JPH049548Y2 - - Google Patents

Description

[Detailed description of the invention] A rotating magnetic head device for a VTR has a fixed drum 1 and a rotating drum 2 as shown in FIG.
H ₁ and H ₂ are installed, and this rotating drum 2
A plurality of magnets, ie, elements for controlling the rotational speed and rotational phase of the rotary drum 2, are further disposed on the lower surface of the rotary drum 2.

In this example, as shown in FIG. 2, a plurality of magnets, for example six magnets _M1 to _M6 , are attached concentrically to the lower surface 2A of the rotating drum 2. magnet
The polarities of M ₁ to _{M 6} are selected to be the same in the direction of rotation, and the passage of these magnets M ₁ to M ₆ is connected to the first and second detection coils (not shown) arranged on the fixed drum 1 side. ) is detected. Then, as the magnet passes, the trapezoidal wave formed based on the pulse signal output from the first detection coil is sampled by the pulse signal output from the second detection coil, and the sampled signal is The rotational speed of the rotary drum 2 is controlled by the rotational speed control means so that the rotational speed of the rotary drum 2 reaches a predetermined level, and the rotational speed of the rotary drum 2 is kept constant.

Further, on the lower surface 2A of this rotating drum 2, an element for detecting a rotational phase is arranged. In FIG. 2, a magnet _M7 is mounted as an element for detecting the rotational phase at a predetermined position on the inner periphery of the mounting positions of the magnets _M1 to _M6 . This magnet _M7 is detected by a detection coil (not shown) disposed on the fixed drum 1, and the rotational phase of the rotary drum 2 relative to the position of the magnetic tape is controlled based on the detection output.

By the way, like this, multiple magnets M ₁ ~
When attaching _M7 to the rotating drum 2, it is necessary to consider the rotational balance of the rotating drum 2. Since there are six magnets for rotational speed detection, there is no problem if they are arranged concentrically at equal angular intervals as shown in the figure, but since there is only one magnet for rotational phase detection, rotation In order to maintain balance, it is absolutely necessary to provide a dummy M _D as shown in the figure. Moreover, this dummy M _D made of metal or the like must be on the same radius as the mounting radius of the magnet _M7 .

Therefore, in this conventional device, the magnet M ₁
~ In addition to M ₆ , it is necessary to arrange magnet M ₇ and dummy M _D on a concentric circle, so rotating drum 2
The disadvantage is that it is difficult to process and requires a large number of parts.

Therefore, the purpose of this invention is to create a rotation detection device for a rotating drum that has a small number of parts to be attached to the rotating drum, allows easy processing of the rotating drum, and can detect the rotational phase of the rotating drum with high accuracy. The goal is to provide the following.

Therefore, in this invention, one element among the plurality of elements for detecting rotational speed is also used as an element for detecting rotational phase.
As shown in the figure, six magnets M ₁ to _{M 6} are installed concentrically, and the polarity of five of them, for example magnets M ₁ to M ₅ , is selected to be the same in the rotation direction, and the remaining magnets are
M ₆ is installed with its polarity reversed.

H _a and H _b are detection coils, and based on the phase difference between the detection signals S _Da and S _Db detected by the pair of detection coils H _a and H _b , a conventionally known rotational speed control circuit, that is, The trapezoidal wave formed based on the pulse signal output from the detection coil H _a is sampled by the pulse signal output from the detection coil H _b , and rotated so that the level of the sampled signal becomes a predetermined level. The rotational speed of the rotary drum 2 is kept constant by a control circuit that controls the rotational speed of the drum 2. Further, at this time, one of the detection coils H _a or H _b is also used as a detector for rotational phase detection. In this example, the detection coil H _a is also used as a rotational phase detector.

FIG. 4 shows an example of a rotational phase detection device that extracts only the detection signal D ₆ of the magnet M ₆ , and the detection signal S _Da detected by the detection coil H _a is detected from the magnets M ₁ to M as shown in FIG. 5A. This detection signal S _Da is supplied to the _first waveform shaping circuit 4 via the terminal 3, and the detection signal S Da is obtained as a signal corresponding to the polarity of the signal S _Da .
Of these, only the positive signal is shaped and output.
Therefore, the first pulse S _P shown in FIG. 5B is obtained.

The detection signal S _Da is further supplied to the second waveform shaping circuit 6 via the inverter 5, and the positive polarity signal of the detection signal _Da , therefore, only the negative polarity signal with respect to the detection signal S _Da is shaped and output. Therefore, the second pulse S _P ' shown in FIG. 5C is obtained. This second pulse S _P ' is supplied to a variable pulse width circuit 7 which can be configured with a delay circuit, etc., to form a pulse S _G shown in FIG. 5D, which is supplied as a gate pulse to an AND gate 8. 1 pulse S _P is gated.

In the relationship between the first pulse S _P and the second pulse S _P ′,
The first one is compatible with magnets M ₁ to M ₅ .
The first pulse S _P corresponding to the magnets M ₁ to _{M 5} is obtained in advance of the second pulse S _P ′.
The pulses P ₁ to _{P 5} of are not gated by the gate pulses G ₁ to _{G 5} .

On the other hand, Magnet M ₆ is similar to other magnets.
Since M ₁ to _{M 5} and their polarities are opposite, the detection signal D ₆
The polarity of is also opposite to that of the other detection signals D ₁ to D ₅ , so that the second pulse P ₆ ' is obtained in advance of the first pulse P ₆ . Therefore, this second pulse
The first pulse P ₆ is gated with a gate pulse G ₆ based on P ₆ ' (FIG. 5E).

Thus, if the configuration is as shown in FIG. 4, the pulse P ₆ corresponding to the magnet M ₆ for detecting the rotational phase will be
Since only the pulse P 6 can be detected, the rotation phase of the rotary drum 2 can be controlled using this pulse P ₆ obtained every rotation.

Since a well-known control circuit for the rotational phase can be used, a description thereof will be omitted.

FIG. 6 shows a specific example of a rotational phase detection device. In this example, operational amplifiers are used as the first and second waveform shaping circuits 4 and 6, respectively, and instead of using the inverter 5, the negative terminal of the operational amplifier 6 is used. The detection signal S _Da is supplied to the Therefore,
Now, when the detection signal D ₆ of FIG. 7A is input, when the detection signal D ₆ becomes positive, the first
A second pulse P ₆ (FIG. 7B) is obtained, whereas a second pulse P ₆ ' (FIG. 7C) is obtained from the other operational amplifier 4 when the detection signal D ₆ becomes negative.

This second pulse P ₆ ' is then passed through the time constant circuit 7.
is supplied to This time constant circuit 7 functions as the pulse width variable circuit 7 shown in FIG. 4, and has a resistor R _a
and a capacitor C, and a resistor R _a is connected to a DC power supply +B. A capacitor C is connected in series with the signal path and via a resistor R _b to the base of a transistor Q which refines the AND gate 8 . Note that the collector of this transistor Q is connected to the output terminal of one operational amplifier 4, and an output terminal 9 is led out from this collector.

When the output of the other operational amplifier 6 is at a low level, a predetermined voltage is applied to the transistor Q via the resistors R _a and R _b , so this turns on, and the level of the output terminal 9 is therefore low. . When the second pulse P ₆ ' rises in this state, the transistor Q remains on, but the capacitor C is charged to the polarity shown in the figure, and from that moment on, when the second pulse P ₆ ' falls. Capacitor C starts discharging. Therefore, the base potential V _B of transistor Q is
Since the voltage suddenly drops to a negative level, this transistor Q is turned off.

The period during which the transistor Q is off is determined by the time constant τ of the time constant circuit 7, and during this off period,
Since the first pulse P ₆ is output from one of the operational amplifiers 4, the level of the output terminal ₉ is high during the period when the first output pulse P 6 is obtained. Therefore, the time constant τ is selected to be at least the pulse width of the first pulse _P6 .

In the case of detection signals D ₁ to _{D 5} other than D ₆ , the timing at which the first and second pulses S _P and S _P ′ are obtained is the seventh
Since the situation is opposite to that shown in the figure, no output pulse can be obtained from the output terminal 9. Therefore, even if the configuration is as shown in FIG. 6, the same operation as in FIG. 4 is achieved.

In Fig. 6, the reference voltages V ₁ and V ₂ (Fig. 7 A) applied to each input terminal of the operational amplifiers 4 and 6 differ by the voltage drop caused by the resistor R _c , but as shown above, the slight potential difference The reason for this is to prevent the operational amplifiers 4 and 6 from oscillating when the detection signal S _Da is not input to the terminal 3.

As explained above, according to this invention, one of the elements for detecting rotational speed is also used as an element for detecting rotational phase, so it is only necessary to attach multiple elements on the same circumference on the rotating drum 2. That's enough. Therefore, the rotary drum 2 can be processed more easily than before, and the number of detection elements itself can be reduced. Since the dual-purpose configuration satisfies the rotational balance of the rotating drum 2, there is no need to install a dummy M _D for rotational balance.
Processing of the rotating drum 2 becomes easier accordingly.

Further, since the passage of the magnet _M6 is detected by the detection coil H _a , the rotational phase of the rotary drum can be detected with high accuracy.

Note that in the above embodiments, the number of magnets may be an odd number. Even in the case of an odd number, the arrangement is done taking rotational balance into consideration.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a rotating magnetic head device, FIG. 2 is a bottom view of a rotating drum, FIG. 3 is a bottom view showing an example of a rotating drum suitable for use in this invention, and FIG.
5 is a system diagram showing an example of the device of this invention, FIG. 5 is an explanatory diagram of its operation, FIG. 6 is a connection diagram showing a specific example of FIG. 4, and FIG. 7 is an explanatory diagram of its operation. 2 is a rotating drum, M ₁ to _{M 6} are magnets, 4,
6 is a first and second waveform shaping circuit, 7 is a variable pulse width circuit, 8 is an AND gate, and P ₆ is a detection pulse used for rotational phase control.

Claims (1)

[Scope of utility model registration request] A plurality of magnets M ₁ , M ₂ , M ₃ , M ₄ , M ₅ , M ₆ arranged at equal intervals in the circumferential direction of the rotating drum ₂ to which the magnetic heads H ₁ and H 2 are attached, and the plurality of magnets mentioned above. magnets M ₁ , M ₂ , M ₃ , M ₄ , M ₅ ,
First and second detection coils H _a and H _b arranged close to M ₆ and the first and second detection coils H _a and
and a rotation speed control means for controlling the rotation speed of the rotary drum 2 based on first and second detection output signals respectively output from H _b . Coil H _a
A first waveform shaping circuit 4 is supplied with an output signal of , and outputs a positive polarity component of the supplied signal, and an output signal of the first detection coil H _a is supplied, and outputs a negative polarity component of the supplied signal. a second waveform shaping circuit 5, 6 that outputs the component of the second waveform shaping circuit 5, a pulse width variable circuit 7 that expands the pulse width of the pulse signal supplied from the second waveform shaping circuit 5, 6, and a pulse width variable circuit 7 that extends the pulse width of the pulse signal supplied from the second waveform shaping circuit 5, 6; The output signal of the shaping circuit 4 and the output signal of the variable pulse width circuit 7 are supplied, and based on the output signal of the variable pulse width circuit 7, the first waveform shaping circuit 4
a gate circuit 8 for selectively outputting a pulse signal supplied from the gate circuit 8; and a rotation phase of the rotary drum 2 relative to the position of the magnetic tape scanned by the magnetic head based on the pulse signal output from the gate circuit 8. Equipped with a rotational phase control circuit that controls the
The above plurality of magnets M ₁ , M ₂ , M ₃ , M ₄ , M ₅ ,
Among _M6 , the first magnet _M6 is rotated as described above so that the direction of its magnetic pole is opposite to the direction of the magnetic pole of the other magnets _M1 , _M2 , _M3 , _M4 , and _M5 . A rotation detection device for a rotating drum, characterized in that it is attached to a drum 2.