JPH0278050A - Automatic tracking device - Google Patents

Abstract

PURPOSE:To always execute automatic tracking in a suitable range for a tape recorded in a different condition by switching an amplifier gain when an envelope outside the prescribed range is detected during the automatic tracking. CONSTITUTION:The output of an envelope detecting circuit 11 inputted through an envelope range comparing circuit 14 to a tracking shift circuit 12. When a voltage in a lower range than the prescribed value continues for >= a prescribed period, the circuit 14 sends an amplifier gain output signal (e) to an amplifying circuit 13, increases the gain, and simultaneously sends a restart signal (d) to the circuit 12. When the high voltage continues, the gain is decreased, and the restart signal (d) is sent to the circuit. On the other hand, when the voltage in the prescribed range continues, the output of the amplifier 13 is sent as an envelope signal (c) as it is. Thus, the automatic tracking can be executed for the tape recorded in the different condition.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to magnetic recording using a helical scan method in which an information signal that is sequentially FM modulated is recorded and reproduced as a recording trajectory inclined with respect to the longitudinal direction of a magnetic tape using a rotating head. This invention relates to an auto-tracking device for a playback device (VTR).

In conventional rotary two-head helical scan type VTRs, it is necessary to accurately trace the recorded video track during playback, and for this reason, the vertical synchronization signal, which is separated from the video signal to be recorded, is used during recording. A controller μ signal synchronized with the A frequency division output is recorded, and during playback, the reproduced controller μ signal is the PG which is the phase information of the cylinder.
A tracking servo is applied so as to lock at a certain phase with the head switching pulse generated by the double signal.

Therefore, as long as the track of the video signal on the recorded magnetic tape and the phase of the control signal are maintained, accurate tracking is always performed (hereinafter referred to as being compatible).

However, a tracking mono multivibrator (hereinafter referred to as tracking MM) is used to adjust the phase of the head switching pulse and the playback control signal when playing back a tape that is not compatible, such as when the VTR used for recording differs from the VTR used for playback. ), and the configuration needs to be such that optimal tracking can be achieved by manually varying this time constant. However, in self-recording playback, it is recommended that manual tracking is not necessary as much as possible.
The tracking volume center is adjusted at the factory for optimal tracking.

However, as long as the recorded tapes are not compatible, the only way to find the optimal tracking position is to turn the tracking volume during playback and monitor the image on a TV receiver.

Therefore, various methods have been proposed for automating manual tracking. Basically, in order to maximize the envelope signal reproduced from the rotating head, the phase of the head switching pulsed reproduction control signal is slightly shifted, and the magnitude of the reproduced envelope signal before and after the displacement is compared to determine the envelope signal. Determine the maximum phase.

A conventionally proposed method will be described below with reference to the drawings. FIG. 3 is a block diagram of auto-tracking during normal playback. 1 is head cylinder 2
9 is a head motor that rotates and drives the head motor, and 9 is a capstan motor. Both are rotated at predetermined speeds in a speed control circuit (not shown), and at the same time, the output of the reference oscillator 4 is divided through a divider 5 to obtain a phase reference signal a, and a phase signal of the head cylinder 2. is P
The phase of the G multiplied signal is compared by the phase comparator 3, and phase control is applied to the head motor 1 so that the phases of both signals are locked. A phase comparator 8 compares the phases of the reproduction control signals from the capstan motor 9 and controls the phase of the capstan motor 9 according to the phase difference, thereby locking the phase to a certain phase φ. At this time,
By making the time constant of the tracking MMe variable, the phase φ can be varied, that is, the relative position between the recorded track and the reproducing head can be changed.

Then, the reproduced signal obtained from the rotary head is guided to the envelope detection circuit 11 via the head amplifier 1o, and an envelope signal C proportional to the amplitude of the reproduced signal is created.

Then, at the start of auto-tracking, a certain unit amount of tracking is sequentially shifted, and the maximum tracking point is found based on the magnitude of the envelope signal C obtained at that time.

The operation beyond the problem to be solved by the invention is the basic idea of auto-tracking, and is sufficiently effective for tapes with good recording conditions.

However, in the conventional method, the gain of the envelope detection output is fixed, so for tapes with very weak recording magnetic fields, changes in the envelope are not noticeable as changes in voltage, and changes in the envelope due to phase displacement are not noticeable. I can't get it exactly right. Conversely, for a tape with a very strong recording magnetic field, the value of the envelope signal comparison circuit becomes saturated, making it impossible to find the maximum point of the envelope signal.

FIG. 2 shows three types of envelope signal waveforms in different recording states recorded in standard speed mode. Symbol C indicates an envelope signal waveform with a weak recording magnetic field, and C indicates an envelope signal waveform with a strong recording magnetic field. B shows an envelope signal waveform on a standard tape.

If you read the envelope signal of a module in the voltage range of Y and find the maximum point of the envelope signal, the change in the envelope will not be noticeable as a change in voltage, so it will not be possible to find the exact maximum point.

Conversely, when reading the envelope signal of C and finding the maximum point of the envelope signal, it becomes saturated from point C-1 to point G-2, and the true maximum point cannot be found.

Additionally, during auto-tracking, the tracking is intentionally shifted and changes in the output signal voltage are examined, so the auto-gain controller output, which automatically switches the amplifier gain of the output signal, can be used as an envelope signal during auto-tracking. I can't do it.

Means for Solving the Problems The auto-tracking device of the present invention increases the gain and performs auto-tracking again if the envelope of the reproduced signal continues to be below a certain voltage during auto-tracking. Similarly, if the voltage continues to exceed a certain level, the gain is lowered and auto-tracking is performed again.

Effect According to the above configuration, the gain is automatically adjusted according to the size of the envelope of the reproduced signal, so even if there are slight differences in the recording state of the information signal on the magnetic tape, optimal auto-tracking is always achieved. It's something to hope for.

EXAMPLE An example of the present invention will be described below with reference to the drawings. 1st
The figure is a block diagram of an auto-tracking device according to an embodiment of the present invention, and the same constituent blocks as those of the conventional example in FIG. 3 are given the same reference numerals. The difference from the conventional example is that instead of inputting the output of the envelope detection circuit 11 directly to the tracking shift circuit 12 as the envelope signal C, the output of the envelope detection circuit 11 is inputted via the amplifier circuit 13 and the envelope range comparison circuit 14. The point is that the signal is configured to be input to the tracking shift circuit 12. The envelope range comparison circuit 14 constantly monitors the level of the envelope detection output, controls the gain of the amplifier circuit 13, and simultaneously outputs an auto-tracking restart command d to the tracking shift circuit 12.

Next, the operation of this envelope range comparison circuit 14 will be explained. The envelope range comparison circuit 14 checks whether the signal has continuously deviated from a predetermined range for a certain period or more. If a voltage lower than a predetermined range continues for a certain period or more, an amplifier gain output signal e is outputted to the amplifier circuit 13 to prompt the amplifier gain to be increased.
At the same time as increasing the gain of the amplifier, an auto-tracking restart command d is output to the tracking shift circuit 12. On the other hand, if a voltage higher than the predetermined range continues for a certain period of time, an amplifier gain output signal e is outputted to the amplifier circuit 13 to urge the amplifier gain to be lowered, and at the same time, the tracking shift circuit 12 outputs the amplifier gain output signal e to lower the amplifier gain. , an auto tracking restart command +1 is output. If there is no problem, try amplifier circuit 1.
The output of No. 3 is directly input to the tracking shift circuit 12 as the envelope signal C, and the tracking maximum point is found from the magnitude of the envelope signal C obtained at this time, as in the conventional example.

Effects of the Invention According to the present invention, the level of the envelope detection circuit is monitored during auto-tracking operation, and when an envelope outside a predetermined range is detected, the amplifier gain of the envelope detection output is adjusted accordingly. By switching, auto-tracking is always possible in the optimum range even for tapes with different recording conditions.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an auto-tracking device of the present invention, FIG. 2 is an envelope signal waveform diagram, and FIG. 3 is a block diagram of a conventional auto-tracking device. 1... Head motor, 2... Head cylinder, 3... Phase comparator, 4... Reference oscillator, 6... Frequency divider, e...Tracking MM, 7. River...Control head, 8...
...Phase comparator, 9... Capstan motor, 1o... Head amplifier, 11... Envelope detector, 12... Tracking shift circuit, 13... ...Amplifier circuit, 14...Mountain envelope range comparison circuit. Name of agent: Patent attorney Shigetaka Awano and 1 other person 1st
Figure 2 Figure L U Nokiso 7゛ Figure 3 θ

Claims (1)

[Claims] By displacing the relative position of a tilted recording track formed on a tape-shaped recording medium and a rotary head that scans the tilted recording track, and by changing the size of the envelope of the reproduced signal obtained by scanning the tilted recording track with the rotary head. , an auto-tracking device that finds the best tracking point, monitors the level of envelope detection output during auto-tracking operation, and adjusts the gain of envelope detection output accordingly if it detects an envelope outside a predetermined range. An auto-tracking device characterized by switching.