WO1997039445A1

WO1997039445A1 - Method and apparatus for detecting the minimum glide height of a flying head and for focusing a lens carried on a flying head

Info

Publication number: WO1997039445A1
Application number: PCT/US1997/006217
Authority: WO
Inventors: John S. Berg; Neville K. S. Lee
Original assignee: Digital Papyrus Technologies
Priority date: 1996-04-15
Filing date: 1997-04-15
Publication date: 1997-10-23

Abstract

A flying head comprises a lens which is movably affixed to the body having an air bearing surface. The flying head system may also comprise a focus sensor and focus controller. A method of focusing a laser beam is also claimed. Another aspect of the application is a flying head comprising a contact sensor having an electrical connection that carries a signal indicative of contact between the flying head and the recording medium. According to another aspect of the application a flying head comprises a lens affixed to a body, and an electric heater mounted to the body, which changes the focus of the lens when a current flows in the electric heater.

Description

METHOD AND APPARATUS FOR DETECTING THE MINIMUM GLIDE HEIGHT OF A FLYING HEAD AND FOR FOCUSING A LENS CARRIED ON A FLYING HEAD

Background 1. Cross-Reference to Related Application

This application is related to the present inventors' copending U.S. Patent Application Serial No. 08/804,301, entitled FLYING HEAD WITH ADJUSTABLE ACTUATOR LOAD, filed February 21, 1997.

2. Field of the Invention

The present invention relates generally to focus systems for optical disk drive heads. More particularly, the invention relates to focus systems in flying optical heads, including those whose flying height is under closed loop control.

3. Related Art

High density disk drive systems based on magneto-optic and optical storage principles generally use a transducer system which does not, under normal operating conditions, contact the surface of the recording medium. Such non-contact transducers are known in this art as flying heads because of the principles upon which they rely to maintain a correct position with respect to the surface of the recording medium.

A brief description of how a flying head flies is now given, with reference to Fig. 15.

During operation of a disk drive, the recording medium, typically in the form of a specially coated disk of aluminum, glass or plastic, rotates at high speeds, e.g., 3600 RPM. The rotary motion of the disk 107 causes an air flow in the direction of rotation, near the surface 106 of the disk 107. The head 101 is placed by a mechanical actuator or load arm 103 in proximity with the surface 106 of the disk so that the air flow passes between the surface of the disk and the lower features of the head, thereby forming a cushion of air 108 which generates an upwards force F_A on the head 101 due to air pressure in the space between the disk surface and the lower features of the head 101. with the lower features of the head defining an air bearing surface 1 10. The cushion of air 108 that develops between the air bearing surface 110 and the surface 106 of the disk is referred to hereinafter as an air bearing.

The flying head 101 flies at a flying height 1 13. defined herein as the separation distance between the air bearing surface 1 10 of the head 101 and the surface 106 of the disk, determined by the force balance between the air. pressure F_A of the air bearing 108 pushing the head 101 away from the surface 106 of the disk, and a downward force F, exerted through a spring 105 or suspension that mounts the head 101 to the load arm or actuator 103.

The force F_L has a magnitude determined by the physical dimensions of the spring, the spring constant of the spring material and the deformation of the spring which occurs in operation. The upward force F_A applied by the air bearing depends on the finish of the disk surface, the linear velocity of the disk surface where it passes under the head, and the shape and size of the air bearing surface of the head. Whenever F_A and F_L are not equal, the head experiences a net force which causes it to move in a vertical direction corresponding to the direction of the net force. When F_L = F_A, the head experiences no net force, and hence no vertical motion.

In conventional systems, as flying height 113 increases, the air bearing 108 grows, lowering F_A, while spring 105 is compressed, raising F_L. The relationship between each of the forces F_L and F_A and flying height 113 can be determined by application of aerodynamic principles to the system configuration, which can be done by making measurements on actual systems, or physical or computer-generated models of the system. The conventional system is designed so that F_L=F_Aat the desired flying height when the disk 107 is spinning at its normal speed. When the disk spins down, i.e., slows to a stop, insufficient air flow occurs to maintain the air bearing between head and disk. Hence, insufficient air pressure and force are generated to counteract the downward force exerted by the spring or suspension, leading to contact between head and disk. Thus, when the disk 107 slows to a stop, the head 101 may come to rest on the disk surface 106. Alternatively, the disk drive may include a mechanism that lifts the suspension 103 to prevent contact between the head and the disk when the disk spins down, but otherwise plays no role in normal disk drive operation. Flying height 113 is one important parameter governing successful operation of a disk drive. At extremely large values for flying height 113. excessive distance from the disk can cause unacceptable functional performance, for example, an inability to discriminate high frequency signals. Close proximity of the head to the disk improves functional performance. However, at extremely small values for flying height 113. insufficient flying height or loss of separation between the head and the disk can result in aerodynamic instability, reliability problems and catastrophic product failure, e.g., a head crash which occurs when the head contacts the disk surface with sufficient force to cause damage to the head or the disk surface - J resulting in a loss of data. Avoiding potential damage often associated with contact between head and disk is the reason that some disk drives move their heads away from the disk surface to avoid contact when the disk spins down. The lowest height at which the head can fly without making contact with the disk surface is defined as the minimum glide height for the disk. Asperities (i.e.. microscopic bumps or roughness) in the disk surface are those features which are likely to be contacted first by the head.

One problem of disk drive manufacturing is that the physical parameters determinative of flying height, e.g., the spring characteristics (affecting load force), the design of the air bearing surface shape, manufacturing variations in the air bearing surface geometry and finish (affecting air bearing force), and the load arm position relative to the surface of the disk (affecting load force), exhibit some variation within a tolerance band which causes a corresponding variation in the load force or air bearing force and. in turn, flying height. Other sources of variation in flying height in a disk drive include variations in altitude (i.e., ambient air density), radial position of the head on the disk which varies the velocity of the air flow due to different track circumferential lengths at different track radii, and skew angle of the head relative to a line tangential to a track, all of which affect the air bearing force.

Conventionally, flying height is set by a mechanical adjustment made at the time of manufacture of a disk drive. The mechanical adjustment sets a static load force selected to provide a desired flying height under nominal conditions. For example, the static load force may be measured manually and adjusted by repositioning or bending the load arm 103. Once set, the static load force remains substantially unaltered for the life of the disk drive, despite variations in operating conditions which may cause variation in other parameters determinative of flying height. Conventional systems are also known which employ closed loop feedback control systems to maintain a substantially constant flying height. Although such systems can compensate for variations in some parameters, there remain other uncompensated tolerance errors, such as variation in the actual minimum glide height from one disk to another.

Thus, flying height in conventional disk drives cannot be set to the minimum glide height. Rather, tolerance variations such as discussed above are typically taken in consideration, adding a tolerance band to the nominal or design minimum glide height of a disk when setting the actual flying height. Therefore, in order to avoid any likelihood of unwanted contact between the head and the surface of the disk, conventional systems set a nominal flying height that is greater than the largest expected actual minimum glide height. Conventional systems use this tolerance band because they have no way of determining the actual minimum glide height for the disk.

In view of the foregoing, one problem encountered in the prior art is that conventional flying head systems are unable to fly at the actual minimum glide height for a disk. An optical flying head and related disk drive components are shown schematically in Fig.

20. The optical flying head 2001 includes a body 2003 having a lower surface defining an air bearing surface 2005. The head 2001 also has a two-element lens 2007 affixed to the body 2003. A laser light source 2009 emits a collimated laser beam 201 1 which is passed through the lens, focused onto the recording medium surface 2013 and returned through a beam splitter 2015 to a detector 2017. When properly focused, the beam is caused to converge exactly at the recording medium surface. The focal length of the lens, i.e., the distance at which the collimated laser beam will converge after passing through the lens, is fixed. This distance depends on the lens element shapes and sizes. It is desired to minimize the spot size of the focused beam. This is achieved by creating a diffraction limited lens system at the wavelength and numerical aperture of interest, i.e. one in which the wavefront error is minimized by correctly setting the distance between lens elements for the flying height. If the beam fails to converge exactly at the recording medium surface due to flying height variation or other tolerances, then the density at which information can be recorded or recovered may be adversely affected.

In view of the foregoing, another problem encountered in conventional flying head systems is controlling the height of the lens above the disk so that it remains at the focal length of the lens. Since conventional systems fixedly mount the lens to the head, variations in flying height of the head necessarily result in variations in the height of the lens above the disk, which can result in degraded performance if that height is not at the focal length of the lens. In addition, variations in other characteristics of the system, including the positioning of the lens relative to the air bearing surface and the shape of the lens, can also affect whether focus is achieved. Conventional systems cannot independently compensate for these variations, because the height of the lens above the disk can be controlled only by varying the height of the head to which the lens is fixed. Summary of the Invention

According to one aspect of the invention, there is a flying head for use with a recording medium, including a body having an air bearing surface; and a lens movably affixed to the body relative to the air bearing surface.

According to another aspect of the invention, there is a flying head for use with a recording medium, including a body having an air bearing surface; and a contact sensor having an electrical connection carrying a signal indicative of contact between the head and the medium. According to yet another aspect of the invention, there is a flying head system for use with a recording medium and a light source projecting a beam onto the recording medium. The system includes a flying head including an air bearing surface, a lens through which the beam is projected onto the recording medium, the lens movable with respect to the air bearing surface; a focus sensor having an output indicative of focus of the laser beam projected onto the recording medium; and a focus controller having an input that receives the focus sensor output and an output carrying a focus control signal, the output being connected to the flying head to cause movement of the lens relative to the air bearing surface.

Finally, according to yet another aspect of the invention, there is a method of focusing a laser beam onto a recording medium, comprising steps of: flying a head carrying a lens so an air bearing surface of the head is substantially at a minimum glide height above a recording medium; projecting the laser beam through the lens onto the recording medium; measuring focus of the laser beam projected onto the recording medium; controlling a position of the lens relative to the air bearing surface, responsive to the step of measuring, to alter focus of the laser beam projected onto the recording medium.

Brief Description of the Drawings

In the Figures in which like reference designations indicate like elements:

Fig. 1 is a schematic block diagram of a feedback controlled flying head load mechanism illustrating aspects of the present invention;

Fig. 2 is a perspective view of a disk drive using a mechanism embodying aspects of the invention;

Fig. 3 is a side elevation view of a head suspension used in the disk drive taken along line 3-3 of Fig. 2:

Fig. 4 is a bottom plan view of the head suspension taken along line 4-4 of Fig. 3:

RECTIFIED SHEET (RULE 91) ISA/EP Fig. 5 is a cross-sectional view of the head suspension taken along line 5-5 of Fig. 4: Fig. 6 is a perspective view of the head suspension of Figs. 2-5;

Fig. 7 is a side elevation view showing the movement of the head suspension of Figs. 2-5: Fig. 8 is an end elevation view of an embodiment of the invention directed to a head including an integrated focus actuator and head/disk interference sensor;

Fig. 9 is a detail view of the head suspension of Figs. 2-6 showing a gimbal; Fig. 10 is a detail view of the gimbal of Fig. 9;

Fig. 11 is a cross-sectional side view of a detail of one embodiment of the head suspension taken along line 11-11 of Fig. 9; Fig. 12 is a cross-sectional side view of a detail of an alternate embodiment of the head suspension of Fig. 9;

Fig. 13 is a cross-sectional side view of a detail of an alternate embodiment of the head suspension which may be used in place of that of Fig. 9;

Fig. 14 is a perspective view of the head suspension of Fig. 13; Fig. 15 is a schematic side elevation of a conventional flying head mechanism;

Fig. 16 is a perspective view of a pivoting head carriage assembly for use with a flying head, such as those shown in Figs. 8, 21 and 22 in accordance with the present invention;

Figs. 17, 18 and 19 are plan views of the pivoting head carriage assembly of Fig. 16, shown in three different positions; Fig. 20 is a schematic side elevation of a conventional optical flying head flying over a disk surface;

Fig. 21 is an end elevation view of an embodiment of the invention directed to a head including an integrated focus actuator; and

Fig. 22 is a plan view of the head of Fig. 21. Detailed Description

The present invention will be better understood upon reading the following detailed description of various illustrative embodiments of the invention, in connection with the figures.

The present inventors' related application entitled FLYING HEAD WITH ADJUSTABLE ACTUATOR LOAD, filed February 21, 1997, Serial No. 08/804.301 (hereafter referred to as "the related application"), which is incorporated herein by reference, teaches a method and apparatus for maintaining a flying head at a flying height substantially equal to the minimum glide height for each data track of the disk over which the head is flown.

RECTIFIED SHEET (RULE 91) ISA/EP despite variation in the minimum glide height from the nominal or design minimum glide height, and despite variations in other parameters affecting flying height. The related application teaches that this can be accomplished by measuring the actual minimum glide height at points along the disk while accessing data. The measurement can be made by detecting whether, and with what frequency, the flying head contacts surface asperities of the disk. The flying head is lowered toward the surface of the disk to a point where a low incidence of contact with surface asperities is detected, that point being just below the minimum glide height as defined above. The flying height of the head is then controlled to maintain the head just out of range of such contacts, i.e.. at the mimmum glide height. In one illustrative embodiment of the present invention, a flying head is provided that can be used in conjunction with a system such as the one disclosed in the related application to measure the actual minimum glide height. In this embodiment, the head includes an integrated head/disk interference or contact sensor that can be used to measure the minimum glide height.

As described above, in the system described in the related application, the head is flown at the minimum glide height, which will vary slightly from disk to disk. For optical systems that employ a lens on the flying head, that variation, in combination with small variations in lens shape and placement of lens elements relative to each other and relative to the air bearing of the head, can cause the lens system to fail to focus optimally at the minimum glide height. According to another aspect of the invention, a flying head is provided that includes a lens with an element that is movably mounted relative thereto, so that the lens can be focused independently of the flying height of the head. In view of current manufacturing tolerances, movement of the lens element of about 0.5μm is useful, but the invention is not limited thereto as other ranges of movement are also useful. A head with an independently focusable lens is useful in the above-described system where the flying height of the head varies to match the minimum glide height. However, it should be understood that the invention is not limited in this respect, and that the embodiment of the invention directed to an independently focusable lens can be used in any optical system, including those where the head is not flown at the minimum glide height.

In another illustrative embodiment of the invention, the above described aspects are advantageously combined by providing a flying head with a single transducer that both generates a signal indicative of head-disk interference, and also is capable of moving and focusing the lens independent of flying height. One embodiment of a flying head incorporating aspects of the invention, as shown in Fig. 8, includes a body 601 formed of a piezoelectric ceramic material, such as PZT. However, it should be understood that the invention is not limited to use of this or any other particular material. Additional illustrative embodiments using other materials are described below. Outriggers 611 defining the air bearing surface 617 are bonded to the block of piezoelectric ceramic, and can be formed of a conventional ceramic material, glass or any of a number of other materials. A lens element 613 is bonded at 615 to a surface of the head away from the air bearing surface 617 and a lens element 614 is bonded at 616 to a lower surface. The surface to which the lens is mounted is movable by body 601 to control focusing of the lens as discussed below. The body 601 includes electrodes 603 and 605 formed thereon. Although two are shown, more can be used. Across the electrodes 603 and 605, a signal is generated representative of stresses under which the body 601 of the head 101 is placed. For example, if the head 101 were to fly too close to the surface of the disk 107, at some point striking the surface of the disk 106, then the head 101 will "ring" or vibrate at a natural frequency dependent upon the mass of head 101 and the characteristics of the air bearing and suspension. A signal is generated across electrodes 603 and 605 at the natural frequency at which the head 101 rings. The amplitude of this signal indicating contact between the head 101 and the disk surface 106 can be used by the controller 11 1 (Fig. 2) as an indicator of head flying height 1 13 below the minimum glide height because more frequent contact between the head 101 and the disk surface 106 causes the ringing to be reinforced, resulting in a larger signal amplitude.

Piezoelectric material of which the body 601 of this embodiment is formed is advantageous because it is a two-way transducer between electrical and mechanical energy. The block of piezoelectric material generates an electrical signal at the conductive electrodes 603 and 605 which varies with mechanical excitation of the head 101. For example, as discussed above, when the head 101 hits an asperity on the surface of the disk 107, the head 101 will ring at a natural frequency of vibration. The mechanical energy of that vibration is then transduced into electrical energy forming the signal at electrodes 603 and 605. The piezoelectric material can also convert electrical energy in the form of an electrical signal applied to the electrodes 603 and 605 into an expansion of the body 601. This expansion can move the lens 613. which is mounted to body 601. independent of changes in the flying height 1 13, thereby allowing focus adjustments without changing flying height 113.

RECTIFIED SHEET (RULE 91 ) ISA/EP Altemate embodiments of thejnvention provide a similar advantage by combining any material that is a two-way transducer between electrical and mechanical energy, such as an electrostrictive material or a magnetostrictive material. When such a material is used as to form the body 601 of the head 101 , or some suitable portion thereof, the head can include an integrated focus actuator and head/disk interference sensor as discussed above.

In the embodiment discussed above, the head advantageously includes at least a portion thereof that is formed from a material that is a two-way transducer so that the head includes both advantageous features of the present invention directed to me independently focusable lens and the contact sensor. However, it should be understood that the present invention also contemplates the use of these features independently. Thus, the aspect of the invention directed to the independently focusable sensor is not limited to the use of a two-way transducer material in the head. Rather, lens elements can be movably mounted to the head in any of a number of other ways that would enable the lens to be focused independent of the flying height of the head. Similarly, the aspect of the invention directed to the contact sensor is not limited to the use of any of the two-way transducer materials discussed above. Rather, all that is required is that the head be provided with some type of sensor capable of detecting contact between the disk and head.

An alternate embodiment for implementing the independently focusable lens is shown in Figs. 21 and 22. In this embodiment, the body 2101 of the head 101 is formed of a conventional ceramic material or other material suitable for flying over the recording medium and supporting the lens. A heating element 2103 is formed on a surface of the body 2101 of the head 101. for example, by depositing a serpentine metallic pattern thereon. Causing an electric current to flow through the heating element 2103 generates heat which is transferred into the body 2101 of the head 101. As the body 2103 of the head 101 is heated it expands, displacing the lens element 2105 relative to the air bearing surface 2107 and causes lens element 2106 to alter its focus. The material used for the body 2101 of the head 101 is not limited to ceramic, as any of a number of other materials could be used, each having a coefficient of thermal expansion that is sufficient to provide the necessary change in position of the lens to focus it.

As discussed above, one application for the heads of the present invention, including those having integrated focus actuators, head/disk interference sensors, or both, is for use in systems such as described in the inventors' related application. This use is now described in greater detail, making reference to Fig. 1.

RECTIFIED SHEET (RULE 91) ISA/EP The load force actuator 109. (Fig. 2) adjusts F_L during normal operation of the head and disk. That is. the actuator adjusts F_L even while the head may be reading information from the disk or writing information to the disk during operation of the disk drive as a component of a computer system. Some embodiments of the system disclosed in the related application control flying height using a closed loop control architecture that, for example, makes adjustments to F, . By controlling F_L even during operation of the head and disk, embodiments of the actuator can adjust F_t to compensate for known or measured variations in F_A or other parameters that vary during such operation. For example, as atmospheric pressure slowly changes over time during operation of the disk drive, flying height can be controlled by automatically adjusting F_L to compensate for changes in F_A caused by the variation in atmospheric pressure.

The load force actuator 109 can control flying height to maintain the head at the minimum glide height for the disk, in contrast to conventional load-setting mechanisms which fly the head above the minimum glide height to accommodate tolerance errors. Maintaining the head at the minimum glide height, without hitting asperities, ensures that reliability remains high, while signal strength is maximized.

The schematic drawing of Fig. 1 is now referred to in connection with a general description of the actuator. As illustrated by the figure, the flying head 101 is resiliently mounted in a conventional manner to load arm 103 by a resilient member 105 which may be a spring, elastomer or other flexible element. Load arm 103 can be positioned by a positioner mechanism (not shown) to maintain head 101 in close proximity to disk 107. Disk 107 is rotated at high speed, generating an air bearing 108 between air bearing surface 1 10 and disk surface 106 that produces an upward force F_A upon head 101. The upward force F_A is balanced by a downward load force F_L generated by actuator 109, and acting on the head 101 through load arm 103 and resilient member 105. This embodiment of the invention further includes a feedback path including a controller 111 having an input which receives a signal 112 including a component indicative of the flying height 113 of the head 101 over the disk 107. and in particular of how close the head 101 is flying relative to the minimum glide height. In some embodiments of the present invention, signal 112 includes a head/disk interference component generated by a head/disk interference sensor integrated into the head 101 in the manner discussed above. A contact sensor (e.g., a piezoelectric sensor, electrostrictive sensor, magnetostrictive sensor or other transducer of mechanical energy to electrical energy) can be built into the head 101 to detect asperities or bumps on the disk 107. Detecting any asperities indicates the head 101 is too low. The controller 1 1 1 produces a control signal output 1 14 that represents either a force or position command. The controller 111 may be a general purpose data processor, special purpose digital signal processing circuits and software, or analog control circuits, for example. The control signal output 1 14 of controller 11 1 is applied to actuator 109, which adjusts the load force F_L in response to the signal 114 to correspondingly adjust the flying height. The actuator 109 can, for example, be a voice coil actuator that produces a force F_L proportional to the control signal.

In the system shown in Fig. 1, the flying head is a damped spring-mass system. The resilient member 105 and the air bearing 108 act as springs suspending the head 101 between the surface of the disk 107 and the load arm 103. The resilient member 105 acts as a spring because of its resiliency. The air bearing 108 acts as a spring because the air itself is a compressible fluid whose pressure varies with the amount of compression.

Damping is an inherent property of both resilient member 105 and air bearing 108, neither of which are perfect springs. The damped spring-mass system enables the flying head to follow rapid (i.e., high frequency) vertical variations in the surface of the disk 107 without imparting vertical motion to load arm 103, much as an automobile suspension enables the tires to follow bumps in the road without imparting vertical motion to the passenger compartment. It should be understood that vertical variations in disk 107 cause variations in F_A which result in variations in flying height. In this art. vertical variations in the surface 106 of the disk 107. whether rapid or not, are called vertical runout. The mass of the head 101 affects the ability of the head 101 to respond to variations in the surface 106 of the disk 107 because greater suspended mass slows the reaction time of the head 101 to variations in the surface 106 of the disk 107, a well-known property of damped spring-mass systems. Therefore, minimizing the mass of the head 101 that moves to follow disk surface variations increases the frequency response of the system (i.e., the ability of the system to follow high frequency surface variations). In addition, increasing the spring constant of the air bearing, i.e., making the air bearing less compressible, for example by changing the geometry of the air bearing surface as is known in this art, also increases frequency response by increasing the mechanical coupling between the disk surface and the head through the air bearing. The resilient member 105, one of whose functions is to permit movement of the head in response to vertical runout, therefore is arranged to permit the head 101 to move vertically by a distance which should be greater than the amplitude of the high frequency component of the vertical runout of the disk. With this rigid

RECTIFIED SHEET (RULE 91 ) ISA EP condition met. the head 101 responds to the high frequency variations in the surface 106 of the disk 107 and maintains a safe functional flying height.

The high frequency variations in the surface 106 of disk 107 often cause a complex combination of roll, pitch, yaw and radially directed forces on the head 101. As in conventional systems, the system disclosed in the related application address these complex forces using a gimbal arrangement, as follows. It should be understood that the disclosed gimbal arrangements are not to be considered limiting, as other conventional gimbal arrangements can also suit this purpose. In one embodiment, the resilient member 105 is arranged to serve as a gimbal to allow some roll and pitch motion of head 101 while preventing motion in undesirable directions. Radial motion and yaw motion are undesirable because they cause mispositioning of the head which hinders data reading and writing operations. However, vertical, roll and pitch motions of the head desirably permit the head to follow variations in the surface of the disk without making contact therewith. Therefore, in one embodiment of the system disclosed in the related application, the effective spring constant of the resilient member 105 is extremely high in radial and yaw directions, and lower in vertical, roll and pitch directions.

Several illustrative embodiments of gimballed resilient members 105 for use in connection with the present invention are discussed later in connection with Figs. 9-14. Although the illustrated gimbals have been found to be advantageous, the invention is not limited to these particular arrangements. Rather, there are many suitable conventional gimbal arrangements that could be used in association with the present invention.

The system described generally above is now described in further detail with respect to an embodiment of the invention directed to a flying head system having a controllable load force and including a head with a head/disk interference sensor. The inventive system has an active suspension, in which load force may be dynamically adjusted during use, as compared to a conventional passive suspension that uses a simple damped spring-mass system in which load force is set mechanically. In the illustrative embodiment described, the head is an optical disk drive head. However, it should be understood that the invention is not limited in this respect, and that the disk drive head can be any type of flying head, including but not limited to magnetic and magneto-optic heads. A simplified perspective view of the elements of an optical disk drive system with which the present invention can be used is shown in Fig. 2. In this simplified view, disk 107 is rotated in direction R by motor 201. A head positioning mechanism 203 radially positions the head 101 at a radius of the disk 107 sought to be read or written to. Each radius of the disk 107 sought to be read or written to is referred to herein as a track. Such radial positioning is referred to as seeking or as motion in a seek direction. The head 101 is connected to the positioning system 203 through an active suspension mechanism 205 that includes load arm 103, gimbal 105 and several additional components shown in greater detail in Figs. 3 - 7.

Referring to Figs. 3 and 4, the rotary motion of disk 107 causes disk 107 to move past the head 101 in the direction R as shown. The head 101 is attached by a resilient member 105, such as described above, to a load arm 103. Load arm 103 is integrated with an actuator mechanism, generally indicated at 109. Finally, the combined load arm 103 and actuator 109 that carry head 101 are mounted to the positioning system 203. A laser light source 301 shines a laser beam 303 through a lens 305 which is part of head 101.

Conventionally, the load arm would be fixedly mounted to the positioning member 203, so that except for the head responding to vertical runout of the disk surface 106 via the resilient member 105 as described above, only positioning system 203 would move the head 101. However, in this embodiment of the invention, the actuator mechanism 109 produces additional motion in two directions independent of the response of the head 101 to vertical runout of the disk surface 106, and independent of any movements produced by positioning mechanism 203. According to this embodiment of the invention, the actuator includes a vertically oriented voice coil 427 that produces vertical motion by acting on steel member 429. The actuator further includes transversely mounted voice coils 431 and 433 that produce an independent horizontal motion H in the seek direction, also by acting on steel member 429. In other embodiments, any one or more of voice coils 427, 431 and 433 can be replaced by a different source of motive force, such as a piezoelectric element. Servo control of horizontal motion H is used to microposition head 101 over a track after seeking of positioning system 203 is complete. Movable mounts 400 connect the actuator components 109 and load arm 103 to a rigid frame 401 (Fig. 6). The rigid frame 401 is attached to the positioning mechanism 203 so that the entire suspension mechanism (Fig. 2, 205) can be quickly positioned in a desired radial location (i.e.. within the micropositioning capability of the actuator mechanism 109 of a desired track) relative to the disk 107. The actuator 109 of Figs. 3-4 and its connection to the positioning system 203 through movable mounts 400 is now described in more detail in connection with Figs. 5-7. Suspension 205 includes a frame 401 which is rigidly connected to the positioning system 203. A pair of members 403 and 405. elongated in a vertical direction, is affixed to the frame 401. At the ends of rigid member 403 are hinged supports 407 and 409, oriented for flexing in a vertical direction. Hinged supports 407 and 409 do not permit substantially any flexure in a horizontal direction. Hinged supports 407 and 409 attach swing arms 411 and 413 to rigid member 403. When at rest. 5 swing arms 411 and 413 extend perpendicular to member 403 and substantially parallel to each other for equal distances to hinges 415 and 417, which are in turn connected to a second vertically oriented member 419. Similarly, vertical member 405 is connected through swing arms 421 and 423 to a second vertical member 425. Actuator 109 includes a voice coil 427 acting upon a steel member 429 rigidly connected to frame 401 to vertically displace vertical l o members 419 and 425. Load arm 103 is rigidly attached to vertical members 419 and 425.

The movable mounts 400 can be formed of a resilient plastic material or another resilient material. Thus, the flexible hinged supports act as spring elements which contribute to the ability of the head 101 to follow vertical runout of the disk surface 106.

Referring specifically to Fig. 5. electrical currents applied to input wires 501 of the voice 15 coil 427 produce up and down displacements of the voice coil 427, as indicated by double- headed arrow V, relative to frame 401. Thus, the load arm 103 and head 101 are also displaced relative to frame 401 as indicated by arrow V. As seen in Fig. 5, disk 107 may include surface perturbations 502 from a nominally flat surface 503. Perturbations 502 are slow variations, relative to the asperities discussed above. Disk motion in direction R causes head 101 to fly a 20 small distance above disk 107. When the vertical runout of the disk 107 causes the surface of the disk 106 to move towards the head 101, the air bearing force F_A increases, forcing the head upward. The head deforms the resilient member 105 as indicated by arrow V. Resilient member 105 and spring 505, when provided, are deformed by the movement of the head 101 , as indicated by arrow V, until the force applied by deformable member 105 is equal to and opposite the air 25 bearing force F_A. The stiffness of resilient member 105 can be set by the choice of materials and configuration of deformable member 105, and can be supplemented by providing the assistance of spring 505. The configurations described are merely illustrative, and the invention is not limited to any one of these.

Actuator 109 is included as part of a closed loop feedback system capable of following at 30 least low frequency vertical runout of the surface 106 of disk 107. When part of a closed loop feedback system as described above in connection with Fig. 1. actuator 109 can produce variations in load force to displace the head 101 and cause the head to follow corresponding low

RECTIFIED SHEET (RULE 91) ISA EP frequency displacements 502 in the disk surface 107 from the nominally flat condition 503. while deformation of the resilient member 105 as described above permits the head 101 to follow high frequency displacements 502 in the disk surface 107.

As previously described in connection with Fig. 1. a signal 1 12 including a component representative of flying height 113, and including a component indicative of head/disk interference, is processed by the controller 11 1 to produce the input signal 1 14 to the actuator 109. When using the embodiment of Figs. 3-7, the controller 11 1 produces a signal 1 14 applied to the voice coil input through wires 501. The magnitude of the signal 1 14 applied depends upon the signal 112. For example, in one illustrative embodiment, the value of the signal representative of flying height is compared to a set point value indicative of the mimmum glide height measured using the head of the present invention. The difference between the set point value and the value of the signal 112 is used to generate the signal 1 14. The load force applied by actuator 109 is set by the application of electrical currents, i.e., signal 1 14, to input wires 501 of the voice coil 427. The component of the signal 1 12 representative of flying height 113 may be derived in any of several ways. In the illustrative embodiment of an optical disk drive system discussed in connection with Fig. 3, flying height can be determined from characteristics of the laser beam 303, using a detector to detect the beam after it is directed from the source 301 , through the lens 305 of the head 101 , to the disk surface and then returned to a detector which can. for example, be co-located with source 301. For example, a laser beam focus signal and read signal amplitude can provide information concerning flying height. Derivation of flying height information from a laser beam focus signal is described below. It is also known that read signal amplitude varies with flying height.

In an illustrative embodiment of the invention in an optical disk drive including a head carrying a solid immersion lens (SIL), a laser focus signal is used to provide the signal 112 representative of flying height. The use of the laser focus signal is advantageous because optical disk drives, such as the one shown in Fig. 20, typically include a focus sensor that, along with its other functions, inherently generates a signal from which flying height of the optical head can be determined. Without any loss of generality, and without limiting the invention to the described embodiment, for the purposes of simplification, the following describes the use of focus signals with SIL heads having a lens with a fixed focal length. Examples of focus sensor systems which are common in optical disk drive applications include Foucault knife-edge sensors, half-aperture

RECTIFIED SHEET (RULE 91) ISA/EP focus sensors, and astigmatic sensors employing quad detectors, all known to those skilled in this art. Astigmatic sensors are used in some embodiments of the invention because of their relative immunity to construction tolerance errors.

Focus sensors produce an output signal, called an s-curve because of its general shape around the ideal focus point, whose signal value represents a distance of the lens of the head 101 from the ideal focus point. The ideal focus point is a distance above the disk surface 106. Therefore, the focus sensor output signal inherently represents the distance of the lens of the head 101 above the disk surface 106. The focus sensor output signal may be calibrated in a simple manner, for example, by measuring the focus sensor output signal value at a flying height of zero, i.e., when the disk is not spinning and the head is resting on the surface 106. The gain of the focus sensor is a substantially constant value known from the design of the sensor and relatively insensitive to construction tolerances. Therefore, the flying height can easily be computed by those skilled in the art, knowing the signal value at a flying height of zero, the signal value at the current unknown flying height and the gain of the focus sensor. When the controller 1 11 adjusts the flying height 113 to the optimum value, i.e., the minimum glide height, the focus sensor may detect an out of focus condition. In the embodiment of the present invention that employs an independently focusable lens mounted to the head, the controller can send a control signal that adjusts the focus of the lens. For example, in the embodiment wherein the head is a two-way transducer or heat element, the controller 1 1 1 can apply an excitation signal to the electrodes on the head 101. causing the integral focus actuator to expand or contract as necessary to achieve optimum focus without changing the flying height from the minimum glide height.

As discussed above, in one embodiment of the invention, a piezoelectric transducer, electrostrictive transducer, magnetostrictive transducer or other mechanical-to-electrical transducer is integrated into the head to provide the component of the signal 112 which represents head/disk interference, or contact. When the frequency of such contacts as indicated by the amplitude of the signal at the natural frequency of vibration of the head is too high, then the control signal 114 to the actuator 109 is adjusted to reduce the force F_L. thereby increasing the flying height of the head. A flying height that is too high is indicated by the flying height component of the signal 112. for example, by observing an inadequate read signal amplitude, or using a focus error signal in an optical system as described above. In other embodiments, the flying height component of the signal 112 can be determined using other proximity sensors. including proximity sensors which may be mounted to the head, such as a capacitive sensor, a magnetic sensor or an independent optical sensor. Such a proximity sensor, the read signal amplitude or the focus error signal can be used in connection with a contact sensor, such as described above, that provides the component of the signal 1 12 indicating head/disk contact. In this manner, the controller 11 1 can not only determine the minimum glide height, but also can measure the displacement of the head from the minimum glide height either toward or away from the surface of the disk. The contact sensor provides a binary indication of whether the head is above or below the minimum glide height. By comparison, the proximity sensor, read signal amplitude or focus error signal provides an output whose value is related to flying height by a predetermined mathematical function. The controller 11 1 uses the value of the proximity sensor output, read signal amplitude or focus error signal at the minimum glide height determined by the contact sensor as a set point to which the system is driven by controlling flying height.

In another embodiment, the head/disk interference sensor described above can be used in connection with circuits or software which simply counts a number of contacts between the head 101 and the disk surface 106. A high frequency of contacts indicates too low a flying height, i.e., below the minimum glide height.

The system described above differs from conventional systems in that a number of tolerances do not affect flying height in this system that do affect flying height in conventional systems. Conventional systems, even those which exercise some dynamic control over flying height, do not drive flying height to equal the minimum glide height because mechanical tolerances and environmental variations that are not compensated for by the dynamic control mechanism could cause such conventional systems to occasionally operate at flying heights less than minimum glide height, resulting in a catastrophic system failure. In contrast, embodiments of the invention determine minimum glide height by detecting contact with surface asperities while controlling flying height, thus ensuring that each unit produced in accordance with the principles of the invention can fly the head at the minimum glide height.

Example gimbal structures for implementing resilient member 105. along with related structures, are now briefly discussed in connection with Figs. 9-14. One embodiment is shown in Figs. 9-10; a variation on that embodiment is shown in Fig. 1 1 : a second variation is shown in Fig. 12; and another embodiment is shown in Figs. 13-14. Although any of these embodiments of a resilient member 105 may be used in connection with the present invention, the present invention is not limited in this respect, and can be used with any of a number of other types of mounting systems.

In the embodiment shown in Figs. 9-10, the flying head 101 is connected to load arm 103 through gimbal 105. Although an optical head is shown, any flying head according to the present invention may be used in connection with this structure. Slots 905, 907, 909 and 911 are etched into gimbal 105 to permit the gimbal to flex at a lower spring rate in some directions than in others. Yaw and radial motion is substantially inhibited by the substantial cross-sections of gimbal material through which such motion must be transmitted, while motion in the roll and pitch directions is very readily permitted by hinge regions 913, 915, 917 and 919, which act as torsion springs. The gimbal 105 can be, for example, a precision etched thin piece of stainless steel. The head 101 can be attached by applying epoxy to the gimbal 105 in region 901 , which is in turn attached to load arm 103 by a quantity of epoxy in region 903. Other adhesives and attachment methods are also suitable, such as high strength glues, interference fits between parts and various clamping arrangements. In alternate embodiments, the gimballed assembly of Figs. 9-10 may further include a spring disposed in a position to exert additional downward force, as now described in connection with Figs. 11-14. Fig. 11 shows an embodiment using a coil spring to exert force at region 901 of the gimbal 105, while Fig. 12 shows an embodiment using a leaf spring to exert force at region 901 of the gimbal 105. Figs. 13 and 14 show an embodiment in which a leaf spring exerts force on the gimbal 105 through an auxiliary arm.

As seen in Fig. 11. the gimbal 105 has considerable flexibility in a purely vertical direction. In the embodiment shown, an additional optional spring 505 is disposed between region 901 of the gimbal 105 and the load arm 103, to increase the spring rate in the vertical direction without appreciably affecting the spring rate in the roll and pitch directions. In Fig. 11 , spring 505 is a coil spring. However, the invention is not limited to using any particular type of spring, as many other types of springs can be used, such as a leaf spring 505A as shown in Fig. 12. These arrangements should suggest numerous others to the skilled artisan, which can be used in embodiments of the invention without departing from the inventive concept.

In yet another alternate embodiment shown in Figs. 13 and 14, load arm 103 is connected through a leaf spring 505B to an auxiliary arm 103A. Head 101 and auxiliary arm 103A are then connected through the gimbal 105 described in connection with Figs. 9-10.

RECTIFIED SHEET (RULE 91) IS One advantage of the system described above, is that setting and maintaining a proper load force does not require the use of a special jig, removing a disk drive from service or any other action which impairs the useful operation of the unit. The setting of load force may be made and varied during normal drive operation. Load force may be substantially continuously 5 updated to follow changing conditions and maintain an optimum flying height as close to the disk surface as possible without coming into contact with the disk surface, i.e., at the minimum glide height.

Performance of some embodiments of the invention is further enhanced by generating and storing in the controller (Fig. 1, 111) a map of the vertical runout of the disk surface which l o the head should follow. The map may be applied as an input to the controller (Fig. 1 , 111 ) to provide a bias to the control signal (Fig. 1, 114). As will be understood by those familiar with feedback control systems, this reduces the amount of error in flying height (Fig. 1. 1 13). as represented by the flying height signal (Fig. 1, 112), that must be compensated for by adjusting the control signal (Fig. 1 , 114). Generation of the map may take place at the time of manufacture 15 or may be performed periodically during periods of non-use of the disk drive. In the latter instance, a special head carriage can be used, as now described in connection with Figs. 16-19.

The head carriage 1601 of this embodiment incorporates the flying head 101 and suspension 105 features already described above. The head carriage is used in conjunction with a laser beam 1609 similar to that shown in Fig. 3 at 303. A load force actuator (not shown) 20 raises and lowers the head carriage 1601 along a shaft 1607 in the same manner as actuator 109 operates on load arm 103 (Figs. 1-7), with the head carriage 1601 performing functions served by the load arm 103 in the system of Figs. 1-7. In addition, the head carriage 1601 includes a fixed, non-contact, non-flying lens element 1603, such as a conventional compact disk lens. The head 101 and suspension 105 are epoxied, glued or otherwise fixedly attached to an adapter ring 1602. 25 The adapter ring 1602 has a spherical base which fits into a spherical socket in the head carriage 1601. This allows the adapter ring to be rotated or rocked to permit the axis of the lens of head 101 to be aligned with the axis of the laser beam 1609, before the adapter ring 1602 is fixedly attached to the head carriage 1601. The described mount using an adapter ring is exemplary, and the invention is not limited to this particular implementation as other mounting techniques are 30 possible. The head carriage 1601 of this embodiment pivots on shaft 1607 between two substantially fixed positions shown in Fig. 17 and Fig. 19. respectively, as now described.

RECTIFIED SHEET (RULE 91) ISA/EP In a first position, shown in Fig. 17, the head 101 is positioned for flying over and accessing the recording medium. Magnetic, magneto-optic, optical and other types of flying heads may be used, as the scope of the invention is not limited to any type of head. In the case of an optical head, the first position locates the head 101 in alignment with a laser light source (Fig. 3, 301) as described previously. The beam from the laser light source is directed along axis 1605.

In a second position shown in Fig. 19, the fixed lens element 1603 is positioned in alignment with the axis along which the laser light beam is directed. A conventional focus sensor of any suitable type, including those previously described, detects a reflection of the beam from the disk surface and produces a time-varying focus signal which varies with the vertical runout of the disk during rotation thereof. A processor included in the controller (Fig. 1 , 111) receives the time- varying focus signal, processes the time-varying focus signal and stores the result in a memory in the controller (Fig. 1, 111) as a map of vertical runout of the disk. As a result of processing, the map may comprise a signal based upon one or more measured revolutions of the disk which may or may not have been filtered. Appropriate processing useful for achieving any desired sensitivity and resolution of the map is known.

After storing the map, the head carriage 1601 is pivoted (Fig. 18) from the second position to the first position, in which the head is flown over the medium surface in accordance with the discussion of Figs. 1-14 to read data, in the normal manner. Magnets 1609 and coils 161 1 cause the head carriage 1601 to pivot about shaft 1607 in a manner similar to a two position stepping motor.

The controller (Fig. 1 , 111) accesses a map signal representing the stored map, and reads the map back in synchronism with the rotation of the disk. The controller (Fig. 1, 111) applies the map signal as a bias to the actuator control signal 114, whereby the control signal (Fig. 1, 114) is preset to a value which compensates for the known vertical runout as represented by the map. In a feedback control system such as this, use of the biasing technique reduces the stress placed on the system, enabling the system to perform with greater speed and resolution, as previously mentioned.

The present invention has now been described in connection with a number of specific embodiments thereof. However, numerous modifications which are contemplated as falling within the scope of the present invention should now be apparent to those skilled in the art.

RECTIFIED SHEET (RULE 91) ISA/EP Therefore, it is intended that the scope of the present invention be limited only by the scope of the claims appended hereto and equivalents thereof.

Claims

C AIMS

1. A flying head for use with a recording medium, comprising: a body having an air bearing surface; and a lens movably affixed to the body relative to the air bearing surface.

2. The flying head of claim 1 , wherein the body includes a controllably movable surface; and the lens is affixed to a portion of the body whose position with respect to the air bearing surface is controlled by the controllably movable surface.

3. The flying head of claim 2, further comprising: a transducer, having an electrical connection thereto, that transduces electrical energy received at the electrical connection into movement of the controllably movable surface.

4. The flying head of claim 3, wherein the transducer includes an electrically driven heater and an expandable component that expands upon application of an electric current to the heater.

5. The flying head of claim 3. wherein the transducer also converts contact between a surface thereof and the recordine medium into electrical energy at the electrical connection, thereby generating a signal indicative of contact between the head and the recording medium.

6. The flying head mechanism of claim 5, wherein the transducer is formed of a piezoelectric material.

7. The flying head mechanism of claim 5, wherein the transducer is formed of an electrostrictive material.

8. The flying head mechanism of claim 5. wherein the transducer is formed of a maenetostrictive material. 9. A flying head for use with a recording medium, comprising: a body having an air bearing surface; and a contact sensor supported by the body, having an electrical connection carrying a signal indicative of contact between the head and the medium.

10. The flying head mechanism of claim 9, wherein the contact sensor is a transducer of mechanical energy into an electrical signal at the electrical connection.

1 1. The flying head mechanism of claim 10, wherein the head further includes a lens moveably affixed to the body relative to the air bearing surface.

12. The flying head mechanism of claim 11 , wherein the body includes a controllably movable surface; and wherein the lens is affixed to a portion of the body whose position with respect to the air bearing surface is controlled by the controllably movable surface.

13. The flying head mechanism of claim 12, wherein the contact sensor also converts an electrical signal at the electrical connection into movement of the controllably movable surface.

14. The flying head mechanism of claim 13, wherein the transducer is formed of a piezoelectric material.

1 . The flying head mechanism of claim 13 , wherein the transducer is formed of an electrostrictive material.

16. The flying head mechanism of claim 13. wherein the transducer is formed of a magnetostrictive material.

17. A flying head system for use with a recording medium and a light source projects a beam of light onto the recording medium, the system comprising: a flying head including an air bearing surface, and a lens through which the beam is projected onto the recording medium, the lens being mounted to the head for movement relative to the air bearing surface; a focus sensor generating an output signal indicative of focus of the laser beam projected onto the recording medium: and a focus controller having an input that receives the focus sensor output signal and an output coupled to the flying head, carrying a focus control signal that causes movement of the lens relative to the air bearing surface to focus the lens.

18. The system of claim 17. further comprising: a contact sensor generating an output signal indicative of contact between the head and the recording medium; and a flying height controller, having an input that receives the contact sensor output signal, that controls flying height of the head responsive the contact sensor output signal.

19. The system of claim 17, wherein the contact sensor is mounted to the flying head.

20. The system of claim 19, wherein the contact sensor is a two-way transducer of electrical energy into mechanical movement and of mechanical movement into electrical energy, the contact sensor being mounted on the head so that mechanical movement of the contact sensor causes movement of the lens relative to the air bearing surface.

21. The flying head mechanism of claim 20, wherein the transducer is formed of a piezoelectric material.

22. The flying head mechanism of claim 20. wherein the transducer is formed of an electrostrictive material.

23. The flying head mechanism of claim 20. wherein the transducer is formed of a magnetostrictive material.

24. A method of focusing a laser beam onto a recording medium, comprising steps of: flying a head carrying a lens so an air bearing surface of the head is substantially at a constant height above a recording medium; projecting the laser beam through the lens onto the recording medium; measuring focus of the laser beam projected onto the recording medium; controlling a position of the lens relative to the air bearing surface, responsive to the step of measuring, to alter focus of the laser beam projected onto the recording medium.

25. The method of claim 24, further comprising steps of: determining when the head contacts the recording medium; setting the constant height to a lowest height at which the head does not contact the recording medium.

25. A flying head for use with a recording medium, comprising: a body; a lens affixed to the body, the lens having a focus; and an electric heater mounted to the body, proximate to the lens, which changes the focus of the lens when a current flows in the electric heater.

27. The flying head of claim 26, wherein the electric heater expands the body when a current flows in the electric heater, thereby changing the focus of the lens.

28. The flying head of claim 26, wherein the electric heater heats the lens, thereby changing the focus of the lens.

29. The flying head of claim 28, wherein heating the lens expands the lens, thereby changing the focus of the lens.