JPH0682497B2 - Headlash detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] The present invention improves the detection sensitivity of head crush by directly attaching a piezoelectric element to a core slider, and configures the output terminal of the piezoelectric element as a pair of electrodes, This is a head crash detection method in which electrical noise generated in the same phase is removed by differentially amplifying the detection signal.

[Industrial application field]

The present invention relates to a head crash detection method in a magnetic disk device.

The magnetic recording medium mounted on the magnetic disk device is disk-shaped and is required to have high smoothness in order to maintain the floating characteristic of the magnetic head and prevent head crash.

A means for further improving the smoothness of the magnetic disk surface in order to further reduce the distance between the magnetic disk and the magnetic head for high-density recording on the magnetic recording medium, and further improve the head crash detection sensitivity. Development is desired.

[Conventional technology]

FIG. 5 is a schematic diagram of a conventional head crash detection method and an explanatory diagram of its features. In the figure, reference numeral 1 denotes a magnetic head, which reads and writes information while levitating on a rotating magnetic disk (not shown) attached to a core slider 2. Reference numeral 3 is a gimbal that supports the core slider 2, and 4 is an arm that supports and accesses the gimbal, and is directly connected to an actuator (not shown). Reference numeral 5 is an ultrasonic wave detector composed of a piezoelectric element, also known as an acoustic wave extraction element (Acoustic Emissi
The following is abbreviated as AE sensor), and is known as an element that efficiently converts minute mechanical vibrations into electrical signals.

A contact source signal 6 is detected by the AE sensor 5 via the gimbal 3 and the arm 4 by contacting the core slider 2. The characteristics of the contact signal at each part will be described according to the signal transmission path with reference to the graphs of FIGS. 6A to 6D in which the horizontal axis represents the frequency and the vertical axis represents the relative value of the AE sensor output.

In the graph (a) of FIG. 6, the output is attenuated as the frequency becomes higher due to the frequency characteristic of the contact source signal 6. The AE sensor 5 cannot be conventionally provided on the core slider 2 or the gimbal 3 due to its inherent size limitation, and the arm 4 is exclusively used.
It is provided at a position (away from the contact signal source 6).

The graph (b) shows the frequency characteristic of the gimbal 3 serving as the transmission path of the contact source signal 6, and has the effect of attenuating the output as the frequency increases. The graph (c) has a characteristic that it has a peak in the vicinity of 100 KHz due to the frequency characteristic of the AE sensor itself, and in order to obtain high sensitivity, there is no choice but to adjust to a low frequency (around 100 KHz).

Graph (d) shows the frequency characteristics of the total detection signal of the conventional AE sensor, and since mechanical noise due to spindle rotation and the like is large in the low-frequency region near 100 KHz, contact signals and mechanical noise coexist. .

[Problems to be Solved by the Present Invention]

As explained above, it is impossible to improve the detection sensitivity of the contact signal with the conventional method due to the increase of the contact signal transmission loss due to the restriction of the attachment position of the AE sensor or the occupation of the low frequency area of mechanical noise. there were.

The present invention was created in view of the above-mentioned conventional drawbacks, and an object of the present invention is to provide a head crash detection method capable of improving the detection sensitivity of a contact signal.

[Means for solving problems]

As shown in FIG. 1, the head crush detecting method of the present invention is provided with a piezoelectric element 7 having a pair of electrodes 8a and 8b on the surface opposite to the floating surface of the core slider 2, that is, the back surface thereof, and the pair of electrodes 8a and 8d. A differential amplifier 14 that differentially amplifies the outputs of the respective outputs and outputs a head crash detection signal is provided.

[Action]

By removing the shield case of the conventional AE sensor 5 and providing the pair of electrodes 8a, 8b on the piezoelectric element 7 inside, the dimensional constraint is released, and it can be directly attached to the core slider 2 for contact signal transmission. You can reduce the loss. Further, since the outputs of the pair of electrodes 8a and 8b are respectively input to the differential amplifier 14 and differentially amplified, electrical noise generated in the same phase can be removed, so that the detection sensitivity of the contact signal can be improved. You can

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings. In addition, in order to make the description of the configuration and the operation easy to understand, the same reference numerals are given to the same portions throughout the entire surface, and duplicate description thereof will be omitted.

FIG. 1 shows a schematic diagram of an embodiment of the present invention. In the figure, 7
Is a piezoelectric element that constitutes the contents of the AE sensor, and is provided with a pair of electrodes 8a and 8b. Reference numeral 8c is a ground electrode interposed between the piezoelectric element 7 and the core slider 2 and electrically connected to the core slider 2. As described above, the electrodes are formed only on the piezoelectric element 7 inside of which the shield case of the AE sensor is removed, so that the dimensional restriction is released and the core slider 2 can be attached to the surface facing the floating surface.

The signal lines 9 connected to the electrodes 8a and 8b are connected to the terminals 10a and 10b provided on the arm 4 along the conductive gimbal 3 and output from here via the shield line 11.

Reference numeral 12 indicates a magnetic disk, and arrow P indicates the rotation direction of the magnetic disk 12.

FIG. 2 shows a block diagram of an embodiment of the present invention. In the figure, 13 is a piezoelectric element head, which is composed of the piezoelectric element 7 and a pair of electrodes 8a and 8b. Reference numeral 14 denotes a differential amplifier which inputs detection signals from the pair of electrodes 8a and 8b. The differential amplifier 14 removes electrical noise generated in the same phase. Reference numeral 15 is a bandpass filter that removes mechanical noise in the low range and electrical noise in the high range to select a target band. Reference numeral 16 is a comparator which sets a required threshold value, removes noise below the threshold value, and detects a target contact signal 17.

The core slider attachment method using the same piezoelectric element head 13 increases the detection sensitivity by about 100 times as compared with the arm attachment method.

As the signal line 9 for guiding the output from the piezoelectric element head, a shield line having a large rigidity cannot be used in terms of rigidity of the gimbal 3. Use an insulated wire with weak rigidity. Therefore, the signal line 9 easily picks up noise in the space, but the noise mixed in the same phase is canceled by the action of the differential amplifier 14. Factual differential amplifier
There is so much noise that it cannot be used in a general environment without 14. Further, the detection sensitivity is increased about twice by using the differential amplifier 14.

FIG. 3 shows a first modification of the piezoelectric element structure of the present invention. In the figure, 18a and 18b indicate a pair of electrodes. In this case, insulation is required between the core slider 2 (or ground) and each electrode.

FIG. 4 shows a second modification of the piezoelectric element structure of the present invention. In the figure, 19a and 19b indicate a pair of electrodes, and in this case as well, insulation is required between the core slider 2 (or ground) and each electrode. As described above, even if the asymmetrical electrode is used, there is no problem in practically detecting the contact signal.

[Effect of the present invention]

As described in detail above, according to the head crash detection method of the present invention, S / N is improved several tens of times as compared with the conventional method, so that it is possible to detect a minute contact situation that has not been seen in the past, It is very effective in developing a magnetic disk device.

[Brief description of drawings]

FIG. 1 is a schematic view of an embodiment of the present invention, FIG. 2 is a block diagram of the embodiment of the present invention, FIG. 3 is a view showing a first modification of the piezoelectric element structure of the present invention, and FIG. 4 is a view of the present invention. The figure which shows the 2nd modification of a piezoelectric element structure, FIG. 5 is a figure which shows the conventional head crash detection structure typically, FIG. 6 is the signal characteristic of each part in the transmission path of the contact source signal of FIG. It is a figure for explaining. In the figure, 1 is a magnetic head, 2 is a core slider, 5 is an ultrasonic wave detector (AE sensor), 7 is a piezoelectric element, 8a and 8b are electrodes, and 14 is a differential amplifier.

Claims (1)

[Claims] 1. A piezoelectric element (7) having a pair of electrodes (8a, 8b) is attached to the back surface of a core slider (2) levitating on a rotating magnetic disk, and the pair of electrodes (8a, 8b). The head crash detection method is characterized in that the output of each is input to the differential amplifier (14) and the head crash is detected by the output of the differential amplifier (14).