Dynamics and Wheel’s Slip Ratio of a Wheel-legged Robot in Wheeled Motion Considering the Change of Height

The existing research on dynamics and slip ratio of wheeled mobile robot (WMR) are derived without considering the effect of height, and the existing models can not be used to analyze the dynamics performance of the robot with variable height while moving such as NOROS-Ⅱ. The existing method of dynamics modeling is improved by adding the constraint equation between perpendicular displacement of body and horizontal displacement of wheel into the constraint conditions. The dynamic model of NOROS-Ⅱ in wheel motion is built by the Lagrange method under nonholonomic constraints. The inverse dynamics is calculated in three different paths based on this model, and the results demonstrate that torques of hip pitching joints are inversely proportional to the height of robot. The relative error of calculated torques is less than 2% compared with that of ADAMS simulation, by which the validity of dynamic model is verified. Moreover, the relative horizontal motion between fore?hind wheels and body is produced when the height is changed, and thus the accurate slip ratio can not be obtained by the traditional equation. The improved slip ratio equations with the parameter of the vertical velocity of body are introduced for fore wheels and hind wheels respectively. Numerical simulations of slip ratios are conducted to reveal the effect of varied height on slip ratios of different wheels. The result shows that the slip ratios of fore?hind wheels become larger?smaller respectively as the height increases, and as the height is reduced, the reverse applies. The proposed research of dynamic model and slip ratio based on the robot height provides the effective method to analyze the dynamics of WMRs with varying height.     

移动机械臂的输出跟踪控制

移动机械臂通常由移动机器人和装在移动机器人上的机械臂组成。它既具有移动机器人的可移动性又具有机械臂的操作灵活性,有极高的实际应用价值。本文针对由二轮驱动的移动平台和二连杆机械臂组成的移动机械臂的输出跟踪问题,利用滑模控制原理为其设计了动态滑模控制器。首先给出了移动机械臂的简化动态模型,然后通过微分同胚和输入变换将其分解为4个低阶子系统,并给出了其输出跟踪的动态滑模控制器的设计方法。仿真实验表明,所设计的动态滑模控制器不仅能很好地跟踪给定轨迹,而且能有效地削弱滑模控制系统的抖振。     

非协调移动机器人的变结构跟踪控制

研究非协调移动机器人系统的跟踪问题。根据反演设计的方法 ,针对双后轮驱动移动机器人的运动学模型 ,设计变结构跟踪控制方案 ,使闭环跟踪系统渐近稳定。对双后轮驱动机器人的仿真证实了控制器的鲁棒跟踪能力     

障碍环境下移动操作机零件移动规划方法研究

将移动操作机应用于装配领域,研究了运动冗余且受非完整约柬的移动操作机系统在障碍环境下完成零件移动任务的运动规划问题。将整个任务划分成移动、夹取和转移3个子任务。将随机道路图法应用于移动操作机的协同避障规划,首先求出了移动平台的一条满足非完整约束的简单路径;然后以此路径作为操作臂位置约束,在操作臂的位形空间内随机采样构造了道路图;最后通过图的搜索获得一条移动操作机的无碰路径。以平面移动操作机为例,通过计算机仿真实现了2维工作空间的零件移动操作,表明了该方法的有效性。     

THEORETICAL DESIGN AND MOTION PLANNING OF NONHOLONOMIC MANIPULATOR

A new nonholonomic transmission mechanism is proposed based on the nonholonomic the-ory and nonlinear control principle, and combined with conditions of the nonholonomic motion plan-ning and control, that is researched to compose method of the motion transfer chain from this transmis-sion mechanism, on which a new nonholonomic manipulator is designed. This nonholonomic manipu-lator is a controllable multi-joint manipulator that actuated only by two-servo electromotor Its motionexpresses the characteristic of nonholonomy constraint and nonlinear, and that also satisfies thechained form convertibility. And then, using the nonlinear control principle of chained system, motioncharacteristic of the nonholonomic manipulator is applied. From simulation verification and analysis,the usefulness of the theoretical design and control strategies is shown, and that is important in designand research of handiness robot and multi-finger robot hand.     

Robust adaptive motion/force control scheme for crawler-type mobile manipulator with nonholonomic constraint based on sliding mode control approach

In this paper, a robust adaptive motion/force control (RAMFC) scheme is presented for a crawler-type mobile manipulator (CTMM) with nonholonomic constraint. For the position tracking control design, an adaptive sliding mode tracking controller is proposed to deal with the unknown upper bounds of system parameter uncertainties and external disturbances. Based on the position tracking results, a robust control strategy is also developed for the nonholonomic constraint force of CTMM. According to the Lyapunov stability theory, the stability of the closed-loop control system, the uniformly ultimately boundedness of position tracking errors, and the boundedness of the force error and adaptive coefficient errors are all guaranteed by using the derived RAMFC scheme. Simulation and experimental tests on a CTMM with two-link manipulator demonstrate the effectiveness and robustness of the proposed control scheme.     

Modeling and motion control of mobile robot for lattice type welding

This paper presents a motion control method and its simulation results of a mobile robot for a lattice type welding. Its dynamic equation and motion control methods for welding speed and seam tracking are described. The motion control is realized in the view of keeping constant welding speed and precise target line even though the robot is driven for following straight line or curve. The mobile robot is modeled based on Lagrange equation under nonholonomic constraints and the model is represented in state space form. The motion control of the mobile robot is separated into three driving motions of straight locomotion, turning locomotion and torch slider control. For the torch slider control, the proportional-integral-derivative (PID) control method is used. For the straight locomotion, a concept of decoupling method between input and output is adopted and for the turning locomotion, the turning speed is controlled according to the angular velocity value at each point of the corner with range of 90° constrained to the welding speed. The proposed control methods are proved through simulation results and these results have proved that the mobile robot has enough ability to apply the lattice type welding line.     

Robust adaptive tracking control for nonholonomic mobile manipulator with uncertainties

In this paper, mobile manipulator is divided into two subsystems, that is, nonholonomic mobile platform subsystem and holonomic manipulator subsystem. First, the kinematic controller of the mobile platform is derived to obtain a desired velocity. Second, regarding the coupling between the two subsystems as disturbances, Lyapunov functions of the two subsystems are designed respectively. Third, a robust adaptive tracking controller is proposed to deal with the unknown upper bounds of parameter uncertainties and disturbances. According to the Lyapunov stability theory, the derived robust adaptive controller guarantees global stability of the closed-loop system, and the tracking errors and adaptive coefficient errors are all bounded. Finally, simulation results show that the proposed robust adaptive tracking controller for nonholonomic mobile manipulator is effective and has good tracking capacity.     

事件触发的自适应移动机器人轨迹跟踪控制

针对纵向滑转对移动机器人轨迹跟踪控制的影响,提出了一种基于事件触发的自适应轨迹跟踪控制方法。引入自适应估计策略,通过两个滑转参数自适应估计驱动轮的纵向滑转情况,克服纵向滑转带来的运动扰动。同时结合事件触发思想,设计触发函数,降低通信频次,节约计算资源。最后,利用Lyapunov稳定性理论对系统的稳定性进行证明。仿真及实验结果表明,在纵向滑转使得位置误差最大值的均方根提升56.85%的情况下,控制系统仍能在短时间内迅速收敛,提高了运动系统的稳定性。     

Design,implementation, and test of skid steering-based autonomous driving controller for a robotic vehicle with articulated suspension

This paper describes an autonomous driving control algorithm based on skid steering for a Robotic Vehicle with Articulated Suspension (RVAS). The driving control algorithm consisted of four parts: speed controller for following the desired speed, trajectory tracking controller to track the desired trajectory, longitudinal tire force distribution algorithm which determines the optimal desired longitudinal tire force and wheel torque controller which determines the wheel torque command at each wheel to keep the slip ratio below the limit value as well as to track the desired tire force. The longitudinal and vertical tire force estimators were designed for optimal tire force distribution and wheel slip control. The dynamic model of the RVAS is validated using vehicle test data. Simulation and vehicle tests were conducted in order to evaluate the proposed driving control algorithm. Based on the simulation and test results, the proposed driving controller was shown to produces satisfactory trajectory tracking performance.     

Design, modelling and errors measurement of wheeled mobile robots

This paper presents the mechanical design process of an omni-directional mobile robot. In addition, the kinematics equations of the final design are derived, and the inverse Jacobian matrix of the robot is presented. The dynamic equations of motion for the final design are derived in a symbolic form, assuming that no slip occurs on the wheel in the spin direction. In order to validate the kinematics and dynamic equation, we carried out consequences of simulation using two pieces of software, Maple and Working Model. Finally, the mobile robot is moved in given trajectories and the systematic errors of the robot are determined. To overcome the problems, a new method was introduced in which the robot was programmed to move in the direction of each wheel shaft.     

考虑轮胎无滑移的智能车辆连续曲率轨迹规划方法

提出了无滑移约束条件下,给定起止点位置和状态的可行运动轨迹规划方法。首先根据前轮转向的单轨车辆模型,建立了7维非线性车辆动力学模型。然后基于无滑移假设,推导出前轮转角及其转角变化率的无滑移表达式;利用MNC轮胎/路面模型推导满足车辆无滑移的动力学约束,并据此给出最大速度轮廓曲线。最后利用闭环操纵稳定性评价指标来优化生成的轨迹。仿真结果验证了该方法的有效性。     

汽车ABS系统的PID控制策略及仿真分析

运用汽车动力学理论,建立了PID控制器模型、制动时整车动力学模型、车轮模型。提出了以滑移率为控制目标的ABS系统的控制仿真分析,将PID控制器应用于单个ABS系统控制研究,以车轮滑移率为控制目标,通过轮速与车速传感器采集汽车速度、车轮转速,计算出汽车各轮胎实际滑移率,与期望滑移率进行比较后,将二者的偏差作为PID控制器的输入量,反复调节控制器的控制参数,使其实际滑移率始终处于最佳滑移率附近,通过PID控制最终使汽车在最佳滑移率所对应的地面制动力下进行制动。     

Maximum load-carrying capacity of autonomous mobile manipulator in an environment with obstacle considering tip over stability

In order to increase the efficiency of wheeled mobile manipulators (WMM), it is preferred to carry the maximum payload, but in the case of a small-sized platform, which is desirable in applications, it may cause dangerous tip over, especially in the presence of obstacles. So, it is necessary to consider stability constraint in the determination of robot motion planning. This paper presents a novel approach for the determination of the maximum payload-carrying capacity of a coordinated mobile manipulator in an environment with presence of obstacle, based on stability. The proposed method considers the tip over stability on zero moment point criterion, which must be considered when the path of the end-effector is predefined but the position of the mobile platform is free, because tipping over in this condition is probable. Hence, the full dynamic model of WMM (including the coordinating vehicle and manipulator) is used, the obstacle avoidance scheme is implied based on potential functions, and the maximum payload path for a specified payload is generated using the optimal control approach. Then, an iterative method based on the stability criterion and motor restriction, including torque and jerk, was implied to calculate the maximum payload capacity. To the best of our knowledge, this is the first paper reporting on some simulation results as well as successful experiments of implementing the algorithm. The proposed approach has been implemented and tested on a nonholonomic WMM consisting of a differential-drive mobile base and a robotic arm to demonstrate the efficiency and effectiveness of the proposed approach.     

基于非线性微分方程的机械臂运动位置控制方法

针对当前机械臂运动位置控制方法存在机械臂关节节点位置的跟踪效果差和机械臂运动位置控制能力差的问题,提出基于非线性微分方程的机械臂运动位置控制方法。首先对机械臂动力学进行分析,获取内部三连杆结构作用原理和机械臂动力学目标函数,再利用坐标求权矩阵重构机械臂动力学目标函数,获取机械臂相关的非线性微分方程,将非线性微分方程的输出结果,即机械臂动力学参数代入 CPG 神经网络中,构建机械臂运动控制模型。实验结果表明,所提方法的械臂关节节点位置跟踪效果好、机械臂运动位置控制能力强。     

Trajectory planning of mobile robots using indirect solution of optimal control method in generalized point-to-point task

This paper presents an optimal control strategy for optimal trajectory planning of mobile robots by considering nonlinear dynamic model and nonholonomic constraints of the system. The nonholonomic constraints of the system are introduced by a nonintegrable set of differential equations which represent kinematic restriction on the motion. The Lagrange’s principle is employed to derive the nonlinear equations of the system. Then, the optimal path planning of the mobile robot is formulated as an optimal control problem. To set up the problem, the nonlinear equations of the system are assumed as constraints, and a minimum energy objective function is defined. To solve the problem, an indirect solution of the optimal control method is employed, and conditions of the optimality derived as a set of coupled nonlinear differential equations. The optimality equations are solved numerically, and various simulations are performed for a nonholonomic mobile robot to illustrate effectiveness of the proposed method.     

四轮驱动全轮差速转向移动焊接机器人运动学分析与仿真

为增加轮式移动焊接机器人稳定性、负载能力和降低控制复杂度,提出了一种四轮驱动全轮差速转向移动焊接机器人机构,介绍了该机构差速转向原理,证明该机构无转向侧滑。采用非完整约束方法建立了其差速转向误差模型,并在该模型基础上对其进行了直线-圆弧-直线轨迹数值仿真,结果为转角误差0.002 137°,转动中心坐标误差小于0.012mm。仿真结果表明该模型满足焊接中的位置精度要求。     

热加工用机械手末端轨迹跟踪控制方法研究

分析机械手横纵向移动、旋转和伸缩等不同动作的动力学,利用拉格朗日法构建机械手动力学模型,以此计算热加工作业时机械手末端移动轨迹误差。考虑机械手移动惯性、重力和向心力角位移等多重因素,设计前馈控制器,将移动轨迹点作为神经网络训练集,通过多次迭代完善轨迹点数据库,利用距离加权法修正轨迹点值,通过控制机械手末端惯性问题完成机械手末端轨迹跟踪控制。仿真实验证明,所提方法路径跟踪误差小,控制稳定性好、响应快,可适用范围广。     

基于自适应滑模控制器的机械臂运动控制方法

由于无法消除机械臂运动过程中存在的高频振动,导致运动控制方法存在跟踪精度低、控制稳定性差和控制性能差等问题。对此,提出一种基于自适应滑膜控制器的机械臂运动控制方法,在机械臂动力学模型的基础上设计非线性观测器,对机械臂控制系统中存在的干扰信号进行观测,设计自适应滑膜控制器对干扰信号进行补偿。将补偿器引入自适应滑膜控制器中,其主要作用是抑制机械臂在运动过程中存在的高频振动,以提高控制稳定性,通过 Lyapunov 函数设计自适应滑膜控制器的总控制律,根据总控制律利用改进后的自适应滑膜控制器完成机械臂的运动控制。实验结果表明,所提方法的跟踪精度高、稳定性好、控制性能高。     

具有外部扰动的参数未知漂浮基柔性空间机械臂的对角递归神经网络控制

讨论载体位置和姿态均不受控情况下,存在外部扰动的参数未知漂浮基柔性空间机械臂系统关节运动的动力学控制问题。由假设模态法,利用拉格朗日方法建立漂浮基柔性空间机械臂的系统动力学方程。以此为基础,针对存在外部扰动和系统参数未知的情况,利用对角递归神经网络逼近柔性空间机械臂系统的逆动力学模型,设计基于对角递归神经网络的控制方案,以控制柔性空间机械臂的关节铰跟踪在关节空间的期望运动轨迹,同时能抑制柔性杆的振动。该方案由于没有专门设计主动控制器抑制柔性振动,因此不需要测量、反馈柔性振动模态,大大简化控制器的结构;无需预知控制对象的精确模型和系统参数,且能克服外部扰动的影响。计算机数值仿真证实所提方案的有效性和可行性。