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Description  |
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BACKGROUND OF THE INVENTION
Tracking control of a digital audio tape recorder (DAT) is made by an
automatic tracking following system (ATF system), the principles of which
will be described with reference to FIGS. 2 through 4.
FIG. 4A illustrates the relationship between a rotary drum 40 of a DAT and
a running path of a magnetic tape 41. The rotary drum 40 has two heads ha
and hb (not shown) provided at the same height but spaced apart from each
other on the periphery of the drum so that the same movement locus can be
obtained. The rotary drum 40 rotates in a direction indicated by J at 2000
r.p.m. The magnetic tape 41 moves in a direction indicated by K at a tape
velocity of v along the tape running path. The magnetic tape is provided
with guide rollers 44 and 45 for controlling its movement in widthwise
direction along the rotary drum 40 and inclined pins 42 and 43. An angle
at which the magnetic tape 41 is wound on the rotary drum 40 is set to be
approximately 90 degrees if an outer diameter of the rotary drum 40 is 30
mm, while an angle between the tape running direction and a rotary axis of
the rotary drum 40 is equal to a reference angle .theta.r.
FIG. 4B illustrates the reference angle .theta.r between the tape running
direction at the tape winding portion and the rotary axis of the rotary
drum 40 in a plane face.
Referring now to FIG. 2, there are shown the ATF areas of track pattern in
an enlarged manner. The ATF areas are indicated by E.sub.1 and E.sub.2
adjacent to the edges of the magnetic tape 41 in a widthwise direction and
a PCM area is indicated by E.sub.3 on which a PCM signal is recorded. The
ATF areas are formed of blocks P (indicated by hatching) on which pilot
signals s.sub.1 are recorded, respective blocks A and B (indicated by
lateral lines and longitudinal lines, respectively) on which synchronizing
signals s.sub.2 of different frequencies corresponding to the heads ha and
hb, respectively, are recorded and blocks D on which IBG signals are
recorded.
On reproduction of the signals, the heads ha and hb, which have a width
equal to 1.5 times the track width, alternately scan the adjacent tracks
of the magnetic tape to reproduce the signals on the magnetic tape. FIGS.
3A, 3B and 3C show the pilot signals s.sub.1 reproduced when the head hb
scans the track t.sub.4. The head hb sequentially scans the blocks
P.sub.51, P.sub.31 and P.sub.41 of the ATF area E.sub.1 and the blocks
P.sub.42, P.sub.52 and P.sub.32 of the ATF are E.sub.2 to reproduce the
pilot signals s.sub.1 recorded on these blocks.
FIG. 3A shows waveforms of the reproduction level of the pilot signals
s.sub.1 when the head hb normally scans the track T.sub.4. As noted from
FIG. 3A, at the ATF area E.sub.1 the reproduced pilot signals s.sub.1 on
the block P.sub.31 on the leftward adjacent track T.sub.3 and the block
P.sub.51 on the rightward adjacent track T.sub.5 have the same level.
Also, at the ATF area E.sub.2, the reproduced signals on the blocks
P.sub.32 and P.sub.52 have the same level. This means that at the ATF
areas E.sub.1 and E.sub.2 the width at which the head hb scans the track
T.sub.3 is equal to the width at which it scans the track T.sub.5 while a
center of the width of the track T.sub.4 aligns with a center of the width
of the head hb.
FIG. 3B shows waveforms of the reproduced signals when the head hb scans
the track T.sub.4 in an offset manner toward the rightward track T.sub.5.
It will be noted that the width at which the head hb scans the rightward
adjacent track T.sub.5 increases while the width at which the head hb
scans the leftward adjacent track T.sub.3 decreases. Accordingly, as noted
from FIG. 3B, the reproduction level of the pilot signal s.sub.1 recorded
on the track T.sub.5 increases in proportion to the offset of the head hb
while the reproduction level of the pilot signal s.sub.1 recorded on the
track T.sub.3 decreases in proportion thereto.
FIG. 3C shows waveforms of the reproduction levels of the pilot signals
s.sub.1 when the head hb scans the track T.sub.3 in an offset manner
toward the leftward adjacent track T.sub.3. At that time, the reproduction
level of the pilot signal s.sub.1 on the track T.sub.3 increases while
that on the track T.sub.5 decreases.
In this manner, it will be noted that if the head scans in an offset manner
from the predetermined track, then the reproduction of the pilot signal
s.sub.1 on the adjacent track increases or decreases in accordance with
the direction and magnitude of offset.
ATF control is accomplished by sequentially detecting a difference between
the pilot signals s.sub.1 reproduced on the blocks on the adjacent tracks
and controlling a rotational velocity of a capstan, which determines the
velocity v of the magnetic tape, so that the reproduction levels are equal
to each other.
FIG. 7 shows a conventional ATF control system which accomplishes the
aforementioned ATF control.
A reproduction signal s.sub.0 amplified by an RF amplifier 1 is applied to
a low-pass filter 2 for detecting the pilot signals s.sub.1 and also to a
band-pass filter 3 for detecting the synchronizing signal s.sub.2. An
envelope detection circuit 4 receives the pilot signal s.sub.1, having a
reproduction frequency of 130.67 kHz, and supplies a level voltage signal
s.sub.3, which corresponding to the level of the pilot signal s.sub.1, to
a subtracter 6 and also to a sample and hold circuit 5 (hereafter referred
to as SH circuit). A control circuit 34 receives the synchronizing signal
s.sub.2 and supplies pulse control signals s.sub.6 and s.sub.7 at a
predetermined timing when the frequency of the synchronizing signal
s.sub.2 corresponding to the scanning head is confirmed. For example,
while the head hb scans the track T.sub.4 in FIG. 2, it detects the
synchronizing signal s.sub.2 when it reaches the block B.sub.41. When the
control circuit 34 confirms that the frequency of the synchronizing signal
s.sub.2 corresponds to the head hb, it outputs the control signal s.sub.6
at the timing t.sub.1 of FIG. 3 and the control signal s.sub.7 at the
timing t.sub.2 of FIG. 3, respectively. The SH circuits 5, 32 hold input
signals by their control signals s.sub.6, s.sub.7, respectively. Thus, it
will be noted that the SH circuit 5 holds the level voltage signal of the
pilot signal detected from the block P.sub.51 on the rightward adjacent
track T.sub.5 while the SH circuit 32 holds a level difference signal
s.sub.4 corresponding to the difference between the level voltage signal
held by the SH circuit 5 and the level voltage of the pilot signal
detected from the block P.sub.31 on the leftward adjacent track T.sub.3.
The holding operations are made every time the respective heads ha and hb
detect the corresponding synchronizing signals s.sub.2 and, therefore, the
hold signal output from the SH circuit 32 becomes a tracking error voltage
signal s.sub.5 (hereafter referred to as TE voltage signal) indicating a
tracking error.
The TE voltage signal s.sub.5 is smoothed by a smoothing circuit 33 to
provide an average voltage signal s.sub.12, which is input to a drive
circuit 12 for a capstan driving motor 13 which forms a tape transport
means. The capstan motor drive circuit 12 rotationally drives a capstan
motor 13 so that the input average voltage signal s.sub.12 becomes 0 level
and the tape velocity v is controlled by negative feedback on the average
voltage signal s.sub.12 by means of the ATF control system.
FIGS. 5A and 5B show variations in loci of the synchronizing signal s.sub.2
' and the level voltage signal s.sub.3 ' detected corresponding to the
head hb when the center position of the head hb scanning the ATF area
E.sub.1 moves over the respective tracks. It should be noted that the
synchronizing signal s.sub.2 ' and the level voltage signal s.sub.3 ' are
different from the synchronizing signal s.sub.2 and the level voltage
signal s.sub.3.
A variation in level of the synchronizing signal s.sub.2 ' shown in FIG. 5A
will be described with reference to FIG. 2. A level Vs.sub.4 of the
synchronizing signal s.sub.2 ' detected on the block B.sub.41 becomes the
maximum level when the center of the head hb scans the center of the track
T.sub.4. The level Vs.sub.4 never varies until the head hb is offset by a
quarter of the track in the positive direction toward the rightward
adjacent track T.sub.5. However, it linearly decreases when the head hb is
further offset in the positive direction because the width at which the
head hb passes through the block B.sub.41 decreases and becomes zero level
when the head hb reaches a position d.sub.4. At position d.sub.4 the head
hb is offset by a quarter of the track width from the center of the track
T.sub.5. On the other hand, a level Vs.sub.6 of the synchronizing signal
s.sub.2 ' detected on the block B.sub.61 of the track T.sub.6 linearly
increases when the head hb passes over a position d.sub.3 and becomes the
maximum level at a position d.sub.6. Thus, the variation in level is
repeated in the same manner as the level Vs.sub.4 in accordance with the
movement of the head hb in the positive direction.
It will be apparent that when the head hb is offset in the negative
direction toward the leftward adjacent track T.sub.3, the synchronizing
signal s.sub.2 ' is also detected and varies as shown in FIG. 5A. In FIG.
5A, a level Vs.sub.2 is a level of the synchronizing signal s.sub.2 '
detected on the block B.sub.21 on the track T.sub.2.
A variation in level of a level voltage signal s.sub.3 ' obtained in
accordance with the movement of the head hb will hereafter be described
with reference to FIGS. 5B and 2.
After it detects the synchronizing signal s.sub.2 ' having a higher level
than a critical value Vf on the blocks B, the control circuit 34 outputs
control signals s.sub.6 and s.sub.7 to detect levels of the pilot signals
on the adjacent tracks at the timings of t.sub.1 and t.sub.2 of FIG.
3A-3C. Thus, when the head hb lies within the range of w.sub.2 and the
level of the level voltage signal s.sub.3 ' is on the blocks P, the head
hb scans at the predetermined timing of t.sub.1 and t.sub.2 after it
passes through the blocks B.sub.21 where the synchronizing signal is
detected. When the head hb lies within the range of w.sub.4, and the level
of the level voltage signal s.sub.3 ' is on the blocks P, the head hb
scans at the predetermined timing of t.sub.1 and t.sub.2 after it passes
through the blocks B.sub.41 where the synchronizing signal is detected.
When the head hb lies within the range of w.sub.6, and the level of the
level voltage signal s.sub.3 ' is on the blocks P, the head hb scans at
the predetermined timing of t.sub.1 and t.sub.2 after it passes through
the blocks B.sub.61 where the synchronizing signal is detected.
Once the control circuit 34 detects the synchronizing signal, the
subsequent synchronizing signal is not detected until the control signals
s.sub.6 and s.sub.7 on the synchronizing signal are output. Therefore, the
synchronizing signal at the dotted line portions of FIG. 5A is never
detected.
Accordingly, when the scanning center of the head hb lies at the center of
the track T.sub.4, a level Vp.sub.1 of the level voltage signal s.sub.3 '
provided at the timing of t.sub.1 and indicated by a solid line and a
level Vp.sub.2 of the level voltage signal s.sub.3 ' provided at the
timing of t.sub.2 and indicated by a dotted line correspond to a detected
level of the pilot signal detected by the head hb on the blocks P.sub.51
and P.sub.31, respectively, and have the same level as each other as shown
in FIG. 5B. When the scanning position of the head hb is offset in the
positive direction, the level Vp.sub.1 linearly increases and the level
Vp.sub.2 linearly decreases. When the head hb reaches the position
d.sub.1, the level Vp.sub.2 becomes zero and, when it reaches the position
d.sub.3, the level Vp.sub.1 becomes maximum. Furthermore, when the head hb
passes over the position d.sub.3, it begins to detect the pilot signal on
the block P.sub. 61 at the timing of t.sub.2 and, therefore, the level
Vp.sub.2 linearly increases. When the head hb passes over the position
d.sub.7, where the detected level of the synchronizing signal on the block
B.sub.61 exceeds the critical value Vf, it falls within the range w.sub.6
and the level of the level voltage signal s.sub.3 ' on the block P at the
predetermined timing of t.sub.1 and t.sub.2 is provided after it passes
over the block B.sub.61. Accordingly, the level Vp.sub.1 becomes zero
after it reaches the position d.sub.6 and remains zero until it reaches
the position d.sub.7 where the pilot signal on the block P.sub.71 is
detected. On the other hand, the level Vp.sub.2 becomes the detected level
of the pilot signal on the block P.sub.51, is kept at the maximum level
until it reaches the position d.sub.4 and linearly decreases when it
passes thereover. Finally, when the scanning center of the head hb reaches
the center of the track T.sub.6, the levels Vp.sub.1 and Vp.sub.2 again
are equal, but the respective levels become the detected levels of the
pilot signals detected by the head hb on the blocks P.sub.51 and P.sub.71,
respectively. Also, when the head hb is offset in the negative direction,
the levels Vp.sub.1 and Vp.sub.2 of the pilot signals s.sub.3 ' are
similarly detected and vary as shown in FIG. 5B.
A variation in locus of the level voltage signal s.sub.3 ' is detected when
the scanning position of the head hb moves over the respective tracks at
the ATF area E.sub.2 will hereafter be described with reference to FIGS.
5A, 5C and 2.
At that time, variation in the locus of the synchronizing signal s.sub.2 ',
varying in accordance with the scanning position of the head hb will be
identical to that at the ATF area E.sub.1. However, variation in the locus
of the level voltage signal s.sub.3 ' is slightly different from the
aforementioned one, as shown in FIG. 5C. More particularly, when the
scanning center of the head hb is offset from the center of the track
T.sub.4 in the positive direction, the respective levels Vp.sub.1 and
Vp.sub.2 vary in the same manner as in the ATF area E.sub.1 to the
position d.sub.3. However, when it passes through the position d.sub.3,
there is no block P detected at the timing of t.sub.2 and therefore the
level of Vp.sub.2 never increases as at the ATF area E.sub.1 and,
therefore, is kept at zero. On the other hand, the level Vp.sub.1 becomes
the detected level of the pilot signal on the block P.sub.42 after the
head hb reaches the position d.sub.7 where the detecting blocks of the
synchronizing signal changes from B.sub.42 to B.sub.62 and linearly
decreases as the head hb moves in the positive direction, as shown in FIG.
5C.
Although only the variation in locus of the level of the pilot signal
detected at the ATF areas E.sub.1 and E.sub.2 when the scanning position
of the head hb moves between the tracks, the above discussion is also true
of the variation in the level of the pilot signal detected when the head
ha moves between the tracks. However, it should be noted that in this
case, the scanning position of the head ha and the variation in locus of
the pilot signal level is offset by one track as indicated by (T.sub.2),
(T.sub.3) ------ and (T.sub.8) in FIGS. 5A through 5C. The variation in
locus of the pilot signal level at the ATF area E.sub.1 is shown by FIG.
5C while that at the ATF area E.sub.2 is shown by FIG. 5B. As noted from
this, they are opposite of those of the head hb. This is due to the fact
that the position of the block B having the synchronizing signal
corresponding to the head hb and the block P having the pilot signal at
the ATF area E.sub.1 is consistent with the relation of position of the
block A having the synchronizing signal corresponding to the head ha and
the block P having the pilot signal at the ATF area E.sub.2.
The TE voltage signal s.sub.5 from the SH circuit 32 of FIG. 7 corresponds
to a differential voltage (Vp.sub.1 -Vp.sub.2) between the levels Vp.sub.1
and Vp.sub.2 obtained in synchronization with the synchronizing signal
meeting the aforementioned conditions. FIG. 5D shows a variation in level
which is obtained by subtracting the dotted line from the solid line of
FIG. 5B while FIG. 5E shows a variation in level which is obtained by
subtracting the dotted line from the solid line of FIG. 5C. Thus, it will
be understood that a differential voltage Va.sub.1 is obtained by
detecting the synchronizing signal corresponding to the ATF area E.sub.1
where the head ha is positioned while the scanning position moves between
the tracks. Likewise, a differential voltage Vb.sub.2 is obtained by
detecting the synchronizing signal corresponding to the ATF area E.sub.2
where the head hb is positioned while the scanning position moves between
the tracks vary, as shown in FIG. 5E. It will also be understood that a
differential voltage Vb.sub.1 is obtained by detecting the synchronizing
signal corresponding to the ATF area E.sub. 1 where the head hb is
positioned while the scanning position moves between the tracks and a
differential voltage Va.sub.2 is obtained by detecting the synchronizing
signal corresponding to the ATF area E.sub.2 where the head ha is
positioned while the scanning position moves between the tracks vary, as
shown in FIG. 5D.
Now, supposing that the rotary drum having heads ha and hb disposed at
identical heights on recording and moving along the identical locus
rotates at 2000 r.p.m. and having an angle between the axis of the rotary
drum and the tape running direction being equal to the reference angle
.theta.r which corresponds to the angle on recording and that the magnetic
tape runs at the tape velocity Vp which is approximately equal to the tape
velocity on recording for reproducing the ATF signal from the magnetic
tape, the scanning positions of the heads ha and hb scanning the ATF area
E.sub.1 and E.sub.2 are identical to each other relative to the center of
the corresponding tracks. In this case, the differential voltages Vb.sub.1
and Va.sub.2 on the variation of FIG. 5D and the differential voltages
Va.sub.1 and Vb.sub.2 on the variation of FIG. 5E move along the identical
axis.
Supposing that the heads ha and hb are offset in height, the scanning
positions of the heads relative to the center of the corresponding to the
tracks Tr at the ATF area E.sub.1 have a height error wh corresponding to
the offset height. This is also true of the relation of their positions at
the ATF area E.sub.2. These height errors wh can be expressed as errors
between the movement positions of the differential voltages Va.sub.1 and
Vb.sub.1 and between those of the differential voltages Va.sub.2 and
Vb.sub.2 in FIGS. 5D and 5E, respectively. These figures correspond to the
case in which the head hb is positioned lower than the head ha and the
lower head is offset in the negative direction.
Supposing that the angle between the axis of the rotary drum and the tape
running direction is inclined relative to the reference angle .theta.r on
recording, the scanning direction of the heads is never parallel to the
direction of the tracks on recording. Thus, the scanning positions of the
head ha relative to the center of the corresponding track at the ATF area
E.sub.1 and relative to the center of the corresponding track at the ATF
area E.sub.2 have an inclination error ws in accordance with their
inclination. This is also true of the head hb. These inclination errors ws
can be expressed as errors between the movement positions of the
differential voltages Va.sub.1 and Vb.sub.1 and between those of the
differential voltages Va.sub.2 and Vb.sub.2 in FIGS. 5D and 5E,
respectively. This corresponds to the case in which the angle between the
axis of the rotary drum and the tape running direction is offset by
-.DELTA..theta. relative to the reference angle .theta.r in the angle
relation of FIG. 4B. In this case, the relation of FIGS. 5D and 5E are
provided because of the scanning direction of the heads offset in the
clockwise direction.
Thus, it will be understood that the errors wh and ws of the movement
position of the heads are inevitably caused by the difference between the
head heights on recording and reproducing and the difference between the
inclinations of the axis of the rotary drum on recording and reproducing.
The variation in the tape velocity and the offset position of the heads
relative to the tracks causes the differential voltages Va.sub.1,
Va.sub.2, Vb.sub.1 and Vb.sub.2 of the TE voltage signals s.sub.5 output
from the SH circuit 32 to move along the variation locus of FIGS. 5D and
5E while the errors wh and ws are maintained. For example, if the
relationship of the tape velocity Vr on recording and the tape velocity Vp
on reproducing is (Vr<Vp), then they move in the positive direction. If it
is (Vr>Vp), then they move in the negative direction.
As noted from the foregoing, since the ATF control is accomplished by
controlling the tape velocity v so that the average level of the TE
voltage signals s.sub.5 is zero, the levels of the respective differential
voltages are stable at the positions of FIGS. 5D and 5E.
One of the disadvantages of the prior ATF control system is that it tends
to deteriorate the reproduction condition. More particularly, the heads ha
and hb scan the corresponding tracks by ATF control but, if there is a
difference between the inclinations of the rotary drum on recording and
reproducing, then the reproduction will be made on the condition that the
scanning locus is not parallel to the track direction and if the heads ha
and hb scan at different height on recording and on reproducing, then the
reproduction will be made on the condition that the center of the track is
inconsistent with the center of the heads. This causes the reproduction
condition to deteriorate. Since the prior ATF control system cannot detect
the height error of the heads and the inclination error of the rotary
drum, whether the reproduction condition is allowable cannot be
determined.
Also, in the prior ATF control system, the TE voltage signals s.sub.5
output from the SH circuit 32 are renewed by the sequential differential
voltages Va.sub.1, Va.sub.2, Vb.sub.1, Vb.sub.2 of FIGS. 5A through 5E
every time the respective heads ha and hb scan the areas E.sub.1 and
E.sub.2. Thus, if there is a head height error and an inclination error of
the rotary drum on recording and on reproducing, then there is a large
variation in the differential voltage levels in proportion to the
magnitude of the errors. The level variation can be normally expressed by
the TE voltage signals s.sub.5.
Thus, to provide for ATF control the average voltage signal s.sub.12 having
the level variation components removed from the TE voltage signal s.sub.5,
which variation components cause the errors of height and inclination.
This average voltage signal can be obtained by a smoothing circuit, but
such a smoothing circuit causes delayed response to information of
movement of the head positions on the variation in the tape velocity.
SUMMARY OF THE INVENTION
Accordingly, it is a principal object of the invention to provide an error
detection circuit adapted to detect an inclination error of a rotary drum
on recording and reproducing.
It is another object of the invention to provide an error detection circuit
adapted to detect a height error of two heads on recording and
reproducing.
It is a further object of the invention to provide an error detection
circuit adapted to detect an average voltage signal for ATF control
without a smoothing circuit.
In accordance with the present invention, there is provided an error
detection circuit for a helical scanning type magnetic reproducing
apparatus including a rotary drum having a first head and a second head
provided on the periphery thereof for reproducing pilot signals recorded
on a first area and a second area on respective tracks of a magnetic tape
adjacent to its end whereby at least one of a height error of said heads,
an inclination error of said rotary drum and the tracking error due to
said height error and said inclination error is detected on said pilot
signals so that tracking control is made, said error detection circuit
comprising:
at least two sample and hold circuits to sequentially sample and hold a
level difference between the pair of pilot signals on either of said first
and second tracks detected by one of said first and second heads with
different first and second timings in synchronization with a detection of
a synchronizing signal recorded on another track corresponding to either
of said first and second areas; and,
an operational circuit to estimate the selected ones of the outputs from
said sample and hold circuits.
In accordance with one aspect of the invention, the sample and hold circuit
group includes a first sample and hold circuit to sequentially sample and
hold a level difference between the pair of pilot signals on another track
detected by the first head with different first and second timings in
synchronization with a detection of a synchronizing signal recorded on
said first track corresponding to the first area, a second sample and hold
circuit to sequentially sample and hold a level difference between the
pair of pilot signals on another track detected by the first head with
different first and second timings in synchronization with a detection of
a synchronizing signal recorded on the first track corresponding to the
second area, a third sample and hold circuit to sequentially sample and
hold a level difference between the pair of pilot signals on another track
detected by the second head with different first and second timings in
synchronization with a detection of a synchronizing signal recorded on the
second track corresponding to the first area, and a fourth sample and bold
circuit to sequentially sample and hold a level difference between the
pair of pilot signals on another track detected by the second head with
different first and second timings in synchronization with a detection of
a synchronizing signal recorded on the second track corresponding to the
second area.
The operational circuit may be a first subtracter to obtain either of a
first level difference information between the outputs from the first and
third sample and hold circuits and a second level difference information
between the second and fourth sample and hold circuits. The first and
second level informations correspond to the angle errors of the scanning
direction of the heads relative to the track direction in which the heads
scan the tracks. In this case, the error detection circuit may comprise
only a pair of first and third sample and hold circuits or only pair of
second and fourth sample and hold circuits to detect the angle error.
The operational circuit may be a second subtracter to obtain either of a
third level difference information between the outputs from the first and
second sample and hold circuits and a fourth level difference information
between the third and fourth sample and hold circuits. The third and
fourth level difference informations correspond to the height errors
between the heads. Also, in this case, the error detection circuit may
comprise only a pair of first and second sample and hold circuits or only
a pair of third and fourth sample and hold circuits to detect the height
error.
The operational circuit may be an adder to add all the output from the
first through fourth sample and hold circuits to provide an average
voltage signal indicating an average center position of the heads relative
to the center of the tracks at the ATF areas which the heads scan.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects and features of the invention will be apparent
from the description of the embodiments of the invention with reference to
the accompanying drawings in which:
FIG. 1 is a schematic diagram of an ATF control system having an error
detecting circuit of the invention;
FIG. 2 is an enlarged front view of ATF areas of track patterns recorded,
on magnetic tape;
FIGS. 3A through 3C illustrate waveforms of reproduction levels when the
heads scan the tracks;
FIG. 4A is a perspective view of a rotary drum and a magnetic tape running
along heads of the rotary drum;
FIG. 4B illustrates a relative angle of the axis of the rotary drum
relative to a tape running direction;
FIGS. 5A through 5E illustrate level variation in synchronizing signals,
level voltage signals and differential voltages, respectively;
FIGS. 6A through 6N are time charts illustrating waveforms at the various
portions of the system of FIG. 1;
FIG. 7 is a schematic diagram of an ATF control system conventionally used
for ATF control;
FIGS. 8A and 8B illustrate examples using the circuit of the invention; and
FIG. 9 is a schematic diagram of a tracking error detection circuit
constructed in accordance with another embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1, there is illustrated an ATF control system using
the error detection circuit of the present invention wherein the same
numerals designate the same components as that of FIG. 7.
A control circuit 14 has output terminals 14.sub.1 through 14.sub.4
connected to AND gates 20 through 23 at one input terminal and, also,
through respective mono-multivibrators 15 through 18 to an input terminal
of an OR gate 19, an output terminal of which is connected to a control
signal input terminal of the sample and hold circuit (SH circuit) 5. A
control circuit 14 also has an output terminal 14.sub.5 connected to the
AND gates 20 through 23 at their other input terminals.
Sample and hold circuits (SH circuits) 7 through 10 have respective control
input terminals connected to output terminals of the AND gates 20 through
23 and normal input terminals connected to an output terminal of the
subtracter 6. An output terminal of the SH circuit 7 is connected to an
input terminal of an adder 11, a positive input terminal of a subtracter
24 and a positive input terminal of a subtracter 26. An output terminal of
the SH circuit 8 is connected to the input terminal of the adder 11, a
negative input terminal of the subtracter 24 and a positive input terminal
of a subtracter 27. An output terminal of the SH circuit 9 is connected to
the input terminal of the adder 11, a positive input terminal of a
subtracter 25 and a negative input terminal of the subtracter 26. An
output terminal of the SH circuit 10 is connected to the input terminal of
the adder 11 and negative input terminals of the subtracters 25 and 27.
An output terminal of the adder 11 is connected to the input terminal of
the capstan motor drive circuit 12 for controlling the capstan motor 13.
Output terminals of the subtracters 24 and 25 are commonly connected to an
input terminal of an adder 28 while output terminals of the subtracters 26
and 27 are commonly connected to an input terminal of an adder 29.
In the ATF control system, the control circuit 14 receives the
synchronizing signal s.sub.2 from the band-pass filter 3 to prove "H"
states of the corresponding output terminals at t.sub.1 of FIGS. 3A-3C and
output the control signal s.sub.7 from the output terminal 14.sub.5 at
timing of t.sub.2 after the frequency of the synchronizing signal s.sub.2
corresponding to the scanning head is confirmed, and after which of the
heads ha and hb detects the signal and at which of the ATF areas E.sub.1
and E.sub.2 of FIG. 2 the signals are detected are confirmed. More
particularly, a waveform of the output signal from the output terminal
14.sub.1, shown in FIG. 6A, is at a state of "H" on the synchronizing
signal s.sub.2 detected at the block A when the head ha scans the
corresponding track at the ATF area E.sub.1. A waveform of the output
signal from the output terminal 14.sub.2, shown in FIG. 6B, is at a state
of "H" on the synchronizing signal s.sub.2 detected at the block A when
the head ha scans the corresponding track at the ATF area E.sub.2.
Similarly, a waveform of the output signal from the output terminal
14.sub.3, shown in FIG. 6C, is at a state of "H" on the synchronizing
signal s.sub.2 detected at the block B when the head hb scans the
corresponding track at the ATF area E.sub.1 and a waveform of output
signal from the output terminal 14.sub.4, shown in FIG. 6D, is at a state
of "H" on the synchronizing signal s.sub.2 detected at the block B when
the head hb scans the corresponding track at the ATF area E.sub.2. As
aforementioned, the timing at which the output terminals of the control
circuit 14 are at the state of "H" is at t.sub.1 of FIG. 3A-3C.
Although how the control circuit 14 distinguishes the heads is not
described in detail herein, it can easily distinguish which of the heads
scans the tracks by obtaining the rotation information of the rotary drum
and, also, whether the scanning heads scan the corresponding tracks by
determining the frequency of the synchronizing signals reproduced by the
heads. Furthermore, it will be noted that there is a regulation of the
synchronizing signals s.sub.2 reproduced. If the synchronizing signals
detected by the head ha at the ATF areas E.sub.1 and E.sub.2 are expressed
by sa.sub.1 and sa.sub.2, respectively, and if the synchronizing signals
detected by the head hb at the ATF areas E.sub.1 and E.sub.2 are expressed
by sb.sub.1 and sb.sub.2, respectively, they regularly appear at the
sequence of sa.sub.1, sa.sub.2, sb.sub.1, sb.sub.2, sa.sub.1 . . . , and
the timings of the state of "H" at the respective output terminals can be
easily obtained by using the regulation of the synchronizing signals.
The mono-multivibrators 15 through 18 output pulses of predetermined width
in synchronization with a raising-up of the input signals. Accordingly,
the pulses of the pulse-like control signal s.sub.6 from the OR gate 19
appear at the timing of t.sub.1 of FIGS. 3A-3C, as shown in FIG. 6E, every
time the heads scan the ATF areas and the SH circuit 5 holds the level
voltage of the level voltage signal s.sub.3 at the timing of "H".
The AND gates 20 through 23 input the respective control signals from the
output terminals 14.sub.1 through 14.sub.4 of the control circuit 14 and
the control signal s.sub.7 from the output terminal 14.sub.5 thereof and
supply AND signals s.sub.8 through s.sub.11, shown in FIGS. 6G through 6J,
to the control signal input terminals of the SH circuits 7 through 10. The
SH circuits 7 through 10 receive the level difference signal s.sub.4 at
their normal input terminal and sample-hold it at the timing of "H" of the
AND signal. Thus, the SH circuit 7 outputs the TE voltage signal s.sub.51,
renewing the differential voltage Va.sub.1, the SH circuit 8 outputs the
TE voltage signal s.sub.52, renewing the differential voltage Va.sub.2,
the SH circuit 9 outputs the TE voltage signal s.sub.53, renewing the
differential voltage Vb.sub.1, and the SH circuit 10 outputs the TE
voltage signal s.sub.54, renewing the differential voltage Vb.sub.2.
FIGS. 6K through 6M show the conditions in which the TE voltage signals
s.sub.51 through s.sub.54, sequentially renewed on the respective
differential voltages, are stable at the state of level of FIGS. 5D and
5E. It will be noted that although there is no variation in the
differential voltages Va.sub.1, Va.sub.2, Vb.sub.1 and Vb.sub.2 of the TE
voltage signals from the SH circuits 7 through 10, there is a variation in
the differential voltage level every sampling when the positions of the
differential voltages of FIGS. 5D and 5E move along their loci.
The adder 11 outputs an added voltage signal s.sub.12 obtained by adding
the TE voltage signals s.sub.51 through s.sub.54. The voltage level of the
added voltage signal s.sub.12 corresponds to the average level of the
sequentially renewed differential voltages Va.sub.1, Va.sub.2, Vb.sub.1
and Vb.sub.2 to indicate an average position of the heads relative to the
center of the tracks at the ATF areas E.sub.1 and E.sub.2 scanned by the
heads ha and hb. This varies in accordance with variation in the tape
velocity. The capstan motor drive circuit 12 and the capstan motor 13 are
operated by receiving the added voltage signal s.sub.12 in the same manner
as the system of FIG. 7.
It should be noted that a smoothing circuit may be provided at a rear stage
of the adder 11 in order to obtain a desired characteristic of ATF
control, if necessary.
The subtracter 24 outputs an inclination error signal s.sub.13 which
corresponds to a level difference (Va.sub.1 -Va.sub.2) between the TE
voltage signals s.sub.51 and s.sub.52. The subtracter 25 outputs an
inclination error signal s.sub.14 which corresponds to a level difference
(Vb.sub.1 -Vb.sub.2) between the TE voltage signals s.sub.53 and s.sub.54.
As noted from the description of FIGS. 5D and 5E, the level of the
inclination error signals s.sub.13 and s.sub.14 appear as a negative
voltage when the angle of the rotary drum on reproducing is inclined in a
negative direction relative to the angle .theta.r of the rotary drum on
recording and as a positive voltage when that the former is inclined in a
positive direction relative to the latter and the magnitude thereof is
approximately proportional to the error angle.
It should be noted that the aforementioned relation can be established only
when the differential voltages Va.sub.1, Va.sub.2, Vb.sub.1, and Vb.sub.2
fall within the range wa of FIG. 5D. Also, it should be noted that the
levels of the inclination error signals s.sub.13 and s.sub.14 are not
positively proportional to the error angle because the locus of movement
within the range is not linear.
The subtracter 26 outputs a height error signal s.sub.16 which corresponds
to a level difference (Va.sub.1 -Vb.sub.1) between the TE voltage signals
s.sub.51 and s.sub.53. The subtracter 27 outputs a height error signal
s.sub.17 which corresponds to a level difference (Va.sub.2 -Vb.sub.2)
between the TE voltage signals s.sub.52 and s.sub.54. As noted from the
description of FIGS. 5D and 5E, the level of the height error signals
s.sub.16 and s.sub.17 appears as a positive voltage when the height of the
head hb relative to the height of the head ha on reproducing is lower than
the height of the had hb relative to the height of the head ha on
recording and as a negative voltage when that the former is higher than
the latter and the magnitude thereof is approximately proportional to the
height error.
It should be noted that the aforementioned relation can be established only
when the differential voltages Va.sub.1, Va.sub.2, Vb.sub.1 and Vb.sub.2
fall within the range wa of FIG. 5D. Also, it should be noted that the
level of the height error signals s.sub.16 and s.sub.17 are not positively
proportional to the height error because the locus of movement within the
range is not linear.
Although, in the embodiment of FIG. 1, the inclination error signal
s.sub.15 may be formed by adding the inclination error signals s.sub.13
and s.sub.14 by the adder 28, it will be considered that the information
the signals have are approximately identical to each other. Also, the
height error signal s.sub.18 may be formed by adding the height error
signals s.sub.16 and s.sub.17 by the adder 29, it will be considered that
the information the signals have are approximately identical to each
other.
FIGS. 8A and 8B illustrate examples of using the circuit of the invention
to visually confirm the inclination error and/or the height error on the
error signals s.sub.15 and s.sub.18.
As noted from FIG. 8A, a display drive circuit 22 at its input terminal 21
receives the error signals to light dots on a display 23 corresponding to
the signal level. If the input level of the error signal is positive, then
the display 23 is lit in a positive direction from the zero position to
the dot position proportional to the input level. Similarly, if the input
level is negative, then the display 23 is lit in a negative direction from
the zero position to the dot position proportional to the input level. If
the input level is zero, then the display is lit only at the zero dot
position. When the input level is not zero, the display 23 may be lit in
the corresponding direction at all the dot positions including the zero
position.
Alternatively, as shown in FIG. 8A, a display drive circuit 22' at its
input terminal 21' inputs the error signals to light either of arrow
indicated portions 23'.sub.1 and 23'.sub.2 of a display 23' in accordance
with the positive and negative directions of the error signals. In this
case, if the input signal level is zero, then both of the arrow indicated
portions are lit.
FIG. 9 shows a tracking error detection circuit constructed in accordance
with another embo | | |
