Compensation actuator for a rotorcraft flight control

1. An actuator comprising:

an auto-synchronous rotary electric motor;

a reversible speed-reducing gearbox coupled to the motor to be driven in rotation thereby;

an outlet shaft coupled to the speed-reducing gearbox to be driven in rotation thereby;

a member responsive to the opposing torque transmitted by the outlet shaft, the member being interposed between and coupled to rotate with the outlet shaft and the speed-reducing gearbox, the member comprising a deformable structure that is deformable by twisting;

two angular position sensors responsive to the angular position of the deformable structure and disposed at opposite ends of the deformable structure, the first angular position sensor responsive to an angular position of the outlet shaft; and

a control circuit connected to the two angular position sensors and to the motor, said circuit delivering a motor power supply signal that varies as a function of a position setpoint signal applied to the control circuit and as a function of signals delivered by the angular position sensor, and the control circuit arranged to determine an opposing torque value as a function of the signals delivered by the two angular position sensors and as a function of a twisting stiffness of the deformable structure;

wherein the gearbox comprises a plurality of speed-reducing stages each stage comprising a pair of gears, the gears being mounted to rotate on two parallel axes of rotation, and wherein said motor comprising a rotor cage, said actuator is provided with a brake lining and with an electromagnetic field winding which is able to engage or disengage said brake lining against said rotary cage, and

wherein the deformable structure comprises a helical spring, two parallel plates connected to the ends of the helical spring, a first finger connecting the two parallel plates and the helical spring to the gearbox, and a second finger connecting the two parallel plates and the helical spring to the outlet shaft of the actuator.

2. An actuator according to claim 1 , in which the speed-reducing gearbox comprises at least three speed-reducing modules or stages, wherein at least two speed-reducing stages presenting an identical reduction ratio.

3. An actuator according to claim 1 , in which the gears are mounted to rotate about only two axes of rotation, wherein the axes are mutually parallel, and one of the two axes coincides with the axis of the outlet shaft.

4. An actuator according to claim 1 , in which the two angular position sensors are magnetic sensors and include said first angular position sensor that is responsive to the angular position of the outlet shaft.

5. An actuator according to claim 1 , in which the two angular position sensors include at least a portion of a magnetized rotary ring and a stationary sensor responsive to variations in the magnetization of the magnetized ring.

6. An actuator according to claim 5 , in which each magnetized ring has two circular or circularly arcuate tracks that are concentric, each having several tens of north poles alternating with south poles, the two tracks being angularly offset, and the sensor responsive to variations in magnetization is a Hall effect sensor.

7. An actuator according to claim 1 , further comprising a weakened structure forming a mechanical “fuse” for interrupting torque transmission between the motor and the outlet shaft when the opposing torque reaches a determined value, the weakened structure being interposed between the angular position sensor of the outlet shaft and the deformable structure that is deformable in twisting.

8. An actuator according to claim 1 , further comprising an electromagnetic brake incorporated in the motor.

9. An actuator according to claim 1 , further comprising an electromagnetic clutch interposed between the speed-reducing gearbox and the deformable structure that is deformable in twisting.

10. An actuator according to claim 1 , further comprising an electromagnetic clutch interposed between two stages of the speed-reducing gearbox.

11. An actuator comprising:

an auto-synchronous rotary electric motor;

a reversible speed-reducing gearbox coupled to the motor to be driven in rotation thereby;

an outlet shaft coupled to the speed-reducing gearbox to be driven in rotation thereby;

a member responsive to the opposing torque transmitted by the outlet shaft, the member being interposed between and coupled to rotate with the outlet shaft and the speed-reducing gearbox, the member comprising a deformable structure that is deformable by twisting;

two angular position sensors responsive to the angular position of the deformable structure and disposed at opposite ends of the deformable structure, the first angular position sensor responsive to the angular position of the outlet shaft; and

a control circuit connected to the two angular position sensors and to the motor, said circuit delivering a motor power supply signal that varies as a function of a position setpoint signal applied to the control circuit and as a function of signals delivered by the angular position sensor, and the control circuit arranged to determine an opposing torque value as a function of the signals delivered by the two angular position sensors and as a function of the twisting stiffness of the deformable structure;

wherein the gearbox comprises a plurality of speed-reducing stages each stage comprising a pair of gears, the gears being mounted to rotate on two parallel axes of rotation, and wherein said motor comprising a rotor cage, said actuator is provided with a brake lining and with an electromagnetic field winding which is able to engage or disengage said brake lining against said rotary cage, a weakened structure forming a mechanical fuse for interrupting torque transmission between the motor and the outlet shaft when the opposing torque reaches a determined value, the weakened structure being interposed between the angular position sensor of the outlet shaft and the deformable structure that is deformable in twisting.