Modelling and Control of a Seat Cushion for Pressure Ulcers Prevention.

Pressure Ulcers are a skin phenomenon that develops in patients with loss of mobility and activity due to a decrease of sensory perception and a transformation in the cardiocirculatory system. These aspects affect mainly: elderly people, people with neurodegenerative disease (as ALS), spinal cord injury patients (SCI) and people suffering from a stroke who are obliged to stand still in bed or on wheelchairs. The aim of this work is the modelling and control of a seat cushion for Pressure Ulcer prevention. In particular, the attention is focused on the definition of level surfaces in order to highlight the highest and lowest risk sites of pressure ulcers formation. Every level surface is defined by the presence of actuators that represent the contact surface of the cushion. The system is able to identify the critical points of pressure ulcer development (Ischial tuberosities) thanks to a closed loop control that maps pressure in real time, offload specific air cells and redistribute the resulting pressure in order to delete the pressure peaks, permitting reperfusion. The following step is the study of the pressure variation of these actuators through an inflation and deflation process, analyzed submitting the cushion to different loads and evaluating two different control systems: the first one where the level surfaces are controlled in series (one at time) and the second one where the level surfaces are controlled simultaneously.