To ensure maximum functional safety on multi-roller calenders with parallel axes, ABB has developed and tested two technical solutions for two different application needs: the safe control of minimum roller rotation speed and the emergency stop with controlled rotation angle.
For ABB, safety is a core value. For this reason, ABB solutions are safe according to the most up-to-date industry standards, in compliance with safety regulations and new market developments. For the plastic industry specifically, to ensure maximum functional safety on multi-cylinder calenders with parallel axes, ABB has developed and tested two technical solutions for two different application needs.
The first solution is designed for the safe control of minimum roller rotation speed. To perform the periodical maintenance and cleaning of calender rollers, you have to guarantee the safety of operators working near the machine. Therefore, you must make sure that the motor rotation speed remains below a preset limit value that is considered “safe” for the maintenance operations to be carried out.
Using the ACS880 industrial drive equipped with FSO-12 safety module, this result can be achieved without mounting any encoder on the motors and simplifying the safety system architecture.
The SLS (“safe limited speed”) functionality keeps the motor rotation speed below a preset threshold; if this limit is exceeded accidentally, the drive triggers the “safe torque off” function and blocks the modulation of current pulses to the motor. In this way, the motor stops by inertia. This functionality, integrated into the frequency converter, avoids using external safety components, simplifying wiring and reducing overall system costs, while meeting the highest safety standards according to the Machinery Directive applicable within the European Union: as a matter of fact, the SLS function is SIL 3 classified according to IEC 61508 e PL and to ISO 13849-1.
Industrial Drives ACS880 with Direct Torque Control (DTC) can control asynchronous, synchronous permanent magnet and synchronous reluctance motors.
The second application ensures the emergency stop with controlled rotation angle. A more and more frequent requirement is stopping the calender rollers (in emergency situations) within a controlled and preset rotation angle. Using ABB automation products, this result can be achieved with a safe and compact architecture meeting the strictest safety standards.
The system is comprised of the safety PLC AC500-S and the industrial drive ACS880. In case of emergency, AC500-S communicates via the safety protocol Profisafe, so that the transmitted signal is interpreted by ACS880 as an emergency command, and consequently, it is handled by the FSO-12 safety module. Through the safety function SS1 (“safe stop category 1”), ACS880 can stop the motor with a controlled and safe procedure and ensure that the calender roller stops within the preset rotation angle. The SS1 function, activated via Profisafe and safety PLC, is SIL 3 classified according to IEC 61508 e PL and to ISO 13849-1.
ABB’s specific solution for safety applications is the AC500-S safety PLC.