Active Spine Modeling Representing a 6 Year-Old Child

In a car crash, properly restrained forward facing children may sustain head injuries due to contact with the car interior. Emergency events such as braking and steering will influence the kinematics of the child, thereby affecting the child’s interaction with the restraint systems. Volunteer experiments (Stockman et al. 2013) have shown that children around six years of age, properly restrained on a booster cushion, may slip out of the shoulder belt during a 1g emergency event, while older children can maintain their posture better. A numerical human body model of the 6 year-old would be a valuable tool to study and improve the performance of restraint systems in the pre-crash phase. Compared to a crash, an emergency event typically has low g and long duration loading; hence, the muscle activity will influence the kinematics of the child. Therefore, the aim of this work is to develop an active 6 year-old human body model.The 6 year-old facet occupant multi body model in the MADYMO code (TASS, Rijswijk, the Netherlands) was selected. The spine is composed of rigid vertebral bodies connected with spherical joints. Muscle activity was implemented by applying torques at each vertebral joint for flexion-extension and lateral bending. The torque actuators were controlled by proportional, integrative and derivative controllers comparing the current joint angles to an initial posture reference value. The controller gains were based on adult data and scaled by 50% for a first version of the active child model. The resulting active 6 year-old model was used to simulate the volunteer experiments by Stockman et al. 2013. The model was seated on a booster cushion and loaded with the average experimental pulse. The first version of the active child model had a significantly improved biofidelity compared to the original facet model, with shape and magnitude of displacements similar to the volunteer data, see Figure.It is concluded that the first version active 6 year-old model can reproduce this specific emergency event. Future work should focus on controller gain optimization and further validation