This paper presents an active control strategy for lower limb exoskeletons by proposing an end-to-end framework employing deep reinforcement learning (DRL) to enable smooth transitions between different movement patterns. The majority of existing methods in exoskeleton literature employ finite state machines (FSM) that have proven successful in predicting the control strategy for the next state on the basis of sensor data such as IMU data, force, etc. However, one drawback of FSM occurs due to their inflexibility regarding sudden changes. Specifically, FSM is based on clear state transitions, which makes it hard to manage smooth continuous movements and increases the chance of sudden changes in control during transitions. These, in turn, raise safety concerns for the user. While learning-based control approaches have been suggested in recent years, the validation was performed in simulation environments. Therefore, the real-world applicability remains an open research question to date. To address this issue, we provide the first contribution in this field that proposes an end-to-end learning framework with a Deep Deterministic Policy Gradient (DDPG) module to enable smooth transitions between movement patterns under real-world conditions. By introducing several evaluation metrics, we demonstrate that our framework outperforms existing methods in terms of the adaptability and smoothness in movement transitions.

This contribution presents a robot path-following framework via Reactive Model Predictive Contouring Control (RMPCC) that successfully avoids obstacles, singularities and self-collisions in dynamic environments at 100 Hz. Many path-following methods rely on the time parametrization, but struggle to handle collision and singularity avoidance while adhering kinematic limits or other constraints. Specifically, the error between the desired path and the actual position can become large when executing evasive maneuvers. Thus, this paper derives a method that parametrizes the reference path by a path parameter and performs the optimization via RMPCC. In particular, Control Barrier Functions (CBFs) are introduced to avoid collisions and singularities in dynamic environments. A Jacobian-based linearization and Gauss-Newton Hessian approximation enable solving the nonlinear RMPCC problem at 100 Hz, outperforming state-of-the-art methods by a factor of 10. Experiments confirm that the framework handles dynamic obstacles in real-world settings with low contouring error and low robot acceleration.

In this paper, we present an approach for quantifying the propagated uncertainty of robot systems in an online and data-driven manner. Especially in Human-Robot Collaboration, keeping track of the safety compliance during run time is essential: Misclassifying dangerous situations as safe might result in severe accidents. According to official regulations (e.g., ISO standards), safety in industrial robot applications depends on critical parameters, such as the distance and relative velocity between humans and robots. However, safety can only be assured given a measure for the reliability of these parameters. While different risk detection and mitigation approaches exist in literature, a measure that can be used to evaluate safety limits online, and succinctly implies whether a situation is safe or dangerous, is missing to date. Motivated by this, we introduce a generalizable method for calculating the propagated measurement uncertainty of arbitrary parameters, that captures the accumulated uncertainty originating from sensory devices and environmental disturbances of the system. To show that our approach delivers correct results, we perform validation experiments in simulation. In addition, we employ our method in two real-world settings and demonstrate how quantifying the propagated uncertainty of critical parameters facilitates assessing safety online in Human-Robot Collaboration.

In this paper, we present a method to engage measurement uncertainties with the probabilistic robustness to one system uncertainty measure. Providing a metric indicating the potential occurrence of dangerous situations is highly essential for safety-critical robot applications. Due to the difficulty of finding a quantifiable, unambiguous representation however, such a metric has not been derived to date. In case of sensory devices, measurement uncertainties are usually provided by manufacturer specifications. Apart from that, several contributions demonstrate that the accuracy of neural networks is verifiable via the robustness. However, state-of-the-art literature is mainly concerned with theoretical investigations such that scarce attention has been devoted to the transfer of the robustness to real-world applications. To fill this gap, we show how the probabilistic robustness can be made useful for evaluating quantitative safety limits. Our key idea is to exploit the analogy between measurement uncertainties and the probabilistic robustness: While measurement uncertainties reflect possible shifts due to technical limitations, the robustness refers to the tolerated amount of distortions in the input data for an unaltered output. Inspired by this analogy, we combine both measures to quantify the system uncertainty online. We validate our method in different settings under real-world conditions. Our findings exemplify that incorporating the novel uncertainty metric effectively prevents the rate of dangerous situations in Human-Robot Collaboration.