Automated Precision Weighing with WMS Weigh Modules


Safety Assured – Airbag Systems Rely on Weighing

WMS Weigh ModulesIn airbag production, accurate filling of propellant tablets is essential for correct deployment in case of an accident. TRW Automotive, a leading global supplier of safety systems for the automotive industry relies on high-precision weigh modules for its propellant dosing applications.

TRW Automotive is one of the world’s largest automotive suppliers. The company has business relations with more than 40 major vehicle manufacturers, and provides equipment for approximately 250 different vehicle models. The leading company in the field of vehicle safety produces advanced brake, steering, suspension, and passenger protection systems. TRW is also one of the leading global companies in the design, development, and production of gas generators for the entire range of airbag systems.

In an accident, the airbag has to deploy extremely fast to ensure the safety of passengers. This is achieved through a special propellant in the form of tablets. The smallest tablets weigh a couple of milligrams; the largest up to 200 milligrams. The uniformity of the tablets in terms of their composition, weight and shape, is one of the requirements for safe and reliable airbag function. Ultimately, the propellant tablet must be placed in the gas generator of an airbag using precise weighing-technology methods.

Below-the-balance load transmission

WMS Weigh ModulesTRW uses the high-precision WM204 weigh modules from METTLER TOLEDO to place the tables in the generators. TRW engineers chose this weigh module because it is both precise and can be easily integrated into the machine mechanically and electrically. The below-the-balance weighing device makes it possible to suspend the dispensing container underneath the weigh module. This provides the advantage of allowing the tablets to flow into the gas generator through the simple and compact dispenser using the weight of the tablets themselves. TRW is able to forgo a handling mechanism for transporting the tablets from the weighing pan to the gas generator.

Easy electrical installation

The weigh module is electrically connected via the ConBlock and Profibus® DP Module from METTLER TOLEDO to the programmable logic controller (PLC). The ConBlock module offers permanent service access, which allows online analysis of the data exchange between the weigh module and the PLC.

Service access also makes it possible to configure and optimize the weigh module even while operations are running via APW-Lint™ software. The connection runs from the ConBlock module to the Profibus DP fieldbus module. Thanks to automatic parameter detection and the integrated interface command set for weighing technology, the system is very easy to put into operation.

Simple integration

TRW engineers developed and built a device for placing the correctly sized tablets in the gas generator themselves. The ease of integrating the WMS weigh module thanks to ConBlock, the fieldbus module and the ergonomic APW Line configuration software made their task significantly less complicated.

The high precision of the weigh module, combined with fast data transmission, provides more consistent quality, and enables high throughput in the production process.

WMS weigh modules

  • WMS Weigh ModulesModels ranging from 120 g to 6,200 g
  • Readability: 0.1 mg – 10 mg
  • Stabilization time: 0.15 – .08 seconds
  • Integrated calibration weight as option
  • IP54 protection, IP66 protection for cleaning

WMS Weigh Modules