Block-Oriented Nonlinear Control of Pneumatic Actuator Systems

Mechatronics is the art of directing the advances of a variety of academic and engineering areas to solve the smart machine problems. Author Supervisor Summary Title Language Keywords Document type Date www.md.kth.se This thesis treats block-oriented modelling, approximate linearization and control of a nonlinear pneumatic actuator system. The definition of the block-oriented nonlinear model is extended to include dynamic nonlinearities. The block-oriented model is a general input/output model structure consisting of series and parallel connections of linear dynamics and nonlinear elements. Based on this extension, a block-oriented approximate feedback linearization method is proposed. For feedback linearization of a block-oriented nonlinear system, the only requirement is that some specific blocks are invertible or approximately invertible so that the manipulating calculation based on the block-units can be implemented. This rather loose constraint makes it possible to apply the linearization technique to a variety of nonlinear systems. In this linearization, each nonlinear block can be compensated in its specific way and many nonlinearity compensation techniques can be directly incorporated. The proposition of the block-oriented approximate feedback linearization is in the hope that it can be further formalized and that it can become a sophisticated but practical nonlinear control and modelling tool. The pneumatic servo control problems are formalized. The dominant nonlinearities in the system are the couplings between motion and pressure, between pressure and flow rate, the valve nonlinearities and the cylinder friction. The nonlinear friction, especially the friction behaviour at velocity reversal, is the big obstacle for high precision motion control of a pneumatic actuator system. Thus, a dynamic friction model structure for friction compensation is necessary. The valve nonlinearities are complicated and it is necessary to consider their integral nonlinear effect. The block-oriented approximate feedback linearization for a rodless pneumatic cylinder motion control system is demonstrated. For the linearized system, high performance force, position and tracking control can be easily achieved with just some simple linear control algorithms. The steady-state positioning error is shown to be less than the sensor's 5 m resolution in almost full cylinder operation range and in the presence of high friction (about 15-20% of the maximum cylinder force). A step-by-step and interactive nonlinear modelling approach for the pneumatic servo system is presented. Further, a robust redesign method, focusing on the characterization of the linearization residuals, is presented. Acknowledgements I am particularly indebted to my supervisor Professor Jan Wikander for the encouragement, support and guidance he has …