Introduction

With the onset of the Industrial Revolution 4.0 (Industrial IoT), communication scenarios are changing rapidly. Machine-to-machine (M2M) communication such as connected robots, warehouse automation, and factory processing machinery are becoming more and more prevalent and demanding higher availability, better robustness, lower latency, and deterministic patterns.

In this revolution, cable-based communication simply cannot fulfil the requirements demanded by the tremendous increase in connected devices in terms of flexibility, mobility and cost. Only wireless communication makes the usage of connected devices economically feasible.

Wireless protocols have made incredible strides forward in two vectors: spectral efficiency to achieve higher throughput for human-to-human/machine applications, and power consumption reduction for low data rate applications like IoT. As of today, standard wireless technologies are unable to meet the required robustness and low latency that industrial M2M applications need and therefore are being underutilized, mostly for monitoring in non-critical applications.

A new wireless standard for mission critical called IO-Link Wireless was recently born (IO-Link Wireless System Extensions). IO-Link Wireless, for the first time, presents a reliable, real-time and deterministic protocol for industrial factory automation control systems. It is expected that this standard will replace the serial wired cables in industrial control applications, taking the Industrial Revolution 4.0 to the next level.

This paper provides a high level description of the IO-Link Wireless protocol.

For more information please have a look at reference [1], the IO-Link Wireless standard, and CoreTigo’s website.

Factory Automation Standard

A defined industry standard provides a basis for mutual understanding, and a tool used to facilitate communication, measurement, commerce and manufacturing. Industry standards play an important role in industrial communication by:

  • facilitating business interaction between vendors, suppliers and customers;

  • speeding up the introduction of innovative products to market;

  • providing interoperability between new and existing products, services and processes; and

  • reducing the risk of a single source.

PROFIBUS & PROFINET International (PI) is the most influential interest group in the field of industrial communication. With a majority share of the fieldbus market, it has grown to become the unequivocal leader in this industry. The Profibus User Organization (PNO) hosts the IO-LINK ORGANIZATION and provides it with administrative services including specification writing, testing and standardization.  IO-Link is the first standardized IO technology worldwide (IEC 61131-9) for communication with sensors and actuators. IO-LINK was chosen to provide the field connections for PI’s standardized wireless solutions for factory automation applications.

With a deployment of more than 5 million new IO-Link nodes in 2016 and an installation base greater than 13 million, IO-Link’s usage has been increasing by 47% year over. There is a tremendous acceptance of communication between sensors, actuators and the control level and a steadily increasing demand for more flexibility in automation solutions. With the wireless extension for the IO-Link standard, the expectation is that more industrial applications will adopt the wireless and that the IO-Link number of nodes (wired and wireless) deployed in 2019 will exceed 18 million.

So, what is it IO-Link Wireless?

IO-Link Wireless defines wireless network communication between sensors, actuators and controllers (PLC) in the factory automation environment. It was designed to provide similar level of performance as with cables so the migration from wired to wireless systems will be smooth. IO-Link Wireless provides real-time latency of 5 msec communicate with 40 nodes (sensors or actuators). It presents reliability that is better than 1e-9 Packet error rate (PER). As an example, other wireless standards like WLAN, Bluetooth and Zigbee show PER that is 6 orders higher (~1e-3) in industrial environment.

IO-Link Wireless supports roaming capabilities and the possibility to include battery-powered or energy-harvesting sensors with very limited energy resources in the real-time network. One of the key features of IO-Link Wireless is the compatibility with the factory and process automation protocols. The system planning, setup, operation and maintenance standard engineering tools of IO-Link can be employed so that the backward compatibility with wireline IO-Link solutions is guaranteed.

IO-Link Wireless System Description

In Industry 4.0 and mostly in smart factories, efficient data collection and intelligent data handling combined with consistent connectivity is increasingly important. In this context and the introduction of the I-IOT (Industrial Internet of Things), IO-Link Wireless is seen as an enabling technology for such services. It offers full networking capabilities vertically down to the sensors and actuators on the shop-floor and up to the enterprise resource planning (ERP) tool. It is also supports horizontally across the various fieldbus platforms on the basis of an already internationally established communication standard.

 Smart factory pyramid

An IO-Link Wireless system typically consists of an IO-Link Wireless fieldbus gateway, and the IO-Link wireless master, providing some number of master ports, each of which is connected to a single IO-Link Wireless device. Devices can be sensors, actuators, RFID-readers, valves, motor starters or simple I/O-modules. Additionally, the standard IO-Link Wireless system comprises engineering tools for sensor/actuator configuration and parameter assignment.

Architecture of Wired IO-Link and Wireless IO-Link

The following basic data types are defined:

  • Process data: with a length of up to 32 Bytes, which are exchanged with every communication cycle.
  • Value status data: indicating if the process data is valid or not, which is information also exchanged cyclically.
  • Parameter and diagnostic data: such as identification information, settings, warnings and errors, which are exchanged on-request.

The next figure depicts an example of a system architecture based on IO-Link wireless and wired according to [1].

 IO-Link Wired and Wireless Architecture

IO-Link Wireless Physical Layer and MAC

In order to meet the high reliability requirements (PER of 1e-9) in industrial environment, a narrow band GFSK (Gaussian Frequency Shift Keying) modulation has been chosen. This modulation enjoys high power efficiency and good rejection to interferers but also immunity to channel fading due to the narrow band, 1MHz. The same modulation serves other protocols like the low energy Bluetooth and 802.15.4 standards, but achieves different performance due to different protocol schemes. To comply with regulatory standards the maximum RF transmission power is 10 mW and 2.45 GHz ISM-band (unlicensed) have been chosen, even though this band suffers from wireless congested environment.

To guarantee highly reliable linkage in a congested environment a combination of a frequency- and time division media access scheme (F/TDMA) has been employed. Downlink (DL) messages from the IO-Link master to the devices and uplink (UL) messages from the devices to the master are exchanged in a half-duplex mode in a defined timeframe.  A cell can support up to 3 masters, while each master communicates with up to 40 sensors over 5 tracks. The next figure illustrates this scheme.

 IO-Link Wireless TDMA

An improved coexistence behavior is achieved by using two mechanisms, frequency hopping and dynamic blacklisting, which allows operation of the wireless sensor/actuator network with low packet-error rates even in industrial plants where three WLAN bands are allocated in the 2.45 GHz band.

In terms of real-time, a cycle-time of 5 msec was specified to meet the reliability and in each cell up to 120 nodes (sensors or actuators) are sampled in each cycle-time. In a duration of 5 msec two retransmits of cyclic data are supported in different channels to get better immunity to narrow band interferrers or channel fading.  The frequency-hopping algorithms mitigate the channel fading but also improves coexistence behavior and allow devices to roam between masters.

Several concepts have been defined to reduce energy consumption to also allow devices with very limited energy resources to be integrated into the wireless communication system, such as long-term operable battery-powered devices.

Summary

Although wireless technology is commonplace, reliable wireless is still something of a Holy Grail for industrial automation applications.

The benefits of using wireless for industrial automation applications are certainly alluring enough in terms of flexibility, cost reduction, higher mobility and better scalability. Modern factories understand the added value of a flexible production line. There is a rising demand for robotic arms, smart sensors and advanced actuators for automation, and unmanned AGVs (automatic guided vehicle) to increase efficiency. Since much of the equipment is portable and the production line needs to be flexible, wireless is a better fit for connectivity. However, the downside of using wireless in industrial applications is that it’s much harder to meet the reliability requirements demanded by industrial automation.

IO-Link Wireless protocol was made to answer these challenges – high reliability, low latency, deterministic communication and compatibility to wired factory automation protocols.

IO-Link Wireless solutions are beginning to transform industrial automation. Companies like CoreTigo are part of this transformation. While the downside of using wireless in industrial applications is that it’s much harder to meet the reliability requirements demanded by industrial automation, CoreTigo is taking on this challenge full force to ensure that IO-Link Wireless surpasses wired cables as they are used today. You may find more information at www.coretigo.com

Reference

[1]: IO-Link Wireless Enhanced Sensors and Actuators for Industry 4.0 Networks, AMA Conferences 2017