WO1998048415A1

WO1998048415A1 - A flying magnetic head positioner having rotational fine positioning and adjustable actuator load

Info

Publication number: WO1998048415A1
Application number: PCT/US1998/008321
Authority: WO
Inventors: Neville K. S. Lee; John S. Berg
Original assignee: Digital Papyrus Corporation
Priority date: 1997-04-24
Filing date: 1998-04-24
Publication date: 1998-10-29

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. A read signal from the flying head may be processed into a signal indicative of flying height. The flying head can also include a contact sensor which detects head/disk contact. The entire suspension is mounted in a shock and vibration immune configuration.

Description

A FLYING MAGNETIC HEAD POSITIONER HAVING ROTATIONAL FINE POSITIONING AND ADJUSTABLE ACTUATOR LOAD

Background

1. Field of the Invention

The present invention relates generally to disk drive systems including an apparatus for positioning a flying magnetic head over a disk. The invention further relates to disk drive systems in which a load force applied to the flying magnetic head is adjustable. The invention yet further relates to disk drive systems including a coarse and fine head positioner.

2. Related Art

As the areal densities for magnetic recording disk drives increase at what is now a 60% annual growth rate, the physical dimensions of marks on a disk correspondingly decrease. Both linear bit density, i.e., bit length, and track density, i.e., track pitch, are decreasing. These recording requirements are placing ever greater demands on the mechanical and electrical hardware.

Extremely high density data storage systems based on magnetic and magneto-optic and optical storage disk media store data in at least one track including a series of very small regions, each region termed either a mark or a space. In some technologies, recording marks are regions altered by a writing process and spaces are the regions between marks. In other recording technologies marks are regions of one magnetic polarity, strength or direction and spaces are regions of another magnetic polarity, strength or direction. The values of one or more bits are encoded as the lengths of the marks and spaces, depending upon the encoding technology. The track may be 0.2 μm wide, with marks and spaces being one or more times that length. Because very small regions of this storage medium are used to represent information, a transducer system which can discriminate those regions with a high degree of resolution is used so that each bit can be accessed separately.

A fine track pitch requires an accurate servo system to position a head over a track. Additionally, current and future disk rotational speeds of the disk drives are high and increasing, e.g., 3,600 RPM and up. This means that not only must a head be positioned extremely accurately it must also be positioned more quickly than when disk rotational speeds were lower.

High density disk drive systems based on magnetic, 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. Some 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.

High storage densities require very low and repeatable flying heights to maximize resolution and signal strength from the media. Simultaneously, customers require ever improving reliability. This despite drives being used in environments ranging from the office to air planes to factories. However, low flying heights increase the likelihood of undesired contact between a head and the medium.

A brief description of how a positive pressure flying head flies is now given, with reference to Fig. 1.

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., 3,600 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 110. 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 113, defined herein as the separation distance between the air bearing surface 110 of the head 101 and the surface 106 of the disk. 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_L exerted through a spring 105 or suspension that mounts the head 101 to the load arm or actuator 103 determines flying height 113.

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 until equilibrium is established. When equilibrium is reached, F_L = F_A, the head experiences no net force, and hence no vertical motion occurs.

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, physical models of the system or computer-generated models of the system. The conventional system is designed so that F_L=F_A at 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 the 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 the 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 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 or recovery of a signal exhibiting a poor signal to noise ratio. 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 resulting in a loss of data. Avoiding potential damage often associated with contact between the 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 this, in turn, causes a variation in 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 into 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. By failing to fly at the minimum glide height, conventional systems exhibit poorer resolution than that of which they are theoretically capable. Moreover, magnetic signal strength varies directly and geometrically with the height of the head above the disk surface. Therefore, in order to maintain an adequate signal at the disk surface, a larger, heavier head with substantially greater magnetic coupling might be required in such a conventional system. Yet another problem with conventional systems is that they are extremely susceptible to externally applied mechanical shocks. As briefly mentioned at the beginning of this description, the head must be positioned with an extremely fine positional resolution to properly discriminate between closely spaced adjacent tracks. However, a requirement for extremely fine positional resolution renders the system more susceptible to mechanical shock and vibration.

Another problem of conventional systems is to provide very fast positioning over a wide range of track positions, while also providing extremely high track position resolution to discriminate between closely spaced tracks. One conventional solution to this problem is to provide both a coarse positioner and a fine positioner which cooperate to position the head at the proper location. A conventional coarse positioner can quickly move the head to an approximate position defined by any track or group of tracks on a disk, but cannot position to or follow the track on which reading and writing are to take place with sufficient accuracy. Therefore, once roughly positioned by the coarse positioner, the head is more finely positioned by the fine positioner. The fine positioner conventionally has a small range of movement covering a distance equal to the span of distance occupied by a small group of tracks, or less, but extremely fine resolution. A problem with this conventional arrangement is that each time the coarse positioner operates to move the head by several tracks to a new track group, the movement has a similar effect upon the fine positioner as an external mechanical shock. That is, the coarse positioner adds to the final position error which the fine positioner will overcome, a transient error due to an induced mechanical shock. When the coarse positioner ceases its movement, the fine positioner must then overcome the induced mechanical shock, as well as position accurately over the target track before reading or writing of data can commence. This movement of the fine positioner takes longer to accomplish than movement of the fine positioner over the same distance would take if made without a movement of the coarse positioner to a different track group because the fine positioner requires additional time to overcome the induced mechanical shock caused by the coarse positioner movement.

An increasing desire to move data into and out of systems for security and data transfer purposes has lead to a continuing popularity of removable media drives. Removable media drives, however, add several unique problems. One is that the disks are less likely to be centered as exactly as in a fixed drive. This results in greater error in the concentricity of the tracks with the axis of rotation. However, in order to recover information from a track, the head must follow the track. This again places greater demands in the performance of servo system of the drive. Furthermore, unloading the disk from the drive presents a problem of what to do with the heads when the disk is either not present, is being loaded or is being unloaded.

Summary of the Invention It is an object of the present invention to provide an improved disk drive system.

A head positioner for a magnetic disk drive according to one embodiment of the invention operates on a magnetic disk. The positioner includes a flying magnetic head; a coarse positioner having a coarse positional resolution; a head carriage mounted to the coarse positioner, the head carriage including a fine positioner, the flying magnetic head being mounted to the fine positioner, and the fine positioner having a fine positional resolution less than the coarse positional resolution; and a load force actuator mechanism having an axis of motion perpendicular to a surface of the disk through which an adjustable load force is applied to the flying magnetic head responsive to a controller output.

According to another embodiment, there is a head positioner for a magnetic drive including a magnetic storage disk having a surface. The head positioner comprises: a flying magnetic head including a reading transducer having an output carrying a readback signal, the magnetic flying head developing an air bearing when flying; a coarse positioner having a coarse positional resolution; a head carriage mounted to the coarse positioner; a fine positioner mounted to the coarse positioner, the flying head being mounted to the fine positioner, and the fine positioner having a fine positional resolution less than the coarse resolution; a load force actuator having an axis of motion perpendicular to the surface of the disk through which an adjustable load is applied responsive to a control input; and a load force controller having a load force controller output, the controller output coupled to the control input.

Finally, according to another embodiment of the invention, there is a method of positioning a flying head relative to a recording medium surface. The method comprises steps of: flying the flying head over the recording medium surface; positioning the flying head over a desired location on the recording medium surface; applying a load force to the flying head; and adjusting the load force applied to the flying head while positioned over the desired location.

Brief Description of the Drawings In the Figures in which like reference designations indicate like elements:

Fig. 1 is a schematic side elevation of a conventional flying head mechanism; Fig. 2 is an end elevation view of a head including an integrated head/disk interference sensor;

Fig. 3 is a schematic block diagram of a feedback controlled flying head load mechanism illustrating aspects of the present invention; Fig. 4 is a perspective view of a disk drive using a mechanism embodying aspects of the invention;

Fig. 5 is a side elevation view of a head suspension used in the disk drive of Fig. 4; Fig. 6 is a top plan view of the head suspension of Fig. 5;

Fig. 7 is a cross-sectional view of the head suspension taken along line 5-5 of Fig. 6; Fig. 8 is a perspective view of the head suspension of Figs. 4-7;

Fig. 9 is a side elevation view showing the movement of the head suspension of Figs. 4-8; Fig. 10 is a detail view of the head suspension of Figs. 4-8 showing a gimbal; Fig. 11 is a detail view of the gimbal of Fig. 10;

Fig. 12 is a side elevation view of a detail of one embodiment of the head suspension of Fig. 10;

Fig. 13 is a side elevation view of a detail of an alternate embodiment of the head suspension of Fig. 10;

Fig. 14 is a side elevation view of a detail of an alternate embodiment of the head suspension which may be used in place of that of Fig. 10; Fig. 15 is a perspective view of the head suspension of Fig. 14;

Fig. 16 is a top view of an alternate head suspension embodying aspects of the invention;

Fig. 17 is a top view of a variation on the embodiment of Fig. 16; and

Fig. 18 is a side elevation view of the embodiment and variation of Figs. 16 and 17.

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 invention solves numerous problems of the prior art and provides additional design flexibility not available in conventional systems. For example, when the principles of the invention are applied, a system may be constructed which combines improved positioning resolution, shock resistance and removable media. In accordance with some principles of the invention, the head may be mounted to a linear fine positioning actuator or to a rotary fine positioning actuator, both described in detail below. In the case of a rotary fine positioner, the head is mounted in a position such that the rotary fine positioner is counterbalanced and rotates about its center of gravity. Such an arrangement improves the immunity of the fine positioning system to externally applied shock and vibration, as well as to extended settling transients when the coarse positioner moves.

Finally, any of the above-described arrangements are advantageously combined with a system for applying an adjustable load force to a flying optical head, as described in detail below. The flying height of the flying head may thereby be controlled through load force adjustments. In addition, a system for applying an adjustable load force can be arranged to move the head far enough from the media surface to permit removal of removable media.

One of the present inventors' related applications, entitled FLYING HEAD WITH ADJUSTABLE ACTUATOR LOAD, filed February 21, 1997, Serial No. 08/804,301 (hereafter referred to as "the actuator load application"), incorporated herein by reference, teaches a method and apparatus for maintaining a flying head at a flying height substantially equal to the actual minimum glide height for each data track of the disk over which the head is flown, despite variation in the minimum glide height from the nominal or design minimum glide height, and despite variations in other parameters affecting flying height. Although the exemplary embodiment disclosed in the actuator load application uses optical recording, the method disclosed is applicable to magnetic recording systems as well. The related application teaches measuring the actual minimum glide height at points along the disk while accessing data. The measurement can be made by detecting whether, and how often, 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 minimum glide height. As discussed further, below, the minimum glide height is determined indirectly by examining a sensor signal for evidence of the head "ringing", i.e., vibrating, at its mechanical resonant frequency. For example, the sensor signal may be measured to detect a signal amplitude at the resonant frequency. Alternatively, the read signal itself may be band pass filtered at the resonant frequency and the resulting signal amplitude measured. As described above, in the system described in the actuator load application, the head is flown at the minimum glide height, which will vary slightly from disk to disk. A flying head may be provided that includes an integrated head/disk interference or contact sensor that can be used to measure the minimum glide height in conjunction with a system such as the one disclosed in the actuator load application. According to another of the present inventors' related applications, entitled METHOD AND APPARATUS FOR DETECTING THE MINIMUM GLIDE HEIGHT OF A FLYING HEAD AND FOR FOCUSING A LENS CARRIED ON A FLYING HEAD, filed March 26, 1997, Serial No. 08/824,625 (hereafter referred to as "the detecting/focusing application"), incorporated herein by reference, a flying head is provided that includes such a sensor.

The aspects of the detecting/focusing application and the actuator load application are advantageously combined in a system including a flying magnetic head with a transducer that generates a signal indicative of head-disk interference, and dynamic adjustment of flying height using closed loop control methods. One embodiment of a flying head that incorporates aspects of the actuator load application and is described in the detecting/focusing application is shown in Fig. 2 and 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 magnetic transducer 613 is incorporated in the head 101. 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 voltage 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 106 of the disk 107, at some point striking the surface 106 of the disk 107, 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 at the ringing frequency indicates contact between the head 101 and the disk surface 107 (Fig. 4) which is related to a head flying height 113 below the minimum glide height. More frequent contact between the head 101 and the disk surface 106 causes the ringing to be reinforced, resulting in a larger signal amplitude. The use of this signal is discussed in greater detail in connection with the controller 111 of Fig. 3.

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.

As discussed in the detecting/focusing application alternate embodiments can provide a similar advantage by employing other materials that act as a transducer of mechanical energy to electrical energy, such as an electrostrictive material or a magnetostrictive material. These are discussed in detail in the detecting/focusing application. All that is required for these embodiments is that the system include some type of sensor capable of detecting contact between the disk and head or some other source of a signal indicative of such contact.

As illustrated in Fig. 3, the flying magnetic 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 110 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. The system includes a load force actuator 109 that 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 actuator load application control flying height using a closed loop control architecture that makes adjustments to F_L. By controlling F_L even during operation of the head and disk, the actuator can adjust F_L 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 and resolution is maximized.

In some embodiments of the present invention, signal 112 includes a head/disk interference component generated by a head/disk contact 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. Alternatively, the data signal read from the disk can be processed to identify and measure a component thereof indicative of head/disk contact. Detecting any asperities indicates the head 101 is too low. The controller 111 produces a control signal output 114 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 114 of controller 111 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. 3, 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 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 systems disclosed in the related actuator load 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 gimbal arrangements can also suit this purpose. In an embodiment described in the actuator load application, 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 actuator load 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 conventional gimballed resilient members 105 for use in connection with the present invention are discussed later in connection with Figs. 10-15. Although the illustrated conventional gimbals have been found to be advantageous, 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 a magnetic 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 optical, magnetic and magneto-optic heads.

A simplified perspective view of the elements of a magnetic disk drive system with which the present invention can be used is shown in Fig. 4. In this simplified view, disk 107 is rotated in direction R by motor 201. A head positioning mechanism 203 radially positions the magnetic 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. 5 - 9. Referring to Figs. 5 and 6, the rotary motion of disk 107 causes the disk 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 the 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. 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 system of the actuator load application, 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 (Fig. 6) 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 target track after seeking of positioning system 203 is complete. The position of the head relative to the target track is determined by conventional means. The voice coils 431 and 433 are then driven by currents which produce horizontal motion H as needed to position the head relative to the target track. Movable mounts 400 connect the actuator components 109 and load arm 103 to a rigid frame 401 (Fig. 8). The rigid frame 401 is attached to the positioning mechanism 203 so that the entire suspension mechanism (Fig. 4, 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. 5-6 and its connection to the positioning system 203 through movable mounts 400 is now described in more detail in connection with Figs. 7-9. Suspension 205 includes a frame 401 which is rigidly connected to the positioning system 203. A pair of rigid 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, 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 members 410 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. 7, electrical currents applied to input wires 501 of the voice 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. 7, 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 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 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 of the actuator 109 described in connection with Figs. 5-9 are merely illustrative, and the invention is not limited to any one of these.

Actuator 109 can be included as part of a closed loop feedback system capable of following at 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. 3, actuator 109 can produce variations in load force to displace the head 101 and cause the head to follow corresponding low frequency displacements (Fig. 7, 502) in the disk surface 107 from the nominally flat condition (Fig. 7, 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. 3, a signal 112 which can include a component representative of flying height 113, and which can also include a component indicative of head/disk contact, is processed by the controller 111 to produce the input signal 114 to the actuator 109. While the components of signal 112 may be independent of each other, as described herein, they may also be supplied in the form of a single signal representing both flying height and contact. When using the embodiment of Figs. 5-9, the controller 111 produces a signal 114 applied to the voice coil input through wires 501. The magnitude of the signal 114 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 minimum 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 114. The load force applied by actuator 109 is set by the application of electrical currents, i.e., signal 114, to input wires 501 of the voice coil 427.

The component of the signal 112 representative of flying height 113 may be derived in any of several ways. In the illustrative embodiment of a magnetic disk drive system using a magneto resistive head discussed in connection with Fig. 5, flying height can be determined from read signal amplitude. Since, read signal amplitude decreases monotonically as flying height increases, read signal amplitude defines a measurement of flying height that can be used as the flying height component of signal 112.

The output of the magneto resistive head can be filtered using a band pass filter centered on the mechanical resonant frequency of the head. The amplitude of the filtered signal indicates how often the head is contacting asperities on the disk surface. When the head contacts the disk more often, the amplitude of the resonance of the head increases, giving an indication that the flying height is too low. Magnetoresistive heads also exhibit a phenomenon known as thermal asperities, which also cause detectable changes in the head output. Incidence of thermal asperities also indicates too low a flying height.

As discussed above, in some embodiments 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 in the related applications. 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 or the read signal amplitude can be used in connection with a contact sensor, such as described above, that provides the component of the signal 112 indicating head/disk contact. In this manner, the controller 111 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 or read signal amplitude provides an output whose value is related to flying height by a predetermined mathematical function. In one embodiment, the controller 111 uses the contact sensor output to find the minimum glide height, and the proximity sensor output or read signal amplitude at the minimum glide height is then determined. The controller 111 then uses as a set point, the value of the proximity sensor output or read signal amplitude determined by the contact sensor at the minimum glide height. The system controls flying height to that at which the value of the proximity sensor output equals the set point.

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 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, several 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 actual minimum glide height for that unit.

Example gimbal structures for implementing resilient member 105, along with related structures, are now briefly discussed in connection with Figs. 10-15. One embodiment is shown in Figs. 10-11; a variation on that embodiment is shown in Fig. 12; a second variation is shown in Fig. 13; and another embodiment is shown in Figs. 14-15. 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. 10-11, 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. 10-11 may further include a spring disposed in a position to exert additional downward force, as now described in connection with Figs. 12-15. Fig. 12 shows an embodiment using a coil spring to exert force at region 901 of the gimbal 105, while Fig. 13 shows an embodiment using a leaf spring to exert force at region 901 of the gimbal 105. Figs. 14 and 15 show an embodiment in which a leaf spring exerts force on the gimbal 105 through an auxiliary arm.

As seen in Fig. 12, 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. 12, 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 505 A as shown in Fig. 13.

In yet another alternate embodiment shown in Fig. 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. 10-11.

One advantage of systems such as those 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 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. 3, 111) a map of the vertical runout of the disk surface which the head should follow. The map may be applied as an input to the controller (Fig. 3, 111) to provide a bias to the control signal (Fig. 3, 114). As will be understood by those familiar with feedback control systems, this reduces the amount of error in the flying height (Fig. 3, 113), as represented by the flying height signal (Fig. 3, 112), that must be compensated for by adjusting the control signal (Fig. 3, 114). Generation of the map may take place at the time of manufacture or may be performed periodically during periods of non-use of the disk drive. In the latter instance, the load actuator can be set to a known, constant, safe position and the flying height signal measured and stored for use as a biasing signal. A processor included in the controller (Fig. 3, 111) receives the time- varying flying height signal, processes the time-varying flying height signal and stores the result in a memory in the controller (Fig. 3, 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 is flown over the medium surface in accordance with the discussion of Figs. 2-15 to read data, in the normal manner.

The controller (Fig. 3, 111) accesses a map signal representing the stored map, and reads the map back, synchronized with the rotation of the disk. The controller (Fig. 3, 11 1) applies the map signal as a bias to the actuator control signal 114, whereby the control signal (Fig. 3, 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.

Another actuator and suspension embodying aspects of the invention is shown in Figs. 16-18.

In Fig. 16, a coarse actuator arm is shown, to which a transducer 1601 is mounted through an air bearing head 101 carried by a suspension. The active part of the transducer 1601 is offset from a pivot point 1603, about which the transducer is rotatable S. Thus, rotating the head 101 through small angles can be used to microposition the active part of the transducer 1601, after the coarse positioner brings the transducer 1601 to within a small distance of a target position. In the illustrated embodiment, the assembly includes an iron or similar piece 1605, upon which one or two micropositioning coils 1607 and 1609 may act. The arrangement described in connection with Fig. 16 may, in some systems, introduce too high a stray magnetic field strength near the active part of the transducer 1601. This problem can be alleviated as shown in Fig. 17. In this embodiment, the iron core 1701 upon which the micropositioning coils 1607 and 1609 act is set perpendicular to the direction of motion of the head 101 relative to the disk, and hence further from the active part of the transducer 1601.

Integration of a micropositioning mechanism such as one of those shown in Figs. 16 and 17 with the load force actuator described in detail, above, is shown in Fig. 18. The assembly is carried on a coarse actuator arm 1801. A head carriage 1803 is rotatably mounted (direction S) to the coarse actuator arm 1801. The head carriage 1803 is also axially positionable (direction L) in accordance with the principles for adjusting load force discussed above. A coil 1805 for adjusting the load force is positioned along the load axis. Rotational motion S of the head carriage is accomplished by the micropositioning coils 1607 and 1609 which act upon an iron core 1807 which may be positioned as shown in Fig. 16 (1605) or Fig. 17 (1701). The suspension also includes a conventional flexure spring 1809 and gimbal 1811, as previously described and known in this art.

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. 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. What is claimed is:

Claims

1. A head positioner for a magnetic disk drive which operates on a magnetic disk, comprising: a flying magnetic head; a coarse positioner having a coarse positional resolution; a head carriage mounted to the coarse positioner, the head carriage including a fine positioner, the flying magnetic head being mounted to the fine positioner, and the fine positioner having a fine positional resolution less than the coarse positional resolution; and a load force actuator mechanism having an axis of motion perpendicular to a surface of the disk through which an adjustable load force is applied to the flying magnetic head responsive to a controller output.

2. The head positioner of claim 1 , wherein the flying magnetic head flies on an air bearing at a flying height over the surface of the disk, the head positioner further comprising: a sensor having an output representative of the flying height; and a controller having an input coupled to the sensor output and having a control output responsive to the controller input, the control output couple to the load force actuator which produces the adjustable load force responsive thereto.

3. The head positioner of claim 2, wherein the sensor further comprises: in the flying magnetic head, a magnetic transducer having an output carrying a readback signal.

4. The head positioner of claim 3 , where said transducer is of an inductive type and the sensor output is related to amplitude of the readback signal.

5. The head positioner of claim 4, where the sensor output is related to the amplitude of the readback signal as an amplitude of a frequency component thereof which is characteristic of a mechanical resonance of a system including the flying magnetic head and the air bearing.

6. The head positioner of claim 3, wherein the transducer further comprises: a magneto-resistive element and the sensor output is related to peaks in the readback signal which are indicative of flying magnetic head contact with a disk asperity.

7. The head positioner of claim 3, wherein the transducer further comprises: a magneto-resistive sensor and the sensor output is related to amplitude of the readback signal.

8. The head positioner of claim 7, where the sensor output is related to the amplitude of the readback signal as an amplitude of a frequency component thereof which is characteristic of a mechanical resonance of a system including the flying head and the air bearing.

9. A head positioner for a magnetic drive including a magnetic storage disk having a surface comprising: a flying magnetic head including a reading transducer having an output carrying a readback signal, the magnetic flying head developing an air bearing when flying; a coarse positioner having a coarse positional resolution; a head carriage mounted to the coarse positioner; a fine positioner mounted to the coarse positioner, the flying head being mounted to the fine positioner, and the fine positioner having a fine positional resolution less than the coarse resolution; a load force actuator having an axis of motion perpendicular to the surface of the disk through which an adjustable load is applied responsive to a control input; and a load force controller having a load force controller output, the controller output coupled to the control input.

10. The head positioner of claim 9, the load force actuator having a degree of motion along the axis of motion perpendicular to the surface of the disk sufficient to load and to completely withdraw the flying head from the surface of the disk.

11. The head positioner of claim 10, for flying the flying magnetic head over a recording medium, the head positioner further comprising: a sensor having an output representative of a flying height of the head above the medium; the controller having an input coupled to the sensor output.

12. The head positioner of claim 11, where the sensor is the reading transducer.

13. The head positioner of claim 12, wherein the reading transducer is of an inductive type and the sensor output is derived from changes in amplitude of the readback signal.

14. The head positioner of claim 13, wherein the sensor output is further defined by changes in amplitude of the readback signal occurring at a frequency characteristic of a mechanical resonance of the magnetic flying head and the air bearing.

15. The head positioner of claim 12, wherein the reading transducer is a magneto- resistive element and the sensor output is derived from a high voltage peak in the readback signal indicative of contact between the magnetic flying head and a disk asperity.

16. The head positioner of claim 12, wherein the reading transducer is a magneto- resistive element and the sensor output is derived from changes in amplitude of the readback signal.

17. The head positioner of claim 16, wherein the sensor output is further defined by changes in amplitude of the readback signal occurring at a frequency characteristic of a mechanical resonance of the magnetic flying head and the air bearing.

18. The head positioner of claim 9, the fine positioner further comprising: a rotary position motor having a rotor and a stator, the flying magnetic head mounted to the rotor and the stator mounted to a moving member of the coarse actuator.

19. The head positioner of claim 10, the fine positioner further comprising: a rotary position motor having a rotor and a stator, the flying magnetic head mounted to the rotor and the stator mounted to a moving member of the coarse actuator.

20. A method of positioning a flying head relative to a recording medium surface, comprising the steps of: flying the flying head over the recording medium surface; positioning the flying head over a desired location on the recording medium surface; applying a load force to the flying head; and adjusting the load force applied to the flying head while positioned over the desired location.

21. The method of claim 20, further comprising the step of: reading magnetically encoded information from the recording medium surface using the flying head.

22. The method of claim 21, wherein the step of adjusting further comprises the steps of: measuring whether the flying head is flying at a minimum glide height; changing the load force to cause the flying head to fly at the minimum glide height.

23. The method of claim 21 , wherein the step of positioning further comprises the step of: coarsely positioning the flying head to within a coarse positional resolution of the desired location; and finely positioning the flying head to within a fine positional resolution of the desired location.

24. The method of claim 23, the flying head having a center of gravity, wherein the step of finely positioning further comprises the step of: applying a force to the flying head substantially parallel to the recording medium surface and through the center of gravity of the flying head.