Magnetic head position adjusting mechanism

A magnetic head adjusting mechanism operable to adjust the position of magnetic heads with respect to a direction of a run of magnetic recording medium independently of the adjustments of the head gap angle, the heights of the heads and other adjustment items. The mechanism includes a head base plate carrying the magnetic heads and formed with a shaft bore in which is fitted a support shaft mounted on a chassis. The head base plate is resiliently biased about the axis of the support shaft. The rotation of the head base plate about the support shaft is limited by a tapered adjusting member formed by a tapered nut having a conical outer surface in contact with the head base plate and a screw shaft in threadable engagement with the tapered nut. The screw shaft is mounted on and extends from the chassis to support the tapered nut such that the generating line of the conical surface of the nut, which includes the point of contact of the nut with the head base plate, is substantially parallel to the axis of the support shaft.

BACKGROUND OF THE INVENTION 
The present invention relates to an adjusting device for magnetic heads in 
a magnetic recording/reproducing apparatus and, more particularly, to an 
adjusting device for magnetic heads which require an adjustment of 
position in the direction of running of the magnetic recording medium. 
Generally, in a magnetic recording/reproducing apparatus for video signals, 
a magnetic tape runs from a reel to a rotary head cylinder having a rotary 
video head via a tape guide pin, eraser head and so forth and, after 
having been wound around the rotary head cylinder, runs past an audio 
control head, tape guide pin, capstan and so forth to another reel. For 
reproducing video or audio signals from a magnetic tape with this tape 
running system, it is often required to adjust the position of the 
magnetic head in order that the control head correctly traces the control 
pulses recorded on the control track on the magnetic tape. 
In, for example, Japanese Utility model Laid-Open Publication No. 39523/80 
(Application No. 120563/78, filed on Sept. 4, 1978), a device for 
adjusting the position of the magnetic head is proposed wherein a support 
and position adjustment for a magnetic head block, usually referred to as 
"ACE head" in which a magnetic heads for audio signal and control signal 
and a magnetic head for erasing audio track are constructed as a single 
unit. In this proposed construction, independent adjustments of not only 
the position of the magnetic head in the direction of running of the tape 
but also other adjustment items such as the azimuth angle of the head gap, 
height of the head, the tilt (inclination) of the head in the back and 
forth direction and so forth. 
While adjustment of an azimuth angle and the adjustment of the position of 
the head in the tape running direction can be made independently of other 
items of adjustment. The adjustment of the tilt of the head and the 
adjustment of the head height, however, affect the azimuth angle and the 
head position in the tape running position, respectively. 
No problem will be caused if predetermined sequences of adjustments are 
followed, namely, adjustment of the azimuth angle after adjustment of the 
tilt of the head and adjustment of magnetic head in the tape running 
direction after the adjustment of magnetic head height. However, with 
readjustment of a height of the head or readjustment of the tilt of the 
head, it is necessary to make troublesome readjustment of the head 
position in the tape running direction or of the azimuth angle even if the 
head position or the tilt of the head has been correctly adjusted. Without 
the subsequent readjustment of the head position in the tape running 
direction or the azimuth angle, problems arise due to incorrect 
adjustment. 
In recent years, there has been a remarkable improvement in the performance 
which, in turn, affords a higher density in recording on a magnetic tape. 
Consequently, the tape running speed suitable for the recording or 
reproduction has been decreased to 1/2 and then to 1/3 of that required 
before. The decrease in the tape running speed has imposed a new problem 
namely, the azimuth angle is now seriously affected by a slight play in 
the fit between the support shaft and the associated sleeve. For instance, 
assuming that the track width is 1 mm and the recording frequency is 4 
KHz, the level of azimuth loss due to 5' (minutes) deviation of azimuth 
angle was as small as about -0.4dB when the tape running speed was 33.35 
mm. However, when the tape running speed is reduced to 11.12 mm which is 
about 1/3 (one third), a large azimuth loss of about -4.3dB is caused by 
the same deviation of the azimuth angle. For instance, the deviation of 5' 
is caused even by a small inclination of the support shaft caused by a 
minute clearance of 36 .mu.m between the support shaft and the shaft hole 
when the axial length of fit between the sleeve and the support shaft is 
25 mm. In order to reduce the azimuth loss down to the level of -0.4dB at 
the low tape speed of 11.12 mm, it is necessary to reduce the clearance 
between the support shaft and the shaft hole to a level of 12 .mu.m which 
can hardly be attained by ordinary machining. Clearly, it is quite costly 
to realize a fit which has small clearance between two members but still 
ensuring smooth relative sliding motion therebetween. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the invention is to provide an inexpensive 
magnetic head adjusting device which does not cause any change in the 
position of the head in the tape running position when the height of the 
head is adjusted, thereby to avoiding the above-described problems of the 
prior art. 
Another object of the invention is to provide a magnetic head adjusting 
device which is improved to eliminate any change in the azimuth angle 
after adjustment. 
To achieve the objects, the present invention provides a magnetic head 
adjusting device which includes a head base plate carrying magnetic heads 
and having a shaft bore; a support shaft mounted on the chassis and fitted 
in the shaft bore in the head base plate; means for applying to the head 
base plate a force acting to rotate the head base plate about the support 
shaft; and a tapered adjusting means including a member having a conical 
outer peripheral surface adapted to contact one end of the head base plate 
so as to limit the rotation of the head base plate about the support 
shaft, and a shaft for moving the member up and down. The tapered 
adjusting means is mounted on the chassis in such a manner that the 
generating line of the conical outer peripheral surface, which includes 
the point of contact between the conical outer peripheral surface and the 
head base plate, extends substantially in parallel with the support shaft. 
In one preferred embodiment of the invention, the magnetic head adjusting 
device further includes adjusting mechanisms carried by the head base 
plate and adapted for adjusting tilt of the head and the azimuth angle; 
means for applying to the head base plate a rotational force or moment 
.alpha. for rotating the latter substantially in a plane including the 
head surfaces contacting the magnetic tape so as to urge the support shaft 
in the shaft bore to eliminate any mechanical play therebetween, a 
rotational force or moment .beta. for rotating the head base plate about 
the support shaft, and a thrust force for urging the head base plate in 
the axial direction of the support shaft; and means for limiting the 
movement of the head base plate caused by the thrust force in the axial 
direction of the support shaft. 
The above and other objects, features and advantages of the invention will 
become clear from the following description with reference to the 
accompanying drawings.

DETAILED DESCRIPTION 
Referring now to the drawings wherein like reference numerals are used 
throughout the various views to designate like parts and, more 
particularly, to FIGS. 1-3, according to these figures, a device for 
adjusting the position of a magnetic head of the type proposed in Japanese 
Utility Model Laid-Open Publication No. 39523/80 includes a head base 
plate 10 carrying an audio control head 2 and an audio erase head 3 in 
such a manner that the heads 2, 3 are held in positions for predetermined 
contact with the magnetic tape 1. The base plate 10 supports mounting 
members 4-9 which are employed for an adjustment of the azimuth angle and 
tilt of the head. A sleeve 11 is secured to the head base plate 10 to 
provide a shaft hole in the head base plate 10. The sleeve 11 together 
with the torsion spring 18 and washer 12 fits around a support shaft 14 
which extends upright from a chassis 15. The torsion spring exerts a 
resilient force for pushing the head base plate 10 upwardly in an axial 
direction of the support shaft 14; however, the upward movement of the 
head base plate 10 is limited by a nut 13 which is screwed to a threaded 
portion 14a of the head portion of the support shaft 14. Consequently, it 
is possible to adjust the position of the "ACE" head as a whole in a 
heightwise direction, that is, in the direction of the arrow Z. The 
torsion spring 18 also produces a rotational force which acts to bias the 
"ACE" head counter-clockwise around the axis of the support shaft 14. The 
rotation of the "ACE" head is limited by a tapered nut 17 screwed to a 
threaded shaft 16 extending upright from the chassis 15. The rotational 
reaction force of the torsion spring 18 is received by a stopper 15a on 
the chassis 15. It is thus possible to adjust the tilt of the head by 
means of the adjusting screw 6, while the adjustment of the azimuth angle 
and adjustment of the height of the head are made by the adjusting screw 5 
and nut 13, respectively. Additionally, the position of the head in the 
direction of running of the tape can be adjusted by the tapered nut 17. 
The members 4, 7, 8, and 9 respectively correspond to a head plate, a 
screw, a center shaft, and a play eliminating spring. 
In accordance with the present invention, as shown in FIGS. 4-9, audio 
control head 2 has an audio head core 2a and a control head core 2b, with 
an audio erase head 3 being adapted to erase signals along the audio track 
on a magnetic tape 1. The audio control head 2 and the audio erase head 3 
are carried by a head plate 4 and contact predetermined portions of the 
magnetic tape 1. The head plate 4 is supported by members such as an 
azimuth angle adjusting screw 5, a head tilt adjusting screw 6, a screw 7, 
a play eliminating spring 9 and a center shaft 8 on a head base plate 19. 
Thus, the head plate 4 is mounted on the head base plate 19 in a manner 
which permits adjustments of the azimuth angle and the tilt of head. More 
specifically, the screws 6 and 7 are threadably accommodated into threaded 
holes in the head plate 4, while the screw 5 is threaded into a threaded 
hole formed in the head base plate 19. The screw 5 extends through a hole 
in the head plate 4 and the screw 7 extends through a hole in the head 
base plate 19. The free end of the screw 6 rests in a recess formed in the 
head base plate 19, while the center shaft 8 is received at its end by a 
hole formed in the head plate 4. The play eliminating spring 9 extends 
around the screw 7 and is loaded between the head of the screw 7 and the 
head base plate 19 so as to bias the head plate 4 towards the head base 
plate 19. 
When the azimuth angle adjusting screw 5 is rotated, the head plate 4 
carrying the heads 2, 3 rocks in a manner within a plane defined by Z and 
X axes about a line joining the head inclination adjusting screw 6 and the 
center shaft 8. It is, therefore, possible to vary the azimuth angle by 
rotating the azimuth angle adjusting screw 5. On the other hand, a 
rotation of the head tilt adjusting screw 6 causes a rotation of the head 
plate 4 about a line extending between the azimuth angle adjusting screw 5 
and the center shaft 8. Thus, both tilt of the head and the azimuth angle 
can be simultaneously varied. 
A sleeve 20 is fixed to the head base plate 19. A shaft bore formed in the 
sleeve 20 extends in the direction of Z axis which is substantially 
parallel to the tape contact surface of the magnetic head and 
perpendicular to the direction of running of the magnetic tape. The shaft 
bore of the sleeve 20 snugly receives a support shaft 14 which extends 
upright from a chassis 22. 
A nut 13 together with a washer 12 is threaded onto a threaded end 14a of 
the support shaft 14 and serves to limit the movement of the sleeve 20 and 
thus of the heads 2 and 3 and other members on the head base plate 19 in 
the positive direction along the Z axis. A tension spring 23 is engaged at 
its one end by a hook 19b on the head base plate 19 and at its other end 
by a hook 22a on the chassis or a portion of a bracket fixed to the 
chassis 22 so as to pull the head base plate 19. Thus, the spring 23 
produces a force or moment .beta. which acts to rotate the head base plate 
19 within the X-Y plane about the support shaft 14, a thrust force which 
acts to slide the head base plate 19 in the direction of Z axis along the 
support shaft 14, and a force or moment .alpha. (indicated by an arrow M 
in FIG. 9) which acts to rotate the head base plate 19 as a whole 
substantially within the X-Z plane. A screw shaft 21 is secured to the 
chassis 22 so as to extend obliquely upwardly at an inclination angle 
which is same as the gradient of the taper of a tapered nut 17 screwed on 
to the screw shaft 21. The direction of inclination of the screw shaft 21 
is selected such that, assuming that the tapered nut 17 is conical, the 
generating line of the tapered nut 17 passing through the point of contact 
between the tapered nut 17 and the base plate 19 extends substantially in 
parallel with the axis of the support shaft 14. The tapered nut 17 limits 
the rotation of the head base plate 19 in the X-Y plane. 
The heights or levels of the heads 2, 3 are adjustable by the rotation of 
the nut 13, while the positions of the heads 2, 3 in the tape running 
direction (direction of X axis) are adjustable by rotating the tapered nut 
17. 
In the embodiment of FIGS. 10 and 11, the role or function played by the 
spring 23 in the first embodiment is shared by two springs, namely, a 
compression spring 25 and a tensile spring 26. The force for moving the 
head base plate 19 in the direction of Z axis is produced by the 
compression spring 25, while the tensile spring 26 produces the force or 
moment .beta. for rotating the head base plate 19 in the X-Y plane and the 
force or moment .alpha. for rotating the same in the X-Z plane. The 
chassis 22 is provided with a hook 24 which is engaged with one end of the 
tensile spring 26. 
In the embodiments described above, a combination of a tapered nut 17 
having a conical outer peripheral surface and a screw shaft 21 threadably 
engaging with the tapered nut is used as tapered adjusting means. This 
combination can be substituted by a construction shown in FIG. 12 wherein 
a tapered member 30 is fastened to a head adjusting shaft 33 by a nut 32 
through a spring 31. The arrangement is such that the tapered member 30 
moves up and down when the nut 32 is rotated. According to this 
arrangement, it is not essential that the entire outer peripheral surface 
has a conical shape. Namely, the member 30 operates satisfactorily 
provided that the portion of the member 30 contacting one end of the head 
base plate is inclined to the axis of the member 30. 
According to the invention, the adjustment of heights or levels of the 
heads is achieved by rotating the nut 13 as in the conventional adjusting 
device. The head adjusting device of the invention, however, is 
distinguished from the known head adjusting device that, in the head 
adjusting device of the invention, the locus of movement of the point of 
contact between the tapered nut 17, limiting the movement of the head 
block as a whole in the tape running direction and, the head base plate 19 
extends substantially in parallel with the direction of height or level 
adjustment of the head. Therefore, the head base plate 19 does not move 
substantially in the tape running direction (substantially parallel with 
the Z axis) even when the head base plate 19 is moved in the direction of 
the axis Z for height or level adjustment. 
In the head adjusting device of the invention, moreover, once the tilt of 
the head has been adjusted optimumly, the azimuth angle, the head heights 
or levels, and the head position in the tape running direction can be 
adjusted independently and in a random sequence by means of the azimuth 
angle adjusting screw 5, the nut 13 and the tapered nut 17, respectively. 
The spring 23 or 26 produces a rotational force which biases the support 
shaft 14 fitted in the shaft bore in the sleeve 20 to cause the support 
shaft 14 to contact always at two fixed points A and B as shown in FIG. 9 
to substantially eliminate any play between the support shaft and the 
inner surface of the sleeve 20 after the adjustment. Consequently, the 
deviation of the azimuth angle which inevitably takes place in the known 
head adjusting device, due to a play between the support shaft and the 
sleeve, is advantageously avoided. The mechanical plays in other portions 
are all eliminated by the combination of the play-eliminating spring 9 and 
the tension spring 23 or by the combination of the play-eliminating spring 
9, the compression spring 25 and the tensile spring 26, thereby avoiding 
any change in other adjusting items. As stated before, in the known head 
adjusting device, the play between the support shaft 14 and the sleeve 20 
could be decreased only by increasing the precision of the machining of 
the support shaft 14 and the sleeve 20, resulting in an increase in the 
production cost and the play still could not be perfectly eliminated even 
by taking such a measure. In contrast, according to the invention, the 
unfavorable effect produced by the play between the support shaft and the 
sleeve can be eliminated without requiring any increase in the machining 
precision and, hence, without incurring substantial increase of the 
production cost. 
As has been described, according to the invention, it is possible to obtain 
an inexpensive head adjusting device which permits easy adjustments while 
overcoming the problem, in the conventional head adjusting mechanism, of 
the undesirable change of the head position in the tape running direction 
caused by a height or level adjustment. Additionally, the head adjusting 
device of the invention provides a head stable support which is improved 
to eliminate changes after adjustment, particularly the change in the 
azimuth angle which has been a problem in the conventional head adjusting 
mechanism. 
Although the invention has been described through specific terms, it is to 
be noted here that the described embodiments are not exclusive and various 
changes and modifications may be imparted thereto without departing from 
the scope of the invention which is limited solely by the appended claims.