Abstract:
An apparatus for measuring vibration of a fan includes a frame having an opening for enclosing a fan; a plurality of accelerometers disposed on the frame; and an elastic support for supporting the frame. An apparatus for measuring fan vibration includes a frame having an opening for enclosing a fan; a plurality of accelerometers disposed on the frame. The plurality of accelerometers output a signal to the signal-analyzing device and at least three of the plurality of accelerometers are disposed on a different surface of the frame from each other. The apparatus for measuring fan vibration includes a mounting block that allows the fan to be secured in the opening of the frame and an elastic support for supporting the frame. A method of measuring fan vibration includes disposing a plurality of accelerometers on a frame; mounting a fan within the frame; turning on the fan; and outputting a signal from each of the plurality of accelerometers to a signal-analyzing device.

Description:
BACKGROUND 
   Hard disk drives (HDDS) in computer products are sensitive to external vibration, either from other devices or from sources outside the system. For example, the effect of external vibration on HDDs is to disturb the tracking of read/write heads on data tracks, to increase the track access time, and to reduce overall data transfer rates. Further, in case of a significant vibration, read performance and, especially, write performance of HDDs can be severely reduced. If the vibration becomes large enough, writing to HDD may be prevented and it may cause a failure of the system. 
   As computers, such as computer servers and storage systems, become more and more dense, the number of internal vibration sources has increased. Because these dense systems require more cooling, the energy to be put into internal cooling fans has increased in terms of the number of fans, total power of motor fan drive, and rotational speed of fans. In particular, fan speeds for the small systems have more than doubled in recent years. In the past, the only significant source of HDD vibration disturbance was other HDDs in the system. On the other hand, now, cooling fans have become the major cause of HDD performance problems in many systems. 
   The vibration sources within fans are many and variable. The most common cause of fan-induced HDD vibration sensitivity is fan torque ripple off and on the axis of fan rotation at frequencies above 300 Hz and especially above 500 Hz to 1 kHz or higher. Despite a common trend toward increasing vibration energy at increasing frequencies, different fan designs in consideration for a single system product may have very different spectrum characteristics. Also, the impact of even the same fan at different speeds is affected by fan motor characteristics, chassis structural response, and HDD servo response. 
   The impact of fans on HDD performance can be serious. Without adequate fan characterization methods, the impact is quite unpredictable. No commercial methods currently exist for the measurement of fan dynamics, especially for the vibration components on top of steady fan torque or for the components off the motor axis. 
   SUMMARY OF INVENTION 
   One or more embodiments of the present invention relate to an apparatus for measuring vibration of a fan comprising: a frame comprising an opening for enclosing a fan; a plurality of accelerometers disposed on the frame; and an elastic support for supporting the frame. 
   One or more embodiments of the present invention relate to an apparatus for measuring fan vibration comprising: a frame comprising an opening for enclosing a fan; a plurality of accelerometers disposed on the frame, wherein the plurality of accelerometers output a signal to the signal-analyzing device and wherein at least three of the plurality of accelerometers are disposed on a different surface of the frame from each other; a mounting block that allows the fan to be secured in the opening of the frame; and an elastic support for supporting the frame. 
   One or more embodiments of the present invention relate to a method of measuring fan vibration comprising: disposing a plurality of accelerometers on a frame; mounting a fan within the frame; turning on the fan; and outputting a signal from each of the plurality of accelerometers to a signal-analyzing device. Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  shows one embodiment of a system for measuring fan vibration. 
       FIG. 2  shows one embodiment of a device for measuring fan vibration. 
       FIG. 3  shows a typical system fan. 
       FIG. 4  shows one embodiment of a device for measuring fan vibration with a fan disposed therein. 
       FIG. 5  shows one embodiment of a device for measuring fan vibration with a fan disposed therein. 
       FIG. 6  shows one embodiment of a device for measuring fan vibration with a fan disposed therein. 
       FIG. 7  shows one embodiment of a device for measuring fan vibration with a fan disposed therein. 
   

   DETAILED DESCRIPTION 
   Specific embodiments of the invention will now be described in detail with reference to the accompanying figures. Like elements in the various figures are denoted by like reference numerals for consistency. 
   In the following detailed description of embodiments of the invention, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to one of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description. 
     FIG. 1  shows a system for measuring fan vibration. A fan vibration measurement apparatus  100  has a fan  110  disposed therein. The fan vibration measurement apparatus  100  is connected to a signal-processing device  120 . The signal-processing device  120  is connected to an output device  130  and a storage device  140 . 
     FIG. 2  shows an apparatus for measuring fan vibration  100  in accordance with one or more embodiments of the present invention. The apparatus  100  has a frame  101 , which has an opening at the center, six accelerometers  111 - 116 , and four elastic supports  150 - 153 . Each accelerometer  111 - 116  is connected to the signal-processing device  120  by a coaxial cable (not shown) or other suitable cable known in the art. There is a mounting block  160  disposed within the opening of the frame  101 . The mounting block  160  supports the base of the fan  110  and prevents the fan  110  from passing through the frame  101  upon insertion. Also, the mounting block  160  may include a hole for allowing a screw or bolt to pass through. As will be appreciated by those skilled in the art, typical fan casings often include holes at locations corresponding to holes in a mounting block or other mounting surfaces such that the fan can be secured by screw, bolt and nut, pin, elastic connector, or other suitable connector. 
     FIG. 3  shows a typical fan, which can be tested by an apparatus for measuring fan vibration in  FIG. 2 . The fan  110  includes a rotor  300  and casing  310 . The casing  310  is generally square or rectangular in shape. Those skilled in the art will appreciate that any other shape fan could also be used. Direction A is perpendicular to the surface of the surface of casing  310 . Air driven by the fan  110  moves in the direction A. Additionally, the casing  310  may be made of plastic or any other suitable material known in the art. As discussed above, the fan casing  310  may include a hole  370  at one or more locations to allow the fan  110  to be securely mounted by a screw, bolt and nut, pin, elastic connector, or other suitable connector. 
     FIG. 4  shows the fan  110  installed into the opening of the frame  101 . The frame  101  is generally square or rectangular in shape. The shape of the frame  101  is selected based on the ease of calculating the mass moments of inertia of the frame  101  and the fan  110  and on the ease of locating the accelerometers  111 - 116  at a useful distance from each other. For these reasons, a square frame  101  is generally preferred. The frame  101  may be made of a rigid material. The rigid material may be steel, aluminum, or any other suitable material known in the art. In one or more embodiments, the material is five to ten times heavier than the fan  110 . The accelerometers  111 - 116  may be mounted on around the corners of frame  101 . Six accelerometers  111 - 116  are used to detect six-axis information, such as, translational and rotational acceleration in three dimensional directions. This information can be used to determine translational force and rotational torque. Those skilled in the art will appreciate that the number and placement of the accelerometers  111 - 116  may be varied. 
   The fan  110  is installed into the opening of the frame  101  rigidly so that force and torque of the fan  110  are transferred without distortion of the dynamic loads. Specifically, the casing  310  is attached, for example, by screw, bolt and nut, pin, elastic connector, or other suitable connector through hole  370  at the corner of the casing  310  and the hole in mounting block  160 . Those skilled in the art will appreciate that the number and type of attachment points between the casing  110  and the frame  101  may be varied. 
   The thickness of the frame in the direction A is almost equal to that of the fan  110  in the direction A. Also, the width of the opening in the frame  101  is almost equal to the width of fan  110  in each direction perpendicular to the direction A. However, so long as the fan  110  is held rigidly in the opening, it is not necessary that the shape of the opening of the frame  101  is exactly matched with the outside shape of the casing  310 . However, in one or more embodiments, when installed, the shape of the opening of the frame  101  may be exactly matched with the outside shape of the casing  310  and the casing  310  may be in an interference fit against the frame  101 . The fan  110  may be also attached to the frame  101  using any other suitable methods known in the art. 
   Frame  101  is suspended in the air by elastic supports  150 - 153 , which may be made of, such as, rubber, plastic, or any other suitable material known in the art. One end of each elastic support  150 - 153  is attached to the corners of frame  101  by tapes, screws, bolts and nuts, adhesives, staking, spot welding, swaging, bonding, or other attachment methods known in the art. In one or more embodiments, duct and adhesive tape or clamping screws are suitable for adjusting the attachment points of each elastic support  150 - 153  to the frame  101  along the length of each elastic support  150 - 153 . The other end of each elastic support  150 - 153  is attached to a mounting bracket (not shown) of the fan vibration measurement apparatus  100 . The end of each elastic support  150 - 153  may be attached to the mounting bracket by tapes, screws, bolts and nuts, adhesives, staking, spot welding, swaging, bonding, or other attachment methods known in the art. Because frame  101  is suspended in the air, the structural resonances associated with the elastic attachment to ground are very low in frequency and do not influence the measurements. Although the number of elastic supports  150 - 153  shown is four, other number of elastic support may be used, so long as the elastic supports suspend the frame  101  and the fan  110  freely in the air. Also, the positions at which elastic supports  150 - 153  are attached to frame  101  are not limited to those shown. Those skilled in the art will appreciate that the elastic supports  150 - 153  could be attached to frame  101  at any other position on the surface of the frame  101 . 
   In the embodiment shown, accelerometers  111 - 116  for three orthogonal directions are disposed around at corners of frame  101 , so that there exists a greater distance among each of the accelerometers  111 - 116  in the same direction. This leads to an improvement in the accuracy of the calculations of torque. Specifically, the accelerometers are disposed on the upper surface, and side surfaces of frame  101  such that motion of the frame  101  in the x-axis, y-axis, and z-axis can be detected. From the output of these accelerometers  111 - 116 , any translation and rotation of fan  110  and the frame  101  can be determined by analog difference and scaling at one of the corners, or at the center of the fan  110 . Although the number of the accelerometers shown is six, fewer or more accelerometers can be used. In one or more embodiments, fewer accelerometers may be used to simplify the device, for example, in order to focus on specific torques. In one or more embodiments, more accelerometers may be used in order to increase precision or in order to provide redundancy for error reduction. Also, those skilled in the art will appreciate other positions where the accelerometers  111 - 116  may be disposed on or within frame  101  in order to measure the motion of fan  110  and the frame  101 . In addition, the dimensions of the frame  101  may be chosen in order to minimize inertia error due to the addition of the fan housing, while maintaining adequate rigidity to elevate device resonance frequency and while allowing sufficient device motion to be captured by ordinary sensors. 
   The signal-processing device  120  is connected electrically to each accelerometer  111 - 116 . The signal-processing device  120  includes a differential amplifier and an FFT device. The differential amplifier adds or subtracts raw analog acceleration waveforms of accelerometers  111 - 116 , and the FFT device generates the spectrum of the combined signals from the differential amplifier. Thus, the signal-processing device  120  converts analog signals from accelerometers  111 - 116  to forces and torques in spectrum form simply and accurately. In one or more embodiments, the signal-processing device  120  may be a multi-channel dynamic signal analyzer, or any other suitable signal-processing device. 
   The signal-processing device  120  is electrically connected to the output device  130 . The output device  130  may include a display device (not shown), which displays the forces and torques in spectrum form. The output device  130  and signal-processing device  120  may be included together in a single computer capable of the functionality described. In one or more embodiments, the output device  130  outputs the force and torque signals to the display device, and may include software for predicting the impact of the fan vibration on HDDs or other parts of a computer system. Because one output from the signal-processing device  120  is a set of force and torque spectra, this information can directly be used by other analysis software to permit comparisons and simulations of structural response. 
   The signal-processing device  120  is connected electrically to the storage device  140 . The storage device  140  stores the force and torque signals from the signal-processing device  120 . The storage device  140  may be a HDD, optical disc drive, or any other suitable storage devices known in the art. The storage device may be included in the processing device  120 . The information stored in the storage device  140  is used for further analysis in output device  130 , or some other computer or apparatus, to predict the impact of the fan vibration on HDDs or other parts of a computer system. 
   In operation, the fan  110  is inserted into the opening of frame  101 . As shown in  FIG. 4 , the frame  101  tightly holds the fan  110  at the mounting block  160  and the attachment points of the casing  301  by screw, bolt, or any other suitable methods in the art. Then, the fan  110  is turned on and the fan motor (not shown) starts the rotor  300  rotating. At this time, the frame  101  and the fan  110  are suspended by the elastic supports  150 - 153  so that the frame  101  and the fan  110  can move freely in the air. As the vibration of the fan  110  increases, each accelerometer  111 - 116  detects the accelerations from forces and torques and sends the signal to the signal-processing device  120 . Then, the signal-processing device  120  converts the signals from accelerometers  111 - 116  to forces and torques, and then the forces and torques are either stored in the storage device  140  or are displayed on the output device  130 . 
     FIG. 5  shows an apparatus for measuring fan vibration according to one embodiment of the present invention. In the embodiment shown, the opening in the frame  501  is not matched to a fan  510  having a circular shape. In the embodiment shown, fan  510  is mounted to the frame  501  via a screw  575 , which passes through a bracket included on fan  510  and the mounting block on frame  501  to secure the fan  510  to the frame  501 . Alternatively, a bolt may pass through the bracket and mounting block and secure the fan  510  to the frame  501  with a nut or an elastic connector designed to pass through the bracket and mounting block and secure the fan  510  to the frame  501  made be used. Otherwise, the elements and operation of the fan vibration measurement apparatus  100  are the same as that shown in  FIG. 4 . 
     FIG. 6  shows an apparatus for measuring fan vibration. In the embodiment shown, the opening in the frame  601  is matched to a fan  610  having a circular shape. Furthermore, the frame  601  has a circular shape. Because frame  601  has a circular shape, there are no corners on which to place accelerometers. Instead, accelerometers  611 - 613  are placed at various positions on the frame  601  such that motion in three dimensions can be detected. Also, elastic supports  650 - 652  are placed at various locations on frame  601  such that frame  101  and fan  610  can be suspended freely in the air. Otherwise, the operation of the fan vibration measurement apparatus  100  is the same as that shown in  FIGS. 4 and 5 . 
     FIG. 7  shows an apparatus for measuring fan vibration. In the embodiment shown, the accelerometers  111 - 116  are positioned on the frame  101  to simplify the calculation of forces and torques at the center of the fan. While the geometry discussed with respect to other embodiments favored calculation at the corner of the frame  101 , which maps well to fan mount points, the geometry shown in this embodiment favors an idealized origin of forces and torques at the center of the fan. Such a configuration does not correspond to fan mounting points for transfer of the dynamic loads to a system chassis, but rather, is independent of the specific fan mounting schemes and, accordingly, may be useful in different applications. Otherwise, the operation of the fan vibration measurement apparatus  100  is the same as that shown in  FIGS. 4-6 . 
   In the embodiment shown, the linear accelerations at the center of the fan are simply the average of the linear accelerations measured in each axis, e.g., (x 1 +x 2 )/2 in the x-axis. Further, the rotational accelerations are simply the difference between measured accelerations around each axis divided by the distance between the accelerometers, e.g., (z 1 -z 2 )/Dc, for rotation around the x-axis, where Dc is the distance between accelerometers z 1  and z 2 . The forces and torques are calculated similar as with other embodiments, i.e., by multiplying the accelerations and mass moment of inertia. Those skilled in the art will appreciate that mass moments of inertia are straightforward to calculate around a mass and geometry center. 
   Methods in accordance with one or more embodiments of the present invention for diagnosing, analyzing, and correcting fan-induced vibration in systems are critical in the early evaluation of systems to avoid these problems, and especially to solve problems which may arise during product development cycles. Mechanical analysis of cooling fans as sources of vibration and the system chassis design as paths of vibration in the time and frequency domains is increasingly important. Measurements of dynamic components, which include forces and torques, in each significant axis are essential to rapid ranking and resolution of fan-induced problems. 
   While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.