1. Technical Field
The present invention generally relates to computer systems, more specifically, to storage devices such as hard disk drives used by computer systems for the permanent retention of user data and software programs. The invention particularly relates to a method of determining the angular position of one or more rotating disks of such a storage device, to provide proper indexing of the disks with respect to an associated servo mechanism.
2. Description of Related Art
Computer systems use a variety of devices for permanently storing data, i.e., in a non-volatile manner such that power to the computer system may be turned off but the data (including both user information and computer programs) are retained for future access. These direct access storage devices (DASDs) typically use a magnetic or optical medium to preserve the data. The most common data storage device has one or more generally circular disks formed from a non-magnetic substrate with a ferromagnetic coating. The disks rotate or spin, and a pivoting arm having electromagnetic transducers is used to read from, and write to, the disks. This magnetic storage device is commonly referred to as a hard disk drive (HDD), and is usually packaged in a modular enclosure so that it may be easily installed in and removed from the computer system. Many computer systems use multiple HDDs for greater storage capability, or for fault tolerance, such as in a redundant array of inexpensive disks (RAID).
FIG. 1 depicts an exemplary HDD 10 constructed in accordance with the prior art. HDD 10 has a shroud or enclosure 12, a plurality of disks 14, a rotary actuator assembly 16, and associated control electronics (not shown). A cover which is part of enclosure 12 has been removed in FIG. 1. Disks 14 are appropriately mounted on a spindle which is attached to a spindle motor, and thus rotatable with respect to enclosure 12.
The upper and lower surfaces of each of the disks 14 are coated with a magnetic material to allowing the writing of data onto the surfaces using the principle of magnetic induction. Rotary actuator assembly 16 has a plurality of arm/suspension members 18 supporting electromagnetic transducers (heads) at their tips, which are used to read data from and write data to the magnetic media-bearing surfaces of disks 14. The movement of actuator assembly 16 is controlled by a voice-coil motor (VCM) 22.
The magnetic media-bearing surfaces of disks 14 have a plurality of generally concentric tracks for recording blocks of information. Each of these tracks is divided into multiple sectors. The theoretical location of any given set of data bits can accordingly be computed based on the track number and position within the particular sector. Based on this assumed location, the HDD control electronics generate appropriate electrical signals that cause VCM 22 to move the read/write heads on arm/suspension members 18 over the desired portions of disks 14. Thus, when the heads have been located over the proper tracks, as the disks 14 are spinning, data can be read from or written to the tracks via the inductive heads.
The magnetic disk of a typical HDD is divided into several different areas according to industry standards. For example, many disks include a master boot record for storing technical specifications of the disk, a boot sector for storing basic operating system data, and multiple tracks for storing other data. The transducers must be precisely aligned with these various areas on the disk in order to properly write to or read from the disk. In the well-known Whitney style technology, the rotary movement and positioning of the actuator assembly is controlled by a series of electrical signals emanating from the computer processor (or from a xe2x80x9ccontrollerxe2x80x9d connected to the processor), which feed into the VCM of the actuator assembly. The VCM includes an electromagnetic coil (solenoid) attached to a portion of the pivoting arm, and one or more permanent magnets are affixed to the HDD enclosure such that a steady-state magnetic field from the magnets can be used in conjunction with the magnetic field from the VCM coil to cause the arm to rotate about its pivot point in a precise manner. Many HDDs provide a special magnetic pattern, or xe2x80x9cservo surface,xe2x80x9d that allows the actuator assembly to identify its relative location on the disk. In this manner, an actuator assembly can be quickly moved to the approximate desired location, and then precisely adjusted to the exact location.
For such accurate registration of the read/write heads, it is necessary to determine the absolute angular position (index) of a disk with respect to the servo mechanism. In order to perform this determination, it is currently necessary to use some form of sensor. The sensor may itself comprise the read/write heads that are used to access the media-bearing surfaces of the disks. This approach has several problems, however. First, it is of course necessary that the heads have been loaded onto the device, which impacts the manufacturing process. It may be desirable under certain circumstances to effectuate disk indexing prior to mounting of the transducer heads. Moreover, for disk drives which utilize a load/unload feature, one of the heads may be loaded directly on top of a surface defect in the loading zone, thus causing more surface damage. Since a spindle position index is not available when the heads are parked on the ramps, the angular spindle location where the heads load onto the disk surfaces becomes random.
Instead of using the transducer heads to index the disks, an external sensor may be employed. One example is the use of a Hall sensor, but this approach also has problems, particularly the increased cost associated with the use of the external sensor. It would, therefore, be desirable to provide an improved method for determining a fixed rotary position reference of the disks in a disk drive, without requiring the recording heads to be loaded, and without the use of any external sensor. It would be further advantageous if the method could facilitate the location of defects in the loading zone without the use of servo sectors.
It is therefore one object of the present invention to provide an improved direct access storage device (DASD) for a computer system.
It is another object of the present invention to provide such a DASD which allows the angular position of disks to be established relative to the index for the servo sectors.
It is yet another object of the present invention to provide a method for generating a fixed angular position index of a DASD using a sensorless spindle motor.
The foregoing objects are achieved in a method of indexing a rotatable disk in a direct access storage device (DASD) having a sensorless spindle motor, generally comprising the steps of monitoring a center-tap voltage of the spindle motor to detect a pattern of commutation spike timing separations associated with the sensorless spindle motor, identifying a sensorless spindle motor index from the commutation spike timing separations pattern, and matching the sensorless spindle motor index with a servo sector index of the disk. The center-tap voltage may not be readily available in some spindle motors. In this case, the individual induced motor phase voltages are added by a summing amplifier to provide a voltage signal that is similar to the center-tap voltage. The commutation spikes may be monitored by connecting a center tap of the sensorless spindle motor to an input of a highpass filter, and connecting an output of the highpass filter to a threshold-and-gate device which triggers on a leading edge of a commutation pulse from the highpass filter based on a predetermined threshold level. A plurality of clock pulses are counted as the disk spins, and count values are captured using the threshold-and-gate device. The threshold-and-gate device stores the count values in an index register; a timing-separation sequence between adjacent count values is computed, and variations in the timing-separation sequence are computing by subtracting an average timing-separation from the sequence. A figure-of-merit may be set based on a sliding window used to sum a portion of the sequence, and the difference between the largest value of the sequence and the next largest value of the sequence is enlarged, based on the figure-of-merit. The rotor magnets of the sensorless spindle motor may be placed in an asymmetric fashion to produce a large deviation in the variation of the timing-sequence. Indexing may be accomplished during servo track write for the disk.
The above as well as additional objectives, features, and advantages of the present invention will become apparent in the following detailed written description.