Automatic tracking system for magnetic recording and/or reproducing apparatus

An automatic tracking system for a magnetic recording and/or reproducing apparatus is provided means for varying a phase relationship between a magnetic head and a recording track and for monitoring the level of signals reproduced by a magnetic head at various phase relationships, and means for detecting an optimal point which is centroid of the reproduced signal levels. The automatic tracking system further includes means for controlling a tape feed speed so as to establish the phase relationship of the magnetic head and the recording track, which phase relationship corresponds to an optimal phase relationship.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates recording and/or reproducing apparatus, 
recorders, pulse-code modulated (PCM) audio signal recorders and so forth. 
more specifically, the invention relates to an automatic tracking system 
for a magnetic recording and/or reproducing apparatus, which can 
satisfactorily control tape feed speed for fine tracking. 
2. Description of the Background Art 
In modern video tape recorders, automatic tracking systems provide 
automatic adjustment of tracking volume without requiring manual 
operation. In a typical automatic tracking system, the speed of a capstan 
motor is so controlled that a control signal recorded in a control track 
on a magnetic tape can be maintained in a predetermined phase relationship 
to a rotary drum. By way of this, the scanning start timing of a magnetic 
head is controlled to the same timing as a recording to assure 
reproduction of a well adjusted video image. 
The ideal reproduced control signal has a symmetric waveform with respect 
to a center and peak signal level. Using such an ideally reproduced 
control signal, the automatic tracking control can be done very 
efficiently by adjusting the capstan motor speed to obtain the peak level 
of the control signal, by adjusting the phase relationship between the 
magnetic head and the control track to obtain the peak level of the 
control signal, optimal video image reproduction can be achieved. 
However, it is not possible to obtain an ideally reproduced control signal 
due to the tolerances involved in the installation of tape drive systems 
and rotary heads, which tolerances necessarily cause slight fluctuation of 
the angle of a scanning trace of the magnetic head, or meandering of the 
scanning trace. Such tolerance in the scanning trace of the magnetic head 
versus the magnetic tape will cause distortion of the reproduced control 
signal. A distorted control signal makes it difficult to detect the 
optimal phase relationship between the magnetic head and the recording 
tracks on the magnetic tape. 
In a typical case, a practically reproduced control signal has an 
asymmetric waveform with respect to the peak level of the control signal 
or has a multi-peak waveform. when a multi-peak waveform control signal is 
reproduced, a conventional automatic tracking system selects one of the 
peaks for adjusting the phase relationship between the magnetic head and 
the tape track. In contrast to this, it has been noted that, through 
manual adjustment by means of a manually operable tracking volume, 
improved fine reproduction of the video image can be obtained at a phase 
relationship intermediate between the points where the peak level of the 
control signal is obtained. Therefore, conventional automatic tracking 
systems fail to provide optimal tracking adjustment. Additionally, in a 
case where an asymmetric waveform control signal is produced, a 
conventional automatic tracking control system adjusts the phase 
relationship between the magnetic head and the tape track at a point where 
the maximum level of the control signal is obtained though such point is 
offset from the center point where the optimal video image reproduction 
performance can be obtained. In such case, jitter causes the phase 
relationship to shift and the reproduced signal level tends to drop 
rapidly, causing a substantial degradation of the reproduced video image. 
SUMMARY OF THE INVENTION 
Therefore, it is an object of the present invention to solve the 
difficulties inherent in prior art systems. 
Another object of the present invention is to provide an automatic tracking 
system for a magnetic recording and/or reproducing apparatus, which 
automatic tracking system can compensate for the tolerance in a scanning 
trace of a magnetic head versus a recording track of a magnetic recording 
medium. 
In order to accomplish aforementioned and other objects, an automatic 
tracking system for a magnetic recording and/or reproducing apparatus, 
according to the present invention, is provided with means for varying the 
phase relationship between a magnetic head and a recording track and for 
monitoring levels of signals reproduced by a magnetic head at various 
phase relationships, and means for detecting an optimal point which is at 
the centriod of reproduced signal levels. The automatic tracking system 
further includes means for controlling a tape feed speed so as to 
establish a phase relationship of the magnetic head and the recording 
track, which corresponds to an optimum point. 
According to one aspect of the invention, a magnetic reproducing apparatus 
comprises: a rotary head drum assembly carrying a magnetic head for 
reproducing information recorded on a recording track of a magnetic 
recording medium; a drive system for feeding the magnetic recording medium 
over the rotary head; first means, associated with the drive system, for 
controlling a feeding speed of the magnetic recording medium for adjusting 
a phase relationship between the magnetic head and the recording track to 
a predetermined phase relationship; second means, cooperative with the 
first means for periodically varying the predetermined phase relationship 
by a predetermined magnitude so that the phase relationship between the 
magnetic head and the recording track is periodically shifted; third means 
for monitoring the level of a signal reproduced by the magnetic head and 
sampling the signal level at every occurrence of a predetermined sampling 
timing; and fourth means for processing a predetermined number of the 
sampled signal levels for deriving a center of integration thereof for 
setting the predetermined phase relationship to the center of integration. 
Preferably, the second means is responsive to the initiation of a 
reproducing operation for causing variation of the predetermined phase 
relationship until the predetermined number of the sampled signal levels 
is obtained by the fourth means. In such case, the second means may vary 
the predetermined phase relationship within a predetermined range defined 
by a maximum advance point and a maximum retard point which maximum 
advance and retard points are determined at points where no substantial 
variation of the reproduced signal level is caused. 
On the other hand, the rotary head drum assembly may carry a plurality of 
magnetic heads, and the fourth means derives the center of integration of 
signal levels with respect to each of the magnetic heads for deriving an 
optimal phase relationship with respect to corresponding magnetic heads 
and derives the predetermined phase relationship to be set on the basis of 
the optimal phase relationship derived with respect to each of the 
magnetic heads. In this case, the fourth means derives the predetermined 
phase relationship to be set by introducing a weighting factor. The 
magnetic reproducing apparatus may comprise a video tape recorder. In such 
case, the video tape recorder may be provided with a rotary head drum 
assembly including at least one video signal reproducing head and at least 
one audio signal reproducing head, and the fourth means derives the center 
of integration of signal levels with respect to each of the magnetic heads 
for deriving an optimal phase relationship with respect a corresponding 
magnetic head and derives the predetermined phase relationship to be set 
on the basis of the optimal phase relationship derived with respect to 
each of the magnetic heads. 
In the latter mentioned case, the magnetic recording medium may comprise a 
video tape having a video recording track on which an audio signal is 
additionally recorded by way of deeper phase recording, and the fourth 
means gives a greater weighting factor to the optimal phase relationship 
derived with respect to the audio signal reproducing head. 
In addition, the third means preferably checks signal level differences 
with adjacent sampling timings for detecting the quality of sampled signal 
level data for rejecting the sampled signal level data when the difference 
is greater than a predetermined threshold value.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, particularly to FIG. 1, there is illustrated 
a rotary head type magnetic tape recording and/or reproducing apparatus 1, 
for which the preferred embodiment of an automatic tracking system, 
according to the present invention, is incorporated. In the shown 
embodiment, the magnetic tape recording and/or reproducing apparatus 
comprises a video tape recorder which records and/or reproduces 
information related to, for example, a video movie, i.e. a video signal 
and an associated audio signal in combination. Though the following 
discussion of the preferred embodiment of the automatic tracking system 
will be concentrated on that incorporated in a video tape recorder, the 
automatic tracking system of the present invention is applicable to 
various types of screwed track type or rotary head type information 
recording, such as that in a PCM audio signal recorder. 
In the shown embodiment, the magnetic tape recording and/or reproducing 
apparatus has a rotary head drum 3, on which a magnetic tape 2 is wrapped. 
To the magnetic tape 2, a capstan is associated to transmit driving torque 
from a capstan motor 4 so that the tape can be fed over the rotary head 
drum 3 at a controlled speed determined by the capstan motor speed. The 
rotary head drum 3 carries a plurality of magnetic heads for video 
recording and/or reproduction and audio recording and/or reproduction. 
When the magnetic recording and/or reproducing apparatus operates for 
reproduction, a reproduced signal S.sub.RF is fed from the magnetic heads 
to a signal processor circuit 7 via an amplifier 6. The signal processor 
circuit 7 processes the reproduced signal S.sub.RF to output a video 
signal S.sub.V and an audio signal S.sub.A. 
A control circuit 10 includes a system controller 11, a rotary drum 
controller 12 and a capstan motor controller 13. The rotary drum 
controller 12 and the capstan motor controller 13 are cooperatively 
controlled by the system controller 11 for adjusting the phase 
relationship between the magnetic head on the rotary head drum 3 and the 
recording track o the magnetic tape 2 for fine tracking. 
For this, the rotary drum controller 12 receives a reference pulse S.sub.FG 
indicative of a predetermined reference position of the rotary head drum 
and a position pulse S.sub.PG at every predetermined angular displacement 
of the rotary head drum. Both the reference pulse and the position pulse 
are output from the rotary head drum for forming a rotary head servo 
network. The rotary drum controller 12 also receives a switching pulse 
from the system controller 11. The rotary drum controller 12 processes 
these reference signals, S.sub.FG the position pulse, S.sub.PG and the 
switching pulse, in a per se known manner to control rotational driving of 
the rotary head drum 3. As is well known, the rotary head network is 
locked in the desired rotational state of the rotary head drum for 
establishing a servo locked state for steady driving of the rotary head 
drum. on the other hand, when the servo locked state is released, the 
rotary drum controller 12 detects the servo lock released state to output 
a servo lock released indicative signal D.sub.RD to the system controller 
11. 
Furthermore, the rotary drum controller 12 is designed to detect the 
envelope of the reproduced signal S.sub.RF to produce a detected signal 
S.sub.RFK as shown in FIG. 2. The rotary drum controller 12 monitors the 
signal level of the detected signal S.sub.RFK for sampling signal level 
data at every predetermined sampling timing to, t.sub.O, t.sub.1 ... 
t.sub.n, which sampling timing is determined with respect to the reference 
signal S.sub.FG and the position signal S.sub.PG. The rotary drum 
controller 12 transfers the sampled signal level data of each magnetic 
head for each field T.sub.F to the system controller 11 at a predetermined 
timing. 
The system controller receives the sampled signal level data of each 
magnetic head and derives a sum value of the sampled level data for each 
one filed and thus derives an integrated signal level data of each 
magnetic head. This permits detection of the signal level of the 
reproduced signal S.sub.RF with high precision. 
On the other hand, the capstan motor controller 13 is designed for 
controlling the driving speed of the capstan motor in terms of the 
reference signal S.sub.FG for synchronization of the capstan speed with 
rotation of the rotary head drum 3. For this, the capstan motor controller 
13 receives a capstan control signal D.sub.C from the system controller. 
The capstan controller 13 thus adjusts the capstan speed so that a 
predetermined phase relationship between the switching pulse and a control 
signal S.sub.CTL can be established. Therefore, the phase relationship of 
the control signal S.sub.CTL stored in the control track of the magnetic 
tape thus the magnetic head in the rotary head drum can be maintained at a 
predetermined phase relationship determined by the capstan control signal 
DC. Therefore, by varying the capstan control signal DC, the phase 
relation can be varied. 
The capstan motor controller 13 detects the establishment of a phase 
relationship coincident with that represented by the capstan control 
signal D.sub.C to output a capstan motor locked state indicative signal 
D.sub.RC to the system controller 11. 
The system controller 11 is responsive to the initiation of a reproduction 
mode operation to perform the process as illustrated in FIG. 3 for 
detecting an optimal phase relationship between the recorded track on the 
magnetic tape Lo be reproduced and the magnetic head of the rotary head 
drum 3. 
The system controller 11 enters a mode of operation for determining the 
optimal phase relationship, as shown in FIG. 3, at a step SP.sub.1 
immediately after starting the process at the step SP.sub.1, initial 
setting is performed at a step SP.sub.2 In the process of the step 
SP.sub.2 control signals are output to the rotary drum controller 12 and 
the capstan motor controller 13 for initialization of the phase 
relationship. Initialization of the phase relationship is performed by 
setting the phase relationship of the magnetic head 3 and the recording 
track at a position corresponding to a neutral position of a manually 
operable tracking volume. 
In addition, the system controller 11 detects the recording mode of the 
magnetic tape to be reproduced, at the step SP.sub.2. In this process, 
discrimination is made between Hi-Fi mode recording which records audio 
signals at a deeper phase recording on a video recording track, and Normal 
mode recording which records audio signals only on an audio track. 
At a step SP.sub.3 a check is performed as to whether the rotary drum servo 
network is locked by checking for the presence of the rotary drum servo 
lock released state indicative signal D.sub.RD. As long as the rotary drum 
servo lock released state indicative signal D.sub.RD is present the answer 
at the step SP.sub.3 is negative, and the checking process is repeatedly 
and cyclically performed, awaiting the establishment of the locked state 
of the rotary drum servo. In response to termination of the rotary drum 
servo lock released state indicative signal D.sub.RD the process goes to a 
step SP.sub.4. At the step SP.sub.4, where a check is performed as to 
whether the capstan motor servo network is locked or not by checking the 
rotary drum servo locked state indicative signal D.sub.RC. At this step 
SP. the presence of the rotary drum servo locked state indicative signal 
D.sub.RC is checked to determine whether the phase relationship between 
the magnetic head and the recording track as commanded by the capstan 
control signal D.sub.C is established or not. Similarly to the step 
SP.sub.3 the process in the step SP.sub.4 is repeated until presence of 
the rotary drum servo locked state indicative signal D.sub.RC is detected. 
After detecting the presence of the rotary drum servo locked state 
indicative signal D.sub.RC at the step SP.sub.4 the sampled signal level 
data of each magnetic head, sampled over four fields by the rotary drum 
controller 12, is read out at a step SP.sub.5. By this, the signal level 
of the reproduced signal S.sub.RF of the locked state of the rotary drum 
servo and the capstan motor servo networks can be obtained. 
Therefore, at a step SP.sub.6 the read out sampled signal level data is 
analyzed for discriminating whether the data obtained is appropriate for 
use in determination of the phase relationship between the magnetic head 
and the recording track on the magnetic tape. Discrimination is 
practically performed by comparing signal level data at respective time 
points t.sub.O, t.sub.1 ... t.sub.n of each magnetic head over four fields 
and by checking whether difference of the signal level over four fields is 
within a predetermined range. When the difference in the signal level is 
out of the predetermined range due to signal drop out in reproduction of 
the recorded information, the process returns to the step SP 5 for 
obtaining fresh data for four fields. On the other hand. if the difference 
of the signal level as checked at the step SP 6 is within the 
predetermined range, a sum value of the signal levels at respective time 
points t.sub.O, t.sub.1 ... t.sub.n of the reproduced signal S.sub.RF 
reproduced by each magnetic head over four fields is derived at the step 
SP.sub.6. Subsequently, the derived sum values are temporarily stored in a 
memory. Then, at a step SP.sub.7, a check is performed whether the number 
of sum values stored in the memory is sufficient for derivation of the 
phase relationship. 
As long as the number of the stored sum values in the memory is smaller 
than a predetermined number which is required for accurately determining 
the phase relationship, the process goes to a step SP.sub.8. At the step 
SP.sub.8, the phase relationship is shifted in an advancing direction for 
a given magnitude and outputs the capstan control signal D.sub.C for 
causing variation of the phase relationship between the magnetic head and 
the recording track on the magnetic tape. By shifting the phase 
relationship the overlapping magnitude of the scanning trace of the 
magnetic head of FIG. 4 relative to the recording track of FIG. 4 can be 
varied as shown in FIG. 5. After commanding shifting of the phase 
relationship, the process returns to the step SP.sub.3. As will be 
appreciated herefrom, the steps SP.sub.3 to SP 8 are repeatedly performed 
until the number of the stored sum values reaches the predetermined 
number. During this process, when the phase relationship is advanced to a 
predetermined maximum advance magnitude, then, the process in the step 
SP.sub.8 is switched to retard the phase relationship for a given 
magnitude toward a predetermined maximum retarding magnitude. When the 
number of the stored sum values reaches the predetermined number, process 
goes to a step SP.sub.9 for deriving the phase relationship. 
The maximum advance and retard magnitudes define a range of variation in 
the phase relationship. The variation range is set in a range 
corresponding to an adjusting range of a manually operable tracking volume 
without causing substantial degradation of the reproduced video image. 
Therefore, during the process of determination of the phase relationship, 
significant degradation of the video image is never caused. 
In the process of the step SP.sub.9, an optimal phase relationship point 
.theta.H is determined by deriving an integration center according to the 
following process. 
With respect to each magnetic head, the optimal phase relationship point 
.theta.H is derived according to the following equation: 
##EQU1## 
wherein k is the phase relationship shifted from the neutral or reference 
phase relationship and 
F(k) is a sum value obtained at each phase relationship. 
The foregoing equation can be expressed as: 
##EQU2## 
In the simplified model in FIGS. 4 and 5, if the scanning trace of the 
magnetic head is smaller than the recording track, the overlapping area of 
the recording track and the scanning trace will vary as illustrated in 
FIG. 6. In general, the signal level of the reproduced signal S.sub.RF is 
variable depending upon the overlap magnitude of the recording track and 
the trace of the magnetic head. Therefore, as shown in FIG. 7, since 
conventional automatic tracking systems adjust the scanning trace 
orientation so that the scanning trace is fully overlapped with the 
recording track, the edge of the trace being overlapped with the side edge 
of the recording track, a slight off-set of the scanning path in a 
direction for reducing the overlapping magnitude may cause substantial 
variation of the signal level. On the other hand, according to the shown 
embodiment, since the scanning trace is generally oriented substantially 
at the center of the recording track (FIG. 8), slight fluctuation will 
never affect the reproduced signal level. Therefore, according to the 
shown embodiment, abrupt variation of the signal level of the reproduced 
signal will not be caused. Accordingly, a high accuracy phase relationship 
adjustment can be realized. 
For example, if the screw or pitch angle of the scanning trace of the 
magnetic head is slightly varied from the screw angle of the recording 
track, the optimal phase relationship point can be derived according to 
the process set out above with respect to FIG. 8. On the other hand, when 
the configuration of the scanning trace of the magnetic head and the 
recording track do not match to each other due to meandering of the 
scanning trace and/or the recording track, as shown in FIG. 9, for 
example, variation of the phase relationship in the advancing or retarding 
directions becomes asymmetric with respect to the point at which the peak 
level of the reproduced signal is obtained. In this case, the conventional 
automatic tracking system adjusts the phase relationship for maximum 
overlapping area so that the upper edge of the scanning trace coincides 
with the upper edge of the recording track, which has been graphically 
represented as a trapezoidal shape for simplification, as shown in FIG. 
11. In such case, slight a off-set of the scanning trace relative to the 
recording track may cause substantial and abrupt variation of the 
reproduced signal level. 
In contrast to this, according to the shown embodiment, the scanning trace 
is so oriented as to establish the optimal phase relationship according to 
the optimal phase relation point .theta.H as set forth above. By 
positioning the scanning trace at the optimal phase relation point, the 
orientation of the scanning trace with respect to the recording track 
assumes a slightly off-set position toward left from an orientation where 
the maximum overlapping area is obtained, as shown in FIG. 12. In this 
position, since the overlapping area will not cause substantial variation 
even when the position of the scanning trace fluctuates in relation to the 
recording track. Therefore, even in this case, the signal level of the 
reproduced signal remains stable. 
In case of Hi-Fi mode video tape, the optimal phase relationships 
.theta..sub.HVA and .theta..sub.HVB for the magnetic head for reproducing 
video signals and the optimal phase relationships .theta..sub.HAA and 
.theta..sub.HAB for the magnetic head for reproducing audio signals can be 
differentiated from each other, as shown in FIG. 13. The difference in the 
optimal phase relationships may represent a measure of the differences 
between the video tape recorder used for reproducing the recorded 
information and the video tape recorder used to originally record the 
information. Namely, when the difference is within a predetermined range, 
it indicates that the video and audio reproducing heads of the reproducing 
video tape recorder are positioned so as to substantially correspond to 
the position of the video tape recorder used for recording the video and 
audio information. In such case, the optimal phase relationship 
.theta..sub.AH may be derived through the following equation: 
EQU .theta..sub.AH =.theta..sub.HVA +.theta..sub.HVB +3.times.{(.theta..sub.HAA 
+.theta..sub.HAB)/2}/5 (4) 
As will be appreciated from the foregoing equation, arithmetic operation is 
not performed for simply deriving an average value but is performed to 
introduce a weighting factor. As can be seen from the foregoing equation, 
the optimal phase relationship .theta..sub.AH derived from the foregoing 
equation (4) will have greater weight for audio signal reproduction. 
On the other hand, when the difference is out of the predetermined range, 
it shows substantially low compatibility between the reproducing video 
tape recorder and the recording video tape recorder. In this case, since 
greater weight is given to the quality of audio reproduction, the optimal 
phase relationship .theta..sub.AH is determined so that the phase 
relationships .theta..sub.HVA and .theta..sub.HVB of the video reproducing 
head are adjusted within a range in which the phase relationships 
.theta..sub.HAA and .theta..sub.HAB of the audio reproduction head can be 
maintained within a given range. 
In practice, it is not possible to avoid tolerance in arrangement of the 
magnetic heads. Therefore, the optimal phase relationship for one of the 
magnetic head is not necessarily the optimal phase relationship for the 
other magnetic heads. The greater the difference between the recording 
video tape recorder and the reproducing video tape recorder the greater 
the difference between the optimal phase relationships between individual 
magnetic heads in the reproducing video tape recorder. Therefore, 
according to the preferred process of determination of the optimal phase 
relationship, the point is determined so as to achieve the optimal balance 
of the phase relationships of the individual magnetic heads. By this the 
optimal overall phase relationship for the video tape recorder can be 
obtained. 
In contrast to the above, the optimal phase relationship .theta..sub.AH in 
the normal mode magnetic tape reproduction can be derived according to the 
following equation: 
##EQU3## 
As can be appreciated herefrom, the preferred embodiment derives the 
optimal phase taking not only the difference of optimal phase 
relationships derived with respect to respective magnetic heads into 
account, but also the recording mode of the information. This assures good 
tracking performance. 
Returning to FIG. 3, after deriving the optimal phase relationship 
.theta..sub.AH through the process set forth above, the capstan motor 
control signal D.sub.C is output at a step SP.sub.10. As set forth, the 
capstan motor controller 13 then adjusts the capstan speed for 
establishing the phase relationship corresponding to the optimal phase 
relationship .theta..sub.AH as commanded by the capstan motor control 
signal D.sub.C. After outputting the capstan motor control signal at the 
step SP.sub.10, process goes EXIT at a step SP.sub.11. 
As will be appreciated herefrom, the present invention fulfills all of the 
objects and advantages sought therefor. 
While the present invention has been disclosed in terms of the preferred 
embodiment in order to facilitate better understanding of the invention, 
it should be appreciated that the invention can be embodied in various 
ways without departing from the principle of the invention. Therefore, the 
invention should be understood to include all possible embodiments and 
modifications to the shown embodiments which can be embodied without 
departing from the principle of the invention as set out in the appended 
claims.