Basic Characteristics of a Multi-pole Spherical Synchronous Motor

A multi pole spherical synchronous motor is developed and tested. The developed motor has a rotor supported by a gymbal mechanism and a stator with two pairs of armature poles. 260 Small permanent magnets are attached on the rotor surface so that the North poles and the South poles appear on the concentric circles alternatively. Four armature winding units are positioned on the stator. Each armature winding unit has three windings. The pitch of the windings is 2/3 of the pitch of permanent magnets. Therefore, locally, the relation between the armature windings and the permanent magnets is almost the same as that of the conventional multi pole synchronous motor. The motor size is 265 times 265 times 266 [mm] and the diameter of the rotor is 130 [mm]. The target maximum output torque is 0.49 [Nm], The motor has two degrees of freedom and the working area is plusmn45 [deg] around x and y axis. The rotor can rotates around x and y axis and also moves in the direction combining two rotations simultaneously. The motor is driven by two pairs of three phase sinusoidal currents, each amplitude is calculated at the DSP board. The repeated positioning accuracy, the moving speed, and the output torque of the vertical position were tested. The maximum repeated positioning error was 0.00348 [deg]. The maximum moving speed was more than 90 [deg/sec], and the output torque is more than 0.59 [Nm]. Additional trajectory control results also showed small positioning errors.