Abstract:
One embodiment provides a system that mitigates vibrations caused by cooling fans in a computer system. More specifically, the system includes a cooling fan mechanically coupled to the chassis of the computer system, wherein vibrations generated by the cooling fan are coupled to the chassis. The system also includes an actuation mechanism that creates a relative displacement between the cooling fan and the chassis when a control signal is applied to the actuation mechanism. The system additionally includes a detection mechanism which detects the relative displacement and generates a feedback signal which represents the relative displacement. The system further includes a control signal generation mechanism which converts the feedback signal into the control signal, which is subsequently applied to the actuation mechanism. When the control signal is applied to the actuation mechanism, the relative displacement between the cooling fan and the chassis vibrationally decouples the cooling fan from the chassis.

Description:
BACKGROUND 
       [0001]    1. Field 
         [0002]    Embodiments of the present invention generally relate to techniques for improving the vibrational health of computer systems. More specifically, embodiments of the present invention relate to techniques for damping vibrations caused by cooling fans in a computer system. 
         [0003]    2. Related Art 
         [0004]    In today&#39;s computer systems, cooling fans are becoming increasingly more powerful and can consequently generate significant mechanical vibrations during computer system operation. Such vibrations can propagate to other computer system components which are mechanically coupled to the same chassis structures. These fan-induced vibrations can cause performance degradation and reliability problems for computer system components, such as interconnects, motors, and hard-disk drives (HDDs). In particular, HDDs have become increasingly sensitive to vibration-induced performance degradation, and excessive vibrations can cause drastic degradation of read and/or write throughput for the HDDs. 
         [0005]    Some conventional techniques for damping the fan-induced vibrations in computer systems involve inserting elastomeric isolation materials, such as foams, polymers, and natural rubber pads of various thicknesses, between the fans and the chassis structures. Unfortunately, these isolation materials typically suffer from long-term deterioration problems due to elastomeric aging mechanisms. 
         [0006]    Hence, what is needed is a method and apparatus that facilitates isolating fan vibrations from vibration-sensitive devices without the above-described problems. 
       SUMMARY 
       [0007]    One embodiment provides a system that mitigates vibrations caused by cooling fans in a computer system. This system includes a cooling fan mechanically coupled to the chassis of the computer system, wherein vibrations generated by the cooling fan are coupled to the chassis. The system also includes an actuation mechanism for creating a relative displacement between the cooling fan and the chassis when a control signal is applied to the actuation mechanism. The system additionally includes a detection mechanism which detects the relative displacement and generates a feedback signal which represents the relative displacement. The system further includes a control signal generation mechanism which converts the feedback signal into the control signal, which is subsequently applied to the actuation mechanism. When the control signal is applied to the actuation mechanism, the relative displacement between the cooling fan and the chassis vibrationally decouples the cooling fan from the chassis. 
         [0008]    In some embodiments, the actuation mechanism includes a first electromagnet embedded in the cooling fan and a second electromagnet embedded in the chassis and located in proximity to the first electromagnet. The first electromagnet and the second electromagnet form an electromagnetic suspension (EMS) across the interface between the cooling fan and the chassis. Consequently, when subjected to the control signal, the first and second electromagnets cause magnetic levitation to vibrationally decouple the cooling fan from the chassis. 
         [0009]    In some embodiments, the detection mechanism includes a first position sensor embedded in the cooling fan which detects the position of the cooling fan. The detection mechanism also includes a second position sensor embedded in the chassis which detects the position of the chassis. 
         [0010]    In some embodiments, the first and second position sensors are accelerometers, wherein each accelerometer is configured to measure both position and trajectory signals. 
         [0011]    In some embodiments, the control signal generation mechanism is a servomechanism controller. 
         [0012]    In some embodiments, the feedback signal includes both position signals and trajectory signals associated with the cooling fan and the chassis. 
         [0013]    In some embodiments, the relative displacement between the cooling fan and the chassis mechanically vibrationally decouples the cooling fan from one or more hard-disk drives (HDDs) which are mechanically coupled to the chassis. 
         [0014]    In some embodiments, the accelerometers can include uni-axial accelerometers; bi-axial accelerometers; and tri-axial accelerometers. 
         [0015]    In some embodiments, the relative displacement between the cooling fan and the chassis can be a one-dimensional displacement; a two-dimensional displacement; or a three-dimensional displacement. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0016]      FIG. 1  illustrates a computer system having multiple cooling fans in accordance with an embodiment of the present invention. 
           [0017]      FIG. 2  illustrates an active controlled electromagnetic suspension (EMS) system for isolating vibrations caused by a cooling fan in a computer system in accordance with an embodiment of the present invention. 
           [0018]      FIG. 3A  illustrates a system for decoupling a fan from a chassis through 2D magnetic levitation in accordance with an embodiment of the present invention. 
           [0019]      FIG. 3B  illustrates a system for decoupling a fan from a chassis through 3D magnetic levitation in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    The following description is presented to enable any person skilled in the art to make and use the embodiments, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. Thus, the present invention is not limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein. 
         [0021]    The data structures and code described in this detailed description are typically stored on a computer-readable storage medium, which may be any device or medium that can store code and/or data for use by a computer system. The computer-readable storage medium includes, but is not limited to, volatile memory, non-volatile memory, magnetic and optical storage devices such as disk drives, magnetic tape, CDs (compact discs), DVDs (digital versatile discs or digital video discs), or other media capable of storing computer-readable media now known or later developed. 
         [0022]    The methods and processes described in the detailed description section can be embodied as code and/or data, which can be stored in a computer-readable storage medium as described above. When a computer system reads and executes the code and/or data stored on the computer-readable storage medium, the computer system performs the methods and processes embodied as data structures and code and stored within the computer-readable storage medium. 
         [0023]    Furthermore, the methods and processes described below can be included in hardware modules. For example, the hardware modules can include, but are not limited to, application-specific integrated circuit (ASIC) chips, field-programmable gate arrays (FPGAs), and other programmable-logic devices now known or later developed. When the hardware modules are activated, the hardware modules perform the methods and processes included within the hardware modules. 
       Computer System 
       [0024]      FIG. 1  illustrates a computer system  100  having multiple cooling fans  116  in accordance with an embodiment of the present invention. As illustrated in  FIG. 1 , computer system  100  includes a processor  102 , which is coupled to a memory  112  and to peripheral bus  110  through bridge  106 . Bridge  106  can generally include any type of circuitry for coupling components of computer system  100  together. 
         [0025]    Processor  102  can generally include any type of processor, including, but not limited to, a microprocessor, a mainframe computer, a digital signal processor, a personal organizer, a device controller, a computational engine within an appliance, and any other processor now known or later developed. Furthermore, processor  102  can include one or more cores. Processor  102  includes a cache  104  that stores code and data for execution by processor  102 . 
         [0026]    Although  FIG. 1  illustrates computer system  100  with one processor, computer system  100  can include more than one processor. In a multi-processor configuration, the processors can be located on a single system board, or on multiple system boards. Computer system  100  can include, but is not limited to, a server, a server blade, a datacenter server, a field-replaceable unit, or an enterprise computer system. 
         [0027]    Processor  102  communicates with storage device  108  through bridge  106  and peripheral bus  110 . Storage device  108  can include any type of non-volatile storage device that can be coupled to a computer system. This includes, but is not limited to, magnetic, optical, and magneto-optical storage devices. In particular, storage device  108  can include one or multiple hard-disk drives (HDDs), or an HDD array. 
         [0028]    Processor  102  communicates with memory  112  through bridge  106 . Memory  112  can include any type of memory that can store code and data for execution by processor  102 . This includes, but is not limited to, dynamic random access memory (DRAM), static random access memory (SRAM), flash memory, read-only memory (ROM), and any other type of memory now known or later developed. Note that processor  102 , cache  104 , bridge  106 , peripheral bus  110  and memory  112  are typically located on a system board/motherboard (not shown). 
         [0029]    Computer system  100  also includes other system components, which include, but are not limited to, power supply  114 , one or more cooling fans  116 , network cards  118 , and cables  120  that interconnect system components. Furthermore, computer system  100  is enclosed by chassis  122 , which provides housing and mechanical supports for the aforementioned computer system components. As cooling fans become increasingly powerful, they can generate significant vibrations during computer system operation. Also note that cooling fans  116  are mechanically coupled to an inner surface of chassis  122 , so that the vibrations generated by cooling fans  116  are coupled to chassis  122  and subsequently propagated to other system components which are also mechanically coupled to chassis  122  (e.g., storage device  108 ). 
         [0030]    Note that although computer system  100  is used for the purposes of illustration, embodiments of the present invention can generally be applied to other computer systems, such as desktop computers, workstations, storage arrays, embedded computer systems, automated manufacturing systems, and other computer systems which use one or more rotational cooling devices for system cooling. Hence, the present invention is not limited to the specific implementation of computer system  100  as illustrated in  FIG. 1 . 
       Using Electromagnetic Suspension for Vibration Isolation 
       [0031]      FIG. 2  illustrates an active controlled electromagnetic suspension (EMS) system  200  for isolating vibrations caused by a cooling fan  202  in a computer system  201  in accordance with an embodiment of the present invention. Note that EMS system  200  may be embedded in computer system  201  (which is not fully shown). 
         [0032]    As illustrated in  FIG. 2 , EMS system  200  includes cooling fan  202  (or “fan  202 ”) to be isolated. The housing of fan  202  may be initially in direct contact with the inner surface  203  of chassis  204  of computer system  201 . However, fan  202  does not have to be affixed to chassis  204 . In one embodiment, fan  202  lightly coupled to chassis  204  through soft springs  205 - 1  and  205 - 2 . These soft springs are configured to limit the movement of fan  202  in the horizontal direction while allow freedom of movement of fan  202  in the vertical direction by means of a very small spring constant. However, many other forms of mechanical coupling between fan  202  and chassis  204  can be used in place of the one illustrated in  FIG. 2 . 
         [0033]    Fan  202  includes an actuator  207  which comprises a first electromagnet  206  and a second electromagnet  208 . As illustrated in  FIG. 2 , electromagnet  206  is embedded in the housing of fan  202  in proximity to the surface which may be in contact with chassis  204 . Electromagnet  206  faces electromagnet  208  which is embedded in chassis  204 . Note that electromagnets  206  and  208  do not have to be the same size. Furthermore, electromagnets  206  and  208  can be driven by respective electromagnetic force (EMF) actuation signals  210  and  212 , which are generated from EMF actuation signal generator  214 . EMF actuation signal generator  214  is described in more detail below. When EMF actuation signals  210  and  212  are applied, electromagnets  206  and  208  repel each other, thereby causing a magnetic levitation force between fan  202  and chassis  204 . This levitation force can create a relative displacement (in the indicated vertical direction next to actuator  207 ) between fan  202  and chassis  204 , allowing fan  202  to be suspended above surface  203 , and decoupled from the chassis structure  204 . Consequently, mechanical vibrations generated by fan  202  are either damped or completely isolated (i.e., vibrationally decoupled) from the chassis structures. Note that EMF actuation signals  210  and  212  control the amount of electromagnetic force generated by electromagnets  206  and  208  and therefore control the amount of actuation between fan  202  and chassis  204 . 
         [0034]    Referring to  FIG. 2 , fan  202  is also integrated with a first accelerometer  216 , which is used to detect the position and trajectory of fan  202  during magnetic levitation. Additionally, a second accelerometer  218  is rigidly affixed to chassis  204  to detect the displacement of chassis  204 . In one embodiment, accelerometer  218  is embedded in chassis  204  underneath inner surface  203 , as shown in  FIG. 2 . In another embodiment, accelerometer  218  may be rigidly affixed to chassis  204  on top of inner surface  203 . In some embodiments, accelerometers  216  and  218  are microelectromechanical system (MEMS) accelerometers. Note that such MEMS accelerometers are typically much smaller than fan  202  and are also inexpensive. Moreover, each accelerometer can be a uni-axial accelerometer, bi-axial accelerometer, or tri-axial accelerometer. 
         [0035]    Accelerometers  216  and  218  together determine the relative displacement between fan  202  and chassis  204  in the vertical direction. More specifically, output signals from accelerometers  216  and  218  are coupled to a displacement signal generator  220 . Typically, prior to applying EMF actuation signals  210  and  212 , the displacement between fan  202  and chassis  204  is set to zero. During the process of magnetic levitation, displacement signal generator  220  determines the displacement of fan  202  from the initial position based on the telemetry signals gathered from both of the accelerometers. 
         [0036]    Note that in addition to the displacement caused by magnetic levitation, the relative displacement between fan  202  and chassis  204  can also include displacements caused by mechanical vibrations of both fan  202  and chassis  204 . As a result, the amount of levitation may be modulated by these vibration-induced displacements, resulting in uncertainty in the amount of magnetic levitation. In order to achieve stable EMS of fan  202  from chassis  204 , the position and trajectory data of fan  202  can be continuously gathered and processed by displacement signal generator  220  to generate real-time displacement data for the fan. This real-time displacement data can then be used to continuously adjust EMF actuation signals  210  and  212  to compensate for the effect of mechanical vibrations. 
         [0037]    More specifically, the output from displacement signal generator  220  is fed into servomechanism controller  222 , which can adjust the amount of EMS based on the real-time displacement data. For example, if it is found that the relative displacement between fan  202  and chassis  204  is below a desirable minimum value, servomechanism controller  222  can cause an increase of magnitudes in the EMF actuation signals. As shown in  FIG. 2 , this is achieved by using the output from servomechanism controller  222  to control EMF actuation signal generator  214 , which is configured to convert the servomechanism controller output into desired EMF actuation signals  210  and  212 . Hence, displacement signal generator  220 , servomechanism controller  222 , and EMF actuation signal generator  214  form a feedback control loop which can achieve stable magnetic levitation of fan  202 . 
         [0038]    Although  FIG. 2  illustrates a system for performing vibration decoupling between chassis and fan in one-dimension (1D), generally the EMS-based vibration-decoupling technique can be performed in 2D or 3D.  FIGS. 3A and 3B  illustrate systems for performing vibration decoupling between fans and chassis structures in multiple dimensions. Specifically,  FIG. 3A  illustrates a system for decoupling a fan  302  from a chassis  304  through 2D magnetic levitation in accordance with an embodiment of the present invention. More specifically, fan  302  which is placed inside a computer system is in contact with two adjacent surfaces of chassis  304 . In one embodiment, fan  302  is lightly coupled to chassis  304  through soft springs  305 - 1  and  305 - 2 . These soft springs are configured to confine the movement of fan  302  in both the horizontal and vertical directions when fan  302  is in contact with chassis  304 . However, many other forms of mechanical coupling between fan  302  and chassis  304  can be used in place of the one illustrated in  FIG. 3 . 
         [0039]    In this embodiment, two actuators wherein each of which is comprised of a set of electromagnets are used to facilitate magnetic levitation in both x-(i.e., the vertical) and y-(i.e., the horizontal) directions. As shown in  FIG. 3A , a first electromagnet  306  is integrated with fan  302  and faces horizontal surface  308  of chassis  304 , while a second electromagnet  310  is rigidly affixed underneath surface  308  of chassis  304 . 
         [0040]    The pair of electromagnets  306  and  310 , when driven by proper EMF actuation signals, magnetically levitate fan  302  in the y-direction, which subsequently achieves damping or isolation of vibrations caused by fan  302  in the same direction. Similarly, a second pair of electromagnets  312  and  314  is embedded in the left-hand side of fan  302  and a vertical surface  316  of chassis  304 , respectively. The second pair of electromagnets magnetically levitates fan  302  in the x-direction, thereby damping out vibration caused by fan  302  in the x-direction. Hence, the two pairs of electromagnets in  FIG. 3A  can create 2D displacement of fan  302  relative to chassis  304  in the x-y plane. 
         [0041]    In one embodiment, the relative displacement between fan  302  and chassis  304  is inferred by real-time telemetry of the vector difference between a pair of bi-axial MEMS accelerometers  318  and  320 , wherein accelerometer  318  is integrated with fan  302 , while accelerometer  320  is rigidly affixed to chassis  304 . In this case, the actuation directions of the bi-axial accelerometers are aligned with the x- and y-directions, respectively. During EMS operation, the bi-axial accelerometers simultaneously measure position and trajectory signals in two orthogonal directions (the x- and y-directions). These electromagnets can be driven by a servomechanism feedback system similar to the one illustrated in  FIG. 2 . More specifically, the 2D accelerometer telemetry signals are used to generate EMF actuation signals for both sets of electromagnets in  FIG. 3A  to adjust the 2D displacement of fan  302  relative to chassis  304  in both x- and y-directions. In some embodiments, tri-axial accelerometers can be used instead of bi-axial accelerometers. 
         [0042]      FIG. 3B  illustrates a system for decoupling a fan  322  from a chassis  324  through 3D magnetic levitation in accordance with an embodiment of the present invention. More specifically, fan  322  which is placed inside a computer system is making contact with three adjacent surfaces of chassis  324 . In this embodiment, for each pair of contacting surfaces (i.e., one from fan  322  and one from chassis  324 ), a pair of electromagnets is used to magnetically levitate in the direction perpendicular to the pair of surfaces (the electromagnets are not shown in  FIG. 3B ). Overall, three electromagnets are integrated with fan  322  and three complementing electromagnets are embedded in chassis  324  underneath the three orthogonal surfaces  326 ,  328 , and  330 . These electromagnets can be driven by a servomechanism feedback system similar to the one illustrated in  FIG. 2  to cause a 3D displacement of fan  322  relative to chassis  324  in a 3D space. In one embodiment, the relative displacement between fan  322  and chassis  324  is inferred by real-time telemetry of the vector difference between a pair of tri-axis MEMS accelerometers (not shown in  FIG. 3B ), wherein one accelerometer is integrated with fan  322 , and the other accelerometer is rigidly affixed to chassis  324 . 
         [0043]    In both fan-chassis configurations of  FIG. 3A  and  FIG. 3B , it is possible to selectively apply magnetic levitation in only one direction. In one embodiment, this direction can be the one which causes the greatest performance degradation for HDDs coupled to the chassis structures. For example in  FIG. 3A , the system can separately apply magnetic levitation in the x- and y-directions, and for each direction, can determine the corresponding improvement on throughput of HDDs. Next, during normal operation, the system can only apply EMF actuation signals to the selected direction, thereby simplifying the feedback control mechanism. In another embodiment of the present invention, this selected direction can be the one which facilitates damping out vibrations in certain frequencies that are similar to the natural resonant frequencies of the HDDs, and/or frequencies to which the HDDs are known to have a high vibrational sensitivity. 
         [0044]    While we have described decoupling vibrations between the fans and the sensitive HDDs by applying magnetic levitation to the fans, it is also possible to magnetically levitate the HDDs, thereby isolating the HDDs from the chassis structures and the fan-induced vibrations. In practice, it may be more efficient to decouple the fans from the chassis because there are typically many fewer fans in computer systems than HDDs. Furthermore, the technique described above can be readily extended to other vibration-sensitive components and vibration sources within a computer system. Hence, the present invention is not limited to the specific implementation of EMS system  200  as illustrated in  FIG. 2 , and those illustrated in  FIGS. 3A and 3B . 
         [0045]    The foregoing descriptions of embodiments of the present invention have been presented only for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art. Additionally, the above disclosure is not intended to limit the present invention. The scope of the present invention is defined by the appended claims.