CAN Cross-Communication: Direct VFD Data Transfer over Two Wires

In a previous article, we explored master-follower configurations and how KEB drives can utilize encoder signals to achieve synchronized motion. While this is a tried and tested method, KEB’s latest generation of drives introduces an even simpler approach: CAN Cross-Communication (or CAN cross). CAN cross enables multiple drives to exchange data directly with remarkably fast cycle rates, facilitating not only master-follower setups, but also the ability for KEB drives to manage additional tasks that would otherwise be handled by a PLC.

What is CAN Cross-Communication?

CAN Cross-Communication is a KEB-exclusive feature introduced in the latest firmware for KEB’s S6 and F6 drives. It allows KEB drives to communicate directly with one another over a CANopen network, eliminating the need for a separate CANopen master in many cases.

NOTE: CAN Cross-Communication is possible with KEB S6 & F6 drives from firmware 3.1+ with control card A or P.

Traditionally in a CANopen network, drives function as command receivers (logical slaves), reliant on a higher control system (the logical master) to transmit commands and manage network traffic. With CAN cross, KEB drives can assume the role of the logical master, transmitting commands and directing network traffic independently – all through just two wires. This not only reduces both cost and complexity, but also unlocks a range of features, including enhanced data transfer rates, subordinate control, and simplified master-follower configurations.

Faster Data Transfer

By enabling direct data exchange between drives, CAN cross-communication circumvents the need to route data through a PLC. Instead of having a drive relay data to a PLC, which then communicates with another drive, data is transferred directly between drives. The inherent speed of CAN bus combined with the ability to avoid unnecessary data detours significantly boosts the speed of data  transmission and processing.

Subordinate Control

In addition to facilitating direct data transfer, CAN cross enables multi-level communication systems. For example, a PLC can control the master drive via EtherCAT or PROFINET, while the master drive manages subordinate drives via CAN cross. This simplifies the control scheme and reduces the PLC’s workload, only requiring it to interface with the master drive. Consequently, commands such as initiating a run state or changing operation modes can be applied across all connected drives.

With CAN cross, the PLC can offload various tasks to the KEB drives, including:

• Simultaneous run commands
• Speed adjustments across the network
• Mode changes for all drives
• Master-Follower

Master-Follower: Synchronized Motion

The most ground-breaking advantage of CAN cross-communication is that it enables master-follower configurations with just a two-wire connection. Given that CAN bus is designed for high-speed data transfer, it is particularly well-suited for applications requiring real-time data exchange like master-follower.

In master-follower setups, rapid cycle times are critical. Even slight misalignment of coupled shafts can lead to operational issues or even destructive results. Through CAN cross, the master drive can transmit position, speed, or torque setpoints to follower drives with cycle times on the order of milliseconds. The follower drives can then reference these setpoints and use them to achieve synchronized motion.

KEB drives can implement three versions of master-follower:

1. Angular Synchronization: Follower drives maintain alignment with the master’s angular position, essential for applications where precise shaft alignment is critical.
2. Speed Synchronization: This mode synchronizes the velocity of follower drives with that of the master, offering a simpler approach that does not account for accumulated positional error.
3. Load Sharing: Torque is synchronized to the master drive to ensure torque is applied equally, allowing load to be distributed and preventing directly couple motors from fighting each other.

This grants maximum flexibility when implementing synchronized motion in new or existing applications. Master-follower configurations are used in various industrial applications where precise control and synchronization are critical. Examples include:

• Material Handling Systems: Synchronizing conveyors to ensure smooth and coordinated movement of materials.
• Winders: Ensuring multiple drives work in perfect harmony, preventing tears and breaks, and delivering flawlessly wound materials.
• Theater: Lifting heavy sets or complex stage structures requires a delicate balance. Master-follower distributes the load effortlessly across multiple drives, ensuring smooth and safe operation.

Conclusion 

By leveraging CAN Cross-Communication, KEB drives not only simplify the implementation of master-follower configurations, but also improve the efficiency of the data system, making it a powerful solution for modern automation applications. CAN cross requires minimal hardware to get started, so please reach out to a KEB applications engineer to learn more about how CAN cross can improve your application.