Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
1994-11-17
2001-06-05
Sniezek, Andrew L. (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
C360S078090, C360S077020, C369S044290
Reexamination Certificate
active
06243226
ABSTRACT:
BACKGROUND OF THE INVENTION The present invention relates to a servo control apparatus of a disk recording system and particularly to a servo control apparatus and process capable of controlling the position of a head for recording and reading digital data on a disk as recording media.
In a current disk recording system, a hard disk drive (hereinafter referred to as HDD) operates in two modes, in accordance with the moving distance, the first of which is called a seek mode, in which a head moves between tracks so as to reach target position, and the second of which is called a track following mode, in which the head is accurately positioned on a data line of the track after the head has reached the target track.
In a method for controlling the position of the head in a hard disk drive, the control of velocity is executed until the head reaches a target position and the control of position is executed at the target position, so that the head lies on the track.
In a typical hard disk drive, the seek mode executes a search mode in the first deceleration phase and executes a transition mode in the second deceleration phase. Therefore, the seek mode is separated into the search mode and transition mode, in which servo information having the course of feedback uses a track number with a gray code. In the track following mode however, servo information uses a position error signal (hereinafter referred to as PES) using A and B bursts.
In such a conventional control method for respective seek (and its search and transition modes) and track following modes, a compensator or a proportional integral derivative controller has been frequently used. A voice coil motor controls the position of head in the disk recording system.
The conventional servo control apparatus may be an analog control apparatus depending upon the hardware to be controlled, or a mixed analog and digital mixing control apparatus. First, the head reads the number of the track in which the head is positioned currently through the gray code value indicating the servo information of track for each sampling period. As a result, the moving distance by which the head should be moved from a current position to a target position is defined. Target velocity corresponding to the moving distance is obtained from a look-up table. When the moving distance is defined, the seek mode is also determined. A real velocity is, however, determined by the difference between the value prior to sampling and current sampling value of the current position. Therefore, in the seek mode being separated as the search mode and transition mode, the control of velocity is executed by a control input derived from the target velocity and real velocity.
The conventional servo control apparatus as discussed above however, has the following problems which should be cleared. First, the real velocity is calculated for each sampling interval. The value calculated tends to be come more inaccurate however, where the sampling interval is short and the real position has changed substantially. Thus, there is a problem when the voice coil motor is required to execute an unexpected or abnormal movement in the search mode the head during the search mode or the transition mode.
Secondly, the track following mode which has a full state feedback which uses position information (a number of track, PES) and velocity information containing expectable errors, has great difficulties in maintaining the complete control due to instability of the real velocity information.
Third, it is possible that a steady state error will occur during the track following mode because there is no method for directly removing an external disturbance. While such an error is capable of being indirectly controlled by using an integral controller, but is not capable of being controlled over the whole range of data on the recording media, so that the error is not completely removed.
U.S. Pat. No. 5,182,684, to Thomas et al. for an
Estimator Positioning System And Method,
endeavors to control the movement of a head of a disk file by generating a position signal in response to servo information read. The current position signal is sampled regularly, and together with a current actuator control signal, updates estimated velocity. The distance from the current position to a specified position, i.e., distance-to-go, is also updated regularly. When the distance-to-go is greater than seven tracks the control signal is generated according to a maximum velocity of the actuator. When a maximum velocity is reached the system switches to a coast mode or when the number of tracks is less than or equal to seven tracks the system switches to a deceleration phase. During the deceleration phase the actuator control signal is generated by squaring the estimated velocity and dividing the result by the distance-to-go. Thomas et al. also suggests using an estimated position instead of the actual current position signal. In practice, only the position information is calculated and is used to modify the distance-to-go at each sampling period. The deceleration phase is followed by a track-following mode when the distance-to-go is between 1.0 and 0.125 tracks, i.e., less than 0.25 tracks.
U.S. Pat. No. 5,164,931, to Yamaguchi et al. for a
Method And Apparatus For Control Of Positioning,
uses a system for controlling positioning of a recording/playback head. The head is initially controlled as a velocity control system wherein a target velocity is generated in response to a track number signal. The difference between the head velocity and the target velocity is determined and the difference is supplied to a power amplifier for controlling the actuator for the heads. When the head reaches the vicinity of a target position, the head is controlled as a position control system utilizing the values of the target position and the position error signal of the current position of the heads.
U.S. Pat. No. 5,126,897, to Ogawa et al. for a
Magnetic Recording/Reproducing Apparatus Capable Of Reducing A Setting Time In A Head Positioning Control Mode,
for a servo type magnetic head drive control device with the moving velocity of the head controlled according to the moving distance to a target position in response to servo data and target velocity data. The servo data is used to generated position information and velocity information. Using the position information and target position information for calculating a moving distance, target velocity information is generated, in accordance with the moving distance. The velocity of the head is controlled for moving the head to a predetermined position on the basis of the difference between the velocity information and the target velocity information. After a certain time period or when a predetermined position is reached, control of the head movement is changed to be dependent upon a central processing unit (CPU) for operating in a positioning control mode having reduced settling time. In the position control mode, the CPU detects the position of the head actuator/driver using the position error signal (PES) from a head position decoder. The velocity signal, generated in response to the position error signal, is also detected by the CPU. The CPU then uses the position error signal and the velocity signal to control the positioning of the head. Use of a velocity estimated by the CPU in the position control mode is also discussed, by using a control model predefined in the CPU.
U.S. Pat. No. 5,051,851, to Sakurai for a
Method And Apparatus For Positioning Head On The Basis Of Premeasured Amount Of Displacement,
describes an apparatus having a plurality of disk-dependent displacement data stored in a table. The apparatus detects the displacement of a head from a designated track of a magnetic disk and controls the positioning of the head in a radial direction in response to disk-dependent displacement data from the table according to the designated track and further in response to the detected head displacement.
U.S. Pat. No. 5,040,084, to Liu for
Disk Drive system And Method,
provide
Bushnell , Esq. Robert E.
Samsung Electronics Co,. Ltd.
Sniezek Andrew L.
LandOfFree
Apparatus and method for digital servocontrol in a data... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus and method for digital servocontrol in a data..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus and method for digital servocontrol in a data... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2447974