Abstract:
A head drum assembly comprises a stationary drum, a rotary drum, and a self-compensating dynamic balancer. The stationary drum is fixed to a shaft, and the rotary drum is rotatably mounted to the shaft so that it faces the stationary drum. The rotary drum supports a magnetic head. The self-compensating dynamic balancer automatically compensates for any eccentricity between the rotational axis and the centroid of the rotary drum by using the centrifugal force of the rotary drum being rotated.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit under 35 U.S.C. § 119(a) of Korean Patent Application No. 2004-90279, filed Nov. 8, 2004, the entire contents of which are hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a head drum assembly which records and reproduces information with a running magnetic tape, and a magnetic recording/reproducing apparatus having the same. More particularly, the present invention relates to a dynamic balancer for a head drum assembly.  
         [0004]     2. Description of the Related Art  
         [0005]     Generally, a magnetic recording/reproducing apparatus records information on a recording medium such as a magnetic tape and reproduces the recorded information. Video cassette tape recorders (VCRs) and camcorders are examples of magnetic recording/reproducing apparatuses.  
         [0006]     A magnetic recording/reproducing apparatus includes a head drum assembly that is rotatably mounted to a deck to record and reproduce information with respect to a magnetic tape as the tape moves past the head drum assembly. The head drum assembly is typically slanted by a predetermined angle with respect to the deck for better recording and reproduction performance.  
         [0007]      FIG. 1  shows an example of a head drum assembly. Referring to  FIG. 1 , a stationary drum  11  is fixed to a shaft  10 , and a rotary drum  12  is rotatably mounted to the shaft  10 . A magnetic head  13  is supported by the rotary drum  12  and scans a running magnetic tape to record and reproduce information on the tape. A drum cover  14  is fixed to the shaft  10  above the rotary drum  12 . The surface of the rotary drum  12  has a rotary transfer  16  and the surface of the drum cover  14  has a stationary transfer  15 . The rotary transfer  16  and stationary transfer  14  face each other and convert a magnetic signal to an electric signal and transmit the converted signal.  
         [0008]     A motor rotor  17  is mounted on the rotary drum  12 . The motor rotor  17  comprises a bracket  17   a  fastened to the rotary drum  12 , and a magnet  17   b  supported by the bracket  17   a.  A motor stator  18  is mounted to the stationary drum  11  and faces the motor rotor  17 . The motor stator  18  and the motor rotor  17  cooperate with one another to generate a driving force for rotating the rotary drum  12 .  
         [0009]     With this construction, the rotary drum  12  supporting the magnetic head  13  rotates with the motor rotor  17  at a high speed. During the rotation of the rotary drum  12 , the magnetic head  13  records or reproduces information on the magnetic tape.  
         [0010]     In the above-structured rotary drum  12 , the rotational axis of the rotary drum may not correspond to the centroid of the rotary drum due to manufacturing and assembly errors. When the centroid is not aligned with the rotational axis (that is, they are eccentric with respect to each other), the rotary drum may be unstable, thereby degrading recording and reproducing performance of the rotary drum  12 .  
         [0011]     Therefore, in the conventional art, a predetermined balancing apparatus is used to measure eccentricity and an eccentric position. Once measured, a mass body  19  is attached to a suitable location that compensates for the measured eccentricity. For instance, a mass body  19  comprising a certain amount of a hard bond may be placed and hardened on the bracket  17   a  to compensate for eccentricity.  
         [0012]     Compensation of the eccentricity of the rotary drum  12  using a dedicated mass body  19  requires complicated processes. In detail, the rotary drum  12  (with the mounted magnetic head  13  and motor rotor  17 ) is rotatably supported by a shaft, which is provided just for measurement. The rotary drum  12  is rotated, and the eccentricity and an eccentric position of the rotary drum  12  are measured. A predetermined mass body  19  is attached to a location that compensates for the eccentricity, according to the measured result. The eccentricity of the rotary drum  12  is then measured again by rotating the drum. If the measured eccentricity of the rotary drum  12  passes a predetermined reference standard, the rotary drum  12  is removed from the shaft and the next processes are performed. Thus, balancing the rotary drum  12  takes considerable time and involves complicated processes, thereby degrading productivity and increasing manufacturing costs.  
         [0013]     Accordingly, there is a need for an improved head drum assembly that compensates for eccentricity more efficiently.  
       SUMMARY OF THE INVENTION  
       [0014]     An aspect of the present invention is to address at least the above problems and/or disadvantages. Accordingly, an aspect of the present invention is to provide a head drum assembly that is capable of automatically compensating for any eccentricity of a rotary drum without requiring a dedicated balancing process, and a magnetic recording/reproducing apparatus having the same.  
         [0015]     In an exemplary embodiment of the present invention, a head drum assembly comprises a stationary drum, a rotary drum, and a self-compensating dynamic balancer. The stationary drum is fixed to a shaft, and the rotary drum is rotatably mounted to the same shaft. The rotary drum faces the stationary drum and supports a magnetic head. The self-compensating dynamic balancer automatically compensates for any eccentricity between the rotational axis and the centroid of the rotary drum by using the centrifugal force of the rotary drum being rotated.  
         [0016]     In another aspect of the present invention, the self-compensating dynamic balancer comprises a recessed race groove. The race groove is annular with respect to the rotational axis of the rotary drum. A plurality of mobile members are received in the race groove and move in a direction that compensates for the eccentricity of the rotary drum when the rotary drum is rotated.  
         [0017]     In yet another aspect of the present invention, the self-compensating dynamic balancer further comprises a cover member that covers an open top portion of the race groove to prevent the mobile members from escaping from the race groove.  
         [0018]     In one more aspect of the present invention, the cover member is connected by press fit with an inner circumferential wall of the race groove.  
         [0019]     In a further aspect of the present invention, the inner circumferential wall of the race groove has a supporting projection for restricting the connection height of the cover member.  
         [0020]     In another aspect of the present invention, the mobile members comprise balls.  
         [0021]     In yet one more aspect of the present invention, the outer circumferential wall of the race groove has a plurality of receiving recesses in which the balls are received when the rotary drum is rotated.  
         [0022]     In a further aspect of the present invention, the receiving recesses are disposed at constant intervals along the outer circumferential wall of the race groove.  
         [0023]     In yet another aspect of the present invention, the receiving recesses are semicircular indentations formed in the outer circumferential wall of the race groove  
         [0024]     In one more aspect of the present invention, the race groove is formed on an upper surface of the rotary drum to face the magnetic head.  
         [0025]     In another exemplary embodiment of the present invention, a magnetic recording/reproducing apparatus comprises a deck and a head drum assembly mounted to the deck. The head drum assembly comprises a stationary drum, a rotary drum, and a self-compensating dynamic balancer. The stationary drum is fixed to a shaft, and the rotary drum is rotatably mounted to the same shaft. The rotary drum faces the stationary drum and supports a magnetic head. The self-compensating dynamic balancer automatically compensates for any eccentricity between the rotational axis and the centroid of the rotary drum by using the centrifugal force of the rotary drum being rotated. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES  
       [0026]     The above and other objects, features, and advantages of certain embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:  
         [0027]      FIG. 1  is a schematic sectional view of a conventional head drum assembly;  
         [0028]      FIG. 2  is a sectional view of a magnetic recording/reproducing apparatus according to an embodiment of the present invention;  
         [0029]      FIG. 3  is a plan view of the rotary drum of  FIG. 2 ; and  
         [0030]      FIG. 4  is a partial, sectional view of certain elements of  FIG. 2 . 
     
    
       [0031]     Throughout the drawings, the same drawing reference numerals will be understood to refer to the same elements, features, and structures.  
       DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0032]     The matters defined in the description such as a detailed construction and elements are provided to assist in a comprehensive understanding of the embodiments of the invention. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness.  
         [0033]     Referring to  FIG. 2 , a magnetic recording/reproducing apparatus according to an embodiment of the present invention comprises a deck  21  and a head drum assembly  100  mounted to the deck  21 . The deck  21  is mounted within a main body of the magnetic recording/reproducing apparatus, such as a camcorder, for recording and reproducing information on a magnetic tape. The deck  21  includes a driving device for transporting the magnetic tape and a guiding device for guiding the magnetic tape. A mechanism using such a deck  21  is generally known by those in the art, and, therefore, a detailed description is omitted for conciseness.  
         [0034]     The head drum assembly  100  comprises a stationary drum  30  fixed to a shaft  22 , a rotary drum  40  rotatably mounted on the shaft  22  above the stationary drum  30 , a drum cover  50  mounted above the rotary drum  40 , a drum motor  60  for rotating the rotary drum  40 , and a self-compensating dynamic balancer  70 .  
         [0035]     The stationary drum  30  fits around the shaft  22  and is fastened to the deck  21  by a screw  24 .  
         [0036]     The rotary drum  40  fits around the shaft  22  to face the stationary drum  30 . A bearing  26  is interposed between the rotary drum  40  and the shaft  22 .  
         [0037]     A magnetic head  80  is supported by the rotary drum  40  and scans a magnetic tape running past the magnetic head  80  to record information on the magnetic tape or reproduce recorded information from the magnetic tape. The magnetic head  80  is preferably disposed under the rotary drum  40 .  
         [0038]     The drum cover  50  is disposed above the rotary drum  50  and fits around the shaft  22 . The rotary drum  50  has a rotary transfer  91 , and the drum cover  40  has a stationary transfer  93 . The rotary transfer  91  and stationary transfer  93  cooperate to transmit the information read from the magnetic head  80 .  
         [0039]     The drum motor  60  comprises a rotor  61  mounted to the rotary drum  40 , and a stator  63  mounted to the stationary drum  30 .  
         [0040]     The self-compensating dynamic balancer  70 , as shown in  FIGS. 3 and 4 , comprises a race groove  41  located in the rotary drum  40 , at least one mobile member  43  received in the race groove  41 , and a cover member  45 .  
         [0041]     The race groove  41  is annular, and is formed around the rotational axis of the rotary drum  40 . More preferably, the race groove  41  is formed on an upper surface  40   a  of the rotary drum  40 , and has a predetermined depth.  
         [0042]     In the illustrated exemplary embodiment, a plurality of mobile members  43  are received in the race groove  41  and are movable. The mobile members  43  may be metal balls. When the rotary drum  40  rotates, the mobile members  43  move in a direction that is symmetrical with the eccentric point of the rotary drum  40 , thereby compensating the eccentricity of the rotary drum  40 . Therefore, to allow the balls to move, the balls can roll freely within the race groove  41 .  
         [0043]     The cover member  45  prevents any mobile members  43  from escaping from the race groove  43 . The cover member  45  is connected, preferably by press fit, with an inner circumferential wall  41   a  of the race groove  41 . A supporting projection  42  for restricting a connection height of the cover member  45  protrudes from the inner circumferential wall  41   a.  Alternatively, the cover member  45  may be sized for a press fit with the outer circumferential wall  41   b  of the race groove  41 .  
         [0044]     The outer circumferential wall  41   b  of the race groove  41  has receiving recesses  41   c  for receiving the mobile members  43 . The receiving recesses  41   c  are preferably arranged at constant intervals along the race groove  41 . Preferably, the receiving recesses  41   c  are substantially semicircular indentation in the outer circumferential wall  41   b  of the race groove  41 .  
         [0045]     When the rotary drum  40  of the above-describe head drum assembly rotates, the mobile members  43  move away from the rotational axis due to centrifugal force. Therefore, the mobile members  43  move in a direction symmetrical to the eccentric point of the rotary drum  40 , and are received in the receiving recesses  41   c.  Once received in the receiving recesses  41   c,  the mobile members  43  compensate for the eccentricity of the rotary drum  40 .  
         [0046]     When the eccentric point occurs at another location in the rotary drum  40 , the mobile members  43  relocate, thereby automatically compensating for any changed eccentricity of the rotary drum  40 .  
         [0047]     In addition, any mobile members  43  that do not move toward the eccentric point are received in the receiving recesses  41   c.  Thus, any mobile members  43  which did not find the eccentric point are prevented from moving around within the race groove  41 .  
         [0048]     Accordingly, the rotary drum  40  can be driven without eccentricity and therefore operates stably without shaking or trembling. As a result, performance of recording and reproducing information on a magnetic tape can be enhanced.  
         [0049]     Also, according to the above structure, the self-compensating dynamic balancer  70  is completely mounted by forming the race groove  41  in the rotary drum  40 , inserting the mobile member  43  in the race groove  41  and connecting the cover member  45 .  
         [0050]     By connecting the rotary drum  40  with the compensation balancer  70  to the shaft  22  and assembling the stationary drum  30  and the drum cover  50 , the head drum assembly  100  can be constructed in a simple manner. That is, the assembly does not require any special balancing processes. Accordingly, assembly steps and assembly time can be saved, thereby improving productivity and reducing manufacturing costs.  
         [0051]     Furthermore, the self-compensating dynamic balancer is able to automatically compensate any eccentricity generated while driving the rotary drum. Thus, the eccentricity does not have to be measured for every rotary drum produced. Therefore, recording and reproducing characteristics can be enhanced by preventing shaking and trembling of the rotary drum.  
         [0052]     While the invention has been shown and described with reference to certain embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.