Patent Publication Number: US-2007119794-A1

Title: Vibration damping unit

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a method of preventing the sway of a rack accommodating a rack-mounted disk array apparatus, for example.  
      2. Description of the Prior Art  
      A rack-mounted disk array apparatus is well known. The disk array apparatus is mounted on a rack located on a seismic isolation apparatus. The seismic isolation apparatus serves to reduce the sway of the rack. The disk array apparatus is thus allowed to keep its normal operation without any interruption. Lifting up the rack is required to place the rack on the seismic isolation apparatus.  
      The rack weighs at least 150 kg. The disk array apparatus or apparatuses mounted in the rack serves to further increase the weight. It is quite difficult to lift up the rack onto the seismic isolation apparatus. What is worse, lifting up the rack should interrupt the operation of the disk array apparatus. In other words, once the disk array apparatus starts operating, the rack cannot normally enjoy the seismic isolation.  
     SUMMARY OF THE INVENTION  
      It is accordingly an object of the present invention to provide a vibration damping unit contributing to prevention of the sway of an existing rack in a facilitated manner.  
      According to the present invention, there is provided a vibration damping unit comprising: a rack-mounted support body removably mounted on a rack; a mass or weight supported on the support body for movement along an imaginary plane; and an elastic member coupled to the support body and the mass.  
      The support body of the vibration damping unit is removable from the rack. The vibration damping unit can be mounted on an existing rack in a facilitated manner without any change in the design of the rack. Workers can be released from troublesome works, such as moving the rack, even when the vibration damping unit is applied to the rack. The means for preventing sway or vibration can be applied to the rack even when an electronic apparatus, including a disk array apparatus and the like, is in operation inside the rack.  
      The mass is supported on the support body for movement along an imaginary plane. The elastic member is interposed between the support body and the mass. The elastic member serves to realize the reciprocation of the mass along the imaginary plane. The reciprocation of the mass contributes to a significant suppression of the sway or vibration of the rack when the rack suffers from an earthquake, for example. The rack is allowed to have a smaller rigidity. The assembling process can be simplified. The simplified process leads to a reduction in the production cost of the rack. A reduction in the rigidity greatly contributes to a significant reduction in the weight of the rack.  
      The mass may comprise: a tray coupled to the support body for movement along the imaginary plane; and at least one weight member removably mounted on the tray. The amount of mass can be adjusted depending on the number of the weight member. This structure enables adjustment of the amount of the mass in accordance with the resonance frequency of the rack, for example.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiment in conjunction with the accompanying drawings, wherein:  
       FIG. 1  is a perspective view schematically illustrating the structure of a rack;  
       FIG. 2  is a perspective view schematically illustrating the structure of a vibration damping unit according to a specific example of the present invention;  
       FIG. 3  is an exploded view schematically illustrating the structure of the vibration damping unit;  
       FIG. 4  is a view schematically illustrating a specific model of the vibration damping unit when the rack moves forward;  
       FIG. 5  is a view schematically illustrating a specific model of the vibration damping unit when the rack moves backward;  
       FIG. 6  is a view schematically illustrating a model of the rack for a computer software analysis;  
       FIG. 7  illustrates a table specifying the values of parameters such as the weight f a mass, spring constants and damper constants;  
       FIG. 8  is a graph illustrating the correlation between the frequency and the acceleration in a comparative example;  
       FIG. 9  is a graph illustrating the correlation between the frequency and the acceleration in a specific example of the present invention;  
       FIG. 10  illustrates a table specifying the peak values of the response acceleration of the comparative example and the specific examples of the present invention;  
       FIG. 11  is a view schematically illustrating another model of the rack for a computer software analysis; and  
       FIG. 12  illustrates a table specifying the peak values of the response acceleration of the comparative example and the specific examples of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       FIG. 1  schematically illustrates a rack  12  containing a rack-mounted disk array apparatus. In this case, a plurality of disk array apparatuses  11  are mounted on the rack  12 , for example. The disk array apparatuses  11  are connected to a host or server computer  13  likewise mounted on the rack  12 , for example. The disk array apparatuses  11  operate in response to instruction signals supplied from the server computer  13 .  
      As conventionally known, recording disk drives or hard disk drives (HDDs) are mounted in the individual disk array apparatus  11 . The hard disk drive may include a recording disk or hard disk (HD) having the rotation axis extending in the vertical direction perpendicular to the floor, for example. In this case, each disk array apparatus  11  holds fifteen hard disk drives. Alternatively, the rotation axis of the hard disk may extend in the horizontal direction in parallel with the floor.  
      A vibration damping unit  14  is mounted on the rack  12  just below the top plate of the rack  12 . The vibration damping unit  14  is capable of sliding on the rack  12  along a horizontal plane. The vibration damping unit  14  can thus be withdrawn from the front side of the rack  12 . The vibration damping unit  14  is coupled to the rack  12  when the vibration damping unit  14  is placed inside the rack  12 . Screws  15  may be utilized to couple the vibration damping unit  14 , for example. The screws  15  may be screwed into support columns of the rack  12 , for example.  
      As shown in  FIG. 2 , the vibration damping unit  14  includes a rack-mounted support body  21 . The support body  21  includes a bottom plate  21   a  and a surrounding wall  21   b  standing upright from the periphery of the bottom plate  21   a . The support body  21  defines an inner space in the shape of a parallelepiped based on the bottom plate  21   a  and the surrounding wall  21   b.    
      A pair of first rails  22 ,  22  is located within the inner space of the support body  21 . The first rails  22 ,  22  are designed to extend in a first direction FD. The first direction FD is set along a horizontal plane in the right and left direction of the vibration damping unit  14 . The first rails  22 ,  22  extend in parallel with each other. The first rails  22  may be fixed to the bottom plate  21   a  of the support body  21 . Screws may be utilized to fix the first rails  22 , for example.  
      Sliders  23  are mounted on the first rails  22 , respectively. The sliders  23  are capable of sliding along the first rails  22  in the first direction FD. A second rail  24  is coupled to the sliders  23 ,  23 . The second rail  24  may be fixed to the sliders  23 . The second rail  24  is designed to extend in a second direction SD perpendicular to the first direction FD. The second direction SD is set along the horizontal plane in the back and front direction of the vibration damping unit  14 . The second rail  24  serves to connect the sliders  23 ,  23  to each other.  
      A tray  25  is mounted on the second rail  24 . The tray  25  is capable of sliding along the second rail  24  in the second direction SD. At least one weight member  26  is mounted on the tray  25 , for example. The weight members  26  are thus coupled to the support body  21  for movement along an imaginary plane defined on the surface of the bottom plate  21   a , for example. The weight members  26  may removably be attached to the tray  25 . Screws may be utilized for attachment, for example. Each weight member  26  may weigh 1 kg, for example. The tray  25  and the weight members  26  in combination serve as a mass according to the present invention.  
      First coil springs  27  and first dampers  28  are incorporated within the inner space of the support body  21 . The first coil spring  27  and the first damper  28  are designed to extend in parallel with the corresponding first rail  22 . Pairs of tabs  29 ,  29  are formed on the bottom plate  21   a  so as to stand from the bottom plate  21   a . The tabs  29 ,  29  of each pair are spaced from each other in the first direction FD. The first coil spring  27  and the first damper  28  are located in a space between the pair of tabs  29 ,  29 .  
      The slider  23  is located in a space between the first coil spring  27  and the first damper  28 . The first coil spring  27  is coupled to the slider  23  at one end and to the tab  29  at the other end. The elasticity of the first coil spring  27  serves to drive the slider  23  for reciprocation along the first rail  22  in a set period. The first damper  28  is likewise coupled to the slider  23  at one end and to the tab  29  at the other end. The first damper  28  serves to attenuate the movement of the slider  23 .  
      Likewise, a pair of second coil springs  31 ,  31  is incorporated within the inner space of the support body  21 . The second coil springs  31 ,  31  are designed to extend in parallel with the second rail  24 . The second coil springs  31 ,  31  are located in series in a space between the sliders  23 ,  23 . A pair of second dampers  32 ,  32  is incorporated within the inner space of the support body  21 . The second dampers  32 ,  32  are designed to extend in parallel with the second rail  24 . The second dampers  32 ,  32  are located in series in a space between the sliders  23 .  
      The tray  25  is located between the second coil springs  31 ,  31  as well as between the second dampers  32 ,  32 . Each of the second coil springs  31  is coupled to the slider  23  at one end and to the tray  25  at the other end. The elasticity of the second coil springs  31  serves to drive the tray  25  for reciprocation along the second rail  24  in a set period. Each of the second dampers  32  is likewise coupled to the slider  23  at one end and to the tray  25  at the other end. The second damper  32  serves to attenuate the movement of the tray  25 .  
      As shown in  FIG. 3 , the first coil springs  27  and the first dampers  28  can be removed from the sliders  23  and the tabs  29 . The second coil springs  31  and the second dampers  32  can likewise be removed from the sliders  23  and the tray  25 . The weight members  26  can also be removed from the tray  25 . Replacement of the first and second coil springs  27 ,  31 , the first and second dampers  28 ,  32  and the weight members  26  can thus be realized in a facilitated manner.  
      As shown in  FIG. 2 , the weight members  26  are located at a standard position when the rack  12  stands still. The tray  25  is positioned at the intermediate position equally spaced from the first rails  22 ,  22 . The slider  23  is simultaneously positioned at the intermediate position equally spaced from both the ends of the first rail  22 . No load affects the first and second coil springs  27 ,  31  and the first and second dampers  28 ,  32 . The first and second coil springs  27 ,  31  and the first and second dampers  28 ,  32  are kept in the original lengths.  
      Now, assume that the rack  12  suffers from a sway in the second direction SD because of an earthquake, for example. As shown in  FIGS. 4 and 5 , the vibration damping unit  14  allows a relative movement between the tray  25  and the support body  21  along a horizontal plane so that the tray  25  stays where it is. The support body  21  is forced to reciprocate in the second direction SD. This results in shrinkage and elongation of the second coil springs  31 ,  31 . The rack  12  and the support body  21  is thus allowed to enjoy a suppression in the amplitude of the sway or vibration. The energy of the sway is transformed into deformation of the second coil springs  31 . The energy of the sway thus stored in the second dampers  32 ,  32  is then consumed in the second dampers  32 . The rack  12  is in this manner allowed to enjoy a suppression of the vibration.  
      The vibration damping unit  14  is removably mounted on the rack  12  in the same manner as the disk array apparatus  11 . The existing rack  12  thus easily receives the vibration damping unit  14  without any change in design. One is released from troublesome works, such as moving the rack  12 , even when the vibration damping unit  14  is applied to the rack  12 . Moreover, the means for preventing sway or vibration can be applied to the rack  12  even after the disk array apparatus  11  is in operation.  
      Since the vibration damping unit  14  serves to sufficiently suppress sway or vibration of the rack  12 , the rack  12  is allowed to have a smaller rigidity. Welding can be replaced with riveting in the production process of the rack  12 . The production process can be simplified. The simplified process leads to a reduction in the production cost of the rack  12 . A reduction in the rigidity greatly contributes to a reduction in the weight of the rack  12 .  
      The first and second coil springs  27 ,  31 , the first and second dampers  28 ,  32  and the weight members  26  can be removed in a facilitated manner. The spring constants of the first and second coil springs  27 ,  31  can thus be adjusted depending on the resonance frequency of the rack  12  and the vibration damping unit  14 . The damper constants of the first and second dampers  28 ,  32  can likewise be adjusted. The amount of the mass can also be adjusted.  
      The inventors have observed the effect of the vibration damping unit  14  based on a computer software analysis. As shown in  FIG. 6 , a model  41  of the rack  12  was defined for the observation. The model  41  included a rack  42  having four support columns  43  and upper and lower frames  44 ,  44  coupling the support columns  43 . The upper frame  44  was located on the upper ends of the support columns  43 . The lower frame  44  was located adjacent to the lower ends of the support columns  43 .  
      Here, the height of the individual support columns  43  in the z-axis was set at 1,800 [mm]. The length of the upper and lower frames  44  in the x-axis was set at 600 [mm]. The length of the upper and lower frames  44  in the y-axis was set at 950 [mm]. The bottom surface of the lower frame  44  was located at a height of 50 [mm] from the bottom ends of the support columns  43 . The movement of the bottom ends of the support columns  43  was restrained. The weight of the rack  42  was set at 150 kg. The Young&#39;s modulus of the rack  42  was set at 193.198 [GPa]. The Poisson&#39;s ratio of the rack  42  was set at 0.3.  
      As is apparent from  FIG. 6 , the aforementioned vibration damping unit  14  was imaginarily incorporated within the upper frame  44 . Four coil springs  45  and four dampers  46  were defined in the upper frame  44 . The coil springs  45  and the dampers  46  were designed to extend inward from the upper frame  44 . A mass  47  of the vibration damping unit  14  was defined at a joint of the coil springs  45  and the dampers  46 . The movement of the mass  47  in the z-axis was restrained in the vibration damping unit  14 . The mass  47  was thus allowed to move only along the xy plane.  
      First to ninth specific examples were prepared for the observation. As shown in  FIG. 7 , the weight [kg] of the mass  47 , the spring constants [N/mm] of the coil spring  45 , and the damper constants [Nmm/s] of the damper  46  were set for the first to ninth specific examples, respectively. Three values were employed in each parameter. A comparative example was also prepared. The vibration damping unit  14  was omitted in the comparative example. The rack  42  was subjected to a sway in the x-axis at the acceleration of 1 [G] or 9.8 m/s 2 . The decrement of the sway was set at 1%. A response acceleration was measured at a measuring point  48  set at one of the corners of the upper frame  44 .  
      As shown in  FIG. 8 , the maximum or peak appears in the response acceleration [G] at the resonance frequency [Hz] of the rack  42  in the comparative example. On the other hand, as shown in  FIG. 9 , the maximums or peaks appear in the response acceleration [G] at the resonance frequency of the rack  42  and the resonance frequency of the vibration damping unit  14  in the seventh specific example. Two peaks were observed in the other specific examples as well.  
      As shown in  FIG. 10 , the response acceleration measured at the measuring point  48  takes the peak at 58.8 [G] in the comparative example. On the other hand, the resonance frequency measured at the measuring point  48  takes the first peak in a range from 27.6 to 38.8 [G], at the resonance frequency of the rack  42 , in the first to ninth specific examples. Likewise, the resonance frequency measured at the measuring point  48  takes the second peak in a range from 27.1 to 38.8 [G], at the resonance frequency of the vibration damping unit  14 , in the first to ninth specific examples. It has been confirmed that the racks  42  of the first to ninth specific examples are allowed to enjoy a remarkable reduction in the response acceleration as compared with the comparative example. It has been confirmed that the vibration damping unit  14  enables a remarkable suppression of the sway or vibration of the rack  42 .  
      Referring also to  FIG. 7 , it has been revealed that a larger weight of the mass  47  contributes to a further suppression of sway or vibration of the rack  42 . Likewise, it has been revealed that a smaller spring constants contributes to a further suppression of sway or vibration of the rack  42 . It has been revealed that the damper constants have little influence on the suppression of sway or vibration of the rack  42 . It has been revealed that the attenuation of sway or vibration depends on the weight of the mass  47  and the spring constants of the coil springs  45 .  
      The inventors have also observed the influence of the position of the vibration damping unit  14  in the rack  12 . A computer software analysis was used for the observation in the same manner as described above. As shown in  FIG. 11 , the rack  42  of a model  41   a  included first and second middle frames  44   a ,  44   b  located in a space between the aforementioned upper and lower frames  44 . The distance between the upper and lower frames  44  may be equally divided into three by inserting the first and second middle frames  44   a ,  44   b . The first middle frame  44   a  was located next to the upper frame  44 . The second middle frame  44   b  was located next to the lower frame  44 .  
      The same values were used for the Young&#39;s modulus, the Poisson&#39;s ratio and the weight of the rack  42 . The same value was also used for the weight of the mass  47 . The spring constants of the coil spring  45  in the vibration damping unit  14  were set at 493 [N/mm]. The damper constants of the dampers  46  in the vibration damping unit  14  were set at 300 [Nmm/s]. The movement of the bottom ends of the support columns  43  was restrained. The vibration damping unit  14  was thus allowed to move only along the xy plane.  
      Specific examples A to C were prepared for the observation. The specific example A had the vibration damping unit  14  imaginarily incorporated within the upper frame  44 . The specific example B had the vibration damping unit  14  imaginarily incorporated within the first middle frame  44   a . The specific example C had the vibration damping unit  14  imaginarily incorporated within the second middle frame  44   b . The same comparative example as described above was prepared. The vibration damping unit  14  was omitted in the comparative example.  
      The rack  42  was subjected to a sway in the x-axis at the acceleration of 1 [G] or 9.8 m/s 2  in the specific example A to C as well as the comparative example. The decrement of the sway was set at 1%. A response acceleration was measured at a measuring point  48  set at one of the corners of the upper frame  44 . The maximum or peak of the response acceleration was observed in the specific example A to C as well as the comparative example, respectively.  
      As shown in  FIG. 12 , the response acceleration measured at the measuring point  48  takes the peak at 64.0 [G] in the comparative example. The response acceleration measured at the measuring point  48  takes the peak at 33.0 [G] in the specific example A. The response acceleration measured at the measuring point  48  takes the peak at 33.6 [G] in the specific example B. The response acceleration measured at the measuring point  48  takes the peak at 36.7 [G] in the specific example C. As is apparent from the ratio to the comparative example, it has been confirmed that the vibration damping unit  14  enables a remarkable suppression of the sway or vibration of the rack  42 .  
      As is apparent from the ratio to the specific example A, it has been confirmed that the specific example A exhibits the minimum value of the response acceleration. In other words, it has been confirmed that the maximum response acceleration reduces as the vibration damping unit  14  gets closer to the top of the rack  12 . It has thus been revealed that the vibration damping unit  14  is preferably located as close to the top as possible in the rack  12 .  
      The vibration damping unit  14  can be applied to a rack containing two or more server computers  13 , other types of electronic apparatus and other types of recording medium drive as well.