KR20080011808A - The method for detecting a head touch-down and for controlling flying height of the head in the hard disk drive - Google Patents

Abstract

A method for detecting head touch-down and a method for controlling flying height of a head in a hard disk drive are provided to reduce an area increase caused by adding a hardware, by detecting touch down time of a head accurately only with self property of an SFF(Small Form Factor) drive. A method for detecting head touch-down includes the steps of: applying current to a heater installed in a head to execute an FOD(flying on demand) function(S101); measuring an RRO variation quantity and the variation quantity of the driving current applied to the spindle motor while increasing the current volume applied to the heater(S102~104); and determining whether the variation quantity of the RRO and the variation quantity of the driving current exceed the threshold(S105).

Description

The method for detecting a head touch-down and for controlling flying height of the head in the hard disk drive}

1 is a diagram showing the distribution of the height of the lift of the head.

FIG. 2 is a schematic diagram illustrating a direction of a moment according to each area when a head is touched down in a small form factor (SFF) drive. FIG.

3A is a graph illustrating a position error signal (PES) output during normal operation.

3B is a graph illustrating PES output when the head is touched down.

4 is a graph showing a spindle motor driving current changed when the head is touched down.

5 is a flowchart illustrating a head touchdown detection method according to the present invention.

6 is a flow chart showing a head floating height control method according to the present invention.

The present invention relates to a method applied to a hard disk drive, and more particularly, in a small form factor (SFF) drive having a FOD (Flying on Demand) function, by using the SFF drive's own characteristics, the FOD function is performed. The present invention relates to a method of detecting a touchdown of a head and a method of controlling a height of floating of the head.

A hard disk drive is a kind of data storage device that reads data written to a disk by a magnetic head or writes data to a disk. Such hard disk drives are gradually increasing in capacity, density, and light weight, and the BPI (Bit Per Inch), which is the density of the disk rotation direction, and the TPI (Track Per Inch), which is the radial density, are increasing. Therefore, for this purpose, the development of a disk drive is being progressed in the direction of lowering the flying height of the magnetic head and increasing the recording frequency.

By the way, one of the most troublesome parts for ensuring the reliability of the disc drive is the occurrence of recording failure due to the contact between the magnetic head and the disc. Such defects may also be caused by external factors such as temperature and pressure, but may also be caused by the mechanical characteristics of the disk drive itself. For example, the recording magnetic head uses a metal material, but the slider supporting the magnetic head uses a non-metallic material, so that when the recording current is applied, the periphery of the pole expands due to the difference in the coefficient of thermal expansion between the metal and the nonmetal. The phenomenon is TPTP (Thermal Pole Tip Protrusion). Such a TPTP phenomenon causes different head heights to vary, resulting in various HDI (Head Disk Interface) problems as well as reducing the reliability of the recording operation.

In order to solve the above problems, a technique applied to a hard disk drive is FOD (Flying on Demand). The FOD is a function of controlling a gap between the head and the disk by mounting a kind of heater inside the head to uniformly maintain heads having different flying heights at a target clearance. In particular, by using the FOD function, it is possible to ensure uniform HDI performance between the head and the disc, and improve bit error rate (BER) performance by controlling the height of injury. The FOD function was mainly used only for a desktop and a laptop computer due to the power consumption problem, but recently, the use of the FOD function has been expanded to MP3 and mobile phones equipped with small form facotr (SFF) drives.

On the other hand, when using the FOD function, a method of detecting whether the head is in contact with the disk (Touch-down) or to control the head by using it, conventionally using an automatic gain control circuit (AGC: Auto Gain Controller) there was. However, since the value of the automatic gain control circuit changes with temperature change, it is difficult to obtain accurate and reliable results. This is especially true for very small devices such as SFF drives.

The technical problem to be achieved in the present invention is the head touchdown detection that can accurately detect when the head is touched down by using the SFF drive's own characteristics when performing FOD (Flying on Demand) in the small form factor (SFF) drive To provide a way.

Another technical problem to be achieved by the present invention is to control the floating height of the head by accurately detecting the time when the head touches down by using the SFF drive's own characteristics when performing FOD (Flying on Demand) in a small form factor (SFF) drive. It is to provide a method of controlling the head injury height that can be.

In the head touchdown detection method according to the present invention, applying a current to a heater (Heater) provided in the head to perform the FOD function, while increasing the amount of current applied to the heater, and the amount of change in the RRO generated accordingly Measuring a change amount of the drive current applied to the spindle motor, and determining whether the change amount of the RRO and / or the change amount of the drive current exceeds a threshold value.

In this case, the amount of change in the RRO is preferably made in an inner diameter (ID) or outer diameter (OD) region of the disk. The RRO change amount measurement is preferably preceded by the change amount of the drive current applied to the spindle motor. The head touchdown detection method according to the present invention can be applied to an SFF drive using a 0.85 inch disk as a medium.

According to an embodiment of the present invention, a method of controlling a head injury height includes applying a current to a heater provided in the head to perform a FOD function, increasing an amount of current applied to the heater, Measuring a change amount of the drive current applied to the spindle motor, measuring a first amount of current supplied to the heater at a moment when the change amount of the RRO and / or the change amount of the drive current exceeds a threshold value, the measured second Calculating a second current amount by multiplying one current amount by a predetermined coefficient α (0 <α <1), and when the head tracks the track, the head uses the calculated second current amount to generate a target interval ( And controlling to float while maintaining a target clearance.

Here, the storing of the calculated second current amount in the maintenance cylinder of the disk may be further added. Therefore, the controlling may be performed by using the second current amount stored in the maintenance cylinder. The predetermined coefficient α may be a value corresponding to a magnetic recording width recorded in the track by the head when no current is supplied to the heater. The RRO change amount measurement is preferably performed in an inner diameter (ID) or outer diameter (OD) region of the disk. The RRO change amount measurement may also be preceded by the change amount of the drive current applied to the spindle motor. The head lift height control method according to the present invention can be applied to an SFF drive using a 0.85 inch disk as a medium.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing the present invention, if it is determined that the detailed description of the related well-known configuration or function may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

When the magnetic disk is rotated by the spindle motor, the load and airflow on the slider cause the slider to float on the recording medium at a very fine flying height. The height of injury has now approached less than 10 nanometers and is expected to decrease further in the future. On the other hand, the size of the magnetic field detected by the head is inversely proportional to the lift height of the head. Therefore, the larger the floating height, the smaller the magnetic recording width MWW recorded in the sector on the disc. In this case, when reading the data recorded in the sector, the data cannot be read normally, which acts as a factor of increasing the error rate, that is, the bit error rate (BER). On the contrary, the smaller the floating height is, the larger the magnetic recording width is, but this is also undesirable because the possibility of scratching between the head and the disk increases. In particular, the spacing between the head and the disk is not always constant due to various factors (temperature, pressure, stress, etc.). Therefore, it is most important that the head has a target clearance, which is the target injury height.

1 is a diagram showing the distribution of the height of the lift of the head.

Here, the right graph is a graph showing a flying height between the head and the disc before performing the FOD (Flying on Demand) function, and the left graph is a FOD function to perform a target interval with a constant height of injury. Graph showing keeping. The height of the head and disk is not always constant, but depends on the surface area. This is due to external or internal factors of the disk drive.

Referring to the graph on the right, samples having a floating height of up to about 15 nm and at least about 5 nm based on 10 nm are distributed. However, if the head has a very high or small floating height compared to the target spacing (here 10nm), a problem occurs as described above. Especially when the height of the injury is high, the BER is increased to reduce the performance of the disk drive. Therefore, it is important to apply the FOD so that the floating height of the head can be concentrated in the target interval (here 6nm) as shown in the left graph.

FIG. 2 is a schematic diagram illustrating a direction of a moment according to each area when a head is touched down in a small form factor (SFF) drive. FIG.

SFF drives use disks that are much smaller (e.g., 0.85 inch) and thinner (e.g., 0.381mm) than the 3.5-inch or 2.5-inch disks used in traditional desktop or laptop computers. It is also small because it is used as a storage medium for MP3s and mobile phones. Due to this size constraint, the SFF drive has a small radius of the motor hub, and the actuator is small, so the inertia is very small (about 1/150 of a drive using a 2.5 inch disk). As a result, the head disk interface (HDI) phenomenon that occurs when the head is touched down to the disk is different from that of a large form factor (LFF) drive.

In the conventional LFF drive, when the HDI is generated by the touchdown of the head, signal modulation is generally caused by the contact of the slider. However, in the case of SFF, due to the small actuator inertia and motor torque as described above, the position error signal (PES) starts to change before contacting the slider disk, and the jitter change in the spindle motor Is detected. Phenomenologically, jitter occurs in the spindle motor after the PES begins to change, but in some cases both occur at the same time.

PES refers to a signal indicating the degree to which the head is out of the center of the track, that is, the size of the off-track. The reason for the PES is that the x direction, which is the track direction rather than the z direction, which is generally the vertical direction of the head, This is caused by the RRO (Repeatable Run-Out) component occurring in the y direction, which is the disk direction. In general, even when the head is in contact with the disk, the hard disk drive has a sufficiently large motor torque or actuator inertia so that the position change in the z direction does not occur in the x direction or the y direction. Therefore, no PES change is detected. However, because the SFF drive has a small actuator inertia as described above, when the head tracks on the track, a force is generated to move in the direction of the head's linear velocity, thereby detecting the PES. Since the PES is a signal generated by the touchdown of the head, the PES is a regular signal, and thus is composed of an RRO (Repeatable Run-Out) component which is a repetitive error component.

Referring to FIG. 2, when the head tracks in the OD or ID region compared to the middle diameter (MD) region, the PES change, that is, the RRO, is largely detected because the skew of the head is in the linear velocity direction of the head. This is because it cannot endure the force to move in the direction of zero. On the other hand, when the head moves in the MD region, since the movement direction of the actuator and the movement direction of the head are the same, the amount of change in the PES is relatively weakly detected. Therefore, in the method for detecting the touchdown of the head according to the present invention, the detection of the PES change amount is preferably measured in the ID or OD region rather than the MD region. As described above, the PES is composed of an RRO component.

FIG. 3A is a graph illustrating a position error signal (PES) output during normal operation, and FIG. 3B is a graph showing a PES output when the head is touched down. Here, the horizontal axis represents the number of sectors, and the vertical axis represents the number of counters. A plurality of counters constitute one track, and typically one track consists of 512 counters.

3A and 3B together, it can be seen that the PES shown in FIG. 3A has a relatively gentle height of at most 61 and at least -76 over 160 sectors in the measurement range. This means that the head is following without deviating from the track's target. In contrast, the PES shown in FIG. 3B is heavily offtracked to a height of up to 256 and a minimum of -229 (not exactly represented in this graph) over 160 sectors in the measurement range. It means that you are following a lot away from the target.

As described above, the reason why the PES signal is different when the head is touched down is that the SFF drive has a small inertia of the actuator. Thus, even if there is a slight contact between the head and the disc, the head has a linear velocity of the track. Because it tries to move in the direction. Accordingly, the present applicant intends to detect the touchdown of the head using the characteristics of the SFF drive itself and to control the height of the head lift using the same. However, since an increase in the amount of PES change does not immediately mean a touchdown of the head, it should also be noted that jitter occurs in the spindle motor and that the amount of change in driving current applied thereto is generated as described below.

4 is a graph showing a spindle motor driving current changed when the head is touched down. Here, the yellow graph shows the current change amount in the OD region, the blue graph shows the current change amount in the ID region, and the purple graph shows the current change amount in the MD region.

When the head is touched down to the disk, the spindle motor is subjected to a force opposite to the direction of rotation. Therefore, if a constant drive current is applied to a constant spindle motor, the speed at which the disk rotates naturally decreases. However, if the speed of the spindle motor is reduced, the controller automatically increases the amount of drive current applied to the spindle motor to compensate for this. In particular, since the torque of the motor is small in the SFF drive, the amount of change in the driving current is easily detected.

4, when the head is touched down, jitter occurs in the spindle motor, which is more prominent in the ID or OD region. Specifically, before the head is touched down (MD area in the graph), the drive current changes to about 556 to 556 and has a value of Δ = 2, but after the head is touched down (ID or OD area in the graph). The drive current changes from about 560 to 566 and has a value of DELTA = 6.

5 is a flowchart illustrating a head touchdown detection method according to the present invention.

The head touchdown detection method according to the present invention is applied in a small form factor (SFF) drive. As described above, the SFF drive is characterized by low torque of the spindle motor and low inertia of the actuator. Thus, in the pre-modulation phase caused by the contact of the slider and the disk, a PES signal consisting of the RRO component is detected and jitter is sensed in the spindle motor. The present invention relates to an SFF drive to which the FOD (Flying on Demand) function is applied. In other words, in order to maintain the floating height between the head and the disk at the target clearance, a disk drive capable of adjusting the gap between the head and the disk by supplying a driving current to the heater provided inside the head to expand the poles. The invention relates to.

First, in order to perform the FOD function, a current is supplied to a heater provided in the head (S101). When the current is supplied to the heater, the gap between the head and the disk gradually decreases because the periphery of the pole expands as described above. The current supplied to the heater is gradually increased by defaulting to 0 (S102). This continues until the head is touched down. As described above, the head touchdown detection is performed through the amount of change in the RRO component included in the PES and the amount of change in driving current applied to the spindle motor.

The amount of change in the RRO component is measured while increasing the current applied to the heater (S103). The RRO component is generally composed of a plurality of signals having different frequencies, and is usually composed of signals having an integer multiple of the motor rotation frequency. In addition, the change amount of the drive current applied to the spindle motor is also measured (S104). If the head is not touched down, the drive current is expressed as a constant constant value. However, when touched down, the value changes. Here, the measurement of the RRO component is preferably measured in the ID region or the OD region rather than the MD region. The RRO change amount measurement and the drive current change amount measurement may be performed at the same time, or the RRO change amount measurement may be prior to the drive current change amount measurement.

It is determined whether the measured RRO change amount and (spindle motor) driving current change amount exceed a threshold value (S103). The threshold is a value that can vary depending on the definition of the user. For example, the change amount of the RRO may be set to a case where the amplitude of the PES signal is out of 100 counters. If the RRO change amount or the drive current change amount does not exceed the threshold value, the current is supplied to the heater again and it is measured again whether the threshold value is exceeded. This is repeated until the threshold is exceeded.

If the amount of change in RRO or the amount of change in drive current exceeds the threshold, then the head is considered to be touched down to the disc. However, in order to improve accuracy, it is based on the time when both the RRO change amount and the drive current change amount exceed a predetermined threshold value. The threshold value is a numerical value applied differently to the RRO change amount and the drive current change amount, respectively. The present invention can be applied to SFF drives using 0.85, 1.0, 1.3, 1.8 inch disks.

6 is a flow chart showing a head floating height control method according to the present invention.

The head lift height control method according to the present invention includes the head touchdown detection method described above, and is a method of controlling the lift height of the head using the same. While increasing the driving current applied to the heater (S201, S202), the change amount of the RRO component and the change amount of the drive current are measured (S203, S204) and the value of the head based on whether the value exceeds the threshold (S205). Since the method of detecting the touchdown has already been described above, a detailed description thereof will be omitted.

The present invention includes the step 206 of measuring, by the head touchdown detection method, a first current amount applied to the heater, that is, a reference current, when the head is considered to be touched down. Using the reference current can also calculate the moving distance of the head. This means that the height of the head can be controlled by adjusting the amount of current. However, this cannot be done for each sample area, but is calculated and applied as an average value.

The second current amount is calculated by multiplying the measured first current amount by a predetermined coefficient α (0 <α <1) (S207). That is, since the first current amount is a current supplied to the heater when the head is touched down, the second current amount for stably floating the head, that is, the target current, is calculated by multiplying a predetermined safety factor. Here, the second current amount is smaller than the first current amount and larger than zero. Preferably, α is a value corresponding to a magnetic recording width recorded in the track by the head when no current is supplied to the heater. For example, when the heater driving current amount is 0, the coefficient α may be differently adjusted to generate a normal magnetic recording width (eg, 200 nm) by differentiating the case where the magnetic recording width is 50 nm and the 100 nm case. .

 When the head tracks the track using the calculated second current amount, the head is controlled to float while maintaining a target interval (S109). However, rather than using the second current amount directly, it is preferable to store it in the maintenance cylinder of the disk and use the controller when necessary. The second current amount is a variable that can be changed at any time by the coefficient α, and the coefficient α can be updated through a test.

Due to the configuration as described above, the head touchdown detection method according to the present invention can accurately detect the time when the head is touched down without using the conventional automatic gain control circuit and only the SFF drive itself, The additional area increase can be reduced and the detection is relatively less affected by the external environment, such as temperature.

The head lift height control method according to the present invention has only the characteristics of the SFF drive itself, accurately detects the point of time when the head is touched down, detects the amount of current applied to the heater at that point, and uses the detected current amount to lift the head. The effect is to control the height accurately.

Claims (8)

In a method of detecting whether a head is touched down to a disk when performing FOD (Flying on Demand) in a small form factor (SFF) drive, Applying a current to a heater provided in the head to perform the FOD function; Increasing the amount of current applied to the heater and measuring the amount of change in the RRO generated accordingly and the amount of change in the drive current applied to the spindle motor; And And determining whether the change amount of the RRO and / or the change amount of the driving current exceeds a threshold value. The method of claim 1, wherein the change in RRO amount, And the ID or OD area of the disc. The method of claim 1, wherein the change in RRO amount, The method of detecting a head touchdown, which precedes the measurement of the change amount of the driving current applied to the spindle motor. In the method of controlling the height of the head floating when FOD (Flying on Demand) in the Small Form Factor (SFF) drive, Applying a current to a heater provided in the head to perform the FOD function; Increasing the amount of current applied to the heater and measuring the amount of change in the RRO generated accordingly and the amount of change in the drive current applied to the spindle motor; Measuring a first amount of current supplied to the heater when the amount of change in RRO and / or the amount of change in drive current exceeds a threshold; Calculating a second current amount by multiplying the measured first current amount by a predetermined coefficient α (0 <α <1); And And controlling the head to float while maintaining a target interval using the calculated second current amount when the head tracks the track. The method of claim 4, wherein The method may further include storing information about the calculated second current amount in a maintenance cylinder of the disk, wherein the controlling may include: And a second current amount stored in the maintenance cylinder. The method according to claim 4, wherein the predetermined coefficient α, And a value corresponding to a magnetic recording width recorded in the track by the head when no current is supplied to the heater. The method of claim 4, wherein the change in RRO amount, The height of the head floating control method, characterized in that made in the ID or OD area of the disk. The method of claim 4, wherein the change in RRO amount, The method of detecting a head touchdown, which precedes the measurement of the change amount of the driving current applied to the spindle motor.

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