Demcon is a company that develops a variety of new high-tech mechatronic systems such as the peristaltic pump system shown in Figure 1. During the design phase, a closed-loop controller was required that regulates the behavior of the system. Traditionally, linear PID-type controllers are designed due to their simplicity and wide use in industry. However, linear PID controllers are limited in suppressing disturbances close to or beyond the bandwidth.
To overcome these limitations in view of disturbance rejection, one can use disturbance observer based control (DOBC) as an add-on to classical PID control. Using DOBC, a real-time estimation of the actual disturbance to the system is made and instantly compensated. In literature, several methods and implementations of DOBC are found. In an earlier project, an M.Sc graduation student implemented an inversion-based DOBC controller for the peristaltic pump system, thereby making use of plant inversion to estimate the disturbance. Although the demonstrated performance improvement was promising, the method itself suffered from some strict constraints regarding causality and stability because inversion-based DOBC is mainly intended for random unknown disturbances.
The goal of this assignment is to replace the inversion-based DOBC by an alternative DOBC method that exploits the periodic nature of disturbances present in peristaltic pumps. Namely, if the disturbances are assumed to be periodic, the strict design constraints related to inversion-based DOBC could be relaxed such that further improvements become possible. A first step would be to design and implement a time-domain repetitive controller (or any other DOBC method that suffices) to improve performance by aiming at a constant rotational speed of the pump. As a second step, a transition to the position domain could be made to make the compensation independent of the actual pump speed. Third, one could add a flow sensor to reduce the flow ripple (which is a primary performance measure of the pump). An alternative development is the implementation of a flow ripple disturbance observer to obtain the same performance improvements but without the need of a flow sensor.