Paolo Cappapaolo.cappa@uniroma1.it

Department of Mechanical and Aerospace Engineering - macroarea 09

WAKE-up!: a Wearable Ankle Knee Exoskeleton

The WAKE-UP! is a Wearable Ankle–Knee Exoskeleton developed to assist the walk in children affected by Cerebral Palsy (CP). It is made up by two modules, one for the Knee and one for the Ankle. These modules can work together or one by one, depending from the gait problem. The WAKE-up! is an active orthosis and it can interact actively with the subject, changing the stiffness value in function of his/her motor improvements. Specifically, the device can apply a corrective/perturbative action on the joint motion assisting or less the subject only when requested. The first design constraint is related to the maximum value of device mass equal to 2.5 kg.

Cerebral PalsyThe prevalence of CP ranges is from 1.5 to 2.5 per 1000 live births and it is influenced by the weight and the gestational age. The CP comports gait disorders and one of the most important is the Drop Foot. In this particular case the children reach the ground with toe and not with the heel.

Mechanical Design The actuation system is based on a Rotary Series Elastic Actuator (RSEA). Power transmission is achieved by timing belt and pulleys (1.5 reduction factor) and it is mediated by a torsion spring of 3.0 Nm/rad. Motors are high-torque digital servos with an embedded positional controller. Torsion spring deflection is measured by an absolute encoder embedded in the transmission shaft. Frame is composed by two braces attached to thigh and shank and its length is adjustable. Quick release system, which is composed by sliding dovetail joints, is designed between motors and brace. Two revolute joints connect the two braces together and the lower brace with a foot steel plate that is inserted into the shoe. An Absolute Magnetic Shaft Encoder was used for each module to measure the degree of rotation of spring and motor.

Orthosis 3D PrototypingThe orthosis, where to fix the mechanical components, are made by the 3D prototyping technique. The first step of the design work was to acquire and digitalize with a 3D scanner (FARO ScanArm V3,UK), the surface of a lower limb. Then, the digital surface of the limb was imported in the 3D design software where the surface was processed to extruded a shells with thickness of 4 mm from the surface acquired. This method is used to obtain a greater homogeneous contact between the skin surface and the internal surface of the orthosis.

Control systemThe main goal of the control system of an active orthosis is the correct and real-time identification of gait phases in order to provide the right assistance based on the subject’s need. For the identification of the gait cycle a sole was sensorized with four footswitches, which can determinate the contact of the foot with the ground. The output of gyroscope embedded into the IMU is used as input of the Hidden Markov Model in order to estimate the correct sequence of gait phases. The sensors are managed by a MyRio board (NI, USA). Next goal of the project is the optimization of the control system based on the

application of Hidden Markov Model. For this reason, each module of the orthosis is equipped with an inertial measurement unit.

First experimental resultsThe main significant obtained results is related to the prevention of the drop-foot. A pilot study was conducted at the Neurorehabilitation Department of the Children’s Hospital Bambino Gesù Italy with both healthy children and children with CP. The synergetic actuation of the ankle and knee joint provided by the WAKE-up! assisted the subjects’ intention to produce voluntary leg movements. These results demonstrate device functionality and lay the groundwork for future studies with larger subject populations.

Paolo Cappa, Full Professor. Paolo Cappa, Full Professor of Mechanical and Thermal

Measurements with the Department of Mechanics and Aeronautics at the “Sapienza”

University of Rome. He earned a Master of Science in mechanical engineering (with

honors) from the “Sapienza” University of Rome, Italy, in 1980. He is currently a Full

Professor of Mechanical Engineering and Biomedical Engineering. He scientifically

cooperates with the MARlab (Movement Analysis and Robotics Laboratory) at the

Neurorehabilitation Division of IRCCS Pediatric Hospital “Bambino Gesù,” in Rome, Italy.

His research interests include experimental mechanics applied in biomedical and

biomechanical fields and he serves as a consultant to industry management or government

policymakers in those fields.

Team

Prof. Paolo CAPPA, Full Professor in Mechanical and Thermal

Measurements

Prof. Fabrizio PATANÉ, Associate Professor at Cusano University

Prof. Stefano ROSSI, Assistant Professor at University of Tuscia

Dr. Eduardo PALERMO, Research Associate

Dr. Alessandra PACILLI, PostDoc

Fausto DEL SETTE, PhD Student

Juri TABORRI, PhD Student

Ilaria MILETI, PhD Student

1. Mechanical Design of WAKE-up! 2. Experimental protocol

3. Experimental results for prevention of drop-foot