Linear displacement actuator

A linear displacement actuator comprising:

• a shaft having an outside diameter and a screw thread;
• a female part in which said male part is engaged having an inside diameter and a plurality of internal circular ribs which collaborate with said screw thread and a plurality of grooves, said inside diameter of said female part being greater than said outside diameter of said male part;
• and
• at least a pair of linear actuators arranged perpendicularly in a cage-like support that is free to be displaced axially with respect to said male part and which places said female part in sinusoidal vibration in a pair of perpendicular directions with an appropriate phase shift between said vibrations, and displaces, rotation-wise, a line of contact between said screw thread and said at least one peripheral rib while said screw thread and said peripheral rib remain motionless in terms of rotation one with respect to each other to bring about relative linear displacement of said female part and said male part, and said female part is placed in said support which is free in terms of axial displacement along said shaft and is positioned between said linear actuators and a pair of corresponding return springs, each of said return springs being diametrically opposite of each of said linear actuator.