How Do I Synchronize Conveyor Speeds

A common application question that arises at KEB is how to synchronize the speed of two or more motors. The best solution depends on the speed, load, precision, and available hardware within the application. Here, we will address the question with respect to a specific application: How can conveyor speeds be synchronized?

This question is frequently asked for applications where one conveyor feeds into another. In some instances, the speeds must match 1:1, while in others, the speeds must follow a different ratio (e.g., 1:2, 1:3, etc.). It is crucial in all cases that the conveyor speeds match to prevent jamming and product damage.

Similar vs. Synchronized Speed

Before setting up the conveyors, determine whether you need them to run at the same speed or have synchronized speed. If you only need them to run at the same speed, you can achieve this by running two induction motors at the same frequency, for example, 60 Hz. However, due to factors such as slip and changes in load, the motors may vary slightly in speed.

If you require synchronized speed, it means the second conveyor will turn a specific number of degrees for every set number of degrees the first conveyor turns. This can be achieved using mechanical linkages, but this method is often large, complex, and prone to wear and failure. An alternative and more efficient option is to electronically couple the two motors using Variable Frequency Drives (VFDs) or servo drives that support a master-follower function (electronic line shaft).

Similar Speed

If you need the same speed, you’ll need a basic VFD that can receive the same command signal as the first VFD. Then you’ll need to set this second drive to the desired ratio (same speed, 3% faster, etc.). If possible, it may be easiest to directly modify the machine’s PLC to send a second command signal to the second VFD so that the user only needs to go to one location to change the product.

Advantages

• Simple to set up
• Easy to adjust

Disadvantages

• Motors will deviate slightly
• No system feedback to account for dynamic load or jams

Synchronized Speed: Fieldbus

If you require synchronized speed, there are options available. You can set up both drives on a fieldbus system that supports synchronous motion, such as EtherCAT or Ethernet/IP. This will need a PLC or IPC, like the KEB C6 Smart, with sufficient processing power to handle the motion profiles of multiple drives. Additionally, you’ll need to use drives that are compatible with the fieldbus system you are using.

Advantages

• Real-time synchronization (accounts for dynamic load and jams)
• Motion Profiles Managed from a Single Device

Disadvantages

• Coding knowledge required
• More powerful PLC/IPC required

Synchronized Speed: Master-Follower

Another option would be to opt for a drive that supports on-board master-follower configurations, such as KEB’s S6 & F6 drives. The S6 & F6 enable synchronized motion between drives with a direct link either over an encoder cable, or even just two wires (CAN). This eliminates the need for a PLC, giving you the flexibility to switch PLC brands or even remove the PLC entirely.

Synchronized motion profiles are set up in the drives, which is much simpler from a hardware standpoint. The fast cycle times mean that this configuration achieves real-time synchronization, ensuring high accuracy and reliability.

Advantages

• Real-time synchronization (accounts for dynamic load and jams)
• No PLC or coding knowledge required
• Not locked into one PLC brand

Disadvantages 

• Longer drive startup process

Conclusion

While similar speed setups are simpler and easier to adjust, they lack the precision needed to handle dynamic loads and prevent jams. On the other hand, synchronized speed setups, whether through fieldbus systems or master-follower drives, offer real-time accuracy and reliability, though they may require more advanced hardware and setup.

Ultimately, the best solution depends on the level of precision and control your application demands. By carefully considering these options, you can select the most appropriate method to ensure your conveyors run smoothly and effectively.