Patent Publication Number: US-10316929-B2

Title: Control strategy for reducing boom oscillation

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a National Stage of PCT/US2014/064651, filed on Nov. 7, 2014, which claims benefit of U.S. Patent Application Ser. No. 61/904,340 filed on Nov. 14, 2013 and which applications are incorporated herein by reference. To the extent appropriate, a claim of priority is made to each of the above disclosed applications. 
    
    
     BACKGROUND 
     Various off-road and on-road vehicles include booms. For example, certain concrete pump trucks include a boom configured to support a passage through which concrete is pumped from a base of the concrete pump truck to a location at a construction site where the concrete is needed. Such booms may be long and slender to facilitate pumping the concrete a substantial distance away from the concrete pump truck. In addition, such booms may be relatively heavy. The combination of the substantial length and mass properties of the boom may lead to the boom exhibiting undesirable dynamic behavior. In certain booms in certain configurations, a natural frequency of the boom may be about 0.3 Hertz (i.e., 3.3 seconds per cycle). In certain booms in certain configurations, the natural frequency of the boom may be less than about 1 Hertz (i.e., 1 second per cycle). In certain booms in certain configurations, the natural frequency of the boom may range from about 0.1 Hertz to about 1 Hertz (i.e., 10 seconds per cycle to 1 second per cycle). For example, as the boom is moved from place to place, the starting and stopping loads that actuate the boom may induce vibration (i.e., oscillation). Other load sources that may excite the boom include momentum of the concrete as it is pumped along the boom, starting and stopping the pumping of concrete along the boom, wind loads that may develop against the boom, and/or other miscellaneous loads. 
     Other vehicles with booms include fire trucks in which a ladder may be included on the boom, fire trucks which include a boom with plumbing to deliver water to a desired location, excavators which use a boom to move a shovel, tele-handlers which use a boom to deliver materials around a construction site, cranes which may use a boom to move material from place-to-place, etc. 
     In certain boom applications, including those mentioned above, a hydraulic cylinder may be used to actuate the boom. By actuating the hydraulic cylinder, the boom may be deployed and retracted, as desired, to achieve a desired placement of the boom. In certain applications, counter-balance valves may be used to control actuation of the hydraulic cylinder and/or to prevent the hydraulic cylinder from uncommanded movement (e.g., caused by a component failure). 
     Conventional solutions for reducing the above mentioned oscillations are typically passive (i.e., orifices) which are tuned for one particular operating point and often have a negative impact on efficiency. Many machines/vehicles with extended booms employ counter-balance valves (CBVs) for safely and safety regulation reasons. These counter-balance valves (CBVs) restrict/block the ability of the hydraulic control valve to sense and act upon pressure oscillations. In certain applications, such as concrete pump truck booms, oscillations are induced by external sources (e.g., the pumping of the concrete) when the machine (e.g., the boom) is nominally stationary. In this case, the counter-balance valves (CBVs) are closed, and the main control valve is isolated from the oscillating pressure that is induced by the oscillations. There are a number of conventional solutions that approach this problem, that typically rely on joint position sensors to sense the oscillations (i.e., ripples) and prevent drift due to flow through a ripple-cancelling valve. Some solutions also have parallel hydraulic systems that allow a ripple-cancelling valve to operate while the counter-balance valves (CBVs) are in place. 
     SUMMARY 
     One aspect of the present disclosure relates to systems and methods for reducing boom dynamics (e.g., boom bounce) of a boom while providing counter-balance valve protection to the boom. 
     Another aspect of the present disclosure relates to a method of controlling vibration in a boom. The method may include: providing a hydraulic actuator with a first and a second chamber; selecting either the first or the second chamber as a locked chamber; selecting the opposite chamber as an active chamber; locking the locked chamber; and transferring a vibration canceling fluid flow to the active chamber. In certain embodiments, the method may further include detecting which of the first and the second chambers is a load holding chamber. The load holding chamber may be selected as the locked chamber and prevent drifting of the hydraulic actuator. A first pressure of the first chamber may, at least intermittently, be measured, and a second pressure of the second chamber may, at least intermittently, be measured. The load holding chamber may be detected by comparing the first and the second pressures. Hydraulic fluid may be prevented from exiting the locked chamber by a first counter-balance valve in a closed configuration. The vibration canceling fluid flow may be transferred to the active chamber via a second counter-balance valve in an open configuration. 
     In certain embodiments, the method may further include providing a first control valve that is adapted to pressurize and drain the first chamber and providing a second control valve that is adapted to pressurize and drain the second chamber. Pressurizing a pilot of the second counter-balance valve may be done with the first control valve and thereby configure the second counter-balance valve in the open configuration. Generating the vibration canceling fluid flow may be done with the second control valve. 
     In certain embodiments, the method may further include measuring pressure ripples at the load holding chamber and reducing a magnitude of the pressure ripples by the transferring of the vibration canceling fluid flow to the active chamber. In certain embodiments the method may further include measuring first pressure ripples at the active chamber and reducing a magnitude of second pressure ripples at the load holding chamber by the transferring of the vibration canceling fluid flow to the active chamber. The measuring of the first pressure ripples at the active chamber and the transferring of the vibration canceling fluid flow to the active chamber may be separated in time. 
     In certain embodiments the method may further include transforming a shape of the first pressure ripples into a flow command that forms the vibration canceling fluid flow by multiplying the shape of the first pressure ripples by a gain and/or phase shifting the shape of the first pressure ripples. The gain may be a fixed gain and/or the phase shifting may be constant phase shifting. The gain may be a variable gain and/or the phase shifting may be variable phase shifting. At least one of the variable gain and the variable phase shifting may be adjusted by feedback. The feedback may include the second pressure ripples at the load holding chamber. The feedback may include a position of the hydraulic actuator. The feedback may include an operator input. 
     In certain embodiments the method may further include generating a reference signal starting prior to transferring the vibration canceling fluid flow to the active chamber, deriving a variable from a characteristic measured from the hydraulic actuator, summing the reference signal and the variable and thereby deriving a control variable, and/or forming a flow characteristic of the vibration canceling fluid flow with the control variable. The reference signal may be filtered with a moving average filter. The reference signal may be generated from a first pressure measured at the first chamber and from a second pressure measured at the second chamber. The first chamber of the hydraulic actuator may be a head chamber, and the second chamber of the hydraulic actuator may be a rod chamber. The first chamber of the hydraulic actuator may be the rod chamber, and the second chamber of the hydraulic actuator may be the head chamber. The first and second chambers may switch between the head and rod chambers as the external load switches direction. 
     A variety of additional aspects will be set forth in the description that follows These aspects can relate to individual features and to combinations of features. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the broad concepts upon which the embodiments disclosed herein are based. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a hydraulic system including a hydraulic cylinder with a pair of counter-balance valves and configured with a hydraulic cylinder control system with a pair of control valves according to the principles of the present is disclosure; 
         FIG. 2  is the schematic illustration of  FIG. 1 , but with a valve blocking fluid flow to a pilot of one of the counter-balance valves of  FIG. 1 ; 
         FIG. 3  is a schematic illustration of a hydraulic cylinder suitable for use with the hydraulic cylinder control system of  FIG. 1  according to the principles of the present disclosure; 
         FIG. 4  is a schematic illustration of a vehicle with a boom system that is actuated by one or more cylinders and controlled with the hydraulic system of  FIG. 1  according to the principles of the present disclosure; 
         FIG. 5  is a schematic illustration of a control system suitable for use with the hydraulic cylinder control system of  FIG. 1  according to the principles of the present disclosure; 
         FIG. 6  is a graph illustrating a simulation of the hydraulic cylinder control system of  FIG. 1 ; 
         FIG. 7  is a schematic illustration of another control system suitable for use with the hydraulic cylinder control system of  FIG. 1  according to the principles of the present disclosure; 
         FIG. 8  is a flow chart of an example method of implementing a control strategy for reducing boom oscillation according to the principles of the present disclosure; and 
         FIG. 9  is a rotary actuator writable for use with the hydraulic system of  FIG. 1  according to the principles of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     According to the principles of the present disclosure, a hydraulic system is adapted to actuate a hydraulic cylinder  110 , including counter-balance valves  300  and  400 , and further provides means for counteracting vibrations to which the hydraulic cylinder  110  is exposed. As illustrated at  FIG. 1 , an example system  600  is illustrated with the hydraulic cylinder  110  (i.e., a hydraulic actuator), the counter-balance valve  300 , and the counter-balance valve  400 . The hydraulic cylinder  110  and the counter-balance valves  300 ,  400  of  FIG. 1  may be the same as those in certain prior art systems. The hydraulic system  600  may therefore be retrofitted to an existing and/or a conventional hydraulic is system. The depicted embodiment illustrated at  FIG. 1  can represent a prior art hydraulic system retrofitted by replacing a conventional hydraulic control valve with a valve assembly  690 , described in detail below, and by adding valves  350  and/or  450 . Certain features of the hydraulic cylinder  110  and the counter-balance valves  300 ,  400  may be the same or similar between the hydraulic system  600  and certain prior art hydraulic systems. 
     It will be understood that certain concepts and principles disclosed herein apply to both linear and rotary actuators. The hydraulic cylinder  110 , illustrated in the Figures, is an example actuator. The hydraulic cylinder  110  is an example hydraulic cylinder and an example linear actuator. In certain applications, the hydraulic cylinder  110  may be replaced with a rotary actuator  1108  (see  FIG. 9 ). The rotary actuator  1108  may operate over a range of less than 360 degrees, a range of 360 degrees, a range of more than 360 degrees, or may have an unlimited range in one or both rotational directions. 
     According to the principles of the present disclosure a control strategy for the hydraulic system  600  includes a method for using the valve assembly  690 , with two independent directional control valves (DCV)  700 ,  800 , in conjunction with a mechanism for opening one of the counter-balance valves  300  or  400  and locking the other of the counter-balance valves  400  or  300  that is the load-holding counter balance valve. Oscillations in a boom  30  may thereby be reduced while also preventing drift in the hydraulic cylinder  110  or rotary actuator  1108 . 
     In certain embodiments, the control strategy uses only pressure sensors (e.g., pressure sensors  610   1 ,  610   2 ,  620   1 ,  620   2 ). The pressure sensors (e.g., the pressure sensors  610   1 ,  610   2 ) may be included in the valve assembly  690 . A position sensor (e.g., position sensors  620   3 ) may not be required. Thus, the hardware and sensors required may be reduced in comparison with conventional arrangements. 
     The control strategy may include a cross-port pressure feedback control system. In particular, the hydraulic cylinder  110  or rotary actuator  110 R is actuated by the pair of independent metering valves  700 ,  800  which can control the flow in and flow out of the two hydraulic cylinder chambers  116 ,  116 R,  118 ,  118 R, respectively. Before active vibration control is turned on, pressures in both chambers  116 ,  116 R,  118 ,  118 R are recorded and are used to initialize a reference pressure to be tracked. When the active vibration control is turned on, the load holding chamber  116 ,  116 R or  118 ,  118 R is locked, and no flow enters or leaves the load holding chamber  116 ,  116 R or  118 ,  118 R via the control valve  700  or  800 , respectively. In certain embodiments, the pressure sensor  620   1 ,  620   2  installed on the load holding chamber  116 ,  116 R or  118 ,  118 R continuously measures the pressure in the load holding chamber  116 ,  116 R or  118 ,  118 R. 
     After the load holding chamber  116 ,  1168  or  118 ,  118 R is locked, the vibration control motions of the hydraulic cylinder  110  or rotary actuator  110 R are accomplished by manipulating the pressure in the chamber  118 ,  118 R or  116 ,  116 R (i.e., the active chamber) that is opposite the load holding chamber  116 ,  116 R or  118 ,  118 R. Position drifting of the hydraulic cylinder  110  or rotary actuator  110 R is effectively prevented by the locked counter-balance valve  300  or  400  on the load-holding side. 
     The control objective for the non-load-holding chamber  118 ,  118 R or  116 ,  116 R is to stabilize the pressure in the load holding chamber  116 ,  116 R or  118 ,  118 R which is defined as the cross-port pressure feedback control. The cross-port pressure feedback control can be illustrated by a repetitive external load force acting as an external vibration  960  applied on the hydraulic cylinder  110  or rotary actuator  110 R. If both chambers  116 ,  116 R and  118 ,  118 R are locked, the pressures in both chambers  116 ,  116 R and  118 ,  118 R will eventually achieve repetitive patterns, with constant mean values (see  FIG. 6 ). The mean pressure values are updated in real time in a controller  640 . The control objective is to reduce pressure ripples in the load-holding chamber  116 ,  116 R or  118 ,  118 R by controlling the flow inflow out of the non-load-holding chamber  118 ,  118 R or  116 ,  116 R. Upon the load-holding chamber pressure being stabilized, the pressure in the non-load-holding chamber  118 ,  118 R or  116   116 R produces enough hydraulic force to compensate the external repetitive load force, acting as the external vibration  960 , and the cylinder position is stabilized. 
     According to the principles of the present disclosure, the control strategy may be implemented on the hydraulic system  600 . The hydraulic system  600  is illustrated at  FIG. 1 . The counter-balance valve  300  controls and/or transfers hydraulic fluid flow into and out of the first chamber  116  of the hydraulic cylinder  110  of the system  600 . Likewise, the second counter-balance valve  400  controls and/or transfers hydraulic fluid flow into and out of the second chamber  118  of the hydraulic cylinder  110 . In particular, a port  302  of the counter-balance valve  300  is connected to a port  122  of the hydraulic cylinder  110 . Likewise, a port  402  of the counter-balance valve  400  is fluidly connected to a port  124  of the hydraulic cylinder  110 . As depicted, a fluid line  562  schematically connects the port  302  to the port  122 , and a fluid line  564  connects the port  402  to the port  124 . The counter-balance valves  300 ,  400  are typically mounted directly to the hydraulic cylinder  110 . The port  302  may directly connect to the port  122 , and the port  402  may directly connect to the port  124 . 
     The counter-balance valves  300 ,  400  provide safety protection to the system  600 . In particular, before movement of the cylinder  110  can occur, hydraulic pressure must be applied to both of the counter-balance valves  300 ,  400 . The hydraulic pressure applied to one of the counter-balance valves  300 ,  400  is delivered to a corresponding one of the ports  122 ,  124  of the hydraulic cylinder  110  thereby urging a piston  120  of the hydraulic cylinder  110  to move. The hydraulic pressure applied to an opposite one of the counter-balance valves  400 ,  300  allows hydraulic fluid to flow out of the opposite port  124 ,  122  of the hydraulic cylinder  110 . By requiring hydraulic pressure at the counter-balance valve  300 ,  400  corresponding to the port  122 ,  124  that is releasing the hydraulic fluid, a failure of a hydraulic line, a valve, a pump, etc. that supplies or receives the hydraulic fluid from the hydraulic cylinder  110  will not result in uncommanded movement of the hydraulic cylinder  110 . 
     Turning now to  FIG. 1 , the system  600  will be described in detail. As depicted, the valve assembly  690  is used to control the hydraulic cylinder  110 . The hydraulic cylinder  110  may be urged to extend by supplying hydraulic fluid to the chamber  116 , and hydraulic fluid in the chamber  118  of the hydraulic cylinder  110  is urged out of the port  124  of the cylinder  110 . Hydraulic fluid leaving the port  124  returns to a hydraulic tank. The hydraulic cylinder  10  may be effectively stopped by the valve assembly  690  by shutting of hydraulic fluid flow to the chambers  116  and  118 . The hydraulic cylinder  110  may be urged to retract by supplying hydraulic fluid to the chamber  118 , and hydraulic fluid in the chamber  116  of the hydraulic cylinder  110  is urged out of the port  122  of the cylinder  110 . Hydraulic fluid leaving the port  122  returns to the hydraulic tank. In certain embodiments, the supply line  502  supplies hydraulic fluid at a constant or at a near constant supply pressure. In certain embodiments, the return line  504  receives hydraulic fluid at a constant or at a near constant return pressure. An operator and/or a control system may control the valve assembly  690  as desired and thereby achieve extension, retraction, and/or locking of the hydraulic cylinder  110 . 
     A function of the counter-balance valves  300 ,  400  when the hydraulic cylinder  110  is extending will now be discussed in detail. Upon hydraulic fluid pressurizing a port  304  of the counter-balance valve  300  and a port  406  of the counter-balance valve  400 . Hydraulic fluid pressure applied at the port  304  of the counter-balance valve  300  flows past a spool  310  of the counter-balance valve  300  and past a check valve  320  of the counter-balance valve  300  and thereby flows from the port  304  to the port  302  through a passage  322  of the counter-balance valve  300 . The hydraulic fluid pressure further flows through the port  122  and into the chamber  116  (i.e., a meter-in chamber). Pressure applied to the port  406  of the counter-balance valve  400  moves a spool  410  of the counter-balance valve  400  against a spring  412  and thereby compresses the spring  412 . Hydraulic fluid pressure applied at the port  406  thereby opens a passage  424  between the port  402  and the port  404 . By applying hydraulic pressure at the port  406  (i.e., a pilot), hydraulic fluid may exit the chamber  118  (i.e., a meter-out chamber) through the port  124 , through the line  564 , through the passage  424  of the counter-balance valve  400  across the spool  410 , through a hydraulic line  554 , through the valve  800 , and through the return line  504  into the tank. The meter-out side may supply backpressure. 
     A function of the counter-balance valves  300 ,  400  when the hydraulic cylinder  110  is retracting will now be discussed in detail. Upon hydraulic fluid pressuring a port  404  of the counter-balance valve  400  and a port  306  of the counter-balance valve  300 . Hydraulic fluid pressure applied at the port  404  of the counter-balance valve  400  flows past the spool  410  of the counter-balance valve  400  and past a check valve  420  of the counter-balance valve  400  and thereby flows from the port  404  to the port  402  through a passage  422  of the counter-balance valve  400 . The hydraulic fluid pressure further flows through the port  124  and into the chamber  118  (i.e., a meter-in chamber). Hydraulic pressure applied to the port  306  of the counter-balance valve  300  moves the spool  310  of the counter-balance valve  300  against a spring  312 . and thereby compresses the spring  312 . Hydraulic fluid pressure applied at the port  306  thereby opens a passage  324  between the port  302  and the port  304 . By applying hydraulic pressure at the port  306  (i.e., a pilot), hydraulic fluid may exit the chamber  116  (i.e., a meter-out chamber) through the port  122 , through the line  562 , through the passage  324  of the counter-balance valve  300  across the spool  310 , through the hydraulic line  552 , through the valve  700 , and through the return line  504  into the tank. The meter-out side may supply backpressure. 
     The hydraulic cylinder  110  may hold a net load  90  that, in general, may urge retraction or extension of a rod  126  of the cylinder  110 . Alternatively, the rotary hydraulic actuator  11  OR may hold a net load that, in general, may urge a first rotation or a second rotation of a shaft  126 R of the rotary hydraulic actuator  110 R (see  FIG. 9 ). The rod  126  is connected to the piston  120  of the cylinder  110 . If the load  90  urges extension of the hydraulic cylinder  110 , the chamber  118  on a rod side  114  of the hydraulic cylinder  110  is pressurized by the load  90 , and the counter-balance valve  400  acts to prevent the release of hydraulic fluid from the chamber  118  and thereby acts as a safety device to prevent uncommanded extension of the hydraulic cylinder  110 . In other words, the counter-balance valve  400  locks the chamber  118 . In addition to providing safety, the locking of the chamber  118  prevents drifting of the cylinder  110 . Vibration control may be provided via the hydraulic cylinder  110  by dynamically pressurizing and depressurizing the chamber  116  on a head side  112  of the hydraulic cylinder  110 . As the hydraulic cylinder  110 , the structure to which the hydraulic cylinder  110  is attached, and the hydraulic fluid within the chamber  118  are at least slightly deformable, selective application of hydraulic pressure to the chamber  116  will cause movement (e.g., slight movement) of the hydraulic cylinder  110 . Such movement, when timed in conjunction with the control strategy, may be used to counteract vibrations of the system  600 . 
     If the load  90  urges retraction of the hydraulic cylinder  110 , the chamber  116  on the head side  112  of the hydraulic cylinder  110  is pressurized by the load  90 , and the counter-balance valve  300  acts to prevent the release of hydraulic fluid from the chamber  116  and thereby acts as a safety device to prevent uncommanded retraction of the hydraulic cylinder  110 . In other words, the counter-balance valve  300  locks the chamber  116 . In addition to providing safety, the locking of the chamber  116  prevents drifting of the cylinder  110 . Vibration control may be provided via the hydraulic cylinder  110  by dynamically pressurizing and depressurizing the chamber  118  on the rod side  114  of the hydraulic cylinder  110 . As the hydraulic cylinder  110 , the structure to which the hydraulic cylinder  110  is attached, and the hydraulic fluid within the chamber  116  are at least slightly deformable, selective application of hydraulic pressure to the chamber  118  will cause movement (e.g., slight movement) of the hydraulic cylinder  110 . Such movement, when timed in conjunction with the control strategy, may be used to counteract vibrations of the system  600 . 
     The load  90  is depicted as attached via a rod connection  128  to the rod  126  of the cylinder  110 . In certain embodiments, the load  90  is a tensile or a compressive load across the rod connection  128  and the head side  112  of the cylinder  110 . 
     As is further described below, the system  600  provides a control framework and a control mechanism to achieve boom vibration reduction for both off-highway vehicles and on-highway vehicles. The vibration reduction may be adapted to reduced vibrations in booms with relatively low natural frequencies (e.g., the concrete pump truck boom). The hydraulic system  600  may also be applied to booms with relatively high natural frequencies (e.g., an excavator boom). Compared with conventional methods, the hydraulic system  600  may achieve vibration reduction of booms with fewer sensors and a simplified control structure. The vibration reduction method may be implemented while assuring protection from failures of certain hydraulic lines, hydraulic valves, and/or hydraulic pumps, as described above. The protection from failure may be automatic and/or mechanical. In certain embodiments, the protection from failure may not require any electrical signal and/or electrical power to engage. The protection from failure may be and/or meet a regulatory requirement (e.g., an ISO standard). The regulatory requirement may require certain mechanical means of protection that is provided by the hydraulic system  600 . 
     Certain booms may include stiffness and inertial properties that can transmit and/or amplify dynamic behavior of the load  90 . As the dynamic load  90  may include external force/position disturbances that are applied to the boom, severe vibrations (i.e., oscillations) may result, especially when these disturbances are near the natural frequency of the boom. Such excitation of the boom by the load  90  may result in safer issues and/or decrease productivity and/or reliability of the boom system. By measuring parameters of the hydraulic system  600  and responding appropriately, effects of the disturbances may be reduced and/or minimized or even eliminated. The response provided may be effective over a wide variety of operating conditions. According to the principles of the present disclosure, vibration control may be achieved using minimal numbers of sensors. 
     According to the principles of the present disclosure, hydraulic fluid flow to the chamber  116  of the head side  112  of the cylinder  110 , and hydraulic fluid flow to the chamber  118  of the rod side  114  of the cylinder  110  are independently controlled and/or metered to realize boom vibration reduction and also to prevent the cylinder  110  from drifting. According to the principles of the present disclosure, the hydraulic system  600  may be configured similar to a conventional counter-balance system. 
     In certain embodiments, the hydraulic system  600  is configured to the conventional counter-balance configuration when a movement of the cylinder  110  is commanded. As further described below, the hydraulic system  600  may enable measurement of pressures within the chambers  116  and/or  118  of the cylinder  110  at a remote location away from the hydraulic cylinder  110  (e.g., at sensors  610 ). This architecture thereby may reduce mass that would otherwise be positioned on the boom and/or may simplify routing of hydraulic lines (e.g., hard tubing and hoses). Performance of machines such as concrete pump booms and/or lift handlers may be improved by such simplified hydraulic line routing and/or reduced mass on the boom. In certain embodiments, the hydraulic system  600  may enable measurement of the pressures within the chambers  116  and/or  118  of the cylinder  110  at the hydraulic cylinder  110  (e.g., at sensors  620   1  and/or  620   2 ). In the embodiment depicted at  FIG. 1 , the sensor  620   1  may measure the pressure within the chamber  116 , and the sensor  620   2  may measure the pressure within the chamber  118 . Signals from some or all of the sensors  610 ,  620  may be sent to the controller  640  (e.g., for use as feedback signals). 
     The counter-balance valves  300  and  400  may be components of a valve arrangement  840  (i.e., a valve set). The valve arrangement  840  may include various hydraulic components that control and/or regulate hydraulic fluid flow to and/or from the hydraulic cylinder  110 . The valve arrangement  840  may further include the control valve  700  (e.g., a proportional hydraulic valve), the control valve  800  (e.g., a proportional hydraulic valve), the valve  350  (e.g., a 2-way valve), and the valve  450  (e.g., a 2-way valve). The control valves  700  and/or  800  may be high bandwidth and/or high resolution control valves. 
     In the depicted embodiment of  FIG. 1 , a node  51  is defined at the port  302  of the counter-balance valve  300  and the port  122  of the hydraulic cylinder  110 ; a node  52  is defined at the port  402  of the counter-balance valve  400  and the port  124  of the hydraulic cylinder  110 ; a node  53  is defined at the port  304  of the counter-balance valve  300 , a port  462 . of the valve  450 , and the port  702  of the hydraulic valve  700 ; a node  54  is defined at the port  404  of the counter-balance valve  400 , a port  362  of the valve  350 , and the port  804  of the hydraulic valve  800 ; a node  55  is defined at the port  306  of the counter-balance valve  300  and a port  352  of the valve  350 ; and a node  56  is defined at the port  406  of the counter-balance valve  400  and a port  452  of the valve  450 . The hydraulic valves  350  and  450  are described in detail below. 
     Turning now to  FIG. 3 , the hydraulic cylinder  110  is illustrated with v blocks  152 ,  154 . The valve blocks  152 ,  154  may be separate from each other, as illustrated, or may be a single combined valve block. The valve block  152  may be mounted to and/or over the port  122  of the hydraulic cylinder  110 , and the valve block  154  may be mounted to and/or over the port  124  of the hydraulic cylinder  110 . The valve blocks  152 ,  154  may be directly mounted to the hydraulic cylinder  110 . The valve block  152  may include the counter-balance valve  300  and/or the valve  350 , and the valve block  154  may include the counter-balance valve  400  and/or the valve  450 . The valve blocks  152  and/or  154  may include additional components of the valve arrangement  840 . The valve blocks  152 ,  154 , and/or the single combined valve block may include sensors and/or sensor ports (e.g., pressure and/or flow sensors and/or corresponding ports). 
     Turning now to  FIG. 4 , an example boom system  10  is described and illustrated in detail. The boom system  10  may include a vehicle  20  and a boom  30 . The vehicle  20  may include a drive train  22  (e.g., including wheels and/or tracks). As depicted at  FIG. 5 , rigid retractable supports  24  are further provided on the vehicle  20 . The rigid supports  24  may include feet that are extended to contact the ground and thereby support and/or stabilize the vehicle  20  by bypassing ground support away from the drive train  22  and/or suspension of the vehicle  20 . In other vehicles (e.g., vehicles with tracks, vehicles with no suspension), the drive train  22  may be sufficiently rigid and retractable rigid supports  24  may not be needed and/or provided. 
     As depicted at  FIG. 4 , the boom  30  extends from a first end  32  to a second end  34 . As depicted, the first end  32  is rotatably attached (e.g., by a turntable) to the vehicle  20 . The second end  34  may be positioned by actuation of the boom  30  and thereby be positioned as desired. In certain applications, it may be desired to extend the second end  34  a substantial distance away front the vehicle  20  in a primarily horizontal direction. In other embodiments, it may be desired to position the second end  34  vertically above the vehicle  20  a substantial distance. In still other applications, the second end  34  of the boom  30  may be spaced both vertically and horizontally from the vehicle  20 . In certain applications, the second end  34  of the boom  30  may be lowered into a hole and thereby be positioned at an elevation below the vehicle  20 , 
     As depicted, the boom  30  includes a plurality of boom segments  36 . Adjacent pairs of the boom segments  36  may be connected to each other by a corresponding joint  38 . As depicted, a first boom segment  36   1  is rotatably attached to the vehicle  20  at a first joint  381 . The first boom segment  36   1  may be mounted by two rotatable joints. For example, the first rotatable joint may include a turntable, and the second rotatable joint may include a horizontal axis. A second boom segment  36   2  is attached to the first boom segment  36   1  at a second joint  38   2 . Likewise, a third boom segment  36   3  is attached to the second boom segment  36   2  at a joint  38   3 , and a fourth boom segment  36   4  is attached to the third boom segment  36   3  at a fourth joint  38   4 . A relative position/orientation between the adjacent pairs of the boom segments  36  may be controlled by a corresponding hydraulic cylinder  110 . For example, a relative position/orientation between the first boom segment  36   1  and the vehicle  20  is controlled by a first hydraulic cylinder  110   1 . The relative position/orientation between the first boom segment  36   1  and the second boom segment  36   2  is controlled by a second hydraulic cylinder  110   2 . Likewise, the relative position/orientation between the third boom segment  36   3  and the second boom segment  362  may be controlled by a third hydraulic cylinder  110   3 , and the relative position/orientation between the fourth boom segment  36   4  and the third boom segment  36   3  may be controlled by a fourth hydraulic cylinder  110   4 . 
     According to the principles of the present disclosure, the boom  30 , including the plurality of boom segments  36   1-4 , may be modeled and vibration of the boom  30  may be controlled by the controller  640 . In particular, the controller  640  may send a signal  652  to the valve  700  and a signal  654  to the valve  800 . The signal  652  may include a vibration component  652   v , and the signal  654  may include a vibration component  654   v . The vibration component  652   v ,  654   v  may cause the respective valve  700 ,  800  to produce a vibratory flow and/or a vibratory pressure at the respective port  702 ,  804 . The vibratory flow arid/or the vibratory pressure may be transferred through the respective counter-balance valve  300 ,  400  and to the respective chamber  116 ,  118  of the hydraulic cylinder  110 . 
     The signals  652 ,  654  of the controller  640  may also include move signals that cause the hydraulic cylinder  110  to extend and retract, respectively, and thereby actuate the boom  30 . As will be further described below, the signals  652 ,  654  of the controller  640  may also include selection signals that select one of the counter-balance valves  300 ,  400  as a holding counter-balance valve and select the other of the counter-balance valves  400 ,  300  as a vibration flow/pressure transferring counter-balance valve. In the depicted embodiment, a loaded one of the chambers  116 ,  118  of the hydraulic cylinder  110 , that is loaded by the net load  90 , corresponds to the holding counter-balance valve  300 ,  400 , and an unloaded one of the chambers  118 ,  116  of the hydraulic cylinder  110 , that is not loaded by the net load  90 , corresponds to the vibration flow/pressure transferring counter-balance valve  400 ,  300 . In certain embodiments, the vibration component  652   v  or  654   v  may be transmitted to the control valve  800 ,  700  that corresponds to the unloaded one of the chambers  118 ,  116  of the hydraulic cylinder  110 . 
     The controller  640  may receive input from various sensors, including the sensors  610 , optional remote sensors  620 , position sensors, LVDTs, vision base sensors, etc. and thereby compute the signals  652 ,  654 , including the vibration component  652   v ,  654   v  and the selection signals. The controller  640  may include a dynamic model of the boom  30  and use the dynamic model and the input from the various sensors to calculate the signals  652 ,  654 , including the vibration component  652   v ,  654   v  and the selection signals. In certain embodiments, the selection signals include testing signals to determine the loaded one and/or the unloaded one of the chambers  116 ,  118  of the hydraulic cylinder  110 . 
     In certain embodiments, a single system such as the hydraulic system  600  may be used on one of the hydraulic cylinders  110  (e.g., the hydraulic cylinder  1100 . In other embodiments, a plurality of the hydraulic cylinders  110  may each be actuated by a corresponding hydraulic system  600 . In still other embodiments, all of the hydraulic cylinders  110  may each be actuated by a system such as the system  600 . 
     Turning now to  FIG. 1 , certain elements of the hydraulic system  600  will be described in detail. The example hydraulic system  600  includes the proportional hydraulic control valve  700  and the proportional hydraulic control valve  800 . In the depicted embodiment, the hydraulic valves  700  and  800  are three-way three position proportional valves. The valves  700  and  800  may be combined within a common valve body. In certain embodiments, some or all of the valves  300 ,  350 ,  400 ,  450 ,  700 , and/or  800  of the hydraulic system  600  may be combined within a common valve body and/or a common valve block. In certain embodiments, some or all of the valves  300 ,  350 ,  400 ,  450 ,  700 , and/or  800  of the valve arrangement  840  may be combined within a common valve body and/or a common valve block. In certain embodiments, the valves  300 ,  350 , and/or  700  of the valve arrangement  840  may be combined within a common valve body and/or a common valve block. In certain embodiments, the valves  400 ,  450 , and/or  800  of the valve arrangement  840  may be combined within a common valve body and/or a common valve block. 
     The hydraulic valve  700  may include a spool  720  with a first configuration  722 , a second configuration  724 , and a third configuration  726 . As illustrated, the spool  720  is at the third configuration  726 . The valve  700  includes a port  702 , a port  712 , and a port  714 . In the first configuration  722 , the port  714  is blocked off, and the port  702  is fluidly connected to the port  712 . In the second configuration  724 , the ports  702 ,  712 ,  714  are all blocked off In the third configuration  726 , the port  702  is fluidly connected to the port  714 , and the port  712  is blocked off. 
     The hydraulic valve  800  may include a spool  820  with a first configuration  822 , a second configuration  824 , and a third configuration  826 . As illustrated, the spool  820  is at the third configuration  826 . The valve  800  includes a port  804 , a port  812 , and a port  814 . In the first configuration  822 , the port  812  is blocked off, and the port  804  is fluidly connected to the port  814 . In the second configuration  824 , the ports  804 ,  812 ,  814  are all blocked off. In the third configuration  826 , the port  804  is fluidly connected to the port  812 , and the port  814  is blocked off. 
     In the depicted embodiment, a hydraulic line  562  connects the port  302  of the counter-balance valve  300  with the port  122  of the hydraulic cylinder  110 . Node  51  may include the hydraulic line  562 . A hydraulic line  564  may connect the port  402  of the counter-balance valve  400  with the port  124  of the hydraulic cylinder  110 . Node  52  may include the hydraulic line  564 . In certain embodiments, the hydraulic lines  562  and/or  564  are included in valve blocks, housings, etc. and may be short in length. A hydraulic line  552  may connect the port  304  of the counter-balance valve  300  with the port  702 . of the hydraulic valve  700  and with the port  462  of the valve  450 . Node  53  may include the hydraulic line  552 . Likewise, a hydraulic line  554  may connect the port  404  of the counter-balance valve  400  with the port  804  of the hydraulic valve  800  and with the port  362  of the valve  350 . Node  54  may include the hydraulic line  554 . A hydraulic line (unnumbered) may connect the port  306  of the counter-balance valve  300  with the port  352  of the valve  350 , and node  55  may include this hydraulic line. Likewise, a hydraulic line (unnumbered) may connect the port  406  of the counter-balance valve  400  with the port  452  of the valve  450 , and node  56  may include this hydraulic line. In other embodiments, the ports  306  and  352  may directly connect to each other. Likewise, the ports  406  and  452  may directly connect to each other. 
     As illustrated at  FIGS. 1 and 2 , the valve  350  is a two-way two position valve. In particular, the valve  350  includes the first port  352  and the second port  362 . The valve  350  includes a spool  370  with a first configuration  372  and a second configuration  374 . In the first configuration  372  (depicted at  FIG. 1 ), the port  352  and the port  362  are fluidly connected. In the second configuration  374  (depicted at  FIG. 2 ), the port  362  and the port  352  are connected with a one-way flow device  364  (e.g., a check valve). As depicted, the valve  350  includes a solenoid  376  and a spring  378 . The solenoid  376  and the spring  378  can be used to move the spool  370  between the first configuration  372  and the second configuration  374 . As depicted, the valve spool  370  is positioned at the first configuration  372  when the solenoid  376  is unpowered. As depicted, the one-way flow device  364  allows flow from node  55  to node  54  and prevents flow from node  54  to node  55  when the valve spool  370  is positioned at the second configuration  374  (see  FIG. 3 ). 
     As depicted, the valve  450  is also a two-way two position valve. In particular, the valve  450  includes the first port  452  and the second port  462 . The valve  450  includes a spool  470  with a first configuration  472  and a second configuration  474 . In the first configuration  472 , the port  452  and the port  462  are fluidly connected. In the second configuration  474 , the port  462  and the port  452  are connected with a one-way flow device  464  (e.g., a check valve). As depicted, the valve  450  includes a solenoid  476  and a spring  478 . The solenoid  476  and the spring  478  can be used to move the spool  470  between the first configuration  472  and the second configuration  474 . As depicted, the valve spool  470  is positioned at the first configuration  472  when the solenoid  476  is unpowered. As depicted, the one-way flow device  464  allows flow from node  56  to node  53  and prevents flow front node  53  to node  56  when the valve spool  470  is positioned at the second configuration  474 . 
     When the valves  350  and  450  are both positioned at the first configurations  372  and  472  (see  FIG. 1 ), respectively, the hydraulic system  600  may function the same as or similar to a conventional hydraulic system. The hydraulic system  600  may include a “conventional” mode that configures the valves  350  and  450  at the first configurations  372 ,  472 . The “conventional” mode may disable and/or deactivate the vibration control features of the hydraulic system  600 . The “conventional” mode may be selected by a machine operator and/or may be selected automatically (e.g., by the controller  640 ). Manual or automatic selection of the “conventional” mode may be implemented by the controller  640  (e.g., by sending electrical signals to the solenoids  376  and/or  476 ). As depicted, a lack of power at the solenoids  376 ,  476  corresponds with the selection of the “conventional” mode. In other embodiments, providing power to the solenoids  376  and/or  476  corresponds with the selection of the “conventional” mode (e.g., configures the valves  350  and/or  450  at the first configurations  372  and/or  472 ). In certain embodiments, the valve spools  370  and/or  470  may be manually positioned (e.g., by a linkage). In certain embodiments, the valve spools  370  and/or  470  may be positioned by pilot hydraulic pressure. In certain embodiments, the “conventional” mode may be selected when cylinder movements of the hydraulic cylinder  110  are executed (e.g., when a position configuration change of the boom  30  is executed). 
     When the vibration control features of the hydraulic system  600  are executed, one of the valves  350  and  450  may be positioned at the second configuration  372 ,  472 . For example, as depicted at  FIG. 2 , the chamber  116  of the hydraulic cylinder  110  is the load holding and/or drift preventing chamber, and the vibratory flow and/or the vibratory pressure is applied to the chamber  118  of the hydraulic cylinder  110 . The vibratory flow and/or the vibratory pressure may be generated by the control valve  800  in response to the signal  654   v  from the controller  640 . A pilot opening pressure (e.g., generated by the control valve  700 ) may be applied to the counter-balance valve  400  thereby allowing the vibratory flow and/or the vibratory pressure generated by the control valve  800  to bi-directionally pass through the counter-balance valve  400  to the chamber  118 . The vibratory flow and/or the vibratory pressure thereby act on nodes  52  and  54  of the hydraulic system  600 . With the valve  350  at the second configuration  374 , the vibratory flow and/or the vibratory pressure is blocked from reaching node  55  of the hydraulic system  600  by the one-way flow device  364  of the valve  350 , and the counter-balance valve  300  is not opened by the vibratory flow and/or the vibratory pressure, even if a pilot opening pressure of the counter-balance valve  300  is exceeded at node  54 . 
     The counter-balance valve  300  may develop/exhibit internal fluid leakage under certain conditions and/or in certain embodiments. For example, the internal fluid leakage may transfer hydraulic fluid from node  51  to node  55  and/or may transfer hydraulic fluid from node  53  to node  55 . If such internal fluid leakage occurs and is not allowed to drain, pressure may develop at node  55 . If the pressure at node  55  exceeds the pilot opening pressure of the counter-balance valve  300 , the spool  310  may be actuated by the pressure at node  55 , and the counter-balance valve  300  may open. However, the one-way flow device  364  of the valve  350  allows node  55  to drain to node  54 . In particular, the vibratory flow and/or the vibratory pressure may be generated so that at least periodically the pressure at node  54  is below the pilot opening pressure of the counter-balance valve  300 . Thus, the one-way flow device  364  of the valve  350  allows node  55  to drain to node  54  when the pressure at node  54  is below the pilot opening pressure of the counter-balance valve  300 , and the pressure at node  55  may remain below the pilot opening pressure of the counter-balance valve  300  in this configuration of the hydraulic system  600 . 
     In another example, the chamber  118  of the hydraulic cylinder  110  is the load holding and/or drift preventing chamber, and the vibratory flow and/or the vibratory pressure is applied to the chamber  116  of the hydraulic cylinder  110 . The vibratory flow and/or the vibratory pressure may be generated by the control valve  700  in response to the signal  652   v  from the controller  640 . A pilot opening pressure (e.g., generated by the control valve  800 ) may be applied to the counter-balance valve  300  thereby allowing the vibratory flow and/or the vibratory pressure generated by the control valve  700  to bi-directionally pass through the counter-balance valve  300  to the chamber  116 . The vibratory flow and/or the vibratory pressure thereby act on nodes  51  and  53  of the hydraulic system  600 . With the valve  450  at the second configuration  474 , the vibratory flow and/or the vibratory pressure is blocked from reaching node  56  of the hydraulic system  600  by the one-way flow device  464  of the valve  450 , and the counter-balance valve  400  is not opened by the vibratory flow and/or the vibratory pressure, even if a pilot opening pressure of the counter-balance valve  400  is exceeded at node  53 . 
     The counter-balance valve  400  may develop/exhibit internal fluid leakage under certain conditions and/or in certain embodiments. For example, the internal fluid leakage may transfer hydraulic fluid from node  52  to node  56  and/or may transfer hydraulic fluid from node  54  to node  56 . If such internal fluid leakage occurs and is not allowed to drain, pressure may develop at node  56 . If the pressure at node  56  exceeds the pilot opening pressure of the counter-balance valve  400 , the spool  410  may be actuated by the pressure at node  56 , and the counter-balance valve  400  may open. However, the one-way flow device  464  of the valve  450  allows node  56  to drain to node  53 . In particular, the vibratory flow and/or the vibratory pressure may be generated so that at least periodically the pressure at node  53  is below the pilot opening pressure of the counter-balance valve  400 . Thus, the one-way flow device  464  of the valve  450  allows node  56  to drain to node  53  when the pressure at node  53  is below the pilot opening pressure of the counter-balance valve  400 , and the pressure at node  56  may remain below the pilot opening pressure of the counter-balance valve  400  in this configuration of the hydraulic system  600 . 
     In other embodiments, other methods of draining nodes  55  and/or  56  may be implemented. 
     In certain applications, the hydraulic actuator (e.g., the hydraulic cylinder  110 ) may always be or may predominantly be loaded in a same direction when the vibration control features (e.g., of the hydraulic system  600 ) are desired. For example, the hydraulic cylinder  110   1  of the boom  30  may always be or may predominantly be loaded in compression, and the chamber  116  of the hydraulic cylinder  110   1  may always be or may predominantly be the load holding and/or drift preventing chamber when the vibration control features are desired. In such applications, one of the valves  350  Of  450  may be removed from the hydraulic system  600 . For example, if the chamber  116  of the hydraulic cylinder  110  is always or is predominantly the load holding and/or drift preventing chamber, the valve  450  may be removed and nodes  53  and  56  may be combined. As another example, if the chamber  118  of the hydraulic cylinder  110  is always or is predominantly the load holding and/or drift preventing chamber, the valve  350  may be removed and nodes  54  and  55  may be combined. 
     The valve  350  allows the vibratory flow and/or the vibratory pressure generated by the control valve  800  to exceed the pilot opening pressure of the counter-balance valve  300  without opening the counter-balance valve  300 . Likewise, the valve  450  allows the vibratory flow and/or the vibratory pressure generated by the control valve  700  to exceed the pilot opening pressure of the counter-balance valve  400  without opening the counter-balance valve  400 . Thus, the valves  350  and  450  allow the vibratory flow and/or the vibratory pressure to reach pressures limited by the supply pressure, and a vibratory response force/displacement  950  can be correspondingly aggressive. 
     In certain environments, the vibratory response force/displacement  950  may be suitable at pressures below the pilot opening pressure of the counter-balance valve  300 ,  400 . In such or similar embodiments and/or environments, the valves  350 ,  450  may remain at the first configuration  372 ,  472 , and/or the hydraulic system  600  may be operated the same as or similar to a hydraulic system  600  of Patent Application Ser. No. 61/872,424, filed on Aug. 30, 2013, entitled Control Method and System for Using a Pair of Independent Hydraulic Metering Valves to Reduce Boom Oscillations, which is hereby incorporated by reference in its entirety. 
     Sensors that measure temperature and/or pressure at various ports of the valves  700 ,  800  and/or at other locations may be provided. In particular, a sensor  610   1  is provided adjacent the port  702  of the valve  700 . As depicted, the sensor  610   1  is a pressure sensor and may be used to provide dynamic information about the system  600  and/or the boom system  10 . As depicted at  FIGS. 1 and 2 , a second sensor  610   2  is provided adjacent the port  804  of the hydraulic valve  800 . The sensor  610   2  may be a pressure sensor and may be used to provide dynamic information about the hydraulic system  600  and/or the boom system  10 . As further depicted at  FIGS. 1 and 2 , a third sensor  610   3  may be provided adjacent the port  814  of the valve  800 , and a fourth sensor  610   4  may be provided adjacent the port  812  of the valve  800 . The sensors  610   3  and  610   4  may also be used to provide dynamic information about the hydraulic system  600  and/or the boom system  10 . A sensor  620   1  may be a pressure sensor provided adjacent the port  122  of the chamber  116  of the hydraulic cylinder  110 , and a sensor  620   2  may be a pressure sensor provided adjacent the port  124  of the chamber  118  of the hydraulic cylinder  110 . In certain embodiments, a sensor  620   3  may be capable of measuring relative position, velocity, and/or acceleration of the rod  126  relative to the head side  112  and/or housing of the hydraulic cylinder  110 . In certain embodiments, a sensor capable of measuring relative position, velocity, and/or acceleration of the rod  126  relative to the head side  112  and/or housing of the hydraulic cylinder  110  is not used. The sensors  620  may also be used to provide dynamic information about the hydraulic system  600  and/or the boom system  10 . The sensors  610  and  620  may provide feedback signals to the controller  640 . 
     In certain embodiments, pressure within the supply line  502  and/or pressure within the tank line  504  are well known, and the pressure sensors  610   1  and  610   2  may be used to calculate flow rates through the valves  700  and  800 , respectively. In other embodiments, a pressure difference across the valve  700 ,  800  is calculated. For example, the pressure sensor  610   3  and the pressure sensor  610   2  may be used when the spool  820  of the valve  800  is at the first position  822  and thereby calculate flow through the valve  800 . Likewise, a pressure difference may be calculated between the sensor  610   2  and the sensor  610   4  when the spool  820  of the valve  800  is at the third configuration  826 . The controller  640  may use these pressures and pressure differences as control inputs. 
     Temperature sensors may further be provided at and around the valves  700 ,  800  and thereby refine the flow measurements by allowing calculation of the viscosity and/or density of the hydraulic fluid flowing through the valves  700 ,  800 . The controller  640  may use these temperatures as control inputs. 
     Although depicted with the first sensor  610   1 , the second sensor  610   2 , the third Sensor  610   3 , and the fourth sensor  610   4 , fewer sensors or more sensors than those illustrated may be used in alternative embodiments. Further, such sensors may be positioned at various other locations in other embodiments. In certain embodiments, the sensors  610  may be positioned within a common valve body. In certain embodiments, an Ultronics® servo valve available from Eaton Corporation may be used. The Ultronics® servo valve provides a compact and high performance valve package that includes two three-way valves (i.e., the valves  700  and  800 ), the pressure sensors  610 , and a pressure regulation controller (e.g., included in the controller  640 ). The Ultronics® servo valve may serve as the valve assembly  690 . The Eaton Ultronics® servo valve further includes linear variable differential transformers (LVDT) that monitor positions of the spools  720 ,  820 , respectively. By using the two three-way proportional valves  700 ,  800 , the pressures of the chambers  116  and  118  may be independently controlled. In addition, the flow rates into and/or out of the chambers  116  and  118  may be independently controlled. In other embodiments, the pressure of one of the chambers  116 ,  118  may be independently controlled with respect to a flow rate into and/or out of the opposite chambers  116 ,  118 . 
     In comparison with using a single four-way proportional valve, the configuration of the hydraulic system  600  can achieve and accommodate more flexible control strategies with less energy consumption. For example, when the cylinder  110  is moving, the valve  700 ,  800  connected with the metered-out chamber  116 ,  118  can manipulate the chamber pressure while the valves  800 ,  700  connected with the metered-in chamber can regulate the flow entering the chamber  118 ,  116 . As the metered-out chamber pressure is not coupled with the metered-in chamber flow, the metered-out chamber pressure can be regulated to be low and thereby reduce associated throttling losses. 
     The supply line  502 , the return line  504 , the hydraulic line  552 , the hydraulic line  554 , the hydraulic line  562 , the hydraulic line  564 , a hydraulic line extending between the ports  306  and  352 , and/or a hydraulic line extending between the ports  406  and  452  may belong to a line set  550 . 
     Upon vibration control being deactivated (e.g., by an operator input), the hydraulic system  600  may configure the valve arrangement  840  as a conventional counter-balance/control valve arrangement. The conventional counter-balance/control valve arrangement may be engaged when moving the boom  30  under move commands to the control valves  700 ,  800 . 
     Upon vibration control being activated by an operator input), the valve arrangement  840  may effectively lock the hydraulic cylinder  110  from moving. In particular, the activated configuration of the valve arrangement  840  may lock one of the chambers  116 ,  118  of the hydraulic cylinder  110  while sending vibratory pressure and/or flow to an opposite one of the chambers  118 ,  116 . The vibratory pressure and/or flow may be used to counteract external vibrations  960  encountered by the boom  30 . 
     Turning again to  FIGS. 1 and 2 , certain components of the counter-balance valve  300 ,  400  will be described in detail. The counter-balance valve  300 ,  400  includes a first port  302 ,  402 , a second port  304 ,  404 , and a third port  306 ,  406 , respectively. As depicted, the port  302 ,  402  is fluidly connected to a hydraulic component (e.g., the hydraulic cylinder  110 ). The port  304 ,  404  is fluidly connected to a control valve (e.g., the control valve  700 ,  800 ). The port  306 ,  406  is a pilot port that is selectively fluidly connected to the port  404 ,  304  of an opposite counter-balance valve via the valve  350 ,  450 . By selectively connecting the port  306 ,  406  to the port  404 ,  304  of the opposite counter-balance valve, the port  306 ,  406  is also selectively fluidly connected to a control valve  800 ,  700  that is opposite the control valve  700 ,  800  that is connected to the port  304 ,  404 . 
     The spool  310 ,  410  is movable within a bore of the counter-balance valve  300 ,  400 . In particular, a net force on the spool  310 ,  410  moves or urges the spool  310 ,  410  to move within the bore. The spool  310 ,  410  includes a spring area and an opposite pilot area. The spring area is operated on by a pressure at the port  304 ,  404 . Likewise, the pilot area is operated on by a pressure at the port  306 ,  406 . In certain embodiments, a pressure at the port  302 ,  402  may have negligible or minor effects on applying a force that urges movement on the spool  310 ,  410 . In other embodiments, the spool  310 ,  410  may further include features that adapt the counter-balance valve  300 ,  400  to provide a relief valve function responsive to a pressure at the port  302 ,  402 . In addition to forces generated by fluid pressure acting on the spring and pilot areas, the spool  310 ,  410  is further operated on by a spring force. In the absence of pressure at the ports  304 ,  404  and  306 ,  406 , the spring force urges the spool  310 ,  410  to seat and thereby prevent fluid flow between the ports  302 ,  402  and  304 ,  404 . As illustrated at  FIG. 1 , a passage  322 ,  422  and check valves  320 ,  420  allow fluid to flow from the port  304 ,  404  to the port  302 ,  402  by bypassing the seated spool  310 ,  410 . However, flow from the port  302 ,  402  to the port  304 ,  404  is prevented by the check valve  320 ,  420 , when the spool  310 ,  410  is seated. 
     A net load direction on the hydraulic cylinder  110  can be determined by comparing the pressure measured by the sensor  620   1  multiplied by the effective area of the chamber  116  and comparing with the pressure measured by the sensor  620   2  multiplied by the effective area of the chamber  118 . 
     If the net load  90  is supported by the chamber  116 , the control valve  700  may supply the pilot opening pressure to the port  406  via the valve  450 , and the control valve  800  may supply a vibration canceling fluid flow to the chamber  118 . The sensors  610   1  and/or  610   2  can be used to detect the frequency, phase, and/or amplitude of any external vibrational inputs to the hydraulic cylinder  110 . Alternatively or additionally, vibrational inputs to the hydraulic cylinder  110  may be measured by an upstream pressure sensor (e.g., the sensors  620   1  and/or  620   2 ), an external position sensor (e.g., the sensors  620   3 ), an external acceleration sensor (e.g., the sensors  620   3 ), and/or various other sensors. If the net load  90  is supported by the chamber  118 , the control valve  800  may supply a pilot opening pressure to the port  306  via the valve  350 , and the control valve  700  may supply a vibration canceling fluid flow to the chamber  116 . The sensors  610   1  and/or  610   2  can be used to detect the frequency, phase, and/or amplitude of any external vibrational inputs to the hydraulic cylinder  110 . Alternatively or additionally, vibrational inputs to the hydraulic cylinder  110  may be measured by an upstream pressure sensor (e.g., the sensors  620   1  and/or  620   2 ), an external position sensor (e.g., the sensors  620   3 ), an external acceleration sensor (e.g., the sensors  620   3 ), and/or various other sensors. 
     The vibration cancellation algorithm can take different forms. In certain embodiments, the frequency and phase of the external vibration may  960  be identified by a filtering algorithm (e.g., by Least Mean Squares, Fast Fourier Transform, etc.). In certain embodiments, the frequency, the amplitude, and/or the phase of the external vibration may be identified by various conventional means. In certain embodiments, upon identifying the frequency, the amplitude, and/or the phase of the external vibration, a pressure signal with the same frequency and appropriate phase shift may be applied at the unloaded chamber  116 ,  118  to cancel out the disturbance caused by the external vibration  960 . The control valves  700  and/or  800  may be used along with the controller  640  to continuously monitor flow through the control valves  700  and/or  800  to ensure no unexpected movements occur. 
     In the depicted embodiments, the sensors  610   1  and  610   2  are shielded from measuring the pressures at the ports  122  and  124  of the hydraulic cylinder  110 , respectively, by the counter-balance valves  300  and  400 . Therefore, methods independent of the sensors  610   1  and  610   2  can be used to determine the direction of the net load  90  on the cylinder  110  and to determine external vibrations acting on the cylinder  110 . In certain embodiments, pressure sensors (e.g., the pressure sensors  620   1  and  620   2 ) at the ports  122  and/or  124  may be used. In other embodiments, the pressure sensors  610   1  and  610   2  may be used. Alternatively or additionally, other sensors such as accelerometers, position sensors, visual tracking of the boom  30 , etc, may be used (e.g., a position, velocity, and/or acceleration sensor  610   3  that tracks movement of the rod  126  of the hydraulic cylinder  110 ). 
     A flow chart  1000  of an example method of implementing the control strategy for reducing boom oscillation, according to the principles of the present disclosure, is given at  FIG. 8 . The boom bounce reduction control is initiated at step  1002 . Step  1004  follows step  1002  and determines which of the chambers  116  or  118  is the load holding chamber. Step  1006  follows step  1004  and locks (e.g., removes pilot pressure from) the counter-balance valve (CBV)  300  or  400  corresponding to the load holding chamber. Step  1008  follows step  1006  and opens (e.g., applies pilot pressure to) the counter-balance valve (CBV)  400  or  300  corresponding to the chamber  116  or  118  opposite the load holding chamber (i.e., the active chamber). Step  1010  follows step  1008  and measures the pressure within the load holding chamber to initialize a reference signal. Step  1012  follows step  1010  and generates a control signal  652  or  654  to the valve  700  or  800  corresponding to the active chamber. In certain embodiments, the control signal  652  or  654  is based on the measurement of the load holding pressure and the reference signal. Step  1014  follows step  1012  and adjusts the control signal based on the measurement of the active chamber pressure. In step  1014 , a specified average level for the pressure in the active chamber is maintained. By maintaining the specified average level, the control pressure is allowed to vary in both directions from the mean. Step  1016  follows step  1014  but may occur continuously. Step  1016  updates the reference signal. Decision point  1018  follows step  1016  and inquires whether boom bounce reduction is still enabled. If the result of decision point  1018  is “yes”, then control is transferred to step  1012 . If the result of decision point  1018  is “no”, then control is transferred to an end  1020  of the flow chart  1000 . 
     The valve arrangement  840  may be configured to apply an anti-vibration (i.e., a vibration cancelling) response as follows. If the net load  90  is determined to be held by the chamber  116 , the control valve  700  pressurizes node  53  thereby opening the counter-balance valve  400  and further urging the counter-balance valve  300  to close. Upon the counter-balance valve  400  being opened, the control valve  800  may apply an anti-vibration fluid pressure/flow to the chamber  118 . The controller  640  may position the valve  350  to the second configuration  374  (see  FIG. 2 ) to preclude opening the counter-balance valve  300 . If the net load  90  is determined to be held by the chamber  118 , the control valve  800  pressurizes node  54  thereby opening the counter-balance valve  300  and further urging the counter-balance valve  400  to close. Upon the counter-balance valve  300  being opened, the control valve  700  may apply an anti-vibration fluid pressure/flow to the chamber  116 . The controller  640  may position the valve  450  to the second configuration  474  to preclude opening the counter-balance valve  400 . 
     In embodiments where the direction of the net cylinder load  90  is independently known to be acting on the chamber  116  but at least some of the parameters of the external vibration acting on the hydraulic cylinder  110  are unknown from external sensor information, the pressure sensor  610   2  may be used to measure pressure fluctuations within the chamber  118  and thereby determine characteristics of the external vibration. If the direction of the net cylinder load is independently known to be acting on the chamber  118  but at least some of the parameters of the external vibration acting on the hydraulic cylinder  110  are unknown from external sensor information, the pressure sensor  610   1  may be used to measure pressure fluctuations within the chamber  116  and thereby determine characteristics of the external vibration. 
     As schematically illustrated at  FIG. 1 , an environmental vibration load  960  is imposed as a component of the net load  90  on the hydraulic cylinder  110 . As depicted at  FIG. 1 , the vibration load component  960  does not include a steady state load component. In certain applications, the vibration load  960  includes dynamic loads such as wind loads, momentum loads of material that may be moved along the boom  30 , inertial loads from moving the vehicle  20 , and/or other dynamic loads. The steady state load may include gravity loads that may vary depending on the configuration of the boom  30 . The vibration load  960  may be sensed and estimated/measured by the various sensors  610 ,  620  and/or other sensors. The controller  640  may process these inputs and use a model of the dynamic behavior of the boom system  10  and thereby calculate and transmit an appropriate vibration signal  652   v ,  654   v . The signal  652   v ,  654   v  is transformed into hydraulic pressure and/or hydraulic flow at the corresponding valve  700 ,  800 . The vibratory pressure/flow is transferred through the corresponding counter-balance valve  300 ,  400  and to the corresponding chamber  116 ,  118  of the hydraulic cylinder  110 . The hydraulic cylinder  110  transforms the vibratory pressure and/or the vibratory flow into the vibratory response force/displacement  950 . When the vibratory response  950  and the vibration load  960  are superimposed on the boom  30 , a resultant vibration  970  is produced. The resultant vibration  970  may be substantially less than a vibration of the boom  30  generated without the vibratory response  950 . Vibration of the boom  30  may thereby be controlled and/or reduced enhancing the performance, durability, safety, usability, etc. of the boom system  10 . The vibratory response  950  of the hydraulic cylinder  110  is depicted at  FIG. 2  as a dynamic component of the output of the hydraulic cylinder  110 . The hydraulic cylinder  110  may also include a steady state component (i.e., a static component) that may reflect static loads such as gravity. 
     According to the principles of the present disclosure, a control method uses independent metering main control valves  700 ,  800  with embedded sensors  610  (e.g., embedded pressure sensors) that can sense oscillating pressure and provide a ripple cancelling pressure with counter-balance valves  300 ,  400  (CBVs) installed. The approach calls for locking one side (e.g., one chamber  116  or  118 ) of the actuator  110  in place to prevent drifting of the actuator  110 . According to the principles of the present disclosure, active ripple cancelling is provided, an efficiency penalty of orifices is avoided, and/or the main control valves  700 ,  800  may be the only control elements. According to the principles of the present disclosure, embedded pressure sensors  610  embedded in the valve  700 ,  800  and/or external pressure/acceleration/position sensors  620  may be used. 
     Turning now to  FIG. 5 , certain aspects of certain embodiments of the control strategy are illustrated according to the principles of the present disclosure. As illustrated, in certain embodiments, no position sensors are used to monitor a position of the rod  126  of the hydraulic cylinder  110 . Furthermore, no angle sensor to show geometric information of the boom  30  is used. The control strategy may be achieved using only pressure sensors. In certain embodiments, two pressure sensors  620   1 ,  620   2  are installed with one measuring each chamber  116 ,  118 . Alternatively, one shuttle pressure sensor may be used, and only the load holding chamber pressure is sensed.  FIG. 5  illustrates a “locking mechanism” activated at chamber  116  thereby locking chamber  116  (i.e., flow into or out of the chamber  116  is zero). 
       FIG. 5  illustrates cross port control. In particular, the flow feeding the unlocked cylinder chamber  118  (i.e., the active chamber) is controlled based on pressure measured at the locked chamber  116 . The control objective is to stabilize the pressure of the locked, load-holding chamber  116 . In certain embodiments, the reference signal Pref is generated by self-learning. The reference signal Pref may be initialized by the pressure before vibration control is turned on. Once the vibration control is engaged, the pressure Pload of the load-holding chamber  116  is filtered to generate Pref. A low-pass filter may be used. In certain embodiments, pressure measured at the active chamber  118  may be used as an input of the controller  640 . 
     Turning now to  FIG. 6 , a graph showing simulation results of the control strategy illustrates the relationships of a position of the cylinder rod  126 , a pressure Phead of the load holding chamber (the upper pressure trace), a pressure Prod of the active chamber (the lower pressure trace), and flow into the active chamber in the time domain. In this simulation, the head chamber  116  of the cylinder  110  is the load holding chamber. The active vibration control is turned on at t=3 seconds. At t=3 seconds, control flow is provided to the rod side cylinder chamber  118 . As illustrated, a size of the head side pressure ripple is reduced, while a size of the rod side pressure ripple is amplified. A cylinder position ripple is correspondingly reduced, and a mean position of the cylinder rod  126  does not drift. 
     Turning now to  FIG. 7 , certain aspects of certain embodiments of the control strategy are illustrated according to the principles of the present disclosure. The control strategy can provide flexibility in the type of feedback sensor used. The frequency and/or shape of the pressure ripple on the load holding side (illustrated as chamber  116 ) can be estimated by observing; the pressure on the non-load-holding side (illustrated as chamber  118 ) which may have an open counter-balance valve and thus may be measured by the sensor  610   2  built in to the valve  800 . The shape of the disturbance  642  can then be multiplied by a gain  646 , phase shifted by a phase shift  648 , and applied as a flow command  654   v  to the valve  800  of the non-load-holding chamber  118 . If no additional sensors are available, the gain  646  and/or the offset  648  could be fixed values. however, this would not be robust to changes in operating conditions. Other available measurements  644  that sense the quality of the ripple reduction (e.g., pressure sensor data, position sensor data, operator feedback, etc.) could be used to adjust the gain  646  and/or the phase shift  648 . 
     Disturbance estimation may be used additionally or alternatively. The pressure measured on the non-load holding side (e.g., by the pressure sensor  610   1 ,  610   2  built into the valve  700 ,  800 ) can be used. Repetitive control may be used to generate an estimate of the disturbance  642 . A gain  646  and/or a phase shift  648  may be applied to the disturbance  642  to cancel the disturbance force  960 . The gain  646  and/or the offset  648  could be constants (i.e., open loop) requiring no additional sensors. 
     Alternately, some method of feedback may be used to measure the disturbance rejection and then adapt the gain  646  and/or the phase shift  648  to improve the performance. The feedback can be any means of judging quality of disturbance rejection (e.g., pressure on the loaded chamber, position feedback of the cylinder rod  126 , operator input, etc.). The method illustrated at  FIG. 7  gives flexibility as to the type of feedback used and allows the possibility of an open-loop (no sensor) implementation. 
     This application relates to U.S. Provisional Patent Applications Ser. No. 61/829,796, filed on May 31, 2013, entitled Hydraulic System and Method for Reducing Boom Bounce with Counter-Balance Protection, and Ser. No. 61/872,424, filed on Aug. 30, 2013, entitled Control Method and System for Using a Pair of Independent Hydraulic Metering Valves to Reduce Boom Oscillations, which are hereby incorporated by reference in their entireties. 
     Various modifications and alterations of this disclosure will become apparent to those skilled in the art without departing from the scope and spirit of this disclosure, and it should be understood that the scope of this disclosure is not to be unduly limited to the illustrative embodiments set forth herein.