Design and Evaluation of an Active Vibration Isolation System for Ambulance Stretchers

Whole-body vibrations (WBV) experienced in vehicles have garnered increasing attention due to their potential impact on occupant health and well-being; their effects range from short-term discomfort and fatigue to long-term muscu-loskeletal disorders. Particularly, during ambulance transportation of patients to hospitals, WBV limit the effectiveness of vital support techniques that are frequently implemented to stabilize such patients, and can even worsen their condition. To mitigate these effects, isolation systems are usually placed in between the stretcher and the ambulance floorboard; however, the passive characteristic of most limits their effectiveness to around 40%, and the active ones involve a more complex mechanism that often results impractical for implementation. Moreover, most proposals are designed at most with a half-car model, which turns in a dynamic decoupling that loses a comprehensive understanding of the entire vehicle's behavior in response to road irregularities. Thus, the aim of this study is to design and evaluate an active isolation system to insulate the patient's stretcher from the vibrations generated by the terrain. A full-car model of the system was implemented and a Skyhook control strategy with zero acceleration reference was established. The obtained RMS body acceleration resulted lower than that indicated by the SAE J6a by 98%, which indicates an efficient reduction of WBV suffered by patients and results beneficial for preserving their health.