High-level motion planning for CPG-driven modular robots

Modular robots may become candidates for search and rescue operations or even for future space missions, as they can change their structure to adapt to terrain conditions and to better fulfill a given task. A core problem in such missions is the ability to visit distant places in rough terrain. Traditionally, the motion of modular robots is modeled using locomotion generators that can provide various gaits, e.g. crawling or walking. However, pure locomotion generation cannot ensure that desired places in a complex environment with obstacles will in fact be reached. These cases require several locomotion generators providing motion primitives that are switched using a planning process that takes the obstacles into account. In this paper, we present a novel motion planning method for modular robots equipped with elementary motion primitives. The utilization of primitives significantly reduces the complexity of the motion planning which enables plans to be created for robots of arbitrary shapes. The primitives used here do not need to cope with environmental changes, which can therefore be realized using simple locomotion generators that are scalable, i.e., the primitives can provide motion for robots with many modules. As the motion primitives are realized using locomotion generators, no reconfiguration is required and the proposed approach can thus be used even for modular robots without self-reconfiguration capabilities. The performance of the proposed algorithm has been experimentally verified in various environments, in physical simulations and also in hardware experiments.     

New Visual Invariants for Terrain Navigation Without 3D Reconstruction

For autonomous vehicles to achieve terrain navigation, obstacles must be discriminated from terrain before any path planning and obstacle avoidance activity is undertaken. In this paper, a novel approach to obstacle detection has been developed. The method finds obstacles in the 2D image space, as opposed to 3D reconstructed space, using optical flow. Our method assumes that both nonobstacle terrain regions, as well as regions with obstacles, will be visible in the imagery. Therefore, our goal is to discriminate between terrain regions with obstacles and terrain regions without obstacles. Our method uses new visual linear invariants based on optical flow. Employing the linear invariance property, obstacles can be directly detected by using reference flow lines obtained from measured optical flow. The main features of this approach are: (1) 2D visual information (i.e., optical flow) is directly used to detect obstacles; no range, 3D motion, or 3D scene geometry is recovered; (2) knowledge about the camera-to-ground coordinate transformation is not required; (3) knowledge about vehicle (or camera) motion is not required; (4) the method is valid for the vehicle (or camera) undergoing general six-degree-of-freedom motion; (5) the error sources involved are reduced to a minimum, because the only information required is one component of optical flow. Numerous experiments using both synthetic and real image data are presented. Our methods are demonstrated in both ground and air vehicle scenarios.     

基于ADAMS的机械四连杆机构运动仿真分析

机械四连杆机构是机械类的典型机构,其设计与运动分析具有很强的理论性和实践性。针对作图法和解析法对该类机构进行运动分析的不足,在基于经典机构学理论的基础上,采用ADAMS(Automatic Dynamic Analysis of Mechanical Systems)动力学仿真方法,可实现对铰链四杆机构的运动特性的直观、高效而准确的计算机辅助分析。然后,采用多体系统动力学理论,通过ADAMS分析了机构的简化方法并进行运动学仿真,对四连杆机构中杆件的传动角、位移、速度及运动轨迹进行了分析。     

Optimal Design of a New Wheeled Mobile Robot Based on a Kinetic Analysis of the Stair Climbing States

In this paper, we propose a new wheeled mobile robot (WMR) with a passive linkage-type locomotive mechanism that allows the WMR to adapt passively to rough terrain and climb up stairs, making it ideal for applications such as building inspection, building security, and military reconnaissance. A simple four-bar linkage mechanism and a limited pin joint are proposed after considering two design needs: adaptability and passivity. To improve the WMR’s ability to climb stairs, we divided the stair-climbing motion into several stages, taking into consideration the status of the points of contact between the driving wheels and the step. For each of the suggested stages, a kinetic analysis was accomplished and validated using the multi-body dynamic analysis software package ADAMS. The object functions are presented for the stages that influence the WMR’s ability to climb stairs. The optimization of the object functions is carried out using the multi-objective optimization method.     

单自由度转动式对心机械夹持器

近年来许多学者提出了各种新型的机械夹持器,对心夹持器就是其中的一种.现有的对心机械夹持器的主要缺点是结构复杂,设计麻烦,加工困难,夹持范围小.本文提出一种新的结构简单,制造容易,使用方便,夹持范围大,对心夹持精度高,能对心夹持各种圆柱体的转动式机械夹持器.这种夹持器是根据同心圆在同一圆心角下的不同圆上的弦相互平行的几何关系和平行四杆机械的运动特点设计的.夹持器的每侧是由摇杆滑块机构外接平行四杆机构组成的.     

复杂环境下群机器人自组织协同多目标围捕

针对动态多目标围捕,提出了一种复杂环境下协同自组织多目标围捕方法.首先设计了多目标在复杂环境下的运动模型,然后通过对生物群体围捕行为的研究,构建了多目标简化虚拟受力模型.基于此受力模型和提出的动态多目标自组织任务分配算法,提出了群机器人协同自组织动态多目标围捕算法,这两个算法只需多目标和个体两最近邻位置信息以及个体面向多目标中心方向的两最近邻任务信息,计算简单高效,易于实现.接着获得了系统稳定时参数的设置范围.由仿真可知,所提的方法具有较好的灵活性、可扩展性和鲁棒性.最后给出了所提方法相较于其它方法的优势.     

A Robust Tracking Controller for Electrically Driven Robot Manipulators: Stability Analysis and Experiment

 In this paper, a robust controller for electrically driven robotic systems is developed. The controller is designed in a backstepping manner. The main features of the controller are: 1) Control strategy is developed at the voltage level and can deal with both mechanical and electrical uncertainties. 2) The proposed control law removes the restriction of previous robust methods on the upper bound of system uncertainties. 3) It also benefits from global asymptotic stability in the Lyapunov sense. It is worth to mention that the proposed controller can be utilized for constrained and nonconstrained robotic systems. The effectiveness of the proposed controller is verified by simulations for a two link robot manipulator and a four-bar linkage. In addition to simulation results, experimental results on a two link serial manipulator are included to demonstrate the performance of the proposed controller in tracking a given trajectory.     

Attitude-based dynamic and kinematic models for wheels of mobile robot on deformable slope

Deformable slope is a type of terrain that wheeled mobile robots (WMRs) and ground unmanned vehicles (GUVs) may have to traverse to accomplish their mission tasks. However, the associated terramechanics for wheels with arbitrary posture is rarely studied. In this paper, based on wheel attitude, dynamics of the wheel–terrain interaction for a rigid wheel on deformable slope is investigated. Through introducing the angular geometry of wheel attitude into terramechanics theory, a generalized dynamic model is developed, involving two inclination angles of slope and three attitude angles of wheel steering axis. Two representative cases are studied: the wheel runs straight forward and perpendicular to the slope, and the wheel is in a steering maneuver with an inclined steering axis. A generalized kinematic model for wheel–terrain contact point and wheel center is also provided, which analytically explicates that trajectory of wheel motion is coupled with wheel attitude while driven by angular rates. The proposed attitude-based models are valid for arbitrary wheel–terrain geometry and can lead to control purpose directly. Effectiveness of the models is confirmed by simulating the influences from attitude to wheel mechanics and motion.     

Mobile Robot Navigation for Moving Obstacles with Unpredictable Direction Changes,Including Humans

In many service applications, mobile robots need to share their work areas with obstacles. Avoiding moving obstacles with unpredictable direction changes, such as humans, is more challenging than avoiding moving obstacles whose motion can be predicted. Precise information on the future moving directions of humans is unobtainable for use in navigation algorithms. Furthermore, humans should be able to pursue their activities unhindered and without worrying about the robots around them. An enhanced virtual force field-based mobile robot navigation algorithm (termed EVFF) is presented for avoiding moving obstacles with unpredictable direction changes. This algorithm may be used with both holonomic and nonholonomic robots. It incorporates improved virtual force functions and an improved method for selecting the sense of the detour force to better avoid moving obstacles. For several challenging obstacle configurations, the EVFF algorithm is compared with five state-of-the-art navigation algorithms for moving obstacles. The navigation system with the new algorithm generated collision-free paths consistently. Methods for solving local minima conditions are proposed. Experimental results are also presented to further verify the avoidance performance of this algorithm.     

Collision-avoidance for redundant robots through control of the self-motion of the manipulator

A new method to on-line collision-avoidance of the links of redundant robots with obstacles is presented. The method allows the use of redundant degrees of freedom such that a manipulator can avoid obstacles while tracking the desired end-effector trajectory. It is supposed that the obstacles in the workspace of the manipulator are presented by convex polygons. The recognition of collisions of the links of the manipulator with obstacles results on-line through a nonsensory method. For every link of the redundant manipulator and every obstacle a boundary ellipse is defined in workspace such that there is no collision if the robot joints are outside these ellipses. In case a collision is imminent, the collision-avoidance algorithm compute the self-motion movements necessary to avoid the collision. The method is based on coordinate transformation and inverse kinematics and leads to the favorable use of the abilities of redundant robots to avoid the collisions with obstacles while tracking the end-effector trajectory. This method has the advantage that the configuration of the manipulator after collision-avoidance can be influenced by further requirements such as avoidance of singularities, joint limits, etc. The effectiveness of the proposed method is discussed by theoretical considerations and illustrated by simulation of the motion of three-and four-link planar manipulators between obstacles.     

未知动态环境下非完整移动群机器人围捕

针对未知动态障碍物环境下非完整移动群机器人围捕,提出了一种基于简化虚拟受力模型的自组织方法.首先给出了个体机器人的运动方程,然后给出了未知动态环境下目标和动态障碍物的运动模型.通过对复杂环境下围捕行为的分解,抽象出简化虚拟受力模型,基于此受力模型,设计了个体运动控制方法,接着证明了系统的稳定性并给出了参数设置范围.不同情况下的仿真结果表明,本文给出的围捕方法可以使群机器人在未知动态障碍物环境下保持较好的围捕队形,并具有良好的避障性能和灵活性.最后分析了本文与基于松散偏好规则的围捕方法相比的优势.     

A combined reactive and reinforcement learning controller for an autonomous tracked vehicle

Unmanned ground vehicles currently exhibit simple autonomous behaviours. This paper presents a control algorithm developed for a tracked vehicle to autonomously climb obstacles by varying its front and back track orientations. A reactive controller computes a desired geometric configuration based on terrain information. A reinforcement learning algorithm enhances vehicle mobility by finding effective exit strategies in deadlock situations. It is capable of incorporating complex information including terrain and vehicle dynamics through learned experiences. Experiments illustrate the effectiveness of the proposed approach for climbing various obstacles.     

“妙手”系统机械结构设计与优化

为了辅助医生更好地完成显微外科手术,开发了一种主从异构的显微外科手术机器人系统——“妙手”系统．“妙手”系统的主手为商业化的Phantom Desktop主手,从手为针对显微外科血管缝合而设计的“妙手”从手．从手包括位置机构和姿态机构．位置机构通过丝传动实现双四连杆机构的运动特性;姿态机构采用三轴交汇于一点的设计思想．通过分析双四连杆机构的运动特性,根据Angeles运动灵活度指标对双四连杆机构进行了优化．结果表明：当双四连杆机构前三级杆等长且I级杆与III级杆垂直时,机构运动灵活度取最大值．     

Dynamic Motion Planning for Mobile Robots Using Potential Field Method

The potential field method is widely used for autonomous mobile robot path planning due to its elegant mathematical analysis and simplicity. However, most researches have been focused on solving the motion planning problem in a stationary environment where both targets and obstacles are stationary. This paper proposes a new potential field method for motion planning of mobile robots in a dynamic environment where the target and the obstacles are moving. Firstly, the new potential function and the corresponding virtual force are defined. Then, the problem of local minima is discussed. Finally, extensive computer simulations and hardware experiments are carried out to demonstrate the effectiveness of the dynamic motion planning schemes based on the new potential field method.     

Terrain-evaluation-based motion planning for legged locomotion on irregular terrain

The path planning of legged locomotion is complex in that path generation is based on constraints not only from body motion, but also from leg motion. A general approach to path planning will fail in generating a feasible path for walking machines when facing the huge searching space of legged locomotion. In this paper, an effective method of path planning is introduced by virtue of terrain evaluation. It maps obstacles into the robot configuration space by evaluating the obstacles' influence on the legged locomotion. The evaluation produces an index of terrain, called terrain complexity, for path planning. Using potential-guided searching, the terrain with mapped obstacles is searched to generate a feasible path.     

Human like trajectory generation for a biped robot with a four-bar linkage for the knees

The design of a knee joint is a key issue in robotics to improve the locomotion and the performances of the bipedal robots. We study a design for the knee joints of a planar bipedal robot, based on a four-bar linkage. We design walking reference trajectories composed of double support phases, single support phases and impacts. The single support phases are divided in two sub-phases. During the first sub-phase the stance foot has a flat contact with the ground. During the second sub-phase the stance foot rotates on its toes. In the double support phase, both stance feet rotate. This phase is ended by an impact on the ground of the toe of the forward foot, the rear foot taking off. The single support phase is ended by an impact of the heel of the swing foot, the other foot keeping contact with the ground through its toes. A parametric optimization problem is presented for the determination of the parameters corresponding to the optimal cyclic walking gaits. In the optimization process this novel bipedal robot is successively, overactuated (double support with rotation of both stance feet), fully actuated (single support sub-phase with a flat foot contact), and underactuated (single support sub-phase with a rotation of the stance foot). A comparison of the performances with respect to a sthenic criterion is proposed between a biped equipped with four-bar knees and another with revolute joints. Our numerical results show that the performances with a four-bar linkage are bad for the smaller velocities and better for the higher velocities. These numerical results allows us to think that the four-bar linkage could be a good technological way to increase the speed of the future bipedal robots.     

Particle filter-based aerial tracking for moving targets

This paper considers the problem of tracking a moving target with a radio transmitter using an aerial robot in an online manner. The aerial robot is equipped with a low-cost directional antenna and Software Defined Radio receiver to obtain the signal emitted by the target. The aerial robot rotates around itself and collects a predefined number of signal recordings from each direction to determine the bearing angle to the target in which the received signal strength is maximized. The measurement uncertainty is assumed to be bounded and represented by two triangular areas divided by a bisector. To localize and track the target, a particle filter-based approach is proposed. In this approach, we integrate the discrete and bounded measurement model with the particle filter in such a way that the particles' weights are updated based on a novel method which considers the measurement wedge and the particle locations with respect to this wedge along with a logistic function. We also incorporate the doubling strategy into the particle filter to determine the next measurement locations and avoid arbitrarily large number of measurements. We choose wildlife monitoring as a use case scenario in which a radio transmitter is put on the animal under consideration to allow wildlife researchers to track it. Since each animal has its own motion behavior, we consider different motion models for the target, which are used in modeling animal movements in wildlife studies. Therefore, the proposed approach is validated using a target moving with varying velocity and acceleration. We verified the tracking performance of the approach through a series of extensive simulations. We compared the proposed approach with the optimal offline strategy in terms of the empirical competitive ratio of the total distance traveled and the tracking distance. We also developed a low-cost hardware platform and software infrastructure for the proposed tracking system. Using this platform, we conducted field experiments for the stationary and moving targets.     

广义Voronoi图求解多机器人运动规划

在拥挤环境中,由于障碍物的边界形状比较复杂,需要使用广义Voronoi图表示空间环境。且在多移动机器人的运动规划过程中,需要协调多个机器人的运动,必须得到Voronoi图通道的宽度。为此提出了一种计算拥挤障碍物环境中生成的广义Voronoi图及其通道宽度的算法。并在生成的Voronoi图上利用A*算法对多个机器人进行路径规划,并利用分布式方法协调多个机器人运动。对协调两个机器人运动的过程进行了仿真,仿真结果表明利用提出的算法生成的具有通道宽度信息的Voronoi图能够满足多移动机器人运动规划的需要。     

非平坦地形下移动机器人安全路径规划

提出一种基于双分辨率2.5D分层栅格地图的Secure A*(SA*)路径规划方法,以解决移动机器人在非平坦地形下的安全路径规划问题.首先,设计一种双分辨率2.5D分层栅格地图,利用双分辨率栅格对环境中的障碍物信息与高程信息进行存储,以节约地图的存储空间;然后,结合移动机器人运动能力,将环境中的高程信息转化为约束因子,...