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TECHNICAL FIELD  
       [0001]     The present disclosure is directed to a control system and method for a vibratory mechanism. More particularly, the disclosure relates to a system and method for controlling amplitude and frequency of a vibratory mechanism.  
       BACKGROUND  
       [0002]     Vibratory work machines such as compactors are often employed to compact soil, gravel, asphalt, and other materials. These vibratory work machines include plate-type compactors and rotating drum compactors. A typical drum compactor has a drum assembly with one or more drums for compacting the material. The drum assembly includes a vibratory mechanism having two or more weights arranged on a shaft rotatable about a common axis within an interior cavity of the drum for inducing vibrations on the drum. The weights are eccentrically positioned with respect to the common axis and are typically movable with respect to each other about the common axis to produce varying degrees of imbalance during rotation of the weights.  
         [0003]     The vibratory mechanism provides one or more frequency and amplitude settings. In operation, the vibration amplitude and frequency of a compactor may be changed by a user to suit a particular application. The suitable amplitude and frequency of the vibration may vary depending on the characteristics of the material to be compacted. For example, the vibration amplitude and frequency suitable for compacting gravel for a road may be different from the vibration amplitude and frequency suitable for compacting soil for a footpath. Also, a compacting process may often require compaction with different amplitude and frequency levels at the beginning and end of the process. Furthermore, when a material such as asphalt cools down, its hardness often changes. As a result, compaction with different amplitude and frequency levels may be required based on the temperature of the material.  
         [0004]     Vibration amplitude and frequency determine the quality of the compaction, as well as the efficiency of the compaction process. Typically, the amplitude of the vibrations produced by the eccentric weights in the drum assembly may be varied by positioning the weights with respect to each other about their common rotational axis to vary the average distribution of mass (i.e., the centroid) with respect to the rotational axis. In general, vibration amplitude increases as the centroid moves away from the rotational axis of the weights and decreases toward zero as the centroid moves toward the rotational axis. It is also known that varying the rotational speed of the weights about their common axis may change the frequency of the vibrations.  
         [0005]     A known vibratory mechanism allows a user to select a desired vibration frequency from one or more possible frequencies independent of the selection of a desired vibration amplitude. In some cases, the vibratory mechanism may enable the user to adjust only vibration amplitude while a vibration frequency remains fixed or uncontrolled, or may enable the user to adjust only vibration frequency while vibration amplitude remains fixed or uncontrolled. For example, U.S. Pat. No. 4,481,835 discloses a device that can continuously adjust a vibration amplitude. However, these known vibratory mechanisms do not establish any relationship or dependency between vibration frequency and vibration amplitude. As a result, a user may be permitted to inadvertently select a vibration frequency and amplitude combination that results in unintended decoupling. Decoupling occurs when a compactor vibrates with a vibratory amplitude that is high enough that the compacting drum becomes airborne.  
         [0006]     Thus, the present control system is directed to solving one or more of the shortcomings associated with prior art designs and providing a system and method for controlling a vibratory mechanism with more stability and less interference with the machine performance.  
       SUMMARY OF THE INVENTION  
       [0007]     In one aspect, a method is provided for controlling a vibratory mechanism. The method includes sensing a vibratory amplitude of the vibratory mechanism and determining a decoupling point of the vibratory mechanism. An output signal is generated based on the determination of the decoupling point for controlling the vibratory amplitude of the vibratory mechanism.  
         [0008]     In another aspect, a control system is provided for controlling a vibratory mechanism. The control system includes a sensor configured to sense a vibratory amplitude and a controller coupled to the sensor. The controller is configured to determine a decoupling point of the vibratory mechanism based on the sensed amplitude and to generate an output signal based on the determination of the decoupling point to control the vibratory amplitude of the vibratory mechanism. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description, serve to explain the principles of the invention.  
         [0010]      FIG. 1  is a diagrammatic representation of a vibratory work machine with a control system according to one exemplary embodiment;  
         [0011]      FIG. 2  is a cross-sectional view of a compacting drum of the vibratory work machine of  FIG. 1 ; and  
         [0012]      FIG. 3  is a block diagram describing the logic of the control system shown in  FIG. 1 . 
     
    
     DETAILED DESCRIPTION  
       [0013]     Reference will now be made in detail to exemplary embodiments that are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.  
         [0014]     As shown in  FIG. 1 , a vibratory work machine may be a double-drum compactor  10  used for compacting a material  12  such as soil, gravel, or asphalt to increase the density of the material. While the control system and method for a vibratory mechanism in a double-drum compactor is described, the control system and method is not limited to this application.  
         [0015]     The compactor  10  has a first compacting drum  14  and a second compacting drum  16  rotatably mounted on a main frame  18 . The compactor  10  also has an engine  20  that may be used to generate mechanical and/or electrical power for propelling the compactor  10 . The first compacting drum  14  includes a first vibratory mechanism  22  that is operatively connected to a first motor  24 . The second compacting drum  16  includes a second vibratory mechanism  26  that is operatively connected to a second motor  28 . It should be understood from this disclosure that the vibratory work machine may have more or less than two compacting drums and vibratory mechanisms.  
         [0016]     The first and second motors  24 ,  28  propel the first and second compacting drums  14 ,  16 , respectively, and the motors may be operatively coupled to a power source  30 , which may be connected to the engine  20 . The power source  30  may be an electric generator, a fluid pump or any other suitable device for propelling the compactor  10  and providing power to the first and second vibratory mechanisms  22 ,  26  and other systems of the compactor  10 . Where the power source  30  provides electrical power, the first and second motors  24 ,  28  may be electric motors. Alternatively, where the power source  30  provides mechanical or hydraulic power, the motors  24 ,  28  may be fluid motors. The motors  24 ,  28  may be operatively coupled to the power source  30  with electrical wires, fluid conduits, or any other suitable connection.  
         [0017]     Also, the compactor  10  includes a controller  40  that determines a decoupling point of the vibratory mechanisms  22 ,  26 . At the decoupling point, compacting drums  14 ,  16  lose their surface contact to the material  12 , and the vibratory mechanisms or compacting drums become airborne. The controller  34  may also be operatively coupled to an operator or user input  42  that enables the operator of the compactor  10  to set, for example, a desired vibratory control characteristic. The vibratory control characteristic may include a vibratory amplitude limit, which will be explained in detail later. The operator input  42  may be a vibratory control knob, lever, switch or any other suitable device that the operator uses to set the vibratory amplitude characteristic. In one exemplary embodiment, the operator input  42  may be a multi-position switch, and each of the switch positions may correspond to one of amplitude limit settings, such as 50%, 100%, and 150% of the decoupling amplitude. The decoupling amplitude is an amplitude at which the compactor  10  decouples.  
         [0018]      FIG. 2  illustrates a cross-sectional view of the first compacting drum  14 . The first vibratory mechanism  22  may be approximately centrally mounted within the first compacting drum  14 . However, the precise location of the vibratory mechanism  22  may be varied to suit a particular application. While the vibratory mechanism will be described with respect to the first vibratory mechanism  22 , the vibratory mechanism shown in  FIG. 2  may be used for one or both of the first and second vibratory mechanisms  22 ,  26  shown in  FIG. 1 .  
         [0019]     In the exemplary embodiment shown in  FIG. 2 , the vibratory mechanism  22  includes a housing  44  that is rigidly fixed to the compacting drum  14 , an inner eccentric weight  32  that is connected to an inner shaft  34 , and an outer eccentric weight  36  that is connected to an outer shaft  38 . An inner flexible coupling  46  and an outer flexible coupling  48  may be provided for rotating the inner shaft  34  and the outer shaft  38 , respectively.  
         [0020]     In general, the vibratory mechanism  22  produces independent continuous or infinite variation of both the amplitude and the frequency. For example, the vibratory mechanism  22  changes the relative positions or relative phase of the inner and outer eccentric weights  32 ,  36  to vary the magnitude of the imbalance and the vibratory amplitude produced by rotation of the inner and outer eccentric weights  32 ,  36  about their axes. Additionally, the frequency of the vibrations produced by the vibratory mechanism  22  may be varied by changing the rotational speed of the inner and outer weights  32 ,  36 . Thus, the frequency of the vibrations produced by the weights  32 ,  36  increases as the rotational speed of the weights  32 ,  36  increases.  
         [0021]     The first motor  24  may be connected to the inner and outer couplings  46 ,  48  via a gearbox  50 . A phase control device  52  may be coupled to the gearbox  50  to change the relative positions of the inner and outer shafts  34 ,  38  and, thus, the relative positions or phase of the inner and outer eccentric weights  32 ,  36  to be continuously or infinitely varied.  
         [0022]     As shown in  FIG. 2 , the compactor  10  also includes a vibratory amplitude sensor  54 . In one example, the vibratory amplitude sensor  54  may be an accelerometer that can sense the amplitude of the vibrations produced by the compactor  10 , and it may be fixed to a portion of the compacting drum  14 . The accelerometer may also sense the frequency of the vibrations. In addition, the compactor  10  may include a phase sensor  56  connected to the gearbox  50  to measure the relative positions or relative phase of the inner and outer weights  32 ,  36  and the inner and outer shafts  34 ,  38 . The compactor  10  may also have a speed sensor  58  to measure the rotational speed of the inner and outer weights  32 ,  36  and the inner and outer shafts  34 ,  38 .  
         [0023]     The compactor  10  has the controller  40  electrically connected to the operator input  42 , the phase control device  52 , and the vibratory amplitude sensor  54 . The controller  40  may also be electrically connected to the other sensors. The controller  40  includes a processor for determining the coupling point and generate an output signal to control the amplitude.  
         [0024]      FIG. 3  illustrates a schematic block diagram describing an exemplary logic that may be used with the controller  40  to control the vibration amplitude of the compactor  10  shown in  FIG. 1 . In one exemplary embodiment, the controller  40  determines a decoupling point of the vibratory mechanism  22  based on the vibratory amplitude sensed by the vibratory amplitude sensor  54  and a predetermined reference vibratory amplitude. The reference vibratory amplitude may be empirically determined, for example, through test runs of the compactor  10  with the drums suspended off the ground, and may be prestored in the controller  40 . This predetermined reference vibratory amplitude corresponds to the decoupling point of the vibratory mechanism  22 . The reference vibratory amplitude may be in a graphic form, such as a sinusoidal wave.  
         [0025]     By comparing the sensed amplitude with the reference amplitude, the controller  40  determines a decoupling point of the vibratory mechanism  22 . For example, when the decoupling occurs, the sinusoidal amplitude signal from the sensor  54  may have large amplitude differences between its polarities. Based on the amplitude differences, the controller  40  generates an amplitude control output signal to the vibratory mechanism. In response, the vibratory mechanism vibrates at an amplitude corresponding to the output signal. In one embodiment, the controller  40  may also generate another signal to vary the vibratory frequency of the vibratory mechanism  22  based on the value of the amplitude control output signal.  
       INDUSTRIAL APPLICABILITY  
       [0026]     Referring to  FIGS. 1-3 , the vibratory amplitude sensor  54 , such as an accelerometer, senses a vibratory amplitude of the compactor  10 . A signal representing the sensed vibratory amplitude is sent to the controller  40 .  
         [0027]     Upon receipt of the sensed vibratory amplitude signal, the controller  40  compares the sensed amplitude with a reference amplitude stored in the controller  40 . In one example, the reference amplitude may be in a sinusoidal wave form that represents the amplitude at which the vibratory mechanism  22  decouples, i.e., the amplitude at which the compactor  10  becomes airborne. By comparing the sensed amplitude and the reference amplitude, the controller  40  determines whether the sensed amplitude is below or above the reference or decoupling amplitude. In one embodiment, the controller  40  determines whether the sensed amplitude is below or above the reference or decoupling amplitude via analysis of the dynamic signal from the sensor  54 . When the controller  40  determines that the sensed amplitude is below the reference amplitude, it will send an output signal to increase the amplitude to the vibratory mechanism  22 . On the other hand, when the controller  40  determines that the sensed amplitude is above the reference amplitude, it will send an output signal to decrease the amplitude to the vibratory mechanism  22 . Based on the output signal from the controller  40 , the vibratory mechanism  22  adjusts the phase or positions of the eccentric weights  32 ,  36  to alter the amplitude of the vibratory mechanism  22 . The controller  40  may repeat these steps in a closed loop manner so that the amplitude of the vibratory mechanism is kept close to the decoupling amplitude.  
         [0028]     In one exemplary embodiment, the operator may set an amplitude characteristic, such as an amplitude limit, via the operator input  42 . When the operator desired to obtain the optimum compaction result without decoupling, then the amplitude limit should be set to 100% of the decoupling amplitude. If the amplitude limit is set, for example, at 50% of the decoupling amplitude, then the output signal is multiplied by 0.5, and the vibratory mechanism  22  provides the amplitude well below the decoupling amplitude, i.e., 50% of the decoupling amplitude. The operator may choose this low setting when a slow compacting process is desired. On the other hand, if the amplitude limit is set, for example, at 150% of the decoupling amplitude, then the output signal is multiplied by 1.5, and the vibratory mechanism  22  provides the amplitude well above the decoupling amplitude, i.e., 150% of the decoupling amplitude. The operator may choose this high setting to intentionally cause decoupling of the vibratory mechanism  22 , for example, when compacting the material at the beginning of the compaction process. Thus, an operator is able to most effectively utilize a compactor for a given application. While these steps are described with respect to the first vibratory mechanism  22 , the controller  40  may control the amplitude of the second vibratory mechanism  26  independently in a similar manner.  
         [0029]     It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed system and method without departing from the scope of the invention. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the invention being indicated by the following claims.

Summary:
A method is provided for controlling a vibratory mechanism. The method includes sensing a vibratory amplitude of the vibratory mechanism and determining a decoupling point of the vibratory mechanism. An output signal is generated based on the determination of the decoupling point for controlling the vibratory amplitude of the vibratory mechanism.