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Smart Gait:A Gait Optimization Framework for Hexapod robots

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Chinese Journal of Mechanical Engineering 2024年第1期37卷 146-159页

作者： Yunpeng Yin Feng Gao Qiao Sun Yue Zhao Yuguang Xiao State Key Laboratory of Mechanical System and Vibration School of Mechanical EngineeringShanghai Jiao Tong UniversityShanghai 200240China Lenovo Corporation ShanghaiChina AI Institute School of Electronic Information and Electrical EngineeringShanghai Jiao Tong UniversityShanghai 200240China

The current gait planning for legged robots is mostly based on human presets,which cannot match the flexible characteristics of natural mammals.This paper proposes a gait optimization framework for hexapod robots called Smart Gait.Smart Gait contains three modules:swing leg trajectory optimization,gait period&duty optimization,and gait sequence optimization.The full dynamics of a single leg,and the centroid dynamics of the overall robot are considered in the respective modules.The Smart Gait not only helps the robot to decrease the energy consumption when in locomotion,mostly,it enables the hexapod robot to determine its gait pattern transitions based on its current state,instead of repeating the formalistic clock-set step cycles.Our Smart Gait framework allows the hexapod robot to behave nimbly as a living animal when in 3D movements for the first time.The Smart Gait framework combines offline and online optimizations without any fussy data-driven training procedures,and it can run efficiently on board in real-time after deployment.Various experiments are carried out on the hexapod robot LittleStrong.The results show that the energy consumption is reduced by 15.9%when in locomotion.Adaptive gait patterns can be generated spontaneously both in regular and challenge environments,and when facing external interferences.

关键词： Gait optimization Swing trajectory optimization legged robot Hexapod robot

北京2022年冬奥会六足冰壶机器人机构设计与运动规划

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Engineering 2024年第4期35卷 15-31页

作者： Ke Yin Yue Gao Feng Gao Xianbao Chen Yue Zhao Yuguang Xiao Qiao Sun Jing Sun School of Electronic Information and Electrical Engineering Shanghai Jiao Tong UniversityShanghai 200240China Key Laboratory of Mechanical System and Vibration School of Mechanical EngineeringShanghai Jiao Tong UniversityShanghai 200240China

When a curling rock slides on an ice sheet with an initial rotation,a lateral movement occurs,which is known as the curling phenomenon.The force of friction between the curling rock and the ice sheet changes continually with changes in the environment;thus,the sport of curling requires great skill and experience.The throwing of the curling rock is a great challenge in robot design and control,and existing curling robots usually adopt a combination scheme of a wheel chassis and gripper that differs significantly from human throwing movements.A hexapod curling robot that imitates human kicking,sliding,pushing,and curling rock rotating was designed and manufactured by our group,and completed a perfect show during the Beijing 2022 Winter Olympics Games.Smooth switching between the walking and throwing tasks is realized by the robot’s morphology transformation based on leg configuration switching.The robot’s controlling parameters,which include the kicking velocity v_(k),pushing velocity v_(p),orientation angle hc,and rotation velocityω,are determined by aiming and sliding models according to the estimated equivalent friction coefficientμ_(equ)and ratio e of the front and back frictions.The stable errors between the target and actual stopping points converge to 0.2 and 1.105 m in the simulations and experiments,respectively,and the error shown in the experiments is close to that of a well-trained wheelchair curling athlete.This robot holds promise for helping ice-makers rectify ice sheet friction or assisting in athlete training.

关键词： legged robot Curling robot Winter Olympics Mechanism design Motion planning

Learning physical characteristics like animals for legged robots

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National Science Review 2023年第5期10卷 22-37页

作者： Peng Xu Liang Ding Zhengyang Li Huaiguang Yang Zhikai Wang Haibo Gao Ruyi Zhou Yang Su Zongquan Deng Yanlong Huang Key Laboratory of robotics and Systems Harbin Institute of Technology School of Computing University of Leeds

Physical characteristics of terrains,such as softness and friction,provide essential information for legged robots to avoid non-geometric obstacles,like mires and slippery stones,in the wild.The perception of such characteristics often relies on tactile perception and vision prediction.Although tactile perception is more accurate,it is limited to close-range us e;by contrast,establishing a supervised or self-supervised contactless prediction system using computer vision re quires adequate labeled data and lacks the ability to adapt to the dynamic environment.In this paper,we simulate the behavior of animals and propose an unsupervised learning framework for legged robots to learn the physical characteristics of terrains,which is the first report to manage it online,incrementally and with the ability to solve cognitive conflicts.The proposed scheme allows robots to interact with the environment and adjust their cognition in real time,therefore endowing robots with the adaptation ability.Indoor and outdoor experiments on a hexapod robot are carried out to show that the robot can extract tactile and visual features of terrains to create cognitive networks independently;an associative layer between visual and tactile features is created during the robot’s exploration;with the layer,the robot can autonomously generate a physical segmentation model of terrains and solve cognitive conflicts in an ever-changing environment,facilitating its safe navigation.

关键词： legged robot unsupervised learning environmental perception cognitive learning

Bio-inspired Leg Design for a Heavy-Duty Hexapod robot

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Journal of Bionic Engineering 2022年第4期19卷 975-990页

作者： Haoyuan Yi Zhenyu Xu Xueting Xin Liming Zhou Xin Luo State Key Laboratory of Digital Manufacturing Equipment and Technology Huazhong University of Science and TechnologyWuhan 430074China Research Institute Inner Mongolia First Machinery Group Co.LtdBaotou 014030China

The leg structure is crucial to the legged robot's motion performance.With the size and load of the legged robot increasing,the difficulty of leg design increases sharply.Inspired by biomechanics,this paper proposes a leg design approach based on effective mechanical advantage(EMA)for developing the heavy-duty legged robot.The bio-inspired design approach can reduce the demand for joint actuation forces during walking by optimizing the ratio relationship between the joint driving force and ground contact force.A dimensionless EMA model of the leg for the heavy-duty legged robot is constructed in this paper.Leg dimensions and hinge point locations are optimized according to the EMA and energy-optimal criterion.Based on the optimal leg structure,an electrically driven tri-segmented leg prototype is developed.The leg's joint hinge points are located near the main support line,and the load-to-weight ratio is 15:1.The leg can realize a swing frequency of 0.63 Hz at the stride length of 0.8 m,and the maximum stride length can reach 1.5 m.

关键词： legged robot EMA Heavy-duty Bio-inspired

Kinematic Calibration of a Six-legged Walking Machine Tool

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Chinese Journal of Mechanical Engineering 2022年第2期35卷 28-44页

作者： Jimu Liu Zhijun Chen Feng Gao State Key Laboratory of Mechanical System and Vibration Shanghai Jiao Tong UniversityShanghai 200240China

This paper presents the kinematic calibration of a novel six-legged walking machine tool comprising a six-legged mobile robot integrated with a parallel manipulator on the body.Each leg of the robot is a 2-universal-prismatic-spherical(UPS)and UP parallel mechanism,and the manipulator is a 6-PSU parallel mechanism.The error models of both subsystems are derived according to their inverse kinematics.The objective function for each kinematic limb is formulated as the inverse kinematic residual,i.e.,the deviation between the actual and computed joint coordinates.The hip center of each leg is first identified via sphere fitting,and the other kinematic parameters are identified by solving the objective function for each limb individually using the least-squares method.Thus,the kinematic parameters are partially decoupled,and the complexities of the error models are reduced.A calibration method is proposed for the legged robot to overcome the lack of a fixed base on the ground.A calibration experiment is conducted to validate the proposed method,where a laser tracker is used as the measurement equipment.The kinematic parameters of the entire robot are identified,and the motion accuracy of each leg and that of the manipulator are significantly improved after calibration.Validation experiments are performed to evaluate the positioning and trajectory errors of the six-legged walking machine tool.The results indicate that the kinematic calibration of the legs and manipulator improves not only the motion accuracy of each individual subsystem but also the cooperative motion accuracy among the subsystems.

关键词： Parallel mechanism legged robot Kinematic calibration

Limb Stiffness Improvement of the robot WAREC-1R for a Faster and Stable New Ladder Climbing Gait

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Journal of Bionic Engineering 2023年第1期20卷 57-68页

作者： Xiao Sun Akira Ito Takashi Matsuzawa Atsuo Takanishi Department of Mechatronics University of YamanashiYamanashi400-8511Japan Faculty of Science and Engineering Waseda UniversityTokyo162-8480Japan

Ladder climbing is a relatively new but practical locomotion style for robots. Unfortunately, due to their size and weight, ladder climbing by human-sized robots developed so far is struggling with the speedup of ladder climbing motion itself. Therefore, in this paper, a new ladder climbing gait for the robot WAREC-1R is proposed by the authors, which is both faster than the former ones and stable. However, to realize such a gait, a point that has to be taken into consideration is the deformation caused by the self-weight of the robot. To deal with this issue, extra hardware (sensor) and software (position and force control) systems and extra time for sensing and calculation were required. For a complete solution without any complicated systems and time only for deformation compensation, limb stiffness improvement plan by the minimal design change of mechanical parts of the robot is also proposed by the authors, with a thorough study about deformation distribution in the robot. With redesigned parts, ladder climbing experiments by WAREC-1R proved that both the new ladder climbing gait and the limb stiffness improvement are successful, and the reduced deformation is very close to the estimated value as well.

关键词： Ladder climbing legged robot Bionic robot Gait.Stiffness improvement Finite element analysis

Explosive Electric Actuator and Control for legged robots

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Engineering 2022年第5期8卷 39-47页

作者： Fei Meng Qiang Huang Zhangguo Yu Xuechao Chen Xuxiao Fan Wu Zhang Aiguo Ming School of Mechatronical Engineering Beijing Institute of TechnologyBeijing 100081China Beijing Advanced Innovation Center for Intelligent robots and Systems Beijing Institute of TechnologyBeijing 100081China Key Laboratory of Biomimetic robots and Systems Ministry of EducationBeijing 100081China Department of Mechanical and Intelligent Systems Engineering The University of Electro-CommunicationsTokyo 182-8585Japan

Unmanned systems such as legged robots require fast-motion responses for operation in complex envi-ronments.These systems therefore require explosive actuators that can provide high peak speed or high peak torque at specific moments during dynamic motion.Although hydraulic actuators can provide a large force,they are relatively inefficient,large,and heavy.Industrial electric actuators are incapable of providing instant high power.In addition,the constant reduction ratio of the reducer makes it difficult to eliminate the tradeoff between high speed and high torque in a given system.This study proposes an explosive electric actuator and an associated control method for legged robots.First,a high-power-density variable transmission is designed to enable continuous adjustment of the output speed to torque ratio.A heat-dissipating structure based on a composite phase-change material(PCM)is used.An integral torque control method is used to achieve periodic and controllable explosive power output.Jumping experiments are conducted with typical legged robots to verify the effectiveness of the proposed actuator and control method.Single-legged,quadruped,and humanoid robots jumped to heights of 1.5,0.8,and 0.5 m,respectively.These are the highest values reported to date for legged robots powered by electric actuators.

关键词： Electric actuator Variable transmission Integral torque control legged robot

Footholds optimization for legged robots walking on complex terrain

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机械工程前沿:英文版 2023年第2期18卷 99-114页

作者： Yunpeng YIN Yue ZHAO Yuguang XIAO Feng GAO State Key Laboratory of Mechanical System and Vibration School of Mechanical EngineeringShanghai Jiao Tong UniversityShanghai 200240China AI Institute School of Electronic Information and Electrical EngineeringShanghai Jiao Tong UniversityShanghai 200240China

This paper proposes a novel continuous footholds optimization method for legged robots to expand their walking ability on complex terrains.The algorithm can efficiently run onboard and online by using terrain perception information to protect the robot against slipping or tripping on the edge of obstacles,and to improve its stability and safety when walking on complex terrain.By relying on the depth camera installed on the robot and obtaining the terrain heightmap,the algorithm converts the discrete grid heightmap into a continuous costmap.Then,it constructs an optimization function combined with the robot’s state information to select the next footholds and generate the motion trajectory to control the robot’s locomotion.Compared with most existing footholds selection algorithms that rely on discrete enumeration search,as far as we know,the proposed algorithm is the first to use a continuous optimization method.We successfully implemented the algorithm on a hexapod robot,and verified its feasibility in a walking experiment on a complex terrain.

关键词： footholds optimization legged robot complex terrain adapting hexapod robot locomotion control

Type Design and Behavior Control for Six legged robots

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Chinese Journal of Mechanical Engineering 2018年第3期31卷 11-22页

作者： Ling Fang Feng Gao State Key Laboratory of Mechanical System and Vibration Shanghai Jiao Tong University

The research on legged robots attracted much attention both from the academia and industry. legged robots are multi-input multi-output with multiple end-e ector systems. Therefore,the mechanical design and control framework are challenging issues. This paper reviews the development of type synthesis and behavior control on legged robots; introduces the hexapod robots developed in our research group based on the proposed type synthesis method. The control framework for legged robots includes data driven layer,robot behavior layer and robot execution layer. Each layer consists several components which are explained in details. Finally,various experiments were conducted on several hexapod robots. The summarization of the type synthesis and behavior control design constructed in this paper would provide a unified platform for communications and references for future advancement for legged robots.

关键词： legged robot Type synthesis Human robot interaction Control framework