Ensuring consistent identification

27 February 2017

Tracing components through the entire production process and then analysing the data to help optimise production has been a goal in the industrial environment for some time. High-precision processes can be improved by implementing component identification with UHF RFID technology, says Ingo Hecker.

The requirement for tracking and tracing in value process chains is constantly increasing due to the fact that a variety of process parameters must be logged and made available for further use, analysis and similar tasks. In addition, government and industry regulations must be observed and documented. In the automotive industry, for example, such documentation requirements must be met when installing specific components such as airbags in a vehicle, and also for many other safety-related tasks. This is all based on the serialisation of goods within the processes. Each component must be clearly identifiable and clearly traceable within the value chain. This is generally defined as ‘track & trace’.

A variety of technologies can be used for the identification of components. Industrial identification systems – mainly optical identification systems or RFID (radio frequency identification) systems – are used for this purpose. For visual identification, for example, a compact Data Matrix Code can be cost-effectively applied to difficult surfaces such as metal and plastics using a variety of methods. The immutability of the data is a basic condition for optical codes. This means that no substantive change can be made to the data after its application. Any status or information changes must be provided in an accompanying database that references the initial code.

Variable data content
RFID systems are employed in many highly automated processes to meet the requirements for the storage and change of data during the process. Direct attachment of the RFID tags (or transponders) to the components ensures that the data is ‘married’ to the component, which enables immediate identification of the components throughout the value chain. Direct attachment offers advantages when compared to indirect identification, where tags are mounted to a workpiece carrier on which the component is transported or processed, for example. Otherwise, the separation of the transponder and component must be taken into consideration in the processes through appropriate redundant structures – for example, by carrying along data in a higher-level IT system.

Since the introduction of UHF RFID at 868 MHz in Europe, the advantages of optical identification systems and established HF RFID systems have been combined. Similar to optical codes, the UHF RFID tags are processed over long read/write distances and also offer the ability to change information. 

Even when different engine blocks – four, six- or eight-cylinders – are manufactured on the same production line in the automotive industry, it can be done using RFID and this is where the UHF technology of the Simatic RF600 system from Siemens is frequently used. To date, mainly optical identification systems with lasered or dot-peened Data Matrix Code have been used. During machining, it was not always possible to reliably read the codes due to drilling fluids, metal shavings or oxidation of surfaces. Due to highly varied production, the documentation of the build status as well as the variants dynamically and directly at the assembly site is often necessary during processing. 

Increasingly greater read and write distances also need to be achieved – due to the interference contour of an engine block along the production line and the installation conditions. It is also an advantage if the process and quality data can be carried along directly on the workpiece, for one because early removal of defective parts due to faulty process steps is possible, and for another because the production history can be read at the end of the production line – directly on the finished power train, for example. This traceability of individual process steps within the context of quality assurance is important for documentation purposes. The process quality can be continuously and permanently optimised in this way. 

Saving space
Using the Simatic RF630T UHF screw-fit transponders these requirements can be optimally met with limited space on the casting. In its assembled state, the footprint of the screw-fit transponder occupies no more space than a lasered Data Matrix Code. Thanks to the concentric and symmetrical field property, the RFID transponder can be detected in the process even at a variety of reading positions. This provides greater flexibility in the assembly of the RFID antennas, and during commissioning of the system as a whole as well. This offer considerable advantages as the available space in fully automated machining equipment is often limited.

The 64 bytes of storage capacity of the Simatic RF630T is sufficient to store the relevant user data of the automated processing stations directly – for example on the crankcase – and thus to control further processes. In this way, each step in the process chain is documented and can also be reviewed at the end. For example, questions can be easily answered later such as which component was handled by a certain station and whether any quality optimisation measures were performed.

With UHF RFID, communication between the reader antenna and transponder is established via radio waves. ‘Cross reads’ may occur due to the reflection of the waves on metallic surfaces, which are common in the production environment. When engine blocks are lined up tightly, for example, this overreach causes several blocks to be detected at one time and not just the one intended for the next processing task. One way to reduce such effects, or even prevent them altogether, is the use of different RFID antenna types. The different detection characteristics of the antennas are based on their size, polarisation (linear, circular), the antenna gain and beam angle. The RF620A UHF antenna is especially suited for confined installation conditions. The adaptive antenna, RF680A – on the other hand – offers reliable detection especially in reflecting radio environments often found in production. This external antenna can be used in conjunction with the RF680R reader, for example, and integrated into automation systems due to its integrated Profinet interface. The Siemens TIA Portal allows a convenient integration of RFID components in control systems. Using standard function blocks, data can be easily read from the RFID tag and processed in the controller or data from the controller can be written to the transponder. 

The goal 
A frequently cited goal in industry is for the identification of a component as consistently as possible along the entire value chain. By attaching a tag, the resulting component – an engine for example – can be consistently identified with a single technology throughout the power train production, starting at the foundry, through mechanical machining, assembly, the concluding test processes and finally the installation in the drive train. This is possible not only in the manufacturing environment, but also in the area of logistics. 

UHF technology has come of age in industrial environments with high process requirements. It is now able to offer great potential for merging continuous identification concepts along existing value chains.

Looking at future concepts such as Industry 4.0 or the Industrial Internet of Things (IIoT), communication technologies such as RFID, as well as network technologies, will be essential pieces of the puzzle. 

Ingo Hecker is product manager for identification for the Process Automation division of Siemens.

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