Connecting your vision system to the factory, everything you need to know

There has been a rapid move over the last few years from using vision systems not just for stand-alone, in-line quality control processes, but to drill down and use the information which is created, assessed and archived through the automated vision system.

When vision systems first started being used in numbers in the early 1990’s, the only real option of connection to the production line PLC (programmable logic controller) was through hardwired digital I/O (PNP/NPN), simply acting like a relay to make a decision on product quality and then to trigger a reject arm or air blast to remove the rogue product. The next evolution from there was to start to save some of the basic data at the same time as the inspection process took place. Simple statistics on how many products had passed the vision system inspection and how many had been rejected. This data could then either be displayed on the PLC HMI in simple form or via rudimentary displays on the vision system. From there, communication started with the RS-232 serial line, and this morphed into USB and onto TCP/IP.

The Fieldbus protocol was the next evolution of communication with vision systems. From the standpoint of the user, the fieldbus looked to be state-based, similar to digital I/O. In reality, the data was exchanged serially through a network. Because these messages were sent on a clock cycle, the information was delayed. The benefit of Fieldbus over digital I/O was that each data exchange package of several hundred to 1,000 bytes was exchanged. PROFIBUS, CC-Link, CANopen, and DeviceNet were among the first protocols to be created. While fieldbuses of the first generation utilised serial connections to exchange data, fieldbuses of the second generation used Ethernet. As a result, the technology was sometimes referred to as “Industrial Ethernet” as it evolved, but the term’s meaning is slightly ambiguous.

When compared to serial data transfer, Ethernet enables substantially more data to be sent. However, using Ethernet as a fieldbus medium has the problem of having non-deterministic transmission timings. To obtain enough real-time performance, several Industrial Ethernet protocols such as PROFINET, EtherNet/IP, Ethernet Powerlink, or EtherCAT typically expanded the Ethernet standard (to the Common Industrial Protocol, CIP). For PC-based vision systems, some of these expansions are implemented in hardware, which necessitates the insertion of an expansion card in the vision controller unit.

So, the big evolution came with the support of this “industrial ethernet” communication, so vision systems now use a unified standard supporting real-time Ethernet and Fieldbus systems for PC-based automation. This allows for data to be transferred and exchanged with the PLC through ethernet protocols on a single connection. The benefit is the reduction in complex and costly cabling, easy integration and fast deployment of vision systems. Ethernet is characterised by the large amount of data that can be transferred.

This allows for the seamless and simple integration with all standard PLCs, such as Allen-Bradley, Siemens, Schneider, Omron and others – directly to the vision systems controller unit. Vision system data can be displayed on the PLC HMI, along with the vision HMI, where required.

The most common protocols are:
Profinet — This industrial communications protocol is defined by Profibus International and allows vision systems to communicate with Siemens PLCs and other factory automation devices which support the protocol.

EtherNet/IP — This Rockwell-defined protocol enables a vision system to connect to Allen-Bradley PLCs and other devices.

ModBus/TCP — This industrial network protocol is defined by Schneider Electric and permits direct connectivity to PLCs and other devices over Ethernet.

This progress was and is being accompanied by an increase in the resolutions of industrial cameras. Industrial cameras for machine vision inspection are not always up to date with the commercial world of smartphones. This is largely because the quality necessary for automatic vision assessment is considerably greater than the quality required for merely seeing a photo (i.e. you don’t worry about a dead pixel when looking at your holiday pics!). As a preserved picture archive for end-of-line photo archiving in an industrial environment, high-resolution image quality is now important. In addition to connecting to the line PLC, vision systems must now link to the whole factory network environment and industrial information systems. Vision systems may now interact directly with production databases, with every image of every product leaving the factory gates being taken, recorded and time-stamped, and even linked to a batch or component number via serial number tracking. Now, vision systems are not only used as a goalkeeper to stop bad products from going out the door, but also as a warranty protection providing tangible image data for historic record keeping.

In conclusion, the industrial ethernet connection is now the easiest and fastest way to integrate vision system devices into an automated environment. The ease of connection, the lower cost of cabling, and the use of standard protocols make it a simple and effective method for high-speed communication, coupled with database connections for further image and data collection from the vision system. Vision systems are now linked to complete factory line control and command centres for fully immersive data collection.

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