Multi-Axis Electric Stepper Motor

Multi-axis stepper motors offer a compact solution to actuate multiple degrees of freedom in a mechanical system by a single device. This research presents an electric stepper motor with three coaxial shafts driven by a single stator. The motor dimensions are 42 x 42 x 44 mm^3 (excluding output shafts), its mass is 0.326 kg and it includes three rotors of height 7 mm and different number of teeth.

The maximum torque for one rotor at low speed and 1 A current is 0.1 Nm, which is comparable to that of a conventional stepper motor with similar rotor size. When multiple rotors are driven simultaneously, then the total power has to be distributed over the three rotors, resulting in 42% lower torque on average. The maximum no-load speed is 4000 revolutions per minute.

The coaxial output shaft configuration poses significant challenges but also unique opportunities in actuating multiple joints of a robotic system. In many applications, the mechanical design can be redesigned to make effective use of the multi-motor design. An example of a three-DOF robot arm is demonstrated that can be efficiently driven by the proposed motor.