I am a control scientist for application and theory of (non) linear control systems currently focusing on autonomous driving and biomedical engineering. Working as a research scientist in the Control Systems Group at Technische Universität Berlin, I received my Ph.D. Herein, I investigated novel control schemes for neuroprosthesis based on Functional Electrical Stimulation to restore lost motor functions, e.g., in case of stroke and Spinal Cord Injury (SCI).
After my Ph.D., I continued as a postdoctoral research fellow in the Neuroengineering and Robotics Lab (NearLab), Politecnico di Milano on the restoration of paralyzed hand functions. Today, I am involved in control for autonomous vehicles with TomTom Location Technology Germany GmbH.
This project considers paralyzed hand functions as a typical cause of stroke. Electrical pulses applied to the motor nerves induce artificial muscle contractions (Functional Electrical Stimulation, FES). Three muscles are involved to control arbitrary angles of wrist extension and to realize grasping. A feedback of the electrical muscle responses (Electromyography, EMG) is used to estimate the muscle-internal states and to ensure the desired reaction of the muscles to FES. Only one EMG-channel is required to observe all three muscles.
In an earlier stage, open-loop control was investigated, which was then superseded by automatic, feedback-controlled approaches (see video). Herein, with feedback being active, the operator manually issued movement commands, e.g., to extend the wrist or grasp.
The control system was tested in ten healthy subjects (not all shown in the video). They were asked to not volitionally participate in the hand movements. Placing the stimulation electrodes involves a trial-and-error procedure before activating the system to find good positions. However, with an increasing number of tested participants, a better, more general understanding of the placement could be found.
This is a system intended for persons who have only weak residual activity in the shoulder deltoid muscle. By Functional Electrical Stimulation (FES) an artificial muscle contraction is added such that the full extent of arm movements is restored. Behind the scenes, a positive-feedback control system measures the elevation-angle to amplify volitional movements. Electromyography (EMG) is used to compensate for the effects of rapidly progressing muscle fatigue under FES.
In effect, the participant (stroke, paresis in shoulder deltoid muscle) shown in this video could elevate his arm much higher than without the arm neuroprosthesis. The entire movement is still under his control, as the system detects his intention to move.
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.
A two-class brain-computer interface (Berlin-BCI) allows the user to select a target position. This position is then continuously realized by a feedback-controlled FES-system attached to the shoulder deltoid to produce horizontal arm movements.
OpenRTdynamics.github.io (ORTD): A framework for the implementation of advanced real-time control systems aiming to be an open-source alternative to Simulink Coder. It provides features including state machines and, as a real-time capable interpreter is used, sub-simulations that can be exchanged during runtime. Besides, this framework properly handles multiple threads, their communication, allows to synchronize control systems to external events (e.g. even irregular timers or incoming network packages) and provides many other nice features. Because of a high-level schematic-description language -- based on Scilab commands provided by a toolbox -- lower implementation-effort results compared to C/C++.
This framework has grown since 2008 along with the needs for the implementation of the feedback-control schemes in the area of neuroprosthetics.