Lift gate load elevator with columnar power assemblies

Abstract

A lifting system includes a vertically extending parallel pair of fixedly spaced apart guide surfaces, a linear actuator suspended vertically between said pair of guide surfaces, a vertically elongate runner member having a pivotal connection to a lower end of said linear actuator to be vertically reciprocated by said actuator, a load bearing member at a lower end of said runner member at a location spaced downwardly from said pivotal connection and a vertically spaced apart pair of sliding contact members on said runner member for relatively slidable contact with said pair of guide surfaces during vertical reciprocation of said runner member by said actuator. Each of said contact members comprises a projecting contact pad having a concave surface for slidable contact with one of said guide surfaces.

What is claimed is: 
     
         1 . A lift comprising:
 a vertically extending parallel pair of fixedly spaced apart guide surfaces;   a linear actuator suspended vertically between said pair of guide surfaces;   a vertically elongate runner member having a pivotal connection to a lower end of said linear actuator to be vertically reciprocated by said actuator;   a load bearing member at a lower end of said runner member at a location spaced downwardly from said pivotal connection; and   a vertically spaced apart pair of sliding contact members on said runner member for relatively slidable contact with said pair of guide surfaces during vertical reciprocation of said runner member by said actuator, a first one of said sliding contact members being mounted at an upper end of said runner member, a second of said sliding contact members being mounted on an intermediate portion of said runner member between said first sliding contact member and said pivotal connection, wherein said pair of sliding contact members are mounted on opposite sides of said runner member for contact with opposite ones of said pair of guide surfaces;   wherein each of said sliding contact members comprises a projecting contact pad having a curved surface for slidable contact with one of said guide surfaces;   wherein each of said sliding contact members comprises a self-adjusting mounting mechanism configured such that each of said contact pads is pivotally mounted on the runner member, allowing axial displacement of each sliding contact member relative to the corresponding one of said guide surfaces, for maintaining substantial uniform contact therebetween substantially throughout the axial width of the contact pad of that sliding contact member.   
     
     
         2 . The lift of  claim 1 , wherein:
 each of said pair of sliding contact members comprises a spaced apart tandem pair of contact pads on a support member pivotally mounted on said runner member, each of the contact pads having a curved surface for slidable contact with one of said guide surfaces.   
     
     
         3 . The lift of  claim 2 , wherein:
 a first one of said sliding contact members is at a rear side of said lift;   a second one of said sliding contact members is at a forward side of said lift; and   said load bearing member is configured to support a load at said rear side of said lift for biasing, via said runner member, said second contact member against a front one of said guide surfaces and biasing said second contact member against a rear one of said guide surfaces.   
     
     
         4 . The lift of  claim 3 , wherein:
 each of said guide surfaces comprises a curved track surface for contact with one of said contact pads;   each of said contact pads and each of said track surfaces has substantially the same radius for substantially uniform mating contact therebetween essentially throughout the axial width of said contact pad;   said contact pads and said track surfaces having the centers of their respective radii within a common vertical plane substantially bisecting said contact pads and said track surfaces.   
     
     
         5 . The lift of  claim 4 , wherein:
 said pair of sliding contact members and said pivotal connection of said runner member are so oriented relative to one another such that said longitudinal axis of said runner member is misaligned relative to a longitudinal axis of said guide surfaces.   
     
     
         6 . The lift of  claim 5 , further comprising:
 a pair of clearance contact members corresponding to the sliding contact members, each clearance contact member mounted on the runner member essentially opposite a corresponding sliding contact member, each clearance contact member configured for slidable contact with one of said guide surfaces.   
     
     
         7 . The lift of  claim 6 , wherein:
 each clearance contact member comprises a clearance pad having a substantially planar surface for slidable contact with one of said guide surfaces.   
     
     
         8 . The lift of  claim 5 , wherein:
 each of said guide surfaces comprises an arcuately convex track surface for contact with one of said contact pads; and   each of said contact pads comprises an arcuately concave surface for mating contact with one of said convex track surfaces.   
     
     
         9 . The lift of  claim 5 , wherein:
 said actuator is pivotally suspended on an axis transverse to a plane including said pair of guide surfaces; and   said pivotal connection of said runner member and said actuator has an axis parallel to said transverse pivot axis of said actuator and horizontally offset from a longitudinal axis of said runner member.   
     
     
         10 . The lift of  claim 5 , wherein:
 wear between said contact pads and said track surfaces permits displacement of said longitudinal axis of said runner member toward alignment with said longitudinal axis between said tracks while maintaining substantially uniform contact between said contact pads and said track surfaces.   
     
     
         11 . A liftgate comprising:
 a vertically spaced apart parallel pair of vertically extending columns having inner open sides confronting one another, each column including:
 a linear actuator suspended vertically between said pair of guide surfaces; 
 a vertically reciprocable runner mechanism telescopically mounted within the column, the runner mechanism comprising a vertically elongate runner member having a pivotal connection to a lower end of said linear actuator to be vertically reciprocated by said actuator; 
 a load bearing member at a lower end of said runner member at a location spaced downwardly from said pivotal connection; 
 a vertically extending parallel pair of fixedly spaced apart guide surfaces; and 
 a vertically spaced apart pair of sliding contact members on said runner member for relatively slidable contact with said pair of guide surfaces during vertical reciprocation of said runner member by said actuator, a first one of said sliding contact members being mounted at an upper end of said runner member, a second of said sliding contact members being mounted on an intermediate portion of said runner member between said first sliding contact member and said pivotal connection, wherein said pair of sliding contact members are mounted on opposite sides of said runner member for contact with opposite ones of said pair of guide surfaces; 
 wherein each of said sliding contact members comprises a projecting contact pad having a curved surface for slidable contact with one of said guide surfaces; 
 wherein each of said sliding contact members comprises a self-adjusting mounting mechanism configured such that each of said contact pads is pivotally mounted on the runner member, allowing axial displacement of each sliding contact member relative to the corresponding one of said guide surfaces, for maintaining substantial uniform contact therebetween substantially throughout the axial width of the contact pad of that sliding contact member. 
   
     
     
         12 . The liftgate of  claim 11 , further comprising:
 a platform section having a pivotal connection along a forward edge thereof to lower ends of said pair of runner members at the load bearing members for movement between a substantially vertically erect position and a rearwardly projecting horizontal load bearing position.   
     
     
         13 . The liftgate of  claim 11 , wherein:
 each of said pair of sliding contact members comprises a spaced apart tandem pair of contact pads on a support member pivotally mounted on said runner member, each of the contact pads having a curved surface for slidable contact with one of said guide surfaces;   a first one of said sliding contact members is at a rear side of said lift;   a second one of said sliding contact members is at a forward side of said lift;   said load bearing member is configured to support a load at said rear side of said lift for biasing, via said runner member, said second contact member against a front one of said guide surfaces and biasing said second contact member against a rear one of said guide surfaces.   
     
     
         14 . The liftgate of  claim 13 , wherein:
 each of said guide surfaces comprises a curved track surface for contact with one of said contact pads;   each of said contact pads and each of said track surfaces has substantially the same radius for substantially uniform mating contact therebetween essentially throughout the axial width of said contact pad;   said contact pads and said track surfaces having the centers of their respective radii within a common vertical plane substantially bisecting said contact pads and said track surfaces;   said pair of sliding contact members and said pivotal connection of said runner member are so oriented relative to one another such that said longitudinal axis of said runner member is misaligned relative to a longitudinal axis of said guide surfaces.   
     
     
         15 . The liftgate of  claim 14 , further comprising:
 a pair of clearance contact members corresponding to the sliding contact members, each clearance contact member mounted on the runner member essentially opposite a corresponding sliding contact member, each clearance contact member configured for slidable contact with one of said guide surfaces;   wherein each clearance contact member comprises a clearance pad having a substantially planar surface for slidable contact with one of said guide surfaces.   
     
     
         16 . The liftgate of  claim 15 , wherein:
 each of said guide surfaces comprises an arcuately convex track surface for contact with one of said contact pads; and   each of said contact pads comprises an arcuately concave surface for mating contact with one of said convex track surfaces.   
     
     
         17 . The liftgate of  claim 15 , wherein:
 said actuator is pivotally suspended on an axis transverse to a plane including said pair of guide surfaces; and   said pivotal connection of said runner member and said actuator has an axis parallel to said transverse pivot axis of said actuator and horizontally offset from a longitudinal axis of said runner member.   
     
     
         18 . The liftgate of  claim 15 , wherein:
 wear between said contact pads and said track surfaces permits displacement of said longitudinal axis of said runner member toward alignment with said longitudinal axis between said tracks while maintaining substantially uniform contact between said contact pads and said track surfaces.