Gyroscope | EPFL Graph Search

Un gyroscope (du grec « qui observe la rotation ») est un appareil constitué d'un disque dont l'axe de rotation est libre de prendre toutes les orientations possibles grâce à un système de cardans. Cet appareil exploite le principe de la conservation du moment cinétique en physique (ou encore stabilité gyroscopique ou effet gyroscopique). Cette loi fondamentale de la mécanique veut qu'en l'absence de couple appliqué à un solide en rotation autour d'un de ses axes principaux, celui-ci conserve son axe de rotation invariable. Lorsqu'un couple est appliqué à l'appareil, il provoque une précession ou une nutation du solide en rotation. Les gyroscopes sont utilisés comme capteur de position angulaire, alors que les gyromètres sont des capteurs de vitesse angulaire. Le gyroscope donne la position angulaire (selon un ou deux axes uniquement) de son référentiel par rapport à un référentiel inertiel (ou galiléen). Dans les smartphones entre autres, les capteurs improprement nommés gyros

Shoulder function and outcome evaluation after surgery using 3D inertial sensors

Brian Coley

The importance of outcome evaluation of a medical treatment in orthopedics is currently recognized. In shoulder disease, a large variety of evaluation tools is employed to assess the results of the surgery. However, even if the majority of these evaluations are largely widespread, none was accepted as a universal standard. Since 1990, few researchers have been evaluating the assumption that the movement analysis (with camera-based or electromagnetic systems) is likely to provide objective results. In clinical practice, these techniques are not always applicable for outcome evaluation of a treatment. The surgeons lack a convenient and simple method of evaluating in an objective way a patient's activity and quality of life after a surgery of the shoulder. This project provides a new tool for the objective functional evaluation of shoulder pathologies, a tool that can be easily used by a doctor at a hospital and by the patient at home. It allows the measurement of the biodynamic changes as well as 3D kinematics of the treated shoulder by noting the effects of these changes on clinical results and on the patient's daily activity. The project was split in four complementary studies. In the first study, a new ambulatory device allowing long-term monitoring of the shoulder movement using several inertial sensors (3D gyroscopes, 3D accelerometers) attached on the trunk, the humerus and the scapula's spine was designed. By combining acceleration and angular velocity features of the both humerus during 9 tests, three kinematic scores for the functional assessment of the shoulder were presented to evaluate the shoulder function in patient before and after surgery. The kinematic scores objectively showed the shoulder improvement after surgery. In the second study, a new method was proposed to detect and quantify the dominant upper-limb segment during daily activity. The method was tested on healthy subjects (N=31) and a patient group (N=10, at baseline, 3, 6 and 12 months after surgery) while carrying the system during 8 hours of their daily life. The results showed the dominance of the arm during standing, sitting and walking periods for healthy subjects and the quantification of the shoulder improvement after surgery, by taking into account the presence of the disease in the dominant or the non dominant arm. In the third study, 3D gyroscopes attached on the humerus were used to identify the movements of flexion-extension, abduction-adduction and internal/external rotation of the humerus and to identify the rates of adjunct (deliberate rotation) and conjunct rotations (inherent or automatic rotation) within each movement. The frequencies of each movement (number/hour) for the different ranges of the arm speed, as well as the rate of adjunct and conjunct rotations for each movement were estimated during daily activity in healthy and patient groups. The results provided the values of frequency of each movement and adjunct/conjunct rate based on the data obtained from the healthy group. In the pathological case, we found that the painful dominant shoulder of the patients lost its predominance in favor of the healthy shoulder, the non dominant shoulder. Patients had less pure internal/external rotations and performed less fast movements while after surgery these parameters presented no significant differences with the healthy group. In the fourth study, a new method of detecting the working level of the shoulder was presented. By measuring the arm elevation during motionless periods, we proposed a new score to evaluate the ability of working at a specific level for a definite duration. We showed that this score had an average of 100% (±31%) for healthy subjects while the working level of the painful shoulder was lower than the healthy shoulder and improved significantly after surgery (up to 87% at 6 months). This study provides preliminary evidence of the effectiveness of the proposed system in clinical practice and objectively assesses upper-limb activity during daily activity.

EPFL2007

An orientation measuring system suitable for routine uses made by the fusion of a 3D gyroscope and a magnetic tracker

Julien Favre

Many studies have shown the efficacy of orientation and three-dimensional joint angle measurement for patient evaluation or rehabilitation purposes. But currently, the use of these systems for routine practice is questionable. The commercially available devices are generally too expensive and complicated-to-use. This study proposed the fusion between two affordable types of orientation measuring systems, which used separately couldn't satisfy the health professionals, needs. One was a portable magnetic tracker limited in accuracy, sampling frequency and possibly distorted. The other was triplets of gyroscopes limited by their bias, which generates orientation drift after integration. The fusion algorithm presented here relay on two cascaded complementary Kalman filters to estimate the bias of the gyroscopes and to provide accurate and high frequency orientation even during distortion periods. This system was assessed during treadmill walking and reported good performances.

Ieee Service Center, 445 Hoes Lane, Po Box 1331, Piscataway, Nj 08855-1331 Usa2007

Ambulatory monitoring of motor functions in patients with Parkinson's disease using kinematic sensors

Arash Salarian

Parkinson's disease (PD) is the second most common neurodegenerative disease in the general population. Cardinal symptoms of Parkinson's disease are resting tremor, rigidity, akinesia and bradykinesia and in advanced stages, gait impairments, postural instability and complications of chronic treatment with levodopa such as motor dysfunctions and dyskinesia. Multitude and complexity of these motor symptoms and their variability over the time have made assessment of them a difficult task. Moreover, following the fluctuations of motor performance (ON/OFF fluctuations) of the PD patients throughout their daily activities by quantifying their motor symptoms is a major challenge. The aim of this thesis was to design and validate a portable ambulatory movement analysis system for long-term monitoring and qualitative and quantitative assessment of motor abnormalities of PD patients during daily activities. We have designed a new measurement system consisting of five independent, lightweight, autonomous sensing units based on kinematic sensors that can continuously record body movements during daily life. Using this system and by performing several clinical studies, both in controlled conditions and on free moving patients, we have prepared a database of different movement patterns of PD patients. This database was the basis to design several new algorithms for the analysis of tremor, bradykinesia, gait and posture. An accurate algorithm based on spectral estimation has been proposed to detect and quantify tremor during daily activities of PD patients with a resolution down to three seconds using gyroscopes attached to the forearms. By quantifying the speed, range and the frequency of the movements, we have proposed a new method to assess the bradykinesia and tested it both in controlled and free conditions. We found out that in the free moving patients, the outcomes of this algorithm show significant and good correlation to the established clinical scores. Regarding the detection and analysis of gait, we have developed and tested a method based on four sensors attached to the lower limbs that provided spatio-temporal parameters of gait with good accuracy. We further improved our method using a new biomechanical model that could predict the movements of thighs from the movements of shanks during walking. This way we could reduce the number of sensor sites on the body while keeping the same accuracy in estimation of the spatio-temporal parameters of gait. By combining a statistical classifier, to detect transitions between sitting and standing postures, and a fuzzy classifier, to detect the basic body postures, we have developed an algorithm to classify basic body posture allocations both in PD patients and aged matched healthy subjects. Finally, while currently no other objective ambulatory method exists to accurately detect the periods of ON and OFF in PD patients, by combining the outcomes of the above algorithms (tremor, gait, bradykinesia and posture) using a statistical approach, we have proposed a method to detect periods of these two states with a resolution of 10 minutes in free moving patients. We believe that the proposed system has a high potential both for the clinical applications and research purposes related to the patient with Parkinson's disease and possibly other neurological movement disorders.

EPFL2006