Patent Publication Number: US-2011056805-A1

Title: Moving floor hydraulic actuator assemblies

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/239,925, filed Sep. 4, 2009. 
    
    
     BACKGROUND OF THE INVENTION 
     This disclosure relates to hydraulic and electro-hydraulic actuator assemblies for slat-type reciprocating conveyors or moving floors, and, more particularly, to hydraulic and/or electro-hydraulic circuitry for controllable operation of slat-type moving floor systems. 
     A slat-type moving floor is generally a hydraulically-driven reciprocating conveyor that uses groups of interconnected floor slats to move a load along a linear path. Typically, the moving floor consists of movable floor slats arranged side-by-side in parallel, with each slat extending longitudinally along the length of a conveyance surface such as a tractor trailer floor. The floor slats are typically divided into three groups of slats, with every third slat interconnected to one another and to one of three cross-drive members, with the cross-drive members hydraulically-driven to extend together in unison to move the load forward and to retract one at a time. A load resting upon the floor slats may be conveyed longitudinally along the floor slats by first extending all slats in the desired direction of travel, retracting the slats one group at a time until all three groups of slats have been retracted to their original starting position, and repeating the sequence until the load has been moved to its desired location. 
     The friction between the load and the stationary slats resists movement of the load while the retracting slats return to their unextended or starting position. More or less groups of slats may be used, but most systems use three groups of slats with each group driven by a hydraulic fluid power actuator such as a piston and cylinder assembly. Such moving floor systems are sometimes referred to as three-cylinder systems. Conceptually, four groups of slats may be used, with all four groups extending in unison to move a load in the desired direction of travel. From an extended position, the slats may then be retracted one group at a time. However, the additional cylinder(s), associated cross-drive member, and other components needed for systems using more than three cylinders render such systems less practical. 
     Two-cylinder systems have been developed. One such system uses two groups of slats, with each group driven by a hydraulic fluid power actuator, and mechanical means for lowering or raising one group of slats at a time. For example, such system may include means for raising one group of slats at a time (with the load thereupon) while the other group of slats is retracted. Or such system may include means for lowering one group of slats at a time while the other group of slats (with the load thereupon) is extended. 
     Another two-cylinder system uses non-movable or static slats positioned between the movable slats, for example a narrower static slat between each movable slat or pair of independently movable slats. The load-contacting surface area of the narrower static slats provide enough friction when combined with the surface area of the non-moving group of slats to substantially prevent the load from moving when one of the movable groups of slats is retracted. 
     Single-cylinder systems may be possible. Conceptually, such systems may use non-longitudinally-movable or longitudinally static slats positioned between slats of a single group of longitudinally movable slats, the longitudinally movable slats driven by a hydraulic fluid power actuator, and mechanical means for alternately lowering and raising either the longitudinally movable group of slats or the non-longitudinally-movable ones. For example, the longitudinally movable slats may be configured so as to raise (with the load thereupon) to above the level of the longitudinally static slats when extending and then lower (allowing the load to rest upon the longitudinally static slats) when retracting. Or, alternatively, the longitudinally static slats may be configured to lower into a lowered position when the longitudinally movable slats (with the load thereupon) are extended and to raise into a raised position (lifting the load from the longitudinally movable slats) when the longitudinally movable slats are retracted. 
     Slat-type moving floors may be used for moving a wide variety of material, from bulk material such as shredded tires or refuse to palletized product, in warehouse, loading, semi-trailer or other applications. A moving floor-equipped trailer, for example, allows for unloading of the trailer without requiring the use of forklifts or other material handling equipment to extract the load, or without the need for tipping the floor of the trailer to dump the load. Prior moving floor-equipped trailers, however, employ so-called three-cylinder slat-type moving floor systems that use a set of three cylinders for actuation of the floor for movement of the load in one direction (i.e. for unloading a trailer) but require (if equipped) a second set of three oppositely oriented cylinders for actuation of the floor for movement of the load in the opposite direction (i.e. for loading). 
     Although different slat-type moving floor systems have been developed, most incorporate less-than-desirable actuator assembly designs requiring multiple hydraulic connections and comprising multiple separate parts, which in turn increases the number of failure modes and disadvantages with such systems. Other actuator assembly designs have been rejected in the marketplace due to poor quality or poor design, a lack of available features, difficulty of use, or other factors. 
     What is needed, therefore, are moving floor actuator assembly designs that offer features, capabilities, and improvements which are unavailable in actuators currently designed systems. 
     The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL DRAWINGS 
       For a more complete understanding of the present invention, the drawings herein illustrate examples of the invention. The drawings, however, do not limit the scope of the invention. Similar references in the drawings indicate similar elements. 
         FIG. 1  is an exemplary slat-type moving floor system incorporating an electro-hydraulic actuator assembly, according to one embodiment. 
         FIG. 2  is a perspective partially transparent view of an exemplary electro-hydraulic actuator assembly as in  FIG. 1 , according to one embodiment. 
         FIG. 3  is an exemplary hydraulic circuit for an electro-hydraulic actuator assembly as in  FIGS. 1 and 2 , according to various embodiments. 
         FIG. 4  is an exemplary partial cross-sectional view of an electro-hydraulic actuator assembly as in  FIG. 2 , according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, those skilled in the art will understand that the present invention may be practiced without these specific details, that the present invention is not limited to the depicted embodiments, and that the present invention may be practiced in a variety of alternate embodiments. In other instances, well known methods, procedures, components, and systems have not been described in detail. 
     Various operations will be described as multiple discrete steps performed in turn in a manner that is helpful for understanding the present invention. However, the order of description should not be construed as to imply that these operations are necessarily performed in the order they are presented, nor even order dependent. 
     By way of general overview and as shown in  FIG. 1 , an exemplary slat-type moving floor system  100  incorporating a hydraulic moving floor actuator assembly  102 , according to one embodiment, may comprise a load-conveying side-by-side (or parallel) arrangement of floor slats  104  upon which a load may be conveyed longitudinally along the slats as the slats reciprocate between a retracted position and an extended position via mechanical linkages to cross drives  106 , which are in turn hydraulically driven by the moving floor actuator assembly  102 . The moving floor actuator assembly  102  may be controlled by a control console  108  or other control device. 
     The system shown in  FIG. 1  includes an arrangement of floor slats  104  having every third floor slat interconnected to one another to form a group of slats that may be extended and retracted together as a group. As shown, slats  112 ,  114 ,  116 , and  118  are interconnected to one another via a cross drive member  132 ; slats  120 ,  122 , and  124  are interconnected to one another via a second cross drive member  134 ; and slats  126 ,  128 , and  130  are interconnected to one another via a third cross drive member  136 . Each of the three cross drives (such as cross drives  132 ,  134 , and  136 ) is hydraulically driven by a separate longitudinally extensible piston rod (such as piston rods  138 ,  140 , and  142 , respectively) extending from the moving floor actuator assembly  102 , which in turn includes hydraulic fluid power cylinders and hydraulic and/or electro-hydraulic circuitry for controlling the longitudinal extensible position and movement of the piston rods. The moving floor actuator assembly  102 , as shown, receives pressurized hydraulic fluid via pump conduit  146 , returns hydraulic fluid via tank conduit  144 , and preferably receives electrical power and control signals via line  148 . In one embodiment a power source  110  (such as a 12 or 24 volt battery supply) may provide the electrical power to the control console  108  via line  150 . Other sub-systems (not shown) may include a power cooling assembly used for conditioning hydraulic fluid provided by a hydraulic pump coupled to, for example, a vehicle engine power-take-off (PTO) unit, a gas engine, a diesel engine, or an electric motor. 
     Although the moving floor actuator assembly  102  is shown and described in the context of a slat-type moving floor system having three groups of interconnected floor slats with each group hydraulically driven by one of three hydraulic fluid power cylinders, less preferred embodiments may employ a moving floor actuator assembly  102  with fewer than three hydraulic fluid power cylinders (for moving floor systems using few than three groups of interconnected floor slats) or more than three hydraulic fluid power cylinders (for moving floor systems using more than three groups of interconnected floor slats). The moving floor actuator assembly  102  is preferably, as shown, a substantially unitary (or integrated) device with a minimum of exposed or external hydraulic line connections and having electronics and hydraulic valving enclosed within the integrated device. Preferably, the moving floor actuator assembly  102  comprises a manifold that includes: hydraulic fluid power cylinders machined into the manifold; embedded electronic piston position sensors; screw-in, cartridge-type solenoid-controlled two-way valves; and an enclosed electronic controller for controlling the two-way valves in response to 1) piston position sensed by the piston position sensors (thereby providing automatic anti-jamming of the moving floor system) and 2) a user selection of desired operation such as, for example, forward for extending or unloading material (i.e. from a moving floor equipped trailer) or reverse for retracting or loading material. The enclosed electronic controller preferably comprises a pre-programmed non-adjustable electronic controller, electrically interconnected with the embedded electronic piston position sensors and the solenoid-controlled two-way valves. Preferably, the moving floor actuator assembly  102  allows for a moving floor system  100  comprising a minimum of tubes, hoses, tie rods, and other components. 
     A perspective partially transparent view of an exemplary electro-hydraulic actuator assembly  200  is shown in  FIG. 2 . In one embodiment, the moving floor actuator  102  comprises, as shown in  FIG. 2 , an actuator manifold  202 , an optional adaptor manifold assembly  266 , and a back cover (or rear housing) assembly  264 . The back cover assembly  264  preferably encloses and protects electronics associated with the actuator manifold  202  and valving extending from the rear portion of the actuator manifold  202 , and the optional adaptor manifold assembly  266  comprises various optional hydraulic circuitry for conditioning hydraulic fluid provided to and received from the actuator assembly  200 . The optional adaptor manifold assembly  266 , if included, may be attached directly to the actuator manifold  202  as shown, remotely located yet still hydraulically connected to the actuator manifold  202 , or integrated within the hydraulic circuitry incorporated within the actuator manifold  202  (with its associated back cover assembly  264 ). 
     As shown in  FIG. 2 , the piston rods  138 ,  140 , and  142  extend from the actuator manifold  202  for engagement with cross drives  132 ,  134 , and  136 , respectively. The piston rods  138 ,  140 , and  142  are shown longitudinally extensible from within substantially (physically) parallel cylindrical cavities  204 ,  206 , and  208 , respectively. The piston rods  138 ,  140 , and  142  are shown inserted into the rod end of the actuator manifold  202  and captured within the actuator manifold  202  by rod-end covers  210 ,  212 , and  214 , respectively, which in turn incorporate various seals so as to retain pressurized hydraulic fluid within the rod-end spaces in the cylinder cavities  204 ,  206 , and  208 . For example, the rod-end enclosures  210 ,  212 , and  214  are shown with rod wipers  216 ,  218 , and  220 , respectively; rod seals  222 ,  224 , and  226 , respectively; and rod wearing rings  228 ,  230 , and  232 , respectively. Also shown (and shown in more detail in  FIG. 4 ) are o-rings  234 ,  236 , and  238  and backup rings  240 ,  242 , and  244  positioned within appropriately dimensioned glands formed radially within the rod-end enclosures  210 ,  224 , and  226 , respectively, so as to provide (static) fluid tight closures for the cylinder cavities  204 ,  206 , and  208 . 
     Pistons  246 ,  248 , and  250  are shown in  FIG. 2  in longitudinally staggered positions within respective cylinder cavities  204 ,  206 , and  208 , with piston sealing rings  252 ,  254 , and  256 , respectively, and each with a pair of piston wear rings  258 ,  260 , and  262 , respectively. 
     Preferably, the manifold  202  comprises an aluminum block within which the cylinder cavities  204 ,  206 , and  208  are machined and within which the pistons and rods and other components are integrally assembled, substantially as shown in  FIG. 2 . In a less preferred embodiment, the manifold  202  may comprise a housing enclosing individual hydraulic fluid power cylinders assembled within the manifold  202  (instead of the cylinder cavities being machined into the manifold material as shown in  FIG. 2 ). Preferably the back cover assembly  264  provides easy access for servicing or replacement of screw-in, cartridge type hydraulic valves for operation of the cylinders and is sealably closable so as to protect the electronics and valving therewithin from exposure to dirt, debris, and other environmental conditions. 
     Exemplary hydraulic circuitry for an electro-hydraulic moving floor actuator assembly  300  is shown in  FIG. 3 , according to various embodiments. The circuitry is shown schematically grouped into circuitry comprising an exemplary optional adaptor manifold assembly  266  and circuitry comprising an exemplary actuator manifold  202  together with valving that may be enclosed or partially housed in a back cover assembly  264  (shown schematically as actuator circuitry  326 ), although other schematic groupings or arrangements may be used. As shown, pressurized hydraulic fluid may be provided to the optional adaptor manifold  266  via a hydraulic fluid pump  306  and supply line  146 , and hydraulic fluid may be exhausted from the optional adaptor manifold  266  via return line  144  (to tank  308 ). 
     The optional adaptor manifold assembly  266  preferably comprises various hydraulic circuitry for conditioning the hydraulic fluid provided to the actuator circuitry  326 . For example, the optional adaptor manifold assembly  266  may include, sequentially along supply line  146 , a pressure regulating valve  312  (or safety relief valve for diverting excess pressure from the supply line  146  to return line  144 ), a filter or strainer  310 , and a flow restrictor (or maximum flow orifice)  314 , which when combined condition pressurized hydraulic fluid received into the actuator circuitry  326  via supply line  322 . Another suitable type of pressure regulating valve variably responsive to the pressure in line  146  can be used in the position of pressure regulating valve  312 , including one or more pilot-controlled relief valves or pressure reducing valves. 
     The optional adaptor manifold assembly  266  is also shown with a pressure regulating valve  318  and check valve  320  in parallel, which together provide a counterbalance valve (or normally closed pressure control with an integral check valve) between the actuator circuitry  326  return line  324  and return line  144 . The pressure regulating valve  318  is shown with a pilot line  316  from supply line  322  that causes  318  to move to an open (or flow) position in response to pressure in supply line  322 . In one embodiment, the pressure regulating valve  318  in combination with check valve  320  may operate as a brake valve; pressure in pilot line  316  causes the pressure regulating valve  318  to open, thus allowing hydraulic fluid to freely exhaust from return line  324  (and return line  144 ), but without pressure in supply line  322 , hydraulic pressure upstream (i.e. hydraulic pressure from two-way valves  358 ,  360 , and/or  362 ) is needed in return line  324  to cause the pressure regulating valve  318  to move to an open (flow) position. In one embodiment, the pressure regulating valve  318  with integral check valve  320  may operate as a meter-out type of flow control circuit, used when a load being moved by cylinders  328 ,  330 , and/or  332  might tend to “run away” or get ahead of hydraulic flow received into the supply line  322 . Such meter-out circuitry may be placed between the cylinders  328 ,  330 , and  332  and the reservoir or tank  308  to limit hydraulic fluid flow from the cylinders and received into return line  324 . 
     As shown, the actuator circuitry  326  preferably comprises three hydraulic fluid power cylinders  328 ,  330 , and  332  that are each individually longitudinally extensible between a retracted position and an extended position in response to hydraulic fluid flow controlled by six two-way valves  352 ,  354 ,  356 ,  358 ,  360 , and  362 . Each of the power cylinders  328 ,  330 , and  332  has a rod side  334 ,  336 , and  338 , respectively, in fluid communication with hydraulic fluid provided by supply line  322 . That is, as shown in  FIG. 3 , supply line (or conduit)  322  is in fluid communication with rod side  334 , conduit  346 , rod side  336 , conduit  348 , rod side  338 , and conduit  350 , although the conduits  346 ,  348 , and  350  may physically comprise a single hydraulic fluid bus or conduit machined into the actuator manifold  202  and further machined so as to fluidly interconnect with the rod sides  334 ,  336 , and  338  of the cylinders  328 ,  330 , and  332 , respectively, and fluidly interconnect with the actuator circuitry  326  supply line  322 . Each of the power cylinders  328 ,  330 , and  332  has a two-way valve  352 ,  354 , and  356 , respectively, permitting hydraulic fluid flow between the power cylinder&#39;s rod side  334 ,  336 , and  338 , respectively, and the power cylinder&#39;s head side  335 ,  337 , and  339 , respectively. Further, each of the power cylinders  328 ,  330 , and  332  has a two-way valve  358 ,  360 , and  362 , respectively, permitting hydraulic fluid to exhaust through return line  324 . The actuator circuitry  326 , as shown, allows for a simpler, more compact manifold design, requiring a minimum number of valves (i.e. two) to control each cylinder. The result is a smaller, lighter weight manifold with fewer failure modes and lower manufacturing and ongoing servicing and maintenance costs. 
     The actuator circuitry  326  may be described as three cylinder sub-circuits interconnected (hydraulically) in parallel, with each cylinder sub-circuit comprising a cylinder with its rod side in fluid communication with the actuator circuitry supply line, a two-way valve interconnecting the rod side and the head side of the cylinder, and a two-way valve interconnecting the head side of the cylinder and the actuator circuitry return line. As shown in  FIG. 3 , a first cylinder sub-circuit may be defined comprising the cylinder  328  with its rod side  334  in fluid communication with the actuator circuitry supply line  322 , the two-way valve  352  interconnecting the rod side  334  (via conduit  346 ) and the head side  335  (via conduit  340 ) of the cylinder  328 , and a two-way valve  358  interconnecting the head side  335  (via conduit  340 ) of the cylinder  328  and the actuator circuitry  326  return line  324 . The first cylinder sub-circuit is shown interconnected in parallel with both a second cylinder sub-circuit and a third cylinder sub-circuit. The second cylinder sub-circuit may be defined comprising the cylinder  330  with its rod side  336  in fluid communication with the actuator circuitry supply line  322  (shown via conduit  346  and rod side  334 ), the two-way valve  354  interconnecting the rod side  336  (via conduit  348 ) and the head side  337  (via conduit  342 ) of the cylinder  330 , and a two-way valve  360  interconnecting the head side  337  (via conduit  342 ) of the cylinder  330  and the actuator circuitry  326  return line  324 . In similar fashion, the third cylinder sub-circuit may be defined comprising the cylinder  332  with its rod side  338  in fluid communication with the actuator circuitry supply line  322  (shown via conduit  348 , rod side  336 , conduit  346 , and rod side  334 ), the two-way valve  356  interconnecting the rod side  338  (via conduit  350 ) and the head side  339  (via conduit  344 ) of the cylinder  332 , and a two-way valve  362  interconnecting the head side  339  (via conduit  344 ) of the cylinder  332  and the actuator circuitry  326  return line  324 . Although circuitry for a three-cylinder actuator is shown in  FIG. 3 , additional cylinder sub-circuits may be included for moving floor systems having more than three groups of interconnected, movable slats. Likewise, fewer sub-circuits than shown in  FIG. 3  may be used for moving floor systems having fewer than three groups of interconnected, movable slats. The actuator circuitry  326  is therefore scalable to accommodate different types of moving floor systems. 
     Preferably, each of the power cylinders  328 ,  330 , and  332  is interconnected as shown so that pressurized hydraulic fluid acts upon one side of the cylinder when both extending and retracting the cylinder. For example, the power cylinders  328 ,  330 , and  332  are shown in  FIG. 3  as being interconnected so that pressurized hydraulic fluid acts upon their rod sides  334 ,  336 , and  338 , respectively, when both extending and retracting the cylinders. Also shown schematically, each of the hydraulic fluid power cylinders  328 ,  330 , and  332  is preferably a double acting, single end rod fluid power device with a predetermined relationship between rod diameter and cylinder bore diameter. When extending a cylinder, for example, cylinder  328 , pressurized hydraulic fluid from supply line  322  acts upon both the rod side  334  and (through two-way valve  352 ) the head side  335 , and the larger surface area of the piston exposed to the pressurized fluid in the head side  335  as compared to the surface area of the piston in the rod side  334  causes extension of the rod  138  and flow of hydraulic fluid from the rod side  334  to the head side  335 . The actuator circuitry  326  requires less hydraulic fluid (i.e. oil) for extension of the cylinder because fluid for extending the cylinder is supplied by the head side of the cylinder (as well as from supply line  322  if needed). The reduced fluid requirement in turn allows for the use of a smaller displacement pump  306  and smaller capacity fluid lines in such as system  300 . A smaller displacement pump also decreases the horsepower and energy/fuel requirements associated with the pump and its operation. When retracting the cylinder  328  pressurized hydraulic fluid from supply line  322  acts upon the rod side  334 , but the flow through the two-way valve  352  is blocked and hydraulic fluid is allowed to exhaust from the head side  335  (through two-way valve  358 ) to the return line  324 . 
     Preferably, rod diameter and cylinder bore diameter are determined so as to approximately match extending and retracting forces. For example, according to a preferred embodiment, the diameter of rod  138  is two inches, the diameter of the cylindrical cavity  204  for cylinder  328  is three inches, and an operating pressure of 3000 psi (pounds-per-square-inch (gage)) is used to extend and then retract cylinder  328 . To extend cylinder  328 , all of the two-way valves (i.e. two-way valves  354 ,  356 ,  358 ,  360 , and  362 ) are held in a closed (no flow) position, with the two-way valve  352  held in an open (flow) position so that pressurized hydraulic fluid at 3000 psi acts upon both the rod side  334  and head side  335  of cylinder  328  simultaneously. The pressure on both sides of the piston (i.e. piston  246 ) will balance each other except for the area of the rod  138 . The net force that cylinder  328  will produce when extending is, therefore, the area of the rod times pressure. The area of the rod is approximately 3.14159 times the radius of the rod  138  (i.e. half of the diameter of rod  138 ) squared, or 3.14159 square inches. The area of the rod times the operating pressure gives a net force during extension of cylinder  328  of approximately 9,425 pounds. The cylinders  330  and  332  are preferably similar to the cylinder  328 , and, therefore, the net force during extension of all three cylinders together is approximately three times that of cylinder  328  alone, or 28,275 pounds. 
     To retract cylinder  328 , the two-way valve  352  is moved to a closed (no flow) position blocking fluid flow between the rod side  334  and the head side  335 , the two-way valve  358  is moved to an open (flow) position allowing fluid to exhaust from head side  335  to return line  324 , and the remaining two-way valves are held in a closed (no flow) position. The pressure on the rod side  334  will be the operating pressure whereas there will be essentially no pressure on the head side  335 . The net force that cylinder  328  will produce when retracting is, therefore, the difference between the areas of the piston and the rod times pressure. The area of the piston is approximately 3.24259 times the radius of the piston (or more accurately the radius of the piston plus radially exposed dimensions of the piston sealing ring  252  and/or piston wear rings  258 , or approximately the radius of the cylindrical cavity  204  for cylinder  328 ) squared, or 7.06858 square inches. Subtracting the area of the rod  138  and multiplying by the operating pressure gives a net force during retraction of cylinder  328  of approximately 11,781 pounds. The cylinders  330  and  332  are preferably similar to the cylinder  328 , and, therefore, the net force during retraction of all three cylinders together is approximately 35,343 pounds. 
     In the above example, the net force during extension (of about 9,425 pounds for each cylinder and 28,275 pounds for all three together) is approximately matched with the net force during retraction (of about 11,781 pounds for each cylinder and 35,343 pounds for all three together). In contrast, hydraulic circuitry (not shown) for actuation of cylinders  328 ,  330 , and  332  (each having, for example, a rod diameter of two inches and a cylinder bore diameter of three inches) whereby the cylinders are extended by providing pressurized hydraulic fluid to only their head sides  335 ,  337 , and  339  (i.e. without pressure being provided to both sides of the respective pistons during extension), provides a net force during extension of about 21,206 pounds (the area of the piston times the pressure, or 7.06858 square inches times 3000 psi) for each cylinder and 63,617 pounds for all three cylinders together, or more than twice the extension forces provided by the hydraulic circuitry shown in  FIG. 3 . In such (prior) systems, components are subjected to much higher extending forces (relative to retracting forces), which may lead to component damage such as, for example, failure of smaller diameter piston rods (which are subjected to twice the force when extending as they are when retracting). The actuator circuitry  326  allows for larger rod diameters (relative to cylinder bore diameter) to be used and for the rod and cylinder bore diameters to be chosen so as to more closely match cylinder extension and retraction forces, thereby reducing potential component shock and subsequent damage. 
     Different rod and cylinder bore diameters may be used for the actuator circuitry  326  in  FIG. 3 . For example, in another preferred embodiment, the power cylinders  328 ,  330 , and  332  each have a rod diameter of 1.375 inches and a cylinder bore diameter of two inches, providing a net force during extension of all three cylinders together of approximately 13,364 pounds and a net force of retraction of 14,910 pounds. In yet another preferred embodiment, power cylinders  328 ,  330 , and  332  each have a rod diameter of 3.5 inches and a cylinder bore diameter of five inches, providing a net force of extension for all three cylinders together of approximately 86,590 pounds and a net force of retraction of 90,125 pounds. The rod and cylinder bore diameters may be chosen so as to more closely match extending and retracting forces. For instance, with the area of the piston approximately equal to twice the area of the rod (or, differently stated, with the rod diameter approximately equal to the piston (or cylinder core) diameter divided by the square root of two), the extending and retracting forces should be approximately the same. For example, a piston (or cylinder bore) diameter of three inches (corresponding to a piston area of 7.06858 square inches) and a rod diameter of approximately 2.12132 inches (corresponding to a rod area of 3.53429 square inches) provides a net force during extension of about (area of rod times pressure) 10,603 pounds and a net force during retraction of about (difference between the areas of the piston and rod times pressure) 10,603 pounds. 
     As shown schematically in  FIG. 3 , the two-way valves  352 ,  354 ,  356 ,  358 ,  360 , and  362  are preferably normally open solenoid-controlled bidirectional two-way (i.e. two-connection) on-or-off type (i.e. flow or no flow) hydraulic valves. In a preferred embodiment, electronics for controlling activation and deactivation of the solenoids are enclosed within the actuator manifold  202  and/or back cover (rear housing)  264 . In alternate embodiments, other types of two-way valves may be used. For example, the two-way valves  352 ,  354 ,  356 ,  358 ,  360 , and  362  may comprise piloted-operated two-way valves with corresponding hydraulic selector valves and associated hydraulic circuitry for controllably piloting open or closed the two-way valves. Hydraulically or mechanically activated two-way valves may be used in less preferred embodiments instead of or in combination with solenoid-controlled valves. 
     Typical operation of a slat-type moving floor system  100  incorporating the hydraulic circuitry shown in  FIG. 3  to, for example, unload material from a trailer equipped with the moving floor system preferably includes extending all of the cylinders  328 ,  330 , and  332  in unison so as to move the respective rods  138 ,  140 , and  142 , their respective cross-drives  132 ,  134 , and  136 , and their respective groups of interconnected slats forward and thereby moving the material forward (i.e. unloading the trailer by moving the load outward toward an open end of the trailer). To extend all of the cylinders  328 ,  330 , and  332  the two-way valves  352 ,  354 , and  356  are opened to allow fluid flow between the rod sides  334 ,  336 , and  338  and the head sides  335 ,  337 , and  339 , and the two-way valves  358 ,  360 , and  362  are closed to block fluid from exhausting to return line  324 . Following extension of all three cylinders  328 ,  330 , and  332 , each of the cylinders is retracted individually, one at a time until all three cylinders are fully retracted. Once all three cylinders are retracted, the sequence is repeated until the load is fully expelled from the trailer. Retracting cylinder  328  individually may be accomplished by closing all of the two-way valves except the two-way valve  358 , which is opened to allow hydraulic fluid to exhaust from head side  335  as pressurized hydraulic fluid is received into the rod side  334  of the cylinder  328 . In similar fashion, retracting cylinder  330  may be accomplished by closing all of the two-way valves except the two-way valve  360 , which his opened to allow hydraulic fluid to exhaust from head side  337 . Likewise, retracting cylinder  332  may be accomplished by closing all of the two-way valves except the two-way valve  362 , which is opened to allow hydraulic fluid to exhaust from head side  339 . 
     The slat-type moving floor system  100  incorporating the hydraulic circuitry shown in  FIG. 3  may be operated in reverse to, for example, load material into a trailer equipped with the moving floor system. The floor slats may be retracted all together in unison by retracting all three of the cylinders  328 ,  330 , and  332 , which may be accomplished by closing the two-way valves  352 ,  354 , and  356  and opening the two-way valves  358 ,  360 , and  362  to allow hydraulic fluid to exhaust from the head sides  335 ,  337 , and  339  as pressurized hydraulic fluid is received into the rod sides  334 ,  336 , and  338  of the cylinders  328 ,  330 , and  332 , respectively. Once all three cylinders  328 ,  330 , and  332  are fully retracted, each of the cylinders is then extended one at a time until all three cylinders are fully extended. The sequence is repeated until the load is conveyed into the trailer to the desired position. Extending cylinder  328  individually may be accomplished by closing all of the two-way valves except the two-way valve  352 , which is opened to allow hydraulic fluid to flow from the rod side  334  to the head side  335  of the cylinder  328 . In similar fashion, extending cylinder  330  may be accomplished by closing all of the two-way valves except the two-way valve  354 , which is opened to allow hydraulic fluid to flow from the rod side  336  to the head side  337 . Likewise, extending cylinder  332  may be accomplished by closing all of the two-way valves except the two-way valve  356 , which is opened to allow hydraulic fluid to flow from the rod side  338  to the head side  339 . 
     In preferred embodiments, the moving floor system  100  provides a load travel speed (i.e. the speed that the load travels longitudinally along the slat-type floor) of approximately ten feet per minute using cylinders  328 ,  330 , and  332  that provide approximately six inches of cylinder stroke (i.e. the longitudinal travel distance between their fully retracted and fully extended positions) and hydraulic fluid supplied by a pump (such as pump  306 ) at a rate of about eleven gallons per minute for a system comprising cylinders  328 ,  330 , and  332  having rod diameters of approximately two inches and cylinder bore diameters of approximately three inches; at a rate of about 4.9 gallons per minute for a system comprising cylinders  328 ,  330 , and  332  having rod diameters of approximately 1.375 inches and cylinder bore diameters of approximately two inches; and at a rate of about 30.6 gallons per minute for a system comprising cylinders  328 ,  330 , and  332  having rod diameters of approximately 3.5 inches and cylinder bore diameters of approximately five inches. 
     In preferred embodiments, each of the cylinders  328 ,  330 , and  332  have a cross-section similar to that shown in  FIG. 4 , which is a cross-sectional view through longitudinal cut line  4 - 4  in  FIG. 2 . As shown, the piston  250  is fastened to the head end of the rod  142  and sealed via piston o-ring  416 . The cylinder preferably includes a limit switch assembly comprising a limit switch housing  404 , which encapsulates an end-of-extension switch element  408  (such as, for example, a reed switch or other type of proximity type), one or more electrical conductor  410  from the end-of-extension switch element  408 , an end-of-retraction switch element  412  (of similar type as the end-of-extension switch element  408 ), and electrical conductors  414  from the switch elements  408  and  412 . As shown, the limit switch housing  404  is inserted within a limit switch cavity  406  machined through the piston  250  and head end of the rod  142  and mounted within the cylinder cavity  208  so as to remain fixed in relation to the cylinder cavity  208  throughout longitudinally extensible movement of the rod  142  and piston  250 , which is shown in  FIG. 4  in a fully retracted position. A magnet  400  or other type of proximity switch target is preferably incorporated into the piston  250 , shown retained by a snap ring  402 , for triggering the end-of-retraction switch element  412  when the piston  250  is in a fully retracted position and triggering the end-of-extension switch element  408  when the piston  250  is in a fully extended position. Electronic controls housed within the back cover  264  (or elsewhere) receive electrical signals from the switch elements  412  and  408  for determining rod/piston position and electronic control of the solenoid-controlled two-way valves  352 ,  354 ,  356 ,  358 ,  360 , and  362 . For example, the two-way valves  352 ,  354 , and  356  are activated to a closed position to stop further extension of the respective rods  138 ,  140 , and  142  once the respective end-of-extension switch elements electrically sense the magnets (or proximity switch targets) incorporated into the respective piston  246 ,  248 , and  250 , thus eliminating mechanical end-of-stroke induced shock and mechanical stress therefrom. The electronic controls preferably use the embedded electronic piston position sensors (i.e. the end-of-extension and end-of-retraction switch elements and targets) in each cylinder to prevent the pistons from being mechanically stopped within their respective cylinder cavities, thus reducing component wear and tear and the potential for hydraulic fluid leaks. Further, sensing end-of-stroke electronically (using sensor switches embedded internally to the cylinder, piston, and rods, as shown in  FIG. 4 , or, alternatively, using similar sensor switches embedded elsewhere in the manifold  202  oriented to sense end-of-extension and end-of-retraction) instead of mechanically (perhaps by triggering end-of-stroke when a mechanical member attached to a moving component physically contacts another mechanical component) provides for quieter actuator operation. 
     Electronic piston position sensing afforded by the internally oriented switches (such as the switch elements  412  and  408 ) provides position information that is preferably used to automatically detect jamming conditions in any of the cylinders  328 ,  330 , and  332  and to subsequently automatically reverse direction of the affected cylinders for clearing the jamming conditions. For example, electronics associated with the moving floor actuator assembly  102  (i.e. included within the manifold  202  and/or rear housing  264 , and/or as part of the control console  108 ) preferably monitor the position sensors within the cylinders  328 ,  330 , and  332  (such as the switch elements  412  and  408 ) and detect when any of the cylinders become jammed, which may be indicated when, for instance, an end-of-extension switch triggering event was expected but did not happen within a prescribed amount of time or not at all. In response to the jamming condition, the particular cylinder(s) involved is(are) automatically reversed momentarily so as to clear the jamming condition. When material becomes jammed between adjacent floor slats, reversing the direction of the reciprocating slats may dislodge the problem causing material so that reciprocation of the moving floor slats may be resumed to advance the load in the direction of desired travel (i.e. to continue unloading a trailer). 
     The terms and expressions which have been employed in the forgoing specification are used therein as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding equivalence of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.