Abstract:
A method of measuring the vibration of an actuator assembly in a disc drive in the plane of rotation of the actuator assembly and determining the resonance behavior of the actuator assembly from the measured vibrations is disclosed. The method involves use of a laser to measure the vibrational behavior of the actuator assembly in the rotational plane. A method is described for adjusting the resonance behavior of the actuator assembly during the manufacturing process without the use of glue or extra parts. The resonance behavior is determined and the preload on the bearings in the actuator assembly is adjusted until a desired resonance behavior is achieved.

Description:
RELATED APPLICATIONS 
     This application claims priority of U.S. provisional application Ser. No. 60/180,709, filed Feb. 7, 2000. 
    
    
     FIELD OF THE INVENTION 
     This application relates generally to disc drive actuator assemblies and more particularly to a discrete bearing assembly for an actuator assembly. 
     BACKGROUND OF THE INVENTION 
     Conventional disc drive actuator assemblies may have discrete bearing assemblies. These discrete bearings are typically preloaded with a preload spring or a glued arrangement. Resonant behavior of such bearing systems is not directly monitored or controlled. The resonant behavior of actuator assemblies utilizing these discrete bearing assemblies is usually related to the amount of preload on the bearings. 
     Other actuator assembly designs utilize a cartridge bearing that includes a separate sleeve. These cartridge bearings typically have their preload set utilizing a dead weight and glue on the cartridge alone. For example, NSK (Nippon Steel K) measures the axial resonant frequency of the cartridge bearing during a push fit operation that sets the preload in the cartridge bearing. This push fit operation does not take into account the radial stiffness of the attachment method to the actuator or the resonance of the whole actuator assembly, however, since it is done on the cartridge alone. In addition, the push fit operation does not take into account resonance of the actuator assembly after it has been fastened to the base plate in the disc drive. Consequently, the radial stiffness and resonance of the whole actuator assembly is simply not addressed. This results in less than predictable actuator assembly resonance performance when the actuator assembly is actually operated and unpredictable performance of the disc drive as a whole. Accordingly, there is a need for a bearing assembly that permits a more predictable resonance behavior when installed in the disc drive. 
     SUMMARY OF THE INVENTION 
     Against this backdrop the present invention has been developed. One embodiment of the present invention is a method of measuring the vibration of the actuator assembly in the plane of rotation of the actuator assembly and determining the resonance behavior of the actuator assembly from the measured vibrations. This method is superior to the prior art in that it directly determines the resonance behavior in the plane of rotation of the actuator assembly and also determines the resonance behavior of the assembly after it has been fastened to the drive. 
     Another embodiment of the present invention permits the easy adjustment of the actuator assembly resonance behavior during the manufacturing process without requiring gluing or extra parts and without the error introduced by measuring the resonance behavior before the final assembly of the actuator assembly to the drive. The pivot bearing assembly in accordance with the present invention incorporates an actuator pivot pin that also functions as a preload adjustment screw. The pivot pin has a head portion, a cylindrical shaft portion, and a distal threaded end portion. The pivot bearing assembly includes a pair of discrete bearing assemblies mounted on the cylindrical shaft portion of the pivot pin. Sandwiched between the bearings on the pivot pin is a pivot portion of the actuator arm. Each bearing assembly includes an outer race sleeve and an inner race sleeve concentrically spaced apart by ball bearings. When the two bearing assemblies are placed on the pivot pin with the actuator pivot portion sandwiched therebetween, and the threaded portion of the pin is threaded into the base plate of the disc drive, the head portion of the pin contacts the inner race of the upper bearing. The inner race of the lower bearing contacts the base plate. The outer races of the upper and lower bearing assemblies each contact the pivot portion of the actuator arm. The base plate is formed with a raised shoulder around the threaded bore receiving the threaded portion of the pivot pin. The outer race of the lower bearing is beyond the shoulder and thus does not contact the base plate. The shoulder permits the actuator arm to rotate freely on the bearings in a plane of rotation orthogonal to the pivot pin. Tightening the pivot pin into the base plate places a preload force through the bearing assemblies onto the actuator arm. 
     A laser measuring device aimed at a benchmark on the actuator arm is used to measure vibration of the actuator arm in the plane of rotation of the actuator arm as the pivot screw is tightened during drive manufacture. Resonance behavior of the actuator assembly in the plane of rotation is determined from the measured vibration. Based on the determined resonance behavior, the pivot screw is further tightened or loosened to adjust the preload on the bearing assemblies to provide optimum resonance performance of the actuator assembly. In this arrangement, the preload is applied during final drive assembly, and thus the preload force can be optimized to account for all sources of resonance vibration from the drive as well as permit adjustment for radial stiffness and actual resonance performance. 
    
    
     These and various other features as well as advantages that characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a disc drive incorporating a preferred embodiment of the present invention showing the primary internal components. 
     FIG. 2 is a simplified sectional view through an actuator assembly in a disc drive in accordance with a preferred embodiment of the present invention shown in FIG. 1 taken along the line  2 — 2 . 
     FIG. 3 is a simplified exploded view of the actuator assembly shown in FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     A disc drive  100  constructed in accordance with a preferred embodiment of the present invention is shown in FIG.  1 . The disc drive  100  includes a base  102  to which various components of the disc drive  100  are mounted. A top cover  104 , shown partially cut away, cooperates with the base  102  to form an internal, sealed environment for the disc drive in a conventional manner. The components include a spindle motor  106 , which rotates one or more discs  108  at a constant high speed. Information is written to and read from tracks on the discs  108  through the use of an actuator assembly  110 , which rotates during a seek operation in a plane about a pivot pin  112  positioned adjacent the discs  108 . The actuator assembly  110  includes an includes an actuator arm  114  that extends towards the disc  108 , with one or more flexures  116  extending from the actuator arm  114 . Mounted at the distal end of each of the flexures  116  is a head  118 , which includes an air bearing slider enabling the head  118  to fly in close proximity above the corresponding surface of the associated disc  108 . 
     During a seek operation, the track position of the heads  118  is controlled through the use of a voice coil motor (VCM)  124 , which typically includes a coil  126  attached to the actuator assembly  110 , as well as one or more permanent magnets  128  which establish a magnetic field in which the coil  126  is immersed. The controlled application of current to the coil  126  causes magnetic interaction between the permanent magnets  128  and the coil  126  so that the coil  126  moves in accordance with the well-known Lorentz relationship. As the coil  126  moves, the actuator assembly  110  pivots in a plane about the pivot pin  112 , and the heads  118  are caused to move across the surfaces of the discs  108 . 
     The spindle motor  106  is typically de-energized when the disc drive  100  is not in use for extended periods of time. The heads  118  are moved over park zones near the inner diameter of the discs  108  when the drive motor is de-energized. The heads  118  are secured over the park zones through the use of an actuator latch arrangement  122 , which prevents inadvertent rotation of the actuator assembly  110  when the heads are parked. 
     A flex assembly  130  provides the requisite electrical connection paths for the actuator assembly  110  while allowing pivotal movement of the actuator assembly  110  during operation. The flex assembly includes a printed circuit board  132  to which head wires (not shown) are connected; the head wires being routed along the actuator arms  114  and the flexures  116  to the heads  118 . The printed circuit board  132  typically includes circuitry for controlling the write currents applied to the heads  118  during a write operation and a preamplifier for amplifying read signals generated by the heads  118  during a read operation. The flex assembly terminates at a flex bracket  134  for communication through the base deck  102  to a disc drive printed circuit board (not shown) mounted to the bottom side of the disc drive  100 . 
     A cross sectional view through the actuator assembly  110  in FIG. 1 is shown in FIG.  2 . The actuator assembly  110  in accordance with the present invention incorporates an actuator pivot pin  112  that also functions as a preload adjustment screw. The pivot pin  112  has a head portion  164 , a cylindrical shaft portion  160 , and a distal threaded end portion  162 . The actuator assembly  110  includes a pair of discrete bearing assemblies  140  mounted on the cylindrical shaft portion  160  of the pivot pin  112 . Sandwiched between the bearings  140  on the pivot pin  112  is a pivot portion  152  of the actuator arm  114 . Each bearing assembly  140  includes an outer race sleeve  142  and an inner race sleeve  144  concentrically spaced apart by ball bearings  146 . When the two bearing assemblies  140  are placed on the pivot pin  112  with the actuator pivot portion  152  sandwiched therebetween, and the threaded portion  162  of the pin  112  is threaded into the base  102  of the disc drive  100 , the head portion  164  of the pin  112  contacts the inner race  144  of the upper bearing assembly  140 . The inner race  144  of the lower bearing assembly  140  contacts the base  102 . The outer races  142  of the upper and lower bearing assemblies  140  each contact the pivot portion  152  of the actuator arm  114 . The base  102  is formed with a raised shoulder  180  around the threaded bore receiving the threaded portion  162  of the pivot pin  112 . The outer race  142  of the lower bearing assembly  140  is beyond the shoulder  180  and thus does not contact the base  102 . The shoulder  180  permits the actuator arm  114  to rotate freely on the bearings  140  in a plane of rotation orthogonal to the pivot pin  112 . Tightening the pivot pin  112  into the base  102  places a preload force through the bearing assemblies  140  onto the actuator arm  114 . This preload force is preferably within a range of 0.5 kg-force to about 2 kg-force and more preferably about 1 kg-force. The threaded portion  162  of the pivot pin  112  preferably has a high friction fit within the threaded bore in the base  102  to provide this preload force. 
     Once the actuator assembly  110  has been installed, the assembly  110  is excited and the vibration of the actuator assembly  110  in the plane of rotation of the actuator assembly  110  resulting from the excitation is measured. The actuator assembly  110  may be excited by any means including deliberately rotating the actuator assembly  110  via current fed to the voice coil  126  of the voice coil motor  124 , delivering an external shock load to the disc drive  100  or vibrating the disc drive  100 . The vibration is measured by shining a laser  202  on a benchmark location  200  on the actuator arm  114  and measuring the attributes of the reflected light, but any measuring method may be used including using an accelerometer or by measuring the current induced in the coil  126  of the actuator assembly  110  by the vibration of the arm  114 . 
     In a preferred embodiment, the measured vibration of the actuator assembly  110  is used to determine the resonance behavior of the actuator assembly  110  in the plane of rotation of the actuator assembly  110 . Based on the determined resonance behavior, actuator assembly  110  may adjusted to change the resonance behavior to achieve a desired resonance behavior. 
     An exploded view of the actuator assembly  110  in accordance with another embodiment of the present invention is shown in FIG.  3 . The figure shows an actuator assembly  110  comprising two discrete bearing assemblies  140 , an actuator arm  114 , and a pivot pin  112 . Each bearing assembly  140  includes an outer race sleeve  142  and an inner race sleeve  144  concentrically spaced apart by a number of ball bearings  146 . The actuator arm  114  consists of a coil  126  opposite an extended arm portion  150  to which the flexure  116  is attached and a pivot portion  152  between the coil  126  and arm portion  150 . The pivot portion  152  has an upper surface  154  for contacting an outer race  142  of an upper bearing assembly  140  and lower surface  158  for contacting the outer race  142  of a lower bearing assembly  140 . In addition, the pivot portion  152  defines a central aperture  156  therethrough, through which the pivot pin  112  can penetrate the actuator arm  114 . The pivot pin  112  comprises a shaft portion  160 , a lower threaded portion  162  for fastening the pin  112  to the disc drive  100 , and an upper flange portion  164 . The upper flange portion  164  comprises a lower surface  166  for contacting the inner race  144  of the upper bearing assembly  140 , an upper surface  168  for contacting the disc drive cover  104  and a central hole  170  threaded for accepting a mounting screw (not shown). 
     The actuator assembly  110  is assembled so that the actuator arm  114  is sandwiched between the upper and lower bearing assemblies  140 , all of which are penetrated by and fastened to the disc drive  100  by the pivot pin  112  as shown in FIG.  3 . The fastening force exerted by the pivot pin flange portion  164  on the inner race  144  of the upper bearing assembly  140  is transferred through the upper bearing assembly&#39;s ball bearings  146  to the outer race  142  of upper bearing assembly  140  and onto the upper surface  154  of the pivot portion  152  of the actuator arm  114 . The force on the actuator arm  114  is subsequently transferred to the outer race  142  of the lower bearing assembly  140 , through its ball bearings  146  to its inner race  144  and onto a surface  180  of the disc drive base  102 . Thus, the fastening force also preloads the bearing assemblies  140  and adjusting the fastening force will simultaneously adjust the preload on the bearing assemblies  140 . 
     In another preferred embodiment, the actuator assembly  110  comprises multiple actuator arms  114  and bearing assemblies  140 . In that embodiment, the actuator arms  114  are shaped such that the fastening force also preloads all the bearing assemblies  140 . 
     In a preferred embodiment of the present invention, the resonance behavior of the actuator assembly  110  is adjusted to achieve a desired resonance behavior. In the embodiment, the actuator assembly  110  is excited and the vibration of the actuator assembly  110  in the plane of rotation of the actuator assembly  110  resulting from the excitation is measured. The actuator assembly  110  is excited by fastening the actuator assembly  110  to the disc drive  100  with the pivot pin  112 , although any means may be used including deliberately rotating the actuator assembly  110 , delivering an external shock load to the disc drive  100  or vibrating the disc drive  100 . The vibration is measured by shining a laser (not shown) on a benchmark location on the actuator arm  114  and measuring the attributes of the reflected light, but any measuring method may be used including using an accelerometer or by measuring the current induced in the coil  126  by the vibration of the actuator assembly  110 . The resonance behavior of the actuator assembly  110  in the plane of rotation is determined from the measured vibration. Based on the determined resonance behavior, the preload on the bearing assemblies  140  is increased by tightening the pivot pin  112 . The preload is increased until the desired resonance behavior is achieved. 
     In a preferred embodiment, the vibration is measured and the resonance behavior is determined during the initial fastening of the actuator assembly  110  to the disc drive  100  so that the desired resonance behavior is achieved at that time. 
     In summary, the present invention can be viewed as a method of measuring vibrational resonance in an actuator assembly (such as  110 ) having an actuator arm (such as  114 ) in a disc drive (such as  100 ). The first step of the method comprises mounting an actuator assembly (such as  110 ) onto a pivot pin (such as  112 ) in a disc drive (such as  100 ) for rotation of the actuator assembly (such as  110 ) in a plane. The second step comprises exciting the actuator assembly (such as  110 ). The third step comprises measuring vibration in the actuator assembly (such as  110 ) resulting from the exciting step in the plane of rotation of the actuator assembly (such as  110 ). The measuring step preferably includes determining a resonant frequency from the measured vibrations of the actuator assembly (such as  110 ). The actuator assembly (such as  110 ) is excited by fastening the actuator assembly (such as  110 ) to the disc drive (such as  100 ), but may also be excited by rotating the actuator assembly (such as  110 ) about the pivot pin (such as  112 ) or delivering an external shock load to the disc drive (such as  100 ). The vibration of the actuator arm (such as  114 ) is measured by shining a laser on the actuator arm (such as  114 ) and measuring the attributes of laser light reflected from the excited actuator assembly (such as  110 ) but may also be measured by an accelerometer placed on the actuator arm (such as  114 ) or by measuring the induced current in a voice coil (such as  126 ) attached to the actuator assembly (such as  110 ) caused by the vibration of the actuator arm (such as  114 ) in the plane of rotation. 
     Alternatively, the invention may be viewed as a method of providing a preload on an actuator assembly (such as  110 ) in a disc drive (such as  100 ) to optimize vibrational resonance of the actuator assembly (such as  110 ). The first step of the method is mounting an actuator assembly (such as  110 ) onto a pivot pin (such as  112 ) having an axis in a disc drive (such as  100 ) for rotation of the actuator assembly (such as  110 ) in a plane normal to the axis. The second step is fastening the actuator assembly (such as  110 ) to the disc drive (such as  100 ) to a predetermined preload with a fastener. The actuator assembly (such as  110 ) is preferably fastened by securing the assembly (such as  110 ) with the pivot pin (such as  112 ), but may also be secured by a screw or by a press-fit fastener. Next, the actuator assembly (such as  110 ) is excited, preferably by the fastening performed in the second step, but the source of the excitation may be rotating the actuator assembly (such as  110 ) about the pivot pin (such as  112 ) by a controlled application of a current to a voice coil (such as  126 ) attached to the actuator assembly (such as  110 ) or an external shock load delivered to the disc drive (such as  100 ). 
     After excitation, the vibration of the actuator assembly (such as  110 ) in the rotational plane caused by the exciting step is measured. The measurement is preferably made by shining a laser beam on the actuator arm (such as  114 ) and measuring the attributes of reflected light from the excited actuator assembly (such as  110 ) but may also be made by using an accelerometer or by measuring the induced current in the voice coil (such as  126 ) caused by vibration of the actuator arm (such as  114 ) in the plane of rotation. The fifth step is determining a resonant frequency from the measured vibrations of the actuator assembly (such as  110 ). The final step is adjusting the fastener preload to change the resonant frequency to a desired value, preferably by increasing the preload. In the preferred embodiment, the vibration of the actuator assembly (such as  110 ) is measured and the resonant frequency determined while the fastener preload is increased. The preload is adjusted a desired resonance state of the actuator assembly (such as  110 ) is obtained. 
     It will be clear that the present invention is well adapted to attain the ends and advantages mentioned as well as those inherent therein. While a presently preferred embodiment has been described for purposes of this disclosure, various changes and modifications may be made which are well within the scope of the present invention. For example, the pivot pin  112  may be press-fit to the disc drive base  102  rather than screwed into the base  102  to fasten the actuator assembly  110  and adjust the preload on the bearing assemblies  140  or the pivot pin  112  may not include a flange  164  and the fastening force and preload is applied by means of a fastener (not shown) fastened to the upper end of the pivot pin  112 . Numerous other changes may be made which will readily suggest themselves to those skilled in the art and which are encompassed in the spirit of the invention disclosed and as defined in the appended claims.