Category Archives: Robotics

Hierarchical RL with continuous options

Zhigang Huang, Quan Liu, Fei Zhu, Hierarchical reinforcement learning with adaptive scheduling for robot control, Engineering Applications of Artificial Intelligence, Volume 126, Part D, 2023 DOI: 10.1016/j.engappai.2023.107130.

Conventional hierarchical reinforcement learning (HRL) relies on discrete options to represent explicitly distinguishable knowledge, which may lead to severe performance bottlenecks. It is possible to represent richer knowledge through continuous options, but reliable scheduling methods are lacking. To design an available scheduling method for continuous options, in this paper, the hierarchical reinforcement learning with adaptive scheduling (HAS) algorithm is proposed. Its low-level controller learns diverse options, while the high-level controller schedules options to learn solutions. It achieves an adaptive balance between exploration and exploitation during the frequent scheduling of continuous options, maximizing the representation potential of continuous options. It builds on multi-step static scheduling and makes switching decisions according to the relative advantages of the previous and the estimated continuous options, enabling the agent to focus on different behaviors at different phases of the task. The expected t-step distance is applied to demonstrate the superiority of adaptive scheduling in terms of exploration. Furthermore, an interruption incentive based on annealing is proposed to alleviate excessive exploration during the early training phase, accelerating the convergence rate. Finally, we apply HAS to robot control with sparse rewards in continuous spaces, and develop a comprehensive experimental analysis scheme. The experimental results not only demonstrate the high performance and robustness of HAS, but also provide evidence that the adaptive scheduling method has a positive effect both on the representation and option policies.

RL to learn not only manipulator skills but also safety skills

A. C. Ak, E. E. Aksoy and S. Sariel, Learning Failure Prevention Skills for Safe Robot Manipulation, IEEE Robotics and Automation Letters, vol. 8, no. 12, pp. 7994-8001, Dec. 2023 DOI: 10.1109/LRA.2023.3324587.

Robots are more capable of achieving manipulation tasks for everyday activities than before. However, the safety of manipulation skills that robots employ is still an open problem. Considering all possible failures during skill learning increases the complexity of the process and restrains learning an optimal policy. Nonetheless, safety-focused modularity in the acquisition of skills has not been adequately addressed in previous works. For that purpose, we reformulate skills as base and failure prevention skills, where base skills aim at completing tasks and failure prevention skills aim at reducing the risk of failures to occur. Then, we propose a modular and hierarchical method for safe robot manipulation by augmenting base skills by learning failure prevention skills with reinforcement learning and forming a skill library to address different safety risks. Furthermore, a skill selection policy that considers estimated risks is used for the robot to select the best control policy for safe manipulation. Our experiments show that the proposed method achieves the given goal while ensuring safety by preventing failures. We also show that with the proposed method, skill learning is feasible and our safe manipulation tools can be transferred to the real environment.

A survey on open hardware robotics

V. V. Patel, M. V. Liarokapis and A. M. Dollar, Open Robot Hardware: Progress, Benefits, Challenges, and Best Practices, IEEE Robotics & Automation Magazine, vol. 30, no. 3, pp. 123-148, Sept. 2023 DOI: 10.1109/MRA.2022.3225725.

Technologies from open source projects have seen widespread adoption in robotics in recent years. The rapid pace of progress in robotics is in part fueled by open source projects, providing researchers with resources, tools, and devices to implement novel ideas and approaches quickly. Open source hardware, in particular, lowers the barrier of entry to new technologies and can further accelerate innovation in robotics. But open hardware is also more difficult to propagate in comparison to open software because it involves replicating physical components, which requires users to have sufficient familiarity and access to fabrication equipment. In this work, we present a review on open robot hardware (ORH) by first highlighting the key benefits and challenges encountered by users and developers of ORH, and then relaying some best practices that can be adopted in developing successful ORH. To accomplish this, we surveyed more than 80 major ORH projects and initiatives across different domains within robotics. Finally, we identify strategies exemplified by the surveyed projects to further detail the development process, and guide developers through the design, documentation, and dissemination stages of an ORH project.

Dealing with affordances in robotics through RL

X. Yang, Z. Ji, J. Wu and Y. -K. Lai, Recent Advances of Deep Robotic Affordance Learning: A Reinforcement Learning Perspective, EEE Transactions on Cognitive and Developmental Systems, vol. 15, no. 3, pp. 1139-1149, Sept. 2023 DOI: 10.1109/TCDS.2023.3277288.

As a popular concept proposed in the field of psychology, affordance has been regarded as one of the important abilities that enable humans to understand and interact with the environment. Briefly, it captures the possibilities and effects of the actions of an agent applied to a specific object or, more generally, a part of the environment. This article provides a short review of the recent developments of deep robotic affordance learning (DRAL), which aims to develop data-driven methods that use the concept of affordance to aid in robotic tasks. We first classify these papers from a reinforcement learning (RL) perspective and draw connections between RL and affordances. The technical details of each category are discussed and their limitations are identified. We further summarize them and identify future challenges from the aspects of observations, actions, affordance representation, data-collection, and real-world deployment. A final remark is given at the end to propose a promising future direction of the RL-based affordance definition to include the predictions of arbitrary action consequences.

Review of algorithms available in ROS-2

Steve Macenski, Tom Moore, David V. Lu, Alexey Merzlyakov, Michael Ferguson, From the desks of ROS maintainers: A survey of modern & capable mobile robotics algorithms in the robot operating system 2, Robotics and Autonomous Systems, Volume 168, 2023, DOI: 10.1016/j.robot.2023.104493.

The Robot Operating System�2 (ROS�2) is rapidly impacting the intelligent machines sector \u2014 on space missions, large agriculture equipment, multi-robot fleets, and more. Its success derives from its focused design and improved capabilities targeting product-grade and modern robotic systems. Following ROS�2\u2019s example, the mobile robotics ecosystem has been fully redesigned based on the transformed needs of modern robots and is experiencing active development not seen since its inception. This paper comes from the desks of the key ROS Navigation maintainers to review and analyze the state of the art of robotics navigation in ROS�2. This includes new systems without parallel in ROS�1 or other similar mobile robotics frameworks. We discuss current research products and historically robust methods that provide differing behaviors and support for most every robot type. This survey consists of overviews, comparisons, and expert insights organized by the fundamental problems in the field. Some of these implementations have yet to be described in literature and many have not been benchmarked relative to others. We end by providing a glimpse into the future of the ROS�2 mobile robotics ecosystem.

Pure pursuit with linear velocity regulation

Macenski, S., Singh, S., Mart�n, F. et al. Regulated pure pursuit for robot path tracking, Auton Robot 47, 685\u2013694 (2023) DOI: 10.1007/s10514-023-10097-6.

The accelerated deployment of service robots have spawned a number of algorithm variations to better handle real-world conditions. Many local trajectory planning techniques have been deployed on practical robot systems successfully. While most formulations of Dynamic Window Approach and Model Predictive Control can progress along paths and optimize for additional criteria, the use of pure path tracking algorithms is still commonplace. Decades later, Pure Pursuit and its variants continues to be one of the most commonly utilized classes of local trajectory planners. However, few Pure Pursuit variants have been proposed with schema for variable linear velocities\u2014they either assume a constant velocity or fails to address the point at all. This paper presents a variant of Pure Pursuit designed with additional heuristics to regulate linear velocities, built atop the existing Adaptive variant. The Regulated Pure Pursuit algorithm makes incremental improvements on state of the art by adjusting linear velocities with particular focus on safety in constrained and partially observable spaces commonly negotiated by deployed robots. We present experiments with the Regulated Pure Pursuit algorithm on industrial-grade service robots. We also provide a high-quality reference implementation that is freely included ROS 2 Nav2 framework at https://github.com/ros-planning/navigation2 for fast evaluation.

UWB for SLAM

H. A. G. C. Premachandra, R. Liu, C. Yuen and U. -X. Tan, UWB Radar SLAM: An Anchorless Approach in Vision Denied Indoor Environments, IEEE Robotics and Automation Letters, vol. 8, no. 9, pp. 5299-5306, Sept. 2023 DOI: 10.1109/LRA.2023.3293354.

LiDAR and cameras are frequently used as sensors for simultaneous localization and mapping (SLAM). However, these sensors are prone to failure under low visibility (e.g. smoke) or places with reflective surfaces (e.g. mirrors). On the other hand, electromagnetic waves exhibit better penetration properties when the wavelength increases, thus are not affected by low visibility. Hence, this letter presents ultra-wideband (UWB) radar as an alternative to the existing sensors. UWB is generally known to be used in anchor-tag SLAM systems. One or more anchors are installed in the environment and the tags are attached to the robots. Although this method performs well under low visibility, modifying the existing infrastructure is not always feasible. UWB has also been used in peer-to-peer ranging collaborative SLAM systems. However, this requires more than a single robot and does not include mapping in the mentioned environment like smoke. Therefore, the presented approach in this letter solely depends on the UWB transceivers mounted on-board. In addition, an extended Kalman filter (EKF) SLAM is used to solve the SLAM problem at the back-end. Experiments were conducted and demonstrated that the proposed UWB-based radar SLAM is able to map natural point landmarks inside an indoor environment while improving robot localization.

Using “empowerment” to better select actions in RL when there are only sparse rewards

Dai, S., Xu, W., Hofmann, A. et al. An empowerment-based solution to robotic manipulation tasks with sparse rewards, Auton Robot 47, 617\u2013633 (2023) DOI: 10.1007/s10514-023-10087-8.

In order to provide adaptive and user-friendly solutions to robotic manipulation, it is important that the agent can learn to accomplish tasks even if they are only provided with very sparse instruction signals. To address the issues reinforcement learning algorithms face when task rewards are sparse, this paper proposes an intrinsic motivation approach that can be easily integrated into any standard reinforcement learning algorithm and can allow robotic manipulators to learn useful manipulation skills with only sparse extrinsic rewards. Through integrating and balancing empowerment and curiosity, this approach shows superior performance compared to other state-of-the-art intrinsic exploration approaches during extensive empirical testing. When combined with other strategies for tackling the exploration challenge, e.g. curriculum learning, our approach is able to further improve the exploration efficiency and task success rate. Qualitative analysis also shows that when combined with diversity-driven intrinsic motivations, this approach can help manipulators learn a set of diverse skills which could potentially be applied to other more complicated manipulation tasks and accelerate their learning process.

Using Deep RL (TRPO) for selecting best interest points in the environment for path planning

Jie Fan, Xudong Zhang, Yuan Zou, Hierarchical path planner for unknown space exploration using reinforcement learning-based intelligent frontier selection, Expert Systems with Applications, Volume 230, 2023 DOI: 10.1016/j.eswa.2023.120630.

Path planning in unknown environments is extremely useful for some specific tasks, such as exploration of outer space planets, search and rescue in disaster areas, home sweeping services, etc. However, existing frontier-based path planners suffer from insufficient exploration, while reinforcement learning (RL)-based ones are confronted with problems in efficient training and effective searching. To overcome the above problems, this paper proposes a novel hierarchical path planner for unknown space exploration using RL-based intelligent frontier selection. Firstly, by decomposing the path planner into three-layered architecture (including the perception layer, planning layer, and control layer) and using edge detection to find potential frontiers to track, the path search space is shrunk from the whole map to a handful of points of interest, which significantly saves the computational resources in both training and execution processes. Secondly, one of the advanced RL algorithms, trust region policy optimization (TRPO), is used as a judge to select the best frontier for the robot to track, which ensures the optimality of the path planner with a shorter path length. The proposed method is validated through simulation and compared with both classic and state-of-the-art methods. Results show that the training process could be greatly accelerated compared with the traditional deep-Q network (DQN). Moreover, the proposed method has 4.2%\u201314.3% improvement in exploration region rate and achieves the highest exploration completeness.

Monte Carlo Tree Search (MTCS) with hybrid discrete-continuous beliefs, applied to robotics

M. Barenboim, M. Shienman and V. Indelman, Monte Carlo Planning in Hybrid Belief POMDPs, IEEE Robotics and Automation Letters, vol. 8, no. 8, pp. 4410-4417, Aug. 2023 DOI: 10.1109/LRA.2023.3282773.

Real-world problems often require reasoning about hybrid beliefs, over both discrete and continuous random variables. Yet, such a setting has hardly been investigated in the context of planning. Moreover, existing online partially observable Markov decision processes (POMDPs) solvers do not support hybrid beliefs directly. In particular, these solvers do not address the added computational burden due to an increasing number of hypotheses with the planning horizon, which can grow exponentially. As part of this work, we present a novel algorithm, Hybrid Belief Monte Carlo Planning (HB-MCP) that utilizes the Monte Carlo Tree Search (MCTS) algorithm to solve a POMDP while maintaining a hybrid belief. We illustrate how the upper confidence bound (UCB) exploration bonus can be leveraged to guide the growth of hypotheses trees alongside the belief trees. We then evaluate our approach in highly aliased simulated environments where unresolved data association leads to multi-modal belief hypotheses.