Rotary actuator

A pole riser for use in a rotary actuator to provide first and second additional flux paths and a mechanical stop for a rotor that rotates about an axis within the rotary actuator responsively to a magnetomotive force generated by an energizable coil, comprising:

• a nominal thickness defined at a preselected plane through said pole riser;
• a latching portion, adapted to abuttingly contact a surface on the rotor when the rotor rotates to a preselected stop position, said latching portion having a generally constant thickness, greater than said nominal thickness, along a length of said latching portion;
• and
• a necked region extending between said preselected plane and said latching portion, said necked region having a varying thickness increasing generally in a direction away from said preselected plane toward said latching portion.

A method of controlling the position of a rotor that rotates about an axis between an initial position and a preselected stop position within a rotary actuator, comprising the steps of:

• (A) causing a magneto motive force to act on said rotor such that said rotor rotates away from said initial position toward said stop position by producing a main magnetic flux, which varies as a function of a rotary position of said rotor, to flow through at least a portion of said rotor in a direction generally parallel to said axis;
• (B) causing a first additional magnetic flux to flow in a direction generally parallel to said axis and along a pathway radially spaced from said rotor, said first additional flux not producing any torque that acts on said rotor;
• and
• (C) causing a latching flux to flow in a direction generally perpendicular to said axis along a pathway at least partially directed generally radially toward said rotor, said latching flux increasing as said rotor rotates toward said stop position such that said latching flux introduces a magneto motive force that acts on said rotor to maintain said rotor in said preselected stop position independent of said main flux.