Robust adaptive output feedback tracking control for flexible-joint robot manipulators based on singularly perturbed decoupling

Abstract

SUMMARYThis paper presents a robust adaptive output feedback tracking controller for the flexible-joint robot manipulators to deal with the unknown upper bounds of parameter uncertainties and external disturbances. With applying the singular perturbation theory and integral manifold concept, the complex nonlinear coupled system of the flexible-joint robot manipulators is divided into a slow subsystem and a fast subsystem. A robust adaptive control scheme based on an improved linear parameterization expression is designed for the slow subsystem, and a saturation function is applied in the robust control term to make the torque output smooth. In the meantime, different from the previous approaches, the second-order derivative term of elastic torque is avoided by using the proposed computed torque method, which simplifies the implementation of the fast control law. Moreover, to carry out the whole control system with only position measurements, an approximate differential filter is involved to generate pseudo velocity signals for links and joint motors. In addition, an explicit but strict stability proof of the control system based on the theory of singularly perturbed systems is presented. Finally, simulation results verify the superior dynamic performance of the proposed controller.

Fault estimation and optimization for uncertain disturbed singularly perturbed systems with time-delay

“…Consequently, the optimization problem can be transformed into the following mathematical form min γ, max ε * s.t. 6,12,13 Optimization algorithm is as follows:…”

“…The research on singularly perturbed systems attracts much attention owning to their wide application in practical engineering [32]. The research methods mainly include H ∞ control [14,25], adaptive control [6], fuzzy control [13,15], sliding mode control [28,4] and their combination [21,29]. In practical engineering applications, due to insufficient understanding of system characteristics or links, unfamiliar with environment and modeling errors, etc., systems are affected by parameter inevitably, and the time-delay caused by signal transmission delays is ubiquitous as well.…”

Reconfigurable control of flexible joint robot with actuator fault and uncertainty

“…So, under the effect of the fault tolerant control (28), we can conclude that the uncertain system in the presence of fault (20) is asymptotically stable at the origin (x, y) = (0, 0). Using the equation (28), the system (20) is rewritten in the following form…”

“…Then, in order to reduce the effect of the actuator fault and the uncertainty on the system, a fault tolerant approach will be introduced, according to equations (21) and (28), it takes the form It can be seen from Fig. 5 that the control applied to the uncertain robotic system with faulty makes it capable of maintaining its performance even in the presence of uncertainty and collision defect.…”

“…The model considered by authors is extracted using singular perturbation (SP) theory. Liu and Huang in [28] designed a robust adaptive controller based on singularly perturbed method, for flexible-joint manipulators with unknown upper bounds of parameter uncertainties and external disturbances. In [29] Asadi and Shandiz presented an adaptive tracking control for a class of flexiblejoint manipulators in the presence of parametric uncertainties.…”