Actuators

A powered linear actuator, comprising

• a screw jack having a non-rotary rectilinearly-moving screwed shaft and a rotary non-rectilinearly-moving screwed sleeve surrounding the shaft in screw engagement therewith;
• an axially aligned pair of electric motors coaxially surrounding the screwed shaft and sleeve;
• differential gearing coupling both said motors in driving relationship with said screwed sleeve, and including a pair of gears each individually driven by a respective one of said motors and a set of planetary pinions mounted on the screwed sleeve and meshing with both said gears, whereby said pair of motors share substantially equally in driving said screw jack;
• a pair of motor locks, one for each motor, each automatically engaging to lock the respective motor against rotation in the event of motor circuit failure;
• output position feedback potentiometer means operatively coupled to said screwed shaft and generating a feedback signal;
• driving circuit means responsive to said feedback signal and an input command signal to derive a drive signal for applicaton to the motors;
• and
• resistor means in series with said potentiometer means the resistance value of which is selectable at will to determine the length of stroke of the shaft of the screw jack.