Transparency up to the process level
11 September 2008
To meet demands for consistent cost reduction and higher system availability in the future, Profibus and Profinet International have initiated a working group of manufacturers several years ago, to make the “final yard” in a continuous automation structure more communicative and intelligent.
Transparency up to the process level
Prior to that, conventional sensors and actuators were becoming more intelligent and providing parameter and diagnostic services. This intelligence however, stopped at the interface of sensors/actuators since there was no standardised and bi-directional communication to the control level at that time. Hence, almost all parameters were configured directly by hand at the conventional sensor before delivery or during the commissioning phase of a machine/system or by means of a PC.
The backup of these configured parameters frequently stayed on the PC or in the document of the commissioning person. If a defect led to a replacement of a sensor or actuator, these parameters were often not available and had to be entered again in the new device by the maintenance personnel. Before the sensor/actuator replacement could take place, the manufacturer and type of sensor/actuator frequently had to be determined by means of the circuit documentation or with an on-site visit since a continuous diagnostics and type recognition was not possible. No meaningful preventive maintenance of a system could be performed.
The IO-Link communication technology offers a solution because it provides benefits for all phases of the system/machine life cycle. In the installation phase, the work of the system/mechanical engineer is made easier since only one cable must be laid in the future, a standardised unshielded 3-wire cable, between control level and the respective sensor/actuator. This simplified installation makes it possible to connect a simple binary-switching sensor/actuator on the one hand, and a multi-level signal light via the same standardised 3-wire cable on the other hand.
The wiring of analogue signals also becomes significantly easier since they are no longer connected with a shielded cable, but with the aforementioned cable. This saves warehousing costs for different cable types, also reduces and simplifies wiring expenses, and significantly lowers the risk of errors during installation. Since the IO-Link interface is derived from the standardised interface for proximity switches IEC 60947-5-2, no additional new tool is required for the installation of the devices. Furthermore, compatibility with existing sensor/actuator interfaces still exists. This allows it to mix IO-Link sensors with conventional sensors. They can then optionally be operated on an IO-Link master with full IO-Link scope of functions or a standard assembly as standard digital input/output.
Sensors/actuators can be configured and parameterised for IO-Link devices from the PC workstation or control room with the central engineering tool, e.g. Step 7, using the fieldbus system up to the sensor/actuator. In the process, the engineering tool reduces parameterisation tools of various manufacturers thanks to the configuration and data maintenance in Step 7, and also ensures the reproducibility of sensor and actuator parameters since they can now be stored centrally within a project in the same data format.
In addition to the central data maintenance, valuable time is also saved during parameterisation through uniform user guidance in the Step 7 engineering tool for all sensors/actuators and by omitting the on-site assignment. If a sensor or actuator should not exist in the central engineering tool, it is possible to import it, as it is known from Step 7, from the IODD or GSD file that is provided by every sensor or actuator manufacturer. The user then has the option to perform the parameterisation via the Step 7 port configurator) or via the TCI (Tool Calling Interface to Step 7) with the help of the sensor/actuator manufacturer tool. When the parameterisation is called via the TCI, the data can be saved in the respective format of the sensor/actuator manufacturer.
IO-Link also achieves significant improvements during the commissioning phase: The electrician/commissioning person only has to check the firm connection of the IO-Link connection during the start phase of the system/machine since wiring faults can nearly be ruled out due to the standardised 3-wire line. In addition, the accessibility/parameterisation of the IO-Link device can be tested using the engineering tool. If several devices within a system/machine require the same configuration/parameterisation, it can be duplicated and sent to every additional device.
To continue increasing the efficiency of systems/machines, it is possible to perform the configuration/parameterisation of IO-Link-capable sensors/actuators during runtime. This enables the commissioning person to adjust optimisations of systems/machines significantly better with the process than it was previously possible and, due to direct data access via fieldbus, also shortens the configuration process since parameters do not have to be adjusted directly at the device.
After completing the commissioning, the customer receives all the diagnostic information through the complete transparency, starting with the control level and down up to the sensor/actuator level. For example, if a system/machine fails, it is now possible to recognise on the control/visualisation level which sensor/actuator from which manufacturer caused the machine standstill. It can then be brought along for the maintenance call at the machine and automatically receives its parameter data after replacing the PLC or the IO-Link master. For this reason, the automatic parameterisation and advance information about the defective sensor/actuator significantly reduce the standstill times of a machine.
If the quality or productivity of a system/machine decreases during the operating phase, it is very easy to investigate the cause by using IO-Link and the Step 7 engineering tool. This allows checking the degree of contamination of an optical sensor or recalibrating the switching point of a distance sensor via the system so that tolerances can be adhered to and the quality level can be increased. The technology is suitable for quality checks and quality increase as well as allowing a flexible and customer-oriented production
The new IO-Link communication technology results in advantages and benefits for every phase of the machine life cycle that are available to every user and customer of automation systems. It is particularly due to these advantages that some machine will certainly have a competitive advantage over another one within the next few years. The great potential of IO-Link and the versatile options offered by this technology are already evident today:
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