Actuator Fault Estimation (FE) and Fault Tolerant Control (FTC) strategies designed with model-based observers for Vertical TakeOff and Landing (VTOL) aerial vehicles are proposed and validated experimentally in this paper. Three observers are considered for FE: a nonlinear adaptive observer and a linear Proportional-Integral Observer (PIO) applied to a Planar VTOL and a quasi-Linear Parameter Varying (qLPV) PIO applied to a quadcopter vehicle. The fault detection is done by comparing the fault estimation signal with a predefined threshold. Fault isolation is achieved by analyzing the sign of the fault estimation signal. The Available Control Authority Index (ACAI) method is used to analyze the controllability properties of the vehicles under actuator faults. The main contribution of this work is the design and the experimental validation of complete active FTC schemes by using the proposed FE systems in order to accommodate a soft actuator fault and reconfigure an aggressive fault, even when the vehicle is flying in a non-hover position. Finally, the proposed FTC schemes are validated in different cases of flight tests for illustrating the effectiveness of the strategies.

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In this article, various investigations on soft exoskeletons are presented and their functional and structural characteristics are analyzed. The present work is oriented to the studies of the last decade and covers the upper and lower joints, specifically the shoulder, elbow, wrist, hand, hip, knee, and ankle. Its functionality, applicability, and main characteristics are exposed, such as degrees of freedom, force, actuators, power transmission methods, control systems, and sensors. The purpose of this work is to show the current trend in the development of soft exoskeletons, in addition to specifying the essential characteristics that must be considered in its design and the challenges that its construction implies.

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