Movement device

Abstract

A device for moving an object relative to a surface, for example for pushing a bar in a bar feed mechanism, comprises a piston mounted for reciprocation within a chamber ( 2 ), and a piston rod ( 8 ) extending from one end of the chamber. Front and rear locking devices ( 12, 10 ) respectively associated with the piston rod ( 8 ) and chamber ( 2 ) are activated alternately in synchronism with the movement of the piston in opposite directions respectively in the chamber ( 2 ).

1 . A device for moving an object relative to a surface, the device being characterised by a piston ( 50 ) mounted for reciprocation within a chamber ( 2 ), a piston rod ( 8 ) extending from one end of the chamber, a first locking device ( 10 ) associated with the chamber for locking the chamber relative to the surface, a second locking device ( 12 ) associated with the piston rod for locking the piston rod relative to the surface, drive means ( 14 ,  56 ) for effecting reciprocating movement of the piston in the chamber, and means ( 52 ,  58 ) for activating alternate locking devices in synchronism with the movement of the piston in opposite directions respectively in the chamber.  
     
     
         2 . A device as claimed in  claim 1 , wherein the drive means comprises means ( 14 ) for applying fluid pressure intermittently to the chamber ( 2 ) on one side of the piston ( 50 ), the fluid pressure forcing the piston along the chamber from an initial position, the drive means further including means ( 56 ) to return the piston to its initial position upon removal of the fluid pressure.  
     
     
         3 . A device as claimed in  claim 2 , wherein the return means comprises a resilient biasing means ( 56 ).  
     
     
         4 . A device as claimed in  claim 1 ,  2  or  3 , wherein the first locking device ( 10 ) comprises at least one locking element ( 21 ) which upon activation of the first locking device is forced laterally outwardly, relative to the axis of the piston rod ( 8 ), into engagement with the surface.  
     
     
         5 . A device as claimed in  claim 4  when directly or indirectly dependent on  claim 2 , wherein the at least one locking element ( 21 ) is forced laterally outwardly by the fluid pressure applied to the chamber ( 2 ).  
     
     
         6 . A device as claimed in  claim 5 , wherein the at least one locking element ( 21 ) is forced laterally outwardly by at least one wedge member ( 58 ) which is moved against a resilient bias ( 90 ) by the fluid pressure.  
     
     
         7 . A device as claimed in  claim 6 , wherein there are a plurality of locking elements ( 21 ) disposed around the axis of the piston rod ( 8 ), and wherein the wedge member ( 58 ) has a conical surface which is substantially coaxial with the axis of the piston rod, the wedge member being moved substantially along its own axis by the fluid pressure to force the locking elements ( 21 ) simultaneously laterally outwardly relative to the piston rod axis.  
     
     
         8 . A device as claimed in  claim 7 , wherein the wedge member ( 58 ) is contained within a housing ( 4 ), and wherein the locking elements ( 21 ) are balls which are forced outwardly through respective apertures ( 19 ) in the wall of the housing.  
     
     
         9 . A device as claimed in any preceding claim, wherein the second locking device ( 12 ) comprises at least one further locking element ( 20 ) which upon activation of the second locking device is forced laterally outwardly, relative to the axis of the piston rod ( 8 ), into engagement with the surface.  
     
     
         10 . A device as claimed in  claim 9 , wherein the at least one further locking element ( 20 ) is forced laterally outwardly by at least one further wedge member ( 52 ) which is fixed to the piston rod ( 8 ).  
     
     
         11 . A device as claimed in  claim 10 , wherein the further wedge member ( 52 ) is contained within a further housing ( 6 ) which is resiliently biased for movement relative to the further wedge member in a direction substantially parallel to the axis of the piston rod ( 8 ), wherein the at least one further locking element ( 20 ) is captured for axial movement with the further housing but is free to move laterally thereof, whereby movement of the further wedge member ( 52 ) relative to the further housing ( 6 ) under the influence of the resilient bias ( 54 ) forces the at least one further locking element laterally outwardly.  
     
     
         12 . A device as claimed in  claim 11 , wherein there are a plurality of further locking elements ( 20 ) disposed around the axis of the piston rod, and wherein the further wedge member ( 52 ) has a conical surface which is substantially coaxial with the axis of the piston rod ( 8 ), the further housing ( 6 ) being resiliently biased substantially along the axis of the conical surface of the further wedge member.  
     
     
         13 . A device as claimed in  claim 12 , wherein the further locking elements ( 20 ) are balls which are forced outwardly through respective apertures ( 18 ) in the wall of the further housing ( 6 ).