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  • Writer's pictureMatt Prellwitz

Why Servo Drives Should Be Your High-performance VFD

When variable frequency drive (VFD) applications need tight speed and torque control, could new servo technologies with highly synchronized EtherCAT fieldbus performance actually be the best solution?

Beckhoff AX5000 and AX8000 servo drives

In applications with high-performance motion from spindle motors or induction motors, VFDs might seem like the logical answer. High-end VFDs promise better current and external position control, but complex configuration keeps the motors and drives from reaching their combined potential. Most often, the necessary incremental or high-end encoder feedback for speed and torque control is simply not available. In these cases, a servo drive with VFD mode in its firmware provides tighter motion control and, perhaps surprisingly, overall cost savings.

This servo approach is becoming more widespread as companies work to get high performance from low-cost motors. Beckhoff servo drives in the AX5000 and AX8000 series offer this capability, easily integrating either incremental or high-end encoder feedback. In addition, these can power induction motors as well as a wide variety of rotary servomotors and linear motors. For example, one AX8000 drive module in VFD mode can control multiple induction motors with feedback and induction motors in the same DC power, and a two-channel AX5000 drive can control a servo or linear motor on one channel and then an induction motor with incremental feedback on the other. This reduces hardware, cabinet space and spare component stock requirements.

Whether using a servo drive or VFD from various vendors, configuration can often be time consuming and trouble prone. But the Beckhoff solution uses a Drive Manager and other tools built into our comprehensive TwinCAT 3 automation software to simplify everything from sizing to commissioning to operation. Programming takes place with either simple point-to-point motion commands or frequency control directly from the PLC. All connected devices, including motors and drives, are automatically identified by the software using the TwinCAT ADS protocol and EtherCAT or a wide range of other fieldbuses. Motor selection remains vendor neutral, and that is important if the application requires induction motors that are very large, which are best suited for AX5000 drives, or otherwise specialized.

While the price of servo drives is higher than VFDs, the Beckhoff drives combine several key functionalities that reduce the overall cost, often up to 10%. The EtherCAT-based drives deliver all of the benefits of the world’s fastest fieldbus: high synchronization, great diagnostics, flexible topology, simple configuration, etc. And both series offer functional safety up to PLe with Safety over EtherCAT (FSoE). This integrated solution provides STO, SS1 and others directly in the drive, with programming again handled in TwinCAT. This makes the application safer and reduces components, programming and software requirements. So whether you have a straightforward application with the AX8000 or need to run large, 30-horsepower induction motors with AX5000s, the benefits and high performance remain the same.

Want to learn more about using AX8000 or AX5000 Servo Drives in high-performance VFD applications? Contact your local Beckhoff sales engineer today.


Matt Prellwitz is the Drive Technology Product Manager for Beckhoff Automation LLC.

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