Patent Application
20070279806
The following description is presented to enable a person of ordinary skill in the art to make and use the various inventions, and is provided in the context of particular applications and examples. Various modifications to the examples will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other examples and applications without departing from the spirit and scope of the invention. Moreover, in the following description, numerous details are set forth for the purpose of explanation. However, one of ordinary skill in the art will realize that the invention might be practiced without the use of these specific details. In other instances, well-known structures and devices are shown in block diagram form in order not to obscure the description of the invention with unnecessary detail. Thus, the present invention is not intended to be limited to the examples shown and described, but is to be accorded the widest scope consistent with the principles and features disclosed herein.
For ease of explanation, the examples are described generally with respect to a magnetic storage tape drive actuator and fine positioner system thereof. It will be appreciated by those of ordinary skill in the art that the examples may be applied (with appropriate modifications) to other data storage systems such as optical, magnetic, or magnetic-optical storage systems.
In one example, a fine positioning system is described that may operate at high servo bandwidths by having a balanced assembly, for example, where the center of the motor force acting on the moving portion of the assembly is substantially through or aligned with the center of mass of the moving portion of the assembly. In one example, the moving portion includes a support frame holding a magnet assembly (including, e.g., at least one permanent magnet and a magnet holder) and a data transducer head. The frame is operable to move relative to a stationary planar coil attached to a base or stationary portion of the actuator. In one example, a major surface of the planar coil is positioned substantially parallel to a supporting surface of the data transducer head.
Aligning the center of the motor force with the moving portion of the positioner may reduce torques thereon and improve performance and operating bandwidth of the system. In one example, the coil is positioned at or near the center of mass of the moving portion of the positioner, and when activated generates a magnetic field and force on the permanent magnet substantially aligned with the center of mass. Additionally, utilizing a stationary coil (as opposed to a moving coil) may simplify the assembly as well as improve the durability and life of the assembly as movement and flexing of the coil or leads to the coil is reduced or eliminated during operation.
In operation, positioner 101, including tape head 108 and magnet 121 attached to head mounting frame 104, moves relative to stationary coil 110 in response to magnetic fields produced by coil 110, resulting in a magnetomotive force exerted on magnet 121. In particular, magnet 121 and coil 110 are configured in a fashion such that upon the application of sufficient electrical current to coil 110, a force is generated therebetween causing relative movement between magnet 121 and coil 110. In this example, coil 110 is held stationary, for example, with respect to a base of the actuator (see, e.g.,
The data transducer head 108 includes a support surface 108s for supporting and engaging tape 111 as passes adjacent at least one data transducer element formed therewith, e.g., read or write elements, for reading from or writing to tape 111. Head 108 may include read/write transducer elements, and tape 111 may include a magnetic data storage tape. Accordingly, a controller (not shown) may energize coil 110 with an appropriate magnitude and polarity/direction of current to generate a desired magnetic force and movement of positioner 101, thereby positioning head 108 and associated transducer elements at a desired location relative to head 111. In particular, positioner 101, including head 108, moves in response to changing current applied to coil 110, generally along axis A2 to access (e.g., read/write) tracks of storage medium 111 during operation.
In this example, magnet 121 is disposed adjacent coil 110 (but not necessarily without an interposed element). Magnet 121, which may include one or more permanent magnets positioned adjacent each other, includes a major surface adjacent, and substantially parallel, to major surface 130 of coil 110. Magnet 121 may be held by a magnet holder 120, which wraps partially or fully around coil 110. In this example, magnet holder 120 is configured to hold magnet 121 at a suitable position such that the center of mass of the moving portions of positioner 101 (other than coil 110) is located at or near the position of the center of coil 110, or at least at or near the center of a magnetic field generated by coil 110. In this manner, the motor force generated by coil 110 is generally aligned with the center of mass of positioner 101. Such an arrangement, e.g., with the center of motor force through the center of mass of positioner 101, may provide a balanced assembly with reduced torques (and without exciting resonances of positioner 101 during operation).
Coil 110 includes, for example, an insulated conductive wire, e.g., a copper wire, wrapped in a spiral shape to form a multi-turn, flat, rectangular coil with two rounded sides, two flat sides, and a major surface 130. Major surface 130 of coil 110 is substantially parallel to a plane defined by the axes A1 and A2. Axes A1 and A2 further generally relate to a plane of tape 111 as it engages supporting surface 108s of data head 108. It will be recognized, of course, that contoured heads, for example, engage tape 111 as it wraps or curves on a contoured surface thereof; accordingly, in one example, it may be stated that major surface 130 of coil 110 is substantially parallel to a portion of support surface 108s of head 108, or alternatively that major surface 130 of coil 110 is substantially parallel to a direction of tape transport over at least a portion of head 108, generally defined by axis A1. It is also noted that the support surface of head 108 does not necessarily physically contact tape 111, e.g., a thin layer of air may be present there between, such that engaging may include supporting tape 111 as it steams by via an air lubricated interface with tape 111.
For illustrative purposes only, the dimensions of an exemplary coil 110 are as follows. The upper and lower flat surfaces of the coil 110 are 0.413 inches in length (i.e., along axis A1). The outer radius of each rounded side of the coil is 0.157 inches. The width of the coil is 0.314 inches (along axis A2) and the overall length of the coil is 0.728 inches (along axis A1; the sum of 0.413, 0.157, and 0.157). The thickness of the coil is 0.049 inches (along axis A3). The coil 110 includes a slot 131, which is an empty area that has an inside surface around which internal windings (not shown) of the coil may be wound. The width of the slot 131 is 0.079 inches (along axis A2). Other examples of the coil 110 may have different dimensions depending, e.g., on the particular application, actuators, mass, center of mass of positioner 101, and so on.
An axis A3 is shown passing generally through the north pole N and south pole S of coil 110. The axis A3 is generally perpendicular to a plane of tape 111, of which the axes A1 and A2 are parallel to. Accordingly, in this example, the major surface 130 of coil 110 is substantially parallel to a supporting surface of head 108 and the direction of tape transport relative to a portion of head 108. Thus, the major surface of coil 110 is substantially parallel to the plane defined by the axes A1 and A2.
In one example, coil 110 is positioned relative to moving portions of fine positioner 101, and more particularly, relative to head 108, magnet 121, and associated structures such as magnetic holder 121 and frame 104, such that the motor force generated by coil 110 is positioned at or aligned substantially with the center of mass of fine positioner 101, or at a relatively small distance from the center of mass of fine positioner 101. The small distance may, for example, allow for structural members between coil 110 and head 108. The term “aligned” is used herein to indicate that the center of motor force generated by coil 110, via the interaction of coil 110 current when energized and the magnet field set-up by the magnet 121, is positioned relative to the center of mass of fine positioner 101 within a predetermined distance and at a predetermined three-dimensional offset. The center of mass is a close approximation to the actual center of mass of the fine positioner 101, because, e.g., the parts of the positioner 101 have tolerances which may cause the exact center of mass to be different from the nominal center by some small amount, and positioner 101 is moving during operation and may only be aligned during a portion of the movement.
In one example, coil 110 and/or the center of magnetic force generated by coil 110 is disposed at or near the center of mass of fine positioner 101 in two of the three spatial dimensions, e.g., at or near zero offset. In one example, the centers are separated by a small distance, e.g., 0.3 inches or less, in the third dimension. In another aspect, the center of force of the coil 110 is at a predetermined spatial offset from the center of mass of the fine positioner 101, e.g., at an offset of 0.3 inches or less in a first dimension, an offset of 0.01 inches or less in a second dimension, and an offset of 0.01 inches or less in a third dimension.
Magnet holder 120 (or a portion of holder 104 engaging magnetic 121) may include a ferrous or ferromagnetic material, e.g., steel or the like, and may serve as a magnetic flux conducting structure (for forming a magnetic circuit). Magnet 121 may include any suitable magnetic material such as a rare earth magnetic material. Additionally, magnet 121 may include any number of permanent magnets, for example, a two-pole magnet or a four-pole magnet, as described in greater detail with respect to
The magnet 121 is positioned adjacent to the major surface 130 of the coil 110, so that magnet holder 121 wraps partially or fully around coil 110. As described, fine positioner 101 is movable relative to coil 110. In one example, fine positioner 101 is not attached to coil 110. That is, neither magnetic holder 120, magnet 121, nor the frame 104 is attached directly to coil 110. In one example, fine positioner 101 is attached to coil 110 in a fashion allowing for relative movement of fine positioner 101 (including frame 104, magnet 121, and head 108) and coil 110 as generally described herein.
In this example, the distal end of upper flexure 100 is attached to a top side 105 of head frame 104 and extends substantially perpendicularly from head frame 104. The distal end of the lower flexure 102 is attached to a bottom side 106 of the head frame 104 and extends substantially perpendicularly from the head frame 104. In this example, flexures 100 and 102 are substantially perpendicular to major surface 130 of coil 110. Further, flexures 100 and 102 are substantially parallel to axis A3 passing through the magnetic poles of the coil 110 when current is applied thereto, e.g., through the center of coil 110 as shown in
In one example, flexures 100 and 102 are formed from a thin sheet of metal. In other examples, flexures 100 and 102 may include any suitable flexible material with elastic properties, such as a flat spring or flat members connected by a spring-loaded hinge. In one aspect, each of the flexures 100 and 102 includes a void, such as a rectangular hole in the center of the flat surface of the flexure. In one aspect, each flexure 100 and 102 has a rectangular void 107, which divides the flexures 100 and 102 into two longitudinal bar regions. Each rectangular flexure 100 and 102 is, for example, 0.512 inches in width (i.e., along axis A1) by 0.551 inches in length (along axis A3) by 0.003 inches in thickness (along axis A2). The thickness of each flexure 100 and 102 may be between 0.002 inches and 0.005 inches (along axis A2). It will be recognized, of course, that flexures 100 and 102 may have various dimensions depending, e.g., on the particular application, design considerations, cost considerations, and the like. Further, the upper flexure 100 need not include the same materials or dimensions as the lower flexure 102.
In operation, an electric current applied to coil 110 moves fine positioner 101 along the axis A2, the motion constrained by flexures 100 and 102 as described herein. For example, as tape 111 moves past head 108 in a direction substantially parallel to an axis A1, the high out-of-plane stiffness of flexures 100 and 102 allows fine positioner 101 to move and follow lateral tape motion of tape 111 (e.g., lateral tape motion, along axis A2), while reducing out-of-plane motions caused by natural resonances in frequency ranges that may influence the tracking system. The flow of electric current through coil 110, which is in the magnetic field created by magnet 121, generates a force which moves magnet 121 and consequently fine positioner 101, including the head 108, in a direction substantially parallel to the axis A2 (e.g., there is or may be some rotational motion depending on the distance moved).
The position of coil 110 between the flexures 100 and 102 and in close proximity to the center of mass of the positioner 101 allows the actuator servo control system to operate at high frequencies, e.g., above 800 Hz, because the center of force produced by the coil is located at or near the center of mass of fine positioner 101. Further, the particular arrangement of this example may reduce torques on the fine positioner 101 because coil 110 is at or near the center of mass of positioner 101 and the relative stiffness of the flexures 100 and 102 in the axes normal to the axis A2. In one aspect, the coil 110 is positioned relative to frame 104, head 108, and magnet 121 such that the center of force of the coil 110 is located at or near the center of mass of the fine positioner 101. The mounting attachment may be secured by screws or other fasteners, and may include plates, e.g., a plate 216, to hold the flexures against the frame 104. Alternatively, some or all of the components, including coil 110, head 108, and flexures 100 and 102 may be integrally formed in a single assembly.
Coil 110 is attached to and stationary with respect to base 212 (or another portion of actuator 200) such that positioner 101 moves relative to coil 110 and base 212. Coil 110 may be electrically connected via wires attached to a fixed flex lead, wire bundle, or the like. Because coil 110 is stationary with respect to base 212, the durability and life of the connection of coil 110 may be improved over existing actuator assemblies where such leads are flexible and move with movement of coil 110.
In this example, coil 110 is positioned between upper flexure 100 and lower flexure 102, and the plane of the flat side of the coil 110 is substantially perpendicular to the upper flexure 100 and the lower flexure 102. That is, the flat side of the coil 110 is typically at a 90 degree angle to the flexures, but other orientations are possible. In other examples, however, flexures may extend at non-right angles from the coil, or the coil may be positioned at a slightly non-right angle.
Base 212 is spaced apart from the head frame 104, and the upper flexure 100 and the lower flexure 102 are affixed to the base 212, e.g., by screws 218 which secure the mounting plate 216 against the upper flexure 100. In another example, the upper flexure 100 and the lower flexure 102 may be integrally formed upon the head frame 104 or base 212.
In one example, a position sensor 109 may be mounted on the base 212 to monitor the position of a portion of positioner 101, e.g., support frame 104, with respect to the base 212. Position information from the position sensor 109 may be used by a drive controller (not shown) to maintain the position of head 108 during shock events. The position sensor 109 may be, for example, an optical interrupter, a miniature Hall-effect sensor, and inductive sensor, or the like. During a mechanical shock event the head 108 and frame 104 may move before the servo system can detect that the head 108 is moving off track. The sensor 109 provides feedback which can be used to correct the position of head 108, e.g., by generating or adjusting a current in coil 110 to move frame 104 and position head 108 in response to the detected movement.
The moving magnet assembly of magnets 421 may include one or more magnets, including an arrangement of two or four-pole magnets, for example. In the present instance, a four-pole magnet (having two north poles and two south poles) is shown
When current flows through coil 410, a magnetic field is created, which interacts with the magnet field of magnets 421 and results in a force and relative movement of magnets 421 and frame 404 relative to coil 410. For example, applying current through coil 410 in a first polarity. or direction results in a magnetic force on magnets 421 and frame 404 in a first direction (along axis A2); conversely, applying current through coil 410 in a second polarity or direction results in a magnetic force on magnets 421 and frame 404 in a second direction, opposite from the first direction. Accordingly, varying the polarity and magnitude of current through coil 410 provides varying forces and displacement of frame 404 relative to coil 410.
For example, if current is applied through coil 410 in a fashion to set-up a magnetic field corresponding to a north pole positioned at the surface 430 of coil 410 facing magnets 421, magnets 421 and frame 404 would be forced up (e.g., the generated north pole of coil 410 attracting the south pole S of lower magnet 421 and repelling the north pole N of upper magnet 421). Reversing the current through coil 410 results in the force acting in the opposite direction. In other examples, a single permanent magnet 421 could be used, offset from the center for the magnetic field generated by coil 410.
Magnets 421 and 422 each have a north pole N and a south pole S and are positioned generally to provide a magnetic field in a direction substantially perpendicular to the major surfaces 430 and 431 of coil 410. The magnetic field is shown in
It is noted, that the term “substantially” as used herein to indicate an approximation of a perpendicular or parallel orientation (with respect to any of the examples) does not require an absolute perpendicular or parallel orientation. In one example, a substantially perpendicular or parallel orientation includes within plus or minus 15 degrees of perpendicular or parallel, and in one example, within 5 degrees of perpendicular or parallel. Accordingly, in one example, coil 130 is described as being substantially parallel to the plane of tape 111 defined by the axes A1 and A2 (at the point where tape 111 passes over head 108) or to the axes A2. The term “substantially” indicates that the coil 130 may be oriented parallel to, i.e., at an angle of 0 degrees to, the plane of the tape 111, or at an angle of up to plus or minus 15 degrees to the axis A1 or to the axis A2, or at up to plus or minus 15 degrees of each axis A1, A2. The 0 degree angle is shown in the figures and is used here for illustrative purposes of one instance. To illustrate the term “substantially perpendicular”, the upper flexure 100 may be perpendicular, i.e., at a 90 degree angle, to the head frame 104, or may be at some other angle within approximately 15 degrees of a right angle, e.g., 75 degrees. The 90 degree angle is shown in the figures and is used for illustrative purposes. However, the flexures may be at others angles to the head frame. Angles other than 90 degrees may cause the flexures to impart a tip of the head 108 into and out of the plane of the tape 111 as the head 108 moves along the axis A2. Therefore, the angle is typically 90 degrees, or close to 90 degrees, e.g., 85 or 95 degrees.
Although various aspects of the invention have been described in connection with some specific embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the claims. Additionally, although a feature may appear to be described in connection with a particular embodiment, one skilled in the art would recognize that various features of the described embodiments may be combined in accordance with the invention. Moreover, aspects of the invention describe in connection with an embodiment may stand alone as an invention.
Moreover, it will be appreciated that various modifications and alterations may be made by those skilled in the art without departing from the spirit and scope of the invention. The invention is therefore not to be limited by the foregoing illustrative details, but is to be defined according to the claims.
