Abstract:
A vehicle access system and method with retractable access means ( 10 ) e.g. ladder or stairs and a retracting mechanism ( 25 ) therefor. Force applied to the access means is sufficient to retract the access means from a fully deployed position to a partially retracted position but not sufficient to not be physically resisted by a user during at least part of the retraction. With the access means in a fully retracted position, force exerted on the retracted access means can be sufficient to hold the access means in a retracted position without the need for auxiliary restraining means.

Description:
RELATED PATENT DOCUMENTS 
     This patent application is the national stage filing under 35 U.S.C. §371 of International Application No. PCT/AU2006/000846 filed on Jun. 16, 2006; which claims foreign priority benefit under 35 U.S.C. §119/365 of Australian Patent Application No. 2005903162 filed on Jun. 16, 2005, both of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     This invention relates to access systems for vehicles, specifically the access system for large earth moving equipment. 
     BACKGROUND OF THE INVENTION 
     Access systems for large earth moving equipment often incorporate a set of deployable stairs so that the operator can climb up into the cab without climbing a vertical ladder that may have a negative inclination if the equipment is not parked on level ground. 
     Once the operator is on the machine the operator retracts the stairs so that they are not hanging down and the ground clearance of the machine is increased thus minimizing the probability of the stairs being damaged by contacting rocks when the machine is in motion. 
     The stairs need to be retracted so that other personnel cannot climb up onto the machine without the operator&#39;s knowledge. Should a person be on the stairs without the operator&#39;s knowledge then the possibilities for injury to that person are numerous. The possible injuries could range from overbalancing the person to crushing or trapping the person between the moving parts of the equipment and the adjoining bodywork of the equipment. 
     The systems used for retracting the stairs can vary but generally they rely on either an electric or hydraulic system that is manually actuated by the operator. 
     Should an emergency occur such as a fire it is necessary for the operator to activate a switch to lower the stairs to evacuate the machine or find an alternative way off the machine or equipment. This can be a particular problem if there is a fire in the vicinity of the stair operating switch. 
     Should the operator forget to retract the stairs and drive the machine off, it is possible to destroy the stairs, causing an expensive repair, downtime and generating safety issues, resulting from damage to an emergency exit. 
     Another known problem of prior art ladder retraction systems is that, when retracted, the ladder is either held retracted by hydraulic/pneumatic pressure, such as provided by the lifting cylinder, or once retracted a locking pin is used to lock the ladder in place. The locking pin itself can be driven by a small hydraulic/pneumatic cylinder. 
     Problems with such systems are typically associated with bounce. The ladder can bounce during movement of the vehicle, causing failure of the lifting system. Also, damage caused to the locking pin by ladder bounce can result in failure of the locking pin mechanism. 
     Where the vehicle has an interlock system, such as a proximity switch, connected to the ladder retraction mechanism or to the locking pin actuating mechanism to prevent movement or starting the vehicle until the interlock is operated, ladder bounce can result in the switch operating thereby stopping or shutting down the vehicle unexpectedly. This results in excess downtime of the vehicle and loss of productivity. 
     With the aforementioned in mind, it is an object of the present invention to provide a system for retracting a ladder that allows a user to physically halt initial retraction but provides sufficient force to maintain the ladder retracted when retracted. 
     SUMMARY OF THE INVENTION 
     With this in view, there is provided a vehicle access system including an access means and a retracting mechanism for the access means, wherein a force applied to the access means is sufficient to retract the access means from a fully deployed position to a partially retracted position but not sufficient to not be physically resisted by a user during at least part of the retraction. 
     Thus, advantageously, an access system for a vehicle is provided that will allow a user to overcome the retraction forces during at least part of the retraction process to thus prevent further retraction, and optionally commence re-deployment of the stairs to alleviate risk of injury to the user. It will be appreciated that a user wishing to prevent retraction of the stairs will be able to safely apply sufficient force or weight to overcome retraction forces and thus halt or reverse the retraction process. 
     It will be appreciated that the term access means may encompass stairs, steps and ladders for accessing vehicles. 
     A further aspect of the present invention provides a retractable access system for a vehicle including an access means and a retracting mechanism for said access means, wherein an applied moving force is translated into a variable force for retracting the access means wherein torque generated to retract the access means exceeds torque required to retract the access means by an amount that is able to be resisted by a user for a portion of the retraction phase and increases to a greater force for a latter portion of the retraction phase. 
     Preferably, when the access means is fully retracted, a force may be exerted on the retracted access means sufficient to hold the access means in a retracted position without the need for auxiliary restraining means. 
     Preferably torque provided to retract the access means may vary through at least part of the retraction cycle. 
     The torque generated may vary throughout the retraction cycle so that the torque provided to retract the access means from 0-70% of the retraction cycle just exceeds the required torque necessary to retract the access means, and between 70-100% of the retraction cycle the torque generated may increase such that when the access means is fully retracted the torque applied to the access means is sufficient to hold the access means in the retracted position without the need for auxiliary restraining means. 
     This provides the advantage that when the access means are within reach or use of ground personnel, the forces retracting the access means may be countered by the user. When the access means are out of the reach of ground personnel, the force applied through the retraction mechanism increases so that the access means are firmly held in the retracted position. 
     Preferably the retracting/deploying system may be connected into a hydraulic pilot control circuit and/or a hand brake hydraulic circuit of the vehicle. This has the advantage that when the hand brake is released the access means are automatically retracted. When the park brake is applied or if there is a hydraulic failure the access means are deployed. 
     The geometry of the parts of the linkage is configured to provide a required torque profile. 
     A further aspect of the present invention provides a method of retracting an access means including the steps of; 
     a) applying a first lifting force during an initial portion of a retraction phase of a deployed access means, the applied first lifting force being equal to or greater than a minimum force required to lift the access means, 
     and b) subsequently applying a second lifting force during a secondary portion of the retraction phase of the deployed access means, the second lifting force being greater than the minimum required to lift the ladder. 
     Preferably the first lifting force may be less than a manual effort required to retard retraction of the access means. Preferably the manual effort may be sufficient to reverse retraction of the access means and commence re-deployment thereof. 
     Preferably the second lifting force (torque) may diverge (and increase) compared to the required lifting force during the secondary portion of the retraction phase. 
     Preferably the initial portion of the retraction phase may be about two thirds of the entire retraction phase from commencement to fully retracted. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of an embodiment of the present invention showing the mechanical arrangement of the retracting mechanism. 
         FIG. 2  is a graph showing the torque required and the torque applied to retract the stair from +45° to −90° according to an embodiment of the present invention. 
         FIG. 3  is a graph showing the torque required and the torque applied to retract the stair from +60° to −120° according to an embodiment of the present invention. 
         FIG. 4  shows a graph of excess lift torque for a ladder retracting through 90° in accordance with an embodiment of the present invention. 
         FIG. 5  shows a graph of excess lift torque for a ladder retracting from 45° extended to −90° retracted, according to an embodiment of the present invention. 
         FIGS. 6   a  to  6   d  show a series of images of a set of vehicle stairs being retracted from a deployed position to a fully retracted position according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     It will be convenient to describe the present invention with reference to the accompanying Figures and examples that illustrate possible arrangements of the present invention. 
       FIG. 1  shows a preferred embodiment where the stairs  10  operate with rotation around a fixed point at the inboard end of the stairs  10 . It would be clear to a person skilled in the art that other possible arrangements are possible. 
     The access system consists of a set of access stairs  10  actuated by a retraction mechanism  25 . 
     The stairs  10  are relatively conventional for large earthmoving equipment and may have a normal operating angle of between 45° and 70° relative to the horizontal direction and retract through an arc of between 90° and 180°. The stairs  10  may also include a hand rail  27  and textured treads (not shown) to provide a secure access way to the equipment. 
     The retraction mechanism  25  has been chosen to provide a unique non linear torque response to the stairs  10  from a fixed force linear output. In the present example the linear force is provided by a hydraulic ram  40 . The retraction mechanism  25  is optimized to provide a varying torque to lift the stairs  10  depending on where in the arc of retraction the stairs  10  are. When the stairs  10  are in the fully deployed position such that an operator could use the stairs  10  to access the equipment the torque force applied to retract the stairs  10  is enough to raise the stairs  10 , however the torque applied only exceeds the torque required by a relatively small amount so that a person would be able to stop the stairs  10  from retracting. This has the advantage that should a person be on the stairs  10  or holding the stairs  10  when they are retracted by the equipment operator, the stairs  10  will not retract and injure the person holding the stairs  10 . 
     Once the stairs  10  are retracted above the reach of any ground personnel or equipment that may get caught up with the stairs  10 , the torque applied to the stairs  10  is increased relative to the torque required. The point of increasing torque is set by the geometry of the retraction mechanism  25 . The point of increasing torque is determined during design of the retraction mechanism  25  and may vary according to the intended application. For example a small earth moving machine or equipment may have the stair travel through 70° before the stairs  10  are out of reach of ground personnel and therefore may be designed to have the torque increase at about this point. If the stairs  10  are being fitted to a larger machine the stairs  10  may only need to be retracted through 45° or even less before they are out of reach of ground personnel. 
     The increase of torque applied to the stairs  10  provides an advantage in that by the time the stairs  10  are in the fully retracted position there is a larger force holding the stairs  10  in the fully retracted position. This increased force applied to the stairs  10  eliminates the need for any additional retention mechanisms to be installed to stop the stairs  10  moving uncontrollably when the equipment is in operation. 
     Another advantage of the retraction mechanism  25  is that should the stairs  10  be restrained, by contact with fixed objects, for example rocks or other vehicles, the retraction mechanism  25  will not be damaged as the torsional force available to retract the stairs  10  is initially not significantly greater than the force required in retracting the stairs  10 . 
       FIG. 1  shows a general arrangement of the retraction mechanism  25 . The stairs  10  are pivotally mounted to the equipment at the stair main pivot  30 . The retraction mechanism  25  includes a hydraulic ram  40 , having a first end  45  pivotally connected to a hydraulic ram  40  via mounting bracket  50  at the hydraulic ram pivot  46 . The hydraulic ram bracket  50  is affixed to the stair  10  at some distance along the stair  10  remote from the stair main pivot  30  that is located on the earth moving equipment (not shown). The hydraulic ram bracket  50  is designed to move the hydraulic ram pivot some distance from the stair  10 . This distance is called the hydraulic ram offset  100 . 
     The second end  47  of the hydraulic ram  40  is pivotally connected to two linkages. One of the linkages is called the ram stair linkage  55 . The ram stair linkage  55  runs from the second end  47  of the hydraulic ram  40  to the intermediate pivot  56  located on the stairs  10  at a point between the main pivot  30  and the hydraulic ram mounting bracket  50 . 
     The second linkage connected to the second end  47  of the hydraulic ram  40  is called the ram body linkage  57 . The ram body linkage  57  runs from the second end  47  of the hydraulic ram  40  to the body pivot point  60  located on the earth moving equipment at some point offset from the stair main pivot  30 . 
     When in operation the hydraulic ram  40  extends and applies a force between the ram pivot  46  and the equipment through the ram body linkage  57 . As the ram pivot  46  is offset by the use of the hydraulic ram mounting bracket  50  (the hydraulic ram offset  100 ) and the ram body linkage  47  is mounted on the earth moving equipment at the body pivot  60  (offset from the main pivot  30 ) the force generated by the extending hydraulic cylinder  40  is converted to a torque applied to the stair  10  around the stair main pivot  30 . 
     The force applied by the hydraulic ram  40  may be adjusted so that when the stairs  10  are in a fully deployed position and an operator would use the stairs  10 . The forces applied through the hydraulic ram  40  and translated into torque are sufficient to counteract the weight of the stairs  10  so that the stairs  10  can be retracted. The torque forces are however not high enough to lift a person, the stairs  10  may even be stopped from raising by being held by a person. Once the arc of retraction has progressed so that the stairs  10  are not within reach of ground personnel the torque applied increases so that once the stairs  10  are fully retracted the torque applied to the stairs  10  is sufficient to hold the stairs  10  in the fully retracted position and prevent them moving when the earth moving equipment is in operation. 
       FIG. 2  shows a typical force profile for a set of stairs  10  operating in the +45° to −90° arc. In this graph the dotted line shows the torque required to raise the stairs  10  while the solid line represents the torque applied. It can be seen that through the arc of +45° to −70° the torque supplied is in excess of the torque required to raise the stairs  10  by approximately 10-20 kgm. When the stair  10  are in the fully retracted position the force required to overcome the tortional force provided through the retraction mechanism  25  is approximately 80 kgm. These values may be changed by adjusting the force output of the hydraulic ram  40 . 
       FIG. 3  shows a typical force profile for a set of stairs operating in the +60° to −120° arc. In this graph the dotted line shows the torque required to raise the access stairs  10  while the solid line represents the force applied to the stairs  10 . It can be seen that through the arc of +60° to −60° the torque supplied in excess of the torque required is approximately 5 kgm. When the stairs  10  is in the fully retracted position the force required to overcome the hydraulic force is substantially more. 
     In general the retraction mechanism  25  is set up so that with a constant output from a hydraulic ram  40  the torsion forces applied to the stairs  10  exceed the forces required to lift the stairs  10  for approximately ⅔ of the arc. In the last third of the arc approaching the fully retracted position the induced torque force increases so that the stairs  10  are firmly held in the retracted position and doesn&#39;t move excessively while the equipment is in operation. 
     Examples of the retraction mechanism  25  are given in Table 1 . . . 
     
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Dimension 
                 Dimension 
               
               
                 Description 
                 45° C. to 90° C. 
                 60° C.-120° C. 
               
               
                   
               
             
             
               
                 Stair main pivot 30 to extreme end 
                 2000 mm 
                 700 mm 
               
               
                 (not shown) 
               
               
                 Hydraulic Ram Offset 100 
                  100 mm 
                 200 mm 
               
               
                 Hydraulic Ram mounting bracket 50 
                 1030 mm 
                 550 mm 
               
               
                 to stair main pivot 30 
               
               
                 Ram stair linkage 55 (pivot centre to 
                  255 mm 
                 150 mm 
               
               
                 pivot centre) 
               
               
                 Ram body linkage 57 (pivot centre to 
                  220 mm 
                 150 mm 
               
               
                 pivot centre) 
               
               
                 Distance from stair pivot 56 to main 
                  160 mm 
                  50 mm 
               
               
                 pivot 30 
               
               
                 Stair main pivot to body pivot 60 
                  200 mm 
                  65 mm 
               
               
                   
               
             
          
         
       
     
     The control for the hydraulic ram  40  of the retraction mechanism  25  may be operated through the pilot circuit for the park brakes on rubber tyred equipment or the pilot circuit for the controls on tracked equipment. In large earth moving equipment the park brakes are normally on and hydraulic pressure is used to release the brakes. Alternately the hydraulic pressure for the retraction mechanism  25  may be provided by the main hydraulic system or from a separate hydraulic pump. 
     The graph in  FIG. 4  depicts excess lift torque for a vehicle ladder or stairs retracting through 90° e.g. from near vertical when deployed to near horizontal when fully retracted. The graph plots Lift torque (kgm) over and above the torque required to commence lifting the ladder against the degrees of extension of the ladder. That is, for example, a graph of the difference between the dotted line and the solid line shown in each of  FIGS. 2 and 3 . 
     In the embodiment shown, excess lift torque is minimal for initial lift (retraction) (right hand portion of curve) and thereafter increases once the ladder has retracted sufficiently that a user or personnel is either not in danger of injury, or the ladder is considered sufficiently retracted that the user has had sufficient warning of retraction or the ladder is out of reach. 
     It may be appreciated that although ideally the excess lift torque would be linear or near linear i.e. a straight line prior to the increase portion of the graph, physical, mechanical and force characteristics of the system approximate or approach the ideal, which is sufficient to provide an effective and efficient working system without requiring over-engineering or more complex configurations. 
       FIG. 5  shows an alternative excess lift torque curve being for a ladder retracting from 45° angle of extension (from the horizontal) to −90° retracted (vertical). Again, ideally the right hand portion of the graph (before the steep sloped section) would be linear. 
     It will be appreciated that the nearer the generated torque (solid line in  FIGS. 2 and 3 ) is to the required lift torque in the right hand side of each graph across the range of angles, the less manual force is required to halt retraction of the ladder. Also, in the left hand (steep) section of the graph, the more the solid (applied force) line deviates away from and above the dotted line, the greater the force (torque) applied, and the greater the holding force can be when the ladder is fully retracted. Thus, for the first approximately two thirds of the retraction process, the difference between required and applied torque can be minimal, though applied should not be less than the required torque, the easier a person can manually stopped retraction (lift) of the ladder. However, once the ladder has approximately one third retraction travel to go, lift force (torque) can be significantly increased, thus speeding up retraction and also providing sufficient force to maintain the ladder retracted without needing additional restraining means such as a locking pin mechanism (though such can be provided if required). 
       FIGS. 6   a  to  6   d  show a series of steps in the retraction process.  FIG. 6   a  shows the steps  101  fully extended (approx  450  from horizontal). The upper end  102  would normally be mounted to a vehicle (not shown). The steps are pivoted to a retracted position, with deployment being the reverse of retraction, though if required, the force curve for deployment may differ from the force curve for retraction.  FIG. 6   b  shows the steps approximately one third through the retraction process. The lower end  103  is almost horizontal with the upper end  102 . It will be appreciated that the steps or ladders etc. may take various forms and arrangements e.g. pivoted in the middle so as to also collapse to a shorter retracted form. Also the steps or ladders may retract sideways e.g. pivot sideways. However, the force curve nature of retraction according to the present invention remains the same. 
     Lifting force is provided via an actuating cylinder  104  applying force between a linkage at the upper end of the steps and a connection  105  approximately halfway down the steps. It will be appreciated that the arrangement of actuators and linkages may vary depending on the form and application of the steps, though the present invention remains unchanged. 
       FIG. 6   c  shows the steps at approximately two thirds retracted. Consequently, the steps are, in this embodiment, considered sufficiently retracted as to be generally out of reach of personnel on the ground or that personnel on the vehicle/steps have had sufficient time (warning) of retraction of the steps and therefore are deemed either clear of the steps or have had sufficient time to apply force during the initial retraction phase to halt retraction or to manually cause the steps to re-deploy by overcoming the applied lift torque. 
       FIG. 6   d  shows the steps fully (vertically) retracted. Between phases  6   c  and  6   d , torque applied to the steps increases, thereby diverging the applied lift torque curve away from the required lift torque curve. Force applied at the fully retracted position is sufficient to prevent or mitigate ladder/step bounce, thereby reducing risk of damage, injury or vehicle failure (eg due to bounce causing a proximity switch to inadvertently operate). 
     While the method and apparatus has been explained by illustrative examples it will be appreciated by those skilled in the art that varying embodiments and applications are within the teaching and scope of the present invention. The examples presented here in are by way of example and should not be construed as limiting the scope of the present invention.