This paper investigates the fixed-time prescribed performance tracking control problem for Euler-Lagrange systems with model uncertainties, external disturbances, and actuator faults. To the best of the authors’ knowledge, achieving prescribed transient and steady-state behaviors within a fixed time under unknown bounded initial conditions, while simultaneously ensuring effective compensation for system uncertainties and faults, still remains an open problem. To address these challenges concerning both performance-related and reliability-related constraints, we propose a novel adaptive neural fault-tolerant control with fixed-time prescribed performance (ANFTC-FPP). The performance-related constraints are handled through a unified framework that synergistically combines novel prescribed performance functions (PPFs) with barrier Lyapunov functions (BLFs). This integration relaxes initialization constraints and characterizes the relationship between initial conditions and transient performance, thereby considering overshoot for tracking errors within a fixed time while achieving specified steady-state accuracy, regardless of initial states. For reliability-related constraints, we establish a fixed-time compensation mechanism where model uncertainties are handled by extending radial basis function neural networks (RBFNNs) for uncertainty approximation, while actuator faults are addressed through adaptive fault-tolerant control (FTC). The semi-global practical fixed-time stability (SPFS) of all closed-loop signals is rigorously established through comprehensive Lyapunov stability analysis. The efficacy of the proposed control strategy is experimentally validated on a physical KINOVA robotic manipulator system through real-world implementation.

3D Gaussian Splatting (3DGS) allows flexible adjustments to scene representation, enabling continuous optimization of scene quality during dense visual simultaneous localization and mapping (SLAM) in static environments. However, 3DGS faces challenges in handling environmental disturbances from dynamic objects with irregular movement, leading to degradation in both camera tracking accuracy and map reconstruction quality. To address this challenge, we develop an RGB-D dense SLAM which is called Gaussian Splatting SLAM in Dynamic Environments (Gassidy). This approach calculates Gaussians to generate rendering loss flows for each environmental component based on a designed photometricgeometric loss function. To distinguish and filter environmental disturbances, we iteratively analyze rendering loss flows to detect features characterized by changes in loss values between dynamic objects and static components. This process ensures a clean environment for accurate scene reconstruction. Compared to state-of-the-art SLAM methods, experimental results on open datasets show that Gassidy improves camera tracking precision by up to 97.9 % and enhances map quality by up to 6 %. Video of experiments is available here: https://www.wixsite.com.com/wen-Gassidy.

Optimal path planning requires finding a series of feasible states from the starting point to the goal to optimize objectives. Popular path planning algorithms, such as Effort Informed Trees (EIT*), employ effort heuristics to guide the search. Effective heuristics are accurate and computationally efficient, but achieving both can be challenging due to their conflicting nature. This paper proposes Direction Informed Trees (DIT*), a sampling-based planner that focuses on optimizing the search direction for each edge, resulting in goal bias during exploration. We define edges as generalized vectors and integrate similarity indexes to establish a directional filter that selects the nearest neighbors and estimates direction costs. The estimated direction cost heuristics are utilized in edge evaluation. This strategy allows the exploration to share directional information efficiently. DIT* convergence faster than existing single-query, sampling-based planners on tested problems in$\mathbb{R}^{4}$to$\mathbb{R}^{16}$and has been demonstrated in real-world environments with various planning tasks. A video showcasing our experimental results is available at: https://youtu.be/2SX6QT2NOek.

This paper proposes a novel dual-filter architecture utilizing RGB-D camera data and dynamic control barrier functions (D-CBFs) for real-time obstacle avoidance in unstructured environments. The proposed method efficiently handles static, suddenly appearing, and dynamic obstacles, maintaining consistent computational performance across diverse scenarios. To achieve this, two key challenges must be addressed. First, the substantial volume of pixel and depth map data requires robust, real-time processing for efficient D-CBF construction. Second, constructing D-CBFs for each obstacle in multi-obstacle scenarios increases optimization solver time. To address these challenges, we adapt the concept of salient object detection (SOD), proposing an enhanced FastSOD (E-FastSOD) method for rapid risk area identification. This approach rapidly filters out low-risk areas, while high-risk regions are mathematically represented utilizing the proposed enhanced minimal bounding circle (E-MBC) technique. We differentiate static and dynamic obstacles by comparing current and previous MBC states, employing Kalman filtering for obstacle state prediction. This setup enables efficient online D-CBF construction for each MBC, balancing computational speed with accurate obstacle representation. Subsequently, the second filter establishes buffer zones around established D-CBFs, activating only those corresponding to zones the robot actually enters, rather than all D-CBFs to increase real-time performance. We prove the system's safety and asymptotic stabilization under this architecture. Simulated and real-world experiments validate our method, demonstrating an equipped mobile robot's ability to accomplish tasks while ensuring safety across diverse, unknown scenarios.

The whisker-inspired tactile sensor is advantageous for enhancing robotic perception in proximate range and darkness via non-intrusive contacts. However, localizing contact along the whisker shaft is challenging due to the non-injective mapping between tangential contacts and the resulting bending moments at the whisker base. Previous studies suggest that incorporating axial force measurements can resolve this ambiguity. In this work, we develop a magnetically transduced whisker sensor that integrates axial force sensing as an additional mechanical signal. The sensor features a tapered whisker with a custom slope and a 3-DoF suspension mechanism, enabling axial displacement at the base, which is proportional to the applied axial force. We construct a Penalized Gaussian Process model trained on synthetic data to estimate the whisker’s motion and refine it with real-data constraints. The design is compact, low-cost, and validated through simulations and real-world experiments to differentiate tangential contacts. Furthermore, we propose an optimization-based approach for estimating instantaneous contact locations. Experimental results demonstrate that the proposed method can effectively track contacts in millimeter-level accuracy with a mean error of 7.17 mm, achieving a higher accuracy with only 4.02 mm in large-deflection and close-to-base regions.

Path planning in robotics often involves solving continuously valued, high-dimensional problems. Popular informed approaches include graph-based searches, such as A*, and sampling-based methods, such as Informed RRT*, which utilize informed set and anytime strategies to expedite path optimization incrementally. Informed sampling-based planners define informed sets as subsets of the problem domain based on the current best solution cost. However, when no solution is found, these planners re-sample and explore the entire configuration space, which is time-consuming and computationally expensive. This article introduces Multi-Informed Trees (MIT*), a novel planner that constructs estimated informed sets based on prior admissible solution costs before finding the initial solution, thereby accelerating the initial convergence rate. Moreover, MIT* employs an adaptive sampler that dynamically adjusts the sampling strategy based on the exploration process. Furthermore, MIT* utilizes length-related adaptive sparse collision checks to guide lazy reverse search. These features enhance path cost efficiency and computation times while ensuring high success rates in confined scenarios. Through a series of simulations and real-world experiments, it is confirmed that MIT* outperforms existing single-query, sampling-based planners for problems in$\mathbb {R}^{4}$to$\mathbb {R}^{16}$and has been successfully applied to real-world robot manipulation tasks. A video showcasing our experimental results is available at:https://youtu.be/30RsBIdexTUNote to Practitioners—The motivation for this work stems from the challenges faced by existing informed path planners in high-dimensional, continuously valued environments, particularly when an initial feasible solution is difficult to find. Traditional asymmetric bidirectional planners rely on the best current solution to define problem subsets. When a lazy path has been found through lazy reverse search, these planners tend to re-sample and explore the entire problem space, which could hinder the path planning process. Our proposed MIT* algorithm addresses this issue by constructing an estimated informed set based on prior admissible solution costs before finding the initial solution. This estimated set helps to narrow the search area, thereby accelerating the initial convergence rate. MIT* also integrates an adaptive sampling strategy that dynamically adjusts based on the ongoing exploration process, enhancing the planner’s ability to efficiently navigate through challenging spaces. Furthermore, MIT* employs adaptive sparse collision checks, which guide the lazy reverse search that balances computational efficiency with accuracy in pathfinding. The proposed algorithm can be applied to industrial robots, humanoid robots, or service robots to achieve efficient path planning.

This paper proposes a novel adaptive fast variational sparse Gaussian process (AFVSGP) framework to ensure real-time safety for high-order systems under model uncertainties and dynamic obstacle environments. The framework effectively addresses the challenge of maintaining real-time safety guarantees during unknown trajectory transitions in nonstationary environments. To achieve this, the proposed framework incorporates three key innovations. First, a specialized kernel function is embedded within the VSGP algorithm to decouple control inputs from uncertainties while preserving the convexity of posterior-based safety constraints. Second, an adaptive online incremental learning mechanism is introduced, integrating forgetting capabilities with dynamic reconstruction rules for training datasets and inducing sets, thereby accelerating inference convergence and enabling compact uncertainty prediction with reduced computational complexity. Third, a high-order control barrier function (HOCBF)-based safety filter is developed to synthesize safe control inputs by leveraging the proposed learning model, thereby establishing rigorous probabilistic bounds on the satisfaction of safety specifications. The effectiveness of the proposed framework is validated through both simulation and real-world obstacle avoidance experiments on a 7-DOF Franka robot. The video is available at: https://www.youtube.com/watch?v=2tCKYM_79S8.

Autonomous robots operating in diverse scenarios are expected to safely and efficiently adapt to new, unknown, and cluttered environments. In this paper, we introduce a real-time goal-seeking and exploration framework incorporating novel meta-signed distance functions (MetaSDFs) and metabuffer robust control barrier functions (Meta-BRCBFs). To adapt to environmental changes in real time, we employ Bayesian meta-learning to construct MetaSDFs. Deep neural network weights are initially trained offline, followed by efficient online adaptation at the last Bayesian layer, allowing for online updates at linear time complexity. Each MetaSDF is individually trained for its corresponding obstacle class, enhancing online distance estimation accuracy. Subsequently, buffer zones are constructed around the MetaSDFs to establish corresponding Meta-BRCBFs. These Meta-BRCBFs are activated only when the robot enters these zones, substantially reducing the number of CBFs required. Outside these specified buffer zones, the robot remains ingoal-seekingmode, focusing on task completion. After entering a buffer zone, it transitions toexplorationmode, prioritizing safety and exploring safe pathways, effectively balancing task execution with environmental adaptability. We demonstrate that, under this framework, the system achieves both safety and asymptotic stabilization. Extensive simulations and experiments are conducted to demonstrate our framework’s effectiveness in both simulated scenarios and real-world environments. These tests confirm our framework’s real-time capabilities and safety assurances in dynamic settings where state-of-the-art methods fail. The video is available at: https://www.youtube.com/watch?v=C6eshldAMxA.

This paper presents an adaptive online learning framework for systems with uncertain parameters to ensure safety-critical control in non-stationary environments. Our approach consists of two phases. The initial phase is centered on a novel sparse Gaussian process (GP) framework. We first integrate a forgetting factor to refine a variational sparse GP algorithm, thus enhancing its adaptability. Subsequently, the hyperparameters of the Gaussian model are trained with a specially compound kernel, and the Gaussian model’s online inferential capability and computational efficiency are strengthened by updating a solitary inducing point derived from newly samples, in conjunction with the learned hyperparameters. In the second phase, we propose a safety filter based on high order control barrier functions (HOCBFs), synergized with the previously trained learning model. By leveraging the compound kernel from the first phase, we effectively address the inherent limitations of GPs in handling high-dimensional problems for real-time applications. The derived controller ensures a rigorous lower bound on the probability of satisfying the safety specification. Finally, the efficacy of our proposed algorithm is demonstrated through real-time obstacle avoidance experiments executed using both simulation platform and a real-world 7-DOF robot.

In path planning, anytime almost-surely asymptotically optimal planners dominate the benchmark of sampling-based planners. A notable example is Batch Informed Trees (BIT*), where planners iteratively determine paths to batches of vertices within the exploration area. However, utilizing a consistent batch size is inefficient for initial pathfinding and optimal performance, it relies on effective task allocation. This paper introduces Flexible Informed Trees (FIT*), a sampling-based planner that integrates an adaptive batch-size method to enhance the initial path convergence rate. FIT* employs a flexible approach in adjusting batch sizes dynamically based on the inherent dimension of the configuration spaces and the hypervolume of the n-dimensional hyperellipsoid. By applying dense and sparse sampling strategy, FIT* improves convergence rate while finding successful solutions faster with lower initial solution cost. This method enhances the planner’s ability to handle confined, narrow spaces in the initial finding phase and increases batch vertices sampling frequency in the optimization phase. FIT* outperforms existing single-query, sampling-based planners on the tested problems in R2to R8, and was demonstrated on a real-world mobile manipulation task.

Path planning has long been an important and active research area in robotics. To address challenges in high-dimensional motion planning, this study introduces the Force Direction Informed Trees (FDIT*), a sampling-based planner designed to enhance speed and cost-effectiveness in pathfinding. FDIT* builds upon the state-of-the-art informed sampling planner, the Effort Informed Trees (EIT*), by capitalizing on often-overlooked information in invalid vertices. It incorporates principles of physical force, particularly Coulomb’s law. This approach proposes the elliptical k-nearest neighbors search method, enabling fast convergence navigation and avoiding high solution cost or infeasible paths by exploring more problem-specific search-worthy areas. It demonstrates benefits in search efficiency and cost reduction, particularly in confined, high-dimensional environments. It can be viewed as an extension of nearest neighbors search techniques. Fusing invalid vertex data with physical dynamics facilitates force-direction-based search regions, resulting in an improved convergence rate to the optimum. FDIT* outperforms existing single-query, sampling-based planners on the tested problems in ℝ4to ℝ16and has been demonstrated on a real-world mobile manipulation task.

This paper proposes a LiDAR-based goal-seeking and exploration framework, addressing the efficiency of online obstacle avoidance in unstructured environments populated with static and moving obstacles. This framework addresses two significant challenges associated with traditional dynamic control barrier functions (D-CBFs): their online construction and the diminished real-time performance caused by utilizing multiple D-CBFs. To tackle the first challenge, the framework’s perception component begins with clustering point clouds via the DBSCAN algorithm, followed by encapsulating these clusters with the minimum bounding ellipses (MBEs) algorithm to create elliptical representations. By comparing the current state of MBEs with those stored from previous moments, the differentiation between static and dynamic obstacles is realized, and the Kalman filter is utilized to predict the movements of the latter. Such analysis facilitates the D-CBF’s online construction for each MBE. To tackle the second challenge, we introduce buffer zones, generating Type-II D-CBFs online for each identified obstacle. Utilizing these buffer zones as activation areas substantially reduces the number of D-CBFs that need to be activated. Upon entering these buffer zones, the system prioritizes safety, autonomously navigating safe paths, and hence referred to as the exploration mode. Exiting these buffer zones triggers the system’s transition to goal-seeking mode. We demonstrate that the system’s states under this framework achieve safety and asymptotic stabilization. Experimental results in simulated and real-world environments have validated our framework’s capability, allowing a LiDAR-equipped mobile robot to efficiently and safely reach the desired location within dynamic environments containing multiple obstacles. Video and code are available: https://zyzhang4.wixsite.com/iros2024.

In this article, neural network (NN)-based sliding mode control schemes are proposed for an n-link robotic manipulator with system uncertainties, input deadzone, and external perturbations. A novel error-shifting function is proposed to release initial conditions. NNs are employed to approximate the unknown parameters of both system uncertainties and input deadzone. To update the sliding mode scheme, two advanced sliding mode surfaces with error-shifting function and barrier function are proposed to reduce the dependency of prior information and to realize a finite time convergence result, collectively. It should be pointed out that the proposed methods do not require initial states to satisfy the prescribed constraint caused by the barrier function and can be applied under unknown initial conditions. Furthermore, finite-time convergence for both tracking errors and NN weights is guaranteed. The effectiveness of the proposed schemes is demonstrated by simulation and experiments on the KINOVA robot.