The following site explains exactly what the machine is in French.

Soudage par résistance à la molette (Procédé RSEW)

C'est une variante du soudage par points dans laquelle les électrodes sont remplacées par des molettes (sorte de disques en cuivre). Le soudage par résistance à la molette permet d'exécuter des soudures continues.

Les molettes animées d'un mouvement de rotation exercent un effort et entraînent les pièces à assembler. Le courant de soudage peut être permanent ou séquentiel; dans ce dernier cas, il est possible d'obtenir des soudures constituées de points imbriqués, alors comparables aux soudures continues, ou tout simplement des points distincts plus ou moins espacés en fonction de la vitesse de rotation des molettes et de la fréquence des trains d'impulsions du courant de soudage.

[visit site to see photographs]

Soudage à la molette : principe (photo 3)
Soudage à la molette : machine (photo 4)

Rotary welding machines are made to work with a wide variety of materials. While some of them are designed to work with metal, others work with thermoplastics (nonwoven textiles [nontissés] : note that the hyphen is not used in these two words within the textile industry itself) in a wide variety of applications. While the rotary welding machine is fusing some ribbons over some seams, that is not the name of the machine itself.

Please see the Miller Weldmaster website for further clarification.
http://www.millerweldmaster.com/technical-applications.htm

I'm sorry that I wasn't here to answer your question sooner. Against my will, I had to let go of my computer long enough to get a new hard drive installed :-)

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Note added at 3 days 9 hrs 43 mins (2004-06-14 07:55:14 GMT)
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Oops. Sorry. I meant to make the answer a 5: I\'m sure; not a 4.

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Note added at 3 days 21 hrs 37 mins (2004-06-14 19:48:59 GMT)
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Q: How can the Miller machines weld fabrics that are not thermoplastic?
A: The Miller machines can weld many non-thermoplastic materials such as Sunbrella and Dixon, by simply guiding a heat activated adhesive tape in between the seam.
http://www.millerweldmaster.com/faq-acrylic-rendering.htm

see an illustration of how the machine works on this page
http://www.millerweldmaster.com/acrylic-welding.htm