Abstract:
A four-bar linkage ladder is used to provide access to the cab of a mobile machine. The ladder is light enough for manual operation and may include a spring assembly, but avoids the need for the electric, pneumatic, or hydraulic actuators of prior art moveable ladders. The ladder swings from bumper height to an ergonomically desirable height for access and egress and allows passage over uneven terrain without ground contact.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure is directed to an access system for mobile machines and more specifically to a linkage ladder for use in connection with mobile machines. 
       BACKGROUND 
       [0002]    Most mobile machines or other heavy equipment, from construction and mining machines to agricultural equipment, have some form of access system to assist an operator in gaining access to an operator station or cab. For example, some trucks are accessible only via a ladder or stairs located at the front bumper. 
         [0003]    These access systems take two general forms. The first is a rigid ladder attached to the machine, such as at the bumper. In one such arrangement, the ladder is permanently fixed to a bumper and extends below the bumper. Because the ladder extends below the bumper and the overall ground clearance of the machine, the ladder can both be damaged by an obstruction and cause damage to an object when encountered. 
         [0004]    The second form of access system is a moveable staircase that uses electric, pneumatic, or hydraulic lifts to position the staircase for use or to stow the staircase away from obstructions. The staircase is generally too heavy for manual operation and must rely on the lift for operation. Furthermore, because the machines are often parked at berms or with the tires in a ditch, unless the staircase is fully deployed the steps are left at an angle that may be at best unsafe and at worst case, unusable. 
         [0005]    U.S. Pat. No. 4,425,983 discloses a four-bar fire escape ladder that is wall-mounted. The ladder uses a cam on an upright rail to hold the ladder in the up position. The ladder fails to disclose upper and lower lift handles and fails to disclose ergonomic lift areas for operator convenience and safety. The ladder also fails to disclose a baseplate for use in attaching the ladder to a mobile machine. 
       SUMMARY OF THE DISCLOSURE 
       [0006]    In one aspect of the present disclosure includes a ladder for use with a mobile machine, such as but not limited to, a loader, a dump truck, a grader, a paver, an articulated truck, an excavator, a mining shovel, and agricultural equipment. The ladder may include a first rail and a second rail with rungs connecting the first rail and the second rail, and a lift handle attached to the first support extending above a top rung to form a step assembly, the lift handle including a grip region at an upper portion of the lift handle. The ladder may also include a baseplate for use in fixedly attaching the ladder to the mobile machine, at least one four-bar linkage that moveably attaches the step assembly to the baseplate, and a latch fastened to the baseplate that engages a feature of the step assembly when in an up position. 
         [0007]    In another aspect of the present disclosure, a method of using a ladder fixedly attached to a mobile machine include providing a ladder having at least one four-bar linkage with opposite linkages being approximately equal in length, a step assembly, a guide having a groove and a stop, a lift handle attached to the step assembly, and a latch. The method may also include receiving a hand motion that releases the latch, lowering the step assembly, and engaging one of the linkages in the groove of the guide. The method also may include raising the step assembly by the lift handle, engaging at least one of the linkages against the stop of the guide, and engaging the latch at a feature of the step assembly. 
         [0008]    In yet another aspect, a machine may include a bumper, grab rails attached to the bumper, and a ladder mounted between the grab rails. The ladder may include a first rail and a second rail, rungs connecting the first rail and the second rail and a lift handle attached to the first rail extending above a top rung, the lift handle, rungs, first rail and second rail forming a step assembly, a baseplate for use in fixedly attaching the ladder to the bumper, and at least four-bar linkage that moveably attaches the step assembly to the baseplate. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a perspective view of a ladder in accordance with the current disclosure; 
           [0010]      FIG. 2  is a perspective view of a portion of the ladder of  FIG. 1  in an up position; 
           [0011]      FIG. 3  is a perspective view of the ladder of  FIG. 1  in a down position; 
           [0012]      FIG. 4  is a side view of the ladder of  FIG. 1  in an up position showing ergonomic lifting areas; 
           [0013]      FIG. 5  is a side view of the ladder of  FIG. 1  in a partially deployed position showing ergonomic lifting areas; 
           [0014]      FIG. 6  is a side view of the ladder of  FIG. 1  in a down position showing ergonomic lifting areas; 
           [0015]      FIG. 7  is a perspective view of a ladder in an up position attached to a bumper of a mobile machine; 
           [0016]      FIG. 8  is a perspective view of a ladder in a down position attached to a bumper of a mobile machine; 
           [0017]      FIG. 9  is a perspective view of a latch suitable for use with the ladder of  FIG. 1 ; 
           [0018]      FIG. 10  is a perspective view of an alternate embodiment of a ladder in accordance with the current disclosure in an up position; 
           [0019]      FIG. 11  is a perspective view of an alternate embodiment of the ladder of  FIG. 10  in accordance with the current disclosure in a down position; and 
           [0020]      FIG. 12  is a flowchart of a method of using a ladder on a mobile machine. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]      FIG. 1  and  FIG. 2  illustrate a ladder  100  in perspective view, suitable for use on a mobile machine, that is, a mobile machine with enough ground clearance so than an operator cannot step directly into the cab or onto a bumper or other foothold. Ladder  100  includes a latch  102  with a release lever  104 . The ladder  100  also includes a first hinge  106  and a second hinge  108 , as well as a first gusset  110  and a second gusset  112 . The first hinge  106  may be formed by a male connector and a female connector, discussed more below, used to attach a linkage  114  to a baseplate  138 . Similarly, the second hinge  108  may be used to attach a linkage  118  to the baseplate  138 . The gussets  110  and  112  may be used to attach respective linkages  118  and  120  the baseplate  138 . Ladder  100  may also include a spring assembly  122  that may optionally be used to assist raising and lowering the ladder  100 . 
         [0022]    A step assembly  123  may include a first rail  124 , a second rail  126 , and one or more handles  128 ,  129 , and a lift handle  130  including a lift handle grip point  131 . The step assembly  123  may also include rungs or steps, hereinafter referred to as rungs  132 , attached on one end to rail  124  and on the other end to rail  126 . There may be other variations of the exact relationship between these components, such as spacing of the rungs  132 , the location of the handles  128 ,  129 , etc. The first hinge  106  and first gusset  110  at hinge  150  define a ground link  115  (see  FIG. 5 ) in a four-bar linkage. The first hinge  106  and the hinge  150  may be referred to as baseplate hinges. A coupler link  117  (see  FIG. 5 ) is formed by the handle  128  between a hinge  146  and a hinge  148  (the support hinges). The ground link  115  and coupler link  117  form two sides of a first four-bar linkage. The linkages  114  and  116  form the other two sides of the first four-bar linkage. In order to keep the step assembly  123  in the same orientation with the baseplate  138  throughout a deployment cycle of the ladder  100 , the ground link  115  and coupler link  117  are approximately equal in length as are the linkages  114  and  116 . That is, the opposite sides of the four-bar linkage are generally equal in length even if the adjacent sides of the four-bar linkage are not equal in length. While the ideal four-bar linkage would have opposite sides exactly equal, at least manufacturing and assembly tolerances may combine in such a manner that the opposite sides are only approximately equal but still within the field of the current disclosure. In other embodiments, some intentional deviation from a perfect parallelogram four-bar linkage may be desired, for example, to allow water to drain from a step during deployment without making the step unusable if deployed only half way. 
         [0023]    A second four-bar linkage may be formed by the second hinge  108 , gusset  112 , the second handle  129  and linkages  118  and  120 . In an embodiment, each element (linkage) of this four-bar linkage is the same length as the corresponding elements of the first four-bar linkage. 
         [0024]    A connector  134  may be installed respectively in each end of each linkage  114 ,  116 ,  118 ,  120 . Additional connectors  135  may be installed in the upper and lower ends of each handle  128  and  129  and the top of baseplate  138 . A bushing  136  may be installed at hinge  146  and at hinge  148  between connectors  134  and  135  at both ends of the linkages  114  and  118 , as well as at the step assembly end of the linkages  116  and  120 . In an embodiment, the connector  134  is male and has an insert that fits into the corresponding female element of connector  135 . Of course, the connectors may be mixed as to the location of male and female connectors. In another embodiment, two female connectors may be used and a pin, rivet, or bolt may be used to mate the connectors. 
         [0025]    Referring to  FIG. 2 , a bushing  136  may also be used at the contact point between the gussets  110 ,  112  and the connector  134  at the baseplate end of linkages  116  and  120 . The bushings  136  may be made of nylon, polytetraflouroethylene (PTFE, such as Teflon® by DuPont), or another smooth compound to reduce friction and act as a wear surface at the moveable joints of the four-bar linkages, that is, where the respective connectors are joined. 
         [0026]    In an alternate embodiment, a connector  134  may be used instead of the gussets  110 ,  112 . In the illustrated embodiment, a flange of the gussets  110 , 112  may help provide additional support to the step assembly in the down position by contacting the linkages  116  and  120 . 
         [0027]    The connectors  134 ,  135  may have a cylindrical base with a shoulder. The cylindrical base may be inserted in baseplate  138 , in the linkage ends, and in the handle ends. The shoulder may set the depth of the connectors  134  and serve as a weld point. A top of the connector  134 ,  135  may be a hemispherical with a flat side positioned to face the flat side of a corresponding connector  134 ,  135 . During assembly of the handle  128 , the baseplate  138 , and the linkages  114 ,  116 ,  118 ,  120 , simple jigs may be used to align the connectors  134 ,  135  to its respective work piece so that the corresponding components are self-aligning during final assembly. 
         [0028]    A stop  140  may be installed in a guide  142  that itself is attached to the baseplate  138 . The guide  142  may include a groove  144 . The guide  142  and stop  140  interact with linkages  114  and  116  as discussed in more detail below. A second guide and stop may be installed to cooperate with the second four-bar linkage. 
         [0029]    When the ladder  100  is in an up position, as shown in  FIG. 2 , the linkage  116  may engage the stop  140  just prior to the latch  102  being captured by a feature  139  (shown in  FIG. 1 ), such as a pin, of the step assembly  123 . The stop  140  may be constructed of a resilient material configured to apply an outward resistance pressure on the step assembly  123  against the latch  102  and may reduce rattling during operation of the mobile machine. The stop  140  may be installed in the angled face of guide  142  with a screw so that the stop  140  may be adjusted in and out to provide more or less pressure to the linkage  116  during latching, for example, to accommodate operating conditions, wear, and an amount of force required for the latch  102  to capture the step assembly  123 . In an alternate embodiment, the stop  140  may be mounted in a slot (not shown) of an angled face of guide  142  so that the stop  140  may be moved up and down along the angled face and provide more or less pressure to the linkage  116  during latching. As discussed above, a second guide and stop may be installed to cooperate with second four-bar linkage on the other side of the step assembly  123 . 
         [0030]      FIG. 3  illustrates the ladder  100  in the down position. In this position, the linkage  114  rests in the groove  144  of the guide  142 . This not only provides a lower limit stop for the step assembly  123 , but also provides side-to side-support to reduce wobble when the ladder  100  is in use in the down position. 
         [0031]      FIGS. 4-6  illustrate operation of ladder  100 . A human representation in each figure shows the relative position of ladder components during deployment. The bumper  200  of the machine and ground level  202  are illustrated. 
         [0032]    In  FIGS. 4-6 , ergonomic lift areas are illustrated by box  204  and by box  206  depending upon whether an operator is standing on the bumper  200  or at ground level  202 . As shown, both the lift handle grip point  131 , that is, the top of the lift handle  130  and at least some portion of the handle  128  or  129  are configured to be located in the respective ergonomic lift areas. This allows the operator to raise and lower the ladder  100  from either ground level  202  or the bumper  200  while maintaining control of the ladder  100  from an ergonomically desirable position. 
         [0033]    Further to  FIGS. 4-6 , the side view of each figure illustrates the relative position of the linkages, for example linkage  116 , in relationship to the spring assembly  122 . In the fully up position shown in  FIG. 4 , the spring assembly  122  and the linkage  116  are virtually parallel so that force applied by the spring assembly  122  toward the baseplate  138  will have little or no leverage on the step assembly  123  in a downward direction. 
         [0034]      FIG. 5  illustrates that midway through the travel of the step assembly  123  (up or down) an angle is formed between the spring assembly  122  and the linkage  116  so that the spring assembly  122  provides a counterbalance force to the step assembly  123 . 
         [0035]      FIG. 6  illustrates that at the bottom of the travel of the step assembly  123  the spring assembly  122  is again virtually parallel with the linkage  116 , and again, the force of spring assembly  122  does not provide any leverage to the step assembly  123 . In one embodiment, the force imparted by the spring assembly  122  will not prevent the ladder  100  from dropping to its fully down position so that if the latch  102  fails, the ladder  100  will deploy on its own and fail in the down position. In an embodiment, the force of the spring assembly  122  may be selected so that the maximum force required at any point in the deployment cycle is about 70-130 Newtons, or more particularly, about 95-105 Newtons. The spring assembly force required may be calculated using the mass of the step assembly  123  and linkages as well as the maximum angle between the spring assembly  122  and a linkage  114 , selected for the purpose of illustration. Simple trigonometry allows development of a vertical component of force needed to provide the desired counterforce for the downward gravitational force on the step assembly  123 . 
         [0036]      FIG. 7  is a perspective view of the ladder  100  in an up position mounted to the bumper  300  of a machine (not fully shown). The machine to which the bumper  300  is attached may be a loader, a dump truck, a grader, a paver, an articulated truck, an excavator, a mining shovel, agricultural equipment, etc. In some embodiments, the ladder  100  may not be attached to a bumper but instead may be attached to another part of the machine. 
         [0037]    As illustrated in  FIG. 7 , the ladder  100  may be attached to a bumper  300 . A left grip  302  and a right grip  304  may be permanently mounted to the bumper  300  on either side of the ladder  100 . Once on the bumper  300  an operator may continue up a fixed staircase (not shown) using a staircase railing  306  to access a cab of the machine. As shown, a lift handle  130  may only be present on a side of the ladder  100  away from the fixed staircase railing  306  so that the lift handle  130  does not interfere with an operator ascending or descending the staircase. As illustrated here, the lift handle  130  is configured as an umbrella handle as opposed to the full loop shown in  FIG. 1 . In other embodiments, lift handle  130  may be provided on both rails  124  and  126 . In some embodiments, this is not necessary because the grips  303 ,  304  can provide required points of contact so that the lift handle  130  is not required as a handhold during ladder use. That is, the lift handle  130  can serve only to raise and lower the ladder  100  when the operator is on the bumper  300 . 
         [0038]      FIG. 8  is similar to  FIG. 7  with the ladder  100  in the down position. The distance from the top of the bumper  300  to the bottom rung  132  when the step assembly  123  is fully down is the total drop of the ladder  100 . The total drop is a function of the length of the linkages  114 ,  116 ,  118 ,  120 . In an embodiment, the step height is between 350 mm and 450 mm above the ground or more particularly between 390 mm and 410 mm Other step heights may be used based on design constraints and applicable regulations. As the total drop is increased, an angle of the lift handle  130  may be increased to keep the lift handle from extending too far out over the edge of the bumper  300  during deployment of the ladder  100 . From the ground, an operator can simply step back if the swing path of the step assembly  123  requires it. 
         [0039]      FIG. 9  illustrates a latch  102  and release lever  104 . The latch  102  can include a double jaw mechanism  320  as shown or any number of other locking mechanisms known in the art. The latch  102  may engage the feature  139 , such as a pin to hold the step assembly  123  in the up position and the double jaw mechanism  320  may open to release the feature  139 . The release lever  104  shown may provide convenient activation both by hand, when an operator is standing on the ground, or by a shoe or boot when an operator is standing on the bumper  300 . 
         [0040]      FIG. 10  and  FIG. 11  show perspective views of another embodiment of a ladder  330 . The ladder  330  may include a step assembly  332 . In this embodiment, a hinge mount  340  is used on both ends of a dog bone linkage  342 . A bushing  346  may be used to reduce friction and act as a wear surface between the hinge mount  340  and the dog bone linkage  342 . The remaining joints of the ladder  330  may be similarly connected. 
         [0041]    When in an up position, as shown in  FIG. 10 , a stop  344  may contact the step assembly  332 . Similar to that of the embodiment described above, the stop  344  may provide an outward resistance pressure as the latch  102  is engaged to reduce vibration while the ladder  330  is stowed. In the down position, shown in  FIG. 11 , the stop  344  may contact a lower one of the dog bone linkages  342  and provide a soft stop when deploying the ladder  330 . In this embodiment, side-to-side support is provided by the wide base of the dog bone linkage  342 . 
       INDUSTRIAL APPLICABILITY 
       [0042]    The ladder  100  may be used on a variety of machines, including but not limited to, a loader, a dump truck, a grader, a paver, an articulated truck, an excavator, a mining shovel, and agricultural equipment. Because it is manually operated, the ladder  100  is readily available and does not depend on power from an external source, such as, hydraulic, electric, or pneumatic power from the machine or an external source. Because the ladder  100  stows at or near bumper height, the overall ground clearance of the machine is improved over fixed ladders. The four-bar linkage construction allows the ladder  100  to remain at a nearly constant angle throughout the deployment so that if the ladder cannot be fully lowered, it is still usable at whatever height it becomes obstructed. In an embodiment, the linkages  114 ,  116 ,  118 ,  120  may be of a length that even at a maximum distance from the bumper  300 , see, e.g.,  FIG. 5 , the ladder  100  may be safely reached by stepping from the bumper  300 . 
         [0043]    Referring to  FIG. 12 , a method  400  of using a linkage ladder  100  for accessing a machine is discussed and described. At block  402 , the ladder  100  may be provided, including four linkages  114 ,  116 ,  118 ,  120 , that may be equal in length, a step assembly  123 , a guide  142  having a groove  144  and a stop  140 , a lift handle  130  attached to the step assembly  123 , and a latch  102 . 
         [0044]    At block  404 , a hand motion that releases the latch  102  may be received at a release lever  104  of the latch  102 . The release lever  104  is operable by hand, with a tool, or with a shoe or boot. 
         [0045]    After operating the release lever  104  to unlock the latch  102 , the step assembly  123  may be lowered at block  406 . If the step assembly  123  cannot be fully deployed, such as when there is an obstruction under the bumper  300 , the step assembly  123  remains at a constant orientation and can be used at any height. 
         [0046]    At block  408 , when in the down position, one or more of the linkages  114 ,  116 ,  118 ,  120  may be engaged in the groove  144  of its respective the guide  142 . At block  410 , after being deployed in the down position, the ladder  100  may be lifted by either a handle  128  or the lift handle  130 . In an alternate embodiment, additional hinges, such as first hinge  106  and second hinge  108  and additional guides and stops, such as guide  142  and stop  140  may be installed instead of the gussets  110  and  112  to provide additional side-to-side stability and weight-bearing capacity. In yet another embodiment, the gussets  110 ,  112  and the hinges  106 ,  108  may be reversed so that the gussets  110 ,  112  are above the hinges  106 ,  108 . In yet another embodiment, a guide  142  and stop  140  may be installed under the spring assembly  122  to provide additional side-to-side stability and support for the step assembly  123  when in the down position. 
         [0047]    At block  412 , at least one of the linkages may be engaged against the stop  140 . At block  414 , the latch  102  may engage a feature of the step assembly, such as a pin, knuckle, barb, etc. to lock the ladder  100  in the up position. At block  416 , a foot motion may be received at the release lever to open the latch and allow the ladder  100  to be deployed. 
         [0048]    The baseplate  138  provides a single mounting point for the ladder as opposed to some four-bar linkage ladders that have multiple attachment points, for example, for wall mounting. When drilled at standard offsets, holes in the baseplate  138  can allow use on any machine that accommodates the standard holes so that the ladder  100  may be used in aftermarket applications as well as in new designs. To accommodate slight mounting variations, some or all of the mounting holes may be slotted to allow for adjustment. Similarly, the mounting holes in the baseplate for the guide  142  may be slotted to accommodate different materials, different diameter linkages  114 , and to account for wear of the components.