IO-Link: Getting straight to the point
23 November 2015
Standardised IO-Link technology makes communication with sensors and actuators simple and economical. This low-cost connection technology, with three or five conductors, achieves point-to-point connection without the need for complex wiring and with minimal material requirements.
IO-Link is not a new bus system but has been further developed as a new kind of communications interface for fieldbus and Ethernet systems. It allows users to download parameter data from the control system to the sensor or actuator, and also to send diagnostic data in the other direction to the control system. Traditionally, integrating a fieldbus interface all the way down to the lowest field level was a costly task. Digital or analogue values and all parameters and diagnostic data can now be transmitted with only a simple 3-wire or 5-wire cable – with no special features required in terms of screening, twisting, impedance or terminating resistance.
The gateway between the fieldbus and one or more IO-Link slaves is normally provided by a fieldbus device with multiple IO-Link master channels. In smaller machines or systems, which may not require a fieldbus due to their size, the PLC can act as the IO-Link master.
IO-Link provides a secure connection for analogue, binary and serial communication devices. Typical IO-Link applications for complex sensor technology and terminals can be found in automotive body-in-white production and assembly, for personal protection with safety fences, in heavy machinery construction and for machine tools, at manual workstations, assembly cells, input/output stations.
IO-Link is a uniform, standardised and therefore efficient technology for installation and wiring. Standardisation also means less investment risk. An international, open and fieldbus-independent IO-Link standard provides support for existing and future connection concepts. Devices can be parameterised simply and conveniently – and can be put back into operation immediately after replacement with no need for engineering software tools.
Software-supported parameterisation of intelligent sensors and actuators via the IO-Link master makes it extremely easy to set and reassign parameters. Simple sensor-actuator wiring combinations with standardised, unscreened cables reduces material costs, simplifies logistics and saves time. This makes installation much easier.
Festo can offer a range of products for IO-Link - from a single source - including several masters, pressure and flow sensors, displacement encoders/position transmitters, five valve terminal series, proportional pressure regulators, stepper motor controllers and connecting cables. In addition, Festo has application knowledge in both factory and process automation and can also offer basic and advanced training for industrial users.
Competent and consistent decentralisation of an installation can be achieved with Festo’s CECC compact controller with four IO-Link master ports. The compact controller operates with electric and pneumatic drives in small installations. It can help to reduce installation and networking costs for intelligent sensors and valve terminals and can also provide diagnostic options inside and outside the control cabinet.
Used as a remote-I/O or in conjunction with Festo’s MPA or VTSA valve terminals, it allows the integration of one or more master interfaces for IO-Link devices. Because of its comprehensive function integration, control of pneumatic and electric drives with the CPX terminal is simplified. In combination with PROFINET or Sercos – the terminal has an I-Port interface with two channels for IO-Link. Individual third-party IO-Link devices can therefore be connected in the near/direct vicinity of the valve terminal
This solution offers a major gain in economic and efficient installation. Multi-pin connecting cables for valve terminals are replaced by standard M12 cables and IO-Link, reducing material costs and offering more flexible, easier installation, energy chain through-feed or adaptation to damp or particularly challenging or harsh operating conditions.
Festo’s CMMO-ST motor controller with integrated web server for configuration and diagnostics is now also equipped with an IO-Link interface. This closed-loop servo controller for stepper motors forms an important part of Festo's Optimised Motion Series (OMS). A package consisting of electric cylinder, stepper motor with servo functionality, motor controller and all the necessary cables offers a cost-effective solution when compared with conventional electric positioning systems.
The OMS with the electric cylinder can be configured in two ways - using Web Config and the parameter cloud on a server. The controller has its own IP address and a catalogue is available with all the necessary data for pre-defined and tested combinations.
When using a Festo VPM proportional pressure regulator connected to IO-Link there is no need for a screened analogue cable, making the signal level less prone to interference. Parameters are set and data saved in the IO-Link master offering a practical solution that allows for a quick restart after component replacement. Because of its point-to-point connection IO-Link allows short cycle times.
The uniform interface within IO-Link replaces individual sensor connections, making complex sensors easier to integrate. That means that even position transmitters and parameterisable pressure and flow sensors can be integrated and installed at low cost. Festo’s SDAT position transmitter, for example, detects a piston position with high repetition accuracy – no matter whether used for process monitoring for screwdriving, riveting, ultrasound welding, pressing and clamping or for object detection.
IO-Link – making an impression in the field
IO-Link is the first standardised IO technology worldwide (IEC 61131-9) for communication with sensors and also actuators. The point-to-point communication standard is based around standard 3-wire sensor and actuator connection without the need for any special cabling requirements.
The majority of IO-Link devices are equipped with M12 connectors which can be used without any restrictions for IO-Link's switching mode and communication mode. Each port of an IO-Link master is capable of processing binary switching signals and analogue values. Serial IO-Link communication takes place via the same port.
As standard, two bytes of process data are available per cycle. The transmission between IO-Link master and device takes 400 µs at a speed of 230 kBaud. The user can also choose larger frame types so greater process data with up to 32 bytes length can also be transmitted at a correspondingly lower cycle time. To ensure that the parameter data of a device are not lost when replacing a device, they can be automatically stored directly in the IO-Link master. If a new, identical substitution device is connected, the parameters of the previous device are automatically transferred onto the new device.
Each IO-Link device has an IODD (IO Device Description) which contains information about the manufacturer, article number, functionality etc. Each device can be identified via the IODD, as well as via an internal device ID.
Earlier this year the IO-Link Community commissioned statistics on the number of installed IO-Link nodes in the field. The counting method used has already been well-proven for many years for the PROFIBUS & PROFINET International (PI) technologies, with members being surveyed regarding the number of devices sold.
The survey revealed that since 2009, over 2.19 million IO-Link nodes have been installed in the field and that IO-Link being well distributed through many industyr sectors including automotive, packaging, machine construction, solar industry, glass manufacturing, biogas production, and wood processing.
The IO-Link Community is also increasing. There are now more than 90 members, with 17 new members added in 2014. Since the start of this year, 11 companies became members.
The success of the technology are said to be due to a vareity of reasons. Besides the simplified installation, automated parameter assignment, and diagnostic capabilities, the fact that users can make use of a wide range of devices and technologies is also a recognised benefit.
IO-Link has now been implemented in all fieldbus systems established on the market and most well-known PLC manufacturers have integrated it in their systems. In doing so, the IO-Link master can undertake the crucial connection between the IO-Link devices and the automation system. All essential sensor and actuator technologies are already offered with an IO-Link interface today.
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