Abstract:
A method of retaining a transducer for a digital storage apparatus that reads and writes data to a tape as the tape is moved in a tape drive path across the transducer. According to the method a head assembly is attached to the base to be movable relative to the base in a linear path that is perpendicular to the tape drive path. Movement of the head assembly is guided on a track that is partially defined by the head and partially defined by the base. At least two balls are disposed in the track between the base and the head assembly. A magnetic coupling retains the balls within the track. A linear motor operatively engages the head assembly to move the head assembly to follow the tape.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a division of U.S. application Ser. No. 11/733,812 filed Apr. 11, 2007, now U.S. Patent No. 7,965,472 issued Jun.  21, 2011, the disclosure of which is incorporated in its entirety by reference herein.    
    
    
     BACKGROUND 
     Linear guides for transducers are used in media drives to align a transducer with respect to a media track or tracks. Examples of transducer positioning devices are disclosed in U.S. Pat. Nos. 6,437,946 and 6,985,430. 
     Linear guides for transducers are generally preloaded to remove play and minimize undesirable head movements. The most common method of preloading is to use springs that bias the linear guides. Spring preloading mechanisms may be a source of reliability and performance issues. Reliability and performance problems may arise due to component fatigue, component wear, and unpredictable frictional forces that may occur at preload component interfaces. Such reliability and performance problems may contribute to poor actuator performance and reduced linear guide and head actuator product life. 
     Linear guide spring preload mechanisms are small parts of considerable complexity. The cost of assembling such small, complex parts increases the cost of assembling the linear guides and head actuator assemblies. 
     The present invention is directed to overcoming the above problems as summarized below. 
     SUMMARY 
     According to one aspect of the present invention, a method is provided for retaining a movable head of a transducer on a base of the transducer. The transducer may include a linear motor that operatively engages the head. The movable head and the base define a track between the head and the base. At least two balls are disposed in the track between the base and the head. The method comprises providing a magnetic field within a track that retains the balls in the track and retains the head on the base. Movement of the tape is tracked in a direction perpendicular to the direction of travel of the tape. A representative signal is provided to a controller that is representative of the movement of the tape in the perpendicular direction. The head is driven by the linear motor in a linear direction in response to a signal from the controller that is based upon the representative signal. 
     According to other aspects of the method of the invention, the tape may have at least one servo track wherein the step of tracking the movement of the tape further comprises determining the location of the servo tracks. The method further comprises providing a permanent magnet on either or both of the base or the head that provides a magnetic field within the track. 
     According to another aspect of the present invention, a transducer is disclosed for a digital storage apparatus that reads and writes data to a tape as the tape is moved in a tape drive path across the transducer. The tape has at least one servo track that is read by the storage apparatus. A controller provides a control signal that is indicative of the position of the tape. The transducer comprises a base and a head assembly that is attached to the base and movable relative to the base in a linear path. The linear path is perpendicular to the tape drive path. A guide assembly guides the movement of the head assembly. The guide assembly has a track that is partially defined by the head and partially defined by the base. The guide assembly includes at least two balls that are disposed in the track between the base and the head assembly. A magnetic coupling retains the balls within the track. A linear motor operatively engages the head assembly to move the head assembly in response to the control signal to follow the tape. 
     According to other aspects of the invention, the magnetic coupling includes at least one magnet disposed adjacent to the track that has a magnetic flux field that retains the balls between the head assembly and the base. The magnetic flux also retains the head assembly in position relative to the base. Movement of the head assembly is guided on the linear path as the head assembly rolls on the balls. 
     In one embodiment, the magnet may be attached to the head assembly (or movable member). Alternatively, the magnets could be placed on the stationary member or magnets could be provided on both the stationary and movable members. A wear plate may be disposed on the head assembly between the magnet and the balls. The wear plate disposed on the head assembly may be referred to as a head wear plate, and a base wear plate may be provided on the face of the base. 
     According to another aspect of the present invention, a linear guide is provided that comprises a stationary member defining a first portion of a track and a movable member defining a second portion of the track. At least two balls are disposed between the first and second portions of the track. A magnet is located proximate the first and second portions of the track that creates a flux field that retains the first and second portions of the track in engagement with the balls. The magnet also holds the first and second tracks in a parallel relationship with the movement of the movable member being limited to movement in a single linear direction. 
     According to other aspects of the invention as they relate to the linear guide, at least one magnet may be disposed on the movable member. Alternatively, the magnets could be placed on the stationary member or magnets could be provided on both the stationary and movable members. The stationary member may be a tower on a base of a read/write transducer with the movable member being a head assembly of the read/write transducer. The head of the read/write transducer may be secured to the frame of the read/write transducer to move in a single linear direction. The head of the read/write transducer may be operatively connected to a linear motor that moves the head of the read/write transducer relative to the base of the read/write transducer. In a further aspect of the invention, the linear motor may be assembled to the base of the read/write transducer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an outer perspective view of a head actuator; 
         FIG. 2  is a front exploded perspective view of the head actuator; 
         FIG. 3  is a rear exploded perspective view of the head actuator; 
         FIG. 4  is a top plan view of the head actuator; 
         FIG. 5  is a diagrammatic top plan view of an alternative embodiment of a head actuator; 
         FIG. 6  is a diagrammatic top plan view of another alternative embodiment of a head actuator; 
         FIG. 7  is a side perspective view of an anti-rotation guide portion of the head actuator; 
         FIG. 8  is a diagrammatic top plan view of an alternative embodiment of an anti-rotation guide portion of a head actuator; and 
         FIG. 9  is a diagrammatic top plan view of an alternative embodiment of an anti-rotation guide portion of a head actuator. 
     
    
    
     DETAILED DESCRIPTION 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
     Referring to  FIG. 1 , a transducer head positioning apparatus  10  is illustrated. The transducer head positioning apparatus  10  includes a base assembly  12  and a head assembly  14 . The head assembly  14  is supported in part by a linear motion track  16  that is defined by both the base assembly  12  and the head assembly  14 . A magnetic coupling system is generally represented by reference numeral  18  that functions in conjunction with the linear motion track  16  to guide the movement of the head assembly  14  relative to the base assembly  12 . The head assembly  14  is used to read and write data to a data storage tape  20  in the illustrated embodiment. However, it should be understood that the invention is not limited to tape storage applications and could be adapted, for example, to disk storage applications. 
     The base assembly  12  includes a base  22  and a linear motor  24 . The linear motor  24  has a plurality of legs  26  that operatively engage the head assembly  14  to move the head assembly  14  in a linear direction reciprocally relative to the base  22 . The base assembly  12  also includes a tower  28  that extends from the base  22 . 
     The head assembly  14  includes a frame  30  that defines a head support  32 . The frame  30  also includes a tripod support  34  that is connected to the three legs  26  of the linear motor  24 . A head  36  is attached to the head support  32 . The head  36  is a read/write head which may also be referred to as a transducer head that is used to read and write data to a data storage tape or other data storage medium. 
     Referring to  FIGS. 2 and 3 , the transducer head positioning apparatus  10  is shown in oppositely oriented exploded perspective views. The linear motion track generally referred to in  FIG. 1  by reference numeral  16  is separated into its component parts wherein a first upper movable track  38  and a second upper movable track  40  are provided on the head assembly  14 . A first upper stationary track  42  and a second upper stationary track  44  are shown in a facing relationship relative to the first and second upper movable tracks  38  and  40 . An upper ball  46  is restrained between the movable tracks  38 ,  40  and the stationary tracks  42 ,  44 . 
     First and second lower movable tracks  48 ,  50  are provided on the frame  30  of the head assembly  14  at locations below the upper movable tracks  38 ,  40 , as viewed in  FIG. 2 . First and second lower stationary tracks  52 ,  54  are provided below the first and second upper stationary tracks  42 ,  44 , as illustrated in  FIGS. 2 and 3 . A lower ball  56  is confined within the movable tracks  48 ,  50  and the stationary tracks  52 ,  54 . 
     The track  16  guides movement of the frame  30  in conjunction with the tower  28 . The frame  30  is moved by the linear motor  24  that has legs  26  that engage the tripod support  34  of the frame  30 . The linear motor  24  drives the legs  26  in a linear direction reciprocally in response to control signals received from a controller (not shown). 
     The magnetic coupling system  18  is described by reference to  FIG. 4 . The transducer head positioning apparatus  10  includes the base assembly  12 . The magnetic coupling system  18  retains the frame  30  of the head assembly  14 . In the embodiment shown in  FIG. 4 , the magnetic coupling system  18  includes a first magnet  60  and a second magnet  62  that cooperate with the first magnetically attracted member  64  and the second magnetically attracted member  66  to support the frame  30  on the upper ball  46 . A lower portion of the linear motion track  16  is not visible in  FIG. 3 , but is aligned with the upper portion of the linear motion track  16 . The oval line with arrowheads illustrates generally the magnetic flux path of the magnetic coupling system  18 . The magnetic flux path holds the ball  46  and magnetically attracted members  64 ,  66  to the magnets  60 ,  62 . The frame  30  is generally free to move along the linear motion track  16  with upper ball  46  and lower ball  56  providing a rolling support for the frame  30  of the head assembly  14 . 
     The legs  26  of the linear motor  24  engage the tripod support  34  of the head assembly  14  to reciprocally drive the head assembly  14  to track movement of the data storage tape perpendicular to the direction of movement of the data storage tape. Base wear plates  70  and head wear plates  68  are shown on the first and second magnets  60 ,  62  and on the first and second magnetically attracted members  64 ,  66 , respectively. The wear plates  68 ,  70  are made of hardened steel or ceramic and reduce wear occurring as a result of the movement of the head assembly  14  as it rolls on the balls  46 ,  56 . 
     Referring to  FIG. 5 , a dual magnet track embodiment  72  is shown. The dual magnet track embodiment  72  includes head assembly magnets  74  and base magnets  76  that are arranged to provide a flux path that retains the ball  46  within the linear motion track  16 . Ball  46  shown in  FIG. 4  is the upper ball, while the lower ball  56  is maintained generally in alignment with the upper ball  46  in a similar arrangement. Wear plates  78  are provided to provide a wear resistant surface upon which the ball  46  may roll when the head assembly  14  is moved relative to the base assembly  12 . 
     Referring to  FIG. 6 , a further embodiment of the present invention referred to as the head assembly magnet embodiment  80  is shown to include a pair of head magnets  82  that are assembled to the frame  30 . Magnetically attracted members  84  are provided on the base assembly  12 . The magnetically attracted members  84  may be steel or other ferrous material. Wear plates  86  may be provided in conjunction with or in addition to the magnetically attracted members  84  and the head magnets  82  to provide a wear surface over which the ball  46  may roll. A lower track may be provided that rolls on a ball  56  in like manner. 
     Referring to  FIG. 7 , an anti-rotation guide system  90  is shown in conjunction with the base assembly  12  and head assembly  14  that define the linear motion track  16  as previously described. The anti-rotation guide system  90  may be used in conjunction with the linear motion track  16  having a magnetic coupling system  18 , as previously described with reference to  FIGS. 1-5 . The anti-rotation guide system  90  includes a magnet  92  and a ball  94  that cooperate with an anti-rotation flange  96  of the frame  30 . The anti-rotation flange  96  extends through a slot  98  formed in the tower  28  of the base assembly  12 . The oval line with arrowheads that passes through the magnet  92 , ball  94  and anti-rotation flange  96  is provided to indicate the flux path of the anti-rotation guide system  90 . The magnet  92  exerts a biasing force through the magnetic flux field that biases the anti-rotation flange  96  into engagement with the ball  94 . A wear plate  100  may be provided on the magnet  92 . Another wear plate  102  may be provided on the anti-rotation flange  96 . The wear plate may be made of ferrous or ceramic material and may form part of the magnetic coupling system that couples the anti-rotation flange  96  to the magnet  92 . The anti-rotation flange  96  may be moved when the linear motor moves the legs  26  to move the head assembly  14  as it tracks the data storage tape. When the frame  30  of the head assembly  14  moves up and down, as shown in  FIG. 6 , the anti-rotation flange  96  rolls the ball  94  between the wear plate  100  on the magnet  92  and wear plate  102  on the flange  96 . 
     Referring to  FIG. 8 , a dual magnet anti-rotation system  110  is shown to include a magnet  112  that is attached to the base assembly  12  and a magnet  114  that is attached to the frame  30 . A magnetic flux path is illustrated by the elliptical line with arrowheads that extends from the magnet  112  to the magnet  114  and through the ball  118 . The magnets  112 ,  114  retain the ball  118  between the anti-rotation flange  116  and the base  12 . Wear plates  120 , as previously described, are provided for engagement with the ball  118  to reduce wear on the component parts of the dual magnet anti-rotation system  110  when the frame  30  rolls on the ball  118  relative to the base assembly  12 . Wear plates  120  may also be included in the flux path if made of ferrous material. 
     Referring to  FIG. 9 , a magnet anti-rotation system  124  is shown to include a magnet  126  that is attached to the frame  30  of the head assembly  14 . A magnetic flux path is illustrated by the elliptical line with arrowheads that extend from the magnet  126  through the wear plates  120  and through the ball  128 . The wear plate  120  on the base  12 , if made of a ferrous material, may function as the magnetically attracted portion of the base  12 . The magnet  126  retains the ball  128  between the anti-rotation flange  116  and the base  12 . Wear plates  120 , as previously described, are provided for engagement with the ball  128  to reduce wear on the component parts of the anti-rotation system  124  when the frame  30  rolls on the ball  128  relative to the assembly  12 . 
     While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.