Custom sizing of lower limb exoskeleton actuators using gait dynamic modelling of children with cerebral palsy

Abstract

The use of exoskeletons as an aid for people with musculoskeletal disorder is the subject to an increasing interest in the research community. These devices are expected to meet the specific needs of users, such as children with cerebral palsy (CP) who are considered a significant population in pediatric rehabilitation. Although these exoskeletons should be designed to ease the movement of people with physical shortcoming, their design is generally based on data obtained from healthy adults, which leads to oversized components that are inadequate to the targeted users. Consequently, the objective of this study is to custom-size the lower limb exoskeleton actuators based on dynamic modeling of the human body for children with CP on the basis of hip, knee, and ankle joint kinematics and dynamics of human body during gait. For this purpose, a multibody modeling of the human body of 3 typically developed children (TD) and 3 children with CP is used. The results show significant differences in gait patterns especially in knee and ankle with respectively 0.39 and -0.33 (Nm/kg) maximum torque differences between TD children and children with CP. This study provides the recommendations to support the design of actuators to normalize the movement of children with CP.

Preliminary design and development of a low-cost lower-limb exoskeleton system for paediatric rehabilitation

“…For Case II, the maximum values of the hip, knee and ankle actuator torques with ELM are increased by 29.78%, decreased by 66.66% and increased by 11.3%, respectively when compared with Samadi et al 26 On the other hand, maximum torque value is increased by 3.88% for hip joint, decreased by 73.85% for knee joint and raised by 8.05% for ankle joint while comparing the results of SMM with the reference work. The difference in torque values between this work and Samadi et al 26 is realized due to dissimilarity in factors like actuator masses, subjects’ heights, subjects’ body masses, level of pathological conditions, upper to lower extremity ratio, percentage body fat, muscle orientation, and bone density. However, the comparative analysis clearly demonstrates the potential of applied dynamic models to estimate the joint actuator torques for the human-exoskeleton coupled system.…”

“…The subjects have post-effects of paraplegic cerebral palsy with no sign of pain and discomfort. Finally, the results of this work are validated by comparing the results with the study by Samadi et al 26…”

“…After gauging the capacity of joint actuator torques using Euler-Lagrange and SimMechanics models, a quantitative comparison is carried out with the results given by Samadi et al 26 and shown in Table 7. It can be observed that the maximum value of hip actuator torque for the Case I increases by 2.94% (ELM) and decreases by 19.19% (SMM) while comparing the results with Samadi et al 26 The maximum magnitude of knee actuator torque show a decrement of 78.43% (ELM) and 83% (SMM) while comparing with the reference work. Further comparing the maximum value of ankle actuator torque, a respective fall of 4% and 23.48% is observed for ELM and SMM.…”

“…The ankle’s dorsiflexion/plantarflexion movement is delivered via an attached link between the shank and thigh. Samadi et al 26 presented a study on adjusting link lengths of exoskeleton for a group of children with cerebral palsy. They showed a comparative analysis of the joint torque requirements for typically developed children and children with cerebral palsy.…”

Optimal control prediction of assisted walking using torque-driven models : application to active orthosis simulation to assist individuals with spinal cord injury

“…Passive devices are usually modelled adding high-stiffness rotational springs in passive joints [67][68][69]. Active devices have been modelled as massless torque actuators in active joints [15,22,49,70]; or embedded in the human limbs, by properly modifying mass and inertia of the corresponding body segments [22,71]. Another option to model both passive and active devices is modelling them as independent bodies connected to the subject by using kinematic constraints, both assuming no subjectdevice relative motion [68,72] or allowing relative motion [73,74]; or by using force constraints (prescribe force acting in parallel to residual muscle force) [75].…”