasmuch as carriage movement is produced by rotation of the cam It, the electrical output from the linear master card, derived through 20, 2|, isin accordance with the law or formula with which the design of the cam conforms. It will be observed in Fig. 1 that the force 12 normal to the tangent defined by the point of contact of the cam and follower can be separated into components one 22 perpendicular to the rail l6 and another 23 longitudinally of the rail. The perpendicular component 22 produces dou- 4 Claims. (01. 201-'-48) cated axes as by headed terminal and brush connections, Y

and frictional resistance driver.

clearance with the rail l5, nuts 4| on the ble-wedge' friction effects at the point of cam contact with the follower and at the points of bearing between the carriage and rail and, assuming that there are no gravity effects on the carriage, these friction forces determine the magnitude of the longitudinal component force 23 required to move the carriage along the rail. The magnitude of these forces is determined largely by the slope of the tangent defining the cam approach angle 24 relative to the longitudinal axis'of the carriage M, these forces in-- creasing as a preponderantly sine function of the angle 25. Accordingly, comparatively enormous friction obtains with large magnitudesof the approach angle 24. In general, gravity forces acting lengthwise of the carriage and rail are not negligible since in practice ithas been found desirable to use a gravity weight to insure close contact between the cam l0 and its follower [3. Even when the gravity pull of a carriage weight or of the carriage itselfis small, it can be" seen that large values of angle 24 require increasingly larger camming forces to overcome both gravity to movement of the carriage along the rail. If the follower l3 were of the rounded chisel point type, friction bind would occur at'a value of approximately 20 for angle 24, whereas friction bind of the antifric tion roller-type follower [3 occurs when the angle 24 is around 45.

Referring now more particularly to Figs. 2 and 3, it is clear that the cam follower roller l3 turns on antifriction bearings 25 about a shaft 26 in the yoke-shaped bracket [5 isv centrally fastened to the carriage M as bya cap screw 28 and dowel pins 29. The rectangular. carriage I4 is equipped at its corners with four antifriction rollers 3l-34 having bevel'ed peripheries of v-shape in cross section. Two of .the rollers 3|, 32 are mounted on antifriction bearings 38 for rotation about fixedly loscrews 31 and nuts 38. The other two rollers 33, 34 are mounted on similar antifriction bearings 36 for rotation about adjustably located axes as by eccentrics 39 fast on mounting screws 40 slotted to receive a screw.- Following screwdriver adjustment of roller mounting screws 40 are tightened to releasably fix. the positionof the rollers 33, 34 on the carriage. If the eccentrics are flanged at tithe rollers 33, 34 will not bind when the nuts 4! are tightened.

' The V-rollers 3l-34 are formed of glass-hard steel beveled by precision grinding to included is. This bracket angles of approximately 44. The rail I6 is a glass-hard precision-ground rectangular crosssection steel bar having oppositely located relieved precision-ground V-grooves or ways 45, 46 with included angles of approximately 46.

Supporting the master brush I! as by a screw 4! is anelectrically insulative block 48 fastened to the carriage M, as by. screws 49 and, following alignment, by dowel pins 50. The wire-wound linear master card I9 is mounted with its longi:-- tudinal axis parallel to that of the rail so that the brush 11 will make good contact throughout the full range of travel of the carriage.

In operation the clearance; between the four carriage rollers and the rail grooves is'adjusted to approximately zero and the perpendicular component 22 of the camming force is carried by the rollers 3|, 32. Because of the high antifriction qualities of carriage rollers acting against the hardened V-grooves in the guide rail, the friction loading is so low that resistance to carriage motion arises mainly from gravitational forces urgingthecarriage follower rollerinto contact with the cam. Loadings on the carriage rollers 33, '34 are generally normal to thetop ofthe carriage but are negligibly low for cam approach angles up "to 60 due tothe substantially frictionless operation of the device. Lost motion is also negligible when the device has been properly designed, constructed and adjusted as hereinbefore outlined. While-a rotary plate cam has been chosen for purposes of description, it is clear that the same principles apply in the use of cams designed for rectilinear motions. It has been found desirable to makeuse'of large slopes of cam approach angles to provide 'a multiplication between resistance card length and master brush travel distance. The present invention by substantially eliminating slide friction makes possible the regular use of cams having approach angles of 60 and which maybe increased, if necessary, to approximately 75 before friction and gravitational forces become limiting factors.

I'Various changes may be made in the form of invention herein shown and described without departing from the spirit of the invention or the scope of the following claims.

'What is claimed is:

I. In a cam-actuated device for "continuously and accurately varying resistance to be included in 'an electrical circuit; a fixed jelongate'd linear resistor, an 'elo'nga'ted guide having opposite side walls paralleling the resistor and provided with parallel grooves one in each of said side walls, a carriage having antifrictionrollers disposed in said grooves and'spa'ced to closely engage said side walls, a brush mounted on said carriage and in contact with said resistor, an 'antifric'tion cam follower mounted on the carriageintermediate of said frollers, a cam rotatable about an axis normal tothe longitudinal axis of said guide and adapted to engage said. follower, whereby the brush may be moved without lost motion across the entire length of the resistor in -a-manner exactly reproducing a motion determined by the contour of said cam.

2. In a cam-actuated device for continuously and accurately varying resistance to be included in an electrical circuit, a fixed elongat'ed l-i n'e'a'r resistor, an elongatedguidehaving opposite side the ball-bearing-mounted walls paralleling the resistor and provided with parallel grooves one in each of said side walls, a carriage having antifriction rollers disposed in said grooves and spaced to closely engage said side walls, said grooves and the peripheries of said rollers being V-shaped in cross section, a brushwmounted said carriage "and inxcontact with the resistor, an antifr iction tcarn.. follower mounted on the carriage intermediate of said rollers, a cam rotatable about an axis normal to the longitudinal axis of said guide and adapted to engage said follower, whereby the brush may be moved across the resistor in a manner exactly cor-responding to a motion determined by the contour of, said cam.

3. In a cam-actuated device for continuously and accurately varying resistance to be included in an electrical circuit, a fixed elongated linear resistor, an elongated guide rail having opposite side walls paralleling the resistor and provided with parallel V-shaped grooves one in each of said side 'walls, ,a carriage plate having ammo, tion rollers on one' sidedisposed in said grooves and spaced to closely engage said side walls, an antifriction cam follower mounted on thejoppoe site side of the plate and offset therefrom, a brush mounted on the carriage plate and engaging the resistor, ai'cam rotatable about an'axis normal to the longitudinal "axis of said guide rail and adapted to engage sai'd follower, whereby'th'e brush may be moved across the le th of the 'resistor in a mannerexac'tly corresponding to a motion determined bythe contour of saidcam.

4. In a cam-actuated device forvarying the amount of resistance to be included in an electrical circuit in order toproduce a predetermined cyclical variation of voltage in said'ic'i'rcuit, an elongated fixed linear resistor, an eiongated'jguiue rail having opposite side walls par'alleIingth'e-resister and provided withi'v shaped g'rooves one in each of said walls, said grooves'bein'g relieved along the bottom portion thereof, a cariia'geplate having a substantially U shaped cross sections. plurality of antifrictionV-shaped rollers mounted on,one side ofsaid plate for rotation'in the grooves 'and in zero 'clearancecontact with "said side walls, an antifriction cam-follower mounted on the opposite side of the plate and oliset therefrom, a 'brush'mounte'd on the carriage and resiliently urgedjto contact the resistor, a cam 10- tatabiy mounted a'bout a'n axis normal to and intersecting the longitudinal axis of said guide rail-"and adapted. to engage said carnefollower, whereby the rate ofgmovement of the brush acrossth'e resistor may be varied in accordance with the contour of saidcam. V I j'.

' BENJAMIN-EfSCBTTQ lfl; REFERENCES CITED I I Q. t

The 'followingreferences are or record inthe rile-cf this patent:

4 UNITED "STATES inrmu'rs Number, Date. I l

V Name. 1,354,781 :Scanlin Got. 5,1920 1,930,297 Welch ',OCii.1'10, 3 19 33 2,273,760, 4 Nelson i Feb. 1-7,-=1942 3 3 uS u r l ;J y* 4 2,427,190 iBr-adleyetal. 'i-Sept,;9, 1947 ..2,520,453

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