Monthly Archives: December 2023

You are browsing the site archives by month.

Learning options in RL and using rewards adequately in that context

Richard S. Sutton, Marlos C. Machado, G. Zacharias Holland, David Szepesvari, Finbarr Timbers, Brian Tanner, Adam White, Reward-respecting subtasks for model-based reinforcement learning, Artificial Intelligence, Volume 324, 2023, DOI: 10.1016/j.artint.2023.104001.

To achieve the ambitious goals of artificial intelligence, reinforcement learning must include planning with a model of the world that is abstract in state and time. Deep learning has made progress with state abstraction, but temporal abstraction has rarely been used, despite extensively developed theory based on the options framework. One reason for this is that the space of possible options is immense, and the methods previously proposed for option discovery do not take into account how the option models will be used in planning. Options are typically discovered by posing subsidiary tasks, such as reaching a bottleneck state or maximizing the cumulative sum of a sensory signal other than reward. Each subtask is solved to produce an option, and then a model of the option is learned and made available to the planning process. In most previous work, the subtasks ignore the reward on the original problem, whereas we propose subtasks that use the original reward plus a bonus based on a feature of the state at the time the option terminates. We show that option models obtained from such reward-respecting subtasks are much more likely to be useful in planning than eigenoptions, shortest path options based on bottleneck states, or reward-respecting options generated by the option-critic. Reward respecting subtasks strongly constrain the space of options and thereby also provide a partial solution to the problem of option discovery. Finally, we show how values, policies, options, and models can all be learned online and off-policy using standard algorithms and general value functions.

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.

Reward machines as reward specification method for RL and their automated learning

Rodrigo Toro Icarte, Toryn Q. Klassen, Richard Valenzano, Margarita P. Castro, Ethan Waldie, Sheila A. McIlraith, Learning reward machines: A study in partially observable reinforcement learning, Artificial Intelligence, Volume 323, 2023 DOI: 10.1016/j.artint.2023.103989.

Reinforcement Learning (RL) is a machine learning paradigm wherein an artificial agent interacts with an environment with the purpose of learning behaviour that maximizes the expected cumulative reward it receives from the environment. Reward machines (RMs) provide a structured, automata-based representation of a reward function that enables an RL agent to decompose an RL problem into structured subproblems that can be efficiently learned via off-policy learning. Here we show that RMs can be learned from experience, instead of being specified by the user, and that the resulting problem decomposition can be used to effectively solve partially observable RL problems. We pose the task of learning RMs as a discrete optimization problem where the objective is to find an RM that decomposes the problem into a set of subproblems such that the combination of their optimal memoryless policies is an optimal policy for the original problem. We show the effectiveness of this approach on three partially observable domains, where it significantly outperforms A3C, PPO, and ACER, and discuss its advantages, limitations, and broader potential.

A PID-based global optimization algorithm

Yuansheng Gao, PID-based search algorithm: A novel metaheuristic algorithm based on PID algorithm, Expert Systems with Applications, Volume 232, 2023, DOI: 10.1016/j.eswa.2023.120886.

In this paper, a metaheuristic algorithm called PID-based search algorithm (PSA) is proposed for global optimization. The algorithm is based on an incremental PID algorithm that converges the entire population to an optimal state by continuously adjusting the system deviations. PSA is mathematically modeled and implemented to achieve optimization in a wide range of search spaces. PSA is used to solve CEC2017 benchmark test functions and six constrained problems. The optimization performance of PSA is verified by comparing it with seven metaheuristics proposed in recent years. The Kruskal-Wallis, Holm and Friedman tests verified the superiority of PSA in terms of statistical significance. The results show that PSA can be better balanced exploration and exploitation with strong optimization capability. Source codes�of PSA are publicly available at

A review of RL algorithms

Ashish Kumar Shakya, Gopinatha Pillai, Sohom Chakrabarty, Reinforcement learning algorithms: A brief survey, Expert Systems with Applications, Volume 231, 2023 DOI: 10.1016/j.eswa.2023.120495.

Reinforcement Learning (RL) is a machine learning (ML) technique to learn sequential decision-making in complex problems. RL is inspired by trial-and-error based human/animal learning. It can learn an optimal policy autonomously with knowledge obtained by continuous interaction with a stochastic dynamical environment. Problems considered virtually impossible to solve, such as learning to play video games just from pixel information, are now successfully solved using deep reinforcement learning. Without human intervention, RL agents can surpass human performance in challenging tasks. This review gives a broad overview of RL, covering its fundamental principles, essential methods, and illustrative applications. The authors aim to develop an initial reference point for researchers commencing their research work in RL. In this review, the authors cover some fundamental model-free RL algorithms and pathbreaking function approximation-based deep RL (DRL) algorithms for complex uncertain tasks with continuous action and state spaces, making RL useful in various interdisciplinary fields. This article also provides a brief review of model-based and multi-agent RL approaches. Finally, some promising research directions for RL are briefly presented.

Interesting way of explaining pointers and arrays of C in teaching programming

W. Rong, T. Xu, Z. Sun, Z. Sun, Y. Ouyang and Z. Xiong, An Object Tuple Model for Understanding Pointer and Array in C Language, IEEE Transactions on Education, vol. 66, no. 4, pp. 318-329, Aug. 2023 DOI: 10.1109/TE.2023.3236027.

Contribution: In this study, an object tuple model has been proposed, and a quasi-experimental study on its usage in an introductory programming language course has been reported. This work can be adopted by all C language teachers and students in learning pointer and array-related concepts. Background: C language has been extensively employed in numerous universities as an introductory programming practice. However, the pointer and array have long been recognized as some of the most difficult concepts for novice students learning C language. To help students become familiar with the concept of pointer and array and also their related operations, a comprehensive understanding from memory management\u2019s perspective might be helpful. Research Questions: 1) How does the object tuple model help students understand all kinds of object types from a generalized perspective? 2) Why is it important to let the students consider multiple arrays from a 1-D perspective? and 3) How do the memory-oriented operations from the object\u2019s perspective help students comprehensively understand the pointer and array? Methodology: The students were divided into experimental and control groups, and the object tuple model was presented in the experimental group. An examination was conducted at end of the semester, and test data were gathered for further analysis. Findings: The proposed object tuple model is effective in giving students clear guidance and helping them further understand the pointer and array in C language.

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 for fast evaluation.


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.