Josep M. Font-Llagunes

Consistent triangulation for mobile robot localization using discontinuous angular measurements

Localization is a fundamental operation for the navigation of mobile robots. The standard localization algorithms fuse external measurements of the environment with the odometric evolution of the robot pose to obtain its optimal estimation. In this work, we present a different approach to determine the pose using angular measurements discontinuously obtained in time. The presented method is based on an Extended Kalman Filter (EKF) with a state-vector composed of the external angular measurements. This algorithm keeps track of the angles between actual measurements from robot odometric information. This continuous angular estimation allows the consistent use of the triangulation methods to determine the robot pose at any time during its motion. The article reports experimental results that show the localization accuracy obtained by means of the presented approach. These results are compared to the ones obtained applying the EKF algorithm with the standard pose state-vector. For the experiments, an omnidirectional robotic platform with omnidirectional wheels is used.

Efficient Dynamic Walking: Design Strategies to Reduce Energetic Losses of a Compass Walker at Heel Strike

Abstract Understanding the dynamics of bipedal locomotion is a key issue for the design of efficient walking systems. The mechanical analysis of the gait involves the study of the single support phase and the impulsive motion of heel strike. The aim of this work is to gain insight into the dynamics and energetics of heel-strike impacts. For this purpose, we use a concept that decouples the dynamics to the spaces of admissible and constrained motions. Detailed analysis and discussions are presented to quantify the effects of various parameters and the configuration of a compass-gait biped on the energetic aspects of heel strike.

An Eigenvalue Problem for the Analysis of Variable Topology Mechanical Systems

Mechanical systems with time-varying topology appear frequently in natural or human-made artificial systems, The nature of topology transitions is a key characteristic in the functioning of such systems. In this paper, we discuss a concept that can offer possibilities to gain insight and analyze topology transitions. This approach relies on the use of impulsive constraints and a formulation that makes it possible to decouple the dynamics at topology change. A key point is an eigenvalue problem that characterizes several aspects of energy and momentum transfer at the discontinuous topology transition.

Analysis of muscle synergies and activation-deactivation patterns in subjects with anterior cruciate ligament deficiency during walking.

BACKGROUND The knowledge of muscle activation patterns when doing a certain task in subjects with anterior cruciate ligament deficiency could help to improve their rehabilitation treatment. The goal of this study is to identify differences in such patterns between anterior cruciate ligament-deficient and healthy subjects during walking. METHODS Electromyographic data for eight muscles were measured in a sample of eighteen subjects with anterior cruciate ligament deficiency, in both injured (ipsilateral group) and non-injured (contralateral group) legs, and a sample of ten healthy subjects (control group). The analysis was carried out at two levels: activation-deactivation patterns and muscle synergies. Muscle synergy components were calculated using a non-negative matrix factorization algorithm. FINDINGS The results showed that there was a higher co-contraction in injured than in healthy subjects. Although all muscles were activated similarly since all subjects developed the same task (walking), some differences could be observed among the analyzed groups. INTERPRETATION The observed differences in the synergy components of injured subjects suggested that those individuals alter muscle activation patterns to stabilize the knee joint. This analysis could provide valuable information for the physiotherapist to identify alterations in muscle activation patterns during the follow-up of the subjects rehabilitation.

New biomechanical model for clinical evaluation of the upper extremity motion in subjects with neurological disorders: an application case

Cervical spinal cord injury and acquired brain injury commonly imply a reduction in the upper extremity function which complicates, or even constrains, the performance of basic activities of daily living. Neurological rehabilitation in specialised hospitals is a common treatment for patients with neurological disorders. This study presents a practical methodology for the objective and quantitative evaluation of the upper extremity motion during an activity of daily living of those subjects. A new biomechanical model (with 10 rigid segments and 20 degrees of freedom) was defined to carry out kinematic, dynamic and energetic analyses of the upper extremity motion during a reaching task through data acquired by an optoelectronic system. In contrast to previous upper extremity models, the present model includes the analysis of the grasp motion, which is considered as crucial by clinicians. In addition to the model, we describe a processing and analysis methodology designed to present relevant summaries of biomechanical information to rehabilitation specialists. As an application case, the method was tested on a total of four subjects: three healthy subjects and one pathological subject suffering from cervical spinal cord injury. The dedicated kinematic, dynamic and energetic analyses for this particular case are presented. The resulting set of biomechanical measurements provides valuable information for clinicians to achieve a thorough understanding of the upper extremity motion, and allows comparing the motion of healthy and pathological cases.

A comparative study of elastic motions in trajectory tracking of flexible RPR planar manipulators moving with high speed

The study of inertial forces effects at high speeds in flexible parallel manipulators, which generate undesired deviations, is a challenging task due to the coupled and complicated equations of motion. A dynamic model of the Revolute Prismatic Revolute (RPR) planar manipulators (specifically 3-RPR, 2-RPR and 1-RPR) with flexible intermediate links is developed based on the assumed mode method. The flexible intermediate links are modeled as Euler-Bernoulli beams with fixed-free boundary conditions. Using the Lagrange multipliers, a generalized set of differential algebraic equations (DAEs) of motion is developed. In the simulations, the rigid body motion of the end-effector is constrained by some moving constraint equations while the vibrations of the flexible intermediate links cause deviations from the desired trajectory. From this analysis, the dynamic performance of the manipulators when tracking a desired trajectory is evaluated. A comparison of the results indicates that in some cases, adding each extra RPR chain in the n-RPR planar manipulators with flexible intermediate links reduces the stiffness and accuracy due to the inertial forces of the flexible links, which is opposite to what would be expected. The study provides insights to the design, control and suitable selection of the flexible manipulators.

Neuromusculoskeletal Model Calibration Significantly Affects Predicted Knee Contact Forces for Walking

Though walking impairments are prevalent in society, clinical treatments are often ineffective at restoring lost function. For this reason, researchers have begun to explore the use of patient-specific computational walking models to develop more effective treatments. However, the accuracy with which models can predict internal body forces in muscles and across joints depends on how well relevant model parameter values can be calibrated for the patient. This study investigated how knowledge of internal knee contact forces affects calibration of neuromusculoskeletal model parameter values and subsequent prediction of internal knee contact and leg muscle forces during walking. Model calibration was performed using a novel two-level optimization procedure applied to six normal walking trials from the Fourth Grand Challenge Competition to Predict In Vivo Knee Loads. The outer-level optimization adjusted time-invariant model parameter values to minimize passive muscle forces, reserve actuator moments, and model parameter value changes with (Approach A) and without (Approach B) tracking of experimental knee contact forces. Using the current guess for model parameter values but no knee contact force information, the inner-level optimization predicted time-varying muscle activations that were close to experimental muscle synergy patterns and consistent with the experimental inverse dynamic loads (both approaches). For all the six gait trials, Approach A predicted knee contact forces with high accuracy for both compartments (average correlation coefficient r = 0.99 and root mean square error (RMSE) = 52.6 N medial; average r = 0.95 and RMSE = 56.6 N lateral). In contrast, Approach B overpredicted contact force magnitude for both compartments (average RMSE = 323 N medial and 348 N lateral) and poorly matched contact force shape for the lateral compartment (average r = 0.90 medial and -0.10 lateral). Approach B had statistically higher lateral muscle forces and lateral optimal muscle fiber lengths but lower medial, central, and lateral normalized muscle fiber lengths compared to Approach A. These findings suggest that poorly calibrated model parameter values may be a major factor limiting the ability of neuromusculoskeletal models to predict knee contact and leg muscle forces accurately for walking.

HYBRID MODELING AND FRACTIONAL CONTROL OF A SCKAFO ORTHOSIS FOR GAIT ASSISTANCE

SCKAFO, stance-control knee-ankle-foot orthosis, is a type of orthosis that permits free knee motion during swing while resisting knee flexion during stance, supporting thereby the limb during weight bearing. This orthosis specially assists patients who have incomplete spinal cord injury and allows them to walk with the aid of canes or crutches, maintaining a proper gait. In this paper, based on the human walking biomechanics, the SCKAFO hybrid modeling is proposed, which consists of eight different stages whose evolution is given by means of four planar sensors on each foot. In the model, it is considered that the patients can move their hip but not their knee that will be controlled using a DC motor. Two fractional order controllers are designed, following decision based control techniques, to control the knee angle. Simulation results are given in order to demonstrate the efficiency of the system performance.

Design and Experimental Evaluation of a Low-Cost Robotic Orthosis for Gait Assistance in Subjects with Spinal Cord Injury

Robotic gait training after spinal cord injury (SCI) is of high priority to maximize independence and improve the living conditions of these patients. Current rehabilitation robots are expensive and heavy, and are generally found only in the clinic. To overcome these issues, we present the design of a low-cost, low-weight robotic orthosis for subjects with SCI. The paper also presents a preliminary experimental evaluation of the assistive device on a subject with SCI. Results show that gait velocity, stride length and cadence of walking increased (24.11, 7.41 and 15.56 %, respectively) when wearing active orthoses compared to the case with standard passive orthoses.

Evaluation of Motion/Force Transmission Between Passive/Active Orthosis and Subject Through Forward Dynamic Analysis

Forward dynamic analysis of the acquired gait of subjects assisted by either passive or active knee-ankle-foot orthoses and crutches is used to evaluate the motion and force transmission between orthosis and subject depending on the connecting stiffness. Unlike inverse dynamic analysis, this approach allows to consider the subject’s limbs and the assistive devices as different entities, so that their relative behavior may be studied. The quality of motion transmission and the intensity of interface forces are evaluated for a range of connecting stiffness values, so that those providing the best trade-off between both aspects can be identified.