机床非线性颤振的描述函数分析

本文采用描述函数方法分析机床的非线性颤振.以描述函数刻划切削过程复杂的非线性特性,并将非线性振动分析所依赖的复平面推广到三维空间进行稳定性分析。从而求出颤振振幅和颤振频率。该法不仅可揭示切削过程等效刚度系数和等效阻尼系数的变化,而且还可考察各切削参数对颤振频率和振幅的影响.结果表明,描述函数方法是分析机床颤振这个极其复杂的非线性系统的一个有效的手段.     

介电弹性作动器主动隔振模糊控制试验研究

采用模糊控制策略,开展介电弹性作动器的主动隔振性能试验研究。基于介电弹性材料的Maxwell应力模型建立了作动器的力电耦合模型,分析了作动器的非线性特性;针对隔振系统设计了Mamdani型模糊控制器,建立了控制电压信号与振动响应之间的关系;在此基础上,开展了介电弹性作动器主动隔振试验研究,并与加速度反馈控制进行了对比。试验结果表明,在相同驱动电压的情况下,基于模糊控制策略的主动隔振性能要优于加速度反馈控制,且能够显著降低由于非线性驱动力导致的倍频响应幅值,有助于提高隔振系统的稳定性。     

机床非线性颤振的分段线性化及其数学模型

通过引入非线性调制环节N(S),本文实现了非线性颤振的分段线性化,建立了统一的切削动力学系统模型。这一模型使线性颤振理论、非线性颤振理论趋于统一,并使超声振动切削抑制颤振的机理从理论上得到解释。     

The identification of the vibration control system parameters designed for continuous miner machines

The Continuous Miner machines are exposed to time dependent loads during normal operation of the rock cutting process. These loads cause vibrations, which have a negative influence on the whole structure of the machine. This phenomenon can be eliminated by applying passive or active vibration control systems (VCS). Generally these systems are coupled with additional elements, which provide dispersion or transfer energy. The energy thus acquired can also reinforce the intended function such as rock cutting operation in the case of mining machines. The objective of this paper is to present the method of numerical identification of VCS parameters for Continuous Miner machines. The main function of the presented system is to reduce displacement of cutting drum by using elastic element joined to machine chassis and applying appropriate algorithm of control of the angular velocity of cutting drum. The method described improves efficiency of mining and increases durability of machine. In order to determine mechanical and control parameters of VCS the genetic algorithm optimisation method conjugated with numerical modal analysis was used. Finally the transient dynamic analysis was performed for the full-scale model of Continuous Miner in order to verify VCS in normal working condition.     

作动器/传感器优化配置的研究进展

给出了作动器／传感器优化配置问题的数学描述,综述了作动器／传感器优化配置方法的发展现状．阐述了振动控制和模态试验中作动器／传感器优化配置的关系．并给出需要进一步研究的几个问题     

Vibration suppression in multi-tool ultrasonic machining to multi-external and parametric excitations

Ultrasonic machining （USM） is of particular interest for the machining of non-conductive, brittle materials such as engineering ceramics. In this paper, a multi-tool technique is used in USM to reduce the vibration in the tool holder and have reasonable amplitude for the tools. This can be done via dynamic absorbers. The coupling of four nonlinear oscillators of the tool holder and tools representing ultrasonic cutting process are investigated. This leads to a four-degree-of-freedom system subjected to multi-external and multi-parametric excitation forces. The aim of this work is to control the tool holder behavior at simultaneous primary, sub-harmonic and internal resonance condition. Multiple scale perturbation method is used to obtain the solution up to the second order approximations. The different resonance cases are reported and studied numerically. The stability of the system is investigated by using both phase-plane and frequency response techniques. The effects of the different parameters of the tools on the system behavior are studied numerically. Comparison with the available published work is reported.     

Analysis of Machining Stability for a Parallel Machine Tool

Abstract

Machine tool chatter is a self-excited vibration generated by chip thickness variation. It severely degrades the quality of the machined surface. The incidence of chatter is greatly affected by the dynamic characteristics of machine tool structure. This article extends chatter stability analysis to a machine tool equipped with a parallel mechanism. The vibration model of a parallel machine tool is derived, in which the legs of the parallel mechanism are considered as spring-damper systems. Then, the regenerative cutting dynamics is combined with the vibration model and stability analysis is performed. The chatter stability charts for various machining parameters are examined, with the example of the cubic parallel mechanism that is specially designed for machine tool use.     

用两种功能材料综合控制智能梁的振动

给出了用两种材料对梁进行振动控制的综合控制方法。采用多层分布压电层进行精密主动控制时,将压电传感层和压电致动层分割成若干单元来设计压电模态传感器和压电模态致动器,进而实现了梁的模态控制,同时利用形状记忆合金的超弹性特性对梁进行被动控制来抑制梁的大振幅振动,取得了很好的控制效果。     

Controlling the vertical shift of an isolated body based on the vibration of nonlinear systems with asymmetric damping forces

Asymmetric damping forces induce the equilibrium position of the isolated body to shift downward. Inspired by this phenomenon, this paper proposes the novel concept of shifting an isolated body based on the vibration of nonlinear systems with asymmetric damping forces. To verify the feasibility of this concept, a piecewise smooth isolation system is established. The incremental harmonic balance method is used to analyze the nonlinear vibration system and to obtain a steady-state analytical solution. The accuracy of the solution is verified by the Runge–Kutta method. Based on the analytical solution, the influences of some key parameters on the system vibration response are analyzed, revealing that the shift in the isolated body height increases with increasing excitation amplitude and damping asymmetry ratio. Additionally, this shift first increases and then decreases with increasing excitation frequency, reaching a peak near the natural frequency of the intermediate body. Finally, considering the complex structure, high energy consumption, and slow response of active suspension actuators, the proposed concept is applied to the tilt control of a vehicle. The simulation results show that the proposed methodology based on this concept can tilt a vehicle body to a certain angle in the turning direction, enabling the use of a semi-active actuator for vehicle tilt control to realize the control effect achieved by an active actuator.

     

非线性振动一种稳定的模糊控制方法研究

由于非线性振动系统的非线性本质,在于传统控制理论的线性控制器用于非线性振动控制效果不佳。本文针对非线性振动系统提出了一种模糊自适应滑模控制方案。     

Cutting process of composite materials: An experimental study

This paper focuses on experimental research of milling process of the epoxide-polymer matrix composite reinforced carbon fibers (EPMC—carbon composite). An influence of two control parameters, namely feed and rotational speed, on cutting forces is investigated. The experiment is conducted on a CNC machine with feed rate ranging from 200 to 720 mm/min and rotational speed from 2000 to 8000 rpm. The experimental time series are analysed by means of the delay coordinates method in order to find stable cutting regions and to recognize the kind of behaviour. Using this information, a new model for the cutting forces is proposed that can be used to build a new regenerative vibration model for EPMC milling.     

Forced vibration analysis of the milling process with structural nonlinearity,internal resonance,tool wear and process damping effects

In this paper, forced vibration analysis of an extended dynamic model of the milling process is investigated, in the presence of internal resonance. Regenerative chatter, structural nonlinearity, tool wear and process damping effects are included in the proposed model. Taking into account the average and first order expansion of Fourier series for cutting force components; their closed form expressions are derived. Moreover, in the presence of large vibration amplitudes, the loss of contact effect is included in this model. Analytical approximate response of the nonlinear system is constructed through the multiple-scales approach. Dynamics of the system is studied for two cases of primary and super-harmonic resonance, associated with the internal resonance. Under steady state motion, the effects of structural nonlinearity, cutting force coefficients, tool wear length and process damping are investigated on the frequency response functions of the system. In addition, existence of multiple solutions, jump phenomenon and energy transfer between vibration modes are presented and compared for tow cases of primary and super-harmonic resonances.     

Active control of vibration in small and medium amplitude range of elements in automotive systems

In this paper two different visco-elastic suspensions active system with pneumatic cylinder, and semi-active system with piezoceramics, are presented. The active suspension controls the vibration in medium-amplitude range and low frequency excitation. The semi-active suppression system controls the vibration in the audio frequency range and small amplitudes. The main aim of proposed solutions is to decrease the amplitude of vibration in resonance of conventional, passive suspensions. Both systems are worked out, especially for the better protection of the human body against harmful sounds and vibrations.     

Nonlinear-forced vibrations of piezoelectrically actuated viscoelastic cantilevers

This paper aims to study the nonlinear-forced vibrations of a viscoelastic cantilever with a piecewise piezoelectric actuator layer on its top surface using the method of Multiple Scales. The governing equation of motion is a second-order nonlinear ordinary differential equation with quadratic and cubic nonlinearities which appear in stiffness, inertia, and damping terms. The nonlinear terms are due to the piezoelectricity, viscoelasticity, and geometry of the system. Forced vibrations of the system are investigated in the cases of primary resonance and non-resonance hard excitation including subharmonic and superharmonic resonances. Analytical expressions for frequency responses are derived, and the effects of different parameters including damping coefficient, thickness to width ratio of the beam, length and position of the piezoelectric layer, density of the beam, and the piezoelectric coefficient on the frequency-response curves are discussed for each case. It is shown that in all these cases, the response of the system follows a softening behavior due to the existence of the piezoelectric layer. The piezoelectric layer provides an effective tool for active control of vibration. In addition, the effect of the viscoelasticity of the beam on passive control of amplitude of vibration is illustrated.     

压电智能环形板的主动控制

对在不同位置粘有任意多组压电传感器和压电执行器的轴对称弹性环形薄板的振动控制进行了研究．根据压电执行元件的等效作用量得到了压电智能环板的振动控制方程和传感方程,再利用分离变量法以及由传感器测得的电量和作用在执行器上电压之间的控制模式得到振动方程的全解．实行了对整体结构的主动控制．对不同的压电片布置进行了数值计算．结果表明：当离散分布压电元件布置越密,振动衰减的效果越佳     

STOCHASTIC VIBRATION CONTROL BASED ON PIEZOELECTRIC STACK INERTIAL ACTUATOR1)

本文主要研究了基于压电叠堆惯性作动器的随机振动控制方法并分析了控制力时滞对控制效果的影响规律。首先,对压电叠堆惯性作动器的动力学特性进行分析,建立了考虑惯性作动器动力学的主结构的随机动力学模型;接着,提出主结构随机振动 "线性"二次高斯控制(linear quadratic Gaussian,LQG)方法,并探讨了作动器惯性质量和刚度等对控制效果的影响规律;最后,研究了控制力时滞对控制效果的影响,并提出了利用时滞优化控制效果的方法。研究结果表明,压电叠堆惯性作动器对结构的随机振动具有较好的控制效果,当控制时滞时间$\tau = 0.025$s时控制效果可以得到进一步优化。     

浮筏的主动吸振控制实验研究

浮筏在低频减振方面存在较大不足,而这恰是主动减振的优势.将两者相结合,研究了浮筏的主动吸振控制问题.研制了一种主动吸振器,建立了以DSP F2812为核心的控制系统;提出了符号LMS算法,与广泛使用的滤波x-LMS等算法相比,该算法不需要精确的模型信息;在此基础上设计了自适应前馈主动吸振控制律,并在浮筏实验平台上进行主动吸振控制实验.实验结果表明,通过主动吸振控制,浮筏的低频减振能力得到了显著的改善.     

微型斯特林制冷机振动主动控制

本文研究了微型斯特林制冷机的振动主动控制问题,设计了一种全新的减振方案,即用直线电机推动一个质量平衡块来抑制制冷机的振动,采用基于前馈的自寻优控制器,控制算法由DSP芯片实现,使用该方案,制冷机的振动水平减小了一个数量级。     

Active control of time-delay in cutting vibration

The system dynamics of turning processes can be described by a delay differential equation. How to improve the stability and suppress the vibration of cutting is of an interesting topic. In this paper, a multiple time-delay controller is developed based on discrete optimal control method for the turning vibrations control. Numerical simulations are carried out to verify the efficiency of the controller. Results indicate the designed controller can suppress the cutting vibration efficiently and improve the stability of the cutting processes. The influence of designed time-delay and sampling time on the control performance is also discussed.