| With the continuous development of the technology and the expansion of the research on the motor, all kinds of novel multi-degree-of-freedom motors were designed one after the other by the scholars all of the world. While the idea and the prototype of the three-degree-of-freedom (three DOF) motor came into being, it is more convenient to realize the motion of the robot joint where the demand on workspace is low but three DOF is required. It also combines the merits of simplified system construction, minimized machine volume, improved dynamic and static performance with high position accuracy. However, control relative problems have seldom been discussed which becomes the bottleneck of the development and practicability of the three DOF motors. The permanent magnet spherical stepper motor (PMSSM) is a novel three DOF stepping configuration spherical motor that laminations are not required, so the realization of a prototype is much easier. It has higher energy and simple working principle with respect to other spherical motors. In view of control problems of the PMSSM, this dissertation is devoted to an in-depth study on the torque model, dynamic model of the rotor, control strategy and algorithm, design of the driver and the controller and so on.The main contribution of this dissertation includes:1. Based on the simple presentation of the configuration characteristic and the calculation of the magnetic field and torque of the PMSSM, the torque-angle characteristic is divided into three kinds to calculate. Then the curves of the torque are approximated with different functions. The simplified torque model and the expressions are concluded.2. The whole model of the motor was simplified to a system using active solenoids. The possible stable positions of the rotor with one or a pair of active stator coils are discussed using Hill-Climbing method while the motor is in stepping mode. It affords the reference of the rotor position for the relay control mode.3. One open loop control algorithm based on quaternion rotation for the PMSSM in relay control mode is proposed. It divides the kinetic trajectory into sections. Thus each segment corresponds one arc and circles around one fixed axis individually, and the continuous movement of the rotor is feasible. This solves the problem of the limited motion trajectory while in point-to-point motion.4. The dynamic model of the rotor expressed with Cardan angle rotation was set up in rotor-fixed coordinates frame using Lagrange equation of second kind. The problem that the PMSSM has no exact mathematical description leading to the trouble of quantitative analysis combined with the torque model and the dynamic model is then resolved. 5. The current control method is applied in the controller to construct the closed loop control of the PMSSM. Later the PD control algorithm for the point-to-point (PTP) motion and the adjusted PD control algorithm for the continuous path (CP) motion in unloaded mode are presented. So the PMSSM can accomplish not only the PTP motion but also the CP motion.6. One control algorithm is designed based on input-output stability theory for the CP motion in unloaded mode. It can drive the motor without the angular accelerations feedback, which reduces the pressure on the position measuring system. Inheriting the advantage of this algorithm, the adaptive control algorithm and the switching control algorithm applied in the situation that the load affected the rotation inertia of the axes are developed to satisfy the requirements of the CP motion. It resolves the problem of assuming the unloaded mode for all the existent control algorithms. It has extended the applications of the PMSSM significantly.7. The simulation examples of all the control algorithms are accomplished. The entire solvent of the control system based on the relay control and the current control are presented, also the driver and controller for the permanent magnet spherical stepper motor is developed.
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