A Survey in the Different Designs of Passive Exoskeletons for Lower Extremities

Assistance exoskeletons are among the requirements for those suffering from strokes, post-polio complications, injuries, osteoarthritis and multiple other health issues. These exoskeletons could also be beneficial for individuals who exert heavy physical activities on a regular basis. Consequently, various academic as well as commercial projects are available in the market in the field of lower limb exoskeletons. The purpose of this article is to investigate passive and quasi-passive lower limb exoskeletons with a focus on knees and categorize these exoskeletons and moreover introduce their basic structures. It is concluded that ppassive exoskeletons are among the most essential subjects of this field due to their simplicity and cost efficiency. The basis of these types of exoskeletons is grounded on energy storage while the knee is in flexion (stored energy to be released in the extension phase). Furthermore, passive exoskeleton designs endeavor to sustain/endure some of the weight force with the aim of reducing pressure on the knee joint. One of the important parameters in choosing an exoskeleton is the user's comfort when using the exoskeleton, which depends on two factors, the first is how the exoskeleton connects to the body and the second is the changes in metabolic energy consumption as a result of using this exoskeleton.