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Industry 4.0 involves the use of high levels of automation and real-time, bi-directional data transfer from the controller to the element being controlled. With the introduction of smart sensors and actuators, now widely available, a new solution – the IO-Link protocol – was established to regulate how these smart devices communicate with the controller in industrial automation applications.
Smart sensors and actuators are the central nervous system of an automated industrial process. The control network for these systems was initially based on parallel wiring, which was cumbersome, not easily scalable, and expensive. Fieldbus protocols improved on this situation but were low in signal levels, requiring expensive shielding. The IO-link protocol solves these bottlenecks and enables the widespread use of smart sensors and actuators in industrial systems.
Reflecting the wide adoption of this standard in factory automation, the global IO-Link market size is expected to increase from $48.3 billion in 2022 to $73.1 billion in 2032, with a compound annual growth rate of 26%, according to Future Market Insights.
What is IO-Link?
IO-Link, first established in 2006 by the IO-Link Consortium, is an international protocol (IEC-61131-9) aimed at I/O technology for communicating with sensors and actuators in industrial automation environments. Some of its core elements include:
- It is a bi-directional, digital, point-to-point communication protocol, also called a single drop communication interface (SDCI).
- At a minimum, it consists of an IO-Link master that can transmit data over a variety of existing networks such as Profibus, Profinet, Devicenet, Ethernet/IP, EtherCAT, CC-Link, and CC-Link IE Field. IO-Link is fieldbus-neutral, which allows for greater flexibility in the control architecture.
- IO-Link devices such as sensors connect to ports on the IO-Link master with standard, unshielded three, four or five wire cables. These can be up to 20 meters long. An IO-Link master can have several ports. A typical pin configuration is shown in Figure 1. Power is provided at 24 V, and the switching and communication signals can be either switching signals (DI/DO) or coded. Each IO-Link device has a unique IO device description identifier called an IODD, which holds information such as the communication setup and device parameters.
- The baud rates for communication are 4.8, 38.4, and 230.4 Kbaud. Data, such as process data and value status, indicating data validity, can be periodic on request from the IO-Link master. These can include device parameter values or event-driven errors and warnings from the IO-Link device.
Advantages of IO-Link
To delve into the advantages of IO-Link, let us consider its usage in two different sensor applications: a hydraulic cylinder and packaging automation system
1) Measure, Control, and Regulation of a Hydraulic Cylinder
As shown in Figure 2, IO-Link can be used to effectively measure and control using analog sense signals such as temperature and flow through Balluff Inc.’s analog IO-Link converters. The Balluff single-channel analog interface devices are fully configurable through IO-Link for resolution and signal type and can convert a variety of analog input data such as current, voltage, or temperature signals from the forced or native voltage sense of RTDs and thermocouples, respectively, to a digital value. In addition, they offer diagnostic capability such as short circuit, temperature, out of range measurements, and thermocouple wire breaks.
Analog signals can make up around 10% of the total data volume and usually require shielded cables and expensive multi-channel input modules. The point-to-point, noise immune decentralization with IO-Link allows basic unshielded cables to be run for the analog signals.
“The advantages of IO-Link come from the cost reductions enabled through simpler wiring, reduced setup times due to easily downloadable parameter files to the sensor, and the ease of scalability from the use of a uniform communication standard across a wide range of sensors from different manufacturers,” said Shishir Rege, automation and technology specialist at Balluff.
Safety interlocks and switches can be easily integrated into an existing IO-Link automation system, as illustrated in Figure 3.
“Whether the need is to connect safety devices, analog devices, smart measurement devices, simple ON/OFF binary devices or even valve manifolds, IO-Link makes it unified and simple to connect to the IO-Link port of an existing IO-Link master to achieve greater flexibility and modularity in the machine architecture,” said Rege.
2) Packaging automation with IO-Link
Packaging automation systems require automation at several steps in the flow such as die cutting, carton erecting, filling, inspecting, and closing, and even multi-packing and palletizing. It demands great flexibility to accommodate different package dimensions and changeovers for small production batches.
Figure 4 illustrates a typical packaging automation setup with Sensata Technologies Inc.’s IO-Link-based sensors. The AHx5 and THx5 are IO-Link absolute encoders with high resolution, while the DHx5 is an incremental encoder for measurement of rotational speed. The ACW4 and TCW4 are robust Hall-effect position sensors.
“IO-Link enables plug-and-play sensor automation. Products can be reconfigured on the fly. Performance parameters can be stored in the IO-Link master so that a replacement sensor could be easily configured. Thanks to the diagnostics and event features, environmental and sensor health conditions are simple to manage,” said Jean-Marc Hubsch, Sensata’s engineering manager for encoders and position sensors. “A quicker real-time remote setting and monitoring capability allows for reduced downtimes.
“Sensata’s encoders offer high resolution on absolute [movement] and 1000 PPR [pulses per revolution] on incremental [movement] for applications requiring high performance,” he added. “They offer dual output of both the incremental channel and the absolute value. The resolution and output are fully configurable with IO-Link. Communication is done at the highest COM3 230.4 Kbaud level, ensuring a minimal cycle time of 1 millisecond.
IO-Link System Extensions
The IO-Link wireless protocol works similarly to the wired one and is useful in factory automation for non-stationary sensors and actuators. It uses the 2.4-GHz band. Each IO-Link master can contain up to five channels, each of which support eight devices, leading to 40 IO devices per master. With a maximum of three masters operating per cell, a total of 120 devices could operate while moving within this cell. IO-Link Wireless is robust even in high electromagnetic interference (EMI) environments.
The IO-Link Safety is an extension to IO-Link that has been recently specified by the IO-Link community. Additional safety communication from both the master and the device makes them functional safety (FS) capable. Electronic safety devices, called output switching sensing devices (OSSD), can be connected via redundant signals to a FS IO device. Pin 2 in Figure 1 is used for this redundancy.
IO-Link enables cost-effective and efficient utilization of sensors and actuators on a factory floor. It offers a single, standardized control interface, allowing smart sensors from various manufacturers to be integrated into a single platform.
Bi-directional flow of process, service, and diagnostic data can be routed over standard, unshielded wires. Sensor setup and debugging can be done remotely in real-time while device replacement can be streamlined, and hence, downtimes minimized. This is an evolving standard and additions such as wireless and functional safety will serve to accelerate its adoption across many industries.