Finding the balance between machine and operational safety

Safety and its possibilities are on everyone’s lips. There are strict sequences of fault reaction chains for typical risk scenarios. In most cases, each of these chains ends with the safe shutdown of the torque, with the machine coming to a standstill until the fault has been rectified. 

What is regulated in European machinery standards is intended to make operating sites safer and to protect people. In extreme cases, a machine that is as functionally safe as possible will therefore react in an extremely safe manner.

“The task now facing mechanical engineering and automation technology is to find a compromise between functional and operational safety,” says Richard Eichele, Head of Export at KEB. Solving this task is a balancing act.

Speed measurement without optical measuring system

Tool spindles are at the heart of TechnoWood’s high-performance woodworking CNC machines. Not only do they have to maintain their milling speed with high precision at maximum loads of over 100kW peak power, they also have to come to a safe standstill in the event of a fault, for example, if the machining speed is set incorrectly.

“In conventional machines, optical encoder systems are used for this purpose, which enable reliable speed detection,” explains Eichele. “Our analyses within the scope of various customer surveys have shown that if there are failures in operation, it is usually related to faulty measuring systems caused by a ‘crash’ of the spindle without a rotating tool with the workpiece.”

In combination with COMBIVERT F6 drive controllers from KEB, a functionally safe speed measurement is made possible without requiring a complex optical measuring system. “This not only enables continuously safe speed detection for synchronous spindles operated without encoder, but also reduces the cost of the spindle while making it more reliable in operation, as no encoder needs to be installed,” explains Mathias Huber, Head of Software/Support at TechnoWood.

He continues: “Compared to machines with a safe encoder, TechnoWood customers work more productively and more reliably. With ourselves and KEB, they no longer have to rely on safe encoder evaluations.”

FSoE and CNC

With the help of CNC controls, the motion sequences in the machine are conveniently programmed and workpieces are produced. Here too, the functional safety of light barriers and door interlocks is a priority when it comes to user-friendly installation of the system. Together with the COMBIVERT S6 servo drive, TechnoWood relies fully on the modern FSoE (Fail Safe Over EtherCAT) protocol to avoid any line-related obstacles. The servo drives receive only the power supply via high voltage and low voltage DC bus and a patch cable for control. They are immediately ready for safe functional operation.

“By using this technology, not only does the control cabinet look incomparably tidy, it enables maximum reliability in continuous operation on the construction site and guarantees the highest possible failure safety on the market,” says Huber.