JPH0460942A - Tape traveling speed controller - Google Patents

Abstract

PURPOSE:To more precisely execute phase control by controlling the traveling speed of a magnetic recording tape while responding to control signals regenerated by first and second regenerating means so that the phases of control signals to be regenerated can not be equal each other. CONSTITUTION:First and second regenerating means 30 and 36 regenerate control signals at respectively different positions. The two regenerated control signals shift the phases each other corresponding to positional deviation between the first and second regenerating means 30 and 36. Therefore, phase control based on the control signal regenerated by the first regenerating means 30 can be executed at certain timing different form timing for phase control based on the control signal regenerated by the second regenerating means 36. Accordingly, a sampling frequency for phase control is practically increased. Thus, since the phase delay of a servo system for adjusting tape traveling speed is decreased, the traveling speed of the magnetic recording tape can be controlled more accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording/reproducing device, and in particular to capstan motor phase control for running a magnetic tape at a constant speed in a helical scan type VTR (video tape recorder). Regarding technology.

[Prior Art] FIG. 3 is a block diagram of a conventional tape running speed control device. Referring to FIG. 3, this apparatus includes a speed control circuit 10 forming a loop for detecting the rotational speed of the rotating body of the capstan and thereby controlling the rotational speed of the capstan, and a magnetic recording tape. Control recorded in (C
T L) A phase control circuit 12 that constitutes a loop for controlling the running speed of the magnetic recording tape by reproducing the signal and comparing the phase with a reference 30 Hz signal, and a phase control circuit 12 connected to the output of the phase control circuit 12. Low pass filter (LP
F) 18 is connected to the output of the speed control circuit 10 and the output of the LPF 18, and the output of the LPF 18 is connected to the speed control circuit ↑
and a subtractor 20 for subtracting the zero output and providing it to a capstan motor drive (not shown) for driving the magnetic recording tape.

The speed control circuit 10 controls F as the capstan rotates.
An FG signal head 24 for generating a G (frequency generator) signal, an amplifier 26 for amplifying the output of the FG signal head 24, and the rotation speed of the capstan, that is, the running speed of the magnetic recording tape from the output of the amplifier 26. speed detector 28 for detecting
including.

The phase control circuit 12 includes a reproduction CTL head 30 for reproducing a CTL signal recorded on a control track of a magnetic recording tape (not shown), and a reproduction CTL head 3.
an amplifier 32 for amplifying the output of 0; connected to the output of the amplifier 32 and receiving a reference 30Hz signal from the outside;
It includes a phase comparator 34 for comparing the phases of the CTL signal and the reference 30 Hz signal and outputting a phase detection signal according to the phase shift.

Referring to FIG. 3, the conventional device operates as follows. The speed control circuit 10 first outputs a signal for driving the capstan motor drive to form a loop according to the rotation speed of the rotating body of the capstan. The reproduction CTL head 30 reproduces a CTL signal recorded on a control track on a magnetic recording tape (not shown). The output of the head 30 is amplified by an amplifier 32 and provided to a phase comparator 34. The phase comparator 34 compares the phase of the reproduced CTL signal given from the amplifier 32 and the phase of the reference 30Hz signal, outputs a phase detection signal, and outputs a phase detection signal.
Give to 8. LPF ↑ 8 removes high frequency component noise from the output of the phase comparator 34 and supplies it to the subtracter 20 . A subtracter 20 subtracts the output of the speed control circuit 10 from the output of the LPF 18, and supplies the subtracted output to a capstan motor drive (not shown). The capstan motor drive, not shown, is
The capstan motor is driven based on the output of the subtracter 20. Therefore, the running speed of the magnetic recording tape is kept constant.

FIG. 4 is a waveform diagram for explaining the operation of the phase comparator 34. Referring to FIG. 4(a), the phase comparator 34 generates a reference sawtooth with a frequency of 30 Hz based on the reference 30 Hz signal. This standard sawtooth is 1/30
It is repeated to linearly change the voltage from, for example, 0■ to 5■ every second.

The reproduced CTL signal reproduced by the reproduced CTL head 30 and waveform-shaped by the amplifier 32 is shown in FIG. 4(b).
It has a waveform as shown in . The phase comparator 34 samples the reference sawtooth voltage at the falling edge (time tl) of the reproduced CTL signal. Depending on the sampled reference sawtooth voltage, the phase comparator 34
A phase detection signal (FIG. 4(C)) is output. When the reference sawtooth fluctuates between 0■ and 5■ as described above, this phase detection signal is determined by the sampled voltage or 2
．． It is set to be O when the voltage is 5V. A capstan motor drive (not shown) controls the capstan motor so that the phase detection output approaches 0 based on the phase detection output shown in FIG. 4(c) and the output of the speed control circuit 10.

By controlling the capstan motor as described above, the running speed of the magnetic recording tape is maintained at a predetermined constant speed.

[Problems to be Solved by the Invention] Conventional tape running speed control devices have the following drawbacks. The period of the CTL signal recorded on the magnetic recording tape is a predetermined constant value, for example, 33 Hz. The sampling frequency for phase control is therefore below this frequency. For example, when the sampling frequency is 30 Hz or less, a phase delay occurs in the servo system due to dead time, which deteriorates the phase margin. Therefore, it is not possible to increase the loop gain of phase control sufficiently,
The phase pull-in was slow, and a phase shift occurred in the magnetic tape running speed during steady running.

Therefore, an object of the present invention is to provide a tape running speed control device that can perform more precise phase control.

[Means for Solving the Problems] A tape running speed control device according to the present invention includes a first reproducing means for reproducing a CTL signal at a predetermined first position along the running direction of the magnetic recording tape. , a second reproducing means for reproducing the CTL signal at a predetermined second position different from the first position along the running direction of the magnetic recording tape. At the second position, the phase of the CTL signal reproduced by the first and second reproduction means is
are chosen so that they are not equal to each other. The apparatus according to the invention further includes means for controlling the running speed of the magnetic recording tape in response to the CTL signals reproduced by the first and second reproduction means.

Operation] The first reproducing means and the second reproducing means reproduce the CTL signal at different positions.

The two reproduced CTL signals are out of phase with each other in accordance with the positional shift of the first and second reproduction means.

Therefore, the phase control based on the CTL signal reproduced by the first reproduction means and the phase control based on the control signal reproduced by the second reproduction means can be performed at different timings. Therefore, the sampling frequency for phase control is substantially increased. Along with that,
The phase delay of the servo system for adjusting the tape running speed is reduced.

[Embodiment] Figure 1 is a block diagram of a tape running speed control device according to an embodiment of the present invention. Referring to FIG. 1, this device includes a speed control circuit 10, a first phase control circuit 12, and a CTL signal that is provided at a different position from the phase control circuit 12 and that is recorded on a magnetic tape (not shown). a second phase control circuit 14 which outputs a phase detection signal for phase control based on the regenerated CTL signal; Based on the CTL signal, the phase control circuit 12
．． A phase control switching circuit 16 for determining which output of 14 is used for phase control, and a phase control circuit 1
A switch 22 whose inputs are respectively connected to the outputs of the phase control circuit 12.14 and selects one of the outputs of the phase control circuit 12.14 in response to the output of the phase control circuit 16;
LPF 18 connected to the output of 2 and speed control circuit 10
and a subtracter 20 connected to the output of the LPF 18 and the output of the LPF 18.

In FIG. 1, parts that are the same as or correspond to those shown in FIG. 3 are given the same reference numerals and names. Their functions are also the same. Therefore, detailed explanations about them will not be repeated here.

Referring to FIG. 1, the second phase control circuit 14 has a reproduction C
A reproduction CTL head 36 provided at a different position from the TL head 30 and for reproducing a CTL signal recorded on a magnetic tape (not shown); and an amplifier 38 for amplifying and waveform-shaping the output of the reproduction CTL head 36; amplifier 38
and a second reference 30 Hz signal, the phase comparator 40 detects a phase shift in tape running and outputs a phase detection signal. Note that the reference 30Hz given to the phase comparator 34 of the first phase control circuit 12
The signal will hereinafter be referred to as the first reference 3QHz signal.

The phase control switching circuit 16 has an input connected to the output of the amplifier 32, and a tri-force pulse generation circuit 42 that generates a tri-force pulse that determines the timing for phase comparison and sampling based on the output of the amplifier 32. and a sampling circuit 46 for setting a flip-flop 50, which will be described later, in response to the falling edge of the l. a trigger pulse generation circuit 44 for generating trigger pulses for phase control and sampling based on the output of;
In response to the timing determined by the falling edge of the trigger pulse generated from the trigger pulse generation circuit 44, a sampling circuit 48 for resetting a flip-flop 50, which will be described later, and a sampling circuit 46 set the signal. The flip-flop circuit (F/F) 50 is reset.

The output of F/F 50 is used to control switch 22.

In the embodiment shown in FIG. 1, the reproduction CTL heads 30, 36 are mounted at positions offset from each other by an odd multiple of 1/2 the period of the CTL signal. The second reference 30Hz signal is half a cycle out of phase compared to the first reference 30Hz signal. As a result, the second phase control circuit 14 samples the second reference signal in the middle of the sampling of the reference signal by the first phase control circuit 12 .

FIG. 2 is a waveform diagram for explaining the operation of this device. The operation of this embodiment will be explained with reference to FIGS. 1 and 2. The speed control circuit 10 outputs a signal for controlling the capstan motor based on the FG multiplied signal as in the conventional case. 1st digit"-1 The coarse control circuit 12 also controls the playback CTL head 30 as in the past.
A phase detection signal indicating a phase shift is output based on the CTL signal reproduced by.

In the second phase control circuit 14 as well, the following operation is performed similarly to the first phase control circuit 12. Regeneration C
The TL head 36 is connected to the head 30 at one cycle of the CTL signal.
The CTL signal is reproduced at a position separated by an odd number of /2. The amplifier 38 amplifies the output of the head 36, shapes the waveform, and supplies the output to a phase comparator 40 and a trigger pulse generation circuit 44. The output of the amplifier 38 is a signal that is shifted by an odd number of half cycles compared to the output of the amplifier 32, depending on the shift in the position of the reproduction CTL head 30.36.

The outputs of amplifiers 32 and 38 are provided to trigger pulse generation circuits 42 and 44, respectively. Trigger pulse generation circuit 4
The reproduced CTL signal given to 2.44 is shown in Fig. 2(b).
, it is shown in (f).

Referring to FIG. 2(c), the trigger pulse generation circuit 42 generates a trigger pulse that rises (at time t1) in response to the rise and fall of the reproduced CTL signal and falls after a predetermined time at time t2. Occur.

The pulse width of the trigger pulse is selected to be long enough for the phase comparison in the phase comparator 34 to be completed. The phase comparator 34 samples the reference sawtooth voltage shown in FIG. 2(a) at the timing determined by the rising edge of the reproduced CTL signal as described above, and samples the reference sawtooth voltage shown in FIG. 2(d). Outputs a phase detection signal. The method of creating the reference sawtooth and phase detection signal is the same as the conventional method.

The trigger pulse generation circuit 44 generates a trigger pulse that rises at the rising edge (time t3) of the reproduced CTL signal (FIG. 2(f)) reproduced by the reproduced CTL head 36 and falls after a predetermined time (second pulse). Figure (g)). Based on the second reference 30Hz signal, the phase comparator 40
A reference sawtooth as shown in FIG. 2(e) is generated. This sawtooth has a waveform similar to that of the sawtooth generated in the phase comparator 34, but is shifted in phase by half a period. The phase comparator 40 samples the reference sawtooth voltage at the rise of the reproduced CTL signal and outputs it as a phase detection signal (FIG. 2(h)). The pulse width of the trigger pulse is wide enough to complete the phase comparison process in the phase comparator 40.

The sampling circuit 46 detects the falling edge of the trigger pulse applied from the trigger pulse generation circuit 42 and sets the F/F 50. The sampling circuit 48 selects the F/F at a timing determined by the falling edge of the trigger pulse given from the trigger pulse generation circuit 44.
Reset 50. This situation is shown in FIG. 2 (1).

The switch 22 selects the output of the first phase control circuit 12 when the output of the F/F 50 is at a high level, and selects the output of the F/F 50.
When the output of 50 is at a low level, the output of the second phase control circuit 14 is selected. Therefore, the value of the phase error output from the switch 22 changes in synchronization with the falling edge of the trigger pulse generated by the trigger pulse generation circuits 42 and 44, as shown in FIG. 2(j). It becomes a signal.

As can be easily seen by comparing FIG. 4(C) and FIG. 2(D), the value of the phase error output obtained in the tape running speed control device according to the present invention is half that of the conventional one. It changes at time intervals.In other words, a phase error signal similar to that obtained when the sampling frequency for phase control is doubled is obtained.The phase error signal more faithfully represents the phase shift. By performing phase control based on this phase error signal, it is possible to increase the loop gain of the servo system and speed up phase pull-in.As a result, it is possible to reduce the phase shift that occurs even in steady state. .

In the embodiment described above, the two reproduction CTL heads are
They were provided at positions separated from each other by an odd number multiple of 1/2 of the period of the CTL signal. However, the invention is not limited thereto. For example, three or more reproduction CTL heads may be used.

As the number of reproduction CTL heads increases, the loop gain of the servo system increases. In this case, the phase shift between each reference sawtooth may also be changed in accordance with the position shift of each reproduction CTL head.

[Effects of the Invention] As described above, according to the present invention, the phase control of the tape running drive system is performed based on the two control signals reproduced by the first reproduction means and the second reproduction means. The sampling frequency for phase control is substantially increased and the dead time in phase control is reduced. Therefore, the loop gain of the phase control can be increased, the phase can be pulled in quickly, and the phase shift of the servo system during steady state can be reduced.

Therefore, it is possible to provide a tape running speed control device that can control the running speed of a magnetic recording tape with more precision.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a tape running speed control device according to the present invention, FIG. 2 is a waveform diagram showing the operation of the device according to the present invention, and FIG. 3 is a conventional tape running speed control device. FIG. 4 is a block diagram of the device, and FIG. 4 is a waveform diagram showing the operation of the conventional device. In the figure, 10 is a speed control circuit, 12.14 is a phase control circuit, 16 is a phase control switching circuit, 18 is an LPF, 20 is a subtracter, 22 is a switch, 30.36 is a reproduction CTL head,
34.40 is a phase comparator, 42.44 is a trigger pulse generation circuit, and 50 is a flip-flop. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] (1) A tape running speed control device for running a magnetic recording tape, on which a control signal having a predetermined period is recorded, at a constant speed by controlling a tape drive device, the tape running speed control device comprising: running the magnetic recording tape at a constant speed by controlling a tape drive device; a predetermined first
a first reproducing means for reproducing the control signal at a position; and a first reproducing means for reproducing the control signal at a predetermined second position different from the first position along the running direction of the magnetic recording tape. a second reproducing means; the second position is selected such that the phases of the control signals reproduced by the first and second reproducing means are not equal to each other; and means for controlling the running speed of the magnetic recording tape in response to the reproduction signal reproduced by the reproduction means.