When we think industry, we can’t deny how the industrial revolution changed how we manufactured everything, from clothes to engines. Over the last few decades, new technological advances kept emerging to improve the manufacturing processes and introduce automation into factories producing all our goods. With time, computers began playing a vital role in industry, and innovations have surfaced that have managed to even further revolutionize manufacturing. One of the most important of these is the Programmable Logic Controller (PLC), an industrial computer that can control the manufacturing processes from assembly lines to fault diagnosis. Let’s dive into industrial automation PLC history and how it has changed how we do things.
PLC
First, it’s important that we understand what PLC means. In very simple terms, a programmable logic controller is a computer we use to monitor inputs. Based on these, decisions are made depending on the PLC’s programming or logic to perform a control function in terms of automation––turning a machine on or off. Another way to define PLCs is a digital device that leverages a programmable memory that can store preset instructions. And based on those instructions, it implements particular functions that range from timing and arithmetic control to logic sequencing. This is done through digital or analog input/output modules. As you can probably tell, this is a sophisticated technology that can basically run an entire factory assembly line or more. It didn’t start out as intricate as that, though, and PLCs were first created to solve particular challenges facing manufacturers and to make their lives a bit easier.
The Old Ways
The initial programmable logic controllers were developed for the automotive industry, and it was the first to implement this technology. PLC development began in the late sixties, around 1968 to be exact, and it was developed based on a request from US car manufacturer General Motors. The goal was to replace hard-wired relay systems and timers, which were becoming too difficult to deal with, with programmable controllers that offered much more flexibility. Since then, PLCs, due to their adaptability to harsher environments, have been widely implemented as highly reliable automation controllers.
Before programmable logic controllers, factories used cam timers, relays, closed-loop controllers, and drum sequencers as control logic for manufacturing. While this system worked, it was extremely rigid and difficult to change. These systems were hard-wired, which made it quite difficult for production line engineers to make any changes to the automation process. If something went wrong with an assembly line, for example, or it needed updating, this meant rewiring and thoroughly updating the documentation. Worst of all, put one wire out of place, and you’d get a faulty system, which meant production would suffer delays that were often very costly. Staff would have to waste hours comparing existing wiring to schematics in an attempt to find the fault, which was counter-productive. With the advent of computers, a better way to automate the process came about. They were quickly implemented in control logic but also proved to be unreliable and required some challenging working conditions to be kept. This included close monitoring of temperature, power, and cleanliness. General-purpose computers also needed special programming, which made them even harder to use in industrial processes.
PLC Programming
With industrial processes suffering due to the lack of an improved and flexible logic controller, a need arose for a better option. In 1968, General Motors came up with a “standard machine controller,” and they designed its specifications, which were then given to vendors for a quote. The specifications were expansive and included some major elements that had to be part of the final product. The design had to have 16 inputs, expandable to 256. It needed to have 16 outputs, expandable to 128. It needed to be easily programmable (and reprogrammable) to avoid the hiccups faced with hard-wired controllers. It had to use solid-state components (modular and expandable). The specification also entailed that the new controller needed to have enough memory to avoid losing stored programs in an outage (1k expandable to 4k).
The white paper that the specifications were based on was written by an engineer called Edward R. Clark. The proposal that won came from Bedford Associates, based in Bedford, Massachusetts. Richard E. Morley worked for Bedford Associates, and he designed the prototype, called Modular Digital Controller. This machine met the specifications presented in General Motors’ proposal. It was tested by the company and showed a whopping 60% reduction in downtime, which was exactly the kind of reduction in time and cost the company was looking for.
Further Development
The first PLC was built in 1969 and was dubbed the 084 (Bedford Associates’ 84th project). After the success of the first mode, Bedford Associates started a new company called Modicon (modular digital controller) that was fully dedicated to the design, development, and production of the PLC. Richard E. Morley (better known as Dick Morley) worked on the development of the PLC with Modicon and is considered to be the father of the programmable logic controllers. And thus, the production of the Modicon 084 began.
The programming technique used in Modicon 084 made it stand out compared to other products in the market. For most other controller systems, Boolean Statements were used to calibrate and program the equipment. Without getting too technical, Boolean mathematics uses ones and zeroes, or in other words, true and false statements. Computers, in general, use this logic, but it wasn’t very suitable for manufacturing processes. Boolean Statements are actually brilliant in their simplicity, but they were too difficult to work with for factory engineers who were accustomed to relay logics that used ladder diagrams. This is where Morley’s clever idea revolutionized the whole process. He came up with a design to implement ladder logic in his system, which is basically using the relay language that engineers understand in Boolean logic. Needless to say, this changed everything.
Using this technique, it was possible to represent Boolean logic as a graphical representation with ladder logic. With the success of the Modicon brand, it was sold in 1977 to Gould Electronics and then finally to its current owner, Schneider Electric. Modicon also created another communication protocol called Modbus that is used with PLCs––it’s a data protocol used to connect many devices.
Allen-Bradley
As interest in PLCs grew, as did the competition in the market and the interest in developing new technologies in that field to further improve the process. Innovation became the only way that a company could grab a part of the market share of PLCs, which was eventually for the greater good. With more companies working on developing new techniques, programmable logic controllers became faster, more efficient, and more powerful. Simultaneously with the development of Modbus, Allen-Bradley developed new technology known as Data Highway. Odo Josef Struger worked for Allen-Bradley and is also known as one of the fathers of programmable logic controllers. He played a huge role in developing PLC programming language standards.
Personal Computers
By the 80s, personal computers were being introduced into offices and becoming more common. This paved the way for more technology interfacing with programmable logic controllers to further facilitate and improve the manufacturing process. It also made it much easier for system designers to get better results at a much faster rate. For them, using a computer was much faster and more accurate than using a drafting board. As the 90s approached, even the old-school designers set aside their drafting boards for the much faster computers, even if they were a lot slower than what we have nowadays.
It wasn’t just in the design room that computers began making things easier. They were also being interfaced with programmable logic controllers directly. This made it much easier and more accurate to monitor machine performance. Paired with PLC’s impeccable––and heavily implemented by that time––troubleshooting and diagnostic tools, machine diagnostics was heading in a whole new, much-improved direction.
The Evolution of Programming Languages
As computers evolved and PLC’s development saw more effort and investment, new programming languages emerged. As we said earlier, many of the early PLCs were not capable of graphical representation of the logic, which is why Boolean algebra was heavily used. As time passed, ladder logic was implemented with Boolean algebra and created the most commonly used programming languages of that time. The 1982 IEC 61131-3 (International Electrotechnical Commission (IEC) 61131-3) was one of the most important steps in the evolution of programmable logic controllers. Struger was involved in this standard and is credited with its development. The introduction of this language standard was crucial because it added much-needed consistency to the market and brought some sort of a benchmark or code that PLCs were compared to. In other words, any programmable logic controller under development was held up against this standard. Using it, the engineers and technicians were much more able to understand logic and program performance in any given PLC software. It didn’t matter if it was designed by one company or the other because they were all built in relation to the standard.
The 90s
Technology rapidly evolved in the 90s, and the development of PLCs was no exception. By then, there was a gradual reduction in new protocols being introduced for the sake of consistency and stability. On the other hand, the physical components of a PLC were undergoing heavy development so that the remnants of the 80s and decades before could be modernized using newer technologies. On the other hand, end-users had a few ideas in mind they wanted to implement. It was possible to allow for such requests because PLCs were flexible and could be easily leveraged.
Factory owners were requesting their new machinery come with PLC monitoring software. Yet, technicians were still heavily involved in the process. Many factory managers wanted the human element and insisted that their technicians do actual troubleshooting, which sort of hindered the development of PLCs for a while since the ones used and requested were simple in design and didn’t need to be sophisticated. As time went by, managers began using the PLCs a lot more so that the software could tell them what was wrong since its troubleshooting performance was much better. Fortunately, a newer technology was introduced that could streamline that relationship between man and machine.
Programmable Human Machine Interface (HMI)
No matter how sophisticated PLC technology was, there still was a need for the human element for configuration, monitoring, and reporting problems or alarms. This is where human machine interface (HMI) came in. At first, it was a simple button replacement, but it was developed over time when plant managers found more uses for this technology. HMI is basically a system that uses buttons and lights so that the user (engineer, technician, and so on) could interact with the system. This made machine monitoring much easier and critical since it was simpler to identify what was wrong.
Using HMI, you could get vital information such as manual intervention, product counts, machine problems, and much more. This would be displayed on the HMI screens using text displays as well as graphical touch screens. Later on, more advanced systems were conceived where monitoring software would be installed on a computer, and the PLC would be connected using a communication interface. More information was being processed and introduced, which eventually reflected on the overall production quality and efficiency.
Today, programmable logic controllers are still undergoing development to make them smaller, easier to maintain, and more efficient. The current size of the circuit boards and processors is insignificant to what it was fifty years ago, and this has not only reduced costs but also improved efficiency and made maintenance easier. Speed is the most crucial factor in PLCs these days, and it’s what any manufacturer is looking for. New solutions are being introduced all the time to give us faster PLCs without compromising durability and stability. There is no telling what the future holds for programmable logic controllers, but we can be certain that there is much in store.
