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The robot as sewing machine

With needle and thread for Airbus

The idea of using robots to automate sewing operations was originated by the company KSL Keilmann Sondermaschinenbau GmbH from the town of Lorsch in the German state of Hesse. Founded in 1964, KSL has many years of experience in sewing technology. The company is thus in a position to supply appropriate custom-developed special solutions at reasonable prices. For example, KSL manufactures sewing systems for airbags, car seats, convertible roofs, filters, mattresses, furniture and safety equipment. Their main customers are the automotive industry, automotive subsuppliers, aerospace engineering companies, the technical textile industry, and the leather, upholstery, environmental protection and packaging industries. Also attesting to the company’s expertise are the patents it holds – for a blindstitch machine and a taffeta sewing machine.

With 106 employees, KSL achieved sales of 12.5 million euros in 2001. The company has two subsidiaries, one also in Lorsch, and the other in Altenburg, Thuringia. KSL is a systems partner of KUKA Roboter GmbH, Augsburg. News about the quality of KSL’s machines has even made the journey to Mecca recently. In the year 2000 the Hessian company shipped the CNC sewing system “Holy Kaaba” to this Saudi Arabian city. This equipment is used to sew the fabric coverings for Islam’s most sacred shrine.


Robot sews Airbus components

At the beginning of March 2002, KSL installed a KUKA KR 125 robot at Airbus Deutschland GmbH in Stade, Germany. The Stade plant is Airbus’s center for the processing of carbon fiber composites (CRP). With about 1,200 employees, it produces among other things the rudder units for all Airbus aircraft. These rudder units are among the world’s largest carbon fiber composite structures for passenger aircraft.

The robot is mounted in inverted position on a seven meter long linear unit. Its tasks include the sewing of pressure shells and wing elements made of carbon fiber composites. In addition, the KR 125 sews parts of the Eurofighter’s outer skin to the aircraft’s structural members.

“In order to ensure that Airbus received a fully-optimized production system, in November 2001 we first set up the robotic cell at our plant and tested it thoroughly, explains Robert Keilmann, Managing Director of KSL. “To program the robot, the data of the components in question were first transferred to CAD software. Next came a CAD simulation to test the feasibility of the concept. After that we downloaded the data from the CAD system to the robot controller.”


Robot with freedom of movement

Keilmann continues: “Each individual carbon fiber composite component receives its shape from the mold in which it is sewed. Since it is necessary for the needle to maintain a 90° angle to the surface, the freedom of movement provided by a six-axis jointed-arm robot is essential for this application.”

There was also no alternative to using a robot because of the high level of flexibility required. After all, the KR 125 has to be able to use three different sewing heads, which are exchanged by means of a quick-change system, while at the same time reliably controlling three different sewing methods.

In taffeta sewing, the KR 125 inserts the thread into the carbon fiber composite at a 90° angle. In the backstitch method, it joins different layers of material to each other; access from below is necessary if this method is to be used. Such access is not required if blindstitch sewing is used. For this reason, when this single-thread chain stitch is used, the material is left in the mold even after sewing. The mold is closed at the bottom, therefore the material can remain there while resin is being pressed into the carbon fiber composite and during subsequent curing of the CRP. The desired shape of the component is thus obtained.

“We also expect that a robot will provide high repeatability and motion coordinated with the sewing head”, says Robert Keilmann. “Equally important is that if the KR 125 has to leave the programmed path due to a broken thread, it will resume work again from the previous position. Such interruptions occur frequently because the needle is subject to heavy wear. Furthermore, the process may be stopped by knots occurring in the thread.”

The KUKA robot is mounted in inverted position because it also has to sew convex and concave shapes, and in any other position it would not be able to reach all of the points. Working from above expands the robot’s work envelope to 5 meters x 3 meters x 1.5 meters (LxWxH).


Robot finds the workpiece carrier

Operators slide a workpiece carrier with the CRP part into the robotic cell. The cell is a steel construction on which the linear unit is mounted in inverted position. The dimensions of the workpiece carrier are determined by the specific application. In order to allow larger elements, such as wing structures, to be indexed through the cell and sewn there, the cell must remain open on all sides. For this reason, there are only four supports in the corners, and it is possible to move the safety equipment to the side.

Once the workpiece carrier is in the cell, the operating personnel can leave it in any position, i.e. without reference to any fixed points. The operator then closes the cell. The KR 125 “finds” the workpiece carrier and measures it in three dimensions by means of a laser measuring system. The data thus obtained are used by the robot to adjust its sewing program to the position of the workpiece carrier. The system operator can monitor the process with the aid of a camera mounted in the sewing head.

In order to program new sewing materials, to check whether the points are sewn as specified, or to reteach points, the operating personnel use the KUKA Control Panel of the PC-based robot controller. This is equipped with a Windows interface, making communication with the KR 125 much easier.


A competitive advantage

Another competitive advantage held by KUKA with regard to Airbus’s choice of robot was that the company had already participated in research projects in Ottobrunn which involved sewing with robots, and Airbus thus had previous experience in working with KUKA as a supplier. Moreover, the aviation industry can look back on other successful applications implemented in cooperation with KUKA. The package supplied by the robot manufacturer included the KR 125 robot, its controller and linear unit, and technical support in adapting the software.


Author: Jürgen Warmbold, freelance technical journalist, 27327 Martfeld, Germany






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