JPS5834029B2 - Head crush prevention device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a head crash prevention device for a magnetic disk device.

In recent years, so-called tracks have been developed, in which a servo trunk in which position information is recorded in advance on a specific surface, that is, a servo surface, in a magnetic disk is set, and the position information is read out with a magnetic head, that is, a servo head, and positioning is performed as a position servo signal. With the realization of a tracking type magnetic head positioning device, its performance has greatly improved.

In such a trunk-following type magnetic head positioning device, various methods have been proposed and put into practical use for the servo trunk formed on the servo surface, and typical examples include the dibit method and the dual-frequency method. Yes, details are in Tokuko Sho 47-32012 and Tokko Sho 41-2586.
However, in both methods, data is recorded on two adjacent servo tracks.
The principle is to read the quantity information simultaneously with one servo head and control the amplitudes of the read signal components from two adjacent servo tracks to be equal. Therefore, the boundary between the two servo trunks is This is the center of the data track where data is recorded.

The outline of the dibit method will be explained below with reference to the figures.

FIG. 1 is an enlarged view of two adjacent servo tracks among a plurality of servo tracks formed concentrically on the servo surface, where N and N+1 are servo trunk numbers;
+ and - are the directions of magnetization recorded in advance on the servo track, 1 is the direction of movement of the servo track caused by the rotation of the magnetic disk, 2 is the servo head, and 3 is the direction of movement of the servo head 2, that is, the positioning direction; tB
yC, D, and E indicate positional changes of the servo head 2 in the movement direction 3.

FIG. 2 is a diagram showing the output of the servo head 2 when the servo head 2 causes the position changes A, B, C, D, and E as shown in FIG. b, c, d
, e correspond to the position changes A, B, C, D, and E in FIG.

In FIGS. 1 and 2, if the servo head 2 moves in the movement direction 3 for positioning to a desired track, the servo head 2 moves in the movement direction 3, B, C, D.
, E, person, and B. song are repeatedly stuttered until the target position is reached.

Therefore, the servo head 2 moves to the movement positions A, B, and C.
,..., as shown in Figure 2, a
, b, c, d.

Outputs e, a, ...... are generated.

On the other hand, when the target position is reached, the output of the servo head 2 is processed by an electronic circuit and then fed back as a position servo signal.
It is controlled as shown below.

Furthermore, as is clear from FIGS. 1 and 2, in this Guipinto method, the sum of the amplitudes of the two readout signal components simultaneously read out by the servo head 2 from the adjacent servo trunks N and N+1 is always constant. One of the characteristics is that.

As mentioned above, the trunk following type magnetic head positioning device is based on the premise of reading out the positional information accurately and reliably, and it is clear that improving the reliability of the device is based on the reliability of reading out the positional information. It comes down to increasing sexuality.

However, the servo head normally has a structure that opposes the servo surface and levitates on the servo surface while maintaining an extremely small gap, that is, the amount of levitation. The purpose of this is to remove dust that is scattered in the air flow on the disk surface, by installing a closed air stem that supplies only air that has passed through a strict air filter into the magnetic disk, or by installing a hard protective layer on the surface of the magnetic disk. In addition, the flotation system, which includes the characteristics of the spatula arm for holding the magnetic head and maintaining the minute gap, and the vibration characteristics of the magnetic disk surface, is more stable. However, various efforts and efforts have been made to research the structure of the levitation system with higher reliability and a design method that makes full use of aerodynamic methods to realize the structure. However, there is a drawback that the contact phenomenon between the servo head and the servo surface (hereinafter referred to as rad crush phenomenon) cannot be completely prevented, and once the phenomenon occurs, the servo head and the servo surface In many cases, both surfaces become unusable. In particular, if the position information pre-recorded on the servo track is damaged, the data head for writing or reading data on the magnetic disk cannot be positioned on the desired track. This was a fatal defect in that the positioning device did not have the same structure, and the reliability of the positioning device was significantly reduced.

Therefore, an object of the present invention is to provide a novel means that eliminates the above-mentioned drawbacks, and makes it possible to significantly improve the axiality of a track-following magnetic head positioning device with a relatively simple structure and inexpensive means. An object of the present invention is to provide a head crash prevention circuit characterized by the following.

According to the present invention, a servo trunk in which position information is recorded in advance on a specific surface, that is, a servo surface, in a magnetic disk is set, and the position information is read out by a magnetic head, that is, a servo head, and positioning is performed as a position servo signal. In a track-following magnetic head positioning device such as the one described above, a generator generates a predetermined head crash prevention voltage Ec and separates two read signal components from adjacent servo tracks included in the output signal of the servo head. an adder that generates a voltage (1) that is the sum of the amplitudes of the read signal components; an output of the adder, that is, a voltage V that is the sum of the amplitudes;
c, and when ■≧Ec, a comparator that generates a head unload signal, a drive circuit that receives the head unload signal and drives the actuator by 1; and an actuator for releasing the floating state of the servo head, that is, bringing the servo head into a head unload state, and the actuator is driven by the herad unload signal to bring the servo head into the head state before the herad crush phenomenon occurs. By maintaining the unloaded state, it is possible to prevent the above-mentioned crush phenomenon.

A head crash prevention circuit is obtained.

The head crash prevention circuit of the present invention takes advantage of the fact that the relationship between the servo head output signal and the amount of levitation is almost inversely proportional. By focusing on the increase in the amount of levitation and comparing it with a preset voltage, it is possible to detect an abnormal decrease in the amount of lift before a head crush phenomenon occurs. A head crash prevention device that can significantly improve the reliability of a follow-up magnetic head positioning device can be realized, and the object of the present invention can be sufficiently achieved.

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

FIG. 3 is a block diagram of an embodiment of the present invention, in which 11 is a servo surface, 12 is a servo head, 13 is an amplifier for amplifying the output signal of the servo head, and 14 is an amplifier. A comparator, 15 is a drive circuit, 16 is an actuator, which in the present invention is a piezoelectric element such as PZT, 17 is a herad crush prevention voltage generator, and 18 is a servo head 13.
2 from adjacent servo tracks included in the output signal of
This adder separates two readout signal components and generates a voltage that is the sum of their amplitudes.This adder is used to output the output signal of the servo head 12 in synchronization with the output signal of the servo head 12 as shown in FIG. An oscillator, or PLO (Phaselocked oscillator), oscillates at the same frequency as the signal, or position information recorded in advance on the servo track.
peak detection of the output signal of the servo head 12 is performed in synchronization with the output signal of the servo head 12, and two readout signal components from adjacent servo tracks, that is, servo tracks numbered N and number N+1 shown in FIGS. 1 and 2, are detected. The output of the adder 18, that is, the sum of the peak levels, is used as a feedback signal for an AGC circuit (Kane control circuit), not shown. ing.

Even if the servo head 12 is in a normal floating state, the AGC circuit is configured such that even if the servo head 12 is in a normal floating state, when it is located on an outer servo track and an inner servo track, the air flowing near each servo track is affected by the difference in circumferential speed between the servo tracks. It is said that the output signal of the servo head 12 fluctuates due to changes in the amount of levitation caused by differences in flow speed, and the output signal of the servo head 12 is kept at a constant value. When the condition is normal, that is, when the levitation amount is within the permissible limit value, the output is always kept constant.

Also, 1oo is a signal line, and the double line is the servo head 12.
This represents the mechanical connection between the actuator 16 and the actuator 16.

Now, in the figure, when a positioning start signal is applied to the head crush prevention voltage generator 17 from a control circuit (not shown) via a signal line 100, the generator 1
7 is the comparator 14 which converts the hedra crash prevention voltage Ec to the comparator 14.
4 stutter.

On the other hand, the position information recorded on the servo track on the servo surface 11 is read out by the servo spatula lower 12 and sent to the adder 18 via the amplifier 13.
The output voltage V is applied to the comparator 14, and the comparator 14 compares the Herad crash prevention voltage Ec with the output voltage V of the adder 18, and if ■≧Ec, generates the Herad unload signal. At the same time, the drive circuit 15
Immediately after the application to the servo head 12, the actuator 16 releases the floating state of the servo head 12, that is, maintains the head unloaded state.

FIGS. 4a and 4b are diagrams for explaining the normal floating state and head unloading state of the servo head, respectively, and are diagrams showing the configuration of an embodiment of the present invention.

In the figure, 12 is a servo head, 16 is an actuator, which in the present invention is a piezoelectric element such as PZT, and 11
is a servo surface; 22 is a helad arm for holding the servo head 12 and allowing the servo surface 11 and the servo head 12 to float while maintaining a small gap; 23 is a helad arm;
24 is a gimbal spring for fixing the heradosh 22 to the helad arm, 25 is a carriage for supporting the servo head 12 and a plurality of data heads (not shown), and the actuator 16 is attached to the head arm 23. are attached to the upper and lower surfaces of the helad arm 23 parallel to the servo surface 11 on the carry-in 25 side.

FIG. 4a shows a head unload signal 75 (not generated) from the comparator 14 in FIG. It shows a state in which it is floating while maintaining a minute gap with 11.

FIG. 4 shows that when the servo head 12 is in the normal floating state shown in FIG. The servo head 12 is separated from the servo surface 11 and the floating state is released, ie, the head is unloaded.

Figure 5 is a diagram for explaining the relationship between the output and the amount of levitation of the servo head and the setting of the head crash prevention voltage. The nominal value of the levitation amount of the head, △δ is its allowable width, δ+△δ is the permissible limit value of the levitation amount, and Em and Em±△Em are the nominal value δ and the allowable limit value of the servo head levitation amount, respectively. It represents the output voltage of the servo head when δ±△δ.

It is generally known that the relationship between the output of a magnetic head and the flying height can be considered to be almost inversely proportional as shown in the figure, and is described in detail in IEICE Magnetic Recording Study Group Material MR7417.

Now, assuming that the floating amount is constant at the nominal value δ, the output voltage of the servo head changes as shown in Figure 2 as the position changes in the positioning direction, but as mentioned above, it is included in the output signal of the servo head. Since the voltage of the sum of the amplitudes of two read signal components from adjacent servo tracks is always constant, the voltage of the sum of the amplitudes is assumed to be .Furthermore, the levitation amount varies within its allowable width △δ. Assuming that the fluctuation of the voltage (2), which is the sum of the amplitudes, is ΔV and referring to FIG. 5, it is true that Em-V and ΔEm-Δ■ are set.

Therefore, the voltage (■), which is the sum of the amplitudes, becomes maximum at the permissible limit value of 8 to △δ of the levitation amount, and its value is ■+△V, so the hedra crash prevention voltage EC is defined as Ec=V+△
■+l (l cow O) is set, and the sum of the width ■ is ■≧EC
When the amount of levitation of the servo head reaches its levitation limit value δ−
This is smaller than Δδ, and as a result, abnormal approach between the servo surface and the servo head can be detected before a head crush phenomenon occurs.

Therefore, the object of the present invention can be fully achieved.

Although the operating principle of the present embodiment has been described in detail above, modifications can be made without departing from the spirit of the present invention, and the above description does not limit the scope of the present invention.

[Brief explanation of the drawing]

Figure 1 is an enlarged view of two adjacent servo tracks out of a plurality of servo tracks formed concentrically on a servo surface, showing an outline of a servo track using the conventional die bit method. Figure 2 is an enlarged view of two adjacent servo tracks. FIG. 3 is a block diagram of an embodiment of the present invention, and FIGS. 4a and 4b each illustrate an embodiment of the present invention. FIG. 5 is a diagram for explaining the normal floating state and head unloading state of the servo head shown in FIG. N, N+1 are the numbers of the servo tracks, 1 is the movement direction of the servo tracks, 2 is the servo head, 3 is the movement direction of the servo tracks, A, B, C, D, E are position changes in the positioning direction of the servo tracks, a . b, c, d, e are the position changes A of the servo head in Fig. 1;
Output signal waveforms of servo heads corresponding to B, C, D, and E, 11 is servo surface, 12 is servo head, 13 is amplifier, 14 is comparator, 15 is drive circuit, 16 is actuator, 17 is head crash prevention Voltage generator, 18 adder, 22 heradosh, 23 head arm, 24 gimbal spring, 25 carriage, 100 signal line.

Claims (1)

[Claims] A track-following magnetic system in which a servo trunk in which positional information is recorded in advance on a specific surface of a magnetic disk, that is, a servo surface, is set, and a magnetic head, that is, a servo head, reads out the positional information and performs positioning as a positional servo signal. The head positioning device includes a head crush prevention voltage generator that generates a preset head crush prevention voltage, and a head crush prevention voltage generator that separates two read signal components from adjacent servo tracks that are determined by the output signal of the servo head. an adder that generates a voltage that is the sum of the amplitudes of the read signal components; a comparator that compares the voltage that is the sum of the amplitudes with the head crash prevention voltage and generates a head unload signal; a drive circuit for driving an actuator in response to a rad unload signal; and an actuator for bringing the servo head into an unload state in response to the head unload signal supplied via the drive circuit. Features a head crush prevention device.