Modern robotic systems with a large number of actuated degrees of freedom can be utilized to perform several tasks at the same time while following a given order of priority. The most frequently used method is to apply null space projections to realize such a strict hierarchy, where lower priority tasks are executed as long as they do not interfere with any higher priority objectives. However, introducing null space projectors inevitably destroys the beneficial and safety-relevant feature of passivity. Here, two controllers are proposed to restore the passivity: one with local energy tanks on each hierarchy level and one with a global tank for the entire system. The formal proofs of passivity show that no energy is generated by these controllers. Once the tanks are empty, passivity is still guaranteed at the cost of some control performance. Simulations and experiments on a torque-controlled robot validate the approaches and predestine them for the usage in safety-relevant applications.
Assistive robots aim to help humans with impairments execute motor tasks in everyday household environments. Controlling the end-effector of such robots directly, for instance with a joystick, is often cumbersome. Shared control methods, like Shared Control Templates (SCTs) [1], have therefore been proposed to provide support for robotic control. Moreover, depending on factors such as workload, system trust or engagement, users may like to freely adjust the level of autonomy, for instance by letting the robot complete a task by itself.In this paper, we present a concept for adjustable autonomy in the context of robotic assistance. We extend the SCT approach with an automatic control module that allows the user to switch between Shared Control and Supervised Autonomy at any time during task execution. As both support modes use the same action representation, transitions are seamless. We show the capabilities of this approach in a set of daily living tasks with our wheelchair-mounted robot EDAN and our humanoid robot Rollin' Justin. We highlight how automatic execution benefits from SCT features, like task-related constraints and whole-body control.
This paper introduces a passivity-based control framework for multi-task time-delayed bilateral teleoperation and shared control of kinematically-redundant robots. The proposed method can be seen as extension of state-of-the art hierarchical whole-body control as it allows for some of the tasks to be commanded by a remotely-located human operator through a haptic device while the others are autonomously performed. The operator is able to switch among tasks at any time without compromising the stability of the system. To enforce the passivity of the communication channel as well as to dissipate the energy generated by the null-space projectors used to enforce the hierarchy among the tasks, the Time-Domain Passivity Approach (TDPA) is applied. The efficacy of the approach is demonstrated through its application to the DLR Suspended Aerial Manipulator (SAM) in a real telemanipulation scenario with variable time delay, jitter, and package loss.
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