Magnetic position indicator and actuator using same

An actuator apparatus for controlling the relative positions of a pair of members, one of which is movable relative to the other along a given path, said apparatus comprising:

• magnetic means forming at least a portion of a first of said members for providing adjoining magnetic fields of opposite polarity and generally equal field strengths extending generally perpendicular to said given path for providing a substantially linear variation in field strength extending over an elongated path which traverses an abutment of said fields;
• a field coil forming at least a portion of a second of said members, said field coil having conductive portions located in said fields, and said field coil portions being energizeable for effecting relative movement between said members along said given path;
• means for sensing magnetic field strength fixedly coupled to said second member and generally centrally located within said field coil for movement along said elongated path responsive to relative movement of said members whereby said sensing means provides a substantially linear response during said relative movement, said sensing means providing an output signal representative of magnetic field strength;
• and,
• means responsive to said output signal for controlling the energization of said field coil to provide closed loop control of the positioning of said members.