Hybrid Actuator for a New Robotic-Aquatic Rehabilitation Paradigm

Robotic technologies has been demonstrated to be effective in the treatment of neurological disorders such as stroke, multiple sclerosis, or severe neuropathies. However, many patients, who suffer severe spasticity, pain and limited range of motion, do not qualify for such robotic training. On the other hand, aquatic therapy seems to be an effective rehabilitation method to improve rehabilitation outcomes of patients with those complications/symptoms. The current actuator technologies used in robotic rehabilitation devices is not enough efficient to deliver therapy in aquatic environments so we present in this paper a new type of hybrid actuator system based on the reaction force produced by a set of micro water jets in opposite configuration and the torque produced by small electric motor to get actuator systems more efficient and lighter than the application of any of the current actuator technologies. This paper presents the first experimental results of this novel hybrid actuation system. A comparative study of step input response parameters is analysed, distinguishing between the water jet propulsion configuration and the hybrid actuation approach. The hybrid configuration shows that the delay time is reduced to 1.0 s, the rise time to 1.5 s, and the peak time to 1.9 s. It is worth noting that the settling time decreases from 7.6 s to 2.4 s, enabling the system to reach the reference value considerably faster. Furthermore, the overshoot is reduced to$\mathbf{1 1. 7 6 \%}$, while the steady-state error drops to 0.14%