Strain relief for an actuator coil

An apparatus and associated method for providing a strain relief in support of a medial portion of a terminal end of an electrical wire that is used in the construction of an actuator coil for a disc drive assembly. The strain relief apparatus has a base that is attached to the actuator assembly, an upstanding post around which the electrical wire is wrapped to provide a frictional engagement between the wire and the post, and a flange depending from a distal portion of the post to urge the wire onto the post and retain the wire about the post during routing of a distal portion of the terminal end that is associated with manufacturing steps of electrically connecting the actuator coil to the disc drive control system. In a preferred embodiment the strain relief has a pair of posts so that each terminal end is wrapped individually about one of the posts. In an alternative preferred embodiment the strain relief has a single post about which both terminal ends are wrapped.

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
 apparatus and a method for providing a strain relief in support of the
 terminal end of an electrical wire used in the construction of the disc
 drive actuator coil.
 BACKGROUND OF THE INVENTION
 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 is 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 storage
 surface divided into a series of generally concentric data tracks that are
 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. The interactive element 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.
 Each of the read/write heads is mounted to a rotary actuator arm and is
 selectively positioned by the actuator arm over a pre-selected data track
 of the disc to either read data from or write data to the data track. The
 read/write head includes a slider assembly having an air bearing surface
 that, in response to air currents caused by rotation of the disc, causes
 the head to fly adjacent to the disc surface with a desired gap separating
 the read/write head and the corresponding disc.
 Typically, multiple center-open 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 a part of an actuator assembly. The actuator assembly
 generally includes head wires which conduct electrical signals from the
 read/write heads to a flex circuit which, in turn, conducts the electrical
 signals to a flex circuit connector mounted to a disc drive base deck.
 When the disc drive is not in use, the read/write heads are parked in a
 position separate from the data storage surfaces of the discs. Typically,
 a landing zone is provided on each of the disc surfaces where the
 read/write heads are positioned before the rotational velocity of the
 spinning discs decreases below a threshold velocity which sustains the air
 bearing. The landing zones are generally located near the inner diameter
 of the discs.
 Generally, the actuator assembly has an actuator body that pivots about a
 pivot mechanism disposed in a medial portion thereof. A motor, such as a
 voice coil motor, selectively positions a proximal end of the actuator
 body. This positioning of the proximal end in cooperation with the pivot
 mechanism causes a distal end of the actuator body, which supports the
 read/write heads, to move radially across the face of the discs.
 The voice coil motor involves an electrical coil and a magnet assembly that
 interact to produce an electro mechanical force that moves one with
 respect to the other. In some designs the magnet assembly is supported by
 the actuator assembly and thereby pivots with respect to a stationary
 electrical coil; conversely the electrical coil can be supported by the
 actuator assembly for pivoting relative to a stationary magnet assembly.
 In either case, the electrical coil is produced from a very fine conductive
 wire which is wound to form a coiled portion. Both ends of the coiled wire
 are left extending from the coiled portion, these terminal ends thereby
 routed and connected to the flex circuit for connection to the control
 system. In this manner, the control system sends controlled currents to
 the electrical coil in order to effectuate movement of the actuator
 assembly.
 The assembly process in manufacturing the disc drive, whether done manually
 or robotically, requires grasping the terminal ends and directing a distal
 portion thereof to the circuit board for electrical connection, such as by
 a suitable soldering process. These tensile forces tend to pull the wires
 loose from the electrical coil, and can lead to wire damage or breakage,
 or damage to the wire insulation.
 There is a long-unresolved need in the industry for a method and
 accompanying apparatus to provide a strain relief support of the wires at
 a position medially disposed between the electrical coil and the distal
 portion of the terminal end. Such a strain relief could prevent expensive
 scrap and rework of actuator assemblies by absorbing tensile forces
 imparted to the terminal ends, and preventing the forces from reaching the
 windings of the electrical coil.
 SUMMARY OF THE INVENTION
 The present invention is directed to a strain relief apparatus and a method
 for routing the electrical leads of an actuator coil relative to the
 strain relief apparatus in order to prevent damage to the actuator coil
 during normal assembly operations involved in routing and electrically
 wiring the actuator assembly of a disc drive.
 The strain relief apparatus has a base that supports one or two upstanding
 posts around which the terminal ends of the electrical wire are wrapped
 thereabout before routing the wires to a circuit board for electrical
 connection. Wrapping the wire about the strain relief post causes a
 frictional engagement between the wire and the post so that tension in the
 wire downstream of the strain relief, that is, between the post and the
 circuit board, is transmitted to the post and thereby not transmitted to
 the wire making up the windings of the actuator coil
 The strain relief base is attached to the actuator assembly in a
 conventional manner, such as by an adhesive. A flange depends from the
 post to urge the wire onto the post and to retain the wire about the post
 during the routing and connection stages of electrically connecting the
 actuator coil to the disc drive control system.
 With the strain relief supported by the actuator assembly, the terminal
 ends extending from the actuator coil are first wrapped around the posts
 of the strain relief and then routed to the circuit board for electrical
 connection. The advantages and features of the present invention will be
 apparent from the following description when read in conjunction with the
 drawings and appended claims.

DETAILED DESCRIPTION
 Referring to the drawings in general, and more particularly to FIG. 1,
 shown therein is a plan view of a disc drive 100 constructed in accordance
 with a preferred embodiment of the present invention. The disc drive 100
 includes a base deck 102 to which various disc drive components are
 mounted, and a cover 104 which together with the base deck 102 and a
 perimeter gasket 105 provide a sealed internal environment for the disc
 drive 100. The cover 104 is shown in a partial cut-away fashion to expose
 selected components of interest. It will be understood that numerous
 details of construction of the disc drive 100 are not included in the
 following description because they are well known to those skilled in the
 art and are believed to be unnecessary for the purpose of describing the
 present invention.
 Mounted to the base deck 102 is a spindle motor 106 to which a plurality of
 discs 108 are mounted and secured by a clamp ring 110 for rotation at a
 constant high speed. Adjacent the discs 108 is an actuator assembly 112
 which rotates about a pivot bearing assembly 114 in a plane parallel to
 the discs 108. The actuator assembly 112 includes an E-block 115 that is
 supported by the pivot bearing assembly 114. The E-block 115 has actuator
 arms 116 (only one shown) that support load arm assemblies 118. The load
 arm assemblies 118, in turn, support read/write heads 120, with each of
 the read/write heads 120 adjacent a surface of one of the discs 108 and
 maintained in a data reading and writing spatial relationship by a
 conventional slider assembly (not shown) which supports each read/write
 head 120 in response to air currents generated by the spinning discs 108
 during operation of the disc drive 100.
 Each of the discs 108 has a data storage location with a data recording
 surface 122 divided into concentric circular data tracks (not shown), and
 the read/write heads 120 are positionably located adjacent data tracks to
 read data from or write data to the tracks. The data recording surface 122
 is bounded at an inner extent by a circular landing zone 124 where the
 read/write heads 120 can come to rest against the discs 108 at times when
 the disc drive 100 is inoperable. The data recording surface 122 is
 similarly bounded at an outer extent by a circular snubber zone 126 where
 a conventional snubber (not shown) can contact the disc 108 to limit an
 axial runout.
 The E-block 115 is positioned by a voice coil motor (VCM) 128, the VCM 128
 having an actuator coil 130 supported by the E-block 115 and immersed in a
 magnetic field generated by a magnet assembly 132. A magnetically
 permeable flux path, such as provided by a pair of steel plates 134
 (sometimes referred to as a pole 134), completes the magnetic circuit of
 the VCM 128. In a preferred embodiment shown in FIG. 1, one pole 134 is
 attached to the base deck 102 and the other pole 134 is attached to the
 cover 104. A pair of magnets 136 are supported about the actuator coil
 130, each magnet 136 supported by one of the poles 134.
 When controlled current is passed through the actuator coil 130, an
 electromagnetic field is set up which interacts with the magnetic circuit
 of the magnet assembly 132 to cause the actuator coil 130 to move relative
 to the magnets 136 in accordance with the well-known Lorentz relationship.
 As the actuator coil 130 moves, the E-block 115 pivots about the pivot
 bearing assembly 114 causing the actuator arms 116 to move the read/write
 heads 120 adjacent to, and radially across, the discs 108.
 To provide the requisite electrical conduction paths between the read/write
 heads 120 and disc drive read/write circuitry (not shown), head wires (not
 separately shown) are routed on the actuator assembly 112 from the
 read/write heads 120, along the load arm assemblies 118 and the actuator
 arms 116, to a flex circuit 138. The head wires are secured by way of a
 suitable soldering process to corresponding pads of a printed circuit
 board (PCB) 140.
 As is conventional, the actuator coil 130 is formed from an electrical wire
 which is shaped to form an active coil portion 143 comprising a plurality
 of adjacent turns of the electrical wire which magnetically interact with
 the magnet assembly 132. A pair of terminal ends 144 extend from the
 active coil portion 143. To provide the controlled current to the actuator
 coil 130, the terminal ends 144 are routed from the active coil portion
 143 to a printed circuit board 146 and secured by way of a suitable
 soldering process. The printed circuit board 146 is likewise connected to
 the flex circuit 138.
 The flex circuit 138 is connected to a flex circuit bracket 142 in a
 conventional manner which, in turn, is connected through the base deck 102
 to a disc drive PCB (not shown) mounted to the underside of the base deck
 102. The disc drive PCB provides the disc drive read/write circuitry which
 controls the operation of the read/write heads 120, as well as other
 interface and control circuitry for the disc drive 100.
 Finally, one skilled in the art will recognize the use of a latching
 assembly 148 that locks the actuator assembly 112 in a parked position
 when the read/write heads 120 have been moved to the landing zone 124 and
 the disc drive is inoperable.
 Turning now to FIG. 2, shown therein is the E-block 115 of the actuator
 assembly 112 of FIG. 1, shown in the manner in which the actuator coil 130
 is supported for operable engagement with the stationary magnet assembly
 132 (see FIG. 1). A strain relief 150 is shown attached to the actuator
 coil 130, such as by the use of a suitable epoxy such as the product 400-5
 manufactured by Ablebond, or a suitable equivalent. The strain relief 150
 provides a rigidly stationary post around which the terminal ends 144 (see
 FIG. 1) of the electrical wire forming the actuator coil 130 are wrapped
 around before routing the wires to the printed circuit board 146 for
 attachment to the flex circuit 138. In this manner the strain relief 150
 provides support to the terminal ends 144 of the wires to prevent damage
 during assembly.
 The strain relief 150 is preferably of a unitary construction, such as an
 injection molded component formed of a relatively hard, high temperature
 plastic material. One such material particularly well suited is the
 product Ultem 1000 manufactured by General Electric, or a suitable
 equivalent.
 FIG. 3 is a side view of the strain relief 150 of FIG. 2. It will be noted
 a base 152 supports a pair of posts 154 in an upstanding manner. The
 electrical wires are wrapped around the posts 154 for frictional
 engagement therewith so that a tensile force placed on the wire downstream
 of the strain relief 150 is born by the strain relief 150 and not the
 actuator coil 130.
 The need for ever lighter actuator assemblies 112 has required lighter
 actuator coils 130. One approach has been to decrease the diameter of the
 wire used in forming the actuator coil 130. Another approach has been to
 use less dense material, such as aluminum for the wire. In either case,
 these advances make the wires more susceptible to damage during handling
 operations in routing and attaching the wires to the flex circuit 138.
 This handling can likewise damage the nylon insulation on the electrical
 wire, resulting in a short circuit between windings of the actuator coil
 130. It has been shown that by routing the terminal ends 144 of the wires
 around the strain relief 150 of the present invention the amount of wire
 breakage and damage is significantly decreased. It has been determined
 that generally two wraps of the wire around the post 154 is sufficient to
 affix the wire, that is, to prevent slippage of the wire around the post
 154.
 FIGS. 3 and 4 further show a flange 156 is supported by a distal end of
 each of the posts 154. The flange 156 has an enlarged cross-sectional area
 in comparison to the posts 154 in order to guide the wire into engagement
 with the post 154 and retain the wire on the post 154 during times when
 attachment of the distal end of the terminal portion can create slack in
 the wire.
 FIGS. 5 and 6 show a strain relief 158 having a base 152 and posts 154 as
 in FIG. 3, but with a round flange 160. It has been determined that the
 rounded edges of the flange 160 facilitate the routing of the wire around
 the post 154 by reducing the obstruction provided by the flange 160 and by
 eliminating the pointed corners which tend to snag the wire.
 FIGS. 7 and 8 show a strain relief 162 having a base 164 of a reduced size,
 and supporting only one post 154 rather than two. Because the electrical
 wire is insulated, typically with an epoxy, the two terminal ends 144 can
 be wrapped together around one post 154. Combining the terminal ends 144
 to one post 154 presents certain logistical difficulties, however, in that
 the terminal ends 144 must be matched with the appropriate pad on the
 printed circuit board 146. Combining the terminal ends 144 around a single
 post 154 makes it more difficult to maintain the identity for appropriate
 connection to the printed circuit board 146, thus making it more likely
 that the actuator coil 130 can be wired backward.
 FIG. 9 is an enlarged view of a portion of the actuator assembly 112 of the
 prior art disc drive 100 of FIG. 1, wherein the terminal ends 144 of the
 electrical wire are shown extending from the actuator coil 130, thereat
 being routed and attached to the printed circuit board 146. The printed
 circuit board 146 is typically attached to the E-block 115 for support by
 a fastener 166 that threadingly engages the E-block 115.
 FIG. 10 is a view from a perspective along the projection line 10--10 of
 FIG. 9 showing the attachment of distal portions 167 of the terminal ends
 144 by a suitable solder 168 to a pad 170 of the printed circuit board
 146.
 Finally, FIG. 11 shows a portion of the actuator assembly 112 of FIG. 2
 that is constructed in accordance with a preferred embodiment of the
 present invention, whereby the terminal ends 144 are wrapped around the
 posts 154 of the strain relief 150 before being routed toward and attached
 to the printed circuit board 146. It will be noted that the flanges 156
 are not shown for clarity in showing the terminal ends passing around the
 posts 154 between the actuator coil 130 and the printed circuit board 146.
 In this manner a resistive force, or strain relieving force, is provided
 for each terminal end 144 in that portion between the strain relief 150
 and the coil 130, so that tension imparted to the terminal end 144
 downstream of the strain relief 150, or between the circuit board 146 and
 the strain relief 150, is not transmitted to the actuator coil 130. One
 skilled in the art will recognize the benefit associated with protecting
 the actuator coil 130 from forces during assembly of the disc drive 100
 which tend to damage the terminal ends 144 at the actuator coil 130.
 The resistive, or strain relieving, force is the result of a frictional
 engagement between the terminal end 144 and the post 154. The amount of
 strain relieving force is thus proportional to the surface area of wire
 that engages the post 154. That is, the strain relieving force increases
 with more wraps of the terminal end 144 around the post 154. It has been
 shown that two wraps provide a sufficient resistance to slippage in light
 of the assembly processes at hand and the tensile strength of the wire.
 The present invention provides an apparatus and a method for supporting a
 terminal end (such as 144) of an electrical wire which is used in the
 construction of an electrical coil (such as 130) for a voice coil motor
 (such as 128) of a disc drive (such as 100). A strain relief (such as 150)
 is provided which has an upstanding post (such as 154) around which the
 wire is wrapped before routing a distal end of the terminal portion to a
 connecting printed circuit board (such as 146). In this manner the wire
 frictionally engages the post so that tension placed on the wire
 downstream of the post is absorbed by the post, and not transmitted along
 the wire upstream of the post.
 The strain relief has a base (such as 152) that is supported by an actuator
 assembly (such as 112) of the disc drive, whereas the actuator assembly
 also supports the actuator coil (such as 130). In a preferred embodiment
 the base can be adhered to the windings of the actuator coil near the
 terminal ends of the electrical wire. The base supports the post, and a
 flange (such as 156) depends from a distal end of the post for urging the
 wire to remain on and about the post.
 In one preferred embodiment the strain relief can have one post, about
 which both terminal ends are wrapped. In an alternative preferred
 embodiment the strain relief can have a pair of posts, about which a
 terminal end is wrapped about each post. It will be recognized by a
 skilled artisan that a two-post strain relief facilitates wire separation
 and routing in a manner less likely to reverse the terminal ends at the
 printed circuit board and thereby electrically connect the actuator coil
 backwards.
 The strain relief of the present invention permits an improved method of
 electrically connecting the disc drive actuator assembly. FIG. 12
 illustrates the following steps of the method:
 (a) winding an electrical wire to form an electrical coil, leaving a pair
 of terminal ends extending from the actuator coil (180);
 (b) attaching a strain relief to the actuator coil (182);
 (c) winding a medial portion of each wire terminal end around an upstanding
 post portion of the strain relief (184);
 (d) attaching the actuator coil to a supporting portion of an actuator
 assembly (186);
 (e) attaching a printed circuit board to the actuator assembly, the circuit
 board having a flex assembly depending therefrom (188);
 (f) electrically connecting each terminal end to the circuit board (190).
 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 details 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.