JPS61162805A - Vertical magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To obtain a reproduction signal which is not affected by an external magnetic field all the time by extracting and comparing two reproduction signals of vertical magnetic recording as representative values at specific intervals of time, and increasing or decreasing a magnetic field for canceling the external magnetic field according to the comparison result. CONSTITUTION:When a power switch is turned on, a driving motor 38 rotates at a constant speed and a reproduction signal picked up by a magnetic head 21 is amplified properly by a preamplifier circuit 31 and supplied to an envelope detecting circuit 32. A PG coil 39 detects magnetic flux generated by a PG yoke 30a through the rotation of a magnetic disk 30 and its detection signal is waveform-shaped by a waveform shaping amplifier circuit 41 and sent out of the amplifier circuit 41 as PG pulses having a constant period; and the PG pulses are sent out as 1/2-frequency-divided pulses. The DC magnetic field generated so as to eliminate the influence of the external magnetic field is controlled, so a minimum holding circuit 33 is reset at intervals of this unit period. Consequently, a reproduction state wherein there is not external magnetic field is realized.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to a perpendicular magnetic recording/reproducing device, more specifically, to a perpendicular magnetic recording/reproducing device, and more specifically, to a perpendicular magnetic recording/reproducing device, in which the reproduction of information signals is affected even when an external DC magnetic field is applied during magnetic recording, recording, and reproduction. The present invention relates to a perpendicular magnetic recording and reproducing apparatus that can perform perpendicular magnetic recording and reproducing without any problems.

(Prior art) In the perpendicular magnetic recording method in which a magnetic recording medium is magnetized in the thickness direction, in principle, the shorter the wavelength (higher frequency) of the magnetization that is magnetically recorded, the more It is known that it is suitable for high-density recording because the self-demagnetizing field is small.

To perform such perpendicular magnetic recording, a magnetic recording medium with large perpendicular magnetic anisotropy and a magnetic recording head that generates a sharp and strong perpendicular component magnetic field are required. And 1. Five methods for perpendicular magnetic recording are known: an auxiliary pole excitation type perpendicular magnetic head type and a main pole excitation type perpendicular magnetic head type.

In the auxiliary pole excitation type perpendicular magnetic head system, as shown in FIG. 10, a main pole 2 and a synchronous pole 3 are disposed facing each other with a 5K perpendicular magnetic recording medium 1 interposed therebetween. Here, the perpendicular magnetic recording medium 1 is a flexible paste made of a polymer film or the like.
It is constructed by forming a high permeability magnetic layer made of Ni permalloy or the like, and further forming a perpendicular magnetic recording layer having an axis of easy magnetization perpendicular to the medium surface. Also,
The main magnetic pole 2 has a main magnetic pole film 5 made of a high magnetic permeability soft magnetic film formed on a nonmagnetic substrate 4a by sputtering, and the main magnetic pole film 5 is sandwiched between nonmagnetic substrates 4b.

Further, the auxiliary magnetic pole 3 is constructed by winding a winding 7 for transmitting and receiving an information signal current around a high permeability magnetic layer B such as ferrite.

Next, in the above-described main pole excitation type perpendicular magnetic head system, as shown in FIG. There is. Here, the main magnetic pole 8 is formed by first forming a main magnetic pole film 9 made of a high magnetic permeability soft magnetic film on a non-magnetic substrate 10a by sputtering, and then forming a block body by sandwiching this main magnetic pole film 9 between non-magnetic substrates 10b. , and is formed by fitting and bonding the block body into the reverse circular groove of a high magnetic permeability magnetic body 12 made of ferrite or the like having a reverse circular groove. Further, a TI human-sensing signal current transmitting/receiving winding 11' is wound around a protrusion formed on the bottom surface of the reverse circular groove.

In the perpendicular magnetic recording system configured as described above, the flow of magnetic flux is in an open magnetic path configuration. After the sharp magnetic field described above flows through the magnetic path of main magnetic pole film 5 → perpendicular magnetic recording medium 1 → auxiliary magnetic pole 5,
It passes through the space and returns to the main magnetic pole film 5.

By the way, in the case of the conventional longitudinal recording method, as shown in FIG.
Recording and playback are performed while sliding contact. The magnetic path in this case has a closed magnetic path configuration as shown by the arrows in FIG. 12, and is therefore less susceptible to external noise and external magnetic fields.

However, the perpendicular magnetic recording method with the above-mentioned open magnetic path configuration is susceptible to external noise and external magnetic fields.

In particular, the influence of a direct current external magnetic field on the playback output level is significant. For example, as shown in Figure 13, if the vertical axis is the playback output (relative value) and the horizontal axis is the external magnetic field, the external magnetic field is If the playback output at 00e (Oersted) is 100ch, there is data that shows that the playback output drops to about 10k when the external magnetic field is ±10e (Television Society technical report).

June 1984 VOL, 8. No. 8 VR635
).

The effects of an external magnetic field are not only a decrease in the recording/reproducing output as described above, but also a decrease in the recording level, or if the magnetic head comes close to or comes into sliding contact with a medium that has already been recorded while no recording/reproducing operation is being performed. This appears as a reducing effect on the residual magnetization of the medium during the busy period. The reason why such an effect of an external magnetic field appears is considered to be due to the following principle.

Figure 14 is a diagram showing the B-H characteristics of the main pole of a perpendicular magnetic head, and Figure 15 is a diagram showing the B-H characteristics of a recording medium magnetized by a perpendicular magnetic head that operates with the characteristics shown in Figure 14. It is a diagram. In the absence of an external magnetic field, the main pole is magnetized in the positive and negative directions around the origin O to a magnetic flux density of approximately the saturation level ±Bs, as shown in FIG. 14, in response to the alternating magnetic field generated by the recording signal. On the other hand, the recording medium is magnetized in the positive and negative directions to a saturation level magnetic flux density by the magnetic field generated by the main magnetic pole magnetized as described above, as shown in FIG. 15, and the residual magnetic flux ±Br is maintained. This state is a state in which normal magnetic recording is performed on the recording medium. When an external magnetic field (for example, a positive DC magnetic field from the earth's magnetism or a spindle motor magnet) is applied,
The magnetizing force (magnetic field) acting on the main magnetic pole is the summation of this external magnetic field acting on the magnetic field due to the recording signal described above (that is, the magnetizing force is in the positive direction on the horizontal axis in Fig. 14). shift). As a result, the operating center point of the magnetization (magnetic flux density) of the main pole moves to point At in Figure 14, so even if it is magnetized to the saturation level +Bs in the positive direction, it reaches the saturation level -Bs in the negative direction. It is possible that it will not be magnetized. In this way, when a recording medium is magnetized by a magnetic field emitted from a main magnetic pole with a biased magnetization state, the residual magnetic flux in the recording medium is maintained at the above-mentioned +Br in the positive direction, but in the negative direction. The absolute value is smaller than this - Bk
(See FIG. 15) will be retained. In other words, the external magnetic field causes a decrease in the magnetic recording level.

Next, a state in which the perpendicular magnetic head approaches or comes into sliding contact with a recording medium whose magnetization state is biased as described above (10th
In the state shown in the figure), when an external magnetic field is applied to the extent that the magnetization of the main pole reaches point A in Figure 14, the magnetizing force due to this external magnetic field (a magnetic field that focuses mainly on the main pole)
As a result, the magnetization state in the recording medium changes from the initial residual magnetization -Bk to the value corresponding to point A' in FIG. After this change, even if the external magnetic field is removed and the magnetizing force by the main pole disappears, the magnetization state of the recording medium will not return to the original residual magnetization -Bk, but will change to -Bk/, which has a smaller absolute value than this. (See Figure 15). This is because, as is well known, the relationship between changes in the magnetic field (magnetizing force) and the corresponding magnetization (magnetic flux density) is irreversible.

As described above, when an external magnetic field is applied to a recorded magnetic recording medium, and furthermore, the applied state is subsequently canceled, the residual magnetization (that is, the magnetic recording level) is reduced. In other words.

This tendency becomes particularly noticeable when the main pole of the perpendicular magnetic head approaches or comes into sliding contact with the recording medium, even when not recording or reproducing.

Next, we will consider the case where an external magnetic field (the same DC magnetic field as described above) is applied when reproducing recorded information from a medium on which normal magnetic recording has been performed as described above. In this case, in response to the magnetic field emitted from the already recorded medium,
Since the external magnetic field acts harmonically, the operating point at the main pole of the perpendicular magnetic head is the origin 0 on the horizontal axis in Figure 14.
It moves in the positive direction, and moves to point A or, if the external magnetic field is particularly strong, to point B. B − in Figure 14
As is clear from the H characteristic, when operating around point A or point B, the magnetization (in the main magnetic pole) corresponding to the change in magnetizing force (in this case, the signal magnetic field from the medium trap plus the external magnetic field) The rate of change in magnetic flux density (magnetic flux density) is significantly reduced and becomes almost zero in the positive direction from point B. Therefore, the reproduction sensitivity decreases.

In this way, the reduction in the recording and/or reproduction level due to the influence of external magnetic fields, as well as the reduction in the recording level of the medium when the magnetic head comes close to or in sliding contact with the medium that has already been recorded, can be prevented by the above-mentioned auxiliary magnetic pole excitation type. Ik-ttt is not only seen in the perpendicular magnetic head system, but also in the main pole excitation type perpendicular magnetic head system. In other words, as mentioned above, it is known that in the perpendicular magnetic recording method, the influence of external magnetic fields is greater than in the conventional longitudinal recording method.

Therefore, for example, in a floppy disk drive device,
In order to suppress leakage magnetic fields from the motor and external magnetic fields from outside the device, measures are taken to shield the motor and the entire device with a high permeability magnetic material such as permalloy. However, even with such means, it is difficult to completely suppress the external magnetic field, and since the influence of the external magnetic field on the magnetic head varies depending on the track position, it is difficult to always obtain a stable reproduction output. Furthermore, the use of the above-mentioned shielding material has the disadvantage that it is not desirable for reducing the size and weight of a floppy disk drive device.

(Objective) An object of the present invention is to provide a perpendicular magnetic recording/reproducing apparatus which prevents the demagnetization effect that occurs when a perpendicular magnetic head comes into sliding contact with a magnetic recording medium due to a DC external magnetic field during reproduction.

(Summary) In order to achieve the above object, the present invention extracts two representative values of reproduction signals of perpendicular magnetic recording affected by an external magnetic field for each predetermined time interval, compares these representative values,
The present invention is characterized in that by increasing or decreasing the magnetic field for canceling the external magnetic field according to the comparison result, a reproduced signal that is not affected by the external magnetic field is always obtained.

(Example) First, before giving a detailed explanation of the present invention, the principle of the present invention will be explained based on FIGS. 1 to 3.

FIG. 1 is a diagram showing the magnetic path of a direct current magnetic field generated from a spindle motor when an auxiliary magnetic pole excitation type perpendicular magnetic head is used in a floppy disk drive device. That is, a perpendicular magnetic recording medium (floppy disk) 1a is attached to the spindle motor 15 by an appropriate chucking member 15a, and an auxiliary magnetic pole consisting of a main magnetic pole 2, an auxiliary magnetic pole 3, etc. is attached near the spindle motor 15. A pole-excited perpendicular magnetic head is used for the medium 1a.
It is arranged so that it moves while sliding in the radial direction of the

In the case of such a configuration, the direct current magnetic field (external magnetic field) emitted from the spindle motor 15 is located at the main magnetic pole 5 as shown by the arrow in Figure 1. Since it is focused on the tip of the main magnetic pole film 5 of No. 2, a bias magnetic field is applied, and an operating point is established, resulting in a reduction in the reproduction ratio.

Therefore, as shown in FIG. 2, a direct current magnetic field generation source 16 is installed near the main pole film 5 of the auxiliary pole excitation type perpendicular magnetic head so that the direction is opposite to the direction of the external magnetic field. When installed in this way, the external magnetic field from the spindle motor 15 shown by the solid line arrow and the magnetic field from the source 16 shown by the dotted line arrow will be applied to the main pole film 5.
It is as if two types of direct current magnetic fields with opposite directions are applied at the tip of the become. That is, during recording and reproduction, the influence of the external magnetic field caused by the spindle motor 15 can be eliminated.

In addition, in Fig. 2, as a direct current magnetic field generation source,
Although the magnetic field generation source 16 is installed outside the perpendicular magnetic head in the explanation, it is not necessarily necessary to install it outside, and it is also possible to apply current to the windings wound around the magnetic head to cancel out the magnetic field in each part. be.

That is, as shown in FIG. 6, one end of the winding 22 wound around the main pole 21 is grounded, and the other end is connected via a variable resistor 26 to a terminal to which a positive operating voltage V is supplied. It is also connected to the variable terminal 25a of the recording/reproduction switch 25 via the DC blocking capacitor 24. The first fixed terminal 25b of the changeover switch 25 is connected to the output end of the recording amplifier 26, and the input end of the amplifier 260 is connected to a recording signal generation circuit (not shown). Further, the second fixed terminal 25C of the changeover switch 25 is connected to the input terminal of the reproduction amplifier 270.
The output end of 7 is connected to a reproduction signal output circuit (not shown).

'In such a configuration, if the positive operating voltage V is applied to the midpoint of the connection between the winding 22 and the capacitor 24 via the variable resistor 26, the direct current flows through the winding both during recording and playback. 22, a direct current magnetic field is generated from the tip of the main pole 21. By changing the resistance value of the variable resistor 23, the value of the current flowing through the winding 22 can be increased or decreased, so that the strength of the generated DC magnetic field can be increased or decreased.

Next, a first embodiment of the present invention will be described based on FIGS. 4 to 6.

FIG. 4 is an electrical circuit diagram showing the main parts when the principle explained in FIG. 3 is applied to the control circuit of this embodiment. That is, one end of the winding 22 wound around the main pole 21 is grounded, and the other end is connected to the collector of the PNP transistor 28, and connected to the control circuit (fifth (see figure) is connected to a preamplifier circuit 31. The emitter of the transistor 28 is connected via a resistor 29 to a terminal for supplying a positive operating voltage V, and the base is connected to the output terminal of the buffer circuit 55 of the control circuit.

In this state, the transistor 28 and resistor 29 constitute a constant current circuit. For example, when the positive operating voltage V is set to +5V, the potential vB of the base of the transistor 28 and the DC current flowing through the winding 22 have the following relationship.

I = (5-(Vn+v''0/resistance.2.) Resistance value Here, VBE is the voltage between the base and emitter of the transistor 28, which is approximately 0.6v to 0.7v. Therefore, the resistance 29
If the resistance value of is set to 1 and Ω, a current of about 4.4 mA at maximum can flow through the winding 22. Note that when the external magnetic field is extremely strong, the current flowing through the winding 22 can be further increased by reducing the value of the resistance value 29.

A control circuit using the above electric circuit configured in this way will be explained based on FIGS. 5 and 6. The outline of the operation of this mlJ control circuit is as follows.

That is, the reproduction R and F signals affected by the external magnetic field are detected as reproduction envelope levels during a unit period given by an integral multiple of the rotation period of the magnetic disk. The minimum value of this envelope level is set to 1. Second
Temporarily accumulates in the sample and hold circuit. On the other hand, the first sampling pulse has a cycle twice as long as the unit period and has a phase different by 180°. The envelope signal is supplied to the second sample and hold circuit, and the envelope signal stored in the first and second sample and hold circuits is taken out, and the level of the signal is compared by a comparator. When making this comparison, the level of the previous unit period J is used as a standard to compare the switch. If it is small, it is judged that the influence of the external magnetic field has not disappeared yet, and the canceling current flowing to the magnetic head is increased to cancel the influence of the external magnetic field, and the level of the inverse K "previous unit period" is increased. If the current is greater than the level of the "current unit period", the current is reduced so that the optimum reproduced signal can be obtained at all times.

Hereinafter, the above-mentioned control circuit will be explained based on FIG. 5.

First, to describe the configuration of this control circuit, a perpendicular magnetic recording medium (hereinafter referred to as a magnetic disk) 30 is mounted on a rotating flange (not shown) fixed to the spindle of a drive motor 38, and is rotated at a predetermined rotational speed. It rotates at high speed. A main magnetic pole (hereinafter referred to as a magnetic head) 21 is disposed on the lower surface of the magnetic disk 300 so as to slide in contact with the disk 30 and move in the radial direction thereof.

A winding 22 for signal transmission and reception is wound around this magnetic head 21, one end of this winding 22 is grounded, and the other end is connected to the collector of a PNP transistor 28 constituting a constant current circuit. , are connected to the input end of the preamplifier circuit 31 via a DC blocking capacitor 24. The output end of the preamplifier circuit 51 is connected to the input end of the envelope detection circuit 32.

This envelope detection circuit 32 detects an envelope signal waveform having a width amplified by the preamplifier circuit 31.
For example, only the top side can be taken out. The output terminal of the envelope detection circuit 32 is connected to the input terminal of a minimum value hold circuit 33 for holding the minimum value of the envelope detection signal in a unit period of a periodic signal, which will be described later. The output end is connected to the first . It is connected to the respective input terminals of second sample and hold circuits 54a and 54b.

The output ends of each of the hold circuits 34a and 34b are connected to two switches 35 for constantly supplying the latest data. That is, the switch 35 is composed of a first set of switches consisting of a movable contact piece 35a and fixed terminals 35b and 35c, and a second set of switches also consisting of a movable contact piece 35d and fixed terminals 35e and 35f. The switch is configured to change over in response to a pulse supplied from a 1/2 frequency divider circuit 43, which will be described later. The output end of the first sample hold circuit 54a is connected to the fixed terminals 35b and 55e, and the output end of the second sample hold circuit 34b is connected to the fixed terminals 55c and 55f. The above movable contact piece 5
5a is connected to the non-inverting input end of the comparator 36, and the movable contact piece 55d is connected to the inverting input end of the comparator 36.

In this way, the sample and hold circuits 54a, 54
b, switch 35, and comparator 36 are constructed by, for example, timings 1, 2, 3, 4, 5, 6, . . . from the minimum value hold circuit 33. . . . Signals are continuously sent out at timings 1, 3, 5° . . . to the first hold circuit 54a.
The signals at timings 2, 4, 6, . . . are held in the second hold circuit 54b. This is to ensure that the signals of... are held. In a "certain period", by switching the switch 35, the signal at timing 1 of the hold circuit 54a is supplied to the non-inverting input terminal of the comparator 36, and at the same time, the signal at timing 2 of the hold circuit 34b is supplied to the comparator 36. It is supplied to the inverting input terminal, and this comparator 36 outputs the above timings 1 and 2.
The magnitude of the signals at is compared. Then, when the "next section" of the "certain section" is reached, the switch 35 is switched, and the signal at timing 2 is applied to the non-inverting input terminal, and at the same time, the signal at timing 6 is applied to the inverting input terminal. applied. In other words, two consecutive intervals to be compared (
timing), always the first half (in this case, "certain section")
The signal at timing 1 in the case and timing 2 in the "next section" is applied to the non-inverting input terminal of the comparator 56, and the reference is always set to the signal in the "first half". '' and the ``second half.'' In other words, the minimum values of the signals in the "first half" and "second half" are compared.

The output terminal of the comparator 36 is a T-flip 70.
It is connected to the trigger input terminal of a tube circuit (hereinafter referred to as T-FF circuit) 670, and the Q output terminal of the T-FF circuit 37 is connected to one input terminal of an AND gate 48. The Q output terminal is connected to one input terminal of AND gate 47.

Further, a PG (pulse generator) yoke 30a that emits magnetic flux is embedded in the center core of the magnetic disk 30, and the magnetic flux is detected so as to face the PG yoke 30a, and the magnetic disk rotates 600 times. A PG coil 69 for detection is attached. The output end of this coil 69 is connected to the input end of a waveform shaping amplifier circuit 410 that amplifies the detected signal, shapes the waveform, and sends out a PG pulse with a constant period, and the output end of the circuit 41 is connected to the input end of a waveform shaping amplifier circuit 410 that amplifies and shapes the detected signal and sends out a PG pulse with a constant period. The input terminal of the circuit 420, the 1/2 frequency divider circuit 45, one input terminal of each of AND gates 45 and 46, and the other input terminal of each of the AND gates 47 and 48 are connected. The output terminal of the reset pulse generation circuit 42 is connected to the reset terminal of the minimum value hold circuit 33, and the output terminal of the 1/2 frequency divider circuit 43 is connected to the other input terminal of the AND gate 46 and the inverter 440. It is connected to the input terminal and the switch switching input terminal 35g of the switch 65. The output terminal of the AND gate 46 is connected to the sample hold circuit 34.
The output terminal of the AND gate 45 is connected to the sampling pulse input terminal of the sample hold circuit 34.
It is connected to the sampling pulse input terminal of b. Further, the output terminal of the inverter 44 is connected to the AND gate 4.
5.

The output terminals of the AND gates 47 and 48 are connected to the first . The output terminal of this counter 49 is connected to the second input terminal of the D/A converter 5.
It is connected to the input terminal of 1. This converter 51. (
7) The output terminal is connected to the input terminal of an inverting amplifier 520 that amplifies the voltage to a voltage suitable for driving the transistor 28, and the output terminal of the amplifier 52 is connected to the above-mentioned voltage via the level shift circuit 56 and the buffer circuit 55. Connected to the pace of transistor 2B. The emitter of this transistor 28 is connected via a resistor 29 to a terminal that supplies an operating voltage +V.

The control circuit is configured as described above.

Next, the operation of the control circuit shown in FIG. 5 will be explained based on the time chart shown in FIG. 6.

When the power switch (not shown) is turned on, the drive motor 3
8 rotates at a constant speed, and the reproduced signal picked up by the magnetic head 21 is appropriately amplified by a preamplifier circuit 31 and supplied to an envelope detection circuit 52K.

At this time, it is assumed that the reproduction signal is influenced by an external magnetic field generated by the motor 58.

On the other hand, due to the 300 rotations of the magnetic disk, the PG coil 3
Reference numeral 9 detects the magnetic flux emitted from the PG yoke 50a, and this detection signal is waveform-shaped by a waveform shaping amplifier circuit 41 and has a constant period as shown in FIG. 6(A).
It is sent out from the amplifier circuit 41 as a Q pulse. Further, the PG pulse is supplied to a 1/2 frequency divider circuit 43,
It is sent out as a 1/2 denominator pulse as shown in FIG. 6(B).

In addition, the reproduction R, F which is the output of the preamplifier circuit 31
The signal waveform of the (radio frequency) signal is the 6th
When the reproduced R and F signals are subjected to envelope detection in the envelope detection circuit 62, an envelope detection signal as shown in FIG. 6(D) is obtained. This envelope detection signal is then input to the minimum value hold circuit 36, and this hold circuit 63 is periodically reset by a reset pulse (see FIG. 6(E)) synchronized with the PG pulse. , this reset pulse is generated by the falling edge of the PG pulse. As shown in FIG. 6 (F'), the signal obtained from the minimum value hold circuit 33 is a signal in which the minimum values of the envelope detection signal in the period having the P and G pulses are continuous.

In this embodiment, the magnetic disk 60 is used as a unit period.
The minimum hold circuit 33 is reset every unit period, and the generated DC magnetic field is controlled to eliminate the shadow j caused by the external end field. Moreover, since the unit period can be selected as an integral multiple of one rotation period, for example, if the unit period is two rotation periods, the period of the reset pulse will also be every two rotations.

The output signal of the minimum value hold circuit 33 is supplied to a first sample hold circuit 54a and a second sample hold circuit 54b. On the other hand, sampling pulses as described below are supplied to these sample and hold circuits 34a and 54b. That is, the above P
The G pulse (see FIG. 6(A)) is divided into 1 by the 1/frequency divider circuit 43.
This 1/2 frequency-divided signal is supplied to the other input terminal of AND gate 46, and also supplied to the other input terminal of AND gate 45 with a phase shift of 180°. And the above PG pulse is also the above A/Toge) 45.
As a result, the output signal obtained from 45.46 is as shown in FIG. 6(G).

As shown in (H), the output signal (
sampling pulses 1 and 2). Therefore, the first
．． Second sampling and hold circuits 34a, 34b
The respective signals held in Fig. 6 (I) and (J)
The signal waveform will be as shown in .

The holding signals of the hold circuits 34a and 54b are supplied to the fixed terminals 35b and 65e of the switch 65, and the fixed terminals 35c and 55f. Here, the above-mentioned 1/2 frequency division signal is applied to the switching signal input terminal 35g of the above-mentioned switch 35, for example, the above-mentioned
While the /2 frequency division signal is at L level, the switch 35
The movable contact pieces 35a and 35d are fixed terminals 55b, respectively.
, 35f, and while the same <1/2 frequency division signal is at H level, the movable contact pieces 35a and 35d are connected to fixed terminals 35c and 35e, respectively. That is, the switching contacts of the first and second switches of the switch 35 are switched every unit period of the PG pulse (the same PG period), and the envelope levels are compared with each other as described in 5 above. The output of the sample and hold circuit that outputs the envelope level in the earlier unit period of two consecutive unit periods is always supplied to the non-inverting input terminal of the comparator 56.

In this way, in the comparator 3611C,
Comparison of envelope levels in five consecutive unit periods that are adjacent to each other is performed. If the busy envelope level in the "current unit period" is higher than the envelope level in the "previous unit period", L
An output of high level is obtained, and when the output is small, an output of H level is obtained.

In this way, the "current" envelope level and the "immediately before current" envelope level are always compared by the comparator 36, and the output signal waveform is as shown in FIG. 6(K).

This output signal is supplied to the trigger input terminal of the T-FF circuit 67, and outputs a Q output whose output level is inverted when the envelope level in the current unit period JK becomes smaller than the envelope level in the previous unit period. signal(
(see FIG. 6(L)) and its inverted signal Qff1 are respectively supplied to one input terminal of an AND gate 48.degree. 47. On the other hand, since the PG pulse (see FIG. 6(A)) is supplied to the other input terminals of these AND gates 47 and 48, the output clock signal of the gate 48 is as shown in FIG. ) is obtained, and similarly, as the output clock signal of the gate 47, the sixth clock signal is obtained.
A signal as shown in Figure (N)K is obtained. These clock signals are supplied to an up/down counter 49 (see FIG. 5). This up/down counter 49 is of a separate clock type, and is shown in FIG. 6(M) above.
The input terminal to which the clock signal shown in FIG. 6(N) is supplied is a count-up clock terminal, and the input terminal to which the clock signal shown in FIG. Then, the counter 49
The output of is supplied to the D/A converter 51, and the count value of the counter 49 is output as an analog voltage.

Therefore, the envelope levels in each consecutive unit period are compared, and if the envelope level in the "previous unit period" is larger, the output of the comparator 66 will not be inverted from the L level to the H level. (See Fig. 6(K)), and by this reversal, the above T-F
The output signal of the F circuit 67 is inverted from H level to L level (see L1 in FIG. 6(L)). For example, if a pulse is being supplied to the counter in the direction of countdown in the previous state, the count value of the counter 49 will decrease by one step, so that the count value of the D/A converter 51 will decrease by one step, as shown in FIG. 6(0). The output voltage drops by one step, and conversely, if the envelope level of the "previous unit period" is smaller, the output signal of the T-FF circuit 37 remains unchanged from the previous state (Fig. 6 (L)). (See L2). Therefore, for example, in the direction of count up, the envelope level is "previous unit period".
As long as the PCx pulse is larger than , the AND gate 47 supplies the PCx pulse to the counter 49 as a count-up clock, and the output of the D/A converter 51 increases by one step. Then, when it becomes smaller than the "previous unit period", the output signal of the T-FF circuit 37 is inverted from the previous state, so for example, from the gate 4th, a PQ pulse is supplied to the counter 49 as a countdown clock. Since the count decreases by one step, the output voltage of the D/A converter 51 decreases by one step.

The output signal of the D/A converter 51 is sent to the inverting amplifier 5.
2. After passing through the level shift circuit 56,
As a result, a control voltage as shown in FIG. 6(P) K is output. When this control voltage is applied to the base of the transistor 2B, the operating voltage +V increases between the resistor 29 and the transistor 28.
The current is supplied to the first winding 22 as a direct current as shown in FIG. 6(Q). Then, the envelopes of the reproduced R and F signals change as shown in FIG. 6(C). In this way, comparing the envelope frequency in adjacent unit periods of 5K continuous unit periods, as long as the envelope level increases, the applied voltage is increased or decreased by 1 step, and conversely, when the envelope level decreases, the applied voltage is increased or decreased. By reversing the direction of voltage increase/decrease by 5K, the optimum direct current can be supplied to the winding 22 and the maximum output can be automatically maintained.

In this embodiment, the period of the PG pulse (rotation period of the magnetic disk) is set to be a unit period, but this is to avoid a case where only a specific location within one track has a good envelope. This unit period may be an integral multiple of the rotation period of the magnetic disk.

In addition, in this embodiment, the representative value for each predetermined time interval is “
Although the "minimum value" was used, the "average value" may also be used.

Furthermore, a tape-shaped medium may be used instead of a disk-shaped magnetic disk. When using this tape-shaped medium, for example, a reference signal is recorded on a successive portion of the tape, and the reproduced signal of this reference signal is compared between representative values of each predetermined cycle, and the What is necessary is to control the magnetic field generating means.

Further, in the first embodiment, the case was described for only the reproduction, but when erasing the recorded information signal, the circuit around the magnetic head having the configuration shown in FIG. 7 can be used. Bye.

That is, the magnetic hexagon 1212 winding 22. The capacitor 24, the transistor 28, and the resistor 29 are constructed in the same manner as in the first embodiment. The pace of the transistor 28 is connected to the movable contact piece 61a of the recording/reproducing/erasing switch 61, and the first fixed terminal 61b is connected to the output terminal of the buffer circuit 55 (see FIG. 5). . Also,
A second fixed terminal 61C of the changeover switch 61 is connected to an output terminal of a control circuit 63 for generating an erasing current.

In the peripheral circuit of the magnetic head configured as described above, in order to eliminate the influence of external magnetic fields during reproduction, the movable contact piece 61a of the changeover switch 61 and the first fixed terminal 61
If the connection is made so that the movable contact piece 61a and the second fixed terminal 61C are connected to each other, the operation is the same as in the first embodiment described above, and in the erase mode in which the recorded information signal is erased, the movable contact piece 61a and the second fixed terminal 61C are connected. Switch so that it is connected. Then,
During erasing, a control signal of an appropriate magnitude is sent from the control circuit 63 to the base of the transistor 28, and an erasing current from the operating voltage V is caused to flow through the winding 22, so that the magnetic head 2
1 generates a magnetic field for erasing.

Next, a second embodiment of the present invention will be described based on FIGS. 8 and 9. In this embodiment, a magnetic field generation source is provided outside the magnetic head, and the magnetic field generated by this source acts on the magnetic head.

As shown in FIG. 8, an electromagnet 65 is disposed near the main magnetic pole 8, and a winding 66 is wound around the electromagnet 65 to generate a magnetic field for canceling an external magnetic field. ing. A piezoelectric element 6 is located approximately in the center of the side surface of this electromagnet 65.
4 is attached to one end surface, and the other end is fixed to a member that moves together with the main magnetic pole 8. Electrodes are provided on the upper and lower surfaces of the piezoelectric element 64, respectively, and these electrodes are connected to the two output ends of the driver circuit 670, respectively. Here, the piezoelectric element 64 is bent (displaced) up and down as shown by the arrow in FIG. 8 in response to a predetermined voltage applied to the electrode. The input terminal of the driver circuit 670 is connected to the movable contact piece 68a of the recording/reproducing/erasing switch 68 as shown in FIG. (See Figure 5) D/A converter 5
It is connected to the output terminal of 1.

Note that in this case, the inverting amplifier 52. Level shift circuit 5
3. Buffer circuit 55. The transistor 28 and the like have been removed. Further, the second fixed terminal 68 of the switch 68
C is connected to an erase current generation source (not shown).

The operation of this embodiment configured as described above will be explained.

First, the operation during playback will be described. During playback, the selector switch 68 is switched so that the movable contact piece 68a and the first fixed terminal 68b are connected. In this state, the signal output from the D/A converter 51 is amplified to an appropriate strength by the driver circuit 67 and applied to the piezoelectric element 64 as a voltage signal. As a result, this piezoelectric element 64 is curved (displaced), and this displacement also causes the electromagnet 65 to be vertically displaced. On the other hand, both ends of a winding 660 wound around this electromagnet 65 are connected to a canceling current generating circuit (not shown), so that a canceling magnetic field is generated.

Since a canceling magnetic field is generated in this way, the strength of the magnetic field acting on the main magnetic pole 81C also changes depending on the displacement of the electromagnet 65. That is, the detected signal of the reproduced envelope signal changes as shown in FIG. 6(D). Here, as the voltage applied to the piezoelectric element 64 increases, the electromagnet 65 approaches the main magnetic pole 8. In other words, even if a magnetic field is applied from the electromagnet 65 to the tip of the main magnetic pole 8, if the external magnetic field is larger, the applied voltage increases, so the electromagnet 65 The closer it gets, the stronger it tries to cancel out the external magnetic field. Conversely, if the level of the reproduction envelope decreases because the electromagnet 65 is too close to the main pole 8, the applied voltage decreases and the electromagnet 65 is displaced away from the main pole 8.

Further, when the movable contact piece 68a of the switch 68 is connected to the second fixed terminal 68c, it is an erase mode in which the recorded information signal is erased, and in this erase mode, the D/A converter 51 DC voltage is applied at a sufficiently higher level than the output voltage of .

Therefore, when this DC voltage is applied to the piezoelectric element 64 through the driver circuit 67, the electromagnet 64 emitting a magnetic field
5 is very close to the main magnetic pole 8 and supplies a DC magnetic field larger than the external magnetic field, so that the information signal recorded on the magnetic disk 1 is erased by DC current.

In this embodiment, a main pole excitation type perpendicular magnetic head has been described, but it goes without saying that the present invention can also be applied to an auxiliary pole excitation type perpendicular magnetic head. Furthermore, it goes without saying that a permanent magnet may be used instead of the electromagnet 650 described above.

(Effects) According to the present invention, it is possible to prevent erasure of recorded information due to an external magnetic field, which is a particular problem in perpendicular magnetic recording systems, and it is possible to prevent the erasure of recorded information due to external magnetic fields, which is a particular problem in perpendicular magnetic recording systems. It is possible to generate just the right amount of magnetic field to cancel out the external magnetic field, thereby realizing a reproducing state similar to that in the absence of the external magnetic field.

[Brief explanation of drawings]

1 is a diagram showing the state in which an external magnetic field affects a perpendicular magnetic head; FIG. 2 is a diagram showing the principle of the present invention for canceling the external magnetic field shown in FIG. 1; 3 is an electric circuit diagram showing the principle of the magnetic field generating section used in the first embodiment of the present invention, FIG. 4 is an electric circuit diagram of the magnetic field generating section used in the first embodiment of the present invention, and FIG. , an electric circuit diagram of a perpendicular magnetic recording and reproducing apparatus showing a first embodiment of the present invention, FIG. 6 is a time chart showing the operation of the perpendicular magnetic recording and reproducing apparatus shown in FIG. 5, and FIG. FIG. 5 is an electric circuit diagram showing a modification of the magnetic field generating section of the perpendicular magnetic recording/reproducing apparatus shown in FIG. The figure is an electric circuit diagram showing the vicinity of the driving part of the piezoelectric element shown in FIG. Figure 12 is a diagram showing the flow of the magnetic field in the conventional longitudinal magnetic recording system. Figure 13 is an enlarged side view of the main part of the main pole excitation type perpendicular magnetic head. Figure 14 is a diagram showing the B-H characteristics of the main pole of the vertical magnetic head; Figure 15 is the characteristic shown in Figure 14 above. FIG. 2 is a diagram showing the B-H characteristics of a recording medium magnetized by a perpendicular magnetic head having the following characteristics. 1, la, 30... Perpendicular magnetic recording medium (magnetic disk) 2.8.21... Main magnetic pole (magnetic spatula)
5.9 Main pole film 28 Transistor (magnetic field generation means) 36 Comparator (comparison means) AF, @118611611611@ Business Xm r
/ m N n /J-! $F! ) Horse 1 Map Ka 20 Plan 3 Kasumi Plan 4 Plan 8 Plan 8 Island 10 Plan 11 Plan 12 Plan

Claims (1)

[Claims] In a perpendicular magnetic recording/reproducing device configured to reproduce information recorded on a perpendicular magnetic recording medium using a perpendicular magnetic head, the information recorded on the perpendicular magnetic recording medium may be reproduced at predetermined time intervals in synchronization with the movement of the perpendicular magnetic recording medium. means for detecting a predetermined representative value of the reproduced signal level in the section; means for comparing the representative values for each of the two different sections; 1. A perpendicular magnetic recording and reproducing device comprising: means for generating an acting magnetic field.