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Servo technology increases filter production by 70%

Servo technology increases filter production by 70%

For its new generation machines to manufacture air filters, Keilmann Group (KSL) in Lorsch near Frankfurt chose servo drives instead of the frequency inverters used on previous machines, and achieved a 70% increase in output. The new KSL FPS 300 machine produces what are known as pocket filters, which consist of a number of panels of filter material that are cut to a waisted profile and stitched together. The servo drives control the material infeed and outfeed plus positioning of sewing heads which run at up to 600 stitches per minute.

Keilmann is one of the world's leading suppliers of automatic pocket filter production systems that use sewing techniques with conical or constant stitch loosening, straight and waisted contours and special shapes in the outer seam area. The pocket filters are used in groups of three to 12 pairs that are held in a frame that forms the shape of the open end. Typical sizes range from 300x300 to 600x600mm.  he pockets make up a filter with high surface area that can efficiently remove dust from the air with the minimum of pressure loss.  

Applications are widespread, including the pharmaceutical industry and healthcare, spray booths, clean-rooms and general HVAC ventilation. Filter materials are glass-fibre or synthetic and in both cases the low density and relative softness create a challenge for precise material handling at speed. The need for precise synchronisation and positioning of the sewing heads led Keilmann to opt for Lenze servo technology. The FPS300 filter pocket system starts with a material infeed where the upper and lower lengths of material are pulled from a reel into the sewing area. Here a multi-needle station sews them into variable lengths across the web followed by fixing with a hot-melt adhesive. Next the sides are waisted with precisely positioned sewing heads, the pockets are cut to length and then fed out into the stacking area.

The multi-needle sewing station strokes at up to 600 stitches per minute and varying thread lengths of 20 to 60mm between the two webs of material. To ensure the 1.4mm diameter needles enter the material cleanly without tearing and then slide out again, the sewing station must be precisely synchronised with the travel of the filter material.

The Lenze drive solution is based around servo drives of the 9400 series. Linked by CANopen, they synchronise with electrical shaft software working to the master drive which is the draw-in roller at the first sewing station. To achieve the high dynamics, Lenze MCS synchronous servo motors were selected for their low inertias and peak torque capacity up to four times nominal. Rather than a conventional option of planetary gears, the motors are connected to Lenze GKR bevel gear-boxes.

Externally resembling worm gearboxes, the GKR design is based on bevel gears giving efficiency of 94%+, virtually no wear and very low backlash with lower costs than planetary designs. "We need a high degree of dynamic responsiveness because we map most of the sub-processes with a modulo positing system," explains Frank Koschnick, who is responsible for the mechanical design. "The Lenze system adjusts the motor very quickly."

For fast data processing the positioning system is integrated into the Lenze 9400 servo drives. For the cross-cutter that divides the material web into individual pockets, KSL use the Lenze flying saw drive solution as a ready-made technology module. This achieves continuous movement of the web rather than a stop-start motion with buffering. The flying saw software is part of the suite of motion software that Lenze call 'FAST', consisting of technology modules with a clear structure and proven high performance. Rather than create their own motion pro-gram, customers have only to configure their application data. This saves considerable programming time, reduces costs and speeds projects.

The KSL FPS 300 filter pocket system demonstrates big gains from use of the Lenze servo system. Previous machines with frequency inverter drives ran at 14m/min.  The target for this machine was 20m/min but 24m/min was achieved. This is a 70% increase and represents 40 pocket filters per minute with a length of 600mm. The success can be attributed to a partnership with on one side the KSL expertise in handling non-woven fabrics and on the other the drive and automation know-how of Lenze.  

"Above all it is Lenze's knowledge that impresses us again and again. For the new machine we therefore brought Lenze on board at an early stage to specify the drives, the motion functions and the performance," comments Koschnick. Lenze sees itself as a development partner who can make a valuable contribution towards choosing and correctly designing a machine that is market-oriented and therefore more profitable.

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