238 Control theory in biomedical engineering Fig. 2 Existing upper limb exoskeletons. (A) MARSE-7 (Rahman et al., 2013a, 2014); (B) CADEN-7 (Perry et al., 2007); (C) Harmony (Kim and Deshpande, 2017); (D) SUFUL-7 (Gopura et al., 2009).