Integrated automation controls rail straightening machine

Turning to the partnership of Siemens' Solution Partner, Independent Control Systems (ICONSYS) and Siemens Industry to deliver a drive/motion system, which would be based upon a new dynamic and flexible automation system, the company now has the largest machine of its type in the world. After successful implementation, the machine is achieving production results exceeding stated parameters and tests.

The new machine straightens a broad range of railway rails including P50, P65, P65K and consists of two machines in series, the horizontal straightener with nine roll drives and the vertical straightener with eight main roll drives. The new drive system from Siemens was required to control these main drive rolls, with both speed and torque control central to the system.

Accurate positioning systems were required to position the rolls both axially and radially to give the correct amount of bending required to achieve straightness, while not introducing residual stress into the material.

In addition, fast changeover of roll position settings was equally important to increase production efficiency and reduce downtime between product changes. Setpoints for all position loops were calculated and saved so all settings are now stored in a database for future use.

Finally, fast roll change was also very important, so two fully automated roll change rigs were supplied, both inverter controlled on two axes with position control for both traverse and height adjustments. Fine torque control was required to just support the weight of the rolls without applying bending forces to the shafts, while their hydraulic clamping mechanisms were released prior to being traversed away on the removal rigs.

At the centre of the drive and motion approach chosen by ICONSYS sits the seamlessly integrated automated system offered by Siemens Industry.

John Inskip from Siemens Industry says: "Our solution offered ICONSYS and the end customer a number of benefits in terms of communications, data acquisition and operational efficiency. The integration of our products through our philosophy of totally integrated automation (TIA) sets the solution apart from others on the market and addresses the holistic needs of the customers."

Sinamics S120 inverter drives

ICONSYS specified the use of Sinamics S120 inverter drives from Siemens configured in a common DC bus arrangement to control the main drives. A suite of cubicles housed the main drive inverters all fed directly from the DC bus. A total of 21 inverter modules were connected and ultimately, controlled by six CU320 controllers, which communicate with the PLC over Profibus. The many auxiliary AC motors were controlled by direct on line starters housed in a separate cubicle.

Overall control was delivered by a Siemens S7 PLC system utilising Profibus to communicate with the drives controllers, the remote I/O and the large number of absolute encoders used for position feedback from the position control loops. The PLC's main functions are to control the speed and torque setpoints of the main drives, calculate theoretical setpoints for the position loops, execute the position control loops, control the overall automatic operation of the machine while in production and also the automatic sequences for roll change operations.

The operator's interface to the machine is via a Siemens WinCC-based HMI, with access to overall status indication, as well as the ancillary hydraulic and lubrication systems. The HMI is linked to a database where recipes for setpoints for all position loops are stored, with the database organised to be sorted either by rail type, rail dimensions or data used.

From a diagnostic perspective, data for all the main drives is displayed via drill down screens for each motor. Calibration of the many Profibus absolute encoders can be carried out via the HMI, but only by authorised personnel due to password protection on certain screens.

Tim Rhodes from ICONSYS concludes: "The metal works company required a flexible and accurate drive and motion system to achieve a high-quality finished product. With no compromise in terms of changeover times between production runs, the integrated and standardised automated control solution provided has met its requirements of enhanced flexibility, production efficiencies and vastly improved overall control."

To learn more about computer-controlled automation from Siemens, please go to www.industry.siemens.co.uk.