Energy efficiency analysis and optimal control of servo pneumatic cylinders

The paper presents a method for energy efficiency analysis of servo pneumatic actuator systems. Simulation study indicated that different quantities of compressed air will be consumed for one cycle of piston movement when the same controller is adopted but with different profiles for servo pneumatic actuators. This motivated the authors to investigate the profile which leads the system to use the least amount of compressed air, that is, the most energy efficient profile. To avoid solving a set of complicated nonlinear differential equations, the nonlinear system is linearized through input/output state feedback and energy efficient optimal control theory is then applied to the linearized system. An optimal control strategy is developed with respect to the transformed states of the linear system model. The solution of the state trajectory results in an energy efficient profile. Through an inverse transformation, the system is converted back to the original states and control variables. The generalized controller has been proved to be a sub-optimal control with respect to the original nonlinear system model. Simulation study has conducted and the results obtained from linear and nonlinear system models are analyzed and compared.