US2647754A - Reproducer mounting - Google Patents

Description

1953 M. F. ROYSTON 2,647,754

REPRODUCER MOUNTING Filed Nov. 28, 1947 2 Sheets-Sheet l 6 x INVENTOR. 1707'!!! I. Iayston ATTORNEYS 1953 M. F. ROYSTON 2,647,754

REPRODUCER MOUNTING Filed Nov. 28, 1947 2 Sheets-Sheet 2 *5 cl 3:. g

ATTORNEYS Patented Aug. 4, 1953 UNITED STATES PATENT OFFICE REPRODUCER MQUNBING Marvin F. Royston, Poughkeepsie, N. Y.,,assign0r to Daystrom, Incorporated, Elizabeth; N; .11, a corporation of'N'ew'Jersey' Application November 28, llll ll'gscriallNot'ldll-fillll" (Cl. MA -23.).

12 Claims. 1

This intention. relates to phonograph reproducer. mounti ngs;.. particularly for thereproductien or phonograph and like records having g roovedisoundtracks: adapted to actuate the re producer through a stylus. or needle.

It is. a. principal obj ect of the: invention to provide an improved pivoted mounting for such a reproducer, particularly advantageous in the playing of records in a horizontal positionwhich eliminatesor greatly reduces the tendency-of the needle in. certain positions and under certain conditions, to leave. the groove with which it is engaged. and slide over thesuriace of the record to. amore stable position. This tendency occurs when the engaged portion of! the groove extends and is advanced in a direction at an angle to the longitudinal axis or? the: reprodncer arm, or to the line: connecting the needle and vertical pivotal axis. ot the arm" if the arm does not follow such lines Actual jumping from one grooveto another is more likely to; take place when light needlepoint pressures are employed. and when the apparatus is; subject. toshock or vibration,

although the. tendency to.- jump grooves is inherent: in the relations]? the forcesacting onthe need-1e.-

When the sound: groove and theieilectivelongitudinal, axis. of the pivoted: reproducer. armare at an angle to one another, there exists: a. component or-. the: frictional force or drag of the I advancing. groom-e: on! the needle which: a moment about the vertical pivotal. axis of the reproducer arm: tending; to rotate.- the: arm: and move the needle to a new groove, or a new convolntioniin thecase ofi a continuous spiral groove,

Where: the longitudinal axis of. the' arm and the engaged groove. are substantially parallel; For example, the recording medium is. a. film strip inwhich ainumher of parallel sound grooves are formedand which: lies and isadvanced substantially in a horizontal plane at the point of en-- gagneme-nta of the reproducer needle therewith,

and it the vertical pivot about which the reproduces arm; swings iscentrally disposed relative to the strip, there isa tendenoy fior the needl'e when following: any out the central. grooves to jump out oii the engaged groove andv slide over thesurface oi thestrip'to a m-orecen-trally located one. This tendency increases as the lengthof the: reproducer arm i's shortened many applications it is highly desirable to use: a: short? reproducer arm, to: facilitate compact design..- It is; also desirable: to use fine record grooves snas: to: obtain as much: information as possible: from a given: area of. record surface- Low: needle-point pressures are desirable to; reduce. record. and needle wear. All these factors increasethe tendency of the. needle, when engaging, a groove. lying. at an angle to the effective longitudinal. axis off the reproducer amp to. jump to a groove. more nearly aligned. with said axis.

The present invention makes. use of. the Weight oii thezpiclcup armto. provide. an outwardly-acting force. to at. least. partially counteract the inwardly-acting force due to contact between needle and. groove. thereby decreasing, the. tendency to jump grooves. This. is accomplished" by tilting the conventional. vertical pivotal axisv of the arm. The relation between the angle or tilt of this axis and. the factors affecting. stability of the needle will be referred. to. more in detailiin the following description of a. specific. embodiment, with reference to the appended drawings in. which Fi 1-: isa iractionalelevatibnal view of asoun'd reproducing apparatus. including a reproducer mounting. in accordance with the invention;

Figs 2. is a plan view. of. the record medium of Fig.- 1., together with a diagram illustrating certainif'orce relationships involved in. the operation oil reproducer mountings;

Fig. Eb is:- a diagrammatic. side. view ofa reproduces mounting. illustrating certain features ottheinventiona Fig-l4 is atop-view oil the reproducer of Figafi'; and- Figs. 5 and 6 are diagrams. illustrating the manner in which the. tilt of. the results in an: outward force. at. the. needle.

Fig, 1 illustrates. theapplication. of the reproducer mounting of the. invention. to sound. apparatns employing as. a record medium an endless loopor film. strip. H, having a portion thereof coiled into. a. roll: rotatably supported on rollers 12,. mounted in. circular array on a panel or supporting member. A3. A pair of rotatably' reversi-bieguardmcmbers I II in. the illustrated position, thereofv prevent the film roll from slipping off the supporting rollers, and may he positioned to permit mounting. the roll thereupon.

Film strip-= ll. isladvancedlongitudinally by the engagement of; edge.v perforations. Iii thereof with at sprocket. I-fi driven. from motive means, not shown The axis of the. film. roll and; the axes ofi rollers 1a are necessarily at. a slight angle to the axisiofi sprocket. its due. to. the endless nature of the; film: strip In its travel. the stripv passes over a slightly curved platen 26' and at a portion thereof where-the film. is substantially horizontal is engagedin one at sound grooves 21'' of. the film, by reproducer; stylus or. needle 22,. is

operatively connected to actuate a reproducer head 23 carried at the front end of reproducer arm 25. The reproducer head converts lateral variations in the sound grooves into an electric wave as is well known.

The reproducer head and its mounting are located within the film roll, as shown, to yield a compact design. The length of arm 25 is hence restricted. In certain designs an effective arm length of the order of 3 inches is the maximum possible. The present invention enables such short arms to be employed while maintaining stable tracking.

Reproducer arm 25, in accordance with the principles of the invention, is pivoted on a movable support member, here shown as bracket 21, about an axis 26 which allows movement of the reproducer head 23 in a direction normal to the plane of the record grooves, that is, in the Vertical direction in the embodiment shown. Bracket 21 in turn is pivoted to a fixed support, here shown as bracket 28, about an axis 30 which is inclined at an acute angle to the vertical (angle a in Fig. 3). Axis 2B is advantageously offset from axis 30 in the direction of the reproducer head, as shown, the amount of offset being small compared to the arm length.

When using a strip film record, it is advantageous to locate axis 30 in a vertical plane passing through a central part of the record groove surface, so that the lateral excursion-s of the reproducer head are approximately equal on each side. Axis 26 is advantageously at right angles to axis 30, and horizontal when the head engages a central groove. As the head moves laterally in either direction, axis 26 moves in an are about axis 30 and accordingly tilts downwardly in the corresponding direction.

In Fig. 2 there are shown certain of the horizontal forces and components thereof acting on a reproducer arm pivoted about a vertical axis through a point centrally located relative to the film, for different positions and lengths of the arm. A vertical axis through 0 in Fig. 2 may be taken to correspond to the line C-C, in Fig; 3, which illustrates the position axis 30 of the reproducer arm mounting would assume if rotated to the vertical about axis 26. Sound grooves 2| are shown broken away, for clarity of illustration, but will be understood to be continuous in ordinary practice.

Assume that a reproducer arm, represented as to effective length and position by the line O-A, mounts a needle at point A subjected to a frictional drag f in the direction in which the sound groove advances. When the film and the sound grooves therein advance in the direction of arrow 35, there is no tendency for the needle at point A to slide laterally over the film, since the force 1, due to the longitudinal drag of the groove on the needle, lies along the effective longitudinal axis of the arm. However, when an arm of the same length is in the position 0A, with the needle at A engaging one of the outer sound grooves 2| of the strip, the force 1 has a component in normal to the arm axis and this component has a moment about 0 tending to slide the needle to the point A. This normal component of the frictional drag decreases as the length of the arm is increased, for example, to a value in if the arm is increased in length to 0-3.

In the diagram the force I, the pull of the needle in the direction in which the groove is advancing, has been assumed constant for simplicity of explanation and the force vector of the resistance to lateral sliding of the needle is not shown. The forces due to lateral movement of the needle produced by the recorded waves in the record grooves have also been omitted, for simplicity.

Considering now the effect of the tilt of the axis, Figs. 5 and 6 will be referred to. Fig. 5 is a force diagram in a horizontal plane with the pickup or reproducer head assumed to be engaging an outer groove of the record. Fig. 6 is a force diagram in a vertical plane through the center of gravity normal to the pickup axis, the point of view being indicated by arrows 66 in Fig. 5.

In Fig. 5, 4| is a center line down the record film H through the tilted axis 30. The center line through the pickup is denoted 42.

In Fig. 6, center line 53 coincides with axis 30, and appears at an angle due to the projection of the angle of tilt of axis 30 onto the vertical plane 6-6. The weight of the pickup arm, acting at its center of gravity, results in a downward force ,fg due to gravity. This force may be resolved into component 44 along the center line 43 and component 45 perpendicular thereto. The latter component may in turn be resolved into a force parallel to j and force in in the horizontal plane.

Referring again to Fig. 5, force in is shown applied at the assumed center of gravity of the pickup arm along center line 42. It is evident that in results in a torque tending to swing the arm outward. The resultant force at the needle is shown as in, and is smaller than it since it is farther from the pivot point.

It is evident that in is opposite to fn in Fig. 2, and hence tends to counteract it. Both forces are zero when the needle is in a center groove, and both increase as the needle moves more and more toward the outer grooves. This is advantageous. Actually it is not necessary that force in exactly counterbalance force ,fn, so long as the resultant force does not exceed that required to lift the needle out of the groove. In addition to diminishing the tendency to jump grooves, the counteracting force f0 reduces record wear by reducing the lateral force on the sides of the grooves.

As the pickup moves toward the outer grooves the axis 26 (Fig. 3) does not remain exactly horizontal, but tilts slightly. This tilt may also contribute somewhat to the outward force at the needle.

The effect of the tilt may also be considered from the point of view that since axis 26 moves in an arc of a circle around axis 30, it moves downward on either side of its central position, and thus the rear end of the pickup arm 25 moves downward. Hence, when the needle engages a non-central groove, work must be done on the arm to move it back to a central position. Force fn is required to do this work, in addition to the work required to lift the needle out of the groove, before the needle can jump a groove.

The above theory, while believed helpful in understanding the effect of tilting the axis, is not insisted upon and is subject to further elaboration.

The optimum angle of tilt is subject to variation depending on several factors, particularly the length and weight of the arm, needle pressure, speed of travel of the record surface, and coeflicient of friction of the needle therewith. It has been found possible to calculate approximately aeeam the performanceef the arm for given parameters but in general the difficulty-01 determining the essential parameters-and making thecalculation renders the direct determination of the" optimum tiltangle far-simpler; This may easily be ascertained by constructing the arm of desired length and needle pressure; and placing the needle on an ungrooved record. surface traveling at the desired speedi The-vertical axis maythen be tilted" until there is little or no tendency-1hr the needle to move from outer to central; portions of th'erecordsurface:

As an example for illustrative purposes 0111s, for one model of thein-vention which operated satisfactorily the following datav applied:

Needle. pressure 24-grams. Tilt" angle (from: vertical) 35:; Distance from axi'sttljto 26 grams. Lengthfrom axis 2b to needle=- v 3% grams. Needlean'gl'e" (from horizontal film)" 7 35 mm. film speed 6'6 fa/min;

As examples of variations in tilt angle with other parameters, the following observations have been made, As the film speed is increased; with other parameters unchanged, larger tilt angles are in general required to prevent or minimize lateral movement of the needle on an ungrooved film. Such increased" film speed increases the force due to needle friction in" and hence requires a somewhatv greater force it to counteract it.

For a light weight pickup arm '7 inches long, as the reprod'ucer head was moved from a distance of 2.75 to 7 inches from the. tiltedaxisand needle pressure maintained constant.- at 35 grams by gram weights over the needle point, the optimum tll'tangle increased somewhat. However, for'arm lengths above about. inches, when used with a-35 mm. film, the force in, was sufii'ci'ently small so that a vertical pivot sufilced Without danger of jumping grooves in normal play. For arms shorter than about 5 inches the tilt angl'eassi'sted materially in improving, tracking stability. In another case where the; arm. length was increased as the reproducer head was moved from, 2.75 to 7 inches, thereby increasing, the weight of the arm itself, while the needle pressure was maintained constant at 35 grams by gram weights over; the

needle point, the optimum tilt angle decreased slightly, averaging, about l!) degrees.

It has also beenfound that the needle. point pressure is increased by added force. applied over the, needle, as by weights, etc.,, without changing other factors, the optimum tilt; angle is. increased somewhat, presumably due; to, the increase force ,fn which requires. additional tilt to. increase the counteracting force It...

It, is believedthat the above discussion oi the efi'ect of, certain parameters on the. optimum tilt anglerwill assist in theready practice. of the invention. Also, as previously pointed out, it is usually easier in practice to simply vary the tilt angle in a given case to determine the optimum, keeping. in, mind that adequate tracking. is ofiten obtained even though the tilt angle is not optimum due to the factor ofsafety introduced by the: force required to:- the needle: outiof the groove In general, it has; been found that backward til-t angles between and 45 degrees suffice to give proper tiackingz. The optimum angle within this range may be selected' tor the particular'conditions applying as above discussed. Angles; greater than .45" have-beentemployedwith 6 success; but appear torbe' unnecessary in most cases't A: preferred embodiment of: the invention has been described above" for use with. a-film record It will be understood that the specificv details given may be departed from to lit the conditions of a given-- application, within the scope of the invention.- It will also be. understood that the invention is applicable to dish records as well as the film records specifically described.

I" claim:

1 A phonograph reproducer mounting for reproducing soundfrom record grooves which are substantially horizontal at the point of reproduction comprising a fixed support, a movable support member pivoted to said fixed support aboutan axis inclined'backwards with respect to the reproducer mounting playing position at a substantial acuteangle with the" normal to the plane'- of therecord grooves at the point of reproduction, and a generally horizontal arm having a free front end bearing a reproducer' head and pivoted. near the rear end thereof tosaid movabl'e' support member about an axis allowing movement of saidheadin the direction normal to sai'dplane of therecord' grooves.

2". A- phonograph reproducer mounting for reproducing. sound from record grooves which are substantially horizontal at the point ofreproduction comprisinga fixed support, a movable support member pivoted" tic-said fixed support about an axis inclined backwards with respect to the reproducermountingin playing position at a substantial acute angle with thenormal to the plane of the record grooves at the point of reproduction, and a generally horizontal arm having a free front and bearing a reproducer head and pivoted'near' the rear end thereof to said movable support member about a lateral axis substantially atright angles to said inclined axis.

3. A phonograph reproduoer mounting for'reproducing sound from record grooves which are substantially horizontal at the point ofreproduction comprising a fixed support, a movable support" member pivoted" to said fixed support about an axis inclined backwards with respect t the reproducer mounting in playing position at a substantial acute angle with the normal to the plane of the record grooves at the point of reproduction, and a generally horizontal arm having afreefront end bearing a reproducer head and pivoted near the rear end thereof to said movable-supportmember-about a lateralaxis substantially at right angles to said inclined axis and-onset with'respect thereto by'a distance small compared to the length of said arm.

4. A phonograph reproducer mounting comprising a generally horizontal arm having a free front end bearing areproducer head for engaging a substantially horizontal record surface, a movable support member pivoting the rear endof said arm" about" a lateral axis; and a fixed support pivotingsaidmovablesupport member about anaxi inclined backwards with respect to the reproducer mounting in playing position at a substantial acute angle to-thevertical.

5 phonograph reproducer mounting comprising afixed support, a movable support member pivoted-tosaid fixed supportabout an axis inclined backwards with respect to the reprodlieer mounting inplaying position: at a substantial acute angle to the vertical, anda generally horizontal arm having a f ree frontend lbearing a reproduce'r he'a'd and pivoted toward the rear end thereon to said movable supportmember" about a lateral axis allowing movement of said head in a vertical direction, said arm being movable through a substantial horizontal angle to permit said reproducer head to traverse a band of record rooves.

6. A phonograph reproducer mounting for reproducing sound from a band of record grooves which are substantially horizontal at the point of reproduction which comprises a fixed support, a movable support member pivoted to said fixed support about an axis inclined backwards with respect to the reproducer mounting in playing position at a substantial acute angle to the vertical, and a generally horizontal arm having a free front end bearing a reproducer head and pivoted toward the rear end thereof to said movable support about a lateral axis substantially at right angles to said inclined axis, said arm being movable through a substantial horizontal angle to permit said reproducer head to traverse a band of record grooves.

'7. A phonograph reproducer mounting comprising a fixed support, a movable support member pivoted to said fixed support about an axis inclined backwards with respect to the reproducer mounting in playing position at a substantial acute angle to the vertical, and a generally hori zontal arm having a free front end bearing areproducer head and pivoted toward the rear end thereof to said movable support member about a lateral axis substantially at right angles to said inclined axis and ofiset with respect thereto by an amount small compared to the length of said arm, said arm being movable through a substantial horizontal angle to permit said reproducer head to traverse a band of record grooves.

8. A phonograph reproducer mounting comprising a fixed support, a movable support member pivoted to said fixed support about an axis inclined backwards with respect to the reproducer mounting in playing position at an acute angle to the vertical greater than about 20 degrees, and a generally horizontal arm having a free front end bearing a reproducer head and pivoted at the rear end thereof to said movable support member about a lateral axis substantially at right angles to said inclined axis and offset with respect thereto by an amount small compared to the length of said arm, said arm being movable through a substantial horizontal angle to permit said reproducer head to traverse a band of record grooves.

9. A phonograph reproducer mounting for reproducing sound from a band of record grooves which are substantially horizontal at the point of reproduction which comprises a fixed support, a movable support member pivoted to said fixed support about an axis inclined backwards with respect to the reproducer mounting at a substantial acute angle to the vertical in a vertical plane passing through a central part of said band of grooves, and a generally horizontal arm having a free front end bearing a reproducer head and pivoted at the rear end thereof to said movable support about a lateral axis substantially at right angles to said inclined axis, said arm being move able through a substantial horizontal angle to permit said reproducer head to traverse said band, said lateral axis being horizontal when the reproducer head is in the central part of said band and tilting as the head engages outer parts of said band.

10. A phonograph reproducer mounting for reproducing sound from a band of record grooves which are substantially horizontal at the point of reproduction which comprises a fixed support, a movable support member pivoted to said fixed support about an axis inclined backwards with respect to the reproducer mounting at a substantial acute angle to the vertical in a vertical plane passing through a central part of said band of grooves, said acute angle being greater than about 20 degrees, and a generally horizontal arm having a free front end bearing a reproducer head and pivoted at the rear end thereof to said movable support about a lateral axis substantially at right angles to said inclined axis and horizontal when the reproducer engages a central part of said band, said arm being movable through a substantial horizontal angle to permit said reproducer head to traverse said band, whereby the Weight of the arm produces an outwardly-acting force as the reproducer head moves laterally from said central part to at least partially counteract the inwardly-acting force due to groove contact.

11. A phonograph reproducer mounting for reproducing sounds from a band of record grooves which are substantially horizontal at the point of reproduction which comprises a fixed support, a movable support member pivoted to said fixed support about an axis inclined backwards with respect to the reproducer mounting at an acute angle to the vertical in a vertical plane passing through a central part of said band of grooves at said point of reproduction, said. acute angle being greater than about 20 degrees, and a relatively short generally horizontal arm having a free front end bearing a reproducer head and pivoted at the rear end thereof to said movable support about a lateral axis substantially at right angles to said inclined axis and horizontal when the reproducer engages a central part of said band, said arm being movable through a substantial horizontal angle to permit said reproducer head to traverse said band, the length of said arm being less than about 5 inches from the lateral axis to said point of reproduction and the lateral axis being offset from the inclined axis toward the reproducer head by a distance small compared to the length of the arm, whereby the weight of the arm produces an outwardly acting force as the reproducer head moves laterally from said central part to at least partially counteract the inwardly-acting force due to groove contact.

12. A phonograph reproducer mounting for reproducing sound from record grooves which are substantially horizontal at the point of reproduction comprising a fixed support, a movable support member pivoted to said fixed support about an axis inclined backwards with respect to the reproducer mounting in playing position at a substantial acute angle to the vertical, and a generally horizontal arm having a free front end bearing a reproducer head and pivoted near the rear end thereof to said movable support memher about an axis allowing movement of said head in the direction normal to the plane of the record grooves at the point of reproduction.

MARVIN F. ROYSTON.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 703,764 Chapman July 1, 1902 1,067,530 Lindstrom July 15, 1913 1,304,404 Swing May 20, 1919 2,267,693 Di Toro Dec. 23, 1941 2,269,263 Guedon Jan. 6, 1942 2,323,066 May June 29, 1943

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