Head actuator velocity control for electrical power off in a disk drive
View Patent ↗A hard disk drive with a voice coil motor coupled to a head. The head is coupled to a disk that is rotated by a spindle motor. The spindle motor generates a back-emf current. The disk drive also includes a drive circuit that causes the voice coil motor to move the head off of the disk. The drive circuit provides at least a portion of the back-emf voltage to the voice coil motor if a head velocity exceeds a first predetermined value and a larger portion of the back-emf voltage if the head velocity exceeds a second predetermined value. For example, a relatively small amount of voltage can be provided if the head velocity falls below a first threshold to accelerate the head and a larger current can be provided if the head velocity falls below a lower threshold to generate a greater head thrust.
1. A hard disk drive, comprising:
a disk;
a spindle motor for rotating said disk and for generating a back-emf voltage and a back-emf current;
a head coupled to said disk;
an actuator arm coupled to said head;
a voice coil motor coupled to said actuator arm, said voice coil motor for moving said head off of said disk; and,
a drive circuit coupled to said voice coil motor for:
providing a portion of said back-emf current at a first acceleration value to said voice coil motor when a head velocity is between a first predetermined value and a second predetermined value, and
providing a portion of said back-emf current at a second acceleration value to said voice coil motor when the head velocity exceeds the second predetermined value, and
providing a portion of said back-emf current at a first deceleration value to said voice coil motor when the head velocity is between a third predetermined value and a fourth predetermined value, and
providing a portion of said back-emf current at a second deceleration value to said voice coil motor when the head velocity exceeds the fourth predetermined value.
2. The hard disk drive of claim 1 , wherein said voice coil motor is for providing at least a portion of said back-emf current at the first acceleration value to accelerate said head when said head velocity is below a first minimum value.
3. The hard disk drive of claim 2 , wherein said voice coil motor is for providing at least a portion of said back-emf current at the second acceleration value to accelerate said head when said head velocity is below a second minimum value.
4. The hard disk drive of claim 1 , wherein said voice coil motor is for providing at least a portion of said back-emf current at the first deceleration to decelerate said head when said head velocity is above a first maximum value.
5. The hard disk drive of claim 4 , wherein said voice coil motor is for providing at least a portion of said back-emf current at the second deceleration value to decelerate said head when said head velocity is above a second maximum value.
6. The hard disk drive of claim 1 , wherein said back-emf voltage is periodically sampled to determine said head velocity.
7. The hard disk drive of claim 1 , further comprising a ramp that supports said head in an off-disk position.
8. The hard disk drive of claim 1 , further comprising a ramp that supports said head in an off-disk position.
9. A hard disk drive, comprising:
a disk;
a head coupled to said disk;
a spindle motor that rotates said disk and generates a back-emf voltage and a back emf-current;
an actuator arm coupled to said head;
a voice coil motor coupled to said actuator arm, said voice coil motor for moving said head off of said disk; and,
circuit means coupled to said voice coil motor for:
providing a first acceleration portion of said back-emf current to said voice coil motor when a head velocity is between a first predetermined value and a second predetermined value, and
providing a second acceleration portion of said back-emf current to said voice coil motor when the head velocity exceeds the second predetermined value, and
providing a first deceleration portion of said back-emf current to said voice coil motor when the head velocity is between a third predetermined value and a fourth predetermined value, and
providing a second deceleration portion of said back-emf current to said voice coil motor when the head velocity exceeds the fourth predetermined value.
10. The hard disk drive of claim 9 , wherein said voice coil motor is for providing at least a portion of said back-emf current at the first acceleration value to accelerate said head when said head velocity is below a first minimum value.
11. The hard disk drive of claim 10 , wherein said voice coil motor is for providing at least a portion of said back-emf current at the second acceleration value to accelerate said head when said head velocity is below a second minimum value.
12. The hard disk drive of claim 9 , wherein said voice coil motor is for providing at least a portion of said back-emf current at the first deceleration value to decelerate said head when said head velocity is above a first maximum value.
13. The hard disk drive of claim 12 , wherein said voice coil motor is for providing at least a portion of said back-emf current at the second deceleration value to decelerate said head if said head velocity is above a second maximum value.
14. The hard disk drive of claim 9 , wherein said back-emf voltage is periodically sampled to determine said head velocity.
15. A method for moving a head off a disk in a hard disk drive, comprising:
initiating movement of a head off of a disk with a voice coil motor;
providing a spindle motor that rotates said disk and generates a back-emf voltage and a back emf-current;
determining a head velocity; and,
providing a circuit for:
providing a portion of said back-emf current at a first acceleration value to said voice coil motor when the head velocity is between a first predetermined value and a second predetermined value, and
providing a portion of said back-emf current at a second acceleration value to said voice coil motor when the head velocity exceeds the second predetermined value, and
providing a portion of said back-emf current at a first deceleration value to said voice coil motor when the head velocity is between a third predetermined value and a fourth predetermined value, and
providing a portion of said back-emf current at a second deceleration value to said voice coil motor when the head velocity exceeds the fourth predetermined value.
16. The method of claim 15 , wherein the voice coil motor is for providing at least a portion of said back-emf current at the first acceleration value to accelerate the head when the head velocity is below a first minimum value.
17. The method of claim 16 , wherein the voice coil motor is for providing at least a portion of the back-emf current at the second acceleration value to accelerate the head when the head velocity is below a second minimum value.
18. The method of claim 15 , wherein the voice coil motor is for providing at least a portion of the back-emf current at the first deceleration value to decelerate the head when said the velocity is above a first maximum value.
19. The method of claim 18 , wherein the voice coil motor is for providing at least a portion of the back-emf current at the second deceleration value to decelerate the head when the head velocity is above a second maximum value.
20. The method of claim 15 , further comprising sampling periodically a back-emf voltage of the voice coil motor to determine the head velocity.