Flying head with adjustable actuator load

• US 6,178,157 B1
• Filed: 02/21/1997
• Issued: 01/23/2001
• Est. Priority Date: 04/15/1996
• Status: Expired due to Fees

• Current Assignee: Digital Papyrus Corporation
• Original Assignee: Digital Papyrus Corporation
• Inventors: Lee, Neville K. S., Berg, John S.
• Primary Examiner(s): KLIMOWICZ, WILLIAM JOSEPH
• Application Number:
  US08/804,301
• Time in Patent Office: 1,432 Days
• Field of Search: 360/75, 360/102, 360/103, 360/104, 360/106, 360/109, 360/114, 360/294.7, 360/234.7, 360/234.3, 360/234.4, 369/300, 369/13, 369/110, 369/112
• US Class Current: 369/300
• CPC Class Codes: G11B 21/21 with provision for maintaining desired spacing of head from record carrier, e.g. fluid-dynamic spacing, slider
• CPC Class Codes: G11B 7/0037 with discs
• CPC Class Codes: G11B 7/093 for focusing and tracking G11B7/0932 - G11B7/0937 take precedence
• CPC Class Codes: G11B 7/0937 Piezoelectric actuators
• CPC Class Codes: G11B 7/12 Heads, e.g. forming of the optical beam spot or modulation of the optical beam disposition or mounting of head elements within housing or with provision for moving of light source, optical beam or detector, irrelevant to the transducing method G11B7/08 ; modulating lasers H01S3/10; controlling the intensity, colour, phase, polarisation or direction of light beams arriving from an independent light source, e.g. switching gating or modulating G02F1/00
• CPC Class Codes: G11B 7/122 Flying-type heads, e.g. analogous to Winchester type in magnetic recording

Abstract

A flying head mechanism includes a flying head, a suspension and an actuator which applies a load force through the suspension. The load force applied by the actuator is adjustable while the head is in operation. The actuator may actively control load force as part of a feedback loop which maintains the flying head at a constant flying height. One embodiment disclosed includes a voice coil actuator. In embodiments using an optical flying head, a conventional focus sensor may provide a signal indicative of flying height, since the focus signal inherently indicates flying height error.

Claims

1. A flying head mechanism having a controllable load force, for flying an optical head at a flying height between a minimum glide height which is just greater than a height of asperities on a recording medium and a height at which evanescent wave coupling at a wavelength of interest occurs, the mechanism comprising:

a suspension;

an optical head having an air bearing surface and a solid inmersion lens (SIL), the head being mounted by the suspension such that relative motion between a surface of the recording medium and the air bearing surface will cause an air bearing to develop therebetween;

a force actuator, connected to the suspension, to apply an adjustable load force to the head through the suspension in opposition to a separating force generated by the air bearing, the force actuator having a control input to receive a control signal and being responsive to the control signal to adjust the load force; and

a controller having a control output, connected to the control input of the force actuator, that carries the control signal, the controller generating the control signal, to cause the actuator to produce a load force which acts to substantially maintain the head at the flying height between the minimum glide height just greater than the height of asperities above the surface of the recording medium and the height at which evanescent wave coupling at the wavelength of interest occurs.

2. The flying head mechanism of claim 1, wherein the control signal is an electrical current and wherein the force actuator includes a voice coil that is coupled to the control input and responsive to the control signal.

3. The flying head mechanism of claim 1, wherein the controller includes a sensor which has an output indicative of when the head flies at a height less than the minimum glide height.

4. The flying head mechanism of claim 3, wherein the sensor detects contacts between the head and the surface of the recording medium.

5. The flying head mechanism of claim 4, wherein the sensor produces as the sensor signal a signal representing an amplitude of a natural frequency of vibration of the head induced by contact between the head and the medium.

6. The flying head mechanism of claim 5, wherein the flying height sensor includes a piezoelectric transducer positioned to detect vibration of the head.

7. The flying head mechanism of claim 5, wherein the flying height sensor includes a piezoelectric transducer positioned to detect vibration of the head, wherein the flying height sensor is integrated with the head.

8. The flying head mechanism of claim 5, wherein the sensor is an optical transducer which detects modulation of an optical signal at the natural frequency.

9. The flying head mechanism of claim 8, wherein the optical transducer reproduces information from the recording medium and includes:

a detector having an output, connected to the flying height sensor output, that provides a signal representing a degree of focus of a light spot projected onto the medium surface by the head.

10. The flying head mechanism of claim 1, wherein the suspension comprises:

a gimbal that mounts the head and has a lower spring rate in roll and pitch directions than in vertical, yaw and seek directions.

11. The flying head mechanism of claim 10, wherein the suspension further comprises:

a load arm supporting the gimbal; and

a resilient member disposed between the load arm and a region of the gimbal connected to the head.

12. The flying head mechanism of claim 10, wherein the suspension further comprises:

a load arm;

an auxiliary load arm to which the gimbal is mounted; and

a spring connecting the load arm and the auxiliary load arm.

13. The flying head mechanism of claim 3, wherein the controller further comprises:

a memory, in which a map of vertical runout measured by the sensor can be stored; and

a bias generator that biases the force actuator according to the map stored in the memory.

14. A flying head mechanism having a controllable load force, for flying an optical head at a flying height between a minimum glide height which is just greater than a height of asperities on a recording medium and a height at which evanescent wave coupling at a wavelength of interest occurs, the mechanism comprising:

a head having a solid inmersion lens (SIL) and further having an air bearing surface oriented relative to a surface of the recording medium such that relative motion between the air bearing surface and the recording medium surface causes an air bearing to develop therebetween; and

a load force controller, coupled to the head, to apply a load force in opposition to a separating force generated on the head by the air bearing, the load force controller including a sensor to measure a flying height and minimum glide height of the head, the load force controller being configured to vary the load force to maintain a constant separation between the air bearing surface and the recording medium surface greater than the minimum glide height just greater than the height of asperities on the recording medium surface and less than the height at which evanescent wave coupling at the wavelength of interest occurs.

15. The flying head mechanism of claim 14, wherein the sensor includes means for detecting a frequency of contact between the air bearing surface and the recording medium, and wherein the minimum glide height is represented by a substantially zero frequency of contact.

16. The flying head mechanism of claim 15, wherein the sensor is a piezoelectric transducer having an output which represents flying heights less than the minimum glide height by an amplitude of a natural frequency of vibration of the head detected by the piezoelectric transducer.

17. The flying head mechanism of claim 15, wherein the means for detecting a frequency of contact is an optical transducer which detects modulation of an optical signal at a natural frequency of vibration of the head.

18. The flying head mechanism of claim 17, wherein the optical transducer reproduces information from the recording medium and includes:

a detector having an output carrying a signal representing a degree of focus of a light spot projected onto the medium surface by the head.

19. The flying head mechanism of claim 14, further comprising:

a controller having an input connected to an output of the sensor to receive a signal representative of a flying height relative to the minimum glide height, the controller having an output in communication with a control input of an actuator, the output carrying a control signal derived from a characteristic of the signal representative of the separation between the air bearing surface and the recording medium surface;

wherein the head includes said lens arranged to focus a laser beam onto the recording medium, and wherein the sensor also includes means for receiving through the lens an optical signal carrying recorded information from the recording medium and means for transducing the optical signal into an electrical signal.

20. The flying head mechanism of claim 19, wherein the sensor further comprises a focus detector in a path of the laser beam that produces focus information of the laser beam on the recording medium, and wherein the controller derives the control signal from the focus information.

21. The method of claim 14, the load force controller receiving from the sensor vertical runout measurements, the load force controller further comprising:

a memory in which a map of vertical runout can be stored; and

a bias generator that biases the load force according to the map stored in the memory.

22. A method of controlling a load force applied to a flying optical head while using the flying optical head to reproduce information recorded on a recording medium, the method comprising steps of:

measuring a flying height of the head above an information track of the recording medium;

determining whether the measured flying height is less than or equal to a minimum glide height just greater than a height of asperities on the recording medium;

adjusting the load force applied to the head when the measured flying height is found less than or equal to the minimum glide height in the step of determining; and

simultaneously with the foregoing steps, reproducing information recorded on the recording medium using a solid inmersion lens (SIL) carried by the flying optical head to evanescently couple an optical signal into the recording medium.

23. The method of claim 22, wherein the step of measuring further comprises steps of:

projecting a laser beam through said lens on the head onto the recording medium;

detecting focus of the projected laser beam; and

computing the measured flying height from the detected focus.

24. The method of claim 23, further comprising a step of:

extracting from the detected focus an amplitude of a variation in focus occurring at a resonant frequency of vibration of the head; and

wherein the step of computing includes computing the measured flying height from the amplitude extracted from the detected focus.

25. The method of claim 22, further comprising:

measuring vertical runout of the recording medium;

storing a map of vertical runout of the recording medium; and

providing a bias to the step of adjusting load force, the bias corresponding to the stored map.

26. A method of loading a flying optical head on a medium, comprising steps of:

applying a load force to the head; and

dynamically varying the load force by means of a controller in response to varying operating conditions to maintain a substantially constant flying height greater than a minimum glide height just greater than a height of asperities on the medium and less than a height at which evanescent wave coupling by a solid inmersion lens (SIL) carried by the head at a wavelength of interest occurs while the head retrieves information from the medium by evanescently coupling an optical signal into the medium.

27. The method of claim 26, further comprising a step of:

measuring a flying height of the head relative to the minimum glide height; and

wherein the step of varying the load force is performed responsive to the step of measuring.

28. The method of claim 26, further comprising a step of:

generating a signal representative of contacts between the head and the medium indicative of a flying height less than the minimum glide height.

29. A flying head mechanism comprising:

a flying optical head carrying a solid inmersion lens (SIL);

a sensor that detects a flying height of the head relative to a minimum glide height just greater than a height of asperities on a medium; and

means for applying a load force to the head that varies in accordance with the detected flying height to maintain the flying height of the flying head greater than the minimum glide height just greater than the height of asperities on the medium and less than a height at which evanescent wave coupling at a wavelength of interest occurs.

30. The mechanism of claim 29, wherein the flying head is to be used in connection with a recording medium, and wherein the means for applying further comprises:

means mounted between head and means for applying, that permit movement of the head relative to the means for applying in response to vertical runout of the recording medium.

31. The mechanism of claim 29, wherein the sensor further comprises:

means for measuring an amplitude of a resonant frequency of vibration of the head indicative of contact between the head and a recording medium, the control output varying responsive to the means for measuring.

32. The mechanism of claim 29, further comprising:

a controller including a memory, the controller receiving vertical runout measurements of the recording medium from the sensor and storing a map thereof in the memory, and the controller further including a bias generator that biases the means for applying a load force according to the stored map.