Abstract:
A method of inserting a removable data cartridge into a disk drive utilizes a cartridge having a registration contour adapted for alignment with a registration member of the disk drive. The registration contour slides along the registration member during insertion. The cartridge has an interlocking recess adapted to interface with an ejector pin of the disk drive, and a door biased to a closed position, where the door has a tab engaging the disk drive and holding the housing door open while the cartridge is in the inserted position. The cartridge is ejected by releasing the ejector pin from the interlocking recess and pushing the cartridge with the ejector pin.

Description:
This application is a Division of Ser. No. 09/170,627, filed Oct. 13, 1998, and which is a Continuation of Ser. No. 08/929,746, filed Sep. 15, 1997, and now U.S. Pat. No. 5,822,162. 
    
    
     FIELD OF THE INVENTION 
     The present invention is directed to a disk drive and in particular a disk drive which will accept a removable cartridge which houses memory media for communication with the disk drive. 
     BACKGROUND OF THE INVENTION 
     At present the industry trend is to provide for greater memory capacity in a reduced form factor at a lower cost with a lower energy consumption. This trend is driven by the increased demand for portable, lap top, notebook and palm top computer configurations which can be easily transported to a desired work site. The desired memory configuration would include, for example, a magnetic or optical hard disk drive as such drives store a considerably higher amount of data than a floppy disk drive and can access that data at a rate substantially in excess of that of a floppy disk drive. 
     With respect to hard disk drives, there are two major types. The first is a hard disk drive with the memory media or magnetic disk permanently fixed therein. The second is a hard disk drive which can accept interchangeable and removable cartridges containing the memory media. 
     The removable cartridge hard disk drives have several significant advantages over the fixed disk hard disk drives. These include the ability to interchange the number of cartridges and thus provide the disk drive with an infinitely large memory capacity. A second advantage is that any information stored on the disk or the memory media in the cartridge can, along with the cartridge, be removed and placed in a secure location should the information be of a confidential or secret nature. This can be accomplished without having to store the computer or the disk drive itself. Additionally, large amounts of data can be transferred between computers and locations by removing the cartridge from one computer and transporting it to a second computer at a different location. Such portability of large amounts of information stored on cartridges has become more necessary, for example, due to the data requirement for graphic presentations. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to providing a removable cartridge disk drive which meets and significantly exceeds the industry trend. The disk drive and removable cartridge of the present invention provides for a disk drive which is configured into a form factor having about a 2.5 inch disk or smaller and having a total disk drive height of about 0.75 inches (19 millimeters) or less. In this form factor, a removable cartridge can be inserted, which removable cartridge has a memory capacity of 40 megabytes or larger. The configuration further affords a reduced power consumption due to among other things, the design of the cartridge receiver mechanism which does not require electrical power for its operation. Accordingly, the present invention provides for the desired form factor for the newest generation of portable, lap top, notebook, and palm top computers while affording infinite memory capacity. Further the removable cartridge disk drive has the advantage that the cartridge can be removed and locked in a secured facility in order to protect confidential and secret information contained on the hard disk. Additionally, large amounts of data can be transferred from location to location as required, for example, for graphic applications by transporting the cartridge to the desired location. 
     It is also to be understood that while the present invention is highly advantageous for the above form factor, that the present invention can be incorporated into disk drives having a disk larger than about 2.5 inches and a height larger than about 0.75 inches. 
     It is also to be understood this the present design configuration with the cartridge being removable provides for much higher shock immunity at a lower cost compared to systems where the entire disk drive must be removed and stored in order to secure the data contained on the disk. In addition, the present invention provides for the ability to create a backup of information for each cartridge by merely copying the information to another cartridge. 
     Accordingly, the present invention provides for a disk drive which can accept cartridges containing a disk having a diameter of greater than and less than about 2.5 inches and preferably having a diameter of about 2.5 inches to about 1.8 inches. The cartridges of the disk drive contain a disk which in conjunction with the disk drive can store 40 megabytes and greater amounts of data. The disk drive includes a spindle motor for engaging and causing the disk in the cartridge to spin at the appropriate speed. Further, a mechanism is provided for movably mounting the spindle motor to the drive housing so that the spindle motor is telescopable movable from a first position out of engagement with the disk to a second position operably engaged with the disk. This mechanism allows the cartridge to be inserted into the drive, without the disk drive having to physically reposition the cartridge onto a spindle motor. Thus, without the need of a cartridge receiver mechanism for repositioning the cartridge onto a spindle motor, the configuration of the present invention can be more compact, and fit within the desired form factor which includes the drive height of about 17.5 millimeters and less. 
     In the present inventive configuration, the cartridge remains on the same plane on which it is inserted into the drive. This allows the cartridge to be received in and more tightly conformed to the dimensions of the disk drive cartridge receiver and thus affords a more accurate positioning of the cartridge in the cartridge receiver of the disk drive. Further, due to the fact that there is a tight fit between the cartridge and the cartridge receiver of the disk drive and due to the fact that there is a long distance between the door of the disk drive and the door of the cartridge as inserted into the disk drive, environmental contamination of the disk inside of the cartridge is greatly diminished due to the long distance which the contamination must travel in order to reach the disk. 
     Further, due to an inventive interlocking mechanism, if a cartridge is not properly seated within the disk drive, the actuation mechanism which positions the heads will not be unlatched and enabled, the heads will be not be unloaded, and the spindle motor will not be enabled. The above interlocking mechanism of the drive also ensures that the cartridge cannot be removed from the cartridge receiver while the spindle motor is engaging the disk, while the head is unloaded onto the disk, or while the head actuator mechanism and spindle motor are enabled. 
     The disk drive of the invention includes an ejecting mechanism, which is part of the above interlocking mechanism, for engaging and lockingly holding the cartridge in place in the cartridge receiver of the disk drive and for ejecting the cartridge from the cartridge receiver. The ejecting mechanism engages another proprietary interlocking mechanism or recess in the cartridge which is directed essentially across the direction of insertion of the cartridge into the drive. These interlocking mechanisms ensure that the cartridge is held in the drive and prevented from being withdrawn. 
     The drive further includes a guide rail which extends into the cartridge receiver and mates with a guide groove in the cartridge, both of which are disposed along the direction of insertion of the cartridge into the drive. The tolerances of the guide rail and guide groove are tight in order to accurately position the cartridge across the direction of insertion of the cartridge into the disk drive. 
     The cartridge receiver of the disk drive provides for guide strips for accurately positioning the cartridge along a direction which is substantially aligned with the height of the cartridge. 
     In another aspect of the invention, the disk drive includes an integral apparatus which provides for a mechanism for ensuring that the door of the cartridge is appropriately opened and able to accept the head actuator arm and heads. If the door is not appropriately opened, the mechanism halts further introduction of the cartridge into the drive. This integral apparatus further includes a ramp mechanism upon which the actuator arm and heads can be loaded and therefrom unloaded onto the disk. Additionally, this integral apparatus includes a mounting mechanism for mounting air filters for the disk drive. 
     In another aspect of the invention, the spindle motor has an inventive magnetic clamp for seating of an armature plate of the hub of the cartridge onto the spindle motor. This magnetic clamp includes in one preferred embodiment, a single uniform pole magnet with a single flux path ring. With this configuration, it is advantageous for the cartridge armature plate to be premagnetized or otherwise acquire a magnetic pole which is attracted by the polarity of the magnetic clamp. This magnetic clamp includes, in another of the preferred embodiments, a plurality of magnetic rings spaced by a plurality of magnetic flux transmitting rings. Such a configuration ensures that there is an adequate magnetic field for properly seating the hub and the armature of the cartridge onto the spindle motor while ensuring that the field is sufficiently weak so that it will not damage any data stored on the magnetic disk of the cartridge. 
     In another aspect of the invention, a proprietary hub chuck is provided for ensuring accurate positioning of the cartridge hub and chuck relative to the spindle motor. The chuck includes a one piece, integral apparatus which includes datum and a spring mechanism for accurately positioning the chuck onto the shaft of the spindle motor. Further, there is provided an appropriate configuration on the internal surface of the housing of the cartridge which insures that during the process of mating the hub and chuck to the spindle motor, that the disk does not become cocked in the cartridge. In a preferred embodiment, this includes a raised ring which projects on the inside of the housing towards the hub. 
     In further aspect of the invention, the cartridge door is removable from a closed position to an open position as a member of drive engages a cam fixed to the door and urges the cam and the door to the open position. The cartridge door is configured with a spring which is imbedded into the door in order to maximize clearance with the door open to ensure that the actuator arms and heads can be positioned through the door opening and unloaded onto the disk without interference between the actuator arms and heads, and the cartridge or door. The door further includes a stiffener for preventing the door from bowing and for also retaining the spring embedded in the door, thus also ensuring that there is appropriate clearance so that there is no interference between the actuator arms and head, and the cartridge and door as the heads are unloaded onto the disk. 
     In another aspect of the invention, a servo pattern embedded in the servo sector of the disk includes a servo address mark (SAM) that is distinguishable and detectable in the presence of media defects. 
     A further aspect of the invention includes improved repetitive runout correction for the disk drive with a removable cartridge having an imbedded servo sector. 
     Other inventive aspects of the disk drive and removable cartridge of the invention can be obtained from a review of the specification, claims and the appended figures. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 depicts a perspective view of an embodiment of the removable cartridge disk drive of the invention. 
     FIG. 2 depicts a perspective view similar to FIG. 1 with the door of the disk drive moved to the open position. 
     FIG. 3 depicts a perspective view of an embodiment of the removable cartridge of the invention. 
     FIG. 4 depicts a perspective view similar to FIG. 3 with the door of the cartridge moved to an open position. 
     FIG. 5 depicts a cutaway and sectioned view of an embodiment of the removable cartridge of the invention inserted into an embodiment of the disk drive of the invention. 
     FIG. 6 depicts a cutaway and sectioned view of the disk drive of FIG. 1 with the cartridge receiver removed and some of the base plate cutaway in order to depict the position of the spindle motor and the various mechanisms, and with the door of the disk drive in an open position. 
     FIG. 7 is a cutaway, sectioned view similar to FIG. 6 with the door of the disk drive in a closed position and the various mechanisms repositioned. 
     FIG. 8 depicts a cutaway and sectioned view of an embodiment of the cartridge with the cartridge hub. 
     FIG. 9 depicts a cross-section view of an embodiment of the spindle motor of the disk drive of the invention. 
     FIG. 10 depicts a cross-sectioned and cutaway view of the hub of FIG. 8 of the cartridge of the invention positioned above the spindle motor of FIG. 9 of the invention. 
     FIG. 11 depicts a view similar to FIG. 10 with the hub of the cartridge seated on the spindle motor of the invention. 
     FIG. 12 a  depicts a side view of an embodiment of an outer housing or barrel for the spindle motor of FIGS. 4 and 10 of the invention with a cam profile. 
     FIG. 12 b  depicts a view similar to FIG. 12 a  but with another cam profile. 
     FIG. 12 c  depicts the cam profiles of FIGS. 12 a  and  12   b  superimposed in order to show the differences in profiles. 
     FIG. 13 a  depicts a plan view of an alternative magnetic clamp for the spindle motor of FIGS. 10 and 13 b  depicts a cross-sectioned view of FIG. 13 a  at line  13   b — 13   b.    
     FIG. 14 depicts another alternative embodiment of the magnetic clamp. 
     FIG. 15 depicts a cross-sectional view of FIG.  14  through line  15 — 15 . 
     FIG. 16 depicts yet another alternative embodiment of the magnetic clamp. 
     FIG. 17 depicts a plan broken-away view showing an embodiment of a transducer or head mounted on an actuator arm of the disk drive of the invention resting in a position away from the disk of the cartridge of the invention. 
     FIG. 18 depicts a view similar to FIG. 17 but with the heads moved toward the disk of the cartridge preparatory to the heads being unloaded onto the disk. 
     FIGS. 19 a  through  19   e  depict the indicated views of an integral apparatus for ensuring that the cartridge door is fully opened, for loading the heads onto the disk, and for mounting an air filter. 
     FIG. 20 depicts a side view along lines  20 — 20  of FIG.  17 . 
     FIG. 21 depicts a plan view of the embodiment of the cartridge of the invention of FIG.  23 . 
     FIG. 22 depicts a bottom view of the cartridge of the invention of FIG.  21 . 
     FIG. 23 depicts a door end or front view of the cartridge of the invention of FIG. 21 with the door in a closed position. 
     FIG. 24 depicts a partially broken-away and sectioned view of an embodiment of the cartridge door of the invention affixed to the housing of the cartridge of FIGS. 3 and 4 with the door in an open position. 
     FIG. 25 depicts a cross-sectioned broken-away view through line  25 — 25  of FIG.  24 . 
     FIG. 26 depicts a cross-sectioned view of the cartridge door of FIG. 24 of the invention with the torsional spring shown in two positions. 
     FIG. 27 depicts the bottom view of the cartridge door of FIG. 24 of the invention. 
     FIG. 28 depicts a cross-sectioned view of an embodiment of the cartridge receiver of the disk drive of the invention with an embodiment of the cartridge of the invention inserted therein. 
     FIG. 29 depicts a plan view of the internal surface of a lower half of the cartridge housing of FIGS. 3 and 4 of the invention. 
     FIG. 30 depicts a plan view of the internal surface of the upper half of the cartridge housing of FIGS. 3 and 4 of the invention. 
     FIG. 31 a  depicts a plan view of an embodiment of the chuck for the hub of the cartridge of the invention. 
     FIG. 31 b  depicts a cross-sectioned view of FIG. 31 a  taken at line  31   b — 31   b.    
     FIG. 32 depicts a current wave form used to encode some of the servo information onto a servo sector on the disk of the cartridge of the invention. 
     FIG. 33 depicts magnetized transitions on the servo section on selected tracks of a disk of the cartridge of the invention formed by the current wave form of FIG.  32 . 
     FIGS. 34 a - 34   b  are a depiction of the waveform for a servo pattern of an embodiment of the invention. 
     FIG. 35 a  is an enlargement of the waveforms for the servo address mark (SAM) of the servo pattern. 
     FIG. 35 b  is a block diagram showing the method of detecting the SAM of FIG. 35 a.    
     FIG. 36 is a schematic of an embodiment for servo loop compensation and for repetitive correction for the invention. 
     FIGS. 37 a - 37   d  are block diagrams for the repetitive runout correction of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to the figures and in particular FIGS. 1 through 4, the disk drive  50  and the removable cartridge  52  of the invention are depicted. In a preferred embodiment, the housing of the disk drive  50  can have a height of about 0.748 inches or 19 mm, a width across the front of 2.76 inches and a length of about 4.0 inches. In an alternative embodiment, the height can be 17.5 mm. The cartridge  52 , in a preferred embodiment, can have a height of about 0.263 inches, a width across the front of the cartridge of about 2.66 inches and a length of about 2.70 inches. The disk contained in the cartridge is about 2.55 inches or 65 mm in diameter. As noted herein, other embodiments of the invention can have other dimensions and come within the spirit and scope of the invention. 
     As can be seen in FIGS. 1 and 2, the disk drive  50  includes an outer housing  54  and a door  56  which is movable between a closed position as shown FIG.  1  and an open position as shown in FIG.  2 . In the open position, the removable cartridge  52  can be inserted through a port  58  into the cartridge receiver  60 . The door  56  includes a spring  62  which, in a preferred embodiment, can be comprised of an elastic form material or other resilient material or a variety of mechanical spring mechanisms, such as for example a leaf spring or a bowed spring retained in a recess of the drive door  56 , to ensure that the closing of the door  56  further urges the cartridge  52  into the drive  50  in order to lockingly position the cartridge  52  as will be more fully explained hereinbelow. 
     Extending from the front panel  64  of the disk drive  50  is a slide  66  which is movable from the first position shown in FIG. 1 to a second position shown in FIG.  2 . This slide  66  operates in conjunction with the interlocking mechanisms, which will be described hereinbelow, that ensures, among other things, that unless the cartridge is properly locked in the drive, that the spindle motor and the motor which positions the head relative to the disk and cartridge will not be enabled. Slide  66  also ensures, among other things, that before a cartridge can be removed from the drive that the heads are removed from the disk and that the motors are disabled. 
     As can be seen in FIGS. 3 and 4, the cartridge  52  includes a cartridge door  68  which is movable from a closed position, shown in FIG. 3, to an open position shown in FIG.  4 . The cartridge door  68  is pivotedly mounted to the housing  70  of the removable cartridge  52  and includes a main door portion  72  and a cam or tab  74 . The main door portion  72  provides a closure for the port or opening  76  in the housing  70  of the removable cartridge  52  through which the heads and actuator arm (described below) are provided in order to load the heads onto the disk contained in the cartridge. The cam  74  extends in a direction opposite to the main portion of the door  72  and is disposed at the beginning of a door opening groove  78  provided in the housing  70 . In a preferred embodiment, the housing  70  includes an upper half  80  and a lower half  82 . The door opening groove  78  is located in the upper half  80  of the cartridge housing  70 . 
     As will be described more fully hereinbelow, the disk drive includes a door opening projection or rail ( 354  in FIG. 28) which upon insertion of the cartridge  52  into the drive  50  comes into contact with the cam  74  of the door  68  causing the cam  74  to rotate from approximately zero degrees to approximately 90 degrees with the door  68  rotating from approximately 180 degrees to approximately 270 degrees, both in a clockwise manner. The door opening rail then proceeds to travel along the door opening groove  78  as the cartridge  52  becomes fully seated in the disk drive  50 . 
     FIG. 5 depicts a cutaway view of the disk drive  50  with the top of the housing  54  removed in order to reveal the cartridge  52  in a fully seated positioned. In this view, it can be seen that a recess  84  defined by the lower half  82  of the housing  54  of the cartridge  52  is received against a stop  86  defined by the cartridge receiver  60  of the disk drive. The stop  86  is upstanding from the base plate  92  of the cartridge receiver  60 . When the door  56  of the disk drive  50  is closed, the spring  62  mounted on the door  56  of the disk drive  50  urges the cartridge  52  against the stop  86  in order to lockingly position the cartridge  52  in the disk drive receiver  60  in a “Y” direction or the direction of insertion of a cartridge into a disk drive. 
     As can be seen in these figures, the cartridge  52  further includes a guide groove  88  (FIG. 5) and an interlocking recess  90  (FIG. 22) which as will be described hereinbelow, are used to accurately position and hold the cartridge in the disk drive. In a preferred embodiment, the cartridge housing and door are molded from one of the high impact and durable plastics which are well known in the industry such as by way of example only, a polycarbonate plastic. The disk drive housing  54  in a preferred embodiment is comprised of a one of a number of metals (such as aluminum) or plastics (such as polycarbonate plastic) which are known in the industry suitable for such housings. 
     As can be seen in FIG. 5, the cartridge  52  is received on a base plate  92  which is the floor of the cartridge receiver  60  and separates the cartridge from the various linkage mechanisms and the spindle motor (described hereinbelow). Also it is noted that the cartridge  52  is tightly received within the cartridge receiver  60 . It is evident from FIG. 5 that the spaces between the sides  94 ,  96  of the drive housing  54  and the cartridge are quite small. This being the case, and given the length of the cartridge and the fact that the cartridge door  56  is located, when inserted in the drive, distally from the drive door ensures that there is a substantially long, narrow path which environmental contamination must follow in order to go through the door  56  of the disk drive  50  and arrive at the cartridge door  68  before potentially contaminating the disk therein. That being the case, the present embodiment provides for a design with a greatly enhanced environmental contamination prevention scheme. 
     Cartridge Interlocking and Spindle Motor Telescoping Mechanisms 
     FIGS. 6 and 7 depict the cartridge interlocking and spindle motor telescoping mechanisms  100  of the invention. Mechanisms  100 , which along with the rest of the drive, afford the ability of the disk drive to store 40 megabytes or greater of information in the above specified desired form factor of a disk drive with about a 2.5 inch diameter disk with a drive height of about 19 millimeters and less. 
     FIG. 6 depicts the mechanisms  100  which resides in the lower portion of the disk drive  50  below the base plate  92 , which base plate  92  has been removed in part to better reveal the mechanisms  100 . FIG. 6 depicts the disc drive  50  with the door  56  provided in the open position and the mechanisms  100  as they would be preparatory to a cartridge being received in the receiver. FIG. 7 depicts the disk drive  50  with the door  56  in the closed position and with the mechanisms  100  positioned in the manner that they would be positioned where a cartridge  52  received in the disk drive  50 . 
     The mechanisms  100  provides for the interlock functions necessary for the insertion and removal of the cartridge into the disk drive. 
     It is noted mechanisms  100  allow the cartridge to be inserted substantially on a horizontal plane and remain in that plane while the disk is spun by the spindle motor and the heads are loaded on the disk in order to read and write information. This design is highly advantageous with respect to other designs where the cartridge itself has to be physically lowered and set down on the spindle motor, whether through mechanical linkages or mechanical linkages in combination with solenoids. Thus, the present design affords for a more compact and reliable design for positioning the cartridge in the disk drive. 
     As the functions of the mechanisms  100  are performed mechanically, the present disk drive is highly suitable for use in a portable computer. There is no electrical power requirement and thus mechanisms  100  do not drain the battery of the portable computer. This allows the portable computer to function for a longer time than would be possible were the mechanism of the disk drive which afforded engagement and seating of the cartridge electrically operated. Further, should there be a power failure, in a solenoid system, it would be difficult to remove the cartridge and secure it. However in a mechanical system provided by the present invention, the cartridge can be removed at any desired time in order to secure or transport it. 
     In general, one of the main features of the mechanisms  100  include the spindle motor  102  being telescopably mounted so that it can move from a lower positioned as depicted in FIGS. 6 and 10 to an upper position as depicted in FIGS. 7 and 11 in order to engage the hub  104  of the cartridge  52 . Further the mechanisms  100  includes an ejector mechanism  106  which has an ejector pin  108  which is used to lockingly receive and hold the cartridge  52  in the cartridge receiver  60 . Ejector pin  108  projects through port  109  defined in base plate  92  into the cartridge receiver  60  in order to engage the cartridge  52 . More specifically, the ejector pin  108  acts in a direction which is across, and in a preferred embodiment generally perpendicular to, the direction of insertion of the cartridge into the drive, which direction of insertion is shown by the arrow  110  on the cartridge in FIG.  5 . 
     The cartridge interlocking and spindle motor telescoping mechanisms  100  perform four separate operations. These include (1) insertion of the cartridge into the drive, (2) enabling of the drive, (3) disabling of the drive and (4) removal of the cartridge from the drive. During the insertion operation, certain elements (described below) are interlocked so that cartridge cannot be removed while the drive is still in use. Further the interlocking elements provide that the drive cannot be enabled if a cartridge is not inserted into the drive. With no cartridge received in the disk drive, the interlocking elements will not allow the heads to be loaded onto the disk or the head arm actuator motor (which in a preferred embodiment is a voice coil motor) to be unlatched and enabled. Additionally, the spindle motor cannot be enabled without the cartridge properly inserted and seated in the cartridge receiver. 
     1. Insertion of Cartridge 
     As the cartridge  52  is inserted into the disk drive, a cam detail or interlocking recess  90  (FIGS. 3,  22 ) on the underside of the housing of the cartridge  52  (discussed hereinbelow in greater detail) is engaged by the ejector pin  108  of the ejector mechanism  106 . The ejector mechanism  106  further includes an ejector arm  114  which pivots about pivot pin  116  with an ejector arm follower pin  118  following an L-shaped cam slot  120  of an index bar  122  until the ejector arm follower pin  118  is lodged in the lower most portion of the L-shaped cam slot  120 . This movement allows the spring  125  which is secured between the index bar  122  and the ejector arm  114  to cause the index bar  122  to move rightwardly to the position as shown in FIG.  7 . The motion of the index bar  122  is guided by the slots  124  and  126  which are defined by the index bar  122 . The previously identified fixed pivot pin  116  and the fixed pivot pin  128  are disposed through slots  126  and  124 , respectively and according guide and limit the motion of the index bar  122 . 
     As the index bar  122  moves to the right from the position in FIG. 6 to the position in FIG. 7, the follower arm assembly  130  which is pivotally mounted at pivot point  132  to index bar  122  is displaced toward the actuating arm  134 . As this occurs, the follower  140  located on the end of follower arm assembly  130  remains in contact with the extended ledge or land  142  of the actuating arm  134  as shown in FIG.  6  and spring  136  which links assembly  130  to index bar  122  is stretched with the pivot point  132  located on index bar  122  being projected into a recess  138  of the actuating arm  134  as shown in FIG.  7 . This action holds the index bar  122  in the rightward position of FIG.  7 . At this point, with the ejector pin  108  moved to the more rearward position as shown in FIG.  7  and engaging the cam detail or interlocking recess  90  of the cartridge  52 , the cartridge is lockingly positioned or held in the cartridge receiver  60  and cannot be withdrawn. This process also stretches spring  143  which is mounted between actuating arm  134  and ejector mechanism  106 . So stretched spring  143  can aid in ejecting cartridge  52 . The reverse of this process causes the cartridge to be ejected from the drive as described hereinbelow. 
     The index box  122  includes an ear  137  located at an extreme leftward position thereon. Ear  127  along with an ear  205  of retract link  204  (described below) form an interlock that prevents (1) heads from unloading onto themselves, (2) the head actuator arm and actuator motor from moving and being enabled, and (3) the spindle motor from being enabled should a cartridge not be seated into the drive so as to cause index bar  122  to be repositioned rightwardly as ejector pin  108  is displaced from the position of FIG. 6 to the position of FIG.  7 . 
     The actuating arm  134  is connected to the door  56  by a door linkage  144 . As the door  56  is moved to the closed positioned as shown in FIG. 7, the door linkage  144  and the actuating arm  134  move rearwardly as guided by slots  146  and  148  which slots are constrained by fix pins  150  and  152  provided through slots  146 ,  148 . During the first half of the motion of the actuating arm  134 , the ejector mechanism  106  is armed for ejection of the cartridge  52  from the disk drive  50 . This is accomplished due to the displacement of the follower  140  rightwardly into the now moved recess  138  of the actuating arm  134  shown in FIG. 7 with the accompanying contraction of spring  136  which is connected between an end of the follower arm assembly  130  and the index bar  122 . Thus, follower  140  is now placed in the path of ramp  139  of recess  138 . For ejection, ramp  139  urges follower  140  and thus index bar  122  leftwardly (as actuating arm  134  is pulled forwardly, by the drive door opening) to the position of FIG. 6, freeing pin  118  from the bottom of the L-shaped cam slot  118  and allowing spring  125  to rotate ejector pin  108  clockwise in order to eject the cartridge. 
     During the second half of the motion of the actuating arm  134  in a rearwardly direction, a follower roller  154  on the spindle motor actuating arm  156  follows the slot cam detail  158  on the actuating arm  134  causing the motor actuating arm  156  to rotate in a counterclockwise direction. As this occurs, the spindle motor actuating arm  156  pivots about fixed pivot pin  160 . Fixed pivot pin  160  is disposed in the slot cam detail  158  of the actuating arm  134  in order to assist in directing the actuating arm  134  in a rearwardly direction. 
     As the spindle motor actuating arm  156  rotates, it pulls the motor drag link  162  to a rightward position as shown in FIG.  7 . The motor drag link  162  is attached to the outer rotating barrel  164  of the motor lifting or telescoping mechanism  168  (more fully described hereinbelow). The spindle motor  102  is accordingly raised into contact with the cartridge and base plate  92  as the rotating barrel  164  is rotated in a counterclockwise direction from the position of FIG. 6 to the position of FIG.  7 . The rotation of the outer rotating barrel  164  is guided by fixed pins  170  which are disposed within curved slots  172  which are defined by the outer rotating barrel  164 . As rotation of barrel  164  occurs, the follower pin  174  affixed to the motor drag link  162  moves in the slit  176  defined in the spindle motor actuating arm  156 . A spring  178  is connected between the motor drag link  162  and the spindle motor actuating arm  156  in order to encourage the motion of the follower  174  in the slit  176  thus ensuring the appropriate freedom of motion between the motor drag link  162  and the spindle motor actuating arm  156 . 
     At this point, the spindle motor  102  has been telescoped upwardly into contact with the hub  104  of the cartridge  52  and also the bottom of base plate  92 . 
     2. Enabling the Drive 
     The disk drive  50  is now enabled by moving the slide  66  rightwardly from the position of FIG. 6 to the position of FIG.  7 . The slide  66  is connected to an interlock bar  180  which slides across the path of the actuating arm  134  when and only when the actuating arm  134  is fully disposed in a rearward position as shown in FIG.  7 . Thus, it can be appreciated that with the disk drive door  56  open, that the slide  66  cannot be moved fully rightwardly as the interlock bar  180  would come into contact with the actuating arm  134  and thus the drive cannot be enabled. 
     A detent arm assembly  182  held by a spring  184  provides positive location of the interlock bar  180  in the first position shown in FIG.  6  and the second position shown in FIG.  7 . The motion of the interlink bar  180  is guided by the slots  186 ,  187  defined by the interlock bar  180  and by the fixed pins  188 ,  189  which are disposed in slots  186 ,  187 . As interlock bar  180  moves between the first and second positions as shown in FIGS. 6 and 7, the roller follower  190 , located on the detent arm assembly  182 , moves between the first and second recesses  192 ,  194  on the interlock bar  180 . With the assistance of the spring  184  the interlocking bar  180  causing the detent arm assembly  182  to pivot about the fixed pin  189 , resulting in the interlock bar  180  being retained in either the position of FIG. 6 or FIG.  7 . 
     Connected to the interlock bar  180  is a linkage assembly  196  which comprises a retract actuating arm  198 . Arm  198  is pivoted about fix pivot pin  200  in a counterclockwise direction as the retract actuating arm  198  is directly connected to the interlock bar  180  by the pin and slot arrangement  202 . The linkage assembly  196  further includes a retract link  204  which is pivotally pinned to the retract actuating arm  198 . Retreat link  204  includes ear  205  which can interlock with ear  127  of index bar  122  to prevent operation of the drive should a cartridge not be properly inserted in the cartridge receiver  60 . FIG. 6 shows how ears  127  and  204  interfere and prevent enablement of the drive and unloading of the heads onto themselves if a cartridge has not be received in cartridge receiver  60 . FIG. 7 shows ear  127  moved out of the way of ear  205  as the cartridge has been properly inserted in the cartridge receiver  60 , so as to move ejection pin  108  and thus causing the index bar  122  to move rightwardly. This action allows slide  66  to enable the disk drive motor and allows the heads to be unloaded onto the disk. 
     The retract link  204  is also pivotally connected to the retract arm  206  by pin  208 . The retract arm  206  is pivotedly mounted about fix pivot pin  210 . The retract arm  206  moves in a clockwise direction from the position in FIG. 6 to the position of FIG. 7 during the motion of the interlock bar  180  to the rightward position as shown in FIG.  7 . This motion of the retract arm  206  takes it out of the path of the motion of the head actuator assembly and in particularly pin  283  of the actuator arm  282  (described below) and thus allows the heads under the control of a voice coil motor to be unloaded onto the disk. Motion of the slide  66  leftwardly to the position of FIG. 6 causes the retract arm  206  to move in a counterclockwise direction causing the heads to be removed from the disk and parked as described below, preparatory to the removable of the cartridge  52  from the drive  50 . It is noted that portion  93  of base plate  92  onto which the voice coil motor and head actuator arm (FIG. 20) are mounted is lower than the rest of the base plate  92  and that the elongate end  207  projects through a port in base plate  92  and over the lower portion  93  in order to engage pin  283  (FIG. 20) of the actuator arm  282  and thus to remove and hold the head actuator arm  282  with the head parked off the disk. 
     The retract arm  206  includes a retract follower pin  212  which moves the down the curved camming surface  214  of the switch lever  216 . The retract follower pin  212  is maintained in contact with the curved camming surface  214  by the spring  218  which is connected between the retract arm  206  and the switch lever  216 . During the last portion of the motion of the retract follower pin  212 , pin  212  drops off shoulder  220  of the curved camming surfaces  214  such that the switch lever  216  rotates in a clockwise direction about fixed pivot pin  124 . The switch lever  216  rotates due to the contraction of spring  218 . This clockwise rotation of the switch lever  216  depresses a switch arm of switch  222 . 
     With the above arrangement, the disk drive  50  is not enabled if a cartridge  52  has not been inserted into the cartridge receiver  60 . With no cartridge  52  in the cartridge receiver  60 , the ejector arm  114  will not have been rotated in a counterclockwise manner from the position of FIG. 6 to the position of FIG.  7  and the index bar  122  would not have been moved to the right as shown in FIG.  7 . With the index bar  122  in the position of FIG. 6, the ear  127 , which is located on the index bar  122 , blocks ear  205  on retract link  204  and thus blocks the rotation of the switch lever  216  during the rotation of the switch lever  216  in a clockwise manner and the switch  222  is not turned on and the motors and drive are not enabled. Further, end  207  cannot move sufficiently to allow the actuator arm to unload the heads onto themselves, there being no cartridge received in the drive. 
     All of the above described linkages and arms are positioned about the telescoping spindle motor  102  and are substantially tangential to the spindle motor. It is this configuration which also affords the present drive  50  the ability to perform all of the interlocking and safety functions while compactly configuring the disk drive  50  into the required form factor as specified about. 
     It is noted that in a preferred embodiment, that the various linkages are comprised of steel, with the rotating barrel being brass. 
     3. Disabling Drive 
     The drive is disabled by moving the slide  66  to the leftward position as shown in FIG.  6 . When this occurs, the above linkages and assemblies move directly opposite to that described above in order to move the switch lever  216  away from engagement with the switch  222  thus disabling the drive. 
     4. Removable of the Cartridge 
     After the slide  66  is moved leftwardly to the position of FIG. 6, the door  56  can be opened as the interlock bar  180  is moved out of the way of the actuating arm  134 , allowing the actuating arm  134  to move frontwardly toward the door as the door is opened. During the first half of the movement of the actuating arm  134  and thus the first half of the motion of door rotating to an open position, the motor is disengaged from the hub. This occurs as outer rotating barrel  164  is moved in a clockwise direction from the position of FIG. 7 to the position of FIG.  6  through the movement of the motor lifting or telescoping mechanism  168  which includes the spindle motor actuating arm  156  and the motor drag link  162 . As this occurs, the spindle motor  102  is telescoped downwardly out of contact with the hub of the cartridge (as will be more fully described hereinbelow). During the second half of rotation of the door to the fully opened position, the cartridge is ejected from the drive due to the motion of the ejector pin  108  from the position of FIG. 7 to the position of FIG. 6 under the influence of the above described linkages and springs associated with the motion of the ejector pin  108 . Essentially, as the actuating arm  134  moves forwardly towards the door  56 , the follower  140  rides up on the cam surface  139  of the recess  138  until it reaches the extending ledge or land  142 . This action urges follower arm assembly  130  against stop  123  of index bar  122 , which urges the index bar  122  leftwardly allowing the spring  125  to rotate the ejector mechanism  106  in a clockwise direction ejecting the cartridge, as the ejector arm follower pin  118  is caused to follow the L-shaped cam slot  120  back to the original position as shown in FIG.  6 . 
     Hub Telescoping Mechanism 
     FIGS. 8 and 9 depict the cartridge  52  and the spindle motor  102  of the disk drive  50 . In particular in FIG. 8, the hub  104  of the cartridge is shown in cross-section with the rest of the cartridge  52  cutaway. FIGS. 10,  11  and  12  depict the spindle motor telescoping mechanism  168  which enables the spindle motor  102  to engage the hub  104 . As can be seen in FIG. 10, the spindle motor is out of engagement with the hub  104 . In FIG. 11, the spindle motor  102  has been telescoped into engagement with the hub  104 . 
     Prior art designs for removable cartridge disk drives require that the cartridge be inserted into a cartridge receiver and that the cartridge receiver be then repositioned using various linkages and/or solenoids causing the cartridge hub to be seated generally downwardly onto the shaft or spindle of the spindle motor. Such an arrangement requires a larger form factor than is desirable and provided by the present invention. In the present invention, the cartridge  52  is received and maintained in the cartridge receiver  60  in a single plane, and remains in that single plane until the cartridge is again ejected from the disk drive  50 . This being the case, the spindle motor must move and preferably telescope from a lower position to an upper position into engagement with the hub  104  of the cartridge  52 . As will be described more fully below, the spindle motor  102  is free to move only axially from the lower position to the upper position into engagement with the hub  104 . The spindle motor  102 , as will be explained hereinbelow, is restrained from rotating in a clockwise or in a counterclockwise direction about the telescoping direction thereby eliminating the stress on any motor flexible cabling. In a preferred embodiment, spindle motor  102  moves substantially perpendicularly to the base plate  92  of the drive which base plate  92  forms the bottom of the cartridge receiver  60  upon which the cartridge is received (FIGS.  10  and  11 ). 
     Accordingly, this present design eliminates the need for a cartridge receiver which must move and set the cartridge down on the spindle motor and thereby affords the advantage of a removable cartridge disk drive which has a thinner form factor. 
     After the cartridge  52  is inserted into the cartridge receiver  60 , the actuating arm  134  through the use of the spindle motor actuating arm  156  and the motor drag link  162  causes the outer rotating barrel  164  to rotate in a counterclockwise direction. The outer barrel has three identical cam profiles, such as profile  228  (FIG.  12 ), which engage three pins, such as pins  230 , which extend from the spindle motor  102 . An inner stationary barrel  232  has slots  234  in which the pins  230  are disposed. These slots  234  are in the preferred embodiment substantially perpendicular to the drive base plate  92  and prevent rotation of the spindle motor  102  as the motor is telescoped upwardly towards the base plate  92  with the pins  230  following the cam detail  228 . To accomplish this, the inner stationary barrel  230  is rigidedly pinned to the base plate  92  while the outer rotating barrel  164  rotates relative thereto as described hereinabove. Accordingly, the motor is telescoped until shoulder  236  of the spindle motor  102  seats against the bottom of base plate  92 . As this occurs, with the cartridge inserted in the cartridge receiver, the motor shaft  252  engages the hub chuck  238  (FIGS. 10,  11 ,  31   a ) of the cartridge. The magnetic clamp  240  on the spindle motor rotor  242  seats the armature plate  244 , the hub chuck  238  and the hub  104  of the cartridge onto the spindle motor  102  by magnetically drawing the armature plate  244  into contact with the magnetic clamp  240 . It is to be understood that the magnetic clamp  240  engages the armature plate  244 , in a preferred embodiment, before the spindle motor  102  has been fully seated against the drive base plate  92 . The spindle motor  102  is finally and fully seated against the drive base plate  92  with the movement of the motor drag link  162  and the spindle motor actuating arm  156  which continues to cause the outer rotating barrel  164  to rotate. The spring  178  secured between the motor drag link  162  and the spindle motor actuating arm  156  transmits force through the rotating barrel  164  so that the spindle motor  102  is positively loaded against the drive base plate  92  as shown in FIG.  11 . 
     An alternative embodiment for the outer rotating barrel  164  is shown in FIG. 12 b.  The outer rotating barrel  165  in FIG. 12 b  includes two cam details, such as cam detail  229  depicted and one cam detail  228  or alternatively three cam details such as cam detail  229 . 
     As indicated, the spindle motor  102  has a down position (cartridge disk disengaged) and an up position (cartridge disk engaged). To assure that the motor is firmly pushed up against three pads on the underside of the base plate  92 , at least two cam details  229  are used. Cam detail  229  includes an integral beam springs  231  with a cam surface  233  that is higher than that of the cam detail  228 . 
     When the motor  102  is -guided up the fixed cam detail  228  with one pin  230 , the two other pins  230  deflect the beam springs  231  in a downward direction, which results in an upward force on the two pins  230  forcing the motor  102  upwards against the pads on the base plate  92 . 
     FIG. 12 b  show beam spring  231  with the cam surface  233  in an undeflected position and an outline of pin  230  where it would be positioned if it were disposed in cam detail  229 . As seen, pin  230  would have displaced beam spring  231  downwardly. FIG. 12 c  shows cam surface  233  of beam spring  231  deflected downwardly, and superimposed thereover the cam detail  228  with pin  230  disposed therein. It is noted that cam surface  233  pushes pin  230  against the upper surface of cam detail  228  but that the upper surface of cam detail  229  does not contact or limit the motion of pin  230 . 
     The above arrangement ensures that the spindle motor  102  makes contact with the three pads on base plate  102  resulting in accurate seating of the motor  102  and no system vibration that could result if motor  102  were not so seated. 
     Disk Drive Spindle Motor and Clamp Magnet 
     In a preferred embodiment, the spindle motor  102  is of the brushless DC spindle motor variety with the above identified clamp magnet  240 . The spindle motor  102 , in a preferred embodiment, is also of the radial gap, outer rotor configuration and includes the rotor  242  as well as the stator  246  (FIG.  9 ). The stator  246  includes the stator windings and lamination  248  and mounts the bearings  250  upon which the spindle shaft  252  and the rotor  240  rotates. The rotor  242  includes, in a preferred embodiment, permanent magnets  254  which cause the rotor  242  to rotate under the influence of the stator windings  248 . 
     In FIG. 9, the combination of the clamp magnet  240  located on the back of the rotor  242  in a magnetic removable cartridge disk drive is a novel configuration. The clamp magnet  240  includes a single-uniform pole magnetic ring  241  with a low reluctance magnetic flux path ring  243  positioned outboard thereof. The flux path ring  243  projects above the magnetic ring  241  and can contact the armature plate  244 . 
     With the embodiment of FIG. 9, it is to be understood that great advantages can be obtained from the production of all of the clamp magnets  240  for all of the disk drives  50  having a single uniform pole magnetic ring  241  which always has the same polarity as seen from a cartridge  52  inserted into the disk drive. By way of example, the magnetic ring  241  could have a north pole facing away from the spindle motor toward the cartridge. The armature plate  244  could then either be premagnetized with a south pole extending away from the cartridge  52 , and thus seen by the clamp magnet  240 , or could be left unmagnetized. In the first arrangement, the south pole of the armature plate  244  would be attracted by the north pole of the clamp magnet  240 . In the second arrangement, after several insertions of the cartridge into the drive, the armature plate  240  would acquire a south pole orientation extending in a direction away from the cartridge and thus be attracted by the north pole of the spindle motor. Alternatively, it is to be understood that the clamp magnets  240  can have a south pole directed away from the spindle motor and the armature plate  244  can have a north pole directed away the removable cartridge  52 . 
     Such arrangements are highly advantageous as the flux lines in the armature plate take a preferred direction with respect to the flux lines in the clamp magnet and thus there is an increase in clamping force between the armature plate and the clamp magnet. Were the same poles outwardly projecting from both the clamp magnet and the armature plate, the clamping force between the two would be decreased. This might occur if some of the clamp magnets for the spindle motors were manufactured with a north pole facing up and some were manufactured with a south pole facing up. Thus, it is advantageous to have all of the clamp magnets, for all of the spindle motors for all of the disk drives manufactured with the same polarity facing up. 
     Alternative embodiments of the below discussed clamp magnet  240  have a novel design for magnetically drawing thereto and holding the armature plate  244  of the cartridge  52 . The novel design meets two goals. First, the clamp magnets have been designed to have a sufficiently high force in order to draw and hold the armature plate thereto under shock loading, while secondly having a sufficiently weak leakage field that any data on the magnetic disk is not affected by or exposed to the leakage field from the clamp magnet as the disk is inserted over the clamp magnet. Thus, the clamp magnet must be designed to have sufficient force to hold the disk in place under shock loading and have a sufficiently weak field to obviate erasure of the data. Greater force requires a greater magnetic field. Hence the design of the clamp magnet provides for sufficient high force with a sufficiently weak leakage field. 
     FIGS. 13 a ,  13   b  depict a first alternative embodiment of the clamp magnet of the invention. In this embodiment, a clamp magnet  245  is comprised of three rings  258  which are comprised of a low reluctance magnetic flux material such as for example steel as well as three magnet rings  260 . As can be seen in FIGS. 13 a ,  13   b  the rings  258  and magnet rings  260  are interposed with each other with the outer most being the low reluctance magnetic flux path ring  258  followed alternatively by a magnet ring  260  and then a ring  258  and progressing inwardly towards the spindle shaft  252 . In this configuration, the low reluctance magnetic flux path rings  258  extend further away from the rotor  242  than do the magnet rings  260 . It is noted that the distance over the top of any of the magnets  260  between two steel rings  258  is relatively short. This decreased distance reduces the flux leakage which would normally occur in a magnetic clamp where there is only one magnet which essentially occupies the radial length of the three magnet rings  260  and the three steel rings  258 . Further, as the three rings  258  come into contact with the armature plate  244 , this contact provides a low reluctance flux path for the magnetic flux and permits the required binding force to be asserted upon the armature plate. 
     In a preferred embodiment, the magnetic rings  260  are comprised of HB061 material and the steel rings  258  are comprised ST461 material. The armature plate  244  in a preferred embodiment is comprised of magnetic stainless steel. With the configuration as shown in FIGS. 13 a ,  13   b , the magnetic force on the armature plate is minus 10.7 N (Newtons). The leakage level is 184×10  −5  T (Tesla) at 4 mm. 
     In a similar configuration, with only two steel rings  258  and two magnetic rings  260  made of the same materials, the force on the armature plate is equal to a minus 8.5 N with the leakage level being 20 G (2 mT) of 4 mm. In such a configuration the leakage is satisfactory but the force is to low for the present embodiment. 
     FIGS. 14 and 15 depict an alternative embodiment of the clamp magnet of the invention which clamp magnet is identified by the numeral  262 . This clamp magnet is made of the same material of the prior clamp magnet but is less expensive to manufacture. This clamp magnet has the same properties of the prior clamp magnet of FIGS. 13 a ,  13   b.  In this embodiment, the magnetic element  264  is configured much like a gear with an inner ring  268  with a plurality of spaced radial projections  270  extending therefrom. The low reluctance magnetic flux path element  272  which is comprised of steel, in a preferred embodiment, is configured as an inwardly directed gear with an outer ring  274  with spaced radial projections  276  which are inwardly directed. It is noted that the spaced radial projections  270  of the magnetic element  264  alternate with the spaced radial projections  276  of the low reluctance flux path element  272 . Such an arrangement gives a force and flux leakage which are comparable to the embodiment of FIGS. 13 a  and  13   b.  In an alternative embodiment for FIG. 14, the positions of the flux path element  272  and the magnetic element  264  can be switched. 
     FIG. 16 depicts yet another embodiment of a clamp magnet  278  of the invention. This clamp magnet  278  includes, in a preferred embodiment, eighteen individual magnetic poles  279  which alternate between north and south poles. The division of the magnetic clamp  278  into a plurality of alternating poles reduces the leakage flux, but has the desired magnetic force in order to pull down the armature plate of the cartridge. In such an arrangement, each of the poles is afforded about 20 degrees with the chuck force predicted to be about minus 5 N and the leakage less than 3 mT at 4 mm distance. 
     Integral Head Loading Ramp, Air Filter and Removable Cartridge Door Safety Stop 
     FIGS. 17,  18 ,  19  and  20  depict another aspect of the invention which includes an integral element  280  which performs among other things the functions of providing for dynamic head loading and unloading, housing a recirculating air filter, and providing for a cartridge door safety stop. Additionally through the proper selection of materials, the integral element can provide for an electrostatic discharge drain for the cartridge. FIG. 19 depicts the integral element  280  by itself while FIGS. 17 and 18 depict the integral element  280  in conjunction with the disk  256  from the cartridge  52  as well as the actuator arm  282  upon which is mounted the head-gimble assembly  284  which includes the magnetic head or transducer  286 . The actuator arm  282  is moved in a clockwise and a counterclockwise direction by the actuator motor  290  which in a preferred embodiment is a voice coil motor. As can be seen in the figures, outboard of the head-gimble assemble  284  is an extension  292  of the actuator arm  282  which rides on a ramp provided by the integral element  280  as will be described more fully hereinbelow. 
     FIG. 17 shows the extension  292  of the actuator arm  282  parked on the ramp of the integral element  280 . FIG. 18 depicts the extension  292  of the actuator arm  282  positioned just before the transducer  286  would be unloaded onto the disk  256 . 
     The integral element  280  which, in a preferred embodiment, is cast as a one-piece, integral, element, includes a base  294  which serves as a holder for an air filter element  296  which can be inserted therein. The base  294  as can be seen in FIG. 19 d  includes two rectangular shaped openings  298  which are placed side-by-side and allow air to flow through air filter elements  296 . Extending from the base  294  is a projection  300 . Projection  300  in a preferred embodiment is substantially perpendicular to the base  294 . Projection  300  is bifurcated into a cartridge door safety stop  302  and a head ramp  304 . The cartridge safety stop  302  (side profile of FIG. 19 b ) includes a projected end  306  which is substantially flat and perpendicular to the plane of the disk  256 . Further as the integral element  280  is secured to the base plate  92  of the disk drive upon which the cartridge is received, the projected end  306  is perpendicular to the base plate  92 . Extending rearwardly and upwardly from projected end  306  is a cartridge door ramping surface  308 . 
     Additionally, the cartridge door safety stop  302  is dispose d in a direction which is parallel to the direction of insertion of the cartridge into the drive and that it extends into the cartridge that is properly seated in the cartridge receiver. 
     As the cartridge is inserted into the disk drive and in particular into the cartridge receiver  60 , the cartridge door  68  (as will be more fully explained hereinbelow) is caused to rotate by the cartridge receiver in order to allow the actuator arm  282  to transport the head-gimble assembly  284  to a position where it can be loaded onto the disk  256 . The cartridge door  68  is opened by rotating it from zero degrees to approximately ninety degrees. Due to assembly and part tolerances, the cartridge door  68  may not reach a full ninety degrees of rotation. This being the case, there might not be enough clearance for allowing the head-gimble assembly  284  to be inserted into the cartridge. Accordingly, the cartridge door safety stop  302  provides for the projected end  306  which will stop the further insertion of the cartridge into the drive if the door has not reached at least approximately a minimum of 80% of the required rotation from zero to ninety degrees. Further, if the cartridge door has reached a minimum of 80% of its full rotation, the cartridge ramp surface  308  will ensure that the door rotates 100% to a position of ninety degrees relative to its closed position, thus ensuring that there will be no interference between the door and the unloading of the head onto the disk. 
     The head ramp  304 , as can be seen in the figures and in particular FIG. 19 f  includes a bifurcated end  310  which includes an upper ramp surface  312  and a lower ramp surface  314 . As can be seen in FIGS. 17 and 18, with the cartridge inserted into the drive, the disk  256  is disposed between the upper and lower ramp surfaces  312 ,  314 . The actuator arm  282  under control of the actuator motor  290  can then move the head-gimble assembly  284  from a parked position as shown in FIG. 17 to a position shown in FIG. 18 where the heads are at the end of the ramps  312 ,  314 , preparatory to being immediately unloaded onto the disk  256 . As can be seen from the figures, the extension  292  of the actuator arm  282  rides up on the upper ramp surface  312 . A similar extension rides on the lower ramp surface  314  in order ramp the lower head away from the lower surface of the disk  256 . In a preferred embodiment it can be seen that the bifurcated end  310  is directed so that it is substantially perpendicular to the actuator arm  282  and substantially along a radius of the disk  256 . 
     The recirculating air filter element  296  as previously indicated, is secured to the base  294 . The air filter element  296  is provided in a semi-circular configuration and is made out of materials which are known in the trade. In operation, a positive pressure field is maintained on the front or convex side of the air filter element  296 , while a negative pressure field is maintained on the back or concave side of the element  296 . The total difference between the positive and negative pressure is proportional to the relative flow of air through the air filter. 
     The integral element  280  additionally includes an air flow diverter  316  which extends from the base  294  at a location distal from where the projection  300  extends. The projection  300  extends from a position which is one end of the air filter  296  while the air flow diverter  316  projects from a position which is on the other side of the air filter  296 . The diverter  316  is substantially a flat plane which projects outwardly in the plane of the disk  256  and has a curved edge  318  which substantially conforms to the portion of the disk  256  that is located adjacent thereto as shown in FIGS. 17 and 18. The air flow diverter  316  is used to maximize the pressure differential across the air filter element  296 . With the disk  256  rotating in a preferred embodiment in a counterclockwise direction, the air flow diverter  316  assists the re-directing of the air rotating with the disk into the cavity which exists in front of the air filter elements  296  (convex side) in order to create a higher positive pressure. 
     Integral element  280  can have affixed thereto a stop mechanism  320  which in a preferred embodiment is comprised of an elastomer or other energy absorbing material or mechanism. The stop mechanism  320  is used to damp and stop uncontrolled rotary motion of the actuator arm  282  and thus the head-gimble assembly  284  and decelerate that motion should the actuator motor  290  attempt to park the heads on the bifurcated end  310  at too rapid a velocity. 
     Accordingly, the stop mechanism  320  prevents rapid deceleration of the actuator arm  282  and thus mechanical damage to the actuator arm  282  and the head-gimble assembly  284 . The elastomer may be in a preferred embodiment, attached to the integral element  280  by a liquid or paste adhesive or pressure sensitive adhesive tape. Alternatively, the elastomer can be mechanically interlocked to the integral element  280  as the integral element  280  is itself being molded. In a preferred embodiment, the elastomer is a thermal plastic elastomer and it can be molded into a liquid crystal polymer plastic which comprises the integral element  280 . 
     The integral element  280  further includes the function of providing for an electro-static discharge drain for the cartridge and drive to protect both the magnetic heads  286  and the disk  256  from damage. This function is performed by the specific material chosen for the integral element  280 . Should the material be of conductive, metallic material, this function is automatically performed. However, in a preferred embodiment, the integral element  280  will be comprised of the above liquid crystal polymer plastic to which will be added a substantial volume, by percent, of a conductive fiber. The amount of conductive fiber, in a preferred embodiment, shall reduce the natural non-conductivity of the polymer to a surface conductivity of less than 5000 ohms. In such an arrangement, the integral element  280  will be able to discharge electrostatic charge built up on the heads and the disk. 
     It is noted that prior disk drives include similar types of ramp functions and recirculating air filter functions. However, none provide the integral element  280  which affords a compact design allowing the inventive disk drive  50  and removable cartridge  52  to fit within the form factor above specified. Additionally, the present design provides for a lower manufacturing costs. 
     Cartridge Receiver Mechanism 
     The present disk drive  50  includes a cartridge receiver  60  which can accurately position the cartridge  52  with respect to the disk drive  50 . 
     It is to be understood that in prior art disk drives, which have removable cartridges, that the cartridge receiver is generally guided along its edges and lowers a cartridge to a rigidly mounted spindle motor. This configuration, while working well, requires large clearances between the inside of the cartridge receiver and the cartridge to prevent wedging due to a drawer effect (unfavorable length-to-width ratio). The present invention does not require the movement of the cartridge receiver (as in the present design, the spindle motor telescopes into contact with the cartridge) and thus clearances can be tighter with the overall form factor of the drive being smaller and preferably, as specified above. The design of the disk drive  50  has a favorable length-to-width ratio and is not susceptible to wedging due to the drawer effect. 
     Further, due to the small size of the form factor for this removable cartridge disk drive  50 , the clearance allowed between the hub  104  of the cartridge  52  and the inside of the cartridge  52  are very small. Thus, very accurate positioning of the cartridge in the drive and the disk in the cartridge is required in order to prevent the rubbing of the disk which is mounted on the hub against the inside of the cartridge during operation. The present embodiment provides for accurate positioning as well as smooth insertion and ejection of the cartridge relative to the drive with low friction forces and without the danger of wedging. 
     These advantages are carried out in the present embodiment which provides for a guide rail  88  used in conjunction with a guide groove  332 , and a fixed stop  86  (FIG. 5) along with a recess  84  in the cartridge, as well as a spring  62  mounted in the disk drive door  56 . In addition guide strips  336 ,  338 ,  340  and  342  are provide for ensuring accurate cartridge positioning. In the present design, the manufacturing tolerances are advantageously smaller across the small width of the guide rail  88  and the guide groove  332  than over the total width of the cartridge and the inside of the cartridge receiver. 
     The above embodiment of the present invention is preferably implemented as follows. The guide rail  88  extends from the cartridge receiver  60  into the cavity  344  which receives the removable cartridge  52 . The guide rail  88  is accurately machined and is received in a precisely molded guide groove  332  which is provided in the upper half  80  of the cartridge housing  70  (FIG.  28 ). The guide rail  88  and the guide groove  332  are disposed in a direction which is parallel to the direction of insertion of the cartridge into the drive. Using the convention shown in FIG. 5, the guide rail and guide groove are disposed in the “Y” direction. Thus, when the cartridge is inserted, the guide rail  88  and guide groove  332  accurately position the cartridge relative to the “X” direction or the direction which is perpendicular to or across the direction of insertion of the cartridge into the drive. 
     Although the guide rail  88  as shown has been provided in the cartridge receiver and the guide groove  332  as shown has been provided in the cartridge that equivalently the guide rail could be extending from cartridge with the guide groove provided in the cartridge receiver of the drive. This alternative embodiment would result in the same function of accurate positioning of the cartridge in the cartridge receiver in a direction which is perpendicular to or across the direction of insertion of the cartridge into the drive. 
     Additionally, for accurately positioning the cartridge in the drive in the “Z” direction or the direction of the height of the cartridge, between its upper and lower substantially parallel surfaces  350  and  352 , guide strips  336 ,  338 ,  340  and  342  are provided extending into the cavity  344  from the cartridge receiver  60 . As can be seen in FIG. 28, guide strip  336  is comprised of two longitudinal elements, one on each side of the guide rail  88 . These guide strips  336  are provided along the direction of insertion of the cartridge into the drive and substantially parallel to the guide rail  88 . Additionally, guide strip  338  is comprised of two longitudinal elements which again are extending from the cartridge receiver into the cavity and are substantially parallel to the direction of insertion of the cartridge into the cartridge receiver. 
     The guide strips  340  and  342  extend from the bottom of the cartridge receiver  60  and again are longitudinal in the direction of insertion of the cartridge into the drive. At the mouth of the cartridge receiver the guide rails and guide strips are slightly beveled to ease the insertion of the cartridge into the drive. 
     At the end of the insertion stroke of the cartridge into the cartridge receiver that is a rigid stop  86  (FIG.  5 ). The rigid stop  86  is upstanding from the base plate  92 . This rigid stop  86  mates with a groove or recess  84  defined in the cartridge. As the door  56  of the disk drive is closed, spring  62  mounted thereon is urged against the cartridge to in turn urge the cartridge firmly against the stop  86  in order to accurately position the cartridge in the “Y” direction or in the direction of insertion of the cartridge into the drive. 
     Finally, as seen in FIG. 28 located between the elements of guide strip  338 , is a door opening rail  354  which is loosely received in a groove  78  of the cartridge. As is more fully described elsewhere, as the cartridge is inserted into the drive, the door opening rail  354  trips or causes the cam or tab  74  of the cartridge door  68  to rotate clockwise as the door opening rail  354  is received into the door opening groove  78  in order to open the cartridge door  68  preparatory to the heads being actuated into the cartridge through the cartridge door and unloaded onto the disk. 
     As can be seen in FIG. 28, the clearances on all sides of the cartridge relative to all sides of the cartridge receiver are relatively small. Also due to the fact that the door of cartridge when opened is positioned at the rearward end of the cartridge receiver, distally located from the door  56  of the disk drive  50 , that contamination from environmental sources is greatly reduced. This is due to the fact that the paths from the door  56  of the disk drive  50  to the door  68  of the cartridge  52  are quite long and narrow thereby providing a significant barrier to the infiltration of environmental contaminates into the inside of the cartridge. 
     Removable Cartridge with Imbedded Interlocking Mechanism 
     As can be seen in FIG. 22, in the lower half  82  of the cartridge housing  70  and more particularly disposed in the lower surface  352  is an interlocking recess  90 . Interlocking recess  90  along with recess  84  are opened to the front face  98  of the cartridge  52  which front face  98  additionally mounts the cartridge door  68 . It is in the interlocking recess  90  that the cartridge engaging ejector pin  108  is received in order to lockingly position the cartridge into the disk drive. As can be seen in FIG. 22, the interlocking recess  90  is essentially a groove which extends in a direction which is perpendicular to or across the direction of insertion of the cartridge into the drive. In particular, the interlocking recess  90  includes an opening  360  which communicates with the front face  98 . Extending from the opening  360  is a ramp surface  362 . Extending from the ramp surface  362  is a flat surface  364  which is also directed substantially perpendicular to or across the direction of insertion of the cartridge into the drive. The ramp surface ends in a semi-circular cavity or stop  366  which is positioned somewhat sidewardly from the opening  360  in a direction which is perpendicular to or across the direction of insertion of the cartridge into the drive. With the cartridge inserted into the drive, the ejection pin  108  comes to a final resting position in the stop  366  after having entered the opening  360  and travelled along the ramp surface  362 . Thus, the ejector mechanism  106  is urged from the uncocked position of FIG. 6 to the cocked position of FIG. 7, with the pin  108  received in the semi-circular stop  336 , the cartridge is locked into the drive and prevented from being withdrawn. It is additionally noted that in this embodiment depicted, the interlocking recess  90  is located below the guide groove  88  which is located on and incorporated into the upper surface  350  of the upper half  80  of the cartridge. The advantages of having these two features closely spaced are found in improved dimensional accuracy and a lesser effect from thermal expansion. Other relationships between these two features are possible and come within the spirit of the invention. 
     Removable Cartridge with Hub Chuck 
     In order to satisfy the present form factor requirement, the hub chuck  238  of the present embodiment is preferably of a one-piece construction, having two integrally formed springs and two datum surfaces. This arrangement allows for a very thin cartridge configuration and a drive with very low height and small spindle motor shaft. Further, the chuck  238  can be inexpensively made. 
     In a preferred embodiment, the hub chuck  238  is formed from a single piece of material which can include, for example, phosphorous bronze. The chuck is circular and has stamped therein a central bore  378  and a lip  380  upstanding therefrom. Formed on the central bore and lip are datum  382  and datum  384 . Datum  382  and  384  are provided with lead-in chamfers which assists in the seating of the hub chuck  238  onto the spindle shaft of the spindle motor. In a preferred embodiment, these datum can be chromed or otherwise plated in order to increase the hardness of the surface. 
     Additionally formed in the hub chuck  238  are first and second beam springs  386 ,  388 . These beam springs are elongate and include adjacently deposed free ends  390 ,  392  respectively, which form part of the circular bore  378 . Free ends  390 ,  392  have bosses  392 ,  393  with lead-in chamfers. 
     The first and second beam springs  386 ,  388  additionally have fixed ends  394 ,  396  which are secured to the remainder of the chuck  238 . As can be seen in FIG. 31 a , slots  398 ,  400  and  402  have been machined or stamped or otherwise formed into the chuck  238  in order to define the first and second beam springs  386 ,  388 . 
     FIG. 31 a  further depicts mounting holes such as mounting holes  404  which are used to mount the chuck  238  to the hub. The chuck  238  is retained between the hub  104  and magnetic coupling armature  244  (FIG. 10) with, in a preferred embodiment, rivets or an adhesive bonding. Further balancing holes  406  are provided in the chuck  238  in order to balance the material removed to form the first and second beam springs  386 ,  388 . In the embodiment shown in FIG. 31 a , it is evident that the first and second datum  382 ,  384  and the free ends  390 ,  392  of the first and second beam springs  386 ,  388  form a triangle and thus essentially three points for holding the chuck onto the spindle of the spindle motor. The lead-in chamfers assist in guiding the chuck  238  onto the spindle of the spindle motor as the motor is lifted into engagement with the cartridge. As previously indicated, as the spindle of the spindle motor engages the chuck  238 , the hub and particularly ring  255  thereof, is first pushed up against the inside top of the cartridge against a ring  257  which was downwardly dependent from the inside surface of the upper half  80  of the cartridge housing. When the hub comes in contact with the ring  257  this prevents the hub and disk from becoming cocked or skewed in the cartridge and thus prevents the disk from touching the inside of the housing, potentially damaging the disk. Substantially simultaneously the spindle shaft penetrates the chuck, the hub is pulled down on the spindle motor by the hub clamp magnet and the spindle motor stops against the underside of the base plate. 
     Cartridge Door Spring Retention and Stiffening Mechanism 
     As previously indicated, it is important that the cartridge door  68  be provided in the appropriate open position and preferably moved to an opened position which is 90 degrees from the closed position in order that the door does not interfere with the positioning of the actuator arm and the heads past the door  68  through the port  76  (FIG. 25) formed in the front of the cartridge  52  preparatory to unloading the heads onto the disk. In order to accomplish this, the door must be made as thin as possible so that the effective opening of the port  76  can be as large as possible and the door must be made in a manner so that it will not bow in the open position again in order to maximize the effective opening of the port  76 . Further, it is necessary that whatever mechanism is used to bias the door to a closed position not interfere with the effective opening of the port  76 . 
     To accomplish these objectives, the present invention provides for the positioning of a torsion spring  412  in a groove  414  molded into the door. The groove is sufficiently large in order to allow the torsion spring  412  to be freely placed therein. The back of the door  68  includes a recess  416  which is designed to receive a stiffening plate  418  with a stiffening lip  417 , which in a preferred embodiment is comprised of a metallic material with the door in a preferred embodiment comprised of a plastic material including polycarbonate. The stiffening plate  418  is adhered to the door with an appropriate bonding agent well known in the trade. Not only does the stiffening plate  418  retain the torsion spring  412  in the groove  414 , but additionally it stiffens the door  68  so that it does not bow in the middle, interfering with the placement of the heads inside the cartridge relative to the disk. 
     As can be seen in the figures and in particular, FIGS. 24 through 27, the portion of the torsion spring  412  which is located in the door  68  is substantially L-shaped and can twist in the groove in order to store energy as the door is urged to an open position as shown in FIG.  25 . The stored energy is used to close the door during the removal of a cartridge from the drive. 
     The other end of the torsion spring is additionally L-shaped and is retained in the cartridge housing itself. This retention is accomplished by a capture cavity  420  which is formed in the upper half  80  of the cartridge and a key  422  which is formed in the lower half  82  of the cartridge. When the upper half and the lower half are mated, the torsion spring is captured between the capture cavity  420  and the key  422  as shown in FIG.  25 . FIG. 26 depicts the torsion spring  412  in a rest position (dotted lines) and in a position where it has been twisted (solid lines) in order to store energy as the door is opened. Further, FIGS. 24 and 27 show the main portion of the cartridge door  68  along with the cam or tab  74  and the pivot shaft  75 . 
     Imbedded Servo System with Servo Address Mark with Robustness in the Presence of Media Defects 
     The disk of the present drive is configured in a preferred embodiment into fifty-six wedges, each wedge having a servo field (with servo pattern  500 ) and with a data field on each side of the servo field. Of these wedges, one is an index wedge with fifty-five being non-index wedges. In order to provide for 40 megabytes of information on the disk, the disk among other things has approximately 1028 tracks or cylinders (average track pitch 1600 TPI) on each of the surfaces. Each track is divided into a first and a second band as shown in FIG.  33 . FIG. 32 shows the write current waveform which is used in order to place head centering servo information in the servo fields of each wedge of each track. The write current provides for a direction of magnetization or transition as shown in FIG.  33 . 
     The possible transitions in the servo patterns caused by the write current are 312.5 nanoseconds apart. This results in a 3.200 megahertz clock which is the servo clock. This frequency assumes a rotation of 3246.7532 revolutions per minute or a rotational period of 18.4800 milliseconds. This gives 59,136 servo clocks (SCLKS) per revolution. As each revolution is divided into fifty-six wedges, each wedge has 1056 servo clock periods with 932 SCLKS for the data fields and the rest for the servo fields. 
     The head centering information (“analog”) section which is depicted in FIG. 33 ( 506  in FIG. 34 a ) of the servo field accounts for head centering. The analog section has four types of bands. These include even.0, even.5, odd.0 and odd.5 bands. The bands for track zero and track one are depicted. Track zero, being an even track, has bands 0.0 and 0.5 and track one being an odd track, has bands 1.0 and 1.5 (FIG.  33 ). The head centering information  506  is thirty-two SCLKS periods long with a pattern of eight SCLKS long which repeats four times during the analog section. There are two periods of “A” transitions followed by two periods of “C” transitions which are followed by two periods of “B” transitions followed by two periods of “D” transitions. Through appropriately circuitry known in the art, the “A” and “B” transitions which straddle track zero are read, amplified and compared in order to determine where the head or transducer is relative to track zero and to adjust the position of the head relative to the track zero. With respect to track one, the “A” and “B” transitions are read and compared in order to determine where the head is with respect to track one and to reposition the head with respect to track one. The same procedure is used in order to center and adjust the head relative to any track on the disk. 
     
       
         
               
               
             
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
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                 EVEN.0 
                 A 
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                 EVEN.5 
                   
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     Further it is noted that a zoned recording scheme is used with lower density recording on the outer tracks and higher density on the inner tracks. The servo fields from are radially aligned track-to-track due to the fact that the placement of the servo fields can be adjusted as each servo field is located between first and second data fields associated with and located on each side of each of the servo fields. 
     In the present removable cartridge disk drive and also in fixed disk drive, the servo fields share the same disk surfaces as user data fields. Servo patterns  500  are regularly spaced around the disk with space for user data in between. These servo patterns  500  include a servo address mark (SAM)  502 . This is a pattern that cannot occur in the user data fields or in the remainder of the servo pattern. Detection circuitry in the drive recognizes the SAM  502  and synchronizes to it so gates may be opened at appropriate time intervals in order to sample head centering information and track number information and thereby derive head position information from the remaining part of the servo pattern. 
     As can be seen in FIG. 34, the servo pattern  500  includes the automatic gain control (AGC) pattern  504 , followed by the SAM  502  which is followed by the head centering information  506  and the track numbering information  508 . The AGC  504  has a transition at each interval. 
     The track number information field  508  is encoded in all 11-bit gray code. Two SCLK periods are used for each bit of gray code. A transition is in the first period if the gray bit is a 1 and the transition is the second period if the gray bit is a 0. The most significant bit (G 10 ) is first and the least significant bit (G 0 ) is last in time. The binary track number determines the gray code bits by the following rule. Gn is the exclusive “or” of Bn with Bn+1 where Gn is the nth gray bit code and Bn is the nth bit of the binary track number and Bn+1 is the next more significant bit of the binary track number. B 11  is assumed to be 0. 
     Most if not all embedded servo disk drives have servo address marks. These SAMs use a gap which is longer than any that can occur in normal user data fields. In many drives as in the present device, after a SAM is detected, the drive uses a timer (counter) to wait until it is almost time for the next SAM before the drive starts looking for the next SAM. 
     The present invention uses a novel SAM in order to provide for robustness in the presences of holes in the magnetic recording material (media defects). These holes can look like SAMs. Thus, an object of this invention is to make a SAM  502  that is distinguishable from media defects and detectable in the presence of media defects. 
     This invention uses information about polarity of the detected transitions  510  and two main gaps  514 ,  516  of different lengths that are each generally longer than media defects. Every transition  510  is the opposite polarity of the one before it. In the servo pattern  500  magnetic transitions are only allowed at regularly spaced intervals  512  or multiplies of such intervals  512 . But not every possible interval has a transition. In a preferred embodiment, in the area before and after the SAM  502 , that is in the AGC area  504  and the head centering information area  506 , two transitions that are an even number of intervals away from each other are of the same polarity. Further, any transitions that are located an odd number of intervals apart are of the opposite polarity. The place where this predefined “rule” is violated is in the SAM  502 . It is also noted that the “rule” is violated in the track number information area  518  (grey code area) but that this is of no concern as it is several microseconds from the SAM and is located after the SAM is detected and synchronization to the SAM has been accomplished. 
     If a media defect wipes out transitions in the region before or after the SAM  502 , the resulting gap in transitions will not look like a gap in the SAM  502  because of the polarity of the pulses read around the defect gap will not match the polarity of pulses read around a gap in the SAM in accordance with the above established “rule”. 
     The SAM  502  of a preferred embodiment of the invention, is fourteen intervals wide and has two major gaps  514 ,  516 . Gap  514  is four intervals long and gap  516  is eight intervals long. In addition, there is a gap  518 , one interval in length, between gaps  514  and  516 . The transitions around each main gap  514 , 516  are an even number of locations apart from each other. This is to make the magnetic transitions around the main gap  514 ,  516  violate the transition polarity “rule” established above. Also two main gaps  514 ,  516  have different lengths so said gaps  514 ,  516  do not look alike. This further adds to the robustness and reduces the possibility of falsely detecting a SAM. 
     In viewing FIG. 35 a,  it can be seen that in a preferred embodiment, in the AGC  504  that the transitions alternate between positive and negative polarity. In the AGC  504 , thus the rule that transitions of the same polarity are spaced even intervals apart (2, 4, 6, etc.) and that transitions of different polarity are spaced odd intervals apart (1, 3, 5, etc.) is maintained. Further, in the area of the head centering information  506  as can be seen partially in FIG.  35  and also in FIG. 34, the “rule” as defined for the AGC area  504  is also maintained. In the area of the SAM  502 , this rule is not maintained. As indicated above, the SAM is fourteen intervals long. A SAM has four transitions. The first transition is identified by the number  520  and is of negative polarity in the example of FIG. 35 a.  It is also to be understood that transition  520  could be of position polarity with the other transitions accordingly change to the opposite of what they are presently denoted in FIG.  35 . 
     The second transition  522  in the SAM  502  is of positive polarity and is located, as indicated above, four intervals from the first transition  520 . Thus, as transitions  520  and  522  are of differing polarity, and as they are spaced an even number of intervals apart, they violate the “rule” established for the AGC and the head centering information. Transition  522 , as can be seen in FIG. 35 a , is located between the fourth and the fifth interval of the SAM  502 . 
     The third transition  524  is of negative polarity and is located between the fifth and the sixth interval of the SAM as is shown in FIG. 35 a.  The fourth transition  526  of the SAM is located eight intervals from the third transition  524 . The fourth transition  526  is of positive polarity, thus violating the “rule” of the AGC that an odd number of intervals is to be located between transitions (transitions  524 ,  526 ) of different polarities. 
     A transition detector, such as by way of example, a pulse read detector with a hystersis comparator, can then decide if it has seen (1) a SAM if it sees the first main gap  514  or the second main gap  516  or (2) the long gap that results from a media defect which wipes out transitions. 
     As can be seen in FIG. 35 b , the SAM detection routine is depicted. This SAM detection routine includes a first step, presented by block  530 , of providing a counter for counting from the last identified SAM and beginning to look for the next SAM just before the counter indicates that the appropriate number of intervals or the appropriate amount of time has passed and thus that the next SAM should be appearing. Once a counter has indicated that the next SAM should be appearing, a detector (block  532 ), for example the detector of the variety described hereinabove, begins to detect the presence of and polarity of the transitions. Simultaneously, the intervals between the transitions are counted (block  534 ) and an association is made and stored between the count of the intervals and the polarity of the transitions (block  536 ). This association is compared with the known pattern for the AGC, the SAM and the head centering information (block  538 ). It is to be understood that such a detection scheme can be implemented with detection hardware, counters and the like which are well known in the art. 
     Embedded Servo System with Repetitive Runout Correction 
     On disk drives, such as drive  50 , the recording and playback heads or transducers must follow nominally circular tracks with great precision. Imbalance and errors in disk centering and disk tilt, due to the reception of the hub chuck of the cartridge  52  onto the spindle motor, cause these tracks to deviate from being perfectly circular. Imperfect reception of the disk in the plane of the magnetic clamp of the spindle motor, so that the disk is not exactly centered on the spindle of the spindle motor, causes error known as “once-around” error or runout. With this error, the disk can be seen to wobble, in the plane of the magnetic clamp, in and out relative to the spindle motor. This once-around error repeats once each time the disk revolves one time. Imperfect reception of the disk so that it is not entirely received in the plane of the magnetic clamp, but is tilted, causes error known as “twice-around” error runout. With this error, the disk can be seen to wobble up and down relative to the plane of the magnetic clamp. This twice-around error repeats twice over one revolutions of the disk. The feedback servo loops reduces the repetitive components, but the degree to which it can reduce such components is limited by structural resonances, sampling rates, and other factors which place limits on servo bandwidth. This invention relates to a technique for correcting for the repeatable (once-around and twice-around) components of disk runout which is not subject to these limitations. This allows cartridge disk drives to reduce tracking errors to levels similar to fixed disk drives and therefore to match the track densities and servo performance of fixed disk drives. This novel aspect as well as the other novel aspects of drive  50  and cartridge  52  allow the disk to contain 40 megabytes of information and greater amounts (with 1600 TPI and greater) in the above specified 2½ inch form factors. 
     Embedded servo cartridge disk drives have a servo system which corrects for both repeatable and non-repeatable tracking errors. Non-repeatable tracking errors (or runout) are caused by such factors as non-repeatable bearing runout, random external force disturbances on the actuator, and random external forces applied to the disk drive. Repeatable runout occurs as a result of repeatable bearing runout, imbalance of the rotating hub assembly and disk, and disk clamping errors. The latter is composed of both of the above centering and tilt components which give rise to repeatable tracking error components at once the rotation frequency (once-around error) and at twice the rotation frequency (twice-around error). Despite great efforts to minimize these errors mechanically, disk clamping errors are usually quite large in cartridge (removable media) disk drives. This error component is usually not present to any significant degree in fixed (non-removable media) disk drives. 
     Tracking errors which repeat cannot be adequately attenuated using classical feedback servo approaches in cartridge disk drives with higher track densities. Thus, the use of a classical servo approach can place a fundamental limit on drive performance by limiting the number of tracks which can be squeezed on each disk, while still allowing adequate margins for tracking error. Fixed disk drives do not have this problem as the media is clamped in place prior to writing servo information and is never removed or shifted on the spindle. 
     This invention takes advantage of the repeatable nature of these tracking errors to suppress these components on removable drive to levels where, after normal feedback servo correction, the servo tracking errors are as low as on fixed disk drives. The net result is reduced tracking error and the achievement of fixed drive performance on a removable cartridge disk drive. 
     This invention uses a microprocessor to analyze and produce a correction function for the repeatable components of the tracking error. This correction is done independently of the feedback servo loop and minimizes the tracking error which the servo loop must attenuate resulting in better overall tracking accuracy. Since this technique uses feedforward instead of feedback correction, it is not limited by factors which traditionally limit the performance of closed loop feedback servo systems such as structural resonances, sample rate limitations, and other dynamic stability constraints, and allows for performance levels similar to fixed disk drives. 
     At power on, when the cartridge is changed, and at times during normal operation (such as for example, when the disk drive temperature rises resulting in weaker magnetic fields in the voice coil actuator motor, and thus resulting in the requirement for greater actuating currents from the servo system  550 ), the repeatable runout of the disk is analyzed by a microprocessor using Fourier Transform techniques, and in a preferred embodiment, Discrete Fourier Transform (DFT) techniques. The error is decomposed into real and imaginary parts which represents both amplitude and phase information of once-around and twice-around repeatable tracking error components. These correspond to two frequency bins of a DFT, which in this embodiment occur at about 60 Hz (once-around errors) and 120 Hz (twice-around errors). Based on this, a correction function table or alternatively, a runout error correction signal table is generated and stored in RAM and is used to output correction forces to the actuator independent of the action of the closed-loop feedback servo system. In this way the repeatable components of runout are reduced to levels similar to a fixed disk drive even before the action of the closed-loop feedback servo system. The residual errors which the closed-loop servo system is left to act upon and reduce are now the same for a cartridge disk drive as for a similar fixed disk drive. This eliminates the servo tracking error disadvantage otherwise inherent in cartridge verses fixed disk drives and which can limit the relative overall capacity and performance of cartridge verses fixed disk drives. 
     FIG. 36 shows an overall block diagram of the servo system  550 . A microprocessor  552  is used to implement feedback servo loop compensation. (This could also be implemented by a microprocessor along with external compensation components, or entirely with external compensation as is known in the art). 
     The block  562  labeled “Repeatable Tracking Error Correction” is the new element introduced by this invention. A microprocessor (which in this case can be the same microprocessor used for feedback servo loop compensation) is used to analyze and perform a Fourier Transform, and in a preferred embodiment, a Discrete Fourier Transform (DFT) on the position error signal (PES) during initial startup and subsequent calibration periods. The index and servo sector reference signals provide the timing information needed to do the DFT and the inverse DFT. Once the repeatable error components have been analyzed and stored, an inverse DFT is performed at each servo sector and a feedforward correction signal is generated and output to the actuator driver in addition to, and independent from, the control signal generated by the normal feedback servo loop compensation. 
     More specifically, the schematic FIG. 36 depicts a servo system  550  of the invention which includes both a feedback loop  551  and a feedforward line  553 . Feedback loop  551  includes an microprocessor  552  which provides for the feedback servo loop compensation calculation. Additionally, feedback loop  551  includes summing point  554 , actuator driver  556  and the actuator (for example a voice coil motor)  558  which causes the head to seek to the actual desired position. The signal from the actuator  558  is then feed back to a summing point  560  which sums the actual position of the head as implemented by the actuator  558  and as determined by the head in reading the servo patterns on the disk and the desired position signal. The error signal is then provided to the microprocessor  552  which outputs an appropriate correction signal, generally as a current in order to drive the actuator driver  556 . 
     The feedforward compensation for correcting for repeatable track error is performed by the microprocessor  562 . As indicated above, in a preferred embodiment, the functions of the microprocessor  560  and of the microprocessor  552  are performed by the same microprocessor at different times. 
     With respect to the feedforward line  553 , it is highly advantageous to initially drive the actuator as close as possible to the desired location before attempting to correct the location with feedback servo loop compensation. Accordingly, the feedforward compensation afforded by microprocessor  562  provides a feedforward correction signal to summing point  554 , which in combination with the feedback correction signal from microprocessor  552 , provides a current to the actuator driver  556  in order to drive and position the actuator  558 . The microprocessor  562  creates and stores a runout table as described in FIGS. 37 a  through  37   d  in order to apply the runout correction. With inputs including an index reference and a sector reference, in addition to input from the summing point  560  over line  561 , the repeatable tracking error correction microprocessor  562  in conjunction with building the runout table, can provide a current signal to summing point  554  in order to drive the actuator  558 . It is noted that line  561  is used to make measurements in order to build the runout table, and that after the table is built, that microprocessor  562  can disable this line. 
     FIGS. 37 a - 37   d  are flow charts of the microprocessor firmware (Exhibit A is a copy of the firmware code listing) used to perform the DFT on the repeatable runout during calibration time, generate the correction function and to do the inverse DFT as part of the processing to generate a runout table for the error correction signal. 
     During the calibration phase the once-around and twice-around runouts are measured by doing the DFT at each servo sector or “wedge”. In the present embodiment, there are 56 servo sectors (one index sector and 55 non-index sectors). These runout measurements are converted to frequency domain measurements by the DFT which resolves the measurement into real and imaginary parts containing both amplitude and phase information of the once-around and twice-around components of runout tracking error. These are stored in the microprocessor  562  as oncereal (once-around real components), onceim (once-around imaginary components), twicereal (twice-around real components) and twiceim (twice-around imaginary components). 
     Runout tables (stored in RAM for example) are then generated by multiplying the DFT by a complex number which takes into account the actuator characteristics and amplifier gains so as to correct for the measured repeatable runout error when applied to the actuator as an independent forcing function. These forcing functions are stored as L 1 RE, L 1 IM, L 2 RE, and L 2 IM which are DFT representations of the once-around and twice-around runout correction functions (FIG. 37 d ). Disk clamp centering, disk tilt, disk thickness, and actuator geometries make the repeatable runout errors dependent on the position in the actuator stroke and on which surface of the disk is being used. For this reason a different table is generated for each surface. A correction function is also applied which is dependant on the track number and which compensates for variations in geometries between the disk and the actuator over the stroke. This is the variable “target” in the flowchart where target is dependant on position in the stroke and represents the desired track. 
     Specifically referring to the flow charts in FIGS. 37 a  through  37   d , a preferred embodiment of the invention is implemented as follows. 
     In FIG. 37 a , the overall structure of the process performed by the microprocessor  562  is set out. In this structure  570 , the operation is initiated by setting all variables equal to zero. The variables include “L” which is the number of sectors, which in a preferred embodiment, is 56. The variables also include the once-around real (ONCEREAL) component of the complex number performed by the Fourier Transform and the once-around imaginary (ONCEIM) component of the Fourier Transform. These are set to zero in block  574 . The next variables which are set to zero are the twice-around real component (TWICEREAL) of the Fourier Transform and the twice-around imaginary component (TWICEIM) of the Fourier Transform. Then measurements are taken at every servo sector until the last servo sector (LMAX) is measured at block  578 . Thus, structure  570  of FIG. 37 a  indicates that structure  580  of FIG. 37 b  should be performed 56 times or LMAX times. 
     For each servo sector (i.e. at each of the 56 wedges described in a preferred embodiment about the disk) a once-around and twice-around runout measurement is made by the microprocessor  562  according to the structure  580  (FIG. 37 b ). In structure  580 , block  582  includes a counter for stepping between successive wedges in order to perform the measurements. Block  584  includes a measurement and calculation for the once-around real component of the runout error. In this block  584 , the once-around real component is equal to the previously calculated once-around real component for the particular track on which the specific servo section or wedge is located, plus the position error signal (PES) times the COS (K′) where K′ is equal to 2 πK/N. 
     The DFTs are listed below with F 1  for the once-around errors (about 60 Hz) and F 2  for the twice-around errors (about 120 Hz). It is the COS portion of F 1  that is performed in block  584 .                F   1     =       1   M            ∑     K   =   0       M   -   1              PES   K          [       COS                     2      π                 k     N       -     i                 Sin                     2      π                 K     N         ]                         F   2     =       1   M            ∑     K   =   0       M   -   1              PES   K          [       COS                 2                     2      π                 k     N       -     i                 Sin                 2                     2      π                 K     N         ]                                 where                 M     =                number                 of                 measurements                 per                 revolution                 of                 the                 disk                 N   =                number                 of                 the                 wedges                 M   =                2      N                 K   =                the                 number                 of                 wedges                              (       integers                 0     ,   1   ,   2   ,     3                 …                  )                                  
     Block  586  calculates the imaginary component of the once-around runout correction in the same manner except that SIN (K′) (the Sin portion of F 1 ) is utilized. As with block  584 , block  590  calculates the twice-around real component of the runout error by adding the previously calculated runout error for the other subsequent wedges in the track to the position error signal, PES, times COS (K′) (which symbolically represents the COS portion of F 2 ). Similarly block  592  performs the same calculation with the position error signal multiplied by the SIN (K′) (which symbolically represents the Sin portion of F 2 . The structure  580  is then performed for each servo on the track and a summation of all of the runout correction errors is made so that for each track there is a once-around real value, a once-around imaginary value, a twice-around real value, and a twice-around imaginary value. 
     In FIG. 37 c,  complex correction functions, including real and imaginary parts, are generated based on the measure runout structure  580  of FIG. 37 b.  In FIG. 37 c,  the runout adaptive structure  600  is performed by first clearing all of the variables in block  602  and then having the head actuated to an outer track as provided for by block  604 . The outer track can be an outer most track or a track which is outwardly of an inner track which is specified in block  612 . Block  606  indicates that the measure runout structure  580  of FIG. 37 b  is then implemented in order to provide the four complex values for each track which are calculated by the structure  580 . Once these values are calculated, then the function of block  608  is implemented. In block  608  for the outer track, a once-around real correction function is generated and thereafter stored in block  620  under the value M 1 RE. The outer once-around real correction function (OUT 1 RE) in block  608  is generated by adding any previous once-around outer correction function for that track to the sum of the once-around value calculated in block  584  times a constant K 1 REAL minus the once-around imaginary value calculated in block  586  times a constant M 1 IM. The constant M 1 REAL and M 1 IM depend on the characteristics of the drive as outlined above. These values, as well as K 2 REAL and K 2 IM listed below, can be calculated from known mathematical relationships for the drive configuration, but practically they are empirically determine with an emulator as is known in the art. The OUT 1 RE function can be performed as many times as desired for each track and summed in order to increase the accuracy for the final OUT 1 RE value for each track. 
     Similarly an outer track once-around imaginary function (OUT 1 IM) is calculated in block  608  and this value is stored in block  620  as M 1 IM. In block  610 , twice-around real and imaginary correction functions for the outer track (OUT 2 RE, OUT 2 IM) are calculated and stored respectively as M 2 RE and M 2 IM in block  620 . In block  610 , the functions calculated in the structure of  580  in FIG. 37 b  are multiplied by the constant K 2 REAL and K 2 IM, which again are constant values determined by the specific structure of the disk drive as set out above. In block  612 , the head is actuated to a track which is inwardly of the track measured in block  604 , and then in block  614 , the runout algorithm of structure  580  is performed on the inner track. Block  616  and  618  are similar to block  608  and  610 , but are performed for the inner track. These blocks result in the storing of values in blocks  620  which include B 1 RE, B 1 IM, B 2 RE and B 2 IM, which stand for inner track once-around real and imaginary correction functions and inner track twice-around real and imaginary correction functions, respectively. 
     It is to be understood that the value of block  620  can be computed and stored in complex, slope intercept form in order to simply the calculation of the flow charts of FIGS. 37 a - 32   d  as is known in the art. 
     It is also to be noted that alternatively instead of making calculations for an outer track and an inner track and then scaling between said tracks as set forth in FIG. 37 d  (blocks  632 ,  634 ) that the measurement for a single track can be made for block  620  and then other values for blocks  632 ,  634  can be scaled from the values for the single track. 
     A structure  630  shown in FIG. 37 d  then makes the correction functions which are complex values having real and imaginary components of blocks  620  and builds a runout table for each track on the disk. It is to be understood that alternatively, instead of building a runout table that it is possible to have the calculations contemplated in FIG. 37 d  done in real time and on the fly. The runout table of FIG. 37 d  is constructed for each individual track and each individual sector on the track. In blocks  632  and  634  the once-around real and imaginary components and twice-around real and imaginary components are calculated for each track and each sector on the track by scaling between the values of the inner track and the outer track or by scaling from a single track, preferably a middle track, as calculated in the runout adaptive structure  600  in FIG. 37 c.  As can be seen block  632  for the once around real component for any particular track and sector, this is calculated by multiplying the once-around real component of the correction factor as stored in block  620  by the target which is a mathematical representation of the track and sector and adding thereto a base value which is the real component of the correction function stored in block  62  for the inner track. In other words, the base value is the inner track value and thereto is added a scale mount which is equivalent to a portion of the outer value in order to calculate the value for a track which falls between the correction function for the inner track and the outer track. The same process is accomplished for the imaginary once-around component in block  620 . Similarly, the same scaling function is accomplished for the twice-around real and imaginary components for each sector in each track by block  634 . Block  638  emphases that the calculations of block  632  and  634  are accomplished for each of the sectors in each track. Again, scaling can occur from a single, preferably, middle track, if desired. 
     In blocks  640  and  644 , the inverse of the discrete Fourier Transform is performed in order to transform the correction functions of blocks  632 ,  634  for each sector on each track into, in a preferred embodiment, a current signal to be provided to the actuator driver  556  in FIG.  36 . Blocks  640  and  644  cause the runout table to be generated. This is accomplished by adding the once-around current value as calculated in block  640  to the twice-around current value as calculated in block  644 . In block  640 , the value which is denoted by FEED(L) is equivalent to the complex value L 1 RE calculated in block  632  times the COS (K′) (which is symbolically used to represent the inverse DFT) in order to perform the inverse Fourier Transform as previously discussed. To this value is added L 1 IM times SIN(K′) (which is symbocially used to represent the inverse DFT). In block  644 , the twice-around correction functions L 2 RE and L 2 IM are used in the same manner as the once-around correction functions are used in block  640 , in order to calculate the error correction signal which is a combination of the FEED(L) value calculated in block  640  plus that calculated in block  644  for each sector on each track. These calculations result in runout tables of current values which are used to drive the actuator  558 . 
     Limited Copyright Waiver 
     A portion of the disclosure of this patent document (Exhibit A, Code Listing) contains material to which the claim of copyright protection is made. The copyright owner has no objection to the facsimile reproduction by any person of the patent document or the patent disclosure, as it appears in the U.S. Patent and Trademark Office file or records, but reserves all other rights whatsoever. 
     Copyright 1991 Iota Memories Corporation 
     INDUSTRIAL APPLICABILITY 
     The operation of the disc drive  50  and removable cartridge  52  of the invention are as disclosed hereinabove. From the above, it is evident that the present invention provides for a disk drive and cartridge which fits into the 2½ inch disk, 17.5 millimeter high drive housing form factor and affords a storage capacity per cartridge of at least 40-megabytes. The present invention provides for reduced power consumption and safety interlocking mechanisms to prevent damage to the drive and cartridge, and also infinite storage capabilities. 
     Other aspects and objects of the invention can be obtained from a review of the appended claims and figures. 
     It is to be understood that other embodiments of the present invention can be fashioned and come within the spirit and scope of the invention as claimed.