Technical development and preliminary physiological response investigation of a tendon-based robotic system for gait rehabilitation

Cable-driven robots are commonly applied in the rehabilitation field. Many tendon-based systems use parallel end-effector structures because of the advantages of fast reactions and high force outputs. We previously developed an active cable-driven robotic system that enabled accurate force control and was applied while walking on a treadmill. However, the kinematic and kinetic assistance methods need to be improved. Given the advantages of tendon-based parallel systems, this study investigated walking generated by four cables that were directly attached around the ankle. The aim of this work was to develop a tendon-based parallel robotic system to provide assisted walking on a treadmill with gait-specific position guidance and force compensation. To demonstrate the assistance effects, preliminary physiological responses of leg muscles during walking with the system were investigated. A parallel robotic system with four cable-driven units was developed. Kinematic and kinetic analyses of walking were performed, followed by the development of control algorithms for walking with impedance assistance only and walking with impedance assistance plus kinetic compensation. The muscle activity of the rectus femoris, vastus lateralis, gluteus maximus, biceps femoris, and gastrocnemius muscles was recorded and analyzed. On the basis of the kinematic and kinetic analyses, the tendon-based parallel robotic system produced treadmill walking with position and force assistance. The force control algorithms tracked the target force profile with a mean error of 6.4 N. During impedance-assisted walking, the rectus femoris, gluteus maximus and biceps femoris muscles produced a mean electromyography of 115.1% of the activity during independent walking (without assistance). However, the activity of the vastus lateralis and gastrocnemius reduced to only 82.5% of that during independent walking. Further kinetic compensation generally reduced the muscle activity, with the mean electromyography result being 88.7% of that during independent walking. From a technical point of view, the tendon-based parallel robotic system provided walking-specific position and force assistance in leg movement, accompanied by reduced muscle activity compared with independent walking. A technical feasibility study will be conducted to evaluate whether the tendon-based parallel robotic system is feasible for assisted treadmill walking in the general population and whether position guidance and force assistance are acceptable.