Step 3 Dual-axis PID tuning and levitation experiment Y-direction static lift-off measurement from back-up bearing position It was demonstrated in section 6.3 that the finite element predicted forces show excellent agreement with the experimental results static uncontrolled lift-off experiments. The simulation results presented previously in section 4.2.1 demonstrated that significant improvements in performance for a given combination of control gains could be achieved by incorporating UMP compensation into the control scheme, in particular the ability to maintain performance with significantly reduced controller gains and hence increased reliance to noise. Hence, for the controller used in the experimental testing of levitation, a look-up table of finite element estimated open-circuit unbalance magnetic pull (UMP) was added into the closed-loop system to compensate for the effect of UMP. Static lift-off is achieved in the Y-direction from the back-up bearing position designed as the step has two major purpose: Identifying the maximum moving clearance, i.e., maximum rotor eccentricities from back-up bearing position at either end. Due to the mechanical tolerance for constructing back-up bearings, the rotor eccentricities at lift-off positions are different as shown in Figure 72 and Figure 73. The corresponding eccentricity values represents the maximum moving clearance at either end of this constructed prototype machine. Determining the minimum value of proportional gain for single-axis (Y-direction) levitation. According to the well-established tuning strategy for PID controllers, proportional gain is usually the first value determined for starting with a marginally stable rotor movement (which means that the rotor is expected to continuously oscillate with a proportional only controller). A higher proportional gain results in increased oscillation frequency, which is unnecessary until an asymptotically stable system achieved. On the other hand, insufficient proportional gain is unable to provide sufficient control action to levitate rotor from back-up bearing position. By using the results from lift-off experiments, the force error at lift-off position can be
Step 3 Dual-axis PID tuning and levitation experiment Y-direction static lift-off measurement from back-up bearing position It was demonstrated in section 6.3 that the finite element predicted forces show excellent agreement with the experimental results static uncontrolled lift-off experiments. The simulation results presented previously in section 4.2.1 demonstrated that significant improvements in performance for a given combination of control gains could be achieved by incorporating UMP compensation into the control scheme, in particular the ability to maintain performance with significantly reduced controller gains and hence increased reliance to noise. Hence, for the controller used in the experimental testing of levitation, a look-up table of finite element estimated open-circuit unbalance magnetic pull (UMP) was added into the closed-loop system to compensate for the effect of UMP. Static lift-off is achieved in the Y-direction from the back-up bearing position designed as the step has two major purpose: Identifying the maximum moving clearance, i.e., maximum rotor eccentricities from back-up bearing position at either end. Due to the mechanical tolerance for constructing back-up bearings, the rotor eccentricities at lift-off positions are different as shown in Figure 72 and Figure 73. The corresponding eccentricity values represents the maximum moving clearance at either end of this constructed prototype machine. Determining the minimum value of proportional gain for single-axis (Y-direction) levitation. According to the well-established tuning strategy for PID controllers, proportional gain is usually the first value determined for starting with a marginally stable rotor movement (which means that the rotor is expected to continuously oscillate with a proportional only controller). A higher proportional gain results in increased oscillation frequency, which is unnecessary until an asymptotically stable system achieved. On the other hand, insufficient proportional gain is unable to provide sufficient control action to levitate rotor from back-up bearing position. By using the results from lift-off experiments, the force error at lift-off position can be
Chenyu%20Nie%20Thesis%20%28Final%20version%29.docx