A precision robotic joint is driven by a d.c. rotary actuator. The actuator consists of a rectangular coil of wire containing N N\,N turns, mounted on a central axle between two permanent magnetic poles. When a direct current is passed through the coil, a torque is generated, causing the axle to rotate.
Explain, in terms of magnetic fields and forces, how the current in the coil generates a torque to rotate the axle.
State two design modifications, one electrical and one magnetic, that could be made to the actuator to increase the torque generated for a given input signal.
Describe how the direction of rotation of the axle can be reversed.
To optimize the actuator's performance, the designer replaces the flat permanent magnets with magnets having curved pole faces, and inserts a cylindrical soft iron core inside the coil, as shown in the diagram below.
Explain how these two modifications improve the actuator's rotational efficiency and consistency.
