Hybrid Control of Powered Orthosis and Functional Neuromuscular Stimulation for Restoring Gait

Abstract

The restoration of motor functions of patients with spinal cord injury (SCI) is one of important subjects for study. For this purpose, methods of functional neuromuscular stimulation (FNS) have been investigated in medical science and practice during these three decades. However, we have not achieved complete restoration of motor functions in SCI patients. On the other hand, we have achieved useful devices in human-scaled transportation by using power assist technology. Thus, applying power assist technology to the problem of restoring motor functions is one of possible solutions and sounds practical. In this paper, we propose a new hybrid system to combine power assist technology and FNS for restoring motor functions of lower extremity in SCI patients. Both powered orthosis and FNS are used to generate and control the joints moments of lower extremity in the proposed hybrid system. The main role of powered orthosis to compensate the joints moments generated by FNS and to enhance the controllability of FNS with the actuators. The proposed hybrid control system has been experimentally evaluated in gait motions by measuring the angle trajectories and generated moments around the knee and hip joints in the cases when only actuators are used and both FNS and actuators of the orthosis are used. The results prove that the control method for the hybrid system is useful to restore motor functions of lower extremity in SCI patients.

Hybrid FES–robotic gait rehabilitation technologies: a review on mechanical design, actuation, and control strategies

“…However, validation results have not yet been published. Obinata et al (2007) proposed HyPO, a new hybrid powered orthosis which comprises a functional neuromuscular stimulator and a control system with four actuators. The controller of the actuators achieved preprogrammed joint trajectories while the functional neuromuscular stimulator system generates muscular forces through stimulation.…”

Review of hybrid exoskeletons to restore gait following spinal cord injury

“…The active control of hip and knee joints by means of actuators was also explored with the hybrid powered orthosis (HyPo) [71]. The HyPo is designed with the motors and gearboxes located in the front part of the orthosis, allowing users to wear it while sitting.…”

“…User evaluation is crucial to generate useful information about the functional performance of hybrid exoskeletons. While testing in both nondisabled subjects [62][63][65][66]71] and SCI subjects has been reported for some systems, the number of subjects is generally limited and heterogeneous. For example, the CBO was tested on four patients with SCI [60][61] and the variable hip constraint mechanism was tested on only one subject with T7 complete paraplegia [56].…”

“…The physiological cost was not evaluated for all the systems reviewed here, and where it was, different variables were used: oxygen consumption normalized as an indirect measure of the physiological cost [50], heart rate, and blood pressure [60][61]. Muscle fatigue has also been related to the physiological cost [60][61]72], assuming that a decrease in the stimulation cycle leads to a decrease in muscle fatigue [62][63][65][66]71]. Other variables analyzed are related to spasticity, coordination [72], and system comfort [69].…”

“…Other exoskeletons have active actuators that can either dissipate or add power to the joints, thereby providing a means of control while allowing complete joint movement to improve system performance [50,[71][72][73].…”