Dynamic trajectory adjustment of lower limb exoskeleton in swing phase based on impedance control strategy

Abstract

<jats:p> The lower limb exoskeleton provides assistance by following the lower limb joints’ desired motion trajectory. However, angle control is not enough to meet the requirements in some special circumstances such as encountering obstacles. In the swing phase of the attached leg with the exoskeleton, there is a different contact force between the sole and the road surface in different road conditions. Therefore, it is particularly important to control the joint angle and contact force simultaneously, that is, it is not only necessary to follow the desired angle but also to minimize the influence of external contact force. In this article, a novel scheme is proposed to adjust the trajectory dynamically in the swing phase. First of all, the physical model is streamlined and the Lagrangian principle is carried out to dynamic analysis and established a model of lower limb exoskeleton in the swing phase. Furthermore, the angle dynamics equation is transformed into a Cartesian coordinate system to calculate the end contact force for the impedance model. Finally, the impedance control strategy together with a disturbance observer is designed which is suitable for nonlinear and strong coupling characteristics. The simulation result shows that the control system can follow the angle accurately in the condition of minimizing external constraints. Hardware experiment shows that lower extremity exoskeleton can adjust motion trajectory actively when encountering obstacles and complete the movement trajectory tracking at the same time. </jats:p>

Precision Interaction Force Control of an Underactuated Hydraulic Stance Leg Exoskeleton Considering the Constraint from the Wearer

“…Theorem 2. For human motion tracking in middle level controller, if output force tracking error z 4 = 0 is realized in inner loop, bounded motion tracking errors can be guaranteed by the control law (19), which is described by…”

“…In [18], a nonlinear disturbance observer was integrated into the conventional proxy-based sliding mode control structure to enhance the robust performance to model uncertainties. Using a disturbance observer, an impedance control structure has been proposed in [19]. In order to improve the performance of the impedance controller, the controller parameter optimization method and human-robot interaction dynamics modeling using some AI algorithms are also proposed [20,21].…”

Precision force control of an underactuated stance leg exoskeleton for human performance augmentation

“…However, the rest two interaction force components in X-and Y-axes can still be minimized. Thus, the control goal is to generate a control input t act = ½t 2 , t 3 T based on equation (12) such that the integral of interaction force at X-and Yaxes (x 1a ) can be minimized.…”

“…8 Another line of thought is to design a cascade force controller with human-machine interaction force measured, such as adaptive scale force control, 9 proportional-integral-derivative (PID) admittance control 10 and human-robot cooperation control. 11 To overcome the negative effect of various model uncertainties and disturbances in the exoskeleton systems, some robust control methods are also proposed, such as the disturbance observer-based impedance control, 12 adaptive assist-as-needed control 13 and adaptive sliding mode control. 14 To realize high-performance controller design of uncertain mechanical systems, an adaptive robust control (ARC) algorithm has been developed, 15,16 which is also successfully applied to robust force control of lower limb hydraulic exoskeletons.…”

Design, control, and experimental verification of a soft knee exoskeleton for rehabilitation during walking

“…With the development of robot technology, exoskeleton robots provide a viable solution to recovering from stroke. [3][4][5] Exoskeleton can be worn in parallel with human limbs, providing additional power or assistive torques for human movement assistance and rehabilitation training. However, for the devices designed to directly apply torques to human joint, the exoskeleton robots with rigid structure may interfere with biological joint movements.…”