A Review on Lower Limb Rehabilitation Exoskeleton Robots

Chinese Journal of Mechanical Engineering

Table 3 Overview of the control methods used for lower limb exoskeletons

Control strategies	Method	Devices	Features
Position control	Finite state machine	eLEGS, Indergo	A finite state machine is used to indicate the intended option of a series of maneuvers. The user’s intended maneuver is then determined based on the provided inputs. Each state is defined by a set of joint angle trajectories, which are enforced by position control loops
Position control	Trajectory tracking control	Rewalk, Rex, MINDWALKER	After selecting the walk mode based on sensors, the participant initiates and propagates programmed motions like walking, turning, sitting, standing and shuffling. This also enables a person to move using a joystick and remote controller
Force controller	Selective control of subtasks	LOPES	Human gait is divided into different subtasks. These subtasks are controlled separately based on the impedance controller
Force controller	Impedance control	Lokomat	Torque is supplied by the robot using a PD controller based on the deviation between the actual and desired angular trajectories. Thresholds of maximum allowed deviations are determined around the reference angular trajectory
EMG-based control	Virtual torque control	HAL	Human joint torque is estimated based on EMG signals to generate virtual torque for controlling the motors
Assist-as-needed control	Force field control	ALEX	Tangential and normal forces are applied at the ankle of the subject based on the deviation of the actual path from the desired path