Controller design and experimental evaluation of a motorised assistance for a patient transfer floor lift

Patient transfer is a critical task in patient care and medical sectors. However, it is challenging because it exposes caregivers to injury risks. Available transfer devices, like floor lifts, lead to improvements but are far from perfect. They do not eliminate the caregivers' risk for musculoskeletal disorders, and they can be burdensome to use due to their poor manoeuvrability. This paper presents a new motorised floor lift with a single central motorised wheel connected to an instrumented handle. It proposes admittance controllers (the reference velocity of the motorised wheel, is computed as a function of the force applied on the handle), 1) to achieve the best manoeuvrability, 2) to reduce the effort required in a task, decreasing the risk of injuries among caregivers and 3) while guaranteeing the security and comfort of patients. Two controller designs, one with a linear admittance law and a non-linear admittance law with variable damping, were developed and implemented on a prototype. Tests were performed on seven participants to evaluate the performance of the assistance system and the controllers. The experimental results show that 1) the motorised assistance with the variable damping controller improves manoeuvrability by 28%, 2) reduces the amount of effort required to push the lift by 66% and 3) provides the same level of patient comfort compared to a standard unassisted floor lift.