Dual load path actuator

An electric motor assembly for an actuator comprising:

• a stator;
• a rotor mounted for rotation with respect to the stator around an axis of rotation (A);
• a first transmission shaft mounted to the rotor;
• a second transmission shaft mounted to the rotor;
• and
• an output shaft;
• wherein the rotor is configured to drive the first transmission shaft and second transmission shaft around the axis of rotation (A);
• wherein the first transmission shaft is secured to the output shaft for rotation with the output shaft around the axis of rotation (A);
• wherein the output shaft comprises a first engagement feature, and wherein the second transmission shaft comprises a second engagement feature arranged to engage with the first engagement feature upon rotation of the second transmission shaft relative to the output shaft;
• wherein the first engagement feature is separated from engagement with the second engagement feature.

A method for detecting a permitted failure condition of an actuator, the actuator comprising:

• a first transmission shaft mounted to a driver;
• a second transmission shaft mounted to the driver;
• and
• an output shaft;
• wherein the output shaft comprises a first engagement feature and wherein the second transmission shaft comprises a second engagement feature for engaging with the first engagement feature;
• wherein, in a functioning condition, the first transmission shaft transmits drive from the driver to the output shaft, the second transmission shaft does not transmit drive from the driver to the output shaft, and the first engagement feature is rotationally separated from the second engagement feature by a predetermined angular gap;
• and
• wherein, in the permitted failure condition, the first transmission shaft does not transmit drive from the driver to the output shaft, the second transmission shaft transmits drive from the driver to the output shaft, and the first engagement feature engages the second engagement feature to transmit drive from the driver to the output shaft;
• the method comprising:
• determining a position of the output shaft relative to a position of the driver;
• comparing the determined position of the output shaft with an expected position of the output shaft;
• determining that the permitted failure condition has occurred if the determined position of the output shaft and the expected position of the output shaft are offset from each other by the predetermined angular gap.