"Sound Weaving," Feature Article, March 2008

sound weaving

Making a fast loom even faster requires special handling of noise and vibration.

This article was prepared by staff writers in collaboration with outside contributors.

Weaving puts the clothes on our backs, but like so many things in life, if you're not in the business, you may not think often about looms or how they perform. Fabric is largely a commodity business, so speed is important, because the faster the loom can go, the more productive it and the mill are.

Picanol NV, a maker of weaving machines based in Ieper, Belgium, markets a variety of models, including a family of high-speed rapier looms sold under the name OptiMax. The rapier loom has no shuttle. Instead, it uses a device called a rapier to pass the weft at high speed through the warp. This kind of loom can weave a variety of fabrics, including voile and crepe, and can handle a range of materials, from wool or cotton to Kevlar or fiberglass.

Kristof Roelstraete, director of rapier weaving machine development at Picanol, said the company has made a number of technical advances in its looms over the past few years. One is a patented direct-drive engine called Sumo, which is controlled electronically. It can stop or slow down immediately, as needed and, according to Roelstraete, reduces a loom's overall power consumption by about 10 percent.

Picanol says that commercial installations of its fastest machines average 650 picks per minute, or better than 10 cycles per second. Some have been clocked at 750 ppm.

Design Considerations

Indeed, the OptiMax looms are so fast that particular care had to be taken in their design to minimize noise and vibration.

When it came to developing its high-speed OptiMax looms, Picanol decided to bring in a noise and vibration specialist early in the design process. Picanol called on another Belgian company, LMS Engineering Services, which is based in Leuven and had worked with Picanol on an earlier-model loom.

According to Roelstraete, a key assembly in the OptiMax is the rapier driver mechanism, which increases speed, and also can raise noise. The circular motion of the mechanism drives the bidirectional linear movement of the rapier. The forces resulting from the high-speed motion put a lot of pressure on the driver mechanism.

Because assembly parts deform slightly during operation, LMS engineers created a dynamic multibody model of the entire rapier driver mechanism. By modeling key components as flexible bodies using finite elements, the effects of deflection and resonance were taken into account when simulating the dynamic assembly load cases.

A CAD model of the OptiMax drive system; the parts were modeled as flexible bodies.

According to the program manager at LMS Engineering Services, Stefan Dutré, deflection of parts introduced slight misalignment of bearings and axial bearing forces. LMS used its own simulation program, Virtual.Lab Motion, to establish optimal bearing performance under real-life operating conditions. It reduced the problem by increasing bearing and housing stiffness, improving bearing alignment, and adjusting bearing pretension.

"Dynamic motion simulations also helped us to trim down radial bearing forces through further weight reduction of moving and oscillating parts," Dutré said.

Simulations also provided a basis for evaluating the fatigue life of rapier driver parts. High durability standards are critical in keeping weaving machines running nonstop for seven to 10 years. Simulations identified locations where stress variations approximated or exceeded endurance limits of materials. According to Picanol, functional holes in some parts required repositioning and resizing to extend their projected service life.

Where the Noise Comes From

A major source of noise were the gears in the driver assembly. Dutré said that each time the rapier reversed direction of motion, the tolerance between teeth resulted in vibration that traveled through the housing structure to radiate noise.

LMS created a model that accounted for gear tolerance and varying contact stiffness of teeth dynamically gripping into one another.

"We derived the dynamic bearing loads through multibody simulation and applied them to the FE model of the housing," Dutré said. "Then, we took the average value of the resulting surface vibrations as a measure for the radiated noise." Simulation results indicated that increasing the damping of the housing structure, and using more expensive gears produced with smaller tolerances and higher-quality tooth finishing techniques would reduce noise radiation.

The high speed of the rapier in the OptiMax weaving machine raised issues of noise and vibration.

Roelstraete said the development process and the product both proved very efficient. "Altogether, simulation eliminated at least one complete prototype iteration step, which firmly reduces both development duration and expenditure," he said.

Picanol claims that its OptiMax looms are 15 percent more productive than earlier models. According to Roelstraete, "This performance boost is realized through higher machine speed and lower downtime, the ability to weave a wider variety of textiles, more flexibility in switching between articles, and lower weaving cost."