EtherNet/IP to DeviceNet Gateway for Rockwell PLC & Delta Servo

ByHANI_AUTOMATION HANI

In modern industrial automation, integrating devices from different manufacturers often means dealing with incompatible communication protocols. A common scenario is connecting a Rockwell Automation PLC, which uses EtherNet/IP, with a Delta servo drive that only supports DeviceNet. Instead of replacing expensive hardware, a protocol gateway provides a cost-effective solution. This article explores how an EtherNet/IP to DeviceNet gateway enables seamless communication between a Rockwell CompactLogix PLC and Delta ASDA-A2 servo drives in a packaging line retrofit.

Project Background: The Integration Challenge

During a packaging line upgrade, the customer required new servo drives to be Delta due to budget constraints. However, the main controller was a Rockwell CompactLogix PLC that only communicated via EtherNet/IP. The selected Delta ASDA-A2 servos came with a DeviceNet interface. Replacing either the PLC or the servos would have blown the budget. The solution was to insert a protocol gateway that converts EtherNet/IP to DeviceNet, acting as a bridge between the two networks.

System Architecture Overview

The communication network is split into two segments:

  • Upper Segment (Information Layer): The Rockwell PLC acts as an EtherNet/IP scanner. It connects via Ethernet to the gateway’s EtherNet/IP adapter port. The PLC sends position and speed commands and receives status feedback.
  • Lower Segment (Device Layer): The gateway’s DeviceNet scanner interface connects to a DeviceNet trunk line, which links four Delta ASDA-A2 servo drives in parallel. The gateway translates EtherNet/IP data into DeviceNet messages and forwards them to the servos.

In essence, the gateway serves as a translator, enabling two otherwise incompatible devices to communicate.

Interface Roles: Master and Slave Configuration

The gateway is configured with DeviceNet as the master and EtherNet/IP as the slave. This arrangement simplifies integration:

  • EtherNet/IP Adapter (Slave): The Rockwell PLC is the scanner, initiating all communication. The gateway responds to the PLC’s requests, requiring no changes to the PLC program.
  • DeviceNet Scanner (Master): The gateway actively polls the four servo drives. Each servo’s node address and baud rate (set to 500 kbps) are configured in the gateway. Connections are established automatically on power-up.

In operation, the EtherNet/IP Requested Packet Interval (RPI) was set to 10 ms, while the DeviceNet polling cycle was approximately 5-8 ms. This performance easily handled a packaging speed of 150 packs per minute.

Delta Servo Technical Specifications

The Delta ASDA-A2 series servos used in this project included:

  • Models: ASDA-A2-0421-L (400W) and ASDA-A2-1021-L (1kW)
  • Encoder: 20-bit incremental with battery backup for absolute position
  • Control Mode: Position mode, with target positions sent via DeviceNet instead of pulse inputs
  • Key Parameters: Speed response bandwidth of 550 Hz, overload capacity of 300% for 3 seconds

The DeviceNet object dictionary of the Delta servos was standard, allowing the gateway to auto-scan and recognize most parameters, significantly reducing configuration time.

Gateway Functionality: Data Mapping, Rate Matching, and Fault Transparency

The gateway performs three core tasks:

  1. Data Mapping: It maps EtherNet/IP Assembly instances from the PLC to DeviceNet I/O data blocks. For example, bytes 0-3 from the PLC (target position) are directly transferred to the DeviceNet output.
  2. Rate Matching: With EtherNet/IP updates every 10 ms and DeviceNet polling every 5 ms, the gateway buffers data to prevent loss.
  3. Fault Transparency: When a servo alarms, the gateway passes the error code to the PLC via EtherNet/IP. The HMI can then display specific messages like “Servo 3 overload,” aiding maintenance.

Performance and Reliability

After six months of continuous operation, the system experienced no communication faults. The key to success was selecting a gateway with full DeviceNet master capability (supporting multiple slaves) and an EtherNet/IP adapter that supports Class 1 I/O connections, which is required by Rockwell PLCs.

Commissioning Tips

For first-time setup of such a heterogeneous network, it is advisable to use Wireshark to capture EtherNet/IP packets and a DeviceNet analyzer to monitor bus traffic. Verify data consistency on both ends before finalizing the PLC program. This approach minimizes debugging time and ensures a smooth startup.

Conclusion

Protocol gateways are a practical solution for integrating legacy or cost-effective devices into modern control systems. By bridging EtherNet/IP and DeviceNet, manufacturers can leverage existing hardware investments while meeting performance requirements. This case study demonstrates that with proper configuration, a gateway can deliver reliable, real-time control in demanding industrial applications.

Similar Posts