JPS5822273Y2 - VTR servo circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a servo circuit for a VTR such as a rotating two-head VTR.

Conventionally, in order to keep the rotational speed of the rotating magnetic head constant, a generator has been provided in conjunction with the rotating shaft of the rotating magnetic head or the motor shaft.

This generator uses a magnetized disk and a multi-gap head to generate a detection output with a frequency or level depending on the rotation speed. For example, a detection signal with a frequency of about IKHz can be obtained, and fluctuations in this frequency or level can be detected. The rotational speed of the rotating magnetic head is kept constant using the error signal obtained.

However, in the above-mentioned generator, if the mechanical precision of the magnetizing disk is poor or if there is uneven magnetization, the average level of the detection signal will fluctuate, which will reduce the stability of the servo, which also results in high costs. It was something.

By the way, improvements in motors such as the development of brushless motors have made it possible to directly drive a rotating magnetic head (or drum if a rotating magnetic head is attached to a rotating drum) to the shaft of the motor. Compared to the case of using a transmission means such as the above, the time delay of the transmission characteristic can be ignored, and it is no longer necessary to generate a high frequency detection signal by the generator as described above.

FIG. 1 shows the positional relationship between a magnet piece and a pickup coil in an example of a DC servo circuit, where 1 indicates a rotating shaft of a DC motor, and 2 indicates a tape guide drum directly connected to the rotating shaft 1.

A pair of rotating magnetic heads (not shown) arranged at an angular interval of 1800 mm are fixed to this drum 2. This is similar to an ordinary rotating two-head VTR in that the two heads are in contact with each other and inclined tracks are drawn on the magnetic tape in sequence.

In this case, a rotating disk may be fixed to the rotating shaft 1 separately from the drum 2.

Then, a button is pressed on the top surface of the drum 2, and position display means, for example, six magnet pieces M1-
M6 is attached and close to this trajectory two fixed sensitive elements, such as pick-up coils 3a and 3b, are provided.

The angular spacing between the pickup coils 3a and 3b is narrower than the angular spacing (approximately 60 degrees) between the magnet pieces M1 to M6.

Furthermore, two magnet pieces M7 and M8 are attached at an angular interval of approximately 1800 degrees on the upper surface of the drum 2 so as to draw a rotation locus different from that of the magnet pieces M1 to M6.

In this case, the magnet pieces M7 and M8 are provided so that their polarities are opposite, and the detection signal generated by the pickup coil 3C provided on these trajectories is different when the magnet piece M7 approaches and when the magnet piece M8 approaches. The polarity is reversed depending on the time.

In the above detection means, the detection outputs Sla and S1b of the pickup coils 3a and 3b are supplied to amplifiers 4a and 4b, respectively, as shown in FIG.

The detection output S1a is detected by the magnet piece M19M as shown in FIG. 3A.
The detection output Slb includes a series of pulses generated each time 29M3... approaches, and the detection output Slb is a series of pulses generated with a delay time corresponding to the interval of the pickup coil: 3av3b, as shown in FIG. 3B. This includes:

Amplifiers 4a and 4b output such detection outputs Sla and Sxb.
A pulse S2a shown in FIG. 3C and a pulse S2b shown in the third diagram corresponding to the positive polarity (curved portion) of the detection output are generated at the outputs of the amplifiers 4a and 4b.

Pulse S2a is supplied as a set input to flip-flop 5, and pulse S2b is supplied as reset input to flip-flop 5, which is triggered on the rising edge of the pulse, so that the output pulse S3 of flip-flop 5 is as shown in FIG. 3E. becomes.

This output pulse S3 is supplied to a monostable multivibrator (referred to as monomulti) 6 as a trigger force,
This generates a pulse S4 with a constant pulse width as shown in FIG. A trapezoidal wave S5 having a dog shape is formed.

On the other hand, the output of the flip-flop 5 (opposite polarity to S3) is supplied to the gate pulse generation circuit 8, and the gate pulse from this causes the sampling gate circuit 9 to generate a pulse S2a.
The slope portion of the trapezoidal wave S5 is sampled at the rising edge of the trapezoidal wave S5.

This sampling output, that is, the phase comparison output is supplied to a hold circuit 10 and smoothed, and the output of the hold circuit 10 is supplied to a drive amplifier 11, and the output of the drive amplifier 11 is used to rotate the drum 1 (therefore, the rotating magnetic head). DC motor 2 is driven.

According to this configuration, as the rotational speed of the drum 1 increases, for example, the frequencies of the detection outputs Sla and S1b increase.

Since the pulse width of the output pulse S4 of the monomulti 6 is constant, the output level of the sampling gate circuit 9 becomes small, and the rotation of the motor 12 becomes slow.

In this way, the motor 12 is controlled to rotate at a constant speed.

On the other hand, the detection output Slc of the pickup coil 3c is
The signal is supplied to an amplification and polarity determination circuit 21 as shown in the figure.

As shown in FIG. 5A, the detection output S1c includes a pulse P7 generated when the magnet piece M7 approaches and a pulse P8 generated when the magnet piece M8 approaches, and these pulses P
7 and P8 have opposite polarities because the polarities of the magnet pieces M7 and M8 are reversed.

Then, by passing through the amplification and polarity discrimination circuit 21, a pulse S6a corresponding to the negative polarity (concave portion) of the detection output S1c shown in FIG. 5B and a pulse corresponding to the positive polarity (convex portion) shown in FIG. 5C are generated. S6b is separated and taken out.

This pulse S6a is supplied to the R8 type flip-flop 22 as a set input, and the pulse S6b is supplied to the flip-flop 22 as a reset input.

Pulses S6a and S6b occur almost simultaneously, but the flip-flop 22 is triggered at the rising edge of the one that occurs later, and the output pulse S7 of the flip-flop 22 becomes as shown in the fifth diagram.

When this pulse S7 is passed through the pulse delay circuit 23, a pulse S8 delayed by a time Ta is generated as shown in FIG. 5E, and when this pulse S8 is further passed through the pulse delay circuit 24, as shown in As shown in F, a pulse S is delayed by a time Tb and whose level is inverted every second.
9 occurs.

This pulse S9 is supplied as a switching pulse to the RF switching circuit of the signal reproduction system of the VTR, and when the pulse S9 is at a high level, the signal extracted from one of the rotating magnetic heads is supplied to the reproduction system, and the pulse S9 is at a low level. In this case, the signal extracted from the other rotating magnetic head is supplied to the reproduction system.

The pulse delay circuit 23 or 24 electrically corrects the deviation in the mounting position of the magnet piece M7 tMs and the pickup coil 3c.

In addition, in the servo circuit of a VTR, one field of the video signal is recorded as one inclined track by controlling the rotational phase of the rotating magnetic head, and a phase servo circuit is used so that the rotating magnetic head correctly scans this track during playback. However, by comparing the phase of the output pulse S7 of the flip-flop 22 with a reference signal (a vertical synchronization signal separated from the video signal during recording, and a playback control signal during playback), a phase error voltage can be easily generated. , by superimposing this on the speed error voltage described above, a phase servo system can be constructed.

For example, the monomulti 6 may be controlled by a phase error voltage, and the pulse width of its output pulse S4 may be controlled.

FIG. 6 shows another example of a speed servo system for the motor 12. In this example, magnet pieces M1 to M are placed in the same positional relationship as in FIG.
8 and pickup coil 3a.

3b and 3c are arranged, but the difference is that the pickup coils 3a and 3b are connected in series (parallel is also possible) with the polarity reversed.
As shown in FIG. 7A, the detection output Sl generated from the sensor is, for example, a pulse Pla generated when the magnet piece Ml approaches the pickup coil 3a, and a pulse Plb generated when the magnet piece M1 approaches the pickup coil 3b.
A series of pulses P2 . of alternating polarities such that P2 . This includes P2b, P3a, P3b...

This detection output Sl is supplied to the amplification and polarity discrimination circuit 13, from which pulses S2'8 and Sz'b shown in FIG. Alternatively, the flip-flop 5 generates an output pulse S3 shown in FIG. 7, which is similar to FIG. 3E.

This output pulse S3 is supplied to the monomulti 6, and the output pulse S4 of the monomulti 6 (FIG. 7E) is supplied to the inclined trapezoidal wave generation circuit 7 to form a trapezoidal wave S5 (FIG. 7F).

Furthermore, by supplying the output pulse of the flip-flop 13 to the gate pulse generation circuit 8, a gate pulse synchronized with the rising edge of the pulse S3 is formed, and a trapezoidal wave S5 is generated.
is sampled by the sampling gate circuit 9, and the sampling output is sent to the hold circuit 10 and the drive amplifier 11.
is supplied to the DC motor 12 via.

The operation of other examples of the DC servo circuit constructed as described above is also similar to the above example.

In the above example, a plurality of magnet pieces M1 to M are placed on the drum.
6 are arranged at equal intervals, the pickup coils 3a and 3b cannot form an RF switching signal.

Therefore, in order to form a switching pulse for the RF switching circuit, a pair of magnet pieces M7 and M8 are arranged on the drum, and a pickup coil 3c is added to detect this.

Therefore, the present invention provides such an additional magnet piece M7. M
8, speed control signals and RF switching signals can be generated with a simple configuration.

FIG. 8 shows the positional relationship between a magnet piece and a pickup coil in an embodiment of a servo circuit for a VTR according to the present invention.

That is, the circumference centered on the rotating shaft 1 is divided into n equal parts, and a magnet piece is attached to each of (n-1) points excluding one of the parts.

In the example shown in the figure (n=6), five magnet pieces Ml~
M5 is provided.

Pick-up coils 3d, 3e, and 3f are arranged on the rotation locus of these magnet pieces.

Then, as shown in FIG. 8, when the angle when divided into n equal parts is α (for example, 600), and the line connecting a pair of magnet pieces, for example, Ml and M4 facing each other with an angular interval of 1800, is used as a reference, A pickup coil 3d is provided at a position corresponding to the magnet piece M0, a pickup coil 3e is provided at a position further advanced by an angle β in the rotational direction of the rotary shaft 1 from the position of the pickup coil 3d, and further advanced by an angle β from the position of the magnet piece M4. A pickup coil 3f is provided at a position advanced by γ.

In this case, the positions of the pickup coils 3d, 3e, and 3f are selected so that these angles have a relationship of, for example, (α>β>γ).

Pickup coil 3a t3e 93f configured as described above
The detected signals are sent to amplifiers 4d and 4d, respectively, as shown in FIG.
4e and 4f.

At the outputs of these amplifiers 4d, 4e, and 4f, pulses S1d, S18, and Stf as shown in FIG. 10A, B, and C, which are amplified and shaped detection signals, are generated.

The flip-flop 5 is set by the rising edge of the pulse S1d, and the flip-flop 5 is reset by the rising edge of the pulse Sle+, and the flip-flop 5 generates an output pulse S3 shown in FIG. 10 and an output pulse S3 having the opposite polarity.

Both of these control the speed servo of the DC motor 12 in the same manner as in FIG. 2 or FIG. 6 described above.

Along with this, one output pulse S3 of the flip-flop 5
-Af is supplied to the AND circuit 14.

A pulse Slf is also supplied to this AND circuit 14, and the output of the AND circuit 14 is a pulse S11 shown in FIG. 10F.
occurs.

Further, the R8 type flip-flop 15 is set at the rising edge of the pulse S1d and reset at the rising edge of the pulse Slf.
An output pulse SIO shown in is generated.

This pulse SIO and pulse S1e are supplied to an AND circuit 16, and a pulse S12 shown in FIG. 10G is generated at the output of the AND circuit 16.

A flip-flop 22 is provided which is set at the rising edge of the output pulse S12 of the AND circuit 16 and reset at the rising edge of the output pulse S11 of the AND circuit 14.
is obtained.

This output pulse S7 passes through pulse delay circuits 23 and 24 to form a switching pulse S9 for the RF switching circuit, which is similar to the configuration shown in FIG. 4.

As is clear from the above, according to the present invention, it is possible to realize a servo circuit that rotates the DC motor 12 at a constant speed without providing a generator consisting of a magnetizing disk and a multi-gap head. It is possible to eliminate instability in servo operation due to unevenness, eccentricity, etc., and the cost is also reduced.

Furthermore, since the configuration is such that the flip-flop 5 is triggered by the detection signal, even if noise is superimposed on the detection signal and the shaped pulse becomes intermittent, the flip-flop will not be set (or reset) once. For example, since the state does not reverse until the next reset input (or set input) is supplied, there is an advantage that the operation can be made more stable without being affected by noise.

Note that the position display means and sensing element are not limited to magnetic ones such as magnet pieces and pickup coils as in the above embodiment, but also photoelectric ones consisting of a rotating disk with slits, a lamp, and a light receiving element. Of course, you may also use other materials.

[Brief explanation of drawings]

Figure 1 is a diagram showing the positional relationship between a magnet piece and a pickup coil in an example of a DC servo circuit, Figures 2 and 4 are system diagrams of an example of a DC servo circuit, and Figures 3 and 5 are its operation. 6 and 7 are respectively a system diagram of another example of the DC servo circuit and a waveform diagram of each part used to explain its operation. FIG. 8 is an implementation of the VTR servo circuit according to the present invention. FIGS. 9 and 10, which show the positional relationship between the magnet piece and the pickup coil, are a system diagram of an embodiment of the servo circuit of a VTR according to the present invention, and diagrams for explaining its operation, respectively. M1-MB is a magnet piece, 3a to 3f are pickup coils, 5, 15.22 are flip-flops, 6 is a monomulti, 7 is an inclined trapezoidal wave generation circuit, 9 is a sampling gate circuit, and 12 is a DC motor.

Claims (1)

[Scope of utility model registration request] n on the same circumference of the member that rotates together with the rotating magnetic head.
(n>2), a position display means provided at the divided (n-1) position, and a sensing element disposed close to the rotating circumference of this position display means. , the first flip-flop is triggered by a detection signal generated each time the position indicating means approaches the sensing element, and the output of the first flip-flop and this output are delayed by a fixed time. Compare the phase with the signal,
The rotational speed of the rotary magnetic head is controlled by this comparison output, and the second flip-flop is triggered by the detection signal from the sensing element.
The VTR gates the detection signal using the output of the flip-flop as a gate signal, and controls the switching of the rotating magnetic head based on the gated detection signal.
sabot circuit.