Sensor-free machine speed control

| Information and Communication Technology

CNC wood-working machinery is protected with in-drive speed control

Modern drive controllers can now perform speed measurements without requiring a complex optical measuring system

For rotating machinery, there are strict sequences of fault reaction chains for typical risk scenarios and, 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.

Speed measurement without optical measuring system

At TechnoWood, high performance woodworking CNC machines have tool spindles that have to maintain their milling speed with high precision at maximum loads of over 100kW peak power, but also have to come to a safe standstill in the event of a fault, for example, if the machining speed is set incorrectly.

According to Richard Eichele, Head of Export at KEB Automation, in conventional machines, optical encoder systems are used for this purpose, which enable reliable speed detection.

“Our analysis has 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,” he says.

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 encoders, but also reduces the cost of the spindle while making it more reliable in operation, as no encoder needs to be installed.


In addition to the control of widely-supported motor types such as synchronous, asynchronous, permanent magnet, reluctance, linear, high-torque motors and high speed motors, the COMBIVERT F6 offers additional functions such as automatic anti-cogging and optimised torque pre-control for linear and non-linear kinematics. Motor operation with encoder feedback or encoderless ASCL/SCL for precise speed control is also possible.

With drive-based safety, safety functions are shifted into the F6 drive platform, which means the cost of separate protective devices and cabling is reduced. The F6 is available in two control versions:

* The F6-K (COMPACT) version is highly integrated with everything onboard, including STO (Safe Torque Off) as standard. This version offers real time Ethernet control (EtherCAT or VARAN) as well as CAN and DIAGNOSTIC RS 232/485 communications interfaces as standard.

* The F6-A (APPLICATION) version is a flexible, modular design that allows scaleable functional safety, from basic STO to encoder-based safe motion. Optional use of current speed-based safety functions (eg Safe Limited Speed, Safe Maximum Speed, Safe Operating Stop, and Safe Direction) is available. All safety functions can be used in applications up to IEC 62061-SIL3 in accordance with IEC 61508 or up to PLe in accordance with ISO 13849. The safety functions are controlled via secure digital inputs or via FSoE (Fail Safe over EtherCAT). The F6-A also provides more real time fieldbus control options and safety PLC communications (EtherCAT, PROFINET, POWERLINK), giving the end user a genuine Industry 4.0/IoT-capable drive.

FSoE and CNC

At TechnoWood, 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 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.

Jonathan Newell
Latest posts by Jonathan Newell (see all)

Related news

Read More News From Unspecified Company: