# Incorporation of Torsion Springs in a Knee Exoskeleton for Stance Phase Correction of Crouch Gait
## 5 Conclusions  
The gait cycle is composed of two major phases; the stance phase and the swing phase, with subphases defined within each. The stance phase comprises 60% of the gait cycle, while the swing phase comprises the final 40% of the gait cycle. The crouch gait is defined by excessive flexion of the knee during the stance phase of the gait cycle. Factors affecting crouch gait are numerous, but they are seen especially in those with cerebral palsy. Excessive flexion in the knee results in the degradation of joints and mobility over time, resulting in a complete loss of ambulation if left untreated. Exoskeletons for rehabilitative purposes are common for many such injuries and complications of the leg. While many exoskeletons are motorized for assistive mobility, the incorporation of passive elements was sought, to reduce the cost of the exoskeleton. Most exoskeletons are designed to be worn on the lower extremity, to correct ankle and hip rotation.  
SolidWorks was used to model a lower limb exoskeleton to counter the reaction forces produced in the knee for four different types of crouch gait. The exoskeleton was modeled using the average circumferences for the thigh and shank and was modeled using passive elements to reduce cost and to reduce invasiveness, to keep the exoskeleton lightweight. Since ankle flexion is more pronounced during knee flexion, the team sought to explore the implications of the device for use solely on the knee. Torsional springs were incorporated to inhibit the overflexion of the knee during the stance phase of the gait cycle. Dampers were included, to reduce the recovery force of the spring entering the swing phase of the gait, to prevent a forced overextension of the knee.  
To establish the parameters for testing the exoskeleton, OpenSim 4.3 was used. The angles of rotation during the gait cycle were plotted for four different crouch gaits and compared to the normal gait. Excessive forces, as well as moments, are produced in the knee because of excessive flexion during the stance phase of the gait cycle. The data points from the forces and moments were exported as CSV files and applied to the exoskeleton, first incorporating only passive elements through the use of torsional springs while simulating the knee rotation of the four crouch gaits.  
The gait cycle was set to 1s, to analyze the proportion of the gait cycle, in SolidWorks. Results from the passive elements indicated the greatest improvements with both 20 k Nmm/deg and 30 k Nmm/deg in CG2 and CG4. The 30 k Nmm/deg torsion spring simulations showed little to no improvement in CG1. The 30 k Nmm/deg torsion springs showed the greatest overall trend toward the normal gait, while the 20 k Nmm torsion springs showed minor improvements over all crouch gaits, except for CG1 in the stance phase. The swing phase requires further improvement in all crouch gaits.  
In the second round of testing, a motor was incorporated to drive the exoskeleton using the normal range of motion of the knee, while simulating forces on the exoskeleton from each crouch gait. All results showed the same trends as the normal knee angular displacement; however, using different spring stiffnesses resulted only in a change of magnitude of the moments generated. Thus, it was determined that the best results would involve the incorporation of both passive and motorized elements while driving the exoskeleton, using the normal range of motion in the knee for both angular and moment correction in the crouch gait.