The SDRE controller and estimator design for flexible joint manipulators in presence of noise and disturbance

ARTICLE INFORMATION ABSTRACT Original Research Paper Received 24 February 2016 Accepted 19 May 2016 Available Online 14 August 2016 Full feedback data is mostly essential in control design. Measurement of the variation of flexible joint robot (FJR) actuators is not as easy as the measurement of the changes of FJR links’ angles. The measurement of the states is also affected by noise, and the disturbance in the workspace of the robot is not ignorable. Hence a state observer or a nonlinear estimator is necessary to improve the performance of the dynamical system. The state-dependent Riccati equation (SDRE) is one of the most promising nonlinear optimal control methods and estimators. Systematic procedure, simple structure, and incorporating a wide range of systems (under observability condition) are some advantages of SDRE method. The majority of nonlinear techniques linearize the model, but the SDRE directly uses the nonlinear state space; it is one of the reasons for its precision and flexibility in design with respect to other methods. The goal of this work is to merge the SDRE controller and estimator simultaneously to reduce the state error of the system in presence of external disturbance and measurement noise. So, first, the controller and the observer formulation haves been stated. Then, the procedure has been applied to design and simulate a 3 DOF robot arm with flexible joints. Next, the process has been tested experimentally using Scout robot and the simulation results have been verified. Finally, the proposed method of this paper has been compared with the optimal sliding mode controller. The results showed that the behavior of the system is more similar to the real behavior of the robot.

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