Structure Design of Lower Limb Exoskeletons for Gait Training

Due to the close physical interaction between human and machine in process of gait training, lower limb exoskeletons should be safe, comfortable and able to smoothly transfer desired driving force/moments to the patients. Correlatively, in kinematics the exoskeletons are required to be compatible with human lower limbs and thereby to avoid the uncontrollable interactional loads at the human-machine interfaces. Such requirement makes the structure design of exoskeletons very difficult because the human-machine closed chains are complicated. In addition, both the axis misalignments and the kinematic character difference between the exoskeleton and human joints should be taken into account. By analyzing the DOF（degree of freedom） of the whole human-machine closed chain, the human-machine kinematic incompatibility of lower limb exoskeletons is studied. An effective method for the structure design of lower limb exoskeletons, which are kinematically compatible with human lower limb, is proposed. Applying this method, the structure synthesis of the lower limb exoskeletons containing only one-DOF revolute and prismatic joints is investigated; the feasible basic structures of exoskeletons are developed and classified into three different categories. With the consideration of quasi-anthropopathic feature, structural simplicity and wearable comfort of lower limb exoskeletons, a joint replacement and structure comparison based approach to select the ideal structures of lower limb exoskeletons is proposed, by which three optimal exoskeleton structures are obtained. This paper indicates that the human-machine closed chain formed by the exoskeleton and human lower limb should be an even-constrained kinematic system in order to avoid the uncontrollable human-machine interactional loads. The presented method for the structure design of lower limb exoskeletons is universal and simple, and hence can be applied to other kinds of wearable exoskeletons.

Effect of robot-assisted gait training on the biomechanical properties of burn scars:a single-blind,randomized controlled trial

Background:Robot-assisted gait training(RAGT)is more effective in the range of motion(ROM)and isometric strength in patients with burns than conventional training.However,concerns have been raised about whether RAGT might negatively affect the scars of patients with burns.Therefore,we investigated the effects of RAGT-induced mechanical load on the biomechanical properties of burn scars.Methods:This was a single-blind,randomized clinical trial conducted on inpatients admitted to the Department of Rehabilitation Medicine between September 2020 and August 2021.RAGT was conducted for 30 min per day,five days a week for 12 weeks and the control group received conventional gait training for 12 weeks.The pre-training ROM of lower extremity joints was evaluated and the levels of melanin,erythema,trans-epidermal water loss,scar distensibility and elasticity were assessed before training and at 4 and 12 weeks after training.Finally,19 patients in the gait assistance robot(GAR)group and 20 patients in the control group completed the 12-week trial and all evaluations.Results:There were no significant differences in the epidemiologic characteristics,pre-training ROM of joints and pre-training biomechanical properties of the burn scar between the groups(p>0.05 for all).None of the patients experienced skin abrasion around the burn scar where the fastening belts were applied or musculoskeletal or cardiovascular adverse events during the training.Scar thickness significantly increased in both groups(p=0.037 and p=0.019)and scar distensibility significantly decreased in the control group(p=0.011)during the training.Hysteresis was significantly decreased in the GAR group during the training(p=0.038).The GAR and control groups showed significant difference in the change in the values of hysteresis between pre-training and 12 weeks after training(p=0.441 and p=0.049).Conclusions:RAGT significantly decreased hysteresis in hypertrophic burn scars and did not cause a significant decrease in skin distensibility.Moreover,no skin complications around the burn scars were detected during RAGT.

Application of Optimal-Jerk Trajectory Planning in Gait-balance Training Robot

To accommodate the gait and balance disorder of the elderly with age progression and the occurrence of various senile diseases,this paper proposes a novel gait balance training robot(G-Balance)based on a six degree-of-freedom parallel platform.Using the platform movement and IMU wearable sensors,two training modes,i.e.,active and passive,are developed to achieve vestibular stimulation.Virtual reality technology is applied to achieve visual stimulation.In the active training mode,the elderly actively exercises to control the posture change of the platform and the switching of the virtual scene.In the passive training mode,the platform movement is combined with the virtual scene to simulate bumpy environments,such as earthquakes,to enhance the human anti-interference ability.To achieve a smooth switching of the scene,continuous speed and acceleration of the platform motion are required in some scenarios,in which a trajectory planning algorithm is applied.This paper describes the application of the trajectory planning algorithm in the balance training mode and the optimization of jerk(differential of acceleration)based on cubic spline planning,which can reduce impact on the joint and enhance stability.

Neurorehabilitation using a voluntary driven exoskeletal robot improves trunk function in patients with chronic spinal cord injury: a single-arm study

Body weight-supported treadmill training with the voluntary driven exoskeleton(VDE-BWSTT) has been shown to improve the gait function of patients with chronic spinal cord injury. However, little is known whether VDE-BWSTT can effectively improve the trunk function of patients with chronic spinal cord injury. In this open-label, single-arm study, nine patients with chronic spinal cord injury at the cervical or thoracic level(six males and three females, aged 37.8 ± 15.6 years, and time since injury 51.1 ± 31.8 months) who underwent outpatient VDE-BWSTT training program at Keio University Hospital, Japan from September 2017 to March 2019 were included. All patients underwent twenty 60-minute gait training sessions using VDE. Trunk muscular strength, i.e., the maximum force against which patient could maintain a sitting posture without any support, was evaluated in four directions: anterior, posterior, and lateral(right and left) after 10 and 20 training sessions. After intervention, lateral muscular strength significantly improved. In addition, a significant positive correlation was detected between the change in lateral trunk muscular strength after 20 training sessions relative to baseline and gait speed. The change in trunk muscular strength after 20 training sessions relative to baseline was greatly correlated with patient age. This suggests that older adult patients with chronic spinal cord injury achieved a greater improvement in trunk muscle strength following VDE-BWSTT. All these findings suggest that VDE-BWSTT can improve the trunk function of patients with chronic spinal cord injury and the effect might be greater in older adult patients. The study was approved by the Keio University of Medicine Ethics Committee(IRB No. 20150355-3) on September 26, 2017.