The control system of the machine is an important part of its design and market strategy. Many engineering teams employ a decentralized approach, using multiple PLC trains for different machine prices, and rely on third-party gateways to integrate legacy systems. This increases the costs associated with engineering, inventory, and site support, thereby reducing operational flexibility. Another approach is to standardize a single unified platform that can be extended across applications and can communicate with modern and traditional protocols.
Using policies that are not related to each other can be inefficient. Managing multiple different PLC trains creates management difficulties in training and inventory, while adding additional hardware, complexity, and potential failure points to the system. However, can these problems be completely solved by one platform? This paper will take Siemens SIMATIC S7-1200 ecosystem as an example to explore how to meet scalability and connectivity requirements.
Scalability Challenges for OEMs
The OEM's product line typically adopts a "good, good, best" model, where the complexity of the machine varies depending on the function included. While this makes sense, it is also a challenge to specify an economical and practical control system for an entry-level aircraft that is sufficient to control a high-end aircraft. For this purpose, the following common solutions can be used.
Multiple control platforms: Using different PLCs for each machine level seems to be cost effective per unit but generates downstream costs such as training, programming and spare parts inventory. With this approach, engineers need to be fully familiar with a variety of programming environments and require OEMs and end users to prepare larger and more complex inventory of spare parts.
Oversize Fixed I/O PLC: Selecting a single large PLC simplifies programming, but causes entry level models to lose competitiveness as BOM costs include redundant capacity that is not used. This approach also provides limited flexibility for future modifications. Since all fixed I/O points are allocated, even if the user adds just one sensor, redesign may be required, which is costly and time consuming.
A practical solution is the use of a modular control platform, characterized by the CPU being precisely configurable via the I/O interfaces required for each machine model.
Meeting Brownfield System Connectivity Challenges
How can state-of-the-art machines communicate effectively in a plant using previous generation technology? This is the core issue facing system integrators in the brownfield dilemma, where new machines using modern protocols such as PROFINET often need to be integrated with existing devices that rely on serial protocols such as Modbus RTUs. Therefore, the new system is required to communicate with traditional VFD, scale and other equipment via RS-485 serial communication. Two common solutions to these problems are as follows:
Third-party protocol gateway: the external gateway can be switched between PROFINET and Modbus RTU, but it will cause additional hardware cost, potential failure point and independent software tools for configuration. The data mapping between two systems can be cumbersome and the fault diagnosis of communication problems can be very complex, requiring the diagnosis of two different devices, usually from different manufacturers.
Industrial PC (IPC) with customized code: IPC running customized communication software is a powerful but expensive complex solution, which introduces the maintenance of PC operating system into the factory. This strategy requires specialized development skills in the IT and software areas, which traditional automation teams do not always have, and may result in solutions that are fragile and difficult to maintain.
Modern controllers shall native support traditional communication protocols to simplify architecture and provide centralized configuration.