Magnetic tape cassette
BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION 
     The present invention relates to magnetic tape cassettes for use in presently avilable tape cassette recorders. More particularly, this invention provides an improved tape cassette which has excellent operating and recording and playback characteristics. 
     The conventional tape cassette includes two hubs or spools of tape wound on rotatably mounted cores adapted to be driven by drive spindles on tape recorders adapted to receive such a cassette. 
     The cassette housing, usually in the form of two shells or trays which are sealed together to form a generally flat rectangular compartment, has various openings to enable cooperation of the recorder with the tape in the cassette, for example, tape heads for record, playback (reproducing), erase, and the tape drive mechanism. 
     The housing of tape cassettes in general have a window provided in the front housing wall for admitting the recording - reproducing head, and at each side of this window is located a pin, integral with the housing, to restrict the position of the magnetic tape. Behind these two pins are provided a pressure assembly comprising a head pressure pad and a shield plate. The cassette includes roller posts and various other guide members defining the path of the tape from one spool past the various openings in the cassette housing to the other spool. With this arrangement of essential elements associated with that portion of the magnetic tape coming into running contact with the head, the tape in motion is compelled to move through a given path. Thus, the running mode of the tape in the window section relative to the magnetic head is determined by the shapes of the two cassette housing halves and is dependent upon the precision with the housing is fabricated. Because of the variations in &#34;identical&#34; cassette housings, due to production tolerances, the tape moving through the magnetic head section of the cassette is biased to one side of the tape path. There is accordingly some difference in sensitivity between the two tracks, &#34;A&#34; side and &#34;B&#34; side, of the tape. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to overcome the disdavantages of conventional tape cassettes, and particularly to provide a cassette having an improved pressure assembly for the magnetic head to reduce variations in recording and playback performance between tracks of the tape and to improve tape running characteristics. 
     In a cassette according to this invention, the magnetic head pressure assembly is not fixed but is held movable in place, so that, when the tape is running in operation, no force acts on it to displace it toward one side. In other words, the tape in sliding contact with the magnetic head remaims evenly pressed and, consequently, there occurs no difference in sensitivity between different tracks of the tape. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a plan view of the bottom half of a conventional tape cassette, from which the top half has been removed to expose the interior. 
     FIG. 2 is a partially sectional view, taken at plane A -- A&#39; of FIG. 1, of the two cassette halves put together. 
     FIG. 3 is a perspective view of a part of the tape cassette of FIG. 1. 
     FIG. 4 is a chart of output sensitivity of a conventional tape cassette. 
     FIG. 5A is a sectional view showing a first embodiment of the invention. 
     FIG. 5B is a partially exploded perspective view showing the first embodiment of the present invention. 
     FIG. 6 is a chart of output sensitivity of a tape cassette according to the first embodiment of this invention. 
     FIG. 7 is a sectional view showing a second embodiment of the present invention. 
     FIG. 8 is a partially exploded perspective view of the structure of FIG. 7. 
    
    
     DETAILED DESCRIPTION 
     Referring now in detail to the drawing, FIG. 1 shows the bottom half 1 of a conventional cassette, from which the top half 1&#39; has been removed to expose the interior. FIG. 2 indicates the cross-section, taken at plane A -- A&#39; of FIG. 1, of two cassette halves put together. 
     FIG. 3 shows window 2, pressure pad 4, tape positioning pins 3, and shield plate 5 in a perspective view. From these views of FIGS. 1 through 3, it will be seen that a conventional cassette construction is characterized by the positioning pins 3 being integral with the half case 1 and standing at both sides of window 2 formed of the front wall for admitting the magnetic head (not shown), and also by the pressure pad 4 and shield plate 5 being located behind the pins. 
     While this arrangement of essential elements associated with that portion of the record medium or magnetic tape 6 coming into running contact with the magnetic head, the tape in motion from hub 7 to hub 7&#39; is compelled to move through a given path. Thus, the position of running tape 6 in the window section relative to the magnetic head is determined by the shapes of the two cassette housing halves 1, 1&#39;, and is dependent upon the precision with which the housing is fabricated. As noted above, the housing consists of two halves 1, 1&#39;, which are shaped by molding a plastic material, and are joined together to form the housing. More or less variations in dimensions and shape, however small they may be, of identical cassette housings constituting a production lot is inevitable, simply because there are limits on the degree of precision attainable in the molding and joining of the two housing halves. 
     By reason of such variation, the tape moving through the magnetic head section of the cassette must be expected to be always to one side of tape movment. Stated specifically, the tape in that section remains displaced to one side relative to the magnetic head in contact therewith. When a cassette with such a tape is set in a recording or playback machine, there is bound to occur some difference in terms of intensity of the magnetic record on the tape or of playback output sensitivity between the two tracks, namely the &#34;A&#34; and &#34;B&#34; sides of the tape as demonstrated in FIG. 4. In FIG. 4, the difference of output sensitivity between the &#34;A&#34; and &#34;B&#34; sides of the tape resulted in about 8 dB at the measuring frequency of 10 KHz. This is a drawback of conventional tape cassettes, to the overcoming of which the present invention is directed. 
     The first preferred embodiment of this invention is shown in FIGS. 5A and 5B, wherein numbered parts 3, 4 and 5 correspond respectively to those similarly numbered in FIGS. 1 through 3. Pressure assembly P, in which the magnetic tape 6 comes into sliding contact with the magnetic head (not shown), comprises pins 3, pad 4 and shield plate 5 mounted together as a unit. Tape transport section 8, formed of the half case 1 has recess 9, and it is in this recess or pocket that the assembly P is movably held. Since pressure assembly P is movable in place, a running tape in that assembly complies with and conforms to the tilt of the magnetic head. 
     Pressure assembly P is sandwiched in place by two split halves, i.e., an upper half case 1&#39; and a bottom case 1, of tape transport section 8, so that it is incapable of leaving recess 9, although it is movable in place. The compliance and conformance of pressure assembly P to a tilted magnetic head results in improved sliding contact between tape and head. Consequently, the aforementioned variations in housing shape and dimension diminish so much as to make the &#34;A&#34; side and &#34;B&#34; side present almost the same output sensitivity to the playback machine, as demonstrated by FIG. 6. 
     FIG. 7 shows a second embodiment of this invention. FIG. 8 indicates the major elements shown in FIG. 7 in an exploded view. In these figures it will be noted that assembly P&#39; includes a round rod or protrusion 10 protruding sideways. This rod is shaped and located so as to be properly supported by supports 11 provided in tape transport section 8, and the pressure assembly P&#39; is capable of freely pivoting in the direction of the arrow 12. This structural arrangement enables pressure assembly P&#39; to comply with and conform to the tilt of the magnetic head, thereby improving the sliding contact between running tape and magnetic head, thus eliminating the aforementioned difference in output sensitivity between the &#34;A&#34; and &#34;B&#34; sides of the tape. 
     It will be noted from the foregoing description that, according to this invention, that portion of the cassette bringing the tape into sliding contact with the magnetic head is made freely movable or tiltable in place. By this feature, representing a distinct departure from a conventional tape cassette, this invention eliminates the uneven sliding contact, inevitable hitherto in conventional tape cassettes, between the running tape and the magnetic head due to the tilt of the head. 
     The present invention has been described in detail with particular reference to the preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention, which is to be taken to be defined by the following claims.