Abstract:
A coil construction for a voice coil motor is disclosed. The coil construction includes a series of stacked planar coils disposed on a substrate material. Each planar coil is separated from its neighboring coil or coils by a viscoelastic material to reduce vibration of the coil construction. The coil construction is attached to an actuator arm. Control circuitry creates a current in the coil construction to position a head on the actuator arm. Also disclosed is a method for making a coil for a voice coil motor. The method includes the steps of masking a substrate having a conductive layer with a photoresist, exposing the mask to create a pattern of planar coils, developing the photoresist, and etching the conductive layer to create a planar coil.

Description:
RELATED APPLICATIONS 
     This application claims priority of U.S. provisional application Serial No. 60/374,079 filed Apr. 18, 2002. 
    
    
     FIELD OF THE INVENTION 
     This application relates generally to voice coil motors and more particularly to a coil construction for a voice coil motor. 
     BACKGROUND OF THE INVENTION 
     In a disc drive, a head for reading and writing data to and from a disc is supported on an actuator arm. The actuator arm controls the position of the head through the use of a voice coil motor (VCM), which typically includes a coil attached to an actuator assembly, as well as one or more permanent magnets which establish a magnetic field in which the coil is immersed. The controlled application of current to the coil causes magnetic interaction between the permanent magnets and the coil so that the coil moves in accordance with the well-known Lorentz relationship. As the coil moves, the actuator assembly pivots about a bearing shaft assembly, and the head (or heads) is caused to move across the surfaces of the discs. 
     The coil is fabricated by winding copper wire around a mandrel. Adhesion of a coil wire to the adjacent wires is accomplished by pre-coating the wire with a bond coat material and then heating the covered wire while winding the coil. The coil is heated to allow plasticizers to outgas from the coating. During this process, voids can form in the bond coat, which can result in delaminating of the bond coat from the wires. The delamination can allow individual wires in the coil to vibrate, causing undesirable noise during operation. A wire may also contact an adjacent wire if it becomes unbonded further causing undesired vibration effects. Another source of noise or unwanted vibration in current coils is out-of-plane forces. These forces cause additional vibration of the voice coil motor. 
     Accordingly there is a need for a coil construction that reduces the undesirable vibration due to delamination and out-of-plane forces. The present invention provides a solution to this and other problems, and offers other advantages over the prior art. 
     SUMMARY OF THE INVENTION 
     Against this backdrop the present invention has been developed. One embodiment of the present invention is directed to a coil construction for a voice coil motor. The coil construction includes a series of planar coils made from electrically conductive material formed on a substrate. The planar coils are disposed on a substrate and the coils are formed into a stacked array wherein each planar coil is separated from its neighboring coil or coils by a dampening material. The coil construction is assembled into an actuator arm for use in a disc drive and used to position a head located on the actuator arm. 
     Another embodiment of the invention is directed to a disc drive assembly including an actuator arm assembly for positioning a head over a disc surface. A coil construction is disposed on the actuator arm assembly and current from control circuitry through the coil construction controls the position of the head over the disc surface. The coil is a part of a voice coil motor that creates forces to move the actuator arm assembly to position the head. The coil construction includes a series of adjacent layers of stacked planar coils disposed on a substrate. The planar coils are electrically connected in series to form a single electrical current path. 
     These and various other features as well as advantages which 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 for incorporating an embodiment of the present invention showing the primary internal components. 
     FIG. 2 is a block diagram of components that control the disc drive of FIG.  1 . 
     FIG. 3A is a perspective view from a first side of an example embodiment of a coil construction of the present invention. 
     FIG. 3B is a perspective view from a second side of the coil construction of FIG.  3 A. 
     FIG. 4 is a top view of the coil construction of FIG. 3A assembled into a coil. 
     FIG. 5 is a perspective view of an actuator arm assembly incorporating the coil construction of FIG.  4 . 
    
    
     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 about a bearing shaft assembly  112  positioned adjacent the discs  108 . The actuator assembly  110  includes a plurality of actuator arms  114  which extend towards the discs  108 , with one or more flexures  116  extending from each of the actuator arms  114 . Mounted at the distal end of each of the flexures  116  is a head  118  that 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 about the bearing shaft assembly  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  120  near the inner diameter of the discs  108  when the drive motor is de-energized. The heads  118  are secured over the park zones  120  through the use of an actuator latch arrangement, 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 . 
     Referring now to FIG. 2, shown therein is a functional block diagram of the disc drive  100  of FIG. 1, generally showing the main functional circuits which are resident on the disc drive printed circuit board and used to control the operation of the disc drive  100 . The disc drive  100  is operably connected to a host computer  200  in a conventional manner. Control communication paths are provided between the host computer  200  and a disc drive microprocessor  216 , the microprocessor  216  generally providing top level communication and control for the disc drive  200  in conjunction with programming for the microprocessor  216  stored in microprocessor memory (MEM)  224 . The MEM  224  can include random access memory (RAM), read only memory (ROM) and other sources of resident memory for the microprocessor  216 . 
     The discs  108  are rotated at a constant high speed by a spindle motor control circuit  226 , which typically electrically commutates the spindle motor  106  (FIG. 1) through the use of back electromotive force (BEMF) sensing. During a seek operation, wherein the actuator  110  moves the heads  118  between tracks, the position of the heads  118  is controlled through the application of current to the coil  126  of the voice coil motor  124 . A servo control circuit  228  provides such control. During a seek operation the microprocessor  216  receives information regarding the velocity of the head  118 , and uses that information in conjunction with a velocity profile stored in memory  224  to communicate with the servo control circuit  228 , which will apply a controlled amount of current to the coil  126 , thereby causing the actuator assembly  110  to be pivoted. 
     Data is transferred between the host computer  200  or other device and the disc drive  100  by way of an interface  202 , which typically includes a buffer  210  to facilitate high speed data transfer between the host computer  200  or other device and the disc drive  100 . Data to be written to the disc drive  100  is thus passed from the host computer  200  to the interface  202  and then to a read/write channel  212 , which encodes and serializes the data and provides the requisite write current signals to the heads  118 . To retrieve data that has been previously stored in the disc drive  100 , read signals are generated by the heads  118  and provided to the read/write channel  212 , which performs decoding and error detection and correction operations and outputs the retrieved data to the interface  202  for subsequent transfer to the host computer  200  or other device. Such operations of the disc drive  100  are well known in the art and are discussed, for example, in U.S. Pat. No. 5,276,662 issued Jan. 4, 1994 to Shaver et al. 
     To improve the acoustical performance and attenuate self-induced vibrations in an actuator arm assembly, the present invention has been developed. Referring to FIG. 5, shown is an actuator arm assembly  310  incorporating an example embodiment of a coil construction  330  of the present invention. The actuator arm assembly  310  includes a bearing housing  312 , a plurality of actuator arms  314 , and a plurality of flexures  316 , each flexure  316  supporting a head  318 , and a coil assembly  330 . While the actuator arm assembly  310  is shown supporting a plurality of heads  318 , it is not uncommon for an actuator arm assembly  310  to support only one head  318 . 
     The coil construction  330  is located on the actuator arm assembly  310  and is also part of the voice coil motor (VCM) (not shown) of the disc drive. Referring to FIGS. 3A-5, the coil construction  330  includes a series of planar coils  336  arranged into a coil  337  that allows the actuator arm assembly  310  to move when a current is applied to the coil  337 . The coil  337  operates in the same manner as conventional coils to position the heads  318  on the actuator arm assembly  310 . The coil construction  330  is shown in FIG. 5 with the coil  337  formed and mounted to the actuator arm assembly  310 . 
     The coil construction  330  is formed by stacking a series of planar coils  336  each disposed on a substrate section  338 . In the example embodiment shown, the substrate sections  338  include first and second end sections  340 ,  342  and a plurality of intermediate sections  344 . Each substrate section  338  is joined to its neighboring section(s) by a folding section  346 . The folding sections  346  allow the coil construction  330  as shown in FIGS. 3A-B to be folded to form the coil  337  shown in FIG. 5, thereby forming a series of adjacent layers of planar coils  336  each bonded to a corresponding substrate section  338 . The coil construction  330  in FIGS. 3A-B is shown in the extended position and is shown in the folded position in FIGS. 4-5. 
     Referring to FIG. 5, the planar coils  336  are electrically connected to form a single coil  337  when the coil construction  330  is in the folded position to form the coil  337 . Each planar coil  336  is electrically connected to the adjacent planar coil  336  by through holes, or vias  360 , formed in the substrate section  338 . The electrical connection can be accomplished in various ways, which are well within the knowledge of one of skill in the art, and are not part of the present invention. Preferably, the electrical connection is made through the vias  360  by plating or a solder connection. 
     The coil construction  330  is mounted to the actuator arm assembly  310  by techniques known to those of skill in the art, but the coil construction  330  is preferably bonded to the actuator arm assembly  310  by an epoxy layer between the actuator arm assembly  310  and the second end section  344  of the coil construction  330 . Another preferred method of joining the coil construction  330  to the actuator arm assembly  310  is by placing the coil construction  330  in its proper position and then overmolding the entire assembly together. Overmolding typically uses a PPS (polyphenylene sulfide) or LCP (liquid crystal polymer) material that is injection molded around the entire assembly to bond all the parts together. 
     The coil construction  330  can also include leads  348 ,  350 . The leads  348 ,  350  are connected to a power source in the control circuitry and allow current to pass through the coil  337 , to move the actuator arm assembly  310  to position the heads  318  during use. The leads  348 ,  350  can be omitted and the wires of the coil  337  can be directly connected to pins in the voice coil motor. 
     Preferably, the coil construction of the present invention is fabricated by starting with a planar sheet of substrate coated on both sides with a layer of conductive material, preferably copper. A substrate coated on a single side can be used to for the coil construction of the present invention, but using a substrate coated on both sides, such as a flex circuit with copper on both sides, lends itself to the accordion-fold embodiment described in FIGS. 3A-5 since it is desirable for the planar coils  336  to have the substrate material  338  between adjacent layers. 
     The substrate is preferably a polyimide such as KAPTON® (made by DuPont) that is suitable for use in the photolithography process, but one of skill in the art will recognize that many materials suitable for flexible circuits can be used. Preferably, the coil construction  330  is then formed using conventional photolithographic techniques. The coated substrate is covered with a photoresist and an image is patterned on the photoresist, which can be of the positive or negative type. The substrate with the photoresist is then developed and etched using techniques well known in the art. The end product is the formation of the coil construction  330  in the extended position. 
     Preferably, the fabrication process uses a KAPTON® substrate 0.001 inches thick that is coated on both sides with a layer of copper 0.0028 inches thick. Preferably, the copper traces that form the planar coils  336  are then processed to be approximately 0.008 inches wide, giving a trace width to material thickness aspect ratio of 2.8. One of skill in the art will recognize that the coil resistance can be controlled changing the width or height of the traces, as well as the total length of the traces through the coil. The metal layer can also be a different material on each side of the coated substrate. 
     After the unfolded coil construction  330  is formed, it is covered with a viscoelastic polymer adhesive and/or adhesive to achieve an optimum level of damping and structural stiffness. Preferably, epoxy or a pressure sensitive adhesive is used. The coil construction  330  is then formed into a coil  337  in the folded position by folding each of the sections  340 ,  342 ,  344  onto its neighboring section(s) of the coil  337 , at a fold made at each folding section  346 . The sections are folded so that there is a substrate section  338  between each planar coil  336 . If necessary, the coil construction  330  is then pressed under heated conditions to bond the successive layers together. After the folded coil construction  330  is formed it is then mounted onto the actuator arm assembly  310  and the leads  348 ,  350  are electrically connected to the control circuitry (not shown) of the disc drive. 
     Additional features can also be integrated into the coil construction  330  of the present invention. Referring to FIGS. 4 and 5, a limit stop  352  is formed by the folding sections  346  when the coil construction  330  is in the folded position. The limit stop  352  engages with a limiting post (not shown) located in the disc drive assembly to limit travel of the actuator arm assembly  310 . 
     An advantage of the coil construction of the present invention is that it can be formed by creating an array of coils on a single substrate, then folding and laminating the coils in one process step, and finally cutting the laminated stack to a desired shape to create individual coils. Another advantage is that the substrate on the viscoelastic material used between the adjacent layers of planar coils acts as a damper to reduce undesirable vibrations in the coil due to the various causes discussed previously. The method of making the coil construction of the present invention also is able to create various coil shapes that are decoupled from having to develop expensive coil winding tools. 
     One example embodiment of the present invention is directed to a coil construction (such as  330 ) for a voice coil motor (such as  124 ). The coil construction (such as  330 ) includes a series of planar coil sections (such as  336 ) made from an electrically conductive material. The planar coil sections (such as  336 ) are electrically connected in series and each planar coil (such as  336 ) is joined to a corresponding substrate section (such as  334 ). The substrate sections (such as  334 ) include first and second end sections (such as  340 ,  342 ) and at least one intermediate section (such as  344 ). Each intermediate section (such as  344 ) has two neighboring sections and each end section (such as  340 ,  342 ) has one neighboring section. The coil construction (such as  330 ) forms a coil (such as  337 ) when the substrate sections (such as  334 ) are stacked. 
     Another example embodiment of the present invention is directed to a disc drive assembly (such as  100 ). The disc drive assembly (such as  100 ) includes an actuator arm assembly (such as  310 ) for positioning a head (such as  318 ) over a surface of a disc (such as  108 ). The disc drive assembly (such as  100 ) further includes a coil construction (such as  300 ) disposed on the actuator arm assembly (such as  310 ). The coil construction (such as  330 ) includes a series of adjacent layers of stacked planar coils (such as  336 ) disposed on a substrate. The planar coils (such as  336 ) are electrically connected in series to form a single electrical current path. The disc drive assembly (such as  100 ) also includes control circuitry electrically connected in series with the coil construction (such as  330 ) and a voice coil motor assembly (such as  124 ) for moving the actuator arm assembly (such as  310 ) to position the head (such as  318 ) when current is passed through the coil construction (such as  330 ) by the control circuitry. 
     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, a metallic surface can be added to the coil construction to enhance heat transfer from the coil or increase structural stiffness. Also, surfaces or sections made of polymers or composites can be added to modify the stiffness of the coil construction. 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.