Abstract:
A disk drive unit mounts an acceleration sensor. A sequence for calculating an amount by which a head actuator is adjusted during recording and readout operations is changed based on an output from the acceleration sensor.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to a disk drive unit mounting an acceleration sensor and a control method for the disk drive unit, and more particularly, to a device and method for compensating for the effects of an external disturbance on a disk drive unit mounting one or more acceleration sensors.  
           [0003]    2. Description of Related Art  
           [0004]    Conventionally, in the field of magnetic disk drive units, the magnetic recording and/or readout (hereinafter recording and readout) of information to and from a rotating recording medium such as a magnetic or optical disk involves positioning the magnetic head appropriately with respect to the rotating disk so as to carry out optimum magnetic recording and readout.  
           [0005]    In such cases, external disturbances imparted to the disk drive unit can affect the positioning of the magnetic head. In particular, the rotary-type actuator that is sometimes used as a magnetic head drive mechanism is particularly susceptible to external disturbances which coincide with a radial direction of the rotating disk (hereinafter referred to as a radial disturbance).  
           [0006]    One method that has been proposed for correcting for the effects of such external disturbances on the positioning of the magnetic head with respect to the rotating disk involves mounting acceleration sensors on the magnetic disk drive unit frame or on top of the printed circuit board, sensing vibrations from external disturbances or from the reaction of the magnetic disk drive unit itself to a seek operation, and using the data so detected to correct for the effects of the vibrations. In particular, one method for sensing vibrations due to external disturbances in a radial direction of the rotating disk involves using a single acceleration sensor to detect directly the angular velocity imparted by the external disturbance.  
           [0007]    The disadvantage of the above-described method is that the acceleration sensor is either expensive, has a low frequency response, or is relatively large.  
           [0008]    In contrast to the above-described method, another, less expensive, method has been proposed in which two acceleration sensors are disposed along a single axis on the magnetic disk drive unit for sensing vibrations along the single axis (including the vibrational component of the external disturbance along such single axis), and processing the output of these acceleration sensors to obtain the effects of the external disturbance along both the single axis and the radial direction.  
           [0009]    Examples of such conventional dual-sensor arrangements are shown in FIG. 1 and FIG. 2.  
           [0010]    [0010]FIG. 1 is an abbreviated plan view of a printed circuit board portion of a conventional magnetic disk drive unit mounting two acceleration sensors. FIG. 2 is a diagram illustrating an operation of a conventional magnetic disk drive unit mounting acceleration sensors.  
           [0011]    As shown in the diagrams, two acceleration sensors  1   a,    1   b  are located at a right edge section of the circuit board  2 , spaced a distance L apart. Servo information recorded on a magnetic disk  3  is read by a magnetic head  4 . A servo signal read from the magnetic head  4  is amplified by a playback amplifier  5   a  and demodulated to position data by servo demodulation circuit  5   b.  The position data from the servo demodulation circuit  5   b  is then taken in by a microprocessor  6 .  
           [0012]    At the same time, data indicating detection of an disturbance by the acceleration sensors  1   a,    1   b  (hereinafter referred to as disturbance data) is also taken in by the A/D converter  6   a  of the microprocessor  6 .  
           [0013]    The position data and disturbance data read in by the microprocessor  6  are then processed by a CPU  6   c  using a program recorded in a memory  6   b  in order to generate a control signal.  
           [0014]    The control signal is then sent via a DA converter  6   d  to a VCM driver  7  in order to drive a voice coil motor (VCM)  8  so as to position the magnetic head  4 , such position being corrected for the effects of the external disturbance.  
           [0015]    In this case, the radial disturbance is obtained as angular acceleration ω (in units of rad/sec 2 ). However, this angular acceleration ω is obtained from outputs G1, G2 (units: G) of the two acceleration sensors and the distance L (in meters) between the two acceleration sensors according to the following formula (where g is 9.8 m/sec 2 ): 
           ω=( G 1− G 2) g/L   
           [0016]    [0016]FIG. 3 is a circuit diagram illustrating the operation of a magnetic disk drive unit mounting the conventional acceleration sensor.  
           [0017]    As shown in the diagram, the disturbance data provided by the acceleration sensors  1   a,    1   b  is then processed by the filter  9   a  and gain adjusted to get a correction signal Sb. By subtracting the correction signal Sb from an output signal Sa of a controller  9   b  of an ordinary feedback control system, a command value S that cancels the disturbance is imparted to a control object  9   c.    
           [0018]    However, a disadvantage of the above-described conventional arrangement arises if there is a disparity in sensitivity between the two acceleration sensors when using the difference between the output values of the two acceleration sensors (which sense movement in a direction parallel to a surface of the disk) in order to obtain an amount of movement in a radial direction, because the vibration component in the direction parallel to the surface of the disk cannot be cancelled, thus producing incorrect radial disturbance data for the difference in detected values leading to improper disturbance correction.  
           [0019]    Another disadvantage of the above-described conventional arrangement arises if there is a phase lag in the radial disturbance data detected by the acceleration sensors, which in turn leads to improper disturbance correction.  
         SUMMARY OF THE INVENTION  
         [0020]    Accordingly, it is a general object of the present invention to provide an improved and useful disk drive unit control method and disk drive unit, in which the above-described disadvantages are eliminated.  
           [0021]    The above-described object of the present invention is achieved by a control method for a disk drive unit mounting an acceleration sensor, the control method comprising the step of changing a sequence for calculating an amount by which a head actuator is adjusted during recording and readout operations based on an output from the acceleration sensor.  
           [0022]    According to the invention described above, adverse effects to the feedback system can be prevented when performing feed forward correction control of a radial disturbance.  
           [0023]    Additionally, the above-described object of the present invention is achieved by a control method for a disk drive unit mounting two acceleration sensors positioned a predetermined distance apart, the control method comprising the step of changing a sequence for calculating an amount by which a head actuator is adjusted during recording and readout operations based on an output from the two acceleration sensors sensing parallel components of an external disturbance on the disk drive unit in a direction parallel to a surface of a disk.  
           [0024]    It should be noted that the direction parallel to the surface of the disk is meant to include, but not be limited to, a radial direction of the disk to be described later, and, as such, constitutes a uniaxial direction. In the invention to be described below, in which acceleration sensors are positioned so as to sense acceleration in a same direction, this uniaxial direction is referred to as the parallel direction for ease of explanation, parallel in the sense that movement is in a direction parallel to a surface of the disk.  
           [0025]    According to the invention described above, adverse effects to the feedback system can be prevented.  
           [0026]    Additionally, the above-described object of the present invention is achieved by a disk drive unit mounting an acceleration sensor, the disk drive unit comprising a correction control unit for changing a sequence for calculating an amount by which a head actuator is adjusted during recording and readout operations based on an output from the acceleration sensor. 
       
    
    
       [0027]    Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]    [0028]FIG. 1 is a partial cutaway plan view of a circuit board of a magnetic disk drive unit mounting a conventional acceleration sensor;  
         [0029]    [0029]FIG. 2 is a diagram illustrating an operation of a magnetic disk drive unit mounting a conventional acceleration sensor;  
         [0030]    [0030]FIG. 3 is a circuit diagram illustrating the operation of a magnetic disk drive unit mounting the conventional acceleration sensor;  
         [0031]    [0031]FIG. 4 is a diagram for illustrating an operation of a magnetic disk drive unit mounting an acceleration sensor according to one embodiment of the present invention;  
         [0032]    [0032]FIG. 5 is a flow chart showing steps in a correction control sequence of a magnetic disk drive unit mounting an acceleration sensor according to a first embodiment of the present invention;  
         [0033]    [0033]FIG. 6 is a flow chart showing steps in a correction control sequence of a magnetic disk drive unit mounting an acceleration sensor according to a second embodiment of the present invention;  
         [0034]    [0034]FIG. 7 is a flow chart showing steps in a correction control sequence of a magnetic disk drive unit mounting an acceleration sensor according to a third embodiment of the present invention;  
         [0035]    [0035]FIG. 8 is a flow chart showing steps in a correction control sequence of a magnetic disk drive unit mounting an acceleration sensor according to a fourth embodiment of the present invention;  
         [0036]    [0036]FIG. 9 is a flow chart showing steps in a correction control sequence of a magnetic disk drive unit mounting an acceleration sensor according to a fifth embodiment of the present invention;  
         [0037]    [0037]FIG. 10 is a flow chart showing steps in a correction control sequence of a magnetic disk drive unit mounting an acceleration sensor according to a sixth embodiment of the present invention;  
         [0038]    [0038]FIG. 11 is a circuit structure diagram for illustrating a correction control unit of a magnetic disk drive unit mounting acceleration sensors according to a seventh embodiment of the present invention;  
         [0039]    [0039]FIG. 12 is a diagram showing an position error gain of a magnetic disk drive unit mounting the acceleration sensor according to one embodiment of the present invention;  
         [0040]    [0040]FIG. 13 is a flow chart showing steps in a process of designing a filter of the magnetic disk drive unit according to the seventh embodiment of the present invention;  
         [0041]    [0041]FIG. 14 is a flow chart illustrating a corrective control unit of a magnetic disk drive unit mounting an acceleration sensor according to an eighth embodiment of the present invention; and  
         [0042]    [0042]FIG. 15 is a diagram illustrating a corrective control unit of a magnetic disk drive unit mounting an acceleration sensor according to a ninth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0043]    A description will now be given of embodiments of the present invention, with reference to the accompanying drawings. It should be noted that identical or corresponding elements in the embodiments are given identical or corresponding reference numbers in all drawings, with detailed descriptions of such elements given once and thereafter omitted. In addition, the following description involves a magnetic disk drive unit the basic configuration of which is essentially unchanged from that of the conventional magnetic disk drive unit shown in FIGS. 1, 2 and  3 , and accordingly a detailed description thereof shall be omitted.  
         [0044]    A description will now be given of a magnetic disk drive unit control method and disk drive unit according to a first embodiment of the present invention.  
         [0045]    [0045]FIG. 4 is a diagram for illustrating an operation of a magnetic disk drive unit mounting an acceleration sensor according to one embodiment of the present invention. FIG. 5 is a flow chart showing steps in a correction control sequence of a magnetic disk drive unit mounting an acceleration sensor according to a first embodiment of the present invention.  
         [0046]    For ease of explanation, a description will first be given of the control method.  
         [0047]    First, in a step S 1 , the two acceleration sensors  1   a,    1   b  detect an external disturbance in a parallel direction as well as a parallel direction component of a radial disturbance, that is, G1 and G2.  
         [0048]    Next, in a step S 2 , it is determined whether or not G1 and G2 have the same sign, that is, whether or not the acceleration is in the same direction. If the signs are different, then it is clear that the radial disturbance is the larger of the two, and normal disturbance correction control is conducted in a step S 3 . In other words, the radial disturbance is calculated from the difference between G1 and G2, with normal disturbance correction control carried out. If, on the other hand, the signs of G1 and G2 are the same, then a differential between G1 and G2, that is, Gsub, is calculated in a step S 4 .  
         [0049]    In a step S 5 , it is determined whether the disturbance G1, G2 difference Gsub meets or exceeds a threshold value given here as A. It should be noted that the threshold value A can be set according to experience or by experiment, taking into consideration the characteristics of the feedback control system of the magnetic disk drive unit microprocessor  6  as well as the vibrational characteristics of the external disturbance. When the difference Gsub of the disturbances G1, G2 meets or exceeds the threshold level, the radial disturbance is large enough so that effective disturbance correction control can be carried out (in the step S 3 ) despite any disparity in sensitivity that might exist between the acceleration sensors. If on the other hand the difference Gsub of G1 and G2 falls below the threshold value A, then in a step S 6  a sum Gadd of G1, G2 is calculated.  
         [0050]    In a step S 7 , it is determined whether or not the sum Gadd of G1, G2 meets or exceeds a threshold value B. If the sum Gadd of G1, G2 is less than the threshold value B, then the parallel disturbance is small and the effect of any disparity in sensitivity between the acceleration sensors is negligible, and normal disturbance correction control is carried out in the step S 3 . If on the other hand the sum Gadd of G1, G2 meets or exceeds a threshold value B, then in a step S 8  an amount of the parallel vibration P is calculated. Here, the parallel vibration amount P is a value defined as the difference of the sum Gadd of G1, G2 minus the difference Gsub between G1, G2. In this case, the absolute value of the sum of the disturbances G1, G2 may also be weighted. Finally, in a step S 9  the disturbance correction control is changed to accord with the amount of the parallel vibration amount P.  
         [0051]    It should be noted that in the step S 6  and the step S 7 , instead of the sum of the disturbances G1 and G2, either one or the other of G1 or G2 may be used.  
         [0052]    According to the magnetic disk drive unit control method and the disk drive unit of the first embodiment of the present invention as described above, the feedback system can be prevented from being adversely affected during feed forward correction control with respect to a radial disturbance by changing the disturbance correction control method as appropriate depending on the output from the acceleration sensors  1   a,    1   b.  Such a method and device is particularly well suited to the rotary-type actuators used as head drive mechanisms in magnetic disk drive units.  
         [0053]    A description will now be given of a magnetic disk drive unit control method according to a second embodiment of the present invention.  
         [0054]    [0054]FIG. 6 is a flow chart showing steps in a correction control sequence of a magnetic disk drive unit mounting an acceleration sensor according to a second embodiment of the present invention.  
         [0055]    As with the magnetic disk drive unit control method according to the first embodiment of the present invention as described above, the steps S 1  (acceleration sensor disturbance detection) through S 8  (calculation of parallel vibration amount P) are performed.  
         [0056]    Next, in a step S 11 , it is determined whether or not the parallel vibration amount P meets or exceeds a threshold value α. Here, the threshold value α is such that performing correction control based on parallel vibration amount P has no practical meaning, but rather, threshold value α should be thought of as a limit at which the control system is adversely affected by false detection of a radial disturbance due to discrepancies between the acceleration sensors and consequent performance of correction control. Additionally, this value can be set to an appropriate level by experiment.  
         [0057]    If the parallel vibration amount P is below the threshold value α, there is no change to the disturbance correction gain and normal disturbance correction control is carried out (see the step S 3  in FIG. 5). If on the other hand the parallel vibration amount P meets or exceeds the threshold value α, then the disturbance correction gain value is changed in a step S 12 , an disturbance correction gain Sb is obtained in a step S 13  and added to a control amount Sa to obtain a control amount S in a step S 14 . In a step S 15 , the control object  9   c  is moved by an amount S to a target position.  
         [0058]    According to the magnetic disk drive unit control method and the disk drive unit of the second embodiment of the present invention as described above, the same advantages can be obtained as with the first embodiment of the present invention described previously.  
         [0059]    A description will now be given of a magnetic disk drive unit control method according to a third embodiment of the present invention.  
         [0060]    [0060]FIG. 7 is a flow chart showing steps in a correction control sequence of a magnetic disk drive unit mounting an acceleration sensor according to a third embodiment of the present invention.  
         [0061]    As with the magnetic disk drive unit control method according to the first embodiment of the present invention as described above, the steps S 1  (acceleration sensor disturbance detection) through S 8  (calculation of parallel vibration amount P) are performed.  
         [0062]    Next, in a step S 21  it is determined whether or not the parallel vibration amount P is above a threshold value β. Here, the threshold value β should be thought of as a limit at which the control system is adversely affected by performance of correction control based on the parallel vibration amount P due to false detection of a radial disturbance because of discrepancies between the acceleration sensors, and taking into account the magnetic disk drive unit microprocessor  6  feedback control system characteristics as well as the vibration characteristics. Additionally, this value can be set to an appropriate level by experiment.  
         [0063]    If the parallel vibration amount P meets or exceeds the threshold value β, then no disturbance correction is carried out in a step S 22 , that is, a command value S that offsets the disturbance assumes the same value as the output signal Sa of the controller  9   b,  and in a step S 25  the control object is moved to the target position by the amount S (refer also to FIG. 3). If on the other hand the parallel vibration amount P is below the threshold value β, then, as with the second embodiment described above, the steps S 13  through S 15  are performed and the disturbance correction gain value is changed, after which the disturbance correction amount Sb is sought in a step S 23 , the disturbance correction amount Sb is added to the control amount Sa to obtain the control amount S in a step S 24 , with the control object being moved to a target position by the control amount S in a step S 25 .  
         [0064]    According to the magnetic disk drive unit control method and the disk drive unit of the third embodiment of the present invention as described above, the same advantages can be obtained as with the first embodiment of the present invention described previously.  
         [0065]    A description will now be given of a magnetic disk drive unit control method according to a fourth embodiment of the present invention.  
         [0066]    [0066]FIG. 8 is a flow chart showing steps in a correction control sequence of a magnetic disk drive unit mounting an acceleration sensor according to a fourth embodiment of the present invention.  
         [0067]    The magnetic disk drive unit control method according to the fourth embodiment of the present invention is related to the magnetic disk drive unit control method according to the third embodiment as described above, wherein it is determined in the step S 21  whether or not parallel vibration amount P meets or exceeds the threshold value β, with the recording of data to the magnetic disk  3  terminated in a step S 26  if the parallel vibration amount P does meet or exceed the threshold value β. By so doing, the data that has already been written to the disk can be protected.  
         [0068]    A description will now be given of a magnetic disk drive unit control method according to a fifth embodiment of the present invention.  
         [0069]    [0069]FIG. 9 is a flow chart showing steps in a correction control sequence of a magnetic disk drive unit mounting an acceleration sensor according to a fifth embodiment of the present invention.  
         [0070]    In this case, a timer incurs a decrement each time the disturbances G1, G2 that are the outputs of the two acceleration sensors  1   a,    1   b  are sampled and an initial value Tnc is set thereto, such that when the timer value T is greater than zero no disturbance correction gain can be conducted. When the parallel vibration amount P is large during the initial value Tnc, the initial value Tnc may for example be set through experimentation to find the value at which false detection of a radial disturbance arising from discrepancies in the sensitivity of the acceleration sensors appears to adversely affect the control system.  
         [0071]    Specifically, acceleration sensor disturbance detection G1, G2 is conducted in the step S 1 .  
         [0072]    Next, in a step S 31  it is determined whether or not the timer value T exceeds zero or not.  
         [0073]    If the time value T does exceed zero, then a timer value T decrement is carried out in a step S 32  such that T=T−1, no disturbance correction control is carried out in a step S 33 , and the control object  9   c  is moved to a target position by control amount S in a step S 34 . If on the other hand the timer value T is zero, then the parallel vibration amount P is calculated in a step S 35  and, as with the step S 21  according to the fourth embodiment described above, it is determined in a step S 36  whether or not the parallel vibration amount P meets or exceeds the threshold value β.  
         [0074]    If the calculated parallel vibration amount P meets or exceeds the threshold value β, then in a step S 37  the timer value T is set to an initial value Tnc, no disturbance correction control is carried out in the step S 33 , and in the step S 34  the control object  9   c  is moved by amount S to the target position. If on the other hand the parallel vibration amount P is less than the threshold value β, then an disturbance correction amount Sb is obtained in a step S 38  and added to a control amount Sa to obtain a control amount S in a step S 39 . In the step S 34 , the control object  9   c  is moved by amount S to the target position.  
         [0075]    According to the magnetic disk drive unit control method and the disk drive unit of the fifth embodiment of the present invention as described above, a repeated turning on and off of the disturbance correction control and consequent adverse effects on the control system when the disk drive unit parallel vibration amount is near the threshold value during operation of the disk drive unit can be prevented.  
         [0076]    A description will now be given of a magnetic disk drive unit control method according to a sixth embodiment of the present invention.  
         [0077]    [0077]FIG. 10 is a flow chart showing steps in a correction control sequence of a magnetic disk drive unit mounting an acceleration sensor according to a sixth embodiment of the present invention.  
         [0078]    As can be seen from the flow chart, the sixth embodiment involves a change to one part of the sequence of the fifth embodiment of the present invention, such that when the parallel vibration amount P again meets or exceeds the threshold value β within a predetermined time period that is the initial value Tnc, a predetermined time period during which disturbance control is not carried out is again continued during predetermined time period Tnc.  
         [0079]    Specifically, the parallel vibration amount P is calculated in the step S 8  using the same sequence as for the first embodiment of the present invention as described above, and in a step S 43  it is determined whether or not the parallel vibration amount P meets or exceeds the threshold value β.  
         [0080]    If the parallel vibration amount P meets or exceeds the threshold value β, then in a step S 44  the timer value T is set to the initial value Tnc, in a step S 45  no disturbance correction control is conducted, and in a step S 50  the control object is moved by control amount S to the target position. If at the next output sampling the parallel vibration amount P continues to meet or exceed the threshold value β in a step S 43 , then the timer value T undergoes no decrement but is reset to the initial value Tnc in a step S 44 . By so doing, as long as the parallel vibration amount P meets or exceeds the threshold value β a condition continues in which no disturbance correction control is carried out.  
         [0081]    If on the other hand the parallel vibration amount P is less than the threshold value β, then in a step S 46  it is determined whether or not the timer value T exceeds zero. If the timer value T exceeds zero, then in a step S 47  the timer value T undergoes a decrement such that T=T−1 and no disturbance correction control is carried out in a step S 45 . By contrast, if the timer value T equals zero, then in a step S 48  the disturbance correction amount Sb is obtained, in a step S 49  the disturbance correction amount Sb is added to the control amount Sa to obtain a control amount S, and in a step S 50  the control object  9   c  is moved by amount S to the target position.  
         [0082]    According to the magnetic disk drive unit control method and the disk drive unit of the sixth embodiment of the present invention as described above, the same advantages of the control method of the magnetic disk drive unit according to the fifth embodiment described above can be obtained even if the parallel vibration amount remains near the threshold level for more than a predetermined period of time.  
         [0083]    A description will now be given of a magnetic disk drive unit control method and disk drive unit according to a seventh embodiment of the present invention. As described below, the seventh embodiment pertains to an embodiment in which the correction control unit for correction control is provided with a filter.  
         [0084]    [0084]FIG. 11 is a circuit structure diagram for illustrating a correction control unit of a magnetic disk drive unit mounting acceleration sensors according to a seventh embodiment of the present invention.  
         [0085]    [0085]FIG. 12 is a diagram showing an position error gain of a magnetic disk drive unit mounting the acceleration sensor according to one embodiment of the present invention.  
         [0086]    As shown in the flow chart and diagram, the correction control unit  18  comprises analog filters  20  such as a low-pass filter for eliminating an acceleration sensor resonance point and a high-pass filter for eliminating a direct current component when amplifying the output from the acceleration sensors  1   a,    1   b,  an operation circuit  22 , and an amplifying circuit  24  for obtaining an amplified correction control signal.  
         [0087]    The seventh embodiment of the present invention further has a phase-advanced correction filter as a digital filter  26 .  
         [0088]    When the correction control unit  18  comprises only an analog filter  20  without the digital filter  26 , an operation circuit  22 , and an amplifying circuit  24 , it can happen that the phase of the disturbance correction value obtained from the characteristics of this circuit can differ from the phase of that disturbance. This phase difference diminishes the effectiveness of the disturbance correction control.  
         [0089]    This tendency is shown in the simulation-based gain graph depicted in FIG. 12. In FIG. 12, A represents a case in which no disturbance correction control by the acceleration sensors is conducted, B represents a case in which disturbance correction control is conducted without the aid of a digital filter, and C represents a case in which disturbance correction control is carried out with the aid of a digital filter. In B as compared to A, a large disturbance correction is obtained in the 200 Hz frequency bandwidth where there is no phase difference, but at frequencies below 200 Hz a phase advance is created by the high-pass filter and at frequencies above 200 Hz a phase lag is created by the low-pass filter and the operation time lag, with a consequent weakening of the disturbance correction in both cases. By contrast, in case C, the phase advance correction filter causes the frequency at which the phase of the disturbance correction value and the phase of the disturbance match to move to 600 Hz, at which frequency a large disturbance correction effect can be obtained.  
         [0090]    For ease of explanation, a description of case D in FIG. 12 shall be deferred.  
         [0091]    [0091]FIG. 13 is a flow chart showing steps in a process of designing a filter of the magnetic disk drive unit according to the seventh embodiment of the present invention acceleration sensor described above.  
         [0092]    First, in a step S 61 , a correction target frequency is provided. In FIG. 12, the correction target frequency is 600 Hz.  
         [0093]    Next, in a step S 62 , the phase lag Δω at the correction target frequency is calculated, and further, in a step S 63  a correction filter is designed that corrects the phase lag Δω at the correction target frequency. In this case, the target frequency transfer function F(s) of the phase advance correction filter centering on the correction target frequency fc can be obtained by the following formula: 
           F ( s )=( s+ 2π fc /{square root}{square root over (Υ)})/( s+ 2π fc {square root}{square root over (Υ)}) 
         [0094]    By varying the value of Υ in the above formula, the amount of the phase advance at the frequency fc can be adjusted. The disturbance correction gain can then be adjusted with respect to the phase correction filter gain change. Then, in a step S 66  the simulation evaluation is carried out and in a step S 67  the results evaluated.  
         [0095]    If the results are poor, then in a step S 65  the target frequency undergoes a fine adjustment and the simulation model is adjusted. If on the other hand the results are good, then in a step S 68  the results undergo a test evaluation and the results evaluated in a step S 69 .  
         [0096]    If these results are poor, then in the step S 65  the target frequency undergoes a fine adjustment and the simulation model is adjusted. If on the other hand the results are good, then the filter design is complete.  
         [0097]    A description will now be given of a magnetic disk drive unit control method according to an eighth embodiment of the present invention.  
         [0098]    [0098]FIG. 14 is a flow chart illustrating a corrective control unit of a magnetic disk drive unit mounting an acceleration sensor according to an eighth embodiment of the present invention.  
         [0099]    The control method according to the eighth embodiment of the present invention concerns filter design for the case C in FIG. 12 discussed above with respect to the seventh embodiment of the present invention. A phase advance correction filter is provided as the digital filter  26  of FIG. 11, with gain as well as phase being corrected for a plurality of correction target frequencies fi (i=1, 2 . . . n).  
         [0100]    Initially, in a step S 81  the correction target frequency is determined from the magnetic disk drive unit.  
         [0101]    Next, in a step S 82 , an disturbance correction value gain shift ΔGi and a phase lag Δωi at the correction target frequency are calculated, and further, in a step S 83 , a filter is designed such that the gain is −ΔGi and a phase advance is Δωi.  
         [0102]    Then, in a step S 84  the filter stability is evaluated and, if the filter is determined to be unstable, then the target frequency fi is adjusted and the simulation model is adjusted in a step S 85 , and the target frequency fi gain shift ΔGi and a phase lag Δωi are recalculated in the step S 82 . If, on the other hand, the filter is determined to be stable, then its control efficacy is verified in a step S 86 .  
         [0103]    If the results are poor, then the target frequency undergoes a fine adjustment and the simulation model is adjusted in a step S 85 . If on the other hand the results are good, then the design of the filter is completed.  
         [0104]    Using the above-described phase advance correction filter in the case D in FIG. 12 mentioned above, a large disturbance correction effect can be obtained at two frequencies, i.e., at approximately 200 Hz and approximately 500 Hz.  
         [0105]    [0105]FIG. 15 is a diagram illustrating a corrective control unit of a magnetic disk drive unit mounting an acceleration sensor according to a ninth embodiment of the present invention.  
         [0106]    As shown in FIG. 15, the correction control unit  30  is provided with a phase correction filter (digital filter)  32  and a notch filter  34  on a stage prior to the phase correction filter  32 , and further, with a band limiting filter  36  provided between the notch filter  34  and the phase correction filter  32 . The notch filter  34  removes the acceleration sensor resonance frequency component and the band limiting filter  36  removes the noise.  
         [0107]    According to the magnetic disk drive unit control method according to the ninth embodiment of the present invention as described above, adverse effects on the correction control can be reduced.  
         [0108]    The above description is provided in order to enable any person skilled in the art to make and use the invention and sets forth the best mode contemplated by the inventor of carrying out the invention.  
         [0109]    The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing from the scope and spirit of the present invention.  
         [0110]    The present application is based on Japanese Priority Application No. 2000-164944, filed on Jun. 1, 2000, the entire contents of which are hereby incorporated by reference.