机械阻尼器对刀具颤振抑制的理论分析及数值模拟

为了抑制高速铣削中的颤振影响,文中提出在刀具中心插入一个分层梁结构机械阻尼器．依靠刀具与阻尼器间的相对运动产生的摩擦阻尼-以耗散振动能量。通过理论分析和数值模拟的方法分别计算了接触压力和阻尼耗散功率．并对两种结果比较分析．找出了造成结果差异的主要原因。     

An intelligent sensor for detection of milling chatter

In this paper, a new real-time sensor system has been developed to detect chatter in milling operations. In the developed sensor system, a pattern recognition technique based on an unsupervised neural network using the adaptive resonance theory (ART) is adopted for detection of milling chatter. The features on the cutting force spectrum are fed into the sensor system to classify the milling process with or without chatter. The experimental results indicate that the proposed sensor system can accurately detect milling chatter regardless of the variation in cutting conditions.     

基于嵌入式系统的切削颤振在线监测技术研究

针对机床切削过程中的颤振现象难于实时、精确监测和控制的问题,设计了一种基于FPGA+ARM结构的切削颤振在线监测系统。切削振动数据采集主控制逻辑用FPGA来实现,ARM则用来实现采集数据的处理及快速发出颤振警报。     

A variable time delay compensator for multivariable linear processes

A variable time delay compensator based on the Smith predictor is proposed. Finite difference and cinematic techniques are employed for a numerical approximation of the variable delay. The resulting multivariable controller is analyzed for robustness using the structured singular value. The technique is demonstrated through two simulated systems: a single-input, single-output numerical example, and a cross-direction paper machine control problem.     

Suppression of nonlinear regenerative chatter in milling process via robust optimal control

During the milling process, self-excited vibration or chatter adversely affects tool life, surface quality and productivity rate. In this paper, nonlinear cutting forces of milling process are considered as a function of chip thickness with a complete third order polynomial (instead of the common linear dependency). An optimal control strategy is developed for chatter suppression of the system described through nonlinear delay differential equations. Counterbalance forces exerted by actuators in x and y directions are the control inputs. For optimal control problem, an appropriate performance index is defined such that the regenerative chatter is suppressed while control efforts are minimized. Optimal control law is determined based on variation of extremals algorithm. Results show that under unstable machining conditions, regenerative chatter is suppressed effectively after applying the optimal control strategy. In addition, optimal controller guarantees robust performance of the process in the presence of model parametric uncertainties.     

Detection of chatter vibration in a drilling process using multivariate control charts

Time series analysis and multivariate control charts are used to devise a real-time monitoring strategy in a drilling process. The process is used to produce holes with high length-to-diameter ratio, good surface finish and straightness. It is subject to dynamic disturbances that are classified as either chatter vibration or spiralling. A new nonparametric control chart for multivariate processes is proposed. It is used to detect chatter vibration which is dominated by single frequencies. The results showed that the proposed monitoring strategy can detect chatter vibration and that some alarm signals are related to changing physical conditions of the process.     

Optimal control for chatter mitigation in milling—Part 1: Modeling and control design

Active structural methods constitute a promising way to mitigate chatter vibrations in milling. This paper presents an active system integrated into a spindle unit. Two different optimal control strategies are investigated. The first one only considers the dynamics of the machine structure in the controller design and minimizes the influence of cutting forces on tool tip deviations. The second one takes explicitly the process interaction into account and attempts to guarantee the stability of the overall closed-loop system for specific machining conditions. The modeling and formulation used for both strategies are presented in this first part. A simulation allows the comparison of their respective working principle. The validation of the proposed concept in experimental conditions is described in the second part.     

Optimal control for chatter mitigation in milling—Part 2: Experimental validation

The productivity of milling operations in chatter-free conditions can be improved using active structural methods. This paper presents the use of a mechatronic system integrated into the spindle unit combined with two different optimal control strategies. The first one aims to minimize the influence of cutting forces on tool tip deviations. The second one explicitly considers the process interaction and attempts to stabilize the overall closed-loop system for specific machining conditions. The first part of this two-part paper describes the modeling and formulation used for both strategies. In this second part, the experimental validation of the proposed concept is presented.     

Iterative analysis of Markov regenerative models

Conventional algorithms for the steady-state analysis of Markov regenerative models suffer from high computational costs which are caused by densely populated matrices. In this paper, a new algorithm is suggested which avoids computing these matrices explicitly. Instead, a two-stage iteration scheme is used. An extended version of uniformization is applied as a subalgorithm to compute the required transient quantities “on-the fly”. The algorithm is formulated in terms of stochastic Petri nets. A detailed example illustrates the proposed concepts.     

不确定LTI-SISO系统的低通滤波时滞观测器控制

合理利用时滞可能获得意想不到的性能.研究表明,系统的不确定性以及受到的外部干扰可以利用时滞观测器来进行观测,从而实现系统的鲁棒控制.本文提出了一种低通滤波时滞观测器.避免了常规时滞观测器控制中出现的控制信号颤振,得到了一种结构新颖的控制器.仿真结果表明时滞观测器控制系统可以很好地抑制系统的不确定性以及受到的外部干扰,是一种性能优良的鲁棒控制方法.     

Observer-based stabilisation of a class of nonlinear systems in the presence of measurement delay

In this paper, the stabilising control problem for a class of nonlinear system in the presence of measurement delay is addressed. A full-order observer is designed to eliminate the effect of variable output time delay, which is bounded and known. Then, the estimated states are utilised for the state feedback control law to stabilise the considered control system. Lyapunov–Razumikhin approach is employed to analyse the stability of the closed-loop system. Unlike the previous work, the exponential convergence of the estimation error is ensured, rather than asymptotic convergence, by designing a delay-dependent gain of the observer. Moreover, comparison with similar work is also made in simulation to illustrate the effectiveness of the proposed strategy.     

Lyapunov matrices: Existence and uniqueness issues

A necessary and sufficient condition for the existence and uniqueness of Lyapunov matrices for neutral type single delay systems is presented.     

Lyapunov–Krasovskii functionals for scalar time delay equations

In this paper a procedure for construction of complete type Lyapunov–Krasovskii functionals for a scalar time delay equation is considered. The functionals depend on a scalar function which satisfies a time delay equation. It is shown that the scalar function satisfies also a high order delay free differential equation. In order to specify the function additional boundary conditions are given.Robust stability conditions based on the Lyapunov–Krasovskii functionals are presented.     

一种应用于DSP的快速位提取和插入实现方法

介绍了一种快速的位提取和插入实现方法。该方法通过使用快速的与或逻辑电路而不是较慢的多选1电路来减小时延;通过器件复用技术来减小面积。仿真和综合结果表明该方法大大优化了DSP的时延和面积,有助于提高DSP整体的运算速度和降低功耗。     

On analytic and algebraic observability of nonlinear delay systems

The observability of nonlinear delay systems has previously been defined in an algebraic setting by a rank condition on modules over noncommutative rings. We introduce an analytic definition of observability to ensure the local uniqueness of state and initial conditions that correspond to a given input-output behaviour. It is shown that an algebraically observable delay system can be reformulated as a system of ordinary differential equations. Analytic observability is then decided by the local uniqueness of solutions to a boundary value problem for this ODE system.     

时滞系统优化控制简介

介绍了时滞系统的优化方法,已基本解决了单变量时滞系统的优化控制问题.     

State‐Feedback Stabilization of Stochastic Nonlinear Systems with Time‐Varying Delay and Different Orders

This paper studies the problem of state feedback stabilization for a class of stochastic time‐varying delay nonlinear systems which are neither necessarily feedback linearizable nor affine in the control input. Based on the backstepping design method and the adding of a power integrator technique, a state feedback controller is constructed to ensure the origin of closed‐loop system is globally asymptotically stable in probability. The main design difficulty is how to deal with the different power orders, time‐varying delay and the nonsmooth system perturbations. The efficiency of the state feedback controller is demonstrated by a simulation example.     

Spectral expansion solution for a class of Markov models: application and comparison with the matrix-geometric method

Many two-dimensional Markov models whose state space is a semi-infinite strip (i.e. finite in one dimension and infinite in the other) can be solved efficiently by means of spectral expansion. This method and its application are described in the context of an M/M//N queue with general breakdowns and repairs. The results of experiments aimed at evaluating the relative merits of the spectral expansion and the matrix-geometric solutions are also presented.