Motion Control Resources
Slitting without edge deformation
by Thorsten Sienk, Freelance Journalist
AMK Automation Posted 01/10/2018
Narrow tapes require high torque stability / HERO relies on decentralized servo technology from AMK.
HERO GmbH uses decentralized servo drive technology to slim down and tidy up their slitting and winding machines. Thanks to drive and control technology from AMK, the solutions of HERO GmbH in Sigmaringendorf, Germany, have done away with anything that is not actually needed to meet the precise product quality standards. This includes control cabinets as well as long cable runs.
Carbon fiber tapes are a typical product that are precisely and quickly converted by HERO machines. The central task involves the lengthwise slitting of "master rolls" with a starting web width of 30 centimeters. For this purpose, the material is unwound, fed through a slitting unit and then rewound. The result is individual rolls that have a tape width of between 3 and 15 millimeters. These tapes are used in aircraft construction, for example. Carbon fibers are regarded here as extremely light and stable while remaining easy to shape.
High torque stability demanded
"There are more and more products in which robots produce the desired shapes fully automatically with a kind of self-adhesive carbon tape," said Richard Balzer, Managing Director at Hero, in describing the current trend in manufacturing. Tapes made of basalt fibers are also currently emerging as another popular material. They have similar properties but are significantly cheaper to make. Regardless of whether carbon or mineral is used, the further conversion of the fiber tapes requires highly precise torque control. Metal foils with a thickness of a few 1/100 millimeters are another field of application. If the tension is uneven or too high, deformation can quickly form at the edges of the tapes having widths of only a few millimeters. They are an indicator that the material was overstretched beyond its elastic range. Because this condition cannot be reversed, this occurrence can thus be classified as production scrap.
The extremely sensitive control of the web tension is thus one of the outstanding features of the automation, or motion control, functionality in the HERO solution. Depending on the material width, tension values between 5 and 1.2 N are used. This is realized with a synchronous group of servo axes from AMK and a slightly leading speed setpoint that the motors of the rewinder don't reach however – which results in the desired torque and tensile weights between 120 and 500 grams. Which force prevails is stored in the product recipe and can be called up with a few clicks on the AMK touch panel before a new production order. In a special design the data can be specified directly from the higher-level production control computer or ERP system.
Unwinding, edge guide control, slitter drives, rewinder on multiple automatically adjustable levels: the new machines from HERO have more than 30 servo axes all of which are interconnected. "The power consumption per axis is low, except for the two slitter drives with a couple of hundred watts, the demands on the speed accuracy although are very high," explained Uwe Gfrörer, Director of the Control Technology Division at HERO. Many axes, little power: these are ideal operating conditions for the distributed servo drives – and namely in the form of an integrated mechatronic solution made up of servo motor and inverter. Specifically, HERO is using the AMK ihXT series. These involve complete units that can easily be integrated into machine designs.
Reduced installation through drive bus
The AMK solution scores points as a result of its connection system that uses a single hybrid cable – and this is also combined with convenient loop-through possibilities. The DC current is fed from one drive to another via the DC bus together with real-time Ethernet communication over the hybrid cable. Up to 40 axes can be supplied in series with a single power supply unit. One power supply for 30 axes in the slitting and winding machine would have been enough for HERO. However, the company decided on two drive trains with one power supply each in order to leave room for future functional expansions or capacity expansion due to additional rewinder units.
This decision was ultimately made to ensure that the new machine design was as future-proof as possible, thereby saving valuable engineering resources in upcoming projects. HERO opened up additional efficiency gains with the single cable connection system – in particular in connection with the mentioned loop-through possibilities. "When I imagine 30 cables coming out of the control cabinet compared to the 2 cables we are dealing with today, the advantages become clear very quickly. There is no reason to complain," said Richard Balzer. For one thing, his company saves a lot of space and time. For another thing, "we have fewer interference sources. That is especially important when movable drives require movable cables and these have to be routed in trailing cables or bridges." For the Managing Director, the distributed servo drive technology implemented jointly with AMK also contributes to better MTBF figures because the failure probabilities go down automatically with the elimination of components. "We are dealing with a drive solution that is modern and sustainably efficient in all respects," said the Managing Director.
HERO also exploits the benefits of a coordinated system in the case of the control technology. The AMKAMAC controller is used as the highest-level control. In this case, the integrated version with rugged touch panel with IP69K degree of protection offered by AMK is used. As a classic PLC, the control unit undertakes the complete sequence control and the visualization. On the other hand, the control unit also operates as powerful motion control for the winding and positioning drives in their synchronized multi-axis group. Everything is programmed with Codesys and thus in the internationally established standard languages of IEC 61131-3.
The lean and straightforward configuration of the decentralized servo technology under a centralized PLC with integrated motion control and visualization has also been made possible in the equipment of HERO because the new AMK AIO series I/O system provides a solution that reaches up to 256 DI/DOs in 20 μs thanks to a high-speed system bus. This architecture is flanked by the real-time Ethernet fieldbus EtherCAT, which ensures consistent communication of all nodes in the slitting and winding machine.
In summary, the combination of decentralized servo technology, centralized DC power supply, EtherCAT communication and controller intelligence with visualization ensures that the machine visually gives off an extremely tidy impression – which is mainly apparent from the cabling. Because the actuator together with the control is integrated directly in the process, bulky control cabinets are a thing of the past.
But, HERO did not do away with a control cabinet completely – and this for reasons of thrift. Actually, only a small enclosure is needed for the two central supply units and the I/O system. HERO nevertheless uses relatively large-scale control cabinets in this case for a very practical reason: it is easier and more economical to combine two standard-sized enclosures into the machine frame, than fabricating individual steel frames of different sizes each time. Consequently, the system provides all sorts of space behind the closed doors that the end user is free to use.
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