Modeling, analysis and non-linear control of a novel pneumatic semi-active vibration isolator: a concept validation study

Abstract

<p>Advanced suspension systems play a crucial role in the performance of vehicles. The essential problem in designing a vibration isolator for a system comprises of controlling the relative motion between the suspended mass and the base due to stroke limitations, while attenuating the vibration transmitted to the mass from the base. These two requirements being conflicting in nature results in a compromised suspension design when purely passive isolation technologies are employed. Active vibration isolation systems which totally eliminated this compromise have cost, maintenance and reliability issues precluding them from being used in many applications. Semi-active technologies on the other hand provide feasible alternative to the active systems, but employ oil based dampers, which deteriorates the performance over a wide range of operating regime.;The thesis presents a novel semi-active pneumatic vibration isolation technology, which is capable of alleviating the drawbacks of both the contemporary active and the semi-active systems currently being researched. The pneumatic system proposed was shown to have the capability to continuously alter its natural frequency and damping characteristics (CVNFD) without needing either a hydraulic actuator or oil based variable damping device. The computational study based on the non-linear mathematical model developed showed the CVNFD behavior of the pneumatic system and the experiments conducted on the research test-rig corroborated the result.;Two non-linear control schemes in the form of Skyhook control and sliding mode control were used to synthesize controllers for the pneumatic system. A modified skyhook control was derived and implemented on the pneumatic system. The performance of this controller was shown to rival that obtained for a conventional semi-active system using the Magneto-Rhealogical (MR) damper and controlled by skyhook control. A more advanced non-linear robust control scheme called sliding mode control was used for the second controller design. The controller was synthesized using the sliding mode control theory applied to the theory of model-matching. Lyapunov stability analysis was applied and the sliding mode controller was modified to guarantee global asymptotic stability. It was demonstrated computationally as well as experimentally that by suitably choosing the several controller design-parameters, the skyhook based sliding mode controller can recover the performance lost by implementing the model independent skyhook law.;In summary, the research conducted in this thesis demonstrated the availability and feasibility of a new and novel semi-active pneumatic vibration isolation technology that can replace and/or enhance the performance of contemporary passive and semi-active systems.</p>