Speaker
Description
ANDES is a neutron diffraction instrument for materials characterization currently under development by the Argentine National Atomic Energy Commission (CNEA) as part of the Argentine Laboratory of Neutron Beams (LAHN) project. One of its key mechanical subsystems, SS03, is responsible for selecting the neutron energy spectrum and orienting the neutron beam by positioning the monochromator assembly. The subsystem comprises two electromechanical devices, including the Monochromator Shielding Device, whose operation requires coordinated motion, fault supervision, and safe interaction between pneumatic and electromechanical actuators.
The development of the automation system for the Monochromator Shielding Device goes from the conceptual design to its implementation and experimental validation. The development included the definition of the control architecture, hardware and software selection, PLC programming, virtual commissioning through simulation, and commissioning of the physical machine.
This works presents the methodology adopted to develop the automation system. The controller was implemented as a hierarchical finite state machine (HFSM) in accordance with the IEC 61131-3 standard and organizes the machine behavior into two operating principal modes: User Mode and Maintenance Mode. User Mode supports the normal operation of the neutron instrument, whereas Maintenance Mode manages machine initialization, homing, calibration, diagnostics, and recovery from abnormal conditions. State transitions are determined by sensor feedback, operator commands, and safety conditions, allowing the controller to respond predictably while maintaining safe machine operation. The HFSM architecture also simplifies the implementation of fault recovery procedures and facilitates future software maintenance and functional expansion.
The controller integrates digital and analog inputs from the machine instrumentation to coordinate two primary actuators: a pneumatic cylinder driven by a proportional 5/3 directional valve and a closed-loop stepper motor that positions the rotating shielding assembly. The implemented logic supervises the complete operational sequence, validates machine states before every motion command, and continuously monitors the process to detect unsafe or unexpected operating conditions.
The proposed automation architecture provides a reliable and maintainable control solution for the Monochromator Shielding Device. The methodology developed for SS03 can be extended to other mechatronic subsystems requiring coordinated motion, state-based supervision, and high operational reliability in large scientific instrumentation facilities.
Key Words
PLC, programming, IEC, Monochromator, logic