A lattice-type reconfigurable robotic system for achieving gaits of chain-type robots

Traditional lattice-type reconfigurable robots can only achieve the flow-style locomotion with low efficiency. Since gaits of chain-type robots are proved to be efficient and practical, this paper presents a novel lattice distortion approach for lattice-type reconfigurable robots to achieve locomotion gaits of chain-type robots. Using this approach, the robotic system can be actuated by local lattice distortion to move as an ensemble. In this paper, a rule that makes the lattice distortion equivalent to joint rotation is presented firstly. Then, a kind of module structure is designed according to requirements of the lattice distortion. Finally, a motion planning for achieving locomotion is developed, which works well in physics-based simulations of completing a serpentine locomotion gait of a snake-like robot and a tripod gait of a hexapod robot.     

仿生机器人运动步态控制:强化学习方法综述

仿生机器人是一类典型的多关节非线性欠驱动系统，其步态控制是一个非常具有挑战性的问题。对于该问题，传统的控制和规划方法需要针对具体的运动任务进行专门设计，需要耗费大量时间和精力，而且所设计出来的控制器往往没有通用性。基于数据驱动的强化学习方法能对不同的任务进行自主学习，且对不同的机器人和运动任务具有良好的通用性。因此，近年来这种基于强化学习的方法在仿生机器人运动步态控制方面获得了不少应用。针对这方面的研究，本文从问题形式化、策略表示方法和策略学习方法3个方面对现有的研究情况进行了分析和总结，总结了强化学习应用于仿生机器人步态控制中尚待解决的问题，并指出了后续的发展方向。     

Development of wheel-less snake robot with two distinct gaits and gait transition capability

Snake robots are mostly designed based on single mode locomotion. However, single mode gait most likely could not work effectively when the robot is subject to an unstructured working environment with different measures of terrain complexity. As a solution, mixed mode locomotion is proposed in this paper by synchronizing two types of gaits known as serpentine and wriggler gaits used for non-constricted and narrow space environments, respectively, but for straight line locomotion only. A gait transition algorithm is developed to efficiently change the gait from one to another. This study includes the investigation on kinematics analysis followed by dynamics analysis while considering related structural constraints for both gaits. The approach utilizes the speed of the serpentine gait for open area locomotion and exploits the narrow space access capability of the wriggler gait. Hence, it can increase motion flexibility in view of the fact that the robot is able to change its mode of locomotion according to the working environment.     

面向仿人机器人自然步态规划的人体步行实验分析

自然步态规划方法是实现仿人机器人步态柔顺和能量优化的可行方法,该方法要求对人体步行及其平衡策略进行定量研究．本文分析自然步态规划方法的原理,建立了一套快捷有效的人体步态测试系统,并通过实验建立了人体步行的参数化数据库．实验结果揭示了人体步行的参数化特征及其平衡策略,对于仿人机器人的自然步态规划及控制提供了理论指导．结论特别指出,仅仅通过规划的方式实现仿人机器人的自然步态是不完备的,自然步态的实现必须同仿生控制策略相结合．同时实验结论对于仿人机器人的本体优化设计也提供了参考．     

仿蚯蚓移动机器人离散步态控制与相位差控制特性比较

从机器人的运动特征、稳态平均速度和波动特性3个方面,对仿蚯蚓移动机器人的离散步态控制策略和相位差控制策略进行比较研究．首先,通过学习蚯蚓的形态学特征,基于舵机－弹簧钢片复合结构,设计并制作了可以执行拮抗变形的仿蚯蚓机器人单元,并将其串联得到一个8单元仿蚯蚓移动机器人．以该机器人为平台,从理论和实验角度研究了机器人在离散步态控制和等相位差控制下的平均速度和运动特征．研究发现,对于2种控制策略,实验得到的平均速度都与理论预测定性吻合,但机器人单元在运动过程中有可能发生显著的向后滑动,使得实验得到的平均速度低于理论预测的平均速度．随后,从波传播的角度对2种控制策略进行了比较．2种控制策略都使得机器人单元的变形以波动的形式沿机器人进行传播,传播方向与机器人运动方向相反,与蚯蚓的后退蠕动波机理保持一致．对于离散步态控制,波传播的波形、波速、波长和周期都与步态参数密切相关;对于相位差控制,波形和周期都由作动规律决定,不能通过相位差进行调节,但波速和波长与相位差成反比．从控制效果来看,机器人在最优的等相位差控制模式下可以实现更高的平均速度,且与蚯蚓的连续特征保持一致,具有一定的优势．     

动态双足机器人的控制与优化研究进展

对动态双足机器人的可控周期步态的稳定性、鲁棒性和优化控制策略的国内外研究现状与发展趋势进行了探讨.首先,介绍动态双足机器人的动力学数学模型,进一步,提出动态双足机器人运动步态和控制系统原理;其次,讨论动态双足机器人可控周期步态稳定性现有的研究方法,分析这些方法中存在的缺点与不足;再次,研究动态双足机器人的可控周期步态优化控制策略,阐明各种策略的优缺点;最后,给出动态双足机器人研究领域的难点问题和未来工作,展望动态双足机器人可控周期步态与鲁棒稳定性及其应用的研究思路.     

Construction and locomotion analysis of modular robots with pneumatic-actuated and binary-controlled expandable cubes

This paper presents the construction and locomotion analysis of the modular robots composed of expandable cubes (E-Cubes). The kinematic properties and experiment research of the assembled modular robots are the main focus of the paper. The E-Cube consisted of only prismatic joints is a cubic module with three degrees of freedom corresponding to three mutually perpendicular directions. The modular robots are constructed by connecting the vertex or edge of the adjacent modules. In this paper, first, the modular robot system including the E-Cube hardware, connection method of modules and a potential binary control strategy is described. And then, the detailed kinematics, stability and motion simulations of three configurations assembled with four modules are analysed. After that, a set of experimental pneumatic-based robotic system is built. At last, the gait experiments of the configurations are carried out to testify the feasibility and validity of design and locomotion functions. The experiment results show the reliability of the mechanical, control and pneumatic systems and the programming and control efficiency of the binary control strategy. As extension, a modular robot with eight modules is assembled, and its different locomotion gaits are simulated accordingly.     

On the Improvement of Walking Performance in Natural Environments by a Compliant Adaptive Gait

It is a widespread idea that animal-legged locomotion is better than wheeled locomotion on natural rough terrain. However, the use of legs as a locomotion system for vehicles and robots still has a long way to go before it can compete with wheels and trucks, even on natural ground. This paper aims to solve two main disadvantages plaguing walking robots: their inability to react to external disturbances (which is also a drawback of wheeled robots); and their extreme slowness. Both problems are reduced here by combining: 1) a gait-parameter-adaptation method that maximizes a dynamic energy stability margin and 2) an active-compliance controller with a new term that compensates for stability variations, thus helping the robot react stably in the face of disturbances. As a result, the combined gait-adaptation approach helps the robot achieve faster, more stable compliant motions than conventional controllers. Experiments performed with the SILO4 quadruped robot show a relevant improvement in the walking gait     

Optimization and evaluation of swing leg retraction for a hydraulic biped robot

To improve the locomotion performance of legged robots, the swing leg retraction (SLR) technique is investigated in a hydraulic biped robot. First, the influence of SLR on the locomotion performance of the hydraulic biped robot is analyzed in theory and simulations based on an extended spring load inverted pendulum model. The influence contains three performance indicators: energy loss/effiency, friction/slipping, and impact/compliance. Second, by synthesizing three performance indicators, using unified objective method and particle swarm optimization algorithm, the optimal SLR rate for gait planning based on Bezier curve is addressed. Finally, experiments are implemented to validate the effectiveness and feasibility of proposed method. And, the results show that the SLR technique is useful to reduce the impact force, improve the robot's locomotion stability and make room for impedance performance improvement of compliance controller. This research provides an insight for locomotion control of hydraulic legged robots.     

Experimental study on the oscillating paddling gait of an ePaddle mechanism with flexible configuration

In this paper, a novel eccentric paddle locomotion mechanism (ePaddle) has been proposed to enhance the mobility of amphibious robots for multi-terrains tasks with diverse locomotion gaits. The oscillating paddling gait of the ePaddle mechanism enables the robot to perform stationary observation or attitude maneuvering operations in shallow water. To increase the thrust generated by this gait, the ePaddle mechanism has a flexible configuration, i.e. a flexible paddle and three rigid paddles. The effects of the oscillating amplitude and period of the gait to thrust are analyzed and compared with the thrusts measured with rigid configuration. Experimental results demonstrate that the flexible configuration is able to produce much more net thrust than the rigid configuration when the ePaddle is oscillating at large amplitude.     

Formation control of underactuated bio-inspired snake robots

This paper considers formation control of snake robots. In particular, based on a simplified locomotion model, and using the method of virtual holonomic constraints, we control the body shape of the robot to a desired gait pattern defined by some pre-specified constraint functions. These functions are dynamic in that they depend on the state variables of two compensators which are used to control the orientation and planar position of the robot, making this a dynamic maneuvering control strategy. Furthermore, using a formation control strategy we make the multi-agent system converge to and keep a desired geometric formation, and enforce the formation follow a desired straight line path with a given speed profile. Specifically, we use the proposed maneuvering controller to solve the formation control problem for a group of snake robots by synchronizing the commanded velocities of the robots. Simulation results are presented which illustrate the successful performance of the theoretical approach.     

Dynamic modelling & simulation of a four legged jumping robot with compliant legs

Legged locomotion is used by most animals and human beings on Earth. Legged locomotion is preferred over the wheeled locomotion as it can be used for both flat and rough terrains. In this paper, an attempt has been made for the dynamic modelling and simulation of four legged jumping robots with compliant legs. Sagittal plane and bounding gait has been considered for the simulation. For energy saving, passive dynamics has been used with the help of compliant legs (linear spring). Different state variables have been obtained for analysis. Control strategies have been implemented on dynamic modelling for forward velocity control.     

Adaptive Robot Biped Locomotion with Dynamic Motion Primitives and Coupled Phase Oscillators

In order to properly function in real-world environments, the gait of a humanoid robot must be able to adapt to new situations as well as to deal with unexpected perturbations. A promising research direction is the modular generation of movements that results from the combination of a set of basic primitives. In this paper, we present a robot control framework that provides adaptive biped locomotion by combining the modulation of dynamic movement primitives (DMPs) with rhythm and phase coordination. The first objective is to explore the use of rhythmic movement primitives for generating biped locomotion from human demonstrations. The second objective is to evaluate how the proposed framework can be used to generalize and adapt the human demonstrations by adjusting a few open control parameters of the learned model. This paper contributes with a particular view into the problem of adaptive locomotion by addressing three aspects that, in the specific context of biped robots, have not received much attention. First, the demonstrations examples are extracted from human gaits in which the human stance foot will be constrained to remain in flat contact with the ground, forcing the “bent-knee” at all times in contrast with the typical straight-legged style. Second, this paper addresses the important concept of generalization from a single demonstration. Third, a clear departure is assumed from the classical control that forces the robot’s motion to follow a predefined fixed timing into a more event-based controller. The applicability of the proposed control architecture is demonstrated by numerical simulations, focusing on the adaptation of the robot’s gait pattern to irregularities on the ground surface, stepping over obstacles and, at the same time, on the tolerance to external disturbances.     

基于能效优化的两足机器人步态控制方法

针对高能耗导致的两足机器人实用化障碍,提出了一种全新的、系统化的步态能效优化控制方法.基于两足机器人运动的重要能耗指标(平均功率、平均功率偏差、平均力矩损耗),提出了能耗预估策略和能效优化算法,获取了零力矩点(ZMP)稳定区域内的能耗极小值.沿着能耗极小值所对应的上体轨迹对机器人步态实施能效优化控制,最终获得满足ZMP稳定判据的低能耗步态.仿真结果证明,该方法能够有效降低机器人能耗并保持其稳定性.     

A simple approach to the control of locomotion in self-reconfigurable robots

In this paper we present role-based control which is a general bottom-up approach to the control of locomotion in self-reconfigurable robots. We use role-based control to implement a caterpillar, a sidewinder, and a rolling track gait in the CONRO self-reconfigurable robot consisting of eight modules. Based on our experiments and discussion we conclude that control systems based on role-based control are minimal, robust to communication errors, and robust to reconfiguration.     

基于X86平台和RSI的工业机器人步态自动控制系统设计

工业环境中的任务和工作场景是动态变化的,机器人需要能够根据环境的变化调整步态,以满足新的任务需求。为此,设计基于X86平台和RSI的工业机器人步态自动控制系统。以复杂指令集计算机为基础的X86架构设计机器人控制器主板,使系统具有高集成度和扩展性。利用超声波传感器和红外线传感器获取步态自动控制传感信号。使用基于AS5040型高精密非接触磁性转动编码器的步态关节控制器,通过总线扩展,定位关节运动方向。分析机械臂前后摆动步态规划轨迹,控制髋关节。使用RSI应用程序包控制点位运动,实现步态自动控制。实验结果表明,设计系统的膝关节x方向与实际轨迹只存在最大为20mm的误差,y方向与实际轨迹一致;髋关节x方向与实际轨迹只存在最大为20mm的误差,y方向与实际轨迹只存在最大为15mm的误差,能够提高控制精度,控制效果较好。     

The gait control system of a quadruped walking vehicle

A walking vehicle has potential capability to be developed to an off-road machine with high mobility and adaptivity by using the coordination control of its multi-degrees of freedom. There have been several discussions on the gait control of a walking vehicle, although few have mentioned the total gait control system and any sub-systems integrated into the total structure. This paper discusses the gait control system based on a quadruped walking vehicle developed by the authors. At first, the premises for the discussion are confirmed. Then, the total structure of the control system, consisting of three levels named A, B and C, is clarified. The control algorithm of each level is studied in detail, particularly the three sub-systems belonging to level B, i.e. gait control in xy coordinates, the same in z coordinate and trajectory control of legs taking account up/down swinging. The control algorithm at level C, which regulates the basic reflex motions, is specifically discussed. Finally, these discussions are verified by walking experiments of a model TITAN III. The joystick control of omnidirectional motions and adaptive locomotion over irregular surfaces are successfully demonstrated.     

Oscillatory motion-based miniature magnetic walking robot actuated by a rotating magnetic field

Magnetic micro-robots have been proposed for use in biomedical applications. These studies focus on locomotion control using a gradient, alternating, and rotating magnetic fields at the sub-micro scale. However, this study focuses on a basic mechanism of active locomotion for diagnostic robots. Furthermore, the digestive intestine in the human body has a complex path in which locomotion methods can become either swimming or walking according to the inner condition. Therefore, we propose a new simple mechanism for amphibious locomotion within a rotating magnetic field using the three-axis Helmholtz coil system. The proposed magnetic robot consists of NdFeB permanent spherical magnets, flexible silicone tubes, and legs. Successive changes of actuation of yaw and roll motions cause alternating and walking motions. Direction of movement is decided by rotating the direction of the magnetic field (clockwise or counter-clockwise). In addition, turning directions are decided by the plane of the rotating magnetic field. A magnetic torque between the rotating magnetic field and the magnetic moments produce a constant walking pattern similar to a trotting gait. In addition, an oscillatory motion of the flexible robot body can generate a thrust force in the liquid. Finally, through the various experiments, we evaluate the capability of the locomotion.     

Intrinsic dynamics and total energy-shaping control of the ballbot system

Research on bipedal locomotion has shown that a dynamic walking gait is energetically more efficient than a statically stable one. Analogously, even though statically stable multi-wheeled robots are easier to control, they are energetically less efficient and have low accelerations to avoid tipping over. In contrast, the ballbot is an underactuated, nonholonomically constrained mobile robot, whose upward equilibrium point has to be stabilised by active control. In this work, we derive coordinate-invariant, reduced, Euler–Poincaré equations of motion for the ballbot. By means of partial feedback linearisation, we obtain two independent passive outputs with corresponding storage functions and utilise these to come up with energy-shaping control laws which move the system along the trajectories of a new Lagrangian system whose desired equilibrium point is asymptotically stable by construction. The basin of attraction of this controller is shown to be almost global under certain conditions on the design of the mechanism which are reflected directly in the mass matrix of the unforced equations of motion.     

六足步行机横向行走最佳步态及其运动特性初探

本文分别以纵向稳定裕量和一般稳定裕量为准则,通过对六足步行机横向行走几何模型的分析和计算机优化计算,得出六足步行机横向运动时的最佳步态为广义三角步态.此外,文中对广义三角步态的运动特性(包括静态稳定性、爬坡能力、越沟能力等)进行了初步研究,阐明了这些运动特性与步行机若干几何参数间的内在联系,为六足步行机的总体尺寸设计提供了理论依据。