Dockboard safety stop

Claim 2

An adjustable dockboard for spanning the gap between a loading dock and a floor of a carrier disposed in a loading or unloading position adjacent the dock, said dockboard having a ramp with front and rear edges and means at its front edge to rest on the floor of a carrier and means hingedly connecting the rear edge of the ramp relative to the dock so that the ramp may rise and fall as the height of the carrier changes, and safety means for supporting the ramp in the event the carrier pulls away from the dock and leaves the ramp unsupported at its front edge, comprising the improvement wherein said safety means includes closed and self-contained telescopic fluid pressure cylinder means acting solely as a safety stop and coacting with said ramp for stationarily supporting same when the load on said ramp exceeds a predetermined magnitude, said cylinder means including wall means defining a substantially closed chamber containing therein a predetermined quantity of a substantially incompressible fluid, said wall means defining a pair of compartments containing therein said incompressible fluid, said cylinder means also including piston means slidably movable relative to said wall means, said piston means defining one of the boundaries of at least one of said compartments, flow passage means extending between said pair of compartments and providing the sole communication therebetween, and valve means associated with said flow passage means for totally closing same and preventing flow between said compartments when a sudden load is imposed on said ramp in excess of said predetermined magnitude and said ramp is unsupported, said valve means remaining closed for holding said piston means stationary relative to said wall means so long as said load remains on said ramp.

Claim 3

A dockboard according to claim 1, wherein said cylinder means includes a cylinder housing defining an elongated piston chamber therein and said piston means being slidably positioned within said housing and slidable longitudinally thereof, said piston means dividing said chamber into said pair of compartments, and said cylinder means further including accumulator means defining therein a reservoir chamber, and means defining a passageway between said reservoir chamber and one of said compartments, said piston and reservoir chambers and said passageway interconnecting same defining a closed system, and said predetermined quantity of substantially incompressible fluid being disposed in said system and completely filling said piston chamber and only partially filling said reservoir chamber, and said passageway always being filled with said fluid.

Claim 4

A dockboard according to claim 2, wherein said piston means has said flow passage means exTending therethrough for permitting flow of said fluid between said compartments, and said valve means being mounted on said piston means and associated with said passage means for preventing flow through said passage means from the other compartment to said one compartment when the pressure of the fluid within said other compartment exceeds a predetermined value.

Claim 5

A dockboard according to claim 2, wherein said piston means has a tapered surface formed on one end thereof, wherein said passage means terminates at said tapered surface, and said valve means comprising a platelike valve member mounted on said piston means adjacent said tapered surface, said valve member being resiliently deflectable into engagement with said tapered surface for closing the terminal end of said passage means.

Claim 6

A dockboard according to claim 1, wherein said ramp has track means of predetermined length formed on the lower side thereof, said track means extending longitudinally in a direction from the rear edge toward the front edge of said ramp, the opposite ends of said track means being closed by stop means, and said fluid pressure cylinder means having slide means mounted on one end thereof and disposed for movement along said track means for enabling said ramp to undergo a limited amount of swinging movement without causing extension or retraction of said cylinder means.

Claim 7

In combination, a vertically swingable dockboard ramp and a safety stop device for preventing free downward swinging of the dockboard ramp when the ramp is unsupported and has a load disposed thereon, said safety stop device comprising: telescopic fluid pressure cylinder means adpted for coaction with said ramp and capable of locking up when a load in excess of a predetermined magnitude is imposed thereon for stationarily holding the ramp, said cylinder means including a substantially closed cylinder housing defining therein an elongated bore and a piston slidably disposed within said bore and dividing same into a compression chamber and a suction chamber, a piston rod fixedly secured to said piston and extending through one of said chambers and outwardly from one end of said cylinder housing, accumulator means disposed adjacent said cylinder housing and defining therein a reserve chamber and means defining a passageway providing communication between said reserve chamber and said suction chamber, said reserve, suction and compression chambers and said passageway defining a closed system containing therein a predetermined quantity of a substantially incompressible fluid, said reserve chamber as defined by said accumulator means having only a portion thereof filled with said fluid, the remaining volume of said reserve chamber containing trapped therein a predetermined quantity of a compressible gas, said passageway providing communication with the portion of said reserve chamber containing said fluid therein, said suction and compression chambers and said passageway and said portion of said reserve chamber always being filled with said fluid, flow control passage means providing the sole communication between said suction chamber and said compression chamber, and load-responsive valve means associated with said flow control passage means for totally closing same and preventing flow of fluid from said compression chamber to said suction chamber when a load in excess of said predetermined magnitude is imposed on the unsupported ramp.

Claim 8

In combination, a vertically swingable dockboard ramp and a safety stop device for preventing free downward swinging of the dockboard ramp when the ramp is unsupported and has a load disposed thereon, said safety stop device comprising: telescopic fluid pressure cylinder means adpted for coaction with said ramp and capable of locking up when a load in excess of a predetermined magnitude is imposed thereon for stationarily holding the ramp, said cylinder means including a substantially closed cylinder housing defining therein an elongated bore and a piston slidably disposed within said bore and dividing same into a compression chamber and a suction chamber, a piston rod fixedly secured to said piston and extending through one of said chambers and outwardly from one end of said cylinder housing, accumulator means disposed adjacent said cylinder housing and defining therein a reserve chamber and means defining a passageway providing communication between said reserve chamber and said suction chamber, said reserve, suction and compression chambers and said passageway defining a closed system containing therein a predetermined quantity of a substantially incompressible fluid, said reserve chamber as defined by said accumulator means having only a portion thereof filled with said fluid, the remaining volume of said reserve chamber containing trapped therein a predetermined quantity of a compressible gas, said passageway providing communication with the portion of said reserve chamber containing said fluid therein, said suction and compression chambers and said passageway and said portion of said reserve chamber always being filled with said fluid, flow control passage means providing the sole communication between said suction chamber and said compression chamber, and load-responsive valve means associated with said flow control passage means for totally closing same and preventing flow of fluid from said compression chamber to said suction chamber when a load in excess of said predetermined magnitude is imposed on the unsupported ramp.

Claim 9

A combination according to claim 6, wherein said flow control passage means extends through and interconnects the opposite end faces of said piston, and said valve means comprising a valve member mounted on said piston and disposed for coaction with said flow control passage means.

Claim 10

A combination according to claim 6, wherein said flow control passage means comprises a plurality of small metering holes formed in said piston and extended axially therethrough for providing communication between said compression chamber and said suction chamber, said plurality of holes beiNg disposed in a circular pattern generated about the axis of said piston, and said valve means comprising a platelike valve disc having the center portion thereof fixedly mounted on said piston and having the annular peripheral portion thereof disposed for overlapping said holes, the annular peripheral portion of said valve disc and the adjacent end face of said piston wherein said holes terminate being angularly inclined relative to one another by means of a small intermediate angle, and the annular peripheral portion of said valve disc being resiliently deflectable so as to move into engagement with the adjacent end face of said piston for covering said holes when the pressure in said compression chamber exceeds a predetermined value.

Claim 11

A safety device according to claim 6, wherein said cylinder means is disposed so as to always extend at least partially in the vertical direction, and said compression chamber being disposed adjacent the lower end of said cylinder housing and said piston rod extending upwardly from said piston and through said suction chamber, said accumulator means comprising an elongated hollow tubular member disposed directly adjacent said cylinder housing and fixedly connected thereto and extending substantially longitudinally thereof, and said passageway comprising conduit means providing communication between the upper end of said suction chamber and the lower end of said reserve chamber, said conduit means including an elongated pipe member disposed within said reserve chamber and having the lower open end thereof disposed adjacent the lower end of said reserve chamber, said flow control passage means being formed within said piston and extending axially therethrough for providing communication between said suction chamber and said compression chamber, and said valve means comprising a valve member mounted on said piston and disposed for coaction with said passage means extending therethrough, said valve member being disposed so as to be acted upon by the pressure fluid contained within said compression chamber.

Claim 12

In an adjustable dockboard for spanning the gap between a loading dock and the bed of a carrier disposed in a loading or unloading position adjacent the dock regardless of the relative height of the dock and the bed of the carrier, said dockboard having a base, a decklike ramp pivotally connected adjacent the rearward edge thereof to said base, a lip plate hingedly connected to the front edge of said ramp and adapted for engagement with the bed of said carrier, spring means coacting between said base and said ramp for normally swingably urging said ramp upwardly into an uppermost position wherein the front edge of said ramp is disposed a substantial distance above the rear edge of said ramp, and safety stop means coacting between said ramp and said base for preventing downward swinging movement of said ramp when same is unsupported and has a large load imposed thereon, the improvement wherein said safety stop means comprises: extendible and contractible fluid pressure cylinder means coacting between said base and said ramp, said cylinder means including load sensing means associated therewith for positively locking said cylinder means in a determined position so as to prevent further telescopic movement thereof when the ramp is unsupported and has a load in excess of a predetermined magnitude imposed thereon, first connecting means structurally interconnecting one end of said cylinder means to said base, and second connecting means operatively interconnecting the other end of said cylinder means to said ramp, one of said first and second connecting means including lost motion means associated therewith for permitting said ramp to be angularly swung downwardly through a predetermined angle from its uppermost position without causing any telescopic movement of said cylinder means.

Claim 13

In an adjustable dockboard for spanning the gap between a loading dock and the bed of a carrier disposed in a loading or unloading position adjacent the dock regardless of the relative height of the dock and the bed of the carrier, said dockboard having a base, a decklike ramp pivotally connected adjacent the rearward edge thereof to said base, a lip plate hingedly connected to the front edge of said ramp and adapted for engagement with the bed of said carrier, spring means coacting between said base and said ramp for normally swingably urging said ramp upwardly into an uppermost position wherein the front edge of said ramp is disposed a substantial distance above the rear edge of said ramp, and safety stop means coacting between said ramp and said base for preventing downward swinging movement of said ramp when same is unsupported and has a large load imposed thereon, the improvement wherein said safety stop means comprises: extendible and contractible fluid pressure cylinder means coacting between said base and said ramp, said cylinder means including load sensing means associated therewith for positively locking said cylinder means in a determined position so as to prevent further telescopic movement thereof when the ramp is unsupported and has a load in excess of a predetermined magnitude imposed thereon, first connecting means structurally interconnecting one end of said cylinder means to said base, and second connecting means operatively interconnecting the other end of said cylinder means to said ramp, one of said first and second connecting means including lost motion means associated therewith for permitting said ramp to be angularly swung downwardly through a predetermined angle from its uppermost position without causing any telescopic movement of said cylinder means.

Claim 14

In a dockboard according to claim 10, further including stop means associated with said one connecting means and coacting with said cylinder mEans for causing telescopic movement of said cylinder means when the downward swinging movement of said ramp from its uppermost position exceeds said predetermined angle.

Claim 15

In a dockboard according to claim 10, wherein said first connecting means pivotally connects the lower end of said cylinder means to said base and said second connecting means connects the upper end of said cylinder means to said ramp, said second connecting means including means permitting relative pivotal movement between said cylinder means and said ramp and said lost-motion means permitting limited linear displacement of the upper end of said cylinder means relative to said ramp in a direction substantially perpendicular to the front edge of said ramp for permitting angular swinging movement of said ramp through said predetermined angle without causing any telescopic movement of said cylinder means.

Claim 16

In a dockboard according to claim 12; wherein said lost motion means includes an elongated guide track of predetermined length fixedly secured to the underside of said ramp, said guide track extending in a direction substantially perpendicular to the front and rear edges of said ramp and having stop means associated with at least one end thereof, and the upper end of said cylinder means having slide means associated therewith and coacting with said guide track for pivotally interconnecting the upper end of said cylinder means to said ramp while also enabling relative linear movement therebetween through said predetermined length.

Claim 17

In a dockboard according to claim 10; wherein said fluid pressure cylinder means includes a cylinder housing defining therein a piston compartment and piston means positioned within said compartment and slidably disposed in sealing engagement with the walls of said cylinder housing for dividing said compartment into first and second chambers, said piston means including a piston rod projecting through one of said chambers and slidably supported on and projecting outwardly of said cylinder housing, wall means defining a reserve chamber and conduit means defining a passageway providing communication between said first chamber and a portion of said reserve chamber, said plurality of chambers defining a closed system containing therein a predetermined quantity of a substantially incompressible pressure fluid, said pressure fluid completely filling said first and second chambers and said passageway and only partially filling said reserve chamber, said pressure fluid in said reserve chamber filling said portion thereof, and a predetermined quantity of a compressible gas located in the remaining portion of said reserve chamber whereby said reserve chamber and said passageway communicating between said reserve chamber and said one chamber always results in said first chamber being filled with said pressure fluid without requiring the use of pumps or the like, said cylinder means including a flow control passage providing for flow of said fluid between said first and second chambers, and valve means associated with said flow control passage for controlling the flow therethrough, said valve means being automatically moved to a closed position when the pressure in a selected one of said first and second compartments exceeds a predetermined maximum for causing said cylinder means to lock up.

Claim 18

In a dockboard according to claim 14, wherein said flow control passage is formed in and extends axially through said piston means, and wherein said valve means comprises a valve member mounted on said piston means.

Claim 19

In a dockboard according to claim 15, wherein said wall means defining said reserve chamber comprises a closed elongated tubular housing disposed directly adjacent and extending longitudinally along said cylinder housing, said tubular housing being fixedly mounted on said cylinder housing, the fluid level in said tubular housing always being at least equal to the uppermost fluid level in said cylinder means irrespective of the position of said piston means within said cylinder means so as to permit the gravity flow of fluid from said reserve chamber into said cylinder means for maintaining said first and second chambers completely filled with fluid.

Claim 20

In a dockboard according to claim 10, wherein said cylinder means comprises a pair of closed and self-contained telescopic fluid pressure cylinders disposed adjacent the opposite edges of said ramp, each of said telescopic fluid pressure cylinders being disposed for coaction between said ramp and said base, and conduit means connected between said pair of fluid pressure cylinders and providing communication between the second chambers disposed within said cylinders for causing said cylinders to act substantially as a single unit.

Claim 21

In a dockboard having a loading ramp for vertical swinging movement, an actuating mechanism coacting with the loading ramp for causing at least upward swinging movement of said ramp, and a safety mechanism coacting with said ramp for preventing undesired downward swinging movement of said ramp when same has a load of at least a predetermined magnitude imposed thereon, the improvement wherein said safety mechanism comprises telescopic fluid pressure cylinder means utilizing therein a substantially incompressible fluid and coacting between said ramp and a stationary support surface, said fluid pressure cylinder means being totally independent of said actuating mechanism.

Claim 22

In a dockboard having a loading ramp for vertical swinging movement, an actuating mechanism coacting with the loading ramp for causing at least upward swinging movement of said ramp, and a safety mechanism coacting with said ramp for preventing undesired downward swinging movement of said ramp when same has a load of at least a predetermined magnitude imposed thereon, the improvement wherein said safety mechanism comprises telescopic fluid pressure cylinder means utilizing therein a substantially incompressible fluid and coacting between said ramp and a stationary support surface, said fluid pressure cylinder means being totally independent of said actuating mechanism.

Claim 23

In a dockboard according to claim 18, wherein said cylinder means includes wall means defining at least a pair of chambers containing said fluid therein, said cylinder means including piston means movable relative to said wall means and defining at least one of the boundaries of at least one of said chambers, movement of said piston means relative to said wall means causing flow of fluid between said chambers, and movement of said piston means relative to said wall means being caused solely by and responsive to swinging movement of said ramp.

Claim 24

In a dockboard according to claim 18, wherein said ramp is swingably movable into a first uppermost position wherein said ramp extends upwardly at a substantial angle relative to a horizontal plane, said ramp being moved into said first position by said actuating mechanism, said ramp also being swingably movable into a second position wherein said ramp projects downwardly relative to said horizontal plane, said ramp also being positionable in the third intermediate position which is spaced between said first and second positions, said ramp when in said third position extending at least slightly upwardly relative to said horizontal plane, said third position being spaced a substantial angular extent from said first position, and said telescopic fluid pressure cylinder means coacting with said ramp for stopping downward swinging of same only when said ramp is located in or between said second and third positions, said fluid pressure cylinder means being ineffective to prevent downward swinging movement of said ramp as said ramp is being moved from said first position to said third position.

Claim 25

In a dockboard according to claim 20, wherein said cylinder means includes a cylinder housing defining therein a piston chamber and piston means slidably disposed within said piston chamber and dividing same into suction and compression compartments located on opposite sides of said piston means, means defining a flow passage for normally permitting fluid communication between said suction and compression compartments, and load responsive valve means coacting with said passage for totally closing same to positively prevent transfer of fluid between said compartments when the pressure within said compression compartment exceeds a preselected value, closing of said valve means causing entrapment of the fluid within said compression compartment for causing locking of said piston means in its previous position to positively prevent movement of said ramp.