KR100326181B1 - Method for compensating servo offset - Google Patents

Abstract

PURPOSE: A method for compensating servo offset is provided to compensate offset of hardware components associated with servo control of a hard disc drive so as to improve the performance of servo control. CONSTITUTION: A bias force of each of designated sample tracks is measured(46). A difference between the bias force measured from each sample track and a standard bias force is calculated to obtain the average bias force value of the overall sample tracks(48,50). Whenever servo control is carried out, a servo control signal from which the average bias force value is removed is output to compensate servo offset. The standard bias force is the bias force value when an offset component is zero, and the standard bias force is stored in a bias force table of a hard disc drive. The step of measuring the bias force and the step of calculating the average bias force value are performed before a drive ready mode.

Description

Servo offset compensation method

The present invention relates to servo offset compensation of a hard disk drive, and more particularly, to a method for compensating offsets of hardware components related to servo control.

A hard disk drive, which is widely used as an auxiliary memory device of a computer system, is generally composed of a mechanical part and a circuit part to transmit and receive data between a host computer and a recording medium. 1 shows a general block diagram of a hard disk drive including a mechanism portion and a circuit portion. The disk 10 used as a recording medium in FIG. 1 rotates at a constant speed by a spindle motor 32. The head 12 is located on a corresponding one of the disks 10, Plater, and is coupled to an E-block assembly 28 with a cyclic voice coil motor (hereinafter referred to as VCM) 28. Corresponding to the support arms extended from the disk 10 toward the disk 10. The preamplifier 14 preamplifies the signal (analog read signal) picked up by one of the heads 12 during data readout and applies the preamplified signal to the read / write channel circuit 16. Encoded write data applied from the read / write channel circuit 18 is written on the disc 10 through one of the heads 12. The read / write channel circuit 16 detects and decodes a data pulse from the read signal applied from the preamplifier 14, applies the data pulse to the disk data controller (DDC) 18, and decodes the write data applied from the DDC 18. To the preamplifier (14). The DDC 18 is controlled by the microcontroller 22 and writes data received from the host computer through the read / write channel circuit 16 and the preamplifier 14 onto the disc or reads data from the host. Send to a computer. The DDC 18 also interfaces the communication between the host computer and the microcontroller 22. The buffer RAM 20 connected to the DDC 18 temporarily stores data transmitted and received between the host computer and the disk 10. The microcontroller 22 performs the overall control operation of the hard disk drive in response to the data read or data write command received from the host computer, and simultaneously performs track search and track tracking according to the servo information input from the disk signal controller 34. To control. Meanwhile, according to an exemplary embodiment of the present invention, the microcontroller 22 includes a bias force table to store the bias force value and the offset value measured in the initialization routine. The ROM 24 stores the control program of the microcontroller 22 and various initial values. The servo driver 26 drives a driving current for position control of the heads 12 according to a control signal input from the microcontroller 22 through a digital-to-analog converter (not shown). Is generated and applied to the voice coil of the actuator (28). The actuator 28 moves the heads 12 horizontally on the disk 10 corresponding to the direction and level of the drive current applied from the servo driver 26. The spindle motor driver 30 controls the driving of the spindle motor 32 according to a control value for controlling the rotation of the disks 10 input from the microcontroller 22. The disk signal controller 34 generates various timing signals necessary for data read / write, decodes the servo information, and applies it to the microcontroller 24.

In the conventional hard disk drive having the above-described configuration, hardware components related to servo control, that is, the D / A converter, the servo driver 26, the spindle motor driver 30, etc., are usually large and small offset amounts and gains ( Gain). In general, the gain difference of hardware components related to servo control is measured in a calibration subroutine performed at power " on " to compensate for gain difference. However, the offset of each hardware component acts as a disturbance of servo control, thereby degrading the servo control performance of the microcontroller 22. Hereinafter, the problems of the servo control in the conventional hard disk drive will be described with reference to FIGS. 2 and 3 showing the bias force change when the hardware components have offsets.

FIG. 2 shows an example of change in bias force due to track variation when the offset of hardware components related to servo control is zero. Typically in Figure 2 the abscissa represents the track (or cylinder) and the ordinate represents the bias force. In general, in the disk 10 (OD) area, the bias force is generated by the magnetic force of the magnetic latch in the inner diameter (ID) area due to the tension of the flexible printed circuit (FPC). Therefore, if the offset of the hardware components related to servo control is zero, connecting a bias force that varies with the track results in a bias force curve as shown in FIG.

3 shows a bias force curve that varies with tracks when an offset exists in hardware components related to servo control. In FIG. 3, (a) shows a bias force curve of a standard (when offset is zero), and (b) shows a bias force curve when hardware components related to servo control have a positive offset. (c) shows a bias force curve when the hardware components related to servo control have a negative offset. That is, the bias force curve is shifted according to the direction and magnitude of the offset of hardware components related to servo control. Normally the bias force is measured in the calibration subroutine immediately after power "on" and compensated for in servo control. In other words, the microcontroller 22 cancels the bias force by applying a current to the actuator 28 corresponding to the bias pose size in the direction opposite to the bias force. However, in the conventional hard disk drive, the bias force compensation is performed only in the track following mode because of the calculation time of the microcontroller 22. Therefore, in the track search mode, there is a problem in that the performance degradation of the servo control occurs due to the offset of hardware components related to the servo control.

Accordingly, an object of the present invention is to provide a servo offset compensation method capable of improving the performance of servo control by compensating for offsets of hardware components related to servo control of a hard disk drive.

It is still another object of the present invention to provide a servo offset compensation method capable of improving the performance of servo control regardless of track search mode and track tracking mode by compensating offset of hardware components related to servo control during servo control. Is in.

In the present invention for achieving the above object, in the servo offset compensation method of a hard disk drive having a bias force table,

Measuring each bias force from the defined sample tracks,

Calculating the difference between the bias force measured in each sample track and the standard bias force and calculating the average bias force of all the sample tracks;

The servo offset is compensated by outputting a servo control signal obtained by removing the bias force average of all the sample tracks calculated at each servo control.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, many specific details such as specific track number, sample track number, etc. are shown to provide a more general understanding of the present invention. It will be apparent to those skilled in the art that the present invention may be practiced without these specific details. And detailed descriptions of well-known functions and configurations that may unnecessarily obscure the subject matter of the present invention will be omitted.

FIG. 4A schematically illustrates a general initialization routine until the drive is switched to the Ready mode when the hard disk drive is powered on. FIG. 4B shows the implementation of the present invention in FIG. 4A. The subroutine for offset compensation according to an example (SubRoutine: hereinafter referred to as SR) is shown. First, referring to FIG. 4A, when the power of the hard disk drive is "on", the microcontroller 22 initializes the variables of the hard disk drive in step 40 and proceeds to step 42. In step 42, the microcontroller 22 performs an unlatch operation for moving the head 12 located in the parking area to a specific track of the data area, and then proceeds to step 44. In step 44, the microcontroller 22 performs an SR to compensate for offsets of hardware components related to servo control, and then switches to the drive ready mode. Hereinafter, an SR process for offset compensation will be described with reference to FIG. 4B.

First, the microcontroller 22 measures the bias force of each sample track defined in step 46 and stores the bias force in the bias force table, and then proceeds to step 48. Hereinafter, the bias force measured in each of the sample tracks will be defined as Bm (Bias Force Measurement). In step 48, the microcontroller 22 calculates a difference between the bias force Bm measured in each sample track and the standard bias force of the sample track and stores the difference in the bias force table. Hereinafter, a standard bias pose of the sample track is defined as a bias force standard (Bs), and the standard bias force Bs is previously stored in the bias force table as an experimentally measured bias force value when the offset is zero. Thereafter, in step 50, the microcontroller 22 calculates an average value of bias force differences (ie, Bm-Bs) for each sample track stored in the bias pose table and stores the average value in the table. The microcontroller 22 then returns to the initialization routine to switch to the drive ready mode. At this time, if the bias value of the bias force difference for each sample track is formulated, the following equation (1) is obtained, and the value calculated by the following equation (1) becomes an offset value of hardware components related to servo control. In formula (1), n represents the total number of sample tracks.

Offset = {sum of (Bm-Bs)} / n (1)

5 shows a bias force table in which 15 sample tracks are defined as one embodiment of the present invention. In the bias pose table of FIG. 5, the sample track means a predefined track number to compensate for offsets of hardware components related to servo control, and Bs represents a standard value of the bias force measured experimentally in the sample tracks. . In addition, Bm represents a bias force measurement of the sample tracks measured in the offset compensation SR described above. Therefore, the offset value according to the embodiment of the present invention is 9.4 (141/15). If the offset value calculated in the initialization routine is 9.4, the bias force for each sample track will show a bias force curve as shown in FIG. Figure 6 shows an example of the change in the bias force according to an embodiment of the present invention, (a) shows the standard value of the bias force Bs according to the sample tracks, (b) is a bias measured in each sample track This is a bias force curve in which the offset value is added to the bias bias standard value. That is, the microcontroller 22 compensates the offset value of the hardware components by compensating the offset value in the inter-output calculation process for controlling the actuator 28 when the servo interrupt is received.

As described above, the present invention has the advantage that the performance of the servo control can be improved by calculating the offset of hardware components related to the servo control in the initialization routine and compensating for each servo control.

1 is a block diagram of a general hard disk drive.

2 shows an example of bias force change caused by track variation when offset zero.

3 shows an example of bias force change according to track variation when offset exists.

4A and 4B are control flow diagrams for sub offset compensation according to an embodiment of the present invention.

5 is a configuration diagram of a bias force table according to an embodiment of the present invention.

6 is a view illustrating a change in bias force according to an embodiment of the present invention.

Claims (3)

In the servo offset compensation method of a hard disk drive having a bias force table, Measuring each bias force from the defined sample tracks, Calculating the difference between the bias force measured in each sample track and the standard bias force and calculating the average bias force of all the sample tracks; Compensating the servo offset by outputting a servo control signal obtained by removing the bias force average value of all the sample tracks calculated every servo control. The method of claim 1, wherein the standard bias force for each of the sample tracks is stored in the bias force table as a bias force value when the offset component is zero. The method of claim 1, wherein the bias force measurement process and the bias force average value calculation process are performed before a drive ready mode.