Werner Reichenfelser

Feedback control of arm movements using Neuro-Muscular Electrical Stimulation (NMES) combined with a lockable, passive exoskeleton for gravity compensation.

Within the European project MUNDUS, an assistive framework was developed for the support of arm and hand functions during daily life activities in severely impaired people. This contribution aims at designing a feedback control system for Neuro-Muscular Electrical Stimulation (NMES) to enable reaching functions in people with no residual voluntary control of the arm and shoulder due to high level spinal cord injury. NMES is applied to the deltoids and the biceps muscles and integrated with a three degrees of freedom (DoFs) passive exoskeleton, which partially compensates gravitational forces and allows to lock each DOF. The user is able to choose the target hand position and to trigger actions using an eyetracker system. The target position is selected by using the eyetracker and determined by a marker-based tracking system using Microsoft Kinect. A central controller, i.e., a finite state machine, issues a sequence of basic movement commands to the real-time arm controller. The NMES control algorithm sequentially controls each joint angle while locking the other DoFs. Daily activities, such as drinking, brushing hair, pushing an alarm button, etc., can be supported by the system. The robust and easily tunable control approach was evaluated with five healthy subjects during a drinking task. Subjects were asked to remain passive and to allow NMES to induce the movements. In all of them, the controller was able to perform the task, and a mean hand positioning error of less than five centimeters was achieved. The average total time duration for moving the hand from a rest position to a drinking cup, for moving the cup to the mouth and back, and for finally returning the arm to the rest position was 71 s.

Functional and usability assessment of a robotic exoskeleton arm to support activities of daily life

An assistive device for upper limb support was developed and evaluated in terms of usability, user satisfaction and motor performance on six end-users affected by neuro-motor disorders (three spinal cord injury; one multiple sclerosis; two Friedreichs ataxia). The system consisted of a lightweight 3-degrees-of-freedom robotic exoskeleton arm for weight relief, equipped with electromagnetic brakes. Users could autonomously control the brakes using a USB-button or residual electromyogram activations. The system functionally supported all of the potential users in performing reaching and drinking tasks. For three of them, time, smoothness, straightness and repeatability were also comparable to healthy subjects. An overall high level of usability (system usability score, median value of 90/100) and user satisfaction (Tele-healthcare Satisfaction Questionnaire - Wearable Technology, median value of 104/120) were obtained for all subjects.

KINEMATIC AND KINETIC ANALYSIS OF HUMAN MOTION AS DESIGN INPUT FOR AN UPPER EXTREMITY BRACING SYSTEM

Upper extremity motion in humans is complex and irregular. An orthosis designer cannot count on cyclic procedures or repetitions. When designing a bracing system for the upper limb, this complexity is challenging and therefore it is essential to know about the necessary torques, angular velocities and joint ranges. In this study, we took a closer look at tasks associated with daily living and defined requirements for an upper limb orthotic device. The required working range of the assistive device in order to cover the required range of motion (ROM) was defined. Furthermore, external torques were assessed to facilitate the dimensioning of locking and weight compensation systems and to support strength calculation. The angular velocity at each joint of interest was calculated, as required e.g. for hydraulic component design. Prior to the development of a prototype, an evaluation of the defined joint ranges was envisioned. Additionally we investigated the effect of restricted joint angle ranges on movement performance.

Modular Instrumented Arm Orthosis with Weight Support for Application with NMES

Activities of daily living can be facilitated for individuals with motor impairment in the upper limb, if the arm weight is compensated by an orthosis. In this work we focused on the design of a modular arm orthosis with weight compensation. Additional brakes and angle encoders at each of the three available degrees of freedom prepare the orthosis for the application in combination with Neuromuscular Electrical Stimulation if the user’s residual motor capabilities are not sufficient to perform self induced arm movements. The prototype was tested by healthy subjects and showed promising results regarding functionality, weight and range of motion.

Design of Feedback Control Strategies for an Arm Neuroprothesis Combined with an Exoskeleton

For restoration of reaching function in patients with upper motor neuron lesion a noval control strategy for a neuroprosthesis was developed within the EU project MUNDUS. By applying controlled Functional Electrical Stimulation (FES) to the shoulder deltoid muscle and the biceps, functional arm movements can be achieved. An exoskeleton with three DOF partially compensates for gravitation and allows to lock joint angles for holding purposes. This is exploited by a feedback control strategy to reduce muscular fatigue. The control algorithm that sequentially controls the joint angles according to a given reference one after another is designed. The feasibility of the approach was demonstrated by successfully applying the strategy to one spinal cord injured (SCI) subject.