2011

Measuring Multiple-Axis Position of Multiple Points at Data-Sampling Rates of 10-20 kHz

Multi-axis measurement of position is important in testing of weapons and in automotive crash testing.

Multi-point, multi-axis measurement of position can be valuable in a variety of applications that require high-speed data acquisition and a high degree of measurement accuracy. Examples include ballistics testing (weapons, ammunition, and protective gear) and automotive crash testing, for which this new technology was originally developed. The electro-optical measurement system uses high-power LEDs and high-speed sensors to generate unprecedented volumes of highly accurate data on 2D and 3D position.

Measurement System for the crash test dummy. Sensors and controller/DAS are built into one enclosure." class="caption" align="right">Current crash test dummies use either a single potentiometer to measure chest deflection at the center of the sternum, or one potentiometer per rib to measure deflection at the center of each rib. To improve occupant safety, automotive restraint engineers and researchers require more information on the motion of dummy ribs under various crash scenarios.

The measurement system uses LEDs at each measurement point on the ribs and optical angle sensors attached to the dummy spine. Using fundamental triangulation techniques, the 3D position of each LED can be measured to better than 1-mm accuracy.

The system leverages advances in LED and optical sensor technology, along with a fast DSP processor, to achieve an overall sample rate of 1020 kHz per LED. Each LED is turned on for only 3 to 4 microseconds, one LED at a time, and the sensor outputs are recorded using fast analog-to-digital converters. In order to make accurate measurements, the LED brightness is optimized for each sample to ensure a near full-scale reading on each sensor.

LEDs mounted on ribs (above), and the measurement system’s dummy thorax (right)." class="caption" align="right">While one LED is on, the processor calculates the drive current for the next LED in the sequence. Due to the inverse square law (where the sensor output is inversely proportional to the square of the LED-to-sensor distance), the LED brightness-control algorithm uses non-linear techniques.

The system’s LEDs, sensors, and controller/data acquisition system (DAS) have been packaged into several different types of current and advanced frontal and side impact dummies. Measurement range can be adapted to the application.

Researchers using the system can get a better understanding of the interaction between the dummy and the airbags, seatbelts, and car interior. For example, in one series of side impact tests, the dummy ribs were being pushed significantly forward during the crash, as indicated by data that previously had not been measurable. After evaluating the data, researchers found that a stiffener bar in the seat structure was causing the problem. Safety engineers have also found that with data, they can differentiate between the loading on the dummy caused by the seatbelt versus that caused by the airbag. This previously had not been possible.

This work was done by Boxboro Systems LLC. For more information, visit http://info.hotims.com/34455-121.

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