Cassette Tape Recorder

The present invention relates to a cassette tape recorder for automatic stereo sets.

It is well known from experience that an ordinary cassette tape recorder may produce a high quality sound when a vehicle in which the cassette tape recorder is installed is in a stationary condition but that the same tape recorder may produce a poor quality sound when the vehicle is in motion and is experiencing large up-and-down vibrations. It is also known that, particularly when the remaining amount of tape to be played is large, wow is increased to thereby result in a poor quality sound production.

Various studies of this wow phenomenon have been made by the present inventors. In one experiment, an up-and-down vibration of 1G was applied to an ordinary cassette tape recorder at a changing frequency, and the resulting wow was measured. The results are shown in FIG. 1, which is a graph shoing the wow (RMS) characteristics vs. frequency. As is apparent from the characteristic curve, wow exceeding 1% was generated at a vibration of 40 Hz and also at 100 Hz or more. These characteristics were measured in another way, that is, with auditory sense compensation, and the results were as shown in FIG. 2. The wow generated at the vibration of 100 Hz or more was less than 0.2% and caused no problem, but the wow generated at about 40 Hz was still more than 0.2%, which caused the quality of sound to be degraded.

Detailed analyses of the wow at 40 Hz were then made, which can be understood with reference to the structure of a conventional tape recorder and the tape cassette and the operations thereof as will be explained in detail with reference to FIGS. 3 through 8.

Referring first to FIGS. 3 and 4, a tape cassette case generally designated by reference numeral 1 is made up of cassette halves 1a and 1b and a tape 2 encased therein. The tape 2 is fixed at either end to a pair or reels 3a and 3b by means of respective clampers 4a and 4b, so that the tape can be wound onto the reels 3a and 3b. Thus, when the winding diameter of the tape on one side is increased, the winding diameter of the tape on the other side is decreased. In the drawings, the tape is fully wound on supply reel 3b. It is a typical feature of the tape cassette that no flanges are provided on the reels 3a and 3b, to thereby decrease the distance between reels 3a and 3b, which in turn leads to a miniaturization of the overall physical cassette size. However, without flange members, the tape may be wound on the reels 3a and 3b non-uniformly in a width wise direction. In order to eliminate this defect, i.e., to prevent the tape from contacting with the inner walls of the cassette halves 1a and 1b, and in order to achieve such prevention without causing any substantial additional friction, a space is provided between the tape and each inner wall of the cassette halves 1a and 1b, and a sheet 5a or 5b, which is a so called "retainer", is interposed in this space so that the reels 3a and 3b are retained at a suitable position within the case 1.

A pair of guide rollers 6a and 6b, a pressure pad 7, and the like are encased in the case together with the tape 2 and the reels 3a and 3b. In the walls of the case 1 are formed a pair of capstan shaft insertion holes 8a and 8b, positioning pin insertion holes 9a, 9b, 9c and 9d, a pair of pinch roller insertion holes 10a, 10b, reel shaft insertion holes 11a and 11b, and a magnetic head insertion hole 12. Reference characters 3a' and 3b' denote engagement lips formed at an angular interval of 60.degree. on the circumferential periphery of the reel 3a or 3b.

On the other hand, the cassette tape recorder comprises a pair of reel shafts 20a and 20b, a capstan shaft 21, a pinch roller 23 and a magnetic head 24. When the tape cassette 1 is mounted on the tape recorder, the reel shafts 20a and 20b are inserted through the reel shaft insertion holes 11a and 11b into the interior of the tape cassette 1 and engage the reels 3a and 3b. At the same time, the capstan shaft 21 is inserted into the capstan shaft insertion hole 8a. Then, when the tape recorder is played, the pinch roller 23 is inserted through the pinch roller insertion hole 10a into the interior of the tape cassette 1 to clamp the tape 2 against the capstan shaft 21 so that the pinch roller cooperates with the capstan shaft 21 rotating at a constant speed to move the tape 2 at a constant speed. At the same time, the magnetic head 24 is inserted through the magnetic head insertion hole 12 into the interior of the cassette case 1 to clamp the tape 2 against the pressure pad 7 to thereby reproduce the information recorded on the tape 2.

In the thus described play condition, the reel shaft 20a serves to take up the tape 2 and is driven by a drive source (not shown), whereas the reel shaft 20b serves to feed the tape 2 and is not driven by the source, but instead is adapted to apply a constant back tension to the tape 2.

The reel shaft 20b on the supply side of the conventional construction is shown in FIGS. 5 and 6, wherein the character C denotes a chassis of the cassette tape recorder, from which an upright shaft 20b.sub.1 extends vertically. A reel shaft member 20b.sub.2 having a regular hexagonal cross section is freely rotatably mounted on the upright shaft 20b.sub.1. A cylindrical hub 20b.sub.3 surrounds the shaft 20b.sub.2 so as to be slidable in the axial direction but to positively engage the shaft member 20b.sub.2 with respect to the horizontal or rotational direction. The cylindrical hub 20b.sub.3 is biased to move in one direction by a spring 20b.sub.4 interposed between the bottom surface of the hub and the facing portion of the shaft member 20b.sub.2. The hub 20b.sub.3 is held at a position shown by a retaining member 20b.sub.5 tightly engaged with the shaft member 20b.sub.2.

As described above, the shaft member 20b.sub.2, the cylindrical hub 20b.sub.3, the spring 20b.sub.4 and the retaining member 20b.sub.5 are formed as a unit which is prevented from being pulled apart from the upright shaft 20b.sub.1 by means of a stopping member 20b.sub.6 mounted on the top end of the upright shaft 20b.sub.1, as shown in FIG. 5. A leaf spring 20b.sub.7 interposed between a flanged portion of the upright shaft 20b.sub.1 and the shaft member 20b.sub.2 is provided in order to produce a constant frictional force between the reel shaft and the upright shaft 20b.sub.1 to thereby apply a back tension to the tape 2. With the thus constructed reel shaft 20b, when the tape cassette is inserted, if the reel lips 3b' of the cassette are not properly meshed with the outer projections 20b'.sub.3 of the cylindrical hub 20b.sub.3, the cylindrical hub 20b.sub.3 may be pressed downwardly so that no damage occurs. If a simpler construction is desired, as shown in FIG. 7, projections 20b'.sub.2 may be formed directly on the shaft member 20b.sub.2 with the shaft member rotatably mounted on the upright shaft 20b.sub.1. The leaf spring 20b.sub.7 provides back tension and is also provided with somewhat more bending range.

Now, when the above-described tape recorder is in the play condition, let us asseme that an up-and-down vibration is applied thereto as shown by the arrow in FIG. 4. When the frequency of vibration is very low, e.g. about 1 Hz, the reels 3a and 3b are vibrated together with the case 1 and chassis C. However, when the frequency is increased, the reels 3a and 3b may remain relatively stationary while only the case 1 vibrates vertically together with the chassis C. For this reason, the upper and lower inner walls of the case 1 collide against the reels 3a and 3b with high energy. In such a condition, the tape 2 may be elongated or shortened between the point a on the tape 2 clamped between the capstan shaft 21 and the pinch roller 23 and the point b at the winding end of the reel 3b.

It is to be noted that the tape 2 between the above described points a and b has a resonance at a resonance frequency f.sub.O which is determined according to the spring constant of the tape 2 and the inertial moment of the tape wound on the reel 3b. Now, when the value of f.sub.O is calculated with a typical back tension of 2 to 3 g, a value of f.sub.O =30-40 Hz, is derived.

When the cassette tape recorder is in its play condition, as shown in FIG. 8a, the projections 3b' of the supply reel 3b are engaged with the projections 20b'.sub.3 of the reel shaft 20b so that the projections 3b' rotate the reel shaft 20b while the supply reel is rotated in the direction of the arrow. However, when the above noted resonance is generaged, the rotation of the reel 3b may be stopped by the elongation of the tape 2 as shown in FIG. 8b. Thereafter, due to the reduction of the tape, the reel 3b is rapidly rotated to thereby rotate the reel shaft 20b with high energy and at a higher speed as shown in FIG. 8c. For this reason, a reactive force occurs whereby the shaft projections 20b'.sub.3 push back on the reel projections 3b' so that, with the next elongation of the tape 2, the projections 3b' and 20b'.sub.3 of both members are separated from each other as shown in FIG. 8d. Once such a state is generated, collision and reaction are alternately generated between the projections 3b' and 20b'.sub.3 to thereby cause so-called jitter. As a result, the travelling speed of the tape 2 on the surface of the magnetic head 24 is changed, which causes wow to be generated at about 40 Hz.

Also, in the reel shaft according to the prior art, there would be a radial displacement between the reel and reel shaft of cassette. Therefore, the reel would not rotate coaxially with the reel shaft. This would cause a vertical fluctuation and a resonance of tape so that the reel might be moved in a radial direction of the reel shaft to produce an unstable travel of tape and to increase a wow.

It is an object of this invention to provide a cassette tape recorder which does not cause a large WRMS, even it vertical vibrations are applied thereto, and which is thus improved in tone quality.

In order to accomplish the above object, in the cassette tape recorder of the invention, at least the reel shaft on the tape supply side comprises a taper portion engaged with a reel of the cassette in such a manner that the reel is coaxial with the reel shaft, and an elastic member for supporting the reel from below through the taper portion, the elastic member having an elastic force which is substantially proportional to the weight of the maximum residual quantity of tape on the reel, whereby when vertical vibrations are applied to the cassette, the elastic member can prevent the reel from violently striking the lower wall of the cassette case to decrease the vertical motion of the reel in the cassette case, and wherein a diametrial motion of the reel is prevented by the taper portion to reduce sympathetic vibrations of the tape, with the result that the collision and reaction between the reel shaft the projections caused by the sympathetic vibrations of the tape are lessened so as to keep the WRMS low.

FIGS. 1 and 2 are graphs showing the WRMS characteristic of a conventional cassette tape recorder before and after auditory sense correction;

FIG. 3 is a plan view showing a cassette tape recorder in an operating condition, with one side of the cassette case detached;

FIG. 4 is a sectional view along the line IV--IV' of FIG. 3;

FIGS. 5 to 7 are sectional views showing a conventional reel shaft on the tape supply side, and especially FIG. 6 is a sectional view along the line VI--VI of FIG. 5;

FIG. 8 is a schematic illustration of a problem caused when using the reel shafts described in FIGS. 5 to 7;

FIG. 9 is a sectional view of one embodiment of the reel shaft on the supply side used in the cassette tape recorder of the present invention;

FIG. 10 is a sectional view along the line X--X of FIG. 9;

FIG. 11 is a perspective view of one portion of FIG. 9;

FIG. 12 is a plan view showing the condition in mounting a reel shaft on a cassette, with one portion of the reel;

FIG. 13 is a sectional view showing the mounting condition of a cassette;

FIGS. 14 and 15 are graphs showing WRMS characteristics before and after hearing correction, respectively, measured by applying vertical vibrations to the cassette tape recorder adopting the reel shaft of FIGS. 9 to 13;

FIG. 16 is a perspective view showing a modification of one portion of FIG. 9;

FIGS. 17 and 18 are sectional views of other embodiments corresponding to FIG. 9;

FIG. 19 is a sectional view of a further embodiment corresponding to FIG. 13; and

FIG. 20 is a perspective view of one portion of FIG. 19.

The present invention will now be described by way of embodiments shown in FIGS. 9 to 20, wherein reference characters similar to those of FIGS. 3 to 8 indicate the same or corresponding members, respectively.

FIGS. 9 to 13 show one embodiment of a reel shaft 20b on the tape supply side, in the case of a cassette tape recorder for one way use. The illustrated reel shaft 20b is structurally similar to the reel shaft of FIG. 6, except that a collar 30 having a diameter larger than that of the protrusions 20b'.sub.3 is formed on the lower side of a cylindrical hub 20, the upper surface of the collar 30 being provided with a taper portion 30' at a selected angle.

With the above reel shaft 20b, however, when a cassette is mounted thereon as shown in FIGS. 12 and 13, the inner peripheral lower edge of the reel 3b and the leading edge of a protrusion 3b' are adapted to seat on the taper portion 30' to support the reel 3b with a spring 20b.sub.4 through the taper portion 30', so that the reel 3b is retained at an intermediate position between the upper and lower cases 1a, 1b of the cassette 1. The spring 20b.sub.4 is selected to have 10 to 20 g of elastic force in such a manner as to be substantially in proportion to the weight of the maximum residual quantity of tape on the reel 3b.

Therefore, in the condition in which the cassette is mounted, as shown in FIG. 13, the upper end surface of the cylindrical hub 20b.sub.3 is slightly separated from a pressing member 20b.sub.5 so as to form a gap 33, and to position the reel 3b coaxially with the reel shaft 20b.

In the above embodiment, the elastic force of the spring 20b.sub.4 is selected to be of a specific strength. But it is possible that a strong spring may be used for the spring 20b.sub.4 and in place of this spring, a leaf spring 20b.sub.7 may satisfy the above conditions. In this case, when the cassette 1 is installed, the whole reel shaft unit moves down so as to form a gap between a stopper 20b and the pressing member 20b.sub.5.

In either case, the reel 3b of the cassette 1 is supported by an elastic member comprising the spring 20b.sub.4 or the leaf spring 20b.sub.7 from below through the taper portion 30', so that the vertical vibrations do not cause the reel 3b to strike the lower inner walls of the cassette case 1, and the vertical motion of the reel 3b is reduced by half so as to decrease the sympathetic vibration of the tape 2. Since the reel 3b is engaged with the taper portion 30' in such a manner as to be retained coaxially with the reel shaft 20b, even if the sympathetic vibrations occur in the tape 2, the reel 3b will not move, resulting in that there is almost no collision and repulsion between the protrusions 3b' of the reel 3b and 20 of the cylindrical hub 20b.sub.3.

Jitter as shown in FIG. 8 will thus not occur, and the speed of the tape 2 travelling on the surface of the magnetic head 24 is kept constant, resulting in an improvement in the WRMS.

FIGS. 14 and 15 show the state of such improvement by way of WRMS characteristic graphs of measurements on the embodiment shown in FIGS. 9 to 13. Conventionally at about 40 Hz, there is 1 percent of WRMS before hearing correction and more than 0.2 percent of WRMS after hearing correction, but this invention eliminates such WRMS, so that the whole characteristic is far below 1 or 0.2 percent, respectively.

FIG. 16 shows a modified form of the cylindrical hub 20b.sub.3 of the reel shaft 20b described in FIGS. 9 to 13, where the taper portion 30' mounted on the collar 30 of the cylindrical hub 20b.sub.3 takes the form of radially projecting rib, resulting in that the finger 3b' of the reel 3b does not engage the taper portion 30', but the inner peripheral lower edge of the reel 3b does engage with the taper portion 30', whereby the taper angle of the taper portion 30' can be larger. The larger the taper angle of the taper portion 30', the more reliably the reel 3b can be positioned coaxially with the reel shaft 20b.

FIGS. 17 and 18 show a reel shaft 20b applicable to a cassette tape recorder for two-way use capable of two way play. In this case, as the reel shaft is used not only for supplying tape, but also for taking up tape, some structures for this additional function are added to the reel shaft.

In the embodiment of FIG. 17, added is a pulley 37 coupled to the shaft main body 20b.sub.2 through a friction mechanism comprising felt pads 35, 36 brought into pressure contact with each other by the leaf spring 20b.sub.7, a gear 38 rotated by a driving source (not illustrated) adapted to selectively engage a gear 37a mounted on the outer periphery of the pulley 37.

In the embodiment of FIG. 18, a flat motor 39 which is rotated at the time of using the reel shaft 20b for take-up is fixed to a chassis C, and the reel shaft unit is secured to the rotary shaft 39a of the motor 39. In this case, when the reel shaft 20b is used for supply, the motor 39 is not driven. A spring 40 mounted on the lower end of the rotary shaft 39a is adapted to produce friction for applying back tension to the tape 2.

With any of the reel shafts 20b described in FIGS. 9, 17 and 18, the cylindrical hub 20b can be slidable along the axis of the shaft main body 20b.sub.2.

In the embodiments of FIGS. 19 and 20, the cylindrical hub is divided into a protrusion portion 30' and a collar portion 30, the protrusion portion being integral with the shaft main body 20b.sub.2, only the collar 30 portion being slidably fitted on the shaft main body 20b.sub.2 in such a manner that the collar 30 is urged upwardly by a spring 20b.sub.4 interposed between a flange 32 secured to the lower end of the shaft main body 20b.sub.2 and the collar 30. In this case, the rib-shaped taper portion 30' is slidably fitted in a slit formed on the shaft main body 20b.sub.2 so as not to rotate the collar 30 with the shaft main body 20b.sub.2.

As described above, this invention provides a cassette tape recorder including a pair of reel shafts having protrusions engaged with a reel of a cassette in the direction of rotation, at least the reel shaft on the tape supply side having a taper portion engaged with the reel of the cassette in such a manner that the reel is coaxial with the reel shaft, and an elastic member for supporting the reel from below via the tape portion, wherein the elastic member has an elastic force which is substantially in proportion to the weight of the maximum residual quantity of tape on the reel.

Therefore, even if vertical vibrations are applied during operation, the reel is prevented from striking the lower inner wall of the cassette case so as to lessen the vertical motion of the reel in the cassette and prevent the diametral movement of the reel in the cassette, resulting in that the sympathetic vibrations of the tape are not so large. Accordingly, even if the tape vibrates sympathetically, no collision and rebounding occurs between the reel and the protrusions of the reel shaft, so that the speed of the tape passing the magnetic head surface is kept substantially constant. Thus, a cassette tape recorder with small WRMS can be obtained, with consequent improvement in tone quality.