Abstract:
The present disclosure generally relates to a railroad track ballast tamping vehicle and associated methods of use, wherein the vehicle comprises: a rigid frame; a variable-displacement servo-pump operatively coupled to the vehicle; at least one linear hydraulic actuator operatively coupled to the frame at a proximal end of the at least one linear hydraulic actuator and comprising: at least one internal cavity for receiving hydraulic fluid from the variable-displacement servo-pump via a hydraulic hose; and an actuator rod passing through a first internal cavity and a second internal cavity of the at least one linear hydraulic actuator; and a tamping tool operatively coupled to a distal end of the at least one linear hydraulic actuator. A tamping pad associated with the tamping tool may be lowered into ballast underlying railroad tracks and between railroad track ties for performing ballast tamping operations.

Description:
TECHNICAL FIELD 
       [0001]    Embodiments disclosed herein related to an apparatus and method for tamping ballast. 
       BACKGROUND 
       [0002]    Railroads are generally constructed of a pair of elongated, substantially parallel rails, which are coupled to a plurality of laterally extending ties via metal tie plates and spikes and/or spring clip fasteners. The rails and ties are disposed on a ballast bed formed of hard particulate material, such as gravel. 
         [0003]    During installation of new railroad and maintenance of existing railroad, the ballast adjacent to and/or under the ties is “tamped,” or compressed, to ensure that the ties, and therefore the rails, do not shift. This tamping process ensures that the rails and ties are sufficiently aligned, stable, and/or durable. 
         [0004]    A rail vehicle for carrying out tamping operations is generally referred to as a “tamper” and includes work heads for carrying out tamping operations. Such work heads typically include a workhead frame, a sub frame, hydraulic actuators linking the sub frame to the tamping arms, a number of tamping tools (often referred to as tynes), attached to the tamping arms and terminating in paddles. The tamping tools are adapted to move towards one another in a pincer-like motion in order to compress the ballast adjacent to and underlying the ties. Vibration of the tamping tools further compresses the ballast. In practice, multiple vibration devices may be employed in order to provide tools for tamping inside and outside the rails as well as forward and aft of the ties. Such tamping operations may be carried out at each tie via a tamper vehicle, which advances along the rails. 
         [0005]    The amplitude and frequency of vibration imparted by the tamping tools in tamping ballast under ties of a railroad track should be controlled. If, for instance, the condition of the ballast under successive ties changes, vibrating the tamping tools with the same amplitude and the same frequency will result in inappropriate track tamping operations. However, adjusting the vibration of the tamping tools by traditional hydraulic valves, such as hydraulic proportional valves, is inefficient as such valves introduce losses due to flow throttling. 
       BRIEF SUMMARY 
       [0006]    The present disclosure relates to an energy efficient hydraulic drive associated with tamping units where the vibration of the tamping tools is adjustable in terms of both amplitude and frequency. In this regard, a hydraulic drive may be installed on the tamping unit to provide a drive for each of the tamping tools. 
         [0007]    Such tamping units may be equipped with a mobile frame (e.g., a subframe) extendable in the vertical and transverse directions, tamping arms pivoting about the sub frame, linear hydraulic actuators that drive each tamping arm and tamping tools for compressing ballast. The position of the tamping tools may be sensed by displacement sensors associated with the linear hydraulic actuators. The vibration of the tamping tools as well as the motion of the tamping tools may be controlled based on the displacement sensor signal. Accordingly, the motion of each linear hydraulic actuator may be controlled by an associated variable-displacement servo-pump. 
         [0008]    Each linear hydraulic actuator may include one or multiple internal chambers (e.g., cavities) into and/or out of which hydraulic fluid flows, as controlled by the variable-displacement servo-pump. In instances where each linear hydraulic actuator includes two chambers, the flow rate going into a first chamber of a linear hydraulic actuator and the flow rate coming out a second chamber of each linear hydraulic actuator may both flow through the associated variable-displacement servo-pump. In this manner, the vibration of each tamping tool may be adjusted in terms of both amplitude and frequency by varying the displacement of the variable-displacement servo-pump, thus enabling an energy-efficient functioning of the system. Accordingly, hydraulic valves may no longer be needed to be positioned between linear hydraulic actuators and variable-displacement servo-pumps, thereby removing the losses due to flow throttling. 
         [0009]    In some embodiments, an apparatus may be provided. The apparatus may comprise: a rigid frame; a variable-displacement servo-pump operatively coupled to the frame; a double rod linear hydraulic actuator operatively coupled to the sub frame at a proximal end of the double rod linear hydraulic actuator and comprising: at least one internal cavity for receiving hydraulic fluid from the variable-displacement servo-pump via a hydraulic hose; and an actuator rod passing through a first internal cavity and a second internal cavity of the double rod linear hydraulic actuator; a tamping arm operatively coupled to a distal end of the double rod linear hydraulic actuator and a tamping tool coupled to the tamping arm. 
         [0010]    In some embodiments, the double rod linear hydraulic actuator is configured to translate in a longitudinal direction along the actuator rod in response to the at least one internal cavity of the double rod linear hydraulic actuator receiving hydraulic fluid, thereby causing movement of at least one of the tamping tools. 
         [0011]    In some embodiments, the apparatus may further comprise: a vibrator operatively coupled to the frame, wherein vibrations of the vibrator cause the tamping tool to vibrate when performing ballast tamping operations. 
         [0012]    In some embodiments, the double rod linear hydraulic actuator comprises at least one of a displacement sensor, a pressure transducer, and a position sensor for collecting sensor data associated with the double rod linear hydraulic actuator. 
         [0013]    In some embodiments, the apparatus may further comprise: an intelligent microcontroller for controlling displacement of hydraulic fluid between the variable-displacement servo-pump and the at least one cavity of the double rod linear hydraulic actuator in response to receiving sensor data associated with the double rod linear hydraulic actuator from at least one of the displacement sensor, the pressure transducer, and the position sensor. 
         [0014]    In some embodiments, the apparatus may further comprise: another linear actuator defining a lower end operatively coupled to the sub frame and an upper end operatively coupled to a workhead frame operatively coupled to the vehicle frame for raising and lowering the apparatus in relation to the tamper vehicle frame. This linear actuator may be a single rod linear actuator. 
         [0015]    In some embodiments, an apparatus may be provided. The apparatus may comprise: a rigid frame; a variable-displacement servo-pump operatively coupled to the frame; a linear hydraulic actuator system operatively coupled to the frame at a proximal end of the linear hydraulic actuator system and comprising: a first single rod linear hydraulic actuator and a second single rod linear hydraulic actuator operatively coupled to each other via one or more pins and oriented in opposite directions on a common plane, wherein each of the first single rod linear hydraulic actuator and the second single rod linear hydraulic actuator comprise: at least one internal cavity for receiving hydraulic fluid from the variable-displacement servo-pump via a hydraulic hose; and an actuator rod passing through only one cavity of the at least one internal cavity; and a tamping arm operatively coupled to a distal end of the linear hydraulic actuator system and a tamping tool coupled to the tamping arm. 
         [0016]    In some embodiments, in response to at least one internal cavity of the first single rod linear hydraulic actuator and the second single rod linear hydraulic actuator receiving hydraulic fluid, the first single rod linear hydraulic actuator is configured to extend along the actuator rod of the first single linear hydraulic actuator in a first longitudinal direction and the second single rod linear hydraulic actuator is configured to extend along the actuator rod of the second single linear hydraulic actuator in a second longitudinal direction opposite the first longitudinal direction, thereby causing movement of the tamping arm and therefore the movement of the tamping arm. 
         [0017]    In some embodiments, the apparatus may further comprise: a vibrator operatively coupled to the frame, wherein vibrations of the vibrator cause the tamping tool to vibrate when performing ballast tamping operations. 
         [0018]    In some embodiments, at least one of the first linear hydraulic actuator and the second linear hydraulic actuator comprises at least one of a displacement sensor, a pressure transducer, and a position sensor for collecting sensor data associated with at least one of the first linear hydraulic actuator and the second linear hydraulic actuator. 
         [0019]    In some embodiments, the apparatus may further comprise: an intelligent microcontroller for controlling displacement of hydraulic fluid between the variable-displacement servo-pump and the at least one cavity of the linear hydraulic actuator in response to receiving sensor data associated with the linear hydraulic actuator from at least one of the displacement sensor, the pressure transducer, and the position sensor. 
         [0020]    In some embodiments, the apparatus may further comprise: another linear actuator defining a lower end operatively coupled to the sub frame and an upper end operatively coupled to a workhead frame operatively coupled to the vehicle frame for raising and lowering the apparatus in relation to the tamper vehicle frame. This linear actuator may be a single rod linear actuator. 
         [0021]    In some embodiments, a method may be provided. The method may comprise: advancing a tamping vehicle along railroad tracks to a first predetermined location; lowering, relative to the tamping vehicle, a frame of a tamping apparatus by extending a first linear hydraulic actuator defining a lower end operatively coupled to the sub frame and an upper end operatively coupled to the workhead frame operatively coupled to the vehicle frame; tamping, using the tamping apparatus, ballast positioned underneath one or more rail ties of the railroad tracks; raising, relative to the tamping vehicle frame by retracting the first linear hydraulic actuator; and advancing the tamping vehicle along the railroad tracks to a second predetermined location. 
         [0022]    In some embodiments, lowering the frame further comprises: lowering a tamping tool into the ballast for performing at least one tamping operation wherein an upper end of the tamping tool is operatively coupled to the tamping arm and the tamping arm is operatively coupled to a distal end of a second linear hydraulic actuator, and wherein a proximal end of the second linear hydraulic actuator is operatively coupled to the sub frame. 
         [0023]    In some embodiments, tamping the ballast comprises: measuring, using at least one of a displacement sensor, a pressure transducer, and a position sensor associated with the second linear hydraulic actuator, at least one of a fluid property and a position of an actuator rod comprised in the second linear hydraulic actuator; receiving, at a microcontroller, sensor data associated with the second linear hydraulic actuator from at least one of the displacement sensor, the pressure transducer, and the position sensor; determining, using the microcontroller, an amount of hydraulic fluid to be displaced within at least one cavity of the second linear hydraulic actuator; and displacing, using a variable-displacement servo-pump, the determined amount of hydraulic fluid to at least one cavity of the second linear hydraulic actuator, thereby causing the second linear hydraulic actuator to extend or retract in a longitudinal direction along the actuator rod, wherein causing the second linear hydraulic actuator to extend or retract in a longitudinal direction along the actuator rod causes the tamping tool to move. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    Reference is now made to the following descriptions taken in conjunction with the accompanying drawings. 
           [0025]      FIG. 1  illustrates an exemplary rail tamper, in accordance with some embodiments of the disclosure; 
           [0026]      FIG. 2  illustrates an exemplary tamping unit, in accordance with some embodiments of the disclosure; 
           [0027]      FIG. 3  illustrates an exemplary schematic of a hydraulic system that utilizes a dual-chambered “double rod” linear hydraulic actuator, in accordance with some embodiments of the disclosure; 
           [0028]      FIG. 4  illustrates an exemplary actuator system that utilizes two dual-chambered “single rod” linear hydraulic actuators, in accordance with some embodiments of the disclosure; 
           [0029]      FIG. 5A  illustrates an exemplary schematic of an actuator system that utilizes two dual-chambered “single rod” linear hydraulic actuators to perform an extension movement, in accordance with some embodiments of the disclosure; and 
           [0030]      FIG. 5B  illustrates an exemplary schematic of an actuator system that utilizes two dual-chambered “single rod” hydraulic actuators to perform a retraction movement, in accordance with some embodiments of the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    Various embodiments of an apparatus and method for moving and vibrating tamping tools according to the present disclosure are described. It is to be understood, however, that the following explanation is merely exemplary in describing the devices and methods of the present disclosure. Accordingly, several modifications, changes and substitutions are contemplated. 
         [0032]    In some embodiments, the apparatus and method for moving and vibrating tamping tools may be employed in a tamping machine rail vehicle  100 , as illustrated in  FIG. 1 . The tamping vehicle  100  may include a frame assembly  102 , a propulsion device  104 , a tamping unit  106  and a cabin  108 . Frame assembly  102  may include a plurality of rigid frame members and a plurality of wheels  110  that are configured to travel on a pair of rails  112 . During operation, the tamping vehicle  100  may travel across the pair of rails  112 , which is disposed over a series of rail ties  114  operatively coupled and/or secured to the rails  112 . The rails  112  and series of ties  114  may be disposed over a bed of ballast  115  (e.g., crushed stones, rocks, gravel, and/or the like). 
         [0033]    The propulsion device  104  of the tamping vehicle  100  may be configured and/or utilized to move tamping vehicle  100  in one or more directions along the pair of rails  112 . As the tamping vehicle  100  moves along the pair of rails  112 , the tamping unit  106  may be configured to tamp ballast between rail ties  114  to reshape the ballast. This reshaping of the ballast may improve the alignment, stability, and/or durability of the rails  112  and/or rail ties  114 . 
         [0034]    The tamping unit  106  may include multiple workheads. In the side view of  FIG. 1 , one workhead can be viewed while another workhead may also be included at an opposite side corresponding with the other rail. Any number of workheads (e.g., 2, 4, etc.) may be included in the tamping unit  106 . 
         [0035]    As described in more detail below, the tamping unit  106  may include tamping arms  116 , which are operatively coupled to tamping tools  126  that may be lowered into the ballast between rail ties  114 . Movement of the tamping arms  116 , and therefore the tamping tools  126 , may be controlled by one or more actuators  118  operatively coupled to a sub frame  124  as further described below. For example, the tamping tools  126  may be actuated (e.g., be caused to move) by one or more hydraulic actuators  118  that squeeze the tamping tools  126  around the rail ties  114  when inserted into the ballast beneath the rail ties to thereby compact and/or otherwise reshape the ballast material. 
         [0036]    The tamping unit  106  may further include a variable-displacement servo-pump  122  for monitoring and/or controlling of the flow of hydraulic fluid being sent to and/or received from each chamber of the hydraulic actuators  118  used to control movement of the tamping unit  106  and/or the tamping tools  126 . The servo-pump  122  may be placed at a variety of positions on the rail vehicle  100 . The amount and/or flow rate of hydraulic fluid being sent to each chamber of the hydraulic actuators  118  may cause the tamping arms  116  and therefore the tamping tools  126  to translate, pivot, and/or otherwise move in a variety of directions. 
         [0037]    In some embodiments, the tamping unit  106  may be operatively coupled to the frame assembly  102  via a workhead frame  120 , the sub frame  124  and an actuator operatively coupled between the workhead frame  120  and the sub frame  124 . For example, the actuator (preferably a hydraulic actuator) may be operable to lower the tamping unit  106  such that the tamping tools  126  may be inserted into the ballast between adjacent rail ties  114  where squeezing and vibration actions may be performed to tamp (e.g., compress, reshape, etc.) the underlying ballast. 
         [0038]    In an exemplary work cycle, the tamping vehicle  100  may advance along the rails  112  to position the tamping unit  106  over a first rail tie  114 . A linear hydraulic actuator may then be actuated in response to hydraulic fluid being sent to and/or from each chamber of the actuator to thereby lower the tamping unit  106  (e.g., the tamping tools  126  into the ballast). Once lowered, the tamping tools  126  may be enabled to carry out the tamping operations of the ballast as desired, where movement of the tamping tools may be controlled by one or more actuators  118  in response to hydraulic fluid being sent to and/or from each chamber of the actuator. In some embodiments, the actuators  118  may cause vibration and thus causing the associated tamping tools  126  to vibrate during operation. Again, the flow of hydraulic fluid being sent to and/or from each chamber of the actuator(s)  118  used to control movement of the tamping unit  106  and/or the tamping tools  126  may be controlled by the variable-displacement servo-pump  122  and/or a hydraulic circuit included in the variable-displacement servo-pump. Once tamping operations are completed, the actuator that lowered the tamping unit may be actuated to raise (and in some cases stow) the tamping tools  126  and/or the tamping unit  106  as a whole for travel to a second rail tie  114 . 
         [0039]    The tamping vehicle  100  may also include a tracking device  125  that measures general linear movement of the rail vehicle  100  along the rail track  112 . In this manner, the tracking device  125  may enable the tamping vehicle  100  to accurately position itself, the tamping unit  106 , and/or the tamping tools  126  in relation to a rail tie  114 . Additionally, cabin  108  of the tamping vehicle  100  may be structured such that it remains stationary relative to the frame assembly  102  as the rail vehicle  100  moves along the rails  112 . 
         [0040]      FIG. 2  illustrates the tamping unit  106  in more detail. As described above, the tamping unit  106  may include a sub frame  124 , which may be extended in the vertical direction (e.g., raised and/or lowered) by an actuator during tamping operations. Additionally, the sub frame  124  of the tamping unit  106  may be operatively coupled to the frame assembly  102  (shown in  FIG. 1  but not shown in  FIG. 2 ) of the tamping vehicle  100  by one or more vertical bars (not pictured) extending downward from the workhead frame assembly  120 . During operation, an actuator may cause the sub frame  124  of the tamping unit  106  to translate in a vertical direction (e.g., raise and/or lower) along the vertical bars. For example, the sub frame  124  may include one or more apertures (not pictured) through which the vertical bars may pass when the tamping unit  106  is raised and/or lowered (e.g., translated vertically) along the longitudinal direction of the vertical bars. 
         [0041]    As described above, the tamping unit  106  may include tamping tools  126 . Each tamping tool  126  may include a tamping pad at its lower end that is to be inserted into the ballast (e.g., lowered into the gravel bed beneath the rails  112  and/or the rail ties  114 ) during operation. In some embodiments, the tamping tools  126  may be mounted on the tamping arms  116  for pivoting about pivot joints  127  (shown in  FIG. 2  and in  FIG. 3 ) having pivot axes extending in a longitudinal direction of the rail ties  114  (e.g., orthogonal to the longitudinal direction of the rails  112 ) when being actuated by actuators  118 . 
         [0042]    The actuators  118  (e.g., linear hydraulic actuators) as described herein may be mechanically connected and/or otherwise operably coupled to each tamping arm  116  of the tamping unit  106  for moving the tamping tools  126  (e.g., pivoting the tamping arms about the pivot joints  127 ), in response to flow of hydraulic fluid in the chambers of the actuators coupled to the tamping arms. In some embodiments, the position of each tamping tool  126  may be sensed by a displacement sensor  128  associated with each actuator  118  and/or each chamber of each actuator. Each displacement sensor  128  may measure, monitor, and/or otherwise determine an amount of fluid (e.g., hydraulic fluid) held in each chamber of an actuator  118 . Each displacement sensor  128  may also measure, monitor, and/or otherwise determine one or more fluid properties (e.g., pressure, volume, temperature, and/or the like) of a fluid being held inside of each chamber of an actuator  118 . 
         [0043]    In some embodiments, each displacement sensor  128  may include an electronic sensor, a transmitter, a transceiver, a wireless communication unit, a wired communication unit, and/or the like for capturing, transmitting, and/or receiving sensor data (e.g., measured values and/or properties of hydraulic fluid in each chamber of an actuator  118 ). Sensor data may be transmitted and/or received between displacement sensors  128  and a communication unit associated with the variable-displacement servo-pump  122  for controlling one or more flows of fluid (e.g., hydraulic fluid) to and/or from one or more chambers of actuators  118 . Each of the displacement sensor  128  and the variable-displacement servo-pump  122  may include electrical circuits, computing processor hardware, and/or the like for making intelligent determinations of how fluid is to be dispersed among different elements of the apparatus described herein. 
         [0044]    In some embodiments, the motion of each actuator  118  may determine the motion of the tamping tools  126 . For example, when an actuator  118  extends outwardly in a direction along its longitudinal axis, the tamping arm and therefore the associated tamping tool  126  may pivot about a pivot joint  127 . This pivoting action of the tamping arm  116  may cause the tamping tool  126  to move in a direction opposite of the direction in which the actuator  118  extends. Similarly, when the actuator  118  retracts inwardly in a direction along its longitudinal axis, the tamping arm  116  and therefore the associated tamping tool  126  may pivot about the pivot joint  127  to thus cause the tamping tool  126  to move in a direction opposite of the direction in which the actuator retracts. 
         [0045]    In some embodiments, each actuator  118  may include one or more internal chambers (e.g., cavities) into which fluid (e.g., hydraulic fluid) is displaced. The displacement of fluid in each chamber of an actuator  118  may cause the actuator  118  to actuate (e.g., retract and/or extend in a linear direction and also vibrate). Additionally, the amount and/or flow of fluid displaced in each chamber of the actuator  118  may be determined and/or monitored by a displacement sensor  128  and/or controlled by the variable-displacement servo-pump  122 . As shown in  FIG. 2 , each chamber of the actuators  118  may be connected to a hydraulic circuit of the variable-displacement servo-pump  122  by means of hydraulic hoses  130 . 
         [0046]      FIG. 3  shows a simplified schematic of a hydraulic system  132  used to power a dual-chambered “double rod” linear hydraulic actuator  118  in a closed-circuit configuration. The schematic may depict a hydraulic circuit included in and/or associated with the variable-displacement servo-pump  122  that is utilized to disperse hydraulic fluid among various elements of the hydraulic system  132 . 
         [0047]    As described above and with reference to  FIG. 3 , a dual-chambered double rod linear hydraulic actuator  118  may be operatively coupled to the sub frame  124 . The actuator  118  may also be hydraulically coupled with an associated variable-displacement servo-pump  122  via hydraulic hoses  130 . For example, each chamber of the actuator  118  may be connected to one port of the associated variable-displacement servo-pump  122  by means of two hydraulic hoses  130 . Additionally, each chamber of the actuator  118  may be connected to a low-pressure source  134  through both check valves  136  and relief valves  138 . In some embodiments, a dedicated charge pump  140  may feed the low-pressure source  134 . 
         [0048]    In some embodiments, the double rod actuator  118  of  FIG. 3  may be actuated when more hydraulic fluid is displaced within a first chamber of the double rod actuator  118  than a second chamber of the double rod actuator  118 . Displacing more hydraulic fluid within the first chamber of the double rod actuator  118  increases the pressure within the first chamber of the double rod actuator  118 , which thus causes the double rod actuator  118  to translate (e.g., move, slide, and/or the like) along the actuator rod  119  disposed within both the interior of the first and second chambers of the double rod actuator  118  in a first direction. 
         [0049]    Each actuator  118  included in the tamping unit  106  may be driven by a dedicated variable-displacement servo-pump  122  or multiple variable-displacement servo-pumps  122 . Alternatively, multiple actuators  118  may be driven by a common variable-displacement servo-pump  122 . Each variable-displacement servo-pump  122  may be powered by a combustion engine  142  of the tamping unit  106 . Each variable-displacement servo-pump  122  may also include an external drain  144  connected to a hydraulic tank of the tamping unit  106  for discharging hydraulic fluid as desired. 
         [0050]    In some embodiments, the check valves  136  may serve the purpose of reintroducing any external losses of hydraulic fluid that have been driven to the hydraulic tank of the tamping unit  106  via the external drain  144  back into the hydraulic system  132  for use. In this manner, hydraulic fluid may be recycled and/or reused as it is collected in the hydraulic tank of the tamping unit  106 . 
         [0051]    Further, the hydraulic system  132  may include an electronic control system that includes electronic sensors for measuring and/or monitoring hydraulic pressure in each chamber (e.g., a pressure transducer  146 ) and/or a position of an actuator rod  119  inside each chamber of an actuator  118  (e.g., a position sensor  148 ). In addition to and/or instead of a position sensor  148 , an angular sensor (not pictured) may be coupled to a pivot joint  127  so as to measure an angle of a tamping tool  126 . In some embodiments, each of the pressure transducer  146  and/or the position sensor  148  may also include the displacement sensor  128  as described above, and/or vice versa. Sensor signals and/or sensor data collected by the sensors  128 ,  146 ,  148  may be electrically transmitted to a digital microcontroller  150 , where a desired hydraulic fluid displacement setting for each variable-displacement servo-pump  122  may be calculated. For example, the microcontroller  150  may execute a feedback control algorithm and send a command signal to an electrohydraulic valve included in a pump adjustment system  152 , which may regulate fluid displacement of the variable-displacement servo-pump  122  to control the flow rate of hydraulic fluid flowing into and/or out of the variable-displacement servo-pump  122  in a suitable manner. 
         [0052]    In some embodiments, a goal of the hydraulic system  132  may be to create a motion of the actuator  118  characterized by a vibration adjustable in terms of both amplitude and frequency. Since the tamping arm  116  and therefore the tamping tool  126  is mechanically coupled to the actuator  118 , vibration of the actuator may result in vibration of the tamping tool  126 . This vibration of the tamping tool  126  may be controlled by adjusting a swashplate angle of the variable-displacement servo-pump  122  based on a measured position of a linear actuator rod  119  inside each chamber of the actuator  118 . In some embodiments, the position of the linear actuator rod  119  inside each chamber of the actuator  118  may be measured using the position sensor  148  and/or displacement sensor  128 . Both frequency and amplitude of the vibration of the tamping tool  126  may be adjusted to any value between zero and the upper limit of the system using the microcontroller  150 . 
         [0053]    Moreover, monitoring the pressure in each chamber of the actuator  118  (e.g., each chamber being in which hydraulic fluid is displaced by the variable-displacement servo-pump  122 ) using the pressure sensor  146  may provide increased safety of operation by enabling the microcontroller  150  to limit a maximum squeezing force being applied to the ballast by the tamping tool  126  during operation (i.e., when tamping the ballast  115 ). For example, if a critical pressure (e.g., a pressure value that exceeds a predetermined threshold pressure value) is sensed by a pressure sensor  146 , a specific control algorithm executed by the microcontroller  150  may cause the variable-displacement servo-pump  122  to destroke (e.g., stop operation, reduce and/or limit fluid flow rate, and/or the like) and thereby limit the maximum squeezing pressure being applied to the ballast  115  by the tamping tool  126 . 
         [0054]    Another advantage of the hydraulic system  132  as described herein is the ability to achieve a desired amount (e.g., amplitude and/or frequency) of vibration of the tamping tool  126  without introducing any throttle loss between the variable-displacement servo-pump  122  and the actuator  118 . In fact, by utilizing a dual-chambered actuator  118  (as well as other embodiments described herein), the hydraulic system  132  may not require any hydraulic valve to be positioned between the actuator  118  and the variable-displacement servo-pump  122  of the hydraulic system  132 . Instead, a direct hydraulic coupling (e.g., the hydraulic hose  130 ) may connect the variable-displacement servo-pump  122  directly to the actuator  118 . This capability of more easily adjusting vibration of the tamping tool  126  without utilizing hydraulic valves between the actuator  118  and the variable-displacement servo-pump  122  may provide a significant improvement to the field of art in terms of overall efficiency and fuel savings of the hydraulic system  132 . Prior to the present disclosure, hydraulic valves have been necessarily positioned between actuators and the displacement pumps in hydraulic systems to adjust vibrations of tamping pads, thereby introducing unwanted metering losses between the displacement pumps and the actuators. 
         [0055]    An alternative to utilizing a double rod actuator  118  as described with reference to  FIG. 3  that achieves the same end result of increased efficiency and fuel savings may include utilizing actuator system  154  as shown in  FIG. 4  instead of a double rod actuator  118 . Now referring to  FIG. 4 , the actuator system  154  may include two dual-chamber “single rod” actuators  118  (e.g., a first single rod actuator  118   a  and a second single rod actuator  118   b ) coupled together via pins  156  as shown in  FIG. 4 . The actuator system  154  may couple to the sub frame  124  of the tamping unit  106  via a first mounting port  158 . The actuator system  154  may couple to a tamping arm  116  via a second mounting port  160 . Each of the single rod actuators  118   a ,  118   b  may be driven by a variable-displacement servo-pump  122 , which may be coupled to each single rod actuator  118   a ,  118   b  via a hydraulic hose  130 . 
         [0056]    Similar to operation of the dual-chamber actuator  118  described with reference to  FIG. 3 , the actuator system  154  of  FIG. 4  may be utilized to control movement of the associated tamping tool  126  (via the tamping arm  116 ) in response to hydraulic fluid flowing into and/or out of a chamber of each single rod actuator  118   a ,  118   b  of the actuator system  154 . However, because the actuator system  154  may utilize two single rod actuators  118   a ,  118   b  to actuate and move the associated tamping arm  116  instead of one double rod actuator  118 , a first single rod actuator  118   a  of the actuator system  154  may be responsible for causing the associated tamping tool  126  to move in a first direction, while a both single rod actuators  118   a  and  118   b  of the actuator system  154  may be responsible for causing the associated tamping tool  126  to move in a second direction that is opposite the first direction. 
         [0057]    For example, with reference to the hydraulic schematic  162  of  FIG. 5A , a first single rod actuator  118   a  may be actuated when more hydraulic fluid is displaced within a first chamber of the first single rod actuator  118   a  than a second chamber of the first single rod actuator  118   a . Displacing more hydraulic fluid within the first chamber of the first single rod actuator  118   a  increases the pressure within the first chamber of the first single rod actuator  118   a , which thereby causes the first single rod actuator  118   a  to extend (e.g., translate, move, slide, and/or the like) along the actuator rod  119  disposed within the interior of the second chamber of the first single rod actuator  118   a  in a first direction. 
         [0058]    Unlike operation of the double rod actuator  118 , the actuator system  154  of  FIG. 4  that utilizes two single rod actuators  118  may require the variable-displacement servo-pump  122  to coordinate hydraulic fluid flow between both single rod actuators  118  of the actuator system  154 . Areas of high and low pressure (p High and p Low) and direction of flow rate (Q) are illustrated in  FIG. 5A  and  FIG. 5B . Accordingly, fluid may be displaced in and/or withdrawn from a first chamber of the second single rod actuator  118   b  to utilize, offset, and/or overcome the exerted force in the second direction. 
         [0059]    While various embodiments of an apparatus and method for moving and vibrating tamping tools have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents. Moreover, the above advantages and features are provided in described embodiments, but shall not limit the application of the claims to processes and structures accomplishing any or all of the above advantages. 
         [0060]    Additionally, the section headings herein are provided for consistency with the suggestions under 37 CFR 1.77 or otherwise to provide organizational cues. These headings shall not limit or characterize the invention(s) set out in any claims that may issue from this disclosure. Specifically and by way of example, a description of a technology in the “Background” is not to be construed as an admission that technology is prior art to any invention(s) in this disclosure. Neither is the “Brief Summary” to be considered as a characterization of the invention(s) set forth in the claims found herein. Furthermore, any reference in this disclosure to “invention” in the singular should not be used to argue that there is only a single point of novelty claimed in this disclosure. Multiple inventions may be set forth according to the limitations of the multiple claims associated with this disclosure, and the claims accordingly define the invention(s), and their equivalents, that are protected thereby. In all instances, the scope of the claims shall be considered on their own merits in light of the specification, but should not be constrained by the headings set forth herein.