Methods and systems for moving a read/write head to a velocity and position where it is useful to switch from a deceleration phase to a settling phase of a seek operation

• US 7,054,099 B2
• Filed: 10/04/2004
• Issued: 05/30/2006
• Est. Priority Date: 10/04/2004
• Status: Expired due to Fees

• Current Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Hansen, Fred R.
• Primary Examiner(s): WONG, KIN C
• Application Number:
  US10/958,013
• Publication Number:
  US 20060072238A1
• Time in Patent Office: 603 Days
• Field of Search: None
• US Class Current: 360/78.06
• CPC Class Codes: G11B 5/5556 with track following after a "seek"
• CPC Class Codes: G11B 5/596 for track following on disks G11B5/5526, G11B5/5552, G11B5/5565, G11B5/5582 take precedence

Abstract

Improved deceleration control for a disk drive is provided. A deceleration profile is selected based on a present velocity (v_i), a present position (x_i) and a BEMF constant associated with a voice coil motor (VCM), wherein the deceleration profile is useful for moving the read/write head to a point in phase space (defined by a target velocity and a target position) where it is efficient to hand-off control of a seek operation from a deceleration controller to a seek controller. A control signal is supplied to a VCM driver in an attempt to have a read/write head follow the selected deceleration profile. As new present velocities and new present positions are obtained, these steps are repeated until the seek operation transitions from the deceleration phase to a settle phase. This description is not intended to be a complete description of, or limit the scope of, the invention. Other features, aspects, and objects of the invention can be obtained from a review of the specification, the figures and the claims.

Claims

1. For use in a disk drive system including a read/write head, an actuator assembly including a voice coil motor (VCM) that is used to control movement of the read/write head, and a VCM driver that drives the VCM, wherein the VCM has an associated back electromagnetic field (BEMF) constant,

a method for controlling the deceleration phase of a seek operation that is used to move the read/write head to a desired velocity and a desired position in phase space, the method comprising:

(a) obtaining a present (v_i) and a present position (x_i) of the read/write head;

(b) selecting a deceleration profile, based on the present velocity (v_i), the present position (x_i) and the BEMF constant,

wherein the deceleration profile defines a path in phase space from the present velocity and present position to a target velocity and a target position where it is useful to switch from the deceleration phase to a settling phase of the seek operation, rather than defining a path in phase space from the present velocity and present position to the desired velocity and the desired position,

wherein the target velocity and the target position are offset, respectively, from the desired velocity and the desired position; and

(c) supplying a control signal to the VCM driver in an attempt to have the read/write head follow the selected deceleration profile.

2. The method of claim 1, wherein:

each present position (x_i) is expressed in terms of a position error from the desired position; and

each present velocity (v_i) is expressed in terms of a velocity error from the desired velocity.

3. The method of claim 1, wherein each deceleration profile is generally of the form

a=f·

(a₀−

K·

v)

where,

a represents a deceleration;

f is a fraction of a predetermined maximum possible deceleration control;

a₀ is a predetermined deceleration associated with a stall current of the VCM;

K is a predetermined BEMF constant of the VCM; and

v is a velocity of the VCM.

4. The method of claim 3, wherein:

each different value for f corresponds to a different deceleration profile; and

each of the different deceleration profiles intersect one another at a point in phase space representing the target velocity and the target position.

5. The method of claim 4, wherein step (b) includes solving for f.

6. The method of claim 5, wherein step (b) includes solving for f in accordance with the following equation

$f=\frac{h}{}$

( v i ) - h ⁡

( v τ

) x i - x τ

where

$h<br><br>\left(v_i\right)=-\frac{v_i}{K}-\frac{a_0}{K^2}<br><br>\ln <br><br>\left(1-\frac{\mathrm{\kappa <br><br>}·<br><br>v_{\mathrm{\tau <br><br>}}}{a_0}\right);<br><br>$

v_i is the present velocity;

x_i is the present position;

$h<br><br>\left(v_{\mathrm{\tau <br><br>}}\right)=-\frac{v_{\mathrm{\tau <br><br>}}}{K}-\frac{a_0}{K^2}<br><br>\ln <br><br>\left(1-\frac{K·<br><br>v_{\mathrm{\tau <br><br>}}}{a_0}\right);<br><br>$

v_T is the target velocity, which is offset from the desired velocity; and

x_T is the target position, which is offset from the desired position.

7. The method of claim 6, wherein, once f is solved for, the selected deceleration profile generally has the form

$a_i=\frac{h}{}$

( v i ) - h ⁡

( v τ

) x i - x τ

⁢

( a 0 - K ·

v i ) .

8. The method of claim 6, wherein step (b) includes determining h(v_i) and h(v_T) on-the-fly.

9. The method of claim 6, wherein values for h(v_i) and h(v_T) that correspond to numerous possible velocities and numerous possible positions that are pre-computed and stored.

10. The method of claim 9, wherein step (b) includes solving for f using the stored values for h(v_i) and h(v_T).

11. The method of claim 1, further comprising repeating steps (a) through (c) at later points in time during the same deceleration phase of the same seek operation, wherein:

each time step (a) is repeated a new present velocity and a new present position is obtained;

each time step (b) is repeated a new deceleration profile is selected based on the new present velocity most recently obtained at step (a), the new present position most recently obtained at step (a), and the BEMF constant; and

each time step (c) is repeated the control signal is supplied to the VCM driver in an attempt to have the read/write head follow the new deceleration profile most recently selected at step (b).

12. The method of claim 11, wherein the new deceleration profile most recently selected at step (b) can be the same as a previously selected deceleration profile if the new present velocity and the new present position most recently obtained at step (a) lie on the previously selected deceleration profile.

13. The method of claim 11, wherein steps (a) through (c) are repeated until the present position and the present velocity, respectively, are substantially equal to the target position and the target velocity, at which point the seek operation transition from the deceleration phase to the settling phase.

14. The method of claim 11, wherein:

each present position (x_i) is expressed in terms of a position error from the desired position; and

each present velocity (v_i) is expressed in terms of a velocity error from the desired velocity.

15. The method of claim 11, wherein each deceleration profile is generally of the form

a=f·

(a₀−

K·

v)

where,

a represents a deceleration;

f is a fraction of a predetermined maximum possible deceleration control;

a₀ is a predetermined deceleration associated with a stall current of the VCM;

K is a predetermined BEMF constant of the VCM; and

v is a velocity of the VCM.

16. The method of claim 15, wherein:

each different value for f corresponds to a different deceleration profile; and

each of the different deceleration profiles intersect one another at a point in phase space representing the target velocity and the target position.

17. The method of claim 16, wherein step (b) includes solving for f.

18. The method of claim 17, wherein step (b) includes solving for f in accordance with the following equation

$f=\frac{h}{}$

( v i ) - h ⁡

( v τ

) x i - x τ

where

$h<br><br>\left(v_i\right)=-\frac{v_i}{K}-\frac{a_0}{K^2}<br><br>\ln <br><br>\left(1-\frac{\mathrm{\kappa <br><br>}·<br><br>v_{\mathrm{\tau <br><br>}}}{a_0}\right);<br><br>$

v_i is the present velocity;

x_i is the present position;

$h<br><br>\left(v_{\mathrm{\tau <br><br>}}\right)=-\frac{v_{\mathrm{\tau <br><br>}}}{K}-\frac{a_0}{K^2}<br><br>\ln <br><br>\left(1-\frac{K·<br><br>v_{\mathrm{\tau <br><br>}}}{a_0}\right);<br><br>$

v_T is the target velocity, which is offset from the desired velocity; and

x_T is the target position, which is offset from the desired position.

19. The method of claim 18, wherein, once f is solved for, the selected deceleration profile generally has the form

$a_i=\frac{h}{}$

( v i ) - h ⁡

( v τ

) x i - x τ

⁢

( a 0 - K ·

v i ) .

20. The method of claim 18, wherein step (b) includes determining h(v_i) and h(v_T) on-the-fly.

21. The method of claim 18, wherein values for h(v_i) and h(v_T) that correspond to numerous possible velocities and numerous possible positions that are pre-computed and stored.

22. The method of claim 21, wherein step (b) includes solving for f using the stored values for h(v_i) and h(v_T).

23. The method of claim 1, wherein the BEMF constant can differ for different positions along a stroke of the drive, and wherein the BEMF constant used for selecting the deceleration profile in step (b) is a predetermined BEMF constant corresponding to the present position.

24. For use in a disk drive system including a read/write head, an actuator assembly including a voice coil motor (VCM) that is used to control movement of the read/write head, and a VCM driver that drives the VCM, wherein the VCM has an associated back electromagnetic field (BEMF) constant,

a method for controlling the deceleration phase of a seek operation that is used to move the read/write head to a desired velocity and a desired position in phase space, the method comprising:

(a) obtaining a present velocity (v_i) and a present position (x_i) of the read/write head;

(b) selecting a deceleration profile, based on the present velocity (v_i), the present position (x_i) and the BEMF constant,

wherein the deceleration profile defines a path in phase space from the present velocity and present position to a target velocity and a target position where it is useful to switch from the deceleration phase to a settling phase of the seek operation, rather than defining a path in phase space from the present velocity and present position to the desired velocity and the desired position,

wherein the target velocity and the target position are offset, respectively, from the desired velocity and the desired position; and

(c) supplying a control signal to the VCM driver, wherein the control signal is a function of the selected deceleration profile, the present velocity, the present position and the BEMF constant.

25. The method of claim 24, wherein the BEMF constant can differ for different positions along a stroke of the drive, and wherein the BEMF constant used for selecting the deceleration profile in step (b) is a predetermined BEMF constant corresponding to the present position.

26. The method of claim 24, further comprising repeating steps (a) through (c) at later points in time during the same deceleration phase of the same seek operation, wherein:

each time step (a) is repeated a new present velocity and a new present position is obtained;

each time step (b) is repeated a new deceleration profile is selected based on the new present velocity most recently obtained at step (a), the new present position most recently obtained at step (a), and the BEMF constant; and

each time step (c) is repeated the control signal is supplied to the VCM driver in an attempt to have the read/write head follow the new deceleration profile most recently selected at step (b).

27. The method of claim 26, wherein steps (a) through (c) are repeated until the seek operation transitions from the deceleration phase to the settling phase.

28. A method for moving a read/write head to a target point in phase where it is efficient to hand-off of a seek operation from a deceleration controller to a seek controller, the method comprising:

(a) obtaining a present velocity (v_i) and a present position (x_i) of the read/write head;

(b) selecting a deceleration profile that can be used to move the read/write head from the present velocity and the present position to a target velocity and a target position that are offset, respectively, from the desired velocity and the desired position, rather than selecting a deceleration profile that can be used to move the read/write head from the present velocity and present position to the desired velocity and the desired position; and

(c) using the selected deceleration profile to control movement of the read/write head toward the target velocity and the target position;

wherein the target velocity and the target position correspond to the target point in phase space where it is efficient to hand-off control of the seek operation from the deceleration controller to the seek controller.

29. The method of claim 28, further comprising repeating steps (a) through (c) at later points in time during the same seek operation, wherein:

each time step (a) is repeated a new present velocity and a new present position is obtained;

each time step (b) is repeated a new deceleration profile is selected based on the new present velocity most recently obtained at step (a) and the new present position most recently obtained at step (a); and

each time step (c) is repeated the selected deceleration profile most recently selected at step (b) is used to control movement of the read/write head.

30. The method of claim 29, wherein each deceleration profile is generally of the form

a=f·

(a₀−

K·

v)

where,

a represents a deceleration;

f is a fraction of a predetermined maximum possible deceleration control;

a₀ is a predetermined deceleration associated with a stall current of a voice coil motor (VCM) that is used to control movement of the read/write head;

K is a predetermined BEMF constant of the VCM; and

v is a velocity of the VCM.

31. A disk drive system, comprising:

a rotatable disk including at least one surface to store information;

a read/write head to read form and write to the disk;

an actuator assembly including a voice coil motor (VCM) that is used to control movement of the read/write head, wherein the VCM has an associated back electromagnetic field (BEMF) constant;

a VCM driver to drive the VCM; and

a deceleration controller to control a deceleration phase of a seek operation that is used to move the read/write head to a desired velocity and a desired position in phase space,

wherein the deceleration controller is configured to select a deceleration profile, based on a present velocity (v_i) and a present position (x_i) of the read/write head and the BEMF constant,

wherein the deceleration profile defined a path in phase space from the present velocity and present position to a target velocity and a target position where it is useful to switch from the deceleration phase to a settling phase of the seek operation, rather than defining a path in phase space from the present velocity and present position to the desired velocity and the desired position,

wherein the target velocity and the target position are offset, respectively, from the desired velocity and the desired position; and

wherein the deceleration controller is further configured to supply a control signal to the VCM driver in an attempt to have the read/write head follow the selected deceleration profile.

32. The system of claim 31, wherein:

each present position (x_i) is expressed in terms of a position error from the desired position; and

each present velocity (v_i) is expressed in terms of a velocity error from the desired velocity.

33. The system of claim 31, wherein each deceleration profile is generally of the form

a=f·

(a₀−

K·

v)

where,

a represents a deceleration;

f is a fraction of a predetermined maximum possible deceleration control;

a₀ is a predetermined deceleration associated with a stall current of the VCM;

K is a predetermined BEMF constant of the VCM; and

v is a velocity of the VCM.

34. The system of claim 33, wherein:

each different value for f corresponds to a different deceleration profile; and

each of the different deceleration profiles intersect one another at a point in phase space representing the target velocity and the target position.

35. The system of claim 34, wherein the deceleration controller is configured to solve for f.

36. The system of claim 35, wherein the deceleration controller is configured to solve for f in accordance with the following equation

$f=\frac{h}{}$

( v i ) - h ⁡

( v τ

) x i - x τ

where

$h<br><br>\left(v_i\right)=-\frac{v_i}{K}-\frac{a_0}{K^2}<br><br>\ln <br><br>\left(1-\frac{\mathrm{\kappa <br><br>}·<br><br>v_{\mathrm{\tau <br><br>}}}{a_0}\right);<br><br>$

v_i is the present velocity;

x_i is the present position;

$h<br><br>\left(v_{\mathrm{\tau <br><br>}}\right)=-\frac{v_{\mathrm{\tau <br><br>}}}{K}-\frac{a_0}{K^2}<br><br>\ln <br><br>\left(1-\frac{K·<br><br>v_{\mathrm{\tau <br><br>}}}{a_0}\right);<br><br>$

v_T is the target velocity, which is offset from the desired velocity; and

x_T is the target position, which is offset from the desired position.

37. The system of claim 36, wherein, once f is solved for, the selected deceleration profile generally has the form

$a_i=\frac{h}{}$

( v i ) - h ⁡

( v τ

) x i - x τ

⁢

( a 0 - K ·

v i ) .

38. The system of claim 36, wherein the deceleration controller is configured to determine h(v_i) and h(v_T) on-the-fly.

39. The system of claim 36, wherein values for h(v_i) and h(v_T) that correspond to numerous possible velocities and numerous possible positions are pre-computed and stored.

40. The system of claim 39, wherein the deceleration controller is configured to solve for f using the stored values for h(v_i) and h(v_T).

41. The system of claim 31, wherein the deceleration controller is configured to:

select a new deceleration profile each time a new present velocity and a new present position are obtained during the same deceleration phase of the same seek operation; and

supply a control signal to the VCM driver in an attempt to have the read/write head follow the new selected deceleration profile.

42. The system of claim 41, wherein the new selected deceleration profile can be the same as a previously selected deceleration profile if the new present velocity and the new present position lie on the previously selected deceleration profile.

43. The system of claim 41, wherein control of a seek operation is transferred from the deceleration controller to a settle controller when a predetermined condition is satisfied.

44. The system of claim 41, wherein:

each present position (x_i) is expressed in terms of a position error from the desired position; and

each present velocity (v_i) is expressed in terms of a velocity error from the desired velocity.

45. The system of claim 41, wherein each deceleration profile is generally of the form

a=f·

(a₀−

K·

v)

where,

a represents a deceleration;

f is a fraction of a predetermined maximum possible deceleration control;

a₀ is a predetermined deceleration associated with a stall current of the VCM;

K is a predetermined BEMF constant of the VCM; and

v is a velocity of the VCM.

46. The system of claim 45, wherein:

each different value for f corresponds to a different deceleration profile; and

each of the different deceleration profiles intersect one another at a point in phase space representing the target velocity and the target position.

47. The system of claim 46, wherein the deceleration controller is configured to solve for f.

48. The system of claim 46, wherein the deceleration controller is configured to solve for f in accordance with the following equation

$f=\frac{h}{}$

( v i ) x i ⁢

where

$h<br><br>\left(v_i\right)=-\frac{v_i}{K}-\frac{a_0}{K^2}<br><br>\ln <br><br>\left(1-\frac{K·<br><br>v_i}{a_0}\right);<br><br>$

v_i is the present velocity; and

x_i is the present position.

49. The system of claim 48, wherein, once f is solved for, the selected deceleration profile generally has the form

$a_i=\frac{h}{}$

( v i ) - h ⁡

( v T ) x i - x τ

⁢

( a 0 - K ·

v i ) .

50. The system of claim 48, wherein the deceleration controller is configured to determine h(v_i) and h(v_T) on-the-fly.

51. The system of claim 48, wherein values for h(v_i) and h(v_T) that correspond to numerous possible velocities and numerous possible positions are pre-computed and stored.

52. The system of claim 51, wherein the deceleration controller is configured to solve for f using the stored values for h(v_i) and h(v_T).

53. The system of claim 31, wherein the BEMF constant can differ for different positions along a stroke of the drive, and wherein the BEMF constant used for selecting the deceleration profile is a predetermined BEMF constant corresponding to the present position.

54. A disk drive system, comprising:

a rotatable disk including at least one surface to store information;

a read/write head from and write to the disk;

an actuator assembly including a voice coil motor (VCM) that is used to control movement of the read/write head, wherein the VCM has an associated back electromagnetic field (BEMF) constant; and

a deceleration controller to control a deceleration phase of a seek operation that is used to move the read/write head to a desired velocity and a desired position in phase space,

wherein the deceleration controller is configured to select a deceleration profile, based on a present velocity (v_i) and a present position (x_i) of the read/write head and the BEMF constant,

wherein the deceleration profile defines a path in phase space from the present velocity and present position to a target velocity and a target position where it is useful to switch from the deceleration phase to a settling phase of the seek operation, rather than defining a path in phase space from the present velocity and present position to the desired velocity and the desired position,

wherein the target velocity and the target position are offset, respectively, from the desired velocity and the desired position; and

wherein the deceleration controller is further configured to control movement of the read/write head using the selected deceleration profile.

55. The system of claim 54, further comprising:

a VCM driver to drive the VCM;

wherein the deceleration controller supplies a control signal to the VCM driver in order to control movement of the read/write head.

56. The system of claim 54, wherein the BEMF constant can differ for different positions along a stroke of the drive, and wherein the BEMF constant used for selecting the deceleration profile is a predetermined BEMF constant corresponding to the present position.

57. The system of claim 54, wherein the deceleration controller is configured to:

select a new deceleration profile each time a new present velocity and new present position are obtained during the same deceleration phase of the same seek operation; and

control movement of the read/write head using the new selected deceleration profile.

58. The system of claim 54, wherein control of a seek operation is transferred from the deceleration controller to a settle controller when a predetermined condition is satisfied.