Digital Theses Archive


Tesi etd-05262021-092505

Type of thesis
Development and validation of control strategies for lower-limb exoskeletons to assist individuals with gait impairments
Scientific disciplinary sector
Istituto di Biorobotica - BIOROBOTICS
relatore Dott.ssa CREA, SIMONA
  • Amputees
  • Control
  • Exoskeleton
  • Lower-limb
  • Rehabilitation
  • Robotics
  • Stroke
Exam session start date
Gait disorders can be the consequence of many pathological conditions and considering their age-related prevalence, they can only be expected to grow. Two of the most incident causes of gait disorders are lower-limb amputation and stroke. Amputees and stroke survivors present both abnormal kinematics and energy inefficiency during walking and other tasks, and these deviations might cause inactivity and reduced quality of life. Early rehabilitation of the lower-limb impaired individuals is essential in improving the rehabilitation outcomes, but only a few studies are dedicated to the rehabilitation community-ambulating amputees or chronic stroke survivors. As there is still an open discussion about the most suitable technique for rehabilitation, new techniques have emerged. Among them, robotic rehabilitation seems to be promising in the rehabilitation of motor deficits, both with treadmill-based and portable exoskeletons. To enhance the effect of the intervention, the exoskeleton has to be comfortable, lightweight, and have an efficient power transmission. The controller is also essential, as it has to provide (i) safety and stability, (ii) high transparency, (iii) accurate tracking of the desired assistance, (iv) smoothness in the assistance profile/command, and (v) low current requirement while (vi) understanding the intention of the user performing instinctive actions and without requiring additional cognitive efforts.<br>This work aims at designing controllers (high, middle, and low-level controllers) for lower-limb portable exoskeletons to assist lower-limb impaired individuals, focusing on transfemoral amputees and stroke survivors. Activities were carried out in the frame of the CYBERLEGs Plus Plus project (grant n°731931), within the H2020 framework (H2020-ICT-25-2016-2017).<br>This thesis started with the preliminary study of the background activities carried out with a Knee-Ankle Foot-Orthosis in the Wearable Robotics Lab. Then, I developed the controllers for two Active Knee Orthoses (AKO and AKO II). Each platform includes a 2 poles-2 zeros low-level controller specifically designed after a preliminary evaluation of the mechanics. The high and middle-level controllers were tested with one healthy subject wearing AKO during treadmill walking and Sit-to-stand/Stand-to-sit transitions but its mechanical performance did not allow a thorough verification. The same controllers were then improved for AKO II and verified with several healthy subjects and two stroke survivors. With these tests, we proved the reliability of the device, and the adequate physical Human-Robot Interface and performance of the controllers. Moreover, in the clinical verification, we saw that when stroke survivors walk with AKO II on the treadmill they slightly reduce knee hyperextension during the stance phase and improve knee flexion during the swing phase.<br>Other studies were carried out during this work with the Active Pelvis Orthosis (APO), a previously-developed and advanced technology. Most of the controllers were already tested and verified in previous studies, but the Sit-to-stand/Stand-to-sit recognition was improved to target a subject-independent algorithm. The effects of training with the APO were tested in two clinical validation studies with transfemoral amputees with promising effects regarding walking speed, efficiency, and symmetry.<br>This thesis was dedicated to designing and validating controllers implemented in portable and stand-alone exoskeletons. We proved that the algorithms could be used in real-time both in in-lab settings and in clinical scenarios. Moreover, it seems that with the current technology it is possible to improve the gait abilities of both community-ambulating transfemoral amputees and chronic stroke survivors. Clinical studies are still ongoing, others are planned for the future and the current technology might require additional improvements, but overall this work has contributed to advance the state of the art of lower-limb exoskeletons towards their adoption in real-life scenarios