Abstract:
A method of positioning a selected recording channel on a recording head relative to an optical servo system includes positioning the optical servo system at a first position relative to the selected recording, processing an alignment tape to determine a lateral offset between the optical servo system and the selected recording channel and positioning the optical servo system at a second position relative to the selected recording channel using the lateral offset. An alignment tape is also provided, which includes an elongated continuous web of flexible plastic substrate material having two edges and defining a front major surface and a back major surface, a magnetic storage medium formed on the front major surface, an inert medium formed on the back major surface and a track of alignment voids for indicating actual lateral displacement of the selected recording channel relative to the optical servo system.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to optical to magnetic alignment in a magnetic tape recording system, and more particularly to a magnetic tape recording system utilizing a laser-guided magnetic recording (LGMR) optical servo system.  
         BACKGROUND  
         [0002]    To increase data storage and retrieval performance, many digital linear magnetic tape recording systems utilize multi-head, multi-channel fixed head structures with narrowed recording gaps and track widths so that many linear data tracks may be achieved on a tape medium of predetermined width. Reliable verification of data is implemented using heads capable of “read while write.” Tape substrates are also being made thinner with increased tape lengths in small diameter packages.  
           [0003]    Head positioning optical servo systems are employed to position a read and/or write head in a magnetic tape system over a selected track of data; these systems are generally referred to as laser-guided magnetic recording (LGMR) systems. Misalignment between the read/write head and the data track may cause data errors during read back and data loss on adjacent tracks during writing.  
           [0004]    To ensure a working head positioning optical servo system (including read while write) and also magnetic tape cartridge interchange capability the optical servo system should be aligned with the magnetic read/write head during its manufacture and prior to shipment to an end-user.  
         SUMMARY  
         [0005]    In a general aspect, the invention features a method of positioning a selected recording channel on a recording head relative to an optical servo system in a read/write assembly including positioning the optical servo system at a first position relative to the selected recording channel in the read/write assembly, processing an alignment tape in the read/write assembly to determine a lateral offset between the optical servo system and the selected recording channel, and positioning the optical servo system at a second position relative to the selected recording channel using the lateral offset.  
           [0006]    In a preferred embodiment, the alignment tape includes a track of longitudinal equally spaced apart alignment voids. Processing includes writing a track of data to the alignment tape over the track of alignment voids, imaging a section of the alignment tape to determine a lateral distance between a center of the track of alignment voids and a center of the track of data, and setting the lateral offset to the lateral distance. Imaging includes placing the section of alignment tape under a Magnetic Force microscope or placing the section of alignment tape under an optical microscope using ferrofluid. The lateral distance is measured in micrometers (μm). The second position is laterally upward from the first position if the lateral offset is a negative number and laterally downward from the first position if the lateral offset is a positive number. Imaging may further include determining an average lateral distance between several alignment voids and the track of data, and setting the lateral offset to the average lateral distance.  
           [0007]    Alternatively, processing includes writing and subsequently reading a track of data to a front major surface of the alignment tape on the track of alignment voids with a write head and a read head of the selected recording channel, monitoring a bit-error ratio (BER) from reading the track of data, and correlating the bit-error ratio (BER) to the lateral offset. Correlating includes relating a maximum BER to the lateral offset. A negative lateral offset value indicates the optical servo system is laterally above the selected recording channel and a positive lateral offset indicates the optical servo system is laterally below the selected recording channel. The BER represents a number of erroneous data bits read divided by the total number of data bits written.  
           [0008]    Alternatively, processing includes providing a plurality of longitudinally arranged equally spaced apart alignment void tracks on the alignment tape, moving the recording head across the tracks in a motion perpendicular to a motion of the alignment tape, writing and reading a magnetic signal to the alignment tape by the selected recording channel at a higher frequency than the frequency of alignment voids moving past the selected recording channel to determine an amplitude demodulated magnetic signal, directing a beam of light by the optical servo system to the alignment tape to determine an optical signal, and determining a timing difference between the envelope of the demodulated magnetic signal and the envelope of the optical signal. Determining may include the timing difference between a peak in the envelope of the demodulated magnetic signal and a peak in the envelope of the optical signal. Determining may include calibrating the timing difference using the velocity measured from the timing difference between peaks in the envelope of the optical signal. Determining may include the cross-correlation function to find the timing difference between the envelope of the demodulated magnetic signal and the envelope of the optical signal. The velocity is determined from the separation of peaks in the cross-correlation function. The lateral offset is set equal to the timing difference divided by the velocity.  
           [0009]    Alternatively, processing includes providing a plurality of longitudinally arranged equally spaced apart alignment void tracks on the alignment tape, moving the recording head across the tracks in a motion perpendicular to a motion of the alignment tape, directing multiple beams of light by the optical servo system to the alignment tape to determine a number of optical signals, and determining a timing difference between the envelope of one optical signal and the envelope of another optical signal. The optics are rotated to bring the timing difference divided by the velocity to a desired value. Determining may include the cross-correlation function to find the timing difference between the envelope of one optical signal and the envelope of another optical signal.  
           [0010]    The alignment tape includes longitudinal tracks on a second major surface of the tape, and recording channel positioning alignment voids. Processing includes suspending the alignment tape in a coupon, positioning the alignment tape with the coupon over a recording channel pair to position a line from one element of a channel pair to another, and positioning the optical servo system such that one generated optical spot is centered on a middle one of the longitudinal tracks and other generated optical spots are offset by a desired amount. Passing the tape through a laser system generates the tracks. Positioning includes viewing the alignment tape under a microscope, and adjusting the alignment tape&#39;s position with a precision translation and rotation stage attached to the coupon.  
           [0011]    In another aspect, the invention features an alignment tape for positioning a selected recording channel of a recording head relative to an optical servo system in a read/write assembly including an elongated continuous web of flexible plastic substrate material having two edges and defining a front major surface and a back major surface, a magnetic storage medium formed on the front major surface, an inert medium formed on the back major surface, and a track of alignment voids for indicating actual lateral displacement of the selected recording channel relative to the optical servo system.  
           [0012]    In a preferred embodiment, the track of alignment voids is formed by ablation by a pulsating laser beam of sufficient power to penetrate the back major surface through to the front major surface leaving visible the flexible plastic substrate of the alignment tape.  
           [0013]    In another aspect, the invention features a method of positioning a selected recording channel on a recording head relative to an optical servo system including fixedly positioning the optical servo system at a position relative to the selected recording channel, processing an alignment tape to determine a lateral offset between the optical servo system and the selected recording channel and storing the lateral offset.  
           [0014]    In a preferred embodiment, the method further includes aligning a data track with the selected recording channel using optical servo system and the stored lateral offset during tape travel across the selected recording channel.  
           [0015]    Embodiments of the invention may have one or more of the following advantages.  
           [0016]    A check of optical alignment both before and after tape drive assembly may be implemented and can be made without disassembly of a completed tape drive. Optical alignment is done rapidly in a manufacturing environment and insures tape interchange between diverse tape drive assemblies by closely aligning the optical servo system to a recording channel, and by providing a measure of residual misalignment, enabling compensation techniques to be implemented.  
           [0017]    The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
       
    
    
     DESCRIPTION OF DRAWINGS  
       [0018]    [0018]FIG. 1 is a block diagram of an exemplary magnetic tape recording system.  
         [0019]    [0019]FIG. 2 is a schematic diagram of a cross section of the read/write assembly of FIG. 1.  
         [0020]    [0020]FIG. 3 is a schematic diagram of an exemplary alignment tape.  
         [0021]    [0021]FIG. 4 is a block diagram of an exemplary optical servo writer system.  
         [0022]    [0022]FIG. 5 is a block diagram of an exemplary microscope.  
         [0023]    [0023]FIG. 6A is an illustration of a first exemplary image of the alignment tape under a microscope.  
         [0024]    [0024]FIG. 6B is an illustration of a second exemplary image of the alignment tape under a microscope.  
         [0025]    [0025]FIG. 7 is an exemplary graph of track offset verses bit-error ratio (BER).  
         [0026]    [0026]FIG. 8 is a schematic diagram of a second exemplary alignment tape.  
         [0027]    [0027]FIG. 9 is an exemplary graph of optical and magnetic signal envelopes.  
         [0028]    [0028]FIG. 10 is an illustration of an alignment tape used in conjunction with a positioning coupon. 
     
    
       [0029]    Like reference symbols in the various drawings indicate like elements.  
       DETAILED DESCRIPTION  
       [0030]    Referring to FIG. 1, an exemplary magnetic tape recording system  10  includes a delivery system  12 , a read/write assembly  14  and a pickup system  16 . The delivery system  12  houses a magnetic tape  18 . The magnetic tape  18  travels past a recording head  20  and an optical servo system  22  contained in the read/write assembly  14  and is delivered to the reel pickup system  16 . The recording head  20  reads and writes information, generally referred to as data, onto one or more data tracks on the magnetic tape  18  as it travels from the delivery system  12  to the pickup system  16 . As the magnetic tape  18  passes over the recording head  20  the magnetic tape  18  may become misaligned with respect to the intended track position due to, for example, lateral tape motion (LTM). Changes in lateral tape position can be detected by the optical servo system  22  in conjunction with optical servo tracks located on the tape  18  and compensated for via a closed servo control loop, described below.  
         [0031]    Referring to FIG. 2, the read/write assembly  14  includes the recording head  20  and the optical servo system  22 . An actuator  24  is shown connected to the read/write assembly  14 . In operation, the magnetic tape  18  moves across the recording head  20  and a set of data tracks (not shown) are written or read from the tape  18 . In one example, the read/write assembly  14  includes a series of recording channels  26 ,  28 ,  30  and  32  residing on the recording head  20 , thus writing four tracks simultaneously on the tape  18 . Four read heads about 0.1 inches downstream (not shown) immediately read and verify the data just written. The optical servo system  22  utilizes one or more optical servo tracks on a second major surface  34  of the magnetic tape  18  to detect lateral tape motion (LTM) of the magnetic tape  18  along an axis  36 . Compensation of LTM is done by positioning the read/write assembly  14  relative to the tape  18  via movement of the actuator  24 . Specifically, the optical servo system  22  directs a beam of light upon a particular one of the optical servo tracks located on the second major surface  34  of the tape  18 . Reflections of the beam of light from the optical servo track result in electronically discernible LTM position error signals. The resultant position error signals are sent to an optical feedback control loop that generates a bi-directional head position correction sending current to a coil motor that results in a servo bias torque. The bias torque is applied to the actuator  24  to pivot the read/write assembly  14  along the axis  36  relative to the tape  18  and thereby follow the tape  18  despite the presence of LTM.  
         [0032]    As indicated above, LTM is an undesirable motion of the tape  18  in a lateral direction along the axis  36  that is transverse to the tape direction. LTM may be caused by many factors including tape slitting variations, tension variations, imperfections in the guiding mechanism, friction variations in the recording head  20 , and environmental factors such as heat and humidity. These factors affect LTM in various ways. Some cause abrupt momentary jumps along the axis  36  while others may cause a slower variation of tape position along the axis  36 . Generally, LTM is unpredictable and unrepeatable and is compensated for by using the optical servo system  22 .  
         [0033]    During manufacture of the read/write assembly  14 , the optical servo system  22  is aligned to one of the recording channels  26 ,  28 ,  30 ,  32 , recording channel  30  for example, using a special alignment tape. The alignment tape provides an offset between the optical servo system  22  and the recording channel  30  that is used to align or position the two before the read/write assembly  14  is shipped to customers. During the manufacture of the read/write assembly  14 , the recording head  20 , and more specifically, one of the recording channels  26 ,  28 ,  30 ,  32 , is aligned with the optics contained in the optical servo system  22 . Without this alignment of a recording channel and the optics, interchange of tapes during operation may be affected. Specifically, if an offset between a recording channel and the optics of the optical servo system in a first read/write assembly is large in one direction along the axis  36 , and an offset between a recording channel and the optics of the optical servo system in a second read/write assembly is large in an opposite direction along the axis  36 , read/write errors will occur when the first read/write assembly writes data to a tape and the second read/write assembly attempts to read the data from the tape. This results because the overall offset of the data from the recording channel will be so great so as to prevent the read/write assembly from moving along the axis  36  to compensate for the offset and thus be aligned properly to the data so that the data can be read. This is referred to as tape interchangeability. The ability of the reading drive to compensate for overall offset introduced on a tape by the writing drive is limited by the finite number of optical servo tracks on major surface  34  of the tape  18 . This limit, caused by the fact that the optical servo system  22  must remain within sight of the optical servo tracks, also limits the ability of a writing drive to compensate for its own known offset. Thus, utilizing the offset gained from using the alignment tape during the manufacture of the read/write assembly  14 , an adjuster  38  can manually move and lock into position the optical servo system  22  relative to the magnetic reading head  20 , minimizing the offsets that must be compensated while in service. The adjuster  38  moves the optical servo system  22  in a direction parallel to the axis  36 . It is worth noting that after final movement of the adjuster  38 , any remaining offset can be measured and stored in the tape system  10 . The tape system  10  could then compensate for this stored offset during writing of data by moving the recording head  20  according to the stored offset to ensure that data tracks are written without such a residual offset.  
         [0034]    Referring to FIG. 3, an alignment tape  50  includes a track of special marks referred as alignment voids  52 . The term void as used herein refers to a location of the alignment tape  50  in which the magnetic material on a first major surface of the alignment tape  50  is absent and in which the generally inert backing material on a second, opposite, major surface of the alignment tape  50  is absent, leaving only an area of exposed base film. Specifically the alignment voids  52  are a series of longitudinally arranged, equally spaced, spots of exposed base film. In operation, the track of alignment voids  52  is utilized during manufacturing of the read/write assembly  14  to align, as mentioned above, the optical servo system  22  with one of the recording channels  26 ,  28 ,  30  or  32 .  
         [0035]    Referring to FIG. 4, an exemplary laser system  60  for producing a track of alignment voids  52  includes a laser source  62 , a servo writer optics system  64  and a lens  66 . The laser source  62  generates a beam of collimated light  68 . In a preferred embodiment, the light  68  is in the ultraviolet (UV) range of the spectrum. The collimated light  68  enters the optics system  64  where it generates a focused beam  70 . The focused beam  70  is passed through the lens  66  and directed on to the alignment tape  50 . Upon hitting the alignment tape  50 , the focused beam  70  removes pieces of inert backing material from the second major surface of the alignment tape  50  and magnetic material from the first major surface of the alignment tape  50 , leaving a track of alignment voids  52 . In operation, the laser source  62  is pulsed at such a frequency to result in generating a longitudinally arranged equally spaced apart track of alignment voids  52 . More specifically, a combination of high power and short wavelength, for example, 31 milliwatts with a wavelength of 355 nanometers, of the focused beam  70  penetrates both the first major surface and the second major surface of the alignment tape  50 . A polyethylene terephthalate (PET) base film of the alignment tape  50  is transparent to UV light  68  of the laser source  62 . Thus, the focused beam  70  penetrates into the first major surface and the second, opposite, major surface of the alignment tape  50 , leaving only the base film of the alignment tape  50  where the focused beam  70  hits. By adjustment of the height of the drive moving the alignment tape  50  relative to the height of the laser source  62  and optics  64  and  66 , the track of alignment voids  52  is positioned on the alignment tape  50  at a distance along axis  36  that can match standard optical servo tracks. This ensures that the actuator  24  is able to move the optical servo system  22  into position to see the track of alignment voids  52 .  
         [0036]    There are many ways to use the alignment tape  50  to perform alignment of a selected recording channel with the optical servo system  22  as part of the manufacturing process and prior to shipment of the fully assembled magnetic tape recording system  10  to an end-user.  
         [0037]    In one operation, a selected recording channel is blindly aligned to the optical servo system  22  and manually set in place using the adapter  38 . This initial alignment is blind since there is no practical way to visually align a selected recording channel to the optical servo system  22  with any high degree of accuracy. Only through extremely tedious methods of trial and error might the selected recorded be visually aligned to the optical servo system  22 . The alignment tape  50  is placed in the magnetic tape recoding system  10 . The selected recording channel writes a single linear track of data while the optics detect the track of alignment voids  52 . After the single track of data is written the alignment tape  50  is removed from the magnetic tape recording system  10  and a section of the alignment tape  50  viewed under a microscope, such as exemplary microscope  75  in FIG. 5. Imaging of the section of alignment tape  50  is used in conjunction with the microscope  75 . Example imaging techniques are magnetic force microscopy and optical microscopy using ferrofluids.  
         [0038]    Referring to FIG. 6A, a first exemplary image  100  of the alignment tape  50  after the track of data has been written illustrates a single track of data  80  and the track of alignment voids  52 , as viewed under the microscope  75 . A center  82  of the track of data  80  is not centered relative to a center  84  of the track of alignment voids  52 . A distance  86  between the center  82  of track of data  80  and the center  84  of the track of alignment voids  52  represents an actual lateral offset  86  between the selected recording channel and the optical servo system  22  measured in, for example, micrometers. Recall that before the alignment tape  50  is placed in the magnetic tape recording system  10 , the selected recording channel and the optical servo system  22  are blindly aligned and positioned relative to each other by using the adjuster  38 . The actual lateral offset  86  can be stored for use during system  10  operation or to finely adjust the position of the selected recording channel and the optical servo system  22  by further manual adjustment using the adjuster  38 . The optical servo system  22  can be locked in place relative to the selected recording channel for further processing of the read/write assembly  14  during its manufacture.  
         [0039]    By way of another example, referring to FIG. 6B, a second exemplary image  102  of the alignment tape  50  after the selected recording channel has written the track of data  88  shows a single track of data  88  and the track of alignment voids  52 . A center  90  of the track of alignment voids  52  is also the center of the track of data  88 . Thus, the actual lateral offset is zero and may be stored for use during system  10  operation. This means that the selected recording channel and the optical servo system  22  are aligned and no further adjustment is needed. The read/write assembly  14  is ready for further processing during its manufacture.  
         [0040]    In another example, an actual lateral offset is determined using the alignment tape  50  and a read-after-write process. Here again, initially, the selected recording channel is blindly aligned to the optical servo system  22  and manually positioned and locked using the adjuster  38 . The alignment tape  50  is placed in the magnetic recording system  10 . It should be noted that the optical azimuth in this example needs to be adjusted first. Vertical alignment of the optics to the magnetics may not be necessary, depending on characteristics of the magnetic recording system  10 . It should also be noted that firmware more flexible than is usual in the magnetic recording system  10  would allow for even large initial misalignments to be tolerated but the optical azimuth would have to be correct for the optical servo system  22  to function properly. The selected recording channel writes a single track of data, as illustrated in FIGS. 6A and 6B, to the track of alignment voids  52 . The selected recording channel includes both read and write heads such that as each datum of the track of data is written by a write head of the selected recording channel it is immediately read by a corresponding read head of the selected recording channel. This process is referred to as read-after-write and occurs during a single pass of the alignment tape  52  across the read and write heads of selected recording channel. A Bit-Error Ratio (BER) is monitored as the read head of the selected recording channel reads the track of data. The Bit-Error-Ratio represents the number of erroneous bits divided by the total number of bits transmitted, received, or processed over some stipulated period. Examples of bit error ratios are (a) transmission Bit-Error-Ratio, i.e., the number of erroneous bits received divided by the total number of bits transmitted; and (b) information Bit-Error-Ratio, i.e., the number of erroneous decoded (corrected) bits divided by the total number of decoded (corrected) bits. The BER is usually expressed as a coefficient and a power of 10. A BER of the selected recording channel that is lined up (or nearly lined up) with the optical servo system  22  greatly increases whenever data is written and read directly over the track of alignment voids  52  because data cannot be written where magnetic material on the alignment tape  50  is missing. The BER decreases when the selected recording channel is not on the track of alignment voids  52  because data can be written where the magnetic material on the alignment tape  50  is present.  
         [0041]    Referring to FIG. 7, an exemplary graph  110  of the BER  114  by the selected recording channel versus track offset  112  across two tracks of the alignment tape  50  is illustrated. Here again, prior to the run, the selected recording channel is blindly aligned to the optical servo system  22  and set in place at a first position using the adjuster  38 . The selected recording channel writes a single track of data to the track of alignment voids  52  as the head moves across two tracks of alignment voids. The optics  22  detects the movement across the two tracks. A first peak  116  represents a following of the BER of reads-after-writes by the selected recording channel across the first track, while a second plot  118  represents a following of the BER of reads-after-writes by the selected recording channel across the second track. The known separation of alignment void tracks allows a calibration to be made of the offset distance  112 .  
         [0042]    In the first track  116 , the plot goes through a maximum BER at point  120  and correlates to a track offset of 0 by the selected recording channel. This indicates the selected recording channel is lined up directly on the track of alignment voids  52 , and thus aligned properly with the optical servo system  22 . For the second track by the selected recording channel, the plot  118  goes through a maximum BER at point  122 . Point  122  correlates to a linear track offset of 24 μm, the separation between tracks on the alignment tape. This can be used to calibrate an offset for those cases when the peak  120  is at a non-zero offset. Thus, if in a separate and unique run of the BER  114  versus track offset  112 , the peak  120  occurs at an offset of count  500  and the peak  122  occurs at an offset count of 1500, then that means that the alignment of the selected recording channel and the optical servo system  22  is off by approximately half of 24, or 12 μm and the optical servo system  22  needs to be adjusted 12 μm laterally by the adjuster  38 . Correlation of the maximum BER to a positive lateral offset means the optical servo system  22  has to be moved laterally up relative to the selected recording channel, while correlation of the maximum BER to a negative lateral offset means the optical servo system  22  has to be moved laterally down relative to the selected recording channel. In each case, the adjuster  38  is used to laterally position the optical servo system  22  an amount equal to the lateral offset. Once the optical servo system  22  is adjusted relative to the selected recording channel into a second position using the determined lateral offset, and the read/write assembly  14  is ready for further processing during its manufacture.  
         [0043]    In another example, a scanning head method is utilized in conjunction with the alignment tape  52  and the optical servo system  22  to determine an offset between the selected recording channel and the optical servo system  22 . Referring to FIG. 8, the laser system  60  for producing tracks of alignment voids (of FIG. 4) is used to generate multiple parallel longitudinal tracks of alignment voids  90  on the alignment tape  50 . This is accomplished by having the laser source  62  direct multiple beams of light to the servo optics system  64  and focusing the multiple beams onto the alignment tape  50  to generate the multiple tracks of alignment voids  90 . The laser source  62  is pulsed at such a frequency to result in generating multiple longitudinally equal spaced apart tracks of alignment voids  90 .  
         [0044]    In operation, the selected recording channel is moved slowly across the multiple tracks of alignment voids  90  in a motion perpendicular to the alignment tape  50 . During the perpendicular motion the selected recording channel writes and reads a single frequency magnetic signal on the first major surface of the alignment tape  50 . The amplitude of the magnetic signal detected by the read head on the selected recording channel decreases whenever an alignment void passes across the read head, then the magnetic signal is amplitude modulated. The optical servo system  22  is turned on and an optical spot directed by a laser source in the optical servo system  22  towards and reflected off of the second, opposite, major surface of the alignment tape  50  where an optical signal is detected by an optical sensor in the optical servo system  22 . The demodulated magnetic signal and the optical signal have the same frequencies, corresponding to the rate at which alignment voids, traveling with the alignment tape, move past the recording head  20  and the optical servo system  22 . The selected recording channel and the optical servo system  22  are aligned when the envelope of the demodulated magnetic signal detected by the read head of the selected recording channel and the envelope of optical signal detected by the optical servo system  22  are in phase.  
         [0045]    Referring to FIG. 9, an exemplary graph  130  tracking the envelope of the demodulated magnetic signal  132  and the envelope of the optical signal  134  is illustrated. When the selected recording channel is centered over an alignment void in any one of the tracks of alignment voids  90  the envelope of the demodulated magnetic signal peaks at point  136 , for example, since the amplitude modulation of the magnetic signal at this point is a maximum. When a spot of light generated by the optical servo system  22  is centered over an alignment void, the light reflected is a minimum, and thus the current photo detector in the optical system  22  is a minimum. However, typically an amplifier generates a voltage signal that peaks when the current is a minimum, thus when a spot of light generated by the optical servo system  22  is centered over the same alignment void in the multiple tracks of alignment voids  90  the envelope of the optical voltage signal peaks at point  138 . Knowing the track pitch of the alignment voids  90 , which can be controlled by adjustment of the servo writer optics  64  and can be measured by the microscope  75 , one knows that each peak in the envelope of the optical signal  134  corresponds to the track pitch. Similarly, the separation of peaks of the envelope of the demodulated magnetic signal  132  also corresponds to the track pitch. The track pitch divided by the timing T between peaks gives the velocity v of the head assembly as it is scanned up and down across the alignment voids  90 . Equally spaced peaks indicate a constant velocity of the head assembly. Then the timing difference t is the difference in time between peaks  136  and  138  and is converted to micrometers by multiplying by the velocity.  
         [0046]    In still another example, the alignment tape  150  is utilized in a static alignment process. Referring to FIG. 10, the laser system  60  is used to generate an alternate alignment tape  150  having multiple continuous longitudinal arranged tracks  152  that imprint the second major surface of the alignment tape  150  but do not expose the base film of the alignment tape. The is accomplished by having the laser source  62  direct one or more beams of light of such power, so as to partially penetrate the second major surface of the alignment tape  150  to mark the second major surface but not expose the base film and cause ejection of material from the front major surface of the alignment tape  150 . In addition, two alignment windows  154  and  156  are generated by a commercial laser micro machining station. A segment of the alignment tape  150  is clamped in a metal coupon  158 . The metal coupon  158  is used to hold the alignment tape  150  in place and position the alignment tape  150  within the read/write assembly  14 . The alignment voids  154  and  156  are spaced apart so as to fit directly over a recording channel pair on  28  and  30  of recording head  20 , e.g., 0.08 inches. The metal coupon  158  is also sized to fit between the recording channels of the recording head  20  and the optical servo system  22  and includes precision translation and rotation stages  160  to manually position the coupon  158 , and consequently the alignment tape  150 , accurately within the read/write assembly  14 . In addition, a microscope, such as the microscope  75  of FIG. 5, is mounted to the read/write assembly  14  to aid in viewing the position of the alignment tape  150  relative to the recording channels and the optical servo system  22 .  
         [0047]    The coupon  158  positions the alignment tape  150  such that the alignment voids  154  and  156  are centered over a recording channel pair. Once oriented properly by using the precision translation stages  160  and the microscope  75 , the coupon  158  is fixed in position. The optical servo system  22  is put in place and turned on and the adjuster  38  moved so that the optics  22  moves laterally up and down in a direction perpendicular to the multiple continuous longitudinal arranged tracks  152 . An optical spot is produced by a laser source in the optical servo system  22  and hits the alignment tape  150 . The adjuster  38  is moved by a precision translation stage  160  to position the optical spot over a center of a middle one of the multiple continuous longitudinal arranged tracks  152 . Once centered, the position is fixed as a final position. The read/write assembly  14  is ready for further processing in its manufacture.  
         [0048]    A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.