RFID for the identification of workpiece carriers certifies smooth logistics flow on the production line at Getrag Ford Transmissions |
There seem to be countless variants of transmissions available today like the five, six speed, in many different power classes, housing types and configurations. The transmissions are manufactured on a semi-automatic production line. At the beginning of the process, the two housing parts are each on a workpiece carrier. While passing the production line they are equipped with shafts, toothed wheels, spacers and other mechanical components – partly automatically, partly manually. Automatic measuring tools tune the components in the 100th millimetre range – this requires highest precision. Finally, the two parts of the transmission are joined, screwed together and filled with oil. Final testing is then carried out on the test rig.
The time has long gone when a production line was set up for a specific transmission type. Today, many variants can be manufactured in a mixed production. The machining centres and pick-and-place machines must identify which transmission gets passed on the production line. The different machine parameters have to be selected accordingly.
At first, the number was limited to four transmission variants. Identification was ensured by means of targets attached to the workpiece carrier. These are metal discs in different arrangements. Proximity sensors were used for detection. The metal disc at the uppermost position was for transmission type A. For transmission type B, the disc was one position lower, etc.
Due to growing requirements, Getrag Ford Transmissions in Köln-Niehl, upgraded and modernised their plant about two years ago. The project was managed by the company Bratz Engineering that specialised in refurbishing and equipping production plants. The goal was to produce as many different transmission types as possible without retrofitting the machines. Therefore, identification of the workpiece carriers was adapted to new requirements. Optical processes such as barcodes were eliminated due to the severe operating conditions (oils, metal swarf) and they decided to use a RFID system from ifm electronic gmbh.
Ford Transmissions makes more than 50 different transmission types and over 40 RFID read heads were installed along the transport belt. The system is controlled via the fieldbus AS-interface and offers real ‘plug and play’. There is no need for complex parallel wiring and this reduces time and cost for installation and setup. Michael Kirchner, project manager, Bratz Engineering said, “For AS-i a simple two-wire cable is sufficient for the power supply and data transfer. Installation and wiring were carried out without problems within some days. We had to just mount the heads, lay the AS-i flat cable along the read units, make branches in the cable and then connect the RFID sensors to the junction box.”
Due to the spatial extension and the number of sensors the AS-i system is divided in five lines. One AS-i controller each is connected per line. The five controllers communicate with the higher-level control system via the Profibus interface. The set-up too was trouble-free. “Setting the parameters of the RFID system was very easy. The system could be handled intuitively thanks to the convenient AS-i controllers with graphic display and pushbuttons. Reading the manual too was not necessary,” stated Kirchner.
The matching parts for the RFID sensors are the ID tags. The tags contain the data the read head reads when they pass. These tiny radio memories were mounted in fixtures on 120 workpiece carriers. When the tags pass, the sensors read the data from a distance up to 20 mm. The pallet number (1 to 120) is saved in each ID tag. This number refers to a transmission-specific dataset saved in the central control system. This dataset controls the different machines of the assembly line by means of the transmission- specific parameters. The read/write distance is maximum 65 mm and the travel speeds up to 0.5 m/s.
The voltage is supplied via AS-i. Therefore, a separate power supply is not necessary. In addition to the antenna, the read/write head includes the complete evaluation and the interface to AS-i. It is simply operated as an analogue slave according to the profile 7.4 in the AS-i system. Additional hardware or software modules are not necessary. Up to 31 read/write heads can be connected to an AS-i line. The transmission of energy between the ID tag and the read/write unit is based on the physical principle of inductive coupling with a frequency of 125 kHz.
The modernised installation has been operating with RFID technology for about a year. Summing up, Kirchner said, “The system works reliably. There were no problems when reading the data nor were there any faults in the AS-i system.” The initial scepticism towards RFID and AS-i turned into enthusiasm. “For sure, this will not be the last installation we will get from ifm electronic,” added Kirchner.