Sharif Digital Repository

The design and implementation of linear and nonlinear control methods for a three-pole active magnetic bearing (AMB) is presented in this paper. It is shown that the system has nearly linear dynamics by adding a bias to coil currents. A decentralized PID feedback law and an integral sliding mode controller are proposed and the unknown state variables of the system are estimated by the Kalman filter. The optimal gains of the linear controller are determined by the LQG technique. To evaluate the effectiveness of the proposed controllers, they are implemented on an experimental setup. The experimental results show that the proposed methods can effectively stabilize the three-pole AMB. The... 

The design and implementation of the hybrid control method for a three-pole active magnetic bearing (AMB) is proposed in this paper. The system is inherently nonlinear and conventional nonlinear controllers are a little complicated while the proposed hybrid controller has a piecewise linear form, i.e., linear in each sub-region. A state-feedback hybrid controller is designed in this study and the unmeasurable states are estimated by an observer. The gains of the hybrid controller are obtained by the LQR method in each sub-region. To evaluate the performance, the designed controller is implemented on an experimental setup. The experimental results show that the proposed method can efficiently... 

In this study, a general methodology has been developed to design the proper bearing in order to eliminate the curvature of the final product in extrusion process. Three smooth curved (advanced-surface) dies with non-symmetric T-shaped sections and different off-centricities have been studied. For each die, the proper bearing has been designed and physical and numerical modeling have been performed to validate the design. The design procedure is as follows: A formulation, based on Bezier curves, has been used to determine the exit velocity profile. Since the result of Bezier method is different from the actual velocity profile, the Chitkara corrective function has been modified and applied... 

Total knee replacement (TKR) surgery is one of the most successful and cost-effective procedures for treating knee injuries performed in orthopedics. However, the knee replacement revision surgery will probably be required after some years. Wear at the contact area between femoral metal component and the polyethylene inserts in TKR is recognized as one of the foremost causes of prosthesis failure and necessity of revision surgery. In the present study, focusing on the patellofemoral joint (PFJ), the wear at the contact area between the patellar and femoral components has been simulated employing the explicit finite element modeling. In this regard, common types of patellar component surface...