Test fixture for digital measurement of vehicle air bag deployment

Abstract

The disclosed invention is a method of and a system for taking digital measurements of vehicle air bag deployment characteristics versus time in which the key parameter measured is air bag envelope throw, outboard from the storage canister from which envelope leading edge velocity is derived. Also measured are squib voltage, squib current, and exhaust gas temperature. Envelope throw is recorded on three axes, the central, left diagonal and right diagonal, which are instrumented on a checkerboard target containing photo-transistors at the checkerboard intersections. The photo-transistors are connected to a stepped voltage ladder, and conduct when they are illuminated, causing their respective output voltages to be low. When illumination is interrupted, the photo-transistors turn off, and allow the output of a voltage which is proportional to position on the checkerboard. Before the air bag is fired, all photo-transistors are illuminated, keeping all outputs low. When the air bag is fired, the expanding envelope interrupts illumination to respective photo transistors and they turn off and cause a stepped voltage output, proportional to their position on the checkerboard, but the still-illuminated photo-transistors stay on and keep their outputs low. The expanding envelope leading edge position is therefore known each time the positional voltage outputs are sampled. The electrical, thermal and distance-proportional signals are simultaneously monitored using a data acquisition system at rates up to 5000 sample words per second.