Applications and How-Tos, KEB Technology

Torque Sharing with KEB’s Yaw Library

Scott Froehle | January 7th, 2026

Introduction

KEB developed a PLC library to turn torque sharing with multiple motors from a daunting PLC code writing task into a simple function block. It was originally developed for the Yaw axis of a wind turbine which is responsible for turning the whole assembly on the top of the tower. This system is comprised of multiple motors mechanically coupled at the output that share the torque load.

KEB’s Yaw library is not limited to controlling a Yaw axis, it’s applicable to many torque-sharing applications such as:

• Industrial Mixers – To overcome high starting torque for viscous material
• Hoists & Cranes – To reduce cable stress
• Stage and Theatre – Multiple lift points on scenery or people
• Extruders – Co-rotating screws
• Gates/Doors – Large sliding units use two motors on one shaft or rail
• AS/RS – Smooth operation even when load shifts
• Mining – Bucket elevators and screw conveyors
• Printing – Web tension control

Library Features

KEB’s torque sharing library supports up to ten axes and is comprised of other KEB function blocks (FBs) which can be called upon by the user program. Several of the FBs are there to improve quality of life for the programmer such as the datalogger and error history FBs. The data types are all included in the library, so the programmer does not need to create their own to interact with it.

screenshot of COMBIVIS 6 software showing the Yaw control function block for easy torque sharing functionality — *Figure 1: Yaw Control Function Block*

Functional Description

The core function of the KEB Yaw Library is to control several axes sharing the load torque. These axes consist of a F6 drive, a servo or induction geared motor, and an application-specific component on the output of the gearing (screw, chain, mixer, etc…).

Typically, one axis works as the master running in speed control operation. The slave drives follow the master speed and torque. Since the load is mechanically coupled, the speed of each axis will be the same while the torque is balanced by the control (PI) to distribute the load and prevent the axes from fighting each other. The master axis can shift periodically to even out the component wear which will prolong the life of the machine.

If you have a load with un-coupled shafts such as a double screw extruder, you can use CAN cross or our Torque Balancer FB.

The Yaw Library uses CiA 402 device profile so the parameters shown in Figure 2 below are what is needed in the PDO:

Screenshot of KEB Combivis 6 Torque Sharing in Yaw Library Overview — *Figure 2: Parameters sent over the real-time EtherCAT bus to run the Yaw Library*

Implementation

There are two FBs running in the KEB torque sharing controller. The first is the master control, which selects the master axis. As mentioned in the last section, the master axis can be changed periodically and based on feedback from the system determining health.

The second is the motion control. This handles the drive control and monitoring of system health all in one FB. All that is required to get torque sharing up and running is basic control setup, homing, scaling, and PI tuning. Everything else is handled in the background which is a huge time saver for the programmer.

Screenshot of KEB Combivis Torque Sharing basic Yaw Implementation — *Figure 3: Torque Sharing FB Implementation*

Summary

KEB’s torque sharing library transforms what would traditionally be a complex, time-consuming programming challenge into a streamlined, efficient solution. By consolidating master control selection, motion control, drive monitoring, and system health management into intuitive function blocks, the library dramatically reduces implementation time while improving reliability across diverse applications.

The flexibility of the library, supporting up to ten axes with CiA 402 device profile compatibility and EtherCAT communication, makes it adaptable to virtually any torque sharing scenario beyond its original wind turbine yaw application. From industrial mixers requiring high starting torque to precision web tension control in printing operations, the same proven architecture delivers consistent performance.

It supports up to ten axes and is comprised of other KEB FBs that make up our extensive library. The master axis is run in speed and torque control and the slaves follow these values via PI controller. A KEB system running this library consists of:

For applications where multiple motors must work in harmony to share mechanical loads, KEB’s torque sharing library provides a battle-tested, industrial-grade solution that balances simplicity with sophisticated control capabilities.

Rather than starting from scratch, leverage the work already done by KEB’s programmers and get your torque sharing machine up and running quickly.

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