Helder Carvalho

Textile moisture sensor matrix for monitoring of disabled and bed-rest patients

This paper presents the development of a moisture sensor matrix based on textile materials provided with conductive yarns. The measurement principle is based on the measurement of electrical resistance of the textile. The main purpose of this work is to support research on the prevention of pressure ulcers in people committed to bed rest or using wheelchairs. In the first stage of development, the project is studying the relation between physical parameters, exposure time and the levels of discomfort and pain experienced by the patients. In a later stage, the underlying measurement and evaluation principles will be used to develop single sensors or sensor matrixes to be connected to active patient monitoring systems able to warn in situations of excess of moisture and/or pressure (produced by sweat, open wounds, incontinence, etc.).

Study of vital sign monitoring with textile sensors in swimming pool environment

This paper presents the results of a series of experiments aiming at the optimisation of vital sign monitoring using textile electrodes to be used in a swimsuit. The swimsuit will integrate sensors for the measurement of several physiological and biomechanical signals; this paper will focus on ECG and respiratory movement analysis. The data obtained is mainly intended to provide tools for evaluation of high-performance swimmers, although applications can be derived for leisure sports and other situations. A comparison between electrodes based on different materials and structures, behaviour in dry and wet environments, as well as the behaviour in different extension states, will be presented. The influence of movement on the signal quality, both by the muscular electrical signals as well as by the displacement of the electrodes, will be discussed. The final objective is the integration of the electrodes in the swimsuit by knitting them directly in the suits fabric in a seamless knitting machine.

Deposition of conductive materials on textile and polymeric flexible substrates

This paper describes the study, analysis and selection of textile and similar materials to be used as flexible substrates for thin conductive film deposition, in the context of integrating electronics into textiles. Kapton® polyimide was chosen as reference substrate material, was characterized regarding mechanical and electrical properties and was used as a basis for a comparison with several textile substrates. Samples were fabricated using physical vapour deposition (thermal evaporation) to deposit a thin layer of aluminium on top of Kapton and textile substrates. The measurement of electrical resistance of the thin aluminum films was carried out using the Kelvin method. To characterize the mechanical behaviour of the substrate and aluminum film, several mechanical tests were performed and results were compared between Kapton and these textile materials. The chemical composition of the textile substrates and aluminum films as well as the continuity of the films was characterized. This selection process identified the material that was closer to the behaviour of polyimide, a flexible, but non-elastic woven textile coated on both sides with PVC.

Measurement and analysis of needle penetration forces in industrial high-speed sewing machine

This paper presents a system that allows the measurement of parameters of needle penetration during high-speed sewing. The system has been developed as a tool for analysis of the most important mechanical effects occurring during high-speed sewing. It allows the measurement of several sewing process variables, namely the needle penetration and withdrawal forces. The objective of this work is the development of real-time control and monitoring devices, as well as offline process planning tools for industrial sewing. The evaluation of needle penetration forces is a particularly critical aspect. A fault-free needle penetration depends mainly on the materials properties and needle choice. Needle penetration force is one of the variables whose measurement is important for the pre-screening analysis of quality problems (‘sewability testing’) and for real-time quality monitoring. This article describes the experimental results obtained and discusses potential applications in process planning tools and monitoring devices.

Measurements and feature extraction in high-speed sewing

This paper presents the development of signal acquisition and analysis equipment for the measurement of sewing parameters on a high-speed overlock sewing machine. The objective of the work was to provide investigators of the textile area with hardware and software to ease the investigation on the dynamical behaviour of the following sewing parameters: force on needle bar; and presser-foot and thread tensions. It should also have enough flexibility to incorporate further signal entries, and provide the user with tools to ease the gathering and analysis of tests on different materials, sewing speeds and machine configurations and settings. Outputs for actuators to implement closed-loop control strategies are also available. The paper presents an overview of the system, which is a development of earlier hardware and software and focuses on the results concerning the measurement of the force on the needle-bar; this parameter is important to investigate needle penetration force in fabrics during sewing. Several signal-processing algorithms, that aim to automate the detection of some characteristics, are described. The purpose of this system, that implements some novel strategies, is to develop an add-on kit to apply to different sewing machines, but presently it has been implemented on a PC as a quality assessment system which will be used by textile technicians to build a quality database.

Health monitoring using textile sensors and electrodes: An overview and integration of technologies

This paper gives an overview of technologies and results of integration and test of textile integrated sensors and electrodes for monitoring of biosignals (electrocardiographic - ECG and electromyographic - EMG), breathing and moisture. Using a seamless jacquard knitting machine, it is possible to integrate these sensors and electrodes directly into the fabrics, which can then be used in clothing for monitoring of elderly people, in sports or in hazardous occupations. The total integration of the sensing elements and connections into the garment presents great advantages in physical as well as psychological comfort of the user. It has been shown that the measurements are of adequate quality for most of the applications. In some cases, as is the case of ECG and EMG, signals acquired are similar to those obtained using conventional electrodes.

Signal feature extraction for sewing analysis using non-linear techniques

This paper describes the measurement of a process variable in industrial sewing machines using a piezoelectric sensing system and non-linear filtering and processing techniques. The objective is to obtain a measure of the needle penetration and withdrawal forces in a fabric, which can be used to detect faulty processing conditions causing second-rate quality products. Aimed for future real-time applications, currently the measurement process has been optimized for laboratory use. It provides the means for experimentation leading to the development of further processing techniques able to detect fault conditions automatically, a completely innovative industrial application. The signal is acquired by a piezoelectric sensor introduced in the needle support bar. With this set-up, the sensor provides not only the forces related to needle-fabric interaction, but also other, undesired components, that are reduced with specifically developed techniques. This paper presents the advantages and drawbacks of the measurement set-up and describes the optimization of the complex processing techniques used to extract the relevant information from the signals.

Actuation, monitoring and closed-loop control of sewing machine presser foot

Sewing is one of the most important processes in the apparel industry for the production of high-quality garments. Although some research and improvements have been carried out in this area, the sewing process has remained almost unchanged throughout the years, staying largely dependent on the operator skills to set up sewing parameters and to handle the fabrics being sewn. Slight changes in sewing machine settings can influence the quality of seams, as well as sewing operation time. To avoid these empirical settings, reduce set-up times and improve machine performance, flexibility and sewing quality, an electromagnetic actuated presser foot, based on the use of a proportional force solenoid, was developed and implemented on an industrial overlock sewing machine. The compression force and displacement waveforms from the presser foot bar will be studied in this paper, as well as the admissible displacement limits used to monitor (on- and offline) fabrics’ feeding efficiency. Following this analysis, a new research programme was established to enable a PC-based open- and closed-loop control of the presser foot system. This paper also highlights these recent developments, presenting and discussing, in detail, a PID closed-loop control strategy. The obtained results show that the presser foot closed-loop control has improved performance for a wide speed variation range.

Treat me well: Affective and physiological feedback for wheelchair users

This work reports a electrocardiograph and skin conductivity hardware architecture, based on E-textile electrodes, attached to a wheelchair for affective and physiological computing. Appropriate conditioning circuits and a microcontroller platform that performs acquisition, primary processing, and communication using Bluetooth were designed and implemented. To increase the accuracy and repeatability of the skin conductivity measuring channel, force measurement sensors were attached to the system certifying measuring contact force on the electrode level. Advanced processing including R-wave peak detector, adaptive filtering and autonomic nervous system analysis based on wavelets transform was designed and implemented on a server. A central design of affective recognition and biofeedback system is described.

Automatic presser‐foot force control for industrial sewing machines

Purpose – The purpose of this paper is to develop and test control methods for real‐time automatic presser‐foot force control in industrial sewing machines. In this work, a closed‐loop controller that controls presser‐foot maximum vertical displacement is presented and compared to existing solutions that adjust force depending on sewing speed. Automatic force control can reduce problems such as stitch irregularity, stitch distortions and material damage, besides making material handling easier.Design/methodology/approach – An electromagnetic force actuator was integrated in an industrial lockstitch machine. A computer‐based control system was designed implementing either speed‐variable force control, closed‐loop control, or emulating a traditional constant‐force system. Maximum presser‐foot displacement values were measured and analysed in relevant sewing situations, and seam quality was assessed.Findings – Constant‐force control does not allow optimal force setting at all speeds. Speed‐variable force con...