Servoactuator having motor-driven actuator with hydraulic force amplification

A mechanism for selectively controlling the movement of a linearly-displaceable member in two directions relative to a frame, comprising:

• a motor mounted on one of said member and frame, and having a rotatable output shaft;
• a first mechanical transmission having a screw with an axial force reaction bearing mounted on one of said member and frame, and having a nut mounted on the other of said member and frame, said nut being in mating engagement with said screw;
• said motor shaft being arranged to rotate one of said screw and nut with respect to the other of said screw and nut so as to displace said member with respect to said frame;
• a hydrostatic second transmission having first and second pistons, said first piston being operatively arranged to generate pressure as a function of the axial force reacted through said first mechanical transmission, said second piston being arranged to produce a pressure-induced force between said frame and member;
• a transfer mechanism operatively arranged to either (a) lock said first piston relative to one of said frame and member and to allow free motion of said second piston relative to the other of said frame and member, or (b) transfer fluid from said first piston to said second piston;
• whereby said motor output shaft maybe selectively coupled to said member either through said first transmission to impart a high-speed low-force drive to said member, or through said second transmission to impart a low-speed high-force drive to said member.

A servoactuator for selectively controlling the movement of an output member in two directions relative to a frame in response to a command signal, comprising:

• an electric motor having an output shaft;
• a motor controller arranged to provide a drive current to said motor for controllably moving said output shaft;
• a first transmission mechanism operatively arranged to displace said output member in either direction at a nominal first ratio with respect to said motor output shaft;
• and
• a hydrostatic second transmission mechanism operatively arranged to displace said output member in either direction at a nominal second ratio with respect to said motor output shaft;
• and
• a transfer mechanism operatively arranged to selectively couple said motor output shaft to said output member either through said first transmission mechanism to impart a high-speed low-force drive to said output member, or through said second transmission mechanism to impart a low-speed high-force drive to said output member.