Design and control of an active mattress for moving bedridden patients

A new mechanism for transporting a bedridden patient in an arbitrary direction while lying comfortably on the bed is developed. A wave-like periodic motion is generated on a mattress surface by activating the individual coil springs which constitute the mattress. The whole or part of the patient body is moved by this periodic surface movement. Varying the periodic trajectory and coordination pattern yields various movements of the patient, i.e. translation and rotation of the whole body, changing the posture of the limbs, etc. First, functional requirements for active mattresses are provided, and a prototype system is designed and built. A variety of control algorithms are developed for moving a patient in various ways. Periodic trajectory and coordination patterns are designed in order to move the patient smoothly despite uncertainties in load distribution and actuator dynamics. A discrete-event control system using a Petri net is developed for coordinating and synchronizing many axes of motion. Furthermore, a high-level controller is developed to perform closed-loop positioning of the human body, based on the estimation of the body's location using pressure sensors distributed across the bed surface. Experiments using a prototype mattress demonstrate smooth body motion in both the x and y directions and rotation within the plane of the mattress surface.