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CABXLexo-7 (Xiao et al., 2018) as shown in Fig. 3B, a 7-DOF cable-
driven upper limb exoskeleton (CABXLexo-7) successor to 6-DOF
CABexo (Xiao et al., 2017), was developed by Feiyun et al. from Harbin
Institute of Technology (HIT), China and Hefei University of Technology
(HFUT), China, as a joint effort in 2017 (Xiao et al., 2018). In order to cre-
ate a lightweight exoskeleton robot capable of providing all seven DOFs, the
development team put all the actuators on the stationary board and transmit-
ted power through a cable-conduit system using two types of cable-driven
differential mechanisms and using a tension device to work with the cable
slag problem. The resulting weight of the moving robot is 3.5 kg. However,
this robot does not consider the movement of CR of the human shoulder.
Experimentation was carried out using surface electromyography on with
five healthy individuals. This robot was designed for providing motion assist
to poststroke patients (Xiao et al., 2018). CABXLexo-7 is yet to go through
clinical trials.
ARMin-III (Nef et al., 2009a, b) as shown in Fig. 5B (successor of
ARMIn and ARMin-II, and predecessor of commercial exoskeleton
Armeopower as shown in Fig. 5A), developed at ETH Zurich, Switzerland,
is one of the early and well-known robotic exoskeletons with high degrees
of freedom for upper extremity rehabilitation. The very first version ARMin
(Nef et al., 2007) was designed with four DOFs intended to provide reha-
bilitation in the human shoulder (giving mobility for shoulder abduction-
adduction, flexion-extension, and internal-external rotation) and elbow
(flexion-extension). Then, the 7-DOF ARMin-II was developed with five
adjustable lengths segments to provide better patient cooperative rehabilita-
tion. Unlike ARMin, the shoulder axis of rotation is not fixed in ARMin-II,
allowing passive elevation/depression and protraction/retraction of the gle-
nohumeral (GH) joint during shoulder vertical flexion-extension. ARMin-
II also includes ergonomic shoulder actuation to provide as much natural
movement as possible for shoulder rehabilitation. The advancement of
the ARMin rehabilitative exoskeleton went through several stages of devel-
opment and is now commercially available (known as ArmeoPower devel-
oped by Hocoma AG, Volketswil, Switzerland) for use in human upper
extremity rehabilitation at clinical settings in hospitals.
ETS-MARSE (Rahman et al., 2013a) as shown in Fig. 2A, a 7-DOF
upper limb exoskeleton for whole arm, used a novel power transmission
mechanism to assist shoulder internal/external rotation and forearm prona-
tion supination (Rahman et al., 2012, 2014). Since it is somewhat difficult to