Patent Publication Number: US-2004057160-A1

Title: Actuator assembly with out-of-plane voice coil

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
     [0001] This application claims the benefit of U.S. Provisional Application No. 60/411,728, filed Sep. 19, 2002. 
    
    
     
       FIELD OF THE INVENTION  
       [0002] The present invention relates generally to actuator assemblies. More particularly, the present invention relates to actuator assemblies operable by voice coil motors.  
       BACKGROUND OF THE INVENTION  
       [0003] Voice coil motor-activated actuator assemblies are used in data storage devices for positioning read/write devices relative to recording media. In some applications, it may be desirable to use an out-of-plane voice coil. However, because such a voice coil cannot be conveniently supported by a yoke that extends in a plane parallel to that of the actuator arms, the manufacture of such actuator assemblies often involves relatively costly molding or extrusion processes. It would therefore be beneficial if there were some cost effective way of overcoming this difficulty.  
       [0004] The following description shows how the present invention addresses this and other issues while providing various advantages over the existing art.  
       SUMMARY OF THE INVENTION  
       [0005] One embodiment of the present invention includes an actuator assembly that has arms that support read/write devices and an out-of-plane voice coil. The arms are configured to be manufacturable by cost effective methods, for example, by stamping processes.  
       [0006] In another aspect, an improved method of making an actuator assembly is provided. The arms are severally formed by stamping processes, and assembled with a spacer there between. An out-of-plane voice coil can be easily attached to the arms, which may be made to provide increased surface area for engaging the voice coil.  
       [0007] These and various other features as well as advantages which characterize the present invention will be apparent upon reading of the following detailed description and review of the associated drawings. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0008]FIG. 1 is a perspective view of a data storage device.  
     [0009]FIG. 2 is a perspective view of an actuator assembly according to one embodiment of the present invention.  
     [0010]FIG. 3 is a perspective view of an actuator assembly according to another embodiment of the present invention.  
     [0011]FIG. 4 is an exploded view of an actuator assembly, illustrating a method of making the actuator assembly according to one embodiment of the present invention.  
     [0012]FIG. 5 is an exploded view of an actuator assembly, illustrating a method of making the actuator assembly according to another embodiment of the present invention.  
    
    
     DETAILED DESCRIPTION  
     [0013] The disc drive  100  illustrated in FIG. 1 is one example of a data storage device in which an actuator assembly of the present invention is applied. Provided within a protective housing, which may be formed from a base deck  102  and a complementary cover  104 , are storage media and apparatus for storing and retrieving data from the storage media. In this example, storage media is provided in the form of one or more discs  106 . Each disc is secured to a spindle motor  108 , forming a disc stack assembly that is rotatable about an axis of rotation. Circuitry required for drive operations is generally located on a printed circuit board assembly  110  attached to an underside of the base deck. Flex cables  112  connect the circuits from the printed circuit board assembly to read/write devices  114  and a voice coil motor  116  in the disc drive.  
     [0014] The voice coil motor may be of various configurations. It is essentially made up of an energizable voice coil  118  and a permanent magnet  120 , oriented such that relative motion between an energized voice coil and the magnetic flux of the permanent magnet produces motion of either the permanent magnet or the voice coil. In this example, the permanent magnet is arranged to be stationary relative to the base deck, with pole pieces  122  located in the vicinity to facilitate closure or containment of the magnetic flux. The voice coil is affixed to an actuator assembly  124  so that energizing the voice coil brings about motion of the actuator assembly.  
     [0015] As is more clearly illustrated in FIGS. 2 and 3, the actuator assembly  124  is constructed to be used with a pivot mechanism  126  which may be, for example, a ball bearing pivot cartridge or a flexural joint. The pivot mechanism  126  may generally be described as having a stationary shaft for mounting to the base deck and a sleeve, rotatable with respect to the shaft, for attachment to the actuator assembly. The pivot mechanism therefore defines an axis of rotation  128  about which the actuator assembly  124  is rotatable with respect to the base deck  102 .  
     [0016] The actuator assembly  124  includes two arms  130 , 132  extending substantially perpendicular to the axis of rotation  128  of the actuator assembly. A first end  134  of each arm is configured to support read/write devices  114 . The read/write devices  114  may be indirectly coupled to the arms  130 ,  132 . For example, the read/write devices may be mounted to suspensions  136  which are then swaged, glued, or otherwise coupled to the first ends  134  of the arms  130 ,  132 . Rotation of the actuator assembly  124  causes the first ends  134  of the arms to describe arcuate paths  140  across corresponding surfaces of the discs  106 . The read/write heads  114  are thus positionable by the actuator assembly  124  such that, during drive operations, they can read/write data from/to various desired radial locations of the discs  106 .  
     [0017] A second end  142  of each arm supports the voice coil  118  of the voice coil motor so that the voice coil is oriented with its coil-plane normal  143  oriented substantially perpendicular to the axis of rotation  128  of the actuator assembly. In other words, the voice coil  118  is attached to the actuator assembly  124  so that it is out-of-plane with respect to the arms  130 ,  132  of the actuator assembly  124 . Thus configured, the actuator assembly  124  is characterized by a greater structural stiffness than a conventional actuator assembly that has a coil-plane normal aligned substantially parallel to the axis of rotation of the actuator assembly. The greater structural stiffness contributes to improved reliability in the positioning of the read/write devices as the actuator assembly is less vulnerable to resonant excitation. In particular, it has been demonstrated that, not only do the first moment of area and the second moment of area improve, the “butterfly” mode of an actuator assembly having an out-of-plane voice coil improves significantly, as compared to the conventional actuator assembly.  
     [0018] Each arm  130 , 132  of the actuator assembly extends from the first end  134  (configured for supporting read/write devices  114 ) to the second end  142  (configured for supporting the voice coil  118 ). The arms  130 , 132  may be described as being substantially planar, by which term is included arms that can be formed by stamping and forming processes, even if not all parts of the arm would lie on the same plane.  
     [0019] Provided on the arm, between the first end  134  and the second end  142 , is a pivot hole  144  suitably sized to engage the pivot mechanism  126 . Various other features may be provided on the arm. For example, swage holes  146  may be provided at the first end for swaging to suspensions  136 . As further examples, the arm may have holes or features  148  between the pivot hole  144  and the first end  134  for decreasing the mass of the arm, or for improving flow characteristics about the arm, or for improving the frequency response of the actuator assembly.  
     [0020] The two arms  130 , 132  are spaced apart a suitable distance along the axis of rotation  128  of the actuator assembly, and each of the second ends  142  of the arms is coupled to a portion of the voice coil  118 . For example, the second ends  142  may be coupled to portions  182 ,  184  of the voice coil that are oriented substantially perpendicular to the axis of rotation  128 .  
     [0021] In one embodiment of the present invention, as shown in FIG. 2, the arms  130 ,  132  are spaced apart about the same distance as the height  150  of the voice coil. Each second end is forked to provide a niche  152  of a suitably sized width  154  to receive a portion of the voice coil  118 . In other words, the coil portions  182 , 184  may be arranged to be at the same elevations as the second ends  142  of the arms  130 ,  132  (where the elevations are measured with respect to a reference plane that is substantially perpendicular to the axis of rotation  128  of the actuator assembly).  
     [0022] The niche surfaces  156  provide additional area for contact and bondage with the voice coil  118 . The length  156  of the niche may vary; a greater length being preferred to provide more surface area for contact and for the application of adhesives between the arms  130 ,  132  and the voice coil  118 .  
     [0023]FIG. 3 shows another embodiment in which the arms  130 ,  132  are spaced apart by a distance  152  so that the voice coil  118  is sandwiched between the second ends  142  of the arms  130 ,  132 . The outer surfaces of the voice coil  118  can be bonded to inner surfaces  158  of arms  130 ,  132  by use of adhesives.  
     [0024] Epoxy has been found to be a suitable adhesive for use in securing the voice coil to the arms. It provides the advantage of forming an actuator assembly that shows improved frequency response. Of course, other attachment methods for attaching the coil to the arms, such as overmolding, may also be used without departing from the spirit of the invention.  
     [0025]FIG. 4 shows one embodiment of the present invention where the sleeve  160  of the pivot mechanism  126  is shaped with a step  162 ,  164  at each of its ends  166 ,  168  so that the sleeve  160  has a smaller diameter at its ends  166 ,  168  than at its middle portion  170 . The pivot hole  144  of each arm  130 ,  132  is sized to receive one end  166 ,  168  of the sleeve, bringing the arms  130 ,  132  into abutment with the respective steps  162 ,  164 . The length  172  of the middle portion thus serves as a spacer to maintain the desired spacing between the two arms  130 ,  132  of the actuator assembly. The arms  130 ,  132  can be secured to the sleeve  172  by an adhesive, for example, an epoxy adhesive. The voice coil  118  can thus be mounted to the arms  130 , 132  in a desired out-of-plane configuration without the need for the rest of the actuator assembly to be formed by molding processes.  
     [0026]FIG. 5 shows an alternative to modifying the sleeve  160  of the pivot mechanism  126 . A separate spacer  174  of a desired height  176  is fitted around the sleeve  160  to keep the arms  130 ,  132  the desired spacing apart. One advantage of this arrangement is that a commercially available pivot mechanism can be used without the need for a customized sleeve. In the example shown, the arms  130 ,  132  are shaped with pivot holes  144  suitably sized to receive the sleeve  160  but not the spacer  174  such that the arms  130 ,  132  come into abutment with respective ends  178 ,  180  of the spacer. The arms  130 , 132  can then be secured to the sleeve  160  and the spacer  174  by an adhesive, for example, an epoxy adhesive. The voice coil  118  can be attached to the arms  130 ,  132 , with the coil-plane normal  143  at an angle with respect to the axis of rotation  128 .  
     [0027] It will be understood that other methods of securing the arms can be used. For example, the spacer  174  can be shaped with varying diameters, similar to the sleeve of FIG. 4, to receive and maintain the arms  130 ,  132  in the desired spatial relationship. Providing an interference fit, tolerance ring or other mechanical fastener are other contemplated attachment methods which may be used without departing from the scope of the present invention.  
     [0028] In some embodiments, the voice coil  118  abuts the sleeve  160 , or as the case may be, the spacer  174 . Epoxy can then be applied between the voice coil  118  and the sleeve  160 , or between the voice coil  118  and the spacer  174 , to provide a more secure mounting of the voice coil  118  to the actuator assembly  124 . Such an arrangement is found to improve the frequency response of the actuator assembly.  
     [0029] Thus configured, the arms  130 ,  132  can be severally and easily coupled to the pivot mechanism  126  and to the voice coil  118  to form an actuator assembly  124 . The present invention accommodates the use of stamped arms  130 ,  132  to form part of the actuator assembly  124  while providing an out-of-plane voice coil  118 . This contributes to the ease of manufacture of the actuator assembly. More advantageously, it costs less to manufacture an actuator assembly of the present invention than to make an actuator assembly using molding or extrusion processes.  
     [0030] It is to be understood that even though numerous characteristics and advantages of various embodiments of the present invention have been set forth in the foregoing description, together with details of the structure and function of various embodiments of the invention, this disclosure is illustrative only, and changes may be made in detail, especially in matters of structure and arrangement of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.