Prototype,control system architecture and controlling of the hexapod legs with nonlinear stick-slip vibrations

The paper introduces the constructed prototype of the hexapod robot designed based on the biomechanics of insects for inspection and operation applications as well as for different research investigations related to the walking robots. A detailed discussion on the design and realization of mechanical construction, electronic control system and devices installed on the robot body are presented. Moreover, the control problem of the robot legs is studied in detail. In order to find the relationship between movements commonly used by insects legs and stable trajectories of mechanical systems, first we analyze different previous papers and leg movements of real insects. Next, we are focus on the control the robot leg with several oscillators working as a so-called Central Pattern Generator (CPG) and we propose other model of CPG based on the oscillator describing stick-slip induced vibrations. Some advantages of the proposed model are presented and compared with other previous applied mechanical oscillators with help of numerical simulations performed for both single robot leg and the whole robot. In order to confirm the mentioned numerical simulations, the conducted real experiments are described and some interesting results are reported. Both numerical and experimental results indicate some analogies between the characteristics of the simulated walking robot and animals met in nature as well as the benefits of the proposed stick-slip vibrations as a CPG are outlined. Our research work has been preceded by a biological inspiration, scientific literature review devoted to the six-legged insects met in nature as well as various prototypes and methods of control hexapod robots which can be found in engineering applications.     

Navigability of multi-legged robots

This paper addresses the improvement of navigability for a six-legged robot through the development of a simple method for measuring heading and drift errors. More specifically, the navigation scheme utilizes both a magnetic compass and landmark navigation to correct these errors with every step, hence limiting error propagation. The approach is aimed at operation in unknown environments. Elaborate data processing in the control algorithm is avoided by using modular sensors capable of processing their own inputs. The robot controller uses the well-known tripod gait, implemented here using the hexapod inverse kinematics. Experimental results show significant improvements in the hexapod's navigability for turning and walking maneuvers.     

Using role-based control to produce locomotion in chain-type self-reconfigurable robots

This paper presents a role-based approach to the problem of controlling locomotion of chain-type self-reconfigurable robots. In role-based control, all modules are controlled by identical controllers. Each controller consists of several playable roles and a role-selection mechanism. A role represents the motion of a module and how it synchronizes with connected modules. A controller selects which role to play depending on the local configuration of the module and the roles being played by connected modules. We use role-based control to implement a sidewinder and a caterpillar gait in the CONRO self-reconfigurable robot. The robot is made from up to nine modules connected in a chain. We show that the locomotion speed of the caterpillar gait is constant even with loss of 75% of the communication signals. Furthermore, we show that the speed of the caterpillar gait decreases gracefully with a decreased number of modules. We also implement a quadruped gait and show that without changing the controller the robot can be extended with an extra pair of legs and produce a hexapod gait. Based on these experiments, we conclude that role-based control is robust to signal loss, scales with an increased number of modules, and is a simple approach to the control of locomotion of chain-type self-reconfigurable robots.     

Prototype development and gait planning of biologically inspired multi-legged crablike robot

In order to investigate the walking gait of the legged robot with multiple redundant walking legs, the motion features of the biologic crab are studied. To study the motion property of multi-legged animals in depth, an event sequence analysis method is proposed, and employed to design the motion pattern of multi-legged robot. A low-consumption environmental self-adaptive bionic gait with its phase factor of 0.25 and duty factor of 0.454 is analyzed based on the analysis of pace order, gait parameters and single leg’s terminal trajectory on uneven terrain. According to the structures and motion patterns of biologic crab, a multi-legged crablike prototype with its experimental platform is developed. The contrast tests of environmental self-adaptive bionic gait and double tetrapod gait are experimented at the same velocity, and slope climbing tests are performed as well. The experimental results show that, although the double tetrapod gait enables four legs to support the robot’s body at any time, there exists halt or backward phenomena periodically. However, the robot using the new gait has lower gravity fluctuation in displacement and velocity without halt or backward problem, and the decreasing of motion speed leads to the increasing of the gravity fluctuation and the toe-force.     

An investigation of the kinematic control of a six-legged walking robot

A semi autonomous six-legged walking machine with hexagonal architecture that has been developed for research on gait control is described. The machine weighs 13 kg; each leg has three d.o.f. with closed-loop kinematics, actuated by D.C. electric drives. The kinematics is designed to achieve gravitational decoupling, which simplifies considerably the velocity control of the legs. The control architecture is decentralized, each leg being controlled by a separate microcontroller. A central computer coordinates the motion of the various legs (gait) and controls the attitude of the vehicle. The gait can be programmed arbitrarily.     

Fault-tolerant gaits of quadruped robots for locked joint failures

This paper lays a theoretical foundation for fault detection and tolerance in static walking of legged robots. Legged robots considered in this paper have symmetric structures and legs which have the form of an articulated arm with three revolute joints. A kind of fault event (locked joint failure) is defined, and its properties are closely investigated in the frame of gait study and robot kinematics. For the purpose of tolerating a locked joint failure, an algorithm of fault-tolerant gaits for a quadruped robot is proposed in which the robot can continue its walking after a locked failure occurs to a joint of a leg. In particular, a periodic gait is proposed as a special form of the proposed algorithm and its existence and efficiency are analytically proven. A case study on applying the proposed scheme to wave gaits verifies its applicability and capability.     

Improving the energy efficiency and speed of walking robots

This study analyses the superior performance of gravitationally decoupled actuation in terms of energy efficiency, and hence autonomy. Based on the decoupling concept, a new design is presented for a 3 dof leg, and its performance is validated by including it in a 84 kg hybrid locomotion robot. The proposed leg obtains a straight-line constant-velocity motion of the foot as only one of its 3 motors is operated at constant speed. This feature, together with the hybrid structure, increases the robot’s efficiency and speed when operating on surfaces without obstacles, and drastically simplifies the walking operation control. A series of simulations have been done comparing the energy consumption of the hybrid robot including traditional coupled legs, and including the proposed decoupled legs. They show a superior performance of the later one. A real prototype has been built including the proposed mechanism. It shows a similar performance to that obtained from simulation, and a natural gait in flat terrains,at speeds up to 0.9 m/s.     

Subsea crab bounding gait of leg-paddle hybrid driven shoal crablike robot

This paper presents the design principles of a novel subsea propulsion pattern named as crab bounding gait for the shoal crablike robot and the gait experimental results. The concept of leg-paddle hybrid driven shoal crablike robot is developed for shoal environment; the robot moves on the seabed by employing six 3DOFs walking legs and swims by two 3DOFs swimming paddles. The proposed gait is derived by mimicking the movement mode of biological swimming crab when preying or being attacked underwater. Three aspects of gait planning, including gait process planning, kinematics modelling and trajectory planning, and subsea dynamics analyzing in back stance phase and flight phase by considering hydrodynamic factors such as water resistance and buoyancy, are discussed in this work. Experimental results of subsea crab bounding gait are presented and used to make a comparison with the bionic wave gait; the current and pitch angle of body centroid are monitored in real time. It is demonstrated that the average motion speed improves by 54%, and the total power consumption of crab bounding gait is 14.5 W, which enables that the total cost of transport (TCoT) decreases from 6.8 to 3.7 against bionic wave gait.     

基于MATLAB的机器人正运动学分析与仿真

鉴于机器人技术的迅猛发展,不同用途的机器人活跃在各个领域.研究机器人,运动学分析是关键,包括运动学方程的正解和逆解.本文应用坐标系变换对机器人进行建模分析,计算出机器人运动方程的正解求解公式,得到了关节末端坐标与各个关节角之间的对应关系.并应用Matlab—Simulink下的SimMechanics仿真模块进行机器人的运动学三维仿真,验证仿真模型,为今后机器人运动学方面的研究提供一个直观有效的环境.     

机器人竞赛创新实践应用实例

智能机器人的迅速崛起带动了一系列学科的发展,吸引着众多学者致力于机器人的研究,同时也催生了一系列围绕机器人展开的竞赛。机器人竞赛因其对参与者综合能力的要求,也受到了中国乃至全世界的广泛关注[1],全国大学生机器人大赛便应运而生。河南省大学生机器人竞赛于每年五月举行,承袭国赛精神,至今已举办六届,特以此为契机,以河南省大学生机器人竞赛参赛项目“竞步机器人”和“循迹小车”为例浅谈机器人竞赛在培养大学生创新实践能力中的作用。     

On the mechanics of functional asymmetry in bipedal walking

This paper uses two symmetrical models, the passive compass-gait biped and a five-link 3-D biped, to computationally investigate the cause and function of gait asymmetry. We show that for a range of slope angles during passive 2-D walking and mass distributions during controlled 3-D walking, these models have asymmetric walking patterns between the left and right legs due to the phenomenon of spontaneous symmetry-breaking. In both cases a stable asymmetric family of gaits emerges from a symmetric family of gaits as the total energy increases (e.g., fast speeds). The ground reaction forces of each leg reflect different roles, roughly corresponding to support, propulsion, and motion control as proposed by the hypothesis of functional asymmetry in able-bodied human walking. These results suggest that body mechanics, independent of neurophysiological mechanisms such as leg dominance, may contribute to able-bodied gait asymmetry.     

Spiral-Shape Fast-Moving Soft Robots

Soft robots typically exhibit limited agility due to inherent properties of soft materials. The structural design of soft robots is one of the key elements to improve their mobility. Inspired by the Archimedean spiral geometry in nature, here, a fast-moving spiral-shaped soft robot made of a piezoelectric composite with an amorphous piezoelectric vinylidene fluoride film and a layer of copper tape is presented. The soft robot demonstrates a forward locomotion speed of 76 body length per second under the first-order resonance frequency and a backward locomotion speed of 11.26 body length per second at the third-order resonance frequency. Moreover, the multitasking capabilities of the soft robot in slope climbing, step jumping, load carrying, and steering are demonstrated. The soft robot can escape from a relatively confined space without external control and human intervention. An untethered robot with a battery and a flexible circuit (a payload of 1.665 g and a total weight of 1.815 g) can move at an absolute speed of 20 mm s⁻¹ (1 body length per second). This study opens a new generic design paradigm for next-generation fast-moving soft robots that are applicable for multifunctionality at small scales.     

一种四足机器人对角步态仿真分析

仿生四足机器人因具有控制简单、多种路况适应性强、环境适应性强等优点而成为仿生学研究的焦点。文中针对四足机器人模型复杂性、对角步态难以控制等问题,搭建了四足机器人仿真平台。从SolidWorks中建立四足机器人模型,并获得其运动学方程。采用ADAMS和Simulink联合仿真的方法,实现了该机器人的对角行走。通过仿真可知机器人在7 s内前进距离约0.65 m,质心在垂直方向波动量较小,证明机器人能实现稳定运行,为机器人动力学和轨迹规划奠定了基础。     

小型仿人机器人的设计及步态规划

针对现有仿人形机器人造价高的缺点,设计一款低成本的小型双足机器人研究平台.根据人类步行过程及人体生理结构.依据模糊控制与专家控制相结合的理论提出一种简单的双足机器人模型.并根据仿生学原理确定机器人的自由度配置及各关节的比例尺寸.然后,利用目前通用的行为规划软件对双足机器人步态规划进行仿真.并在平坦地面上进行相应行走试验.实验证明.根据人行走模式对机器人进行步态规划的算法稳定可行.为机器人的教学和科研提供了良好的实验平台.     

未知不平整地面上的双足步行稳定控制

 针对未知的不平整地面环境,提出了双足机器人稳定步行控制算法,该算法由步态规划和传感器反馈控制两部分组成.采用被动倒立摆模型设计双足机器人的步态,使得双足机器人能够自然、节能的稳定行走.实时反馈控制用来适应地面环境的凹凸不平以及处理外部环境的扰动.控制器包括上身姿态控制、期望ZMP控制以及非线性落地控制三部分.双足机器人机构柔性的存在对机器人稳定性以及控制效果造成很坏的影响,甚至使反馈控制造成负面的效果,因此柔性的影响也被考虑到步行控制器的设计当中.利用双足机器人不平地面上的步行实验验证所提出步行控制算法的有效性.     

小型仿人机器人的设计及步态规划

针对现有仿人形机器人造价高的缺点,设计一款低成本的小型双足机器人研究平台。根据人类步行过程及人体生理结构．依据模糊控制与专家控制相结合的理论提出一种简单的双足机器人模型,并根据仿生学原理确定机器人的自由度配置及各关节的比例尺寸。然后,利用目前通用的行为规划软件对双足机器人步态规划进行仿真,并在平坦地面上进行相应行走试验。实验证明,根据人行走模式对机器人进行步态规划的算法稳定可行,为机器人的教学和科研提供了良好的实验平台。     

压电驱动的六足爬行机器人的设计与制造

该文提出了一种基于压电驱动的六足爬行机器人的整体设计与制造方案,并对六足爬行机器人进行了动力学建模。介绍了爬行机器人碳纤维连杆传动机构的原理,并提出了各部分零部件的加工方案。介绍了压电驱动器多层材料叠合的复合结构加工工艺,对压电驱动器进行了性能测试,并将其应用到爬行机器人样机上。在280 V的直流偏置电压下,总质量4.631 g的爬行机器人样机完成了爬行运动测试,验证了压电驱动的六足爬行机器人设计方案的可行性。     

Efficient rolling motion for snake-like robots utilizing center of gravity shift

Snake-like robots have attracted attention as robots that can travel over rough terrain where wheeled mobility mechanisms cannot. Previous research on snake-like robots has mainly focused on the biological movement of snakes; therefore, the issue of power consumption caused by driving a large number of actuators still remains unaddressed. In this study, we propose an efficient movement method using the movement of the center of gravity (COG) as a solution to the above-mentioned problem. In the proposed method, the snake-like robot is first transformed into a wheel shape, and then, some motors of the joint are moved to shift the COG and rotate the robot. Therefore, good movement efficiency can be achieved on leveled terrain by the rolling movement, and a snake-like undulating drive with high running performance can be selected on underwater and rough terrain. To realize the proposed movement method, we propose a method for switching between the rotational movement and undulation drive modes. However, the rolling motion with a COG shift needs a design of an appropriate orbit of the eccentric COG and timing of the motion stage transition. In this study, we demonstrate the rolling motion design with a simplified equation of motion. Next, experiments are conducted to verify the traveling efficiency in the proposed rolling mode, and it is proven that the method can achieve twice the traveling efficiency of the undulating motion.     

Towards stable and efficient legged race-walking of an ePaddle-based robot

ePaddle mechanism is a novel hybrid locomotive mechanism designed for accessing terrestrial, aquatic and amphibious terrains with versatile locomotion gaits. Among those gaits, race-walking gait has a promised gait that is potential for achieving highly stable, and highly energetic efficient legged walking. This paper studies the motion planning method of this unique race-walking gait for an ePaddle-based quadruped robot. The standard gait sequence that consists of four phases is firstly presented. The selection of wheel-center trajectory for achieving the gait is then discussed based on kinematic models of the ePaddle module in these phases. Two motion planning methods are presented for an ePaddle-based quadruped robot to track planar path with the proposed race-walking gait. Stability and energetic performances of the proposed race-walking gait are discussed by evaluating duty factor of the ePaddle module, and by measuring stability margin and specific resistance of the robot. A set of simulations on tracking straight and circular paths verifies the idea of the race-walking gait as well as its stability and efficiency.