PLC & PC networking
23 June 2014
By linking PLCs with PC-based data acquisition and analysis, shops that fabricate customsed products can achieve better consistency and quality, explains Eamonn Walsh, chairman and managing director at Brainboxes
Advanced CNC machines allow the fabrication of intricate, large parts with complexity and tolerances that were not achievable even just a few years ago. Combined with advances in CAD/CAM analysis, planning and machine set-up, these improvements have also heightened expectations by designers and fabrication shops. As usual, technological advancement has widened the goal posts of possibility but it’s still a world where a mistaken automation instruction is costly.
The long-established PLC is a very good fit as the controller for a CNC machine given it can handle the demands of tight tool control and feedback while also functioning amid the harsh environment of the shop floor. Implementing the individual fabrication steps with the tight tolerances and intricate motions to defined precision shapes to precise dimensions is a task well suited to the PLC.
But the PLC is not the appropriate controller for analyzing and preparing the machine's operation, or for providing the long, carefully timed set of instructions to the CNC machine—a process which may span hours. It is limited in both computation capability and sequencing ability. Furthermore, it is limited in its ability to provide work-in-process updates or production-related data.
PCs working in conjunction with PLCs are the solution for those tasks. With their computational power, PCs can provide the necessary calculation-intensive capabilities for CAD/CAM applications to work out the complex dimensional analysis needed for the various cuts, machining paths, critical angles and their overall production sequencing.
In addition, PCs and their multi-faceted networking options can easily link to other PCs to provide Ethernet connectivity and other standard I/O ports. Critically they also support legacy interfaces such as RS-232. Their capabilities go beyond the basic hardware interfaces, as well, as they can support the myriad formats and protocols required by a diverse array of PLC-based CNC machines.
Pulling PLCs & PCs together
The PLC has its well-established role at the production line, while the PC provides higher-level access to an almost unlimited array of application software for advanced data analysis to support production planning, tracking, traceability and scheduling. Adding the considerable resources of PCs and their networks to a PLC test or production system takes advantage of the substantial benefits of each while avoiding their traditional weaknesses. Using CAD/CAM application tools, the PC can work out machining specifics and then feed the CNC a long sequence of precise instructions. The PC also enables further optimisation including improved yields, margins, and profits, as well as improved regulatory compliance.
PC-based analysis and connectivity gives management insight into production flow, along with a broad view of the process shifts which affect output, ranging from materials to operational to maintenance issues. Management can integrate additional factors including market data, availability and pricing of raw materials, and inventory situation, as part of the ERP (enterprise resource planning) goal.
The right modules can bridge the divide
There are multilevel approaches which meet the issues of the PLC and PC worlds, along with multiple networking and interoperability concerns, plus legacy factors. In the right combinations, these integrate the vertical path from transducer I/O and its basic interfaces, to factory protocols and advanced network compatibility. A new highly-integrated digital networking module for industrial machine control demonstrates this. The Brainboxes ED-204 combines a dual-port Ethernet switch, an Ethernet to RS-232 serial interface and an Ethernet to 4-channel digital I/O in a compact 3-in-1 solution that saves the cost of deploying three separate units.
At the networking and management levels this module can be configured, monitored and controlled using a Windows COM port driver, which enables legacy software support by providing an interface to the Windows platform. Seamlessly networking the older serial modules extends their life for many years to come, keeping costs low and investment return high; plant engineers don’t need to retrain to use these devices. The port is compatible with industry-standard PC packages.
Further, it's important to look ahead while not obsoleting the installed base; even the venerable RS-232 interface still has an important place in the PLC/CNC world. That's why there are adapter modules which provide connectivity and protocol compatibility between well-established serial interface standard and the ubiquitous Ethernet port.
As PCs increase their role with respect to PLC-based test and production, modules such as Brainboxes' ED units can support manufacturers who stay with PLCs for basic control, but who also want to have access to the system-wide, analysis-focused, and networked advantages which PCs can bring—especially when integrated with PLCs where appropriate. Selecting a module with PC and network interfaces and compatibility allows them to keep their options open for the future.
- The PLC is a good fit as the controller for a CNC machine, handling the demands of tight tool control and feedback in harsh environments
- PCs and their multi-faceted networking options can easily link to other PCs to provide Ethernet connectivity and other standard I/O ports
- The Brainboxes ED-204 combines a dual-port Ethernet switch, an Ethernet to RS-232 serial interface and an Ethernet to 4-channel digital I/O in one compact solution