Tape cassette with tape tension controlled by grease of a specified range of viscosity

A tape cassette comprises a supply and a take-up reel on which tape is wound, a cassette casing for rotatably enclosing the reels therein, a plurality of tape guide pins, each being press-fitted through the inner wall of the casing, for defining a tape path for the tape travelling between the pair of reels. The press-fit section of each guide pin is formed in a predetermined taper in such a manner as to gradually decrease its outer diameter towards its end. The straight press-fit section of the guide pin is formed in such a manner as to include a predetermined geometry of chamfered circumference at its end. In a tape guide pin used in conjunction with a tape guide roller, grease having a predetermined viscosity coefficient is disposed between the associated pin and roller. An electrical insulating cover is provided for surrounding the exposed underside of the electrically conductive lower half of the casing.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a tape cassette which is optimally adapted 
for use in recording and/or reproducing apparatus. Specifically to a tape 
cassette wherein tape guide pins are press-fitted onto a cassette casing. 
2. Description of the Prior Disclosure 
Recently, there have been proposed and developed various magnetic tape 
cassettes to serve as an external data storage medium. 
One such magnetic tape cassette has been disclosed in U.S. Pat. No. 
4,198,013. This conventional tape cassette includes a pair of reels, 
namely a supply reel and a take-up reel, rotatably supported in the 
cassette casing. As is generally known, magnetic tape is wound on the pair 
of reels through a plurality of tape guide pins by which the travelling 
path of the tape is controlled in such a manner that the tape is wound on 
the reels at a predetermined contact angle. That is, the tape travelling 
path is defined by the upstanding guide pins, each arranged at a 
predetermined location on the cassette casing. As shown in FIG. 1, a 
conventional guide pin 90 is integrally formed with a tape contact section 
90a, upper and lower flange sections 90b, and a press-fit section 90c 
extending from the bottom surface of the lower flange section. Each 
section 90a, 90b, or 90c has a specific, constant outer diameter. As seen 
in FIG. 1, the guide pin 90 is fixed on the cassette casing such that the 
press-fit section 90c is press-fitted onto the aluminum alloy lower half 
of the casing. Such guide pins are traditionally formed by lathe 
machining. The machining accuracy may be affected by various machining 
conditions, such as deflection of the workpiece, fluctuation in bite by a 
cutting tool, and fluctuation in lubrication by a cutting lubricant. For 
example, as shown in FIG. 2, the press-fit section 90c is often formed in 
a reverse taper fashion in which the outer diameter is gradually increased 
from its root connected to the bottom surface of the lower flange section 
90b to its end. Therefore, the outer diameter a at the root is slightly 
smaller than that b at the end. If such a reverse tapered press-fit 
section of the guide pin is press-fitted into the lower half of the 
casing, the greatest outer diameter of end of the press-fit section 90c 
expands a preformed hole and forms a hole 33 slightly greater than a 
required outer diameter of hole, over the whole length of press-fit 
section 90c. As a result, after pressing, pressure occurring between the 
outer periphery of the press-fit section 90c and the inner periphery of 
the hole formed in the lower half of the cassette casing is decreased. 
Under these conditions, since the guide pin 90 is not press-fitted tightly 
enough into the lower half, the guide pin 90 may be easily removed from 
the lower half. Therefore, there is a possibility that the guide pins may 
dislodge due to external forces, such as vibration. 
During press-fitting of a guide pin, a maximum impact with regard to the 
lower half occurs at the beginning of pressing. Specifically, since the 
end of the reverse tapered press-fit section 90c has a maximum outer 
diameter, the initial impact during pressing becomes excessively high, 
thereby resulting in deformation or damage to the lower half. Therefore, 
the flatness of the lower half may be compromised and as a result tape 
travel may become unstable. The above mentioned defect of a 
reverse-tapered press-fit section for a guide pin may also occur to some 
degree in a non-tapered, or straight press-fit section for a guide pin. If 
a reverse-tapered or straight press-fit section is press-fitted onto the 
lower half of a cassette without any preformed hole, the flatness of the 
lower half may be comprimised to a greater degree, due to the excessively 
high, initial impact necessary during pressing and in addition such guide 
pins may also be dislodged relatively easily by external forces. 
Traditionally, such a guide pin is used in the lower half of a casing in 
such a manner as to directly guide magnetic tape on its cylindrical outer 
peripheral surface or to guide magnetic tape via a guide roller rotatably 
assembled therearound. In general, since the surfaces of such conventional 
guide pins are finished within a range of a maximum surface-roughness Rmax 
0.5 to 0.8 .mu.m, there is a possibility that dust may be generated at the 
point of contact between the guide pins and the coated tape surface, 
resulting in so-called dropout error if the tape cassette is used for a 
relatively long time. In a guide pin employing the guide roller, since 
magnetic tape is guided by the outer peripheral surface of the guide 
roller, generation of the previously described dust is reduced. Such guide 
rollers may provide extremely smooth tape feed, however this makes tape 
tension control quite difficult. 
Furthermore, in tape cassettes including such press-fitted guide pins, the 
lower half, receiving the guide pins, is made of electrically conductive 
material, such as aluminum alloy, as previously described. Therefore, were 
an user, charged with static electricity to touch the lower half of the 
casing of the tape cassette while loading the recording and/or reproducing 
apparatus for operation, static electricity may be discharged through the 
lower half of the cassette, through the cassette holder of the apparatus 
into the electrical control unit including logical circuits, resulting in 
error of logical circuits because of their low degree of tolerance to 
static electricity. 
SUMMARY OF THE INVENTION 
It is, therefore in view of the above disadvantages, an object of the 
present invention to provide a tape cassette in which a tape guide pin is 
firmly press-fitted into a cassette casing. 
It is another object of the invention to provide a tape cassette which is 
capable of maintaining a high degree of flatness in the casing even after 
guide pins have been press-fitted to the casing. 
It is a further object of the invention to provide a tape cassette which 
can provide optimal tape tension during tape travel. 
It is another object of the invention to provide a tape cassette which is 
capable of preventing static electricity from a user from being introduced 
through the cassette casing to electric or electronic elements in the 
associated recording and/or reproducing apparatus. 
It is a still further object of the invention to provide a tape cassette 
which has high durability and high reliability to maintain high quality as 
a recording medium. 
In order to accomplish the aforementioned and other objects, a tape 
cassette comprises a pair of reels mounted side by side, on which tape is 
wound, a cassette casing for rotatably enclosing the pair of reels 
therein, at least one tape guide pin being press-fitted through the wall 
of the casing, for defining a tape path for tape travel between the pair 
of reels. The guide pin include a press-fit section press-fitted into the 
casing. The press-fit section is formed in a taper fashion in such a 
manner as to gradually decrease its outer diameter towards the end of the 
press-fit section. Preferably, the press-fit section may be 
frusto-conical, and its taper may be within a range of 1/250 to 1/38 to 
insure optimum press-fit with the casing. 
According to another aspect of the invention, a tape cassette comprises a 
pair of reels mounted side by side, on which tape is wound, a cassette 
casing for rotatably enclosing the pair of reels therein, an upstanding 
pin being press-fitted through the wall of the casing. The pin includes a 
cylindrical press-fit section to be press-fitted into the casing without 
need of a preformed hole. The press-fit section includes a cylindrical 
outer peripheral surface coaxial to the axis of the pin, a chamfered 
annular circumference at the lower tip of the cylindrical surface, 
terminating in a flat circular end perpendicular to the axis and having an 
outer diameter less than that of the cylindrical surface. The chamfered 
annular circumference is formed with a curved surface, the curve, in 
cross-section, corresponding to the perimeter of a circle with a radius in 
a range of 0.2 to 0.3 mm, or with a 45.degree. sloped, frusto-conical 
surface essentially corresponding to the dimension of the curved surface. 
The tape guide pin or upstanding pin may be formed of non-magnetic 
stainless steel material by lathe machining. When the tapered or chamfered 
pin is used in a manner so as to contact with a tape surface having 
magnetic substance, its contacting surface has a maximum surface roughness 
of Rmax 0.1 to 0.4 .mu.m to provide smooth tape travel. The contacting 
surface is finished by super-finishing after centerless grinding so as to 
accomplish a maximum surface-roughness of Rmax 0.1 to 0.4 .mu.m. 
The casing is comprised of an upper half formed of electrical insulating 
material and a lower half formed of electrically conductive metal material 
suitable for the press-fitting of the tape guide pin or the upstanding 
pin. When a portion of the conductive lower half is exposed outside of a 
recording and/or reproducing apparatus in a state wherein the tape 
cassette is set to a predetermined loaded position, the casing may 
preferably include an insulating member for electrically insulating the 
conductive half, for preventing static electricity from being introduced 
through an exposed portion of the conductive half into the apparatus. The 
insulating member comprises the outer wall of the casing surrounding the 
outer perimeter of the conductive half. The insulating member overlaps the 
exposed underside of the conductive half by substantially 20 mm. 
According to a further aspect of the invention, a tape cassette comprises a 
pair of reels mounted side by side, on which tape is wound, a cassette 
casing for rotatably enclosing the pair of reels therein, a driven roller 
being rotated by a drive device of a recording and/or reproducing 
apparatus, associated with the tape cassette, the driven roller rotatably 
supported by an upstanding roller shaft fixed on the wall of the casing, a 
pair of idle rollers, each rotatably supported by an upstanding roller 
shaft fixed on the wall of the casing, an endless flexible drive belt for 
drivingly engaging the driven roller and the idle rollers to rotate the 
reels, such that a portion of the drive belt between the driven roller and 
each idle roller pressingly contacts a portion of the outermost peripheral 
surface of the tape wound on each reel, the drive belt being driven 
according to rotation of the driven roller, and means for controlling tape 
tension of the tape during operation of the tape cassette, the means 
including grease disposed between the associated rollers and shafts for 
lubricating the contacting surfaces therebetween, with a predetermined 
viscous drag. The grease includes a viscosity coefficient of 50 to 500 P 
(poise) within a grease temperature range of -10.degree. to 60.degree. C. 
Each of the roller shafts may be press-fitted through the wall of the 
casing. The roller shaft includes a press-fit section formed in taper 
fashion such as to gradually decrease its outer diameter towards its end. 
Preferably, the press-fit section is frusto-conical, and its taper is 
within a range of 1/250 to 1/38. The roller shaft may also include a 
cylindrical press-fit section press-fitted into the casing without a 
preformed hole. The press-fit section includes a cylindrical outer 
peripheral surface coaxial to the axis of the pin, a chamfered annular 
circumference at the lower tip of the cylindrical surface, terminating in 
a flat circular end perpendicular to the axis and having an outer diameter 
less than that of the cylindrical surface. The chamfered annular 
circumference is formed with a curved surface, the curve, in 
cross-section, corresponding to the perimeter of a circle with a radius in 
a range of 0.2 to 0.3 mm, or with a 45.degree. sloped, frusto-conical 
surface essentially corresponding to the dimension of the curved surface. 
According to a still further aspect of the invention, a tape cassette 
comprises a pair of reels mounted side by side, on which tape is wound, a 
cassette casing for rotatably enclosing the pair of reels therein, the 
casing partially including an electrically conductive section constructed 
such that a portion of the conductive section is exposed outside of a 
recording and/or reproducing apparatus in a state wherein the tape 
cassette is set to a predetermined loaded position, an insulating member 
for electrically insulating the conductive section, for preventing static 
electricity from being introduced through an exposed portion of the 
conductive section into the apparatus. The insulating member comprises the 
outer wall of the casing surrounding the outer perimeter of the conductive 
section. The casing is comprised of a pair of halves. The insulating 
member overlaps the exposed underside of the conductive section by 
substantially 20 mm.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The principles of the present invention, applied to a tape cassette for 
recording and/or reproducing apparatus, are illustrated in FIGS. 3A to 13. 
Referring now to FIGS. 5 and 6, a tape cassette according to the invention 
includes an upper half 2 formed of electrical insulating synthetic resin 
and a flat, lower half 3 formed of aluminum alloy together forming a 
cassette casing 1. The upper half 2 is comprised of a substantially flat, 
upper wall and a side wall 4 extending downward from the outer perimeter 
of the upper wall. The casing 1 defines an internal space for rotatably 
supporting a pair of reels, one being a supply reel 5 and the other a 
take-up reel 6, in such a manner that the edge of side wall 4 abuts the 
outer perimeter of the lower half 3. Magnetic tape 7 is wound on the pair 
of reels 5 and 6 through a plurality of upstanding tape guide pins which 
are firmly disposed on the lower half 3. The path of tape travel is 
defined by the guide pins, each arranged at a predetermined location on 
the lower half 3 of the casing 1. As best seen in FIG. 6, two flanged 
guide pins 9 and 10, are located near the front face of the casing 1, and 
straight guide pins 11, 12, and 13, are respectively located between the 
supply reel 5 and the guide pin 9, between the two guide pins 9 and 10, 
and between the guide pin 10 and the take-up reel 6. Tape from the supply 
reel 5 is drawn over the guide pin 9 at a predetermined contact angle, 
thus changing the direction of tape travel. Thereafter, the tape travels 
parallel to and in the vicinity of the front face of the casing 1. 
Subsequently, the tape is drawn over the guide pin 10 at a predetermined 
contact angle and again the tape travelling direction is changed to 
facilitate the tape being wound finally on the take-up reel 6. 
As clearly seen in FIGS. 3A and 3B, the flanged guide pins 9, 10 are 
integrally formed with tape contact sections 9a, 10a, upper and lower 
flange sections 9b, 10b, and frusto-conical press-fit sections 9c, 10c, 
respectively. These guide pins 9 and 10 are formed of non-magnetic 
stainless steel material by lathe machining. As previously described, the 
tape contact sections 9a, 10a permit tape to be wound there on at the 
predetermined contact angle. The upper and lower flange sections 9b, 10b, 
restrict lateral movement of the tape 7. The press-fit sections 9c, 10c 
are formed in a taper fashion wherein the outer diameter is gradually 
decreased from the root, connected to the bottom surface of the lower 
flange section 9b, to the end. Assuming that dimensions A, B, and are 
taken as shown in FIG. 3A, it is desirable that the taper (A-B) of the 
press-fit section 9c, 10c be selected within a range between 1/250 to 
1/38. If the taper dimensions exceed the above mentioned desirable taper, 
it is difficult to insure that high flatness of the lower half 3 is 
reliably maintained due to the high stress that would be generated in 
pressing the guide pins to the lower half 3. Conversely, if the taper 
dimensions are less than the desirable taper, there is a possibility that 
the press-fit section of the guide pin will become straight, or a reverse 
taper may be formed which would be unsuited to press-fitting, due to 
fluctuations in lathe machining accuracy. 
As clearly seen in FIGS. 4A and 4B, the straight guide pins 11, 12, and 13 
are integrally formed with tape contact sections 11a, 12a, and 13a, and 
frusto-conical press-fit sections 11b, 11b, and 13b, respectively. The 
guide pins 11, 12, and 13 are formed of non-magnetic stainless steel 
material by lathe machining. The press-fit sections 11b, 12b, and 13b are 
formed within the same taper range as the press-fit sections 9c, 10c. As 
seen in FIG. 6, out of the three straight guide pins 11, 12, and 13, only 
guide pins 11 and 13 come into contact with the oxide (recording) surface 
of the tape, while the guide pin 12 comes into contact only with the 
uncoated surface of the tape. In this embodiment, the maximum 
surface-roughness Rmax 0.1 to 0.4 .mu.m of the pins 11 and 13 is less than 
the maximum surface-roughness Rmax 0.5 to 0.8 .mu.m of conventional guide 
pins, thereby reducing dust generated at the point of contact between the 
guide pins and the coated tape surface. In this manner, so-called dropout 
error, due to abrasion of the magnetic oxide at a certain point on the 
tape, is prevented. The magnetic tape cassette according to the embodiment 
has high durability and high reliability as a high quality recording 
medium. Desirably, the outer peripheral surfaces of the guide pins 11 and 
13 are finished by super-finishing after centerless grinding, so as to 
accomplish a maximum surface-roughness of Rmax 0.1 to 0.4 .mu.m with 
regard thereto. If the surface-roughness Rmax is less than 0.1 .mu.m, 
there is a tendency for the tape surface and the outer peripheral surfaces 
of the guide pins 11 and 13 to adhere to each other. Therefore, as set 
forth, it is desirable that the surface-roughness Rmax of the outer 
peripheral surface of the two pins 11 and 13 be selected within a range of 
0.1 to 0.4 .mu.m. In constructions according to the embodiment, the 
flanged guide pins 9 and 10 are aligned with holes 32 formed is the lower 
half 3 as shown in FIG. 3A and thus the guide pins 9 and 10 are 
press-fitted onto the lower half 3 as shown in FIG. 3B. While as shown in 
FIG. 4A, the straight guide pins 11 to 13 are directly pressed into the 
lower half 3 without preformed holes and thus the guide pins 11 to 13 are 
press-fitted onto the lower half 3 as shown in FIG. 4B. As shown in FIG. 
4A, note that the circular end surface of each press-fit section of the 
straight guide pins 11, 12, and 13 is flat and perpendicular to the axis 
of the guide pin so as to provide an optimal pressing. In the above 
mentioned pressing method, the necessity of having preformed holes with 
regard to the lower half is determined depending on the outer diameter of 
the press-fit section of the guide pin in conjunction with the mechanical 
strength of the lower half of the casing. 
In the pressing process, since the press-fit sections 9a to 13a are formed 
in a taper fashion, pressing is accomplished in such a manner that the 
hole is gradually expanded over the entire surface of the press-fit 
section according to the press-fitting stroke, so that after the pressing 
is completed, pressure occurring between the press-fit section and the 
lower half exceeds a required pressure over the whole surface of the 
press-fit section. When these conditions are met, the guide pins 9 to 13 
are firmly connected to the lower half 3, such that these guide pins 
cannot be easily removed. In such tapered guide pins, since the end of the 
press-fit section has the smallest diameter, the initial impact occurring 
at the beginning of the pressing stroke is suppressed to a minimum value, 
thereby providing smooth pressing. This prevents the lower half 3 from 
deforming due to excessive initial impact during pressing. As a result, 
high flatness of the lower half 3 may be maintained. 
As shown in FIGS. 7A to 7D, the previously described straight guide pins 11 
to 13, each including a tapered press-fit section and directly 
press-fitted into the lower half without preformed holes, may be replaced 
with a guide pin 28 including a chamfered press-fit section 29 which has a 
chamfered annular circumference 29c at the end. The guide pin 28 will be 
referred to as a "chamfered guide pin". The pressing process is started 
from the starting state of FIG. 7A, and continues via the intermediate 
pressing states of FIGS. 7B and 7C, to the pressing completed state of 
FIG. 7D, in that order. In FIGS. 7A to 7D, the press-fit section 29 
corresponds to the section lower than the phantom line. As clearly seen in 
FIG. 7A, the chamfered press-fit section 29 includes a cylindrical outer 
peripheral surface 29b of an outer diameter D.sub.2 and a circular, flat 
end surface 29a of an outer diameter D.sub.1 less than the diameter 
D.sub.2. The press-fit section 29 also includes the chamfered annular 
circumference 29c joining the flat end surface 29a and the outer 
peripheral surface 29b. Preferably, the chamfered circumference 29c may be 
formed with a surface curved (in cross-section) within the range of a 
radius R of 0.2 to 0.3 mm or with a 45.degree. sloped, frusto-conical 
surface essentially equivalent to the above mentioned curved surface. 
The pressing process of FIGS. 7A to 7D is achieved according to the 
following steps. 
First, as shown in FIG. 7A, the press-fit section 29 is pressed downwardly 
to the upper press-fit surface of the lower half 3 in a state therein the 
flat end surface 29a and the press-fitted surface are parallel with each 
other and the axis of the guide pin is arranged perpendicularly to the 
upper surface of the lower half 3. 
As shown in FIG. 7B, the end surface 29a reaches and pressingly abuts the 
upper surface of the lower half 3. Thereafter, shearing fracture indicated 
by reference numeral s of FIG. 7B occurs at an essentialy cylindrical 
portion of the lower half 3 along the outermost circumference (diameter 
D.sub.1), of the end surface 29a. According to subsequent pressing, the 
shearing fracture grows gradually towards the lower surface of the lower 
half 3. As seen in FIG. 7C, a hole 34 formed by the shearing fracture 
includes a substantially cylindrical sheared surface and a substantially 
frusto-conical broken-out surface extending or growing gradually from the 
sheared surface to the lower surface of the lower half 3. Assuming that 
the length of the press-fit section 29 is set to a length of 2T/3 with 
regard to a thickness T of the lower half 3, the sheared surface and the 
broken-out surface respectively correspond to a length 2T/3 and a length 
T/3, as shown in FIG. 7C. In other words, the shearing fructure reaches 
the 2T/3 length of the lower half 3 and thereafter the lower section of 
the lower half corresponding to the T/3 length is broken out. In this 
manner, while a portion of the lower half is punched out as a punched 
portion 35, the press-fit section 29 is gradually press-fitted into the 
hole 34 in such a manner as to expand the inner diameter of the hole 34 by 
means of the chamfered lower circumference 29c. Thus, the pressing is 
completed as seen in FIG. 7D. If the guide pin 28 is forcibly removed from 
the lower half 3 after completion of the pressing as shown in FIG. 7D, the 
inner diameter of the hole 34 may become substantially equal to the outer 
diameter D.sub.1 of the outermost circumference of the end surface 29a as 
shown in FIG. 8. That is, after completion of pressing, the hole 34 is 
expanded by the difference between the inner diameter of the hole 34 
(substantially equal to the diameter D.sub.1) and the outer diameter 
D.sub.2 of the cylindrical outer periphery of the press-fit section 29. In 
other words, according to the above pressing method, pressure generated 
due to elastic deformation of the inner periphery of the hole 34 
corresponding to the above mentioned difference is applied to the outer 
peripheral surface 29b of the press-fit section 29. 
In conventional straight guide pins, the curved surface of the chamfered 
circumference of the press-fit section is formed at a relatively small 
radius, such as 0.1 mm, according to research by the inventors of this 
invention. When comparing the radii R of 0.1 mm and 0.2 to 0.3 mm, the 
force F required to remove the guide pin 28 from a lower half 3 having a 
thickness T of 2 mm is indicated, according to the outer diameter D.sub.2 
of the press-fit section 29 of the guide pin 28, in the Table 1. This data 
was experimentally confirmed by the inventors. 
TABLE 1 
______________________________________ 
Thickness T 
Diameter D.sub.2 
Radius R Force F 
(mm) (mm) (mm) (kg) 
______________________________________ 
2 2.3 0.2-0.3 80 
0.1 70 
2 3.4 0.2-0.3 90 
0.1 70 
2 3.9 0.2-0.3 130 
0.1 90 
______________________________________ 
As will be appreciated from Table 1, a chamfered guide pin 28 having a 
curved surface along a radius R of 0.2 to 0.3 mm according to the 
invention is inferior to conventional guide pins having a curved surface 
along a radius R of 0.1 mm, with regard to the removing force F. If the 
radius R exceeds 0.3 mm, the hole 34 is excessively, elastically deformed 
and, as a result, high flatness of the lower half 3 may not be maintained. 
Although the previously described pins, including tapered or chamfered 
press-fit sections, serve as tape guide pins or tape guide roller shafts, 
these pins may also serve as a pivot shaft, a supporting shaft or the 
like. 
The tape cassette casing 1 also includes a tape exposure section 20 through 
which some of the tape 7 is exposed to the outside of the casing 1. The 
tape exposure section 20 is provided within the straight tape travel path 
between the flanged guide pins 9 and 10, such that the coated tape surface 
and a recording and/or reproducing head may come into contact with each 
other during recording and/or reproducing. The cut-out portion 21 of the 
tape exposure section 20 is hermetically covered by a pivotable cover 23 
to prevent dust from entering the casing 1. The cover 23 is pivotably 
supported by an upstanding pin 30 provided on the lower half 3. The cover 
23 is normally biased in a closed position by means of a coil spring 31. 
During recording and/or reproducing, the cover 23 is opened by a releasing 
device (not shown) provided in the recording and/or reproducing apparatus 
(not shown). 
A tape travelling mechanism 14 includes a driven roller 15, disposed 
substantially midway between the two flanged guide pins 9 and 10, and two 
idle rollers 16 and 17, disposed in the vicinity of both corners of the 
rear surface of the casing 1. These rollers 15, 16, and 17 are rotatably 
supported by means of upstanding roller shafts 18 provided on the lower 
half 3. The driven roller 15 is comprised of a drive belt contact section, 
on which a flexible drive belt 25 is wound, and a drive roller abutting 
section 15a, which has an outer diameter greater than the drive belt 
contact section and is driven by a drive roller (not shown) of a tape 
drive device (not shown) provided in the recording and/or reproducing 
apparatus, during recording and/or reproducing. For this reason, a portion 
of the drive roller abutting section 15a is exposed through an opening 19 
formed substantially in the center of the front face of the casing 1. As 
best seen in FIG. 6, the flexible drive belt 25 is endless and is wound in 
a manner so as to engage the above mentioned rollers 15, 16, and 17. Since 
the endless belt 25 is flexible, a portion of the drive belt between the 
driven roller 15 and the idle roller 17 pressingly contacts a portion of 
the outermost peripheral surface of magnetic tape 7 wound on the supply 
reel 5, while a portion of the drive belt between the driven roller 15 and 
the idle roller 16, pressingly contacts a portion of the outermost 
peripheral surface of magnetic tape 7 wound on the take-up reel 6 to turn 
the reels 5 and 6 when the belt 25 is driven via the driven roller 15. 
As shown in FIG. 9, contacting surfaces between the respective associated 
rollers 15, 16, and 17 and shafts 18 are greased to prevent abrasion. 
According to the invention, grease 24 includes a viscosity coefficient of 
50 to 500 poise within a range of grease temperature from -10.degree. to 
60.degree. C. In this embodiment, a maximum surface roughness Rmax of the 
inner peripheral surface of the roller is designed to a value less than 
0.1 .mu.m and a maximum surface roughness Rmax of the outer peripheral 
surface of the shaft 18 is designed within a range of 0.2 to 0.6 .mu.m. In 
FIG. 8, reference numeral 22 denotes a snap ring provided to restrict 
movement of the roller 16 in the axial direction of the shaft 18. 
The magnetic tape cassette according to the invention operates as follows. 
When the tape cassette is inserted into a loading holder (not shown) 
provided in the recording and/or reproducing apparatus and tape loading is 
started, the cover 23 is rotated to an open position against the spring 
force generated by the spring 31. Upon sufficient opening of the cover 23, 
the recording and/or reproducing head (not shown) of the recording and/or 
reproducing apparatus is pressed against the magnetic tape exposed through 
the tape exposure section 20 and simultaneously the drive roller (not 
shown) of the tape drive device (not shown) is pressed on the abutting 
section 15a of the driven roller 15. According to rotation of the drive 
roller of the tape drive device, the driven roller 15 is rotated and as a 
result the idle rollers 16 and 17 are driven by means of the drive belt 
25. As shown in FIG. 6, assuming the drive belt 25 is driven in one 
direction indicated by the three arrows g, the magnetic tape 7 will be 
driven in the opposite direction indicated by two arrows h by frictional 
force created at the contacting portions between the magnetic tape 7 and 
the endless drive belt 25. In this manner, tape recording and or 
reproducing may be executed. 
When the drive belt 25 is driven according to rotation of the drive roller 
of the tape drive device, each idle roller (16,17) is rotated against the 
viscous drag of grease 24 disposed between the inner peripheral surface of 
the roller and the outer peripheral surface of the shaft. As best seen in 
FIG. 6, assuming the drive belt 25 is driven in the direction indicated by 
the arrows g, the tension of the drive belt between the driven roller 15 
and the idle roller 16 is slightly decreased by viscous drag of grease 
disposed between the idle roller 16 and the shaft 18 and while the tension 
of the drive belt between the driven roller 15 and the idle roller 17 is 
slightly increased by viscous drag of grease disposed between the idle 
roller 17 and the shaft 18. Conversely, when the drive belt 25 is driven 
in the opposite direction, the belt tension between the driven roller 15 
and the idle roller 16 is slightly increased and the belt tension between 
the driven roller 15 and the idle roller 17 is slightly decreased, for the 
same reasons described above. In this manner, the viscous drag of the 
grease results in belt tension adjustment between a belt section tightened 
between the two rollers (15, 16) via the outer periphery of the magnetic 
tape wound on the reel 6, and a belt section tightened between the two 
rollers (15, 17) via the outer periphery of the magnetic tape wound on the 
reel 5. As set forth above, since the magnetic tape 7 is driven by 
frictional force created at the contacting portions between the magnetic 
tape 7 and the drive belt 25, assuming that the drive belt 25 is driven in 
one direction indicated by the arrows g, the slightly increased belt 
tension is applied to the outer periphery of the magnetic tape wound on 
the reel 5 serving as a take-up reel and the slightly decreased belt 
tension is applied to the outer periphery of the magnetic tape wound on 
the reel 6 serving as a supply reel. In other words, the tape tension 
difference between the take-up end supply reels is proportional to the 
belt tension difference. In this way, the tape tension is optimally 
adjusted by the viscous drag of grease 24 having a predetermined viscosity 
coefficient, such that the tension of the take-up reel side becomes 
slightly higher than the supply reel side. As shown in FIG. 10, it has 
been experimentally proven by the inventors that the tape tension is 
stable within an optimal tape tension range of 30 to 90 g when the 
viscosity coefficient of grease 24 is within a range of 50 to 500 P 
(poise). 
In magnetic tape cassettes employing tape guide pins press-fitted into the 
lower half of the casing, since the lower half 3 of the cassette casing 1 
is conventionally made of an electrically conductive material, such as 
aluminium alloy, if the tape cassette is set in the cassette holder of the 
recording and/or reproducing apparatus 100 as shown in FIG. 11, such that 
a portion of the cassette casing 1 is exposed outside of the apparatus 
100, there is the possibility that a user may touch the exposed portion of 
the tape cassette. As previously described, during operation of the 
apparatus 100 there is a tendency for static electricity from the user to 
be discharged through the exposed portion of the electrically conductive 
lower half into the electrical control unit of the apparatus. To prevent 
this, an electrically insulating cover or frame 24 is attached to the 
lower half 3 in such a manner as to border the outer perimeter of the 
bottom surface of the lower half 3 at a width of substantially 20 mm, as 
clearly seen in FIG. 12. With these constructions, the magnetic tape 
cassette according to the invention, has high durability and high 
reliability to maintain high quality as a recording medium. 
As shown in FIG. 13, when comparing a conventional magnetic tape cassette C 
and a magnetic tape cassette I of the present embodiment, the tape 
cassette I ameliorates the degree of tracking error or reading error 
relative to the number of completed tape travels. 
As will be appreciated from the above, although in the present embodiments 
according to the invention, a tape cassette including magnetic tape is 
used as a recording medium, another type tape cassette may be used as such 
a recording medium. 
While the foregoing is a description of the preferred embodiments for 
carrying out the invention, it will be understood that the invention is 
not limited to the particular embodiments shown and described herein, but 
may include variations and modifications without departing from the scope 
or sprit of this invention as described by the following claims.