Fail-safe hydraulic actuator with constant force retraction springs

A fail-safe hydraulic actuator, comprising:

• a housing having a first end and a second end and defining a piston chamber;
• a piston assembly that includes a piston slidably disposed within the piston chamber and a piston rod connected to the piston and movable with the piston, the piston rod having an end thereof that extends through the first end of the housing;
• the housing includes a hydraulic fluid cavity that is configured to contain a hydraulic fluid and that is in fluid communication with the piston chamber to allow passage of hydraulic fluid between the hydraulic fluid cavity and the piston chamber;
• at least first and second constant force retraction spring mechanisms, the first and second constant force retraction spring mechanisms each include a constant force retraction spring having an end fixed to the piston on a side of the piston opposite of where the piston rod is connected to the piston;
• a sensor that detects linear position of the piston within the piston chamber.