US2112894A

US2112894A - Film motion filter

Info

Publication number: US2112894A
Application number: US71532A
Authority: US
Inventors: Jr Harold J Hasbrouck
Original assignee: United Research Corp
Current assignee: United Research Corp
Priority date: 1936-03-28
Filing date: 1936-03-28
Publication date: 1938-04-05
Anticipated expiration: 1955-04-05

Description

April "5; 1938. H. J. HASBROUCK. JR 2,112,894

FILM MOTION FILTER Filed March 28, 1936 INVENTOR Harald LT. Hashrnunk. LII.

BY W/FMW ATTORNEY Patented Apr. 5, 1938 FILM MOTION FILTER Harold J. Hasbrouck, 11-, Merchantville, N. 1.,- signor to United Research Corporation,-Burbank, Calif., a corporation of Delaware Application March 28, 1936, Serial No. 71,532

13 Claim.

This invention relates to talking motion picture apparatus and particularly to the film drive portion of the sound recording or reproducing unit wherein the motion-of the film past the translation point is maintained constant. It is well understood that a necessary prerequisite for perfect sound recording and reproduction is that the film be advanced at a constant and uniform speed through the light beam, the point of contact between the film and beam being known as the translation point. Stabilizing devices such as flywheels have been and are employed for stabilizing the motion at this point against the effects of starting surges, take-up reel jerks, me-

chanical faults of the driving mechanism, or other extraneous causes of speed variations. The flywlieels may be supplemented byother mechanical filter elements having, for example, elastic and/or resistive characteristics toaid instabilization.

In the types of filter elements having mechanical resistance are included dash pots employing viscous mediums such as oil. Such an oil dash pot has heretofore been used to control the movement of a resilient restoring element acting on a loop in the film between the drive sprocket and the flywheel roller which guides the film at the translation point.

The present invention is directed to an improvement in -a filter of this type, this improvement consisting of a particular form of sliding friction as the damping element instead of a viscous friction such as produced by oil in the dash pottype of'damping element. Many advantages of the sliding friction damper, if designed in accordance with this invention, are found over the viscous damper, some of which are, freedom from attention, independence of temperature changes, no oil leakage. problem and less counterforce during rapid displacements, thereby permitting an adjustment which results in a more rapid decayof filter oscillations initie-ted, for example, by the starting surge.

In the normal sound unit, some of the causes of speed variations not minimized by the flywheel and oil dash pot may be traced to the starting surge, film reel take-up Jerks, and the variations in friction of bearings due to poormaintenance. These causes of speed variations produce different rates or velocities of filmspeed changes which lie within determinable frequenoy limits. It has been found in the use of an oil dash pot damper in a filter having a lowperiod that, if the damperis adjusted to provide the proper damping to quickly dissipate the (o1. z'u-aa) Y oscillations initiated by the starting surge, which generally produces a low velocity variation, it will ofler such a large counterforce during any later rapid displacements or variations that the angular "velocityof the flywheel may be substan- 5 tlally altered or the film caused to slip on-its roller or drum. Also if it were adjusted properly for the rapid variations, it would be insumcient to dampen out the slower variations.

To avoid flywheel speed variations therefore, the damper should not offer a counterforce so large as to prevent the moving elements of the filter from promptly accommodating the changed length of loop between the drive sprocket and the drum of .the flywheel caused by rapid variations nor, should it be so small as to permit the moving elements to oscillate for an appreciable time. 1 If a viscous type of damper is adjusted to provide sufllcient damping of the fundamental period of the filter to quickly dissipate the oscillations caused by'the starting surge, then sudden film speed changes produce sumcient coun-l teri'orce to permit a sudden transfer of energy to the flywheel and consequently appreciably alter the speed of the film at the translation point. This is becausewith viscous dampers the counterforce increases directly with velocity, particularly within the velocity limits required by film drive filters, while 1 for :further increased velocities a c'ounterforceproportional to higher powers ,ofthe velocity may. be produced caused bythe onset of turbulence in the fluid.

It has also been found that-the ordinary or" usual typeof sliding frictionhas a static friction greater than its initial kinetic friction with the result that the force required to start it in motion is considerably greater than the force required to maintain movement thereafter, the trcnsitionoccurring quite rapidly. Such types of sliding friction are not suitable for the invention since damping would only be accomplished after a surge of suillcient force was in-- troduced to overcome the staticfriction counterforce. There would thus be set up a. series of transient surges or. parasitic oscillations caused by such forceacting on the film elastance, and flywheel mass. It has been discovered therefore-that the static friction should be substantially' zero or negligible compared'with the operating kinetic friction.

As stated above, if the viscous damper produced sufficient damping at the low velocities, it would produce entirely too, great a counterforce at the higher velocities, and if it had the Y proper damping efiectat the higher-velocities,

locity above the critical range of film variation velocities and which has a static friction of substantially zero.

For instance. to illustrate with a particular case. a starting surge may result in a shortening of the film loop, due to the film being taken out of the loop faster than it is fed thereto by the flywheel roller during its acceleration up to normal film speed. 'Ihe result is the storing of energy in the tensioning means beyond that required for normal film This energy is released when the drum has reached normal speed and, without a damper, this energy release will maintain excess tension in'the mm and continue to accelerate thefiywheel. The result of this acceleration is a transfer of energy from the spring to the flywheel which increases the loop beyond its normal size as more film is fed into it by the drum than: istaken out by :the drive sprocket. a f

'Ihis inter-transfer of energybetween the tensioning means and flywheel produces oscillations or variations in film speed which are deleterious to good sound recording or reproduction. Thus, to prevent these oscillations,the energy should preferably be absorbed by the damperas fast as it isreleased; This is accomplishedby placing a drag on the tensioning means'which will absorb its stored energy. 4

The damper mumalso absorb the energy arising from surges entering thesystem when normally operating. We can assume for illustration, surges of a higher velocity than that encountered in starting. Now since .the counterforce of the damper of this invention increases less rapidly than the velocity. we minimise the transfer of energy to the flywheel, store it in the tensionlng means, and dissipate. it at the low free period velocities of-the V An obiect oftheinvention therefore is to obtain a substantially. comtant counterforce to film speed changes overs dcfiniterange, of speedvalocitybelow this range.

This object is accomplished by providing a sliding friction in: a film loop between the riations andacounterforce proportional to vedrive sprocket and flywheel roller, which damper I has negligiblestatic friction, a counterforce proportional to velocity for a predetermined low range of velocities .and substantialiyvconstant counterforce, for a predetermined higher range of velocities. v 1

One set of materials providing the proper sliding friction characteristicvwas found to be soft 1 felt against stainless steel polished'to a very high degree. Adeviceemploying these materials-and constructed to operate with a roller positioned in a loop in the-film betweenthe drive sprocket and-fiywheel'roller of a sound recording or reproducing machine was found to. provide a much superior damper for a film motion filter than the viscous type previously known in the art. It was found that by adjusting the pressure between thefelt and the steel, the proper damping could be obtained to dissipate the starting surge before completing the first oscillation of the mechanical filter and hence in a muchshorter time than possible with the oil type damper.

With the oil damper, provision against oil leakage and change in viscosity with temperature had to be provided. The present invention avoids these provisions, is rugged in construction, and may be conveniently adjusted'by a screw for controlling the pressure between the felt and the steel to change the damping. A coil spring maintains the pressure between the felt and steel substantially uniform.

The details of the invention will be more fully Fig. 6 is a graph showing the relationship between the counterforce of friction and velocity for different dampers. Referring now to'the figures, in which the same numeral indicates identical elements, the

soundreproducer of Fig. i is 'includedin ahousing tdivided into two sections 6 and 1. Section 8 enclosesa lamp ll of constant intensity, the light rays therefrom being projected through a lens and silt assembly tube ll into compartment 1. In compartment I afilm i3 is continuously advanced through the lightbeam from tube ll,

the. driving force being applied by asprocket it having a pad roller ll associated therewith. The film is pulled by the right hand side ofthe sprocket, under a roller ll, over a roller I, under a tension roller 20, over a roller II; around the flywheel roller or spool 22 having a guide or pressure roller 23 associated therewith-around a roller 24 and then from the left hand-side of sprocket M which feeds the film II to form a.

slight upper loop between

rollers

23 and 24. The roller or spool 22 is mounted on the same shaft with'the fiywheei shown by the dotted lines 21.

An optical system It and photo-sensitive device ll projects the emergent light from the sound track portion of the film i3 and translates it into electrical currents, respectively, as is well known in the art. The particular system shown at 2! and ll in combination with thespool I2, is disclosed and claimed in my co-pending application Serial No. 54,885 filed December 17, 1935.

The present invention utilizes the damper shown as a unit at 32 and having an arm 33 extending therefrom to the roller 20. A tension spring is attached to arm I! and to lever 30 pivoted at 42 and having a notch and screw adjustment arrangement 81, provides the means of varying the tension on the arm a. 7

Referring now to the details of the film motion damper shown in Figs. 2 to 5inclusive, the arm is fixedly attachedtoa shaft 38 through a hub 34, the shaft having mounted thereon a light metal plate 3! Attached to the plate I! in any suitable manner such as by glueor coupled by roughening the surface of plate 3!, is a soft felt pad 40. A cup-shaped housing 40 encloses the plate -39 and felt II and also a stainless steel plate 4| pressed into the bottom of the cup.

This plate is'polished preferably by'rotary mo- 75 tion to a very high degree on the side thereof contacting felt 40. The felt 4| and plate 4| have a motion relative to one another to provide the sliding friction characteristic of the invention, the static friction therebetween being less than the kinetic friction, although satisfactory op; eration is obtainable with materials in which these frictions are equal in, value. Other materials or constructions having similar characteristics may, therefore, be used.

To maintain a uniform pressure between the plate and felt 40, a'coil spring 43 is employed, one end of which abuts the end of shaft 38 and the other end of, which is fitted into a notch of a lever arm 44 pivoted on a projection 45. The

lever arm 44 may be adjusted to'increase or decrease the compression of spring 43 and consequently the pressure between plate 4| and felt 40, by a long screw 46 threaded through a back plate 4'! of the casing or housing 48. This particular arrangement permits the adjustment to be made from the front of the reproducer. As shown in Fig. 5, the steel plate 39 and felt 40 have V-type slots 49 provided therein to permit oscillation of the shaft. 38. The back plate 41 is attached to the casing 48 by means of a plurality of screws 5| while the entire unit is fixed against rotation by attachment to the frame or housing 5 by screws 3i through holes Si in the casing 48.

It will be seen in Fig. 1 that the film advance by the sprocket l4 drives or rotates the spool 22 and the flywheel 21. In starting a. sudden ten- .sion is placed on the film 13 between the sprocket l4 and the spool 22 which'pulls the arm 32 upward, decreases the loop and stores energy in the tensioning spring 35.

Referring now to Fig. 6 in which the counter:

force of friction F of the damper is plotted against the relative velocities "V of the friction surfaces of the damper caused by film speed variations or surges, there is shown a pair of dotted lines B and BI" which illustrate the action of two usual types of sliding friction resistance, a'pair of dot and dash lines A and Al" which illustrate the action of two viscous types of dampers, and a solid line "1 illustrating the action of an ideal damper of this invention. These curves may be considered as the force-velocity characteristics of difierent types of dampers.

It will be observed from curve 'i" that the slope is initially steep so that adequate damping is obtained at the low velocities which are encountered in the free period oscillation. For higher velocities the slope rapidly decreases so that rapid surges do not generate high counterforces which accelerate the flywheel or cause slipping of the film on the drum or spool. Now, in curve A", which illustrates a viscous type .damper adjusted to rapidly damp the free period oscillation, there will be unduly high counterforces offered to high velocity surges which will cause appreciable acceleration of the flywheel or slippage of the film. While the latter objection is eliminated with curve Al", the damping in this case would not be suflicient. v In the case of curves B and BI where the usual characteristics of sliding friction are illustrated, there are abrupt changes in counteriorce wherever the velocity passes through zero. These changes set up transient surges which are objectionable in film drive filters.

What is claimed is:

1. In a film drive system, the combination of a drive sprocket, a stabilizing means adapted to be driven by a fllmadvanced by said sprocket,

said film, having a loop therein between said drive sprocket and said meansrsaid loop varying in size in accordance with variations in speed of said film and means including a sliding friction damper located in said loop and offering, av substantially constant counterforce to vsaid variations in the size of said loop over a certain range of velocities of variations and proportional counterforces to variations in velocities outside of said range.

2. A film drive system comprising a continuously driven sprocket, a fiywheelroller, means for guiding the film between said roller and said sprocket in the form of a loop tending to move said guiding means during changes in speed of said film, and means including a sliding friction damper movable by said guiding means for introducing a substantially constant counterforce to changes in speed of said film within a predetermined range and proportional counterforces to changes in speed of said film below said range.

3. A film motion damper comprising a steel plate, felt material positioned in contact with said plate and adapted to be oscillated, means for adjusting the pressure between said felt and said plate, and means interconnecting a moving film and said felt for oscillating said felt, the friction between said felt and said plate constituting a counterforce to variations in speed of said film.

4. A film drive system comprising means for driving a motion picture film at a substantially constant speed, means adapted to be rotated by a film, means between said driving means and said rotatable means for forming a loop in said film, means attached to said loop forming means and adapted to be displaced by changes in speed of said film, and a sliding friction damper in- 'cluding a metal, and soft pliable material in contact therewith. for resisting the displacement of said loop forming means and preventing speed changes from affecting said rotatable means.

5. A film drive system comprising a drive sprocket for a motion picture film, means adapted to be driven by the pull of said film for stabilizing the motion thereof, and .a sliding friction damper interposed between said sprocket and said stabilizing means for reacting to changes in motion of said film at a substantially constant counterforce and negligible static friction..

6. A film drive system in accordance with I claim 5 in which said sliding friction damper includes steel in contact with soft felt, said damper having a resilient restoring member.

7. A film drive system comprising a sprocket adapted to advance a film at a substantially constant speed, a stabilizing device adapted to be rotated by the pull of said film, said device having considerable mass, and means including a sliding friction damper intermediate said sprocket and said device and adapted to be displaced by speed variations of said film, said means providing a substantially constant counterforce to displacement for variations in speed of said film at differentamplitudes and frequencies within a certain range of amplitudes and frequencies.

8. A film drive in accordance with claim '7 in which said sliding friction damper includes soft felt and steel adapted to be moved by film speed variations relatively to one another, the pressure therebetween being controllable.

9. In a film drive system the combination of a tension roller adapted to engage a loop in the film and a sliding friction brake device operated by movements of said roller, said device having a 7 lower static friction than kinetic friction;

10. A film drive system comprising means for continuously advancing a iilm,-means for stabilizing the movement of said film, and a sliding friction damper in a loop of'said film and directly operative by changes in size of said loop for absorbing mm speed variations and oscillations of variations within the time of said stabilizing means. i

12. A drive system 1 comprising a. source of power, a mass adapted to be rotated bysaid power. resilient means adapted to store and reone oscillation of lease energy during variations in speed of said source of power, and a sliding friction damper connected to said resilientmeans, the rate of absorption of energy by said damper being proportional to certain velocities of movement of said resilient meansand constant to certain other velocities of movement of said resilient means.

13. A drive system in accordance with claim 12 in which said sliding friction damper comprises felt and steel in contact with one another. I v

mow J. HABBROUCK, Jin