Abstract:
An magnetorheological damper useful in structural vibration control has a damper body and a moveable portion relative to the damper body. The damper includes an magnetorheological material contained within the damper body for resisting movement of the moveable portion. Rheology changes can be generated in the magnetorheological material owing to changes in a magnetic field, to which the magnetorheological material is exposed. The damper further includes at least a sensor embedded in the damper for monitoring an external force exerted on the damper, and for generating a signal to control the magnetic field and hence the resulting yield force and rheological damping of the damper in response to a variance in the external force.

Description:
BACKGROUND  
       [0001]     1. Field of the Invention  
         [0002]     The present application relates to structural vibration control mechanism, and particularly to magnetorheological (MR) dampers useful in such controls.  
         [0003]     2. Background of the Invention  
         [0004]     Magnetorheological (MR) dampers have been used in vibration control of civil and mechanical structures. Application examples include vibration damping of the suspension cables in cable-stayed bridges, vibration damping of automotive seats and suspension systems, and vibration isolation of automation and/or precision equipment/machines, to name a few. The MR materials used in the MR dampers have the ability to reversibly change their rheological characteristics upon applying a magnetic field. In more details, they can change themselves from a free-flowing, linear viscous fluid to a semi-solid with adjustable/controllable yield stress in milliseconds when exposed to an applied magnetic field. By inputting different electrical currents to the electromagnet of such an MR damper, it can adjust/control the magnetic field applied to the MR material so that the yield stress of the material and hence the yield force and rheological damping of the damper can readily be adjusted/controlled in milliseconds. While possessing adjustable/controllable yield force and rheological damping capabilities, the existing MR dampers are incapable of sensing structural vibrations for implementing real-time, close-loop vibration controls; they are only limited to an open-loop mode of operation instead, and their adjustable/controllable capability cannot be fully utilized.  
         [0005]     Technological advancement of structural vibration controls from an open-loop to a close-loop operation of MR dampers requires the development of an accurate inverse dynamic model for the dampers so as to determine appropriate current inputs for facilitating the desired yield force and rheological damping. Nevertheless, it is still a challenge to develop such an inverse dynamic model for these highly nonlinear dampers. Alternatively, a force feedback control loop is often deployed to overcome the deficiency of implementing inverse dynamic modeling via an installation of force sensors between the vibrating structures and the dampers at the expense of reducing the control effectiveness and increasing both the implementation difficulty and engineering cost.  
       OBJECT OF THE INVENTION  
       [0006]     Therefore, it is an object of the present invention to provide an improved magnetorheological damper, wherein real-time adjustment/control of its yield force and rheological damping can be achieved, or at least provide the public with a useful choice.  
         [0007]     It is a further object of the present invention to provide an improved structural vibration control system, which can be sensitive to, variances in structural vibrations, or at least provide the public with a useful choice.  
       SUMMARY OF THE INVENTION  
       [0008]     According to an aspect of the present invention, an magnetorheological damper useful in structural vibration control has a damper body and a moveable portion relative to the damper body. The damper includes an magnetorheological material contained within the damper body for resisting movement of the moveable portion. Rheology changes can be generated in the magnetorheological material owing to changes in a magnetic field, to which the magnetorheological material is exposed. The damper further includes at least a sensor embedded in the damper for monitoring an external force exerted on the damper, and for generating a signal to control the magnetic field and hence the resulting yield force and rheological damping of the damper in response to a variance in the external force.  
         [0009]     According to a second aspect of the present invention, a structural vibration control system includes: 
        at least an magnetorheological damper, having a damper body and a moveable portion relative to the damper body, including 
            an magnetorheological material contained within the damper body for resisting movement of the moveable portion, wherein rheology changes can be generated in the magnetorheological material owing to changes in a magnetic field, to which the magnetorheological material is exposed; and     at least a sensor embedded in the damper for monitoring an external force exerted on the damper, and for generating a signal to control the magnetic field and hence the resulting yield force and rheological damping of the damper in response to a variance in the external force; and    
            means for receiving the signal from the sensor and for varying the magnetic field in accordance with the signal.        
 
         [0014]     Preferably, the sensor is a piezoelectric sensor.  
         [0015]     Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which description illustrates by way of example the principles of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is a plan view of a traditional linear magnetorheological damper;  
         [0017]      FIG. 2  is a plan view of an exemplary magnetorheological damper according to an embodiment of the present intention;  
         [0018]      FIG. 3  is an exploded isometric view of sensor components of a first sensor useful in the damper of  FIG. 2 :  
         [0019]      FIG. 4  is an exploded isometric view of sensor components of a second sensor useful in the damper of  FIG. 2 ;  
         [0020]      FIG. 5  is an exploded isometric view of sensor components of a third sensor useful in the damper of  FIG. 2 ;  
         [0021]      FIG. 6  is an exploded isometric view of sensor components a fourth sensor useful in the damper of  FIG. 2 ;  
         [0022]      FIG. 7  is an isometric view of piezoelectric wafers of the sensor of  FIGS. 3-6 , made of different piezoelectric materials;  
         [0023]      FIG. 8  is an isometric view of piezoelectric wafers of the sensor of  FIGS. 3-6 , with different electrical patterns; and  
         [0024]      FIG. 9  illustrates two test results of the sensor. 
     
    
     DETAILED DESCRIPTION  
       [0025]      FIG. 1  illustrates a conventional magnetorheological (MR) damper  100  known in the art. The conventional MR damper  100  generally includes a pair of electrical wires  11 , a bearing and seal unit  12 , a cylinder housing MR material or fluid  13 , an electromagnet  14 , a diaphragm  15 , an accumulator  16 , a piston  17 , an upper connection support  18 , and a lower connection support  19 . The bearing and seal unit  12  guides the movement of the piston  17  and prevents the leakage of the MR material  13 . By applying different current inputs to the electromagnet  14  through a pair of electrical wires  11 , the MR material  13  may be reversibly changed from a free-flowing, linear viscous fluid to a semi-solid with adjustable/controllable yield stress such that the yield force and rheological damping of the damper can be changed accordingly.  
         [0026]     Such or similar conventional dampers are generally known in the field. See, for example, U.S. Pat. No. 6,394,239, entitled “Controllable medium device and apparatus utilizing same” and filed by David J. Carlson on Oct. 29, 1997; U.S. Pat. No. 6,378,631 entitled “Apparatus for recovering core samples at in situ conditions” and filed by Aumann et al. on Jun. 30, 2000; U.S. Pat. No. 6,158,470 entitled “Two-way magnetorheological fluid valve assembly and devices utilizing same” and filed by Ivers et al. on Feb. 11, 2000; U.S. Pat. No. 6,131,709 entitled “Adjustable valve and vibration damper utilizing same” and filed by Jolly et al. on Nov. 25, 1997; U.S. Pat. No. 6,095,486 entitled “Two-way magnetorheological fluid valve assembly and devices utilizing same” and filed by Ivers et al. on Mar. 5, 1997; U.S. Pat. No. 5,878,851 entitled “Controllable vibration apparatus” and filed by Carlson et al. on Jul. 2, 1999; U.S. Pat. No. 5,398,917 entitled “Magnetorheological fluid devices” and filed by Carlson et al. Feb. 7, 1994: U.S. Pat. No. 5,284,330 entitled “Magnetorheological fluid devices” and filed by Carlson et al. on Jun. 18, 1992; U.S. Pat. No. 5,277,281 entitled “Magnetorheological fluid dampers” and filed by Carlson et al. on Jun. 18, 1992. All these references are herein incorporated by reference.  
         [0027]      FIG. 2  illustrates an exemplary MR damper embodiment  200  of the present invention. Similar to the conventional MR damper  100  of  FIG. 1 , the MR damper  200  also includes a pair of electrical wires  11 , a bearing and seal unit  12 , a cylinder housing MR material or fluid  13 , an electromagnet  14 , a diaphragm  15 , an accumulator  16 , and a piston  17 . The MR damper  200  further includes a first piezoelectric sensor  28  and a second piezoelectric sensor  29  for measuring the external forces exerted on the damper due to structural vibrations. The piezoelectric sensors  28  and  29  are, respectively, attached to the lower part  38  of the upper connection support  18  and the lower part  39  of the lower connection support  19  in this invention by substituting part of the upper connection support  18  and lower connection support  19  of the conventional damper  100  shown in  FIG. 1 . These locations may essentially assure the MR damper  200  that its embedded piezoelectric sensors  28  and  29  are: 1) capable of producing strong output signals in proportional to the external forces (i.e., good mechanical coupling and linearity); 2) sensitive to the variances in the external forces; and 3) ease of installation. The piezoelectric sensors  28  and  29  sense the variances in the external forces exerted on the damper due to structural vibrations and generate electrical signals in accordance with the variances in the external forces imposed onto their electroded surfaces (i.e., the pressures; to be is described in  FIG. 8 ), which signals can be used to assist adjusting/controlling the current inputs to the electromagnet  14  so as to adjust/control the magnetic field applied to the damper and hence the resulting yield force and rheological damping of the damper. Since the piezoelectric sensors  28  and  29  are capable of monitoring real-time variances in the external forces (or pressures), real-time adjustment/control of the yield force and rheological damping of the damper can also be achieved.  
         [0028]     As understood in the art, the piezoelectric sensors  28  and  29  can be all the same except that their sizes may be different. As also understood in the art, MR dampers with a single sensor can be developed by solely using either piezoelectric sensor  28  or piezoelectric sensor  29  of  FIG. 2 . However, the duel-sensor design shown in  FIG. 2  provides a more accurate and reliable measurement of structural vibrations as compared with the single-sensor designs.  
         [0029]     In  FIG. 3 , sensor components of a first exemplary sensor are shown and include two wafer electrodes  31  and  32  mounted on either side of a piezoelectric wafer  30 . For simplicity of description, wafer electrode  31  is set as the positive, while electrode  32  is set as the negative. Insulating wafer  33  is mounted between the electrode  31  and the neighboring surface  40  of the lower part of a connection support that, referring to  FIG. 2 , corresponds to the lower part  38  of the upper connection support  18  or the lower part  39  of the lower connection support  19 . These sensor components are sandwiched centrally in a stack  35  under the mechanical pressure by using a threaded shaft  41  protruding from a new connection support  42  to a shaft hole  43  opened in the lower part ( 38  or  39 ) of a connection support ( 38  or  39 ). The preloading pressure is large enough so that the piezoelectric wafer  30  remains in compression during operation. The threaded shaft  41  should be insulated from the wafer electrodes  31  and  32  and piezoelectric wafer  30 . Electrical wires (not shown) are connected in use to the wafer electrodes  31  and  32  to deliver electrical charges (and hence voltages) generated from the piezoelectric wafer  30 , through a signal conditioning unit  24 , and a data acquisition unit  25 . The results can be recorded and processed using a personal computer  26  and displayed on a monitor  27 . This enables the external forces (or pressures) to be monitored in the operation of the damper. In addition, as understood in the art, real-time adjustment/control of the yield force and rheological damping can also be achieved by using said results to adjust/control the current inputs to the electromagnet  14 .  
         [0030]     In  FIG. 4 , a stack  36  including another two piezoelectric wafers  30  and two wafer electrodes  31  and  32  are added to the sensor shown in  FIG. 3 . The piezoelectric wafers and the wafer electrodes are placed in alternating order. By connecting all the positive wafer electrodes together as one node, and all the negative ones as another, the charges generated from the two nodes representing the effect of all the three piezoelectric wafers can be obtained to monitor the external forces exerted on the damper. In such a way, the sensitivity of the sensor can be enhanced. Similarly, by adding more stacks  36 , five, seven, and more piezoelectric wafers can be deployed to enhance the sensor sensitivity.  
         [0031]     In  FIG. 5 , two piezoelectric wafers  30  are deployed with three wafer electrodes (two  32  and one  31 ) in an alternating order to form the stack  37 . The charges generated from the positive wafer electrode  31  and the two negative wafer electrodes  32  can be obtained for monitoring the external forces exerted on the damper. In this case of deploying two piezoelectric wafers, the insulating wafer  33  as in the stack  35  (of  FIGS. 3 and 4 ) may not be necessary in that one of the piezoelectric wafers also functions as an insulating wafer.  
         [0032]     In  FIG. 6 , by adding a stack  36  (the same as in  FIG. 4 ) to the stack  37 , four piezoelectric wafers can be deployed. Similarly, by adding more stacks  36 , six, eight, and more piezoelectric wafers can be deployed in monitoring the external forces with improved sensor sensitivity.  
         [0033]     The piezoelectric wafer  30  can be any suitable piezoelectric material including piezoelectric ceramics, polymers, and composites due to their effectiveness over a large frequency range, simplicity, reliability, compactness, and light weight. In  FIG. 7 , a piezoelectric ceramic element and four piezoelectric ceramic/polymer composite elements with different configurations: namely, the 0-3, 1-3, radial 2-2, and parallel 2-2 configurations, are presented in this invention. Usually piezoelectric ceramic sensors have sharp resonances and high sensitivity within a narrow bandwidth. Signals with frequencies within their resonances will be greatly amplified and artifacts may be created. As ceramics are hard and brittle, it is difficult to produce ceramic sensors with large element size and complex shape and damage caused by mechanical shock or vibration is more serious. Piezoelectric polymer sensors, however, have wider bandwidth, and all signals will be received with more or less equal sensitivity over a wide range of frequency. They can be fabricated into complex shapes and are more resilient to mechanical stress as they are more flexible. Their major drawbacks are lower sensitivity and less temperature stability. Piezoelectric composite sensors, on the other hand, can be tailored to combine the desired properties of ceramics and polymers and may be most suitable for this sensor.  
         [0034]     In  FIG. 8 , different electrode patterns for the wafer  30  are presented by the forms of an “active” area  51  and an “inactive” area  50 . According to the relative position of the “active” and “inactive” areas, whole-face ( FIG. 8   a ), inner ( FIG. 8   b ), in-between ( FIG. 8   c ), and outer ( FIG. 8   d ) electrode patterns are clarified. Such electrode patterns can be used for the wafer  30  of any kind of material among ceramics, polymers, and composites as mentioned before.  
         [0035]     In  FIG. 9 , two test results show that the quasi-sinusoidal ( FIG. 9   a ) and square ( FIG. 9   b ) forces exerted on the damper including both the amplitude and phase can be finely monitored by measuring the charges generated from the piezoelectric sensor(s) ( 28  and/or  29 ) and displayed on the monitor  27  of  FIG. 3  as voltages.  
         [0036]     Whereas all the described wafers are cylindrical, embodiments of the invention can be provided with other shaped wafers including irregular and rectangular cross-sectioned uniform or composite wafers.