Semi-active control of ambulance stretcher system based on parallel mechanism with MR dampers and perturbation analysis

The recumbent patients on ambulance stretcher experience multi-dimensional excitations due to road roughness. In order to isolate the multi-dimensional vibrations validly, a novel ambulance stretcher system based on 4-PUU parallel mechanism with Magneto-Rheological dampers is proposed. Firstly, the kinematic and dynamic equation are deduced by geometric relation and Lagrange equation respectively. Subsequently, the vibration isolation performance is investigated in time and frequency domain. The robustness of LQR algorithm is addressed with parameters perturbation by deducing Lyapunov equation. Further, selecting RMS values as the index of vibration isolation performance, the index which includes geometric parameters perturbation, mass and spring uncertainties is discussed. Simulations demonstrate the stretcher system can effectively isolate multi-dimensional vibrations in sensitive frequency range for supine patients with perturbation and uncertainties. The RMS values show different characteristics because of altering Jacobin matrix of the stretcher.