The stability of six degree of freedom dynamics with magnus effects

The equations of motion of a rigid body are developed in body fixed axes; the aerodynamic forces and moments are expressed as elements of a Taylor series in the six kinematic rates (body velocities and spins). Stability is approached firstly by forcing Jacobi elliptic functions into the equations of motion; stability criteria follow either as unconditional system stability or as a conditional criterion dependent upon the launch conditions. Stability is also considered by way of the motion invariants and their relation to kinetic energy. Three basic systems are considered and numerical integration gives detailed system responses; pertubation of the various aerodynamic effects changes the responses and the stability from unconditional stability to instability or conditional stability.     

Application of graph theory to the determination of potential energy of systems consisting of rigid bodies and springs

The process of determining the potential energy, as a function of generalized coordinates, of a system consisting of rigid bodies and springs is often extremely laborious. In this paper, a method is presented by means of which all the potential energy terms of a system are calculated in a systematic manner. It is assumed that the system of rigid bodies has a topological tree structure, and that linear springs are situated arbitrarily between the rigid bodies. The method is based on a graph-theoretical approach and is consistent with that of the calculation of kinetic energy presented in (2, J. Franklin Inst., Vol. 324, No. 3, pp. 351–367, 1987). The paper contains the derivation of general formulae for potential energies of gravity and elastic forces. These formulae are implemented for the case of a planar system; an example is also provided.     

On the Computation of Functionals Over Sample Paths of a Randomly Rotating Rigid Body

This paper deals with the computation of the values of two functionals which are defined over the sample paths of a randomly rotating rigid body. It is assumed that the body is subjected to two different kinds of perturbation. The first kind of perturbation is represented by the standard Wiener process and the second kind by a homogeneous process with independent increments, finite second-order moments, mean zero and no continuous sample functions. In order to measure quantitatively the stochastic stability of the body's motion, two functionals are defined over its sample paths. It is shown that each of these functionals is a solution to a corresponding partial integro-differential equation. A numerical procedure for the solution of these equations is suggested, and its efficiency and applicability are demonstrated with examples.     

Bio-inspired untethered fully soft robots in liquid actuated by induced energy gradients

Soft robotics with new designs, fabrication technologies and control strategies inspired by nature have been totally changing our view on robotics. To fully exploit their potential in practical applications, untethered designs are preferred in implementation. However, hindered by the limited thermal/mechanical performance of soft materials, it has been always challenging for researchers to implement untethered solutions, which generally involve rigid forms of high energy-density power sources or high energy-density processes. A number of insects in nature, such as rove beetles, can gain a burst of kinetic energy from the induced surface-energy gradient on water to return to their familiar habitats, which is generally known as Marangoni propulsion. Inspired by such a behavior, we report the agile untethered mobility of a fully soft robot in liquid based on induced energy gradients and also develop corresponding fabrication and maneuvering strategies. The robot can reach a speed of 5.5 body lengths per second, which is 7-fold more than the best reported, 0.69 (body length per second), in the previous work on untethered soft robots in liquid by far. Further controlling the robots, we demonstrate a soft-robot swarm that can approach a target simultaneously to assure a hit with high accuracy. Without employing any high energy-density power sources or processes, our robot exhibits many attractive merits, such as quietness, no mechanical wear, no thermal fatigue, invisibility and ease of robot fabrication, which may potentially impact many fields in the future.     

Hybrid position/force control of a flexible parallel manipulator

In this paper, simultaneous position/force control of a closed-chain planar manipulator with the last link flexible is studied when the manipulator is in contact with an environment. The proposed manipulator consists of a flexible link connected to three rigid linkages whichare optimized for kinematic and force manipulability in the region of interest. The flexible link is modeled as a series of rigid links connected by virtual torsion springs. A hybrid position/force control algorithm is developed and implemented on the manipulator. Experimental results are presented to verify the performance of the controller.     

技术创新,还是结构升级效率?——推动高质量发展的主导动能分析

不同经济发展阶段的主导动能不同，文章基于动能转换视角，探讨了实现经济高质量发展所需的技术创新与产业结构升级两大主导动能之间的动态互动机制，并运用CHD模型来实证分析我国两大主导动能之间的关联关系，进一步利用GRA得到影响我国现阶段主导动能的关键因素。结果表明：在样本初期，两大主导动能的发展水平较低，耦合协调度受二者发展水平的影响较大，但随着两个子系统发展水平的不断提高后，协调度受二者耦合度的影响较大，表明我国为了实现经济高质量发展，需要两大主导动能之间协调发挥作用，但是由于我国现在面临着技术成果产品化低效率的难题，即技术创新成果可以专利化，却不能产品化，两大主导动能之间传递信息时存在一定的滞后性，且影响现阶段我国经济发展主导动能的关键因素有：专利申请授权数、R&D人员投入占比、生产性服务业占比和改进后的泰尔系数。最后为我国实现经济高质量发展提出政策建议。     

Cooperative payload transportation with real-time formation control of multi-quadrotors in the presence of uncertainty

This paper considers the trajectory tracking for a cable-suspended rigid body carried by multiple quadrotors while maintaining the desired formation. A three-loop control structure is proposed based on the Super Twisting Sliding Mode (STSM) controller with high robustness to compensate for uncertainties and disturbances. In the proposed structure, a proper formation based on a centralized approach creates advantages such as collision avoidance and non-entanglement of the cables, which leads to uniform load distribution on all quadrotors to optimize energy consumption. The corresponding equations are formulated as a convex constrained optimization problem with an analytical solution for calculating the cables' tension. This approach is a straightforward and computationally efficient method for real-time applications. In addition to proving the system's stability by Lyapunov theory, the simulation results show good performance in the presence of disturbance and uncertainty.     

Determination method for power-saved driving motions of manipulators by heuristic algorithms (in case of PTP control)

This study proposed a method for suppressing torques and consumed energy of manipulators considering an effect of inertial forces in order to achieve power-saved drive. The present paper describes the case that the start and end points of a work path of a manipulator are specified and the path between the points can be determined arbitrarily, which is so-called point-to-point (PTP) control. The proposed method determines both the initial pose of a manipulator and input motions of its joints so that the torque or consumed energy is suppressed. The input motion of the joint is expressed by a motion curve that indicates the time profiles of input displacements, velocities and accelerations. The proposed method determines the motion curve as a polynomial with appropriate coefficients. Those coefficients and their values are decided by a heuristic algorithm in order to suppress the input torques or consumed energy of a manipulator. The paper actually determines the power-saved drive motion of “PUMA560” by the proposed method and reveals its effectiveness.     

Attitude tracking control of a quadrotor UAV in the exponential coordinates

A new approach to control the attitude of a quadrotor UAV in terms of the exponential coordinates is developed in this paper. The exponential coordinate is a minimal representation of the rotation matrix, but it can avoid singularities. Since the quadrotor UAV can be considered as a rigid body aircraft, the analytic closed-form expressions of a rigid body's attitude kinematics are derived from differential of exponential on SO(3). Furthermore, based on the exponential expressions of attitude kinematics, the controller of a fully actuated rigid body is designed using trajectory linearization control method. The overall attitude controller contains two loops, which are designed according to the torque equation and the angular velocity equation respectively. In the numerical simulation, the proposed attitude controller is compared to a controller in the Euler angles, showing that singularities induced by Euler angles are avoided by using exponential coordinates. The robustness test of the attitude controller is also demonstrated in the simulation. The simulation results indicate that the proposed method can be applied to the attitude tracking control of an aerial robot especially when the robot needs to make aggressive maneuverings.     

The energetic structure of multi-body dynamic systems

Dynamic systems containing particles and rigid bodies capable of movement in two- or three-dimensions may be represented by equations of motion in several basic forms. In all cases geometric nonlinearities are involved and terms arise in the equations which are difficult to understand and interpret. The equations often conceal the basic structure of the dynamic model of the system since only combinations of parameters and combined effects of various constraints finally appear.In this paper the basic relations for the dynamic elements as well as the transformations among internal forces and velocities are depicted using bond graphs. The energetic structure of the system is thus exhibited in multiport form. This aids in the exploration of alternative equation formulation and in understanding of the assumptions involved in any particular equation set. Further, a bond graph model is easily coupled with nonmechanical dynamic models through force or motion generators.     

Chaotic attitude motion of a magnetic rigid spacecraft in a circular orbit near the equatorial plane

This paper deals with chaotic attitude motion of a magnetic rigid spacecraft in a circular orbit near the equatorial plane of the earth. The dynamical model of the problem is derived. The Melnikov analysis is carried out to prove the existence of a complicated nonwandering Cantor set. The dynamical behavior is numerically investigated by means of time history, Poincare map, power spectrum and Lyapunov exponents. Numerical simulations indicate that the onset of chaos is characterized by break of torus as the torque of the magnetic forces is increased.     

Crack stability of an adhesive layer

The stability of crack which is present in an adhesive layer is investigated. The adhesive layer bonds an elastic plate to a rigid base. A Wieghardt base is assumed as the model for the adhesive layer. The crack is loaded by internal pressure. An energy criterion and a critical load intensity criterion are used. Explicit results are given for a relatively rigid plate and for a relatively flexible plate and a comparison of the two criteria is discussed.     

基于特征缺失修复的人脸三维运动形变估计算法

人脸由于其非刚性明显,受到运动背景变化、形变程度复杂、特征丢失等因素的影响,使得在进行三维动态人脸形变估计时,面临着估计不准,误差较大的问题。为了解决这些问题,提出一种基于特征缺失修复的人脸三维运动形变估计算法,将非刚体人脸运动的形变估计过程中,运用特征补偿方法,补偿由于噪声、形变程度复杂带来的特征丢失缺陷,运用较多的人脸形变特征进行形变分析,准确计算人脸的形变程度。实验结果表明,这种方法得到的解误差较小,效果明显。     

科技成果的表观水平与科技评价

提出了"科技成果表观水平"的概念。论述了表观水平流行于科技成果评价的原因,运用表观水平进行科技评价存在的弊端以及提高科技成果质量的对策。指出科技评价可以发现差距,有差距就会产生"势能",科技奖励是将"势能"转化成"动能"和动力的外在条件;只有正确评价才能正确鉴别,才能奖罚得当,才能正确引导;制度改革应以科技评价和激励政策为主线,从上到下的各种制度都应围绕这条主线进行创新。     

节能量交易问题的思考

随着工业化、城镇化进程加快和消费结构持续升级,我省能源消费需求在相当长一段时间内仍将呈刚性增长,资源环境压力仍将持续。节能工作必须改变过去主要依靠行政手段一条腿走路的方式,主动适应当前节能工作新变化,积极推进节能市场机制建设,把政府、企业、金融机构等各方面的积极性充分调动起来,建立起均衡持续推进节能工作的长效机制,才能确保实现节能目标任务。为深入贯彻落实党的十八大和十八届三中全会精神,本文围绕推行节能量交易进行了深入思考,明确了政府在节能量交易中的作用,提出了节能量分类交易、目标分配及核查的作用、工作重点及体会。     

K型铸钢节点刚域研究

本文利用ANSYS对K型铸钢节点与钢管相贯节点在节点转动刚度上进行了对比,K型铸钢节点存在刚域,既不是铰接,也不是简单刚接,本文提出了一种计算K型铸钢节点刚域长度的方法。     

Energy regulation of torque–driven robot manipulators in joint space

The energy regulation of fully actuated torque–driven robot manipulators in joint space is addressed in this paper. The proposed controller is designed via an energy shaping plus damping injection approach. The contribution is the proposal of an energy regulator with partial damping injection capable of inducing oscillations in the undamped joints of robot manipulators, with an user specified desired frequency and amplitude, by adding only damping in the rest of the joints, which may require less control effort than a trajectory tracking controller with full damping injection. Although viscous friction is considered in all joints of robot manipulator, it has been compensated via the proposed energy regulator. Moreover, the controlled periodic motion oscillates around a desired joint position as reference, and this provides a nice feature in the robot, mainly when there is not interest in the undamped joint to follow an specified time-varying sinusoidal function, but generating an oscillatory motion of constant amplitude and frequency. Instrumental in stability analysis is the Lyapunov’s theory and LaSalle’s theorem, which allows concluding that the closed-loop trajectories approach an invariant set that could include a unique equilibrium or periodic orbits. Numerical simulations on a manipulator arm model of two degrees of freedom illustrate the main results.     

On the matching equations of kinetic energy shaping in IDA-PBC

Interconnection and damping assignment passivity-based control scheme has been used to stabilize many physical systems such as underactuated mechanical systems through total energy shaping. In this method, some partial differential equations (PDEs) related to kinetic and potential energy shaping shall be solved analytically. Finding a suitable desired inertia matrix as the solution of nonlinear PDEs relevant to kinetic energy shaping is a challenging problem. In this paper, a systematic approach to solving this matching equation for systems with one degree of underactuation is proposed. A special structure for desired inertia matrix is proposed to simplify the solution of the corresponding PDE. It is shown that the proposed method is more general than that of some reported methods in the literature. In order to derive a suitable desired inertia matrix, a necessary condition is also derived. The proposed method is applied to three examples, including pendubot, VTOL aircraft, and 2D SpiderCrane.     

On the dynamics of an axially moving beam

The equations of motion of a beam whose length changes with time are derived. These take the form of four nonlinear partial differential equations and one algebraic relation. By assuming that the deflection gradients of the beam are small, and that the beam is axially rigid, the equations of motion are linearized. One closed-form similarity solution and a semi-analytic solution is obtained for specific axial velocities. Also, a procedure is described for obtaining approximate solutions for various axial velocities of the beam.