Quadruped robots have demonstrated remarkable versatility in various applications, from search and rescue to exploration. Recent advancements have shifted focus from individual robots to swarms, recognizing the potential of collaborative behaviors to achieve complex tasks beyond the capabilities of a single robot. Inspired by the cooperative hunting behaviors observed in nature, this paper presents a reinforcement learning framework for a swarm of quadruped robots to learn decentralized end-to-end hunting locomotion. In particular, we integrate stable and dynamic locomotion with hunting objectives and utilize a guidance vector as privileged information for efficient training. The framework concerns the control dynamics of quadruped robots, ensuring both low-level stability and high-level hunting coordination in muti-robot environments. The trained policy is deployed onto a real robot system, and the experimental results demonstrate coordinative behavior in various scenarios. The implementation code is released to benefit the community.

Safe corridor-based Trajectory Optimization (TO) presents an appealing approach for collision-free path planning of autonomous robots, because its convex formulation can guarantee global optimality. The safe corridor is constructed based on the obstacle map, however, the non-ideal perception induces uncertainty, which is rarely considered in the context of trajectory generation. In this paper, we propose Distributionally Robust Safe Corridor Constraints (DRSCCs) to consider the uncertainty of the safe corridor. Then, we integrate DRSCCs into the trajectory optimization framework using Bernstein basis polynomials. Theoretically, we rigorously prove that the proposed trajectory optimization problem is equivalent to a convex quadratic program, which is computationally efficient to deploy onto real robots. The simulation results show that our method enhances navigation safety by significantly reducing the infeasible motions compared to the baseline. Moreover, the proposed approach is validated through two robotic applications, a micro Unmanned Aerial Vehicle (UAV) and a quadruped robot Unitree A1.

This paper presents a collaborative quadrotor-quadruped robot system for the manipulation of a cable-towed payload. In particular, we aim to solve the challenge from the unknown dynamics of the cable-towed payload. To this end, we first propose novel dynamic models for both the quadrotor and the quadruped robot, taking into account the nonlinear robot dynamics and the uncertainties associated with the cable-towed load. Moreover, we design observers for the hybrid interaction between the robots and the payload. Theoretically, the convergence of these observers is analyzed using Lyapunov functions under mild technical assumptions. Finally, we seamlessly integrate the dynamics models and the observers into a distributed Model Predictive Control (MPC) framework with kinematics limitations and collision avoidance constraints. The proposed system is validated through challenging field experiments in indoor and outdoor environments, involving push disturbances, varying and unknown payloads, uneven terrains, etc.

In this paper, we propose a reactive planning system for quadruped robots based on prescribed-time control. The navigation of the quadruped robot is fundamentally depicted as omnidirectional movements, while a feedback control law is formulated to address any deviations the robot may encounter. In particular, our proposed feedback control system is theoretically proven to achieve convergence within a predefined finite time that is specified by the user. To further compute the optimal convergent time and the local goal state, we present a high-level planning node encompassing terrain-aware kinodynamic search and spatiotemporal trajectory optimization, which can generate collision-free, smooth, and efficient trajectories. The effectiveness of our proposed framework is validated through both numerical simulation and real-robot experiments in indoor and outdoor environments, including scenarios with cluttered obstacles, slopes, and external disturbances.

This paper presents a Kalman filter based LiDAR-Inertial-Leg Odometry (KLILO) system for legged robots to navigate in challenging environments. In particular, we employ the iterated error-state extended Kalman filter framework on manifolds to fuse measurements from the inertial measurement unit (IMU), LiDAR, joint encoders, and contact force sensors in a tightly coupled manner. To assess the performance of KLILO, we build a dataset that encompasses intricate environments with challenging conditions such as dynamic objects and deformable terrains. The results demonstrate that our algorithm can provide efficient and reliable localization in all tests. It exhibits an average improvement of around 40% in positioning accuracy compared to the baselines. Furthermore, we validate KLILO in a challenging navigation task on a real robot, where the LiDAR encounters ineffective measurements.

Quadruped robots demonstrate robust and agile movements in various terrains; however, their navigation autonomy is still insufficient. One of the challenges is that the motion capabilities of the quadruped robot are anisotropic along different directions, which significantly affects the safety of quadruped robot navigation. This paper proposes a navigation framework that takes into account the motion anisotropy of quadruped robots including kinodynamic trajectory generation, nonlinear trajectory optimization, and nonlinear model predictive control. In simulation and real robot tests, we demonstrate that our motion-anisotropy-aware navigation framework could: (1) generate more efficient trajectories and realize more agile quadruped navigation; (2) significantly improve the navigation safety in challenging scenarios. The implementation is realized as an open-source package at https://github.com/ZWT006/agile_navigation.

In this paper, we present a fully distributed framework for multiple quadruped robots in environments with obstacles. Our approach utilizes Model Predictive Control (MPC) and multi-robot consensus protocol to obtain the distributed control law. It ensures that all the robots are able to avoid obstacles, navigate to the desired positions, and meanwhile synchronize the gaits. In particular, via MPC and consensus, the robots compute the optimal trajectory and the contact profile of the legs. Then an MPC-based locomotion controller is implemented to achieve the gait, stabilize the locomotion and track the desired trajectory. We present experiments in simulation and with three real quadruped robots in an environment with a static obstacle.

Markov decision processes (MDPs) often suffer from the sensitivity issue under model ambiguity. In recent years, robust MDPs have emerged as an effective framework to overcome this challenge. Distributionally robust MDPs extend the robust MDP framework by incorporating distributional information of the uncertain model parameters to alleviate the conservative nature of robust MDPs. This paper proposes a computationally efficient solution framework for solving distributionally robust MDPs with Wasserstein ambiguity sets. By exploiting the specific problem structure, the proposed framework decomposes the optimization problems associated with distributionally robust Bellman updates into smaller subproblems, which can be solved efficiently. The overall complexity of the proposed algorithm is quasi-linear in both the numbers of states and actions when the distance metric of the Wasserstein distance is chosen to be $L_1$, $L_2$, or $L_{\infty}$ norm, and so the computational cost of distributional robustness is substantially reduced. Our numerical experiments demonstrate that the proposed algorithms outperform other state-of-the-art solution methods.

This article considers quadruped locomotion control in the presence of uncertainties. Two types of structured uncertainties are considered, namely, uncertain friction constraints and uncertain model dynamics. Then, a min-max optimization model is formulated based on robust optimization, and a robust min-max model predictive controller is proposed by recurrently solving the optimization model. We prove that the min-max optimization model is equivalent to a convex quadratic constrained quadratic program by exploiting the structure of uncertainties. Moreover, a two-stage optimization algorithm is proposed to solve the optimization problem efficiently, allowing for the deployment of the controller onto the real robot. The results show that the proposed optimization algorithm can improve solving frequency by$\sim$11× compared with Gurobi. The proposed controller is able to stabilize quadruped locomotion in challenging scenarios where the uncertainties are caused by significant disturbances and unknown environments.

Four-legged animals are able to change their gaits adaptively for lower energy consumption. However, designing a robust controller for their robot counterparts with multi-modal locomotion remains challenging. In this paper, we present a hierarchical control framework that decomposes this challenge into two kinds of problems: high-level decision-making for gait selection and robust low-level control in complex application environments. For gait transitions, we use reinforcement learning (RL) to design a gait policy that selects the optimal gaits in different environments. After the gait is decided, model predictive control (MPC) is applied to implement the desired gait. To improve the robustness of the locomotion, a model adaptation policy is developed to optimize the input parameters of our MPC controller adaptively. The control framework is first trained and tested in simulation, and then it is applied directly to a quadruped robot in real without any fine-tuning. We show that our control framework is more energy efficient by choosing different gaits and is more robust by adjusting model parameters compared to baseline controllers.

BACKGROUND: Tandem mass spectrometry (MS/MS) followed by database search is a main approach to identify peptides/proteins in proteomic studies. A lot of effort has been devoted to improve the identification accuracy and sensitivity for peptides/proteins, such as developing advanced algorithms and expanding protein databases. RESULTS: Herein, we described a new strategy for enhancing the sensitivity of protein/peptide identification through combination of mRNA and peptide abundance in Percolator. In our strategy, a new workflow for peptide identification is established on the basis of the abundance of transcripts and potential novel transcripts derived from RNA-Seq and abundance of peptides towards the same life species. We demonstrate the utility of this strategy by two MS/MS datasets and the results indicate that about 5% ~ 8% improvement of peptide identification can be achieved with 1% FDR in peptide level by integrating the peptide abundance, the transcript abundance and potential novel transcripts from RNA-Seq data. Meanwhile, 181 and 154 novel peptides were identified in the two datasets, respectively. CONCLUSIONS: We have demonstrated that this strategy could enable improvement of peptide/protein identification and discovery of novel peptides, as compared with the traditional search methods.

BACKGROUND: Peptide identification based upon mass spectrometry (MS) is generally achieved by comparison of the experimental mass spectra with the theoretically digested peptides derived from a reference protein database. Obviously, this strategy could not identify peptide and protein sequences that are absent from a reference database. A customized protein database on the basis of RNA-Seq data is thus proposed to assist with and improve the identification of novel peptides. Correspondingly, development of a comprehensive pipeline, which provides an end-to-end solution for novel peptide detection with the customized protein database, is necessary. RESULTS: A pipeline with an R package, assigned as a PGA utility, was developed that enables automated treatment to the tandem mass spectrometry (MS/MS) data acquired from different MS platforms and construction of customized protein databases based on RNA-Seq data with or without a reference genome guide. Hence, PGA can identify novel peptides and generate an HTML-based report with a visualized interface. On the basis of a published dataset, PGA was employed to identify peptides, resulting in 636 novel peptides, including 510 single amino acid polymorphism (SAP) peptides, 2 INDEL peptides, 49 splice junction peptides, and 75 novel transcript-derived peptides. The software is freely available from http://bioconductor.org/packages/PGA/ , and the example reports are available at http://wenbostar.github.io/PGA/ . CONCLUSIONS: The pipeline of PGA, aimed at being platform-independent and easy-to-use, was successfully developed and shown to be capable of identifying novel peptides by searching the customized protein database derived from RNA-Seq data.

UNLABELLED: Single nucleotide variations (SNVs) located within a reading frame can result in single amino acid polymorphisms (SAPs), leading to alteration of the corresponding amino acid sequence as well as function of a protein. Accurate detection of SAPs is an important issue in proteomic analysis at the experimental and bioinformatic level. Herein, we present sapFinder, an R software package, for detection of the variant peptides based on tandem mass spectrometry (MS/MS)-based proteomics data. This package automates the construction of variation-associated databases from public SNV repositories or sample-specific next-generation sequencing (NGS) data and the identification of SAPs through database searching, post-processing and generation of HTML-based report with visualized interface. AVAILABILITY AND IMPLEMENTATION: sapFinder is implemented as a Bioconductor package in R. The package and the vignette can be downloaded at http://bioconductor.org/packages/devel/bioc/html/sapFinder.html and are provided under a GPL-2 license.