1. Field of the Invention
The present invention relates to a magnetic disk drive capable of precisely controlling the flying height of a magnetic head, and a method for controlling the flying height of the magnetic head.
2. Description of the Related Art
In magnetic disk drives (hard disk drives (HDD)), technological improvements of magnetic disks, magnetic heads, signal processing, and the like have increased capacity in a very high growth rate, thereby leading to a finer track pitch. In this situation, in the case of a magnetic disk drive including a flying head, holding the minute flying height of the magnetic head constant is important for the improvement of reliability.
A slider on which the magnetic head is mounted is used to float the magnetic head. The slider receives airflow generated by the rotation of the magnetic disk to allow the magnetic head to float in an appropriate flying height. The flying height of the magnetic head is affected by the shape of the slider because of such a mechanism. Thus, variations in flying height disadvantageously occur among drives. Furthermore, the flying height of the magnetic head disadvantageously changes in response to a change in atmospheric pressure.
To overcome the foregoing problem of the variations in the flying height of the magnetic head, Japanese Unexamined Patent Application Publication No. 06-267219 discloses a method for adjusting the flying height by means for adjusting a lifting force acting on the magnetic head. According to the patent document, the magnetic disk drive described in the patent document includes a piezoelectric element in a slider. The deformation of the piezoelectric element is controlled in response to an operation mode. The deformation of the piezoelectric element deforms the shape of the slider (amount of crown) to change the lifting force acting on the magnetic head.
In the magnetic disk drive disclosed in the patent document, the flying height of the magnetic head is controlled by adjusting the lifting force acting on the magnetic head. Thus, in the art disclosed in the patent document, variations in the flying height of the magnetic head due to the operation mode and environmental factors can be reduced. However, the flying height of the magnetic head with respect to the surface of the magnetic disk cannot be controlled. That is, disadvantageously, the absolute value of the flying height of the magnetic disk cannot be precisely controlled.
According to an aspect of an embodiment, a magnetic disk drive includes: a magnetic head; a magnetic disk; an actuator for changing the position of the magnetic head with respect to the magnetic disk; a sensor for detecting vibration of the magnetic head; and a controller for detecting contact between the magnetic head and the magnetic disk on the basis of the detected vibration and for controlling the actuator.
Embodiments of the present invention will be described in detail below with reference to the drawings.
The magnetic head 30 reads data from the magnetic disk 100 and writes data into the magnetic disk 100, as described above. The magnetic head 30 includes a read head element (not shown) that reads data from the magnetic disk 100 and a write head element (not shown) that writes data into the magnetic disk 100. The magnetic head 30 also includes a heater (not shown) that produces heat by being supplied with a current so as to protrude a surface of the slider 24 facing the magnetic disk 100. The heater is supplied with a current from a current supply circuit 18 in a controller 10. The heater produces heat in response to the amount of current supplied so as to expand the bottom of the slider 24 facing the magnetic disk 100. The expansion of the bottom of the slider 24 reduces the distance between the surface of the magnetic disk 100 and an end of the read head element adjacent to the magnetic disk 100 and between the surface of the magnetic disk 100 and an end of the write head adjacent to the magnetic disk 100. That is, the position of the magnetic head 30 with respect to the surface of the magnetic disk 100 shifts in response to the amount of current (amount of energy) fed into the heater. In this case, the position of the slider 24 with respect to the surface of the magnetic disk 100, i.e., the flying height of the slider, does not shift substantially. The amount of protrusion of the bottom of the slider 24 is equal to the amount of displacement of the magnetic head 30. A specific arrangement of the read head, the write head, and the heater will be described below.
As stated above, a part that changes the position of a magnetic head with respect to a magnetic disk is also referred to as an “actuator”.
The sensor 50 is disposed between the substrate 40 and the magnetic head 30. The sensor 50 converts mechanical vibration of the slider 24 into an electric signal 11a. The electric signal 11a is transmitted to a signal amplifying circuit 12 in the controller 10 through a lead 28.
The controller 10 is mounted on, for example, a control board (not shown) that controls operations of a magnetic disk drive 1. As shown in
The signal amplifying circuit 12 receives the electric signal 11a from the sensor 50 and then amplifies the electric signal 11a according to a command from the CPU 10a. Alternatively, the signal amplifying circuit 12 does not directly receive the electric signal 11a but may receive the electric signal 11a via the input/output circuit 10d. The amplified signal 11b is send to the filter circuit 14 through, for example, the bus 10c. For example, the signal amplifying circuit 12 amplifies the voltage level of the electric signal 11a while the S/N ratio of the electric signal 11a is maintained. The amplification operation of the electric signal 11a may be performed not by the command from the CPU 10a but with the signal amplifying circuit 12 alone.
The filter circuit 14 receives the signal 11b from the sensor 50 and then filters the signal 11b. The filter circuit 14 sends the filtered signal 11c to the comparator circuit 16 through, for example, the bus 10c. For example, the filter circuit 14 filters out frequency components of several tens of kilohertz or less and frequency components of several megahertz or more to improve the S/N ratio of the amplified signal 11b. The filtering of the signal 11b may be performed not by a command from the CPU 10a but with the filter circuit 14 alone.
The comparator circuit 16 receives the signal 11c from the filter circuit 14. The comparator circuit 16 compares a peak value of the signal 11c with a reference value according to a command from the CPU 10a. The comparator circuit 16 provides a notification 11d of the comparison result to the current supply circuit 18. Specifically, when the peak value of the signal 11c is larger than the predetermined reference value, the notification 11d is made to the current supply circuit 18. The notification 11d to the current supply circuit 18 is made through, for example, the bus 10c. The comparison of the peak value of the signal 11c with the reference value may be performed not by a command from the CPU 10a but with the comparator circuit 16 alone.
The term “reference value” defined here refers to a value determined by actual measurement of a plurality of magnetic disk drives 1 that are of the same type. Specifically, in each of the magnetic disk drives 1 prepared, the magnetic head 30 is brought into contact with a surface of the magnetic disk 100. The signal 11c is measured before contact. Then the signal 11c is measured when the magnetic head 30 is in contact with the surface of the magnetic disk 100. A frequency component of the signal 11c having a largest change in peak value is determined from the measurement results. A substantially intermediate value between the peak value before contact and the peak value of the determined frequency component when the magnetic head 30 is in contact with the surface of the magnetic disk 100 is defined as the reference value. Alternatively, the reference value may be determined by a simulation. In addition, the reference value may be determined by the use of the magnetic disk drive 1 in which the flying height of the magnetic head 30 will be adjusted. In this case, for example, the housing (not shown) of the magnetic disk drive 1 is provided with a small transparent window (not shown). After the completion of the magnetic disk drive 1, vibration of the magnetic head 30 is observed through the transparent window in order to determine when the magnetic head 30 comes into contact with the magnetic disk 100. In the case where vibration of the magnetic head 30 is observed through the transparent window, a measuring apparatus, such as a laser Doppler vibrometer that irradiates an object with laser light and measures a relative velocity on the basis of the phase difference of the reflected light may be used.
The current supply circuit 18 receives the notification 11d from the comparator circuit 16 and then limits the value of a current 11e fed into the heater. For example, the ROM in the controller 10 stores the relationship between the current 11e fed into the heater and the flying height of the magnetic head 30. The relationship between the current 11e fed into the heater and the flying height of the magnetic head 30 is desirably obtained by measurement with the magnetic disk drive 1 in which the flying height will be adjusted. Thus, for example, the relationship is determined by automatically performing measurement immediately after power-on and writing the measurement result into the ROM at a predetermined address. Alternatively, the relationship determined by a simulation may be written from the outside into the ROM at a predetermined address. The CPU 10a may carry out all of these tasks on the basis of a program stored in the ROM. In addition, the current 11e fed into the heater may be a pulse current.
When the current supply circuit 18 receives the notification 11d from the comparator circuit 16, the current supply circuit 18 recognizes that the magnetic head 30 is in contact with the surface of the magnetic disk 100. The current supply circuit 18 allows the value of current fed into the heater (for example, the value of the current 11e) when the current supply circuit 18 receives the notification to be temporarily stored into the RAM in the controller 10 according to a command from the CPU 10a. In the case where the current 11e fed into the heater is a pulse current, for example, the current supply circuit 18 regards the integral of the current per unit time as the value of the current 11e fed and allows the integral to be stored into the RAM. In addition, the CPU 10a may carry out all of the storage tasks on the basis of a program stored in the ROM. Then, according to commands from the CPU 10a, the current supply circuit 18 determines a current Is corresponding to an optimum flying height Hs from the value of the current 11e when the magnetic head 30 is in contact with the surface of the magnetic disk 100, and sets the current fed into the heater to the current Is. When a read operation and a write operation are performed, the current Is is fed into the heater through a lead 29. In this case, the current 11e fed into the heater is not directly supplied from the current supply circuit 18 but may be supplied from the current supply circuit 18 via the input/output circuit 10d.
A method for adjusting the flying height of the magnetic head with the magnetic disk drive 1 shown in
The power to the magnetic disk drive 1 is turned on. Then the CPU 10a in the controller 10 rotates a spindle on which the magnetic disk 100 is mounted to rotate the magnetic disk 100.
The controller 10 moves the head unit 20 in such a manner that the magnetic head 30 is located directly above the non-storage region 104 of the magnetic disk 100. Specifically, for example, the head unit 20 is moved in the direction of an arrow shown in
The CPU 10a increases a current fed into the heater in the magnetic head 30 by a predetermined increment. A current equal to the predetermined increment is fed into the heater because the current fed into the heater is initially zero. In the case where this step is performed after step 6 is performed, the current fed into the heater is gradually increased. The heater protrudes the bottom 24b of the slider 24 toward the magnetic disk 100 in response to the current fed.
The CPU 10a starts sampling the electric signal 11a from the sensor 50. The CPU 10a commands the signal amplifying circuit 12 to amplify the voltage level of the electric signal 11a from the sensor 50 and then to send the amplified signal 11b to the filter circuit 14.
The CPU 10a commands the filter circuit 14 to filter the signal 11b from the signal amplifying circuit 12 and then to send the filtered signal 11c to the comparator circuit 16. As described above, for example, the S/N ratio of the amplified signal 11b is improved by filtering out frequency components of several tens of kilohertz or less and frequency components of several megahertz or more. Alternatively, a plurality of magnetic disk drives 1 that are of the same type is tested in order to determine a frequency component required, and then frequency components other than the determined frequency component may be filtered out.
The CPU 10a allows the comparator circuit 16 to check whether the strength of the signal 11c exceeds the reference value. When the strength of the signal 11c does not exceed the reference value, the CPU 10a gives a command to return to Step 3. When the strength of the signal 11c exceeds the reference value, the CPU 10a commands the comparator circuit 16 to provide notification of an excess of the strength of the signal 11c over the reference value to the current supply circuit 18. Then the CPU 10a gives a command to go to Step 7. Alternatively, only when the strength of the signals 11c exceeds the reference value multiple times (e.g., three times) in succession, the process may go to step 7. This process ensures reliable determination impervious to noise.
The CPU 10a commands the current supply circuit 18 to store the current value Ic (collision energy E2) fed into a heater 70 when the strength of the signal 11c exceeds the reference value into the RAM in the memory 10b.
The CPU 10a determines the optimum current Is (optimum energy level E1) on the basis of the relationship between the current 11e fed into the heater and the flying height of the magnetic head 30, the relationship being stored in the ROM in advance.
The CPU 10a commands the current supply circuit 18 to set the current 11e fed into the heater at the optimum current Is (optimum energy level E1) determined in Step 8.
The CPU 10a reads data (read operation) from the magnetic disk 100 and writes data (write operation) into the magnetic disk 100 while the optimum current Is is fed into the heater.
The flying height of the magnetic head 30 is controlled through the above-described steps. The above-described control precisely adjusts the flying height of the magnetic head with respect to the surface of the magnetic disk. In the case where the relationship between the flying height of the magnetic head 30 and the current 11e fed into the heater 70 in the read operation is different from that in the write operation, the adjustment of the flying height of the magnetic head 30 in the read operation may be different from that in the write operation. Furthermore, in Steps 3 to 6, processing may be performed by each circuit without a command from the CPU 10a.
A method for detecting a point (reference point of the flying height) where the magnetic head 30 is in contact with the magnetic disk 100 on the basis of a sampled signal waveform will be described below.
The contact between the magnetic head 30 and the surface of the magnetic disk 100 steeply increases only a signal component having a predetermined frequency (fp). As a result, the peak value of the signal having the predetermined frequency fp exceeds the reference value. In this way, a frequency component that is maximized when the magnetic head 30 is in contact with the magnetic disk 100 is defined as the predetermined frequency. The predetermined frequency fp is a value determined in response to, for example, the shape of the slider 24. Thus, the predetermined frequency fp can vary slightly among devices that are of the same type. As shown in
Examples of a structure in which the sensor 50 is mounted on the slider 24 will be shown.
As shown in
An outline of a process for producing the slider 24 according to the first embodiment will be described below. In particular, a process for producing the sensor 50 will be described in detail.
As shown in
As shown in
As shown in
As shown in
Steps shown in
As shown in
The other surface of the substrate 40a (a side opposite the sensor 50 side) is cleaned. Then the magnetic head 30 is formed on the other surface.
The substrate 40a is separated into the sliders 24 by dicing. Each of the separated sliders 24 is mounted on the arm end 22a. The arm end 22a has spring properties and thus is also referred to as a “suspension”. The electrodes 54 and 62 (ground electrodes) and the electrode 58 (sensor electrode) of the sensor 50 are connected to the lead 28 formed on the arm end 22a. Alternatively, the substrate 40 of the slider 24 may be connected to a ground, and the electrodes 54 and 62 may be connected to the substrate 40.
The above-described steps are steps in the case where the sensor 50 is disposed at position B (
In the case where the sensor 50 is disposed at position C (
In this embodiment, the flying height of a magnetic head 30 with respect to a surface of a magnetic disk 100 is adjusted by vertically moving an arm 22 of a head unit 20. In this embodiment, the arm 22 is moved in directions of arrows shown in
A magnetic disk drive 1 adjusts the flying height of the magnetic head 30 with the driving unit in the same way as in the first embodiment. The flying height of the magnetic head 30 is set at an optimum flying height with respect to the surface of the magnetic disk 100. Then a read operation or a write operation is performed. As a result, the magnetic disk drive 1 performs the read operation or the write operation while the optimum flying height of the magnetic head 30 is maintained.
Number | Date | Country | Kind |
---|---|---|---|
2006-346760 | Dec 2006 | JP | national |