Electromechanical actuator

An electromechanical actuator, EMA, having a plurality of modes, the EMA comprising:

• a housing;
• a motor fixed relative to the housing, the motor having an output shaft, the output shaft defining an axis (X) of the EMA;
• a first sun gear connected for rotation with the output shaft;
• an output arranged to be driven by rotation of the first sun gear, wherein the output is arranged to have a neutral position and to be movable away from the neutral position within a positive quadrant and away from the neutral position within a negative quadrant;
• a ratchet comprising a ratchet wheel and a pawl;
• a torque limiter having a predetermined torque limit, wherein the torque limiter is arranged to limit torque transfer between the first sun gear and the output;
• a synchroniser comprising a first conical portion connected to an end of the output shaft, and a second conical portion connected to the ratchet wheel, wherein the synchroniser has an engaged position in which rotation of the first conical portion is transmitted to the second conical portion, and a disengaged position wherein the second conical portion is axially spaced apart from the first conical portion, along the axis (X), such that rotation of the first conical portion is not transmitted to the second conical portion;
• a solenoid mounted to a floating frame within the housing and connected to the second conical portion, the solenoid configured to pull the second conical portion along the axis (X) away from the first conical portion when the solenoid is energised;
• and
• a spring arranged to bias the frame along the axis (X) away from the first conical portion, wherein the frame abuts against a cam surface of the output;
• wherein, in an active mode of the plurality of modes, the solenoid is energised and wherein rotation of the output shaft in either direction of rotation drives the output to rotate;
• wherein in an anti-extension mode, the solenoid is not energised and, when the output is at the neutral position or in the positive quadrant, the output shaft is connected for rotation, via the synchroniser, to the ratchet, wherein the ratchet is arranged to prevent rotation of the output shaft in a predetermined direction of rotation;
• and
• wherein when the output is in the negative quadrant, the cam surface is in a position such that the frame is biased away from the first conical portion, along the axis (X), such that the second conical portion is axially spaced apart from the first conical portion both while the solenoid is energised and while the solenoid is not energised.