Most sensors still provide a binary or analog output signal, but sensors with an IO-Link interface are on the rise. This is not surprising, as the standardized, digital point-to-point connection offers system manufacturers and operators many advantages. The interface ensures uncomplicated, bidirectional signal and data exchange at field level. As an internationally certified standard in accordance with IEC 61131-9, it also significantly simplifies installation and cabling processes because, in conjunction with an IO-Link master, a standard, unshielded, three-core cable is sufficient for all communication tasks. IO-Link is downward compatible with all standard sensors and insensitive to interference. This means that there is no need for any special cables or additional connection boxes.

Thanks to a standardized device description, IO-Link can be used as easily as USB on a computer. All device functions are mapped in the IODD (IO Device Description). Whereas it used to be necessary to search for these on the device manufacturer's homepage, users can now usually download them from the IODD portal of the IO-Link community.

With IO-Link, intelligent diagnostic and parameterization concepts can be implemented down to field level, as envisaged by the Industry 4.0 concept. Switching points can be changed or configurations adapted from the PLC via IO-Link. The standard also makes it possible to clearly verify the origin of the data using two ID fields stored in the sensor. And there's more: using a software tool, such as the one offered by Balluff, direct access to the lowest device level is possible. All IO-Link process devices in a system can be monitored, parameterized and tested centrally via various interfaces such as UDP and TC/IP or protocols such as http, SNMP and others from almost any location and parallel to the control system.

IO-Link complements Ethernet and fieldbuses in terms of data continuity right down to the last meter, as a direct connection to IT systems via the Internet is not worthwhile for the large number of simple, switching sensors. In addition, IO-Link makes users independent of the market and country-specific conditions, circumstances and control systems, as it supports the various fieldbus systems by itself.

Additional information in real time

Increasing digitalization requires intelligent sensors to enrich plant models with real-time data and provide clarity on plant and production status. To this end, the 'eyes and ears' of automation must provide additional information that goes beyond their primary function. In addition to data on service life, load level and damage detection, this also includes environmental information such as temperature, contamination or the quality of alignment with the object to be detected.

Self-diagnosis increases system safety in difficult environments.

© Balluff

Balluff offers such an 'all-rounder' with the optoelectronic sensor 'BOS 21M ADCAP'. The multi-function sensor works with red light and allows a choice of four sensor modes: background suppression, energetic diffuse sensor, retro-reflective sensor or through-beam sensor. All functions can be configured via IO-Link, even during operation, so that a remote teach-in can be triggered via the controller. In addition, the sensor records far more data than just the pure switching signal: detection signals are already prepared and pre-processed in the sensor, which relieves the system controller and reduces data traffic on the fieldbus systems. Comprehensive, smart diagnostic functions provide important information, for example on service life, operating hours and function reserve. Increasing soiling, sensor misalignment, setting errors or other irregularities can be detected at an early stage by monitoring the light emission values - as a measure of the quality of the sensor signal.

Automate format changes

With position measuring systems with an IO-Link interface, a format change of the system, for example during a product change, can be achieved 'at the push of a button' in the shortest possible time.

© Balluff

If such Industry 4.0-capable sensors are used, machines and systems can be automated and controlled more efficiently. One example of this is a packaging system on which products of different sizes - i.e. different formats - have to be packaged. In a conventional system, the rails and guides usually have to be manually adjusted or replaced each time the format is changed. In addition, the switching points of the sensors have to be set manually directly on the sensor. All of this is time-consuming and sometimes also prone to errors. However, if IO-Link sensors are installed, they can be parameterized to the new format directly from the PLC. In the best case, this is done automatically controlled by format recognition. In a second step, the same procedure also applies to guides and rails, provided they are equipped with electric drives.

However, it is not only the variety of sensor functions that will increase overall; the number of sensors themselves is also growing rapidly in the course of Industry 4.0. Where previously only the PLC derived an action from the information, today the IIoT world is increasingly being added. Here, too, a large number of variables from the very heart of the processes must be recorded and analyzed with sensors in order to be able to view processes holistically.

The challenge of big data

This results in data volumes that are too large, too complex, too transient or too poorly structured to be analyzed using manual and conventional data processing methods. Methods are needed to be able to interpret big data in a simple way. Mechanisms are also required for its transmission and pre-processing.

An inductive sensor on its own, for example, usually generates a status value - such as 'part there' or 'part not there'. In order to be able to interpret this information in a meaningful way, it is important for big data to know who provided this information, where and when. In addition, earlier and later values must be included in the analysis. Only when this information is attached to the status value can it be included in a meaningful analysis.

Integrate data into higher-level systems

Industry 4.0 cannot be implemented without manufacturer- and platform-independent networking of devices and systems. This is precisely what OPC UA is designed for. The protocol is based on the client-server principle and is considered the ideal communication protocol for implementing Industry 4.0. Fieldbus-independent integration via OPC UA is very interesting for IO-Link, as it increases the range of possible automation solutions:

The OPC UA RFID reader with Secure Element prevents data from being spied on or manipulated during production.

© Balluff

IO-Link masters or edge gateways, which bundle the data from sensors and actuators, can not only process this data as fieldbus participants, but also make it available to higher levels within and outside the automation pyramid via OPC UA. In this way, sensor data can be seamlessly integrated into MES and ERP systems with little effort. This is often referred to as 'sensor-to-cloud' functionality.

Such data transmission from the field to the control level is nothing fundamentally new; it has been done before: In numerous RFID applications, the data was not only intended for a control system, but also for an MES or ERP system - after all, this is where the evaluation, data acquisition and tracking of production data takes place.

However, this information was previously transferred to the IT system via the PLC, which was associated with a corresponding programming effort. Today, IO-Link offers a lean alternative. For this reason, the IO-Link community has developed the companion specification 'OPC-UA for IO-Link' as a standard for the data and function model in order to be able to represent IO-Link devices and IO-Link masters accordingly in OPC UA in the future. The specification was reviewed by the IO-Link community and the OPC Foundation and approved as final version V1.0. The first implementations and examples were on display at SPS IPC Drives 2018.

The IUNO research project

Balluff and partner companies in the IUNO research project have demonstrated how communication can be designed securely using an RFID application. The research project, funded by the German Federal Ministry of Education and Research, is a national reference project for Industry 4.0 IT security. Using the example of furniture production, the participants examined the individual process steps from product development, product planning and production through to service. From this, they were able to derive appropriate protective measures and implement them as examples.

The researchers focused on two risks: firstly, the threat posed by hackers and secondly, the challenge of ensuring that a workpiece always finds the right path through production and can be reliably identified at all times. The problem with this is that conventional RFID tags are generally not data-secure and unauthorized persons can intercept or manipulate them.

To remedy this, Balluff has developed an OPC UA RFID reader with Secure Element from Wibu-Systems, a specialist in the protection and licensing of software and documents. It uses the OPC UA protocol with end-to-end encryption. The data on the RFID tag is digitally signed and optionally encrypted. The authenticity of the RFID tag data can be checked using the key, which is located in the secure element directly in the RFID reader. The reader thus effectively prevents data from being spied on or manipulated during production.

Author:
Dr. Detlef Zienert is Press Relations Manager at Balluff in Neuhausen a.d.F.