Abstract:
A system for evaluating a head stack assembly used in an optical or optically assisted hard drive is provided. The system utilizes a reflective surface that is provided in a forward and return optical path that includes an optical head and associated optical components.

Description:
RELATED APPLICATIONS 
     The present application is related to and claims priority from U.S. Provisional Application Ser. No. 60/103,691 filed Oct. 10, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to the evaluation of light through an optical head, and more particularly to the evaluation of light in sub assembly testing of a multi-head optical storage system. 
     2. Background 
     Read-write optical heads that include active optics may be characterized by verification testing of an optical path of light that is altered by the optics. This testing may include a determination of the magnitude of a vector angle or a frequency response obtained based on the characterization of the optics. 
     Problems may result when evaluating the light during sub-assembly testing of read-write optical heads in a multi-head disk storage system, for example, when placing a light sensitive detector for monitoring the light between each of a plurality of flying heads comprising the subassembly. In this type of system, only one detector typically fits between the heads, requiring one fixture for up facing heads and a separate fixture for down facing heads. This approach also requires external circuitry to acquire a signal from separate detectors, preventing the use of a standard drive controller board to perform the test process. These detectors and fixturing add additional process steps to the assembly of the storage system, resulting in increased cost and handling of parts as well as potential damage to components. In this approach, there also does not exist any provision for measuring light in the return leg of the light and, thus, the complete optical path cannot be evaluated. 
     What is needed, therefore, is an improved method and apparatus for evaluating optical components in sub-assembly testing of multiple heads of a multi-disk optical system. 
     SUMMARY OF THE INVENTION 
     The present invention includes an apparatus for testing a head stack assembly, comprising: a substrate, wherein the substrate receives a light from the head stack assembly and directs a reflection of the light back to the head stack assembly, and wherein the head stack assembly is characterized based on the reflection of the light. The substrate may comprise a first surface, wherein first surface comprises a plurality of features for disrupting the reflection of the light. The substrate may further comprise a second surface disposed in generally parallel opposition to the first surface, wherein second surface comprises a plurality of features for disrupting the reflection of the light. The head stack assembly may comprise at least two optical heads, wherein the substrate comprises a surface, wherein the surface is disposed between the at least two optical heads, wherein the light from the head stack assembly received by the surface is delivered from a one of the at least two optical heads, and wherein the one of the at least two optical heads is characterized based on the reflection of the light from the surface. The light from the head stack assembly may be directed to the surface by a moveable part disposed on the optical head, wherein the moveable part acts to direct the light across the plurality of features. The present invention may further comprise and analyzer for analyzing the reflection of the light. The moveable part may comprise a steerable mirror, wherein the characterization comprises measurement of a voltage applied to the steerable mirror to deflect the steerable mirror. The head stack may comprise a plurality of optical fibers, wherein the characterization may be based on measurement of the reflection of the light from a particular one of the plurality of optical fibers. The characterization may also comprise an identification of a particular one of the plurality of optical fibers. 
     The present invention may also comprise a substrate, wherein the substrate receives light from the moveable optics; reflection means for providing a reflection of the light; and analyzing means for characterizing the moveable optics based on the reflection of the light. The reflection means may comprise disruption means for disrupting the light from the moveable optics. The moveable optics may comprise a steerable mirror. 
     The present invention may also comprise a method of testing a head stack assembly comprising the steps of: directing a light with optics of the head stack assembly toward a substrate, receiving a reflection of the light form the substrate, and characterizing the head stack assembly based on the reflection of the light. The present invention may further comprise a step of disrupting the light with substrate features. The present invention may further comprise a step of wherein the step of directing the light with the optics toward the substrate comprises directing the light with dynamic optics. The dynamic optics may comprise steerable optics. The present invention may further comprise a step of wherein the step of directing the light and receiving the reflection of the light comprises directing the light and receiving the reflection of the light with optics comprising an optical fiber. The present invention may further comprise a step of wherein the characterization includes detection of the reflected light from the optical fiber. The present invention may further comprise a step of wherein the characterization includes evaluating a functionality of the steerable optics. The present invention may further comprise a step of wherein the characterization includes evaluating a frequency response of the steerable optics. 
     Accordingly, several objects and advantages of the present invention are: 
     (a) to provide for the use of a computer to take, transfer, and store test results for head stack assemblies for later retrieval and analysis; 
     (b) to provide a means of testing a complete light path of an optical head-stack subassembly; 
     (c) to provide a means of testing micro-machined components; 
     (d) to provide a means of testing rotatable micro-machined mirrors for proper movement when a voltage is applied; 
     (e) to provide a measurement of the natural frequency of a micro-machined mirror; 
     (f) to provide a means of determining which optical fiber in a fiber bundle is attached to which flying optical head; 
     (g) to provide a means of determining which optical fiber attached to an optical head is located in an optical switch; and 
     (h) to accomplish the aforementioned testing using a single fixture and single installation of an optical head-stack sub-assembly. 
     The present invention may also comprise a data storage and retrieval system including a set of flying optical heads that are adapted for use with a set of spinning disks. The set of flying optical heads are coupled to a rotary actuator magnet and coil assembly by a respective suspension and actuator arm for positioning the set of heads over the surfaces of the set of spinning disks. In operation, lift forces are generated by aerodynamic interactions between the set of heads and the spinning disks. A flying height of a head (above the disk surface) is a balance of the lift force opposed by an equal and opposite spring force applied by each suspension. The optics of a given head are designed to be focused at a distance equal to said flying height. 
     In the present invention, a force measuring device known as a gram-load fixture may be modified to comprise an additional fixture providing a number of adapter plates preferably equaling one half the number of flying optical heads. These adapter plates are stacked such that they simulate disks of a drive assembly. A gram-load fixture is a device used to measure spring load force on each head of a head sub-assembly of a standard hard drive. As those skilled in the are aware, the gram-load measuring device individually determines the spring force acting on each head of the head sub-assembly. In this invention the adapter plates are included with the gram-load fixture to provide testing optics on the head. 
     The adapter plates provide a features from which a return beam of light is evaluated. The features can be made on any suitable substrate, the fixture design being such as to provide dimensions that approximate a typical flying head gap over a read-write surface while in operation. The evaluation may include determination of a vector angle and/or a mirror frequency response, provided the optics components on the head exhibit a dynamic component. In one embodiment of the invention, the dynamic component is provided by a moveable mirror, and features on the reflective surface contribute to evaluating head performance. Thus, in addition to measuring spring load force of the subassembly, optics components on the head can also be evaluated with one apparatus. In addition, bundled optical fibers coupled to the heads can be characterized by a determination as to which optical head is attached to which fiber. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an optical hard drive; 
     FIG. 2 a  is an exploded view of an optical head; 
     FIG. 2 b  is a side view of an optical head; 
     FIG. 3 is a perspective view of a steerable micro-machined mirror; 
     FIGS. 4 a-c  are views of an optical head stack-assembly installed onto a gram-load device that includes a support assembly of the present invention; 
     FIG. 5 is a perspective view of a load fixture comprising load cams; 
     FIG. 6 shows a support assembly and adapter plates of the present invention; 
     FIG. 7 a  is cross-sectional view of an adapter plate; 
     FIG. 7 b  is a top view of a adapter plate and features formed therein/thereon; 
     FIG. 7 c  is an alternative embodiment of the present invention; 
     FIG. 7 d  is another alternative embodiment of the present invention; and 
     FIG. 8 is a view of an upper optical head (down facing) positioned in an unloaded position by a load cam and an opposing lower optical head (upper facing) resting on a lower side of an adapter plate. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring in detail to the drawings wherein similar parts are identified by like reference numbers, there is seen in FIG. 1 a perspective view of a multi-disk optical drive  100 . In this view it is seen that a head stack assembly  105  may comprise individual optical heads  125 , each of which is coupled to individual arms  120  through respective suspensions  122 . In one embodiment, the optical heads  125  may comprise flying optical heads. Flying optical heads are understood to comprise air bearing surfaces that interact to aerodynamically maintain the optical heads  125  a distance above respective rotating disks  155 . While the present invention is described with reference to flying optical heads, it is understood that other optical heads used in the disk drive industry are also with the scope of use with the present invention, for example, optical heads that do not utilize air bearing surfaces. It is understood that in other embodiments, the optical heads  125  may alternatively comprise magneto-optical heads. FIG. 1 further illustrates a group of individual optical fibers  115 , which are all coupled to an optical switch  130  at one end and to individual ones of the optical heads  125  at an opposite end. The optical switch  130  selectively directs a light  160  from a source (not shown) to a particular one of the individual optical fiber  115 . The optical fibers  115  function to route the light  160  between the optical switch  130  and a particular optical head  125 . 
     Referring now to FIGS. 2 a  and  2   b , there is seen in FIG. 2 a  an exploded view of an optical head  125  in which is shown attached to a body  150 , the optical fiber  115 , a steerable micro-machined mirror  140 , and a focusing lens  145 . Illustrated in FIG. 2 b  is a cross-section of the optical head  125  and a path of the light as it travels along the optical fiber  115 . The light  160  is vectored and reflected by the steerable micro-machined mirror  140  and focused by the lens  145 . During normal drive operation, the light  160  is directed by the lens  145  onto a surface of a particular disk  155 , and reflected light  161  is returned from the disk  155 . The reflected light  161  is transmitted by the optical fiber  115  in an opposite direction to that of light  160  to the optical switch  130  and for processing by optics and electronics (not shown). 
     Referring now FIG. 3, the steerable micro-machined mirror  140  is seen to include a moveable portion  146  attached to a body  147  by beams  142 . Bond pads  143  and  144  are connected electrically to drive electrodes (not shown) located underneath moveable portion  146  and separated from moveable portion  146  by an air gap. When a differential voltage is applied to pads  143 / 144  relative to a ground pad  148 , a differential electrostatic force is applied to the moveable portion  146  to cause it to torsionally vector about the beams  142  by a desired angle  141  about axis  149 . The mirror  140  is manufactured by utilizing micro-machining techniques and is described in commonly assigned and U.S. application Ser. No. 08/844,207, entitled “Data Storage System Having An Improved Surface Micro-Machined Mirror.” 
     Referring now to FIGS. 4 a  and  4   b , there is shown side and top views of an optical head-stack assembly  105  installed onto a force-measuring tool or gram-load device  177  that is modified to include a support assembly  195  of the present invention. The support assembly  195  comprises adapter plates  199 , which are described in detail below. In use with the present invention, prior to assembly as part of drive  100 , the head stack assembly  105 , (including the optical heads  125 , optical fibers  115 , mirrors  140 , and optical switch  130 ) is mounted onto the gram-load device  177 . 
     FIG. 4 c  is an end view showing the gram-load device  177  comprising a load fixture  196  and fixture plate  175 . The load fixture  196  comprises load cams  180  of a generally semi-circle or half-circle shape in a cross-section, which when engaged between suspensions  122  and turned in a direction  185  rotate to allow a spring force from the suspensions  122  in the head stack assembly  105  to be applied to the load cams  180 . The fixture plate  175  is bolted on top and electronically connected to the scale  170 , which is capable of reading forces exerted by the suspensions  122  of the head stack assembly  105 . 
     Referring now to FIG. 5, there is shown a close up perspective view of a representative load fixture  196  comprising the load cams  180  wherein although a 3 cam embodiment is shown it is understood that other numbers of cams are within the scope of the present invention. 
     Referring now to FIG. 6 there is seen a side view of the support assembly  195  of present invention. The support assembly  195  includes adapter plates  199 . The adapter plates  199  each comprise an upper side and a lower side  200 . 
     Referring now to FIG. 7 a , there is shown a cross-section through a particular adapter plate  199 . In the preferred embodiment, the adapter plate  199  may comprise pattern of features  210  that may include, for example, grooves or the like, which may be etched or formed into or onto a suitable substrate  201 , such as glass, over which may be deposited a reflective layer  204 , such as gold, to provide a reflective surface. A transparent protective coating  206 , such as silicon dioxide, may be deposited over the reflective layer  204 . It is understood that the reflective layer  204  may not be required if the substrate  201  itself is sufficiently reflective. FIG. 7 b  illustrates a top view of an adapter plate  199  and one particular pattern of the features  210  formed therein/thereon. 
     Referring now to FIG. 8, there is seen an upper optical head  125  (down facing) positioned in an unloaded position by a load cam  180  and an opposing lower optical head  125  (upper facing) resting on a lower side  200  of the adapter plate  199 . Alternatively, the load cam  180  may be rotated in a direction  185  by 180 degrees such that the upper head  125  is resting on an upper side  200  of the adapter plate  199  and the opposing lower optical head is positioned in an unloaded position. As is well known in the art, spring forces of the springs  122  associated with the respective unloaded optical heads  125  may be measured. Unlike the prior art, however, the present invention provides that the optical heads  125  resting against the lower surface  200 , as well as fixed and dynamic optical components thereon, may be tested. 
     During testing of the optical heads  125  and fixed and dynamic optical components thereon, the light  160  from the optical switch  130  is directed down an optical fiber  115 . The light exits the optical fiber  115  and is directed by the optics of the optical head  125  that is in contact with the adapter plate  199  onto the reflective layer  204 . The reflected light  161  is reflected from the reflective surface  204  and returns through the optics and optical fiber  115 . Preferably, when the optical head  125  is in contact with the adapter plate  199 , the lens  145  will be a correct focal distance above at least a portion of the reflective layer  204  to reflect sufficient light back through the head  125 . In the embodiment shown in FIG. 7 a , the raised portion of the features  210  provides the sufficient light, while the lowered portion provides a physical discontinuity at a different focal length from the lens  145  of sufficient magnitude to cause a change in the reflected light  161  to be sensed. Preferably, the total outer dimensional thickness of the substrate  199  simulates the dimensional operating condition that would be encountered by the optical head  125  when used in the disk drive  100 . Accordingly, a transparent protective coating  206  may be deposited over the adapter plate  199  to a thickness that simulates the flying height of the optical head  105  when used in the drive  100 . It is understood that the adapter plate  199  of the present invention provides that that both upper and lower optical heads  125  may be tested with one test setup, as opposed to an embodiment that might rely on bulky detectors, the dimensions of which would require two setups, one for an upper optical head and second for a lower optical head. 
     One evaluation test that may be performed by the present invention includes functionality of the mirror  140 , for example, the vector angle  141  of the moveable portion  146  of the mirror  140  as a function of applied voltage to the pads  143 / 144 . In this test, as light  160  is vectored across the adapter plate  199  by the moveable portion  146 , the pattern of features  210  will interrupt the reflected light  161 . An optical measuring device that is sensitive to the changes in the reflected light  161  caused by the interruptions, for example, a photo-detector in the optical switch  130 , may be positioned in the return path of the reflected light  161 . An output from the optical detector may be used to provide a signal representative of these changes, such that, the vector angle  141  of the moveable portion  146  may be related to a count of how many times and at what rate the light  160  is reflected from the known number and dimensions of the features  210 , verses an applied voltage to the electrodes  143 ,  144  of the mirror  140 . 
     At the time that the vector angle  141  characterization is made, the mirror  140  may also be evaluated for frequency response. Several approaches may be taken to determine the mirror  140  frequency response, but the simplest is to output to the mirror  140  a series of voltage signals of varying voltage in a cyclic pattern. These signals may be applied in increasing frequencies up to the bandwidth of the mirror  140 , and a corresponding number of pulses caused by the features  210  in the reflected light  161  may be observed. As the source frequency continues to increase, due to harmonic response limitations, the moveable portion  146  will not be able to reach its full deflection and fewer pulses per source cycle will be observed at some point. Eventually, the moveable portion  146  will not move at all for much higher frequencies. The mirror  140  and associated optics may then be evaluated based on the frequency response. For a quick go/no-go test, the number of pulses at a specified frequency may be counted. 
     Evaluation of the amplitude of the reflected light  161  may also provide an indication of the alignment between the optical components on the optical head  125 , for example, between the optical fiber  115  and the mirror  140 , the mirror and the lens  145 , and the optical fiber  115  and the lens  145 . 
     Also, the reflected light  161  may be detected to provide an indication of which optical fiber  115  at the optical switch end is attached to which optical head  125 . This is beneficial in an embodiment in which the optical fibers  115  are bundled together at the optical switch end, wherein in such an embodiment it is difficult to distinguish and identify which optical fiber  115  is connected to which optical head  125   
     The adapter plate  199  is not limited to the embodiment described above. For example, in an alternative embodiment shown in FIG. 7 c , the features  210  may be etched to include a depth equivalent to approximately the flying height of the optical head  125 . In this first alternative embodiment, a protective coating  206  would not necessarily be required. In a second alternative embodiment shown in FIG. 7 d  the features  210  could be deposited on the substrate  201  rather than etched, other methods could include staining, burnishing, thin-film vapor deposition, and anodizing. It will be recognized that while the present invention has been described for use in conjunction with a gram-load fixture, with suitable modifications the invention&#39;s functionality can be provided as a stand alone device. It will also be identified that the present invention is not limited to testing of flying optical heads, but may be used to test magneto-optical heads, flying or otherwise. In a magneto-optical head embodiment, it is understood by those skilled in the art that a magnetic field generating element and/or other optical components may be required on the optical head. Furthermore, it is understood that the present invention is not limited to testing of dynamic components on optical heads but has utility in testing functionality of fixed optics. 
     Thus, while the present invention has been described herein with reference to particular embodiments thereof, a latitude of modification, various changes, and substitutions are intended with the present invention, and it will be appreciated that in some instances some features of the invention will be employed without a corresponding use of other features without departure from the scope of the invention.