Abstract:
A Hard Disk Drive (HDD) includes a write-inhibit signal that is generated by a head-disk interaction sensor during a write process that is integrated with a suspension of the HDD when fly-height modulation of the slider is detected during a write process. The suspension load beam includes a dimple and a laminated flexure. The laminated flexure includes a surface that is adapted to receive a slider and a surface that is adapted to contact the dimple. The head-disk interaction sensor is fabricated as part of the laminations of the flexure. The head-disk interaction sensor can be an accelerometer that senses an acceleration of the flexure when the slider contacts the disk of the disk drive and/or a pressure sensor that senses a pressure between the flexure and the dimple when the slider contacts the disk. A write-inhibit circuit is responsive to the sensor signal by inhibiting the write process.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     The present application is related to co-pending, co-assigned and concurrently filed patent application Ser. No. (Attorney Docket No. HSJ920030073US1), entitled “Head-Disk Interaction Sensor Integrated With Suspension,” which is incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to disk drives. More particularly, the present invention relates to a sensor system for improving write operations for a hard disk drive (HDD).  
         [0004]     2. Description of the Related Art  
         [0005]      FIG. 1  shows an exemplary hard disk drive (HDD)  100  having a magnetic read/write (R/W) head (or a recording slider)  101  that includes, for example, a tunnel-valve read sensor, that is positioned over a selected track on a magnetic disk  102 . As the fly-height of slider  101  becomes smaller, the chance of slider  101  hitting asperities on disk  102 , for example, disk defects, particles, and/or lubricant bumps, becomes greater, resulting in a higher probability of fly-height modulation, i.e., “slider jump-up”. When fly-height modulation occurs during a write process, that portion of data being written during slider jump-up can be lost because the data is not properly written on the disk due to greater than expected write-head-to-disk distance. There is no current technique available for detecting fly-height modulation during a write process. Consequently, write processes are performed essentially “blind” with the hope that the data is properly written on the disk.  
         [0006]     Conventional approaches for minimizing slider modulation include minimization of head-disk interaction by, for example, reducing the take-off height of a disk, reducing the number of particles, and using less mobile lubricant on the disk. These approaches, however, will reach their respective limits for minimizing head-disk interaction as slider fly-height is further reduced.  
         [0007]     Consequently, what is needed is a technique for detecting slider fly-height modulation during a write process. Further, what is needed is a technique for inhibiting a write operation when slider fly-height modulation is detected.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     The present invention provides a technique for detecting slider fly-height modulation during a write process. Additionally, the present invention provides a technique for inhibiting a write operation when slider fly-height modulation is detected.  
         [0009]     The advantages of the present invention are provided by a suspension for a disk drive having a suspension load beam having a dimple and a laminated flexure. The laminated flexure is coupled to the suspension load beam and has a surface that is adapted to receive a slider and a surface that is adapted to contact the dimple. According to the invention, the flexure includes a head-disk interaction sensor that outputs a sensor signal when the slider contacts a disk of the disk drive. One embodiment of the head-disk interaction sensor is an accelerometer that senses an acceleration of the flexure that is generated by the slider contacting the disk of the disk drive. The accelerometer includes a piezoelectric material layer and a conductive material layer that are each formed as a layer of the laminated flexure and are each patterned to substantially correspond to a top surface of a back portion of the slider.  
         [0010]     An alternative or an additional embodiment of the head-disk interaction sensor is a pressure sensor that senses a pressure between the flexure and the dimple that is generated by the slider contacting the disk of the disk drive. One configuration of the pressure sensor includes a piezoelectric material layer and a conductive material layer that are each formed as a layer of the laminated flexure and each are patterned to substantially correspond to a surface region of the flexure corresponding to the dimple. One pattern is substantially a square shape. An alternative pattern is a substantially circular shape. The piezoelectric material layer generates a voltage between a top portion and a bottom portion of the piezoelectric material layer when the slider contacts the disk of the disk drive that corresponds to a magnitude of a force with which the slider contacts the disk of the disk drive.  
         [0011]     An alternative configuration of the accelerometer includes a piezoelectric material layer and a conductive material layer that are each formed as a layer of the laminated flexure and are each patterned to form a first region and a second region. The first and second regions respectively correspond to a front portion and a back portion of the slider and respectively corresponding to first and second surface regions of the surface of the flexure adapted to contact the dimple. The first region of the piezoelectric material layer generates a first voltage between a top portion and a bottom portion of the first region of the piezoelectric material layer when the slider contacts the disk of the disk drive. Similarly, the second region of the piezoelectric material layer generates a second voltage between a top portion and a bottom portion of the second region of the piezoelectric material layer when the slider contacts the disk of the disk drive. The first and second voltages respectively generated between the top portions and the bottom portions of the first and second regions of the piezoelectric material layer each correspond to a magnitude of a force with which the slider contacts the disk of the disk drive. A pitch mode of the slider can be determined based on a difference between the first voltage and the second voltage. Additionally, a first bending mode of a body of the slider body can be determined based on a sum of the first and second voltages.  
         [0012]     The suspension of the present invention further includes a write-inhibit circuit that is responsive to the sensor signal by inhibiting a write operation of the disk drive. The write-inhibit circuit includes a filter circuit that condition the sensor signal. One embodiment of the filter circuit is a low-pass filter having a passband that is greater than about 20 kHz. Another embodiment of the filter circuit is a high-pass filter having a passband that is less than about 2 MHz. Yet another embodiment of the filter circuit is a bandpass filter having a passband between about 20 kHz and about 2 MHz. Further, the filter circuit can be a bandpass filter having a passband corresponding to about a pitch frequency of the slider. For example, the filter circuit can have a narrow passband at about 200 kHz. Further still, the filter circuit can be a bandpass filter having a passband corresponding to about a bending mode frequency of a body of the slider. For example, the filter circuit can have a narrow passband at about 1.6 MHz. Alternatively, the filter circuit can be a passband filter having a passband that includes about 200 kHz and about 1.6 MHz. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The present invention is illustrated by way of example and not by limitation in the accompanying figures in which like reference numerals indicate similar elements and in which:  
         [0014]      FIG. 1  shows an exemplary disk drive having a magnetic read/write head;  
         [0015]      FIG. 2A  shows a side view of a slider, a suspension and a flexure having a first exemplary embodiment of an integrated accelerometer according to the present invention;  
         [0016]      FIG. 2B  shows a top view of a piezoelectric material layer of the first exemplary embodiment of the integrated accelerometer shown in  FIG. 2A ;  
         [0017]      FIG. 2C  shows a cross-sectional view of the first exemplary embodiment of accelerometer according to the present invention shown in  FIG. 2A  as view A;  
         [0018]      FIG. 3A  shows a side view of a slider, a suspension and a flexure having an exemplary embodiment of an integrated pressure sensor for detecting dimple pressure according to the present invention;  
         [0019]      FIG. 3B  shows a top view of a piezoelectric material layer of the exemplary embodiment of the integrated pressure sensor for detecting dimple pressure according to the present invention shown in  FIG. 3A ;  
         [0020]      FIG. 3C  shows a cross-sectional view of the first exemplary embodiment of a pressure sensor for detecting dimple pressure according to the present invention shown in  FIG. 3A  as view B;  
         [0021]      FIG. 4A  shows a side view of a slider, a suspension and a flexure having a second exemplary embodiment of an integrated accelerometer for detecting vertical acceleration and first pitch mode of the slider according to the present invention;  
         [0022]      FIG. 4B  shows a top view of a piezoelectric material layer of the second exemplary embodiment of the integrated accelerometer shown in  FIG. 4A ;  
         [0023]      FIG. 5A  shows a side view of a slider, a suspension and a flexure having a third exemplary embodiment of an integrated accelerometer for detecting pitch motion and bending motion of the slider according to the present invention;  
         [0024]      FIG. 5B  shows a top view of a piezoelectric material layer of the third exemplary embodiment of the integrated accelerometer shown in  FIG. 5A ; and  
         [0025]      FIG. 6  shows a schematic block diagram of a circuit for detecting head-disk interaction and enabling write-inhibit followed by a data rewrite according to the present invention 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]     The present invention detects head-disk interaction in an HDD by using at least one sensor that is integrated with suspension. Slider motion caused by Head-Disk Interference (HDI) is detected by using a force (or pressure) sensor for monitoring the force (or pressure) between the back of the slider and the suspension dimple, and/or by using an accelerometer for measuring the acceleration of the slider. Both the pressure sensor and the acceleration sensor are integrated with a suspension having a laminated flexure.  
         [0027]     The signal output from the sensors includes both air-flow-related noise and write-current-related noise. Noise that is caused by air-flow typically has a very low frequency component, i.e., less than 20 kHz. Noise that is caused by write current typically has a very high frequency, i.e., greater than 2 Mhz. Accordingly, the present invention passes the frequency component at the pitch mode frequency of the slider at approximately 200 kHz, and at the first bending mode frequency of the slider body at approximately 1.7 MHz, while removing low-frequency noise caused by air flow and high-frequency noise caused by write current.  
         [0028]     Tables 1-3 below respectively set forth simulation results of the expected acceleration of the R/W element of a slider and the expected force applied to a dimple of a suspension for soft, medium-soft and hard asperities on a disk  
                                                                           TABLE 1                           Slider/Lubrication Interaction                Remarks                        Force:                   Fz   1.5   mN       Fx   1.5   mN       Duration:   6   μs   Assumed 0.5 μs risetime,                   5.0 μs peak duration, and                   0.5 μs decay.       Results:       FHM at R/W   10   nm       Acceleration at R/W   8,000   m/s 2     200 kHz oscillation       Acceleration at dimple   2,400   m/s 2         Stress (x)   200,000   N/m/m            Strain (x)   4.00 × 10 −7                  Force at the dimple   0.6   mN                      
 
         [0029]    
       
         
               
             
               
               
             
               
               
               
               
             
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                   
               
               
                 Slider/Medium Hardness Asperity Interaction 
               
             
          
           
               
                   
                 Remarks: 
               
               
                   
                   
               
             
          
           
               
                 Force: 
                   
                   
                   
               
               
                 Fz 
                 1.5 
                 mN 
               
               
                 Fx 
                 1.5 
                 mN 
               
               
                 Duration: 
                 1 
                 μs 
                 Assumed 0.2 μs risetime, 
               
               
                   
                   
                   
                 0.6 μs peak duration, and 
               
               
                   
                   
                   
                 0.2 μs decay. 
               
               
                 Results: 
               
               
                 FHM at R/W 
                 5 
                 nm 
               
               
                 Acceleration at R/W 
                 26,000 
                 m/s 2   
                 200 kHz and 1.7 MHz 
               
               
                   
                   
                   
                 oscillations 
               
               
                 Acceleration at dimple 
                 7,000 
                 m/s 2   
               
               
                 Stress (x) 
                 75,000 
                 N/m/m 
               
             
          
           
               
                 Strain (x) 
                 1.9 × 10 −7   
                   
               
             
          
           
               
                 Force at the dimple 
                 0.5 
                 mN 
               
               
                   
               
             
          
         
       
     
         [0030]    
       
         
               
             
               
               
             
               
               
               
               
             
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                   
               
               
                 Slider/Hard Asperity Interaction 
               
             
          
           
               
                   
                 Remarks 
               
               
                   
                   
               
             
          
           
               
                 Force: 
                   
                   
                   
               
               
                 Fz 
                 1.5 
                 mN 
               
               
                 Fx 
                 1.5 
                 mN 
               
               
                 Duration: 
                 0.5 
                 μs 
                 Assumed 0.1 μs risetime, 
               
               
                   
                   
                   
                 0.3 μs peak duration, and 
               
               
                   
                   
                   
                 0.1 μs decay. 
               
               
                 Results: 
               
               
                 FHM at R/W 
                 1.4 
                 nm 
               
               
                 Acceleration at R/W 
                 30,000 
                 m/s 2   
                 1.7 MHz oscillation 
               
               
                 Acceleration at dimple 
                 8,000 
                 m/s 2   
               
               
                 Stress (x) 
                 80,000 
                 N/m/m 
                 1.7 MHz 
               
             
          
           
               
                 Strain (x) 
                 2.0 × 10 −7   
                 1.7 MHz 
               
             
          
           
               
                 Force at the dimple 
                 0.22 
                 mN 
               
               
                   
               
             
          
         
       
     
         [0031]     Simulated acceleration at the R/W element is calculated to be between 8,000 to 30,000 m/s 2  (or 800-3000 G). The simulated force applied to a dimple is calculated to be between 0.22 mN to 0.6 mN.  
         [0032]      FIG. 2A  shows a side view of a slider, a suspension and a flexure having a first exemplary embodiment of an integrated accelerometer according to the present invention.  FIG. 2B  shows a top view of a piezoelectric material layer of the first exemplary embodiment of the integrated accelerometer shown in  FIG. 2A . In  FIG. 2A , a slider  201  is attached to a suspension flexure  202  in a well-known manner. Flexure  202  is a laminated flexure, such as disclosed by U.S. Pat. No. 4,996,623 to Erpelding et al. or by U.S. Pat. No. 5,491,597 to Bennin et al., both of which are incorporated by reference herein. Flexure  202  contacts a suspension load beam  203  through a dimple  204 , which provides a gimbal function. An accelerometer  205  is fabricated as an integral part of flexure  202 .  
         [0033]      FIG. 2C  shows a cross-sectional view of the first exemplary embodiment of accelerometer  205  according to the present invention shown in  FIG. 2A  as view A. Flexure  202  includes a metal layer  206  that is formed from, for example, stainless steel. A first insulative material layer  207  is formed on metal layer  206  using well-known techniques. First insulative layer  207  is formed from, for example, polyimide. A first conductive material layer  208  is formed on first insulative layer  207  using well-known techniques and is formed from, for example, copper. A piezoelectric material layer  209 , such as Poly(vinilyden fluoride) (PVDF), is formed on first conductive material layer  208  as a film using well-known techniques. A second conductive material layer  210  is formed on piezoelectric material layer  209  using well-known techniques and is formed from, for example, copper. A second insulative layer  211  is formed on second conductive layer  210  using well-known techniques and is formed from, for example, polyimide. After flexure  202  is attached to suspension load beam  203 , slider  201  is glued to flexure  202  and integrated accelerometer  205 .  
         [0034]     Piezoelectric material layer  209  and the first and second conductive material layers  208  and  210  (not shown in  FIG. 2B ), which are formed on both sides of piezoelectric material layer  209 , are patterned so that these three layers correspond to only the top of the trailing edge of slider  201  (i.e., the R/W element end of slider  201 ). When HDI occurs and a force  212  is applied to the trailing edge of slider  201 , slider  201  typically moves in a pitch direction, as indicated by arrows  213  and  214 . The resulting acceleration compresses piezoelectric material layer  209  caused by the inertia and rigidity of metal layer  206 . When piezoelectric material layer  209  is compressed, a voltage difference of a few millivolts is generated across piezoelectric material layer  209 , as depicted by voltage V. The voltage difference is easily detected using a well-known voltage detection technique. By monitoring the voltage generated across piezoelectric material layer  209 , the acceleration imparted to slider  201  by HDI can be determined. Detection accuracy can be further improved by adding a low-pass and/or high-pass, and/or peak filter between the output of piezoelectric material layer  209  and the voltage detection device. The best center frequency for a peak filter is at the pitch frequency of the slider.  
         [0035]      FIG. 3A  shows a side view of a slider, a suspension arid a flexure having an exemplary embodiment of an integrated pressure sensor for detecting dimple pressure according to the present invention.  FIG. 3B  shows a top view of a piezoelectric material layer of the exemplary embodiment of the integrated pressure sensor for detecting dimple pressure according to the present invention shown in  FIG. 3A . In  FIG. 3A , a slider  301  is attached to a suspension flexure  302  in a well-known manner. Flexure  302  is a laminated flexure, such as disclosed by U.S. Pat. No. 4,996,623 to Erpelding et al. or by U.S. Pat. No. 5,491,597 to Bennin et al., both of which are incorporated by reference herein. Flexure  302  contacts a suspension load beam  303  through a dimple  304 , which provides a gimbal function. A pressure sensor  305  is fabricated as an integral part of flexure  302 .  
         [0036]      FIG. 3C  shows a cross-sectional view of the exemplary embodiment of a pressure sensor  305  for detecting dimple pressure according to the present invention shown in  FIG. 3A  as view B. Flexure  302  includes a metal layer  306  that is formed from, for example, stainless steel. A first insulative material layer  307  is formed on metal layer  306  using a well-known technique. First insulative layer  307  is formed from, for example, polyimide. A first conductive material layer  308  is formed on first insulative layer  307  using a well-known technique and is formed from, for example, copper. A piezoelectric material layer  309 , such as PVDF, is formed on first conductive material layer  308  as a film using a well-known technique. A second conductive material layer  310  is formed on piezoelectric layer  309  using a well-known technique and is formed from, for example, copper. A second insulative layer  311  is formed on second conductive material layer  310  using a well-known technique and is formed from, for example, polyimide. After flexure  302  is attached to suspension load beam  303 , slider  301  is glued to flexure  302  and integrated pressure sensor  305 .  
         [0037]     Piezoelectric material layer  309  and the first and second conductive material layers  308  and  310  (not shown in  FIG. 3B ), which are formed on both sides of piezoelectric material layer  309 , are patterned so that these three layers exist around dimple contact region  314 .  FIG. 3B  shows a substantially circularly shaped patterning, although it should be understood that alternative shapes can also be used. When HDI occurs and a force  312  is applied to the trailing edge of slider  301 , slider  301  moves toward dimple  304  along the z-axis, the inertia of the suspension compresses piezoelectric material layer  309 , resulting in a detectable voltage of several millivolts across piezoelectric material layer  309 . Detection accuracy can be further improved by adding a low-pass and/or high-pass, and/or peak filter between the output of piezoelectric material layer  309  and the voltage detection device. The best center frequency for a peak filter is at the pitch frequency of the slider.  
         [0038]      FIG. 4A  shows a side view of a slider, a suspension and a flexure having a second exemplary embodiment of an integrated accelerometer for detecting vertical acceleration and the first pitch mode of the slider according to the present invention.  FIG. 4B  shows a top view of a piezoelectric material layer of the second exemplary embodiment of the integrated accelerometer shown in  FIG. 4A . In  FIG. 4A , a slider  401  is attached to a suspension flexure  402  in a well-known manner. Only the portion of flexure  402  corresponding to the integrated accelerometer is shown in  FIG. 4A . Flexure  402  is a laminated flexure, such as disclosed by U.S. Pat. No. 4,996,623 to Erpelding et al. or by U.S. Pat. No. 5,491,597 to Bennin et al., both of which are incorporated by reference herein. Flexure  402  contacts a suspension load beam  403  through a dimple  404 , which provides a gimbal function. An accelerometer  405  is fabricated as an integral part of flexure  402 .  
         [0039]     Flexure includes a metal layer  406  that is formed from, for example, stainless steel. A first insulative material layer  407  is formed on metal layer  406  using a well-known technique and is formed from, for example, polyimide. A first conductive material layer  408  is formed on first insulative layer  407  using a well-known technique and is formed from, for example, copper. A piezoelectric material layer  409 , such as PVDF, is formed on first conductive material layer  408  as a film using a well-known technique. A second conductive material layer  410  is formed on piezoelectric layer  409  using a well-known technique and is formed from, for example, copper. A second insulative layer  411  is formed on second conductive layer  410  using a well-known technique and is formed from, for example, polyimide. After flexure  402  is attached to suspension load beam  403 , slider  401  is glued to flexure  402  and integrated accelerometer  405 .  
         [0040]     Piezoelectric material layer  409  and the first and second conductive material layers  408  and  410  (not shown in  FIG. 4B ) formed on both sides of piezoelectric material layer  409  are patterned so that these three layers corresponding to the entire top side of slider  401  around dimple contact region  414 .  FIG. 4B  shows the patterning of piezoelectric material layer  409 . While  FIG. 4B  shows a substantially square shaped patterning, it should be understood that alternative shapes can also be used. Accelerometer  405  covers entire top side of slider  401  and thereby provides a substantially flat bonding surface on the top side of slider  401  for bonding slider  401  to flexure  402 . Accelerometer  405  detects the translation acceleration of slider  401  in the z-axis direction and the first bending mode amplitude of slider body  401 . When HDI occurs and slider  401  moves toward dimple  404 , the inertia of the suspension compresses piezoelectric material layer  409 , resulting in a detectable voltage of several millivolts across piezoelectric material layer  409 . Detection accuracy can be further improved by adding a low-pass and/or high-pass, and/or peak filter between the output of piezoelectric material layer  409  and the voltage detection device. The best center frequency for a peak filter is at the pitch frequency of the slider.  
         [0041]      FIG. 5A  shows a side view of a slider, a suspension and a flexure having a third exemplary embodiment of an integrated accelerometer for detecting pitch motion and bending motion of the slider according to the present invention.  FIG. 5B  shows a top view of a piezoelectric material layer of the third exemplary embodiment of the integrated accelerometer shown in  FIG. 5A . In  FIG. 5A , a slider  501  is attached to a suspension flexure  502  in a well-known manner. Only the portion of flexure  502  corresponding to the integrated accelerometer is shown in  FIG. 5A . Flexure  502  contacts a suspension load beam  503  through a dimple  504 , which provides a gimbal function. Accelerometers  505   a  and  505   b  are fabricated as an integral part of slider  501 .  
         [0042]     Flexure  502  includes a metal layer  506  that is formed from, for example, stainless steel. A first insulative material layer  507  is formed on metal layer  506  using a well-known technique. First insulative layer  507  is formed from, for example, polyimide. A first conductive layer  508  is formed on first insulative layer  507  and is formed from, for example, polyimide. Piezoelectric material layer  509  is formed on first conductive material layer  508 . Piezoelectric material layer  509  is formed as a film from, for example, PVDF, using a well-known technique. Two second conductive material layers  510   a  and  510   b  are formed on piezoelectric material layer  509  using a well-known technique and are formed from, for example, copper. Second conductive material layers  510   a  and  510   b  are patterned to be separate, as shown in  FIG. 5B . A second insulative layer  511  is formed on second conductive material layers  510   a  and  510   b  using a well-known technique and is formed from, for example, polyimide. After flexure  502  is attached to suspension load beam  503 , slider  501  is glued to flexure  502  and integrated accelerometer  505 .  
         [0043]     The first and second conductive material layers  510   a  and  510   b  are patterned so that they respectively correspond to the front and back sides of the top side of slider  501  around dimple contact region  514 , as shown in  FIG. 5B . Additionally or alternatively, piezoelectric material layer  508  can be patterned as shown in  FIG. 5B . Second conductive material layer  510  can also be patterned as shown in  FIG. 5B . When piezoelectric material layer  508  is patterned as shown in  FIG. 5B , at least one of the first conductive material layer  508  or the second conductive material layer  510  must be patterned as shown in  FIG. 5B . In any alternative configuration, accelerometer  505   a  corresponds to the front, or leading, side of the top of slider  501  and accelerometer  505   b  corresponds to the back, or trailing, side of the top of slider  501 , thereby providing a mostly flat bonding surface on the top side of slider  501  for bonding slider  501  to flexure  502 . The pitch mode of slider  501  can be detected based on the difference of measured voltages V 1  and V 2 , i.e., V 1 -V 2 . The first bending mode of slider body  501  can be detected based on the sum of voltages V 1  and V 2 , i.e., V 1 +V 2 . Detection accuracy can be further improved by adding a low-pass and/or high-pass, and/or peak filter between the output of piezoelectric material layer  509  and the voltage detection device.  
         [0044]      FIG. 6  shows a schematic block diagram of a circuit  600  for detecting HDI according to the present invention.  FIG. 6  shows a slider  601  that is attached in a well-known manner to a laminated suspension flexure  602  having an integrated accelerometer and/or pressure sensor according to the present invention. Flexure  602  contacts a suspension load beam  603 , of which only a portion is shown in  FIG. 6 , through a dimple  604 , which provides a gimbal function. An HDI sensor  605  is fabricated as an integral part of flexure  602 , as described above. HDI sensor  605  can be an accelerometer and/or a pressure sensor, also as described above.  
         [0045]     When there is a head-disk interaction event, slider  601  physically vibrates in a vertical direction. HDI sensor  605 , which has been integrated with flexure  602 , detects the vibration and generates a corresponding sensor signal  606 . The vibration mode of slider  601  can be either a single impulse when, for example, slider  601  contacts a hard asperity, or a periodic oscillation at the pitch frequency of slider  601  when, for example, when slider  601  makes contact with the disk (not shown in  FIG. 6 ) through an abnormally thick lubricant. Sensor signal  606  is input to a signal amplifier  607 . The output of signal amplifier  607  is coupled to a filter circuit  608 . Filter circuit  608  can be a high-pass filter so that low-frequency noise is rejected. The cut-off frequency the high-pass filter should preferably be set to be below the pitch-mode frequency of slider  601  so that sensor signal  606  generated in response to the slider pitch motion passes through filter circuit  608 . Filter circuit  608  can also be a low-pass filter so that electrical noise generated by the write current can be rejected. Usually, the write current has frequency content that is greater than 1 MHz, whereas the slider pitch-mode frequency is a few hundred of kilohertz. Thus, it is preferred to set the cut-off frequency of low-pass filter to a frequency that is between typical write current frequency and slider pitch-mode frequency. It is even more preferable to combine both a low-pass and a high-pass filter. Alternatively, a bandpass filter can be used that only transmits a sensor signal having particular frequency. When a bandpass filter is used, it is preferred to select the pitch mode frequency of slider  601 . The sequential order of signal amplifier  607  and filter circuit  608  can be reversed, that is, the signal can be first filtered and then amplified.  
         [0046]     After the sensor signal has been conditioned by filter circuit  608 , the signal amplitude is input to a comparator circuit  609 . Comparator circuit  609  compares the conditioned sensor signal with a predetermined threshold value  610 . When the amplitude of the conditioned sensor signal is greater than threshold value  610 , comparator circuit  609  generates a write inhibit signal  611 . When an HDD controller  612  (or a read/write channel that controls the write process) receives write-inhibit signal  611 , HDD controller  612  immediately stops the write current that is being output to the magnetic head (not shown in  FIG. 6 ) so that the head is the proper distance from the disk during the write process. Additionally, HDD controller  612  stops the write current so that data on an adjacent track is not mistakenly overwritten because sometimes HDI causes off-track motion of the write head. Subsequently, when write-inhibit signal is removed, controller  612  re-tries to write the same data to the same location.  
         [0047]     Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced that are within the scope of the appended claims. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.