Abstract:
A disk drive system includes a light source ( 110 ), such as an LED, mounted on the magnetic head. The LED ( 110 ) is patterned to form a fine pitched mask. The diverging light off the LED radiates toward a fixed, faceted optical reflector ( 112 ). The faceted array includes a plurality of spaced aspherical reflectors. The faceted array projects a portion of the light to a diffraction limited focus detector ( 114 ).

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to magnetic disk drives and, in particular, to magnetic head positioning.  
           [0003]    2. Description of the Related Art  
           [0004]    In magnetic disk drives, the data is stored as a series of magnetic field transitions on a magnetic recording surface. The transitions are placed on the surface by a magnetic transducer commonly referred to as a magnetic recording head. The transducer converts electrical energy into a magnetic field, the polarity of which is switched according to the information to be recorded. The magnetic field causes magnetization to remain in the media after the field is removed. The data is stored as binary information in the polarity reversals, or transitions, remaining in the media. The transducer used with magnetic media may also act as a detector to detect data stored as magnetic transitions. The transducer senses a magnetic field emanating from the magnetized media. The sensed magnetic field is converted into an electric signal which varies depending on the polarity of the magnetic field. Data is then decoded from the electrical signal. When the transducer places data on the recording media, the transducer is said to have written data to the media. When the transducer detects previously written data on the media, the transducer is said to have read data from the media. In general, systems for storing and retrieving data to/from magnetic media may employ a single transducer to both read and write data, or they may employ dual transducers, one to read and one to write.  
           [0005]    The recording media is in the form of a disk, typically with data being recorded on both surfaces. Multiple disks may be provided to increase the aggregate storage capacity of the disk drive. The center hole in the media is typically called a hub. The hub is the means by which the recording media attaches to a motor, through a spindle shaft, which rotates the recording media. The head is flown over the surface of the recording media by virtue of the air movement created when the disk rotates. The flying height must be large enough to minimize the probability of head and disk contacts that could be detrimental to data integrity, but small enough so that the magnetic field generated by the write transducer establishes magnetic transitions in the recording media surface and so that a magnetic field in the media can be sensed by the transducer.  
           [0006]    The head is placed in proximity to the recording surface and positioned over the desired data track by an actuator arm, to which it is attached via a suspension. The actuator arm moves the head radially with respect to the media surface from a position near the hub (the inside diameter (ID)) to a position near the rim (the outside diameter (OD)). Data is commonly written onto the media surface between the ID and OD in the form of sequential concentric tracks. The track width is usually slightly larger than the width of the write transducer. The concentric tracks may be subdivided into one or more sectors.  
           [0007]    The head must be accurately positioned over the desired data track to read or write data. Head positioning is typically accomplished by way of an actuator positioning servo controller driving a voice coil motor (VCM) attached to the actuator arm. The actuator positioning servo controller makes use of pre-recorded head positioning information as well as track and sector identification information to move the head from one track to another, known as seeking to a desired track, and to position the head over the center of the desired track and at the appropriate sector along the track. The positioning and identification information is pre-recorded on one or more of the disk surfaces, in magnetic patterns which vary in both the radial and circumferential direction to provide the actuator positioning servo controller with feedback indicating the current position of the head relative to the desired track and sector.  
           [0008]    The data head must be accurately positioned over the desired data track and data sector before user data can be stored or retrieved from a disk drive. The actuator positioning system accomplishes this by reading the pre-written positioning and identification information and using it to update the position of the actuator. The positioning and identification information is encoded onto the disk surface in the form of a pattern of accurately sized and spaced magnetic transitions, known as servo patterns, precisely recorded in both the radial and circumferential directions. These servo burst provide a radial error signals which when fed back to the radial arm position control mechanism reduce tracking error to acceptable levels.  
           [0009]    A limiting factor in the performance of this control mechanism is the mechanical resonate frequency of the tracking arm, radial inertia, and the number of servo bursts per disk rotation. To increase the resonate frequency of the structure, and to decrease mechanical inertia, the effective size and weight of the head arm must be reduced. One way of doing so is through a two stage mechanical control of the head radial position. Coarse positioning is provided through a conventional head arm and fine positioning is provided using a piezo-electrical or electromechanical actuator. However, this approach must be combined with an increase in servo boost sectors, resulting in both significantly increased mechanical complexity and a reduction in the available storage space.  
           [0010]    Another approach has been through the use of optical sensors. One such method focuses light beams from a laser onto a reflector attached to the tracking arm. Another approach mounts a light source and associated optics on the arm itself. However, these approaches, too, suffer from either an increase in the mechanical complexity or from poor detectors.  
           [0011]    As such, there is a need for an improved position detector associated with a magnetic drive tracking arm.  
         SUMMARY OF THE INVENTION  
         [0012]    These disadvantages in the prior art are overcome in large part by a system and method according to the present invention. A disk drive system according to an embodiment of the present invention includes a light source, such as an LED, mounted on the magnetic head, for fine positioning. The LED is patterned to form a fine pitched mask. The diverging light off the LED radiates toward a fixed, faceted optical reflector. The faceted array includes a plurality of spaced reflectors. The faceted array projects a portion of the light to a diffraction limited focus detector.  
           [0013]    A method for fine positioning of a disk drive actuator arm according to an embodiment of the present invention includes projecting a light beam through a mask from an end of the disk drive actuator arm. The beam is reflected from facets on a reflector onto first and second quadrature detectors. The reflector facets are configured such that a pattern from the mask impinges on at least one of the detectors at all times. Fine movements of the actuator arm, such as those induced by mechanical vibrations, are detected and the position of the arm is sensed at all times.  
           [0014]    A disk drive positioning apparatus according to an embodiment of the present invention includes a light source positioned on an actuator arm that produces one or more incident beams; a faceted reflector configured to reflect the one or more incident beams; and a detector adapted to receive one or more incident beams from the reflector and correlate reflected beams with a position of the actuator arm. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    A better understanding of the invention is obtained when the following detailed description is considered in conjunction with the following drawings in which:  
         [0016]    [0016]FIG. 1 is a diagram illustrating disk drive system according to an embodiment of the invention;  
         [0017]    [0017]FIG. 2 is a diagram illustrating the position sensor of an embodiment of the present invention;  
         [0018]    [0018]FIG. 3 is a diagram illustrating a detector according to an embodiment of the present invention;  
         [0019]    FIGS.  4 A-E illustrate detector operation according to an embodiment of the present invention;  
         [0020]    [0020]FIG. 5 is a block diagram of detector electronics according to an embodiment of the present invention;  
         [0021]    [0021]FIG. 6 is a graph illustrating degrees of resolution;  
         [0022]    [0022]FIG. 7 is a flowchart illustrating operation of an embodiment of the present invention; and  
         [0023]    [0023]FIG. 8 is a graph illustrating residue error which may be corrected in embodiments of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]    Turning now to the drawings and, with particular attention to FIG. 1, a diagram of a magnetic disk drive according to an embodiment of the invention is shown therein. Any suitable disk drive system having servo electronics and read/write electronics may be suitable for use with detection according to the present invention. The disk drive includes a disk  102 , actuator arm  104  having a pivot point  108 , data head  106 , voice coil motor  109 , LED or laser diode  110  (or VCSEL laser), detector electronics  111 , reflector  112 , detector  114 , read/write electronics  116 , and servo electronics  118 .  
         [0025]    In operation, the read/write electronics  116  sends and receives user data and provides signals to read and write the user data from and to the disk  102  through head  106 . The servo electronics  118  receives signals from the read/write head when the read/write head  106  reads a servo pattern on the disk. The servo electronics  118  are used to obtain relatively precise positioning information at relatively widely spaced intervals. The servo electronics  118  receive position information and issue servo signals to provide actuator control through voice coil motor  109 , effecting movement of the actuator arm  104 . The disk  102  is rotated past the data head  106  at a constant rate.  
         [0026]    The LED  110 , reflector  112 , reflector electronics  111 , and detector  114  are used to provide additional position reference information during operation. In particular, these are used to follow position changes between sector updates. In this way, fine movements of the actuator arm, such as those induced by mechanical vibrations, are detected. As will be explained in greater detail below, in operation, once the actuator arm is in a relatively fixed position, the LED  110  directs a light beam in the direction of reflector  112 . The reflector  112  directs the reflected beam into detector  114 . Detector electronics  111  read the input and determine a position of the actuator arm from the received signal.  
         [0027]    More particularly, FIG. 2 and FIG. 3 illustrate the motion detection according to embodiments of the present invention in greater detail. Shown in FIG. 2 is the platter  102 , actuator arm  104 , light source  110 , reflector array  112 , and detector  114 . Shown at  103  is a detail of the light source  102 &#39;s emitter mask  103 . The emitter mask  103  includes a plurality of slits  105 . The mask  103  may be 500 microns square and the slits  105  may have a width of 40 microns and be spaced 40 microns, center to center. The reflector array  112  includes a plurality of facets or elements  113 . In on embodiment, the elements are aspherical reflectors, though any reflector suitable to direct or focus the beam(s) from the light source to the detector may be used. As shown, the reflector array  112  includes a plurality of aspherical reflectors  113  having a spacing of 2 millimeters.  
         [0028]    [0028]FIG. 3 illustrates in greater detail the detectors  114 . In the embodiment illustrated, the detector  114  is implemented as a pair of quadrature detectors  114   a ,  114   b . Each detector  114   a ,  114   b  includes a pair of rows of slits  117   a ,  117   b . As shown, the slits  117   a  are partially offset from the slits  117   b . In particular, the slits  117   a  may be 25% offset from slits  117   b . The offset quadrature detectors provide two signal channels per detector and allow for more precise detection. The detectors  114   a ,  114   b  may be implemented on a single semiconductor chip to ensure uniformity and improve mask registration. The slits may be implemented as a metal layer deposited on the semiconductor (or over an insulation layer disposed on the semiconductor layer.)  
         [0029]    Also shown in FIG. 3 are beams  302  and beams  304  impinging on the detectors after being reflected from different facets of the reflector. As shown, the beam  302  reflects off element  113   a  onto detector  114   a , and beam  304  reflects off element  113   b  onto detector  114   b . In operation, each element  113  of the reflector array  112  generates an image independently of the others on the detectors  114 . The orientation of the reflector facets  113  is chosen such that only one complete image of the emitter mask is present on the position detector at a given time. Thus, a series of images are formed on or intersecting the plane of the detectors which are used to derive a relative position reference.  
         [0030]    More particularly, as shown, at least two of the reflector elements  113  are illuminated at a given time. The focus position of the reflector elements is chosen such that only two images  119   a ,  119   b , however, appear on the detectors  114   a ,  114   b  at a given time and, in particular, only one per detector. As the actuator arm moves or wobbles, different elements (or different portions of the same elements) are illuminated and the images move on the detectors  114   a ,  114   b . As the actuator arm moves, before one of the images  119   a ,  119   b  moves out of the field of view of one of the position detectors  114   a ,  114   b , a full image is present on the other.  
         [0031]    This is illustrated by way of example with reference to FIGS.  4 A-E. Shown in FIG. 4A are detectors  114   a ,  114   b  and impinging patterns  119   a ,  119   b . In the example illustrated, the image  119   a  is wholly on detector  114   a . The image  119   b  is only partially on detector  114   b . In certain embodiments, therefore, the receiver electronics  111  will track only the image  119   a . For example, the amplitude and/or power of the signal that results from image  119   a  on detector  114   a  will be greater than that for the image  119   b  on detector  114   b . This will be detected, and the image  199   a  tracked.  
         [0032]    [0032]FIG. 4B illustrates impinging patterns  119   a ,  119   b  if the arm has moved in a direction such that the images move in the direction of the arrow (left). In this case, both patterns  119   a ,  119   b  are wholly on their respective detectors  114   a ,  114   b . In this case, the amplitude or power of the two signals resulting from the images  119   a ,  119   b  on each of the detectors  114   a ,  114   b  should be the same. However, since the pattern  119   a  previously had been detected as completely on the detector  114   a , it will continue to be tracked.  
         [0033]    In FIG. 4C, the arm continues to move such that the images  119   a ,  119   b  continue to move left. Now, however, the image  119   a  is detected as being only partially on the detector  114   a , while the image  119   b  is wholly on the detector  119   b . That is, the amplitude or power resulting from the signal corresponding to the detected image  119   a  on detector  114   a  will decrease, and be less than that for the image  119   b  on detector  114   b . Thus, the receiver electronics will track the image  119   b.    
         [0034]    In FIG. 4D, the images continue to move left across the faces of the detectors  114   a ,  114   b . As shown, the image  119   a  is completely off the detector  114   a  while the image  119   b  is transitioning between the detectors  114   a ,  114   b . In this case, the amplitude or power of the signal from image  119   b  will be split between the detectors  114   a ,  114   b . That is, the quadrature information provided is the sum of the signals from the detectors  114   a ,  114   b  (i.e., the signal from the top slits of both detectors  114   a ,  114   b  are summed, and the signals from the bottom slits of both detectors are summed).  
         [0035]    In FIG. 4E, the leftward movement continues and image  119   b  continues to be tracked and is wholly on detector  119   a . A new image  119   c  now begins to impinge on the detector  114   b , but the amplitude or signal power resulting from the image  119   c  is still less than that resulting from the image  119   b  on detector  114   a . Thus, the image  119   c  will not be tracked until it is wholly on the detector  114   b  and the image  119   b  transitions off the detector  114   a.    
         [0036]    The images may continue to proceed left (e.g., as shown in FIG. 4A) and so on. Movement of the images in the rightward direction is tracked similarly.  
         [0037]    Turning now to FIG. 5, a block diagram of receiver electronics according to an embodiment of the present invention are shown. It is noted that the receiver electronics may be any combination of hardware, software, or firmware suitable to detect and process the detector signals. Thus, FIG. 5 is exemplary only.  
         [0038]    Shown in FIG. 5 are receivers  502 ,  504 , a selector unit  506 , and a quadrature detector  508 . Quadrature signals  501 ,  503  are received at receivers  502 ,  504  respectively. The signals, which are square waves, are the signals from the top and bottom rows  117   a ,  117   b  (FIG. 3) of slits (The optical signal is a square wave to support synchronous detection and the amplitude of the synchronous signal is used for quadrature demodulation. The modulation of the envelope of the signal is due to the movement of the image over the mask. The resulting quadrature signals are two sine waves separated by 90 degrees in phase.).  
         [0039]    The signals are then provided to a selector unit  506 . The selector unit  506  makes the determination of which of the images  119   a ,  119   b  is to be tracked. That is, as discussed above, the selector  506  examines the amplitude or signal power from the detector  114   a  and the detector  114   b . Thus, in tracking, the selector  506  will select detector  114   a  or  114   b  or both  114   a  and  114   b  (i.e., receiver  502 , receiver  504  or both). The resulting tracking information is provided to a quadrature detector  508 . It is noted that the detector may be any appropriate detector, for detecting baseband or modulated signals. The output of the quadrature detector  508  is then used for the position determination or correlation. Processing of such a signal may be accomplished in a known manner.  
         [0040]    It is noted that, in certain embodiments, such as those in which the detectors are formed on separate semiconductors (i.e., separate pieces of silicon), a gain control may need to be provided after one of the receivers (FIG. 5). However, if typically, the detectors are formed on a common piece of silicon, such a gain control would likely not be necessary, although localized nonuniformities resulting in a residue positional error may need to be corrected. For example, shown in FIG. 8, is a graph of actual vs. estimated positions of the actuator arm. Graph  800  illustrates the theoretical values, and  802  represents actual values. These may be compensated for through knowledge of the position information obtained using the servo. That is, since the coarse position is known, as the images  119   a ,  119   b  move across the detectors, a coarse position is known since it is known when the images begin to impinge. This information may be used to compensate for the residue positional errors.  
         [0041]    The optically-based position measurement apparatus of the present invention thus provides for higher resolution than is possible with the servo method described earlier. In particular, shown in FIG. 6 is a graph  602  representing degrees of precision for servo  602   a  and for the optical method of the present invention  602   b . As the degree of resolution increases, the limits of capabilities of the servo  602   a  are reached and the optical system of the present invention takes over.  
         [0042]    Finally, FIG. 7 is a flowchart illustrating operation of an embodiment of the present invention. In step  702 , the light is projected from the end of the actuator arm through the mask. In step  704 , the mask image(s) is reflected onto the detectors  114   a ,  114   b . In step  706 , an image is selected for tracking and correlated with a position. In an ongoing manner, the receiver electronics also determine, in step  708 , if the tracked image has moved off the detector being tracked. In  710 , the current image is continued to be tracked and correlated, if the image has not moved off the corresponding detector. However, if the image has, then the other image will be tracked and correlated, in step  712 .  
         [0043]    The invention described in the above detailed description is not intended to be limited to the specific form set forth herein, but is intended to cover such alternatives, modifications and equivalents as can reasonably be included within the spirit and scope of the appended claims.