Abstract:
A slider assembly for an optical disc drive includes a flyable slider supporting a pad with a pair of piezoelectric beams mounted to the pad to extend in spaced relation over the slider. An objective lens is mounted to the beams as to be cantilevered over the slider body. The beams are operable to deflect along the yawl axis of the slider to thereby move the objective lens and alter the position of the focal point. When operated independently, the beams rotate the objective lens about the roll axis of the slider to alter the radial position of the focal point. When operated together, the beams move the objective lens to focus the focal point relative to the recording medium. The beams are optionally operable to deflect along the pitch axis of the slider to thereby radially move the objective lens and alter the position of the focal point.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority of Provisional Application No. 60/055,912 filed Aug. 18, 1997 for “MICRO-POSITIONING METHOD FOR LENSES” by Zine-Eddine Boutaghou and Lowell James Berg. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to optical disc drives, and particularly to high density optical disc drives that employ lenses supported on sliders that aerodynamically control head/disc spacing. 
     Run-out, in an optical disc drive, is the condition of variations in distance between the head and disc surface that leads to defocus of the objective lens. Run-out is caused by a lack of parallelism between the lens and disc surface, which in turn is caused by a number of factors, including unbalanced forces acting on the disc drive spindle, vibration, external noise, disc warpage, lack of perpendicularity of the disc spindle, and lateral motion of the spindle caused by ball bearing imperfections, to name a few. Many optical disc drives employ an objective lens positioned at a fixed location relative to the platform supporting the disc. Variations in the flatness in the disc, therefore, is the most common cause of run-out in such optical disc drives. Where the objective lens is mounted to a flying slider, disc run-out will be of less impact on lens focus because the slider follows undulations of the disc surface. 
     The density, or radial spacing, between concentric data tracks, on optical discs continue to increase, requiring greater precision of lens positioning. Conventional drives employing flying sliders accomplish lens positioning by operating an actuator arm with a large scale motor, such as a voice coil motor, to position a lens\slider on a gimbal at the end of the actuator arm. However, the large scale motor lacks sufficient resolution to effectively accommodate high track-density discs. Thus, a high resolution lens positioning mechanism is necessary to accommodate more densely spaced tracks. 
     BRIEF SUMMARY OF THE INVENTION 
     A slider assembly for an optical disc drive in accordance with the present invention comprises a slider body having an aerodynamic surface arranged to fly a design distance from a recording surface of a recording medium when the recording medium is rotated about a medium axis at its operating velocity. An objective lens is supported by the slider and defines a focal point located at a fixed position relative to the lens. A microactuator is mounted to the slider body and supports the objective lens to selectively alter the radial position of the focal point relative to the medium axis. 
     In a preferred embodiment of the slider assembly, the microactuator includes a pad supported by the slider body. A micromotor beam, such as a pair of piezoelectric beams, are mounted to the pad and extend in spaced relation over the slider body. The objective lens is mounted to the micromotor beam as to be cantilevered over the slider body. The micromotor beam is operable to move the objective lens relative to the slider body to thereby rotate the objective lens about the roll axis and radially alter the position of the focal point. 
     In one form of the slider assembly, the pair of piezoelectric beams include conductive patterns to operate the piezoelectric beams to deflect in a direction along the yawl axis of the slider body. The first and second beams rotate the objective lens about the roll axis when operated at different voltages, and operate to rotate the objective lens about the pitch axis of the slider body to adjust the focus of the objective lens when operated at design polarities. 
     In another form of the slider assembly, the piezoelectric beans include conductive patterns having first portion to operate the piezoelectric beams to deflect in a direction along the yawl axis of the slider body to focus the objective lens relative to the recording surface, and a second portion to operate the piezoelectric beams to deflect in a direction along the pitch axis of the slider body to radially position the focal point. 
     In a preferred embodiment, the objective lens defines a light path through the slider body between the lens and the focal point, and a solid immersion lens is mounted to the slider body in the light path. 
     In accordance with another aspect of the present invention, an optical disc drive has a rotatable optical recording medium having a recording surface with a plurality of concentric radial tracks along which data may be recorded as marks having distinctive optical characteristics and along which data may be recovered by optically sensing marks when the recording medium is rotated at an operating velocity. An optical system has a light source for supplying light, an objective lens for directing light supplied by the light source at the recording surface, and a light detector operatively associated with the objective lens to receive light reflected from the recording surface. The objective lens defines a focal point at a position relative to the lens. A slider assembly supports the objective lens. An actuator arm supports the slider at a selected radial position adjacent the optical recording medium. The slider has an aerodynamic surface to fly a design distance from the recording surface when the recording medium is rotated at the operating velocity. A microactuator on the slider assembly is operable to selectively alter the radial position of the focal point relative to the slider. 
     Another aspect of the present invention is a method of radially positioning the focal point of an objective lens of a disc drive optical system in which the optical system includes an actuator arm having a slider which supports the objective lens and is arranged to fly a design distance from a recording surface of an optical recording medium when the recording medium is rotated at an operating velocity. The method comprises flying the slider a design distance from the recording surface, and selectively positioning the objective lens relative to the slider to selectively alter the radial position of the focal point relative to the recording surface. 
     The objective lens is advantageously mounted to a pair of cantilevered micromotor beams. In one embodiment, the beams are independently deflected in a direction along the yawl axis of the slider to rotate the objective lens about the roll axis. 
     In another embodiment, the beams are independently deflected in a direction along the pitch axis of the slider to move the objective lens along the pitch axis. In this embodiment, the beams may also be deflected along the yawl axis of the slider to focus the objective lens relative to the recording surface. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an optical disc drive in accordance with the presently preferred embodiment of the present invention. 
     FIG. 2 is a section view of a rotary actuator arm and optics of the disc drive of FIG.  1 . 
     FIG. 3 is a schematic diagram of the optical paths of an optical module used in the optical disc drive of FIG.  1 . 
     FIGS. 4A,  5 A,  6 A and  7 A are perspective views, and 
     FIGS. 4B,  5 B,  6 B and  7 B are section views taken at lines  4 A— 4 A,  5 A— 5 A,  6 A— 6 A and  7 A— 7 A, respectively, illustrating a succession of steps in fabricating a slider containing an objective lens and focus mechanism for the apparatus illustrated in FIG.  1 . 
     FIG. 8 is a perspective view, as in FIG. 7B, of a slider for use in the optical drive illustrated in FIG. 1 in accordance with a second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2 illustrate a rotary actuator assembly for an optical disc drive in accordance with the presently preferred embodiment of the present invention. The actuator assembly includes an actuator spindle  12  having a hollow actuator arm  14  mounted thereto for rotation about actuator axis  16 . A gimbal spring  18  is mounted to actuator arm  14  and carries a slider  20 . In one embodiment, the body of slider  20  is formed of transparent cubic zirconia, and one or more rails  22  (FIGS. 4B-7B) having smooth aerodynamic surfaces  24  extend along the slider body to confront optical disc  30 . Disc  30  is mounted to spindle  32  to rotate about disc axis  34  at a design operational velocity. When so rotating, windage associated with disc  30  reacts against aerodynamic surfaces  24  of slider  20  to cause slider  20  to “fly” a design distance above surface  36  of disc  30 . As is well known in the art, the aerodynamic characteristics of slider  20 , together with the spring bias of gimbal  18  and any load beam (not shown) imposed on gimbal  18 , causes slider  20  to “fly” the design distance from confronting surface  36  of disc  30 . Lens assembly  40  is supported by slider  20  and includes an objective lens  96  having a focal point  42  in fixed position to the lens. Actuator arm  14  supports mirror  52  immediately adjacent lens assembly  40 . Housing  54  is supported by actuator spindle  12  and contains optical module  56  shown in greater detail in FIG.  3 . 
     Slider  20  includes a microactuator  44  connected to slider  20  and supporting lens assembly  40 . Microactuator  44  is arranged to adjust the position of lens  70  with respect to the body of slider  40  to alter the radical position of focal point  42  with respect to the slider to thereby move the focal point radially with respect to disc  30 . Thus, when the disc is rotated at its operational velocity, microactuator  44  selectively adjusts the position of focal point  42  relative to a selected radial track. 
     As shown particularly in FIG. 3, optical module  56  includes a laser light source  58  arranged to emit collimated light in the form of a beam, and a detector  60  arranged to detect collimated light. Splitter  62  is well-known in the art as a device that is partially transparent to light impinging it from one side and partially reflective of light impinging it from the opposite side. Splitter  62  is arranged in respect of source  58  to direct source light radiation from source  58  through splitter  62  and along a light path within arm  14  (FIG. 2) to mirror  52  where it is redirected through lens assembly  40  to focal point  42 . Light reflected from disc  30  is transmitted through lens assembly  40 , reflected by mirror  52  to splitter  62 , reflected by splitter  62  to mirror  64  to impinge on detector  60 . Source  58 , which is a typical laser source well-known in the art, is operated via input leads  66  from the disc drive controller (not shown) and signals generated by detector  60  are provided via leads  68  to the controller. Other light paths may be included within module  56  as is well-known in the art. For example, light from the source  58  may be reflected by splitter  62  away from the detection light path for control purposes. 
     As is well-known in the art, information is written to disc  30  by applying digital signals from the controller to light source  58  to provide a pulsed laser output through lens assembly  40  to the surface of disc  30 . The strength and wavelength of the laser pulses are such as to heat the surface of the optical disc to form optically distinctive marks or optical modifications in the otherwise reflective optical disc. Because the disc is rotating, these marks are recorded as a series of optical modifications along concentric tracks, the marks being recorded at a frequency and representing data in a matter well-known in the art. In the read mode, source  58  is operated continuously, usually at a lower power and slightly different optical wavelength than a write operation to provide light through lens assembly  40  to impinge on the surface  36  of disc  30 . Marks on the disc have distinctive optical characteristics, to reflect the light differently than from areas where there are no such marks. As a result, the reflected light constitutes a series of light pulses representing the marks, and hence the data recorded on the disc. The reflected light is transmitted through lens assembly  40  and reflected by mirror  52 , splitter  62  and mirror  64  to be detected by detector  60  as a series of light pulses of varying intensity, based on the reflections of light from the marks and regions where there are no marks (non-marks). The impinging light on detector  60  creates a digital signal which is transmitted back to the controller and recovered as data. While the present invention will be described in connection with an intensity-based readout, as might be employed with erasable phase change media, the invention is equally applicable to phase-based readout, as employed with CD-ROM media, and polarization-readout as employed with magneto-optical media. 
     The present invention is directed to a slider having a microactuator arranged to radially shift the position of the focal point  42  of lens assembly  40  for focusing on a track center, or even selecting different tracks. More particularly, the present invention is directed to a micromotor beam mechanism that is cantilevered to the slider and supports the lens assembly to move the focal point of the objective lens relative to the slider. The slider, micromotor and lens assembly may be explained with reference to FIGS. 4-7. 
     As shown in FIGS. 4A and 4B, a slider body  70  having rails  22  is formed of a transparent cubic zirconia material. Rails  22  have aerodynamic surfaces  24  to react against windage caused by rotating disc  30  to “fly” slider  70  a design distance from the disc surface. Solid immersion lens (SIL)  72  is formed on an upper surface of slider body  70  and a pad  74  formed of insulating material thermally compatible with the slider body is formed on the top surface of the of the slider at the leading edge. For example, pad  74  may be formed of a ceramic material. As shown in FIGS  5 A and  5 B, a layer of sacrificial material  76 , such as a dissolvable resist, is formed on the top surface of slider body  70  to abut pad  74  and at the same height as pad  74 . Piezoelectric layers  78  and  80  are formed on the sacrificial layer and on pad  74 . As shown particularly, in FIG. 5B, there are two such piezoelectric layers  78  and  80  extending outwardly from pad  74  and together form an aperture  82  partly surrounding SIL  72 . 
     As shown in FIGS. 6A and 6B, lens base  84  is mounted to the distal or trailing ends of piezoelectric layers  78  and  80 . Interleaved conductive leads  86  and  88  are formed on the upper surface of the proximal end of piezoelectric layer  78  and interleaved conductive leads  90  and  92  are formed on the upper surface of the proximal end of piezoelectric layer  80 . The interleaved conductive patterns are disposed forwardly of lens base  84 , which in turn forms an aperture  94  exposing SIL  72 . Finally, and as illustrated particularly in FIGS. 7A and 7B, objective lens  96  is formed on base  84 , covering apertures  94  and  82 . Sacrificial layer  76  is dissolved away leaving space  98  below the distal or trailing ends of piezoelectric layers  78  and  80 , beneath lens base  84  and lens  96 . As a result piezoelectric layers  78  and  80  form cantilevered piezoelectric beams attached at one end to pad  74  and supporting the lens base  84  and lens  96  at the other end in a cantilevered fashion. 
     In operation, application of a voltage signal to leads  86  and  88  of cantilevered piezoelectric beam  78 , and application of a different voltage signal to leads  90  and  92  of cantilevered piezoelectric beam  80 , causes the cantilevered distal or trailing ends of those piezoelectric beams to bend in respectively different amounts around the pitch axis  102  extending across the width of slider body  70  so that the respective distal or trailing ends of beams  78  and  80  bend toward or away from slider body  70  along yawl axis  106  to different levels relative to the disc surface. Because piezoelectric beams  78  and  80  are bent to different levels, lens base  84  and lens  96  are rotated about the roll or longitudinal axis  104  of the slider. As a result, the focal point  42  of lens  96  is selectively moved radially inwardly or outwardly with respect to axis  34  of disc  30  (FIG. 1) to selectively position focal point  42  to a selected track. 
     While application of oppositely poled voltages to the contacts on beams  78  and  80  will result in the most dramatic movement of beams  78  and  80  around the pitch axis  102 , resulting in roll of base  84  and lens  96  for track selection purposes, it is also possible to simultaneously adjust the focus of lens  96  on the selected track. More particularly, the focal position of lens  96  with respect to the surface of disc  30  may be adjusted by application of the same voltage to both piezoelectric beams  78  and  80 , thereby causing equal bending of the beams around the pitch axis, thereby adjusting the focus of lens  96  with respect to a selected track. This might be done, for example, to correct for run-out, or to adjust the focal position of lens  96  for changes in wavelength between read and write modes as explained in the co-pending Gage et al. application Ser. No. 08/895,257, filed Jul. 15, 1997 for “Microactuator for Fine Focusing a Slider-Mounted Lens of an Optical Disc Drive”, and assigned to the same assignee as the present application. Moreover, by selectively adjusting the voltage signals to piezoelectric beams  78  and  80 , lens base  84  and lens  96  may be adjusted both around the roll axis  104  of slider body  70  to selectively position focal point  42  to a selected track, and around the pitch axis  102  of slider body  70  to selectively position focal point  42  for purposes of focusing lens  96 . 
     FIG. 8 illustrates a modification of the slider illustrated in FIG.  7 B. Conductors  112  and  114  on piezoelectric beam  78  include a first section  116  to provide bending of piezoelectric layer  80  toward or away from disc  30  (around the pitch axis and along the yawl axis of the slider), and a second section  118 , normal to the pattern of section  116 , to bend piezoelectric beam  78  toward or away from disc axis  34  (around the yawl axis and along the pitch axis of the slider). Likewise, piezoelectric beam  80  includes patterns  120  and  122  having first and second portions  124  and  126  normal to each other to provide bending of piezoelectric beam  80  toward or away from disc  30  around the pitch axis  102  and toward or away from axis  34  around the yawl axis  106 , respectively. As a result, the lens base and lens are controlled for movement about the pitch axis by bending beams  78  and  80  about the pitch axis, and for movement about the yawl axis by bending beams  78  and  80  about the yawl axis, to control both track selection and lens focus. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.