Flywheel for Small Size Tape Recorder

The invention relates to a flywheel for small size tape recorders.

A tape drive mechanism for a small size tape recorder generally comprises a capstan for transporting a tape at a uniform rate, a flywheel for rotating the capstan at a uniform rate, a drive motor, and a transmission disposed between the motor and the flywheel. A miniature motor used as a drive source in a tape recorder has a rotor with a very large moment of inertia, and a flywheel also has a very large moment of inertia in order to achieve a uniform rotational speed of the capstan. When an idle pulley is interposed between these components, which have an increased moment of inertia, in order to permit their rotation in the same direction, inconveniences are caused in that a greater starting torque is required of the motor or an increased braking effort must be applied to stop the capstan.

In particular, with a tape recorder of miniature size which employs a micro-cassette tape and which is adapted to be gripped by hand during use, any swinging motion of the recorder which is very likely to occur may add the influence of external forces to the angular momentum of the motor rotor and the flywheel. Some means must be provided therefore to compensate for any variation in the angular momentum in order to assure a satisfactory recording response. If an idle pulley is used which rotates in the opposite direction from the rotor and the flywheel, the diameter of such idle pulley would be limited by design considerations, and the limited diameter of the idle pulley makes it almost impossible to achieve a full compensation.

It is a first object of the invention to provide a flywheel for a small size tape recorder which is peripherally engaged with an output wheel of a motor and which is designed to exhibit a moment of inertia having a given relationship with the moment of inertia of the motor, thereby overcoming the difficulty of the prior art.

It is a second object of the invention to provide a flywheel for a small size tape recorder of the kind described which includes a rubber ring fitted into the periphery of the flywheel to increase the friction between the output wheel and the flywheel.

It is a third object of the invention to provide a flywheel for a small size tape recorder which is molded from synthetic resin integrally with or mechanically coupled with a hollow shaft capstan, thereby reducing the number of parts and the space requirement therefor.

FIG. 1 is a top view of the flywheel for small size tape recorder constructed in accordance with one embodiment of the invention;

FIG. 2 is an elevational section taken along the line II--II shown in FIG. 1;

FIG. 3 is a fragmentary view in elevational section of the flywheel; and

FIG. 4 is an elevational section of another flywheel which is molded from synthetic resin integrally with a hollow shaft capstan.

Referring to FIGS. 1 and 2, there is shown a flywheel constructed in accordance with the invention. Specifically, there is shown a miniature motor 5 for driving a tape in a tape recorder. The motor is mounted on a support plate 3 by set screws 7a, 7b, 7c with its output shaft 5a extending downward into an opening 3a (FIG. 2) formed in the plate 3. An output wheel 6 is fixedly mounted on the shaft 5a and is in closed (i.e. firm) engagement with a frictional transmission member 4 such as rubber ring which is applied to the peripheral surface of a flywheel 2.

In the example shown, a capstan 1 is formed integrally with the flywheel 2 for coaxial rotation, and is disposed in parallel relationship with the output shaft 5a of the motor 5. In such an arrangement, the moment of inertia of the rotating portion of the motor 5 inclusive of the output wheel 6 about the shaft 5a, the moment of inertia of the flywheel 2 about its support shaft, and the relative direction of rotation of the output wheel 6 and the flywheel 2 have a complex relationship among them, which is avoided by providing a direct coupling between the output wheel and the flywheel, which thus rotate in opposite directions from each other. Rotation in the opposite directions permits a cancellation of the moments of inertia if they have a substantial magnitude.

In accordance with the invention, the size and weight of the flywheel are chosen so that the following relation applies;

or

where I.sub.M represents the moment of inertia of the rotating portion of the motor inclusive of the output wheel 6 about the shaft 5a, I.sub.F that of the flywheel, .omega..sub.M and .omega..sub.F the angular velocity of the output wheel 5a and the flywheel 2, respectively, and n the ratio therebetween which is equal to .omega..sub.M /.omega..sub.F. The equal angular momentum of the motor and the flywheel, coupled with their rotation in opposite directions, permits a substantial balancing of the respective angular momenta, thereby enabling the starting torque or the braking effort required upon stopping to be reduced.

If an external force is applied to the flywheel 2 to cause a change .DELTA..omega..sub.F in its angular velocity, the resulting change .DELTA..omega..sub.M in the angular velocity of the output shaft 5a is calculated as follows;

Hence,

In other words, the equality between the angular momentum of the motor and the flywheel is maintained in the presence of the influence of an external force, still permitting their substantial balancing. As a result, the arrangement of the invention permits the rotational speed of the capstan to be maintained constant, minimizing the wow or flutter.

As shown in FIG. 3, the flywheel 2 is peripherally formed with a groove 2b into which is fitted the transmission member 4, which may comprise a rubber ring, for example, having an increased coefficient of friction. The member 4 as prepared has a perimeter which is slightly less than the circumferential length of the flywheel, and is fitted into the groove by stretching it. This assures a strong frictional engagement while simplifying the required process than when a frictional member is staked around the periphery of the flywheel.

As shown in FIG. 4, the flywheel 2 is molded from synthetic resin integrally with the capstan 1. The flywheel is centrally formed with an integral hub 2b extending upward therefrom, with a step 2c formed above the hub and which is contiguous with an upwardly extending hollow shaft of a reduced diameter, the hollow shaft constituting the capstan 1. The capstan 1 and the flywheel 2 are fitted closely over a support shaft 9 secured to the support plate 3, with a bearing 8 interposed between the hub and the shaft 9 to make the flywheel rotatable relative to the latter. An upper interior surface 2d of the hub 2b rests on the top end face of the bearing 8 to prevent a downward movement of the flywheel. The top end of the shaft 9 is internally threaded to receive a locking screw 10 having a dished head 10a, which bears against the top end of the capstan 1 to prevent its upward movement.

In the region of a cassette receiving chamber, a panel 11 in the recorder is formed with an opening 11a, through which the capstan 1 extends into the chamber. A stationary baseplate 12 is located intermediate the panel 11 and the support plate 3 and fixedly mounted on the latter, with an opening 12a formed therein to pass the hub 2b therethrough. The step 2c is located slightly above the upper surface of the baseplate 12, and has a small diameter drive gear 13 rigidly mounted thereon as by shrinkage fit for driving a tape supply or rewind shaft.

The above construction of the capstan 1 as a hollow shaft integral with the flywheel 2 enable a substantial reduction in the spacing H (FIG. 4) between the panel 11 and the support plate 3 and hence in the thickness of the tape recorder. Another advantage occurs from the fact that the shaft 9 is located to counter the pressure exerted upon the capstan 1 by a pinch roller, not shown, thus effectively avoiding a tilting of the capstan and preventing undue stresses from being applied to the bearing.

The integral molding of the capstan and the flywheel is not essential. Instead, the capstan may be formed by a pipe of a reduced diameter and integrally joined with the flywheel for the ease of mass production.