- October 30, 2014
- Cognex Corporation
By John Lewis, Cognex
The need to use PCs to interface with vision systems and ID readers required the purchase of expensive hardware and development of sometimes complex software. A new generation of vision systems and ID readers with built-in EtherNet/IP connectivity streamlines factory network integration.
By John Lewis, Cognex
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. Traditional machine vision interfaces at device level The traditional method of interfacing between factory networks and ID readers and machine vision systems uses 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. The number of code readers or vision systems that can be connected to a single PC is limited so this approach is not easily scalable. Companies that are required to maintain Good Manufacturing Practices (GMP) incur additional expenses for validation of the PC and software. Another limitation of the traditional approach is that the ID reader or vision system communicates only with the PC it is directly connected to. So it can be challenging to interface with other applications such as statistical process control (SPC) or to download configurations to multiple vision systems such as during model changeover. Ethernet-based vision systems interfaces 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. Direct Ethernet communications between the ID reader or machine vision system and the factory network improves scalability by making it possible to add ID readers or vision systems without having to add other hardware or software. The latest generation of vision systems and ID readers also generally includes RS-232 and USB connectivity which enables direct connection to a PC for setup and troubleshooting was well as implementation in legacy applications. 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. Networking also allows vision systems to increase manufacturing agility by automating procedures such as changeovers for mixed-model processing. Advanced vision systems and sensors offer software tools to centralize application development and network administration. An engineer can set up and modify vision applications, share applications with other plant sites and remotely troubleshoot problems with technicians, all without ever leaving the office. Such tools make it very easy to add new vision sensors to an existing line or copy existing vision sensor applications to new vision sensors for reuse on a new line. 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. A number of industrial Ethernet protocols are most commonly used for this purpose:
- EtherNet/IP — This Rockwell-defined protocol enables vision systems to be linked to Allen-Bradley PLCs and other devices over a single Ethernet cable, eliminating the need for complex wiring schemes and costly network gateways.
- ModBus/TCP — This industrial network protocol is defined by Schneider Electric and permits direct connectivity to Modicon PLCs and other devices over Ethernet.
- Profinet — This industrial communications protocol is defined by Profibus International and allows vision systems to communicate with Siemens PLCs and other factory automation devices.
Typical communications capabilities include pre-configured drivers, ready-to-use templates and sample code to accelerate system set-up and ensure smooth communication with factory automation robots and controllers. An array of visualization options are typically provided for integrating inspection images into a central operator interface. A point and click configuration interface is used to control multiple vision systems from a network PC and allows users to easily transfer data and images to an enterprise file server or display them in the user’s own operator interface. 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. Pre-configured drivers, ready-to-use templates and sample code are available for robots by ABB, Denso, Fanuc, Kawasaki, Kuka, Motoman and Staubli. Communications with robots by Mitsubishi, Adept, Epson and many other manufacturers is also supported. Discrete I/O and serial protocols are available to support older PLCs and devices without network connectivity. Fieldbus support is provided for established standards, including CCLink, DeviceNet, and Profibus. 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. ID reader/PLC connectivity example Add on profile loaded with Rockwell AOP setup utility New module set up on PLC Definition of input and output nodes 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. Case histories Before a foundry can deliver 40-pound aluminum clutch housings to its customer, it must saw off the sprues and remove flash. Previously, one operator loaded the castings into a machine that sawed the sprue off and a second operator held the castings while another cutter removed flash. Odyssey Machine Company of Bowling Green, Ohio, developed a vision-guided robot application that eliminates both of these difficult and potentially dangerous tasks. A machine vision system identifies which of eight different parts is on the infeed conveyor and the location of that part. The robot then picks up the part and loads it into the three-stage sprue saw. Next, the robot takes the part from the saw and moves it around a high speed cutter in a secondary fixture to remove flash. Guided by vision system, robot picks clutch housing from conveyor The workcell runs under the control of an Allen-Bradley programmable logic controller (PLC) which is connected to the vision system with an Ethernet cable. The robot used in this application is a Fanuc S900W that the customer had previously retired, but was rebuilt by Fanuc for this application. The PLC was easily connected to the vision system via an Ethernet connection because it contains protocols needed to communicate with the PLC. The vision system is connected to the RJ2 robot control with digital input/outputs to communicate with the robot controller. The vision system sends the part identification information and the coordinate information on the part to the PLC which sends information directly to the robot controller. In the state of Texas, a tax stamp must be applied to each liquor bottle sold at the wholesale level, such as to hotels and restaurants. Good-Goody Liquor, Dallas, Texas, wanted to automate the process of reading the stamps to ensure each bottle has a tax stamp and to store its number in a database with the bottle number for audit purposes. The application presents a major barcode reading challenge. The system processes bottles at the rate of one per second and the bottles have different shapes and different backgrounds. In addition, the label position varies and the lighting continually changes. ID reader reads tax stamp barcode for verification and tracking Cisco-Eagle, the company that built the automated system for applying the stamps, worked with Goody-Goody Liquor to develop a system that automatically applies the tax stamps with 1D barcodes and reads the barcode for verification and tracking. Machine vision is used to identify bottles that do not have a stamp on them so they can be removed from the line. Machine vision is also used to capture the tax stamp number so it can be entered into a database along with the bottle number in case of an audit. The ID reader communicates using Rockwell’s Ethernet/IP protocol and has a driver for Rockwell PLCs that simplifies the integration task. Once the driver is installed in the PLC, the camera shows up as a component in the PLC. The PLC can then be easily programmed to issue any commands to the camera such as to capture an image with minimal programming. In this application, issuing the command to the barcode reader to capture an image, provide feedback on whether or not a barcode was detected, and send the barcode number was accomplished with only three lines of code. Conclusion 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.Learn More
Did you enjoy this great article?
Check out our free e-newsletters to read more great articles..Subscribe