JPH061580B2 - Servo mechanism of magnetic recording / reproducing apparatus - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotary head type helical scan type magnetic recording / reproducing apparatus, and more particularly to a servo mechanism for performing a stable reproducing operation.

[Background of the Invention]

A magnetic recording / reproducing device of a rotary head type helical scan system in which a magnetic tape is spirally wound around a head drum equipped with a pair of rotary heads to run, and the magnetic tapes are alternately scanned by each rotary head ( (Hereinafter, simply referred to as a magnetic recording / reproducing device),
A servo mechanism is provided so that the rotary head accurately scans a track on the magnetic tape during normal reproduction. This servo mechanism controls the speed and phase of the drum motor that rotationally drives the rotary head pair and the capstan motor that drives the magnetic tape to drive the rotation of the rotary head pair and the running of the magnetic tape in the same state as during recording. I am trying to do it.

FIG. 6 is a block diagram showing an example of a conventional servo mechanism of such a magnetic recording / reproducing apparatus. 1 is a magnetic tape, 2 is a capstan motor, 3 is a frequency generator, 4 is a control head, 5 is motor control. Circuit, 6 is a summing amplifier, 7
Is a speed control circuit, 8 is a switch, 9 is a sample hold circuit, 10 is a trapezoidal wave generation circuit, 11 is a head drum, 1
2 is a head pair, 13 is a drum motor, 14 is a frequency generator, 15 is a rotational phase detector, 16 is a motor control circuit, 1
7 is a summing amplifier, 18 is a speed control circuit, 19 is a switch,
20 is a head switching signal generation circuit, 21 is a trapezoidal wave generation circuit,
22 is a sample hold circuit, 23 is a reference signal generator,
24 is an input terminal.

In the figure, the frequency generator 14-speed control circuit 18-
The summing amplifier 17-the motor control circuit 16 is the drum motor 1
3, the rotational phase detector 15-head switching signal generation circuit 20-trapezoidal wave generation circuit 21-sample and hold circuit 22-switch 19-summing amplifier 17-motor control circuit 16 is a phase control system for the drum motor 13. In addition, the frequency generator 3-speed control circuit 7-summing amplifier 6-motor control circuit 5 is the capstan motor 2
The control head 4, the trapezoidal wave generating circuit 10, the sample and hold circuit 9, the switch 8, the summing amplifier 6 and the motor control circuit 5 constitute the phase control system of the capstan motor 2.

First, the operation at the time of normal reproduction of this prior art will be described with reference to FIG. 7 showing the signal waveform of each part in FIG.

At this time, the capstan motor 2 rotates to drive the magnetic tape 1, and the drum motor 13 also rotates to drive the rotary head pair 12 to rotate, and the rotary heads of the rotary head pair 12 are alternately magnetically driven. The track on the tape 1 is scanned to reproduce the video signal. The switches 8 and 19 are closed.

The frequency generator 14 generates a rotation signal having a frequency proportional to the rotation speed of the drum motor 13, and the rotation signal is supplied to the speed control circuit 18 to generate a voltage proportional to the cycle of the rotation signal, that is, the speed control signal. Is generated.

Further, the rotation phase detector 15 generates a tack pulse TP synchronized with the rotation phase of the drum motor 13, the tack pulse TP is supplied to the head switching signal generation circuit 20, and has a cycle equal to the rotation cycle of the drum motor 13. Then, a rectangular head switching signal SP having a duty ratio of 50% is generated. The head switching signal SP is supplied to a switching circuit (not shown) to alternately switch the video signals reproduced by the rotary heads of the rotary head pair 12 to obtain a continuous video signal. Wave generation circuit 21
Will also be supplied. The trapezoidal wave generation circuit 21 generates a trapezoidal wave signal LH rising at a predetermined inclination angle from the falling edge of the head switching signal SP, and the trapezoidal wave signal LH is supplied to the sample hold circuit 22. The sample-hold circuit 22 is also supplied with a pulse-shaped reference signal RP from the reference signal generator 23, and uses the reference signal RP as a sampling pulse to sample and hold the trapezoidal wave signal LH. The voltage obtained by this represents the phase difference between the head switching signal SP and the reference signal RP, and hence the difference between the rotation phase of the drum motor 13 and the phase of the reference signal RP, and is added as a phase control signal via the switch 19. It is supplied to the amplifier 17 and added to the speed control signal from the speed control circuit 18.

The output signal of the summing amplifier 17 is supplied to the motor control circuit 16, and as a result, the drum motor 13 is speed-controlled by the speed control signal so as to rotate at a steady rotation speed, and the rotation phase is changed to the reference signal by the phase control signal. The phase is controlled so as to have a predetermined relationship with the phase of RP.

The above is the operation of the control system of the drum motor 13, and next,
The operation of the control system of the capstan motor 2 will be described.

The frequency generator 3 generates a rotation signal having a frequency proportional to the rotation speed of the capstan motor 2, and the rotation signal is supplied to the speed control circuit 7 to generate a voltage proportional to the cycle of the rotation signal, that is, the speed control signal. Is generated.

Further, the reference signal RP from the reference signal generator 23 is supplied to the trapezoidal wave generation circuit 10, and a trapezoidal wave signal LT which rises at a predetermined inclination angle after a certain time delay is generated from the reference signal RP to generate the sample hold circuit 9. Is supplied to. On the other hand, the control signal CP recorded in the longitudinal direction of the magnetic tape 1 is reproduced by the control head 4. The control signal CP is supplied to the sample hold circuit 9 as a sampling pulse to sample and hold the trapezoidal wave signal LT. The voltage obtained by this represents the phase difference between the control signal CP and the reference signal RP, and as a phase control signal, via the switch 8,
It is supplied to the adding amplifier 6 and added with the speed control signal from the speed control circuit 7.

The output signal of the summing amplifier 6 is supplied to the motor control circuit 5, and as a result, the capstan motor 2 is speed-controlled by the speed control signal so as to rotate at a steady rotation speed,
Further, the phase control signal controls the phase of the control signal CP and the reference signal RP so that they have a predetermined phase relationship.

In this way, the rotary head pair 12 rotates at a steady speed and the magnetic tape 1 runs at a steady speed, and the rotation phase of the rotary head pair 12 and the control signal CP phase by the control head 4 are the reference signal RP. The rotary head pair 12 accurately reproduces and scans a track (not shown) on the magnetic tape 1 by setting a predetermined relationship via the.

By the way, in this conventional technique in which the speed control and the phase control are performed on the drum motor 13 and the capstan motor 2, respectively, the drum motor 13 and the capstan motor 2 are activated when the stop mode is changed to the reproduction mode. Since the respective rotation speeds change in sequence from the beginning until the steady rotation speed is reached, there is no point in performing the phase control during that time. Rather, if the phase control is performed from the start-up, this affects the speed control, and the drum motor 13
Also, the time from the activation of the capstan motor 2 to the reaching of the steady rotation speed becomes unduly long. Therefore, at the time of startup, only the speed control system is operated, and the phase control system is operated after the drum motor 13 and the capstan motor 2 reach the steady rotation speed.

That is, if it is now in the stop mode, the drum motor 13 and the capstan motor 2 are stopped, and at this time, the switches 8 and 19 are open.

Therefore, when the start command signal ST is supplied from the input terminal 24, the speed control circuits 7 and 18 are activated respectively,
At this time, since the rotation signal is not supplied, a high voltage speed control signal is generated. The speed signal output from the speed control circuit 18 is sent to the motor control circuit 16 via the adding amplifier 17.
Is supplied to the drum motor 13 and the drum motor 13 is activated and starts to rotate. Similarly, the speed control signal output from the speed control circuit 7 is supplied to the motor control circuit 5 via the addition amplifier 6, and the capstan motor 2 starts to rotate.

When the drum motor 13 and the capstan motor 2 start to rotate, a rotation signal is supplied to each of the speed control circuits 18 and 7, and thereafter, the speed control control described above is performed,
The drum motor 13 and the capstan motor 2 are accelerated until the steady rotation speed is reached. During that time, the phase control signal is output from the sampling and holding circuits 22 and 9, but the phase control is not performed because the switches 19 and 8 are open.

When the drum motor 13 and the capstan motor 2 start to rotate at a steady rotation speed, the speed control circuits 18 and 7 detect this from the frequency of the supplied rotation signal and output a switch signal respectively to output a switch 19, Close 8.

Then, the phase control of the drum motor 13 and the capstan motor 2 is started. In the phase control system of the drum motor 13, when the phase relationship between the operation start reference signal RP and the head switching signal SP is random, as shown in FIG. 7, the reference signal RP is the trapezoidal wave signal LH. A phase control signal, which changes greatly until it is located in the vicinity of the center of the inclined portion of the, is supplied to the motor control circuit 16. Further, in the phase control system of the capstan motor 2, the phase relationship between the control signal CP and the reference signal RP is also random, as shown in FIG. 7, a trapezoidal wave whose phase is delayed from the reference signal RP. A phase control signal that greatly changes until it is located near the center of the inclined portion of the signal LT is supplied to the motor control circuit 5.

By the way, in the magnetic recording / reproducing apparatus, the rotational speed of the capstan motor 2 is switchable so that standard recording / reproducing, long-time recording / reproducing, or special reproduction such as slow-motion reproduction or search reproduction can be performed. In addition, the switching of the rotation speed is performed quickly,
After this switching, the inertia applied to the capstan motor 2 is made sufficiently small so that the running speed of the magnetic tape 1 is quickly stabilized. For this reason, as shown in FIG. 8, a period from when the start signal ST is supplied from the input terminal 24 to when the capstan motor 2 reaches the steady rotation speed and the switch 8 is closed (hereinafter referred to as a speed pull-in period). t '
_B1 and the period from the closing of the switch 8 until the rotational phase of the capstan motor 2 stabilizes (hereinafter referred to as the phase pull-in period, during which the phase control signal EB supplied to the summing amplifier 6 greatly fluctuates). _t'B2 is relatively short.

On the other hand, the uneven rotation of the rotary head pair 12 is lost,
In order to always rotate at a constant rotation speed, the inertia of the drum motor 13 is sufficiently increased by increasing the weight of the head drum 11. As a result, the responsiveness of the speed and phase of the drum motor 13 is significantly inferior to that of the capstan motor 2, and as shown in FIG. 8, the drum 8 is supplied after the start command signal ST is supplied to the input terminal 24. When the motor 13 reaches the steady speed, the switch 1
9 closes speed retraction period t _{'A1 up,} and, phase pull period a significant variation occurs in the phase control signal EA supplied to the summing amplifier 17 to the rotational phase is stabilized in the drum motor 13 from the switch 19 is closed _t'A2 becomes very long.

In this way, the drum motor 13 and the capstan motor 2 are
If at least one of the two is in an unstable state during the velocity pull-in period or the phase pull-in period, the rotary head pair 12 cannot accurately scan the track on the magnetic tape 1, and as a result, the reproduced image is disturbed. Will be lost.

Therefore, in order to prevent such disturbed playback images from being displayed on the monitor, the unstable operation period of the servo mechanism (hereinafter referred to as the start-up transition period) during the transition from the stop mode to the playback mode, the playback to the monitor The video signal is being cut. As described above, the length of the transition period at the time of start-up is determined by the control system of the drum motor 13, and is the longest when the head switching signal SP is 180 ° out of phase with the reference signal RP, The cut period of the reproduced video signal to the monitor (hereinafter, monitor cut period) must be set longer than this.

From this, the transition period at the time of startup reaches several seconds and is very long, and during that time, many necessary screens are lost due to the monitor cut.

[Object of the Invention]

An object of the present invention is to provide a servo mechanism of a magnetic recording / reproducing apparatus, which can shorten the transient period at the time of startup and obtain a stable reproduced image quickly after the startup, except for the above-mentioned drawbacks of the prior art. There is.

[Outline of Invention]

To achieve this object, the present invention uses a head switching signal phase-synchronized with the drum motor during a period until the drum motor reaches a steady rotation speed by speed control when shifting from the stop mode to the reproduction mode. Phase control the generator to set the head switching signal and the reference signal in a predetermined phase relationship, and after the drum motor reaches a steady rotation speed, the head switching signal set in the predetermined phase relationship It is characterized in that the phase of the drum motor is controlled by using the reference signal so that the period during which the drum motor is brought into the steady rotation phase state is significantly shortened.

Example of Invention

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a servo mechanism of a magnetic recording / reproducing apparatus according to the present invention, in which 23 'is a reference signal generator, 25 is a switch, 26 is a control signal generating circuit, and FIG. The same reference numerals are given to the portions corresponding to, and the overlapping description will be omitted.

The operation of this embodiment will be described with reference to FIG.
It will be described with reference to the drawings.

In the stop mode, the switch 19 is open and the switch 25 is closed. As described above, when the start command signal ST is supplied from the input terminal 24, the speed control circuit 18 starts operating, and the drum motor 13 is started, the tack pulse 15 of the frequency generator 15 is generated and the head switching signal is generated. The circuit 20 generates the head switching signal SP, and therefore the trapezoidal wave generation circuit 21 generates the trapezoidal wave signal LH. This trapezoidal wave signal LH, together with the sample hold circuit 22,
It is supplied to the reference signal generator 23 ′ via the switch 25.

The reference signal generator 23 'is phase-controlled by the trapezoidal wave signal LH supplied through the switch 25 so that the reference signal RP is located at the center of the inclined portion of the trapezoidal wave signal LH. As a specific example of the reference signal generator 23 ',
A reference oscillator, a frequency divider that divides the clock from the reference oscillator, and a pulse generator that generates a pulse that is phase-synchronized with the trapezoidal wave signal LH, and the frequency divider is preset by this pulse. , Reference signal R from frequency divider
P is obtained. Therefore, until the drum motor 13 reaches the steady rotation speed, the rotation speed of the drum motor 13 changes and the phase of the trapezoidal wave signal 21 changes with it, and the phase of the reference signal RP also follows this. By changing, the phase relationship between the reference signal RP and the trapezoidal wave signal LH is kept constant.

After that, when the drum motor 13 reaches the steady rotation speed,
The switch signal from the speed control circuit 18 causes the switch 19 to close and the switch 25 to open. As a result, the phase of the reference signal RP holds the phase set immediately before the switch 25 is opened, and the reference signal RP is located at the center of the slope of the trapezoidal wave signal LH supplied to the sample hold circuit 22. There is. The phase control signal output from the sample hold circuit 22 is fed back to the drum motor 13 via the switch 19, the addition amplifier 17, and the motor control circuit 16 to control the phase of the drum motor 13. In the rotating state, the reference signal RP is phase-locked so that the reference signal RP is positioned slightly displaced from the center of the inclined portion of the trapezoidal wave signal LH by the offset of each element forming the loop of the phase control system. For this reason, when the switch 19 is closed and the switch 25 is opened, the reference signal RP is located at the center of the inclined portion of the trapezoidal wave signal LH and deviates from the position of the drum motor 13 in the steady rotation state. A phase control signal is output from the sample-hold circuit 22 so that the shift amount is eliminated (that is, the reference signal RP is drawn into a position slightly shifted from the center of the inclined portion of the trapezoidal wave signal LH as described above). Then, a phase pull-in period occurs in which the phase of the drum motor 13 is controlled. However, since the shift amount is very small, as shown in FIG. 3, the fluctuation of the phase control signal EA supplied to the summing amplifier 17 to lose it is very small. The phase pull-in period t _A2 becomes extremely short, and the period until the drum motor 13 reaches a steady rotation state is a period t during which only speed control is performed when the drum motor 13 is started.
Almost equal to _A1 (Fig. 3). In the above-mentioned prior art, the period until the phase control system operates to stabilize the rotational phase of the drum motor 13 is substantially equal to or longer than the period t _A1 during which only speed control is performed. Then, it means that the period from the start of the drum motor 13 to the time when the drum motor 13 reaches the steady rotation state is significantly shortened.

The offset of each element forming the loop of the phase control system of the drum motor 13 varies depending on the magnetic recording / reproducing apparatus. Therefore, the trapezoidal wave signal LH and the reference signal in the steady rotation state of the drum motor 13 are used. The phase relationship with RP differs depending on the magnetic recording / reproducing apparatus, but by setting the loop gain sufficiently large, the reference signal RP should be set near the center of the sloped portion of the trapezoidal wave signal LH even with respect to the above variations in offset. And therefore switch 2
By setting the reference signal RP immediately before the opening of 5 at the center of the inclined portion of the trapezoidal wave signal LH, the phase pull-in period t _A2 can be made extremely short even if there is a variation in the offset.

On the other hand, in the control system of the capstan motor 2, the start signal ST is supplied from the input terminal 24 to control the speed of the capstan motor 2 as in the prior art.
When it rotates at a steady rotation speed, the switch 8 is closed and phase control is performed.
The phase of the reference signal RP from the reference signal generator 23 'changes until the velocity pull-in is completed. Drum motor
When the speed pull-in period t _A1 (FIG. 3) of 13 is completed, the phase control system of the capstan motor 2 operates normally and the phase pull-in operation is performed.

Therefore, as shown in FIG. 3, the phase control signal EB supplied to the summing amplifier 6 has a period t until the speed pull-in of the drum motor 13 is completed after the speed pull-in period t _B1 of the capstan motor 2 has elapsed. _B2 greatly fluctuates, and after this period t _B2 ends, a fluctuation for normal phase pull-in occurs in the phase pull-in period t _B3 .

As described above, the transient period at the time of startup in this embodiment can be greatly shortened.
As a result of changing the phase of the reference signal RP during the speed pull-in period t _A1 , the phase pull-in period of the capstan motor 2 is equivalently the sum of the period t _B2 and the period t _{B3 in} FIG. This is longer than the above-mentioned conventional technique, and the normal phase pull-in period t _B3 of the capstan motor 2 is longer than the phase pull-in period t _A2 of the drum motor 13. For this reason, the transition period at the time of startup in this embodiment is determined by the period from the startup of the capstan motor 13 to the steady rotation state.

The control signal generation circuit 26 shown in FIG. 1 further shortens the phase pull-in period t _B3 of the capstan motor 2 shown in FIG. 3 and further shortens the transient period at the time of startup.

The operation for this will be described with reference to FIGS. 4 and 5.

The control signal generation circuit 26 includes a control signal CP reproduced by the control head 4, a head switching signal SP generated by the head switching signal generation circuit, and the speed control circuit 1.
The switch signal generated in 8 is supplied to form a control signal representing the phase difference between the control signal CP and the falling edge of the head switching signal SP. Here, this control signal is a pulse-like signal which rises in synchronization with the control signal CP and falls at the next falling edge of the head switching signal SP.

The activated drum motor 13 reaches a steady rotation speed, and the speed control circuit 18 outputs a switch signal to switch 19
Is closed and the switch 25 is opened, the control signal generation circuit 26
Is supplied with the switch signal and outputs only the first control signal after that, and the motor control circuit 5 outputs the brake signal CB.
Supply to. The motor control circuit 5 uses this brake signal CB.
During the period T _CB , the capstan motor 2 is braked, and as shown in FIG. 5, the circuit speed S of the capstan motor 2 is forcibly changed to delay the rotational phase thereof.
As a result, the phase of the control signal CP is delayed. In this case, the control signal CP is applied during the period of the brake signal CB.
And the head switching signal SP, the control signal CP is phase-shifted toward the falling edge of the head switching signal SP after the capstan motor 2 is braked.

On the other hand, since the head switching signal SP and the reference signal RP are set in a fixed phase relationship as described above,
The phase relationship between the control signal CP and the reference signal RP is set to a predetermined value, and by appropriately selecting the braking strength, the control signal CP is placed near the center of the inclined portion of the trapezoidal wave signal LT from the trapezoidal wave generation circuit 10. It can be set and the phase pull-in period t of the capstan motor 2 is set.
_B3 (FIG. 3) can be shortened and the phase pull-in can be performed instantaneously.

Since the braking of the capstan motor 2 is applied only once during the transient period at the time of starting, it does not affect the phase characteristic of the capstan motor 2 in the steady rotation state.

Although one embodiment of the present invention has been described above, the present invention is not limited to this embodiment, and the reference signal generator 2
3'may be phase-controlled based on the head switching signal SP, and the brake signal CB may be changed to the control signal CP.
And the rising edge of the head switching signal SP, the brake signal CB may be a signal corresponding to the phase difference between the reference signal RP and the control signal CP, and the capstan may be a capstan. It is needless to say that the braking strength of the motor 2 may be changed by the brake signal CB, or may be changed within the scope of the claims.

〔The invention's effect〕

As described above, according to the present invention, since the phase pull-in period of the drum motor having low responsiveness can be significantly shortened, the transition period at the time of start-up can be greatly shortened, and the reproduced image at the time of start-up can be quickly obtained. Therefore, it is possible to provide a servo mechanism of a magnetic recording / reproducing apparatus which is stable and can greatly reduce the cut portion of the reproduced image and which has an excellent function except for the above-mentioned drawbacks of the prior art.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a servo function of a magnetic recording / reproducing apparatus according to the present invention, FIGS. 2 to 4 are waveform diagrams showing signals of respective parts in FIG. 1, and FIG. Explanatory drawing showing the rotation speed change of the capstan motor, 6th
FIG. 7 is a block diagram showing an example of a servo mechanism of a conventional magnetic recording / reproducing apparatus, and FIGS. 7 and 8 are waveform charts showing signals of respective parts in FIG. 12 ... Rotating head pair, 13 ... Drum motor, 14 ...
… Frequency generator, 15 …… Rotation phase detector, 17 …… Adding amplifier, 18 …… Speed control circuit, 19 …… Switch, 2
0 ... Head switching signal generation circuit, 21 ... Trapezoidal wave generation circuit, 22 ... Sample and hold circuit, 23 '... Reference signal generator, 24 ... Start command signal input terminal, 25 ...
…switch.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideo Nishijima 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Prefecture Home Appliances Research Laboratory, Hitachi, Ltd. (72) Inventor Takashi Takahashi 1479, Kamimizumoto-cho, Kodaira, Tokyo Hitachi My Cross Computer Engineering Co., Ltd. In-house (56) References JP-A-49-99007 (JP, A)

Claims (1)

[Claims] 1. A drum motor that rotationally drives a pair of rotary heads, starts its operation from the start, detects the rotational speed of the drum motor, obtains a speed control signal, and makes the drum motor a steady rotational speed by the speed control signal. The speed control system to set,
The phase difference between the head switching signal synchronized with the rotation phase of the drum motor and the reference signal is started after the transient period from the start of the drum motor until the state of the steady rotation speed is reached. In a servo mechanism, a magnetic recording / reproducing apparatus equipped with a phase control system for controlling the rotational phase of the drum motor with a phase control signal according to the phase control system and setting the rotational phase and the phase of the reference signal in a predetermined relationship , The phase of the reference signal of the drum motor during the transition period is synchronized with the head switching signal, and the phase of the reference signal after the passage of the transition period of the drum motor becomes the phase at the end of the transition period of the drum motor. A means for fixing the drum motor is provided so that the phase control system can quickly pull the phase of the drum motor to the reference signal after the transient period of the drum motor. Servomechanism of the magnetic recording and reproducing apparatus, wherein a configured to allow it.