Surveillance and control of the yarn input tension on circular weft knitting machines : new approaches

The Yarn Input Tension - YIT is one of the most important parameters in weft knitting industry. This parameter must be maintained between limits in order to produce knitted fabric without faults. However, YIT is not the only parameter to control and monitor for preventing faults. The knitting elements and the knitting machine itself should be monitored to improve productivity and quality. The monitoring of the YIT can be used to detect the faults and at the same time controlled inside tight limits to prevent machine’s premature stop due to yarn break . This paper will present the recent developments made for monitoring and control the YIT. A surveillance system will be presented, a low cost force sensor will be suggested to substitute the present industrial solutions, and a new actuator for control of the YIT will be introduced.FCT - Fundação para a Ciência e a Tecnologia POSI/SRI/39824/200

Using multivariate statistics on detection of particular signals during production of knitwear

This paper reports the recent developments in the pursuit to correctly locate, identify and distinguish faults during production of weft knitted fabrics. For this purpose a major textile parameter – yarn input tension (YIT) - is analyzed by means of signal processing techniques. An overview of the entire process of gathering the information and fault detection is presented. For the purpose of distinguishing faults, Multivariate statistical methods, namely cluster and discriminant analysis are used, results presented and discussed. Finally, some conclusions are drawn from the obtained results and future developments are addressed.Fundação para a Ciência e a Tecnologia (FCT) - project POSI/SRI/39824/2001

Knitting process surveillance using time and frequency analysis

This paper will present and discuss the two major techniques used when inspecting an important parameter of the weft knitting industry: yarn input tension. The two techniques are frequency and time analysis. In this paper, the major features of each technique will be discussed and some examples will be presented.Fundadação para a Ciência e a Tecnologia (FCT

A new system for monitoring and analysis of the knitting process

Production monitoring is an important task for proper production planning. For this task the information that a system of this nature can possibly gather assumes significant importance. Among all the information available during production, the detection of faults assumes a crucial role since it directly affects the quality and productivity. This paper presents a system which was developed with the purpose of performing the analysis in real time of the knitting process, supplying the parameters of major concern for production and furthermore, allowing the detection, identification and location of faults.Fundação para a Ciência e a Tenologia (FCT)projecto POSI/SRI/39824/200

A system for knitting process monitoring and fault detection on weft circular knitting machines

From the production manager point of view, the knowledge of how well a knitting machine is working during production is very important. This information allows the manager to schedule all plans and also to know the overall production level of a manufacturing plant. For this purpose there are many system information packages. One of the most important items for production is the number of faults occurred while producing a fabric, since it directly influences productivity. With this subject in mind, this paper presents a system with a special emphasis on surveillance of the knitting process in order to detect, identify and locate faults during production, by monitoring the yarn input tension. The system also provides the user with a valuable set of information related with production. Finally, the paper presents some of the techniques used to detect the faults.Fundação para Ciência e Tecnologia (FCT) project POSI/SRI/39824/200

Techniques for unveiling faults during knitting production

Detection of faults during production of knitted fabric is crucial for improved quality and productivity. The yarn input tension is an important parameter that can be used for this purpose. This paper will present and discuss a computer-based monitoring system which was developed for the detection of faults and malfunctions during the production of weft knitted fabric, using the yarn input tension. In particular, it will present the method used to unveil the appearance of faults, based on two different approaches: comparison with a previously acquired waveform and a particular pattern matching technique - Average Magnitude Cross-Difference.Fundação para a Ciência e a Tecnologia (FCT)

Electromagnetic energy harvesting using magnetic levitation architectures: a review

Motion-driven electromagnetic energy harvesters have the ability to provide low-cost and customizable electric powering. They are a well-suited technological solution to autonomously supply a broad range of high-sophisticated devices. This paper presents a detailed review focused on major breakthroughs in the scope of electromagnetic energy harvesting using magnetic levitation architectures. A rigorous analysis of twenty-one design configurations was made to compare their geometric and constructive parameters, optimization methodologies and energy harvesting performances. This review also explores the most relevant models (analytical, semi-analytical, empirical and finite element method) already developed to make intelligible the physical phenomena of their transduction mechanisms. The most relevant approaches to model each physical phenomenon of these transduction mechanisms are highlighted in this paper. Very good agreements were found between experimental and simulation tests with deviations lower than 15%. Moreover, the external motion excitations and electric energy harvesting outputs were also comprehensively compared and critically discussed. Electric power densities up to 8 mW/cm^3 (8 kW/m^3) have already been achieved; for resistive loads, the maximum voltage and current were 43.4 V and 150 mA, respectively, for volumes up to 235 cm^3. Results highlight the potential of these harvesters to convert mechanical energy into electric energy both for large-scale and small-scale applications. Moreover, this paper proposes future research directions towards efficiency maximization and minimization of energy production costs.in publicatio

Advancements in on-line monitoring and control of parameters in knitting and sewing processes

This paper presents a summary of the developments in process control in textile processes at the University of Minho, by a multidisciplinary research group involving three different departments (Textile, lectronic and Mechanical Engineering). The studies target the automatic process parameter monitoring and control in the areas of industrial sewing and knitting.Fundação para a Ciência e a Tecnologia (FCT)