Dynamic recursive decoupling method for closed-loop flexible mechanical systems

Optimization of noisiness of mechanical system by using a pneumatic tuner during a failure of piston machine

Sensor-based force decouple controller design of macro–mini manipulator

Control of dynamic vibration is critical to the operational success of many flexible mechanism systems. This paper addresses the problem of vibration control of such mechanisms through passive damping, using constrained layer damping treatment technique. A new type of shape function for three layer frame element containing a viscoelastic layer is developed. The equations of motion of the damped flexible mechanism are derived. Modal loss factors of this kind mechanisms are predicated from undamped normal mode by means of the modal strain energy method. Comparisons between the results obtained by this paper and the results obtained by exact solution of the governing equations for a well known sandwich beam demonstrate that the method presented in this paper is correct and reliable. Application of this method in predication of modal damping ratios for damped mechanisms is discussed. It is believed that the method of this paper hold the greatest potential for optimal design of damped flexible mechanism systems.

This paper presents a flexible mechanical system of the snake-like robot type. Our mechanical system is a hyper-redundant system consisting of 23 rigid solid-type elements (vertebra) actuated by means of 6 flexible wires. The developed constructive solution is intended to be a system with very high flexibility with applicability in various fields of activity in which exploration and operation in small or dangerous spaces is a priority. Also, due to the small size of the components, the geometry of the active surfaces, and the mode of operation, the proposed system can be a solution for medical applications such as Single Port Access (SPA) surgery. The virtual design is made using SOLIDWORKS software. The kinematic and dynamic simulation of the constructive solution is performed with the ADAMS software. The ADAMS-View module allows dynamic analysis on models that contain both rigid and deformable bodies, such as drive wires. Using dynamic simulation, depending on the mode of actuation (sequence and duration) of the elastic wires, the deformed shape as well as the working space of the flexible unit is obtained, which allows us to validate the constructive solution. Using rapid prototyping techniques based on the virtual prototype we will create a flexible mechanical system.

In this paper, an efficient normalization based adaptive algorithm is used for active noise control in mechanical systems in order to reject extensive disturbances. The proposed implementations are suitable in applications like various motors, generators, aircrafts, battle field and elevators, etc where noise reduction is very important. In the experiments, the authors used several variants of the familiar Filtered X Least Mean Square (FXLMS) algorithm. In FXLMS the vector of past inputs is first filtered by the secondary path transfer function, hence it is named as filtered X LMS. These modified results normalized FXLMS (NFXLMS) and normalized clipped FXLMS (NCFXLMS) algorithms, leads to fast convergence, better noise rejection capability. The NCFXLMS algorithm requires only half of the multiplications requires than NFXLMS. This type of low complexity strategy is not used in active noise control application in mechatronic systems. Simulation results prove that the proposed active noise cancellers provide better performance in terms of signal to noise ratio than the conventional FXLMS.

Magnetorheological (MR) dampers have received remarkable attention due to being a potential technology to conduct semi-active control in mechanical systems in order to effectively suppress vibration. It is therefore important to understand the dynamic behaviour of such devices whose non-linear hysteresis is a complicated phenomenon. In the study, an MR damper has been designed, fabricated, tested and then its dynamic behaviour has been modelled with the classical Bouc-Wen hysteretic model. After that, the seven parameters of this model have been expressed in terms of only current excitation. By this, the total damping force has been given by a compact form in which the only independent variable is the current excitation. Finally, the model has been verified with experimental data and a good agreement has been observed.

We propose a class of second order mechanical systems on Grassmann manifolds that converge to the dominant eigenspace of a given symmetric matrix. Such second order flows for principal subspace analysis are derived from a modification of the familiar Euler-Lagrange equation by inserting a suitable damping term. The kinetic energy of the system is defined by the Riemannian metric on the Grassmannian while the potential energy is given by a trace function, that is defined by the symmetric matrix. Convergence of the algorithm to the dominant subspace is shown for generic initial conditions and a comparison with the Oja flow is made.

Dynamic responses of flexible linkage mechanisms with viscoelastic constrained layer damping treatment

<abstract> <p>In this paper, in order to provides a powerful new tool for quantitative and qualitative analysis of dynamics properties in flexible mechanical multibody systems, the symmetry theory and numerical algorithms for preserving structure in modern analytical mechanics is introduced into flexible multibody dynamics. First, taking the hub-beam systems as an example, the original nonlinear partial differential-integral equations of the system dynamics model are discretized into the finite-dimensional Lagrange equations by using the assumed modal method. Second, the group analysis theory is introduced and the criterion equations and the corresponding conserved quantities of Noether symmetries are given according to the invariance principle, which provide an effective way for analytic integral theory of dynamic equations. Finally, a conserved quantity-preserving numerical algorithm is constructed by coordinates incremental discrete gradient, which makes full use of the invariance of conserved quantity to eliminate the error consumption for a long time. The simulation results show that the deeper mechanical laws and motion characteristics of flexible mechanical multibody systems dynamics can be obtained with the help of symmetries and conserved quantities, which can provide reference for more precise dynamic optimization design and advanced control of systems.</p> </abstract>

The purpose of this study is to develop a design method of a flexible mechanical system using a hydrostatic skeleton driving mechanism. The system consists of two types of flexible bags in order to separate the roles into a structural part and an actuator part. One is a constant pressure bag as a structural part, and the other is a pressure tunable bag as an actuator part. There are remarkable advantages of using this system as listed below: i) Because of the flexibility, the system can be applied safely to various kinds of workspaces where living beings and mechanical systems work together. ii) Because of using two types of bags, driving efficiency of the system is higher than that of other flexible systems using only one type of bag. The theoretical design method of the system is required to realize these advantages. In order to realize the design method, it is important to calculate the structural strength of the structural part and driving force generated by the actuator part. In this paper, strength evaluation of the structural part is performed by nonlinear FEA. From the comparison between the analytical result and measurement results, deflection of the structural part is obtained. On the other hand, the driving force that is generated by the actuator part is also analyzed. Based on the analytical results, an empirical equation about the driving force is induced. The validity of the empirical equation is confirmed by the comparison between measurement values and the values of the empirical equation. These results will contribute to an optimum design of the proposed flexible mechanical system.

This investigation is concerned with the thermoelastic analysis of flexible multibody machine-tool mechanisms using the finite-element method. Thermoelastic response of the machine tool is obtained by discretizing the machine tool into a number of simple elements and calculating the thermal stress and strain of each element under the average temperature rise. The generalized thermoelastic forces associated with the generalized elastic coordinates are then determined using the virtual work. The nonlinear dynamic behavior of the machine-tool mechanism due to the application of a constant cutting force as well as a chattering (dynamic) force, with and without thermal effects, is analyzed. The chattering force is obtained by considering the cutting force variations due to the variation of undeformed chip thickness and the rate of penetration of the tool, as a result of tool deformation. In this investigation, the machine-tool mechanism is considered as a multibody system consisting of interconnected rigid and flexible bodies that undergo large angular rotations. Bending and axial deformation of the elastic bodies in the system are considered. Component mode synthesis techniques are employed in order to reduce the number of elastic coordinates and the system differential equations of motion and nonlinear algebraic constraint equations are written in terms of a coupled set of reference and modal elastic coordinates. The formulation is exemplified using a crank-shaper mechanism wherein the flexibility of the tool as well as the flexibility of the mechanism links are considered.

摘要: 双框架磁悬浮控制力矩陀螺(Double-gimbal magnetically suspended control moment gyroscope, DGMSCMG)的框架伺服系统是一个多变量、非线性且强耦合的复杂系统. 为了进一步提高框架伺服系统的控制精度,本文提出了一种基于电流模式的动态逆系统解耦方法,通过对功放系统的动态补偿有效克服了未建模动态对解耦性能的影响,采用自适应滑模控制器有效提高了系统的跟踪特性. 对比仿真结果证明了该方法的有效性和优越性 关键词: 双框架磁悬浮控制力矩陀螺 / 框架伺服系统 / 动力学耦合 / 动态逆解耦 / 动态补偿

Horizontal axis wind turbine (HAWTs) structures, throughout the years, have presumed to be of relatively simple construction, but wind-induced aerodynamic vibrations, wind-field conditions, and power requirements tend to lead to the need for increasingly complicated designs. One phenomenon that requires special attention is the gyroscopic or Coriolis effect. In general, blades design codes are written to optimize for lightness and slenderness, but also to withstand excitations at high frequency. As a result, gyroscopic motion derives as a nonlinear dynamic condition in the out-of-plane direction that is difficult to characterize by means of the well-known vibrational theory that has been established for their design and analysis. The present study develops and presents a probabilistic analysis of the precession — gyroscopic — effects of a wind turbine model developed for tapered-swept cross-sections of nt degree with nonlinear variations of mass and geometry along the body of the blade. A dynamic orthogonal decoupling method is utilized to successfully perform the aeroelastic analysis by decoupling the damped-gyroscopic equations of motion, as a result of the addition of Rayleigh damping — symmetric proportional mass and stiffness — within the linear system in study. Results are valid for yaw-free rotor configurations by means of unknown and random (though bounded) yaw rates. Simultaneously, those results can easily be expanded for yaw-controlled mechanisms. The yaw-free assumption presents a higher risk of potential reliability expectations, given the stochastic impairment of the gyroscopic nature that is present for out-of-plane axis motions, requiring special attention at higher frequencies. This impairment becomes particularly troublesome for blade profiles with tapered-swept cross-section variations. This uncertainty can be minimized by incorporating a mathematical framework capable of characterizing properly the yaw action such that gyroscopic effects can be fully interpreted and diagnosed. In summary, the main goal is to decipher the complexity of gyroscopic patterns of flexible rotor blades with complex shape configurations, but also to provide substantial elements to successfully approach yaw-mechanics of tapered-swept rotor blades.

<div class="htmlview paragraph">In this paper methods for the nonlinear dynamic analysis of multibody vehicle systems are presented. A total Lagrangian finite element formulation for deformable bodies of the vehicle systems that undergo large translational and rotational displacements is developed. A set of nonlinear dynamic differential equations are developed in a closed form for each finite element in terms of the reference as well as the nodal elstic coordinates and their time derivatives. These equations are expressed in terms of a set of element invariants that depend on the assumed displacement field. The invariants of the deformable body that undergoes large reference translational and rotational displacements can be obtained by assembling the invariants of its elements using a standard finite element procedure. The nonlinear dynamic equations of the deformable body can then be obtained by assembling the nonlinear element equations. Both the consistent and lumped mass finite element formulations are discussed. The dynamic formulations presented in this paper are exemplified using multibody vehicle systems that consist of interconnected rigid and deformable bodies. Numerical results are obtained using the general purpose computer program <b>DAMS</b> (Dynamic Analysis of Multibody Systems).</div>

By analyzing recent schemes for preparing the chain cluster state, we find that the existence of long-range couplings between qubits will induce a quick decay of the fidelity of the cluster state. We propose some schemes for eliminating the effect of the next-nearest-neighbor interactions in the XY and Ising models by dynamical decoupling method. In our approach, the undesired next-nearest-neighbor interactions are effectively suppressed and the fidelity of the generated cluster state is greatly improved by the pulse operations.