Fluid actuator

Claim 1

A linear fluid actuator comprising housing means having a fluid chamber, a folded diaphragm forming a movable wall of said chamber, the central part of said diaphragm being cylindrical and normally projecting into said chamber, a piston having a hollow central cylindrical section closely contained within the like part of said diaphragm, the admittance of fluid under pressure to said chamber causing said diaphragm to roll to expand said chamber and thereby move said piston, a piston rod at least partly contained within said hollow central cylindrical section of said piston, said rod being rotatable freely relative to said piston whereby said rod can turn without twisting of said piston and diaphragm, and said rod also being capable of withdrawal axially from said piston without moving the latter, said housing means including cap means containing at least part of each of said piston and rod for guiding the same for substantially linear movement in the axial direction of the actuator, said piston being axially longer than the axial length of the central part of said diaphragm and including skirt means having a diameter larger than the diameter of the piston section within the central part of said diaphragm and closely fitting with respect to said cap means for accurately guiding said piston for such linear movement, said skirt means including an appreciable surface area along the axial extent of the actuator in such closely fitting relationship with said cap means and being cooperable with the latter to hold said piston and said diaphragm in relatively fixed radially spaced relationship with respect to said housing means, return spring means between said cap means and said rod for normally urging the latter to engagement with said piston and said piston and diaphragm in a direction in said housing means to reduce said chamber, a portion of said spring means being accommodated within said piston, said housing means including fluid inlet means in a wall thereof for supplying fluid to said chamber, and said diaphragm including exteriorly projecting bumper means on the movable wall thereof directly facing said fluid inlet means for abutting said wall of said housing means in covering relationship with respect to said fluid inlet means to space said movable wall from said housing means when the actuator is not energized and said chamber is unexpanded, said bumper means having channel means therein for passing fluid from said fluid inlet means into said chamber for substantially uniform distribution of fluid in said chamber to energize the actuator and to expand said chamber.