1. Field of the Invention
The present invention relates to disk drives. More particularly, the present invention relates to a disk drive employing adjustable seek profiles for variable seek times to reduce power dissipation.
2. Description of the Prior Art
FIG. 1A shows a prior art disk drive comprising a disk 2 having a plurality of tracks 4 which are partitioned into a number of data sectors. A head 6 coupled to a distal end of an actuator arm 8 is actuated over the disk 2 to access a target data sector by rotating the actuator arm 8 about a pivot in a seek operation. The disk drive typically employs a voice coil motor (VCM) 10 for rotating the actuator arm 8 about the pivot by energizing a voice coil with current. Control circuitry 12 generates a VCM control signal 13 applied to the VCM 10 according to a predetermined seek profile. During at least part of the seek operation, the control circuitry 12 implements a closed-loop servo system in response to the position of the head 6 as determined from position information (e.g., track address and servo bursts) recorded in embedded servo sectors 140–14N. A read channel 16 processes the read signal 18 emanating from the head 6 in order to demodulate the position information recorded in the embedded servo sectors 140–14N.
The ability of the VCM 10 to follow a predetermined seek profile depends on the acceleration/deceleration capability of the VCM 10 as controlled by the magnitude of current energizing the voice coil. Aggressive seek profiles require aggressive acceleration/deceleration currents which increases the heat and mechanical stress on the VCM, as well as increases power dissipation. FIG. 1B shows a prior art seek profile during the seek operation wherein the control circuitry 12 generates the VCM control signal 13 to apply a saturated acceleration current to the voice coil in order to accelerate the actuator arm 8 open-loop. The magnitude (Aaccel) of the saturated acceleration current is limited by the supply voltage, VCM coil resistance, and the VCM driver voltage drops and resistances. In addition, as the back EMF voltage of the VCM increases with increasing velocity, there is a corresponding decrease in the saturated acceleration current as shown in FIG. 1B. During deceleration, the control circuitry 12 generates the VCM control signal 13 to control the velocity of the actuator arm 8 in a closed-loop system to follow a predetermined velocity/distance deceleration profile (described below with reference to FIG. 6). An aggressive deceleration profile is typically selected relative to the deceleration capability of the VCM 10 in order to minimize the seek time. The maximum deceleration current is also a function of the back EMF voltage which decreases with decreasing velocity as illustrated in FIG. 1B. Under certain conditions, it may be unnecessary to minimize seek times using aggressive seek profiles. For example, if the disk drive disables predictive caching, less aggressive seek profiles may be employed in order to reduce VCM heating and power dissipation.
There is, therefore, a need to adjust the seek profile in a disk drive to accommodate variable seek times.