# Perspectives and Challenges in Robotic Neurorehabilitation
## 2 An Overview of Robotic Devices for Neurorehabilitation
### Robotic Neurorehabilitation for the Lower Limb  
As for the upper limb, robotic devices for lower limb neurorehabilitation can also differ in terms of mechanical design (i.e., end-effector devices vs. exoskeletons), mechanism of actuation, training modality, number of degrees of freedom, and control architecture [7; 83]. End-effector robots (see Table 3) are grouped in \"footplate-based\", such as the Gait Trainer GTI [84], Haptic Walker [85], and G-EO Systems (EO, from latin: I walk) [86] robots, where the patient's feet are firmly strapped onto platforms that are able to simulate the different gait cycles [87], and in \"platform-based\" robots, such as Hunova [88] (Movendo Technology, Genova, Italy) and Rutgers Ankle [89]. These robots are characterized by a fixed platform that does not simulate the walking pattern [90], but instead applies a controlled motion to the joints, specifically focusing on the ankle. One of the first examples of a footplate-based robot was the GTI [84], which allows partial or complete assistance support to both stance and swing phases of gait, depending on the subject's residual abilities. The Haptic Walker, developed by the same research group of GTI, represents its improvement. Figure 1: Lateral view of WristBot during combined movements in the flexion–extension and pronation–supination DOFs (degrees of freedom) (**A**) and movements in the radial–ulnar deviation DOF (**B**); posterior–lateral view of the handle of WristBot (**C**) and a frontal view of the device connected to the case, with the integrated PC and electronic control unit (**D**). Therefore, it allows for complex exercises, such as up and down stair-climbing or walking on rough surfaces, and it even simulates sliding or stumbling events [87]. G-EO Systems is similar to the Haptic Walker, but with reduced dimensions and with some precautions to comply for use in a clinical setting. Concerning \"platform-based\" end-effector robots, the recent Hunova platform has been developed, starting from the ARBOT device [91]. Hunova consists of two robotic platforms, one at the foot level and one at the seat level, allowing for rehabilitative exercises in both seated and upright mono and bipodalic conditions. It integrates force sensors to regulate the interaction with the patient and a wireless inertial sensor placed on the body of the subject, which allows detection of compensatory trunk movements and gives sensory feedback during exercise. Hunova can target rehabilitation of the lower limbs, from ankle to knee and hip, the pelvis, and trunk, by providing a large variety of training modalities, including the assistive resistive one [92]. On the other hand, exoskeletons (see Table 4) are classified as \"treadmill-based\", like Lokomat [99] (Hocoma, Volketswil, Switzerland), LokoHelp [100] (Woodway, Waukesha, WI, USA), LOPES [101], and ALEX [102], and as devices that directly allow for \"overground walking\", such as Eko [103] (Ekoo Bionics, Richmond, VA, USA), HAL (Cyberdyne, Tsukuba, Japan), Rewalk [104] (Rewalk Robotics, Marlborough, MA, USA), and Indego Therapy [105] (Parker Hannifin, Macedonia, OH, USA). In this category, new emerging devices include EXOATLET [106] (Exoaltet, Moscow, Russia), PhoenixX (SuitX, Berkeley, CA, USA), for which limited information is currently available, and REX (REX Bionics, London, UK). In addition, some of these exoskeletons, such as Lokomat and REX, have been employed to develop brain machine interfaces (BMIs) (for a review, see [107]). Then, albeit still in progress, the development of self-balancing exoskeletons might allow for arm swing, which is an important feature during locomotion