Matjaz Mihelj

ARMin II - 7 DoF rehabilitation robot: mechanics and kinematics

Task-oriented repetitive movements can improve motor recovery in patients with neurological or orthopaedic lesions. The application of robotics can serve to assist, enhance, evaluate, and document neurological and orthopaedic rehabilitation. ARMin II is the second prototype of a robot for arm therapy applicable to the training of activities of daily living. ARMin II has a semi-exoskeletal structure with seven active degrees of freedom (two of them coupled), five adjustable segments to fit in with different patient sizes, and is equipped with position and force sensors. The mechanical structure, the actuators and the sensors of the robot are optimized for patient-cooperative control strategies based on impedance and admittance architectures. This paper describes the mechanical structure and kinematics of ARMin II.

Real-Time Closed-Loop Control of Cognitive Load in Neurological Patients During Robot-Assisted Gait Training

Cognitively challenging training sessions during robot-assisted gait training after stroke were shown to be key requirements for the success of rehabilitation. Despite a broad variability of cognitive impairments amongst the stroke population, current rehabilitation environments do not adapt to the cognitive capabilities of the patient, as cognitive load cannot be objectively assessed in real-time. We provided healthy subjects and stroke patients with a virtual task during robot-assisted gait training, which allowed modulating cognitive load by adapting the difficulty level of the task. We quantified the cognitive load of stroke patients by using psychophysiological measurements and performance data. In open-loop experiments with healthy subjects and stroke patients, we obtained training data for a linear, adaptive classifier that estimated the current cognitive load of patients in real-time. We verified our classification results via questionnaires and obtained 88% correct classification in healthy subjects and 75% in patients. Using the pre-trained, adaptive classifier, we closed the cognitive control loop around healthy subjects and stroke patients by automatically adapting the difficulty level of the virtual task in real-time such that patients were neither cognitively overloaded nor under-challenged.

Emotion-aware system for upper extremity rehabilitation

Immersive and multimodal sensory feedback was implemented to improve neurorehabilitation movement training. A major aspect of feedback is to reflect back the patients psychophysiological state into the environment, and also to use this as a guidance mechanism as to how events within the virtual environment unfold. The virtual environment was constructed using haptic, visual and acoustic primitives (basic sets of changes applied to the multimodal virtual environment that are expected to change the psychophysiological state of the patient). State transitions between primitives are defined as a response to changes in the users psychological state and motor performance. The mapping of biomechanical and physiological measurements to motor performance and psychological state and then to changes in action primitives was implemented using a fuzzy-logic system.

Virtual Reality Technology and Applications

As virtual reality expands from the imaginary worlds of science fiction and pervades every corner of everyday life, it is becoming increasingly important for students and professionals alike to understand the diverse aspects of this technology. This book aims to provide a comprehensive guide to the theoretical and practical elements of virtual reality, from the mathematical and technological foundations of virtual worlds to the human factors and the applications that enrich our lives: in the fields of medicine, entertainment, education and others. After providing a brief introduction to the topic, the book describes the kinematic and dynamic mathematical models of virtual worlds. It explores the many ways a computer can track and interpret human movement, then progresses through the modalities that make up a virtual world: visual, acoustic and haptic. It explores the interaction between the actual and virtual environments, as well as design principles of the latter. The book closes with an examination of different applications, focusing on augmented reality as a special case. Though the content is primarily VR-related, it is also relevant for many other fields.

HEnRiE - Haptic environment for reaching and grasping exercise

Task-oriented repetitive movements can improve motor recovery in patients with neurological or orthopaedic lesions. HEnRiE is a robot based haptic environment for simultaneous training of reaching and grasping movements. It consists of a robot with three active and two passive degrees of freedom and a grasping device with one degree of freedom. A training scenario that includes a virtual physiotherapist is introduced. Presented are results of a preliminary study that requires reaching and grasping coordination.

Upper limb and grasp rehabilitation and evaluation of stroke patients using HenRiE device

This paper presents a case study with a HenRiE (Haptic environment for reaching and grasping exercises) device with two hemiparetic subjects. The HenRiE device is intended for use in a robot-aided neurorehabilitation for training of reaching and grasping in haptic environments. The goal of the study is to develop a single system that retrains both hand grasping and releasing movements (which are essential to perform activities of daily living) and arm movements. The system combines a haptic interface and a grasping device, which is mounted on the end-effector of the haptic interface. The paper focuses on experimental training sessions with two hemiparetic subjects. Results show favourable effect both on arm and grasping.

Introduction to Robotics

This book is focused on geometrical models of robot mechanisms. Rotation and orientation of an object are described by Rodriguess formula, rotation matrix and quaternions. Pose and displacement of an object are mathematically dealt with homogenous transformation matrices. The geometrical robot model is based on Denavit Hartenberg parameters. Direct and inverse model of six degrees of freedom anthropomorphic industrial robots are also presented.

Measuring motor actions and psychophysiology for task difficulty estimation in human-robot interaction

In this paper, we describe a method for estimating task difficulty in human-robot interaction using a combination of motor actions and psychophysiology. A number of variables are calculated from kinematics, dynamics, heart rate, skin conductance, respiration and skin temperature. Discriminant analysis of the variables is used to determine whether the user finds the task too easy or too hard. The discriminant function is recursively updated with Kalman filtering in order to better adapt to the current user. The method was tested offline in a task with 20 subjects. In cross-validation, nonadaptive discriminant analysis yielded a classification accuracy of 80.2% while adaptive discriminant analysis yielded a classification accuracy of 84.3%.

CareToy: An Intelligent Baby Gym for Intervention at Home in Infants at Risk for Neurodevelopmental Disorders

This article describes the design of an innovative system for early intervention (EI) at home in infancy. The aim is to develop a smart device capable of promoting and measuring the actions of infants in the first months of life. The CareToy system, inspired by a commercially available gym for infants and equipped with a variety of sensors, can provide an intensive, individualized, home-based and family-centered EI program remotely telemonitored by clinicians. An array of sensors measures the activity of infants inside the gym. The sensor signals related to infants movement, interaction with toys, and pressure distribution are acquired and processed in real time to classify the infants activities and behavior. Rewards (feedback) are provided to the infants on the basis of their activity. Data are interpreted offline in terms of clinical meaning, and experimental tests are also reported.

An affordable, adaptable, and hybrid assistive device for upper-limb neurorehabilitation

The paper presents a multisensory and multimodal device for neuromuscular rehabilitation of the upper limb, designed to enable enriched rehabilitation treatment in both clinical and home environments. Originating from an existing low-cost, variable-stiffness rehabilitation device, it expands its functionalities by integrating additional modules in order to augment application scenarios and applicable clinical techniques. The newly developed system focuses on the integration of a wearable neuromuscular electrical stimulation system, a virtual rehabilitation scenario, a low-cost unobtrusive sensory system and a patient model for adapting training task parameters. It also monitors the user behavior during each single session and its evolution throughout the entire training period. The result is a modular, integrated and affordable rehabilitation device, enabling a biomechanical, neurological, and physiological-based training of patients, including innovative features currently unavailable within off-the-shelf rehabilitation devices.