Motion Analysis and Tactile-Based Impedance Control of the Chest Holder of a Piggyback Patient Transfer Robot.

Patient transfer, such as carrying a bedridden patient from a bed to a pedestal pan or a wheelchair and back, is one of the most physically challenging tasks in nursing care facilities. To reduce the intensity of physical labor on nurses or caregivers, a piggyback transfer robot has been developed by imitating the motion when a person holds another person on his/her back. As the chest holder supports most of the weight of the care-receiver during transfer, a human-robot dynamic model was built to analyze the influences of the motion of the chest holder on comfort. Simulations and experiments were conducted, and the results demonstrated that the rotational motion of the chest holder is the key factor affecting comfort. A tactile-based impedance control law was developed to adjust the rotational motion. Subjective evaluations of ten healthy subjects showed that adjusting the rotational motion of the chest holder is a useful way to achieve a comfortable transfer.