Hardware Circuits Design and Performance Evaluation of a Soft Lower Limb Exoskeleton

Soft lower limb exoskeletons (LLEs) are wearable devices that have good potential in walking rehabilitation and augmentation. While a few studies focused on the structure design and assistance force optimization of the soft LLEs, rarely work has been conducted on the hardware circuits design. The main purpose of this work is to present a new soft LLE for walking efficiency improvement and introduce its hardware circuits design. A soft LLE for hip flexion assistance and a hardware circuits system with scalability were proposed. To assess the efficacy of the soft LLE, the experimental tests that evaluate the sensor data acquisition, force tracking performance, lower limb muscle activity and metabolic cost were conducted. The time error in the peak assistance force was just 1%. The reduction in the normalized root-mean-square EMG of the rectus femoris was 7.1%. The net metabolic cost in exoskeleton on condition was reduced by 7.8% relative to walking with no exoskeleton. The results show that the designed hardware circuits can be applied to the soft LLE and the soft LLE is able to improve walking efficiency of wearers.

I. Introduction

The lower limb exoskeletons (LLEs) have been widely researched to restore walking ability of people with spinal cord injury and strengthen stamina of manual workers and soldiers [1]–[4]. The LLEs are mainly divided into rigid and soft types according to materials used and characteristics of structures [5]. The rigid LLEs usually include rigid links and joints which act like an external skeleton. The soft LLEs are made up of textile components which wrap around the lower limb of people and work like an external layer of muscles. The soft LLEs have no frame to bear own load and mainly transfer reaction forces between different segments of lower limb and other parts [6]. Compared to rigid LLEs, the soft LLEs have less restraint on the human body and more potential in wearability due to materials used.