IO-Link is a short distance, bi-directional, digital, point-to-point, wired (or

wireless Wireless communication (or just wireless, when the context allows) is the transfer of information between two or more points without the use of an electrical conductor, optical fiber or other continuous guided medium for the transfer. The most ...

), industrial communications networking standard ( IEC 61131-9) used for connecting digital sensors and actuators to either a type of industrial fieldbus or a type of industrial Ethernet. Its objective is to provide a technological platform that enables the development and use of sensors and actuators that can produce and consume enriched sets of data that in turn can be used for economically optimizing industrial automated processes and operations. The technology standard is managed by the industry association Profibus and Profinet International.

System overview

An IO-Link system consists of an IO-Link master and one or more IO-Link devices, i.e. Sensors or Actuators. The IO-Link master provides the interface to the higher-level controller ( PLC) and controls the communication with the connected IO-Link devices. An IO-Link master can have one or more IO-Link ports to which only one device can be connected at a time. This can also be a "hub" which, as a concentrator, enables the connection of classic switching sensors and actuators. An IO-Link device can be an intelligent sensor, actuator, hub or, due to bidirectional communication, also a mechatronic component, e.g. a gripper or a power supply unit with IO-Link connection. Intelligent with regard to IO-Link means that a device has identification data e.g. a type designation and a serial number or parameter data (e.g. sensitivities, switching delays or characteristic curves) that can be read or written via the IO-Link protocol. This allows parameters to be changed by the PLC during operation, for example. Intelligent also means, however, that it can provide detailed diagnostic information. IO-Link and the data transmitted with it are often used for preventive maintenance and servicing, e.g. it is possible to set an optical sensor in such a way that it reports via IO-Link in good time if it threatens to become dirty. Cleaning no longer comes as a surprise and blocks production; it can now be put on a production break. The parameters of the sensors and actuators are device- and technology-specific, which is why parameter information in the form of an IODD (IO Device Description) with the description language

XML Extensible Markup Language (XML) is a markup language and file format for storing, transmitting, and reconstructing arbitrary data. It defines a set of rules for encoding documents in a format that is both human-readable and machine-readable ...

. The IO-Link community provides interfaces to an "IODD Finder", which can be used by engineering or master tools to present the appropriate IODD for a device.

Connector

Cabling is in the form of an unshielded, three or five conductor cables, not longer than twenty meters, and a standardized four or five pin connector. The master and device pin assignment is based on the specifications in IEC 60947-5-2. For a master, two port classes are defined, port class A and port class B. Port class A uses M5, M8, or M12 connectors, with a maximum of four pins. Port class B uses only M12 connectors with 5 pins. M12 connectors are mechanically "A"-coded according to IEC 61076-2-101. Female connectors are assigned to the master and male connectors to the device. At the master pin 1 to pin 3 provides 24V DC power with max. 200 mA for an optional power supply of the IO-Link device. Pin 4 is used as a digital input (DI) or digital output (DO) according to the IEC 61131-2 specification to allow backward compatibility to

proximity sensor A proximity sensor is a sensor able to detect the presence of nearby objects without any physical contact. A proximity sensor often emits an electromagnetic field or a beam of electromagnetic radiation (infrared, for instance), and looks for ...

s according to IEC60947-5-2 or other sensors or electrical

switch In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...

es. The IO-Link master sends a wake-up current pulse to get the IO-Link device from the serial input-output (SIO) state into the single-drop digital communication interface (SDCI) state. In the SDCI state the IO-Link master exchanges information frames with the IO-Link device. In a port class A the pins 2 and 5 are not specified and are left to the manufacturer to define. In a port class B the pins 2 and 5 are configured as an additional power supply.

Protocol

The IO-Link communications protocol consists of communication ports, communication modes, data types, and transmission speeds. The ports are physically located on the master, and provide it a means for connecting with terminal devices and for bridging to a fieldbus or Ethernet. There are four communication modes that can be applied to a port connected to a terminal device: IO-Link, DI, DQ, and Deactivated. IO-Link mode configures the port for bi-directional communications, DI mode configures it as an input, DQ configures it as an output, and Deactivated just simply deactivates the port. There are four data types: process data, value status data, device data, and event data. The protocol can be configured to operate at transmission speeds of either 4.8 kilobaud, 38.4 kilobaud, or 230.4 kilobaud. The minimum transmission time at 230.4 kilobaud is 400 microseconds. An engineering tool is used for configuring the master to operate as the network bridge.

IO-Link Wireless

IO-Link Wireless is an extension of IO-Link on the physical level. An IO-Link Wireless Master ("W-Master") behaves like a Master to the superordinate system. There are only virtual ports "down" to the IO-Link Wireless Devices ("W-Devices"). A transmission cycle consists of two phases. To transmit output data, the W master sends a

Multicast In computer networking, multicast is group communication where data transmission is addressed to a group of destination computers simultaneously. Multicast can be one-to-many or many-to-many distribution. Multicast should not be confused with ...

-W frame (

Downlink In a telecommunications network, a link is a communication channel that connects two or more devices for the purpose of data transmission. The link may be a dedicated physical link or a virtual circuit that uses one or more physical links or shar ...

) with data for the W devices in assigned time slots. Then the W-Master goes on reception and collects in the

Uplink In a telecommunications network, a link is a communication channel that connects two or more devices for the purpose of data transmission. The link may be a dedicated physical link or a virtual circuit that uses one or more physical links or sha ...

Data from the W-Devices which transmit one after the other according to an agreed fixed scheme. To secure the transmission

Frequency Hopping Frequency-hopping spread spectrum (FHSS) is a method of transmitting radio signals by rapidly changing the carrier frequency among many distinct frequencies occupying a large spectral band. The changes are controlled by a code known to both tra ...

and Channel-Blacklisting are used.

IO-Link Safety

IO-Link Safety is an extension of IO-Link by providing an additional safety communication layer on the existing master and device layers, which thus become the "FS master" and "FS device". One also speaks of the Black Channel principle. The concept has been tested by TÜV SÜD. IO-Link Safety has also extended the OSSD (Output Switching Signal Device) output switching elements commonly used for

functional safety Functional safety is the part of the overall safety of a system or piece of equipment that depends on automatic protection operating correctly in response to its inputs or failure in a predictable manner (fail-safe). The automatic protection syste ...

in a non-contact protective device like a

light curtain Light curtains was first introduced as a "Light barrier" by invertor Dr. Erwin Sick on Sept 26, 1972 when he formally described this device as "Safety devices acting in conjunction with the control or operation of a machine; Control arrangements ...

to OSSDe. As with standard IO-Link, an FS-Device can be operated both in switching mode as OSSDe and via functionally safe IO-Link communication. During implementation, the safety rules of

IEC 61508 IEC 61508 is an international standard published by the International Electrotechnical Commission consisting of methods on how to apply, design, deploy and maintain automatic protection systems called safety-related systems. It is titled ''Functio ...

and/or

ISO 13849 ISO 13849 is a safety standard which applies to parts of machinery control systems that are assigned to providing safety functions (called safety-related parts of a control system). The standard is one of a group of sector-specific functional saf ...

must be observed.

Literature

* Joachim R. Uffelmann, Peter Wienzek, Myriam Jahn: ''IO-Link. The DNA of Industry 4.0.'' Edition 1. Vulkan-Verlag GmbH, Essen 2018, .

References

{{DEFAULTSORT:IO-Link Serial buses Industrial automation Communications protocols
Io-Link Communication