Role of CNCs and PLCs in the factory of the future

As automation in manufacturing increases, industrial controllers and control systems are becoming more complex and efficient, which will change the role of computer numerical controls (CNCs) and programmable logic controllers (PLCs) in the factory of the future.

12/21/2017


Computer numerical controls (CNCs) and programmable logic controllers (PLCs) will have different role to play in the factory of the future, which is becoming more automated and focused on minimizing downtime. Courtesy: Fanuc/Control Engineering EuropeThe concept of automation is changing as Industrie 4.0 and the Industrial Internet of Things (IIoT) become more prevalent. Automation encompasses concepts such as zero downtime, increased precision, high speeds, efficiency, and proactive maintenance. This is powered by digital, programmable systems that have been developed and perfected over the last several decades.

Computer numerical controls (CNCs), for example, facilitate the automation of machine tools through computers that execute pre-programmed sequences. "CNC was developed during the 50s and 60s as a logical progression from computer-aided manufacturing (CAM) and tracer-based automation," said Ian Baird, CNC applications manager for Fanuc's Factory Automation Division. "Established alongside computer and servo system developments, it helped manufacturers to meet their increasing requirements for repeatable, high-precision production.

Today, five main parts form the CNC—a sequencer, interpolator, servo controllers, logic controller, and operator control interface—and it is synonymous with precision and control." Twenty years after the CNC was introduced, a cheaper and simpler form of computer-aided control was developed: the programmable logic controller (PLC).

"The PLC was developed in the 1980s to supersede relay logic control systems, which were often less cost-effective, flexible, and easy to use because they relied on hardware to perform their key functions. PLC has input and output functionality and can be programmed to perform sequential operations, data processing, or simple axes control."

However, the PLC was never intended to replace the CNC. "Both serve very different purposes and marketplaces, with their own advantages and disadvantages. Therefore, it would be limiting for anyone in industry to say, 'I've invested in CNC—there's no room for PLC here,' because they are two entirely different controls," continued Baird.

CNC is associated more with automation because its usage extends beyond a simple input/output (I/O) algorithm. The modern CNC is a flexible, digitally-controlled system designed to suit a manufacturer's specific needs without having to reprogram the entire system.

"Most modern CNCs also include user interfaces with built-in operation, maintenance, and diagnostic screens. For this reason, CNC is popular with people who want full control over their machines, because its functionality does allow you to fly solo after a bit of training," said Baird. The flexibility of CNC lends it to complex, multi-axis machining in almost any industry. "A CNC's applications are limited only by imagination. Any application that requires precision motion control needs CNC, whether that be the manufacture of watch parts and medical devices, or reactive atomic plasma etching."

Simple control tasks

The PLC, according to Baird, is useful for simple control tasks. "If you've got an application that doesn't need a high level of accuracy or flexible motion control, such as an ac motor conveyor, then PLC is often the best choice. It is cheaper than CNC, which would arguably be better invested in more complex applications."

However, Baird said there are some disadvantages to the PLC's simplicity. "PLC does not have the flexibility of CNC. If you need to change the program even slightly, you have to reprogram it entirely. It also doesn't offer the precision of CNC and is therefore best used as a low-cost solution for basic tasks." According to Baird, despite PLC's low cost many manufacturers are choosing CNC, due in part to its lower total cost of ownership. "It is interesting to see many designers turning to CNC after investing in PLC, largely for reasons of flexibility, reliability, and cost. The initial cost of CNC is higher than that of PLC, but the return on investment can be higher in the long term because of the CNC's higher reliability and control. It also gives system designers the flexibility to dictate how much control they want users to have over their machines."

The long-term cost-effectiveness of CNC can be attributed to its advanced user-programmable features, which can minimize downtime and control the energy usage or output of the machine.

Many CNCs are equipped with artificial intelligence (AI) contour control. This means the machine can be controlled to operate within a certain workload, or adaptively control the machine for working overnight. For example, it can be programmed so it only works at 80% load, allowing the company to be more economical with their energy usage. CNCs also come equipped with energy efficiency functions such as energy charge modules.

CNCs also have safety functions, which lend themselves well for collaborative operations with humans. "CNCs come equipped with a digital algorithm that looks after the motion control," Baird said. "This digital system is formed of two parts—a real digital data system and an observer digital system. The observer acts like the 'ideal', providing the machine with the parameters in which it should be working. The real and the observer are both driven by the same command, so they should be working in exactly the same way.

"If the real system encounters a disruption, such as an unexpected load, then this causes the real data to deviate from the observer data. The machine will translate this as a collision and respond in one of two ways. If it's moving slowly, it will stop, and if it's moving quickly, it will perform a 'vectored back-off', where it will retract any moving machinery to avoid damage. For high-end machines, you can also incorporate 3-D technology, which stops five-axis machinery from moving outside of its pre-determined work envelope."

Zero downtime also is an important consideration for manufacturers looking to automate their processes. Unplanned downtime is expensive and can halt production for days, weeks, or even months. An undetected fault could cause irreversible damage to machinery and could even be hazardous to workers. 

Minimizing downtime

"Although it's unrealistic to expect factories to work seamlessly 24/7, we can aim to minimize downtime caused by minor faults or errors," Baird said. This is where the concept of predictive maintenance comes in, which, as Baird explained, is facilitated by CNC technology. "Predictive maintenance allows us to spot potential problems before they occur, and act accordingly before they become serious. We do this by employing the automation technology that controls the machine as a kind of watchman."

Does this mean the CNC is destined to become the sole tool of the factory of the future? Baird doesn't think so. He believes the PLC still has a critical role to play. "The best example of this is a production line. CNC may be controlling the robot arms, the tooling, milling, and grinding, but PLC is powering the belt that takes a product or material from one part of the line to the next. The complexity of CNC does not lend it well to such tasks and would be wasted. As part of a factory floor, where simple and complex tasks are done simultaneously, CNC and PLC work perfectly together."

With CNC and PLC both maintaining a place in manufacturing's toolkit, it is now important to look at how they can be developed. "Industrial control systems (ICSs) will continue to evolve, and this will largely come in the form of specializations suited to specific industries," Baird said.

"Third-parties will also exploit the concept of an open interface in order to integrate the factory with the Internet of Things (IoT). With this will come intelligent machines and data collection and analysis on a vast scale, which will help us to identify further process improvements."

While it isn't clear what role CNCs and PLCs will play in the factory of the future, they will both form a part of it, even if they aren't always working in collaboration.

Suzanne Gill, editor, Control Engineering Europe. Fanuc provided additional information for this article, which originally appeared in an October 15 Control Engineering Europe article online. Edited by Chris Vavra, production editor, Control Engineering, CFE Media, cvavra@cfemedia.com.

MORE INSIGHTS

www.controleng.com keywords: PLC, CNC

  • Computer numerical controls (CNCs), which have been around since the 1950s, facilitate the automation of machine tools through computers.
  • Programmable logic controllers (PLCs) are designed for more simple control tasks than CNCs and are useful on the production line and for applications that aren't as dependent on accuracy.
  • PLCs and CNCs will have different roles in the factory of the future, but they will remain useful to manufacturers. 

Consider this

What new roles will PLCs and CNCs play in the factory of the future and what new benefits might they provide to companies?

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Control Engineering Europe article: Will there be room for CNCs and PLCs in the factory of the future?



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