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

From: A Review on Lower Limb Rehabilitation Exoskeleton Robots

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
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
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