振动驱动移动系统平面避障运动分析

近年来,工业机器人的应用领域日益广泛,可移动机器人的发展备受关注,为了在一些复杂环境中准确地完成作业,学者们提出并研究了振动驱动移动系统.本文研究了在各向异性黏性摩擦环境中一类有两个在平行轨道内做正弦运动的内部质量块的振动驱动移动系统的运动规律,提出了使系统完成包括避障等规定作业的驱动设计方法.首先利用第二类拉格朗日方程,建立了系统的动力学方程;然后,利用速度Verlet积分法分析了系统的运动规律,得到了内部驱动参数与系统运动轨迹、运动速度的关系;最后,结合振动驱动移动系统的运动规律,提出了使系统沿预设路径运动和实现避障运动的驱动设计方法.通过曲线离散得到了系统沿预设路径运动的移动轨迹,进而通过改变内部质量块的驱动参数,使系统沿预设路径运动.为了使移动系统在障碍物环境中达到目标位置,提出了结合栅格法,Floyd算法及最小顶点圆法的优化的路径规划计算方法,得到了振动驱动移动系统在障碍物环境中运动的最优路径,并通过改变内部质量块的驱动参数实现了移动系统的避障运动.     

三相驱动下非光滑振动驱动系统的动力学分析

可移动式机器人已成为机器人研究领域的重要分支,为实现其在狭小特殊环境中的运动, 学者们提出并研究了振动驱动移动系统.本文基于二维LuGre摩擦模型和拉格朗日方程,给出了一类振动驱动系统在各向同性摩擦环境中的动力学建模方法和数值算法.这类振动驱动系统结构简单且密封性好,依靠箱体与地面间的摩擦力实现自身的定向运动.该系统由一个外部箱体和两个内部质量块构成,两个质量块在箱体内的两个平行轨道上作三相振动驱动,箱体通过三个刚性支撑足与地面保持接触. 二维LuGre摩擦模型的利用,可有效避免库伦摩擦模型的不连续性给动力学方程的数值求解带来的困难,且可有效揭示该系统在运动过程中的黏滞-滑移切换现象. 数值仿真结果表明,通过调整其内部质量块的驱动参数,可实现箱体的直线平移、定轴转动和平面一般运动,且箱体在移动和转动过程中会出现擦滑、穿滑、回滑和不黏等4种现象; 另外,通过调节驱动参数, 不仅可以改变箱体移动和转动的快慢,还可以改变箱体形心运动轨迹的曲率半径.      

振动驱动移动机器人直线运动的滑移分岔

近年来,随着移动型机器人设计技术水平的不断提高,其运动形式日趋多样. 借助于仿生学的思想,模仿蚯蚓等动物的蠕动成为不少机器人设计者所追求的目标. 为了实现这一目标,学者们提出并研究了振动驱动系统. 本文研究了各向同性干摩擦下,单模块三相振动驱动系统的粘滑运动. 考虑到库伦干摩擦力的不连续性,振动驱动系统属于Filippov 系统. 基于此,运用Filippov 滑移分岔理论,分析了振动驱动系统不同的粘滑运动情况. 根据驱动参数的不同,系统运动的滑移区域被分成4 种基本情形. 对这些情形分类讨论,得到系统的6 种运动情况. 然后对这6 种运动情况进行归纳,最终得出系统一共存在4 种不同的粘滑运动,而且也解析地给出了发生这4 种粘滑运动的分岔条件. 分岔条件包含系统的3 个驱动参数,通过变化这些参数,得到了系统运动的分岔图. 借助分岔图,详细分析了随着驱动参数的变化,系统如何实现不同粘滑运动类型之间的切换,并从分岔角度给出了相应的物理解释. 最后,通过数值方法直接求解原运动方程,数值解法得到的4 种运动图像与理论分析一致,验证了系统运动分岔研究的正确性.      

KINETICS ANALYSIS OF NON-SMOOTH VIBRATION-DRIVEN SYSTEM WITH THREE-PHASE CONTROL 1)

可移动式机器人已成为机器人研究领域的重要分支,为实现其在狭小特殊环境中的运动, 学者们提出并研究了振动驱动移动系统.本文基于二维LuGre摩擦模型和拉格朗日方程,给出了一类振动驱动系统在各向同性摩擦环境中的动力学建模方法和数值算法.这类振动驱动系统结构简单且密封性好,依靠箱体与地面间的摩擦力实现自身的定向运动.该系统由一个外部箱体和两个内部质量块构成,两个质量块在箱体内的两个平行轨道上作三相振动驱动,箱体通过三个刚性支撑足与地面保持接触. 二维LuGre摩擦模型的利用,可有效避免库伦摩擦模型的不连续性给动力学方程的数值求解带来的困难,且可有效揭示该系统在运动过程中的黏滞-滑移切换现象. 数值仿真结果表明,通过调整其内部质量块的驱动参数,可实现箱体的直线平移、定轴转动和平面一般运动,且箱体在移动和转动过程中会出现擦滑、穿滑、回滑和不黏等4种现象; 另外,通过调节驱动参数, 不仅可以改变箱体移动和转动的快慢,还可以改变箱体形心运动轨迹的曲率半径.     

磁耦合悬臂梁双稳动力学分析与实验

研究了一个自由端附加小磁铁的悬臂梁在磁力作用下的双稳态动力学行为．首先,利用Hamilton原理和Euler-Bernoulli梁的基本方程建立了系统在非零平衡点处做微幅振动的动力学方程．其次,利用多尺度法对建立的模型进行理论分析,得到悬臂梁在非零平衡点处振动的幅频方程和位移解,并对解进行了稳定性分析．最后,通过建立实验装置,得到悬臂梁不同运动形式下的参数平面分类和悬臂梁在非零平衡点处振动的幅频关系,通过观察系统在非零平衡点处振动的理论预测,实验结果验证了非零平衡点处振动的理论分析的正确性．对照理论、实验和数值结果得到：在不同的外激励幅值和频率作用下,悬臂梁有三种不同的运动形式：在非零平衡点处的微幅振动;大范围往返运动;在两个非零平衡点之间的无规律运动．     

两自由度的Burridge-Knopoff模型的一种近似分析方法

Burridge-Knopoff模型是速度驱动的多质量的质量弹簧系统.它是用来进行地震机理研究的一种摩擦动力系统的模型.本文考查了具有两个自由度的Burridge-Knopoff模型的摩擦激振问题.摩擦的不光滑性给系统的求解带来了很大的困难.又系统带有两个摩擦接触面,运动情况更加复杂.本文通过对摩擦力取平均的方法,得到了系统在各个运动形式下的通解,采用半解析的方法对此两自由度的系统进行了研究.通过以上方法,给出了一种周期运动的具体运动形式以及位移和速度的时程关系;并且发现在不同驱动速度的情况下,随着驱动速度的增大,系统的运动形式存在简单和复杂交替出现的现象,并给出了不同系统参数下的分岔图.     

两自由度参数激励摆旋转运动分析和实验

研究具有支撑参数激励摆系统的支撑结构振动对摆旋转的影响,其中支撑结构是受到扭簧约束的刚性悬臂梁,参数激励摆与刚性悬臂梁的悬臂段铰接．首先,通过拉格朗日方程建立了系统两自由度的动力学方程．其次,利用多尺度法对建立的模型进行理论分析,得到悬臂梁的振动与上摆不同运动形式的关系,从而得到上摆不同运动形式下的参数平面分类和悬臂梁在上摆转动时的振动频响．最后,通过建立实验装置,观察理论预测,实验结果验证了理论分析的正确性．实验与理论对照得到,当参数激励频率接近悬臂梁的一阶固有频率时,悬臂梁的振幅变大,会破坏摆的转动稳定性．     

基于积分本构黏弹性带的横向非线性动力学

研究了黏弹性传动带在1:1内共振时的横向非平面非线性动力学特性. 首先,利用Hamilton原理建立了黏弹性传动带横向非平面非线性动力学方程. 然后综合应用多尺度法和Galerkin离散法对偏微分形式的动力学方程进行摄动分析,得到了四维平均方程. 对平均方程的稳定性进行了分析,从理论上讨论了动力系统解的稳定性变化情况. 最后数值模拟结果表明黏弹性传动带系统存在混沌运动、概周期运动和周期运动.      

双驱动布鲁塞尔振子系统混沌运动的控制

本言语以强迫布鲁塞尔振子方程为例，研究了外加第二驱动对振子系统混沌运动的控制影响，第二驱面与原强是为某些有理比值时，可以通过适当选择第二驱动的频率或强度抑制方程的混沌运动，得到周期轨道，这时系统混沌运动的控制与初始相位有限敏感的依赖关系；而对某些无理比的外驱动则可以改变方程的运动性质，产生非混沌的奇怪吸引子。     

一种压电驱动的三足爬行机器人

机器人领域涉及到力学、机械、材料、控制、电子和计算机等多个学科. 其中, 爬行机器人可在极端环境下工作, 进而可有效降低人工作业的危险性并提高工作效率. 因此, 爬行机器人一直是机器人领域的重点研究对象. 压电陶瓷是一种能够将机械能和电能互相转换的新型功能陶瓷材料. 逆压电效应是指当在电介质的极化方向施加电场, 这些电介质就在一定方向上产生机械变形或机械压力, 当外加电场撤去时, 这些变形或应力也随之消失. 本文基于压电陶瓷的逆压电效应设计了一种由3条弯曲变截面梁支撑的一体化三足爬行机器人. 利用理论力学方法对该三足爬行机器人建立整体受力分析方程, 再用哈密顿原理对变截面、变角度梁建立动力学方程, 最终得到了可求解该三足爬行机器人的压电驱动腿固有频率的方程. 设计并制作了三足爬行机器人实物, 通过实验测试了不同弯折角度、不同驱动频率、不同负载、不同电压波形对运动方向及运动速度的影响. 最后利用不对称的驱动电压使三足爬行机器人实现了左转、右转以及不加导轨的近似直线运动, 实现了设计的3个方向的运动, 最后分析了该机器人的能耗问题. 该研究可为微型爬行机器人设计和实验提供参考依据.      

Controlled motion of a two-module vibration-driven system induced by internal acceleration-controlled masses

The rectilinear motion of a vibration-driven mechanical system composed of two identical modules connected by an elastic element is considered in this paper. Each module consists of a main body and an internal mass that can move inside the main body. Anisotropic linear resistance is assumed to act between each module and the resistant medium. The motion of the system is excited by two acceleration-controlled masses inside the respective main bodies. The primary resonance situation that the excitation frequency is close to the natural frequency of the system is considered, and the steady-state motion of the system as a whole is mainly investigated. Both the internal excitation force and the external resistance force contain non-smooth factors and are assumed to be small quantities of the same order when compared with the maximum value of the force developed in the elastic element during the motion. With this assumption, method of averaging can be employed and an approximate value of the average steady-state velocity of the entire system is derived through a set of algebraic equations. The analytical results show that the magnitude of the average steady-state velocity can be controlled by varying the time shift between the excitations in the modules. The optimal value of the time shift that corresponds to the maximal average steady-state velocity exists and is unchanging with the external coefficients of resistance. For a system with specific parameters, numerical simulations are carried out to verify the correctness of the analytical results. The optimal value of the time shift is numerically obtained, and the optimal situation is studied to show the advantages of the control.     

Analysis of worm-like locomotion driven by the sine-squared strain wave in a linear viscous medium

In this paper, a worm-like locomotion in a linear resistive medium is studied to achieve controlled shape changes of the worm-like body by choosing a kind of driving with low energy expended and high-velocity locomotion in certain condition. To this end, we first develop the full dynamic model of the system under consideration to obtain the mean velocity related to friction coefficient, wave speed, linear density, body length and wave width. Correspondingly, a quasi-static model is also given from which the velocity can be expressed analytically. In the case of the shape change driven by the sine-squared strain wave (SSSW), it is seen that these two velocities will tend to uniformity with the friction coefficient or length of the body increasing or the wave speed decreasing when keeping the other parameters unchanged. Thus, the inertia term is ignorable for a large friction, a long body-length but a small wave-speed of the SSSW, which implies that the dynamical model can be reduced to the quasi-static one. The relative criterion is approximately given. As a result, the corresponding quasi-static model is employed to consider two typical drives, namely, the SSSW and the square strain wave (SSW). The result shows the shape change driven by the SSSW has an advantage in both the mean velocity and the average energy expended over that by the SSW when the necessary condition is satisfied. The analytical results are verified by numerical simulation.     

Dynamical behavior of a mobile system with two degrees of freedom near the resonance

The design of mobile robots that can move without wheels or legs is an important engineering and technological problem.Self-propelling mechanisms consisting of a body that has contact with a rough surface and moveable internal masses are considered.Mathematical models of such systems are presented in this paper.First,a model of a vibration driven robot that moves along a rough horizontal plane with isotropic dry friction is studied.It is shown that by changing the off-resonance frequency detuning in sign,one can control the direction of motion of the system.In addition,a locomotion system which moves in an environment with anisotropic viscous friction is considered.For all models,the method of averaging to obtain an algebraic equation for the steady-state"average"velocity of the system is used. Prototypes were constructed to compare the theoretical results with experimental ones.     

Kinematic analysis of a rolling tensegrity structure with spatially curved members

In this work, a tensegrity structure with spatially curved members is applied as rolling locomotion system. The actuation of the structure allows a variation of the originally cylindrical shape to a conical shape. Moreover, the structure is equipped with internal movable masses to control the position of the center of mass of the structure. To control the locomotion system a reliable actuation strategy is required. Therefore, the kinematics of the system considering the nonholonomic constraints are derived in this paper. Based on the resulting insight in the locomotion behavior a feasible actuation strategy is designed to control the trajectory of the system. To verify this approach kinematic analyses are evaluated numerically. The simulation data confirm the path following due to an appropriate shape change of the tensegrity structure. Thus, this system enables a two-dimensional rolling locomotion.

     

Global synchronization in fixed time for semi-Markovian switching complex dynamical networks with hybrid couplings and time-varying delays

This paper is concerned with the global synchronization in fixed time for semi-Markovian switching complex dynamical networks with hybrid couplings and time-varying delays in the presence of disturbances. Firstly, the property with respect to the global stability in fixed time is developed for semi-Markovian switching nonlinear systems. Subsequently, a novel sliding manifold with double integration is presented based on the proposed principle of convergence in fixed time. Under the designed sliding mode controller, the state trajectory of synchronization error system is driven to the prescribed sliding manifold in fixed time. In addition, the global stability in fixed time of sliding mode dynamics is proved analytically. By means of the stochastic Lyapunov–Krasovskii functional approach, the synchronization condition is established in terms of linear matrix inequalities; moreover, the stochastic fixed settling-time can be determined to any desired values in advance, via the configuration of parameters in the proposed controller. Finally, two numerical examples are provided to demonstrate the validity of the theoretical results and the feasibility of the proposed approach.

     

Magnetically driven foldable shell type swimmers at Stokes flow

This paper focuses on the interaction of low Reynolds number (Re) flows and thin shell type deformable structures in the context of flexible body locomotion and addresses the coupled field problem through a numerical solution framework. The thin structure is discretized by enhanced three-node finite elements and coupled with boundary element based treatment of Stokes flow in a monolithic manner. The locomotion is triggered and driven by an external magnetic field that generates displacement dependent body couples over the magnetically sensitive parts of the flexible structure. A particular novelty of the paper is the use of internal hinges through which very large rotations and structural deformations can be combined in an efficient way. Using this concept; new, on the fly locomotion direction reversal mechanisms can be generated as demonstrated by the foldable bi-directional swimmer.