JEC COMPOSITES MAGAZINE - Issue #76 - October/November 2012 - 76

cost effectiveness
Requirements The patterning possibilities of warp-knitting yarns are limited through the mechanical activation of the guide bar by means of the pattern discs. Therefore an electro-mechanically driven guide bar is necessary to be able to change the Fig. 8: Principle of the new guide bar control stitch type from stitch course to stitch course. Such a guide bar is integrated in the Copcentra MAX 3 CNC is to specify the yarn run in independently from the stitch type warp-knitting machine with multiaxial non-course wise weft to be able to control the tension of the warp-knitting yarns. insertion manufactured by LIBA Maschinenfabrik GmbH This tension also has an effect on drapability because a higher (Naila, Germany). The electro-mechanical driven guide bar has tension generally leads to smaller knitting loops and therefore to fulfil the following requirements: to a higher bending stiffness. - No adverse effect on production speed - Processing of all well-established stitch types Development and implementation - Closed-loop control The modification of the machine operating system and develop- Computer-controlled yarn run-in ment of the hardware were carried out by the machine manuDue to production speeds higher than 100 m/h, stitch types facturer LIBA Maschinenfabrik GmbH. with a large underlap, like satin, and coarse gauges (needles/ An extension of the machine operation system was required to inch) such as E6, high accelerations up to 250 m/s² can occur. control the new technologies. The machine operation system These accelerations lead to forces up to 10,000 N for a guide bar is based on a B&R control system from Bernecker + Rainer weighing around 4 kg. Therefore, powerful drive systems which Industrie Elektronik Ges.m.b.H. (Eggelsberg, Austria). Figure 8 can achieve high accelerations, forces and a displacement of shows the principle of the new guide bar control. more than 20 mm are necessary. The electro-mechanical drive was developed with a linear drive, which generates the longitudinal motion of the guide bar. The integration of the linear drive into the warpknitting unit demanded a complete re-design of the connection between the linear drive and the machine frame. These modifications required heavy machinery for Fig. 7: Displacement and acceleration of the guide bar in dependency of the position of the main machine shaft milling and drilling. Therefore, the comIn state-of-the-art machines, the motion of the compound and plete warp-knitting closure needles is conveyed to the pattern discs mechanically. unit, weighing nearly Therefore, a synchronous motion of the pattern discs and the 6 tons, was sent to knitting elements is enforced. If electro-mechanical drives are LIBA Maschinenfabrik used, there is no mechanical connection between the motion of GmbH. Figure 9 shows the knitting elements and the guide bars. A closed-loop control the integrated electrosystem is thus necessary to avoid asynchronous motion of the mechanically driven Fig. 9: Integrated electro-mechanical driven guide bar knitting elements and the guide bar. The closed-loop control guide bar. makes a high-resolution, fast measurement system necessary. This system has to work contactless to avoid wear. The newly developed and integrated technology fulfils all Varying stitch types during production requires an adjustthe above listed requirements. It was recently successfully ment of the yarn run-in from stitch course to stitch course. A proved and tested. One of the first non-crimp fabrics procomputer controlled beam control is necessary to specify the duced with adjusted stitch type and yarn run-in is shown in yarn run-in depending on the stitch type. Another requirement Figure 10.

76 jec composites magazine / No76 October - November 2012

JEC COMPOSITES MAGAZINE - Issue #76 - October/November 2012

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #76 - October/November 2012