الفهرس Only 14 pages are availabe for public view
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Abstract
Vibration caused by mass unbalance is a common problem in rotating machinery. Vibration control and damping is essential for achieving longer bearing and spindle life, improving machining surface finish, long tool life in high-speed machining and reducing the number of unscheduled shutdowns. Active magnetic bearings are electromagnetic actuators, which can solve classical bearing problems such as the vibration that appears at the critical speeds of the shaft-bearing system. Such systems require an active control: This thesis investigates the application of the fuzzy logic control (FLC) to the active magnetic bearing (AMB) systems to control and damp the shaft vibration while passing the critical speeds.
The shaft mathematical model was derived using the transfer matrix method. The free and the forced vibration analysis that involve both the natural frequencies and the corresponding mode shapes were performed.
The active magnetic bearing general equation was derived. The active magnetic bearing function, applications, parameters (displacement stiffness, current stiffness and air gab) and characteristics were presented.
A proportional derivative controller, adaptive proportional integrator controller (use a fuzzy controller as ’adaptive proportional), fuzzy controller (using the displacements at the bearings as input) and fuzzy controller (using the displacements as well as the change of displacements at the bearings as inputs) were designed to damp the shaft vibration in the presence of unbalance force while runs at the first critical speed. The capability of the controllers, to compensate the losses occurred in the control current, were tested. The simulations of the controlled shaft-bearing systems were conducted with MATLAB/SIMULINK software.
The results showed that the proportional integral controller (fuzzy) eliminates the shaft deflections but its performance was degraded as the control current losses increased. The two fuzzy controllers resulted in an acceptable performance with respect to the damping of the shaft deflections, Fuzzy controller which used the displacement of the shaft as input gives better performance and was capable to compensate 60% of the controller current losses while fuzzy controller which used the displacement as well as the change of the displacement ’of the shaft was capable to compensate only 40% of the control current losses, The proportional derivative rendered the worst dynamic performance as compared to the fuzzy controllers.