KR100255206B1 - Torque constant calibration method of voice coil motor - Google Patents

Abstract

PURPOSE: A method for calibrating a torque constant of a VCM(Voice Coil Motor) is provided to multiply torque constant gains having different values by a control output value of the VCM. Therefore, it is possible to calibrate the difference between the measured torque constant and a torque constant used for a servo design. Also, the stability of a servo control can be accomplished. CONSTITUTION: A microprocessor successively seeks disk sections in a forward direction to generate torque constant gains each the first seeking section, and successively seeks the disk sections in a reverse direction to generate reverse torque constant gains each the second seeking section. The microprocessor performs a swapping for the torque constant gains in the forward/reverse directions, and calculates torque constant gain slopes of each section in the forward/reverse directions, then stores the calculated torque constant gain slopes. The microprocessor generates torque constant gains corresponding to cylinder information from the torque constant gain slopes, and multiplies the torque constant gains by a control output value, then calibrates torque constants.

Description

Torque constant compensation method of voice coil motor

The present invention relates to a servo control system of a magnetic disk drive apparatus, and more particularly, to a method for compensating torque constants of a voice coil motor having a different value according to each cylinder of a disk surface.

Magnetic disk drives, such as hard disk drives, floppy disk drives, and the like, are widely used as auxiliary storage devices in computer systems today. In particular, hard disk drives have the advantage of being able to stably store large amounts of data as well as accessing data at high speed. In general, a hard disk drive records or records data on a disk 2 that is rotated at high speed by an internal spindle motor 22 and a track on the surface of the disk 2, as shown in FIG. An actuator 20 is provided with a magnetic head 4 (hereinafter referred to as a head) 4 for reproducing the data. The actuator 20 is rotatably installed about the pivot shaft 10 and bobbin 12 and a coil installed at one end thereof operate the voice coil motor (hereinafter referred to as VCM) 18. As the head moves, the head 4 attached to the end of the suspension 6 at the other end moves to both ends of the disc 2, and records or reproduces data on the track of the disc 2 surface. At this time, the head 4 attached to the end of the suspension 6, which moves to both ends of the disk 2, is lifted by the airflow generated by the high speed rotation of the disk 2, and moves while maintaining a fine floating height.

In a typical hard disk drive having the above-described mechanical structure, the ability for the head 4 to move to and hold a specific position on the disk 2 is required for recording and reproducing data. In addition, given the trend of larger applications and faster seek times, the average seek time and location maintenance (ie track tracking) of a hard disk drive are important factors in determining the overall performance of the product. As an element for controlling such average search time and position holding characteristic, VCM 18 can be mechanically mentioned, and a servo control system including firmware can be mentioned as a circuit. In particular, the VCM 18 is responsible for the movement of the actuator 20 attached to the end of the head 4, which is responsible for recording and reproducing the actual data, and a permanent magnet for forming a magnetic field, and a yoke that is a passage for the magnetic field. It consists of a plate and a winding coil which flows an electric current and induces the movement of the actuator 20. The torque constant (hereinafter referred to as Kt) of the VCM 18 having such a configuration is represented by the following equation (1).

Kt = Bg * Le * R * Nc

Bg: magnetic flux density,

Le: Effective length per turn of coil

R: Torque-arm length

Nc: Number of turns of the winding coil

The torque constant Kt of the ideal VCM 18 should be uniform over the entire surface of the disk 2, but the nonuniformity of the magnetic field density formed by the permanent magnet, the loss by the spindle motor 22 or the actuator flexible printed circuit (FPC), the actuator (20) Due to various disturbance factors such as friction of the bearing, a difference in torque constant Kt actually occurs depending on the rotation angle of the actuator 20. In other words, the torque constant Kt is small in both of the data areas (ID, OD) on the disk 2 surface, and the torque constant Kt is maximum in the vicinity of the center. As described above, in order to compensate torque constants Kt having different values according to the position of the disk 2 surface, in the conventional hard disk drive, the search value of the constant distance is repeatedly performed several times to calculate the average value of torque constants Kt in a predetermined section. . However, the torque constant Kt value calculated by repeating only a certain distance search operation is valid only in the corresponding section, and instability of servo control is avoided in a typical drive where the torque constant Kt value is not constant over the entire disc 2 section. It becomes impossible. This is because the torque constant Kt, which is used as a default for modeling the VCM 18 in the servo design, cannot be the same for each drive (even in the same drive, it is different for each cylinder). Therefore, if the torque constant Kt of the actual hard disk drive differs from that used in the servo design, a large error occurs between the servo information calculated by the estimator and the servo information reproduced in the actual system, thereby making the servo control impossible. do.

Accordingly, an object of the present invention is to measure the torque constant of the VCM 18, which is the basis for servo control in a magnetic disk drive, for all cylinders, and to determine the difference between the measured torque constants and the torque constant used in the servo design. And torque constant gain) to provide a stable torque constant compensation method.

A magnetic disk drive apparatus comprising a disk which is a recording medium, a transducer for recording predetermined data on the disk surface and reproducing the recorded data, and an actuator for moving the transducer on the disk.

Calculating a torque constant gain for each first search section while sequentially searching a plurality of partitioned disk sections in a forward direction, and calculating a reverse torque constant gain for each second search section while sequentially searching the disk sections in a reverse direction;

Swept the forward and reverse torque constant gains calculated in each section of the disk with each other to calculate and store forward and reverse torque constant gain gradients in each section;

In the servo control, the torque constant gain is calculated from the torque constant gain inclination corresponding to the cylinder information at which the transducer is located and multiplied by the control output value to compensate for the torque constant.

1 is a perspective view of a hard disk drive that is a magnetic disk drive.

2 is a general block diagram of a hard disk drive that is a magnetic disk drive.

3 is a block diagram of a disk 2 according to an embodiment of the present invention.

4 is a general initialization flow chart performed at power on.

5 is a search routine execution flowchart for calculating torque constant_gain according to an embodiment of the present invention of FIG. 4.

6 is a control flowchart of the microprocessor 30 for explaining the torque constant (Kt) compensation process according to an embodiment of the present invention.

Hereinafter, an operation according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. In the following description and the annexed drawings, many specific details are set forth in order to provide a more general understanding of the invention, such as the number of partition sections on the disk surface, the number of searches performed, and the specific processing flow. It will be apparent to those skilled in the art that the present invention may be practiced without these specific details. In the following description, detailed descriptions of well-known functions and configurations that may unnecessarily obscure the subject matter of the present invention will be omitted.

Figure 2 shows a general block diagram of a hard disk drive that is a magnetic disk drive. Referring to FIG. 2, the microprocessor 30 may include a programmable read memory 32 that stores a predetermined control program and an estimator algorithm of the microprocessor 30, and a static RAM (PROM). Static random access memory (hereinafter referred to as sram) 34 to control the overall operation of the drive. The head 4 is attached to one end of the actuator to perform horizontal movement on the disc 2, which is a recording medium, and to record and reproduce data on / from the disc 2 surface. The voice coil motor (VCM) 18 located at the other end of the actuator with the head 4 attached to one end is horizontally driven on the disk 2 in correspondence with the applied current level and direction. The spindle motor 22 rotates the disk 2 mounted on the drive shaft in accordance with a control signal input from the motor driver 40. The VCM driver 36 is connected to the VCM 18 to control the driving of the VCM 18. A digital-to-analog converter (DAC) 38 is connected to the microprocessor 30 and the VCM driver 36 to receive a digital control input signal U (k) from the microprocessor 30 and to output the analog signal. Convert to and outputs to the VCM driver (36).

The motor driver 40 is connected to the spindle motor 22 and the microprocessor 30 and controls the driving of the spindle motor 22 under the control of the microprocessor 30. A pre-amplifier 42 is connected to the head 4 to amplify and output the reproduced signal and output an input signal to the head 4 to be recorded. The read / write channel circuit 44 is connected to the microprocessor 30, the preamplifier 42, and the interface controller 50 and receives recording data from the interface controller 50 under the control of the microprocessor 30. This is encoded and output to the preamplifier 42. The read / write channel circuit 44 digitally converts the analog reproduction signal input from the preamplifier 42 and outputs the encoded read data as encoded read data (ERD). An analog-to-digital converter (ADC) 48 is connected to the read / write channel circuit 44 to receive an analog servo reproduction signal, and digitally converts it to PES and outputs it to the microprocessor 30. A gate array 46 is connected to the read / write channel circuit 44 to receive an ERD signal and detects and outputs servo information such as gray codes in the servo region of the disk 2 from the ERD signal. do. The interface controller 50 transmits and receives data between an external data input device (for example, a host computer) and the disk 2.

3 shows a partition diagram of a disc 2 according to an embodiment of the invention. In FIG. 3, ID (Inner Diameter) and OD (Outer Diameter) indicate the inner circumference and outer circumference of the disk 2 surface, respectively, and each disk 2 surface is divided into six sections as shown in FIG. 2. have. Numbers 1 to 7 used for dividing the disk 2 surface into six sections are position information values indicating issue points that are set in advance for performing a search routine described later. Meanwhile, in FIG. 3, the SC (segment cylinder) indicates a cylinder located at the center of each section, and this is an ID and OD direction slope in the corresponding section using the calculated torque constant_gain value (hereinafter referred to as Kt_gain value). It is used to find the slope.

FIG. 4 is a flowchart illustrating a general initialization execution performed at power on. When the power is “on”, the microprocessor 30 initializes variables necessary for the drive operation in step 60 and proceeds to step 62. . After that, the microprocessor 30 unlatches the head latched in the parking zone in step 62, and then proceeds to step 64, and the search routine for calculating Kt_gain for all cylinders of the disk 2 surface. Perform (Seek Routine). After the completion of the search routine, the microprocessor 30 switches to the standby mode. Hereinafter, a search routine performing process for calculating Kt_gain will be described with reference to FIGS. 3 and 5.

)를 이용하여 하기 수학식 2에 의해 Kt_게인을 산출한다.FIG. 5 is a flowchart illustrating a search routine execution for calculating Kt_gain according to an embodiment of the present invention. First, referring to FIG. 5, the microprocessor 30 moves to the first reference point (issue point 2) in step 70 to calculate Kt_gain according to an embodiment of the present invention. ) Start searching. In this case, the forward search means a search from the OD direction to the ID direction of the partition diagram of the disk 2 shown in FIG. 3, and the forward search is performed for each of the preset first sections (2 sections, 4 sections, 6 sections). It is to carry out. That is, the microprocessor 30 starts the forward search in the order of issue point 2 (X1)-> 4 (X2)-> 6 (X) in step 72. In the forward search, the microprocessor 30 proceeds to step 74 and calculates Kt_gain in each partitioned section (2 sections and 4 sections), and converts the value to the forward Kt_ gain of 2 sections and 4 sections, respectively. Save it. The method of calculating the Kt_gain may be obtained by dividing the distance that the head 4 moves for a predetermined distance by a reference value set in the servo design. That is, before starting the search, the state updated head position of the estimator (if A1) is stored and the head position after completion of a certain number of servo sector counting is obtained (this is A2). In this case, the acceleration of the actuator 20 becomes the absolute value | A2-A1 |. Since the reference acceleration used in servo design

Kt_Gain is calculated by the following equation (2).

／｜A2-A1｜

／ ｜ A2-A1 ｜

On the other hand, if the forward search is completed in step 76, the microprocessor 30 proceeds to step 78 to start the backward search. The backward search means a search in the OD direction from the disk ID surface ID. In the reverse search, the microprocessor 30 proceeds to step 80 to calculate Kt_gain in the preset second sections (5 sections and 3 sections), and converts the value into the reverse Kt_ gain of 5 sections and 3 sections, respectively. Save it. Thereafter, the microprocessor 30 proceeds to step 82 and checks whether the backward search is completed. If so, the microprocessor 30 proceeds to step 84 to check whether the number of forward (or reverse) search executions is less than two. As a result of the inspection, if the number of forward search execution times is less than 2, the microprocessor 30 proceeds to step 86, moves to the second reference point (issue point 1), and returns to step 72. Thereafter, the microprocessor 30 may calculate the forward Kt_gain of one section, three sections, and five sections by the second forward search by repeatedly performing the above steps 72 to 82, and the six reverse sections and the four sections by the second reverse search. It is possible to calculate the reverse Kt_gain of 2 sections. Since the number of forward (or reverse) searches is 2 in step 84, the microprocessor 30 proceeds to step 88 to calculate the forward Kt_ gain of 6 sections and the backward Kt_ gain of 1 section. This is because the forward Kt_gain of 6 sections and the reverse Kt_gain of 1 section cannot be calculated by the two search operations described above. Therefore, in step 88, the microprocessor 30 partitions the six-section backward Kt_gain into six sections of forward Kt_gain and shifts the one-section forward Kt_gain into one section of backward Kt_gain to six sections. Kt_gain in the forward direction (ID direction) and in the reverse direction (OD direction) can be calculated for the entire disk 20 surface. Thereafter, the microprocessor 30 proceeds to step 90 and swipes forward and backward Kt_gains calculated from the above processes and stores them in a table. The reason for this is as follows.

The Kt_gain is typically mainly affected in the deceleration mode and the linear velocity mode of the actuator 20. Therefore, since the Kt_gain calculated in the forward 1 section is actually a value to be used in the deceleration and constant velocity mode parts in the reverse search in the 1 section, the forward Kt_ gain in the 1 section should be stored as the reverse Kt_ gain in the 1 section. In addition, the Kt_gain calculated in 6 reverse sections should be used in the deceleration and constant velocity modes during forward search of 6 sections. Therefore, the reverse Kt_gain of 6 sections should be stored as the forward Kt_ gain of 6 sections. As described above, the microprocessor 30 swept the Kt_gains calculated in the forward and reverse directions and stores them in a table, and then proceeds to step 92 to calculate the forward and backward gradients in each section. And store it in the SRAM 34. In the method of calculating the inclination, the center cylinder of each section is used as the segment cylinder SC, and using the Kt_gain calculated above, the inclination of the forward (ID) and the reverse (OD) in each section can be calculated. The Kt_gain of the entire cylinder can be calculated.

As described above, the microprocessor 30 that calculates the Kt_gain of the entire cylinder of the disk 2 surface returns to the initialization routine and performs an operation according to a series of initialization operations, and then switches to the standby mode. Hereinafter, a process of compensating the torque constant Kt by using the Kt_gain calculated for the entire cylinder of the disk 2 surface will be described with reference to FIG. 6.

FIG. 6 illustrates a control flow diagram of the microprocessor 30 for explaining the torque constant Kt compensation process according to an embodiment of the present invention, and the torque constant Kt compensation process is performed on-track from the beginning of the search. until each servo interrupt occurs until just before it is tracked. That is, in the track search mode, the microprocessor 30 checks whether a servo interrupt occurs in step 94. As a result of the test, when the servo interrupt occurs, the microprocessor 30 proceeds to step 96 and interpolates the search routine result for calculating the Kt_gain using the current head position information, and then Kt_gain corresponding to the corresponding cylinder. To calculate. The microprocessor 30 then multiplies the control output value U (k) by outputting the Kt_gain calculated in step 98 again. As such, by multiplying the Kt_gain corresponding to the current head position every time the servo interrupt is generated and outputting it to the VCM 18, it is possible to compensate for the difference in torque constants having different values according to the position of the head 4.

On the other hand, the Kt_gain multiplied by the control output value U (k) varies depending on the current drive mode. That is, from the unlatching search of the head 4 until the search routine for calculating the Kt_gain is used, the Kt_gain made using the default table is used, and the constant velocity is performed during the search routine for the Kt_gain calculation. In mode and fixation mode, 1.1 is multiplied to output the control output value U (k) .After completion of the search routine for calculating Kt_gain, the output output U (k) interpolated with the updated table value is converted to the control output value U (k). By multiplying by k) and outputting it, the torque constant Kt at the time of track search can be compensated.

As described above, the present invention multiplies the torque constant_gain having a different value according to the search direction by the control output value of the voice coil motor to compensate for the difference from the torque constant set when designing the servo control system, thereby ensuring the accuracy of the servo control. There is an advantage.

Claims (3)

A magnetic disk drive apparatus comprising a disk which is a recording medium, a transducer for recording predetermined data on the disk surface and reproducing the recorded data, and an actuator for moving the transducer on the disk. Calculating a torque constant gain for each first search section while sequentially searching a plurality of partitioned disk sections in a forward direction, and calculating a reverse torque constant gain for each second search section while sequentially searching the disk sections in a reverse direction; Swept the forward and reverse torque constant gains calculated in each section of the disk with each other to calculate and store forward and reverse torque constant gain gradients in each section; Torque constant compensation method comprising the step of compensating the torque constant by multiplying the control output value by calculating the torque constant gain corresponding to the cylinder information of the current transducer is located from the torque constant gain slope during servo control. The torque constant compensation as claimed in claim 1, wherein the torque constant gain is calculated by dividing a distance traveled by the actuator during a unit time by a distance traveled by the actuator for a unit time in each search section. Way. 3. The slope of the forward and reverse torque constant gains according to claim 2, wherein the slope of the forward and reverse torque constant gains is set by using a bidirectional torque constant calculated for each section after setting the median value of each section of the disc as a segment cylinder. Torque constant compensation method characterized in that the calculation.

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