KR20010111511A - Dual stage servo controller - Google Patents

Abstract

The servo controller 250 controls the servo system in the disk drive 110. Proportional integrator member 166 receives a target track signal indicative of a target track and a measured track signal indicative of an activity or measured data head position. During the search mode, an output signal based on the measured track signal and the target track signal is provided to the proportional integrator 166. A profile signal based on the output signal from the proportional integrator is provided to the profile generator member 170. The overview actuator 120 is driven based on the profile signal. The filter member 252 is connected to the profile generator 170 and filters the profile signal to provide a filtered profile signal. The fine actuator 127 is driven based on the filtered profile signal.

Description

Dual stage servo controller {DUAL STAGE SERVO CONTROLLER}

Typical disk drives include one or more disks mounted for rotation on a hub or spindle. Conventional disk drives also include one or more transducers that fly on each disk and are supported by air bearings. Transducers and air bearings are collectively called data heads. Conventional drive controllers are used to control a disk drive system based on commands received from a host system. The drive controller controls the disk drive to retrieve information from and store information on the disk.

Typically the actuators operate in a closed loop-loop servo system. Typically the actuator supports the flexure of the flexure assembly, which in turn includes an actuator arm supporting the data head. The actuator moves the data head in a radial direction on the disk surface for a track search operation and secures the transducer directly on the track on the disk surface for a track following operation. Just before starting track following, the state in which the data head is near the target track and finely adjusts the position of the head is called track seating or search seating.

Information is typically stored on the disc by providing a recording signal to the data head to encode the information on the surface of the disc representing the data to be stored. When retrieving data from the disc, the drive controller controls the servo actuator so that the data head can fly onto the disc, sense the disc, and generate a read signal based on the sensed information. The read signal is then decoded by the drive controller to reproduce the data represented by the information stored on the disc, thus appearing as a read signal provided by the data head.

Fine positioning of the data head on the track of the disc is very important when writing data to and reading data from the disc.

In conventional systems, servo operation is based on a dedicated servo head. In the dedicated servo form of the system, the servo information is all written to one dedicated disk surface in the disk drive. All the heads in the disk drive are mechanically coupled to a servo head that accesses servo information. Thus, all heads in the dedicated servo disk drive are located based on servo information read from the servo surface. This type of system facilitates the disk drive to perform parallel read and write operations. In other words, using specific circuitry of the drive controller, read and write operations can be performed using multiple data heads mounted on the actuators in parallel, the data heads being based on servo information read from a dedicated servo surface. Are located at the same time.

However, the track density of magnetic disks has increased over the years. Increased track density on magnetic disks necessitates more sophisticated and advanced positioning solutions. The mechanical offset between the heads in the dedicated servo system can exceed one track width. Thus, the art has shown a tendency to change the embedded servo information in any application.

In an embedded servo system, servo information is embedded in each track on each surface of every disk. Thus, each data head recovers a position signal independent of the other data heads. Thus, the servo actuator positions each individual data head while a particular data head is accessing information on the disk surface. Positioning is done using built-in servo data for the track and the data head moves on the track.

Conventional servo controllers have a proportional-integral-differential (PID) controller comprising two members: an observer and a regulator. The observer receives input position information each time it traverses the servo sector and measures position and velocity. Feedback on the observed signal is then provided to the regulator. In search mode, the regulator typically zeros the error between the reference velocity trajectory and the observed velocity. In the track following mode, the regulator zeroes the error between the desired track position and the observed track position. The regulator controls according to the PID control technique.

However, implementing a PID controller to all disk drives can be difficult. For example, it may be desirable to provide a microactuator between the flexure assembly and the transducer or in the slider assembly or on the actuator arm or on the suspension or in the flexure assembly. Servo actuator systems, provided with a microactuator, receive various inputs from the microactuator in a single input single output (SISO) system where the input is an error signal and the output is a voice coil current signal and the position output is output to the voice coil motor and each microactuator. It can be enhanced with a multiple input multiple output (MIMO) system that provides a signal. This system can also be controlled by simply distributing the PID controller and receiving two target track inputs, providing two outputs, one for the voice coil motor and one for the microactuator. This may indicate a problem. For example, it is difficult to control two actuators with a single controller while maintaining the desired gain and stability for the two control loops during track search as well as track tracking. Messner discusses Schroeck and Messner's systems, on controller design for linear time-invariant dual-input single-output systems. ) Track tracking with a PQ controller.

BACKGROUND OF THE INVENTION The present invention generally relates to servo systems in disc drives, and more particularly to dual stage servo control systems.

1 illustrates a disk drive according to an embodiment of the present invention.

2 shows an actuator assembly according to one embodiment of the invention.

3 shows a head gimbal assembly according to one embodiment of the invention.

4 shows a servo control system.

5 and 6 show partial schematic diagrams consistent with the control system shown in FIG. 4.

7-1 through 7-6 show board plots and phases consistent with the control system shown in FIGS. 4 through 6.

8 shows a block diagram of a control system according to an embodiment of the present invention.

9, 9A and 9B show a more detailed block diagram of the control system shown in FIG.

10-1 through 10-10 show board plots and phase diagrams consistent with the members of the control system shown in FIG.

11-1 through 11-4 are graphs showing the output of the profile generator and the speed and current of the voice coil actuator versus the number of tracks going to the target track.

12-1 and 12-2 show board plots and phase diagrams of each of the delay circuits according to an embodiment of the present invention.

13-1 and 13-2 show board plots and phase diagrams of notched members in accordance with one embodiment of the present invention.

14-1 and 14-2 show board plots and phase diagrams of error functions.

15-20 show graphs of position error samples, track errors, speed profiles, speed tachometer outputs, voice coil motor currents and microactuator voltages, respectively.

The servo controller controls the servo system of the disk drive. During operation of the track search mode, the proportional integrator member receives a target track signal indicative of the target track and a measured track signal indicative of the measured or operating data head position. An external signal based on the measured track signal and the target track signal is provided to the proportional integrator. A profile signal based on the target track signal and the output signal from the proportional integrator is provided to the profile generator member. Coarse actuators are driven based on the profile signal. The filter element is coupled to the profile generator and filters the profile signal to provide a filtered profile signal. The fine actuator is driven based on the filtered profile signal.

1 is a top view of one embodiment of a disk drive 110. The disk drive 110 includes a disk pack 112 mounted on a spindle motor (not shown) by the disk clamp 114. In one embodiment, disk pack 112 includes a plurality of individual disks mounted for simultaneously rotating about central axis 115. Each disk surface where data is stored on the surface has a head gimbal assembly (HGA) 116 mounted to an actuator assembly 118 within the data head or disk drive 110. The actuator assembly shown in FIG. 1 is in a form known as a rotary moving coil actuator and includes a voice coil motor (VCM), shown generally at 120. Voice coil motor 120 rotates actuator assembly 118. In control of the electrical circuitry contained within the disk drive 110, the voicecoil motor 120 rotates the actuator assembly 118 with the HGAs 116 around the pivot axis 121 on the desired data track on the disk surface. Place the HGAs 116 in.

In particular, the actuator assembly 118 is pivoted about the axis 121 to rotate the head gimbal assembly 116 typically along the arc 119 such that each head gimbal assembly 116 has a disk surface within the disc pack 112. It is located on the desired track among the tracks on the screen. HGAs 116 may be moved from a track lying on the innermost radius of the disk to a track lying on the outermost radius. In one embodiment, each head gimbal assembly 116 has a gimbal and the gimbal supports the slider relative to the load beam so that the slider can follow the topography of the disc. This again means that the slider comprises the transducer, which is used to encode information on the disk surface on which the transducer is moving above and to read information from the disk surface. The information can be encoded magnetically, optically, and many others.

2 is a perspective view of the actuator assembly 118. Actuator assembly 118 may include a base portion 122, a plurality of actuator arms 126, a plurality of microactuators 127 (existing between sliders and suspensions, between data heads and sliders, or elsewhere), A load beam 128 and a plurality of head gimbal assemblies or suspensions 116 are provided.

Base portion 122 includes a bore, in one embodiment, the bore is coupled for pivoting motion about axis 121. Actuator arm 126 extends from base portion 122 and is coupled to each first end of one or two load beams 128, respectively. Each load beam 128 has a second end connected to the head gimbal assembly 116.

3 shows an expanded view of one embodiment of the head gimbal assembly 116, although many other embodiments may be used. The head gimbal assembly 116 includes a gimbal 130, which has a pair of struts 132 and 134 and gimbal bond tongues 136. Head gimbal assembly 116 also includes a slider 138 having an upper surface 140 and a lower air bearing surface 142. The transducer is also illustratively located on the leading edge of the slider 138. The particular mounting between the slider 138 and the gimbal 130 is made in any desired manner, such as by mounting the microactuator 127 to the assembly to move the transducer. In summary, in one embodiment, a compliant sheer layer is connected with an adhesive between the top surface 140 of the slider 138 and the bottom surface of the gimbal bond tongue 136. The compliant shear layer allows for relatively horizontal operation between the slider 138 and the gimbal bond tongue 136. The compliant shear layer is, for example, a mylar film having a thickness of approximately 150 microns. The gimbal bond tongue 136 also ends at the trailing edge of the slider 138 with the mounting tab 146 by way of example to provide a surface on which the slider 138 is mounted to the gimbal bond tongue 136. .

4 is a block diagram illustrating the servo control system 150. System 150 illustrates controlling plant 152 corresponding to voice coil motor 120 and microactuator 127 by way of example. In one embodiment, the microactuator 127 is a PZT member. Although many other embodiments can be implemented, the description continues with regard to the implementation of the microactuator as a PZT member.

System 150 also includes PZT driver 154, VCM driver 156, notch filter 158, differentiator 160, summing nodes 162 and 164), proportional integrator (PI), summing node 168 and Profile generator 170. The position error specimen (PES) signal 172 is based on the information read from the disc and indicates the position of the data head in relation to the target track center. PES signal 172 is provided to notch filter 158 to filter notches at a desired frequency and provide notch PES signal 174. Notched PES signal 174 is provided to differential integrator 160, proportional integrator 166 and summing node 164.

A commanded track signal (or cock mark track signal) 176 is provided and carries a track to be accessed on the disc in the disc drive. The commanded track signal 176 is provided to summing node 164 and summing node 168. An output signal 178 based on the notched PES signal 174 and an output from summing node 164 are provided to proportional integrator 166. The output signal from PI 166 is summed with the commanded track signal and provided to profile generator 170. The PES signal 174 is also provided to the differentiator 160 where the differentiated output signal 162 is provided.

The profile generator 170 generates a voice coil motor current profile (or speed profile) based on the distance the data head is from the target track. When the datahead is located far from the target track, profile generator 170 creates a non-linear profile that quickly accelerates the movement of the datahead in the direction of the target track. As the data head approaches the target track, a linear gain is provided to the profile generator 170 corresponding to the distance the data head is away from the target track. This allows the data head speed to slow down as it approaches the target track. The output of the profile generator is provided to the PZT driver 154 and the summation node 162.

This, in turn, provides an output 162 of the summing node to the voice coil motor (VCM driver) 156. PZT driver 154 provides an output signal (example voltage) to the PZT microactuator of plant 152 to drive the microactuator. Similarly, the VCM driver 156 provides an output signal (example current) to the voice coil motor of plant 152 for the voice coil motor to rotate.

Looking differently at control system 150, PZT driver 154, VCM driver 156, plant 152 and differentiator 160 can all be considered as part of a “new” plant, The portion can be shown by the block diagram starting from FIG. The circuit includes a differentiator 160, summing nodes 180, 182, 184, gain blocks 186, 188, 190, 192, 194 and integrators 196, 198, 200, 202. The input of the VCM path may be defined by the I _VCM provided to summing node 180. Block 186 represents the torque constant, etc., as seen in the circuit, and blocks 196 and 198 are integrators that integrate the signal twice and provide to summing node 182. Block 194 represents a demodulation constant and the like, and an output signal Y is provided. Signal Y is fed back to summing node 180 via differential 160. The PZT path is represented by the input voltage V _PZT returning to block 188, which also represents the torque constant. The output 188 of the block is provided to the summing node 184, which in turn is integrated twice through the integrators 200 and 202, and the output is supplied through the summing node 182. The output from integrator 200, which also represents a speed feedback signal, is fed back to summing node 184 via block 190. The output of integrator 202, which also indicates position feedback, is provided to summing node 184 via block 192.

The circuit shown in FIG. 5 can be rewritten as shown in FIG. The K _DS block has been moved to the left of the summation node 180. This is represented by block 204. This removes the differentiator 160 from the feedback path and removes one of the integrators. Block 186 is also slightly modified by including a gain constant K _D therein.

The transfer functions for the VCM path and the PZT path are shown below by Equations 1 and 2:

Equation 1

Equation 2

From the rewritten circuit and transfer function shown in FIG. 6, the sum of the input currents into the VCM path is zero, and the feedback from Y to summing node 180 through integrator 198 affects the PZT signal. In other words, the PZT path, which generally appears as a low pass filter, looks like a differentiator. The integrator in the feedback path to the PZT makes the path appear as a differentiator, so if there is no change in the input signal (as during a long search operation), the PZT signal moves the microactuator relative to the coarse actuator closer to the center. This eliminates the benefit of reduced search time resulting from the microactuator which extends completely in the search direction.

This can be well illustrated with reference to FIGS. 7-1 through 7-6. 7-1 and 7-2 show board plots and phase diagrams for the differentiator 160, respectively. Differentiator 160 introduces 20 dB per 10 unit gain of approximately 7 * 10 ⁴ radians per second at very low frequencies, where the gain is limited. 7-3 and 7-4 show board plots and phase diagrams, respectively, for a VCM path with differential feedback. With feedback from this figure, the VCM path has -20 dB per 10 unit gain outputting approximately 20,000 radians per second, where the slope of the curve switches from -20 dB per 10 units to -40 dB per 10 units. This change in slope is due to the divergence.

7-5 and 7-6 show board plots and phase diagrams for the PZT path. + 20dB per 10-unit ramp continues at approximately 20,000 radians per second.

Since the log width of the transfer function shown in FIGS. 7-5 continues at a rate of 20 dB per 10 units throughout the frequency of approximately 20,000 radians per second, during the next long search operation, the input frequency is transferred to the transfer function of FIG. The point branching down the curve shown in Fig. 5 is reduced, thus providing a reduced gain even while the search operation continues. This effect on the PZT actuator is that as soon as the long search operation is started, the PZT actuator is moved to the longest distance in the search operation direction. However, as the search operation continues, the input frequency will be reduced to the point where the gain provided by the PZT transfer function is reduced and the PZT actuator will move gradually gradually toward the center position relative to the microactuator. This is undesirable because any gain of the reduced search time obtained through the movement of the microactuator is eliminated or reduced.

8 shows a block diagram of another servo control circuit 250 in accordance with an aspect of the present invention. Many blocks are similar to those of FIG. 4, and reference numerals are similar. However, circuit 250 also includes a delay circuit 252 provided in the PZT path. The delay circuit 252 consists of modifying the sensitive response of the microactuator by moving the breakpoints of the board plots shown in FIGS. 7-5 to very low frequencies so that the gain through the PZT path remains constant at very low frequencies. Delay circuit 252 does this by virtually acting as a bandpass filter, with a low corner frequency, and by raising the low frequency components and leading the phase loss. Thus, the control circuit can be performed better during the long search operation.

9, 9A and 9B show a more detailed block diagram of the data system 250 shown in FIG. Corresponding members have similar reference numerals.

Profile generator 170 has a non-linear gain step 256, a gain member 258, and a switch 260. The delay circuit 252 has a gain member 262, a summing node 264, a saturation clipping circuit 266, a delay unit 268, a gain member 270, a summing node 272 and a gain member 274. . The remaining members do not form part of the invention and are referred to briefly in the following description.

The output of summing node 168 is provided to a nonlinear gain step 256. This signal indicates the distance of the read head (or data head) away from the target track. When the read head is at a distance from the target track, the switch 260 switches to the position shown in FIG. 9 and outputs a non-linear velocity profile to quickly accelerate the read head in the direction of the target track. When the read head approaches the target track and is within the track of a predetermined threshold number of target tracks, the switch 260 is switched so that a constant gain member 258 is selected. A constant gain from profile generator 170 is provided when the data head is close to the target track. 11-1 and 11-2 show the response of the nonlinear gain step 256 along two different scales. Two are graphs of input counts versus output counts, where one count corresponds to one track. The output of profile generator 170 is provided to gain member 262 and summing node 162 of delay circuit 252. Summing node 162 also receives the output of differentiator 160 at the inverting input of the summing node and provides the output to the VCM path.

In delay circuit 252, gain member 262 provides a constant gain K to summing node 264 that provides an output signal to saturation circuit 266. In one embodiment, the saturation circuit 266 is provided as an anti-windup circuit. As an example, the saturation circuit 266 is a clipping circuit that clips the signal level received from the summing node 264 just below the level at which the PZT driver 154 is saturated. The clipped output of saturation circuit 266 is provided to delay circuit 268 and summing node 272. Delay unit 268 provides a feedback output, via constant gain member 274, to summing node 264. The output of delay unit 268 also provides to the inverting input of summing node 272 via a constant gain member 270. The output of summing node 272 is provided to PZT driver circuit 154.

10-1 and 10-2 are diagrams of board plots and phases for delay circuit 252, respectively. This figure shows that the log width of the delay circuit 252 transfer function has -20 dB per 10 units of slope at the relevant frequency.

10-3 and 10-4 are for the transfer function from the input of the gain member 262 (ie, the input of the delay circuit 252) to the output of the notched PES filter 158, which is included in the feedback path. The board plot and phase diagram are shown with a differentiator 160, assuming that the transfer function of notch filter 158 sums up simply canceling the sway mode in the PZT microactuator. The logarithmic width of the transfer function is constant at very low frequencies such that the microactuator hardly responds to the gain frequency so that the gain remains at a low frequency.

As the PZT microactuator approaches saturation, the residual circuit simplifies the VCM path. 10-5 and 10-6 are respective open loop board plots and phase diagrams for the VCM path. The board plots shown in Figures 10-5 show that this path is stable. Thus, even if the PZT actuator is saturated, the controller will be stable.

As mentioned in the background, Messner noted that for a dual stage actuator, in order for the two paths to interfere structurally, the two paths must have a phase difference less than 120 degrees at the point where the two paths have approximately the same gain. . According to the circuit of the present invention, the output of the switch 260 has two paths, one through the PZT path and one through the VCM path. At low frequencies, the VCM path dominates. At intermediate frequencies (approximately 2500 radians per second), the two paths have approximately the same gain. In this regard, the phase difference between the two paths should be less than approximately 120 degrees to obtain structural interference. On each of these frequencies, the PZT path is dominant. 10-7 and 10-8 show board plots and phase diagrams for the transfer function from the output of switch 260 to the output of notch filter 158. Both paths are driven simultaneously and a suitable phase margin is obtained.

A full open loop board plot for circuit 252 is shown in FIGS. 10-9 and a phase diagram is shown in FIGS. 10-10. At the 0 dB crossover point, there is a significant amount of phase margin. Thus, the present invention is provided to prevent termination (or saturation) of the PZT driver, and to modify the sensitive response of the PZT path to accommodate long search operations, which is less than 120 degrees. At the 0 dB crossover point, the phase difference between the VCM and PZT paths is provided. The residual circuit member can be described simply. 9 shows that differentiator 160 includes summing nodes 300, 302, gain members 304, 306 and delay unit 308. Board plots and phase diagrams for the differentiator 160 are shown and described above.

PZT driver 154 includes a quantizer 310, a digital analog (DAC) gain stage 312, a zeroth order fixed circuit 314, and an active driver circuit 316. Quantizer 310 quantizes the input from delay circuit 252 and provides it to driver 316 through gain stage 312 and zero order lock circuit 314. The driver 316 converts the digital input signal into an analog voltage output signal and provides it to a PZT microactuator. The VCM driver 156 includes a quantizer 318, a DAC gain member 320, a zero order lock circuit 322, and an active driver 324. These members operate in a similar manner as the members 310, 312, 314 and an analog signal is applied to the VCM.

Proportional integrator 166 includes a switch 330, summing nodes 332, 334, 336, a number of input circuit steps 338, 340, 342, switches 350, 352, a gain member 354, and a delay member 356.

11-3 and 11-4 show the distance versus speed and current of the read head from the target track. In proportional integrator 166, switches 330, 350 and 352 are configured to accommodate three different loops for track search, track seating and track following. For the track following mode, the switch 260 of the profile generator 170 selects a constant gain member 258. Switch 352 selects the output of gain member 354, and switch 350 selects the output of summing node 164. Board plots and phase diagrams for proportional integrator 166 are shown, respectively, by FIGS. 12-1 and 12-2.

In track seating mode, switch 260 selects the output of constant gain member 258, switch 352 selects the zero input and switch 350 selects the zero input. The switch 330 applies a bias value to the unit delay 356. The bias value initializes proportional integrator 166 with cable bias so that it can be easily applied during the track following mode.

In the track search mode, the switches are set the same as in the track seat mode except that the switch 260 selects the output of the nonlinear gain stage 256 instead of the constant gain block 258. Input steps 342 and 343 are also identical and represent the desired track position (or target track signal) in the diagram shown in FIG. The remaining two step functions 340 and 338 place the proportional integrator 155 within the above mentioned configuration for searching, seating and track following.

Notch filter 158 operates in a known manner and filters arbitrary frequencies (eg, frequencies associated with microactuator sway) from the PES signal. 13-1 and 13-2 show board plots and phase diagrams for notch filter 158.

14-1 and 14-2 show board plots and phase diagrams for error functions. The logarithmic width of the error function is very monotonous, from about 2000 radians per second to about 10,000 per second, and actually remains negative at about 17,000-18,000 radians per second and peaks at about 30,000 radians per second. This performance is a significant improvement over conventional systems.

15-20 are time domain plots for the Example 100 track search operation. This step is initiated at one millisecond represented on all plots 15-20. 15 shows a position error sample (PES) of tracks plotted against time in milliseconds. 16 shows the track error of track increment plotted against time in milliseconds. 17 shows the speed characteristic of the data head in tracks per second over milliseconds of time. FIG. 18 shows the speed tachometer output in tracks per second plotted against time in milliseconds. FIG. 19 shows voice coil motor current plotted against millisecond time, and FIG. 20 shows PZT voltage plotted against time in millisecond. Saturation of the PZT voltage, which means that the microactuator is fully extended, can be seen in FIG. 20. Thus, the microactuator first reaches the track and then slowly pulls the reminder of the general actuator onto the center of the target track.

In the present invention, the servo controller controls the servo system in the disc drive 110. Servo system 250 has an overview actuator 120 and at least one fine actuator 127. The actuator is connected to the data head 116 to move the data head 116 (or its transducers) relative to the surface of the disk 112. The servo controller includes a proportional integrator 166 that receives the target track signal and the error signal and, in any mode of operation, provides an output signal based on the error signal and the target track signal. Profile generator 170 provides a profile signal based on the target track signal and, in any mode of operation, the output from proportional integrator 166 with the active or measured track signal. The overview actuator 120 is driven based on the profile signal. The filter member 252 is connected to the profile generator 170 and filters the profile signal providing the filtered profile signal. The fine actuator 127 is driven based on the filtered profile signal.

Notch filter 158 receives a position error signal indicating a difference between the seed position and the target track center and filters the notch frequency to provide an error signal. Differential member 160 is coupled to notch filter 158 and differentiates the error signal. Outline The actuator is driven based on a combination of profile and differential signals.

In one embodiment, the filter element is configured to offset the gain relative to the differentiator through the operating frequency range. In one embodiment, the frequency range is less than or equal to about 20,000 radians per second, and may be from about 7000 to about 12,000 radians per second.

In one embodiment, the differentiator 160 has a slope of approximately 20 dB per 10 unit radians per second over the operating frequency range and the filter element 252 has a slope of approximately -20 dB per 10 unit radians per second over the operating frequency range.

The fine actuator 127 includes a fine actuator driver 154 that receives the filtered signal and drives the fine actuator 127 based on the filtered signal. Filter member 252 includes a clamping member 266 configured to clamp the level of the filtered profile signal based on the saturation level of the fine actuator driver 154.

Although the present invention has been described in connection with the preferred embodiment, those skilled in the art can change the structure and implementation without departing from the spirit and scope of the invention.

Claims (10)

A servo controller that controls a servo system in a disk drive, An overview actuator and at least one fine actuator, the actuators being coupled to the data head to move the data head relative to the disk surface within the disk drive: Receive a target track signal indicative of a target track, a measured track signal indicative of an active head position, and an error signal indicative of a head position relative to the target track, and during the search mode, the measured track signal and the target track A proportional integrator (PI) that is based on the signal and provides a PI output signal based on the target track signal, the error signal and the integral bias signal during the seating mode; A profile generator member for providing a profile signal based on a PI output signal, wherein the general actuator is driven based on the profile signal; And And a filter member coupled to the profile generator for filtering the profile signal to provide a filtered profile signal having a reduced low corner frequency, wherein the fine actuator is driven based on the filtered profile signal. The method of claim 1, A notch filter receiving a position error signal indicative of a distance between the head position and the target track and filtering a notch frequency to provide the error signal; And And a differentiator member coupled to the notch filter and differentially differentiating an error signal to provide a differentiator signal, wherein the general actuator is driven based on a combination of the profile signal and the differentiator signal. The method of claim 2, And the filter member is configured to offset the gain with respect to the differentiator through an operating frequency range. 4. The servo controller of claim 3 wherein the operating frequency range is less than or equal to approximately 20,000 radians per second. 5. The servo controller of claim 4 wherein the operating frequency range is about 7000 radians per second to about 12000 radians per second. The micro actuator of claim 1, wherein the micro actuator includes a micro actuator configured to receive the filtered profile signal and to drive the micro actuator based on the filtered profile signal, wherein the filter member is disposed at a saturation level of the micro actuator driver. And a clamping member configured to clamp the level of the filtered profile signal based thereon. 4. The method of claim 3, wherein the differentiator has a slope of approximately 20 decibels per 10 units of radian per second over the operating frequency range, and the filter element is approximately -20 decibels per 10 units of radian per second over the operating frequency range. Servo controller having a slope of). 9. The servo controller of claim 8, wherein the filter member comprises a delay circuit. A servo system that controls the positioning of a data head relative to a disk surface on a disk in a disk drive, An overview actuator coupled to the data head to move the data head; A fine actuator coupled to the data head to move the data head in relation to the general actuator; And And a control system having a fine actuator control member and an overview actuator control member, wherein the fine and outline actuator control members comprise the fine and outline actuators during a track search operation at a frequency at which the two fine and outline actuator control members have the same gain. A servo system configured to have a phase difference between the actuator control member outputs to be approximately 120 degrees or less. The system of claim 9, wherein the servo system is Receive a target track signal indicative of a target track and a measured track signal indicative of an active track corresponding to the current head position, and during a track search, a PI output signal based on the measured track signal and the target track signal No proportional integrator (PI) to provide; A profile generator member for providing a profile signal based on the PI output signal, wherein the general actuator is driven based on the profile signal; And And a filter member coupled to the profile generator and filtering to provide a filtered profile signal, wherein the fine actuator is driven based on the filtered profile signal.