University of Twente Student Theses
Hybrid and disturbance-observer-based control of a peristaltic pump
Tijman op Smeijers, T.J.C. (2024) Hybrid and disturbance-observer-based control of a peristaltic pump.
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| Abstract: | Peristaltic pumps are used for transporting liquids within disposable tubes and are commonly found in medical devices. A rotating pump wheel with several rollers is placed against the tube, such that a certain amount of liquid is trapped between two consecutive rollers and subsequently ”pushed” through the tube. The peristaltic pump principle, however, introduces disturbances, thereby distorting the desired rotational speed of the pump. Demcon recently developed a peristaltic pump for one of its medical devices. The pump uses linear proportional plus double integral (PI2) control to reject the aforementioned disturbances. However, linear control suffers from fundamental trade-offs between performance and stability, thereby posing limits on disturbance rejection. To further improve upon disturbance rejection of the peristaltic pump, this thesis proposes both a hybrid and a disturbance-observer-based control strategy. The hybrid control strategy makes use of the hybrid integrator-gain system (HIGS). The HIGS can be exploited for constructing nonlinear filter elements that mimic the amplification characteristics of classical linear filters such as integrators and low-pass filters, but with reduced phase lag. From a design point-of-view, these HIGS-based filters provide additional freedom in controller tuning as gain and phase are no longer related via Bode’s gain-phase relationship. This, in turn, allows for achieving higher bandwidths and improved disturbance rejection capabilities without compromising transient performance and robustness margins. This thesis presents a novel HIGS-based PI2 controller that reduces the steady-state error of the motor speed while additionally improving transient performance and maintaining robustness margins compared to linear PI2 control. An initial design is presented by means of a conference paper. Subsequent thorough analysis of HIGS-based PI2 controller design resulted in a structured tuning methodology for HIGS-based PI2 controllers, eventually presenting an improved design compared to the paper. Simulation studies indicate comparable performance at higher speeds but up to 24.7% improvement in root-mean-square (RMS) value at lower speeds with the new HIGS-based PI2 design compared to the HIGS-based PI2 design from the paper. Experimental validation of the new design on the peristaltic pump demonstrates up to 30.1% RMS improvement over linear PI2 control, with additional transient improvements up to 50.0% in overshoot for similar rise time, all while maintaining the same robustness margins. The disturbance-observer-based control strategy considered is called inversion-based disturbance-observer-based control (IBDOBC). The basic idea behind IBDOBC is to estimate input disturbances and/or uncertainties using an inverse nominal plant model and directly compensate the controller output with the estimate. IBDOBC is an addition to a conventional feedback controller, which could for example be linear or HIGS-based. The feedback controller can conventionally be designed according to tracking performance specifications and stability, whilst IBDOBC is used to further reject disturbances and suppress uncertainties. This thesis presents an IBDOBC design that allows for reducing the steady-state error of the motor speed of the peristaltic pump. Experimental validation of the IBDOBC design in combination with linear PI2 control showed improvements up to 44.8% in terms of RMS value compared to linear PI2 control, whereas the IBDOBC design in combination with HIGS-based PI2 control showed improvements up to 50.5%. |
| Item Type: | Essay (Master) |
| Faculty: | ET: Engineering Technology |
| Subject: | 52 mechanical engineering |
| Programme: | Mechanical Engineering MSc (60439) |
| Link to this item: | https://purl.utwente.nl/essays/98277 |
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