Introduction to the Problem
Many companies have Programmable Logic Controllers (PLCs). The main function of a PLC is to manage low-level control and automation in an industrial environment. The robustness of existing PLCs and the expense of replacing and reprogramming them means that PLCs are often used well beyond their 20-year lifespan.
PLC data can be a rich source of information about manufacturing operations and processes. For example, live PLC data could improve operational efficiency, anomaly detection, machine utilisation, and the identification of possible safety issues. Many companies, including the PLC manufacturers, offer ethernet, WiFi or serial connection to collect data from PLCs.
This is great for newer PLCs or machines, but there are three scenarios where this cannot be used:
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The PLC is an older model without this built-in capability (e.g., no ethernet or serial connection).
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A third party installed the PLC or came as part of an existing machine. Editing the PLC code or adding new functionality could void the warranty or agreement with the equipment supplier.
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Connecting the PLC to the factory network could expose that machine and make it vulnerable to costly attacks.
Many of these problems could be solved by spending money on help from industry experts or new equipment. However, this is not accessible to many SMEs. Even when a company has the money it is still worth testing to see if the PLC data could be useful.
Technology Solution - PLC-MS
The technology solution to the problem mentioned is to create a low-cost PLC monitoring system (PLC-MS). The PLC-MS uses a Raspberry Pi, a touch screen and a low-cost webcam mounted on the door of the PLC cabinet, as shown in the images on the right. The equipment for the PLC-MS can be purchased for under £150. The camera faces the PLC I/O module of the PLC. A docker-based program runs on the Raspberry PI, collecting images at 9-10Hz; the PLC images are processed to capture the state of the PLC light (on or off).
This data provides insight into the PLC program and the utilisation of different machines and equipment. The solution has been extended to include a self-realigning function which can correct for any movement of the camera. The solution has been successfully deployed in SMEs. See the Trox case study in case studies for more details. An example of a dashboard showing the use of one production line is shown in the image below. Because the solution does not connect directly to the PLC, it does not open up potential vulnerabilities in the PLC. It also does not interfere with the existing equipment and can be easily removed and added as needed.
Potential Impact
This solution provides an excellent, fast way to upgrade any legacy equipment to a smart factory. The solution generates extensive useful data which can be used to improve factory operations. For example, if an SME has clear data about when a CNC machine or robot is in use, it can see if it can become more productive by investing in new equipment or improving its current equipment usage. The low-cost hardware used makes this solution acceptable to all SMEs, which comprise most of the UK's manufacturers.
