**2.1 Modular exoskeleton robot**

There are many researches about exoskeleton with human-robot cooperation [12]. Due to the wearability, convenience, comfort and easy portability, modular exoskeleton robot is becoming a trend in the industrial work environment nowadays such as construction site, heavy industry, medical care, logistics, maintenance, manufacturing process, etc. In this study, the modular means the modular type according to the body parts of human being. For example, shoulder modular exoskeleton, knee modular exoskeleton. Biggest merit of modular exoskeleton may be the bringing more comfortability rather than full-body exoskeleton robots. Of course, it is possible only in the industrial area. If we look for the purpose of rehabilitation in hospital, it may be different story. Also, once we narrow down the application area, modular exoskeleton robot can be lighter, have more simple structure and can be more compact. Some area, you do not need active exoskeleton robot, and just passive exoskeleton is fine. Also, modular exoskeleton robot is applicable either together or separate case by case. Furthermore, modular exoskeleton is more economical compare to the full-body exoskeleton robot. The following **Figure 1** shows the concept design of modular exoskeleton robot which we are currently developing. In this study, exoskeleton assistive force can be applied human body as an external force through the optimization process.
