Abstract:
A servo positioned carriage and actuator assembly in which a part of the carriage is positioned within the central portion of the motor. The motor, typically a voice coil motor, includes a coil of electrically conductive windings and a magnet or magnets adjacent to the coil. In one embodiment of the invention, the central portion of the motor is defined by a perimeter of the magnets and the carriage is positioned at least partially inside this perimeter. The carriage, for example, will typically include a ring shaped center portion in which the coil is mounted. This ring shaped center portion mounting the coil is positioned inside the magnets to help minimize the overall mass of the carriage elements of the assembly.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to servo positioned actuators, and more particularly, to a carriage and positioning actuator assembly in which at least part of the carriage is positioned within the central portion of the motor. 
     BACKGROUND OF THE INVENTION 
     Information is recorded on and read from a moving magnetic tape with a magnetic read/write head positioned next to the tape. The magnetic “head” may be a single head or, as is common, a series of read/write head elements stacked individually and/or in pairs within the head unit. Data is recorded in tracks on the tape by moving the tape lengthwise past the head. The head elements are selectively activated by electric currents representing the information to be recorded on the tape. The information is read from the tape by moving the tape longitudinally past the head elements so that magnetic flux patterns on the tape create electric signals in the head elements. These signals represent the information stored on the tape. 
     Data is recorded on and read from each of the parallel tracks on the tape by positioning the head elements at different locations across the tape. That is, head elements are moved from track to track as necessary to either record or read the desired information. Movement of the magnetic head is controlled by an actuator operatively coupled to some type of servo control circuitry. Tape drive head positioning actuators often include a lead screw driven by a stepper motor, a voice coil motor, or a combination of both. The carriage that supports the head is driven by the actuator along a path perpendicular to the direction that the tape travels. The head elements are positioned as close to the center of a track as possible based upon the servo information recorded on the tape. 
     SUMMARY OF THE INVENTION 
     The present invention is directed in general to a servo positioned carriage and actuator assembly and, more particularly, to a head carriage and actuator assembly for a tape drive. A part of the carriage is positioned within the central portion of the motor. The motor, typically a voice coil motor, includes a coil of electrically conductive windings and a magnet or magnets adjacent to the coil. In one embodiment of the invention, the central portion of the motor is defined by a perimeter of the magnets and the carriage is positioned at least partially inside this perimeter. The carriage, for example, will typically include a ring shaped center portion in which the coil is mounted. This ring shaped center portion mounting the coil is positioned inside the magnets to help minimize the overall mass of the carriage elements of the assembly. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top down plan view of a tape drive incorporating a head positioning actuator constructed according to one embodiment of the invention. 
     FIG. 2 is a perspective view of the moveable carriage and head positioning actuator of FIG.  1 . 
     FIGS. 3A and 3B are side elevation and partial section views of the moveable carriage and head positioning actuator of FIGS. 1 and 2 in different positions along the guide rails. 
     FIG. 4 is a top down plan and partial section view of the moveable carriage and head positioning actuator taken along the line  4 — 4  in FIG.  3 A. 
     FIG. 5 is a front elevation and partial cut-away view of the moveable carriage and head positioning actuator as viewed along the line  5 — 5  in FIG.  4 . 
     FIGS. 6A,  6 B and  6 C are detail perspective views of the head carriage. FIG. 6A illustrates the carriage without the coil. FIG. 6B illustrates the carriage with the coil installed in the carriage. FIG. 6C illustrates a carriage in which a non-conductive break is made between the center portions of the carriage and the back portion of the carriage. 
     FIG. 7 is a detail side elevation view of the back portion of the carriage showing one type of bearing preload mechanism. 
     FIG. 8 is a representational side view of the actuator showing the magnetic flux in the voice coil motor. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring first to FIG. 1, a magnetic tape  12  is wound on a single supply spool  14  and tape cartridge  16 . Tape cartridge  16  is inserted into tape drive  10  for read and write operations. Tape  12  passes around tape guide  17 , over a magnetic read/write head  18 , around tape guide  19  to take up spool  20 . Head  18  is mounted to a head carriage and actuator assembly  22  that includes a variety of operational features related to head  18 . Head carriage and actuator assembly  22  is also referred to for convenience as actuator  22 . Magnetic head  18  engages tape  12  as tape  12  moves across the face of head  18  to record data on tape  12  and to read data from tape  12 . 
     FIG. 2 is a perspective view of the actuator  22 . FIGS. 3,  4  and  5  are elevation and plan views of actuator  22 . The operative components of actuator  22  are best seen in FIGS. 3-5. Referring to FIGS. 2-5, head  18  is carried by a moveable carriage  24 . Carriage  24  moves up and down along a primary guide rail  26  and a secondary guide rail  28  at the urging of voice coil motor  30 . Head  18 , which is carried by carriage  24 , therefore, also moves up and down in a direction perpendicular to the direction of tape travel as desired to properly position head  18  for reading and writing operations. FIGS. 3A and 3B show carriage  24  and head  18  in different positions along the guide rails. 
     Voice coil motor  30  includes a coil  32  and magnets  34 . Magnets  34  are attached to the inside of sidewalls  54  of actuator base  50 . Top flux plate  36  fits on top of sidewalls  54  of base  50 . Actuator base  50  is secured to the frame or another stable component of tape drive  10 . Coil  32  is mounted to carriage  24 . 
     The details of carriage  24  are best seen in FIGS. 6A and 6B. FIG. 6A is a perspective view of carriage  24  without coil  32 . FIG. 6B is a perspective view of carriage  24  with coil  32  installed. Referring to FIGS. 6A and 6B, carriage  24  includes a front portion  38 , a back portion  40  and truncated ring shaped center portions  42 A and  42 B that join the front and back portions  38 ,  40 . Center portions  42 A and  42 B are positioned inside a circumferential perimeter defined by magnets  34 . The ring shaped center portions  42 A and  42 B are spaced apart a distance equal to or slightly greater than the height (the axial dimension) of coil  32 . Coil  32  is sandwiched between and firmly attached to ring shaped center portions  42 B and  42 C in carriage  24 . Coil  32  is exposed at cavities  44  formed on each side of carriage  24  between ring shaped center portions  42 A and  42 B. 
     Referring again to FIGS. 2-5, a post  46  extends vertically through the center portion of coil  32 . In the embodiment of the invention shown in the drawings, post  46  is the upright core portion of actuator base  50 . Primary guide rail  26  extends up along a V-shaped trough  48  formed in the front side of core  42 . Secondary guide rail  28  is positioned at the back of carriage  24  just outside coil  32 . Head  18  is mounted to front piece  38  of carriage  24 . If necessary or desirable, a position sensor  52  that reads the vertical position of carriage  24  may be mounted between back piece  40  and actuator base  50 . Carriage  24  travels along primary guide rail  26  on two pairs of bearings  56 A and  56 B mounted in the front piece  38  of carriage  24 . Carriage  24  travels along secondary guide rail  28  on one pair of bearings  58  mounted in the back piece  40  of carriage  24 . Preferably, bearings  56 A are mounted at the top of carriage  24 , bearings  56 B are mounted at the bottom  62  of carriage  24 , and bearings  58  are mounted at the middle of carriage  24 . In this configuration, bearings  56 A and  56 B control the position of carriage  24  in the azimuth direction, indicated by arrow A in FIG. 5, and the zenith direction, indicated by arrow Z in FIG.  3 A. Bearings  58  control the position of carriage  24  in the yaw direction, indicated by arrow Y in FIG.  4 . 
     It may be desirable to preload one or both bearings  58  against secondary rail  28  to maintain contact of all of the bearings against the rails. One type of bearing preload mechanism is shown in FIG.  7 . Referring to FIG. 7, one or both of the secondary rail bearings  58  are spring mounted against secondary guide rail  28 . A spring  64  extends between back portion  40  of carriage  24  and bearing shaft  59 . Spring  64  generates a spring force F that pushes bearing  58  against secondary guide rail  28  and to pulls carriage  24  rearward. The rearward pull of carriage  24  urges the primary guide rail bearings  56  against primary guide  26 . 
     In operation, actuator  22  positions head  18  relative to tape  12  according to positional information recorded on tape  12 . It may be desirable, and in some cases necessary, to make one or all of top flux plate  36 , post  46  and actuator base  50  from a soft magnetic steel to carry the magnetic flux  66  generated by magnets  34  through the space occupied by coil  32 , as shown in FIG. 8. A servo control signal is generated from the positional information on tape  12  through servo control circuitry (not shown) and delivered as an electrical current to voice coil  32 . The presence of current in coil  32  in the magnetic field generated by magnets  34  creates a vertical force on coil  32  and, correspondingly, on carriage  24 . This vertical force moves carriage  24  and head  18  up or down as necessary to properly position head  18  relative to tape  12 . 
     The position of primary guide rail  26  inside coil  32  and the position of bearings  56 A and  56 B above and below coil  32  minimizes the amount of mass needed at the back of carriage  24  to place the center of gravity of carriage  24  at the same location as the center of force exerted by voice coil motor  30 . Positioning the center of gravity of carriage  24  at the same location as the center of force of voice coil motor  30  reduces the amplitude of the carriage rocking modes. So, by locating primary guide rail  26  inside coil  32 , the overall mass of carriage  24  can be reduced. A more compact design can also be achieved by positioning coil  32  between primary guide rail bearings  56 A and  56 B. This configuration allows the positioning of head  18  closer to the center of force of voice coil motor  30  to further reduce the size and mass of carriage  24 . 
     It is desirable to glue or otherwise fasten primary guide rail  26  to post  46  to increase the stiffness of primary guide rail  26 . In addition, fastening primary guide rail  26  to post  46  eliminates the need to provide other support for primary guide rail  26 , particularly at the ends of the primary guide rail. The added stiffness allows higher resonant frequencies of the rocking modes of carriage  24  and, hence, a higher band width for the servo control system. It is also desirable to separate upper guide bearings  56 A from lower guide bearings  56 B as much as possible without exceeding the vertical height limitations of actuator  22  and tape drive  10 . Since the lowest stiffness member in determining the carriage rocking frequencies is the bearings, spreading the bearings as far apart as possible increases the effective stiffness of the carriage guide system. So, by maximizing the spacing between bearings  56 A and  56 B, the resonant frequency of the carriage rocking modes can be made as high as possible for a given stiffness of bearings. 
     If carriage  24 , or at least one of the center portions  42 A and  42 B, are made of conductive material, then the carriage will form an electrically conductive loop in the magnetic flux of voice coil motor  30 . The movement of carriage  24  as it is driven by motor  30 , therefore, will generate an electrical current through this conductive loop. The current in carriage  24  generates a damping force that acts on carriage  24  in a direction opposite the direction of travel and is proportional to the velocity of the carriage. This damping force can be avoided by making carriage  24 , or at least the center portions  42 A and  42 B, from a non-conductive material or by forming a non-conductive break in the otherwise conductive carriage loop. FIG. 6C shows such a non-conductive break in carriage  24 . Referring to FIG. 6C, a strip  41  of adhesive material fills a break made in carriage  24  near one of the junctions of back portions  40  and center portions  42 A and  42 B. Although any electrically non-conductive material may be used, an epoxy or other strong adhesive is preferred to help maintain the structural integrity of carriage  24 . 
     “Bearings” as used in this Specification and in the Claims means any suitable object, structure or surface that moveably supports the carriage for travel along the rails. Suitable bearings may include, for example, ball bearings, roller bearings, Gothic arch bearings, journal bearings, bushings and the like. 
     Although the invention has been shown and described with reference to a head carriage and actuator assembly for a tape drive, the invention may be embodied in other carriage and actuator assemblies, structures and designs. For example, the invention could be incorporated in many different types of servo positioned actuators that use a voice coil motor. The voice coil motor might be configured so that the magnets are secured to the carriage and the coil remains stationary. And, the coil need not be annular. A square or rectangular coil may be appropriate in some applications. The post and the primary guide rail could be formed as an integral unit, rather the discrete components described above. The sidewalls of the actuator base might be formed integral to the base foundation, as shown in FIGS. 2,  5  and  6 , or the sidewalls might be formed integral with the top plate and separate from the base. Therefore, it is to be understood that these and other variations of and modifications to the embodiments shown and described may be made without departing from the spirit and scope of the invention as defined in following claims.