With the advent of the fourth industrial revolution and Industry 4.0, comprehensive and intelligent automation came to be defined by advanced controls, monitoring, and diagnostics. Such capabilities are only possible through industrial connectivity — through which controls and machine devices are unified on some platform (such as IO-Link) for continual data exchange.
Figure 1: IO-Link complements existing network protocols by easily integrating into fieldbus or Ethernet networks via the IO-Link primary. The connection between an IO-Link primary and its IO-Link devices is through unshielded and unscreened three or five-wire cable also capable of supplying power to the IO-Link devices. Here, power from the primary is 24-Vdc. (Image source: Pepperl+Fuchs)
The key enabling technologies underpinning industrial connectivity are standardized networks and devices with onboard communications features. Protocols abound for these functions. However, not all industrial protocols satisfy the data-exchange and intelligence requirements required by today’s automation. IO-Link was created to satisfy a wide array of these modern applications.
As covered in a previous digikey.com article, IO-Link is a wired point-to-point communication protocol that facilitates smart bidirectional data communication between devices. Typically, IO-Link primaries (local controllers) have several IO-Link ports (channels) into which various IO-Link devices independently plug. These node-to-node endpoint connections are what render IO-Link a point-to-point communication protocol.
Launched in 2009 by a consortium of 41 members that is now hundreds of members strong, IO-Link is has become a widely accepted communication protocol to harness data crucial for:
- Optimizing operations
- Reducing downtime and streamlining maintenance
- Trimming raw material costs and making strategic operational decisions.
The harmonized IO-Link interface is defined by the IEC 61131-9 standard and supported by Siemens, Omron Corp., ifm Efector, Balluff, Cinch Connectivity, Banner Engineering, Rockwell Automation, SICK, Pepperl+Fuchs, and dozens of other component and system manufacturers. No wonder IO-Link connectivity is widely leveraged in operations involving assembly automation, machine tools, and intralogistics. Its three main uses in these and other industrial settings include status communications, machine control, and rendering devices intelligent.
IO-Link controller modes correlate to uses
Figure 2: The type of connector used with the connecting cable depends on the type of port. IO-Link class-A primary ports accept M8 or M12 (like the AL1120 from ifm efector shown here) connectors with up to four pins, while class-B counterparts accept connections with devices having five-pin M12 connectors (for bidirectional data communication). The mode assigned to a primary’s port at any given time is determined by the device to which it’s connected and the current operation. (Image source: ifm Efector)
Recall from previous digikey.com articles that the IO-Link communication protocol renders each connector port on an IO-Link high-level primary (controller) capable of four communication modes. These include a fully deactivated mode as well as IO-Link, digital input (DI), and digital output (DQ) operating modes. The modes loosely correlate to the three main IO-Link uses listed above.
The IO-Link operating mode supports bidirectional data communications with field devices and is typically used during data collection for monitoring, testing, and diagnostics. A primary’s port in DI mode accepts digital inputs and works when the port is connected to sensors — in this context, acting as input devices. In contrast, a port in DQ mode acts as a digital output, typically when the port is connected to an actuator (in this context, effectively an output device) or when a system PLC is set up to directly send instructions to another IO-Link device.
Though beyond the scope of this article, it’s worth noting that the ports on an IO-Link primary can readily switch between modes. For example, a primary’s port connected to a sensor can run in DI mode — and then switch to IO-Link communication mode when diagnostics and monitoring data from the sensor is requested by the primary.
IO-Link application 1 of 3: actionable status communications
Figure 3: IO-Link facilitates the creation of highly advanced control and automation systems. The machine-tool industry makes copious use of IO-Link sensors to verify appropriate workpiece clamping and milling end-tool pressures and positions. (Image source: Getty Images)
Machine monitoring is possible with IO-Link devices set up to report status that can, in turn, inform the system of necessary adjustments and corrections. Consider one use in the machine-tool industry — that of IO-Link pressure sensors which verify workpieces are clamped with a pressure appropriate for damage-free yet secure holding during material-removal operations. Here, IO-Link sensors essentially support the optimization of machine tasks for fewer rejected workpieces.
IO-Link devices can also make actionable status communications to support enhanced maintenance routines for minimized downtime. For example, IO-Link position sensors on an assembly machine might continually report the locations of end effectors to ensure none are out of range or alignment.
By analyzing diagnostics data provided by IO-Link devices, a plant’s machine technicians can predict and correct errors and potential breakdowns before they happen. Technicians can also identify weak links in a machine or plant — to inform enterprise-level operational changes, purchasing decisions, and captive machine designs in the future.
IO-Link application 2 of 3: advanced control and automation
Figure 4: An IO-Link system involved in advanced controls includes an IO-Link primary (controller), like the Omron NX-ILM400 shown here, and various IO-Link-enabled sensors, power supplies, and mechatronic devices connected to that primary. IO-Link systems for such applications typically yoke the IO-Link primary and devices to a PLC or other automation system. (Image source: Omron)
Control and automation are other application functions supported by IO-Link. Where an IO-Link installation supports functions that run sans intervention of personnel, the IO-Link primary often connects to a host system or higher-level PLC that processes received data and then directly or indirectly commands actuators in the design to the appropriate coordinated responses. Such automated control requires that the IO-Link system connect to a higher-level controller via standardized fieldbus or Ethernet protocols and cabling. In fact, most IO-Link primaries have fieldbus or Ethernet ports for such connections.
Devices in advanced control applications involving IO-Link systems integrate in one of three ways:
- They directly connect to the host computer or PLC
- They connect to an IO-Link primary and communicate via the IO-Link protocol
- They use IO-Link compatible communications and connect to an IO-Link primary via an IO-Link hub
The latter essentially acts as an intermediary to connect non-IO-Link devices to the primary.
An added benefit of IO-Link systems having fieldbus and Ethernet-communications connectivity is that long-distance connections are allowable — which in turn lets installers locate IO-Link primaries in a control cabinet or at the outermost machine reaches if that makes the most sense for a given application.
Consider how IO-Link primaries benefit advanced assembly applications by serving as low-level controllers capable of processing both digital and analog signals. Here, primaries might:
- Accept the data generated by IO-Link linear encoders on the axes of an XY stage
- Process that data as a gateway
- Submit that processed IO-Link field-device data to the PLC or other system controller
IO-Link application 3 of 3: device intelligence
Figure 5: The IO-Link connection interface is very small and can fit on most compact field devices. Shown here is a Balluff BUS004Z proximity sensor with IO-Link connectivity. (Image source: Balluff)
The third application of IO-Link is to render devices smart. Especially common in sensor designs that resemble legacy sensor options with no (or more modest) programming, these IO-Link-enabled devices can receive instructions, monitor, and execute self-testing routines — and generate data. Because IO-Link also lets devices provide more than basic two-value (yes-no or pass-fail) data, the reporting of precise values is also possible. For example, process-automation tasks benefit from IO-Link temperature sensors that go beyond reporting high or low temperature status by continually reporting the exact temperature value of a monitored zone or volume.
Another benefit of IO-Link for smart field devices is the way in which its physical connections are compact. That’s in contrast with the physical connections of fieldbus and Ethernet interfaces, which can sometimes be too big to fit on field microdevices.
IO-Link smart components can also be precisely controlled. For example, instead of basic off-and-on controls, an actuator can be commanded to turn off once a scenario satisfies a set of conditions.
Input devices such as pushbutton switches from RAFI can leverage IO-Link functions to support smart-device features — including color-coded indicator lights.
There are some caveats to the use of IO-Link for smart-device applications. Though there is a wireless form of IO-Link under development, it’s still a wired communication protocol — so it is still subject to all the limitations of hard wiring. To maintain data integrity, IO-Link primary-to-device cabling mustn’t exceed 20 m. Plus, because the IO-Link protocol can only transmit up to 32 bytes of data per cycle, it’s insufficient for use with field devices such as cameras, which can generate many MB of data per minute.
Uses for IO-Link systems abound to complement existing protocols underpinning virtually limitless controls and data-collection systems. Spurring adoption has been the simplicity of IO-Link systems —comprising only an IO-Link primary and its devices and their connectorized three or five-wire cables. Plug-and-play installation and cost-effectiveness are other IO-Link benefits.
Efforts by the IO-Link consortium of member companies have ensured wide compatibility between controllers, devices, and actuators from various manufacturers, which has given design engineers the widest selection of equipment for their specific use cases.