How to unlock the power of IO-Link for automation

Most of the history of industrial automation has been about big machines talking to other big machines. Over time, however, many devices have been getting smaller and smarter. In particular, sensors and actuators are no longer limited to being told whether they should be on or off. They can talk back to the control system, function with greater precision, and provide real-time data about their health and performance. 

In the recent past, sending that much information back and forth between small devices and higher-level controllers would have required thick bundles of wiring or cost-prohibitive chipsets. Today, however, a growing number of integrators and device manufacturers are recognizing the potential of IO-Link. This open-source communication protocol enables robust two-way data transfer and advanced capabilities at relatively low cost over single-wire connections. 

Although IO-Link has been around since 2006, it has seen much more widespread use since 2020. This trend is being driven by the rapid growth of industrial Internet of Things (IIoT) devices and more integrated manufacturing facilities.

Growing demand for remote configuration and predictive maintenance is also speeding the pace of adoption. But another key factor in IO-Link’s success is that it augments, rather than replaces, familiar technologies.

What is IO-Link?

IO-Link is the first globally standardized protocol (IEC 61131-9) for point-to-point communication between sensors, actuators, and control systems such as programmable logic controllers (PLCs) or human-machine interfaces (HMIs). It was developed by a consortium of automation companies and other industry stakeholders in response to the increasing complexity and miniaturization of devices, plus the need for more detailed data than binary signals.

A single standard, unshielded wire enables fast, two-way communication with an IO-Link master hub, which enables easy integration with higher-level systems. Although most often used with PROFINET, IO-Link also has specifications for integration with EtherNet/IP, EtherCAT, and other major field bus systems. Common uses of the technology include factory automation, condition-based monitoring, asset management, and quality control. 

The primary limitation of IO-Link is distance. Packet loss can occur if a cable exceeds 20 meters or so. This is a minor concern, however, since electric sensors and actuators typically don’t require cables that long. 

Evolution, not revolution

Although greater efficiency and throughput are common goals of industrial automation, big disruptive changes aren’t always welcome. It’s a rare operation that’s willing to rip and replace an expensive system that’s getting the job done, and even greenfield facilities hesitate to become early adopters. 

One of the great advantages of IO-Link, therefore, is its ability to integrate seamlessly with established higher-level control systems. Existing systems and expertise can be leveraged and enhanced, not replaced.

Individual wires from devices connect to IO-Link hubs, known as “masters,” via standard M5, M8, or M12 connectors. The master then communicates with the PLC using whatever fieldbus protocol you prefer.

Key benefits of IO-Link

• Lower cost and weight: IO-Link requires less wiring, minimal power, and there are no software licensing fees. In addition, it allows point-to-point communication without requiring more expensive components like linear encoders. This makes it a lighter-weight technology that’s easier to justify incorporating into smaller and less-expensive devices. It also allows many more devices to be included in a sensor network than ever before by reducing the number of ports required to manage them.
• More robust communication: Instead of just responding to simple binary instructions, sensors and actuators can now communicate data back and forth in real time, providing detailed device and process data, plus status and fault messages. For example, IO-Link compatible sensors can provide the PLC with specific position data, making them more capable and flexible. 
• Flexibility of open-source technology: No proprietary hardware or software is required. Device configuration and performance can be easily customized or simplified with basic XML programming. A multi-vendor, centralized IO-Link database makes end-user changes even simpler. Virtually any type of sensor or actuator can be built with IO-Link capability. The system is easily scaled and simplifies process changes.
• Simplified installation and integration: IO-Link devices are practically plug-and-play. Individual devices may have unique setup needs depending on the manufacturer, but typically work seamlessly and are easy to maintain once up and running. Setup for similar devices can be automated using parameter data from the end user’s server.
• Faster data: IO-Link offers three communication speeds: 4.8kBaud, 38.4kBaud, and 230.4kBaud.
• Remote maintenance and monitoring capabilities: Bidirectional communication enables remote alerts, diagnostics, and maintenance. Many troubleshooting issues that used to require on-site hardware adjustments can now be resolved via any secure internet connection. Integrators can also use device data to deliver real-time monitoring and predictive maintenance capabilities. 
• Uses existing infrastructure: IO-Link can be implemented with minimal disruption to either integrators or end users. An established international standard allows IO-Link devices to be easily integrated into any standard control system anywhere in the world.
• Proven technology: The IO-Link standard was established in 2006 and began to see major adoption within three years. Global industry acceptance is widespread, and many sensors and actuators sold today are already IO-Link ready.

Real-world applications

Minimizing wiring is highly beneficial in itself. If you’re building a robotic arm, for example, every ounce of weight you can eliminate delivers performance advantages. It also gives you the flexibility to incorporate more devices (e.g., grippers) into end-of-arm tooling. This makes many more precise and advanced capabilities possible.

Another huge benefit is the ability to get variable data from sensors. In the past, many small devices could only tell the system if they were on or off. Now it’s possible to track movements or distances down to a fraction of a millimeter. 

For example, a proximity switch or laser sensor can not only tell the controller that it’s detected an object, but how far away it is. Data like this can be used to make adjustments on a case-by-case basis (e.g., a robot gripper picking up eggs). The size or position of a box may determine whether a sortation system diverts it to another line or keeps it on the current conveyor path. 

Movements outside a certain threshold can provide early warning signs of performance loss or component failure. This is one of the key drivers of predictive maintenance. Alert thresholds can be set by the integrator or, in some cases, the end user.

Cutting the cable

Eliminating wires is the obvious next frontier. The IO-Link Wireless standard is already making this possible. Up to three IO-Link wireless masters can operate in the same airspace, each supporting up to 40 wireless devices. 

In this way, as many as 120 wireless devices can be controlled within a 20-by-20-meter production cell, using the same processing methodology as the wired version of IO-Link with minor programming changes.

What the future holds

Low cost, flexibility, real-time data, and easy integration have brought IO-Link into the industrial mainstream. Today, tens of thousands of products already offer IO-Link compatibility, and the technology shows no sign of slowing down. 

Although higher-level protocols like PROFINET, EtherNet/IP, and EtherCAT are likely to remain relevant for years to come, IO-Link is expanding into applications, like safety, that have long been dominated by traditional protocols. In the long term, there may be potential to extend its capabilities further up the control network, creating new options for efficiency, flexibility, and cost-effectiveness.

About the author

Dr. Dave Sessoms is the senior lead engineer for Johnson Electric’s Warehouse Automation business unit. He specializes in developing technical solutions to optimize efficiency and solve complex customer challenges.

With a strong background in innovation, Sessoms previously worked on developing conformal printed electronics for the biomedical and consumer electronics industries. He is passionate about automation and emerging technologies, bringing a deep technical expertise to the forefront of modern warehouse automation solutions. Sessoms holds a Ph.D. in physics from the University of Fribourg, Switzerland.