Figure 2.

(A) A novel haptic device by Fraunhofer Institute IPK, Berlin, Germany, Department of Automation and Robotics, the Haptic Walker. This haptic locomotion interface is skilled at reproducing slow and smooth trajectories, simulating walking on the floor and up and down the stairs. It is a footplate-based training device and possesses the training mode of passive, active, and resist. Position control and impedance control are used (Schmidt et al., 2005; Chen et al., 2014). (B) Lokomat. The Lokomat's hip and knee joints are initiated by linear drives incorporated in the exoskeletal design. A passive foot lifter prompts ankle dorsiflexion during the swing phase (Fang et al., 2020; Lin et al., 2020). (C) Lower extremity rehabilitation exoskeleton platform. The exoskeleton is composed of two mechanical lower limbs (Chen et al., 2020). (D) LOPES or treadmill-based LLREs. The LOPES has superior performance due to the innovative design of the joint drive, which uses a flexible cable drive instead of the traditional drive (De Rossi et al., 2010). (E) The LLRE robot developed by Zhejiang University. A semi-automatic control strategy can be based on the patient's gait during training for exclusion and adaptation of gait curves with appropriate amendments to reduce patient discomfort in the rehabilitation process (Lyu et al., 2016; Pinheiro et al., 2020). (F) The mechanical framework of the exoskeleton (Lyu et al., 2016). Briefly, many robotic rehabilitation techniques consist of robotic external skeletons adapted for a particular body part connected to the program, which sends information and data training to the exoskeleton and vice versa. The amount of assistance or force contributed by the robot can be adapted, and the systems come with pre-programmed routines that can be set to the patient's level of movability.