Active Inference and Behavior Trees for Reactive Action Planning and Execution in Robotics

We propose a hybrid combination of active inference and behavior trees (BTs) for reactive action planning and execution in dynamic environments, showing how robotic tasks can be formulated as a free-energy minimization problem. The proposed approach allows to handle partially observable initial states and improves the robustness of classical BTs against unexpected contingencies while at the same time reducing the number of nodes in a tree. In this work, the general nominal behavior is specified offline through BTs, where a new type of leaf node, the prior node, is introduced to specify the desired state to be achieved rather than an action to be executed as typically done in BTs. The decision of which action to execute to reach the desired state is performed online through active inference. This results in the combination of continual online planning and hierarchical deliberation, that is an agent is able to follow a predefined offline plan while still being able to locally adapt and take autonomous decisions at runtime. The properties of our algorithm, such as convergence and robustness, are thoroughly analyzed, and the theoretical results are validated in two different mobile manipulators performing similar tasks, both in a simulated and real retail environment

Sampling-based Model Predictive Control Leveraging Parallelizable Physics Simulations

We present a method for sampling-based model predictive control that makes use of a generic physics simulator as the dynamical model. In particular, we propose a Model Predictive Path Integral controller (MPPI), that uses the GPU-parallelizable IsaacGym simulator to compute the forward dynamics of a problem. By doing so, we eliminate the need for manual encoding of robot dynamics and interactions among objects and allow one to effortlessly solve complex navigation and contact-rich tasks. Since no explicit dynamic modeling is required, the method is easily extendable to different objects and robots. We demonstrate the effectiveness of this method in several simulated and real-world settings, among which mobile navigation with collision avoidance, non-prehensile manipulation, and whole-body control for high-dimensional configuration spaces. This method is a powerful and accessible tool to solve a large variety of contact-rich motion planning tasks.Comment: Submitted to RA-L. Code available at https://github.com/tud-airlab/mppi-isaac and video of the experiments at https://youtu.be/RSkJ670uoK

Active inference for adaptive and fault tolerant control: An application to robot manipulators

Dealing with inherently unmodeled dynamics and large parameter variations or faults, is a challenging task while controlling robot manipulators. Classical control techniques cannot usually provide satisfactory responses, and often external supervision systems have to be designed to handle the faults. Recent research has shown that active inference, a unifying neuroscientific theory of the brain, bares the potential of intrinsically coping with strong uncertainties in the system, mimicking the adaptability capabilities of humans. However, the current state-of-the-art regarding active inference in robotics is very narrow and limited. This thesis presents a novel active inference controller as a general adaptive fault tolerant solution for control of robot manipulators. The goal of this work is threefold. First, we demonstrate the applicability of active inference in robotics, deriving a control scheme which is computationally efficient and with high performance. Second, we verify the claimed adaptability properties of active inference against a model reference adaptive controller, in a simulated on-line pick and place task with a 7 degrees-of-freedom robot arm. Third, we propose a method to exploit the controller's structure to perform fault detection, isolation and recovery, without the use of external supervision systems. This work showed that not only active inference is applicable to robotics, but it also outperforms the model reference adaptive controller, and it allows to efficiently deal with sensory faults. This thesis represents a leap forward with respect to the current state-of-the-art of active inference for robotics, and it lays the foundations for further research in this direction.Mechanical Engineering | Systems and Contro