Patent Publication Number: US-6981572-B2

Title: Foldable access device

Description:
The present invention relates generally to an access device for providing access between a lower level and an upper level. 
   In applicant&#39;s Australian Patent Specification No. 738307 (48282/97) there is described an access device of this general type and the contents of that specification are incorporated into the present specification by way of cross reference. 
   In the aforementioned Australian patent specification the access device comprises a main body in the form of a ladder or stairway which is mounted for pivotal movement about a fixed pivot mounting between an access position in which it enables access between the upper and lower levels and a stowed position in which a substantial part thereof is disposed above the fixed pivot mounting. The device further includes a drive mechanism operable to cause movement of the main body between the access and stowed positions. The drive mechanism includes a drive device and a drive link mechanism, the drive device comprising a linear actuator which includes a body portion pivotally mounted to a fixed structure and a drive member which can move in the direction of its longitudinal axis in a linear fashion relative to the body portion. The drive link mechanism includes a control drive link means mounted for pivotal movement about a drive control link fixed pivot mounting. The drive control link means is operatively connected to the drive member at a first connecting point, the fixed pivot mounting of the main body and the control link fixed pivot mounting being laterally disposed to the same side by longitudinal axis of the drive member. The link mechanism further includes coupling link means operatively connecting the main body to the control link means, the coupling link means being connected to the main body at a second connecting point, spaced from the fixed pivot mounting of the main body. The arrangement is such that actuation of the drive member causes linear movement thereof which causes the connection between the coupling link means and the main body to be displaced upwardly or downwardly to move the main body between the access position and the stowed position. 
   In Australian Patent Specification No. 738307 (48282/97) the main body includes an elongated member which as described above is in the form of a ladder or stairway which in the access position extends between the upper and lower positions with one end thereof being adjacent or resting on the lower level and the other end being adjacent the upper level. In this position, the main body is inclined with respect to a vertical axis and in the stowed position it is disposed generally upright above the upper level and preferably vertically above the main body pivot mounting point. 
   It is an object of the present invention to provide an access device in which the main body can be folded when in the stowed position. 
   According to one aspect of the present invention there is provided an access device for providing access between a lower level and an upper level, the access device including a main body which includes an upper section and a lower section which is pivotally connected to the upper section. The upper section is mounted for pivotal movement about an upper section fixed pivot mounting between an access position and a stowed position. The device further includes a drive mechanism operable to cause movement of the upper section between the access and stowed positions. The upper and lower body sections are pivotally movable relative to one another between an extended position in which they are disposed generally end to end and a retracted position in which they disposed generally side by side in a folded configuration. The device further includes a control link assembly for controlling the movement of the upper and lower sections between the extended and retracted positions, the control link assembly being movable in response to movement of the upper section between the access and stowed positions. 
   In one form the control link assembly may include a motion generating link operatively mounted for pivotal movement in response to movement of the upper section between the access and stowed positions. To this end, the motion generating link may be operatively connected to the drive mechanism. The control link assembly may further include a first transfer link assembly operatively connected to the motion generating link and being movable by the motion generating link in response to movement of the upper section between the access and stowed positions. The assembly further includes a coupling link pivotally mounted to the upper section of the main body and operatively connected to the first transfer link assembly and a second transfer link assembly operatively connected to the coupling link and the lower section of the main body. 
   Preferably, the first transfer link assembly includes a first link member having one end portion pivotally connected to upper section of the main body, and a second link member operatively connected to the first link member in spaced relation to the aforementioned one end thereof. Preferably, the first and second link members, the coupling link and a portion of the upper section of the main body form a typical four bar linkage. Preferably, the first link member is operatively connected to the motion generating link. 
   The coupling link may, in one form include two arms which extend away from one another from a junction region, one of the arms being connected to the second link member. Preferably, the two arms form a generally V-shaped configuration. There may further be provided a cross arm extending between the two arms in spaced relating from the junction region. 
   In one form the second transfer link assembly may include a third link member and a fourth link member, the third link member being connected between the coupling link and the fourth link member which in turn is operatively connected to the lower section of the main body. 
   Adjustable link means may be provided which is operatively connected between the coupling link and the lower section of the main body so as to urge it towards either the fully extended or retracted positions. The adjustable link means may be in the form of an elongated element, similar to a turnbuckle, one end of which is operatively connected to the lower section of the main body and the other end is operatively connected to the other arm of the coupling link. 

   
     Preferred embodiments of the invention will hereinafter be described with reference to the accompanying drawings, and in those drawings: 
       FIG. 1  is a schematic perspective view of an access device according to the invention in an access and extended position; 
       FIG. 2  is a schematic side elevation of the device shown in  FIG. 1 ; 
       FIG. 3  is a similar view to  FIG. 2  with the device in an intermediate position; and 
       FIG. 4  is a similar view to that of  FIGS. 2 and 3  with the device in a stored and retracted position. 
   

   The access device of the invention can be mounted to a vehicle which may be an excavating vehicle as described in Australian Patent Specification No. 738307 (48282/97). 
   Referring to the drawings the access device generally indicated at  210  includes a stairway  212  comprising an upper section  214  and a lower section  216 . The upper and lower sections are pivotally connected together via pivot mounting  218  so that the two parts can pivot relative to one another between a fully extended as shown in  FIGS. 1 and 2  and fully retracted or folded position as shown in  FIG. 4 . 
   The drive mechanism  220  comprises a support frame  221 , the upper section of the stairway being pivotally mounted to the support frame. The drive mechanism further includes a linear actuator  222 , and a drive link mechanism  224  which includes a control link  225  and a coupling link  228 . This drive mechanism is substantially the same and acts in the same fashion as has been described in the earlier Patent Specification 738307 (48282/97). 
   There is further provided a stairway control link assembly which is duplicated on both sides of the stairway and which includes a motion generating link  232  which is pivotally mounted to the support frame  221  and is operatively connected to drive and control link mechanism for moving the stairway between the access and stowed positions, the link  232  being moved in response to movement of the stairway by the drive and control link mechanism. The control link assembly further includes a first transfer link assembly including first transfer link  234  to which the motion generating link  232  is operatively connected. A second transfer link  236  has one end connected to link  234  with the other end being operatively connected to coupling link  237 . The coupling link  237  is pivotally connected to the upper section  214  of the stairway at pivot point  242 . 
   The coupling link  237  comprises two arms  238  and  239  and a cross member  247 . Arm  238  forms part of a four bar link mechanism comprising links  234  and  236  as well as arm  238 . The other arm  239  of the coupling link is operatively connected to the lower section  216  of the staircase via an adjustable link  240 , similar to a turnbuckle. 
   The handrail for the upper section  214  of the staircase is connected to the linkage formed by arm  238  and links  234  and  236 . The handrail for the lower section  216  of the staircase is connected to the coupling link  237  via transfer links  244  and  246  which form a second transfer link assembly. 
   In operation actuation of the primary linear actuator  222  causes pivotal movement of the stairway as described in the earlier patent specification. The pivotal movement of the stairway causes a pivotal movement of the link assembly comprising links  232 ,  234 ,  236  and coupling link  237  in the direction of the arrows as shown. This pivotal movement causes pivotal movement of the lower section  216  of the stairway  212  relative to the upper section  214 . When the coupling link has reached a selected position, the adjustable link  240  causes the lower section to fully retract the lower section  216  of the stairway relative to the upper section  214 . 
   Throughout this specification and the claims which follow, unless the context requires otherwise, the word “comprise”, and variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. 
   The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that the prior art forms part of the common general knowledge in Australia. 
   Finally, it is to be understood that various alterations, modifications and/or additions may be incorporated into the various constructions and arrangements of parts without departing from the spirit or ambit of the invention.