Electromechanical equivalent of fluid powered cylinder

An electromechanical actuator for taking the rotational motion of an electric motor and varying the spacing between first and second actuator ends from a first close disposition to a second spaced disposition comprising:

• an electric motor including a current input and a rotating power output;
• a rotating and threaded lead screw attached for rotation with respect to said first actuator end;
• transmission means generally at one end of said lead screw for transmitting said rotating power output of said motor to rotate said lead screw, said lead screw having an unthreaded portion at the end remote from said transmission means;
• a drive nut having threads complementary to said lead screw;
• a hollow inner cylinder coaxially surrounding said lead screw, and linking said drive nut to said second actuator end;
• compression means linked to said second actuator end;
• a casing devoid of limit switches therein, and having said electric motor mounted thereto, said casing including a hollow outer cylinder coaxially surrounding said lead screw and said hollow inner cylinder, a head abutting said outer cylinder at its end farthest from said transmission means, a cap remote from said head, and a plurality of tie rods holding said head and said cap in spaced relation with said outer cylinder therebetween;
• means within said casing for preventing relative rotation between said casing and said drive nut, whereby axial movement of said drive nut along said lead screw occurs upon rotation of said lead screw;
• spring means surrounding said unthreaded portion on said lead screw and retained thereon, wherein said drive nut compresses said spring means when said actuator ends are at said spaced disposition and wherein said compression means compresses said spring means when said actuator ends are at said close disposition, said spring means imparting to said electric motor through said transmission means an increasing load upon movement of said actuator to either of said close or spaced dispositions;
• current sensing means attached to said current input of said electric motor for detecting change of current due to said increasing load;
• and
• current interrupting means connected to said current input and responsively communicated to said current sensing means for interrupting said current upon said increase in current due to said increase in load;
• such that movement of said actuator ends to either of said close or spaced dispositions is detected, and movement interrupted, despite said casing's being devoid of limit switches therein;
• said casing's being devoid of limit switches therein further facilitating a shortening of said actuator wherein said actuator may be shortened by a predetermined decrement by shortening said lead screw by said decrement, shortening said outer cylinder by said decrement, shortening said inner cylinder by said decrement, and shortening said tie rods by said decrement.