Towards Design Guidelines for Multidirectional Patient Transfer on a Bed Surface Using Traveling Waves

Patients who have limited body movement ability need assistance with frequent repositioning and transfers from their caregivers. These common manual tasks are physically strenuous for caregivers. To minimize caregiver physical effort, several assistive devices have been proposed. However, most devices have complex designs, are expensive, can only move the patient in one direction, or still need the caregiver's intervention. Inspired by natural waves such as water waves that can carry objects, this study presents actuator-agnostic design guidelines for moving a body on a bed surface using traveling waves as an alternative solution. Specifically, this study explores how transportation speed and movement smoothness are affected by wave parameters such as the wavelength, wave amplitude, number of the actuators used to create the wave profile, and their movement pattern. Additional requirements for moving an elastic object, such as a human body, were also established to minimize the stiffness of the interface layer between the body and wave particles. Results suggest that transportation speed is linearly proportional to wave frequency and horizontal displacement of the wave actuators. Maximizing the number of actuators while minimizing wave amplitude and wavelength will increase the smoothness. Meanwhile, the wavelength must be at least half of the object length to ensure motion stability while also exceeding a critical value to guarantee that feasible waves are achieved in practice. Additionally, the wavelength, wave amplitude, and number of actuators will determine the minimum required stiffness of the interface layer.