Disk drive servo control system with low power consumption for long seeks
A disk drive has a servo control system that implements just-in-time (JIT) seeks with low power consumption for all long seeks. The servo controller receives a seek command to move the transducer to a target data track and sector, calculates rotational latency from the seek command, and limits the transducer velocity for seeks longer than a predetermined seek length. The servo controller then generates a JIT gain from the calculated rotational latency, modifies the transducer acceleration and deceleration using the JIT gain, and modifies the transducer velocity limit using the JIT gain. Positive current is applied to the actuator to move the transducer with the JIT gain-modified acceleration until the transducer reaches the modified velocity limit. The servo controller determines when to initiate deceleration of the transducer, and applies negative current to the actuator to move the transducer with the JIT gain-modified deceleration until the transducer reaches the target track.
1. In a hard disk drive, an improvement comprising:
a rotatable disk having a plurality of data tracks containing data sectors;
a transducer for accessing the data sectors;
an actuator for moving the transducer to seek from one track to another track, wherein the actuator cannot move the transducer faster than a predetermined maximum velocity (Vmax); and
a servo control system coupled to the actuator and responsive to a seek command, the servo control system configured to:
calculate track seek length, rotational latency of a target sector, and a just-in-time (JIT) gain (JITGain) from the calculated rotational latency, the JITGain being inversely proportional to the rotational latency,
calculate an initial transducer velocity limit (Vlim) from the JITGain,
generate a seek profile comprising a transducer acceleration phase, a transducer coast phase at Vlim and a transducer deceleration phase,
apply an acceleration current to the actuator,
determine when the transducer velocity and position intersects a predetermined velocity-position phase-plane curve (Phase-Plane Profile), and
in response to said Phase-Plane Profile intersection, apply a deceleration current to the actuator;
an improvement comprising wherein the servo control system, for seek lengths greater than a predetermined value, is configured to:
modify the acceleration current with an acceleration gain (AccelGain), the AccelGain being a function of JITGain,
modify the Phase-Plane Profile with a Phase-Plane Profile gain (Phase-Plane Profile Scalar), the Phase-Plane Profile Scalar being a function of JITGain,
calculate a reduced Vlim less than said initial Vlim as a function of Phase-Plane Profile Scalar and Vmax, and
modify the deceleration current with a deceleration gain (DecelGain), the DecelGain being a function of Phase-Plane Profile Scalar.
2. The improvement according to claim 1 wherein the servo control system is configured to calculate AccelGain according to the following:
AccelGain=((1.0−AccelGainMin)/JITGainMax)*JITGain+AccelGainMin,
where AccelGainMin is a predetermined value less than 1.0.
3. The improvement according to claim 1 wherein the servo control system is configured to calculate Phase-Plane Profile Scalar according to the following:
Phase-Plane Profile Scalar=((1.0−Phase-Plane Profile ScalarMin)/JITGainMax)*JITGain+Phase-Plane Profile ScalarMin,
where Phase-Plane Profile ScalarMin is a predetermined value less than 1.0.
4. The improvement according to claim 1 wherein the servo control system is configured to calculate said reduced Vlim equal to Phase-Plane Profile Scalar*Vmax.
5. The improvement according to claim 1 wherein the servo control system is configured to calculate DecelGain equal to 1/Phase-Plane Profile Scalar.
6. A hard disk drive comprising:
a rotatable disk having a plurality of data tracks containing data sectors;
a transducer for accessing the data sectors;
an actuator for moving the transducer to seek from one track to another track; and
a servo controller coupled to the actuator and responsive to a seek command to move the transducer to a target sector in a target track, the controller being capable of performing just-in-time (JIT) seeks by calculation of rotational latency of target sectors from the seek commands, increasing the velocity of the transducer according to a predetermined acceleration, limiting the transducer velocity to coast at a velocity limit for seeks longer than a predetermined seek length, and decreasing the velocity of the transducer according to a predetermined deceleration, wherein the controller, for a seek greater than a predetermined seek length, is configured to:
generate a JIT gain (JITGain) from the calculated rotational latency, the JITGain being inversely proportional to the calculated rotational latency,
modify the transducer acceleration and deceleration using the JITGain,
reduce the transducer velocity limit using the JITGain,
apply positive current to the actuator to move the transducer with the JITGain-modified acceleration until the transducer reaches the reduced velocity limit,
determine when to initiate deceleration of the transducer, and
apply negative current to the actuator to move the transducer with the JITGain-modified deceleration until the transducer reaches the target track.
7. The disk drive of claim 6 wherein the controller is configured to modify the acceleration with an acceleration gain (AccelGain) and to calculate AccelGain according to the following:
AccelGain=((1.0−AccelGainMin)/JITGainMax)*JITGain+AccelGainMin,
where AccelGainMin is a predetermined value less than 1.0.
8. The disk drive of claim 6 wherein the controller is configured to access a velocity-position phase plane curve (Phase-Plane Profile), to modify the Phase-Plane Profile with a Phase-Plane Profile gain (Phase-Plane Profile Scalar), and to calculate Phase-Plane Profile Scalar according to the following:
Phase-Plane Profile Scalar=((1.0−Phase-Plane Profile ScalarMin)/JITGainMax)*JITGain+Phase-Plane Profile ScalarMin,
where Phase-Plane Profile ScalarMin is a predetermined value less than 1.0.
9. The disk drive of claim 8 wherein the actuator cannot move the transducer faster than a predetermined maximum velocity (Vmax), and wherein the controller is configured to reduce the limiting velocity by calculation of said reduced velocity limit (Vlim) equal to Phase-Plane Profile Scalar*Vmax.
10. The disk drive of claim 8 wherein the controller is configured to modify the deceleration by multiplying it by a deceleration gain (DecelGain) and to calculate DecelGain equal to 1/Phase-Plane Profile Scalar.