Patent Grant
7167333
U.S. patent application Ser. No. 09/923,570 filed Aug. 6, 2001 is specifically incorporated herein by reference in its entirety.
The present invention relates to computer disk drives. More particularly, the present invention relates to writing servo information onto and reading servo information from one or more disk surfaces of a disk drive, wherein the servo information is written in a spiral fashion.
Computer disk drives store information on magnetic disks. Typically, the information is stored on each disk in concentric tracks that are divided into sectors. Information is written to and read from a disk by a transducer that is mounted on an actuator arm capable of moving the transducer radially over the disk. Accordingly, the movement of the actuator arm allows the transducer to access different tracks. The disk is rotated by a spindle motor at high speed which allows the transducer to access different sectors on the disk.
A conventional disk drive, generally designated 10, is illustrated in
The actuator arm assembly 18 includes a transducer 20 (having a write head and a read head) mounted to a flexure arm 22 which is attached to an actuator arm 24 that can rotate about a bearing assembly 26. The actuator arm assembly 18 also contains a voice coil motor 28 which moves the transducer 20 relative to the disk 12. The spin motor 14, voice coil motor 28 and transducer 20 are coupled to a number of electronic circuits 30 mounted to a printed circuit board 31. The electronic circuits 30 typically include a read channel chip, a microprocessor-based controller and a random access memory (RAM) device.
The disk drive 10 typically includes a plurality of disks 12 and, therefore, a plurality of corresponding actuator arm assemblies 18. However, it is also possible for the disk drive 10 to include a single disk 12 as shown in
In addition to the components of the disk drive 10 shown and labeled in
The actuator arm assembly 18 is a semi-rigid member that acts as a support structure for the transducer 20, holding it above the surface of the disk 12. The actuator arm assembly 18 is coupled at one end to the transducer 20 and at another end to the VCM 28. The VCM 28 is operative for imparting controlled motion to the actuator arm 18 to appropriately position the transducer 20 with respect to the disk 12. The VCM 28 operates in response to a control signal icontrol generated by the controller 36. The controller 36 generates the control signal icontrol in response to, among other things, an access command received from the host computer 32 via the interface 40.
The read/write channel 38 is operative for appropriately processing the data being read from/written to the disk 12. For example, during a read operation, the read/write channel 38 converts an analog read signal generated by the transducer 20 into a digital data signal that can be recognized by the controller 36. The channel 38 is also generally capable of recovering timing information from the analog read signal. During a write operation, the read/write channel 38 converts customer data received from the host 32 into a write current signal that is delivered to the transducer 20 to “write” the customer data to an appropriate portion of the disk 12. As will be discussed in greater detail, the read/write channel 38 is also operative for continually processing data read from servo information stored on the disk 12 and delivering the processed data to the controller 36 for use in, for example, transducer positioning.
It should be understood that, for ease of illustration, only a small number of tracks 42 and servo spokes 44 have been shown on the surface of the disk 12 of
During the disk drive manufacturing process, a special piece of equipment known as a servo track writer (STW) is used to write the radially-aligned servo information which forms servo spokes 44. A STW is a very precise piece of equipment that is capable of writing servo information on the disk surface with a high degree of positional accuracy. In general, a STW is a very expensive piece of capital equipment. Thus, it is generally desirable that a STW be used as efficiently as possible during manufacturing operations. Even a small reduction in the amount of data needed to be written by the STW per disk surface can result in a significant cost and time savings.
In order to write servo information on to a disk surface 12, the disk drive 10 is loaded onto the STW 50 and is held securely in place. One of a variety of push-pin systems 58 (e.g., a mechanical push-pin system or an optical push-pin system) is used to create an interface between the actuator arm assembly 18 of disk drive 10 and the actuator arm assembly 56 of the servo track writer 50. By properly positioning the STW actuator arm assembly 56, the actuator arm assembly 18 and, hence, the transducer 20 of the disk drive 10 may be positioned at an appropriate location relative to the center of the disk surface 12. In order to effectuate this positioning, the STW 50 uses a servo loop formed by an external relative encoder (see block 70 in
Once the transducer 20 is appropriately positioned relative to the disk surface 12, servo information is then written by the transducer 20 onto the disk surface 12 at the particular radial location. Subsequently, the STW actuator arm assembly 56 is used to position the actuator arm assembly 18 of the disk drive 10 at a next radial location and servo information is written at this radial location. The process repeats until servo information is written at all predetermined radial locations across the disk surface 12.
As shown in
Because servo information is currently written by placing transducers at radial locations across the disk surface and then writing servo information which is used to define a track, the time for writing servo information increases as the total number of tracks able to be placed on a disk surface increases. Since the number of tracks per inch (TPI) continues to increase, manufacturing times are likely to continue to increase, unless more servo track writers are supplied. However, as alluded to above, the purchase of additional servo track writers involves a significant capital expense.
In order to solve this problem and to expedite the manner by which servo information is written onto a disk surface (among other things), it has been determined that it would be beneficial to write servo information in spiral patterns. U.S. patent application Ser. No. 09/853,093 filed May 9, 2001 and U.S. patent application Ser. No. 09/923,570 filed on Aug. 6, 2001, both of which are incorporated herein by reference in their entireties, relate to writing servo information in spiral patterns.
In such applications, among other things, reference is made to writing spiral servo patterns at a constant velocity by following a constant velocity profile. However, writing spiral servo patterns at a constant velocity may require certain tradeoffs. Accordingly, it would be desirable to write spiral servo patterns at a variable velocity, as an alternative to writing spiral patterns at a constant velocity, to capitalize on benefits gained therefrom.
The present invention is designed to meet the aforementioned, and other, needs. The invention is directed to a method and apparatus for writing spiral servo information onto one or more disk surfaces at a variable velocity using a servo track writer (STW). In one embodiment, a variable velocity profile is chosen so that spiral crossing angles across the disk surface are set to be equal. In another embodiment, a variable velocity profile is chosen so that spiral crossing angles across groups of tracks (i.e., two or more tracks) are set to be equal. In yet another embodiment, a variable velocity profile is chosen to adjust the number of tracks per inch (TPI) across the disk surface.
Other embodiments, objects, features and advantages of the invention will be apparent from the following specification taken in conjunction with the following drawings.
While this invention is susceptible of embodiments in many different forms, there are shown in the drawings and will herein be described in detail, preferred embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspects of the invention to the embodiments illustrated.
Additional spirals of servo information may be written on the disk surface 210 depending upon the servo sample rate (that is, the number of servo samples required for each track 120 to keep the disk drive's transducer on-track). For example, if a servo sample rate of 120 equally-spaced servo sectors per track was required, 120 equally-spaced spirals would be written on the disk surface 110. Accordingly, by using the present technique, the time necessary to write servo information on disk surface 110 is a function of the servo sample rate (i.e., the number of spirals of servo information to be written) rather than the number of tracks.
At any given track 220 (Data Tracks 24–40 are depicted in
It should be noted that a read head 230 placed on a track 220 closer to the inner diameter (ID) of the disk surface 210 will cross a given spiral of servo information at a time slightly delayed from a track 220 closer to the outer diameter (OD) of the disk surface. For example, suppose that: (1) time zero (t=0) is defined towards the right side of
Referring again to
In
The transducer is preferably enabled for its entire stroke (i.e., from OD to ID or visa-versa). As a result, a continuous spiral of servo information is written.
As described in U.S. patent application Ser. No. 09/853,093 filed May 9, 2001, each of the spirals of servo information include sync marks written at fixed time intervals by the transducer. Furthermore, the transducer is moved at some fixed velocity in a generally radial direction across the disk surface. If the time intervals between sync marks is known and the velocity of the transducer is known, the distance between sync marks along a spiral can be determined. Specifically, the following formula may be applied: Distance=(Velocity)(Time), where Distance represents the distance between sync marks, Velocity represents the velocity of the transducer and Time represents the interval between sync marks.
For example, the interval between sync marks may be set at 1 microsecond, while the transducer may be controlled to move at a velocity of 10 inches per second along its stroke. Thus, the distance between sync marks can be calculated to be 10 microinches along each spiral.
Each sync mark along a given spiral corresponds to unique radius. Accordingly, the sync marks may be used to accurately position a transducer of a disk drive over the disk surface.
It should be noted that, as an alternative to writing sync marks relative to a fixed time interval, sync marks may be written at some fixed distance interval by the transducer. If the transducer was moved at a fixed velocity when writing a spiral, the above formula could be applied to determine a time interval between sync marks.
Importantly, the position of the read signal envelope in time changes based upon the position of the reader 230. Although the read signal envelope moves relative to the position of the reader 230, the sync pattern within the spiral being read does not move. Accordingly, the envelope moves relative to the sync marks. Since the sync marks are at known radial positions, the sync marks provide a position reference for the reader 230.
As a convention, the position of the reader 230 is given by the centroid of the read signal envelope. For example, the centroid of the read signal envelope may be determined by integrating over the read signal envelope to determine its area and, then, dividing by two. It should be noted that other conventions may be adopted for the position of the reader 230.
In U.S. patent application Ser. No. 09/853,093 and U.S. patent application Ser. No. 09/923,570, among other things, reference is made to following a constant velocity profile (e.g., moving the STW actuator arm at 10–20 inches per second) when writing spiral information. In writing spiral servo information in such a manner, the angle at which a spiral crosses generally circular tracks (hereinafter defined as the spiral crossing angle, γ) varies along the spiral. Accordingly, the shape of the read signal envelope (shown in
The inventors of the present invention have determined that the change in spiral crossing angle, γ, requires the use of dynamic gain adjustments in the disk drive's position demodulation algorithm. That is, read signal amplitudes associated with spiral servo information are track dependent, and therefore, require compensation.
In an effort to provide an alternative to compensating for changes in spiral crossing angle, γ, the inventors of the present invention have devised a method and apparatus for providing a constant spiral crossing angle by varying the velocity at which spiral information is written onto the disk surface. Accordingly, a system could be designed so that spiral crossing angles are constant for some or all tracks across a disk surface.
In order to derive a variable velocity profile which allows for constant spiral crossing angles, one must identify factors on which the spiral crossing angle depends. Changes in spiral crossing angle may be due to a number of different factors including: (1) the velocity at which a transducer writes servo information onto the disk surface; (2) the velocity of the disk at the particular radial location at which the servo information is being written; and, (3) skew angle.
With reference to
As shown in
γ=arctan(VA/ωDR) [1]
In order to keep the spiral crossing angle at a constant value, the above equation could be solved for VA. It should be noted that the vectors shown in
In practice, disk drives do not have a zero skew angle across their entire disk surface. Like
Due to the skew angle, θskew, a component of VA exists in the direction of the disk velocity VD. Accordingly, for a disk drive that may include a skew angle, the spiral crossing angle, γ, is given by the following equation:
γ=arctan(VA cos(θskew)/(ωDR−VA sin(θskew))) [2]
While the skew angle, θskew, is shown as being zero at the disk's inner diameter and greatest at the disk's outer diameter, the above equation is equally applicable to situations where the skew angle, θskew, is zero at other locations.
In order to implement a profiled movement of the positioner on the STW, the linear velocity profile must be converted to the angular velocity of the positioner and then the desired position profile must be computed using the integral of the angular velocity.
The radius as a function of actuator angle is given by the following equation:
R(φ)=(A2+M2−2AM cos(φ))1/2 [3]
The skew angle can be expressed as a function of actuator angle and is given by the following equation:
θskew(φ)=arcsin((A2+R(φ)2−M2)/2AR(φ)) [4]
Substituting equations [3] and [4] into equation [2] allows the spiral crossing angle to be computed at any actuator position. An alternative formulation of equation [2] involves solving for VA as a function of φ and is given by the following equation:
VA(φ)=tan(γ)wDR(φ)/(tan(γ)sin(θskew(φ))+cos(θskew(φ))) [5]
By setting γ to a constant, equation [5] can be used to compute the variable velocity profile.
To contrast a constant velocity profile with a variable velocity profile, reference is made to
The lower portion of
It should be noted that the sharply angled portions near the left and right ends of
It should also be noted that variable velocity profiles may also be used to purposefully change the number of tracks per inch (TPI) on the disk surface, since the velocity at which the spiral servo information is being written onto the disk surface is used to define the TPI. More specifically, as mentioned above, sync marks may be written at constant time intervals by the transducer. Furthermore, the sync marks are used to define the tracks (i.e., the track pitch). When the transducer is moving across the disk surface at a constant velocity over a region of the disk surface, the number of tracks per inch is constant over that region of the disk surface. If the transducer is moved across the disk surface at a variable velocity instead of a constant velocity, the number of tracks per inch will change across the disk surface in accordance with the varying velocity of the transducer.
While an effort has been made to describe some alternatives to the preferred embodiment, other alternatives will readily come to mind to those skilled in the art. Therefore, it should be understood that the invention may be embodied in other specific forms without departing from the spirit or central characteristics thereof. The present examples and embodiments, therefore, are to be considered in all respects as illustrative and not restrictive, and the invention is not intended to be limited to the details given herein.
Priority is claimed from U.S. Provisional Patent Application Ser. No. 60/285,055 filed Apr. 19, 2001, which is incorporated by reference herein in its entirety. This is a continuation-in-part of U.S. patent application Ser. No. 09/853,093 now abandoned, filed May 9, 2001, which claims priority from U.S. Provisional Patent Application Ser. No. 60/203,159 filed May 9, 2000, U.S. Provisional Patent Application Ser. No. 60/223,446 filed Aug. 4, 2000, and U.S. Provisional Patent Application Ser. No. 60/285,055 filed Apr. 19, 2001. All of the aforementioned patent applications are specifically incorporated herein by reference in their entireties.
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| Number | Date | Country | |
|---|---|---|---|
| 60285055 | Apr 2001 | US | |
| 60223446 | Aug 2000 | US | |
| 60203159 | May 2000 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 09853093 | May 2001 | US |
| Child | 10126917 | US |
