US2611292A - Claw pulldown mechanism - Google Patents

Description

JASPER S. CHINDLER INVENTOR 1;? P Q ..;@.2M 3/ 2 j ATTORNEYX Sept. 23, 1952 J. s. CHANDLER 2,611,292

CLAW PULLDOWN MECHANISM Filed Feb. 24, 1950 3 Sheets-Sheet 1 P 1952 J. s. CHANDLER 2,611,292

CLAW PULLDOWN MECHANISM Filed Feb. 24, 1950 v 3 Sheets-Sheet 2 JASPER S. CHANDLER INVENTOR P 1952 J. s. CHANDLER 2,611,292

CLAW PULLDOWN MECHANISM Filed Feb. 24, 1950 5 Sheets-Sheet 3 (1, ANGLE 0F CAMSHAFT ROTATION, DEG/FEES JASPER S. CHANDLER 2 7 kNVENTOR BY z Z W ATTORNEi Patented Sept. 23, 1952 CLAW PULLDOWN MECHANISM Jasper S. Chandler, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application February 24, 1950, Serial No. 146,110

11 Claims.

1 The present invention relates to improvements in claw-type intermittent film-advancing mechanisms for handling perforated motion-picture Although many types of intermittent film-adyancing mechanisms for motion-picture cameras,

projectors, perforators, printers, etc., have been designed, these known mechanisms possess certain disadvantages in spite of the great amount of effort and development work which has been devoted to this problem.

The primary object of the present invention is the provision of an intermittent film transport mechanism of the claw-type which possesses the following advantages strived for in the art: The mass and dimensions of the moving parts are substantially reduced to the end that high-speed operation is possible with reduced forces of acceleration, reduced rubbing velocity and, hence, reduced wear on the parts; the follower is normally held in contact with the driving cam by a spring which not only provides the force for effecting the return and film-engaging motions to the claw, but providesautomatic take-up in the event of wear on the cam and cam follower surfaces, thus providing accurate positioning of the film and reduced noise of operation over a long period of time; the spring is tuned to cancel out the fundamental harmonic, and actually certain portions of the higher harmonics of the claw accelerational forces, to thereby reduce the working pressure between the cam and follower surfaces; the cam has a configuration primarily useful for apparatus other than projectors, although it could be modified for use thereon; the cam provides a pull-down angle of approximately 130 characterized by the fact that approximately one-half of this pull-down angle produces positive acceleration and the remainder produces negative acceleration with a gradual tapering off at the end position where the claw comes to a stop before being withdrawn from'the film path and, as a result of which, the advance of the film is smoothly and accurately stopped at the desired end position; the top and bottom edges of the claw tip are tapered inwardly to a slight degree and the cam is so designed that the claw completely fills the perforation when moved into engagement therewith, whereby the claw has control of the film both during the positive and negative accelerating movements thereof, and there is no sawing action between the bottom claw edge and the bottom edge of the engaged perforation; an auxiliary cam and follower are provided which preventsthe cam follower from accidentally leaving the driving cam due to. any unusual occurrence during the engagement of the claw with the film, and which auxiliary cam takes over, in combination with the driving cam and its followers, to permit reverse operation of the claw mechanism for feeding the film in the opposite direction; and guiding means are provided on said driving cam or auxiliary cam follower which cooperate with their companion parts to guide the claw laterally in a given plane of movement; and the contour of the driving cam is so designed as to eliminate any sudden changes in the acceleration of the cam-driven parts during the operation cycle.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its methods of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

Fig. 1 is a schematic showing of a pull-down mechanism constructed in accordance with one embodiment of the present invention and shown in association with a film gate and film path of any type of apparatus adapted to handle motionpicture film;

Fig. 2 is an enlarged elevational view of the pull-down mechanism showing the position the parts assume when the claw is at the top of the pull down stroke;

Fig. 3 is a view corresponding to Fig. 2 but showing the claw at the bottom of its pull-down stroke; V

Fig. 4. is an enlarged view of the tip-0f the claw showing the configuration thereof and the position it assumes relative tothe engaged film perforation'when at thetop of the pull-down stroke, or in the position shown in Fig. 2;

Fig. 5 is similar to Fig. 4, but showing the tip of the claw in the position it assumes relative to the engaged filmperforation when the claw is at the bottom of its pull-down stroke, or the mechanism is in the position shown in Fig. 3;

Fig. 6 is a diagrammatic illustration of the path described by the tip of the pull-down claw during operation of the mechanism;

Fig. 7 is a sectional view taken substantially on line ll of Fig. 2 and showing how the fianges on the driving cam guide the claw member laterally; I

Figs. 8, 8-a and 8-22 diagrammatically illustrate how the parts of the follower mechanism enter into the design of the spring in order to tune the spring so as to cancel out the fundamental harmonic; H I

Fig. 9 is an enlarged elevational view showing another embodiment of the present invention, particularly designed to permit feeding of the film in the reverse direction, as well as to prevent accidental separation of the follower surfaces from the driving cam;

Fig. 10 is a sectional view taken substantially on line l0|0 of Fig.9;

Fig. 11 is a diagrammatic view of the cam and Like reference characters refer to corresponding parts throughout the drawing.

Referring to Fig. 1, basically this pull-down mechanism operates in the same manner as conventional claw pull-down mechanisms-'inthat the film-at the gate. This shaft may be rotated at a constant desired speed by any suitable mechanism including a driving wheel 14 coaxial therewith and located to one side of the film path;

Engaging the periphery of the driving cam 12 is a follower in the form of a Y, which is pivoted on a pin I 5 carried on the end of an arm 11 and which arm is, in turn, pivoted on a fixed pin 18 whose axis is parallel to that of the cam shaft 13. A coiled spring S wrapped around pivot pin 18 has one end [9 engaging arm I! and normally acting to move it and the follower in a clockwise direction, or toward the cam. The inside edges of the two branch arms 20 and 2| of the Y-shaped follower engage the periphery of the cam and constitute follower surfaces 22 and 23 which, as indicated, may be separate hard-wearing inserts, i. e., sapphire, carboloy,- etc. On the end of-arm 2| is formed the film-engagingclaw 24-.

As will be apparent from an inspection of Figs. 2 and 3, the periphery of the driving cam I2 is completely irregularwith respect to its axis of rotation. In advancing the film, the cam rotates counterclockwise and the cam and follower are so designedthat both follower surfaces 22 and 23 are in simultaneous engagement with spaced points on the cam surface-atall times. The cam is so formed that it, in combination with the pring S, causes the claw tip to describe a path of the type shown in Fig- 6. The cam positively drives the claw downwardly: and out of engagement with the film perforation at the end of the pull-down stroke, while the spring S provides the power to return the claw to the top of its stroke and then back into engagement with the successive film perforation. The opposite sides of the cam extend slightly beyond the periphery of the cam surface to constitute guide flanges 25 which overhang opposite edges of the follower surfaces 22 and 23, and thus serve to laterally guide the follower and claw in their given plane of movement. This guiding action of flanges 25 is most clearly apparent from an inspection of Fig. 7.

This cam i2 is so designed that the pull-down stroke takes approximately 130 of the cam rotation as distinguished from 60 to 72 pull-down angles normally used in the cams of claw mechanisms of this type. While this pull-down angle is not suitable for use on motion-picture projectors, wherein quick pull-down times are required, it is suitable for all other types of motionpicture apparatus including perforators, printers, cameras, etc. The advantage" of this large pulldown angle is that the accelerational forces re- '4 quired to move the film can be reduced to onefourth of those requiredfor a-65.pull -down angle due to the fact that more cam movement is available to get the film up to speed, and to stop it, and this relationship varies inversely as the square of the pull-down angle. It will be ap- --parent-that -this cam shape could be redesigned ,-to..gi ve a-smaller pull-down angle and thus be adaptedfojr use on projectors, but then certain advantagesof the-same (so far as low accelerational forces are concerned) would be lost. Also, a skip stroke arrangement without alteration of the cam could be used for projector operation.

01' this pull-down angle, approximately half thereof is used toaccelerate the claw. The remainder of'the-pull-down'angle is used to decelerate the clawsothat it will come' to a stop gradually at the 'endofits stroke and only very low inertia forces of the claw, or film, will be present and tend to carry the film past -a given bottom position. The last 4 or -5 degrees of the pull-down movement take place at a very much reduced value of deceleration prior to withdrawal of the claw from the" engagedperforatidn; This insures the film being completely 'stoppedand accurately located at the'time'the claw leaves the engaged perforation. Thecam' surface is so designed that the characteristic curveot the'acceleration forces during the entire motionhas no sharp. corners, as is characteristicfiof the Lumiere, constant acc'elerationand other' type cams; but the changes innc'oelerational forces, bothin direction and magnitude, are'smo'othed out. This results in. less wear in the cam and follower surfaces dueto accelerational-forces and appreciably reduces noise. ofroperation. This is done by the technique of Fourier analysis .and the elimination of-all-harmonics above the 10th.

With this cam and follower constructiomthe parts can be reduced-in size and-mass-as compared with conventional claw mechanisms for doing the same job; Forexample,I have found that, a cam approximately long in the long dimension :and long onthe short dimension, will give the advance'stroke' required when using a 16 mm. movie filmr Reduction in'overall dimensions of the cam results in reducing the rubbing velocity, and, hence, we'ambetween the cam and follower surfaceswhile reduction in m'ass makes possible-higheroperating speed'sL--- I have found that a claw mechanism of this type can be operated at speeds at least as high 1 as 1950 R; P. M. for long-periods of timewithout difficulty. An examination of thecam' and follower arrangement will show that actually thecam and follower surfaceshave only a two-point'contact at any one position of the mechanism.

As clearly indicated in Figs. 4 and 5, the tip of the .film claw Z'l'has its top and bottom edges 28 and 21 respectively inclined toward one another result of which, no impact between'the edges-of th perforation and edges 'of thef claw-are encountered at any time. Smallamounts of pitch variation in the film 'are accommodated before the-start of the adva'nce'stroke. I have'fo'und that the edges26 and of 'th'eclaw are inclined 4 inwardly relative to the remainder of the 'corresponding portions of the claw, very satisfactory results are obtained.

The cam and follower are so designed that at the top of the stroke the top edge 26 of the claw is horizontal and parallel ,to the top edge of the perforation. See Fig. 4. This means that the bottom edge 21 of the claw lies at anangle of 8 relative to the bottom edge of the perforation. At the bottom of the pull-down stroke, these conditions are reversed; namely, the bottom edge 21 of the claw is horizontal and parallel to the bottom edge of theperforation, and the top edge 26 makes an 8 angle with the top edge of the perforation. See Fig. 5. This condition makes for accurate positioning of the film in either forward or reverse direction of operation, even if the claw tip has not entered to the full depth. This rocking motion of the claw tip through 8 during the pull-down stroke does not introduce a sawing action between the bottom edge '21 of the claw and the bottom edge of the perforation, because the cam and follower mechanism are so designed that, during the slight rocking motion of the claw, the dimension X, shown in Figs. 4 and 5, remains constant throughout the pull-down stroke of the claw. This indicates that the same point on the edge 21 of the claw which engages the bottom edge of the perforation of the claw at the top of the stroke also engages the perforation at the same point at the bottom of the stroke.

Coming now to the primary novel feature of my pull-down mechanism which distinguishes it from the prior art more than any other mentioned up to this point, I have found that certain definite advantages can be obtained by tuning the spring S to the operating speed of the pull-down mechanism, whatever it might .be. This tuningof the spring S cancels out the fundamental harmonic, and actually certain amounts of the higher harmonics, in themechanism. The result of this is that the spring actually takes care of part of the accelerations and dec'elerations of the springmoved mass when operated at the specified speed with the result that the remaining forces between the cam and follower surfaces are appreciably re: duced, along with a corresponding reduction in wear on the cam and follower surfaces. In fact, I have found that by tuning the spring, the forces between the cam and follower as compared to those for a low rate spring are reduced by 30 to -75 per cent, depending upon the portions of the claw stroke being considered. For instance, the forces between the cam and follower surfaces are reduced 30 per cent at the peaks in the pull-down stroke and in the return stroke; the peak forces occur at the points where the downward accelerational forces, plus the upward spring forces, are at a maximum. This reduction in accelerational forces becomes significant when it is noted that the acceleration may amount to as much as 42 gs at the film for an operating speed of'l950 R. P. M.,see Fig. 12. v

The tuning of this spring involves calculating the spring constant, or spring stiffness, required to vibrate the movable follower mechanism at the frequency the device is to operate and then from this constantto compute the size of spring having this desired constant. The calculation of the spring constant involves solving the following formula:

in which fr is the operating frequency in cycles per second to which the spring is to be tuned; K is the spring constant referred to'agiven convenient point in the moving system; and M is the equivalent mass of themoving parts acted on by the spring including follower l5, arm [1, and pivot pin le (the mass is equal to the. weight divided by g, the standard acceleration of gravity or 386 in./sec. referred to the same convenient point in the moving system. After the value K" is determined, the spring can be computed from the following formula forra. cylindrical helical spring of circular cross-section, if that is the type used, as in the present instance.

where f is the deflection and P is the force, both referred to the radius r,

l is the wire length,

E is Youngs modulus, and

d is the wire diameter of scale for purposes of clarity, the first step is to find the. equivalent mass of each part or the follower mechanism with reference to a given point in the moving system.

The weight of the claw member part shown in Fig. 8 and being s thick was found to be 1.574 gr.=.00347 lb. The natural frequency of the claw part wasjthen found to be 140 C. P. M. by suspending it as a pendulum at a radius of 2.145 from the normal film plane. This center of suspension indicatedat A in Fig. ;8 was found by the intersectionof vlinesdrawn at 4*, to the'film plane at the top and bottom of the claw stroke which is .300" in a single frame of 16 mm. film. This point of suspension was chosen because it represents the equivalent center about which the claw tip must rotate so that the same will enter the film perforation with its inclined upper edge perpendicular to'the film plane and leave the film perforationat the bottom of the stroke with its lower. edge perpendicular to the film plane. The weight of arm H was found to be 1.97 gr.= .00434 lb. and its natural frequency when suspended at the right-hand edgeof the 3%" hole was found to be 212 C. P. M. The location of the center of gravity and its distance from the point of suspension was next determined for both the claw and the arm.

is The radius of gyration"lc was then found for both the arm andclaw member from the formu a:

mzw

per minute, and 0 1s the distance of the'center of gravity from the suspension point Weight of pivot pin-16 connecting arm "z'whichsiszderived iromithe .formulaeior-aygravity or physical'pendulumand-is For 'arm' where i=radius of gyration neferred'tocenter of gravity at :center of hole to claw member :.=.000328'lb.

Equivalent weight oi clawmember: at (l;741 zmdosgs 1b.

left-end of arm 17 1 .625

. Equivalent weight of arm at lcitaend ct it 001535 1b V 1 K=..63l 1114.111. 7 T To compute a spring havingi-the-Rduird .con-' I stant, it is -necessary toassumea 'giverr diameter --ofspring andsubstitute: in: the iollowmgcior- -mula:

If we zallowthecspringi to have 5.coi1s;then the mean coil diameter and outside diameter: .488

It. is also necessary to calculateithe maximum spring stress to determine if this is a safe value. We use the formula,

. -IardJS, a?

where 85 is tensile and compressive stress The value P must 1be-determined first. Total travel at arm end= :where r'r' is the' period-mi thewpezidulumimsec- I onds For, claw member .=Allowing about eiadditionai motion .for initial loading of spring l1 Max P=-(.'238+:L094).;631

. '.2Q911b. Substituting "this valuenof Pain ,theiorm'ula 1 and solvingliorss Accordingly; f or tuningjthe-spring in question, f-the spring shouldihave'- 5 turns; an outside coil diameter. equal :to:..488f'; a #wire diameter equal *t0fi0390 hand about initial springdeflection measurediat arm end.

The contours ofconventionalcams usedin film pul'ldown' mechanisms -have "characteristic accoloration curves; having: sharp corners and sud- ;den'changesoflarge-magnitude as evidenced by verticallines "in the solid line curve of Fig. 12. Theselsharpcurves are :the result of high" harmonics .being present in the Fourier, analysis of "theoperation cycle. I--have discovered that if "the contour ofthe'camis'modified to smooth out "the sharp corners and eliminate sudden changes "in-'accelerational forces '-without changing the path of movement of the-clawfrom that desired, that anappreciableamount of noise and'wear between-the cam, and "follower; surfaces can be eliminated.

In the following table I show the "comparison "oi-the camcontoursfor a conventional cam designed to "give the desired path ofjclaw travel -shown'inFig. 6 and one having a contourmod- :ified 1 according to 'fthe' present ,invention to smooth-out the acceleration curve.

' Table 345 a B (modifled) .3351. 111. :19 111.40 0 1 112.45 112.186 9 11s. 15 118149 .118 :1 130.86 .1130. so 21 148. .149. 01 7 -60 36 112.49 112.72 names 199.- 14 .64 .225.11 225.68 7 63 149.13 249; 81 I 12 11,0; 26 210. ,1 81 287.74 287.70 -90 301. 44 301. 56 99 311.02 311.11 108 316. 25 315, 13 111 1 316.48 316.22

v :;In this .table: 6o wfi=Cam rotation angle relativexto follower,- in

I ,-degrees B=Perpendicular distance from'camaxis of'ronation .to ..left lffaceoi scam followerv surface, in ,mils.

. .See .Fig l-lrnln this table only. thezadvance portion oflthe motion-is shown, .but .the modifioationlwill extend in similar fashion. throughoutjthe. 3602M. rotation. Theacceleration curves .,iorcthesetwoflcams areshown in- Fig. 12.

'The unmodified cam contour is characterized by portions having a parabolic relationship between ;8 and B and portions of circular arcs so chosen as to provide the required him advance in the specified angle of rotation, and the rewrmaining portionsof.1c1aw travel; due considerily calculated.

ation being given to the fact that both followers ride on the same cam and to the arrangement which gives a minimum cam size. The modified contour is found by taking as few terms as necessary of the Fourier series for the unmodified case (10 termsfor this example) in order to provide the desired claw motion without undue rounding of the corners or departure from the straight portion of the claw path shown in Fig. 6.

Cams with straight followers employing the parabolic relationship between 18 and B (also called constant acceleration cams since the seoond derivative of B with respect to 18 is a constant) and cams made up partly, or entirely, of circular arc segments of finite valuesat different radii and center locations (usually called Lumiere cams) are well known. The most common cams. are usually symmetrical in shape,

and quite often are of constant diameter so that,

they will work between parallel straight followers. Such cams need not be symmetrical, however, as in the unmodified profile of the example given in the above table.

Both the .constant acceleration cams and the Lumiere cams have the'advantage of being eas- Constant acceleration cams produce a given motion with the minimum possible peak value oft-he second derivative of B with respect to c (for rectilinear motion of the follower, this also means minimum acceleration for constant drive shaft speed). owe considerable of their popularity to the fact that in the absence of cam generating and re producing equipment they offer some simplicity of layout and construction.

Referring to Fig. 12, it will be seen that in the acceleration curve for the unmodified cam, the first or negative acceleration portion corresponds to a portion of the cam following the parabolic relation, and that the second or positive acceleration portion corresponds to a portion of the cam consisting of a circular arc. .In both cases there are sharp corners andsudden changes of large magnitude. Since the forces between the claw tip and the film, and between the cam and its follower, are both directly related to the acceleration, it follows that shock loadings would exist in the unmodified case. The sudden force changes are productive of vibrational noise and wear. The situation is analogous to the sudden application of full throttle or full braking force on any moving vehicle. The sharp corners and the vertical lines of the unmodified acceleration curve are l the result of high harmonics being present in the Fourier analysis of the operation cycle.

The modified curve results from the elimination of all of the harmonics above the 10th. The change in the acceleration curve is very pronounced while the actual change in the cam shape and claw path, although important, is small, see table above. Another mannerof distinguishing a cam modified according to this invention from a constant acceleration cam or a Lumiere cam is that in my modified cam no finite length of the cam sur'faceis arcuate in shape, and each curved portion of the cam surface blends into the adjacent curved portions so that there are no suddenchanges. in curvature, and hence acceleration, caused by .a follower passing from one portion to the next. As mentioned above, a Lumiere camflis characterized by being made up either partly or entirely of circular arc segments offinite. length,

Lumiere cams whereas constant acceleration cams, although their surface does not include arcuate portions, are characterized by sudden changes in curvature and acceleration between successive parabolic portions. I

In addition to the reduction of noise-and wear, the modified acceleration curve provides the significant advantage of gradual reduction of the force near the end of the advance stroke. This reduces the tendency of the film to over-shoot or travel past the correct stopping position, for a given frictional retarding force applied to the film, probably. at the gate. The accuracy of film location is thereby improved, and in some types of apparatus this of considerable importance (i. e;, to produce steady pictures in oin-camerasor in step-printers), and. it is anticipated thatan even more pronounced reduction in the acceleration force near the end of the advance stroke may be desirable. It will be appreciated that in the curves of Fig. 12 only that portion of the claw travel constituting the actual pull-down stroke of the claw has been shown. This includes approximately 130 (from 350-120) and is indicated on Fig-6.

, Referring now to Figs. 9 and l0, a modification of the claw pull-down mechanism already described whichpermits feeding of thefilm in the opposite direction for any reason will now be described. As before, this modified mechanism comprises a Y-shaped follower l5 pivoted to the end of arm IT by a pivot pin l5; said arm, in turn, being pivoted at its other end to a fixed pivot E8. The follower surfaces 22 and 23' on the follower I5 are normally pressed into engagement with a driving cam 12 by a coiled spring S, the driving cam having the same contour as in the first embodiment and aloneserving to drive the film in a forward direction and withdraw'the claw from the film path, while in combination with spring S controlling the-return travel .of the claw and its return stroke into the film path. Also as before, the follower includes a claw 24' adapted to engage the film perforations for driving purposes. I have also shown it as including a second claw 39 which is spaced from claw 24' by a distance equal to theframe or perforation spacing of the film and engages the perforation immediately following the; one engaged by the feeding claw. This second claw 30 is provided to take over the feeding of thefilm in the event the claw 24' misses its intended perforation engagement for any reason, such as, ir-

regular perforation spacing due to film splices,

mutilated perforations, etc. Normally, the second claw 30 does no Work whatever. Up to this point, this modification of the pull-down'mechanism is the same as that first disclosed,both in structure and principle of operation. r

In order to. permit reverse film-feeding operation a second cam was added to the cam shaft to work in conjunction with cam 12', the two cams being then boxed in by an addition to the follower [5' which includes a third follower surface for engaging the second cam. To this end, I have shown the second cam referred to as being two like peripheral cams 3! of the form best shown in Fig. 9 and mounted in alignment with one another on opposite sides of driving cam l2 and having the same axis of rotation as cam, l2.

Branch arms of follower 15 are then joinedby arcuate portion 32 lying in same plane as cam l2 and supporting arcuate follower surfaces 33 disposed to engage the peripheral cams 3|. The .arcuate follower surfaces 33 are each provided with -aflange 34--whiehyoverhang the periphery of its-corresponding-camiiand cooperates with a machined or facedborder-35 thereon to laterally guide-the claw and follower during operation. See Fig. 10. These flanges serve the samef-unction asfiangeslion cam I2 in-the-first-embodiment ofthe mechanism disclosed. See Fig. 7.

It is pointed out-that in thenormalforward feeding ofthe film, cams 3 l-and'followersurfaces 33 are ca1led-uponto -do' nothing. Accordingly,

these-parts are so designed that when thedevice isoperating in aforWard-direction'there isa slight clearance; i. e., .001 or .002'in.between -follower surfaces 33 andcams 3l,"as indicatedat "36'inFig. l0. By virtue of this clearancathere is-no wear between-cams 3| and follower-surfaces 33 when the pull-down mechanism is operating in its forward direction and under normal-conditions.

However,--when it is I desired to -feed-thefilm in the reverse direction; the direction of rotation of thecam shaft I 3-is reversed and cams'3l and "follower surfaces -33 come into-engagement -to positively drive the claw into-engagement with the film at the bottom of the stroke and upwardly during the' time'the claw is in engagement with the film-perforation. It will be appreciated that in this movement'the-forces between the cams-3| and their follower surf aces I 33 are reduced by the normal action of sprin --S, which constantly tends to move, the claw arm in'thesctwo directions. Withdrawal -of-the claw 'from the "film path at the top of the stroke and downward movernent thereof'is then-takenover by cam' 12' engaging follower surfaces 22' and =23-on' the claw member, followers 33 being removed from require more force than the springpressurealone to hold follower surfaces 2-2 and 23' 'in engage- -ment with cam l2.

Cams 3! are-so designed that, in reverse operation'of the mechanism, the claw tipwill-follow exactly the same path that it-does-in 'forward operation; namely, that shown in Fig. '6. Such a cam configuration-is readily obtained without calculation by deciding where-thefdllower surfaces 33 should be and operating. a claw arm of the typeshownin Fig. 9 in the forward direction-by only the cam -l2 but with a blank of metal fixed to the -face'-thereof in overhanging relation with one -of the followers 33. As the claw mechanism is operated intermittently, the points at which the follower '33 passes over the metal blank can be scribed thereon, and'thenthe scribed'blank can be cut toshape on a milling-machine. -By such a procedure, a large scale master can be made in conjunction with the master already made for cam l2. From such a master cam any number duplicates can be reproduced readily and ac curately on a pantograph profile milling machine, as is well known. Asindicated in Fig. .10, both cams 3|, as well as cam I2, along with the cam shaft 13', are preferably cut from a :12 single piece "of stock so as to eliminate the problem of; properly orienting the several parts.

"The hole -i-I shown in-each of the cams 3| and-l2 in'-Figs. 9 and 10 is for the purpose of reducing-the mass'of these parts.

while-'cams 3l-"appear to be regular in shape, actually they are completely irregular relative to the- 'cam' shaft'axisas is the driving cam l2.

"Ofihand, it might be confusing that cams -3I differ in shape from cams [2, although the claw -tip traversesthesame-pathin both directions of "film feed. This is required, however, by the location and shape of the followers 33 as compared to the followers 22 and 23'. It will be obvious thatlt-he two cams "3| and the two fol- *lowers 33 could-be" replaced by a single cam and follower placed on either side of the oam [2' and its "followers- 22'and 23 and still obtain :specific :emhodiments :of :my invention, I am xfullyaware .thatmanymodification's thereof are possible. invention, :therefore, is not to be limited to :the.:precise details of construction shown and' zdescribed, .but .is intended to cover ;all:modificationszcoming:within the scope of the appended claims.

,1 .Having. thus described .my invention, what I zclaimasirnew rand-desire .to secure by letters Patent of .the United States is:

1-1. .A .cameoperated gpull-down mechanism for intermittently advancing-a perforated film along a rgivenrpath-rand comprising a rotatable pezripheral cam-whose axis .of rotation extends substantially ;parallel to, and laterally of, the @film .path, a :cam follower having two follower surfaces disposed in acute angular relation to onexan'other andradapted to engage said cam, :a :claw'on' said-follower for engaging and adyancing-thefllm once for each revolution of "saidzcamrmeans for mounting said cam follower -so that .it is free to move relative to the .filmgpath zunder :control -.of said cam in directionsto move the claw thereon longitudinally and -;perpendicularlyof said film path, means for rotatingsaid cam .at aespeed .to oscillate said claw ata frequency of m. strokes per minute, and means. including a spring normally urging said ifollowerein a-direction to hold the two followersurfaces thereof .in contact with said cam, -.-said .-follower and .spring.-urging means having anatural freguemzyequal to n oscillations per minute whereby .the working pressure between -sazid cam [and follower surfaces, .and hence wear on said two parts, is reduced.

v2. Aram-operated pull-down mechanism in accordance with claim. .1, and characterized by :the fact that'zsaid team has .a contour no finite portion of. which-is arcuate with respect to a singlewcenteraand allv adjacent curve portions thereof blendin'to each other without a sudden chan'gexin'. curvature, whereby the acceleration curve thereofi's devoid rofsharp corners and sudden:;changes :of elargexmagnitude.

35A icam operated ipull-down mechanism for intermittently advancing a perforated film along a given path and comprising a rotatable peripheral cam whose axis of rotation extends substantially parallel to,and laterally of, said film path, a cam follower having two follower surfaces disposed in acute angular relation to one another and adapted to engage said cam, a claw on said follower for engaging and advancing the film once for each revolution of said cam, means for mounting said follower so that it is free to move under control of said camto move said claw through a closed path to ad vance the film and has its follower surfaces nor: mally held in contact with said cam'and including an arm pivoted at one end on an axis parallel to the cam axis, an extension on said follower pivoted to the other end of said'arm, a spring acting on said arm, means for rotating said cam at a speed to oscillate said claw at a frequency of n strokes per minute, said arm, spring and follower combination having a natural frequency of n oscillations per minute, whereby the spring and parts moved thereby are tuned to cancel out the fundamental harmonics and certain portions of the higher harmonics and thereby reduce the working pressure between the cam and follower surfaces.

4. A cam-operated pull-down mechanism; according to claim 3, characterized by the fact that said cam includes flanges extending from opposite sides beyond the entire peripheral face thereof, said flanges arranged to engage opposite edges of said follower faces to laterally guide said follower in a given plane of movement.

5. A cam-operated pull-down mechanism according to claim 3, characterized by the fact that said cam has a configuration to impart to the claw a pull-down stroke consuming approximately 130 of rotation of the cam and characterized by a positive acceleration, through approximately one-half of said Pull-down stroke followed by negative acceleration through the remainder of the stroke until substantially the end of the stroke where the negative acceleration is gradually reduced to zero at the end of the pull-down stroke.

6. A cam-operated pull-down mechanism according to claim 3, characterized by the fact that the top and bottom edges of the claw are inclined toward one another by substantially 4 from the horizontal, and the cam configuration being such as to cause the claw to enter the film perforation at the top of the stroke with the top edge of the claw substantially horizontal and parallel to the top edge of the engaged perforation and to a depth such that the claw fills said perforation and leaves the perforation at the bottom of the stroke with the bottom edge of the claw substantially horizontal and parallel to the lower or engaged edge of the perforation.

'7. A cam-operated pull-down mechanism for intermittently advancing a perforated film along a given path and comprising a rotatable shaft whose axis lies substantially in a plane parallel to that of said film path, a first peripheral cam on said shaft for feeding the film forwardly when the shaft is rotated in the direction of forward movement of the film, a cam follower including a claw thereon for engaging and advancing said film, two follower surfaces on said follower disposed in and adapted to simultaneously engage two spaced points on said cam in all positions of said cam, means for mounting said follower so that it is capable of movement under control of said cam in directions to move the claw thereon longitudinally and perpendicularly of said film path as necessary to intermittent movement of the film thereby, a spring normally urging said follower toward said cam to maintain-both of said follower surfaces in contact, therewith at all times, and means for positively preventing said cam follower from jumping off said cam for any reason and for intermittently feeding the film in the opposite direction upon rotation of said cam shaft in the opposite direction. 7

8 A cam-operated pull-down mechanism for intermittently advancing a perforated film along a given path and comprising a rotatable shaft whose axis lies substantially in a plane parallel to that of said film path, a first peripheral cam on said shaft for feeding the film forwardly when the shaft is rotated in the direction of forward movement of the film, a cam follower including a claw thereon for engaging and advancing said film, two follower surfaces on said follower disposed in and adapted to simultaneously engage two spaced points on said cam in all positions of said cam, means for mounting said follower so that it is capable of movement under control of said'cam in directions to move the claw thereon longitudinally and perpe'ndicularlyof said film path as necessary to'intermittent movement of the film thereby, a spring normally urging said follower toward said cam to maintain both of said follower surfaces in contact therewith at alltimes, and means for positively preventing said cam follower from jumping off said cam for any reason and for intermittently feeding the film in the opposite direction upon rotation of said cam shaft in the opposite direction, and including a, second peripheral cam mounted on said shaft in side-by-side relation with said first cam, a third follower surface fixed to said cam follower substantially opposite the vertex of the angle formed by said first two follower surfaces and in a position to engage said second cam, said third follower surface and second cam relatively disposed to be free from engagement when the first cam and two follower surfaces are operating normally to advance the film in a forward direction and adapted to come into engagement only when said two follower surfaces tend to leave said first cam for any reason and when the shaft is rotated in a direction opposite to that in which it is rotated to advance the film.

9. A cam-operated pull-down mechanism for intermittently advancing a perforated film along a given path and comprising a rotatable shaft whose axis lies substantially in a plane parallel to that of said film path, a first peripheral cam on said shaft for feeding the film forwardly when the shaft is rotated in the direction of forward movement of the film, a cam follower including a claw thereon for engaging and advancing said film, two follower surfaces on said follower disposed in and adapted to simultaneously engage two spaced points on said cam in all positions of said cam, means for mounting said follower so that it is capable of movement under control of said cam in directions to move the claw thereon longitudinally and perpendicularly of said film path as necessary to intermittent movement of the film thereby, a spring normally urging said follower toward said cam tomaintain both of said follower surfaces in contact therewith at all times, and means for positively preventing said cam follower from jumping off said cam for any reason and for intermittently feeding the film in the opposite direction upon rotation of said cam shaft in the opposite direction, and including a second peripheral cam mounted on said shaft in side-by-side relation with said first cam, a third follower surface fixed to said 0am follower substantially Oppositethe vertex of the angle formedbysaidfirsttwo follower surfaces and in a position to engage said second cam, said third follower surface and second cam relatively dis-' posed to be free from engagement when the first cam and two'follower surfaces are operating normally to advance the film in a. forward direction and adapted to come into engagement only when said two follower surfaces'tend to leave said first cam for any reason andwhen the shaft is rotated in a direction opposite to that in which it is rotated to advance the film,- and flanges extending from opposite sides of said third follower into overhanging relation with opposite sides of said second ca'm to laterally guide said two fol lowers to movement in a given plane.

10. A' cam-operated p'ulldown mechanism for intermittently advancing a perforated film along a, given path, and comprising a rotatable peripheral cam whose axis of rotation extends substantially parallel to, and laterally of, the film path; a claw arm having a, follower surface normally engaging said cam; a claw on said arm foren gaging and advancing the film; means for mounting said claw am so that it is free to move rela tive to the film path under control of said cam in directions to move the claw longitudinally and perpendicularlyof said film path; said cam having a contour no flnite portion of which is arcuate with respect to a single center and all adjacent curve portions of which blend into'each other without a sudden change in curvature whereby the acceleration curve thereof is devoid of sharp corners and sudden changes of large magnitude.

11. A; cam-operatecl'pull-down mechanism for intermittently advancing a perforated film along a given pathand comprising a rotatable peripheral cam whose axis of rotation extends substantially parallelto,- and laterally of, the film path; a claw arm having a follower surface normally engaging said cam; a claw on said arm for engaging and advancing the film; means for mounting said claw arm so that it is free to move relative to the filin path under control of said cam in directions to move the claw longitudinally and perpendicularly-of said film path; said cam having a contounwhich eliminates all harmonics above the tenth from that portion of the operation cycle of the claw comprising the filmadvancing portion-thereof,- whereby the acceleration curve of that portion of the claw is devoid of sharp corners and sudden changes in magnitude.

JASPER S. CHANDLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number 7 Name Date 1,978,878 Bundick Oct. 20; 1934 2,059,206 v Carson l s= s Nov. 3, 1936 2,461,159 Hutchison Feb. 8, 1949 FOREIGN PATENTS Number Country Date 521,086 Germany Mar. 18, 1931v

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