US3170331A

US3170331A - Cam mechanism

Info

Publication number: US3170331A
Application number: US263016A
Authority: US
Inventors: Harold T Lyman
Original assignee: INTERSTATE Manufacturing CORP
Current assignee: INTERSTATE Manufacturing CORP
Priority date: 1963-03-05
Filing date: 1963-03-05
Publication date: 1965-02-23
Anticipated expiration: 1982-02-23

Description

3 Sheets-Sheet 1 H. T. LYMAN CAM MECHANISM Feb. 23, 1965 Filled March 5, 1963 H. T. LYMAN CMI IIECHANISII- Feb. 23, 1965 3 Sheets-Sheet 2 Filed March 5, 1963 mvEm-oa Harald giada Que@ Feb. 23, 1965 H. 1'. LYMAN 3,170,331

CAII IIECHANISM Filed March 5, 1963 3 Sheets-Sheet 3 TURNS 0F FAD SCREW z5 M y' 24 25 24 INVENTOR. Harold I. ymaffz United States Patent O 3,170,331 CAM MECHANISM Harold T. Lyman, Milford, Conn., assignor to Interstate Manufacturing Corporation, Orange, Connecticut Filed Mar. 5, 1963, Ser. No. 263,016 2 Claims. (Cl. 74-10.6)

This invention relates to improvements in cam mechanisms and in particular to a cam mechanism for radio frequency tuners.

One object of my invention is to provide a cam surface which can be varied to suit the required conditions.

Another object is to provide means for readily and easily making required variation in the cam surface.

Yet another object is to provide a cam mechanism which automatically compensates for wear, backlash and varying tolerances in the construction of the cam mechanism.

Another object is to provide a cam mechanism which is compact and economical as to space requirements.

Still another object is to provide a cam mechanism which is long lasting, accurate and produces precise results in radio frequency tuning.

Other objects and a fuller understanding of the invention may be had by referring to the following description and claims, -taken in conjunction with the accompanying drawings in which:

FIGURE 1 shows a longitudinal view of a micro module tuner partly sectioned; showing application of cam mechanism;

FIGURE 2 is an enlarged longitudinal section of the end of the tuner showing some of the tuning elements;

FIGURE 3 is a cross section taken on line 3-3 of FIGURE 2;

FIGURE 4 is a cross section taken on line 4-4 of FIGURE 2;

FIGURE 5 is an enlarged perspective partly in section showing cam followers and tracking cam washers;

FIGURE 6 shows an enlarged view of the biasing means;

FIGURE 7 is a graph showing an untracked tuning curve plotted against -the desired or tracked curve;

FIGURE 8 is an enlarged cross section taken on line 8-8 of FIGURE 1;

FIGURE 9 is a partial section on line 9--9 of FIG- URE 8, greatly enlarged.

Referring now to the drawings, the numeral 10 denotes a general reference to a radio frequency tuner represented by a micro module tuner containing the cam mechanism. This module is merely exemplary of the use to Vwhich my improvement may be applied to devices requiring my improvement.

The numeral 11 denotes a removable metal casing or enclosure cover and the numeral 12 denotes a bearing housing which comprises the main supporting base for the several component parts as will be subsequently described.

The shaft 13 mounted in the housing 12 extends to the right, as viewed in FIGURE 1, to receive ahand knob 16 for purposes of rotating the shaft 13 as, may be desired for tuning.

A cover plate 51 mounted over a gasket 52 of pliable material seals the right hand end of the housing 12 upon tightening of the knurled annular nut 53 on the threads 54 on the housing 12.

A gland stuing box assembly of the customary type seals the opening between the right extension ofthe shaft 13 and the housing 12 to keep out dust and moisture.

The shaft 13 is mounted in ball bearing units 14 which in turn are mounted in the bearing housing 12. The ball bearing units 14 are spaced apart by spacer member 14a so that the shaft 13 has ample support for any cantilever "ice tendency. The shaft 13 is prevented from longitudinal movement by means of a retaining washer 12a riding in a groove 13a in the shaft 13. (See FIGURE 1.)

The shaft 13 also extends to the left of the bearing housing 12, as viewed in FIGURE 1, in the form of a precision cut thread comprising a lead screw 17.

Mounted on lead screw 17 are two axially spaced

drive nuts

18 and 19 respectively; drive nut 18 being to the right of drive nut 19 to the left thereof as shown in FIGURE 2.

Each drive nut has a follower arm 18a and 19a protruding radially outward to each of which is attached a ball cam 18e and 19C respectively as clearly shown in FIGURES 2 and 5.

A pile 23 is formed at the left of housing 12, as viewed in FIGURE 1, comprising a series of concentric discs constituting cam tracking washer 20 each of which is rotatable in its own slightly thinner guide washer 2S as more clearly shown in FIGURES 8 and 9. The tracking washers 20 are longitudinally separated from each other by thin spacing washers 24. The spacing washers 24 have a concentric central opening slightly smaller in diameter than the concentric central opening in the guide washer 25 (which hold the tracking washer 20) so that while the tracking washer 20 is free to rotate in the concentric central opening in its guide washer 25, it is prevented from contacting adjacent tracking washers 20 thus making it possible for independent rotations of the tracking washers 20 for adjusting purposes.

The pile 23 is held together by corner bolts 26 mounted in the bearing housing 12 and provided with end plates 56 to receive abutting clamp nuts 28. Upon tightening of the appropriate nuts 28 the tracking washers 20 are firmly held against any movement by the pressure transmitted through the tracking washers 20 and the spacer washers 24.

Each cam tracking washer 20 is provided with a con- `centric central opening 20a into which opening protrude two oppositely located radial cam ledges 21 and 22 respectively. These tracking washers 20 are assembled into the pile 23 with the cam ledges 21 and 22 so aligned that their

cam surfaces

21 and 22 respectively form a pair of sinuous like paths or

cam tracks

31 and 32 respectively the cylindrical zone in which these tracks lie being concentric with the axis of the lead screw 17 along which the ball cams 18C and 19C ride in firm contact therewith as will be subsequently described.

A notch 29 (See FIGURE 4) in the periphery of each tracking cam washer 20 enables the washer 20 to be rotated slightly in the pile 23 to vary the slope of the

cam tracks

31 and 32 formed by the series of

cam ledges

21 and 22 respectively for purposes of adjusting the desired tuning characteristics of the tuner 10 for the precise tracking as will also be subsequently described. scribed, a plurality of notches 29 may be used to assist in the precise adjustment of the respective slopes of the

cam tracks

31 and 32.

It will be noted particularly in FIGURES 4 and 5 that the ball cams 18e and 19C each bear on the

surfaces

21 and 22 respectively which face toward the left but on opposite sides ofthe axis of the lead screw 17 hence these ball cams 18C and 19C act in opposite directions, one clockwise and the other counter clockwise.

To prevent any backlashwhich might occur when the rotation of lead screw 17 is reversed and to take up wear in the threads and on cam surfaces, the

drive nuts

18 and 19 are biased by a coiled spring 30 which is under compression both axiallyv and angularly as shown in FIG- URES 5 and 6. The effect of this biasing is to always provide a force to push the

drive nuts

18 and 19 axially apart and to force a tendency to clockwise rotation to one drive nut and counter clockwise rotation to the other drive If denut for angular bias. This results in an opposing axial pressure on the threads of the lead screw 17 and an opposing angular pressure on the pair of cam tracks 3l and 32 formed by cam ledges 21 and 22 by the follower ball cams 18C and i90 respectively and insures positive contact between ball cams 18C and 19C and their respective tracks and hence accurate tracking resulting in precise tuning.

I'prefer to make the follower arms 13a and 19a as short as possible and to arrange the ball cams 13C and 19C in the same plane transverse to the axis of lead screw i7 so that I may have a negligible or a low rocking moment about an axis perpendicular to the lead screw axis which might be caused by friction of the ball cams riding along their tracks and particularly wherrsteep inclines are encountered in the

cam tracks

31 and 32. Furthermore by locating the centers of the ball cams 18e and 19C in a common axially transverse plane balanced rotative moments are provided which resist sidewise rocking. These features together with the long bearing support between the bearing units 14 insure an accurate constant concentric alignment of the moving tuning element throughout its entire travel.

The tuning units describediherein, as an example, cover both capacitive and inductance tuning. The elements constituting the inductive unit comprise a stationary helically wound coil 4d wound on a coil form 41 mounted on a hoilowed out stationary core 42 which in turn is mounted on a core support` 43. The core support i3 is composed of a ceramic like material known in this trade as Mycalex Supra mica 500 whichis secured in place by extension of the four corner bolts.

A movable core unit is composed of two coaxial cylinders secured to a drive bushing 37 by cementing with preferably an epoxy resin. The inner core is designated by the numeral 34 and the outer core by the numeral 35. The free end 34a of the inner core is convex tapered to align with a concave taper 42a of the stationary core 42. The free end 35a of the outer core 35 is concave tapered to correspond with a convex taper 42h of the stationary core 42. As clearly shown in FIGURE 2 this annular space between the inner core 34 and the outer core 3S permits telescoping ofthe

movable core elements

34 and 35 with the coil 46. All of the core elements are preferably made of powdered iron held together with a suitable plastic binding material, such as carbonyl iron, known in the trade as Permacore #12, used in the preferred embodiment; but ferrites may also be used.

The variable capacity portion of the tuner is used to extend the tuning range, but is not necessarily a part of this invention. The unit comprises three comb like pattern cylindrical members known Faraday Shields of very thin iiat copper in the neighborhood of .001 inch thick cemented to dielectric cylindrical forms respectively preferably of glass filled Rexolite Numeral 44 denotes a stationary shield mounted coaxially on the stationary core 42 and extending over a portion of coil 4t). Numeral 45 denotes `a coaxial shield mounted on the movable outer core 35.

Numeral 46 denotes a shield coaxially mounted in the core support 43 and surrounding both the above shields 44 and 45.

The drive bushing 37 is attached to the drive nut 19 by any suitable means preferablypinned with layer of adhesive resin. Hence any axial or rotative movement of the drive nut 19 will be directly transmitted to movable tuning elements by the drive bushing 37.

The comb like capacitor plates or

Faraday Shields

44, 45 and 46 with the narrow conductors and open ends are inhibitory to the flow of large circulating currents. No severe eddy current losses exist with this type of capacitor plate. Solid plates cause high resistance R which would drastically reduce the quality factor Q in the formula Q=X /R where X is the reactance of coil or capacitor.

The circuit connections provide the `usual grounding either by conductor leads or through the metal structures A of the tuner and by conductor leads to appropriate outside load. Trimmers for both capacity and inductance (not marked on drawings) may be located on one end of the tuner and included in the circuit as required.

As the rotation of the lead screw drives the movable tuning units back and forth the core mesh changes the radio frequency magnetic field strength of the coil to perform the inductive tuning and the mesh of the shields changes the radio frequency dielectric iield energy between the shields (plates) to perform the capacitance tuning.

The inherent electrical and mechanical characteristics of complicated tuner constructions so vary that it becomes necessary to compensate for this variation to make the circuits track, that is, tune to the same frequency at each setting of the tuning control.

The practical application of my cam.mechanism will now. be clearly evidentlby referring to FIGURE 7 for example where curve A represents the desired tuning curve. Although line A is shown in this ligure as a straight line it may be a smooth curve depending on the particular tuner circuits.

The curve B represents a tuning curve for a given tuner for which it is desired to make compensating adjustments to coincide with the desired tuning curve A or as nearly coincide therewith as is practical.

Since the lead screw 17 is uniformly threaded, a single revolution of the hand knob lo will ordinarily move the drive nuts a uniform distance per revolution no matter in what axial positions these

drive nuts

13 and 19 are resting and of course the movable tuning element connected thereto. Such a uniform axial movement of the tuning elements might result in a tuning curve represented by curve B for example instead of the desired curve A. The difference might be represented for example by the line C D and line E F at these two particular points. To effect the desired tuning, the slope of the cam tracks may be adjusted by rotating the proper tracking washers 2i) resulting in the proper advance of the movable tuning elements to correspond to curve A.

This will be clarified by the following explanation. By connecting the drive nut 19 to the ball cam 19C in its respective track 31, theV advance of the movable tuning element and drive nut 1.9 depends on how much the drive nut is allowed to turn relative to the axis of the lead screw 17 as the latter turns. For example if the slope of the cam track 31 is zero that is it is parallel to the axis of the lead screw 17, the lead screw will move axially according to the pitch of the lead screw 17. Now if the slope of the track 31 is steep the drive nut 19 will be caused to partly rotate about its axis and its axial travel will be more or less depending on which way the track 31 slopes. If the slope of track 31 is perpendicularto the axis of the lead screw 17 there will be no axial movement of the drive nut 19.

Hence by adjusting the position of the cam tracking washers 2@ using the adjusting notch 29 the slope of the cam tracks 31 and 32 may be set to make the necessary compensation in the advance of the movable tuning eiement resulting in the desired turning curve.

Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only byway of example and that numerous changes in the details of construction and arrangements of parts may be resorted to without departing from the spirit and scope of the invention as hereinafter claimed. i

I claim as my invention:

1. In a radio frequency tuner having a stationary tuning element and a movable tuning element in which the latter is precisely operated in accordance with a cam track adjustable to correspond to a desired characteristic tuning curve, a lead screw terminating at one end in a shaft `journaled in a supporting bearing and fixed against axial displacement, a plurality of cam track washers mounted in pile formation about said lead screw each said washer having a central opening concentric with the axis of said lead screw, each of said cam track washers having a first ledge and a second ledge on the periphery of said central opening extending toward said lead screw and located substantially diametrically opposite each other, a first cam surface on said first ledge and a second cam surface on said second ledge both of said cam surfaces facing in the same general direction, said cam track washers being rotatively adjustable to align said cam surfaces to form substantially continuous cam tracks respectively having the necessary contours to correspond to such a desired tuning curve, means for adjustably rotating each washer, means for retaining said washers in adjusted position, first and second drive nuts threaded on said lead screw in spaced relation to each other, said first drive nut having a first arm extending toward said second drive nut in close proximity and parallel to said lead screw, said second drive nut having a second arm extending toward said first drive nut in close proximity and parallel to said lead screw, a first and second cam follower mounted on said first and second arms engaging said first and second cam surfaces respectively, said arms being substantially equal in length and positioned relative to each other so that said cam followers engage said lirst and second cam surfaces respectively in a plane normal to the axis of said lead screw, a resilient member disposed between and engaging said drive nuts to bias them axially and rotatively to take up thread back-lash and maintain said followers in operating engagement with said first and second cam surfaces repectively as said lead screw is rotated and means connecting said movable element with one of said drive nuts.

2. In a device of claim l said means for adjustably rotating said cam track washers and retaining same in adjusted position comprising a guide washer fixed against rotation having a concentric central opening to receive said cam track washer therein and having a thickness less than said cam track washer, said cam track washer rotatable in said guide washer, a spacer washer disposed between adjacent cam track washers, a ledge on the periphery of said cam track washer, an access opening in the periphery of said guide washer to enable said ledge to be engaged to rotate said cam track washer to a desired position and means extending through said pile formation to apply longitudinal pressure to said pile formation to press said cam track washers and said spacer washers together to retain said cam track washers in said adjusted position.

References Cited by the Examiner UNITED STATES PATENTS 2,392,880 l/46 Reed 7422 2,468,071 4/49 Hunter 74-567 XR 2,641,709 6/53 Stover 74-10.6 XR 2,728,235 12/55 Mifflin 74-10.85 2,984,776 5/61 Barnes 74-l0.85 XR 3,094,011 6/63 Bradley 74-424.8 XR

FOREIGN PATENTS 819,615 9/59 Great Britain.

BROUGHTON G. DURHAM, Primary Examiner.

MILTON KAUFMAN, Examiner.

Claims

1. IN A RADIO FREQUENCY TUNER HAVING A STATIONARY TUNING ELEMENT AND A MOVABLE TUNING ELEMENT IN WHICH THE LATTER IN PRECISELY OPERATED IN ACCORDANCE WITH A CAM TRACK ADJUSTABLE TO CORRESPOND TO A DESIRED CHARACTERISTIC TUNING CURVE, A LEAD SCREW TERMINATING AT ONE END IN A SHAFT JOURNALED IN A SUPPORTING BEARING AND FIXED AGAINST AXIAL DISPLACEMENT, A PLURALITY OF CAM TRACK WASHERS MOUNTED IN PILE FORMATION ABOUT SAID LEAD SCREW EACH SAID WASHER HAVING A CENTRAL OPENING CONCENTRIC WITH THE AXIS OF SAID LEAD SCREW, EACH OF SAID CAM TRACK WASHERS HAVING A FIRST LEDGE AND A SECOND LEDGE ON THE PERIPHERY OF SAID CENTRAL OPENING EXTENDING TOWARD SAID LEAD SCREW AND LOCATED SUBSTANTIALLY DIAMETRICALLY OPPOSITE EACH OTHER, A FIRST CAM SURFACE ON SAID FIRST LEDGE AND A SECOND CAM SURFACE ON SAID SECOND LEDGE BOTH OF SAID CAM TRACK WASHERS BEING THE SAME GENERAL DIRECTION, SAID CAN TRACK WASHERS BEING ROTATIVELY ADJUSTABLE TO ALIGN SAID CAM SURFACES TO FORM SUBSTANTIALLY CONTINUOUS CAM TRACKS RESPECTIVELY HAVING THE NECESSARY CONTOURS TO CORRESPOND TO SUCH A DESIRED TUNING CURVE, MEANS FOR ADJUSTABLY ROTATING EACH WASHER, MEANS FOR RETAINING SAID WASHERS IN ADJUSTED POSITION, FIRST AND SECOND DRIVE NUTS THREADED ON SAID LEAD SCREW IN SPACED RELATION TO EACH OTHER, SAID FIRST DRIVE NUT HAVING A FIRST ARM EXTENDING TOWARD SAID SECOND DRIVE NUT IN CLOSE PROXIMITY AND PARALLEL TO SAID LEAD SCREW, SAID SECOND DRIVE NUT HAVING A SECOND ARM EXTENDING TOWARD SAID FIRST DRIVE NUT IN CLOSE PROXIMITY AND PARALLEL TO SAID LEAD SCREW, A FIRST AND SECOND CAM FOLLOWER MOUNTED ON SAID FIRST AND SECOND ARMS ENGAGING SAID FIRST AND SECOND CAM SURFACES RESPECTIVELY, SAID ARMS BEING SUBSTANTIALLY EQUAL IN LENGTH AND POSITIONED RELATIVE TO EACH OTHER SO THAT SAID CAM FOLLOWERS ENGAGE SAID FIRST AND SECOND CAM SURFACES RESPECTIVELY IN A PLANE NORMAL TO THE AXIS OF SAID LEAD SCREW, A RESILIENT MEMBER DISPOSED BETWEEN AND ENGAGING SAID DRIVE NUTS TO BIAS THEM AXIALLY AND ROTATIVELY TO TAKE UP THREADED BACK-LASH AND MAINTAIN SAID FOLLOWERS IN OPERATING ENGAGMENT WITH SAID FIRST AND SECOND CAM SURFACES RESPECTIVELY AS SAID LEAD SCREW IS ROTATED AND MEANS CONNECTING SAID MOVABLE ELEMENT WITH ONE OF SAID DRIVE NUTS.