Patent Publication Number: US-8966792-B2

Title: Machine having dipper actuator system

Description:
TECHNICAL FIELD 
     The present disclosure is directed to a dipper actuator system and, more particularly, to a machine having a dipper actuator system. 
     BACKGROUND 
     Power shovels are in a category of excavation equipment used to remove large amounts of overburden and ore during a mining operation. One type of power shovel is known as a rope shovel. Another type of power shovel is known as a dredge, and dredges are typically used to remove material from below a waterline. A rope shovel includes a boom, a dipper handle pivotally connected to a mid-point of the boom, and a bucket (also known as a dipper) pivotally connected at one end of the dipper handle. A cable extends over a sheave at a distal end of the boom and terminates at the end of the dipper handle supporting the dipper. The cable is reeled in or spooled out by electric, hydraulic, and/or mechanical motors to selectively raise and lower the dipper. 
     In most rope shovels or dredges, the dipper includes a door that is selectively swung open to dump material from the dipper into a waiting haul vehicle. The door is pivotally connected at one edge to a dipper body, and mechanically latched at an opposing edge. A cable extends from an operator cabin over a boom-mounted sheave to the dipper latch. In this configuration, an operator can actuate the latch from inside a cabin of the shovel by tensioning the cable. When the dipper is held vertically, tensioning the cable causes the latch to release the door and the door falls open under the force of gravity. When the dipper is held horizontally, the door swings shut against the dipper body under the force of gravity, and the latch is biased to re-engage and hold the door in the closed position. 
     Although adequate for some applications, use of the cable to manually cause actuation of the dipper latch can be problematic. In particular, typical latches and associated cable linkages are under tremendous strain and cycle continuously. As a result, these components suffer high-cycle fatigue and must be serviced frequently to ensure that the latch operates effectively when manipulated by the operator via the cable. This frequent servicing results in machine downtime and lost productivity. Accordingly, an alternative source of control at the dipper latch is desired. 
     One attempt to improve durability of the dipper is disclosed in U.S. Pat. No. 8,136,272 that issued to Hren et al. on Mar. 20, 2012 (“the &#39;272 patent”). Specifically, the &#39;272 patent discloses a dipper door latch having a hydraulic cylinder that is remotely activated to selectively lock and unlock movement of the door. The cylinder is a double-acting cylinder having opposing chambers connected to each other by way of a closed loop. A solenoid operated valve, powered by a battery pack located at the dipper, controls fluid flow between the chambers in response to a remotely-transmitted signal from the operator. An accumulator is connected to the loop to accommodate volume differences between the chambers. 
     Although the dipper door latch of the &#39;272 patent may have improved durability because it no longer requires mechanical connection to the cab of the power shovel, it may still be problematic. In particular, the double-acting nature of the cylinder increases a complexity of the latch and the potential for malfunction. Further the location and configuration of the latch and hydraulic cylinder could result in elevated wear. 
     The exemplary embodiments of the present disclosure solve one or more of the problems set forth above. 
     SUMMARY 
     In an exemplary embodiment of the present disclosure, an actuator system for a machine includes a linear hydraulic actuator connected to a dipper of the machine, and a hydraulic system fluidly connected to the actuator and configured to selectively direct fluid to the actuator. A component of the hydraulic system is mounted on the dipper. The system also includes an overcenter link coupled to a door of the dipper and biased to maintain the door in a closed position. A piston assembly of the actuator is configured to move the overcenter link in a first direction, via contact between the piston assembly and the overcenter link, thereby transitioning the door from the closed position to an open position. 
     In another exemplary embodiment of the present disclosure, an actuator system for a machine includes a linear hydraulic actuator connected to a dipper of the machine The actuator includes a tube and a piston assembly associated with the tube. The dipper includes a body having a front side including an excavation opening, a back side opposite the front side, a top surface, and a door. The door is moveable between a closed position in which the door is disposed adjacent to the back side and an open position in which the door is disposed away from the back side. The dipper is connected to the machine via a boom extending from the machine, and via a dipper handle pivotally connected to a midpoint of the boom. The actuator system also includes a hydraulic system having a component disposed on the dipper. The hydraulic system is configured to selectively direct fluid to the actuator. The actuator system further includes an overcenter link connected to the door. The piston assembly contacts the overcenter link such that selectively directing fluid to the actuator causes the piston assembly to move the overcenter link relative to the body, and transitions the door between the open and closed positions. 
     In a further exemplary embodiment of the present disclosure, a method of operating a machine includes selectively directing fluid between a hydraulic system, having a component disposed on a dipper of the machine, and a linear hydraulic actuator connected to the dipper. The actuator includes a tube and a piston assembly associated with the tube. The method also includes contacting an overcenter link connected to a door of the dipper with the piston assembly. In such a method, selectively directing fluid between the hydraulic system and the actuator causes the piston assembly to move the overcenter link and transitions the door to an open position in which the door is disposed away from a body of the dipper. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic illustration of an exemplary disclosed machine; 
         FIG. 1   a  is a diagrammatic illustration of another exemplary disclosed machine; 
         FIG. 2  is a diagrammatic illustration of an exemplary disclosed actuator system associated with the machines of  FIGS. 1 and 1   a , the actuator system being in a closed position; 
         FIG. 3  is another diagrammatic illustration of the actuator system shown in  FIG. 2 , the actuator system being in an open position; 
         FIG. 4  is a further diagrammatic illustration of the actuator system shown in  FIG. 2 , the actuator system being transitioned to the closed position; 
         FIG. 5  is an illustration of another exemplary disclosed actuator system associated with the machines of  FIGS. 1 and 1   a;    
         FIG. 6  is a side view of a portion of the actuator system shown in  FIG. 5 ; 
         FIG. 7  is an illustration of another exemplary disclosed actuator system associated with the machines of  FIGS. 1 and 1   a;    
         FIG. 8  is a side view of a portion of the actuator system shown in  FIG. 7 ; and 
         FIG. 9  is an illustration of another exemplary disclosed actuator system associated with the machines of  FIGS. 1 and 1   a.    
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 and 1   a  illustrate exemplary embodiments of a machine  10 . Machine  10  may perform any type of operation associated with an industry such as mining, construction, excavation, or any other industry known in the art. For example, machine  10  may embody an earth moving machine such as the power shovel depicted in  FIG. 1  or the dredge depicted in  FIG. 1   a . In the exemplary embodiment of  FIG. 1 , machine  10  may include a base  12 , a body  14  operatively connected to base  12 , a gantry member  16  rigidly mounted to a top side of body  14  opposite base  12 , a boom  18  pivotally connected to a leading end of body  14 , a dipper handle  20  pivotally connected to a midpoint of boom  18 , a tool  22  pivotally connected to a distal end of dipper handle  20 , and cabling connecting gantry member  16 , boom  18 , dipper handle  20 , and tool  22 . In the exemplary embodiment of  FIG. 1   a , machine  10  may include each of the components noted above, except that base  12  may be placed with a barge  12   a  configured to support machine  10  in aqueous and/or semi-aqueous environments. 
     Base  12  (or barge  12   a ) may be a structural unit that supports movements of machine  10 . In the disclosed exemplary application, base  12  is itself movable, having one or more traction devices such as feet, tracks (shown in  FIG. 1 ), and/or wheels that are driven to propel machine  10  over a work surface  24 . In other applications, however, base  12  may be a stationary platform configured for fixed engagement with work surface  24 . As shown in  FIG. 1   a , in still further embodiments, barge  12   a  may be stationary and/or moveable over a body of water, and a work surface  24   a  may embody an underwater trench and/or other like underwater surface. In exemplary embodiments, at least a portion of barge  12   a  may be configured for fixed engagement with an underwater surface proximate work surface  24   a.    
     Body  14  may pivot relative to base  12  or barge  12   a  ( FIG. 1   a ). Specifically, body  14  may pivot relative to base  12  or barge  12   a  about a substantially vertical axis  26 . As body  14  is pivoted about axis  26 , attached gantry member  16 , boom  18 , dipper handle  20 , and tool  22  may likewise pivot to change a radial engagement angle of tool  22  with work surface  24 ,  24   a . In the exemplary embodiment of  FIG. 1 , tool  22  typically engages with the vertical portion of work surface  24 , and the horizontal portion of work surface  24  may be formed as a result of such engagement. The horizontal portion of work surface  24  may be removed by tool  22  in subsequent passes and/or by additional machines located proximate word surface  24 . Alternatively, in the exemplary embodiment of  FIG. 1   a , tool  22  may engage a working face and/or other portion of work surface  24   a  disposed below the waterline (i.e., underwater). Body  14  may house, among other things, a power source  28  that powers the movements of machine  10 . For ease of description, the exemplary embodiment of  FIG. 1  will be referred to for the duration of this disclosure unless otherwise specified. It is understood, however, that the exemplary actuator systems and/or other components described herein, as well as their respective methods of operation, may be used with the machines  10  (i.e., the power shovel of  FIG. 1  and the dredge of  FIG. 1   a ) illustrated in either of  FIGS. 1 and 1   a.    
     Gantry member  16  may be a structural frame member, for example a general A-frame member, that is configured to anchor one or more cables  30  to body  14 . Gantry member  16  may extend from body  14  in a vertical direction away from base  12 . Gantry member  16  may be located rearward of boom  18  relative to tool  22  and, in the disclosed exemplary embodiment, fixed in a single orientation and position. Cables  30  may extend from an apex of gantry member  16  to a distal end of boom  18 , thereby transferring a weight of boom  18 , tool  22 , and a load contained within tool  22  into body  14 . 
     Boom  18  may be pivotally connected at a base end to body  14 , and constrained at a desired vertical angle relative to work surface  24  by cables  30 . Additional cables  32  may extend from body  14  over a sheave mechanism  34  located at the distal end of boom  18  and around a sheave mechanism  36  of tool  22 . Cables  32  may connect tool  22  to body  14  by way of one or more motors and/or transmissions coupled to a drum (not shown), such that a rotation of the motors (and/or transmissions coupled to a drum) functions to reel in or spool out cables  32 . The reeling in and spooling out of cables  32  may affect the height and angle of tool  22  relative to work surface  24 . For example, when cables  32  are reeled in, the decreasing effective length of cables  32  may cause tool  22  to rise and tilt backward away from work surface  24 . In contrast, when cables  32  are spooled out, the increasing effective length of cables  32  may cause tool  22  to lower and tilt forward toward work surface  24 . 
     Dipper handle  20  may be pivotally connected at one end to a general midpoint of boom  18 , and at an opposing end to a corner of tool  22  adjacent sheave mechanism  36  (e.g., rearward of sheave mechanism  36 ). In this position, dipper handle  20  may function to maintain a desired distance of tool  22  away from boom  18  and ensure that tool  22  moves through a desired arc as cables  32  are reeled in and spooled out. In the disclosed embodiment, dipper handle  20  may be connected to boom  18  at a location closer to the base end of boom  18 , although other configurations are also possible. In some configurations, dipper handle  20  may be provided with a crowd cylinder (not shown) that functions to extend or retract dipper handle  20 . In this manner, the distance between tool  22  and boom  18  (as well as the arcuate trajectory of tool  22 ) may be adjusted. 
     Tool  22 , in the exemplary embodiments of the present disclosure, is known as a “dipper,” and the terms “tool  22 ” and “dipper” may be used interchangeably throughout this disclosure. A dipper is a type of shovel bucket having a dipper body  38 , and a dipper door  40  located at a back side of dipper body  38  opposite a front side excavation opening  42 . Dipper door  40  may be hinged along a base edge at the back side of dipper body  38 , so that it can be selectively pivoted to open and close dipper body  38  during an excavating operation. Dipper door  40  may be pivoted between the open and closed positions by gravity, and held closed or released by way of an actuator system  44 . For example, when tool  22  is lifted upward toward the distal end of boom  18  by reeling in of cables  32 , a releasing action of actuator system  44  may allow the weight of dipper door  40  (and any material within tool  22 ) to swing dipper door  40  downward toward work surface  24  and away from dipper body  38 . This motion may allow material collected within tool  22  to spill out the back side of dipper body  38 . In contrast, when tool  22  is lowered toward work surface  24 , the weight of dipper door  40  may cause dipper door  40  to swing back toward dipper body  38 . Actuator system  44  may then be caused to lock dipper door  40  in its closed position. 
     In the disclosed embodiments, actuator system  44  may be remotely controlled, such as by way of an electric signal, a hydraulic signal, a pneumatic signal, a radio signal, a wireless signal, or another type of signal known in the art. It is contemplated, however, that a cable may alternatively be mechanically connected to and used to activate actuator system  44 , if desired. 
       FIGS. 2-4  provide partial schematic illustrations of actuator system  44  in use to open and close dipper door  40 . Additional exemplary embodiments of actuator system  44  will be described in greater detail below with respect to  FIGS. 5-9 . As shown in  FIG. 2 , actuator system  44  may include a powered-type of hydraulic actuator that forms a part of and/or that is fluidly connected to an isolated hydraulic system  46  located at and, in some embodiments, mounted to tool  22 . For purposes of this disclosure, actuator system  44  may be construed as including hydraulic system  46  and/or various components thereof. For example, actuator system  44  may include one or more linear hydraulic actuators, such as hydraulic cylinders. Actuator system  44  may also include one or more rotary hydraulic actuators, such as hydraulic motors. The hydraulic actuators of actuator system  44  may be selectively activated to initiate opening of dipper door  40 , and/or to assist in closing and/or locking dipper door  40  in the closed position. Hydraulic system  46  may be considered an isolated system, as it may be self-contained and self-powered, not requiring fluid connection or powered support from other components or systems within base  12  or body  14  of machine  10 . 
     In the exemplary partial schematic illustrations of  FIGS. 2-4 , actuator system  44  is shown as including a single-acting linear hydraulic actuator (i.e., a hydraulic cylinder) operatively connected between dipper body  38  and the base edge of dipper door  40 . In such exemplary embodiments, the linear hydraulic actuator of actuator system  44  includes a tube  48 , and a piston assembly  50  disposed within and extendable from tube  48  to form a head-end chamber  52  and a rod-end chamber  54 . One of tube  48  and piston assembly  50  may be pivotally connected to dipper body  38 , while the other may be pivotally connected to dipper door  40  by way of one or more eccentric links  56  and an overcenter link  58  that is coupled to eccentric links  56 . In exemplary embodiments, such links  56 ,  58  may also be construed as components of actuator system  44 . 
     As a single-acting cylinder, only one of head-end chamber  52  and rod-end chamber  54  may ever be filled with hydraulic fluid. In the exemplary configuration shown in  FIG. 2 , head-end chamber  52  functions as the sole pressure chamber for the linear actuator. As door  40  opens under the force of gravity (see  FIG. 3 ), piston assembly  50  may be forced to retract into tube  48 , thereby discharging any fluid within head-end chamber  52  at high-pressure from the linear actuator. In contrast, as door  40  closes under the force of gravity (see  FIG. 4 ), piston assembly  50  may be forced to extend from tube  48 , thereby drawing low-pressure fluid into head-end chamber  52 . It is contemplated that rod-end chamber  54  could alternatively function as the sole pressure chamber for the linear actuator (e.g., when the orientation of the linear actuator is reversed), if desired. It is further contemplated that actuator system  44  could alternatively include a double-acting linear actuator or a double-acting rotary actuator. It should be noted that, in some embodiments, more than one substantially identical linear or rotary hydraulic actuators may be associated with a single tool  22 . In these embodiments, the hydraulic actuators may be disposed in parallel and controlled simultaneously to cooperatively open and close dipper door  40 . 
     Hydraulic system  46  may include additional components that interact with actuator system  44  to selectively allow or block movement of dipper door  40 , as well as recuperate energy associated with the movement. In particular, although not illustrated in  FIGS. 2-4 , in exemplary embodiments hydraulic system  46  may include a low-pressure reservoir, an accumulator, and/or one or more control valves disposed between actuator system  44 , the reservoir, and the accumulator. Such a low-pressure reservoir may be fluidly connected to actuator system  44  via a supply passage  63 , while such a control valve may be fluidly connected to actuator system  44  via one or more additional passages (not shown) such as a control or return passage. The control valve may also be fluidly connected to the accumulator and the reservoir via a high-pressure passage and a low-pressure passage (not shown), respectively. Such components may provide a supply of pressurized fluid to and may receive pressurized fluid from actuator system  44  to assist in opening and closing dipper door  40 . For example, the control valve may include a valve element movable between different positions to selectively allow fluid to flow between head-end chamber  52 , accumulator, and reservoir. For example, the valve element may be movable from a first position (associated with dipper door  40  being in the closed position shown in  FIG. 2 ), at which fluid flow between head-end chamber  52 , accumulator, and reservoir, via control valve, may be inhibited, to a second flow-passing position (associated with dipper door  40  being in the open position shown in  FIG. 3 ) or a third flow-passing position (associated with the dipper door  40  returning to the closed position as shown in  FIG. 4 ). 
     Movement of the valve element described above with respect to hydraulic system  46  may be controlled to regulate operation of actuator system  44  and tool  22 . Specifically, the valve element may be solenoid-operable to move from the first position described above with respect to  FIG. 2 , to either of the second or third flow-passing positions based on a wired or wirelessly transmitted control signal generated by an operator of machine  10 . In exemplary embodiments, the valve element may be spring-biased toward the first position. When the valve element is moved to the first position (referring to  FIG. 2 ) and all fluid flow through the associated control valve of hydraulic system  46  is inhibited, actuator system  44  may be hydraulically locked. That is, fluid within head-end chamber  52  may be trapped when the valve element is in the first position, thereby blocking extension and retraction of piston assembly  50 . When dipper door  40  is closed and actuator system  44  is hydraulically locked, it may not be possible for dipper door  40  to open. 
     Further, due to interaction between overcenter link  58  and eccentric link  56 , and/or between overcenter link  58  and other dipper door linkages, overcenter link  58  may be biased to maintain dipper door  40  in the closed position shown in  FIG. 2 . In particular, the limited path of travel, shape, size, and/or other configurations of eccentric link  56 , alone or in combination with other dipper door linkages, may assist in providing a mechanical advantage and/or other like biasing force to overcenter link  58  while dipper door  40  is in the closed position. Such mechanical advantage and/or other like biasing force may assist in maintaining dipper door  40  in the closed position until this biasing force is overcome by actuator system  44 . 
     In contrast, when the valve element of hydraulic system  46  is moved to the second flow-passing position (referring to  FIG. 3 ), actuator system  44  may no longer be hydraulically locked. In this state, when dipper body  38  is oriented upward (i.e., such that excavation opening  42  is oriented away from work surface  24 ) and the force of dipper door  40  (and any material contained within dipper body  38 ) urges dipper door  40  to rotate clockwise (as viewed in  FIG. 3 ) toward work surface  24 , piston assembly  50  may be forced to retract within tube  48  and push fluid out of head-end chamber  52  at high pressure. This high-pressure fluid, containing significant potential energy in the form of pressure, may be directed from the hydraulic actuator of actuator system  44 , through the control valve, and into hydraulic system  46  where it may be collected and stored for later use. 
     When the valve element of hydraulic system  46  is moved to the third flow-passing position and dipper body  38  is oriented forward (e.g., rotated about 90° clockwise from the upward orientation), the gravitational force acting on dipper door  40  may urge dipper door  40  to rotate counterclockwise (as viewed in  FIG. 4 ), causing piston assembly  50  to extend from tube  48  and draw in fluid from hydraulic system  46  via supply passage  63 . In further exemplary embodiments, such valve element movement, positions, fluid flow directions, and/or other operations of hydraulic system  46  may be reversed such that hydraulic system  46  may direct pressurized fluid to actuator system  44  to assist in, for example, transitioning dipper door  40  from the closed position illustrated in  FIG. 2  to the open position illustrated in  FIG. 3 . In such embodiments, fluid directed from hydraulic system  46  to actuator system  44  may, for example, extend piston assembly  48  from tube  50 . Due to one or more connections and/or contact between, for example, piston assembly  48  and overcenter link  58 , such movement of piston assembly  48  may result in corresponding movement of overcenter link  58 , thereby transitioning dipper door  40  from the closed position to the open position. 
     It is understood that components of hydraulic system  46  may additionally be used as a “snubber” for actuation system  44 , if desired. In particular, in some embodiments, the control valve described above may be moveable to a position between the first and second positions (shown in  FIGS. 2 and 3 , respectively) and/or to a position between the first and third positions (shown in  FIGS. 2 and 4 , respectively). In either of these intermediate positions, the flow of fluid from head-end chamber  52  and/or into head-end chamber  52  may be metered to a rate that effectively slows and cushions the pivoting movement of dipper door  40 . Further, although the operation of actuator system  44  and hydraulic system  46  have been described above with respect to the linear hydraulic actuator shown in  FIGS. 2-4 , in exemplary embodiments in which actuator system  44  comprises one or more rotary hydraulic actuators, the operation of actuator system  44  and hydraulic system  46  may be substantially identical to that described above. 
     The embodiments shown in  FIGS. 5-9  illustrate various additional exemplary actuator systems  44  configured for use with machine  10 . Although not illustrated in  FIGS. 5-9 , it is understood that hydraulic system  46  may be fluidly, operably, and/or otherwise connected to the various actuators of actuator system  44 , and configured to selectively direct fluid, such as such as oil, hydraulic fluid, and/or other incompressible working fluids, to the various actuators. In such exemplary embodiments, at least one component of hydraulic system  46  may be disposed and/or otherwise mounted on tool  22 . 
     As shown in  FIGS. 5 and 6 , an exemplary embodiment of actuator system  44  may comprise at least one linear hydraulic actuator  47  connected to the dipper. Linear actuator  47  may be connected directly to a top surface  62  of dipper body  38 . Alternately, linear actuator  47  may be connected proximate top surface  62 , and may be spaced from top surface  62  by one or more mounting brackets, flanges, spacers, and/or other like mounts  76 . In exemplary embodiments, linear actuator  47  may be rotatably connected to and/or proximate top surface  62 . For example, tube  48  of linear actuator  47  may be rotatably connected to the dipper, such as proximate top surface  62 , via mounts  76 . In such embodiments, tube  48  may be configured to rotate relative to top surface  62  in response to activation of linear actuator  47 . It is understood that linear actuator  47  may be activated by directing fluid from hydraulic system  46  to linear actuator  47  and/or by directing fluid from linear actuator  47  to hydraulic system  46 . In further embodiments, the orientation of linear actuator  47  may be reversed such that piston assembly  50  may be rotatably connected to the dipper, such as proximate top surface  62 . 
     Mounts  76  may project substantially perpendicularly from top surface  62  and may have any shape, size, and/or other configuration required to assist in securing linear actuator  47  to top surface  62 . In exemplary embodiments, one or more bearings, bushings, washers, and/or other like components may be disposed at the interface between linear actuator  47  and flange mounts  76  to assist in rotation of, for example, tube  47  relative to mounts  76  while minimizing friction and/or wear caused by such relative motion. 
     As described above, overcenter link  58  may be coupled to tool  22  (i.e., the dipper of machine  10 ) via eccentric link  56 , and in the embodiment of  FIGS. 5 and 6 , linear actuator  47  may be in direct contact with eccentric link  56  and/or overcenter link  58 . Due to such contact, activation of linear actuator  47  may result in movement of overcenter link  58  and/or eccentric link  56  relative to, for example, top surface  62 . For example, as will be described in greater detail below, at least one component of linear actuator  47  may be configured to slide, roll, push, and/or otherwise move along overcenter link  58 , such as along an underside and/or other outer surface of overcenter link  58 . Such movement along overcenter link  58  may cause movement of overcenter link  58  in a first direction, and may thereby transition dipper door  40  from the closed position to the open position. 
     It is understood that movement of overcenter link  58  in such a first direction may comprise one or more of linear, arcuate, rotational, pivotal, and/or other like movement of overcenter link  58 . For example, movement of overcenter link  58  may be governed by the connection between overcenter link  58 , eccentric link  56 , and the various other linkages illustrated but not explicitly labeled in  FIG. 5 . Accordingly, movement of overcenter link  58  in such a first direction may be characterized generally as movement toward the back side of dipper body  38  and/or away from front side excavation opening  42  ( FIG. 1 ). In exemplary embodiments, such movement in the first direction may transition dipper door  40  from the closed position described above in which dipper door  40  is disposed adjacent to the back side of dipper body  38  to the open position in which dipper door  40  is disposed away from the back side of dipper body  38 . Further, in some embodiments, such movement of overcenter link  58  in the first direction may comprise a combination of one or more movements. Such a combination of movements may be required to overcome the mechanical advantage and/or other biasing force applied to overcenter link  58  by, for example, eccentric link  56 , and may comprise a pivoting and/or rotational movement of overcenter link  58  toward the back side of dipper body  38  as the eccentric link  56  shown in  FIG. 5  rotates counterclockwise. Such a combination of movements may also include an arcuate and/or substantially linear movement of overcenter link  58  away from top surface  62  of dipper body  38  and/or toward front side excavation opening  42  when dipper door  40  swings open. 
     As shown in at least  FIG. 5 , eccentric link  56  may be rotatably coupled to overcenter link  58 , and may be coupled to top surface  62  via one or more flanges  64  projecting from top surface  62 . Flanges  64  may project substantially perpendicularly from top surface  62  and may have any shape, size, and/or other configuration required to assist in securing eccentric link  56  to top surface  62 . In exemplary embodiments, one or more bearings, bushings, washers, and/or other like components may be disposed at the interface between eccentric link  56  and flange  64  to assist in rotation of eccentric link  56  relative to flange  64  while minimizing friction and/or wear caused by such relative motion. In the exemplary embodiment of  FIGS. 5 and 6 , overcenter link  58  may be movably connected to the dipper via first and second eccentric links  56 . 
     As shown in  FIGS. 5 and 6 , in exemplary embodiments of the present disclosure, piston assembly  50  may include a cam  66  configured to contact overcenter link  58 . In such embodiments, activation of linear actuator  47  may move cam  66  against and/or otherwise along a surface of overcenter link  58 . Such movement may push and/or otherwise move overcenter link  58  in the first direction and may thereby transition dipper door  40  from the closed position to the open position. 
       FIG. 6  illustrates a side view of a portion of the exemplary actuator system  44  shown in  FIG. 5 . As shown in  FIG. 6 , in an exemplary embodiment, cam  66  may be connected to piston assembly  50  and may be moveable with piston assembly  50  relative to tube  48  as one or more components of piston assembly  50  enters and/or exits tube  48 . In some exemplary embodiments, cam  66  may include one or more rollers  80 . Rollers  80  may comprise, for example, bearings, bushings, substantially cylindrical wheels, and/or other like structures configured to facilitate relative movement between cam  66  and overcenter link  58  while reducing friction and/or wear caused by such relative movement. In exemplary embodiments, rollers  80  may contact a surface of overcenter link  58 , and may rotate against and/or otherwise act on the surface of overcenter link  58  as cam  66  moves along overcenter link  58 . Accordingly, rollers  80  may be moveable relative to cam  66  and overcenter link  58  during movement of cam  66  against overcenter link  58 . Such relative movement of rollers  80  may facilitate movement of overcenter link  58  in the first direction to open dipper door  40 . As shown in  FIG. 5 , cam  66  may be positioned proximate top surface  62  such that at least a portion of cam  66 , such as rollers  80  ( FIG. 6 ), may be disposed beneath overcenter link  58  while dipper door  40  is in the closed position. For example, rollers  80  and/or other portions of cam  66  may be disposed between overcenter link  58  and top surface  62  while dipper door  40  is in the closed position. 
     In exemplary embodiments, cam  66  may move in a direction substantially parallel to top surface  62  to facilitate movement of overcenter link  58  in the first direction, and to thereby open dipper door  40 . In such embodiments, cam  66  may move along and/or on top surface  62 . In further exemplary embodiments, actuator assembly  44  may include a ramp  92  disposed proximate and/or on top surface  62 . In such embodiments, ramp  92  may be in contact with cam  66 , and cam  66  may move along a surface of ramp  92  in response to activation of linear actuator  47 . For example, ramp  92  may include a top surface oriented at an inclined angle relative to top surface  62 . Ramp  92  may include, for example, a first end disposed adjacent cam  66 , and a second end disposed away from cam  66  and/or closer to dipper door  40  than the first end of ramp  92 . In such embodiments, the first end of ramp  92  may be disposed closer to top surface  62  (i.e., relatively lower than) the second end of ramp  92 . Accordingly, movement of cam  66  along ramp  92  from the first end to the second end (i.e., from front to back) thereof may elevate cam  66  from top surface  62 . In exemplary embodiments, a top surface of ramp  92  interfacing with cam  66  may be substantially linear from the first end to the second end. Alternatively, as shown in  FIG. 6 , a top surface of ramp  92  may be curved and/or substantially arcuate from the first end to the second end. 
     In exemplary embodiments, at least a portion of cam  66  may be disposed between overcenter link  58  and ramp  92 . Accordingly, movement of cam  66  along ramp  92  from the first end of ramp  92  to the second end thereof may push overcenter link  58  away from top surface  62  and/or otherwise move overcenter link  58  in the first direction described above. Ramp  92  may be configured such that movement of cam  66  from the first end to the second end thereof may overcome the mechanical advantage and/or other biasing force applied to overcenter link  58 , and may assist in transitioning dipper door  40  from the closed position to the open position. Additionally, movement of cam  66  from the first end to the second end of ramp  92  may rotate linear actuator  47  relative to top surface  62 . From the perspective of  FIGS. 5 and 6 , such rotation of linear actuator  47  may be in the clockwise direction. 
       FIGS. 7 and 8  illustrate an exemplary embodiment of actuator system  44  similar to the embodiment shown in  FIGS. 5 and 6 , however, in the exemplary embodiment of  FIGS. 7 and 8 , actuator system  44  includes one or more cam guides in place of ramp  92 . For example, cam guides  94 ,  96  may be disposed proximate top surface  62  of dipper body  38  and adjacent to cam  66 . In exemplary embodiments, cam guides  94 ,  96  may be structurally similar to flanges  64 . For example, cam guides  94 ,  96  may project substantially perpendicularly from top surface  62  and may have any shape, size, and/or other configuration required to assist in guiding movement of cam  66  relative to top surface  62  and/or overcenter link  58 . 
     In exemplary embodiments, each cam guide  94 ,  96  may include one or more slots  98  configured to assist in guiding motion of cam  66  upon activation of linear actuator  47 . For example, cam  66  may contact, extend at least partially into, and/or otherwise be in communication with each respective slot  98  such that activation of linear actuator  47  may move cam  66  along slot  98 . In exemplary embodiments, one or more bearings, bushings, washers, and/or other like components may be disposed at the interface between cam  66  and slot  98  to assist in movement of cam  66  along, adjacent to, and/or within slot  98 , while minimizing friction and/or wear caused by such relative motion. In exemplary embodiments, cam  66  may include one or more pins  100  extending at least partially into and/or otherwise engaged with a respective slot  98 . In such embodiments, pin  100  may be configured to move along slot  98  in response to activation of linear actuator  47 , and movement of pin  100  within and/or otherwise along slot  98  may govern the movement of cam  66 . 
     As described above with respect to ramp  92 , each slot  98  may include a first end disposed closer to top surface  62  (i.e., relatively lower than) a second end of ramp  92 . Accordingly, movement of cam  66  along slot  98  from the first end to the second end thereof may elevate cam  66  from top surface  62 . In exemplary embodiments, slot may be substantially linear from the first end to the second end. Alternatively, as shown in  FIGS. 7 and 8 , slot  98  may be curved and/or substantially arcuate. 
     In exemplary embodiments, movement of cam  66  along slot  98  from the first end to the second end thereof may push overcenter link  58  away from top surface  62  and/or otherwise move overcenter link  58  in the first direction described above. Slot  98  may be configured such that movement of cam  66  from the first end to the second end thereof may overcome the mechanical advantage and/or other biasing force applied to overcenter link  58 , and may assist in transitioning dipper door  40  from the closed position to the open position. Additionally, movement of cam  66  from the first end to the second end of slot  98  may rotate linear actuator  47  relative to top surface  62 . From the perspective of  FIGS. 7 and 8 , such rotation of linear actuator  47  may be in the clockwise direction. 
     As shown in  FIG. 9 , in another exemplary embodiment of actuator system  44 , tube  48  of linear actuator  47  may be fixedly mounted proximate top surface  62 . In exemplary embodiments, tube  48  may be fixedly mounted to top surface  62  and configured such that activation of linear actuator  47  may cause piston assembly  50  to push against overcenter link  58  to thereby transition dipper door  40  between the closed and open positions, Alternatively, as shown in  FIG. 9 , the dipper may include a channel  104  formed within and/or otherwise proximate top surface  62 . In such embodiments, channel  104  may include a bottom surface  106  extending substantially parallel to top surface  62 , and a pair of opposing sidewalls extending substantially perpendicular to bottom surface  106 . As shown in  FIG. 9 , in such embodiments, tube  48  may be fixed at an inclined angle relative to bottom surface  106 . For example, the dipper may include one or more brackets, flanges, and/or other like mounts  76  connected to bottom surface  106  and/or sidewalls. Such mounts  76  may assist in fixing tube  48  at an inclined angle relative to bottom surface  106 . Due to this configuration, movement of piston assembly  50  against overcenter link  58  may cause overcenter link  58  to move in the first direction described above, thereby transitioning dipper door  40  from the closed position to the open position. In particular, due to the positioning of linear actuator  47  relative to overcenter link  58 , a portion of piston assembly  50  may maintain a substantially fixed orientation relative to overcenter link  58  upon activation of linear actuator  47 . For example, piston assembly  50  may maintain a substantially fixed orientation relative to overcenter link  58  as overcenter link  58  moves in the first direction. 
     As shown in  FIG. 9 , in exemplary embodiments, piston assembly  50  may include a rounded and/or substantially spherical ball end  102 . Ball end  102  may be configured to mate with overcenter link  58  and, as described above, ball end  102  may maintain a substantially fixed orientation relative to overcenter link  58  upon activation of linear actuator  47  and/or as overcenter link  58  moves in the first direction. In such exemplary embodiments, overcenter link  58  may include a substantially rounded and/or concave pocket  108  configured to mate with ball end  102  upon activation of linear actuator  47 . Such a pocket  108  may assist in maintaining the substantially fixed relationship between ball end  102  and overcenter link  58  during movement of overcenter link  58 . 
     It is understood that linear actuator  47  illustrated in  FIGS. 5-9  may be substantially structurally and/or functionally identical to the linear hydraulic actuators described above with respect to  FIGS. 2-4 . For example, each linear actuator  47  may include a tube  48  and a piston assembly  50 , and although not shown in  FIGS. 5-9 , each linear actuator  47  may also include a head-end chamber  52 , a rod-end chamber  54 , and/or various other fluid control components as described above with respect to  FIGS. 2-4 . Additionally, although  FIGS. 5-9  illustrate exemplary embodiments employing a single linear actuator  47 , in further exemplary embodiment, actuator system  44  may comprise more than one linear actuator  47  configured to act on overcenter link  58  and/or eccentric link  56 . Moreover, it is contemplated that in the embodiments of  FIGS. 5-9 , actuator system  44  may comprise one or more rotary hydraulic actuators in addition to and/or instead of the linear actuators  47  illustrated therein. 
     Industrial Applicability 
     The disclosed dipper actuator systems and associated hydraulic system may be used in any power shovel application where component longevity and reliability are desired. The disclosed actuator systems may have improved longevity and reliability because of the reduction of conventional components (e.g., latches, cables, wires, passages, etc.) that stretch and shrink during dipper handle extensions and retractions. Operation of hydraulic system  46  and actuator system  44  will now be explained. 
     Referring to  FIG. 1 , the operator of machine  10  may raise, lower, and tilt tool  22  by causing cables  32  to be reeled in or spooled out. When tool  22  is oriented in the appropriate position (oriented such that the force of gravity generates a clockwise moment on dipper door  40 ) and the operator of machine  10  desires dipper door  40  of tool  22  to open, the operator may indicate this desire by way of an input device (not shown) located within the cabin of machine  10 . A corresponding signal may be generated and wirelessly transmitted to, for example, dipper control valve (not shown) of hydraulic system  46 , causing control valve to open. As shown in the exemplary configuration of  FIGS. 2 and 3 , such control may hydraulically unlock an actuator of actuator system  44  such that, for example, fluid within head-end chamber  52  may be free to flow through supply passage  63  into hydraulic system  46 . At this time, the gravitational force acting on dipper door  40  may cause dipper door  40  to rotate away from dipper body  38  and push piston assembly  50  into tube  48 . This retraction of piston assembly  50  may effectively reduce the volume of head-end chamber  52 , causing fluid to be discharged from dipper actuator  40  at high-pressure. The high-pressure fluid may be collected within hydraulic system  46  for later use. Such dipper door movement and corresponding fluid flow is illustrated in, for example,  FIG. 3 . In some embodiments, the flow of fluid discharged from head-end chamber  52  may be restricted to some degree to slow and/or cushion the opening movements of dipper door  40 . In exemplary embodiments, hydraulically unlocking actuator system  44  as described above may not necessarily result in movement of dipper door  40 . Instead, dipper door  40  may only move when tool  22  is oriented to allow gravity to pull dipper door  40  open after actuator system  44  has been unlocked by, for example, movement of the control valve associated with hydraulic system  46 . 
     Dipper door  40  may close any time its orientation is such that gravity pulls dipper door  40  closed (i.e., any time that gravity generates a moment in the counterclockwise direction—as viewed from the perspective of  FIG. 4 ). During the closing movement of dipper door  40 , piston assembly  50  may be retracted out of tube  48 , thereby increasing the effective volume of head-end chamber  52 . This expansion may draw fluid from hydraulic system  46  through supply passage  63  into actuator system  44 . 
     It is understood that the high-pressure fluid collected by actuator system  44  and hydraulic system  46  during, for example, opening of dipper door  44  may be used as a remote power source for other actuators associated with tool  22 . The remote and isolated nature of actuator system  44  and hydraulic system  46  may reduce cost and routing complexity, while at the same time improving durability of machine  10 . 
     Additionally, although the above methods of operation of actuator system  44  and hydraulic system  46  have been explained with respect to the hydraulic actuators of  FIGS. 2-4 , the exemplary embodiments of  FIGS. 5-9  may be characterized by substantially similar methods of operation. For example, the fluid communication between hydraulic system  46  and linear actuators  47  shown in  FIGS. 5-9  may be substantially identical to that described above with respect to the hydraulic actuators shown in  FIGS. 2-4 . 
     It is also understood that although  FIGS. 2-4  illustrate high pressure fluid passing from actuator system  44  to hydraulic system  46  during the transition of dipper door from the closed position ( FIG. 2 ) to the open position ( FIG. 3 ), in additional exemplary embodiments, such fluid flow may be reversed. For example, in further embodiments, hydraulic system  46  may be configured to direct pressurized fluid to linear actuators  47  of actuator system  44  to facilitate opening dipper door  40 . In particular, in such exemplary embodiments, pressurized hydraulic fluid may be directed to linear actuators  47  to activate such actuators  47 . Such activation, in response to receipt of pressurized fluid from hydraulic system  46 , may be sufficient to move overcenter link  58  in the first direction described above, thereby transitioning dipper door  40  from the closed position to the open position. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed power shovel and dipper actuator. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed power shovel and dipper actuator. It is intended that the specification and example be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.