Head height adjustment construction in magnetic recording and reproducing apparatus with rotary cylinder

A head height adjustment construction in a magnetic recording and reproducing apparatus with a rotary cylinder for use in a VTR, for example, includes a lower fixed drum, an upper rotary drum axially spaced from and rotatable with respect to the lower fixed drum, the upper rotary drum having a tapered surface slanted upwardly in a radially outward direction thereof, a head attachment plate having one end mounted on the upper rotary drum and supporting a head on an opposite end thereof, and an adjustment screw threaded in the upper rotary drum and held against the head attachment plate. When the height of the head is to be adjusted, the adjustment screw is turned about its own axis for spacing the opposite end of the head attachment plate away from the tapered surface. After the head height has been adjusted, a surface of the head which is held in sliding contact with a magnetic tape is directed upwardly toward a plane in which the upper rotary drum is rotatable.

BACKGROUND OF THE INVENTION 
The present invention relates to a head height adjustment construction in a 
magnetic recording and reproducing apparatus with a rotary head for use in 
a video tape recorder (hereinafter referred to as "VTR") or the like. 
FIG. 4 of the accompanying drawings illustrates a conventional head height 
adjustment construction, the view showing in cross section a magnetic 
recording and reproducing apparatus having a rotary drum, prior to fine 
adjustment thereof, for use in a VTR. The prior arrangement includes head 
attachment plates 2 each supporting a head 1 on one end thereof and 
fastened at an opposite end to the lower surface of an upper rotary drum 4 
with an attachment screw 3. The head attachment plates 2 extend parallel 
to a plane A in which the rotary drum 4 is rotatable. Each head 1 defines 
a gap having a lower end spaced from a reference surface 5a of a lower 
fixed drum 5 by a distance which is greater than a prescribed height H by 
a small interval (about 10 m). By depressing each of the head attachment 
plates 2 with an adjustment screw 6 threaded in a threaded hole defined in 
the upper rotary drum 4, the height of the head 1 exposed in a head 
attachment window 7 can be adjusted little by little in the direction of 
the arrow B. Such height adjustment is completed when the height of the 
head 1 has reached the prescribed height H. It would actually be of 
importance to measure the head height from a lead 8 of the lower fixed 
drum 5. Since it would be highly difficult to measure such a height, 
however, the heat height is normally measured with a microscope from the 
reference surface 5a of the lower fixed drum 5. 
A rotatable shaft 10 is fixed centrally to the upper rotary drum 4 by a 
sleeve 9 and is rotatably supported on the lower fixed drum 5 by bearings 
11, 12. A rotary transformer 13 for transmitting signals is disposed 
between the upper rotary drum 4 and the lower fixed drum 5. A bushing 14 
is mounted on an end of the shaft 10 which projects from the lower fixed 
drum 5. A head cable 15 is connected to the heads 1. 
FIG. 5 shows the manner in which a tape travels in the magnetic recording 
and reproducing apparatus. A magnetic tape 16 travels in the direction of 
the arrow D while wound around the upper rotary drum 4 and the lower fixed 
drum 5 through more than 180.degree., with a lower tape edge extending 
along the lead 8. Since the upper rotary drum 4 rotates at high speed in 
the direction of the arrow D to rotate the heads 1, the gaps of the heads 
1 where thet are slidably contact the tape 16 slide on a magnetic surface 
of the magnetic tape 1 for recording and reproducing signals on and from 
the magnetic tape 1. 
With the prior head height adjustment construction, the surfaces of the 
upper rotary drum 4 which confront the head attachment plates 2 lie 
parallel to the plane A. Therefore, when fine adjustment of the head 
height is completed by depressing the free end of the head attachment 
plate 2 toward the lower fixed drum 5 with the adjustment screw 6, a 
surface 1a of the head 1 for slidable contact with the tape 16 is directed 
dowardly as shown in FIG. 6. Inasmuch as the lower edge of the magnetic 
tape 16 is especially subjected to smaller tension and held against the 
heads 1 under smaller presser in the position E where the magnetic tape 16 
starts engaging the drums 4, 5, the head 1 is liable to disengage from the 
magnetic tape 16 in the vicinity of a lower end n of the gap of the head 
1. Designated at m is an upper end of the gap of the head 1. As the 
clearance between the gap (m - n) of the head 1 and the magnetic tape 16 
is increased, the head 1 has difficulty in picking up the magnetic flux 
from the magnetic tape 16, resuling in a so-called spacing loss which 
reduces a reproduced output produced from the magnetic tape 16 as it 
starts engaging the drums 4, 5. As a consequence, the waveform of the 
reproduced output has rounded portions as shown in FIG. 7 and the head 
sensitivity is reduced particularly when the magnetic tape begins to 
engage the drums 4, 5, with the result that a reproduced image will suffer 
from noise in its upper portion. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a head height 
adjustment construction in a magnetic recording and reproducing apparauts 
with a rotary cylinder, the head height adjustment construction being free 
from any spacing loss which would otherwise occur as a magnetic tape 
starts engaging rotary and fixed drums, thus preventing any reduction in a 
reproduced signal output. 
According to the present invention, a head height adjustment construction 
in a magnetic recording and reproducing apparatus with a rotary cylinder, 
includes a lower fixed drum, an upper rotary drum axially spaced from and 
rotatable with respect to the lower fixed drum, the upper rotary drum 
having a tapered surface slanted upwardly in a radially outward direction 
thereof, a head attachment plate having one end mounted on the upper 
rotary drum and supporting a head on an opposite end thereof, and an 
adjustment screw threaded in the upper rotary drum and held against the 
head attachment plate. When the height of the head is to be adjusted, the 
adjustment screw is turned about its own axis for spacing the opposite end 
of the head attachment plate away from the tapered surface. After the head 
height has been adjusted, a surface of the head which is held in sliding 
contact with a magnetic tape is directed upwardly toward a plane in which 
the upper rotary drum is rotatable. 
The above and other objects, features and advantages of the present 
invention will become more apparent from the following description when 
taken in conjunction with the accompanying drawings in which a preferred 
embodiment of the present invention is shown by way of illustrative 
example.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention will be described with reference to FIGS. 1 through 
3. Like or corresponding parts in FIGS. 1 and 2 are denoted by like or 
corresponding reference characters in FIGS. 4 through 6. 
FIG. 1 shows a head height adjustment construction according to the present 
invention. A head attachment plate 2 with a head 1 mounted on one end 
thereof has an opposite end secured by an attachment screw 3 to a lower 
tapered surface 4a of an upper rotary drum 4. The tapered surface 4a is 
slanted upwardly in a radially outward direction of the upper rotary drum 
4 and has an outer edge contiguous to a head attachment window 7. 
Therefore, the head attachment plate 2 extending along the tapered surface 
4a is also slanted with respect to a plane A in which the upper rotary 
drum 4 is rotatable. With the parts thus assembled, the head 1 defines a 
gap having a lower end spaced from a reference surface 5a of a lower fixed 
drum 5 by a distance which is greater than a prescribed height H by a 
small interval (about 10 m). 
By depressing the head attachment plate 2 with an adjustment screw 6 
threaded in a threaded hole defined in the upper rotary drum 4, the free 
end of the head attachment plate 2 is spaced from the tapered surface 4a 
to adjust the height of the head 1 little by little in the direction of 
the arrow B. Such height adjustment is finished when the height of the 
head 1 has reached the prescribed height H. Since the head attachment 
plate 2 is attached to the tapered surface 4a, a surface 1a of the head 1 
which is held in sliding contact with a magnetic tape 16 is slightly 
directed obliquely upwardly toward the plane A, as illustrated in FIG. 2. 
With the sliding surface 1a of the head 1 being slightly directed obliquely 
upwardly toward the plane A, the magnetic tape 16 can be brought into 
reliable contact with the gap (m - n) in the head 1 in the vicinity of a 
position in which the magnetic tape 16 starts engaging the drums 4, 5. 
This arrangement avoids any spacing loss which would be produced in the 
position wherein the magnetic tape 16 starts engaging the drums 4, 5. As a 
result, the waveform of a reproduced output has an envelope as shown in 
FIG. 3, which is free from unwanted rounded portions and is uniform 
throughout. Accordingly, the magnetic recording and reproducing apparatus 
can generate reproduced images of good quality at all times. 
With the head height adjustment construction of the present invention, as 
described above, the head attachment plate is held against and attached to 
the tapered surface of the upper rotary drum, so that the sliding surface 
of the head will be directed obliquely upwardly to the plane of rotation 
of the upper rotatry drum, after the head height has been adjusted. The 
head gap and the magnetic tape can therefore be held in reliable contact 
with each other in the position in which the magnetic tape starts engaging 
the drums, and hence the output reproduced by the head is prevented from 
attenuation. 
Although a certain preferred embodiment has been shown and described, it 
should be understood that many changes and modifications may be made 
therein without departing from the scope of the appended claims.