Method and apparatus for positioning a magnetoresistive head

Description: TECHNICAL FIELD [Detailed description of the invention]

Technical field to which the invention belongs The present invention relates generally to data storage systems, and more specifically to methods, devices and disks for positioning a magnetoresistive (MR) head relative to a storage medium. Conventional technology A typical data storage system includes a magnetic medium for storing the data in a magnetic form and a converter used to read the magnetic data from the storage medium and write the magnetic data to the storage medium. For example, a disk storage device includes one or more data storage disks coaxially mounted on the hub of a spindle motor. Spindle motors typically rotate discs at speeds of several thousand revolutions per minute. Digital information representing various types of data is typically written to and read from a data storage disk by one or more converters or read / write heads, which the converter or head is an actuator. It is attached to the assembly and passes over the surface of a fast-rotating disc. Actuator assemblies typically include a coil assembly and multiple arms that have a flexible suspension and extend outwards, the suspension to which one or more transducers and slider bodies are attached. There is. Suspension is typically inserted into a stack of rotating discs by an arm assembly (E / block) attached to the actuator assembly. In general, the coil assembly responds to the controller by magnetic action with the permanent magnet structure. The actuator assembly also has a voice coil motor (VCM) mounted in the exact opposite position of the actuator arm. In a typical digital data storage system, digital data is stored in the form of magnetic transitions on a series of concentric, equidistant tracks that include the surface of a magnetizable rigid data storage disc. Generally, a track is divided into a plurality of sectors, and each sector contains a plurality of information fields. Normally, one of the information fields is designated for data storage, and the remaining fields contain track and sector position IDs, synchronization information, and so on. Data is transferred to and retrieved from designated track and sector locations by transducers that track a given track and move between tracks, usually under the servo control of a controller. Normally, the slider body of the head raises the MR head from the surface of the disc as the rotation speed of the spindle motor increases, and air is used to hover the MR head over the disc on the air bearing cushion generated by the high-speed disc rotation. Designed as an object that receives lift. The distance between the MR head and the disc is usually 0.1 micron or less, and is generally called the head / disc distance. In general, writing data to a data storage disc involves passing an electric current through the write element of the transducer assembly to generate magnetic flux lines that magnetize a particular location on the surface of the disc. Reading data from a given disk position is typically done by a reading element in the transducer assembly that senses the magnetic or magnetic flux lines emanating from the magnetized position of the disk. As the reading element passes over the surface of the rotating disk, an electrical signal is generated on the reading element as a result of the action of the magnetic flux lines from a predetermined position on the disk surface on the reading element. This electronic signal corresponds to the transition (sometimes called transition) of the magnetic field at the magnetization position. Traditional data storage systems typically use a closed-loop / servo control system to position actuators and read / write transducers at designated storage locations on the data storage disk. During normal data storage system operation, a servo converter, typically mounted near the read / write transducer or incorporated as the read element of the transducer, is used to track the specified track (track tracking) and on disk. Reads information to seek the specified track and data sector position (track seek). A servo write procedure is typically performed to first record servo pattern information on the surface of one or more data storage discs. Also, to facilitate the transfer of servo pattern data to one or more data storage disks during the manufacturing process, data storage system manufacturers typically use servo writer assemblies. In one of the known servo techniques, embedded servo pattern information is written to the disc, generally along a segment extending outward from the center of the disc. Therefore, the built-in servo pattern is formed between the data storage sectors of each track. However, servo sectors are typically used to maintain optimal read / write transducer alignment on the track centerline when reading and writing data in the specified data sector on the track. Note that it contains one data pattern called the burst pattern. The servo information can also include sector and track identification codes used to identify the location of the transducer. Since the servo information is co-located with the target data information (and the servo information can be taken from one single disk surface), the built-in servo allows for significantly higher track densities than dedicated servos. In an attempt to further increase disk capacity, a proposed servo information format called pre-embossed rigid magnetic (PERM) disk technology was developed. Tanaka et al. characterization of Magnetizing As described and illustrated in Process for Pre-Embossed Servo Pattern of Plastic Hard Disks, IEEE Transactions on Magnetics 4209 (Vol.30, No.2, November 1994), PERM disks have a radius around the disk. Servo information is included in a plurality of servo zones provided at equal intervals in the direction. Each servo zone contains pre-formed indentations and ridges to form fine patterns, clock marks, and address codes. The fine pattern and address code are used to generate the servo information signal. In order to generate a servo signal, the magnetization direction of the ridge and the depression must be opposite. The magnetization process involves first magnetizing the entire disk in one direction using a high magnetic field magnet. Next, a conventional write head is used to magnetize the raised portion in the opposite direction. Although PERM discs can be used to increase disk capacity, such techniques have some drawbacks. As mentioned above, the servo information is provided on the PERM servo disk in a two-step magnetization process. Therefore, the time required to write the servo information to the disk is greatly increased. Moreover, during the second step of the process, the servo information is not yet available on the disk. Therefore, an external positioning system must be used, which increases the cost of the servo write process. Other concerns related to PERM disc technology include durability. Finally, PERM disks, like other embedded servo techniques, store servo information in a disk space that is originally available for data storage. As a result, PERM disc technology, while still at the research level, has not been widely accepted by the industry. Problems to be solved by the invention There is a need in the data storage system manufacturing industry for servo information formats that can be provided inexpensively and that optimize the data capacity of the disk. The present invention addresses the above and other needs. Means to solve problems The present invention relates to methods, devices and discs for positioning a magnetoresistive (MR) head within a storage device relative to a storage medium. The storage medium is mounted in the storage device so that the relative movement between the MR head and the storage medium is possible. The storage medium contains servo information provided to induce a thermal response at the MR head. The control device uses the thermal response induced by the MR head to control the relative motion between the MR head and the storage medium. .. A brief description of the drawing FIG. 1 is a plan view of the data storage system with its upper housing cover removed. FIG. 2 is a side view of a data storage system including a plurality of data storage disks. FIG. 3 is an enlarged side view showing a data storage disc presenting various surface defects and features and the thermal and magnetic responses of the MR head to such defects and features. FIG. 4 is a cross-sectional view of the transducer reluctance element shown in the orientation on the track on the centerline of the track of the disc. FIG. 5 is a plan view of the disk according to the present invention. FIG. 6 is a perspective view of two adjacent tracks on the disc, separated by track markers. FIG. 7 is a plan view of a series of tracks and track markers on an optical disc. FIG. 8 shows the thermal frequency response of the MR head as a function of the MR head position on the track of the disc. FIG. 9 is a block diagram of a system consisting of components for demodulating the read-back signal of the MR head. FIG. 10 is a general-purpose block diagram of system components for servo-positioning the MR head using the thermal frequency response signal of the MR head according to the present invention. FIG. 11 (a) is a diagram showing the segments of the calibration zone according to the present invention, and FIG. 11 (b) is a detailed view of the segments of the calibration zone. FIG. 12 is a diagram showing the mapping of the MR head to the physical track for the cylinder. FIG. 13 is a block diagram of a device for extracting a thermal signal from the read-back signal induced by the MR head. FIG. 14 is a diagram showing a read-back signal induced by the MR head, which presents the strain of the DC baseline. FIG. 15 is a diagram showing the read-back signal of FIG. 14, which presents the restoration of the DC baseline after processing by the signal separation / conversion module. FIG. 16 is a block diagram of a signal separation / modulation module for extracting a thermal signal and a magnetic signal from the read-back signal induced by the MR head. FIG. 17 (a) is a diagram showing a thermal signal extracted from a read-back signal induced by an MR head at a specific track position, and FIG. 17 (b) is a diagram obtained from the same track position after AC erasing. Is a read-back signal. Fig. 18 (a), Fig. 18 (b), and Fig. 18 (c) show the read-back signal induced by the MR head, the restored magnetic signal component of the read-back signal, and the unrestored magnetism of the read-back signal. The signal components are shown respectively. Figures 19 and 20 show the phase and scale responses of the finite impulse response (FIR) filter and windowed FIR filter used in the signal separation / restoration module. 21 and 22 are views showing a conventional MR head. FIG. 23 is a diagram showing the scale and phase response of the high frequency pass filter behavior of a typical AE module. Figures 24 and 25 compare the scale and phase response of a typical AE module's high-pass filter behavior with an inverse filter that has a transfer function opposite to that of the AE module's effective high-pass filter. Are shown respectively. FIG. 26 is a signal flow diagram showing the inverse filters of FIGS. 24 and 25. FIG. 27 is a block diagram of another embodiment of a signal separation / restoration module using an infinite impulse response (IIR) filter. FIGS. 28 (a) to 28 (c) show three waveforms generated at various processing points in the signal separation / restoration module of FIG. 27. FIG. 29 is a comparison diagram of the restored magnetic signal and the thermal signal showing the presence of a hump on the surface of the disk. .. Embodiment of the invention Then referring to the accompanying drawings, more specifically FIGS. 1 and 2, the figure shows the data storage system 20 with its cover (not shown) removed from the base 22 of the housing 21. ing. Typically, the data storage system 20 includes one or more rigid data storage disks 24 that rotate around a spindle motor 26. Typically, the actuator assembly 37 includes a plurality of plug-in actuator arms 30, each arm having one or more suspensions 28 and a converter 27. Typically, the transducer 27 includes a reluctance (MR) element for reading information from a data storage disc 24 and writing the information to that disc. For example, the converter 27 can be an MR head with a write element and an MR read element. The actuator assembly 37 cooperates with the permanent magnet structure 38 to act as an actuator voice coil motor (VCM) 39 in response to a control signal generated by the controller 58. Includes coil assembly 36. The controller 58 coordinates the transfer of data on the data storage disk 24 and brings the actuator arm 30, suspension 28, and transducer 27 to the specified track 50 and sector 52 positions when reading and writing data on disk 24. It is preferable to include a control circuit that cooperates with VCM39 to move it. FIG. 3 shows an enlarged side view of the MR head slider 79 floating near the surface 24a of the magnetic data storage disk 24. The disk surface 24a generally has a microscopically variable topology and often contains various surface defects such as pits 122, humps 124, and voids 126 of magnetic material. According to the judgment of the inventors, the thermal response of the MR head 80 changes as a function of the distance (indicated by the parameter y) between the MR element 78 of the MR head 80 and the disk surface 24a. As the head / disk spacing changes, the amount of heat transferred between the MR element 78 and the disk 24 changes concomitantly. As a result of this change in the amount of heat transfer, the temperature of the MR element 78 changes. As a result of the temperature change of the MR element 78, the electrical resistance of the MR element 78 changes accordingly, and therefore the output voltage of the MR element 78 changes. As the instantaneous head / disk spacing (y) increases, the amount of air space insulation between the MR head 80 and the disk surface 24a increases, thus increasing the temperature of the MR element 78. .. As a result of the temperature rise of the MR element 78, the electrical resistance of the MR head 80 increases accordingly. This is because the temperature coefficient of the MR element material normally used to manufacture the MR element 78 is positive. For example, permalloy is the preferred material used to make MR element 78 and exhibits a temperature coefficient of + 3 × 10-3 / ° C. For example, when the MR head 80 passes over the hump 124 on the disk surface 24a, the amount of heat transferred from the MR element 78 to the disk surface 24a increases, and thus the temperature of the MR element 78 decreases. Due to such a decrease in the temperature of the MR element 78, the resistance of the MR element 78 decreases, and the voltage VTH of the MR element 78 decreases when the bias current is constant. The amplitude of the thermal voltage signal VTH119 obtained by the MR element 78 is expressed as a function of the head / disk separation distance (y), and it is shown on the disk surface 24a that VTH119 increases as y increases. And the corresponding VTH119. Furthermore, it should be seen that VTH119 decreases as y decreases by referring to the hump 124 shown on the disk surface 24a and the corresponding VTH119. Therefore, the thermal signal component that changes as a function of the head / disk separation distance in the signal contained in the read-back signal is actually the presence of topological changes on the surface of the magnetic data storage disk 24 and the head-disk interval. An information signal that can be used to detect the relative distance of. FIG. 3 also shows a magnetic spacing signal 121 conditioned to accommodate changes in the disk surface 24a. It should be seen that the magnetic spacing signal 121 incorrectly indicates the presence of some surface feature, such as the magnetic void 126, as a change in the topology of the disk surface 24a. In addition, it should be found that the magnetic spacing signal 121 is a poor indication of other surface features such as humps when compared to the information on the changes in disk surface topology brought about by the use of thermal signal 119. As detailed below, the thermal component of the read-back signal of the MR element can be extracted to obtain information about the surface properties of the rotating disk 24. According to one embodiment of the present invention, the servo information is encoded in the surface profile of the disk 24 and read using a transducer having an MR element such as an MR head 80. As can be seen from the examples described below, the servo information is provided in the profile of the disc and can be read at the same time as the magnetically stored data, so that an additional 15% to 20% of the disc is required to store the data. It becomes available (ie, a portion of the pre-used disk for embedded magnetic servo information). Next, moving to FIG. 4, the figure shows the MR element 78 of the MR head 80 oriented on the center line 51 of the track 50. The MR head 80 can be of the type used in conventional data storage systems, facilitating the use of the present invention in conventional storage systems. As the MR element 78 passes over track 50 of the rotating disc 24, a magnetic transition that occurs on the surface of the disc 24 results in a read-back signal induced by the MR head 80. By way of example, but not by limitation, the read-back signal is preferably a voltage signal. FIG. 5 shows a disk with track markers 108 and sector markers 106 pre-embossed or engraved to provide servo information on the disk in the form of changes in surface profile such as head / disk spacing. Twenty-four examples are shown. The disk 24 is provided with a concentric data track 50 used to store the data. Each data track 50 can be divided into a series of sectors 52 identified by the sector marker 106. Adjacent data tracks 50 are separated by track markers 108. The track marker 108 and the sector marker 106 are formed as changes in the disk 24 that can be identified by using the thermal component of the read-back signal of the MR head. As best shown in FIGS. 6 and 7, the track marker 108 can be a circumferential groove that results in a change in head / disk spacing between adjacent data tracks 50. , The sector marker 106 can be a radial groove that causes a change in head / disk spacing between adjacent sectors 52. As detailed below, the track marker 108 and the sector marker 106 are used to provide servo information. The disk 24 is also provided with a calibration zone 110 and an index marker 112, which can be formed by a pair of closely spaced sector markers 106. The purpose of the calibration zone 110 and the index marker 112 will become clear later. As shown in FIG. 7, the data track 50 of the disk 24 is provided with serrated edges 50 ID and 50 OD corresponding to the inner diameter (ID) edge and the outer diameter (OD) edge of the track. For each track, the ID edge 50 ID serrations have a different serration frequency than the OD edge 50 OD serrations to provide radial servo information. The serrations can be in the form of square or sine waves. Also, the serrations can have frequencies f1 and f2 that are twice as different, but if each track has edges 50ID and 50OD of different frequencies, the serrations can have many different frequencies. Please note. As shown, the serrated edges 50ID and 50OD of track 50 can alternate serration frequencies. For example, some tracks 50, called odd tracks, may have a (ID) edge 50 ID with serration frequency f1 and a (OD) edge 50 OD with serration frequency f2. The even data track 50, on the other hand, should have an OD edge 50 OD at frequency f1 and an ID edge 50 ID at frequency f2. By alternating the serration frequencies between adjacent data tracks 50, the serration edges of adjacent tracks 50 correspond to each other. This makes it easier to detect the track marker 108 that separates the adjacent tracks 50 from each other, and makes it easier to manufacture the disc 24. In addition, the serrations can be aligned radially. That is, the serrations can be further spaced as they move outward in the radial direction. This should be useful in constant angular velocity systems. This is because the serration frequency relative to the MR head 80 is expected to be constant across the surface of the disk 24. Moreover, the number of serrations around the data track 50 can be a power of 2 so that the oscillation frequencies of the data storage system can be split to accurately determine the serration frequencies f1 and f2, respectively. In Figure 8, the frequency scale responses t (f1) and t (f2) of the thermal component of the MR head readback signal are shown as a function of the position of the MR head 80 on the even data track 50. That is, the data track 50 has a frequency f2 with an ID edge 50ID and a frequency f1 with an OD edge 50OD. When the MR head 80 is positioned on the center 51 of the data track 50, the thermal frequency scale responses t (f1) and t (f2) should be close to zero. As the MR head 80 moves towards the ID edge 50 ID of the even track 50, the MR head 80 senses edge serrations and the thermal signal t (f2) increases. Similarly, as the MR head 80 moves towards the OD edge 50 OD, the thermal signal t (f1) increases. However, keep in mind that the thermal signals t (f1) and t (f2) reach the horizontal range as the head continues to move off the track. As described in detail below, by inspecting the frequency content of the thermal component of the read-back signal, the direction and degree of deviation from the track of the MR head 80 is determined, an appropriate control signal is output, and the track is on the center line. The actuator 30 can be positioned. Note that the thermal frequency scale responses t (f1) and t (f2) from which the servo information is obtained are derived from the periodic changes in the spacing between the disk 24 and the MR head 80. In the illustrated embodiment, servo information is obtained by sensing the change in thermal frequency response that results from the MR head 80 passing over the serrated circumferential groove. Alternatively, the change in disc / head spacing can be achieved by providing raised portions between the tracks. However, in a typical environment, grooves are preferred. This is because in the case of a groove, the storage system 20 can operate even if the distance between the MR head and the data track is the minimum. In an alternative embodiment of the present invention, servo information is derived from other changes in disk characteristics that can be reflected in the thermal component of the read-back signal. For example, track marker 108 may differ from data track 50 in terms of thermal emissivity or other parameters that can be reflected in the thermal components. Similar changes in disk characteristics can be used for sector marker 106. Moving on to FIG. 9, the figure shows a block diagram of an example system consisting of components for demodulating the read-back signal and generating servo positioning control signals 221 and 223. The demodulation system shown in Fig. 9 is realized as a digital system, but an equivalent analog system can also be used. During operation, the demodulation system amplifies the read-back signal 81 obtained using the MR head 80. This amplification can be done, for example, by using the Arm Electronics (AE) module 202. The amplified read-back signal 203 is sampled by the sampler 204 at a predetermined sampling rate to generate the read-back signal 205. Typical sampling rates will be above 100 MHz (MHz). The sampled read-back signal 205 is fed to the data channel for normal processing and is also fed to the track crossover detector 230 for the purposes described below. The read-back signal 205 is also supplied to a filter 206, such as an inverse infinite impulse response (IIR) filter, to correct the high frequency pass filter in the AE module 202. The output signal 207 of the filter 206 passes through a filter 208, such as a moving average low pass finite impulse response (FIR) filter, to recover the thermal component of the readback signal. The output of filter 208 is supplied to the heterodyne demodulation circuit 210, which determines whether the thermal frequency scale components t (f1) and t (f2) of the read-back signal 81 exceed the thresholds ta and tb, respectively. judge. The operation of the heterodyne demodulation circuit 210 will be described in detail below. The signal 209 received by the heterodyne demodulation circuit 210 during the read operation is supplied directly from the filter 208. However, during the writing operation, the writing element generates heat, and this heat is transferred to the MR head. The heat transfer between the write head and MR head distorts the heat component of the read-back signal. The dynamics of heat transfer between the write head and MR head can be estimated by the first-order transfer function of the low-pass filter. The distortion generated by the heat transfer between the write head and the MR head is caused by passing the signal exiting the filter 208 through an adaptive inverse filter 240, which counts the transfer functions opposite to those of the lowpass filter transfer function. It can be significantly reduced. A signal 233 indicating a read or write operation can be supplied to selectively couple the adaptive inverse filter 240. For example, during the write operation, the signal 233 can be used to couple the adaptive inverse filter 240 so that the signal exiting the filter 208 before being received by the heterodyne demodulator circuit 210 passes through the adaptive inverse filter 240. During the read operation, signal 233 can be used to pass the signal exiting filter 208 directly to the heterodyne demodulation circuit 210. The electrode position of the transfer function of the adaptive inverse filter 240 may vary between MR heads. The electrode position of a given MR head can be estimated by using the thermal cooling response of the MR head after the write operation has started. For example, the cooling curve can be a simple decay exponential function that uses a time constant, but this constant is by the time the cooling curve reaches about 36.8% of its maximum value, i.e. e-1 = .368. It can be calculated from the required time. The electrode position value, which is the time constant or the opposite of the time constant, can be estimated in the field for each MR head and stored in random access memory (RAM). In that case, the transfer function of the adaptive inverse filter 240 can be updated based on the time constant of the selected MR head. The transfer function of the adaptive inverse filter 24 for each MR head over time to compensate for changes in heat transfer between write heads / MR heads and between MR heads / disks that are likely to result from the collection of debris on the heads. Can be updated as you go. Therefore, the adaptive inverse filter 240 restores the distorted thermal component to a component that is likely to be present during the reading operation. When the read-back signal whose thermal component is restored by the adaptive inverse filter 240 is used as an input to the heterodyne demodulation circuit 210, the misalignment (TMR) of the track during writing is reduced. In addition, sensing during both read and write operations eliminates the need to use accelerometers or other external sensors to monitor shocks and vibrations in the drive. The heterodyne demodulation circuit 210 includes first and second multipliers 212 and 214, filters 216 and 218, and first and second comparators 220 and 222. The heterodyne demodulation circuit 210 extracts the thermal frequency scale response signals t (f1) and t (f2) from the signal 209 and compares these signals with the thresholds ta and tb to generate servo positioning control signals 221 and 223. .. During operation, the heterodyne demodulator circuit 210 receives signal 209 and supplies it to the first and second multipliers 212 and 214. The multipliers 212 and 214 multiply the read-back signal 209 by two or more split oscillator signals 225 and 227, respectively. Oscillator signals 225 and 227 may have frequencies and waveforms similar to the serration frequencies of the serrated edges that occur when the disk 24 is rotated at rated speed. The multipliers 212 and 214 output signals 213 and 215 whose frequency components are amplified at frequencies f1 and f2, respectively. Signals 213 and 215 are lowpass filtered by filters 216 and 218, thereby rejecting the high frequency components of signals 213 and 215 and the low frequency thermal scale response signals t (f1) and indicated by 217 and 219, respectively. Generate t (f2). Thermal signals 217 and 219 are supplied to comparators 220 and 222 for comparison with thresholds ta and tb. As best shown in Figure 8, the thresholds ta and tb are for the thermal signals t (f1) and t (f2) when the MR head 80 moves off the track and needs to be repositioned. Corresponds to the limit amplitude. However, note that the thresholds ta and tb are predetermined values for each MR head 80 and are stored in random access memory (RAM). The thresholds ta and tb are determined by taking into account the difference in thermal sensitivity along the width W of the MR element for each MR head 80 and may vary from one MR head to another as detailed below. There is. The comparator output signals 221 and 223 from the comparators 220 and 222 can have a logical value of 0 or 1. For example, if the MR head 80 is centered on track 50, outputs 221, 223 can both have a logical value of 0. If the thermal frequency response signal 217 exceeds the threshold ta, the comparator output signal 221 can have logic 1. Similarly, if the signal 219 exceeds the threshold tb, the comparator output signal 223 can have logic 1. If the signals 217 and 219 have frequency components of serration frequencies f1 or f2 below their respective thresholds, the comparator outputs 221 and 223 are both zero. As described below, comparator outputs 221 and 223 can be used by the track tracking servo control system to control the position of the MR head 80. Next, referring to FIG. 10, at the same time, an example of a servo control system using the comparator signals 221 and 223 to servo-position the MR head 80 on the data track 50 is shown. This servo control system includes a servo demodulator 200, a read / write (R / W) controller 340, a seek controller 302, a speed profile controller 304, a feedforward generator (FFG) 306, and a first. And a second adder 308 and 310, a multiplier 312, a servo compensator 318, a digital-to-analog converter (DAC) 314, and a driver 316. During operation, the R / W controller 340 supplies a signal 340 to a servo control system such as the servo demodulator 200. Signal 340 can be used to control the type or mode of operation such as read / write, track tracking, seek, settling, etc. For example, during track tracking, comparator output signals 221 and 223 control switches 320 and 322, respectively, to couple the digital values + I0 and -I0 to adder 310. If the comparator output 221 has logic 1, switch 310 is calibrated to close so that the value + I0 is supplied to adder 310. Similarly, if the comparator output signal 223 has logic 1, the value -I0 is supplied to adder 310. The digital values + I0 and -I0 are supplied as pulse injection values to control the movement of the actuator. If the comparator output signals 221 and 223 are both 0, then switches 320 and 322 both remain open and no pulse injection is supplied to the adder 310. However, note that the comparator output can be ignored as there is an error if both comparator outputs have logic 1. The adder 310 sums the pulse injection value + I0 or -I0 (if any) with the feedforward generator (FFG) value 307 and supplies the total signal 311 to the servo compensator 318. However, although the adder 310 is configured to receive signal 313, is this signal used primarily during track seek and is ignored during track tracking operations, as described below? Or note that it may not be supplied. The FFG value 307 expresses the axial offset of the MR head and the track runout as a function of the rotation of the disk 24, and is supplied to the adder 310 by the feed forward generator (FFG) 306. The FFG306 stores a predetermined axial offset and track runout of the MR head 80 in random access memory (RAM) for each MR head 80 of the storage device. The track runout and head offset of each MR head 80 can be determined using the configuration procedure described below. Servo compensator 318 is typically a microprocessor that processes signal 311 and generates servo positioning control signal 319, taking into account the type of data track 50, odd or even. The control signal 319 is converted into an analog signal 315 by the DAC 314 and supplied to the driver 316, which in response supplies a current 317 to the voice coil motor (VCM) 39 to move the actuator 30. In this way, the movement of the actuator 30 is controlled so that the MR head 80 tracks a given data track 50. The servo control system can also be used to seek a track, i.e. move the MR head 80 to a position on the designated track 50 on disk 24. During track seek operation, the servo control system uses the speed difference between the estimated radial speed of the MR head 80 and the desired radial speed to control the radial speed of the actuator arm 30, and thus the MR head 80. Generate a signal for. For example, if the estimated speed is lower than the desired speed, the servo compensator 318 will generate a signal to increase the radial speed of the MR head 80 by increasing the rotation of the actuator arm 30. On the other hand, if the desired speed of the MR head 80 is lower than the estimated radial speed of the MR head 80, the servo compensator 318 generates a signal to reduce the radial speed of the actuator arm 30. The seek controller 302 generates an estimated head velocity (EV) signal 303 that is subtracted by the adder 308 from the desired head velocity (DV) signal 305 generated by the velocity profile controller 30. The velocity difference (DV-EV) signal 309 is multiplied by the velocity gain + K or -K on the multiplier 312, and the product 313 is supplied to the adder 310. The seek controller 302 can also supply a seek direction signal 300 for use by the multiplier 312 to determine whether to use the velocity gain -K or + K. The adder 310 adds the speed difference signal 313 to the feed forward generator (FFG) value 307 and supplies the total value 311 to the servo compensator 318, which processes the value 311 and the servo positioning control signal. Generate 319. The control signal 319 is converted into an analog signal 315 by the DAC 314 and supplied to the driver 316. The driver 316 generates a current 317 for the VCM 39 of the actuator assembly 37, thereby allowing the MR head 80 to efficiently seek and position the desired position over the radial velocity of the MR head 80. Increase or decrease. The seek controller 302 uses a transmitter pulse to measure the time between dropouts of the magnetic component of the read-back signal 81 that occurs when the MR head 80 passes over the track marker 108, at this time. Generate an estimated head velocity by dividing the fixed track pitch. This velocity estimation can be further refined by compensating for the track runout of the MR head 80. Such additional refinement can be performed at low head speeds, such as when the MR head 80 is fixed on the designated data track 50. However, it should be noted that the estimated speed can also be determined using the thermal component peaks that occur on the track marker 106, similar to the magnetic dropout when the disk 24 is magnetically recorded. However, the magnetic component increases the signal-to-noise ratio. In addition to estimating the speed of the MR head 80, the seek controller 302 records the track number of the current data track on which the MR head 80 is positioned and also counts data track crossings. Data track crossing is detected by track crossing detection by amplitude detection of the thermal component peak or magnetic component dropout of the readback signal that occurs when the recording head crosses the track marker 106, as shown in FIG. It is counted by the vessel 230. Each time the head intersects the track marker 106, a pulse is generated on the output side line 201 of the track intersection detector 230. The seek controller 302 uses the current track number and track count to determine the difference between the current data track number where the MR head 80 is positioned and the target data track number that the MR head 80 is seeking. .. This track number difference is called the number of passing tracks (TTG) and is supplied from the seek controller 302 to the speed profile controller 304. During the seek operation, the seek controller 302 counts the track crossing pulses present on line 201 and continues to update the TTG count signal 353. As the TTG signal approaches zero, i.e. as the MR head approaches the target track, the radial velocity drops rapidly and actuator control tracks crossing detection of track tracking demodulator outputs 221 and 223 for speed estimation. You can switch to a fixed mode that can be used with the output of the device. Switching to fixed mode can be triggered if the TTG is less than a given count, for example if TTG <1-2 tracks. The speed profile controller 304 receives the TTG signal 353 and uses it to determine the desired speed of the MR head 80. The desired head speed is determined from the relationship between the desired head speed and TTG. This relationship is predetermined and can be stored in a reference table in RAM attached to the speed profile controller 304. Since the thermal component of the MR head 80 can be sampled at the same time as the magnetic signal component, it is advantageous for the servo control system to provide continuous servo control. Unlike traditional magnetic servo techniques, thermal servo control can reach sampling rates above 100 KHz. The higher the sampling rate of the thermal servo control, the smaller the corresponding actuator coil current. In addition, the mechanical inertia of the actuator integrates these small currents to produce a very smooth movement, which reduces actuator jerk. The more precise the actuator control, the higher the track density (closer to 16,000 tracks per inch for dual actuators) and significantly better shock and vibration detection on disk 24. Moreover, due to predictive failure analysis (PFA), any defects on disk 24 that could potentially cause track misalignment (TMR) can be detected. Similarly, any modulation of the MR head 80, eg, modulation by the MR head 80 that has not risen from disk 24, can be detected. However, it should be noted that in order to use the pre-embossed disc 24, it is necessary to form servo information on the disc before assembling it into the disc drive. When using multiple discs, the alignment of servo information between the discs must be considered. For example, depending on the mechanical tolerance of the disc 24 during manufacture and installation of the disc 24 in the storage device, each disc 24 in the disc pack may exhibit a different degree of eccentricity or runout. Moreover, due to the mechanical tolerance, an axial offset occurs between the MR heads 80. Therefore, a calibration procedure is required to determine the individual disc runouts with respect to the radial index marker 112, the axial offset of the MR head, and the difference in rotational alignment. To calibrate and format the discs 24 in storage, each disc 24 has an outer diameter (OD) crash stop or an inner diameter (ID) crash of the disc 24 anywhere on the disc 24, for example. -There is an annular calibration zone 110 that can be placed at the stop. The calibration zone 110 must have a width equal to at least the worst eccentricity of the disc 24 plus the maximum axial offset of the MR head. An example of the width is 32 tracks. As shown in FIGS. 11 (a) and 11 (b), the calibration zones 110 can be evenly spaced to 6-8 bits. It consists of an iterative Gray code pattern. Gray code patterns can be interlaced with blank spaces or frequency patterns 384 and 386. Gray code patterns 382 and frequency patterns 384 and 386 consist of changes in disk characteristics, which can be read by heat. The gray code pattern 382 of the illustrated embodiment is encoded as an embossed indentation, and the frequency patterns 384 and 386 include radial grooves. MR head 80 gives a positive spiked signal perform the thermal response against Therefore recess or groove. However, it should be noted that the patterns shown in FIGS. 11 (a) and 11 (b) have a linear density on the disc such that their frequency at the rated disc speed is commensurate with the frequency range of the thermal signal. For example, the magnetic frequency is typically about 100-200 MHz, but the thermal frequency is much lower, for example, this pattern can be at a frequency of 100-200 kHz. FIG. 11 (a) shows one segment of the example calibration zone 110. This segment consists of eight tracks n-1, n-1, n, n + 1, n + 2, ..., n + 5, and a 4-bit gray code {b3, b2, b1, b0}. The code and frequency patterns 384 and 386 are shown. Gray code can be written at a pitch of 1/2 track width with a 1/4 track width offset, but is indicated by ..., j-2, j-1, j + 1, ... ing. In the example of FIG. 11 (a), the MR head 80 is located on track n + 2 in the calibration zone. When the head crosses the gray code 1/2 track (j + 4), the result is two positive spikes {b3, b2}. Since the part of the head that crosses the 1/2 track (j + 3) of the Gray code is smaller, the resulting spike (b0) is also smaller. This spike is compared to the threshold, and if it exceeds the threshold, it can output logic 1, otherwise it can output logic 0. For example, in the illustrated embodiment, if only the spike (b3, b2) exceeds the threshold, the code {1, 1, 0, 0} is decoded. Gray code 382 is processed to determine the axial and relative head offset and track runout of each MR head 80 in storage. As mentioned above, the head offset and track runout can be stored in RAM coupled to the feedforward generator 302 and used in the servo control system for track tracking and track seek. The axial offset of the MR head 80 is determined by rotating the disk 24 completely one revolution, reading the Gray code pattern 382 by the MR head 80, and then averaging the signals. A thermal Gray code signal is created in the MR head 80 read-back signal as the MR head 80 passes over the indentations and ridges of the Gray code pattern 382. The thermal Gray code signal is processed to determine the absolute average measurement of disc eccentricity or runout. Axial head offset is determined by averaging the absolute average measurements of disk eccentricity for one complete revolution. By doing this, the relative position of each MR head 80 with respect to the other MR head 80 can be determined. Axial head offsets can be used in multiple disk systems to determine the physical track of each MR head 80 in the cylinder. However, it should be noted that the cylinder represents the physical track on which the MR head 80 is positioned. In the placement example, the physical track 0 of the MR head 80, which maximizes the axial offset, is mapped to cylinder 0. MR heads 80 with a smaller axial offset are mapped to physical track numbers greater than 0 based on the maximum axial offset. An example of this mapping for a storage system with 3 disks and 6 MR heads 80 is shown in Figure 12. The black circle represents the position of each MR head 80 in the calibration zone 110. The distance between the black circle and the horizontal axis represents the axial offset of each MR head 80 from its physical track 0. MR head number 5 has a maximum axial offset of 5.5 tracks, which is mapped to that physical track 0. The remaining MR head 80 is mapped to a physical track that is 5.5 tracks apart from that position in calibration zone 110. By mapping cylinder 0 to physical track 0 of MR head 80 with maximum axial offset, seek required during head switching is minimized. Frequency calibration patterns 384 and 386 are used to measure the thermal sensitivity of the MR head 80 to determine the appropriate servo thresholds ta and tb for a given head. The servo thresholds ta and tb compensate for the various thermal sensitivities between MR heads 80 that arise from differences in MR element dimensions, indentations, shield spacing and dimensions, MR reed thermal conductivity, and so on. Frequency patterns 384 and 386 have serration frequencies to determine the servo thresholds ta and tb for each MR head 80 in the storage system, for example serration frequencies for serrated edges 50 ID and 50 OD. Can be equal to f1 and f2. The threshold calibration procedure for a multi-disk device includes the following steps: First, move all MR heads 80 of the storage system to the calibration zone 110 of each disk 24. Select one MR head 80 and rotate its respective disc 24. Thermal frequency scale responses t (f1) and t (f2) are created as the MR head 80 passes over frequency patterns 384 and 386. The thresholds ta and tb can be calibrated using the thermal frequency scale responses t (f1) and t (f2). For example, as shown in Fig. 8, based on the assumption that the thermal sensitivity along the width W of the MR element is constant, the ratio of the threshold value to the horizontal amplitude becomes constant, or ta = kat ( The threshold can be determined from the relationship f1) and t (f2) and tb = kbt (f2). The selected MR head 80 thresholds ta and tb are stored in RAM and repeat the above process for another MR head 80 until the thresholds for all MR heads 80 in the storage system are calibrated. .. An example of a calibration procedure for determining the position of all index markers 112 on the surface of a disc 24 in a disc pack includes the following steps. The index marker 112 of the reference disk 24 is identified, and the time difference (including the head switching time) between the index marker 112 of the reference disk 24 and the index marker 112 of the second disk 24 is measured. This is repeated until a time lag between all index markers 112 and the sectors 52 for them is established. Relative timing calibration is advantageous because it can be performed at the same time as thermal signal calibration. Next, referring to FIG. 13, a device for reading an information signal having a magnetic signal component and a thermal signal component from a magnetic storage medium and separating the thermal signal component and the magnetic signal component from the information signal is shown in the figure. It is shown. The MR head 80 is shown near the surface of the data storage disk 24. The read-back signal induced by the MR head 80 is usually amplified by the AE module 202. Filtering of the read-back signal by the AE module 202 can also be performed. As shown graphically on the output side of the AE module 202, the analog read-back signal 460 containing the relatively high frequency magnetic signal component 461a shows the distortion of the DC baseline due to the presence of the low frequency modulated signal component. For those skilled in the art, the modulated magnetic signal component 61a of the modulated read-back signal 460, or more specifically the read-back signal 460, may cause servo control errors or inaccuracies, or reduced reliability of data storage and retrieval. It should be noted that some have long been recognized as the source of some of the harmful effects of data storage systems, including the irreparable loss of data. According to the discoveries of the inventors, the read-back signal 460 is a composite signal containing an independent magnetic signal component and a thermal signal component, and the low-frequency modulated read-back signal baseline is actually an independent thermal signal of the read-back signal 460. It is an ingredient. Further, at the discretion of the inventors, as detailed below, the modulation of the unwanted read-back signal 460 can be eliminated or significantly reduced in scale, resulting in the representation of data or servo information. A pure magnetic signal can be obtained. 14 and 15 show the distorted read-back signal and the undistorted read-back signal restored by the signal separation / restoration module 476 shown in FIG. 13, respectively. The signal separation / restoration module 476 processes the read-back signal 460 by removing unwanted baseline modulation and thereby producing a pure, undisturbed magnetic signal 461b, which is read as shown in FIG. Restore the return signal baseline. However, it should be noted that the signal separation / restoration module 476 generally represents the read-back signal filter device of the servo demodulator 200 shown in FIG. 9, which is required to extract the thermal signal from the read-back signal. The independence of the magnetic signal and the thermal signal is demonstrated by the waveform in Fig. 17. The waveform shown in FIG. 17 (a) represents a thermal signal extracted from a composite read-back signal using a digital filter configured as a low-pass filter and an MR head. After the waveform shown in Fig. 17 (a) was obtained, AC erasing was performed on the track on which the waveform was generated. The same MR head was moved to the same track position of the erased track, and the waveform shown in Fig. 17 (b) was obtained. It should be noted that the extraction heat signal shown in Fig. 17 (a) and the read-back signal derived from the erasure track shown in Fig. 17 (b) are almost the same. The two waveforms shown in FIG. 17 confirm that the two thermal and magnetic signals read at the same time are independent and separable. With reference to FIG. 16, FIG. 16 shows an embodiment of the signal separation / restoration module 476 described above in connection with FIG. The signal separation / restoration module 476 performs a single task of separating the magnetic signal independent of the read-back signal 460 in order to remove the low frequency modulation component of the read-back signal 460 due to the influence of the thermal signal. Note that it can be used for. In another embodiment, the signal separation / restoration module 476 separates the magnetic signal component from the read-back signal 460 to remove the low frequency thermal signal component and further extracts the thermal signal, resulting in a pure magnetic signal. And pure thermal signals can both be used to perform the dual task of making them available for subsequent processing independently. As shown in FIG. 16, the read-back signal is sensed by the MR head 80 located near the magnetic data storage disk 24. In one embodiment, the read-back signal received from the AE module 202 by the MR head 80 is converted from analog format to digital format by the analog-to-digital converter 204. The digitized read-back signal is then communicated to the delay device 486 and further to the programmable filter 488. The programmable filter 488 is a finite impulse response (FIR) filter having a length N, where N represents the impulse response coefficient or the number of taps of the programmable filter 488. For the read-back signal applied to the input of the programmable filter 488, a total signal delay corresponding to the length N of the programmable filter 488 is applied as the read-back signal passes through the programmable filter 488. According to this embodiment, the programmable filter 488 has an appropriate tap factor and weight to pass the relatively low frequency thermal signal component of the readback signal and filter the relatively high frequency magnetic signal component. Programmed using. As such, the programmable filter 488 is configured as a low pass filter and provides a thermal signal that can be generally characterized as an intermediate frequency in which most of its energy falls in the frequency range from about 10 kHz (KHz) to about 100 to KHz. Programmed to pass. However, it should be noted that the magnetic signal component of the read-back signal has a frequency range between about 20 MHz (MHz) and 100 MHz. The thermal signal 480 on the output side of the programmable filter 488 is communicated to the signal adder 490. The thermal signal 480 can be transmitted from the output of the programmable filter 488 to other components within the data storage system, such as servo control to control track tracking and track seek operation. The delay device 86 receives the read-back signal 460 from the analog-to-digital converter 204 and goes to the signal adder 490 for a duration corresponding to the delay time required for the read-back signal 460 to pass through the programmable filter 488. Delays the transmission of the read-back signal. Therefore, the read-back signal 460 including both the magnetic signal component and the thermal signal component and the thermal signal 480 extracted from the read-back signal by the programmable filter 488 arrive at the signal adder 490 almost at the same time. The signal adder 490 performs a demodulation operation on the read-back signal 460 and the thermal signal 480 to generate a restore read-back signal 478. As a result, the signal separation / restoration module 476 shown in the embodiment of FIG. 16 can separate the magnetic signal component and the thermal signal component of the composite read-back signal, and further, the restoration magnetic read-back signal 478 without distortion. To generate. For more information on designing, implementing, and programming FIR filters for use with the Signal Separation / Restoration Module 476, see Digital Signal Proces sing by ECIfeachor, BW Jervis (Addison-Wesley Publishing Company, Inc., 1993). I want to. Returning to FIGS. 14 and 15, the modulated read-back signal 460 shown in FIG. 14 represents the appearance of the read-back signal before being processed by the signal separation / restoration module 476. The representation of the read-back signal in FIG. 15 shows the read-back signal in FIG. 14 after being processed by the signal separation / restoration module 476. The unwanted effect of the thermal component of the distorted read-back signal shown in FIG. 14 uses a 9-tap FIR filter in the signal separation / recovery module 476 to generate the restore magnetic read-back signal 478 shown in Figure 15. It has been removed by. The scale and phase characteristics of the 9-tap FIR filter used to generate the restored magnetic read-back signal 478 shown in Fig. 15 are shown in Fig. 19. In particular, in Figure 19 (b), you can see that the 9-tap filter shows a perfect linear phase response over the frequency range of interest. The effectiveness of the 9-tap FIR filter in removing the baseline shift or modulation of the read-back signal is shown in Figure 18. Figure 18 (a) shows a read-back signal demonstrating an unstable or time-varying baseline. In Figure 18 (b), after passing the distorted read-back signal through a properly programmed 9-tap FIR filter, the modulation baseline of the read-back signal that is apparent in Figure 18 (a) is removed. The tap weights for the 9-tap filter used to restore the baseline of the read-back signal are defined to include the following tap weights: B (i) = (1/9) * (-1, -1, -1, -1,8, -1, -1, -1, -1) Or B (i) = (-.111, -.111, -.111, -.111, .889, -.111, -.111, -.111, -.111) The waveform shown in Fig. 18 (c) is generated by passing the modulated read-back signal shown in Fig. 18 (a) through a conventional high-pass pass towers filter, which is a single-pole high-pass filter. .. After passing the read-back signal through a conventional high-pass filter, it should be seen that the size of the unwanted modulation baseline of the read-back signal has not been significantly reduced. As described above, the scale and phase characteristics of the 9-tap FIR filter used to restore the baseline of the read-back signal shown in Fig. 18 (b) are shown in Fig. 19 (a) and Fig. 19 (b). Each is shown in. In Figure 19 (a), it should be seen that some ripple can occur within the passband of the filter, which can be eliminated by applying a window function to the tap weights of the 9-tap FIR filter. As an example, a humming window can be applied to the tap weights of a 9-tap FIR filter to generate a windowed restore filter with the following tap weights. B (i) = (-.0089, -.0239,-.06,-.0961, .8889,-.0961, -.06, -.0239, -.0089) In the output of the 9-tap window type FIR filter having the above tap weight, ripples are removed as shown in FIG. 20 (a). Furthermore, as shown in Figure 20 (b), the windowed 9-tap FIR filter retains its perfect linear phase response. However, keep in mind that applying a window function such as a humming window to the tap weights of the programmable FIR filter 488 expects some increase in non-zero DC gain and low frequency response. Next, moving to FIGS. 23 to 29, at the same time, another embodiment of the signal separation / restoration module 476 is shown. In the design of the AE module 202 shown in FIG. 13, it is desirable to include a high frequency pass filter together with the preamplifier in order to reject the relatively low frequency signal content of the composite readback signal generated by the MR head 80. There are many. The high frequency pass filter of the AE module 202 distorts the thermal signal component of the composite read-back signal in terms of both amplitude and phase. The magnitude of the thermal signal distortion due to the high pass filter varies in severity depending on the frequency and phase response of the particular high pass filter used. For example, a high pass filter suitable for use with the AE module 202 has a cutoff frequency of approximately 500 KHz and may exhibit non-linear phase behavior. However, the frequencies associated with changes in head / disk spacing are typically in the range below 200 KHz. Moreover, the thermal signal of the read-back signal usually has a frequency in the range of 10 KHz to about 100 KHz. It should be noted that a high pass filter with a cutoff frequency of about 500 KHz significantly distorts the amplitude and phase of the thermal component of the readback signal. However, the magnetic signal component of the read-back signal is still unaffected by the high frequency pass filter. This is because the frequency range of the magnetic signal is approximately 20 to 40 times the cutoff frequency of the high frequency pass filter. Figures 23 (a) and 23 (b) show graphs showing the magnitude and phase response of a typical AE module 202 high pass filter behavior, respectively. This high frequency pass filter has a cutoff frequency of about 500 KHz. The scale and phase response shown in Fig. 23 and the transfer function for a high frequency pass filter with a single pole of 500 KHz can be defined as follows. Bh (1) + Hb (2) z-1 H = .. 1 + ah (2) z-1 During the ceremony: bh (1) = .9876 bh (2) =-.9876 ah (2) =-.9752 The amplitude and phase distortion of the thermal signal caused by the high pass filter of the AE module 202 is effectively eliminated by using an inverse filter with a transfer function opposite to that of the high pass filter. When the read-back signal output from the AE module 202 is passed through an inverse filter, the thermal signal is restored to its original form in both amplitude and phase. For example, the transfer function of the inverse filter for adjusting the condition of the read-back signal that has passed through the high-pass filter having the transfer function of the above equation [1] is as follows. 1 + ah (2) z-1 H-1 = .. Bh (1) + bh (2) z-1 The scale and phase response of the high frequency pass filter of AE module 202 and the above inverse filter are shown in FIGS. 24 and 25, respectively. In particular, the scale responses of the inverse filter and the high pass filter of the AE module 202 are shown in Figure 24 as curves 570 and 572, respectively. The phase responses of the inverse filter and the high pass filter are shown as curves 576 and 574, respectively. The infinite impulse response (IIR) filter of one embodiment is programmed to respond as an inverse filter to restore the thermal content of the high pass filtered readback signal. Although analog filters can be used in alternative embodiments, IIR filters are suitable for use as inverse filters to restore the amplitude and phase of thermal signals distorted by the high frequency pass filter behavior of the AE module 202. It brings several advantages. The signal flow diagram shown in FIG. 26 represents a first-order IIR filter configured as an inverse filter. The coefficients related to the signal flow diagram of Fig. 26 for the first-order IIR inverse filter having the transfer function shown by the above equation [2] are as follows. a1 = .9876 a2 =-.9876 b1 = .1 b2 =-.9752 FIG. 28 shows three waveforms demonstrating the effectiveness of the inverse filter to restore the original amplitude and phase of the thermal component of the readback signal passed through the high pass filter. FIG. 28 (a) shows the read-back signal detected from the pit on the surface of the data storage disk. The read-back signal shown in FIG. 28 (a) is detected from a track written at a write frequency of 20 MHz. This read-back signal is sampled at 100 MHz with an 8-bit resolution. The graph shown in Fig. 28 (b) shows the peak-to-peak scale calculated for the read-back signal in Fig. 28 (a). Therefore, the signal shown in FIG. 28 (b) represents the magnetic interval signal 560, which clearly indicates the loss of the magnetic signal due to the MR reading element passing over the pit. FIG. 28 (c) shows the thermal signal component of the read-back signal after passing through the high frequency pass filter 550 of the AE module 202. The fact that the magnetic spacing information and the thermal spacing information do not correspond closely to each other due to the distortion of the thermal signal component generated by the high frequency pass filter 550, which essentially distinguishes the thermal signal, is shown in FIGS. 28 (b) and 28. It should be understood by comparing the waveforms in Fig. 28 (c). For details on the design, implementation, and programming of IIR filters for use as inverse filters, see "Digital Signal Processing" by ECIfeachor, BW Jervis (Addison-Wesley Publishing Company, Inc., 1993). FIG. 29 shows the thermal spacing signal 562 processed by the inverse filter 556 and the average filter 558, as well as the magnetic spacing signal 560 processed by the digital filter 552 and the logarithmic device 554. However, it should be noted that the linearized magnetic spacing signal 560 is usually calculated by taking the logarithm of the peak-to-peak signal and multiplying it by the known sensitivity of the output voltage change to the well-known Wallace-based magnetic spacing change. In Figure 29, you should see that the magnetic spacing signal 560 and the thermal spacing signal 562 show pits on the disk surface, except that the signal height difference and the time constant associated with the thermal spacing signal 562 are slightly longer. .. Therefore, the integration effect on the inverse filter 556 on the distorted thermal signal shown in FIG. 28 (c) produces the correct thermal interval signal 562. Referring to FIG. 27, the figure shows a system for processing the read-back signal to obtain magnetic and thermal head / disk spacing information in block diagram format. The read-back signal is detected from the disk surface 24 by the MR head 80. The read-back signal is assumed to be a composite signal containing both a magnetic signal component and a thermal signal component. The read-back signal detected by the MR head 80 is communicated to the AE module 202 and then to the high frequency pass filter 550. The high pass filter 550 is shown as an external component of the AE module 202. However, in a common practice, the high pass filter 550 is incorporated into the AE module 202. The transfer function of the high frequency pass filter is shown as H0. The output signal from the high pass filter 550 is sampled by the analog-to-digital converter 551 to produce a digitized sample of the high pass filtered read-back signal. The digitized read-back signal is then communicated to an inverse filter 556 that corrects the distortion caused by the high pass filter 150 of the AE module 202. The transfer function of the inverse filter 556 is shown as H0-1. The averaging of the signals that have passed through the inverse filter 556 is obtained by digital filtering using the averaging filter 558 to generate a thermal signal that is linearly related to the head / disk spacing. The read-back signal obtained on the output side of the analog-to-digital converter 551 also communicates with a digital filter 552 such as a FIR filter that extracts the peak-to-peak amplitude of the read-back signal so as to extract the magnetic signal component from the read-back signal. can do. The logarithm of the magnetic signal is obtained by passing the magnetic signal through the logarithmic device 554, which produces a magnetic signal that is linearly related to the head / disk spacing. The thermal signal can be calibrated by extracting both the magnetic spacing signal 560 and the thermal spacing signal 562, respectively. This is because magnetic calibration is known and depends only on the wavelength of the recorded signal. However, it is important to note that both the magnetic spacing signal 560 and the thermal spacing signal 562 are linearly proportional to the head / disk spacing (y). In order to better understand the various aspects of the present invention, conventional MR heads will be briefly described. The general layout of the basic elements of a typical integrated MR head 600 is shown in Figures 21 and 22. These figures are not drawn to a fixed scale, but are meant to show the relative orientation of the various MR head elements. This MR head contains a pair of shields 601 and 603. The MR element 602 is located between the shields 601 and 603. The MR element 602 operates as a reading element for the MR head 600. The element 603, together with the element 604, forms a thin film magnetic head that functions as a writing element for the MR head 600. Elements 603 and 604 act as the first and second magnetic poles of the thin film writing element, respectively. The dual function of element 603 (ie, acting as the first magnetic pole of the write element as well as the second shield) results in the integrated characteristics of the MR head 600. Insulation layers such as glass (not shown for clarity) are usually formed between the various elements of the MR head 600. As further shown in FIGS. 21 and 22, the first shield 601, MR element 602, and second shield 603 extend upward from surface 501A of disk 501 in their respective vertical planes. ing. For clarity, the second magnetic pole 604 is not shown in FIG. The planes of the various elements are shown parallel to the plane direction in the figure. In these figures, the plane of the first pole / second shield 603 is closest, followed by the MR element 602, and the first shield 601 is the furthest. Negative and positive MR leads 701A and 701B are also shown, respectively. These leads are formed in the plane between the first shield 601 and the first magnetic pole / second shield 603. Leads 701A and 701B are electrically coupled to MR element 602 in a known manner and operate normally. Extension leads 705A and 705B are connected to the leads 701A and 701B, respectively. The extension leads 705A and 705B have connection points 707A and 707B, which are connected to leads 709A and 709B, respectively, which are then connected to the preamplifier module 711. The physical phenomenon that causes the thermal voltage response VTH in the MR head element 602 is that as the instantaneous head / disk spacing increases, the space between the head 600 and the disk surface 101A increases and the MR element 602 heats up. That is. Due to this heating, the resistance of the MR head 600 increases because the temperature coefficient of the material constituting the MR element 602 is positive. For example, as mentioned above, permalloy has a temperature coefficient of + 3 × 10-3 / ° C. When the bias current is constant, the voltage VTH at the resistor of MR element 602 increases. When the MR element 602 approaches the disk surface 501A, the heat transfer generated between the MR element 602 and the disk surface 501A increases, and the MR element 602 is cooled. As a result, the resistance of the MR head 600 decreases, and the voltage VTH of the MR element 602 decreases when the bias current is constant. It should be noted that, of course, various modifications and additions can be made to the above embodiments without departing from the scope or spirit of the invention. For example, this new servo positioning method and device can be used in systems that use optical data discs, or discs with spiral or other non-concentric track configurations. Therefore, the scope of the present invention is not limited to the specific embodiment described above, but is defined only by the complete and justified scope of the claims described below.