基于步态切换的欠驱动双足机器人控制方法

由于高维、非线性、欠驱动等特点, 3-D双足机器人的稳定性控制依然是一个研究难点. 一些传统的控制方法, 如基于事件的反馈控制方法和PD控制方法, 抗扰动能力较弱, 鲁棒性较差. 通过观察, 人类受到外部扰动影响时, 会通过调整步态重新获得稳定性,相较之下仅依靠一个步态获得的稳定性是有限的. 受此启发, 本文针对上述问题提出一种基于步态切换的欠驱动3-D双足机器人控制方法. 首先, 以能耗最少为优化目标, 通过非线性优化方法预先设计多组不同步长、步速的步态作为参考步态, 以构建一个步态库; 然后, 通过综合考虑步态切换过程中的稳定性与能效, 建立了多目标步态切换函数; 最后, 将该步态切换函数作为优化目标, 并求解该最小化问题获得下一步的参考步态, 从而实现步态切换, 达到使用步态库?多轨迹方法来提高鲁棒性的目的. 在仿真实验中运用该步态切换控制方法, 欠驱动3-D双足机器人可实现相对高度在[-20, 20] mm内随机变化的不平整地面上行走, 而仅采用单步态控制策略则无法克服这样的外部扰动, 从而说明了基于步态切换的欠驱动双足机器人控制方法的有效性.      

倒摆的一类控制问题

本文从理论上阐明了倒摆的一类控制能实现的依据,并初步地讨论了实现这类控制的具体方法.     

基于能量准则的板振动控制的LQR法

针对压电层合结构振动的主动控制问题，为了优化控制效果，本文基于现代控制理论提出了选用结构振动能量和控制信号能量作为控制目标函数的LQR法。首先，按能量准则推导了控制目标函数中权系数矩阵(Q矩阵和R矩阵)的理论计算公式，为权系数矩阵的选取提供了一定的理论依据。然后，运用该算法，分析了压电层合板受到初始位移激励和冲击载荷作用下的控制过程，用Matlab进行系统仿真，得到了板中心点的位移和控制电压大小随时间变化的曲线。数值模拟的结果表明，该方法能达到更有效控制结构振动和减小控制能量消耗的目的，与一般的LQR控制方法相比，能满足系统多方面的设计要求且控制效果更优，从而验证了该LQR方法运用到结构振动主动控制中的可行性。     

弹性板振动的多模态主动控制

采用多对压电片对板振动的多阶模态进行主动控制。为了改善结构振动控制的效果，本文对选用结构振动能量和控制信号能量作为控制目标函数的LQR控制算法作了初步研究。首先，按能量准则推导了控制目标函数中权系数矩阵(Q矩阵和R矩阵)的理论计算公式，为权系数矩阵的选取提供了一定的理论依据。然后，运用该算法，在研究了单对压电片进行振动主动控制的基础上．本文深入分析了压电层合板振动的多阶模态控制的问题，用Matlab进行系统仿真，得到了压电层合板受到初始位移激励下板中心点的位移和控制电压大小随时间变化的曲线。数值模拟的结果表明，该方法能达到更有效控制结构振动和减小控制能量消耗的目的．进一步验证了该方法能达到有效控制结构振动和减小控制能量消耗的目的。     

"气体摆"式惯性器件的机理研究

本文用能量分析的方法论述了气体摆式惯性器件的敏感机理，并与固体摆式惯性器件的原理作了类比分析。ＡＢＳＴＲＡＣＴ＿＿Ｔｈｉｓｐａｐｅｒ＿＿ＴｈｉｓｐａｐｅｒｄｉｓｃｕｓｓｅｄｔｈｅｇａｓｆｌＯｗｉｎｅｒｔｉａｌｓｅｎｓｏｒ’ｓｓｅｎｓｉｔｉｖｅｍｅｃｈａｎｉｓｍｂｙｕｓｉｎｇｔｈｅｐｏｗｅｒａｎａｌｙｓｉｓｍｅｔｈｏｄａｎｄｃｏｍｐａｒｅｄｉｔｗｉｔｈｓＯｌｉｄｍａｓｓｓｅｎｓｏｒ＇ｓ。     

旋转圆板振动的热力控制

本文研究发现,热力对旋转圆盘动力特性有明显影响.可将此特征应用于旋转圆盘振动的热力自适应控制.仿真和试验均表明,这种控制方法对一些结构振动控制将是一种有效的方法.     

基于能量准则的梁振动多模态主动控制的LQR法

选用以结构振动能量和控制信号能量作为控制目标函数的LQR算法,在单对压电元件进行梁振动主动控制的基础上,使用多对压电元件进行主动控制.运用该算法对压电层合梁的振动控制进行了分析计算.数值算例表明该方法能够有效地控制多阶模态并减小控制能量的消耗.由此,进一步验证了以结构振动能量和控制信号能量作为控制目标函数的LQR算法的正确性.     

一类双层薄膜结构振动能量采集器的数据驱动建模方法及应用

随着工程研究对象日益复杂化、系统化,单纯依赖先验知识的力学建模手段难以满足日渐复杂的系统建模需求.相比而言,数据驱动通过大数据处理方法得到准确反映系统当前运动状态的数学模型,体现了数据科学融入基础与应用科学领域的发展趋势.特别是稀疏非线性动力系统辨识算法(SINDy)的出现,解决了直接构建非线性数学模型的难点问题,实现了由实验数据到非线性控制方程的直接过渡.然而,受制于噪声数据的影响显著以及奇异矩阵难以准确分析等因素, SINDy在实际应用中的可靠性仍有待加强.有鉴于此,文章在已有SINDy算法基础上提出增强型稀疏筛选辨识算法(ESINDy),改进了数据滤波模块以强化其对于含噪信号的处理能力,并且改变了原有算法的循环函数体,以提高其对于奇异问题的识别能力,使之更适于分析工程信号中常见的强噪声、高奇异性等问题.作为应用,研究了一类双层薄膜结构电磁式振动能量采集器(EMH),利用理论建模与ESINDy方法相结合的手段建立了采集器动力学方程,并通过实验和仿真对理论结果进行验证.结果表明:相比于SINDy算法, ESINDy算法能够更加准确地识别该动力学系统的信息,刻画系统蕴含的复杂振动行为....     

旋转振荡板尾流的控制研究

桥跨结构发生颤振时的旋涡尾流可由二维强迫旋转振荡板绕流模拟. 在弦厚比B/H = 5的振荡板两侧对称地放置两个宽度比均为b/H = 0.33的窄条, 对尾流的锁频旋涡脱落进行控制. 采用数值模拟和实验验证方法, 对旋涡场、尾流平均和脉动速度, 以及板所受扭转力矩和升力进行研究, 研究的振幅范围β = 0° ~ 10°, 振频范围f_eH/V_∞ = 0 ~ 0.0857, 雷诺数Re = V_∞H/V = 2800. 窄条位置分为板的前缘、中央和尾缘3种, 控制参数为窄条横向坐标y/H. 根据实验结果, 当窄条位置y/H在一定范围, 振幅β = 0° ~ 7.5°, 振频f_eH/V_∞ = 0 ~ 0.08时, 有控制和无控制尾流脉动速度功率谱主峰的比值远低于1, 最低可达0.3左右. 根据数值模拟结果, 当中央控制件位于y/H = ±1附近时, 在振幅β = 0° ~ 7.5°, 和一定频率范围内, 脉动扭转力矩均方根和升力均方根都有大幅下降, 最多可分别降低43%和80%. 引入第一和第二涡黏系数, 将尾流无规则脉动形成的湍流法向和切向应力, 分别与扰动速度幅值的法向和切向梯度相联系, 得到线性稳定性方程. 稳定性分析表明, 施加控制后, 最大扰动放大因子ω_{i max}大幅降低, 扰动增长的频率范围显著收窄. 窄条改变尾流速度剖面形状并增大湍流涡黏系数, 从而减弱尾流的不稳定性.      

旋转倒立双摆摆起控制量的动态设计变量优化

倒立摆的摆起过程是复杂的非线性力学与控制的综合问题,当力学模型和参数确定时,寻求有效方法计算控制律函数是实现摆起的关键。本文以倒立双摆模型为研究对象,将动态设计变量优化方法引入对摆起开环控制律的分析,编制计算机程序进行数值仿真,确定了控制律函数与状态量随时间变化的状态,为复杂强非线性系统的控制提出了一种有效方法。     

On Stability of a Nonlinear Pendulum

Using the Lyapunov method, we establish a sufficient condition for the stability of a nonlinear pendulum.     

On the Need for Control of Nonlinear Oscillations in Machine Systems

Oscillations in machines are invariably nonlinear. This is either because of inertial coupling effects between different motions of the moving components, material and constitutive phenomena giving rise to stiffness modifications, nonlinear dissipation mechanisms, large deflections, or, as is most likely, some sort of combination of all of these. The net effect of nonlinear vibrations is that at best the machine may well behave a little differently from the way the designer intended, or at worst, in a manner which renders it completely unsuitable for the job. The extent of such problems depends on the nature and the scale of the nonlinearities that are present but it is safe to say that nonlinear oscillations can rarely be completely overlooked in precision machinery analysis and design. The unifying theme in this paper is pendulum motion, firstly in the case of a mobile gantry crane for container stacking where we wish to minimise such motion and converge on a target, and then secondly in the case of a vibration absorber in which we choose to initiate pendulum motion within a special absorber, for the purposes of vibration minimisation. The third example involves the potential for pendulum motion at a very much larger scale and summarises the main control problem that is likely to be encountered in a fully deployed momentum exchange propulsion tether operating in space. The paper discusses the general mathematical issues that pertain to pendulum motion in each of the three cases. This motion is investigated initially in the context of the mobile gantry crane, in the form of a basic three dimensional dynamical model. A feedback linearised controller is shown to offer some advantages for the control of such a system and then a simulation based on data from a practical implementation of this within a real-time control system on a 1/10 laboratory scale model is discussed. It is recalled that the real-time effectiveness of the controller can be compromised by relatively slow sensing and data logging hardware but that despite this some useful performance gains can still be obtainable using this sort of control strategy. The second example comprises an autoparametric vibration absorber and here it is shown how even a simple hunting controller can exploit the mode-locking and wide detuning region effects inherent in autoparametric systems. Further experimental results are discussed in the case of a hunting controller for detuning a vertically oriented parametrically excited pendulum in order to exploit and enhance the powerful and persistent absorption available during autoparametric interaction. The paper concludes with a summary review of the third problem in which the theoretical attitude dynamics of a motorised momentum exchange space propulsion tether are summarised and it is shown that they need to be controlled for reliable and optimal payload velocity boost from both circular parking orbits and elliptical transfer orbits about the Earth.     

An Optimal Nonlinear Feedback Control Strategy for Randomly Excited Structural Systems

A strategy for optimal nonlinear feedback control of randomlyexcited structural systems is proposed based on the stochastic averagingmethod for quasi-Hamiltonian systems and the stochastic dynamicprogramming principle. A randomly excited structural system isformulated as a quasi-Hamiltonian system and the control forces aredivided into conservative and dissipative parts. The conservative partsare designed to change the integrability and resonance of the associatedHamiltonian system and the energy distribution among the controlledsystem. After the conservative parts are determined, the system responseis reduced to a controlled diffusion process by using the stochasticaveraging method. The dissipative parts of control forces are thenobtained from solving the stochastic dynamic programming equation. Boththe responses of uncontrolled and controlled structural systems can bepredicted analytically. Numerical results for a controlled andstochastically excited Duffing oscillator and a two-degree-of-freedomsystem with linear springs and linear and nonlinear dampings, show thatthe proposed control strategy is very effective and efficient.     

A Moment Specification Algorithm for Control of Nonlinear Systems Driven by Gaussian White Noise

Covariance control methods have been applied to linearstochastic multivariable control systems to ensure good behavior of eachstate variable separately. Recent attempts to extend these ideas tononlinear systems have been reported, including an example of a systemexhibiting hysteresis nonlinearity which employed describing functions.As nonlinearities, including hysteresis, occur frequently in structuralsystems, the development of effective control algorithms to accommodatethem is desirable. Recently, the authors designed covariance controllersfor several hysteretic systems using the method of stochastic equivalentlinearization. Performance of the closed loop system employing thecovariance control was verified through simulation. In the present work,a new control design method is adopted that uses the principle ofmaximum entropy, which has been used as an alternative procedure forclosure of moment equations arising in stochastic dynamical systems. Themaximum entropy-based method leads to a result equivalent to that ofstochastic linearization when covariances alone are specified; however,the method readily accommodates the specification of higher orderresponse moments.     

同心旋转圆柱间粘弹性流的非线性动力学模型

基于小间隙假设,将速度场和应力场有杉Ｆｏｕｒｉｅｒ展开式截断近似,推导了同心旋转圆柱间Ｏｌｄｒｏｙｄ－Ｂ型流体的六维动力系统,探讨了高分子添加对滑动轴承间油膜稳定性的影响。结果表明,少量的高分子添加剂具有推迟流体层流失稳的作用。     

Exploiting Parallel Computing to Control Uncertain Nonlinear Systems in Real-Time

Experimental Techniques - Control is a critical element in many applications and research such as experimental testing in real-time. Linear approaches for control and estimation have been widely...     

Adaptive Control of Nonlinear Dynamical Systems Using a Model Reference Approach

In this paper we consider using a model reference adaptive control approach to control nonlinear systems. We consider the controller design and stability analysis associated with these type of adaptive systems. Then we discuss the use of model reference adaptive control algorithms to control systems which exhibit nonlinear dynamical behaviour using the example of a Duffing oscillator being controlled to follow a linear reference model. For this system we show that if the nonlinearity is small then standard linear model reference control can be applied. A second example, which is often found in synchronization applications, is when the nonlinearities in the plant and reference model are identical. Again we show that linear model reference adaptive control is sufficient to control the system. Finally we consider controlling more general nonlinear systems using adaptive feedback linearization to control scalar nonlinear systems. As an example we use the Lorenz and Chua systems with parameter values such that they both have chaotic dynamics. The Lorenz system is used as a reference model and a single coordinate from the Chua system is controlled to follow one of the Lorenz system coordinates.     

Inertialess Nonlinear Systems for Information Coding

Linear properties of primary information converters are mostly used in conventional information coding methods and devices. The more converters are considered suitable for information transmission purposes, the more linear their characteristics are. However, purely linear converters are usually unavailable. Therefore, the devices should operate only in a narrow range, where the converter characteristic is close to linear. Unfortunately, only a low signal-to-noise ratio can be thus obtained. When trying to increase the output level, nonlinear distortions are encountered. If nonlinear elements are employed for information transmission, they are only constituents of the entire conversion system. However, even in this case only linear properties of the system are used. The above conflict is characteristic not only of primary information converters, but also of converters operating on the basis of amplitude, phase, or frequency modulation. A new information coding method is proposed in this work that employs the nonlinear properties of a converter described by a monotonous conversion function f(x). It allows one to avoid the effect of nonlinear distortions and to increase the signal-to-noise ratio. Calculations are presented that concern application of the proposed method for measurements, in the transmission of analog and digital information. Possible applications of the method in analog-to-digital converters are discussed.     

Global Nonexistence for Nonlinear Kirchhoff Systems

In this paper we consider the problem of non-continuation of solutions of dissipative nonlinear Kirchhoff systems, involving the p(x)-Laplacian operator and governed by nonlinear driving forces f = f (t, x, u), as well as nonlinear external damping terms Q = Q(t, x, u, u _t ), both of which could significantly dependent on the time t. The theorems are obtained through the study of the natural energy Eu associated to the solutions u of the systems. Thanks to a new approach of the classical potential well and concavity methods, we show the nonexistence of global solutions, when the initial energy is controlled above by a critical value; that is, when the initial data belong to a specific region in the phase plane. Several consequences, interesting in applications, are given in particular subcases. The results are original also for the scalar standard wave equation when p ≡ 2 and even for problems linearly damped.