Design of a Knee Exoskeleton actuated with Artificial Muscles of SMA

This project presents the preliminary design of a powered exoskeleton for the knee joint, build upon the structural framework of DonJoy’s X-Act Rom Lite - Knee Brace. The device allows exclusively one degree of freedom, intended for the flexion and extension of the lower limb. The actuation mechanism is based on artificial muscles of Nitinol fibers, which are a type of Shape Memory Alloys (SMA). These wires contract 4% of its original length as the temperature rises due to the Joule Effect, when connected to a power supply. Thanks to this phenomenon, the proposed robotic orthosis presents portability, lightness and noiseless performance, in comparison to similar products. The main role of these instruments is to conduct medical rehabilitation therapy for those patients who have suffered from neurological diseases, musculoskeletal lesions or spinal cord injuries. Consequently, the wearer might recover -partially or fully- the movement on the joint. The results from several trials were obtained after mimicking real rehabilitation positions -like sitting, standing or lying down- and are analyzed thoroughly in this thesis. All in all, this prototype proves how the SMA actuators are a viable alternative to create lower extremity robotic devices for rehabilitation.Ingeniería Biomédic

Real-time EMG Control for Hand Exoskeletons

The goal of this project is to develop a system for hand exoskeletons control in real time. Robotic systems are useful for rehabilitation therapies due to their ability to help patients perform repetitive movements. Hand recovery is especially critical because hands are necessary to perform many daily life activities. Exoskeletons developed for hand rehabilitation can benefit from a real-time control system that activates the robotic devices at the same time as the patient is performing a movement. Real-time control of these systems can be achieved using different methods. In this project, electromyographic (EMG) signals from the patient’s forearm are used. The controlled robotic systems are soft hand exoskeletons actuated with Shape-Memory Alloys (SMA) wires. The SMA wires are controlled with a microcontroller. The main objective of these exoskeletons is to help the patient with the movement of grasping an object and releasing it afterwards. Machine learning is used to detect the intention of the patient to grasp or release an object based on the patient’s EMG signals. Once one of these movements is detected, real-time communication with the microcontroller is achieved and the necessary SMA wires are activated. The system is developed in Matlab, and it involves signal acquisition, signal rectification, signal segmentation, feature extraction, dimensionality reduction, signal classification, and communication with the microcontroller. To differentiate between the movements of grasping and releasing an object, three different classifiers will be tested: Artificial Neural Networks (ANN), Support Vector Machine (SVM) and K-Nearest Neighbors (KNN). Their performance will be compared using a confusion matrix and the best one will be selected for the system’s algorithm. Control is achieved with a time delay of less than 1 second for the action of grasping and of less than 2 seconds for the action of releasing is achieved, almost accomplishing the objective of developing a real-time control system. Several improvements are proposed to decrease this time delay.Ingeniería Biomédic

Soft hand exoskeleton actuated with SMA fibres

The current project is based on developing a wearable and comfortable soft hand exoskeleton actuated with Shape Memory Alloy (SMA) fibres. The main purpose of this device is both, to be involved in rehabilitation exercises and assistive therapies for patients suffering from hands’ damage. This innovative idea presents an affordable and convenient alternative in the exoskeletons’ field, combining a light and non-expensive actuation along with biocompatible materials specifically tailored to patient’s hand anatomy. To generate the perfectly fitting glove, plastic moulds were 3D-printed after sketching them with Creo Parametric software. Then, silicone was poured into the casts and it cured maintaining the desired shape. Taking advantage of Joule’s effect, the current which flows though the SMA wires is capable of increasing temperature, causing a microstructure change and thus inducing contraction. This motion can be accurately controlled by a MATLAB-Simulink interface, achieving both flexion and extension so as to perform pincer grip. Furthermore, a force sensor embedded on silicone finger’s tip is used as a force feedback to evaluate the pressure applied by the subject when holding distinct objects.Ingeniería Biomédica (Plan 2010

Are Functional Measures Sufficient to Capture Acceptance? A Qualitative Study on Lower Limb Exoskeleton Use for Older People

Lower limb exoskeletons (LLE) are robotic devices developed to assist walk. In the field of healthcare, this technology has been available for almost a decade, yet it still faces important acceptance issues. While LLE were first developed for patients with spinal cord injuries, we expect their use to expand to everyday settings to benefit other populations, namely that of older people with reduced mobility (RM). We propose a qualitative approach to unearth key psychosocial themes on the acceptance of LLE in daily living for older people. The study analyses perceptions of older people with RM, as well as their entourage, including informal and professional caregivers. Using a grounded theory approach we analysed 12 semi-structured interviews with older people with RM; 2 focus groups with informal caregivers, and 2 focus groups with professional caregivers. LLE were introduced to participants through photo-elicitation. Older people with RM believed that LLE would increase their autonomy. They also perceived that using LLE would make them feel less of a burden for their entourage. Beyond these expected benefits, results captured participants' ambivalence, dependent on their experiences of the ageing process and perceptions on the human-machine interaction. Informal caregivers highlighted that LLE could provide important relief related to the burden of care. Nonetheless, professional caregivers raised the fear of LLE leading to dehumanization of care. While each group had specific concerns on how LLE use would impact their lives, psychosocial considerations played a key role in LLE acceptance

A novel approach to user controlled ambulation of lower extremity exoskeletons using admittance control paradigm

The robotic lower extremity exoskeletons address the ambulatory problems confronting individuals with paraplegia. Paraplegia due to spinal cord injury (SCI) can cause motor deficit to the lower extremities leading to inability to walk. Though wheelchairs provide mobility to the user, they do not provide support to all activities of everyday living to individuals with paraplegia. Current research is addressing the issue of ambulation through the use of wearable exoskeletons that are pre-programmed. There are currently four exoskeletons in the U.S. market: Ekso, Rewalk, REX and Indego. All of the currently available exoskeletons have 2 active Degrees of Freedom (DOF) except for REX which has 5 active DOF. All of them have pre-programmed gait giving the user the ability to initiate a gait but not the ability to control the stride amplitude (height), stride frequency or stride length, and hence restricting users’ ability to navigate across different surfaces and obstacles that are commonly encountered in the community. Most current exoskeletons do not have motors for abduction or adduction to provide users with the option for movement in coronal plane, hence restricting user’s ability to effectively use the exoskeletons. These limitations of currently available pre-programmed exoskeleton models are sought to be overcome by an intuitive, real time user-controlled control mechanism employing admittance control by using hand-trajectory as a surrogate for foot trajectory. Preliminary study included subjects controlling the trajectory of the foot in a virtual environment using their contralateral hand. The study proved that hands could produce trajectories similar to human foot trajectories when provided with haptic and visual feedback. A 10 DOF 1/2 scale biped robot was built to test the control paradigm. The robot has 5 DOF on each leg with 2 DOF at the hip to provide flexion/extension and abduction/adduction, 1 DOF at the knee to provide flexion and 2 DOF at the ankle to provide flexion/extension and inversion/eversion. The control mechanism translates the trajectory of each hand into the trajectory of the ipsilateral foot in real time, thus providing the user with the ability to control each leg in both sagittal and coronal planes using the admittance control paradigm. The efficiency of the control mechanism was evaluated in a study using healthy subjects controlling the robot on a treadmill. A trekking pole was attached to each foot of the biped. The subjects controlled the trajectory of the foot of the biped by applying small forces in the direction of the required movement to the trekking pole through a force sensor. The algorithm converted the forces to Cartesian position of the foot in real time using admittance control; the Cartesian position was converted to joint angles of the hip and knee using inverse kinematics. The kinematics, synchrony and smoothness of the trajectory produced by the biped robot was evaluated at different speeds, with and without obstacles, and compared with typical walking by human subjects on the treadmill. Further, the cognitive load required to control the biped on the treadmill was evaluated and the effect of speed and obstacles with cognitive load on the kinematics, synchrony and smoothness was analyzed