Patent Publication Number: US-11387705-B2

Title: Torsional mass tuned damper

Description:
TECHNICAL FIELD 
     The present disclosure relates to torsional mass tuned damper, and in particular, to torsional mass tuned damper for electric machines. 
     BACKGROUND 
     Conventional topology of a permanent magnet electric motor includes a permanent magnet rotor positioned inside a wound stator where electric current in the windings interact with the magnetic field of the permanent magnet to generate rotational motion of a shaft. An alternative induction motor topology is the external rotor design where the stator is placed inside a rotor. This configuration may allow for a longer air gap radius and hence capable of generating more drive torque compared to that of a conventional internal rotor motor of similar size. 
     For external rotor electric machines, the stator is often secured in a cantilever arrangement where one end of the stator is bolted onto a casing, such as a back plate of the electric machine, while the axially opposing end is free hanging. Those skilled in the art may appreciate that such cantilever arrangement may be more vulnerable to the negative effects of stator torsional resonance. 
     As mentioned above, the operating principle of electric machines is based on the magnetic field interaction between the rotor and stator. This interaction may create multiple force vectors acting on the external rotor, the sum of which may create a resulting torque on the rotor. Each of the forces acting on the external rotor may have an equal and opposite counterpart force acting on the internal stator. Thus, the internal stator may experience similar torque loading as the external rotor but in an opposite direction. The torque typically contains a mean value along with some parasitic torque ripples. These torque ripples may vary with the relative positioning between the rotor and the stator, and thus, may have frequencies proportional to the motor speed. The torque acting on the internal stator tend to excite the stator and causing movement in the form of vibration, particularly in the free hanging end. As the motor can be use in a broad range of speed defined in terms of revolutions per minute (RPM), the exciting forces on the internal stator may have a broad range of frequency. At some specific RPM, the exciting forces become synchronized with the torsional mode of the stator, which is defined as torsional resonance. During torsional resonance, the vibration amplitude increases significantly, which in turn can lead to high noise emission and/or mechanical damage. 
     Accordingly, there is a need for a device that at least partially ameliorates torsional resonance in external rotor motors. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present disclosure, there is provided a tuned mass damper for an electric machine having an rotor coaxially aligned with a stator, the damper comprising: a body; and a mounting mechanism configured to couple the body onto a mounting surface of the stator, the mounting mechanism is configured with a rigidity; wherein the rigidity permits the body to oscillate at a first frequency at least partially out of phase with the stator at a stator resonance frequency. 
     In another aspect of the present disclosure, there is provided a tuned mass damper for an electric machine having an rotor coaxially aligned with a stator, the damper comprising: a first body fixedly coupled to a mounting surface of the rotor; a second body; a compression element positioned in between and thereby coupling the first and second bodies; wherein the compression element is configured to permit the second body to oscillate at a first frequency at least partially out of phase with stator oscillation at a stator resonance frequency. 
     In a further aspect of the present disclosure, there is provided a tuned mass damper for an electric machine having an rotor coaxially aligned with a stator, the damper comprising: a first body fixedly coupled to a mounting surface of the stator; a second body concentric to the first body; a compression element positioned in between and for coupling the first and second bodies; wherein the compression element is configured to permit the second body to oscillate at a first frequency at least partially out of phase with stator oscillation at a stator resonance frequency. 
     In a further still aspect of the present disclosure, there is provided a tuned mass damper for an electric machine having an rotor coaxially aligned with a stator, the damper comprising: a body; a fastener configured to couple the body to a mounting surface of the stator; an insert mechanism configured to receive the fastener therethrough; and a compression element having a rigidity and is configured to permit the body to oscillate at a first frequency at least partially out of phase with stator oscillation at a stator resonance frequency; wherein the fastener is adjustable to vary a compressive force exerted onto the compression element by the insert mechanism thereby adjusting the rigidity of the compression element. 
     In any of the above, the first frequency may be naturally out of phase with the stator resonance frequency. 
     In any of the above, the body may have a mass; and wherein the mass and the rigidity determine the first frequency. 
     In any of the above, the mounting mechanism may comprise a compression element configured to be deformed during the damper oscillation, wherein the compression element defines the rigidity of the mounting mechanism. 
     In any of the above, the mounting mechanism may further comprise a plurality of openings that are evenly spaced along a periphery edge of the body. 
     In any of the above, the mounting mechanism may further comprise a plurality of openings that are unevenly spaced along a periphery edge of the body. 
     In any of the above, the plurality openings may be grouped into a plurality of groups of openings that are spaced along a periphery edge of the body. 
     In any of the above, the mounting mechanism may comprise a connection arm configured to couple a fastener to the body; wherein the connection arm defines a rigidity of the mounting mechanism. 
     In any of the above, the mounting mechanism may comprise a fastener configured for coupling the body onto the mounting surface; an opening formed on the body; and a compression element partially filling the opening and configured to receive the fastener therethrough; wherein during stator resonance frequency, the body and the fastener cause the compression element to deform such that the body oscillates at the first frequency. 
     In any of the above, the mounting mechanism may comprise a fastener configured for coupling the body onto the mounting surface; an opening formed on the body; and a spring member configured to secure the fastener to the body; wherein the spring member is configured with a spring constant that permits the body to oscillate at the first frequency. 
     In any of the above, the mounting mechanism may be an adhesive couples the body onto the mounting surface and permits relative movement thereinbetween. 
     In any of the above, the rotor may be an external rotor, and the stator is an internal stator, and the electric machine is in a cantilever arrangement with the external rotor and internal stator fixedly mounted at a first end, while a second end opposing the first end is left free hanging. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference will now be made, by way of example, to the accompanying drawings which show example embodiments of the present application, and in which: 
         FIG. 1  shows a partially exploded isometric view of an electric machine comprising a tuned mass damper in accordance with one example embodiment of the present disclosure; 
         FIG. 2  shows an isometric view of the tuned mass damper in  FIG. 1 ; 
         FIG. 3  shows an elevation cross-sectional view of one of the openings  46  as taken along the A-A line in  FIG. 2 ; 
         FIG. 4  shows a front elevation view of a mass tuned damper in accordance with another example embodiment of the present disclosure; 
         FIG. 5  shows a front elevation view of a mass tuned damper in accordance with a further example embodiment of the present disclosure; 
         FIG. 6A  shows an enlarged elevation view of a mounting mechanism in accordance with the present disclosure where spring members are in their natural state; 
         FIG. 6B  shows an enlarged elevation view of the mounting mechanism in  FIG. 6A  where the two spring members are in their stretched and compressed states respectively in response to damper body movement in a first direction; 
         FIG. 6C  shows an enlarged elevation view of the mounting mechanism in  FIG. 6A  where the two spring members are in their stretched and compressed states respectively in response to damper body movement in a second direction, opposite to the first direction in  FIG. 6B ; 
         FIG. 7A  shows a partial top view of a tuned mass damper in accordance with another aspect of the present disclosure; 
         FIG. 7B  shows an elevation cross-sectional view of the mounting mechanism shown in  FIG. 7A  taken along the A-A line; 
         FIG. 7C  shows an elevation cross-sectional view of the mounting mechanism shown in  FIG. 7A  taken along the B-B line; 
         FIG. 8A  shows a partial top view of a tuned mass damper in accordance with a further aspect of the present disclosure; 
         FIG. 8B  shows an elevation cross-sectional view of the mounting mechanism shown in  FIG. 8A  taken along the A-A line; 
         FIG. 8C  shows an elevation cross-sectional view of the mounting mechanism shown in  FIG. 8A  taken along the B-B line; 
         FIG. 9A  shows a partial top view of a tuned mass damper in accordance with a still further aspect of the present disclosure; and 
         FIG. 9B  shows an elevation cross-sectional view of the mounting mechanism shown in  FIG. 9A  taken along the A-A line. 
     
    
    
     Similar reference numerals may have been used in different figures to denote similar components. 
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
       FIG. 1  is a partially exploded isometric view of selected components of an electric machine  10 , showing one possible implementation of a tuned mass damper in accordance with exemplary embodiments of the present disclosure. It may be apparent from the present disclosure that the tuned mass damper disclosed herein can be applied to any motor topology, and especially for an external-rotor type of electric machine in cantilever arrangement. The electric machine  10  may be of any suitable electric system, such as a dual output motor as shown in  FIG. 1 . 
     In the illustrated embodiment of  FIG. 1 , the electric machine  10  includes a mass tuned damper  12 , which is mounted onto an internal stator  14 . An external rotor  16  is configured to be in coaxially sleeved relationship with the internal stator  14 . Although an external rotor electric machine  10  is shown, it is to be appreciated that the tuned mass damper in accordance with the present disclosure may also be applied to other types of electric machine configuration, such as the internal rotor type. 
     The stator  14  may be made out of multiple stacked laminations  18  forming outwardly facing slots  20  typically filled with coils, which are omitted in the figures for clarity. The stator  14  includes a first longitudinal end  22   a  and an opposing second longitudinal end  22   b  as shown. As shown in  FIG. 1 , the first end  22   a  is coupled to a base  24 , which, in a cantilever arrangement, may be securely fastened onto a rigid structure such as a motor casing (not shown) while the second longitudinal end  22   b  of the stator  14  is left free hanging. A skilled person may appreciate that other cantilever arrangement of the electric machine  10  may be possible. In  FIG. 1 , one embodiment of the base  24  is shown to include one or more connectors  26  for receiving electrical cables carrying alternating current used to energize the coils. In the illustrated embodiment, the tuned mass damper  12  is coupled onto an end mounting surface  28  of the stator  14  at the free hanging second longitudinal end  22   b.    
     As shown, the external rotor  16  comprising a cylindrically shaped receptacle  30  defining a first longitudinal end  32   a  and an axially opposing second longitudinal end  32   b . The receptacle  30  which may be fitted with inwardly facing permanent magnets (not shown) on an interior surface. In the illustrated embodiment, the rotor  16  further comprises a front plate  34  fastened onto the receptacle  30  at the longitudinal end  32   b . The front plate  34 , on an interior surface, may comprise one or more bearings for supporting the rotor  16 . A hub  36  is provided in the cap  34  coaxially with the receptacle  30 . The hub  36  may be configured to receive therethrough an input/output shaft  38  internally or externally with respect to the receptacle  30 . When the internal stator  14  is coaxially received within the external rotor  16 , the longitudinal ends  32   a ,  32   b  align with longitudinal ends  22   a ,  22   b  of the stator  14 , respectively. 
     As mentioned above, an alternating current received at base  24  may be used to energize the coils on the stator  14 . The energized coils in turn create electromagnetic field that interacts with the permanent magnets on the stator  14  to rotate rotor  16 , which then rotates the shaft  38 . This magnetic interaction may create multiple force vectors acting on the external rotor  16 , the sum of which may create a resulting torque on the rotor. Each of the force vector acting on the external rotor  16  may have an equal and opposite counterpart force acting on the internal stator  14 . Thus, the internal stator  14  may experience similar torque loading as the external rotor  16  but in an opposite direction. The torque typically contains a mean value along with some parasitic torque ripples. These torque ripples may vary with the relative positioning between the rotor  16  and the stator  14 , and thus, may have frequencies proportional to the motor speed. The torque acting on the internal stator  14  tends to excite the stator and thereby causes movement in the form of vibration, particularly in the free hanging end  22   b . At a specific rotational speed, the exciting forces become synchronized with the torsional mode of the stator  14 , which is defined as stator torsional resonance. 
     By attaching a tuned mass damper in accordance with the present disclosure to the stator via a mounting mechanism, the effects of the stator torsional resonance experienced at resonance frequency may be minimized. Specifically, in one embodiment, the tuned mass damper in accordance with the present disclosure may be configured to oscillate at the stator&#39;s natural frequency, but naturally out of phase with that of the stator, thereby resulting in the overall displacement of the stator being at least partially lessened. In another embodiment, the tuned mass damper in accordance with the present disclosure may convert kinetic energy of the stator to another form of energy, such as thermal energy for example, which may also lessen the displacement of the stator. 
       FIG. 2  illustrates one exemplary embodiment of tuned mass damper  12  as shown in  FIG. 1  in greater detail. The illustrated tuned mass damper  12  comprises a discoidal body  40  with a central bore  42 . In the illustrated embodiment, the tuned mass damper  12  is coupled to the stator  14  at a plurality of mounting points  44  that are evenly spaced along the circumference of damper body  40 . Each of the mounting points  44  is configured to receive a fastener  46  for securing the tuned mass damper  12  onto the mounting surface  28 . The fastener  46  may be configured to threadingly engage a corresponding mounting hole on the mounting surface  28  of stator  14 . A skilled person may appreciated that any other suitable types of mounting mechanism may also be used as discussed in more detail below. 
     Even though body  40  is shown to be discoidal, it is understood that any other shape may be suitable. However, a circular disc may possess even weight distribution in all directions and thus may be preferred for simpler tuning and configuration. The body  40  may be configured to have a mass value that is suitable for counteracting the torsional movement of the stator  14 . By way of a non-limiting example, the mass tuned damper  12  may be configured to have approximately 10% of the modal mass of the natural mode of the stator  14 . As known by those skilled in the art, the modal mass refers to the amount of mass that is in motion during the resonance event. The modal mass may vary based on the mass of the resonating component and the shape of the motion. 
     Central bore  42  may be configured with a sufficient diameter to at least permit the shaft  38  to pass therethrough unimpeded, while also taking into consideration possible torsional movement of the stator. In embodiments where space for accommodating the tuned mass damper  12  within electric machine  10  is limited, it may be preferred to decrease the size of bore  42  to achieve desired damper mass. In embodiments where the shaft  38  is not required to fit through the tuned mass damper  12 , central bore  42  may be omitted and/or decreased in size to possibly serve as a mounting point  44 . 
       FIG. 3  shows each of the mounting point  44  from  FIGS. 1 and 2  in greater detail. Specifically, each of the plurality of mounting point  44  comprises a mounting opening  48  that, in some embodiments, coaxially receives a compression limiter  50 . In the illustrated embodiment, a compression element  52  may be press fitted, or any other suitable means such as attached via adhesive, to fill the space between the compression limiter  50  and the interior wall of the mounting opening  48 . In the embodiment shows in  FIG. 3 , the compression limiter  52  is coaxially positioned within the mounting opening  48  with equal amount of compression element  52  surrounding the compression limiter  52  in all radial directions. As shown, the compression limiter  50  is a tubular structure that is configured to receive a fastener  46  therethrough. The compression limiter  50  may be resiliently fitted around the fastener  46  such it presents a fixed barrier against further movement of the compression element  52  along the lateral direction perpendicular to the lengthwise direction of the fastener  46 . As mentioned above, in some embodiments, the fastener  46  may threadingly engage a fastening hole formed on the mounting surface  28 . In some further embodiments, the fastener  46  may also threadingly engage the interior surface of the compression limiter  50 . In further still embodiments, once the fastener  46  is received through the compression limiter  50 , a gap may exist between the interior surface of the compression limiter  50  and the fastener  46 . In  FIG. 3 , the fastener  46  includes a head  54  that is of larger diameter than that of the central bore of the compression limiter  50  such that the head  54  rests upon, and is prevented from going through, the compression limiter  50 . 
     The compression element  52  preferably possesses a predetermined rigidity such that it may be compressible when force is exerted thereon. In some embodiments, the compression element  52  may be made out of a synthetic silicon polymer material. Those skilled in the art may appreciate that any other suitable material may be used. Upon movement of the damper body  40  during resonance, the damper body  40  may vibrate and exert force upon the compression element  52  and cause the compression element  52  to be compressed between the interior surface of mounting opening  48  and the compression limiter  50 . The rigidity of the compression element  52  would dictate the amount of compression and the hence the amount of movement of the damper body  40  with respect to the fixed mounting point  44  centered on a securely fastened fastener  46 . 
     The tuned mass damper is, in at least one aspect, a spring-mass dynamic system. Thus, its resonance frequency may directly correlate with the ratio of compression element rigidity over the damper mass. Accordingly, the resonance frequency of the damper may be adjusted by modifying the rigidity of the compression element  52  and/or the mass of the damper body  40 . In some preferred embodiments, the rigidity of the compression element  52  remains constant or with minimal variation over the entire operating temperature range of the electric machine  10 . In some embodiments, the resonance frequency of the tuned mass damper  12  is naturally out of phase with the torsional resonance of the stator. 
     In the embodiment shown in  FIGS. 1 and 2 , even though the mounting points  44  is shown to include six mounting openings  48 , it is to be understood that any number of mounting openings  48  may be used. As it may be appreciated that an increase number of mounting points  48  may result in the damper  12  being more rigid with respect to the stator  14  as each point of connection offers added resistance to damper movement. Conversely, the less number of mounting points for forming connections, the more flexible the damper movement may be. In some embodiments, the mounting mechanism may include at least two points of connection formed on diametrically opposing ends of the body  40 . In embodiments where the shaft  38  does not pass through the mounting surface  28 , the tuned mass damper  12  may be attached to the mounting surface  28  via a single point of connection, preferably located directly over the center of the tuned mass damper  12 . 
     In some embodiments, the points of connection of the mounting mechanism  44  may be evenly spaced along the peripheral edge of the damper body  40  as shown in  FIG. 2 . In some other embodiments, a subset of points of connection may be located in close proximity to one another thereby forming a connection point group, and a plurality of connection point groups may be evenly spaced along the peripheral edge of the body  40 . In some further embodiments, the points of connection, or connection point groups, may be unevenly distributed along the periphery edge to, for example, counteract uneven force distribution on the free hanging end  22   b  of the stator  14 . It is to be appreciated that other arrangements of the points of connection may be possible. By way of a non-limiting example, in some embodiments, the damper body  40  may be coupled to the mounting surface  28  via an adhesive thereby defining practically infinite number of points of connection. In some embodiments, the adhesive may serve as the compression element  52  between the tuned mass damper  12  and the stator  14 . Fasteners  46  may be omitted from such embodiments. In some other embodiments, the adhesive may be applied to select areas of the damper body  40 . By way of non-limiting example, the adhesive may be applied to a bottom surface of the damping elements  50 , which may completely fill the mounting openings  48  with no fasteners  46 . 
     Each of the openings  46  is circular in shape in the illustrated embodiment. As may be appreciated by those skilled in the art, circular openings may allow simpler tuning process as the range of motion in all directions may be equal. Additionally, the compression element  52  located within a circular opening  44  may experience equal compression in all directions and thus present similar rigidity regardless of the direction of movement. It is to be appreciated that other opening shapes are permissible with proper tuning. 
       FIG. 4  shows a tuned mass damper  100  in accordance with another example embodiment of the present disclosure. The tuned mass damper  100  comprises a body  140  that defines a central opening  141  for permitting other components, such as the shaft  38 , to pass therethrough. The mounting mechanism consists of six cavities  142  formed on the outer circumferential edge  144  of the damper body  140 . A mounting ring  146  is attached to the nadir point of the cavity  142  via a connection arm  148 . The mounting ring  146  is configured to receive a fastener (not shown) therethrough. Each mounting ring  146  may be partially filled with a damping element (not shown) of a predetermined rigidity that fittingly receives a fastener and provide damping function similar as disclosed above. Alternatively, the connection arm  148  may be formed from a material of predetermined rigidity that permits movement of the tuned mass damper  100  within the confines of the cavity  142 . Although six cavities, or points of connection, are shown, it may be appreciated the number of cavities may vary. 
       FIG. 5  shows a tuned mass damper  200  in accordance with another example embodiment of the present invention. The damper  200  comprises a body  240  that defines a central opening  241  for permitting other components, such as the shaft  38 , to pass therethrough. In the illustrated embodiment, the mounting mechanism includes four generally circular opening  242   a ,  242   b ,  242   c , and  242   d  (collectively referred to as openings  242 ) even spaced along the circumferential direction of the body  240 , each of the openings  242  is configured to receive a fastener  244  for mounting damper  200  onto the mounting surface  28  of stator  14 . Alternatively, a compression limiter (not shown) may be received in the opening  242 , and the fastener  244  is received within the compression limiter. As shown, each fastener  244  is located concentrically within each circular opening  242 . Two spring members  246  with a predefined spring constant connects the fastener  244 , or compression limiter, to body  240  in each opening  242 . The spring constant of the spring members  246  may be configured to achieve the desired resonance frequency of the damper  200 . In the illustrated embodiment, the spring members  246  in openings  242   a  and  242   c  are oriented along the X-direction for allowing movement primarily in the X-direction; while the spring members in openings  242   b  and  242   c  are oriented along the Y-direction for allowing movement primarily in the Y-direction. The number of X-axis oriented spring members may be equal to, or greater than, or less than, the number of Y-axis oriented spring members  246 . It may be appreciated that in some embodiments, the spring members  246  may be oriented in any direction in the X-Y plane. 
     As may be appreciated, the circular shape of openings  242  may permit any number of spring members  246  to be used. In some further embodiments, each fastener  244  or compression limiter (not shown) may be coupled to the body  240  via multiple spring members  246  that are oriented in any direction, preferably evenly spaced around the fastener  244  within each opening  242 . 
     In the embodiment show in  FIG. 5 , the damper body  240  preferably vibrates naturally out of phase with the stator  14 . The fasteners  244 , which may be received in a compression limiter (not shown), remains fixed in position while the spring members  246  either extend or retract depending on the motion of the damper body  240 . 
       FIGS. 6A-6C  illustrate a further embodiment of the spring member based mass tuned damper in accordance with the present disclosure. Specifically,  FIG. 6A  shows a partial view of damper body  250  that includes a generally rectangular opening  252 . A fastener  254  is positioned within the opening  252 , preferably near the half way point along the lengthwise direction of the opening. Two spring members  256   a  and  256   b  attach the fastener  254 , or the compression limiter, to either lengthwise ends of the opening  252   a  as shown. The spring members  256   a  and  256   b  may be compressed to a first compressed state or to be stretched to an extended state.  FIG. 6B  shows the damper body  250  moving in the general direction indicated by the arrow. During damper body  250  movement in the indicated direction, the left side of the opening  252  is moving away from the fixed fastener  254 , thus stretching the spring member  256   a  to an extended state. Correspondingly, the right side of the opening  252  moves closer to the fixedly placed fastener  254  and compresses the spring member  256   b  to a compressed state. The tendencies in spring members  256   a  and  256   b  to return to their normal states may counter damper body  240  kinetic force.  FIG. 6C  shows damper body  250  movement in the opposite direction as indicated by the arrow, which causes spring member  256   a  to extend and spring member  256   b  to compress. The same operating principle may be applied mutatis mutandis to embodiments with any number of spring members in other orientations. 
       FIGS. 7A-7C  show yet another embodiment of the present invention. Specifically,  FIG. 7A  shows a top elevation view of a section of a tuned mass damper  300  in accordance with the present invention. One mounting point  302  is shown to be situated on the damper body  304 . Similar to other embodiments discloses herein, any number of mounting points  302  may be positioned along the circumferential length of the damper body  304 . 
       FIG. 7B  shows a cross-sectional view of the damper body  304  taken along the line A-A in  FIG. 7A . As can be seen, the damper body  304  consists of two vertically stacked rings, a top moving ring  306  and a bottom fixed ring  308  separated by a layer of compression element  52 . 
       FIG. 7C  shows a cross-sectional view of the damper body  304  taken along the line B-B in  FIG. 7A . As shown, the mounting point  302  includes an opening  310  with a first diameter dimensioned to permit passage of a fastener  314 . A similar sized opening is also formed in the compression element  52  layer. The fixed ring  308  has a hole  312  formed at the corresponding location with a second diameter configured to permit the body of the fastener  314  to pass therethrough. In the illustrated embodiment, the first diameter is greater than the second diameter such that the head portion  316  of the fastener  314  is estopped and rests upon the fixed ring  308 . The fastener  314  extends through the hole  312  and may further securely engage a corresponding opening on the mounting surface  28  on the stator  14 . 
     Accordingly to  FIGS. 7A-7C , the fixed ring  308  is secured onto the mounting surface  28  of the stator  14  by fasteners  314 . During stator resonance, the shear deformation of the compression element  52  may permit vibrational movement of the top moving ring  306  above the bottom fixed ring  308 . In some embodiments, the vibrational movement of the top moving ring  306  is primarily in the plane parallel to the mounting surface  28  of the stator  14 , and may be naturally out of phase with the stator oscillation during resonance. 
       FIGS. 8A-8C  show yet another embodiment of the present invention. Specifically,  FIG. 8A  shows a top elevation view of a section of a tuned mass damper  400  in accordance with the present invention. In the illustrated section, one mounting point  402  is shown to be situated on the damper body  404 . Similar to other embodiments discloses herein, any number of mounting points  402  may be positioned along the circumferential length of the damper body  404 . 
       FIG. 8B  shows a cross-sectional view of the damper body  404  taken along the line A-A in  FIG. 8A . As can be seen, the damper body  404  consists of two concentric rings, an inner moving ring  406  and an outer fixed ring  408  separated by a layer of compression element  52 . The fixed ring  408  includes a vertical body  410  with a horizontal flange  412  perpendicularly extending from one end of the body  410 . 
       FIG. 8C  shows a cross-sectional view of the damper body  404  taken along the line B-B in  FIG. 8A . As shown, the mounting point  402  includes a hole  414  formed through the horizontal flange  412  of the fixed ring  408  for receiving a fastener  416 . In the illustrated embodiment, the fastener  416  extends through the hole  414  so as to be able to securely fasten to a corresponding opening on the mounting surface  28  of the stator  14 , and thus fixedly maintaining the outer ring  408  on the mounting surface  28 . The fastener  46  extends through the hole  312  and may further securely engage a corresponding opening on the mounting surface  28  on the stator  14 . 
     Accordingly to  FIGS. 8A-8C , the fixed outer ring  408  is secured onto the mounting surface  28  of the stator  14  by fasteners  416 . During stator resonance, the shear deformation of the compression element  52  may permit vibrational movement of the inner moving ring  406 . In some embodiments, the vibrational movement of the moving ring  406  is primarily in the plane parallel to the mounting surface  28  of the stator  14 , and may be naturally out of phase with the stator oscillation during resonance. 
     It may be appreciated that in further embodiments where the tuned mass damper consists of concentric rings, the inner ring may be fixed and the outer ring may be the moving ring that functions mutatis mutandis as embodiments shown in  FIGS. 8A-8C . Specifically, a circumferential flange may extend from the inner edge of the inner fixed ring where mounting points may be located for securely fastening the damper onto the mounting surface of the stator. A layer of compression element separates the inner and outer rings so as to permit movement of the outer ring during stator resonance that may be naturally out of phase with the vibration of the stator. 
       FIGS. 9A-B  show an adjustable tuned mass damper  500  in accordance with yet another embodiment of the present invention. Specifically,  FIG. 9A  shows a top elevation view of a portion of the tuned mass damper  500  where one mounting point  502  is located on the damper body  504 . Similar to other embodiments discloses herein, any number of mounting points  502  may be positioned along the entire circumferential length of the damper body  504 . 
       FIG. 9B  shows a cross sectional elevation view of the damper body  504  along the A-A line in  FIG. 9A . The mounting point  502  includes a mounting opening  506  formed through damper body  504  where an insert mechanism is received that includes a top insert  508  and a bottom insert  510  are received therein. In the illustrated embodiment, mounting opening  506  is substantially an “hour-glass” shape where the diameter of the opening gradually narrows until approximately half way point and then gradually enlarges to its original size. It is to be appreciated that other shapes of the opening  506  may be possible. 
     As shown, in order to be fitted into the hour-glass shaped mounting opening  506 , both of the top insert  508  and bottom insert  510  are generally in the shape of truncated cones. In some embodiments, the dimensions of the top and bottom inserts  508  and  510  are identical. In other embodiments, differently dimensioned inserts  508  and  510  may be used. As shown in the figures, the inserts  508  and  510  may be separate pieces. When the top and bottom inserts  508  and  510  are received within the opening  506  with the narrow ends facing each other. 
     In some embodiments, such as the one shown in  FIG. 9B , a shim plate  512  is positioned between the two inserts  508  and  510 . The shim plate  512  may be of variable thickness, which in turn allows different amount of compression between inserts  508  and  510 . 
     The top insert  508  includes a central bore  514   a  and the bottom insert  510  includes a central bore  514   b . When the top and bottom inserts  508  and  510  are positioned within mounting opening  506 , the central bores  514   a  and  514   b  align to form fastener bore  514  for receiving a fastener  516  therethrough. The fastener  516  may extend through the fastener bore  514  to be fastened onto a corresponding opening on the mounting surface  28  of the stator  14 . In some embodiments, the fastener  516  may be a bolt or screw that is configured to have a downward movement upon being tightened. 
     In the illustrated embodiment, a compression element  518   a  is sandwiched between the top inserts  508  and the upper portion of the damper body  504 . Similarly, a compression element  518   b  is sandwiched between the bottom inserts  510  and the lower portion of the damper body  504 . Collectively referred to as compression elements  518 , compression elements  518   a  and  518   b , may be configured to generally conform to the contours of the inserts  508  and/or  510  on an interior surface and that of the mounting opening  506  on the exterior surface. In some embodiments, compression element  518  may be a single continuous piece that covers both inserts  508  and  510 . In further embodiments, the compression element may comprise a plurality of pieces. 
     Accordingly, the embodiment shown in  FIGS. 9A and 9B  may provide an “adjustable” tuned mass damper  500 . Specifically, the bottom insert  510  may sit on top of the mounting surface  28  which provides a backstop for the insert. As mentioned above, the fastener  516  may be configured to have a downward movement when tightened, which would in turn exert a similar downward force onto the top insert  508 . The top insert  508  may then move closer to the bottom insert  510 . The inserts  508  and  510  would exert a compressive force onto the compression element  518  against damper body  504 , thereby causing shearing deformation of the compression element  518 . Accordingly, by adjusting the fastener  516 &#39;s downward movement, the rigidity of the compression element  518  may be adjusted. The thickness of the shim plate  512  or the space between inserts  508  and  510  allow tuning of the compression amount of the compression elements  518 . During stator resonance, the damper body  504  may come in contact with the compression elements  518  and causing further deformation. Hence, the more deformation the compression elements  518  experience from the inserts  508 ,  510 , the less deformation may be possible from force exerted by the damper body  504 . 
     The shim plate  512  also includes a central bore that aligns with bores  514   a  and  514   b  to form central bore  514  for permitting fastener  516  to pass therethrough. The central bore of the shim plate  512  may be configured to threadingly engage the fastener  516  and provide additional fastening surface with which to maintain the fastener  516  in place. Further, as it may be appreciated by those skilled in the art, some synthetic polymer material may have the tendency to deform and may creep into any gap that may exist between the top and bottom inserts  508  and  510 , which could impact the rigidity of the compression element  518  and hence the damping ability of the tuned mass damper. Thus, shim plate  512  may provide a physical barrier to prevent the compression element  518  from entering the gap between the inserts  508  and  510  and help to maintain the physical integrity of the compression element  518 . 
     Certain adaptations and modifications of the described embodiments can be made. Therefore, the above discussed embodiments are considered to be illustrative and not restrictive. The present disclosure is not to be limited in scope by the specific embodiments described herein. Further example embodiments may also include all of the steps, features, compositions and compounds referred to or indicated in this description, individually or collectively and any and all combinations or any two or more of the steps or features. 
       FIGS. 1-9B  show example configurations with relative positioning of the various components. If shown directly contacting each other, or directly coupled, then such elements may be referred to as directly contacting or directly coupled, respectively, at least in one example. Similarly, elements shown contiguous or adjacent to one another may be contiguous or adjacent to each other, respectively, at least in one example. As an example, components laying in face-sharing contact with each other may be referred to as in face-sharing contact. As another example, elements positioned apart from each other with only a space there-between and no other components may be referred to as such, in at least one example. As yet another example, elements shown above/below one another, at opposite sides to one another, or to the left/right of one another may be referred to as such, relative to one another. Further, as shown in the figures, a topmost element or point of element may be referred to as a “top” of the component and a bottommost element or point of the element may be referred to as a “bottom” of the component, in at least one example. As used herein, top/bottom, upper/lower, above/below, may be relative to a vertical axis of the figures and used to describe positioning of elements of the figures relative to one another. As such, elements shown above other elements are positioned vertically above the other elements, in one example. As yet another example, shapes of the elements depicted within the figures may be referred to as having those shapes (e.g., such as being circular, straight, planar, curved, rounded, chamfered, angled, or the like). Further, elements shown intersecting one another may be referred to as intersecting elements or intersecting one another, in at least one example. Further still, an element shown within another element or shown outside of another element may be referred as such, in one example. 
     Throughout this document, the use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and/or the specification may mean “one”, but it is also consistent with the meaning of “one or more”, “at least one”, and “one or more than one”. Similarly, the word “another” may mean at least a second or more. The words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “include” and “includes”) or “containing” (and any form of containing, such as “contain” and “contains”), are inclusive or open-ended and do not exclude additional, unrecited elements or process steps. 
     In the present specification and in the appended claims, various terminology which is directional, geometrical and/or spatial in nature such as “longitudinal”, “horizontal”, “front”, “forward”, “backward”, “back”, “rear”, “upwardly”, “downwardly”, etc. is used. It is to be understood that such terminology is used for ease of description and in a relative sense only and is not to be taken in any way as specifying an absolute direction or orientation. 
     The embodiments described herein may include one or more range of values (for example, size, displacement and field strength etc.). A range of values will be understood to include all values within the range, including the values defining the range, and values adjacent to the range that lead to the same or substantially the same outcome as the values immediately adjacent to that value which defines the boundary to the range. For example, a person skilled in the field will understand that a 10% variation in upper or lower limits of a range can be totally appropriate and is encompassed by the disclosure. More particularly, the variation in upper or lower limits of a range will be 5% or as is commonly recognized in the art, whichever is greater. 
     Throughout this specification relative language such as the words ‘about’ and ‘approximately’ are used. This language seeks to incorporate at least 10% variability to the specified number or range. That variability may be plus 10% or negative 10% of the particular number specified.