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Fotos und technische Daten  Fujitsu  MHV2060BH

(7) VCM current sense resistor (CSR) This resistor controls current at the power amplifier by converting the VCM current into voltage and feeding back. 4-14 C141-E224 4.7 Servo Control 4.7.2 Data-surface servo format Figure 4.7 describes the physical layout of the servo frame. The three areas indicated by (1) to (3) in Figure 4.7 are described below. (1) Inner guard band This area is located inside the user area, and the rotational speed of the VCM can be controlled on this cylinder area for head moving. (2) Data area This area is used as the user data area SA area. (3) Outer guard band This area is located at outer position of the user data area, and the rotational speed of the spindle can be controlled on this cylinder area for head moving. C141-E224 4-15 Theory of Device Operation Figure 4.7 Physical sector servo configuration on disk surface 4-16 C141-E224 4.7 Servo Control 4.7.3 Servo frame format As the servo information, the IDD uses the phase signal servo generated from the gray code and servo EVEN and ODD. This servo information is used for positioning operation of radius direction and position detection of circumstance direction. The servo frame consists of 5 blocks; write/read recovery, servo mark, gray code, Burst EVEN1, Burst ODD, Burst EVEN2, and PAD. Figure 4.8 shows the servo frame format. Write/read recovery Servo mark Gray code Burst EVEN1 Burst ODD Burst EVEN2 PAD Figure 4.8 Servo frame format (1) Write/read recovery This area is used to absorb the write/read transient and to stabilize the AGC. (2) Servo mark This area generates a timing for demodulating the gray code and position- demodulating the burst signal by detecting the servo mark. (3) Gray code (including sector address bits) This area is used as cylinder address. The data in this area is converted into the binary data by the gray code demodulation circuit (4) Burst Even1, Burst Odd, Burst Even2 These areas are used as position signals between tracks and the IDD control so that target phase signal is generated from Burst Even and Burst Odd. (5) PAD This area is used as a gap between servo and data. C141-E224 4-17 Theory of Device Operation 4.7.4 Actuator motor control The voice coil motor (VCM) is controlled by feeding back the servo data recorded on the data surface. The MPU fetches the position sense data on the servo frame at a constant interval of sampling time, executes calculation, and updates the VCM drive current. The servo control of the actuator includes the operation to move the head to the reference cylinder, the seek operation to move the head to the target cylinder to read or write data, and the track-following operation to position the head onto the target track. (1) Operation to move the head to the reference cylinder The MPU moves the head to the reference cylinder when the power is turned. The reference cylinder is in the data area. When power is applied the heads are moved from the outside of media to the normal servo data zone in the following sequence: a) Micro current is fed to the VCM to press the head against the outer direction. b) The head is loaded on the disk. c) When the servo mark is detected the head is moved slowly toward the inner circumference at a constant speed. d) If the head is stopped at the reference cylinder from there. Track following control starts. (2) Seek operation Upon a data read/write request from the host, the MPU confirms the necessity of access to the disk. If a read/write instruction is issued, the MPU seeks the desired track. The MPU feeds the VCM current via the D/A converter and power amplifier to move the head. The MPU calculates the difference (speed error) between the specified target position and the current position for each sampling timing during head moving. The MPU then feeds the VCM drive current by setting the calculated result into the D/A converter. The calculation is digitally executed by the firmware. When the head arrives at the target cylinder, the track is followed. (3) Track following operation Except during head movement to the reference cylinder and seek operation under the spindle rotates in steady speed, the MPU does track following control. To position the head at the center of a track, the DSP drives the VCM by feeding micro current. For each sampling time, the VCM drive current is determined by filtering the position difference between the target position and the position clarified by the detected position sense data. The filtering includes servo compensation. These are digitally controlled by the firmware. 4-18 C141-E224 4.7 Servo Control 4.7.5 Spindle motor control Hall-less three-phase twelve-pole motor is used for the spindle motor, and the 3phase full/half-wave analog current control circuit is used as the spindle motor driver (called SVC hereafter). The firmware operates on the MPU manufactured by Fujitsu. The spindle motor is controlled by sending several signals from the MPU to the SVC. There are three modes for the spindle control; start mod...

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