Abstract: A system for positioning a read/write head having a voice coil suitable for coarse control and a piezoelectric transducer (PZT) suitable for fine control. A voice coil control signal and a PZT control signal are generated from a position-indicative signal, both receiving power via a shared supply having a nominal rectified voltage V1. In a preferred method, control signals are both applied to the voice coil and PZT when amplified so that each has a saturation voltage smaller than |V1|.

Abstract: An actuator arm assembly is provided in a disc drive. The disc drive includes a disc with a surface for storing information and a first actuator for moving the actuator arm assembly relative to the surface of the disc. The actuator arm assembly includes an actuator arm coupled to the first actuator, a load beam coupled to the actuator arm, a suspension coupled to the load beam and an air bearing coupled to the suspension. A transducer is mounted on the air bearing and positioned to access the surface of the disc. A second actuator is coupled to the air bearing and the load beam and is controllable to move the air bearing relative to the surface of the disc and relative to the load beam.

Abstract: A head positioner has a configuration employing a dual-stage actuator method, wherein positioning control is performed for a write/read according to cooperative operations of a coarse actuator and a fine actuator, and the fine actuator is configured using a piezoelectric device. A positioning control unit for controlling the coarse actuator and the fine actuator is configured to include a coarse control system including a coarse drive unit for driving the coarse actuator and coarse control unit for controlling the coarse drive unit, a fine control system including a fine drive unit for driving the fine actuator and a fine control unit for controlling the fine drive unit. In addition, a driving-signal limiting unit is provided. The piezoelectric device is prone to property deterioration because of erosion due to an electrochemical reaction.

Abstract: A method and apparatus are provided for testing a microactuator that forms part of a suspension assembly in a disc drive. The method and apparatus test the microactuator before placing the suspension assembly in a disc drive. In the invention, the head is positioned over a track on a disc based in part on servo information read from the disc. At least one input signal is then applied to at last one microactuator on the suspension assembly. Servo information is then read from the disc to determine a change in the position of the head. By comparing the change in the position of the head to the input signal applied to the microactuator, a performance characteristic of a microactuator can be determined.

Abstract: A head position control system for a dual stage actuation disk drive system. A feedback system is provided for modifying a primary and a secondary input command signal to produce primary and secondary error signals. A controller receives the primary error signal and transmits primary actuator arm positioning information to the primary actuator. A secondary controller receives the secondary error signal and transmits secondary actuator arm positioning information to the secondary actuator. The feedback system creates a position error signal (PES) using information from servo wedges and runout information and the PES is used to produce the secondary error signal. The feedback system produces a reconstructed error signal including angular position information for the primary actuator arm by processing a back electromotive force signal from the primary actuator. The primary error signal is produced by modifying the primary input signal with the reconstructed error signal.

Abstract: A disc drive head positioning apparatus includes a head, a suspension which supports the head, a piezoelectric microactuator which is operatively coupled to the suspension, and a charge feedback driver which is operatively coupled to the piezoelectric microactuator. A method of positioning the head relative to a storage medium is also provided.

Abstract: A high bandwidth, large stroke spin-stand for testing components of a disc drive includes a coarse positioning stage and a rotary micropositioning stage. The spin-stand is capable of positioning a transducer head relative to the data storage disc based on one or both of: (1) an angular position of a rotary actuator arm in the rotary micropositioning stage; and (2) servo data read from the data storage disc. The angular position of the rotary actuator arm is detected by an encoder. In one embodiment, position adjustments are based on the detected angular position. In another embodiment, position adjustments are based on servo data read from the data storage disc, but are also conditional on angular position being consistent with the servo data. In yet another embodiment, both angular position and servo data from a track are linearized to generate PES adjustment parameters that are recorded on the data storage disc to redefine the track as more circular or to linearize the PES.

Abstract: The present invention is directed to utilizing the capabilities of multi-stage actuators in disk drives to write servo tracks that have a variable number of tracks-per-inch (TPI) from head to head, thereby improving both the performance of the drive and manufacturing yields. An appropriate TPI for a particular head has been found to depend on a number of factors that vary from head to head. Consequently, the initial step is to determine an appropriate TPI for at least one of the heads or, more preferably, all of the heads in the drive. The determination typically involves measurements such as read and write width measurements and off-track performance tests for the relevant heads. Once an appropriate TPI format has been determined, the servo tracks are written according to the TPI formats using either a servo track writer or self servo track writing.

Abstract: Apparatus and method for positioning a head in a disc drive using a dual stage actuator having a primary actuator motor for coarse head positional control and a microactuator motor for fine head positional control. The microactuator motor includes a strain gauge affixed to a piezoelectric transducer measuring actual dimensional change of the microactuator motor resulting from response by the piezoelectric transducer to a request for head repositioning. A closed loop servo control circuit generates control inputs for the dual stage actuator to carry out track following and seek operations while adjusting head position by correcting piezoelectric transducer hysteresis and reducing seek and settle times.

Abstract: There is provided a technique for controlling drive of a voice coil motor which can select, with priority for effective reduction, any one of heat generation and EMI noise which are presumed to induce a read/write error and for simultaneously realizing the positioning control of magnetic head with higher accuracy during the tracking operation and the high speed access with shortening of the seek operation period. The magnetic disc storage apparatus introducing this technique is provided with a mode to drive with linear control a coil of the voice coil motor from both terminals and a mode to drive one terminal of coil with linear control and the other terminal with pulse width control. Thereby, the coil is driven in the drive mode of linear control during the tracking operation, while one terminal of coil is driven with linear control and the other terminal with pulse width control during the seek operation.

Abstract: Apparatus and method which provide accelerated servo control value calculations for a control processor controlling an actuator maintaining a head adjacent a rotatable disc f a disc drive. A dedicated multiply-accumulate hardware core of a servo micro engine calculates sum-of-products terms common in servo control loops. The multiply-accumulate hardware core uses a pipeline with stages for fetch, read, multiply, accumulate, and write-back as an arithmetic core to fully utilize all of the hardware during every servo interval. Feeding this arithmetic core is a dedicated state memory, from which a first signed servo state and a second signed servo state are read and where calculation results may be optionally written. Another, independent, coefficient memory provides predetermined coefficients used in resolving servo control loop algorithms. A final dedicated instruction memory provides shifter control values and the addresses of the states and coefficients.

Abstract: A method and apparatus are provided for positioning a head over a disc in a disc drive while maintaining servo loop stability. The apparatus includes an actuator-head assembly having a large scale actuator and a micro-actuator that are both able to move the head over the disc. An anti-windup compensation component detects when a micro-actuator controller is producing a micro-actuator control value that will saturate the micro-actuator. Using the micro-actuator control value, the anti-windup compensation component generates a saturation tracking error signal. A summing component then combines a position value that the head generates based on its position over the disc with the saturation tracking error signal to form a position error value that masks the saturation of the micro-actuator.

Abstract: Apparatus and method for generating control inputs for a disc drive dual stage actuator having primary and secondary actuator motors used to maintain a head adjacent a rotatable disc surface. An h-infinity hardware controller generates the control inputs in relation to an actual position signal, a desired position signal and a unique set of coefficients for each selected head. The coefficients are selected by obtaining an output response for each head, selecting the coefficients in relation to the output response for each head, and storing the coefficients in a nonvolatile memory location of the disc drive. The appropriate set of coefficients are thereafter loaded as each head is selected in turn during normal drive operation.

Abstract: A method and system for providing plant variation compensation for a microactuator in a dual-stage servomechanism of a disc drive. The method includes performing indirect adaptive filtering to identify plant variation in the microactuator, and tuning a compensator for the microactuator based on the plant variation. The indirect adaptive filtering can be performed using a two-stage process, including a first stage of adaptive modeling for the dual-stage servomechanism and a second stage of generating an indirect mode-reference inverse for the microactuator. A combined process can alternatively be employed. The microactuator can be a piezoelectric microactuator which forms a PZT system. The dual-stage servomechanism also includes a coarse actuator such as a voice coil motor.

Abstract: A disk drive capable of controlling two or more high-response small-stroke precise-movement actuators and a low-response large-stroke rough-movement actuator to be operated in cooperation with each other so that two or more heads can be fast and precisely positioned at a time by those actuators. The disk drive includes a rough-movement actuator having a stroke enough to cover all disk, a first precise-movement actuator having a small stroke, and a second precise-movement actuator having a small stroke, wherein a head is positioned at a track on a disk surface by the first precise-movement actuator, at the same time a head is positioned at a track on a second disk surface by the second precise-movement actuator, and the rough-movement actuator is operated to follow and to be brought to a center position between the located heads.

Abstract: A micro-actuator of a head suspension either is wired in a reverse polarity to effect movement of the suspension arms in opposing directions relative to the magnetic disks or reversed in physical orientation and wired identically. This permits a single micro-actuator control signal to control all micro-actuators and thereby cancel the affects of inertia of the suspension arms and the read/write heads on the actuator arms as half of the suspension arms and magnetic heads move in one direction while, simultaneously, the other half of the suspension arms and magnetic heads move in a second, opposite direction in response to a single control signal, simplifying wiring and control electronics. The counter-movement of the suspension arms and magnetic counter the inertia and inertial forces and expedite the settling into their stable recording/reading positions, thereby reducing seek times and improving disk drive performance.

Abstract: A head retraction circuit receives a retraction signal from a microprocessor and sequentially turns on first and second drivers connected across a voice coil motor (VCM) winding of a hard disk drive system. The retraction circuit generates a first control signal to turn on a first driver in response to receiving the retraction signal and generates a second control signal to turn on the second driver a predetermined time interval after receiving the retraction signal. The retraction circuit thereby provides current to the VCM winding to retract a head to a safety zone of a disc after the predetermined time interval so that any momentum in the VCM has substantially dissipated prior to retracting the head.

Abstract: A method and apparatus are provided for positioning a head over a disc in a disc drive while maintaining servo loop stability. The apparatus includes an actuator-head assembly having a large-scale actuator and a micro-actuator that are both able to move the head over the disc. A saturation adjustment component detects when a micro-actuator controller is producing a micro-actuator control value that will saturate the micro-actuator. Using the micro-actuator control value, the saturation adjustment component generates a saturation error value. An adaptive anti-windup circuit transfers control to the large-scale actuator when the saturation error value is generated by the saturation adjustment component.

Abstract: A sensor system for a disk device by using a floating head, comprising a head element that floats over a data recording area of a rotating disk so as to write data thereon or read data therefrom, a first actuator for moving the head element over the data recording area of the disk, and a second actuator supported by the first actuator and supporting the head element for precisely positioning the head element against the data recording area of the disk. The sensor system is capable of detecting any contact between the disk and the head element by utilizing a signal generated by the second actuator when the disk contacts the head element during an operation of the disk.

Abstract: In the magnetic disk unit comprising suspensions in each of which an IC is mounted on a load beam, a magnetic head displacement caused by the warp of the load beam occurring due to heat generated from the IC is compensated, whereby the shortening of an access speed and high reliability of reading/writing are realized. The thermal displacement of the magnetic head is compensated by operating micro actuators on the load beam in accordance with the temperature rise of the IC which is measured by a temperature sensor. Namely, by driving the micro actuators so that the magnetic head may move in a direction reverse to the direction of the magnetic head movement caused by the thermal displacement, the thermal displacement of the magnetic head is made to be substantially zero.

Abstract: The present invention is directed to a disk drive that utilizes a multi-stage actuator associated with two or more heads that are each associated with a separate disk surface to realize high speed data transfers. In one embodiment, the multi-stage actuator is used to simultaneously transfer portions of a data file between the heads and the associated disk surfaces and to perform simultaneous seek operations for the heads between data transfer operations. In another embodiment, the multi-stage actuator is used to alternatingly transfer portions of a data file between the heads and the associated disk surfaces and to perform alternating seek operations for the heads such that one head is transferring data while another head is performing a seek operation.

Abstract: An actuator control system for a two-stage actuator system of a disc drive has a first, or primary, stage actuator consisting of a voice coil motor that positions the head relative to a disc and a microactuator that alters the actuator system without operation of the voice coil motor. A control loop includes a controller responsive to seek commands to operate the voice coil motor, thereby moving the head relative to the disc. An active damping circuit is coupled to the head to operate the microactuator to damp resonance modes of the actuator system.

Abstract: A hard disk drive system (10) includes a rotating magnetic disk (16), and a support arm (22) which is supported for movement relative to the disk under control of a voice coil motor (21). a microactuator (26) supports a read/write head (27) on the support arm for movement relative thereto a control arrangement (13) controls the voice coil motor and the microactuator in response to position information (31), which is read by the read/write head from the disk and which indicates the position of the read/write head relative to the disk. The system is free of a sensor for detecting the actual position of the support arm relative to the read/write head or the disk.

Abstract: The position information of the magnetic head is generated also from the data area to improve the positioning accuracy. The magnetic disk drive has a function of oscillating the magnetic head in the radial direction in the data area at a specific frequency and a function of detecting a read signal during the execution of the oscillation function and detects position information of the magnetic head from the detected read signal. The magnetic head position control can be performed in the data area. The magnetic head position signal not dependent on the frequency of a sampling signal generated from the servo information area can be generated. This in turn improves the data recording density and allows a highly precise position control of the magnetic head, thus improving the reliability of the magnetic disk drive.

Abstract: The frequency rectification filter, in principle, measures an amplitude and phase of a particular frequency and compresses the frequency. Accordingly, if no initial value is present, it is necessary to take a time more than one turning cycle. Consequently, no effect can be seen immediately after the rise of an apparatus, and head positioning takes much time. The object of the present invention is to reduce this time. According to the present invention, a state amount of the frequency rectification filter is stored in memory before unloading the head from the disc, so that at apparatus rise, the spindle rotation angle is matched so as to operate the filter, thus increasing the speed of the rise of the effect of the frequency rectification filter. Thus, the risa of the frequency entire apparatus can be performed rapidly.

Abstract: A magnetic disk tester has a head clamp (35, 218) to position a magnetic head (15, 289). The head clamp has a micromotion stage (55, 273) provided with a stage (59, 205) which is horizontally moved by a piezo-element (77). The magnetic head is attached to the piezo-stage (55, 273).

Abstract: A method is used for moving a transducing head between tracks of a disc in a dual-stage actuation assembly. The dual-stage actuation assembly has a main actuator for coarse positioning of the transducing head and a microactuator for fine positioning of the transducing head. The method comprises accelerating the main actuator during coarse positioning of the transducing head and applying control pulses to the microactuator during coarse positioning by the main actuator to eliminate oscillation of the microactuator during and after coarse positioning.

Abstract: A head drive device for positioning a read and/or write head for reading and/or writing information to and from a disk coated with a recording medium, the head drive device including a carriage, a main actuator for moving the carriage, a plurality of heads for reading and/or writing information to and from the disk, and a vibration control portion comprising a plurality of micro-actuators positioned between the carriage and the heads, such that when the main actuator and a first micro-actuator are driven to enable precise positioning of a desired head with respect to a surface of the disk a second micro-actuator is driven so as to offset vibrations generated at the carriage by the operation of the desired micro-actuator.

Abstract: An apparatus and method for sensing the position of a read/write head or transducer carried by a microactuator at a distal end of a primary actuator in a head disc assembly of a disc drive. The position sensing system has a fixed member attached to the primary actuator and a moveable member attached to the fixed member by an attachment device. The attachment device permits the moveable member to move in relation to the fixed member along a predetermined pathway. A secondary voice coil motor (VCM) drives the movement of the microactuator via a VCM coil that is affixed to the moveable member, wherein a high frequency signal is applied to the VCM coil. At least one sense coil is attached to the fixed member and positioned near the VCM coil, such that the sense coil will receive a portion of the high frequency signal transmitted from the VCM coil through mutual magnetic coupling.

Abstract: By increasing the gain of a controller for coarse motion CFBV within a frequency band in which the gain of a sensitivity function SP=1/(1+PP·CFBP) of fine motion actuator DP and controller for fine motion CFBP exceeds 0 dB, the gain of a sensitivity function SV=1/(1+PP·CFBV) of coarse motion actuator PV and coarse motion controller CFBV is decreased. Through this, in a two-stage actuator control system, a disk apparatus can be provided in which a sensitivity function SPES=1/(1+PP·CFBP)·1/(1+PP·CFBV) indicative of a disturbance compressive ratio in a signal path ranging from disturbance components to a head position error signal is rendered to be 0 dB or less at all frequencies concerned.

Abstract: An actuator driving method and an actuator driving device for PWM-driving an actuator of a storage disk device are disclosed. This method and device prevent a servo signal from being overlapped with switching noises. The storage disk device includes a head for reading information from a storage disk, a PWM driver for generating a drive current having a pulse width corresponding to a current indication value, a linear driver for generating a drive current of which a magnitude corresponds to the current indication value, an actuator, driven by the drive current, for moving the head, and a control circuit for generating the current indication value for positioning the head from the servo information read by the head from the storage disk. The driving method includes a step of PWM-driving the actuator by the PWM driver, and a step of effecting a switchover from the PWM drive to a linear drive by the linear driver during a period for which the control circuit reads the servo information.

Abstract: To provide head-positioning system which can control tracking movement of the magnetic head reliably and smoothly with a high speed, enlarging the controllable frequency band of a fine tracking actuator by suppressing interference between the fine tracking actuator and a main actuator (27), a head-position control circuit of the head-positioning system comprises: a phase compensating controller (31) for obtaining deviation information of the read/write head relative to a designated position from the positional information (S12) detected by the read/write head, and generating a positioning correcting signal (S31) for feedback-controlling the fine tracking actuator to drive the slider supporting spring (22) with a torque value to make the read/write head follow the designated position, according to the deviation information (S12); and a vibration suppressing controller (32) for forward-controlling the main actuator to maintain an angular position of carriages (25) to be fixed by controlling the main actuator (2

Abstract: A disc drive including a rotatable data track, a dual-stage actuator with a primary actuator motor supporting an actuator arm, a read/write head supported by the actuator arm and communicating with a secondary actuator motor, and steps for controlling range of motion of the secondary actuator motor. The controlling steps include supplying and sustaining a bias signal to a single-sided unipolar device driver that then apply a bias voltage the secondary actuator motor to induce the secondary actuator motor to expand substantially one half of its expansion capabilities. And, confining correction signals provided by a control circuit of the disc drive, used in correcting mechanical position of the secondary actuator motor, to a voltage ranging substantially between a positive “+” and negative “−” voltage substantially equal to the applied bias voltage.

Abstract: A disc drive having a voice coil actuator with an attached suspension and head, the head including a micro-actuator. The micro-actuator having at least one natural frequency and at least one natural frequency time period. The voice coil actuator is adapted to attenuate a resonance of the micro-actuator at the at least one natural frequency using a stepped acceleration.

Abstract: A method and apparatus for controlling the position of a computer hard disk drive transducer head are provided. According to the invention, an initial value compensation scheme is applied to a signal derived from available states of the transducer head when the control mode of the disk drive switches from a track seek mode to a settling mode. In particular, at least portions of a the compensation signal are provided to both a coarse actuator and a microactuator associated with the transducer head. According to one embodiment of the present invention, high frequency components of the compensation signal are generally provided to the microactuator, while low frequency components of the compensation signal are generally provided to the coarse actuator. The method and apparatus of the present invention provide a computer hard disk drive having improved performance due to reduced settling times and improved audible characteristics.

Abstract: A system for positioning a transducing head in a disc drive device over a selected track of a rotatable disc includes an actuator arm which is rotatable about an axis, a head suspension mechanism connected to the actuator arm, and a slider carrying a transducing head and supported by the head suspension mechanism. A low resolution motor moves the actuator arm about the axis to effect coarse movement of the head between tracks of the disc. A piezoelectric element is embedded in the actuator arm to distort the arm to effect fine positioning of the head. Control circuitry distributes electrical signals to the low resolution motor and the piezoelectric element to selectively control movement thereof. The piezoelectric element is embedded in the actuator arm by removing a predetermined amount of material from the actuator arm and bonding the piezoelectric element in the resulting space in the actuator arm.

Abstract: A driving section of a head actuator mechanism rotatably supporting a magnetic disk includes a voice coil, and a piezo-electric element for cutting off a resonance resulting from a drive of the voice coil. The driving section is arranged on a side opposite to an arm across a rotational axis of the head actuator mechanism. The voice coil and the piezo-electric element are held by a holding frame which is molded of a resin integrally with these voice coil and piezo-electric element.

Abstract: In a disk drive having a dual stage actuator, a method to improve head switching time by aligning a target head with a target track before a head switch occurs by using a second stage actuator attached to the target head to align the target head with the new track. The radial offset required to align the target head with the target track is either calibrated at startup or is measured dynamically during normal disk operations. A dual stage actuator with either a milli-actuator second stage or a micro-actuator second stage, positions a read/write head over a disk surface. The disk drive has a radial offset table for storage of radial offsets for head switches.

Abstract: In a magnetic recording device, a control element placed on a flexible wiring board between a control device and first actuators includes a plurality of actuator-driving-signal connecting terminals connected to a plurality of second actuators, an actuator-driving-signal input terminal to which driving voltage for the second actuators is input from the control device, connecting wires for connecting the actuator-driving-signal input terminal to the actuator-driving-signal connecting terminals, signal selection elements incorporated in the connecting wires, and a decoder for selecting one of the signal selection elements so that a specific actuator-driving-signal connecting terminal is connected to the actuator-driving-signal input terminal.

Abstract: A dual-stage disc drive actuation system for positioning a transducing head over a selected track of a rotatable disc having a plurality of concentric tracks includes a low resolution actuator and a high resolution microactuator. An input circuit provides a signal corresponding to the selected track. The actuator and microactuator are then operated to position the head over the selected track. The dual-stage actuation system positions the head over the selected track without significant off-track error within about 0.5 milliseconds for a track density of at least about 12,000 tracks-per-inch.

Abstract: A magnetic storage system having one or more rotating disks is disclosed. In a preferred embodiment, each rotating disk has two magnetic surfaces which each contain a number of tracks. Each track has one or more data regions and one or more embedded servo sectors. First and second transducers are respectively suspended over first and second tracks corresponding to first and second magnetic surfaces. The second transducer determines an off-track position with respect to the second track by reading from the data region of the second track. Once the off-track position is determined for the second transducer, that information is used to position the first transducer with respect to the first track and position the second transducer with respect to the second track as the first transducer writes to the first track. Furthermore, the first transducer is positioned at a correction rate that exceeds the rate at which the first transducer encounters embedded servo sectors in the first track.

Abstract: A magnetic disk apparatus includes head bases placed one on another and supported for pivotal motion on a common pivot shaft, and sliders provided at free ends of the head bases and having magnetic heads mounted thereon with suspensions interposed therebetween, respectively. A coil for a voice coil motor serving as a first driving apparatus is provided on the opposite side to the sliders with respect to the pivot shaft. Second driving apparatus formed from piezoelectric elements and hinges are provided between the pivot shaft and the sliders. For faces of a plurality of magnetic disks, recording and/or reproduction operations can be performed simultaneously by integral tracking control of the sliders by the first driving apparatus and individual tracking control of the sliders by the second driving apparatus.

Abstract: A magnetic disk device comprises at least a disk having information, at least a head for reading or writing information from or into the disk, at least a micro actuator for supporting said head and positioning said head, a coarse actuator for carrying the micro actuator and positioning the head, a controller for controlling the micro actuator and the coarse actuator based on the servo information read by the head, and a host controller for determining that information is to be read. In the case where the host controller determines that the operation is in wait mode, the positioning operation of the micro actuator is stopped.

Abstract: An apparatus and method for reducing the number of interconnections in a disc drive through microactuator control and write current signal superpositioning. The disc drive includes a rotatable disc on which a plurality of tracks are defined and an actuator assembly supporting a read/write head having a write element. An actuator motor provides coarse (primary) positional control of the head and a microactuator disposed adjacent the head provides fine (secondary) positional control. A filter circuit is operably coupled between the write element and the microactuator and receives, by way of a common set of conductors, a combined signal comprising high frequency write current signals superimposed upon lower frequency microactuator control signals. The filter circuit filters the combined signal so as to pass the low frequency microactuator control signals to the microactuator and pass the high frequency write current signals to the write element.

Abstract: A hard disk drive system (10) includes a rotating magnetic disk (13), an arm (16) moved by a voice coil motor (18), and a read/write head (21) movably supported on the arm by a microactuator (22). The read/write head is moved approximately radially of the disk in response to operation of the microactuator or movement of the arm. The microactuator has a nonlinear transfer function. A control system (62) for controlling the microactuator and the voice coil motor includes a control technique (126) having a nonlinear transfer function which is substantially an inverse of the nonlinear transfer function of the microactuator. Control of the microactuator is effected through the control technique, the control technique linearizing the control of the microactuator.

Abstract: A disk drive system includes a servo system for driving mechanical parts, including a read/write head, to a desired track on a disk. The mechanical parts undesirably resonate at a frequency f, where f is a function of a temperature t of those mechanical parts. The servo system includes a notch filter responsive to an indication of temperature t, to attenuate the amplitude of frequency f in a broadband control signal that is applied to move the mechanical parts.