Pneumatically actuatable linear drive for automatic spot welding machines

A pneumatically actuatable linear drive for automatic spot welding machines, comprising:

• a) a cylinder having ends, a piston rod, first and second pistons guided in tandem on said piston rod in said cylinder, a cylinder bottom closing one of said ends of said cylinder, a guide ring being disposed in the vicinity of the other of said ends of said cylinder and being penetrated by said piston rod;
• an intermediate bottom being attached to said cylinder between said pistons and being penetrated by said piston rod, said cylinder being divided into at least a first pressure chamber between said cylinder bottom and said first piston, a second pressure chamber between said first piston and said intermediate bottom, and a third pressure chamber between said second piston and said intermediate bottom;
• b) said piston rod having a first segment and a second end segment extending between said pistons, an axial conduit being disposed in said segments and having an end facing toward said cylinder bottom, a check valve disposed at said end of said axial conduit for conducting a discharge from said axial conduit into said first pressure chamber, radial conduits communicating between said axial conduit and said first and third pressure chambers, a throttle valve, said cylinder having a first air line connection leading into said first pressure chamber and communicating with said third pressure chamber, and a second air line connection leading into said second pressure chamber through said throttle valve;
• c) said second end segment having a smaller diameter than said first segment defining a shoulder between said segments, said first piston being disposed on said second end segment for axial movement toward said cylinder bottom into an end position closing said radial conduits leading out of said axial conduit into said first pressure chamber and away from said cylinder bottom into a terminal position opening said radial conduits leading out of said axial conduit into said first pressure chamber,
• d) a helical compression spring axially surrounding said second end segment with prestressing between said first piston and said shoulder;
• said check valve having a housing disposed on said second end segment in the form of a cap screw with an axially parallel conduit disposed therein;
• said end position of movement of said first piston toward said cylinder bottom being determined by said housing, and said terminal position of movement of said first piston away from said cylinder bottom being defined by a maximum compression of said helical compression spring;
• e) a connecting conduit containing said throttle valve, at least said intermediate bottom having a peripheral annular conduit communicating directly with said second air line connection and communicating through said connecting conduit with said second pressure chamber;
• f) at least said intermediate bottom having a peripheral region with an at least approximately axially parallel extending slide cylinder being open toward said second and third pressure chambers, a ventilation conduit extending in said intermediate bottom, connecting said second pressure chamber to said annular conduit and intersecting said slide cylinder, and a ventilation slide being axially movable as a function of pressure differences between said second pressure chamber and said third pressure chamber for blocking off said ventilation conduit.