Reset Control for Vibration Isolation

Abstract

Floor vibrations are a common problem in high tech engineering where good tracking, precision and bandwidth have utmost importance. They are mainly present at low frequencies, and they need to be suppressed. PID control is the go-to controller in the industry because of its ease of design, simple implementation and good performance. However, PID is subjected to the fundamental limitations of linear control theory - the waterbed effect and bode's gain-phase relationship. Therefore, it is not possible to improve one performance criterion, like stability, without negatively influencing the other. The need for overcoming the fundamental limitations of linear control initiates research towards nonlinear controllers.

Reset control is a type of nonlinear controller as a solution to overcome the limitations of a linear control. It reduces phase lag within the system, gives the advantage to reach higher bandwidth and results in lower overshoot or a faster settling time compared to linear controllers. However, using reset control comes with a price of unwanted dynamics due to the higher order harmonics. The main focus of this thesis is to improve disturbance rejection performance against floor vibrations by attenuating the power of high order harmonics. This problem has been tackled within the thesis, and a band-pass reset control is proposed.

Proposed reset controller applies reset only within the frequency range where floor vibrations are present, and it uses integrator as a reset variable. Results show reset controller that has a broadband phase compensation, like CgLp, is more advantageous towards phase lag reduction methods. CgLp is a reset element, which is an abbreviation of Constant-Gain Lead Phase. It gives broadband phase compensation within the desired range of frequencies by using generalized first order reset element. Also, CgLp controller achieved disturbance rejection performance of PI extsuperscript{2}D with the phase behavior of Clegg.