Patent Application
20080204924
The instant nonprovisional patent application claims priority to Japanese Patent Application No. 2007-040464 filed Feb. 21, 2007 and which is incorporated by reference in its entirety herein for all purposes.
To increase the data-recording density of a hard disk, it is necessary to reduce the spacing between a recording/reproducing head and a magnetic film of the hard disk. On the other hand, reducing the spacing increases the risk of the head touching the disk and damaging it. Thus, the reliability of the hard disk is reduced. While maintaining the reliability and reading and writing data, the spacing should be as small as possible. Therefore, it is necessary to reduce the mechanical variation of the spacing between the head and the disk due to environmental variations such as the variations of atmospheric pressure and temperature and manufacturing errors such as dimensional errors of the floating surface of the floating head slider. Accordingly, an art to dynamically control the spacing after the hard disk being mounted was developed. To make the best use of the art, it is necessary to determine the spacing between the head and the disk accurately. The spacing can be determined accurately by reducing the spacing gradually until the head touches the disk and treating the touch point as the datum, or basis for measurement. According to this method, the spacing margin for manufacturing errors and environmental variations can be dispensed with and, therefore, data can be recorded and reproduced with a smaller spacing on the average.
According to the above method, however, because the head is put into contact with the disk once, there may be damage due to the contact. To minimize the risk, it is important to detect the heads' contact with the disk with high sensitivity.
Disclosed in Japanese Patent Publication No. 2002-74686 (“Patent document 1”) is an approach to detect such contact. That is, according to the art disclosed in Patent document 1, an optical disk device of the art comprises: an actuator which has a first objective lens and approaches and leaves a disk-type recording medium under focusing control; and a floating slider which has a second objective lens and moves along with the actuator and is floated over the surface of the disk-type recording medium by an airflow caused by the rotation of the disk-type recording medium. Signals are produced by removing the components of frequencies in the vicinity of the rotational frequency of the disk-type recording medium from the level changes of the focusing-error signals of the first and second objective lenses and comparing the signals so produced with a reference level to move the floating slider away from the surface of the recording medium.
Disclosed in Japanese Patent Publication No. 2005-4909 (“Patent document 2”) is a magnetic disk device with an actuator which moves slightly. The heads' contact with the disk is detected by monitoring the output signals from the slightly-moving actuator. Besides, in this regard, a method of detecting the contact by monitoring frequencies other than the natural frequency of the mechanical system is disclosed.
As described above, in the case of the method of estimating the fly-height of the head by detecting the head's contact with the disk, the head and the disk may be damaged by the contact. To minimize the risk, it is important to detect the head's slight contact with the disk with high sensitivity while the fly-height of the head is decreased. The detecting power can be improved by monitoring the variation of reproduced signals. It is difficult, however, to set a boundary between the variations in the steady state and the variations at the time of contact because the inherent system noise of the device is superimposed on those variations. As a result, the head is put into contact with the disk for a long time, which increases the risk of damaging the head and the disk.
An object in accordance with embodiments of the present invention is to compute controlling quantity to make the spacing between a floating head slider and a recording medium optimum without damaging the floating head slider and the recording medium by detecting the floating head slider's contact with the recording medium with high sensitivity.
According to the particular embodiment disclosed in
Embodiments of the invention relate to an information recording device, and particularly to a magnetic disk device with a mechanism to control the fly-height of a floating head slider.
Embodiments of the present invention were made under the above circumstances. Specifically, an object of embodiments of the present invention is to provide an information recording device wherein (i) the spacing between the floating head slider and the recording medium is dynamically controlled, and (ii) controlling quantity to make the spacing between the floating head slider and the recording medium optimum is computed without damaging the floating head slider and the recording medium by detecting the floating head slider's contact with the recording medium with high sensitivity.
In order to achieve the above object, according to a first feature of embodiments of the present invention, there is provided an information recording device which comprises (i) a recording medium, (ii) a floating head slider with a recording head, a reproducing head, and a fly-height-control mechanism, and (iii) a controller for controlling the fly-height-control mechanism, wherein, when the floating head slider is floating over the recording medium, the controller (i) takes samples of a notable characteristic value from signals reproduced by the reproducing head, (ii) retains the variation of the sample characteristic value as a reference signal, (iii) takes samples of the notable characteristic value from signals reproduced by the reproducing head while reducing the spacing between the floating head slider and the recording medium gradually, (iv) produces a signal which is the sample characteristic value from which the reference signal is subtracted, (v) detects the floating head slider's contact with the recording medium when the fluctuation of the signal so produced exceeds a reference value, and (vi) computes the fly-height-control mechanism's controlling quantity for making the spacing between the floating head slider and the recording medium optimum on the basis of the controlling quantity of the fly-height-control mechanism at the time of detecting the contact and retains the controlling quantity so computed.
It may be desirable that the above notable characteristic value is one of the amplitude of reproduced signals, the waveform of reproduced signals, timing jitters, and position data.
It may be desirable that the fly-height-control mechanism's controlling quantity for making the spacing between the floating head slider and the recording medium optimum is computed after the assembly of the information recording device.
According to a second feature of embodiments of the present invention, the controller of the information recording device (i) takes samples of a notable characteristic value from signals reproduced by the reproducing head while reducing the spacing between the floating head slider and the recording medium gradually, (ii) produces a signal which is the sample characteristic value from which components, whose frequencies are not higher than five times the rotational frequency of the recording medium, are removed, (iii) detects the floating head slider's contact with the recording medium when the fluctuation of the signal so produced exceeds a reference value, and (iv) computes the fly-height-control mechanism's controlling quantity for making the spacing between the floating head slider and the recording medium optimum on the basis of the controlling quantity of the fly-height-control mechanism at the time of detecting the contact and retains the controlling quantity so computed.
According to a third feature of embodiments of the present invention, the controller of the information recording device (i) takes samples of a notable characteristic value from signals reproduced by the reproducing head while reducing the spacing between the floating head slider and the recording medium gradually, (ii) produces a signal which is the sample characteristic value from which components of frequencies in the vicinity of the resonance frequency of the floating head slider are extracted, (iii) detects the floating head slider's contact with the recording medium when the fluctuation of the signal so produced exceeds a reference value, and (iv) computes the fly-height-control mechanism's controlling quantity for making the spacing between the floating head slider and the recording medium optimum on the basis of the controlling quantity of the fly-height-control mechanism at the time of detecting the contact and retains the controlling quantity so computed.
According to embodiments of the present invention, contact between the floating head slider and the information recording medium can be detected without damaging them, and controlling quantity for making the spacing between the floating head slider and the information recording medium optimum can be computed on the basis of the condition at the time of detecting the contact.
By referring to drawings, preferred embodiments of the present invention will be described.
As shown in
The preamplifier 7 receives signals representing data to be recorded through the read/write channel 8, amplifies them, and feeds them to the recording head 3a of the floating head slider 3. Besides, the preamplifier 7 amplifies the signals reproduced by the reproducing head 3b and outputs them. Moreover, the preamplifier 7 of the present embodiment receives a signal representing an electric-current value (controlling quantity) and feeds an electric current (or voltage or electric power) of the inputted electric-current value to the heater 3c. Provided between the floating head slider 3 and the read/write channel 8 is a flexible cable (FPC) 11 to cope with the rotational motion caused by the VCM 5. The preamplifier 7 is fitted onto the FPC 11 with solder.
As shown in
The read/write channel 8 encodes signals from the controller 9 and feeds the encoded signals to the preamplifier 7 as electric signals. The read/write channel 8 also decodes reproduced signals from the reproducing head 3b through the preamplifier 7 and feeds the decoded signals to the controller 9. The controller 9, through the read/write channel 8 of the present embodiment, controls the spacing between the floating head slider 3 and the magnetic disk 1.
The controller 9 may be a microprocessor and functions in accordance with a program stored in the memory 10. The controller 9 receives data to be recorded from a host computer of the magnetic disk device and feeds the data to the read/write channel 8. The controller 9 outputs signals to the VCM controller 6 so as to move the floating head slider 3 to data-recording positions on the magnetic disk 1. According to the present embodiment, when data is recorded or reproduced, the floating head slider 3 is moved under the control of the VCM controller 6 to an address on a track designated by the servo data.
Besides, when the controller 9 receives instructions from the host computer to read out data from the magnetic disk 1, it outputs a signal to the VCM controller 6 so as to move the floating head slider 3 to the address related to the instruction where the data is recorded and, then, receives decoded signals from the read/write channel 8 and feeds them to the host computer.
In summary, the magnetic disk device is connected to the host computer and receives (i) instructions from the host computer to record data and (ii) electric signals representing the data to be recorded and, then, the controller 9 feeds the data to be recorded to the read/write channel 8, which encodes the data and feeds the it to the preamplifier 7, which produces the electric signals, and the recording head 3a converts the electric signals into magnetic signals and magnetizes the magnetic disk 1 to record the data onto it.
On the other hand, when the magnetic disk device receives instructions from the host computer to read out data from the magnetic disk 1, the controller 9 outputs a signal to the VCM controller 6, which controls the carriage assembly 4 through the VCM 5 to move the floating head slider 3 to the address where the data are recorded. The reproducing head 3b of the floating head slider 3 reads out the recorded data and feeds the data signals to the preamplifier 7, which amplifies the data signals and feeds the amplified data signals to the read/write channel 8, which decodes the data signals and feeds the decoded data signals to the controller 9, which feeds the decoded data signals to the host computer.
Operation of the controller 9 will be described. When data are to be recorded, the controller 9, following a prescribed procedure and taking environmental conditions into account, gives the read/write channel 8 instructions to make the spacing between the magnetic disk 1 and the floating head slider 3 optimum. According to the instructions, the read/write channel 8 controls the fly-height-control mechanism 3c to control the spacing. With the spacing controlled to be optimum, data are recorded onto concentric tracks on the magnetic disk 1. Similar processing is carried out to read out data. Thus, data can be recorded densely and reproduced efficiently.
According to the present embodiment, after the assembly of the magnetic disk device but before its shipment, or at prescribed intervals, or when the magnetic disk device lies idle, the controller 9 estimates environmental factors and the spacing and computes the controlling quantity (electric-power value) of the fly-height-control mechanism for making the spacing optimum. To estimate the spacing, it is set wide enough first, and then gradually narrowed. While the spacing is gradually narrowed, reproduced signals are monitored to detect the floating head slider 3's contact with the magnetic disk 1. The electric-power value of the fly-height-control mechanism at the time of the contact is treated as the datum, or basis for measurement, and the spacing is computed backward from the datum. The backward computation of the original spacing (fly-height) requires the proportional coefficient, or “spacing-reducing efficiency,” between the electric-power value and the change of fly-height. As for the “spacing-reducing efficiency,” a value peculiar to the floating head slider may be calculated from Wallace's formula of spacing loss during the inspection before shipment. Alternatively, a typical value found beforehand by simulation or a sample test may be used.
With reference to
As described above, according to the contact detection in Example 1, because low-frequency noise due to the rotation of the magnetic disk is removed by removing, from sample signals, components whose frequencies are not higher than five times the rotational frequency of the magnetic disk, the floating head slider's contact with the magnetic disk can be detected with high sensitivity.
If the above processing is made after the assembly of the magnetic disk device but before its shipment, the controller can control the fly-height-control mechanism by using the electric-power value stored in the memory so as to make the spacing between the floating head slider and the magnetic disk, or floating amount of the floating head slider, optimum when the magnetic disk device is turned on. If the above processing is made at regular intervals or while the magnetic disk device is idle after the shipment of the magnetic disk device, the controller can control the fly-height-control mechanism by using the electric-power value stored in the memory, until the next processing, so as to make the spacing between the head and the disk optimum.
In Example 1, although the amplitude of reproduced signals is chosen as a notable characteristic value, the waveform of reproduced signals, timing jitters, position data, etc. may be chosen as other items to be sampled. Desirable methods of taking samples of notable characteristic values will be as follows.
Method of Taking Samples of Amplitude of Reproduced Signals:
(1) The AGC gain of the read/write channel 8 is monitored.
(2) User-data sections or servo-data sections or both the user-data and servo-data sections of the tracks are monitored.
(3) Periodic sampling is made.
(4) To be precise, a periodic sampling is regarded as pseudo-periodic sampling.
Method of Taking Samples of Waveform of Reproduced Signals:
(1) The coefficient of the adaptively functioning filter of the read/write channel 8 is monitored.
(2) The variation (change) of resolution is monitored.
(3) The asymmetry of waveform of reproduced signals with respect to the x-axis is monitored.
(4) The errors in equalization of waveform are monitored at the read/write channel 8.
(5) The quantity of noise is monitored at the read/write channel 8.
(6) The bit error rate is monitored.
Method of Taking Samples of Timing Jitters:
(1) The result of the phase-lock loop of the read/write channel is monitored.
Method of Taking Samples of Position Data:
(1) Position signals are produced from position data stored in the medium and the fluctuation of the signals is monitored.
In Example 1, variance is used as a method to quantify fluctuation. However, the maximum value of signals may be used by using a comparator.
With reference to
Although the example of taking samples of the amplitude of reproduced signals is also shown in Example 2, as in Example 1, the waveform of reproduced signals, timing jitters, position data, etc. may be chosen.
With reference to
In the processing according to Example 3, too, various noises due to the rotation of the medium are subtracted from the amplitude of reproduced signals by using the reference signal. Therefore, the floating head slider's contact with the magnetic disk can be detected with high sensitivity.
Further, two or three of the above examples may be adopted at the same time. Besides, two or more of the items to be sampled may be chosen. In such a case, the contact can be detected with higher sensitivity. For example, Examples 1 and 2 can be implemented in such a way that reference signals are produced and the reference signals are subtracted from sample reproduced signals in the first place and, then, the signals are subjected to the processing of Example 1 or Example 2.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-040464 | Feb 2007 | JP | national |
