Legged robots can have a unique role in manipulating objects in dynamic, human-centric, or otherwise inaccessible environments. Although most legged robotics research to date typically focuses on traversing these challenging environments, many legged platform demonstrations have also included "moving an object" as a way of doing tangible work. Legged robots can be designed to manipulate a particular type of object (e.g., a cardboard box, a soccer ball, or a larger piece of furniture), by themselves or collaboratively. The objective of this review is to collect and learn from these examples, to both organize the work done so far in the community and highlight interesting open avenues for future work. This review categorizes existing works into four main manipulation methods: object interactions without grasping, manipulation with walking legs, dedicated non-locomotive arms, and legged teams. Each method has different design and autonomy features, which are illustrated by available examples in the literature. Based on a few simplifying assumptions, we further provide quantitative comparisons for the range of possible relative sizes of the manipulated object with respect to the robot. Taken together, these examples suggest new directions for research in legged robot manipulation, such as multifunctional limbs, terrain modeling, or learning-based control, to support a number of new deployments in challenging indoor/outdoor scenarios in warehouses/construction sites, preserved natural areas, and especially for home robotics.
Georgia Institute of Technology（佐治亚理工学院）；Facebook AI Research（Facebook人工智能研究院）
Recent work has shown results on learning navigation policies for idealized cylinder agents in simulation and transferring them to real wheeled robots. Deploying such navigation policies on legged robots can be challenging due to their complex dynamics, and the large dynamical difference between cylinder agents and legged systems. In this work, we learn hierarchical navigation policies that account for the low-level dynamics of legged robots, such as maximum speed, slipping, contacts, and learn to successfully navigate cluttered indoor environments. To enable transfer of policies learned in si…
The recent availability of commercial-off-the-shelf (COTS) legged robot platforms have opened up new opportunities in deploying legged systems into different scenarios. While the main advantage of legged robots is their ability to traverse unstructured terrain, there are still large gaps between what robot platforms can achieve and their animal counterparts. Therefore, when deploying as part of a heterogeneous robot team of different platforms, it is beneficial to understand the different scenarios where a legged platform would perform better than a wheeled, tracked or aerial platform. Two COT…
Soft pneumatic legged robots show promise in their ability to traverse a range of different types of terrain, including natural unstructured terrain met in applications like precision agriculture. They can adapt their body morphology to the intricacies of the terrain at hand, thus enabling robust and resilient locomotion. In this paper we capitalize upon recent developments on soft pneumatic legged robots to introduce a closed-loop trajectory tracking control scheme for operation over flat ground. Closed-loop pneumatic actuation feedback is achieved via a compact and portable pneumatic regulat…
Active Embodiment Identification with Reinforcement Learning for Legged Robots
Department of Computer Science, Technical University of Darmstadt（德累斯顿技术大学计算机科学系）；Robotics Institute Germany (RIG)（德国机器人研究所（RIG）；德国人工智能研究中心（DFKI）；hessian.AI）；German Research Center for AI (DFKI)；hessian.AI
Boston University（波士顿大学）；Carnegie Mellon University（卡内基梅隆大学）
Legged robots constructed from soft materials are commonly claimed to demonstrate safer, more robust environmental interactions than their rigid counterparts. However, this motivating feature of soft robots requires more rigorous development for comparison to rigid locomotion. This article presents a soft legged robot platform, Horton, and a feedback control system with safety guarantees on some aspects of its operation. The robot is constructed using a series of soft limbs, actuated by thermal shape memory alloy (SMA) wire muscles, with sensors for its position and its actuator temperatures. …
MUJICA: Multi-skill Unified Joint Integration of Control Architecture for Wheeled-Legged Robots
College of Intelligent Robotics and Advanced Manufacturing, Fudan University（智能机器人与先进制造学院，复旦大学）；Power China Huadong Engineering Corporation Limited（中国电力工程顾问集团华东分公司）
University of Illinois at Urbana-Champaign（伊利诺伊大学厄巴纳-香槟分校）
Industrial manipulators do not collapse under their own weight when powered off due to the friction in their joints. Although these mechanism are effective for stiff position control of pick-and-place, they are inappropriate for legged robots which must rapidly regulate compliant interactions with the environment. However, no metric exists to quantify the robot's perform degradation due to mechanical losses in the actuators. This letter provides a novel formulation which describes how the efficiency of individual actuators propagate to the equations of motion of the whole robot. We quantitativ…
Istituto Italiano di Tecnologia (IIT)（意大利技术研究院）；PAL Robotics（PAL机器人公司）
For legged robots to perform agile, highly dynamic and contact-rich motions, whole-body trajectories computation of under-actuated complex systems subject to non-linear dynamics is required. In this work, we present hands-on applications of Horizon, a novel open-source framework for trajectory optimization tailored to robotic systems, that provides a collection of tools to simplify dynamic motion generation. Horizon was tested on a broad range of behaviours involving several robotic platforms: we introduce its building blocks and describe the complete procedure to generate three complex motion…
University of Leeds（利兹大学）；University College London（伦敦大学学院）
Human life is invaluable. When dangerous or life-threatening tasks need to be completed, robotic platforms could be ideal in replacing human operators. Such a task that we focus on in this work is the Explosive Ordnance Disposal. Robot telepresence has the potential to provide safety solutions, given that mobile robots have shown robust capabilities when operating in several environments. However, autonomy may be challenging and risky at this stage, compared to human operation. Teleoperation could be a compromise between full robot autonomy and human presence. In this paper, we present a relat…
In this paper, the supervisory control of a Discrete Event System (DES) analyses states and events to construct an autonomous package delivery system. The delivery system includes a legged robot in order to autonomously navigate uneven indoor terrain and a conveyor belt for transporting the package to the legged robot.The aim of the paper is using the theory of supervisory control of DES to supervise and control machine's state and event and ensure robots autonomously collaborate. By applying the theory, we show the collaboration of two individual robots to deliver goods in a multi-floor envir…
This work reports on developing a deep inverse reinforcement learning method for legged robots terrain traversability modeling that incorporates both exteroceptive and proprioceptive sensory data. Existing works use robot-agnostic exteroceptive environmental features or handcrafted kinematic features; instead, we propose to also learn robot-specific inertial features from proprioceptive sensory data for reward approximation in a single deep neural network. Incorporating the inertial features can improve the model fidelity and provide a reward that depends on the robot's state during deployment…
Faculty of Mechanical Engineering, University of Tabriz（大不里士大学机械工程学院）；School of Engineering Emerging Technologies（新兴技术工程学院）
Ants are six-legged insects that can carry loads ten times heavier than their body weight. Since having six-legs, they are intrinsically stable. They are powerful and can carry heavy loads. For these reasons, in this paper a new parallel kinematic structure is proposed for a six-legged ant robot. The mechanical structure is designed and optimized in Solidworks. The mechanism has six legs and only two DC motors actuate the six legs so from mechanical point of view the design is an optimal one. The robot is lightweight and semiautonomous due to using wireless modules. This feature makes this rob…
University of Illinois at Urbana-Champaign（伊利诺伊大学厄巴纳-香槟分校）
Industrial manipulators do not collapse under their own weight when powered off due to the friction in their joints. Although these mechanism are effective for stiff position control of pick-and-place, they are inappropriate for legged robots that must rapidly regulate compliant interactions with the environment. However, no metric exists to quantify the robot's performance degradation due to mechanical losses in the actuators and transmissions. This paper provides a fundamental formulation that uses the mechanical efficiency of transmissions to quantify the effect of power losses in the mecha…
Saratoga High School（萨拉托加高中）；University of Michigan（密歇根大学）
We propose a mechanically simple and cheap design for a series elastic actuator with controllable stiffness. Such characteristics are necessary for animals for running, jumping, throwing, and manipulation, yet in robots, variable stiffness actuators are either complicated or mimicked at low bandwidth through feedback controllers. A robust and simple design is needed to build reliable and cheap robots with animal capabilities. The key insight of our design is attaching torsional springs to timing belts to create a variable stiffness linear spring. In an antagonistic pair, varying the distance b…
Music-Driven Legged Robots: Synchronized Walking to Rhythmic Beats
Academy for Engineering and Technology, Fudan University（复旦大学工程技术研究院）；School of Information and Communication Engineering, Hainan University（海南大学信息与通信工程学院）
This work develops a learning-based contact estimator for legged robots that bypasses the need for physical sensors and takes multi-modal proprioceptive sensory data as input. Unlike vision-based state estimators, proprioceptive state estimators are agnostic to perceptually degraded situations such as dark or foggy scenes. While some robots are equipped with dedicated physical sensors to detect necessary contact data for state estimation, some robots do not have dedicated contact sensors, and the addition of such sensors is non-trivial without redesigning the hardware. The trained network can …
Korea Advanced Institute of Science and Technology (KAIST)（韩国科学技术院）
We propose a novel state estimator for legged robots, STEP, achieved through a novel preintegrated foot velocity factor. In the preintegrated foot velocity factor, the usual non-slip assumption is not adopted. Instead, the end effector velocity becomes observable by exploiting the body speed obtained from a stereo camera. In other words, the preintegrated end effector's pose can be estimated. Another advantage of our approach is that it eliminates the necessity for a contact detection step, unlike the typical approaches. The proposed method has also been validated in harsh-environment simulati…
FZI Research Center for Information Technology（弗劳恩霍夫研究所信息技术研究中心）；Machine Intelligence and Robotics Lab at the Karlsruhe Institute for Technology (KIT)（卡尔斯鲁厄理工学院机械智能与机器人实验室）
Space Control and Inertial Technology Research Center（空间控制与惯性技术研究中心）；Harbin Institute of Technology（哈尔滨工业大学）
Impact mitigation is crucial to the stable locomotion of legged robots, especially in high-speed dynamic locomotion. This paper presents a leg locomotion system including the nonlinear active compliance control and the active impedance control for the steel wire transmission-based legged robot. The developed control system enables high-speed dynamic locomotion with excellent impact mitigation and leg position tracking performance, where three strategies are applied. a) The feed-forward controller is designed according to the linear motor-leg model with the information of Coulomb friction and v…
Arm-Constrained Curriculum Learning for Loco-Manipulation of the Wheel-Legged Robot
The Hong Kong University of Science and Technology (Guangzhou)（香港科技大学（广州））；Institute for AI Industry Research (AIR), Tsinghua University（清华大学人工智能产业研究院）；Tsinghua University（清华大学）；Harbin Institute of Technology（哈尔滨工业大学）；Xi’an Jiaotong-Liverpool University（西交利物浦大学）
Robotics Institute, Carnegie Mellon University（卡内基梅隆大学机器人研究所）
Our goal is to make robotics more accessible to casual users by reducing the domain knowledge required in designing and building robots. Towards this goal, we present an interactive computational design system that enables users to design legged robots with desired morphologies and behaviors by specifying higher level descriptions. The core of our method is a design optimization technique that reasons about the structure, and motion of a robot in coupled manner in order to achieve user-specified robot behavior, and performance. We are inspired by the recent works that also aim to jointly optim…
The functional demands of robotic systems often require completing various tasks or behaviors under the effect of disturbances or uncertain environments. Of increasing interest is the autonomy for dynamic robots, such as multirotors, motor vehicles, and legged platforms. Here, disturbances and environmental conditions can have significant impact on the successful performance of the individual dynamic behaviors, referred to as "motion primitives". Despite this, robustness can be achieved by switching to and transitioning through suitable motion primitives. This paper contributes such a method b…
Integrable Whole-body Orientation Coordinates for Legged Robots
University of Pennsylvania（宾夕法尼亚大学）；Boardwalk Robotics（博德沃克机器人公司）；Boston Dynamics Artificial Intelligence Institute（波士顿动力人工智能研究所）；Florida Institute for Human and Machine Cognition（佛罗里达人机认知研究所）
Control of Legged Robots using Model Predictive Optimized Path Integral
University of Calgary, Department of Mechanical Engineering（卡尔加里大学机械工程系）；Munich Institute of Robotics and Machine Intelligence (MIRMI), Technical University of Munich (TUM)（慕尼黑机器人与智能机械研究所（MIRMI），慕尼黑技术大学）
This paper introduces a novel proprioceptive state estimator for legged robots based on a learned displacement measurement from IMU data. Recent research in pedestrian tracking has shown that motion can be inferred from inertial data using convolutional neural networks. A learned inertial displacement measurement can improve state estimation in challenging scenarios where leg odometry is unreliable, such as slipping and compressible terrains. Our work learns to estimate a displacement measurement from IMU data which is then fused with traditional leg odometry. Our approach greatly reduces the …
Kyoto University（京都大学）；Dokkyo Medical University（独协医科大学）
Legged robots have excellent terrestrial mobility for traversing diverse environments and thus have the potential to be deployed in a wide variety of scenarios. However, they are susceptible to falling and leg malfunction during locomotion. Although the use of a large number of legs can overcome these problems, it makes the body long and leads to many legs being constrained to contact with the ground to support the long body, which impedes maneuverability. To improve the locomotion maneuverability of such robots, the present study focuses on dynamic instability, which induces rapid and large m…
University of Lisbon（里斯本大学）；Instituto Superior Técnico（高等技术学院）
We present a solvable biped walking model based on an inverted pendulum with two massless articulated legs capable of walking on uneven floors and inclined planes. The stride of the two-legged robot results from the pendular motion of a standing leg and the articulated motion of a trailing leg. Gaiting is possible due to the alternating role of the legs, the standing and the trailing leg, and the conservation of energy of the pendular motion. The motion on uneven surfaces and inclined planes is possible by imposing the same maximal opening angle between the two legs in the transition between s…
We introduce a robust control architecture for the whole-body motion control of torque controlled robots with arms and legs. The method is based on the robust control of contact forces in order to track a planned Center of Mass trajectory. Its appeal lies in the ability to guarantee robust stability and performance despite rigid body model mismatch, actuator dynamics, delays, contact surface stiffness, and unobserved ground profiles. Furthermore, we introduce a task space decomposition approach which removes the coupling effects between contact force controller and the other non-contact contro…
PIE: Parkour with Implicit-Explicit Learning Framework for Legged Robots
Institute of Cyber-Systems and Control, Zhejiang University（浙江大学控制科学与工程学院 cyber-system 研究所）；State Key Laboratory of Industrial Control Technology（工业控制技术国家重点实验室）
University of Oslo（奥斯陆大学）；Norwegian Defence Research Institute（挪威国防研究所）
Legged robots promise higher versatility and the ability to traverse much more difficult terrains than their wheeled counterparts. Even though the use of legged robots have increased drastically in the last few years, they are still not close to the performance seen from legged animals in nature. Robotic legs are typically fairly simple mechanically, and few feature an ankle joint, even though most land mammals have one. The ankle could be a key to better performance and stability for legged robots, and in this paper we investigate how the use of an ankle in a bipedal robot could improve its p…
ATRos: Learning Energy-Efficient Agile Locomotion for Wheeled-legged Robots
Shanghai Huawei Technologies Co., Ltd.（上海华为技术有限公司）；College of Future Information Technology, Fudan University（复旦大学未来信息科技学院）；Robotics Institute, Carnegie Mellon University（卡内基梅隆大学机器人研究所）；School of Aeronautic and Astronautics, Zhejiang University（浙江大学航空宇航学院）；School of Electronics and Communication Engineering, Sun Yat-sen University（中山大学电子与通信工程学院）
UniLegs: Universal Multi-Legged Robot Control through Morphology-Agnostic Policy Distillation
Wuxi Research Institute of Applied Technologies, Tsinghua University（清华大学应用技术研究院（无锡））；School of Internet of Things Engineering, Department of Automation, Jiangnan University（江南大学物联网工程学院）；Shanghai Jiao Tong University（上海交通大学）；School of Automation Science and Electrical Engineering, Beihang University（北航自动化科学与电气工程学院）
Georgia Institute of Technology（佐治亚理工学院）；Florida Institute for Human & Machine Cognition（佛罗里达人机认知研究所）；University of West Florida（西佛罗里达大学）
Legged robot locomotion is a challenging task due to a myriad of sub-problems, such as the hybrid dynamics of foot contact and the effects of the desired gait on the terrain. Accurate and efficient state estimation of the floating base and the feet joints can help alleviate much of these issues by providing feedback information to robot controllers. Current state estimation methods are highly reliant on a conjunction of visual and inertial measurements to provide real-time estimates, thus being handicapped in perceptually poor environments. In this work, we show that by leveraging the kinemati…
Unleashing the Agility of Wheeled-Legged Robots for High-Dynamic Reflexive Obstacle Evasion
School of Mechanical Engineering, Tianjin University（天津大学机械工程学院）；School of Computing, National University of Singapore（新加坡国立大学计算机学院）；Beijing Zhongguancun Academy（北京中关村学院）；DeepRobotics（深睿科技）
This paper describes the design and control of a support and recovery system for use with planar legged robots. The system operates in three modes. First, it can be operated in a fully transparent mode where no forces are applied to the robot. In this mode, the system follows the robot closely to be able to quickly catch the robot if needed. Second, it can provide a vertical supportive force to assist a robot during operation. Third, it can catch the robot and pull it away from the ground after a failure to avoid falls and the associated damages. In this mode, the system automatically resets t…
University of Edinburgh（爱丁堡大学）；Heriot-Watt University（赫瑞-瓦特大学）
We present a versatile framework for the computational co-design of legged robots and dynamic maneuvers. Current state-of-the-art approaches are typically based on random sampling or concurrent optimization. We propose a novel bilevel optimization approach that exploits the derivatives of the motion planning sub-problem (i.e., the lower level). These motion-planning derivatives allow us to incorporate arbitrary design constraints and costs in an general-purpose nonlinear program (i.e., the upper level). Our approach allows for the use of any differentiable motion planner in the lower level and…
