Electricity and Control April 2022

SAFETY OF PLANT, EQUIPMENT + PEOPLE

Safe motion monitoring in automation systems Carsten Gregorius (Dipl.-Ing.(FH)), Senior Safety Specialist, Automation Infrastructure, Phoenix Contact Electronics GmbH, Germany UdoTappe, Product Manager Safety, Automation Infrastructure, Phoenix Contact Electronics GmbH, Germany.

Carsten Gregorius, Phoenix Contact Electronics, Germany.

S afe motion monitoring (Safe Motion) is becoming an integral part of safety and automation technology. Various systems are used for this, depending on the degree of automation. From simple switching devices for zero-speed and speed monitoring to configurable safety systems, safety controllers, and safe drives, these solutions have many things in common. With Safe Motion functionality, the availability and efficiency of machines and systems can be increased. It often makes more sense to move the drive with the safety door open so that setup and maintenance work can be performed. To protect the user, the safety technology monitors the hazardous movement. Productivity can potentially be increased if the ‘enable’ signal is output to an electromechanical guard-locking device when actual zero- speed is detected. Compared to a time-controlled enable signal, this allows the operator to access the machine more quickly and more safely. Systems for safe movement monitoring are also used in situations where large systems need to be secured against mechanical damage due to increased speed. The use of Safe Motion functions allows the rotor speed in wind turbine generators to be monitored, for example, or the movement of supporting structures in the case of movable bridges. Safety functions in accordance with EN 61800-5-2 The EN 61800-5-2 standard describes the demands on functional safety for power drives with adjustable speed, also known as Power Drive Systems Safety Related PDS(SR). For this purpose, standardised partial safety

functions have been defined as a basis for further validation. The most important functions are listed below. ƒ Safe Torque Off (STO), that is, shutting down the drive by means of immediate energy disconnection (stop category 0), which prevents unexpected startup

Udo Tappe, Phoenix Contact Electronics, Germany. ƒ Safe Operating Stop (SOS) to prevent a drive from deviating from a defined position while supplying energy; SOS is used to safeguard vertical axes ƒ Safely Limited Speed (SLS) to stop the drive when a maximum permissible speed is exceeded; used in setup mode on machine tools in conjunction with inching mode ƒ Safe Speed Range (SSR) as a function that stops the drive when a permissible speed range is exceeded or not reached; SSR is used in fans and ventilators to safeguard exhaust processes in potentially explosive areas ƒ Safe Speed Monitor (SSM) for generating a safe signal that can be further processed if a maximum permissible speed is exceeded; one area of application is enabling a guard-locking device on a safety door until the speed is below the permissible range ƒ Safe Direction (SDI) to prevent the drive shaft from moving in the unintended direction; used to prevent direction reversal on power-driven rollers. Improved encoder signal diagnostics Often, proximity switches or rotary transducers (encoders) are used to record the movement. If proximity switches are used, two sensors are to be attached to a gear wheel or a perforated disk to implement a redundant architecture. The frequency generated by the motion pulses depending on time is evaluated in the logic system in the Safe Motion module. The measured frequency can be used as a comparison value against the configured switching thresholds for overspeed or underspeed monitoring. Movement monitoring by an encoder installed on the drive train works similarly. Although rotary

Safe motion monitoring is becoming an integral part of safety and automation technology.

22 Electricity + Control APRIL 2022