Retrofit boosts quality and availability

When the electronics started to fail more and more often, Vetex – based in Herzebrock – realized it was time to retrofit one of its tufting machines and migrate to PC-based control. The compact drive technology from Beckhoff enabled a new type of yarn infeed: 424 integrated ASI8114 stepper motor drives replace the usual yarn feed rollers and feed the system with around 1,700 yarn threads – complete with individual and very fast control of the thread length and monitoring of the thread tension.

Herzebrock-based carpet specialist Vetex offers carpets in a wide variety of patterns, colors, and dimensions. The spectrum of products marketed worldwide under the Infloor-Girloon brand is large and encompasses standard commercial products in several quality levels from 500 g/m² to over 2,000 g/m² pile weight. “Other highlights include carpets with individually printed motifs and our self-adhesive carpet tiles, which can be laid directly on dust-free, smooth subfloors and removed again at any time without leaving any residue,” says Josef Röttgers, Head of Production and Product Management at Vetex.

The most commonly used process for carpets worldwide is tufting, a technique between sewing and embroidery. Needles threaded with the pile yarn (tufting yarn) pierce the backing material, which is moved synchronously to the machine cycle by a feed roller and a take-off roller. The vertical needles are arranged across the entire width of the tufting machine – in the case of the Vetex machine, exactly 1,696 needles across a width of 4.29 meters. “That corresponds to ten needles per inch of carpet width,” explains Ralf Bosch, production manager for the Vetex tufting and weaving division. Grippers form the pile thread loops on the back of the pierced backing layer and fix their height. If these grippers are also equipped with blades, the loops can be cut open so that the pile loop fabric becomes a velour carpet.

For Infloor-Girloon’s target markets – hotel chains, offices, insurance companies, specialist retailers, and the construction industry – quality and durability are extremely important, as is the ability to create customized carpet designs with regard to coloring, texture, and pattern. “It is essential that the production process is as smooth and precise as possible, which was no longer possible with the previous control technology,” says Ralf Bosch, emphasizing the necessity of the retrofit implemented by Beckhoff and machine builder Gierecker & Brökelmann in Rheda-Wiedenbrück. For this reason, the tufting machine’s electronics, which had become increasingly susceptible to faults, were completely replaced with powerful and flexible control and drive technology – PC-based control. “We have been using PC-based control technology from Beckhoff for about seven years and are modernizing our machines with it step by step,” says Josef Röttgers.

Yarn feed with over 400 compact stepper motor drives

During the retrofit of the tufting machine, the previous drive technology was replaced with various AM8000 synchronous servomotors and AX5000 compact servo drives, which control aspects such as the needle stroke, the feed of the tufting fabric, the press foot, and the lifting table. “For the most important part of the retrofit – the precise yarn feed and thread tension – Vetex relies on a new concept that could only be implemented in this form with the compact integrated ASI8114 stepper motor drives,” explains Jens Hülsebusch, project manager and programmer of the retrofit at Beckhoff. A total of 424 stepper motors with integrated amplifiers each pull four threads from the creel via corresponding shafts and make them available to the machine via scramble box and puller rolls. The speeds of the yarn drives can change up to ten times per second.

“Due to their compact dimensions, the flange dimension of 42 mm, and the low power consumption, the stepper motor drives could be mounted very closely,” adds Christian Mische, Senior Product Manager Drive Technology at Beckhoff. “Compared to other solutions, the design effort required for the infeed of the 1,696 individual yarns is therefore much lower and more precise,” confirms Ralf Bosch.

The compact drive technology with 48 V DC supply voltage saves valuable installation space – but that’s not all. Its internal feedback system turns the stepper motors into a precise servo drive with field-oriented control. Compared to traditional stepper motors, this means that energy consumption and heat generation are much lower, reducing the power consumption from just under 8 kW for a conventional machine to around 4 kW after the retrofit. “With 2-shift operation and several machines, this is definitely noticeable in terms of energy consumption and the CO₂ balance,” says Ralf Bosch. The necessary power for the stepper motor drives is provided by 19 PS3000 power supplies.

PC-based control regulates the thread tension via the motor current or the resulting torque and detects whether the tension is too high or a thread is broken. “Both have a direct effect on the quality of the carpet,” says Josef Röttgers. The thread tensions are displayed to the machine operator on the CP2918 Control Panel via a dot matrix. “The operator can immediately see from the colors where the thread infeed is hooked and can intervene if necessary,” says Jens Hülsebusch. To ensure that this display works synchronously with the machine cycle, the visualization was created with the TwinCAT 3 PLC HMI (TF1800).

Eight processor cores for short cycle times

TwinCAT calculates the motor current or torque for the required thread tension with a cycle time of 1 ms. “To ensure this short cycle, the many stepper motors and other tasks were divided between the eight CPU cores of the C6032 ultra-compact Industrial PC and several EtherCAT segments,” explains Jens Hülsebusch. One Ethernet interface connects 100 of the stepper motor drives to the industrial PC in each case. A fifth junction connects the remaining EtherCAT Terminals and EP box modules as well as the AX5000 compact servo drives for the other drives of the tufting machine. The NC part, the visualization, and the slow and fast processes are each assigned to a further CPU core. “In this application, we make full use of the flexibility of PC-based control and the performance of the industrial PC,” says Jens Hülsebusch.

Josef Röttgers confirms this: “The retrofit of the machine was the most complicated conversion at Vetex to date, but thanks to the excellent preparation and expertise of Beckhoff systems engineering, it went off without a hitch.” Some of the challenges included the individual control of the many drives depending on the carpet design, and the interpretation and handling of the bitmap of a pattern in the control system. “The individual patterns are created when the threads are stitched through the base fabric at different lengths,” says Ralf Bosch. To do this, TwinCAT must translate the pattern planned by a graphic designer pixel by pixel into position setpoints and yarn lengths for each of the 424 stepper motor drives and generate the motion profiles. PC-based control can make full use of its strengths here, as the C6032 ultra-compact Industrial PC – in conjunction with TwinCAT 3 – provides sufficient real-time memory to read and process the approximately 10 MB files. The connection between the controller and the design department or order planning is established via TwinCAT 3 XML Server (TF6421). The demanding motion sequences were implemented with TwinCAT 3 PLC/NC PTP (TC1250) and NC Camming (TF5050).

Following the extremely positive experience, Vetex is getting ready for further modernizations: In addition to the conversion of a cutting system for the self-adhesive carpet tiles, Josef Röttgers is already planning the retrofit of another tufting machine for next year.