JPS6218979B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic tape drive device in a video tape recorder or the like.

In video signal magnetic recording and reproducing devices using magnetic tape such as video tape recorders, in order to obtain control signals indicating the phase reference of magnetic recording even at ultra-low speeds or even still images, it is necessary to adjust the relative speed between the conventional tape and the head. It has been announced that it is more advantageous to use a magnetoresistive head (hereinafter referred to as an MR head), which is a type of magnetically responsive head, than a wire-wound ring head, which has proportional output characteristics.

A drawback of this MR head is that the output DC voltage level changes with temperature. Therefore, the applicant of the present invention has already proposed an AC coupling type control signal reproducing device that has a sufficiently small time constant with respect to temperature changes and can provide a stable control signal even when driving at very low speeds.

However, when this device stops during running and starts running again, depending on the stop position of the magnetic tape, the electric charge stored in the capacitor that makes up the AC coupling is discharged, resulting in the average control signal at the time of running again. It has been found that the difference in value levels causes trouble in the waveform shaping circuit at the next stage (see, for example, FIG. 3).

In view of the above points, the present invention detects whether or not a reproduction output signal of an AC coupled amplifier that amplifies the reproduction output of a magnetically responsive head is between a first predetermined level and a second predetermined level. A stopping prohibited area detection means is provided, and the magnetic tape is configured to be prohibited from stopping when the reproduction output signal of the AC coupled amplifier is lower than a first predetermined level or higher than a second predetermined level, By stopping the magnetic tape when the playback output signal of the AC coupling amplifier is near zero level, that is, near the average level of the playback output signal, the charging load on the capacitor of the AC coupling amplifier when stopped is minimized. However, the average level of the regenerated output signal of the AC coupled amplifier during re-running is made to remain the same as before the stop.

An embodiment of the present invention will be described below based on the drawings. FIG. 1 is a schematic overall configuration diagram of a video tape recorder in playback mode using a magnetic tape drive device according to the present invention, and 1 and 2 are video heads;
3 is a rotational phase detection magnet, and these video heads 1, 2 and rotational phase detection magnet 3 are attached to a rotating disk 4. This rotating disk 4
is rotationally driven by a DC motor 5. Reference numeral 6 denotes a rotational phase detector provided on the fixed side corresponding to the rotational phase detection magnet 3. Reference numeral 7 denotes a magnetic tape, and the magnetic tape 7 is caused to run in the direction of arrow a by a capstan 9 and a pinch roller 10, which are rotationally driven by a DC motor 8. 11
is a head switching pulse generator for switching the video heads 1 and 2; the head switching pulse generator 11 generates a rectangular wave pulse based on the signal generated by the rotational phase detector 6; The outputs of video heads 1 and 2 are alternately switched. 12
is an MR head, and the signal generated by the MR head 12 is amplified by an AC coupling type control signal regenerative amplifier 13. Reference numeral 14 denotes a stop prohibited area detection circuit composed of a window type comparator. The output of the stop prohibited area detection circuit 14 and the output of the tape stop detection circuit 15 are input to an AND gate 16, and the output of the AND gate 16 The drive information on/off switch 17 is opened/closed. Note that 18 is a drive circuit, and 19 is a differential circuit.

FIG. 2 is an output waveform diagram of the control signal regeneration amplifier 13 and the stop prohibited area detection circuit 14,
The downwardly protruding portion B of the reproduced output signal A of the control signal regenerative amplifier 13 is waveform-shaped and used as a control signal. C and D are prohibited stop area detection circuit 1
4, E and F are the stop areas of the reproduction output signal A when the magnetic tape 7 stops;
G and G indicate the same stop-prohibited areas, and correspond to the low level and high level of the output of the stop-prohibited area detection circuit 14, respectively. In other words, the end of the output waveform of the control signal reproducing amplifier 13 when the magnetic tape 7 is stopped is limited to be located at the flat portion of the reproduced output signal A.

FIG. 3 is an output waveform diagram of the control signal reproducing amplifier 13 when the magnetic tape 7 is re-traveled from a stopped state in stop-prohibited areas T and J of the reproducing output signal A, where A is the running section before stopping and B is the running section. Stop section, C
is the rerun section. The broken line O shows the correspondence of waveforms from immediately after the stop to immediately before the re-running, and within the stop section B, even the time constant of the AC coupling circuit of the control signal regenerative amplifier 13 approaches zero level. In the rerun section C, the average waveform level is different from the average waveform level before the stop. Note that the waveform average level in the rerun section C approaches the zero level even with the time constant of the AC coupling circuit.

FIG. 4 shows a specific circuit example of the control signal regenerative amplifier 13 of AC coupling type. MR head 12
is the output point 2 due to power supply Vcc and bias resistor _R1 .
0 and generates a control signal to capacitor C ₁
and a resistor R ₂ , and is amplified by an amplifier section composed of an operational amplifier 21 and resistors R ₃ and R ₄ that determine the degree of amplification, and a second signal is output to an output point 22. A reproduced output signal A as shown in the figure is obtained.

FIG. 5 shows a specific circuit example of the main part. Input point 2
A reproduction output signal A of the control signal reproduction amplifier 13 as shown in FIG. 2 is input to 3. The voltages corresponding to the threshold values C and D in Fig. 2 are set using variable resistors VR ₁ and VR ₂ , and the operational amplifier 2
The signals are input to the inverting input and non-inverting input sides of numbers 4 and 25, respectively. The operational amplifiers 24 and 25 compare the levels of the regenerated output signal A of the control signal regenerative amplifier 13 with the voltages corresponding to the levels of the thresholds C and D, and the output signals are passed through the low resistors R ₅ and R ₆ . Input to the base of transistor Tr. In this way, a rectangular wave output as shown in FIG. 2 is obtained at the collector of the transistor Tr. The output of the stop prohibited area detection circuit 14 and the output of the tape stop detection circuit 15, which becomes high level when the magnetic tape 7 stops, are input to an AND gate 16, and when the output of the AND gate 16 is high level, Switch 17 is closed. That is, the switch 17 is closed only when the magnetic tape 7 has stopped and the reproduction output signal A of the control signal reproduction amplifier 13 corresponds to the stop prohibited areas T and H. This switch 17 supplies a signal obtained by differentiating the head switching pulse from the head switching pulse generator 11 with a differentiating circuit 19 consisting of a capacitor C ₂ and a resistor R ₇ to a drive circuit 18 (FIG. 1). As a result, the magnetic tape 7 is caused to travel slightly, and the magnetic tape 7 is stopped at a position where the reproduction output signal A of the control signal reproduction amplifier 13 corresponds to the stop areas E and F. Note that a fixed resistor divided type may be used instead of the variable resistors VR ₁ and VR ₂ . Further, a corresponding logic circuit may be used in place of the AND gate 16. Further, the tape stop detection circuit 15
It determines the presence or absence of an output from a frequency generator (not shown) that is directly connected to the DC motor 8 that drives the capstan 9 (a generator that generates a frequency voltage proportional to the rotational speed, and does not generate output when the motor is stopped). This can be easily realized using a logic configuration that outputs a high level when the tape 7 is stopped.

In this way, in this embodiment, the stop prohibited area detection circuit 14 detects whether the output level of the control signal reproducing amplifier 13 is within a predetermined range, and the output of the stop prohibited area detection circuit 14 and the tape stop detection circuit 14 are used. The output of the circuit 16 and the AND gate 16
, the magnetic tape 7 stops, and the reproduction output signal A of the control signal reproduction amplifier 13 becomes the second
The switch 17 is closed by the output of the AND gate 16 only when it corresponds to the prohibited stop area G and H in the figure. Since the differentiated signal is input to the drive circuit 19, when the reproduction output signal A of the control signal reproduction amplifier 13 is stopped at a position corresponding to the prohibited stop areas G and H, the magnetic tape 7 is always in the prohibited stop area. Therefore, the DC voltage level of the regenerated output signal A of the control signal regenerative amplifier 13 does not change as shown in Fig. 3 when the control signal regenerative amplifier 13 travels slightly to the positions corresponding to E and F. .

FIG. 6 is an explanatory diagram of the recording pattern of the magnetic tape 7, 26 is a recorded video track, 27 is a recorded control signal, and this control signal 27 is used by the control signal reproducing amplifier 13 shown in FIG. This corresponds to the downwardly protruding portion B of the reproduced output signal A.

As explained above, according to the magnetic tape drive device according to the present invention, the reproduction output signal of the AC coupling type amplifier that amplifies the reproduction output of the magnetic response head has a difference between the first predetermined level and the second predetermined level. A stop-prohibited area detection means is provided for detecting whether or not the stop prohibited area detection means is located between the first and second
is lower than a predetermined level or higher than a second predetermined level. Since the magnetic tape is stopped when the magnetic tape is near the level, the charging load on the capacitor of the AC-coupled amplifier is extremely small when the magnetic tape is stopped, and the average level of the reproduction output signal of the AC-coupled amplifier is stopped when running again. It can be made almost the same as before. Therefore, when the vehicle runs again, there is no possibility that the signal processing of the reproduction control signal by the waveform shaping circuit at the next stage of the AC coupled amplifier will be hindered.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention; FIG. 1 is a schematic overall configuration diagram of a video tape recorder in playback mode using a magnetic tape drive device according to the present invention, and FIG. 2 is a diagram showing a control signal playback amplifier and a prohibited stop area. Figure 3 is a diagram of the output waveform of the detection circuit, and Figure 4 is a diagram of the output waveform of the control signal regeneration amplifier assuming that the magnetic tape has once stopped at a position corresponding to the stop-prohibited area. An example of a specific circuit of a control signal reproducing amplifier, FIG. 5 is an example of a specific circuit of the main part, and FIG. 6 is an explanatory diagram of a recording pattern of a magnetic tape. 7... Magnetic tape, 8... DC motor (capstan motor), 9... Capstan, 12...
MR head (magnetic response type head), 13... control signal regeneration amplifier (AC coupling type amplifier),
14... No-stop area detection circuit.

Claims (1)

[Scope of Claims] 1. A capstan motor that drives a magnetic tape having a control track, a magnetically responsive head that reproduces a control signal from the control track, and an AC coupling that amplifies the reproduction output of the magnetically responsive head. type amplifier, and the reproduction output signal of the AC coupled type amplifier is at a first predetermined level and the first predetermined level.
and a second predetermined level that is higher than the predetermined level of the signal, and detects whether the reproduced output signal of the AC coupled amplifier is lower than the first predetermined level. Alternatively, a magnetic tape drive device characterized in that the magnetic tape drive device is configured to prohibit the stoppage of the magnetic tape when the level is higher than a second predetermined level. 2. Claim 1, characterized in that the stop-prohibited area detection means is constituted by a window-type comparator having two levels of threshold values.
The magnetic tape drive described in Section 1.