Patent Publication Number: US-2018044114-A1

Title: Kiln cart pusher

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of and claims priority to U.S. patent application Ser. No. 15/364,237 filed Nov. 29, 2016, which is a continuation of and claims priority to U.S. patent application Ser. No. 15/182,323, filed Jun. 14, 2016, now U.S. Pat. No. 9,534,842, which claims priority to U.S. Patent Application No. 62/300,770, filed Feb. 27, 2016, all titled “KILN CART PUSHER,” the entire disclosures of which are incorporated by reference herein. 
    
    
     BACKGROUND 
     Conventional track-type lumber kilns are provided with a set of rails that extend through the kiln. Lumber packages are loaded onto wheeled carts, or trams, which typically include a series of transverse supports mounted to a wheeled frame. The trams are moved through the kiln along the track in an end-to-end arrangement. As each tram is moved into the kiln, it is forced against the lagging end of the next to advance the entire line of trams. 
     A pusher device is typically used to push the trams through the kiln. One type of conventional pusher device uses a hydraulic cylinder to exert force against the trams. However, conventional pusher devices may be prone to breakage or failure under harsh conditions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments will be readily understood by the following detailed description in conjunction with the accompanying drawings. Embodiments are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings. 
         FIGS. 1A-1B  are perspective views of a prior kiln pusher; 
         FIG. 2  is a perspective view of an embodiment of a pusher device; 
         FIGS. 3A-3B  are perspective and plan views, respectively, of components of a pusher device as shown in  FIG. 2 ; 
         FIG. 4  is a perspective view of the pusher device of  FIG. 2  in use; 
         FIG. 5  is a perspective view of another embodiment of a pusher device; 
         FIGS. 6 and 7  are perspective views of components of a pusher device as shown in  FIG. 6 ; 
         FIG. 8  is a perspective view of the pusher device of  FIG. 6  in use; 
         FIG. 9  is a perspective view of another embodiment of a pusher device in use; 
         FIG. 10  is a perspective view of another embodiment of a pusher device; 
         FIG. 11A  is a perspective view of components of a pusher device as shown in  FIG. 10 ; 
         FIGS. 11B-C  are side and rear elevational views of components shown in  FIG. 11A ; 
         FIGS. 11D-E  are additional side elevational views of components shown in  FIG. 11A ; 
         FIG. 11F  is a schematic sectional view of some of the components shown in  FIG. 11B , taken along lines A-A of  FIG. 11B ; 
         FIGS. 12A-12B  are plan and side elevational views, respectively, of a pusher device as shown in  FIG. 10 ; 
         FIG. 12C  is a magnified view of a portion of  FIG. 12B ; 
         FIG. 13  is an exploded view of a pusher device as shown in  FIG. 10 ; 
         FIG. 14  is a perspective view of an alternative embodiment of a pusher device carriage; 
         FIG. 15  is a plan view of the pusher device carriage of  FIG. 14 ; 
         FIGS. 16A-B  are rear elevational and side elevational views, respectively, of the pusher device carriage of  FIG. 14 ; and 
         FIGS. 17A-B  are side elevational and perspective views, respectively, of components of a pusher device, all in accordance with various embodiments. 
     
    
    
     DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS 
     In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which are shown by way of illustration embodiments that may be practiced. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of embodiments is defined by the appended claims and their equivalents. 
     Various operations may be described as multiple discrete operations in turn, in a manner that may be helpful in understanding embodiments; however, the order of description should not be construed to imply that these operations are order dependent. 
     The description may use perspective-based descriptions such as up/down, back/front, and top/bottom. Such descriptions are merely used to facilitate the discussion and are not intended to restrict the application of disclosed embodiments. 
     The terms “coupled” and “connected,” along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. Rather, in particular embodiments, “connected” may be used to indicate that two or more elements are in direct physical or electrical contact with each other. “Coupled” may mean that two or more elements are in direct physical or electrical contact. However, “coupled” may also mean that two or more elements are not in direct contact with each other, but yet still cooperate or interact with each other. 
     For the purposes of the description, a phrase in the form “A/B” or in the form “A and/or B” means (A), (B), or (A and B). For the purposes of the description, a phrase in the form “at least one of A, B, and C” means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B and C). For the purposes of the description, a phrase in the form “(A)B” means (B) or (AB) that is, A is an optional element. 
     The description may use the terms “embodiment” or “embodiments,” which may each refer to one or more of the same or different embodiments. Furthermore, the terms “comprising,” “including,” “having,” and the like, as used with respect to embodiments, are synonymous. 
     The present disclosure describes embodiments of a pusher device for use to move trams or carts along a track. Corresponding methods and systems are also disclosed herein. In exemplary embodiments, a computing device may be endowed with one or more components of the disclosed apparatuses and/or systems and may be employed to perform one or more methods as disclosed herein. 
     Rail-mounted trams, or kiln carts, are often used to convey lumber through a kiln for drying. A typical tram has a pair of wheeled longitudinal supports connected by a series of transverse members mounted on the longitudinal supports at increments, with gaps between adjacent transverse members. Collectively, the transverse members form a lumber support surface. 
     The tram&#39;s wheels are mounted on rails that extend through the kiln. Green lumber is placed onto the transverse members of the tram, and the tram is pushed or pulled along the track through the kiln. Some facilities push the trams through the kiln in series, abutting end-to-end, using a pusher device positioned along the track upstream of the kiln entrance. One type of conventional pusher device uses a carriage with rotatable lugs to exert force against the upstream-most tram. 
     For the purposes of the present description, a lug has opposed faces, at least two sides that are transverse to the faces, at least one end that is transverse to the faces and sides, a pivot axis that extends through the opposed faces, and a longitudinal axis. The “cross-sectional shape” of a lug (i.e., the shape of the lug “in profile”) is the shape of the outer periphery of the lug within a plane that extends through the lug normal to the pivot axis and equidistant from the opposed faces. The cross-sectional shape of a lug is generally a polygon with multiple sides, the longest of which is one “side” of the lug. If the polygon has only three sides, the second-longest side is another “side” of the lug, the last (shortest) side is one “end” of the lug, and the intersection of the longest and second-longest sides of the polygon is considered the other (or opposite) “end” of the lug. If the polygon has four or more sides, the longest side is a “side” of the lug, the sides of the polygon that are adjacent to the longest side are the “ends” of the lug, and the remaining side(s) of the polygon is/are the other “side(s)” of the lug. 
     Each of the sides, ends, and faces lies within a corresponding plane, and each may be either continuous (e.g., a flat uninterrupted surface) or discontinuous (e.g., textured, notched, etc.) within that plane. In other words, two or more surfaces that lie within the same plane are part of the same side, end, or face. In addition, unless stated otherwise, the cross-sectional shape of a lug is defined without reference to the shape(s) of the intersections of the sides and ends (“corners”), any or all of which may be curved/rounded, chamfered, beveled, or angular in profile. For example, a lug with parallel faces, parallel sides, and parallel ends is considered to have a rectangular cross-sectional shape, whether the corners are curved, beveled, angular, etc. 
     The “longitudinal axis” of a lug is defined as an axis that extends through the lug, and through the pivot axis, parallel to the longest side of the lug. 
       FIGS. 1A-1B  illustrate a conventional pusher device  10  positioned between the rails of a track. 
     The conventional pusher device  10  includes a frame  12 , a carriage  14  with front and rear wheels  16 , and a hydraulic cylinder  18 . The carriage  14  has front, side, and rear vertical walls coupled together to form a generally square frame with an open center. The rod of the hydraulic cylinder is connected to the rear wall of the carriage, and the cylinder body is coupled to a pair of elongate support plates that are in turn coupled to the side walls. Pairs of lugs  20  are rotatably mounted to the carriage on a shaft  22  that passes through the lugs and the side walls of the carriage. The lugs are rotatable in a forward direction (in the view of  FIG. 1A , counter-clockwise) on the shaft from a resting position as shown to a lowered position (not shown). Stops  24  are fixedly coupled to the side walls within the frame, forward of the pivot axis of the lugs (i.e., between the front wall of the carriage and the shaft  22 ). Stops  24  are thus positioned to engage the front sides of the lugs near the bottom ends of the lugs to prevent backward rotation of the lugs. 
     The lugs of pusher device  10  are substantially rectangular in profile, with rounded corners at the intersection of the upper end and the sides. The lugs have parallel faces, parallel top and bottom ends, and parallel front and back sides that are longer than the ends. In the resting position, the lugs are upright, such the longitudinal axis and the front and rear sides of each lug are substantially vertical and the ends are vertically aligned with the pivot axis. In the lowered position (not shown), the lugs  20  are rotated forward, such that the top ends of the lugs are forward of the pivot axis and the longitudinal axis is inclined from rear to front. 
     The hydraulic cylinder  18  is selectively actuable to move the carriage  14  forward and backward within the frame  12  on wheels  16  to push a tram ( FIG. 1B ). As illustrated, a tram  2  has a pair of longitudinal supports  6  with wheels  8 , and transverse members  4  arranged on the longitudinal supports to form a support surface. The transverse members  4  are substantially coplanar and positioned at regular intervals along the length of the tram. The wheels  8  of each longitudinal support engage the corresponding rail of the track. 
     In the resting position, the upper ends of the lugs extend into or through the plane of the transverse members  4 . In the lowered position, the lugs are below the plane of the transverse members  4 . The other components of carriage  14 , as well as the frame  12  and hydraulic cylinder  18 , remain below the plane of the transverse members regardless of the position of the lugs. The lugs are rotatable from the resting position to the lowered position by application of pressure against the rear/lagging side of the lugs. 
     In operation, the pusher device is positioned between the rails of the track upstream of the kiln entrance. A push cycle begins when the hydraulic cylinder  18  is extended to move the carriage  14  forward by an increment of distance. The lugs  20  are in the resting position as the carriage  14  moves forward. The forward movement of the carriage  14  brings the front sides of the lugs into engagement with the rear side of a transverse support  4  to push the corresponding tram forward. The hydraulic cylinder  18  is then retracted to move the carriage  14  backward, which brings the rear side of the lugs into contact with the front side of another transverse support  4 . The force exerted against the lugs by this contact causes them to rotate forward to the lowered position, which is maintained by the contact between the rear side of the lugs and the underside(s) of the transverse support(s) as the carriage continues to move backward. When the lugs reach a gap between transverse supports, the lugs return to the resting position. The retraction of hydraulic cylinder  18  to the initial position completes one push cycle. Successive push cycles can be used to move a line of trams incrementally along the rails in an end-to-end arrangement. 
     This design has several disadvantages. First, if the transverse supports become warped, bent, or damaged, or if the carriage encounters debris between the rails, one of the lugs may contact the tram before the others. The resulting force may bend or break the lug. In addition, a moment developed by the hydraulic cylinder piston tends to cause the front of the carriage to lift. The resulting increase in force against the rear wheels may cause them to seize or break. In addition, damage to the wheels, uneven contact of the lugs with the trams, or debris along the track can cause lateral or twisting carriage motion, which can cause failure of the rear guide wheels, breakage of the vertical lugs at the welds, or sticking/seizing of the vertical lugs in one position. 
     Embodiments described herein may overcome some or all of these disadvantages of conventional pusher devices. In various embodiments, a pusher device may be configured such that when the lugs are in the resting position, the longitudinal axis of each lug is inclined or tilted forward (as opposed to vertical) to contact the tram with the front end (as opposed to a side) of the lugs. The lugs may be rotatably mounted to a carriage that is slideably mounted on linear bearings. 
     The lugs may have a front end, a back end, a lower side, and an upper side. The upper side may be longer than the ends and, optionally, the lower side. When the lugs are in the resting position, the upper side may be inclined from rear to front and the back end may be generally horizontal. 
     In some embodiments the lugs may be generally trapezoidal in profile, with neither end forming a right angle to either of the sides. In other embodiments the lugs may be generally triangular in profile, with the front end and the upper and lower sides forming the three sides of the triangle, and the intersection of the upper and lower sides considered the back end of lug. In still other embodiments the lugs may have generally the shape of a concave polygon in profile, with the front end being curved or angled in contour to define an interior angle of more than 180 degrees. 
     The lugs may be rotatably mounted to a pusher carriage disposed within a frame. The pusher carriage may have guide members (e.g., linear bushings or bearing carriages) that are slideable along corresponding guide rails (e.g., profile rails). A linear positioner (e.g., a hydraulic cylinder, pneumatic cylinder, roller screw, planetary screw, etc.) may be used to move the carriage forward and backward within the frame along the guide rails. In some embodiments the guide rails may be attached to an underlying support that is coupled to the frame. 
     In some embodiments one or more stop members may be provided rearward of the shaft/pivot around which the lugs rotate. The stop member may be positioned to engage the back end of a corresponding lug in the resting position to prevent backward rotation of the lug. Other embodiments may lack a stop member. For example, in some embodiments the lugs may be shaped and dimensioned such that the bottom sides of the lugs are in contact with the carriage while the lugs are in the resting position, preventing backward rotation of the lugs. 
     Configurations and features described herein may provide for reduced stress on the lugs, thereby reducing fatigue-related lug failure, in comparison to conventional configurations with vertical lugs. The rotation required for the lugs to move under the trams may be comparatively less, which may reduce sticking and/or slow return of the lugs to the resting position. The use of linear bushings/bearings instead of wheels for movement of the carriage may reduce lifting, twisting, and other non-linear carriage motion, which may help to limit the frequency and severity of damage to the lugs, carriage, and other components of the pusher device during use under harsh conditions. 
       FIG. 2  illustrates a perspective view of a pusher device  100 , in accordance with various embodiments. 
     Pusher device  100  may include a frame  102 , a carriage  104 , a hydraulic cylinder  108  connected at opposite ends  112 ,  114  to the rear of the carriage and the rear of the frame, respectively, and lugs  116 . Lugs  116  may be mounted to the carriage on shaft  134 , such that the lugs  116  are rotatable in a forward direction. 
     Shaft  134  may extend through opposite sides of the carriage. As illustrated, some embodiments may have two pairs of lugs  116  arranged on opposite sides of the carriage, with the lugs of each pair positioned on opposite sides of the corresponding side wall. Other embodiments may have two, three, five, six, or more than six lugs. 
     Carriage  104  may have front, back, and opposed side walls joined together to form a frame. The carriage may be slideable along a pair of guide rails  130 . The guide rails may help to reduce or prevent lifting, twisting, and/or lateral movements of carriage  104  that could damage components of the pusher device and cause early failure of the system. Using guide rails instead of (or in addition to) wheels may reduce or eliminate wheel failures that can occur in prior pushers operated under harsh conditions. In some embodiments, a bellows (not shown) may be provided on or over the guide rails to protect the guide rails from dirt or other debris that could otherwise stick to the guide rails. 
     Guide rails  130  may be mounted to the frame  102  above the underlying floor surface with mount blocks  146  that are bolted to the frame  102 . The forward ends of the guide rails  130  may be retained in/through corresponding mount blocks  146  that are bolted to a front end of the frame, and the rearward ends of the guide rails  130  may be retained in/through corresponding mount blocks  146  that are bolted to the support  138 . Support  138  may be rigidly attached (e.g., welded or bolted) to the frame  102 . The use of mount blocks may allow for convenient disassembly of the guide rails for maintenance or replacement. Mounting the guide rails to forward end of the frame and to support  138  may reduce deflection of the guide rails during use. 
     Optionally, a support  140  may also be rigidly attached (e.g., welded or bolted) to the frame rearward of support  138 . Supports  138  and  140  may be plates, bars, beams, or the like, made of steel or any other suitable material. The ends  114  and  112  of the hydraulic cylinder  108  may be bolted or otherwise rigidly attached to the supports  140  and  138 , respectively, using one or more mount blocks, plates, or the like. As illustrated, in some embodiments the hydraulic cylinder may be coupled to support  138  by an L-shaped bracket  148  that has a vertical portion and a horizontal portion. The vertical portion may have an open-ended slot dimensioned to receive the outer body of the hydraulic cylinder, such that the hydraulic cylinder is cradled within the slot. The horizontal portion may be bolted to support  138 . Optionally, the bracket may have reinforcing gussets at each side. The bracket may help to support and stabilize the hydraulic cylinder during operation while facilitating its removal for maintenance purposes. 
     Referring now to  FIGS. 3A-B , guide rails  130  may be disposed through corresponding guide members  132  in the front and rear walls of carriage  104  (see  FIG. 3A ). In some embodiments, guide members  132  may be linear bushings. The guide rails may be greased to aid smooth travel of the carriage on the guide rails. Optionally, carriage  104  may have reinforcing gussets  140  at some of the intersections of the front, back, and sides of carriage  104 . 
     Lugs  116  may be rotatably mounted on shaft  134  ( FIG. 2 ). In some embodiments, shaft  134  may be fixed relative to the carriage frame, and the lugs may be rotatable on the shaft. In other embodiments, lugs  116  may be fixed in position on shaft  134 , and shaft  134  may be rotatable such that the lugs and shaft rotate as a single unit. Optionally, lug spacer rings  144  may be provided along the shaft on one or both sides of the lugs to maintain a desired spacing between lugs  116  and the sides of the carriage  104 . This may facilitate cleaning and maintenance of the lugs and/or help to prevent jamming caused by lugs contacting the carriage frame. 
     Some embodiments may include one or more counterweights  136 . Counterweight  136  may be coupled to one or more of the lugs  116  (e.g., at the back end of the lug) to aid in returning the lug(s) to the resting position. 
     Lugs  116  may have front and back ends  118  and  120 , respectively, and upper and lower sides  122  and  124 , respectively, as well as opposite faces. The lugs may be trapezoidal in shape, such that the front and back ends do not form right angles with the upper and lower sides. Upper side  122  may be longer than the front and back ends  118 ,  120  and the lower side  124 . In some embodiments, the lug may have curved or rounded edges/corners at some or all of the intersections between the ends and the sides. 
     Carriage  104  may have one or more stops  126 . In various embodiments, stop(s)  126  may be positioned rearward of the pivot axis of the lugs. Stop(s)  126  may be positioned to contact the back end  120  of the lugs when the lugs are in the resting position. Alternatively, stop(s)  126  may be positioned to contact the lower side  124  proximal to the back end  120  when the lugs are in the resting position. In either case, the stop(s)  126  may be configured to prevent backward rotation of the lugs from the resting position. 
     In some embodiments the front ends  118  and/or back ends  120  of the lugs may be provided with an elastomeric or compressible pad  128 . The compressible pad may help to reduce stress concentrations on the lugs when pushing a tram that is bent or otherwise damaged. 
     When the lugs  116  are in the resting position, the upper and lower sides of lugs  116  may be inclined and front ends  118  may be substantially vertical. In some embodiments the back ends  120  may be substantially horizontal when lugs  116  are in the resting position. 
     Referring now to  FIG. 4 , the hydraulic cylinder may be actuated to push the carriage forward. As the carriage moves forward with the lugs in the resting position, the forward ends of the lugs are brought into contact with the rear surface of a corresponding transverse member  4  of a tram, and the tram is pushed forward. As the hydraulic cylinder is retracted and the carriage is moved backward, the upper side  122  of the lugs contacts the leading edge of the next successive transverse member  4 . The lugs are rotated forward to the lowered position by the engagement of the upper side  122  with the underside of the transverse member. Once the lugs have passed beneath the transverse member, they begin to rotate back to the resting position. 
       FIGS. 5-9  illustrate perspective views of another example of a pusher device  200  and components thereof, in accordance with various embodiments. Elements that generally correspond to elements of  FIGS. 2-4  are indicated with like reference characters. 
     Pusher device  200  may have a frame  202 , a carriage  204 , a linear positioner (e.g., a hydraulic cylinder)  208  connected at opposite ends to the rear of the carriage and the rear of the frame, respectively, and lugs  216 . 
     The frame  202  may have generally vertical front, rear, and side walls. The linear positioner/hydraulic cylinder  208  may be coupled with the frame via supports  238  and  240  and bracket  248  in the same or similar manner as described above. In addition, a plate  256  may be welded or otherwise rigidly attached to the frame. Plate  256  may be a sheet of steel or other such material. Optionally, plate  256  may extend below both side walls of the frame  102 , and/or from the front end of the frame to the body of the linear positioner  208 . 
     Carriage  204  may include a carriage plate  250 , brackets  252 , and a cylinder mount  254 . In some embodiments carriage plate  250  may be a plate of steel or other such material. Cylinder mount  254  may be disposed at the back end of plate  250  and the brackets  252  may be disposed on the upper surface of plate  250 . Brackets  252  and cylinder mount  254  may be coupled to the plate  250  by welds, bolts, or the like. Optionally, the carriage plate and the cylinder mount and/or brackets may have complementary notches, slots, or the like, along which these components are fitted together. 
     Guide rails  230  may be affixed to the rail plate  256  ( FIG. 5 ), and corresponding guide members  232  may be affixed to the bottom surface of carriage plate  250 , with welds, bolts, or other suitable fasteners ( FIGS. 6-7 ). In a particular example, the guide members  232  are Rexroth 55 mm roller blocks, and the guide rails  230  are Rexroth 1845 size 55 rails. Alternatively, other suitable sizes and/or types of linear motion bearings may be used instead. 
     Referring now to  FIGS. 6-7 , lugs  216  may be arranged along shaft  234 , which may extend through the brackets  252 . A pair of lugs and a corresponding bracket may be provided on both sides of the carriage. The lugs of each pair may be positioned on opposite sides of the corresponding bracket  252 . 
     Lugs  216  may be generally triangular in shape, with the front end  218 , upper side  222 , and lower side  224  as the three sides of the triangle. The intersection of the upper and lower sides  222  and  224  may be the back end  220 . The upper side may be longer than the lower side and the front end. As best illustrated in  FIG. 6 , the lugs may be curved at the intersection of the front end  218  and the lower side  224 . In the resting position (shown), the front end  218  may be substantially vertical, the lower side  224  may be substantially horizontal, and the upper side  222  may be inclined from rear to front. The thickness of the lugs (distance between the opposed faces) may vary among embodiments. In some embodiments, lugs  216  may be 1-3 inches thick. In a particular example, lugs  216  are approximately 2 inches thick. 
     The number and arrangement of the lugs and brackets  252  may vary among embodiments. As shown by way of example in  FIG. 9 , in some embodiments the carriage may have additional brackets  252 , such that each lug is disposed between two brackets. Other embodiments may have one or more additional brackets and/or lugs located nearer to the center of the carriage or the shaft. 
     Optionally, pusher device  200  may further include various other features (e.g., lug spacer rings, gussets, elastomeric pads, guide rail protective bellows, etc.) described above with regard to pusher device  100 . For example, as shown in  FIG. 9 , in some embodiments carriage  204  may include gussets  258  connected to the upper surface of the carriage plate  250  and the forward surface of the cylinder mount  254 . 
     Another example of a pusher device is shown in  FIGS. 10-13 . Referring first to  FIG. 10 , pusher device  300 . Again, elements that generally correspond to elements of  FIGS. 2-9  are indicated with like reference characters. 
     Pusher device  300  may have a frame  302  and a carriage  304 . A linear positioner (not shown) may be connected at opposite ends to the rear of the carriage and the rear of the frame, respectively. 
     Again, the frame  302  may have generally vertical front, rear, and side walls. Supports  338  and  340  and the linear positioner may be coupled with the frame in the same or similar manner as described above. 
     A plate  356  may be welded or otherwise rigidly attached to the frame. Plate  356  may be a sheet of steel or other such material. Again, plate  356  may be coupled to the underside of the frame and extend below both side walls of the frame. However, plate  356  may have a series of open-ended slots  360  around the outer edge thereof (see also  FIG. 12A ). The slots  360  may extend inwardly toward a longitudinal center of the frame, passing beyond the vertical walls of the frame. This configuration may allow drainage of water or other fluids through the plate  356 . Alternatively, plate  356  may be provided with interior holes to provide drainage. 
     Optionally, a removable bracket  262  may be coupled with the forward end of carriage plate  350  and plate  356  by bolts or the like. Bracket  262  may be used to secure carriage plate  350  in place for shipping and/or during maintenance, and removed before resuming operation of the pusher device. 
     Carriage  304  may include a carriage plate  350 , brackets  352 , and a cylinder mount  354 . In some embodiments carriage plate  350  may be a plate of steel or other such material. Cylinder mount  354  may be disposed at the back end of plate  350  and the brackets  352  may be disposed on the upper surface of plate  350 . Brackets  352  and cylinder mount  354  may be coupled to the plate  350  by welds, bolts, or the like. Again, the carriage plate and the cylinder mount and/or brackets may have complementary notches, slots, or the like, along which these components are fitted together, and/or reinforcing gussets  358 . In some embodiments carriage plate  350  may include one or more grease fitting ports  364 . A grease fitting/zerk fitting may be disposed within each port  364 . 
     Guide rails  330  may be affixed to the rail plate  356  ( FIG. 10 ). Referring now to  FIGS. 11A-C , corresponding guide members  332  may be affixed to the bottom surface of carriage plate  350  (e.g., with bolts or other suitable fasteners). In some embodiments, guide members  332  and guide rails  330  may be linear recirculating roller bearing and guideway assemblies. For example, guide members  332  may be INA double sealed roller guide carriages with anti-corrosion coating, and guide rails  330  may be corresponding INA 55 mm profile rails with brass closure plugs. Alternatively, any other suitable size or type of linear motion bearing may be used instead. 
     A pair of brackets  352  may be provided on opposite sides of the upper surface of carriage plate  350 . Optionally, the brackets may be constructed with chamfered lower surfaces and welded to the carriage plate to fill the chamfer with weld. In some embodiments, brackets  352  may have an open-ended slot  372  ( FIG. 11D ). 
     A lug  316  may be disposed between the brackets of each pair. Lugs  316  may be generally triangular in shape, with the front end  318 , upper side  322 , and lower side  324  as the three sides of the triangle and the intersection of the upper and lower sides  222  and  224  forming back end  220 . The upper side may be longer than the lower side and the front end, and the lugs may be curved at the intersection of the front end  318  and the lower side  324 . In the resting position (shown), the front end  318  may be substantially vertical, the lower side  324  may be substantially horizontal, and the upper side  322  may be inclined from rear to front. 
       FIGS. 11E-F  show additional details of the bracket and lug configuration. As best illustrated in  FIG. 11F , which shows a sectional view taken along a vertical plane that passes through the center of the pivot axis of the lugs, brackets  252  may be provided with bushing sleeves  368 . Corresponding bushings  370  may be disposed within the bushing sleeves. In some embodiments, bushings  370  may be self-lubricating bushings. In other embodiments, bushings  370  may be pre-lubricated bushings, metallic bushings, composite bushings, or any other suitable type of bearing. A shaft  334  may extend through the bushings  370  and lug  316 . Another shaft  334  may extend through the bushings and lug on the opposite side of the carriage. A retaining flange  366  may be provided at each end of each shaft. 
     Again, the number and arrangement of the lugs  316  and brackets  352  may vary among embodiments. Optionally, the lugs  316  may be more than three inches thick. For example, the lugs may be approximately 4 inches thick, or 3-5 inches thick. 
       FIG. 13  is an exploded view of a pusher device as shown in  FIG. 10 . In some embodiments, a pusher device may include a cover  374 , such as a sheet of metal or other durable material, configured to cover the linear positioner  308  during use. The cover  374  may be removably coupled to the frame  302  with bolts, screws, brackets, or with any other suitable type of fastener. 
     Some pusher devices may include a linear alignment coupler  376  coupled to the front end/rod of linear positioner  308 . The use of a linear alignment coupler may reduce wear on linear positioner  308  and/or components thereof. Other embodiments may lack linear alignment coupler  376 . 
     Optionally, a shaft  334  and corresponding lug  316  may be provided as a unitary component. For example, the shaft may be press-fitted through the corresponding lug. Alternatively, the shaft and lug may be welded together. In other embodiments, the shaft and lug may be provided as separate components. 
     The shapes and dimensions of the lugs and brackets may vary among embodiments. For example,  FIGS. 14-15 and 16A -B illustrate a carriage  404  with brackets  452  that are generally rectangular. Optionally, brackets  452  may extend toward the back of the carriage  452  beyond the back ends of lugs  416 . Carriage  404  may further include supports  478  affixed to the upper surface of the carriage plate  450 . Each support  478  may be, or may include, a block or plate positioned in contact with the back end of a corresponding bracket  452 . In some embodiments, supports  478  may be constructed with a chamfered lower edge and welded to the carriage plate  450  such that the chamfer is substantially filled. 
     Brackets  452  may be removably coupled to the carriage plate  350  with bolts  482  ( FIGS. 16A-B ). Removably coupling the brackets to the carriage plate may allow damaged or worn brackets to be replaced, and/or allow the brackets and corresponding lug to be removed as a single unit. Supports  478  may help to reinforce the brackets, and may serve as alignment guides for installing or replacing the brackets. 
     In some embodiments a lug may have two ends and more than two sides. Some lugs may have the shape of a concave polygon in profile. Others may have the shape of a convex polygon in profile. Again, any or all of the intersections between two sides or an end and a side may be angled or curved, chamfered, beveled, or the like. 
     A lug with a concave polygon cross-sectional shape/profile is illustrated by way of example in  FIG. 17A . Lug  416  may have a front end  418 , a back end  420 , an upper side  422 , a lower side  424 , and a third side  480 . Front end  418  and third side  480  may form an interior angle of more than 180 degrees. For example, they may form an interior angle of 190-230°, 200-220°, 205-212°, or about 208°. Optionally, the upper side  422  and the bottom side  424  may be generally parallel to one another. Lower side  424  and third side  480  may form an angle of 80-100°, or 85-95°, 88-92°, or about 90°. Lower side  424  and back end  420  may form an interior angle of 140-160°, 145-155°, 150-154°, or about 152°. Any or all of the corners (e.g., corner  482  of upper side  422  and front end  482 ) may be curved, rounded, beveled, etc. 
     In the resting position, the back end  420  of the lug  416  may rest on a surface of the carriage plate  450 , preventing further backward rotation of the lug. When the lug is rotated forward to the lowered position, lower side  424  may rest on another surface of carriage plate  450 , preventing further forward rotation of the lug. As such, carriage plate  450  may lack stop members. Optionally, carriage plate  450  may have replaceable plates/pads at some or all of the surfaces contacted by an end or side of the lugs to thereby reduce wear on the carriage plate and/or lugs, or to facilitate smooth motion of the lugs. 
     Again, shaft  434  may be press fitted or welded to the corresponding lug  416 , or rigidly affixed thereto by any other suitable means. 
     A pusher device may have any of the features (e.g., lug spacer rings, gussets, elastomeric pads, guide rail protective bellows, etc.) of any of the embodiments described herein, in any suitable combination. 
     In some embodiments, an existing pusher device may be modified by replacing the carriage, lugs, wheels, and/or other existing components with components of pusher devices as described herein. For example, pusher device  10  could be modified by removing the existing carriage, coupling guide rails (and optionally a rail plate) to the frame of the existing pusher device, and coupling a pusher carriage as described herein to the guide rails and the existing hydraulic cylinder. Alternatively, pusher device  10  could be modified by replacing the lugs with lugs as described herein (either on the existing shaft or on separate shafts) and reinstalling the stop members rearwardly of the pivot axis of the lugs, and/or replacing the wheels with linear bearings coupled to the existing carriage and existing frame. In any case, existing components such as the frame, hydraulic cylinder and hydraulic system may be reused for a more cost-efficient upgrade of an existing pusher device. 
     Although certain embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent embodiments or implementations calculated to achieve the same purposes may be substituted for the embodiments shown and described without departing from the scope. Those with skill in the art will readily appreciate that embodiments may be implemented in a very wide variety of ways. This application is intended to cover any adaptations or variations of the embodiments discussed herein. Therefore, it is manifestly intended that embodiments be limited only by the claims and the equivalents thereof.