Magnetic tape cassette with improved guide roller means

A magnetic tape cassette is provided with an improved guide roller means. The magnetic tape cassette is of a type having an upper and lower half case with two hubs around which a magnetic tape is wound. Two guide rollers are rotatably mounted on a supporting shaft and are improved by providing each guide roller with a supporting annular seat which is protruded from one or both of the cassette half cases in such a manner as to surround the base end portion of the supporting shaft. Further, ribs with a height equal to or slightly smaller than the height of the annular seat, are disposed between the annular seat and the supporting shaft so as to connect the seat and the shaft.

BACKGROUND OF THE INVENTION 
This invention relates to magnetic tape cassettes, and more particularly to 
an improvement of a so-called "Phillips" type magnetic tape cassette in 
which a magnetic tape is wound on a pair of hubs. 
In general, in a magnetic tape cassette used for audio devices or the like, 
a pair of hubs on which a magnetic tape is wound are arranged in a 
cassette case made up of the upper and lower half cases. The magnetic tape 
is laid against right and left guide rollers arranged in the front part of 
the cassette so that the magnetic tape may be run through the front 
opening of the cassette. 
Each of the guide rollers is rotatably provided in the cassette, and the 
magnetic tape is partially wound around each guide roller. Thus, when the 
guide rollers are rotated, one guide roller smoothly changes the direction 
of movement of the magnetic tape toward the recording and reproducing 
region in the front part of the cassette and the other guide roller 
smoothly changes the direction of movement of the magnetic tape toward the 
hub incorporating region. Accordingly, during a recording or reproducing 
operation, the tape running characteristic is greatly affected by the 
performance of rotation of the guide rollers. Especially in a magnetic 
tape cassette in which the guide rollers are rotatably mounted on guide 
roller supporting shafts which are extended from the lower half case, the 
performance of the guide rollers suffers from the following difficulty. 
In general, in order to prevent the negative effects due to shrinkage which 
occurs in molding the half cases, an annular seat is formed in such a 
manner as to surround the base part of the supporting shaft. However, the 
lubrication between the upper end face of the seat and the roller end face 
is insufficient; therefore, the guide roller cannot turn smoothly, thus 
producing squeaks sometimes. If the guide roller is rotated for a long 
period under the condition which produces squeaks as described above, the 
aforementioned two end faces become worn. As a result, the guide roller is 
able to move up and down, which considerably decreases the smoothness of 
the tape running characteristic. 
In the case where the above-described guide rollers are employed for a 
magnetic tape cassette, such as that operated in a digital system, which 
is higher in recording or reproducing density than a conventional audio 
magnetic tape cassette, the above-described difficulty is especially 
serious because the number of recording or reproducing tracks is large. 
SUMMARY OF THE INVENTION 
In view of the foregoing, an object of this invention is to provide a 
magnetic tape cassette which is so improved that the guide rollers thereof 
can smoothly rotate for a long period. 
The foregoing object of the invention has been achieved by the provision of 
an improved guide roller means in a magnetic tape cassette having guide 
rollers which are brought into contact with a magnetic tape to guide the 
magnetic tape while the tape rotates. According to the invention, each of 
the guide rollers is rotatably mounted on a supporting shaft which is 
extended from one of the cassette half cases. One end face of each roller 
is supported by an annular seat which is protruded from the one cassette 
half case in such a manner as to surround the base end portion of the 
supporting shaft. In addition, at least one rib the height of which is 
equal to or slightly smaller than the height of the annular seat is 
provided between the annular seat and the supporting shaft in such a 
manner as to bridge the seat and the shaft.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Similar to a conventional magnetic tape cassette, a magnetic tape cassette 
1 shown in FIG. 1 is made up of upper and lower half cases 10 and 11, 
respectively. Furthermore, similar to a conventional magnetic tape 
cassette, recording and reproducing region A of the magnetic tape cassette 
1 is closer to the front of the cassette 1 than are two guide rollers 2, 
and a hub incorporating region of the cassette 1 is closer to the rear of 
the cassette 1 than the guide rollers 2. The two guide rollers 2 are 
arranged on the right and left sides of the cassette case. 
Each guide roller 2 is rotatably mounted on a supporting shaft 8 with 
roller end faces 6 of a boss 5 of the roller being supported by seats 9 
which protrud from the upper and lower half cases 10 and 11, respectively, 
in such a manner as to surround the supporting shaft 8. Flanges 4 are 
formed at the upper and lower ends of the guide roller 2. The flanges 4 
are larger in diameter than drum part 3 of the guide roller on which 
magnetic tape T is laid. The flanges 4 are used to limit the vertical 
movement of the magnetic tape T when the tape T is being run. 
Four ribs 7 are provided between the supporting shaft 8 and each seat 9 in 
such a manner as to bridge the shaft 8 and seat 9. The inside ends of the 
ribs 7 are flush with the inside ends of the seats 9. As is apparent from 
FIG. 2, adjacent ribs 7 form an angle of 90.degree.. 
The seat 9 of the upper half case 10 into which the upper end portion of 
the supporting shaft 8 is inserted has the ribs 7 similarly disposed as in 
the case of the seat 9 of the lower half case 11. However, the ribs 7 may 
be eliminated from the seat 9 of the upper half case 10. For instance, the 
seat 9 of the upper half case 10 may be designed similar to a seat in a 
conventional magnetic tape cassette where the seat's width (that is, the 
distance between the inside and outside radii of the seat) is 
substantially equal to the thickness of the roller end face 6. 
Similar to a conventional magnetic tape cassette, the upper and lower half 
cases 10 and 11, respectively, are made of ABS resin, PS resin, or the 
like. The guide rollers 2 are also made of a conventional plastic material 
such as polyacetal resin. 
When the guide rollers 2 are set in the cassette case, in general, 
liquid-state lubricant such as silicone grease is applied to the 
supporting shafts 8 so that the guide rollers 2 can rotate smoothly. 
Accordingly, as the rollers 2 rotate, or with the lapse of time, the 
lubricant between the supporting shaft 8 and the boss 5 of the guide 
roller 2 flows down onto the upper end faces of the ribs 7 and the seat 9 
of the half case set on the lower side. When the cassette is turned over, 
the lubricant spreads over the other seat 9. 
As was described above, the ribs 7 serve to spread the lubricant applied to 
the supporting shaft 8 over the seat 9. That is, the ribs 7 cause the 
lubricant to spread over all the sliding surfaces of the guide rollers 2 
and of the cassette case. 
In the above-described embodiment, the upper end faces of the ribs 7 are 
flush with the upper end face of the seat 9; however, the invention is not 
limited thereby or thereto. That is, the height of the ribs 7 may be 
slightly smaller than that of the seat 9. 
In the above-described embodiment, four ribs 7 are formed on each half 
case; however, the invention is not limited thereby or thereto. That is, 
only a minimum of one rib need be provided between the seat 9 and the 
supporting shaft 8. 
As was described above, according to the invention, the lubricant applied 
to the supporting shaft 8 is spread to the seat 9 with the aid of the ribs 
7. Thus, lubricant is spread over all the sliding surfaces of the guide 
rollers 2 and of the cassette case. Therefore, the roller end faces 6 and 
the seats 9 are less worn, and the sliding condition thereof is improved. 
Thus, according to the invention, it is possible to provide a magnetic 
tape cassette in which, unlike the conventional one, no squeaks are 
produced when the mating end faces of the guide rollers 2 and seats 9 
slide on each other, and the rotational characteristic of the guide 
rollers 2 is improved.