KR19980080235A - Optical Head Servo Writer - Google Patents

Abstract

Method and apparatus for servo recording a disc. The clock track is recorded on a reference surface that is subsequently sealed in a sealed head disc assembly. A detector outside the sealed head disk assembly reads the clock track and causes a transducer inside the sealed head disk assembly to record the servo track.

Description

Optical Head Servo Writer

The present invention relates to an apparatus for a servo recording disk. The invention relates in particular to servotrack recording in a sealed head disc assembly.

A disk drive is a data storage device having a stack of one or more magnetic recording disks mounted to rotate about a common axis. Data is stored in a concentric track on the disc and read from or written to the disc surface by the transducer. Typically there is one read / write head per disc surface, and normally a single head / disk surface combination reads or writes user data at one specified time. The heads are attached to the actuator. The actuator has a voice coil motor that moves the head radially across the disk. Heads typically fly over a disk surface that rotates at a constant height (1 μm), causing dust and other contaminants on the disk surface to cause head failure, loss of data, and possible damage to the head and disk. easy. For this reason, the disc, actuator and head are placed in a sealed unit known as a head disc assembly (HDA).

The movement of the actuator is controlled by the servo system utilizing the servo information recorded on one or more disks. By reading this servo information, the actual radial position of the head can be determined, and after comparing the radial position of the desired head, a control signal can be transmitted to move the actuator accordingly. Typically, two types of servo systems are used. The first is commonly referred to as a dedicated servo system, where one disk surface (servo disk) is exclusively used to store servo information. The servohead constantly reads this information to provide a continuous signal indicating the position of the servohead relative to the servodisk, and by extension provides the position of all other dataheads on the actuator. In the second type of servo system, sectors of servo information are interspersed with sectors of data on each disk surface (this type of system is known as sector servo). As the head turns along the datatrack, it regularly reads new samples of servo information from each servosector used to control its position. In both types of servo systems, servo guard bands are formed at inner and outer diameters to indicate radial limits of the data storage area on the disk. Sometimes one of the servo guardband regions is used as the landing zone of the head when the disk drive is powered off.

Therefore, the servo pattern is composed of whole tracks or sectors of aerial seam tracks. Each track is identified by an index number and allows the radial position of the entirety of the nearest number of tracks to be easily determined. More detailed radial positional information is provided by error signals derived from the relative strength of the signals from two or more adjacent servotracks. The head position on the angular or azimuth angle is defined as the origin of the angle using some particular indication on the track and is obtained from the circumferentially aligned transitions in the servo track. Radial and angular measurements in the polar coordinates allow full positioning of the head over the disk surface.

Initial writing of the servo pattern onto the disc is an important step in the manufacture of the disc drive. It is essential that the servo tracks be recorded as accurately as possible while preventing contamination of the disk surface. Until now, this has been accomplished by using its own transducer head as a special servo recording device. Conventionally, the clock track is recorded on a disk already in the HDA. The disc is then mounted into a disc drive assembly having a plurality of heads. The servo information is then recorded on the disc using the clock signal recorded on the outer periphery of the disc. The angular information is a form of visual information that notifies the product head when to record a particular transition, and is provided by synchronization with a clock track and simultaneously read by a servo recorder. The head is controlled at a resolution better than 1 micro inch and moved from one track to another during servo recording. In this way, it is possible to obtain circular servotracks which are all set in angular reference to the clock track.

Although conventional servo recorders can produce high accuracy servo patterns, they have a major drawback in price. Conventional machines require large optical (vibration isolation) tables and therefore require large space and are expensive. Also, since the disk surface is exposed during the servo recording process, this process must be performed in a clean room. Installing and operating a clean room is relatively expensive. Constraints in terms of the amount of space available, the number of cleanrooms available, or the cost of a servo writer limit the overall throughput of a disk drive manufacturing line. Because of this, various attempts have been made to find a simpler and less expensive method and servo recording.

EPA 327207 discloses a method in which only one disc is servo recorded outside the sealed HDA. The remaining disk surface is servo-recorded after the HDA is sealed by effectively copying the pattern from the disk that already has the servo pattern. Similarly, US Pat. No. 4,531,167 discloses a servo recorder for copying a servo pattern onto a disc inside the HDA from a master disc cartridge attached to a disc spindle outside the HDA. In EPA 327207, a clean room is required to create the original mast disk. In '167, it is necessary to remove the master disc after recording the servo track. In addition, the method disclosed in '167 above is only applicable to the assembly of a particular disk drive.

According to U.S. Patent No. 5,339,204, which is assigned to IBM, a clock track is recorded inside a sealed disk assembly, and then the optical track effect is read out of the clock track, and servo information is read on the disk in the sealed HDA. Control the transducer to record to. Clock tracks are recorded using transducers located within the HDA. Using a transducer inside the sealed disc assembly to record the clockhead results in a narrower clock track. These narrow clock tracks cause signal-to-noise problems when they are read optically by standard optical magnetic heads. Many optical systems require a signal-to-noise ratio of 30 dB or more over a 5 KHz bandwidth for reliable performance.

Thus, an improved method for servo recording tracks on disk is desired.

The present invention discloses an improved method and apparatus for servo writing to a disc. The clock track is recorded or stamped on a reference plane that remains fixed relative to the disk as the disk rotates. The disc is sealed inside a substantially sealed head disc assembly. The clock track is used to control the transducer head to read and write the servo track.

1 is a block diagram of one embodiment of a disk clock recorder and verification system.

Fig. 2 is a plan view showing a typical pattern of tracks on a magnetic disc recorded by the clock recorder and the calibration system.

3 is an exploded perspective view of a magnetic disk drive in brief.

4 is a plan view of a typical sector servo pattern used in a magnetic drive.

5A is a block schematic diagram of a conventional magneto-optical head.

5B is a block schematic diagram of a magneto-optical system adapted for use in the present invention.

6 illustrates a focusing orthogonal detector.

Fig. 7 is a schematic diagram showing the Kerr effect on light reflected from the magnetic disk.

The objects and advantages of the invention are described in more detail below with reference to the accompanying drawings.

Many techniques can be used to write a clock track on a surface that remains fixed with respect to the rotation of the disk. One such technique is shown in FIG. 1. 1 shows an example of a disk clock recorder and verifier system 100 (clock recorder). This system is controlled by a personal computer (PC) or other type of computer controller 104, which may include a keyboard 106 and a monitor 108. Computer controller 104 is coupled to bus 106 to send instructions from computer controller 104 to an expansion board that controls the remainder of clockwriter 100.

The clock recorder 100 is designed to record an ultra-light clock track on a magnetic medium or a disk 112. The disk 112 rotates on a spindle 114 driven by a motor located directly below the head disk mount 116. The motor of the disc mount 116 may be coupled to the user expansion board 118 which sends a signal to the robotics board 120 which links the drive motor which controls the rotation of the disc 112 and the other motors which control the movement of the reference head 122 and the clock recording head 124. Can be. The robotics board 120 may include a separate display 126, a keypad 128, a robotics motor, and a sensor 130.

The reference head 122 is controlled by a reference read / write preamp board 132 that amplifies the signals generated by the reference and pattern generation board 134. The reference and pattern generation board 134 may include modules 136 and 138 for amplifying a signal transmitted to the reference read / write preamp board 132.

The reference head 122 records the reference track on the disc 112 using the instructions generated by the reference pattern generation board 134. The reference track can be generated using a closure technique similar to the technique used for recording clock tracks. The reference track is recorded with the reference head 122 held at a constant radius. Reference head 122 records a reference track including a transition on a disc. The transition is a change in magnetic direction that occurs at the predicted transition frequency based on the total number of desired transitions during one revolution of the disc 112. After the disc has completed one revolution, when the reference head again encounters the start of the reference track, the spacing between the first transition and the final transition is correct (i.e., the phase of the reference pattern at 0 ° and 360 ° is properly Reference tracks are read to see if they match. When used in conjunction with the recording of clock tracks, this process is often referred to as checking for track closure. If the phase pattern is properly matched and there is a desired number of transitions (usually checked by a counter), then an acceptable reference track is recorded. If no acceptable reference track is recorded, the whole process is repeated until another test reference track is recorded and checked and an acceptable reference track is obtained.

In principle, the transition frequency for each reference track can be adjusted for the lack of closure in the preceding reference track record, but in practice it remains even if the disc's rotational speed changes slightly between the records of the test reference track. do. Alternatively, a crystal controlled oscillator having a fixed frequency can be used for the test reference track, with a discrepancy in the disc rotational speed generating a slightly different reference track for each test. Within a short time, one of these tracks will represent an acceptable reference track. Such Monte Carlo approaches to clock tracks are known in the art (see, eg, US Pat. No. 4,131,920, 'Regenerated Clock Technoque for Servo-Track Writers') and typically take only a few seconds per disc.

Typically, the desired reference pattern may be generated from a ROM located in the reference pattern generation board 134. However, in some cases, if a different reference pattern is desired, the pattern into the pattern RAM 141 communicating with the pattern generation board 134 via the module 142 may be a pattern. You can put The reference track will be used to control the recording of the clock track transition.

In one embodiment, the transition frequency of the desired clock track matches the transition frequency of the reference track. In this configuration, the transition frequency is selected such that the Kerr system's diffraction limit optics used to focus the locklock track can focus on the beat of the clock track. Since electronics on commercially available disk drives often operate at about 1 MHz, a 1 MHz clock signal has been found to be appropriate. Also, a clock of 1 MHz can be read by the system by making the length of the clock track long enough. The lens will focus the readout laser beam typically at a spot size of 1 to 100 microns, although higher frequency (e.g. visible light) lasers allow for smaller spot sizes. Bit sizes of less than 7 microns in general will produce spot sizes that transcend the bit boundaries and possibly overlap with other bits. Spot sizes larger than the bit size greatly reduce the signal-to-noise ratio and increase the probability of error. In a preferred embodiment, the spot size is adjusted to the bit size so that most of the energy is put into the fundamental frequency of the clock signal. The bit length produced by the clock signal at 1 MHz is about 10 microns long, suitable for a spot size of 7 microns typically used in large effect detection. Proper closure of the reference track is monitored by the electronics of the pattern inspection board 142.

After the reference track is recorded by the reference head 122, the clock track is recorded by the clock head 124. Clockhead 124 records the clock track using the output of reference head 122 as a guide. Thus, in one embodiment, the clockhead transition is timed to coincide with the reference track transition to produce a clock track that is substantially similar to the reference track at different predetermined radii. The transition may be offset because the reference head offsets from the clock head. Since the ultra-fast clock track is desired, the clock head 124 is moved radially across the disk 112 by a distance less than the width of the clock head 124, and the process of recording the clock track is repeated. Thus, each recording of a clock track is made at a different radius, but the edges of different recordings of a single clock track match or overlap. Matching the time of the transition of the clock track by the reference track transition ensures that the transitions of the different clock regions are properly aligned. Therefore, the process of recording the area of the clock track using the reference track as a guide is repeated at a radius between, and each repetition increases the width of the clock track. The process is repeated until the clock track reaches the desired width, and when the desired track is reached the reference track can be erased or ignored for later purposes.

In one embodiment, the position of the clock writehead is monitored with a laser position transducer using an array of interferometers and comprising a laser 144. Laser 144 emits a light beam passing through beam splitter 146. A portion of the beam reflected from the beam splitter 146 enters the reference mirror 148, passes through the beam splitter 146, and is reflected from the mirror 150 to enter the light receiving unit 152. The second portion of the original beam from laser 144 passes through beam splitter 146 and is reflected from mirror 154 coupled to clockhead 124. The beam transmitted through the beam splitter 146 is reflected from the mirror 154 and returns to the beam splitter 146 where it is reflected from the beam splitter 146 and refracted by the mirror 150 to enter the light receiving unit 152. The poor light beam generates an interference pattern, which is detected by the light receiving unit 152. The light receiving unit 152 sends the detected interference pattern to the laser electronics 156, and the laser electronics process the information to determine the position of the clock head 124. The output of the laser electronics 156 is sent to the servo board 158, which uses it to control the DC servo drive motor 160. The DC servo drive motor 160 moves the assembly 162 coupled to the clock head 124 and the mirror 154.

Using the system described above, a clock track having a width of several hundred microns can be generated using a standard clock writehead. By varying the number of times the clockhead reads the reference track and writes tracks that overlap or are adjacent to previously recorded clock tracks, the exact width can be easily varied.

Although the embodiment described above is a preferred embodiment, other methods of recording clock tracks may also be used. One such method is to meet the ultra-wide clockhead by avoiding the need for the disk to rotate several times to record a wide clock track.

The second embodiment utilizes laser writing on an external disk or an internal disk in a texture zone located outside of the area where data is typically written. Various reference surfaces can be used for excretion of the clock track. The only requirement for the location where the clock track is written is that the clock track must remain stationary with respect to the rotating disk. In one embodiment, the clock track is written on the hub of the disk drive. Since disk hubs are uniform in size and inexpensive, recording clock tracks on a hub allows a large number of different types of disks to be recorded using standard processes.

To record the clock tracks, laser ablation can be performed at any convenient stage of disc manufacturing, including the process of forming the disc substrate. Another technique for recording clock tracks is to use lithography. In lithographic techniques, a photoresist mask including a written clock track is applied to a substrate. Illumination light is then irradiated onto the mask and clock marks are exposed on the photoresist cover substrate. Next, the clock display is etched into the substrate. This technique is widely developed for silicon wafer processing. The obtained clock track can be read by detecting the amount of light reflected from the read laser.

Other methods of recording clock tracks on reference surfaces may be more suitable for mass production techniques. For example, the clock track is stamped onto a fixed surface with respect to the rotating disk. This technique can be realized by making a master disk and then stamping the reference surface. The technique used for stamping has been developed for mass production of compact discs and is suitable for mass production of clock tracks. Stamping and lithography also rule out the need for a Monte Carlo approach to clock track recording.

FIG. 2 is a plan view of a typical pattern of tracks on a magnetic disk, as recorded by the clock recorder and verifier 100 embodiment shown in FIG. The disc 200 rotates on the spindle 204 while the magnetic reference head 208 records the reference track 212. The reference track includes a number of transitions 214 and 216. These transitions run along the periphery of reference track 212, and in properly closed tracks, all transitions 214, 216 on reference track 212 are evenly arranged. After reference track 212 is written, reference head 208 is used to read the reference track 212 and provide a reference signal for clockhead 220.

Clockhead 220 is used to record clocktrack 224. Reading of transitions 214 and 216 by reference head 208 is used to determine the timing at which transitions 228 and 232 should be written on clock track 224. Clockhead 220 is narrower than the desired width of clocktrack 224. Thus, multiple writes are needed while clockhead 220 moves radially across disk 200 to generate the entire clock track. In the first rotation of the disc, the first part 236 of the clock track is recorded. Clockhead 220 then moves radially across disk 200, where a second portion 240 of clocktrack 224 is recorded in the second path. The recording from the first path that produces the first portion 236 of the clock track 224 and the recording from the second path that produces the second portion 240 of the clock track 224 overlap or overlap each other to form the first portion 236 of the clock track 224. There is no space between and second portion 240. This process is repeated for additional parts of the clock track until the entire clock track width is recorded. In a typical system, recording the full width of clocktrack 224 may take hundreds of revolutions of the disk or pass through clockhead 220. After clock track 224 is written, reference track 212 may no longer be needed and may be erased or deleted.

After the recording of the clock track is pigmented, the disc is inserted into the disc drive. 3 is a schematic diagram showing main components of the disc drive 300. Drive 300 includes a disk stack 304 comprising a data storage disk 308 coaxially mounted on a shaft 312 using a hub and clamp 316. The shaft is rotated by an electric motor in a hub (not shown). Each data storage surface has a respective transducer head 320 supported by an arm 324 attached to an actuator 328. The actuator is rotated by the coil 331 and the voice coil motor magnet 332 to move the head radially across the disk surface in unison. The present invention is applicable to a disk drive having a linear or radial actuator. In order to prevent contamination of the disk surface, the disk stack is contained in a sealed unit together with the actuator and the attached head, which is called a head disk assembly (HDA). The HDA housing consists of an outer shell 336 and a mating cover 340 thereof which support the disk spindle at both ends to impart structural rigidity to the disk drive. The HDA cover has a transparent window at 344, which is arranged to observe the circular clock track of one of the disks, which will be described in more detail below. Other features typically included in HDA housings, such as for example through filters, are not shown. The HDA is shock mounted in the casing 348, and the casing is also provided with most of the electronic components associated with the disk drive.

The movement of the actuator 328 (and thus the head 320) is controlled by the servo system utilizing the servo information recorded on one or more disc surfaces.

4 shows a simplified form of sector servo information recorded on one surface of the disk 400 (note that the present invention can be equally applied to a dedicated servo system). The clock track 404 recorded by the embodiment of the clock recorder 100 of FIG. 1 includes a transition 408 indicating a change in magnetic polarity on the clock track. The remainder of the disk surface is divided between the inner and outer diameters up to a series of concentric tracks 412 (representing only a few tracks for clarity only). These tracks are circumferentially divided up to sector 416 available for data storage, alternating with sector 420 information, as is known in the art. The inner and outer servo guard bands 424 and 428, respectively, are not used for data storage but represent the limits of the data recording band of the disc. On each disk surface there is a similar arrangement of servo information.

Clocktrack 404 is recorded before installing the disc in the HDA unit. The remainder of the servo pattern shown in Fig. 2 is recorded after the disc is installed in the HDA unit. The clock track 404 is used as a guide for recording other disc information. According to a preferred embodiment of the present invention, this includes the writing of the servo track and the reading of the clock track through the window 344 simultaneously, at different radii. This is achieved by providing the timing information for transducer head 320, which magneto-optically reads clocktrack 404 from outside of the HDA via window 344 to record the servo pattern.

Conventional magneto-optical (MO) heads are commercially available for magneto-optical recorders. A typical example is shown in FIG. 5. Such heads are well known in the art and will only be described briefly. The magneto-optic head 500 contains three main components. That is, the diode laser 504, the optics, and the photodiode detector 508 are the same. Light (with a frequency of about 820 nm) passes through the collimating lens 512 and the polarizer 516 and through the beam splitter 520 through the window 344 of the HDA cover 340 by the objective lens 528 before being reflected by the mirror 524 onto the disk surface 532. Focus on.

The objective lens focuses the spot of light on the clock track. A typical spot size using a conventional MO head is about 8 μm, but a spot size of 1 μm can be obtained. Therefore, in order to improve signal-to-noise, a clock track that is wider than the spot size is desirable. In addition, since the spindle used in HDA to record servo tracks is different from the spindle used in clock recording unit 100, the clock can form a slightly elliptical path during rotation and is wider to compensate for slightly eccentric rotation. Requires a clock track.

The light reflected from the clock track returns to the beam splitter 520 where it travels through the linearizing phase plate 536 towards the polarizing beam splitter 540, where the beam splitter produces two beams. Each of its beams respectively passes through an asstigmatic or cylindrical lens 544 to reach each photodiode detector 508.

The differential signal from the two photodiodes 508 is used to measure the Kerr rotation of the light reflected from the disk surface and thus to detect the magnetic transition of the clock track. In one embodiment, orthogonal photodiode 508 is used in conjunction with cylindrical lens 544 to monitor the focus of objective 528 on the disk surface, as illustrated in FIG. 6. The asstigmatic or cylindrical lens forms an ellipse on the photodiode if the objective lens is not properly focused. The directionality of the ellipse calculated from the signals (P1 + P3) / (P2 + P4) determines whether the objective lens needs to approach the disk surface or further distance and sends the appropriate command signal to the focus controller 548. . (A circle is created in the quadrature detector when the objective is correctly focused.) Another controller 552 ensures that the mirror is directed exactly to the clock track. More details on MO heads can be found in Magnetic Recording, Vol. 2: Computer Data Storage, Ed. C. Denis Mee and Ed Daniel, 1988. McGraw-Hill (Chapter 6) and references cited therein.

Kerr rotation of the light reflected from the magnetization medium is shown in simplified form in FIG. 7. Substrate 700 is coated with a magnetic layer that can be magnetized in two different directions 704 and 708. The linearly polarized light beams A, B and C enter the magnetic layer and are reflected to cause their polarization planes to rotate in one direction and beam B in the opposite direction as shown (in the propagation of light). The polarization plane is always substantially orthogonal to the direction of the beam; however, Figure 7 uses a somewhat distorted geometry to represent the cross section through the beam). The measurement of the change in linearly polarized light thus provides information about the magnetization direction on the disc.

As can be seen in Fig. 7, the polarker effect is used when the direction of magnetization is perpendicular or perpendicular to the disk surface. Most typical disk drives utilize either longitudinal or transverse Kerr effects when horizontal magnetization (ie parallel to the disk surface) is used. In this second case, a simple normal incidence will be reflected without large rotation, and therefore cannot be used for the MO readout beam (except for transitions between oppositely magnetized segments). Therefore, in practice, the apparatus shown in Fig. 5 should be suitable for a servo recording disk drive using horizontal magnetic recording.

5B illustrates a suitable modification of the MO head of FIG. 5A for use in the present invention. Essentially, the laser beam has been narrowed and moved upward so that only one side of the objective lens 528 is illuminated. This beam naturally slopes in the normal direction of incidence and will therefore be sensitive to Kerr effects. Some components of FIG. 5A (eg, photo detector 508) have been simply rearranged to center the beam through them. It should be appreciated that the beam splitter 520 is strictly no longer needed and can be replaced by a simple mirror in the path of the beam reflected from the disk. The size of the objective lens should be increased to obtain a sufficiently large angle of incidence (the value of the required angle of incidence relates to the read back signal to noise ratio). The difference between the MO heads of FIG. 5A and the MO heads of FIG. 5B will add to the latter cost, but only one such head is needed for servo recording of many disk drives.

Those skilled in the art will appreciate that the optical arrangement shown in FIG. 5B is only one of many possible alternatives. An alternative embodiment is to separate the input and output optics, where only the incident beam is reflected at the tracking mirror 524 and focused by the objective lens 528. The reflected light then proceeds to a separate optical set that requires some collimation before sending the reflected signal onto a detector similar to the detector of FIG. 5B. This approach will increase the angle of incidence, but requires a more complex device since the objective lens and its focusing system 548 as shown in FIG. 5B must be effectively excreted. Also, making the paths of the incident and reflected beams as similar as possible in FIG. 5B has the advantage of simplicity and will minimize the distortion caused by the paths of different light passing through the HDA window, for example. The MO head of FIG. 5B is used to provide a signal representing transition 408 along clock track 404 in accordance with the method of the present invention.

The Kerr effect described above is one of several possible ways of reading the written clock track. The second method of reading the clock track utilizes laser intensity read back. In laser intensity reverse reading, the physical deformation of the medium or hub itself is detected by a change in reflected or scattered light intensity. The intensity of the reflected light indicates to the detector whether the reading of the clock track has been completed. Bright or dark field detection can be utilized, but bright field detection provides the simplest and most suitable signal-to-noise ratio. Laser intensity back read is particularly useful for reading clock tracks recorded by techniques that result in physical deformation of the medium. Such techniques include lithography, stamping and laser writing.

Kerr reading and laser intensity reverse reading method both require focusing small light spots on the clock track. In particular, the clock track should be less than 1 bit of the trolltrack, so the spot size should typically be less than 10 microns. Such small spot size makes focusing difficult, especially through the window of the head disc assembly. Laser diffraction reader techniques allow the use of larger spot sizes. In particular, a spot size covering several transitions can be used. Since the clock cycle is periodic, the clock track acts as a diffraction grating for the point of incidence. The light reflected from the spot produces a diffraction peak. By analyzing the time-dependent nature of the higher diffraction peaks using an intensity detector, a clock signal can be obtained that servo writes the remainder of the disc.

The periodic nature of the clock also allows the use of higher harmonics in various clock reading techniques.

Conventionally, the detected fundamental frequency is multiplied by a multiplier factor generated by the phase-locked loop multiplier circuit to produce a higher frequency suitable for the clock signal. Large multipliers reduce the accuracy of the clock signal. Thus, by using harmonics instead of the base of the detected clock tracks, multipliers can be reduced and enable more accurate cleat signals. In such a system, the spot size is preferably formed as small as possible with respect to the bit size in order to produce higher harmonics of higher amplitude.

Finally, the clock signal is designed to be generated without recording the clock track. In this method of generating a clock signal, the detection and measurement of repeatable runout provides a rotation and synchronization signal of the disc. The measured runout is a change in the periodic disk height, typically the warpage of the disk caused by clamping of the disk hub or other structural manufacturing defects. Since non-periodic effects, such as wobbling of the disc, should not be input into the analysis and should be considered noise, the system should be designed to detect only periodic disc deflection. Periodic signals due to disk deflection and other effects are detected by various techniques, including the change in the capacitance of the disk relative to the head sensor, the method of detecting the displacement of the disk drive head, or other electronic or magnetic Techniques include, but are not limited to. Optical techniques can also be used to detect periodic runout of the rotating medium. One example of such an optical technique is to use an interferometer to detect the distance from the disk to a fixed point on the disk. In order to derive a high frequency clock signal, it is desirable that the repeatable runout of the rotating medium has a high harmonic content. Otherwise, a multiplier will be needed to generate the proper clock signal.

Regardless of the method used to read the clock track or generate the clock signal, the clock signal controls the transducer head (s) 320 to write servo patterns at different radii in the sealed head disk assembly. This is repeated until the entire disk drive is servo written with the product head at various different radii. One technique for obtaining a high-precision servo pattern (see US Pat. No. 4,068,268, for example) is to move the product head less than one full width between recordings of adjacent tracks (i.e., to fix many of the preceding tracks). Overwriting). The present invention is equally applicable whether the servo pattern is a simple servo or a dedicated servo. In the former case this process will generally be repeated every disk surface (since only one surface can be written by the product head at any given time).

It is necessary to keep the product head at a constant radius while recording the servo pattern. In the present invention, this involves monitoring the position of the actuator from the outside of the HDA. Suitable techniques are generally based on laser interferometry and include optical reflection of light from the actuator. For example, the plane mirror may be attached to the linear actuator so as to be orthogonal to the direction of movement of the actuator. At this time, the position of the actuator is measured using a laser beam from outside of the HDA moving parallel to the direction of movement of the actuator, and the beam is reflected from the HDA to the mirror through the window 344 toward the interferometer. Similar techniques may be used with the rotary actuator, where a corner cube mirror should be used to ensure that the reflected laser beam exits the HDA through the same window in which it is incident. Various other methods are also disclosed in the literature: for example, European Patent Application No. 91111003.9 (YO9-90-013) or IBM TDB Vol. See 33-11, p. 428, Head Positioning to Servowrite Magnetic Disk Files.

In the present invention, the most convenient arrangement is to record the clock track on the top or bottom disk surface and read the clock track using the Kerr effect. In this case, a window in the HDA can be placed directly above or just below (as appropriate) the clock track, so that the MO head has immediate access to the disc surface. The window may be made of glass, perspex or other suitable transparent material. In order to avoid acoustic problems or loss of stiffness, which typically occurs in aluminum castings, and to prevent leakage into or out of the HDA, care must be taken to couple the window 344 to the interior of the HDA housing 340, but this difficulty is conventional. It is not greater than the difficulty that must be overcome to enclose the vent filter.

The magneto-optical head as in FIG. 5A can be purchased as a complete unit

It is designed to operate with a track pitch of μm. In contrast, magnetic hard disk drives use a track pitch of about 10μm. The length of bits used in the two systems is about 1 to 2 [mu] m, which is similar, and the recent magnetic hard disks have optical characteristics that provide a high degree of reflectivity. In addition, the two systems use materials with high coercivity for the magnetic layer on the disk, whereby the magnetic field strengths are comparable. Thus, one embodiment of the present invention can be easily implemented by simply adapting the conventional MO head.

The invention described herein can be designed in many different ways and using many different configurations. While the invention has been described in terms of various embodiments, other embodiments may occur to those skilled in the art without departing from the spirit and scope of the invention. Therefore, the present invention should be evaluated by the following claims.

As described above, the present invention can achieve an improved method and apparatus for servo writing to a disc.

Claims (32)

Recording a clock track on a magnetic storage disk external to the head disk assembly; Positioning a magnetic storage disk in the head disk assembly and sealing the substantially sealed housing; Reading a clock track to obtain a clock signal by measuring polarization of light reflected from the surface of a magnetic storage disk through a window in the head disk assembly; Recording a servo track based on the clock signal; And servo recording the magnetic storage disk in a head disk assembly having a substantially sealed housing. The method of claim 1, wherein the clock track has a width greater than 1 micron. The method of claim 1, wherein recording of the servotrack is performed by at least one transducer inside the head disk assembly. 2. The method of claim 1, further comprising using an assay unit to assay the magnetic storage disk and performing recording of the clock track on the assay unit. 5. The method of claim 4, wherein the assay unit for assaying a magnetic storage disk records a reference track using a closure technique. 5. The method according to claim 4, wherein said verification unit for validating a data storage disk records clock tracks using a staged technique. The method of claim 1, wherein the clock track is recorded such that the magnetization direction of the clock track is parallel to the surface of the magnetic storage disk. The method of claim 1, wherein recording the clock track Recording a reference track on the magnetic storage disk using the reference head; Reading a reference track on the disc and outputting transition information using the reference head; Using the transition information as a guide, recording a first portion of a clock track in which the first portion of the clock track forms a first complete ring around the spindle; Using the transition information as a guide, recording a second portion of the clock track in contact with the first portion, forming a second complete ring around the spindle, How to include more. A substantially sealed housing containing a transparent window and containing a magnetic disk recorded with a clock track of width greater than 1 micron; An optical magnetic head positioned outside of the sealed housing and adjacent to the transparent window and configured to read a clock track by generating a light beam and measuring the polarization of the light beam reflected from the clock track through the transparent window; A magnetic transducer head located within the sealed housing and configured to record the servo track in response to reading the optical magnetic head of the clock track, System for servo recording of a magnetic disk comprising a. 10. The system of claim 9, wherein the clock track is located on the outermost surface of the disk and adjacent to the transparent window. 10. The system of claim 9, wherein the optical magnetic head includes a beam splitter and at least two photodiode detectors that receive light reflected from the surface of the magnetic disk. 12. The system of claim 11, wherein the outputs of each of the at least two photodiode detectors combine to produce a differential signal. 13. The system of claim 12, wherein the clock track is magnetized in a vertical direction perpendicular to the surface of the magnetic disk. A magnetic disk for use in a sealed head disk assembly, A clock track recorded on the magnetic disk and having a width exceeding 1 micron; And a servo track recorded on the magnetic disk and recorded using a clock track as a guide. The magnetic disk of claim 10 wherein the width of the clock track is less than 100 microns. Recording the reference track using the reference head, Generating reference data by reading the reference track using the reference head; Using the reference data as a guide to record the first portion of the clock track such that the first portion forms a ring around the spindle; Using the reference data as a guide to record a second portion of the clock track such that a second portion forms a ring around the spindle, Method of recording a wide clock track comprising a. 17. The method of claim 16, wherein the first portion of the clock track is recorded on the first rotation of the disk and the second portion is recorded on the subsequent rotation of the disk. The method of claim 16 wherein said first portion and said second portion overlap. 17. The method of claim 16, wherein the first portion and the second portion are contiguous and form a single comprehensive clock track. 17. The method of claim 16, wherein an additional portion of the clock track is recorded upon further rotation of the disc. 17. The method of claim 16, further comprising deleting the reference track after the clock track is complete. 17. The method of claim 16, further comprising recording a servotrack using the clocktrack as a guide. A magnetic disk including an area for storing magnetic data, A clock track recorded on a hub coupled to the area storing magnetic data; System for servo recording of a magnetic disk comprising a. 24. The system of claim 23, wherein the system further comprises a substantially sealed housing that houses the magnetic disk. Recording a clock track on a reference surface that remains fixed relative to the rotating disk; Sealing the reference surface in the substantially sealed head disk assembly including the clock track and the rotating disk; Reading the clock track to generate a clock signal used to control a servo write head for servo recording the rotating disk; Method for servo recording of a rotating disk comprising a. 27. The method of claim 25, wherein said reading of said clock track is performed by measuring the intensity of light reflected from said clock track. 27. The method of claim 25, wherein the writing of the clock track is by stamping the clock track on the reference surface. 27. The method of claim 25, wherein the recording of the clock track is made using lithographic technique. 27. The method of claim 25, wherein said reading of said clock track is made by measuring the intensity of light reflected from said clock track. Rotating the disc, Measuring repeatable disc runout, Recording a servo track using a clock signal generated from repeatable disc runout as a reference, And servo recording the disc without a clock track. 33. The method of claim 30, using an interferometer to measure repeatable disc runout. 33. The method of claim 30, wherein the repeatable disc runout is bending of the disc.