Magnetic head component mounting system

A magnetic tape unit comprising a head component having a rotatable drum provided with a magnetic head, a guide plate having a tape guide mechanism for leading a magnetic tape into contact with the head component, a supporting base for supporting the head component with the rotation surface of the magnetic head inclined at predetermined angle against the guide plate, the thermal coefficient of expansion thereof being different from that of the guide plate, and mounting means for fitting the supporting base to the guide plate and for absorbing the difference in the degree of expansion and contraction therebetween appeared in a direction in parallel with the surface of the guide plate due to the difference of the thermal coefficient of expansion therebetween. As described above, by use of the magnetic tape unit according to the present invention, the expanded portion of the supporting base is absorbed due to the fact that the thermal coefficient thereof is greater than that of the guide plate, whereby the tape inclination angle formed between the rotation surface of the magnetic head and the guide plate is not easily affected by any temperature fluctuation, so that the predetermined angle becomes invariable.

BACKGROUND OF THE INVENTION 
The present invention relates to a magnetic tape unit such as a DAT 
(Digital Audio Tape Recorder), specially to the construction of the 
rotatable drum portion thereof. 
Conventionally, there has been proposed a magnetic tape unit as disclosed 
in the Japanese Utility Model Laid-open Publication No. 61-61611, wherein 
as shown in FIG. 6, the components such as a rotatable drum 2 provided 
with a magnetic head (not shown) that spins around a rotational shaft 1, a 
fixed drum 3 for supporting the rotatable drum 2, a supporting member 4 
for supporting the fixed drum 3 and a motor 5 to rotate the rotatable drum 
2 altogether compose a rotative head component 6, which is fixed to a base 
plate 8 through a screw 7 at the outer edge portion 4a of the supporting 
member 4. 
In the magnetic tape unit of the above construction, the supporting member 
4 is generally constructed from a diecast Zinc or a resin-formed material, 
whereas the base plate 8 is made from a metal plate mainly adopted for 
economical reason. The materials of the above two objects are thus 
different from each other in the respective coefficients of thermal 
expansion and also in the degrees of expansion and contraction against the 
temperature fluctuation therearound, whereby at least one of these 
materials is deformed to produce a positional error between the base plate 
8 and the rotative head component 6. On the other hand, the magnetic tape 
(not shown) is brought into contact with the rotatable drum 2 and the 
fixed drum 3 through a tape guide mechanism (not shown) provided on the 
base plate 8, thereby a predetermined angle (hereinafter referred to as 
"tape inclination angle") against the rotation surface of the magnetic 
head is formed so as to write/read signals to/from the surface of the 
magnetic tape. 
Accordingly, when the subtle positional error occurs between the base plate 
8 and the rotative head component 6 in accordance with the temperature 
fluctuation, the above tape inclination angle is not possibly maintained, 
and the magnetic head thereby becomes unable to read the signals stored on 
the magnetic tape. This phenomenon is applied specially to the 
vehicle-mounted type magnetic tape unit which is seriously affected to its 
proper operation by the abrupt temperature fluctuation generated inside 
the vehicle. 
The primary object of the present invention therefore is to eliminate the 
above problems contained by the conventional unit, in other words, to 
provide a magnetic tape unit, wherein the predetermined tape inclination 
angle is not affected by any temperature fluctuation therearound. 
SUMMARY OF THE INVENTION 
The magnetic tape unit according to the present invention comprises a guide 
plate having a tape guide mechanism for supporting a head component in 
such a manner that the rotation surface of the magnetic head is inclined 
at the predetermined angle against the surface of the guide plate, a 
supporting plate having a different coefficient of thermal expansion from 
that of the guide plate, and a buffer means for absorbing the difference 
of the degrees of expansion and contraction in the direction of the guide 
plate surface caused by the mentioned difference of the coefficients of 
the thermal expansion between the above plates. 
By utilization of the magnetic tape unit of the above structure, the buffer 
means absorbs the difference of the level of expansion and contraction 
between the guide plate and the supporting base in the direction of the 
guide plate surface generated by the difference of the respective thermal 
coefficient of expansion between the above two plates, so that the 
inclination angle provided therebetween is always maintained at the 
predetemined level against the temperature fluctuation caused therearound.

DETAILED DESCRIPTION OF THE EMBODIMENT 
Below shows a detailed description of an embodiment of the present 
invention. 
In FIGS. 1 to 3, 9 denotes a rotatable drum provided with a magnetic head 
10, 11 a fixed drum provided for supporting the rotatable drum 9, 12 a 
motor to activate the rotatable drum 9, wherein the above rotatable drum 9 
and the fixed drum 11 together compose a head component 13. 14a to 14d are 
guide shafts for leading the magnetic tape 15 into contact with the head 
component 13, 16a and 16b are respectively guide-shaft supporting members, 
and 17 is a guide plate made of a material wherein the guide grooves 17a 
and 17b are provided. 
As mentioned above, the guide shafts 14a to 14d, the guide-shaft supporting 
members 16a and 16b, and the guide grooves 17a and 17b get together 
composing a tape guide mechanism 18. The guide plate 17 having the above 
tape guide mechanism 18 regulates the running position of the magnetic 
tape 15 in such a manner that the magnetic tape 15 can form a 
predetermined tape inclination angle in accordance with the rotation 
surface A of the magnetic head 10. 19 is a supporting base made of diecast 
Zinc or a resin-formed material provided for fixedly supporting the head 
component 13 through a fixing screw 20, whose coefficient of thermal 
expansion is different from that of the guide plate 17, and the fitting 
portions 19a and 19b thereof are fixedly connected to the fitting portions 
17c and 17d of the guide plate 17. 
Further, the central portion of supporting base 19 is as shown in FIG. 1, 
inclined downwardly to the left, thereby the angle formed by the rotation 
surface A of the magnetic head 10 and the surface B of the guide plate 17 
is settled at the predetermined mounting angle. In this case, the 
predetermined mounting angle is exactly synchronized with the magnetic 
tape inclination angle. Furthermore, the rotational surface A and the 
surface C of the supporting base 19 are in parallel, whereby the angle 
formed by the surface C of the supporting base 19 and the surface B of the 
guide plate 17 is settled to be also at the mounting angle. 
Concerning the related fitting portions 17c and 19a, 21a is a fixing screw 
to fix the supporting base 19 to the guide plate 17. Concerning the 
related portions 17d and 19b, as seen in FIG. 1, 21b is a fixing screw 
that is fixed to the guide plate 17 through a fitting hole 17e, and that 
extends through the fitting hole 19d, in the supporting base 19. Also, a 
predetermined space is formed in the supporting base 19 side, wherein 22 
is a coil spring loosely inserted on the fixing screw 21a and compressedly 
provided between the supporting base 19 and the head portion of the fixing 
screw 21b. In this structure above, the screw 21b and the fitting portions 
17d and 19b forming a mounting means 23 together, whereby the 
predetermined space provided in the fitting hole 19d is formed in such a 
manner that the difference in the degrees of expansion and contraction 
between the guide plate 17 and the supporting base 19 caused by the 
temperature fluctuation is substantially absorbed since as seen from FIG. 
1 the supporting base 19 is slidingly held to the guide plate 17 by the 
screw 21b and the coil spring 22. 
In the embodiment of the above construction, the guide shafts 14a to 14d 
draw out the magnetic tape 15 from a cassette case (not shown), then each 
of the guide-shaft supporting members 16a and 16b are shifted along the 
guide grooves 17a and 17b thereby to lead the magnetic tape 15 into 
contact with respectively the rotatable drum 9 and the fixed drum 11. By 
this operation, the magnetic tape 15 and the rotation surface A of the 
magnetic head 10 maintain a predetermined tape inclination angle so as to 
correctly perform write or read operation of the signals stored on the 
tape. 
In the above construction, even when the ambient temperature thereof 
arises, the fitting portions 17c and 19a are not affected since they are 
firmly fixed to each other, whereas concerning the mounting portions 17d 
and 19b, since the coefficient expansion rate of the supporting base 19 is 
greater than that of the guide plate 17, the expanded portion of the 
supporting base 19 is shifted towards right, as shown in FIG. 1, starting 
from the both fitting portions 17c and 19a in parallel with the surface B 
of the guide plate 17. Accordingly, the mounting angle formed between the 
rotation surface A of the magnetic head 10 and the surface B of the guide 
plate 17 can be maintained at one level in spite of the rise of 
temperature. By this, it is obvious that the above angle is maintained at 
one level also when the temperature lowers. Accordingly, the tape 
inclination angle can be maintained against any temperature fluctuation, 
so that precise writing or reading operation of the signals stored on the 
tape can be performed. Similarly, an angle between the guide plate 17 and 
a rotational axis R of the rotatable drum 9 will also necessarily remain 
constant during temperature fluctuations which result in thermal expansion 
or contraction of the supporting base 19 and the guide plate 17. 
Furthermore, in the above embodiment, since the fitting portion 19b of the 
supporting base 19 is suppressively attached to the fitting portion 17d of 
the guide plate 17 by function of the coil spring 22, the supporting base 
19 is not easily affected by vibration or shock, thereby the tape 
inclination angle is maintained, and in the case that rather strong shock 
to vibrate the supporting base 19 is caused, the inner constituents of the 
head component 13 can be protected as the coil spring 22 absorbs it. FIGS. 
4 and 5 show another embodiment of the present invention, wherein the 
resilient plate 24 to suppressively and slidingly attach the fitting 
portion 19b of the supporting base 19 to the fitting portion 17d of the 
guide plate 17 is fastened to the guide plate 17 through a fixing screw 
25, providing the same effect as the first embodiment. 
In the both embodiments above, the fitting portions 17c and 19a are fixed 
to each other, these portions can also be constructed as the other 
portions 17d and 19b. 
Furthermore, as well as to the DAT, these embodiments can also be applied 
to other types of magnetic tape unit such as VTRs wherein a head component 
is adopted.