Communications & Networks
Integrating Ethernet-based machine vision and image-based ID readers into factory networks
By John Lewis Cognex
By John Lewis Cognex
Oct. 8, 2015 – The traditional approach to integrating machine vision systems or image-based ID readers with factory automation involves connecting to a personal computer (PC) with a dedicated serial line or USB port and running a translator program on the PC to interface to the programmable logic controller (PLC) running the line.
The latest generation of machine vision systems and ID readers offer substantial improvements by providing Ethernet connectivity and tools to communicate directly with PLCs, robot controllers, PCs and human machine interfaces (HMIs). Key benefits include eliminating the need for the PC and cabling from the PC to the vision system or ID reader, eliminating the need for software on the PC, and the ability to communicate with the vision system or ID reader from anywhere on the factory network. This article will discuss recent advances in interfacing factory networks with vision systems and ID readers, explain how the new interfaces work and provide several case studies.
Using the conventional method, machine vision systems interface with factory networks and ID readers using RS-232 serial lines or USB connections to a personal computer. The personal computer runs translation software or a custom script that parses the data and pushes it to a PLC and sometimes to other network destinations. This approach involves expenses such as purchasing and programming the PC and providing cabling to the ID reader or vision system. In the past, manufacturers would often multiplex vision systems from a single PC in order to distribute vision at multiple points on the production line. The traditional method can involve considerable expense in purchasing the PCs and cabling used to connect vision systems and ID readers. Even greater expenses may be involved in developing or purchasing and configuring the translation software running on the PC.
Ethernet-based vision systems interface at control level
The latest generation of ID code readers and machine vision systems incorporate Ethernet ports that enable them to be directly connected to any switch or hub on a factory network and in turn communicate with all other devices on the network. The latest visions systems and ID readers also include tools that make it easy to interface directly to common factory automation hardware such as PLCs, robot controllers, HMIs and PCs. This approach eliminates the need for the PC and cabling from the PC to the ID reader or machine system, providing significant cost savings.
Additional cost savings arise from the elimination of software on the PC and, for industries subject to GMP, the elimination of the need to validate the PC and its software. Because they can be easily linked together and managed as a system over a network, the overall cost and effort involved in implementing and maintaining vision is reduced. Networked vision systems, vision sensors and ID readers enable data and images from all devices to be collected at a central point, viewed on a single monitor and archived for trend analysis and continuous process improvement. Advanced vision systems and sensors offer software tools to centralize application development and network administration.
Integrating vision with factory networks
In order to achieve these benefits, the ID reader or machine vision system must communicate with other factory automation devices such as PLCs over the network.
The latest generation of vision systems provides drivers, templates and sample code for open standard industrial Ethernet communications protocols such as MC Protocol, EtherNet/IP and Profinet for connection to a wide range of PLCs and other automation devices from Mitsubishi, Rockwell, Siemens and other manufacturers. Vision systems can communicate with most any make or model of robot.
Visualization options are provided to integrate inspection images, quality data, and interactive controls into an operator interface. One typical approach embeds the vision system image and custom display into a NET or ActiveX compatible custom application, or a PC-based HMI system from Rockwell, Wonderware, Citect and others. Open Process Control (OPC) Servers can be used to uplink vision data to HMI displays, SPC systems, plant supervisory systems and Microsoft Excel to monitor operations and record statistical data. Software development kits can be used to create a custom user interface for managing vision systems.
Here’s an example of how a vision system or ID reader can be connected via EtherNet/IP using a Rockwell Add-on Profile (AOP). The first step is to load an electronic data sheet (EDS) file supplied with the vision system into Rockwell’s EDS wizard software, RSLogix. EDS files are simple text files used by network configuration tools to help identify products and commission them on a network. The vision system or ID reader AOP is then loaded using Rockwell’s AOP setup utility. The third step is to set up a new module on the PLC, add a unique name and set the IP address of the reader itself. The final step is defining the input and output nodes. Then the engineer can write the application and define the associated logic in the familiar Rockwell environment.
The need in the past to use PCs to interface with vision systems and ID readers required the purchase of expensive hardware and development of sometimes complex software to interface with factory networks. A new generation of vision systems and ID readers with built-in Ethernet connectivity and tools for interfacing directly with common factory automation devices streamlines factory network integration. In addition to reducing the time and cost required for implementation, the new devices also increase the value of vision systems and ID readers by enabling the information they generate to be more easily accessed and utilized in other applications.
John Lewis, market development manager of Cognex, has written about machine vision and factory automation since 1996, and holds a B.S. degree in chemical engineering.