Abstract:
A hard disk is provided with tools for limiting the duty cycle (a group of variations of load with time). The write current is controlled by, e.g., limiting the duration of a given write cycle. The write cycle may involve writing data continuously along adjacent portions of the disk media (e.g., writing of data in adjacent segments of a track in the outer diameter (OD) region of a platter), with an intermittent duty write current.

Description:
Priority is hereby claimed to U.S. Provisional Application No. 60/269,761, filed on Feb. 16, 2001, the content of which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Related Application Data 
     1. Copyright Notice 
     This patent document contains information subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent, as it appears in the U.S. Patent and Trademark Office files or records but otherwise reserves all copyright rights whatsoever. 
     2. Field of the Invention 
     The present invention, in certain respects, may relate to hard disks. In other respects, the present invention may relate to a hard disk&#39;s read/write heads and to hindering pole tip protrusion (PTP). 
     3. Description of Background Information 
     Hard disks are being manufactured with increased access speeds and storage capacities. Manufacturers of these (present day and future) improved-performance hard disks have decreased the distance between the hard disk&#39;s read/write heads and its disk media. As a result, slight variations in the positioning or dimensions of the heads or of the disk media can cause the heads and the disk media to collide. For example, such a collision can be caused by protrusion of the pole tips of the write portion of a given read/write head, a phenomenon referred to as pole tip protrusion (PTP). 
     PTP can be caused by high frequency writing, which causes the thermal expansion of the pole tips. Such thermal expansion is caused by eddy current heating and coil heating. PTP can cause problems such as off-track writing (due to frictional forces) and high servo PES (due to the dragging of the head by the pole tip). PTP can result in drive failure. 
     SUMMARY OF THE INVENTION 
     The present invention is provided to hinder the occurrence of PTP in the write elements of hard disk read/write heads. 
     In accordance with one aspect of the invention, a hard disk is provided with tools for limiting the duty cycle (a group of variations of load with time). The write current is controlled by, e.g., limiting the duration of a given write cycle. The write cycle may involve writing data continuously along adjacent portions of the disk media (e.g., writing of data in adjacent segments of a track in the outer diameter (OD) region of a platter), with an intermittent duty write current. The invention may also be directed to any portion of such a hard disk or to any set or subset of acts performed by the hard disk. The invention may also be directed to computer readable media encoded to perform any acts disclosed herein. 
     In one embodiment, the write cycle is limited to a thermal time constant of approximately 0.5 to 1.0 msec. In another embodiment the write cycle is limited to a longer period, e.g., 2-100 msec. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is further described in the detailed description which follows, by reference to the noted drawings, by way of non-limiting exemplary embodiments, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein: 
     FIG. 1 is a schematic diagram illustrating certain elements of a hard disk, provided with mechanisms for limiting the duration of a given write cycle; 
     FIG. 2 is a block diagram of a personal computer system; 
     FIG. 3 is a flow chart of a write operation; and 
     FIG. 4 is a flow chart of a PTP hindering process. 
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings in greater detail, FIG. 1 shows a hard disk having a unitary housing schematically depicted by a rectangle  11 . Within the hard disk housing  11 , disk media is provided, including a stack of disk platters (not shown). A given disk platter  12  is shown in the simplified diagram. For each side of a disk platter, a different read/write head  10  is provided. Each read/write head  10  may comprise a read element  13  and a write element  14 . These elements are provided in some of the newer higher-performance hard disks which utilize a traditional U-shaped head for writing data onto the disk while using a magneto-resistive (MR) read element for reading data from-the disk media. 
     FIG. 1 includes an enlarged view of write element  14  comprising pole tips  17 . Write element  14  comprises a U-shaped head made of conductive material. The U-shaped member is wrapped with coils of wire. A magnetic field is generated and transferred to the disk media in accordance with disk drive write signals that are passed through the coils. By changing the polarity of the electric current passed through the coils, the polarity of the field generated is also changed. The pattern of such magnetic conditions is transferred to the surface of the disk media on disk platter  12  to form a pattern which comprises the resulting encoded version of the data to be retrieved at a later point. 
     Poles  17  are positioned very close to the surface of disk platter  12 , and are maintained at a specified distance from the surface of the disk platter  12  by an air bearing. If there is contact, or if the distance between the surface of the disk platter  12  and the pole tips  17  becomes unacceptably small, there can be problems with the disk. The head or the disk media can be damaged, and errors can be encountered when retrieving the data and reading the data from the disk media. 
     Such contact between the pole tips and the disk media occurs when there is pole tip protrusion (PTP). PTP can be caused by high frequency writing which causes thermal expansion of the pole tips  17  due to, for example, the combined effects of eddy current heating and coil heating. Such PTP phenomena can cause problems while writing data onto the disk media, such as off track writing, due to frictional forces, as well as high servo PES (position error signal), because the pole tip is dragging the head. These effects could cause drive failure. 
     A write current duty cycle control mechanism may be provided to hinder PTP by controlling the write current duty cycle so as not to exceed a maximum level. 
     The write current duty cycle control mechanism may be implemented as part of a collection of the circuitry within the hard disk, e.g., as shown in FIG. 2 (below), including collectively the control portion, the hardware interaction circuitry, and the internal memory. More specifically, the write current duty cycle control mechanism may be implemented as part of the controller running software within internal ROM and/or RAM of the hard disk. Such a write current duty cycle control mechanism may also be implemented with circuitry provided as part of the read channel. 
     The write current duty cycle control mechanism may comprise a write current duty cycle monitor, a comparator to compare data representing the write current duty cycle to reference data, and a write cycle interrupter to interrupt the write cycle when the write current duty cycle exceeds a reference level as indicated by the reference data. 
     An exemplary embodiment is shown in FIG.  1 . As shown, PTP can be prevented or hindered by monitoring the duty cycle of the write signal  18 , using a counter  20 . A compare and stop write operation mechanism  22  may be provided to compare the counter value (which counts the number of pulses over a predetermined time period) to a threshold value and to stop the write operation when the threshold value is exceeded. Write signal source  18 , counter  20 , and compare and stop write operation mechanisms may be provided as part of a read/write channel chip of the hard disk. 
     FIG. 2 is a block diagram of one embodiment of a personal computer system. The illustrated computer system has a hard disk  17 . The illustrated hard disk  17  comprises, among other elements, disk media  46 . In the illustrated embodiment, disk media  46  comprises magnetic media sputtered onto a metal substrate (the metal may be aluminum). 
     The illustrated computer system comprises a host system  23  and a hard disk  17 . Hard disk  17  comprises a unitary hard disk housing which houses an input/output interface  26 , a cache buffer memory  28 , a controller  30 , a RAM (random access memory)  36 , and a ROM (read only memory)  34 . Input/output interface  26  is connected to cache buffer memory  28 , which is connected to controller  30 . Each of the RAM and ROM portions  36 ,  34  is coupled to controller  30 . 
     The hard disk housing further houses motor and servo mechanisms  38 , read/write electronics  40 , and a read channel  42 . Read channel  42  is coupled to read/write heads  44 , which interact with disk media  46 . Read/write heads  44  and disk media  46  are also provided within the unitary hard disk housing (depicted with a schematic dotted line). 
     Input/output interface  26  may comprise a SCSI, IDE, or ADA interface, just to name a few examples. While a cache buffer memory  28  is not required, such is common. 
     In the embodiment, controller  22  serves as a control portion of the hard disk. Motor and servo control portions (not shown) of motor and servo mechanisms  38 , read/write electronics  40 , and read channel  42  collectively comprise hardware interaction circuitry coupling controller  30  to a head/disk assembly, which comprises a spindle motor (not shown), a servo (not shown), read/write heads  44 , and disk media  46 . 
     In the illustrated embodiment, hard disk  17 , has in its housing, internal memory, including RAM  36  and ROM  34 . All or a portion of such memory (and any other devices or mechanisms that may be provided in the hard disk and that serve as memory) may serve as the internal memory for the hard disk, and may contain information pertinent to the functions and operation of the hard disk. 
     FIG. 3 shows a flow chart of a write operation. In act  50 , a block write command is received by controller  30  from host  23 . Then, in act  52 , data is written from host  23  to cache  28 , while keeping track of LBA (logical block address) and PBA (physical block address) information as appropriate. 
     In act  54 , the block is written from cache  28  to the disk media. At act  56 , a determination is made as to whether the write cycle was stopped early—e.g., because of a process for controlling the duty cycle of the write current (the process depicted in FIG.  4 ). If the write cycle was stopped early, the process proceeds to act  58 , where the controller  30  will make sure a minimum delay passes before proceeding to act  60 . At act  60 , the write cycle is completed, by completing the writing of any unfinished sectors to the disk media. 
     The write operation is completed by proceeding from act  56  if the write cycle was not stopped early, or by proceeding from act  60 . 
     FIG. 4 shows one embodiment of a PTP hindering process, which allows the duty cycle of the write current to be controlled to hinder PTP effects in the write portions of the respective read/write heads of the hard disk. In an initial act  61 , the process waits for certain PTP susceptibility conditions to exist, before proceeding. This act is an optional part of the illustrated embodiment. The conditions may be, e.g., the hard disk being in a cold condition or the detection of a sudden increase in the PES signal. Such condition(s) may be detected by a respective detector (not shown) or otherwise indicated by a signal received by the controller. 
     If the PTP susceptible condition exists, the process proceeds to act  62 , where write operations at the outer diameter portion of the disk media (at the OD) are controlled. Specifically a determination is made at act  62  to determine if the duty cycle of the write current reaches a certain level. If the pulses counted within a given time period are greater than a threshold, then the process proceeds to act  66 , where the write cycle is stopped. If the counted pulses do not exceed the threshold, the process proceeds to act  64 , where a determination is made as to whether the write cycle is completed. If it is, the PTP hindering process is ended. If it is not, the process returns to act  62 . 
     The determination at act  62  may perform a calculation of the duty cycle by comparing the number of pulses within a time period Td. If that number exceeds a given value, which can be determined empirically, then the duty cycle of the write current may be deemed likely to cause an undesired PTP effect on the write element of the read/write head. 
     Alternately, the duty cycle may be determined in act  62  to likely lead to undesired PTP by simply determining when the write operation is occurring with a constant intermittent duty write current lasting at least a given “PTP danger time.” The PTP danger time may be deemed to be equal to a value somewhere in the range of 0.5 to 1.0 msec. In another embodiment the PTP danger time is a longer period, e.g., a value in the range of 2-100 msec. 
     For purposes of the disclosure herein, a computer-readable media may comprise any form of data storage mechanism, including temporary memory such as a RAM, or longer-term storage devices, including ROM, magnetic disks, rewritable optical disks, and so on. Computer-readable media can also comprise hardware or circuit representations of structures or data. The above described system and method embodiments can be implemented with software controlling a general purpose processor or with specialized processing components and circuitry. 
     While the invention has been described with reference to certain illustrated embodiments, the words which have been used herein are words of description, rather than words of limitation. Changes may be made, within the purview of the appended claims, without departing from the scope or spirit of the invention in its aspects. Although the invention has been described herein with reference to particular structures, acts, and materials, the invention is not to be limited to the particulars disclosed, but rather extends to all equivalent structures, acts, and materials, such as are within the scope of the appended claims.