Method of manufacturing a disc device and program product

Abstract

A method and procedure for manufacturing a disk device capable of improving head positioning accuracy in a disk device controlled by multi-rate actuators using two-stage actuators are provided. In this embodiment, before applying an additional MA filter, a test signal is applied at 1 / N cycles to measure the head position error spectrum and frequency characteristics for both the VCM and MA operation values. Based on the frequency characteristics, a multi-rate sensitivity characteristic is calculated, and the frequency to be corrected by the MA filter is determined based on the head position error spectrum and the multi-rate sensitivity characteristic. Furthermore, with each candidate of a plurality of MA filter candidates applied, a test signal is applied at 1 / N cycles to measure the frequency characteristics for both the VCM and MA operation values. Based on the frequency characteristics, a multi-rate sensitivity characteristic is calculated, and the candidate with the lowest head position error and a peak value of the multi-rate sensitivity characteristic below a threshold is selected as the MA filter to be used.

Description

[0001] This application enjoys priority based on Japanese Patent Application No. 2022-144372 (filed on September 12, 2022). This application incorporates the entire contents of the basic application by reference. Technical Field

[0002] The embodiments of the present invention relate to a method and procedure for manufacturing a disc device. Background Technology

[0003] Generally, disk drives, such as hard disk drives, include a controller (software) for positioning a head, such as a read / write head, on the target position on the disk, which serves as the recording medium, i.e., on the track to be accessed. The head then performs data read / write operations at the positioned position on the disk.

[0004] In addition, in recent years, research and development of so-called two-stage actuators has been underway in the field of disc actuators. This involves using a voice coil motor (VCM) to move an arm with a head at its front end, and a micro-actuator (MA) located at the front end of the arm to move the head minutely. In this case, the controller is divided into a controller for the VCM and a controller for the MA.

[0005] In addition, research and development are underway on multi-rate control of the VCM and MA, which controls the disk device of the two-stage actuator by multiples of the observation period of the position error signal (PES) (N is an integer greater than 2).

[0006] However, in the existing technology, the positioning accuracy of the head in disk devices controlled by two-stage actuators at multiple rates is still insufficient and there is room for improvement. Summary of the Invention

[0007] This embodiment provides a method and procedure for manufacturing a disk device that can improve the positioning accuracy of the head in a disk device controlled by a two-stage actuator at multiple rates.

[0008] This embodiment relates to a method for manufacturing a disk device, the disk device comprising: a disk for storing data; a head for reading / writing data relative to the disk; a first actuator for moving an arm to which the head is disposed as a whole; a second actuator disposed at the front end of the arm for moving the head; a first controller for controlling the first actuator at a multi-rate of 1 / N periods (N being an integer greater than or equal to 2) as the head position observation period, based on the target position of the head; a second controller for controlling the second actuator at the same 1 / N periods, based on the target position of the head; and a first additional filter attached between the first controller and the first actuator, outputting output data to the first actuator based on input data from the first controller. The manufacturing method includes the following steps: before attaching the first additional filter... In the first additional filter, the arithmetic unit applies test signals at 1 / N cycles to measure the head position error spectrum and frequency characteristics for the operation amounts of the first actuator and the second actuator, respectively; calculates multi-rate sensitivity characteristics based on the frequency characteristics; and determines the frequency that should be corrected by the first additional filter based on the head position error spectrum and multi-rate sensitivity characteristics. In the second additional filter, with each candidate among multiple candidates of the first additional filter attached, the arithmetic unit applies test signals at 1 / N cycles to measure the frequency characteristics for the operation amounts of the first actuator and the second actuator, respectively; calculates multi-rate sensitivity characteristics based on the frequency characteristics; and determines the candidate whose peak value of the multi-rate sensitivity characteristics is below a threshold and has the smallest head position error as the first additional filter to be used. Attached Figure Description

[0009] Figure 1 This is a block diagram of a feedback control system for a disk device with a two-stage actuator in the prior art.

[0010] Figure 2 This is an illustration of a method for measuring the sensitivity characteristics of a disk drive with a two-stage actuator in the prior art.

[0011] Figure 3 This is a diagram schematically illustrating the configuration of a disk device according to an embodiment.

[0012] Figure 4A This is an explanatory diagram of the method for measuring the sensitivity characteristics of the disk device in the embodiment.

[0013] Figure 4B This is an explanatory diagram of the method for measuring the sensitivity characteristics of the disk device in the embodiment.

[0014] Figure 5 This is a block diagram of the feedback control system for the disk device in the implementation method.

[0015] Figure 6 This is a diagram showing the four modes of the MA additional filter candidates in the implementation method.

[0016] Figure 7 This is a flowchart illustrating the generation process of the MA-added filter when the maximum gain value of the multi-rate sensitivity characteristics in the implementation is below a threshold.

[0017] Figure 8 This is a flowchart illustrating the generation process of the MA additional filter when the maximum gain value of the multi-rate sensitivity characteristic in the implementation method is greater than a threshold.

[0018] Figure 9 This is a graph showing the head position error spectrum before and after the design of the MA-added filter in the implementation method.

[0019] Figure 10 This is a graph showing the single-rate sensitivity characteristics of the MA-added filter before and after design in the implementation method.

[0020] Label Explanation

[0021] 1. Disc; 2. Head; 3. Arm; 4. VCM; 9. Signal processing circuit; 10. Position detection circuit; 11. CPU; 12. ROM; 13. Controller; 14. VCM drive circuit; 15. MA drive circuit; 17. Vibration sensor; 18. A / D conversion circuit. Detailed Implementation

[0022] Hereinafter, with reference to the accompanying drawings, embodiments of the manufacturing method and procedure for the disk device of the present invention will be described. Furthermore, the present invention is not limited to the following embodiments. To facilitate understanding of the embodiments, the prior art will first be described again.

[0023] (Prior art)

[0024] Figure 1 This is a block diagram of the feedback control system (software) for a disk device with a two-stage actuator in the prior art. Figure 2 This is an illustration of a method for measuring the sensitivity characteristics of a disk drive with a two-stage actuator in the prior art.

[0025] like Figure 1 As shown, the VCM control object Pv and the MA control object Pm are arranged side by side. A VCM controller Cv is set for the VCM control object Pv, and an MA controller Cm is set for the MA control object Pm. The symbols Mv and Mm represent the implementation of a more than 2x rate control. Furthermore, feedback control corresponding to the target position T of the head is performed by the VCM controller Cv and the MA controller Cm. In addition, sometimes an additional filter is added in parallel to the MA controller Cm.

[0026] Next, refer to Figure 2 This paper describes a method for measuring the sensitivity characteristics of a two-stage actuator disk device. A single PES test signal ST, containing multiple frequencies such as a swept-frequency signal, white noise, or an M-sequence signal, is applied to the head position error. The head position error is observed, and the time-series data of both the PES single test signal ST and the head position error are transformed to the frequency domain using Fourier transforms. The transfer characteristics are then calculated based on the absolute value of the ratio of the complex values ​​and the phase angle. The transfer characteristics are recorded as a PES single log SL.

[0027] In this existing controller design technology, a numerical model of the controlled object is used for controller design, and sensitivity characteristics are simulated. However, calibration of the numerical model is required to correct the measured sensitivity characteristics. Even with calibration, due to modeling errors, the expected sensitivity characteristics will deviate from the measured values. Therefore, the positioning accuracy of the head is still insufficient and there is room for improvement.

[0028] Therefore, the following describes a technique for improving the positioning accuracy of the head in a disc device controlled by a two-stage actuator at multiple rates.

[0029] (Implementation Method)

[0030] Figure 3 This is a schematic diagram illustrating the configuration of a disk drive 100 according to an embodiment. The disk drive 100 includes a disk 1 for storing data, a head 2 for reading / writing data relative to the disk 1, and an arm 3 equipped with a microactuator 16 and the head 2.

[0031] Disk 1 rotates via a spindle motor (not shown). A large number of concentric tracks 5 are arranged on the surface of disk 1. Each track 5 contains a servo sector 6. Each servo sector 6 contains a servo area 7 and a data area 8. Each track 5 contains a predetermined number of servo areas 7 arranged at predetermined intervals in the circumferential direction. Servo information (position information) is recorded within the servo areas 7. During normal read / write operations, this servo information is used in the head positioning control system to detect the position of head 2. Additionally, the data areas 8 between the servo areas 7 record user data.

[0032] Head 2, for example, has a structure where the read head and write head are separately mounted on the slider. The read head reads servo information and user data recorded on disk 1. During head positioning control, the read head reads servo information at regular intervals according to the rotational speed of disk 1. The write head writes user data onto disk 1.

[0033] VCM4 (first actuator) causes the arm 3, with head 2 at its front end, to move as a whole in the radial direction of disk 1. Microactuator 16 (second actuator) causes head 2 to move slightly.

[0034] Furthermore, the disk drive 100 includes a read / write channel (signal processing circuit 9 and position detection circuit 10), a controller 13, a VCM drive circuit 14, an MA drive circuit 15, and a vibration sensor 17.

[0035] Signal processing circuit 9 processes read signals and write signals corresponding to servo information and / or user data read from the read head contained in head 2. Additionally, position detection circuit 10 extracts servo information from the read signals and generates a position detection signal for detecting the position of head 2.

[0036] The controller 13 includes a CPU (Central Processing Unit) 11, which is a key component of the head positioning control system, and a ROM 12 storing its program (e.g., firmware) and various control parameters. The CPU 11 implements a feedback control system and / or a feedforward control system that constitutes the head positioning control system. The CPU 11 calculates control values ​​(including operational quantities), controls the drive current supplied to the VCM4 and the microactuator 16 via the VCM drive circuit 14 and the MA drive circuit 15, and executes the head positioning action.

[0037] Vibration sensor 17 detects (observes) the acceleration of an disturbance (external vibration or excitation force) equivalent to the vibration or impact applied to disk drive 100, and outputs the detected signal (analog signal) to A / D conversion circuit 18. A / D conversion circuit 18 converts the detected signal (acceleration signal) of vibration sensor 17 into a digital value and outputs it to CPU 11. Vibration sensor 17 is, for example, a vibration sensor and / or an RV sensor.

[0038] In addition, controller 13 functions as the first controller, which controls VCM4 at a multi-rate of 1 / N periods (N is an integer greater than 2) as the head position observation period, based on the target position of head 2.

[0039] In addition, controller 13 functions as a second controller, which controls microactuator 16 in 1 / N cycles according to the target position of the first 2.

[0040] The following describes the additional filter Ca(MA). Figure 5 The method for constructing the (second additional filter) will be explained. Sometimes the entity performing the calculations is called the "arithmetic unit." The arithmetic unit is implemented, for example, by CPU11, but it can also be implemented by other arithmetic units.

[0041] The outline of the fabrication of the MA additional filter Ca is explained. First, the arithmetic unit performs the following steps: In the state before the MA additional filter Ca is applied, test signals are applied at 1 / N cycles to measure the head position error spectrum and frequency characteristics for the operation quantity of VCM4 and the operation quantity of microactuator 16, respectively. Based on the frequency characteristics, the multi-rate sensitivity characteristics are calculated, and based on the head position error spectrum and multi-rate sensitivity characteristics, the frequency that should be corrected by the MA additional filter Ca is determined.

[0042] Next, the computation unit performs the following steps: In each candidate state among the candidates for which multiple MA additional filters Ca are attached, with respect to the determined frequency, a test signal is applied at 1 / N cycles for the operation of VCM4 and the operation of microactuator 16, and the frequency characteristics are measured. Based on the frequency characteristics, a multi-rate sensitivity characteristic is calculated, and the candidate with the lowest peak value of the multi-rate sensitivity characteristic below a threshold and the smallest head position error is selected as the MA additional filter Ca to be used. This will be explained in detail below.

[0043] Figure 4A , Figure 4B This is an explanatory diagram of the method for measuring the sensitivity characteristics of the disk device 100 in the embodiment. Hereinafter, VCM4 will sometimes be referred to as "VCM" and microactuator 16 as "MA".

[0044] like Figure 4A , Figure 4B As shown, for VCM and MA operations at more than twice the rate, multi-rate test signals are applied respectively, and the time series of the multi-rate operations are recorded as a log (recorded as VCM multi-log ML). Let the VCM multi-rate test signal time series be Tv, the MA multi-rate test signal time series be Tm, the VCM multi-rate operation with the added test signal be Iv, and the MA multi-rate operation be Im, and the frequency characteristics Kv and Km be defined as follows (1).

[0045] Kv = FFT(Iv) / FFT(Tv)

[0046] Km = FFT(Im) / FFT(Tm) Equation (1)

[0047] Here, FFT represents the High-Speed ​​Fourier Transform of the time series. Furthermore, FFT(Iv), FFT(Tv), FFT(Im), and FFT(Tm) are vectors computed using the High-Speed ​​Fourier Transform, with complex numbers as their elements. Additionally, FFT(Iv) / FFT(Tv) and FFT(Im) / FFT(Tm) represent element-wise division operations between the vectors.

[0048] After measuring the frequency characteristics Kv and Km, the predicted value of the sensitivity measurement of the feedback system is obtained in the post-processing of numerical data. Here, if the VCM controller characteristic is Cv, the VCM controlled object characteristic is Pv, the MA controller characteristic is Cm, and the MA controlled object characteristic is Pm, then the frequency characteristics that can be measured are expressed as the transfer characteristics of the following equation (2).

[0049] Kv=(1+Cm×Pm) / (1+Cv×Pv+Cm×Pm)

[0050] Km=(1+Cv×Pv) / (1+Cv×Pv+Cm×Pm) (Equation 2)

[0051] By using Matlab (one of the numerical computing platforms) to perform post-operations (formula transformation) on this property, the following (Equation 3) can be obtained.

[0052] Cv×Pv=(Kv-1) / (1-Kv-Km)

[0053] Cm×Pm=(Km-1) / (1-Kv-Km) (Equation 3)

[0054] Furthermore, the open-loop characteristics of the multi-rate system are as follows (Equation 4).

[0055] Om=Cv×Pv+Cm×Pm (Equation 4)

[0056] Furthermore, considering the foldback of the Nyquist frequency (half of the sampling frequency), the open-loop characteristic of a single rate becomes as follows (Equation 5).

[0057] Os=Om+conj(flipud(Om)) (Formula 5)

[0058] Here, conj represents the conjugate complex number operation, and flipud represents the flip-over operation. Furthermore, the following (Equation 6) is ultimately obtained as the sensitivity characteristic.

[0059] Multi-rate sensitivity characteristics: 1 / (1+Om)

[0060] Single-rate sensitivity characteristic: 1 / (1+Os) (Equation 6)

[0061] Figure 5 This is a block diagram of the feedback control system of the disk device 100 in the embodiment. Figure 5 In, relative to Figure 1 An additional MA filter Ca is added. The MA filter Ca is attached between the MA controller Cm (the second controller) and the MA controlled object Pm (the second actuator), and outputs output data to the MA controlled object Pm based on the input data from the MA controller Cm.

[0062] Based on the above multi-rate sensitivity measurement results, the order of setting the MA additional filter Ca is as follows.

[0063] First, the VCM characteristic Cv×Pv, MA characteristic Cm×Pm, multi-rate sensitivity characteristic Km, and single-rate sensitivity characteristic Sm are measured. For Km, the maximum gain value Xm = max(abs(Km)) and the frequency Fm at this point are calculated. Furthermore, "abs" means absolute value.

[0064] Furthermore, when Xm is below a predetermined threshold, entry Figure 7 The processing involves proceeding to the next step if Xm is greater than the threshold. Figure 8 The processing.

[0065] Figure 7 This is a flowchart illustrating the generation process of the MA additional filter when the maximum gain value Xm of the multi-rate sensitivity characteristic in the implementation is below the threshold (that is, when the current multi-rate sensitivity characteristic Km is not problematic).

[0066] First, in step S11, the arithmetic unit measures the gain value Sp of the spectrum of the head position error time series data, and calculates the frequency value Fp and the cumulative spectrum value Rp that the maximum gain value can take.

[0067] Next, in step S12, the arithmetic unit calculates the interference characteristic Gp = Sp / Sm based on the single-rate sensitivity characteristic Sm and the gain value Sp of the spectrum.

[0068] Next, in step S13, the computation unit calculates the feature points at frequency Fp. Figure 6 The four MA additional filter candidate modes shown (gain-up, gain-down, phase-up, phase-down) have multiple additional filters Ca1, Ca2, ... with certain strengths (here, "strong", "standard", and "weak").

[0069] Next, in step S14, the arithmetic unit uses the VCM characteristic Cv×Pv, the MA characteristic Cm×Pm, and the additional filter candidates Ca1, Ca2, ... to calculate the multi-rate sensitivity characteristic Km', the maximum gain value Xm', and the single-rate sensitivity characteristic Sm' after adding Ca.

[0070] Next, in step S15, the arithmetic unit calculates the expected spectrum gain value Sp' = Gp × Sm' based on the interference characteristic Gp and the single-rate sensitivity characteristic Sm', and obtains its spectrum accumulation value Rp'.

[0071] Next, in step S16, the arithmetic unit selects an additional filter Ca whose maximum gain value Xm' is below a predetermined threshold and whose cumulative spectral value Rp' is the minimum, and ends the design.

[0072] Figure 8 This is a flowchart illustrating the generation process of the MA additional filter when the maximum gain value of the multi-rate sensitivity characteristic in the implementation is greater than a threshold (that is, when the current multi-rate sensitivity characteristic Km is problematic).

[0073] First, in step S21, the arithmetic unit measures the gain value Sp of the spectrum of the head position error time series data.

[0074] Next, in step S22, the arithmetic unit calculates the interference characteristic Gp = Sp / Sm based on the single-rate sensitivity characteristic Sm and the gain value Sp of the spectrum.

[0075] Next, in step S23, the computation unit calculates the feature points at frequency Fm. Figure 6 The four candidate modes of additional filters shown (gain increase, gain decrease, phase increase, phase decrease) have multiple additional filters Ca1, Ca2, ... with certain strengths.

[0076] Next, in step S24, the arithmetic unit uses the VCM characteristic Cv×Pv, the MA characteristic Cm×Pm, and the additional filter candidates Ca1, Ca2, ... to calculate the multi-rate sensitivity characteristic Km', the maximum gain value Xm', and the single-rate sensitivity characteristic Sm' after adding Ca.

[0077] Next, in step S25, the arithmetic unit calculates the expected spectrum gain value Sp' = Gp × Sm' based on the interference characteristic Gp and the single-rate sensitivity characteristic Sm', and obtains its spectrum accumulation value Rp'.

[0078] Next, in step S26, the arithmetic unit determines whether there is an additional filter Ca whose maximum gain value Xm' is below a predetermined threshold and whose cumulative spectral value Rp' is the minimum. If there is ("Yes"), proceed to step S27; if there is not ("No"), proceed to step S28.

[0079] In step S27, the arithmetic unit selects a suitable additional filter Ca and the design ends.

[0080] In step S28, since the maximum gain value Xm' is not lower than a predetermined threshold among all MA additional filter candidates, the arithmetic unit records it as an error in the non-volatile memory inside the drive or in the drive management information on disk 1.

[0081] Next, the effects of the additional MA filter Ca will be explained. Figure 9 This is a graph showing the head position error spectrum before and after the design of the MA-added filter in the implementation method.

[0082] It can be seen that by adding an additional filter Ca to the MA filter at a specific frequency, the gain of the head position error spectrum decreases ( Figure 9 In addition, the positioning accuracy was also improved in the cumulative head position error spectrum. Figure 9 (b)

[0083] Figure 10 This is a graph showing the single-rate sensitivity characteristics before and after the design of the MA additional filter in the implementation method. By adding the MA additional filter Ca at a specific frequency, the gain of the single-rate sensitivity decreases, and the positioning accuracy is improved.

[0084] Thus, according to this embodiment, in the disk device 100 that performs multi-rate control by a two-stage actuator, by attaching the MA supplementary filter Ca, which is manufactured as described above, between the MA controller Cm and the MA controlled object Pm, the positioning accuracy of the head can be improved.

[0085] Furthermore, while the MA-attached filter was described in the above embodiments, the VCM-attached filter can also be fabricated in the same way.

[0086] Some embodiments of the present invention have been described, but these embodiments are given by way of example and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included within the scope and / or spirit of the invention, and are included within the scope of the invention as described in the claims and its equivalents.

[0087] For example, in Figure 7 , Figure 8 In the processing, the case without additional filters can also be used as an object for comparison.

[0088] Alternatively, both MA supplementary filters and VCM supplementary filters can be made and used simultaneously.

Claims

1. A method for manufacturing a disc device, The disk device includes: Disk, which stores data; The head, which reads / writes data relative to the disk; The first actuator moves the entire arm on which the head is mounted at the front end; A second actuator, disposed at the front end of the arm, moves the head; The first controller controls the first actuator at a multi-rate of 1 / N cycles, which is the head position observation period, according to the target position of the head. The second controller controls the second actuator according to the target position of the head in the 1 / N cycle; as well as A first additional filter, attached between the first controller and the first actuator, outputs output data to the first actuator based on input data from the first controller. Where N is an integer greater than or equal to 2. The manufacturing method includes the following steps: Before the first additional filter is applied, the arithmetic unit applies test signals to the operation quantities of the first actuator and the second actuator at 1 / N cycles to measure the head position error spectrum and frequency characteristics obtained by transforming the time series data of the head position error into the frequency domain through Fourier transform. The step of calculating the multi-rate sensitivity characteristic based on the measured frequency characteristics includes: performing a post-operational formula transformation based on the measured frequency characteristics to calculate a first characteristic (Cv×Pv) represented by the product of the first controller characteristic and the controlled object characteristic of the first actuator, and a second characteristic (Cm×Pm) represented by the product of the second controller characteristic and the controlled object characteristic of the second actuator; calculating the multi-rate open-loop characteristic (Om) by adding the first characteristic and the second characteristic (Cv×Pv+Cm×Pm); and obtaining the multi-rate sensitivity characteristic (1 / (1+Om)) based on the multi-rate open-loop characteristic (Om). The step of determining the frequency that should be corrected by the first additional filter based on the head position error spectrum and multi-rate sensitivity characteristics; and In a state where each of the multiple candidates of the first additional filter is attached, the arithmetic unit applies a test signal with a period of 1 / N to measure the frequency characteristics for the operation amount of the first actuator and the operation amount of the second actuator, respectively. The step of calculating the multi-rate sensitivity characteristic based on the frequency characteristics measured in the state with the first additional filter candidates attached includes: performing a post-operational formula transformation based on the frequency characteristics measured in the state with the first additional filter candidates attached, and calculating the first characteristic (Cv×Pv) and the second characteristic (Cm×Pm) respectively; calculating the open-loop characteristic (Om) of the multi-rate by adding the first characteristic and the second characteristic (Cv×Pv+Cm×Pm); and obtaining the multi-rate sensitivity characteristic (1 / (1+Om)) based on the open-loop characteristic (Om) of the multi-rate. The step of determining the candidate filter to be used as the first additional filter is the one whose peak value of the multi-rate sensitivity characteristic is below the threshold and whose head position error is minimal.

2. A method for manufacturing a disc device, The disk device includes: Disk, which stores data; The head, which reads / writes data relative to the disk; The first actuator moves the entire arm on which the head is mounted at the front end; A second actuator, disposed at the front end of the arm, moves the head; The first controller controls the first actuator at a multi-rate of 1 / N cycles, which is the head position observation period, according to the target position of the head. The second controller controls the second actuator according to the target position of the head in the 1 / N cycle; as well as A second additional filter, attached between the second controller and the second actuator, outputs output data to the second actuator based on input data from the second controller. Where N is an integer greater than or equal to 2. The manufacturing method includes the following steps: Before the second additional filter is applied, the arithmetic unit applies test signals to the operation amounts of the first actuator and the second actuator at 1 / N periods to measure the head position error spectrum and frequency characteristics obtained by transforming the time series data of the head position error into the frequency domain through Fourier transform, and calculates the multi-rate sensitivity characteristics based on the measured frequency characteristics. The step of calculating the multi-rate sensitivity characteristics based on the measured frequency characteristics includes: performing a post-operation-based formula transformation based on the measured frequency characteristics. The steps include: calculating the first characteristic (Cv×Pv) represented by the product of the first controller characteristic and the controlled object characteristic of the first actuator, and the second characteristic (Cm×Pm) represented by the product of the second controller characteristic and the controlled object characteristic of the second actuator; adding the first characteristic (Cv×Pv) and the second characteristic (Cm×Pm) (Cv×Pv+Cm×Pm) to calculate the multi-rate open-loop characteristic (Om); and determining the multi-rate sensitivity characteristic (1 / (1+Om)) based on the multi-rate open-loop characteristic (Om). The step of determining the frequency that should be corrected by the second additional filter based on the head position error spectrum and multi-rate sensitivity characteristics; and In a state where each of the multiple candidates of the second additional filter is attached, the arithmetic unit applies a test signal with a period of 1 / N to measure the frequency characteristics for the operation amount of the first actuator and the operation amount of the second actuator, respectively. The step of calculating the multi-rate sensitivity characteristic based on the frequency characteristics measured in the state with the second additional filter candidates attached includes: performing a post-operational formula transformation based on the frequency characteristics measured in the state with the second additional filter candidates attached, and calculating the first characteristic (Cv×Pv) and the second characteristic (Cm×Pm) respectively; calculating the open-loop characteristic (Om) of the multi-rate by adding the first characteristic (Cv×Pv) and the second characteristic (Cm×Pm) (Cv×Pv+Cm×Pm); and determining the multi-rate sensitivity characteristic (1 / (1+Om)) based on the open-loop characteristic (Om). The step of determining the candidate filter to be used as the second additional filter is the one whose peak value of the multi-rate sensitivity characteristic is below the threshold and whose head position error is minimal.

3. A computer program product comprising a computer program for enabling a computer used in a disc manufacturing apparatus to function as a unit, The disk device includes: A disk, which stores data; The head, which reads / writes data relative to the disk; The first actuator moves the entire arm on which the head is mounted at the front end; A second actuator, disposed at the front end of the arm, moves the head; The first controller controls the first actuator at a multi-rate of 1 / N cycles, which is the head position observation period, according to the target position of the head. The second controller controls the second actuator according to the target position of the head in the 1 / N cycle; as well as A first additional filter, attached between the first controller and the first actuator, outputs output data to the first actuator based on input data from the first controller. Where N is an integer greater than 2. The unit includes: Before the first additional filter is applied, for the operating quantities of the first actuator and the second actuator, a test signal is applied at 1 / N cycles to measure the head position error spectrum and frequency characteristics obtained by transforming the time series data of the head position error into the frequency domain through Fourier transform. The unit that calculates the multi-rate sensitivity characteristics based on the measured frequency characteristics includes: a unit that performs post-operational formula transformation based on the measured frequency characteristics to calculate a first characteristic (Cv×Pv) represented by the product of the first controller characteristic and the controlled object characteristic of the first actuator; and a second characteristic (Cm×Pm) represented by the product of the second controller characteristic and the controlled object characteristic of the second actuator; a unit that calculates the open-loop characteristic (Om) of the multi-rate by adding the first characteristic and the second characteristic (Cv×Pv+Cm×Pm); and a unit that calculates the multi-rate sensitivity characteristic (1 / (1+Om)) based on the open-loop characteristic (Om). Based on the head position error spectrum and multi-rate sensitivity characteristics, determine the cell whose frequency should be corrected by the first additional filter; and In a state where each of the multiple candidates of the first additional filter is attached, the frequency characteristic is measured by applying a test signal with a period of 1 / N for the operation amount of the first actuator and the operation amount of the second actuator, respectively, with respect to the frequency. A unit calculates a multi-rate sensitivity characteristic based on the frequency characteristic measured in the state with the first additional filter candidates attached. This unit comprises: a unit that, based on the frequency characteristic measured in the state with the first additional filter candidates attached, performs a post-operational formula transformation to calculate the first characteristic (Cv×Pv) and the second characteristic (Cm×Pm), respectively; a unit that calculates the open-loop characteristic (Om) of the multi-rate by adding the first characteristic and the second characteristic (Cv×Pv+Cm×Pm); and a unit that calculates the multi-rate sensitivity characteristic (1 / (1+Om)) based on the open-loop characteristic (Om) of the multi-rate. The candidate whose peak value of the multi-rate sensitivity characteristic is below the threshold and whose head position error is minimal is selected as the unit of the first additional filter to be used.

4. A computer program product comprising a computer program for enabling a computer used in a disc manufacturing apparatus to function as a unit, The disk device includes: A disk, which stores data; The head, which reads / writes data relative to the disk; The first actuator moves the entire arm on which the head is mounted at the front end; A second actuator, disposed at the front end of the arm, moves the head; The first controller controls the first actuator at a multi-rate of 1 / N cycles, which is the head position observation period, according to the target position of the head. The second controller controls the second actuator according to the target position of the head in the 1 / N cycle; as well as A second additional filter, attached between the second controller and the second actuator, outputs output data to the second actuator based on input data from the second controller. Where N is an integer greater than 2. The unit includes: Before the second additional filter is applied, for the operating quantities of the first actuator and the second actuator, a unit measures the head position error spectrum and frequency characteristics obtained by transforming the time series data of the head position error into the frequency domain through Fourier transform for each of the 1 / N period test signals. The unit calculates multi-rate sensitivity characteristics based on the measured frequency characteristics, and the unit includes: performing a post-operation-based formula transformation based on the measured frequency characteristics. The system includes units for calculating the first characteristic (Cv×Pv) represented by the product of the first controller characteristic and the controlled object characteristic of the first actuator; and the second characteristic (Cm×Pm) represented by the product of the second controller characteristic and the controlled object characteristic of the second actuator; units for adding the first characteristic (Cv×Pv) and the second characteristic (Cm×Pm) (Cv×Pv+Cm×Pm) to calculate the multi-rate open-loop characteristic (Om); and units for calculating the multi-rate sensitivity characteristic (1 / (1+Om)) based on the multi-rate open-loop characteristic (Om). Based on the head position error spectrum and multi-rate sensitivity characteristics, determine the cell whose frequency should be corrected by the second additional filter; and In a state where each of the multiple candidates of the second additional filter is attached, the frequency characteristic is measured by applying a test signal with a period of 1 / N for the operation of the first actuator and the operation of the second actuator, respectively, with respect to the frequency. A unit calculates a multi-rate sensitivity characteristic based on the frequency characteristic measured in the state with the second additional filter candidates attached. This unit comprises: a unit that performs a post-operational formula transformation based on the frequency characteristic measured in the state with the second additional filter candidates attached, and calculates the first characteristic (Cv×Pv) and the second characteristic (Cm×Pm) respectively; a unit that calculates the open-loop characteristic (Om) of the multi-rate by adding the first characteristic (Cv×Pv) and the second characteristic (Cm×Pm) (Cv×Pv+Cm×Pm); and a unit that calculates the multi-rate sensitivity characteristic (1 / (1+Om)) based on the open-loop characteristic (Om) of the multi-rate. The candidate whose peak value of the multi-rate sensitivity characteristic is below the threshold and whose head position error is minimal is selected as the unit of the second additional filter to be used.

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