Linear drive; has pneumatic piston system containing hydraulic cylinder fixed to pneumatic cylinder and hydraulic piston and has membrane around hydraulic cylinder to form hydraulic accumulator

摘要

The drive has a pneumatic piston system (5) in a pneumatic cylinder (2) that holds a hydraulic cylinder (8) containing a plunger (26) fixed to the pneumatic cylinder and a hydraulic piston (28) that drives a drive rod (29). A space (27) between the plunger and the hydraulic cylinder has a volume that depends on the axial position of the pneumatic piston system. The pneumatic piston system has a sleeve-like membrane (9) that surrounds the hydraulic cylinder to form a hydraulic accumulator (32), which communicates to the interior (34) of the hydraulic cylinder. During a fast stroke phase, the hydraulic connection is open and the hydraulic piston is biased in the forwards stroke direction of the drive rod and is still with respect to the pneumatic piston system. During a force stroke phase, the hydraulic connection is closed and the pneumatic system moves with respect to the hydraulic cylinder, so that a high pressure is formed inside the hydraulic cylinder until the drive rod meets an obstacle. An intermediate layer (38) is formed inside the membrane to surround the hydraulic accumulator. A pneumatic connection (39) applies an evacuating pressure to the intermediate layer, which is less than a pneumatic pressure applied outside the membrane.