CONTROL SYSTEMS

Modular and individually customized flat and profile wire rolling mills manufactured by Bühler & Co GmbH (of Pforzheim, Germany) are in use around the world by leading wire processing companies. These rolling mills form round or preshaped material into wire and profiles for a wide range of end products. The last step is always the laying of the wire or profiles on either standard reels or customer-specific or product-specific reels (e.g. annealing reels). This must be performed neatly and precisely layer by layer, not only to optimally load the reel, but also to prevent the winding layer from tipping and the wire from catching or breaking during subsequent uncoiling or recoiling, which could result in stoppages in production. It sounds very simple, but it is anything but simple. With current rolling mill production speeds of up to 600 m/min, very short control times are required in order to synchronize the traversing arm with the varying speed of the winding axis adapted to the rolling speed. "In particular at the start of the winding when the coil diameter and therefore the material length is still small, very high demands are placed on the precise achievement of the acceleration, deceleration and delay angles in the reversing points", commented Marco Kunkel, technical director and executive officer of Bühler & Co.
In the past, the machine manufacturer had exclusively used dedicated controllers (Unix-based controllers) for the open-loop and closed-loop control of this motion sequence. Although the purchased "black box" had an integrated 4ms position controller and a number of parameters could be set, the control times increasingly proved inadequate for particularly fast coiling processes and the controller manufacturer had to be consulted in advance when special tasks were to be undertaken or when modifications were required. In addition, defective controllers could only be repaired by the manufacturer, so that either a production outage of several weeks resulted or a replacement controller had to be kept in stock.

Into the future with innovative motion control

Bühler & Co continuously works on maintaining its leading technological leadership and constantly searches for ways to increase this lead. This was the reason that the decision was taken in the middle of the boom phase to depart from the proven path (which had reached its technological limits) and to look for a future-oriented controller solution. As this Pforzheim company has already been successfully using Siemens PLC, HMI and drives technology (Masterdrives) for some time, they also turned to the market leader with this task, more specifically the Motion Control Systems business unit in Erlangen, which works intensively on automation and drives solutions for production machines.
A large number of applications in this sector already use the Simotion motion control system, which is available in three variants: PC, controller and drives-based. The latter is also available with scalable performance. A suitable device was quickly found in the form of the Simotion D425 drives-based motion controller, which can control individual axes with cycle times up to 2ms. This alone results in a halving of the previous control times and therefore a theoretical doubling of the traversing unit performance. This increased performance is most notable in the reversing points of the traversing unit where increased resolution and improved control properties enable a more precise approach and dwell time at the end positions, even at high speeds. Immediate or imprecise switching at the end positions may result in the coil being thinner at the edges. The well-proven Masterdrives drives generation has been retained by the decision-makers in the first applications. However, the defined goal is the uniform use of the Sinamics S120 modular drives family from Siemens, which has already been implemented in a first plant. The motion controller and drives are then very compact in the drives line-up (booksize format), which save space in the control cabinet and reduces the number of interfaces. This also eliminates the external PROFIBUS connection between the controller and the drives. Communication at the drives level is performed exclusively via a digital system bus (drive-cliq). This simplifies and speeds up commissioning and maintenance as all drive components are automatically identified via their electronic type plates and therefore do not have to be parameterized manually, which would be very time-consuming. This keeps downtimes short and increases plant availability.

Based on standard applications

A further decisive criterion for the use of Simotion is the fact that Siemens has developed a whole range of standard applications ("converting toolbox") for the motion control system that can be adapted to various customer-specific conditions with comparatively little work. The standard applications are fully executable sample projects including basic visualization and documentation. Also included is the "traversing unit example application" for Simotion. "It was therefore clear that Siemens already had the required know-how for the task and didn't need time to become familiarized with our technology", says Marco Kunkel.
As time was tight, the above example was modified jointly with the drive specialists from Siemens for a traversing spooler from Bühler. This mainly affected the already existing and accustomed Simatic WinCC user interface in a flexible way. (The major advantage is that the engineering for the motion controller, drives and HMI is performed on one platform, with central access to all components.) The basic technological functions are already integrated in the standard application for Simotion and therefore the set tasks could be performed with minimum effort. The user can enter all of the relevant parameters at a Simatic MP277 Multi Panel or MP377 Touch Panel, including
– Reel core diameter
– Flange positions (drive/operator side)
– Winding start position
– Material width and thickness
– Winding step
– Waiting angle and
– Displacement angle
In this way, the entire process can be adapted to various product and reel dimensions in a rapid and flexible way. The Bühler & Co rolling mills can produce round and profile wires with cross-sections of 0.3 x 0.01mm2 to 25 x 8mm2. The range of reels is also correspondingly wide with inner diameters of 80 to 400mm, winding diameters of up to 1200mm and widths of 100 to 600mm.
The entries are checked in the background for plausibility and then processed in the motion control section of the controller. This ensures highly dynamic and precise electronic synchronous operation of the winder and the traversing arm drive axes. The motion is performed by 1FK7 servo motors (Siemens) of the High Dynamic version. The operator can use softkeys to intervene during operations even when the traversing unit is running, e.g. to correct the edge positions; an animated visualization of the results is immediately displayed. Recipes for frequently recurring products can be stored directly at the operating device, managed and, if required, the proven settings can be called up on the operator panel.
The progress, the results that have been achieved and also the costs confirm the machine manufacturer’s choice of technology and equipment supplier. The first customers are also welcomed by the use of a modern and above all open motion control system that is quickly available worldwide and can be quickly adapted to the particular requirements of the customer. The integration of a measuring system for the reels and the transfer of the measurement data to the traversing unit application are already being considered.

Additional functionality for more productivity and quality

The results speak for themselves: even in the initial constellation with Simotion D425 and Masterdrives drives technology, productivity increases of 25 to 50 percent were achieved, depending on the material and type of reel. Further improvements should and will be provided by the integrated solution in the Sinamics line-up.
By that time, Siemens will also have done the "homework" set by Bühler & Co and introduced the functions still missing for biconical laying and laying with a gap at the edge (also in the standard application). All of the prerequisites are then satisfied for a consistent use of Simotion and Sinamics on all traversing spoolers of the Pforzheim company.

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