Impact of an uncooperative passenger on the control of an externally guided self-balancing patient-transport system

Patient transport is a physically demanding task for paramedics. The risk of injuries is high and the early retirement rate in emergency medical services is among the highest compared to other industries. The aim of the SEBARES project is to reduce the workloads for paramedics by introducing a self-balancing patient-transport system with a stair climbing mechanism, which is externally guided by a paramedic. In an earlier study a prototype for flat terrain was set up with a sliding mode controller for the self-balancing mechanism. The performance of the prototype without a patient was evaluated in respect of the ergonomic requirements of the paramedic/user. Furthermore, a simulative study demonstrated a considerable impact of an uncooperative passenger on the self-stabilizing mechanism. Although control of self-stabilizing human transporters in general are well researched, possible negative influences of passengers are currently neglected during modelling and control design. For the described patient-transport application uncooperative behavior is very common. Therefore, this experimental study focuses on the impact of uncooperative patients on the dynamic behavior and influences on controller robustness. The prototype of the transport aid was adapted and 128 trials were conducted with 8 subjects who had to perform 4 different scenarios to simulate uncooperative passengers. The tasks were repeated with different parameter values to evaluate the robustness of a sliding mode controller. The results showed that increasing the robustness can reduce the average force on the paramedic's handle from 60 N to 35 N, while the passenger was performing cyclic movements of the upper body. However, a drawback of high robustness is the occurrence of chattering around the control reference. Further studies will consider adaptive controller design.