SUMMARY

Because magnetic fields are instantaneous and invariant to environmental factors (such as pressure and temperature) and can be measured inexpensively with miniature sensors, they are widely used as a medium of energy conversion and signal transmission in a variety of motion systems. Of particular interest in this research is to develop methods to control the orientation of an electromagnetic spherical actuator (capable of providing 3-DOF continuous orientation with one joint). Unlike traditional methods that often rely on orientation information estimated from single-axis encoders (connected in parallel/series that normally introduce unwanted frictions) or computationally demanding vision-based solutions, this research proposes a novel control method utilizing existing magnetic fields in the actuator for real-time feedback control without the need to explicitly measure the orientation. The major challenges encountered in developing such a system are two folds: The first is to determine the torque required to track a desired orientation from the magnetic field measurements. The second is to compute the corresponding torque coefficient vectors (which relate the currents to torque) in order to determine the current inputs to realize the desired torque. To address these challenges, this proposed research utilizes the relationship between orientation and magneic fields to build a control law, and develops a method to compute the torque coefficient vectors directly from magnetic field measurements. This novel method, which eliminates the need to compute sequentially the orientation then the torque coefficient vectors, dramatically reduces the computational time and improves the performances. While the immediate application of this proposed research is to develop a spherical actuator controlled system, it is expected that this new method can also be applied to a broad spectrum of motion systems that utilize magnetic fields for actuation.