Dynamic magnetic information storage or retrieval – General recording or reproducing – Signal switching
Reexamination Certificate
1995-09-08
2001-10-16
Neal, Regina Y. (Department: 2651)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Signal switching
C360S070000, C386S349000, C386S349000
Reexamination Certificate
active
06304399
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a head switching control apparatus and method for use in a video cassette recorder having at least two heads, and more particularly to an automatic head switching control method and apparatus which detects whether a delay time between a head switching point of time and a vertical sync signal is within a predetermined range, and generates a head switching signal according to head switching delay data in order to control a head switching operation.
The head switching control is necessarily needed to maintain a uniform relative position between a video head attached to a drum and a video signal recorded on a tape, when one frame is formed of signals picked up by a plurality of heads.
The head switching point of time is determined by the head switching signal. In a VHS system, the head switching point of time is produced at an interval of time prior to a rising edge of a vertical sync signal of a video signal ranging between five horizontal sync intervals (5H) and eight horizontal sync intervals (8H).
FIG. 1
is a waveform timing diagram showing a process of producing a head switching signal in the VHS system.
FIG. 1
shows a drum phase generation DPG signal (wave form A) and a drum frequency generation DFG signal (waveform B), which are generated from a head drum, respectively. Waveform C of
FIG. 1
shows a head switching signal for determining a head switching point of time. Waveform D of
FIG. 1
shows a vertical sync signal of a video signal. In the VHS system, the head switching point of time of the head switching signal should lead the vertical sync of the video signal by 5H through 8H centered at 6.5H. As shown by waveforms C and D in
FIG. 1
, the head switching point of time leads the vertical sync signal by 6.5H.
An interval t
H′D
for determining the head switching point of time is determined by a time t
fg
from a falling edge of the DPG signal to a first rising edge of the DFG signal and a delay time t
D
which is determined by head switching delay data which is controlled by a controller.
The relationship between the head switching delay data (hereinafter referred to as the delay data) and the delay time follows an equation (1).
t
D
=
(
N
+
1
)
·
32
f
sc
(
1
)
Here, t
D
is a delay time, N is delay data of which the unit is one byte (8 bits), and f
sc
is a color subcarrier sync frequency.
Since time t
fg
is a fixed value in a drum system, an automatic head switching control represents that the delay data varies stepwisely and delay time t
D
is controlled by the controller, in order to match a head switching point of time.
FIG. 2
is a block diagram of a conventional automatic head switching control apparatus.
In
FIG. 2
, a video processor
1
includes a pre-amplifier (not shown). The pre-amplifier detects an envelope state, that is, an amount of a video signal which is currently picked up by the video heads, and supplies the detected information to controller
2
. Controller
2
generates delay data for altering delay time t
D
according to the envelope detection signal. The output end of controller
2
is connected to a servo portion
3
. A head switching signal is determined by signals DPG and DFG applied from a drum
4
and the delay data output from controller
2
. Servo portion
3
supplies a control signal to a motor in drum
4
according to the head switching signal. The controlled drum motor rotates in drum
4
and a video signal is read out from a recording medium by the video heads attached to the drum. The read video signal is supplied to video processor
1
to detect a new envelope state. Such an operation repeats while altering the delay data, until the envelope detection signal becomes a high-level state. When a high-level envelope detection signal is applied to controller
2
from video processor
1
, the delay data at this time is stored in controller
2
.
However, the above conventional automatic head switching control method has a problem. The interval between the head switching point of time and the vertical sync signal cannot be maintained invariably in the VHS system when the pre-amplifier does not have an accurate envelope detection performance. Since the drum motor is controlled every time with respect to the delay data varying in the controller, it is another problem that it takes a considerable time to control a head switching operation due to a time taken until the velocity of the drum motor is stabilized.
SUMMARY OF THE INVENTION
Therefore, to solve the above problems, it is an object of the present invention to provide an automatic head switching control method and apparatus which detects whether an interval between a head switching point of time and a vertical sync signal is within a predetermined range, and uses delay data in order to control a head switching operation, irrespective of an envelope detection performance.
Another object of the present invention is to provide an automatic head switching control method and apparatus which alters only a head switching point of time of one head among a plurality of heads attached to a drum while finding delay data meeting a format, and then maintains the consistent velocity of a drum motor while controlling a head switching operation, thereby shortening a control time.
Thus, to accomplish the above object of the present invention, there is provided an automatic head switching control apparatus, the apparatus comprising:
a head switching signal generator for generating a head switching signal according to a drum phase generation (DPG) and a drum frequency generation (DFG) signal supplied from the drum, delay data, and a shift command signal of a head switching point of time; a format detector coupled to an output end of the head switching signal generator, for comparing the head switching signal with a vertical sync signal of a video signal and detecting whether an interval of time between both the head switching signal and the vertical sync signal meets a predetermined range; a controller for supplying the delay data and the shift command signal of the head switching point of time for each head to the head switching signal generator according to the output of the format detector; a storage portion for storing the delay data generated when the format detector judges that the format is met; and a drum phase detector for detecting a drum phase according to a drum reference signal output from a drum reference counter and the head switching signal output from the head switching signal generator, and supplying a drum phase control signal to the drum.
Also, the above object of the present invention is to provide an automatic head switching control method, the method comprising the steps of:
obtaining delay data adapted to a format while shifting the head switching point of time for a only one head; generating a head switching signal of which a head switching point of time for each head is shifted by the determined appropriate adapted delay data; and controlling a head switching operation by varying the velocity of a drum motor according to the head switching signal.
REFERENCES:
patent: 5243474 (1993-09-01), Mitsuhashi
patent: 5448367 (1995-09-01), Park et al.
Neal Regina Y.
Samsung Electronics Co,. Ltd.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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