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Top1. Introduction
As per World Health Organization (WHO) report, about 15% of people experience some form of disability (World Bank, n.d.). Several people suffer from movement-related disabilities (World Health Organisation, 2011) which includes quadriplegia, muscular dystrophy, stroke, cerebral palsy, Hemiplegia and similar conditions. Stroke patients suffer more from residual limb disability (Shandilya et al., 2015) as well as mobility impairment resulting due to spinal cord injury in comparison to age-related pathologies (Cao et al., 2014; O’Connor, 2006). People in the age group of 30 years are more prone to spinal cord injury (SCI) (Brown-Triolo et al., 2002; McDonald & Sadowsky, 2002) which has severe socio-economic impact (Shandilya et al., 2015). Patients with a complete SCI, lose sensory functions and also motor functions in their lower limbs, and this leads to increased risk for several secondary medical consequences of paralysis (Chen et al., 2016). There is dysfunction in the lower extremities of patients who have cerebral paralysis and orthopaedic injuries. The life expectancy of the patient is significantly reduced due to impaired mobility, and thus training is required to help these patients recover and regain mobility from rehabilitation. Therefore, assistive devices are developed using state-of-the-art technologies to help disabled people to stand and walk aid physiotherapist in rehabilitation training schedule (Huo et al., 2014).
Though the demands in rehabilitation and industries are high for robotic assistive devices, they are also used for human strength augmentation and it is a major requirement. Heavy objects are usually transported by vehicles and it is challenged by rocky slopes and terrain. Legs can adapt to a wide range of extreme terrains, and seems to be a desired method of transportation in these circumstances. Therefore, a lower limb exoskeleton can improve the efficiency of work (Huo et al., 2014) and lessen the burden of manual work and injury that results due to carrying heavy loads. An exoskeleton is a wearable orthotic assistive device attached to the human body consisting of an outer framework and a powered system consisting of motors/hydraulics that delivers an adequate amount of energy required for routine or enhanced limb movement. It senses signals from the wearer's legs and automatically assists the wearer in walking by providing extra kinetic power for the leg for enhanced walking and running. The exoskeleton enhances the strength of the wearer's joints. On comparing with the traditional physical therapy, this assistive rehabilitation reduces intensive and repetitive training the subjects undergo and also the presence of therapists, and hence quantitatively assess the recovery level by measuring force and movement patterns. The person can also carry heavy loads, and the high-performance level achieved with the help of an exoskeleton.
The progress in the development of exoskeletons (Dollar & Herr, 2008) has been remarkable in the past few decades as several exoskeleton systems have been developed (Liu et al., 2016; Lovrenovic & Doumit, 2016; Young & Ferris, 2016). This paper primarily focuses on the various sensing methodologies and mechanism developed for efficient detection of gait events and to trigger the actuators. Figure 1 describes the extensive literature survey carried out in various aspects for this paper.
Figure 1.
Flow chart demonstrating the literature survey in various aspects