In order to develop a device for the elderly on bed for long-term to do legs rehabilitation exercise, a small-sized magnetic hydro-cylinder without piston rod is researched. The finite element analysis software--Ansoft Maxwell and an experiment device developed by us are used to analyze and to research the magnetic coupling force performance, the effects of the arrangement of the magnet, the separation distance between the magnets and the magnet thickness on the cylinder performance. Finite element analysis and experimental results show that the cylinder wall thickness should be thinned under the premise of meeting the strength requirement, the magnets should be arranged in the reverse direction, the separation distance between the adjacent magnets should be set to 4 mm, the thickness of magnet should be set to about 10 mm. Under those conditions, the better performance of magnetic hydro-cylinder without piston rod can be gotten, and the miniaturization of the cylinder structure can be realized.
