Abstract:
An improved actuator assembly for a disc drive, the actuator assembly having an E-block which at a proximal end supports an array of read/write heads in reading and writing data relationship to a plurality of spinning data discs which create air currents that convectively cool the E-block, the E-block supporting at a distal end an electrical coil which interacts with a magnet assembly of the disc drive to selectively position the actuator assembly in response to control voltages introduced to the electrical coil. A portion of the control voltage is dissipated as heat energy by the electrical coil, and a heat transfer plate is provided to thermally connect the electrical coil and the E-block to provide conductive heat transfer of the heat energy to the E-block which acts as a heat sink for the electrical coil.

Description:
RELATED APPLICATIONS 
     This application claims priority to Provisional Application No. 60/075,713 entitled HARD DISC DRIVE ACTUATOR WITH A HEAT CONDUCTING PLATE, filed Feb. 24, 1998 and is a continuation of U.S. patent application Ser. No. 09/126,112 filed Jul. 30, 1998, now U.S. Pat. No. 6,078,477, issued Jun. 20, 2000. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to the field of disc drive data storage devices, and more particularly but not by way of limitation, to an improved actuator for a disc drive. 
     BACKGROUND 
     Modern disc drives are commonly used in a multitude of computer environments, ranging from super computers to notebook computers, to store large amounts of data in a form that can be made readily available to a user. Typically, a disc drive has one or more magnetic discs that are rotated by a spindle motor at a constant high speed. Each disc has a data recording surface divided into a series of generally concentric data tracks radially spaced across a band having an inner diameter and an outer diameter. 
     The data is stored within the data tracks on the disc surfaces in the form of magnetic flux transitions. The flux transitions are induced by an array of read/write heads. Typically, each data track is divided into a number of data sectors where data is stored in fixed size data blocks. 
     The read/write head includes an interactive element such as a magnetic transducer which senses the magnetic transitions on a selected data track to read the data stored on the track. Alternatively, the interactive element transmits an electrical signal that induces magnetic transitions on the selected data track to write data to the track. 
     As is known in the art, each read/write head is mounted to a load arm that is supported by an actuator arm and is selectively positionable by a rotary actuator assembly over a selected data track of the disc to either read data from or write data to the selected data trace. The read/write head includes a slider assembly having an air bearing surface that, in response to air currents caused by rotation of the discs, causes the read/write head to fly adjacent the disc surface with a desired gap separating the read/write head and the corresponding disc. 
     Typically, a plurality of open-center discs and spacer rings are alternately stacked on a spindle motor hub. The hub, defining the core of the stack, serves to align the discs and spacer rings around a common axis. Collectively the discs, spacer rings, and spindle motor hub define a disc pack assembly. The surfaces of the stacked discs are accessed by the read/write heads which are mounted on a complementary stack of actuator arms which form part of an actuator assembly. The actuator assembly generally includes head wires which conduct electrical signals from the read/write heads to the flex circuit which, in turn, conducts the electrical signals to a flex circuit connector. The flex circuit connector is mounted to a flex circuit mounting bracket, and the mounting bracket is mounted to a disc drive basedeck. External to the basedeck, the flex circuit connector is secured to a printed circuit board assembly (PCB). 
     The actuator assembly interacts with a magnet assembly of the disc drive to selectively move the actuator arms so as to selectively position the read/write heads. This interaction generally involves the relative movement or an electrical coil and a magnetic circuit created by a pair of opposing magnets. In one embodiment the coil is attached to the actuator assembly and rotates therewith within the magnetic field of stationary magnets. In an alternative embodiment it is known to attach the magnets to the actuator assembly and rotate them adjacent an electric coil. 
     In either case, the electric coil is energized with a control current to create an electromagnetic Field which interacts with the magnetic circuit to move and position the actuator assembly. The recent trend in the industry is to reduce drive seek time, the time required to move the read/write head from a current data track to a target data track. One way of reducing seek time is to increase the relative amount of current to the electric coil. As the current is increased the operating temperature of the coil likewise increases, as a proportionate amount of the electrical energy is dissipated as heat energy. One skilled in the art will understand that the amount of current that can be passed through a coil is generally a function of its electrical resistance, which is directly proportional to the temperature of the coil. As the temperature of the coil increases, the magnitude of the control current is limited, adversely affecting the drive seek time. Moreover, elevated coil temperatures can also adversely affect the seek time performance by generally weakening the strength of the magnetic circuit of the magnet assembly. 
     There is a long-felt need in the industry for an improved actuator assembly that provides thermal heat transfer from the electric coil of the voice coil motor, so as to reduce the accumulation of heat energy in the coil to reduce the coil operating temperature. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a disc drive assembly having an actuator assembly that conductively transfers heat energy from a voice coil motor and convectively dissipates the heat energy to cool the voice coil motor. In a preferred embodiment the actuator assembly has an E-block that is pivotally supported by the disc drive, the E-block supporting an array of read/write heads in data reading and writing relationship to a plurality of spinning data discs. The spinning discs create air currents which convectively cool the E-block. 
     Opposite the read/write heads the E-block supports an electrical coil as part of a voice coil motor, which selectively positions the actuator assembly by the introduction of a control current to the electrical coil. A portion of the control current is dissipated as heat energy which tends to increase the operating temperature of the electrical coil. 
     A heat transfer plate thermally connects the electrical coil to the E-block so that the heat energy call be conductively transferred from the electrical coil to the E-block. The cooling of the E-block by the spinning discs results in a thermal gradient such that the E-block(functions as a heat sink to cool the electrical coil. 
     The electrical coil is formed from the combination of an outer coil portion and an inner coil portion. The heat transfer plate has projecting legs interposed between the coil portions to increase the contact surface area between the heat transfer plate and the electrical coil. 
    
    
     The heat transfer plate of the present invention cools the electrical coil reducing the electrical resistance and allowing the use of a larger control current to reduce seek time. Reducing the operating temperature of the voice coil motor also lessens the temperature degradation of the magnetic circuit strength. Other advantages and features of the present invention will be apparent from the following description when read in conjunction with the drawings and appended 
     BRIEF DESCRIPTION OF TILE DRAWINGS 
     FIG  1  is a plan view of a disc drive constructed in accordance with the prior art. 
     FIG. 2 is a perspective view of all actuator assembly utilized by the prior art disc drive of FIG.  1 . 
     FIG. 3 is a perspective view of a portion of an actuator assembly of the present invention. 
     FIG. 4 is a partially broken view of a portion of the actuator assembly of FIG. 3 
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings in general, and more particularly to FIG. 1, showing therein is a plan view of a typical prior art disc drive  100  in which the present invention is especially useful. The disc drive  100  includes a head disc assembly (HDA)  102 , which includes a basedeck  104  to which various disc drive components are mounted, a gasket  106 , a top cover  108  (partially cutaway), and fasteners  110 , which together provide a sealed internal environment for the HDA  102 . It will be understood that numerous details of construction of the disc drive  100  are not included in the following description as such are well known to one skilled in the art and are unnecessary for the purpose of describing the present invention. 
     Mounted to the basedeck  104  is a disc pack assembly  112  having a spindle motor  114  with a plurality of alternately stacked discs  116  and spaces (not shown) disposed about a spindle motor hub  118  and secured thereto by a clamping ring  120 . Adjacent the discs  116  is an actuator assembly  122  which pivots about a cartridge bearing  124 . The actuator assembly  122  has a centrally disposed E-block  126  (FIG. 2) which forms a plurality of actuator arms  128  (only one shown) that support load arm assemblies  130 . Each of the load arm assemblies  130  supports a read/write head  132 , with each of the read/write heads  132  corresponding to a surface of one of the discs  116 . Each of the discs  116  has a data recording surface divided into concentric circular data tracks (not shown), and the read/write heads  132  are positioned adjacent the data tracks to read data from or write data to the tracks. An outer extremity of the data recording surface is circumscribed by a guard band  134 , and the inner extremity by a landing zone (not shown). 
     The actuator assembly  122  of the prior art disc drive  100  is pivotally positioned by way of a voice coil motor assembly (VCM)  138 , having an actuator coil  140  immersed in the magnetic field generated by a magnet assembly  142 . The magnet assembly  142  is mounted to the basedeck  104  and to the top cover  108 , and consists of a pair of opposing magnets (not shown) each supported by a magnetically permeable flux path (such as a steel plate  144 ) to complete the magnetic circuit of the VCM  138 . When a control current is passed through the actuator coil  140 , an electromagnetic field is set up which interacts with the magnetic circuit of the magnet assembly  142  to cause the actuator coil  140  to move relative to the magnet assembly  142  in accordance with the well-known Lorentz relationship. 
     To provide the requisite electrical conduction paths between the read/write heads  132  and the disc drive read/write circuitry (not shown), read/write head wires (not separately shown) are routed on the actuator assembly  122  from the read/write heads  132 , along the load arm assemblies  130  and the actuator arms  128 , to a flex circuit assembly  146 . The flex circuit assembly  146  has a flex circuit  148 , a flex circuit mounting bracket  150 , a printed circuit board (PCB)  152  and a disc drive PCB connector  154 . The read/write head wires are secured by way of a suitable soldering process to corresponding pads of the PCB  152 . The flex circuit  148  is connected to the flex circuit mounting bracket  150  in a conventional maniner which in turn is connected by the disc drive PCB connector  154  through the basecdeck  104  to a disc drive PCB (not shown) mounted to the underside of the basedeck  104 . The disc drive PCB provides the disc drive read/write circuitry to control the operation of the read/write heads  132 , as well as other interface and control circuitry for the disc drive  100 . 
     FIG. 2 is a perspective view of a portion of the prior art actuator assembly  122  which is pivotally supported by the cartridge bearing  124 . The cartridge bearing  124  is of a conventional design known in the art, having a stationary shaft  156  and a rotatable sleeve  158  supported by a number of ball bearings (not shown) therebetween. The E-block  126  is attached to the sleeve  158  for pivotal movement about the stationary shaft  156 . A fastener (not shown) engages an aperture  160  at an tipper end of the stationary shaft  156  to secure the cartridge bearing  124  to the top cover  108 . Likewise, a fastener engages another aperture (not shown) at a lower end of the stationary shaft  156  to secure the cartridge bearing  124  to the basedeck  104 . 
     The E-block  126  forms the actuator arms  128  at a proximal end as well as a pair of coil support arms  162  at a distal end. The coil  140  is formed by winding an epoxy coated wire about a forming mandrel in a conventional manner to achieve the desired number of windings. After winding the wire the formed coil  140  is heated to meld the epoxy. In this manner the epoxy joins and supports the wire in the final coil  140  shape, and insulates the wire to prevent short circuiting of the coil  140 . The formed coil  140  is disposed within and supported by the coil support arms  162  by an epoxy material injected therebetween. 
     FIG. 3 is a perspective view of a portion of an actuator assembly  164  constructed in accordance with a preferred embodiment of the present invention. It will be noted that the actuator assembly  164  of the present invention, modified as described below, is well suited for use in the prior art disc drive of FIG.  1 . 
     It will be noted that an actuator coil  168  supports a heat transfer plate  170  that has an upstanding portion  172  pressingly engaging an E-block  174  by an attaching fastener  176  cooperating with a receiving aperture (not shown) in the E-block  174 . In this manner the heat transfer plate  170  is mechanically connected to both the coil  168  and the E-block  174  to permit conductive heat transfer therebetween. In a preferred embodiment the upstanding portion  172  has an abutting surface  178  that is formed to accommodate the shape of an abutting surface  180  of the E-block  174 , so as to maximize the surface-to-surface contact area between the upstanding portion  172  and the E-block  174  for maximum heat transfer therebetween. In the preferred embodiment shown in FIG. 3, for example, the abutting surface  180  forms a generally convex surface and the abutting surface  178  accommodatingly forms a generally concave surface. In an alternative preferred embodiment these face-to-face surfaces may both be flat formed portions, as represented by the upstanding portion  172  shown in FIG.  4 . 
     FIG. 4 is a partially cutaway perspective view of the coil  168  showing an inner coil  182  and an outer coil  184  and the heat transfer plate  170  having leg members  186  (only one shown) sandwiched between the inner coil  182  and the outer coil  184 . 
     In a preferred embodiment of the present invention the inner coil  182  and the outer coil  184  are individually formed. The heat transfer plate  170  is placed over the inner coil  182  and the outer coil  184  is then placed around both the inner coil  182  and the heat transfer plate  170 . After all three components are thus combined, the assembled components can be heated to meld the epoxy coating on the coil wire. Where the heat transfer plate  170  and the wire abuttingly contact, the epoxy on the wire melds to join the wire to the heat transfer plate  170 . 
     Where the inner coil  182  and outer coil  184  are formed independently and married together as previously described, each of the coils  182 ,  184  will have a pair of terminal leads. These leads are preferably joined so as to electrically connect the coils  182 ,  184  in series to effectuate a single coil made up of the two individually formed coils  182 ,  184 . For example, the output lead of the outer coil  184  can be connected to the input lead of the inner coil  182  to electrically bridge the coils  182 ,  184  in series. In this manner the input lead of the outer coil  184  and the output lead of the inner coil  182  are connected to a disc drive power circuit providing the control current to position the actuator assembly  164 . 
     In an alternative preferred embodiment the coil  168  is formed as a single coil with the heat transfer plate  170  inserted into the coil winding process. In this embodiment the coil  168  is partially wound to form the inner coil  182  and then the winding process is paused. The heat transfer plate  170  is then placed over the inner coil  182  and the winding process is resumed to form the outer coil  184 . An advantage of a single wound coil is that the intermediate electrical connection between individual coils  182 ,  184  is eliminated. 
     The heat transfer plate  170  is thus interposed between the inner coil  182  and the outer coil  184  in order to provide a thermal link between the coil  168  and the E-block  174 . Actuator arms  188  (FIG. 3) are positioned adjacent the spinning discs  116  which produce air currents that convectively cools the proximal end of the E-block  174 . The coil  168  produces a localized hot spot as heat energy is generated by the control voltage used to position the actuator assembly  164 . The heat transfer plate  170  provides a thermal link between the coil  168  and the E-block  174 , establishing a heat transfer path for the thermal gradient established between the relatively hot coil  168  and the relatively cool actuator arms  188 . 
     To provide the thermal link, the heat transfer plate  170  made of a thermally conductive material. In a preferred embodiment the heat transfer plate  170  is made of a metal material. It is advantageous to form the heat transfer plate  170  from the same metal as the E-block  174 , typically aluminum or magnesium, so that the heat transfer plate  170  and the E-block  174  have a common heat transfer coefficient to expand and contract in unison. This eliminates potential induced strain on the heat transfer plate  170  and the electrical coil  168  from relative movement between the heat transfer plate  170  and E-block  174 . Such relative movement could damage the melded connection of the wire to the heat transfer plate  170 . 
     To minimize cost, the heat transfer plate  170  is preferably stamped and formed to the described configuration including the upstanding portion  172  and the oppositely projecting legs  186 . Edges of the heat transfer plate  170  which contact the coil  168  must be smooth to prevent scarring or chaffing of the epoxy insulation on the wire of the coil  168 . Otherwise the insulation can be penetrated resulting in a short circuit between wire loops of the coil  168  or between the coil  168  and the heat transfer plate  170 . Because stamping inherently produces sharp sheared edges, a secondary operation such as deburring or etching is desirable to provide none-damaging smooth edges on the heat transfer plate  170 . 
     The present invention provides an improved actuator assembly (such as  164 ) for use in a hard disc drive (such as  100 ). The actuator assembly has an E-block (such as  174 ) which is pivotally supported by attachments to a sleeve (such as  158 ) of a cartridge bearing (such as  124 ). The E-block forms a plurality of actuator arms (such as  188 ) which are disposed adjacent a plurality of spinning discs (such as  116 ) that produce air currents to convectively cool the E-block. Opposite the actuator arms the E-block(supports an electrical coil (such as  168 ) which receives a control current to produce an electromagnetic field which interacts with a magnetic circuit or a magnet assembly (such as  142 ) to pivotally position the actuator assembly. 
     The coil supports a heat transfer plate (such as  170 ) which is also connected to the E-block to provide a thermal link between the electrical coil and the E-block for conductive heat transfer. The electrical coil is cooled as heat is conductively transferred to the E-block, which by being cooled by the air currents thus acts as a heat sink for the electrical coil. 
     Although the preferred embodiment described hereinabove describes the use of the pivoting actuator assembly, it will be recognized that alternative embodiments are likewise within the scope of the present invention, such as a linear positionable actuator assembly. 
     It is 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 of the invention has been described for purposes of the disclosure, it will be understood that numerous changes may be made which will readily suggest themselves to those skilled in the art and which are encompassed within the spirit of the invention disclosed and as defined in the appended claims.