Investigation of joint clearances in a large-scale flexible solar array system

This paper is concerned with the effect of joint clearances in a large-scale flexible solar array system. The adopted solar array system is introduced and dynamics equation of the solar array system is presented by the Jourdain velocity variation principle firstly. Then detection of clearance contact and calculation of contact force are discussed. And finally the effect of joint clearances on the solar array system is studied in detail during the deployment process. Simulation results indicate that joint clearances will affect dynamic behaviors of the deployable mast, the container and the sub-panels in the solar array system. Furthermore, the presented method and simulation result have innovation and reference value for future researches.     

航天器帆板展开过程动力学建模与仿真

阐述了应用柔性多体动力学和Kane方程进行航天器帆板展开过程建模的方法，将帆板视为柔性体并进行模态分析，采用有限元法与模态缩聚技术建立了帆板的离散化模型．以国产某型号航天器为例，同时考虑4块帆板的柔性，应用ADAMS软件对帆板的展开过程进行了建模与仿真，得到了帆板的变形、大范围运动等动力学参量，为航天器帆板的设计提供了一定的依据．     

运动滑道含摩擦多体系统的建模和数值方法

研究了运动约束面含摩擦多体系统动力学方程的建立和算法问题．首先利用第一类Lagrange方程给出了系统的动力学方程,并以矩阵形式给出了这类系统摩擦力的广义力的一般表达式．为便于摩擦力和铰链约束力的分析与计算,采用笛卡尔坐标和约束方程的局部方法,使得系统的约束力与Lagrange乘子一一对应．应用增广法将微分一代数方程组转化为常微分方程组并用分块矩阵的形式给出,以便于方程的编程与计算,提高计算效率．最后用一个算例验证了该方法的有效性．     

柔性关节柔性连杆机械臂的动力学建模

柔性关节柔性连杆机械臂是典型的非线性、强耦合、欠驱动系统,其控制难度高.对于这类系统,选择合适的动力学模型进行控制器设计对于提高控制性能是非常有帮助的.为此,研究了具有柔性关节柔性连杆机械臂的动力学建模问题,并提出了一种改进的建模方法.在该方法中,连接柔性连杆的柔性关节首先被简化为刚性关节和柔性连杆的弹性约束边界.然后,根据结构动力学理论、哈密顿原理和假设模态法建立系统的刚柔耦合动力学方程.相较于将柔性关节简化为刚性关节和扭簧的传统处理方式,所采用的简化方式一方面可以降低系统的自由度,另一方面可以得到更适合控制器设计的动力学模型.最后,通过数值仿真验证了本文方法的有效性和优势.     

太阳电池阵展开与锁定过程的多体动力学分析

柔性太阳电池阵展开动力学分析一般将板间的铰链视为理想铰,展开到位时施加与角度相关的撞击力矩模拟锁定过程.本文采用多体动力学方法,在动力学建模时将板间铰链视为物体,考虑太阳电池阵的刚柔耦合效应,基于Hertz接触理论,建立锁销和锁槽的碰撞模型.然后实现了太阳电池阵展开锁定全过程的动力学数值仿真,并研究了碰撞模型中参数的选取对仿真结果的影响.研究结果表明,碰撞参数的选取不仅影响铰间碰撞力的大小,还会影响整个系统锁定后的频率响应.最后给出了如何选取碰撞参数进行太阳电池阵展开与锁定动力学仿真的策略.     

Pose Control of a Lake Surface Cleaning Robot Using Backstepping and Polar Coordinates

In this paper, the stabilization control problem of a lake surface cleaning robot (LSCR) that is driven by a driving and steering mechanism is addressed. Since the LSCR has more degrees of freedom than the number of control inputs, its motion is subject to non-holonomic constraints. Generally, this kind of system cannot be asymptotically stabilized using a time-invariant smooth feedback controller in the Cartesian coordinates. A novel controller using the vector backstepping technique for controlling the position and orientation of the LSCR is presented. We first represent the pose of the LSCR by a polar coordinate system centered at the desired pose and transform the dynamics equation of the LSCR from the Cartesian coordinates to the polar coordinates. Then a feedback control law is derived to yield global asymptotic convergence of the position and orientation of the system to the desired values using the vectorial backstepping design scheme. We prove the asymptotic stability of the system under the control of the proposed method using the Lyapunov theory. Simulations have been carried out to demonstrate the performance of the proposed controller.     

Dynamics of satellite with deployable rigid solar arrays

This research is concerned with the dynamic modeling of satellite with deployable solar arrays equipped with strain energy hinges (SEH). The SEH is a new deployment device consisting of a strip tape measure, which utilizes the buckling behavior of a thin curved shell to produce nonlinear dynamic characteristics during deployment of solar arrays. For dynamic simulation, the SEH is assumed to be a massless-nonlinear elastic member and the solar panels are assumed to be rigid bodies which are connected by the SEHs. The planar deployment is of interest in this study since the deployment of solar arrays mainly occurs in a two-dimensional plane. In deriving the equations of motion, we developed a new systematic approach suitable for the simulation of solar array deployment in space. The simulation results were compared to the ground experimental results obtained at the laboratory of Korea Aerospace Research Institute. In the ground experiments, the hub of the solar arrays was attached to the frictionless rotational bearing, and the solar arrays were hanged by bungee cables. Even though the dynamic model was derived for the space deployment of the solar arrays, the simulation result corresponding to the solar array deployment was similar to the ground experimental results thus validating the simulation model developed in this paper.     

Modeling and simulation of longitudinal dynamics coupled with clutch engagement dynamics for ground vehicles

During the engagement of the dry clutch in automotive transmissions, clutch judder may occur. Vehicle suspension and engine mounts couple the torsional and longitudinal models, leading to oscillations of the vehicle body that are perceived by the driver as poor driving quality. This paper presents an effective formulation for the modeling and simulation of longitudinal dynamics and powertrain torsional dynamics of the vehicle based on non-smooth dynamics of multibody systems. In doing so friction forces between wheels and the road surface are modeled along with friction torque in the clutch using Coulomb’s friction law. First, bilateral constraint equations of the system are derived in Cartesian coordinates and the dynamical equations of the system are developed using the Lagrange multiplier technique. Complementary formulations are proposed to determine the state transitions from stick to slip between wheels and road surface and from the clutch. An event-driven scheme is used to represent state transition problem, which is solved as a linear complementarity problem (LCP), with Baumgarte’s stabilization method applied to reduce constraint drift. Finally, the numerical results demonstrate that the modeling technique is effective in simulating the vehicle dynamics. Using this method stick-slip transitions between driving wheel and the road surface and from the clutch, as a form of clutch judder, are demonstrated to occur periodically for certain values of the parameters of input torque from engine, and static and dynamic friction characteristics of tire/ground contact patch and clutch discs.     

Cartesian control of robots without dynamic model and observer design

Most control algorithms for rigid robots are given in joint coordinates. However, since the task to be accomplished is expressed in Cartesian coordinates, inverse kinematics has to be computed in order to implement the control law. Alternatively, one can develop the necessary theory directly in workspace coordinates. This has the disadvantage of a more complex robot model. In this paper, a control-observer scheme is given to achieve exact Cartesian tracking without the knowledge of the manipulator dynamics nor computing inverse kinematics. Also, only joint measurements are used.     

欠驱动球棒系统不动点控制器设计

针对欠驱动系统的Benchmark球棒系统,考虑球与棒之间的摩擦系数系统动力学及球质心与棒支点之间垂直于棒方向上的距离,建立其精确的数学模型。基于部分反馈线性化,利用坐标变换将系统动力学转换为便于控制器设计的非三角结构级联规范型,并采用不动点控制方法设计控制器,实现球棒系统的稳定控制。仿真实验表明,在球棒系统的控制过程中考虑系统摩擦系数及球质心与棒支点之间垂直于棒方向上的距离十分必要,并且不动点控制器具有良好的动态性能和强鲁棒性。     

Application of Fuzzy Logic for the Solution of Inverse Kinematics and Hierarchical Controls of Robotic Manipulators

In this paper, hierarchical control techniques is used for controlling a robotic manipulator. The proposed method is based on the establishment of a non-linear mapping between Cartesian and joint coordinates using fuzzy logic in order to direct each individual joint. The hierarchical control will be implemented with fuzzy logic to improve the robustness and reduce the run time computational requirements. Hierarchical control consists of solving the inverse kinematic equations using fuzzy logic to direct each individual joint. A commercial Microbot with three degrees of freedom is utilized to evaluate this methodology. A decentralized fuzzy controller is used for each joint, with a Fuzzy Associative Memories (FAM) performing the inverse kinematic mapping in a supervisory mode. The FAM determines the inverse kinematic mapping which maps the desired Cartesian coordinates to the individual joint angles. The individual fuzzy controller for each joint generates the required control signal to a DC motor to move the associated link to the new position. The proposed hierarchical fuzzy controller is compared to a conventional controller. The simulation experiments indeed demonstate the effectiveness of the proposed method.     

Model reference adaptive impedance control in Cartesian coordinates for physical human–robot interaction

In this paper, a nonlinear model reference adaptive impedance controller is proposed and tested. The controller provides asymptotic tracking of a reference impedance model for the robot end-effector in Cartesian coordinates applicable to rehabilitation robotics or any other human–robot interactions such as haptic systems. The controller uses the parameters of a desired stable reference model which is the target impedance for the robot’s end-effector. It also considers uncertainties in the model parameters of the robot. The asymptotic tracking is proven using Lyapunov stability theorem. Moreover, the adaptation law is proposed in joint space for reducing the complexity of its calculations; however, the controller and the stability proof are all presented in Cartesian coordinates. Using simulations and experiments on a two DOFs robot, the effectiveness of the proposed controller is investigated.     

Dynamic Analysis and Control Synthesis of Undesired Slippage of End-Effectors in a Cooperative Grasping

This paper addresses dynamic analysis and control synthesis of object grasping in a cooperative multirobot system with n-serial manipulators from an undesired slippage point of view. Two control approaches are presented in this article; a modified version of a conventional method in grasp synthesis and a new method based on a new modeling of system dynamics. A new formulation for frictional contact is used in dynamical modeling, where equality and inequality equations of the standard Coulomb friction model are all converted to a single second-order differential equation. A multiphase controller is utilized to control the object trajectory tracking as well as object slippage in the new control approach. Performance and robustness of both approaches are studied numerically. The results show superiority of the new method and its desirable and excellent performance.     

Robust nonlinear task space control for 6 DOF parallel manipulator

This paper presents a robust nonlinear controller equipped with a friction estimator for a 6 degree of freedom (DOF) parallel manipulator in the task space coordinates. The requisite 6 DOF system states for the task space control are acquired by an alpha-beta tracker and a numerical forward kinematic solution. The Friedland-Park friction observer in the joint space coordinates provides friction estimates that help to improve the control performance. Finally, the RNTC turns out to outper form a nonlinear task space control and a popularly adopted PID control with the friction estimator in the joint space coordinates.     

基于一种改进的BP神经网络光伏电池建模

由于光伏电池具有高度非线性特性，难以建模，而传统的数学模型难以满足光伏控制系统设计和应用的要求。该文利用神经网络具有逼近任意复杂非线性函数的能力，将神经网络技术应用到光伏阵的建模中，避开了该模块内部的复杂性。模型以太阳能日照、温度以及负载电压作为神经网络辨识模型的输入量，光伏阵输出电流为输出量，采用改进型BP算法，建立了光伏电池的动态响应模型，然后预测了最大功率点。文中给出模型的结构，训练步骤和仿真结果。仿真结果表明，方法可行，建立的模型精度较高，从而为设计光伏实时控制系统奠定了基础。     

DSP/FPGA-based Controller Architecture for Flexible Joint Robot with Enhanced Impedance Performance

Some practical issues associated with enhancing the Cartesian impedance performance of flexible joint manipulator are investigated. A digital signal processing/field programmable gate array (DSP/FPGA) structure is proposed to realize the singular perturbation based impedance controller. To increase the bandwidth of torque control and minimize the joint torque ripple, boundary layer system and field-oriented control (FOC) are fully implemented in a FPGA of each joint. The kernel of the hardware system is a peripheral component interface (PCI)-based high speed floating-point DSP for the Cartesian level control, and FPGA for high speed (200 us cycle time) multipoint low-voltage differential signaling (M-LVDS) serial data bus communication between robot Cartesian level and joint level. Experimental results with a four-degree-of-freedom flexible-joint manipulator under constrained-motion task, demonstrate that the controller architecture can enhance the robot impedance performance effectively.     

Task-space neuro-sliding mode control of robot manipulators under Jacobian uncertainties

Cartesian robot control is an appealing scheme because it avoids the computation of inverse kinematics, in contrast to joint robot control approach. For tracking, high computational load is typically required to obtain Cartesian robot dynamics. In this paper, an alternative approach for Cartesian tracking is proposed under assumption that robot dynamics is unknown and the Jacobian are uncertain. A neuro-sliding second order mode controller delivers a low dimensional neural network, which roughly estimates inverse robot dynamics, and an inner smooth control loop guarantees exponential tracking. Experimental results are presented to confirm the performance in a real time environment.     

Robust Saturated PI Joint Velocity Control for Robot Manipulators

It is well known that many industrial manipulators use an embedded linear proportional‐integral (PI) joint velocity controller to guarantee motion control through proper velocity commands. However, although this control scheme has been very successful in practice, not much attention has been paid to designing new PI velocity control structures. The problem of analyzing a saturated PI velocity joint velocity controller is addressed in this paper. By using the theory of singularly perturbed systems, the closed‐loop system is studied. The robot dynamics assumed in this paper take into account bounded time–varying disturbances which may include the friction at the joints. An experimental study in a planar two degrees‐of‐freedom direct‐drive robot is also presented, confirming the advantage of the new saturated PI joint velocity controller.     

Cooperative tracking of vessel trajectories based on curved dynamic coordinates

A novel cooperative motion problem for multiple surface vessels is investigated based on multiple referential points and a terminal sliding mode control method. To overcome the difficulties of modeling some special tracking trajectories like rivers and coastlines in a traditional Cartesian coordinate system, a novel local curved‐dynamic coordinate system is constructed, and multiple referential points with given intervals on the curved coordinates are used as the consensus reference for the group. Then cooperative cruise of surface vessels is analyzed, based on which a local‐to‐global terminal sliding mode controller is designed to keep the relative pose of the dynamic unmanned vessels. At last, the formation trajectory constraint conditions are further discussed and some simulation results show the validity of the presented methods.     

作业型飞行机器人动态滑翔抓取的鲁棒自适应控制

作业型飞行机器人是指将多自由度机械臂固连在飞行机器人上的一类新型机器人系统,它能够对周围环境施加主动影响,同时也存在较为复杂的动力学性能.本文针对作业型飞行机器人滑翔抓取物体时所受到的摩擦力和接触力问题以及在飞行过程中产生的转动惯量变化问题,设计了一种整体式鲁棒自适应控制策略.首先在作业型飞行机器人系统动力学建模中引入摩擦力和接触力模型,考虑飞行机器人转动惯量为有界变量,提高了建模和抓取的精度.然后,为减弱滑翔抓取产生的剧烈扰动对飞行控制性能的影响,设计了一种抗扰动的鲁棒自适应控制器,并使用区间矩阵法对转动变量变化进行补偿控制.接着,通过Lyapunov稳定性理论证明了系统的稳定性.最后通过仿真对比实验,验证了所提出方法的有效性和优势.