Patent ID: 7536984

Claim:
An actuator, comprising a fluid driver including a housing defining a longitudinal axis and first and second directions, an actuation mechanism comprising an actuation cylinder and an actuation piston slideably disposed in the actuation cylinder, with the actuation mechanism generating actuation force at least in the first direction; at least one return spring operably connected with the actuation mechanism and biasing the actuation mechanism in the second direction; and a pneumatic booster operably connected with the actuation mechanism and biasing the actuation mechanism in the first direction, whereby giving the driver a boost force in the first direction; and wherein: the pneumatic booster further including a pneumatic cylinder; a pneumatic piston, slideably disposed in the pneumatic cylinder for at least part of its travel range; and a charge mechanism, whereby charging the pneumatic cylinder and balancing its pressure with pressurized air from a high-pressure gas source during at least part of an actuation cycle of the actuator; the charge mechanism including a control mechanism, whereby substantially closing off the charge flow during a substantial portion of a period when the pneumatic cylinder is not at its minimum volume; the actuation mechanism being operably connected with a load of the actuator through a stem; the control mechanism of the charge mechanism including an orifice gate and an undercut on the stem; and the charge flow being open and closed when the orifice gate and the undercut longitudinally overlap and underlap respectively.