JPH0566795B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to an automatic tracking device for a VTR capable of intermittent slow playback.

(b) Prior art During intermittent slow playback in which a tape is played by repeatedly moving and stopping in an azimuth recording helical scan VTR with field still playback.
Starting and braking of the capstan motor were controlled by RF switching pulses and playback control pulses (CTL) so that the rotary head could optimally trace the recording track. In FIG. 6, a is a track pattern diagram showing a head trace state during intermittent slow playback, with time t plotted on the horizontal axis and distance traveled by the head on the vertical axis. Conventionally, the brake pulse (P ₂ ) shown in e is applied to the capstan motor based on the fall timing of the pulse (P ₁ ) shown in d from the RF switching pulse shown in b and the regeneration control pulse shown in c. Intermittent driving was performed by applying a start pulse ( _P4 ) to the capstan motor at the falling timing of the pulse ( _P3 ) generated by the switching pulse after a certain period of time.

Here, a problem arises regarding tracking during intermittent slow playback.

During intermittent slow playback, the time from control pulse playback to the generation of brake pulses can be made variable, and the time can be adjusted using the tracking volume provided on the VTR body to prevent compatibility, changes over time, and temperature changes. We have responded, but
In particular, with respect to changes in the tape drive mechanism over time, there is no guarantee that the optimal tracking amount will be maintained permanently with the tracking amount once set, and frequent adjustments are required, which is inconvenient. For this reason, Japanese Patent Laid-Open No. 57-206182 proposes automatic tracking to optimize slow playback.
However, in this known method, the pulse width of a pulse generated in synchronization with a playback control signal is determined to be the same as the pulse that indicates that the playback envelope of the rotating head has fallen below a certain level and the head switching pulse when the tape is stopped. This is changed according to the phase difference, and the brake is started at the falling edge of this pulse whose width is controlled.
Only the information on the lower limit side of the reproduction envelope of the rotary head is involved in the timing of braking, and if the information on the lower limit side is not accurate due to errors in the recording track or driving conditions, the lower limit will be below a certain level. It must be said that controlling the timing of the brakes based on information about when the brakes are applied is inferior in terms of achieving the goal of not producing noise. Furthermore, the known example requires a large number of circuits for forming a sawtooth wave prior to phase comparison between the pulse indicating that the reproduction envelope has fallen below a certain level and the head switching pulse, which is undesirable in terms of circuit configuration.

(c) Problems to be Solved by the Invention The present invention enables reliable tracking during slow playback with a simple configuration.

(d) Measures to solve the problem The first head of A azimuth and the second head of B azimuth
A head and an auxiliary head disposed adjacent to the second head at A azimuth, and when the A azimuth track is played in still mode in intermittent slow playback, the A azimuth track is in the first position.
In a VTR in which the tape is stopped corresponding to the head and the auxiliary head, there is provided a detection means for detecting the difference between the start and end of the trace of the playback output obtained from the second head during still mode playback; Control means for controlling the braking timing of the capstan motor based on the output.

(e) Effect If the stop position during still mode playback is accurate, the playback output of the head trace start and end will be the same, but if the stop position is shifted, the playback output will be different, and the trace start and end will be different. There will be a difference in the playback output of the parts. At this time, the difference between the trace start and end portions is larger in the output of the second head than in the outputs of the first head and the auxiliary head. Therefore, the detection means detects the output difference between the trace start and end portions of the reproduced output from the second head, and can accurately detect even a slight deviation of the tape. This detection output is applied to a brake pulse forming circuit or the like of the control means to control the braking timing of the capstan motor so that the deviation is corrected.

(F) Example Head 1 in a VTR targeted by the present invention,
As shown in FIG. 3, the cylinders 2 and 3 are arranged at 180° different positions on the cylinder 4 via a rotary head base (not shown). At the same time, FIG. 3 schematically shows them in an enlarged manner. The first head 1 has an A azimuth, the second head 2 has a B azimuth, and the auxiliary head 3 disposed adjacent to the second head 2 has an A azimuth similarly to the first head 1.

FIG. 1 is a circuit diagram of a tracking device embodying the present invention, in which 9 is a first mono-multivibrator that generates a pulse in synchronization with the reproduction control pulse I applied to the first input terminal 4; This is a second mono-multivibrator that generates a brake pulse with a constant time width in synchronization with the fall of the output pulse low of the mono-mono-multivibrator 9. This output is given to the capstan motor 12 through the OR gate 11. Reference numeral 13 denotes a gate that masks the RF switching pulse 2 applied from the second input terminal 5 in accordance with the intermittent control signal applied via the third input terminal 6, and allows only one RF switching pulse to pass every fixed period. The intermittent control signal is formed based on a signal given from a system control circuit (not shown) during the slow playback mode. 14 is a third mono-multivibrator that generates a pulse H in synchronization with the falling edge of the RF switching pulse that has passed through the gate, and 15 generates a start pulse with a constant time width in synchronization with the falling edge of the pulse H. This is the fourth mono multivibrator. This start pulse is applied to the capstan motor 12 through the OR gate 11.

The above circuit is also provided in a conventional slow playback tracking circuit. Reference numeral 16 denotes an exclusive OR circuit to which the head switching pulse N from the second input terminal 5 is applied, and its output H is applied to the first AND gate 19. 18 is an R-S flip-flop to which a pulse obtained by inverting the output of the second mono multivibrator 10 by the inverter 17 is given as a set signal, and an output of the third mono multivibrator 14 is given as a reset signal; As shown in Figure 2, it shows a low level in standard mode playback and a high level in still playback mode, and the output is the first AND
is given as an input to gate 19 and the
Also applied to 2AND gate 20. The RF switching pulse 2 at the second input terminal 5 is applied to the fifth mono-multivibrator 21 and also to the sixth mono-multivibrator 23 via the inverter 22. The outputs of the fifth and sixth mono-multivibrators 21 and 23 are applied to a NOR gate 24, and the output of the NOR gate 24 is supplied to the second AND gate 20 as shown in FIG. The RF switching pulse number of the second input terminal 5 is the first,
It is directly applied to the second AND gates 19, 20 through the line 25, so that the outputs of the first and second AND gates 19, 20 become as shown in FIG. The reproduced output of the rotary head applied from the fourth input terminal 7 is detected by the detector 26 and is also detected by the outputs of the first and second AND gates 19 and 20 in the first and second sampling circuits 27 and 28. The signal is sampled and held by the first and second hold circuits 29 and 30. The output pulse of the first AND gate 19 corresponds to the start of the trace of the second head 2 of the B azimuth, as can be seen from the relationship between R and W or F in FIG. Since this corresponds to the trace end portion of the second head 2, the playback signal outputs at the trace start portion and end portion of the second head are held in the hold circuits 29 and 30. reference〕. These outputs are compared by a comparator 31, and the comparison output is given so as to vary the time constant of the first mono-multivibrator 10.
32 is a switching circuit for switching the rotation direction of the capstan motor 12, which is normally determined by a signal applied from the fifth input terminal 8. The signal at the fifth input terminal 8 is given from the system control circuit, and exhibits a low level (rotates the capstan in the opposite direction) during reverse playback, reverse search, and shot winding during succession. is at a high level (rotating the capstan in the forward direction). However, in addition to this, when braking for still reproduction, the output of the switching circuit 32 is forcibly set to a low level during the period of the brake pulse given from the second mono multivibrator 10, so the capstan motor is It will be driven in the opposite direction when braking.

Next, the operation shown in FIG. 1 will be explained with reference to FIG. 2. First, when the slow playback button installed on the VTR is operated, an intermittent control pulse is given from the third input terminal 6 by the function of the system control circuit, so the RF switching pulse number at the second input terminal 5 is The gate can only be passed through the gate intermittently, and a pulse synchronized with the falling edge of the RF switching pulse that has passed through the gate is generated from the third mono-multivibrator 14 at regular intervals as shown in FIG. This pulse passes through the fourth mono-multivibrator 15 and is applied as a start pulse to the capstan motor 12 via the OR gate 11. This causes the capstan motor to start and rotate. Since the tape is transferred in accordance with the rotation of the capstan motor 12, a reproduction control pulse occurs as shown in FIG. 2A. In response to this, a pulse low occurs from the first mono multivibrator 9 as shown in FIG. This will brake the stun motor. At this time, a brake pulse is applied to the switching circuit 32, and the output of the switching circuit 32 is reduced to a low level only during the brake pulse period, so that the capstan motor 12 is driven in the opposite direction during braking, and effective braking is performed. . The generation timing of the brake pulse C can be controlled by controlling the time constant of the first mono-multivibrator 9 and changing the pulse width of the output pulse L of the first mono-multivibrator 9. Control of this pulse width is performed as follows. In response to the falling of the brake pulse generated from the second mono-multivibrator 10,
RS flip-flop 18 is set and its Q
The output becomes high level, making the first and second AND gates 19 and 20 conductive. In this state, in response to the RF switching pulse 2 from the second input terminal 5, the exclusive OR circuit 16 outputs an appropriate width corresponding to the beginning of the RF switching pulse 2, that is, the beginning of the head trace. This pulsech is further applied directly from the second terminal 5 to the first AND gate 19 to select only those pulses that match the trace start part of the second head 2, and the first AND gate The signal is applied from the gate 19 to the first sampling circuit 27 as a sampling pulse. On the other hand, the same
A pulse of suitable width is formed from the RF switching pulse 2 and corresponds to the end of the RF switching pulse, that is, the end of the trace, at the output side of the NOR gate 24, and of this pulse Monowo is the 2nd AND gate 1
It is applied as a sampling pulse to the second sampling circuit 28 through 9b. Therefore, the first sampling circuit 27 samples the head reproduction output of the trace start portion of the second head, and the second sampling circuit 28 samples the head reproduction output of the trace end portion of the second head. These sampled playback outputs are sent to hold circuit 2.
9 and 30 as shown in FIG. 2, respectively, and compared by a comparator 31.

In the case of an undesired trace position as shown in FIG. 4c in the still playback mode, the time constant of the first mono-multivibrator 9 is controlled to be small by the output of the comparator 31, so that the brake pulse is generated at an earlier timing. and set at the preferred trace position in FIG. 4b. Conversely, in the case of an undesired trace position as shown in FIG. 4. It is set to the preferred state shown in Fig. 4b. In addition, in FIG. 4, the arrow 33 indicates the tape 3.
4, the arrow 35 indicates the moving direction of the head, A indicates the A azimuth track, and B indicates the B azimuth track.

FIG. 5 shows the reproduction output by the heads in the three states of FIG. 4, where a, b, and c correspond to a, b, and c in FIG.
and the reproduction output by the auxiliary head 3 are the reproduction output by the second head. As can be seen from Fig. 5, when the trace position deviates from the desired trace position (Fig. 4 b) as shown in Fig. 4 a or c, it is better to use the regenerated output to trace the control signal than to use the regenerated output to form the control signal. Since the difference between the start part and the end part is large, control sensitivity is high, and reliable control can be performed even with slight deviations.

(G) Effects of the Invention According to the present invention, reliable tracking control can be performed during slow playback, and the circuit can have a simple configuration that does not require many sawtooth wave forming circuits. There is, and it is useful.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an automatic tracking device for a VTR embodying the present invention, and FIGS. 2, 3, 4, and 5 are explanatory diagrams thereof. FIG. 6 is a diagram for explaining a conventional automatic tracking device. 1...first head, 2...second head, 3...
Auxiliary head, 9...first mono-multivibrator, 12...capstan motor, 27, 28...
...First and second sampling circuits, 29, 30...
First and second hold circuits, 31... comparator, A...
...A azimuth track, B...B azimuth track.

Claims (1)

[Claims] 1. The head has first and second heads with different azimuths, and an auxiliary head having the same A azimuth as the first head and disposed adjacent to the second head, and alternately performs standard mode playback and still mode playback. In a helical scan type VTR, in which intermittent slow playback is possible by repeating the following steps, the tape is stopped during still mode playback so that the A azimuth track corresponds to the first head and the auxiliary head. a detection means for detecting a difference between a trace start part and a trace end part of the reproduction output obtained from the second head during the still mode reproduction, and means for controlling the braking timing of the capstan motor based on the output of the detection means. An automatic tracking device for a VTR, characterized by comprising: