US3051798A

US3051798A - Device for the recording or reproduction of sound tracks

Info

Publication number: US3051798A
Application number: US796655A
Authority: US
Inventors: Knudsen Einer Kristian
Original assignee: FONOFILM IND
Current assignee: FONOFILM IND; FONOFILM INDUSTRI AS
Priority date: 1958-03-05
Filing date: 1959-03-02
Publication date: 1962-08-28
Anticipated expiration: 1979-08-28
Also published as: GB832891A; DE1138560B

Description

Aug. 28, 1962 E. K. KNUDsEN DEVICE FOR THE RECORDING OR REPRDUCTION OF' SOUND TRACKS Filed MaI'Gh 2. 1959 2 Sheets-Sheet 1 Illini Aug. 2s, 1962 E. K. KNUDSEN 3,051,798

DEVICE FOR THE RECORDING OR REPRODUCTION OF SOUND TRACKS Filed March 2, 1959 2 Sheets-Sheet 2 United States Patent O mark Filed Mar. 2, 1959, Ser. No. 796,655 Claims priority, application Denmark Mar. 5, 1958 3 Claims. (Cl. 179-100.41)

The present invention relates to an electromechanical recording and reproducing head of the type having two movable electromechanical members connected to a mechanical oscillating system, comprising `an armature and la needle responsive to both vertical and lateral modulation.

The operating principles of devices of this class, for uses such yas disc recording, are known. As a practical matter, however, the cross modulation produced by the mechanical interaction of the two electromechanical members through the armature has prevented satisfactory results from being obtained. Previous attempts to reduce this cross modulation have proceeded on the basis that the masses of the electromechanical members must be increased while the mass of the oscillating system must he reduced.

The results of these attempts have not been acceptable since the attendant increase in the dimensions `and weight of the apparatus, together with the loss of mechanical rigidity of the armature, which limits the high frequency response of the head, have rendered these solutions to the problem both impractical and unsatisfactory Accordingly, it is an object of this invention to provide an electromechanical head structure which is not subject to the aforementioned problems and limitations.

Another object of the invention is to provide a recording and reproducing head which possesses a substantially uniform frequency response throughout the usable frequency spectrum.

A further object of the invention is to provide a head structure capable of response to both vertical and lateral modulation characteristics and which is substantially free from any cross modulation effects.

A still further object of the invention is to provide a head structure capable of recording or reproducing two channels with a single needle.

Y According to a preferred embodiment of the invention, an elongated armature with a needle mounted centrally thereon has an electromechanical member connected to the armature symmetrically on each side of the needle, the distance between each of the points of action of the two electromechanical members on the armature and the centre of gravity of said oscillating system being equal to where I is the moment of inertia of the oscillating system about an axis through the centre of gravity of said oscillating system perpendicular to the plane formed by the points of the needle and said two points of action of the electromechanical members on the armature, While M is the mass of the oscillating system. Energizing either or both of the electromechanical members produces mechanical oscillation of the yarmature which in turn causes the needle to be oscillated either vertically or laterally, or in both directions simultaneously.

In a preferred embodiment of the invention said centre of gravity is located substantially on a straight line through said two points of action.

Preferably a mechanical rigid elongated armature is used connected to two coils forming the two movable electromechanical members. It can thus be seen that 3,051,798 Patented Aug. 28, 1962 lCC this structure implies some increase in the mass of the armature beyond the minimum requirements for mechanical rigidity. On the other hand, however, the coil structures, which are considerably heavier than the armature, may be made `as light as possible, thereby enabling an overall reduction in massi.

This preferred embodiment of the invention is illustrated in the accompanying dnawings in which:

FIG. 1 is a front view of `a part of a device according to the invention;

FIG. Z is an oscillating system under the action of the two electromechanical members operating in in-phase relation;

FIG. 3 is the oscillating system under the action of the two electromechanical members operating in counter phase relation;

FIG. 4 is the oscillating system under the action of one of the two electromechanical members only, and

FIGS. 5, 6 and 7 illustrate various types of track recording under various combined actions of the electromechanical members.

In FIG. 1 a device is shown comprising two electromechanical members in the form of oscillating coils 1 and 2 having parallel directions of motion. Each of the oscillating coils is connected to an armature 3 at points of

action

4 and 5, respectively. The yarmature 3 has a needle 6, the point of which is so located that the lines connecting the point of the needle 6 with each of the two points of

action

4 and 5 form an angle of 90. The coils 1 and 2 are supported conventionally in housing 9 by Ameans of leaf springs .10 and 11 which are arranged radially in relation to the 'axis of the coils.

The armature 3 has a center of gravity 7 located on or near `a straight line through the two points of

action

4 and 5, and the armature is symmetrically constructed so that the .two points of `

action

4 and 5 are located at the same distance x from the center of gravity on each side thereof.

FIG. 2 shows how such a device will cut into a record when the two oscillating coils 1 and 2. are operating in in-phase relation. The armature then move vertically up and down, and in `a record 8 =a track will be cut with vertical or hill-and-dale modulation as indicated by dotted lines.

If the two oscillating coils 1 and 2 are operating in counter phase relation, the armature 3 will be moved as shown in FIG. 3. In view of the very small movements, the curvature of the paths of motion may be neglected and the point of needle 6 `will therefore make a transverse movement only as shown by dotted lines, a transverse modulation being thereby eifected.

FIG. 4 illustrates how the armature will move, if only one of the oscillating coils is operating. Provided that the above-stated condition is fulilled, an action of the oscillating coil 2 at the point of Vaction 5 cause the `armature to pivot about the point of action 4, and the point of the needle 6 will therefore perform a movement which may be considered rectilinear in a direction forming an angle of 45 with the horizontal plane. Thereby a sound track as shown in FIG. 5 will be recorded, and it appears from FIG. 6 how the corresponding recording of a sound track will be effected when the oscillating coil 1 is operating alone.

The combined movements will appear from FIG. 7 Where, -two independent modulations may be recorded in a two-channel system for instance, for stereophonic reproduction.

It will be seen from FIG. 2. that by hill-.and-dale movement each of the ltwo oscillating coils will be loaded by half of the the armature, i.e. by M/Z. When the needle is moving transversely as shown in FIG. 3, and if the armature is so designed that the load become i.e. the same load as for hill-and-dale movement.

In FIG, 4 the armature is operated by one of the oscillating coils only. Still provided the armature will pivot about the point of action of the other coil, and no power wll'l be transferred thereto.

A one-sided action 'of a force P `at the point of action will, according to the laws of physics, impart a movement to the armature composed of two components, i.e. a translatory movement in the direction of. the force P thereby setting up a resistance of inerti-a equal to an opposite the direction of Ithe force P, and, owing to the fact that the resistance of inertia will act in the center of gravity 7, a rotation of the larmature about the center of gravity set up by the torque P-x. The point S will therefore have two accelerations i.e.

O51=I I owing to the tr-anslatory movement, andv 1 -P P a2 1 Ma M owing to the rotation, the effective mass in the point 5 during pivoting about the center of gravity being equal to the moment of inertia divided by x2. It will be seen that when the armature is designed according to the invention, the two components of acceleration will have the same size, and the resulting 'acceleration in the point 5 will therefore be 4x2 I 4x2 2 because the moment of inertia `of the oscillating system by rotation about the point 4 is I -l-Mx2. It will be understood that the load of masses be the same for all the types of motion mentioned, and cross modulation is avoided by the fact .that one of the oscillating coils only set up a pure rotation or 'pivoting ofthe osv 4 cillating system about the point of action of the other coil on the armature.

While the invention has been illustrated and described in one embodiment, it is recognized that variations and changes may be made therein without departing from the invention yas set forth in the claims.

vHaving described my invention, I claim:

1. In an electromechanical recording and reproducing device, a mechanical oscillating system comprising an elongated iarmature .including a needle mounted centrally thereon, a plurality of electromechanical members connected to the armature symmetrically on each side of said needle, the connection between each of the electromechanical members and the armature being so arranged that the larmature is carried by said electromechanical members and that two fixed and sharp points of action are defined through which no turning moment may be transmitted, the armature being fur-ther provided with extensions extending outwardly from said points of action, said extensions being so arranged that the center of gravity of the armature is l'positioned substantially on a straight line` through the two points of action so that the distance between each of the two points of action and said center of gravity is equal to where I is the moment of inertia of the armature about an axis through said center of gravity perpendicular to the plane formed by the point of the needle and said two points of action, while M is the mass of the armature.

v2. In Ia device of the class described, a mechanical oscillating system comprising a mechanical rigid elongated armature with `a needle mounted on said armature at the center of gravity thereof, a coil connected to the armature symmetrical on each side of the center of gravity dening ia point of action therefor, the distance between each of the points of action of the two coils on the armature and the center of gnavity of said oscillating system being equal to where I is the moment of inertia ofthe Aoscillating system about an axis through thel centre of gravity of said oscillating system perpendicular to the plane formed by the points of the needle and said two points of action of the coils on the armature, while M the mass vof the oscillating system. v

3. In a deviceof the class described, and according to claim 2, wherein said center of gravity is located sub stantially on a straight line through said two points of action.

References Cited in the le of this patent v UNITED STATES PATENTS 2,025,388 Henning Dec. 24, 1935 2,027,168 Harrison Jan. 7, 1936 2,093,540 B1um1ein sept. a1, 1937 2,864,897 Kaar Dec. 16, 1958 FOREIGN PATENTS 688,804 Great Britain Mar. l1., 1'953