Head actuator assembly for a tape drive

A head actuator assembly includes a coarse positioner base assembly that is mounted on a guide shaft and an anti-rotation shaft and provides increased structural rigidity due to a four-point support and spring loading of the coarse positioner base against the anti-rotation shaft. A two-part head-carriage and voice coil holder system permits different materials to be used for the head-carriage and the voice coil holder, obviating structural problems of a single-structured head-carriage and coil-holder system. A flexible printed circuit bracket eases manufacture and allows flexible printed circuits to be slid into the bracket and retained in place without the need for locating tabs and screws.

FIELD OF THE INVENTION

The present invention relates to the field of tape drives, and more particularly, to the head actuator assembly for a tape drive.

BACKGROUND OF THE INVENTION

A tape drive head assembly generally comprises three main components: a magnetic read/write head, a movable carriage supporting the head, and a flexible circuit electrically connected to the head. The flexible circuit includes a fine positioner loop and a coarse positioner loop. A flexible printed circuit provides communication between the main control circuitry of the tape drive and the head positioning apparatus. Generally, a voice coil serves as an actuator for the fine positioner.

Magnetic tape data storage devices, or tape drives, are used for storing large quantities of computer data. As storage capacities of tape drives increase, the overall performance and structural integrity of the drives needs to improve. One of the areas needing improvement is found in the performance of the head positioning system.

Lateral motion at the read/write head needs to be controlled within a few micrometers in order to achieve a LTO (linear tape open) cartridge capacity of 400 GB, for example. Conventional techniques of controlling this lateral motion include a camming arrangement between a pivoting beam structure and the head structure that translates a rotational motion into a linear motion of the head traverse. The fine positioner prime mover is a rotary voice coil actuator. One of the major concerns with such an arrangement is the friction associated with both the pivot and cam follower systems. Unlike hard disk drives, a tape drive is an open system and subject to contamination. This makes pivot and cam-follower guide friction problems even worse. Further, there is a potential loss of accuracy during a rotary to linear motion conversion due to clearance in the cam-follower system, as well as wear in the pivot system. Thus, problems in servoing due to friction and the rotary to linear approach makes the requirement of controlling the lateral motion within two micrometers, for example, difficult to achieve.

Another concern of conventional head positioning systems is the lack of adequate structural rigidity in the coarse positioner construction to achieve a necessary frequency response requirement to perform adequate servoing. Conventional systems employ a single guide shaft, resulting in a cantilever beam with a low first mode of resonance. Due to this low first mode of resonance, it is difficult to maintain the required servo-bandwidth to satisfy the necessary accuracy requirement of high capacity tape drives.

Additional concerns with conventional coarse positioner constructions, which are required to hold the head carriage assembly and the voice coil system, include the inability to avoid structural problems of the voice coil holder structure, exacerbating resonance-related problems.

A still further problem with conventional coarse positioner constructions is the integral nature of such systems. The magnetic head is a high cost element, while the voice coil system is a much lower cost element. However, in an integral system, if a voice coil element is defective, the entire coarse positioner system, including the relatively expensive head, needs to be replaced.

Another concern with conventional systems is the use of a flexible printed circuit (FPC) routing system that requires locating tabs and corresponding screws for attachment of the locating tabs. The resulting design presents manufacturing assembly issues and increased cost of parts. Further, the tab system provides for an FPC registration on a single edge. This requires additional assembly instructions for the proper routing of the FPC.

SUMMARY OF THE INVENTION

There is a need for a head actuator assembly for a tape drive with an improved fine positioner system and coarse positioner base mounting that increases the accuracy of the fine positioning as well as improves the structural rigidity of the coarse positioner. Further, there is a need for a head actuator assembly that allows for more efficient assembly, especially with respect to the flexible printed circuit routing.

These and other needs are met by embodiments of the present invention which provide a head actuator assembly for a tape drive comprising a coarse positioner base assembly and first and second shafts that are vertically mounted at first ends on the coarse positioner base assembly. A coarse positioner base is provided that is configured to carry a head carriage assembly and voice coil holder. The coarse positioner base has at least first and second bores and at least first and second bushings respectively in the first and second bores. The coarse positioner base is vertically mounted on the first and second shafts so that the first and second shafts respectively extend through the first and second bushings and the first and second bores.

By providing a two-shaft system, with one of the shafts being a guide shaft, for example, and the other shaft being an anti-rotation shaft, for example, the coarse positioner base can be supported at both of the shafts. This results in an improved structural construction compared to a cantilever system, thereby providing a much stiffer system as compared to a single shaft-guide system.

The earlier stated needs are also met by embodiments of the present invention which provide a head actuator assembly for a tape drive comprising a head carriage assembly and a voice coil holder removably coupled to the head carriage assembly. By employing a separated head carriage assembly and voice coil holder, different materials may be employed for these elements, resulting in improved rigidity and structural stability. Further, this system allows replacement of a defective voice coil after assembly, since the entire head does not have to be discarded. This saves costs during manufacture.

In certain embodiments, the fine positioner system includes a linear voice coil motor and uses flexures to improve the fine positioning without a rotary to linear motion conversion, such as that employed in conventional devices.

In certain embodiments of the invention, a flexible printed circuit bracket is provided that contains slots through which an FPC is routed and retained. This avoids the use of locating tabs and corresponding screws for attachment. Hence, no additional hardware is needed to secure the flexible printed circuit in place, easing assembly and reducing material costs as well as improving registration.

The earlier stated needs are met by other embodiments of the present invention which provide an assembly for a tape drive comprising a magnetic read/write head and means for positioning the head.

DETAILED DESCRIPTION OF THE INVENTION

The present invention addresses and solves problems related to performance and structural integrity in magnetic tape data storage devices. These problems include friction and vibration concerns associated with conventional pivot and cam following systems, and inadequate structural rigidity to produce a frequency response required to perform adequate servo functions, as well as inefficient assembly concerns related to flexible printed circuit routing. The present invention solves these problems, in part, by providing a head actuator assembly for a tape drive that employs a linear voice coil motor and use of flexures, thereby avoiding a pivot and cam-follower arrangement. Since a tape drive is an open system and subject to contamination, the arrangement of the invention avoids the additional problems an open system experiences due to contamination. Embodiments of the invention employ a coarse positioner base mounting system that uses two shafts with a force bias applied at one shaft to create a much stiffer system as compared to single shaft-guide systems. Further, embodiments of the invention provide for a separate head-carriage and voice coil holder system that allows different materials to be employed instead of a single-structured integral head-carriage and voice coil-holder system. The separation of the head and voice coil allows an inexpensive voice coil to be simply replaced if defective during assembly, and prevents the waste of an expensive magnetic head that is not defective. In addition, separation of the voice coil holder and head-carriage assembly allows the use of an alternate stiffer material of the voice coil holder.

FIGS. 1 and 2are front and back perspective views of a head positioner assembly constructed in accordance with embodiments of the present invention. The head positioner assembly10includes a coarse positioner base assembly12on which many of the components of the head positioner assembly10are mounted.

A coarse positioner base14is slidably mounted on first and second shafts16,18. The first shaft is a guide shaft16, affixed to the coarse positioner base assembly12, and the second shaft is an anti-rotation shaft18, also affixed to the coarse positioner base assembly12. This two shaft system prevents a low first mode of resonance, as normally occurs in a single shaft system having a cantilever beam with a low first mode of resonance. Because of the structural rigidity provided by the combination of the coarse positioner base14and guide shaft16, and anti-rotation shaft18, a required servo-bandwidth is achieved to meet the necessary accuracy requirement of high capacity tape drives.

At the top, the guide shaft16is supported by a guide shaft support arrangement20which comprises a brace22that is vertically mounted to the coarse positioner base assembly12. A horizontally extending plate24is provided at the top of the brace22and includes a bore through which a fastener26secures the guide shaft16. This guide shaft support arrangement20provides a very stable securement of the guide shaft16.

The anti-rotation shaft18is similarly supported by an anti-rotation shaft support arrangement28that includes two support shafts30that are securely mounted on the coarse positioner base assembly12. A horizontal connecting plate32connects the top of the support shafts30and the anti-rotation shaft18. Fasteners34secure the anti-rotation shaft18and the support shafts30to the connecting plate32. The anti-rotation shaft support arrangement28provides a very secure and rigid structure for the anti-rotation shaft18.

In certain embodiments of the invention, the anti-rotation shaft18has a smaller diameter than the guide shaft16to allow for manufacturing tolerances. The coarse positioner base14is spring loaded by a biasing element, such as a spring plunger36(depicted inFIG. 2) against the anti-rotation shaft18. This ensures that the coarse position base14is always supported at the anti-rotation shaft18, which in turn, provides further structural rigidity to the coarse positioner assembly.

The coarse positioner base14is moved vertically through a lead screw38that extends through the coarse positioner base14. The lead screw38is driven by a motor40through a gear train42(only depicted inFIG. 2). Springs44bias the coarse positioner base14against the lead screw nut54. The coarse positioner base assembly12, the guide shaft support arrangement20, the anti-rotation shaft18and the coarse positioner base14are depicted in isolation inFIG. 3. Also,FIGS. 4aand4bshow top and bottom perspective views, respectively, of the coarse positioner base14.

The coarse positioner base14includes top bushings46and bottom bushings48through which the guide shaft16and the anti-rotation shaft18extend. The top and bottom bushings46,48provide a four-point support for the coarse positioner base14, resulting in increased structural rigidity in comparison to conventional designs. As best illustrated inFIGS. 4a–4b, the coarse positioner base12includes a lead screw bore50. A notch52is provided for the lead screw nut54(FIG. 2).

A fine positioner assembly is depicted in isolation inFIGS. 5 and 6, and is depicted assembled within the head positioner assembly10inFIG. 1. The fine positioner assembly60includes a head carriage assembly62, a voice coil holder assembly64and a voice coil motor holder assembly66. As will be appreciated from the following description, these assemblies62–66are separable, thereby providing significant advantages over conventional designs, including performance and cost advantages. The fine positioner assembly60is carried by the coarse positioner base14that provides a coarse positioning of the magnetic head. The fine positioner system of the invention uses a linear voice coil motor and flexures to provide for fine positioning of the head.

The head carriage assembly62carries a magnetic read/write head68. The head carriage assembly62is depicted in isolation in a back perspective view ofFIG. 7. For weight purposes, the head carriage assembly62may be made substantially out of a lighter weight material, such as plastic with some conductive filler such as carbon to provide an anti-static property to the head-carriage assembly. A magnetic read/write head holder70is supported by horizontal support elements72that are connected together by a vertical support bar74. A screw hole76receives a fastening screw78that connects the voice coil holder assembly64to the head carriage assembly62at a top portion thereof. A horizontal support member80extends from the lower horizontal support element72. The horizontal support member80includes a screw hole82through which the voice coil holder assembly64is secured by another fastener (not shown inFIGS. 5–7).

The voice coil holder assembly64includes a voice coil holder84(seen in isolation inFIG. 8) and a voice coil96seen inFIG. 9. The voice coil holder may be of a stiffer material, such as aluminum to provide structural rigidity that is many times stronger than the plastic material employed in the head carriage assembly62. At the same time, the separate nature of the head carriage assembly62and the voice coil holder assembly64provides for easy manufacture.

The voice coil holder84includes an attachment section86with a hole88to attach the voice coil holder84to the head carriage assembly62at the threaded hole76. The voice coil holder84includes a top flexure mounting surface90to which a top flexure92(seeFIG. 9) is attached.

A voice coil mounting cylinder94of the voice coil holder84fits within the voice coil motor, as will be described later. The voice coil96is mounted to the cylinder94. A threaded hole98is provided at the bottom of the voice coil holder84and provides a means for attaching the voice coil holder84to the head carriage assembly62at the horizontal support member80through the screw hole82(seeFIG. 7).

A head flexible printed circuit (FPC) bracket100is shown inFIG. 9and routes the head FPCs102through head FPC locating features104a,104bas will be described in more detail later.

FIG. 10is a perspective view of the voice coil motor holder assembly66in isolation. The voice coil motor108is securely held within a voice coil motor holder110of the voice coil motor holder assembly66. Referring toFIGS. 7–10and12, voice coil holder assembly64is assembled into the voice coil motor holder assembly66in order to place the voice coil96into the magnetic gap of the voice coil motor108. The top flexure92is assembled first at its center portion using the screw113and then at its outer portion such that it is secured to the mounting surfaces114of the assembly66. Head-carriage assembly62is assembled to the voice coil holder assembly64, using the screw78such that the holes88and76are aligned. Bottom flexure122is assembled at its outer portions at the surfaces120of assembly66. The center portion of bottom flexure122and the support82of the head-carriage assembly62are secured to the voice coil holder assembly64, using the screw112by fastening it into the threaded hole98.

The voice coil motor holder110has a pair of top flexure mounting surfaces114on which the top flexure92is mounted. Locating posts116help to locate the top flexure92during assembly and fasteners118(seeFIG. 6) secure the top flexure92to the top flexure mounting surfaces114.

Bottom flexure mounting surfaces120provide a surface for mounting the bottom flexure122(seeFIG. 9) by fasteners that are not shown.

The voice coil motor108has a substantially cylindrical design but includes a novel tapered center pole124. The tapering of the center pole124of the voice coil motor108provides room for the voice coil mounting cylinder94to easily fit between the center pole124and the magnet126of the motor108.

The voice coil motor holder110also has fastener holes in the bottom flexure mounting surfaces120for attaching a FPC bracket100with head FPC locating features104a,104bas previously shown inFIG. 9. In conventional construction, the flexible printed circuit has tabs that needed to be precisely located and screwed in to locate and secure the head FPCs. However, the present invention provides an improved head FPC bracket100, shown in isolation inFIG. 11, that obviates the need for screws on the head FPC. After attachment by the fasteners through bores142of the head FPC to the voice coil motor holder110, the head FPCs102may be slid through the opening144into the slots140of the head FPC bracket100. The head FPCs102are securely held in place and prevented from moving by the head FPC locating features104a,104b. When the head positioner assembly10is moved, the head FPC bracket100securely holds the head FPCs102and protects them from unwanted contact with other parts of the tape drive.

FIG. 12depicts the fine positioner assembly60in cross-section. The tapering of the center pole124is clearly illustrated in this Figure, as well as the routing of the head FPCs102through the head FPC bracket100. Also, the fastening of the voice coil holder84to the head carriage of the head carriage assembly62may be better understood from this Figure.

The present invention thus provides an arrangement that improves accuracy of the fine positioning of the head by improving on conventional system arrangements that involve translation of a rotational motion into a linear motion of a head traverse. Further, the invention provides an increased structural rigidity of the coarse positioner and avoids resonance related problems of conventional coarse positioner constructions. The invention also provides for efficient assembly by employing an improved flexible printed circuit routing system that reduces the cost of parts and eases the manufacturing assembly of the flexible printed circuit in the system. Further, the separation of the head-carriage and voice coil holder systems allows the use of different materials for the two systems, preventing any structural problems relating to single-structured head-carriage and coil-holder systems. Also, the invention provides the advantage of providing a separated head and voice coil. Thus, if for any reason the voice coil is defective after assembly, the entire head assembly does not have to be discarded. Rather, a relatively inexpensive voice coil may be exchanged.