On sufficient conditions to keep differential flatness under the addition of new inputs

It is well known that a controllable nonlinear system will retain its controllabality when new actuator inputs are added to it. In this article, we ask the question if a system, linearisable by static or dynamic feedback, will retain this property when new actuator inputs are added to it. Alternatively, a system may be linearisable after removing one or more inputs from it. This question is important in the design of robotic systems from the perspective of trajectory planning and control, specially if they are under-actuated. The goals of this article are as follows: (i) using counter examples, we first show that feedback linearisability may not be preserved when new inputs are added to a robotic system, (ii) sufficient conditions are determined when a system will retain this property under the addition of new inputs. The theory is illustrated through some examples from the robotics field.     

Interference checking approach with tolerance based on assembly dimension chain

CAD model with nominal dimension is implemented in interference checking of assembly simulation of aircraft complex parts at present,which causes inadequate availability.In order to address this challenging issue,interference checking method with tolerance based on assembly dimension chain was proposed.Worst case and maximum error probability of tolerance of composing loop were used,and CAD models were respectively re-constructed and inserted into simulation system.Before dynamic interference checking,engineering semantic interference condition was set to assembly requirements.Finally,the interface checking result was a basis for reasonability of assembly process and tolerance.A prototype system was developed based on the above research.     

A new approach for predicting and collaborative evaluating the cutting force in face milling based on gene expression programming

Cutting force is one of the fundamental elements that can provide valuable insight in the investigation of cutter breakage, tool wear, machine tool chatter, and surface finish in face milling. Analyzing the relationship between process factors and cutting force is helpful to set the process parameters of the future cutting operation and further improve production quality and efficiency. Since cutting force is impacted by the inherent uncertainties in the machining process, how to predict the cutting force presents a significant challenge. In the meantime, face milling is a complex process involving multiple experts with different domain knowledge, collaborative evaluation of the cutting force model should be conducted to effectively evaluate the constructed predictive model. Gene Expression Programming (GEP) combines the advantages of the Genetic Algorithm (GA) and Genetic Programming (GP), and has been successfully applied in function mining and formula finding. In this paper, a new approach to predict the face milling cutting force based on GEP is proposed. At the basis of defining a GEP environment for the cutting force prediction, an explicit predictive model has been constructed. To verify the effectiveness of the proposed approach, a case study has been conducted. The comparisons between the proposed approach and some previous works show that the constructed model fits very well with the experimental data and can predict the cutting force with a high accuracy. Moreover, in order to better apply the constructed predictive models in actual face milling process, a collaborative model evaluation method is proposed to provide a distributed environment for geographical distributed experts to evaluate the constructed predictive model collaboratively, and four kinds of collaboration mode are discussed.     

A linear differential operator approach to flatness based tracking for linear and non-linear systems

This contribution presents a flatness based solution to the tracking for linear systems in differential operator representation. Since the differential operator representation is a flat system representation, tracking controllers can easily be designed using dynamic output feedback. Then, the differential operator approach for flatness based tracking of linear systems is extended to non-linear systems. The design of the resulting linear time varying dynamic output feedback controller is based on a linearization about the trajectory, which directly yields the differential operator representation. Different from the non-linear flatness based controller design the new approach uses linear methods, both in stabilizing the tracking and in computing the output feedback controller. The proposed design procedure assures exact tracking in the steady state when no disturbances are present. A simple example demonstrates the design of a dynamic output feedback controller for the tracking of a non-linear system.     

A Lie-Backlund approach to equivalence and flatness of nonlinearsystems

A new system equivalence relation, using the framework of differential geometry of jets and prolongations of infinite order, is studied. In this setting, two systems are said to be equivalent if any variable of one system may be expressed as a function of the variables of the other system and of a finite number of their time derivatives. This is a Lie-Backlund isomorphism. The authors prove that, although the state dimension is not preserved, the number of input channels is kept fixed. They also prove that a Lie-Backlund isomorphism can be realized by an endogenous feedback. The differentially flat nonlinear systems introduced by the authors (1992) via differential algebraic techniques, are generalized and the new notion of orbitally flat systems is defined. They correspond to systems which are equivalent to a trivial one, with time preservation or not. The endogenous linearizing feedback is explicitly computed in the case of the VTOL aircraft to track given reference trajectories with stability     

DHNN优化设计新方法及在板形模式识别的应用

基于离散Hopfield神经网络(DHNN)的联想记忆能力,提出了随机扰动优化设计DHNN的新方法.该方法降低了DHNN对权值矩阵的苛刻要求,避免进入伪稳定点;并将其用于板形模式识别,采用勒让德多项式表示常见的6种板形基模式,不需大量的测试样本来训练网络,是一种更简单、实用的板形模式识别新方法,为实现板形控制提供依据,仿真结果证明了这种方法的可行性     

A model-based approach to form tolerance evaluation using non-uniform rational B-splines

Tolerance evaluation is critical to quality assurance in modern manufacturing. In contrast to traditional measurement which relies on specific hard gauges, coordinate measuring machines provide more flexibility for dimensional measurement and tolerance evaluations. To fully automate CMM inspection and tolerance evaluation, CAD/CMM integration is an important key. Although the subject of CAD-directed inspection has been widely researched, CAD model-based tolerance evaluation has received less attention. This paper presents a CAD model-based approach for evaluating general form tolerances using non-uniform rational B-splines. Unlike classical methods which construct substitute geometric features from the measurement data, this method evaluates form tolerances by comparing the measurement data with a nominal CAD model. Non-uniform rational B-spline (NURBS) is used to represent general form features since NURBS offers a common format for modeling different form features. With this unified database, a general best-fit algorithm is developed that can be applied to the evaluation of various form tolerances. Computer simulations have been performed on different form features to study the robustness and efficiency of the algorithm. Application to the profile analysis of turbo charger housing and turbine blade die segments are also presented.     

一种基于相容关系的群体共识达成方法

针对一类评价信息不完全的多属性群决策问题中的群体判断的共识性进行研究,提出一种基于相容关系的群体共识达成方法。该方法不需进行群体共识度的计算,避免了评价信息不完全时直接计算群体共识度的困难;对于专家没有给出的评价信息,不需要进行评估和填充,避免了评估和填充缺失值时所需进行的复杂计算。最后通过一个实例对所提出方法的有效性和实用性进行了说明。     

A comprehensive study on fault tolerance in stream processing systems

Stream processing has emerged as a useful technology for applications which require continuous and low latency computation on infinite streaming data. Since stream processing systems (SPSs) usually require distributed deployment on clusters of servers in face of large-scale of data, it is especially common to meet with failures of processing nodes or communication networks, but should be handled seriously considering service quality. A failed system may produce wrong results or become unavailable, resulting in a decline in user experience or even significant financial loss. Hence, a large amount of fault tolerance approaches have been proposed for SPSs. These approaches often have their own priorities on specific performance concerns, e.g., runtime overhead and recovery efficiency. Nevertheless, there is a lack of a systematic overview and classification of the state-of-the-art fault tolerance approaches in SPSs, which will become an obstacle for the development of SPSs. Therefore, we investigate the existing achievements and develop a taxonomy of the fault tolerance in SPSs. Furthermore, we propose an evaluation framework tailored for fault tolerance, demonstrate the experimental results on two representative open-sourced SPSs and exposit the possible disadvantages in current designs. Finally, we specify future research directions in this domain.     

A new optimization model to support a bottom-up approach to facility design

The facility layout problem is typically solved in what is referred to as a “top-down approach” of block layout design followed by detailed layout determination. However, a number of research efforts recently have challenged this approach, producing a reformulated bottom-up approach to the facility layout problem. In this paper we consider the bottom-up approach, applying a tighter formulation than prior efforts and investigating the solvability limits of the new model. Empirical testing of the new bottom-up layout model indicates that although this model produces more usable output, as judged by industry experts, it is approximately three times harder to solve. Valid inequalities and special cases are identified to help improve the formulation's solvability.