With the advent of Industry 4.0, intelligent automation has been defined as advanced control, monitoring, and diagnostics. However, this is only possible through industrial connectivity, which unifies control and machine equipment on the same platform for continuous data exchange.

　　The key enabling technologies that support industrial connectivity are standardized networks and devices with onboard communication capabilities. There are many protocols that support these features. However, not all industrial protocols can meet the data exchange and intelligence requirements required for today's automation, and the IO-Link protocol was created to meet the broad needs of these modern applications.

　　IO-Link is a wired point-to-point communication protocol that facilitates intelligent two-way data communication between devices.Typically, the IO-Link master (local controller) has multiple IO-Link ports into which various IO-Link devices can be plugged in. These node-to-node endpoint connections make IO-Link a peer-to-peer communication protocol. The unified IO-Link interface is defined by the IEC 61131-9 standard.

　　IO-Link offers three ways to integrate devices into advanced control systems, enabling smart devices in the field to work without human intervention.

　　01   Application-related communication modes

　　The IO-Link communication protocol enables four communication modes for each connector port on the IO-Link controller. These include a full deactivation mode as well as IO-Link, digital input (DI) and digital output (DQ) operating modes.

　　The IO-Link operating mode supports bidirectional data communication with field devices and is often used for monitoring, testing, and diagnostics during data acquisition. The local controller port in DI mode accepts digital inputs and functions when the port is connected to the sensor, in which case the port acts as an input device. In contrast, the DQ mode port acts as a digital output, typically when the port is connected to an actuator (in this case, actually the output device) or when the system programmable logic controller (PLC) is set up to send instructions directly to another IO-Link device.

　　It is worth noting that the ports on the IO-Link master can be switched between different modes at any time. For example, a controller port connected to a sensor can operate in DI mode and then switch to IO-Link communication mode when the controller requests diagnostic and monitoring data from the sensor.

　　02  Actionable state communication

　　Machine monitoring is possible by setting up IO-Link devices to report status and inform the system to make the necessary adjustments and corrections. For example, in the machine tool industry, one of the uses of IO-Link pressure sensors is to verify that the clamping pressure of the workpiece is appropriate for non-destructive and safe clamping during the operation of unloading the material. Here, IO-Link sensors mainly support the optimization of machine tool tasks in order to reduce the occurrence of failures.

　　IO-Link devices can also enable operationally available status communication to support enhanced maintenance routines, minimizing downtime. For example, IO-Link position sensors on assembly machines can continuously report the position of the end effector to ensure that no position is out of range or misaligned.

　　By analyzing the diagnostic data provided by IO-Link devices, plant technicians can predict and correct errors and potential failures before they occur. Technicians can also identify weak points in a machine or plant to inform future enterprise-level operational changes, purchasing decisions, and the design of dedicated machines.

　　03  Advanced control and automation

　　In cases where IO-Link devices support functions that can operate without human intervention, IO-Link controllers are typically connected to a host system or a higher level PLC to process the received data and then directly or indirectly command the actuator to respond appropriately and coordinated. This automated control requires IO-Link systems to be connected to higher-level controllers via standardized fieldbus or Ethernet protocols and cabling. In fact, most IO-Link controllers have a fieldbus or Ethernet port for this type of connection.

　　Devices in advanced control applications involving IO-Link systems are integrated in one of three ways:

　　1. Direct connection to the main unit or PLC

　　2.Connect to the IO-Link master and communicate via the IO-Link protocol

　　3. Use IO-Link-compatible communication and connect to the IO-Link master via the IO-Link hub.

　　Another benefit of IO-Link systems with fieldbus and Ethernet communication connections is that they allow long-distance connectivity, which in turn enables installers to install IO-Link controllers in control cabinets or on outermost machines, which is useful for some specific applications.

　　IO-Link controllers can be used as low-level controllers capable of processing digital and analog signals, benefiting advanced combined applications. Here, they can:

　　■  Receives data generated by IO-Link linear encoders on the XY platform axis.

　　■ Acts as a gateway to process data.

　　■ Submit the processed IO-Link field device data to the PLC or other system controller.

　　04  Intelligent equipment

　　An important application of IO-Link is to make devices intelligent. These IO-Link-enabled devices are especially common in designs similar to traditional sensors with no (or few) programming, which can receive instructions, monitor, and perform self-test routines and generate data. Since IO-Link allows devices to provide more data in addition to providing basic double-valued (yes, no, or pass, fail) data, precise values can also be reported. For example, process automation tasks benefit from IO-Link temperature sensors, which continuously report precise temperature values in the monitored area or space instead of simple high or low temperature status alarms.

　　Another benefit of IO-Link for smart field devices is the compactness of its physical connection. This is in contrast to the physical connections of fieldbuses and Ethernet interfaces, which are sometimes too bulky to install on micro-devices in the field. IO-Link intelligent components can also be precisely controlled. For example, once a scene meets a set of conditions, the drive can be commanded to shut down instead of the basic shutdown and on controls.

　　However, there are some considerations to the use of IO-Link in smart device applications. Although IO-Link in its wireless form is under development, it is still primarily a wired communication protocol for now – so it is still limited by hard wiring. To maintain data integrity, the wiring from the IO-Link master to the device must not exceed 20 meters. In addition, since the IO-Link protocol can only transmit up to 32 bytes of data per cycle, it cannot be used with field devices such as cameras, which can generate a few megabytes of data per minute.

　　IO-Link systems are extremely versatile and complement the shortcomings of existing protocols, supporting virtually unlimited control and data acquisition systems. IO-Link systems are widely used because they are easy to use and require only an IO-Link master, application equipment, and a three- or five-wire cable connected to them. Plug-and-play installation and cost-effectiveness are also advantages of IO-Link.

　　Key concepts:

　　■ O-Link offers three ways to integrate devices into advanced control systems.

　　■ Precise control and compactness are the benefits of using IO-Link for intelligent devices.

　　Think about it:

　　How does applying IO-Link help enterprises achieve device intelligence?

*部分信息来源于：控制工程网。