Distributed state estimation is essential for modern industrial systems, especially in sensor networks and multi-agent frameworks constrained by limited communication and computational resources. This article presents a novel$\ell$-step Distributed Moving Horizon Estimation (DMHE$\ell$) algorithm that explicitly addresses sporadic measurements. The algorithm employs an information diffusion mechanism, enabling each sensor to leverage measurements from its$\ell$-step neighbors. A comprehensive stability analysis proves that the estimation error remains uniformly bounded, thereby establishing convergence guarantees, regardless of the sporadic nature of the measurements. The effectiveness of DMHE$\ell$is demonstrated through simulations in a realistic industrial scenario involving an autonomous mobile robot. The results confirm that the method achieves high estimation accuracy while requiring significantly less communication and data exchange than existing distributed estimators for comparable accuracy levels.

In this paper, a Deep Reinforcement Learning (DRL) algorithm is proposed, to learn a control policy for dynamic systems with input and state constraints. The system dynamics are assumed to be unknown for control design, the only available a priori information being the formulation of input and state constraints. Elements of Control Theory are leveraged to obtain safety certificates along with the learned policy: Control Lyapunov Functions (CLF) for closed loop stability, and Control Barrier Functions (CBF) for state constraint satisfaction. These two notions are transformed into conditions to be numerically verified in a PPO-based DRL algorithm, where a neural network CLF is also learned along with the control policy. Simulation results are presented for two application examples, illustrating closed-loop stability and constraint satisfaction resulting from the learned controllers.

For humans, fast, efficient walking over flat ground represents the vast majority of locomotion that an individual experiences on a daily basis, and for an effective, real-world humanoid robot the same will likely be the case. In this work, we propose a locomotion controller for efficient walking over near-flat ground using a relatively simple, model-based controller that utilizes a novel combination of several interesting design features including an ALIP-based step adjustment strategy, stance leg length control as an alternative to center of mass height control, and rolling contact for heel-to-toe motion of the stance foot. We then present the results of this controller on our robot Nadia, both in simulation and on hardware. These results include validation of this controller’s ability to perform fast, reliable forward walking at 0.75 m/s along with backwards walking, side-stepping, turning in place, and push recovery. We also present an efficiency comparison between the proposed control strategy and our baseline walking controller over three steady-state walking speeds. Lastly, we demonstrate some of the benefits of utilizing rolling contact in the stance foot, specifically the reduction of necessary positive and negative work throughout the stride.

Humanoid robots possess the ability to perform complex tasks in challenging environments. However, they require a model of the surroundings in a representation that is sufficient enough for downstream tasks such as footstep planning. The maps generated by existing mapping algorithms are either sparse, insufficient for footstep planning, memory intensive, or too slow for dynamic humanoid behaviors. In this work, we develop a mapping algorithm that combines planar region measurements along with kinematic-inertial state estimates to build a dense but efficient map of bounded planar surfaces. We present novel algorithms for plane feature matching, tracking and registration for mapping within a factor graph framework. The generated map is not only memory efficient, but also offers higher reliability and speed in bipedal footstep planning, than was possible earlier. The complete algorithm is also demonstrated using a full-scale humanoid robot, Nadia, walking over both flat ground and rough terrain utilizing the generated terrain map.

The ability to accomplish manipulation and locomotion tasks in the presence of significant time-varying external loads is a remarkable skill of humans that has yet to be replicated convincingly by humanoid robots. Such an ability will be a key requirement in the environments we envision deploying our robots: dull, dirty, and dangerous. External loads constitute a large model bias, which is typically unaccounted for. In this work, we enable our humanoid robot to engage in loco-manipulation tasks in the presence of significant model bias due to external loads. We propose an online estimation and control framework involving the combination of a physically consistent extended Kalman filter for inertial parameter estimation coupled to a whole-body controller. We showcase our results both in simulation and in hardware, where weights are mounted on Nadia’s wrist links as a proxy for engaging in tasks where large external loads are applied to the robot.

Legged robots require fast and accurate representation of their surrounding terrain to achieve behaviors such as running, push recovery, continuous walking, backflips, while also utilizing on-board computational resources efficiently. The desired tasks can be achieved efficiently by representing the environment using planar regions. However, existing methods for planar region extraction are either too slow or require significant compute time on the Central Processing Unit (CPU). In this work we exploit key properties of depth images and Graphical Processing Unit (GPU) to estimate planar regions around the robot at very high frame rates of 150-200 Hz. The proposed algorithm uses a set of fully customizable and interchangeable set of kernel layers on the GPU to process the depth map in parallel and generate a locally connected graph structure, which is later separated into planar components using a basic depth-first search. We test the proposed algorithm on the Atlas robot while performing different walking behaviors on oriented cinder blocks, as well as in simulation with simulated sensor and robot. The algorithm is open-sourced for research on legged robots and other fields.

This paper presents a tele-operation system that enables a MAV to be controlled on virtual surfaces by an unskilled operator using high-level inputs. These virtual surfaces can be placed relatively to the infrastructure to be inspected, in order to ensure safety of the flight and repeatability of the acquisition conditions of the inspection data (e.g. at a constant distance from the infrastructure). The architecture, interface and embedded controller of the tele-operation system are described, and results from flight experiments in an industrial warehouse are provided for three typical inspection scenarios of infrastructures.

A new distributed algorithm is presented for waypoint navigation of a multi-robot system. The proposed two-level architecture (reference generator and local controller) exploits Voronoi partitioning and purely geometric considerations to distributively generate references for each robot in order to ensure collision avoidance and convergence of the fleet to the waypoint. Flexibility in the obtained formation pattern is made possible by the algorithm, by not pre-fixing as usually done its geometric form. In addition, the gain tuning is easy and the setting allows to naturally obtain certain formation patterns and adjust the rigidity of the fleet. Moreover the distributed nature of the algorithm also allows robustness to online modification of the number of vehicles (in the fleet or within range of communication), also addressing the 2-robot scenario. Field experiments on ground mobile robots are provided to illustrate the performance of the algorithm.

Awareness of the environment is essential for mobile robots. Perception for legged robots requires high levels of reliability and accuracy in order to walk stably in the types of complex, cluttered environments we are interested in. In this paper, we present a usable environmental perception algorithm designed to detect steppable areas and obstacles for the autonomous generation of desired footholds for legged robots. To produce an efficient representation of the environment, the proposed perception algorithm is desired to cluster point cloud data to planar regions composed of convex polygons. We describe in this paper the end-to-end pipeline from data collection to generation of the regions, where we first compose an octree in order to create a more efficient data representation. We then group the leaves in the tree using a nearest neighbor search into a planar region, which is composed of the concave hull of points that is decomposed into convex polygons. We present a variety of environments, and illustrate the usability of this approach by the Atlas humanoid robots walking over rough terrain. We also discuss various challenges we faced and insights we gained in the development of this approach.

Performing large step-ups is a challenging task for a humanoid robot. It requires the robot to perform motions at the limit of its reachable workspace while straining to move its body upon the obstacle. This paper presents a non-linear trajectory optimization method for generating step-up motions. We adopt a simplified model of the centroidal dynamics to generate feasible Center of Mass trajectories aimed at reducing the torques required for the step-up motion. The activation and deactivation of contacts at both feet are considered explicitly. The output of the planner is a Center of Mass trajectory plus an optimal duration for each walking phase. These desired values are stabilized by a whole-body controller that determines a set of desired joint torques. We experimentally demonstrate that by using trajectory optimization techniques, the maximum torque required to the full-size humanoid robot Atlas can be reduced up to 20% when performing a step-up motion.

Legged humanoid robots promise revolutionary mobility and effectiveness in environments built for humans. However, inefficient use of energy significantly limits their practical adoption. The humanoid biped walking anthropomorphic novelly-driven efficient robot for emergency response (WANDERER) achieves versatile, efficient mobility, and high endurance via novel drive-trains and passive joint mechanisms. Results of a test in which WANDERER walked for more than 4 h and covered 2.8 km on a treadmill, are presented. Results of laboratory experiments showing even more efficient walking are also presented and analyzed in this article. WANDERER's energetic performance and endurance are believed to exceed the prior literature in human-scale humanoid robots. This article describes WANDERER, the analytical methods and innovations that enable its design, and system-level energy efficiency results.

In this paper we address the problem of dot painting on a wall by a quadrotor Micro Air Vehicle (MAV), using on-board low cost sensors (monocular camera and IMU) for localization. A method is proposed to cope with uncertainties on the initial positioning of the MAV with respect to the wall and to deal with walls composed of multiple segments. This method is based on an online estimation algorithm that makes use of information of physical contacts detected by the drone during the flight to improve the positioning accuracy of the painted dots. Simulation results are presented to assess quantitatively the efficiency of the proposed approaches.

We present an approach for achieving a natural, efficient gait on bipedal robots using straightened legs and toe-off. Our algorithm avoids complex height planning by allowing a whole-body controller to determine the straightest possible leg configuration at run-time. The controller solutions are biased towards a straight leg configuration by projecting leg joint angle objectives into the null-space of the other quadratic program motion objectives. To allow the legs to remain straight throughout the gait, toe-off was utilized to increase the kinematic reachability of the legs. The toe-off motion is achieved through underconstraining the foot position, allowing it to emerge naturally. We applied this approach of under-specifying the motion objectives to the Atlas humanoid, allowing it to walk over a variety of terrain. We present both experimental and simulation results and discuss performance limitations and potential improvements.

When walking at high speeds, the swing legs of robots produce a non-negligible angular momentum rate. To accommodate this, we provide a reference trajectory generator for bipedal walking that incorporates predicted centroidal angular momentum at the planning stage. This can be done efficiently as the Centroidal Moment Pivot (CMP), Instantaneous Capture Point (ICP) and the center of mass (CoM) all have closed-form trajectory solutions due to their linear dynamics. This is then used to produce smooth, continuous trajectories. We furthermore provide a lightweight model to estimate angular momentum as induced during leg swing of the gait cycle. Our proposed trajectory generator is tested thoroughly in simulation and has been shown to successfully operate on the real hardware.

While humans are highly capable of recovering from external disturbances and uncertainties that result in large tracking errors, humanoid robots have yet to reliably mimic this level of robustness. Essential to this is the ability to combine traditional “ankle strategy” balancing with step timing and location adjustment techniques. In doing so, the robot is able to step quickly to the necessary location to continue walking. In this work, we present both a new swing speed up algorithm to adjust the step timing, allowing the robot to set the foot down more quickly to recover from errors in the direction of the current capture point dynamics, and a new algorithm to adjust the desired footstep, expanding the base of support to utilize the center of pressure (CoP)-based ankle strategy for balance. We then utilize the desired centroidal moment pivot (CMP) to calculate the momentum rate of change for our inverse-dynamics based whole-body controller. We present simulation and experimental results using this work, and discuss performance limitations and potential improvements.

In this paper we introduce STEPPR (Sandia Transmission-Efficient Prototype Promoting Research), a bipedal robot designed to explore efficient bipedal walking. The initial iteration of this robot achieves efficient motions through powerful electromagnetic actuators and highly back-drivable synthetic rope transmissions. We show how the addition of parallel elastic elements at select joints is predicted to provide substantial energetic benefits: reducing cost of transport by 30 to 50 percent. Two joints in particular, hip roll and ankle pitch, reduce dissipated power over three very different gait types: human walking, human-like robot walking, and crouched robot walking. Joint springs based on this analysis are tested and validated experimentally. Finally, this paper concludes with the design of two unique parallel spring mechanisms to be added to the current STEPPR robot in order to provide improved locomotive efficiency.

This paper works with the concept of Divergent Component of Motion (DCM), also called `(instantaneous) Capture Point'. We present two real-time DCM trajectory generators for uneven (three-dimensional) ground surfaces, which lead to continuous leg (and corresponding ground reaction) force profiles and facilitate the use of toe-off motion during double support. Thus, the resulting DCM trajectories are well suited for real-world robots and allow for increased step length and step height. The performance of the proposed methods was tested in numerous simulations and experiments on IHMC's Atlas robot and DLR's humanoid robot TORO.

This paper presents a method to design guidance and control laws for small vertical take off and landing unmanned aerial vehicles when no measurement of linear velocity or angular velocity is available. The control strategy is based on the introduction of virtual states in the state equation of the system and allows the design of stabilizing feedback controllers without using any observer. Simulation results are provided for six degrees of freedom model of a small rotorcraft-based unmanned aerial vehicle.