Sensors and Measurement Quality control and traceability in the dust Ex Zone – with RFID Achim Weber Micro gas generators in seat belt pretensioners and head restraints ensure that vehicle safety systems respond immediately in the event of an emergency. For this the capsules are filled with a precisely defined quantity of powder in a fully automated assembly system. The system builder uses an RFID system that is approved for the dust Ex zone. “Atex zones are not routine environments for machine builders,” says Andreas Gradl, project manager at IMA Automation in Amberg, Bavaria. The company manufactures assembly and production systems for different sectors. However, none of these sectors typically operates in the explosion hazardous area. IMA was therefore breaking new ground when it developed a system for producing micro gas generator capsules in dust Ex zone 22. Micro gas generators are small explosive capsules that are fitted in active seat belt pretensioners or head restraints in vehicles. In the event of collision, Author: Achim Weber is sales specialist at Turck Germany Company name: Hans Turck GmbH & Co. KG Headquarters: Mülheim an der Ruhr, Germany Turnover: € 450 m (2013) Employees: more than 3,350 Products: sensors, fieldbuses, interfaces, RFID About AUTOMATION TECHNOLOGIES 5/2014
Sensors and Measurement next page the active belt pretensioner initiates a pre-tightening of the safety belt. An active head restraint is primarily used for a rear collision which causes the heads of passengers to be thrown forward rapidly. Through the automatic safety mechanism, the head restraint moves forward with the head and reduces the distance between the head and the head restraint. This therefore prevents the so-called “whiplash effect”. Fault-free production The manufacturer of the capsules turned to IMA Automation Amberg GmbH to build an automated assembly system for micro gas generator capsules. Part of the explosion protection concept involved the location of the hazardous processes in a separate Atex zone. The empty capsules are inserted in the workpiece holder and weighed in the safe area. The loaded workpiece holders are transported via a conveyor system into the hazardous area where they are filled at various metering stations. Besides its requirements regarding explosion protection, the customer also wanted the ability to fill the capsules with milligram precision and to integrate quality control and quality assurance in the plant. Any faulty capsules have to be detected as early as possible in the manufacturing process and rejected immediately. With a limited window for quality control of the explosive capsules an absolutely fault-free production process had to be ensured. To ensure this quality control, the manufacturer specified in its initial order that each individual capsule must be identified during the manufacturing process. Production in detail The empty aluminum capsules are firstly weighed in the safe area since the weight of these thimble-sized receptacles varies only by milligrams. The controller stores the weight in a database to determine after each filling exactly how many milligrams of powder are added. 150 workpiece holders transport the capsules in the closed circuit system. They are identified using Turck’s BL ident RFID system. An RFID tag is embedded in each workpiece holder for this purpose. In the first process step, the machine weighs the capsules and writes the tare weight to the database. The read/write head links the database entry with the 01 The RFID heads read out the tag on the workpiece holder
