Time Delay Estimation Control of Permanent Magnet Spherical Actuator Based on Gradient Compensation

A multi-degree-of-freedom Permanent Magnet Spherical Actuator (PMSpA) has a special mechanical structure and electromagnetic fields, and is easily affected by nonlinear disturbances such as modeling errors and friction. Therefore, the quality of a PMSpA control system may be deteriorated. In order to keep the PMSpA with good trajectory tracking performance, this paper designs a time delay estimation controller based on gradient compensation. Firstly, the dynamic model of the PMSpA with nonlinear terms is derived. The nonlinear terms in the complex dynamic model can be simplified and estimated by the time delay estimation method. Secondly, for the estimation errors caused by time delay control, a gradient compensator is introduced to further correct and compensate for it. Furthermore, the stability of the designed controller is proved by the Lyapunov equation. Finally, the correctness and effectiveness of the controller are validated by comparison with other controllers through simulation. In addition, experimental results have also shown that the control accuracy of the spherical motor can be effectively improved using the proposed controller.

Proposal of 5-phase 3-degree-of-freedom spherical actuator with auxiliary poles

Multi-Degree-of-Freedom (Multi-DOF) actuating systems are usually composed of several single-DOF motors, which results in large, heavy and complicated structures. In order to solve these problems, various multi-DOF spherical actuators have been actively studied. However, a large number of current phases are required in the spherical actuator. In this paper, in order to reduce the number of current phases, a 3-DOF spherical actuator with auxiliary poles which is driven using 5-phase currents is proposed. Finally, the torque characteristics of the proposed actuator are evaluated through 3-D finite element analysis.

Dynamics of trunk type robot with spherical piezoelectric actuators

<p class="Abstract">Trunk type robots (TTRs) are exclusive. These robots can provide a high level of maneuverability and have a potential in medicine or high risk zones. TTRs are determined as a long serial linkage of similar segments. They are usually connected using tendons or small actuators. A spherical actuator is the most appreciable option. The motion of real spherical actuator (RSA) can be easily obtained applying an inverse piezoelectric effect. It has three independent spinning axes. These axes are perpendicular to each other despite the history of excitation. Kinematics and dynamics of RSA almost have no basics regardless of mentioned features. This situation can be explained according to common disadvantages of other SAs: sophisticated structure and complex control. The structures and abilities of TTRs are reviewed in the first section of this article. At the beginning of the fourth section the kinematics of piezoelectric TTR with two different RSAs is introduced. Its results of inverse dynamics using Euler-Lagrange equations are presented at the end of the fourth section. Similar results are derived using an analytical-potential method in the fifth section. It is quite accurate and effective option to determine inverse dynamics of the TTR employing an analytical-potential method.</p>