Linear Actuator Using the Switched Reluctance Motor

A novel linear actuator is proposed as a one-for-one replacement for the existing hydraulic actuators on Naval vessels, specifically the actuator that positions the steering rudders on the LCAC. Alternative approaches will be considered, but only two seempractical - a linear motor and a linear actuator using a rotating screw. The preferred of the two uses a rotating screw since it is difficult to gain mechanical advantage with a straight linear motor. Hydraulics applications are characterized by lowspeed and high force requirements, leading to an alternative that can be leveraged using some means of mechanical gearing. Driving the rotating linear actuator screw is an advanced switched reluctance motor with associated power electronics. The SR motoris the most rugged of all known types and is fault tolerant in that a phase in either the motor or electronics can fail without a failure of the overall actuator. This approach can be implemented without any position sensing and with all hardware andcontrols integrated into a single package which can replace the existing actuator without mechanical modifications to the LCAC. Other advantages include much better control flexibility, dramatically reduced maintenance and complete elimination ofhydraulic fluid and equipment. Upon completion of the project (all phases), the rudder actuators on the LCAC could be immediately replaced thus providing the benefits intended by the STTR topic. Versions of the actuator could replace most other hydraulicactuators currently used on military and civilian ships where high force is a requirement. In addition, the SR motor drive can be used in innumerable rotating applications without the linear screw mechanism - pumping, HVAC, hoists/cranes, materialhandling, elevators, and so on. The annual worldwide market for motor drives of all types is about $10 billion.