Abstract
In this paper, a sliding mode (SM)-based online fault compensation control scheme is investigated for modular reconfigurable robots (MRRs) with actuator failures via adaptive dynamic programming. It consists of a SM-based iterative controller, an adaptive robust term and an online fault compensator. For fault-free MRR systems, the SM surface-based Hamilton–Jacobi–Bellman equation is solved by online policy iteration algorithm. The adaptive robust term is added to guarantee the reachable condition of SM surface. For faulty MRR systems, the actuator failure is compensated online to avoid the fault detection and isolation mechanism. The closed-loop MRR system is guaranteed to be asymptotically stable under the developed fault compensation control scheme. Simulation results verify the effectiveness of the present fault compensation control approach.
Highlights
(1) The scheme extends the adaptive dynamic programming (ADP)-based sliding mode control (SMC) method to fault tolerant control (FTC) problem for modular reconfigurable robots (MRRs) with unknown actuator failures, and the online fault compensation is achieved without fault detection and identification (FDI)
Where Wc ∈ RM and σc(s) denote the ideal weight vector and the activation function, respectively, M denotes the number of neurons in the hidden layer, and εc(s) denotes the approximation error caused by critic neural network (NN) (CNN) approximation
We can see that the control input of joint 1 under the SM-based online fault compensation control (SMOFCC) has a slight change after the actuator failure occurs at t = 30 s due to the online fault compensation
Summary
As modular reconfigurable robots (MRRs) take advantages of structural flexibility, low cost, excellent adaptability, etc., they often work in perilous and complex working environments, such as disaster rescue, deep space/sea exploration, smart manufacturing, and many other hazardous environments that human cannot involve directly [1,2,3]. In [40], an ADP-based stabilizing scheme for nonlinear systems with unknown actuator saturation was developed via NN compensation. These literatures have solved stabilizing problems, rather than trajectory tracking, which is feasible to MRRs. To get rapid response and convergence, sliding modebased control schemes have been presented. Motivated by [47], this paper develops a SM-based online fault compensation control (SMOFCC) scheme for MRRs with unknown actuator failures. (1) The scheme extends the ADP-based SMC method to FTC problem for MRRs with unknown actuator failures, and the online fault compensation is achieved without FDI.
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