Roush Develops Passenger Side Airbag Measuring System Using LabVIEW and NI Data Acquisition Technologies

Author(s):
Mike Hawkins - Roush Industries, Inc.

Industry:
Automotive

Products:
Vision, LabVIEW

The Challenge:
Measuring the pressure, strain, and acceleration placed on an automotive instrument panel (IP) when a passenger side airbag is deployed and converting the data into a format that can be used in a computer automated engineering (CAE) model.

The Solution:
Creating a 48-channel measurement system using the NI SCXI-1000 chassis and NI DAQCard-6062E, which is capable of measuring 32 pressure channels, 15 strain or acceleration channels, and a 20-volt input channel, and managing the test with an NI LabVIEW--------based software application capable of recording up to 20,000 samples per channel, per second.

Combining High-Speed Measurement Devices and Custom Software
In the past, engineers used high-speed cameras alone to measure the timing and dynamics of an airbag deployment. However, while the camera can show only what takes place outside the IP, much of the dynamic of the deployment takes place inside the IP. To measure what takes place prior to the airbag becoming visible by the camera, engineers must rely on high-speed measuring devices and custom software. We used National Instruments software and hardware to perform this function quickly and cost-effectively.

Creating an Accurate, Easy-to-Use Measurement System
To meet requirements, we had to build a high-speed, high-channel-count, portable, and user-friendly system. We chose an SCXI-1000 chassis because it accommodates four SCXI modules, which satisfies the required channel count, and because it is small, light, and easy to transport. The data from the SCXI-1000 chassis is digitized and transmitted to a laptop through a DAQCard-6062E, which samples at 500 kS/s, meeting the high-speed requirement of the system.

We used two SCXI-1520 modules, one SCXI-1102C module, and one SCXI-1181 module in the SCXI-1000 chassis. We configured the first SCXI-1520 module for one channel of ±20 V. The other seven channels on the first SCXI-1520 module, as well as the eight channels on the second SCXI-1520 module, are software configurable for strain or acceleration input. We configured the SCXI-1102C module for 32 pressure sensor inputs and used the SCXI-1181 module to supply excitation to all 32 of these sensors.

To make connectivity more technically friendly, we used a custom connector panel with two BNC inputs wired to the ±20 V input channel on the SCXI-1520 module. One BNC input is designed for a contact-style trigger and the other is designed for a voltage-input trigger. There are six 8-channel connectors; we use two for the 15 strain and acceleration channels and the other four for the 32 pressure channels. Each connector is labeled and color-coded.

Custom cabling also comes with the system. Each of the eight connectors has a labeled and color-coded 15-foot cable that the user can bring into an environmental chamber, and each cable also has a color-coded and labeled pigtail.

We designed the software that manages the test to be used by a computer novice. It is intended to be passed around to many different users and must be easy to run with just the help of a user manual. Additionally, because each single deployment costs up to $5,000, the software reliability is critical. We wrote the software code used to set up and control the hardware and to view and process recorded data in LabVIEW version 6.1. We chose this software platform because of its easily programmable icon-based code and its easy integration with National Instruments hardware.

Using the main screen in the software, the user can record and view data from a previous deployment or navigate to the acquisitions or trigger setup sections of the software or the CAE postprocessing screen.

There are four screens in the acquisition setup section. With the first screen the user can enter all information relevant to the type of IP being tested along with the test conditions. He can use the second screen to configure which channels are recorded. Using the third screen, the user can identify the pressure sensor locations relative to the IP for postprocessing of data and with the final screen he can set the sample rate and duration of the data recorded.

In the trigger setup screen, the user can set the threshold and duration of the trigger used to deploy the airbag. The trigger setup portion of the software is very important because the deployment takes place in a mere 15 milliseconds. If the trigger is not properly detected there is a chance that the data could be missed. Additionally, the trigger is used as a marker for the start of the deployment from which the duration can be calculated.

The CAE postprocessing section is designed to view and report the pressure data in a specific format for input into different commercial CAE software packages. In this section, the recorded data, along with the location setup information, is used to extrapolate and interpolate the data across the area of the door throughout the duration of the deployment. That data is then plotted on a 3-D graph for viewing.

Designing Safer, Faster Airbags in Less Time
Using National Instruments software and hardware, engineer now can easily measure and record information about an airbag deployment that previously had never been quantified. Additionally, they can convert this data into a format that can be read directly into a CAE model. In this way, they can make safer, faster passenger side airbags in less time and with more efficiency than ever before.


For more information, contact:
Mike Hawkins, Development Engineer
Roush Industries, Inc.
28152 Plymouth Rd.
Livonia, MI 48150
Tel: 734-466-6215
Fax: 734-466-6905
mjhawk@roushind.com

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