Torque Control Method of an Electromagnetic Spherical Motor Using Torque Map

This paper describes a new method for driving electromagnetic type spherical motors that has arranged permanent magnets on a rotor and arranged electromagnets on a stator. The most significant feature of this method is, in principle, applicable to any permanent magnets arrangement and electromagnets arrangement, and it can generate torque to any direction from any rotor attitude. In the spherical motor, cogging torque between permanent magnets and electromagnets causes not only instability of rotation but also causes rotor attitude error because the rotor has three degrees of freedom. The method of canceling the cogging torque is introduced. In the case of arranging four or more electromagnets, the combination of the electric current supply becomes infinite in number and generally not determined uniquely. However, we have developed a method for deciding the electric current distribution that generates maximum torque under the limited supply of each electromagnet. In the experiment of open-loop control, it was confirmed that the rotor was able to rotate about the axes that had been set by the calculation.