Storage medium and method for actuator movement control

A storage device employing the ramp load/unload technique for an actuator is disclosed that has high shock-resistance, high vibration-resistance, and is capable of rapid and stable ramp load/unload operations. A position detection unit integrates the speed of the actuator, obtained by detecting a back electromotive force generated in a VCM, to calculate the present position of the magnetic head. A position determination unit compares the present position of the magnetic head with a series of position thresholds, and based on the comparison results, a bandwidth switching unit switches the bandwidth of a PI controller for feedback control of the actuator, from a narrow bandwidth to a wide bandwidth and vice versa. At positions where the speed starts to change or the speed change becomes small, the position determination is performed and the bandwidth is appropriately switched.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a storage medium including an actuator employing a ramp loading/unloading technique, and a method of controlling movement of the actuator.

2. Description of the Related Art

In the recent years and continuing, technologies have been developed at an accelerating rate to increase recording density of storage media, such as hard disks, and the recording density per area is increasing by 100% annually. One subject in this development is to improve reproduction performance.

In a hard disk, a magnetic head records or reproduces data in a magnetic disk while floating over the surface of the magnetic disk at a certain height. The amount of space between the magnetic head and the magnetic disk is called “floating height”, or “flying height”, or “head gap”. It is known that the reproduction performance improves when the floating height decreases, and as the state of the art of the technology, a floating height as small as 10 nm has been achieved. To achieve such a small floating height, the surfaces of the magnetic head and the magnetic disk have to be made smooth.

In the related art, the magnetic head is operated in a CSS (Contact Start Stop) mode, in which the magnetic head comes to rest on the surface of the magnetic disk when the drive is not in operation, and the surface of the magnetic disk has to be textured (roughened) to prevent adhesion of the magnetic head to the surface of the magnetic disk to prevent impact on rotation of the magnetic disk.

However, as mentioned above, to achieve a smaller floating height, the surfaces of the magnetic head and the magnetic disk have to be made smooth to improve surface perfection, and due to this, adhesion of the magnetic head to the surface of the magnetic disk becomes remarkable.

One of the solutions to this problem is the so-called ramp load/unload technique, in which the magnetic head is moved away from the surface of the magnetic disk to be laid on a ramp when the disk is not rotating.

With the ramp load/unload technique, surfaces of the magnetic head and the magnetic disk can be made smooth. Further, because the magnetic head and the magnetic disk are not in contact when the drive is not in operation, resistance against shock of the drive is highly improved. For example, even when one moves around while carrying a personal computer, shock to the computer can be suppressed, and trouble can be reduced. Because of these benefits, the use of the ramp load/unload technique is wide-spread.

FIG. 1is view for schematically explaining the ramp load/unload technique.

In the ramp load/unload technique, as shown inFIG. 1, when unloading a magnetic head100, the following operations are performed.

As shown inFIG. 1, an actuator102supports the magnetic head100floating over a magnetic disk101in operation. First, the actuator102, which is at a position A, moves in the right direction inFIG. 1. When the actuator102moves to a position B, a lift tab103formed in the actuator102comes in contact with a ramp104located near the magnetic disk101, and the actuator102is lifted up along the slope of the ramp104. When the actuator102moves further in the right direction to a position C, the magnetic head100is moved beyond the outer diameter of the magnetic disk101.

At the position C, because the magnetic head100and the magnetic disk101are not in contact, even when a shock or any outer force is imposed on the magnetic head100, contact of the magnetic head100with the magnetic disk101can be avoided.

When loading the magnetic head100, the above operations are performed in the reversed order. That is, the actuator102moves from the position C to the position B and finally the position A. Because of an air bearing formed between the magnetic head100and the magnetic disk101, the magnetic head100can stably float over the magnetic disk101.

When the magnetic head100is raised (unloading operation) with the air bearing existing between the magnetic head100and the magnetic disk101, or when the magnetic head100is lowered down to the magnetic disk101(loading operation) with the air bearing to be formed, while the ramp104raises the lift tab103upward, the actuator102, which holds the lift tab103, is engaged with a springy suspension and tends to move downward. Therefore, for example, in the unloading operation, if the upward speed of the magnetic head100is not sufficiently high, the magnetic head100may be pulled down to contact the surface of the magnetic disk101. Similarly, in the loading operation, if the downward speed of the magnetic head is too high, the same problem may occur.

To solve this problem, it is proposed to control the moving speed of the actuator to be in an appropriate region so that the vertical speed of the magnetic head100relative to the magnetic disk101is in an appropriate range, thereby, preventing contact of the magnetic head100with the surface of the magnetic disk101.

Specifically, the vertical speed of the actuator102is determined by the shape of the ramp104, and the horizontal speed of the actuator102is related to a voice coil motor (VCM) that drives the actuator102.

FIG. 2is a graph showing variation of the speed of the actuator102in feedback control in the related art, in which the bandwidth of the feedback control is fixed.

InFIG. 2, in the unloading direction, (the right direction), the speed of the actuator102is expressed by a negative value. For example, an increase of the speed of the actuator102in the unloading operation corresponds to an increase of the graph in the downward direction inFIG. 2.

When the lift tab103comes into contact with the ramp104at the position B, the moving speed of the actuator102drops notably, as shown by the solid line inFIG. 2. Accordingly, the vertical speed of the magnetic head100decreases remarkably, and the magnetic head100may contact the surface of the magnetic disk101.

As a solution to this problem, it is proposed to detect the decrease of the speed of the lift tab103when the lift tab103comes into contact with the ramp104, or detect an increase of a control variable in control of the voice coil motor, and increase a gain of the feedback control or add a feed-forward control variable according the detection results. Thereby, the speed decrease can be suppressed.

For example, Japanese Laid-Open Patent Application No. 2001-052458 discloses such a technique.

In this technique, as shown inFIG. 2, a threshold value of speed is used for detecting the speed decrease, and it is required that the threshold of speed be set sufficiently far away from a target speed so as not to make unnecessary response to even a small speed change caused by external shock or vibration. With such a threshold, however, the detection time Δt increases. Here, the detection time Δt is defined to be the time period from the time when the lift tab103comes into contact with the ramp104to the time when the contact is detected by detecting the decrease of the moving speed. During the detection time Δt, measures cannot be taken to compensate the decrease of the speed, and thus it is difficult to suppress the speed drop, as shown by the solid line inFIG. 2.

On the other hand, for convenience of usage, it is required that the loading and unloading operations of the magnetic head100be completed in a short time. Hence, it is necessary to shorten the detection time and increase the moving speed of the actuator.

However, if the threshold value of the moving speed is set close to the target value so as to shorten the detection time Δt, detection errors may occur, and this may cause unintended large changes of the speed.

If the gain in the feedback control is set higher, oscillation may be induced easily, and this may degrade the stability of speed control. For example, when the device is being carried or used in a vibratory environment, such as in a train, operational stability of the device cannot be secured.

SUMMARY OF THE INVENTION

It is a general object of the present invention to solve one or more of the problems of the related art.

It is a more specific object of the present invention to provide a storage device having high shock-resistance and vibration-resistance and capable of fast and stable loading/unloading operations, and a method of controlling movement of an actuator.

According to a first aspect of the present invention, there is provided a storage device, comprising a disk medium; a recording and reproducing head that floats over the disk medium and records information in the disk medium or reproduces information in the disk medium; an actuator that supports the recording and reproducing head and moves the recording and reproducing head in a radial direction of the disk medium; a driving unit that drives the actuator; a speed detection unit that detects a moving speed of the actuator; a speed control unit that controls the moving speed of the actuator by a feedback control based on a difference between the detected moving speed of the actuator and a target speed; a ramp member arranged outside the disk medium used for loading and unloading the recording and reproducing head; a position detection unit that detects a position of the recording and reproducing head; and a position determination unit that determines whether the detected position of the recording and reproducing head reaches a first predetermined position in operations of loading or unloading the recording and reproducing head. The speed control unit comprises one of a bandwidth switching unit that switches a bandwidth of the feedback control to a wide bandwidth based on a result of the position determination, and a feed-forward compensation unit that adds a predetermined feed-forward control variable to a control variable of the feed-back control based on the result of the position determination.

In an embodiment, the first predetermined position may be a position where the recording and reproduction head is nearly in contact with the ramp member in the operation of unloading the recording and reproducing head.

According to the present invention, in operations of loading or unloading a recording and reproducing head, a position determination unit determines whether the recording and reproducing head detected by the position detection unit reaches a first predetermined position, and based on the position determination, a bandwidth switching unit switches the bandwidth of a feedback control to a wide bandwidth, or a feed-forward compensation unit adds a predetermined feed-forward control variable to a control variable of the feed-back control.

Accordingly, when it is detected that the recording and reproducing head is at the first predetermined position, for example, the position where the actuator comes into contact with the ramp member in the unloading operation, or the position where the actuator starts to ascend the ramp member in the loading operation, a control variable can be quickly changed before or during a speed change of the actuator, for example, a rapid drop of the speed.

In addition, the bandwidth of the feedback control is switched to a wide bandwidth, or a feed-forward control variable is added to the feed-back control variable based on the position of the recording and reproducing head, thereby, the device is not influenced by external shock or vibration, and even at positions where the speed change of the actuator is small, operational errors do not occur. Consequently, it is possible to achieve highly stable loading and unloading operations.

In an embodiment, if the position determination unit determines that the position of the recording and reproducing head reaches the first predetermined position, the bandwidth switching unit may switch the bandwidth of the feedback control to the wide bandwidth, or the feed-forward compensation unit may add the predetermined feed-forward control variable to the control variable of the feed-back control.

According to the present invention, because the bandwidth of the feedback control is switched to the wide bandwidth, or the predetermined feed-forward control variable is added to the feed-back control variable directly based on the result of the position determination, the control of movement of the actuator can be simplified, and can be performed quickly and easily.

In an embodiment, the storage device may further comprise a speed change determination unit that determines whether the speed difference is greater than a predetermined value when the position determination unit determines that the position of the recording and reproducing head reaches the first predetermined position. If the speed change determination unit determines that the speed difference is greater than the predetermined value, the bandwidth switching unit may switch the bandwidth of the feedback control to the wide bandwidth, or the feed-forward compensation unit may add the predetermined feed-forward control variable to the control variable of the feed-back control.

According to the present invention, because the speed change determination of the actuator is performed only when the position of the recording and reproducing head reaches the first predetermined position, and the bandwidth of the feedback control is switched to the wide bandwidth, or the predetermined feed-forward control variable is added to the feed-back control variable according to the determination result, the detection sensitivity of speed change determination is high, and for example, the threshold value of speed deviation from the target speed can be set small.

In addition, because the speed change determination is not performed at usual positions where the speed change of the actuator is small, at these positions operational errors due to influence from external shock or vibration do not happen. As a result, the control operation is stable.

In an embodiment, the ramp member may include a slope portion having a surface inclined relative to a surface of the disk medium, said slope portion raising the recording and reproducing head away from the disk medium in the operation of unloading the recording and reproducing head; and a flat portion parallel to the surface of the disk medium and connecting with the slope portion. In the operation of loading the recording and reproducing head, the first predetermined position includes a position at a boundary of the slope portion and the flat portion.

In an embodiment, the position detection unit may detect the position of the recording and reproducing head by calculating a distance from a reference position to the position of the recording and reproducing head. Specifically, the position detection unit may calculate the distance by integrating the moving speed of the actuator detected by the speed detection unit.

Alternatively, the storage device may further comprise a position displaying unit that displays the position of the actuator. The position detection unit may calculate the distance by using the position of the actuator displayed in the position displaying unit. For example, the position displaying unit may include one of a rotary encoder mounted on the actuator and an optical scale mounted on the actuator.

In an embodiment, the reference position may include a position where the actuator is mechanically limited and mechanically stopped. Alternatively, the disk medium may be a magnetic disk medium; and the reference position may include a predetermined cylinder position based on servo information recorded in the magnetic disk medium. For example, the predetermined cylinder position may be a position of a cylinder at the periphery of the magnetic disk medium. Furthermore, the cylinder at the periphery of the magnetic disk medium may be the outermost cylinder of the magnetic disk medium.

In an embodiment, a second predetermined position may be provided. When the position determination unit determines that the position of the recording and reproducing head reaches the second predetermined position, the bandwidth switching unit may switch the bandwidth of the feedback control to a narrow bandwidth, or the feed-forward compensation unit may stop adding the predetermined feed-forward control variable to the control variable of the feed-back control.

In an embodiment, in the operation of unloading the recording and reproducing head, the second predetermined position may be a position at a boundary of the slope portion and the flat portion; and in the operation of loading the recording and reproducing head, the second predetermined position may be a position where the recording and reproducing head is substantially out of contact with the slope portion.

According to a second aspect of the present invention, there is provided a method of controlling movement of an actuator that supports a recording and reproducing head floating over a disk medium and recording or reproducing information in the disk medium, moves the recording and reproducing head in an in-plane direction of the disk medium, and loads or unloads the recording and reproducing head by using a ramp member arranged outside the disk medium. The method comprises the steps of detecting a moving speed of the actuator; controlling the moving speed of the actuator by a feedback control based on a difference between the detected moving speed and a target speed; detecting a position of the recording and reproducing head in operations of loading or unloading the recording and reproducing head; determining whether the detected position of the recording and reproducing head reaches a predetermined position; and switching a bandwidth of the feedback control to a wide bandwidth or adding a predetermined feed-forward control variable to a control variable of the feed-back control based on the result of the position determination.

According to the present invention, in operations of loading or unloading the recording and reproducing head, the position of the recording and reproducing head is detected, and it is determined whether the position of the recording and reproducing head reaches a first predetermined position, and based on the result of the position determination, the bandwidth of the feedback control is switched to a wide bandwidth, or a predetermined feed-forward control variable is added to the feed-back control variable. As a result, it is possible to quickly and stably control the speed of the actuator.

In an embodiment, the step of switching may be executed when it is determined that the detected position of the recording and reproducing head reaches the predetermined position in the step of determining.

In an embodiment, after the step of determining and before the step of switching, the method may further comprise a step of determining whether the speed difference is greater than a predetermined value when it is determined that the position of the recording and reproducing head reaches the predetermined position. The step of switching may be executed when it is determined that the speed difference is greater than the predetermined value.

These and other objects, features, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments given with reference to the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Below, preferred embodiments of the present invention are explained with reference to the accompanying drawings.

First Embodiment

FIG. 3is a plan view of a magnetic disk device10related to a first embodiment according to the present invention.

As shown inFIG. 3, the magnetic disk device10includes a magnetic disk11, a magnetic head12for recording or reproducing information in the magnetic disk11, and a disk enclosure13for accommodating the magnetic disk11and the magnetic head12.

Furthermore, the magnetic disk device10includes an actuator14supporting and moving the magnetic head12, a suspension15attached to the end of the actuator14, a voice coil motor (VCM)16joined to the base portions14aand14bof the actuator14, a pair of permanent magnets18arranged above and below the voice coil motor16, a ramp20arranged close to the outer side of the magnetic disk11for unloading the magnetic head12, a lift tab21attached to the end of the suspension15to raise the magnetic head12perpendicularly when the lift tab21moves on the ramp20, an outer stopper22and an inner stopper23to limit the movement range of the magnetic head12, a flexible printed circuit board (FPC)24, and a pre-amplifier25.

The magnetic disk11has a disk substrate formed from strengthened glass or others, and a stacked structure on the substrate, including a magnetic layer in which information is sustained as directions of magnetization, a protection layer formed on the magnetic layer to protect against mechanical damage to or oxidation of the magnetic layer, and a lubrication layer formed on the protection layer. The magnetization of the magnetic layer11may be parallel to the substrate, that is, the information is recorded by means of in-plane magnetic recording, or the magnetization of the magnetic layer11may also be perpendicular to the substrate, that is, the information is recorded by means of perpendicular magnetic recording. The magnetic layer11may be formed from well known ferromagnetic materials, for example, CoCrPt-based alloys, such as CoCrPtB.

The magnetic disk11is driven to rotate by a spindle motor26(SPM) (illustrated inFIG. 4) fixed by a hub17.

The magnetic disk device10may include only one magnetic disk11, or a number of magnetic disks11, and these magnetic disks11may be stacked but separated from each other.

In the magnetic disk11, servo information (not illustrated) is recorded for the magnetic head12to track relative to cylinders (not illustrated). The magnetic head12tracks while reading the servo information, thereby reading data recorded in cylinders.

The magnetic head12is arranged to face the magnetic disk11, and is supported by the suspension15connected to the end of the actuator14. In the magnetic head12, a recording/reproduction unit is installed, for example, the recording and reproducing unit includes an inductive write element for recording and a magneto-resistive element for reproduction.

The inductive write element may be a ring-shaped element in the case of in-plane magnetic recording, and may be a single-pole element in the case of perpendicular magnetic recording. The magneto-resistive element may be, for example, a spin-valve Giant Magneto-Resistive (GMR) element, or a Tunneling Magneto-Resistive (TMR) element, or a Ballistic Magneto-Resistive (BMR) element.

Each magnetic head12is installed to track one surface of a magnetic disk11. But not all of the magnetic disks11have a magnetic head12installed on each of their surfaces.

The actuator14is installed to support the magnetic head12and move the magnetic head12on the magnetic disk11. The voice coil motor (VCM)16is joined to the base of the actuator14. Due to the interaction with the magnetic fields from the permanent magnets18, which are applied on the voice coil motor16, the actuator14rotates in an arc relative to a rotational axis19so as to change radial positions on the magnetic disk11while being parallel to the magnetic disk11. Below, this arc-induced direction of movement by the actuator14relative to the magnetic disk11is referred to as “in-plane direction”.

The suspension15, formed from, for example, an SUS sheet, is attached to the end of the actuator14.

The lift tab21is attached to the end of the suspension15to raise the magnetic head12in a direction perpendicular to the surface of the magnetic disk11when the lift tab21moves on the ramp20. Below, the direction perpendicular to the surface of the magnetic disk11is referred to as “perpendicular direction”.

InFIG. 3, one end of the lift tab21is fixed at the center of one end of the suspension15, and the other end of the lift tab21is outside the suspension15along the long side of the suspension15. But the lift tab21may be mounted in other ways. For example, the lift tab21may be fixed to the end portion of the suspension15.

The ramp20is arranged close to the outer side of the magnetic disk11, and is placed on a circle through which the lift tab21passes. The ramp20superposes a vertical motion on the in-plane motion of the actuator14.

The outer stopper22and the inner stopper23are arranged in the area where the base portions14aand14b, respectively, of the actuator14move in arcs so as to limit the range in which the magnetic head12moves. When either of the base portions14aor14bcomes in contact with the outer stopper22or the inner stopper23, respectively, the actuator14comes to rest.

Recording signals and reproduction signals for driving the magnetic head12are supplied from an IC of a hard disk controller (HDC), arranged on an electric board (not illustrated) placed below a housing of the magnetic disk device10, through the pre-amplifier25, the magnetic head12, and the flexible printed circuit board (FPC)24.

A driver IC for controlling and driving the spindle motor and the voice coil motor16are also placed on the electric board. An upper lid (not-illustrated) is used to close the enclosure13so as to prevent entrance of dust and other foreign matter from the atmosphere.

FIG. 4is a block diagram showing a configuration of the magnetic disk device10of the first embodiment.

As shown inFIG. 4, the magnetic disk device10includes the magnetic disk11, the magnetic head12, the actuator14, a spindle motor (SPM)26, the voice coil motor (VCM)16, the ramp20, the pre-amplifier25, a VCM/SPM driver30, a controller31, a Read-Write-Channel IC (RDC)32, and a hard disk controller(HDC)33.

The VCM/SPM driver30includes a SPM driving circuit34, a VCM driving circuit35, and a back electromotive force detection circuit36.

The Read-Write-Channel IC (RDC)32includes a signal processing circuit40and a servo demodulation circuit41.

The spindle motor26is mechanically connected to the magnetic disk11via the hub17, and is driven by a SPM driving current supplied from the SPM driving circuit34in the VCM/SPM driver30.

The voice coil motor16drives the actuator14to move in the in-plane direction by a VCM driving current supplied from the VCM driving circuit35in the VCM/SPM driver30, and controls the moving speed of the actuator14by using the magnitude and direction of the VCM driving current. A back electromotive force proportional to the moving speed of the actuator14is generated in the voice coil motor16. The back electromotive force detection circuit36in the VCM/SPM driver30detects the magnitude of the back electromotive force in the voice coil motor16, converts the analog signal to a digital signal, and sends the value of the magnitude of the back electromotive force (BEMF) to the controller31.

The controller31includes a MPU (Micro processor)38, a memory39, and an Input/Output circuit (not illustrated) that connects the MPU38with the VCM/SPM driver30, the RDC32, and the hard disk controller33.

In the memory39, programs, parameters and a table for feed-forward (FF) control are stored. The MPU38send control signals to the VCM driving circuit35based on the programs in the memory39and the BEMF value supplied from the VCM driving circuit35.

The controller31receives a loading command and an unloading command from the HDC33, and the MPU38performs appropriate processing (described below) and sends a VCM control signal to the VCM driving circuit35.

The pre-amplifier25converts the recording signal to a recording current. It also amplifies the reproduction signal and a servo signal output from the magnetic head12when reproducing data in the magnetic disk11, and sends these signals to RDC32.

In the RDC32, the signal processing circuit40demodulates the amplified reproduction signal to obtain read data, and sends the data to the hard disk controller33. In addition, the servo demodulation circuit41demodulates the servo signal to obtain a head position signal indicating the position of the magnetic head12, and sends the head position signal to the MPU38of the controller31.

FIG. 5is an enlarged plan view of a portion of the magnetic disk device10of the first embodiment, showing a position relation of the ramp20and the lift tab21of the actuator14.

FIG. 6is a cross-sectional view of the portion of the magnetic disk device10along the line indicated by the arrows X inFIG. 5. Here, the line indicated by the arrow X—X forms an arc along which the actuator14moves.

Referring toFIG. 5andFIG. 6, when the magnetic disk device10in operation is set to be out of operation, for example, to be turned off, the actuator14performs the unloading operation to move the magnetic head12, which is floating over the magnetic disk11, to a shelter position P5outside of the magnetic disk11. Here, it is assumed that the magnetic disk11is presently in an on-track state, and at a position P0on the outermost cylinder of the magnetic disk11.

Once the HDC33sends an unloading command to the controller31, the MPU38in the controller31sends a VCM control signal to move the actuator14in the outer direction of the magnetic disk11, the actuator14moves in the direction indicated by an arrow X1shown inFIG. 5andFIG. 6, and the lift tab21comes into contact with the slope SL1of the ramp20at a position P1. Further, driven by the VCM control signal, the lift tab21ascends the slope SL1of the ramp20, passes a flat portion FL1and a descending slope SL2, and finally stops at the shelter position P5.

The shelter position P5, for example, is a position where the base portion14acomes into contact the outer stopper22. In addition, the boundary between the slope SL1and the flat portion FL1is denoted as position P2, the boundary between the flat portion FL1and the slope SL2is denoted as position P3, and the boundary between the slope SL2and the flat portion FL2is denoted as position P4.

FIG. 7is a block diagram showing a configuration of a portion of a speed control system used in the magnetic disk device10according to the first embodiment, which is capable of switching the bandwidth of a feedback speed control system based on the position of the magnetic head12.

The speed control system shown inFIG. 7includes a comparator45, a PI controller46, a bandwidth switching unit47, a position detection unit48, and a position determination unit49.

The comparator45compares the BEMF value with a target speed stored in memory39, and calculates the difference between them. The BEMF value, which is proportional to the moving speed of the actuator14, is supplied by the back electromotive force detection circuit36connected to the voice coil motor16. The PI controller46outputs a control variable to the voice coil motor16through the VCM driving circuit35. The position detection unit48calculates the position of the lift tab21based on the BEMF value supplied by the back electromotive force detection circuit36. The position determination unit49sends a bandwidth switching signal according to the thus obtained position, and the bandwidth switching unit47switches the bandwidth for PI control performed by the PI controller46.

Specifically, the back electromotive force detection circuit36sends the BEMF value, which is the magnitude of the back electromotive force generated in the voice coil motor16, to the position detection unit48.

The position detection unit48integrates the BEMF value from a reference position to calculate the present position of the lift tab21, and sends a signal indicating the present position of the lift tab21to the position determination unit49.

The position determination unit49compares the present position of the lift tab21with position thresholds TH1through TH5stored in memory39inFIG. 4, and sends a bandwidth switching signal to the bandwidth switching unit47based on the comparison results.

The bandwidth switching unit47changes the bandwidth of the PI control performed by the PI controller according to the bandwidth switching signal.

Here, for example, the reference position is the position P0of the outermost cylinder of the magnetic disk11illustrated inFIG. 6. The position thresholds TH1through TH5are set equal to the position P1through P5illustrated inFIG. 6, respectively.

The bandwidth switching unit47is able to switch the bandwidth of the PI control performed by the PI controller between two bandwidths, a wide bandwidth and a usual bandwidth narrower than the wide bandwidth. For example, when the bandwidth is switched to the usual bandwidth, parameters resulting in a low gain of the feedback loop are set in use; when the bandwidth is switched to the wide bandwidth, parameters resulting in a high gain of the feedback loop are set in use. In other words, relative to the control deviation output from the comparator45, when the bandwidth is switched to the wide bandwidth, the control variable increases compared with the case when the bandwidth is switched to the usual bandwidth.

Here, the bandwidth of the PI control is dependent on a proportional gain Kp and an integration gain Ki; usually Kp associated with the wide bandwidth is greater than that associated with the usual bandwidth; Ki is appropriately set so as not to induce oscillation when Kp increases, and Ki associated with the wide bandwidth and may be greater or lower than that associated with the usual bandwidth.

Operations performed by the comparator45, the PI controller46, the bandwidth switching unit47, the position detection unit48, and the position determination unit49are executed by the MPU38in the controller31shown inFIG. 4.

[Actuator Movement Control in Unloading Operation]

Below, an explanation is made of a method of the present embodiment for controlling movement of the actuator14in the operation of unloading the magnetic head12.

FIG. 8is a flowchart showing the method of movement control of the actuator14in the operation of unloading the magnetic head12according to the present embodiment.

FIG. 9Ais a cross-sectional view of the portion of the magnetic disk device10along the line indicated by the arrows X inFIG. 5, schematically showing a sequence of positions of the lift tab21in the operation of unloading the magnetic head12according to the present embodiment.

FIG. 9Bis a graph showing correspondence of the integration of the BEMF (IntglBEMF) and the position thresholds Th1through Th5with the sequence of positions of the lift tab21in the operation of unloading the magnetic head12according to the present embodiment.

FIG. 9Cis a graph showing a relation between the bandwidth of the PI control and the sequence of positions of the lift tab21in the operation of unloading the magnetic head12according to the present embodiment.

FIG. 9Dis a graph showing a relation between the speed of the magnetic head12and the sequence of positions of the lift tab21in the operation of unloading the magnetic head12according to the present embodiment.

InFIG. 9A, for simplicity, only the lift tab21is illustrated, and illustration of the magnetic head12is omitted. InFIG. 9BthroughFIG. 9D, the abscissas represent distances from the reference position.

Referring toFIG. 8, in step102, receiving an unloading command from the HDC33inFIG. 4, MPU38in the controller31sets the integration of the BEMF value (IntglBEMF) to zero, and the bandwidth switching unit47sets the PI control bandwidth to the usual bandwidth.

Here, it is assumed that the magnetic head12is at the position P0of the outermost cylinder of the magnetic disk11illustrated inFIG. 6, that is, the reference position is the position P0of the outermost cylinder of the magnetic disk11. Because the outermost cylinder of the magnetic disk11is the cylinder closest to the ramp20, noise hardly causes errors to the integration of BEMF (IntglBEMF) (as described below), and it is possible to accurately calculate the position of the lift tab21.

It should be noted that the reference position is not limited to the outermost cylinder of the magnetic disk11, but may be set to other peripheral cylinders. If the magnetic head12is at positions other than the outermost cylinder of the magnetic disk11when the unloading command is received, first, the magnetic head12is moved to the outermost cylinder of the magnetic disk11as a usual seek operation, and then step102is executed. Because the moving speed of the magnetic head12is much higher in the usual seek operation than in the unloading operation, moving the magnetic head12by a usual seek operation can shorten the time required for the unloading operation.

In step104, in order to drive the actuator14to move, MPU38sends an activating current to the voice coil motor16through the VCM driving circuit35. The magnitude of the activating current is adjusted to a specified value by, for example, the feedback control of the moving speed of the actuator14.

In step106, the back electromotive force detection circuit36detects the back electromotive force generated in the voice coil motor16due to movement of the actuator14, and the detected magnitude of the back electromotive force (BEMF) is assigned to a parameter Vbemf in the position detection unit48.

In step108, the position detection unit48accumulates the parameter Vbemf to IntgBEMF to continue integration of BEMF.

In step110, the position determination unit49determines whether the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH1. If the integration of BEMF is less than the position threshold TH1, step106through step110are repeated to move the actuator14on at a target speed until the integration of BEMF (IntglBEMF) becomes equal to the position threshold TH1.

If the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH1, the routine proceeds to step112.

In step112, as shown inFIG. 9C, the bandwidth switching unit47sets the PI control bandwidth to the wide bandwidth. As shown inFIG. 9AandFIG. 9B, equality of the integration of BEMF (IntglBEMF) and the position threshold TH1indicates that the lift tab21reaches the position P1, where the lift tab21is nearly in contact with the ramp20.

As described above, in the related art, the speed decrease is detected when the lift tab21is brought into contact with the ramp20, and based on the detection results, the PI control bandwidth is switched. In contrast, in the present control method, the PI control bandwidth is switched based on positions, therefore, the time delay of switching can be suppressed. Especially, as shown by the solid line inFIG. 9D, the notable speed drop (shown by the dashed line inFIG. 9D) of the actuator14after contact with the ramp20occurring in the related art can be effectively suppressed.

In step114, with the PI control in the wide bandwidth mode, the lift tab21ascends the slope SL1.

Similarly, the back electromotive force detection circuit36detects the back electromotive force generated in the voice coil motor16due to movement of the actuator14, and the position detection unit48assigns the detected magnitude of the back electromotive force (BEMF) to the parameter Vbemf.

In step116, the position detection unit48accumulates the parameter Vbemf to IntgBEMF to continue integration of BEMF.

In step118, the position determination unit49determines whether the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH2. If the integration of BEMF is less than the position threshold TH2, step114through step118are repeated to move the actuator14on at the target speed with the PI control in the wide bandwidth mode, until the integration of BEMF (IntglBEMF) becomes equal to the position threshold TH2.

If the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH2, the routine proceeds to step120.

In step120, as shown inFIG. 9C, the bandwidth switching unit47switches the PI control bandwidth to the usual bandwidth. As shown inFIG. 9A, the lift tab21reaches the position P2, that is, the boundary of the slope SL1and the flat portion FL1. In the flat portion FL1, the PI control is more stable in the usual bandwidth mode than in the wide bandwidth mode.

In step122, with the PI control in the usual bandwidth mode, the lift tab21moves in the flat portion FL1of the ramp20.

Similarly, the back electromotive force detection circuit36detects the back electromotive force generated in the voice coil motor16due to movement of the actuator14, and the position detection unit48assigns the detected magnitude of the back electromotive force (BEMF) to the parameter Vbemf.

In step124, the position detection unit48accumulates the parameter Vbemf to IntgBEMF to continue integration of BEMF.

In step126, the position determination unit49determines whether the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH3. If the integration of BEMF is less than the position threshold TH3, step122through step126are repeated to move the actuator14on at the target speed with the PI control in the usual bandwidth mode, until the integration of BEMF (IntglBEMF) becomes equal to the position threshold TH3.

If the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH3, the routine proceeds to step128.

In step128, as shown inFIG. 9C, the bandwidth switching unit47switches the PI control bandwidth to the wide bandwidth.

As shown inFIG. 9AandFIG. 9B, equality of the integration of BEMF (IntglBEMF) and the position threshold TH3indicates that the lift tab21reaches the position P3, the boundary of the flat portion FL1and the slope SL2of the ramp20.

In the present method, the PI control bandwidth is also switched to the wide bandwidth based on positions of the lift tab21when the lift tab21descends the slope SL2. Therefore, as shown by the solid line inFIG. 9D, both the time delay of switching and the increase of the speed can be suppressed. As a result, it is possible to precisely control the speed of the magnetic head12when the lift tab21passes through the slope SL2, and thereby this enables suppression of the deviation from the target speed when the lift tab21passes through the position P4. Consequently, it is possible to accurately control the speed of the lift tab21when the lift tab21finally reaches the position P5, and stop the lift tab21at a specified position. Furthermore, if the lift tab21is stopped when the base portion14aand the outer stopper22come into contact, it is possible to reduce the shock due to the contact between the base portion14aand the outer stopper22.

In step130, with the PI control in the wide bandwidth mode, the lift tab21descends the ramp20along the slope SL2.

Similarly, the back electromotive force detection circuit36detects the back electromotive force generated in the voice coil motor16due to movement of the actuator14, and the position detection unit48assigns the detected magnitude of the back electromotive force (BEMF) to the parameter Vbemf.

In step132, the position detection unit48accumulates the parameter Vbemf to IntgBEMF to continue integration of BEMF.

In step134, the position determination unit49determines whether the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH4. If the integration of BEMF is less than the position threshold TH4, step130through step134are repeated to move the actuator14on at the target speed with the PI control in the wide bandwidth mode, until the integration of BEMF (IntglBEMF) becomes equal to the position threshold TH4.

If the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH4, the routine proceeds to step136.

In step136, as shown inFIG. 9C, the bandwidth switching unit47switches the PI control bandwidth to the usual bandwidth. As shown inFIG. 9A, the lift tab21reaches the position P4, that is, the boundary of the slope SL2and the flat portion FL2. In the flat portion FL2, the PI control is more stable in the usual bandwidth mode than in the wide bandwidth mode.

In step138, with the PI control in the usual bandwidth mode, the lift tab21moves in the flat portion FL1of the ramp20.

Similarly, the back electromotive force detection circuit36detects the back electromotive force generated in the voice coil motor16due to movement of the actuator14, and the position detection unit48assigns the detected magnitude of the back electromotive force (BEMF) to the parameter Vbemf.

In step140, the position detection unit48accumulates the parameter Vbemf to IntgBEMF to continue integration of BEMF.

In step142, the position determination unit49determines whether the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH5. If the integration of BEMF is less than the position threshold TH5, step136through step142are repeated to move the actuator14on at the target speed with the PI control in the usual bandwidth mode, until the integration of BEMF (IntglBEMF) becomes equal to the position threshold TH5.

If the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH5, the routine proceeds to step144.

In step144, as shown inFIG. 9AandFIG. 9B, equality of the integration of BEMF (IntglBEMF) and the position threshold TH5indicates that the lift tab21reaches the shelter position P5. Thus, the target speed is set to zero and the actuator14is stopped. Hence, the unloading operation is completed.

Instead of the position P5, the actuator14may also be stopped when the base portion14aof the actuator14mechanically contacts the outer stopper22. Further, step122through step134and step138through step142are not indispensable, and can be omitted if necessary.

[Actuator Movement Control in Loading Operation]

Below, an explanation is made of a method of the present embodiment for controlling movement of the actuator14in the operation of loading the magnetic head12.

FIG. 10is a flowchart showing the method of movement control of the actuator14in the operation of loading the magnetic head12according to the present embodiment.

FIG. 11Ais a cross-sectional view of the portion of the magnetic disk device10along the line indicated by the arrows X inFIG. 5, schematically showing a sequence of positions of the lift tab21in the operation of loading the magnetic head12according to the present embodiment.

FIG. 11Bis a graph showing correspondence of the integration of the BEMF (IntglBEMF) and the position thresholds Th1through Th5with the sequence of positions of the lift tab21in the operation of loading the magnetic head12according to the present embodiment.

FIG. 11Cis a graph showing a relation between the bandwidth of the PI control and the sequence of positions of the lift tab21in the operation of loading the magnetic head12according to the present embodiment.

FIG. 11Dis a graph showing a relation between the speed of the magnetic head12and the sequence of positions of the lift tab21in the operation of loading the magnetic head12according to the present embodiment.

InFIG. 11A, for simplicity, only the lift tab21is illustrated, and illustration of the magnetic head12is omitted. InFIG. 11BthroughFIG. 9D, the abscissas represent distances from the reference position.

In the following description, initially the reference position is the shelter position P5; the position thresholds TH11, TH12, TH13, TH14and TH15correspond to the position P4, P3, P2, P1, and P0, respectively; the PI control bandwidth is switched to the wide bandwidth at positions P2and P4, with the position P2being the boundary between the slope SL1and the flat portion FL1, and the position P4being the boundary between the slope SL2and the flat portion FL2.

Referring toFIG. 10, in step152, receiving a loading command from the HDC33shown inFIG. 4, MPU38in the controller31sets the integration of the BEMF value (IntglBEMF) to zero, and the bandwidth switching unit47sets the PI control bandwidth to the usual bandwidth.

In this step, the magnetic head12is at the shelter position P5, that is, the reference position, and as shown inFIG. 3, the base portion14aand the outer stopper22are in contact with each other.

In step154, in order to drive the actuator14to move, MPU38sends an activating current to the voice coil motor16through the VCM driving circuit35. The magnitude of the activating current is adjusted to a specified value by, for example, the feedback control of the moving speed of the actuator14.

In step156, the back electromotive force detection circuit36detects the back electromotive force generated in the voice coil motor16due to movement of the actuator14, and the position detection unit48assigns the detected magnitude of the back electromotive force (BEMF) to the parameter Vbemf.

In step158, the position detection unit48accumulates the parameter Vbemf to IntgBEMF to continue integration of BEMF.

In step160, the position determination unit49determines whether the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH11. If the integration of BEMF is less than the position threshold TH11, indicating that the lift tab21has not reached the position P4, that is, the lift tab21has not reached the slope SL2, step156through step160are repeated to move the actuator14on at a target speed until the integration of BEMF (IntglBEMF) becomes equal to the position threshold TH11.

If the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH11, the routine proceeds to step162.

In step162, as shown inFIG. 1C, the bandwidth switching unit47sets the PI control bandwidth to the wide bandwidth. As shown inFIG. 11AandFIG. 11B, equality of the integration of BEMF (IntglBEMF) and the position threshold TH11indicates that the lift tab21reaches the position P4, that is, the lift tab21is nearly reaches the slope SL2.

Subsequently, the lift tab21ascends the slope SL2. As described above, in the related art, the speed drop occurs as shown by the dashed line inFIG. 1D. In contrast, in the present control method, by switching the PI control bandwidth to the wide bandwidth, the speed drop is suppressed, and the seed of the lift tab21can be controlled to vary as shown by the solid line.

In step164, with the PI control in the wide bandwidth mode, the lift tab21ascends the slope SL2. The back electromotive force detection circuit36detects the back electromotive force generated in the voice coil motor16due to movement of the actuator14, and the position detection unit48assigns the detected magnitude of the back electromotive force (BEMF) to the parameter Vbemf.

In step166, the position detection unit48accumulates the parameter Vbemf to IntgBEMF to continue integration of BEMF.

In step168, the position determination unit49determines whether the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH12. If the integration of BEMF is less than the position threshold TH2, step164through step168are repeated to move the actuator14on at the target speed with the PI control in the wide bandwidth mode, until the integration of BEMF (IntglBEMF) becomes equal to the position threshold TH12.

If the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH12, the routine proceeds to step170.

In step170, as shown inFIG. 1C, the bandwidth switching unit47switches the PI control bandwidth to the usual bandwidth. As shown inFIG. 11A, the lift tab21reaches the position P3, that is, the boundary of the slope SL2and the flat portion FL1. In the flat portion FL1, the PI control is more stable in the usual bandwidth mode than in the wide bandwidth mode.

In step172, with the PI control in the usual bandwidth mode, the lift tab21moves in the flat portion FL1of the ramp20.

Similarly, the back electromotive force detection circuit36detects the back electromotive force generated in the voice coil motor16due to movement of the actuator14, and the position detection unit48assigns the detected magnitude of the back electromotive force (BEMF) to the parameter Vbemf.

In step174, the position detection unit48accumulates the parameter Vbemf to IntgBEMF to continue integration of BEMF.

In step176, the position determination unit49determines whether the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH13. If the integration of BEMF is less than the position threshold TH13, step172through step176are repeated to move the actuator14on at the target speed with the PI control in the usual bandwidth mode, until the integration of BEMF (IntglBEMF) becomes equal to the position threshold TH13.

If the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH13, the routine proceeds to step178.

In step178, as shown inFIG. 11C, the bandwidth switching unit47switches the PI control bandwidth to the wide bandwidth.

As shown inFIG. 11AandFIG. 11B, equality of the integration of BEMF (IntglBEMF) and the position threshold TH13indicates that the lift tab21reaches the position P2, the boundary of the flat portion FL1and the slope SL1of the ramp20.

In the present method, when the lift tab21descends the slope SL1, the PI control bandwidth is switched to the wide bandwidth based on positions of the lift tab21. Therefore, as shown by the solid line inFIG. 1D, the time delay of switching can be suppressed, and the increase of the speed can be suppresses quickly. As a result, the lift tab21descends the slope SL1at a moving speed nearly equal to the target speed, thereby, a normal air bearing can be formed between the magnetic head12and the surface of the magnetic disk11, and it is possible to prevent contact of the magnetic head12with the magnetic disk11.

In step180, with the PI control in the wide bandwidth mode, the lift tab21descends the slope SL1.

Similarly, the back electromotive force detection circuit36detects the back electromotive force generated in the voice coil motor16due to movement of the actuator14, and the position detection unit48assigns the detected magnitude of the back electromotive force (BEMF) to the parameter Vbemf.

In step182, the position detection unit48accumulates the parameter Vbemf to IntgBEMF to continue integration of BEMF.

In step184, the position determination unit49determines whether the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH14. If the integration of BEMF is less than the position threshold TH14, step180through step184are repeated to move the actuator14on at the target speed with the PI control in the wide bandwidth mode, until the integration of BEMF (IntglBEMF) becomes equal to the position threshold TH14.

If the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH14, the routine proceeds to step186.

In step186, as shown inFIG. 1C, the bandwidth switching unit47switches the PI control bandwidth to the usual bandwidth. As shown inFIG. 11A, the lift tab21reaches the position P1, that is, to be out of contact with the ramp20. When the magnetic head12is floating over the magnetic disk11, the PI control is more stable in the usual bandwidth mode than in the wide bandwidth mode.

In step188, the magnetic head12reproduces servo information recorded in the magnetic disk11, and moves to an on-track position of the outermost cylinder. So far, the loading operation is completed.

In the method for actuator movement control according to the present embodiment in the operations of loading and unloading the magnetic head12, with the outermost cylinder as a reference position, the position detection unit48calculates the present position of the lift tab21based on the BEMF value sent from the back electromotive force detection circuit36, and determines whether the present position of the lift tab21equals specified positions P1through P4, and based on the determination results, the bandwidth switching unit47switches the bandwidth of the PI control. Therefore, it is possible to switch the bandwidth of the PI control to rapidly suppress fast change of the speed before or during a change of the moving speed of the actuator, for example, a rapid drop of the moving speed. Meanwhile, in a region where the speed change of the actuator is small, the bandwidth is switched to the usual bandwidth, and thereby it is possible to improve stability of the speed control.

Second Embodiment

A second embodiment of the actuator movement control method of the present invention is described below. The magnetic disk device of the present embodiment is the same as that of the first embodiment, and the same reference numbers are used for the same elements.

Specifically, the present embodiment relates to a method of controlling movement of the actuator14in the operation of loading and unloading the magnetic head12.

The actuator movement control method of the present embodiment is basically the same as that of the first embodiment, except that the definitions of the position thresholds are different.

FIG. 12Ais a cross-sectional view of a portion of the magnetic disk device10schematically showing a sequence of positions of the lift tab21in the operation of unloading the magnetic head12according to the present embodiment.

FIG. 12Bis a graph showing correspondence of the integration of the BEMF (IntglBEMF) and the position thresholds Th1athrough Th4awith the sequence of positions of the lift tab21in the operation of unloading the magnetic head12according to the present embodiment.

FIG. 12Cis a graph showing a relation between the bandwidth of the PI control and the sequence of positions of the lift tab21in the operation of unloading the magnetic head12according to the present embodiment.

FIG. 12Dis a graph showing a relation between the moving speed of the magnetic head12and the sequence of positions of the lift tab21in the operation of unloading the magnetic head12according to the present embodiment.

As shown inFIG. 12B, comparing the position thresholds Th1athrough Th4awith the position thresholds Th1through Th4in the first embodiment, which correspond to the positions P1through P4, it is set that Th1a<Th1, Th2a>Th2, Th3a<Th3, Th4a>Th4. That is, relative to the positions P1through P4inFIG. 12A, in the unloading direction, that is, the right direction inFIG. 12B, the position threshold Th1ais prior to the position P1, the position threshold Th2ais behind (after) the position P2, the position threshold Th3ais prior to the position P3, and the position threshold Th4ais behind the position P2.

By setting the position thresholds in this way, it is possible to easily reduce the delay of bandwidth switching caused by noise, which is generated in the integration of the BEMF (IntglBEMF), corresponding to the moving speed of the actuator14.

Preferably, the respective differences between the position thresholds Th1a, Th2a, Th3a, and Th4aand the position thresholds Th1, Th2, Th3, and Th4are in the range from 10 μm to 150 μm. If the difference is less than 10 μm, the effect is not sufficient, and if the difference is above 150 μm, the stability of the speed control is degraded.

With thus defined position thresholds Th1a, Th2a, Th3a, and Th4a, and following steps similar with the flowchart inFIG. 8, the actuator14can be controlled so that the speed of the actuator14follows the solid inFIG. 12D, specifically, the decrease of the speed occurring when the lift tab21comes into contact with the ramp20is better suppressed than that in the first embodiment (FIG. 11D) as shown by the dashed line inFIG. 12D.

In addition, even if errors are incorporated into the IntglBEMF, switching to the wide bandwidth can be reliably achieved between P1and P2and between P3and P4.

In the operation of loading and unloading the magnetic head12, by modifying the definitions of the position thresholds Th1, Th2, Th3, and Th4, in the same manner as above, the same effect can be achieved.

Third Embodiment

The magnetic disk device of the present embodiment is basically the same as that of the first embodiment, except that in control of movement of an actuator when loading and unloading a magnetic head, instead of switching the bandwidth of PI control, a feed-forward control variable is superposed on a control variable of a feedback speed control system.

Below, the same reference numbers are used for the same elements as in the first embodiment.

FIG. 13is a block diagram showing a configuration of a portion of a speed control system according to the third embodiment, which is capable of superposing a feed-forward control variable on a feedback control variable of a feedback speed control system.

FIG. 14AandFIG. 14Bshow tables containing data of the feed-forward control variable used in the operation of unloading the magnetic head12, where,FIG. 14Ashows a first table containing the feed-forward control variables used when the lift tab21comes into contact with the ramp20and ascends the slope SL1of the ramp20, andFIG. 14Bshows a second table containing the feed-forward control variables used when the lift tab21decends the slope SL2of the ramp20.

The speed control system shown inFIG. 13includes a comparator45, a PI controller46, a feed-forward controller51, a position detection unit48, and a position determination unit49.

The feed-forward controller51includes a clock counter52, a clock generator53, and a feed-forward control variable reader54.

The comparator45compares the BEMF value with a target speed stored in memory39, and calculates the difference between them. The BEMF value, which is proportional to the moving speed of the actuator14, is supplied by the back electromotive force detection circuit36connected to the voice coil motor16. The PI controller46outputs a control variable to the voice coil motor16through the VCM driving circuit35. The position detection unit48calculates the position of the lift tab21based on the BEMF value supplied by the back electromotive force detection circuit36. The position determination unit49sends a counting start signal to the clock counter52in the feed-forward controller51, and the feed-forward control variable reader54reads out a feed-forward control variable from a feed-forward control variable table loaded in the memory39. The feed-forward control variable from the feed-forward control variable reader54is superposed on the feedback control variable from the PI controller46, and the sum is used to control the voice coil motor16via the VCM driving circuit35.

Specifically, the back electromotive force detection circuit36sends the BEMF value, which is the magnitude of the back electromotive force generated in the voice coil motor16, to the position detection unit48.

The position detection unit48integrates the BEMF value from a reference position to calculate the present position of the lift tab21, and sends a signal indicating the present position of the lift tab21to the position determination unit49.

The position determination unit49compares the present position of the lift tab21with position thresholds TH1through TH5stored in memory39inFIG. 4, and sends the counting start signal when the present position of the lift tab21equals one of the position thresholds TH1through TH5, to start the clock counter52. Based on the time counted by the clock counter52, the feed-forward control variable reader54reads out a feed-forward control variable from the feed-forward control variable tables shown inFIG. 14AorFIG. 14B. The feed-forward control variable from the feed-forward control variable reader54is superposed on the feedback control variable from the PI controller46, and the sum is used to control the voice coil motor16via the VCM driving circuit35.

Operations performed by the comparator45, the PI controller46, the position detection unit48, the position determination unit49, clock counter52, a clock generator53, and a feed-forward control variable reader54are executed by the MPU38in the controller31shown inFIG. 4.

Below, an explanation is made of a method for controlling movement of the actuator14in the operation of unloading the magnetic head12according to the present embodiment.

FIG. 15is a flowchart showing the method of movement control of the actuator14in the operation of unloading the magnetic head12according to the present embodiment.

FIG. 16Ais a cross-sectional view of a portion of the magnetic disk device10along the line indicated by the arrows X inFIG. 5, schematically showing a sequence of positions of the lift tab21in the operation of unloading the magnetic head12according to the present embodiment.

FIG. 16Bis a graph showing correspondence of the integration of the BEMF (IntglBEMF) and the position thresholds Th1through Th4with the sequence of positions of the lift tab21in the operation of unloading the magnetic head12according to the present embodiment.

FIG. 16Cis a graph showing a relation between the feed-forward control variable and the sequence of positions of the lift tab21in the operation of unloading the magnetic head12according to the present embodiment.

FIG. 16Dis a graph showing a relation between the speed of the magnetic head12and the sequence of positions of the lift tab21in the operation of unloading the magnetic head12according to the present embodiment.

Referring toFIG. 15, in step202, receiving an unloading command from the HDC33inFIG. 4, MPU38in the controller31sets the integration of the BEMF value (IntglBEMF) to zero.

Here, the bandwidth of the PI controller46is set to the usual bandwidth. It is assumed that the magnetic head12is on the outermost cylinder of the magnetic disk11, that is, the reference position is the position of the outermost cylinder of the magnetic disk11.

If the magnetic head12is at positions other than the outermost cylinder of the magnetic disk11when the unloading command is received, as already shown with reference toFIG. 8, the magnetic head12is moved to the outermost cylinder of the magnetic disk11as a usual seek operation before step202.

In step204, in order to drive the actuator14to move, MPU38sends an activating current to the voice coil motor16through the VCM driving circuit35. The magnitude of the activating current is adjusted to a specified value by a feedback control.

In step206, the back electromotive force detection circuit36detects the back electromotive force generated in the voice coil motor16due to movement of the actuator14, and the position detection unit48assigns the detected magnitude of the back electromotive force (BEMF) to the parameter Vbemf.

In step208, the position detection unit48accumulates the parameter Vbemf to IntgBEMF to continue integration of BEMF.

In step210, the position determination unit49determines whether the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH1. If the integration of BEMF is less than the position threshold TH1, step206through step210are repeated to move the actuator14on at a target speed until the integration of BEMF (IntglBEMF) becomes equal to the position threshold TH1.

If the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH1, the routine proceeds to step214.

In step214, the position determination unit49inFIG. 13sends a counting start signal to the clock counter52in the feed-forward controller51. Based on the time counted by the clock counter52, the feed-forward control variable reader54reads out a feed-forward control variable from the first table shown inFIG. 14A. The feed-forward control variable obtained by the feed-forward control variable reader54is superposed on the feedback control variable from the PI controller46, as shown inFIG. 16C.

As shown inFIG. 16AandFIG. 16B, equality of the integration of BEMF (IntglBEMF) and the position threshold TH1indicates that the lift tab21reaches the position P1, where the lift tab21is nearly in contact with the ramp20.

As described above, in the related art, the speed decrease is detected when the lift tab21comes into contact with the ramp20, and the feed-forward control variable is superposed based on the detection results. In contrast, in the present control method, as shown inFIG. 16C, the feed-forward control variable is superposed based on positions, therefore, the time delay of superposition can be suppressed. Especially, as shown by the solid line inFIG. 16D, the notable speed drop (shown by the dashed line inFIG. 16D) of the actuator14after contact with the ramp20occurring in the related art can be effectively suppressed.

Data in the first feed-forward control variable table may be obtained by numeric simulations, or by measurement of each magnetic disk device product in a quality check process before shipment. Since the feed-forward control variable can be determined taking into account influence of friction between and uncertainties of the ramp20and the lift tab21in each magnetic disk device product, it is possible to achieve uniform operation of the actuator14.

Data in the second feed-forward control variable table inFIG. 14Bcan be determined in a similar way.

In step215, while the feed-forward control variable is being superposed, the lift tab21ascends the slope SL1.

During the movement of the actuator14, the position determination unit49determines whether the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH2. If the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH2, the routine proceeds to step216.

In step216, superposition of the feed-forward control variable is completed.

In step218, while the actuator14is moving on, the back electromotive force detection circuit36detects the back electromotive force generated in the voice coil motor16due to movement of the actuator14, and the position detection unit48assigns the detected magnitude of the back electromotive force (BEMF) to the parameter Vbemf.

In step220, the position detection unit48accumulates the parameter Vbemf to IntgBEMF to continue integration of BEMF during and after superposition of the feed-forward control variable.

In step222, the position determination unit49determines whether the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH3. If the integration of BEMF is less than the position threshold TH3, step218through step222are repeated to move the actuator14on at the target speed until the integration of BEMF (IntglBEMF) becomes equal to the position threshold TH3.

If the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH3, the routine proceeds to step224.

In step224, the position determination unit49inFIG. 13sends a counting start signal to the clock counter52in the feed-forward controller51. Based on the time counted by the clock counter52, the feed-forward control variable reader54reads out a feed-forward control variable from the first table shown inFIG. 14B. The feed-forward control variable obtained by the feed-forward control variable reader54is superposed on the feedback control variable from the PI controller46, as shown inFIG. 16C.

As shown inFIG. 16AandFIG. 16B, equality of the integration of BEMF (IntglBEMF) and the position threshold TH3indicates that the lift tab21reaches the position P3, that is, the lift tab21reaches the boundary of the flat portion FL1and the slope SL2.

In the present control method, corresponding to an otherwise further negative increase of the speed (the dashed line inFIG. 16Dat position P3), a positive feed-forward variable is superposed as shown inFIG. 16Cso as to positively decrease the speed (the solid line inFIG. 16Dat position P3). At the same time, the feed-forward control variable is superposed based on positions of the actuator14as shown inFIG. 16C. Therefore, the time delay of superposition can be suppressed, and deviation of the moving speed of the actuator14from the target speed can be more effectively suppressed than in the related art.

In step225, while the feed-forward control variable is being superposed, the lift tab21descends the slope SL2of the ramp20.

During the movement of the actuator14, the position determination unit49determines whether the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH4. If the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH4, the routine proceeds to step226.

In step226, superposition of the feed-forward control variable is completed.

In step228, with the actuator14being at the target speed, the base portion14aof the actuator14is brought into contact with the outer stopper22, and the actuator14is stopped mechanically. Alternatively, as in the first embodiment, the actuator14may also be stopped by setting the target speed and the InfglBEMF to zero.

The method of movement control of the actuator14in the operation of loading the magnetic head12according to the present embodiment is similar to the method described above. Specifically, with the position thresholds Th11and Th13as the starting points of superposition, which are defined in the description of the actuator movement control method of the first embodiment, a feed-forward control variable can be superposed by using the feed-forward control variable table used in the above description but with time order of the table reversed.

In the method for actuator movement control in the operations of loading and unloading the magnetic head12according to the present embodiment, with the outermost cylinder as a reference position, the position detection unit48calculates the present position of the lift tab21based on the BEMF value sent from the back electromotive force detection circuit36, and determines whether the present position of the lift tab21equals specified positions P1through P3, and based on the determination results, a feed-forward control variable is superposed. Therefore, it is possible to superpose a feed-forward control variable before or during a change of the moving speed of the actuator, for example, a rapid drop of the moving speed, thus enabling rapid suppression of fast change of the speed. Meanwhile, in a region where the speed change of the actuator14is small, the feed-forward control variable is set to zero, and thereby stability of speed control can be improved.

In the speed control system of the present embodiment, the clock generator53inFIG. 13may also be placed outside MPU38, and clock signals from other circuits, such as HDC33as shown inFIG. 4, may also be used.

The position thresholds Th1, Th2, Th3, and Th4may also be modified to position thresholds Th1a, Th2a, Th3a, and Th4a, respectively, as described in the second embodiment. By setting the position thresholds in this way, it is possible to easily reduce the delay of feed-forward control variable superposition caused by noise occurring in the integration of the BEMF (IntglBEMF) corresponding to the moving speed of the actuator14.

In addition, instead of the feed-forward control variable tables inFIG. 14AandFIG. 14B, a feed-forward control variable table expressing a relation between a distance from a reference position and the feed-forward control variable may be used. The feed-forward control variable reader54in the feed-forward controller51may make reference to the present position of the lift tab21given by the position detection unit48inFIG. 13, read out a feed-forward control variable from the feed-forward control variable table, and output them. For example, data in the feed-forward control variable table may be set in the following way. The feed-forward control variable is set equal to zero at a position in the range from the reference to the position threshold Th1, to be the same as those in the table inFIG. 14Aat a position in the range from the position threshold Th1to the position threshold Th2, to be zero at a position in the range from the position threshold Th2to the position threshold Th3, to be the same as those in the table inFIG. 14Bat a position in the range from the position threshold Th3to the position threshold Th4, and to be zero at a position beyond the position threshold Th4. Further, the time variable in the first table and the second table is converted to position by using the moving speed. In this way, the position determination unit49, the clock counter52, and the clock generator53may be omitted, and thereby the control process can be simplified.

Fourth Embodiment

The magnetic disk device of the present embodiment is basically the same as that of the first embodiment, except that in control of movement of an actuator, a speed change detection window signal is generated based on positions of a lift tab, and the bandwidth of a PI controller is switched when the speed change detection window signal is OPEN and the speed changes by at least a predetermined amount. Below, the same reference numbers are used for the same elements as in the previous embodiments.

FIG. 17is a block diagram showing a configuration of a portion of a speed control system according to the fourth embodiment, which is capable of detecting and determining the speed of the actuator14based on the position of the actuator14and switching the bandwidth of a feedback speed control system according to the detection and determination results.

The speed control system shown inFIG. 17includes a comparator45, a PI controller46, a bandwidth switching unit47, a position detection unit48, a position determination unit49, a speed detection window generator55, and a speed determination unit56.

The comparator45compares the BEMF value with a target speed stored in memory39, and calculates the difference between them. The BEMF value, which is proportional to the moving speed of the actuator14, is supplied by the back electromotive force detection circuit36connected to the voice coil motor16. The PI controller46outputs a control variable to the voice coil motor16through the VCM driving circuit35.

The position detection unit48calculates the position of the lift tab21based on the BEMF value supplied by the back electromotive force detection circuit36. Based on the position of the lift tab21, the position determination unit49sends a signal to the speed detection window generator55to set the state of the speed detection window signal OPEN or CLOSED.

When the speed detection window signal generated by the speed detection window generator55is OPEN, and when the difference between the speed of the actuator14and a target speed exceeds a threshold value, the speed determination unit56sends a signal to the bandwidth switching unit47to change the bandwidth of the PI control performed by the PI controller46.

Specifically, the back electromotive force detection circuit36sends the BEMF value, which is the magnitude of the back electromotive force generated in the voice coil motor16, to the position detection unit48.

The position detection unit48integrates the BEMF value from a reference position to calculate the present position of the lift tab21, and sends a signal indicating the present position of the lift tab21to the position determination unit49.

The position determination unit49compares the present position of the lift tab21with position thresholds TH1through TH4stored in memory39inFIG. 4, and sends a speed detection window changing signal to the speed detection window generator55based on the determination results.

Here, for example, the reference position is the position P0of the outermost cylinder of the magnetic disk11illustrated inFIG. 6. The position thresholds TH1through TH4are set equal to the position P1through P4illustrated inFIG. 6, respectively.

The speed detection window generator55sets the speed detection window signal OPEN or CLOSED based on the speed detection window changing signal.

The speed determination unit56compares the BEMF value sent from the back electromotive force detection circuit36, indicating the present speed of the actuator14, with the threshold value of speed difference and the target speed when the speed detection window signal is OPEN, and sends a bandwidth switching signal to the bandwidth switching unit47when the difference between the present speed of the actuator14and the target speed is greater than or equal to the threshold value of the speed difference.

The bandwidth switching unit47changes the bandwidth of the PI control performed by the PI controller according to the bandwidth switching signal.

Operations performed by the comparator45, the PI controller46, the bandwidth switching unit47, the position detection unit48, the position determination unit49, the speed detection window generator55, and the speed determination unit56are executed by the MPU38in the controller31shown inFIG. 4.

Below, an explanation is made of a method of movement control of the actuator14in the operation of unloading the magnetic head12.

FIG. 18is a flowchart showing the method of movement control of the actuator14in the operation of unloading the magnetic head12according to the present embodiment.

FIG. 19Ais a cross-sectional view of the portion of the magnetic disk device10schematically showing a sequence of positions of the lift tab21in the operation of unloading the magnetic head12according to the present embodiment.

FIG. 19Bis a graph showing the integration of the BEMF (IntglBEMF) and the position thresholds Th1through Th4, which correspond to specified positions of the lift tab21in the operation of unloading the magnetic head12according to the present embodiment.

FIG. 19Cis a graph showing the speed of the magnetic head12, which changes with the position of the lift tab21in the operation of unloading the magnetic head12according to the present embodiment.

FIG. 19Dis a graph showing the speed detection window signal in the operation of unloading the magnetic head12according to the present embodiment.

FIG. 19Eis a graph showing the bandwidth switching signal in the operation of unloading the magnetic head12according to the present embodiment.

FIG. 19Fis a graph showing the bandwidth of the PI control, which changes with the position of the lift tab21in the operation of unloading the magnetic head12according to the present embodiment.

Here, it is assumed that initially the magnetic head12is at the position P0of the outermost cylinder of the magnetic disk11illustrated inFIG. 6, that is, the reference position is the position P0of the outermost cylinder of the magnetic disk11.

Referring toFIG. 18, in step302, receiving an unloading command from the HDC33, MPU38in the controller31sets the integration of the BEMF value (IntglBEMF) to zero, and the bandwidth switching unit47sets the PI control bandwidth to the usual bandwidth.

In step304, MPU38sends an activating current to the voice coil motor16to drive the actuator14to move.

In step306, the back electromotive force detection circuit36detects the back electromotive force generated in the voice coil motor16due to movement of the actuator14, and the position detection unit48assigns the detected magnitude of the back electromotive force (BEMF) to the parameter Vbemf.

In step308, the position detection unit48accumulates the parameter Vbemf to IntgBEMF to continue integration of BEMF.

In step310, the position determination unit49determines whether the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH1. If the integration of BEMF is less than the position threshold TH1, step306through step310are repeated to move the actuator14on at a target speed until the integration of BEMF (IntglBEMF) becomes equal to the position threshold TH1.

If the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH1, the routine proceeds to step312.

In step312, the position determination unit49sends the speed detection window changing signal to the speed detection window generator55. Based on the speed detection window changing signal, the speed detection window generator55sets the speed detection window signal to a high level, that is, to the OPEN state, as shown inFIG. 19D.

In step314, the speed determination unit56determines whether the parameter Vbemf, the present speed of the actuator14, is greater than or equal to a sum of the target speed Vt and the threshold (Va) of the speed difference.

If the parameter Vbemf is less than the sum of the target speed Vt and the threshold Va, the actuator14moves on with the usual bandwidth mode being maintained. Here, it is assumed that the threshold Va of the speed difference is positive.

If the parameter Vbemf is greater than or equal to the sum of the target speed Vt and the threshold Va, as shown inFIG. 19C, the routine proceeds to step316.

In step316, as shown inFIG. 19E, the speed determination unit56sends the bandwidth switching signal to the bandwidth switching unit47. Then, as shown inFIG. 19F, the bandwidth switching unit47sets the PI control bandwidth to the wide bandwidth.

As described above, determination concerning the speed is performed only when the speed change detection window signal is OPEN, therefore, by setting a smaller threshold Va of the speed difference than in the related art, it is possible to rapidly detect a speed change with high sensitivity. As a result, it is possible to more effectively suppress the speed change than in the related art, and the notable speed drop of the actuator14after contact with the ramp20occurring in the related art can be effectively suppressed.

In step318, while the actuator14is moving on, the back electromotive force detection circuit36detects the back electromotive force generated in the voice coil motor16due to movement of the actuator14, and the position detection unit48assigns the detected magnitude of the back electromotive force (BEMF) to the parameter Vbemf.

In step320, the position detection unit48accumulates the parameter Vbemf to IntgBEMF to continue integration of BEMF.

If the parameter Vbemf is less than the sum of the target speed Vt and the threshold Va (as shown inFIG. 19C), the routine proceeds to step326.

If the parameter Vbemf is not less than the sum of the target speed Vt and the threshold Va, the routine proceeds to step324.

In step324, the position determination unit49determines whether the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH2. If the integration of BEMF is less than the position threshold TH2, step322and step324are repeated to move the actuator14on at the target speed until the integration of BEMF (IntglBEMF) becomes equal to the position threshold TH2.

If the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH2, the routine proceeds to step326.

In step326, the position determination unit49sends the speed detection window changing signal to the speed detection window generator55. Based on the speed detection window changing signal, the speed detection window generator55sets the speed detection window signal to a low level, that is, to the CLOSED state, as shown inFIG. 19D. Then, the speed determination unit56changes the level of the bandwidth switching signal (inFIG. 19E), and the bandwidth switching unit47switches the PI control bandwidth to the usual bandwidth, as shown inFIG. 19F.

As described above, when the lift tab21come into contact with the ramp20and ascends the slope SL1, the bandwidth switching unit47switches the PI control bandwidth to the wide bandwidth only when the speed of the actuator14changes by an amount greater than the threshold value Va of the speed difference. In doing so, switching to the wide bandwidth is performed only when a rapid speed change occurs and the usual bandwidth mode cannot compensate. Therefore, it is possible to achieve both high responding performance and high control stability.

In step328, the back electromotive force detection circuit36detects the back electromotive force generated in the voice coil motor16due to movement of the actuator14, and the position detection unit48assigns the detected magnitude of the back electromotive force (BEMF) to the parameter Vbemf.

In step330, the position detection unit48accumulates the parameter Vbemf to IntgBEMF to continue integration of BEMF.

In step332, the position determination unit49determines whether the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH3. If the integration of BEMF is less than the position threshold TH3, step328through step330are repeated to move the actuator14on at the target speed until the integration of BEMF (IntglBEMF) becomes equal to the position threshold TH3.

If the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH3, the routine proceeds to step334.

In step334, the position determination unit49sends the speed detection window changing signal to the speed detection window generator55. Corresponding to the speed detection window changing signal, the speed detection window generator55sets the speed detection window signal to a high level (OPEN state), as shown inFIG. 19D.

In step336, the speed determination unit56determines whether the parameter Vbemf, the present speed of the actuator14, is less than or equal to a difference between the target speed Vt and the threshold Va of the speed difference.

If the parameter Vbemf is greater than the difference between the target speed Vt and the threshold Va, the actuator14moves on with the usual bandwidth mode being maintained.

If the parameter Vbemf is less than or equal to the difference between the target speed Vt and the threshold Va, as shown inFIG. 19C, the routine proceeds to step336.

In step338, as shown inFIG. 19E, the speed determination unit56sets the bandwidth switching signal to the high level, accordingly, as shown inFIG. 19F, the bandwidth switching unit47sets the PI control bandwidth to the wide bandwidth.

In step340, while the actuator14is moving on, the back electromotive force detection circuit36detects the back electromotive force generated in the voice coil motor16due to movement of the actuator14, and the position detection unit48assigns the detected magnitude of the back electromotive force (BEMF) to the parameter Vbemf.

In step342, the position detection unit48accumulates the parameter Vbemf to IntgBEMF to continue integration of BEMF.

If the parameter Vbemf is less than the difference between the target speed Vt and the threshold Va (as shown inFIG. 19C), the routine proceeds to step348.

If the parameter Vbemf is not less than the difference between the target speed Vt and the threshold Va, the routine proceeds to step346.

In step346, the position determination unit49determines whether the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH4. If the integration of BEMF is less than the position threshold TH4, step344through step346are repeated to move the actuator14on at the target speed until the integration of BEMF (IntglBEMF) becomes equal to the position threshold TH4.

If the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH4, the routine proceeds to step348.

In step348, the position determination unit49sends the speed detection window changing signal to the speed detection window generator55. Based on the speed detection window changing signal, the speed detection window generator55sets the speed detection window signal to a low level, that is, to the CLOSED state, as shown inFIG. 19D. Accordingly, the speed determination unit56changes the level of the bandwidth switching signal (inFIG. 19E), and the bandwidth switching unit47switches the PI control bandwidth to the usual bandwidth, as shown inFIG. 19F.

As described above, when the lift tab21descends the slope SL2of the ramp20, the bandwidth switching unit47switches the PI control bandwidth to the wide bandwidth only when the speed of the actuator14changes by an amount greater than the threshold value Va of the speed difference. In doing so, switching to the wide bandwidth is performed only when a rapid speed change occurs and the usual bandwidth mode cannot compensate. Therefore, it is possible to achieve both high responding performance and high control stability.

It should be noted that step328through step348for speed control on the slope SL2are not indispensable. These steps may be executed only when otherwise speed control becomes unstable.

In step350, as described in the first embodiment, the actuator14may be stopped by changing setting of the target speed. Alternatively, the actuator14may be mechanically stopped by using the outer stopper22, specifically, when the base portion14aof the actuator14mechanically contacts the outer stopper22, the actuator14is stopped.

So at this point, the unloading operation is completed.

The method for movement control of the actuator14in loading the magnetic head12according to the present embodiment is similar to the method described above. Specifically, the actuator movement control method for loading operation can be achieved by combining the corresponding method in the first embodiment and the method described above.

In the method for actuator movement control according to the present embodiment in the operations of loading and unloading the magnetic head12, speed determination is performed only when the speed change detection window signal, which depends on the position of the lift tab21, is OPEN, and the bandwidth switching unit47switches the bandwidth of the PI control according to the determination result. Because the speed change detection window signal is set OPEN depending on the position of the lift tab21, during normal seek operations or in regions where high responding performance is not required, it is possible to prevent operation of erroneously switching PI control to the wide bandwidth in speed control due to speed changes caused by external shock and vibration, thereby enabling stable speed control.

In addition, because the threshold Va of the speed difference, which is used in speed determination, can be set small, it is possible to rapidly detect a speed change with high sensitivity. As a result, it is possible to effectively suppress the speed drop of the actuator after contact with the ramp.

Fifth Embodiment

The magnetic disk device of the fifth embodiment is basically the same as that of the fourth embodiment, except that in control of movement of an actuator when loading and unloading a magnetic head, instead of switching bandwidth of a PI controller corresponding to determination of a speed change, a feed-forward control variable is superposed on a control variable of the feedback speed control system.

Below, the same reference numbers are used for the same elements as in the previous embodiment.

FIG. 20is a block diagram showing a configuration of a portion of a speed control system according to the fifth embodiment, which is capable of detecting and determining the speed of the actuator14based on the position of the actuator14and superposing a feed-forward control variable on a feedback speed control variable of a feedback speed control system.

The speed control system shown inFIG. 20includes a comparator45, a PI controller46, a feed-forward controller51, a position detection unit48, a position determination unit49, a speed detection window generator55, and a speed determination unit56.

The feed-forward controller51includes a clock counter52, a clock generator53, and a feed-forward control variable reader54.

As shown inFIG. 20, instead of the bandwidth switching unit47for switching the bandwidth of the PI control as shown inFIG. 17in the fourth embodiment, the speed control system of the present embodiment includes a feed-forward controller51for superposing a feed-forward control variable on a control variable of a feedback speed control system.

In the speed control system of the present embodiment, the comparator45compares the BEMF value, which is proportional to the moving speed of the actuator14, with a target speed stored in memory39, and calculates the difference between them. The PI controller46outputs a control variable to the voice coil motor16through the VCM driving circuit35. The position detection unit48calculates the position of the lift tab21based on the BEMF value supplied by the back electromotive force detection circuit36. Based on the position of the lift tab21, the position determination unit49sends a signal to the speed detection window generator55to set the state of the speed detection window signal OPEN or CLOSED. When the speed detection window signal generated by the speed detection window generator55is OPEN, and when a difference between the speed of the actuator14and a target speed exceeds a threshold value, the speed determination unit56sends a counting start signal to the clock counter52in the feed-forward controller51, and the feed-forward control variable reader54reads out a feed-forward control variable from a feed-forward control variable table loaded in the memory39. The feed-forward control variable from the feed-forward control variable reader54is superposed on the feedback control variable from the PI controller46, and the sum is used to control the voice coil motor16via the VCM driving circuit35.

Specifically, the back electromotive force detection circuit36sends the BEMF value, which is the magnitude of the back electromotive force generated in the voice coil motor16, to the position detection unit48.

The position detection unit48integrates the BEMF value from a reference position to calculate the present position of the lift tab21, and sends a signal indicating the present position of the lift tab21to the position determination unit49.

The position determination unit49compares the present position of the lift tab21with position thresholds TH1through TH4stored in memory39inFIG. 4, and sends a speed detection window changing signal to the speed detection window generator55based on the determination results. For example, the reference position is the position P0of the outermost cylinder of the magnetic disk11illustrated inFIG. 6. The position thresholds TH1through TH4are set equal to the position P1through P4illustrated inFIG. 6, respectively.

The speed detection window generator55sets the speed detection window signal OPEN or CLOSED based on the speed detection window changing signal.

The speed determination unit56compares the BEMF value sent from the back electromotive force detection circuit36, indicating the present speed of the actuator14, with the threshold value of speed difference and the target speed when the speed detection window signal is OPEN, and sends the counting start signal to start the clock counter52when the difference between the present speed of the actuator14and the target speed is greater than or equal to the threshold value of the speed difference.

Based on the time counted by the clock counter52, the feed-forward control variable reader54reads out a feed-forward control variable from feed-forward control variable tables, for example, the tables shown inFIG. 14AorFIG. 14B. The feed-forward control variable from the feed-forward control variable reader54is superposed on the feedback control variable from the PI controller46, and the sum is used to control the voice coil motor16via the VCM driving circuit35.

Operations performed by the comparator45, the PI controller46, the position detection unit48, the position determination unit49, clock counter52, a clock generator53, a feed-forward control variable reader54, the speed detection window generator55, and the speed determination unit56are executed by the MPU38in the controller31shown inFIG. 4.

Below, an explanation is made of a method for controlling movement of the actuator14in the operation of unloading the magnetic head12according to the present embodiment.

FIG. 21is a flowchart showing the method of movement control of the actuator14in the operation of unloading the magnetic head12according to the present embodiment.

FIG. 22Ais a cross-sectional view of the portion of the magnetic disk device10schematically showing a sequence of positions of the lift tab21in the operation of unloading the magnetic head12according to the present embodiment.

FIG. 22Bis a graph showing the integration of the BEMF (IntglBEMF) and the position thresholds Th1through Th4, which correspond to specified positions of the lift tab21in the operation of unloading the magnetic head12according to the present embodiment.

FIG. 22Cis a graph showing the speed of the magnetic head12, which changes with the position of the lift tab21in the operation of unloading the magnetic head12according to the present embodiment.

FIG. 22Dis a graph showing the speed detection window signal in the operation of unloading the magnetic head12according to the present embodiment.

FIG. 22Eis a graph showing the counting start signal in the operation of unloading the magnetic head12according to the present embodiment.

FIG. 22Fis a graph showing the feed-forward control variable, which changes with the position of the lift tab21in the operation of unloading the magnetic head12according to the present embodiment.

Here, it is assumed that initially the magnetic head12is at the position P0of the outermost cylinder of the magnetic disk11illustrated inFIG. 6, that is, the reference position is the position P0of the outermost cylinder of the magnetic disk11.

Referring toFIG. 21, in step402, receiving an unloading command from the HDC33, MPU38in the controller31sets the integration of the BEMF value (IntglBEMF) to zero. Here, it is assumed that the bandwidth switching unit47sets the PI control bandwidth to the usual bandwidth.

In step404, MPU38sends an activating current to the voice coil motor16to drive the actuator14to move.

In step406, the back electromotive force detection circuit36detects the back electromotive force generated in the voice coil motor16due to movement of the actuator14, and the position detection unit48assigns the detected magnitude of the back electromotive force (BEMF) to the parameter Vbemf.

In step408, the position detection unit48accumulates the parameter Vbemf to IntgBEMF to continue integration of BEMF.

In step410, the position determination unit49determines whether the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH1. If the integration of BEMF is less than the position threshold TH1, step406through step410are repeated to move the actuator14on at a target speed until the integration of BEMF (IntglBEMF) becomes equal to the position threshold TH1.

If the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH1, the routine proceeds to step412.

In step412, the position determination unit49sends the speed detection window changing signal to the speed detection window generator55. Based on the speed detection window changing signal, the speed detection window generator55sets the speed detection window signal to a high level, that is, to OPEN state, as shown inFIG. 22D.

In step414, the speed determination unit56determines whether the parameter Vbemf, the present speed of the actuator14, is greater than or equal to a sum of the target speed Vt and the threshold (Va) of the speed difference.

If the parameter Vbemf is less than the sum of the target speed Vt and the threshold Va, the actuator14moves on. Here, it is assumed that the threshold Va of the speed difference is positive.

If the parameter Vbemf is greater than or equal to the sum of the target speed Vt and the threshold Va, as shown inFIG. 22C, the routine proceeds to step416.

In step416, as shown inFIG. 22E, the speed determination unit56sends the counting start signal to the clock counter52in the feed-forward controller51. Based on the time counted by the clock counter52, the feed-forward control variable reader54reads out a feed-forward control variable (as shown inFIG. 22F) from a feed-forward control variable table, for example that shown inFIG. 14A. The feed-forward control variable obtained by the feed-forward control variable reader54is superposed on the feedback control variable from the PI controller46.

Due to superposition of the feed-forward control variable on the feedback control variable for the actuator14, the lift tab21is moved to ascend the slope SL1of the ramp20.

During superposition of the feed-forward control variable on the feedback control variable, the back electromotive force detection circuit36detects the back electromotive force generated in the voice coil motor16due to movement of the actuator14, and the position detection unit48assigns the detected magnitude of the back electromotive force (BEMF) to the parameter Vbemf. The position detection unit48accumulates the parameter Vbemf to IntgBEMF to continue integration of BEMF.

As described above, determination concerning the speed is performed only when the speed change detection window signal is OPEN, which depends on the position of the lift tab21, and the feed-forward controller51superposes the feed-forward control variable on a feedback control variable according to the determination result. Therefore, during normal seek operations or in regions where high responding performance is not required, it is possible to prevent operation of erroneously superposing a feed-forward control variable on a feedback control variable due to speed changes caused by external shock and vibration, and thereby enabling stable speed control.

In step418, the position determination unit49determines whether the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH2. If the integration of BEMF is less than the position threshold TH2, superposition of the feed-forward control variable on the feedback control variable is continued to move the actuator14on at the target speed until the integration of BEMF (IntglBEMF) becomes equal to the position threshold TH2.

If the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH2, the routine proceeds to step420.

In step420, superposition of the feed-forward control variable is completed.

Also after superposition of the feed-forward control variable on the feedback control variable, the back electromotive force detection circuit36detects the back electromotive force generated in the voice coil motor16due to movement of the actuator14, and the position detection unit48assigns the detected magnitude of the back electromotive force (BEMF) to the parameter Vbemf. The position detection unit48accumulates the parameter Vbemf to IntgBEMF to continue integration of BEMF.

When the lift tab21descends the slope SL2of the ramp20, similarly, the speed detection window signal is set OPEN depending on the position of the lift tab21, and after speed determination, a feed-forward control variable is superposed on a feedback control variable. This process is described by the following steps.

In step422, the back electromotive force detection circuit36detects the back electromotive force generated in the voice coil motor16due to movement of the actuator14, and the position detection unit48assigns the detected magnitude of the back electromotive force (BEMF) to the parameter Vbemf.

In step424, the position detection unit48accumulates the parameter Vbemf to IntgBEMF to continue integration of BEMF.

In step426, the position determination unit49determines whether the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH3. If the integration of BEMF is less than the position threshold TH3, step422through step425are repeated to move the actuator14on at a target speed until the integration of BEMF (IntglBEMF) becomes equal to the position threshold TH3.

If the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH3, the routine proceeds to step428.

In step428, the position determination unit49sends the speed detection window changing signal to the speed detection window generator55. Based on the speed detection window changing signal, the speed detection window generator55sets the speed detection window signal to a high level, that is, to the OPEN state, as shown inFIG. 22D.

In step430, the speed determination unit56determines whether the parameter Vbemf, the present speed of the actuator14, is greater than or equal to a difference between the target speed Vt and the threshold Va of the speed difference.

If the parameter Vbemf is greater than the difference between the target speed Vt and the threshold Va, the actuator14moves on.

If the parameter Vbemf is less than or equal to the difference between the target speed Vt and the threshold Va, as shown inFIG. 22C, the routine proceeds to step432.

In step432, as shown inFIG. 22E, the speed determination unit56sends the counting start signal to the clock counter52in the feed-forward controller51. Based on the time counted by the clock counter52, the feed-forward control variable reader54reads out a feed-forward control variable (as shown inFIG. 22F) from a feed-forward control variable table, for example that shown inFIG. 14B. The feed-forward control variable obtained by the feed-forward control variable reader54is superposed on the feedback control variable from the PI controller46.

In step434, the position determination unit49determines whether the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH4. If the integration of BEMF is less than the position threshold TH4, superposition of the feed-forward control variable on the feedback control variable is continued to move the actuator14on at the target speed until the integration of BEMF (IntglBEMF) becomes equal to the position threshold TH4.

If the integration of BEMF (IntglBEMF) is greater than or equal to the position threshold TH4, the routine proceeds to step436.

In step436, the position determination unit49sends the speed detection window changing signal to the speed detection window generator55. Based on the speed detection window changing signal, the speed detection window generator55sets the speed detection window signal to a low level, that is, to the CLOSED state, as shown inFIG. 22D. The superposition of the feed-forward control variable is completed.

In step438, as described in the fourth embodiment, the actuator14may be stopped by changing setting of the target speed. Alternatively, the actuator14may be mechanically stopped by using the outer stopper22, specifically, when the base portion14aof the actuator14mechanically contacts the outer stopper22, the actuator14is stopped.

So at this point, the unloading operation is completed.

The method for movement control of the actuator14in loading the magnetic head12according to the present embodiment is similar to the method described above.

In the method for actuator movement control according to the present embodiment in the operations of loading and unloading the magnetic head12, speed determination is performed only when the speed change detection window signal is OPEN, which depends on the position of the lift tab21, and the feed-forward controller51superposes the feed-forward control variable on a feedback control variable according to the determination result. Therefore, during normal seek operations or in regions where high responding performance is not required, it is possible to prevent operation of erroneously superposing a feed-forward control variable on a feedback control variable due to speed changes caused by external shock and vibration, and thereby enabling stable speed control.

In addition, while the feed-forward control variable is being superposed, stable feedback control can be maintained.

Furthermore, the position thresholds Th1through Th4may also be modified to the position thresholds Th1athrough Th4aas described in the second embodiment.

Sixth Embodiment

The magnetic disk device of the sixth embodiment is basically the same as that of the first embodiment, except that a rotary encoder or an optical scale is used to detect the position of the lift tab, instead of integrating the BEMF value, which is a back electromotive force proportional to the moving speed of the actuator14.

Below, the same reference numbers are used for the same elements as in the previous embodiment.

FIG. 23is a block diagram showing a configuration of a portion of a speed control system according to the sixth embodiment, which is capable of switching the bandwidth of a feedback speed control system based on the position of a magnetic head.

The speed control system shown inFIG. 23includes a comparator45, a PI controller46, a bandwidth switching unit47, a position detection unit48a, a position determination unit49, and a position indicator58.

In the present embodiment, the position detection unit48aobtains the position of the magnetic head12from the position indicator58. The position indicator58may be a rotary encoder mounted on the rotational axis19of the actuator14. Alternatively, the position indicator58may include an optical scale arranged on the outer coil16aor on the inner coil16bof the voice coil motor16, and in addition, a detector for reading scales arranged on the side of a permanent magnet. For example, the smallest scale of the optical scale is 1 μm.

The position detection unit48acalculates the present position of the lift tab21from a predetermined reference position and the indication of the position indicator58, and sends a signal indicating the present position of the lift tab21to the position determination unit49.

The position determination unit49compares the present position of the lift tab21with position thresholds TH1through TH4stored in memory39inFIG. 4, and sends a bandwidth switching signal to the bandwidth switching unit47based on the comparison results.

The bandwidth switching unit47changes the bandwidth of the PI control performed by the PI controller according to the bandwidth switching signal.

Here, for example, the reference position is the position P0of the outermost cylinder of the magnetic disk11illustrated inFIG. 6. The position thresholds TH1through TH4are set equal to the position P1through P4illustrated inFIG. 6, respectively.

The other part of the magnetic disk device of the present embodiment is the same as that of the first embodiment, and the explanation is omitted.

According to the present embodiment, by using the position indicator58to detect the position of the lift tab21, there are few errors caused by electrical noise that occur when easily integrating the BEMF value, and the position of the lift tab21can be determined accurately. Consequently, switching from the usual bandwidth to the wide bandwidth, or vise versa can be performed accurately and quickly, thereby reducing time delay in control and suppressing speed increase.

Certainly, the present embodiment may be combined with the second through sixth embodiments, and the same effects can be obtained.

While the invention is described above with reference to specific embodiments chosen for purpose of illustration, it should be apparent that the invention is not limited to these embodiments, but numerous modifications could be made thereto by those skilled in the art without departing from the basic concept and scope of the invention.

For example, in the above embodiments, it is described that the ramp is placed outside the outer diameter of the magnetic disk, but the ramp may also be set inside the outer diameter of the magnetic disk, and the method for actuator movement control is still applicable.

In the above embodiments, instead of the PI controller, a P (proportional) controller to a PID (proportional integration differentiation) controller may also be used.

In the above embodiments, a magnetic disk is used as the storage medium, but the present invention is not limited to this, and may be applied to any other storage media which employ the ramp load/unload technique.

Summarizing the effect of the present invention, because the moving speed of a recording and reproducing head is controlled based on the position of the recording and reproducing head, it is possible to present operation errors caused by external shock and vibration in the speed control, and at the same time, it is possible to reduce deviation of the speed of the recording and reproducing head from a target value by rapidly and stably switching the bandwidth of the feedback control. Consequently, it is possible to realize a storage device and actuator movement control method capable of highly stable operations of loading and unloading the recording and reproducing head.

This patent application is based on Japanese Priority Patent Application No. 2003-388146 filed on Nov. 18, 2003, the entire contents of which are hereby incorporated by reference.