Abstract:
The present invention is a method and system to determine a quality of a head in a hard disk drive. The method comprises providing a disk having a at least one side with a plurality of tracks, writing on a predetermined track on the plurality of tracks and reading a profile of the predetermined track to provide a first profile value. The head is then moved to an adjacent track where it writes on the adjacent track. A profile of the predetermined track is then read to provide a second profile value. A quality of the head can then be determined based on the first and second values.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to disk storage systems and more particularly, to methods and apparatus for distinguishing the effects of adjacent track encroachment from head thermal movement. 
     2. Description of the Related Art 
     Disk drives are magnetic recording devices used for the storage of information. The information is typically recorded on concentric tracks on either surface of one or more magnetic recording disks. The disks are rotatably mounted to a spin motor and information is accessed by means of read/write heads that are mounted to actuator arms which are rotated by a voice coil motor. The voice coil motor is excited with a current to rotate the actuator and move the heads. The read/write heads must be accurately aligned with the storage tracks on the disk to ensure proper reading and writing of information. The read/write heads read recorded information from the surface of the disk by sensing the magnetic transitions emanating from the surface of the disk. To write on a data track, current is applied to the read head. The current generates a magnetic field, which magnetizes the surface of the disk. 
     Recording density may be increased by reducing the width of recording tracks. However, as recording tracks become narrower in physical dimensions, the amount of write current applied to the head may result in erasing data located on adjacent tracks. This is of concern when the write current that is applied is too high. Such a characteristic of the head is known as adjacent track encroachment (ATE). The increase in temperature resulting from the write current may also cause the slider on which the head is mounted to move off the centerline of the track. When the slider cools down, the head may move in the opposite direction. Such movement may be as much as 5 micro-inches for certain heads. Such an effect is typically referred to as head thermal movement. The effects of head thermal movement is typically similar to that of ATE. As a result, it is difficult to distinguish between the effects of ATE and head thermal movement. However, ATE results from an intrinsic property of the head, while head thermal movement is a system characteristic. It desirable to be able to distinguish the effects of these two factors, so as to be able to determine the quality of a head and system performance. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a method and system to determine a quality of a head in a hard disk drive. The method comprises providing a disk having a at least one side with a plurality of tracks, writing on a predetermined track on the plurality of tracks and reading a profile of the predetermined track to provide a first profile value. The head is then moved to an adjacent track where it writes on the adjacent track. A profile of the predetermined track is then read to provide a second profile value. A quality of the head can then be determined based on the first and second values. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a hard disk drive which utilizes the methods of the invention. 
     FIG. 2 illustrates the general layout of the servo field region of a track. 
     FIG. 3 is a block diagram of portions of an integrated circuit read channel in accordance with the present invention. 
     FIG. 4 is a flow chart illustrating one embodiment of a process for distinguishing the effects of adjacent track encroachment from head thermal movement. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is an apparatus and methods for distinguishing the effects of adjacent track encroachment from head thermal movement. 
     Referring to the drawings more particularly by reference numbers, FIG. 1 shows a hard disk drive  100 . The disk drive  100  includes a disk  102  that is rotated by a spin motor  104 . The spin motor  104  is mounted to a base plate  106 . Also mounted to the base plate  106  is an actuator arm assembly  108 . The actuator arm assembly  108  includes a number of heads  110  mounted to corresponding flexure arms  112 . The flexure arms  112  are attached to an actuator arm  114  that can rotate about a bearing assembly  116 . The assembly  108  also contains a voice coil  118  that is coupled to the magnets  119  that are mounted to the base plate  106 . Energizing the voice coil  118  moves the heads  110  relative to the disk  102 . There is typically a single head for each disk surface. The spin motor  104 , voice coil  118  and the heads  110  are coupled to a number of electronic circuits  120  mounted to a printed circuit board  122 . In the following discussion, only one head  110  is referenced. The electronic circuits  120  typically include a read channel circuit, a microprocessor-based controller and a random access memory (RAM) device. 
     As shown in FIG. 2, data is typically stored within sectors of radially concentric tracks located across the disk  102 . A typical sector will have an automatic gain control (AGC) field  130 , a synchronization (sync) field  132 , a gray code field  134  that identifies the track, an identification (ID) field  136  that defines the sector, a servo field  138  which includes a number of servo bits A, B, C, D, a data field  140  which contains the data and an error correction code field  142 . In operation, the head  110  is moved to a track and the servo information provided in servo field  138  is read and provided to the electronic circuits  120 . The electronic circuits  120  utilize the variation in the servo bits (A-B) or (C-D) to generate Q, a positioning signal for aligning the head  110 . 
     FIG. 3 is a block diagram of an electronic circuit  120  of the drive. The electronic circuit  120  includes a preamplifier  152  which is coupled to a read/write (R/W) channel circuit  154 . The R/W channel circuit  154  includes a R/W Automatic Gain Control (AGC), a filter circuit  156 , a fullwave rectifier  158  and a peak detector  160 . The electronic circuit  120  further comprises a microprocessor-based servo controller  162  which includes an analog-to-digital converter (ADC)  164 , a digital signal processor (DSP)  166 , a burst sequencer and timing circuit  168  and a memory  170 , such as a random access memory (RAM) device. The DSP  166  includes a logic circuit  172 . 
     The electronic circuit  120  is coupled to one of the magnetic heads  110  which senses the magnetic field of a magnetic disk  102 . When reading the servo information located in the servo field region  10  on the disk  102 , the head  110  generates a read signal that corresponds to the magnetic field of the disk  102 . The read signal is first amplified by the preamplifier  152 , and then provided to the R/W channel circuit  154 . The AGC data included in the read signal is provided to the R/W AGC and filter circuit  156 . The R/W AGC circuit in circuit  156  monitors the AGC data provided by the read signal and the read signal is then filtered by the filter circuit located in the R/W AGC and filter circuit  156 . The fullwave rectifier  158  rectifies the read signal and provides the rectified read signal to the peak detector  160 . The peak detector  160  detects the amplitude of the read signal. The read signal is then provided to the ADC  164  which provides digitized samples of the analog read signal. The digitized signal is then provided to a logic circuit  172  located within the DSP  166 . The logic circuit  172  generates a position signal Q, based on the servo bits A, B, C and D that are read by the head  110 . The position signal Q may be stored in memory and used to control the position of the actuator arm assembly  108 . 
     In accordance with the present invention, the DSP  166  may direct the magnetic heads  110  to erase a selected band or group of tracks. In one embodiment, the band is erased using medium (e.g., 130 MHz) or low frequency (30-40 MHz). The frequency to be applied depends on the density of information on the disk. If the density of the disk is 20 Gbits per square inch, a frequency of 130 MHz may be applied. In one embodiment, the DSP  166  sets the write gate (or circuitry controlling writing of information by the write element of the read/write head  110 ) to write over a predetermined portion a track (or group of tracks) when the read/write head  110  is instructed to write. The DSP  166  also sets the read gate (or circuitry controlling reading of information by the read sensor in the read/write head  110 ) to read data within limits (i.e., X%) set by the write gate. In other words, the read sensor is programmed to read the portions of the track which have been written to. In one embodiment, X is 25%. The DSP  166  then instructs the read/write head  110  to write on a selected track. Such as track N. The profile of the track is then read to provide a read signal. Based on the track profile, the peak amplitude of the read signal TAA 0  is obtained. The read/write head  110  is then instructed to move to an adjacent track, such as track (N−1) or (N+1), and is instructed to write a predetermined number of times Y, over the portion of the track, e.g., X% of the track previously specified to the write gate. This writing process (writing Y times over the adjacent track) may be interspersed with periods of delay or non-writing intervals. Upon completion of the writing process, the track profile of the track N is read again, to obtain the peak amplitude TAA 1  of the read signal. The ATE value may be determined based on TAA 0  and TAA 1 . The ATE value may then be stored along with information regarding the corresponding read/write head. This information may be used to determine the quality of the read/write head due to effects of ATE. 
     FIG. 4 is a flow chart that illustrates one embodiment of the quality identification process provided in accordance with the principles of the invention. Proceeding from a start state, the process  400  proceeds to conduct a band erase, as shown in process block  402 . In one embodiment, the band erase may be performed for a band comprising a predetermined number of tracks. Next, the process  400  sets the write gate within the logic circuit  172  to X% of one revolution of a track (process block  404 ). In other words, the write head will be instructed to write over X% of a selected track or number of tracks. The process  400  also sets the read gate within the logic circuit  172  to ensure that the read head will read data within the limits set by the write gate (process block  406 ). Once the read and write gates have been initialized, the process  400  advances to process block  408 , where it writes on a selected track, N. When writing has been completed, the process  40  reads the data written on the track so as to obtain the profile of the read signal, also known as the track profile (process block  410 ). From the track profile, the process  400  determines the peak amplitude TAA 0  of the track profile. 
     The process  400  then proceeds to process block  412 , where the read/write head is moved to an adjacent track, such as (N−1) or (N+1). Data is then written on the track (N−1) or (N+1) a predetermined number of times Y, over the portion of the track (e.g., X% of the track) specified by the write gate. Writing of the data may be interspersed between non-writing or rest intervals. This facilitates cooling of the read/write head. Once this has been completed, the process  400  moves back to track N to determine the peak amplitude TAA 1  of the track profile after data has been written to the adjacent track (N−1) or (N+1), as shown in process block  414 . 
     Once TAA 1  has been determined, the ATE value may be determined (process block  416 ). In one embodiment, the ATE value may be determined from the following expression: 
     
       
           ATE  value=[( TAA   0 − TAA   1 )/ TAA   0 ]*100% 
       
     
     Thus, if TAA 1  is equal to TAA 0 , it means that there is no change in the read signal after writing on an adjacent track has been performed. As a result, the ATE value will be zero. Otherwise, if the ATE value is non-zero, it means that writing on the adjacent track (N−1) or (N+1) has affected the track profile on track N. In this manner, the effects of ATE may be determined. 
     Once the ATE value has been calculated, it may be stored along with information regarding the corresponding read/write head (process block  418 ). The process  400  then terminates. 
     Through the implementation of the technique of the present invention, the effects of ATE and head thermal movement may be distinguished. Once the value of ATE is determined, the quality of a read/write head may also be determined. 
     While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art.