Artificial neural networks and acoustic emission applied to stability analysis in gas metal arc welding

Abstract

The present paper describes the application of neural networks to obtain a model for estimating the stability of gas metal arc welding (GMAW) process. A neural network has been developed to obtain and model the relationships between the acoustic emission (AE) signal parameters and the stability of GMAW process. Statistical and temporal parameters of AE signals have been used as input of the neural networks; a multilayer feedforward neural network has been used, trained with back propagation method, and using Levenberg Marquardt's algorithm for different network architectures. Different welding conditions have been studied to analyse the incidence of the parameters of the process in acoustic signals. The AE signals have been processed by using the wavelet transform, and have been characterised statistically. Experimental results are provided to illustrate the proposed approach. Finally a statistical analysis for the validation of the experimental results obtained is presented. As a main result of the study, the effectiveness of the application of the artificial neural networks for modelling stability analysis in welding processes has been demonstrated. The regression analysis demonstrates the validity of neural networks to predict the stability of welding process using the statistical characterisation of the signal parameters of AE that have been calculated.     

Towards a simple and safe Objective Caml compiling framework for the synchronous language SIGNAL

This paper presents a simple and safe compiler, called MinSIGNAL, from a subset of the synchronous dataflow language SIGNAL to C, as well as its existing enhancements. The compiler follows a modular architecture, and can be seen as a sequence of source-to-source transformations applied to an intermediate representation which is named Synchronous Clocked Guarded Actions (S-CGA) and translation to sequential imperative code. Objective Caml (OCaml) is used for the implementation of MinSIGNAL. As a modern functional language, OCaml is adapted to symbolic computation and so, particularly suitable for compiler design and implementation of formal analysis tools. In particular, the safety of its type checking allows to skip some verification that would be mandatory with other languages. Additionally, this work is a basis for the formal verification of the compilation of SIGNAL with a theorem prover such as Coq.     

Towards a verified compiler prototype for the synchronous language SIGNAL

SIGNAL belongs to the synchronous languages family which are widely used in the design of safety-critical real-time systems such as avionics, space systems, and nuclear power plants. This paper reports a compiler prototype for SIGNAL. Compared with the existing SIGNAL compiler, we propose a new intermediate representation (named S-CGA, a variant of clocked guarded actions), to integrate more synchronous programs into our compiler prototype in the future. The front-end of the compiler, i.e., the translation from SIGNAL to S-CGA, is presented. As well, the proof of semantics preservation is mechanized in the theorem prover Coq. Moreover, we present the back-end of the compiler, including sequential code generation and multithreaded code generation with time-predictable properties. With the rising importance of multi-core processors in safetycritical embedded systems or cyber-physical systems (CPS), there is a growing need for model-driven generation of multithreaded code and thus mapping on multi-core. We propose a time-predictable multi-core architecture model in architecture analysis and design language (AADL), and map the multi-threaded code to this model.     

Process parameter selection for optimising weld bead geometry in stainless steel cladding using Taguchi's approach

Abstract

In the present study, the Taguchi method, a tool to design optimisation for quality, is used to find the optimal welding process parameters for cladding of austenitic stainless steel. An orthogonal array, the signal to noise (S/N) ratio, and the analysis of variance (ANOVA) are employed to investigate the effect of process parameters on weld bead characteristics. The present study was conducted by depositing AISI 317L onto an IS : 2062 structural steel substrate by the flux cored arc welding (FCAW) process under the shield of 95%Ar and 5%CO₂ gas mixture. The weld bead parameters are optimised individually (single objective) as well as collectively (multiobjective) to get the desired quality characteristics. The results show that these techniques can be used effectively to control the process parameters in cladding with certain limitations.     

Time–frequency diagram applied to stability analysis in gas metal arc welding based on acoustic emission

Abstract

Time–frequency diagram is applied to estimating the stability of gas metal arc welding process. A methodology has been developed to obtain indexes based on image processing of the spectrogram in order to evaluate the relationship between the spectrogram and the stability of process. The acoustic emission (AE) signals have been processed and characterised to obtain the spectrogram of the acoustic signals generated by arc. Statistical analysis of image generated by spectrogram and temporal parameters of AE signals has been used as a tool to obtain a method for stability evaluation. As a main result of the research, it demonstrates the effectiveness of the application of image processing of the time–frequency diagram for evaluating the stability in the welding processes. The results demonstrate the validity of this method to characterise the stability using the image characterisation.     

Enhancing the Signal-to-Interference Ratio in Digital Direct-Sequence Spread-Spectrum Receivers

Digital direct-sequence spread-spectrumreceivers are known to suffer from severe impairments indeterministic types of interference, due to inherentanalog-to-digital converter nonlinearities. In thepresent paper a noncoherent digital direct-sequencespread-spectrum receiver with an integrated adaptiveinterference reduction scheme is presented. Adaptiveinterference reduction is accomplished by exploring the nonlinearity of a 2-bit analog-to-digitalconverter with a pair of magnitude thresholds centeredaround a fixed sign threshold. The magnitude thresholdsare adjusted by means of a statistical control loop. The received signal's magnitudedistribution and zero crossings are used to estimate thecomposition of the interference. The performance of theproposed receiver in the presence of combined additive white Gaussian noise and continuous-waveinterference has been investigated and compared to thebehavior of ideal digital receivers of comparably lowcomplexity as the approach presented. The digitalreceivers studied for comparison use either single-bithard-limiters or 2-bit analog-to-digital converters withadaptive thresholds.     

平顶山某矿PC控制井下电机车运输信集闭系统的设计与研究

本文对平顶山某矿可编程控制器(PC)在井下电机车运输信集闭系统的设计与研究进行了探讨,文章较详细介绍了设计方案确定原则,PC机的硬件配置和软件设计框图,对PC机在井下电机车信集闭的推广运用有一定的参考价值.     

New stability index for short circuit transfer mode in GMAW process using acoustic emission signals

Abstract

A new index for the analysis of stability of GMAW processes taking as a base the acoustic emission generated by the arc during the short circuit metal transfer is presented in the present work. The incidence of parameters of process is analysed in the indices of the acoustic emission signal, as well as its influence on the stability, evaluated through a new proposed index. The results obtained allowed having a relationship between acoustic signals and arc voltage signals, and demonstrated the validity of proposed index of acoustic emission for analysis of stability of GMAW process. The obtained results were then compared with other classic stability analysis methods based on statistical analysis of temporal signals of arc voltage. Finally a statistical analysis for the validation of the obtained experimental results was carried out. As a result of the investigation, the effectiveness of the method proposed as a new way for the analysis of stability is demonstrated. The research can contribute towards a new standard to evaluate the stability in welding processes.     

面向同步规范的并行代码自动生成

随着对安全攸关实时系统功能与非功能要求的日益增加,使用多核技术将成为发展趋势.如何在多核平台条件下保证系统运行的可信任性及可靠性是学术上和应用上的关键问题.目前基于形式化方法的系统设计、验证以及自动代码生成已经在单核平台上形成很多研究成果,但在多核平台上的研究仍面临许多科学问题.同步语言SIGNAL是一种被广泛应用于安全攸关实时系统功能设计的形式化方法,适用于对系统确定性并发行为的描述.SIGNAL编译器也支持将同步规范SynchronousSpecification）生成仿真代码,以对其进行验证与分析.然而现有研究较少关注从SIGNAL同步规范到支持跨平台并行代码的生成方法.本文研究面向SIGNAL同步规范的并行自动代码生成方法.提出了方程依赖图EDG的概念,将SIGNAL规范转换为EDG以分析其全局数据依赖关系;研究了对EDG进行任务划分获取规范中可以并行执行部分的算法;最后,以跨平台并行编程API-OpenMP作为对象,结合程序中信号的时钟关系,将并行任务映射到OpenMP并行代码,并进行了实例验证.     

Accumulation of coincidence site lattice boundaries during grain growth

Abstract

Monte Carlo simulations were used to investigate the effect of grain growth on the coincidence site lattice (CSL) boundary content of randomly textured polycrystals. Each grain was assigned an orientation, and grain boundary properties were dependent on both the boundary misorientation and the CSL character. While low misorientation angle boundaries (LABs) increase during growth, the fraction of CSL boundaries does not change with time. Decreasing CSL boundary energy and mobility did not alter these results. In contrast with LABs, which are characterised by a scalar misorientation angle, a particular combination of three independent rotation variables is required to create a low energy CSL boundary; thus, these boundaries are unlikely to form or to persist in a random polycrystal. While texture influences boundary formation, a texture that can enhance CSL boundaries is not apparent. Boundary plane effects should not increase CSL fraction during grain growth.