Mitsunobu Shibata

Development of a spherical stepping motor rotating around six axes

Spherical motors have an advantageous feature that they can rotate around multiple axes. From the advantage, spherical motors are expected to be applied to driving mechanisms of holonomic mobile robots, joints of robots, and so on. This study develops a spherical motor called 14–12 spherical stepping motor that can rotate around 6 axes. This paper describes the structure of the motor, rotation principle by five-phase ACs (Alternative Currents), a five-phase AC power supply, and rotation experiments to confirm the applicability of the motor.

Basic experimental results of a 14-12 spherical motor

Spherical motors have been studied widely because they have several advantageous features and are applicable to driving mechanisms of holonomic mobile robots, joints of robots, and so on. This study develops a 14-12 spherical motor and evaluates cogging torque and rotation torque for the rotation around one of two kinds of rotation axes. This paper describes the structure of the developed 14-12 spherical motor, working principle of rotation by five-phase alternative current (AC), and some evaluation results of rotation performance. The evaluation results of rotation torque exhibit the applicability of the 14-12 spherical motor.

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.