Available Models
- Humanetics - 370-0000 (ATD Assembly)
Overview
Occupant Classification is a developing science designed to address the need to adjust or suppress the deployment of an airbag depending on the size of the person sitting in the seat. New regulations in the US are expected to require the airbag to be suppressed if a child smaller than the average six year old is occupying the front passenger seat.
This is driving the development of new in-vehicle sensors to classify the size of the seat occupant. One technology uses a matrix of force sensors in the seat cushion to measure the pressure distribution of the occupant on the seat. The sensing system looks for human characteristics in this weight pattern and can determine if this is a human adult, a child, a child seat or a bag of groceries, and modify the airbag deployment accordingly.
Current crash test dummies do not have human-like weight patterns and cannot be used for this purpose. It is possible to use real people for testing, but human testing is typically unrepeatable and logistically difficult.
To address the need for human surrogates for these sensors, the Alliance of Automobile Manufacturers contracted First Technology Safety Systems to develop a small female OCATD5 and a six year old child OCATD6.
OCATD5 represents a small adult female with a mass of 46.7 kg and a standing height stature of 145cm.
Dummy Features
Background
OCATD is based on the Biofidelic Seating Surrogate program, developed by Lear Corporation and Humanetics in 1998 and 1999. The fundamental construction is a soft deformable material molded over a humanlike skeleton. Originally designed for automotive seating comfort, NVH, and ingress/egress applications, the product also has a human-like weight distribution on a seating surface. The Biofidelic Seating surrogate represents a 50th percentile adult male and is reported in SAE Paper 1999-01-0627.
Anthropometry
OCATD5 represents a small adult female representing the 5th percentile of the US population. Key landmarks and exterior surfaces are taken from the 1983 UMTRI Anthropometry study. The skeleton model is derived from a Viewpoint Datalabs female skeleton polygonal model scaled to the UMTRI anthropometry. Mass based on Hybrid III and UMTRI mass segmentations.
Components
The OCATD skeleton is a molded plastic with metal inserts at the joints. Pivots at the T12/L1 and L5/S1 vertebrae locations allow the spine to rotate in the sagital plane. Ball joints at the femur to pelvis allow hip rotation and leg abduction/adduction to simulate various human postures. The joints can be locked for the dummy to sit erect without external support.
Flesh
The flesh material was developed during the Lear/FTSS research program. Currently the dummy uses a urethane based material to simulate human flesh stiffness. The thorax section is divided into three segments - upper thorax, abdomen and the pelvis/upper legs. The abdomen segment is removable to allow access to the ballast weights. The abdomen segment is made of a compressible urethane foam to allow the device to lean forward.
Surface Contours
The original UMTRI surface shell model buttocks were derived from subjects in the deformed seated position. These shell models are resurfaced to approximate a partially deformed human seat while maintaining a constant flesh volume. This initial surface shape provides a more accurate weight pattern when the OCATD is seated in an actual seat.
Postures
The OCATD is designed and molded to a back angle of 24.6 degrees to the vertical. This is measured as the straight line through the palpated surface landmarks of the T8 and L5 spinous processes. OCATD can recline back to 48 deg and sit upright unsupported.
For development and validation testing the OCATD will be raised and lowered into the subject seat many times and in different positions. For maximum repeatability, a hoist system is being developed to vertically raise and lower the OCATDs. The OCATD is suspended from the hoist by a cable system attached at the sternum, pelvis, and knees. The hoist system will allow for positioning in vehicle.
OCATD will be positioned above the test seat on the hoist system. Te device is pre-positioned in to one of three positions, design, reclined to 48 degrees, or erect. If erect, the spine joints are locked into position. The H-point will be aligned to the seat SGRP, and the OCATD lowered into the seat. The suspension cables will go slack and OCATD will settle into the seat.
OCATD is equipped with tilt sensors in the pelvis and spine These are acceleration based sensors to measure the variation of acceleration due to gravity. They are steady output instruments. Further tilt sensors may be added to OCATD if necessary. The tilt sensors connect to signal conditioning unit with a USB serial output a notebook PC. Software is supplied to calculate, display and record the OCATD orientations for each test.
The operating temperature of OCATD will be limited because of the flesh material stiffness varies with temperature. The temperature is expected to be limited to 72F +/- 5F. OCATD will be supplied with thin cotton clothing. Heavy clothing should be simulated by blankets, pads, etc according to the customers internal test procedures. OCATD should not be stored in the seated position. It is possible the flesh material can take a permanent set. The device should be suspended by the same cables used for the hoist. A roller stand will be available for storage and transport of the devices.
The University of Michigan Transport Research Institute (UMTRI) is undertaking a large research program to generate anthropometric data and analysis for small adult females and six year old children to validate the biofidelity of OCATDs with reference to the weight pattern distribution.
