CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Patent Application 62/305,156 filed Mar. 8, 2016, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD 
       [0002]    This application relates to soil working implements, more particularly to an implement for rolling land. 
       BACKGROUND 
       [0003]    Land rollers are implements used to level land to facilitate further working of the land, particularly for seed bed preparation in agriculture. Land rollers generally have large heavy cylindrical rollers whose central axes are oriented substantially horizontally with respect to the ground and substantially transversely with respect to the direction of travel of the implement when the implement is in a working configuration. The circumferential surfaces of the rollers engage the ground as the rollers roll over the ground to flatten the soil and level the ground. 
         [0004]    Land rollers are also generally equipped with transport wheels to permit towing of the implement on a road to transport the implement between sites. During towing, the implement is in a transport configuration where the wheels are on the ground and the rollers are raised off the ground. When the implement is in the working configuration, the rollers are on the ground and the wheels are raised off the ground. 
         [0005]    Land rollers are often provided with a hydraulic system for pivoting the wheels to convert the implement between the transport configuration and the working configuration. Additionally, land rollers are often constructed with side sections or “wings”, which have further hydraulic systems for pivoting the side sections between a substantially horizontally oriented (unfolded) position and a substantially upwardly oriented (folded) position. Upwardly folding the side sections narrows the overall width of the implement to permit the implement to be better towed on a public road. 
         [0006]    When the implement is in the transport configuration and/or the side sections are in the folded position, the great weight of the rollers poses a significant safety hazard to people and property in the vicinity of the implement. In the event of a failure of one or more of the hydraulic systems, the rollers may inadvertently fall down into the working configuration or unfold into the unfolded position. Anything caught under the rollers would be crushed, suffering considerable damage. To avoid this problem, land rollers have been equipped with locking mechanisms or other supports so that the hydraulic system is not supporting the entire weight of the rollers. In many implements, the locking mechanisms are simple pins that are manually inserted by an operator. However, should the hydraulic system experience a catastrophic failure while the operator is trying to insert the pins but before the pins are inserted, the roller could fall, causing injury to the operator. 
         [0007]    There remains a need for a simpler and safer way of ensuring that rollers remain stable when the implement is in the transport configuration. 
       SUMMARY 
       [0008]    There is provided a land roller comprising: a frame comprising a first frame section mountable on a transport vehicle for towing the land roller and a side frame section pivotally mounted on the first frame section, the side frame section pivotable between an unfolded position and a folded position; a first roller mounted on the first frame section; a second roller mounted on the side frame section; at least one transport wheel pivotally mounted on the first frame section, the at least one transport wheel pivotable between a ground-engaging wheel position and a ground-disengaged wheel position for conversion of the land roller between a transport configuration and a working configuration, the transport configuration having the at least one wheel in the ground-engaging wheel position and the first and second rollers in ground-disengaged roller positions, the working configuration having the at least one wheel in the ground-disengaged wheel position and at least the first roller in a ground-engaging roller position; a first actuator connecting the first frame section to the at least one transport wheel, the first actuator operable to pivot the at least one wheel between the ground-engaging wheel position and the ground-disengaged wheel position; an over-center locking linkage arrangement connected between the first actuator and the at least one wheel, the first actuator configured to transmit force through the over-center locking linkage arrangement to the at least one transport wheel to pivot the at least one wheel; and, a second actuator connecting the first frame section to the side frame section, the second actuator operable to pivot the side frame section between the unfolded and folded positions, the side frame section pivoting about a side-frame pivot axis when pivoting between the unfolded and folded positions, the second actuator connected to the side frame section at a connection point on the side frame section, the connection point disposed outward of the side-frame pivot axis when the side frame section is in the unfolded positon and inward of the side-frame pivot axis when the side frame section is in the folded position. 
         [0009]    There is also provided a land roller comprising: a frame; a roller mounted on the frame; a longitudinally extending tongue configured to be mounted on a transport vehicle; and, at least one shock absorber mounted between the tongue and the frame. 
         [0010]    The frame has a longitudinal axis in the direction of motion of the land roller as the land roller is being towed. The longitudinal axis runs from front to rear (or rear to front) of the frame. The cultivator frame has a transverse axis that is perpendicular to the longitudinal axis and runs left to right (or right to left) of the frame. The front end of the frame is mounted to a transport vehicle (e.g. a tractor or a truck) that tows the land roller. The frame may have longitudinally spaced apart transverse frame members and transversely spaced apart longitudinal frame members. The rollers are generally mounted on one or more of the frame members so that circumferential surfaces of the rollers engage the ground as the rollers roll over the ground to flatten the soil and level the ground when the land roller is in the working configuration. In one embodiment, the land roller may comprise two side frame sections, one disposed on a left side of a longitudinal center line through the first frame section and one disposed on a right side of the longitudinal center line through the first frame section. 
         [0011]    The over-center locking linkage arrangement in connection with the first actuator and the at least one wheel provides for improved operational simplicity and safety, helping to lock the frame into an elevated transport configuration to reduce the likelihood that a failure of the first actuator could cause the frame to inadvertently fall and injure a person or cause damage to property while the land roller is in the transport configuration. Further, the over-center locking linkage arrangement in conjunction with an inward of center folded position for the side frame section and an actuator system where the first and second actuators are linked to permit an operator to raise the land roller and lock it in the elevated transport position, followed by folding the side frame section and locking the wings in an upright inward of center folded position all via operation of a single controller. Unfolding the side frame section followed lowering the land roller into the working configuration may be likewise controlled from the same single controller. 
         [0012]    Prior implements often required separate controllers for raising the implement and folding the wings, and often required use of locking pins both to secure the implement in the elevated position and to secure the wings in the folded position. The operator was therefore required to operate the two controllers in a specific order to avoid potentially unstable conditions that could occur if the wings were folded prior to raising the implement thereby exposing the operator to potential hazards during manual insertion of the locking pins. The present invention simplifies raising and folding for safe transport between sites in a locked transport configuration. 
         [0013]    In one embodiment, the over-center locking linkage arrangement may comprise a first linkage and a second linkage. The first linkage may be pivotally connected to the first actuator at a first pivot point. The first linkage may be pivotally connected to the second linkage at a second pivot point. The first linkage may be pivotally connected to the first frame section at a third pivot point disposed between the first and second pivot points. The second linkage may be pivotally linked to a wheel lifting structure at a fourth pivot point. The second pivot point may be to one side of a line between the first and fourth pivot points when the land roller is in the transport configuration. The second pivot point may be to the other side of the line between the first and fourth pivot points when the land roller is in the working configuration. Whether the second pivot is forward or rearward of the line when the land roller is in the transport configuration depends on the overall arrangement of the over-center locking linkage arrangement. The second pivot point is preferably forward of the line when the land roller is in the transport configuration. 
         [0014]    An edge of the first linkage proximate the second pivot point may form an acute angle at the second pivot point with an edge of the second linkage proximate the second pivot point when the land roller is in the transport configuration. The edge of the first linkage and the edge of the second linkage may form an obtuse angle at the second pivot point when the land roller is in the working configuration. The edges of the first and second linkages that form the angle may be posterior or anterior edges depending on the overall arrangement of the over-center locking linkage arrangement, but the edges are preferably posterior edges. 
         [0015]    In one embodiment, the first linkage may be pivotally connected to the first frame section at a bracket rigidly mounted to the first frame section to prevent the third pivot point from translating when the first and second linkages pivot. In one embodiment, the second pivot point may translate in an arcuate path about the third pivot point in response to operation of the first actuator. The third pivot point may represent a center of rotation about which the second pivot point rotates. The point during operation of the first actuator when the linkage arrangement passes over center may occur when the second pivot point is collinear with the first and fourth pivot points. In some embodiments, the edges of the first and second linkages may be collinear or parallel at the over center point. 
         [0016]    In one embodiment, the at least one wheel may be mounted the wheel lifting structure. In one embodiment, the wheel lifting structure may be a transversely oriented axle bar. An axis of rotation of the at least one wheel may be parallel to but spatially offset from a rotation axis of the axle bar. The axle bar may be connected to the second linkage. The axle bar may rotate in response to movement of the second linkage to pivot the at least one wheel between the ground-engaging wheel position and the ground-disengaged wheel position. The second linkage may be movable in response to movement of the first linkage. The first linkage may be moveable in response to operation of the first actuator. In one embodiment, the second linkage may be connected to the axle bar by a third linkage. The third linkage may be pivotally connected to the second linkage and rigidly connected to the axle bar. In one embodiment, the at least one wheel may comprise two transversely spaced-apart wheels. 
         [0017]    In one embodiment, the first and second actuators may be controlled by a single controller. The first and second actuators may be configured to actuate in temporal series when signaled by the controller to actuate. In one embodiment, the first actuator may pivot the at least one wheel to the ground-engaging wheel position, followed by the second actuator pivoting the side frame section to the folded position to convert the land roller to the transport configuration from the working position. In one embodiment, the second actuator may pivot the side frame section to the unfolded position, followed by the first actuator pivoting the at least one wheel to the ground-disengaged wheel position to convert the land roller to the working configuration from the transport configuration. 
         [0018]    The first and/or second actuators may be any suitable device, for example electric actuators (e.g. linear actuators), hydraulic cylinders (e.g. dual acting hydraulic cylinders) and the like. In one embodiment, the first actuator, second actuator or both the first and second actuators may comprise hydraulic cylinders. The first and second actuators may comprise hydraulic cylinders operated from a common hydraulic fluid reservoir through a common hydraulic circuit. The common hydraulic circuit may comprise a pressure relief circuit in fluid communication with the first and second actuators. The pressure relief circuit may prevent hydraulic fluid from flowing into the first actuator when the second actuator is pivoting the side frame section to the unfolded position when hydraulic fluid pressure in the common hydraulic circuit is less than a pre-determined value. The pressure relief circuit may permit hydraulic fluid to flow into the first actuator when hydraulic fluid pressure in the common hydraulic circuit reaches or exceeds the pre-determined value. In one embodiment, when the second actuator is finished pivoting the side frame section, pressure in the common hydraulic circuit may spike triggering opening of a hydraulic fluid path to the first actuator. 
         [0019]    The second actuator is connected to the side frame section at a connection point on the side frame section, the connection point disposed outward of the side-frame pivot axis when the side frame section is in the unfolded position and inward of the side-frame pivot axis when the side frame section is in the folded position. Such an arrangement permits the center of gravity of the side frame section to be over the first frame section when the side frame section is in the folded position, while permitting the center of gravity of the side frame section to be transversely outward of the first frame section when the side frame section is in the unfolded position. With the side frame section in the folded position when the land roller is in the transport configuration, having the center of gravity of the side frame section over the first frame section provides for a locked and more stable arrangement for transporting the land roller between sites. 
         [0020]    In one embodiment, the connection point for the second actuator on the side frame section is configured to permit translation of the actuator within the connection point to permit the side frame section to move relative to the first frame section during operation of the land roller. In one embodiment, the connection point for the second actuator on the side frame section may comprise a pin in an elongated slot to permit translation of the actuator within the connection point to permit the side frame section to move relative to the first frame section during operation of the land roller. 
         [0021]    In another embodiment, at least one shock absorber may be mounted between a tongue and a frame, particularly a center frame section, of the land roller. The tongue may comprise one or more longitudinally extending elongated central tow bars. The at least one shock absorber is preferably pivotally mounted to a central tow bar and a vertically oriented frame member of a center frame section of the frame. Preferably, the at least one shock absorber comprises two shock absorbers. The at least one shock absorber is particularly useful to absorb vertical forces while the land roller is towed in the transport position to reduce vertical displacement of the land roller especially when being towed over rough surfaces. 
         [0022]    Further features will be described or will become apparent in the course of the following detailed description. It should be understood that each feature described herein may be utilized in any combination with any one or more of the other described features, and that each feature does not necessarily rely on the presence of another feature except where evident to one of skill in the art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    For clearer understanding, preferred embodiments will now be described in detail by way of example, with reference to the accompanying drawings, in which: 
           [0024]      FIG. 1A  depicts a rear perspective view of a land roller in accordance with the present invention, where right and left side sections are in unfolded positions; 
           [0025]      FIG. 1B  depicts the land roller of  FIG. 1A  with the right and left side sections in folded positions; 
           [0026]      FIG. 2A  depicts a rear view of the land roller of  FIG. 1A ; 
           [0027]      FIG. 2B  depicts a rear view of the land roller of  FIG. 1B ; 
           [0028]      FIG. 3A  depicts a front view of the land roller of  FIG. 1A ; 
           [0029]      FIG. 3B  depicts a front view of the land roller of  FIG. 1B ; 
           [0030]      FIG. 4A  depicts a top view of the land roller of  FIG. 1A ; 
           [0031]      FIG. 4B  depicts a top view of the land roller of  FIG. 1B ;  FIG. 5A  depicts a bottom view of the land roller of  FIG. 1A ; 
           [0032]      FIG. 5B  depicts a bottom view of the land roller of  FIG. 1B ; 
           [0033]      FIG. 6A  depicts a side view of the land roller of  FIG. 1A ; 
           [0034]      FIG. 6B  depicts a side view of the land roller of  FIG. 1B ; 
           [0035]      FIG. 7A  depicts a magnified rear perspective view of the land roller of  FIG. 1A ; 
           [0036]      FIG. 7B  depicts a magnified rear perspective view of the land roller of  FIG. 1B ; 
           [0037]      FIG. 8A  depicts a magnified side view of the land roller of  FIG. 1A  without side frames, with an implement-elevation hydraulic cylinder fully extended and the land roller in a transport configuration with wheels in a lowered ground-engaging position and rollers in a raised ground-disengaged position; 
           [0038]      FIG. 8B  depicts the land roller of  FIG. 8A  with the implement-elevation hydraulic cylinder in a first partially retracted position; 
           [0039]      FIG. 8C  depicts the land roller of  FIG. 8A  with the implement-elevation hydraulic cylinder in a second partially retracted position; 
           [0040]      FIG. 8D  depicts the land roller of  FIG. 8A  with the implement-elevation hydraulic cylinder fully retracted and the land roller in a working configuration with the wheels in a raised ground-disengaged position and the rollers in a lowered ground-engaging position; 
           [0041]      FIG. 9  depicts a side view of an over-center locking linkage arrangement connecting an implement-elevation hydraulic cylinder to wheels when the land roller is in the transport configuration; 
           [0042]      FIG. 10A  depicts a hydraulic circuit diagram for a hydraulic system of the land roller in a working configuration; 
           [0043]      FIG. 10B  depicts the hydraulic circuit diagram of  FIG. 10A  when the land roller is in a transport configuration with right and left side sections in unfolded positions; 
           [0044]      FIG. 10C  depicts the hydraulic circuit diagram of  FIG. 10A  when the land roller is in a transport configuration with right and left side sections in folded positions; 
           [0045]      FIG. 11A  depicts a front perspective view of a land roller equipped with shock absorbers between a tow bar and a center frame; and, 
           [0046]      FIG. 11B  depicts a magnified view of the shock absorbers on the land roller of  FIG. 11A . 
       
    
    
     DETAILED DESCRIPTION 
       [0047]    Referring to the Figures, a land roller  1  comprises a center section having a center frame  10 , a right side section having a right side frame  30  and a left side section having a left side frame  50 , each of the frames  10 ,  30 ,  50  comprising longitudinal and transverse elongated frame members on which a center roller  11 , a right side roller  31  and a left side roller  51 , respectively, are rotatably mounted. Generally longitudinally extending elongated tow bars  2 ,  3 ,  4  may be pivotally connected to the center frame  10  at tow bar pivot mounts  5 ,  6 ,  7 , respectively, the tow bars  2 ,  3 ,  4  converging to and connected to a hitch  8  at a front end of the land roller  1  where the hitch  8  may be connected to a towing vehicle. 
         [0048]    The right side frame  30  may be pivotally mounted on the center frame  10  at right side frame pivot mounts  32   a ,  32   b . The right side frame pivot mounts  32   a ,  32   b  may comprise any suitable structure permitting upward and downward pivoting of the right side frame  30  about a right side frame pivot axis R-R, for example pivot pins inserted through corresponding apertures in mounting brackets secured to the right side frame  30  and the center frame  10 . The right side frame pivot axis R-R may be parallel to the longitudinal axis of the land roller  1 . Upward and downward pivoting of the right side frame  30  permits moving the right side frame  30  between the folded and unfolded positions. The right side frame  30  may be disposed both to the right and behind the center frame  10 . In order to provide for the right side frame pivot mounts  32   a ,  32   b  at both a rear and front of the center frame  10 , an angled right side pivot support frame member  33  may be used to provide a mounting location for one of the right side frame pivot mounts  32   b  on an opposite side of the center frame  10 . Alternatively, the right side frame  30  may be disposed both to the right and in front of the center frame  10 . A similar arrangement may be provided for the left side frame  50  involving left side frame pivot mounts  52   a ,  52   b , left side frame pivot axis L-L and angled right side pivot support frame member  53 . 
         [0049]    To move the right side frame  30  between the folded and unfolded positions, a right side hydraulic cylinder  34  may be connected between the center frame  10  and the right side frame  30 . Either a barrel-end or a rod-end of the right side hydraulic cylinder  34  may be mounted on the center frame  10  with the other end mounted on the right side frame  30 . In the embodiment shown in the Figures, the barrel-end of the right side hydraulic cylinder  34  is pivotally mounted on the center frame  10  at right side cylinder mount  35  and the rod-end is pivotally mounted on the right side frame  30  at right side cylinder rod mount  37 . Retraction of cylinder rod  36  of the right side hydraulic cylinder  34  causes the right side frame  30  to pivot around the right side frame pivot axis R-R thereby raising the right side frame  30  to the folded position. Extension of cylinder rod  36  of the right side hydraulic cylinder  34  causes the right side frame  30  to pivot around the right side frame pivot axis R-R thereby lowering the right side frame  30  to the unfolded position. The right side cylinder rod mount  37  may advantageously comprise a pin in a clevis  38 , the clevis  38  having elongated slots  39  within which a mounting pin may translate (see  FIG. 7A  and  FIG. 7B ). Translation of the pin in the clevis  38  permits the right side frame  30  to move relative to the center frame  10  during operation of the land roller  1 . Further, as especially shown in  FIG. 4A  and  FIG. 4B , when the right side frame  30  is in the unfolded position ( FIG. 4A ), the right side cylinder rod mount  37  is located transversely outward of the right side frame pivot axis R-R. However, the right side hydraulic cylinder  34  may be configured so that when the right side frame  30  is in the folded position ( FIG. 4B ), the right side cylinder rod mount  37  is located transversely inward of the right side frame pivot axis R-R. With the right side cylinder rod mount  37  located transversely inward of the right side frame pivot axis R-R, the weight of the right side frame  30  is now over the center frame  10  to be supported on a pair of transport wheels  12  instead of just by the right side hydraulic cylinder  34  when the land roller  1  is in the transport configuration. Therefore, should the right side hydraulic cylinder  34  fail during transport of the land roller  1 , the right side frame  30  will not inadvertently crash down to the unfolded position. Therefore, configuring the right side hydraulic cylinder  34  so that the right side cylinder rod mount  37  is located transversely inward of the right side frame pivot axis R-R when the right side frame  30  is in the folded position enhances safety of the land roller  1 . A similar arrangement may be provided for the left side frame  50  involving left side hydraulic cylinder  54 , left side cylinder mount  55 , cylinder rod  56 , left side cylinder rod mount  57 , clevis  58 , elongated slots  39  and left side frame pivot axis L-L. 
         [0050]    The pair of transport wheels  12  may be provided to permit efficient transport of the land roller  1  between sites. With particular reference to  FIG. 7A ,  FIG. 7B ,  FIG. 8A ,  FIG. 8B ,  FIG. 8C ,  FIG. 8D  and  FIG. 9 , to convert the land roller  1  between a transport configuration and a working configuration, the transport wheels  12  may be pivoted upward or downward. When pivoted downward, the wheels  12  eventually reach a ground-engaging position ( FIG. 8A ) with the rollers  11 ,  31 ,  51  in ground-disengaged positions so that the land roller  1  is in the transport configuration. When pivoted upward, the wheels  12  eventually reach a ground-disengaged position with at least the center roller  11  in a ground-engaging position so that the land roller  1  is in the working configuration ( FIG. 8D ). In the working configuration, the right and left side sections with the right and left side frames  30 ,  50  are usually in the unfolded position so that the right and left rollers  31 ,  51  are also in ground-engaging positions. Under normal operation, the right and left side frames  30 ,  50  are only folded when the land roller  1  is in the transport configuration; however, it may be possible in some circumstances for the right and left side frames  30 ,  50  to be in the folded positions when the land roller  1  is in the working configuration, in which case only the center roller  11  would be in the ground-engaging. 
         [0051]    Pivoting of the wheels  12  may be accomplished with an implement-elevation hydraulic cylinder  14  mounted on the center frame  10 . The implement-elevation hydraulic cylinder  14  may be operatively connected to the wheels  12  by linkages that provide an over-center locking arrangement for the center frame  10  when the land roller  1  is in the transport configuration. An over-center locking arrangement advantageously permits the land roller to be locked in the transport configuration without the use of pins or other securing devices and without relying on hydraulic cylinders to hold the land roller in the transport configuration. Such an over-center locking arrangement therefore reduces the chance that the land roller will inadvertently lower into the working configuration while the land roller is being transported between sites. 
         [0052]    In the embodiment illustrated in the Figures, the implement-elevation hydraulic cylinder  14  may be pivotally mounted on a frame member  15  at a center cylinder mount  16 . A cylinder rod  17  of the implement-elevation hydraulic cylinder  14  may be pivotally connected to a first linkage  18  at a first pivot point  19 , for example with a pivot pin. The first linkage  18  may be pivotally connected to a second linkage  20  at a second pivot point  21 , for example with a pivot pin. The first linkage  18  may also be pivotally connected to a mounting plate  22  at a third pivot point  23 , for example by a pivot pin. The mounting plate  22  may be rigidly secured to the center frame  10 , for example by bolting or welding to a frame member, for example a vertical frame member  9 . The third pivot point  23  may be disposed between the first and second pivot points  19 ,  21 . Together, the first linkage  18 , second linkage  20  and mounting plate  22  form a linkage assembly. The linkage assembly is generally vertically disposed in relation to the longitudinal axis of the land roller  1 . The second linkage  20  may be pivotally connected to a lift axle  24  so that pivoting of the second linkage  20  causes the lift axle  24  to rotate. For example, the second linkage  20  may be pivotally connected to an axle crank  25  by a pivot pin at a fourth pivot point  26 , the axle crank  25  being rigidly secured to the lift axle  24 . The lift axle  24  may be connected to wheel axles  27  by struts  28  depending at an angle, for example perpendicularly, from a rotation axis of the lift axle  24 . The wheels  12  may be mounted on wheel hubs  13 , the wheel hubs  13  rotatably mounted on the wheel axles  27 . Longitudinal axes of the wheel axles  27  are preferably parallel to and spatially offset from the rotation axis of the lift axle  24 . The longitudinal axes of the wheel axles  27  are preferably collinear. 
         [0053]    Extension and retraction of the cylinder rod  17  imparts force through the linkage assembly, which causes the lift axle  24  to rotate, rotation of the lift axle  24  causing the struts  28  to pivot thereby lifting or lowering the wheels  12 . Correlation between extension and retraction of the cylinder rod  17  and the overall direction of rotation of the lift axle  24  depends on the orientation of the hydraulic cylinder  14 . The third pivot point  23  represents a center of rotation about which the linkage assembly rotates as the cylinder rod  17  is extended or retracted. 
         [0054]    With particular reference to  FIG. 8A  and  FIG. 9 , when the land roller  1  is in the transport position, the wheels  12  (shown in dashed line in  FIG. 8A  to illustrate structures behind the wheels  12 ) are in the ground-engaging position and the struts  28  depend from the lift axle  24  in a downward and rearward orientation. In the transport configuration, the frames  10 ,  30 ,  50  remain raised with the rollers  11 ,  31 ,  51  in the ground-disengaged position. The land roller  1  is locked in the transport configuration because abutment of an anterior edge  29  of the first linkage  18  against the vertical frame member  9  of the center frame  10  prevents the first linkage  18  from pivoting counterclockwise, which in turn prevents further pivoting of the second linkage  20  and thus prevents further pivoting of the wheels  12 . Because the first, second and fourth pivot points  19 ,  21 ,  26 , respectively, form a triangle with the second pivot point  21  forward of a line C-C between the third pivot point  23  and the fourth pivot point  26 , representing an arrangement of the linkage assembly to one side of a center formed by the line C-C, the weight of the land roller  1  itself helps hold the anterior edge  29  of the first linkage  18  against the vertical frame member  9  of the center frame  10  thereby discouraging clockwise pivoting of the first linkage  18 . Also, because the first, second and fourth pivot points  19 ,  21 ,  26 , respectively, form a triangle, a line A-A along a posterior edge  62  of the first linkage  18  proximate the second pivot point  21  forms an acute posterior angle with a line B-B along a posterior edge  64  of the second linkage  20  proximate the second pivot point  21 . Thus, the weight of the land roller  1  itself helps lock the land roller  1  in the transport configuration in addition to the force applied by the hydraulic cylinder  14 . 
         [0055]    With particular reference to  FIG. 8A ,  FIG. 8B ,  FIG. 8C ,  FIG. 8D  and  FIG. 9 , to convert the land roller  1  from the transport configuration to the working configuration, retraction of the cylinder rod  17  causes the first pivot point  19  to translate forwardly (to the right in  FIG. 9 ) causing the first linkage  18  to pivot clockwise about the third pivot point  23 , the third pivot point  23  remaining stationary because the mounting plate  22  is rigidly connected to the center frame  10 . Clockwise pivoting of the first linkage  18  causes counterclockwise pivoting of the second linkage  20 , which in turn initially causes counterclockwise rotation of the lift axle  24 . Counterclockwise rotation of the lift axle  24  causes the struts  28  to initially pivot to a more vertical orientation, thereby lifting the center frame  10  and the entire land roller  1  higher off the ground. Counterclockwise pivoting of the second linkage  20  causes the second pivot point  21  to translate rearward toward the line C-C between the third pivot point  23  and the fourth pivot point  26  (the fourth pivot point  26  shown as a dashed circle behind the wheel  12  in  FIG. 8B ,  FIG. 8C  and  FIG. 8D ). Thus, the sum of the distance between the first and second pivot points  19 ,  21 , respectively, and the distance between the second and fourth pivot points  21 ,  26 , respectively, approaches the distance between the first and fourth pivot points  19 ,  26 , respectively. When the third, second and fourth pivot points  23 ,  21 ,  26 , respectively, all become aligned along line C-C between the third pivot point  23  and the fourth pivot point  26 , the sum of the distance between the first and second pivot points  19 ,  21 , respectively, and the distance between the second and fourth pivot points  21 ,  26 , respectively, equals the distance between the first and fourth pivot points  19 ,  26 , respectively. At this point the first and second linkages  18 ,  20 , respectively, are over center. Further retraction of the cylinder rod  17  causes the second pivot point  21  to pass rearward of the line C-C, which causes the sum of the distance between the first and second pivot points  19 ,  21 , respectively, and the distance between the second and fourth pivot points  21 ,  26 , respectively, to once again become greater than the distance between the first and fourth pivot points  19 ,  26 , respectively (see  FIG. 8B ). The counterclockwise rotation of the second linkage  20  then causes clockwise rotation of the lift axle  24 , which causes the struts  28  to pivot towards a horizontal orientation (see the sequence of  FIG. 8B  to  FIG. 8C  to  FIG. 8D ), and as the struts  28  become horizontal, the center frame  10  lowers. 
         [0056]    Also, because the second pivot point  21  translates in an arcuate path about the third pivot point in response to retraction of the hydraulic cylinder  14 , the posterior angle between the line A-A along a posterior edge  62  of the first linkage  18  and the line B-B along a posterior edge  64  of the second linkage  20  becomes less acute and starts to approach 180°. The lines A-A and B-B become collinear or parallel or close to collinear or parallel when the first, second and fourth pivot points  19 ,  21 ,  26 , respectively, become aligned at the over center point. Continued retraction of the cylinder rod  17  causes the second pivot point  21  to further travel arcuately clockwise so that the posterior angle between the line A-A along a posterior edge  62  of the first linkage  18  and the line B-B along a posterior edge  64  of the second linkage  20  becomes obtuse ( FIG. 8B ,  FIG. 8C ,  FIG. 8D ), with the second pivot point  21  rearward of the line C-C. 
         [0057]    At some point during the retraction of the cylinder rod  17 , the center roller  10 , as well as the side rollers  31 ,  51  if the side rollers  31 ,  51  are in the unfolded position, is lowered sufficiently to contact the ground to begin supporting the weight of the land roller  1 . Once the second pivot point  21  is rearward of the line C-C, the weight of the land roller  1  can no longer be supported against the vertical frame member  9  of the center frame  10 , but by this time the center roller  11  is in the ground-engaging position so the hydraulic cylinder  14  does not need to be solely responsible for supporting the weight of the land roller  1 . At the same time or at a time after the center roller reaches the ground-engaging position, the wheels  12  completely lift off the ground. By the time the cylinder rod  17  is fully retracted ( FIG. 8D ), the center roller  11  is in the ground-engaging position and the wheels  12  have pivoted rearward and upward completely into the ground-disengaged position with the struts  28  oriented horizontally to bring the land roller  1  into the working configuration. 
         [0058]    With the land roller  1  in the working configuration, extending the cylinder rod  17  reverses the movements to convert the land roller  1  to the transport configuration. 
         [0059]    With the land roller  1  in the transport configuration as depicted in  FIG. 8A  and  FIG. 9 , in the event of a failure of the hydraulic cylinder  14 , the arrangement of the linkage assembly permits the weight of the land roller  1  to be supported by the vertical frame member  9  of the center frame  10 , requiring significant upward forces to overcome the weight of the land roller  1  to effect clockwise pivoting of the first linkage  18 . While the arrangement of the linkage assembly in the transport configuration of the land roller  1  enhances safety by not requiring pins to be inserted to support the land roller  1  in the transport configuration, such pins may still be employed to further enhance safety, and the linkage arrangement makes the operation of inserting such pins safer than on prior art land roller implements. 
         [0060]      FIG. 10A ,  FIG. 10B  and  FIG. 100  depict hydraulic circuit diagrams for a hydraulic system  70  of the land roller  1 . The hydraulic system  70  may comprise the implement-elevation hydraulic cylinder  14 , the right side hydraulic cylinder  34  and the left side hydraulic cylinder  54  hydraulically connected to a common hydraulic fluid reservoir (not shown) through hydraulic line connectors  72 ,  73 . Delivery of hydraulic fluid pressure from the reservoir through hydraulic line connector  72  or hydraulic line connector  73  may be selected by actuation of a single actuating device, for example a single lever, that may be actuated from a cab of a towing vehicle (e.g. a tractor). The hydraulic system  70  may further comprise a pressure relief valve  71  on a rod-side port of the implement-elevation hydraulic cylinder  14 , a  50 / 50  fluid flow splitter  74 , a T-block  75 , T-joint  76  and a plurality of hydraulic fluid lines  81 ,  82 ,  83 ,  84 ,  85 ,  86 ,  87 ,  88  (shown in dashed lines) connecting the various elements of the hydraulic system  70 . 
         [0061]      FIG. 10A  depicts the hydraulic system  70  when the land roller  1  is in the working configuration. In  FIG. 10A , the cylinder rod  17  of the implement-elevation hydraulic cylinder  14  is fully retracted, and the cylinder rods  36 ,  56  of the right and left side hydraulic cylinders  34 ,  54 , respectively, are fully extended.  FIG. 10B  depicts the hydraulic system  70  when the land roller  1  is in the transport configuration with the right and left side frames in the unfolded position. In  FIG. 10B , the cylinder rod  17  of the implement-elevation hydraulic cylinder  14  is fully extended, and the cylinder rods  36 ,  56  of the right and left side hydraulic cylinders  34 ,  54 , respectively, are also fully extended.  FIG. 100  depicts the hydraulic system  70  when the land roller  1  is in the transport configuration with the right and left side frames in the folded position. In  FIG. 100 , the cylinder rod  17  of the implement-elevation hydraulic cylinder  14  is fully extended, and the cylinder rods  36 ,  56  of the right and left side hydraulic cylinders  34 ,  54 , respectively, are fully retracted. 
         [0062]    To convert the land roller  1  between the working configuration ( FIG. 10A ) and the transport configuration with right and left side frames folded ( FIG. 100 ), the land roller  1  passes through the transport configuration with right and left side frames unfolded ( FIG. 10B ). 
         [0063]    Starting with the land roller in the working configuration ( FIG. 10A ), the hydraulic line at the hydraulic line connector  72  may be pressurized with hydraulic fluid so that hydraulic fluid flows into the line  81  to the T-joint  76 . Hydraulic fluid then flows both into the line  82  and into the  50 / 50  splitter  74 . Hydraulic fluid flowing in the line  82  flows into a barrel-side port of the hydraulic cylinder  14  forcing the cylinder rod  17  to extend thereby forcing the wheels of the land roller  1  into the ground-engaging position raising the center frame off the ground to achieve the transport configuration illustrated in  FIG. 10B . Hydraulic fluid in the splitter  74  is divided equally into two streams, one stream flowing into the line  84  and the other into the line  85 . The lines  84 ,  85  lead to rod-side ports on the right and left side hydraulic cylinders  34 ,  54 , respectively. While the cylinder rod  17  is extending, there is not enough hydraulic fluid pressure in the system  70  to overcome the torque that the right and left side frames are placing on the cylinder rods  36 ,  56  of the right and left side hydraulic cylinders  34 ,  54 , respectively. The torque experienced by the cylinder rods  36 ,  56  arises, at least in part, from a combination of the weight of the right and left side frames and the geometry of where the left side hydraulic cylinders  34 ,  54  are mounted on the center frame and the right and left side frames. Lifting the center frame is thus easier than lifting the right and left side frames; therefore the cylinder rods  36 ,  56  do not start to retract while the cylinder rod  17  is extending. Once the cylinder rod  17  is fully extended, the cylinder rod  17  dead-heads and the pressure begins to spike in the system  70 . When the pressure in the system  70  spikes sufficiently, the cylinder rods  36 ,  56  begin to retract. Once the cylinder rods  36 ,  56  are fully retracted ( FIG. 100 ), the right and left side frames have achieved the folded position. Hydraulic fluid flows out of the hydraulic cylinder  14  through the line  83  to the T-block  75  where the fluid flow is joined with hydraulic fluid flowing from the right and left side hydraulic cylinders  34 ,  54  through the lines  86 ,  87 , respectively. Hydraulic fluid then flows from the T-block  75  through the line  88  out through the hydraulic line connector  73  and back to the reservoir. 
         [0064]    Hydraulic fluid flow may be reversed to convert the land roller from the transport configuration with right and left side frames in the folded position ( FIG. 100 ) to the working configuration ( FIG. 10A ). With the land roller from the transport configuration with right and left side frames in the folded position ( FIG. 100 ), the hydraulic line connector  73  may be pressurized with hydraulic fluid so that hydraulic fluid flows into the line  88  to the T-block  75 . From the T-block  75 , hydraulic fluid flows through the lines  86 ,  87  to barrel-side ports on the right and left side hydraulic cylinders  34 ,  54 , respectively, causing the cylinder rods  36 ,  56  to extend. Extension of the cylinder rods  36 ,  56  causes the right and left side frames to unfold to achieve the transport configuration illustrated in  FIG. 10B . Hydraulic fluid also flows from the T-block  75  through the line  83  to the rod-side port on the implement-elevation hydraulic cylinder  14 . However, the rod-side port on the implement-elevation hydraulic cylinder  14  is equipped with the pressure relief valve  71 , which provides a back pressure into the line  83 . The pressure relief valve  71  is configured to open only when the pressure in the system  70  exceeds a pre-determined value. While the cylinder rods  36 ,  56  of the right and left side hydraulic cylinders  34 ,  54 , respectively, are extending, the back pressure caused by the pressure relief valve  71  is sufficient to prevent hydraulic fluid flow into the hydraulic cylinder  14 . Therefore, the right and left side frames achieve the unfolded position before the land roller is lowered into the working configuration. Once the cylinder rods  36 ,  56  are fully extended, the cylinder rods  36 ,  56  dead-head and the pressure begins to spike in the system  70 . When the pressure in the system  70  exceeds the pre-determined value, the pressure relief valve  71  opens to permit hydraulic fluid to flow into the hydraulic cylinder  14  thereby causing the cylinder rod  17  to retract lowering the land roller into the working configuration when the cylinder rod  17  is fully retracted ( FIG. 10A ). Hydraulic fluid flows out of the hydraulic cylinder  14  through the line  82  to the T-joint  76  where the fluid flow is joined with hydraulic fluid flowing from the right and left side hydraulic cylinders  34 ,  54  through the lines  84 ,  85 , respectively, and through the splitter  74 . Hydraulic fluid then flows from the T-joint  76  through the line  81  out through the hydraulic line connector  72  and back to the reservoir. 
         [0065]    Referring to  FIG. 11A  and  FIG. 11B , in another embodiment, a land roller  90  is generally the same as the land roller  1  of  FIG. 1A  except that the land roller  90  is equipped with two shock absorbers  101 ,  102  connected between a longitudinally extending elongated central tow bar  92  and a vertically oriented frame member  96  of a center frame of the land roller  90 , the central tow bar  92  also mounted on the frame member  96  by a tow bar pivot mount  95 . The land roller  90  also comprises right and left tow bars  93 ,  94 , respectively, with all three tow bars  92 ,  93 ,  94  joined at a hitch  98  at a front of the land roller  90 . The shock absorbers  101 ,  102  may be pivotally mounted to the frame member  96 . For example, shock absorber pivot mount  104  may be mounted on the central tow bar  92  while shock absorber pivot mount  105  may be mounted on the frame member  96 , with the shock absorber  101  pivotally mounted to both shock absorber pivot mounts  104 ,  105  by pins. A similar arrangement may be used with the shock absorber  102 . The shock absorbers  101 ,  102  are particularly useful to absorb vertical forces while the land roller  90  is towed to reduce vertical displacement of the land roller  90  especially when being towed over rough surfaces. 
         [0066]    The novel features will become apparent to those of skill in the art upon examination of the description. It should be understood, however, that the scope of the claims should not be limited by the embodiments, but should be given the broadest interpretation consistent with the wording of the claims and the specification as a whole.
A land roller is provided with an over-center locking linkage arrangement to help lock a roller frame of the land roller into a raised transport configuration to reduce the likelihood that a failure of the actuator system could cause the roller frame to inadvertently fall and injure a person or cause damage to property. The land roller may be further provided with actuators that are controlled in temporal series from a single controller to simplify and increase the safety of both converting the land roller between the transport configuration and a working configuration and converting side frame sections of the land roller between folded and unfolded positions.