Browsing by Subject "Robust Control"

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Open Access
Modelling and robust controller design for a multi-axis micro-milling machine
(2016-09) Karagöz, Mümtazcan
In the current era of miniaturization, micro manufacturing had became one of the most popular topics. Even tough there are new promising methods such as laser sintering and 3D printing; conventional manufacturing methods continue to hold a unique and irreplaceable position. This thesis aims to design a robust control algorithm for a three axis micro-machining system. In order to synthesize the controller, first the system is modeled. After the modeling, a system identification due to non-linearities is also performed. X, Y and Z axis's identified using prepared Sum of sines identification input. Verification data shows these identified transfer functions represent the physical system well while avoiding over-fit. Using these identified transfer functions, a robust H1 controller is synthesized with designed weighting functions. In simulations, this robust H1 controller showed significantly better performance with or without disturbance. Machining experiments are also done in order to compare the performance of robust controller with the PID controller. According to results of experiments, robust controller showed similar tracking performance with improved surface quality and less oscillations vibrations.
Open Access
On mixed H2=H∞ controller design for systems with time delay
(2018-07) Ghomi, Meysam
This study discusses mixed H2=H∞ controller design problem for uncertain Linear Time-Invariant (LTI) systems with a time delay. More precisely, the goal is to find an internally stabilizing controller that minimizes the H2 performance measure subject to robust stability condition which bounds the H∞ norm of the weighted closed loop transfer function. Two different methods are used to find the optimal H2 controller. The first method is inspired from the H∞ control design to reduce the two block problem into one block. Second method, however is the implementation of the Mirkin's formula. These methods are compared and their pros and cons are discussed. The key point in the optimal controller is that, it is in Smith predictor form that includes an internal feedback in the form of an Finite Impulse Response (FIR) filter. These types of controllers are easy to implement and programmed in physical systems. A case study is considered to show the exact way to controller design. The simulation results and the effects of delay term on the performance measure are also provided.